Prostacyclin-mediated activation of peroxisome proliferator-activated receptor delta in colorectal cancer

Tamoxifen resistance in MCF7 cells promotes EMT-like behaviour and involves modulation of beta-catenin phosphorylation

We have previously demonstrated that, following acquisition of endocrine resistance, breast cancer cells display an altered growth rate together with increased aggressive behaviour in vitro. Since dysfunctional cell-cell adhesive interactions can promote an aggressive phenotype, we investigated the integrity of this protein complex in our breast cancer model of tamoxifen resistance. In culture, tamoxifen-resistant MCF7 (TamR) cells grew as loosely packed colonies with loss of cell-cell junctions and demonstrated altered morphology characteristic of cells undergoing epithelial-to-mesenchymal transition (EMT). Neutralising E-cadherin function promoted the invasion and inhibited the aggregation of endocrine-sensitive MCF7 cells, whilst having little effect on the behaviour of TamR cells. Additionally, TamR cells had increased levels of tyrosine-phosphorylated beta-catenin, whilst serine/threonine-phosphorylated beta-catenin was decreased. These cells also displayed loss of association between beta-catenin and E-cadherin, increased cytoplasmic and nuclear beta-catenin and elevated transcription of beta-catenin target genes known to be involved in tumour progression and EMT. Inhibition of EGFR kinase activity in TamR cells reduced beta-catenin tyrosine phosphorylation, increased beta-catenin-E-cadherin association and promoted cell-cell adhesion. In such treated cells, the association of beta-catenin with Lef-1 and the transcription of c-myc, cyclin-D1, CD44 and COX-2 were also reduced. These results suggest that homotypic adhesion in tamoxifen-resistant breast cancer cells is dysfunctional due to EGFR-driven modulation of the phosphorylation status of beta-catenin and may contribute to an enhanced aggressive phenotype and transition towards a mesenchymal phenotype in vitro.

Chemoprevention of colorectal cancer: ready for routine use?

In the third millennium, preventive medicine is becoming a cornerstone in our concept of health. Colorectal cancer (CRC) prevention, in particular, has become an important goal for health providers, physicians and the general public. CRC fits the criteria of a disease suitable for chemopreventive interventions. It is a prevalent disease that is associated with considerable mortality and morbidity rates, with more than 1,000,000 new cases and 500,000 deaths expected, worldwide, in 2004. CRC has a natural history of transition from precursor to malignant lesion that spans, on average, 15-20 years, providing a window of opportunity for effective interventions and prevention. A pre-malignant precursor lesion (i.e. adenoma) usually precedes cancer, and helps to identify a subset of the population that is at increased risk of harbouring and developing cancer. Science and technology have evolved to a point where we are able to use our knowledge of cancer biology to identify individuals at risk and interrupt the process of malignant transformation at the level of the pre-cancerous lesion. Recent progress in molecular biology and pharmacology enhances the likelihood that cancer prevention will increasingly rely on chemoprevention. Chemoprevention, a new emerging science, means the use of agents to inhibit, delay or reverse carcinogenesis. Recent observations suggest a number of potential targets for chemoprevention. Many agents have potential benefit but only modest chemopreventive efficacy in clinical trials. There is much evidence suggesting an inverse relationship between aspirin or non-steroidal anti-inflammatory drug (NSAID) consumption and CRC incidence and mortality. However, NSAID consumption is not problem-free; 1997 data show 107,000 hospitalisations and 16,500 deaths due to NSAID consumption in the U.S. alone. Therefore, although chemoprevention of CRC is already possible, drugs that have more acceptable side-effect profiles than the currently available NSAIDs are required. Cyclo-oxygenase (COX)-2-specific inhibitors, which have an improved safety profile compared to traditional NSAIDs that inhibit both the COX-1 and COX-2 enzymes, seem to be well-suited drug candidates for CRC prevention. The inhibition of the growth of pre-cancerous and cancerous cells without affecting normal cells is the ultimate aim of cancer treatment and is of particular importance in chemoprevention studies, which may be long term in nature, involving healthy subjects and minimal toxicity. Cancer prevention is certain to be a significant focus of research and intervention in the coming years, propelled by the realisation that we will be able to identify both individuals susceptible to specific cancers as well as the molecular targets that can alter or stop the carcinogenesis process. Pharmacology and genetics are collaborating to develop new chemoprevention agents designed to affect molecular targets linked to specific premalignant or predisposing conditions.

Expression patterns of the chicken peroxisome proliferator-activated receptors (PPARs) during the development of the digestive organs

Peroxisome proliferator-activated receptors (PPARs) play very important roles in various biological phenomena such as regulation of lipid metabolism, homeostasis, cell differentiation and proliferation, in a variety of organs and tissues. However, their functions in the development of the digestive organs have not been studied yet, although it has been supposed that they are involved in the tumor development and regression of digestive organs. To provide fundamental data to analyze functions of PPARs in the developing digestive organs in the chicken embryos, we performed thorough analysis of expression of PPARalpha, beta (delta) and gamma in the esophagus, proventriculus (glandular stomach), gizzard (muscular stomach), small and large intestines from early developmental stages to post hatch stages. The results showed that each PPAR is expressed in spatio-temporally regulated manner. In general, PPARbeta is widely expressed among digestive organs whereas PPARalpha and gamma showed restricted expression. In the intestine, all PPARs are expressed after hatch, indicating that they play important roles in the physiology of the adult intestine.

Cyclooxygenase-2 plays a suppressive role for induction of apoptosis in isoliquiritigenin-treated mouse colon cancer cells

Cellular damage induced by chronic inflammation is a well known cause of colon carcinogenesis. Cyclooxygenase-2 (COX-2), the enzyme that converts arachidonic acid to prostanoids, is known to play an important role in inflammation. Herbal flavonoid isoliquiritigenin (ILTG) has previously been reported to be a strong suppresser of the COX-2 pathway as well as an inducer of apoptosis. Here we report that the susceptibility to apoptosis by ILTG is dependent on the level of COX-2 in mouse colon adenocarcinoma Colon 26, which spontaneously expresses COX-2. This dependency was observed to be enhanced by blockage of the lipoxigenases (LOXs)-mediated metabolic pathway and attenuated by addition of a number of prostaglandins and thromboxanes. Taken together, these findings indicate that ILTG-induced apoptosis is negatively regulated by the COX-2 expression level.

Quantitative analysis of PPARdelta mRNA by real-time RT-PCR in 86 rectal cancer tissues

AIM

The purpose of this study is to clarify the expression change of PPARdelta gene in human colorectal cancer tissues.

METHODS

Applying real-time RT-PCR, we quantified PPARdelta mRNA in a series of 86 tissues from excised primary rectal cancers. In each case, accompanying normal mucosa was collected for comparison.

RESULTS

Among the 86 rectal cancer tissues, 48 cases showed PPARdelta overexpression: 39 tumours gave an expression level 1.5-5 times, five tumours 10-20 times, and four tumours more than 20 times relative to normal mucosa. However, the general level of PPARdelta mRNA in rectal cancer tissues is not statistically different from normal mucosa.

CONCLUSIONS

The expression of PPARdelta gene in rectal cancers is not statistically different from normal mucosa.

