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.

Extracellular UDP-Glucose Activates P2Y14 Receptor and Induces Signal Transducer and Activator of Transcription 3 (STAT3) Tyr705 Phosphorylation and Binding to Hyaluronan Synthase 2 (HAS2) Promoter, Stimulating Hyaluronan Synthesis of Keratinocytes

“…It has been reported to promote the transcriptional activity of STAT3 by recruiting coactivators (53-55). On the other hand, it may enhance Tyr 705 dephosphorylation, and thereby inhibit transcription (56). The reciprocal changes we found in Tyr 705 and Ser 727 phosphorylations of STAT3 are in line with the latter report, supporting the role of Tyr 705 as an activating modification (56).…”

“…On the other hand, it may enhance Tyr 705 dephosphorylation, and thereby inhibit transcription (56). The reciprocal changes we found in Tyr 705 and Ser 727 phosphorylations of STAT3 are in line with the latter report, supporting the role of Tyr 705 as an activating modification (56). Of course, the function of Ser 727 phosphorylation may depend on the specific gene and cell type.…”

Erk1/2 activation and modulation of STAT3 signaling in oral cancer

“…Similarly, Decker and Kovarik proposed that STAT3 phosphorylation on Ser727 either inhibits tyrosine phosphorylation or increases tyrosine dephosphorylation (9). A negative relationship between STAT3 serine and tyrosine phosphorylation has also been suggested by venkatasubbarao et al (10) and Wakahara et al (63), who described that phospho-Ser727 determines the duration of STAT3 activity by enhancing dephosphorylation of phosphoTyr705 largely through TC45 phosphatase.…”

Interleukin 18 activates MAPKs and STAT3 but not NF-κB in hippocampal HT-22 cells

“…Phosphorylation on Tyr705 has been considered as the most important event that activates STAT3 and results in DNA binding and gene expression regulation. However, another phosphorylation site in Ser727 has been described for STAT3 and the most recent finding reported that it regulated negatively the duration of STAT3 activity in HepG2 cell line (Wakahara et al, 2012). We found decreased levels of P-STAT3 (Ser727)\ STAT3 specifically in the nucleus of HT-22 cells treated with mrIL-18 compared to vehicle exposed cells.…”