Modulation of histone deacetylase activity

HCMV replication is stimulated when permissive cells are treated with inhibitors of histone deacetylases (Murphy et al., 2002) or when virus is propagated in cells in which expression of histone deacetylases has been inhibited (Tavalai et al., 2006). Two viral gene products have been implicated in derepression. One major tegument protein, ppUL82 (pp71), also known as the virion transactivator, appears to inactivate Daxx (Cantrell et al., 2005; Everett, 2006; Hofmann et al., 2002; Ishov et al., 2002; Staffert and Kalejta, 2006). The major immediate early protein, IE 1-p72, long known to disrupt nuclear domain 10 (ND-10) sites early after infection (Korioth et al., 1996), has been ascribed a role in inactivate a family of promyelocytic leukemia protein (PML) proteins, that also act as repressors of viral gene expression (tavalai et al., 2006).

Modulation of IRF –3

HCMV entry into cells is associated with a dramatic induction of NF -κB (Yurochko et al., 1997a) that is likely to drive the interferon-like response of cells exposed to infectious virus, viral particles, or soluble envelope glycoprotein gB (Simmen et al., 2001; Yurochko et al., 1997a; Zhu et al., 1997, 1998). Although the interferon β transcript is induced in virus-infected cells, even following high MOI infection, interferon itself is only produced in cell cultures subjected to low MOI infection (Rodriguez et al., 1987; Zhu et al., 1997). Several investigators, have described the induction of IRF -3 immediately after infection of permissive fibroblasts (Boehme et al., 2004; Browne and Shenk, 2003; Navarro et al., 1998; Preston et al., 2001), using a variety of viral strains and infection conditions. Induction has been associated with the appearance of a novel IRF -3 complex (Navarro et al., 1998). In contrast, experiments that included both uniform high MOI and use of a monoclonal antibody to detect IRF-3 demonstrated that wild type strains of HCMV fail to induce IRF-3 (Abate et al., 2004), a property that may be shared by rhesus CMV (DeFilippis and Fruh, 2005). Experimental differences in MOI and time post infection, as well as in choice of viral strains and strain variants, may contribute to differences in IRF-3 activation and level of inhibition by pp65 (ppUL83) during infection. Virion pp65 reduces the level of activation of IRF-3 immediately following infection and pp65 expression independent of viral infection is sufficient to inhibit IRF-3 activation by a variety of signals (Abate et al., 2004). In the presence of pp65, there appears to be a transient activation of IRF-3 (Yang et al., 2005) that does not exhibit kinetics consistent with the dramatic impact of virus infection on cells. NF-kB, which has been a topic of study for many years (see below), may also be a target of pp65 depending on experimental conditions (Browne et al., 2003). Even though IRF-3 activation that occurs within 2 h postinfection is likely to be dependent on preformed cytoplasmic protein, the ability of IRF-3 siRNA to increase expression of certain IRF-3 responsive genes and decrease HCMV replication levels has been reported (DeFilippis et al., 2006). The mechanism of IRF -3 regulation over the first few hours of infection will emerge from further mechanistic studies.

Activation of NK -κB and interferon response genes

A classical NF -κB response occurs in two distinct phases following HCMV infection of fibroblasts (Johnson et al., 2001a; Kowalik et al., 1993; Sambucetti et al., 1989; Yurochko et al., 1995). The first phase follows as early as 5 minutes after exposure of cells to virus or virus particles and apparently results from the release of preformed NF -κB mediated by the binding and postattachment events (Boyle et al., 1999; Yurochko et al., 1997a; Netterwald et al., 2004). This initial NF -κB activation may underlie the virion-induced interferon-like response (Browne et al., 2001; Zhu et al., 1997, 1998) and enhance expression of immediate early (IE) genes through the enhancer (DeMeritt et al., 2004). Based on studies with MCMV, the NF -κB sites in the enhancer region may not be essential in all settings (Benedict et al., 2004). NF -κB activation requires phosphorylation-dependent degradation of an inhibitor of NF -κB (IκB), and this degradation is activated in response to infection and continues throughout the infection cycle (Kowalik et al., 1993). Phosphorylation is dependent on a three subunit IκB kinase (IKK) that is both activated and, based solely on the use of chemical inhibitors, required for initiation of viral replication (Caposio et al., 2004) in quiescent fibroblasts. Activation is not critical in actively growing astrocytoma cells (Eickhoff and Cotten, 2005). Deletions made through the enhancer reduce viral replication efficiency in a pattern that suggests a possible role of NF -κB as well as other transcription factor binding sites (Isomura et al., 2004). Another phase of NF -κB activation due to the initiation of NF -κB transcription, allowing continued expression throughout infection (Kowalik et al., 1993; Yurochko et al., 1997b). A physiological role for activation is masked by the relative complexity of events as well as the activities of viral regulatory gene products (Castillo et al., 2000).

The interferon-like and likely NF -kB-dependent activation of cellular gene expression begins within a few hours after virus particle contact with cells (Browne et al., 2001; Simmen et al., 2001) and the response includes a wide range of signaling pathways in addition to those that activate NF -κB (Albrecht et al., 1992; Boldogh et al., 1990, 1991, 1997; Evers et al., 2004; Wang et al., 2003). The production of interferon β itself during HCMV infection is inversely associated with MOI (Rodriguez et al., 1987). Levels of this interferon sufficient to influence the behavior of cells is only induced following exposure of cells to low MOIs or to inactive virus particles (Boehme et al., 2004; Compton, 2004). There is little detectable interferon in the medium or associated with virus particles following high MOI infection (Abate et al., 2004; Rodriguez et al., 1987; Zhu et al., 1997). Interferon has long been known to be relatively ineffective against this group of viruses, whether tested in culture (Holmes et al., 1978) or in patients (Cheeseman et al., 1977). HCMV infected cells do not support interferon receptor signaling or the translation of interferon β transcripts but viral functions that carry out these activities remain to be identified. HCMV deflects major interferon regulated pathways through the action of the closely related viral TRS 1 and IRS 1 gene products (Child et al., 2002, 2004; Cassady, 2005). These can replace either the vaccinia dsRNA binding protein E3L or the herpes simplex virus-1 (HSV-1) γ34.5 gene product and suppress both protein kinase R (PKR) and the 2–5 oligoadenylate (2–5OAS) synthetase/RNase L system. Despite the lack of obvious motifs, pTRS1 binds dsRNA and includes an unconventional dsRNA-binding domain conserved in pIRS1; however, this domain is not sufficient to rescue E3L mutant virus (Hakki and Geballe, 2005). Thus, TRS 1 primarily, but IRS 1 secondarily, impede PKR -mediated inactivation of eukaryotic intiation factor 2 as well as the activation of RN ase L by products of 2–5A synthetases and the resultant degradation of mRNA and rRNA. IRS 1 mutants are fully growth proficient, but growth of TRS 1 mutants is reduced (Blankenship and Shenk, 2002; Dunn et al., 2003) and impacts virion assembly (Adamo, et al., 2004).

Impact on the host cell cycle

Betaherpesvirus genomes are transcribed and replicated within the nucleus, the same cellular compartment that regulates the cell cycle and controls apoptosis following DNA damage or aberrant protooncogene expression. Cellular DNA is damaged, the cell cycle is dysregulated, and protooncogene expression is increased following cytomegalovirus infection. DNA damage induced by HCMV includes both randomly distributed and specific chromosomal breaks and gaps (AbuBakar et al., 1988; Deng et al., 1992; Fortunato et al., 2000a). It is not evident that any of these processes requires viral replication.

Cell cycle dysregulation occurs during HCMV productive infection and gives the impression of progression into S phase and mitosis, although cellular DNA synthesis and cell division are blocked. Initial reports of a G2/M arrest, defined by presence of what appeared to be a 4N chromosomal peak (Jault et al., 1995; Lu and Shenk, 1996) were clarified by further work showing host cell DNA content does not increase in infected cells (Bresnahan et al., 1996; Dittmer and Mocarski, 1997; Salvant et al., 1998). Specific inhibition of viral and cellular DNA replication showed that this increase was due to the accumulation of viral DNA (Dittmer and Mocarski, 1997]. Interestingly, viral replication is delayed in cells infected during S phase until after the cell cycle has progressed at least to G2/M, and the majority of cells must apparently cycle to G1 prior to the initiation of viral gene expression (Salvant et al., 1998; Fortunato et al., 2002). It remains possible that the CMV -induced block to cellular DNA synthesis and dysregulation of the cell cycle will vary with each differentiated cell type tested, as detailed studies have not been undertaken in relevant cell types such as endothelial cells, myeloid cells, or epithelial cells. It is notable that studies in MCMV have suggested that induction of apoptosis as a result of viral infection is cell type dependent and that viral inhibitors of apoptosis show cell type specificity (Brune et al., 2001, 2003; Menard et al., 2003).

