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

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

Waardenburg syndrome type 2 (WS2) is a dominantly inherited disorder characterized by a pigmentation anomaly and hearing impairment due to lack of melanocyte. Previous work has linked a subset of families with WS2 (WS2A) to the MITF gene that encodes a transcription factor with a basic-helix-loop-helix-leucine zipper (bHLH-Zip) motif and that is involved in melanocyte differentiation. Several splice-site and missense mutations have been reported in individuals affected with WS2A. In this report, we have identified two novel point mutations in the MITF gene in affected individuals from two different families with WS2A. The two mutations (C760--> T and C895--> T) create stop codons in exons 7 and 8, respectively. Corresponding mutant alleles predict the truncated proteins lacking HLH-Zip or Zip structure. To understand how these mutations cause WS2 in heterozygotes, we generated mutant MITF cDNAs and used them for DNA-binding and luciferase reporter assays. The mutated MITF proteins lose the DNA-binding activity and fail to transactivate the promoter of tyrosinase, a melanocyte-specific enzyme. However, these mutated proteins do not appear to interfere with the activity of wild-type MITF protein in these assays, indicating that they do not show a dominant-negative effect. These findings suggest that the phenotypes of the two families with WS2A in the present study are caused by loss-of-function mutations in one of the two alleles of the MITF gene, resulting in haploinsufficiency of the MITF protein, the protein necessary for normal development of melanocytes.
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PMID:Analyses of loss-of-function mutations of the MITF gene suggest that haploinsufficiency is a cause of Waardenburg syndrome type 2A. 865 47

MITF (microphthalmia-associated transcription factor) encodes a transcription factor with a basic-helix-loop-helix-zipper (bHLH-Zip) motif. MITF mutations occur in patients with Waardenburg syndrome type 2, a disorder associated with melanocyte abnormalities. Here we show that ectopic expression of MITF converts NIH/3T3 fibroblasts into cells with characteristics of melanocytes. MITF transfectants formed foci of morphologically altered cells, which resemble those induced by oncogenes, but did not exhibit malignant phenotypes. Instead, they contained dendritic cells that express melanogenic marker proteins such as tyrosinase and tyrosinase-related protein 1. Most cloned cells of MITF transfectants exhibited dendritic morphology and expressed melanogenic markers, but such properties were not observed in cells transfected with closely related TFE3 cDNA. Our findings indicate that MITF is critically involved in melanocyte differentiation.
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PMID:Ectopic expression of MITF, a gene for Waardenburg syndrome type 2, converts fibroblasts to cells with melanocyte characteristics. 878 19

Waardenburg syndrome (WS) is a clinically and genetically heterogeneous disease accounting for >2% of the congenitally deaf population. It is characterized by deafness in association with pigmentary anomalies and various defects of neural crest-derived tissues. At least four types are recognized (WS1, WS2, WS3 and WS4) on the basis of clinical and genetic criteria. Two previously described families seemed to delineate a new subtype characterized by WS2 in conjunction with ocular albinism (OA). Since mutations in the MITF gene are responsible for some instances of WS2, we screened for mutations in one of the WS2-OA families and discovered a 1 bp deletion in exon 8 of MITF. OA previously has been associated with compound heterozygosity for a mutant TYR allele and the TYR(R402Q) allele, a functionally significant polymorphism that is associated with moderately reduced tyrosinase catalytic activity. In this family, all of the individuals with the OA phenotype are either homozygous or heterozygous for TYR(R402Q), and heterozyous for the 1 bp deletion in MITF This suggests that the WS2-OA phenotype may result from digenic interaction between a gene for a transcription factor (MITF) and a gene that it regulates (TYR).
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PMID:Apparent digenic inheritance of Waardenburg syndrome type 2 (WS2) and autosomal recessive ocular albinism (AROA). 915 38

