Colorectal cancer expression of peroxisome proliferator-activated receptor gamma (PPARG, PPARgamma) is associated with good prognosis

The obesity paradox in cancer: clinical insights and perspectives

A series of evidence demonstrated that obesity represents an established risk factor for an increase in the incidence of multiple cancer types and for poor cancer survival. Nevertheless, recent studies suggested that, in a series of cancers, patients with a normal body mass index (BMI) have worse outcomes than obese patients. This phenomenon, named 'obesity paradox' or 'reverse epidemiology' in cancer, is not well understood and presents controversial aspects. Therefore, this review aims to explore the available studies concerning the relationship between obesity and cancer incidence or survival and to highlight the hypothetical explanations and the methodological framework. In this regard, we underline the limits of BMI as a potential marker of adiposity and the relevance to assessing body composition, beyond the body size. Further studies are needed to define the impact of obesity in cancer patients, to tailor weight management after cancer diagnosis and to hopefully improve overall clinical outcome.

The role of the lipidome in obesity-mediated colon cancer risk

Obesity is a state of chronic inflammation influenced by lipids such as fatty acids and their secondary oxygenated metabolites deemed oxylipids. Many such lipid mediators serve as potent signaling molecules of inflammation, which can further alter lipid metabolism and lead to carcinogenesis. For example, sphingosine-1-phosphate activates cyclooxygenase-2 in endothelial cells resulting in the conversion of arachidonic acid (AA) to prostaglandin E₂ (PGE₂). PGE₂ promotes colon cancer cell growth. In contrast, the less studied path of AA oxygenation via cytochrome p450 enzymes produces epoxyeicosatetraenoic acids (EETs), whose anti-inflammatory properties cause shrinking of enlarged adipocytes, a characteristic of obesity, through the liberation of fatty acids. It is now thought that EET depletion occurs in obesity and may contribute to colon cell carcinogenesis. Meanwhile, gangliosides, a type of sphingolipid, are cell surface signaling molecules that contribute to the apoptosis of colon tumor cells. Many of these discoveries have been made recently and the mechanisms are still not fully understood, leading to an exciting new chapter of lipidomic research. In this review, mechanisms behind obesity-associated colon cancer are discussed with a focus on the role of small lipid signaling molecules in the process. Specifically, changes in lipid metabolite levels during obesity and the development of colon cancer, as well as novel biomarkers and targets for therapy, are discussed.

PPARγ-activation increases intestinal M1 macrophages and mitigates formation of serrated adenomas in mutant KRAS mice

To identify novel hubs for cancer immunotherapy, we generated C57BL/6J mice with concomitant deletion of the drugable transcription factor PPARγ and transgenic overexpression of the mutant KRASG12V oncogene in enterocytes. Animals developed epithelial hyperplasia, transmural inflammation and serrated adenomas in the small intestine with infiltration of CD3+ FOXP3+ T-cells and macrophages into the lamina propria of the non-malignant mucosa. Within serrated polyps, CD3+ CD8+ T-cells and phosphorylated ERK1/2 were reduced and the senescence marker P21 and macrophage counts up-regulated, indicative of an immunosuppressive tissue microenvironment. Treatment of mutant KRASG12V mice with the PPARγ-agonist rosiglitazone augmented M1 macrophage numbers, reduced IL4 expression and diminished polyp load in mice. Rosiglitazone also promoted M1 polarisation of human THP1-derived macrophages and decreased Il4 mRNA in isolated murine lymphocytes. Thus, inhibition of the oncogenic driver mutant RAS by PPARγ in epithelial and immune cell compartments may be a future target for the prevention or treatment of human malignancies associated with intestinal inflammation.

Noncanonical agonist PPARγ ligands modulate the response to DNA damage and sensitize cancer cells to cytotoxic chemotherapy

The peroxisome-proliferator receptor-γ (PPARγ) is expressed in multiple cancer types. Recently, our group has shown that PPARγ is phosphorylated on serine 273 (S273), which selectively modulates the transcriptional program controlled by this protein. PPARγ ligands, including thiazolidinediones (TZDs), block S273 phosphorylation. This activity is chemically separable from the canonical activation of the receptor by agonist ligands and, importantly, these noncanonical agonist ligands do not cause some of the known side effects of TZDs. Here, we show that phosphorylation of S273 of PPARγ occurs in cancer cells on exposure to DNA damaging agents. Blocking this phosphorylation genetically or pharmacologically increases accumulation of DNA damage, resulting in apoptotic cell death. A genetic signature of PPARγ phosphorylation is associated with worse outcomes in response to chemotherapy in human patients. Noncanonical agonist ligands sensitize lung cancer xenografts and genetically induced lung tumors to carboplatin therapy. Moreover, inhibition of this phosphorylation results in deregulation of p53 signaling, and biochemical studies show that PPARγ physically interacts with p53 in a manner dependent on S273 phosphorylation. These data implicate a role for PPARγ in modifying the p53 response to cytotoxic therapy, which can be modulated for therapeutic gain using these compounds.

Lipidome in colorectal cancer

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths. Understanding its pathophysiology is essential for developing efficient strategies to treat this disease. Lipidome, the sum of total lipids, related enzymes, receptors and signaling pathways, plays crucial roles in multiple cellular processes, such as metabolism, energy storage, proliferation and apoptosis. Dysregulation of lipid metabolism and function contributes to the development of CRC, and can be used towards the evaluation of prognosis. The strategies targeting lipidome have been applied in clinical trails and showed promising results. Here we discuss recent advances in abnormal lipid metabolism in CRC, the mechanisms by which the lipidome regulates tumorigenesis and tumor progression, and suggest potential therapeutic targets for clinical trials.

