P53-mediated induction of Cox-2 counteracts p53- or genotoxic stress-induced apoptosis

Clinicopathological correlations of cyclooxygenase-2, MDM2, and p53 expressions in surgically resectable pancreatic invasive ductal adenocarcinoma

OBJECTIVES

Cyclooxygenase-2 (COX-2) and p53 represent molecules linked to oncogenesis of pancreatic cancer, and there is also a known regulatory loop between mouse double minute 2 (MDM2) and p53. The complex cross talks between p53 and COX-2 and scenarios explaining patterns of p53 and COX-2 expressions in precursor and cancer lesions have been recently reported.

METHODS

The expressions of COX-2, p53, and MDM2 were examined using immunohistochemistry in 85 resection specimens of pancreatic ductal adenocarcinoma.

RESULTS

The positive tumor expression rates of COX-2, p53, and MDM2 were 69.4%, 60.0%, and 41.2%, respectively. Significant correlations between COX-2 and p53 expressions and between p53 and MDM2 expressions were revealed. In the Kaplan-Meier analysis, no statistically significant correlations were found among the levels of COX-2, p53, and MDM2 expressions and survival rates. In the multivariate Cox proportional hazards regression model, grade and nodal status showed to be a valuable predictor of a worse overall survival.

CONCLUSIONS

The reported findings confirmed the relationship of p53, MDM2, and COX-2 with the biological process of pancreatic cancer. The expression of none of the examined proteins showed to be a valuable independent prognostic factor. On the contrary, grade and nodal status showed to be a valuable predictor of a worse survival.

Cyclooxygenase-2 functionally inactivates p53 through a physical interaction with p53

Cyclooxygenase-2 (COX-2), an endoplasmic reticulum-resident protein, has been known to promote tumorigenesis, but the exact mechanisms involved have not been identified. We have previously reported that COX-2 physically interacts with the tumor suppressor p53 and regulates its function. However, it remains to be elucidated how COX-2 can interact with p53 residing in different compartments and whether their interaction is involved in the regulation of p53 function. We here demonstrated that upon genotoxic stress, COX-2 and p53 accumulate in the nucleus, where they physically interact with one another. We also showed that an amino-terminal region (amino acids 1-126) of COX-2 interacts with the DNA-binding domain of p53. The p53-interacting region was critical for COX-2-mediated inhibition of p53 DNA-binding and transcriptional activity as well as p53- and genotoxic stress-induced apoptosis. In addition, an active site mutant of COX-2 (S516Q) as well as wild-type COX-2 potently inhibited p53 transcriptional activity and genotoxic stress-induced apoptosis. These results suggest that COX-2 principally inhibits p53 function through a catalytic activity-independent mechanism and that COX-2 inhibits p53 function through a physical interaction with p53 in the nucleus. These findings provide novel insight into the action mechanisms of COX-2 and strongly suggest that the functional inactivation of p53 by COX-2 can be one of the mechanisms by which COX-2 promotes tumorigenesis.

Inhibition of p53 by pifithrin-alpha reduces myocyte apoptosis and leukocyte transmigration in aged rat hearts following 24 hours of reperfusion

Ischemic heart disease is a common age-related disease. Apoptotic cell death and inflammation are the major contributors to I/R injury. The mechanisms that trigger myocyte apoptosis and inflammation during myocardial I/R (MI/R) remain to be elucidated. Published data from our laboratory demonstrated that pretreatment of MI/R rats with pifithrin-alpha (PFT), a specific p53 inhibitor, reduced myocyte apoptosis and improved cardiac function compared with MI/R rats pretreated with saline at 4 h of reperfusion. In the present study, we investigated the effects of PFT on the occurrence of myocyte apoptosis and leukocyte transmigration in the later period of reperfusion. Aged (20-month-old) male F344 rats were subjected to 30 min of myocardial ischemia via ligature of the LCA, followed by 24 h of reperfusion. Pifithrin-alpha (2.2 mg/kg, intraperitoneally) or saline was administered to rats before ischemia. The results indicate that pretreatment of MI/R rats with PFT significantly decreased the percentage of infarct area to ischemic area (33 +/- 8 vs. 54 +/- 9, P < 0.05) and improved cardiac output (79 +/- 11 vs. 38 +/- 9 mL/min per 100 g body weight, P < 0.05) when compared with rats pretreated with saline at 24 h of reperfusion. The protective effects of PFT may involve the p53/Bax-mediated apoptosis because treatment of MI/R rats with PFT attenuated the ratio of Bax to Bcl2 (0.97 +/- 0.1 vs. 2.1 +/- 0.2, P < 0.05) and reduced myocyte apoptosis. Interestingly, inhibition of p53 transcriptional function by PFT alleviated leukocyte infiltration into the ischemic area of the heart (339 +/- 37 vs. 498 +/- 75 cells/10 high-power fields, P < 0.05). These data suggest that inhibition of p53 transcriptional function by PFT attenuates myocyte apoptosis and alleviates leukocyte transmigration at 24 h of reperfusion. The mechanisms by which p53 modulates leukocyte transmigration require further investigation.

Transcriptional regulation of estrogen receptor-alpha by p53 in human breast cancer cells

Estrogen receptor alpha (ER) and p53 are critical prognostic indicators in breast cancer. Loss of functional p53 is correlated with poor prognosis, ER negativity, and resistance to antiestrogen treatment. Previously, we found that p53 genotype was correlated with ER expression and response to tamoxifen in mammary tumors arising in mouse mammary tumor virus-Wnt-1 transgenic mice. These results lead us to hypothesize that p53 may regulate ER expression. To test this, MCF-7 cells were treated with doxorubicin or ionizing radiation, both of which stimulated a 5-fold increase in p53 expression. ER expression was also increased 4-fold over a 24-h time frame. In cells treated with small interfering RNA (siRNA) targeting p53, expression of both p53 and ER was significantly reduced (>60%) by 24 h. Induction of ER by DNA-damaging agents was p53 dependent as either ionizing radiation or doxorubicin failed to up-regulate ER after treatment with p53-targeting siRNA. To further investigate whether p53 directly regulates transcription of the ER gene promoter, MCF-7 cells were transiently transfected with a wild-type (WT) p53 expression vector along with a luciferase reporter containing the proximal promoter of ER. In cells transfected with WT p53, transcription from the ER promoter was increased 8-fold. Chromatin immunoprecipitation assays showed that p53 was recruited to the ER promoter along with CARM1, CBP, c-Jun, and Sp1 and that this multifactor complex was formed in a p53-dependent manner. These data show that p53 regulates ER expression through transcriptional control of the ER promoter, accounting for their concordant expression in human breast cancer.

Gallbladder cancer: a morphological and molecular update

Gallbladder cancer (GBC) shows a marked geographical variation in its incidence, with the highest figures being seen in India and Chile and relatively low levels in many Western countries. Risk factors for its development include the presence of gallstones, infection and the presence of an anomalous pancreatobiliary ductal junction. It can arise from either a pathway involving metaplasia or dysplasia or one in which there is a pre-existing adenoma. The former is the more common and, because it is often not associated with a macroscopically recognizable lesion, leads to the recommendation that all gallbladders need to be examined microscopically. Accurate staging of invasive cancers is essential to determine prognosis and treatment, and this requires extensive tumour sampling. A number of genetic alterations have been identified in the preinvasive and invasive stages of GBC and they support the morphological evidence of there being two pathways by which tumours develop. Some of these genetic changes are associated with particular risk factors. For example, cases with anomalous pancreatobiliary ductal junction show a higher frequency of K-ras mutations. Some changes are associated with differences in prognosis. For example, cancers without expression of p21 but with expression for p27 have a better prognosis, whereas those that express c-erb-B2 have a worse one. Work has also been done on identifying clinical, imaging and other factors that indicate that patients have a higher risk of having GBC. This is particularly important in high-incidence areas in which GBC is a significant public health problem.

