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

Department of Molecular Biology, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.
Journal of Biological Chemistry (Impact Factor: 4.57). 01/2007; 281(52):39891-6. DOI: 10.1074/jbc.M608155200
Source: PubMed


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.

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    • "We found that LPS activated TAK1 and its downstream IKK and p38 in macrophages (Figure 4A, middle 4 lanes), and Tak1 deficiency reduced activation of both IKK and p38 (Figure 4A, left 4 lanes). TAK1 activity was monitored by phosphorylation of Thr 187 (Figure 4A, top panel), which is known to be associated with activation of TAK1 [40] However, non-specific bands were detected around the phosphorylated TAK1 in macrophages protein extracts, which were seen even in unstimulated macrophagse (Figure 4A, asterisks). Thus, we also utilized retardation of TAK1 band on SDS-PAGE to monitor TAK1 activation, which is caused by phosphorylation of several sites associated with TAK1 activation [41], [42]. "
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    • "VopZ might interfere with induction of the TAK1 conformational shift that is thought to enable activating autophosphorylation, either via interacting with a TAB protein or with TAK1 itself. Alternatively, VopZ might increase the activity of a TAK1-associated phosphatase , such as the type 2A protein phosphatase PP6 (Kajino et al., 2006), or possess phosphatase activity itself, although no conserved enzymatic domains were detected. The TAK1- inhibitory activity of VopZ was correlated with punctate localization of VopZ; however, it is currently unclear whether VopZ's localization directly contributes to its activity. "
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    • "ItisthoughtthatdysregulatedandprolongedTGF-b signalingisimplicatedindiseasestates.Inordertoprevent excessiveactionsofTGF-b1,amechanismforefficientdown- regulationofTAK1activitywouldbeimportant.Ingeneral, tightregulationofintracellularsignalingcascadesisaccomplishedbycyclicphosphorylationanddephosphorylation .In thecaseofTAK1inactivation,severalmembersoftheSer/Thr proteinphosphatasefamilyhavebeendemonstratedtonega- tivelyregulateTAK1activity.PP2Ciscapableofbindingand dephosphorylatingTAK1in293cellsundernonstimulated condition[88] [89].AnotherSer/Thrproteinphosphatase familymember,PP6,interactswithandnegativelyregulates IL-1-inducedTAK1in293cells[90]andTNF-a-inducedTAK1 infibroblasts[91]. WehavereportedthatTAK1activationbyTGF-b1in glomerularmesangialcellsisnegativelyregulatedbyanother Ser/Thrproteinphosphatasefamilymember,PP2A[92], whichwaspreviouslyshowntomediateTGF-binhibitionof p70S6kinase(p70S6K)toinducecell-cycleG1arrest[49]. "
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