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Molecular and Cellular Biology, November 2001, p. 7207-7217, Vol. 21, No. 21
Department of Molecular Biology, Cell Biology, and
Biochemistry, Brown University, Providence, Rhode Island
029121; Department of Medicine and
Whittier Diabetes Program, University of California
Received 8 January 2001/Returned for modification 14 March
2001/Accepted 2 August 2001
The Raf kinase inhibitor protein (RKIP) acts as a negative
regulator of the mitogen-activated protein (MAP) kinase (MAPK) cascade
initiated by Raf-1. RKIP inhibits the phosphorylation of
MAP/extracellular signal-regulated kinase 1 (MEK1) by Raf-1 by
disrupting the interaction between these two kinases. We show here that
RKIP also antagonizes the signal transduction pathways that mediate the
activation of the transcription factor nuclear factor kappa B (NF-
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.21.7207-7217.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Raf Kinase Inhibitor Protein Interacts with
NF-
B-Inducing Kinase and TAK1 and Inhibits NF-
B
Activation

San Diego, La
Jolla, California 92093-06732; and
Beatson Institute for Cancer Research, CRC Beatson
Laboratories, Bearsden, Glasgow G61 1BD, United
Kingdom3
B)
in response to stimulation with tumor necrosis factor alpha (TNF-
)
or interleukin 1 beta. Modulation of RKIP expression levels affected
NF-
B signaling independent of the MAPK pathway. Genetic epistasis
analysis involving the ectopic expression of kinases acting in the
NF-
B pathway indicated that RKIP acts upstream of the kinase complex
that mediates the phosphorylation and inactivation of the inhibitor of
NF-
B (I
B). In vitro kinase assays showed that RKIP antagonizes
the activation of the I
B kinase (IKK) activity elicited by TNF-
.
RKIP physically interacted with four kinases of the NF-
B activation
pathway, NF-
B-inducing kinase, transforming growth factor
beta-activated kinase 1, IKK
, and IKK
. This mode of action bears
striking similarities to the interactions of RKIP with Raf-1 and MEK1
in the MAPK pathway. Emerging data from diverse organisms suggest that
RKIP and RKIP-related proteins represent a new and evolutionarily
highly conserved family of protein kinase regulators. Since the MAPK
and NF-
B pathways have physiologically distinct roles, the function
of RKIP may be, in part, to coordinate the regulation of these pathways.
*
Corresponding author. Present address: Medical College
of Ohio, Department of Biochemistry & Molecular Biology, 3035 Arlington Ave., Toledo, OH 43614-5804. Phone: (419) 383-6658. Fax: (419) 383-6228. E-mail: kyeung{at}mco.edu.
Present address: Rhode Island Hospital, Providence, RI 02903.
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