Differential responses of PPARalpha, PPARdelta, and PPARgamma reporter cell lines to selective PPAR synthetic ligands

To characterize the specificity of synthetic compounds for peroxisome proliferator-activated receptors (PPARs), three stable cell lines expressing the ligand binding domain (LBD) of human PPARalpha, PPARdelta, or PPARgamma fused to the yeast GAL4 DNA binding domain (DBD) were developed. These reporter cell lines were generated by a two-step transfection procedure. First, a stable cell line, HG5LN, expressing the reporter gene was developed. These cells were then transfected with the different receptor genes. With the help of the three PPAR reporter cell lines, we assessed the selectivity and activity of PPAR agonists GW7647, WY-14-643, L-165041, GW501516, BRL49653, ciglitazone, and pioglitazone. GW7647, L-165041, and BRL49653 were the most potent and selective agonists for hPPARalpha, hPPARdelta, and hPPARgamma, respectively. Two PPAR antagonists, GW9662 and BADGE, were also tested. GW9662 was a selective PPARgamma antagonist, whereas BADGE was a low-affinity PPAR ligand. Furthermore, GW9662 was a full antagonist on PPARgamma and PPARdelta, whereas it showed partial agonism on PPARalpha. We conclude that our stable models allow specific and sensitive measurement of PPAR ligand activities and are a high-throughput, cell-based screening tool for identifying and characterizing PPAR ligands.

Interactions of peroxisome proliferator-activated receptor {gamma} and diet in etiology of colorectal cancer

The peroxisome proliferator-activated receptor gamma (PPARgamma) is one of a group of ligand-activated nuclear receptors responsible for regulation of glucose, lipid homeostasis, cell differentiation, and apoptosis. The 12 proline-to-alanine (Pro12Ala) substitution polymorphism in PPARgamma produces proteins with lower activity. Variation in PPARgamma expression in the bowel and the role of dietary fatty acids as ligands for PPARgamma led investigation of whether the associations of diet with colon and rectal cancer risk were modified by PPARgamma genotype. Data (diet, lifestyle, and DNA) came from case-control studies of colon (1,577 cases and 1,971 controls) and rectal cancer (794 cases and 1,001 controls) conducted in Northern California, Utah, and the Twin City, Minnesota Metropolitan area (colon cancer study only). Unconditional logistic regression models were adjusted for age at selection, body mass index, physical activity, energy intake, dietary fiber, and calcium. We found no significant interactions between macronutrient (fat, protein, and carbohydrate) and colorectal cancer. High lutein intake [odds ratio (OR), 0.63; 95% confidence interval (95% CI), 0.44-0.89], low refined grain intake (OR, 0.70; 95% CI, 0.53-0.94), or a high prudent diet score (OR, 0.66; 95% CI, 0.49-0.89) and PA/AA PPARgamma genotype were associated with reduced colon cancer risk. Risk of rectal cancer was increased among those with the PA/AA PPARgamma genotype and a high mutagen index (OR, 1.63; 95% CI, 1.12, 2.36). Its unclear whether the alterations in risk in those with the less active phenotype for PPARgamma is related to activation of PPARgamma by nutrients or dietary patterns acting as ligands or direct influences of these nutrients on colon and rectal cancer processes that are important with lower PPARgamma activity.

Peroxisome proliferator-activated receptor-beta as a target for wound healing drugs

Healing of cutaneous wounds, which is crucial for survival after an injury, proceeds via a well-tuned pattern of events including inflammation, re-epithelialisation, and matrix and tissue remodelling. These events are regulated spatio-temporally by a variety of growth factors and cytokines. The inflammation that immediately follows injury increases the expression of peroxisome proliferator-activated receptor (PPAR)-beta in the wound edge keratinocytes and triggers the production of endogenous PPARbeta ligands that activate the newly produced receptor. This elevated PPARbeta activity results in increased resistance of the keratinocytes to the apoptotic signals released during wounding, allowing faster re-epithelialisation. The authors speculate that, in parallel, ligand activation of PPARbeta in infiltrated macrophages attenuates the inflammatory response, which also promotes repair. Thus, current understanding of the roles of PPARbeta in different cell types implicated in tissue repair has revealed an intriguing intercellular cross-talk that coordinates, spatially and temporally, inflammation, keratinocyte survival, proliferation and migration, which are all essential for efficient wound repair. These novel insights into the orchestrating roles of PPARbeta during wound healing may be helpful in the development of drugs for acute and chronic wound disorders.

The Toxicology of Ligands for Peroxisome Proliferator-Activated Receptors (PPAR)

Peroxisome proliferator-activated receptors (PPARs) are ligand activated transcription factors that modulate target gene expression in response to endogenous and exogenous ligands. Ligands for the PPARs have been widely developed for the treatment of various diseases including dyslipidemias and diabetes. While targeting selective receptor activation is an established therapeutic approach for the treatment of various diseases, a variety of toxicities are known to occur in response to ligand administration. Whether PPAR ligands produce toxicity via a receptor-dependent and/or off-target-mediated mechanism(s) is not always known. Extrapolation of data derived from animal models and/or in vitro models, to humans, is also questionable. The different toxicities and mechanisms associated with administration of ligands for the three PPARs will be discussed, and important data gaps that could increase our current understanding of how PPAR ligands lead to toxicity will be highlighted.

NSAIDs in neuroblastoma therapy

Cyclooxygenases (COX) catalyse the conversion of arachidonic acid to prostaglandins. COX-2 is upregulated in several adult epithelial cancers. In neuroblastoma it has been shown that the majority of primary tumours and cell lines express high levels of COX-2, whereas normal adrenal medullas from children do not express COX-2. Treatment of neuroblastoma cells with nonsteroidal anti-inflammatory drugs (NSAIDs), inhibitors of COX, induces caspase-dependent apoptosis via the intrinsic mitochondrial pathway. Established neuroblastoma xenografts in nude rats treated with the dual COX-1/COX-2 inhibitor, diclofenac, or the COX-2 specific inhibitor, celecoxib significantly inhibits neuroblastoma growth in vivo. In vitro, arachidonic acid and diclofenac synergistically induces neuroblastoma cell death. This effect is further pronounced when lipoxygenases is inhibited simultaneously. Proton MR-spectroscopy (1H MRS) of neuroblastoma cells treated with COX-inhibitors demonstrates accumulation of polyunsaturated fatty acids and depletion of choline compounds. Thus, 1H MRS, which can be performed with clinical MR-scanners, is likely to provide pharmacodynamic markers of neuroblastoma response to COX-inhibition. Taken together, these data suggest the use of NSAIDs as a novel adjuvant therapy for children with neuroblastoma.

Non-COX-2 targets and cancer: Expanding the molecular target repertoire of chemoprevention

Chemoprevention represents a highly promising approach for the control of cancer. That nonsteroidal anti-inflammatory drugs (NSAIDs) prevent colon and other cancers has led to novel approaches to cancer prevention. The known inhibitory effect of NSAIDs on the eicosanoid pathway prompted mechanistic and drug development work focusing on cyclooxygenase (COX), culminating in clinical trials of cyclooxygenase 2 (COX-2) inhibitors for cancer prevention or treatment. However, two COX-2 inhibitors have been withdrawn due to side effects. Here we review several pathways of the eicosanoid cascade that are relevant to cancer; summarize the evidence regarding the role of COX-2 as a target for cancer prevention; and discuss several of the molecular targets that may mediate the chemopreventive effect of NSAIDs. The clinically modest results obtained to date with COX-2 specific inhibitors used in cancer prevention; the multiple COX-2-independent targets of both NSAIDs and COX-2 inhibitors; and the limitations of some COX-2 inhibitors indicate that exploiting these (non-COX-2) molecular targets will likely yield effective new approaches for cancer chemoprevention.

The role of peroxisome proliferator-activated receptor-beta/delta in epithelial cell growth and differentiation

The physiological and pharmacological roles of peroxisome proliferator-activated receptor-beta (PPARbeta-also referred to as PPARdelta) are just beginning to emerge. It has recently become clear that PPARbeta has a function in epithelial tissues, but controversy exists due to inconsistencies in the literature. There is strong evidence that ligand activation of PPARbeta can induce terminal differentiation of keratinocytes, with a concomitant inhibition of cell proliferation. However, the role of PPARbeta in keratinocyte-specific apoptosis is less clear. Additionally, the role of PPARbeta in colonic epithelium remains unclear due to conflicting evidence suggesting that ligand activation of PPARbeta can potentiate, as well as attenuate, intestinal cancer. Recent studies revealed that ligand activation of PPARbeta can induce fatty acid catabolism in skeletal muscle and is associated with improved insulin sensitivity, attenuated weight gain and elevated HDL levels thus demonstrating promising potential for targeting PPARbeta for treating obesity, dyslipidemias and type 2 diabetes. Therefore, it becomes critical to determine the safety of PPARbeta ligands. This review focuses on recent literature describing the role of PPARbeta in epithelial tissues and highlights critical discrepancies that need to be resolved for a more comprehensive understanding of how this receptor modulates epithelial homeostasis.

