51
|
Sturm RA, Teasdale RD, Box NF. Human pigmentation genes: identification, structure and consequences of polymorphic variation. Gene 2001; 277:49-62. [PMID: 11602344 DOI: 10.1016/s0378-1119(01)00694-1] [Citation(s) in RCA: 253] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The synthesis of the visible pigment melanin by the melanocyte cell is the basis of the human pigmentary system, those genes directing the formation, transport and distribution of the specialised melanosome organelle in which melanin accumulates can legitimately be called pigmentation genes. The genes involved in this process have been identified through comparative genomic studies of mouse coat colour mutations and by the molecular characterisation of human hypopigmentary genetic diseases such as OCA1 and OCA2. The melanocyte responds to the peptide hormones alpha-MSH or ACTH through the MC1R G-protein coupled receptor to stimulate melanin production through induced maturation or switching of melanin type. The pheomelanosome, containing the key enzyme of the pathway tyrosinase, produces light red/yellowish melanin, whereas the eumelanosome produces darker melanins via induction of additional TYRP1, TYRP2, SILV enzymes, and the P-protein. Intramelanosomal pH governed by the P-protein may act as a critical determinant of tyrosinase enzyme activity to control the initial step in melanin synthesis or TYRP complex formation to facilitate melanogenesis and melanosomal maturation. The search for genetic variation in these candidate human pigmentation genes in various human populations has revealed high levels of polymorphism in the MC1R locus, with over 30 variant alleles so far identified. Functional correlation of MC1R alleles with skin and hair colour provides evidence that this receptor molecule is a principle component underlying normal human pigment variation.
Collapse
Affiliation(s)
- R A Sturm
- Centre for Functional and Applied Genomics, Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD 4072, Australia.
| | | | | |
Collapse
|
52
|
Le Borgne R, Planque N, Martin P, Dewitte F, Saule S, Hoflack B. The AP-3-dependent targeting of the melanosomal glycoprotein QNR-71 requires a di-leucine-based sorting signal. J Cell Sci 2001; 114:2831-41. [PMID: 11683416 DOI: 10.1242/jcs.114.15.2831] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Quail Neuroretina clone 71 gene (QNR-71) is expressed during the differentiation of retinal pigmented epithelia and the epidermis. It encodes a type I transmembrane glycoprotein that shares significant sequence homologies with several melanosomal proteins. We have studied its intracellular traffic in both pigmented and non-pigmented cells. We report that a di-leucine-based sorting signal (ExxPLL) present in the cytoplasmic domain of QNR-71 is necessary and sufficient for its proper targeting to the endosomal/premelanosomal compartments of both pigmented and non-pigmented cells. The intracellular transport of QNR-71 to these compartments is mediated by the AP-3 assembly proteins. As previously observed for the lysosomal glycoproteins LampI and LimpII, overexpression of QNR-71 increases the amount of AP-3 associated with membranes, and inhibition of AP-3 synthesis increases the routing of QNR-71 towards the cell surface. In addition, expression of QNR-71 induces a misrouting of endogenous LampI to the cell surface. Thus, the targeting of QNR-71 might be similar to that of the lysosomal integral membrane glycoproteins LampI and LimpII. This suggests that sorting to melanosomes and lysosomes requires similar sorting signals and transport machineries.
Collapse
Affiliation(s)
- R Le Borgne
- Institut de Biologie de Lille, CNRS EP525, Institut Pasteur de Lille, France
| | | | | | | | | | | |
Collapse
|
53
|
Leszczyniecka M, Roberts T, Dent P, Grant S, Fisher PB. Differentiation therapy of human cancer: basic science and clinical applications. Pharmacol Ther 2001; 90:105-56. [PMID: 11578655 DOI: 10.1016/s0163-7258(01)00132-2] [Citation(s) in RCA: 228] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Current cancer therapies are highly toxic and often nonspecific. A potentially less toxic approach to treating this prevalent disease employs agents that modify cancer cell differentiation, termed 'differentiation therapy.' This approach is based on the tacit assumption that many neoplastic cell types exhibit reversible defects in differentiation, which upon appropriate treatment, results in tumor reprogramming and a concomitant loss in proliferative capacity and induction of terminal differentiation or apoptosis (programmed cell death). Laboratory studies that focus on elucidating mechanisms of action are demonstrating the effectiveness of 'differentiation therapy,' which is now beginning to show translational promise in the clinical setting.
