Phospho-Ser727 of STAT3 regulates STAT3 activity by enhancing dephosphorylation of phospho-Tyr705 largely through TC45
Phospho-Ser727 of STAT3 regulates STAT3 activity by enhancing dephosphorylation of phospho-Tyr705 largely through TC45
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DOI：
10.1111/j.1365-2443.2011.01575.x
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发表时间：
2012-02-01
期刊：
影响因子：
2.1
通讯作者：
Nakajima, Koichi
中科院分区：
文献类型：
--
作者：
Wakahara, Ryohei;Kunimoto, Hiroyuki;Nakajima, Koichi
信号转导子和转录激活子3（STAT 3）是一种潜伏的细胞质转录因子。它通过Tyr 705（pY 705）处的磷酸化被细胞因子（包括白细胞介素-6（IL-6））激活，这是其二聚化和核转位所需的。然而，Ser 727磷酸化的作用，发生在活化过程中，仍然知之甚少。使用用各种STAT 3突变体和蛋白激酶抑制剂重建的HepG 2-stat 3敲除细胞的组合，我们表明磷酸化S727具有缩短STAT 3活性持续时间的内在机制，从而缩短socs 3 mRNA表达的持续时间。STAT 3 WT和STAT 3Ser 727 Asp（S727 D）在抑制酪氨酸激酶后均显示pY 705快速去磷酸化，而STAT 3Ser 727 Ala（S727 A）则没有。我们发现，细胞核中的TC 45磷酸酶很可能是磷酸-S727依赖的pY 705去磷酸化的原因，因为TC 45敲低导致STAT 3 WT中pY 705的持续socs 3 mRNA表达延长，而在STAT 3S 727 A中则没有，并且过表达的TC 45导致STAT 3 WT中pY 705的快速去磷酸化，而在STAT 3S 727 A中则没有。我们进一步表明磷酸化S727不影响TC 45与STAT 3的相互作用，并且在磷酸化S727之后发生的STAT 3的K140处的甲基化不参与pY 705调节。这些发现表明磷酸化Ser 727主要通过TC 45决定STAT 3活性的持续时间。
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.