Inhibition of phosphatidylinositol-3 kinase/Akt or mitogen-activated protein kinase signaling sensitizes endothelial cells to TNF-alpha cytotoxicity

Bovine carotid artery endothelial (BAE) cells are resistant to tumor necros is factor-alpha (TNF), like most other cells. We examined if mitogen-activa ted protein (MAP) kinase and phosphatidylinositol-3(Pl3) kinase/Akt pathway s are involved in this effect. In BAE cells, TNF activates MAP kinase in a MAP kinase kinase 1 (MEK1) manner and Akt in Pl3-kinase-dependent manner, P retreatment with either the MEK1 Inhibitor U0126 or Pl3 kinase inhibitor LY 294002 sensitized BAE cells to TNF-induced apoptosis. Neither U0126 nor LY2 94002 pretreatment affected TNF-induced activation of NF-kappaB, suggesting that the MAP kinase or Pl3-kinase/Akt-mediated anti-apoptotic effect induc ed by TNF was not relevant to NF-kappaB activation, Both MAP kinase and P13 kinase/Akt-mediated signaling could prevent cytochrome c release and mitoc hondrial transmembrane potential (Delta Psi) decrease. Pl3-kinase/Akt signa ling attenuated caspase-8 activity, whereas MAP kinase signaling impaired c aspase-9 activity. These results suggest that TNF-induced MAP kinase and Pl 3-kinase/Akt signaling play important roles In protecting BAE cells from TN F cytotoxicity.