Mechanisms underlying DNA damage resistance in a Xiphophorus melanoma cell line

The Xiphophorus hybrid fish model is an important resource for investigating the genetics and molecular biology of melanoma. Consistent with studies using human melanoma cell lines, the Xiphophorus melanoma cell line PSM, survives the lethal effects of ultraviolet-B radiation (UV-B) radiation much better than a cell line derived from normal fish tissue. In contrast to human melanoma cells, which show enhanced nucleotide excision repair, we do not see any differences in the efficiencies of photoenzymatic or nucleotide excision repair in normal and melanoma cell lines. We do, however, observe a significantly reduced growth rate in the melanoma cell line compared with the normal cell line and considerably less effect of UV-B radiation on DNA synthesis. The data suggest that the UV resistance phenotype of PSM cells is due more to the rate of proliferation and increased ability to replicate on a damaged template rather than enhanced repair of DNA photoproducts as observed in human melanoma cells. The putative increase in lesion bypass by DNA polymerase could result in higher mutation frequencies and enhanced genetic lability in fish melanoma cells.