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Multiple lines of evidence have suggested a role for both bile acids and prostaglandins (PG) in gastrointestinal carcinogenesis. Levels of PGE2 are determined by both synthesis and catabolism. Previously, bile acid-mediated induction of cyclooxygenase-2 (COX-2) was found to stimulate PGE2 synthesis. NAD+-dependent 15-hydroxyprostagIandin dehydrogenase (15-PGDH), the key enzyme responsible for the catabolism of PGE2, has been linked to colorectal carcinogenesis. In this study, we determined whether bile acids altered the expression of 15-PGDH in human colon cancer cell lines. Treatment with unconjugated bile acids (chenodeoxycholate and deoxycholate) suppressed the transcription of 15- PGDH, resulting in reduced amounts of 15-PGDH mRNA, protein, and enzyme activity. Conjugated bile acids were less potent suppressors of 15-PGDH expression than unconjugated bile acids. Treatment with chenodeoxycholate activated protein kinase C (PKC), leading in turn to increased extracellular signal-regulated kinase (ERK) ½ activity. Small molecules that inhibited bile acid-mediated activation of PKC and ERK½ also blocked the downregulation of 15-PGDH. Bile acids induced early growth response factor-1 (Egr-1) and Snail, a repressive transcription factor that bound to the 15-PGDH promoter. Silencing Egr-1 or Snail blocked chenodeoxycholate-mediated downregulation of 15-PGDH. Together, these data indicate that bile acids activate the signal transduction pathway PKC → ERK½ → Egr-1 → Snail and thereby suppress 15-PGDH transcription. Bile acids appear to increase the release of PGs from cells by downregulating catabolism in addition to stimulating synthesis. These results provide new mechanistic insights into the link between bile acids and gastrointestinal carcinogenesis. [ABSTRACT FROM AUTHOR]

Cyclooxygenase-2 (COX-2) and Id-1 are overexpressed in avariety of human malignancies. Recently, each of these genes was found to play a role in mediating breast cancer metastasis to the lungs, but their potential interdependence was not evaluated. Hence, the main objective of the current study was to determine whether COX-2-derived prostaglandin (PGE2) activated Id-1 transcription, leading in turn to increased invasiveness of mammary epithelial cells. In MDA-MB-231 cells, treatment with PGE2 induced Id-1, an effect that was mimicked by an EP4 agonist. PGE2 via EP4 activated the epidermal growth factor receptor (EGFR) → ERK1/2 pathway, which led to increased expression of Egr-1. PGE2 stimulated EGFR signaling by inducing the release of amphiregulin, an EGFR ligand. The ability of PGE2 to activate Id-1 transcription was mediated by enhanced binding of Egr-1 to the Id-1 promoter. Silencing of COX-2 or pharmacological inhibition of COX-2 led to reduced PGE2 production, decreased Id-1 expression, and reduced migration of cells through extracellular matrix. A similar decrease in cell migration was found when Id-1 was silenced. The interrelationship between COX-2, PGE2, Id-1, and cell invasiveness was also compared in nontumorigenic SCp2 and tumorigenic SCg6 mammary epithelial cells. Consistent with the findings in MDA-MB-231 cells, COX-2-derived PGE2 induced Id-1, leading in turn to increased cell invasiveness. Taken together, these results suggest that PGE2 via EP4 activated the EGFR → ERK1/2 → Egr-1 pathway, leading to increased Id-1 transcription and cell invasion. These findings provide new insights into the relationship between COX-2 and Id-1 and their potential role in metastasis. [ABSTRACT FROM AUTHOR]