Cellular and molecular biology of prostacyclin synthase

Prostacyclin synthase (PGIS) cDNA comprises 1500 nucleotides coding for a 500 amino acid protein. It is a heme protein with spectral characteristics of cytochrome p450 (CYP). It does not possess the typical CYP mono-oxygenase activity but catalyzes the rearrangement of prostaglandin H2 to form PGI2. Analysis of its structure-function by molecular modeling and site-directed mutagenesis reveals a long substrate channel lined by hydrophobic residues. Cys-441 has been identified as the proximal axial ligand of heme. Tyr-430 is nitrated by peroxynitrite which results in reduced PGIS catalytic activity, suggesting that Tyr-430 is located close to the heme pocket. PGIS is constitutively expressed and may be upregulated by cytokines, reproductive hormones, and growth factors. It is physically colocalized with cyclooxygenases and phospholipases, and functionally coupled with these enzymes. PGIS coupling with COX-2 has been shown to play an important role in vascular protection, embryo development and implantation, and cancer growth.

Protective effects of a peroxisome proliferator-activated receptor-beta/delta agonist in experimental autoimmune encephalomyelitis

Agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma) exert anti-inflammatory and anti-proliferative effects which led to testing of these drugs in experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. In contrast, the effect of PPARdelta (PPARdelta) agonists in EAE is not yet known. We show that oral administration of the selective PPARdelta agonist GW0742 reduced clinical symptoms in C57BL/6 mice that had been immunized with encephalitogenic myelin oligodendrocyte glycoprotein (MOG) peptide. In contrast to previous results with PPARgamma agonists, GW0742 only modestly attenuated clinical symptoms when the drug was provided simultaneously with immunization, but a greater reduction was observed if administered during disease progression. Reduced clinical symptoms were accompanied by a reduction in the appearance of new cortical lesions, however cerebellar lesion load was not reduced. Treatment of T-cells with GW0742 either in vivo or in vitro did not reduce IFNgamma production; however GW0742 reduced astroglial and microglial inflammatory activation and IL-1beta levels in EAE brain. RTPCR analysis showed that GW0742 increased expression of some myelin genes. These data demonstrate that PPARdelta agonists, like other PPAR ligands, can exert protective actions in an autoimmune model of demyelinating disease.

Both PPARγ and PPARδ influence sulindac sulfide-mediated p21WAF1/CIP1 upregulation in a human prostate epithelial cell line

Nonsteroidal anti-inflammatory drugs (NSAIDs) including sulindac sulfide are known to exert cancer chemopreventative activity in a range of cell lines. This activity has been shown to involve the upregulation of the cyclin-dependent kinase inhibitor p21WAF1/CIP1. It is also known that NSAIDs can act as peroxisome proliferator-activated receptor (PPAR) agonists and antagonists. In this study, we show that sulindac sulfide acts both as a PPARgamma agonist and a PPARdelta antagonist in an immortalized prostatic epithelial cell line (PNT1A). We utilized siRNA technology to show that PPARgamma is required for both growth inhibition and p21WAF1/CIP1 upregulation in response to sulindac sulfide treatment in PNT1A cells. In addition, the overexpression of PPARdelta partially rescued these cells from growth inhibition and also dramatically inhibited sulindac sulfide-mediated p21WAF1/CIP1 upregulation. Together these data identify a novel link between PPARgamma/PPARdelta/p21WAF1/CIP1 and the cancer chemo-preventative properties of NSAIDs.

Activation of peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) increases the expression of prostaglandin E2 receptor subtype EP4. The roles of phosphatidylinositol 3-kinase and CCAAT/enhancer-binding protein beta

The prostaglandin E2 receptor subtype EP4 has been implicated in the growth and progression of human non-small cell lung carcinoma (NSCLC). However, the factors that control its expression have not been entirely elucidated. Our studies show that NSCLC cells express peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) protein and that treatment with a selective PPARbeta/delta agonist (GW501516) increases EP4 mRNA and protein levels. GW501516 induced NSCLC cell proliferation, and this effect was prevented by PPARbeta/delta antisense or EP4 short interfering RNA (siRNA). GW501516 increased the phosphorylation of Akt and decreased PTEN expression. The selective inhibitor of phosphatidylinositol 3-kinase (PI3-K), wortmannin, and PPARbeta/delta antisense, abrogated the effect of GW501516 on EP4 expression, whereas that of the inhibitor of Erk did not. GW501516 also increased EP4 promoter activity through effects on the region between -1555 and -992 bp in the EP4 promoter, and mutation of the CCAAT/enhancer-binding protein (C/EBP) site in this region abrogated the effect of GW501516. GW501516 increased not only the binding activity of C/EBP to the NF-IL6 site in the EP4 promoter, which was prevented by the inhibitor of PI3-K, but also increased C/EBPbeta protein in a dose- and PPARbeta/delta-dependent manner. The effect of GW501516 on EP4 protein was eliminated in the presence of C/EBPbeta siRNA. Finally, we showed that pretreatment of NSCLC with GW501516 further increased NSCLC cell proliferation in response to exogenous dimethyl-prostaglandin E2 (PGE2) that was diminished in the presence of PPARbeta/delta antisense and EP4 siRNA. Taken together, these findings suggest that activation of PPARbeta/delta induces PGE2 receptor subtype EP4 expression through PI3-K signals and increases human lung carcinoma cell proliferation in response to PGE2. The increase in transcription of the EP4 gene by PPARbeta/delta agonist was associated with increased C/EBP binding activity in the NF-IL6 site of EP4 promoter region and C/EBPbeta protein expression that were mediated through both PI3-K/Akt and PPARbeta/delta signaling pathways.

Expression of peroxisome proliferator-activated receptor delta in human gastric cancer and its response to specific COX-2 inhibitor

Peroxisome proliferator-activated receptor delta (PPARdelta) is ligand-activated transcription factor of the nuclear receptor superfamily which is recently implicated in carcinogenesis. We examined the expression profiles of PPARdelta in human gastric cancer, normal gastric mucosa and gastric cancer cell lines by RT-PCR, Western blot and immunohistochemistry. PPARdelta mRNA and protein was found to be ubiquitously expressed in all 5 gastric cancer cell lines, 40 gastric cancer samples and 10 normal gastric mucosa from non-cancer patients. Positive immunoreactivity was detected in the nuclei of normal and malignant gastric epithelium. Treatment of gastric cell line MKN45 that overexpressed cyclooxygenase-2 (COX-2) with specific COX-2 inhibitor NS398 resulted in a time- and dose-dependent suppression of PPARdelta expression. In contrast, there was no suppression of PPARdelta in MKN28 gastric cell line with low COX-2 expression. Our results demonstrated the ubiquitous expression of PPARdelta in normal and cancer gastric epithelium. Suppression of PPARdelta may be one of the mechanisms underlying the chemopreventive effects of COX-2 inhibitor.

