Peroxisome-proliferator-activated receptors and cancers: complex stories

A complex between 6-iodolactone and the peroxisome proliferator-activated receptor type gamma may mediate the antineoplastic effect of iodine in mammary cancer

Recently we and other groups have shown that molecular iodine (I(2)) exhibits potent antiproliferative and apoptotic effects in mammary cancer models. In the human breast cancer cell line MCF-7, I(2) treatment generates iodine-containing lipids similar to 6-iodo-5-hydroxy-eicosatrienoic acid and the 6-iodolactone (6-IL) derivative of arachidonic acid (AA), and it significantly decreases cellular proliferation and induces caspase-dependent apoptosis. Several studies have shown that AA is a natural ligand of the peroxisome proliferator-activated receptors (PPARs), which are nuclear transcription factors thought to participate in regulating cancer cell proliferation. Our results show that in MCF-7 cells: (1) 6-IL binds specifically and with high affinity to PPAR proteins (EMSA assays), (2) 6-IL activates both transfected (by transactivation assays) and endogenous (by lipid accumulation) peroxisome proliferator response elements, and (3) 6-IL supplementation increases PPAR gamma and decreases PPAR alpha expression. These results implicate PPARs in a molecular mechanism by which I(2), through formation of 6-IL, inhibits the growth of human breast cancer cells.

Rosiglitazone synergizes anticancer activity of cisplatin and reduces its nephrotoxicity in 7, 12-dimethyl benz{a}anthracene (DMBA) induced breast cancer rats

BACKGROUND

Antineoplastic drug cisplatin remains the drug of choice for various solid tumours including breast cancer. But dose dependent nephrotoxicity is the major drawback in majority of platinum based chemotherapy regimens. Recent reports have shown that inflammatory pathways are the main offender for cisplatin induced nephrotoxicity. The present study was undertaken to assess the effect of rosiglitazone, a PPARgamma agonist and an anti-inflammatory agent, on cisplatin induced nephrotoxicity, and its anticancer activity in DMBA induced breast cancer rats.

METHODS

Mammary tumours were induced in female Sprague-Dawley rats by feeding orally with dimethylbenz [a]anthracene (DMBA) (60 mg/kg). Cisplatin induced nephropathy was assessed by measurements of blood urea nitrogen, albumin and creatinine levels. Posttranslational modifications of histone H3, mitogen-activated protein (MAP) kinase p38 expression and PPAR-gamma expression were examined by western blotting.

RESULTS

Our data shows involvement of TNF-alpha in preventing cisplatin induced nephrotoxicity by rosiglitazone. Rosiglitazone pre-treatment to cisplatin increases the expression of p38, PPAR-gamma in mammary tumours and shows maximum tumour reduction. Furthermore, cisplatin induced changes in histone acetylation, phosphorylation and methylation of histone H3 in mammary tumours was ameliorated by pre-treatment of rosiglitazone. Suggesting, PPAR-gamma directly or indirectly alters aberrant gene expression in mammary tumours by changing histone modifications.

CONCLUSION

To best of our knowledge this is the first report which shows that pre-treatment of rosiglitazone synergizes the anticancer activity of cisplatin and minimizes cisplatin induced nephrotoxicity in DMBA induced breast cancer.

Exploring the pathogenesis of renal cell carcinoma: pathway and bioinformatics analysis of dysregulated genes and proteins

We recently identified a group of proteins which are dysregulated in renal cell carcinoma (RCC). In this study, we performed bioinformatics and pathway analysis of these proteins. Proteins were mapped to gene ontology biological processes. The upregulated proteins tend to cluster in processes, such as cancer initiation and progression. In addition, we identified a number of pathways that are significantly enriched in RCC. Some of these are 'common' pathways which are dysregulated in many cancers, but we also identified a number of pathways which were not previously linked to RCC. In addition to their potential prognostic values, many of these pathways have a potential as therapeutic targets for RCC. To verify our findings, we compared our proteins to a pool of datasets from published reports. Although there were only a minimal number of common proteins, there was a significant overlap between the identified pathways in the two groups. Moreover, out of 16 individually discovered genes identified by a literature search, 10 were found to be related to our dysregulated pathways. We also verified the upregulation of the mammalian target of rapamycin signaling pathway in RCC by immunohistochemistry. Finally, we highlight the potential clinical applications of pathway analysis in kidney cancer.

Multiple aberrations of chromosome 3p detected in oral premalignant lesions

The study of oral premalignant lesions (OPL) is crucial to the identification of initiating genetic events in oral cancer. However, these lesions are minute in size, making it a challenge to recover sufficient DNA from microdissected cells for comprehensive genomic analysis. As a step toward identifying genetic aberrations associated with oral cancer progression, we used tiling-path array comparative genomic hybridization to compare alterations on chromosome 3p for 71 OPLs against 23 oral squamous cell carcinomas. 3p was chosen because although it is frequently altered in oral cancers and has been associated with progression risk, its alteration status has only been evaluated at a small number of loci in OPLs. We identified six recurrent losses in this region that were shared between high-grade dysplasias and oral squamous cell carcinomas, including a 2.89-Mbp deletion spanning the FHIT gene (previously implicated in oral cancer progression). When the alteration status for these six regions was examined in 24 low-grade dysplasias with known progression outcome, we observed that they occurred at a significantly higher frequency in low-grade dysplasias that later progressed to later-stage disease (P < 0.003). Moreover, parallel analysis of all profiled tissues showed that the extent of overall genomic alteration at 3p increased with histologic stage. This first high-resolution analysis of chromosome arm 3p in OPLs represents a significant step toward predicting progression risk in early preinvasive disease and provides a keen example of how genomic instability escalates with progression to invasive cancer.

Peroxisome proliferator-activated receptor gamma agonist pioglitazone prevents the hyperglycemia caused by phosphatidylinositol 3-kinase pathway inhibition by PX-866 without affecting antitumor activity

The phosphatidylinositol 3-kinase (PI3K)/Akt signaling cascade is an important component of the insulin signaling in normal tissues leading to glucose uptake and homeostasis and for cell survival signaling in cancer cells. Hyperglycemia is an on-target side effect of many inhibitors of PI3K/Akt signaling including the specific PI3K inhibitor PX-866. The peroxisome proliferator-activated receptor gamma agonist pioglitazone, used to treat type 2 diabetes, prevents a decrease in glucose tolerance caused by acute administration of PX-866. Our studies have shown that pioglitazone does not inhibit the antitumor activity of PX-866 in A-549 non-small cell lung cancer and HT-29 colon cancer xenografts. In vitro studies also showed that pioglitazone increases 2-[1-(14)C]deoxy-D-glucose uptake in L-6 muscle cells and prevents inhibition of 2-deoxyglucose uptake by PX-866. Neither pioglitazone nor PX-866 had an effect on 2-deoxyglucose uptake in A-549 lung cancer cells. In vivo imaging studies using [18F]2-deoxyglucose (FDG) positron emission tomography showed that pioglitazone increases FDG accumulation by normal tissue but does not significantly alter FDG uptake by A-549 xenografts. Thus, peroxisome proliferator-activated receptor gamma agonists may be useful in overcoming the increase in blood glucose caused by inhibitors of PI3K signaling by preventing the inhibition of normal tissue insulin-mediated glucose uptake without affecting antitumor activity.

