METTL3-Modulated circUHRF2 Promotes Colorectal Cancer Stemness and Metastasis through Increasing DDX27 mRNA Stability by Recruiting IGF2BP1

SIMPLE SUMMARY: Colorectal cancer (CRC) is the third leading cause of cancer deaths worldwide, and no cure exists for most patients at advanced stages with distant metastasis. CircUHRF2 has been aberrantly expressed in CRC, but its role in CRC growth and metastasis remains largely unclear. This study demonstrated that circUHRF2 was upregulated in CRC and correlated with poor prognostic outcomes in CRC patients. Methyltransferase-like 3 (METTL3) facilitated circUHRF2 expression through N6-methyladenine modification (m(6)A) modification. circUHRF2 or METTL3 silencing suppressed in vitro cell stemness, migration, and invasion; and in vivo tumor growth and liver metastasis. Furthermore, circUHRF2 is bound with insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) and increases the stability and expression of DEAD-box helicase 27 (DDX27) mRNA. Anti-cancer effect of circUHRF2 silencing was counteracted by DDX27 overexpression. Our identification of the oncogenic roles of circUHRF2 and METTL3 in CRC progression as well as their regulatory function through the IGF2BP1-DDX27 axis, has broadened our current knowledge about CRC and may help the future development of more efficient treatments. ABSTRACT: Increasing evidence has implicated that circular RNAs (circRNAs) exert important roles in colorectal cancer (CRC) occurrence and progression. However, the role of a novel circRNA, circUHRF2, remains unknown in CRC. Our work aimed at identifying the functional roles of circUHRF2 in CRC and illustrating the potential mechanisms. As assessed by quantitative real-time PCR (qRT-PCR), circUHRF2 and methyltransferase-like 3 (METTL3) were highly expressed in CRC specimens and cells. Sanger sequencing and RNase R assays were performed to verify the ring structure of circUHRF2. Notably, aberrantly increased expression of circUHRF2 was positively correlated with poor prognosis of CRC patients. Functional experiments indicated that CRC stemness, migration, and epithelial-mesenchymal transition (EMT) were suppressed by the knockdown of circUHRF2 or METTL3. Mechanistically, METTL3 enhanced circUHRF2 expression through N6-methyladenine (m(6)A) modification. Rescue experiments showed that overexpression of circUHRF2 reversed the repressive effect of METTL3 silencing on CRC progression. Moreover, circUHRF2 inhibited the loss of DEAD-box helicase 27 (DDX27) protein via promoting the interaction between insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) and DDX27 mRNA. DDX27 knockdown repressed CRC malignant properties, which was counteracted by circUHRF2 overexpression. The in vivo assays in nude mice demonstrated that circUHRF2 or METTL3 silencing exerted a suppressive effect on CRC growth and liver metastasis via repressing DDX27 protein expression. Taken together, METTL3-mediated m(6)A modification upregulated circUHRF2 and subsequently inhibited loss of DDX27 protein via recruitment of IGF2BP1, which conferred CRC stemness and metastasis. These findings shed light on CRC pathogenesis and suggest circUHRF2 as a novel target for CRC treatment.