Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.10.3.1 (tyrosinase)
9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have cloned and sequenced the human genomic DNA segments encoding the 5'-flanking region and the first two exons of the DOPAchrome tautomerase (DT)/tyrosinase-related protein 2 (TRP-2) gene. The DT gene is a member of the tyrosinase gene family and specifically expressed in melanin-producing cells. A transcriptional initiation site of the DT gene was identified by S1 nuclease-mapping and primer-extension analyses using RNA prepared from human pigmented melanoma cells. To study the mechanism for pigment cell-specific expression of the human DT gene, we analyzed the promoter function of its 5'-flanking region by transient expression assays. The fusion genes, containing the DT gene promoter upstream from a firefly luciferase reporter gene, were introduced into human pigmented melanoma cells and HeLa cells, and the pigment cell-specific promoter activity was evaluated by comparing the luciferase activity expressed in both cell lines. A series of 5' deletion studies of the human DT gene promoter revealed that the 32-bp element, located between -447 and -415, is sufficient to confer pigment cell-specific expression of a reporter gene on a homologous promoter, but not on a heterologous simian virus 40 promoter. Internal deletion studies using a homologous or a heterologous promoter revealed that the pigment cell-specific expression of a reporter gene mediated by the 32-bp element is dependent on the presence of another region of the DT gene spanning from -268 to -56, which was termed the proximal region. However, the proximal region by itself is not sufficient to confer cell type-specific expression. These results indicate that the presence of two regulatory regions, the 32-bp element and the proximal region, is required for pigment cell-specific expression of the DT gene. Both regulatory regions contain a CANNTG motif, a well known binding site for a large family of transcription factors possessing a basic helix-loop-helix structure.
...
PMID:Cloning of the human DOPAchrome tautomerase/tyrosinase-related protein 2 gene and identification of two regulatory regions required for its pigment cell-specific expression. 792 51

Tyrosinase, the key enzyme in melanin synthesis, is expressed specifically in pigment-producing cells. Studies with transgenic mice and gene transfer experiments have demonstrated that the 270-base pair 5'-flanking sequence of the mouse tyrosinase gene leads to weak but cell type-specific and developmentally regulated expression. To elucidate the underlying transcriptional control, we focused on the identification of cis-acting elements within this 270-base pair minimal promoter. We also addressed the potential role of promoter elements in the control of cAMP regulation of the tyrosinase gene. Deletion and linker scanning mutagenesis revealed that promoter activity is modulated by two positive elements and one negative element. One of the positive elements includes the M-box, a sequence motif shared with the promoter of two other melanocyte-specific genes, trp-1 and trp-2. Cotransfection experiments provide evidence that a basic helix-loop-helix-zipper protein, encoded at the microphthalmia gene locus, transactivates the tyrosinase promoter, probably by binding to the M-box. Activating cis elements are bound by nuclear factors in vitro and confer increased expression to a reporter gene both in melanoma cells and in fibroblasts. We therefore suggest that the positive promoter elements modulate tyrosinase expression rather than determine cell specificity in vivo, whereas the negative element acts cell type specifically.
...
PMID:The mouse tyrosinase gene. Promoter modulation by positive and negative regulatory elements. 796 73

The tyrosinase gene is expressed specifically in melanocytes and the cells of the retinal pigment epithelium, which together are responsible for skin, hair, and eye color. By using a combination of DNase I footprinting and band shift assays coupled with mutagenesis of specific DNA elements, we examined the requirements for melanocyte-specific expression of the human tyrosinase promoter. We found that as little as 115 bp of the upstream sequence was sufficient to direct tissue-specific expression. This 115-bp stretch contains three positive elements: the M box, a conserved element found in other melanocyte-specific promoters; an Sp1 site; and a highly evolutionarily conserved element located between -14 and +1 comprising an E-box motif and an overlapping octamer element. In addition, two further elements, one positive and one negative, are located between positions -185 and -150 and positions -150 and -115, respectively. We also found that the basic helix-loop-helix factor encoded by the microphthalmia gene, which is essential for melanocyte differentiation, can transactivate the tyrosinase promoter via the M box and the conserved E box located close to the initiator. Since in vitro assays failed to identify any melanocyte-specific DNA-binding activity, the possibility that the specific arrangement of elements within the basal tyrosinase promoter determines melanocyte-specific expression is discussed.
...
PMID:Melanocyte-specific expression of the human tyrosinase promoter: activation by the microphthalmia gene product and role of the initiator. 796 39