In vitro and in vivo anti-melanoma effects of ciglitazone

Activation of PPARgamma by synthetic ligands, thiazolidinediones, inhibits the proliferation of cancer cells. In this report, focusing our attention on ciglitazone, we show that ciglitazone inhibits melanoma growth by inducing apoptosis and cell-cycle arrest, whereas normal melanocytes are resistant to ciglitazone. In melanoma cells, ciglitazone-induced apoptosis is associated with caspase activations and a loss of mitochondrial membrane potential. Induction of cell-cycle arrest by ciglitazone is associated with changes in expression of key cell-cycle regulators such as p21, cyclin D1, and pRB hypophosphorylation. Cell-cycle arrest occurs at low ciglitazone concentrations and through a PPARgamma-dependent pathway, whereas the induction of apoptosis is caused by higher ciglitazone concentrations and independently of PPARgamma. These results allow an effective molecular dissociation between proapoptotic effects and growth inhibition evoked by ciglitazone in melanoma cells. Finally, we show that in vivo treatment of nude mice by ciglitazone dramatically inhibits human melanoma xenograft development. The data presented suggest that ciglitazone might be a better candidate for clinical trials in melanoma treatment than the thiazolidinediones currently used in the treatment of type 2 diabetes, such as rosiglitazone, which is devoid of a proapoptotic PPARgamma-independent function.

Friend or foe? Role of peroxisome proliferator-activated receptor-gamma in human bladder cancer

The peroxisome proliferator-activated receptor (PPAR) family is an important group of transcription factors that regulates immune surveillance, cell proliferation, fatty acid regulation, and angiogenesis--functions which have all been implicated in the pathogenesis of bladder cancer. One particular subtype, PPARgamma, is expressed at higher levels in bladder cancer specimens than in benign urothelium, and is an attractive molecular target for the development of novel treatment strategies for bladder cancer. In this review, we summarize the data available regarding relevance of PPARgamma in bladder cancer and discuss the potential value of PPAR-targeted treatment of bladder cancer.

Expression of the peroxisome proliferator-activated receptors-alpha, -beta, and -gamma in ovarian carcinoma effusions is associated with poor chemoresponse and shorter survival

Peroxisome proliferator-activated receptors regulate lipid metabolism, affecting inflammation and cancer. The present study analyzed the anatomical site-related expression and prognostic role of peroxisome proliferator-activated receptors in ovarian carcinoma. Fresh-frozen effusions (n = 79), primary carcinomas (n = 44), and solid metastases (n = 16) were studied for peroxisome proliferator-activated receptor-alpha, -beta, and -gamma messenger RNA expression using reverse transcriptase polymerase chain reaction. Peroxisome proliferator-activated receptor-gamma messenger RNA expression was further assessed in 60 tumors (30 effusions, 20 primary carcinomas, 10 metastases) using in situ hybridization. Peroxisome proliferator-activated receptor-gamma protein expression was immunohistochemically analyzed in 160 effusions. All peroxisome proliferator-activated receptors were expressed in most tumors at all anatomical sites using reverse transcriptase polymerase chain reaction, but peroxisome proliferator-activated receptor-alpha (P = .004) and peroxisome proliferator-activated receptor-beta (P = .002) messenger RNA levels were higher in effusions compared with primary carcinomas and solid metastases. In situ hybridization localized peroxisome proliferator-activated receptor-gamma messenger RNA to carcinoma cells in both effusions and solid lesions. Peroxisome proliferator-activated receptor-gamma protein was detected in carcinoma cells in 102 of 160 (64%) effusions. Higher effusion messenger RNA levels of all peroxisome proliferator-activated receptors were associated with less favorable response to chemotherapy at diagnosis (P = .009). In univariate survival analysis, higher messenger RNA expression of all peroxisome proliferator-activated receptors was associated with poor progression-free (P = .045) and overall (P = .014) survival. Higher peroxisome proliferator-activated receptor-gamma protein expression was similarly associated with poor overall survival for the entire cohort (P = .046) and for patients with disease recurrence effusions (P = .009). Peroxisome proliferator-activated receptors were not independent predictors of survival in Cox multivariate analysis. Peroxisome proliferator-activated receptor members are frequently expressed in ovarian carcinoma, with upregulated expression in effusions. Peroxisome proliferator-activated receptor expression in effusions is associated with poor response to chemotherapy at disease recurrence and poor survival, suggesting a role in tumor biology at this unique microenvironment.

Curcumin exerts antidifferentiation effect through AMPKalpha-PPAR-gamma in 3T3-L1 adipocytes and antiproliferatory effect through AMPKalpha-COX-2 in cancer cells

Curcumin has been reported to have the potential to prevent obesity as well as cancers. The downstream targets regulated by AMP-activated protein kinase (AMPK) for inhibiting adipocyte differentiation or cancer cell proliferation of curcumin were investigated. The activation of AMPK by curcumin was crucial for the inhibition of differentiation or growth in both adipocytes and cancer cells. Stimulation of AMPK by curcumin resulted in the down-regulation of PPAR (peroxisome proliferator-activated receptor)-gamma in 3T3-L1 adipocytes and the decrease in COX-2 in MCF-7 cells. Application of a synthetic AMPK activator also supported the evidence that AMPK acts as an upstream signal of PPAR-gamma in 3T3-L1 adipocytes. In cancer cells, AMPK was found to act as a regulator of ERK1/2, p38, and COX-2. Regulation of AMPK and its downstream targets such as PPAR-gamma, Mapkinases, and COX-2 by curcumin appears to be important in controlling adipocytes and cancerous cells.

Regulation of Wnt/beta-catenin pathway by cPLA2alpha and PPARdelta

Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) is a rate-limiting key enzyme that releases arachidonic acid (AA) from membrane phospholipid for the production of biologically active lipid mediators including prostaglandins, leukotrienes and platelet-activating factor. cPLA(2)alpha is translocated to nuclear envelope in response to intracellular calcium increase and the enzyme is also present inside the cell nucleus; however, the biological function of cPLA(2)alpha in the nucleus remains unknown. Here we show a novel role of cPLA(2)alpha for activation of peroxisome proliferator-activated receptor-delta (PPARdelta) and beta-catenin in the nuclei. Overexpression of cPLA(2)alpha in human cholangiocarcinoma cells induced the binding of PPARdelta to beta-catenin and increased their association with the TCF/LEF response element. These effects are inhibited by the cPLA(2)alpha siRNA and inhibitors as well as by siRNA knockdown of PPARdelta. Overexpression of PPARdelta or treatment with the selective PPARdelta ligand, GW501516, also increased beta-catenin binding to TCF/LEF response element and increased its reporter activity. Addition of AA and GW501516 to nuclear extracts induced a comparable degree of beta-catenin binding to TCF/LEF response element. Furthermore, cPLA(2)alpha protein is present in the PPARdelta and beta-catenin binding complex. Thus the close proximity between cPLA(2)alpha and PPARdelta provides a unique advantage for their efficient functional coupling in the nucleus, where AA produced by cPLA(2)alpha becomes immediately available for PPARdelta binding and subsequent beta-catenin activation. These results depict a novel interaction linking cPLA(2)alpha, PPARdelta and Wnt/beta-catenin signaling pathways and provide insight for further understanding the roles of these key molecules in human cells and diseases.

Reduced beta-catenin and peroxisome proliferator-activated receptor-gamma expression levels are associated with colorectal cancer metastatic progression: correlation with tumor-associated macrophages, cyclooxygenase 2, and patient outcome

Recent studies have reported cross talk between beta-catenin, peroxisome proliferator-activated receptor-gamma, and cyclooxygenase 2 signaling pathways. We examined whether molecular changes of these pathways could be related to colorectal cancer metastatic progression. Seventy-two sporadic colorectal cancers and the distant nonneoplastic mucosa were analyzed for beta-catenin, peroxisome proliferator-activated receptor-gamma, cyclooxygenase 2, and nuclear factor kappaB levels by immunohistochemistry and Western blot. The expression profiles were correlated with patient outcome and 5-year survival. Nuclear beta-catenin staining was detected in only 18.1% of tumors and correlated with poor survival as compared with cases showing cytosolic/membrane accumulation (59.7%, P < .05). This latter group and tumor samples showing cytosolic/nuclear peroxisome proliferator-activated receptor-gamma expression (70.8%) were significantly associated with a favorable prognosis (P < .001). Remarkably, reduction or loss of beta-catenin (22.2%) and peroxisome proliferator-activated receptor-gamma (29.2%) expression was strongly correlated with marked infiltration of tumor-associated macrophages (P < .01), presence of liver metastases, and very short survival (P = .0001). Moreover, beta-catenin and peroxisome proliferator-activated receptor-gamma levels were inversely correlated with cyclooxygenase 2 (P < .01) and nuclear factor kappaB expression (P < .05). Our results suggest that reduced expression of beta-catenin and peroxisome proliferator-activated receptor-gamma could play a key role in aggressive colorectal cancer behavior. This finding may provide a relevant prognostic tool and contribute to early identification of patients at high risk of mortality.

