p97/VCP as a dual regulator of UPS and autophagy in ovarian cancer: a novel therapeutic target.

Ovarian cancer is among the most lethal gynecologic malignancies worldwide, with high mortality rates largely attributable to late diagnosis and the development of therapeutic resistance. Cellular proteostasis in cancer cells is tightly regulated by the ubiquitin-proteasome system (UPS) and autophagy, two major protein quality control pathways. Key proteins involved in these pathways, including p97/valosin-containing protein (p97/VCP), ubiquitin (Ub), p62/SQSTM1, and LC3B, have been implicated in cancer progression; however, their coordinated regulation in ovarian cancer remains incompletely understood. In this study, we investigated the expression and regulation of UPS- and autophagy-related proteins in the human ovarian cancer cell line MDAH-2774 under pharmacological modulation of autophagy. Cells were treated with rapamycin (10 µM), an autophagy inducer, or chloroquine (50 µM), an autophagy flux inhibitor, for defined incubation periods. Protein expression levels and cellular localization of p97/VCP, Ub, p62, and LC3-II were analyzed using Western blotting, immunofluorescence staining, and siRNA-mediated p97/VCP silencing. Our results demonstrated that p97/VCP and ubiquitin were expressed at relatively high levels in ovarian cancer cells, whereas autophagy markers p62 and LC3B showed reduced basal expression, suggesting dysregulated autophagic activity. Rapamycin treatment markedly increased p97/VCP expression, supporting its involvement in autophagy induction. In contrast, chloroquine treatment significantly reduced p97/VCP levels while inducing a pronounced accumulation of Ub, p62, and LC3-II (p < 0.05), consistent with impaired autophagic flux and disrupted proteasomal degradation. Furthermore, siRNA-mediated suppression of p97/VCP significantly decreased the expression of p97/VCP, LC3-II, ubiquitin, and the autophagy-modulating responses to rapamycin and chloroquine compared with control siRNA (p < 0.05). p97/VCP suppression was associated with alterations in endoplasmic reticulum-associated degradation (ERAD) and a concomitant reduction in unfolded protein response (UPR)-related protein levels, indicating increased cellular stress. Collectively, these findings highlight p97/VCP as a central regulator of proteostasis in ovarian cancer through its coordinated roles in both the UPS and autophagy pathways. Dysregulation or pharmacological inhibition of p97/VCP may exacerbate proteotoxic stress by disrupting the balance between autophagy and UPR signaling, potentially contributing to tumor progression and therapy resistance. Further mechanistic studies are warranted to elucidate the underlying signaling networks and to evaluate p97/VCP-mediated proteostasis pathways as potential therapeutic targets in ovarian cancer.