Role of cyclins in epithelial response to oxidants

The molecular mechanisms associated with the physiological responses to inflammation and oxidative stress in cardiovascular diseases

The complex physiological signal transduction networks that respond to the dual challenges of inflammatory and oxidative stress are major factors that promote the development of cardiovascular pathologies. These signaling networks contribute to the development of age-related diseases, suggesting crosstalk between the development of aging and cardiovascular disease. Inhibition and/or attenuation of these signaling networks also delays the onset of disease. Therefore, a concept of targeting the signaling networks that are involved in inflammation and oxidative stress may represent a novel treatment paradigm for many types of heart disease. In this review, we discuss the molecular mechanisms associated with the physiological responses to inflammation and oxidative stress especially in heart failure with preserved ejection fraction and emphasize the nature of the crosstalk of these signaling processes as well as possible therapeutic implications for cardiovascular medicine.

Tris (1,3-dichloro-2-propyl) phosphate treatment induces DNA damage, cell cycle arrest and apoptosis in murine RAW264.7 macrophages

Tris (1,3-dichloro-2-propyl) phosphate (TDCPP) is the most widely used organophosphorus flame retardant, which is now used instead of polybrominated diphenyl ethers (PBDEs). TDCPP has frequently been detected in inorganic environmental matrices, such as soil, water and air as well as biota. In vitro effects of TDCPP on cells had not been previously elucidated. Therefore, in the present study, cytotoxicity, DNA damage, cell cycle distribution, apoptosis caused by TDCPP was studied in RAW264.7 macrophage cells. TDCPP reduced viability of RAW264.7 cells in a concentration-dependent manner and caused damage to DNA that was detected by use of the comet assay and caused up-regulation of the level of γ-H2AX. TDCPP increased the intracellular reactive oxygen species (ROS) level in RAW264.7 cells up to 1.44-fold compared to the control group at 12 hr. Percentages of cells in G1 and G2 phases of the cell cycle were dose-dependently greater in cells exposed to TDCPP. TDCPP significantly down-regulated expression of CDK-4, Cyclin D1, Cyclin B1, CDC-2, which are regulators of G1 and G2 phases of the cell cycle. These results demonstrated that TDCPP is cytotoxic and damages DNA in RAW264.7 cells, which resulted in arrest of the cell cycle at G1 and G2 phases and resulted in apoptosis, suggest the necessity to evaluate the effects of TDCPP on the immune system at the cellular level.

Expression profiling and biochemical analysis suggest stress response as a potential mechanism inhibiting proliferation of polyamine-depleted cells

Polyamines are small organic polycations that are absolutely required for cell growth and proliferation; yet the basis for this requirement is mostly unknown. Here, we combined a genome-wide expression profiling with biochemical analysis to reveal the molecular basis for inhibited proliferation of polyamine-depleted cells. Transcriptional responses accompanying growth arrest establishment in polyamine-depleted cells or growth resumption following polyamine replenishment were monitored and compared. Changes in the expression of genes related to various fundamental cellular processes were established. Analysis of mirror-symmetric expression patterns around the G(1)-arrest point identified a set of genes representing a stress-response signature. Indeed, complementary biochemical analysis demonstrated activation of the PKR-like endoplasmic reticulum kinase arm of the unfolded protein response and of the stress-induced p38 MAPK. These changes were accompanied by induction of key growth-inhibitory factors such as p21 and Gadd45a and reduced expression of various cyclins, most profoundly cyclin D1, setting the basis for the halted proliferation. However, although the induced stress response could arrest growth, polyamine depletion also inhibited proliferation of PKR-like endoplasmic reticulum kinase and p38α-deficient cells and of cells harboring a nonphosphorylatable mutant eIF2α (S51A), suggesting that additional yet unidentified mechanisms might inhibit proliferation of polyamine-depleted cells. Despite lengthy persistence of the stress and activation of apoptotic signaling, polyamine-depleted cells remained viable, apparently due to induced expression of protective genes and development of autophagy.

