NOVEL LAMININ E8 CELL-ADHESION SITE REQUIRED FOR LUNG ALVEOLAR FORMATION IN-VITRO

Basement membrane-adherent type II alveolar cells isolated from lung a ssemble into lumen-containing cellular spheres which retain the correc t polarity and thereby approximate the earliest fetal stage of alveola r morphogenesis. The molecular basis of this process, determined in in itial experiments to be attributable mainly to the large heterotrimeri c glycoprotein laminin, was probed with laminin proteolytic fragments, antibodies, and synthetic peptides. The carboxy-terminal fragment E8, but not equimolar amounts of fragment P1, blocked alveolar formation. To pursue this observation, we used several anti-E8 antibodies and id entified one, prepared against A chain residues 2179-2198 (''SN-peptid e'') from the first loop of the G domain, as inhibitory. These results were confirmed by use of SN-peptide alone and further defined by tryp sin digestion of SN-peptide to the sequence SINNNR. This conserved sit e promoted divalent cation dependent adhesion of both type II alveolar and HT1080 cells, was inhibitable with equimolar amounts of fragment E8 but not P1, and derives from a form of laminin present in fetal alv eolar basement membranes. These studies point to an important novel ce ll adhesion site in the laminin E8 region with a key role in lung alve olar morphogenesis.