microRNA-99a is downregulated and promotes proliferation, migration and invasion in non-small cell lung cancer A549 and H1299 cells

There is increasing evidence that microRNAs (miRNAs) are able to play a key role in the diagnosis and therapy of cancer. miRNA-99a (miR-99a), which is downregulated in several human malignancies, has been reported as a potential tumor suppressor. However, to the best of our knowledge, the expression and function of miR-99a has not been investigated in human non-small cell lung cancer (NSCLC) at present. The aim of the current study was to evaluate the association between NSCLC and miR-99a. miR-99a expression was analyzed in 15 pairs of NSCLC and non-cancerous tissue samples by reverse transcription-quantitative polymerase chain reaction. In addition, the NSCLC A549 and H1299 cell lines were transfected with miR-99a mimics, and the effect of miR-99a on the cell cycle, cell proliferation, migration and colony formation of A549 and H1299 cells was investigated. It was found that the level of miR-99a expression was significantly downregulated in NSCLC tissues and that ectopic overexpression of miR-99a significantly inhibited the growth of A549 and H1299 cells. Additionally, ectopic overexpression of miR-99a inhibited A549 and H1299 cell migration and invasion by inhibiting epithelial to mesenchymal transition. The downregulation of insulin-like growth factor 1 receptor (IGF-1R) by miR-99a and knockdown of IGF-1R mediated by siRNA were each found to phenocopy the effect of miR-99a overexpression in NSCLC. To the best of our knowledge, the present study demonstrated for the first time that, in NSCLC, miR-99a is downregulated and thus regulates proliferation, colony formation and migration through the IGF-1R pathway, which indicates that miR-99a is a diagnostic biomarker for NSCLC.