The elusive factor Xa receptor: failure to detect transcripts that correspond to the published sequence of EPR-1

The coagulation protease factor Xa induces cellular responses implicated in cardiovascular and inflammatory disease. Effector-cell protease receptor 1 (EPR-1) is a functionally characterized receptor of factor Xa, and the EPR-1 complementary DNA (cDNA) was published. Remarkably, the cDNA encoding an inhibitor of apoptosis, survivin, is reportedly identical to that of EPR-1 except for a few nucleotide differences and its orientation opposite to EPR-1. To isolate the EPR-1 cDNA and gene, we surveyed gene databases for expressed sequence tags (ESTs) that could be derived from EPR-1. All ESTs with strong homology to EPR-1/survivin were derived from survivin and could not encode EPR-1. By polymerase chain reaction and Southern blot hybridization, EPR-1 was not detectable in the human or murine genome, but survivin was. Our data suggest that EPR-1 is either highly cell-specific or the published EPR-1 cDNA includes sequences from clones derived from survivin messenger RNA. The means by which factor Xa mediates its cellular effects requires further evaluation.