Alternative titles; symbols
HGNC Approved Gene Symbol: AMER1
SNOMEDCT: 254129003;
Cytogenetic location: Xq11.2 Genomic coordinates (GRCh38): X:64,185,117-64,205,708 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| Xq11.2 | Osteopathia striata with cranial sclerosis | 300373 | X-linked dominant | 3 |
AMER1 interacts with beta-catenin (CTNNB1; 116806) in a complex with AXIN1 (602816), beta-TRCP2 (FBXW11; 605651), and APC (611731) and promotes its proteasomal degradation. In addition to this repressive action on WNT (see 164820) signaling, AMER1 also regulates the distribution of APC between the microtubular cytoskeleton and the plasma membrane (summary by Jenkins et al., 2009).
Rivera et al. (2007) searched for genetic abnormalities in sporadic Wilms tumor (see 194070) and found deletions at chromosome Xq11.1 in tumors from 5 of 26 male patients. The only gene in the interval was WTX, also known as FLJ39827 (Kimura et al., 2006; Ota et al., 2004). Rivera et al. (2007) named the gene WTX for 'Wilms tumor gene on the X chromosome.' Rivera et al. (2007) found that the endogenous WTX transcript differed from that predicted by database annotation in the 3-prime end and required assembly with the use of RACE and RT-PCR from human and mouse cDNA. The full-length 7.5-kb transcript encodes a protein of 1,135 amino acids containing a nuclear localization signal, 2 coiled-coil domains, an acidic domain that overlaps the first coiled-coil, and a proline-rich domain. WTX orthologs are present in vertebrates, including zebrafish, but do not share substantial homology with other genes of known function.
Grohmann et al. (2007) described a splice variant of WTX, which they called AMER1. Full-length AMER1 contains 3 APC (611731)-binding sites. The AMER1 variant encodes a deduced 804-amino acid protein that is identical to full-length AMER1 for the first 785 amino acids, but it is truncated in the third APC-binding domain. RT-PCR of 24 adult and fetal tissues detected ubiquitous AMER1 expression, with highest levels in fetal brain and adult adrenal gland. Endogenous and fluorescence-tagged AMER1 localized to the plasma membrane in human MCF7 breast cancer cells. Western blot analysis detected endogenous AMER1 at an apparent molecular mass of 190 kD. Database analysis revealed orthologs of AMER1 in vertebrates, but not Drosophila.
Jenkins et al. (2009) noted that WTX possesses a beta-catenin (see 116806)-binding site located C-terminal to gly368 and 3 binding sites for APC, another component of the beta-catenin-sequestering complex. In cells transfected with a WTX expression construct, WTX localized to the plasma membrane via phosphatidylinositol (4,5)-bisphosphate-binding sites localized between residues 2 through 209. Although the open reading frame (ORF) of WTX is annotated as lying within a single exon, Jenkins et al. (2009) detected by RT-PCR an alternatively spliced transcript that encodes an isoform (WTXS2) lacking residues 50 through 326 from the full-length protein (WTXS1), including most of APC-binding domain-1 (APCBD1) and at least 1 predicted binding site for phosphatidylinositol (4,5)-bisphosphate.
Grohmann et al. (2007) determined that the AMER1 gene contains 3 exons. Exon 2 contains the translation initiation site used by both AMER1 splice variants reported by Grohmann et al. (2007). Stop codons are located in exons 2 and 3 and are used in the long and short AMER1 splice variants, respectively.
Kimura et al. (2006) and Ota et al. (2004) mapped the WTX gene to chromosome Xq11.1. Rivera et al. (2007) identified the WTX gene on chromosome Xq11.1 based on deletions in this region in tumors from patients with Wilms tumor.
Grohmann et al. (2007) stated that the mouse Amer1 gene maps to a region of chromosome XC3 that shares homology of synteny with human chromosome Xq11.1.
Rivera et al. (2007) found that in the mouse Wtx expression was relatively high in neonatal brain and kidney and declined substantially in mature organs. Lung and spleen also expressed Wtx, but with a less notable developmental profile. Temporal patterns of Wtx and Wt1 (607102) expression within the kidney were virtually identical, consistent with a wave of differentiation that is ongoing at birth and completed by postnatal week 3. As assessed by RNA in situ hybridization, Wt1 and Wtx display a high, but not complete, degree of overlap in expression in the kidney. Similar to Wt1, Wtx is expressed in the condensing metanephric mesenchyme and in early epithelial structures that are precursors to glomeruli. Thus both genes are present in the pluripotent cells that are the presumed precursors of Wilms tumor.
