MIR133B-SEPT9 axis suppresses colorectal cancer progression by inhibiting β-catenin-mediated EMT signaling and is associated with poor prognosis.

Abstract

Background: MIR133B is a colorectal cancer (CRC)-associated gene, and its mature product, miR-133b, is significantly downregulated in CRC tissues.

Methods: We aimed to elucidate the tumor-suppressive role of miR-133b in CRC. To identify its downstream target genes, we compared the transcriptome of miR-133b-overexpressing cells with bioinformatic predictions and identified 23 potential target genes. We focused on SEPT9, a gene involved in tumor progression. We confirmed that SEPT9 is a direct target of miR-133b and investigated its role in cell proliferation, invasion, and epithelial-mesenchymal transition (EMT). In addition, we evaluated the expression and prognostic relevance of SEPT9 and active β-catenin in 219 patients with CRC.

Results: We confirmed the direct interaction between miR-133b and SEPT9 using luciferase reporter assay, qRT-PCR, and western blot. SEPT9 expression was significantly upregulated in CRC tissues compared with that in adjacent normal controls. In HCT116 and SW48 CRC cell lines, overexpression of miR-133b or knockdown of SEPT9 significantly reduced SEPT9 protein levels; suppressed proliferation, colony formation, and invasiveness; inhibited KRAS, BRAF, PI3K, pAKT, and pERK expression; and regulated EMT by downregulating N-cadherin, Vimentin, Snail, Twist, and active β-catenin while upregulating E-cadherin. Nuclear SEPT9 expression positively correlated with active β-catenin in human CRC tissues. In multivariate analysis, SEPT9 positivity independently predicted poor OS and RFS, and the combined SEPT9/active β-catenin expression pattern was an independent predictor of OS for both subgroups and of RFS specifically for the co-positive (SEPT9+/active β-catenin+) subgroup.

Conclusion: This study suggests that miR-133b suppresses CRC progression by directly targeting SEPT9 and inhibiting β-catenin-mediated EMT, as well as identifies the miR-133b-SEPT9-β-catenin axis as a potential prognostic indicator in patients with CRC.