title: Glutathione depletion increases tyrosinase activity in human melanoma cells.
abstract: The aim of the present work was to estimate the effect of intracellular glutathione depletion on melanogenesis in human melanoma cells. We determined tyrosine hydroxylation activity, the rate-limiting step of the pathway, and 14C-melanin formation, an assay reflecting the global eumelanogenic pathway. Intracellular glutathione was depleted by treatment with buthionine-S-sulfoximine, a well-known inhibitor of gamma-glutamylcysteine synthetase. The intracellular depletion of glutathione was substantial after 20 h of incubation with 50 microM buthionine-S-sulfoximine, although a significant effect could be observed after 6 h. Tyrosine hydroxylase activity increased in parallel with glutathione depletion, to reach 160% with respect to the control values during 24 h of buthionine-S-sulfoximine treatment. We have found the response to buthionine-S-sulfoximine to be dose dependent and the two different human cell lines HBL and LND1 to have similar, if not identical, responses. 14C-melanin formation assay revealed even greater activation, up to 400% of the control values. This indicates that glutathione depletion may have two distinct effects: first, a direct one on tyrosinase activity and, second, an effect on the promotion of eumelanogenesis. The stimulation of tyrosine hydroxylase can be explained by a possible inactivation of the enzyme by endogenous thiol compounds rather than by a direct effect of buthionine-S-sulfoximine itself on tyrosinase. The data suggest that thiol compounds may play a role for stimulation of melanogenesis by ultraviolet radiation.
authors.affiliation: L.O.C.E, Faculty of Medicine, University of Brussels, Belgium.
authors.forename: V
authors.initials: V
authors.lastname: del Marmol
authors.forename: F
authors.initials: F
authors.lastname: Solano
authors.forename: A
authors.initials: A
authors.lastname: Sels
authors.forename: G
authors.initials: G
authors.lastname: Huez
authors.forename: A
authors.initials: A
authors.lastname: Libert
authors.forename: F
authors.initials: F
authors.lastname: Lejeune
authors.forename: G
authors.initials: G
authors.lastname: Ghanem
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D019328:Buthionine Sulfoximine; D005978:Glutathione / Q000172:deficiency*; D006801:Humans; D008543:Melanins / Q000096:biosynthesis; D008545:Melanoma / Q000201:enzymology* / Q000473:pathology; D008717:Methionine Sulfoximine / Q000031:analogs & derivatives / Q000494:pharmacology; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000964:Antimetabolites, Antineoplastic; D008543:Melanins; D013438:Sulfhydryl Compounds; D008717:Methionine Sulfoximine; D019328:Buthionine Sulfoximine; D014446:Tyrosine 3-Monooxygenase; D014442:Monophenol Monooxygenase; D005978:Glutathione