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

Dose-dependent suppression of hyperlipidemia and intestinal polyp formation in Min mice by pioglitazone, a PPAR gamma ligand

In our previous study, a peroxisome proliferator-activated receptor gamma (PPAR gamma) agonist, pioglitazone, suppressed both hyperlipidemia and intestinal polyp formation in Apc(1309) mice at doses of 100 and 200 ppm in the diet. In contrast, it has been reported that doses of 1500 or 2000 ppm of another PPAR gamma agonist, troglitazone, enhanced colon polyp development in Min mice. In the present study, we therefore investigated the effects of a wide range of pioglitazone doses on both hyperlipidemia and intestinal polyp formation in Min mice. Serum triglycerides and very low density lipoprotein (VLDL) cholesterol in the basal diet group were elevated to levels 13-15 times higher than those in the wild-type counterparts at 20 weeks of age. They were reduced dose-dependently by treatment with 100, 200, 400 and 1600 ppm pioglitazone from 6-20 weeks of age with suppression to almost the wild-type level at the highest dose. Moreover, up-regulation of the liver mRNA levels for lipoprotein lipase (LPL) was evident in the pioglitazone-treated animals. Dose-dependent reduction of intestinal polyps was observed in Min mice given 100-1600 ppm for 14 weeks, total numbers being decreased to 63-9% of the control value. A suppressive effect of pioglitazone on colon polyp formation was also found. The PPAR gamma agonist, pioglitazone, may thus be a promising candidate chemopreventive agent for colon cancer.

Inhibitors of cyclo-oxygenase 2: a new class of anticancer agents?

Experimental studies have shown that cyclo-oxygenase 2 (COX2) is involved in tumour development and progression. Selective inhibitors of COX2 (coxibs) block tumour growth through many mechanisms, especially by antiangiogenic and proapoptotic effects. In experimental models, coxibs potentiate the activity of cytotoxic agents, hormones, and radiotherapy. Large clinical studies have shown chemopreventive activity of coxibs in colorectal cancer. The findings of preclinical studies coupled with the overexpression of COX2 observed in advanced human tumours are the basis for new therapeutic anticancer strategies based on combinations of coxibs with other anticancer treatment modalities. Early clinical studies have documented the feasibility, good tolerability, and promising activity of coxibs combined with chemotherapy in patients with advanced colorectal and non-small-cell lung cancers. Here, we describe the recent findings on the antitumour effects of coxibs with particular focus on the opportunities that have emerged for treatment of cancer.

Cyclo-oxygenase inhibition in colorectal adenomas and cancer

Increasing evidence indicates that Non-steroidal anti-inflammatory drugs (NSAIDs), compounds that inhibit the enzymatic activity of cyclooxygenase (COX), can reduce the number and size of adenomas in patients with familial adenomatous polyposis as well as the incidence of colorectal cancer. The COX enzyme family consists of the classic COX-1 and a second enzyme, COX-2, which is induced by various stimuli, such as mitogens and cytokines. While it is well proven that COX-2 overexpression is a central event in colorectal carcinogenesis, that prostaglandins (PGs) can contribute to tumorigenesis, and that COX-2 selective inhibitors are active chemopreventive agents, the molecular mechanisms by which NSAIDs exert their chemopreventive effect is not fully understood. However, significant advances have been made in understanding the interference of NSAIDs with the pathways that control cell growth and survival even independently from their COX-inhibiting properties, making their use attractive both alone and in combination with standard therapies in the treatment of advanced colorectal cancer. In addition, the recently recognized anti-angiogenic and radiosensitizer properties of COX-2 inhibitors support, further suggest their use in the adjuvant setting.

Cyclooxygenase-independent induction of apoptosis by sulindac sulfone is mediated by polyamines in colon cancer

Sulindac, a non-steroidal anti-inflammatory prodrug, is metabolized into pharmacologically active sulfide and sulfone derivatives. Sulindac sulfide, but not sulindac sulfone, inhibits cyclooxygenase (COX) enzyme activities, yet both derivatives have growth inhibitory effects on colon cancer cells. Microarray analysis was used to detect COX-independent effects of sulindac on gene expression in human colorectal cells. Spermidine/sperm-ine N1-acetyltransferase (SSAT) gene, which encodes a polyamine catabolic enzyme, was induced by clinically relevant sulindac sulfone concentrations. Northern blots confirmed increased SSAT RNA levels in these colon cancer cells. Deletion analysis and mutational studies were done to map the sulindac sulfone-dependent response sequences in the SSAT 5'-flanking sequences. This led us to the identification of two peroxisome proliferator-activated receptor (PPAR) response elements (PPREs) in the SSAT gene. PPRE-2, at +48 bases relative to the transcription start site, is required for the induction of SSAT by sulindac sulfone and is specifically bound by PPAR gamma in the Caco-2 cells as shown by transfection and gel shift experiments. PPRE-1, at-323 bases relative to the start site, is not required for the induction of SSAT by sulindac sulfone but can be bound by both PPAR delta and PPAR gamma. Sulindac sulfone reduced cellular polyamine contents in the absence but not in the presence of verapamil, an inhibitor of the export of monoacetyl diamines, inhibited cell proliferation and induced apoptosis. The induced apoptosis could be partially rescued by exogenous putrescine. These data suggest that apoptosis induced by sulindac sulfone is mediated, in part, by the COX-independent, PPAR-dependent transcriptional activation of SSAT, leading to reduced tissue polyamine contents in human colon cancer cells.

Peroxisome proliferator-activated receptor delta expression and regulation in mouse uterus during embryo implantation and decidualization

The aim of this study was to examine the expression and regulation of peroxisome proliferator-activated receptor (PPAR) PPARdelta gene in mouse uterus during early pregnancy by in situ hybridization and immunohistochemistry. PPARdelta expression under pseudopregnancy, delayed implantation, hormonal treatment, and artificial decidualization was also investigated. There was a very low level of PPARdelta expression on days 1-4 of pregnancy. On day 5 when embryo implanted, PPARdelta expression was exclusively observed in the subluminal stroma surrounding the implanting blastocyst. No corresponding signals were seen in the uterus on day 5 of pregnancy. There was no detectable PPARdelta signal under delayed implantation. Once delayed implantation was terminated by estrogen treatment and embryo implanted, a strong level of PPARdelta expression was induced in the subluminal stroma surrounding the implanting blastocyst. Estrogen treatment induced a moderate level of PPARdelta expression in the glandular epithelium, while progesterone treatment had no effects in the ovariectomized mice. A strong level of PPARdelta expression was seen in the decidua on days 6-8 of pregnancy. PPARdelta expression was also induced under artificial decidualization. These data suggest that PPARdelta expression at implantation sites require the presence of an active blastocyst and may play an essential role for blastocyst implantation.

Selective cyclo-oxygenase-2 inhibitors impair adipocyte differentiation through inhibition of the clonal expansion phase

Selective cyclo-oxygenase-2 (COX-2) inhibitors are nonsteroidal antiinflammatory drugs used in the management of inflammatory diseases. We demonstrate here that inhibition of the COX-2 enzyme impairs adipocyte differentiation. The inhibition of adipogenesis occurs in the early clonal expansion phase. In particular, COX-2 inhibition limits cell cycle reentry required before terminal adipocyte differentiation. This inhibition of adipogenesis is independent of the production of the peroxisome proliferator activated receptor gamma ligand prostaglandin J2, but dependent on the production of proliferative prostaglandins, such as prostaglandin E2. Modulation of the activity of the COX-2 enzyme via COX-2 selective inhibitors might open up new perspectives in the control of obesity and related metabolic diseases.

