miR-181a initiates and perpetuates oncogenic transformation through the regulation of innate immune signaling

Genomic instability predisposes cells to malignant transformation, however the molecular mechanisms that allow for the propagation of cells with a high-degree of genomic instability remains unclear. Here we report that miR-181a is able to transform fallopian tube secretory epithelial cells- the precursor cell type for the majority of high-grade serous ovarian cancers- through the inhibition of RB1 and simultaneously drives a cell protective inhibition of the stimulator-of-interferon-genes (STING) in order to maintain a microenvironment conducive to the propagation of cells with a high-degree of genomic instability. We found that miR-181a inhibition of RB1 leads to profound nuclear defects, genomic instability, and nuclear rupture resulting in a persistence of genomic material in the cytoplasm. While normally, this persistence of genomic material in the cytoplasm induces interferon response through STING to drive cell death, miR-181a directly downregulates STING and prevents apoptosis. The most common mechanism by which oncogenic miRNAs promote tumorigenesis is through the direct inhibition of tumor suppressor genes, however our studies highlight a new mechanism of oncomiR transformation through the combination of tumor suppressor gene inhibition and abrogation of immune surveillance that initiates and propagates tumor cell survival. Importantly, we found that miR-181a induction in ovarian patient tumors is tightly associated with decreased IFNg response and downregulation of lymphocyte infiltration amd leukocyte fraction. To date, DNA oncoviruses are the only known inhibitors of STING that allow for cellular transformation thus, our findings are the first to identify a genetic factor, miR-181a, that can downregulate STING expression, suppress activation of the immunosurveillance machinery, and impair signaling in cancer cells creating a survival advantage. Our studies support the notion that the induction of STING-mediated signaling in cancer cells could lead directly to cancer cell death however these effects are abrogated by miR-181a. Given the recent interest in the development of STING agonists as a strategy to harness the immune system to treat cancer, this study introduces novel patient selective biomarker as well as potent therapeutic target for development of the most effective combination treatments.

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Knarr M, Avelar RA, Sekhar SC, Kwiatkowski LJ, Dziubinski ML, McAnulty J, Skala S, Avril S, Drapkin R, DiFeo A