Inhibition of Melanin Synthesis by Cystamine in Human Melanoma Cells

Abstract

In studies to determine whether pigmentation can be regulated physiologically by thiols, human melanoma cells (MM418c5) and melanocytes were found to become depigmented when cultured continuously in 50 microM cystamine. Cystamine was depleted from the culture medium and the treatment was nontoxic and reversible. Cysteamine, dithiothreitol, and phenylthiourea were less effective, and glutathione, cysteine, and cystine were inactive. Tyrosinase (dopa oxidase) activity was not greatly affected except for induction of a lag period. In contrast, tyrosinase activity in an amelanotic melanoma cell line (MM96L) was rapidly inhibited without consumption of cystamine/cysteamine, in association with the generation of free thiol in the culture medium, and could be enhanced by the cystine transport inhibitor, glutamate. Tyrosinase expressed by a recombinant vaccinia virus was inhibited by cystamine treatment of MM96L and HeLa cells. Cystamine treatment lowered the degree of cross-linking of the pigmentation antigen gp75/TRP-1 in MM418c5 cells. Tyrosinase protein and mRNA levels in MM418c5 cells were not affected by cystamine. The results show that cystamine at a concentration close to physiologic levels has multiple effects on the melanogenic pathway. In amelanotic cells, tyrosinase has a short half-life and is readily inhibited by cystamine/cysteamine whereas tyrosinase in the more mature melanosomes of the pigmented cell appears to be less accessible to proteolytic and thiol attack. Inhibition of melanin synthesis in the latter cell type may arise to a significant degree from reduction of cystamine to cysteamine, which sequesters quinones.

Cell density-dependent reduction of dihydroceramide desaturase activity in neuroblastoma cells

“…9 suggest that reducing agents, like free thiols, in the media of high-density cells were responsible for the decreased activity of dihydroceramide desaturase. In support of our fi ndings in neuroblastoma cells, a study in cultured melanoma cells have shown that, at high density, cultures rapidly accumulate free thiols in the media ( 37 ). The results from the metabolic-labeling experiments with C 17 sphingosine ( Fig.…”

Discovery and Characterization of a Second Mammalian Thiol Dioxygenase, Cysteamine Dioxygenase

“…To some cultures cystamine was added at a final concentration of 0.5 mM 6 h after transfection. Cystamine is a disulfide form of cysteamine that is efficiently taken up by cells and reduced to cysteamine intracellularly (23,24). Cells were harvested 30 h after transfection for Western blot analysis and measurement of intracellular hypotaurine/taurine content by HPLC.…”

“…When cells were incubated in the presence of cystamine, a disulfide form of cysteamine that is efficiently taken up by cells and reduced to cysteamine intracellularly (23,24), transfection with wild-type ADO significantly increased hypotaurine content in a dose-dependent fashion relative to control cells transfected with the empty vector alone (Fig. 5B).…”

Inhibitory Effect of Ammonium Tetrathiotungstate on Tyrosinase and Its Kinetic Mechanism

“…6,7) Therefore, the chelation of copper ions in this enzyme by flavonoid compounds or any other agents has been targeted as a strategy for the attenuation of tyrosinase activity, an objective relevant to cosmetic concerns, darkening problems in agricultural products, and certain medicinal reasons. [8][9][10][11][12][13][14] Melanin pigments are synthesized by melanocytes, and are deposited throughout the epidermis. This process determines skin color.…”

“…[8][9][10][11][12][13][14] Melanin pigments are synthesized by melanocytes, and are deposited throughout the epidermis. This process determines skin color.…”