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)

A radioreceptor assay for alpha-MSH is described which is based on cultured mouse B16 melanoma cells and bioactive monoiodinated [Nle4]-alpha-MSH tracer. The assay was used (1) to study the binding characteristics of alpha-MSH to B16 cells, (2) to determine the relative binding activity of MSH peptides, and (3) to measure MSH in tissue extracts. The association of alpha-MSH to B16 cells reached a stable plateau after 3 h at 15 degrees C. At 25 degrees or 37 degrees C, the binding was transient and at 0-1 degree C, the association was very slow. The hormone-receptor complex was relatively stable between 0 degrees and 15 degrees C whereas a 50% dissociation was reached after 90 min at 25 degrees C and after 35 min at 37 degrees C. The mean KD for alpha-MSH of four saturation experiments was 1.3 nM and the number of receptors 9570 per cell. 1,10-Phenanthroline had a stabilizing effect in the binding assay when used at a 0.3 mM concentration. From the MSH peptides tested in the binding assay, some showed similar potencies in three bioassays (tyrosinase, melanin and Anolis skin), whereas others displayed considerably lower bioassay values than expected from the binding data. This shows that binding and bioactivity can be dissociated in some of the MSH peptides. The biological activity of MSH from the neurointermediate lobe of the rat pituitary as measured by its binding to B16 cells corresponds fairly well with RIA results; in the anterior lobe, alpha-MSH values are overestimated because of the large amount of ACTH present.
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PMID:Radioreceptor assay for alpha-MSH using mouse B16 melanoma cells+. 283 20

The binding of adrenocorticotropic hormone (ACTH) to B16/C3 murine melanoma cells was found to be specific and saturable. The binding capacity of the cells changed as a function of the age of the culture. Scatchard analysis revealed one class of high-affinity ACTH binding sites. The specificity of ACTH binding to the cells was tested by displacement experiments with human leukocyte interferon (alpha-IFN) and alpha-melanocyte stimulating hormone (alpha-MSH) as the competitors. Structure-activity relationship of ACTH, alpha-MSH and alpha-IFN was discussed.
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PMID:Adrenocorticotropin binding activity of B16/C3 melanoma cells. 285 10

Calcium ionophore A23187 lowers basal levels of tyrosinase and inhibits the MSH-induced increase in tyrosinase in Cloudman S-91 mouse melanoma cell cultures. Ionophore at a concentration of 10(-6) g/ml causes a 50% reduction in basal levels of tyrosinase and inhibits the MSH stimulated level of enzyme. Ionophore A23187 also inhibits the PGE1 mediated stimulation of tyrosinase, as well as the rise in enzyme activity observed in cells exposed to either theophylline (1 mM) or dbcAMP (10(-4)M). Ionophore does not affect basal levels of cyclic AMP nor the elevated levels produced by either MSH or PGE1, suggesting then, that the antagonistic activity of A23187 is localized to a point in the pathway of tyrosinase activation distal to the formation of cAMP. Ionophore causes a rapid and marked (greater than 50%) inhibition of cellular protein synthesis and it is possible that this calcium mobilizing compound may exert its inhibitory effects on tyrosinase activity by causing a general reduction in cellular translation. Since the inhibition of protein synthesis occurs in cells exposed to ionophore in either the presence or absence of calcium in the medium, it seems, likely that the ionophore may exert its effects by causing the release of calcium from intracellular sites.
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PMID:Inhibition of tyrosinase activity and protein synthesis in melanoma cells by calcium ionophore A23187. 285 56

L-dopa is a key metabolite in the process of melanogenesis. However, it is difficult to use in biological experiments because it is subject to auto-oxidation and relatively insoluble at neutral pH. Dopa phosphates contain phosphate ester linkages at positions 3 and/or 4 of the phenylalanine ring of L-dopa, rendering them highly soluble and stable to auto-oxidation when compared to L-dopa. Dopa phosphates are readily taken up by melanoma cells in culture and converted to L-dopa and inorganic phosphate by cellular phosphatases, making them useful for studying L-dopa effects in vivo. Here we investigated the effects of dopa phosphates on receptors for MSH in cultured melanoma cells. We found that dopa phosphates caused a 3-fold stimulation of MSH binding capacity by the cells which probably occurred through an increase in the number of receptors for MSH with no apparent change in affinity of the receptors. The increased binding capacity for MSH was followed by increased cellular tyrosinase activity and melanogenesis. Thus dopa phosphates and/or L-dopa can act as regulators of the MSH receptor system. The observations suggest a novel mechanism for regulation of hormonal responsiveness: hormonal signal amplification by a metabolite in the target pathway.
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PMID:Phosphorylated isomers of L-dopa stimulate MSH binding capacity and responsiveness to MSH in cultured melanoma cells. 288 96

