p53 gene status modulates the chemosensitivity of non-small cell lung cancer cells

This study examined the effects of p53 gene status on DNA damage-induced cell death and chemosensitivity to various chemotherapeutic agents in non-small cell lung cancer (NSCLC) cells. A mutant p53 gene was introduced into cells carrying the wild-type p53 gene and also vice versa to introduce the wild-type p53 gene into cells carrying the mutant p53 gene. Chemosensitivity and DNA damage-induced apoptosis in these cells were then examined. This study included five cell lines, NCI-H1437, NCI-H727, NCI-H441 and NCI-H1299 which carry a mutant p53 gene and NCI-H460 which carries a wild-type p53 gene. Mutant p53-carrying cells were transfected with the wild-type p53 gene, while mutant p53 genes were introduced into NCI-H460 cells. These p53 genes were individually mutated at amino acid residues 143, 175, 248 and 273. The representative cell line NCI-H1437 cells transfected with wild-type p53 gene (H1437/wtp53) showed a dramatic increase in susceptibility to three anticancer agents (7-fold to cisplatin, 21-fold to etoposide, and 20-fold to camptothecin) compared to untransfected or neotransfected H1437 cells. An increase in chemosensitivity was also observed in wild-type p53 transfectants of H727, H441, H1299 cells. The results of chemosensitivity were consistent with the observations on apoptotic cell death. H1437/wtp53 cells, but not H1437 parental cells, exhibited a characteristic feature of apoptotic cell death that generated oligonucleosomal-sized DNA fragments. In contrast, loss of chemosensitivity and lack of p53-mediated DNA degradation in response to anticancer agents were observed in H460 cells transfected with mutant p53. These observations suggest that the increase in chemosensitivity was attributable to wild-type p53 mediation of the process of apoptosis. In addition, our results also suggest that p53 gene status modulates the extent of chemosensitivity and the induction of apoptosis by different anticancer agents in NSCLC cells.     

Anti-tumor effects by a synthetic chalcone compound is mediated by c-Myc-mediated reactive oxygen species production

Overexpression of c-Myc represents the most frequently deregulated genetic event in cancer, and therefore c-Myc may represent a good molecular target for cancer therapy. The human lung carcinoma cell line, NCI-H1299, shows resistance to conventional cancer treatments, such as ionizing radiation (IR) and cisplatin, while the lung carcinoma cell line, NCI-H460, is sensitive to treatment with these agents. However, when treated with a chalcone compound [toluenesulfonylamido-chalcone, 4′-(p-toluene sulfonyl amino)-3,4-dihydroxy chalcone (TSHDC)], cell death was dramatically induced in NCI-H1299 cells as compared to NCI-H460 cells. TSHDC-mediated cytotoxicity was not dependent on the status of p53 and p21. However, TSHDC exerted increased c-Myc-dependent reactive oxygen species (ROS) production in NCI-H1299 cells in which c-Myc is overexpressed, while increased ROS production did not occur in A549 or NCI-H460 cells with a low c-Myc level. Several colon and brain cancer cells also showed a correlation between c-Myc expression and TSHDC-mediated increased cell death. Tumor regression by TSHDC was more dramatic in NCI-H1299 cells than NCI-H460 cells, when these cells were grafted to nude mice. However, in the case of IR and cisplatin, NCI-H460 cells were more sensitive than NCI-H1299 cells. From these results, c-Myc-mediated ROS production may be a good target for screening of novel cancer drugs and TSHDC might be a good candidate as a cancer drug, specifically in cancer cells that overexpress c-Myc.     

BCI induces apoptosis via generation of reactive oxygen species and activation of intrinsic mitochondrial pathway in H1299 lung cancer cells

The compound(E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1 H-inden-1-one(BCI) is known as an inhibitor of dual specific phosphatase 1/6 and mitogen-activated protein kinase. However, its precise anti-lung cancer mechanism remains unknown. In this study, the effects of BCI on the viability of non-small cell lung cancer cell lines NCI-H1299, A549, and NCI-H460 were evaluated. We confirmed that BCI significantly inhibited the viability of p53(-) NCI-H1299 cells as compared to NCI-H460 and A549 cells, which express wild-type p53. Furthermore, BCI treatment increased the level of cellular reactive oxygen species and pre-treatment of cells with N-acetylcysteine markedly attenuated BCI-mediated apoptosis of NCI-H1299 cells. BCI induced cellular morphological changes, inhibited viability, and produced reactive oxygen species in NCI-H1299 cells in a dose-dependent manner. BCI induced processing of caspase-9, caspase-3, and poly ADP-ribose polymerase as well as the release of cytochrome c from the mitochondria into the cytosol. In addition, BCI downregulated Bcl-2 expression and enhanced Bax expression in a dose-dependent manner in NCI-H1299 cells. However, BCI failed to modulate the expression of the death receptor and extrinsic factor caspase-8 and Bid, a linker between the intrinsic and extrinsic apoptotic pathways in NCI-H1299 cells. Thus, BCI induces apoptosis via generation of reactive oxygen species and activation of the intrinsic pathway in NCI-H1299 cells.     