The relationship between IGF2BP2 and PPARG polymorphisms and susceptibility to esophageal squamous-cell carcinomas in the eastern Chinese Han population

The aim of this case–control study was to assess whether PPARG and IGF2BP2 polymorphisms confer susceptibility to esophageal squamous-cell carcinoma (ESCC). A total of 507 patients pathologically confirmed for ESCC and 1,496 age-, sex-, and residence-matched healthy individuals were enrolled. The PPARG rs1801282 C>G and rs3856806 C>T and IGF2BP2 rs1470579 A>C and rs4402960 G>T polymorphisms were selected and genotyped by SNPscan genotyping assays. Multivariable logistic analysis suggested that the PPARG rs3856806 C>T polymorphism might increase the risk of ESCC. In different stratified analyses, there were significant associations between PPARG rs3856806 C>T and risk of ESCC in female, never-smoking, drinking, and never-drinking subgroups. In addition, we also found that PPARG rs1801282 C>G increased ESCC risk in the never-smoking subgroup. There was significant difference in C_rs1470579G_rs4402960C_rs1801282C_rs3856806-haplotype distribution among ESCC cases and control subjects. In conclusion, our findings highlight that PPARG rs1801282 C>G and rs3856806 C>T polymorphisms are candidates for susceptibility to ESCC in the eastern Chinese Han population. The C_rs1470579G_rs4402960C_rs1801282C_rs3856806 haplotype is associated with susceptibility to ESCC.

mRNA expression of nuclear factor of activated T-cells, cytoplasmic 2 (NFATc2) and peroxisome proliferator-activated receptor gamma (PPARG) transcription factors in colorectal carcinoma

Transcription factors are involved in cell cycle and apoptosis regulation and thus have a key role in the carcinogenesis of different tumors. Nuclear factor of activated T-cells, cytoplasmic 2 (NFATc2) and peroxisome proliferator-activated receptor gamma (PPARG) transcription factors are important in the carcinogenesis of colorectal cancer (CRC). In this study, we examined whether the expression of NFATc2 and PPARG genes is significantly altered during the carcinogenesis of CRC. A total of 47 tumor samples and matched normal tissue margins were collected during surgery from patients with CRC. In addition, three CRC cell lines (HCT119, SW480, and HT29) and healthy cell line were used. After total RNA extraction and cDNA synthesis, mRNA expression levels of NFATc2 and PPARG were examined by real-time polymerase chain reaction. The results showed that NFATc2 is overexpressed in the tumor tissues compared with normal tissue margins (p ≤ 0.05). However, the mRNA expression levels of PPARG were not significantly different between the tumor tissues and tissue margins. Our results indicate that NFATc2 may be used as an early diagnostic or predictive biomarker for CRC as well as a therapeutic target, providing that upcoming studies confirm these results.

Biomarker correlation network in colorectal carcinoma by tumor anatomic location

Background

Colorectal carcinoma evolves through a multitude of molecular events including somatic mutations, epigenetic alterations, and aberrant protein expression, influenced by host immune reactions. One way to interrogate the complex carcinogenic process and interactions between aberrant events is to model a biomarker correlation network. Such a network analysis integrates multidimensional tumor biomarker data to identify key molecular events and pathways that are central to an underlying biological process. Due to embryological, physiological, and microbial differences, proximal and distal colorectal cancers have distinct sets of molecular pathological signatures. Given these differences, we hypothesized that a biomarker correlation network might vary by tumor location.

Results

We performed network analyses of 54 biomarkers, including major mutational events, microsatellite instability (MSI), epigenetic features, protein expression status, and immune reactions using data from 1380 colorectal cancer cases: 690 cases with proximal colon cancer and 690 cases with distal colorectal cancer matched by age and sex. Edges were defined by statistically significant correlations between biomarkers using Spearman correlation analyses. We found that the proximal colon cancer network formed a denser network (total number of edges, n = 173) than the distal colorectal cancer network (n = 95) (P < 0.0001 in permutation tests). The value of the average clustering coefficient was 0.50 in the proximal colon cancer network and 0.30 in the distal colorectal cancer network, indicating the greater clustering tendency of the proximal colon cancer network. In particular, MSI was a key hub, highly connected with other biomarkers in proximal colon cancer, but not in distal colorectal cancer. Among patients with non-MSI-high cancer, BRAF mutation status emerged as a distinct marker with higher connectivity in the network of proximal colon cancer, but not in distal colorectal cancer.

Conclusion

In proximal colon cancer, tumor biomarkers tended to be correlated with each other, and MSI and BRAF mutation functioned as key molecular characteristics during the carcinogenesis. Our findings highlight the importance of considering multiple correlated pathways for therapeutic targets especially in proximal colon cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-017-1718-5) contains supplementary material, which is available to authorized users.

Subcutaneous adiposity is an independent predictor of mortality in cancer patients

BACKGROUND

Prognostic significance of adiposity, at the time of cancer diagnosis, on survival is not clear. Body mass index (kg m^-2) does not provide an appropriate assessment of body composition; therefore, the concept of the 'obesity paradox' needs to be investigated based on the prognostic significance of fat and muscle. Independent prognostic significance of adipose tissue in predicting mortality, importance of visceral and subcutaneous adiposity in the presence and absence of sarcopenia on survival, was investigated.

METHODS

Adiposity markers including total adipose index (TATI), visceral adipose tissue index (VATI) and subcutaneous adipose tissue index (SATI) were estimated for 1473 gastrointestinal and respiratory cancer patients and 273 metastatic renal cell carcinoma patients using computed tomography. Univariate and multivariate analysis to determine mortality hazard ratios (HR) were conducted using cox proportional hazard models.

RESULTS

Low SATI (SATI <50.0 cm² m^-2 in males and <42.0 cm² m^-2 in females) independently associated with increased mortality (HR: 1.26; 95% CI: 1.11-1.43; P<0.001) and shorter survival (13.1 months; 95% CI, 11.4-14.7) compared to patients with high SATI (19.3 months; 95% CI, 17.6-21.0; P<0.001). In the presence of sarcopenia, the longest survival was observed in patients with high subcutaneous adiposity.

CONCLUSIONS

Subcutaneous adipose tissues appear to associate with reduction in mortality risk demonstrating the prognostic importance of fat distribution. The effect of sarcopenia on survival was more pronounced in patients with low subcutaneous adiposity.

Tryptase expression as a prognostic marker in patients with resected gastric cancer

BACKGROUND

Mast cells play important roles in the progression of various malignancies, but their prognostic value in gastric cancer is unknown. Tryptase expression, as an indicator of mast cell activity, was therefore evaluated to see whether this could be incorporated usefully into a prognostic nomogram after surgery in patients with gastric cancer.

