Differential regulation of IκB kinase α and β by two upstream kinases, NF-κB-inducing kinase and mitogen-activated protein kinase/ERK kinase kinase-1

Differential regulation of IκB kinase α and β by two upstream kinases, NF-κB-inducing kinase and mitogen-activated protein kinase/ERK kinase kinase-1

^*Department of Immunology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113, Japan; ^†Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, 2-3 Surugadai, Kanda, Chiyoda-ku, Tokyo 101, Japan; and ^¶Department of Dermatology, Faculty of Medicine, Tottori University, 86 Nishi-machi, Yonago, Tottori 683, Japan

Communicated by Leonard A. Herzenberg, Stanford University School of Medicine, Stanford, CA (received for review December 17, 1997)

Abstract

NF-κB is activated by various stimuli including inflammatory cytokines and stresses. A key step in the activation of NF-κB is the phosphorylation of its inhibitors, IκBs, by an IκB kinase (IKK) complex. Recently, two closely related kinases, designated IKKα and IKKβ, have been identified to be the components of the IKK complex that phosphorylate critical serine residues of IκBs for degradation. A previously identified NF-κB-inducing kinase (NIK), which mediates NF-κB activation by TNFα and IL-1, has been demonstrated to activate IKKα. Previous studies showed that mitogen-activated protein kinase/ERK kinase kinase-1 (MEKK1), which constitutes the c-Jun N-terminal kinase/stress-activated protein kinase pathway, also activates NF-κB by an undefined mechanism. Here, we show that overexpression of MEKK1 preferentially stimulates the kinase activity of IKKβ, which resulted in phosphorylation of IκBs. Moreover, a catalytically inactive mutant of IKKβ blocked the MEKK1-induced NF-κB activation. By contrast, overexpression of NIK stimulates kinase activities of both IKKα and IKKβ comparably, suggesting a qualitative difference between NIK- and MEKK1-mediated NF-κB activation pathways. Collectively, these results indicate that NIK and MEKK1 independently activate the IKK complex and that the kinase activities of IKKα and IKKβ are differentially regulated by two upstream kinases, NIK and MEKK1, which are responsive to distinct stimuli.

Footnotes

↵ ‡ H.N. and M.S. contributed equally to this work.
↵ § To whom reprint requests should be addressed. e-mail: hnakano{at}med.juntendo.ac.jp.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. AF026524).
ABBREVIATIONS:

GST,

glutathione S-transferase;

HA,

hemagglutinin;

IKK,

IκB kinase;

IL,

interleukin;

JNK,

c-Jun N-terminal kinase;

MAPKKK,

MAP kinase kinase kinase;

MEKK1,

mitogen-activated protein kinase/ERK kinase kinase-1;

NIK,

NF-κB-inducing kinase;

SAPK,

stress-activated protein kinase;

TNF,

tumor necrosis factor;

TRAF,

tumor necrosis factor receptor-associated factor