p53 Regulates Cellular Responses to Environmental Carcinogen Benzo[a]pyrene-7,8-diol-9,10-epoxide in Human Lung Cancer Cells

The p53 tumor suppressor is a mutational target of environmental carcinogen anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE). We now demonstrate that p53 plays an important role in regulation of cellular responses to BPDE. Exposure of p53-null H1299 human lung cancer cells to BPDE resulted in S and G2 phase cell cycle arrest, but not mitotic block, which correlated with induction of cyclin B1 protein expression, down-modulation of cell division cycle 25C (Cdc25C) and Cdc25B protein levels, and hyperphosphorylation of Cdc25C (S216), cyclin-dependent kinase 1 (Cdk1; Y15), checkpoint kinase 1 (Chk1; S317 and S345) and Chk2 (T68). The BPDE-induced S phase block, but not the G2/M phase arrest, was significantly attenuated by knockdown of Chk1 protein level. The BPDE-mediated accumulation of sub-diploid fraction (apoptotic cells) was significantly decreased in H1299 cells transiently transfected with both Chk1 and Chk2 specific siRNAs. The H460 human lung cancer cell line (wild-type p53) was relatively more sensitive to BPDE-mediated growth inhibition and enrichment of sub-diploid apoptotic fraction compared with H1299 cells. The BPDE exposure failed to activate either S or G2 phase checkpoint in H460 cells. Instead, the BPDE-treated H460 cells exhibited a nearly 8-fold increase in sub-diploid apoptotic cells that was accompanied by phosphorylation of p53 at multiple sites. Knockdown of p53 protein level in H460 cells attenuated BPDE-induced apoptosis but enforced activation of S and G2 phase checkpoints. In conclusion, the present study points towards an important role of p53 in regulation of cellular responses to BPDE in human lung cancer cells.     

Knockdown of hepatoma-derived growth factor-related protein-3 induces apoptosis of H1299 cells via ROS-dependent and p53-independent NF-κB activation

We previously identified hepatoma-derived growth factor-related protein-3 (HRP-3) as a radioresistant biomarker in p53 wild-type A549 cells and found that p53-dependent induction of the PUMA pathway was a critical event in regulating the radioresistant phenotype. Here, we found that HRP-3 knockdown regulates the radioresistance of p53-null H1299 cells through a distinctly different molecular mechanism. HRP-3 depletion was sufficient to cause apoptosis of H1299 cells by generating substantial levels of reactive oxygen species (ROS) through inhibition of the Nrf2/HO-1 antioxidant pathway. Subsequent, ROS-dependent and p53-independent NF-κB activation stimulated expression of c-Myc and Noxa proteins, thereby inducing the apoptotic machinery. Our results thus extend the range of targets for the development of new drugs to treat both p53 wild-type or p53-null radioresistant lung cancer cells.     

X-ray irradiation altered chemosensitivity of a p53-null non-small cell lung cancer cell line

Radiotherapy is an effective approach to treating many types of cancer. Recent progress in radiotherapy technology, such as intensity-modulated radiation therapy (IMRT) and three-dimensional (3D) radiotherapy, allow precise energy transfer to the tumor, which has improved local control rates. However, the emergence of tolerant cells during or after radiotherapy remains problematic. In the present study, we first established a cell population from H1299, the p53-null non-small cell lung cancer cell line, by 10 Gy irradiation using 6 MV X-rays. The radio- and chemosensitivity of this cell population (referred to as H1299-IR) was determined using colony formation analyses and MTS assays. Compared with the parental cell line, the radiosensitivity of H1299-IR was apparently the same. H1299 and H1299-IR were both more radio tolerant than the A549 cell line. However, H1299-IR became significantly more sensitive to cisplatin, an antitumor agent. After exposure to 25 mug/ml cisplatin for 2 h, parental cells steadily grew during the MTS assay, whereas the sensitivity of H1299-IR cells doubled both at 24 and 48 h. Microarray analysis of over 30,000 H1299-IR genes (Agilent Technology) revealed that 12 and 15 genes were up- (> 2.0) and down- (< 2.0) regulated, respectively. Rad51d (homologous recombination repair protein) gene was down-regulated 2.8-fold, whereas matrix metalloproteinase 1 (collagenase-1) gene was up-regulated 4.4-fold. These results indicated that some p53-null non-small cell lung cancers could be successfully treated when X-ray radiotherapy was administered with subsequent or concurrent cisplatin chemotherapy.     