Cyclooxygenase-1 is a potential target for prevention and treatment of ovarian epithelial cancer

The precise genetic and molecular defects underlying epithelial ovarian cancer (EOC) remain largely unknown, and treatment options for patients with advanced disease are limited. Cyclooxygenases (COX-1 and COX-2) catalyze the conversion of arachidonic acid to prostaglandins. Whereas overwhelming evidence suggests a role for COX-2 in a variety of cancers, the contribution of COX-1 remains much less explored. The expression status of COX isoforms in ovarian cancers also remains confusing. We have previously shown that human epithelial ovarian tumors have increased levels of COX-1 but not COX-2. To more carefully examine the role of COXs in ovarian cancer, we used a mouse model of EOC in which genetic and oncogenic modifications were experimentally engineered into ovarian surface epithelial cells (OSE) thought to be the cells of origin for human EOC. These OSE cells produce tumors when allografted into host mice. Using multiple approaches, we observed that OSE cells and the tumors comprised of these cells express high levels of COX-1 but not COX-2. Prostacyclin (PGI(2)) is the major prostaglandin generated downstream of COX-1 in these cells, and SC-560, a COX-1-selective inhibitor, dramatically inhibits PGI(2) production. More importantly, SC-560 reduced the growth of tumors when OSE cells were allografted in nude female mice. In contrast, the COX-2-selective inhibitor celecoxib had little effect on tumor growth. The growth inhibitory effects of SC-560 result from reduced cell proliferation and/or accelerated apoptosis. Our results imply COX-1 as a target for the prevention and/or treatment of EOC.

The Human Peroxisome Proliferator-activated Receptor δ Gene is a Primary Target of 1α,25-Dihydroxyvitamin D3 and its Nuclear Receptor

Peroxisome proliferator-activated receptor (PPAR) delta is the most widely expressed member of the PPAR family of nuclear receptor fatty acid sensors. Real-time PCR analysis of breast and prostate cancer cell lines demonstrated that PPARdelta expression was increased 1.5 to 3.2-fold after three hours stimulation with the natural vitamin D receptor (VDR) agonist, 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3). In silico analysis of the 20 kb of the human PPARdelta promoter revealed a DR3-type 1alpha,25(OH)2D3 response element approximately 350 bp upstream of the transcription start site, which was able to bind VDR-retinoid X receptor (RXR) heterodimers and mediate a 1alpha,25(OH)2D3-dependent upregulation of reporter gene activity. Chromatin immuno-precipitation assays demonstrated that a number of proteins representative for 1alpha,25(OH)2D3-mediated gene activation, such as VDR, RXR and RNA polymerase II, displayed a 1alpha,25(OH)2D3-dependent association with a region of the proximal PPARdelta promoter that contained the putative DR3-type VDRE. This was also true for other proteins that are involved in or are the subject of chromatin modification, such as the histone acetyltransferase CBP and histone 4, which displayed ligand-dependent association and acetylation, respectively. Finally, real-time PCR analysis demonstrated that 1alpha,25(OH)2D3 and the synthetic PPARdelta ligand L783483 show a cell and time-dependent interference in each other's effects on VDR mRNA expression, so that their combined application shows complex effects on the induction of VDR target genes, such as CYP24. Taken together, we conclude that PPARdelta is a primary 1alpha,25(OH)2D3-responding gene and that VDR and PPARdelta signaling pathways are interconnected at the level of cross-regulation of their respective transcription factor mRNA levels.

Effect of inflammation on cyclooxygenase (COX)-2 expression in benign and malignant oesophageal cells

Chronic inflammation has been linked to carcinogenesis in various tissue sites. Barrett's oesophageal epithelium (BE) is a premalignant condition in which cyclooxygenase-2 (COX-2) levels are increased. However, it is not clear whether the primary stimulus for the high COX-2 levels is related to inflammation or malignancy. The effect of exogenous cytokines (IL-1beta, IL-10 and IL-13) on COX-2 expression was assessed by western blotting in three BE cancer cell lines (SEG-1, BIC-1 and OE33) and a squamous cancer cell line (OE21). Primary tissue was assessed from 17 patients with long BE segments, 13 oesophagitis, 30 oesophageal adenocarcinoma (EAC), and 40 normal oesophageal (NE) and duodenal (DU) controls. COX-2 protein expression was determined by western blotting and its tissue localization was examined using immunohistochemistry. COX-2 protein and the neutrophil marker myeloperoxidase (MPO) were quantified along BE segments. The leukocyte marker CD45 was used to identify any correlation between COX-2 expression and leukocyte cell distribution in EAC. IL-1beta induced COX-2 expression in SEG-1 cells (P < 0.05), whereas IL-10 and IL-13 had no effect. COX-2 protein levels were found to be increased in distal BE > proximal BE > oesophagitis > NE (P < 0.001). COX-2 expression in EAC was heterogeneous and the overall levels were not significantly increased. The increased COX-2 expression in distal BE was not associated with inflammation (MPO expression). In addition, there was no correlation between COX-2 and CD45 in AC. COX-2 protein expression in the oesophagus appears to be independent of the degree of inflammation.

The role of prostaglandins and other eicosanoids in the gastrointestinal tract

Nonsteroidal anti-inflammatory drugs (NSAIDs) are generally prescribed to ameliorate symptoms associated with acute pain and chronic inflammatory diseases such as arthritis. Recent epidemiologic studies and clinical trials indicate that use of NSAIDs and cyclooxygenase (COX)-2 selective inhibitors are associated with a reduced risk of certain malignancies, especially gastrointestinal cancer. The cyclooxygenase enzymes are the best known targets of NSAIDs; this diverse class of compounds blocks conversion of arachidonic acid to prostanoids. Prostaglandins and other eicosanoids derived from COX-1 and COX-2 are involved in a variety of physiologic and pathologic processes in the gastrointestinal tract. Recent efforts to identify the molecular mechanisms by which COX-2-derived prostanoids exert their proneoplastic effects have provided a rationale for the possible use of NSAIDs alone or in a combination with conventional or experimental anticancer agents for the treatment or prevention of gastrointestinal cancers.

Enhanced expression of peroxisome proliferator-activated receptor gamma in epithelial ovarian carcinoma

The peroxisome proliferator-activated receptors (PPARs) belong to a subclass of nuclear hormone receptor that executes important cellular transcriptional functions. Previous studies have demonstrated the expression of PPARγ in several tumours including colon, breast, bladder, prostate, lung and stomach. This study demonstrates the relative expression of PPARγ in normal ovaries and different pathological grades of ovarian tumours of serous, mucinous, endometrioid, clear cell and mixed subtypes. A total of 56 ovarian specimens including 10 normal, eight benign, 10 borderline, seven grade 1, nine grade 2 and 12 grade 3 were analysed using immunohistochemistry. Immunoreactive PPARγ was not expressed in normal ovaries. Out of eight benign and 10 borderline tumours, only one tumour in each group showed weak cytoplasmic PPARγ expression. In contrast, 26 out of 28 carcinomas studied were positive for PPARγ expression with staining confined to cytoplasmic and nuclear regions. An altered staining pattern of PPARγ was observed in high-grade ovarian tumours with PPARγ being mostly localized in the nuclei with little cytoplasmic immunoreactivity. On the other hand, predominant cytoplasmic staining was observed in lower-grade tumours. Significantly increased PPARγ immunoreactivity was observed in malignant ovarian tumours (grade 1, 2 and 3) compared to benign and borderline tumours (χ²=48.80, P<0.001). Western blot analyses showed significant elevation in the expression of immunoreactive PPARγ in grade 3 ovarian tumours compared with that of normal ovaries and benign ovarian tumours (P<0.01). These findings suggest an involvement of PPARγ in the onset and development of ovarian carcinoma and provide an insight into the regulation of this molecule in the progression of the disease.

