Interactome and Proteome Dynamics Uncover Immune Modulatory Associations of the Pathogen Sensing Factor cGAS

Abstract

<p id="P3">Viral DNA sensing is an essential component of mammalian innate immune response. Upon binding viral DNA, the cyclic-GMP-AMP synthase (cGAS) catalyzes the production of cyclic dinucleotides to induce type I interferons. However, little is known about how cGAS is homeostatically maintained or regulated upon infection. Here, we define cytoplasmic cGAS interactions with cellular and viral proteins upon herpes simplex virus (HSV-1) infection in primary human fibroblasts. We compare several HSV-1 strains (wild-type, <i>d109</i>, <i>d106</i>) that induce cytokine responses and apoptosis, and place cGAS interactions in the context of temporal proteome alterations using isobaric-labeling mass spectrometry. Follow-up analyses establish a functional interaction between cGAS and 2’−5’-oligoadenylate synthase-like protein OASL. The OAS-like domain interacts with the cGAS Mab21 domain, while the OASL ubiquitin-like domain further inhibits cGAS-mediated interferon response. Our findings explain how cGAS may be inactively maintained in cellular homeostasis, with OASL functioning as a negative feedback loop for cytokine induction. </p><p id="P4">Lum, <i>et al.</i> characterize the global protein interactome of the DNA sensor, cGAS, in cellular homeostasis and during HSV-1 infection. Integrating quantitative proteomics, CRISPR-Cas9 technology, reciprocal isolations, and cytokine assays, the function of the discovered cGASOASL interaction suggests negative interferon regulation and crosstalk between the DNA and RNA sensing pathways. </p><p id="P5"> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/d2f117db-ca86-4422-9b84-f75d12180e7f/PubMedCentral/image/nihms-1510741-f0008.jpg"/> </div> </p>