Usp5 links suppression of p53 and FAS levels in melanoma to the BRAF pathway

Abstract

Usp5 is a deubiquitinase (DUB) previously shown to regulate unanchored polyubiquitin (Ub) chains, p53 transcriptional activity and double-strand DNA repair. In BRAF mutant melanoma cells, Usp5 activity was suppressed by BRAF inhibitor (vemurafenib) in sensitive but not in acquired or intrinsically resistant cells. Usp5 knockdown overcame acquired vemurafenib resistance and sensitized BRAF and NRAS mutant melanoma cells to apoptosis initiated by MEK inhibitor, cytokines or DNA-damaging agents. Knockdown and overexpression studies demonstrated that Usp5 regulates p53 (and p73) levels and alters cell growth and cell cycle distribution associated with p21 induction. Usp5 also regulates the intrinsic apoptotic pathway by modulating p53-dependent FAS expression. A small molecule DUB inhibitor (EOAI3402143) phenocopied the FAS induction and apoptotic sensitization of Usp5 knockdown and fully blocked melanoma tumor growth in mice. Overall, our results demonstrate that BRAF activates Usp5 to suppress cell cycle checkpoint control and apoptosis by blocking p53 and FAS induction; all of which can be restored by small molecule-mediated Usp5 inhibition. These results suggest that Usp5 inhibition can provide an alternate approach in recovery of diminished p53 (or p73) function in melanoma and can add to the targeted therapies already used in the treatment of melanoma.

Targeting deubiquitinase activity with a novel small-molecule inhibitor as therapy for B-cell malignancies

“…11 Although some improvement was achieved in selectivity, we were unable to fully modify DUB selectivity with G9 because we retained Usp5 inhibition, which was previously noted as a WP1130 target. 10,22 However, Usp5 was activated in myeloma cells, and its inhibition increases p53 accumulation, as we have shown in this study and as others have shown in their studies and in other tumor types. 10,22,28 Because p53 is infrequently inactivated by mutation in B-cell tumors, it remains a potential effector of apoptosis.…”

“…10,22 However, Usp5 was activated in myeloma cells, and its inhibition increases p53 accumulation, as we have shown in this study and as others have shown in their studies and in other tumor types. 10,22,28 Because p53 is infrequently inactivated by mutation in B-cell tumors, it remains a potential effector of apoptosis. Therefore, G9-mediated inhibition of Usp5 and p53 accumulation may amplify the effects of Usp9x/Usp24 inhibition in some tumors rather than pose a disadvantage as a result of partial selection.…”

“…22 Dose-dependent inhibition of Usp9x/Usp24 and Usp5 were noted in G9-treated MM1. S cells (Figure 6C), which was associated with a reduction in Mcl-1 levels, an increase in p53 stability, and the rapid onset of apoptosis (cleaved PARP).…”

The deubiquitinase Leon/USP5 regulates ubiquitin homeostasis during Drosophila development

“…Thus, different DUBs may target the same substrate, providing a multi-facet regulation or a cell-context dependent regulation. Until now, USP5 has been shown to link two carcinomas: alterations of USP5 isoforms in glioblastoma tumorigenesis and USP5 linked-suppression of p53 in melanoma [25,26]. Treatment of DUBs inhibitor EOAI3402143, targeting to USP9X and USP5, succeed to suppress melanoma growth [26].…”

“…Until now, USP5 has been shown to link two carcinomas: alterations of USP5 isoforms in glioblastoma tumorigenesis and USP5 linked-suppression of p53 in melanoma [25,26]. Treatment of DUBs inhibitor EOAI3402143, targeting to USP9X and USP5, succeed to suppress melanoma growth [26]. Thus, DUBs could be the important targets for disease therapy [27].…”