MicroRNA-212 functions as an epigenetic-silenced tumor suppressor involving in tumor metastasis and invasion of gastric cancer through down-regulating PXN expression.

Altered expression of paxillin (PXN) is closely linked to the pathogenesis progression, metastasis and prognosis of different malignancies including gastric cancer (GC). Epigenetic silencing of tumor-suppressive microRNAs (miRNAs) is a crucial component of the mechanism underlying activation of oncogenes in tumor. To screen for epigenetically silenced miRNAs which target PXN in GC, we performed bioinformatics algorithms and real-time PCR analysis, and identified miR-212 as the optimum candidate gene. A luciferase reporter gene assay validated that miR-212 directly targets the 3'UTR region of PXN. Importantly, miR-212 levels were inversely correlated with PXN expression in GC cell lines and clinical tumor tissues. The use of miR-212 minics decrease PXN mRNA and protein level in GC cell lines. Moreover, low expression of miR-212 and its promoter hypermethylation were causally related and were associated with aggressive tumor phenotype and adverse prognosis in GC. Restoring mir-212 expression by exogenous mirprecursor molecules transfection or reexpression of endogenous miR-212 treated by 5-aza-2'-deoxycytidine (5-aza) can exert similar effect that reduce GC cells invasion and metastasis abilities in vitro by interacting PXN gene. In addition, 5-aza-induced PXN reduction could be partically blocked by miR-212 inhibitor, resulting in a reversal of weankening cell migration and invasion ability of 5-aza. A rescue experiment and a loss-of-function experiment in vitro and vivo showed that PXN restoration rescues migration and invasion phenotype in miR-212 overexpressed GC cell lines and PXN knockdown blocks GC cells migration and invasion in the presence miR-212 inhibitors. Taken together, our results clearly show that overexpression of PXN induced by methylationsuppressed miR-212 promotes tumor metastasis and invasion, and regulation of miR-212 expression may be a novel therapeutic strategy for gastric cancer.