Overexpression of heme oxygenase-1 in human pulmonary epithelial cells results in cell growth arrest and increased resistance to hyperoxia.
Heme oxygenase (HO) catalyzes the rate-limiting step in the degradation of heme to biliverdin, which is reduced by biliverdin reductase to bilirubin. Heme oxygenase-1 (HO-1) is inducible not only by its heme substrate, but also by a variety of agents causing oxidative stress. Although much is known about the regulation of HO-1 expression, the functional significance of HO-1 induction after oxidant insult is still poorly understood. We hypothesize and provide evidence that HO-1 induction serves to protect cells against oxidant stress. Human pulmonary epithelial cells (A549 cells) stably transfected with the rat HO-1 cDNA exhibit marked increases of HO-1 mRNA levels which were correlated with increased HO enzyme activity. Cells that overexpress HO-1 (A549-A4) exhibited a marked decrease in cell growth compared with wild-type A549 (A549-WT) cells or A549 cells transfected with control DNA (A549-neo). This slowing of cell growth was associated with an increased number of cells in G0/G1 phase during the exponential growth phase and decreased entry into the S phase, as determined by flow cytometric analysis of propidium iodide-stained cells and pulse experiments with bromodeoxyuridine. Furthermore, the A549-A4 cells accumulated at the G2/M phase and failed to progress through the cell cycle when stimulated with serum, whereas the A549-neo control cells exhibited normal cell cycle progression. Interestingly, the A549-A4 cells also exhibited marked resistance to hyperoxic oxidant insult. Tin protoporphyrin, a selective inhibitor of HO, reversed the growth arrest and ablated the increased survival against hyperoxia observed in the A549-A4 cells overexpressing HO-1. Taken together, our data suggest that overexpression of HO-1 results in cell growth arrest, which may facilitate cellular protection against non-heme-mediated oxidant insult such as hyperoxia.
Lee
P J
PJ
Division of Pulmonary and Critical Care, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Alam
J
J
Wiegand
G W
GW
Choi
A M
AM
D000818:Animals; D015152:Blotting, Northern; D002453:Cell Cycle; D002455:Cell Division; D002470:Cell Survival / Q000187:drug effects; D015342:DNA Probes; D018076:DNA, Complementary; D004847:Epithelial Cells; D004848:Epithelium / Q000201:enzymology; D005434:Flow Cytometry; D006419:Heme Oxygenase (Decyclizing) / Q000096:biosynthesis*; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis; D007700:Kinetics; D008175:Lung Neoplasms; D010100:Oxygen / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D015342:DNA Probes; D018076:DNA, Complementary; D007527:Isoenzymes; D012333:RNA, Messenger; D011994:Recombinant Proteins; D006419:Heme Oxygenase (Decyclizing); D010100:Oxygen