Role of p53 in the induction of cyclooxygenase-2 by cisplatin or paclitaxel in non-small cell lung cancer cell lines

Non-small cell lung Cancer (NSCLC) is extremely resistant to chemotherapeutic agents, such as cisplatin. High expression of the inflammatory enzyme cyclooxygenase-2 (COX-2) has been shown to inhibit chemotherapy-induced apoptosis, but little is known about COX-2 regulation upon drug treatment. Recent data indicate the tumor suppressor protein p53 as an important regulator of COX-2. Therefore, TP53 status could change tumor sensitivity to chemotherapy through induction of the anti-apoptotic protein COX-2. The main objective of this work was to analyze the effect of chemotherapy on the expression of COX-2, according to TP53 status. We report herein that lung cancer cell lines expressing wild-type p53, when exposed to cisplatin treatment, induced COX-2 (mRNA and protein), with concurrent synthesis of prostaglandins (PGE(2)). In contrast, COX-2 expression was not changed after cisplatin treatment of cells containing an inactive form of p53. Further, after silencing of wild-type p53 expressed in A549 cells by RNA interference, cisplatin was no longer able to induce COX-2 expression. Therefore, we suggest that induction of COX-2 by cisplatin in NSCLC cell lines is dependent on p53. For paclitaxel treatment, an increase in COX-2 mRNA expression was observed in H460 and A549 (wild-type p53 cell lines). Moreover, paclitaxel treatment increased COX-2 expression in ACC-LC-319 cell lines (p53 null), showing a p53-independent effect. These data may have therapeutic implications in the selection of patients and strategy for future COX-2 inhibition trials.

Advance in relationship between COX-2 and gastric cancer

COX-2 is an inducible enzyme which is over expressed in gastric cancer tissues and plays an important role in the incidence, development and prognosis of gastric cancer by regulating the formation of vessel, inducing mutations, immune suppression, suppression of apoptosis, changing the activity of adhesion molecule to promote tumor metastasis, and so on. COX selective inhibitors can be used as one of the basic anti-tumor drugs because of their tumor suppression function in the future.

Evaluation of the immunoexpression of COX-1, COX-2 and p53 in Crohn's disease

BACKGROUND: Crohn's disease accompanied by nonspecific or idiopathic ulcerative proctocolitis corresponds to a condition called intestinal inflammatory disease. The immunoexpression of cyclooxygenase 2 (COX-2) in Crohn's disease becomes more marked with progression of the disease and the presence of wild-type p53 suppresses the transcription of COX-2. AIMS: To investigate the immunoexpression of cyclooxygenase 1 (COX-1), COX-2 and p53 in Crohn's ileocolitis and to correlated this expression with clinical and histopathological parameters. METHODS: Forty-five cases of Crohn's disease, 16 cases of actinic colitis (diseased-control group) and 11 cases without a history of intestinal disease (normal control group) were studied. Hematoxylin-eosin-stained sections were submitted to histopathological analysis and the immunohistochemical expression of COX-1, COX-2 and p53 was evaluated by the streptavidin-biotin-peroxidase method. RESULTS: Sixty percent of the Crohn's disease patients were women and 40% were men, with 75.5% whites and 25.5% non-whites. The disease involved the terminal ileum in 44.5% of cases, ileum in 33.3%, colon in 20% and duodenum-ileum in 2.2%. A significant association was observed between COX-2 immunoreactivity and age <40 years. Histopathological analysis of Crohn's disease samples showed mild or moderate crypt distortion (57.8% and 35.6% of cases), atrophy (6.6%), mild, moderate and marked chronic inflammation (46.7%, 26.7% and 20%), acute inflammatory activity (93.3%), ulceration (24.4%), mucin depletion (37.8%), Paneth's cells (24.4%), intraepithelial lymphocytes (93.3%), and subepithelial collagen (6.7%). In the CD group, COX-1 immunoreactivity in epithelial and inflammatory cells was observed in 26.7% and 22.2% of cases, respectively. COX-2 immunoreactivity was detected in epithelial cells in 68.9% of cases and in inflammatory cells in 46.7%. A marginal difference in COX-2 reactivity was observed between epithelial and inflammatory cells in association with acute inflammatory activity and increase in intraepithelial lymphocytes. Comparison of the date among the threes groups (Crohn's disease, actinic colitis and normal controls) showed a higher proportion of cases presenting COX-2 immunoreactivity in inflammatory cells in the Crohn's disease group. No p53 reactivity was observed in all cases. CONCLUSIONS: COX-2 immunoexpression is high in Crohn's disease, which suggest a possible role of the protein in the pathogenesis of the inflammation. The absence of epithelial dysplasia in all Crohn's disease samples was correlated with the lack of expression of p53.

Resveratrol causes COX-2- and p53-dependent apoptosis in head and neck squamous cell cancer cells

Cyclooxygenase-2 (COX-2) content is increased in many types of tumor cells. We have investigated the mechanism by which resveratrol, a stilbene that is pro-apoptotic in many tumor cell lines, causes apoptosis in human head and neck squamous cell carcinoma UMSCC-22B cells by a mechanism involving cellular COX-2. UMSCC-22B cells treated with resveratrol for 24 h, with or without selected inhibitors, were examined: (1) for the presence of nuclear activated ERK1/2, p53 and COX-2, (2) for evidence of apoptosis, and (3) by chromatin immunoprecipitation to demonstrate p53 binding to the p21 promoter. Stilbene-induced apoptosis was concentration-dependent, and associated with ERK1/2 activation, serine-15 p53 phosphorylation and nuclear accumulation of these proteins. These effects were blocked by inhibition of either ERK1/2 or p53 activation. Resveratrol also caused p53 binding to the p21 promoter and increased abundance of COX-2 protein in UMSCC-22B cell nuclei. Resveratrol-induced nuclear COX-2 accumulation was dependent upon ERK1/2 activation, but not p53 activation. Activation of p53 and p53-dependent apoptosis were blocked by the COX-2 inhibitor, NS398, and by transfection of cells with COX-2-siRNA. In UMSCC-22B cells, resveratrol-induced apoptosis and induction of nuclear COX-2 accumulation share dependence on the ERK1/2 signal transduction pathway. Resveratrol-inducible nuclear accumulation of COX-2 is essential for p53 activation and p53-dependent apoptosis in these cancer cells.

Expression of COX-2 is associated with accumulation of p53 in pancreatic cancer: analysis of COX-2 and p53 expression in premalignant and malignant ductal pancreatic lesions

OBJECTIVES

Cyclooxygenase-2 (COX-2) and tumor suppressor p53 are molecules that are linked to the oncogenesis of pancreatic cancer. COX-2 represents a key modulatory molecule in inflammation and carcinogenesis, and is known to be implicated in the positive regulation of growth and tumorigenesis. Abnormal expression of p53 is common in many human neoplasms including pancreatic cancer. Recent studies demonstrated functional interactions between p53 and COX-2. The p53-dependent upregulation of COX-2 was proposed to be another mechanism by which p53 could abate its own growth-inhibitory and apoptotic effects.

METHODS

In this study, we immunohistochemically analyzed the expression of COX-2 and p53 in 95 pancreatic resection specimens [adenocarcinomas, 95 lesions; pancreatic intraepithelial neoplasias (PanINs), 155; normal ducts, 70].

RESULTS

The expression of COX-2 increased progressively with the grade of ductal lesions (P<0.00001). A statistically significant difference of COX-2 expression between normal ducts and low-grade PanINs was revealed (P=0.0042). COX-2 overexpression was demonstrated in 82 PanINs (52.9%), and in 76 adenocarcinomas (80%). No significant correlation between the grade of adenocarcinoma and COX-2 expression was revealed (P=0.2). The expression of p53 again increased progressively with the grade of lesions (P<0.00001) with a significant increase in high-grade PanINs. A correlation between COX-2 and p53 expression levels in carcinomas was revealed (P=0.0002), and an accumulation of p53 was associated with COX-2 overexpression in premalignant and malignant ductal lesions.

CONCLUSION

These findings confirmed the generally accepted pancreatic cancer progression model, and supported the concept of the interactive role of COX-2 and p53 in pancreatic cancer carcinogenesis, which offers opportunities for targeted therapy and chemoprevention of pancreatic cancer using COX-2 inhibitors.

COX2 and p53 risk-alleles coexist in COPD

BACKGROUND

Cigarette smoke stimulates airway epithelial cells to release pro-inflammatory cytokines which influence various inflammation-related genes, including COX2, whereas p53 expression is known to alter in such a condition. Since both the genes share several common physiological functions including inflammation and oxidative stress, we investigated within gene and gene-gene interactions towards susceptibility to the disease.

METHOD

In a prospective gene-association study we conducted PCR-RFLP for genotyping the COX2 -765G/C and 8473T/C and p53 72Pro/Arg polymorphisms in 229 COPD patients and 147 healthy controls.

