VCP at the crossroads of UPS and autophagy in cancer.

Proteostasis is maintained by the coordinated action of the ubiquitin-proteasome system (UPS) and autophagy-lysosome pathways. Valosin-containing protein (VCP/p97), an AAA + unfoldase, sits at its intersection by extracting ubiquitinated clients and assembling cofactor-defined complexes that determine substrate fate. In cancer, VCP up-regulation and altered cofactor recruitment rewire these ubiquitin-dependent routing decisions. By recruiting E3 ligases and deubiquitinases that remodel K48- and K63-linked ubiquitin chains, VCP biases substrates toward Ufd1-Npl4-coupled proteasomal turnover or autophagy-linked clearance, enabling oncogene stabilization or tumor suppressor loss. These principles are reflected in cancer axes that modulate autophagy flux, invasion and metastasis, PI3K/AKT/mTOR signaling, and immune evasion. The tumor suppressor p53 illustrates this complexity with state-dependent outcomes: VCP promotes proteasomal turnover of wild-type p53 through the canonical Ufd1-Npl4 complex, whereas it can stabilize the R273H hotspot mutant in a chaperone/holdase-like manner, prolonging gain-of-function phenotypes. Opposing regulators further control VCP function: PLAC8 enhances VCP-Ufd1-Npl4 activity and is linked to wild-type p53 turnover, PI3K/AKT/mTOR activation, and context-dependent autophagy effects. In contrast, SVIP can outcompete other VCP cofactors and, via acylation-dependent membrane targeting, redirect VCP toward lysosome-associated functions with predominantly tumor-suppressive effects. Collectively, this framework motivates therapeutic strategies that modulate VCP-cofactor interactions to regulate substrate degradative fate. Approaches include disrupting the Ufd1-Npl4 axis, biasing VCP from UPS to autophagy, altering subcellular localization, and reprogramming VCP for targeted proteolysis, with implications for cancer, fibrosis, neurodegeneration, and multisystem proteinopathy.