Selective activation of PPARgamma in breast, colon, and lung cancer cell lines

Polyunsaturated Fatty Acids: Conversion to Lipid Mediators, Roles in Inflammatory Diseases and Dietary Sources

Polyunsaturated fatty acids (PUFAs) are important components of the diet of mammals. Their role was first established when the essential fatty acids (EFAs) linoleic acid and α-linolenic acid were discovered nearly a century ago. However, most of the biochemical and physiological actions of PUFAs rely on their conversion to 20C or 22C acids and subsequent metabolism to lipid mediators. As a generalisation, lipid mediators formed from n-6 PUFAs are pro-inflammatory while those from n-3 PUFAs are anti-inflammatory or neutral. Apart from the actions of the classic eicosanoids or docosanoids, many newly discovered compounds are described as Specialised Pro-resolving Mediators (SPMs) which have been proposed to have a role in resolving inflammatory conditions such as infections and preventing them from becoming chronic. In addition, a large group of molecules, termed isoprostanes, can be generated by free radical reactions and these too have powerful properties towards inflammation. The ultimate source of n-3 and n-6 PUFAs are photosynthetic organisms which contain Δ-12 and Δ-15 desaturases, which are almost exclusively absent from animals. Moreover, the EFAs consumed from plant food are in competition with each other for conversion to lipid mediators. Thus, the relative amounts of n-3 and n-6 PUFAs in the diet are important. Furthermore, the conversion of the EFAs to 20C and 22C PUFAs in mammals is rather poor. Thus, there has been much interest recently in the use of algae, many of which make substantial quantities of long-chain PUFAs or in manipulating oil crops to make such acids. This is especially important because fish oils, which are their main source in human diets, are becoming limited. In this review, the metabolic conversion of PUFAs into different lipid mediators is described. Then, the biological roles and molecular mechanisms of such mediators in inflammatory diseases are outlined. Finally, natural sources of PUFAs (including 20 or 22 carbon compounds) are detailed, as well as recent efforts to increase their production.

Proteomics analysis reveals promotion effect of 1α,25-dihydroxyvitamin D3 on mammary gland development and lactation of primiparous sows during gestation

1α,25(OH)₂VD₃ is the most active form of vitamin D₃ in animals, and it plays an important role in regulating mineral metabolism and reproduction. In this study, 140 crossbred gilts (Landrace × Yorkshire) were selected, randomly divided into four groups, and fed with a commercial diet supplemented with 0, 1, 2, and 4 μg/kg of 1α,25(OH)₂VD₃ in the form of 1α,25(OH)₂VD₃-glycosides. The mammary gland tissues were sampled from sows on day 114 of gestation. The production data of sows in each group were analyzed, and the colostrum quality was evaluated. Differentially abundant proteins (DAPs) in the mammary tissues were identified by tandem mass tag (TMT) technique and were verified by Western blot and parallel reaction monitoring (PRM). The results showed that 4 μg/kg 1α,25(OH)₂VD₃-glycosides significantly promoted the piglet birth weight, weaning weight, colostrum quality, and lactation ability of primiparous sows. The proteomics analysis showed that of the identified 53,118 peptides, 48,868 were unique peptides. A total of 5029 DAPs were identified, of which 4292 DAPs contained quantitative information. Our data indicated that 1α,25(OH)₂VD₃ was involved in the regulation of the mammary gland development and lactation in a dose-dependent manner through multiple pathways during gestation of primiparous sows. SIGNIFICANCE: The mammary gland is an important lactation organ of female mammals. Our research aims to reveal the effect of dietary supplementation with 1α,25(OH)₂VD₃ on mammary gland development and lactation of primiparous sow. This study identified potential signaling pathways and DAPs involved in regulating the mammary gland development and lactation in sows. Our findings provides theoretical basis for improving the fecundity of sows.

Blocking PPARγ interaction facilitates Nur77 interdiction of fatty acid uptake and suppresses breast cancer progression

Nuclear receptor Nur77 participates in multiple metabolic regulations and plays paradoxical roles in tumorigeneses. Herein, we demonstrated that the knockout of Nur77 stimulated mammary tumor development in two mouse models, which would be reversed by a specific reexpression of Nur77 in mammary tissues. Mechanistically, Nur77 interacted and recruited corepressors, the SWI/SNF complex, to the promoters of CD36 and FABP4 to suppress their transcriptions, which hampered the fatty acid uptake, leading to the inhibition of cell proliferation. Peroxisome proliferator-activated receptor-γ (PPARγ) played an antagonistic role in this process through binding to Nur77 to facilitate ubiquitin ligase Trim13-mediated ubiquitination and degradation of Nur77. Cocrystallographic and functional analysis revealed that Csn-B, a Nur77-targeting compound, promoted the formation of Nur77 homodimer to prevent PPARγ binding by steric hindrance, thereby strengthening the Nur77's inhibitory role in breast cancer. Therefore, our study reveals a regulatory function of Nur77 in breast cancer via impeding fatty acid uptake.

Retinoic Acids in the Treatment of Most Lethal Solid Cancers

Although the use of oral administration of pharmacological all-trans retinoic acid (ATRA) concentration in acute promyelocytic leukaemia (APL) patients was approved for over 20 years and used as standard therapy still to date, the same use in solid cancers is still controversial. In the present review the literature about the top five lethal solid cancers (lung, stomach, liver, breast, and colon cancer), as defined by The Global Cancer Observatory of World Health Organization, and retinoic acids (ATRA, 9-cis retinoic acid, and 13-cis retinoic acid, RA) was compared. The action of retinoic acids in inhibiting the cell proliferation was found in several cell pathways and compartments: from membrane and cytoplasmic signaling, to metabolic enzymes, to gene expression. However, in parallel in the most aggressive phenotypes several escape routes have evolved conferring retinoic acids-resistance. The comparison between different solid cancer types pointed out that for some cancer types several information are still lacking. Moreover, even though some pathways and escape routes are the same between the cancer types, sometimes they can differently respond to retinoic acid therapy, so that generalization cannot be made. Further studies on molecular pathways are needed to perform combinatorial trials that allow overcoming retinoic acids resistance.

Troglitazone Inhibits Matrix Metalloproteinase-9 Expression and Invasion of Breast Cancer Cell through a Peroxisome Proliferator-Activated Receptor γ-Dependent Mechanism

Purpose

Peroxisome proliferator-activated receptor γ (PPARγ) is involved in the pathology of numerous diseases including atherosclerosis, diabetes, obesity, and cancer. Matrix metalloproteinases (MMPs) play a significant role in tissue remodeling related to various processes such as morphogenesis, angiogenesis, tissue repair, invasion, and metastasis. We investigated the effects of PPARγ on MMP expression and invasion in breast cancer cells.

Methods

MCF-7 cells were cultured and then cell viability was monitored in an MTT assay. Western blotting, gelatin zymography, real-time polymerase chain reaction, and luciferase assays were performed to investigate the effect of the synthetic PPARγ ligand troglitazone on MMP expression. Transcription factor DNA binding was analyzed by electrophoretic mobility shift assay. A Matrigel invasion assay was used to assess the effects of troglitazone on MCF-7 cells.

Results

Troglitazone did not affect MCF-7 cell viability. 12-O-tetradecanoylphorbol-13-acetate (TPA) induced MMP-9 expression and invasion in MCF-7 cell. However, these effects were decreased by troglitazone. TPA increased nuclear factor κB and activator protein-1 DNA binding, while troglitazone inhibited these effects. The selective PPARγ antagonist GW9662 reversed MMP-9 inhibition by troglitazone in TPA-treated MCF-7 cells.

Conclusion

Troglitazone inhibited nuclear factor κB and activator protein-1-mediated MMP-9 expression and invasion of MCF-7 cells through a PPARγ-dependent mechanism.