Ochratoxin A induces oxidative DNA damage and G1 phase arrest in human peripheral blood mononuclear cells in vitro

Ochratoxin A is one of the most abundant food-contaminating mycotoxins worldwide, and its immunosuppressive effects in human caused more and more concern in biomedical field. In the present study, the toxicity of OTA on human peripheral blood mononuclear cells (hPBMC) was explored by analyzing the involvement of oxidative pathway. It was found that OTA treatment led to the release of reactive oxygen species (ROS) and the increase of 8-hydroxydeoxyguanosine (8-OHdG), an important biomarker of oxidative DNA stress. Moreover, we found that OTA treatment induced DNA strand breaks in hPBMC as evidenced by DNA comet tails formation and increased γ-H2AX expression. In addition, OTA could induce cell cycle arrest at G1 phase by down-regulating the expression of CDK4 and cyclinD1 protein, as well as apoptosis in hPBMC in vitro. Pre-treatment of hPBMC with antioxidant, N-acetyl-L-cysteine (NAC), could reduce OTA-induced ROS release and DNA damage, thus confirming the involvement of oxidative DNA damage in the OTA genotoxicity in hPBMC. NAC pre-treatment could also significantly prevent OTA-induced down-regulation of CDK4 and cyclinD1 expression in hPBMC. All the results demonstrated the involvement of oxidative pathway in OTA mediated cytotoxicity in human immune cells, which including the ROS accumulation-oxidative DNA damage-G1 arrest and apoptosis. Our results provide new insights into the molecular mechanisms by which OTA might promote immunotoxicity.

Alteronol inhibits proliferation in HeLa cells through inducing a G1-phase arrest

Objectives

Alteronol is a novel compound purified from fermentation products of a microorganism in the bark of the yew tree. The study was designed to evaluate the anticancer effects of alteronol.

Methods

Human cervical carcinoma cell line HeLa was cultured in vitro. The cell viability was evaluated by using sulforhodamine B assay. The cell cycle distribution was analysed by flow cytometry. The level of cyclin D1 protein was evaluated using Western blot analysis. The changes in cyclinD1, CDK4 and p21 were detected by ELISA assay and the changes in G1-related regulators were detected by RT-PCR assay.

Key findings

Our data showed that alteronol inhibited the proliferation of HeLa cells and induced G1 phase arrest. Downregulation of the mRNA levels of CDK2, CDK4 and cyclin D1 and upregulation of p21 in alteronol-treated cells were observed.

Conclusions

Downregulation of the mRNA levels of CDK2, CDK4 and cyclin D1 and upregulation of p21 might be a possible mechanism for the inhibition of proliferation induced by alteronol in HeLa cells.

Prolonged mechanical ventilation induces cell cycle arrest in newborn rat lung

RATIONALE

The molecular mechanism(s) by which mechanical ventilation disrupts alveolar development, a hallmark of bronchopulmonary dysplasia, is unknown.

OBJECTIVE

To determine the effect of 24 h of mechanical ventilation on lung cell cycle regulators, cell proliferation and alveolar formation in newborn rats.

METHODS

Seven-day old rats were ventilated with room air for 8, 12 and 24 h using relatively moderate tidal volumes (8.5 mL.kg⁻¹).

MEASUREMENT AND MAIN RESULTS

Ventilation for 24 h (h) decreased the number of elastin-positive secondary crests and increased the mean linear intercept, indicating arrest of alveolar development. Proliferation (assessed by BrdU incorporation) was halved after 12 h of ventilation and completely arrested after 24 h. Cyclin D1 and E1 mRNA and protein levels were decreased after 8-24 h of ventilation, while that of p27(Kip1) was significantly increased. Mechanical ventilation for 24 h also increased levels of p57(Kip2), decreased that of p16(INK4a), while the levels of p21(Waf/Cip1) and p15(INK4b) were unchanged. Increased p27(Kip1) expression coincided with reduced phosphorylation of p27(Kip1) at Thr¹⁵⁷, Thr¹⁸⁷ and Thr¹⁹⁸ (p<0.05), thereby promoting its nuclear localization. Similar -but more rapid- changes in cell cycle regulators were noted when 7-day rats were ventilated with high tidal volume (40 mL.kg⁻¹) and when fetal lung epithelial cells were subjected to a continuous (17% elongation) cyclic stretch.

CONCLUSION

This is the first demonstration that prolonged (24 h) of mechanical ventilation causes cell cycle arrest in newborn rat lungs; the arrest occurs in G₁ and is caused by increased expression and nuclear localization of Cdk inhibitor proteins (p27(Kip1), p57(Kip2)) from the Kip family.

