Abstract
We found that microRNA-320a (miR-320a) was an attractive prognostic biomarker in breast cancer (BC) previously, whereas its regulatory mechanism in BC was not well understood. Our aim was to identify miR-320a target gene, examine the clinical relationship between miR-320a and its target, and further explore the functions of its target in BC. In this study, miR-320a downstream target gene was determined in HEK-293T cells by dual luciferase reporter assay. Then western blotting and immunohistochemistry were used to assess miR-320a target gene expression in fresh frozen (n=19, breast cancer and matched non-malignant adjacent tissue samples) and formalin-fixed paraffin-embedded (FFPE) (n=130, invasive BC tissues, the same panel detected for miR-320a expression previously) breast tissues, respectively. The results suggested that miR-320a could significantly suppressed Rab14 3'-untranslated region luciferase-reporter activity, and thus Rab14 was first identified as miR-320a target in BC. In 19 matched breast tissues, 12 (63%) breast cancer tissues showed high expression of Rab14 compared with the corresponding normal tissues. Rab14 immunoreactivity was mainly detected in the cytoplasm, 77/130 (59.2%) showed high expression. Furthermore, Rab14 expression was found to be inversely correlated with miR-320a expression in fresh-frozen breast tissues as well as in FFPE invasive breast cancer samples. In addition, Rab14 expression levels were positively related to tumor size (P = 0.034), lymph node metastasis (P < 0.001), distant metastasis (P = 0.001), histological grade (P = 0.035) and clinical tumor lymph-node metastasis stage (P = 0.001). Patients with higher Rab14 expression showed shorter overall survival time. Moreover, silencing of Rab14 could suppress proliferation, migration and invasion in breast cancer cell lines. Collectively, our results indicate that miR-320a could target Rab14 and that they could interact biologically in BC.