PPARs in the central nervous system: roles in neurodegeneration and neuroinflammation

Over 25 years have passed since peroxisome proliferators-activated receptors (PPARs), were first described. Like other members of the nuclear receptors superfamily, PPARs have been defined as critical sensors and master regulators of cellular metabolism. Recognized as ligand-activated transcription factors, they are involved in lipid, glucose and amino acid metabolism, taking part in different cellular processes, including cellular differentiation and apoptosis, inflammatory modulation and attenuation of acute and chronic neurological damage in vivo and in vitro. Interestingly, PPAR activation can simultaneously reprogram the immune response, stimulate metabolic and mitochondrial functions, promote axonal growth, induce progenitor cells to differentiate into myelinating oligodendrocytes, and improve brain clearance of toxic molecules such as β-amyloid peptide. Although the molecular mechanisms and cross-talk with different molecular pathways are still the focus of intense research, PPARs are considered potential therapeutic targets for several neuropathological conditions, including degenerative disorders such as Alzheimer's, Parkinson's and Huntington's disease. This review considers recent advances regarding PPARs, as well as new PPAR agonists. We focus on the mechanisms behind the neuroprotective effects exerted by PPARs and summarise the roles of PPARs in different pathologies of the central nervous system, especially those associated with degenerative and inflammatory mechanisms.

High FABP5 Versus CRABPII Expression Ratio in Recurrent Craniopharyngiomas: Implications for Future Treatment

BACKGROUND AND OBJECTIVE

Recurrence is a major problem in craniopharyngioma (CP) management. Recent study shows that high FABP5/CRABPII may be related to tumor growth and that all-trans retinoic acid (ATRA) may suppress primary CP growth. We studied the expression profile of FABP5 and CRABPII in recurrent CP tissue and the effect of ATRA on recurrent CP cells.

METHODS

Fifty cases of patients with CP were enrolled in the retrospective study. Among them, 15 were recurrent. Fresh specimens were collected for immunohistochemistry, reverse transcription polymerase chain reaction, and western blotting analysis of FABP5 and CRABPII. Fresh specimens from 6 primary and recurrent CPs were collected and subjected to cell culture using an explants method. ATRA at various concentrations was applied to recurrent CP cell culture, and cell growth was recorded and analyzed.

RESULTS

Immunohistochemistry, reverse transcription polymerase chain reaction, and western blot study showed that FABP5 was expressed significantly higher in recurrent tumors, whereas CRABPII was expressed significantly higher in primary tumors. The FABP5/CRABPII ratio was significantly higher in recurrent rather than primary tumors. Recurrent CP cells grew faster than primary cells, and ATRA induced cellular apoptosis and inhibited CP cell growth in a dose-dependent manner.

CONCLUSIONS

A high expression ratio between FABP5 and CRABPII may be related to CP tumor recurrence and ATRA could be a potential therapeutic agent for CP chemotherapy.

15-Deoxy-Δ(12,14)-prostaglandin J2 Induces Apoptosis and Upregulates SOCS3 in Human Thyroid Cancer Cells

The cyclopentenone prostaglandin 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is a natural ligand of peroxisome proliferator-activated receptor gamma (PPAR-γ) and a potential mediator of apoptosis in cancer cells. In the present study, we evaluated the effect of 15d-PGJ₂ in human thyroid papillary carcinoma cells (TPC-1) using different doses of 15d-PGJ₂ (0.6 to 20 μM) to determine IC₅₀ (9.3 μM) via the MTT assay. The supernatant culture medium of the TPC-1 cells that was treated either with 15d-PGJ₂ or with vehicle (control) for 24 hours was assessed for IL-6 secretion via CBA assay. RT-qPCR was used to evaluate mRNA expression of IL-6, SOCS1, SOCS3, and STAT3. TPC-1 cells treated with 15d-PGJ₂ decreased the secretion and expression of IL-6 and STAT3, while it increased SOCS1 and SOCS3. Overall, we demonstrated that 15d-PGJ₂ downregulated IL-6 signaling pathway and led TPC-1 cells into apoptosis. In conclusion, 15d-PGJ₂ shows the potential to become a new therapeutic approach for thyroid tumors.

Docosahexaenoic Acid Induces Growth Suppression on Epithelial Ovarian Cancer Cells More Effectively than Eicosapentaenoic Acid

Omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been shown to possess definitively suppressive effects on the growth of epithelial ovarian cancer cells. This study investigated the differential effects of pure EPA and DHA on the growth of epithelial ovarian cancer cells and the potential molecular mechanisms that may be involved. There were significant time- and dose-dependent inhibitory effects of both EPA and DHA on cellular proliferation of the epithelial ovarian cancer cell line TOV-21G (P < 0.05). TOV-21G cells pretreated with peroxisome proliferator receptor activator gamma (PPARγ) antagonist, GW9662, markedly suppressed EPA/DHA-induced apoptosis as determined by TUNEL assay, Annexin V-FITC/PI staining, and caspase-3 activity. EPA/DHA significantly induced PPARγ and p53 overexpression as observed in immunoblotting assay and the induction of p53 by EPA/DHA was abolished by GW9662. In all cases, the effect of DHA was significantly more potent than that of EPA (P < 0.05). Our findings suggested that DHA may be more effective than EPA in growth suppression of TOV-21G cells and the biologic effects may be partly mediated by PPARγ and p53 activation. Further research is required to elucidate additional divergent mechanisms to account for apparent differences between EPA and DHA.

Fatty acids, eicosanoids and PPAR gamma

Peroxisome proliferator-activated receptor γ (PPARγ) belongs to the family of nuclear nuclear receptors and is mainly expressed in adipose tissue, hematopoietic cells and the large intestine. Contrary to other nuclear receptors that mainly bind a single specific ligand, there are numerous natural PPARγ ligands, in particular fatty acids or their derivatives called eicosanoids. PPARγ have pleiotropic functions: (i) glucose and lipid metabolism regulation, (ii) anti-inflammatory properties, (iii) oxidative stress inhibition, (iv) improvement of endothelial function. Its role has been mainly studied by the use synthetic agonists. In this review, we will focus on the effects of PPARγ mediated through fatty acids and how these have beneficial health properties.

Increasing doxorubicin activity against breast cancer cells using PPARγ-ligands and by exploiting circadian rhythms

BACKGROUND AND PURPOSE

Doxorubicin is effective against breast cancer, but its major side effect is cardiotoxicity. The aim of this study was to determine whether the efficacy of doxorubicin on cancer cells could be increased in combination with PPARγ agonists or chrono-optimization by exploiting the diurnal cycle.

EXPERIMENTAL APPROACH

We determined cell toxicity using MCF-7 cancer cells, neonatal rat cardiac myocytes and fibroblasts in this study.

KEY RESULTS

Doxorubicin damages the contractile filaments of cardiac myocytes and affects cardiac fibroblasts by significantly inhibiting collagen production and proliferation at the level of the cell cycle. Cyclin D1 protein levels decreased significantly following doxorubicin treatment indicative of a G1/S arrest. PPARγ agonists with doxorubicin increased the toxicity to MCF-7 cancer cells without affecting cardiac cells. Rosiglitazone and ciglitazone both enhanced anti-cancer activity when combined with doxorubicin (e.g. 50% cell death for doxorubicin at 0.1 μM compared to 80% cell death when combined with rosiglitazone). Thus, the therapeutic dose of doxorubicin could be reduced by 20-fold through combination with the PPARγ agonists, thereby reducing adverse effects on the heart. The presence of melatonin also significantly increased doxorubicin toxicity, in cardiac fibroblasts (1 μM melatonin) but not in MCF-7 cells.

CONCLUSIONS AND IMPLICATIONS

Our data show, for the first time, that circadian rhythms play an important role in doxorubicin toxicity in the myocardium; doxorubicin should be administered mid-morning, when circulating levels of melatonin are low, and in combination with rosiglitazone to increase therapeutic efficacy in cancer cells while reducing the toxic effects on the heart.

