Letters to Nature
Nature 401, 173-177 (9 September 1999) | doi:10.1038/43686; Received 8 April 1999; Accepted 8 July 1999
Suppression of Raf-1 kinase activity and MAP kinase signalling by RKIP
Kam Yeung1,2, Thomas Seitz1,2, Shengfeng Li4, Petra Janosch, Brian McFerran, Christian Kaiser3, Frances Fee, Kostas D. Katsanakis, David W. Rose6, Harald Mischak7, John M. Sedivy1,2 and Walter Kolch2
- Brown University, Department of Molecular Biology, Cell Biology and Biochemistry, Richmond 02912, USA
- GSF-Research Centre for Health and Environment, Institute for Clinical Molecular Biology, Marchioninstrasse 25, 81377 München, Germany
- Beatson Institute for Cancer Research, CRC Beatson Laboratories, Switchback Road, Bearsdon, Glasgow G61 1BD, UK
- University of California San Diego, Department of Medicine and Whittier Diabetes Program, 9500 Gilman Drive, La Jolla, California, 92093-0673, USA
- Franz-Volhard Klinikum, Max Delbrück Centre, Wiltbergstrasse 50, 13122 Berlin, Germany
- These authors contributed equally to this work
- Present address: Cor Therapeutics Inc., South San Francisco, California 94080, USA.
Correspondence to: John M. Sedivy1,2Walter Kolch2 Correspondence and requests for materials should be addressed to W.K. (e-mail: Email: wkolch@beatson.gla.ac.uk) or J.M.S. (e-mail: Email: john_sedivy@brown.edu).
Raf-1 phosphorylates and activates MEK-1, a kinase that activates the extracellular signal regulated kinases (ERK). This kinase cascade controls the proliferation and differentiation of different cell types1, 2. Here we describe a Raf-1-interacting protein, isolated using a yeast two-hybrid screen. This protein inhibits the phosphorylation and activation of MEK by Raf-1 and is designated RKIP (Raf kinase inhibitor protein). In vitro, RKIP binds to Raf-1, MEK and ERK, but not to Ras. RKIP co-immunoprecipitates with Raf-1 and MEK from cell lysates and colocalizes with Raf-1 when examined by confocal microscopy. RKIP is not a substrate for Raf-1 or MEK, but competitively disrupts the interaction between these kinases. RKIP overexpression interferes with the activation of MEK and ERK, induction of AP-1-dependent reporter genes and transformation elicited by an oncogenically activated Raf-1 kinase. Downregulation of endogenous RKIP by expression of antisense RNA or antibody microinjection induces the activation of MEK-, ERK- and AP-1-dependent transcription. RKIP represents a new class of protein-kinase-inhibitor protein that regulates the activity of the Raf/MEK/ERK module.