A review of the studies done at Yale on the role of MSH in regulating pigmentation and growth of Cloudman (S91) melanoma cells is presented. The areas covered include the isolation and analyses of mutant cell lines unresponsive to MSH; the role of cyclic AMP, cyclic AMP-dependent protein kinases, and protein phosphorylation reactions in the response of MSH; new regulators of the melanogenesis pathway; the cytotoxicity of melanin precursors; the development of methodology for synthesizing 125I-beta-MSH; the use of this ligand to study receptors for MSH; and the chemical and biological properties of phosphorylated isomers of L-dopa, a new class of compounds exhibiting potent bio-activity toward melanocytes. All of the experiments described were carried out in the Department of Dermatology at the Yale University School of Medicine during the tenure of Dr. Aaron B. Lerner as chairman.
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PMID:Studies on the Cloudman melanoma cell line as a model for the action of MSH. 300 51

The superpotent and ultraprolonged melanotropic properties of an alpha-melanotropin analog, [Nle4, D-Phe7]-alpha-MSH, were investigated in a Cloudman S91 (CCL 53.1) melanoma cell line. [Nle4, D-Phe7]-alpha-MSH is 100-fold more effective than the native hormone, alpha-melanocyte stimulating hormone (alpha-MSH), in stimulating melanoma cell tyrosinase activity, as determined from their minimum effective doses (10(-11)M and 10(-9)M, respectively). [Nle4, D-Phe7]-alpha-MSH also exhibits a more sustained effect than alpha-MSH on tyrosinase after removal of the melanotropins from the incubation medium. When cells were exposed to alpha-MSH (10(-7)M) for 24 h, residual activity after removal of the hormone was minimally significant. In contrast, under the same experimental conditions [Nle4, D-Phe7]-alpha-MSH treatment induced tyrosinase activity 2-3 fold above basal level, and maintained remarkable stimulatory effects up to 72 h following melanotropin removal. When the exposure time to melanotropins was reduced to 4 h, alpha-MSH failed to elicit significant tyrosinase activity, whereas [Nle4, D-Phe7]-alpha-MSH stimulated significant tyrosinase activity during the first 24 h subsequent to melanotropin removal. Interestingly, this stimulation by the analog increased at 48 h, reached a maximum at 72 h following removal of the melanotropin analog, and remained significantly stimulated for 6 consecutive days in the absence of the analog.
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PMID:[Nle4, D-Phe7]-alpha-MSH: a superpotent melanotropin that "irreversibly" activates melanoma tyrosinase. 300 69

We have examined adenylate cyclase (AC) in the M2R melanoma cell line, a novel clone of transplantable B16 melanoma cells. It has been found that activity of this enzyme is highly responsive to beta-melanotropin (beta-MSH) and other hormones possessing melanotropic activity (e.g., alpha-melanotropin (alpha-MSH) and adrenocorticotrophic hormone (ACTH1-24)). beta-MSH stimulation of adenylate cyclase, both in the intact cell and in a plasma membrane-enriched fraction derived thereof, was shown to be saturable and dose-dependent. In addition, prostaglandin E1 (PGE1) was found to be a potent stimulator of AC activity in these cells. Hormone stimulation of enzyme activity in the intact cell was strongly potentiated by forskolin which not only enhanced maximal AC activity 3-fold, but lowered by 40-fold the concentration of beta-MSH required for half-maximal stimulation. Using biologically active [125I]iodo-beta-MSH prepared in our laboratory we have examined the specificity of beta-MSH binding to its receptor in both intact M2R cells and plasma membranes derived thereof. Among a series of hormones tested only alpha-MSH and ACTH1-24 competed with [125I]iodo-beta-MSH for binding to the melanotropin receptor in accordance with the results obtained with AC. In contrast to the strong effect on cyclic 3',5'-adenosine monophosphate (cAMP) accumulation in M2R cells forskolin has no effect on [125I]iodo-beta-MSH binding. It appears that the kinetic properties of beta-MSH binding and beta-MSH stimulation of adenylate cyclase activity are essentially identical, the half-maximal effects of which are demonstrated at approximately 20 nM beta-MSH.
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PMID:Regulation of adenylate cyclase by beta-melanotropin in the M2R melanoma cell line. 301 5