Differential cell growth/apoptosis behavior of 13-hydroxyoctadecadienoic acid enantiomers in a colorectal cancer cell line

Cyclooxygenases (COXs) and lipoxygenases (LOXs) are important enzymes that metabolize arachidonic and linoleic acids. Various metabolites generated by the arachidonic acid cascade regulate cell proliferation, apoptosis, differentiation, and senescence. Hydroxyoctadecadienoic acids (HODEs) are synthesized from linoleic acid, giving two enantiomeric forms for each metabolite. The aim was to investigate the effect of 13-HODE enantiomers on nondifferentiated Caco-2 cell growth/apoptosis. Our results indicate that 13(S)-HODE decreases cell growth and DNA synthesis of nondifferentiated Caco-2 cells cultured with 10% fetal bovine serum (FBS). Moreover, 13(S)-HODE showed an apoptotic effect that was reduced in the presence of a specific peroxisome proliferator-activated receptor-γ (PPARγ) antagonist. In addition, we observed that 13(S)-HODE but not 13(R)-HODE is a ligand to PPARγ, confirming the implication of this nuclear receptor in 13(S)-HODE actions. In contrast, 13(R)-HODE increases cell growth and DNA synthesis in the absence of FBS. 13(R)-HODE interaction with BLT receptors activates ERK and CREB signaling pathways, as well as PGE2 synthesis. These results suggest that the proliferative effect of 13(R)-HODE could be due, at least in part, to COX pathway activation. Thus both enantiomers use different receptors and have contrary effects. We also found these differential effects of 9-HODE enantiomers on cell growth/apoptosis. Therefore, the balance between (R)-HODEs and (S)-HODEs in the intestinal epithelium could be important to its cell growth/apoptosis homeostasis.

Anti- and Protumorigenic Effects of PPARγ in Lung Cancer Progression: A Double-Edged Sword

Peroxisome proliferator-activated receptor-γ (PPARγ) is a member of the nuclear receptor superfamily of ligand-activated transcription factors that plays an important role in the control of gene expression linked to a variety of physiological processes, including cancer. Ligands for PPARγ include naturally occurring fatty acids and the thiazolidinedione class of antidiabetic drugs. Activation of PPARγ in a variety of cancer cells leads to inhibition of growth, decreased invasiveness, reduced production of proinflammatory cytokines, and promotion of a more differentiated phenotype. However, systemic activation of PPARγ has been reported to be protumorigenic in some in vitro systems and in vivo models. Here, we review the available data that implicate PPARγ in lung carcinogenesis and highlight the challenges of targeting PPARγ in lung cancer treatments.

Peroxisome proliferator-activated receptor gamma overexpression suppresses proliferation of human colon cancer cells

Peroxisome proliferator-activated receptor gamma (PPARγ) plays an important role in the differentiation of intestinal cells and tissues. Our previous reports indicate that PPARγ is expressed at considerable levels in human colon cancer cells. This suggests that PPARγ expression may be an important factor for cell growth regulation in colon cancer. In this study, we investigated PPARγ expression in 4 human colon cancer cell lines, HT-29, LOVO, DLD-1, and Caco-2. Real-time polymerase chain reaction (PCR) and Western blot analysis revealed that the relative levels of PPARγ mRNA and protein in these cells were in the order HT-29>LOVO>Caco-2>DLD-1. We also found that PPARγ overexpression promoted cell growth inhibition in PPARγ lower-expressing cell lines (Caco-2 and DLD-1), but not in higher-expressing cells (HT-29 and LOVO). We observed a correlation between the level of PPARγ expression and the cells' sensitivity for proliferation.

Research resource: Diagnostic and therapeutic potential of nuclear receptor expression in lung cancer

Lung cancer is the leading cause of cancer-related death. Despite a number of studies that have provided prognostic biomarkers for lung cancer, a paucity of reliable markers and therapeutic targets exist to diagnose and treat this aggressive disease. In this study we investigated the potential of nuclear receptors (NRs), many of which are well-established drug targets, as therapeutic markers in lung cancer. Using quantitative real-time PCR, we analyzed the expression of the 48 members of the NR superfamily in a human panel of 55 normal and lung cancer cell lines. Unsupervised cluster analysis of the NR expression profile segregated normal from tumor cell lines and grouped lung cancers according to type (i.e. small vs. non-small cell lung cancers). Moreover, we found that the NR signature was 79% accurate in diagnosing lung cancer incidence in smokers (n = 129). Finally, the evaluation of a subset of NRs (androgen receptor, estrogen receptor, vitamin D receptor, and peroxisome proliferator-activated receptor-γ) demonstrated the therapeutic potential of using NR expression to predict ligand-dependent growth responses in individual lung cancer cells. Preclinical evaluation of one of these receptors (peroxisome proliferator activated receptor-γ) in mouse xenografts confirmed that ligand-dependent inhibitory growth responses in lung cancer can be predicted based on a tumor's receptor expression status. Taken together, this study establishes NRs as theragnostic markers for predicting lung cancer incidence and further strengthens their potential as therapeutic targets for individualized treatment.

Beta-eleostearic acid induce apoptosis in T24 human bladder cancer cells through reactive oxygen species (ROS)-mediated pathway

Beta-eleostearic acid (β-ESA, 9E11E13E-18:3), a linolenic acid isomer with a conjugated triene system, is a natural and biologically active compound. Herein, we investigated effects of β-eleostearic acid on T24 human bladder cancer cells. In this study, results showed that β-eleostearic acid had strong cytotoxicity to induce cell apoptosis, which was mediated by reactive oxygen species (ROS) in T24 cells. The cell viability assay results showed that incubation with β-eleostearic acid concentrations of 10-80μmol/L caused a dose- and time-dependent decrease of T24 cell viability, and the IC(50) value was 21.2μmol/L at 24h and 13.1μmol/L at 48h. Annexin V/PI double staining was used to assess apoptosis with flow cytometry. Treatment with β-eleostearic acid caused massive ROS accumulation and GSH decrease, which lead to activation of caspase-3 and down-regulation of Bcl-2 indicating induction of apoptosis. Subsequently, N-acetyl-l-cysteine (NAC) and PEG-catalase effectively blocked the ROS elevated effect of β-eleostearic acid, which suggested that β-eleostearic acid-induced apoptosis involved ROS generated. Additionally, we found that treating T24 cells with β-eleostearic acid induced activation of PPARγ. A PPARγ-activated protein kinase inhibitor was able to partially abrogate the effects of β-eleostearic acid. These results suggested that β-eleostearic acid can induce T24 cells apoptosis via a ROS-mediated pathway which may be involved PPARγ activation.

Expression of peroxisome proliferator activated receptor-gamma (PPAR-γ) in human non-small cell lung carcinoma: correlation with clinicopathological parameters, proliferation and apoptosis related molecules and patients' survival

Peroxisome proliferator-activated receptor-γ (PPAR-γ) has currently been considered as molecular target for the treatment of human metabolic disorders. PPAR-γ has also been implicated in the pathogenesis and progression of several types of cancer, being associated with cell differentiation, growth and apoptosis. The present study aimed to evaluate the clinical significance of PPAR-γ expression in non-small cell lung carcinoma (NSCLC). PPAR-γ protein expression was assessed immunohistochemically in tumoral samples of 67 NSCLC patients and was statistically analyzed in relation to clinicopathological parameters, proliferation and apoptosis related molecules and patients' survival. Positive PPAR-γ expression was prominent in 30 (45 %) out of 67 NSCLC cases. PPAR-γ positivity was more frequently observed in squamous cell lung carcinoma cases compared to lung adenocarcinoma ones (p = 0.048). PPAR-γ positivity was significantly associated with bcl-2 positivity (p = 0.016) and borderline with c-myc positivity (p = 0.052), whereas non associations with grade of differentiation, TNM stage, Ki-67, p53, bax proteins' expression and patients' survival were noted. In the subgroup of squamous cell lung carcinoma cases, PPAR-γ positivity was significantly associated with tumor size (p = 0.038), while in lung adenocarcinoma ones with histopathological grade of differentiation (p = 0.026). The present study supported evidence for possible participation of PPAR-γ in the biological mechanisms underlying the carcinogenic evolution of the lung. Although the survival prediction using PPAR-γ expression as a marker seems uncertain, the observed correlation with apoptosis related proteins reinforces the potential utility of PPAR-γ ligands as cell cycle modulators in future therapeutic approaches in lung cancer.