RESULTS

The -765GC+CC genotypes of COX2 and Pro/Pro+Pro/Arg genotypes of p53 were prevalent in patients with significant odds ratio, 2.05 and 2.30, respectively (p=0.001; p=0.009, respectively), as a consequence, the -765C and 72Pro alleles were prevalent (p<or=0.001). Individually, the 8473T/C polymorphism did not associate with the disease (p=NS), however, it did in the haplotype -765C:8473C, which was significantly higher in patients (p<0.0001). Based on its prevalence, the three alleles were identified as risk-alleles in patients. The combinations of the genotypes containing 3, 4 and 5 risk alleles of the 3 polymorphisms were significantly over-represented in patients, whereas, the genotypes combinations containing 0, 1 and 2 risk alleles were significantly higher in controls (p=0.0004). The pairwise gene-gene interactions validated prevalence of risk-alleles associated pairing of genotypes such as the Pro/Pro+ Pro/Arg with -765GC+-765CC in patients (p=0.01).

CONCLUSION

The prevalence of COX2 and p53 risk-alleles contributes towards susceptibility to the disease.

COX-2 and p53 in human sinonasal cancer: COX-2 expression is associated with adenocarcinoma histology and wood-dust exposure

The causal role of wood-dust exposure in sinonasal cancer (SNC) has been established in epidemiological studies, but the mechanisms of SNC carcinogenesis are still largely unknown. Increased amounts of COX-2 are found in both premalignant and malignant tissues, and experimental evidence link COX-2 to development of cancer. Many signals that activate COX-2 also induce tumor suppressor p53, a transcription factor central in cellular stress response. We investigated COX-2 and p53 expressions by immunohistochemistry in 50 SNCs (23 adenocarcinomas, and 27 squamous cell carcinomas (SCC); 48 analyzed for COX-2; 41 for p53). Occupational histories and smoking habits were available for majority of the cases. Most of the adenocarcinoma cases with exposure history data had been exposed to wood dust at work in the past (88%, 14/16). For smokers, 63% (12/19) presented with SSC, whereas 64% (7/11) of nonsmokers displayed adenocarcinoma. COX-2 was expressed at higher levels in adenocarcinoma as compared to SSC (p < 0.001). COX-2 expression showed significant association with occupational exposure to wood dust (p = 0.024), and with nonsmoking status (p = 0.001). No statistically significant associations between the exposures and p53 accumulation were found; however, the p53 accumulation pattern (p = 0.062 for wood dust exposure) resembled that of COX-2 expression. In summary, our findings show increased COX-2 expression in SNC adenocarcinoma with wood dust exposure, suggesting a role for inflammatory components in the carcinogenesis process. In contrast, SCCs predominated among smokers and expressed COX-2 rarely; this may suggest at least partially different molecular mechanisms.

Deregulated expression of pro-survival and pro-apoptotic p53-dependent genes upon Elongator deficiency in colon cancer cells

Elongator, a multi-subunit complex assembled by the IkappaB kinase-associated protein (IKAP)/hELP1 scaffold protein is involved in transcriptional elongation in the nucleus as well as in tRNA modifications in the cytoplasm. However, the biological processes regulated by Elongator in human cells only start to be elucidated. Here we demonstrate that IKAP/hELP1 depleted colon cancer-derived cells show enhanced basal expression of some but not all pro-apoptotic p53-dependent genes such as BAX. Moreover, Elongator deficiency causes increased basal and daunomycin-induced expression of the pro-survival serum- and glucocorticoid-induced protein kinase (SGK) gene through a p53-dependent pathway. Thus, our data collectively demonstrate that Elongator deficiency triggers the activation of p53-dependent genes harbouring opposite functions with respect to apoptosis.

Inflammation and cancer: an ancient link with novel potentials

Infection and chronic inflammation contribute to about 1 in 4 of all cancer cases. Mediators of the inflammatory response, e.g., cytokines, free radicals, prostaglandins and growth factors, can induce genetic and epigenetic changes including point mutations in tumor suppressor genes, DNA methylation and post-translational modifications, causing alterations in critical pathways responsible for maintaining the normal cellular homeostasis and leading to the development and progression of cancer. Recent discovery of an interaction between microRNAs and innate immunity during inflammation has further strengthened the association between inflammation and cancer.

Discoidin domain receptor 1 receptor tyrosine kinase induces cyclooxygenase-2 and promotes chemoresistance through nuclear factor-kappaB pathway activation

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by various types of collagens and is known to play a role in cell attachment, migration, survival, and proliferation. However, little is known about the molecular mechanism(s) underlying the role of DDR1 in cancer. We report here that DDR1 induces cyclooxygenase-2 (Cox-2) expression resulting in enhanced chemoresistance. Depletion of DDR1-mediated Cox-2 induction using short hairpin RNA (shRNA) results in increased chemosensitivity. We also show that DDR1 activates the nuclear factor-kappaB (NF-kappaB) pathway and blocking this activation by an I kappaB superrepressor mutant results in the ablation of DDR1-induced Cox-2, leading to enhanced chemosensitivity, indicating that DDR1-mediated Cox-2 induction is NF-kappaB dependent. We identify the upstream activating kinases of the NF-kappaB pathway, IKK beta and IKK gamma, as essential for DDR1-mediated NF-kappaB activation, whereas IKK alpha seems to be dispensable. Finally, shRNA-mediated inhibition of DDR1 expression significantly enhanced chemosensitivity to genotoxic drugs in breast cancer cells. Thus, DDR1 signaling provides a novel target for therapeutic intervention with the prosurvival/antiapoptotic machinery of tumor cells.

Hzf Determines cell survival upon genotoxic stress by modulating p53 transactivation

A critical unresolved issue about the genotoxic stress response is how the resulting activation of the p53 tumor suppressor can lead either to cell-cycle arrest and DNA repair or to apoptosis. We show here that hematopoietic zinc finger (Hzf), a zinc-finger-containing p53 target gene, modulates p53 transactivation functions in an autoregulatory feedback loop. Hzf is induced by p53 and binds to its DNA-binding domain, resulting in preferential transactivation of proarrest p53 target genes over its proapoptotic target genes. Thus, p53 activation results in cell-cycle arrest in Hzf wild-type MEFs, while in Hzf(-/-) MEFs, apoptosis is induced. Exposure of Hzf null mice to ionizing radiation resulted in enhanced apoptosis in several organs, as compared to in wild-type mice. These findings provide novel insights into the regulation of p53 transactivation function and suggest that Hzf functions as a key player in regulating cell fate decisions in response to genotoxic stress.

Elevated expression of cyclooxygenase-2 is a negative prognostic factor for overall survival in intrahepatic cholangiocarcinoma

The production of prostaglandins is regulated by cyclooxygenases (COXs), which also have a role in tumour development and progression in various human malignancies, including cholangiocarcinoma. Limited information is available of the correlation of COX-2 protein expression and prognosis in intrahepatic cholangiocarcinoma (ICC). The aim of the present study was to determine the clinical significance of COX-2 expression in ICC. In addition the correlation of COX-2 expression and apoptosis/proliferation was analysed. COX-2 expression was determined immunohistochemically in 62 resected ICCs. Proliferation was assessed using Ki67-immunohistochemistry, and apoptosis was measured with the TdT-mediated dUTP nick-end-labelling technique. COX-2 was identified as an independent prognostic factor (P = 0.028) in resected ICC by survival analysis. High levels of COX-2 expression were found to be associated both with reduced apoptosis and increased proliferation of tumour cells. This study demonstrates the independent prognostic value of the COX-2 expression in resected ICC, thus, offering a potential additional adjuvant therapeutic approach with COX-2 inhibitors.

