Septin 2 accelerates the progression of biliary tract cancer and is negatively regulated by mir-140-5p

• SEPT2 expression is upregulated in biliary tract cancer.
• SEPT2 overexpression accelerates proliferation and invasion of biliary tract cancer cells.
• miR-140-5p expression is downregulated in biliary tract cancer.
• SEPT2 expression is negatively regulated by miR-140-5p.
• Overexpression of SEPT2 is associated with increased invasion of biliary tract cancer cells.

Aberrant expression of septin family members (SEPTs) has been noticed in various carcinomas; however, few studies have been conducted to determine their function in biliary tract cancer (BTC). In this study, we identified SEPT2 as a tumor-promoting gene that is regulated by miR-140-5p in BTC. Although miR-140-5p has been reported to be an anti-oncomiR for several types of cancer, this has not previously been shown for BTC. We found that the expression levels of SEPT2 and miR-140-5p were inversely correlated; SEPT2 was aberrantly upregulated in both primary tumor specimens and cell lines whereas miR-140-5p was significantly downregulated. Ectopic expression of miR-140-5p markedly decreased SEPT2 protein concentration in BTC cells and suppressed cell proliferation and colony formation in vitro. Interaction between miR-140-5p and the 3′UTR of SEPT2 was confirmed by luciferase assays and rescue experiments. Furthermore, overexpression of SEPT2 and low expression of miR-140-5p were associated with increased invasion of BTC as indicated by clinical parameters and confirmed by invasion assays in vitro. Xenografts formation assay also showed that SEPT2 overexpression significantly facilitated the growth of tumor in vivo. This finding may provide a novel therapeutic strategy for the treatment of biliary tract cancer.