Cytochrome P450 aromatase (aromatase), a product of the CYP19 gene, catalyzes the synthesis of estrogens from androgens. Because aromatase-dependent estrogen biosynthesis has been linked to hormone-dependent breast carcinogenesis, it is important to elucidate the mechanisms that regulate CYP19 gene expression. The main objective of this study was to identify the receptors (EP) for prostaglandin E2 (PGE2) that mediate the induction of CYP19 transcription in human adipocytes and breast cancer cells. Treatment with PGE2 induced aromatase, an effect that was mimicked by either EP2 or EP4 agonists. Antagonists of EP2 or EP4 or small interference RNA-mediated down-regulation of these receptors suppressed PGE2-mediated induction of aromatase. PGE2 via EP2 and EP4 stimulated the cAMP->protein kinase A pathway resulting in enhanced interaction between P-CREB, p300, and the aromatase promoter I.3/II. Overexpressing a mutant form of p300 that lacks histone acetyltransferase activity suppressed PGE2-mediated induction of aromatase promoter activity. PGE2 via EP2 and EP4 also caused a reduction in both the amounts of BRCA1 and the interaction between BRCA1 and the aromatase promoter I.3/II. Activation of the aromatase promoter by PGE2 was suppressed by overexpressing wild-type BRCA1. Silencing of EP2 or EP4 also blocked PGE2-mediated induction of the progesterone receptor, a prototypic estrogen-response gene. In a mouse model, overexpressing COX-2 in the mammary gland, a known inducer of PGE2 synthesis, led to increased aromatase mRNA and activity and reduced amounts of BRCA1; these effects were reversed by knocking out EP2. Taken together, these results suggest that PGE2 via EP2 and EP4 activates the cAMP->PKA->CREB pathway leading to enhanced CYP19 transcription and increased aromatase activity. Reciprocal changes in the interaction between BRCA1, p300, and the aromatase promoter I.3/II contributed to the inductive effects of PGE2. [ABSTRACT FROM AUTHOR]

The p53 tumor suppressor gene encodes a homotetrameric transcription factor which is activated in response to a variety of cellular stressors, including DNA damage and oncogene activation. p53 mutations occur in>50% of human cancers. Although p53 has been shown to regulate Wnt signaling, the underlying mechanisms are not well understood. Here we show that silencing p53 in colon cancer cells led to increased expression of Aha1, a co-chaperone of Hsp90. Heat shock factor-1 was important for mediating the changes in Aha1 levels. Increased Aha1 levels were associated with enhanced interactions with Hsp90, resulting in increased Hsp90 ATPase activity. Moreover, increased Hsp90 ATPase activity resulted in increased phosphorylation of Akt and glycogen synthase kinase-3β (GSK3β), leading to enhanced expression of Wnt target genes. Significantly, levels of Aha1, Hsp90 ATPase activity, Akt, and GSK3β phosphorylation and expression of Wnt target genes were increased in the colons of p53-null as compared with p53 wild type mice. Using p53 heterozygous mutant epithelial cells from Li-Fraumeni syndrome patients, we show that a monoallelic mutation of p53 was sufficient to activate the Aha1/Hsp90 ATPase axis leading to stimulation of Wnt signaling and increased expression of Wnt target genes. Pharmacologic intervention with CP-31398, a p53 rescue agent, inhibited recruitment of Aha1 to Hsp90 and suppressed Wnt-mediated gene expression in colon cancer cells. Taken together, this study provides new insights into the mechanism by which p53 regulates Wnt signaling and raises the intriguing possibility that p53 status may affect the efficacy of anticancer therapies targeting Hsp90 ATPase. [ABSTRACT FROM AUTHOR]

Background/Aims: Cyclooxygenase-2 (COX-2) has been implicated in a number of hepatic stellate cell (HSC) functions but its relationship to transforming growth factor-β1 (TGF-β1)-mediated fibrogenesis is unknown. We assessed the impact of COX-2 inhibition and PGE2 on the regulation of TGF-β1-stimulated matrix synthesis in an immortalized human HSC line, LX-1 and corroborated these findings in primary stellate cells.Methods: Expression of COX-2 was assessed by Western blotting and real time quantitative PCR. The effect of NS398, a selective COX-2 inhibitor, and PGE2 on TGF-β1-mediated fibrogenesis was examined by measuring mRNA levels of collagen α1(I). PGE2 receptor expression was analyzed by RT-PCR.Results: Under basal conditions, NS398 suppressed PGE2 synthesis and induced collagen α1(I) whereas exogenous PGE2 suppressed expression of collagen α1(I). TGF-β1 induced COX-2 mRNA, COX-2 protein and PGE2 biosynthesis. Importantly, TGF-β1-mediated induction of collagen α1(I) was markedly suppressed by the addition of exogenous PGE2. All four major PGE2 receptors were expressed in LX-1 cells.Conclusions: These results suggest that COX-2-derived PGE2 inhibits both basal and TGF-β1-mediated induction of collagen synthesis by HSC. Based on these findings, it will be important to determine whether inhibiting COX-derived PGE2 synthesis alters the progression of liver fibrosis in vivo. [Copyright &y& Elsevier]

