ADHESION OF CULTURED HUMAN KIDNEY MESANGIAL CELLS TO NATIVE ENTACTIN - ROLE OF INTEGRIN RECEPTORS

Entactin is an extracellular matrix glycoprotein which binds to lamini n and is found in most renal basement membranes and in the glomerular mesangial matrix. In the present study, we have characterized specific integrin receptors on cultured human mesangial cells (CHMC) responsib le for adhesion to native entactin. The integrin receptors alpha 2 bet a 1, alpha 3 beta 1, alpha 5 beta 1, alpha v beta 3, alpha v beta 5, a nd alpha 6 complexed with either beta 1 or beta 4 could be immune prec ipitated from detergent extracts of metabolically labeled CHMC. Adhesi on assays with inhibitory anti integrin monoclonal antibodies (mab) de monstrated that CHMC use both alpha v beta 3 and a beta 1-containing i ntegrin to bind surfaces coated with native entactin. Optimal binding of CHMC to native entactin required the participation of cations. Usin g wild type and mutant recombinant entactin fragments, the binding sit e for the alpha v beta 3 receptor was localized to the RGD sequence on the rod or E domain of entactin. CHMC adhesion to mutant full length recombinant entactin ligands lacking the E domain RGD sequence confirm ed the presence of ligand binding site(s) for beta 1 integrin receptor (s). Differences in CHMC binding characteristics to recombinant and fu ll length entactin compared to native bovine basement membrane entacti n were observed. This suggests that tertiary molecular structure may c ontribute to entactin ligand binding properties. Primary amino acid re sidue sequences and tertiary structure of entactin may play roles in f orming functional cell attachment sites in native basement membrane en tactin.