Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.10.3.1 (tyrosinase)
 9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

In skin of the C57BL/6 mouse, the production of mRNA transcripts that hybridized to the coding region of the MC1 receptor (MC1-R) gene was undetectable in telogen, increased during hair growth, and, after reaching the highest values in anagen VI, decreased during the anagen-catagen transition phase. This production was associated with anagen-dependent expression of the tyrosinase gene and enzyme activity. In contrast, the production of 4.5- and 2.0-kb mRNAs hybridizable to the coding region of the MC2 receptor (MC2-R) gene was similar throughout the entire hair cycle. Previously, dexamethasone was demonstrated to induce premature catagen development accompanied by an abrupt termination of melanogenesis. Here we demonstrate that topical application of dexamethasone during anagen VI decreased the concentration of POMC, MC1-R, and tyrosinase mRNA in the skin. The decrease in tyrosinase mRNA concentration was accompanied by a decrease in tyrosinase protein concentration and enzyme activity. These results support the hypothesis that murine hair growth and attendant melanogenesis can be regulated through coordinated changes in local expression of POMC, MC1-R, and tyrosinase genes.
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PMID:Production of POMC, CRH-R1, MC1, and MC2 receptor mRNA and expression of tyrosinase gene in relation to hair cycle and dexamethasone treatment in the C57BL/6 mouse skin. 900 28

We have previously reported that melatonin was an effective lightening agonist in the teleost Synbranchus marmoratus, the amphibians Rana pipiens and Bufo ictericus, and in the lizard Anolis carolinensis. The hormone, previously applied to the preparations, effectively inhibited alpha-MSH darkening activity in a dose-independent manner, and was also able to reverse MSH-induced darkening. We presently describe the inhibitory effect of the indoleamine on the murine melanoma cell proliferation. Interestingly, the hormone also stimulated tyrosinase activity, with a correlated increase in melanin content. We also demonstrate that in a diverse lizard species, Urosaurus ornatus, the indoleamine was totally ineffective. The competitive MSH antagonistic activity of H-His-D-Arg-Ala-Trp-D-Phe-Lys-NH2 has been demonstrated previously in R. pipiens and U. ornatus. Herein, its inhibitory activity is also reported in another lizard species, A. carolinensis. However, this MSH analogue was inactive in S. marmoratus, and in murine melanoma cells. On the other hand, the 7 thru 10 alpha-MSH fragment, Ac-Phe-Arg-Trp-Gly-NH2, although ineffective in S. marmoratus and R. pipiens, was an alpha-MSH antagonist in A. carolinensis. Surprisingly, in the melanoma cell line, the MSH fragment exhibited no agonist or antagonist activity, but dramatically potentiated the MSH-induced increase in tyrosinase activity. These data might suggest that the fragment is participating either in the process of facilitation or in positive cooperativity. The present results, taken together with our previously reported data, demonstrate a major interspecies diversity of the MC1 subtype of melanocortin receptor, and point out the relevance of the membrane microenvironment for the final receptor configuration.
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PMID:Comparative biological activities of alpha-MSH antagonists in vertebrate pigment cells. 907 3

Melanocytes synthesise two types of melanin: the brown-black eumelanin and the red-yellow phaeomelanin. In mice, the relative proportions of these two melanins are regulated by alpha-MSH, which preferentially increases the synthesis of eumelanin and by the Agouti protein (AP), the expression of which correlates with the growth of yellow phaeomelanin-containing hair. It has been proposed that AP acts by antagonizing the action of alpha-MSH at the MC1 receptor, although it has been suggested that it may also act independently of alpha-MSH. In the present study we show that AP inhibits melanogenesis in B16F1 melanoma cells in the presence and absence of alpha-MSH and also causes dose-related decreases in the synthesis of both eumelanin and phaeomelanin. In the presence of alpha-MSH AP had a greater effect on eumelanin production and this is consistent with an antagonistic action at the MC1 receptor. In the absence of alpha-MSH however, AP produced similar reductions in the synthesis of both melanins. These changes were not seen in B16G4F cells which lack the MC1 receptor, suggesting that even in the absence of alpha-MSH AP acts at the MC1 receptor. How this action is mediated at the intracellular level is not yet clear, although it appears to be associated with a decrease in tyrosinase activity.
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PMID:Agouti protein inhibits the production of eumelanin and phaeomelanin in the presence and absence of alpha-melanocyte stimulating hormone. 935 25

