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)

Melanogenesis is a cascade of events significantly controlled by regulatory genes which are associated with the melanosomal membrane. This report introduces our current research efforts dealing with (a) the gene and protein expressions of tyrosinase and Lamp (lysosome-associated membrane protein) families by human melanoma cells after repeated exposures to UV light, (b) the coordinated alterations in the expression of the Lamp family gene and its encoding product after transfection of two genes of the tyrosinase family in human melanoma cells and (c) cloning and sequencing of a Ca(2+)-binding phosphoprotein, calnexin, which could be a candidate as a chaperone for sorting and maturation of tyrosinase and Lamp family glycoproteins in melanogenesis cascade. Our UV exposure study, as well as gene transfection and antisense hybridization experiments, has clearly indicated a marked and coordinated interaction of the Lamp-1 gene with the tyrosinase and TRP-1 genes in this process. We propose that melanogenesis is controlled at least by two major gene family products, i.e., (a) the tyrosinase family of tyrosinase, TRP-1 and TRP-2, and the Lamp family of Lamp-1, Lamp-2 and Lamp-3. These two gene families probably derived from primordial melanogenesis-associated genes which are common or closely related to each other.
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PMID:Molecular control of melanogenesis in malignant melanoma: functional assessment of tyrosinase and lamp gene families by UV exposure and gene co-transfection, and cloning of a cDNA encoding calnexin, a possible melanogenesis "chaperone". 753 26

Monoclonal antibodies against melanosomal components (human melanosome specific antigens; HMSAs) have been developed in our laboratory. HMSA-1-4 recognizes structural matrix proteins of melanosomes. HMSA-5 is identical to TRP-1, equivalent to the b (brown) locus of murine melanocytes and expressed in early stages of melanosomal maturation. HMSA-6 is a protein associated with melanosomes but its role is still unclarified, and HMSA-7 is identical to the lysosomal protein CD63. We have also recently identified p90 calnexin-like, Ca(2+)-binding protein p97 melanotransferrin, and p64 beta-D-galactosidase-like protein associated with melanosomes through immunological screening of our melanocytes (melanoma cells) cDNA library. Approximately 150 genes and 60 loci are known to influence eye, skin and hair colour in mammals. Tyrosinase is a rate-limiting enzyme responsible for melanin synthesis. In addition, tyrosine-related proteins (TRPs) and their genes have been identified and cloned. Tyrosinase and TRPS (e.g., TRP-1; b-locus protein identical to HMSA-5 and TRP-2; dopachrome tautomerase) are synthesized according to underlying genetic programmes, and are up- and/or down-regulated to create various forms of abnormal melanin pigmentation. We herein propose the importance of investigating the role of non-tyrosinase related proteins such as those which we have recently identified.
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PMID:Characterization of melanosome-associated proteins by establishment of monoclonal antibodies and immunoscreening of a melanoma cDNA library through an anti-melanosome antibody. 829 89

Oxygen free radical (OFR)-mediated oxidative stress in myocardial cells following ischemia could damage unit membrane and macromolecules such as nucleic acids (DNA). It is being reported that under this condition these cells produce antioxidants and heat shock proteins (HSP 70). It is implied that this family of proteins could function as a "molecular chaperone" in the cell and hence has to be transported to various target sites. This process is comparable to the induction of oxygen free radicals in melanocytes and its response, melanin production following UV light exposure stress. Lamp-1, trp-1 and tyrosinase are melanosomal-associated stress relief proteins which are involved in the production of melanin in the subcellular organelle, melanosomes. UV exposure studies as well as gene transfection studies and antisense hybridization in human melanoma cells clearly indicated an increase and marked coordinated interaction of all these stress relief proteins in melanogenesis. These proteins are synthesized in the endoplasmic reticulum and have to undergo posttranslation modification, sorting and posting to their respective target sites. We simultaneously identified and characterized an ER resident protein, calnexin. It became the potential candidate for "chaperoning" these proteins following translation. Based on the computer analysis of HSP 70 cDNA, we postulate that similar to stress response proteins in melanogenesis, stress relief proteins in myocardial cells may also be modulated by the same ER resident protein, calnexin.
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PMID:Stress relief protein modulation by calnexin. 890 96