Cytotoxicity of 15-deoxy-Δ(12,14)-prostaglandin J(2) through PPARγ-independent pathway and the involvement of the JNK and Akt pathway in renal cell carcinoma

INTRODUCTION

Agonists of peroxisome proliferator-activated receptor gamma (PPARγ) have been examined as chemopreventive and chemotherapeutic agents. The aim was to investigate the cytotoxicity and action mechanisms of 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), one of endogenous ligands for PPARγ, in terms of PPARγ-dependency and the mitogen-activated protein kinase (MAPK) and Akt pathway in three human renal cell carcinoma (RCC)-derived cell lines.

METHODS

786-O, Caki-2 and ACHN cells were used as human RCC-derived cell lines. Cell viability and caspase-3 activity was detected by fluorescent reagents, and chromatin-condensation was observed with a brightfield fluorescent microscope after staining cells with Hoechst33342. The expression levels of proteins were detected by Western blot analysis.

RESULTS

15d-PGJ(2) showed cytotoxicity in dose-dependent manner. 15d-PGJ(2) induced chromatin-condensation and elevated caspase-3 activity, and the cell viability was restored by co-treatment with a pan-caspase inhibitor, Z-VAD-FMK, indicating the involvement of caspase-dependent apoptosis. The cytotoxicity was not impaired by a PPARγ inhibitor, GW9662, suggesting that 15d-PGJ(2) exerted the cytotoxicity in a PPARγ-independent manner. Some antioxidants rescued cells from cell death induced by 15d-PGJ(2), but some did not, suggesting that reactive oxygen species (ROS) did not contribute to the apoptosis. 15d-PGJ(2) also increased the expression levels of phospho-c-Jun N terminal kinase (JNK) in Caki-2 cells, and decreased those of phospho-Akt in 786-O cells, indicating that the JNK MAPK and the Akt pathways participated in the anticancer effects of 15d-PGJ(2) in some cell lines.

CONCLUSION

15d-PGJ(2) exerted cytotoxic effects accompanying caspase-dependent apoptosis, and this effect was elicited in a PPARγ-independent manner in three cell lines. In addition, the JNK MAPK and Akt pathway was involved in the cytotoxicity of 15d-PGJ(2) to some extent in some cell line. Therefore, our study showed the 15d-PGJ(2) to potentially be an interesting approach for RCC treatment.

Peroxisome proliferator-activated receptors in lung cancer

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. Their discovery in the 1990s provided insights into the cellular mechanisms involved in the control of energy homeostasis; the regulation of cell differentiation, proliferation, and apoptosis; and the modulation of important biological and pathological processes related to inflammation, among others. Since then, PPARs have become an exciting therapeutic target for several diseases. PPARs are expressed by many tumors including lung carcinoma cells, and their function has been linked to the process of carcinogenesis in lung. Consequently, intense research is being conducted in this area with the hope of discovering new PPAR-related therapeutic targets for the treatment of lung cancer. This review summarizes the research being conducted in this area and focuses on the mechanisms by which PPARs are believed to affect lung tumor cell biology.

Activated PPARgamma Targets Surface and Intracellular Signals That Inhibit the Proliferation of Lung Carcinoma Cells

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. Their discovery in the 1990s provided insights into the cellular mechanisms involved in the control of energy homeostasis, the regulation of cell differentiation, proliferation, and apoptosis, and the modulation of important biological and pathological processes related to inflammation and cancer biology, among others. Since then, PPARs have become an exciting target for the development of therapies directed at many disorders including cancer. PPARs are expressed in many tumors including lung cancer, and their function has been linked to the process of carcinogenesis. Consequently, intense research is being conducted in this area with the hope of discovering new PPAR-related therapeutic targets for the treatment of lung cancer. This review summarizes the research being conducted in this area, and focuses on the mechanisms by which a member of this family (PPARγ) is believed to affect lung tumor cell biology.

Omega-3 Fatty Acids and PPARgamma in Cancer

Omega-3 (or n-3) polyunsaturated fatty acids (PUFAs) and their metabolites are natural ligands for peroxisome proliferator receptor activator (PPAR)gamma and, due to the effects of PPARgamma on cell proliferation, survival, and differentiation, are potential anticancer agents. Dietary intake of omega-3 PUFAs has been associated with a reduced risk of certain cancers in human populations and in animal models. In vitro studies have shown that omega-3 PUFAs inhibit cell proliferation and induce apoptosis in cancer cells through various pathways but one of which involves PPARgamma activation. The differential activation of PPARgamma and PPARgamma-regulated genes by specific dietary fatty acids may be central to their distinct roles in cancer. This review summarizes studies relating PUFAs to PPARgamma and cancer and offers a new paradigm relating an n-3 PUFA through PPARgamma to the expression of the cell surface proteoglycan, syndecan-1, and to the death of cancer cells.

Peroxisome proliferator-activated receptor γ and colorectal cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and ligand-activated transcription factors. PPARγ plays an important role in adipocyte differentiation, lipid storage and energy dissipation in adipose tissue, and is involved in the control of inflammatory reactions as well as in glucose metabolism through the improvement of insulin sensitivity. Growing evidence has demonstrated that activation of PPARγ has an antineoplastic effect in tumors, including colorectal cancer. High expression of PPARγ is detected in human colon cancer cell lines and adenocarcinoma. This review describes the molecular mechanisms by which PPARγ regulates tumorigenesis in colorectal cancer, and examines current clinical trials evaluating PPARγ agonists as therapeutic agents for colorectal cancer.

Induction of apoptosis by 15d-PGJ2 via ROS formation: an alternative pathway without PPARγ activation in non-small cell lung carcinoma A549 cells

Cyclopentenone prostaglandin 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), which is generated from the dehydration of PGD(2), is a natural ligand of peroxisome proliferator-activated receptor gamma (PPARγ) and a potential apoptotic mediator. The synthetic PPARγ ligands, troglitazone and ciglitazone, inhibit tumor progression in many cells by PPARγ activation, but the mechanism of 15d-PGJ(2) is still unclear. In this study, GW9662, an antagonist of PPARγ, and quercetin, a natural antioxidant, were used to study the apoptotic mechanism of 15d-PGJ(2) in A549 cells. Results showed that 15d-PGJ(2) induced apoptosis, which was associated with the production of reactive oxygen species (ROS) and the decrease of GSH levels. Furthermore, quercetin reduced the activity of caspases in 15d-PGJ(2)-induced apoptotic processes. These results suggest that 15d-PGJ(2) induces apoptosis in A549 cells mainly through the formation of ROS; it does not depend on PPARγ activation. Moreover, these findings support the use of quercetin and PPARγ agonists in non-small cell lung carcinoma.

Specific thiazolidinediones inhibit ovarian cancer cell line proliferation and cause cell cycle arrest in a PPARγ independent manner

BACKGROUND

Peroxisome Proliferator Activated Receptor gamma (PPARγ) agonists, such as the thiazolinediones (TZDs), have been studied for their potential use as cancer therapeutic agents. We investigated the effect of four TZDs--Rosiglitazone (Rosi), Ciglitazone (CGZ), Troglitazone (TGZ), and Pioglitazone (Pio)--on ovarian cancer cell proliferation, PPARγ expression and PPAR luciferase reporter activity. We explored whether TZDs act in a PPARγ dependent or independent manner by utilizing molecular approaches to inhibit or overexpress PPARγ activity.

