Submitted August 1, 2007
Accepted December 7, 2007
Alternative mRNA splicing is favored by the A3 haplotype of the EPCR gene PROCR and generates a novel soluble form of EPCR in plasma
Beatrice Saposnik, Elodie Lesteven, Anna Lokajczyk, Charles T Esmon, Martine Aiach, and Sophie Gandrille*
Inserm U765, Paris, France
UFR des Sciences Pharmaceutiques, Universite Paris Descartes, Paris, France
Howard Hughes Medical Institute, and Cardiovascular Biology Research Program, Oklahoma Medical Research Fundation, Oklahoma City, OK, United States
AP-HP, Hopital Europeen Georges Pompidou, Service d'Hematologie Biologique A, Paris, France
* Corresponding author; email: sophie.gandrille{at}univ-paris5.fr.
The endothelial cell protein C receptor also exists in soluble form in plasma (sEPCR), resulting from ADAM17 cleavage. Elevated sEPCR levels are observed in subjects carrying the A3 haplotype, which is characterized by a Ser219Gly substitution in the transmembrane domain that renders the receptor more sensitive to cleavage. As sEPCR production is not completely blocked by metalloprotease inhibition, we looked for another mechanism. On comparing mRNA expression patterns and levels in A3 and non A3 cells from 32 human umbilical cord veins, we detected a truncated mRNA, in addition to the full-length mRNA. This truncated mRNA was 16 times more abundant in A3 HUVEC than in non A3 HUVEC, and encoded a protein lacking the transmembrane domain. We stably expressed a recombinant form of this protein (rEPCRisoform), and also a protein mimicking the plasma sEPCR (rEPCRsol). Functional studies of the purified recombinant proteins revealed that the rEPCRisoform bound to recombinant protein C (rPC) with similar affinity than rEPCRsol and that it also inhibited the anticoagulant activity of APC. Trace amounts of the EPCR isoform were found in the plasma of A3 subjects. These results suggest that the sEPCR isoform could contribute to the regulatory effect of sEPCR in plasma.
