Integrin β3 expression is regulated by let-7a miRNA in malignant melanoma

Although integrin beta(3) is known to play an important role in melanoma progression and invasion, regulation of integrin beta(3) expression in melanoma has not been analysed in detail until today. As transcriptional regulation of integrin beta(3) was ruled out by our analysis, we concentrated on the regulation by microRNAs (miRNAs). Comparing primary melanocytes and malignant melanoma cell lines, we found that one candidate miRNA, miR-let-7a, was lost in melanoma and sequence analysis suggested an interaction with the 3'-untranslated region (3'-UTR) of integrin beta(3) mRNA. Transfection of melanoma cells with let-7a pre-miR (TM) molecules resulted in the downregulation of integrin beta(3) mRNA and protein expression. In addition, we cloned the 3'-UTR of the integrin beta(3) mRNA containing the let-7a target sequence into a reporter plasmid and revealed that let-7a negatively regulates reporter gene expression. The repressed expression of integrin beta(3) accompanies with reduced invasive potential of melanoma cells transfected with synthetic let-7a molecules observed in Boyden chamber assays. On the other hand, the induction of integrin beta(3) expression was achieved in melanocytes by transfection with let-7 a anti-miRs, resulting in invasive behavior of transfected melanocytes. In summary, we determined miRNA let-7a to be an important regulator of integrin beta(3) expression and showed that the loss of let-7a expression is involved in development and progression of malignant melanoma.