Glycosaminoglycans that bind cold-insoluble globulin in cell-substratum adhesion sites of murine fibroblasts

Abstract

Glycosaminoglycans (GAGs) and glycoprotein-derived glycopeptide from mouse BALB/c3T3 and simian virus 40-transformed 3T3 whole cells or their adhesion sites, which are left bound to the serum-coated tissue culture substratum after detachment of cells mediated by [ethylenebis-(oxyethylenenitrilo]tetraacetic acid (EGTA), were analyzed for specific binding to Sepharose columns derivatized with cold-insoluble globulin (CIg). CIg is the serum-contained form of fibronectin and is required for the adhesion of these fibroblasts to the substratum. Of the various GAGs present in these fractions of either cell type, only the highly N-sulfated sequences of heparan sulfate and a small subset of dermatan sulfate bind to CIg-Sepharose. There was no detectable binding of glycopeptide, undersulfated heparan sulfate, the various chondroitin species, or hyaluronate. Adhesion sites from newly attaching cells were greatly enriched in CIg-binding heparan sulfate when compared to long-term-growth adhesion sites or EGTA-detached cells. Various properties of binding were determined. The reference standard standard GAGs heparin (or heparan sulfate) and dermatan sulfate were able to displace bound radiolabeled adhesion site GAG from the column, whereas the other GAGs had no effect. CIg has been shown to be the only adhesion-promoting activity in the serum layer of this culture system. Because these fibroblast adhesion sites do not contain collagen, which could potentially mediate adhesion to the substratum-bound CIg, these data support other evidence that multivalent heparan sulfate proteoglycans mediate substratum adhesion of these cells by coordinate binding to fibronectin on the cell surface and CIg on the substratum.