THE PROTEINASE-ACTIVATED RECEPTOR-2 IS INDUCED BY INFLAMMATORY MEDIATORS IN HUMAN ENDOTHELIAL-CELLS - COMPARISON WITH THE THROMBIN RECEPTOR

The proteinase-activated receptor 2 (PAR-2) belongs to the family of s even transmembrane region receptors, and, like the related thrombin re ceptor, it is activated by specific proteolytic cleavage of its extrac ellular amino terminus. It is not known which proteinase is the physio logical activator of the PAR-2, but candidates can be found among the enzymes involved in the inflammatory cascade systems. Here, we have st udied the effects of various mediators on the expression of the PAR-S and the thrombin receptor in cultured human umbilical vein endothelial cells. Stimulation with the cytokines tumor necrosis factor alpha or interleukin-1 alpha as well as bacterial lipopolysaccharide elevated t he expression of PAR-S in a dose-dependent manner. The time course of induction after cytokine stimulation was similar to those published fo r the adhesion molecules intercellular adhesion molecule-1 and vascula r cell adhesion molecule-1. After 20 h of stimulation, PAR-2 mRNA and protein levels were increased to 5-10-fold basal values, and, in the c ontinued presence of tumor necrosis factor cu, PAR-2 mRNA expression w as found to remain elevated for up to 4 days, In contrast, the thrombi n receptor gene was not induced by any of these inflammatory mediators , The responses to phorbol ester treatment also differed between the t wo genes. Thrombin receptor mRNA levels decreased steadily up to 20 h, whereas PAR-2 mRNA levels first rose to about 3-fold basal values at 4 h before decreasing again. Cell surface protein levels of both recep tors were decreased after 20 h of phorbol ester stimulation, Elevating intracellular cAMP levels by treatment with forskolin resulted in dec reased expression of both receptors, and inhibition of cAMP degradatio n appeared to blunt the cytokine-induced increase in PAR-2 expression. The induction of the PAR-2 by cytokine treatment supports the concept of PAR-2 involvement in the acute inflammatory response.