PPARdelta activation induces COX-2 gene expression and cell proliferation in human hepatocellular carcinoma cells

Cyclooxygenase-2 (COX-2) has been suggested to be associated with carcinogenesis. Recently, many studies have shown increased expression of COX-2 in a variety of human malignancies, including hepatocellular carcinoma (HCC). Therefore, it becomes important to know more about what determines COX-2 expression. In this work, we have studied the effect of PPARdelta activation on COX-2 expression using a selective agonist (GW501516) in human hepatocellular carcinoma (HepG2) cells. Activation of PPARdelta resulted in increased COX-2 mRNA and protein expression. The mechanism behind the induction seems to be increased activity of the proximal promoter of the COX-2 gene, spanning nucleotides -327 to +59. The increased COX-2 protein expression and promoter activity induced by the GW501516 was also confirmed in the monocytic cell line THP-1. Induced levels of COX-2 have previously been associated with resistance to apoptosis and increased cell proliferation in many cell types. In HepG2 cells, we observed a dose-dependent increase in cell number by GW501516 treatment for 72h. The levels of PCNA, used as an indicator of cell division were induced, and the cell survival promoting complex p65 (NF-kappaB) was phosphorylated under GW501516 treatment. We conclude that PPARdelta activation in HepG2 cells results in induced COX-2 expression and increased cellular proliferation. These results may suggest that PPARdelta plays an important role in the development of HCC by modulating expression of COX-2.

The 15-lipoxygenase-1 product 13-S-hydroxyoctadecadienoic acid down-regulates PPAR-delta to induce apoptosis in colorectal cancer cells

Diminished apoptosis, a critical event in tumorigenesis, is linked to down-regulated 15-lipoxygenase-1 (15-LOX-1) expression in colorectal cancer cells. 13-S-hydroxyoctadecadienoic acid (13-S-HODE), which is the primary product of 15-LOX-1 metabolism of linoleic acid, restores apoptosis. Nonsteroidal antiinflammatory drugs (NSAIDs) transcriptionally up-regulate 15-LOX-1 expression to induce apoptosis. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors for linoleic and arachidonic acid metabolites. PPAR-delta promotes colonic tumorigenesis. NSAIDs suppress PPAR-delta activity in colon cancer cells. The mechanistic relationship between 15-LOX-1 and PPAR-delta was previously unknown. Our current study shows that (i) 13-S-HODE binds to PPAR-delta, decreases PPAR-delta activation, and down-regulates PPAR-delta expression in colorectal cancer cells; (ii) the induction of 15-LOX-1 expression is a critical step in NSAID down-regulation of PPAR-delta and the resultant induction of apoptosis; and (iii) PPAR-delta is an important signaling receptor for 13-S-HODE-induced apoptosis. The in vivo relevance of these mechanistic findings was demonstrated in our tumorigenesis studies in nude mouse xenograft models. Our findings indicate that the down-regulation of PPAR-delta by 15-LOX-1 through 13-S-HODE is an apoptotic signaling pathway that is activated by NSAIDs.

Peroxisome proliferator-activated receptors and the cardiovascular system

Insulin resistance syndrome (also called syndrome X) includes obesity, diabetes, hypertension, and dyslipidemia and is a complex phenotype of metabolic abnormalities. The disorder poses a major public health problem by predisposing individuals to coronary heart disease and stroke, the leading causes of mortality in Western countries. Given that hypertension, diabetes, dyslipidemia, and obesity exhibit a substantial heritable component, it is postulated that certain genes may predispose some individuals to this cluster of cardiovascular risk factors. Emerging data suggest that peroxisome proliferator-activated receptors (PPARs), including alpha, gamma, and delta, are important determinants that may provide a functional link between obesity, hypertension, and diabetes. It has been well documented that hypolipidemic fibrates and antidiabetic thiazolidinediones are synthetic ligands for PPAR alpha and PPAR gamma, respectively. In addition, PPAR natural ligands, such as leukotriene B4 for PPAR alpha, 15-deoxy-delta 12,14-prostaglandin J2 for PPAR gamma, and prostacyclin for PPAR delta, are known to be eicosanoids and fatty acids. Studies have documented that PPARs are present in all critical vascular cells: endothelial cells, vascular smooth muscle cells, and monocyte-macrophages. These observations suggest that PPARs not only control lipid metabolism but also regulate vascular diseases such as atherosclerosis and hypertension. In this review, we present structure and tissue distribution of PPAR nuclear receptors, discuss the mechanisms of action and regulation, and summarize the rapid progress made in this area of study and its impact on the cardiovascular system.

Peroxisome proliferator-activated receptors: are they involved in atherosclerosis progression?

Peroxisome proliferator-activated receptors (PPAR) are nuclear receptors present in several organs and cell types. They are subdivided into PPAR alpha, PPAR gamma and PPAR delta (or beta). PPAR alpha and gamma are the two main categories of these receptors, which are both characterized by their ability to influence lipid metabolism, glucose homeostasis, cell proliferation, differentiation and apoptosis, as well as the inflammatory response, by transcriptional activation of target genes. PPAR alpha are activated by fatty acids, eicosanoids and fibrates, while PPAR gamma activators include arachidonic acid metabolites, oxidized low density lipoprotein and thiazolidinediones. Atherosclerosis is now considered a chronic inflammatory condition. Thus, PPAR activation appears a promising approach to favorably affect atherosclerosis development through both metabolic and anti-inflammatory effects. However, the clinical data in favor of an anti-atherosclerotic action of PPAR agonists are still scanty, and some experimental data would even indicate possible pro-atherogenic effects, or a lack of effect in the female sex. New controlled clinical studies will provide the information necessary to understand the true significance and usefulness of PPAR alpha, gamma and delta activators in the control of atherosclerotic disease.

Peroxisome proliferator-activated receptor gamma-mediated differentiation: a mutation in colon cancer cells reveals divergent and cell type-specific mechanisms

Activation of the nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma) inhibits cell growth and induces differentiation in both adipocyte and epithelial cell lineages, although it is unclear whether this occurs through common or cell-type specific mechanisms. We have identified four human colon cancer cell lines that do no undergo growth inhibition or induce markers of differentiation after exposure to PPARgamma agonists. Sequence analysis of the PPARgamma gene revealed that all four cell lines contain a previously unidentified point mutation in the ninth alpha-helix of the ligand binding domain at codon 422 (K422Q). The mutant receptor did not exhibit any defects in DNA binding or retinoid X receptor heterodimerization and was transcriptionally active in an artificial reporter assay. However, only retroviral transduction of the wild-type (WT), but not mutant, receptor could restore PPARgamma ligand-induced growth inhibition and differentiation in resistant colon cancer cell lines. In contrast, there was no difference in the ability of fibroblast cells expressing WT or K422Q mutant receptor to undergo growth inhibition, express adipocyte differentiation markers, or uptake lipid after treatment with a PPARgamma agonist. Finally, analysis of direct PPARgamma target genes in colon cancer cells expressing the WT or K422Q mutant allele suggests that the mutation may disrupt the ability of PPARgamma to repress the basal expression of a subset of genes in the absence of exogenous ligand. Collectively, these data argue that codon 422 may be a part of a co-factor(s) interaction domain necessary for PPARgamma to induce terminal differentiation in epithelial, but not adipocyte, cell lineages and argues that the receptor induces growth inhibition and differentiation via cell lineage-specific mechanisms.

