MicroRNA-200b inhibits pituitary tumor cell proliferation and invasion by targeting PKCα

The present study aimed to investigate the expression of miR-200b and protein kinase C alpha (PKC alpha) in pituitary tumors and to determine whether miR-200b may inhibit proliferation and invasion of pituitary tumor cells. The regulation of PKC alpha expression was targeted in order to find novel targets for the treatment of pituitary tumors. In total, 53 pituitary tumor tissue samples were collected; these included 28 cases of invasive pituitary tumors and 25 cases of non-invasive tumors, in addition to 5 normal pituitaries. The expression level of miR-200b in the pituitary tumor tissue was detected by quantitative polymerase chain reaction (qPCR) and the expression of PKC alpha protein was detected by immunohistochemistry. A PKC alpha 3'untranslated region (UTR) luciferase vector was constructed and a dual luciferase reporter gene assay was employed in order to examine the effect of miR-200b on the PKC alpha 3'UTR luciferase activity. AtT-20 cells were transfected with miR-200b mimics, PKC alpha siRNA and miR-200b mimics + PKC alpha, and the changes in cellular proliferation, invasion and apoptosis were observed via MTT, Transwell assay and flow cytometric analysis. Furthermore, PKC alpha mRNA expression was determined by qPCR, and Western blotting was performed to detect the expression of PKC alpha protein. miR-200b revealed downregulation in invasive pituitary tumor tissue, and the expression level was significantly down-regulated compared with normal and non-invasive pituitary tumor tissue (P<0.01). In addition, the positive rate of PKC alpha protein expression in invasive pituitary tumor tissues was significantly higher than in normal and non-invasive tissues (P<0.01). PKC alpha protein levels are inversely correlated with miR-200b levels in invasive pituitary tumor tissues (r=-0.436, P=0.021). The dual luciferase reporter gene assay revealed that miR-200b could specifically bind to the 3'UTR of PKC alpha and significantly inhibit the luciferase activity by 39% (P<0.01). Upregulation of miR-200b or downregulation of PKC alpha could suppress cell proliferation and invasion, and increase apoptosis of AtT-20 cells. It was revealed that PKC alpha siRNA could suppress both proliferation and invasion of AtT-20 cells and partially simulate the function of miR-200b. Expression of PKC alpha mRNA and protein decreased significantly in AtT-20 cells overexpressing miR-200b. Additionally, miR-200b was significantly down-regulated in invasive pituitary tumor tissue and inversely correlated with PKC alpha protein levels. In conclusion, miR-200b inhibited proliferation and invasiveness and promoted the apoptosis of pituitary tumor cells by targeting PKC alpha. The observations of the present study indicate that miR-200b and PKC alpha may serve as promising therapeutic targets for invasive pituitary tumors.