Expression of cyclooxygenase-2 in breast carcinogenesis and its relation to HER-2/neu and p53 protein expression in invasive ductal carcinoma

Potential of Anti-inflammatory Molecules in the Chemoprevention of Breast Cancer

Breast cancer is a global issue, affecting greater than 1 million women per annum. Over the past two decades, there have been numerous clinical trials involving the use of various pharmacological substances as chemopreventive agents for breast cancer. Various pre-clinical as well as clinical studies have established numerous anti-inflammatory molecules, including nonsteroidal anti-inflammatory drugs (NSAIDs) and dietary phytochemicals as promising agents for chemoprevention of several cancers, including breast cancer. The overexpression of COX-2 has been detected in approximately 40% of human breast cancer cases and pre-invasive ductal carcinoma in-situ lesions, associated with aggressive elements of breast cancer such as large size of the tumour, ER/PR negative and HER-2 overexpression, among others. Anti-inflammatory molecules inhibit COX, thereby inhibiting the formation of prostaglandins and inhibiting nuclear factor-κBmediated signals (NF-kB). Another probable explanation entails inflammation-induced degranulation, with the production of angiogenesis-regulating factors, such as vascular endothelial growth factor, which can be possibly regulated by anti-inflammatory molecules. Apart from NSAIDS, many dietary phytochemicals have the ability to decrease, delay, or stop the progression and/or incidence of breast cancer by their antioxidant action, regulating inflammatory and proliferative cell signalling pathways as well as inducing apoptosis. The rapid progress in chemoprevention research has also established innovative strategies that can be implemented to prevent breast cancer. This article gives a comprehensive overview of the recent advancements in using antiinflammatory molecules in the chemoprevention of breast cancer along with their mechanism of action, supported by latest preclinical and clinical data. The merits of anti-inflammatory chemopreventive agents in the prevention of cardiotoxicity have been described. We have also highlighted the ongoing research and advancements in improving the efficacy of using antiinflammatory molecules as chemopreventive agents.

The Role of NSAIDs in Breast Cancer Prevention and Relapse: Current Evidence and Future Perspectives

Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) have received considerable interest as potential chemopreventive agents. The aim of this review is to summarize the accumulated knowledge on the effect of NSAIDs on breast cancer incidence and natural history, and the underlying pathophysiology. NSAIDs mainly block inflammation by inhibiting cyclooxygenase enzymes, leading to lower prostaglandin synthesis. The latter has been reported to affect breast cancer risk through hormonal and inflammation-related pathways. Intensity, dose, frequency, duration, and timing of administration may also be significant. There is currently enough evidence to support a role of NSAIDs in breast cancer prevention and relapse, which deserves further large-scale experimental and clinical investigation.

Cyclooxygenase-2 (COX2) and p53 protein expression are interdependent in breast cancer but not associated with clinico-pathological surrogate subtypes, tumor aggressiveness and patient survival

In the last decade, different molecular subtypes of breast cancer have been proposed. Although displaying appreciable association with disease prognosis and the prognostic value of cytotoxic and endocrine therapeutic modalities, the subtypes seem to fail at completely explaining disease behavior and response to treatment. Molecules such as those of the cyclocooxigenase (COX) family, currently composed of three entities (COX 1, 2 and 3) have been shown to be associated with breast carcinogenesis, and the analysis of p53 expression in breast tumors may also offer some additional prognostic clues. Our study is aimed at assessing COX2 and p53 expression in these clinico-pathological surrogate subtypes, and to evaluate whether the expression of these molecules can help further explain the variability in prognosis still found within the clinico-pathological subtypes groups of breast cancer.

METHODS

A total of 183 breast cancer samples were obtained from women treated at the Womeńs Hospital of Campinas State University, Campinas, Brazil, between June 2008 and January 2011. Immunohistochemistry was performed to detect the expression of ER, PR, ki67, COX2, and p53 and the HER2 status of the 183 specimens was assessed using FISH. Two COX2 staining thresholds were used to define COX2 positivity: low threshold (LT): moderate and intense staining were considered positive; high-threshold (HT): only intense staining was considered positive.

