Establishment of a novel melanoma cell line SMYM-PRGP showing cytogenetic and biological characteristics of the radial growth phase of acral melanomas.

We established a novel melanoma cell line, SMYM-PRGP, which was non-tumorigenic in vivo, from an acral melanoma in radial growth phase under a low-oxygen environment. SMYM-PRGP was wild-type for known mutation sites in the BRAF and NRAS genes, and showed focal amplification of the human telomerase reverse transcriptase and cyclin D1 genes as well as the fibroblast growth factor-3 and fibroblast growth factor-4 genes. Neither mutation nor copy number loss of the CDKN2A gene was observed. The p16(INK4A) protein was expressed at a level equal to that in normal melanocytes. Among the various melanocyte growth factors added to the culture of SMYM-PRGP cells, endothelin-1 was the strongest growth stimulator, the effect of which was significantly augmented by the addition of calcium chloride. The growth stimulatory effect of endothelin-1 was shown to be mediated via the endothelin B receptor. The protein level of cyclin D1 in SMYM-PRGP cells was approximately 10 times higher than that in normal melanocytes. Although the stimulation with endothelin-1 plus calcium chloride increased cyclin D1 protein levels after 4-6 h, the level of phosphorylated retinoblastoma protein did not increase, suggesting that overexpression of cyclin D1 protein may have little effect on cell cycle progression but rather act as a pro-survival factor. SMYM-PRGP is an excellent tool for investigating the development and progression of acral melanoma.