METHODS

Tissue microarrays from patients with gastric cancer were created from formalin-fixed, paraffin-embedded resection specimens. Tryptase density was assessed by immunohistochemistry, and the association between tryptase expression and prognosis was evaluated. Semiquantitative scoring was devised to determine an optimal cut-off value that correlated with survival. A prognostic nomogram was then developed incorporating tryptase expression scores along with other variables known to be related to survival.

RESULTS

Tissue microarrays were generated from 419 patients having surgery for gastric cancer. Increased tryptase expression was associated with better overall and recurrence-free survival (both P < 0·001). Tryptase expression was an independent favourable prognostic factor for overall (HR 0·72; P = 0·027) and recurrence-free (HR 0·74; P = 0·044) survival. The accuracy of an established prognostic model was improved when tryptase expression was added.

CONCLUSION

Tryptase expression is an independent prognostic factor for overall and recurrence-free survival in patients with gastric cancer after surgical resection.

Musashi-1 promotes a cancer stem cell lineage and chemoresistance in colorectal cancer cells

Colorectal cancers (CRCs) are a critical health issue worldwide. Cancer stem cell (CSC) lineages are associated with tumour transformation, progression, and malignant transformation. However, how lineages are transformed and how chemoresistance is acquired by CRCs remain largely unknown. In this report, we demonstrated that the RNA-binding protein Musashi-1 enhanced the development of CD44⁺ colorectal CSCs and triggered the formation of anti-apoptotic stress granules (SGs). Our results indicated that CD44⁺ CSC lineage-specific induction of tumour malignancies was controlled by Musashi-1. In addition, Musashi-1 formed SGs when CRC cell lines were treated with 5-fluorouracil. The C-terminal domain of Musashi-1 was critical for recruitment of Musashi-1 into SGs. Intracellular Musashi-1 SGs enhanced the chemoresistance of CRCs. Analysis of clinical CRC samples indicated that Musashi-1 expression was prominent in CRC stage IIA and IIB. In summary, we demonstrated that Musashi-1, a stemness gene, is a critical modulator that promotes the development of CD44⁺ colorectal CSCs and also enhances CRC chemoresistance via formation of SGs. Our findings elucidated a novel mechanism of CRC chemoresistance through increased anti-apoptotic effects via Musashi-1-associated SGs.

Fatty acid-binding protein 1 is preferentially lost in microsatellite instable colorectal carcinomas and is immune modulated via the interferon γ pathway

Fatty acid-binding protein 1 (FABP1) is an intracellular protein responsible for the transportation of long chain fatty acids. Aside from its functions in lipid metabolism and cellular differentiation, FABP1 also plays a role in inflammation through its interaction with peroxisome proliferator-activated receptors (PPARs). Previously, we compared expression of colonic epithelium genes in a subset of microsatellite instable (MSI) colorectal carcinomas (medullary carcinomas) to normal colonic mucosa and found that FABP1 expression was markedly decreased in the tumors. Further analysis of RNA expression in the colorectal subtypes and The Cancer Genome Atlas data set found that FABP1 expression is decreased in the CMS1 subset of colorectal carcinomas, which is characterized by microsatellite instability. As MSI colorectal carcinomas are known for their robust immune response, we then aimed to link FABP1 to the immune microenvironment of MSI carcinomas. To confirm the gene expression results, we performed immunohistochemical analysis of a cohort of colorectal carcinomas. FABP1 was preferentially lost in MSI carcinomas (123/133, 93%) compared with microsatellite stable carcinomas (240/562, 43%, P<0.0001). In addition, higher numbers of tumor-infiltrating lymphocytes were present in tumors with loss of FABP1 (P<0.0001). Decreased expression of the fatty acid storage and glucose regulator, PPARγ, was associated with the loss of FABP1 (P<0.0001). Colorectal cancer cell lines treated with interferon γ exhibited decreased expression of FABP1. FABP1 expression was partially recovered with the treatment of the cell lines with rosiglitazone, a PPARγ agonist. This study demonstrated that the loss of FABP1 expression is associated with MSI carcinomas and that interferon γ stimulation plays a role in this process via its interaction with PPARγ.

Tumor Infiltrating Mast Cells (TIMs) Confers a Marked Survival Advantage in Nonmetastatic Clear-Cell Renal Cell Carcinoma

PURPOSE

The role played by the innate immune system in determining the clinical outcome of clear-cell renal cell carcinoma (ccRCC) was still blurred. This study was designed to investigate the prognostic significance of tumor infiltrating mast cells (TIMs) in ccRCC.

METHODS

The study retrospectively enrolled a training set (474 patients) and a validation set (188 patients) with nonmetastasis (pT1-4N0M0) ccRCC from two institutional medical centers of China. TIMs was evaluated by immunohistochemical staining of tryptase and its association with clinicopathologic features and prognosis were evaluated.

RESULTS

In ccRCC tissues, TIMs ranged from 0 to 103 cells/mm² and 0 to 113 cells/mm² in the training set and validation set, respectively. TIMs was negatively correlated with tumor size (P < 0.001 and P < 0.001, respectively), pathological T stage (P = 0.005 and P = 0.007, respectively) and Fuhrman grade (P < 0.001 and P < 0.001, respectively). Patients with abundant TIMs infiltration showed significantly longer cancer-specific survival in the training cohort and the validation cohort (P < 0.001 and P < 0.001). Patients with abundant mast cell infiltration showed significantly longer overall survival in the TCGA cohort (P < 0.001). Moreover, multivariate analysis identified TIMs as an independent prognostic factor for cancer-specific survival (CSS) and relapse-free survival (RFS). Also, TIMs was significantly correlated with CSS and RFS of the mediate and high-risk patients in the training cohort and the validation cohort.

CONCLUSIONS

TIMs density is a powerful independent prognostic factor for CSS and RFS in patients with nonmetastasis (pT1-4N0M0) ccRCC.

Activation of peroxisome proliferator-activated receptor-gamma inhibits tumor growth by negatively regulating nuclear factor-κB activation in patients with hepatocellular carcinoma

BACKGROUND

The prognosis of advanced hepatocellular carcinoma (HCC) is poor because of its rapid progression. Peroxisome proliferator-activated receptor-gamma (PPARγ) is known to inhibit tumor growth in vitro; however, the behavior of PPARγ in clinical cases of HCC remains uncertain.

