MSG1 is a 27 kDa nuclear protein that is expressed strongly in melanotic B16 melanoma cells but very weakly in amelanotic B16 cells. Transient expression of B16 cells with an expression vector for MSG1 resulted in an increase in levels of the enzyme dopachrome tautomerase but not tyrosinase, as detected by western blotting. Stable transfection of B16 melanoma cells with plasmids containing the full length MSG1 or its deletion mutants, however, generated cell lines that showed an increase in levels of tyrosinase, dopachrome tautomerase and cellular melanin when compared with control transfected cells. Our results suggest that MSG1 plays an important role in melanogenesis, by regulating the levels of the enzymes of the pigmentary system via tyrosinase and dopachrome tautomerase.
Metabolism of glutathione by gamma-glutamyl transpeptidase (gamma-GT) at the level of cell membrane has been shown to generate hydrogen peroxide in many cell types including human melanomas. gamma-GT does not appear to be involved in cysteine uptake for pheomelanin production in melanoma cells and does not contribute significantly to the pheomelanin synthesized in B16 melanoma cells. We have therefore examined the possibility of gamma-GT mediated production of prooxidant reactions and its effect, if any, on pigmentation using B16 melanoma cells. Our results indicate that in B16 melanoma cells, gamma-GT activity leads to the production of hydrogen peroxide. We further show that the nuclear levels of the redox sensitive transcription factor NF-kappa B is regulated by H2O2 formed by the action of gamma-GT: stimulation and inhibition of gamma-GT affect the levels of NF-kappa B. Tumor necrosis factor alpha, a hypopigmenting cytokine, known to activate NF-kappa B also up-regulates the gamma-GT messenger RNA and activity. Stimulation of gamma-GT generated prooxidant reactions led to a decrease in tyrosinase activity. We therefore propose that prooxidant reactions mediated by gamma-GT in turn regulate the levels of tyrosinase in pigment cells. Our findings thus introduce a new aspect in the regulation of pigmentation and ascribe a novel role for gamma-GT in pigment cells.
Gamma-glutamyl transpeptidase (gamma-GT), an ectoenzyme involved mainly in glutathione metabolism, is expressed in B16 melanoma cells. B16 melanoma cells under continuous culture conditions show a phenotypic drift from melanotic to amelanotic and re-melanotic stages. We have investigated the regulation of gamma-GT in B16 melanoma cells under such different pigmentary conditions. High levels of gamma-GT messenger RNA (mRNA) and activity were detected in pigmented B16 melanoma cells, whereas in amelanotic B16 melanoma cells the levels were very low. Treatment with lactic acid, a known inhibitor of tyrosinase gene expression, also led to the down-regulation of gamma-GT mRNA and activity. Thus our results indicate that gamma-GT regulation depends on the pigmentation status in pigment cells. We have also assessed the levels of gamma-GT in normal murine melanocytes (melan-a cells). It was seen that melan-a cells express very low levels of gamma-GT. As gamma-GT is known to be regulated in a tissue-specific manner, and is expressed from as many as six promoters giving rise to six different types of mRNAs each having unique 5' ends, we have further investigated the type of gamma-GT mRNA expressed in B16 melanoma and melan-a cells. In this study, we have conclusively demonstrated that type I mRNA transcript of gamma-GT is expressed in B16 melanoma and melan-a cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.