Vertebrates possess 2 proteins with vitamin K oxidoreductase (VKOR) activity: VKORC1, whose vitamin K reduction supports vitamin K–dependent (VKD) protein carboxylation, and VKORC1-like 1 (VKORC1L1), whose function is unknown. VKD proteins include liver-derived coagulation factors, and hemorrhaging and lethality were previously observed in mice lacking either VKORC1 or the γ-glutamyl carboxylase (GGCX) that modifies VKD proteins. Vkorc1–/– mice survived longer (1 week) than Ggcx–/– mice (midembryogenesis or birth), and we assessed whether VKORC1L1 could account for this difference. We found that Vkorc1–/–;Vkorc1l1–/– mice died at birth with severe hemorrhaging, indicating that VKORC1L1 supports carboxylation during the pre- and perinatal periods. Additional studies showed that only VKORC1 sustains hemostasis beyond P7. VKORC1 expression and VKOR activity increased during late embryogenesis and following birth, while VKORC1L1 expression was unchanged. At P0, most (>99%) VKOR activity was due to VKORC1. Prothrombin mRNA, protein, and carboxylation also increased during this period, as did mRNA levels of coagulation factors encoding genes F7, F9, and F10. VKORC1L1 levels in Vkorc1–/– mouse liver may therefore be insufficient for supporting carboxylation beyond day 7. In support of this conclusion, VKORC1L1 overexpression in liver rescued carboxylation and hemostasis in adult Vkorc1–/– mice. These findings establish that VKORC1L1 supports VKD protein carboxylation in vivo.
Julie Lacombe, Mark A. Rishavy, Kathleen L. Berkner, Mathieu Ferron