Protein kinase B/Akt activates c-Jun NH2-terminal kinase by increasing NO production in response to shear stress

Laminar shear stress activates c-Jun NH2-terminal kinase (JNK) by the mecha nisms involving both nitric oxide (NO) and phosphatidylinositide 3-kinase ( PI3K). Because protein kinase B (Akt), a downstream effector of PI3K, has b een shown to phosphorylate and activate endothelial NO synthase, we hypothe sized that Akt regulates shear-dependent activation of JNK by stimulating N O production. Here, we examined the role of Akt in shear-dependent NO produ ction and JNK activation by expressing a dominant negative Akt mutant (Akt( AA)) and a constitutively active mutant (Akt(Myr) in bovine aortic endothel ial cells (BAEC). As expected, pretreatment of BAEC with the PI3K inhibitor (wortmannin) prevented shear-dependent stimulation of Akt and NO productio n. Transient expression of AktAA in BAEC by using a recombinant adenoviral construct inhibited the shear-dependent stimulation of NO production and JN K activation. However, transient expression of Akt(Myr) using a recombinant adenoviral construct did not induce JNK activation. This is consistent wit h our previous finding that NO is required, but not sufficient on its own, to activate JNK in response to shear stress. These results and our previous findings strongly suggest that shear stress triggers activation of PI3K, A kt, and endothelial NO synthase, leading to production of NO, which (along with O-2(-), which is also produced by shear) activates Ras-JNK pathway. Th e regulation of Akt, NO, and JNK by shear stress is likely to play a critic al role in its antiatherogenic effects.