A novel natural compound, a cycloanthranilylproline derivative (Fuligocandin B), sensitizes leukemia cells to apoptosis induced by tumor necrosis factor related apoptosis-inducing ligand (TRAIL) through 15-deoxy-Delta 12, 14 prostaglandin J2 production

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis in many transformed cells; however, not all human tumors respond to TRAIL, potentially limiting its therapeutic utility. Although there is substantial evidence that cytotoxic drugs can augment sensitivity to TRAIL, it has become important to know what kinds of nontoxic drugs can be used together with TRAIL. We thus screened several natural compounds that can overcome resistance to TRAIL and found that a cycloanthranilylproline derivative, Fuligocandin B (FCB), an extract of myxomycete Fuligo candida, exhibited significant synergism with TRAIL. Treatment of the TRAIL-resistant cell line KOB with FCB and TRAIL resulted in apparent apoptosis, which was not induced by either agent alone. FCB increased the production of 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)), an endogenous PPAR gamma ligand, through activation of cyclooxygenase-2 (COX-2). This unique mechanism highlighted the fact that 15d-PGJ(2) directly enhanced sensitivity to TRAIL by inhibiting multiple antiapoptotic factors. More importantly, similar effects were observed in other leukemia cell lines irrespective of their origin. The enhancement was observed regardless of PPAR gamma expression and was not blocked even by peroxisome proliferator-activated receptor-gamma (PPAR gamma) siRNA. These results indicate that 15d-PGJ(2) sensitizes TRAIL-resistant cells to TRAIL in a PPAR gamma-independent manner and that the use of 15d-PGJ(2) or its inducers, such as FCB, is a new strategy for cancer therapy.

p53 modulation of the DNA damage response

The tumor suppressor p53 plays a central role in the DNA damage response. After exposure to genotoxic stress, p53 can both positively and negatively regulate cell fate. Initially, p53 promotes cell survival by inducing cell cycle arrest, DNA repair, and other pro-survival pathways. However, when cells accumulate DNA damage or demonstrate aberrant growth, p53 can direct the elimination of damaged cells. In this review, we will discuss the transcriptional-dependent and -independent roles of p53 in regulating the DNA damage response.

Cyclooxygenase-2 induction by arsenite through the IKKbeta/NFkappaB pathway exerts an antiapoptotic effect in mouse epidermal Cl41 cells

BACKGROUND

Arsenic contamination has become a major public health concern worldwide. Epidemiologic data show that long-term arsenic exposure results in the risk of skin cancer. However, the mechanisms underlying carcinogenic effects of arsenite on skin remain to be studied.

OBJECTIVES

In the present study we evaluated cyclooxygenase-2 (COX-2) expression, the signaling pathways leading to COX-2 induction, and its antiapoptotic function in the response to arsenite exposure in mouse epidermal JB6 Cl41 cells.

METHODS

We used the luciferase reporter assay and Western blots to determine COX-2 induction by arsenite. We utilized dominant negative mutant, genetic knockout, gene knockdown, and gene overexpression approaches to elucidate the signaling pathway involved in COX-2 induction and its protective effect on cell apoptosis.

RESULTS

The induction of COX-2 by arsenite was inhibited in Cl41 cells transfected with IKKbeta-KM, a dominant mutant inhibitor of kbeta (Ikbeta) kinase (IKKbeta), and in IKKbeta-knockout (IKKbeta(-/-)) mouse embryonic fibroblasts (MEFs). IKKbeta/nuclear factor kappaB (NFkappaB) pathway-mediated COX-2 induction exerted an antiapoptotic effect on the cells exposed to arsenite because cell apoptosis was significantly enhanced in the Cl41 cells transfected with IKKbeta-KM or COX-2 small interference RNA (siCOX-2). In addition, IKKbeta(-/-) MEFs stably transfected with COX-2 showed more resistance to arsenite-induced apoptosis compared with the same control vector-transfected cells.

CONCLUSIONS

These results demonstrate that arsenite exposure can induce COX-2 expression through the IKKbeta/NFkappaB pathway, which thereby exerts an antiapoptotic effect in response to arsenite. In light of the importance of apoptosis evasion during carcinogenesis, we anticipate that COX-2 induction may be at least partially responsible for the carcinogenic effect of arsenite on skin.

p53 downstream target DDA3 is a novel microtubule-associated protein that interacts with end-binding protein EB3 and activates beta-catenin pathway

We have previously identified mouse DDA3 as a p53-inducible gene. To explore the functional role of DDA3, we screened a mouse brain cDNA library by the yeast two-hybrid assay, and identified the microtubule plus-end binding protein EB3 as a DDA3-interacting protein. Binding of DDA3 to EB3 was verified by glutathione S-transferase (GST) pull-down assay and subcellular colocalization; co-immunoprecipitation further indicated that interaction of these two proteins within cells required intact microtubules. Domains of DDA3-EB3 interaction were mapped by GST pull-down assay to amino acids 118-241 and 242-329 of DDA3 and the N- and C-termini of EB3. Immunofluorescence analysis revealed colocalization of DDA3 with microtubules in various cell phases, and regions encompassing aa 118-241 and 242-329 contained microtubule-interacting and bundling activities. In vitro microtubule-binding assay showed that DDA3 and EB3 associated directly with microtubules, and cooperated with each other for microtubule binding. In addition, DDA3 bound to the EB3 interacting partner adenomatous polyposis coli 2 (APC2), a homolog of the tumor suppressor APC, which is a component of the beta-catenin destruction complex. Ectopic expression of DDA3 and EB3 enhanced beta-catenin-dependent transactivation and cyclin D1 production, whereas knockdown of endogenous DDA3 or EB3 inhibited beta-catenin-mediated transactivation and the ability of cells to form colonies. Together, our results identify DDA3 as a novel microtubule-associated protein that binds to EB3, and implicate DDA3 and EB3 in the beta-catenin-mediated growth signaling.

A role for cyclooxygenase-2 in ultraviolet light-induced skin carcinogenesis

Nonmelanoma skin cancer is the most prevalent cancer in the United States and its incidence is on the rise. These cancers generally arise on sun-exposed areas of the body and the ultraviolet (UV) B spectrum of sunlight has been clearly identified as the major carcinogen responsible for skin cancer development. Besides inducing DNA damage directly, UV exposure of the skin induces the expression of the enzyme cyclooxygenase-2 (COX-2), which catalyzes the first step in the conversion of arachidonic acid to prostaglandins, the primary product in skin being prostaglandin E(2) (PGE(2)). COX-2 has been shown to be overexpressed in premalignant lesions as well as in nonmelanoma skin cancers in both humans and mice chronically exposed to UV. Through the use of COX-2-selective inhibitors and COX-2 knockout mice, it has been shown that UV-induced COX-2 expression plays a major role in UV-induced PGE(2) production, inflammation, edema, keratinocyte proliferation, epidermal hyperplasia, and generation of a pro-oxidant state leading to oxidative DNA damage. Chronic exposure to UV leads to chronic up-regulation of COX-2 expression and chronic inflammation along with the accumulation of DNA damage and mutations, all of which combine to induce malignant changes in epidermal keratinocytes and skin cancers. Both inhibition of COX-2 activity and reduction in COX-2 expression by genetic manipulations significantly reduce, while overexpression of COX-2 in transgenic mice significantly increases UV-induced skin carcinogenesis. Together these studies demonstrate that COX-2 expression/activity is critical to the development of UV-related nonmelanoma skin cancers.

Cross-talks between cyclooxygenase-2 and tumor suppressor protein p53: Balancing life and death during inflammatory stress and carcinogenesis

Overexpression of Cyclooxygenase-2 (COX-2) is observed in most tumor types. Increased COX-2 activity and synthesis of prostaglandins stimulates proliferation, angiogenesis, invasiveness and inhibits apoptosis. Many stress and proinflammatory signals induce COX-2 expression, including oxyradicals or DNA-damaging agents. The latter also induces p53, a transcription factor often inactivated by mutation in cancer. Several studies have identified complex cross-talks between p53 and COX-2, whereby p53 can either up- or down-regulate COX-2, which in turn controls p53 transcriptional activity. However, the molecular basis of these effects are open to debate, in particular since no p53 binding sequences have been identified in COX-2 regulatory regions. In this review, we summarize the molecular mechanisms by which COX-2 contributes to carcinogenesis and discuss the experimental set-up, results and conclusions of studies analyzing cross-talks between p53 and COX-2. We propose 2 scenarios accounting for overexpression of COX-2 in precursor and cancer lesions. In the "inflammatory" scenario, p53, activated by DNA damage induced by oxygen and nitrogen species, recruits NF-kappaB to activate COX-2, resulting in antiapoptotic effects that contribute to cell expansion in inflammatory precursor lesions. In the "constitutive proliferation" scenario, oncogenic stress due to activation of growth signaling cascades may upregulate COX-2 promoter independently of NF-kappaB and p53, synergizing with TP53 mutation to promote cancer progression. These 2 scenarios, although not mutually exclusive, may account for the diversity of the correlations between COX-2 expression and TP53 mutation, which vary according to cancer types and biological contexts, and have implications for the use of COX-2 inhibitors in cancer prevention and therapy.