PPARs Mediate Lipid Signaling in Inflammation and Cancer

Lipid mediators can trigger physiological responses by activating nuclear hormone receptors, such as the peroxisome proliferator-activated receptors (PPARs). PPARs, in turn, control the expression of networks of genes encoding proteins involved in all aspects of lipid metabolism. In addition, PPARs are tumor growth modifiers, via the regulation of cancer cell apoptosis, proliferation, and differentiation, and through their action on the tumor cell environment, namely, angiogenesis, inflammation, and immune cell functions. Epidemiological studies have established that tumor progression may be exacerbated by chronic inflammation. Here, we describe the production of the lipids that act as activators of PPARs, and we review the roles of these receptors in inflammation and cancer. Finally, we consider emerging strategies for therapeutic intervention.

Troglitazone inhibits cell migration, adhesion, and spreading by modulating cytoskeletal rearrangement in human breast cancer cells

Metastatic tumors are the primary cause of death in patients with breast cancer. Recent data indicate that the peroxisome proliferator-activated receptor gamma (PPARgamma) ligands, thiazolidinediones (TZDs), possess anti-invasive activities on human breast cancer cells. However, the effects of TZDs on other metastatic properties of breast cancer cells such as adhesion, spreading, and migration are not well established. In this study, we show that troglitazone (TG), a member of the TZD family, inhibits lamellipodia formation or membrane ruffling as well as actin polymerization at these structures in MDA-MB-231 and T47D breast cancer cells. In addition, TG reduces migration, adhesion, and spreading on fibronectin (FN)-coated plates. These phenomena were associated with the dramatic decrease of Tyr397 and Tyr576 phosphorylation of focal adhesion kinase (FAK) and the detergent-insoluble Rac1. We also found that TG upregulates Tyr416 phosphorylation of Src, but downregulates the Src-FAK complex. Moreover, we use a PPARgamma-inactive derivative of TG (STG28) and a PPARgamma antagonist (GW9662) to eliminate PPARgamma-mediated effects. We found that treatment with STG28 or GW9662 plus TG showed similar effects compared to TG treatment alone on tyrosine phosphorylation of FAK and Src, indicating that these effects are not the result of PPARgamma activation. Interestingly, we found that TG upregulates actin filament assembly at the point of cell-cell contact in T47D cells, indicating that TG may also upregulate cell-cell adhesion in breast cancer cells which express E-cadherin. These results suggested that TG should be investigated further for its therapeutic potential in metastatic breast cancer.

Regression of drug-resistant lung cancer by the combination of rosiglitazone and carboplatin

PURPOSE

Current therapy for lung cancer involves multimodality therapies. However, many patients are either refractory to therapy or develop drug resistance. KRAS and epidermal growth factor receptor (EGFR) mutations represent some of the most common mutations in lung cancer, and many studies have shown the importance of these mutations in both carcinogenesis and chemoresistance. Genetically engineered murine models of mutant EGFR and KRAS have been developed that more accurately recapitulate human lung cancer. Recently, using cell-based experiments, we showed that platinum-based drugs and the antidiabetic drug rosiglitazone (PPARgamma ligand) interact synergistically to reduce cancer cell and tumor growth. Here, we directly determined the efficacy of the PPARgamma/carboplatin combination in these more relevant models of drug resistant non-small cell lung cancer.

EXPERIMENTAL DESIGN

Tumorigenesis was induced by activation of either mutant KRAS or EGFR. Mice then received either rosiglitazone or carboplatin monotherapy, or a combination of both drugs. Change in tumor burden, pathology, and evidence of apoptosis and cell growth were assessed.

RESULTS

Tumor burden remained unchanged or increased in the mice after monotherapy with either rosiglitazone or carboplatin. In striking contrast, we observed significant tumor shrinkage in mice treated with these drugs in combination. Immunohistochemical analyses showed that this synergy was mediated via both increased apoptosis and decreased proliferation. Importantly, this synergy between carboplatin and rosiglitazone did not increase systemic toxicity.

CONCLUSIONS

These data show that the PPARgamma ligand/carboplatin combination is a new therapy worthy of clinical investigation in lung cancers, including those cancers that show primary resistance to platinum therapy or acquired resistance to targeted therapy.

PPARdelta is a ligand-dependent negative regulator of vitamin D3-induced monocyte differentiation

A number of reports indicate that peroxisome proliferator-activated receptor (PPAR) delta is involved in the molecular control of monocyte-macrophage differentiation. In this regard, the recent demonstration that PPARdelta is a primary response gene of 1alpha,25-dihydroxyvitamin D3 (VD), i.e. a powerful inducer of such process, allowed us to hypothesize the existence of a cross talk between PPARdelta and VD receptor pathways. To address this issue, we analyzed the effects promoted by stimulation with PPARdelta ligands and by overexpression of this nuclear receptor in monoblastic cell lines undergoing exposure to VD. The results obtained evidenced that, although promoting a weak differentiation effect by themselves, PPARdelta ligands efficiently co-operated with VD treatment. In spite of this, PPARdelta overexpression exerted a remarkable inhibitory effect on monocyte-macrophage differentiation induced by VD that was, at least partly, reverted by stimulation with a highly specific PPARdelta ligand. These data indicate that, although acting through a ligand-dependent modality, PPARdelta is a negative regulator of VD-mediated monocyte differentiation, allowing us to hypothesize a role of the investigated nuclear receptor in the differentiation block of M5 type (monoblastic) acute myeloid leukemias (AMLs). Bioinformatic analysis of a microarray database, containing the expression profiles of 285 AML cases, further supported this hypothesis demonstrating the existence of a subset of M5 type (monoblastic) AMLs that overexpress PPARdelta gene.

Low-penetrance alleles predisposing to sporadic colorectal cancers: a French case-controlled genetic association study

Background

Sporadic colorectal cancers (CRC) are multifactorial diseases resulting from the combined effects of numerous genetic, environmental and behavioral risk factors. Genetic association studies have suggested low-penetrance alleles of extremely varied genes to be involved in susceptibility to CRC in Caucasian populations.

Methods

Through a large genetic association study based on 1023 patients with sporadic CRC and 1121 controls, we tested a panel of these low-penetrance alleles to find out whether they could determine "genotypic profiles" at risk for CRC among individuals of the French population. We examined 52 polymorphisms of 35 genes – drawn from inflammation, xenobiotic detoxification, one-carbon, insulin signaling, and DNA repair pathways – for their possible contribution to colorectal carcinogenesis. The risk of cancer associated with these polymorphisms was assessed by calculation of odds ratios (OR) using multivariate analyses and logistic regression.

Results

Whereas all these polymorphisms had previously been found to be associated with CRC risk, especially in Caucasian populations, we were able to replicate the association for only five of them. Three SNPs were shown to increase CRC risk: PTGS1 c.639C>A (p.Gly213Gly), IL8 c.-352T>A, and MTHFR c.1286A>C (p.Ala429Glu). On the contrary, two other SNPs, PLA2G2A c.435+230C>T and PPARG c.1431C>T (p.His477His), were associated with a decrease in CRC risk. Further analyses highlighted genotypic combinations having a greater predisposing effect on CRC (OR 1.97, 95%CI 1.31–2.97, p = 0.0009) than the allelic variants that were examined separately.