The structural proteins that modulate host cells most dramatically include two relatively abundant viral tegument proteins, ppUL82 (pp71) (Bresnahan and Shenk, 2000; Kalejta and Shenk, 2002) and pUL69 (Hayashi et al., 2000; Lu and Shenk, 1999). Both are introduced into cells during viral entry. In addition, the IE 2 p86 regulatory protein encoded immediately following entry (Murphy et al., 2000; Song and Stinski, 2002) has a dramatic impact on the cell. All three have been characterized for their impact on cell cycle independent of viral replication. pUL69 and IE 2 p86 inhibit cell progression past G1 and S, respectively, and pUL82 (pp71) induces quiescent cells to enter the cell cycle. The impact of any of these during viral infection remains poorly understood, but ppUL82 (pp71) may act through derepression of HDACs (Cantrell et al., 2005; Hofmann et al., 2002; Ishov et al., 2002; Saffert and Kalejta, 2006). The situation is complicated by the fact that virus-infected cells do not remain at any distinct stage of the cell cycle but can have characteristics that extend from resting, Go-like to a pseudomitotic state (Hertel and Mocarski, 2004). HHV -7 infection apparently promotes accumulation of polyploid cells with enlarged single cells that have a polylobated nucleus and >4N genome content (Secchiero et al., 1998).

HCMV and HHV -7 grossly alter cyclin and other cell cycle regulatory protein expression patterns (Fortunato et al., 2000b; Hertel and Mocarski, 2004), as described in Chapter 18. Cell cycle dysregulation is accompanied by increases in cyclin E and cdk2 (Bresnahan et al., 1996; Jault et al., 1995) as well as cdk2 translocation to the nucleus (Bresnahan et al., 1997). Additionally, infected cells accumulate hyperphosphorylated pRB (Jault et al., 1995), consistent with induced E2F-specific gene transcription (Song and Stinski, 2002). Proteins that are normally involved in cellular DNA replication, including PCNA (Dittmer and Mocarski, 1997; Mate et al., 1998) and RPA (Fortunato and Spector, 1998), increase and accumulate within sites of viral DNA replication in the nucleus. Increases in cyclin B and cdc2 activity were first demonstrated in infected cells that appeared to have progressed to the G2/M boundary based on DNA content (Jault et al., 1995), but cyclin B levels clearly increase in fibroblasts arrested by CMV at a G1/S-like boundary (Dittmer and Mocarski, 1997). Despite the presence of regulatory factors required for transition through S phase, cellular DNA synthesis is restricted through virus-specific inhibition of licensing factors (Biswas et al., 2003; Wiebusch et al., 2003). All of these studies provide clear evidence of severe dysregulation by HCMV. Although less well characterized, HHV -7 will likely differ from CMV since cdc2 activity decreases after HHV -7 infection. Similar to CMV, cyclin B increases in HHV -7 infected cells despite a G1/S-like arrest. In conjunction with cell cycle alterations, HCMV infection increases expression of the protooncogenes c-jun, c-fos, c-myc (Boldogh et al., 1990), and the tumor suppressor p53 (Jault et al., 1995; Speir et al., 1994). p53 is a transcription factor that promotes growth arrest or apoptosis in response to cell stress (Haupt et al., 2003) or other regulators of intrinsic cell death such as oncogene activation, nucleotide depletion, hypoxia, redox modulation, and loss of normal cell contacts (Giaccia and Kastan, 1998). p53-induced cell death is primarily due to trans-activation of specific apoptosis regulators including several proapototic Bcl-2 family members that promote mitochondria membrane permeability transition. The outcome of p53 activity, growth arrest or induction of apoptosis, depends on many factors including p53 expression levels, p53 co-activators, cell type, and type of stress (Haupt et al., 2003). p53 levels are controlled via Mdm2 (mice) or Hdm2 (humans), which direct degradation via the proteasome. Early during HCMV infection, p53 levels increase due to a decrease in protein turnover (Jault et al., 1995; Muganda et al., 1998; Speir et al., 1994). Further, specific coactivators of p53, such as myc, are induced but apoptosis is not induced, possibly due to accumulation in discrete subnuclear regions colocalizing with the viral DNA polymerase processivity factor, ppUL44 (Fortunato and Spector, 1998), a marker of viral DNA replication compartments (Penfold and Mocarski, 1997). A direct physical interaction with IE 2 p86 may inhibit p53-mediated transactivation (Speir et al., 1994). One reported interaction of IE 2 p86 and p53 (Bonin and McDougall, 1997), however, was carried out in cells that expressed a non-functional IE 2 p86 (Murphy et al., 2000), such that this area needs additional investigation. IE 2 p86-deficient viruses fail to replicate at all (Heider et al., 2002; Marchini et al., 2001), and a variety of deletions have been made within the protein coding sequences to delineate regions that are necessary for viral replication (Sanchez et al., 2002; White et al., 2004), as described in Chapter 18. In addition to sequestration of the protein, HCMV may have additional means of negating p53 activity, including the increased expression of inhibitory proteins in the p53-family. p53-mediated transcription of apoptotic genes is influenced by the presence of p73 (Flores et al., 2002). In p53 deficient astrocytoma cells, the presence of p73 confers sensitivity to DNA damaging agents such as cisplatin, and HCMV infection alters sensitivity to such agents (Allart et al., 2002) and increases the expression of a cellular dominant negative isoform of p73 that may interfere with both p53- and p73-dependent activities.

Suppression of apoptosis

Apoptosis is an evolutionarily conserved cellular process that removes cells during infection, development, or homeostasis. Apoptosis is initiated by intrinsic stress or DNA damage within the cell that accompanies infection by obligate intracellular parasites and viruses (Ferri and Kroemer, 2001; Polster et al., 2004). Death of the cell early after viral infection prevents the production of progeny, and such mechanisms would exert a strong impact on the slow growing betaherpesviruses. This evolutionarily ancient host defense strategy may be induced in mammals through intrinsic signals, as a consequence of cell stress induced by virus infection, or extrinsic signals through the engagement of death receptors on the cell surface or other immune effector mechanisms. Apoptotic bodies and cellular debris from dead cells are cleared by professional phagocytic cells, such as MΦ and DC s, which carry out critical roles priming the adaptive immune response. A wide range of cellular sensors may be triggered by viral infection, including alterations of the cellular tumor-suppressor p53 or other cell cycle regulators, alterations in mitochondrial function, nuclear changes resulting from DNA damage and repair, modification of endoplasmic reticulum, and activation of PKR (Everett and McFadden, 1999, 2001). A wide range of antiapoptotic proteins encoded by DNA and RNA viruses have been recognized (Cuconati and White, 2002; Polster et al., 2004), and many target the mitochondrion (Boya et al., 2004). These inhibitors suppress cell death resulting from the intrinsic impact of virus infection or from extrinsic inducers or stimuli that accompany the host immune response. The consequence of keeping cells alive is enhancement of viral replication levels that increase the chances of a virus gaining a foothold in the host.

Betaherpesviruses rely on a variety of virus-encoded regulators that prevent cells from showing molecular or morphological hallmarks of apoptosis (Allart et al., 2002; Brune et al., 2003; Goldmacher et al., 1999; Reboredo et al., 2004; Skaletskaya et al., 2001), as depicted in Fig. 21.1. Two HCMV genes, UL 37x1 (Goldmacher et al., 1999; Reboredo et al., 2004), which encodes the viral mitochondrial localized inhibitor of apoptosis (vMIA), and UL 36 (Skaletskaya et al., 2001), which encodes the viral inhibitor of caspase 8 activation (vICA), inhibit apoptosis through clearly defined mechanisms. The major IE gene products have also been suspected of blocking apoptosis but little mechanistic insights have been gained. Four MCMV gene products inhibit apoptosis, with one (M36) being homologous to HCMV UL 36 (McCormick et al., 2003a; Menard et al., 2003), one (m38.5) being a positional and functional homolog of vMIA (McCormick, 2005) and two (m41 and M45) functioning differently than any known HCMV gene product (Brune et al., 2001, 2003; Hahn et al., 2002; Patrone et al., 2003). HHV -6B infected CD 4+ cultures include apoptotic cells and virus-positive cells are more resistant to apoptosis than neighboring cells (Inoue et al., 1997), suggesting that this virus also encoded genes that are antiapoptotic. The homologue of UL 36 is the most likely candidate. There is also evidence that apoptosis may occur following exposure of non-permissive cells to betaherpes-viruses or in non-infected cells in productively infected cultures. Thus, all evidence is consistent with a role for betaherpesvirus gene products regulating apoptosis to prolong the life of the infected cell or make it resistant to host immune defense mechanisms. A role for suppression of apoptosis in species specificity of MCMV replication has also been demonstrated by converting human cells to a susceptible state using HCMV vMIA (Jurak and Brune, 2006).

