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Induction of melanocyte-specific microphthalmia-associated transcription factor by Wnt-3a
K Takeda1, K Yasumoto, R Takada
1Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Aoba-ku, Sendai, Miyagi 980-8575, Japan.
Abstract:
Microphthalmia-associated transcription factor (Mitf) plays a critical role in the development of neural crest-derived melanocytes. Here, we show that exogenously added Wnt-3a protein, an intercellular signaling molecule, up-regulates the expression of endogenous melanocyte-specific Mitf (Mitf-M) mRNA in cultured melanocytes. The melanocyte-specific promoter of the human MITF gene (MITF-M promoter) contains a functional LEF-1-binding site, which is bound in vitro by LEF-1 and confers the preferential expression on a reporter gene in melanocytes and melanoma cells, as judged by the transient transfection assays. Moreover, the LEF-1-binding site is required for the transactivation of a reporter gene by LEF-1, beta-catenin, or their combination. Exogenously added Wnt-3a protein also transactivates the MITF-M promoter via the LEF-1-binding site; this activation was abolished when a dominant-negative form of LEF-1 was coexpressed. These results suggest that Wnt-3a signaling recruits beta-catenin and LEF-1 to the LEF-1-binding site of the MITF-M promoter. Therefore, the present study identifies Mitf-M/MITF-M as a direct target of Wnt signaling.
Insights
Wnt signaling activates melanocyte development by up-regulating Microphthalmia-associated transcription factor (Mitf-M). This study reveals Mitf-M is a direct target of Wnt signaling through the LEF-1 binding site on its promoter.
Area of Science:
- Cellular and Molecular Biology
- Developmental Biology
- Signaling Pathways
Background:
- Microphthalmia-associated transcription factor (Mitf) is crucial for melanocyte development.
- Melanocyte-specific Mitf (Mitf-M) expression is regulated by various factors.
Purpose of the Study:
- To investigate the role of Wnt-3a protein in regulating endogenous Mitf-M expression.
- To elucidate the mechanism by which Wnt signaling affects the MITF-M promoter.
Main Methods:
- Cultured melanocytes were treated with Wnt-3a protein.
- Transient transfection assays were used to analyze the MITF-M promoter activity.
- LEF-1 binding site functionality was assessed using reporter gene assays and dominant-negative LEF-1 expression.
Main Results:
- Wnt-3a protein up-regulates endogenous Mitf-M mRNA expression in cultured melanocytes.
- The MITF-M promoter contains a functional LEF-1-binding site that binds LEF-1 in vitro.
- Wnt-3a transactivates the MITF-M promoter via the LEF-1-binding site, dependent on LEF-1 and beta-catenin.
Conclusions:
- Mitf-M is a direct transcriptional target of Wnt signaling.
- Wnt-3a signaling pathway, involving beta-catenin and LEF-1, directly regulates the MITF-M promoter.
- This identifies a key regulatory mechanism in melanocyte development.