The identification and functional characterization of a novel mast cell isoform of the microphthalmia-associated transcription factor.
The microphthalmia-associated transcription factor (Mitf) is critical for mast cell development based on the severe mast cell deficiency seen in Mitf mutant mice. Mitf also is important for the development of melanocytes, osteoclasts, and retinal pigment epithelium. The lineage-restricted phenotypes of Mitf mutations correlate with tissue-restricted expression of Mitf, a feature due in part to the presence of several distinct Mitf isoforms. We report the identification and characterization of a novel mast cell isoform, Mitf-mc. This isoform arises from alternative splicing of a novel 5'-exon onto the common body of the gene and is predicted to encode a unique 43-amino acid sequence at its amino terminus. It is specifically expressed in mast cells. The mast cell isoform functions differently from the melanocyte isoform in its ability to activate cell type-specific Mitf gene targets. Mitf-mc functions only on a mast cell target promoter and fails to activate a melanocyte target promoter despite binding to its E-box element. Moreover, Mitf-mc heterodimerizes with a closely related transcription factor, Tfe3, and dominantly inhibits the ability of Tfe3 to transactivate a melanocyte-specific promoter. These studies identify a new isoform of Mitf with tissue-specific features that may underlie key aspects of the mast cell phenotype of Mitf mutations.
Takemoto
Clifford M
CM
Division of Pediatric Hematology, The Johns Hopkins University, Baltimore, Maryland 21205, USA. ctakemot@jhmi.edu
Yoon
Yo-Jin
YJ
Fisher
David E
DE
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001665:Binding Sites; D002460:Cell Line; D004247:DNA; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008407:Mast Cells / Q000378:metabolism*; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000235:genetics; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism; D015533:Transcriptional Activation
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D020033:Protein Isoforms; C069203:TFE3 protein, human; D014157:Transcription Factors; D004247:DNA; D014442:Monophenol Monooxygenase