Costin GE, Valencia JC, Wakamatsu K et al.Mutations in dopachrome tautomerase (DCT) affect eumelanin/pheomelanin synthesis, but do not affect intracellular trafficking of the mutant protein. Biochem J 391:249-259

Pigment Cell Biology Section, Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health (NIH), Bethesda, MD 20892, USA.
Biochemical Journal (Impact Factor: 4.4). 11/2005; 391(Pt 2):249-59. DOI: 10.1042/BJ20042070
Source: PubMed


Dopachrome tautomerase (Dct) is a type I membrane protein and an important regulatory enzyme that plays a pivotal role in the biosynthesis of melanin and in the rapid metabolism of its toxic intermediates. Dct-mutant melanocytes carrying the slaty or slaty light mutations were derived from the skin of newborn congenic C57BL/6J non-agouti black mice and were used to study the effect(s) of these mutations on the intracellular trafficking of Dct and on the pigmentation of the cells. Dct activity is 3-fold lower in slaty cells compared with non-agouti black melanocytes, whereas slaty light melanocytes have a surprisingly 28-fold lower Dct activity. Homology modelling of the active site of Dct suggests that the slaty mutation [R194Q (Arg194-->Gln)] is located in the active site and may alter the ability of the enzyme to transform the substrate. Transmembrane prediction methods indicate that the slaty light mutation [G486R (Gly486-->Arg)] may result in the sliding of the transmembrane domain towards the N-terminus, thus interfering with Dct function. Chemical analysis showed that both Dct mutations increase pheomelanin and reduce eumelanin produced by melanocytes in culture. Thus the enzymatic activity of Dct may play a role in determining whether the eumelanin or pheomelanin pathway is preferred for pigment biosynthesis.

Download full-text


Available from: Adina L Milac,
  • Source
    • "In our study, IFN-γ promoted the accumulation of melanin in melanocytes, and increased the transcription of some of the melanogenesis-related genes. However, it also significantly decreased the mRNA level of DCT, which encodes a critical enzyme in the synthesis of eumelanin [39]. Thus, IFN-γ might change the eumelanin/pheomelanin ratio in melanocytes. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Interferon-γ (IFN-γ) plays an important role in the proceedings of vitiligo through recruiting lymphocytes to the lesional skin. However, the potential effects of IFN-γ on skin melanocytes and the subsequent contribution to the vitiligo pathogenesis are still unclear. To investigate the effects of IFN-γ on viability and cellular functions of melanocytes. Primary human melanocytes were treated with IFN-γ. Cell viability, apoptosis, cell cycle melanin content and intracellular reactive oxygen species (ROS) level were measured. mRNA expression was examined by real-time PCR. The release of interleukin 6 (IL-6) and heat shock protein 70 (HSP-70) was monitored by ELISA. β-galactosidase staining was utilized to evaluate melanocyte senescence. Persistent IFN-γ treatment induced viability loss, apoptosis, cell cycle arrest and senescence in melanocytes. Melanocyte senescence was characterized as the changes in pigmentation and morphology, as well as the increase of β-galactosidase activity. Increase of p21Cip1/Waf1 protein was evident in melanocytes after IFN-γ treatment. IFN-γ induction of senescence was attenuated by siRNAs against p21, Janus kinase 2 (JAK2) or signal transducer and activator of transcription 1 (STAT1), but not by JAK1 siRNA nor by p53 inhibitor pifithrin-α. IFN-γ treatment increased the accumulation of intracellular ROS in melanocytes, while ROS scavenger N-acetyl cysteine (NAC) effectively inhibited IFN-γ induced p21 expression and melanocyte senescence. IL-6 and HSP-70 release was significantly induced by IFN-γ treatment, which was largely inhibited by NAC. The increase of IL-6 and HSP-70 release could also be observed in senescent melanocytes. IFN-γ can induce senescence in melanocytes and consequently enhance their immuno-competency, leading to a vitiligo-prone milieu.
    PLoS ONE 03/2014; 9(3):e93232. DOI:10.1371/journal.pone.0093232 · 3.23 Impact Factor
  • Source
    • "Tyrosinase (TYR) is the most important enzyme of melanin synthesis, and its expression is induced by exposure to UVR as part of the pigmentation process. TYR acts with TYR-related protein 1 and dopachrome tautomerase to synthesize melanin (Costin et al., 2005). The TYR gene family members such as TYR and TYR-related protein 1 contribute to the initiation of pigment synthesis in stage-3 melanosomes (Raposo and Marks, 2007). "
    [Show abstract] [Hide abstract]
    ABSTRACT: MicroRNA (miR)-203 is known to be downregulated and to act as an anti-oncomir in melanoma cells. Presently we found that exogenous miR-203 increased pigmentation and protein expression levels of the melanoma antigen recognized by T-cells (Melan-A/MART1) and/or tyrosinase (TYR) in the human melanoma cells tested. Inversely, treatment with an inhibitor of miR-203 downregulated the expression level of TYR. The target gene of miR-203 involved in the mechanism was kinesin superfamily protein 5b (kif5b), which was revealed by gene silencing using siRNA and luciferase activity assay. Furthermore, immunocytochemistry showed obvious accumulation of melanosomes around nuclei of human melanoma Mewo cells transfected with miR-203 or siR-kif5b. Importantly, treatment with the miR-203 inhibitor, but not miR-203 exhibited effects on human normal epidermal melanocytes (HEMa-LP) similar to those on melanoma cells. In addition, the data indicated that exogenous miR-203 also negatively regulated the CREB1/MITF/Rab27a pathway, which is one of the main pathways active in melanoma cells. In conclusion, our data indicated that anti-oncogenic miR-203 played a pivotal role in melanoma through reducing melanosome transport and promoting melanogenesis by targeting kif5b and through negative regulation of the CREB1/MITF/Rab27a pathway.Journal of Investigative Dermatology accepted article preview online, 24 July 2013. doi:10.1038/jid.2013.310.
    Journal of Investigative Dermatology 07/2013; 134(2). DOI:10.1038/jid.2013.310 · 7.22 Impact Factor
  • Source
    • "Groups have also shown that mutations in Dct (dopachrome tautomerase) affect eumelanin/pheomelanin synthesis , but do not affect intracellular trafficking of the mutant protein, leading to a mild iris phenotype (Costin et al., 2005). Despite this biological significance, Dct did not fulfill our inclusion criteria. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the contributions of Tyrp1 and Gpnmb to the iris transillumination defect (TID) in five age cohorts of BXD mice. Using systems genetics, we also evaluated the role of other known pigmentation genes (PGs). Mapping studies indicate that Tyrp1 contributes to the phenotype at all ages, yet the TID maps to Gpnmb only in the oldest cohort. Composite interval mapping reveals secondary loci viz. Oca2, Myo5a, Prkcz and Zbtb20 that modulate the phenotype in the age groups up to 10-13 months. The contributions of Tyrp1 and Gpnmb were highly significant in all age cohorts. Moreover, in young mice, all six gene candidates had substantial interactions in our model. Our model accounted for 71-88% of the explained variance of the TID phenotype across the age bins. These results demonstrate that along with Tyrp1 and Gpnmb, Oca2, Myo5a, Prkcz and Zbtb20 modulate the TID in an age-dependent manner. This article is protected by copyright. All rights reserved.
    Pigment Cell & Melanoma Research 04/2013; 26(4). DOI:10.1111/pcmr.12106 · 4.62 Impact Factor
Show more