Activation of protein kinase C is crucial in the regulation of ICAM-1 expression on endothelial cells by interferon-gamma.

ICAM-1 (CD54) is expressed on endothelial cells and serves as an important ligand for the white cell adhesion molecule CD11a/CD18 (LFA-1). Many studies have demonstrated that increased numbers of white cells binding to endothelial cells correlate with the level of ICAM-1 expression on endothelial cells. Several cytokines, including IFN-gamma, increase ICAM-1 expression in cultured human endothelial cells. We have analysed the second intracellular messenger pathways involved in IFN-gamma-induced up-regulation of ICAM-1 expression in endothelial cells. IFN-gamma induced a rapid activation of phospholipase C, leading to a breakdown of phosphoinositoldiphosphate (PIP2) into diacyglycerol (DAG) and inositoltriphosphate (IP3). DAG is a natural activator of the protein kinase C pathway. We were able to show that the effect induced by IFN-gamma could be inhibited by a protein kinase C inhibitor, H7, in a dose-dependent manner and mimicked by PMA, which stimulates protein kinase C. IFN-gamma induced a 5-fold translocation (activation) of protein kinase C from the cytosol into the endothelial cell membrane. Elevation of the IP3 levels led to activation of the calcium-dependent pathway. An inhibitor of calcium calmodulin, W7, decreased the IFN-gamma induced ICAM-1 expression, and addition of calcium ionophore to endothelial cells could replace IFN-gamma in the up-regulation of ICAM-1. Finally, IFN-gamma caused a significant increase in the calcium flux of endothelial cells. cAMP and cGMP had no effect on the regulation of ICAM-1 expression on cultured human endothelial cells.