USP3 stabilizes NPM1 to sustain nucleosome assembly and promote bladder cancer chemoresistance

Abstract Cisplatin-based chemotherapy remains a cornerstone for treating advanced bladder cancer (BCa). However, the frequent emergence of chemoresistance and high recurrence rates poses formidable clinical challenges. Although nucleophosmin 1 (NPM1) is known to orchestrate chromatin homeostasis and cancer cell survival, the upstream regulatory mechanisms governing its stability in BCa remain largely elusive. Here, we report that the deubiquitinating enzyme USP3 is upregulated in BCa and correlates with poor prognosis. USP3 silencing markedly impedes BCa cell proliferation in vitro and xenograft tumor growth in vivo and profoundly sensitizes BCa cells to cisplatin treatment; these effects are partially reversed by ectopic NPM1 expression. Mechanistically, USP3 directly interacts with NPM1 and actively removes its K48-linked polyubiquitination, which stabilizes NPM1 to sustain nucleosome assembly and thereby buffers cells against DNA damage, as evidenced by altered MNase digestion patterns, elevated H3K56ac levels, and exacerbated γ-H2AX signaling. Clinically, USP3 is significantly upregulated in BCa tissues and positively correlated with NPM1 protein levels. In summary, our findings unveil a novel USP3-NPM1 signaling axis that critically maintains chromatin homeostasis and drives chemoresistance, highlighting that targeting USP3 may be a highly promising therapeutic strategy for advanced BCa.