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Department of Medicine, University of Florida, and Medical Research Service, Veterans Affairs Medical Center, Gainesville, Florida 32608-1197
The effects of exposure to hypoxia on the catalytic activity and
mRNA expression of calpain, a calcium-regulated neutral cysteine protease, were examined in porcine pulmonary artery endothelial cells
(PAECs). Specificity of the response to hypoxia was determined by
comparing the effects of hypoxic exposure with exposure to oxidants
such as nitrogen dioxide (NO2) and nitric oxide (NO), as
well as to the sulfhydryl reactive chemical acrolein. Exposure of cells
to hypoxia (0% O2) for 1 and 12 h significantly increased catalytic activity (P < 0.01 for both 1 and 12 h vs.
control cells), as well as mRNA expression (P < 0.01 for 1 h and P < 0.05 for 12 h vs. control cells) of calpain. With
more prolonged exposure to 24 h of hypoxia, calpain activity remained
significantly elevated, whereas calpain mRNA expression returned to the
control level. Calpain activities in cells exposed to NO2
[5 parts/million (ppm)] or NO (7.5 ppm) for 1 h or to acrolein (5 µM) for 1 and 24 h were unchanged. However, calpain activities in
cells exposed to NO2 or NO for 24 h were significantly
(P < 0.05) reduced compared with control cells. The
hypoxia-induced increases in calpain mRNA content were prevented by the
transcriptional inhibitor actinomycin D and by calpain inhibitor I. In
addition, hypoxia increased the degradation of nuclear factor-
B
(NF-
B) inhibitor I
B and enhanced the translocation of the p50
subunit of NF-
B to the nuclear membrane. Pretreatment with the
calpain-specific inhibitor E-64d prevented hypoxia-induced mRNA
expression and degradation of I
B
, as well as translocation of p50
subunit to the nuclear membrane. These results demonstrate for the
first time that hypoxia upregulates calpain activity and mRNA
expression in PAECs and that the upregulation is specific to hypoxia.
Upregulation appears to involve activation of the transcription factor
NF-
B.
endothelium
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