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)

Polyclonal antibodies to hamster melanoma tyrosinase were raised in rabbits, and series of immunoinhibition experiments with a purified enzyme and specific immunoglobulins were carried out. Tyrosinase activity was determined by a set of radiochemical and spectrophotometric methods utilizing tyrosine, dopa, dopamine, or dihydroxyindole (DHI) as substrates. The quantitative data obtained indicated that the complexing of tyrosinase with its specific antibody inhibited melanogenesis in a specific manner: dopachrome formation from dopa and dopamine conversion to melanin were not affected and all other enzyme activities comprising the DHI oxidation step were inhibited to various degrees. Additionally, tyrosine hydroxylation was also slightly inhibited. The data obtained implied that melanogenesis was restricted at the point of DHI oxidation. From observations on the immunoinhibition of a DHI oxidation at varying dopa-cofactor concentrations, we propose that dopa-cofactor may be bound at separate site than DHI and thus may act as a positive allosteric effector for DHI oxidation by tyrosinase. Study of tyrosinase immunoinhibition by the antibodies against the enzyme thus seems to provide a valuable system for investigating the tyrosinase-mediated melanogenesis.
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PMID:Specific inhibition by antityrosinase antibodies of tyrosinase-mediated melanogenesis. 309 7

The B16/C3 murine melanoma is a pigmented tumor that is rich in the copper-containing enzyme, tyrosinase. This enzyme, which converts tyrosine to melanin precursors, is largely associated with membrane fractions of cells and exists in a number of discrete isozymic forms ranging in molecular mass from 58,000 to 150,000 daltons and pI from 3.4 to 5.2. One of these isozymes (Mr = 58,000, pI 3.4) has been purified to homogeneity. The purified enzyme catalyzes the hydroxylation of L-tyrosine to L-dihydroxyphenylalanine (L-DOPA) and the conversion of L-DOPA to dopaquinone. Ascorbic acid, tetrahydrofolate, and dopamine can serve as cofactors in the hydroxylase reaction. The Michaelis constants for the purified enzyme were 7 X 10(-4) M for L-tyrosine and 6 X 10(-4) M for L-DOPA. The Vmax for L-DOPA was much greater than the Vmax for L-tyrosine indicating that tyrosine hydroxylation is rate-limiting in melanin precursor biosynthesis. Two putative copper chelators, phenylthiourea and diethyldithiocarbamide inhibited both the tyrosine hydroxylase and L-DOPA oxidase activities of the enzyme. Phenylthiourea was a noncompetitive inhibitor while diethyldithiocarbamide was a competitive inhibitor indicating that these agents act by different mechanisms. When digested with proteases and glycosidases, higher molecular weight forms of tyrosinase co-migrated with the purified enzyme in isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggesting that the isozyme was derived from larger precursors. Thus, post-translational processing of tyrosinase may underlie isozyme diversity and this may be important in the control of melanogenesis in this tumor model.
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PMID:Tyrosinase isozyme heterogeneity in differentiating B16/C3 melanoma. 309 4

Significant levels of intracellular catecholamines were found in a human melanoma cell line and were enhanced by increasing the extracellular tyrosine concentration. Intracellular dopa, 5-cysteinyldopa, tyrosinase, and melanin also rose under these conditions. 5-HT (serotonin) was synthesized by the melanoma cells but further study was hindered by the high level of 5-HT in fetal calf serum. A 5-HT uptake antagonist, DU 24565 (6-nitroquipazine), was employed as an alternative method for studying 5-HT action. This compound, which in contrast to tunicamycin had no inhibitory effects on cell proliferation or tyrosinase activity, strongly inhibited melanization and decreased the levels of dopa, 5-cysteinyldopa, dopamine, noradrenaline, adrenaline, and 3,4-dihydroxyphenylacetic acid. DU 24565 had little effect on 5-HT or tyrosine accumulation in these cells but suppressed the uptake of extracellular dopa. The results show that human melanoma cells synthesize a wide range of biogenic amines in culture and suggest a new approach to regulating intracellular levels of dopa and of a variety of dopa products.
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PMID:Inhibition of melanization in human melanoma cells by a serotonin uptake inhibitor. 311 Feb 97

