Targeting of p38 Mitogen-Activated Protein Kinases to MEF2 Transcription Factors

Abstract

Mitogen-activated protein (MAP) kinase-mediated signalling to the nucleus is an important event in the conversion of extracellular signals into a cellular response. However, the existence of multiple MAP kinases which phosphorylate similar phosphoacceptor motifs poses a problem in maintaining substrate specificity and hence the correct biological response. Both the extracellular signal-regulated kinase (ERK) and c-Jun NH₂-terminal kinase (JNK) subfamilies of MAP kinases use a second specificity determinant and require docking to their transcription factor substrates to achieve maximal substrate activation. In this study, we demonstrate that among the different MAP kinases, the MADS-box transcription factors MEF2A and MEF2C are preferentially phosphorylated and activated by the p38 subfamily members p38α and p38β₂. The efficiency of phosphorylation in vitro and transcriptional activation in vivo of MEF2A and MEF2C by these p38 subtypes requires the presence of a kinase docking domain (D-domain). Furthermore, the D-domain from MEF2A is sufficient to confer p38 responsiveness on different transcription factors, and reciprocal effects are observed upon the introduction of alternative D-domains into MEF2A. These results therefore contribute to our understanding of signalling to MEF2 transcription factors and demonstrate that the requirement for substrate binding by MAP kinases is an important facet of three different subclasses of MAP kinases (ERK, JNK, and p38).

ACKNOWLEDGMENTS

We thank Margaret Bell and Katherine Stewart for excellent technical and secretarial assistance and Bob Liddell for DNA sequencing. We are grateful to John McDermott, Alan Whitmarsh, and members of our laboratories for comments on the manuscript and for stimulating discussions and to Nic Jones and John McDermott for communicating data prior to publication. We also thank Adam West for help with the inception of this project and Fei-Ling Lim for constructing some of the intermediate plasmids. We are grateful to Stuart Lipton, Richard Treisman, Alan Whitmarsh, and Roger Davis for providing reagents and to Simon Ridley for helpful advice about p38 activation.

This work was supported by the North of England Cancer Research Campaign, the Cancer Research Campaign (CRC), the Wellcome Trust, and a Jeffcock Ph.D. studentship from the University of Newcastle Upon Tyne to A.G. A.D.S. is a Research Fellow of the Lister Institute of Preventative Medicine.