Fig. 21.1

Betaherpesvirus inhibition of apoptosis and interferon response. Grey arrows represent proapoptotic pathways while black arrows indicate prosurvival pathways and black lines indicate interruption of proapoptotic pathways. Cellular functions are listed (more...)

vMIA (pUL37×1)

The genomic region of HCMV encoding the ORFs UL 36, UL 37, and UL 38 is transcriptionally complex (Fig. 21.2). Sequence analysis combined with transcription and in vitro translation studies (Kouzarides et al., 1988; Tenney and Colberg-Poley, 1990, 1991a, 1991b) indicated the presence of two immediate–early transcripts that include UL 37x1. The larger transcript, 3.2–3.4 kb in length, is present only at immediate early times, encodes the glycoprotein gpUL37, and terminates at a polyadenylation signal located between UL 36 and UL 35. The more abundant, 1.7kb transcript, encoding pUL37x1, is present at immediate early times as well as throughout the remainder of infection. This transcript terminates at a polyadenylation signal located between UL 38 and UL 37x2. A splice variant encoding gpUL37_M includes UL 37x1, UL 37x2, and a portion of UL 37x3 (Goldmacher et al., 1999). Transcription and translation in vitro predicted apparent molecular weights of 58 kDa and 24 kDa, respectively for gpUL37 and pUL37x1 (Tenney and Colberg-Poley, 1990). More recently, cDNA cloning has revealed that transcription through this region may produce as many as 11 spliced and unspliced transcripts (Adair et al., 2003), including all those that had been previously identified. HCMV -induced alterations to the cellular splicing machinery apparently ensures the continued production of the unspliced transcript encoding pUL37x1 throughout infection (Su et al., 2003).

Fig. 21.2

Presence of functional antiapoptotic genes in HCMV strains. (top) Depiction of the commonly used laboratory strains AD 169, Towne, and Toledo genomes. Rectangles represent repeated ab - b′a′ sequence flanking the unique long (U_L) and the (more...)

The fact that UL 37x1-containing gene products provide antiapoptotic activity emerged from transient expression of viral DNA fragments and functional analyses of pUL37x1, gpUL37 and gpUL37M clones in a cell death suppression assay (Goldmacher et al., 1999). The name vMIA is reserved for the most potent of these, pUL37x1. vMIA prevents cell death induced by TNF, Fas ligand (Goldmacher et al., 1999), TRAIL (Skaletskaya et al., 2001), E1B19K deficient adenovirus (Goldmacher et al., 1999), HIV Vpr (Roumier et al., 2002), doxorubicin (Goldmacher et al., 1999), nitric oxide, peroxynitrite, 4-hydroxynonenal (Vieira et al., 2001), hydroxychloroquine (Boya et al., 2003a), ionidamine, arsenite, the retinoid derivative CD 437 (Belzacq et al., 2001), propionibacterial short chain fatty acids (Jan et al., 2002), N-(4-hydroxyphenyl)retinamide (Boya et al., 2003b), and macroautophagy (Boya, 2005). vMIA increases the susceptibility of human cells to MCMV productive infection (Jurak and Brune, 2006). vMIA mediates protection at the level of the mitochondria and prevents release of cytochrome c and subsequent downstream events (Fig. 21.1), but does not prevent upstream events including cleavage of either procaspase-8 or Bid (Goldmacher, 1999). vMIA can be immunoprecipitated with adenine nucleotide transporter, a component of the mitochondria membrane pore that interacts with Bax and other Bcl-2 family members but for vMIA, this interaction is non-specific. vMIA also interacts with Bax in cells (Arnoult et al., 2004; Poncet et al., 2004), and Bax also localizes to mitochondria during MCMV infection (Andoniou et al., 2004). More recently an interaction with growth arrest and DNA damage 45 alpha (GADD45α) was established through yeast two hybrid and significantly, this interaction was shown to be critical for cell-death protection since addition of any GADD 45 family member (alpha, beta, or gamma) enhanced survival and function was impaired by siRNA-mediated GADD 45 family reduction. vMIA lacks the BH domains that characterize Bcl-2 family members and Bax also localizes to mitochondria during MCMV infection (Andoniou et al., 2004). Rather this, protein is composed of an amino terminal region, aa 5–34, that is important for localization to mitochondria and a carboxyl terminal region, aa 118–147, that is critical for anti-apoptotic activity (Hayajneh et al., 2001). This domain also mediates the interaction with GADD 45 family members that facilitates vMIA activity (Smith et al., 2005).

vMIA does not exhibit sequence variation in HCMV (Hayajneh et al., 2001) and sequence homologs can only be found in primate CMV s. The regions of highest sequence conservation are coincident with regions defined by mutational studies to be required for vMIA activity (McCormick et al., 2003b). “In fact, a minimal 69 aa protein that includes amino acids 1–34 and 112–147 of vMIA retains full activity (Hayajneh et al., 2001) and is very similar to homologues in monkey CMVs (McCormick et al., 2003b).” At a positionally conserved location in the viral genome, MCMV and rat CMV retain a functional homolog which despite limited sequence homology, functions in cell death assays (McCormick et al., 2005). A UL 37x1 homolog has not been identified in other betaherpesviruses, although all betaherpesviruses carry a gene homologous to UL 37x3, which as the largest exon, has been annotated as UL 37 in most betaherpesviruses but that lacks independent anti-apoptotic activity (Chapter 15; McCormick et al., 2003b). UL 37x1 is not essential for viral replication in TownevarATCC, a strain carrying a functional vICA (McCormick et al., 2005). In contrast, transposon mutants disrupting HCMV UL 37x1 fail to produce infectious virus, in AD 169varATCC, a strain carrying a mutant UL 36 (Reboredo et al., 2004). Other, independently derived UL 37x1 deletion mutants made in AD 169varATCC had also suggested that vMIA is required for viral replication (Brune et al., 2003; Dunn et al., 2003; Yu et al., 2003). Thus, vMIA is dispensable unless other mutations are present which render the virus dependent on the gene to prevent apoptosis. (Dunn et al., 2003; Brune et al., 2003; Reboredo et al., 2004; Yu et al., 2003; Skaletskaya et al., 2001). Consistent with this conclusion and in contrast to the caspase-dependent cell death noted for strains that require vMIA, premature death in TownevarATCC mutant virus is caspase-independent (McCormick et al., 2005).

vICA (pUL36)

This betaherpesvirus-conserved anti-apoptotic gene product is dispensable for HCMV replication in cultured fibroblasts and is mutated in many common laboratory strains (Patterson and Shenk, 1999; Skaletskaya et al., 2001), as depicted in Fig. 21.2. Evidence that UL 36 encodes the antiapoptotic protein vICA first emerged from transient expression of viral DNA fragments in a cell death suppression assay (Skaletskaya et al., 2001). Caspase 8, the target of pUL36, is also known as FLICE. vICA is mechanistically similar to the viral and cellular FLICE inhibitory proteins (v-FLIP and c-FLIP), but lacks any sequence similar to death effector domains typical of this class of protein. Like FLIP s, vICA prevents cleavage by binding to the pro-domain of procaspase-8 and provides protection from apoptosis initiated by death receptors TNFR, TRAILR, or Fas that require caspase 8 activation. vICA only slightly delays cell death induced by E1B19K deficient adenovirus or doxorubicin. The presence of vICA correlates with an increased resistance of HCMV to inducers of extrinsic cell death (Skaletskaya et al., 2001). Mutants of the MCMV homologue M36 show a reduced growth phenotype in macrophages (IC-21, J774-A1, and peritoneal exudate cells) but not in fibroblasts or endothelial cells, but this behavior does not appear to extend to the HCMV gene product (Dunn et al., 2003). M36 mutant infected cells are, however, more susceptible to induction of apoptosis by the Fas pathway similar to HCMV viruses defective in UL 36 (Skaletskaya et al., 2001).

UL36 homologs and vICA function are widely conserved among betaherpesviruses and sequence conservation includes regions outside the boundaries of the US 22-family domains (McCormick et al., 2003a). The homolog is an immediate early gene in MCMV, while the rhesus macaque CMV homolog is an early gene similar to vMIA in that virus. The homologs of UL 36 in HHV -6A and HHV -7 are each encoded by a spliced transcript. The HHV -6A is regulated as an immediate–early gene (Flebbe-Rehwaldt et al., 2000), whereas the HHV -7 spliced RNA seems to be regulated as an early gene (Menegazzi et al., 1999).

Other cell death suppressors

Ribonucleotide reductases convert ribonucleoside diphosphates to deoxyribonucleoside diphosphates and are generally important for DNA synthesis and repair. While alphaherpesviruses and gammaherpesviruses encode both ribonucleotide subunits RR 1 and RR 2 and make an active enzyme, the betaherpesviruses only encode a homolog of the RR 1 subunit that lacks enzymatic activity (Chapter 15). Viral mutants of MCMV M45, but not the HCMV homolog UL 45, show cell-type dependent growth properties (Brune et al., 2001; Hahn et al., 2002). Insertional mutants of M45 grow similar to wild-type viruses in cultured fibroblasts, bone marrow stromal cells, and hepatocytes but fail to grow in either endothelial cells or macrophages (Brune et al., 2001), which enter apoptosis by about 1 day post-infection. Cell to cell spread is thus severely restricted. The alphaherpesvirus HSV -2 RR 1 subunit prevents cell death upstream of caspase 8 activation due to an amino-terminal extention relative to other RR 1 homologs (Langelier et al., 2002) in addition to being a component of an active ribonucleoside reductase enzyme. It is possible that M45 has preserved such an antiapoptotic function, although there is little sequence similarity to guide how the two may be related. Cell-type restricted growth and induced apoptosis are not observed in HCMV UL 45 mutants, which grow poorly and are less efficient at cell-to-cell spread (Patrone et al., 2003), but do not exhibit cell type specific defects in fibroblasts, macrophages, or endothelial when used at high MOIs (Hahn et al., 2002). Mutant HCMV is somewhat reduced compared to wt in ability to withstand Fas-induced apoptosis (26% survival vs. 50% survival), however; HCMV UL 45 is unable to independently block cell death in the absence of viral infection.

