title: Interleukin-6 regulation of transforming growth factor (TGF)-beta receptor compartmentalization and turnover enhances TGF-beta1 signaling.
abstract: Transforming growth factor (TGF)-beta1 is a key cytokine involved in the pathogenesis of fibrosis in many organs, whereas interleukin (IL)-6 plays an important role in the regulation of inflammation. Recent reports demonstrate interaction between the two cytokines in disease states. We have assessed the effect of IL-6 on TGF-beta1 signaling and defined the mechanism by which this occurred. Stimulation of Smad-responsive promoter (SBE)4-Lux activity by TGF-beta1 was significantly greater in the presence of IL-6 than that induced by TGF-beta1 alone. Augmented TGF-beta1 signaling following the addition of IL-6 appeared to be mediated through binding to the cognate IL-6 receptor, the presence of which was confirmed by fluorescence-activated cell sorting and Stat-specific signaling. TGF-beta1 receptors internalize by both caveolin-1 (Cav-1) lipid raft and early endosome antigen 1 (EEA-1) non-lipid raft pathways, with non-lipid raft-associated internalization increasing TGF-beta1 signaling. Affinity labeling of TGF-beta1 receptors demonstrated that IL-6 stimulation resulted in increased partitioning of TGF-beta receptors to the non-lipid raft fraction. There was no change in expression of Cav-1; however, following IL-6 stimulation, co-immunoprecipitation demonstrated decreased association of IL-6 receptor with Cav-1. Increased TGF-beta1-dependent Smad signaling by IL-6 was significantly attenuated by inhibition of clathrin-mediated endocytosis and augmented by depletion of membrane cholesterol. These results indicate that IL-6 increased trafficking of TGF-beta1 receptors to non-lipid raft-associated pools results in augmented TGF-beta1 Smad signaling.
authors.affiliation: Institute of Nephrology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, Wales, United Kingdom.
authors.forename: Xiao Liang
authors.initials: XL
authors.lastname: Zhang
authors.forename: Nicholas
authors.initials: N
authors.lastname: Topley
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ito
authors.forename: Aled
authors.initials: A
authors.lastname: Phillips
mesh_terms: D015153:Blotting, Western; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation; D002469:Cell Separation; D004268:DNA-Binding Proteins / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D004705:Endocytosis; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D015850:Interleukin-6 / Q000378:metabolism / Q000502:physiology*; D007668:Kidney / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D015398:Signal Transduction; D051785:Smad Proteins; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D033921:Vesicular Transport Proteins
chemical_list: C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D004268:DNA-Binding Proteins; D003902:Detergents; D015850:Interleukin-6; D008565:Membrane Proteins; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; C508960:TGFB1 protein, human; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1