Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025202 (melanoma)
 69,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human tyrosinase prepared from cultured melanoma cells is inactivated by 10 mM cysteine. The inactivation of the enzyme by cysteine is less pronounced in the presence of catalase and superoxide dismutase. Thus, oxygen radicals and/or hydrogen peroxide may contribute to the inactivation of human tyrosinase by cysteine. Dopa and/or tyrosine protects tyrosinase against inactivation by cysteine. The protection observed with tyrosine alone indicates that oxidation of substrate is not necessary for the protection. The effect of dopa and/or tyrosine is probably due to steric hindrance at the active site preventing the access of cysteine to the copper.
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PMID:Inactivation of human tyrosinase by cysteine. Protection by dopa and tyrosine. 620 5

Ascorbate-Cu2+ shows considerable cytotoxicity for human melanoma cells at a dose which has very little effect on human fibroblasts. Ascorbate itself inhibits DNA synthesis in melanoma cells but does not fragment the parental DNA. However, the combined action of ascorbate-Cu2+ generates fragmentation of the parental DNA due to the induction of alkali-labile bonds in the DNA. In contrast, if DNA polymerase alpha is inhibited by aphidicolin prior to treatment with ascorbate-Cu2+ one cannot detect the fragmentation of the DNA. The generated fragments show a discrete appearance in agarose gel electrophoresis with a single-stranded size of approximately 5 kb. When fibroblasts were analyzed using the same experimental protocol it was not possible to detect the fragmentation of the DNA.
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PMID:Ascorbate-Cu2+ fragments melanoma DNA but not fibroblast DNA into a discrete DNA population. 640 86

The effect of Ca2+, Cd2+, Cu2+, Mg2+ and Zn2+ as acetates (10(-3) - 10(-5)M) and of 2% DMSO on the proliferation and differentiation of clone M3 of the Cloudman S91 mouse melanoma was studied and compared with the behaviour of GPK (keratocyte) and MRC5 (fibroblast) cell lines. Whereas neither calcium nor magnesium ions influenced the proliferation of the cells as measured by [3H]-thymidine incorporation, absorbance at 280 nm of NaOH cell digests and cell counts, cadmium, zinc and copper ions selectively inhibited the melanoma line. Cd2+ (10(-5)M) and Zn2+ (10(-4)M) were selectively cytotoxic to melanoma cells in contrast to keratocytes and fibroblasts. No direct effect of the cations on melanogenesis, as estimated from the ratio of absorbance at 350 nm and 280 nm and by tyrosinase assays, was demonstrated. DMSO stimulated melanogenesis in melanoma cells but inhibited their growth. Experiments with ouabain indicate that active transport is involved in the uptake of zinc by melanoma cells.
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PMID:The effect of divalent cations on Cloudman melanoma cells. 668 80

Six of eight human melanoma lines showed increased sensitivity to killing by dopa and by ascorbate:copper compared with two fibroblast strains and four other human cell lines of nonmelanoma origin. Catechol, epinephrine, and alpha-methyldopa, but not 5,6-dihydroxyindole, exhibited a similar degree of selectivity. Toxicity was greatly reduced when brief exposure times or high cell densities were used. Depending upon culture conditions, melanoma cells accumulated more [3H]dopa- and [14C]ascorbate-derived isotopic label within the first five min than fibroblasts, but after one hr this difference was less marked. The catalase activity in melanoma cells was not less than that in fibroblasts. Using two independent methods to determine each type of damage, dopa and ascorbate:copper were found to induce DNA breaks in both cell types but not DNA repair synthesis or DNA interstrand cross-links. More DNA breaks were found in melanoma cells (two lines) than in fibroblasts. Semiconservative DNA synthesis was inhibited immediately, recovered within six hr, and in melanoma cells, was again inhibited after 24 hr. RNA synthesis was inhibited less than DNA synthesis. Human cell lines with differential sensitivity to gamma-radiation, ultraviolet light, cross-linking agents, or monofunctional alkylating agents, exhibited normal survival levels when treated with dopa or ascorbate:copper.
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PMID:DNA damage and selective toxicity of dopa and ascorbate:copper in human melanoma cells. 680 13