METHODS

Surgical specimens were collected from 104 HCC patients. The anti-neoplastic effects of PPARγ were evaluated.

RESULTS

PPARγ and its ligand expression were increased in some cases of HCC. When HCC patients were divided into two groups, tumor size was larger in patients with low PPARγ expression. Moreover, low PPARγ expression in HCC was an independent predictor of poorer prognosis. PPARγ expression was positively correlated with PPARγ activation and negatively correlated with NF-κB activation in HCC. PPARγ activation inhibited cell proliferation by inducing cell cycle arrest, through increased expression of p27(kip1) and decreased expression of cyclin D1 and interleukin-8. When HCC cells were treated with PPARγ ligands, PPARγ activation was increased and cell proliferation was inhibited in a dose-dependent manner. In contrast, PPARγ ligands negatively regulated NF-κB activation.

CONCLUSIONS

Activation of PPARγ induces cell cycle arrest and inhibits tumor progression by negatively regulating NF-κB activation in HCC. Therefore, PPARγ is an important endogenous regulator of HCC progression, and is a potential therapeutic target for HCC.

Commonalities in the Association between PPARG and Vitamin D Related with Obesity and Carcinogenesis

The PPAR nuclear receptor family has acquired great relevance in the last decade, which is formed by three different isoforms (PPARα, PPARβ/δ, and PPAR ϒ). Those nuclear receptors are members of the steroid receptor superfamily which take part in essential metabolic and life-sustaining actions. Specifically, PPARG has been implicated in the regulation of processes concerning metabolism, inflammation, atherosclerosis, cell differentiation, and proliferation. Thus, a considerable amount of literature has emerged in the last ten years linking PPARG signalling with metabolic conditions such as obesity and diabetes, cardiovascular disease, and, more recently, cancer. This review paper, at crossroads of basic sciences, preclinical, and clinical data, intends to analyse the last research concerning PPARG signalling in obesity and cancer. Afterwards, possible links between four interrelated actors will be established: PPARG, the vitamin D/VDR system, obesity, and cancer, opening up the door to further investigation and new hypothesis in this fascinating area of research.

Proteomic characterization of peroxisome proliferator-activated receptor-γ (PPARγ) overexpressing or silenced colorectal cancer cells unveils a novel protein network associated with an aggressive phenotype

Peroxisome proliferator-activated receptor-γ (PPARγ) is a transcription factor of the nuclear hormone receptor superfamily implicated in a wide range of processes, including tumorigenesis. Its role in colorectal cancer (CRC) is still debated; most reports support that PPARγ reduced expression is associated with poor prognosis. We employed 2-Dimensional Differential InGel Electrophoresis (2-D DIGE) followed by Liquid Chromatography (LC)-tandem Mass Spectrometry (MS/MS) to identify differentially expressed proteins and the molecular pathways underlying PPARγ expression in CRC progression. We identified several differentially expressed proteins in HT29 and HCT116 CRC cells and derived clones either silenced or overexpressing PPARγ, respectively. In Ingenuity Pathway Analysis (IPA) they showed reciprocal relation with PPARγ and a strong relationship with networks linked to cell death, growth and survival. Interestingly, five of the identified proteins, ezrin (EZR), isoform C of prelamin-A/C (LMNA), alpha-enolase (ENOA), prohibitin (PHB) and RuvB-like 2 (RUVBL2) were shared by the two cell models with opposite expression levels, suggesting a possible regulation by PPARγ. mRNA and western blot analysis were undertaken to obtain a technical validation and confirm the expression trend observed by 2-D DIGE data. We associated EZR upregulation with increased cell surface localization in PPARγ-overexpressing cells by flow cytometry and immunofluorescence staining. We also correlated EZR and PPARγ expression in our series of CRC specimens and the expression profiling of all five proteins levels in the publicly available colon cancer genomic data from Oncomine and Cancer Genome Atlas (TCGA) colon adenocarcinoma (COAD) datasets. In summary, we identified a panel of proteins correlated with PPARγ expression that could be associated with CRC unveiling new pathways to be investigated for the selection of novel potential prognostic/predictive biomarkers and/or therapeutic targets.

Increased Calcineurin A Expression Is Associated with a Lower Relapse-Free Survival Rate after Colorectal Cancer Surgery

OBJECTIVE

Increased expression of calcineurin in colorectal cancer (CRC) has been reported. Although the oncogenic function has been suggested, the clinical relevance is still unclear. We herein studied calcineurin expression as a prognostic biomarker in patients receiving curative surgery for stages I-III CRC.

METHODS

In 121 patients with stages I-III CRC treated at Hiroshima University between 1997 and 2003, calcineurin A expression was examined using immunohistochemistry (IHC) staining of surgical specimens. Specimens were considered positive for calcineurin A if any IHC-stained cells were observed within the carcinomatous area, and clinicopathological characteristics and survival outcomes were compared between IHC-positive and -negative groups.

RESULTS

Calcineurin A was preferentially expressed in the cytoplasm of cancer cells, and a median of 8% of the cells (range: 0-80%; interquartile range: 0-22.5%) were stained within the carcinomatous areas. Of 121 cases, 81 were determined as IHC positive while 40 were determined to be negative. Positive expression of calcineurin A, as well UICC-TNM stage, was associated with low relapse-free survival (RFS) rates in multivariate analyses (hazard ratio = 2.92; 95% CI: 1.27-7.92; p = 0.010).

CONCLUSION

Increased calcineurin A expression is associated with lower RFS rates and may have clinical value in predicting recurrence.