Obesity increases the risk of hormone receptor-positive breast cancer in postmenopausal women. Levels of aromatase, the rate-limiting enzyme in estrogen biosynthesis, are increased in the breast tissue of obese women. Both prostaglandin E 2 (PGE 2 ) and hypoxia-inducible factor 1α (HIF-1α) contribute to the induction of aromatase in adipose stromal cells (ASCs). Sirtuin 1 (SIRT1) binds, deacetylates, and thereby inactivates HIF-1α. Here, we sought to determine whether SIRT1 also plays a role in regulating aromatase expression. We demonstrate that reduced SIRT1 levels are associated with elevated levels of acetyl-HIF-1α, HIF-1α, and aromatase in breast tissue of obese compared with lean women. To determine whether these changes were functionally linked, ASCs were utilized. In ASCs, treatment with PGE 2 , which is increased in obese individuals, down-regulated SIRT1 levels, leading to elevated acetyl-HIF-1α and HIF-1α levels and enhanced aromatase gene transcription. Chemical SIRT1 activators (SIRT1720 and resveratrol) suppressed the PGE 2 -mediated induction of acetyl-HIF-1α, HIF-1α, and aromatase. Silencing of p300/CBP-associated factor (PCAF), which acetylates HIF-1α, blocked PGE 2 -mediated increases in acetyl-HIF-1α, HIF-1α, and aromatase. SIRT1 overexpression or PCAF silencing inhibited the interaction between HIF-1α and p300, a coactivator of aromatase expression, and suppressed p300 binding to the aromatase promoter. PGE 2 acted via prostaglandin E2 receptor 2 (EP 2 ) and EP 4 to induce activating transcription factor 3 (ATF3), a repressive transcription factor, which bound to a CREB site within the SIRT1 promoter and reduced SIRT1 levels. These findings suggest that reduced SIRT1-mediated deacetylation of HIF-1α contributes to the elevated levels of aromatase in breast tissues of obese women., (© 2019 Subbaramaiah et al.)

Multiple lines of evidence have suggested a role for both bile acids and prostaglandins (PG) in gastrointestinal carcinogenesis. Levels of PGE(2) are determined by both synthesis and catabolism. Previously, bile acid-mediated induction of cyclooxygenase-2 (COX-2) was found to stimulate PGE(2) synthesis. NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH), the key enzyme responsible for the catabolism of PGE(2), has been linked to colorectal carcinogenesis. In this study, we determined whether bile acids altered the expression of 15-PGDH in human colon cancer cell lines. Treatment with unconjugated bile acids (chenodeoxycholate and deoxycholate) suppressed the transcription of 15-PGDH, resulting in reduced amounts of 15-PGDH mRNA, protein, and enzyme activity. Conjugated bile acids were less potent suppressors of 15-PGDH expression than unconjugated bile acids. Treatment with chenodeoxycholate activated protein kinase C (PKC), leading in turn to increased extracellular signal-regulated kinase (ERK) 1/2 activity. Small molecules that inhibited bile acid-mediated activation of PKC and ERK1/2 also blocked the downregulation of 15-PGDH. Bile acids induced early growth response factor-1 (Egr-1) and Snail, a repressive transcription factor that bound to the 15-PGDH promoter. Silencing Egr-1 or Snail blocked chenodeoxycholate-mediated downregulation of 15-PGDH. Together, these data indicate that bile acids activate the signal transduction pathway PKC --> ERK1/2 --> Egr-1 --> Snail and thereby suppress 15-PGDH transcription. Bile acids appear to increase the release of PGs from cells by downregulating catabolism in addition to stimulating synthesis. These results provide new mechanistic insights into the link between bile acids and gastrointestinal carcinogenesis.

A series of novel derivatives of the nonsteroidal anti-inflammatory drug (NSAID) sulindac sulfide were synthesized as potential agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma). Nonpolar and aromatic substitutions on the benzylidene ring as well as retention of the carboxylic acid side chain were required for optimal activity. Compound 24 was as potent a compound as any other in the series with an EC50 of 0.1 microM for the induction of peroxisome proliferator response element (PPRE)-luciferase activity. Direct binding of compound 24 to PPARgamma was demonstrated by the displacement of [(3)H]troglitazone, a PPARgamma agonist, in a scintillation proximity assay. Compound 24 also stimulated the binding of PPARgamma to a PPRE-containing oligonucleotide and induced expression of liver fatty-acid binding protein (L-FABP) and adipocyte fatty acid-binding protein (aP2), two established PPARgamma target genes. Taken together, these compounds represent potential leads in the development of novel PPARgamma agonists.