Peroxisome proliferator-activated receptor delta suppresses 11beta-hydroxysteroid dehydrogenase type 2 gene expression in human placental trophoblast cells

Accumulating evidence suggests that the human placental enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) plays a key role in fetal development by controlling fetal exposure to maternal glucocorticoids. Recently, the nuclear peroxisome proliferator-activated receptor delta (PPAR delta) has been found to be the most abundantly expressed PPAR subtype in the human placenta, but its function in this organ is unknown. Given that PPAR delta-null mice exhibited placental defects and consequent intrauterine growth restriction, the present study was undertaken to examine the hypothesis that PPAR delta regulates human placental function in part by targeting 11beta-HSD2. Using cultured human trophoblast cells as a model system, we demonstrated that 1) the putative PPAR delta agonist carbaprostacyclin (cPGI2) reduced 11beta-HSD2 activity as well as 11beta-HSD2 expression at both protein and mRNA levels; 2) GW610742 (a selective PPAR delta agonist) mimicked the effect of cPGI2, whereas indomethacin (a known ligand for PPARalpha and PPAR gamma) had no effect; 3) the cPGI2-induced down-regulation of 11beta-HSD2 mRNA did not require de novo protein synthesis; 4) cPGI2 suppressed HSD11B2 promoter activity, but did not alter the half-life of 11beta-HSD2 mRNA; and 5) the inhibitory effect of cPGI2 on HSD11B2 promoter activity was abrogated in trophoblast cells cotransfected with a dominant negative PPAR delta mutant. Taken together, these findings suggest that activation of PPAR delta down-regulates HSD11B2 gene expression in human trophoblast cells, and that this effect is mediated primarily at the transcriptional level. Thus, the present study reveals 11beta-HSD2 as an additional target for PPAR delta and identifies a molecular mechanism by which this nuclear receptor may regulate human placental function.

Inhibition of cell invasion by indomethacin on glioma cell lines: in vitro study

Malignant glioma invasion into the surrounding brain tissue is still a major problem for any therapeutical methods. Matrix metalloproteinases (MMPs) have been implicated as important factors in this pathological process. In this study, one of the non-steroidal anti-inflammatory drugs (NSAIDs) indomethacin was employed to investigate the effect of inhibition of cell invasion mediated by MMP-2 and MMP-9 in human malignant glioma cell lines, A172, U87MG, U251MG, and U373MG in vitro. MTT assay was firstly examined to determine non-cytotoxic dose range, then gelatin zymography, matrigel invasion assay, migration assay and MMP-2 activity assay for 24 h exposure in indomethacin were employed to assess the inhibitory effect of indomethacin. MTT assay revealed that dose with 0, 50, and 500 microM/ml were non-cytotoxic. Zymography demonstrated: (a) expression of MMP-2 and MMP-9 activity was downregulated along with elevated dose of indomethacin. (b) MMP-2 activity that changed from pro-MMP-2 to active form of MMP-2 in supernatants of cell lines could not be inhibited by indomethacin. Invasion assay disclosed that the number of invading cells through the matrigel were significantly decreased in a dose dependent manner. Migration assay indicated indomethacin did not affect cells migration. MMP-2 activity assay showed the total and active MMP-2 secretion was suppressed by 500 microM/ml of indomethacin. Our present study is the first report on inhibitive effect of indomethacin mediated by MMP-2 and MMP-9 in invasion assay of glioma cell lines. The current study suggested that non-cytotoxic level of indomethacin was able to reduce the cell invasion of malignant gliomas mediated by MMP-2 and MMP-9, but it did not affected on cell motility. It also lowered down the activity of MMP-2 and MMP-9, and could reduce of MMP-2 secretion of cell lines. Thus, high concentration of indomethacin within non-cytotoxic dose might offer a new therapeutic strategy to impair cell invasion of gliomas.

Peroxisome proliferator-activated receptor expression and activation in normal human colonic epithelial cells and tubular adenomas

OBJECTIVE

Peroxisome proliferator-activated receptor (PPAR) ligands, widely used in type 2 diabetes treatment, have variably been shown to promote or prevent colon tumor formation in animal models and cell lines, but their role in normal human colon is unknown. The aim of this study was to determine PPAR expression and function in normal human colonic epithelial cells and tubular adenomas.

MATERIAL AND METHODS

Short-term cultures of normal human colonic epithelial cells were established from biopsies obtained in 42 patients with normal colonoscopy. PPAR and adipophilin mRNA expression was assessed by real-time RT-PCR. PPARs were activated by ligands for PPAR alpha (Wy-14643), PPAR delta (GW-501516) and PPAR gamma (rosiglitazone or troglitazone). Cell viability was measured using the methyltetrazoleum assay, proliferation by thymidine incorporation, and DNA profiles by flow cytometry. PPAR mRNA levels in tubular adenomas or metaplastic polyps (n=12) were compared with those in controls.

RESULTS

PPAR alpha and gamma were consistently expressed in normal colonocytes while no PPAR delta expression could be detected. PPAR gamma activation induced a 7.5-fold increase in adipophilin expression (a PPAR-activated gene). PPAR gamma activation had no effect on viability or DNA profiles, but led to a 25% significant decrease in cell proliferation. Finally, a selective and significant 2.5-fold decrease in PPAR alpha expression was observed in tubular adenomas, but not in metaplastic polyps, compared to controls.

CONCLUSIONS

Our findings support the view that PPAR gamma ligands act as anti-proliferative agents rather than as promoters of tumorigenesis in normal human colon. Moreover, they raise interest in investigation of PPAR alpha as a therapeutic target to prevent adenoma formation.

Colon cancer: genomics and apoptotic events

Colon cancer is the third most common cancer globally. The risk of developing colon cancer is influenced by a number of factors that include age and diet, but is primarily a genetic disease, resulting from oncogene over-expression and tumour suppressor gene inactivation. The induction and progression of the disease is briefly outlined, as are the cellular changes that occur in its progression. While colon cancer is uniformly amenable to surgery if detected at the early stages, advanced carcinomas are usually lethal, with metastases to the liver being the most common cause of death. Oncogenes and genetic mutations that occur in colon cancer are featured. The molecules and signals that act to eradicate or initiate the apoptosis cascade in cancer cells, are elucidated, and these include caspases, Fas, Bax, Bid, APC, antisense hTERT, PUMA, 15-LOX-1, ceramide, butyrate, tributyrin and PPARgamma, whereas the molecules which promote colon cancer cell survival are p53 mutants, Bcl-2, Neu3 and COX-2. Cancer therapies aimed at controlling colon cancer are reviewed briefly.

Gastrin-induced cyclooxygenase-2 expression in Barrett's carcinogenesis

PURPOSE

Cyclooxygenase (COX)-2 has been causally implicated in carcinogenesis. The evidence for increased COX-2 in the malignant progression of Barrett's esophagus is contradictory. We hypothesize that COX-2 expression may be causally affected by the gastrin status via the cholecystokinin 2 (CCK(2)) receptor.

EXPERIMENTAL DESIGN

COX-2 and prostaglandin E(2) expression were evaluated by Western blotting and enzyme-linked immune assay in samples of squamous esophagus, Barrett's esophagus with varying degrees of dysplasia to adenocarcinoma, and normal duodenum. Differentiation status was evaluated by histopathology and villin expression. A longitudinal case-control study compared COX-2 in patients who progressed to adenocarcinoma with nonprogressors matched for age and length of follow-up. Messenger RNA levels of gastrin and CCK(2) receptor in biopsies and cell lines were evaluated by reverse transcription-PCR, and in vitro gastrin stimulation was conducted with and without inhibitors for CCK(2) (YM022) and COX-2 (NS-398). Cell proliferation was evaluated using minichromosome maintenance protein 2 (Mcm2) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays.

RESULTS

COX-2 expression is significantly increased in Barrett's esophagus before dysplasia development. Expression is highly variable within Barrett's dysplasia and adenocarcinoma samples independent of differentiation status. In a longitudinal case-control study, the expression levels within patients increased over time, regardless of the degree of malignant progression. Biopsies from nondysplastic Barrett's esophagus expressed increased gastrin mRNA levels compared with other biopsies. Gastrin significantly induced COX-2, prostaglandin E(2), and cell proliferation in biopsies and cell lines. Gastrin-induced proliferation can be inhibited by YM022 and NS-398.

