Differences in basal and hyperoxia associated heme oxygenase
expression in oxidant resistant hamster fibroblasts.
Dennery, Phyllis A ., Kunju J. Sridhar, Pam Rodgers, Julia E. Sim,
Douglas R. Spitz.
Department of Pediatrics, Stanford University School of Medicine,
Stanford, CA, Department of Radiology, Cancer Biology Section,
Washington University, Saint Louis, MO
APStracts 3:0107L, 1996.
Heme oxygenase (HO) is the rate limiting enzyme in the production of
bilirubin from heme and HO-1 is its inducible isoenzyme. In the
metabolic pathway of HO, a potential oxidant, heme is degraded, a
potential antioxidant, bilirubin is generated, and a potent
sequestering agent of redox active iron, ferritin is thought to be
coinduced. Therefore, the sum of the reactions of HO may be useful in
antioxidant defense. To explore the role of HO in protection against
oxidative stress, we examined HO-1 expression in Chinese hamster
fibroblasts (HA-1) as well as stable hydrogen peroxide (H2O2)
resistant (OC-14) and 95% O2 resistant (O2R95) variant cell lines
derived from HA-1, after exposure to 72 hours of hyperoxia (95% O2 /
5% CO2). Total HO activity, HO-1 protein and HO-1 mRNA steady state
levels were assessed prior to, and daily during exposure to
hyperoxia. Controls were exposed to 95 % air / 5% CO2. Confluent
monolayers of O2R95 and OC-14 cells had increased basal
immunoreactive HO-1 protein levels relative to HA-1 cells when the
cells were grown in normoxia and O2R95 had higher total basal HO
activity. When exposed to hyperoxia for up to 3 days, O2R95 cells
which were resistant to oxygen induced killing, did not show
induction of HO-1 mRNA or increased immunoreactive protein, whereas
OC-14 and HA-1, which were relatively more sensitive than O2R95 to
oxygen related cytotoxicity, demonstrated significant increases in
HO-1 expression during exposure to hyperoxia. Basal ferritin protein
levels were highest in the O2R95 cells, intermediate in OC-14 and
lowest in HA-1 but ferritin protein did not increase further in any
of the cell lines with hyperoxic exposure. We conclude that increased
constitutive HO-1 expression is associated with resistance to
hyperoxia, whereas, induction of HO-1 mRNA is an index of oxidative
injury since it only occurs after cells have sustained cytotoxic
injury. We also conclude that increased ferritin expression does not
necessarily accompany increased HO-1 expression in oxidant stress. We
speculate that HO-1 plays a role in protection against hyperoxic
damage.
Received 30 November 1995; accepted in final form 22 May 1996.
APS Manuscript Number L348-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96