title: Assembly of fibrillin microfibrils governs extracellular deposition of latent TGF beta.
abstract: Control of the bioavailability of the growth factor TGFbeta is essential for tissue formation and homeostasis, yet precisely how latent TGFbeta is incorporated into the extracellular matrix is unknown. Here, we show that deposition of a large latent TGFbeta complex (LLC), which contains latent TGFbeta-binding protein 1 (LTBP-1), is directly dependent on the pericellular assembly of fibrillin microfibrils, which interact with fibronectin during higher-order fibrillogenesis. LTBP-1 formed pericellular arrays that colocalized with microfibrils, whereas fibrillin knockdown inhibited fibrillar LTBP-1 and/or LLC deposition. Blocking alpha5beta1 integrin or supplementing cultures with heparin, which both inhibited microfibril assembly, disrupted LTBP-1 deposition and enhanced Smad2 phosphorylation. Full-length LTBP-1 bound only weakly to N-terminal pro-fibrillin-1, but this association was strongly enhanced by heparin. The microfibril-associated glycoprotein MAGP-1 (MFAP-2) inhibited LTBP-1 binding to fibrillin-1 and stimulated Smad2 phosphorylation. By contrast, fibulin-4, which interacted strongly with full-length LTBP-1, did not induce Smad2 phosphorylation. Thus, LTBP-1 and/or LLC deposition is dependent on pericellular microfibril assembly and is governed by complex interactions between LTBP-1, heparan sulfate, fibrillin-1 and microfibril-associated molecules. In this way, microfibrils control TGFbeta bioavailability.
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK.
authors.forename: Teresa
authors.initials: T
authors.lastname: Massam-Wu
authors.forename: Maybo
authors.initials: M
authors.lastname: Chiu
authors.forename: Rawshan
authors.initials: R
authors.lastname: Choudhury
authors.forename: Shazia S
authors.initials: SS
authors.lastname: Chaudhry
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Baldwin
authors.forename: Amanda
authors.initials: A
authors.lastname: McGovern
authors.forename: Clair
authors.initials: C
authors.lastname: Baldock
authors.forename: C Adrian
authors.initials: CA
authors.lastname: Shuttleworth
authors.forename: Cay M
authors.initials: CM
authors.lastname: Kielty
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D003285:Contractile Proteins / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D000071838:Fibrillin-1; D000071837:Fibrillins; D005347:Fibroblasts / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology; D006497:Heparan Sulfate / Q000378:metabolism; D006801:Humans; D053779:Latent TGF-beta Binding Proteins / Q000378:metabolism*; D020894:Microfibrils / Q000378:metabolism*; D008840:Microfilament Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D000072260:RNA Splicing Factors; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D054392:Adipokines
chemical_list: D003285:Contractile Proteins; D016326:Extracellular Matrix Proteins; D000071838:Fibrillin-1; D000071837:Fibrillins; D006493:Heparin; D006497:Heparan Sulfate; D053779:Latent TGF-beta Binding Proteins; D008840:Microfilament Proteins; D000072260:RNA Splicing Factors; D016212:Transforming Growth Factor beta; C403672:EFEMP2 protein, human; C000605722:FBN1 protein, human; D054392:Adipokines; C509032:LTBP1 protein, human; C016598:microfibrillar protein