MicroRNA‐331‐3p inhibits epithelial‐mesenchymal transition by targeting ErbB2 and VAV2 through the Rac1/PAK1/β‐catenin axis in non‐small‐cell lung cancer

: MicroRNAs have been reported to play critical roles in the regulation of non-small-cell cancer (NSCLC) development, but the role of microRNA (miR)-331-3p in NSCLC is still unclear. In this study, the expression levels of miR-331-3p in NSCLC tumor tissues and adjacent normal tissues were examined by quantitative RT-PCR, and the relationship between miR-331-3p expression and patient clinicopathological characteristics was analyzed. The effects of miR-331-3p on epithelial-mesenchymal transition (EMT), migration, and metastasis of NSCLC cells were determined in vitro and vivo. Direct functional targets of miR-331-3p were identified by luciferase reporter assay, western blot assay, immunohistochemical staining, and rescue assay. The downstream pathway regulated by miR-331-3p was identified by immunofluorescence, immunoprecipitation, and Rac1 activity examination. Our results showed that miR-331-3p was significantly downregulated in NSCLC tumor tissues and was correlated with clinicopathological characteristics, and miR-331-3p could be an independent prognostic marker for NSCLC patients. Furthermore, miR-331-3p significantly suppressed EMT, migration and metastasis of NSCLC cells in vitro and in vivo. Both ErbB2 and VAV2 were direct functional targets of miR-331-3p. The activities of Rac1, PAK1, and β-catenin were regulated by miR-331-3p through ErbB2 and VAV2 targeting. These results indicated that miR-331-3p suppresses EMT, migratory capacity, and metastatic ability by targeting ErbB2 and VAV2 through the Rac1/PAK1/β-catenin axis in NSCLC.