Tyrosinase is a rate-limiting enzyme in melanin biosynthesis and is specifically expressed in differentiated melanocytes. We have identified the enhancer element in the 5'-flanking region of the human tyrosinase gene that is responsible for its pigment cell-specific transcription and have termed it tyrosinase distal element (TDE) (positions -1861 to -1842). Transient expression assays showed that TDE confers efficient expression of a firefly luciferase reporter gene linked to the tyrosinase gene promoter in MeWo pigmented melanoma cells but not in HeLa cells, which do not express tyrosinase. TDE was specifically bound by nuclear proteins of MeWo and HeLa cells, the binding properties of which were indistinguishable in gel mobility shift assays. TDE contains the CATGTG motif in its center, and mutation analysis indicates that the CA dinucleotides of this motif are crucial for protein binding and pigment cell-specific enhancer function. The CATGTG motif is consistent with the consensus sequence recognized by a large family of transcription factors with a basic helix-loop-helix structure, which prompted us to examine the possible involvement of a ubiquitous transcription factor, USF, and a novel factor, microphthalmia-associated transcription factor (MITF), recently cloned as the human homolog of the mouse microphthalmia (mi) gene product. The mi phenotype is associated with a mutant mi locus and characterized by small eyes and loss of melanin pigments. Both USF and MITF are predicted to contain a basic helix-loop-helix structure and a leucine zipper structure. We provide evidence that USF binds to TDE, whereas we were unable to detect the DNA-binding activity of MITF. Transient coexpression assays showed that MITF specifically transactivates the promoter activity of the tyrosinase gene through the CATGTG motif of TDE but not the promoter of the ubiquitously expressed heme oxygenase gene, while USF is able to activate both promoters. These results indicate that MITF is a cell-type-specific factor that is capable of activating transcription of the tyrosinase gene.
...
PMID:Microphthalmia-associated transcription factor as a regulator for melanocyte-specific transcription of the human tyrosinase gene. 786 73

In the DNA binding domain of microphthalmia-associated transcription factor (MITF), four mutations are reported: mi, Mi wh, mi ew, and mi or. MITFs encoded by the mi, Mi wh, mi ew, and Mi or mutant alleles (mi-MITF, Mi wh-MITF, Mi ew-MITF, and Mi or-MITF, respectively) interfered with the DNA binding of wild-type MITF, TFE3, and another basic helix-loop-helix leucine zipper protein in vitro. Polyclonal antibody against MITF was produced and used for investigating the subcellular localization of mutant MITFs. Immunocytochemistry and immunoblotting revealed that more than 99% of wild-type MITF and Mi wh-MITF located in nuclei of transfected NIH 3T3 and 293T cells. In contrast, mi-MITF predominantly located in the cytoplasm of cells transfected with the corresponding plasmid. When the immunoglobulin G (IgG)-conjugated peptides representing a part of the DNA binding domain containing mi and Mi wh mutations were microinjected into the cytoplasm of NRK49F cells, wild-type peptide and Mi wh-type peptide-IgG conjugate localized in nuclei but mi-type peptide-IgG conjugate was detectable only in the cytoplasm. It was also demonstrated that the nuclear translocation potential of Mi or-MITF was normal but that Mi ew-MITF was impaired as well as mi-MITF. In cotransfection assay, a strong dominant negative effect of Mi wh-MITF against wild-type MITF-dependent transactivation system on tyrosinase promoter was observed, but mi-MITF had a small effect. However, by the conjugation of simian virus 40 large-T-antigen-derived nuclear localization signal to mi-MITF, the dominant negative effect was enhanced. Furthermore, we demonstrated that the interaction between wild-type MITF and mi-MITF occurred in the cytoplasm and that mi-MITF had an inhibitory effect on nuclear localization potential of wild-type MITF.
...
PMID:The recessive phenotype displayed by a dominant negative microphthalmia-associated transcription factor mutant is a result of impaired nucleation potential. 862 64

