Interaction with Heparin and Matrix Metalloproteinase 2 Cleavage Expose a Cryptic Anti-adhesive Site of Fibronectin

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Abstract
We recently found that fibronectin (FN) had a functional site [YTIYVIAL sequence in the heparin-binding domain 2 (Hep 2)] that was capable of suppressing the integrin-mediated cell adhesion to extracellular matrix. However, our results also indicated that this anti-adhesive site seemed to be usually buried within the Hep 2 domain structure because of its hydrophobic nature, raising a question as to the physiological significance of the cryptic anti-adhesive activity of FN. The present study demonstrates that the cryptic anti-adhesive activity can be exposed through the physiological processes. A 30-kDa chymotryptic FN fragment derived from Hep 2 domain (Hep 2 fragment), which had no effect on adhesion of MSV-transformed nonproducer 3T3 cell line (KN78) to FN, expressed the anti-adhesive activity after treatment with 6 M urea. Light scattering and circular dichroism measurements showed that the urea treatment induced the conformational change of the Hep 2 fragment from a more compact form to an unfolded one. Incubation of the Hep 2 fragment with heparin also induced similar conformational changes and expression of anti-adhesive activity. Additionally, both the urea and heparin treatments made the Hep 2 fragment and intact FN much more accessible to the polyclonal antibody (αIII14A), with a recognition site near the anti-adhesive site of FN. Specific cleavage of either the Hep 2 fragment or intact FN by matrix metalloproteinase 2 (MMP-2) released a 10-kDa fragment with the anti-adhesive activity, which was shown to have the exposed anti-adhesive site on the amino-terminal region. Thus, the cryptic anti-adhesive activity of FN can be expressed upon conformational change and proteolytic cleavage of Hep 2 domain.