In B16 melanocytes, tyrosinase activity and melanin formation are upregulated by alpha-MSH and downregulated by TGF beta1 and TNF alpha. Since TGF beta1 or TNF alpha block the differentiation programs induced by throphic hormones in other cell types, we studied tyrosinase regulation by alpha-MSH in the presence of the hypopigmenting cytokines, as well as the effects of the cytokines on several aspects of alpha-MSH signaling. TGF beta1 and TNF alpha only slightly diminished MC1 receptor gene expression, and had no effect on the intracellular levels of cAMP, or on the alpha-MSH-dependent cAMP rise. The intracellular levels of tyrosinase mRNA, protein and enzymatic activities were also upregulated by alpha-MSH in cells pretreated with TGF beta1 or TNF alpha. Therefore the cytokines do not block the response to alpha-MSH. However, the cytokine-induced inhibition of tyrosinase gene expression, protein levels and the reduction of tyrosinase intracellular half-life also occurred in the presence of alpha-MSH, indicating that the hormone does not override TGF beta1 or TNF alpha inhibition. Thus, tyrosinase activity and the rate of melanin formation in B16 melanocytes might reflect simply the balance between alpha-MSH stimulation and TGF beta1 or TNF alpha inhibition, acting by independent mechanisms.
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PMID:Independent regulation of tyrosinase by the hypopigmenting cytokines TGF beta1 and TNF alpha and the melanogenic hormone alpha-MSH in B16 mouse melanocytes. 1064 3

Objective To observe the molecular mechanism of Bushen Quban Granule (BQG) for inhibiting the synthesis of intracellular melanin. Methods Twenty SPF grade female SD rats were di- vided into four groups by completely randomized method, i.e., the control group (fed with normal saline) , high, middle, and low dose BQG groups (administered with BQG at 4. 8, 2. 4, 1. 2 g/kg by gastrogavage, equivalent to 24, 12, and 6 times clinical doses, respectively, twice per day for 3 days in total) , 5 in each group. Drug containing serum was collected. Expressions of melanocortin 1 receptor (MC1 R) , mi- crophthalmia-associated transcription factor ( MITF) , tyrosinase ( TYP) , tyrosinase-related protein I (TYRP1) , and tyrosinase-related protein 2 (TYRP2) at the mRNA level were detected by RT-PCR. Ex- pressions of phosphorylated-extracellular regulated MAP kinasel/2 (p-ERK) , TYP, TYRP1 and TYRP2 at the protein level were detected by Western blot. Intracellular melanin contents were determined by NaOH dissolving method. Activities of tyrosinase were determined by Dopa pigment method, and the cell viability was detected by MTT. Results Compared with the control group, expressions of MC1R, MITF, TYP, TYRP1 and TYRP2 at the mRNA level were down-regulated (P <0. 05), and those of TYP, TYRP1 and TYRP2 at the protein level were also down-regulated (P <0. 05), intracellular contents of melanin and the activity of tyrosinase decreased (P <0. 05) , but the level of p-ERK and the proliferation of cells increased in each medicated group (P <0. 05). When ERK was inhibited by its inhibitor PD98059, there was no sta- tistical difference in expressions of MC1 R or MITF at the mRNA level among all medicated groups (P > 0. 05). Compared with the control group, mRNA expressions of TYP, TYRP1 and TYRP2 decreased in the high dose BQG group (P <0. 05), but with no significant difference in protein expressions of p-ERK, TYP, TYRP1 and TYRP2 (P >0. 05). There was no statistical difference in the content of melanin, the activity of TYP, or the proliferation of cells between the control group and the high dose BQG group (P >0. 05). Con- clusion BQG could inhibit the synthesis of intracellular melanin through up-regulating p-ERK to inhibit the expression of tyrosinase and its related proteins.
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PMID:[Mechanisms Involved in the Inhibition of Melanin Synthesis by Bushen Quban Granule]. 3064 34