MCMV mutant defective in m41 prematurely kills cells and replicates to reduced levels compared to parental virus (Brune et al., 2003). Caspase inhibition reduces but does not eliminate cell death, suggesting that apoptosis may underlie the process. Expression of epitope-tagged m41 during viral infection shows localization to Golgi. The mechanism of protection remains to be elucidated.

HCMV IE 1 p72 and IE 2 p86 are nuclear proteins that regulate transcription of cellular and viral genes (Chapters 17 and 18) and each can associate with cellular proteins. Cellular transcription factor E2F is modulated by IE 1 p72 interaction with the Rb-pocket protein p107 (Poma et al., 1996) or by IE 2 p86 interaction with pRB (Hagemeier et al., 1994). Regulation of E2F1 is mediated by binding to IE 1 p72 (Margolis et al., 1995). IE 1 p72 and IE 2 p86 suppress apoptosis induced by TNF or E1B19K defective adenovirus (Zhu et al., 1995) and anti-apoptotic activity maps to disparate sequences without any hint of mechanism. Importantly, fibroblasts constitutively expressing IE 1 p72 that have been used to complement growth of IE 1 p72 mutant viruses do not exhibit any obvious altered cell cycle progression or susceptibility to apoptosis. In transient assays, a genomic clone including IE 1 p72 and IE 2 p86 rescues a temperature sensitive derivative of TAF _II250 mutant cells (ts 13) from transcriptional repression and apoptosis but not cell cycle arrest (Lukac et al., 1997). Further analysis indicated either IE 2 p86 or IE 1 p72 activates the PI 3 kinase pathway and AKT as a consequence (Yu and Alwine, 2002) similar to the response of these prosurvival pathways to infection (Johnson et al., 2001b), but the role of IE 1 p72 and IE 2 p86 as suggested by the TAF _II250 mutant cells has not been extended to natural infection. IE 2 p86 but not IE 1 p72 protects from overexpression of p53 in smooth muscle cells (Tanaka et al., 1999). In contrast IE 2 p86 but not IE 1 p72 expression in endothelial cells induces apoptosis (Wang et al., 2000). Control of cell-intrinsic responses is the suggested mechanism for HCMV IE 1 facilitation of MCMV replication in human cells (Tang and Maul, 2006). These data may suggest that any potential protective role includes both an induction-specific and a cell-type specific component.

Alteration of extrinsic cell death pathways during infection

TNF-R1 surface expression levels decrease following HCMV infection of macrophage or astrocytoma cell lines (Baillie et al., 2003) as well as following MCMV infection of bone marrow derived macrophages (Popkin and Virgin, 2003). Although the viral factors required for the down-regulation have not been identified, either virus seems to employ a post-transcriptional mechanism. Uninfected fibroblasts insensitive to TRAIL mediated apoptosis become sensitive to TRAIL following HCMV infection (Sedger et al., 1999). Infection increases expression of death-inducing TRAIL -R1 and TRAIL -R2, but not decoy receptors TRAIL -R3 and TRAIL -R4. Analysis of HHV -7 revealed downregulation of TRAIL -R1 but not TRAIL -R2, TNF -R1, TNF -R2, or Fas during infection of CD 4 cells (Secchiero et al., 2001). Infections by other betaherpesviruses maintain the Fas receptor available for activation. Fibroblasts infected by HCMV and MCMV are susceptible to Fas-mediated apoptosis (Chaudhuri et al., 1999; Goldmacher et al., 1999; Menard et al., 2003; Skaletskaya et al., 2001) and some, but not all, strains of HCMV may increase Fas receptor surface expression (Chaudhuri et al., 1999; Chiou et al., 2001).

HCMV encodes a potential TNF -receptor homolog (Benedict et al., 1999), although this protein has not been assigned any role in blocking apoptosis. UL 144 encodes a glycoprotein consisting of a leader peptide, cysteine-rich domains (CRD), membrane extension region, transmembrane domain, and a short cytoplasmic tail. UL 144 exhibits dramatic strain-to-strain sequence variability (Bale, 2001; Lurain, 1999), although the protein has highly conserved transmembrane and cytoplasmic domains. UL 144 is the closest known relative of the cell surface herpesvirus entry mediator (HVEM; Chapter 7) protein, whose normal function is as a cognate ligand for the B- and T-lymphocyte attenuator (Sedy et al., 2005). UL 144 binds B and T lymphocyte attenuator (BTLA) and inhibits T-cell proliferation.

Summary

The betaherpesviruses all appear to alter cell cycle and to block rather than promote apoptosis during infection. Cytomegaloviruses prevent cellular DNA synthesis whereas roseolaviruses allow continued cellular DNA synthesis during productive infection, although cell division is blocked in all of these viruses. While none of the betaherpesviruses has been implicated in malignancy, such an impact on the host cell has raised interest of persistent betaherpesvirus infection in certain chronic diseases. These viruses encode a wide variety of functions that modulate the cellular environment, including functions that modulate cell cycle progression and that derail apoptosis induced by either intrinsic or extrinsic mediators.

