Rat hepatocytes attach to laminin present in liver biomatrix proteins by an Mg ++-dependent mechanism

Abstract

Laminin belongs to a family of proteins that contains at least seven variants. Together with fibronectin, it is the most important cell-adhesion protein. Recent data from various laboratories have suggested that liver sinusoidal laminins differ from Engelbert-Holmes-Swarm tumor laminin (laminin 1), because the former contain α2 instead of αl chains. Therefore, we compared the adhesion of hepatocytes to laminin 1 and a matrix extracted with dilute acetic acid from liver biomatrix (LBP). We show that LBP contains laminin and that this extracellular matrix protein is the main adhesion protein. Close to 70% of the hepatocytes attach to LBP after 15 minutes of incubation at 37°C. Cell adhesion was Mg ++ and Mn ++-dependent and Ca +- and insulin-independent. Ethylenediaminetetraacetic acid prevented cell adhesion in the presence of divalent cations. We show that synthetic cell-adhesion peptide sequences present in laminin 1 (RGD and YIGSR) or an antibody to the cell-binding domain (SIKVAV) of the α1 chain do not prevent hepatocyte adhesion to LBP. We also show that LBP has cell specificity; hepatocytes adhere to it preferentially when compared with other epithelial and mesenchymal cell lines. We suggest that because of the differences in chain composition of laminin 1 and liver sinusoidal laminins as well as the described differences in cell adhesion to the two substrata, further studies are needed to determine the actual composition of liver laminin and establish the chains and domains to which hepatocytes adhere.