title: Protein phosphatase 2A is a negative regulator of transforming growth factor-beta1-induced TAK1 activation in mesangial cells.
abstract: TAK1 (transforming growth factor (TGF)-beta-activated kinase 1) is a serine/threonine kinase that is rapidly activated by TGF-beta1 and plays a vital function in its signal transduction. Once TAK1 is activated, efficient down-regulation of TAK1 activity is important to prevent excessive TGF-beta1 responses. The regulatory mechanism of TAK1 inactivation following TGF-beta1 stimulation has not been elucidated. Here we demonstrate that protein phosphatase 2A (PP2A) plays a pivotal role as a negative regulator of TAK1 activation in response to TGF-beta1 in mesangial cells. Treatment with okadaic acid (OA) induces autophosphorylation of Thr-187 in the activation loop of TAK1. In vitro dephosphorylation assay suggests that Thr-187 in TAK1 is a major dephosphorylation target of PP2A. TGF-beta1 stimulation rapidly activates TAK1 in a biphasic manner, indicating that TGF-beta1-induced TAK1 activation is tightly regulated. The association of PP2A(C) with TAK1 is enhanced in response to TGF-beta1 stimulation and closely parallels TGF-beta1-induced TAK1 activity. Attenuation of PP2A activity by OA treatment or targeted knockdown of PP2A(C) with small interfering RNA enhances TGF-beta1-induced phosphorylation of TAK1 at Thr-187 and MKK3 (MAPK kinase 3). Endogenous TAK1 co-precipitates with PP2A(C) but not PP6(C), another OA-sensitive protein phosphatase, and knockdown of PP6(C) by small interfering RNA does not affect TGF-beta1-induced phosphorylation of TAK1 at Thr-187 and MKK3. Moreover, ectopic expression of phosphatase-deficient PP2A(C) enhances TAK1-mediated MKK3 phosphorylation by TGF-beta1 stimulation, whereas the expression of wild-type PP2A(C) suppresses the MKK3 phosphorylation. Taken together, our data indicate that PP2A functions as a negative regulator in TGF-beta1-induced TAK1 activation.
authors.affiliation: Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Sung Il
authors.initials: SI
authors.lastname: Kim
authors.forename: Joon Hyeok
authors.initials: JH
authors.lastname: Kwak
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.forename: Mary E
authors.initials: ME
authors.lastname: Choi
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D008297:Male; D050527:Mesangial Cells / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000378:metabolism; D013912:Threonine / Q000737:chemistry; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D000099151:MAP Kinase Kinase Kinase 7
chemical_list: D020930:MAP Kinase Kinase Kinases; D054648:Protein Phosphatase 2; D034741:RNA, Small Interfering; D013912:Threonine; D053773:Transforming Growth Factor beta1; D000099151:MAP Kinase Kinase Kinase 7