Promoter mutation of tumor suppressor microRNA-7 is associated with poor prognosis of lung cancer.

The significance of promoter mutations of microRNAs (miRNAs) in lung cancer is poorly understood. Recent evidence demonstrated that miRNA-7 (miR-7), a unique member of the miRNA family, exhibited decreased expression and has emerged as an important regulator in lung tumorigenesis. However, the mechanism underlying the downregulation of miR-7 in lung cancer remains largely unknown. In this study, we investigated the sites of mutation of the miR-7 promoter in lung cancer tissues using DNA sequencing. We identified a G→C change at the -617 site (25/39, 64.1%) and an A→G change at the -604 site (20/39, 51.3%) in the miR-7 promoter region in lung cancer tissues. Moreover, the expression of miR-7 in cancer tissue with promoter site mutations was lower compared with that in cancer tissue without mutations (P<0.05). Furthermore, we demonstrated that mutations at these sites may decrease the activity of the miR-7 promoter and alter the expression of miR-7. Notably, mutations at these sites of the miR-7 promoter were found to be closely associated with poor prognosis of lung cancer patients (P=0.037). These data may provide novel insight on the altered expression of specific miRNA molecules in lung cancer and ultimately prove to be helpful in the development of prognostic and therapeutic strategies against lung cancer.