The proto-oncogene c-Src phosphorylates cGAS to reduce DNA binding and activation

cGMP-AMP synthase (cGAS) is a DNA sensor and responsible for inducing an anti-tumor immune response. Recent studies reveal cGAS is frequently inhibited in cancer, and therapeutic targets to promote anti-tumor cGAS function remain elusive. c-Src is a proto-oncogene tyrosine kinase and is expressed at elevated levels in numerous cancers. Here, we demonstrate that c-Src expression in tumors from various cancers negatively correlates with innate immune gene expression and patient survival. We determine that c-Src restricts cGAS signaling in human cell lines through c-Src small molecule inhibitors, depletion, and overexpression. cGAS and c-Src interact in cells and in vitro, while c-Src directly inhibits cGAS enzymatic activity and DNA binding in a kinase-dependent manner. c-Src phosphorylates cGAS, and inhibition of cGAS Y248 phosphorylation partially reduces c-Src inhibition. Collectively, our study demonstrates that cGAS anti-tumor signaling is hindered by the proto-oncogene c-Src and describes how cancer-associated proteins can regulate the innate immune system.