The cGAS-STING pathway senses cytosolic DNA in infected cells and cancer cells and triggers production of type I interferon and other cytokines, thus eliciting immune responses. Deficiency in the pathway prevents T cell responses to several viruses and to transplanted tumor lines. Our new results show that the pathway is critical for activating spontaneous NK cell responses against cancer, and virus infections. Furthermore, in probing the underlying mechanisms, our research has uncovered a new cellular mechanism whereby cGAS and STING activate immune responses. Using genetic approaches, we found that the NK response to transferred tumor cells depends on cGAS expression in tumor cells and STING expression in host cells. We interpret these data to indicate that cGAS activation is the key event that occurs in infected or transformed cells resulting in the production of the cyclic dinucleotide cGAMP. cGAMP is then transferred from the infected/transformed cells to other immune cells, such as antigen presenting cells, which are induced to initiate the immune response. Hence, we propose that cGAMP transfer between cells is a fundamental mechanism in immune activation. In considering how cGAMP is transferred between cells, we hypothesized that specific membrane transporters must play a role. Using a genome-wide CRISPRi screen, we identified a transporter molecule that specifically imports cGAMP into cells. Using a series of knockout mice and conditional knockout mice, and cellular manipulations and transfers, we propose to test the requirement of cGAS-STING signaling in NK and T cell responses to cancer and DNA viruses, the generality of the requirement of the transfer mechanism in viral infections and cancer models and for T cell and NK cell responses, the roles of the newly identified transporters in the process, and to define the specific cells that must import the cGAMP for immune responses to occur. Specifically, we will: (1) Determine the sites of action of cGAMP and STING and intercellular transfer of cGAMP in anti-viral responses, including NK and T cell responses; (2) Determine sites of action of cGAMP and STING and intercellular transfer of cGAMP in T cell responses to cancer, in transfer models and GEM cancer models; (3) Determine roles of cGAMP transporters in anti-viral and anti-tumor and immune responses. Using conditional knockout mice and inhibitor studies, we will test their function in anti-herpesvirus and anti-tumor responses, including a GEM model of cancer.
We have discovered that an innate immune signaling pathway, mediated by the cGAS and STING proteins, is necessary to elicit natural killer cells to reject tumors, and that the two proteins act in different cells: cGAS in the tumor cells and STING in non-tumor cells. Our results suggest that cGAMP, an intermediary molecule that is made by cGAS and activates STING, is made in the tumor cells and transferred to other cells to induce the response, and we have identified transporter molecules that may be responsible for transfer of cGAMP from cell to cell. We propose to investigate the role of the cGAS-STING pathway, cGAMP transfer and the transporters we have discovered, in T and NK cell responses to cancer and viral infections in vivo. 1
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