m6A-modified circFADS2 promotes hepatocellular carcinoma progression through CAPRIN1-mediated TYMS mRNA stability

Circular RNAs (circRNAs) are vital regulators in multiple cancers. However, the biological function of circFADS2 (circBase ID: hsa_circ_0022382) in hepatocellular carcinoma (HCC) remains unknown. Integrative analysis of three Gene Expression Omnibus (GEO) datasets (GSE155949, GSE235991, and GSE263134) was performed to identify candidate circRNAs. circFADS2 expression was validated in HCC tissues and cell lines by RT-qPCR. The circular structure of circFADS2 was confirmed by RNase R resistance and Sanger sequencing. Functional assays, including EdU incorporation, Transwell invasion, and flow cytometric apoptosis analyses, were performed. The underlying mechanisms were investigated using bioinformatic prediction, RNA pull-down, RNA immunoprecipitation (RIP), MeRIP-qPCR, actinomycin D treatment, Western blot, and rescue experiments. circFADS2 was significantly upregulated in both HCC tissues and cell lines. circFADS2 expression was positively correlated with tumor size, microvascular invasion, and advanced TNM stage in HCC patients. Functionally, circFADS2 knockdown inhibited HCC cell proliferation and invasion, and induced apoptosis. Methyltransferase-like 3 (METTL3) mediated the N6-methyladenosine (m 6 A) modification of circFADS2 and promoted its upregulation. circFADS2 downregulation attenuated the tumor-promoting effects induced by METTL3 overexpression in HCC cells. Mechanistically, circFADS2 bound to cell cycle associated protein 1 (CAPRIN1) to enhance thymidylate synthase (TYMS) mRNA stability. TYMS upregulation partly reversed the effects of circFADS2 knockdown on the malignant phenotypes of HCC cells. m 6 A-modified circFADS2 promotes HCC progression by enhancing CAPRIN1-mediated TYMS mRNA stability.