Conclusion

The identification of CRC-predisposing combinations, composed of alleles PTGS1 c.639A, PLA2G2A c.435+230C, PPARG c.1431C, IL8 c.-352A, and MTHFR c.1286C, highlights the importance of inflammatory processes in susceptibility to sporadic CRC, as well as a possible crosstalk between inflammation and one-carbon pathways.

Biomarkers for early effects of carcinogenic dual-acting PPAR agonists in rat urinary bladder urotheliumin vivo

Small-molecule agonists of the peroxisome proliferator-activated receptor (PPAR) alpha and gamma isoforms (dual-acting PPAR agonists) can cause urothelial cancers in rodents. Rats were dosed orally for 16 days with bladder carcinogenic (ragaglitazar) as well as non-bladder carcinogenic (fenofibrate and rosiglitazone) PPAR agonists and protein changes were assayed in the urinary bladder urothelium by Western blotting. Dose levels reflected 10-20 x human exposure, and the ragaglitazar dose was in the carcinogenic range. Ragaglitazar induced expression of the transcription factor Egr-1, phosphorylation of the c-Jun transcription factor and phosphorylation of the ribosomal S6 protein were observed. These changes were also observed in rats dosed with either rosiglitazone or fenofibrate. However, the protein changes were stronger (Egr-1 induction) or of a longer duration (S6 phosphorylation) in ragaglitazar-treated animals. Animals co-administered fenofibrate (a specific PPARalpha agonist) and rosiglitazone (a specific PPARgamma agonist) exhibited Egr-1 and S6 protein changes more similar to those induced by ragaglitazar (a dual-acting PPARalpha/gamma agonist) than either fenofibrate or rosiglitazone alone. The findings suggest that ragaglitazar causes Egr-1, c-Jun and S6 protein changes in the urothelium by a mechanism involving PPARalpha as well as PPARgamma, and that the Egr-1, c-Jun and S6 protein changes might have potential biomarker value.

PPAR gamma ligands, rosiglitazone and pioglitazone, inhibit bFGF- and VEGF-mediated angiogenesis

OBJECTIVE

To study the effect of peroxisome proliferator-activated receptor-gamma (PPAR gamma) agonists, pioglitazone and rosiglitazone, on vascular endothelial growth factor (VEGF)- and basic fibroblast growth factor (bFGF)-induced angiogenesis and on endothelial cell migration.

METHODS

Chick chorioallantoic membrane (CAM) model was used to evaluate the efficacy of pioglitazone and rosiglitazone on VEGF- and bFGF-induced angiogenesis. In addition, the effect of pioglitazone and rosiglitazone on endothelial cell migration was evaluated using 8 mm pore filter to a feeder layer containing vitronectin as chemoattractant.

RESULTS

Pioglitazone and rosiglitazone inhibited the pro-angiogenic effects of bFGF and VEGF in the CAM model significantly (P < 0.001) to the same extent. Endothelial cell migration was also inhibited by both pioglitazone and rosiglitazone (P < 0.001).

CONCLUSIONS

These results suggest that PPAR gamma ligands, pioglitazone and rosiglitazone, in addition to their important regulatory role in adipogenesis and inflammation, possess anti-angiogenic properties. Thus, PPAR gamma ligands may be useful in the treatment of diabetic retinopathy, macular degeneration, and other ocular disorders and may lower the risk to develop cancer in diabetic patients.

Mesodermal fate decisions of a stem cell: the Wnt switch

Stem cells are a powerful resource for cell-based transplantation therapies in osteodegenerative disorders, but before some kinds of stem cells can be applied clinically, several aspects of their expansion and differentiation need to be better controlled. Wnt molecules and members of the Wnt signaling cascade have been ascribed a role in both these processes in vitro as well as normal development in vivo. However some results are controversial. In this review we will present the hypothesis that both canonical and non-canonical signaling are involved in mesenchymal cell fate regulation, such as adipogenesis, chondrogenesis and osteogenesis, and that in vitro it is a timely switch between the two that specifies the identity of the differentiating cell. We will specifically focus on the in vitro differentiation of adipocytes, chondrocytes and osteoblasts contrasting embryonic and mesenchymal stem cells as well as the role of Wnts in mesenchymal fate specification during embryogenesis.

Role of peroxisome-proliferator-activated receptor beta/delta (PPARbeta/delta) in gastrointestinal tract function and disease

PPARbeta/delta (peroxisome-proliferator-activated receptor beta/delta) is one of three PPARs in the nuclear hormone receptor superfamily that are collectively involved in the control of lipid homoeostasis among other functions. PPARbeta/delta not only acts as a ligand-activated transcription factor, but also affects signal transduction by interacting with other transcription factors such as NF-kappaB (nuclear factor kappaB). Constitutive expression of PPARbeta/delta in the gastrointestinal tract is very high compared with other tissues and its potential physiological roles in this tissue include homoeostatic regulation of intestinal cell proliferation/differentiation and modulation of inflammation associated with inflammatory bowel disease and colon cancer. Analysis of mouse epithelial cells in the intestine and colon has clearly demonstrated that ligand activation of PPARbeta/delta induces terminal differentiation. The PPARbeta/delta target genes mediating this effect are currently unknown. Emerging evidence suggests that PPARbeta/delta can suppress inflammatory bowel disease through PPARbeta/delta-dependent and ligand-independent down-regulation of inflammatory signalling. However, the role of PPARbeta/delta in colon carcinogenesis remains controversial, as conflicting evidence suggests that ligand activation of PPARbeta/delta can either potentiate or attenuate this disease. In the present review, we summarize the role of PPARbeta/delta in gastrointestinal physiology and disease with an emphasis on findings in experimental models using both high-affinity ligands and null-mouse models.

Thiazolidinediones downregulate Wnt/beta-catenin signaling via multiple mechanisms in breast cancer cells

BACKGROUND

Thiazolidinediones (TZDs) have been demonstrated to possess antitumor effects in breast cancer cells, although the mechanisms are not well established. We sought to better define TZDs' antitumor effects and molecular mechanisms to permit rational utilization of these agents.

MATERIALS AND METHODS

We studied the effects of TZDs on DNA synthesis (BrdU enzyme-linked immunosorbent assay), gene expression (microarray, quantitative reverse transcription-polymerase chain reaction, and immunoblot), serine phosphorylation and localization of beta-catenin (nuclear/cytoplasmic fractionation and immunoblot), transactivation activity of beta-catenin/T cell factor 4 (TCF4) (luciferase assay with wild-type and mutant TCF4 responsive element), and beta-catenin/TCF4 complex (immunoprecipitation) in human breast cancer cells MDA-MB-231 and T47D.

RESULTS

Troglitazone (TG) down-regulated DNA synthesis in MDA-MB-231 and T47D and decreased mRNA expression of the Wnt co-receptors frizzled-1 and low-density lipoprotein-related protein 6 (LRP6) as well as protein level of LRP6. TG also targets downstream Wnt signaling molecules in T47D cells. TG down-regulates p-beta-catenin (S33/S37/T41) and promotes translocation of beta-catenin into the nucleus. However, TG inhibits beta-catenin-mediated transactivation by down-regulating TCF4 protein levels, thereby inhibiting beta-catenin/TCF4 complex formation. Finally, we found that inhibition of Akt augments TG-mediated down-regulation of DNA synthesis and this result was accompanied with the decreased protein levels of Wnt signaling molecules: LRP6, beta-catenin, and TCF4.

CONCLUSION

These results suggest that the Wnt/beta-catenin signaling pathway, which plays an important role in breast cancer pathogenesis, may be a target for TZD treatment. Moreover, a combination of TZDs and a specific Akt inhibitor may serve as a new approach to target Wnt/beta-catenin directly and via PI3K/Akt action on glycogen synthase-3beta.

