title: Phospho-Ser727 of STAT3 regulates STAT3 activity by enhancing dephosphorylation of phospho-Tyr705 largely through TC45.
abstract: Signal transducer and activator of transcription 3 (STAT3) is a latent cytoplasmic transcription factor. It is activated by cytokines, including interleukin-6 (IL-6) through phosphorylation at Tyr705 (pY705), which is required for its dimerization and nuclear translocation. However, the role of Ser727 phosphorylation, occurring during activation, remains poorly understood. Using a combination of HepG2-stat3-knockdown cells reconstituted with various STAT3 mutants and protein kinase inhibitors, we showed that phospho-S727 has an intrinsic mechanism for shortening the duration of STAT3 activity, in turn shortening the duration of socs3 mRNA expression. Both STAT3WT and STAT3Ser727Asp (S727D) but not STAT3Ser727Ala (S727A) showed rapid dephosphorylation of pY705 after the inhibition of tyrosine kinases. We found that the nuclear TC45 phosphatase is most likely responsible for the phospho-S727-dependent pY705 dephosphorylation because TC45 knockdown caused prolonged pY705 with sustained socs3 mRNA expression in STAT3WT but not in STAT3S727A, and overexpressed TC45 caused rapid dephosphorylation of pY705 in STAT3WT but not in STAT3S727A. We further showed that phospho-S727 did not affect the interaction of TC45 with STAT3, and that a reported methylation at K140 of STAT3 occurring after phospho-S727 was not involved in the pY705 regulation. These findings indicate that phospho-Ser727 determines the duration of STAT3 activity largely through TC45.
authors.affiliation: Department of Immunology, Graduate School of Medicine, Osaka City University, Osaka 545-8585, Japan.
authors.forename: Ryohei
authors.initials: R
authors.lastname: Wakahara
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kunimoto
authors.forename: Kanae
authors.initials: K
authors.lastname: Tanino
authors.forename: Hirotada
authors.initials: H
authors.lastname: Kojima
authors.forename: Akira
authors.initials: A
authors.lastname: Inoue
authors.forename: Haruo
authors.initials: H
authors.lastname: Shintaku
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakajima
mesh_terms: D004257:DNA Polymerase II / Q000378:metabolism; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D056945:Hep G2 Cells; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2 / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics
chemical_list: D012333:RNA, Messenger; C106644:SOCS3 protein, human; D050796:STAT3 Transcription Factor; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D012694:Serine; D004257:DNA Polymerase II; D054578:Protein Tyrosine Phosphatase, Non-Receptor Type 2