Transient Transfection of a Wild-Type p53 Gene Triggers Resveratrol-Induced Apoptosis in Cancer Cells

Resveratrol is a promising chemopreventive agent that mediates many cellular targets involved in cancer signaling pathways. p53 has been suggested to play a role in the anticancer properties of resveratrol. We investigated resveratrol-induced cytotoxicity in H1299 cells, which are non-small lung cancer cells that have a partial deletion of the gene that encodes the p53 protein. The results for H1299 cells were compared with those for three cell lines that constitutively express wild-type p53: breast cancer MCF-7, adenocarcinomic alveolar basal epithelia A549 and non-small lung cancer H460. Cell viability assays revealed that resveratrol reduced the viability of all four of these cell lines in a dose- and time-dependent manner. MCF-7, A549 and H460 cells were more sensitive to resveratrol than were H1299 cells when exposed to the drug for 24 h at concentrations above 100 µM. Resveratrol also increased the p53 protein levels in MCF-7 cells without altering the p53 mRNA levels, suggesting a post-translational modulation of the protein. The resveratrol-induced cytotoxicity in these cells was partially mediated by p53 and involved the activation of caspases 9 and 7 and the cleavage of PARP. In H1299 cells, resveratrol-induced cytotoxicity was less pronounced and (in contrast to MCF-7 cells) cell death was not accompanied by caspase activation. These findings are consistent with the observation that MCF-7 cells were positively labeled by TUNEL following exposure to 100 µM resveratrol whereas H1299 cells under similar conditions were not labeled by TUNEL. The transient transfection of a wild-type p53-GFP gene caused H1299 cells to become more responsive to the pro-apoptotic properties of resveratrol, similarly to findings in the p53-positive MCF-7 cells. Our results suggest a possible therapeutic strategy based on the use of resveratrol for the treatment of tumors that are typically unresponsive to conventional therapies because of the loss of normal p53 function.     

A1E inhibits proliferation and induces apoptosis in NCI-H460 lung cancer cells via extrinsic and intrinsic pathways

It has been reported that extracts from Asian traditional/medical herbs possess therapeutic agents against cancers, metabolic diseases, inflammatory diseases, and other intractable diseases. In this study, we assessed the molecular mechanisms involved in the anticancer effects of A1E, the extract of Korean medicinal herbs. We examined the role of the cytotoxic and apoptotic pathways in the cancer chemopreventive activity in non-small-cell lung cancer (NSCLC) cell lines NCI-H460 and NCI-H1299. A1E inhibited the proliferation of NCI-H460 more efficiently than NCI-H1299 (p53^?/?) cells. The apoptosis was detected by nuclear morphological changes, annexin V-FITC/PI staining, cell cycle analysis, western blot, RT-PCR, and measurement of mitochondrial membrane potential. A1E induced cellular morphological changes and nuclear condensation at 24 h in a dose-dependent manner. A1E also perturbed cell cycle progression at the sub-G1 stage and altered cell cycle regulatory factors in NCI-H460 cells. Furthermore, A1E inhibited the PI3K/Akt and NF-κB survival pathways, and it activated apoptotic intrinsic and extrinsic pathways. A1E increased the expression levels of members of the extrinsic death receptor complex FasL and FADD. In addition, A1E treatment induced cleavage of caspase-8, caspase-9, caspase-3, and poly ADP-ribose polymerase (PARP), whereas the expression levels of Bcl-2 and Bcl-xl were downregulated. A1E induced mitochondrial membrane potential collapse and cytochrome C release. Our results suggest that A1E induces apoptosis via activation of both extrinsic and intrinsic pathways and inhibition of PI3K/Akt survival signaling pathways in NCI-H460 cells. In conclusion, these data demonstrate the potential of A1E as a novel chemotherapeutic agent in NSCLC.     

hMTH1 depletion promotes oxidative-stress-induced apoptosis through a Noxa- and caspase-3/7-mediated signaling pathway