Peroxisome proliferator-activated receptor beta/delta expression and activation in lung cancer

Peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) is a ligand-binding inducible transcriptional factor linked to carcinogenesis. Important functions of PPARbeta/delta were demonstrated in series of human epithelial cancers; however, its role in lung cancer remains controversial. We investigated the differential expression level and localization of PPARbeta/delta in tumors and adjacent normal lung tissue, and the effect of PPARbeta/delta activation on lung cancer cell proliferation and apoptosis. PPARbeta/delta was expressed in all studied human non-small cell lung cancers, and strong PPARbeta/delta immunoreactivity was observed in epithelial cells of more than 75% of studied lung tumors. PPARbeta/delta expression was consistently limited to the cancer cells in tumor tissue, while in adjacent normal lung tissue it was limited predominantly to the mononuclear cells. We found that ligand-binding activation of PPARbeta/delta stimulates cell proliferation (an effect that was blocked by a dominant-negative construct of PPARbeta/delta), stimulates anchorage-independent cell growth, and inhibits apoptosis in lung cancer cell lines. Importantly, the activation of PPARbeta/delta induces Akt phosphorylation correlated with up-regulation of PDK1, down-regulation of PTEN, and increased expression of Bcl-xL and COX-2. These findings indicate that PPARbeta/delta exerts proliferative and anti-apoptotic effects via PI3K/Akt1 and COX-2 pathways. In conclusion, PPARbeta/delta is strongly expressed in the majority of lung cancers, and its activation induces proliferative and survival response in non-small cell lung cancer.

PPAR{gamma} accelerates cellular senescence by inducing p16INK4{alpha} expression in human diploid fibroblasts

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays an important role in the inhibition of cell growth by promoting cell-cycle arrest, and PPARgamma activation induces the expression of p16(INK4alpha) (CDKN2A), an important cell-cycle inhibitor that can induce senescence. However, the role of PPARgamma in cellular senescence is unknown. Here, we show that PPARgamma promotes cellular senescence by inducing p16(INK4alpha) expression. We found several indications that PPARgamma accelerates cellular senescence, including enhanced senescence-associated (SA)-beta-galactosidase staining, increased G1 arrest and delayed cell growth in human fibroblasts. Western blotting studies demonstrated that PPARgamma activation can upregulate the expression of p16(INK4alpha). PPARgamma can bind to the p16 promoter and induce its transcription, and, after treatment with a selective PPARgamma agonist, we observed more-robust expression of p16(INK4alpha) in senescent cells than in young cells. In addition, our data indicate that phosphorylation of PPARgamma decreased with increased cell passage. Our results provide a possible molecular mechanism underlying the regulation of cellular senescence.

Statins and prostate cancer prevention: where we are now, and future directions

Statins are cholesterol-lowering drugs that are widely used to prevent and treat atherosclerotic cardiovascular disease. Recent research from both in vitro and in vivo studies suggests that there is an association between the use of statins and a reduction in the incidence of and mortality from prostate cancer. Several mechanisms of action that might bring about these beneficial effects of statins have been proposed, most of which include direct effects of statins on intracellular signaling. In this Review we discuss the current knowledge on the use of statins to prevent prostate cancer. We will also look at future directions for clinical research on this topic.

A gut feeling of the PXR, PPAR and NF-kappaB connection

Bowel diseases reveal the complex interplay of sensing and signalling pathways in maintaining healthy homeostasis of the intestine. Recent studies of the xenobiotic nuclear receptor, pregnane X receptor and the inflammatory mediator nuclear transcription factor kappaB (NF-kappaB) reveal a functional link between xenobiotic neutralization and inflammation and explain how certain xenobiotics can affect the immune response. Furthermore, another nuclear receptor, peroxisome proliferator-activated receptor gamma (PPAR gamma) has been shown to produce beneficial effects in experimental inflammatory bowel diseases by repression of NF-kappaB thereby reducing inflammation, whilst its close relative PPAR beta/delta appears at a central position in signalling pathways involved in the progression of colon cancer. Recently accumulated knowledge on the action of these nuclear receptors and NF-kappaB in intestinal homeostasis may provide the rationale for the development of innovative treatment strategies with selective receptor modulators.

Analysis of Pro12Ala PPAR gamma polymorphism and Helicobacter pylori infection in gastric adenocarcinoma and peptic ulcer disease

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-dependent transcription factor involved in various disease processes including inflammation and carcinogenesis. We investigated the association of Pro12Ala PPARgamma polymorphism and Helicobacter pylori infection with gastric cancer and peptic ulcer disease (PUD).

PATIENTS AND METHODS

In total, 348 adult patients [62 gastric adenocarcinoma, 45 PUD and 241 nonulcer dyspepsia (NUD)] who underwent an upper gastrointestinal endoscopy were enrolled. PPARgamma polymorphism was analyzed by PCR-based restriction fragment length polymorphism. H. pylori infection was diagnosed by rapid urease test, culture, histopathology and PCR.

RESULTS

PPARgamma G carrier had significant association with gastric adenocarcinoma [P = 0.023, odds ratio (OR) = 2.136, 95% CI = 1.112-4.104] and PUD (P = 0.028, OR = 2.165, 95% CI = 1.008-4.306) when compared with NUD. Combination of G carrier and H. pylori infection further increased the risk of gastric adenocarcinoma (OR = 3.054, 95% CI = 1.195-7.807) and PUD (OR = 11.161, 95% CI = 3.495-35.644). PPARgamma polymorphism did not increase the risk of gastric adenocarcinoma and PUD in H. pylori-negative subjects.

CONCLUSIONS

The study suggests that Pro12Ala PPARgamma polymorphism is associated with gastric adenocarcinoma and PUD, and is a potential marker for genetic susceptibility to these two diseases in the presence of H. pylori infection.

Peroxisome proliferator-activated receptors (PPARs) and the human skin: importance of PPARs in skin physiology and dermatologic diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that regulate lipid, glucose, and amino acid metabolism. More recently, PPARs and corresponding ligands have been shown in skin and other organs to regulate important cellular functions, including cell proliferation and differentiation, as well as inflammatory responses. These new functions identify PPARs and corresponding ligands as potential targets for the treatment of various skin diseases and other disorders. It has been shown that in inflammatory skin disorders, including hyperproliferative psoriatic epidermis and the skin of patients with atopic dermatitis, the expression of both PPARalpha and PPARgamma is decreased. This observation suggests the possibility that PPARalpha and PPARgamma activators, or compounds that positively regulate PPAR gene expression, may represent novel NSAIDs for the topical or systemic treatment of common inflammatory skin diseases such as atopic dermatitis, psoriasis, and allergic contact dermatitis. Moreover, recent findings indicate that PPAR-signaling pathways may act as a promising therapeutic target for the treatment of hyperproliferative skin diseases including skin malignancies. Studies in non-diabetic patients suggest that oral thiazolidinediones, which are synthetic ligands of PPARgamma, not only exert an antidiabetic effect but also may be beneficial for moderate chronic plaque psoriasis by suppressing proliferation and inducing differentiation of keratinocytes; furthermore, they may even induce cell growth arrest, apoptosis, and terminal differentiation in various human malignant tumors. It has been reported that PPARalpha immunoreactivity is reduced in human keratinocytes of squamous cell carcinoma (SCC) and actinic keratosis (AK), while PPARdelta appears to be upregulated. Additionally, the microvessel density is significantly higher in AK and SCC that express high levels of PPARdelta. PPARdelta has been demonstrated to have an anti-apoptotic role and to maintain survival and differentiation of epithelial cells, whereas PPARalpha and PPARgamma activators induce differentiation and inhibit proliferation and regulate apoptosis. In melanoma, the growth inhibitory effect of PPARgamma activation is independent of apoptosis and seems to occur primarily through induction of cell cycle arrest in the G1 phase of the cell cycle or induction of re-differentiation. PPARalpha activation causes inhibition of migration of melanoma cells and anchorage-independent growth, whereas primary tumor growth remains unaltered. In clinical trials of gemfibrozil, a PPARalpha ligand, significantly fewer patients treated with this lipid-lowering drug were diagnosed with melanoma as compared to those in the control group. In conclusion, an increasing body of evidence indicates that PPAR signaling pathways may represent interesting therapeutic targets for a broad variety of skin disorders, including inflammatory skin diseases such as psoriasis and atopic dermatitis, and skin malignancies.

