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Query: UMLS:C0025202 (melanoma)
 69,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several properties of the MSH receptor in solid melanotic and amelanotic mouse M2R tumour isografts were studied in C57BL mice. Using cell membrane fractions prepared from such tumours and the superpotent [Nle4,D-Phe7]alpha MSH analogue, the affinity and receptor contents of the two tumour variants were found to be similar. When occupied by MSH, the receptor-MSH complex (R.MSH) was readily soluble in cholate. In the solubilized form, R.MSH was extremely stable and dissociated to an extent of only 30% within 12 days at 4 degrees C. While this high stability can be maintained in the pH range of 7.0-8.5, the solubilized R.MSH complex becomes increasingly unstable below pH 7.0 and totally dissociates at a pH < 6.0. In the membrane-bound form, the R.MSH complex shows a parallel pH stability profile which is shifted down by approximately two pH units. In addition to low pH, the R.MSH complex becomes unstable and totally dissociates in the presence of 10 mM EGTA, suggesting that the calcium-sensitive function of the receptor is still associated with the receptor in the detergent-soluble state. The R.MSH complexes in the soluble and membrane-bound forms are also totally resistant to proteolytic digestion by V8 protease, but were slowly digested by trypsin. Treatment of R.MSH with 1-ethyl-3-(3-dimethylamino-propyl)carbodiimide hydrochloride or bis (sulphosuccinimidyl) suberate led to covalent crosslinking of MSH to the receptor molecule. The electrophoretic mobility on SDS-PAGE of the 43/46 kD doublet of the receptor-MSH conjugate (R*MSH) was identical to the photoaffinity labelled MSH receptor product described earlier in cultured M2R cells. However, the efficiency of production of the crosslinked product was approximately 30%, much higher than that achieved previously by photoaffinity labelling. Using rabbit polyclonal anti-alpha MSH antibodies, the R*MSH conjugate was identifiable on Western immunoblots. These results provide a basis for further development of procedures for purification of the MSH receptor molecule and studying its protein structure.
Melanoma Res 1993 Jun
PMID:The melanocyte-stimulating hormone (MSH) receptor in M2R mouse melanoma tumours: solubilization and properties of the receptor-MSH complex and its covalently crosslinked conjugate. 840 Aug 53

The two mouse melanoma cell lines B16-F1 and B16-G4F retain their melanogenic capacity when cultured in vitro. Melanotropic peptides such as alpha-melanocyte-stimulating hormone (alpha-MSH) induce formation and release of melanin pigment in B16-F1 cells. In contrast, B16-G4F cells do not respond to alpha-MSH. Using receptor-binding analysis and photoaffinity crosslinking we demonstrate that the lack of response of B16-G4F cells to alpha-MSH is due to the absence of functional MSH receptors from the cell surface. Northern blot analysis of receptor mRNA revealed that MSH receptor mRNA is not expressed in B16-G4F cells. These cells represent a new tool for the study of signal pathways related to the control of melanogenesis in melanoma cells.
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PMID:B16-G4F mouse melanoma cells: an MSH receptor-deficient cell clone. 848 88

4 clonal sublines of Cloudman S91 melanoma cells, S91/mel, S91/I3, S91/6 and S91/amel, were evaluated for changes in growth, pigment content and plating efficiency during and after treatment with a cyclic-AMP phosphodiesterase inhibitor-melanin-stimulating agent, 3-isobutyl-1-methyl-xanthine (IBMX) plus beta-melanocyte stimulating hormone (beta-MSH) or IBMX alone. After combined treatment, increases in melanin content on day 3 were 48, 27, 11, and 2 pg/cell in the four cell lines respectively. In each case IBMX alone was less effective than IBMX plus beta-MSH. Doubling time increased and plating efficiency decreased with increased melanization. The increases in doubling time and decreases in plating efficiency were cell line dependent. The greatest rate of increase in doubling time and decrease in plating efficiency as a function of melanin content were seen in S91/amel, which produced the least pigment. The lowest rates of increase/decrease were seen in S91/mel, which produced the most pigment. Melanin pigment induced in the cells was classified as eumelanin by EPR determination. The differential response to induction of pigmentation makes these cell lines suitable models for comparative studies on the role of melanin in pigment cell biology.
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PMID:Growth and pigmentation in genetically related Cloudman S91 melanoma cell lines treated with 3-isobutyl-1-methyl-xanthine and beta-melanocyte-stimulating hormone. 853 13

