Functional Interactions of Transforming Growth Factor β-activated Kinase 1 with IκB Kinases to Stimulate NF-κB Activation

Hiroaki Sakurai,Hidetaka Miyoshi,Wataru Toriumi,Takahisa Sugita

doi:10.1074/jbc.274.15.10641

Abstract

Several mitogen-activated protein kinase kinase kinases play critical roles in nuclear factor-kappaB (NF-kappaB) activation. We recently reported that the overexpression of transforming growth factor-beta-activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase family, together with its activator TAK1-binding protein 1 (TAB1) stimulates NF-kappaB activation. Here we investigated the molecular mechanism of TAK1-induced NF-kappaB activation. Dominant negative mutants of IkappaB kinase (IKK) alpha and IKKbeta inhibited TAK1-induced NF-kappaB activation. TAK1 activated IKKalpha and IKKbeta in the presence of TAB1. IKKalpha and IKKbeta were coimmunoprecipitated with TAK1 in the absence of TAB1. TAB1-induced TAK1 activation promoted the dissociation of active forms of IKKalpha and IKKbeta from active TAK1, whereas the IKK mutants remained to interact with active TAK1. Furthermore, tumor necrosis factor-alpha activated endogenous TAK1, and the kinase-negative TAK1 acted as a dominant negative inhibitor against tumor necrosis factor-alpha-induced NF-kappaB activation. These results demonstrated a novel signaling pathway to NF-kappaB activation through TAK1 in which TAK1 may act as a regulatory kinase of IKKs.

Highlights

Transcription factor nuclear factor ␬B (NF-␬B)1 is composed of homodimers and heterodimers of Rel family proteins and plays a pivotal role in the gene expression involved in inflammatory and immune responses [1,2,3]
Transforming growth factor (TGF) ␤-activated kinase 1 (TAK1) was first identified as a mitogen-activated protein kinase kinase kinase (MAPKKK) that can be activated by TGF-␤ and bone morphological protein [26]
A gel shift assay showed that wild-type transforming growth factor-␤-activated kinase 1 (TAK1) together with TAK1-binding protein 1 (TAB1) induced the nuclear translocation of NF-␬B, whereas TAK1K63W could not induce the translocation even when TAB1 was coexpressed (Fig. 1A)

Summary

Introduction

Transcription factor nuclear factor ␬B (NF-␬B) is composed of homodimers and heterodimers of Rel family proteins and plays a pivotal role in the gene expression involved in inflammatory and immune responses [1,2,3]. The phosphorylation of two Ser residues at an N-terminal regulatory domain of I␬B proteins triggers polyubiquitination of I␬B proteins, which targets them for rapid degradation through a proteasome-dependent pathway, thereby releasing NF-␬B to enter the nucleus (9 –15) Diverse extracellular stimuli such as tumor necrosis factor (TNF)-␣ and interleukin-1␤, phorbol esters, and environmental stresses lead to NF-␬B activation utilizing the common mechanism for the I␬B degradation, suggesting the diversity of the upstream signaling pathways for phosphorylation of I␬B proteins. MAPK/extracellular signalregulated kinase kinase kinase 1 (MEKK1), another member of the MAPKKK family, stimulates NF-␬B activation by preferentially activating IKK␤ over IKK␣ [23,24,25] These findings suggest that several MAPKKKs play a key role in the NF-␬B activation pathway by regulating the kinase activity of the IKK complex. In the activation of TAK1induced IKKs, two Ser residues in the activation loop of the IKKs were critically involved

Methods

Results

Conclusion