Abstract 1263: Hypoxia induces down-regulation of stimulator of interferon genes (STING) that is synergized with oncometabolites
Authors: Lu Yuhong , Yurkevicz Annali , Liu Yanfeng , Dow Jonathan , Glazer Peter M. 
Published: June 2023

Abstract
The cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway, a component of the innate immune system, functions to detect the presence of cytosolic DNA, and STING signaling is necessary for the anti-cancer immune response. However, STING expression is suppressed or lost in the majority of cancers, which correlates with poor survival in cancer patients. Hypoxia is a key feature of solid tumors that adversely affects prognosis by altering gene expression, creating an immunosuppressive tumor microenvironment, promoting genome instability, and hampering therapy responses. In this study, we found that that prolonged moderate hypoxia induces downregulation of STING expression in multiple cancer cell lines, causing decreased STING pathway activation after treatment with a STING agonist, or with DNA damaging chemotherapy. Mechanically, we found that hypoxia suppressed histone 3 lysine 4 (H3K4) methylation at the STING promoter based on chromatin immunoprecipitation (ChIP) assays in H1975 cells, a non-small cell lung cancer cell line, and knockdown of the H3K4 demethylases, KDM5A or KDM1A, prior to hypoxic exposure prevented hypoxia-induced down-regulation of STING expression. Moreover, decreased STING expression in hypoxic cells was reversed by treatment with the DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine. Next, we found that prolonged hypoxia increased both D-2-hydroxyglutarate (D-2-HG) and L-2-HG levels in H1975 cells, and that 2-HG treatment, by itself, decreased STING expression under normoxic conditions in H1975 cells. These findings are consistent with analysis of TCGA data showing that STING expression at the mRNA level is reduced in malignancies with mutations in isocitrate dehydrogenase 1 (IDH1) which causes elevated D-2-HG. Furthermore, we found that hypoxia increased Branched Chain Amino Acid Transaminase 1 (BCAT1) expression, and overexpression of BCAT1 accelerated STING downregulation in hypoxic condition. Functionally, expression of interferon (IFN)-stimulated genes (ISGs), CCL5 and interferon-β, was low in hypoxic H1975 cells compared to normoxic cells after treatment with poly(dA:dT), a small molecule STING agonist, and doxorubicin. Immunogenic cell death (ICD) was also reduced in hypoxic H1975 cells. In summary, the results suggest that hypoxia suppresses STING expression through epigenetic regulation, leading to STING silencing, and that this process synergizes with oncometabolites. The decreased STING caused by hypoxia further causes reduction of innate immune responses in cancer cells. Our study provides new understanding of the underlying mechanisms for STING silencing, which will help not only to study cancer immunity but also to develop novel therapeutic strategies.
Citation Format: Yuhong Lu, Annali Yurkevicz, Yanfeng Liu, Jonathan Dow, Peter M. Glazer. Hypoxia induces down-regulation of stimulator of interferon genes (STING) that is synergized with oncometabolites [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1263.