Although the accumulation of 8-oxo-dGTP in DNA is associated with apoptotic cell death and mutagenesis, little is known about the exact mechanism of hMTH1-mediated suppression of oxidative-stress-induced cell death. Therefore, we investigated the regulation of DNA-damage-related apoptosis induced by oxidative stress using control and hMTH1 knockdown cells. Small interfering RNA (siRNA) was used to suppress hMTH1 expression in p53-proficient GM00637 and H460 cells, resulting in a significant increase in apoptotic cell death after H(2)O(2) exposure; however, p53-null, hMTH1-deficient H1299 cells did not exhibit H(2)O(2)-induced apoptosis. In addition, hMTH1-deficient GM00637 and H460 cells showed increased caspase-3/7 activity, cleaved caspase-8, and Noxa expression, and gamma-H2AX formation in response to H(2)O(2). In contrast, the caspase inhibitors, p53-siRNA, and Noxa-siRNA suppressed H(2)O(2)-induced cell death. Moreover, in 8-week (long-term) cultured H460 and H1299 cells, hMTH1 suppression increased cell death, Noxa expression, and gamma-H2AX after H(2)O(2) exposure, compared to 3-week (short-term) cultured cells. These data indicate that hMTH1 plays an important role in protecting cells against H(2)O(2)-induced apoptosis via a Noxa- and caspase-3/7-mediated signaling pathway, thus conferring a survival advantage through the inhibition of oxidative-stress-induced DNA damage.     

Ganoderic acid Me induces G1 arrest in wild-type p53 human tumor cells while G1/S transition arrest in p53-null cells

The mechanism of cell cycle arrest of tumor cells induced by ganoderic acid Me (GA-Me) is not understood. In this work, GA-Me was found to possess remarkable cytotoxicity on highly metastatic lung carcinoma 95-D cell line in both dose- and time-dependent manners. The effect of GA-Me on cell cycle arrest was found in 95-D, p53-null lung cancer cells H1299, HCT-116 p53^+/+ and HCT-116 p53^?/? human colon cancer cells. To obtain an insight into the role of p53 in cell cycle arrest by GA-Me, 95-D, H1299, HCT-116 p53^+/+ and HCT-116 p53^?/? cells were used for further investigation. GA-Me arrested cell cycle at G₁ phase in 95-D and HCT-116 p53^+/+ cells while S phase or G₁/S transition arrest in H1299 and HCT-116 p53^?/? cells. The results suggested that p53 may be a target of GA-Me, and it may be looked at as a new promising candidate for the treatment of carcinoma cells.     

A benzoxazine derivative specifically inhibits cell cycle progression in p53-wild type pulmonary adenocarcinoma cells

A fundamental aspect of cancer development is cancer cell proliferation. Seeking for chemical agents that can interfere with cancer cell growth has been of great interest over the years. In our study, we found that a benzoxazine derivative, (6-tert-butyl-3,4-dihydro-2H-benzo[b][1,4]oxazin-3-yl) methanol (TBM), could inhibit cell growth and caused significant cell cycle arrest in pulmonary adenocarcinoma A549 and H460 cells with wild-type p53, while not affecting the cell cycle distribution in p53-deleted H1299 lung adenocarcinoma cells. Since P53 plays an important role in regulating cell cycle progression, we analyzed the protein level of p53 by Western blot, and detected a significant elevation of p53 level after TBM treatment in A549 and H460 cells. The data suggested that TBM might specifically inhibit the proliferation of p53 wild-type lung adenocarcinoma cells through a p53-dependent cell cycle control pathway. More interestingly, results indicated that TBM might serve as a useful tool for studying the molecular mechanisms of lung cancer cell growth and cell cycle control, especially for the biologic process regulated by P53.     

p14ARF inhibits the growth of p53 deficient cells in a cell-specific manner

While p14(ARF) suppression of tumorigenesis in a p53-dependent manner is well studied, the mechanism by which p14(ARF) inhibits tumorigenesis independently of p53 remains elusive. A variety of factors have been reported to play a role in this latter process. We report here that p14(ARF) displays different effects on the anchorage-dependent and -independent growth of p53-null/Mdm2 wild type cells. p14(ARF) blocks both the anchorage-dependent and-independent (soft agar) proliferation of 293T and p53(-/-) HCT116, but not p53-null H1299 lung carcinoma cells. While p14(ARF) had no effect on the anchorage-dependent proliferation of p53(-/-) MEFs and Ras12V-transformed p53(-/-) MEFs, it inhibited the growth of Ras12V-transformed p53(-/-) MEFs in soft agar. Furthermore, ectopic expression of p14(ARF) did not lead to degradation of the E2F1 protein and did not result in the reduction of E2F1 activity detected by two E2F1 responsible promoters, Apaf1 and p14(ARF) promoter, in 293T, p53(-/-) HCT116, and H1299 cells. This is consistent with our observations that p14(ARF) did not result in G1 arrest, but induced apoptosis via Bax up-regulation. Taken together, our data demonstrate that the response of p53-null cells to ARF is cell type dependent and involves factors other than Mdm2 and E2F1.     

