Abstract
Endocytosis plays an important role in down-regulation of several cell-surface receptors such as protease-activated receptor 1 (PAR1), a thrombin receptor. The endocytosis of PAR1 is triggered by irreversible activation induced by thrombin, and then the activated PAR1 transduces thrombin signals into cells. Activated PAR1 is rapidly internalized via clathrin-coated pits and sorted to lysosomes for degradation to terminate thrombin signals. As for Chinese hamster ovary-K1 (CHO-K1) cells, a kind of caveolin-1-enriched cells, the endocytic pathway of PAR1 is still unknown. In this study, the endocytic pathway of PAR1 and its agonist-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation in CHO-K1 cells were investigated. The endocytosis of PAR1 was found to be blocked in cells overexpressing dominant-negative dynamin-1 K44A or dominant-negative clathrin hub mutant. In addition, the levels of agonist-induced transient ERK1/2 activation were significantly increased in CHO-K1 cells stably expressing FLAG-tagged PAR1 compared to those in CHO-K1 cells not expressing FLAG-tagged PAR1. These results indicated those the endocytic pathway of PAR1 is clathrin-dependent and dynamin-dependent in CHO-K1 cells and that activation of PAR1 can stimulate ERK1/2 activation in CHO-K1 cells.