NOS3 and melanoma: Since decreased BH4 levels or BH4:BH2 ratio were not observed in melanoma cells and increased expression of Nos3 has been observed in melan-a melanocytes submitted to sustained stress condition, which resulted in melanocyte malignant transformation [5] and gave rise to the cells used in this study, we evaluated eNOS expression in these melanoma cell lines by real-time qPCR.