CONCLUSIONS

COX-2 is up-regulated early in the Barrett's metaplasia sequence. During carcinogenesis, gastrin is a significant determinant of COX-2 activity levels via the CCK(2) receptor.

Peroxisome proliferator-activated receptor-beta/delta inhibits epidermal cell proliferation by down-regulation of kinase activity

Recent work has shown that peroxisome proliferator-activated receptor beta (PPARbeta) attenuates cell proliferation and skin carcinogenesis, and this is due in part to regulation of ubiquitin C expression. In these studies, the role of PPARbeta in modulating ubiquitin-dependent protein kinase Calpha (PKCalpha) levels and phosphorylation signaling pathways was evaluated. Intracellular phosphorylation analysis showed that phosphorylated PKCalpha and other kinases were lower in wild-type mouse skin treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) as compared with PPARbeta-null mouse skin. No differences in expression levels of other PKC isoforms present in skin were observed. Lower ubiquitination of PKCalpha was found in TPA-treated PPARbeta-null skin as compared with wild-type, and inhibition of ubiquitin-dependent proteasome degradation prevented TPA-induced down-regulation of PKCalpha. The activity of PKCalpha and downstream signaling kinases is enhanced, and expression of cyclooxygenase-2 (COX-2) is significantly greater, in PPARbeta-null mouse skin in response to TPA compared with wild-type mouse skin. Inhibition of PKCalpha or COX-2 reduced cell proliferation in TPA-treated PPARbeta-null keratinocytes in a dose-dependent manner, whereas it only slightly influenced cell proliferation in wild-type keratinocytes. Combined, these studies provide strong evidence that PPARbeta attenuates cell proliferation by modulating PKCalpha/Raf1/MEK/ERK activity that may be due in part to reduced ubiquitin-dependent turnover of PKCalpha.

PPARdelta status and Apc-mediated tumourigenesis in the mouse intestine

Based on recent reports that peroxisome proliferator-activated receptor delta (PPARdelta) activation promotes tumourigenesis, we have investigated the role of this protein in Apc-mediated intestinal tumourigenesis. We demonstrate that the inactivation of Apc in the adult small intestine, while causing the expected nuclear accumulation of beta-catenin, does not cause the expected increase in PPARdelta mRNA or protein but conversely, the levels of PPARdelta mRNA and protein are lowered. Furthermore, we find that ApcMinPPARdelta-null mice exhibit an increased predisposition to intestinal tumourigenesis. Our data suggest that PPARdelta is not directly regulated by beta-catenin, and that inhibition of PPARdelta activity is unlikely to be an appropriate strategy for the chemoprevention or chemotherapy of intestinal malignancies.

Cyclooxygenase-2 is expressed in neuroblastoma, and nonsteroidal anti-inflammatory drugs induce apoptosis and inhibit tumor growth in vivo

Neuroblastoma is the single most common and deadly tumor of childhood and is often associated with therapy resistance. Cyclooxygenases (COXs) catalyze the conversion of arachidonic acid to prostaglandins. COX-2 is up-regulated in several adult epithelial cancers and is linked to proliferation and resistance to apoptosis. We detected COX-2 expression in neuroblastoma primary tumors and cell lines but not in normal adrenal medullas from children. Treatment of neuroblastoma cells with nonsteroidal anti-inflammatory drugs, inhibitors of COX, induced caspase-dependent apoptosis via the intrinsic mitochondrial pathway. Treatment of established neuroblastoma xenografts in nude rats with the dual COX-1/COX-2 inhibitor diclofenac or the COX-2-specific inhibitor celecoxib significantly inhibited tumor growth in vivo (P < 0.001). In vitro, arachidonic acid and diclofenac synergistically induced neuroblastoma cell death. This effect was further pronounced when lipooxygenases were simultaneously inhibited. Proton magnetic resonance spectroscopy ((1)H MRS) of neuroblastoma cells treated with COX inhibitors demonstrated accumulation of polyunsaturated fatty acids and depletion of choline compounds. Thus, (1)H MRS, which can be performed with clinical magnetic resonance scanners, is likely to provide pharmacodynamic markers of neuroblastoma response to COX inhibition. Taken together, these data suggest the use of nonsteroidal anti-inflammatory drugs as a novel adjuvant therapy for children with neuroblastoma.

Dietary (n-6) PUFA and intestinal tumorigenesis

Cancer is the second leading cause of death in the United States, and mortality due to colorectal cancer is only surpassed by lung cancer. Epidemiological studies demonstrate that dietary polyunsaturated fats can have a profound effect on colorectal cancer risk. Experimental data indicate that modulation of cellular (n-6) PUFA metabolism can affect the progression of the disease. This paper discusses the role (n-6) PUFA play in promoting intestinal tumorigenesis and how dietary PUFA from different families interact to modify the neoplastic process. Dietary PUFA that attenuate arachidonic acid metabolism [such as (n-3) PUFA] have antineoplastic properties, whereas those that augment arachidonic acid metabolism, such as linoleic, gamma-linolenic, and arachidonic acids do not appear to enhance tumorigenesis when added to the Western diet but may diminish the beneficial effects of other dietary lipids. It is the relative contributions of the different dietary PUFA that may determine overall risk for and progression of the disease.

Up-regulation of the enzymes involved in prostacyclin synthesis via Ras induces vascular endothelial growth factor

BACKGROUND AND AIMS

The constitutive activation of Ras is an important step in the development and progression of several different cancers and is known to increase the level of cyclooxygenase 2 (COX-2). Prostaglandins are the downstream bioactive lipid mediators produced by the COX-2 enzyme. We sought to determine the role of Ras-induced up-regulation of the enzymes involved in prostacyclin biosynthesis in nontransformed rat intestinal epithelial cells (IECs).

METHODS

Messenger RNA (mRNA) and protein expression were analyzed by Northern and Western analysis, respectively, to determine the level of enzymes induced by Ras. In vitro assays were used to determine the production of vascular endothelial growth factor (VEGF) and prostaglandins as well as the promoter and enzymatic activation of the rate-limiting enzyme in prostaglandin production (phospholipase A(2) [cPLA(2)]).

RESULTS

The inducible expression of Ha-Ras(V12) increased the production of prostaglandin (PG)F(2alpha) and prostacyclin by 2- and 13-fold, respectively. The induction of Ha-Ras(V12) also up-regulated the mRNA and protein levels of cPLA(2), COX-2, and prostacyclin synthase, as well as the promoter and enzyme activity of cPLA(2). Furthermore, oncogenic Ras increased the production of the pro-angiogenic factor VEGF. The increase of VEGF was abolished after treatment with celecoxib, a selective COX-2 inhibitor. The addition of PGI 2 alone also induced the expression of VEGF.

CONCLUSIONS

Inducible Ha-Ras(V12) increases the production of PGI(2) through the coordinate up-regulation of cPLA(2), COX-2, and prostacyclin synthase (PGIS). The production of PGI(2) leads to an increase in the level of the pro-angiogenic factor VEGF, which is known to play a crucial role in the regulation of tumor-associated angiogenesis.