An immunohistochemical perspective of PPAR beta and one of its putative targets PDK1 in normal ovaries, benign and malignant ovarian tumours

Peroxisome proliferator-activated receptor beta (PPAR beta) is a member of the nuclear hormone receptor family and is a ligand-activated transcription factor with few known molecular targets including 3-phosphoinositide-dependent protein kinase 1(PDK1). In view of the association of PPAR beta and PDK1 with cancer, we have examined the expression of PPAR beta and PDK1 in normal ovaries and different histological grades of ovarian tumours. Normal ovaries, benign, borderline, grades 1, 2 and 3 ovarian tumours of serous, muciuous, endometrioid, clear cell and mixed subtypes were analysed by immunohistochemistry for PPAR beta and PDK1 expression. All normal ovarian tissues, benign, borderline and grade 1 tumours showed PPAR beta staining localised in the epithelium and stroma. Staining was predominantly nuclear, but some degree of cytoplasmic staining was also evident. Approximately 20% of grades 2 and 3 tumours lacked PPAR beta staining, whereas the rest displayed some degree of nuclear and cytoplasmic staining of the scattered epithelium and stroma. The extent of epithelial and stromal PPAR beta staining was significantly different among the normal and the histological grades of tumours (chi(2)=59.25, d.f.=25, P<0.001; chi(2)=64.48, d.f.=25, P<0.001). Significantly different staining of PPAR beta was observed in the epithelium and stroma of benign and borderline tumours compared with grades 1, 2 and 3 tumours (chi(2)=11.28, d.f.=4, P<0.05; chi(2)=16.15, d.f.=4, P<0.005). In contrast, PDK1 immunostaining was absent in 9 out of 10 normal ovaries. Weak staining for PDK1 was observed in one normal ovary and 40% of benign ovarian tumours. All borderline and malignant ovarian tumours showed positive cytoplasmic and membrane PDK1 staining. Staining of PDK1 was confined to the epithelium and the blood vessels, and no apparent staining of the stroma was evident. Significantly different PDK1 staining was observed between the benign/borderline and malignant ovarian tumours (chi(2)=22.45, d.f.=5, P<0.001). In some borderline and high-grade tumours, staining of the reactive stroma was also evident. Our results suggest that unlike the colon, the endometrial, head and neck carcinomas, overexpression of PPAR beta does not occur in ovarian tumours. However, overexpression of PDK1 was evident in borderline and low- to high-grade ovarian tumours and is consistent with its known role in tumorigenesis.

RNA interference against peroxisome proliferator-activated receptor delta gene promotes proliferation of human colorectal cancer cells

PURPOSE

This study was designed to investigate the effects of peroxisome proliferator-activated receptor delta (PPAR delta) on the proliferation and apoptosis of human colorectal cancer cells.

METHODS

For RNA interfering (RNAi), HCT-116 cells were transfected with short hairpin RNA (shRNA)-expressing plasmids against PPAR delta or negative control vectors, and the stably transfected cells were selected with G418. The efficacy of RNAi was assessed by real-time reverse transcription polymerase chain reaction (RT-PCR) and Western blotting analysis. The proliferation, cell cycle, and apoptosis of HCT-116 cells treated by RNAi, compared with those containing control vectors or untreated, were analyzed respectively by using MTT (methyl thiazolyl tetrazolium), flow cytometry, and TdT (terminal deoxynucleotidyl transferase)-mediated dUTP nick end-labeling (TUNEL) assay.

RESULTS

RNAi targeting PPAR delta resulted in substantial suppression of PPAR delta expression and significantly promoted the proliferation of HCT-116 cells relative to those with control vectors or untreated, obviously decreasing the frequency of G1-phase cells but had no effect on cell apoptosis.

CONCLUSIONS

PPAR delta may inhibit the proliferation of CRC cells and increase the number of cells in G1 phase, without any function in cell apoptosis.

Meta-analysis of primary target genes of peroxisome proliferator-activated receptors

A combined experimental and in silico approach identifies Peroxisome Proliferator Activated Receptor (PPAR) binding sites and six novel target genes in the human genome.

Background

Peroxisome proliferator-activated receptors (PPARs) are known for their critical role in the development of diseases, such as obesity, cardiovascular disease, type 2 diabetes and cancer. Here, an in silico screening method is presented, which incorporates experiment- and informatics-derived evidence, such as DNA-binding data of PPAR subtypes to a panel of PPAR response elements (PPREs), PPRE location relative to the transcription start site (TSS) and PPRE conservation across multiple species, for more reliable prediction of PPREs.

Results

In vitro binding and in vivo functionality evidence agrees with in silico predictions, validating the approach. The experimental analysis of 30 putative PPREs in eight validated PPAR target genes indicates that each gene contains at least one functional, strong PPRE that occurs without positional bias relative to the TSS. An extended analysis of the cross-species conservation of PPREs reveals limited conservation of PPRE patterns, although PPAR target genes typically contain strong or multiple medium strength PPREs. Human chromosome 19 was screened using this method, with validation of six novel PPAR target genes.

Conclusion

An in silico screening approach is presented, which allows increased sensitivity of PPAR binding site and target gene detection.

Genetically determined susceptibility to COX-2 inhibitors: a report of exaggerated responders to diclofenac 3% gel in the treatment of actinic keratoses

Diclofenac 3% gel is an effective treatment for actinic keratoses (AKs) and is reported to be generally well tolerated with only mild local reactions. However, there is a subset of patients that seem to be susceptible to developing severe local reactions following application of diclofenac 3% gel. Although some of these reactions can be explained as being allergic contact dermatitis and/or photoallergic contact dermatitis, others cannot. We report a series of 10 patients who all developed severe local reactions following application of diclofenac 3% gel, despite negative diclofenac patch testing. This raises the question as to whether there is a subset of patients with skin cancer or AK lesions that are highly/more susceptible to local reactions caused by cyclo-oxygenase-2 (COX-2) inhibitors and peroxisome proliferator-activated receptor (PPAR) agonists? We speculate that underlying molecular differences exist in these patients that make the skin more susceptible to COX-2 inhibitors.

PPARalpha agonist fenofibrate suppresses tumor growth through direct and indirect angiogenesis inhibition

Angiogenesis and inflammation are central processes through which the tumor microenvironment influences tumor growth. We have demonstrated recently that peroxisome proliferator-activated receptor (PPAR)alpha deficiency in the host leads to overt inflammation that suppresses angiogenesis via excess production of thrombospondin (TSP)-1 and prevents tumor growth. Hence, we speculated that pharmacologic activation of PPARalpha would promote tumor growth. Surprisingly, the PPARalpha agonist fenofibrate potently suppressed primary tumor growth in mice. This effect was not mediated by cancer-cell-autonomous antiproliferative mechanisms but by the inhibition of angiogenesis and inflammation in the host tissue. Although PPARalpha-deficient tumors were still susceptible to fenofibrate, absence of PPARalpha in the host animal abrogated the potent antitumor effect of fenofibrate. In addition, fenofibrate suppressed endothelial cell proliferation and VEGF production, increased TSP-1 and endostatin, and inhibited corneal neovascularization. Thus, both genetic abrogation of PPARalpha as well as its activation by ligands cause tumor suppression via overlapping antiangiogenic pathways. These findings reveal the potential utility of the well tolerated PPARalpha agonists beyond their use as lipid-lowering drugs in anticancer therapy. Our results provide a mechanistic rationale for evaluating the clinical benefits of PPARalpha agonists in cancer treatment, alone and in combination with other therapies.

