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Molecular and Cellular Biology, October 2004, p. 9165-9175, Vol. 24, No. 20
0270-7306/04/$08.00+0     DOI: 10.1128/MCB.24.20.9165-9175.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Germinal Center Kinase Is Required for Optimal Jun N-Terminal Kinase Activation by Toll-Like Receptor Agonists and Is Regulated by the Ubiquitin Proteasome System and Agonist-Induced, TRAF6-Dependent Stabilization{dagger}

Jian Zhong and John M. Kyriakis*

Molecular Cardiology Research Institute and Department of Medicine, Tufts-New England Medical Center, and Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts

Received 16 April 2004/ Returned for modification 21 May 2004/ Accepted 23 July 2004

Germinal center kinase (GCK), a member of the Ste20 family, selectively activates the Jun N-terminal kinase (JNK) group of mitogen-activated protein kinases. Here, we show that endogenous GCK is activated by polyinosine-polycytidine [poly(IC)] and lipopolysaccharides (LPS), lipid A, interleukin-1 (IL-1), and engagement of CD40, all agonists that require TRAF6 for JNK activation. RNA interference experiments indicate that GCK is required for the maximal activation of JNK by LPS, lipid A, poly(IC), and, to a lesser extent, IL-1 and engagement of CD40. GCK is ubiquitinated in situ and stabilized by inhibitors of the proteasome, indicating that GCK is subject to proteasomal turnover. GCK is constitutively active, and the kinase activity of GCK is required for GCK ubiquitination. Agonist activation of GCK involves the TRAF6-dependent transient stabilization of the GCK polypeptide rather than an increase in intrinsic kinase activity. Our results identify a physiologic function and unexpected mode of regulation for GCK.


* Corresponding author. Mailing address: Molecular Cardiology Research Institute Tufts-New England Medical Center, 750 Washington St., Box 8486, Boston, MA 02111. Phone: (617) 636-5190. Fax: (617) 636-5204. E-mail: jkyriakis{at}tufts-nemc.org.

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


Molecular and Cellular Biology, October 2004, p. 9165-9175, Vol. 24, No. 20
0022-538X/04/$08.00+0     DOI: 10.1128/MCB.24.20.9165-9175.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.




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