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Biosynthesis of factor XIII B subunit by human hepatoma cell lines
JA Nagy, P Henriksson and J McDonagh
The plasma transglutaminase, factor XIIIa (FXIIIa), circulates as a zymogen
containing two proteins, A and B, arranged in a noncovalent tetrameric
complex, A2B2. Biosynthesis of plasma FXIII has not previously been
demonstrated. In the present study, direct evidence has been obtained that
two human hepatoma cell lines, Hep G2 and PLC/PRF/5, synthesize and secrete
FXIII B protein. Secretion of the B subunit of FXIII by Hep G2 was
demonstrated by immunoblotting. De novo synthesis by Hep G2 was confirmed
in 35S-methionine-labeled cultures. Radiolabeled conditioned medium was
concentrated, mixed (1:1) with purified B protein, and examined by crossed
immunoelectrophoresis with antiserum to the B subunit. The single protein
precipitin arc of purified B protein comigrated with the radiolabeled FXIII
from Hep G2 visualized by autoradiography, indicating both electrophoretic
and antigenic identity. The data presented here represent the first
demonstrations of biosynthesis of FXIII B protein by any cell type and
suggest that the liver is the site of synthesis of FXIII B protein. Further
analysis of concentrated Hep G2 serum-free conditioned medium (SFCM) and
cell lysate by immunoblotting following nondenaturing agarose gel
electrophoresis demonstrated the FXIII A protein as well as the B protein
and also revealed synthesis and secretion of the A and B proteins by
PLC/PRF/5. Crossed immunoelectrophoresis studies of Hep G2 SFCM and cell
lysate suggest that Hep G2 cells also synthesize and secrete the plasma
FXIII zymogen. With a specific radioimmunoassay for B protein, FXIII was
found in Hep G2 SFCM at approximately 4 ng/mL; with an amplified rocket
immunoelectrophoresis technique the level was approximately 5 ng/mL.
Volume 68,
Issue 6,
pp. 1272-1279,
12/01/1986
Copyright © 1986 by The American Society of Hematology
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