Evidence for the progression through S-phase in the ectopic cell cycle re-entry of neurons in Alzheimer disease

Aberrant neuronal re-entry into the cell cycle is emerging as a potential pathological mechanism in Alzheimer disease (AD). However, while cyclins, cyclin dependent kinases (CDKs), and other mitotic factors are ectopically expressed in neurons, many of these proteins are also involved in other pathological and physiological processes, generating continued debate on whether such markers are truly indicative of a bona fide cell cycle process. To address this issue, here we analyzed one of the minichromosome maintenance (Mcm) proteins that plays a role in DNA replication and becomes phosphorylated by the S-phase promoting CDKs and Cdc7 during DNA synthesis. We found phosphorylated Mcm2 (pMcm2) markedly associated with neurofibrillary tangles, neuropil threads, and dystrophic neurites in AD but not in aged-matched controls. These data not only provide further evidence for cell cycle aberrations in AD, but the cytoplasmic, rather than nuclear, localization of pMcm2 suggests an abnormal cellular distribution of this important replication factor in AD that may explain resultant cell cycle stasis and consequent neuronal degeneration.

Ambient particulate matter induces alveolar epithelial cell cycle arrest: role of G1 cyclins

We hypothesized that the ambient air pollution particles (particulate matter; PM) induce cell cycle arrest in alveolar epithelial cells (AEC). Exposure of PM (25microg/cm(2)) to AEC induced cells cycle arrest in G1 phase, inhibited DNA synthesis, blocked cell proliferation and caused decrease in cyclin E, A, D1 and Cyclin E- cyclin-dependent kinase (CDK)-2 kinase activity after 4h. PM induced upregulation of CDK inhibitor, p21 protein and p21 activity in AEC. SiRNAp21 blocked PM-induced downregulation of cyclins and AEC G1 arrest. Accordingly, we provide the evidence that PM induces AEC G1 arrest by altered regulation of G1 cyclins and CDKs.

Fibroblast growth factor-10 prevents H2O2-induced cell cycle arrest by regulation of G1 cyclins and cyclin dependent kinases

We studied the effects of fibroblast growth factor (FGF-10) on H2O2-induced alveolar epithelial cell (AEC) G1 arrest and the role of G1 cyclins. FGF-10 prevented H2O2-induced AEC G1 arrest. FGF-10 induced 2-4-fold increase in cyclin E, cyclin A and CDKs (2,4) alone and in AEC treated with H2O2. H2O2 downregulated cyclin D1; FGF-10 blocked these effects. FGF-10 prevented H2O2-induced upregulation of CDK inhibitor, p21. SiRNAp21 blocked H2O2-induced downregulation of cyclins, CDKs and AEC G1 arrest. Accordingly, we provide first evidence that FGF-10 regulates G1 cyclins and CDKs, and prevents H2O2-induced AEC G1 arrest.

Cadmium induces cell cycle arrest in rat kidney epithelial cells in G2/M phase

Cadmium (Cd) has been reported to cause cell cycle arrest in various cell types by p53-dependent and -independent mechanisms. This study was designed to investigate cell cycle progression in kidney cells that are the target of chronic Cd toxicity. Rat renal proximal tubular epithelial cells, NRK-52E, were treated with up to 20 microM CdCl2 in DMEM containing 10% calf serum for up to 24 h. Flow cytometric analysis revealed time- and concentration-dependent increases in cells in G2/M phase of the cell cycle. As compared to the control cells, the cells exposed to 20 microM Cd showed a doubling of the number of cells in this phase after 24 h. The cell cycle arrest was associated with a decrease in protein levels of both cyclins A and B. Further investigation into the mechanism revealed that Cd treatment led to down-modulation of cyclin-dependent kinases, Cdk1 and Cdk2, apparently by elevating the expression of cyclin kinase inhibitors, KIP1/p27 and WAF1/p21. Furthermore, the wild-type p53 DNA-binding activity was up-regulated. Based on these observations, it appears that Cd causes G2/M phase arrest in NRK-52E cells via elevation of p53 activity, increasing the expression of cyclin kinase inhibitors p27 and p21, and decreasing the expression of cyclin-dependent kinases Cdk1 and 2, and of cyclins A and B.

