INTEGRIN BETA-1 CYTOPLASMIC DOMAIN DOMINANT-NEGATIVE EFFECTS REVEALEDBY LYSOPHOSPHATIDIC ACID TREATMENT

Integrin receptors localize to focal contact sites and interact with t he cytoskeleton via the beta 1 cytoplasmic domain. To study the role o f this domain in adhesion, we have expressed in NIH 3T3 cells a cDNA c onsisting of the interleukin 2 receptor alpha subunit extracellular an d transmembrane domains, connected to the integrin beta 1 cytoplasmic domain (IL2R-beta 1). Since the extracellular domain of the chimeric p rotein has no role in adhesion, this protein could uncouple adhesion f rom intracellular events. As expected, in a cell line expressing IL2R- beta 1, this chimera was directed to focal contact sites. Unexpectedly , the cells exhibited normal adhesion to fibronectin (FN). However, wh en a rapid reorganization of the cytoskeleton was induced using lysoph osphatidic acid (LPA), IL2R-beta 1 cells detached from FN in contrast to wild-type cells. The detachment in response to LPA could be prevent ed with cytochalasin D, an inhibitor of actin polymerization. These re sults imply that a pi cytoplasmic domain, which is uncoupled from adhe sion, can compete with the cytoplasmic domain of native integrin beta 1 for cytoskeletal proteins. As a consequence, the IL2R-beta 1 protein acts as a dominant negative effector of adhesion by disrupting the in tegrin-cytoskeleton connection.