Major et al. (2007) used tandem-affinity protein purification and mass spectrometry to define the protein interaction network of the beta-catenin destruction complex. This assay revealed that WTX, a protein encoded by a gene mutated in Wilms tumors, forms a complex with beta-catenin, AXIN1 (603816), beta-TrCP2 (605651), and APC (611731). Functional analyses in cultured cells, Xenopus, and zebrafish demonstrated that WTX promotes beta-catenin ubiquitination and degradation, which antagonizes WNT/beta-catenin signaling. Major et al. (2007) concluded that their data provide a possible mechanistic explanation for the tumor suppressor activity of WTX.
Using mutation analysis and coimmunoprecipitation experiments, Grohmann et al. (2007) found that 3 distinct domains within full-length AMER1 interacted with the armadillo repeat domain of APC. Knockdown of AMER1 in human cell lines via small interfering RNA reduced APC protein, but not mRNA levels, redistributed APC from the plasma membrane to tips of microtubules, and disrupted cell-cell junctions in MCF7 cells. In transfected MCF7 cells, both AMER1 and AMER2 (614659) recruited APC to the plasma membrane from filamentous structures, which were likely microtubules. Deletion analysis revealed that AMER1 interacted with several phospholipids and 3-sulfogalactosylceramide in vitro via 2 lysine-rich lipid-binding domains in its N terminus. Membrane localization of full-length AMER1 and APC was abolished following ionomycin-induced calcium mobilization or by inhibition of phosphatidylinositol 4-kinases (see 600286). Depletion of phosphatidylinositol 4,5-bisphosphate abolished AMER1 and APC localization at the plasma membrane.
Jenkins et al. (2009) found that mutations in WTX similar to those found to cause OSCS (300373) resulted in enhanced WNT signaling. A WTX construct truncated at gly368 (immediately N terminal to the acidic domain) enhanced translocation of beta-catenin to the nucleus, and siRNA-mediated knockdown of WTX (analogous to whole-gene deletions) increased transcription of WNT-responsive reporter genes.
Osteopathia Striata with Cranial Sclerosis
In 18 of 19 unrelated families with osteopathia striata with cranial sclerosis (OSCS; 300373), Jenkins et al. (2009) detected germline mutations in the WTX gene (300647.0001-300647.0005). All mutations either deleted the entire gene or predicted premature termination of translation. All point mutations identified clustered in the 5-prime region of WTX; mutations leading to lethality in males were located more 5-prime than those associated with survival. Jenkins et al. (2009) pointed out that mechanisms governing nonsense-mediated mRNA decay predict that transcripts with a truncating mutation within the single-exon splice form (WTXS1) or mutations lying within the intron of splice form-2 (WTXS2) would not be subject to degradation. Accordingly, they detected both WTX splice forms (the full-length WTXS1 and the spliced, shorter WTXS2) by quantitative RT-PCR on cDNA from cells from an affected surviving male with a mutation in exon 2 of WTXS2. Patients with germline mutations in WTX did not appear to be at increased risk of Wilms tumor (see 194070).
In affected members of 3 unrelated families and 5 singleton patients with osteopathia striata with cranial sclerosis, Perdu et al. (2010) identified 4 different mutations in the WTX gene and 1 gene deletion (300647.0003; 300647.0005; 300647.0007-300647.0008). One of the male patients had a 5-prime truncating mutation, which did not fully support the hypothesis raised by Jenkins et al. (2009) regarding a genotype/phenotype correlation for male lethality.
Perdu et al. (2011) reported a 17-year-old boy with osteopathia striata with cranial sclerosis due to a hemizygous truncating mutation in the 5-prime end of the WTX gene (C143X; 300647.0006). The mutation was predicted to result in a very short truncated form of the WTXS1 isoform and most likely complete absence of a functional protein. The patient had a severe phenotype with dysmorphic features, mental retardation, seizures, mixed hearing loss, cranial sclerosis with dolichocephaly, atrial septal defect, and intestinal malrotation. Perdu et al. (2011) noted that although this mutation occurred in the 5-prime region of the gene, which Jenkins et al. (2009) postulated would be correlated with reduced survival, the patient had unusually long survival. The report indicated that genotype/phenotype correlations are not absolute.