The effect of cyclin D1 (CCND1) G870A-polymorphism on breast cancer risk is modified by oxidative stress among Chinese women in Singapore

Cyclin D1 (CCND1), an intracellular cell-cycle regulatory protein with checkpoint function, can promote cell proliferation or induce growth arrest and apoptosis depending on the cellular context. We hypothesized that the direction of the association between the (CCND1) G870A-polymorphism and breast cancer risk may be modified by dietary and genetic factors influencing the oxidant-antioxidant balance, such as a dietary pattern with a high intake of n-6 fatty acids and a low intake of n-3 fatty acids, or a genetic profile that is deficient in glutathione S-transferases. We tested our hypothesis in a case-control study nested into the Singapore Chinese Health Study, a prospective investigation of diet and cancer in 63,000 Chinese men and women. Genomic DNA collected from 258 incident cases of breast cancer and 670 female cohort controls was examined for CCND1, GSTM1, GSTT1 and GSTP1 genes using fluorogenic 5'-nuclease assay. Unconditional logistic regression models were used to assess the effects with adjustment for potential confounders. All statistical tests were two-sided. The heterozygous CCND1 GA genotype significantly reduced the breast cancer risk in all subjects (OR=0.67, 95% CI 0.45-0.99) when compared with the GG genotype. The association was restricted to women with a high (above median value) intake level of n-6 fatty acids (OR=0.51, 95% CI 0.30-0.87), a low (below median value) intake level of the antagonistic marine n-3 fatty acids (OR=0.54, 95% CI 0.32-0.93) or a total lack of the antioxidative GSTM1 (OR=0.44, 95% CI 0.25-0.80) or GSTT1 genes (OR=0.46, 95% CI 0.24-0.87). The effects were consistently stronger in cases with advanced disease. The AA genotype did not affect breast cancer risk. The results of this study are compatible with the hypothesis that the oxidant-antioxidant balance in cells is an important determinant of the direction of the cyclin D1 effect, leading either to cell proliferation or cell death.

Protection of pulmonary epithelial cells from oxidative stress by hMYH adenine glycosylase

Background

Oxygen toxicity is a major cause of lung injury. The base excision repair pathway is one of the most important cellular protection mechanisms that responds to oxidative DNA damage. Lesion-specific DNA repair enzymes include hOgg1, hMYH, hNTH and hMTH.

Methods

The above lesion-specific DNA repair enzymes were expressed in human alveolar epithelial cells (A549) using the pSF91.1 retroviral vector. Cells were exposed to a 95% oxygen environment, ionizing radiation (IR), or H₂O₂. Cell growth analysis was performed under non-toxic conditions. Western blot analysis was performed to verify over-expression and assess endogenous expression under toxic and non-toxic conditions. Statistical analysis was performed using the paired Student's t test with significance being accepted for p < 0.05.

Results

Cell killing assays demonstrated cells over-expressing hMYH had improved survival to both increased oxygen and IR. Cell growth analysis of A549 cells under non-toxic conditions revealed cells over-expressing hMYH also grow at a slower rate. Western blot analysis demonstrated over-expression of each individual gene and did not result in altered endogenous expression of the others. However, it was observed that O₂ toxicity did lead to a reduced endogenous expression of hNTH in A549 cells.

Conclusion

Increased expression of the DNA glycosylase repair enzyme hMYH in A549 cells exposed to O₂ and IR leads to improvements in cell survival. DNA repair through the base excision repair pathway may provide an alternative way to offset the damaging effects of O₂ and its metabolites.

Heme: a determinant of life and death in renal tubular epithelial cells

Heme oxygenase-1 (HO-1) and p21 influence cell fate, and genetic HO-1 overexpression upregulates p21 and confers resistance to apoptosis. The present study examined the effects of heme, a metabolite incriminated in renal injury, on sensitivity to apoptosis and cell growth in conjunction with cellular expression of HO-1 and p21. Immortalized rat proximal tubular epithelial cells (IRPTCs) were exposed to hemin (10 microM) in serum-deplete media (0.1% FBS) and in standard cell culture media (5.0% FBS). In the presence of 0.1% FBS media, hemin induced p21 through an HO-dependent, p53-independent mechanism; certain products of HO activity (iron and carbon monoxide), but not others (ferritin, apoferritin, bilirubin), recapitulated these inductive effects on p21 expression. Along with this inductive effect on HO-1 and p21, hemin worsened apoptosis, the latter exacerbated by the inhibition of HO activity and loss of p21 expression. In IRPTCs maintained in 5% FBS, hemin induced HO-dependent p21 expression, provoked cell cycle arrest, and inhibited cell growth without inducing apoptosis; this inhibitory effect of hemin on cell growth was blocked by the concomitant inhibition of HO activity and loss of p21 expression. We conclude that hemin is a potent HO-dependent inducer of p21 and that hemin increases the sensitivity to apoptosis in serum-deplete conditions and decreases cell growth in serum-replete conditions; inhibiting HO activity and concomitantly ablating p21 expression exacerbate apoptosis and reverse the growth-inhibitory actions of hemin. We suggest that these effects of heme may influence the nature of, and recovery from, ischemic and nephrotoxic insults to the kidney.

