PSMD14 promotes hepatocellular carcinoma cell proliferation through E2F4-dependent PHF5A transcription and alternative splicing.

Dysregulation of the ubiquitin-proteasome system contributes to hepatocellular carcinoma (HCC), but how deubiquitination is linked to transcriptional regulation and alternative splicing remains unclear. In this study, proteomic analysis identified E2F4 as a PSMD14-interacting protein. Co-immunoprecipitation and ubiquitination assays showed that PSMD14 removed K48-linked polyubiquitin chains from E2F4, thereby reducing its degradation and increasing its protein stability. Stabilized E2F4 directly bound to the PHF5A promoter and promoted PHF5A transcription. As a component of the spliceosome, PHF5A regulated alternative splicing in HCC cells, including exon 3 skipping of NASP and exon 3 inclusion of POLA1. Silencing PSMD14, E2F4, or PHF5A inhibited HCC cell proliferation, whereas re-expression of the corresponding downstream factors partially restored cell growth, supporting a functional PSMD14-E2F4-PHF5A regulatory axis. Treatment with the proteasome-associated inhibitor O-phenanthroline (OPA) reduced E2F4 and PHF5A expression, altered NASP and POLA1 splicing, and suppressed xenograft tumor growth. Moreover, overexpression of E2F4 or PHF5A partially reversed OPA-induced splicing changes and growth inhibition in vitro. These findings identify a PSMD14-E2F4-PHF5A pathway that connects protein deubiquitination with transcriptional regulation and alternative splicing, and suggest that this pathway may represent a potential therapeutic vulnerability in HCC.