Lipoxygenase metabolism: roles in tumor progression and survival

The metabolism of arachidonic acid through lipoxygenase pathways leads to the generation of various biologically active eicosanoids. The expression of these enzymes vary throughout the progression of various cancers, and thereby they have been shown to regulate aspects of tumor development. Substantial evidence supports a functional role for lipoxygenase-catalyzed arachidonic and linoleic acid metabolism in cancer development. Pharmacologic and natural inhibitors of lipoxygenases have been shown to suppress carcinogenesis and tumor growth in a number of experimental models. Signaling of hydro[peroxy]fatty acids following arachidonic or linoleic acid metabolism potentially effect diverse biological phenomenon regulating processes such as cell growth, cell survival, angiogenesis, cell invasion, metastatic potential and immunomodulation. However, the effects of distinct LOX isoforms differ considerably with respect to their effects on both the individual mechanisms described and the tumor being examined. 5-LOX and platelet type 12-LOX are generally considered pro-carcinogenic, with the role of 15-LOX-1 remaining controversial, while 15-LOX-2 suppresses carcinogenesis. In this review, we focus on the molecular mechanisms regulated by LOX metabolism in some of the major cancers. We discuss the effects of LOXs on tumor cell proliferation, their roles in cell cycle control and cell death induction, effects on angiogenesis, migration and the immune response, as well as the signal transduction pathways involved in these processes. Understanding the molecular mechanisms underlying the anti-tumor effect of specific, or general, LOX inhibitors may lead to the design of biologically and pharmacologically targeted therapeutic strategies inhibiting LOX isoforms and/or their biologically active metabolites, that may ultimately prove useful in the treatment of cancer, either alone or in combination with conventional therapies.

Quantitative analysis of the effect of Helicobacter pylori on the expressions of SOX2, CDX2, MUC2, MUC5AC, MUC6, TFF1, TFF2, and TFF3 mRNAs in human gastric carcinoma cells

OBJECTIVE

To investigate the phenotypic characters of carcinoma cells and the response of gastric epithelial cells to Helicobacter pylori (H. pylori) infection using the gastric carcinoma cell lines.

MATERIAL AND METHODS

Real-time reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the effect of H. pylori infection on mRNA levels of transcription factors (SOX2 and CDX2), mucin core proteins (MUC2, MUC5AC, and MUC6), and trefoil factor family peptides (TFF) (TFF1, TFF2, and TFF3) in gastric carcinoma cells (AGS, MKN45, and KATO III cells). H. pylori ATCC 43504 and its isogenic cag pathogenicity island (PAI) deleted mutant were used.

RESULTS

These cell lines expressed mixed gastric and intestinal phenotypes. The intestinal phenotype predominated in AGS cells and gastric phenotypes in MKN45 and KATO III cells. In all three cell lines, H. pylori infection inhibited SOX2 mRNA expression, but induced the three TFFs mRNAs. In AGS cells, H. pylori induced cag PAI-dependent mRNA expression of CDX2, MUC2, MUC5AC, and MUC6. mRNA expressions of CDX2, MUC5AC, and MUC6 were inhibited in KATO III cells, whereas MUC2 mRNA expression was unchanged. In MKN45 cells, H. pylori induced the three MUCs mRNAs but inhibited CDX2 mRNA expression.

CONCLUSIONS

This study provides a useful platform for selecting appropriate cell lines to model H. pylori-related changes in the gastric epithelium that mirror the changes seen in vivo. The outcome of H. pylori infection may reflect changes in the mucus gel layer caused by altered expression of mucins and TFF peptides.

Synergistic Effects of PPARgamma Ligands and Retinoids in Cancer Treatment

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily. The activation of PPARs by their specific ligands is regarded as one of the promising strategies to inhibit cancer cell growth. However, recent clinical trials targeting several common cancers showed no beneficial effect when PPAR ligands are used as a monotherapy. Retinoid X receptors (RXRs), which play a critical role in normal cell proliferation as a master regulator for nuclear receptors, preferentially form heterodimers with PPARs. A malfunction of RXRalpha due to phosphorylation by the Ras/MAPK signaling pathway is associated with the development of certain types of human malignancies. The activation of PPARgamma/RXR heterodimer by their respective ligands synergistically inhibits cell growth, while inducing apoptosis in human colon cancer cells when the phosphorylation of RXRalpha was inhibited. We herein review the synergistic antitumor effects produced by the combination of the PPAR, especially PPARgamma, ligands plus other agents, especially retinoids, in a variety of human cancers. We also focus on the phosphorylation of RXRalpha because the inhibition of RXRalpha phosphorylation and the restoration of its physiological function may activate PPAR/RXR heterodimer and, therefore, be a potentially effective and critical strategy for the inhibition of cancer cell growth.

PPARalpha Ligands as Antitumorigenic and Antiangiogenic Agents

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor family of ligand-activated transcription factors. This subfamily is composed of three members-PPARalpha, PPARdelta, and PPARgamma-that differ in their cell and tissue distribution as well as in their target genes. PPARalpha is abundantly expressed in liver, brown adipose tissue, kidney, intestine, heart, and skeletal muscle; and its ligands have been used to treat diseases such as obesity and diabetes. The recent finding that members of the PPAR family, including the PPARalpha, are expressed by tumor and endothelial cells together with the observation that PPAR ligands regulate cell growth, survival, migration, and invasion, suggested that PPARs also play a role in cancer. In this review, we focus on the contribution of PPARalpha to tumor and endothelial cell functions and provide compelling evidence that PPARalpha can be viewed as a new class of ligand activated tumor "suppressor" gene with antiangiogenic and antitumorigenic activities. Given that PPAR ligands are currently used in medicine as hypolipidemic drugs with excellent tolerance and limited toxicity, PPARalpha activation might offer a novel and potentially low-toxic approach for the treatment of tumor-associated angiogenesis and cancer.

Peroxisome proliferator-activated receptor-beta/delta protects against chemically induced liver toxicity in mice

Potential functional roles for the peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta) in skeletal muscle fatty acid catabolism and epithelial carcinogenesis have recently been described. Whereas PPARbeta/delta is expressed in liver, its function in this tissue is less clear. To determine the role of PPARbeta/delta in chemically induced liver toxicity, wild-type and PPARbeta/delta-null mice were treated with azoxymethane (AOM) and markers of liver toxicity examined. Bile duct hyperplasia, regenerative hyperplasia, and increased serum alanine aminotransferase (ALT) were found in AOM-treated PPARbeta/delta-null mice, and these effects were not observed in similarly treated wild-type mice. Exacerbated carbon tetrachloride (CCl(4)) hepatoxicity was also observed in PPARbeta/delta-null as compared with wild-type mice. No differences in messenger RNAs (mRNAs) encoding cytochrome2E1 required for the metabolic activation of AOM and CCl(4) were observed between wild-type or PPARbeta/delta-null mice in response to CCl(4). Significant differences in the expression of genes reflecting enhanced nuclear factor kappa B (NF-kappaB) activity were noted in PPARbeta/delta-null mice.

CONCLUSION

Results from these studies show that PPARbeta/delta is protective against liver toxicity induced by AOM and CCl(4), suggesting that this receptor is hepatoprotective against environmental chemicals that are metabolized in this tissue.

PPARbeta/delta protects against experimental colitis through a ligand-independent mechanism

Peroxisome proliferator-activated receptors (PPARs) beta/delta and gamma have overlapping roles in the negative regulation of inflammatory response genes. Ligand activation of PPARgamma protects against experimental colitis in mice. PPARbeta/delta can negatively regulate inflammation and is highly expressed in the epithelial cells of the colon, therefore PPARbeta/delta may also have a role in experimental colitis. In these studies, colitis was induced by dextran sodium sulfate (DSS) treatment in wild-type and PPARbeta/delta-null mice, with and without the PPARbeta/delta specific ligand GW0742. PPARbeta/delta-null mice exhibited increased sensitivity to DSS-induced colitis, as shown by marked differences in body weight loss, colon length, colonic morphology, myeloperoxidase activity and increased expression of mRNAs encoding the inflammatory markers interferon gamma, tumor necrosis factor-alpha, and interleukin-6 compared to similarly treated wild-type mice. Interestingly, these differences were not affected by ligand activation of PPARbeta/delta in either genotype. These studies demonstrate that PPARbeta/delta expression in the colonic epithelium inhibits inflammation and protects against DSS-induced colitis through a ligand-independent mechanism.