References

• Abate D. A., Watanabe S., Mocarski E. S. Major human cytomegalovirus structural protein pp65 (ppUL83) prevents interferon response factor 3 activation in the interferon response. J. Virol. 2004;78:10995–11006. [PMC free article: PMC521853] [PubMed: 15452220]
• AbuBakar S., Au W. W., Legator M. S., Albrecht T. Induction of chromosome aberrations and mitotic arrest by cytomegalovirus in human cells. Environ. Mol. Mutagen. 1988;12:409–420. [PubMed: 2847923]
• Adair R., Liebisch G. W., Poley A. M., and Colberg-2003Complex alternative processing of human cytomegalovirus UL 37 pre-mRNA J. Gen. Virol. 843353–3358. [PubMed: 14645916]
• Adamo J. E., Schroer J., Shenk T. Human cytomegalovirus TRS 1 protein is required for efficient assembly of DNA-containing capsids. J. Virol. 2004;78:10221–10229. [PMC free article: PMC516402] [PubMed: 15367587]
• Albrecht T., Boldogh I., Fons M. P. 1992Receptor-initiated activation of cells and their oncogenes by herpes-family viruses J. Invest. Dermatol. 98(6 Suppl), 29S–35S. [PubMed: 1316926]
• Allart S., Martin H., Detraves C., Terrasson J., Caput D., Davrinche C. Human cytomegalovirus induces drug resistance and alteration of programmed cell death by accumulation of deltaN-p73alpha. J. Biol. Chem. 2002;277:29063–29068. [PubMed: 12034725]
• Andoniou C. E., Andrews D. M., Manzur M., Ricciardi-Castagnoli P., Degli-Esposti M. A. A novel checkpoint in the Bcl-2-regulated apoptotic pathway revealed by murine cytomegalovirus infection of dendritic cells. J. Cell Bio. 2004;166:827–837. [PMC free article: PMC2172116] [PubMed: 15353550]
• Arnoult D., Bartle L. M., Skaletskaya A., et al. Cytomegalovirus cell death suppressor vMIA blocks Bax- but not Bak-mediated apoptosis by binding and sequestering Bax at mitochondria. Proc. Natl Acad. Sci. USA. 2004;101:7988–7993. [PMC free article: PMC419544] [PubMed: 15148411]
• Baillie J., Sahlender D. A., Sinclair J. H. Human cytomegalovirus infection inhibits tumor necrosis factor alpha (TNF-alpha) signaling by targeting the 55-kilodalton TNF -alpha receptor. J. Virol. 2003;77:7007–7016. [PMC free article: PMC156201] [PubMed: 12768019]
• Belzacq A. S., Hamel, Vieira H. L., et al. Adenine nucleotide translocator mediates the mitochondrial membrane permeabilization induced by lonidamine, arsenite and CD 437. Oncogene. 2001;20:7579–7587. [PubMed: 11753636]
• Benedict C. A., Butrovich K. D., Lurain N. S., et al. Cutting edge: a novel viral TNF receptor superfamily member in virulent strains of human cytomegalovirus. J. Immunol. 1999;162:6967–6970. [PubMed: 10358135]
• Benedict C. A., Angulo A., Patterson G., et al. Neutrality of the canonical NF -kappaB-dependent pathway for human and murine cytomegalovirus transcription and replication in vitro. J. Virol. 2004;78:741–750. [PMC free article: PMC368812] [PubMed: 14694106]
• Biswas N., Sanchez V., Spector D. H. Human cytomegalovirus infection leads to accumulation of geminin and inhibition of the licensing of cellular DNA replication. J. Virol. 2003;77:2369–2376. [PMC free article: PMC141111] [PubMed: 12551974]
• Blankenship C. A., Shenk T. Mutant human cytomegalovirus lacking the immediate-early TRS 1 coding region exhibits a late defect. J. Virol. 2002;76:12290–12299. [PMC free article: PMC136912] [PubMed: 12414969]
• Boehme K. W., Singh J., Perry S. T., Compton T. Human cytomegalovirus elicits a coordinated cellular antiviral response via envelope glycoprotein B. J. Virol. 2004;78:1202–1211. [PMC free article: PMC321386] [PubMed: 14722275]
• Boldogh I., AbuBakar S., Albrecht T. Activation of proto-oncogenes: an immediate early event in human cytomegalovirus infection. Science. 1990;247:561–564. [PubMed: 1689075]
• Boldogh I., AbuBakar S., Millinoff D., Deng C. Z., Albrecht T. Cellular oncogene activation by human cytomegalovirus. Lack of correlation with virus infectivity and immediate early gene expression. Arch. Virol. 1991;118:163–177. [PubMed: 1712580]
• Boldogh I., Bui T. K., Szaniszlo P., Bresnahan W. A., Albrecht T., Hughes T. K. Novel activation of gamma-interferon in nonimmune cells during human cytomegalovirus replication. Proc. Soc. Exp. Biol. Med. 1997;215:66–73. [PubMed: 9142139]
• Bonin L. R., McDougall J. K. Human cytomegalovirus IE 2 86-kilodalton protein binds p53 but does not abrogate G1 checkpoint function. J. Virol. 1997;71:5861–5870. [PMC free article: PMC191841] [PubMed: 9223475]
• Boya P., Polo R. A., Poncet D., et al. , Gonzalez-2003aMitochondrial membrane permeabilization is a critical step of lysosome-initiated apoptosis induced by hydroxychloroquine Oncogene 223927–3936. [PubMed: 12813466]
• Boya P., Morales M. C., Polo R. A., et al. , Gonzalez-2003bThe chemopreventive agent N-(4-hydroxyphenyl)retinamide induces apoptosis through a mitochondrial pathway regulated by proteins from the Bcl-2 family Oncogene 226220–6230. [PubMed: 13679861]
• Boya P., Pauleau A. L., Poncet D., Polo R. A., Zamzami N., Kroemer G., Gonzalez-2004Viral proteins targeting mitochondria: controlling cell death Biochim. Biophys. Acta 1659178–189. [PubMed: 15576050]
• Boyle K. A., Pietropaolo R. L., Compton T. Engagement of the cellular receptor for glycoprotein B of human cytomegalovirus activates the interferon-responsive pathway. Mol. Cell. Biol. 1999;19:3607–3613. [PMC free article: PMC84158] [PubMed: 10207084]
• Bresnahan W. A., Shenk T. E. UL82 virion protein activates expression of immediate early viral genes in human cytomegalovirus-infected cells. Proc. Natl Acad. Sci. USA. 2000;97:14506–14511. [PMC free article: PMC18949] [PubMed: 11121054]
• Bresnahan W. A., Boldogh I., Thompson E. A., Albrecht T. Human cytomegalovirus inhibits cellular DNA synthesis and arrests productively infected cells in late G1. Virology. 1996;224:150–160. [PubMed: 8862409]
• Bresnahan W. A., Thompson E. A., Albrecht T. Human cytomegalovirus infection results in altered Cdk2 subcellular localization. J. Gen. Virol. 1997;78:1993–1997. [PubMed: 9266999]
• Browne E. P., Shenk T. Human cytomegalovirus UL 83-coded pp65 virion protein inhibits antiviral gene expression in infected cells. Proc. Natl Acad. Sci. USA. 2003;100:11439–11444. [PMC free article: PMC208776] [PubMed: 12972646]
• Browne E. P., Wing B., Coleman D., Shenk T. Altered cellular mRNA levels in human cytomegalovirus-infected fibroblasts: viral block to the accumulation of antiviral mRNAs. J. Virol. 2001;75:12319–12330. [PMC free article: PMC116128] [PubMed: 11711622]
• Brune W., Menard C., Heesemann J., Koszinowski U. H. A ribonucleotide reductase homologue of cytomegalovirus and endothelial cell tropism. Science. 2001;291:303–305. [PubMed: 11209080]
• Brune W., Nevels M., Shenk T. Murine cytomegalovirus m41 open reading frame encodes a Golgi-localized antiapoptotic protein. J. Virol. 2003;77:11633–11643. [PMC free article: PMC229354] [PubMed: 14557649]
• Cantrell S. R., Bresnahan W. A. Interaction between the human cytomegalovirus UL 82 gene product (pp71) and hDaxx regulates immediate-early gene expression and viral replication. J. Virol. 2005;79:7792–7802. [PMC free article: PMC1143679] [PubMed: 15919932]
• Caposio P., Dreano M., Garotta G., Gribaudo G., Landolfo S. Human cytomegalovirus stimulates cellular IKK 2 activity and requires the enzyme for productive replication. J. Virol. 2004;78:3190–3195. [PMC free article: PMC353729] [PubMed: 14990741]
• Cassady K. A. Human cytomegalovirus TRS 1 and IRS 1 gene products block the double-stranded-RNA-activated host protein shutoff response induced by herpes simplex virus type 1 infection. J. Virol. 2005;79:8707–8715. [PMC free article: PMC1168740] [PubMed: 15994764]
• Castillo J. P., Yurochko A. D., Kowalik T. F. Role of human cytomegalovirus immediate–early proteins in cell growth control. J. Virol. 2000;74:8028–8037. [PMC free article: PMC112335] [PubMed: 10933712]
• Chaudhuri A. R., Jeor S., Maciejewski J. P., St. 1999Apoptosis induced by human cytomegalovirus infection can be enhanced by cytokines to limit the spread of virus Exp. Hematol. 271194–1203. [PubMed: 10390195]
• Cheeseman S. H., Rinaldo C. J., Hirsch M. S. Use of interferon in cytomegalovirus infections in man. Tex. Rep. Biol. Med. 1977;35:523–527. [PubMed: 211670]
• Child S. J., Jarrahian S., Harper V. M., Geballe A. P. Complementation of vaccinia virus lacking the double-stranded RNA -binding protein gene E3L by human cytomegalovirus. J. Virol. 2002;76:4912–4918. [PMC free article: PMC136161] [PubMed: 11967308]
• Child S. J., Hakki M., Niro, Geballe A. P. Evasion of cellular antiviral responses by human cytomegalovirus TRS 1 and IRS 1. J. Virol. 2004;78:197–205. [PMC free article: PMC303427] [PubMed: 14671101]