Somatic Mutations in Wilms Tumor
Rivera et al. (2007) found that 5 of 26 male patients with Wilms tumor had overlapping deletions at chromosome locus Xq11.1 with the only overlap gene implicated being WTX. Furthermore, Rivera et al. (2007) found that of 51 tumors tested for both gene copy alterations and intragenic mutations, 11 (21.6%) had WTX deletions and 4 (7.8%) had point mutations, for a total of 15 of 51 (29.4%). Five of the 6 WTX mutations were nonsense. In these tumors, WT1 mutations were detected in 3 cases and beta-catenin (116806) mutations in 4 cases; as expected, there was overlap between WT1 and beta-catenin mutations (2 of 3 cases with WT1 mutations). In contrast, no tumor with a deletion or point mutation in WTX contained a mutation in WT1 or beta-catenin. WTX deletions and point mutations occurred on the single X chromosome in Wilms tumors from males and on the active X chromosome in Wilms tumors from females.
Jenkins et al. (2009) suggested a putative genotype/phenotype correlation for OSCS: mutations producing a WTXS1 isoform with an intact phosphatidylinositol (4,5)-bisphosphate binding domain and APC-binding domain-1 resulted in survival of males, whereas mutations causing truncation of WTXS1 5-prime to these domains resulted in male lethality. The presence of intact WTXS2 was not protective against the disease, most likely because the WTXS2 isoform is not localized to the plasma membrane. However, Perdu et al. (2010) and Perdu et al. (2011) reported 3 surviving males with mutations in the 5-prime region of the gene (300647.0006 and 300647.0008), indicating that the hypothesis presented by Jenkins et al. (2009) is not absolute.
Holman et al. (2011) found that 5 male patients with severe OSCS had truncating WTX mutations 5-prime to the beta-catenin binding domain; the sixth patient had a whole gene deletion. In contrast, 4 male patients with a milder form of OSCS and survival into the second or third decade had mutations 3-prime to the beta-catenin binding domain.
In a 39-year-old female with osteopathia striata with cranial sclerosis (OSCS; 300373), Jenkins et al. (2009) detected a de novo deletion of a C at nucleotide 671 (671delC) in the WTX gene. The patient's similarly affected male fetus also carried the mutation.
In a 35-year-old female with osteopathia striata with cranial sclerosis (OSCS; 300373), Jenkins et al. (2009) detected a de novo insertion of an adenine at nucleotide 780 of the WTX gene (780insA), resulting in a premature termination frameshift at amino acid 260 with 16 novel amino acids prior to termination (Pro260fs+16Ter). She had skewed X inactivation. She had an affected female child who exhibited orofacial clefting in addition to bony sclerosis at 2 months of age, and a male fetus who also manifested bony sclerosis and orofacial clefting.
In 2 unrelated females with osteopathia striata with cranial sclerosis (OSCS; 300373), Jenkins et al. (2009) identified deletion of the entire AMER1 gene with undetectable protein and normal X-inactivation ratio.
In affected female members of a large family with OSCS originally reported by Savarirayan et al. (1997), Perdu et al. (2010) identified a deletion of the WTX gene. The family showed a highly variable phenotype. The proband had multiple congenital abnormalities, whereas her mother, maternal grandmother, and maternal great-grandmother were less severely affected. The mother of the proband had a subsequent pregnancy; the fetus was found to have alobar holoprosencephaly, cleft lip and palate, and partial absence of the nose. The pregnancy was terminated, and radiographs showed abnormal sclerosis of the maxilla, mandible, and orbital roofs.
In 2 unrelated females with osteopathia striata with cranial sclerosis (OSCS; 300373), Jenkins et al. (2009) identified a 1057C-T transition in the WTX gene, resulting in an arg353-to-stop (R353X) substitution. In both cases this was a de novo occurrence. This mutation had been reported as a somatic mutation in Wilms tumor (see 194070); however, neither of these patients had any history of cancer.
