4157

MC1R

melanocortin 1 receptor (alpha melanocyte stimulating hormone receptor);MC1R;melanocortin 1 receptor (alpha melanocyte stimulating hormone receptor)

MC1-R|melanocyte-stimulating hormone receptor|melanotropin receptor

16q24.3

protein-coding

The melanocortin 1 receptor is a G-protein-coupled receptor, described to be expressed on melanomas and melanocytes. Subsequent RT-PCR studies demonstrated the presence of melanocortin 1 receptor mRNA in other tissues such as pituitary gland and testis. Previously, we have demonstrated that three HLA-A2 binding nonamer peptides derived from melanocortin 1 receptor can elicit peptide-specific CTL which can recognize target cells transfected with the melanocortin 1 receptor gene and MHC class I matched melanoma lines. The potential of targeting melanocortin 1 receptor in therapy and diagnosis will depend on a preferential expression of this receptor in the majority of primary and metastatic melanomas vs normal tissues. We tested a panel of melanomas, carcinomas and other cell lines for the presence of melanocortin 1 receptor, using two monoclonal antibodies. The receptor was detected in 83% of the tested melanoma cell lines but not in other carcinoma lines. Immunohistochemistry revealed a strong expression of melanocortin 1 receptor in all tested primary and metastatic melanomas, but also demonstrated low levels of expression in adrenal medulla, cerebellum, liver and keratinocytes. Flow cytometry studies showed that melanocortin 1 receptor was expressed in in vitro activated monocytes/macrophages and in the THP-1 monocytic leukaemia line at levels of about 1 in 3 to 1 in 5 of that found in melanomas. Peripheral blood-derived dendritic cells, also express melanocortin 1 receptor in vitro. This extensive analysis of melanocortin 1 receptor tissue distribution may be of relevance not only for melanoma immunology, but also for research on the pathogenicity of inflammatory conditions in the skin and neurologic tissues. It remains to be seen if the over-expression of melanocortin 1 receptor in melanomas is sufficiently high to allow a 'therapeutic window' to be exploited in cancer immunotherapy.

We studied the behaviour of three novel human sporadic melanoma cell lines (hmel1, hmel9, hmel11) extracted from tumors with different degrees of malignancy, concerning the cell signalling pathways controlled by MC1R, BRAF, NRAS and beta-catenins. The novel cell lines were compared to metastatic cell lines (HBL, LND1), wild type (wt) for MC1R and BRAF genes, that have been extensively characterised and were used as control. All the novel cell lines have silent or no MC1R mutations even though MC1R signalling is severely impaired. Conversely, they harbour BRAF mutations at the V600 residue. These mutations determine a constitutive ERK phosphorylation in all the three cell lines. Our new melanoma cell lines were BRAF mutated in hetero- and homozygosis, even with a wild type MC1R, and unresponsive to NDP-MSH treatment. Quantity and subcellular localization of beta-catenin were analyzed in both novel and control cell lines. In HBL and LND1 there were high levels of beta-catenin distributed in the cytoplasm/nucleus, while in the novel melanoma cell lines beta-catenins were less abundant and seemed to be located at the plasma membrane/cytoplasm and absent in the nucleus. We sequenced beta-catenin cDNA for all the melanoma cell lines, and found mutations in HBL, LND1 and hmel1, while hmel9 and hmel11 were wt. We found that beta-catenin levels were not influenced by the RAS/RAF/MAPK pathway because inhibition with PD98059 (a MEK inhibitor) did not produce any effect on beta-catenin stability and/or localization.