Increased apoptosis and expression of p21 and p53 in premature infant baboon model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a major complication of premature infants who receive prolonged ventilatory support. The pathophysiology of BPD involves oxidant injury, baro/volutrauma, and disordered lung repair. Exposure of premature lung that is poorly adapted for air breathing (>3% oxygen in fetal lung) to a higher concentration of oxygen can cause significant oxidant injury. Cell growth and differentiation of the developing lung require selective and ordered cell division. As hyperoxia can increase the expression of cell-cycle checkpoints that can cause growth arrest of lung cells, in this report we examined the expression of checkpoint proteins p53 and p21 in a premature infant the baboon model of BPD. Additionally, we also determined whether enhanced apoptosis occurs in baboon BPD model. We have shown that p53 and p21 expression are increased in 125-day as well as 140-day premature baboons with BPD. We also demonstrate increased apoptosis in lung tissue of premature baboons with BPD. These results demonstrate that cell growth inhibition is a likely factor in the evolution of BPD. Additionally, lung cells may undergo increased apoptosis that can impair the repair process in the postventilatory recovery period.

Altered expression of cyclins and cdks in premature infant baboon model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of premature infants, which results in substantial morbidity. The pathophysiology of BPD includes oxidant injury, baro/volutrauma, and disordered lung repair. As lung development, differentiation, and repair require cell division, we hypothesized dysregulation of the cell cycle in oxygen exposure of premature infants that may contribute to the evolution of BPD. In this investigation, we studied the expression of cyclins and cyclin-dependent kinases (cdks) that regulate transition from G1 and G2 phases of the cell cycle. We report here that expression of cyclin D1, cyclin E, and cyclin A is modulated in premature baboons in respiratory distress. In addition, the expression of cdk1 or cdk4 was also modulated in these premature animals. The phosphorylation of retinoblastoma protein was progressively decreased in 125-day animals and in 140-day animals exposed to 6 or 14 days of PRN oxygen. These results indicate that due to altered cyclin and cdk expression, the repair of injured epithelium may proceed in a disordered manner that is characteristic of BPD. Thus, altered cell cycle regulation may be an important factor in the evolution of BPD.

Role of tumor necrosis factor receptor 1 (p55) in hepatocyte proliferation during acetaminophen-induced toxicity in mice

Hepatocyte proliferation represents an important part of tissue repair. In these studies, TNF receptor 1 (TNFR1) knockout mice were used to analyze the role of TNF-alpha in hepatocyte proliferation during acetaminophen-induced hepatotoxicity. Treatment of wild-type (WT) mice with acetaminophen (300 mg/kg) resulted in centrilobular hepatic necrosis. This was associated with proliferation of hepatocytes surrounding the damaged areas, which was evident at 24 h. The cell cycle regulatory proteins, cyclin D1 and cyclin A, were also up regulated in hepatocytes. In contrast, in TNFR1-/- mice, which exhibit exaggerated acetaminophen hepatotoxicity, hepatocyte proliferation, and expression of cyclin D1 and cyclin A, as well as the cyclin dependent kinases, Cdk4 and Cdk2, were reduced. The cyclin-dependent kinase inhibitor p21 was also induced in the liver following acetaminophen administration. This was greater in TNFR1-/- mice compared to WT mice. To investigate mechanisms mediating the reduced hepatic proliferative response of TNFR1-/- mice, we analyzed phosphatidyl inositol-3-kinase (PI-3K) signaling. In both WT and TNFR1-/- mice, acetaminophen caused a rapid increase in total PI-3K within 3 h. Acetaminophen also increased phosphorylated PI-3K, but this was delayed 6-12 h in TNFR1-/- mice. Expression of Akt, a downstream target of PI-3K, was increased in both WT and TNFR1-/- mice in response to acetaminophen. However, the increase was greater in WT mice. Acetaminophen-induced expression of phosphorylated STAT3, a key regulator of cytokine-induced hepatocyte proliferation, was also delayed in TNFR1-/- mice relative to WT. These data suggest that TNF-alpha signaling through TNFR1 is important in regulating hepatocyte proliferation following acetaminophen-induced tissue injury. Delayed cytokine signaling may account for reduced hepatocyte proliferation and contribute to exaggerated acetaminophen-induced hepatotoxicity in TNFR1-/- mice.

