A Regulatory Circuit Mediating Convergence between Nurr1 Transcriptional Regulation and Wnt Signaling

Abstract

The orphan nuclear receptor Nurr1 is essential for the development and maintenance of midbrain dopaminergic neurons, the cells that degenerate during Parkinson's disease, by promoting the transcription of genes involved in dopaminergic neurotransmission. Since Nurr1 lacks a classical ligand-binding pocket, it is not clear which factors regulate its activity and how these factors are affected during disease pathogenesis. Since Wnt signaling via β-catenin promotes the differentiation of Nurr1⁺ dopaminergic precursors in vitro, we tested for functional interactions between these systems. We found that β-catenin and Nurr1 functionally interact at multiple levels. In the absence of β-catenin, Nurr1 is associated with Lef-1 in corepressor complexes. β-Catenin binds Nurr1 and disrupts these corepressor complexes, leading to coactivator recruitment and induction of Wnt- and Nurr1-responsive genes. We then identified KCNIP4/calsenilin-like protein as being responsive to concurrent activation by Nurr1 and β-catenin. Since KCNIP4 interacts with presenilins, the Alzheimer's disease-associated proteins that promote β-catenin degradation, we tested the possibility that KCNIP4 induction regulates β-catenin signaling. KCNIP4 induction limited β-catenin activity in a presenilin-dependent manner, thereby serving as a negative feedback loop; furthermore, Nurr1 inhibition of β-catenin activity was absent in PS1^−/− cells or in the presence of small interfering RNAs specific to KCNIP4. These data describe regulatory convergence between Nurr1 and β-catenin, providing a mechanism by which Nurr1 could be regulated by Wnt signaling.

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A Regulatory Circuit Mediating Convergence between Nurr1 Transcriptional Regulation and Wnt Signaling

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We thank T. Iwatsubo for the kind gift of KCNIP4 antibodies, Ung-il Chung for technical support with handling retrovirus, and J. Yanagisawa for critical reading of the manuscript. We also thank H. Higuchi and Y. Nagasawa for manuscript preparation.

This work was partially supported by the 19th Research Fellowship from the Naito Memorial Foundation (2003) and by a research fellowship from the Uehara Memorial Foundation (2004).