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EZH2 Inhibition Activates a dsRNA-STING-Interferon Stress Mechanism that Potentiates Response to PD-1 Check-Point Blockade in Prostate Cancer

ABSTRACT: Prostate cancers are considered immunologically ‘cold’ tumors given the very few patients who respond to checkpoint inhibitor therapy (CPI). Recently, enrichment of interferon stimulated genes (ISGs) predicts a favorable response to CPI across various disease sites. The enhancer of zeste homolog-2 (EZH2) is over-expressed in prostate cancer and is known to negatively regulate ISGs. Here, we demonstrate that a majority of ISGs are not directly silenced by EZH2 mediated H3K27me3 deposition, but instead in a poised chromatin state associated with accessible chromatin (ATAC+) and H3K27ac deposition. Inhibition of EZH2 catalytic activity in prostate cancer models activates a dsRNA-STING-ISG cellular stress response upregulating genes involved in antigen presentation, Th-1 chemokine signaling, and interferon (IFN) response, including PD-L1 that is dependent on STING activation. EZH2 inhibition combined with PD-1 CPI significantly enhances anti-tumor response dependent on up-regulation of tumor PD-L1 expression. Further, combination therapy significantly increases intratumoral trafficking of activated CD8+ T-cells and M1 tumor associated macrophages (TAMs) with concurrent loss of M2 TAMs. Our study identifies EZH2 as a potent inhibitor of antitumor immunity and responsiveness to CPI. This data suggests EZH2 inhibition is a novel therapeutic direction to enhance prostate cancer response to PD-1 CPI.

ORGANISM(S): Mus musculus

PROVIDER: GSE146076 | GEO | 2020/10/01

REPOSITORIES: GEO

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Project description: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.

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EZH2 Inhibition Activates a dsRNA-STING-Interferon Stress Mechanism that Potentiates Response to PD-1 Check-Point Blockade in Prostate Cancer

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