2-deoxy-D-glucose combined with ferulic acid enhances radiation response in non-small cell lung carcinoma cells

The present study was undertaken to investigate the radiosensitizing effects of 2-deoxy-D-glucose (2DG), a glycolytic inhibitor, and ferulic acid (FA), a phenolic prooxidant, in relatively radioresistant human non-small cell lung carcinoma cells (NCI-H460). NCI-H460 cells were treated with 4 mM 2DG and/or 53.8 μM FA for 24 h and then exposed to 2 Gy irradiation. Compared to cells that were 2 Gy-irradiated alone (50%), FA and 2DG with radiation (FA+2DG+IR) showed additional decrease in cell viability (15%). This has been further validated by decreased (86%) colony formation in 2DG+FA+IR group compared to 2DG (29%), FA (24%) and IR (37%) group alone. Increased apoptotic cells (84%) in 2DG+FA+IR group further confirm the radiosensitizing property of 2DG or FA. In NCI-H460 cells 2DG decreased NADPH levels (10%) and FA increased ROS levels leading to enhanced oxidative damage in the 2DG+FA+IR group. This was reflected as altered mitochondrial membrane potential, increased lipid peroxidative markers (TBARS), DNA damage and decreased intracellular glutathione (GSH) levels in combined treatment groups when compared to radiation or 2DG or FA treatment alone. The present study suggests that FA and 2DG act by increasing oxidative damage in NCI-H460 cells.     

Two-dimensional gel analysis of apoptosis-specific p53 isoforms induced by 2-methoxyestradiol in human lung cancer cells

The natural metabolic byproduct of estradiol, 2-methoxyestradiol (2-MeOE2), induces apoptosis in human lung cancer cells by a p53-dependent mechanism. The expression of wild-type p53 isoforms was investigated in H1299 non-small cell lung carcinoma cells induced into apoptosis by 2-MeOE2. H1299 cells lack endogenous p53 and undergo predominantly a G1 arrest when infected with a recombinant wild-type p53 adenovirus. However, when H1299 cells transfected with p53 were treated with 2-MeOE2, they underwent rapid and extensive apoptosis. H1299 cells expressing mutant his273 p53 were unaffected by 2-MeOE2, indicating a dependence of 2-MeOE2-mediated apoptosis on the presence of a functional p53. Analysis of wild-type p53 phosphoisoforms in H1299 cells by two-dimensional gel electrophoresis revealed that 2-MeOE2 induced a unique group of acidic p53 isoforms. Although most of the wild-type p53 in untreated H1299 cells migrated as at least five diffuse species with isoelectric points from pH 5.5–6.3, as many as nine additional forms migrating toward the acidic region with pI values from 4.4–5.3 were detected in 2-MeOE2-treated apoptotic cells. Two other agents known to induce apoptosis, vinblastine and actinomycin D, induced a similar pattern of acidic p53 species as that observed for 2-MeOE2. The results indicated that the induction of apoptosis in H1299 cells by 2-MeOE2 is dependent on the upregulation of specific p53 isoforms. Identification of the specific p53 phosphoisoforms induced by MeOE2 will be an important step in understanding the regulation and function of p53 in apoptosis.     

Golgi-SNARE GS28 potentiates cisplatin-induced apoptosis by forming GS28-MDM2-p53 complexes and by preventing the ubiquitination and degradation of p53