Protection of lungs from hyperoxic injury: gene expression analysis of cyclosporin A therapy

We have previously shown that cyclosporin A (CsA), an inhibitor of protein phosphatase 2B (calcineurin), attenuates hyperoxia-induced reductions in murine lung compliance. CsA protected against hyperoxia-induced changes in neutrophil infiltration, capillary congestion, edema, and hyaline membrane formation. Gene expression studies were conducted to identify the gene expression patterns underlying the protective effects of CsA during hyperoxic lung injury. After 72 h of simultaneous treatment with >95% oxygen and CsA (50 mg x kg(-1) x day(-1)), RNA was isolated from murine lungs. RNA from treated and untreated lungs was reverse transcribed to cDNA, competitively hybridized, and used to probe 8,734 complimentary DNAs on the Incyte mouse GEM 1 array. Several known genes and expressed sequence tags (ESTs) showed increased (GenBank accession numbers: AA125385, AA241295, W87197, syntaxin, and cyclin G) or decreased [AA036517, AA267567, AA217009, W82577, uteroglobin, stromal cell-derived factor 1, and surfactant protein C (SP-C)] expression after hyperoxia. Hyperoxia-stimulated reductions in SP-C gene expression were confirmed through Northern blot analysis. The increase in gene expression of one expressed sequence tag (AA125385) with hyperoxia was reversed by CsA treatment. Sequence data demonstrated that this EST has high homology to murine cyclin B1. Western blot analysis did not demonstrate any changes in distal lung cyclin B1 expression after hyperoxia. Protein expression of cyclin B1 in the distal lung was observed in the endothelial cells, bronchiolar epithelial cells, and both the type I and type II alveolar epithelial cells. Further analysis of cyclin B1 may elucidate the protective actions of CsA in hyperoxic injury.

The effect of oxidative stress on histone acetylation and IL-8 release

Acetylation of histone residues regulates the expression of inflammatory genes and is controlled by the activities of histone acetyltransferases (HAT) and histone deacetylases (HDAC). Analysis of histone acetylation in human cells is limited by the large numbers needed to perform activity assays or Western blotting. We have used flow cytometry to investigate changes in HAT and HDAC activities at the single cell level and to investigate the effect of hydrogen peroxide (H(2)O(2)) on histone H4 acetylation and cell-cycle progression. Using an anti-acetylated histone H4 antibody we show that H(2)O(2) induced a time-dependent increase in histone acetylation that was maintained for 12h. This was associated with increased IL-8 production. H(2)O(2) also affected cell-cycle progression. HAT activity was found to be highest in G2/M and equivalent in G0/G1 and S phases of the cell cycle. These data show that detection of acetylated histone residues at the single cell level using FACs may be a powerful new tool for the analysis of modulation of cell proliferation and gene transcription.

Protection of human lung cells against hyperoxia using the DNA base excision repair genes hOgg1 and Fpg

Hyperoxia causes pulmonary toxicity in part by injuring alveolar epithelial cells. Previous studies have shown that toxic oxygen-derived species damage DNA and this damage is recognized and repaired by either human enzyme 8-oxoguanine DNA glycosylase (hOgg1) or Escherichia coli enzyme formamidopyrimidine DNA glycosylase (Fpg). To determine whether these DNA repair proteins can reduce O(2)-mediated DNA damage in lung cells, A549 lung epithelial cells were transduced with either hOgg1 or Fpg using a retroviral vector containing enhanced green fluorescent protein. Expression of each gene in the transduced cells was confirmed by fluorescent microscopy, Northern blotting, Western blotting, and an enzymatic oligonucleotide cleavage assay. A549 cells expressing either hOgg1 or Fpg were protected from hyperoxia as evidenced by a decrease in DNA damage and a corresponding increase in cell survival. Further, we determined that overexpression of hOgg1 or Fpg partially mitigated the toxic effects of hydrogen peroxide in lung cells. Our data suggest that increased expression of DNA base excision repair genes might represent a new approach for protecting critical lung cells from the toxic effects of hyperoxia.