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Molecular and Cellular Biology, December 2007, p. 8296-8305, Vol. 27, No. 23
0270-7306/07/$08.00+0     doi:10.1128/MCB.00598-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

RACK1 Targets the Extracellular Signal-Regulated Kinase/Mitogen-Activated Protein Kinase Pathway To Link Integrin Engagement with Focal Adhesion Disassembly and Cell Motility ^,

Tomas Vomastek,^1,2 Marcin P. Iwanicki,¹ Hans-Joerg Schaeffer,^1, Adel Tarcsafalvi,¹ J. Thomas Parsons,¹ and Michael J. Weber^1*

Department of Microbiology and Cancer Center, University of Virginia Health System, Charlottesville, Virginia 22908,¹ Cell and Molecular Microbiology Division, Institute of Microbiology, Prague, Czech Republic²

Received 5 April 2007/ Returned for modification 11 May 2007/ Accepted 14 September 2007

The extracellular signal-regulated kinase (ERK) cascade is activated in response to a multitude of extracellular signals and converts these signals into a variety of specific biological responses, including cell differentiation, cell movement, cell division, and apoptosis. The specificity of the biological response is likely to be controlled in large measure by the localization of signaling, thus enabling ERK activity to be directed towards specific targets. Here we show that the RACK1 scaffold protein functions specifically in integrin-mediated activation of the mitogen-activated protein kinase/ERK cascade and targets active ERK to focal adhesions. We found that RACK1 associated with the core kinases of the ERK pathway, Raf, MEK, and ERK, and that attenuation of RACK1 expression resulted in a decrease in ERK activity in response to adhesion but not in response to growth factors. RACK1 silencing also caused a reduction of active ERK in focal adhesions, an increase in focal adhesion length, a decreased rate of focal adhesion disassembly, and decreased motility. Our data further suggest that focal adhesion kinase is an upstream activator of the RACK1/ERK pathway. We suggest that RACK1 tethers the ERK pathway core kinases and channels signals from upstream activation by integrins to downstream targets at focal adhesions.

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

Published ahead of print on 1 October 2007.

Present address: Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Munich, Germany.

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