RESULTS

There was no trend in COX2 overexpression from Luminal A-like to Triple-negative subtypes. By contrast, p53 was expressed in roughly 67% of the Luminal A-like tumors, 50% of the Luminal B-like HER2 positive tumors, 60.9% of the Luminal B-like HER2 negative, approximately 82% of the HER2 positive (non-luminal) and 87% of the Triple-negative tumors (p for trends=0.06). There was a significantly higher proportion of COX2 positive (LT) tumors (66.9%) when p53 was also positive compared to when the tumor was negative for p53 (in which case only18.0% of the tumors were positive for COX2; p<0.001). Neither marker was found to be associated with patients' survival.

CONCLUSIONS

There seems to be a positive association between the expressions of COX2 and p53. Otherwise, neither the expression of COX nor that of p53 was associated with clinico-pathological subtypes, tumor features and prognosis. It seems to be too early to elect the detection of COX2 using IHC as prognostic or predictive tool, but incipient evidence points toward a possible role for the marker.

Cyclooxygenase-2 expression in invasive breast carcinomas of no special type and correlation with pathological profiles suggest a role in tumorigenesis rather than cancer progression

BACKGROUND

COX-2 has been shown to play an important role in the development of breast cancer and increased expression has been mooted as a poor prognostic factor. The purpose of this study was to investigate the relationship between COX-2 immunohistochemical expression and known predictive and prognostic factors in breast cancer in a routine diagnostic histopathology setting.

MATERIALS AND METHODS

Formalin-fixed paraffin- embedded tumour tissue of 144 no special type (NST) invasive breast carcinomas histologically diagnosed between January 2009 and December 2012 in Hospital Sultanah Bahiyah, Alor Setar, Kedah were immunostained with COX-2 antibody. COX-2 overexpression was analysed against demographic data, hormone receptor status, HER2- neu overexpression, histological grade, tumour size and lymph node status.

RESULTS

COX-2 was overexpressed in 108/144 (75%) tumours and was significantly more prevalent (87%) in hormone receptor-positive tumours. There was no correlation between COX-2 overexpression and HER2/neu status. Triple negative cancers had the lowest prevalence (46%) (p<0.05). A rising trend of COX-2 overexpression with increasing age was observed. There was a significant inverse relationship with tumour grade (p<0.05), prevalences being 94%, 83% and 66% in grades 1, 2 and 3 tumours, respectively. A higher prevalence of COX-2 overexpression in smaller size tumours was observed but this did not reach statistical significance. There was no relationship between COX-2 expression and lymph node status.

CONCLUSIONS

This study did not support the generally held notion that COX-2 overexpression is linked to poor prognosis, rather supporting a role in tumorigenesis. Larger scale studies with outcome data and basic studies on cancer pathogenetic pathways will be required to cast further light on whether COX-2 inhibitors would have clinical utility in cancer prevention or blockage of cancer progression. In either setting, the pathological assessment for COX-2 overexpression in breast cancers would have an important role in the selection of cancer patients for personalized therapy with COX-2 inhibitors.

Immunohistochemical expression of COX-2, mPGES and EP2 receptor in normal and reactive canine bone and in canine osteosarcoma

Accumulating evidence suggests that cyclooxygenase (COX)-2 is involved in the pathogenesis of human and canine osteosarcoma. The aim of this study was to investigate the expression of COX-2 in normal, reactive and neoplastic canine bone and the events downstream to COX-2 that lead to prostaglandin E(2) (PGE(2)) production. COX-2, microsomal PGE(2) synthase-1 (mPGES-1) and the PGE(2) receptor (EP2) were assessed by immunohistochemistry in 12 samples of normal bone, 14 cases of fracture callus and 27 appendicular osteosarcomas. No immunoreactivity to COX-2, mPGES-1 or EP2 receptor was observed in normal bone. Fifty percent of reactive bone samples expressed COX-2 and 57% expressed mPGES-1 and EP2 receptor, although with weak labelling intensity. Ninety-three percent of osteosarcomas expressed COX-2, while mPGES-1 was expressed by 85% and EP2 receptor by 89% of the tumours. The data confirm that COX-2 is expressed at high level in osteosarcoma and support the use of COX-2 inhibitors to improve the response to chemotherapy. The possibility of blocking the EP2 or the selective inhibition of mPGES-1, rather than COX-2 activity, might decrease the incidence of adverse effects that occur due to the inhibition of prostanoids other than PGE(2).

