title: Hyaluronan regulates transforming growth factor-beta1 receptor compartmentalization.
abstract: Transforming growth factor-beta1 (TGF-beta1) is a key cytokine involved in the pathogenesis of fibrosis in many organs. We previously demonstrated in renal proximal tubular cells that the engagement of the extracellular polysaccharide hyaluronan with its receptor CD44 attenuated TGF-beta1 signaling. In the current study we examined the potential mechanism by which the interaction between hyaluronan (HA) and CD44 regulates TGF-beta receptor function. Affinity labeling of TGF-beta receptors demonstrated that in the unstimulated cells the majority of the receptor partitioned into EEA-1-associated non-lipid raft-associated membrane pools. In the presence of exogenous HA, the majority of the receptors partitioned into caveolin-1 lipid raft-associated pools. TGF-beta1 increased the association of activated/phosphorylated Smad proteins with EEA-1, consistent with activation of TGF-beta1 signaling following endosomal internalization. Following addition of HA, caveolin-1 associated with the inhibitory Smad protein Smad7, consistent with the raft pools mediating receptor turnover, which was facilitated by HA. Antagonism of TGF-beta1-dependent Smad signaling and the effect of HA on TGF-beta receptor associations were inhibited by depletion of membrane cholesterol using nystatin and augmented by inhibition of endocytosis. The effect of HA on TGF-beta receptor trafficking was inhibited by inhibition of HA-CD44 interactions, using blocking antibody to CD44 or inhibition of MAP kinase activation. In conclusion, we have proposed a model by which HA engagement of CD44 leads to MAP kinase-dependent increased trafficking of TGF-beta receptors to lipid raft-associated pools, which facilitates increased receptor turnover and attenuation of TGF-beta1-dependent alteration in proximal tubular cell function.
authors.affiliation: Institute of Nephrology, University of Wales College of Medicine, Cardiff CF14 4XN, Wales.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ito
authors.forename: John D
authors.initials: JD
authors.lastname: Williams
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Fraser
authors.forename: Aled O
authors.initials: AO
authors.lastname: Phillips
mesh_terms: D051242:Caveolin 1; D022461:Caveolins / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology; D006801:Humans; D018960:Hyaluronan Receptors / Q000502:physiology; D006820:Hyaluronic Acid / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D051899:Smad2 Protein; D015534:Trans-Activators / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D033921:Vesicular Transport Proteins
chemical_list: C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D004268:DNA-Binding Proteins; D018960:Hyaluronan Receptors; D008565:Membrane Proteins; D018125:Receptors, Transforming Growth Factor beta; C497782:SMAD2 protein, human; D051899:Smad2 Protein; 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; D006820:Hyaluronic Acid