SPARC regulates extracellular matrix organization through its modulation of integrin-linked kinase activity.
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.
Barker
Thomas H
TH
Hope Heart Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington 98101, USA.
Baneyx
Gretchen
G
Cardó-Vila
Marina
M
Workman
Gail A
GA
Weaver
Matt
M
Menon
Priya M
PM
Dedhar
Shoukat
S
Rempel
Sandra A
SA
Arap
Wadih
W
Pasqualini
Renata
R
Vogel
Viola
V
Sage
E Helene
EH
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
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