Submitted March 4, 2009
Accepted June 22, 2009
Endothelial cell protein C receptor cellular localization and trafficking
Ramesh C. Nayak, Prosenjit Sen, Samit Ghosh, Ramakrishnan Gopalakrishnan, Charles T. Esmon, Usha R. Pendurthi, and L. Vijaya Mohan Rao*
Center for Biomedical Research, The University of Texas Health Science Center at Tyler, Tyler, TX, United States
Cardiovascular Research Program, Oklahoma Medical Research Foundation, and Howard Hughes Medical Institute, Oklahoma City, OK, United States
* Corresponding author; email: vijay.rao{at}uthct.edu.
Although the binding of endothelial cell protein C receptor (EPCR) to its ligands is well characterized at the biochemical level, it remains unclear how EPCR interaction with its ligands at the cell surface impacts its cellular trafficking. In the present study, we characterized the cellular localization and trafficking of EPCR in endothelial cells and a heterologus expression system. Immunofluorescence confocal microscopy studies revealed that a majority of EPCR is localized on the cell surface in membrane microdomains that are positive for caveolin-1. A small fraction of EPCR is also localized intracellularly in the recycling compartment. FVIIa or APC binding to EPCR promoted the internalization of EPCR. EPCR and EPCR-bound ligands were endocytosed rapidly via dynamin- and caveolar-dependent pathway. The endocytosed receptor-ligand complexes were accumulated in a recycling compartment before being targeted back to the cell surface. EPCR-mediated FVIIa endocytosis/recycling also resulted in transport of FVIIa from the apical to the basal side. In vivo studies in mice showed that blockade of EPCR with EPCR blocking antibodies impaired the early phase of FVIIa clearance. Overall our results show that FVIIa or APC binding to EPCR promotes EPCR endocytosis via the dynamin-dependent caveolar pathway, and EPCR-mediated endocytosis may facilitate the transcytosis of FVIIa and its clearance from the circulation.