Many specific gene products are sequentially made and utilized by the melanocyte as it emigrates from its embryonic origin, migrates into specific target sites, synthesizes melanin(s) within a specialized organelle, transfers pigment granules to neighboring cells, and responds to various exogenous cues. A mutation in many of the respective encoding genes can disrupt this process of melanogenesis and can result in hypopigmentary disorders. Following are examples highlighting this scenario. A subset of neural crest derived cells emigrate from the dorsal surface of the neural tube, become committed to the melanoblast lineage, and are targeted along the dorsal lateral pathway. The specific transcription factors PAX3 and MITF (microphthalmia transcription factor) appear to play a regulatory role in early embryonic development of the pigment system and in associated diseases (the Waardenburg syndromes). During the subsequent development and commitment of the melanoblast, concomitant expression of the receptors for fibroblasts growth factor (FGFR2), endothelin-B (EDNRB), and steel factor (cKIT) also appears essential for the continued survival of migrating melanoblasts. Lack or dysfunction of these receptors result in Apert syndrome, Hirschsprung syndrome and piebaldism, respectively. Once the melanocyte resides in its target tissue, a plethora of melanocyte specific enzymes and structural proteins are coordinately expressed to form the melanosome and to convert tyrosine to melanin within it. Mutations in the genes encoding these proteins results in a family of congenital hypopigmentary diseases called oculocutaneous albinism (OCA). The tyrosinase gene family of proteins (tyrosinase, TRP1, and TRP2) regulate the type of eumelanin synthesized and mutations affecting them result in OCA1, OCA3, and slaty (in the murine system), respectively. The P protein, with 12 transmembrane domains localized to the melanosome, has no assigned function as of yet but is responsible for OCA2 when dysfunctional. There are other genetically based syndromes, phenotypically resembling albinism, in which the synthesis of pigmented melanosomes, as well as specialized organelles of other cell types, is compromised. The Hermansky-Pudlak syndrome (HPS) and the Chediak-Higashi syndrome (CHS) are two such disorders. Eventually, the functional melanocyte must be maintained in the tissue throughout life. In some cases it is lost either normally or prematurely. White hair results in the absence of melanocytes repopulating the germinative hair follicle during subsequent anagen stages. Vitiligo, in contrast, results from the destruction and removal of the melanocyte in the epidermis and mucous membranes.
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PMID:Molecular basis of congenital hypopigmentary disorders in humans: a review. 917 Jan 58

MITF (microphthalmia-associated transcription factor) encodes a transcription factor with a basic-helix-loop-helix-leucine zipper (bHLH-Zip) motif. Ectopic expression of MITF is found to convert NIH/3T3 fibroblasts into cells with characteristics of melanocytes. MITF transfectants formed foci, which superficially resembled those induced by oncogenes, but did not exhibit malignant phenotypes. Instead, they contained dendritic cells that express melanogenic marker proteins such as tyrosinase and tyrosinase-related protein 1. Such properties were not observed in cells transfected with the closely related gene, TFE3. These findings indicated that MITF is involved in melanocyte differentiation. Two mutations (C760-->T and C895-->T) in MITF are found to be associated with individuals with Waardenburg syndrome type 2 (WS2). These mutations create stop codons in exon 7 and 8, respectively, and probably result in truncated proteins lacking HLH-Zip or Zip structure. To understand how these MITF mutations cause WS2 in heterozygotes, mutant MITF proteins were generated and used for DNA-binding and luciferase reporter assays. The mutated MITF proteins lose their DNA-binding activity and fail to transactivate the promoter of the tyrosinase gene. However, these mutated proteins do not appear to interfere with the activity of wild-type MITF protein in these assays, indicating that they do not show a dominant-negative effect. These findings suggest that the phenotypes of the two WS2 families are caused by loss-of-function mutations in one of the two MITF alleles, resulting in haploinsufficiency of the MITF protein, the transcription factor necessary for normal melanocyte differentiation.
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PMID:Evidence to suggest that expression of MITF induces melanocyte differentiation and haploinsufficiency of MITF causes Waardenburg syndrome type 2A. 917 Jan 59

Waardenburg syndrome (WS) is a hereditary disorder that causes hypopigmentation and hearing impairment. Depending on additional symptoms, WS is classified into four types: WS1, WS2, WS3 and WS4. Mutations in MITF (microphthalmia-associated transcription factor) and PAX3, encoding transcription factors, are responsible for WS2 and WS1/WS3, respectively. We have previously shown that MITF transactivates the gene for tyrosinase, a key enzyme for melanogenesis, and is critically involved in melanocyte differentiation. Absence of melanocytes affects pigmentation in the skin, hair and eyes, and hearing function in the cochlea. Therefore, hypopigmentation and hearing loss in WS2 are likely to be the results of an anomaly of melanocyte differentiation caused by MITF mutations. However, the molecular mechanism by which PAX3 mutations cause the auditory-pigmentary symptoms in WS1/WS3 remains to be explained. Here we show that PAX3, a transcription factor with a paired domain and a homeodomain, transactivates the MITF promoter. We further show that PAX3 proteins associated with WS1 in either the paired domain or the homeodomain fail to recognize and transactivate the MITF promoter. These results provide evidence that PAX3 directly regulates MITF and suggest that the failure of this regulation due to PAX3 mutations causes the auditory-pigmentary symptoms in at least some individuals with WS1.
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PMID:Epistatic relationship between Waardenburg syndrome genes MITF and PAX3. 950 May 54