• Chiou S. H., Liu J. H., Hsu W. M., et al. Up-regulation of Fas ligand expression by human cytomegalovirus immediate-early gene product 2: a novel mechanism in cytomegalovirus- induced apoptosis in human retina. J. Immunol. 2001;167:4098–4103. [PubMed: 11564832]
• Compton T. Receptors and immune sensors: the complex entry path of human cytomegalovirus. Trends Cell Biol. 2004;14:5–8. [PubMed: 14729174]
• Cuconati A., White E. Viral homologs of BCL -2: role of apoptosis in the regulation of virus infection. Genes Dev. 2002;16:2465–2478. [PubMed: 12368257]
• DeMeritt I. B., Milford L. E., Yurochko A. D. Activation of the NF -kappaB pathway in human cytomegalovirus-infected cells is necessary for efficient transactivation of the major immediate–early promoter. J. Virol. 2004;78:4498–4507. [PMC free article: PMC387686] [PubMed: 15078930]
• DeFilippis V., Fruh K. Rhesus cytomegalovirus particles prevent activation of interferon regulatory factor 3. J. Virol. 2005;79:6419–6431. [PMC free article: PMC1091669] [PubMed: 15858025]
• DeFilippis V. R., Robinson B., Keck T. M., Hansen S. G., Nelson J. A., Fruh K. J. Interferon regulatory factor 3 is necessary for induction of antiviral genes during human cytomegalovirus infection. J. Virol. 2006;80:1032–1037. [PMC free article: PMC1346858] [PubMed: 16379004]
• DeFilippis V., Fruh K. Rhesus cytomegalovirus particles prevent activation of interferon regulatory factor 3. J. Virol. 2005;79(10):6419–31. [PMC free article: PMC1091669] [PubMed: 15858025]
• Deng C. Z., AbuBakar S., Fons M. P., et al. Cytomegalovirus-enhanced induction of chromosome aberrations in human peripheral blood lymphocytes treated with potent genotoxic agents. Environ. Mol. Mutagen. 1992;19:304–310. [PubMed: 1376251]
• Dittmer D., Mocarski E. S. Human cytomegalovirus infection inhibits G1/S transition. J. Virol. 1997;71:1629–1634. [PMC free article: PMC191221] [PubMed: 8995690]
• Dunn W., Chou C., Li H., et al. Functional profiling of a human cytomegalovirus genome. Proc. Natl Acad. Sci. USA. 2003;100:14223–14228. [PMC free article: PMC283573] [PubMed: 14623981]
• Eickhoff J. E., Cotten M. NF-kappaB activation can mediate inhibition of human cytomegalovirus replication. J. Gen. Virol. 2005;86:285–295. [PubMed: 15659747]
• Everett R. D. Interactions between DNA viruses, ND 10 and the DNA damage response. Cell Microbiol. 2006;8:365–374. [PubMed: 16469050]
• Everett H., McFadden G. Apoptosis: an innate immune response to virus infection. Trends Microbiol. 1999;7:160–165. [PubMed: 10217831]
• Everett H., McFadden G. Viral proteins and the mitochondrial apoptotic checkpoint. Cytokine Growth Factor Rev. 2001;12:181–188. [PubMed: 11325601]
• Evers D. L., Wang X., Huang E. S. Cellular stress and signal transduction responses to human cytomegalovirus infection. Microbes. Infect. 2004;6:1084–1093. [PubMed: 15380778]
• Ferri K. F., Kroemer G. 2001Organelle-specific initiation of cell death pathways Nat. Cell Biol. 3E255–E263. [PubMed: 11715037]
• Rehwaldt L. M., Wood C., Chandran B.Flebbe-2000Characterization of transcripts expressed from human herpesvirus 6A strain GS immediate-early region B U16–U17 open reading frames J. Virol. 7411040–11054. [PMC free article: PMC113184] [PubMed: 11069999]
• Flores E. R., Tsai K. Y., Crowley D., et al. p63 and p73 are required for p53-dependent apoptosis in response to DNA damage. Nature. 2002;416:560–564. [PubMed: 11932750]
• Fortunato E. A., Spector D. H. p53 and RPA are sequestered in viral replication centers in the nuclei of cells infected with human cytomegalovirus. J. Virol. 1998;72:2033–2039. [PMC free article: PMC109496] [PubMed: 9499057]
• Fortunato E. A., Aquila M. L., Spector D. H., Dell’2000aSpecific chromosome 1 breaks induced by human cytomegalovirus Proc. Natl Acad. Sci. USA 97853–858. [PMC free article: PMC15420] [PubMed: 10639169]
• Fortunato E. A., McElroy A. K., Sanchez I., Spector D. H. Exploitation of cellular signaling and regulatory pathways by human cytomegalovirus. Trends Microbiol. 2000b;8:111–119. [PubMed: 10707064]
• Fortunato E. A., Sanchez V., Yen J. Y., Spector D. H. Infection of cells with human cytomegalovirus during S phase results in a blockade to immediate–early gene expression that can be overcome by inhibition of the proteasome. J. Virol. 2002;76:5369–5379. [PMC free article: PMC137046] [PubMed: 11991965]
• Giaccia A. J., Kastan M. B. The complexity of p53 modulation: emerging patterns from divergent signals. Genes Dev. 1998;12:2973–2983. [PubMed: 9765199]
• Goldmacher V. S. Cell death suppressors encoded by cytomegalovirus. Prog. Mol. Subcell Biol. 2004;36:1–18. [PubMed: 15171604]
• Goldmacher V. S., Bartle L. M., Skaletskaya A., et al. A cytomegalovirus-encoded mitochondria-localized inhibitor of apoptosis structurally unrelated to Bcl-2. Proc. Natl Acad. Sci. USA. 1999;96:12536–12541. [PMC free article: PMC22976] [PubMed: 10535957]
• Hagemeier C., Caswell R., Hayhurst G., Sinclair J., Kouzarides T. Functional interaction between the HCMV IE 2 transactivator and the retinoblastoma protein. EMBO J. 1994;13:2897–2903. [PMC free article: PMC395171] [PubMed: 8026474]
• Hahn G., Khan H., Baldanti F., Koszinowski U. H., Revello M. G., Gerna G. The human cytomegalovirus ribonucleotide reductase homologue UL 45 is dispensable for growth in endothelial cells, as determined by a BAC -cloned clinical isolate of human cytomegalovirus with preserved wild-type characteristics. J. Virol. 2002;76:9551–9555. [PMC free article: PMC136448] [PubMed: 12186938]
• Hakki M., Geballe A. P. Double-stranded RNA binding by human cytomegalovirus pTRS1. J. Virol. 2005;79:7311–7318. [PMC free article: PMC1143672] [PubMed: 15919885]
• Haupt S., Berger M., Goldberg Z., Haupt Y. Apoptosis – the p53 network. J. Cell Sci. 2003;116:4077–4085. [PubMed: 12972501]
• Hayajneh W. A., Poley A. M., Skaletskaya A., et al. , Colberg-2001The sequence and antiapoptotic functional domains of the human cytomegalovirus UL 37 exon 1 immediate early protein are conserved in multiple primary strains Virology 279233–240. [PubMed: 11145905]
• Hayashi M. L., Blankenship C., Shenk T. Human cytomegalovirus UL 69 protein is required for efficient accumulation of infected cells in the G1 phase of the cell cycle. Proc. Natl Acad. Sci. USA. 2000;97:2692–2696. [PMC free article: PMC15991] [PubMed: 10706637]
• Heider J. A., Bresnahan W. A., Shenk T. E. Construction of a rationally designed human cytomegalovirus variant encoding a temperature-sensitive immediate-early 2 protein. Proc. Natl Acad. Sci. USA. 2002;99:3141–3146. [PMC free article: PMC122486] [PubMed: 11867756]
• Hertel L., Mocarski E. S. Global analysis of host cell gene expression late during cytomegalovirus infection reveals extensive dysregulation of cell cycle gene expression and induction of Pseudomitosis independent of US 28 function. J. Virol. 2004;78:11988–12011. [PMC free article: PMC523267] [PubMed: 15479839]
• Hofmann H., Sindre H., Stamminger T. Functional Interaction between the pp71 Protein of Human Cytomegalovirus and the PML-Interacting Protein Human Daxx. J. Virol. 2002;76:5769–5783. [PMC free article: PMC137040] [PubMed: 11992005]
• Holmes A. R., Rasmussen L., Merigan T. C. Factors affecting the interferon sensitivity of human cytomegalovirus. Intervirology. 1978;9:48–55. [PubMed: 202571]
• Inoue Y., Yasukawa M., Fujita S. Induction of T-cell apoptosis by human herpesvirus 6. J. Virol. 1997;71:3751–3759. [PMC free article: PMC191525] [PubMed: 9094650]
• Ishov A. M., Vladimirova O. V., Maul G. G. Daxx-mediated accumulation of human cytomegalovirus tegument protein pp71 at ND 10 facilitates initiation of viral infection at these nuclear domains. J. Virol. 2002;76:7705–7712. [PMC free article: PMC136388] [PubMed: 12097584]
• Isomura H., Tsurumi T., Stinski M. F. Role of the proximal enhancer of the major immediate-early promoter in human cytomegalovirus replication. J. Virol. 2004;78:12788–12799. [PMC free article: PMC525030] [PubMed: 15542631]
• Jan G., Belzacq A. S., Haouzi D., et al. Propionibacteria induce apoptosis of colorectal carcinoma cells via short-chain fatty acids acting on mitochondria. Cell Death Differ. 2002;9:179–188. [PubMed: 11840168]
• Jault F. M., Jault J. M., Ruchti F., et al. Cytomegalovirus infection induces high levels of cyclins, phosphorylated Rb, and p53, leading to cell cycle arrest. J. Virol. 1995;69:6697–6704. [PMC free article: PMC189579] [PubMed: 7474079]
• Johnson R. A., Ma X. L., Yurochko A. D., Huang E. S. The role of MKK 1/2 kinase activity in human cytomegalovirus infection. J. Gen. Virol. 2001a;82:493–497. [PubMed: 11172089]
• Johnson R. A., Wang X., Ma X. L., Huong S. M., Huang E. S. Human cytomegalovirus up-regulates the phosphatidylinositol 3-kinase (PI3-K) pathway: inhibition of PI 3-K activity inhibits viral replication and virus-induced signaling. J. Virol. 2001b;75:6022–6032. [PMC free article: PMC114318] [PubMed: 11390604]
