Proceedings of the National Academy of Sciences of the United States of America ( IF 9.412 ) Pub Date : 2021-04-13 , DOI: 10.1073/pnas.2013598118 Rana Falahat, Anders Berglund, Ryan M. Putney, Patricio Perez-Villarroel, Shota Aoyama, Shari Pilon-Thomas, Glen N. Barber, James J. Mulé
Lack or loss of tumor antigenicity represents one of the key mechanisms of immune escape and resistance to T cell–based immunotherapies. Evidence suggests that activation of stimulator of interferon genes (STING) signaling in tumor cells can augment their antigenicity by triggering a type I IFN-mediated sequence of autocrine and paracrine events. Although suppression of this pathway in melanoma and other tumor types has been consistently reported, the mechanistic basis remains unclear. In this study, we asked whether this suppression is, in part, epigenetically regulated and whether it is indeed a driver of melanoma resistance to T cell–based immunotherapies. Using genome-wide DNA methylation profiling, we show that promoter hypermethylation of cGAS and STING genes mediates their coordinated transcriptional silencing and contributes to the widespread impairment of the STING signaling function in clinically-relevant human melanomas and melanoma cell lines. This suppression is reversible through pharmacologic inhibition of DNA methylation, which can reinstate functional STING signaling in at least half of the examined cell lines. Using a series of T cell recognition assays with HLA-matched human melanoma tumor-infiltrating lymphocytes (TIL), we further show that demethylation-mediated restoration of STING signaling in STING-defective melanoma cell lines can improve their antigenicity through the up-regulation of MHC class I molecules and thereby enhance their recognition and killing by cytotoxic T cells. These findings not only elucidate the contribution of epigenetic processes and specifically DNA methylation in melanoma-intrinsic STING signaling impairment but also highlight their functional significance in mediating tumor-immune evasion and resistance to T cell–based immunotherapies.
肿瘤抗原性的缺乏或丧失代表了免疫逃逸和对基于T细胞的免疫疗法产生抗性的关键机制之一。有证据表明，肿瘤细胞中干扰素基因（STING）信号刺激物的激活可以通过触发I型IFN介导的自分泌和旁分泌事件序列来增强其抗原性。尽管已经一致报道了在黑色素瘤和其他肿瘤类型中抑制该途径，但是其机制基础仍不清楚。在这项研究中，我们询问这种抑制作用是否部分受到表观遗传调控，是否确实是黑色素瘤对基于T细胞的免疫疗法产生抗药性的驱动因素。使用全基因组DNA甲基化分析，我们显示了cGAS和STING的启动子超甲基化基因介导其协调的转录沉默，并在临床相关的人类黑素瘤和黑素瘤细胞系中导致STING信号功能的广泛损害。这种抑制作用可通过药理学抑制DNA甲基化来逆转，DNA甲基化可在至少一半的受检细胞系中恢复功能性STING信号传导。使用一系列与HLA匹配的人黑素瘤肿瘤浸润淋巴细胞（TIL）进行的T细胞识别测定，我们进一步证明，在STING缺陷型黑素瘤细胞系中，去甲基化介导的STING信号转导的恢复可以通过上调HLA的表达来改善其抗原性。 MHC I类分子，从而增强了它们对细胞毒性T细胞的识别和杀伤力。