Role of Cbl in shear-activation of PI 3-kinase and JNK in endothelial cells.

Fluid shear stress can activate PI-3 kinase and JNK in vascular endothelial cells. This study was designed to establish the role of Cbl as an upstream molecule in the shear stress activation of PI-3 kinase and JNK. Confluent monolayers of bovine aortic endothelial cells (BAECs) were subjected to a shear stress of 12 dyn/cm(2) over intervals ranging from 0.5 to 30 min. Shear stress increased Cbl phosphorylation to 2.9-fold of control and Cbl association with the regulatory PI-3 kinase subunit p85 to 5.4-fold. The PI-3 kinase activity measured in Cbl-immunoprecipitated complexes increased to 11.7-fold in response to shear, suggesting that the shear stress activation of PI-3 kinase involves its association with Cbl. Furthermore, the shear stress induction of JNK was attenuated by a negative mutant of Cbl. Finally, shear stress caused an activation of PI 3-kinase only in BAECs seeded onto fibronectin, vitronectin, or laminin, but not poly-l-lysine. Our results suggest that Cbl plays a critical role in the shear stress induction of PI 3-kinase and JNK activities, and that this shear-induced activation requires the interaction of endothelial integrins with extracellular matrix proteins.