Effect of the peroxisome proliferator-activated receptor beta activator GW0742 in rat cultured cerebellar granule neurons

The ligand-activated transcription factor peroxisome proliferator-activated receptor beta (PPARbeta) is present in the brain and is implicated in the regulation of genes with potential roles in neurotoxicity. We sought to examine the role of PPARbeta in neuronal cell death by using the PPARbeta ligand GW0742. Primary cultures of rat cerebellar granule neurons were prepared from 7-day-old pups. Reverse transcriptase-polymerase chain reaction and in situ hybridization were used to verify that PPARbeta mRNA was present in neurons. After 10-12 days in culture, the neuronal cells were incubated in the presence of GW0742, and cell death was measured with a lactate dehydrogenase release (LDH) assay. After 24 hr of exposure, PPARbeta activation by GW0742 was not inherently toxic to cerebellar granule neurons. However, toxicity was observed after 48 hr, with cell death mediated via an apoptotic mechanism. In an effect opposite to that observed with PPARalpha-activating ligands, PPARbeta activation exhibited neuroprotective properties. Treatment with GW0742 significantly reduced cell death during a 12-hr exposure to low-KCl media. These results clearly reinforce very specific roles for the PPAR isoforms in neurons and suggest that PPARbeta is worthy of further investigation regarding its potential role as a therapeutic target in neurodegenerative states.

Prostaglandin E(2) promotes colorectal adenoma growth via transactivation of the nuclear peroxisome proliferator-activated receptor delta

Cyclooxygenase-derived prostaglandin E(2) (PGE(2)) is the predominant prostanoid found in most colorectal cancers (CRC) and is known to promote colon carcinoma growth and invasion. However, the key downstream signaling pathways necessary for PGE(2)-induced intestinal carcinogenesis are unclear. Here we report that PGE(2) indirectly transactivates PPARdelta through PI3K/Akt signaling, which promotes cell survival and intestinal adenoma formation. We also found that PGE(2) treatment of Apc(min) mice dramatically increased intestinal adenoma burden, which was negated in Apc(min) mice lacking PPARdelta. We demonstrate that PPARdelta is a focal point of crosstalk between the prostaglandin and Wnt signaling pathways which results in a shift from cell death to cell survival, leading to increased tumor growth.

Cyclooxygenase-2 modulates cellular growth and promotes tumorigenesis

Cyclooxygenase (COX)-2 and the prostaglandins resulting from its enzymatic activity have been shown to play a role in modulating cell growth and development of human neoplasia. Evidence includes a direct relationship between COX-2 expression and cancer incidence in humans and animal models, increased tumorigenesis after genetic manipulation of COX-2, and significant anti-tumor properties of non-steroidal anti-inflammatory drugs in animal models and in some human cancers. Recent data showed that COX-2 and the derived prostaglandins are involved in control of cellular growth, apoptosis, and signal through a group of nuclear receptors named peroxisome proliferator-activated receptors (PPARs). In this article we will review some of the findings suggesting that COX-2 is involved in multiple cellular mechanisms that lead to tumorigenesis.

PPAR trilogy from metabolism to cancer

PURPOSE OF REVIEW

This review highlights recent advances related to malignancies in the field of peroxisome proliferator-activated receptors (PPARs). It also discusses the implications of cancer research and therapy.

RECENT FINDINGS

In the last few years, genetic evidence has implicated the PPARs, specifically PPARgamma and PPARbeta/delta, in tumorigenesis. Also, new insights into the regulation of the nuclear hormone receptors have emerged.

SUMMARY

Exciting research in PPAR biology has established these nuclear factors as key regulators of metabolism and energy homeostasis. Evidence indicates that PPARs can also affect the pathogenesis and development of tumors. However, the type of effects observed thus far appears to depend on the experimental context. As a result, the findings are generating much debate, as PPAR agonists are widespread targets in the treatment of metabolic disorders such as diabetes and dyslipidemia. Here, we summarize the most recent advances in this field, outline the conflicting reports and discuss their overall implications in cancer research.

Activation of peroxisome proliferator-activated receptor delta stimulates the proliferation of human breast and prostate cancer cell lines

The nuclear receptor peroxisome proliferator-activated receptor delta [PPARdelta/beta (NR1C2)] has been implicated in colorectal carcinogenesis by various molecular genetic observations. These observations have recently been supported by studies of activation of PPARdelta by pharmacological agents. Here we present the first report of the stimulation of breast and prostate cancer cell growth using PPARdelta selective agonists. Activation of PPARdelta with compound F stimulated proliferation in breast (T47D, MCF7) and prostate (LNCaP, PNT1A) cell lines, which are responsive to sex hormones. Conversely, we have found that several steroid-independent cell lines, including colon lines, were unresponsive to compound F. These findings were confirmed with an additional high-affinity PPARdelta agonist, GW501516. Conditional expression of PPARdelta in MCF7 Tet-On cells resulted in a doxycycline-enhanced response to GW501516, thus providing direct genetic evidence for the role of PPARdelta in the proliferative response to this drug. Activation of PPARdelta in T47D cells resulted in increased expression of the proliferation marker Cdk2 and also vascular endothelial growth factor alpha (VEGFalpha) and its receptor, FLT-1, thus, suggesting that PPARdelta may initiate an autocrine loop for cellular proliferation and possibly angiogenesis. Consistent with this hypothesis, we demonstrated a pro-proliferative effect of GW501516 on human umbilical vein endothelial cell cultures and found that GW501516 also regulated the expression of VEGFalpha and FLT-1 in these cells. Our observations provide the first evidence that activation of PPARdelta can result in increased growth in breast and prostate cancer cell lines and primary endothelial cells and supports the possibility that PPARdelta antagonists may be of therapeutic value in the treatment of breast and prostate cancer.

PPAR gamma signaling exacerbates mammary gland tumor development

Breast cancer cell lines that express the nuclear peroxisome proliferator-activated receptor gamma (PPAR gamma) can be prompted to undergo growth arrest and differentiation when treated with synthetic PPAR gamma ligands. To evaluate the therapeutic potential of increased PPAR gamma signaling in vivo, we generated transgenic mice that express a constitutively active form of PPAR gamma in mammary gland. These mice are indistinguishable from their wild-type littermates. However, when bred to a transgenic strain prone to mammary gland cancer, bigenic animals develop tumors with greatly accelerated kinetics. Surprisingly, in spite of their more malignant nature, bigenic tumors are more secretory and differentiated. The molecular basis of this tumor-promoting effect may be an increase in Wnt signaling, as ligand activation of PPAR gamma potentiates Wnt function in an in vivo model of this pathway. These results suggest that once an initiating event has taken place, increased PPAR gamma signaling serves as a tumor promoter in the mammary gland.

Characterization of the PGI2/IP system in cultured rat mesangial cells

Mesangial cells play an important role in glomerular function. They are an important source of cyclooxygenase (COX)-derived arachidonic acid metabolites, including prostaglandin E(2) and prostacyclin. Prostacyclin receptor (IP) mRNA was amplified from cultured mesangial cell total RNA by RT-PCR. While the prostaglandin E(2) receptor subtype EP(2) was not detected, EP(1,3,4) mRNA was amplified. Also, IP protein was noted in mesangial cells, proximal tubules, inner medullary collecting ducts, and the inner and outer medulla. But no protein was detected in whole cortex preparations. Prostacyclin analogues: cicaprost and iloprost, increased cAMP levels in mesangial cells. On the other hand, arginine-vasopressin and angiotensin II increased intracellular calcium in mesangial cells, but cicaprost, iloprost and prostaglandin E(2) had no effect. Moreover, a 50% inhibition of cicaprost- and iloprost-cAMP stimulation was observed upon mesangial cell exposure to 25 and 35 mM glucose for 5 days. But no change in IP mRNA was observed at any glucose concentration or time exposure. Although 25 mM glucose had no effect on COX-1 protein levels, COX-2 was increased up to 50%. In contrast, PGIS levels were reduced by 50%. Thus, we conclude that the prostacyclin/IP system is present in cultured rat mesangial cells, coupling to a cAMP stimulatory pathway. High glucose altered both enzymes in the PGI(2) synthesis pathway, increasing COX-2 but reducing PGIS. In addition, glucose diminished the cAMP response to prostacyclin analogues. Therefore, glucose attenuates the PGI(2)/IP system in cultured rat mesangial cells.