The loss of tyrosinase, the key enzyme in melanin synthesis, has been implicated in the dedifferentiation of malignant melanocytes. The presence of tyrosinase transcripts and antigenic peptides in melanoma tumors prompted us to investigate whether the basis for the loss of the enzyme was proteolytic degradation. Toward this aim, we followed the kinetics of synthesis, degradation, processing, chaperone binding, inhibitor sensitivity, and subcellular localization of tyrosinase in normal and malignant melanocytes. We found that, in amelanotic melanoma cell lines, tyrosinase failed to reach the melanosome, the organelle for melanin synthesis, because it was retained in the endoplasmic reticulum (ER) and then degraded. Tyrosinase appeared mostly as a 70-kDa core-glycosylated, endoglycosidase H-sensitive, immature form bound to the ER chaperone calnexin and had a life-span of only 25% of normal. Maturation and transit from the ER to the Golgi compartment was facilitated by lowering the temperature of incubation to 31 degrees C. Several proteasome inhibitors caused the accumulation of an approximately 60-kDa tyrosinase doublet that was more prominent in malignant than in normal melanocytes and promoted, to various degrees, the maturation of tyrosinase in melanoma cells and the translocation of the enzyme to melanosomes. The appearance of ubiquitinated tyrosinase after treatment of normal melanocytes with N-acetyl-L-leucinyl-L-leucinal-L-norleucinal reinforced our notion that some tyrosinase is normally degraded by proteasomes. Proteolysis of tyrosinase by proteasomes is consistent with the production of antigenic tyrosinase peptides that are presented to the immune system by major histocompatibility complex class I molecules.
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PMID:Aberrant retention of tyrosinase in the endoplasmic reticulum mediates accelerated degradation of the enzyme and contributes to the dedifferentiated phenotype of amelanotic melanoma cells. 917 96

Tyrosinase-related protein (TRP)-1 is one of the most abundant melanosomal glycoproteins involved in melanogenesis. This report summarizes our recent research efforts related to the biological role and biosynthesis of TRP-1 and its transport from TGN (trans-Golgi network) to the stage I melanosome. Our UV irradiation and tyrosinase and TRP-1 cDNA co-transfection studies indicated that human TRP-1 is involved in not only melanogenesis but also prevention of melanocyte death, which may occur during biosynthesis of melanin pigment in the presence of tyrosinase. Furthermore, a coordinated gene interaction was indicated between tyrosinase and TRP-1, resulting in upregulation of mRNA and protein expression of LAMP (lysosome-associated membrane protein)-1 that would directly prevent the tyrosinase-mediated programmed cell death of melanocytes. Similar to tyrosinase, however, TRP-1 appears to require a molecular chaperone, calnexin, which we have cloned recently. Our cDNA transfection study of tyrosinase with calnexin showed clearly the necessity of calnexin in order to have efficient, functional activity of melanosomal glycoprotein, especially tyrosinase. Once glycosylation is completed, TRP-1 will be transported from TGN to the stage I melanosome. At this stage, TRP-1 will have its own target signal, in particular, tyrosine-rich leucine residues in cytoplasmic tail. Our TRP-1 cDNA transfection and immunoelectron microscopy study shows that TRP-1 will be transported through small vesicles, probably non-clathrin-coated type, to large vacuoles, identical to the MPR (mannose-6-phosphate receptor)-positive, late endosomes. In this transport process a low molecular weight G-protein, rab-7, was isolated from the purified melanosomal protein on 2D-PAGE and identified by subsequent sequencing and PCR amplification. Confocal microscopy with double immunostaining and immunoelectron microscopy confirmed the co-localization of rab-7 and TRP-1 in the melanosomes with early stages of maturation (I-HI). Furthermore, this process will also be regulated by phosphatidylinositol 3-kinase (PI-3 kinase).
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PMID:Biological role of tyrosinase related protein and its biosynthesis and transport from TGN to stage I melanosome, late endosome, through gene transfection study. 926 27

Melanin biosynthesis (melanogenesis) is a metabolic pathway exclusively expressed by melanocytes and melanoma cells, and is often altered and/or markedly elevated in the latter cells. The changes in melanogenesis may be responsible for some of the clinical and histopathological features unique to melanoma. Melanogenesis may also contribute to the malignant transformation of melanoma precursors (i.e., atypical moles [or dysplastic nevi]) to melanoma as seen in patients with the familial atypical multiple-mole-melanoma (FAMMM) syndrome. However, it does not appear to affect the multi-step growth phases of melanoma cells from radial to vertical and lastly metastatic growth phases. Within the melanosomal compartment, eu- and pheomelanin pigments are synthesized. Both tyrosinase and lysosome-associated membrane protein (LAMP) gene products play important roles in this process. A coordinated interaction between these two gene family products is required for melanogenesis to occur properly. p90 calnexin is a new melanosome-associated molecule that is presumed to function as a melanogenesis chaperone by controlling the assembly and folding of glycoprotein intermediates of tyrosinase and LAMP gene families.
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PMID:Induction of melanogenesis during the various melanoma growth phases and the role of tyrosinase, lysosome-associated membrane proteins, and p90 calnexin in the melanogenesis cascade. 962 16