Effects of brief cutaneous JP-8 jet fuel exposures on time course of gene expression in the epidermis

The jet fuel jet propulsion fuel 8 (JP-8) has been shown to cause an inflammatory response in the skin, which is characterized histologically by erythema, edema, and hyperplasia. Studies in laboratory animal skin and cultured keratinocytes have identified a variety of changes in protein levels related to inflammation, oxidative damage, apoptosis, and cellular growth. Most of these studies have focused on prolonged exposures and subsequent effects. In an attempt to understand the earliest responses of the skin to JP-8, we have investigated changes in gene expression in the epidermis for up to 8 h after a 1-h cutaneous exposure in rats. After exposure, we separated the epidermis from the rest of the skin with a cryotome and isolated total mRNA. Gene expression was studied with microarray techniques, and changes from sham treatments were analyzed and characterized. We found consistent twofold increases in gene expression of 27 transcripts at 1, 4, and 8 h after the beginning of the 1-h exposure that were related primarily to structural proteins, cell signaling, inflammatory mediators, growth factors, and enzymes. Analysis of pathways changed showed that several signaling pathways were increased at 1 h and that the most significant changes at 8 h were in metabolic pathways, many of which were downregulated. These results confirm and expand many of the previous molecular studies with JP-8. Based on the 1-h changes in gene expression, we hypothesize that the trigger of the JP-8-induced, epidermal stress response is a physical disruption of osmotic, oxidative, and membrane stability which activates gene expression in the signaling pathways and results in the inflammatory, apoptotic, and growth responses that have been previously identified.

Role of cyclooxygenase-2 induction by transcription factor Sp1 and Sp3 in neuronal oxidative and DNA damage response

Cyclooxygenase-2 (COX-2) has been implicated in neuronal survival and death. However, the precise regulatory mechanisms involved in COX-2 function are unclear. In the present study we found that COX-2 is induced in response to glutathione depletion-induced oxidative stress in primary cortical neurons. Two proximal specific Sp1 and Sp3 binding sites are responsible for the COX-2 promoter activity under normal as well as oxidative stress conditions through enhanced Sp1 and Sp3 DNA binding activity. Site-directed mutagenesis confirmed that -268/-267 positions serve as specific Sp1 and Sp3 recognition sites under oxidative stress. Enforced expression of Sp1 and Sp3 using HSV vectors increased the promoter activity, transcription, and protein level of COX-2 in cortical neurons. The dominant negative form of Sp1 abrogated the oxidative stress-induced promoter activity and expression of COX-2. We also demonstrated that adenovirus-mediated COX-2 gene delivery protected neurons from DNA damage induced by oxidative, genotoxic, and excitotoxic stresses and by ischemic injury. Moreover, COX-2(-/-) cortical neurons were more susceptible to DNA damage-induced cell death. These results indicate that in primary neurons Sp1 and Sp3 play an essential role in the modulation of COX-2 transcription, which mediates neuronal homeostasis and survival by preventing DNA damage in response to neuronal stress.

Cyclooxygenase inhibitors modulate the p53/HDM2 pathway and enhance chemotherapy-induced apoptosis in neuroblastoma

Cyclooxygenase-2 (COX-2) is upregulated in many tumors including neuroblastoma, and its overexpression has been implicated in resistance to p53-dependent apoptosis. Although p53 is rarely mutated in neuroblastoma, the p53 protein is rendered inactive via several mechanisms including sequestration in the cytoplasm. Here, we show that COX inhibitors inhibit the growth of neuroblastoma and when combined with low doses of chemotherapy, exert synergistic effects on neuroblastoma cells. Following COX inhibitor treatment, HDM2, which targets p53 for ubiquitin-mediated degradation, is downregulated, resulting in an attenuation of p53 ubiquitination and an increase in p53 half-life. The level of HDM2 phosphorylation at ser166, which influences both HDM2 and p53 subcellular distribution, is markedly diminished in response to COX inhibitors and is associated with increased p53 nuclear localization. Combining COX inhibitors with low-dose chemotherapy potentiates apoptosis and p53 stability, nuclear localization, and activity. p53 knockdown by siRNA resulted in the rescue of COX-inhibitor-treated cells, indicating that COX inhibitor-induced apoptosis is, at least in part, p53-dependent. Taken together, these results provide the first evidence that COX inhibitors enhance chemosensitivity in neuroblastoma via downregulating HDM2 and augmenting p53 stability and nuclear accumulation.

Gene interaction network analysis suggests differences between high and low doses of acetaminophen

Bayesian networks for quantifying linkages between genes were applied to detect differences in gene expression interaction networks between multiple doses of acetaminophen at multiple time points. Seventeen (17) genes were selected from the gene expression profiles from livers of rats orally exposed to 50, 150 and 1500 mg/kg acetaminophen (APAP) at 6, 24 and 48 h after exposure using a variety of statistical and bioinformatics approaches. The selected genes are related to three biological categories: apoptosis, oxidative stress and other. Gene interaction networks between all 17 genes were identified for the nine dose-time observation points by the TAO-Gen algorithm. Using k-means clustering analysis, the estimated nine networks could be clustered into two consensus networks, the first consisting of the low and middle dose groups, and the second consisting of the high dose. The analysis suggests that the networks could be segregated by doses and were consistent in structure over time of observation within grouped doses. The consensus networks were quantified to calculate the probability distribution for the strength of the linkage between genes connected in the networks. The quantifying analysis showed that, at lower doses, the genes related to the oxidative stress signaling pathway did not interact with the apoptosis-related genes. In contrast, the high-dose network demonstrated significant interactions between the oxidative stress genes and the apoptosis genes and also demonstrated a different network between genes in the oxidative stress pathway. The approaches shown here could provide predictive information to understand high- versus low-dose mechanisms of toxicity.

Pifithrin-alpha, an inhibitor of p53 transactivation, alters the inflammatory process and delays tendon healing following acute injury

Transcription factor p53, which was initially associated with cancer, has now emerged as an important regulator of inflammation and extracellular matrix homeostasis, two processes highly relevant to tendon repair. The goal of this study was to evaluate the effect of a p53 transactivation inhibitor, namely, pifithrin-alpha, on the pathophysiological sequence following collagenase-induced tendon injury. Administration of pifithrin-alpha during the inflammatory phase reduced the accumulation of neutrophils and macrophages by 30 and 40%, respectively, on day 3 postinjury. Pifithrin-alpha failed to reduce the percentage of apoptotic cells following collagenase injection but delayed functional recovery. In uninjured Achilles tendons, pifithrin-alpha increased metalloprotease activity 2.4-fold. Accordingly, pifithrin-alpha reduced the collagen content in intact tendons as well as in injured tendons 7 days posttrauma compared with placebo. The effect of pifithrin-alpha on load to failure and stiffness was also evaluated. The administration of pifithrin-alpha during the inflammatory phase did not significantly decrease the functional deficit 3 days posttrauma. More importantly, load to failure and stiffness were significantly decreased in the pifithrin-alpha group from day 7 to day 28 compared with placebo. Overall, our results suggest that administration of pifithrin-alpha alters the inflammatory process and delays tendon healing. The present findings also support the concept that p53 can regulate extracellular matrix homeostasis in vivo.

N-(3-oxo-acyl)homoserine lactones signal cell activation through a mechanism distinct from the canonical pathogen-associated molecular pattern recognition receptor pathways

Innate immune system receptors function as sensors of infection and trigger the immune responses through ligand-specific signaling pathways. These ligands are pathogen-associated products, such as components of bacterial walls and viral nuclear acids. A common response to such ligands is the activation of mitogen-activated protein kinase p38, whereas double-stranded viral RNA additionally induces the phosphorylation of eukaryotic translation initiation factor 2alpha (eIF2alpha). Here we have shown that p38 and eIF2alpha phosphorylation represent two biochemical markers of the effects induced by N-(3-oxo-acyl)homoserine lactones, the secreted products of a number of Gram-negative bacteria, including the human opportunistic pathogen Pseudomonas aeruginosa. Furthermore, N-(3-oxo-dodecanoyl)homoserine lactone induced distension of mitochondria and the endoplasmic reticulum as well as c-jun gene transcription. These effects occurred in a wide variety of cell types including alveolar macrophages and bronchial epithelial cells, requiring the structural integrity of the lactone ring motif and its natural stereochemistry. These findings suggest that N-(3-oxo-acyl)homoserine lactones might be recognized by receptors of the innate immune system. However, we provide evidence that N-(3-oxo-dodecanoyl)homoserine lactone-mediated signaling does not require the presence of the canonical innate immune system receptors, Toll-like receptors, or two members of the NLR/Nod/Caterpillar family, Nod1 and Nod2. These data offer a new understanding of the effects of N-(3-oxo-dodecanoyl)homoserine lactone on host cells and its role in persistent airway infections caused by P. aeruginosa.