The tobacco industry markets potentially reduced exposure products (PREPs) as less harmful or addictive alternatives to conventional cigarettes. This study compared the effects of mainstream smoke from Quest, Eclipse, and 2R4F reference cigarettes on the development of atherosclerosis in apolipoprotein E-deficient (apoE -/-) mice. Mice were exposed to smoke from four cigarette types for 12 weeks beginning at age of 12 weeks, and in a separate study for 8 weeks, beginning at age of 8 weeks. In both studies, mice exposed to smoke from high-nicotine, high-tar Quest 1, and 2R4F cigarettes developed greater areas of lipid-rich aortic lesions than did non-smoking controls. Exposure to smoke from the lower-nicotine products, Eclipse, and Quest 3, was associated with smaller lesion areas, but animals exposed to smoke from all of the tested types of cigarette had larger lesions than did control animals not exposed to smoke. Urinary levels of isoprostane F2 alpha VI, increased proportionally to cigarette nicotine yield, whereas induction of pulmonary cytochrome P4501A1 was proportional to tar yield. Lesion area was associated with both nicotine and tar yields, although in multiple regression analysis only nicotine was a significant predictor of lesion area. Smoke exposure did not alter systolic blood pressure (SBP), heart rate (HR), blood cholesterol, or leukocyte count. Taken together, these observations suggest that smoking may accelerate atherosclerosis by increasing oxidative stress mediated at least in part via the actions of nicotine.

NFAT family is recognized as a transcription factor for inflammation regulation by inducing the expression of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), the key mediator of inflammation, which was reported to induce cell transformation in mouse epidermal Cl41 cells. In this study, we demonstrated that TNF-alpha was able to induce NFAT activation, as well as the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). The induction of COX-2 by TNF-alpha was abolished by knockdown of NFAT3 with its siRNA, while the induction of iNOS was not effected. Moreover, TNF-alpha-induced anchorage-independent cell growth was significantly inhibited by NFAT3 siRNA and cyclosporine A, a chemical inhibitor for the calcineurin/NFAT pathway, which suggests the importance of NFAT3 in regulating TNF-alpha-induced anchorage-independent cell growth. Consequently, impairment of COX-2 by its siRNA or selective inhibitor also inhibited TNF-alpha-induced anchorage-independent cell growth. Taken together, our results indicate that NFAT3 plays an important role in the regulation of TNF-alpha-induced anchorage-independent cell growth, at least partially, by inducing COX-2 expression in Cl41 cells. These findings suggest that NFAT3/cyclooxygenase-2 act as a link between inflammation and carcinogenesis by being involved in the tumor promotion stage.

Increased amounts of PGE(2) have been detected in the inflamed mucosa of patients with inflammatory bowel disease (IBD). This increase has been attributed to enhanced synthesis rather than reduced catabolism of PGE(2). 15-Hydroxyprostaglandin dehydrogenase (15-PGDH) plays a major role in the catabolism of PGE(2). In this study, we investigated whether amounts of 15-PGDH were altered in inflamed mucosa from patients with IBD. Amounts of 15-PGDH protein and mRNA were markedly reduced in inflamed mucosa from patients with Crohn's disease and ulcerative colitis. In situ hybridization demonstrated that 15-PGDH was expressed in normal colonic epithelium but was virtually absent in inflamed colonic mucosa from IBD patients. Because of the importance of TNF-alpha in IBD, we also determined the effects of TNF-alpha on the expression of 15-PGDH in vitro. Treatment with TNF-alpha suppressed the transcription of 15-PGDH in human colonocytes, resulting in reduced amounts of 15-PGDH mRNA and protein and enzyme activity. In contrast, TNF-alpha induced two enzymes (cyclooxygenase-2 and microsomal prostaglandin E synthase-1) that contribute to increased synthesis of PGE(2). Overexpressing 15-PGDH blocked the increase in PGE(2) production mediated by TNF-alpha. Taken together, these results suggest that reduced expression of 15-PGDH contributes to the elevated levels of PGE(2) found in inflamed mucosa of IBD patients. The decrease in amounts of 15-PGDH in inflamed mucosa can be explained at least, in part, by TNF-alpha-mediated suppression of 15-PGDH transcription.