The peroxisome proliferator activated receptor gamma agonist pioglitazone increases functional expression of the glutamate transporter excitatory amino acid transporter 2 (EAAT2) in human glioblastoma cells

Glioma cells release glutamate through expression of system xc-, which exchanges intracellular glutamate for extracellular cysteine. Lack of the excitatory amino acid transporter 2 (EAAT2) expression maintains high extracellular glutamate levels in the glioma microenvironment, causing excitotoxicity to surrounding parenchyma. Not only does this contribute to the survival and proliferation of glioma cells, but is involved in the pathophysiology of tumour-associated epilepsy (TAE). We investigated the role of the peroxisome proliferator activated receptor gamma (PPARγ) agonist pioglitazone in modulating EAAT2 expression in glioma cells. We found that EAAT2 expression was increased in a dose dependent manner in both U87MG and U251MG glioma cells. Extracellular glutamate levels were reduced with the addition of pioglitazone, where statistical significance was reached in both U87MG and U251MG cells at a concentration of ≥ 30 μM pioglitazone (p < 0.05). The PPARγ antagonist GW9662 inhibited the effect of pioglitazone on extracellular glutamate levels, indicating PPARγ dependence. In addition, pioglitazone significantly reduced cell viability of U87MG and U251MG cells at ≥ 30 μM and 100 μM (p < 0.05) respectively. GW9662 also significantly reduced viability of U87MG and U251MG cells with 10 μM and 30 μM (p < 0.05) respectively. The effect on viability was partially dependent on PPARγ activation in U87MG cells but not U251MG cells, whereby PPARγ blockade with GW9662 had a synergistic effect. We conclude that PPARγ agonists may be therapeutically beneficial in the treatment of gliomas and furthermore suggest a novel role for these agents in the treatment of tumour associated seizures through the reduction in extracellular glutamate.

Subcellular compartmentalization of docking protein-1 contributes to progression in colorectal cancer

Full-length (FL) docking protein-1 (DOK1) is an adapter protein which inhibits growth factor and immune response pathways in normal tissues, but is frequently lost in human cancers. Small DOK1 variants remain in cells of solid tumors and leukemias, albeit, their functions are elusive. To assess the so far unknown role of DOK1 in colorectal cancer (CRC), we generated DOK1 mutants which mimic the domain structure and subcellular distribution of DOK1 protein variants in leukemia patients. We found that cytoplasmic DOK1 activated peroxisome-proliferator-activated-receptor-gamma (PPARγ) resulting in inhibition of the c-FOS promoter and cell proliferation, whereas nuclear DOK1 was inactive. PPARγ-agonist increased expression of endogenous DOK1 and interaction with PPARγ. Forward translation of this cell-based signaling model predicted compartmentalization of DOK1 in patients. In a large series of CRC patients, loss of DOK1 protein was associated with poor prognosis at early tumor stages (*p = 0.001; n = 1492). In tumors with cytoplasmic expression of DOK1, survival was improved, whereas nuclear localization of DOK1 correlated with poor outcome, indicating that compartmentalization of DOK1 is critical for CRC progression. Thus, DOK1 was identified as a prognostic factor for non-metastatic CRC, and, via its drugability by PPARγ-agonist, may constitute a potential target for future cancer treatments.

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Forward translation of a cell-based signaling model predicted clinical relevance for DOK1 in colorectal cancer (CRC).

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DOK1 is an independent prognostic factor in CRC patients, and its loss associated with poor survival.

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Cancer cell growth inhibition by DOK1 was increased (“drugable”) by PPARγ-agonist.

Poor survival due to failure to respond to clinical therapies prevents effective treatment of cancer. Thus, there is a high medical need for novel drug targets and biomarkers. DOK1 blocks pro-cancer signaling in the healthy body, but is often lost in tumors. We show that colorectal cancer patients who are positive for DOK1 have a better survival outcome than patients who are negative. Anti-diabetic drugs up-regulated DOK1 and promoted its protective actions against tumor cells. Our study therefore suggests DOK1 as a marker for good prognosis and as a potential drug target for therapy of colorectal cancer.

EGFR/MDM2 signaling promotes NF-κB activation via PPARγ degradation

Dysregulated expression of epidermal growth factor receptor (EGFR) has been implicated in many cancer events, while peroxisome proliferator-activated receptor γ (PPARγ) negatively regulates cancer progression. The molecular mechanism of EGFR interaction with PPARγ is still unclear. Here, we found that nuclear EGFR induced phosphorylation of PPARγ at Tyr-74 leading to PPARγ ubiquitination and degradation by mouse double minute 2 (MDM2) ubiquitin ligase. PPARγ degradation by EGFR/MDM2 signaling resulted in accumulation of nuclear factor-kappaB (NF-κB)/p65 protein levels and increasing NF-κB activation. In contrast, PPARγ-Y74A mutant reversed this event. Moreover, PPARγ-Y74A mutant suppressed cell proliferation and increased chemotherapeutic agent-induced cancer cell sensitivity. Importantly, the clinical findings show that the nuclear phosphorylation of PPARγ-Y74 and EGFR expression in colonic cancer tissues was higher than that in control normal tissues. Thus, our study revealed a novel molecular mechanism that nuclear EGFR/NF-κB signaling promoted cell proliferation by destructing PPARγ function, which provides a novel strategy for cancer treatment.

Prognostic role of PPAR-γ and PTEN in the renal cell carcinoma

OBJECTIVE

To explore association of peroxisome proliferator-activated receptor gamma (PPAR-γ) and phosphatase and tensin homolog (PTEN) expressions with prognosis of renal cell carcinoma (RCC).

METHODS

Our study subjects included 87 RCC tissues, 28 paracarcinoma tissues and 21 normal renal tissues. PPAR-γ and PTEN detection was conducted using immunohistochemistry staining. The association of PPAR-γ and PTEN with the clinical parameters and prognosis of RCC was analyzed. Kaplan-Meier method and Cox's proportional hazards regression model were used for exploring the relation between variables and prognosis.

RESULTS

Among normal renal tissues, para-carcinoma tissues and renal cell carcinomas, positive PPAR-γ expression presented with a progressive tendency (P < 0.001), while positive PTEN expression a degressive tendency (P < 0.001). PPAR-γ expressions were closely related to tumor size, clinical stage and lymph node metastases (all P < 0.05). PTEN expressions were in close association with tumor size, Fuhrman grading, lymph node metastases (all P < 0.05). PPAR-γ expressions were in a negative relation with PTEN expressions (r = -0.417, P < 0.001). Negative PPAR-γ expressions confer a significantly higher overall survival rate than positive PPAR-γ expressions (P = 0.015), while negative PTEN expressions confer a significantly lower overall survival rate than positive PTEN expressions (P = 0.003). Clinical staging, Fuhrman grading, lymph node metastases, PPAR-γ and PTEN were independent prognostic factors for prognosis (all P < 0.05).