p53 and its downstream proteins as molecular targets of cancer

The p53 tumor suppressor gene plays a key role in prevention of tumor formation through transcriptional dependent and independent mechanisms. Transcriptional-dependent mechanisms are mainly mediated by p53 regulation of downstream targets, leading to growth arrest and apoptosis. Mutational inactivation of the p53 gene is detected in more than 50% of human cancers. Mutation of p53 renders cancer cells more resistant to current cancer therapies due to lack of p53-mediated apoptosis. Extensive studies have been conducted to identify small molecules that manipulate p53, including restoration of mutant p53 conformation to wild-type, disruption of murine double minute-2 (Mdm2)-p53 binding to increase p53 level and inhibition of Mdm2 E3 ubiquitin ligase activity to prevent p53 degradation. Another approach was to identify and validate "drugable" target(s) in p53 signaling pathways that modulate p53-induced apoptosis. We profiled a p53 temperature-sensitive lung cancer cell model with the Affymetrix human HG-U133 GeneChip, covering the entire human transcriptome. We identified thousands of unique genes that were either induced or repressed in response to p53-induced apoptosis. A follow-up study characterized a p53-repressed gene, SAK, a polo-like kinase (PLK) family member, as an appealing cancer drug target. Snk/Plk-akin kinase (SAK) silencing via small interfering RNA (siRNA) induced apoptosis, whereas SAK overexpression attenuated p53-induced apoptosis. Thus, SAK repression by p53 contributes to p53-induced apoptosis. Future work is directed at determining the normal cell response to SAK silencing. If a therapeutic window is obtained, a SAK inhibitor identified from high throughput screening (HTS) could serve as a lead compound for development of a novel class of apoptosis-inducing anticancer drugs.

Myosin VI is a mediator of the p53-dependent cell survival pathway

Myosin VI is an unconventional motor protein, and its mutation is responsible for the familiar conditions sensorineural deafness and hypertrophic cardiomyopathy. Myosin VI is found to play a key role in the protein trafficking and homeostasis of the Golgi complex. However, very little is known about how myosin VI is regulated and whether myosin VI has a function in the DNA damage response. Here, we found that myosin VI is regulated by DNA damage in a p53-dependent manner and possesses a novel function in the p53-dependent prosurvival pathway. Specifically, we show that myosin VI is induced by p53 and DNA damage in a p53-dependent manner. We found that p53 directly binds to, and activates, the promoter of the myosin VI gene. We also show that the intracellular localization of myosin VI is substantially altered by p53 and DNA damage in a p53-dependent manner such that the pool of myosin VI in endocytic vesicles, membrane ruffles, and cytosol migrates to the Golgi complex, perinuclear membrane, and nucleus. Furthermore, we show that knockdown of myosin VI attenuates activation of p53 and impairs Golgi complex integrity, which makes myosin VI-deficient cells susceptible to apoptosis upon DNA damage. Taken together, we found a novel function for p53 in the maintenance of Golgi complex integrity and for myosin VI in the p53-dependent prosurvival pathway.

Expression of cyclooxygenase-2 is associated with p53 accumulation in premalignant and malignant gallbladder lesions

AIM: To examine the relationship between cyclooxygenase-2 (COX-2) overexpression and p53 accumulation in gallbladder carcinoma and its precursor lesions.

METHODS: Sixty-eight gallbladder tissue samples comprising 14 cases of normal gallblader epithelium, 27 cases of dysplasia (11 low-grade dysplasia and 16 high-grade dysplasia) and 27 adenocarcinomas were evaluated by immunohistochemistry for COX-2 expression and p53 accumulation. The relationship among COX-2 expression, p53 accumulation and clinicopathological characteristics was analysed.

RESULTS: COX-2 was expressed in 14.3% of normal gallbladder epithelium, 70.3% of dysplastic epitehlium, and 59.2% of adenocarcinomas. When divided into low- and high-grade dysplasia, COX-2 was positive in 5 (45.4%) cases of low-grade and 14 (87.5%) of high-grade dysplasia (P = 0.019). Accumulation of p53 was detected in 5 (31.2%) cases of high-grade dysplasia and in 13 (48.1%) of carcinomas. No p53 accumulation was found in normal epithelium or low-grade dysplasia. COX-2 overexpression was observed in 17 of 18 (94.4%) cases with p53-accumulation in comparison with 20 (40.0%) out of 50 cases without p53 accumulation (P < 0.001).

CONCLUSION: The significant differences in COX-2 expression among normal epithelium, low-grade dysplasia and high-grade dysplasia suggest that overexpression of COX-2 enzyme is an early event in gallbladder carcinogenensis. Furthermore, since accumulation of p53 correlates with COX-2 expression, COX-2 overexpression observed in gallbladder high-grade dysplasia and carcinoma might be partly due to the dysfunction of p53.

Transcriptional activation of cyclooxygenase-2 by tumor suppressor p53 requires nuclear factor-kappaB

Overexpression of cyclooxygenase-2 (Cox-2) is thought to exert antiapoptotic effects in cancer. Here we show that the tumor suppressor p53 upregulated Cox-2 in esophageal and colon cancer cell lines by inducing the binding of nuclear factor-kappaB (NF-kappaB) to its response element in the COX-2 promoter. Inhibition of NF-kappaB prevented p53 induction of Cox-2 expression. Cooperation between p53 and NF-kappaB was required for activation of COX-2 promoter in response to daunomycin, a DNA-damaging agent. Pharmacological inhibition of Cox-2 enhanced apoptosis in response to daunomycin, in particular in cells containing active p53. In esophageal cancer, there was a correlation between Cox-2 expression and wild-type TP53 in Barrett's esophagus (BE) and in adenocarcinoma, but not in squamous cell carcinoma (P<0.01). These results suggest that p53 and NF-kappaB cooperate in upregulating Cox-2 expression, promoting cell survival in inflammatory precursor lesions such as BE.

Disruption of COX-2 modulates gene expression and the cardiac injury response to doxorubicin

To determine the role of cyclooxygenase (COX)-2 in anthracycline-induced cardiac toxicity, we administered doxorubicin (Dox) to mice with genetic disruption of COX-2 (COX-2-/-). After treatment with Dox, COX-2-/- mice had increased cardiac dysfunction and cardiac cell apoptosis compared with Dox-treated wild-type mice. The expression of the death-associated protein kinase-related apoptosis-inducing protein kinase-2 was also increased in Dox-treated COX-2-/- animals. The altered gene expression, cardiac injury, and dysfunction after Dox treatment in COX-2-/- mice was attenuated by a stable prostacyclin analog, iloprost. Wild-type mice treated with Dox developed cardiac fibrosis that was absent in COX-2-/- mice and unaffected by iloprost. These results suggest that genetic disruption of COX-2 increases the cardiac dysfunction after treatment with Dox by an increase in cardiac cell apoptosis. This Dox-induced cardiotoxicity in COX-2-/- mice was attenuated by a prostacyclin analog, suggesting a protective role for prostaglandins in this setting.

Potentiation of tumor formation by topical administration of 15-deoxy-delta12,14-prostaglandin J2 in a model of skin carcinogenesis

The effect of prostaglandins on the development of papillomas has been investigated in mice receiving prostaglandins E2 (PGE2) or the cyclopentenone 15-deoxy-delta(12,14)-PGJ2 (15dPGJ2) topically, using the 7,12-dimethylbenz[a]anthracene (DMBA)-induced tetradecanoylphorbol acetate (TPA)-promoted model of skin carcinogenesis. The presence of 15dPGJ2 during DMBA and TPA treatment inhibited apoptosis and increased the rate, number, size and vascularization of the papillomas, some of them progressing into carcinomas. Moreover, skin sections from mice treated for one week with DMBA and 15dPGJ2 showed a much reduced rate of apoptotic cells, and an enhanced expression of vascular epithelial growth factor when compared with animals receiving DMBA, with or without PGE2. The analysis of molecular events in the MCA3D keratinocyte cell line showed that 15dPGJ2 activated Ras and improved cell viability by inhibiting DMBA-dependent apoptosis. In addition to this, cell adhesion was impaired in MCA3D keratinocytes co-treated with 15dPGJ2 and DMBA, at the same time when the expression of cyclooxygenase-2 (COX-2) was observed under these conditions. These effects mediated by 15dPGJ2 might contribute to understand the role of COX-2 metabolites in carcinogenesis, leading to an increase of cell viability after mutagenic injury and therefore in the progression of tumors.

