Laminar flow inhibits TNF-induced ASK1 activation by preventing dissociation of ASK1 from its inhibitor 14-3-3

The inflammatory cytokine TNF-a stimulates several presumed pro-atherogenic signaling events in endothelial cells (ECs), including activation of c-Jun NH2-terminal kinase (JNK) and induction of E-selectin. Here, rye show that apoptosis signal-regulating kinase 1 (ASK1), a MAP kinase kinase kinase, i s required for TNF-mediated JNK activation. TNF activates ASK1 in part by d issociating ASK1 from its inhibitor 14-3-3. Because the risk of atheroscler osis is decreased in regions of steady laminar flow, we hypothesized that l aminar flow inhibits proinflammatory cytokine-mediated activation of JNK. S teady laminar flow inhibited both TNF activation of ASK1 and JNK. Inhibitio n of ASK1 by flow correlated with increased association of ASK1 with 14-3-3 . A constitutively active form of ASK1 lacking the 14-3-3-binding site (ASK 1-Delta NS367A) was not inhibited by flow These data establish ASK1 as a ta rget for flow-mediated inhibition of cytokine signaling and indicate a nove l role for 14-3-3 as an anti-inflammatory mediator in ECs.