Murine melanoma melanosomal tyrosinase, solubilised at pH 6.8 and 1% Igepal, exhibits a lag in cresolase activity which increases with increasing concentration of tyrosine. The enzyme, solubilised at pH 5.0 and assayed at pH 5.0, does not exhibit lag even at inhibitory concentrations of tyrosine while the same enzyme when assayed at pH 6.8 exhibits characteristic lag. When the enzyme was solubilised from a melanosomal fraction with detergent/water without any buffer, significant linear activity for 2 h was seen at an inhibitory concentration of tyrosine, indicating for the first time the presence of a form of tyrosinase without lag and inhibition by excess tyrosine. Exposure of the enzyme solubilised in buffer/detergent at pH 6.8 to rapid decrease in pH to 5.0 or 4.7 makes the enzyme remain irreversibly in the form without characteristic lag, even at an inhibitory concentration of tyrosine and at pH 6.8. These results may be interpreted as follows. The enzyme at pH 6.8 exists in the E form with an allosteric site for tyrosine. Decrease of the pH of the enzyme solution from 6.8 to 5.0 or 4.7 by dialysis results in the reversible protonation of the enzyme, which no longer binds tyrosine at its allosteric site and consequently inhibition by excess tyrosine and lag were not observed at acidic pH. However, if the enzyme was rapidly brought to pH 5.0 from 6.8 it remains irreversibly in the protonated form even at pH 6.8. Ascorbic acid acts as an effective reductant for the hydroxylation of tyrosine by tyrosinase, while 3,4-dihydroxyphenylalanine is both an effective reductant and counteracts the inhibition by tyrosine at pH 6.8.
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PMID:pH-dependent interconvertible allosteric forms of murine melanoma tyrosinase. Physiological implications. 311 52

A spontaneous, hypomelanotic variant (MI) of the highly melanotic transplantable hamster melanoma of Bomirski (Ma) is the subject of this report. Tyrosinase activity is 2-3 times higher, but melanin content significantly lower than in the parental Ma melanotic melanoma. Acid phosphatase activity is similar in both, but beta-glucuronidase and aryl-sulfatase A are 2-3 times higher in the hypomelanotic variant. Transplanted MI melanomas grow more slowly than the parental tumor, but metastasize with similar incidence and localization. Hypomelanotic variant melanoma cells, even those in grossly nonnecrotic parts of the transplants, show signs of low viability like swelling of the cytoplasm or cellular condensation, and disintegration. Autophagic vacuoles are numerous. They appear to be formed by enclosure of a portion of cytoplasm by cisternae of smooth endoplasmic reticulum or trans-Golgi network. These limiting cisternae contain tyrosinase as evidenced by deposition of electron dense reaction product on incubation with tyrosine or DOPA. Other sites of ultrastructural tyrosinase reaction are melanosomes and the smooth-surfaced cisternae and vesicles of the trans-Golgi network. We postulate the low cell viability, associated with autophagosome formation, is the cause for the growth retardation of the MI variant, and that the lower melanin content of these tyrosinase-rich cells is due to sequestration of a substantial portion of newly synthesized enzyme into autophagic vacuoles before it has the chance of being incorporated into melanosomes.
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PMID:Pathology and ultrastructural characteristics of a hypomelanotic variant of transplantable hamster melanoma with elevated tyrosinase activity. 311 4

Nuclear estrogen binding was characterized in HM-1, a malignant hamster melanoma cell line transplanted into male and female athymic mice following acute, subchronic, and chronic injection of estradiol. Nuclear binding was saturable, of high affinity (10(10) M-1) and readily soluble in low salt buffer. Saturation analyses revealed that [3H]estradiol in excess of 5.0 nM apparently bound to a second class of lower affinity (10(9) M-1), higher capacity cytosol sites. Enzyme-linked immunoassay with a specific monoclonal antibody (H222 Sp gamma) directed against the human estrogen receptor protein was in excellent agreement (r = 0.93) with values obtained using hydroxyapatite to separate bound from free ligand. Nuclear estrogen receptor content in HM-1 cells was increased maximally 1 h after acute s.c. injection of a low dose (0.1 microgram) of estradiol. The increase in nuclear receptor content was accompanied by an apparent rapid reduction in cytosol binding. Subchronic (3 days) and chronic exposure (35 days) to estradiol also produced a significant, dose-related increase in tumor nuclear estrogen receptor content. Cytosol binding for progestin was low (less than or equal to 2 fmol) to absent in HM-1 xenografts not exposed to estradiol. Subchronic and chronic exposure to estradiol induced a dose-related, specific, high affinity (10(9) M-1) cytosol binding protein for progestin(s) in HM-1 xenografts carried in male and female athymic mice. In contrast, progestin binding to nuclear receptor was not increased in estrogen-primed animals, nor did acute injection of progesterone (100 micrograms s.c.) increase the amount of saturable, high affinity (10(9) M-1) nuclear progestin receptor in control or estradiol-primed athymic mice. In contrast to the induction of progestin binding, tyrosinase activity was not altered by a similar exposure to estradiol when assayed at a saturating concentration of tyrosine. These observations suggest that the estrogen receptor in HM-1 cells may be functional but that pigmentary changes observed in mammals following chronic exposure to estradiol may not be mediated by a direct effect on the rate limiting enzyme of melanin synthesis.
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PMID:Effects of estradiol on estrogen receptor, progesterone receptor, and tyrosinase in hamster melanoma transplanted into athymic mice. 313 19

