The Noncatalytic Amino Terminus of Mitogen-Activated Protein Kinase Phosphatase 1 Directs Nuclear Targeting and Serum Response Element Transcriptional Regulation

Abstract

The mitogen-activated protein kinase (MAPK) phosphatase 1 (MKP-1) is an immediate-early gene comprised of a dual-specificity phosphatase domain and a noncatalytic NH₂ terminus. Here, we show that the NH₂ terminus of MKP-1, containing the cdc25 homology domains A (CH2A) and B (CH2B), mediates MKP-1 nuclear targeting and modulates MAPK-mediated gene expression. An LXXLL motif which is known to mediate protein-protein interactions with nuclear-targeted hormone receptors was identified proximal to the CH2A domain of MKP-1. The NH₂ terminus alone of MKP-1 containing this LXXLL motif was sufficient to direct nuclear targeting, and mutating this motif to LXXAA resulted in the exclusion of MKP-1 from the nucleus. We found that the LXXLL motif proximal to the CH2A domain was present in other nuclear-localized MKPs but was absent in MKPs that localized to the cytoplasm. These data suggest that this LXXLL motif confers nuclear targeting properties to the MKPs. The NH₂ terminus of MKP-1 was also found to inhibit the activation of the serum response element (SRE) by preventing MAPK-mediated phosphorylation of the regulatory serine 383 residue on Elk-1. Moreover, we show that MKP-1 plays a major role in the attenuation of serum-induced SRE activity, since MKP-1 null fibroblasts exhibited enhanced SRE activity in response to serum compared with wild-type fibroblasts. The NH₂ terminus of MKP-1, when reconstituted into MKP-1 null fibroblasts to levels similar to endogenous MKP-1 following serum stimulation, reduced serum-mediated SRE activity. Collectively, these data reveal novel roles for the NH₂ terminus of MKP-1 in nuclear targeting and transcriptional regulation.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/.

ACKNOWLEDGMENTS

We thank members of the Bennett lab for comments and helpful discussions during the course of this study. We also thank Michael Nathanson and Barbara Ehrlich for their helpful discussions and review of this work. We are grateful to Thomas Hughes for providing the pWay21 plasmid and Andrew Sharrocks for the Elk-1 reagents.

This work was supported by a Burroughs Wellcome Foundation New Investigators Award and NIH grant and P01-DK-57751 to A.M.B.