USP33 enhances cell survival and stemness by deubiquitinating CTNNB1 in BXPC-3 and SW1990 cells.

Ubiquitin-specific protease 33 (USP33) has been implicated in various cancers, but its biological function and mechanism of action remain unknown in pancreatic cancer (PCa) as a deubiquitinating enzyme. Herein, we report that USP33 silencing inhibits PCa cell survival and self-renewal. USPs highly expressed in spherical PCa cells were screened by comparing the levels of ubiquitin-specific proteases in spherical PCa cells and adherent PCa cells. After silencing USP, the effect of USP on the proliferation of PCa cells was detected by CCK-8 and colony formation assay, and the effect of USP on cell stemness was detected by tumor sphere formation assay, flow analysis, and western blot analysis. The interaction of USP with CTNNB1 and the effect of USP on the ubiquitination of CTNNB1 were verified by coimmunoprecipitation assay. After replenishing CTNNB1, cell proliferation and cell stemness were examined. USP33 is upregulated in spheric BXPC-3, PCNA-1, and SW1990, compared with adherent BXPC-3, PCNA-1, and SW1990. USP33 interacts with CTNNB1, and stabilizes CTNNB1 by suppressing its degradation. Furthermore, cell proliferation, colony-forming, and self-renewal abilities of PCa cells in vitro, and the expression of stem cell markers EpCAM and CD44, C-myc, Nanog, and SOX2, were suppressed when USP33 was knocked down, which was reversed when CTNNB1 was ectopically expressed in PCa cells. Thus, USP33 promotes PCa cell proliferation and self-renewal by inhibiting the degradation of CTNNB1. USP33 inhibition may be a new treatment option for PCa patients.