PRINCIPAL FINDINGS

Treatment with CGZ or TGZ for 24 hours decreased proliferation in three ovarian cancer cell lines, Ovcar3, CaOv3, and Skov3, whereas Rosi and Pio had no effect. This decrease in Ovcar3 cell proliferation was due to a higher fraction of cells in the G(0)/G(1) stage of the cell cycle. CGZ and TGZ treatment increased apoptosis after 4 hours of treatment but not after 8 or 12 hours. Treatment with TGZ or CGZ increased PPARγ mRNA expression in Ovcar3 cells; however, protein levels were unchanged. Surprisingly, luciferase promoter assays revealed that none of the TZDs increased PPARγ activity. Overexpression of wild type PPARγ increased reporter activity. This was further augmented by TGZ, Rosi, and Pio indicating that these cells have the endogenous capacity to mediate PPARγ transactivation. To determine whether PPARγ mediates the TZD-induced decrease in proliferation, cells were treated with CGZ or TGZ in the absence or presence of a dominant negative (DN) or wild type overexpression PPARγ construct. Neither vector changed the TZD-mediated cell proliferation suggesting this effect of TZDs on ovarian cancer cells may be PPARγ independent.

CONCLUSIONS

CGZ and TGZ cause a decrease in ovarian cancer cell proliferation that is PPARγ independent. This concept is supported by the finding that a DN or overexpression of the wild type PPARγ did not affect the changes in cell proliferation and cell cycle.

Steroid receptor coactivator 1 deficiency increases MMTV-neu mediated tumor latency and differentiation specific gene expression, decreases metastasis, and inhibits response to PPAR ligands

Background

The peroxisome proliferator activated receptor (PPAR) subgroup of the nuclear hormone receptor superfamily is activated by a variety of natural and synthetic ligands. PPARs can heterodimerize with retinoid X receptors, which have homology to other members of the nuclear receptor superfamily. Ligand binding to PPAR/RXRs results in recruitment of transcriptional coactivator proteins such as steroid receptor coactivator 1 (SRC-1) and CREB binding protein (CBP). Both SRC-1 and CBP are histone acetyltransferases, which by modifying nucleosomal histones, produce more open chromatin structure and increase transcriptional activity. Nuclear hormone receptors can recruit limiting amounts of coactivators from other transcription factor binding sites such as AP-1, thereby inhibiting the activity of AP-1 target genes. PPAR and RXR ligands have been used in experimental breast cancer therapy. The role of coactivator expression in mammary tumorigenesis and response to drug therapy has been the subject of recent studies.

Methods

We examined the effects of loss of SRC-1 on MMTV-neu mediated mammary tumorigenesis.

Results

SRC-1 null mutation in mammary tumor prone mice increased the tumor latency period, reduced tumor proliferation index and metastasis, inhibited response to PPAR and RXR ligands, and induced genes involved in mammary gland differentiation. We also examined human breast cancer cell lines overexpressing SRC-1 or CBP. Coactivator overexpression increased cellular proliferation with resistance to PPAR and RXR ligands and remodeled chromatin of the proximal epidermal growth factor receptor promoter.

Conclusions

These results indicate that histone acetyltransferases play key roles in mammary tumorigenesis and response to anti-proliferative therapies.

Inhalation delivery of a novel diindolylmethane derivative for the treatment of lung cancer

The purpose of this study was to determine the anticancer efficacy of 1,1-bis (3'-indolyl)-1-(p-biphenyl) methane (DIM-C-pPhC₆H₅) by inhalation delivery alone and in combination with i.v. docetaxel in a murine model for lung cancer. An aqueous DIM-C-pPhC₆H₅ formulation was characterized for its aerodynamic properties. Tumor-bearing athymic nude mice were exposed to nebulized DIM-C-pPhC₆H₅, docetaxel, or combination (DIM-C-pPhC₆H₅ plus docetaxel) using a nose-only exposure technique. The aerodynamic properties included mass median aerodynamic diameter of 1.8 ± 0.3 μm and geometric SD of 2.31 ± 0.02. Lung weight reduction in mice treated with the drug combination was 64% compared with 40% and 47% in mice treated with DIM-C-pPhC₆H₅ aerosol and docetaxel alone, respectively. Combination treatment decreased expression of Akt, cyclin D1, survivin, Mcl-1, NF-κB, IκBα, phospho-IκBα, and vascular endothelial growth factor (VEGF) and increased expression of c-Jun NH₂-terminal kinase 2 and Bad compared with tumors collected from single-agent treatment and control groups. DNA fragmentation was also enhanced in mice treated with the drug combination compared with docetaxel or DIM-C-pPhC₆H₅ alone. Combination treatment decreased expressions of VEGF and CD31 compared with single-agent treated and control groups. These results suggest that DIM-C-pPhC₆H₅ aerosol enhanced the anticancer activity of docetaxel in a lung cancer model by activating multiple signaling pathways. The study provides evidence that DIM-C-pPhC₆H₅ can be used alone or in combination with other drugs for the treatment of lung cancer using the inhalation delivery approach.

Peroxisome proliferator activated receptor-γ and the ubiquitin-proteasome system in colorectal cancer

Peroxisome proliferator activated receptor-γ (PPARγ), a transcription factor of the nuclear receptor superfamily plays a significant role in colorectal cancer pathogenesis. In most experimental systems PPARγ activation has tumor suppressing effects in the colon. PPARγ is regulated at multiple levels by the ubiquitin-proteasome system (UPS). At a first level, UPS regulates PPARγ transcription. This regulation involves both PPARγ transcription specific factors and the general transcription machinery. At a second level UPS regulates PPARγ and its co-factors themselves, as PPARγ and many co-factors are proteasome substrates. At a third level of regulation, transduction pathways working in parallel but also having interrelations with PPARγ are regulated by the UPS, creating a network of regulation in the colorectal carcinogenesis-related pathways that are under UPS control. Activation of PPARγ transcription by direct pharmacologic activators and by stabilization of its molecule by proteasome inhibitors could be strategies to be exploited in colorectal cancer treatment.

Anticancer actions of PPARγ ligands: Current state and future perspectives in human lung cancer

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent nuclear transcription factors and members of the nuclear receptor superfamily. Of the three PPARs identified to date (PPARγ, PPARβ/δ, and PPARα), PPARγ has been studied the most, in part because of the availability of PPARγ agonists (also known as PPARγ ligands) and its significant effects on the management of several human diseases including type 2 diabetes, metabolic syndrome, cardiovascular disease and cancers. PPARγ is expressed in many tumors including lung cancer, and its function has been linked to the process of lung cancer development, progression and metastasis. Studies performed in gynogenic and xenograft models of lung cancer showed decreased tumor growth and metastasis in animals treated with PPARγ ligands. Furthermore, data are emerging from retrospective clinical studies that suggest a protective role for PPARγ ligands on the incidence of lung cancer. This review summarizes the research being conducted in this area and focuses on the mechanisms and potential therapeutic effects of PPARγ ligands as a novel anti-lung cancer treatment strategy.

Peroxisome proliferator-activated receptor γ and colorectal cancer

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and ligand-activated transcription factors. PPARγ plays an important role in adipocyte differentiation, lipid storage and energy dissipation in adipose tissue, and is involved in the control of inflammatory reactions as well as in glucose metabolism through the improvement of insulin sensitivity. Growing evidence has demonstrated that activation of PPARγ has an antineoplastic effect in tumors, including colorectal cancer. High expression of PPARγ is detected in human colon cancer cell lines and adenocarcinoma. This review describes the molecular mechanisms by which PPARγ regulates tumorigenesis in colorectal cancer, and examines current clinical trials evaluating PPARγ agonists as therapeutic agents for colorectal cancer.

