Laminin isoforms promote attachment of hepatocytes via different integrins

Three isoforms of laminin were compared for the ability to promote adhesion of primary rat hepatocytes. In tests of initial attachment to these substrates, kidney laminin (alpha k, beta 1, gamma 1, and alpha k, beta 2, gamma 1) was shown to be a more efficient substrate than Engelbreth Holm Swarm (EHS) (alpha 1, beta 1, gamma 1) or heart laminin (alpha 2, beta 1, gamma 1, and alpha 2, beta 2, gamma 1). Hepatocyte attachment to EHS laminin and heart laminin was completely inhibited by antibodies specific for the integrin subunit beta 1, while a combination of beta 1 integrin antibodies and GRGDS peptide was needed for total inhibition of hepatocyte attachment to kidney laminin. Antiserum directed to the integrin subunit beta 3 could not substitute for the GRGDS peptide in this inhibition. Antibodies against the integrin subunit alpha 1 efficiently blocked adhesion of hepatocytes to collagen type I and to the P1 domain of EHS laminin. However, this antibody had essentially no effect on the attachment to kidney laminin and had only a minor inhibitory effect on attachment to heart laminin, to intact EHS laminin, or to the isolated fragment E8 of EHS laminin. Combining the alpha 1 integrin antibody with GRGDS peptide gave no further inhibition on these substrates. These results show that a recently described isoform of laminin from bovine kidney is an efficient substrate for initial attachment of hepatocytes, interacting with at least one beta 1-containing integrin and an RGD-dependent integrin not containing beta 1 or beta 3 subunits. Native EHS laminin uses integrin alpha 1 beta 1 for hepatocyte binding to the center of the cross (fragment P1) and other beta 1 integrin(s) in addition to alpha 1 beta 1 as receptors for the distal part of the long arm (fragment E8).