6-Ethynyluracil (3) was prepared by two different synthetic procedures. In one approach, 6-formyluracil was reacted with (dibromomethylene)triphenylphosphorane to give 6-(2,2-dibromovinyl)uracil (2), which was silylated and treated with phenyllithium to yield 3. Alternatively, silylated 6-iodouracil was reacted with trimethylsilylacetylene in dry triethylamine in the presence of a palladium/copper catalyst to give 6-[(trimethylsilyl)ethynyl]uracil (5). Compound 5 was converted to 3 in refluxing methanol. At neutral pH, 3 reacted with thiols, such as glutathione, 2-mercaptoethanol, and L-cysteine, but did not react with glycine or L-lysine. This reaction was accompanied by a shift in the UV maximum of 3 from 286 nm to 321-325 nm. The reaction of 3 with 2-mercaptoethanol gave cis-6-[2[(2-hydroxyethyl)-thio]vinyl]uracil as the predominant product. Compounds 2 and 3 inhibited the growth of leukemia L1210, B-16 melanoma, and lewis lung carcinoma cells at concentrations ranging from 1 x 10(-6) to 2 x 10(-5) M. As determined with L1210 cells, the inhibition of growth caused by 2 and 3 was not prevented by the natural pyrimidines, indicating that the agents do not act as antimetabolites.
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PMID:Synthesis and biological evaluation of 6-ethynyluracil, a thiol-specific alkylating pyrimidine. 714 68

Serum copper levels (SCL) and serum zinc levels (SZL) were evaluated in malignant melanoma patients at various clinical stages. Copper levels were generally found to be elevated, reflecting the degree and extent of tumor activity. Zinc levels and, hence, SCL:SZL ratios did not reflect tumor activity. SCL appeared to prognosticate disease progression in that all patients whose values never declined below 150 micrograms/100 ml died during the course of the study. However, not all patients who died from tumor metastases displayed persistent elevations of SCL. Patients receiving BCG immunotherapy appeared to have higher SCL than untreated patients.
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PMID:Serum copper and zinc levels in melanoma patients. 722 78

Vitamin C has been suggested and disputed as an anti-cancer agent. For cells in culture, no preferential effect against any type of cancer has yet been demonstrated. Our aim here is to show that vitamin C is selectively toxic to at least one type of malignant cell--a melanoma--at concentrations that might be attained in humans. Copper ions react with ascorbate and generate free radicals in solution. Ascorbate when combined with copper rapidly reduces the viscosity of DNA solutions and has exhibited some carcinostatic effects on transplanted sarcoma 180 tumours in mice. We reasoned that the elevated copper concentration in melanoma could result in a more selective toxicity for ascorbate.
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PMID:Vitamin C preferential toxicity for malignant melanoma cells. 736 35

Deficiency of cystathionine beta-synthase (CBS) is a genetic disorder of transsulfuration resulting in elevated plasma homocyst(e)ine and methionine and decreased cysteine. Affected patients have multisystem involvement, which may include light skin and hair. Reversible hypopigmentation in treated homocystinuric patients has been infrequently reported, and the mechanism is undefined. Two CBS-deficient homocystinuric patients manifested darkening of their hypopigmented hair following treatment that decreased plasma homocyst(e)ine. We hypothesized that homocyst(e)ine inhibits tyrosinase, the major pigment enzyme. The activity of tyrosinase extracted from pigmented human melanoma cells (MNT-1) that were grown in the presence of homocysteine was reduced in comparison to that extracted from cells grown without homocysteine. Copper sulfate restored homocyst(e)ine-inhibited tyrosinase activity when added to the culture cell media at a proportion of 1.25 mol of copper sulfate per 1 mol of DL-homocysteine. Holo-tyrosinase activity was inhibited by adding DL-homocysteine to the assay reaction mixture, and the addition of copper sulfate to the reaction mixture prevented this inhibition. Other tested compounds, L-cystine and betaine did not affect tyrosinase activity. Our data suggest that reversible hypopigmentation in homocystinuria is the result of tyrosinase inhibition by homocyst(e)ine and that the probable mechanism of this inhibition is the interaction of homocyst(e)ine with copper at the active site of tyrosinase.
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PMID:Tyrosinase inhibition due to interaction of homocyst(e)ine with copper: the mechanism for reversible hypopigmentation in homocystinuria due to cystathionine beta-synthase deficiency. 761 Dec 81