Expression of cyclooxygenase-2 (COX-2) and p53 in neighboring invasive and in situ components of breast tumors

The aim of the study was to assess the relationship between the expression of COX-2 and p53, hormone receptors and HER-2 in the in situ (DCIS) and invasive components of ductal carcinomas (IDC) of the same breast. The expression of COX-2, p53, and hormone receptors was assessed in 87 cases of IDC with contiguous areas of DCIS. Results showed that there was no difference in COX-2 expression comparing the in situ and invasive components of the tumors. In the in situ component, there was a statistically borderline increase in p53 expression in tumors that also expressed COX-2. ER-positive specimens were more common in the group of tumors that expressed COX-2 in the invasive component. From this study we conclude that the expression of COX-2 was similar in the in situ and invasive components of the breast carcinomas. COX-2 positivity was marginally related with the expression of p53 in the in situ components, and with the ER expression in the invasive components.

COX-2 expression and tumor angiogenesis in thyroid carcinoma patients among northeast Chinese population-result of a single-center study

OBJECTIVE

Cyclooxygenase-2 (COX-2), one of the rate-limiting enzymes in the metabolism of arachidonic acid which is reported to be involved in the pathogenesis of many human tumors. As well, Vascular endothelial growth factor (VEGF) is well known to be involved in the infiltration and metastasis of many kinds of cancers. The aim of this study was to further elucidate the clinicopathologic significance of the immunohistochemical expressions of COX-2 and VEGF in thyroid carcinoma.

METHODS

Eighty-five patients with thyroid neoplasms were enrolled in our study from December 2003 to January 2010 from the authors' institution retrospectively. Their tumors were examined in the Department of Pathology, the First Bethune Hospital of Jilin University. Immunohistochemistry was performed on paraffin-embedded tissues sections using monoclonal anti-human COX-2 and VEGF antibodies. The tissues were classified into four types: papillary, follicular, medullary and undifferentiated. The patients ranged in age from 23 to 71 years. Breast cancer slides acted as control slides. The immunohistochemical stains were quantified by staining intensity and by the proportion of positively stained cells which were stained brown or yellow.

RESULTS

The results were analysed by χ(2) test. COX-2 and VEGF expressions were stronger in thyroid carcinoma than in thyroid adenomas and normal tissues (P<0.01). COX-2 and VEGF expressions in thyroid carcinoma correlated with the tumor type and TNM stage.

CONCLUSION

Our results suggest that expression of COX-2 and VEGF may promote angiogenesis of thyroid carcinoma, its infiltration, and metastasis.

Cyclooxygenase-2 and human epidermal growth factor receptor type 2 (HER-2) expression simultaneously in invasive and in situ breast ductal carcinoma

CONTEXT AND OBJECTIVE

Cyclooxygenase-2 (COX-2) and human epidermal growth factor receptor type 2 (HER-2) are associated with tumorigenesis. Studies have shown that HER-2 can regulate COX-2 expression. The aim of this study was to evaluate the correlation between COX-2 and HER-2 expression in normal breast epithelium and in ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) present in the same breast.

DESIGN AND SETTING

Cross-sectional study at the Mastology Unit of the Department of Gynecology and Obstetrics, Santa Casa de Misericórdia de São Paulo Hospital.

METHODS

COX-2 and HER-2 were detected using immunohistochemistry on 100 tissue fragments. HER-2 > +2 was subjected to fluorescence in situ hybridization (FISH).

RESULTS

COX-2 expression was detected in 87%, 85% and 75% of IDC, DCIS and normal epithelium, respectively. HER-2 expression was detected in 34% of IDC and 34% of DCIS. COX-2 in DCIS correlated with HER-2 in IDC (P = 0.049) and DCIS (P = 0.049). COX-2 in normal epithelium correlated with HER-2 in IDC (P = 0.046) and DCIS (P = 0.046). COX-2 in IDC was not associated with HER-2 (P = 0.235). Comparison between COX-2 and HER-2 in DCIS showed that there was a statistically significant difference with regard to nuclear grades II and III and presence of comedonecrosis (P < 0.001). In IDC, there was significant expression with nuclear grades II and III and histological grade II (P < 0.001).

CONCLUSIONS

Our findings provide evidence that HER-2 and COX-2 regulate each other.

