Phosphatase 2A participates in interferon-gamma's induced upregulation of
C1 inhibitor mRNA expression
GD Heda, KJ Kehoe, F Mahdi and AH Schmaier
Thrombosis Research Center, Temple University School of Medicine,
Philadelphia, PA, USA.
C1 inhibitor (C1 INH) is the major inhibitor of the proteolytically active
subcomponents of C1, kallikrein, activated forms of factor XII, and factor
XIa in plasma. We determined the mechanism(s) how interferon- gamma
(IFN-gamma) regulates C1 INH mRNA expression in HepG2 cells. Cycloheximide
or anisomycin treatment alone did not increase C1 INH mRNA nor did it
potentiate C1 INH mRNA expression after IFN-gamma stimulation. C1 INH mRNA
levels on Northern blot from untreated and IFN- gamma-treated cells did not
change for more than 20 hours after actinomycin D treatment. Actinomycin D
and 5,6-dichloro-1-beta- ribofuranosylbenzimidazole abolished
IFN-gamma-induced C1 INH mRNA expression. Relatively more C1 INH mRNA
precursor (heterogeneous nuclear RNA [hnRNA]) was detected in total RNA
from IFN-gamma-treated HepG2 cells than unstimulated cells. Treatment of
HepG2 cells with the phosphatase 1 and 2A inhibitors, okadaic acid (> or
= 50 nmol/L) and calyculin (> or = 25 nmol/L), decreased IFN-gamma's
ability to upregulated C1 INH mRNA. The phosphatase 2A inhibitor,
cantharidin (> or = 10 micromol/L), also blocked the IFN-gamma induction
of the C1 INH gene. In HepG2 cells total phosphatase 2A activity was
significantly increased by C6 ceramide but not IFN-gamma. However, C6
ceramide itself did not increase C1 INH mRNA expression. These data
indicate that phosphatase 2A is required to dephosphorylate a substrate in
order for IFN-gamma to induce the transcriptional upregulation of C1 INH
mRNA, but phosphatase 2A is not a direct stimulator of C1 INH gene
expression.
Volume 87,
Issue 7,
pp. 2831-2838,
04/01/1996
Copyright © 1996 by The American Society of Hematology