Effects of PPAR gamma ligands on TGF-beta1-induced epithelial-mesenchymal transition in alveolar epithelial cells

Background

Transforming growth factor β1 (TGF-β1)-mediated epithelial mesenchymal transition (EMT) of alveolar epithelial cells (AEC) may contribute to lung fibrosis. Since PPARγ ligands have been shown to inhibit fibroblast activation by TGF-β1, we assessed the ability of the thiazolidinediones rosiglitazone (RGZ) and ciglitazone (CGZ) to regulate TGF-β1-mediated EMT of A549 cells, assessing changes in cell morphology, and expression of cell adhesion molecules E-cadherin (epithelial cell marker) and N-cadherin (mesenchymal cell marker), and collagen 1α1 (COL1A1), CTGF and MMP-2 mRNA.

Methods

Serum-deprived A549 cells (human AEC cell line) were pre-incubated with RGZ and CGZ (1 - 30 μM) in the absence or presence of the PPARγ antagonist GW9662 (10 μM) before TGFβ-1 (0.075-7.5 ng/ml) treatment for up to 72 hrs. Changes in E-cadherin, N-cadherin and phosphorylated Smad2 and Smad3 levels were analysed by Western blot, and changes in mRNA levels including COL1A1 assessed by RT-PCR.

Results

TGFβ-1 (2.5 ng/ml)-induced reductions in E-cadherin expression were associated with a loss of epithelial morphology and cell-cell contact. Concomitant increases in N-cadherin, MMP-2, CTGF and COL1A1 were evident in predominantly elongated fibroblast-like cells. Neither RGZ nor CGZ prevented TGFβ1-induced changes in cell morphology, and PPARγ-dependent inhibitory effects of both ligands on changes in E-cadherin were only evident at submaximal TGF-β1 (0.25 ng/ml). However, both RGZ and CGZ inhibited the marked elevation of N-cadherin and COL1A1 induced by TGF-β1 (2.5 ng/ml), with effects on COL1A1 prevented by GW9662. Phosphorylation of Smad2 and Smad3 by TGF-β1 was not inhibited by RGZ or CGZ.

Conclusions

RGZ and CGZ inhibited profibrotic changes in TGF-β1-stimulated A549 cells independently of inhibition of Smad phosphorylation. Their inhibitory effects on changes in collagen I and E-cadherin, but not N-cadherin or CTGF, appeared to be PPARγ-dependent. Further studies are required to unravel additional mechanisms of inhibition of TGF-β1 signalling by thiazolidinediones and their implications for the contribution of EMT to lung fibrosis.

PPARgamma ligands inhibit telomerase activity and hTERT expression through modulation of the Myc/Mad/Max network in colon cancer cells

In human cells the length of telomeres depends on telomerase activity. This activity and the expression of the catalytic subunit of human telomerase reverse transcriptase (hTERT) is strongly up-regulated in most human cancers. hTERT expression is regulated by different transcription factors, such as c-Myc, Mad1 and Sp1. In this study, we demonstrated that 15d-PG J2 and rosiglitazone (an endogenous and synthetic peroxisome proliferators activated receptor γ (PPARγ) ligand, respectively) inhibited hTERT expression and telomerase activity in CaCo-2 colon cancer cells. Moreover, both ligands inhibited c-Myc protein expression and its E-box DNA binding activity. Additionally, Mad1 protein expression and its E-box DNA binding activity were strongly increased by 15d-PG J2 and, to a lesser extent, by rosiglitazone. Sp1 transcription factor expression and its GC-box DNA binding activity were not affected by both PPARγ ligands. Results obtained by transient transfection of CaCo-2 cells with pmaxFP-Green-PRL plasmid constructs containing the functional hTERT core promoter (including one E-box and five GC-boxes) and its E-box deleted sequences, cloned upstream of the green fluorescent protein reporter gene, demonstrated that 15d-PG J2, and with minor effectiveness, rosiglitazone, strongly reduced hTERT core promoter activity. E-boxes for Myc/Mad/Max binding showed a higher activity than GC-boxes for Sp1. By using GW9662, an antagonist of PPARγ, we demonstrated that the effects of 15d-PG J2 are completely PPARγ independent, whereas the effects of rosiglitazone on hTERT expression seem to be partially PPARγ independent. The regulation of hTERT expression by 15d-PG J2 and rosiglitazone, through the modulation of the Myc/Max/Mad1 network, may represent a new mechanism of action of these substances in inhibiting cell proliferation.

New target genes for the peroxisome proliferator-activated receptor-γ (PPARγ) antitumour activity: Perspectives from the insulin receptor

The insulin receptor (IR) plays a crucial role in mediating the metabolic and proliferative functions triggered by the peptide hormone insulin. There is considerable evidence that abnormalities in both IR expression and function may account for malignant transformation and tumour progression in some human neoplasias, including breast cancer. PPARγ is a ligand-activated, nuclear hormone receptor implicated in many pleiotropic biological functions related to cell survival and proliferation. In the last decade, PPARγ agonists—besides their known action and clinical use as insulin sensitizers—have proved to display a wide range of antineoplastic effects in cells and tissues expressing PPARγ, leading to intensive preclinical research in oncology. PPARγ and activators affect tumours by different mechanisms, involving cell proliferation and differentiation, apoptosis, antiinflammatory, and antiangiogenic effects. We recently provided evidence that PPARγ and agonists inhibit IR by non canonical, DNA-independent mechanisms affecting IR gene transcription. We conclude that IR may be considered a new PPARγ “target” gene, supporting a potential use of PPARγ agonists as antiproliferative agents in selected neoplastic tissues that overexpress the IR.

Distinct modulation of voltage-gated and ligand-gated Ca2+ currents by PPAR-gamma agonists in cultured hippocampal neurons

Type 2 diabetes mellitus is a metabolic disorder characterized by hyperglycemia and is especially prevalent in the elderly. Because aging is a risk factor for type 2 diabetes mellitus, and insulin resistance may contribute to the pathogenesis of Alzheimer's disease (AD), anti-diabetic agents (thiazolidinediones-TZDs) are being studied for the treatment of cognitive decline associated with AD. These agents normalize insulin sensitivity in the periphery and can improve cognition and verbal memory in AD patients. Based on evidence that Ca(2+) dysregulation is a pathogenic factor of brain aging/AD, we tested the hypothesis that TZDs could impact Ca(2+) signaling/homeostasis in neurons. We assessed the effects of pioglitazone and rosiglitazone (TZDs) on two major sources of Ca(2+) influx in primary hippocampal cultured neurons, voltage-gated Ca(2+) channel (VGCC) and the NMDA receptor (NMDAR). VGCC- and NMDAR-mediated Ca(2+) currents were recorded using patch-clamp techniques, and Ca(2+) intracellular levels were monitored with Ca(2+) imaging techniques. Rosiglitazone, but not pioglitazone reduced VGCC currents. In contrast, NMDAR-mediated currents were significantly reduced by pioglitazone but not rosiglitazone. These results show that TZDs modulate Ca(2+)-dependent pathways in the brain and have different inhibitory profiles on two major Ca(2+) sources, potentially conferring neuroprotection to an area of the brain that is particularly vulnerable to the effects of aging and/or AD.

