The pathological significance of the circular RNA DDIT4 (CircDDIT4), which is formed by back-splicing at the 3'-untranslated region (UTR) with a 5' splice acceptor site in exon 2 of linear DDIT4 mRNA, has yet to be determined. Our study found that circDDIT4 is downregulated in prostate cancer (PCa) and functions as a tumor suppressor during PCa progression. By competitively binding to ELAV-like RNA binding protein 1 (ELAVL1/HuR) through its 3'-UTR, circDDIT4 acts as a protein sponge to decrease the expression of PCa-overexpressed anoctamin 7 (ANO7). This promotes PCa cell apoptosis while inhibiting cell proliferation and metastasis. Furthermore, we discovered that N6-methyladenosine (m6A) modification facilitates the biogenesis of circDDIT4. The methyltransferase complex consisting of WTAP/METTL3/METTL14 increases the level of circDDIT4, while the RNA demethylase FTO decreases it. Implications: These findings suggest that abnormal co-transcriptional modification of m6A promotes PCa initiation and progression via a circular RNA-protein-cell signaling network.