Abstract 1690 Repression of cancer-immunity regulator STING by Kaposi's Sarcoma-Associated Herpesvirus (KSHV) microRNA

Kaposi sarcoma-associated herpesvirus (KSHV) is the etiologic agent of multiple severe malignancies including primary effusion lymphoma (PEL), multicentric Castleman disease (MCD), and Kaposi sarcoma (KS). Given that KSHV results in lifelong infections, viral mechanisms must compete at length against host immunity factors. A key pathway in innate immunity, the cGAS/STING pathway, detects abnormal cytosolic DNA often resulting from viral infections or cancer-derived DNA damage. The cGAS/STING pathway is suppressed during KSHV infection by several virally encoded proteins; however, these proteins are predominantly expressed only in the lytic phase of the virus. This raises the question of how KSHV suppresses the cGAS/STING pathway during latency, allowing the virus to remain undetected for decades. Notably, we identified several KSHV miRNAs, which are highly expressed during latency, to bind STING mRNA via qCLASH, an approach that combines immunoprecipitation and sequencing to identify direct miRNA-mRNA interactions. We have validated these miRNA-mRNA interactions using luciferase assay and have shown that endogenous STING expression is suppressed upon overexpression of these KSHV miRNAs. Additionally, we have shown that STING expression can be rescued though treatment of KSHV miRNA inhibitors in KSHV+ cell lines. KSHV fitness is dependent on the expression of these virally-encoded miRNAs, as shown by a reduced ability to undergo lytic reactivation in the absence or reduction of miRNA expression. Of note, lytic reactivation can be partially rescued in these miRNA-deprived cells through the knockdown of STING expression, highlighting the importance of their role in supporting viral fitness through the repression of STING. In all, these data represent the first identification of miRNAs that target STING, describe a novel KSHV immune evasion strategy, and provide insight into the development of immunomodulatory RNA-based therapeutics. Funding was provided by NIH T32AI007110, R00 CA230178-04, and American Cancer Society Institutional Research Grant 35544.