Valosin‐containing protein (VCP) has been shown to colocalize with abnormal protein aggregates, such as nuclear inclusions of Huntington disease and Machado‐Joseph disease, Lewy bodies in Parkinson disease. Several mis‐sense mutations in the human VCP gene have been identified in patients suffering inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD). Recently, we have shown that VCP possesses both aggregate‐forming and aggregate‐clearing activities. Here, we showed that in cells treated with proteasome inhibitors VCP first appeared as several small aggregates throughout the cells; and then, these small aggregates gathered together into a single big aggregate. Subcellular localization and ATPase activity of VCP clearly influenced the localization of the aggregates. Furthermore, all tested IBMPFD‐causing mutant VCPs, possessed elevated ATPase activities and enhanced aggregate‐forming activities in cultured cells. In Drosophila, these mutants and VCP(T761E), a super active VCP, did not appear to spontaneously induce eye degeneration, but worsened the phenotype when co‐expressed with polyglutamines. Unexpectedly, these VCPs did not apparently change sizes and the amounts of polyglutamine aggregates in Drosophila eyes. Elevated ATPase activities, thus, may be a hidden primary defect causing IBMPFD pathological phenotypes, which would be revealed when abnormal proteins are accumulated, as typically observed in aging.

p97/valosin‐containing protein (VCP) is a member of the AAA family proteins, which plays various important roles in cells by using its ATPase activity. But mechanism of regulating its ATPase activity is mostly unknown. We report here that VCP is highly modified throughout the protein via acetylation and phosphorylation. In addition to six previously identified phosphorylation sites, we identified at least 14 serines, 14 threonines, 6 tyrosines and 22 lysines as potential modification sites. Interestingly, these sites included Lys251 and Lys524, which are very critical for the ATP binding in Walker A motif of D1 and D2 domains, respectively. It is notable that 16 sites are in the N‐terminal region and 16 sites are clustered in D2α domain (from Pro646 to Gly765). Indeed, amino acid substitution of Lys696 and Thr761 profoundly affect VCP ATPase activities. From these results, we propose that D2α domain acts as a VCP ATPase Regulatory domain or “VAR domain”. VCP modifications including those in this VAR domain may endorse adaptive and multiple functions to VCP in different cell conditions such as in the cell cycle and with abnormal protein accumulation.

Valosin-containing protein (p97/VCP) has been proposed as playing crucial roles in a variety of physiological and pathological processes such as cancer and neurodegeneration. We previously showed that VCP(K524A), an ATPase activity-negative VCP mutant, induced vacuolization, accumulation of ubiquitinated proteins, and cell death, phenotypes commonly observed in neurodegenerative disorders. However, any regulatory mechanism of its ATPase activity has not yet been clarified. Here, we show that oxidative stress readily inactivates VCP ATPase activity. With liquid chromatography/tandem mass spectrometry, we found that at least three cysteine residues were modified by oxidative stress. Of them, the 522nd cysteine (Cys-522) was identified as the site responsible for the oxidative inactivation of VCP. VCP(C522T), a single-amino acid substitution mutant from cysteine to threonine, conferred almost complete resistance to the oxidative inactivation. In response to oxidative stress, VCP strengthened the interaction with Npl4 and Ufd1, both of which are essential in endoplasmic reticulum-associated protein degradation. Cys-522 is located in the second ATP binding motif and is highly conserved in multicellular but not unicellular organisms. Cdc48p ( yeast VCP) has threonine in the corresponding amino acid, and it showed resistance to the oxidative inactivation in vitro. Furthermore, a yeast mutant (Delta cdc48 + cdc48[T532C]) was shown to be susceptible to oxidants-induced growth inhibition and cell death. These results clearly demonstrate that VCP ATPase activity is regulated by the oxidative modification of the Cys-522 residue. This regulatory mechanism may play a key role in the conversion of oxidative stress to endoplasmic reticulum stress response in multicellular organisms and also in the pathological process of various neurodegenerative disorders.