CONCLUSION

PPAR-γ and PTEN expressions are related to the clinical parameters and prognosis of RCC and may be a biomarker for prognosis of RCC.

Beneficial health effects of Chios Gum Mastic and peroxisome proliferator-activated receptors: indications of common mechanisms

For thousands of years, Chios Gum Mastic (CGM), the resin produced by the trunk of Pistachia lentiscus var Chia, has been used for culinary and medicinal purposes and several therapeutic properties have been attributed to it. CGM has been used in traditional medicine of various nations in the eastern Mediterranean area. This survey was carried out to identify biological mechanisms that could explain traditional usage and recent pharmacological findings. We reviewed the related scientific literature available from the NCBI PUBMED database on CGM studies and on natural products showing peroxisome proliferator-activated receptor (PPAR) agonist effects. We investigated whether CGM qualifies as a PPAR modulator. A large number of studies demonstrate that CGM has antioxidant, anti-inflammatory, hypolipidemic, and anticancer properties. Recently, the first evidence of CGM antidiabetic effect became known. CGM chemical composition has been extensively analyzed and the presence of several compounds, especially triterpenoids is well documented. Some of them, oleanonic acid, oleanolic acid, and gallic acid are considered to act as PPAR modulators. PPARs are nuclear receptors functioning as transcription factors and thereby controlling cellular functions at the level of gene expression. PPARs are involved in the pathways of significant diseases, such as metabolic syndrome, diabetes mellitus, dyslipidemia, inflammation, atheromatosis, and neoplasias, constituting a key target for pharmacological interventions. This article proposes that the synergistic action of some constituents of CGM on PPARs and more precisely on both PPARs isotypes-α and -γ, may be one of the major biological mechanisms via which CGM exerts its multiple effects.

Clinical Significance of Peroxisome Proliferator-Activated Receptor γ and TRAP220 in Patients with Operable Colorectal Cancer

Purpose

The peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor that regulates expression of mediators of lipid metabolism and the inflammatory response. Thyroid hormone receptor-associated proteins 220 (TRAP220) is an essential component of the TRAP/Mediator complex. The objective of this study was to clarify whether PPARγ or TRAP220 are significant prognostic markers in resectable colorectal cancer (CRC).

Materials and Methods

A total of 399 patients who underwent curative resection for CRC were enrolled. We investigated the presence of PPARγ and TARP220 in CRC tissues and adjacent normal tissues by immunohistochemistry. Correlation between the expression of these factors and clinicopathologic features and survival was investigated.

Results

Median age of the patients was 63 years (range, 22 to 87 years), and median follow-up duration 61.1 months (range, 2 to 114 months). PPARγ and TRAP220 expression showed significant correlation with depth of invasion (p=0.013 and p=0.001, respectively). Expression of TRAP220 also showed association with lymph node metastasis and TNM stage (p=0.001). Compared with patients with TRAP220 negative tumors, patients with TRAP220 positive tumors had longer 5-year disease-free survival (DFS) tendency (p=0.051). Patients who were PPARγ positive combined with TRAP220 positive had a better 5-year DFS (64.8% vs. 79.3%, p=0.013). In multivariate analysis expression of both PPARγ and TRAP220 significantly affected DFS (hazard ratio, 0.620; 95% confidence interval, 0.379 to 0.997; p=0.048).

Conclusion

TRAP220 may be a valuable marker for nodal metastasis and TNM stage. Tumor co-expression of PPARγ and TRAP220 represents a biomarker for good prognosis in CRC patients.

Activation of mucosal mast cells promotes inflammation-related colon cancer development through recruiting and modulating inflammatory CD11b(+)Gr1(+) cells

Mast cells (MCs) have been reported to be one of the important immunoregulatory cells in promoting the development of colitis-related colon cancer (CRC). It is not clear which MC subtypes play critical roles in CRC progression from colitis to cancer because mucosal mast cells (MMCs) are distinct from connective tissue mast cells (CTMCs) in maintaining intestinal barrier function under homeostatic and inflammatory conditions. In the current study, we found that MMC numbers and the gene expressions of MMC-specific proteases increased significantly in an induced CRC murine model. The production of mast cell protease-1 (mMCP-1) after MMC activation not only resulted in the accumulation of CD11b(+)Gr1(+) inflammatory cells in the colon tissues but also modulated the activities of CD11b(+)Gr1(+) cells to support tumor cell growth and to inhibit T cell activation. Blocking the MMC activity in mice that had developed colitis-related epithelium dysplasia, CD11b(+)Gr1(+) infiltration was reduced and CRC development was inhibited. Our results suggest that MMC activation recruited and modulated the CD11b(+)Gr1(+) cells to promote CRC and that MMCs can be potential therapeutic targets for the prevention of CRC development.

Reporting in studies of protein biomarkers of prognosis in colorectal cancer in relation to the REMARK guidelines

PURPOSE

The REMARK guidelines give authors comprehensive and specific advice on the complete and transparent reporting of studies of prognostic tumor markers. The aim of this study was to use the REMARK guidelines to evaluate the quality of reporting in a sample of studies assessing tissue-based protein markers for survival after resection of colorectal cancer.

EXPERIMENTAL DESIGN

Eighty pertinent articles were scored according to their conformity to 26 items derived from the REMARK criteria.

RESULTS

Overall, on a scale of adequacy of reporting that potentially ranged from 26 to 78, the median for these studies was 60 (interquartile range 54-64) and several criteria were adequately covered in a large proportion of studies. However, others were either not dealt with or inadequately covered, including description of the study design (35%), definition of survival endpoints (48%), adjuvant therapy (54%), follow-up procedures and time (59%), neoadjuvant therapy (63%), inclusion/exclusion criteria (73%), multivariable modeling methods and results (74%), and discussion of study limitations (85%).

CONCLUSIONS AND CLINICAL RELEVANCE

Inadequacies in presentation militate against comparability among protein marker studies and undermine the generalizability of their findings. The quality of reporting could be improved if journal editors were to require authors to ensure that their work satisfied the REMARK criteria.