Collapse
Affiliation(s)
- M Leszczyniecka
- Department of Urology, Herbert Irving Comprehensive Cancer Center, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA
| | | | | | | | | |
Collapse
|
54
|
Raposo G, Tenza D, Murphy DM, Berson JF, Marks MS. Distinct protein sorting and localization to premelanosomes, melanosomes, and lysosomes in pigmented melanocytic cells. J Cell Biol 2001; 152:809-24. [PMID: 11266471 PMCID: PMC2195785 DOI: 10.1083/jcb.152.4.809] [Citation(s) in RCA: 352] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Melanosomes and premelanosomes are lysosome-related organelles with a unique structure and cohort of resident proteins. We have positioned these organelles relative to endosomes and lysosomes in pigmented melanoma cells and melanocytes. Melanosome resident proteins Pmel17 and TRP1 localized to separate vesicular structures that were distinct from those enriched in lysosomal proteins. In immunogold-labeled ultrathin cryosections, Pmel17 was most enriched along the intralumenal striations of premelanosomes. Increased pigmentation was accompanied by a decrease in Pmel17 and by an increase in TRP1 in the limiting membrane. Both proteins were largely excluded from lysosomal compartments enriched in LAMP1 and cathepsin D. By kinetic analysis of fluid phase uptake and immunogold labeling, premelanosomal proteins segregated from endocytic markers within an unusual endosomal compartment. This compartment contained Pmel17, was accessed by BSA-gold after 15 min, was acidic, and displayed a cytoplasmic planar coat that contained clathrin. Our results indicate that premelanosomes and melanosomes represent a distinct lineage of organelles, separable from conventional endosomes and lysosomes within pigmented cells. Furthermore, they implicate an unusual clathrin-coated endosomal compartment as a site from which proteins destined for premelanosomes and lysosomes are sorted.
Collapse
Affiliation(s)
- Graça Raposo
- Curie Institute, Research Section, Paris, 7505 France
| | | | - Diane M. Murphy
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Joanne F. Berson
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Michael S. Marks
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| |
Collapse
|
55
|
Hume AN, Collinson LM, Rapak A, Gomes AQ, Hopkins CR, Seabra MC. Rab27a regulates the peripheral distribution of melanosomes in melanocytes. J Cell Biol 2001; 152:795-808. [PMID: 11266470 PMCID: PMC2195786 DOI: 10.1083/jcb.152.4.795] [Citation(s) in RCA: 273] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2000] [Accepted: 11/22/2000] [Indexed: 12/11/2022] Open
Abstract
Rab GTPases are regulators of intracellular membrane traffic. We report a possible function of Rab27a, a protein implicated in several diseases, including Griscelli syndrome, choroideremia, and the Hermansky-Pudlak syndrome mouse model, gunmetal. We studied endogenous Rab27a and overexpressed enhanced GFP-Rab27a fusion protein in several cultured melanocyte and melanoma-derived cell lines. In pigmented cells, we observed that Rab27a decorates melanosomes, whereas in nonpigmented cells Rab27a colocalizes with melanosome-resident proteins. When dominant interfering Rab27a mutants were expressed in pigmented cells, we observed a redistribution of pigment granules with perinuclear clustering. This phenotype is similar to that observed by others in melanocytes derived from the ashen and dilute mutant mice, which bear mutations in the Rab27a and MyoVa loci, respectively. We also found that myosinVa coimmunoprecipitates with Rab27a in extracts from melanocytes and that both Rab27a and myosinVa colocalize on the cytoplasmic face of peripheral melanosomes in wild-type melanocytes. However, the amount of myosinVa in melanosomes from Rab27a-deficient ashen melanocytes is greatly reduced. These results, together with recent data implicating myosinVa in the peripheral capture of melanosomes, suggest that Rab27a is necessary for the recruitment of myosinVa, so allowing the peripheral retention of melanosomes in melanocytes.
