1
|
Fock V, Gudmundsson SR, Gunnlaugsson HO, Stefansson JA, Ionasz V, Schepsky A, Viarigi J, Reynisson IE, Pogenberg V, Wilmanns M, Ogmundsdottir MH, Steingrimsson E. Subcellular localization and stability of MITF are modulated by the bHLH-Zip domain. Pigment Cell Melanoma Res 2018; 32:41-54. [PMID: 29938923 DOI: 10.1111/pcmr.12721] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Revised: 06/01/2018] [Accepted: 06/19/2018] [Indexed: 12/15/2022]
Abstract
Microphthalmia-associated transcription factor (MITF) is a member of the basic helix-loop-helix leucine zipper (bHLH-Zip) family and functions as the master regulator of the melanocytic lineage. MITF-M is the predominant isoform expressed in melanocytes and melanoma cells, and, unlike other MITF isoforms, it is constitutively nuclear. Mutational analysis revealed three karyophilic signals in the bHLH-Zip domain of MITF-M, spanning residues 197-206, 214-217, and 255-265. Structural characterization of the MITF protein showed that basic residues within these signals are exposed for interactions in the absence of DNA. Moreover, our data indicate that neither DNA binding nor dimerization of MITF-M are required for its nuclear localization. Finally, dimerization-deficient MITF-M mutants exhibited a significantly reduced stability in melanoma cells when compared to the wild-type protein. Taken together, we have shown that, in addition to its well-established role in DNA binding and dimer formation, the bHLH-Zip domain of MITF modulates the transcription factor's subcellular localization and stability.
Collapse
Affiliation(s)
- Valerie Fock
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Sigurdur Runar Gudmundsson
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Hilmar Orn Gunnlaugsson
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Jon August Stefansson
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Vivien Ionasz
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Alexander Schepsky
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Jade Viarigi
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Indridi Einar Reynisson
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | | | | | - Margret Helga Ogmundsdottir
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| | - Eirikur Steingrimsson
- Faculty of Medicine, Department of Biochemistry and Molecular Biology, BioMedical Center, University of Iceland, Reykjavik, Iceland
| |
Collapse
|
2
|
Zeng Z, Johnson SL, Lister JA, Patton EE. Temperature-sensitive splicing of mitfa by an intron mutation in zebrafish. Pigment Cell Melanoma Res 2014; 28:229-32. [PMID: 25469769 DOI: 10.1111/pcmr.12336] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zhiqiang Zeng
- MRC IGMM, MRC Human Genetics Unit, University of Edinburgh Cancer Research UK Centre, Edinburgh, UK
| | | | | | | |
Collapse
|
3
|
Kohli S, Ahuja S, Rani V. Transcription factors in heart: promising therapeutic targets in cardiac hypertrophy. Curr Cardiol Rev 2013; 7:262-71. [PMID: 22758628 PMCID: PMC3322445 DOI: 10.2174/157340311799960618] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 01/08/2012] [Accepted: 01/08/2011] [Indexed: 12/16/2022] Open
Abstract
Regulation of gene expression is central to cell growth, differentiation and diseases. Context specific and signal dependent regulation of gene expression is achieved to a large part by transcription factors. Cardiac transcription factors regulate heart development and are also involved in stress regulation of the adult heart, which may lead to cardiac hypertrophy. Hypertrophy of cardiac myocytes is an outcome of the imbalance between prohypertrophic factors and anti-hypertrophic factors. This is initially a compensatory mechanism but sustained hypertrophy may lead to heart failure. The growing knowledge of transcriptional control mechanisms is helpful in the development of novel therapies. This review summarizes the role of cardiac transcription factors in cardiac hypertrophy, emphasizing their potential as attractive therapeutic targets to prevent the onset of heart failure and sudden death as they can be converging targets for current therapy.
Collapse
Affiliation(s)
- Shrey Kohli
- Department of Biotechnology, Jaypee Institute of Information Technology University, NOIDA 210307, India
| | | | | |
Collapse
|
4
|
In vivo role of alternative splicing and serine phosphorylation of the microphthalmia-associated transcription factor. Genetics 2012; 191:133-44. [PMID: 22367038 DOI: 10.1534/genetics.111.135996] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The microphthalmia-associated transcription factor (MITF) is a basic helix-loop-helix leucine zipper protein that plays major roles in the development and physiology of vertebrate melanocytes and melanoma cells. It is regulated by post-translational modifications, including phosphorylation at serine 73, which based on in vitro experiments imparts on MITF an increased transcriptional activity paired with a decreased stability. Serine 73 is encoded by the alternatively spliced exon 2B, which is preferentially skipped in mice carrying a targeted serine-73-to-alanine mutation. Here, we measured the relative abundance of exon 2B+ and exon 2B- RNAs in freshly isolated and FACS-sorted wild-type melanoblasts and melanocytes and generated a series of knock-in mice allowing forced incorporation of either alanine, aspartate, or wild-type serine at position 73. None of these knock-in alleles, however, creates a striking pigmentation phenotype on its own, but differences between them can be revealed either by a general reduction of Mitf transcript levels or in heteroallelic combinations with extant Mitf mutations. In fact, compared with straight serine-73 knock-in mice with their relative reduction of 2B+ Mitf, forced incorporation of alanine 73 leads to greater increases in MITF protein levels, melanoblast and melanocyte numbers, and extent of pigmentation in particular allelic combinations. These results underscore, in vivo, the importance of the link between alternative splicing and post-translational modifications and may bear on the recent observation that exon 2B skipping can be found in metastatic melanoma.
Collapse
|
5
|
The role of MITF phosphorylation sites during coat color and eye development in mice analyzed by bacterial artificial chromosome transgene rescue. Genetics 2009; 183:581-94. [PMID: 19635938 DOI: 10.1534/genetics.109.103945] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The microphthalmia-associated transcription factor (Mitf) has emerged as an important model for gene regulation in eukaryotic organisms. In vertebrates, it regulates the development of several cell types including melanocytes and has also been shown to play an important role in melanoma. In vitro, the activity of MITF is regulated by multiple signaling pathways, including the KITL/KIT/B-Raf pathway, which results in phosphorylation of MITF on serine residues 73 and 409. However, the precise role of signaling to MITF in vivo remains largely unknown. Here, we use a BAC transgene rescue approach to introduce specific mutations in MITF to study the importance of specific phospho-acceptor sites and protein domains. We show that mice that carry a BAC transgene where single-amino-acid substitutions have been made in the Mitf gene rescue the phenotype of the loss-of-function mutations in Mitf. This may indicate that signaling from KIT to MITF affects other phospho-acceptor sites in MITF or that alternative sites can be phosphorylated when Ser73 and Ser409 have been mutated. Our results have implications for understanding signaling to transcription factors. Furthermore, as MITF and signaling mechanisms have been shown to play an important role in melanomas, our findings may lead to novel insights into this resilient disease.
Collapse
|