Reduced expression of alpha 5 beta B1 integrin prevents spreading-dependent cell proliferation

Cell adhesion to substratum results in the initiation of integrin signaling and an integrin-dependent organization of the cytoskeleton (cell spreading ). To address the potential relationships between these events and cell pro liferation, we transfected NRK fibroblasts with an antisense cDNA encoding a 1.3 kb ATG-spanning portion of alpha 5 integrin subunit and obtained stab le clones in which the surface expression of alpha 5 beta 1 integrin was se lectively reduced. alpha 5-antisense NRK cells are less spread than the con trol transfectants, have poorly defined stress fibers, and an increased amo unt of cortical actin. The antisense clones remained anchorage-dependent, b ut they proliferated very slowly. Serum dose-response curves showed that th ey have an impaired response to mitogens, Importantly, cell spreading and s tress fiber formation could be completely restored by plating the antisense cells on collagen, but cell spreading failed to rescue proliferation, Thes e data indicate that cell spreading can be uncoupled from cell proliferatio n and that cytoskeletal organization is important for NRK cell proliferatio n because it enforces the proliferative effect of alpha 5 beta 1 integrin, Our results also indicate that reduced surface expression of alpha 5 beta 1 integrin is not sufficient to confer the anchorage-independent phenotype t o nontransformed cells.