Understanding the mechanisms underlying carcinogenesis provides insights that are necessary for the development of therapeutic strategies to prevent cancer. Chemoprevention, the use of drugs or natural substances to inhibit carcinogenesis, is a rapidly evolving aspect of cancer research. Evidence is presented that cyclooxygenase-2 (COX-2) and epidermal growth factor receptor (EGFR) are potential pharmacologic targets to prevent cancer. In this paper, we review key data implicating a causal relationship between COX-2, EGFR, and carcinogenesis and possible mechanisms of action. We discuss evidence of crosstalk between COX-2 and EGFR in order to strengthen the rationale for combination chemoprevention, and review plans for a clinical trial that will evaluate the concept of combination chemoprevention targeting COX-2 and EGFR.

There is a significant body of evidence suggesting that enzymes involved in arachidonic acid metabolism and their eicosanoid products play a role in various cancers, having both pro- and antitumorigenic effects. The goal of this study was to further define the role microsomal prostaglandin E synthases (mPGES-1) play in lung tumorigenesis. Transgenic mice were created with targeted over-expression of human mPGES-1 in the alveolar and airway epithelial cells using an SP-C promoter driven construct. Transgene positive (mPGES-1+) mice were shown to significantly over-express functional mPGES-1 in the lung and more specifically in alveolar type II cells. To study the effects of mPGES-1 over-expression in lung tumor formation, mice were exposed to a complete carcinogen protocol with a single injection of urethane or an initiation/promotion model with a single injection of 3-methylcholanthrene (MCA) followed by multiple injections of butylated hydroxytoluene (BHT). mPGES-1+ mice did not show a significant difference in tumor multiplicity or tumor size at 10, 16, 19 or 30 weeks after urethane injection compared with mPGES-1- mice. No significant difference was seen in tumor incidence, multiplicity or size at 19 weeks after treatment with MCA/BHT. Western blots verified that mPGES-1 expression was increased in tumors versus uninvolved tissue of both mPGES-1+ and mPGES-1- mice with overall expression being significantly higher in mPGES-1+ mice. Cyclooxygenase-2 levels were elevated in tumors in both groups. From these studies we conclude that over-expression of mPGES-1 and highly elevated PGE2 production are not sufficient to induce lung tumors.

Several members of the P450 family, including cytochrome P450 1B1 (CYP1B1), can convert tobacco smoke (TS) procarcinogens, including benzo[a]pyrene (B[a]P), to carcinogenic intermediates. In this study we investigated the effects of TS condensate and B[a]P on the expression of CYP1B1 in vitro and in vivo. CYP1B1 mRNA and protein were induced by both TS condensate and B[a]P in cell lines derived from the human aerodigestive tract. Treatment with TS condensate stimulated binding of the aryl hydrocarbon receptor (AhR) to an oligonucleotide containing a canonical xenobiotic response element (XRE) site and induced XRE-luciferase activity. These findings are consistent with prior evidence that polycyclic aromatic hydrocarbons, known ligands of the AhR, stimulate CYP1B1 transcription by an XRE-dependent mechanism. To determine whether these in vitro findings applied in vivo, both murine and human studies were carried out. Short-term exposure to TS induced CYP1B1 in the tongue, esophagus, lung and colon of experimental mice. In contrast, CYP1B1 was not induced by TS in the aorta of these mice. Levels of CYP1B1 mRNA were also elevated in the bronchial mucosa of human tobacco smokers versus never smokers (P < 0.05). Taken together, these results support a role for CYP1B1 in TS-induced carcinogenesis in the aerodigestive tract.

Background/aims: Cyclooxygenase-2 (COX-2) has been implicated in a number of hepatic stellate cell (HSC) functions but its relationship to transforming growth factor-beta 1 (TGF-beta 1)-mediated fibrogenesis is unknown. We assessed the impact of COX-2 inhibition and PGE(2) on the regulation of TGF-beta 1-stimulated matrix synthesis in an immortalized human HSC line, LX-1 and corroborated these findings in primary stellate cells., Methods: Expression of COX-2 was assessed by Western blotting and real time quantitative PCR. The effect of NS398, a selective COX-2 inhibitor, and PGE(2) on TGF-beta 1-mediated fibrogenesis was examined by measuring mRNA levels of collagen alpha1(I). PGE(2) receptor expression was analyzed by RT-PCR., Results: Under basal conditions, NS398 suppressed PGE(2) synthesis and induced collagen alpha 1(I) whereas exogenous PGE(2) suppressed expression of collagen alpha1(I). TGF-beta 1 induced COX-2 mRNA, COX-2 protein and PGE(2) biosynthesis. Importantly, TGF-beta 1-mediated induction of collagen alpha 1(I) was markedly suppressed by the addition of exogenous PGE(2). All four major PGE(2) receptors were expressed in LX-1 cells., Conclusions: These results suggest that COX-2-derived PGE(2) inhibits both basal and TGF-beta 1-mediated induction of collagen synthesis by HSC. Based on these findings, it will be important to determine whether inhibiting COX-derived PGE(2) synthesis alters the progression of liver fibrosis in vivo.