• Jurak I., Brune W. Induction of apoptosis limits cytomegalovirus cross-species infection. EMBO J. 2006;25:2634–2642. [PMC free article: PMC1478185] [PubMed: 16688216]
• Kalejta R. F., Shenk T. 2002Manipulation of the cell cycle by human cytomegalovirus Front Biosci. 7D295–D306. [PubMed: 11779699]
• Khan S., Zimmermann A., Basler M., Groettrup M., Hengel H. A cytomegalovirus inhibitor of gamma interferon signaling controls immunoproteasome induction. J. Virol. 2004;78:1831–1842. [PMC free article: PMC369451] [PubMed: 14747547]
• Korioth F., Maul G. G., Plachter B., Stamminger T., Frey J. The nuclear domain 10 (ND10) is disrupted by the human cytomegalovirus gene product IE 1. Exp. Cell. Res. 1996;229:155–158. [PubMed: 8940259]
• Kouzarides T., Bankier A. T., Satchwell S. C., Preddy E., Barrell B. G. An immediate early gene of human cytomegalovirus encodes a potential membrane glycoprotein. Virology. 1988;165:151–164. [PubMed: 2838954]
• Kowalik T. F., Wing B., Haskill J. S., Azizkhan J. C., Baldwin A. J., Huang E. S. Multiple mechanisms are implicated in the regulation of NF -kappa B activity during human cytomegalovirus infection. Proc. Natl Acad. Sci. USA. 1993;90:1107–1111. [PMC free article: PMC45820] [PubMed: 8381532]
• Langelier Y., Bergeron S., Chabaud S., et al. The R1 subunit of herpes simplex virus ribonucleotide reductase protects cells against apoptosis at, or upstream of, caspase-8 activation. J. Gen. Virol. 2002;83:2779–2789. [PubMed: 12388814]
• Lodoen M. B., Lanier L. L. Viral modulation of NK cell immunity. Nat. Rev. Microbiol. 2005;3:59–69. [PubMed: 15608700]
• Lu M., Shenk T. Human cytomegalovirus infection inhibits cell cycle progression at multiple points, including the transition from G1 to S. J. Virol. 1996;70:8850–8857. [PMC free article: PMC190981] [PubMed: 8971013]
• Lu M., Shenk T. Human cytomegalovirus UL 69 protein induces cells to accumulate in G1 phase of the cell cycle. J. Virol. 1999;73:676–683. [PMC free article: PMC103874] [PubMed: 9847373]
• Lukac D. M., Harel N. Y., Tanese N., Alwine J. C. TAF-like functions of human cytomegalovirus immediate-early proteins. J. Virol. 1997;71:7227–7239. [PMC free article: PMC192063] [PubMed: 9311796]
• Marchini A., Liu H., Zhu H. Human cytomegalovirus with IE -2 (UL122) deleted fails to express early lytic genes. J. Virol. 2001;75:1870–1878. [PMC free article: PMC114097] [PubMed: 11160686]
• Margolis M. J., Pajovic S., Wong E. L., et al. Interaction of the 72-kilodalton human cytomegalovirus IE 1 gene product with E2F1 coincides with E2F-dependent activation of dihydrofolate reductase transcription. J. Virol. 1995;69:7759–7767. [PMC free article: PMC189718] [PubMed: 7494286]
• Mate J. L., Ariza A., Munoz A., Molinero J. L., Lopez D., Palacios J. J., and Navas-1998Induction of proliferating cell nuclear antigen and Ki-67 expression by cytomegalovirus infection J. Pathol. 184279–282. [PubMed: 9614380]
• McCormick A. L., Skaletskaya A., Barry P. A., Mocarski E. S., Goldmacher V. S. Differential function and expression of the viral inhibitor of caspase 8-induced apoptosis (vICA) and the viral mitochondria-localized inhibitor of apoptosis (vMIA) cell death suppressors conserved in primate and rodent cytomegaloviruses. Virology. 2003a;316:221–233. [PubMed: 14644605]
• McCormick A. L., Smith V. L., Chow D., Mocarski E. S. Disruption of mitochondrial networks by the human cytomegalovirus UL 37 gene product viral mitochondrion-localized inhibitor of apoptosis. J. Virol. 2003b;77:631–641. [PMC free article: PMC140587] [PubMed: 12477866]
• McCormick A. L., Meiering C. D., Smith G. B., Mocarski E. S. Mitochondrial cell death suppressors carried by human and murine cytomegalovirus confer resistance to proteasome inhibitor-induced apoptosis. J. Virol. 2005;79:12205–12217. [PMC free article: PMC1211555] [PubMed: 16160147]
• Menard C., Wagner M., Ruzsics Z., et al. Role of murine cytomegalovirus US 22 gene family members in replication in macrophages. J. Virol. 2003;77:5557–5570. [PMC free article: PMC154053] [PubMed: 12719548]
• Menegazzi P., Galvan M., Rotola A., et al. Temporal mapping of transcripts in human herpesvirus-7. J. Gen. Virol. 1999;80:2705–2712. [PubMed: 10573164]
• Mocarski E. S. Immunomodulation by cytomegaloviruses: manipulative strategies beyond evasion. Trends Microbiol. 2002;10:332–339. [PubMed: 12110212]
• Mocarski E. S. Jr. Immune escape and exploitation strategies of cytomegaloviruses: impact on and imitation of the major histocompatibility system. Cell Microbiol. 2004;6:707–717. [PubMed: 15236638]
• Knipe, Howley, Griffin, et al. Mocarski, E. S., Jr. and Courcelle, C. T. (2001). Cytomegaloviruses and their replication. ed. In Fields Virology 4th edn., ed. . Vol. 2, pp. 2629–2673. Philadelphia: Lippincott, Williams & Wilkins;
• Muganda P., Carrasco R., Qian Q. The human cytomegalovirus IE 2 86 kDa protein elevates p53 levels and transactivates the p53 promoter in human fibroblasts. Cell Mol. Biol., (Noisy-le-grand). 1998;44:321–331. [PubMed: 9593583]
• Murphy E. A., Streblow D. N., Nelson J. A., Stinski M. F. The human cytomegalovirus IE 86 protein can block cell cycle progression after inducing transition into the S phase of permissive cells. J. Virol. 2000;74:7108–7118. [PMC free article: PMC112229] [PubMed: 10888651]
• Navarro L., Mowen K., Rodems S., et al. Cytomegalovirus activates interferon immediate-early response gene expression and an interferon regulatory factor 3-containing interferon- stimulated response element-binding complex. Mol. Cell Biol. 1998;18:3796–3802. [PMC free article: PMC108963] [PubMed: 9632763]
• Netterwald J. R., Jones T. R., Britt W. J., Yang S. J., McCrone I. P., Zhu H. Postattachment events associated with viral entry are necessary for induction of interferon- stimulated genes by human cytomegalovirus. J. Virol. 2004;78:6688–6691. [PMC free article: PMC416537] [PubMed: 15163760]
• Patrone M., Percivalle E., Secchi M., et al. The human cytomegalovirus UL 45 gene product is a late, virion-associated protein and influences virus growth at low multiplicities of infection. J. Gen. Virol. 2003;84:3359–3370. [PubMed: 14645917]
• Patterson C. E., Shenk T. Human cytomegalovirus UL 36 protein is dispensable for viral replication in cultured cells. J. Virol. 1999;73:7126–7131. [PMC free article: PMC104234] [PubMed: 10438798]
• Penfold M. E., Mocarski E. S. Formation of cytomegalovirus DNA replication compartments defined by localization of viral proteins and DNA synthesis. Virology. 1997;239:46–61. [PubMed: 9426445]
• Polster B. M., Pevsner J., Hardwick J. M. Viral Bcl-2 homologues and their role in virus replication and associated diseases. Biochim. Biophys. Acta. 2004;1644:211–227. [PubMed: 14996505]
• Poma E. E., Kowalik T. F., Zhu L., Sinclair J. H., Huang E. S. The human cytomegalovirus IE 1–72 protein interacts with the cellular p107 protein and relieves p107-mediated transcriptional repression of an E2F-responsive promoter. J. Virol. 1996;70:7867–7877. [PMC free article: PMC190858] [PubMed: 8892909]
• Poncet D., Larochette N., Pauleau A. L., et al. An anti-apoptotic viral protein that recruits Bax to mitochondria. J. Biol. Chem. 2004;279:22605–22614. [PubMed: 15004026]
• Popkin D. L., Virgin H. W. Murine cytomegalovirus infection inhibits tumor necrosis factor alpha responses in primary macrophages. J. Virol. 2003;77:10125–10130. [PMC free article: PMC224571] [PubMed: 12941924]
• Preston C. M., Harman A. N., Nicholl M. J. Activation of interferon response factor-3 in human cells infected with herpes simplex virus type 1 or human cytomegalovirus. J. Virol. 2001;75:8909–8916. [PMC free article: PMC114459] [PubMed: 11533154]
• Reboredo M., Greaves R. F., Hahn G. Human cytomegalovirus proteins encoded by UL 37 exon 1 protect infected fibroblasts against virus-induced apoptosis and are required for efficient virus replication. J. Gen. Virol. 2004;85:3555–3567. [PubMed: 15557228]
• Rodriguez J. E., Loepfe T. R., Swack N. S. Beta interferon production in primed and unprimed cells infected with human cytomegalovirus. Arch. Virol. 1987;94:177–189. [PubMed: 3034207]
• Roumier T., Vieira H. L., Castedo M., et al. The C-terminal moiety of HIV -1 Vpr induces cell death via a caspase-independent mitochondrial pathway. Cell Death Differ. 2002;9:1212–1219. [PubMed: 12404120]
• Saffert R. T., Kalejta R. F. Inactivating a cellular intrinsic immune defense mediated by Daxx is the mechanism through which the human cytomegalovirus pp71 protein stimulates viral immediate-early gene expression. J. Virol. 2006;80:3863–3871. [PMC free article: PMC1440479] [PubMed: 16571803]
