title: Hyperosmotic stress sustains cytokine-stimulated phosphorylation of STAT3, but slows its nuclear trafficking and impairs STAT3-dependent transcription.
abstract: Persistent STAT3 phosphorylation and nuclear retention are hallmarks of a range of pathologies suggesting the importance of STAT3 transcriptional responses in disease progression. Since hyperosmotic stress (HOS) is a hallmark of diseases such as diabetes and asthma, we analysed the impact of HOS on cytokine-stimulated STAT3 signalling. In contrast to transient STAT3 Y705 and S727 phosphorylation in murine embryonic fibroblasts (MEFs) stimulated by the interleukin-6 family cytokine, leukemia inhibitory factor (LIF), under non-stress conditions, HOS induced by sorbitol treatment increased STAT3 S727 but not Y705 phosphorylation. Strikingly, combined LIF+HOS treatment stimulated persistent STAT3 Y705 and S727 phosphorylation and nuclear localisation, but STAT3 nuclear accumulation was slowed during HOS, likely reflecting the mislocalisation of Ran and importin-α3 during HOS that also reduced the nuclear localisation of classical importin-α/β-recognised nuclear import cargoes. Strikingly, combined LIF+HOS exposure, even though stimulating STAT3 phosphorylation and nuclear accumulation did not elicit a transcriptional output, as demonstrated by qPCR analyses of its target genes SOCS3 and c-Fos. Our analysis thus shows for the first time that HOS can disconnect nuclear, phosphorylated STAT3 from transcriptional outcomes, and emphasizes the importance of assessing STAT3 target gene changes in addition to STAT3 phosphorylation status and localisation.
authors.affiliation: Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia; Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia.
authors.forename: Ivan H W
authors.initials: IH
authors.lastname: Ng
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Victoria 3800, Australia. Electronic address: david.jans@monash.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Jans
authors.affiliation: Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia. Electronic address: marieb@unimelb.edu.au.
authors.forename: Marie A
authors.initials: MA
authors.lastname: Bogoyevitch
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology; D053612:Janus Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D053605:Leukemia Inhibitory Factor / Q000494:pharmacology*; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D013012:Sorbitol / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects*; D028901:alpha Karyopherins / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000378:metabolism
chemical_list: D007211:Indoles; D053605:Leukemia Inhibitory Factor; C102460:Ran protein, mouse; D050796:STAT3 Transcription Factor; C416927:SU 6656; D013449:Sulfonamides; D028901:alpha Karyopherins; D013012:Sorbitol; D053612:Janus Kinases; D020931:ran GTP-Binding Protein
keywords: Cytokines; Hyperosmotic stress; Nuclear transport; STAT3; Transcription