Nitric oxide upregulates the cyclooxygenase-2 expression through the cAMP-response element in its promoter in several cancer cell lines

We previously showed that nitric oxide (NO) induces overexpression of cyclooxygenase-2 (COX-2) and production of prostaglandin E(2) in cancer cells. Here, we investigated the mechanisms by which NO induces COX-2 expression in cancer cells. We found that the cAMP-response element (CRE) is a critical factor in NO-induced COX-2 expression in all cells tested. We found that in cancer cells, three transcription factors (TFs) - cAMP response element-binding protein (CREB), activating transcription factor-2 (ATF-2) and c-jun, bound the CRE in the COX-2 promoter, and their activities were increased by addition of the NO donor, S-nitroso-N-acetyl-D,L-penicillamine (SNAP). NO-induced activation of soluble guanylate cyclase (sGC), p38 and c-Jun NH(2)-terminal kinase (JNK) upregulated the three TFs, leading to COX-2 overexpression. Addition of dibutyryl-cGMP (db-cGMP) induced COX-2 expression in a manner similar to SNAP; this induction was blocked by a p38 inhibitor (SB202190), but not by a JNK inhibitor (SP600125). NO-induced cGMP was found to activate CREB and ATF-2 in a p38, but not c-jun-dependent manner, while NO induced JNK in a cGMP-independent manner, leading to subsequent activation of c-jun and ATF-2. These results suggest that the low concentrations of endogenous NO present in cancer cell may induce the expression of many genes, including COX-2, which promotes the growth and survival of tumor cells.

Inhibition of DNA repair as a mechanism of enhanced radioresponse of head and neck carcinoma cells by a selective cyclooxygenase-2 inhibitor, celecoxib

PURPOSE

Previously, we reported that inhibitors of cyclooxygenase-2 (COX-2) enzyme enhanced murine and human tumor cell response to radiation in vitro and in vivo. However, the molecular mechanisms mediating the effects of COX-2 inhibitors are not clear. The present study was designed to investigate the ability of celecoxib, a selective COX-2 inhibitor, to sensitize human head-and-neck cancer cell line, HN5, to radiation, and examine its effects on DNA repair, which may be a potential mechanism of radiosensitization.

METHODS AND MATERIALS

Cells were assessed for the effect of celecoxib (5-50 microM), by 3-[4,5-dimethylthiozol-2-yl]-2,5-diphenyltetrazolium bromide assay for growth inhibition and by clonogenic cell survival assay for the radiosensitizing effect. Kinase assay and Western analysis were conducted to assess the effect of celecoxib on DNA-dependent protein kinase catalytic subunit (PKcs) and Ku proteins. Electrophoretic mobility shift assays (EMSA) were performed to determine the DNA-binding activity of Ku/DNA-PKcs protein complex and nuclear factor kappa B (NFkappaB).

RESULTS

Celecoxib (10 and 50 microM, for 2 days) inhibited the HN5 cell growth and significantly enhanced the cell radiosensitivity in a dose-dependent manner. It also reduced the shoulder region on the radiation-survival curve, suggesting that inhibition of DNA repair processes may have occurred. Western blot analysis demonstrated that celecoxib downregulated the expression of Ku70 protein and inhibited the kinase activity of DNA-PKcs, which are involved in the double-stranded DNA-break repair machinery. By EMSA, it was further shown that celecoxib reduced DNA-binding activity of Ku/DNA-PKcs protein complex. In addition, celecoxib inhibited the constitutively active NFkappaB and the radiation-induced NFkappaB in HN5 cells, suggesting that NFkappaB may play a role in mediating the effects of celecoxib.

CONCLUSIONS

Celecoxib strongly enhanced the sensitivity of HN5 carcinoma cells to radiation, which, mechanistically, can be attributed to the inhibition of DNA repair processes in radiation-damaged cells.

Significance of Cox-2 expression in rectal cancers with or without preoperative radiotherapy

PURPOSE

Radiotherapy has reduced local recurrence of rectal cancers, but the result is not satisfactory. Further biologic factors are needed to identify patients for more effective radiotherapy. Our aims were to investigate the relationship of cyclooxygenase-2 (Cox-2) expression to radiotherapy, and clinicopathologic/biologic variables in rectal cancers with or without radiotherapy.

METHODS AND MATERIALS

Cox-2 expression was immunohistochemically examined in distal normal mucosa (n = 28), in adjacent normal mucosa (n = 107), in primary cancer (n = 138), lymph node metastasis (n = 30), and biopsy (n = 85). The patients participated in a rectal cancer trial of preoperative radiotherapy.

RESULTS

Cox-2 expression was increased in primary tumor compared with normal mucosa (p < 0.0001), but there was no significant change between primary tumor and metastasis. Cox-2 positivity was or tended to be related to more p53 and Ki-67 expression, and less apoptosis (p < or = 0.05). In Cox-2-negative cases of either biopsy (p = 0.01) or surgical samples (p = 0.02), radiotherapy was related to less frequency of local recurrence, but this was not the case in Cox-2-positive cases.

CONCLUSION

Cox-2 expression seemed to be an early event involved in rectal cancer development. Radiotherapy might reduce a rate of local recurrence in the patients with Cox-2 weakly stained tumors, but not in those with Cox-2 strongly stained tumors.

T-oligo treatment decreases constitutive and UVB-induced COX-2 levels through p53- and NFkappaB-dependent repression of the COX-2 promoter

Chronically irradiated murine skin and UV light-induced squamous cell carcinomas overexpress the inducible isoform of cyclooxygenase (COX-2), and COX-2 inhibition reduces photocarcinogenesis in mice. We have reported previously that DNA oligonucleotides substantially homologous to the telomere 3'-overhang (T-oligos) induce DNA repair capacity and multiple other cancer prevention responses, in part through up-regulation and activation of p53. To determine whether T-oligos affect COX-2 expression, human newborn keratinocytes and fibroblasts were pretreated with T-oligos or diluent alone for 24 h, UV-irradiated, and processed for Western blotting. In both cell types, T-oligos transcriptionally down-regulated base-line and UV light-induced COX-2 expression, coincident with p53 activation. In fibroblasts with wild type versus dominant negative p53 (p53(WT) versus p53(DN)), T-oligos decreased constitutive expression of a COX-2 reporter plasmid by >50%. We then examined NFkappaB, a known positive regulator of COX-2 transcription. In p53(WT) but not in p53(DN) fibroblasts and in human keratinocytes, T-oligos decreased readout of an NFkappaB promoter-driven reporter plasmid and decreased NFkappaB binding to DNA. After T-oligo treatment and subsequent UV irradiation, binding of the transcriptional co-activator protein p300 to NFkappaB was decreased, whereas binding of p300 to p53 was increased. Human skin explants provided with T-oligos had markedly decreased COX-2 immunostaining both at base-line and post-UV light, coincident with increased p53 immunostaining. We conclude that T-oligos transcriptionally down-regulate COX-2 expression in human skin via activation and up-regulation of p53, at least in part by inhibiting NFkappaB transcriptional activation. Decreased COX-2 expression may contribute to the observed ability of T-oligos to reduce photocarcinogenesis.

COX-2 regulates p53 activity and inhibits DNA damage-induced apoptosis

We have previously shown that p53 induces cyclooxygenase-2 (COX-2) expression and COX-2 inhibits p53- or genotoxic stress-induced apoptosis. However, the COX-2 effects have been demonstrated indirectly by the use of a selective inhibitor, NS-398, and the molecular mechanisms by which COX-2 inhibits apoptosis have not been identified. In the present study, we demonstrated that COX-2 inhibits genotoxic stress-induced apoptosis by using an adenoviral COX-2 overexpression system. In addition, we found that COX-2 regulates the transcription function of p53 as evidenced by suppression of p53 target gene induction by COX-2 cotransfection. Furthermore, COX-2 interacted with p53 in vitro and in vivo, which was inhibited by the treatment with NS-398. Taken together, these results suggest a novel function of COX-2 that inhibits DNA damage-induced apoptosis through direct regulation of p53 function.