Protective Effects of Turbinaria ornata and Padina pavonia against Azoxymethane-Induced Colon Carcinogenesis through Modulation of PPAR Gamma, NF-κB and Oxidative Stress

The aim of this study was to investigate the antiproliferative and protective effects of the brown seaweeds, Turbinaria ornata and Padina pavonia, against azoxymethane (AOM)-induced colon carcinogenesis in mice. Both algal extracts showed anti-proliferative effects on the human carcinoma cell line HCT-116 in vitro, with T. ornata demonstrating a more potent effect. Male albino Swiss mice received intraperitoneal injections of AOM (10 mg/kg) once a week for two consecutive weeks and 100 mg/kg of either T. ornata or P. pavonia extracts. AOM-induced mice exhibited alterations in the histological structure of the colon, elevated lipid peroxidation and nitric oxide, declined glutathione content and reduced activity of superoxide dismutase and glutathione peroxidase. In addition, AOM induced downregulation of peroxisome proliferator activated receptor gamma (PPARγ) and p53 mRNA expression, with concomitant upregulation of nuclear factor-kappa B (NF-κB) in colon tissue. Administration of either algal extract markedly alleviated the recorded alterations. In conclusion, the current study suggests that T. ornata and P. pavonia, through their antioxidant and anti-inflammatory effects, are able to attenuate colon inflammation by downregulating NF-κB expression. Furthermore, the protective effects of both algae against AOM-initiated carcinogenesis were attributed, at least in part, to their ability to upregulate colonic PPARγ and p53 expression.

Chemotherapy and chemoprevention by thiazolidinediones

Thiazolidinediones (TZDs) are synthetic ligands of Peroxisome-Proliferator-Activated Receptor gamma (PPARγ). Troglitazone, rosiglitazone, and pioglitazone have been approved for treatment of diabetes mellitus type II. All three compounds, together with the first TZD ciglitazone, also showed an antitumor effect in preclinical studies and a beneficial effect in some clinical trials. This review summarizes hypotheses on the role of PPARγ in tumors, on cellular targets of TZDs, antitumor effects of monotherapy and of TZDs in combination with other compounds, with a focus on their role in the treatment of differentiated thyroid carcinoma. The results of chemopreventive effects of TZDs are also considered. Existing data suggest that the action of TZDs is highly complex and that actions do not correlate with cellular PPARγ expression status. Effects are cell-, species-, and compound-specific and concentration-dependent. Data from human trials suggest the efficacy of TZDs as monotherapy in prostate cancer and glioma and as chemopreventive agent in colon, lung, and breast cancer. TZDs in combination with other therapies might increase antitumor effects in thyroid cancer, soft tissue sarcoma, and melanoma.

A three-gene signature and clinical outcome in esophageal squamous cell carcinoma

It is increasingly apparent that cancer development depends not only on genetic alterations, but also on epigenetic changes involving histone modifications. GASC1, member of the histone demethylases affecting heterochromatin formation and transcriptional repression, has been found to be dysregulation in many types of cancers including breast cancer, prostate cancer, metastatic lung sarcomatoid carcinoma, and leukemia. In this study, we examined the expression of GASC1 and certain GASC1-targeted genes (KLF4, MYC, SOX2, PPARG, MDM2, and NANOG) and identified a three-gene prognostic signature (PPARG, MDM2, and NANOG), using risk scores based on immunohistochemical analyses of 149 tumor specimens from patients with esophageal squamous cell carcinoma (ESCC). The presence of a high-risk three-gene signature in the ESCC tumors was significantly associated with decreased overall survival (OS) of the patients. We validated the predictive value of the three-gene signature in a second independent cohort of 101 patients with ESCC in order to determine whether it had predictive value. The results were similar to those in 149 patients. According to multivariate Cox proportional hazards analyses, the predictive model of a three-gene signature was an independent predictor for OS (p = 0.005 in cohort 1, p = 0.025 in cohort 2). In addition, ROC analysis indicated that the predictive ability of the three-gene model was more robust than that of a single biomarker. Therefore, our three-gene signature is closely associated with OS among patients with ESCC and may serve as a predictor for the poor prognosis of ESCC patients.

Prognostic significance and therapeutic implications of peroxisome proliferator-activated receptor γ overexpression in human pancreatic carcinoma

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated nuclear receptor which has been implicated in carcinogenesis and angiogenesis in a wide range of cancers, including pancreatic carcinoma (PC). We aimed to characterize the prognosis and potential therapeutic implications of PPARγ in PC. Real-time RT-PCR and western blotting were used to quantify PPARγ expression in immortalized pancreatic epithelial cells, PC cell lines and freshly isolated matched tumor and non-tumor tissues. PPARγ protein expression was analyzed by immunohistochemistry (IHC) in archived tumor tissues from 101 PC patients. Furthermore, the effect of PPARγ on the cytotoxic action of gemcitabine (Gem) and 5-fluorouracil (5-FU) in PC cell lines was investigated in vitro using RNA interference techniques. Both PPARγ protein and mRNA were expressed at markedly higher levels in all of the PC cell lines and freshly isolated PC tissues, compared to normal immortalized pancreatic epithelial cells and the matched adjacent non-tumor tissues. High levels of PPARγ expression correlated significantly with tumor-node-metastasis (TNM) staging (P<0.001) and poor overall survival (P<0.001), especially in patients with advanced disease who received postoperative chemotherapy. While silencing of PPARγ significantly inhibit the cytotoxic effects of both gemcitabine and 5-fluorouracil in PC cells in vitro. This study suggests that high levels of PPARγ expression are associated with poor overall survival in PC. Additionally, PPARγ promotes chemoresistance in PC cells, indicating that PPARγ may represent a novel therapeutic target for PC.

PPARγ E3 ubiquitin ligase regulates MUC1-C oncoprotein stability

MUC1-C oncoprotein is associated with colon, breast, ovarian, lung and pancreatic cancers. MUC1-C interacts with intracellular proteins to elicit signaling cascades that induce cell proliferation and tumor growth. Here we report that peroxisome proliferator-activated receptor gamma (PPARγ), an E3 ubiquitin ligase, is an inhibitor of MUC1-C-mediated cell proliferation. PPARγ does so by binding to and inducing MUC1-C proteasome-dependent degradation that was independent of PPARγ transcriptional activity. Lys134 residue was found to be critically important for PPARγ-mediated MUC1-C degradation, as it terminated MUC1-C-mediated cell proliferation. These findings demonstrate PPARγ induces MUC1-C ubiquitination and degradation that is critical to terminate MUC1-C signaling pathway-elicited cancer.