In 5 unrelated patients with osteopathia striata with cranial sclerosis (OSCS; 300373), Jenkins et al. (2009) identified a 1072C-T transition in the WTX gene, resulting in an arg358-to-stop (R358X) substitution. In all tested cases, there was skewed X inactivation. This mutation had been reported as a somatic mutation in Wilms tumor; however, none of the females affected, ranging from age 11 to 56 years, had a history of cancer. One affected patient was a male fetus.
Perdu et al. (2010) identified the R358X mutation in 4 unrelated females with OSCS and suggested that this was a hotspot location due to a CpG dinucleotide. Two of the patients had mild developmental delay.
In a boy and his mother with osteopathia striata with cranial sclerosis (OSCS; 300373), Perdu et al. (2011) identified a 429T-A transversion in the WTX gene, resulting in a cys143-to-ter (C143X) substitution predicted to result in a very short truncated form of the WTXS1 isoform and most likely complete absence of a functional protein. The mother, who was heterozygous for the mutation, had macrocephaly, a long face, a long philtrum, thin lips, narrow palate, mild scoliosis, and a mild asymmetry of the legs. Radiographic studies showed cranial sclerosis and striations of the tubular bones. Her 17-year-old son had a severe phenotype, but had survived. He had severe mental retardation, seizures, mixed hearing loss, severe cranial sclerosis with dolichocephaly, atrial septal defect, patent ductus arteriosus, and intestinal malrotation. Dysmorphic facial features included high forehead, hypertelorism, downslanting palpebral fissures, broad nasal tip, cleft lip and palate, dysplastic low-set ears, dysplastic teeth, and short neck. Brain imaging showed ventricular dilatation and hypoplasia of the corpus callosum. Radiographs showed short, broad clavicles, proximal fibular hypoplasia, and scoliosis, but no clear metaphyseal striations of the tubular bones. Perdu et al. (2011) noted that this mutation occurred in the 5-prime region of the gene, which Jenkins et al. (2009) postulated would be correlated with reduced survival. However, the patient reported by Perdu et al. (2011) had unusually long survival, indicating that this genotype/phenotype correlation is not absolute.
In affected members of a family with osteopathia striata with cranial sclerosis (OSCS; 300373) originally reported by Keymolen et al. (1997), Perdu et al. (2010) identified a 1-bp deletion (1267delC) in the WTX gene, resulting in a frameshift and premature termination (Leu423fs+25Ter). There were 2 affected females and 1 mildly affected male who was alive at age 41 years.
In affected members of a family with osteopathia striata with cranial sclerosis (OSCS; 300373) originally reported by Konig et al. (1996), Perdu et al. (2010) identified an 811C-T transition in the WTX gene, resulting in a gln271-to-ter (Q271X) substitution. There were 4 affected females and 1 mildly affected male who was alive at age 20 years. The mutation was predicted to result in a truncated protein with an intact phosphatidylinositol (4,5)-bisphosphate binding domain, but without the APCBD1 domain. Perdu et al. (2010) noted that this mutation occurred in the 5-prime region of the gene, which Jenkins et al. (2009) postulated would be correlated with reduced survival. However, the male patient in this family had unusually long survival, indicating that this genotype/phenotype correlation is not absolute.