A systematic review to establish the frequency of cyclooxygenase-2 expression in normal breast epithelium, ductal carcinoma in situ, microinvasive carcinoma of the breast and invasive breast cancer

Background:

Epidemiological studies have suggested a protective effect of cyclooxygenase (COX)-inhibiting non-steroidal anti-inflammatory drugs in breast cancer risk and disease progression. We performed a systematic review to evaluate the frequency of COX-2 expression in normal breast epithelium, ductal carcinoma in situ of breast (DCIS), DCIS-adjoining invasive breast cancer, microinvasive carcinoma of the breast (MICB) and invasive breast cancer.

Methods:

Literature searches were carried out on MEDLINE, EMBASE and Web of Science from their commencement until September 2010. Primary studies examining COX-2 expression by immunohistochemistry methodology were included. Meta-analyses were carried out using random effects models for individual study estimates of COX-2 expression and pooled to give an overall estimate.

Results:

The pooled prevalences (95% confidence intervals) of COX-2 expressions were 53% (44–61) in DCIS studies and 42% (36–49) in the invasive breast cancer studies. There were too few studies involving normal breast epithelium, DCIS-adjoining invasive breast cancer and MICB to conduct meta-analyses.

Conclusion:

The findings from our meta-analyses have shown similar COX-2 expression in DCIS and invasive breast cancer. This may suggest the involvement of COX-2 in early carcinogenesis. Further studies of COX-2 expression in DCIS are required to investigate the use of COX-2 as a potential drug target for prevention of disease progression in DCIS.

Non-steroidal anti-inflammatory drugs (NSAIDs) and breast cancer risk: differences by molecular subtype

Use of non-steroidal anti-inflammatory drugs (NSAIDs) has been associated with reduced risk of breast cancer, though findings have been inconsistent. This inconsistency may result from differences in etiology for breast tumors of different subtypes. We examined the association between NSAID use and breast cancer characterized by molecular subtypes in a population-based case-control study in Western New York. Cases (n = 1,170) were women with incident, primary, histologically confirmed breast cancer. Controls (n = 2,115) were randomly selected from NY Department of Motor Vehicles records (<65 years) or Medicare rolls (≥ 65 years). Participants answered questions regarding their use of aspirin and ibuprofen in the year prior to interview and their use of aspirin throughout their adult life. Logistic regression models estimated odds ratios (OR) and 95% confidence intervals (95% CI). Recent and lifetime aspirin use was associated with reduced risk, with no differences by subtype. Recent use of ibuprofen was significantly associated with increased risk of ER+/PR+(OR 1.33, 95% CI: 1.09-1.62), HER2- (OR 1.27, 95% CI: 1.05-1.53), and p53- breast cancers (OR 1.28, 95% CI: 1.04-1.57), as well as luminal A or B breast cancers. These findings support the hypothesis of heterogeneous etiologies of breast cancer subtypes and that aspirin and ibuprofen vary in their effects.

COX-2 expression and outcome in canine nasal carcinomas treated with hypofractionated radiotherapy

The expression of cyclooxygenase isoform 2 (COX-2) in canine nasal carcinomas has been well documented. COX-2 expression has proven to be a prognostic factor in several human tumours. The aims of this study were to assess the correlation between immunohistochemical COX-2 expression and prognosis using rhinoscopic biopsies from 42 dogs with nasal carcinomas treated with hypofractionated radiotherapy, and to establish a replicable COX-2 scoring system. Ninety per cent of sections evaluated were COX-2 positive with a mean score of 6.6 (median 8.0; range 0-12). Neither COX-2 expression nor tumour type had a significant correlation with survival. There are likely to be many as yet unidentified variants which contribute to length of survival in dogs with nasal carcinomas. Immunohistochemical COX-2 expression appears unlikely to be of prognostic significance for canine nasal carcinoma.

