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

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 β-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 β-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 β-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.

Molecular characterization of novel melanoma cell lines

We isolated two novel cell lines from different types of sporadic human malignant melanoma: the hmel1 line was obtained from a melanoma skin metastasis and the hmel9 cell line from a primary superficial spreading melanoma. The karyotype and pigmentation parameters were assessed in these cell lines. Cytogenetic analysis in early stages of culture revealed that both cell lines had chromosome instability and simultaneous growth of heteroploid subpopulations. The molecular analysis of some genes involved in melanoma showed that both cell lines harbor BRAF mutations. The unpigmented hmel1 and the pigmented hmel9 lines were found to express the tyrosinase gene. The tyrosine hydroxylase activity was detectable only in hmel9 cells and practically absent in the hmel1 cell line. This activity was found to be correlated with the relative tyrosinase protein amount in both melanoma cell lines. The biological behaviour in the two melanoma cell lines, derived from two different types of melanoma lesions displaying distinct clinical and histopathological features, confirms the heterogeneous characteristics of sporadic melanoma. Similarities and/or differences between cell lines extracted from different melanoma cases could be useful in the future for diagnostic, prognostic and therapeutic purposes.