In order to investigate the possibility of using [1-11C] labelled 3,4-dihydroxyphenylalanine (DOPA) and tyrosine as radiopharmaceuticals for the detection of eye melanoma, the biodistributions of the same 1- and 3-14C-labelled compounds were investigated in Syrian golden hamsters with Greene melanoma. The results of these investigations were compared with positron emission tomography (PET) images of 11C labelled DOPA and tyrosine. The synthesis of these 11C labelled compounds procures of DL mixture, from which D and L forms can be separated. One h after intravenous injection, both 14C labelled DL-, L- and D-DOPA showed a high uptake in tumour tissue, that of DL- and D-DOPA being the highest. These high uptakes, together with relatively low uptake in bone, skin and eye resulted in high tumour/non tumour ratio (for DL-DOPA 5.9, 4.5 and 6.6 respectively). Extraction of the tumour tissue with trichloroacetic acid showed that L-DOPA was mainly incorporated into melanin, whereas D-DOPA was not. Also, the uptake 1 h after intravenous injection of 1-14C-L- and DL-tyrosine into the tumour were high, but L- and DL- were less different; tumour/non tumour ratios were favorable. PET images of the tumour obtained 40-80 min after injection of the [1-11C] labelled DOPA and tyrosine confirmed that melanoma detection was promising and that D-DOPA produced a better melanoma image than L-DOPA.
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PMID:Potential radiopharmaceuticals for the detection of ocular melanoma. Part III. A study with 14C and 11C labelled tyrosine and dihydroxyphenylalanine. 314 Nov 89

We describe results demonstrating the positive regulation of melanogenesis by two substrates of the melanogenic pathway. We have found that L-tyrosine and L-dihydroxyphenylalanine (L-dopa), whose metabolic fates are affected by the activity of that pathway, can also act as its regulators. In living pigment cells, tyrosinase (EC 1.14.18.1), a crucial and rate-limiting enzyme of melanogenesis, acts in subcellular organelles known as melanosomes. Melanin is laid down only in these organelles. We demonstrate that supplementing Ham's F-10 medium with additional L-tyrosine or L-dopa during the culture of amelanotic Bomirski hamster melanoma cells results in a rapid increase in melanin formation, which is not simply due to greater availability of substrate. There is a rapid increase in tyrosinase activity and a large scale synthesis of melanosomes. The effects of L-tyrosine and L-dopa are prevented by the addition of cycloheximide. The actions of L-tyrosine and L-dopa are specific in that under similar conditions D-tyrosine, D-dopa, N-acetyl-L-tyrosine, L-phenylalanine, L-tryptophan and L-valine have little or no effect. The two substrates, L-tyrosine and L-dopa, appear to act through related but distinct mechanisms. Our findings provide an example of a little-known phenomenon: regulation of a differentiated eukaryotic phenotype through positive control by substrates in the pathway.
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PMID:Positive regulation of melanin pigmentation by two key substrates of the melanogenic pathway, L-tyrosine and L-dopa. 314 38

4-S-cysteinylphenol (4-S-CP), the S-homologue of tyrosine, has been recently synthesized as a selective chemotherapeutic agent against malignant melanoma and has been shown to be a specific substrate for tyrosinase in vitro. In vivo incorporation of 4-S-CP into the B16 and Harding Passey (HP) melanomas and the systemic organs have been evaluated by the autoradiographic method. The distribution of the silver grains indicated that 4-S-CP was selectively incorporated into both the B16 and HP melanomas. 4-S-CP was excreted mainly from the kidneys and there was an accumulation of 4-S-CP in the reticulo-endothelial system. These results seemed to contribute to the utilization of 4-S-CP and other related compounds as chemotherapeutic agents against malignant melanoma.
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PMID:Histological localization of 4-S-cysteinylphenol in melanoma-bearing mice. 332 27

The incorporation of 4-S-cysteinylphenol (4-S-CP), a tyrosine analog, into malignant melanoma cells was evaluated. 4-S-CP was specifically incorporated into the melanotic melanoma cells (HMV-II), which have activity for melanin synthesis, but was scarcely incorporated into HeLA S3 or HMV-I cells, which have no activity for melanin synthesis. Electron microscopic autoradiography revealed that the intracellular localization of 4-S-CP was closely correlated with melanogenesis and that 4-S-CP served as an initial substrate for tyrosinase and was utilized in melanin synthesis. On the basis of these findings we hypothesize that tyrosinase is required for intracellular incorporation of 4-S-CP. This specific incorporation of 4-S-CP into melanoma cells should be useful in the development of an effective procedure for chemotherapy of malignant melanomas and in analysis of melanin synthesis.
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PMID:Specific incorporation of 4-S-cysteinylphenol into human melanoma cells. 336 Nov 42


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