Two compounds have been synthesized based on [Nle4,D-Phe7]alpha-melanocyte stimulating hormone (NDP-MSH) in which either one or two peptide sequences were covalently linked through their N'-termini to a single molecule of diethylenetriamine pentaacetic acid (DTPA). These two compounds (monoNDP-MSH-DTPA and bisNDP-MSH-DTPA, respectively) bound indium-111 (111In) stably and showed hormonal activity as great or greater than alpha-melanocyte stimulating hormone (alpha-MSH). Both compounds were able to target 111In to Cloudman S91 melanomas in DBA2 mice. MonoNDP-MSH-DTPA gave the highest tumour:blood and tumour:tissue ratios and showed least unspecific radioactivity in the liver and kidney. Radioscintigraphy of mice showed good tumour localization of 111In with both compounds, clear images being obtainable within 2 h of injection. Scans with monoNDP-MSH-DTPA showed some kidney and thyroid but no liver radioactivity, whereas bisNDP-MSH-DTPA gave extensive abdominal radioactivity, most of which was associated with the liver and kidneys. MonoNDP-MSH-DTPA was cleared from the tumour much less rapidly and gave more favourable tumour:blood ratios than other alpha-MSH derivatives previously investigated. It is concluded that monoNDP-MSH-DTPA offers promise as a melanoma imaging agent in man.
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PMID:An improved imaging agent for malignant melanoma, based on [Nle4,D-Phe7]alpha-melanocyte stimulating hormone. 857 Jan 17

We have explored the role of protein kinase C (PKC) in pigmentation induced by alpha-melanocyte stimulating hormone (alpha-MSH). Using the well-studied S91 Cloudman mouse melanoma model system in which 10(-7) M alpha-MSH is known to produce a time-dependent increase in pigmentation, we found an increase in the activity of tyrosinase, the key enzyme in pigmentation, between Days 2 and 6 accompanied by an increase in mRNA and protein levels of tyrosinase, as well as an increase in the level of specifically the beta isoform of PKC. When S91 cells were treated with phorbol dibutyrate, 95% of PKC activity was lost within 48 h and the alpha-MSH-induced melanogenesis was completely blocked, as was the induction of tyrosinase mRNA and protein. Serially passaged S91 cells no longer capable of responding to alpha-MSH had an undetectable level of PKC-beta, although the tyrosinase protein level was identical to that of alpha-MSH-responsive cells. Furthermore, in these S91 cells alpha-MSH also did not increase the level of tyrosinase mRNA. Thus, induction of murine melanogenesis by alpha-MSH involves up-regulation of tyrosinase mRNA and protein mediated in part by the PKC-dependent pathway, associated with an up-regulation of the beta isoform previously demonstrated to specifically activate tyrosinase in human melanocytes.
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PMID:Alpha-melanocyte stimulating hormone-induced pigmentation is blocked by depletion of protein kinase C. 880 53

The human melanocortin-1 (MC1) receptor was stably expressed in the amelanotic mouse melanoma cell clone B16-G4F which does not express its own (mouse) MC1 receptor and hence is unresponsive to alpha melanocyte stimulating hormone (alpha MSH). From several stable transfectant cell lines expressing the human MC1 receptor in relatively high numbers, three melanin producing clones (G4F-12, 14, and 15) and one amelanotic clone (G4F-7) were further analyzed in competition binding experiments and in cAMP and melanin assays. The dissociation constants (KD) for [Nle4, D-Phe7]-alpha MSH in all four clones ranged from 0.187 to 0.705 nmol/l, thus corresponding to the KD observed with the different human melanoma cell lines so far studied. Intracellular cAMP content was 3- to 5-fold higher than that of control cells, and alpha MSH induced an additional 1.5- to 1.7-fold increase. G4F-15 cells secreted melanin into the medium whereas the other clones did not secrete melanin. The extent of melanin secretion was similar to that of fully alpha MSH-stimulated B16-F1 mouse melanoma cells but the onset of secretion was delayed. alpha MSH induced an additional dose-related increase (up to 1.3-fold) in melanin production which could be suppressed by the addition of specific alpha MSH antibodies without altering the constitutive part of melanogenesis. Human and mouse agouti proteins, which inhibit basal and alpha MSH-induced melanogenesis in B16-F1 cells, both reduced alpha MSH-induced melanin production in G4F-15 cells but did not affect the constitutive melanogenesis. These results indicate that human MC1 receptor expressed in mouse B16-G4F cells induces constitutive activation of the signalling pathway controlling melanogenesis, most likely by tightly coupling to Gs alpha, in a similar manner to that reported for constitutively active receptor mutants in other systems.
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PMID:Induction of constitutive melanogenesis in amelanotic mouse melanoma cells by transfection of the human melanocortin-1 receptor gene. 885 98

