Protein Phosphatase 6 Down-regulates TAK1 Kinase Activation in the IL-1 Signaling Pathway

Hong Ren,Taisuke Kajino,Jun Ninomiya-Tsuji,Tohru Natsume,David L. Brautigan,Kunihiro Matsumoto,Bjarki Stefansson,Shun-ichiro Iemura

doi:10.1074/jbc.m608155200

Abstract

TAK1 (transforming growth factor beta-activated kinase 1) is a serine/threonine kinase that is a mitogen-activated protein kinase kinase kinase and an essential intracellular signaling component in inflammatory signaling pathways. Upon stimulation of cells with inflammatory cytokines, TAK1 binds proteins that stimulate autophosphorylation within its activation loop and is thereby catalytically activated. This activation is transient; it peaks within a couple of minutes and is subsequently down-regulated rapidly to basal levels. The mechanism of down-regulation of TAK1 has not yet been elucidated. In this study, we found that toxin inhibition of type 2A protein phosphatases greatly enhances interleukin 1 (IL-1)-dependent phosphorylation of Thr-187 in the TAK1 activation loop as well as the catalytic activity of TAK1. From proteomic analysis of TAK1-binding proteins, we identified protein phosphatase 6 (PP6), a type-2A phosphatase, and demonstrated that PP6 associated with and inactivated TAK1 by dephosphorylation of Thr-187. Ectopic and endogenous PP6 co-precipitated with TAK1, and expression of PP6 reduced IL-1 activation of TAK1 but did not affect osmotic activation of MLK3, another MAPKKK. Reduction of PP6 expression by small interfering RNA enhances IL-1-induced phosphorylation of Thr-187 in TAK1. Enhancement occurred without change in levels of PP2A showing specificity for PP6. Our results demonstrate that PP6 specifically down-regulates TAK1 through dephosphorylation of Thr-187 in the activation loop, which is likely important for suppressing inflammatory responses via TAK1 signaling pathways.

Highlights

TAK12 is a member of the mitogen-activated protein kinase kinase kinase (MAPKKK) family and is activated by transforming growth factor ␤ and by proinflammatory cytokines including interleukin-1 (IL-1) and tumor necrosis factor [1,2,3]
Inhibition of Type 2A Phosphatase Activity Increases IL-1induced Phosphorylation of TAK1—TAK1 is activated through its autophosphorylation within the activation loop induced by binding of proteins such as TAB1, TAB2, and tumor necrosis factor receptor-associated factor (TRAF) and is rapidly down-regulated [8, 22, 23]
To further address which protein phosphatases reverse stimuliinduced TAK1 activation, we examined the effects of protein phosphatase inhibitors on IL-1-induced TAK1 phosphorylation

Summary

Introduction

TAK12 (transforming growth factor ␤-activated kinase 1) is a member of the mitogen-activated protein kinase kinase kinase (MAPKKK) family and is activated by transforming growth factor ␤ and by proinflammatory cytokines including interleukin-1 (IL-1) and tumor necrosis factor [1,2,3]. Catalytic activity of TAK1 is required for this phosphorylation, suggesting that TAK1 autophosphorylates its activation loop. TAK1 autophosphorylation is induced presumably through the conformational change due to assembly of the signaling complex, which converts TAK1 into a catalytically active form. TAK1 activity is known to be regulated by protein phosphatase PP2C family members in the unstimulated state [24, 25].

Results

Conclusion