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)

Fotemustine is a chemotherapeutic drug for the treatment of melanoma. In this study, we investigated the metabolic and chemical stability of fotemustine with 31P-NMR and FAB-MS. In the absence of GSH, 95% of fotemustine decomposed rapidly into a reactive diethyl ethylphosphonate (DEP) isocyanate, both in rat liver S9 fraction and in HEPES buffer (pH = 7.4). DEP-isocyanate in turn hydrolyzed rapidly into diethyl (1-aminoethyl)phosphonate, which reacted subsequently with the parent DEP-isocyanate. The remaining 5% of fotemustine was shown to decompose via dechlorination into diethyl [1-(3-nitroso-2-oxoimidazolidin-1-yl)ethyl]-phosphonate. In the presence of GSH, hydrolysis of DEP-isocyanate was blocked, and a glutathione conjugate (DEP-SG) was formed instead. DEP-SG was relatively stable at 37 degrees C in HEPES buffer. Only two minor and as yet unidentified decomposition products were formed. Addition of N-acetyl-L-cysteine (NAC) to DEP-SG in HEPES buffer converted DEP-SG rapidly into the corresponding NAC conjugate of DEP-isocyanate (DEP-NAC). The formation of DEP-SG from DEP-isocyanate and GSH appeared to be spontaneous. The extent of formation of DEP-SG from fotemustine and GSH was equal in both enzymatically active and inactive rat liver S9 fractions. In the presence and in the absence of GSH, the half-lives of decomposition (t1/2) of fotemustine were 33 +/- 6 and 27 +/- 3 min, respectively. The formation of the DEP-isocyanate and 2-chloroethanediazohydroxide intermediates from fotemustine appeared to be rate limiting, and not the hydrolysis of the DEP-isocyanate nor its conjugation to GSH. Active or inactive rat liver S9 fractions accelerated the decomposition of fotemustine slightly; i.e., the t1/2 of fotemustine decreased from 39 +/- 3 to 29 +/- 1 min. Further knowledge of the metabolic and chemical stability of fotemustine and DEP-isocyanate will contribute to a better understanding of fotemustine-related cytostatic effects and toxic side effects and to the design of chemoprotection against undesired toxic side effects.
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PMID:Chemical and glutathione conjugation-related degradation of fotemustine: formation and characterization of a glutathione conjugate of diethyl (1-isocyanatoethyl)phosphonate, a reactive metabolite of fotemustine. 807 70

Most of the natural melanin pigments consist of not only indolic eumelanin but also sulfur-containing pheomelanin. Previous methods for spectrophotometric assay of melanins use solubilization in alkaline media; a major disadvantage of these procedures is that they do not distinguish between eumelanin and pheomelanin. A spectrophotometric method for assaying eumelanin in tissue samples is described. Sepia melanin serves as a standard. Hair and melanoma samples were hydrolyzed in hot hydriodic acid, and insoluble eumelanic pigments were solubilized in hot sodium hydroxide in the presence of hydrogen peroxide and analyzed for absorbance at 350 nm (A350). The detection limit of eumelanin was ca. 2 micrograms. Eumelanins prepared from dopa, 5,6-dihydroxyindole and its carboxy derivative gave similar A350 values. Mixed-type melanins prepared from dopa and various ratios of cysteine gave A350 values inversely proportional to their sulfur contents. Excellent correlations were observed between A350 values and contents of pyrrole-2,3,5-tricarboxylic acid, an oxidation product specific for eumelanin, in hair samples from sheep and humans of various colors and in melanomas and eyes from mice. The present method provides a specific and direct measurement of eumelanin contents in tissue samples.
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PMID:Spectrophotometric assay of eumelanin in tissue samples. 812 89

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

A sulfur-containing amino acid compound, S-allyl cysteine (SAC), derived from garlic extract inhibited proliferation of nine human and murine melanoma cell line in a dose-dependent manner (1.2-10 mM) assessed by a [3H]thymidine incorporation assay. Three control human lymphoblastoid cell lines were not inhibited by SAC concentrations < 5 mM. Four human melanoma cell lines in a soft-agar assay also showed dose-dependent inhibition of colony formation by SAC. Melanin content was increased up to 95% compared to the same untreated cell lines in these four human melanoma and two B16 murine melanoma sublines. Expression of cell surface gangliosides, cellular-differentiation and transformation markers, decreased after SAC treatment. Significant morphological changes including 'flattening and/or dendritic-like elongations' were also observed. Thus SAC inhibited cellular growth and proliferation and modulated major cell differentiation markers of melanoma.
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PMID:Growth inhibition and modulation of cell markers of melanoma by S-allyl cysteine. 842

