CDC-48/p97 is required for proper meiotic chromosome segregation via controlling AIR-2/Aurora B kinase localization in Caenorhabditis elegans

Valosin-Containing Protein (VCP)/p97: A Prognostic Biomarker and Therapeutic Target in Cancer

Valosin-containing protein (VCP)/p97, a member of the AAA+ ATPase family, is a molecular chaperone recruited to the endoplasmic reticulum (ER) membrane by binding to membrane adapters (nuclear protein localization protein 4 (NPL4), p47 and ubiquitin regulatory X (UBX) domain-containing protein 1 (UBXD1)), where it is involved in ER-associated protein degradation (ERAD). However, VCP/p97 interacts with many cofactors to participate in different cellular processes that are critical for cancer cell survival and aggressiveness. Indeed, VCP/p97 is reported to be overexpressed in many cancer types and is considered a potential cancer biomarker and therapeutic target. This review summarizes the role of VCP/p97 in different cancers and the advances in the discovery of small-molecule inhibitors with therapeutic potential, focusing on the challenges associated with cancer-related VCP mutations in the mechanisms of resistance to inhibitors.

The coordinated action of VCP/p97 and GCN2 regulates cancer cell metabolism and proteostasis during nutrient limitation

VCP/p97 regulates numerous cellular functions by mediating protein degradation through its segregase activity. Its key role in governing protein homoeostasis has made VCP/p97 an appealing anticancer drug target. Here, we provide evidence that VCP/p97 acts as a regulator of cellular metabolism. We found that VCP/p97 was tied to multiple metabolic processes on the gene expression level in a diverse range of cancer cell lines and in patient-derived multiple myeloma cells. Cellular VCP/p97 dependency to maintain proteostasis was increased under conditions of glucose and glutamine limitation in a range of cancer cell lines from different tissues. Moreover, glutamine depletion led to increased VCP/p97 expression, whereas VCP/p97 inhibition perturbed metabolic processes and intracellular amino acid turnover. GCN2, an amino acid-sensing kinase, attenuated stress signalling and cell death triggered by VCP/p97 inhibition and nutrient shortages and modulated ERK activation, autophagy, and glycolytic metabolite turnover. Together, our data point to an interconnected role of VCP/p97 and GCN2 in maintaining cancer cell metabolic and protein homoeostasis.

A Mighty "Protein Extractor" of the Cell: Structure and Function of the p97/CDC48 ATPase

p97/VCP (known as Cdc48 in S. cerevisiae or TER94 in Drosophila) is one of the most abundant cytosolic ATPases. It is highly conserved from archaebacteria to eukaryotes. In conjunction with a large number of cofactors and adaptors, it couples ATP hydrolysis to segregation of polypeptides from immobile cellular structures such as protein assemblies, membranes, ribosome, and chromatin. This often results in proteasomal degradation of extracted polypeptides. Given the diversity of p97 substrates, this "segregase" activity has profound influence on cellular physiology ranging from protein homeostasis to DNA lesion sensing, and mutations in p97 have been linked to several human diseases. Here we summarize our current understanding of the structure and function of this important cellular machinery and discuss the relevant clinical implications.

Proteomic analysis and immunodetection of antigens from early developmental stages of Trichinella spiralis

Trichinella spiralis is an ubiquitous parasitic nematode that lives in muscle tissue of many hosts and causes trichinellosis in humans. Numerous efforts have been directed at specific detection of this infection and strategies for its control. TSL-1 and other antigens, mainly from muscle larvae (ML), have been used to induce partial protection in rodents. An improvement in protective immunity may be achieved by using antigens from other parasite stages. Further, identification of other parasite antigens may provide insights into their role in the host-parasite interaction. In this study, T. spiralis antigens from early developmental parasite stages, namely ML and pre-adult (PA) obtained at 6h, 18h and 30h post-infection, were identified by proteomic and mass spectrometry analyses. Our findings showed a differential expression of several proteins with molecular weights in the range of 13-224kDa and pI range of 4.54-9.89. Bioinformatic analyses revealed a wide diversity of functions in the identified proteins, which include structural, antioxidant, actin binding, peptidyl prolyl cis-trans isomerase, motor, hydrolase, ATP binding, magnesium and calcium binding, isomerase and translation elongation factor. This, together with the differential recognition of antigens from these parasite stages by antibodies present in intestinal fluid, in supernatants from intestinal explants, and in serum samples from mice infected with T. spiralis or re-infected with this parasite, provides information that may lead to alternatives in the design of vaccines against this parasite or for modulation of immune responses.

Ring of Change: CDC48/p97 Drives Protein Dynamics at Chromatin

The dynamic composition of proteins associated with nuclear DNA is a fundamental property of chromosome biology. In the chromatin compartment dedicated protein complexes govern the accurate synthesis and repair of the genomic information and define the state of DNA compaction in vital cellular processes such as chromosome segregation or transcription. Unscheduled or faulty association of protein complexes with DNA has detrimental consequences on genome integrity. Consequently, the association of protein complexes with DNA is remarkably dynamic and can respond rapidly to cellular signaling events, which requires tight spatiotemporal control. In this context, the ring-like AAA+ ATPase CDC48/p97 emerges as a key regulator of protein complexes that are marked with ubiquitin or SUMO. Mechanistically, CDC48/p97 functions as a segregase facilitating the extraction of substrate proteins from the chromatin. As such, CDC48/p97 drives molecular reactions either by directed disassembly or rearrangement of chromatin-bound protein complexes. The importance of this mechanism is reflected by human pathologies linked to p97 mutations, including neurodegenerative disorders, oncogenesis, and premature aging. This review focuses on the recent insights into molecular mechanisms that determine CDC48/p97 function in the chromatin environment, which is particularly relevant for cancer and aging research.