Des-, mono-, and diacetylated melanotropin (des-, mono-, and di-Ac MSH, respectively) were compared for their dose-related effects on content of adenosine 3':5'-monophosphate (cAMP) and tyrosinase activity in the Cloudman S91 mouse melanoma tumor. Des-Ac MSH was more potent than the acetylated forms of MSH at increasing cellular levels of cAMP; mono- and di-Ac MSHs, however, were more potent than des-Ac MSH at elevating the activity of the enzyme, tyrosinase. Lysine-gamma1 MSH, a melanotropin from the amino terminus of pro-opiomelanocortin, exhibited slight stimulatory effects on tyrosinase and these actions were less than additive to those of mono-Ac MSH. Unlike their actions on amphibian skin-darkening or in mammalian behavior, neither beta-endorphin1-31 nor its derivatives, N-Ac-beta-endorphin1-27 or beta-endorphin30-31 (glycylglutamine), exhibited any influence on tyrosinase activity evoked by mono-Ac MSH in the tumor cells.
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PMID:The effects of pro-opiomelanocortin peptides on cyclic AMP and tyrosinase in melanoma cells. 302 51

alpha-MSH (melanocyte-stimulating hormone) causes an increase in tyrosinase activity (O-diphenol-O2 oxidoreductase; EC 1.14.18.1) in Cloudman S-91 mouse melanoma cell cultures following a lag period of approximately 9 h. Treatment of cells with 2 X 10(-7)M alpha-MSH for 6 days results in a 90-fold increase in the specific activity of the enzyme. The hormone-mediated increase in tyrosinase activity is dependent upon continued transcription since the enzyme induction is suppressed by either cordycepin (1 microgram/ml) or alpha-amanitin (10 micrograms/ml). Immunoprecipitation analysis of pulse-labeled tyrosinase from control and MSH-treated cultures (48-h exposure) has demonstrated that MSH stimulates tyrosinase synthesis by approximately 4-fold, a level of induction which does not correspond to the observed 14-fold increase in enzyme activity. When immunotitration curves were developed from cell extracts of control and MSH-treated cultures using immunoprecipitation and competitive enzyme-linked immunosorbent assay protocols, evidence for the presence of immunologically active but catalytically less active enzyme in untreated melanoma cell cultures was demonstrated. Degradation rates of tyrosinase were found to be similar in control cultures or in cells treated with MSH for up to 48 h. Taken together, these results suggest that in addition to stimulating tyrosinase synthesis, MSH may also promote an increase in the catalytic efficiency of the enzyme.
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PMID:Alpha-melanocyte-stimulating hormone regulation of tyrosinase in Cloudman S-91 mouse melanoma cell cultures. 303 Oct 58

We show that Cloudman melanoma cells undergo rapid arborization in response to [Nle4,D-Phe7]alpha-melanocyte-stimulating hormone, a potent analogue of alpha-melanocyte stimulating hormone (alpha-MSH). The arbors were established by extension of processes and resembled dendrites. We used this system to study the regulation of cell shape. alpha-MSH is known to induce increases in cAMP levels, and agents such as forskolin and isobutylmethylxanthine that led to increased cAMP also caused arborization. However, equally dramatic arbors were formed after incubation with the protein kinase C inhibitor H-7 [1-(5-isoquinolinesulfonyl)-alpha-methyl-piperazine]. Phorbol diesters that activate protein kinase C led to cell rounding and antagonized alpha-MSH. The actions of protein kinase C cannot be rationalized in terms of indirect effects on cAMP: neither H-7 nor phorbol diesters alone altered cAMP levels, nor did they affect the increase in cAMP induced by MSH. We show also that MSH produced longer-term effects that cannot be mimicked by cAMP. Specifically, even in the continued presence of alpha-MSH, arborization was followed by morphological reversal to the unstimulated flattened configuration within 2 hr. (This did not occur with other agents that increase cAMP or with H-7.) Most importantly, whereas MSH-induced arborization occurred in the presence of cycloheximide, actinomycin D, or in enucleated cells, the reversal of arborization did not. Thus, MSH induced a program of rapid shape change that was dependent on new protein synthesis and gene transcription.
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PMID:Regulation of cell shape in the Cloudman melanoma cell line. 303 40


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