Localization of PPARdelta in murine central nervous system: expression in oligodendrocytes and neurons

The peroxisome proliferator-activated receptors (PPARs), PPARdelta, PPARgamma and PPARalpha, comprise a subclass of the supergene family of nuclear receptors. As such they are ligand-regulated transcription factors whose major effects are mediated by altering expression of target genes. PPARdelta has been shown to be ubiquitously expressed in mammals. However, its primary biological role(s) has yet to be defined. Several recent studies have demonstrated that PPARdelta is the most highly expressed PPAR isoform in the central nervous system, but ambiguity still exists as to the specific brain sub-regions and cells in which it is expressed. Here, utilizing novel, isoform-selective PPARdelta riboprobes and an anti-peptide antibody, we performed a series of in situ hybridization and immunolocalization studies to determine the distribution of PPARdelta in the central nervous system (CNS) of mice. We found that PPARdelta mRNA and protein is expressed throughout the brain, with particularly high levels in the entorhinal cortex, hypothalamus and hippocampus, and lower levels in the corpus callosum and caudate putamen. At the cellular level, PPARdelta mRNA and protein were found to be expressed in oligodendrocytes and neurons but not astrocytes. Such results suggest a role for PPARdelta in both myelination and neuronal functioning within the CNS.

Peroxisome proliferator-activated receptors beta/delta: emerging roles for a previously neglected third family member

PURPOSE OF REVIEW

Peroxisome proliferator-activated receptors alpha, beta/delta and gamma are members of the nuclear receptor superfamily. They mediate the effects of fatty acids and their derivatives at the transcriptional level, and are considered to be lipid sensors that participate in the regulation of energy homeostasis. Compared with the alpha and gamma peroxisome proliferator-activated receptor isotypes, peroxisome proliferator-activated receptor beta functions have long remained an enigma. In this review, we focus on emerging knowledge about peroxisome proliferator-activated receptor beta activation and roles.

RECENT FINDINGS

We review recent data that suggest key roles in basic cell functions, such as proliferation, differentiation and survival, and in embryonic development and lipid metabolism in peripheral tissues.

SUMMARY

The newly unveiled roles of peroxisome proliferator-activated receptor beta in important basic cell functions certainly justify a further exploration of its potential as a therapeutic target in pathologies such as metabolic syndrome X or skin diseases.

Peroxisome proliferator-activated receptors: a critical review on endogenous pathways for ligand generation

Lipid mediators can exert their effects by interactions with well-characterised cell surface G-protein-linked receptors. Recently, a group of intracellular receptors have been identified that are activated by a large variety of lipid-derived mediators. Amongst these novel targets, the peroxisome proliferator-activated receptors (PPARs), a family of three (PPARalpha, beta/delta and gamma) nuclear receptor/transcription factors have become a major area for investigation. PPARs are found throughout the body, where they have diverse roles regulating lipid homeostasis, cellular differentiation, proliferation and the immune response. There is a great interest, therefore, in the roles of PPARs in a variety of pathological conditions, including diabetes, atherosclerosis, cancer and chronic inflammation. Although, a number of naturally occurring compounds can activate PPARs, it has been difficult, as yet, to characterise any of these mediators as truly endogenous ligands. These findings have lead to the suggestion that PPARs may act just as general lipid sensors. Acting as lipid sensors, PPARs may take changes in lipid/fatty acid balance in the diet or local metabolism and translate them to tissue-specific ligands, exerting tissue-specific effects. Using classical pharmacological criteria for endogenous mediator classification we will critically discuss the variety of pathways for putative ligand generation.

Peroxisome proliferator-activated receptor gamma and transforming growth factor-beta pathways inhibit intestinal epithelial cell growth by regulating levels of TSC-22

Peroxisome proliferator-activated receptor gamma (PPARgamma) and transforming growth factor-beta (TGF-beta) are key regulators of epithelial cell biology. However, the molecular mechanisms by which either pathway induces growth inhibition and differentiation are incompletely understood. We have identified transforming growth factor-simulated clone-22 (TSC-22) as a target gene of both pathways in intestinal epithelial cells. TSC-22 is member of a family of leucine zipper containing transcription factors with repressor activity. Although little is known regarding its function in mammals, the Drosophila homolog of TSC-22, bunched, plays an essential role in fly development. The ability of PPARgamma to induce TSC-22 was not dependent on an intact TGF-beta1 signaling pathway and was specific for the gamma isoform. Localization studies revealed that TSC-22 mRNA is enriched in the postmitotic epithelial compartment of the normal human colon. Cells transfected with wild-type TSC-22 exhibited reduced growth rates and increased levels of p21 compared with vector-transfected cells. Furthermore, transfection with a dominant negative TSC-22 in which both repressor domains were deleted was able to reverse the p21 induction and growth inhibition caused by activation of either the PPARgamma or TGF-beta pathways. These results place TSC-22 as an important downstream component of PPARgamma and TGF-beta signaling during intestinal epithelial cell differentiation.

Peroxisome proliferator-activated receptor-beta signaling contributes to enhanced proliferation of hepatic stellate cells

BACKGROUND & AIMS

The peroxisome proliferator-activated nuclear receptors (PPAR-alpha, PPAR-beta, and PPAR-gamma), which modulate the expression of genes involved in energy homeostasis, cell cycle, and immune function, may play a role in hepatic stellate cell activation. Previous studies focused on the decreased expression of PPAR-gamma in hepatic stellate cell activation but did not investigate the expression and role of the PPAR-alpha and -beta isotypes. The aim of this study was to evaluate the expression of the different PPARs during hepatic stellate cell activation in vitro and in situ and to analyze possible factors that might contribute to their expression. In a second part of the study, the effect of a PPAR-beta agonist on acute liver injury was evaluated.

METHODS

The effects of PPAR isotype-specific ligands on hepatic stellate cell transition were evaluated by bromodeoxyuridine incorporation, gel shifts, immunoprecipitation, and use of antisense PPAR-beta RNA-expressing adenoviruses. Tumor necrosis factor alpha-induced PPAR-beta phosphorylation and expression was evaluated by metabolic labeling and by using specific P38 inhibitors.

RESULTS

Hepatic stellate cells constitutively express high levels of PPAR-beta, which become further induced during culture activation and in vivo fibrogenesis. No significant expression of PPAR-alpha or -gamma was found. Stimulation of the P38 mitogen-activated protein kinase pathway modulated the expression of PPAR-beta. Transcriptional activation of PPAR-beta by L165041 enhanced hepatic stellate cell proliferation. Treatment of rats with a single bolus of CCl(4) in combination with L165041 further enhanced the expression of fibrotic markers.

CONCLUSIONS

PPAR-beta is an important signal-transducing factor contributing to hepatic stellate cell proliferation during acute and chronic liver inflammation.

