Pathogenic Mutations in the Valosin-containing Protein/p97(VCP) N-domain Inhibit the SUMOylation of VCP and Lead to Impaired Stress Response

Abstract

Valosin-containing protein/p97(VCP) is a hexameric ATPase vital to protein degradation during endoplasmic reticulum stress. It regulates diverse cellular functions including autophagy, chromatin remodeling, and DNA repair. In addition, mutations in VCP cause inclusion body myopathy, Paget disease of the bone, and frontotemporal dementia (IBMPFD), as well as amyotrophic lateral sclerosis. Nevertheless, how the VCP activities were regulated and how the pathogenic mutations affect the function of VCP during stress are not unclear. Here we show that the small ubiquitin-like modifier (SUMO)-ylation of VCP is a normal stress response inhibited by the disease-causing mutations in the N-domain. Under oxidative and endoplasmic reticulum stress conditions, the SUMOylation of VCP facilitates the distribution of VCP to stress granules and nucleus, and promotes the VCP hexamer assembly. In contrast, pathogenic mutations in the VCP N-domain lead to reduced SUMOylation and weakened VCP hexamer formation upon stress. Defective SUMOylation of VCP also causes altered co-factor binding and attenuated endoplasmic reticulum-associated protein degradation. Furthermore, SUMO-defective VCP fails to protect against stress-induced toxicity in Drosophila. Therefore, our results have revealed SUMOylation as a molecular signaling switch to regulate the distribution and functions of VCP during stress response, and suggest that deficiency in VCP SUMOylation caused by pathogenic mutations will render cells vulnerable to stress insults.Valosin-containing protein (VCP/p97, cdc48, 2 is a highly conserved member of AAA (ATPase associated with diverse cellular activities) family proteins. It is mainly composed of N-domain and two ATPase domains. By forming a homohexamer and binding various co-factors via the N-domain, VCP helps to remodel, unfold, or degrade protein substrates using the energy derived from ATP hydrolysis (1-3). Due to its cellular abundance and broad interaction with a number of co-factors, key substrates, and regulators of the ubiquitin proteasome system, VCP has emerged as a vital modulator of a large variety of cellular activities, including protein degradation, ER stress response, autophagy/mitophagy, endosomal trafficking, cell cycle, and DNA repair (2, 5, 6). However, the factors that regulate VCP activities are not clear.The importance of VCP is also demonstrated by its association with cancer and degenerative diseases. VCP is highly expressed in non-small cell lung carcinoma (7), and its expression is correlated with tumor progression and prognosis (8). On the other hand, mutations in VCP have been associated with degenerative diseases, including inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD) and amyotrophic lateral sclerosis (ALS) (6, 9). Most pathogenic mutations of VCP are found in the N-domain, with a few in the ATPase domains (10). The pathology of VCP-associated degenerative diseases features ubiquitin-positive inclusions. Although some of the pathogenic VCP mutation...

C9orf72 Dipeptide Repeats Cause Selective Neurodegeneration and Cell-Autonomous Excitotoxicity in Drosophila Glutamatergic Neurons

“…Although NMDA receptors were best characterized as a postsynaptic component to relay excitatory potentials, mounting evidence has shown that presynaptic NMDA receptors are widely present in the CNS (Bouvier et al, 2015). At excitatory terminals, NMDA receptors could be activated by glutamate released from axon terminals as autoreceptors to increase calcium influx and to further regulate neurotransmitter release and excitotoxicity (Suárez et al, 2005;Bouvier et al, 2015). Our results support a model whereby C9 DPRs could stimulate synapses' overgrowth, promote glutamate release, and activate presynaptic NMDA receptors to exacerbate excitotoxicity.…”

“…commonly considered a noncell-autonomous event caused by the loss of glial glutamate transporter or altered expression of AMPA receptors (Cleveland and Rothstein, 2001). Recent studies using C9 patient-derived iPSCs motor neurons showed increased susceptibility of these neurons to glutamate toxicity, likely contributed by AMPA receptor activation Selvaraj et al, 2018;Shi et al, 2018) and/or decreased glutamate uptake by astrocytes (Shi et al, 2018). Interestingly, in our in vivo model of C9 DPRs, we have found that a presynaptic cellautonomous mechanism in glutamatergic neurons contributes to the neurodegenerative phenotypes.…”

“…The roles of C9 repeat expansion in excitotoxicity are gradually being recognized. A few studies suggested increased expression of glutamate receptors in C9 patient-derived induced pluripotent stem cells (iPSCs) motor neurons Selvaraj et al, 2018;Shi et al, 2018). Furthermore, the splicing of EAAT2 could be affected by C9 DPR (Kwon et al, 2014) and lead to decreased glutamate uptake by astrocytes and increased excitotoxicity in motor neurons (Shi et al, 2018).…”

“…A few studies suggested increased expression of glutamate receptors in C9 patient-derived induced pluripotent stem cells (iPSCs) motor neurons Selvaraj et al, 2018;Shi et al, 2018). Furthermore, the splicing of EAAT2 could be affected by C9 DPR (Kwon et al, 2014) and lead to decreased glutamate uptake by astrocytes and increased excitotoxicity in motor neurons (Shi et al, 2018). However, most of the studies on C9 repeat expansion products have been focused on the survival and function of motor neurons, and the contribution of those toxic products to neurons affected in FTD, such as excitatory spindle neurons, is unknown.…”

Minimotifs dysfunction is pervasive in neurodegenerative disorders

“…Pathogenic mutation of sumoylated residues in valosin‐containing protein/p97 inhibits its translocation to the nucleus, the formation of stress granules, reduction of hexamer formation, and eventually, inhibition of its clearance. The amino acid substitutions for these mutants are prevalent in FTDs [48].…”