EZH2 Inhibition Enhances PD-L1 Protein Stability through USP22-Mediated Deubiquitination in Colorectal Cancer
Background: Previous studies have shown that EZH2 regulates tumor PD-L1 expression at the transcriptional level and has an impact on tumor immune environment and prognosis. However, whether EZH2 can regulate PD-L1 expression at the post-translational level remains unclear. Therefore, this study aims to investigate the effects of EZH2 inhibition on PD-L1 expression and protein stability in colorectal cancer cells, uncover its underlying mechanisms, and provide new therapeutic strategies for anti-tumor immune therapy. Methods: Multiple colorectal cancer cell models were used to examine the effects of EZH2 inhibition on PD-L1 expression and protein stability at both the protein and transcriptional levels. Transcriptome analysis was performed to identify differentially expressed genes associated with EZH2 inhibition and potential effectors involved in EZH2-mediated regulation of PD-L1 protein stability. Validation of candidate genes was conducted through public database analysis and knockdown or overexpression models. Finally, the combined effects of EZH2 inhibitors and anti-PD-1 immune therapy were evaluated using a mouse xenograft model. Results: We observed that inhibition of EZH2 function upregulated PD-L1 expression and enhanced its protein stability in colorectal cancer cells. Transcriptome analysis revealed that ubiquitin-specific protease 22 (USP22) played a crucial role in mediating EZH2-regulated PD-L1 protein stability. EZH2 affected USP22 expression through its classical epigenetic regulatory function, thereby modulating PD-L1 expression stability and influencing the tumor immune microenvironment. Combination treatment with EZH2 inhibitors and anti-PD-1 immune therapy improved the tumor microenvironment, promoted immune cell infiltration, and exerted synergistic anti-cancer effects. Conclusion: This study elucidated the mechanisms by EZH2 regulate PD-L1 expression and stability, providing new insights into therapeutic strategies for colorectal cancer. The combination of EZH2 inhibitors and anti-PD-1 immune therapy can synergistically enhance anti-tumor effects. These findings offer a potential therapeutic approach to improve the effectiveness of EZH2 inhibitors in cancer treatment and contribute to a better understanding of the role of EZH2 in tumor immune regulation. Overall design: To investigate the effects of EZH2 inhibition on PD-L1 expression and protein stability in colorectal cancer cells, we performed  RNA sequencing profiles of EPZ-6438-treated and DMSO-treated HCT116 cells.