Molecular cloning and characterisation of peroxisome proliferator activated receptor gamma1 (PPARgamma1) cDNA gene from guinea pig (Cavia porcellus): tissue distribution

The coding region of guinea pig peroxisome proliferator activated receptor gamma1 (gpPPARgamma1) cDNA was successfully cloned from adipose tissue by reverse transcription polymerase chain reaction (RT-PCR) using the designated primers based on the conserved regions of the other mammalian PPARgamma1 sequence. From RT-PCR, a combination of three cDNA fragments that comprised of the full length coding region PPARgamma1 cDNA gene were amplified, with the size of 498, 550 and 557 bp, respectively. All three fragments were then successfully assembled by utilising the internal restriction sites present at the overlapping regions to give rise to the full-length coding region of gpPPARgamma1 with the size of 1428 bp and consisting of 475 amino acids. Guinea pig PPARgamma1 is highly conserved with those of other species at protein and nucleotide levels. Gene expression studies showed that gpPPARgamma mRNA was predominantly expressed in adipose tissue followed by lung and spleen. However, at the protein level, PPARgamma was also found to be expressed in skeletal muscle.

Peroxisome proliferator-activated receptors (PPARs) in health and disease

Peroxisome proliferator-activated receptors (PPARs) belong to the superfamily of steroid-thyroid-retinoid nuclear receptors. PPARs are transcription factors activated by specific ligands and play an important role during cell signalling. Intensive study of PPARs during recent years has revealed their importance in both normal physiology and in the pathology of various tissues. They participate in the regulation of lipid metabolism, inflammation and the development of atherosclerosis or diabetes. They also play a role in the regulation of growth and differentiation of cancer. It has been suggested that PPAR ligands may have potent anticancer effects and therefore may serve as potential anticancer drugs. In this review we focus on a role of PPARs in breast cancer and in glial tumors of the brain.

Docosahexaenoic acid suppresses the activity of peroxisome proliferator-activated receptors in a colon tumor cell line

Fatty acids are generally considered as agonists for peroxisome proliferator-activated receptors (PPARs). Fatty acids have been shown to bind to and transactivate PPARs; it is not known whether fatty acids act as generalized agonists for PPARs in different cell types, and thus, stimulate the expression of PPAR-regulated target genes. Here, we investigated the potency of unsaturated fatty acids on transactivation of PPRE, DNA-binding activity of PPARs, and the expression of a PPAR-regulated gene product, CD36. Docosahexaenoic acid (DHA) suppressed the basal and PPAR agonist-induced transactivation of PPRE, and DNA binding of PPARs in colon tumor cells (HCT116). The suppression of PPAR transactivation by DHA leads to reduced expression of CD36 in HCT116 cells and human monocytic cells (THP-1) as determined by promoter reporter gene assay and flow cytometric analysis. Our results demonstrate that DHA and other unsaturated fatty acids act as antagonists instead of agonists for transactivation of PPRE and PPAR-regulated gene expression in the cell lines tested. These results suggest that PPAR-mediated gene expression and cellular responses can be dynamically modulated by different types of dietary fatty acids consumed.

Prostacyclin-deficient mice develop ischemic renal disorders, including nephrosclerosis and renal infarction

BACKGROUND

Prostacyclin (PGI2) is a short-lived endogenous inhibitor of platelet aggregation and a potent vasodilator and regulator of the growth of vascular smooth muscle cells. To study the role of PGI2 in the vascular system in vivo, PGI2-deficient (PGID) mice were established by genetic disruption of the PGI2 synthase gene.

METHODS AND RESULTS

PGI2 synthase-null mice were generated by replacing the exons of PGI2 synthase gene that encodes for the catalytic site of the enzyme with a neomycin resistance gene. In these mice, PGI2 levels in the plasma, kidneys, and lungs were reduced, whereas thromboxane and prostaglandin E2 levels became elevated. Blood pressure and the amounts of urea nitrogen and creatinine in plasma of the PGID mice were significantly higher than those of wild-type mice (P<0.05). They developed progressive morphological abnormalities in the kidneys, accompanied by atrophy, surface irregularity, fibrosis, cyst, arterial sclerosis, and hypertrophy of vessel walls. Thickening of the thoracic aortic media and adventitia were observed in aged PGID mice. Importantly, these phenotypes have not been reported in PGI2 receptor-deficient mice.

CONCLUSIONS

PGI2 deficiency resulted in the development of vascular disorders with the thickening of vascular walls and interstitial fibrosis, especially in mouse kidneys. The findings demonstrated in vivo that PGI2 is important in the homeostasis of blood vessels. Our established PGID mice are useful for studies on the initiation and development of vascular diseases, such as ischemic renal disorders with arterial sclerosis and infarction, and also for studies on the novel signaling pathway of PGI2.

Localization of IP in rabbit kidney and functional role of the PGI(2)/IP system in cortical collecting duct

To clarify the role of the PGI(2)/PGI(2) receptor (IP) system in rabbit cortical collecting duct (RCCD), we characterized the expression of IP receptors in the rabbit kidney. We show by Northern and Western blotting that IP mRNA and protein was detectable in all three regions of the kidney. To determine how PGI(2) signals, we compared the effects of different PGI(2) analogs [iloprost (ILP), carba-prostacyclin (c-PGI(2)), and cicaprost (CCP)] in the isolated perfused RCCD. PGI(2) analogs did not increase water flow (L(p)). Although PGI(2) analogs did not reduce an established L(p) response to 8-chlorophenylthio-cAMP, they equipotently inhibited AVP-stimulated L(p) by 45%. The inhibitory effect of ILP and c-PGI(2) on AVP-stimulated L(p) is partially reversed by the protein kinase C inhibitor staurosporine and abolished by pertussis toxin; no effect was obtained with CCP. In fura 2-loaded RCCD, CCP did not alter cytosolic Ca(2+) concentration ([Ca(2+)](i)), but, in the presence of CCP, individual infusion of ILP and PGE(2) increased [Ca(2+)](i), suggesting that CCP did not cause desensitization to either ILP or PGE(2). We concluded that ILP and c-PGI(2) activate PKC and the liberation of [Ca(2+)](i) but not CCP. This suggested an important role for phosphatidylinositol hydrolysis in mediating ILP and c-PGI(2) effects but not CCP in RCCD.

Metabolism of the endocannabinoids, 2-arachidonylglycerol and anandamide, into prostaglandin, thromboxane, and prostacyclin glycerol esters and ethanolamides

Cyclooxygenase-2 (COX-2) action on the endocannabinoids, 2-arachidonylglycerol (2-AG) and anandamide (AEA), generates prostaglandin glycerol esters (PG-G) and ethanolamides (PG-EA), respectively. The diversity of PG-Gs and PG-EAs that can be formed enzymatically following COX-2 oxygenation of endocannabinoids was examined in cellular and subcellular systems. In cellular systems, glycerol esters and ethanolamides of PGE(2), PGD(2), and PGF(2alpha) were major products of the endocannabinoid-derived COX-2 products, PGH(2)-G and PGH(2)-EA. The sequential action of purified COX-2 and thromboxane synthase on AEA and 2-AG provided thromboxane A(2) ethanolamide and glycerol ester, respectively. Similarly, bovine prostacyclin synthase catalyzed the isomerization of the intermediate endoperoxides, PGH(2)-G and PGH(2)-EA, to the corresponding prostacyclin derivatives. Quantification of the efficiency of prostaglandin and thromboxane synthase-directed endoperoxide isomerization demonstrated that PGE, PGD, and PGI synthases catalyze the isomerization of PGH(2)-G at rates approaching those observed with PGH(2). In contrast, thromboxane synthase was far more efficient at catalyzing PGH(2) isomerization than at catalyzing the isomerization of PGH(2)-G. These results define the in vitro diversity of endocannabinoid-derived prostanoids and will permit focused investigations into their production and potential biological actions in vivo.