Relationship between cyclooxygenase-2 and human epidermal growth factor receptor 2 in vascular endothelial growth factor C up-regulation and lymphangiogenesis in human breast cancer

Both cyclooxygenase (COX)-2 and human epidermal growth factor receptor (HER)-2 promote breast cancer progression; however, the relationship between the two molecules remains unclear. We utilized human breast cancer tissues and cell lines to examine whether COX-2 and HER-2 played independent or interdependent roles in vascular endothelial growth factor (VEGF)-C up-regulation and lymphangiogenesis. A paired correlation of immunodetectable levels of COX-2, VEGF-C, and HER-2 proteins and lymphovascular density (LVD; D2-40-immunolabeled) in 55 breast cancer specimens revealed a positive correlation between COX-2 and HER-2 irrespective of clinicopathological status. However COX-2 alone positively correlated with LVD. In 10 independent specimens, mRNA levels showed a positive correlation between HER-2 and COX-2 or VEGF-C but not LYVE-1 (lymphovascular endothelial marker). These findings implicate COX-2, but not HER-2, in breast cancer-associated lymphangiogenesis. Manipulation of the COX-2 or HER-2 genes in breast cancer cell lines varying widely in COX-2 and HER-2 expression revealed a direct role of COX-2 and an indirect COX-2 dependent role of HER-2 in VEGF-C up-regulation: (i) high VEGF-C expression in high COX-2/low HER-2 expressing MDA-MB-231 cells was reduced by siRNA-mediated down-regulation of COX-2, but not HER-2; (ii) integration of HER-2 in these cells simultaneously up-regulated COX-2 protein as well as VEGF-C secretion; and (iii) low VEGF-C secretion by high HER-2/low COX-2 expressing SK-BR-3 cells was stimulated by COX-2 overexpression. These findings of the primary role of COX-2 and the COX-2-dependent role of HER-2, if any, in VEGF-C up-regulation and lymphangiogenesis suggest that COX-2 inhibitors may abrogate lymphatic metastasis in breast cancer irrespective of HER-2 status.

The value of COX-2 expression in the prognostic parameters of invasive ductal carcinoma of the breast

Cyclooxygenase is an enzyme that changes the immune response to malign cells and catalyzes prostaglandins that may have an impact on cell proliferation. The purpose of this study was to examine the relation between established clinicopathological parameters in breast carcinomas and COX-2 protein expression. COX-2, estrogen receptor (ER), progesterone receptor (PR) and c-erB-2 primary antibodies were assessed in the slides prepared from the paraffin blocks of 62 invasive ductal carcinoma cases. The relation between ER, PR, and c-erbB-2 positivity, histological grade, nuclear grade, lymphovascular invasion, tumor diameter, lymph node positivity, metastasis, and age were evaluated. The results were analyzed statistically. Cytoplasmic COX-2 expression was seen in 75.8% of all breast carcinomas. In both univariate and multivariate logistic regression analysis, there was a positive correlation between COX-2 expression and negative ER status, respectively (P=0.0173) (P=0.016). There was any statistically significant relation between PR positivity, c-erbB-2 positivity, histological grade, nuclear grade, lymphovascular invasion, tumor diameter, lymph node positivity, metastasis, and age (P≥0.05). Given that there was found a statistically significant relation between COX-2 expression and negative ER status, which is considered a poor prognostic parameter, suggests that COX-2 expression can have a place among the other prognostic parameters of breast carcinoma.

EGFR, HER-2 and COX-2 levels in colorectal cancer

AIMS

Receptor tyrosine kinases epidermal growth factor receptor (EGFR) and HER-2 and cyclooxygenase-2 (COX-2) are promising molecular targets for cancer therapy and/or prevention. The aim was to evaluate EGFR, HER-2 and COX-2 mRNA and protein expression in colorectal cancer patients.

METHODS AND RESULTS

EGFR, HER-2 and COX-2 protein levels were evaluated by immunohistochemistry in malignant tissue, dysplastic tissue and normal mucosa samples from 124 cases with primary colorectal carcinoma. Moreover, the corresponding mRNA levels were assessed by quantitative reverse transcriptase-polymerase chain reaction in 46 colorectal carcinomas. There was strong correlation between mRNA and protein expression for EGFR (P < 0.001), HER-2 (P < 0.004) and COX-2 (P < 0.007). EGFR levels did not correlate with stage of the disease or tumour differentiation. HER-2 and COX-2 levels increased in advanced stages and in differentiated carcinomas. Furthermore, a correlation between HER-2 and COX-2 expression was revealed in neoplastic tissue.

CONCLUSIONS

EGFR as well as HER-2 and COX-2 overexpression represent important alterations that are related to the molecular pathways underpinning colorectal carcinogenesis. Further investigation is required to evaluate the impact of these markers on the management of patients with colorectal cancer.

