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ERK5 is a novel type of mitogen-activated protein kinase containing a transcriptional activation domain
H G Kasler1, J Victoria, O Duramad
1Cancer Research Lab and Division of Immunology, Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3200, USA.
Abstract:
Previous studies have shown that upregulation of the orphan steroid receptor Nur77 is required for the apoptosis of immature T cells in response to antigen receptor signals. Transcriptional upregulation of Nur77 in response to antigen receptor signaling involves two binding sites for the MEF2 family of transcription factors located in the Nur77 promoter. Calcium signals greatly increase the activity of MEF2D in T cells via a posttranslational mechanism. The mitogen-activated protein (MAP) kinase ERK5 was isolated in a yeast two-hybrid screen using the MADS-MEF2 domain of MEF2D as bait. ERK5 resembles the other MAP kinase family members in its N-terminal half, but it also contains a 400-amino-acid C-terminal domain of previously uncharacterized function. We report here that the C-terminal region of ERK5 contains a MEF2-interacting domain and, surprisingly, also a potent transcriptional activation domain. These domains are both required for coactivation of MEF2D by ERK5. The MEF2-ERK5 interaction was found to be activation dependent in vivo and inhibitable in vitro by the calcium-sensitive MEF2 repressor Cabin 1. The transcriptional activation domain of ERK5 is required for maximal MEF2 activity in response to calcium flux in T cells, and it can activate the endogenous Nur77 gene when constitutively recruited to the Nur77 promoter via MEF2 sites. These studies provide insights into a mechanism whereby MEF2 activity can respond to calcium signaling and suggest a novel, unexpected mechanism of MAP kinase function.
Insights
The orphan steroid receptor Nur77, crucial for T cell apoptosis, is upregulated by MEF2 transcription factors. Mitogen-activated protein kinase ERK5 coactivates MEF2, linking calcium signaling to Nur77 gene activation.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Upregulation of the orphan steroid receptor Nur77 is essential for T cell apoptosis following antigen receptor signaling.
- The Nur77 promoter contains MEF2 transcription factor binding sites, mediating its transcriptional upregulation.
- Calcium signals enhance MEF2D activity in T cells through posttranslational modifications.
Purpose of the Study:
- To investigate the role of mitogen-activated protein kinase (MAP) ERK5 in regulating MEF2 activity and Nur77 expression.
- To elucidate the functional domains within ERK5 and their interaction with MEF2D.
- To understand the mechanism linking calcium signaling to MEF2-mediated gene transcription.
Main Methods:
- Yeast two-hybrid screening to identify MEF2D-interacting proteins.
- Co-immunoprecipitation and in vitro assays to study protein interactions.
- Reporter gene assays to assess transcriptional activation of the Nur77 promoter.
- Analysis of ERK5 C-terminal domain function.
Main Results:
- The C-terminal region of ERK5 possesses a MEF2-interacting domain and a potent transcriptional activation domain.
- ERK5 coactivates MEF2D, with both identified domains being essential for this function.
- The MEF2-ERK5 interaction is activation-dependent in vivo and inhibited by Cabin 1.
- ERK5's transcriptional activation domain is crucial for calcium flux-induced MEF2 activity in T cells, activating the Nur77 gene.
Conclusions:
- Mitogen-activated protein kinase ERK5 plays a novel role in coactivating MEF2 transcription factors.
- ERK5 links calcium signaling pathways to the transcriptional regulation of genes like Nur77.
- These findings reveal an unexpected mechanism of MAP kinase function in cellular responses.