Grohmann, A., Tanneberger, K., Alzner, A., Schneikert, J., Behrens, J. AMER1 regulates the distribution of the tumor suppressor APC between microtubules and the plasma membrane. J. Cell Sci. 120: 3738-3747, 2007. [PubMed: 17925383] [Full Text: https://doi.org/10.1242/jcs.011320]
Holman, S. K., Daniel, P., Jenkins, Z. A., Herron, R. L., Morgan, T., Savarirayan, R., Chow, C. W., Bohring, A., Mosel, A., Lacombe, D., Steiner, B., Schmitt-Mechelke, T., and 13 others. The male phenotype in osteopathia striata congenita with cranial sclerosis. Am. J. Med. Genet. 155A: 2397-2408, 2011. [PubMed: 22043478] [Full Text: https://doi.org/10.1002/ajmg.a.34178]
Jenkins, Z. A., van Kogelenberg, M., Morgan, T., Jeffs, A., Fukuzawa, R., Pearl, E., Thaller, C., Hing, A. V., Porteous, M. E., Garcia-Minaur, S., Bohring, A., Lacombe, D., and 13 others. Germline mutations in WTX cause a sclerosing skeletal dysplasia but do not predispose to tumorigenesis. Nature Genet. 41: 95-100, 2009. [PubMed: 19079258] [Full Text: https://doi.org/10.1038/ng.270]
Keymolen, K., Bonduelle, M., De Maeseneer, M., Liebaers, I. How to counsel in osteopathia striata with cranial sclerosis. Genet. Counsel. 8: 207-211, 1997. [PubMed: 9327263]
Kimura, K., Wakamatsu, A., Suzuki, Y., Ota, T., Nishikawa, T., Yamashita, R., Yamamoto, J., Sekine, M., Tsuritani, K., Wakaguri, H., Ishii, S., Sugiyama, T., and 20 others. Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes. Genome Res. 16: 55-65, 2006. [PubMed: 16344560] [Full Text: https://doi.org/10.1101/gr.4039406]
Konig, R., Dukiet, C., Dorries, A., Zabel, B., Fuchs, S. Osteopathia striata with cranial sclerosis: variable expressivity in a four generation pedigree. Am. J. Med. Genet. 63: 68-73, 1996. [PubMed: 8723089] [Full Text: https://doi.org/10.1002/(SICI)1096-8628(19960503)63:1<68::AID-AJMG14>3.0.CO;2-S]
Major, M. B., Camp, N. D., Berndt, J. D., Yi, X., Goldenberg, S. J., Hubbert, C., Biechele, T. L., Gingras, A.-C., Zheng, N., MacCoss, M. J., Angers, S., Moon, R. T. Wilms tumor suppressor WTX negatively regulates WNT/beta-catenin signaling. Science 316: 1043-1046, 2007. [PubMed: 17510365] [Full Text: https://doi.org/10.1126/science/1141515]
Ota, T., Suzuki, Y., Nishikawa, T., Otsuki, T., Sugiyama, T., Irie, R., Wakamatsu, A., Hayashi, K., Sato, H., Nagai, K., Kimura, K., Makita, H. {and 143 others}: Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature Genet. 36: 40-45, 2004. [PubMed: 14702039] [Full Text: https://doi.org/10.1038/ng1285]
Perdu, B., de Freitas, F., Frints, S. G. M., Schouten, M., Schrander-Stumpel, C., Barbosa, M., Pinto-Basto, J., Reis-Lima, M., de Vernejoul, M.-C., Becker, K., Freckmann, M.-L., Keymolen, K., Haan, E., Savarirayan, R., Koenig, R., Zabel, B., Vanhoenacker, F. M., Van Hul, W. Osteopathia striata with cranial sclerosis owing to WTX gene defect. J. Bone Miner. Res. 25: 82-90, 2010. [PubMed: 20209645] [Full Text: https://doi.org/10.1359/jbmr.090707]
Perdu, B., Lakeman, P., Mortier, G., Koenig, R., Lachmeijer, A. M. A., Van Hul, W. Two novel WTX mutations underscore the unpredictability of male survival in osteopathia striata with cranial sclerosis. Clin. Genet. 80: 383-388, 2011. [PubMed: 20950377] [Full Text: https://doi.org/10.1111/j.1399-0004.2010.01553.x]
Rivera, M. N., Kim, W. J., Wells, J., Driscoll, D. R., Brannigan, B. W., Han, M., Kim, J. C., Feinberg, A. P., Gerald, W. L., Vargas, S. O., Chin, L., Iafrate, A. J., Bell, D. W., Haber, D. A. An X chromosome gene, WTX, is commonly inactivated in Wilms tumor. Science 315: 642-645, 2007. [PubMed: 17204608] [Full Text: https://doi.org/10.1126/science.1137509]
Savarirayan, R., Nance, J., Morris, L., Haan, E., Couper, R. Osteopathia striata with cranial sclerosis: highly variable phenotypic expression within a family. Clin. Genet. 52: 199-205, 1997. [PubMed: 9383023] [Full Text: https://doi.org/10.1111/j.1399-0004.1997.tb02547.x]