Peroxisome proliferator-activated receptor-delta attenuates colon carcinogenesis

Peroxisome proliferator-activated receptor-delta (PPAR-delta; also known as PPAR-beta) is expressed at high levels in colon tumors, but its contribution to colon cancer is unclear. We examined the role of PPAR-delta in colon carcinogenesis using PPAR-delta-deficient (Ppard(-/-)) mice. In both the Min mutant and chemically induced mouse models, colon polyp formation was significantly greater in mice nullizygous for PPAR-delta. In contrast to previous reports suggesting that activation of PPAR-delta potentiates colon polyp formation, here we show that PPAR-delta attenuates colon carcinogenesis.

Peroxisome proliferator-activated receptor beta (delta)-dependent regulation of ubiquitin C expression contributes to attenuation of skin carcinogenesis

The role of peroxisome proliferator-activated receptor-beta (PPARbeta) in the molecular regulation of skin carcinogenesis was examined. Increased caspase-3 activity associated with apoptosis was found in the skin of wild-type mice after tumor promotion with 12-O-tetradecanoylphorbol-13-acetate, and this effect was diminished in PPARbeta-null mice. The onset of tumor formation, tumor size, and tumor multiplicity induced from a two-stage carcinogen bioassay (7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate) were significantly enhanced in PPARbeta-null mice compared with wild-type mice. To begin to characterize the molecular changes underlying this PPARbeta-dependent phenotype, microarray analysis was performed and a number of differentially regulated gene products were identified including ubiquitin C. Subsequent promoter analysis, reporter gene assays, site-directed mutagenesis, and electrophoretic mobility shift assays provide evidence that PPARbeta regulates ubiquitin C expression, and that ubiquitination of proteins is influenced by PPARbeta. These results strongly suggest that activation of PPARbeta-dependent target genes provides a novel strategy to inhibit tumor promotion and carcinogenesis.

Activation of nuclear hormone receptor peroxisome proliferator-activated receptor-delta accelerates intestinal adenoma growth

We treated Apc(min) mice, which are predisposed to intestinal polyposis, with a selective synthetic agonist of peroxisome proliferator-activated receptor-delta (PPAR-delta). Exposure of Apc(min) mice to the PPAR-delta ligand GW501516 resulted in a significant increase in the number and size of intestinal polyps. The most prominent effect was on polyp size; mice treated with the PPAR-delta activator had a fivefold increase in the number of polyps larger than 2 mm. Our results implicate PPAR-delta in the regulation of intestinal adenoma growth.

Peroxisome proliferator-activated receptors (PPARs) and associated transcription factors in colon cancer: reduced expression of PPARγ-coactivator 1 (PGC-1)

Peroxisome proliferator-activated receptors (PPARs) alpha,beta/delta and gamma are fatty acid sensitive transcription factors that have been implicated in colorectal cancer. To better understand their role, we studied the expression levels of all PPAR-isoforms and transcriptional partners such as the retinoid X receptor alpha (RXRalpha) and PPARgamma-coactivator-1 (PGC-1) by means of real-time PCR in 17 patients with colon cancer. While a heterogeneous pattern was observed for the expression level of the PPAR-isoforms alpha,beta/delta and gamma, the coactivator PGC-1 was significantly decreased in 15 of 17 tumors. Taken together our data suggest that the transcriptional activity of PPARgamma may not only be decreased by mutation but also by downregulation of the coactivator PGC-1 of PPARgamma.

Suppression of polyamine catabolism by activated Ki-ras in human colon cancer cells

An activated Ki-ras was expressed in the human colon adenocarcinoma cell line Caco-2 to study the effects of Ki-ras oncogene on polyamine metabolism during gastrointestinal tumorigenesis. Multiple clones selected for expression of the mutant Ki-ras transgene displayed a suppression of transcription of a key catabolic enzyme in polyamine catabolism spermidine/spermine N1-acetyltransferase (SSAT). Gene expression analysis, with cDNA microarrays, showed that Ki-ras transfected clones had decreased levels of expression, compared to mock transfected cells, of peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear hormone receptor family and an important regulator of cell proliferation and differentiation. The activated Ki-ras suppressed SSAT expression by a mechanism involving the PPARgamma response element (PPRE) located at +48 bp relative to the transcription start site of the SSAT gene. Transient expression of the PPARgamma protein in Ki-ras expressing Caco-2 clones, or treatment with the PPARgamma ligand ciglitazone, led to an increase in the SSAT promoter activity. A MEK1/2 inhibitor PD98059 induced transcription of both PPARgamma and SSAT genes in the activated Ki-ras clones, suggesting that the mitogen-activated protein kinases (MAPKs) were involved in the regulation of SSAT expression by PPARgamma. We concluded that mutated Ki-ras suppressed SSAT via a transcriptional mechanism involving the PPARgamma signaling pathway.

An overview of the effect of linoleic and conjugated-linoleic acids on the growth of several human tumor cell lines

Both n-6 and n-3 polyunsaturated fatty acids are dietary fats important for cell function, being involved in several physiologic and pathologic processes, such as tumorigenesis. Linoleic acid and conjugated linoleic acid, its geometrical and positional stereoisomer, were tested on several human tumor cell lines originating from different tissues and with different degrees of malignancy. This was to provide the widest possible view of the impact of dietary lipids on tumor development. While linoleic acid exerted different effects, ranging from inhibitory to neutral, even promoting growth, conjugated linoleic acid inhibited growth in all lines tested and was particularly effective against the more malignant cells, with the exception of mammary tumor cells, in which behavior was the opposite, the more malignant cell line being less affected. The inhibitory effect of conjugated linoleic acid on growth may be accompanied by different contributions from apoptosis and necrosis. The effects of conjugated linoleic acid on growth or death involved positive or negative variations in PPARs. The important observation is that a big increase of PPARalpha protein occurred in cells undergoing strong induction of apoptosis, whereas PPARbeta/delta protein decreased. Although PPARalpha and PPARbeta/delta seem to be correlated to execution of the apoptotic program, the modulation of PPARgamma appears to depend on the type of tumor cell, increasing as protein content, when inhibition of cell proliferation occurred. In conclusion, CLA may be regarded as a component of the diet that exerts antineoplastic activity and its effect may be antiproliferative or pro-apoptotic.

Negative growth effects of ciglitazone on kidney interstitial fibroblasts: role of PPAR-gamma

BACKGROUND/AIMS

Ciglitazone and other thiazolidinedione compounds are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligands and improve renal function in diabetic nephropathy independent of blood glucose control. Because interstitial fibroblasts and glomerular mesangial cells are important cell types affected in diabetic nephropathy, the major aim of the present study was to examine the effect of ciglitazone on apoptosis and growth of renal interstitial fibroblasts (NRKs) and glomerular mesangial cells (MMCs).

METHODS

The effect of ciglitazone on apoptosis and cell growth of cultured NRKs and MMCs was done using DNA fragmentation and MTS cell-growth assays, respectively. The potential role of PPAR-gamma in these two cell types was examined by reporter gene analysis.

RESULTS

Ciglitazone induced caspase-dependent apoptosis of both NRKs and MMCs and caused a significant decrease in cell growth. Other PPAR-gamma ligands also mimicked this effect. Interestingly, ciglitazone did not activate the PPRE-TK-CAT (peroxisome proliferator regulatory element, a thymidine kinase promoter and a chloramphenicol acetyltransferase gene) when transfected into NRKs, suggesting that ciglitazone does not activate the endogenous PPAR-gamma system in NRKs. On the other hand, ciglitazone activated the endogenous PPAR-gamma in MMCs.

CONCLUSIONS

Apoptotic and negative growth effects of ciglitazone, in NRKs, are not mediated through PPAR-gamma. The thiazolidinediones have important cellular effects on renal interstitial fibroblasts and glomerular mesangial cells that may be therapeutically useful in non-diabetic renal disease.