OTUD4 stabilizes CYLD and counteracts BCL3 K63-linked polyubiquitination to suppress melanoma progression.

Melanoma is a highly aggressive malignancy in which dysregulated ubiquitin-dependent signaling contributes to tumor progression. OTUD4 is frequently downregulated in melanoma, but the functional significance of this alteration remains unclear. Here, we identify OTUD4 as a dual-mode deubiquitinase that suppresses melanoma progression by coordinating K48- and K63-linked polyubiquitination. OTUD4 directly binds and stabilizes CYLD by counteracting K48-linked polyubiquitination, whereas it independently binds BCL3 and counteracts BCL3 K63-linked polyubiquitination. OTUD4 depletion promotes BCL3 ubiquitination and nuclear translocation in melanoma cells, leading to increased melanoma cell proliferation and tumor growth in clonogenic and xenograft assays. Clinically, expression of OTUD4 and CYLD progressively decreases from normal skin through benign nevi to melanoma, with a further reduction in highly metastatic tumors. Reduced expression of OTUD4 and CYLD is associated with poor prognosis in patients with melanoma. Together, these results reveal an OTUD4-CYLD-BCL3 regulatory axis in melanoma, in which OTUD4 stabilizes CYLD and inhibits BCL3 activity.