The Role of RNA Methylation in the Regulation of Viral Mimicry in Ovarian Cancer

Project Summary Ovarian cancer (OC) is the most lethal malignancy of the female reproductive system with poor responses to immunotherapies due to a highly immunosuppressive tumor microenvironment. In contrast, higher levels of infiltrating lymphocytes are associated with better survival in OC, emphasizing the need to develop strategies to enhance immune cell recruitment and activation. One strategy is the use of DNA methyltransferase inhibitors (DNMTis), which include the FDA approved 5-Azacytidine and 5-Aza-2’-deoxycytidine, to increase the expression of transposable elements (TEs) to promote an antitumor immune response. The removal of DNA methylation upregulates TEs which form double-stranded RNAs (dsRNAs) that can be sensed by immune sensors, triggering type I interferon signaling in a response termed “viral mimicry”. Following type I interferon induction, immune cells are recruited and activated to promote antitumor immunity. However, many cancers exhibit high baseline levels of TE expression without signaling an immune response. This highlights the potential role of post-transcriptional regulation, such as RNA methylation, in the negative regulation of the viral mimicry response. Indeed, RNA methylation, specifically N6-methyladenosine (m6A), has been shown to promote the degradation of TE RNA and prevent dsRNA formation. In OC, the main m6A writer, METTL3, has been described as an oncogene. Additionally, other m6A readers are overexpressed compared to normal tissue and associated with poor survival and reduced immune cell infiltration. These specific aims will test the overall hypothesis that m6A modulates transposable element RNA to limit dsRNA sensing and dampens the viral mimicry response. Aim 1 will determine how m6A of TEs change throughout the transformation of fallopian tube cells, the common cell of origin for high-grade serous OC. Aim 2 will elucidate the role of m6A in regulating TEs and downstream immune signaling following epigenetic therapy. Collectively, the proposed aims will investigate the role of m6A in regulating TE RNA and downstream innate immune signaling during OC transformation and in response to epigenetic therapy. Results from these studies will provide insight into the potential for pharmacologically inhibiting m6A alone or synergistically with epigenetic therapy to promote antitumor immunity in OC.