Sunlight and melanoma

Is UV an etiological factor of acral melanoma?

Ultraviolet (UV) radiation is a major environmental risk factor for melanoma, particularly among Caucasians. However, studies have generated conflicting results on the role of UV exposure in the development of acral melanoma, the most prevalent subtype of melanoma in non-Caucasians. In this review, we analyzed studies that have examined the relationship between acral melanoma and UV and show that acral melanoma has specific epidemiological and genetic characteristics, with a lower frequency or absence of UV-induced features. Therefore, we postulate that UV is probably not involved in the etiology of acral melanoma. However, further epidemiological and laboratory studies are required to fully address this controversial issue, which may lead to a better understanding of the pathogenesis and prevention of acral melanoma.

Similar nucleotide excision repair capacity in melanocytes and melanoma cells

Sunlight UV exposure produces DNA photoproducts in skin that are repaired solely by nucleotide excision repair in humans. A significant fraction of melanomas are thought to result from UV-induced DNA damage that escapes repair; however, little evidence is available about the functional capacity of normal human melanocytes, malignant melanoma cells, and metastatic melanoma cells to repair UV-induced photoproducts in DNA. In this study, we measured nucleotide excision repair in both normal melanocytes and a panel of melanoma cell lines. Our results show that in 11 of 12 melanoma cell lines tested, UV photoproduct repair occurred as efficiently as in primary melanocytes. Importantly, repair capacity was not affected by mutation in the N-RAS or B-RAF oncogenes, nor was a difference observed between a highly metastatic melanoma cell line (A375SM) or its parental line (A375P). Lastly, we found that although p53 status contributed to photoproduct removal efficiency, its role did not seem to be mediated by enhanced expression or activity of DNA binding protein DDB2. We concluded that melanoma cells retain capacity for nucleotide excision repair, the loss of which probably does not commonly contribute to melanoma progression.

DNA replication and repair in a human melanoma cell-line resistant to ultra-violet-radiation

The effect of ultra-violet (U.V.)-irradiation on DNA replication was studied in a U.V.-resistant, human melanoma cell-line (MM96). Semi-conservative synthesis of DNA was decreased about five-fold by a U.V.-dose of 100 ergs/mm2. The size of DNA fragments synthesized in irradiated cells at short times after U.V. was smaller than those synthesized in unirradiated cells. Elongation of these fragments occurred with time, and 6 hours after irradiation cells synthesized DNA in fragments of the same size as obtained in unirradiated cells. In this post-replication repair process, elongation appeared to involve de novo synthesis and was not inhibited by theophylline.