Evidence for the postulated role of glutathione reductase in melanin pigmentation has been obtained by determinations of the glutathione concentrations in Tortoiseshell guinea pig skin of different colors (black, yellow, red, and white). As expected, the lowest levels of reduced glutathione (GSH) were found associated with eumelanin type pigmentation, whereas the highest ones were found in the skin with phaeomelanin producing melanocytes. On the other hand, white skin of guinea pig having no active melanocytes showed GSH levels which were intermediate between those of the black and yellow areas. These results are consistent with the view that the activity of the enzyme glutathione reductase, though not primarily related to pigmentation, plays an important role in the regulation and control of the biosynthetic activity of melanocytes leading to various types of melanin pigments.
Previously, we reported evidence suggesting that, in addition to tyrosinase, glutathione-reductase plays an important role in the regulation and control of the biosynthetic activity of melanocytes. Further investigations were performed on a mammal presenting a well-defined genotype for coat pigmentation, the mutant mouse [subline C57 BL (6J)], namely the nonagouti black (a/a) mutant and the yellow (Ay/a) mutant showing, respectively, pure uniform eumelanin and phaeomelanin pigmentation. Analysis of thiol compounds and glutathione-related enzyme levels in mouse skin gave similar results to those found in tortoise-shell guinea pig skin. The observed differences in the glutathione and glutathione-related enzyme content between black and yellow (or red) skin provide evidence that the increase of glutathione-reductase activity in the environment of the melanocytes may stimulate the pigment cells to produce phaeomelanin instead of eumelanin pigment.
Variants of the B16 melanoma exhibiting markedly different tumorigenic and metastatic potential in Ay/a and a/a C57BL/6J syngeneic mice were investigated and compared, with respect to their relative growth and metastatic potential after culture under different conditions. Over 2 to 6 months of growth, in vitro cells demonstrated a rapid and significant decrease in their ability to form spontaneous lung colonies. Such a decrease depended on the conditions of culture. We suggest that the in vitro environment influences the phenotype of cells with respect to their capacity for spontaneous metastasis. This possibility must not be ignored, when conclusions obtained from studies of established cell lines are extended to cancers.
B 16 mouse melanoma maintained on nonagouti a/a mice (C 57 Bl 6j subline) was transplanted to 'Yellow' Ay/a mutants. B 16 melanoma has now been maintained for 1 year on the 'Yellow' strain. A microscopic and ultrastructural study of transplanted tumors is described. Several enzymatic activities including tyrosinases are investigated. A marked depigmentation of the B 16 melanoma is noted after its transplantation to the 'Yellow' strain, and melanogenic characteristics of the tumor are modified.
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