Cell-Collagen Adhesion Is Inhibited by Monoclonal Antibody 33.4 against the Rat α1-Integrin Subunit

A monoclonal antibody (mAb 33.4) is described which inhibits the adhesion and spreading of an adherent cell line (A-cells), established from Morris hepatoma 7777 and isolated hepatocytes on collagen IV but not on laminin, fibronectin, and vitronectin. mAb 33.4 retains its immunological activity after immobilization and covalent cross-linking to Protein G-Sepharose and is therefore a suitable tool for the preparative equimolar purification of two proteins with M(r) of 130 and 190 kDa from detergent-solubilized membrane fractions by immunoaffinity chromatography. The 190-kDa protein was identified as rat alpha 1-integrin subunit by N-terminal amino acid sequencing, while the 130-kDa protein was specifically stained by a beta 1-integrin subunit-specific antiserum. In immunoblot analysis mAb 33.4 recognized the 190-kDa band, suggesting that it is specific for the rat alpha 1-integrin subunit. The epitope recognized by mAb 33.4 is conformation-dependent because the staining in immunoblots was very strong if the SDS-PAGE was performed in the absence of reducing agents. The expression of alpha 1 beta 1-integrin in sinusoidal hepatocyte membrane domains of liver sections is shown by mAb 33.4 and antisera raised against the rat alpha 1- and beta 1-integrin subunits.