Curcumin ameliorates renal failure in 5/6 nephrectomized rats: role of inflammation

TNF-α and NF-κB play important roles in the development of inflammation in chronic renal failure (CRF). In hepatic cells, curcumin is shown to antagonize TNF-α-elicited NF-κB activation. In this study, we hypothesized that if inflammation plays a key role in renal failure then curcumin should be effective in improving CRF. The effectiveness of curcumin was compared with enalapril, a compound known to ameliorate human and experimental CRF. Investigation was conducted in Sprague-Dawley rats where CRF was induced by 5/6 nephrectomy (Nx). The Nx animals were divided into untreated (Nx), curcumin-treated (curcumin), and enalapril-treated (enalapril) groups. Sham-operated animals served as a control. Renal dysfunction in the Nx group, as evidenced by elevated blood urea nitrogen, plasma creatinine, proteinuria, segmental sclerosis, and tubular dilatation, was significantly reduced by curcumin and enalapril treatment. However, only enalapril significantly improved blood pressure. Compared with the control, the Nx animals had significantly higher plasma and kidney TNF-α, which was associated with NF-κB activation and macrophage infiltration in the kidney. These changes were effectively antagonized by curcumin and enalapril treatment. The decline in the anti-inflammatory peroxisome proliferator-activated receptor γ (PPARγ) seen in Nx animals was also counteracted by curcumin and enalapril. Studies in mesangial cells were carried out to further establish that the anti-inflammatory effect of curcumin in vivo was mediated essentially by antagonizing TNF-α. Curcumin dose dependently antagonized the TNF-α-mediated decrease in PPARγ and blocked transactivation of NF-κB and repression of PPARγ, indicating that the anti-inflamatory property of curcumin may be responsible for alleviating CRF in Nx animals.

Down-regulation of PPARgamma1 suppresses cell growth and induces apoptosis in MCF-7 breast cancer cells

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear hormone receptor superfamily and is highly expressed in many human tumors including breast cancer. PPARgamma has been identified as a potential target for breast cancer therapy based on the fact that its activation by synthetic ligands affects the differentiation, proliferation, and apoptosis of cancer cells. However, the controversial nature of current studies and disappointing results from clinical trials raise questions about the contribution of PPARgamma signaling in breast cancer development in the absence of stimulation by exogenous ligands. Recent reports from both in vitro and in vivo studies are inconsistent and suggest that endogenous activation of PPARgamma plays a much more complex role in initiation and progression of cancer than previously thought.

RESULTS

We have previously demonstrated that an increase in expression of PPARgamma1 in MCF-7 breast cancer cells is driven by a tumor-specific promoter. Myc-associated zinc finger protein (MAZ) was identified as a transcriptional mediator of PPARgamma1 expression in these cells. In this study, using RNA interference (RNAi) to inhibit PPARgamma1 expression directly or via down-regulation of MAZ, we report for the first time that a decrease in PPARgamma1 expression results in reduced cellular proliferation in MCF-7 breast cancer cells. Furthermore, we demonstrate that these changes in proliferation are associated with a significant decrease in cell transition from G1 to the S phase. Using a dominant-negative mutant of PPARgamma1, Delta462, we confirmed that PPARgamma1 acts as a pro-survival factor and showed that this phenomenon is not limited to MCF-7 cells. Finally, we demonstrate that down-regulation of PPARgamma1 expression leads to an induction of apoptosis in MCF-7 cells, confirmed by analyzing Bcl-2 expression and PARP-1 cleavage.

CONCLUSION

Thus, these findings suggest that an increase in PPARgamma1 signaling observed in breast cancer contributes to an imbalance between proliferation and apoptosis, and may be an important hallmark of breast tumorigenesis. The results presented here also warrant further investigation regarding the use of PPARgamma ligands in patients who are predisposed or already diagnosed with breast cancer.

Troglitazone enhances tamoxifen-induced growth inhibitory activity of MCF-7 cells

Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands have been identified as a potential source of therapy for human cancers. However, PPARgamma ligands have a limitation for breast cancer therapy, since estrogen receptor alpha (ER(alpha)) negatively interferes with PPARgamma signaling in breast cancer cells. Here we show that ER(alpha) inhihits PPARgamma transactivity and ER(alpha)-mediated inhibition of PPARgamma transactivity is blocked by tamoxifen, an estrogen receptor blocker. The activation of ER(alpha) with 17-beta-estradiol blocked PPRE transactivity induced by troglitazone, a PPARgamma ligand, indicating the resistance of ER(alpha)-positive breast cancer cells to troglitazone. Indeed, troglitazone inhibited the growth of ER(alpha)-negative MDA-MB-231 cells more than that of ER(alpha)-positive MCF-7 cells. Combination of troglitazone with tamoxifen led to a marked increase in growth inhibition of ER(alpha)-positive MCF-7 cells compared to either agent alone. Our data indicates that troglitazone enhances the growth inhibitory activity of tamoxifen in ER(alpha)-positive MCF-7 cells.

Peroxisome proliferator-activated receptor-gamma and growth inhibition by its ligands in prostate cancer

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is expressed in certain human cancers. Ligand-induced PPAR-gamma activation can result in growth inhibition and differentiation in these cancer cells; however, the precise mechanism for the anti-proliferative effect of PPAR-gamma ligands is not clear.

METHODS

In this study, we examined the expression of PPAR-gamma in human prostate cancer and the effect of two PPAR-gamma ligands, 15 deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) and troglitazone, on prostate cancer cell growth.

RESULTS

PPAR-gamma is frequently over-expressed in androgen independent prostate cancer cell lines and human prostate cancer tissues (22 of 47; 47%). Both 15d-PGJ2 and troglitazone inhibited proliferation and DNA synthesis of prostate cancer cell lines in a dose-dependent manner, and slightly increased the proportion of cells with S-phase DNA content. Prostate specific antigen (PSA) promoter reporter assays showed that troglitazone and 15d-PGJ2 down-regulated androgen stimulated reporter gene activity in prostate cancer cell lines LNCaP. Interestingly, LNCaP with troglitazone dramatically suppressed PSA protein expression without suppressing AR expression.

CONCLUSIONS

Taken together, these results suggest that PPAR-gamma ligands may be a useful therapeutic agent for the treatment of prostate cancer.

PGJ2 antagonizes NF-kappaB-induced HIV-1 LTR activation in colonic epithelial cells

Intestinal epithelial cells play an important role in early stages of HIV-1 infection and long-term persistence of the virus. Here we determined the mechanism that regulates HIV-1 activation via prostaglandin J(2) (PGJ(2)) in Caco-2 cells. We showed that treatment of Caco-2 cells with PGJ(2) decreased the infectivity of a luciferase reporter virus, pHXB-luc, as well as HIV production following infection of cells with a X4-tropic virus by antagonizing sodium butyrate, a cellular activator known to induce HIV-1 transcription. Transfection of intestinal epithelial cells such as Caco-2, HT-29 and SW620 cells with full-length HIV-1 LTR (pLTR-luc) revealed that PGJ(2) reduced HIV-1 LTR-mediated reporter gene activity. The involvement of NF-kappaB in the PGJ(2)-dependent down-regulation of HIV-1 transcription was further assessed using the kappaB-regulated luciferase-encoding vectors. In Caco-2 cells, PGJ(2) decreased IKK activity, resulting in reduced NF-kappaB translocation to the nucleus. Since sodium butyrate has been associated with a chronic stress response in AIDS patients, our results suggest that addition of PGJ(2) in the environment of infected intestinal epithelial cells could reduce HIV-1 transcription.

Loss of XIAP sensitizes colon cancer cells to PPARgamma independent antitumor effects of troglitazone and 15-PGJ2

We investigated whether the anticancer effect of a combination of XIAP down-regulation and PPAR gamma activation on colon cancer is PPARgamma receptor dependent. HCT116-XIAP(+/+) cells and HCT116-XIAP(-/-) cells were treated with troglitazone or 15-deoxy-Delta(12,14)-prostaglandin J2 (15-PGJ2) with or without prior exposure to PPARgamma inhibitor GW9662. Cell proliferation and apoptosis was evaluated. Athymic mice carrying HCT116-XIAP(-/-) cells-derived tumors were treated with troglitazone in the presence or absence of GW9662. Inhibition of cell proliferation and induction of apoptosis by troglitazone and 15-PGJ2 were more prominent in HCT116-XIAP(-/-) cells. PPARgamma ligand-induced growth inhibition, apoptosis, caspase and PARP cleavage could not be blocked by GW9662. Troglitazone significantly retarded growth of xenograft tumors and this effect was not blocked by GW9662. Marked apoptosis and an up-regulation of E-cadherin were observed in xenograft tumor tissues, and GW9662 did not affect these effects. Thus, a combination of XIAP down-regulation and PPARgamma ligands exert a significant anticancer effect in colon cancer via a PPARgamma independent pathway.

