Figure 8.

Effect of APC on thrombin signaling pathway in epithelial cells. (a) Activated protein C (APC) reverses thrombin-induced extracellular-regulated kinase 1/2 (ERK) and cytosolic Phospholipase A₂ (cPLA₂) activation in A549 cells. Immunoblotting detection of activated (phosphorylated) ERK and cPLA₂. A549 cells were incubated with serum-free medium, thrombin for 15 minutes, APC for 60 minutes or APC for 60 minutes followed by thrombin for 15 minutes. APC alone induced minimal ERK and cPLA₂ activation. In contrast, thrombin addition was associated with increased activation of ERK and cPLA₂, both of which were abrogated in the presence of APC (Representative of five experiments). (b) ERK phosphorylates cPLA₂ downstream of the thrombin receptor. ERK activation was blocked by MEK inhibitor UO126 in A549 cells challenged with thrombin. Inhibition of ERK activation led to abrogated cPLA₂ phosphorylation (representative of three experiments).