PSMD14通过E2F4依赖的PHF5A转录和可变剪切促进肝细胞癌细胞增殖。

Abstract

PSMD14 deubiquitinates and stabilizes E2F4 by removing K48-linked ubiquitin chains. • Stabilized E2F4 directly activates PHF5A transcription in HCC cells. • PHF5A regulates NASP and POLA1 alternative splicing to support HCC proliferation. • The PSMD14–E2F4–PHF5A axis links protein deubiquitination to RNA 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. High PSMD14 interacts with E2F4 by suppressing E2F4 ubiquitination and its degradation, resulting in the transcriptional upregulation of PHF5A, then maintaining the appropriate AS of NASP and POLA1 for tu