The Response of microRNAs to Solar UVR in Skin-Resident Melanocytes Differs between Melanoma Patients and Healthy Persons

The conversion of melanocytes into cutaneous melanoma is largely dictated by the effects of solar ultraviolet radiation (UVR). Yet to be described, however, is exactly how these cells are affected by intense solar UVR while residing in their natural microenvironment, and whether their response differs in persons with a history of melanoma when compared to that of healthy individuals. By using laser capture microdissection (LCM) to isolate a pure population of melanocytes from a small area of skin that had been intermittingly exposed or unexposed to physiological doses of solar UVR, we can now report for the first time that the majority of UV-responsive microRNAs (miRNAs) in the melanocytes of a group of women with a history of melanoma are down-regulated when compared to those in the melanocytes of healthy controls. Among the miRNAs that were commonly and significantly down-regulated in each of these women were miR-193b (P<0.003), miR-342-3p (P<0.003), miR186 (P<0.007), miR-130a (P<0.007), and miR-146a (P<0.007). To identify genes potentially released from inhibition by these repressed UV-miRNAs, we analyzed databases (e.g., DIANA-TarBase) containing experimentally validated microRNA-gene interactions. In the end, this enabled us to construct UV-miRNA-gene regulatory networks consisting of individual genes with a probable gain-of-function being intersected not by one, but by several down-regulated UV-miRNAs. Most striking, however, was that these networks typified well-known regulatory modules involved in controlling the epithelial-to-mesenchymal transition and processes associated with the regulation of immune-evasion. We speculate that these pathways become activated by UVR resulting in miRNA down regulation only in melanocytes susceptible to melanoma, and that these changes could be partially responsible for empowering these cells toward tumor progression.