COX-2 expression in invasive breast cancer: correlation with prognostic parameters and outcome

Lipoxygenases (LOX) and cyclooxygenases (COX) are key mediators of arachidonic acid metabolism. Recently, studies have reported that human breast carcinomas aberrantly express LOX and cyclooxygenase-2 (COX-2), and that decreased levels of 15-lipoxygenase (15-LOX) and raised levels of COX-2 and 12-LOX have prognostic value in patients with breast cancer. 15-LOX was significantly reduced with increasing stage, and in patients who developed metastatic disease, local recurrence, and/or died. With high COX-2, patients developed local recurrence, died from breast cancer and had reduced disease-free and disease-related overall survival in estrogen receptor (ER)-negative but not ER-positive disease. COX-2 expression is also associated with increased angiogenesis, lymph node metastasis, and Her2-neu overexpression. The purpose of this study is to evaluate COX-2 expression in breast cancer and to determine its correlation with prognostic parameters and outcome. Five tissue microarrays were constructed from 43 breast carcinomas and 5 normal breast tissues, represented by 1 mm cores in triplicate from each of 3 foci. Tissue microarray cores were immunostained with monoclonal COX-2. Expression was assessed as intensity and scored as percentage of cells positive. Prognostic parameters and follow-up information were obtained from the hospital records of Mexican Oncology Hospital, Mexico, where the carcinomas were diagnosed. Ninety-five percent (41/43) of the breast carcinomas showed cytoplasmic COX-2 expression. COX-2 intensity and percentage of cells positive correlated significantly with size of carcinoma (P=0.0271; P=0.0539, respectively). COX-2 intensity correlated significantly with histologic grade (P=0.0182). COX-2 did not correlate with outcome (disease-free and overall survival). There was no significant correlation between COX-2 and ER. In conclusion, COX-2 correlates with poor prognostic markers in breast cancer (large tumor size and high tumor grade), but not with outcome. The therapeutic value of COX-2 inhibitors in COX-2 positive breast cancer patients requires further investigation.

Abrogated response to cellular stress identifies DCIS associated with subsequent tumor events and defines basal-like breast tumors

Approximately 15%-30% of women diagnosed with ductal carcinoma in situ (DCIS) develop a subsequent tumor event within 10 years after surgical lumpectomy. To date, little is known about the molecular pathways that confer this differential risk for developing subsequent disease. In this study, we demonstrate that expression of biomarkers indicative of an abrogated response to cellular stress predicts DCIS with worse outcome and is a defining characteristic of basal-like invasive tumors. Mechanistic studies identify the Rb pathway as a key regulator of this response. Conversely, biomarkers indicative of an intact response to cellular stress are strongly associated with a disease-free prognosis. Assessment of these biomarkers in DCIS begins to allow prediction of tumor formation years before it actually occurs.

GSTP1 promoter hypermethylation is an early event in breast carcinogenesis

Promoter hypermethylation in precursor lesions of the breast cancer may be biomarkers of cancer risk and targets for cancer chemoprevention. Pi-class glutathione-S-transferases (GSTP1) is inactivated by promoter hypermethylation in invasive breast cancers. However, little is known about epigenetic silencing of GSTP1 gene by promoter hypermethylation in precursor lesions. To determine the significance of GSTP1 promoter hypermethylation in breast carcinogenesis, methylation status of GSTP1 gene was studied by nested methylation-specific polymerase chain reaction, and GSTP1 expression was studied by immunohistochemistry in invasive ductal carcinoma (IDC), ductal carcinoma in situ (DCIS), usual ductal hyperplasia (UDH), and normal breast tissue. GSTP1 promoter hypermethylation was detected in 4/24 (16.7%) of UDH, 18/49 (36.7%) of DCIS, and 14/36 (38.9%) of IDC. No hypermethylation was detected in normal breast tissues. GSTP1 promoter hypermethylation was found to be progressively elevated during breast carcinogenesis (p < 0.01). GSTP1 promoter hypermethylation was associated with loss of GSTP1 expression (p < 0.01 for UDH, p < 0.001 for DCIS and IDC). Our results suggest that GSTP1 promoter hypermethylation is an early event in breast carcinogenesis and appears to functionally silence GSTP1 expression. GSTP1 promoter hypermethylation in the precursor lesions of breast cancer may be used as a target for cancer chemoprevention.

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.