title: SPARC regulates extracellular matrix organization through its modulation of integrin-linked kinase activity.
abstract: SPARC, a 32-kDa matricellular glycoprotein, mediates interactions between cells and their extracellular matrix, and targeted deletion of Sparc results in compromised extracellular matrix in mice. Fibronectin matrix provides provisional tissue scaffolding during development and wound healing and is essential for the stabilization of mature extracellular matrix. Herein, we report that SPARC expression does not significantly affect fibronectin-induced cell spreading but enhances fibronectin-induced stress fiber formation and cell-mediated partial unfolding of fibronectin molecules, an essential process in fibronectin matrix assembly. By phage display, we identify integrin-linked kinase as a potential binding partner of SPARC and verify the interaction by co-immunoprecipitation and colocalization in vitro. Cells lacking SPARC exhibit diminished fibronectin-induced integrin-linked kinase activation and integrin-linked kinase-dependent cell-contractile signaling. Furthermore, induced expression of SPARC in SPARC-null fibroblasts restores fibronectin-induced integrin-linked kinase activation, downstream signaling, and fibronectin unfolding. These data further confirm the function of SPARC in extracellular matrix organization and identify a novel mechanism by which SPARC regulates extracellular matrix assembly.
authors.affiliation: Hope Heart Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington 98101, USA.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Barker
authors.forename: Gretchen
authors.initials: G
authors.lastname: Baneyx
authors.forename: Marina
authors.initials: M
authors.lastname: Cardó-Vila
authors.forename: Gail A
authors.initials: GA
authors.lastname: Workman
authors.forename: Matt
authors.initials: M
authors.lastname: Weaver
authors.forename: Priya M
authors.initials: PM
authors.lastname: Menon
authors.forename: Shoukat
authors.initials: S
authors.lastname: Dedhar
authors.forename: Sandra A
authors.initials: SA
authors.lastname: Rempel
authors.forename: Wadih
authors.initials: W
authors.lastname: Arap
authors.forename: Renata
authors.initials: R
authors.lastname: Pasqualini
authors.forename: Viola
authors.initials: V
authors.lastname: Vogel
authors.forename: E Helene
authors.initials: EH
authors.lastname: Sage
mesh_terms: D000199:Actins / Q000737:chemistry; D000256:Adenoviridae / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D019921:Biotinylation; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation; D004305:Dose-Response Relationship, Drug; D005109:Extracellular Matrix / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D005353:Fibronectins / Q000737:chemistry / Q000378:metabolism; D005434:Flow Cytometry; D031541:Fluorescence Resonance Energy Transfer; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000737:chemistry; D015151:Immunoblotting; D047468:Immunoprecipitation; D039482:Integrin alpha5 / Q000378:metabolism; D019012:Integrin beta1 / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D043263:Myosin-Light-Chain Phosphatase / Q000737:chemistry; D015676:Osteonectin / Q000378:metabolism / Q000502:physiology*; D019151:Peptide Library; D010766:Phosphorylation; D011489:Protein Denaturation; D017510:Protein Folding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D013997:Time Factors; D000099200:Scaffold Protein ILK
chemical_list: D000199:Actins; D005353:Fibronectins; D006023:Glycoproteins; D039482:Integrin alpha5; D019012:Integrin beta1; D043263:Myosin-Light-Chain Phosphatase; D015676:Osteonectin; D019151:Peptide Library; D017346:Protein Serine-Threonine Kinases; D000099200:Scaffold Protein ILK