Mi protein encoded at the mouse microphthalmia (mi) locus is a transcription factor with a basic helix-loop-helix/leucine zipper structure. To assess the function of the human homolog of Mi protein, termed microphthalmia-associated transcription factor (MITF), we analyzed the effects of MITF on the promoter function of the mouse tyrosinase and tyrosinase-related protein 1 (TRP-1) genes. These two gene promoters are able to direct transcription preferentially in melanin-producing cells, and an enhancer element M box of 11 bp, containing a CATGTG motif, is conserved in both promoters. By transient expression assays, we have localized the cis-acting element of the tyrosinase gene responsible for pigment cell-specific expression to the proximal 82-bp region, which contains a CATGTG motif (positions -12 to -7) but lacks the M box (positions -107 to -97). We also provide evidence that the 82-bp region and the M box are involved in the transactivation of the tyrosinase promoter by MITF and that the M box is bound by MITF in vitro. Furthermore, MITF activated the TRP-1 gene promoter possibly through the M box (positions -44 to -34). These results suggest that MITF is a common factor regulating transcription of the pigment cell-specific genes.
...
PMID:Transcriptional activation of the melanocyte-specific genes by the human homolog of the mouse Microphthalmia protein. 874 2

TFEC is a transcriptional repressor originally identified in rat chondrosarcoma and contains a basic helix-loop-helix and leucine zipper (bHLH/LZ) structure. TFEC shares a closely related bHLH/LZ structure with microphthalmia-associated transcription factor (MITF) and TFE3. In the course of cDNA cloning for a factor structurally related to MITF which is also a regulator for cell differentiation, we have isolated cDNA clones from a THP-1 human monocytic leukemia cell line. These cDNAs encode a protein of 347 amino acids, termed TFECL, a human homolog of a putative rat TFEC isoform. TFECL contains an acidic domain that corresponds to a transcriptional activation domain of TFE3 but its equivalent region is deleted in rat TFEC. We explored a function of TFECL using a melanocyte-specific tyrosinase gene and a ubiquitously expressed heme oxygenase-1 gene, each promoter containing the cis-acting CANNTG motifs. By transient coexpression assays, we showed that TFECL is able to activate or inhibit transcription of a reporter gene linked to either the tyrosinase or the heme oxygenase-1 gene promoter, depending on cell types. These results suggest that TFECL may function as a transcriptional activator under certain conditions.
...
PMID:Molecular cloning of cDNA encoding a human TFEC isoform, a newly identified transcriptional regulator. 925 61

The rate-limiting step in melanogenesis is catalyzed by tyrosinase, a multifunctional enzyme encoded by the albino locus. We have previously reported that depletion of protein kinase C by long-term treatment of B16 mouse melanoma cells with phorbol dibutyrate (PDBu) prevented cell density-dependent melanogenesis. This was accompanied by a lack of induction of tyrosinase protein and mRNA. We report here the effect of PDBu on the functional activity of the mouse tyrosinase promoter by reporter gene assay and its effect on the binding of nuclear proteins from B16 cells to the "M-box" region of the mouse tyrosinase promoter. Short-term PDBu treatment of B16 cells transfected with a mouse tyrosinase promoter-luciferase construct resulted in increased reporter gene activity, while long-term PDBu treatment inhibited reporter gene activity. Using an oligonucleotide containing the M-box and its flanking residues in electrophoretic mobility shift assays, we found a density-dependent change in the pattern of DNA-protein complexes. One complex was found to be negatively regulated by long-term PDBu treatment. Competition experiments with various mutated oligonucleotides demonstrated that both the M-box and flanking residues are important for nuclear protein binding. The complex whose formation was inhibited by long-term PDBu treatment was shown to contain the basic helix-loop-helix leucine zipper protein microphthalmia-associated transcription factor (MITF). These results suggest that chronic PDBu treatment might inhibit tyrosinase expression (and subsequent melanogenesis) by affecting the amount or function of MITF.
...
PMID:Characterization of density-dependent regulation of the tyrosinase gene promoter: role of protein kinase C. 941 70

