DIFFERENTIAL-EFFECTS OF WARFARIN ON THE INTRACELLULAR PROCESSING OF VITAMIN-K-DEPENDENT PROTEINS

The vitamin K-dependent carboxylation of specific glutamyl residues to gamma-carboxyglutamyl residues occurs during the endoplasmic reticulu m processing of a limited number of proteins. The fate of the under-ga mma-carboxylated proteins during protein processing was studied. When human hepatoma (HepG2) cells were grown in the presence of warfarin, u nder-gamma-carboxylated prothrombin was secreted into the medium. In c ontrast, prothrombin secretion from a rat hepatoma (H-35) cell line wa s blocked by warfarin, and intracellular forms which were retained wer e degraded. When rat prothrombin (rFII) was stably transfected into wa rfarin treated HepG2 cells, endogenous human prothrombin (hFII) was se creted in an under-gamma-carboxylated form, while rFII accumulated int racellularly. These data indicate that retention and degradation of un der-gamma-carboxylated prothrombin by human hepatocytes is related to a structural difference in rFII and hFII, When rFII and hFII were tran sfected into a warfarin treated transformed human embryonic kidney cel l line (293), both proteins were secreted in an under-gamma-carboxylat ed form and intracellular retention was not observed, However, the sec retion of rFII was greatly diminished. Cellular retention of under-gam ma-carboxylated forms is therefore tissue specific, but degradation is not.