Reduced expression of microRNA-432-5p by DNA methyltransferase 3B leads to development of colorectal cancer through upregulation of CCND2

Background: The tumor suppressive function of microRNA-432-5p (miR-432-5p) has been reported in several human malignances. This study aimed to probe the expression profile and role of miR-432-5p in colorectal cancer (CRC) and the molecular mechanism. Methods: Differentially expressed miRNAs between CRC and healthy samples were screened using a miRNA expression dataset GSE136020. The related molecules were identified by integrated bioinformatic analyses. A murine model of primary CRC was established and xenograft tumors were induced in mice. Altered expression of DNMT3B, miR-432-5p and cyclin D2 (CCND2) were introduced in CRC cells to determine their roles in the development of CRC. Results: miR-432-5p was downregulated in CRC according to the GSE136020 dataset. CCND2 mRNA was confirmed as a target of miR-432-5p. miR-432-5p was downregulated, whereas CCND2 was abundantly expressed in CRC tissues and cells. DNA methyltransferase 3B (DNMT3B) induced DNA methylation at the CpG island of miR-432-5p to inhibit its expression. miR-432-5p mimic significantly suppressed tumorigenesis of primary CRC in mice. Downregulation of DNMT3B weakened viability, invasiveness, blocked the cell cycle progression of CRC cells in vitro, and inhibited xenograft tumor growth and metastasis in nude mice. However, additional downregulation of miR-432-5p or upregulation of CCND2 restored the malignant behaviors of CRC cells. Conclusion: This study showed that DNMT3B induced DNA methylation and downregulation of miR-432-5p to promote development of CRC by upregulating CCND2.

Automated summary

miR-432-5p was found to be downregulated in CRC, while CCND2 was abundantly expressed. DNMT3B induced DNA methylation at the CpG island of miR-432-5p to inhibit its expression. The introduction of miR-432-5p mimic significantly suppressed tumorigenesis of primary CRC.