Identification of the Heparin-binding Determinants within Fibronectin Repeat III₁: ROLE IN CELL SPREADING AND GROWTH

Fibronectins are high molecular mass glycoproteins that circulate as soluble molecules in the blood, and are also found in an insoluble, multimeric form in extracellular matrices throughout the body. Soluble fibronectins are polymerized into insoluble extracellular matrix (ECM) fibrils via a cell-de...

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Bibliographic Details
Published in:The Journal of biological chemistry 2006-11, Vol.281 (46), p.34816-34825
Main Authors: Gui, Liqiong, Wojciechowski, Katherine, Gildner, Candace D, Nedelkovska, Hristina, Hocking, Denise C
Format: Article
Language:English
Subjects:
Amino Acid Motifs
Amino Acid Sequence
Animals
Binding Sites
Cell Enlargement
Cell Proliferation
Cell Size
Extracellular Matrix
Fibroblasts
Fibronectins - chemistry
Fibronectins - metabolism
Heparin - metabolism
Humans
Integrins - genetics
Integrins - metabolism
Mice
Mutation
Protein Binding
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Summary:Fibronectins are high molecular mass glycoproteins that circulate as soluble molecules in the blood, and are also found in an insoluble, multimeric form in extracellular matrices throughout the body. Soluble fibronectins are polymerized into insoluble extracellular matrix (ECM) fibrils via a cell-dependent process. Recent studies indicate that the interaction of cells with the ECM form of fibronectin promotes actin organization and cell contractility, increases cell growth and migration, and enhances the tensile strength of artificial tissue constructs; ligation of integrins alone is insufficient to trigger these responses. Evidence suggests that the effect of ECM fibronectin on cell function is mediated in part by a matricryptic heparin-binding site within the first III₁ repeat (FNIII₁). In this study, we localized the heparin-binding activity of FNIII₁ to a cluster of basic amino acids, Arg⁶¹³, Trp⁶¹⁴, Arg⁶¹⁵, and Lys⁶¹⁷. Site-directed mutagenesis of a recombinant fibronectin construct engineered to mimic the ECM form of fibronectin demonstrates that these residues are also critical for stimulating cell spreading and increasing cell proliferation. Cell proliferation has been tightly correlated with cell area. Using integrin- and heparin-binding fibronectin mutants, we found a positive correlation between cell spreading and growth when cells were submaximally spread on ECM protein-coated surfaces at the time of treatment. However, cells maximally spread on vitronectin or fibronectin still responded to the fibronectin matrix mimetic with an increase in growth, indicating that an absolute change in cell area is not required for the increase in cell proliferation induced by the matricryptic site of FNIII₁.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M608611200