The lack of HLA class I antigen expression by the melanoma cell line SK-MEL-33 is caused by a unique lesion in beta 2-microglobulin (beta 2-mu). Sequencing of beta 2-mu mRNA detected a guanosine deletion at position 323 in codon 76 that causes a frameshift with a subsequent introduction of a stop codon at a position 54 base upstream of the normal position of the stop codon in the message. The loss of 18 amino acids and the change of 6 amino acids, including a cysteine at position 80 in the carboxy terminus of beta 2-mu, are likely to cause marked changes in the structure of the polypeptide. The latter may account for the inability of beta 2-mu to associate with HLA class I heavy chains and for its lack of reactivity with the anti-beta 2-mu mAb tested. HLA class I antigen expression on SK-MEL-33 cells was reconstituted after transfection with a wild-type B2m gene, therefore indicating that the abnormality of endogenous B2m gene is the only mechanism underlying lack of HLA class I antigen expression by SK-MEL-33 cells. The guanosine deletion in B2m gene was detected also in the melanoma tissue from which SK-MEL-33 cells had originated. Therefore, the molecular lesion identified in the SK-MEL-33 melanoma cell line is not caused by a mutation acquired during growth in vitro but is likely to reflect a somatic mutation during tumor progression.
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PMID:Lack of HLA class I antigen expression by melanoma cells SK-MEL-33 caused by a reading frameshift in beta 2-microglobulin messenger RNA. 843 69

The course of melanogenesis in (malignant) melanocytes is determined by several relatively independent metabolic processes such as tyrosine uptake and compartmentation, the activity of tyrosinase, and the capacity of melanosomes to produce and store melanin. There is experimental evidence that tyrosine is transported across the cell membrane with a Na(+)-independent L transport system. Tyrosine designated for melanogenesis is probably localized in compartments different from those for protein synthesis. The maturation and subsequent activation of tyrosinase occurs primarily in the Golgi-associated endoplasmatic reticulum and coated vesicles. In these locations, the interaction between tyrosine and tyrosinase has some limitations because no melanin polymer can be detected in these structures. Nevertheless, the coated vesicles were shown to contain unpolymerized monomeric indols. Individual skin types differ in their ability to produce mature, fully pigmented, melanosomes. Whereas eumelanin content in melanocytes corresponds to the phenotypic appearance of the skin, the formation of pheomelanin varies considerably. Precursors of pheomelanin, such as glutathione and cysteine, are responsible for scavenging potentially toxic quinoid products of melanogenesis that escape from melanogenic compartments. Pheomelanogenesis can therefore be considered as one of the protective mechanisms of melanocytes. Significant leakage of reactive intermediates of melanogenesis may occur from aberrant melanosomes and explain the frequent incidence of necrosis in melanoma tissue. The presence of O-methylated derivatives of 5,6-dihydroxyindole (5,6DHI) and 5,6-dihydroxyindole-2-carboxylic acid (5,6DHI2C) in medium of melanoma cell cultures gives evidence of intracellular O-methylating ability. The O-methylation of o-dihydroxyphenols and indols by catechol-O-methyltransferase localized in microsomes and cytoplasma prevents their oxidation to reactive quinones. It is suggested, however, that this protective mechanism can be unreliable because catechol-O-methyltransferase can be inactivated by its oxidated substrates.
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PMID:Dynamics of melanogenesis intermediates. 843 3

The effects of systems generating active oxygen species (superoxide anion, hydrogen peroxide, hydroxyl radical) on tyrosinase have been studied in cultured human melanoma cells. Tyrosinase activity was determined by measuring the quantity of 5-S-L-cysteinyl-L-dopa (5-S-CD) formed in the presence of D,L-dopa and L-cysteine. In some experiments, the enzyme protein was determined by radio immunoassay [RIA]. Exposure of cells to xanthine/xanthine oxidase or glucose/glucose oxidase resulted in a dose-related elevation of tyrosinase. Catalase, but not superoxide dismutase, prevented this increase indicating that hydrogen peroxide may be the agent responsible for the action, whereas superoxide anion is not involved. Hydroxyl radicals formed by the Haber-Weiss or Fenton type reactions were not found to produce elevation of tyrosinase. Catalase determinations showed no enzyme in the medium but a high concentration in the cells. Inhibition of intracellular catalase by 3-amino-1,2,4-triazole caused an increase in the tyrosinase level. The effects of dopac, xanthine/xanthine oxidase, and glucose/glucose oxidase all producing hydrogen peroxide, and increasing tyrosinase, were enhanced by the inhibition of catalase. It is concluded that hydrogen peroxide, formed by the systems, accounts for the elevation of tyrosinase level. When tyrosinase activities determined by 5-S-CD formation were compared to enzyme amounts found by RIA, the ratios of these values were always constant. This fact indicates that the increase in the tyrosinase activities was not due to an activation of the enzyme, but mirrored the quantities of enzyme protein present in the samples. On the basis of our findings, it is assumed that hydrogen peroxide is a regulator of tyrosinase in normal melanocytes and melanoma cells.
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PMID:Hydrogen peroxide as an inducer of elevated tyrosinase level in melanoma cells. 843 9

