MicroRNA-148b enhances proliferation and apoptosis in human renal cancer cells via directly targeting MAP3K9

Increasing evidence revealed that miRNAs, the vital regulators of gene expression, are involved in various cellular processes, including cell growth, differentiation, apoptosis and progression. In addition, miRNAs act as oncogenes and/or tumor suppressors. The present study aimed to verify the potential roles of miR148b in human renal cancer cells. miR-148b was found to be downregulated in human renal cancel tissues and human renal cancer cell lines. Functional studies demonstrated that plasmid-mediated overexpression of miR-148b promoted cell proliferation, increased the S-phase population of the cell cycle and enhanced apoptosis in the 786-O and OS-RC-2 renal cancer cell lines, while it did not appear to affect the total number of viable cells according to a Cell Counting Kit-8 assay. Subsequently, a luciferase reporter assay verified that miR148b directly targeted mitogen-activated protein kinase (MAPK) kinase kinase 9 (MAP3K9), an upstream activator of MAPK kinase/c-Jun N-terminal kinase (JNK) signaling, suppressing the protein but not the mRNA levels. Furthermore, western blot analysis indicated that overexpression of miR148b in renal cancer cells inhibited MAPK/JNK signaling by decreasing the expression of phosphorylated (p)JNK. In addition, over-expression of MAP3K9 and pJNK was detected in clinical renal cell carcinoma specimens compared with that in their normal adjacent tissues. The present study therefore suggested that miR-148b exerts an oncogenic function by enhancing the proliferation and apoptosis of renal cancer cells by inhibiting the MAPK/JNK pathway.