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)

The role of protein phosphorylation in MSH-induced melanogenesis was investigated with an in vivo phosphorylation assay using intact cultured Cloudman S91 mouse melanoma cells preincubated with [32P]orthophosphate. Exposure of the cells to alpha-MSH increased the extent of labelling of two protein bands on SDS gel electrophoresis with estimated molecular weights of 43 and 34 kDa, respectively. The 32P incorporation was concentration-dependent and reached a maximal value at 10(-8) M alpha-MSH for the 43 kDa band (156% of controls) and at 10(-5) M alpha-MSH for the 34 kDa band (250% of controls). The corresponding ED50s were 5 X 10(-10) M (43 kDa) and 3 X 10(-8) M (34 kDa). The 32P incorporation into the 34 kDa band reached a maximum after a 5 min exposure to alpha-MSH whereas 43 kDa phosphorylation was maximal after a 30-60 min incubation with hormone. The effect was completely reversible after removal of the hormone and specific for melanotropic peptides. Dibutyryl cAMP (10(-3) M) and forskolin (10(-4) M) together with isobutylmethylxanthine (10(-4) M) mimicked the effect of alpha-MSH, pointing to an involvement of adenylate cyclase activation in the phosphorylation of both the 34 kDa and the 43 kDa protein. Preliminary observations showed that the 34 kDa protein is membrane-bound whereas the 43 kDa protein is of mitochondrial or melanosomal origin.
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PMID:alpha-MSH-induced changes in protein phosphorylation of Cloudman S91 mouse melanoma cells. 243 92

The melanotropin (MSH) receptor of mouse B16-F1 melanoma cells was characterized by photoaffinity cross-linking, using a potent alpha-MSH photolabel, [norleucine4, D-phenylalanine7, 1'-(2-nitro-4-azidophenylsulfenyl)-tryptophan9]-alpha-melanotropin (Naps-MSH). Its monoiodinated form, 125I-Naps-MSH, displayed a approximately 6.5-fold higher biological activity than alpha-MSH. Scatchard analysis of the saturation curves with 125I-Naps-MSH revealed approximately 20,000 receptors/B16-F1 cell and an apparent KD of approximately 0.3 nM. Analysis of the cross-linked MSH receptor by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that a photolabeled band of approximately 45 kDa occurs in B16-F1, B16-F10, and Cloudman S91 mouse melanoma, as well as in human D10 and 205 melanoma but not in non-melanoma cells. The labeled 45-kDa protein had an isoelectric point of 4.5-4.9 as determined by two-dimensional gel electrophoresis. Treatment of the labeled 45-kDa protein of B16-F1 cell membranes by neuraminidase shifted the band to approximately 42 kDa. A similar band of about 42 kDa was also observed after receptor labeling of B16-W4 cells, a cell line with a decreased number of terminal N-linked neuraminyl residues. These results indicate that the labeled 45-kDa glycoprotein contains terminal sialic acid residues, explaining the low pI of this protein, and that it is characteristic for melanoma cells and hence part of the MSH receptor.
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PMID:The receptor for alpha-melanotropin of mouse and human melanoma cells. Application of a potent alpha-melanotropin photoaffinity label. 254 92

Two analogues of alpha-MSH (Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2), Ac-[Nle4, Asp5, D-Phe7, Lys10]alpha-MSH4-10NH2 and Ac-[Nle4, Asp5, D-Phe7, Lys10] alpha-MSH4-10-NH2, were synthesized, and the melanotropic activities of the peptides were compared in several bioassays. Potencies were determined in the in vitro frog and lizard skin bioassays and in the S91 melanoma cell tyrosinase assay. Both analogues were equipotent or more potent than alpha-MSH in all bioassays, and the activities of the analogues were prolonged compared to alpha-MSH. The two analogues were very resistant to inactivation by purified proteolytic enzymes (alpha-chymotrypsin, trypsin, and pepsin). The two peptides could be topically applied and transdermally delivered across the skin of mice in vivo, resulting in a shift from pheomelanogenesis to eumelanogenesis within follicular melanocytes. The cyclic analogue exhibited greater potency, prolonged activity, and stability against enzyme inactivation than did the linear peptide. The significance of the findings for the further design of melanotropin analogues is discussed, as in the possible relevance of these melanotropin analogues for use in biomedical studies.
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PMID:Linear and cyclic alpha-melanotropin [4-10]-fragment analogues that exhibit superpotency and residual activity. 255 3

