E-twenty-six-specific sequence variant 5 (ETV5) facilitates hepatocellular carcinoma progression and metastasis through enhancing polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC)-mediated immunosuppression

Background Despite the success of immune checkpoint blockade, a lack of understanding of the hepatocellular carcinoma (HCC) immune microenvironment impedes its development. Objective We aim to elucidate the essential function of E-twenty-six-specific sequence variant 5 (ETV5) in regulating the immune microenvironment in HCC. Design Humanised mouse models, murine orthotopic models and diethylnitrosamine/carbon tetrachloride (DEN/CCl 4 )-induced HCC models were used to examine the function of ETV5. The downstream targets of ETV5 were screened using chromatin immunoprecipitation sequencing, CUT&Tag and RNA sequencing. Immune cells were examined using flow cytometry and immunofluorescence. S100 calcium-binding protein A9 (S100A9) was targeted by neutralising antibodies. Results Overexpression of ETV5 in HCC cells facilitated HCC metastasis and immune escape by recruiting and enhancing the immunosuppressive capabilities of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs). Mechanistically, ETV5 transactivated programmed death ligand 1 (PD-L1) and S100A9 expression. Inhibition of S100A9 or myeloid-specific knockout of toll-like receptor 4 (TLR4)/receptor for advanced glycation endproducts (RAGE), the receptors of S100A9, impeded ETV5-induced PMN-MDSC recruitment. Meanwhile, S100A9 within the tumour microenvironment elevated ETV5 expression via the extracellular signal-regulated kinase (ERK)/nuclear factor-kappa B pathway. Additionally, ETV5 transcriptionally upregulated PD-L1 in MDSCs as well, thereby augmenting their immunosuppressive functions. Myeloid-specific Etv5 knockout attenuated HCC progression. We developed monoclonal neutralising-S100A9 antibodies that effectively inhibited ETV5-mediated PMN-MDSC infiltration. Synergistic application of anti-S100A9 or TLR4/RAGE inhibitors with anti-PD-L1 therapy significantly suppressed ETV5-mediated HCC progression. Conclusion ETV5 facilitates HCC progression and metastasis by promoting the recruitment, infiltration and activation of PMN-MDSCs. Synergistic application of anti-S100A9 or TLR4/RAGE inhibitors with anti-PD-L1 therapy holds great promise as an effective combinational treatment strategy for ETV5-positive HCC.