Context: Use of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) has been associated with a decrease in the risk of several cancers, including breast cancer. NSAIDs inhibit cyclooxygenase activity and thereby reduce prostaglandin synthesis; prostaglandins stimulate aromatase gene expression and thereby stimulate estrogen biosynthesis. Given the importance of estrogen in the pathogenesis of breast cancer, the ability of aspirin and other NSAIDs to protect against breast cancer could vary according to hormone receptor status., Objectives: To determine the association between the frequency and duration of use of aspirin and other NSAIDs and breast cancer risk and to investigate whether any observed association is more pronounced for women with hormone receptor-positive breast cancers., Design, Setting, and Patients: Population-based case-control study of women with breast cancer, including in-person interviews conducted on Long Island, NY, during 1996-1997 (1442 cases and 1420 controls)., Main Outcome Measure: Incident invasive and in situ breast cancer by aspirin and NSAID use and hormone receptor status., Results: Ever use of aspirin or other NSAIDs at least once per week for 6 months or longer was reported in 301 cases (20.9%) and 345 controls (24.3%) (odds ratio [OR], 0.80; 95% confidence interval [CI], 0.66-0.97 for ever vs nonusers). The inverse association was most pronounced among frequent users (> or =7 tablets per week) (OR, 0.72; 95% CI, 0.58-0.90). The results for ibuprofen, which was used by fewer women on a regular basis, were generally weaker (OR, 0.78; 95% CI, 0.55-1.10 for <3 times per week vs OR, 0.92; 95% CI, 0.70-1.22 for > or =3 times per week). Use of acetaminophen, an analgesic that does not inhibit prostaglandin synthesis, was not associated with a reduction in the incidence of breast cancer. The reduction in risk with aspirin use was seen among those with hormone receptor-positive tumors (OR, 0.74; 95% CI, 0.60-0.93) but not for women with hormone receptor-negative tumors (OR, 0.97; 95% CI, 0.67-1.40)., Conclusion: These data add to the growing evidence that supports the regular use of aspirin and other NSAIDs (which may operate through inhibition of estrogen biosynthesis) as effective chemopreventive agents for breast cancer.

Evidence continues to accumulate that cyclooxygenase-2 (COX-2), an inducible COX isoform, represents a potential pharmacological target for the prevention and treatment of cancer, including tumors affecting the entire upper aerodigestive tract. Studies in experimental models of these malignancies show that selective COX-1 inhibitors reduce tumor formation and growth. Clinical studies have been initiated to determine the chemoprotective effects of selective COX-2 inhibitors in patients with oral leukoplakia and Barrett's esophagus, and other studies are assessing the feasibility of incorporating these agents into existing treatment modalities for patients with locally advanced or metastatic cancer.

Bryostatin-1 (bryostatin) is a macrocyclic lactone derived from Bugula neritina, a marine bryozoan. On the basis of the strength of in vitro and animal studies, bryostatin is being investigated as a possible treatment for a variety of human malignancies. Severe myalgias are a common dose-limiting side effect. Because cyclooxygenase-2 (COX-2)-derived prostaglandins can cause pain, we investigated whether bryostatin induced COX-2. Bryostatin (1-10 nM) induced COX-2 mRNA, COX-2 protein, and prostaglandin biosynthesis. These effects were observed in macrophages as well as in a series of human cancer cell lines. Transient transfections localized the stimulatory effects of bryostatin to the cyclic AMP response element of the COX-2 promoter. Electrophoretic mobility shift assays and supershift experiments revealed a marked increase in the binding of activator protein-1 (AP-1)(c-Jun/c-Fos) to the cyclic AMP response element of the COX-2 promoter. Pharmacological and transient transfection studies indicated that bryostatin stimulated COX-2 transcription via the protein kinase C-->mitogen-activated protein kinase-->AP-1 pathway. All-trans-retinoic acid, a prototypic AP-1 antagonist, blocked bryostatin-mediated induction of COX-2. Taken together, these results suggest that bryostatin-mediated induction of COX-2 can help to explain the myalgias that are commonly associated with treatment. Moreover, it will be worthwhile to evaluate whether the addition of a selective COX-2 inhibitor can increase the antitumor activity of bryostatin.