In the present study, we observed that the Golgi-SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) GS28 forms a complex with p53 in HEK (human embryonic kidney)-293 cells. Given that p53 represents a tumour suppressor that affects the sensitivity of cancer cells to various chemotherapeutic drugs, we examined whether GS28 may influence the level of sensitivity to the DNA-damaging drug cisplatin. Indeed, knockdown of GS28 using short-hairpin RNA (shGS28) induced resistance to cisplatin in HEK-293 cells. On the other hand, overexpression of GS28 sensitized HEK-293 cells to cisplatin, whereas no sensitization effect was noted for the mitotic spindle-damaging drugs vincristine and taxol. Accordingly, we observed that knockdown of GS28 reduced the accumulation of p53 and its pro-apoptotic target Bax. Conversely, GS28 overexpression induced the accumulation of p53 and Bax as well as the pro-apoptotic phosphorylation of p53 on Ser(46). Further experiments showed that these cellular responses could be abrogated by the p53 inhibitor PFT-α (pifithrin-α), indicating that GS28 may affect the stability and activity of p53. The modulatory effects of GS28 on cisplatin sensitivity and p53 stability were absent in lung cancer H1299 cells which are p53-null. As expected, ectopic expression of p53 in H1299 cells restored the modulatory effects of GS28 on sensitivity to cisplatin. In addition, GS28 was found to form a complex with the p53 E3 ligase MDM2 (murine double minute 2) in H1299 cells. Furthermore, the ubiquitination of p53 was reduced by overexpression of GS28 in cells, confirming that GS28 enhances the stability of the p53 protein. Taken together, these results suggest that GS28 may potentiate cells to DNA-damage-induced apoptosis by inhibiting the ubiquitination and degradation of p53.     

ICAM-3 endows anticancer drug resistance against microtubule-damaging agents via activation of the ICAM-3-AKT/ERK-CREB-2 pathway and blockage of apoptosis

In a previous study, we showed that induction of ICAM-3 endows radioresistance in cervical cancer [1]. To ascertain whether ICAM-3 also promotes anticancer drug resistance, mock control (H1299/pcDNA3) or ICAM-3-expressing stable transfectants (H1299/ICAM-3) of the non-small cell lung cancer (NSCLC) cell line, NCI-H1299, were generated and treated with the microtubule-damaging agents, paclitaxel (TXL) and vincristine (VCS). TXL-/VCS-treated H1299/ICAM-3 cells showed significantly lower levels of apoptosis, activation of caspases-3, 8 or 9, and decrease in anti-apoptotic protein levels, compared to H1299/pcDNA3 cells. Our data clearly indicate that ICAM-3 promotes drug resistance via inhibition of apoptosis. We additionally showed that Akt, ERK, and CREB-2 are located downstream of ICAM-3, and activation of the ICAM-3-Akt/ERK-CREB-2 pathway induces resistance against TXL and VCS. ICAM-3-expressing stable NCI-H460/ICAM-3 transfectant cells and radioresistant SiHa cells endogenously overexpressing ICAM-3 additionally showed drug resistance against TXL and VCS via activation of the ICAM-3-Akt/ERK-CREB-2 pathway. The finding that ICAM-3 endows drug resistance as well as radioresistance supports its potential utility as a major therapeutic target against cancer.     

Human 8-oxoguanine DNA glycosylase suppresses the oxidative stress induced apoptosis through a p53-mediated signaling pathway in human fibroblasts

Human 8-oxoguanine DNA glycosylase (hOGG1) is the main defense enzyme against mutagenic effects of cellular 7,8-dihydro-8-oxoguanine. In this study, we investigated the biological role of hOGG1 in DNA damage-related apoptosis induced by hydrogen peroxide (H(2)O(2))-derived oxidative stress. The down-regulated expression of hOGG1 by its small interfering RNA prominently triggers the H(2)O(2)-induced apoptosis in human fibroblasts GM00637 and human lung carcinoma H1299 cells via the p53-mediated apoptotic pathway. However, the apoptotic responses were specifically inhibited by hOGG1 overexpression. The p53-small interfering RNA transfection into the hOGG1-deficient GM00637 markedly inhibited the H(2)O(2)-induced activation of p53-downstream target proteins such as p21, Noxa, and caspase-3/7, which eventually resulted in the increased cell viability. Although the cell viability of hOGG1-knockdown H1299 p53 null cells was similar to that of the hOGG1 wild-type H1299, after the overexpression of p53 the hOGG1-knockdown H1299 showed the significantly decreased cell viability compared with that of the hOGG1 wild-type H1299 at the same experimental condition. Moreover, the array comparative genome hybridization analyses revealed that the hOGG1-deficient GM00637 showed more significant changes in the copy number of large regions of their chromosomes in response to H(2)O(2) treatment. Therefore, we suggest that although p53 is a major modulator of apoptosis, hOGG1 also plays a pivotal role in protecting cells against the H(2)O(2)-induced apoptosis at the upstream of the p53-dependent pathway to confer a survival advantage to human fibroblasts and human lung carcinomas through maintaining their genomic stability.