MicroRNA-200c is involved in proliferation of gastric cancer by directly repressing p27(Kip1).

P27(Kip1), also known as Cyclin-dependent kinase inhibitor 1B, is an important check-point protein in the cell cycle. It has been identified that although as a tumor suppressor, P27(Kip1) is expressed in different cancer cell types, which shows the therapeutic potential in tumor genesis. In this study, we examined the upstream regulatory mechanism of P27(Kip1) at the microRNA (miRNA) level in gastric carcinogenesis. We used bioinformatics to predict that microRNA-200c (miR-200c) might be a direct upstream regulator of P27(Kip1). It was also verified in gastric epithelial-derived cell lines that overexpression of miR-200c significantly inhibited the expression levels of P27(Kip1), whereas knockdown of miR-200c promoted P27(Kip1) expression in AGS and BGC-823 cells. Furthermore, we identified the direct binding of miR-200c on the P27(Kip1) 3' -UTR sequence by luciferase assay. MiR-200c could enhance the colony formation of cells by repressing P27(Kip1) expression. In addition, the negative correlation between P27(Kip1) and miR-200c in human gastric cancer tissues and matched normal tissues further supported the tumor-promoting action of miR-200c in vivo. Our finding suggested that miR-200c directly regulates the expression of P27(Kip1) and promotes cell growth in gastric cancer as an oncogene, which may provide new clues to treatment.