Cyclooxygenase-2 interacts with p53 and interferes with p53-dependent transcription and apoptosis

Cyclooxygenase-2 (COX-2) has been implicated in a variety of human malignancies and, accordingly, COX-2 selective inhibitors are being investigated as important chemopreventive and therapeutic agents. How COX-2 overexpression results in tumorigenesis and how COX-2 selective agents mediate their chemopreventive effects are issues that remain poorly understood. Here we report that the tumor suppressor p53 upregulates COX-2 expression and that COX-2 can in turn inhibit p53-dependent transcription. Additionally, a COX-2-selective inhibitor potentiates p53-induced apoptosis, which also supports the notion that COX-2 activity appears to interfere with p53 function. Expression of exogenous COX-2 in p53 wild-type cells does not affect the cytoplasmic or nuclear levels of p53, suggesting that COX-2 may not affect p53 turnover or subcellular localization. We further demonstrate that endogenous COX-2 interacts with p53 and that COX-2 and p53 interactions are a physiologically relevant event. Thus, p53 upregulates COX-2 and COX-2 in turn appears to negatively affect p53 activity via mechanisms that could involve physical interactions between COX-2 and p53. Based on our results, we propose that p53-dependent upregulation and activation of COX-2 appear to be yet another novel mechanism by which p53 could abate its own growth-inhibitory and apoptotic effects.

The intimate relation between nitric oxide and superoxide in apoptosis and cell survival

Intra- and intercellular communication in or between cells allows adaptation to changes in the environment. Formation of reactive oxygen (ROS) and nitrogen (RNS) species in response to external insults gained considerable attention in provoking cell demise along an apoptotic subroute of cell death, thus attributing radical formation to pathologies. In close association, stabilization of the tumor suppressor p53 and activation of caspases convey proapoptotic signaling. Complexity was added with the notion that ROS and RNS signals overlap and/or produce synergistic as well as antagonistic effects. With respect to nitric oxide (NO) signaling, it became clear that the molecule is endowed with pro- or antiapoptotic signaling capabilities, depending to some extend on the concentration and cellular context, i.e., ROS generation. Here, some established concepts are summarized that allow an explanation of p53 accumulation under the impact of NO and an understanding of NO-evoked cell protection at the level of caspase inhibition, cyclic GMP formation, or expression of antiapoptotic proteins. In addition, the overlapping sphere of ROS and RNS signaling is recapitulated to appreciate cell physiology/pathology with the notion that marginal changes in the flux rates of either NO or superoxide may shift vital signals used for communication and cell survival into areas of pathology in close association with apoptosis/necrosis.

p53CSV, a Novel p53-Inducible Gene Involved in the p53-Dependent Cell-Survival Pathway

Although a number of p53 target genes have been identified, the mechanisms of p53-dependent activities that determine cellular survival or death are still not fully understood. Here we report isolation of a novel p53 target gene, designated p53-inducible cell-survival factor (p53CSV). p53CSV contains a p53-binding site within its second exon and the reduction of expression by small interfering RNA enhanced apoptosis, whereas overexpression protected cells from apoptosis caused by DNA damage. p53CSV is induced significantly when cells have a low level of genotoxic stresses, but not when DNA damage is severe. p53CSV can modulate apoptotic pathways through interaction with Hsp70 that probably inhibits activity of apoptosis protease activating factor-1. Our results imply that under specific conditions of stress, p53 regulates transcription of p53CSV and that p53CSV is one of the important players in the p53-mediated cell survival.

Inhibition of cyclooxygenase-1 and -2 expression by targeting the endothelin a receptor in human ovarian carcinoma cells

PURPOSE AND EXPERIMENTAL DESIGN

New therapies against cancer are based on targeting cyclooxygenase (COX)-2. Activation of the endothelin A receptor (ET(A)R) by endothelin (ET)-1 is biologically relevant in several malignancies, including ovarian carcinoma. In this tumor, the ET-1/ET(A)R autocrine pathway promotes mitogenesis, apoptosis protection, invasion, and neoangiogenesis. Because COX-1 and COX-2 are involved in ovarian carcinoma progression, we investigated whether ET-1 induced COX-1 and COX-2 expression through the ET(A)R at the mRNA and protein level in HEY and OVCA 433 ovarian carcinoma cell lines by Northern blot, reverse transcription-PCR, Western blot, and immunohistochemistry; we also investigated the activity of the COX-2 promoter by luciferase assay and the release of prostaglandin (PG) E(2) by ELISA.

RESULTS

ET-1 significantly increases the expression of COX-1 and COX-2, COX-2 promoter activity, and PGE(2) production. These effects depend on ET(A)R activation and involve multiple mitogen-activated protein kinase (MAPK) signaling pathways, including p42/44 MAPK, p38 MAPK, and transactivation of the epidermal growth factor receptor. COX-2 inhibitors and, in part, COX-1 inhibitor blocked ET-1-induced PGE(2) and vascular endothelial growth factor release, indicating that both enzymes participate in PGE(2) production to a different extent. Moreover, inhibition of human ovarian tumor growth in nude mice after treatment with the potent ET(A)R-selective antagonist ABT-627 is associated with reduced COX-2 and vascular endothelial growth factor expression.

CONCLUSIONS

These results indicate that impairing COX-1 and COX-2 and their downstream effect by targeting ET(A)R can be therapeutically advantageous in ovarian carcinoma treatment. Pharmacological blockade of the ET(A)R is an attractive strategy to control COX-2 induction, which has been associated with ovarian carcinoma progression and chemoresistance.

5-lipoxygenase antagonizes genotoxic stress-induced apoptosis by altering p53 nuclear trafficking

5-lipoxygenase (5-LO) promotes cancer cell proliferation and survival by unclear mechanisms. Here, we show that 5-LO expression and activity were induced by genotoxic agents in a p53-independent manner and antagonized p53- or genotoxic drug-induced apoptosis in a variety of cancer cells. 5-LO inhibited p53-governed transactivation of the pro-apoptotic genes bax and pig3 but not of p21(WAF1/CIP1) or mdm2. This may be explained by 5-LO capability to inhibit the binding of p53 to promyelocytic leukemia protein (PML) and p53 subnuclear relocalization into PML-nuclear bodies in response to genotoxic stress. Interestingly, 5-LO activity appears to be involved in nuclear retention and inactivation of wild-type p53 in malignant mesothelioma cells. In these cells, genetic or pharmacological inhibition of 5-LO enabled suppression of in vitro tumorigenicity by low doses of chemotherapeutic drugs. Together, these results uncover novel functions of 5-LO and contribute to the understanding of 5-LO involvement in tumor progression. Moreover, they provide a rationale to the therapeutic use of 5-LO inhibitors to enhance cancer chemosensitivity in selected tumors.

Cyclooxygenase-2 and p53 expressions in endometrial cancer

Cyclooxygenase-2 (COX-2) has been known to be related with various types of carcinoma, but we have insufficient knowledge about the association between COX-2 and endometrial cancer. Many have reported a close relationship between p53 expression and a poor prognosis in endometrial cancer, but it is unclear whether p53 is an independent prognostic factor. To clarify these uncertainties, we examined the expressions of COX-2 and p53 in endometrial cancer tissues. The study was carried on 152 endometrial cancer patients who had operation at Seoul National University Hospital. Paraffin-embedded tissue blocks were sectioned and immunostained using monoclonal anti-COX-2 and anti-p53 antibodies. Twenty-seven (17.8%) specimens stained as COX-2 positive. COX-2 positivity was more frequently observed in postmenopausal patients than in premenopausal patients (8.8% versus 25.0%; P = 0.009). However, COX-2 positivity did not show a statistically significant association with any other clinicopathologic characteristic (parity, body mass index, histotype, International Federation of Gynecology and Obstetrics stage, grade, lymph node metastasis, deep myometrial invasion, or p53 overexpression). Thirty-one (20.4%) specimens showed p53 overexpression and this was significantly correlated with an advanced stage (P = 0.001), poor differentiation (P < 0.001), lymph node metastasis (P = 0.012), and deep myometrial invasion (P < 0.001). Multivariate Cox regression analysis showed that advanced stage was an independent prognostic factor of survival, but p53 overexpression was not. COX-2 may be associated with endometrial cancer carcinogenesis during the postmenopausal period but not with tumor aggressiveness and p53 overexpression. The p53 overexpression was found to be strongly associated with endometrial cancer aggressiveness.