Mitf encodes a basic helix-loop-helix-leucine-zipper (bHLHzip) protein that is known to function in the development of melanocytes, pigmented epithelial cells (PECs), osteoclasts, and mast cells. In this paper, we report on the isolation, expression, and overexpression of the chicken Mitf and discuss the role of its protein product in the differentiation and transdifferentiation of PECs. Northern blotting showed that chicken Mitf is predominantly expressed in embryonic retinal pigmented epithelium (PE), but is expressed at low levels in other tissues. A 5' RACE analysis revealed differences in the 5' region Mitf nRNA in PE and other tissues. Immunological analysis revealed that Mitf, the protein encoded by Mitf, is first detected in the nuclei of the optic vesicle cells at embryonic stage 13 in a restricted region covered with mesenchymal cells. From stage 14 to 24, the specific staining is observable in the PE and precursor of the PE, the outer layer of the optic cup. In embryos at stages later than stage 29 the signals for Mitf in the future iris, ciliary body, and posterior retinal regions become faint. These results show that expression of Mitf starts at the optic vesicle stage at which no other marker genes for PECs such as mmp115 and tyrosinase are expressed. Dedifferentiation of cultured retinal PECs (rPECs) was induced by phenylthiourea and testicular hyaluronidase, bFGF, or TGF-beta. Mitf expression was inhibited by these factors and reactivated during redifferentiation of the dedifferentiated cells into rPECs, showing the correlation between Mitf expression and rPEC differentiation. Retrovirus-mediated overexpression of Mtif inhibited bFGF-induced dedifferentiation and transdifferentiation of rPECs to both lens and neural cells. These findings showed that downregulation of Mitf expression is essential for the transdifferentiation of rPEC. Mitf overexpression caused hyperpigmentation in cultured rPECs and suppressed the changes in gene expression induced by bFGF. Mitf overexpression promoted expression of mmp115 and tyrosinase in bFGF-treated rPECs suggesting a critical role for Mitf in rPEC differentiation. Mitf overexpression, however, did not promote expression of another rPEC-specific gene, pP344, in bFGF-treated rPECs. This result suggests the presence of other regulatory genes promoting rPEC differentiation. The expression patterns of pax6 and Mitf are complementary both in vivo in vitro. Overexpression of Mitf inhibited expression of pax6 in cultured rPECs. These observations suggest that Mitf regulates pax6 expression negatively.
...
PMID:Role of Mitf in differentiation and transdifferentiation of chicken pigmented epithelial cell. 946 87

The development of melanocytes, which are pigment-producing cells responsible for skin, hair, and eye color, is absolutely dependent on the action of the microphthalmia basic helix-loop-helix-leucine zipper (bHLH-LZ) transcription factor (Mi); mice lacking a functional Mi protein are entirely devoid of pigment cells. Mi has been shown to activate transcription of the tyrosinase, TRP-1, TRP-2, and QNR-71 genes through specific E-box elements, most notably the highly conserved M box. We investigated the mechanism which enables Mi to be recruited specifically to a restricted subset of E boxes in target promoters while being prevented from binding E-box elements in other promoters. We show both in vitro and in vivo that the presence of a T residue flanking a CATGTG E box is an essential determinant of the ability of Mi to bind DNA, and we successfully predict that the CATGTG E box from the P gene would not bind Mi. In contrast, no specific requirement for the sequences flanking a CACGTG E box was observed, and no binding to an atypical E box in the c-Kit promoter was detected. The relevance of these observations to the control of melanocyte-specific gene expression was highlighted by the fact that the E-box elements located in the tyrosinase, TRP-1, TRP-2, and QNR-71 promoters without exception possess a 5' flanking T residue which is entirely conserved between species as diverse as man and turtle. The ability of Mi to discriminate between different E-box motifs provides a mechanism to restrict the repertoire of genes which are likely to be regulated by Mi and provides insight into the ability of bHLH-LZ transcription factors to achieve the specificity required for the precise coordination of transcription during development.
...
PMID:Targeting the microphthalmia basic helix-loop-helix-leucine zipper transcription factor to a subset of E-box elements in vitro and in vivo. 981 81


1 2 Next >>

---