Seven human melanoma metastases were extracted in order to check the possible presence of any alpha-melanocyte stimulating hormone (MSH) immunoreactivity. The aim of that study was to provide some explanation for, mainly, two observations that we have already made and reported: 1) increased plasma alpha-MSH levels in melanoma of tumour-bearing patients as compared with tumour-free patients; 2) the presence of specific alpha-MSH receptors on human melanoma cells in culture. We could measure large amounts of immunoreactive alpha-MSH in all tumours ranging from 0.31 to 4.27 pmoles per g of wet tissue. Further identification of the extracted material by high-performance liquid chromatography revealed compounds of higher molecular weight and more hydrophobic than synthetic alpha-MSH. In addition, purified extracts could also displace 125I-labelled alpha-MSH from its cellular binding sites in an alpha-MSH specific radio-receptor binding assay. Our findings would suggest a possible presence of some hormone precursor(s) inside the melanoma tumours.
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PMID:Alpha-melanocyte-stimulating hormone immunoreactivity in human melanoma metastases extracts. 255 7

We examined the cultured mouse melanoma cell line B16 (clone F1) and its wheat germ agglutinin-resistant variant Wa4 that suffers from abnormal protein glycosylation (a high fucose:sialic acid ratio in glycoproteins). In both cell lines the adenylate cyclase system was endowed with a functional guanine nucleotide binding protein Gs and was efficiently coupled to alpha-MSH receptors. In the B16 cell line F1 studied we also observed an efficient stimulation of adenylate cyclase activity by helodermin, VIP and the VIP analogue [acetyl-His1]VIP, and also by PGE1. In membranes from the lectin-resistant variant Wa4, the stimulations by VIP-like peptides and by PGE1 were reduced by 60% and 50%, respectively, while the stimulation by alpha-MSH remained normal. As other components of the adenylate cyclase system (Gs site, catalytical unit) appeared unchanged in the Wa4 variant, we conclude that impaired glycosylation essentially affected the number of both VIP-like peptide receptors and PGE1 receptors.
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PMID:Decreased adenylate cyclase activation by helodermin and PGE1 in the lectin-resistant variant Wa4 of the mouse melanoma cell line B16. 255 62

The various physiological effects of alpha-MSH, mainly on the CNS and on pigmentation in animal models, are well documented in the literature. Only a few investigators have confirmed similar properties in the human. However, the possible physiopathological role played by this hormone in human melanoma is still poorly defined. In order to approach this subject in a manner as complete as possible, we have performed, during the past four years, three different series of experiments: 1) alpha-MSH measurements in plasma samples from: a. melanoma and other cancer patients, b. whole body UVA irradiated healthy adults, c. circadian rhythm determinations in melanoma patients and in healthy male adults; 2) alpha-MSH measurements in human melanoma tumours; 3) alpha-MSH receptor expression on human melanoma cells in culture involving: a. alpha-MSH radio-binding assays and b. tyrosinase assay. Our results so far show 1) increased alpha-MSH levels in melanoma patients' plasma, alpha-MSH responsiveness to UVA stimulated skin, large immunoreactive alpha-MSH content in melanoma metastases and an alpha-MSH circadian rhythm in some individuals different from cortisol; 2) alpha-MSH receptor expression in melanoma cells could be increased by various effectors able to stimulate melanogenesis.
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PMID:Studies on factors influencing human plasma alpha-MSH. 256 Jun 23

