ADHESION COMPLEXES FORMED BY OVCAR-4 CELLS ON LAMININ-1 DIFFER FROM THOSE OBSERVED ON FIBRONECTIN

Cell adhesion to laminin 1 or to fibronectin is mediated by distinct s ets of integrins and is differentially regulated by protein kinase C ( PKC). It suggests that upon integrin ligation to laminin 1 or to fibro nectin different intracellular signaling pathways could be activated. We have therefore investigated the formation of signaling complexes in duced during cell adhesion to laminin 1 or to fibronectin. Following c ell adhesion to laminin 1 the re-arrangement of the cytoskeleton was s lower than that observed on fibronectin and it was activated by treati ng the cells with H-7, an inhibitor of PKC. Conversely, treatment of l aminin-adhering cells with a PKC activator resulted in a rapid disorga nization of the actin cytoskeleton while a similar treatment had no ef fect on fibronectin-adhering cells. These results suggested that the s tructural organization of the adhesion complexes might be substrate-sp ecific and might correspond to a different arrangement of cytoskeletal and/or cytoplasmic proteins. Reflection interference contrast microsc opy (RICM) images revealed that cell-substratum contacts formed on lam inin 1 were not well differentiated in contrast to those developed on fibronectin. However, immunofluorescence staining revealed a similar o rganisation of actin microfilaments, talin and phosphotyrosyl-containi ng proteins on both substrates. In contrast, differences were observed for vinculin distribution within cells spread on fibronectin or on la minin 1. Following cell adhesion to fibronectin most of the vinculin a ppeared as thick patches at the tips of the actin stress fibers while in laminin-adhering cells vinculin was recruited into thin streaks loc alized at the end of only some actin stress fibers.