Proteolysis regulates exposure of the IIICS-1 adhesive sequence in plasma fibronectin

Tatiana P. Ugarova, Alexander V. Ljubimov, Lynn Deng, Edward F. Plow

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Abstract

The alternatively spliced type III connecting segment (IIICS) of fibronectin (Fn) contains an amino acid sequence, CS-1, which is recognized by the integrin receptor, α4β1. Plasma Fn inhibits α4β1-dependent binding of lymphocytes and monocytes to CS-1 containing Fn derivatives poorly, suggesting limited exposure of the CS-1 sequence in Fn. To test the availability of CS-1 in plasma Fn, an antibody was raised to the synthetic peptide CS-1. The CS-1 sequence was found to be minimally exposed in plasma Fn: and immobilization of Fn, a model of matrix deposition, caused only a modest increase in its exposure. Digestion of Fn with selected proteases, however, induced substantial expression of the CS-1 sequence. The acid protease cathepsin D generated fragments of 31-33.5 kDa from the COOH- terminal heparin-binding domain of Fn which possessed high immunoreactivity with anti-CS-1. Digestion of Fn with cathepsin B also resulted in the exposure of CS-1 sequence in a 140 kDa fragment. Although the digestion of Fn with neutral proteases (neutrophil elastase, cathepsin G, chymotrypsin, trypsin) generated fragments from the COOH-terminal heparin-binding domain of similar molecular weight as with cathepsin D, the exposures of CS-1 did not occur. Exposure of the CS-1 region by the cathepsins was supported by cell adhesion experiments; digestion of Fn with cathepsins D and B transformed inert plasma Fn to an effective inhibitor of adhesion of lymphoblastoid B and T cells (Ramos, Jurkat, Molt-4) to an immobilized CS-1 conjugate. These results suggest that exposure of the CS-1 sequence in plasma Fn by proteolysis with cathepsins D and B, enzymes implicated in several pathological processes, may serve a regulatory function in cell adhesion. The adhesive function of the CS-1 region in intact Fn appears to be suppressed by the native conformation of the molecule.

Original languageEnglish (US)
Pages (from-to)10913-10921
Number of pages9
JournalBiochemistry
Volume35
Issue number33
DOIs
StatePublished - Sep 4 1996
Externally publishedYes

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ASJC Scopus subject areas

  • Biochemistry

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