title: Plasma membrane rafts and chaperones in cytokine/STAT signaling.
abstract: We and others have recently obtained data suggesting that cytokine-STAT signaling in many different cell-types is a chaperoned pathway initiated at the level of specialized plasma membrane microdomains called "rafts" (the "raft-STAT signaling hypothesis"). These findings are of broad significance in that all cytokines and growth factors initiate signaling in target cells by interacting with respective cell-surface receptors. The new data suggest that raft microdomains represent the units of function at the cell-surface through which ligand-stimulated STAT signaling is initiated. Moreover, recent evidence shows the involvement of chaperone proteins in regulating the STAT signaling pathway. These chaperones include the human homolog of the tumorous imaginal disc 1 protein (hTid1) which associates with Janus kinase 2 (JAK2) at the level of the plasma membrane, heat shock protein 90 (HSP90) which associates with STAT3 and STAT1 proteins in caveolin-1-containing raft and cytoplasmic complexes, and glucose regulated protein 58 (GRP58/ER-60/ERp57), a thiol dependent protein-disulfide isomerase, found in association with STAT3 "statosome" complexes in the cytosol and in the raft fraction. We suggest a function of the HSP90 chaperone system in preserving IL-6/STAT3 signaling in liver cells in the context of fever. The identification and function of protein partners associated with specific STAT species in rafts and in cytosolic complexes, and in the efficient departure of cytokine-activated STATs from the cytosolic face of rafts towards the cell nucleus are now areas of active investigation.
mesh_terms: D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism; D002451:Cell Compartmentation / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D016207:Cytokines / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D053614:Janus Kinase 2; D021962:Membrane Microdomains / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D016207:Cytokines; D004268:DNA-Binding Proteins; C120664:DNAJA3 protein, human; D050956:HSP40 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2