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Human hepatoma cells secrete single chain factor X, prothrombin, and
antithrombin III
DS Fair and BR Bahnak
The human hepatoma cell line, Hep G2, was analyzed for the ability to
synthesize and secrete several coagulation proteins. Using specific
radioimmunoassays, factor X, prothrombin, and antithrombin III were present
in 8-day culture supernatants at 62, 405, and 1,220 ng/mL, respectively.
Factor IX was not detected, either in supernatants or in cell extracts.
Intrinsically labeled factor X was secreted as a single- chain polypeptide
of 66,000 daltons, as measured by sodium dodecylsulfate-polyacrylamide gels
under nonreduced and reduced conditions. Immunoblots of Hep G2 supernatants
and normal human plasma also indicate the presence of single-chain factor
X. These findings support the hypothesis of a postsecretion proteolytic
cleavage of factor X into the two-chain form. Prothrombin and antithrombin
represented their plasma protein counterparts structurally, with molecular
weights of 73,000 and 61,000, respectively. Secreted factor X, prothrombin,
and antithrombin III were biologically active, as determined in coagulation
or chromogenic assays, and all three activities were neutralized by
monospecific antibodies. Vitamin K increased the quantity of prothrombin
secreted by twofold, without affecting the rate of secretion over a
five-day culture period, and had an apparent transient inhibitory effect on
secretion of antithrombin III. Warfarin caused a three to fourfold decrease
in the rate and quantity of secreted prothrombin, but did not affect
intracellular concentrations. The intracellular and extracellular
concentrations and rate of secretion of antithrombin III were not modulated
by warfarin. These data suggest that the Hep G2 cell line may provide a
useful model for assessing the regulation of biosynthesis and secretion of
human coagulation proteins.
Volume 64,
Issue 1,
pp. 194-204,
07/01/1984
Copyright © 1984 by The American Society of Hematology
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