Mutations at the mouse locus encoding microphthalmia-associated transcription factor (Mitf) affect the development of many cell types, including retinal pigment epithelium (RPE), melanocytes, mast cells, and osteoclasts. Here we have identified a novel Mitf isoform, Mitf-a, and its human homologue MITF-A by cDNA cloning. MITF-A consists of 520 amino acid residues and differs in the amino-terminus from authentic melanocyte-type MITF (MITF-M). MITF-A mRNA is widely expressed and represents a predominant MITF isoform in cultured RPE cells, whereas MITF-M mRNA is exclusively expressed in melanocytes and melanoma cells. In situ hybridization analysis suggested that Mitf-a mRNA is enriched in the prospective RPE of mouse embryo. Moreover, transient cotransfection assays suggested that MITF-A activated transcription of the tyrosinase and tyrosinase-related protein 1 genes. MITF-A/Mitf-a therefore may play an important role in melanogenesis in RPE.
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PMID:Identification of a novel isoform of microphthalmia-associated transcription factor that is enriched in retinal pigment epithelium. 964 58

Among more than 80 different loci related to mouse coat color, microphthalmia-associated transcription factor (Mitf) encoded at the mouse microphthalmia locus is one of the most exciting molecules that regulates the development and survival of many cell types, including melanocyte, retinal pigment epithelium (RPE), and mast cells. Mitf and its human homolog MITF consist of at least three isoforms, referred to as Mitf-A/MITF-A, the heart-type Mitf-H/MITF-H, and the melanocyte lineage-specific Mitf-M/MITF-M, respectively. These isoforms differ in the amino-terminal domains but share a transactivation domain and a basic helix-loop-helix and leucine-zipper structure that is required for DNA binding and dimerization. MITF-M is exclusively expressed in melanocytes and melanoma cells, but not in other cell types, including RPE cells. In contrast, MITF-A mRNA is widely expressed in many cell types. These three isoform mRNAs are possibly generated by differential usage of the gene promoters and by alternative splicing. We predict that the entire MITF gene spans about 200 kb of DNA. Like MITF-M, MITF-A is able to activate the two melanogenesis gene promoters, tyrosinase and tyrosinase-related protein 1. These results suggest that melanogenesis may be regulated by different MITF isoforms in melanocyte and RPE. Possible implications of the multiplicity in Mitf/MITF isoforms are discussed.
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PMID:A big gene linked to small eyes encodes multiple Mitf isoforms: many promoters make light work. 987 May 44

Tyrosinase and a family of tyrosinase-related proteins (TRPs) are melanocyte differentiation gene products involved in melanin pigmentation. Members of the tyrosinase family share upstream transcriptional regulatory elements suggesting that expression of these genes is regulated by shared mechanisms. Microphthalmia transcription factor MITF, a melanocyte-specific basic helix-loop-helix protein, has been shown to transactivate tyrosinase and TRP-1 genes in vitro by binding to a shared regulatory sequence known as M box. The role of MITF in concomitant regulation of these genes in vivo is not clear. We showed earlier that in human melanoma cells TRP-1 can be regulated independently of tyrosinase and pigmentation. To investigate the role of MITF in TRP-1 regulation, we studied the effect of pharmacological agents that modulate transcription of tyrosinase and TRP-1 on MITF. In melanoma cells treated with hexamethylene bisacetamide (HMBA), transcription of TRP-1 gene was selectively and completely inhibited while steady state levels of tyrosinase, TRP-2, MITF mRNA and melanin content showed a modest increase. HMBA caused no detectable change in cellular MITF or its nuclear localization. This MITF-independent regulation of TRP-1 required continued synthesis of RNA and protein. Selective down-regulation of TRP-1 by HMBA occurred even in the presence of cholera toxin which up-regulates TRP-1 by cAMP-mediated pathways. These data show that TRP-1 gene can be down-regulated independently of MITF by de novo activation of negative regulatory factors. Thus, both activation of positive factors such as MITF and inactivation of negative regulatory factors may be required for TRP-1 gene expression during melanocytic differentiation.
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PMID:Role of microphthalmia transcription factor in regulation of melanocyte differentiation marker TRP-1. 1008 Sep 55

On some occasions, mutations of a gene cause different syndromes that may have similar phenotypes. For example, mutations of the MITF gene cause Waardenburg syndrome type 2 (Tassabehji et al, 1994; Nobukuni et al, 1996) as well as Tietz syndrome (Smith et al, 1997). On other occasions, mutations of different genes cause an identical syndrome. Molecular analyses of these genes may provide a good opportunity to not only understand such syndromes themselves but also the biologic aspects of cells relevant to these syndromes. By analyzing the genes for Waardenburg syndrome, we showed that PAX3, the gene responsible for Waardenburg syndrome type 1, regulates MITF, the gene responsible for Waardenburg syndrome type 2. Such epistatic relationships have been shown between other genes related to Waardenburg syndrome, and likely to construct a cascade. This paper proposes such a cascade, one that involves genes for PAX3, MITF, human MyoD, MYF5, c-MET, c-KIT, tyrosinase, TRP-1, human QNR-71, SOX10, EDNRB, and EDN3.
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PMID:A cascade of genes related to Waardenburg syndrome. 1053 86


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