Genomic organization of the mouse peroxisome proliferator-activated receptor beta/delta gene: alternative promoter usage and splicing yield transcripts exhibiting differential translational efficiency

Peroxisome proliferator-activated receptor (PPAR) beta/delta is ubiquitously expressed, but the level of expression differs markedly between different cell types. In order to determine the molecular mechanisms governing PPARbeta/delta gene expression, we have isolated and characterized the mouse gene encoding PPARbeta/delta. The gene spans approx. 41 kb and comprises 11 exons of which the six exons located in the 3'-end of the gene are included in all transcripts. Primer-extension and 5'-rapid amplification of cDNA ends experiments revealed the presence of multiple transcription start points and splice variants, originating from the use of at least four different promoters. One of these transcription start points was found to be used predominantly in all tissues examined. Initiation from this major transcription start point gives rise to a transcript with a 548 nt 5'-untranslated leader containing eight upstream AUG codons. We show that the presence of the 548 nt leader resulted in a low translational efficiency of the corresponding PPARbeta/delta mRNA and propose, based on structural features of the 5'-untranslated region, that translational initiation may be mediated via an internal ribosome entry site-dependent mechanism.

A novel pathway of prostacyclin signaling-hanging out with nuclear receptors

Prostacylin (PGI(2)), one of the major prostaglandins, is derived from arachidonic acid by the action of the cyclooxygenase (COX) system coupled to PGI(2) synthase (PGIS). The presence of the COX-2/PGIS at the nuclear and endoplasmic reticular membrane suggests differential signaling pathways of PGI(2) actions involving both cell surface and nuclear receptors. Although the signaling of PGI(2) via its cell surface receptor, prostacyclin receptor (IP), is well documented in vascular biology, its action via nuclear receptors in other physiological responses is gradually being more appreciated. Peroxisomal proliferator-activated receptors (PPARs), PPARalpha, PPARgamma, and PPARdelta, though initially cloned as a family of orphan receptors, are now known for their ligand promiscuity. The ligands range from free fatty acids and their derivatives produced by the cyclooxygenase or lipoxygenase pathway to certain hypolipidemic drugs. The predisposition of PPARs to use a wide spectrum of ligands is well explained by their unusually large ligand-binding pocket. The promiscuous ligand usage by PPARs is also reflected by their involvement in various pathophysiological events. Several recent independent reports show that endogenously produced PGI(2) indeed activates PPARdelta in vivo, indicating that a novel signaling mechanism for this abundant eicosanoid is operative in certain systems. This review attempts to cover recent developments in nuclear actions of PGI(2) in diverse biological functions.

Peroxisome proliferator-activated receptor beta expression in human breast epithelial cell lines of tumorigenic and non-tumorigenic origin

Peroxisome proliferator-activated receptor beta (PPARbeta) is a member of the nuclear hormone receptor superfamily and is a ligand activated transcription factor, although the precise genes that it regulates and its physiological and pathophysiological role remain unclear. In view of the association of PPARbeta with colon cancer and increased mRNA levels of PPARbeta in colon tumours we sought in this study to examine the expression of PPARbeta in human breast epithelial cells of tumorigenic (MCF-7 and MDA-MB-231) and non-tumorigenic origin (MCF-10A). Using quantitative RT-PCR we measured PPARbeta mRNA levels in MCF-7, MDA-MB-231 and MCF-10A cells at various stages in culture. After serum-deprivation, MDA-MB-231 and MCF-10A cells had a 4.2- and 3.8-fold statistically greater expression of PPARbeta compared with MCF-7 cells. The tumorigenic cell lines also exhibited a significantly greater level of PPARbeta mRNA after serum deprivation compared with subconfluence whereas such an effect was not observed in non-tumorigenic MCF-10A cells. The expression of PPARbeta was inducible upon exposure to the PPARbeta ligand bezafibrate. Our results suggest that unlike colon cancer, PPARbeta overexpression is not an inherent property of breast cancer cell lines. However, the dynamic changes in PPARbeta mRNA expression and the ability of PPARbeta in the MCF-7 cells to respond to ligand indicates that PPARbeta may play a role in mammary gland carcinogenesis through activation of downstream genes via endogenous fatty acid ligands or exogenous agonists.

Inflammation and cancer, the mastocytoma P815 tumor model revisited: triggering of macrophage activation in vivo with pro-tumorigenic consequences

Subcutaneous in vivo injections of cells of the mastocytoma line P815 in syngenic DBA/2 mice induce locally fast growing solid tumors. These have been used extensively as a cancer model to analyze and manipulate the relationship between tumor cells and host's immune defenses. We report that progression of P815 tumors in vivo was accompanied by a burst (Days 5-7) of local inflammatory cells recruitment and angiogenesis observed histologically, corroborated in vivo by MRI with gadolinium, overtranscription of macrophage activation marker genes, secretion of TNF-alpha by regional lymph node cells and concomitant systemic inflammation. No substantial overtranscriptions of either VEGF or IL-10 or TGF-beta genes were observed. Induction of COX-2 gene was a late event. To establish a possible relationship between the tumor-induced local, regional and systemic increase of pro-inflammatory mediators and progression of tumors in vivo, we carried out experiments deliberately modulating the inflammatory status of the recipient animals. Pretreatment of recipient animals by i.p. injection of thioglycolate accelerated P815 tumor growth. At the opposite, treatment of mice with either a COX-1 + COX-2 inhibitor (aspirin, 1 mg/day/mouse) or a specific COX-2 inhibitor (celecoxib, 0.13 mg/day/mouse) for 2 weeks after injection of tumor cells, significantly reduced the size and growth rate of tumors compared to control mice. Experiments carried out in vitro indicated that peritoneal macrophages from untreated animals were strongly activated by live P815 cells and by P815 membrane preparations. The tumor-induced inflammatory reaction could establish a local micro environment favoring tumor progression. The P815 tumor model might be helpful to recognize important factors controlling host/tumor relationship.

The peroxisome proliferator-activated receptor alpha (PPARalpha): role in hepatocarcinogenesis

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the nuclear receptor superfamily and mediates most of the known biological effects of peroxisome proliferators. The latter represents a large group of chemicals that include the fibrate hyperlipidemic drugs, the pthalate plasticizers, various solvents and degreasing agents, and endogenous hormones and fatty acids. Peroxisome proliferators are classical members of the nongenotoxic group of chemical carcinogens that do not require metabolic activation to electrophiles in order to exert their harmful effects. These chemicals are of particular concern to regulatory agencies since they can only be detected by long-term carcinogen bioassays using rodents. The mechanism of the carcinogenic action of peroxisome proliferators is beginning to emerge. PPARalpha-null mice are resistant to hepatocarcinogenesis indicating that this receptor is necessary for cancer. However, recent studies indicate that Kupffer cells, in a PPARalpha independent manor, are required for the major effects of peroxisome proliferators on cell proliferation. An interaction between PPARalpha and estrogen carcinogenesis has also been elucidated.