To understand the process of expression of tyrosinase, a key enzyme of melanogenesis, we examined its maturation in the endoplasmic reticulum (ER) by using a heterogeneous expression system. When human tyrosinase cDNA was introduced into COS 7 cells, tyrosinase activity was minimally detected. Immunofluorescence study revealed that tyrosinase was immunolocalized in the nuclear rim, the reticular network, and the punctuated structures. Because a cytoplasmic tail of tyrosinase-gene family protein functions as a lysosomal targeting signal in non-melanocytic cells, and immature and/or misfolded molecules are selectively retained in the ER, the observed localization suggested the inefficient maturation in the COS 7 cells. We thus examined if supplementation of calnexin, a membrane-bound chaperone with affinity for oligosaccharide-processing intermediates containing monoglucose, could improve the process. As expected, the activity was enhanced approximately 2-fold by co-transfection of cDNA encoding calnexin. In contrast, co-transfection of the cytosolic tail-free calnexin, which inhibits calnexin function by allowing premature egress of its ligands from the ER, suppressed expression of this enhanced tyrosinase activity. When alpha-glucosidase activity, which is required for calnexin function, was inhibited by castanospermine (CST) treatment, expression of tyrosinase activity was completely abolished. To confirm the direct involvement of calnexin in tyrosinase maturation, the interaction of calnexin with tyrosinase was examined. Immunoprecipitation of calnexin from extracts of [35S]methionine labeled cells with anti-calnexin antibody revealed that the association is highest immediately after the pulse and that nascent tyrosinase is gradually dissociated upon chase. The association was completely inhibited when CST was included in the medium. Hence, we suggest that the proper folding of tyrosinase is largely dependent on its direct interaction with calnexin for the determined duration in the ER.
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PMID:Promotion of tyrosinase folding in COS 7 cells by calnexin. 988 Aug 1

Tyrosinase is the key enzyme of melanin biosynthesis. It is a multiply glycosylated metalloenzyme, which has a long maturation time making it an ideal in vivo model system to probe protein folding and metal loading events. The use of NB-DNJ, an alpha-glucosidase I and II inhibitor has allowed us to dissect these processes. Here we show that tyrosinase folds through several inactive intermediates, at least two of which are recognised by the ER chaperone, calnexin. If the association with calnexin is prevented, more rapid folding occurs, the resulting protein fails to bind copper and is inactive. If dissociation from calnexin is inhibited, folding is prevented; the protein does not go through the normal secretory pathway and is targeted for degradation. Thus, tyrosinase folds off calnexin, giving alpha-glucosidase II a critical role, but the association with calnexin is essential to promote the correct folding which enables it to acquire copper.
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PMID:Tyrosinase folding and copper loading in vivo: a crucial role for calnexin and alpha-glucosidase II. 1044 92

Tyrosinase is a copper-containing enzyme that regulates melanin biosynthesis in mammals. Mutations at a single N-glycosylation sequon of tyrosinase have been reported to be responsible for oculocutaneous albinism type IA in humans, characterized by inactive tyrosinase and the total absence of pigmentation. To probe the role that each N-glycosylation site plays in the synthesis of biologically active tyrosinase, we analyzed the calnexin mediated folding of tyrosinase N-glycosylation mutants. We have determined that four of the six potential N-glycosylation sites, including that associated with albinism, are occupied. Analysis of the folding pathway and activity of 15 tyrosinase mutants lacking one or more of the occupied N-glycosylation sites shows that glycans at any two N-glycosylation sites are sufficient to interact with calnexin and give partial activity, but a specific pair of sites (Asn(86) and Asn(371)) is required for full activity. The mutants with less than two N-glycosylation sites do not interact with calnexin and show a complete absence of enzyme activity. Copper analysis of selected mutants suggests that the observed partial activity is due to two populations with differential copper content. By correlating the degree of folding with the activity of tyrosinase, we propose a local folding mechanism for tyrosinase that can explain the mechanism of inactivation of tyrosinase N-glycosylation mutants found in certain pigmentation disorders.
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PMID:Mutations at critical N-glycosylation sites reduce tyrosinase activity by altering folding and quality control. 1071 40

The effect of glucosidase and mannosidase inhibitors on the ER-associated degradation of tyrosinase was assessed in transiently transfected COS-7 cells. We found that the glucosidase inhibitors castanospermine and deoxynojirimycin had very little effect on tyrosinase degradation, whereas the mannosidase inhibitors deoxymannojirimycin and kifunensine significantly delayed the rate of tyrosinase degradation as measured by pulse-chase analysis. In addition, we show that tyrosinase degradation is sensitive to the proteasome inhibitor lactacystin and that tyrosinase associates with endogenous calnexin in COS-7 cells. Our data support a model of tyrosinase degradation that involves mannose trimming, calnexin association, and the retrograde transport of tyrosinase from the ER to the cytosol for proteasomal degradation. The pathways of tyrosinase degradation have important ramifications with regard to the exact types of antigenic epitopes that are presented to the immune system.
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PMID:Oligosaccharide trimming plays a role in the endoplasmic reticulum-associated degradation of tyrosinase. 1077 75


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