In humans the major stimulus for cutaneous pigmentation is ultraviolet radiation (UVR). Little is known about the mechanism underlying this response, in part because of the complexity of interactions in whole epidermis. Using a recently developed culture system, human melanocytes were exposed daily to a physiologic range of UVR doses from a solar simulator. Responses were determined 24 hours after the last exposure. There was a dose-related increase in melanin content per cell and uptake of 14C-DOPA, accompanied by growth inhibition. Cells from donors of different racial origin gave proportionately similar increases in melanin, although there were approximately tenfold differences in basal values. Light and electron microscopy revealed UVR-stimulated increases in dendricity as well as melanosome number and degree of melanization, analogous to the well-recognized melanocyte changes following sun exposure of intact skin. Similar responses were seen with Cloudman S91 melanoma cells, although this murine cell line required lower UVR dosages and fewer exposures for maximal stimulation. These data establish that UVR is capable of directly stimulating melanogenesis. Because cyclic AMP elevation has been associated in some settings with increased pigment production by cultured melanocytes, preliminary experiments were conducted to see if the effects of UVR were mediated by cAMP. Both alpha-MSH and isobutylmethylxanthine (IBMX), as positive controls, caused a fourfold increase in cAMP level in human melanocytes and/or S91 cells, but following a dose of UVR sufficient to stimulate pigment production there was no change in cAMP level up to 4 hours after exposure. Thus it appears that the UVR-induced melanogenesis is mediated by cAMP-independent mechanisms.
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PMID:Ultraviolet radiation directly induces pigment production by cultured human melanocytes. 282 34

The presence of alpha-MSH receptors on human melanoma has so far been suggested in the literature but not proved. We describe a reproducible and specific binding assay of alpha-MSH on human melanoma cells, using a high-specific-activity 125I-labelled hormone (1.5 to 2 mCi/micrograms) with consistent receptor binding (usually exceeding 2 pg/10(6) cells) and stable for 3 weeks. Asynchronized cells in suspension were incubated for 15 min at 37 degrees C with the tracer and various concentrations of unlabelled hormones. Synthetic alpha-MSH was compared to beta-MSH, ACTH1-24, ACTH4-10, beta-LPH, CLIP, CRF, MIF I, A8VP and beta-endorphin. Out of a panel of 8 human melanoma cell lines, 3 showed specific and reproducible alpha-MSH binding curves. No significant binding to human fibroblast and human carcinoma cells was seen. alpha-MSH, beta-MSH and, to a lesser extent ACTH4-10 (a part of the alpha-MSH sequence) were the only peptides able to displace labelled alpha-MSH from its binding sites, indicating the high specificity of the MSH receptor. Affinity constants (Ka) ranged from 10(8) to 10(9) l/mole and the estimated receptor number was 1,000 to 2,000 per cell. We conclude that some human melanoma cell lines expressed specific MSH receptors with stable affinity but which are low in number.
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PMID:Evidence for alpha-melanocyte-stimulating hormone (alpha-MSH) receptors on human malignant melanoma cells. 282 46

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 structure-activity relationships in vitro of alpha-MSH (alpha-melanocyte-stimulating hormone, alpha-melanotropin) analogs as determined on normal and transformed (melanoma cell) melanocyte bioassays are summarized. Specifically, the characterization of potent and metabolically stable melanotropic agonist analogs and a newly discovered antagonist of alpha-MSH are highlighted. Comparison of these data versus the known structure-activity relationships of alpha-MSH related to CNS bioactivities suggests the existence of nonclassical alpha-MSH receptor-mediated pathways or, perhaps, a yet undefined endogenous neuropeptidergic pathway(s) having different selectivities for alpha-MSH analogs. In summary, several of the alpha-MSH analogs reported here may be useful molecular probes in future strategies aimed at the identification and systematic characterization of both peripheral and central alpha-MSH receptors.
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PMID:Alpha-melanocyte-stimulating hormone structure-activity studies: comparative analysis of melanotropic and CNS bioactivities. 285 Jun 30


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