Analysis of alpha 1 beta 1, alpha 2 beta 1 and alpha 3 beta 1 integrins in cell‐‐collagen interactions: identification of conformation dependent alpha 1 beta 1 binding sites in collagen type I

Integrins can mediate the attachment of cells to collagen type I. In the present study we have investigated the possible differences in collagen type I recognition sites for the alpha 1 beta 1 and alpha 2 beta 1 integrins. Different cyanogen bromide (CB) fragments of the alpha 1 (I) collagen chain were used in cell attachment experiments with three rat cell types, defined with regard to expression of collagen binding integrins. Primary rat hepatocytes expressed alpha 1 beta 1, primary rat cardiac fibroblasts alpha 1 beta 1 and alpha 2 beta 1, and Rat‐1 cells only alpha 2 beta 1. All three cell types expressed alpha 3 beta 1 but this integrin did not bind to collagen‐‐Sepharose or to immobilized collagen type I in a radioreceptor assay. Hepatocytes and cardiac fibroblasts attached to substrata coated with alpha 1(I)CB3 and alpha 1(I)CB8; Rat‐1 cells attached to alpha 1(I)CB3 but only poorly to alpha 1(I)CB8‐coated substrata. Cardiac fibroblasts and Rat‐1 cells spread and formed beta 1‐integrin‐containing focal adhesions when grown on substrata coated with native collagen or alpha 1(I)CB3; focal adhesions were also detected in cardiac fibroblasts cultured on alpha 1(I)CB8. The rat alpha 1 specific monoclonal antibody 3A3 completely inhibited hepatocyte attachment to alpha 1(I)CB3 and alpha 1(I)CB8, as well as the attachment of cardiac fibroblasts to alpha 1(I)CB8, but only partially inhibited the attachment of cardiac fibroblasts to alpha 1(I)CB3. 3A3 IgG did not inhibit the attachment of Rat‐1 cells to collagen type I or to alpha 1(I)CB3.