title: Interactions of STAT3 with caveolin-1 and heat shock protein 90 in plasma membrane raft and cytosolic complexes. Preservation of cytokine signaling during fever.
abstract: Interleukin-6 (IL-6) initiates STAT3 signaling in plasma membrane rafts with the subsequent transit of Tyr-phosphorylated STAT3 (PY-STAT3) through the cytoplasmic compartment to the nucleus in association with accessory proteins. We initially identified caveolin-1 (cav-1) as a candidate STAT3-associated accessory protein due to its co-localization with STAT3 and PY-STAT3 in flotation raft fractions, and heat shock protein 90 (HSP90) due to its inclusion in cytosolic STAT3-containing 200-400-kDa complexes. Subsequent immunomagnetic bead pullout assays showed that STAT3, PY-STAT3, cav-1, and HSP90 interacted in plasma membrane and cytoplasmic complexes derived from uninduced and stimulated Hep3B cells. This was a general property of STAT3 in that these interactions were also observed in alveolar epithelial type II-like cells, lung fibroblasts, and pulmonary arterial endothelial cells. Exposure of Hep3B cells to the raft disrupter methyl-beta-cyclodextrin for 1-10 min followed by IL-6 stimulation for 15 min preferentially inhibited the appearance of PY-STAT3 in the cav-1-enriched sedimentable cytoplasmic fraction, suggesting that these complexes may represent a trafficking intermediate immediately downstream from the raft. Because IL-6 is known to function in the body in the context of fever, the possibility that HSP90 may help preserve IL-6-induced STAT3 signaling at elevated temperature was investigated. Geldanamycin, an HSP90 inhibitor, markedly inhibited IL-6-stimulated STAT3 signaling in Hep3B hepatocytes cultured overnight at 39.5 degrees C as evaluated by DNA-shift assays, trafficking of PY-STAT3 to the nucleus, cross-precipitation of HSP90 by anti-STAT3 polyclonal antibody, and reporter/luciferase construct experiments. Taken together, the data show that IL-6/raft/STAT3 signaling is a chaperoned pathway that involves cav-1 and HSP90 as accessory proteins and suggest a mechanism for the preservation of this signaling during fever.
authors.affiliation: Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595, USA.
authors.forename: Mehul
authors.initials: M
authors.lastname: Shah
authors.forename: Kirit
authors.initials: K
authors.lastname: Patel
authors.forename: Victor A
authors.initials: VA
authors.lastname: Fried
authors.forename: Pravin B
authors.initials: PB
authors.lastname: Sehgal
mesh_terms: D000818:Animals; D016227:Benzoquinones; D002417:Cattle; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003505:Cyclodextrins / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D005372:Filipin / Q000378:metabolism; D017930:Genes, Reporter; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D007535:Isomerases / Q000378:metabolism; D047029:Lactams, Macrocyclic; D046911:Macromolecular Substances; D021962:Membrane Microdomains / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D019704:Protein Disulfide-Isomerases; D021381:Protein Transport / Q000502:physiology*; D011809:Quinones / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism; D047392:beta-Cyclodextrins
chemical_list: D016227:Benzoquinones; C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D003505:Cyclodextrins; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D015850:Interleukin-6; D047029:Lactams, Macrocyclic; D046911:Macromolecular Substances; D018832:Molecular Chaperones; D011809:Quinones; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D014443:Tyrosine; D007371:Interferon-gamma; D005372:Filipin; D007535:Isomerases; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human; C001277:geldanamycin