MicroRNA-dependent regulation of cKit in cutaneous melanoma.

Loss of cKit receptor in cutaneous melanomas was attributed to the down-regulation of AP2 transcription factor. Our analysis of 27 melanoma cell lines showed no correlation between AP2 and c-kit expression. Suggesting a post-transcriptional mechanism of cKit down-modulation, we performed genome-wide microRNA (miRNA) expression profiling and found that several miRNA species are commonly up-regulated in melanomas. Among them was mir-221, which can directly interact with c-kit 3'UTR and inhibit cKit protein translation. Observed inverse correlation of the c-kit and mir-221 expression in various melanocytic cells pointed to its involvement in regulation of cKit in melanoma. Moreover, a series of functional assays demonstrated that mir-221 could directly inhibit cKit, p27(Kip1) and, possibly, other pivotal proteins in melanoma. Collectively, the studies presented here indicate that mir-221 could be a novel therapeutic target for the treatment of cutaneous melanoma. They also suggest that regulation of expression and functional activity of identified up-regulated miRNAs should be further studied in the context of malignant melanoma.