We have integrated preparative two-dimensional polyacrylamide gel electrophoresis with high-performance tandem mass spectrometry and Edman degradation. By using this approach, we have isolated and identified, by partial sequencing, a human melanoma protein (34 kDa, pI 6.4) as lipocortin I. To our knowledge, this protein was not previously known to be associated with melanoma cells. The identity of the protein was confirmed by two-dimensional immunoblot analysis. High-energy collision-induced dissociation analysis revealed the sequence and acetylation of the N-terminal tryptic peptide and an acrylamide-modified cysteine in another tryptic peptide. Thus, knowledge concerning both the primary structure and covalent modifications of proteins isolated from two-dimensional gels can be obtained directly by this approach, which is applicable to a broad range of biological problems.
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PMID:Mass spectrometric and Edman sequencing of lipocortin I isolated by two-dimensional SDS/PAGE of human melanoma lysates. 844 11

We report a constitutional mutation of codon 273 in exon 8 of the p53 gene. The affected individual has developed multiple independent benign and malignant tumours (tricholemmoma of the scalp, multiple trichoepitheliomata of the face, osteosarcoma of the ovary, bilateral breast cancer, malignant fibrous histiocytoma of the thigh and endometrial adenocarcinoma) and belongs to a family with some, but not all, features of the Li-Fraumeni syndrome. The mutation, found in both blood lymphocyte and tumour specimens, is a cytosine to thymine transition at codon 273, resulting in an amino acid change from arginine to cysteine. The mother and sister of the index case both died of tumours at an early age. We have demonstrated that formalin-preserved material from these tumours contains the same C-->T mutation at codon 273, indicating that this mutation has probably been transmitted through the germline. All tumours from the index case, both benign and malignant, showed immunohistochemical positivity with four antibodies to the p53 protein. Positive staining was also seen in scattered nuclei of morphologically normal epidermal keratinocytes and pilosebaceous cells, but not in lymphocytes or other morphologically normal cells from the index case. However, a similar staining pattern in apparently normal tissue was also observed in 13/48 sections from other individuals with various skin conditions (melanocytic naevi, psoriasis and normal skin adjacent to malignant melanoma and fibrous histiocytomas), suggesting that this pattern of p53 staining may not be unique to individuals with constitutional p53 mutations.
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PMID:Constitutional mutation in exon 8 of the p53 gene in a patient with multiple primary tumours: molecular and immunohistochemical findings. 847 49

Shedding by cultured human melanoma cells of a well-characterised cell- surface glycoprotein antigen known as "melanotransferrin" was studied with two monoclonal antibodies, 140.240 and 96.5. By means of [35S]-cysteine metabolically-labelled melanoma cells and immunoprecipitation studies, identification was made, by 140.240 in the spent media of two of six melanoma cell lines, of a new molecule of 100-kDa, aside from the 88-kDa molecule. Only the 88-kDa shed molecule was detected in the remaining four melanoma cell lines with both antibodies. None of nine clonal sublines derived from the two melanoma cell lines were found to shed the 100-kDa or 88-kDa molecule exclusively. Both shed antigens were released spontaneously to the medium from the live melanoma cells rather than as a result of cell death and lysis, since there was no obvious cell death or debris in the spent medium nor in the monolayer cells detected at the time of spent medium collection. Digestion of the isolated 100-kDa and 88-kDa shed molecules with N-glycanase followed by SDS-polyacrylamide gel electrophoresis resulted in the appearance of a single band of the 77-kDa molecule, which is deduced to be the polypeptide precursor of the cell-associated 87-kDa antigen. It is concluded that some melanoma lines shed the variant 100-kDa molecule, in addition to the 88-kDa molecule, and that both shed molecules and their cellular counterpart 87-kDa differ in their degrees of glycosylation.
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PMID:Identification with monoclonal antibody 140.240 of a structural variant of melanotransferrin shed by human melanoma cell lines in vitro. 861 5


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