Certain aspects of current progress in melanin biology and its possible clinical relevances are reviewed with emphasis on some of our recent research activities. The important aspects discussed are (a) the biological properties of melanin pigments and their relevance to biological functions, (b) functional interaction of melanogenic/melanogenesis-associated genes in melanin biosynthesis process (melanogenesis, and (c) the targeting of proteins involved in melanogenesis and assembly by melanosomal proteins. Upon exposure to UV light radiation (UVR), melanin pigments revealed two distinct photobiological reactions, i.e. photoprotective and phototoxic reactions. The precursor intermediate of brown-black eumelanin, 5-6-dihydroxyindole, appears to possess the most potent photoprotective (antioxidant) property. Eumelanin pigment also had some antioxidant property. Similarly, yellow-red pheomelanin and its precursor intermediate, 5-S-cysteinyldopa also revealed some antioxidant property, but they became prooxidant in the presence of the ferric iron upon exposure to UVR. Melanosomes are known to possess several metal ions including Fe2+, Fe3+, Cu2+ and Zn2+. In addition, upon exposure to UV-light, there is an increase in ferric/ferrous iron in the skin. Therefore, in the in vivo system, pheomelanin intermediate, 5-S-cysteinyldopa, may show significant prooxidant property in conjunction with metal ions (e.g. Fe2+, Fe3+). When atypical moles (previously called dysplastic nevi) were analysed chemically for quantitative and qualitative properties of melanin pigment, they revealed a high ratio of pheomelanin/eumelanin content. This finding may partly explain our clinical observation that these moles are frequently the precursors of malignant melanoma and that the intermittent heavy exposure of UVR can be the major direct cause of their transformation. How, then, the melanosomal compartment, where active new melanin synthesis occurs after exposure to UVR, is protected from the cytotoxicity of melanin precursor intermediates. To study this question, two major experiments were conducted; (a) expression of melanogenesis-associated genes upon exposure of melanocytes to UVR and (b) transfection of cDNAs from the melanogenesis-associated genes. There was coordinated gene expression (mRNA) of tyrosinase and tyrosinase-related protein, TRP-1 and this coordinated gene expression was also accompanied by the upregulation of LAMP-1 (lysosome-associated membrane protein-1). Furthermore, human tyrosinase and TRP-1 mRNAs were expressed successfully in individual transfectants or co-transfectants of cDNAs from the two genes. Co-transfectants of human tyrosinase and TRP-1 cDNAs produced many lysosomal granules and melanin-containing granules, melanosomes. LAMP-1 gene was upregulated simultaneously in co-transfectants of tyrosinase and TRP-1, but not in individual transfectants of the two genes.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Current update and trends in melanin pigmentation and melanin biology. 776 May 35

We have isolated cDNAs for the human TRP-2 gene which represents a third member of the tyrosinase-related gene family and encodes the dopachrome tautomerase activity that functions in the synthesis of melanin pigment. The human TRP-2 protein has 83% identity/90% similarity to the mouse sequence and has all the structural characteristics of the tyrosinase protein family, including a signal peptide, 15 conserved cysteine residues, two copper-binding domains and a C-terminal membrane-spanning region. Northern blot analysis reveals that TRP-2 is expressed at high levels in human melanoma cells.
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PMID:Sequence of the human dopachrome tautomerase-encoding TRP-2 cDNA. 820 91


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