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Query: UMLS:C0025202 (melanoma)
 69,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hybrids between Syrian hamster melanoma cells and mouse fibroblasts, containing one genome (1s) of each parent, produce neither melanin nor DOPA-oxidase ("extinction"). Attempts to induce loss of the fibroblast chromosomes by irradiation of the fibroblasts before fusion with melanoma cells resulted in the formation of colonies comprising pigmented hybrid cells, which contained 2s melanoma and 1s fibroblast chromosome-complements suggesting that extinction or re-expression of melanogenesis is a function of genic balance. This interpretation was confirmed by crosses between 2s melanoma cells with unirradiated 1s fibroblasts, which produced both pigmented and unpigmented hybrids. No correlation has thus far been established between karyotype and phenotype of the hybrid cells, but analysis of the karyological data suggests that the fibroblast chromosomes responsible for extinction cannot be numerous.
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PMID:Gene dosage dependence of pigment synthesis in melanoma x fibroblast hybrids (hamster cells-mouse fibroblast-DOPA-oxidase-irradiation). 462 32

Gamma-glutamyl transpeptidase (GGT), an enzyme of the gamma-glutamyl cycle, was demonstrated in 3 of 6 cell lines derived from a single B16 murine melanoma. Its activity in these cells varied a great deal, appeared to be correlated with the developmental cycle of the cells, and was greatest in young, actively melanogenic cells. Generally, the activity seemed parallel to that of tyrosinase, an enzyme specific for melanin synthesis. The levels of both enzymes tended to decline with prolonged in vitro cultivation, but could be readily renewed after one animal passage. The 3 cell lines that were GGT-negative were nonpigmented and DOPA-negative; so was a nonmelanogenic and nonmelanocytic rhesus cell line. Melanocyte-stimulating hormone (MSH) and theophylline both enhanced pigmentation in murine melanoma cells. The mechanisms of their action apparently differed. We found that theophylline increased both DOPA- and GGT- reactive cells, whereas MSH only increased DOPA-reactive cells. All 3 GGT-positive lines were tumorigenic, and 2 GGT-negative line were not tumorigenic. Our observations suggest that GGT plays a role in the melanin biosynthetic pathway and the its activity is greater in melanoma cells that are tumorigenic.
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PMID:Theophylline and melanocyte-stimulating hormone effects on gamma-glutamyl transpeptidase and DOPA reactions in cultured melanoma cells. 612 37

A tyrosinase purified from cultured human melanoma cells was studied for dopa oxidation and tyrosine oxygenation. Km for oxidation of L-dopa was 0.5 mM, and for D-dopa 3 mM. L-tyrosine was oxygenated only in the presence of a cosubstrate. L-Dopa was superior to D-dopa, dopamine, L- and D-alpha-methyldopa, dopac, and 5,6-dihydroxyindole-2-carboxylic acid as cosubstrate. Ascorbic acid, 5-S-cysteinyldopa, and 5-OH-dopa did not function as cosubstrates. The rate of tyrosine hydroxylation was much lower than that of dopa oxidation. Tyrosine inhibits dopa oxidation, and dopa in high concentrations inhibits tyrosine hydroxylation. The cosubstrate function of dopa, the substrate functions of dopa and tyrosine, and the mutual inhibition of tyrosinase by these compounds are explained in three equations.
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PMID:Dopa oxidation and tyrosine oxygenation by human melanoma tyrosinase. 619 34

This study elucidates the nature of melanogenesis in B16 and Harding-Passey (HP) mouse melanomas producing melanin and melanosomes of different color and fine structure, i.e., brown-black eumelanosome-like B16 granules and reddish brown pheomelanosome-like HP granules, and compares them with "typical" 3,4-dihydroxyphenylalanine (DOPA) and sepia eumelanins and sepia eumelanosomes. The melanin content of B16 melanosomes was more than three times higher than that of HP melanosomes. The content of free and protein-bound DOPA and 5-S-cysteinyldopa varied greatly in B16, HP, and sepia melanosomes and was unrelated to melanin content. Chemical analysis of the eumelanin: pheomelanin ratio in melanosomes and elemental analysis of isolated melanin showed that B16 and HP melanins are primarily eumelanic, with a higher ratio of pheomelanic component in HP melanin. The spectra of electron spin resonance and IR and X-ray small-angle scattering of B16 and HP melanins were basically similar to those of sepia and DOPA melanins. B16, HP, and DOPA melanins were dissolved in aqueous NH3, while sepia melanin was dissolved to a far lesser extent. It was concluded that both B16 and HP melanomas are primarily involved in eumelanogenesis, although the fine structure of their melanosomes is entirely different, and that the marked color difference in the two melanosomes is related to a difference in the absolute content of eumelanin, the presence of a small amount of pheomelanin, and the mode of chemical bindings of melanin to structural proteins. In contrast to normal skin and hair, melanosome morphogenesis may not directly correspond to melanogenesis type in malignant melanoma.
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PMID:Characterization of melanogenesis and morphogenesis of melanosomes by physicochemical properties of melanin and melanosomes in malignant melanoma. 631 81

