title: Elevated expression of cav-1 in a subset of SSc fibroblasts contributes to constitutive Alk1/Smad1 activation.
abstract: Previous studies have shown that the transforming growth factor (TGF)β/Alk1/Smad1 signaling pathway is constitutively activated in a subset of systemic sclerosis (SSc) fibroblasts and this pathway is a critical regulator of CCN2 gene expression. Caveolin-1 (cav-1), an integral membrane protein and the main component of caveolae, has also been implicated in SSc pathogenesis. This study was undertaken to evaluate the role of caveolin-1 in Smad1 signaling and CCN2 expression in healthy and SSc dermal fibroblasts. We show that a significant subset of SSc dermal fibroblasts has up-regulated cav-1 expression in vitro, and that cav-1 up-regulation correlates with constitutive Smad1 phosphorylation. In addition, basal levels of phospho-Smad1 were down-regulated after inhibition of cav-1 in SSc dermal fibroblasts. Caveolin-1 formed a protein complex with Alk1 in dermal fibroblasts, and this association was enhanced by TGFβ. By using siRNA against cav-1 and adenoviral cav-1 overexpression we demonstrate that activation of Smad1 in response to TGFβ requires cav-1 and that cav-1 is sufficient for Smad-1 phosphorylation. We also show that cav-1 is a positive regulator of CCN2 gene expression, and that it is required for the basal and TGFβ-induced CCN2 levels. In conclusion, this study has revealed an important role of cav-1 in mediating TGFβ/Smad1 signaling and CCN2 gene expression in healthy and SSc dermal fibroblasts.
authors.affiliation: Arthritis Center-Rheumatology, Boston University School of Medicine, Boston, MA 02118, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Haines
authors.forename: Faye N
authors.initials: FN
authors.lastname: Hant
authors.forename: Robert
authors.initials: R
authors.lastname: Lafyatis
authors.forename: Maria
authors.initials: M
authors.lastname: Trojanowska
authors.forename: Andreea M
authors.initials: AM
authors.lastname: Bujor
mesh_terms: D030301:Activin Receptors, Type II / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D055513:Connective Tissue Growth Factor / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D012595:Scleroderma, Systemic / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D015398:Signal Transduction; D012867:Skin / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D051898:Smad1 Protein / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
chemical_list: C495540:CAV1 protein, human; C526317:CCN2 protein, human; D051242:Caveolin 1; D034741:RNA, Small Interfering; C497399:SMAD1 protein, human; D051898:Smad1 Protein; D016212:Transforming Growth Factor beta; D055513:Connective Tissue Growth Factor; C425364:ACVRL1 protein, human; D030301:Activin Receptors, Type II