Tyrosinase may protect against oxidative stress by using the superoxide anion (O2-1.) in the production of melanin. We have examined this by comparing its cytotoxic effects in B16/F10 and B16/F10-differential deficient (-DD) mouse melanoma cells that express high and low levels of tyrosinase activity respectively. Xanthine oxidase (XO) was used to generate O2.1 and cytotoxicity assessed by measuring cell survival. XO increased O2.- concentrations and 3 h later dose related decreases in cell survival were seen. F10 cells were more resistant to these cytotoxic effects than the F10-DD cells. [Nle4, DPhe7]MSH increased tyrosinase activity and melanin content, reduced O2.- concentration and increased the resistance of F10 cells to the cytotoxic effects of O2.-. No such effects were seen in F10-DD cells. The effect of [Nle4, DPhe7]MSH on the resistance of the F10 cells was time-dependent and noticeable when tyrosinase activity but not melanin was increased. This suggests that it was the activation of tyrosinase rather than the increase in the melanin that provided the protection against O2.-. In support of this, inhibition of tyrosinase with phenylthiocarbamide reduced the increased resistance induced by [Nle4, DPhe7]MSH. Moreover, although melanin was capable of scavenging O2.- it had little effect at concentrations comparable to those in the activated F10 cells. XO also increased the melanin content of F10 but not F10-DD cells. We conclude that tyrosinase is able to utilise O2.- to produce melanin and this provides pigment cells with a unique anti-oxidant mechanism.
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PMID:Activation of tyrosinase reduces the cytotoxic effects of the superoxide anion in B16 mouse melanoma cells. 885 70

Stable expression of the MSH receptor in a homologous system is important for the study of the function and mechanism of signalling of this receptor. This is the first report on the stable expression of the human alpha-MSH receptor in the mouse melanoma G4F clone which lacks an endogenous MSH receptor. Several stable transfectant cell lines were obtained all of which express the human MSH receptor in high numbers. Human MSH receptor mRNA expression was detected by Northern blot analysis. Competition binding experiments showed that the MSH receptors expressed in these cells have the same affinity for [Nle4,D-Phe7]-alpha-MSH as the MSH receptors of the human HBL melanoma cell line. Several of the transfectant cell lines produced melanin constitutively, some of them secreting melanin into the medium whereas other clones did not secrete melanin. MSH and cholera toxin did not or only marginally increase melanogenesis in these clones, and forskolin had an opposite effect. These results suggest that the human MSH receptor may be constitutively active in these transfected mouse melanoma cells.
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PMID:Stable expression of the human MSH receptor in a mouse melanoma cell line. 890 30

MSH receptors and their binding characteristics of [125I]-labelled derivatives of alpha-MSH have been studied extensively on various mouse and human melanoma cell lines in culture. The aim of this study was to determine the binding characteristics of alpha-MSH radioligands to MSH receptors occurring in experimental mouse and human melanoma tumours as well as in human melanoma biopsies. For this reason, solid tumours were grown on experimental animals by inoculation of murine B16-F1 and human D10 and HBL melanoma cells. After excision and cryosectioning of the tumours, frozen tissue sections were incubated with [(125I)Tyr2]-alpha-MSH or [(125I)Tyr2,Nle4,D-Phe7]-alpha-MSH and specific alpha-MSH binding sites were visualized by subsequent autoradiography. The presence of increasing concentrations of unlabelled alpha-MSH during incubation with tracer led to a dose-dependent displacement of the radioligand. Quantitative analysis of the autoradiograms produced dissociation constants which were comparable with those obtained with cell binding assays: KD = 1.87 and 1.31 nmol/l for B16 tumours and cells, respectively; 0.32 and 0.33 nmol/l for D10, and 2.24 and 1.36 nmol/l for HBL tumours and cells, respectively. This indicates similar binding properties of alpha-MSH radioligands to both cultured melanoma cells and tissue sections of melanoma tumours from experimental animals. Similar binding characteristics were also observed with human melanoma tissue sections originating from biopsies of melanoma patients.
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PMID:alpha-MSH receptor autoradiography on mouse and human melanoma tissue sections and biopsies. 890 55

Cyclic alpha-melanocyte-stimulating hormone (alpha-MSH) analogues produced by disulphide bridging (e.g. [Cys4,Cys10] alpha-MSH) are known to be almost equipotent to the native hormone in amphibian skin bioassays and as a consequence have been proposed as a paradigm for the active conformation of native MSH at the pigment cell MC1 receptor. However this proposal has been somewhat speculative as there is no published data comparing biological activity of cyclic MSH analogues with data on receptor binding. This study addresses this problem by comparing tyrosinase stimulatory activity with their receptor binding affinity in B16 murine melanoma cells expressing the native MC1 melanocortin receptor. Cyclic [Cys4,Cys10] alpha-MSH showed almost the same affinity for the MC1 receptor as alpha-MSH, but the linear analogue [Cys4,Cys10] alpha-MSH bound less strongly. Both had biological activities similar to that of the natural ligand. Introduction of D-Phe into the ring in position 7 increased both affinity and activity of the cyclic compound. The study suggests that the intrinsic efficacy of cyclic [Cys4,Cys10] alpha-MSH analogues is similar to native alpha-MSH. Our studies support the proposal that the cyclic structure serves as a good model for the active conformation of linear alpha-MSH.
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PMID:Receptor binding affinities and biological activities of linear and cyclic melanocortins in B16 murine melanoma cells expressing the native MC1 receptor. 893 71


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