Elevated levels of prostaglandin E(2) (PGE(2)) occur in head and neck squamous cell carcinoma (HNSCC) and have been associated with a poor prognosis. Recently, an inducible microsomal prostaglandin E synthase-1 (mPGES) was identified. This enzyme converts the cyclooxygenase product prostaglandin H(2) (PGH(2)) to PGE(2). Given the apparent significance of PGE(2) in carcinogenesis, it is important to elucidate the mechanisms that account for increased amounts of PGE(2) in HNSCC. By immunoblot analysis, mPGES was overexpressed in 11 of 14 (79%) cases of HNSCC compared with adjacent normal tissue. Immunohistochemistry localized mPGES expression to neoplastic epithelial cells. Cell culture was used to determine whether cellular transformation was associated with increased amounts of mPGES. Levels of mPGES protein and mRNA were markedly elevated in HNSCC cell lines (1483 and Ca9-22) versus a nontumorigenic oral epithelial cell line (MSK-Leuk1). Interestingly, treatment of MSK-Leuk1 cells with PGE(2) caused both dose- and time-dependent stimulation of cell growth. Each of the four known receptors for PGE(2) (E-prostanoid receptor subtypes 1-4) was detected in head and neck squamous mucosa. Taken together, these results suggest that overexpression of mPGES contributes to the increased levels of PGE(2) found in HNSCC. Additional studies will be needed to determine whether this enzyme is a bona fide target for anticancer therapy.

Background: The objective of this prospective cross-sectional study was to determine if cyclo-oxygenase-2, or COX-2, is overexpressed in the inflamed gingival tissue of patients diagnosed as having moderate-to-severe chronic periodontitis, or CP., Methods: The authors evaluated clinical measures, crevicular fluid and gingival biopsy specimens from patients with moderate or severe CP (n = 16) and from healthy volunteers (n = 8). Patients were diagnosed as having CP based on clinical attachment loss, or CAL, of at least 5 millimeters at two sites in each quadrant and on evidence of alveolar bone loss as assessed from standard periapical or bite-wing radiographs. Healthy patients exhibited no sites with CAL of more than 2 mm and no evidence of alveolar bone loss. The authors used standard techniques to perform biochemical measures., Results: Levels of interleukin-1 beta, or IL-1beta, in crevicular fluid were more than doubled in the CP group (P < .05). The amounts of COX-2 mRNA and protein also were elevated in gingival tissues from subjects with CP compared with those from healthy subjects. To gain further mechanistic insights, the authors conducted in vitro studies. The results showed that lipopolysaccharide and tumor necrosis factor alpha, or TNF-alpha, induced COX-2 in macrophages, while IL-1beta and TNF-alpha induced COX-2 in oral epithelial cells., Conclusions: Taken together, these results suggest that levels of COX-2 in gingivae reflect clinical measures of periodontitis and gingival inflammation., Clinical Implications: The discovery of increased levels of COX-2 in inflamed gingival tissue suggests that COX-2 represents a pharmacological target for the prevention or treatment of CP.

Cyclooxygenase2 (COX-2), an inducible prostaglandin G/H synthase, is overexpressed in several human cancers. Here, the potential utility of selective COX-2 inhibitors in the prevention and treatment of cancer is considered. The mechanisms by which COX-2 levels increase in cancers, key data that indicate a causal link between increased COX-2 activity and tumorigenesis, and possible mechanisms of action of COX-2 are discussed. In a proof-of-principle clinical trial, treatment with the selective COX-2 inhibitor celecoxib reduced the number of colorectal polyps in patients with familial adenomatous polyposis. Selective COX-2 inhibitors appear to be sufficiently safe to permit large-scale clinical testing and numerous clinical trials are currently under way to determine whether selective inhibitors of COX-2 are effective in the prevention and treatment of cancer.