Inadequate fine-tuning of protein synthesis and failure of amino acid homeostasis following inhibition of the ATPase VCP/p97

The cellular mechanisms that control protein degradation may constitute a non-oncogenic cancer cell vulnerability and, therefore, a therapeutic target. Although this proposition is supported by the clinical success of proteasome inhibitors in some malignancies, most cancers are resistant to proteasome inhibition. The ATPase valosin-containing protein (VCP; p97) is an essential regulator of protein degradation in multiple pathways and has emerged as a target for cancer therapy. We found that pharmacological depletion of VCP enzymatic activity with mechanistically different inhibitors robustly induced proteotoxic stress in solid cancer and multiple myeloma cells, including cells that were insensitive, adapted, or clinically resistant to proteasome inhibition. VCP inhibition had an impact on two key regulators of protein synthesis, eukaryotic initiation factor 2α (eIF2α) and mechanistic target of rapamycin complex 1 (mTORC1), and attenuated global protein synthesis. However, a block on protein translation that was itself cytotoxic alleviated stress signaling and reduced cell death triggered by VCP inhibition. Some of the proteotoxic effects of VCP depletion depended on the eIF2α phosphatase, protein phosphatase 1 regulatory subunit 15A (PPP1R15A)/PP1c, but not on mTORC1, although there appeared to be cross-talk between them. Thus, cancer cell death following VCP inhibition was linked to inadequate fine-tuning of protein synthesis and activity of PPP1R15A/PP1c. VCP inhibitors also perturbed intracellular amino acid levels, activated eukaryotic translation initiation factor 2α kinase 4 (EIF2AK4), and enhanced cellular dependence on amino acid supplies, consistent with a failure of amino acid homeostasis. Many of the observed effects of VCP inhibition differed from the effects triggered by proteasome inhibition or by protein misfolding. Thus, depletion of VCP enzymatic activity triggers cancer cell death in part through inadequate regulation of protein synthesis and amino acid metabolism. The data provide novel insights into the maintenance of intracellular proteostasis by VCP and may have implications for the development of anti-cancer therapies.

The UBXN-2/p37/p47 adaptors of CDC-48/p97 regulate mitosis by limiting the centrosomal recruitment of Aurora A

UBXN-2, a substrate adaptor of the AAA ATPase CDC-48/p97, is required to coordinate centrosome maturation timing with mitosis.

Coordination of cell cycle events in space and time is crucial to achieve a successful cell division. Here, we demonstrate that UBXN-2, a substrate adaptor of the AAA ATPase Cdc48/p97, is required to coordinate centrosome maturation timing with mitosis. In UBXN-2–depleted Caenorhabditis elegans embryos, centrosomes recruited more AIR-1 (Aurora A), matured precociously, and alignment of the mitotic spindle with the axis of polarity was impaired. UBXN-2 and CDC-48 coimmunoprecipitated with AIR-1 and the spindle alignment defect was partially rescued by co-depleting AIR-1, indicating that UBXN-2 controls these processes via AIR-1. Similarly, depletion in human cells of the UBXN-2 orthologues p37/p47 resulted in an accumulation of Aurora A at centrosomes and a delay in centrosome separation. The latter defect was also rescued by inhibiting Aurora A. We therefore postulate that the role of this adaptor in cell cycle regulation is conserved.

Role of p97/VCP (Cdc48) in genome stability

Ubiquitin-dependent molecular chaperone p97, also known as valosin-containing protein (VCP) or Cdc48, is an AAA ATPase involved in protein turnover and degradation. p97 converts its own ATPase hydrolysis into remodeling activity on a myriad of ubiquitinated substrates from different cellular locations and pathways. In this way, p97 mediates extraction of targeted protein from cellular compartments or protein complexes. p97-dependent protein extraction from various cellular environments maintains cellular protein homeostasis. In recent years, p97-dependent protein extraction from chromatin has emerged as an essential evolutionarily conserved process for maintaining genome stability. Inactivation of p97 segregase activity leads to accumulation of ubiquitinated substrates on chromatin, consequently leading to protein-induced chromatin stress (PICHROS). PICHROS directly and negatively affects multiple DNA metabolic processes, including replication, damage responses, mitosis, and transcription, leading to genotoxic stress and genome instability. By summarizing and critically evaluating recent data on p97 function in various chromatin-associated protein degradation processes, we propose establishing p97 as a genome caretaker.

Create and preserve: proteostasis in development and aging is governed by Cdc48/p97/VCP

The AAA-ATPase Cdc48 (also called p97 or VCP) acts as a key regulator in proteolytic pathways, coordinating recruitment and targeting of substrate proteins to the 26S proteasome or lysosomal degradation. However, in contrast to the well-known function in ubiquitin-dependent cellular processes, the physiological relevance of Cdc48 in organismic development and maintenance of protein homeostasis is less understood. Therefore, studies on multicellular model organisms help to decipher how Cdc48-dependent proteolysis is regulated in time and space to meet developmental requirements. Given the importance of developmental regulation and tissue maintenance, defects in Cdc48 activity have been linked to several human pathologies including protein aggregation diseases. Thus, addressing the underlying disease mechanisms not only contributes to our understanding on the organism-wide function of Cdc48 but also facilitates the design of specific medical therapies. In this review, we will portray the role of Cdc48 in the context of multicellular organisms, pointing out its importance for developmental processes, tissue surveillance, and disease prevention. This article is part of a Special Issue entitled: Ubiquitin-Proteasome System. Guest Editors: Thomas Sommer and Dieter H. Wolf.