title: Signal integration and gene induction by a functionally distinct STAT3 phosphoform.
abstract: Aberrant activation of the ubiquitous transcription factor STAT3 is a major driver of solid tumor progression and pathological angiogenesis. STAT3 activity is regulated by numerous posttranslational modifications (PTMs), including Tyr(705) phosphorylation, which is widely used as an indicator of canonical STAT3 function. Here, we report a noncanonical mechanism of STAT3 activation that occurs independently of Tyr(705) phosphorylation. Using quantitative liquid chromatography-tandem mass spectrometry, we have discovered and characterized a novel STAT3 phosphoform that is simultaneously phosphorylated at Thr(714) and Ser(727) by glycogen synthase kinase 3α and -β (GSK-3α/β). Both Thr(714) and Ser(727) are required for STAT3-dependent gene induction in response to simultaneous activation of epidermal growth factor receptor (EGFR) and protease-activated receptor 1 (PAR-1) in endothelial cells. In this combinatorial signaling context, preventing formation of doubly phosphorylated STAT3 by depleting GSK-3α/β is sufficient to disrupt signal integration and inhibit STAT3-dependent gene expression. Levels of doubly phosphorylated STAT3 but not of Tyr(705)-phosphorylated STAT3 are remarkably elevated in clear-cell renal-cell carcinoma relative to adjacent normal tissue, suggesting that the GSK-3α/β-STAT3 pathway is active in the disease. Collectively, our results describe a functionally distinct, noncanonical STAT3 phosphoform that positively regulates target gene expression in a combinatorial signaling context and identify GSK-3α/β-STAT3 signaling as a potential therapeutic target in renal-cell carcinoma.
authors.affiliation: Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Waitkus
authors.forename: Unni M
authors.initials: UM
authors.lastname: Chandrasekharan
authors.forename: Belinda
authors.initials: B
authors.lastname: Willard
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Tee
authors.forename: Jason K
authors.initials: JK
authors.lastname: Hsieh
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Przybycin
authors.forename: Brian I
authors.initials: BI
authors.lastname: Rini
authors.forename: Paul E
authors.initials: PE
authors.lastname: Dicorleto
mesh_terms: D002292:Carcinoma, Renal Cell / Q000378:metabolism; D002478:Cells, Cultured; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000502:physiology; D066246:ErbB Receptors / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D061307:Human Umbilical Vein Endothelial Cells / Q000378:metabolism; D006801:Humans; D007680:Kidney Neoplasms / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D044463:Receptor, PAR-1 / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000502:physiology*; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D044463:Receptor, PAR-1; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D004815:Epidermal Growth Factor; C512478:EGFR protein, human; D066246:ErbB Receptors; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha