Impaired secretion of mutant alpha 2-plasmin inhibitor (alpha 2 PI- Nara)
from COS-7 and HepG2 cells: molecular and cellular basis for hereditary
deficiency of alpha 2-plasmin inhibitor
O Miura and N Aoki
First Department of Internal Medicine, Tokyo Medical and Dental University,
Japan.
The elongated mutant of alpha 2-plasmin inhibitor (alpha 2 PI) designated
as alpha 2 PI-Nara is caused by a frameshift mutation found near the 3' end
of the coding region of the alpha 2 PI gene. To elucidate the mechanism by
which this molecular abnormality leads to alpha 2 PI deficiency in plasma,
we transfected an expression plasmid for alpha 2 PI-Nara into a monkey
kidney cell line COS-7 or human hepatoma cell line HepG2 synthesizing alpha
2 PI, and analyzed the secretory process of the expressed alpha 2 PI-Nara
by radioimmunoprecipitation followed by sodium dodecyl sulfate
polyacrylamide gel electrophoresis and fluorography. The results obtained
showed that the recombinant alpha 2 PI-Nara was retained within the cells
for prolonged periods as an endoglycosidase H- sensitive precursor form,
and only a small portion of the recombinant protein was secreted into the
medium as a neuraminidase-sensitive mature form. These results suggest that
instead of being secreted from the cells, most of the alpha 2 PI-Nara
undergoes degradation within the cells while its transport is retarded in
the intracellular secretory pathway; thus, alpha 2 PI-Nara should lead to
the alpha 2 PI deficiency primarily by causing a block in the intracellular
transport from the endoplasmic reticulum to the Golgi complex.
Volume 75,
Issue 5,
pp. 1092-1096,
03/01/1990
Copyright © 1990 by The American Society of Hematology
