Protein kinase C-δ regulates thrombin-induced ICAM-1 gene expression in endothelial cells via activation of p38 mitogen-activated protein kinase

The procoagulant thrombin promotes the adhesion of polymorphonuclear leukocytes to endothelial cells by a mechanism involving expression of intercellular adhesion molecule 1 (ICAM-1) via an NF-κB-dependent pathway. We now provide evidence that protein kinase C-δ (PKC-δ) and the p38 mitogen-activated protein (MAP) kinase pathway play a critical role in the mechanism of thrombin-induced ICAM-1 gene expression in endothelial cells. We observed the phosphorylation of PKC-δ and p38 MAP kinase within 1 min after thrombin challenge of human umbilical vein endothelial cells. Pretreatment of these cells with the PKC-δ inhibitor rottlerin prevented the thrombin-induced phosphorylation of p38 MAP kinase, suggesting that p38 MAP kinase signals downstream of PKC-δ. Inhibition of PKC-δ or p38 MAP kinase by pharmacological and genetic approaches markedly decreased the thrombin-induced NF-κB activity and resultant ICAM-1 expression. The effects of PKC-δ inhibition were secondary to inhibition of 1KKβ activation and of subsequent NF-κB binding to the ICAM-1 promoter. The effects of p38 MAP kinase inhibition occurred downstream of IκBα degradation without affecting the DNA binding function of nuclear NF-κB. Thus, PKC-δ signals thrombin-induced ICAM-1 gene transcription by a dual mechanism involving activation of IKIKβ, which mediates NF-κB binding to the ICAM-1 promoter, and p38 MAP kinase, which enhances transactivation potential of the bound NF-κB p65 (RelA).