15-Lipoxygenase metabolism of 2-arachidonylglycerol. Generation of a peroxisome proliferator-activated receptor alpha agonist

The recent demonstrations that cyclooxygenase-2 and leukocyte-type 12-lipoxygenase (LOX) efficiently oxygenate 2-arachidonylglycerol (2-AG) prompted an investigation into related oxygenases capable of metabolizing this endogenous cannabinoid receptor ligand. We evaluated the ability of six LOXs to catalyze the hydroperoxidation of 2-AG. Soybean 15-LOX, rabbit reticulocyte 15-LOX, human 15-LOX-1, and human 15-LOX-2 oxygenate 2-AG, providing 15(S)-hydroperoxyeicosatetraenoic acid glyceryl ester. In contrast, potato and human 5-LOXs do not efficiently metabolize this endocannabinoid. Among a series of structurally related arachidonyl esters, arachidonylglycerols serve as the preferred substrates for 15-LOXs. Steady-state kinetic analysis demonstrates that both 15-LOX-1 and 15-LOX-2 oxygenate 2-AG comparably or preferably to arachidonic acid. Furthermore, 2-AG treatment of COS-7 cells transiently transfected with human 15-LOX expression vectors or normal human epidermal keratinocytes results in the production and extracellular release of 15-hydroxyeicosatetraenoic acid glyceryl ester (15-HETE-G), establishing that lipoxygenase metabolism of 2-AG occurs in an eukaryotic cellular environment. Investigations into the potential biological actions of 15-HETE-G indicate that this lipid, in contrast to its free-acid counterpart, acts as a peroxisome proliferator-activated receptor alpha agonist. The results demonstrate that 15-LOXs are capable of acting on 2-AG to provide 15-HETE-G and elucidate a potential role for endocannabinoid oxygenation in the generation of peroxisome proliferator-activated receptor alpha agonists.

Peroxisome proliferator-activated receptor delta activation promotes cell survival following hypertonic stress

COX2-selective non-steroidal anti-inflammatory drugs (NSAIDs) cause selective apoptosis of renal medullary interstitial cells (RMIC) in vivo and reduce their ability to tolerate hypertonic stress in vitro. To determine the mechanism by which COX2 activity promotes RMIC viability, we examined the capacity of COX2-derived prostanoids to promote RMIC survival. Although RMICs synthesize prostaglandin E2 (PGE2) PGI2 > PGF2a > TxA2, only PGI2 enhanced RMIC viability following hypertonic stress. RMICs do not express the prostacyclin receptor, but they do express the prostacyclin responsive nuclear transcription factor peroxisome proliferator-activated receptor delta (PPARdelta). Hypertonic stress increased PGI2 synthesis 330% above base line and also activated a PPARdelta specific reporter (delta response element (DRE)) by 90% above base line. Conversely DRE activity was only inhibited by the COX2-selective inhibitor SC236 but not by a COX1-selective NSAID (SC560). Overexpression of PPARdelta using an adenovirus not only drove DRE activity but also prevented RMIC death due to COX2 inhibition. These studies are consistent with a model whereby hypertonicity activates COX2-derived prostaglandin production, which promotes RMIC viability through PPARdelta. Inhibition of PPARdelta activity may contribute to the renal papillary necrosis associated with analgesic and/or NSAID use.

New factors in the regulation of adipose differentiation and metabolism

Obesity and lipoatrophy are major risks for insulin resistance, type 2 diabetes and cardiovascular diseases. The molecular links between adipocyte dysfunction and metabolic disorders were elusive until the discovery that adipose tissue operates as an endocrine organ and releases factors targeting a wide range of organs. This article attempts to review the more recent advances from research on the transcriptional control of adipogenesis and on new adipocyte-secreted proteins that have been proposed as molecular links between adipose tissue and insulin resistance.

Site-specific molecular design and its relevance to pharmacogenomics and chemical biology

The emergence of the new discipline of pharmacogenomics reflects the growing convergence of chemical and genomic space. The massive information-driven growth in both computational chemistry and structural biology is leading to unprecedented opportunities in both chemical and biological design. In this paper we relate current opinion in structural biology to recent developments in computational drug design. Sequence information now permits protein structure prediction and, together with experimental protein structure determination, a complete database of ligand-binding sites and protein-protein interactions can be assembled. When aligned with site exploration and virtual screening, this information provides a foundation for structure-based pharmacogenomics. In association with chemical genomics, structure-based design will allow major new insights into a compound's biological and pharmaceutical properties.

COX-2: a target for colon cancer prevention

Disease prevention is one area that both public and governmental agencies strongly support owing to its potential for an improved lifestyle and a reduction in health care costs. In this review, we focus on the clinical development of one target for cancer prevention, the COX-2 enzyme. This provides an excellent example of how basic research in biochemistry and pharmacology can lead to translational studies and eventually to approval of a drug by the FDA for use as a chemopreventive agent in humans. It is hoped that, as the genome sequence is understood more clearly, other targets will emerge that will provide even more effective drugs for future cancer prevention.

Nuclear receptors. I. PPAR gamma in the gastrointestinal tract: gain or pain?

The peroxisome proliferator-activated receptor gamma (PPAR gamma) has recently been implicated in the pathogenesis of inflammatory bowel disease (IBD) and colon cancer. The observation that PPAR gamma agonists, through immune modulation, protect against inflammatory processes in the intestine justified their expedient evaluation in the clinical management of IBD. PPAR gamma agonists are reported to have both tumor-promoting and -inhibiting effects in models of colon cancer. These differences can, in part, be explained by PPAR gamma-independent effects of PPAR gamma agonists and by differences in the models used. Because it is still unclear how PPAR gamma impacts on colon cancer, careful monitoring of patients receiving PPAR gamma agonists and additional basic research is indicated before recommendations on the use of PPAR gamma ligands in colon cancer can be made.

Nuclear receptor corepressor-dependent repression of peroxisome-proliferator-activated receptor delta-mediated transactivation

The nuclear receptor corepressor (NCoR) was isolated as a peroxisome-proliferator-activated receptor (PPAR) delta interacting protein using the yeast two-hybrid system. NCoR interacted strongly with the ligand-binding domain of PPAR delta, whereas interactions with the ligand-binding domains of PPAR gamma and PPAR alpha were significantly weaker. PPAR-NCoR interactions were antagonized by ligands in the two-hybrid system, but were ligand-insensitive in in vitro pull-down assays. Interaction between PPAR delta and NCoR was unaffected by coexpression of retinoid X receptor (RXR) alpha. The PPAR delta-RXR alpha heterodimer bound to an acyl-CoA oxidase (ACO)-type peroxisome-proliferator response element recruited a glutathione S-transferase-NCoR fusion protein in a ligand-independent manner. Contrasting with most other nuclear receptors, PPAR delta was found to interact equally well with interaction domains I and II of NCoR. In transient transfection experiments, NCoR and the related silencing mediator for retinoid and thyroid hormone receptor (SMRT) were shown to exert a marked dose-dependent repression of ligand-induced PPAR delta-mediated transactivation; in addition, transactivation induced by the cAMP-elevating agent forskolin was efficiently reduced to basal levels by NCoR as well as SMRT coexpression. Our results suggest that the transactivation potential of liganded PPAR delta can be fine-tuned by interaction with NCoR and SMRT in a manner determined by the expression levels of corepressors and coactivators.

