Human melanoma cells generate leukotrienes B-4 and C-4 from leukotriene A(4)

We examined the synthesis of leukotrienes (LTs) in human melanoma cells in order to assess the function of LTs in human melanocytes. LTA(4) hydrolase, which catalyzes the conversion of LTA(4) to LTB4, was detected in the supernatant of cultured human melanoma (MeWo) cells and melanoma cells obtained from patients, Immunoblotting analysis using an antihuman LTA(4) hydrolase antibody showed LTA(4) hydrolase to be a 70-kDa protein in both MeWo and melanoma cells, Considerable activity of LTC4 synthase, which catalyzes the conversion of LTA(4) to LTC4, was detected in the microsomal fraction of both MeWo and melanoma cells, The HPLC profile of the LTC4 synthase reaction products revealed that LTC4 was the main product, LTC4 was not detected under these conditions, indicating that the microsomal fraction of human melanoma cells lacks the membrane-bound gamma-glutamyl transferase that converts LTC4 to LTD4. LTC4 synthase activity was inhibited by the additon of MK-886, and was not altered by treatment with N-ethylmaleimide or 1-chloro-2,4-dinitrobenzene, These results indicate that the enzyme responsible for the conversion of LTA(4) to LTC4 in human melanoma cells is LTC4 synthase rather than a nonspecific or microsomal glutathione-S-transferase. These results also suggest that human melanoma cells can generate LTB4 and LTC4 from LTA(4), and that this process is catalyzed by two enzymes: LTA(4) hydrolase and LTC4 synthase.