MicroRNA-135b regulates the stability of PTEN and promotes glycolysis by targeting USP13 in human colorectal cancers

Dysregulation of microRNAs has been reported to be involved in the progression of human colorectal cancers (CRCs). Loss of the adenomatous polyposis coli (APC) gene is a common initiating event in CRCs. PTEN inactivation by mutation or allelic loss also occurs in CRCs. miR-135b was reported to be upregulated in CRCs and its overexpression was due to APC/beta-catenin and PTEN/PI3K pathway deregulation. APC was proven to be a target of miR-135b and forms a feedback loop with miR-135b. In the present study, we found that ubiquitin-specific peptidase 13 (USP13) was a target of miR-135b. miR-135b downregulated the expression of USP13, and reduced the stability of PTEN. miR-135b promoted cell proliferation and glycolysis that could be reversed by the overexpression of USP13 or PTEN. Moreover, knockdown of USP13 upregulated the levels of endogenous miR-135b, but not those in CRC cells with PTEN mutation. The results showed positive feedback loops between miR-135b and PTEN inactivation in CRCs.