Peroxisome proliferator-activated receptor delta is up-regulated during vascular lesion formation and promotes post-confluent cell proliferation in vascular smooth muscle cells

Although peroxisome proliferator-activated receptor (PPAR) delta is widely expressed in many tissues, the role of PPARdelta is poorly understood. In this study, we report that PPARdelta was up-regulated in vascular smooth muscle cells (VSMC) during vascular lesion formation. By using Northern blot analysis, we demonstrated that PPARdelta was increased by 3-4-fold in VSMC treated with platelet-derived growth factor (PDGF) (20 ng/ml). In addition, PDGF-induced PPARdelta mRNA expression neither needs de novo protein synthesis nor affects the stability of PPARdelta mRNA in VSMC. Preincubation of VSMC with phosphatidylinositol 3-kinase inhibitor (LY294002, 50 micromol/liter) or infection of VSMC with an adenovirus carrying the gene for a dominant negative form of Akt abrogated PDGF-induced PPARdelta mRNA expression, suggesting that phosphatidylinositol 3-kinase/Akt signaling pathway is involved in the regulation of PDGF-induced PPARdelta mRNA expression in VSMC. To explore the role of PPARdelta in VSMC, we generated rat vascular smooth muscle cells (A7r5) stably overexpressing PPARdelta and the control green fluorescent protein. Overexpression of PPARdelta in VSMC increased post-confluent cell proliferation by increasing the cyclin A and CDK2 as well as decreasing p57(kip2). Taken together, the results suggest that PPARdelta plays an important role in the pathology of diseases associated with VSMC proliferation, such as primary atherosclerosis and restenosis.

The antiproliferative effects of biologically active isomers of conjugated linoleic acid on human colorectal and prostatic cancer cells

The antiproliferative effects of two commercial preparations of conjugated linoleic acid (CLA) and their constituent isomers, cis-9, trans-11 (c9,t11)-CLA, c9,c11-CLA, and t10,c12-CLA, were determined in vitro using human colorectal (HT-29, MIP-101) and prostate (PC-3) carcinoma cells adapted to serum-free medium. The antiproliferative effects of the preparations were dependent upon the type and concentration of CLA isomer present. The t10,c12-CLA isomer exhibited the greatest potency against colorectal cancer proliferation, and the c9,t11 and t10,c12 isomers were moderately effective against prostate cancer. The t10,c12 isomer induced caspase-dependent apoptosis in MIP-101 and PC-3 cells. The results are the first to demonstrate that physiologic levels of two CLA preparations, their constituent isomers, and the c9,t11-CLA elongation product, c11,t13-conjugated eicosadienoic acid, induce dose-dependent inhibitory effects on cancer proliferation in vitro. Novel CLA preparations may prove effective as chemopreventive supplements for individuals at risk of or diagnosed with colorectal or prostate cancer.

Nonsteroidal anti-inflammatory drugs, apoptosis, and colon-cancer chemoprevention

Nonsteroidal anti-inflammatory drugs (NSAIDs) can inhibit colorectal tumorigenesis and are among the few agents known to be chemopreventive. Epidemiological studies and experiments with animals have shown that NSAIDs have powerful anticolorectal cancer properties, but the mechanism of these effects remains unclear. NSAIDs can inhibit neoplastic growth by inducing apoptosis in cancer cells; the way they do this is currently an area of intense investigation. The most well-characterised pharmacological feature of NSAIDs is their inhibition of the enzyme cyclo-oxygenase (COX), which catalyses the synthesis of prostaglandins. Several studies have shown that COX inhibition prevents cell proliferation and promotes apoptosis. The chemopreventive effects of NSAIDs are thought to occur via this pathway. Other observations indicate that NSAIDs also promote apoptosis through mechanisms that are independent of COX inhibition. This idea is supported by the finding that compounds that are structurally similar to NSAIDs, but do not inhibit COX, also have chemopreventive and proapoptotic properties. COX-dependent and COX-independent mechanisms of apoptosis induction are not mutually exclusive, and it is likely that both have a role in the biological activity of NSAIDs. Knowledge of how NSAIDs prevent neoplastic growth will greatly aid the design of better chemopreventive drugs and novel treatments for colorectal cancer.

Chemoprevention of human skin cancer

The incidence of skin cancer has been rising in recent years with significant effects on public health. Primary prevention has proven inadequate in impacting the incidence of skin cancer, thus stimulating the development of chemopreventive strategies. The majority of skin cancer chemoprevention studies focus on occurrence of new nonmelanoma skin cancers (NMSC) in individuals with a previous NMSC, or on reduction in the number of premalignant skin lesions such as actinic keratoses (AK). Dysplastic nevi, a likely precursor of melanoma, are also potential targets for chemoprevention strategies. Premalignant lesions are especially attractive as endpoints since they are more common than frank cancer, resulting in reduced sample size, length, and cost of clinical trials. Development of new agents that affect the pathogenesis of skin cancer will be discussed, from elucidation of molecular targets to implementation of trials designed to determine the effects of chemopreventive interventions on human skin cancer.

Cyclooxygenase-2 expression in endometrial cancer: correlation with microvessel count and expression of vascular endothelial growth factor and thymidine phosphorylase

Cyclooxygenase-2 (COX-2), known to be elevated in several human cancers, regulates angiogenesis by inducing production of angiogenic factors. These mechanisms require clarification in endometrial cancer. COX-2 expression was examined by immunohistochemistry and reverse-transcription polymerase chain reaction (RT-PCR) in endometrial cancer, endometrial hyperplasia, and normal endometrium in various phases. We investigated the relationship between COX-2 expression and clinicopathologic variables, microvessel count, and expression of vascular endothelial growth factor (VEGF) and thymidine phosphorylase (TP). Immunohistochemistry demonstrated COX-2 protein in cancerous epithelial cells but not in stromal cells. COX-2 expression in epithelial cells was significantly greater in endometrial cancer (n = 63) and endometrial hyperplasia (n = 6) than in normal endometrium in any phase (n = 53). Although COX-2 did not correlate with any conventional clinicopathologic factor in patients with endometrial cancer, COX-2 expression was associated with high microvessel count, VEGF expression, and TP expression. By combined analysis of COX-2, VEGF, and TP, tumors with high expression of at least one factor had a significantly higher microvessel count than tumors expressing little of the three factors. We confirmed upregulation of COX-2 mRNA expression by RT-PCR in endometrial cancer (n = 17) compared to normal endometrium (n = 12). COX-2 mRNA expression significantly correlated with VEGF mRNA expression in these tumors. COX-2 is upregulated in endometrial cancer and facilitates tumor growth via angiogenesis produced in associated with VEGF and TP. Specific inhibition of COX-2 may be a useful therapeutic intervention in endometrial cancer.

Involvement of caveolae and caveolae-like domains in signalling, cell survival and angiogenesis

Caveolae, the flask-shaped membrane invaginations abundant in endothelial cells, have acquired a prominent role in signal transduction. Evidence, that events occurring in caveolae participate in cell survival and angiogenesis, has been recently substantiated by the identification of two novel caveolar constituents: prostacyclin synthase (PGIS) and the cellular form of prion protein (PrP(c)). We have shown that PGIS, previously described as an endoplasmic reticulum component, is bound to caveolin-1 (cav-1) and localized in caveolae in human endothelial cells. By generating prostacyclin, PGIS is involved in angiogenesis. Previous observations regarding the localization of PrP(c) in caveolae-like membrane domains (CLDs) have been recently confirmed and extended. It has been demonstrated that PrP(c) is bound to cav-1 and, by recruiting Fyn kinase, can participate in signal transduction events connected to cell survival and differentiation. The new entries of PGIS and PrP(c) in caveolar components place caveolae and CLDs at the centre of a network, where cells decide whether to proliferate or differentiate and whether to survive or to suicide by apoptosis.

