MC1R RECEPTOR IN MALIGNANT MELANOMA: MOLECULAR AND FUNCTIONAL ANALYSIS

Pigmentation in mammals and cutaneous phenotype are due to the relative amount two types of melanins: pheomelanins and eumelanins. Brown/black eumelanins are more photoprotective, and yellow/red pheomelanins are less photoprotective and probably even phototoxic. The key enzyme for the melanogenesis is tyrosinase: low tyrosinase levels mean that L-tyrosine is preferably converted to pheomelanins; rising levels of tyrosinase push the melanogenesis versus the eumelanin synthesis. Alpha-MSH and its receptor MC1R are key regulation of cutaneous pigmentation and tanning response. The human MC1R is highly polymorphic, and some of its genetics forms are associated with various pigmentary phenotypes. Malignant melanoma (MM) is a type of cancer due both to genetic predisposition and environmental factors such as UV exposure. The genes involved in melanoma development are of various type: high penetrance genes such as CDKN2A and CDK4, and low penetrance one such as the MC1R gene. In this study we obtained primary lines of melanoma cell cultures from South Italy Caucasian patients’ biopsies. We screened for their MC1R genotype, particularly in two different melanoma cell lines, hmel 1 (from MM metastasis) and hmel 9 (from primary MM). The MC1R sequencing revealed that the two analysed cell lines are omozygous for the wild type receptor. These cultures showed histological and morphological differences. Moreover, we demonstrated higher levels of the MC1R transcripts in hmel 1 than hmel 9 cell lines. Functional analysis of MC1R receptor have been performed. Endocellular cAMP level in response to alpha-MSH treatment has been tested at different time of incubation. The cAMP assay revealed that the hmel 1 are able to respond to the alpha-MSH treatment producing higher quantities of cAMP within 15 min incubation in comparison to hmel 9 cell line. The tyrosinase activity was very high in hmel 9 cell line and very low or absent in hmel 1one. These different behaviours of the two cell lines suggests that the cAMP pathway may be impaired, in certain human melanoma cells even when they express the wild type MC1R receptor.