title: Transforming growth factor-beta1 downregulates caveolin-1 expression and enhances sphingosine 1-phosphate signaling in cultured vascular endothelial cells.
abstract: In vascular endothelial cells, specialized microdomains of plasma membrane termed caveolae modulate various receptor signal transduction pathways regulated by caveolin-1, a resident protein of caveolae. We examined whether transforming growth factor-beta1 (TGF-beta1), a multifunctional cytokine, alters expression levels of caveolin-1 and influences heterologous receptor signaling. Treatment of cultured bovine aortic endothelial cells (BAEC) with TGF-beta1 induces marked decreases in caveolin-1 expression in a time- and dose-dependent fashion at both levels of protein and mRNA. A pharmacological inhibitor of activin receptor-like kinase 5 (ALK-5) counteracts caveolin-1 downregulation by TGF-beta1, indicating the involvement of ALK-5 receptor subtype for TGF-beta1. Sphingosine 1-phosphate (S1P) is a serum-borne angiogenic lipid growth factor that exerts a wide variety of biological actions. S1P modulates G protein-coupled S1P receptors, activating downstream molecules kinases AMP-activated protein kinase (AMPK), and Akt as well as a small G protein Rac1, ultimately to promote migration. Because S1P receptor signaling is associated with caveolae/caveolin-1, we examined whether pretreatment with TGF-beta1 enhances effects of S1P on BAEC. Whereas S1P alone evokes robust BAEC responses to S1P, pretreatment with TGF-beta1 leads to even higher magnitudes of S1P-elicited signaling responses and cell migration. Conversely, genetic knockdown of caveolin-1 using small interfering RNA mimics TGF-beta1-induced promotion of BAEC responses to S1P. Collectively, these data demonstrate that TGF-beta1 downregulates caveolin-1 of cultured endothelial cells, involving ALK-5 receptor subtype. Because downregulation of caveolin-1 by TGF-beta1 promotes subsequent heterologous receptor signaling by S1P, these results may also identify novel point of cross-talk between cytokines and sphingolipids within endothelial signal transduction machineries.
authors.affiliation: Department of Cardiovascular, Faculty of Medicine, Kagawa University, Kagawa, Japan. igarashi@med.kagawa-u.ac.jp
authors.forename: Junsuke
authors.initials: J
authors.lastname: Igarashi
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Shoji
authors.forename: Takeshi
authors.initials: T
authors.lastname: Hashimoto
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Moriue
authors.forename: Kozo
authors.initials: K
authors.lastname: Yoneda
authors.forename: Tomoko
authors.initials: T
authors.lastname: Takamura
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Yamashita
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kubota
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kosaka
mesh_terms: D000818:Animals; D002417:Cattle; D051242:Caveolin 1 / Q000096:biosynthesis*; D002465:Cell Movement / Q000502:physiology; D002478:Cells, Cultured; D015536:Down-Regulation; D042783:Endothelial Cells / Q000378:metabolism*; D015151:Immunoblotting; D008246:Lysophospholipids / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: D051242:Caveolin 1; D008246:Lysophospholipids; D034741:RNA, Small Interfering; D018125:Receptors, Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C060506:sphingosine 1-phosphate; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D013110:Sphingosine