Summary

Protein Z (PZ) is a vitamin K-dependent protein isolated fromhuman plasma, and acts as a cofactor for a serpin, called proteinZ-dependent protease inhibitor (ZPI).A prothrombotic phenotypehas been reported in PZ deficient mice, and PZ deficiencieshave been observed in patients with arterial thrombotic events.PZ was immunologically detected in the endothelium of atheroscleroticarteries,suggesting that endothelial cells could be involvedin the production of PZ.In this study we analyzed the synthesisand release of PZ and ZPI by human umbilical vein endothelialcells (HUVEC), representative of the macrovasculature,and by HMEC-1, a microvascular endothelial cell line. PZwas quantified by a specific ELISA in the supernatant and in thelysates of both cellular types. Western blotting of the supernatantsshowed the presence of a band of 62 kDa,identical to PZ synthesized by the hepatoma cell line HepG2. mRNA of PZ wasalso detected in each cellular type. PZ biosynthesis was unaffectedby inflammatory cytokines in HUVEC, whereas a slightdecrease of mRNA and PZ antigen (53.5 ± 14.5% of protein synthesisas compared to the control, p < 0.01) and a modest increase(126 ± 8.5 % as compared to the control, p< 0.05) wereinduced respectively byTumor Necrosis Factor (TNF)-alpha (25ng/ml) and oncostatin M (5 ng/ml) in HMEC-1. Immunologicalstudies showed the presence of PZ near the nucleus and a possibleexpression of PZ at the membrane.In addition,PZ was presentin the endothelial cells of both normal arterial and venousvessel sections. In contrast, neither ZPI nor its mRNA was detectedin endothelial cells.