Collapse
Affiliation(s)
- Alistair N. Hume
- Cell and Molecular Biology Section, Division of Biomedical Sciences
| | - Lucy M. Collinson
- Department of Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AZ, United Kingdom
| | - Andrzej Rapak
- Cell and Molecular Biology Section, Division of Biomedical Sciences
| | - Anita Q. Gomes
- Cell and Molecular Biology Section, Division of Biomedical Sciences
| | - Colin R. Hopkins
- Department of Biochemistry, Imperial College of Science, Technology and Medicine, London SW7 2AZ, United Kingdom
| | - Miguel C. Seabra
- Cell and Molecular Biology Section, Division of Biomedical Sciences
| |
Collapse
|
56
|
Olivares C, Jiménez-Cervantes C, Lozano JA, Solano F, García-Borrón JC. The 5,6-dihydroxyindole-2-carboxylic acid (DHICA) oxidase activity of human tyrosinase. Biochem J 2001; 354:131-9. [PMID: 11171088 PMCID: PMC1221637 DOI: 10.1042/0264-6021:3540131] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Melanin synthesis in mammals is catalysed by at least three enzymic proteins, tyrosinase (monophenol dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) and tyrosinase-related proteins (tyrps) 1 and 2, whose genes map to the albino, brown and slaty loci in mice, respectively. Tyrosinase catalyses the rate-limiting generation of L-dopaquinone from L-tyrosine and is also able to oxidize L-dopa to L-dopaquinone. Conversely, mouse tyrp1, but not tyrosinase, catalyses the oxidation of the indolic intermediate 5,6-dihydroxyindole-2-carboxylic acid (DHICA) into the corresponding 5,6-indolequinone-2-carboxylic acid, thus promoting the incorporation of DHICA units into eumelanin. The catalytic activities of the human melanogenic enzymes are still debated. TYRP1 has been reported to lack DHICA oxidase activity, whereas tyrosinase appears to accelerate DHICA consumption, thus raising the question of DHICA metabolism in human melanocytes. Here we have used two different approaches, comparison of the catalytic activities of human melanocytic cell lines expressing the full set of melanogenic enzymes or deficient in TYRP1, and transient expression of TYR and tyr genes in COS7 cells, to demonstrate that human tyrosinase actually functions as a DHICA oxidase, as opposed to the mouse enzyme. Therefore, human tyrosinase displays a broader substrate specificity than its mouse counterpart, and might be at least partially responsible for the incorporation of DHICA units into human eumelanins.
Collapse
Affiliation(s)
- C Olivares
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Apto 4021, Campus Espinardo, 30100 Murcia, Spain
| | | | | | | | | |
Collapse
|
57
|
van Adelsberg J. Peptides from the PKD repeats of polycystin, the PKD1 gene product, modulate pattern formation in the developing kidney. DEVELOPMENTAL GENETICS 2000; 24:299-308. [PMID: 10322638 DOI: 10.1002/(sici)1520-6408(1999)24:3/4<299::aid-dvg13>3.0.co;2-j] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Mutations in the PKD1 gene cause the majority of cases of autosomal dominant polycystic kidney disease. The PKD1 gene codes for a protein of unknown function, polycystin-1, that is predicted to be a receptor. Its large extracellular domain contains 16 copies of novel motif, the PKD repeat, that is likely to be a ligand binding domain based on its similarity to immunoglobulin domains. These observations suggested that soluble fragments of the extracellular domain of polycystin-1 could be used as competitive inhibitors of polycystin function in a suitable model system. Polycystin-1 is highly expressed in the ureteric bud and other branching epithelia during development and interacts with beta-catenin, a molecule known to play a role in branching morphogenesis. These data suggested that polycystin-1 might play a role in branching morphogenesis. I show here that peptides derived from the PKD repeats of polycystin-1 caused an asymmetric pattern of ureteric bud branching in cultured kidney rudiments. Treatment of kidney rudiments with experimental but not control peptides reduced both the number of ureteric bud branches and the number of nephrons. Experimental peptides produced significant morphogenetic effects at concentrations < or = 0.1 mM. These data suggest that polycystin-1 plays a role in branching morphogenesis by the ureteric bud.
Collapse
Affiliation(s)
- J van Adelsberg
- Department of Medicine, Columbia University, New York, New York 10032, USA.