Growth inhibition and apoptosis induced in human leiomyoma cells by treatment with the PPAR gamma ligand ciglitizone

The nuclear receptors PPARs (peroxisome proliferator-activated receptors) are transcription factors that play important roles in multiple disease conditions. The activation of PPARs by specific ligands is associated with growth suppression of several different types of human cancer, but the molecular mechanism responsible for this growth suppressive effect remains elusive. The aim of this study was to determine the distribution of PPARgamma protein/mRNA expression in uterine leiomyomas and to identify the PPARgamma induced signaling pathways responsible for the growth inhibition induced by treatment with ciglitizone, a synthetic ligand of PPARgamma, in view of identifying targets that could possibly affect the viability and proliferation of uterine leiomyoma cells. Dose-response studies on proliferation found that uterine leiomyoma was more sensitive to inhibition by ciglitizone treatments than normal myometrium. We also found that ciglitizone significantly stimulated gene expression driven by a PPAR-responsive element in cultured leiomyoma cells and reduced the survival of leiomyoma cells relative to the control cells. The reduced survival of ciglitizone treated leiomyoma cells resulted from a mechanism that involved the Fas receptor-mediated apoptosis signaling cascade. These results suggest that uterine leiomyomas growth and differentiation might be modulated through PPARgamma receptors and that PPARgamma ligands may be of potential use for uterine leiomyoma treatment.

Targeting mitochondria in the treatment of human cancer: a coordinated attack against cancer cell energy metabolism and signalling

Mitochondria have major roles in bioenergetics and vital signalling of the mammalian cell. Consequently, these organelles have been implicated in the process of carcinogenesis, which includes alterations of cellular metabolism and cell death pathways. Multiple molecular routes of malignant transformation appear to result in the common ability of many tumours to take up large amounts of glucose. This metabolic twist has been explained by phenomena such as aerobic glycolysis and impaired mitochondrial function, and is linked to tumour growth potential via major cellular signalling pathways. This paper reviews the literature on central mechanisms through which energy metabolism merges with growth, proliferation and death signalling, which tend to include mitochondria at some level. These processes can potentially be targeted by pharmacological agents for therapeutic and chemosensitising purposes.

The non-genomic crosstalk between PPAR-gamma ligands and ERK1/2 in cancer cell lines

Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor superfamily acting as transcription factors. PPAR-gamma, one of the three PPAR subtypes, is expressed in many malignant and non-malignant cells and tissues. PPAR-gamma ligands influence cancer biology via both genomic as well as non-genomic events. The non-genomic action of PPAR-gamma ligands, including the activation of MAPK signaling pathways, is under intense investigation. In the presence of PPAR-gamma ligands, a rapid phosphorylation of ERK1/2 is observed in many cancer cell lines. Activated ERK1/2 elicits rapid, non-genomic cellular effects and can directly repress PPAR-gamma transcriptional activity by phosphorylation. This paper reviews the interrelation of PPAR-gamma ligands and activated ERK1/2, in relation to their antineoplastic actions in cancer cell lines, which may offer the potential for improved anticancer therapies.

Expression level and agonist-binding affect the turnover, ubiquitination and complex formation of peroxisome proliferator activated receptor beta

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily that modulate target gene expression in response to fatty acid ligands. Their regulation by post-translational modifications has been reported but is poorly understood. In the present study, we investigated whether ligand binding affects the turnover and ubiquitination of the PPARbeta subtype (also known as PPARdelta). Our data show that the ubiquitination and degradation of PPARbeta is not significantly influenced by the synthetic agonist GW501516 under conditions of moderate PPARbeta expression. By contrast, the overexpression of PPARbeta dramatically enhanced its degradation concomitant with its polyubiquitination and the formation of high molecular mass complexes containing multiple, presumably oligomerized PPARbeta molecules that lacked stoichiometical amounts of the obligatory PPARbeta dimerization partner, retinoid X receptor. The formation of these apparently aberrant complexes, as well as the ubiquitination and destabilization of PPARbeta, were strongly inhibited by GW501516. Our findings suggest that PPARbeta is subject to complex post-translational regulatory mechanisms that partly may serve to safeguard the cell against deregulated PPARbeta expression. Furthermore, our data have important implications regarding the widespread use of overexpression systems to evaluate the function and regulation of PPARs.

Peroxisome proliferator-activated receptor-alpha is required for the neurotrophic effect of oleic acid in neurons

Oleic acid synthesized by astrocytes behaves as a neurotrophic factor for neurons, up-regulating the molecular markers of axonal and dendritic outgrowth, growth-associated protein 43 and microtubule-associated protein 2. In this work, the nature of the receptor involved in this neurotrophic effect was investigated. As oleic acid has been reported to be a ligand and activator of the peroxisome proliferator-activated receptor (PPAR), we focus on this family of receptors. Our results show that PPARalpha, beta/delta, and gamma are expressed in neurons in culture. However, only the agonists of PPARalpha, Wy14643, GW7647 and oleoylethanolamide, promoted neuronal differentiation, while PPAR beta/delta and gamma agonists did not modify neuronal differentiation. Consequently, we investigated the involvement of PPARalpha (Nr1c1) in oleic acid-induced neuronal differentiation. Our results indicate that oleic acid activates PPARalpha in neurons. In addition, the effect of oleic acid on neuronal morphology, growth-associated protein 43 and microtubule-associated protein 2 expression decreases in neurons after PPARalpha has been silenced by small interfering RNA. Taken together, our results suggest that PPARalpha could be the receptor for oleic acid in neurons, further broadening the range of functions attributed to this family of transcription factors. Although several works have reported that PPARalpha could be involved in neuroprotection, the present work provides the first evidence suggesting a role of PPARalpha in neuronal differentiation.

Present concepts and future outlook: function of peroxisome proliferator-activated receptors (PPARs) for pathogenesis, progression, and therapy of cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily of transcriptional regulators that regulate lipid, glucose, and amino acid metabolism. In recent studies it also has been shown that these receptors are implicated in tumor progression, cellular differentiation, and apoptosis and modulation of their function is therefore considered as a potential target for cancer prevention and treatment. PPAR ligands and other agents influencing PPAR signalling pathways have been shown to reveal chemopreventive potential by mediating tumor suppressive activities in a variety of human cancers and could represent a potential novel strategy to inhibit tumor carcinogenesis and progression. This review summarizes the currently available data on the roles of PPARs in relation to the processes of cell differentiation and carcinogenesis as well as their role as promising future therapeutic targets.

PPARbeta agonists trigger neuronal differentiation in the human neuroblastoma cell line SH-SY5Y

Neuroblastomas are pediatric tumors originating from immature neuroblasts in the developing peripheral nervous system. Differentiation therapies could help lowering the high mortality due to rapid tumor progression to advanced stages. Oleic acid has been demonstrated to promote neuronal differentiation in neuronal cultures. Herein we report on the effects of oleic acid and of a specific synthetic PPARbeta agonist on cell growth, expression of differentiation markers and on parameters responsible for the malignancy such as adhesion, migration, invasiveness, BDNF, and TrkB expression of SH-SY5Y neuroblastoma cells. The results obtained demonstrate that many, but not all, oleic acid effects are mediated by PPARbeta and support a role for PPARbeta in neuronal differentiation strongly pointing towards PPAR ligands as new therapeutic strategies against progression and recurrences of neuroblastoma.