• Salvant B. S., Fortunato E. A., Spector D. H. Cell cycle dysregulation by human cytomegalovirus: influence of the cell cycle phase at the time of infection and effects on cyclin transcription. J. Virol. 1998;72:3729–3741. [PMC free article: PMC109595] [PubMed: 9557655]
• Sambucetti L. C., Cherrington J. M., Wilkinson G. W. G., Mocarski E. S. NF-kB activation of the cytomegalovirus enhancer is mediated by a viral transactivator and by T cell stimulation. EMBO J. 1989;8:4251–4258. [PMC free article: PMC401626] [PubMed: 2556267]
• Sanchez V., McElroy A. K., Spector D. H. Mechanisms governing maintenance of Cdk1/cyclin B1 kinase activity in cells infected with human cytomegalovirus. J. Virol. 2003;77:13214–13224. [PMC free article: PMC296097] [PubMed: 14645578]
• Sanchez V., Clark C. L., Yen J. Y., Dwarakanath R., Spector D. H. Viable human cytomegalovirus recombinant virus with an internal deletion of the IE 2 86 gene affects late stages of viral replication. J. Virol. 2002;76:2973–2989. [PMC free article: PMC135995] [PubMed: 11861863]
• Secchiero P., Bertolaso L., Casareto L., et al. Human herpesvirus 7 infection induces profound cell cycle perturbations coupled to disregulation of cdc2 and cyclin B and polyploidization of CD 4(+) T cells. Blood. 1998;92:1685–1696. [PubMed: 9716597]
• Secchiero P., Mirandola P., Zella D., et al. Human herpesvirus 7 induces the functional up-regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) coupled to TRAIL -R1 down-modulation in CD 4(+) T cells. Blood. 2001;98:2474–2481. [PubMed: 11588045]
• Sedger L. M., Shows D. M., Blanton R. A., et al. IFN-gamma mediates a novel antiviral activity through dynamic modulation of TRAIL and TRAIL receptor expression. J. Immunol. 1999;163:920–926. [PubMed: 10395688]
• Sedy J. R., Gavrieli M., Potter K. G., et al. B and T lymphocyte attenuator regulates T cell activation through interaction with herpesvirus entry mediator. Nat. Immunol. 2005;6:90–98. [PubMed: 15568026]
• Simmen K. A., Singh J., Luukkonen B. G., et al. Global modulation of cellular transcription by human cytomegalovirus is initiated by viral glycoprotein B. Proc. Natl Acad. Sci. USA. 2001;98:7140–7145. [PMC free article: PMC34636] [PubMed: 11390970]
• Skaletskaya A., Bartle L. M., Chittenden T., McCormick A. L., Mocarski E. S., Goldmacher V. S. A cytomegalovirus-encoded inhibitor of apoptosis that suppresses caspase-8 activation. Proc. Natl Acad. Sci. USA. 2001;98:7829–7834. [PMC free article: PMC35427] [PubMed: 11427719]
• Smith G. B., Mocarski E. S. 2005GADD45a directly enhances the mitochondrial apoptosis inhibitors Bcl-xL and vMIA Nat. Cell Biol. (submitted for publication).
• Song Y. J., Stinski M. F. Effect of the human cytomegalovirus IE 86 protein on expression of E2F-responsive genes: A DNA microarray analysis. Proc. Natl Acad. Sci. USA. 2002;99:2836–2841. [PMC free article: PMC122434] [PubMed: 11867723]
• Speir E., Modali R., Huang E. S., et al. Potential role of human cytomegalovirus and p53 interaction in coronary restenosis. Science. 1994;265:391–394. [PubMed: 8023160]
• Su Y., Adair R., Davis C. N., DiFronzo N. L., Poley A. M., and Colberg-2003Convergence of RNA cis elements and cellular polyadenylation factors in the regulation of human cytomegalovirus UL 37 exon 1 unspliced RNA production J. Virol. 7712729–12741. [PMC free article: PMC262569] [PubMed: 14610195]
• Tanaka K., Zou J. P., Takeda K., et al. Effects of human cytomegalovirus immediate-early proteins on p53- mediated apoptosis in coronary artery smooth muscle cells. Circulation. 1999;99:1656–1659. [PubMed: 10190872]
• Tavalai N., Papior P., Rechter S., Leis M., Stamminger T. Evidence for a role of the cellular ND 10 protein PML in mediating intrinsic immunity against human cytomegalovirus infections. J. Virol. 2006;80:8006–8018. [PMC free article: PMC1563799] [PubMed: 16873257]
• Tang Q., Maul G. G. Mouse cytomegalovirus crosses the species barrier with help from a few human cytomegalovirus proteins. J. Virol. 2006;80:7510–7521. [PMC free article: PMC1563706] [PubMed: 16840331]
• Tenney D. J., Poley A. M. and Colberg-1990RNA analysis and isolation of cDNAs derived from the human cytomegalovirus immediate-early region at 0.24 map units Intervirology 31203–214. [PubMed: 2165045]
• Tenney D. J., Poley A. M. and Colberg-1991aExpression of the human cytomegalovirus UL 36–38 immediate early region during permissive infection Virology 182199–210. [PubMed: 1850901]
• Tenney D. J., Poley A. M. and Colberg-1991bHuman cytomegalovirus UL 36–38 and US 3 immediate-early genes: temporally regulated expression of nuclear, cytoplasmic, and polysome-associated transcripts during infection J. Virol. 656724–6734. [PMC free article: PMC250752] [PubMed: 1658371]
• Vieira H. L., Belzacq A. S., Haouzi D., et al. The adenine nucleotide translocator: a target of nitric oxide, peroxynitrite, and 4-hydroxynonenal. Oncogene. 2001;20:4305–4316. [PubMed: 11466611]
• Wang J., Marker P. H., Belcher J. D., et al. Human cytomegalovirus immediate early proteins upregulate endothelial p53 function. FEBS Lett. 2000;474:213–216. [PubMed: 10838087]
• Wang X., Huong S. M., Chiu M. L., Traub N., Huang E. S., Raab-2003Epidermal growth factor receptor is a cellular receptor for human cytomegalovirus Nature 424456–461. [PubMed: 12879076]
• White E. A., Clark C. L., Sanchez V., Spector D. H. Small internal deletions in the human cytomegalovirus IE 2 gene result in nonviable recombinant viruses with differential defects in viral gene expression. J. Virol. 2004;78:1817–1830. [PMC free article: PMC369462] [PubMed: 14747546]
• Wiebusch L., Asmar J., Uecker R., Hagemeier C. Human cytomegalovirus immediate-early protein 2 (IE2)-mediated activation of cyclin E is cell-cycle-independent and forces S-phase entry in IE 2-arrested cells. J. Gen. Virol. 2003a;84:51–60. [PubMed: 12533700]
• Wiebusch L., Hagemeier C. Human cytomegalovirus 86-kilodalton IE 2 protein blocks cell cycle progression in G(1). J. Virol. 1999;73:9274–9283. [PMC free article: PMC112962] [PubMed: 10516036]
• Wiebusch L., Hagemeier C. The human cytomegalovirus immediate early 2 protein dissociates cellular DNA synthesis from cyclin-dependent kinase activation. Embo. J. 2001;20:1086–1098. [PMC free article: PMC145458] [PubMed: 11230132]
• Wiebusch L., Uecker R., Hagemeier C. Human cytomegalovirus prevents replication licensing by inhibiting MCM loading onto chromatin. EMBO Rep. 2003;4:42–46. [PMC free article: PMC1315807] [PubMed: 12524519]
• Yang S., Netterwald J., Wang W., Zhu H. Characterization of the elements and proteins responsible for interferon-stimulated gene induction by human cytomegalovirus. J. Virol. 2005;79:5027–5034. [PMC free article: PMC1069545] [PubMed: 15795288]
• Yu D., Silva M. C., Shenk T. Functional map of human cytomegalovirus AD 169 defined by global mutational analysis. Proc. Natl Acad. Sci. USA. 2003;100:12396–12401. [PMC free article: PMC218769] [PubMed: 14519856]
• Yu Y., Alwine J. C. Human cytomegalovirus major immediate–early proteins and simian virus 40 large T antigen can inhibit apoptosis through activation of the phosphatidylinositide 3‘-OH kinase pathway and the cellular kinase Akt. J. Virol. 2002;76:3731–3738. [PMC free article: PMC136103] [PubMed: 11907212]
• Yurochko A. D., Kowalik T. F., Huong S. M., Huang E. S. Human cytomegalovirus upregulates NF -kappa B activity by transactivating the NF -kappa B p105/p50 and p65 promoters. J. Virol. 1995;69:5391–5400. [PMC free article: PMC189383] [PubMed: 7636984]
• Yurochko A. D., Hwang E. S., Rasmussen L., Keay S., Pereira L., Huang E. S. The human cytomegalovirus UL 55 (gB) and UL 75 (gH) glycoprotein ligands initiate the rapid activation of Sp1 and NF -kappaB during infection. J. Virol. 1997a;71:5051–5059. [PMC free article: PMC191738] [PubMed: 9188570]
• Yurochko A. D., Mayo M. W., Poma E. E., Baldwin A. S. Jr, Huang E. S. Induction of the transcription factor Sp1 during human cytomegalovirus infection mediates upregulation of the p65 and p105/p50 NF -kappaB promoters. J. Virol. 1997b;71:4638–4648. [PMC free article: PMC191685] [PubMed: 9151857]
• Zhu H., Shen Y., Shenk T. Human cytomegalovirus IE 1 and IE 2 proteins block apoptosis. J. Virol. 1995;69:7960–7970. [PMC free article: PMC189741] [PubMed: 7494309]
• Zhu H., Cong J. P., Shenk T. Use of differential display analysis to assess the effect of human cytomegalovirus infection on the accumulation of cellular RNA s: induction of interferon-responsive RNA s. Proc. Natl Acad. Sci. USA. 1997;94:13985–13990. [PMC free article: PMC28419] [PubMed: 9391139]
• Zhu H., Cong J. P., Mamtora G., Gingeras T., Shenk T. Cellular gene expression altered by human cytomegalovirus: global monitoring with oligonucleotide arrays. Proc. Natl Acad. Sci. USA. 1998;95:14470–14475. [PMC free article: PMC24397] [PubMed: 9826724]