Molecular mechanism of USP15-mediated post-transcriptional regulation of CXCR4 via PTBP1 ubiquitination in macrophage M2 polarization and immune evasion in colorectal cancer

Objective Colorectal cancer (CRC) is a common gastrointestinal malignancy with elevated morbidity and mortality rates, posing a severe hazard to human health. This research aims to investigate the role of USP15 in immune evasion of CRC and identify new targets for CRC treatment. Methods USP15, PTBP1, and CXCR4 were detected by qRT-PCR and Western blot. Tumor-associated macrophage infiltration and CD8 + T cell function were detected. USP15 was overexpressed or silenced in CRC cells, which were co-cultured with PMA-induced THP-1 cells, followed by measurement of CD206 + /CD86 + proportion and PD-L1, iNOS, and Arg-1 expression. Polarized macrophages were co-cultured with CD8 + T cells. CD8 + T cell apoptosis was assayed. IL-10, TGF-β, TNF-α, and IL-12 were assessed. The bindings of USP15 to PTBP1 and PTBP1 to CXCR4 were assayed. PTBP1 ubiquitination was analyzed after treatment with MG132. CT26 cells with stably low USP15 expression were injected into BALB/c mice to investigate immune evasion in vivo . Results USP15 exhibited high expression levels in CRC and correlated with unfavorable prognosis of CRC patients. USP15 inhibition suppressed tumor-associated macrophage M2 polarization, reduced PD-L1 and Arg-1 expression, increased iNOS expression, inhibited CD8 + T cell apoptosis, and suppressed immune evasion of CRC cells. USP15 upregulated PTBP1 expression through deubiquitination, thereby promoting the binding of PTBP1 to CXCR4 mRNA and increasing CXCR4 expression. Overexpression of PTBP1 or CXCR4 partially reversed the inhibitory effect of USP15 inhibition on macrophage M2 polarization and promoted CRC immune evasion. Conclusion USP15 promotes M2 polarization of tumor-associated macrophages through the PTBP1/CXCR4 axis, thereby facilitating immune evasion of CRC cells.