Abstract 4443: Targeting the mutual regulation between EZH2 and FADS2 to suppress ovarian cancer by synergistic inhibition of Notch signaling and mitochondrial function

Abstract Ovarian cancer (OC) is the most aggressive and lethal gynecological cancer associated with abnormal lipid metabolism. Enhancer of zeste homolog 2 (EZH2), the catalytic subunit of the polycomb repressive complex 2, is overexpressed in OC and other various cancers. It functions as a tumor promoter through canonical H3K27me3 modification and non-canonical ways, and is considered as a potential anticancer target. Although numerous EZH2 inhibitors have been developed and tested in clinical trials, the therapeutic effect of EZH2 inhibitors on solid tumors is still very limited. Here, we report that EZH2 bi-directionally regulates transcription of fatty acid desaturases 2 (FADS2) transcript variant 1 (v1) and 2/3 (v2/3) in canonical and non-canonical ways respectively. FADS2 is considered the rate-limiting enzyme in the synthesis of long chain polyunsaturated fatty acids (PUFAs). The transcript v1 encodes the full-length isoform, and v2/3 encodes the shorter protein predicted to lack the desaturase activity. EZH2 deficiency increased FADS2 v1 and decreased v2/3 at mRNA and protein level. In fact, the transcriptional start site for FADS2 v2/3 is located about 12 kb upstream of v1. EZH2 occupied at the promoter of FADS2 v1 and v2/3, but the enrichment of H3K27me3 at v2/v3 promoter was significantly lower than that at v1 promoter. These data indicate that EZH2 inhibits FADS2 v1 transcription by catalyzing H3K27me3, and promotes FADS2 v2/v3 transcription in a non-canonical way. In most OC cell lines tested, FADS2 v2/3 was dominant at the protein level compared to v1, which may be due to the advantage in protein stability of v2/3. EZH2 inhibitors reversed the FADS2 expression pattern by especially upregulating FADS2 v1, and increased PUFA abundance in OC cells. In reverse, targeting FADS2 by shRNA or inhibitor impaired EZH2 level and Notch signaling, resulting in suppressed cell proliferation and increased sensitivity to EZH2 inhibition. Proteomics analysis revealed that SDHD (succinate dehydrogenase complex subunit D, a subunit of mitochondrial complex II) was one of the most down-regulated protein under the combined treatment of FADS2 and EZH2 inhibitors. The combined treatment suppressed mitochondrial function and activated AMPK signaling, leading to inhibition of protein synthesis and cell cycle arrest. Furthermore, we found that combined targeting EZH2 and FADS2 induced synergistic inhibition of Notch signaling and mitochondrial function, and enhanced the therapeutic effect of OC in vitro and in vivo. In conclusion, this study reveals the regulation between EZH2 and FADS2, and provides a novel potential therapeutic strategy for ovarian cancer. Citation Format: Zhengyang Guo, Xiao Huo, Ying Song, Jiagui Song, Yang Bai, Tong Liu, Lixiang Xue. Targeting the mutual regulation between EZH2 and FADS2 to suppress ovarian cancer by synergistic inhibition of Notch signaling and mitochondrial function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4443.