miR-381 suppresses C/EBPα-dependent Cx43 expression in breast cancer cells

Cx43 (connexin43) is an enhancer of the metastasis of breast cancer cells. Our previous study identified miR-381 as an indirect suppressor of Cx43 gene expression, with the precise mechanism being not understood. In the present study, using a reporter gene assay, we found that miR-381 suppressed Cx43 gene expression via the promoter region-500/-250. With site-directed gene mutation, we demonstrated that miR-381 could directly bind with the sequences CACUUGUAU in the 3 '-UTR so as to inhibit C/EBP alpha (CCAAT/enhancer-binding protein alpha) expression. C/EBP alpha was further identified as a novel transcription factor by binding to a canonic element (AATTGTC) locating at-459/-453 in the promoter region of the Cx43 gene. Functionally, we demonstrated that miR-381 suppressed C/EBP alpha- and Cx43-dependent migration and invasion of breast cancer cells. Finally, we revealed that decreased levels of miR-381 as well as increased expression of C/EBPa and Cx43 in the metastatic breast cancer cells and tissues. Therefore we are the first to identify that miR- 381 suppresses C/EBP alpha- dependent Cx43 expression in breast cancer cells. The miR-381-C/EBP alpha- Cx43 axis might be a useful diagnostic and therapeutic target of metastatic breast cancer.