| |
Collapse
|
58
|
Rieder S, Stricker C, Joerg H, Dummer R, Stranzinger G. A comparative genetic approach for the investigation of ageing grey horse melanoma. J Anim Breed Genet 2000. [DOI: 10.1111/j.1439-0388.2000x.00245.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
59
|
Hill HZ, Hill GJ, Cieszka K, Plonka PM, Mitchell DL, Meyenhofer MF, Xin P, Boissy RE. Comparative action spectrum for ultraviolet light killing of mouse melanocytes from different genetic coat color backgrounds. Photochem Photobiol 1997; 65:983-9. [PMID: 9188277 DOI: 10.1111/j.1751-1097.1997.tb07958.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The photobiology of mouse melanocyte lines with different pigment genotypes was studied by measuring colony-forming ability after irradiation. The cell lines were wild-type black (melan-a) and the mutants brown (melan-b) and albino (melan-c). Four lamps emitting various UV wavelengths were used. These were germicidal (UVC, 200-280 nm), 82.3% output at 254 nm, TL01 (UVB, 280-320 nm), 64.2% at 310-311 nm, FS20, broadband with peak output at 312 nm and Alisun-S (UVA, 320-400 nm), broadband with peak output at 350-354 nm. Appropriate filtration reduced the contaminating UVC to nonlethal levels for the longer waverange lamps. Wild-type melan-a was resistant to UVC and UVA compared to the other two cell lines, but the differences were small. The melan-c cell line was more resistant to UVB and markedly more resistant to FS20 than the pigmented lines. With the exception of FS20 responses, melan-b was more sensitive than melan-a to killing by the various UV lamps. There were more pyrimidine dimers (cyclobutane dimers and 6-4 photoproducts) produced in melan-a than in melan-c cells by UVC, UVB and FS20 lamps. Unlike melan-c, melan-a and melan-b showed a strong free radical signal of melanin character with a detectable contribution of pheomelanin-like centers. The contribution of pheomelanin was higher in melan-b than in melan-a, while the total melanin content in these two cell lines was comparable. The abundant melanin granules of wild-type melan-a melanocytes were well melanized and ellipsoidal, whereas those of melan-b melanocytes tended to be spherical. In the albino line (melan-c) the melanocytes contained only early-stage melanosomes, all of which were devoid of melanin. The results indicate that pigment does not protect against direct effect DNA damage in the form of pyrimidine dimers nor does it necessarily protect against cell death. High pigment content is not very protective against killing by UVC and UVA, and it may photosensitize in UVB the very wavelength range that is of greatest concern with respect to the rising incidence in skin cancer, especially melanoma. It is clear from these studies that, in pigment cells, monochromatic results cannot predict polychromatic responses and that cell death from solar irradiations is a complex phenomenon that depends on more than DNA damage.
Collapse
Affiliation(s)
- H Z Hill
- Department of Radiology, NJ Medical School, Newark 07103-2714, USA.
| | | | | | | | | | | | | | | |
Collapse
|
60
|
Palumbo A, di Cosmo A, Gesualdo I, Hearing VJ. Subcellular localization and function of melanogenic enzymes in the ink gland of Sepia officinalis. Biochem J 1997; 323 ( Pt 3):749-56. [PMID: 9169609 PMCID: PMC1218379 DOI: 10.1042/bj3230749] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The ink gland of the cuttlefish Sepia officinalis has traditionally been regarded as a convenient model system for investigating melanogenesis. This gland has been shown to contain a variety of melanogenic enzymes including tyrosinase, a dopachrome-rearranging enzyme and peroxidase. However, whether and to what extent these enzymes co-localize in the melanogenic compartments and interact is an open question. Using polyclonal antibodies that recognize the corresponding Sepia proteins, we have been able to demonstrate that peroxidase has a different subcellular localization pattern from tyrosinase and dopachrome-rearranging enzyme. Whereas peroxidase is located in the rough endoplasmic reticulum and in the matrix of premelanosomes and melanosomes, tyrosinase and dopachrome-rearranging enzyme are present in the rough endoplasmic reticulum-Golgi transport system, at the level of trans-Golgi cisternae, trans-Golgi network and coated vesicles, and in melanosomes on pigmented granules. These results fill a longstanding gap in our knowledge of the melanin-producing system in Sepia and provide the necessary background for dissection at the molecular level of the complex interaction between melanogenic enzymes. Moreover, the peculiar and complex organization of melanin in an invertebrate such as Sepia officinalis is surprising and could provide the basis for understanding the process in more evolved systems such as that of mammals.