PPARgamma1 as a molecular target of eicosapentaenoic acid in human colon cancer (HT-29) cells

Diets high in (n-3) PUFA decrease colon cancer development and suppress colon tumor growth, but the molecular mechanism through which these compounds act is largely unknown. We sought to determine whether PPARgamma1 serves as a molecular link between the physiological actions of eicosapentaenoic acid (EPA) in human colon cancer cells (HT-29). At nutritionally relevant concentrations, EPA stimulated a PPAR response element (PPRE) reporter assay in a dose-responsive manner in HT-29 cells. Cotreatment with GW9662 (GW), a PPARgamma antagonist, significantly inhibited this effect, whereas overexpressing the receptor enhanced it. EPA also stimulated the PPRE reporter in a PPARgamma negative cancer cell line (22Rv1) when the cells were cotransfected with a PPARgamma1 expression plasmid and this effect was again inhibited by GW. Furthermore, in vitro incubation of EPA with PPARgamma1 enhanced binding of the protein to DNA containing a PPRE. Next, we sought to determine whether EPA or a prostaglandin formed from EPA is the functional ligand of PPARgamma. Cotreatment in HT-29 and 22Rv1 cells with EPA and acetyl salicylic acid, an inhibitor of cyclooxygenase activity, activated the PPRE reporter at levels similar to EPA alone, suggesting that EPA itself is a ligand of PPARgamma. Finally, EPA suppressed HT-29 cell growth and this effect was significantly reversed by the addition of GW, suggesting that in part the physiological actions of EPA are the result of PPARgamma activation. These studies identify PPARgamma as a molecular mediator of (n-3) PUFA actions in colon cancer cells.

Disruption of ERalpha signalling pathway by PPARgamma agonists: evidences of PPARgamma-independent events in two hormone-dependent breast cancer cell lines

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor that can be activated by natural ligands such as 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ(2)) as well as synthetic drugs such as thiazolidinediones. The treatment of human breast cancer cell lines with PPARgamma agonists is known to have antiproliferative effects but the role of PPARgamma activation in the process remains unclear. In the present study, we investigated the effects of four PPARgamma agonists, Rosiglitazone (RGZ), Ciglitazone (CGZ), Troglitazone (TGZ) and the natural agonist 15d-PGJ(2), on estrogen receptor alpha (ERalpha) signalling pathway in two hormone-dependent breast cancer cell lines, MCF-7 and ZR-75-1. In both of them, TGZ, CGZ and 15d-PGJ(2) induced an inhibition of ERalpha signalling associated with the proteasomal degradation of ERalpha. ZR-75-1 cells were more sensitive than MCF-7 cells to these compounds. Treatments that induced ERalpha degradation inhibited cell proliferation after 24 h. In contrast, 24 h exposure to RGZ, the most potent activator of PPARgamma disrupted neither ERalpha signalling nor cell proliferation. 9-cis retinoic acid never potentiated the proteasomal degradation of ERalpha. PPARgamma antagonists (T0070907, BADGE and GW 9662) did not block the proteolysis of ERalpha in MCF-7 and ZR-75-1 cells treated with TGZ. ERalpha proteolysis still occurred in case of PPARgamma silencing as well as in case of treatment with the PPARgamma-inactive compound Delta2-TGZ, demonstrating a PPARgamma-independent mechanism. The use of thiazolidinedione derivatives able to trigger ERalpha degradation by a PPARgamma-independent pathway could be an interesting tool for breast cancer therapy.

The Peroxisome Proliferator-Activated Receptor Gamma Regulates Trophoblast Cell Differentiation in Mink (Mustela vison)1

Nuclear receptors of the peroxisome proliferator-activated receptor (PPAR) family are implicated in implantation and early placental formation. In carnivores, the trophoblast invades to develop intimate contact with the endothelial cells of the maternal circulation, resulting in an endothelio-chorial form of placentation. Spatio-temporal investigation demonstrated that peroxisome proliferator-activated receptor gamma (PPARG) was strongly and specifically expressed in the mink trophoblast at the time of formation of the syncytiotrophoblast during early implantation, and in trophoblast of the placental labyrinth. The retinoid-X-receptor alpha (RXRA), the heterodimeric partner of PPARG in transcriptional regulation, is, with very few exceptions, co-expressed with PPARG in mink trophoblast. We used mink trophoblast cell lines together with a natural (15-deoxy-delta(12,14)-prostaglandin J(2) ) or a synthetic (troglitazone) PPARG ligand to demonstrate that PPARG is an authentic regulator of gene expression in this tissue. Ligand-activated PPARG stimulated transcription of the PPRE-luc reporter gene transfected into these cell lines. The prostaglandin-induced morphologic changes were accompanied by attenuation in cell proliferation, an increase in PPARG mRNA and protein levels, and the appearance of enlarged and multinuclear cells. Furthermore, 15-deoxy-delta(12,14)-prostaglandin J(2) stimulated the expression of invasion-related genes in trophoblast cells, namely, adipophilin and osteopontin. The results demonstrate that PPARG ligands attenuate proliferation and induce differentiation of mink trophoblast cells to the multlinuclear phenotype. The upregulation of differentiation-specific genes in the placenta under the influence of PPARG ligands provides a mechanism by which blastocyst and endometrial prostanoids regulate implantation, as well as the formation and maintenance of the placenta.

MAZ drives tumor-specific expression of PPAR gamma 1 in breast cancer cells

The peroxisome proliferator-activated receptor gamma 1 (PPARgamma1) is a nuclear receptor that plays a pivotal role in breast cancer and is highly over-expressed relative to normal epithelia. We have previously reported that the expression of PPARgamma1 is mediated by at least six distinct promoters and expression in breast cancer is driven by a tumor-specific promoter (pA1). Deletional analysis of this promoter fragment revealed that the GC-rich, 263 bp sequence proximal to the start of exon A1, is sufficient to drive expression in breast cancer cells but not in normal, human mammary epithelial cells (HMEC). By combining the disparate technologies of microarray and computer-based transcription factor binding site analyses on this promoter sequence the myc-associated zinc finger protein (MAZ) was identified as a candidate transcription factor mediating tumor-specific expression. Western blot analysis and chromatin immunoprecipitation assays verify that MAZ is overexpressed in MCF-7 cells and is capable of binding to the 263 bp promoter fragment, respectively. Furthermore, the over-expression of MAZ in HMEC is sufficient to drive the expression of PPARgamma1 and does so by recruiting the tumor-specific promoter. This results in an increase in the amount of PPARgamma1 capable of binding to its DNA response element. These findings help to define the molecular mechanism driving the high expression of PPARgamma1 in breast cancer and raise new questions regarding the role of MAZ in cancer progression.

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.

Peroxisome proliferator-activated receptor γ (PPARγ) and colorectal carcinogenesis

Peroxisome proliferator-activated receptor gamma (PPARgamma) a member of the nuclear transcription factor superfamily is playing a role in colon carcinogenesis. Although not all in vivo models agree, PPARgamma seems to have suppressive effects in this process favoring apoptosis and inhibiting the cell cycle by inducing expression of apoptosis and senescence proteins. With the recent discovery that anti-diabetic class of drugs thiazolidinediones act through activation of PPARgamma, interest in this transcription factor has increased as it can now be pharmacologically activated in order to obtain tumor suppression. In addition, thiazolidinediones and other PPARgamma agonists possess PPARgamma-independent anti-tumor effects. Although PPARgamma agonists may not by themselves be capable to induce clinical tumor regression, their combination with chemotherapy drugs or other targeted therapies is worth pursuing in the treatment of colorectal carcinoma.