Cyclooxygenase 2 (HER-2) (Cox-2), an inducible form of Cox, is overexpressed in HER-2/neu-positive human breast cancers. The aim of this study was to determine whether celecoxib, a selective Cox-2 inhibitor, protected against HER-2/neu-induced experimental breast cancer. Cox-2 protein was detected in breast carcinomas from mouse mammary tumor virus (MMTV)/neu mice. Treatment with celecoxib (500 ppm) significantly reduced the incidence of mammary tumors in MMTV/neu mice (P = 0.003) and caused about a 50% reduction in mammary prostaglandin E2 (PGE2) levels. Because mammary glands from MMTV/neu mice expressed all four PGE2 receptor subtypes, we speculate that signaling through PGE2 receptors is important for mammary tumorigenesis. These results strengthen the rationale for developing clinical trials to determine whether selective Cox-2 inhibitors possess anticancer properties in humans at risk for breast cancer.

Treatment with retinoic acid (RA) or carnosol, two structurally unrelated compounds with anticancer properties, inhibited phorbol ester (PMA)-mediated induction of activator protein-1 (AP-1) activity and cyclooxygenase-2 (COX-2) expression in human mammary epithelial cells. The induction of COX-2 transcription by PMA was mediated by increased binding of AP-1 to the cyclic AMP response element (CRE) of the COX-2 promoter. Inhibition of the histone acetyltransferase activity of CREB- binding protein (CBP)/p300 blocked the induction of COX-2 by PMA. Treatment with carnosol but not RA blocked increased binding of AP-1 to the COX-2 promoter. Because AP-1 binding was unaffected by RA, we investigated whether RA inhibited COX-2 transcription via effects on the coactivator CBP/p300. Treatment with RA stimulated an interaction between RA receptor-alpha and CBP/p300; a corresponding decrease in the interaction between CBP/p300 and c-Jun was observed. Importantly, overexpressing CBP/p300 or dominant-negative RA receptor-alpha relieved the suppressive effect of RA on PMA-mediated stimulation of the COX-2 promoter. To elucidate the mechanism by which carnosol inhibited COX-2 transcription, its effects on protein kinase C (PKC) signaling were determined. Carnosol but not RA inhibited the activation of PKC, ERK1/2, p38, and c-Jun NH2-terminal kinase mitogen-activated protein kinase. Overexpressing c-Jun but not CBP/p300 reversed the suppressive effect of carnosol on PMA-mediated stimulation of COX-2 promoter activity. Thus, RA acted by a receptor-dependent mechanism to limit the amount of CBP/p300 that was available for AP-1-mediated induction of COX-2. By contrast, carnosol inhibited the induction of COX-2 by blocking PKC signaling and thereby the binding of AP-1 to the CRE of the COX-2 promoter. Taken together, these results show that small molecules can block the activation of COX-2 transcription by distinct mechanisms.

The induction of cyclooxygenase (COX)-2 expression has been implicated as a mechanism for the formation of non-hepatic tumors. Recent investigations have demonstrated COX-2 expression in human hepatocellular carcinomas, but little is known about the regulation of hepatocyte COX-2 expression. Employing the adult, rat hepatocyte line RALA255-10G, the effects of cellular transformation or expression of the alcohol-inducible cytochrome P450 2E1 (CYP2E1) on COX-2 expression were examined. Transformed and non-transformed hepatocytes did not express COX-2 by western and northern blot analysis. The tumor promoters phorbol 12-myristate 13-acetate (PMA) and chenodeoxycholic acid (CD) induced COX-2 protein expression in transformed, but not non-transformed cells. CYP2E1-expressing cells lacked constitutive COX-2 expression, and PMA but not CD induced COX-2 in these cells. PMA-treated transformed and CYP2E1-expressing cells expressed functional COX-2 as demonstrated by marked inductions in prostaglandin E(2) synthesis. PMA-induced COX-2 expression in both transformed and CYP2E1-expressing cells resulted from an induction in COX-2 mRNA, and was dependent on extracellular signal-regulated kinase, p38 mitogen-activated protein kinase and phosphatidylinositol 3-kinase. The differential induction of COX-2 by PMA in transformed and non-transformed cells could not be explained by differences in NF-kappaB or C/EBPalpha activation. PMA did not induce COX-2 transcriptional activity as determined by transient transfections with a luciferase reporter gene driven by the COX-2 promoter. The data demonstrate that cellular transformation and CYP2E1 expression fail to lead to the induction of COX-2 expression in hepatocytes. However, these conditions do render hepatocytes susceptible to COX-2 induction from tumor promoters by post-transcriptional mechanisms.