Collapse
Affiliation(s)
- A Palumbo
- Laboratory of Biochemistry and Molecular Biology, Zoological Station, Villa Comunale, 80121 Naples, Italy
| | | | | | | |
Collapse
|
61
|
Martínez-Esparza M, Jiménez-Cervantes C, Beermann F, Aparicio P, Lozano JA, García-Borrón JC. Transforming growth factor-beta1 inhibits basal melanogenesis in B16/F10 mouse melanoma cells by increasing the rate of degradation of tyrosinase and tyrosinase-related protein-1. J Biol Chem 1997; 272:3967-72. [PMID: 9020101 DOI: 10.1074/jbc.272.7.3967] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Current evidence suggests that melanogenesis is controlled by epidermal paracrine modulators. We have analyzed the effects of transforming growth factor-beta1 (TGF-beta1) on the basal melanogenic activities of B16/F10 mouse melanoma cells. TGF-beta1 treatment (48 h) elicited a concentration-dependent decrease in basal tyrosine hydroxylase and 3,4-dihydroxyphenylalanine (Dopa) oxidase activities, to less than 30% of the control values but had no effect on dopachrome tautomerase activity (TRP-2). The inhibition affected to similar extents the Dopa oxidase activity associated to tyrosinase-related protein-1 (TRP-1) and tyrosinase. This inhibition was noticeable between 1 and 3 h after the addition of the cytokine, and maximal after 6 h of treatment. The decrease in the enzymatic activity was paralleled by a decrease in the abundance of the TRP-1 and tyrosinase proteins. TGF-beta1 mediated this effect by increasing the rate of degradation of tyrosinase and TRP-1. Conversely, after 48 h of treatment, the expression of the tyrosinase gene decreased only slightly, while TRP-1 and TRP-2 gene expression was not affected. An increased rate of proteolytic degradation of TRP-1 and tyrosinase seems the main mechanism accounting for the inhibitory effect of TGF-beta1 on the melanogenic activity of B16/F10 cells.
Collapse
Affiliation(s)
- M Martínez-Esparza
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, 30100 Espinardo, Murcia, Spain
| | | | | | | | | | | |
Collapse
|
62
|
Furumura M, Sakai C, Abdel-Malek Z, Barsh GS, Hearing VJ. The interaction of agouti signal protein and melanocyte stimulating hormone to regulate melanin formation in mammals. PIGMENT CELL RESEARCH 1996; 9:191-203. [PMID: 8948501 DOI: 10.1111/j.1600-0749.1996.tb00109.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Important regulatory controls of melanogenesis that operate at the subcellular level to modulate the structural and/or the functional nature of the melanins and melanin granules produced in melanocytes are reviewed. Melanocyte stimulating hormone and agouti signal protein have antagonistic roles and possibly opposing mechanisms of action in the melanocyte. In the mouse, melanocyte stimulating hormone promotes melanogenic enzyme function and elicits increases in the amount of eumelanins produced, while agouti signal protein reduces total melanin production and elicits the synthesis of pheomelanin rather than eumelanin. We are now beginning to understand the complex controls involved in regulating this switch at the molecular and biochemical levels. The quality and quantity of melanins produced by melanocytes have important physiological consequences for melanocyte function and undoubtedly play important roles in the various functions of the melanins per se, including hair and skin coloration and photoprotection.
Collapse
Affiliation(s)
- M Furumura
- Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | | | | | | | | |
Collapse
|
63
|
Halaban R, Böhm M, Dotto P, Moellmann G, Cheng E, Zhang Y. Growth regulatory proteins that repress differentiation markers in melanocytes also downregulate the transcription factor microphthalmia. J Invest Dermatol 1996; 106:1266-72. [PMID: 8752668 DOI: 10.1111/1523-1747.ep12348972] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Expression of basic fibroblast growth factor cDNA or dominantly acting oncogenes, e.g., E1A, in immortalized mouse melanocytes leads to autonomous growth in vitro, depigmentation, and in the case of the oncogenes, tumorigenesis. Because downregulation of pigmentation is a common event in human metastatic melanoma cells grown in culture, we determined the molecular basis of depigmentation in a mouse melanocyte model system. We tested the effect of E1A mutants deficient in their ability to neutralize several regulatory proteins and determined changes in melanogenic gene expression. We identified Microphthalmia as the affected, downregulated transcription factor in melanocytes rendered amelanotic by E1A, basic fibroblast growth factor, or the oncogenes ras or neu, and in an amelanotic cell variant of Cloudman S91 mouse melanoma. Against expectations, sequestration of p300, a transcriptional adaptor that mediates responses to cyclic adenosine monophosphate, was not required for the full transforming effects of E1A. Our results suggest that in addition to controlling tyrosinase (albino locus) and tyrosinase-related protein 1 (TR-P1/gp75/brown locus), both known to possess the DNA consensus site for binding the Microphthalmia protein, this transcription factor also controls other melanocyte-specific genes such as pink-eyed dilution and Pmel 17 (silver), but not tyrosinase-related protein 2 (slaty locus). Furthermore, these findings show that microphthalmia is downregulated not only by experimentally introduced dominantly acting oncogenes but also by the aberrant expression of basic fibroblast growth factor and by spontaneous tumorigenic transformation.
Collapse
Affiliation(s)
- R Halaban
- Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut 06520-8059, USA
| | | | | | | | | | | |
Collapse
|