1. Harding-Passey mouse-melanoma tyrosinase (EC 1.14.18.1) is inhibited during L-3,4-dihydroxyphenylalanine oxidation by reaction products. L-3,4-dihydroxyphenyl 3-[14C]alanine oxidation products bind to the enzyme, as demonstrated by gel electrophoresis and radioactivity measurements. 2. The enzyme interacts with indoles and oxidizes dopamine and norepinephrine. 3. L-epinephrine activates tyrosinase at non hormonal concentrations and bovine serum albumin protects the enzyme from auto-inhibition. 4. The inhibition of the Harding-Passey mouse-melanoma tyrosinase, during substrate oxidation, is very similar to that of mushroom enzyme.
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PMID:Harding-passey mouse-melanoma tyrosinase inactivation by reaction products and activation by L-epinephrine. 640 91

The activities of NADP-linked dehydrogenases in the cytosol of amelanotic, black melanotic and brown melanotic hamster melanoma are presented. It has been shown that the tyrosine to DOPA hydroxylation is stimulated by the NADPH produced in the reaction catalyzed by either isocitrate dehydrogenase or glucose-6-phosphate dehydrogenase. The significance of NADPH in the hydroxylation of tyrosine to dopa in hamster melanoma is discussed.
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PMID:The role of NADP-dependent dehydrogenases in hydroxylation of tyrosine in hamster melanoma. 640 89

The sera of patients who suffer from melanoma and mammary carcinoma show higher tyrosinase activity than normal sera. The enzyme tyrosinase oxidizes tyrosine to DOPA and also catalizes the oxidation of DOPA to Melanin. The catalytic oxidation might also occur in tyrosine while it is conjugated to other amino acids in a polypeptide or a protein molecule. It is theorized here that gamma globulins and interferons are vulnerable to this catalytic oxidation which eventually denaturates them and diminishes their immunological properties.
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PMID:The possible role of tyrosinase in malignant growth. 641 Jan 61

Histochemical findings of primary and metastatic amelanotic melanomas were shown by the formaldehyde-induced fluorescence method (Falck and Hillarp). All or some of the amelanotic melanoma cells were discovered to emit green specific fluorescence. Results of the determination of 5-S-cysteinyldopa and DOPA in amelanotic melanoma tissues indicated that the specific fluorescence emitted by these cells is primarily due to the presence of 5-S-cysteinyldopa. The values of 5-S-cysteinyldopa in these tissues were lower than those in melanotic melanoma, but were approximately the same as those in pigmented nevus. When unpigmented tumors were histopathologically revealed to be malignant, amelanotic melanoma could be definitely diagnosed by the fluorescence method of Falck and Hillarp and the biochemical analysis of 5-S-cysteinyldopa in the tissues.
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PMID:Studies on amelanotic melanoma with the fluorescence method (Falck and Hillarp) and biochemical analysis of 5-S-cysteinyldopa in the tissues. 641 80

The synthetic glucocorticoid, triamcinolone acetonide, was found to increase melanogenesis in the human melanoma cell line NEL. Treatment of NEL cells for 24 hr with triamcinolone acetonide (1 X 10(-7) M) increased the activity of the enzyme tyrosinase by 43% and the incorporation of the melanin precursor, L-3,4-dihydroxyphenylalanine, by 23%. Additional studies revealed no change in cyclic AMP levels over an 18-hr test period. A 2-hr preincubation of NEL cells with actinomycin D (10 micrograms/ml) prevented the increase in tyrosinase activity by triamcinolone acetonide. When triamcinolone acetonide was added to a synchronized population of NEL cells, an increase in tyrosinase activity was observed at 16 hr, coinciding with the late S phase of the cell cycle. These results suggest that glucocorticoids are involved in the regulation of melanogenesis in NEL cells by increasing the activity of the rate-controlling enzyme tyrosinase.
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PMID:Effect of triamcinolone acetonide on tyrosinase activity in a human melanoma cell line. 642 29

In an attempt to diagnose a suspected amelanotic melanoma tumour, we examined a variety of tissue and cell samples from one patient at the ultrastructural level, which consisted of single cell suspensions of tumour cells with and without DOPA treatment, tumour cells after culture in agar with and without DOPA treatment, and single tumour cells hetero-transplanted into a nude mouse. Premalanosomes were not observed in sections of the amelanotic tumour with routine electron microscopy. Osmophilic-dense bodies, suggestive of melanosomes, were noted in the single cells in suspension treated with DOPA and cells grown in agar without DOPA treatment. Definitive premelanosomes, with an identifiable striated matrix, were only observed in cells grown into colonies in agar and treated with DOPA. Positive L-DOPA reaction products were noted in the golgi complex, endoplasmic reticulum closely related to the golgi (GERL), and in vacuoles from cells grown in agar. As controls, Cloudman S91 53.1 melanoma cells were evaluated as single cells in suspension or as colonies after culture in agar, both with and without DOPA treatment. Premelanosomes were always observed in this established melanoma cell line while DOPA-treated cells contained positive L-DOPA reaction products. The overall findings identified the tumour as amelanotic melanoma and indicated that both DOPA treatment and culture in agar were needed for the demonstration of premelanosomes.
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PMID:Diagnostic electron microscopy for amelanotic melanoma: correlation of patient biopsy, soft agar assay, and xenograft. 662 8


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