Three novel human sporadic melanoma cell lines: signalling pathways controlled by MC1R, BRAF and beta-catenins

We studied the behaviour of three novel human sporadic melanoma cell lines (hmel1, hmel9, hmel11), having different degree of malignancy, for 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, extensively characterised and 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 three cell lines. Our new melanoma cell lines BRAF mutated in hetero- and homozygosis, even with a wild type MC1R, are unresponsive to NDP-MSH treatment. The quantity and subcellular localization of beta-catenin were analyzed both in novel and control cell lines. In HBL and LND1 there are high levels of catenin distributed in the cytoplasm/nucleus, while in novel melanoma cell lines catenins are less abundant and seem to be located at plasma membrane/cytoplasm and absent in the nucleus. We sequenced catenin cDNA for all the melanoma cell lines, and we found it mutated in HBL, LND1 and hmel1, while hmel9 and hmel11 were wt. We found that catenin levels are not influenced by the RAS/RAF/MAPK pathway because its inhibition with PD98059 (a MEK inhibitor) does not produce any effect on catenin stability and/or localization.