Prothrombin synthesis and degradation in rat hepatoma (H-35) cells: effects
of warfarin
P Zhang and JW Suttie
Department of Biochemistry, College of Agricultural and Life Sciences,
University of Wisconsin-Madison 53706.
Vitamin K is a substrate for the enzyme catalyzing the carboxylation of
specific glutamyl residues to gamma-carboxyglutamyl residues in hepatic
precursors of a limited number of plasma proteins, including prothrombin.
The gamma-carboxylation of these proteins can be blocked by the
anticoagulant warfarin; and in the bovine and human, warfarin treatment
results in the secretion of under-gamma-carboxylated forms of prothrombin
into plasma. In the rat, this response is not seen, but plasma prothrombin
concentrations are drastically decreased. This response has now been
studied in rat hepatoma (H-35) cells in which prothrombin secretion is
decreased 90% by incubation in the presence of warfarin. Neither
prothrombin mRNA levels nor the apparent rate of prothrombin message
translation were decreased when cells were cultured in the presence of
warfarin rather than of vitamin K. The pool of intracellular prothrombin
precursors is increased threefold by warfarin treatment, and this pool is
rapidly secreted when vitamin K is administered. In contrast, continued
incubation in the presence of warfarin resulted in the degradation of 60%
of this pool in 24 hours. When transport of secretory proteins to the golgi
apparatus was blocked with Brefeldin A, this precursor pool was
gamma-carboxylated in the presence of vitamin K and no degradation
occurred. Lysosomal enzyme inhibitors did not block the degradation, and
the data suggest that, in rat hepatocytes, under-gamma-carboxylated
prothrombin is specifically targeted to a pathway of protein degradation
located in the endoplasmic reticulum.
Volume 84,
Issue 1,
pp. 169-175,
07/01/1994
Copyright © 1994 by The American Society of Hematology
