HEPATOCYTE ATTACHMENT TO LAMININ IS MEDIATED THROUGH MULTIPLE RECEPTORS

The interaction of hepatocytes with the basement membrane glycoprotein laminin was studied using synthetic peptides derived from laminin sequences. Rat hepatocytes bind to laminin and three different sites within the A and B1 chains of laminin were identified. Active laminin peptides include the PA22-2 peptide (close to the carboxyl end of the long arm in the A chain), the RGD-containing peptide, PA21 (in the short arm of the A chain) and the pentapeptide YIGSR (in the short arm of the B1 chain). PA22-2 was the most potent peptide, whereas the other two peptides had somewhat lower activity. Furthermore, hepatocyte attachment to laminin was inhibited by the three peptides, with PA22-2 being the most active. Various proteins from isolated membranes of cell-surface iodinated hepatocytes bound to a laminin affinity column including three immunologically related binding proteins: M(r) = 67,000, 45,000, and 32,000. Several proteins - M(r) = 80,000, 55,000, and 38,000-36,000 - with lower affinity for laminin were also identified. Affinity chromatography on peptide columns revealed the PA22-2 peptide specifically bound the M(r) = 80,000, 67,000, 45,000, and 32,000 proteins, the PA21 peptide bound the M(r) = 45,000 and 38,000-36,000 proteins and the YIGSR peptide column bound the 38,000-36,000 protein. Antisera to a bacterial fusion protein of the 32-kD laminin-binding protein (LBP-32) reacted strongly with the three laminin-binding proteins, M(r) = 67,000, 45,000, and 32,000, showing that they are immunologically related. Immunoperoxidase microscopy studies confirmed that these proteins are present within the plasma membrane of the hepatocyte. The antisera inhibited the adhesion of hepatocytes to laminin by 30%, supporting the finding that these receptors and others mediate the attachment of hepatocytes to several regions of laminin.