Abstract
Protease-activated receptors (PARs), which are also called thrombin receptors, contain PAR1, PAR3 and PAR4. They are irreversibly activated by thrombin and then transduce thrombin signals into cells. Endocytosis has been reported to play an important role in down-regulation of cell-surface receptors such as G protein-coupled receptors. Activated PAR1 is rapidly internalized via clathrin-coated pits and sorted to lysosome to terminate its signaling. Also, PAR1 and PAR4 are found to be internalized with distinct tempos. However, the regulation of endocytosis in the signaling and trafficking of thrombin receptors is still unclear. In this study, I investigated whether different rates of endocytosis of PAR1 and PAR4 would affect their degradation after receptor activation. Whether endocytosis of PAR1 is involved in PAR1-induced ERK activation and Src degradation was also investigated. I found that the rate of endocytosis of PAR4 was lower and that the extent of endocytosis of PAR4 was less compared with PAR1. Also, PAR1 was degraded after agonist stimulation but PAR4 was not. In addition, PAR1 and PAR1-induced Src degradation were inhibited by blocking endocytosis of the activated receptor. However, the activation of ERK induced by PAR1 was not inhibited by blocking the receptor endocytosis. These findings indicate that endocytosis of thrombin receptors indeed mediates the trafficking and signaling of thrombin receptors.