IBMPFD Disease-Causing Mutant VCP/p97 Proteins Are Targets of Autophagic-Lysosomal Degradation

PLoS One. 2016 Oct 21;11(10):e0164864. doi: 10.1371/journal.pone.0164864. eCollection 2016.

Abstract

The ubiquitin-proteasome system (UPS) degrades soluble proteins and small aggregates, whereas macroautophagy (autophagy herein) eliminates larger protein aggregates, tangles and even whole organelles in a lysosome-dependent manner. VCP/p97 was implicated in both pathways. VCP/p97 mutations cause a rare multisystem disease called IBMPFD (Inclusion Body Myopathy with Paget's Disease and Frontotemporal Dementia). Here, we studied the role IBMPFD-related mutants of VCP/p97 in autophagy. In contrast with the wild-type VCP/p97 protein or R155C or R191Q mutants, the P137L mutant was aggregate-prone. We showed that, unlike commonly studied R155C or R191Q mutants, the P137L mutant protein stimulated both autophagosome and autolysosome formation. Moreover, P137L mutant protein itself was a substrate of autophagy. Starvation- and mTOR inhibition-induced autophagy led to the degradation of the P137L mutant protein, while preserving the wild-type and functional VCP/p97. Strikingly, similar to the P137L mutant, other IBMPFD-related VCP/p97 mutants, namely R93C and G157R mutants induced autophagosome and autolysosome formation; and G157R mutant formed aggregates that could be cleared by autophagy. Therefore, cellular phenotypes caused by P137L mutant expression were not isolated observations, and some other IBMPFD disease-related VCP/p97 mutations could lead to similar outcomes. Our results indicate that cellular mechanisms leading to IBMPFD disease may be various, and underline the importance of studying different disease-associated mutations in order to better understand human pathologies and tailor mutation-specific treatment strategies.

MeSH terms

  • Adenosine Triphosphatases / physiology*
  • Animals
  • Autophagy*
  • Cell Cycle Proteins / physiology*
  • Cell Line, Tumor
  • Frontotemporal Dementia / genetics*
  • HEK293 Cells
  • Humans
  • Lysosomes / metabolism*
  • Male
  • Mice, Inbred C57BL
  • Muscular Dystrophies, Limb-Girdle / genetics*
  • Mutation*
  • Myositis, Inclusion Body / genetics*
  • Osteitis Deformans / genetics*
  • Valosin Containing Protein

Substances

  • Cell Cycle Proteins
  • Adenosine Triphosphatases
  • VCP protein, human
  • Valosin Containing Protein
  • Vcp protein, mouse

Supplementary concepts

  • Inclusion Body Myopathy With Early-Onset Paget Disease And Frontotemporal Dementia

Grants and funding

This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) 1001 Grant Project Number 110T405 and Sabanci University. OB, NMK and YA are recipients of TUBITAK-BIDEB 2211A PHD scholarships. KE was supported by a TUBITAK 2216 postdoctoral grant.