Canonical and Kinase Activity-Independent Mechanisms for Extracellular Signal-Regulated Kinase 5 (ERK5) Nuclear Translocation Require Dissociation of Hsp90 from the ERK5-Cdc37 Complex

Abstract

The mitogen-activated protein (MAP) kinase extracellular signal-regulated kinase 5 (ERK5) plays a crucial role in cell proliferation, regulating gene transcription. ERK5 has a unique C-terminal tail which contains a transcriptional activation domain, and activates transcription by phosphorylating transcription factors and acting itself as a transcriptional coactivator. However, the molecular mechanisms that regulate its nucleocytoplasmatic traffic are unknown. We have used tandem affinity purification to identify proteins that interact with ERK5. We show that ERK5 interacts with the Hsp90-Cdc37 chaperone in resting cells, and that inhibition of Hsp90 or Cdc37 results in ERK5 ubiquitylation and proteasomal degradation. Interestingly, activation of cellular ERK5 induces Hsp90 dissociation from the ERK5-Cdc37 complex, leading to ERK5 nuclear translocation and activation of transcription, by a mechanism which requires the autophosphorylation at its C-terminal tail. Consequently, active ERK5 is no longer sensitive to Hsp90 or Cdc37 inhibitors. Cdc37 overexpression also induces Hsp90 dissociation and the nuclear translocation of a kinase-inactive form of ERK5 which retains transcriptional activity. This is the first example showing that ERK5 transcriptional activity does not require kinase activity. Since Cdc37 cooperates with ERK5 to promote cell proliferation, Cdc37 overexpression (as happens in some cancers) might represent a new, noncanonical mechanism by which ERK5 regulates tumor proliferation.

ACKNOWLEDGMENTS

We thank Philip Cohen and Maria Deak (MRC PPU, Dundee, United Kingdom) for ERK5 antibody and the generation of the TAP-tagged ERK5 vectors, respectively. We also thank Nathanael Gray (Dana-Farber Cancer Institute, Boston, MA) for providing us with the ERK5 competitive inhibitor XMD2-98 and Cathy Tournier (The University of Manchester, United Kingdom) for the MEF MEK5^−/− cells. We are grateful to Ana Cuenda for helpful discussions, Cristina Gutierrez for tissue culture assistance, Anna Vilalta for technical support, and Isabelle Gelot for editorial assistance. We are grateful to the Servei de Genòmica from the UAB.

This work was supported by grants from the Spanish Ministerio Educación (BFU2004-00757 and BFU2007-60268).