Published ahead of print on September 8, 2005, doi:10.1165/rcmb.2004-0361OC Am. J. Respir. Cell Mol. Biol., Volume 33, Number 6, December 2005, 555-564 A more recent version of this article appeared on December 1, 2005
Submitted on November 17, 2004 PARP Activation Mediates Lung Epithelial Cell Death in vitro but is not Essential in Hyperoxia-induced Lung InjuryAlessandra Pagano1,1 Department of Pediatrics, University of Geneva, Medical School, Geneva, Switzerland; Department of Pathology/Immunology, University of Geneva, Medical School, Geneva, Switzerland * To whom correspondence should be addressed. E-mail: constance.barazzone{at}hcuge.ch.
Hyperoxia induces extensive DNA damage and lung cell death by both apoptotic and non apoptotic pathways. We analyzed the regulation of Poly(ADP-ribose)polymerase-1 (PARP-1), a nuclear enzyme activated by DNA damage, and its relation to cell death during hyperoxia in vitro and in vivo. In lung epithelial-derived A549 cells, known to die by necrosis when exposed to oxygen, a minimal amount of PARP-1 was cleaved, correlating with the absence of active caspase-3. Conversely, in primary lung fibroblasts, dying mainly by apoptosis, the complete cleavage of PARP-1 was concomitant to the induction of active caspase-3, as assessed by western blot and caspase activity. Blockade of caspase activity by Z-VAD reduced the amount of cleaved PARP-1 in fibroblasts. Hyperoxia induced PARP activity in both cell types, as revealed by poly-ADP-ribose (PAR) accumulation. In A549 cells, the final outcome of necrosis was dependent on PARP activity, since it was prevented by the PARP inhibitor 3-aminobenzamide (3-AB). In contrast, apoptosis of lung fibroblasts was not sensitive to 3-AB and was not affected by PARP-1 deletion. In vivo, despite evidence of PARP activation in hyperoxia-exposed mouse lungs, absence of PARP-1 did not change the extent of lung damage, arguing for redundant oxidative stressinduced cell death pathways.
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