The Role of Uncoupled Nitric Oxide Synthase in Melanoma Development

Cancer is one of the leading causes of death in the world. Increased levels of reactive oxygen species, including superoxide anion (O 2 •‒ ), and the consequent installation of a pro-oxidant environment, contribute to the development of this disorder. The enzyme nitric oxide synthase (NOS), responsible for the production of nitric oxide, becomes the source of O 2 •‒ when it is in a state referred as uncoupled. The presence of tetrahydrobiopterin cofactor (BH4) is critical to keeping the enzyme coupled. The objective of this study was to evaluate the uncoupling of nitric oxide synthase and its contribution to carcinogenesis in human melanoma cells. The data obtained suggest that BH4 synthesis is compromised in melanoma lineages. Through qPCR we show that the expression levels of the transcripts from via de novo , salvage and recycling pathways are altered in tumors when compared to melanocytes, suggesting low levels of BH4 and uncoupling of NOS in tumor cells. When treated with BH4, cells from the SK-MEL-28 melanoma cell line showed decreased superoxide anion levels. Treatment with BH4 decreased the cell viability of SK-MEL-28 cells. These same cells when treated with BH4 showed reduced ability to form colonies and tumorspheres. It has been shown that treatment with BH4 rendered SK-MEL-28 cells more sensitive to apoptosis. This work contributed to evaluate the importance of BH4, as a cofactor of nitric oxide synthase, in the progression of melanoma.