PCIF1-mediated m6Am modification activates USP5/BRD4 axis to promote glycolysis-driven immunosuppression in multiple...

Multiple myeloma (MM) is a malignant plasma cell disorder, with aberrant glycolysis being a key feature driving tumor progression and immune escape. PCIF1, an RNA modification-related protein, has been implicated in tumorigenesis, but its role in regulating MM progression remains unclear.

Molecular expression was analyzed in bone marrow plasma cells (PCs), MM cell lines, using qRT-PCR and Western blot. Cell viability, apoptosis and glycolysis were examined by CCK-8, flow cytometry, glucose uptake, lactate production and ECAR and OCR analysis, respectively. The CD8⁺ T cell function and cytotoxic effect were determined by CCK-8, flow cytometry and ELISA analysis. Mechanistic studies involved RIP, RNA pull-down and Co-IP to explore the relationship between PCIF1, USP5, and BRD4.

PCIF1 was upregulated in MM-PCs (vs. N-PCs) and correlated with poor patient survival and hypoxic microenvironment. PCIF1 knockdown inhibited MM cell growth, induced apoptosis, reduced PD-L1-mediated immune escape, alleviated CD8⁺ T cell exhaustion by suppressing glycolysis. Mechanistically, PCIF1 increased USP5 expression via m⁶Am modification, thus stabilizing BRD4 protein via reducing its ubiquitination level. Rescue experiments confirmed that BRD4 or USP5 overexpression reversed PCIF1 knockdown-mediated inhibitory effects on MM cell survival, glycolysis, tumor growth and immune escape.

In summary, PCIF1 activated USP5/BRD4 axis to promote MM cell survival and immune escape, suggesting that targeting PCIF1 may represent a novel therapeutic strategy for MM.