STRUCTURAL FEATURES OF THE KRINGLE DOMAIN DETERMINE THE INTRACELLULARDEGRADATION OF UNDER-GAMMA-CARBOXYLATED PROTHROMBIN - STUDIES OF CHIMERIC RAT HUMAN PROTHROMBIN/

Vitamin K antagonist such as warfarin inhibit the vitamin K-dependent gamma-glutamyl carboxylation during protein processing and block the s ecretion of under-gamma-carboxylated prothrombin (FII) in the rat but not in the human or bovine. Under-gamma-carboxylated prothrombin is al so secreted from warfarin-treated human (HepG2) cell cultures but is d egraded in the endoplasmic reticulum in warfarin-treated rat (H-35) ce ll cultures. This differential response to warfarin has been shown Po be determined by the structural difference in the proteins rather than by the origin of the cell line, When recombinant rat prothrombin (rFI I) and human prothrombin (hFII) were expressed in a transformed human kidney cell line (HEK293), secretion of rFII but not hFII was drastica lly dea eased in response to warfarin. To determine the structural sig nal required for this differential response, chimeric cDNAs with the p ropeptide/Gla domains, kringle domain, and serine protease domain exch anged between rFII and hFII were generated (FIIRHH and FIIHRR, FIIRRH and FIIHHR, FIIRHR and FIIHRH) and expressed in both warfarin-treated HEK293 cells and UepG2 cells, The presenctt of the hFII kringle domain changed the stability of rFII to that of hFII, and the rFII kringle d omain changed the stability of hFII to that of rFII, The kringle domai n therefore is critical in determining the metabolic fate of under-gam ma-carboxylated prothrombin precursors during processing, Prothrombin contains two kringle structures, and expression of additional rFII/hFI I chimeras (FIIHrhII and FIIHhrH, FIIRrhR, and FIIRhrR) was used to de termine that the first of the two kringles plays a more important role in the recognition process.