title: Cytokine signaling: STATS in plasma membrane rafts.
abstract: STAT transcription factors signal from the plasma membrane to the nucleus in response to growth factors and cytokines. We have investigated whether plasma membrane "rafts" are involved in cytokine-activated STAT signaling. Cytokine-free human hepatoma Hep3B cells or cells treated with interleukin-6 (IL-6) or orthovanadate (a general activator of STATs) were fractionated, and plasma membrane raft fractions were obtained by equilibrium sedimentation or flotation through discontinuous sucrose gradients using either non-detergent or detergent-based (saponin or Triton X-100) methods. By Western blotting the plasma membrane raft fractions obtained using either non-detergent or detergent-based methods contained significant amounts of STAT1 and STAT3 (up to approximately 10% of the total cytoplasmic amount) as well as the integral raft proteins caveolin-1 and flotillin-1, the IL-6-receptor signal transducing chain gp130, the interferon-gamma receptor alpha chain (IFN-gammaRalpha), and the chaperone glucose-regulated protein 58 (GRP58/ER-60/ERp57). Upon activation of signaling by IL-6 or orthovanadate the respective Tyr-phosphorylated STAT species were now also observed in the membrane raft fraction but in a form deficient in DNA binding. The data show pre-association of STATs with plasma membrane rafts in flotation fractions, which also contained caveolin-1 and flotillin-1, and suggest that Tyr phosphorylation may not in itself be sufficient to cause the departure of PY-STATs from plasma membrane rafts. Methyl-beta-cyclodextrin, which sequesters cholesterol and disrupts plasma membrane rafts, markedly inhibited IL-6- and IFN-gamma-induced STAT signaling. Signaling through specialized raft microdomains may be a general mechanism operating at the level of the plasma membrane through which cytokines and growth factors activate STAT species (the "raft-STAT signaling hypothesis").
authors.affiliation: Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York 10595, USA. pravin_sehgal@nymc.edu
authors.forename: Pravin B
authors.initials: PB
authors.lastname: Sehgal
authors.forename: Gary G
authors.initials: GG
authors.lastname: Guo
authors.forename: Mehul
authors.initials: M
authors.lastname: Shah
authors.forename: Vinita
authors.initials: V
authors.lastname: Kumar
authors.forename: Kirit
authors.initials: K
authors.lastname: Patel
mesh_terms: D015153:Blotting, Western; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D003505:Cyclodextrins / Q000378:metabolism / Q000494:pharmacology; D016207:Cytokines / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism / Q000494:pharmacology; D021962:Membrane Microdomains / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D017830:Octoxynol / Q000494:pharmacology; D010766:Phosphorylation; D011485:Protein Binding; D017471:Receptors, Interferon / Q000378:metabolism; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology; D047392:beta-Cyclodextrins; D000096743:Interferon gamma Receptor
chemical_list: D051242:Caveolin 1; D022461:Caveolins; D002784:Cholesterol; D003505:Cyclodextrins; D016207:Cytokines; D004247:DNA; D004268:DNA-Binding Proteins; D003902:Detergents; D005947:Glucose; D007371:Interferon-gamma; D015850:Interleukin-6; D008565:Membrane Proteins; D017830:Octoxynol; D017471:Receptors, Interferon; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; D014443:Tyrosine; D014638:Vanadates; D047392:beta-Cyclodextrins; D000096743:Interferon gamma Receptor; C495540:CAV1 protein, human; C494079:STAT1 protein, human; C494086:STAT3 protein, human; C106354:flotillins; C108732:methyl-beta-cyclodextrin