Genomic approaches to research in pulmonary hypertension

Genomics, or the study of genes and their function, is a burgeoning field with many new technologies. In the present review, we explore the application of genomic approaches to the study of pulmonary hypertension (PH). Candidate genes, important to the pathobiology of the disease, have been investigated. Rodent models enable the manipulation of selected genes, either by transgenesis or targeted disruption. Mutational analysis of genes in the transforming growth factor-beta family have proven pivotal in both familial and sporadic forms of primary PH. Finally, microarray gene expression analysis is a robust molecular tool to aid in delineating the pathobiology of this disease.

Peroxisome proliferator-activated receptor ligands as antiatherogenic agents: panacea or another Pandora's box?

Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor super family that modulate gene expression upon ligand activation. They are 3 major subtypes of PPARs: alpha, delta (also called beta), and gamma. PPAR-gamma is widely expressed in the cardiovascular system and is involved in the regulation of tissue inflammation and smooth muscle cell growth pathways as well as in lipoprotein metabolism and coagulation cascades. PPAR-gamma ligands of (e.g., rosigitazone and pioglitazone) have been shown to exert antiatherogenic effects both in vitro and in vivo. PPAR-alpha ligands (e.g., clofibrate and benzofibrate) modulate lipoprotein metabolism, and affect inflammation and coagulation cascade. These effects may be helpful in resolving the dilemma arising from studies that showed significant mortality and morbidity benefits of fibrates in the face of minimal changes in HDL-cholesterol levels. The role of PPAR-delta in atherogenesis remains largely unknown, although it appears that PPAR-delta activation affects lipoprotein metabolism. PPAR ligands appear to be promising agents in limiting atherosclerosis; however, large-scale clinical trials are required to assess their safety and efficacy before they can be added to the clinicians' arsenal of antiatherosclerotic agents.

Inflammation and colorectal cancer: IBD-associated and sporadic cancer compared

Ulcerative colitis and colonic Crohn's disease (together known as inflammatory bowel disease or IBD) are both associated with increased risk for colorectal cancer. Although it is customary to emphasize differences in the biology of IBD-associated and sporadic colon cancer, we believe these are far outweighed by the similarities. These similarities suggest that they might have similar pathogenic mechanisms. Because the normal colon is arguably in a continual state of low-grade inflammation in response to its microbial flora, it is reasonable to speculate that both IBD-associated and sporadic colon cancer might be the consequence of bacteria-induced inflammation.

Prostacyclin-dependent apoptosis mediated by PPAR delta

Prostacyclin (PGI(2)) plays important roles in hemostasis both as a vasodilator and an endogenous inhibitor of platelet aggregation. PGI(2) functions in these roles through a specific IP receptor, a G protein-coupled receptor linked to G(s) and increases in cAMP. Here, we report that intracellular prostacyclin formed by expressing prostacyclin synthase in human embryonic kidney 293 cells promotes apoptosis by activating endogenous peroxisome proliferator-activated receptor delta (PPAR delta). In contrast, treatment of cells with extracellular prostacyclin or dibutyryl cAMP actually reduced apoptosis. On the contrary, treatment of the cells with RpcAMP (adenosine 3',5'-cyclic monophosphothioate, Rp-isomer), an antagonist of cAMP, enhanced prostacyclin-mediated apoptosis. The expression of an L431A/G434A mutant of PPAR delta completely blocked prostacyclin-mediated PPAR delta activation and apoptosis. These observations indicate that prostacyclin can act through endogenous PPAR delta as a second signaling pathway that controls cell fate.

Prostaglandins and leukotrienes: advances in eicosanoid biology

Prostaglandins and leukotrienes are potent eicosanoid lipid mediators derived from phospholipase-released arachidonic acid that are involved in numerous homeostatic biological functions and inflammation. They are generated by cyclooxygenase isozymes and 5-lipoxygenase, respectively, and their biosynthesis and actions are blocked by clinically relevant nonsteroidal anti-inflammatory drugs, the newer generation coxibs (selective inhibitors of cyclooxygenase-2), and leukotriene modifiers. The prime mode of prostaglandin and leukotriene action is through specific G protein-coupled receptors, many of which have been cloned recently, thus enabling specific receptor agonist and antagonist development. Important insights into the mechanisms of inflammatory responses, pain, and fever have been gleaned from our current understanding of eicosanoid biology.

COX-2 inhibition and prevention of cancer

The potential for cyclo-oxygenase inhibition in cancer prevention and treatment is founded on epidemiology (reduction of colorectal cancer in aspirin users), animal experiments and molecular genetics. Trials using the NSAID sulindac also reduced the number of polyps in patients with familial adenomatous polyposis, but the well-known gastrointestinal toxic effects of aspirin and NSAIDs have discouraged the exploitation of their antineoplastic potential. The advent of specific COX-2 inhibitors, which do not interfere with the cytoprotective constitutive COX-1 enzyme, and the demonstration of increased COX-2 expression in many common malignancies beside colorectal cancer, has opened up new therapeutic possibilities. Recently a non-cyclo-oxygenase effect of COX-2 inhibitors, which combines the PPARdelta and the APC tumour suppressor activity, was also demonstrated. The selective COX-2 inhibitor celecoxib has been approved by the FDA for adjuvant treatment of familial adenomatous polyposis, and a large number of prevention and treatment trials of colorectal and other common cancers (prostate and breast cancer) have been started.

Colorectal cancer prevention and treatment by inhibition of cyclooxygenase-2

Population-based studies have established that long-term intake of non-steroidal anti-inflammatory drugs (NSAIDs), compounds that inhibit the enzymatic activity of cyclooxygenase (COX), reduces the relative risk for developing colorectal cancer. These studies led to the identification of a molecular target, COX-2, that is involved in tumour promotion during colorectal cancer progression. Recent studies in humans indicate that therapy with specific COX-2 inhibitors might be an effective approach to colorectal cancer prevention and treatment.

Cyclooxygenase-independent actions of cyclooxygenase inhibitors

Several studies have demonstrated unequivocally that certain nonsteroidal anti-inflammatory drugs (NSAIDs) such as sodium salicylate, sulindac, ibuprofen, and flurbiprofen cause anti-inflammatory and antiproliferative effects independent of cyclooxygenase activity and prostaglandin synthesis inhibition. These effects are mediated through inhibition of certain transcription factors such as NF-kappaB and AP-1. The respective NSAIDs might interfere directly with the transcription factors, but their effects are probably mediated predominantly through alterations of the activity of cellular kinases such as IKKbeta, Erk, p38 MAPK, or Cdks. These effects apparently are not shared by all NSAIDs, since indomethacin failed to inhibit NF-kappaB and AP-1 activation as well as Erk and Cdk activity. In contrast, indomethacin was able to activate PPARgamma, which was not affected by sodium salicylate or aspirin. The differences in cyclooxygenase-independent mechanisms may have consequences for the specific use of these drugs in individual patients because additional effects may either enhance the efficacy or reduce the toxicity of the respective compounds.