Colonic mucosal fatty acid synthase as an early biomarker for colorectal neoplasia: modulation by obesity and gender

BACKGROUND

We have previously reported that colonic pericryptal microvascular blood flow is augmented in the premalignant colonic epithelium, highlighting the increased metabolic demand of the proliferative epithelium as a marker of field carcinogenesis. However, its molecular basis is unexplored. In this study, we assessed the expression of a regulator of the "lipogenic switch," fatty acid synthase (FASN), in early colon carcinogenesis for its potential biomarker utility for concurrent neoplasia.

METHODS

FASN expression (IHC) in the colonic epithelium from azoxymethane and polyposis in rat colon (Pirc) models of colorectal cancer was studied. FASN mRNA expression from endoscopically normal rectal mucosa was evaluated and correlated with colonoscopic findings (pathologic confirmation of neoplasia).

RESULTS

FASN expression progressively increased from premalignant to malignant stage in the azoxymethane model (1.9- to 2.5-fold; P < 0.0001) and was also higher in the adenomas compared with adjacent uninvolved mucosa (1.8- to 3.4-fold; P < 0.001) in the Pirc model. Furthermore, FASN was significantly overexpressed in rectal biopsies from patients harboring adenomas compared with those with no adenomas. These effects were accentuated in male (∼2-fold) and obese patients (1.4-fold compared with those with body mass index < 30). Overall, the performance of rectal FASN was excellent (AUROC of 0.81).

CONCLUSIONS

FASN is altered in the premalignant colonic mucosa and may serve as a marker for colonic neoplasia present elsewhere. The enhanced effects in men and obesity may have implications for identifying patient subgroups at risk for early-onset neoplasia.

IMPACT

These findings support the role of rectal FASN expression as a reliable biomarker of colonic neoplasia.

Specific metabolic biomarkers as risk and prognostic factors in colorectal cancer

Advances in genomics, molecular pathology and metabolism have generated many candidate biomarkers of colorectal cancer with potential clinical value. Epidemiological and biological studies suggest a role for adiposity, dyslipidaemia, hyperinsulinemia, altered glucose homeostasis, and elevated expression of insulin-like growth factor (IGF) axis members in the risk and prognosis of cancer. This review discusses some recent past and current approaches being taken by researches in obesity and metabolic disorders. The authors describe three main systems as the most studied metabolic candidates of carcinogenesis: dyslipidemias, adipokines and insulin/IGF axis. However, each of these components is unsuccessful in defining the diseases risk and progression, while their co-occurrence increases cancer incidence and mortality in both men and women.

Peroxisome proliferator-activated receptor γ upregulates galectin-9 and predicts prognosis in intestinal-type gastric cancer

The importance of PPARγ (peroxisome proliferator-activated receptor γ) in gastric cancer (GC) is unclear. We investigated the role of PPARγ in GC cell lines and an animal model, and its prognostic significance of PPARγ in GC patients. We controlled PPARγ and galectin-9 expression by using siRNAs and lentiviral constructs. Interaction between PPARγ and galectin-9 was evaluated using luciferase and chromatin immunoprecipitation assays. PPARγ expression in GCs was determined by immunohistochemical staining of tissue microarrays and survival analysis was done. Overexpression of PPARγ was accompanied by increased galectin-9. Enhanced PPARγ or galectin-9 expression increased E-cadherin expression; decreased expression of N-cadherin, fibronectin, snail, twist and slug and reduced cell invasion and migration. PPARγ bound to the galectin-9 promoter region. Galectin-9 activity increased in PPARγ-overexpressing cells but decreased in PPARγ siRNA-treated cells. In a zebrafish xenograft model, the number of migrated cancer cells and number of fish with AGS cells in the tail vein were reduced in PPARγ-overexpressing GC cells. PPARγ was expressed in 462 of the 688 patients (69.2%) with GC. In 306 patients with intestinal-type GC, those with PPARγ-positive tumors had lower overall and cancer-specific mortalities than those with PPARγ-negative tumors. PPARγ expression was an independent prognostic factor for overall and GC-specific mortality in patients with intestinal-type GC (adjusted hazard ratio, 0.42; 95% CI, 0.22-0.81). PPARγ inhibits cell invasion, migration and epithelial-mesenchymal transition through upregulation of galectin-9 in vitro and in vivo.

Chemopreventive drugs: Mechanisms via inhibition of cancer stem cells in colorectal cancer

Recent epidemiological studies, basic research and clinical trials on colorectal cancer (CRC) prevention have helped identify candidates for effective chemopreventive drugs. However, because of the conflicting results of clinical trials or side effects, the effective use of chemopreventive drugs has not been generalized, except for patients with a high-risk for developing hereditary CRC. Advances in genetic and molecular technologies have highlighted the greater complexity of carcinogenesis, especially the heterogeneity of tumors. We need to target cells and processes that are critical to carcinogenesis for chemoprevention and treatment of advanced cancer. Recent research has shown that intestinal stem cells may serve an important role in tumor initiation and formation of cancer stem cells. Moreover, studies have shown that the tumor microenvironment may play additional roles in dedifferentiation, to enable tumor cells to take on stem cell features and promote the formation of tumorigenic stem cells. Therefore, early tumorigenic changes of stem cells and signals for dedifferentiation may be good targets for chemoprevention. In this review, I focus on cancer stem cells in colorectal carcinogenesis and the effect of major chemopreventive drugs on stem cell-related pathways.

MicroRNA-130b promotes tumor development and is associated with poor prognosis in colorectal cancer

MicroRNA-130b (miR-130b) is involved in several biologic processes; its role in colorectal tumorigenesis has not been addressed so far. Herein, we demonstrate that miR-130b up-regulation exhibits clinical relevance as it is linked to advanced colorectal cancers (CRCs), poor patients' prognosis, and molecular features of enhanced epithelial-mesenchymal transition (EMT) and angiogenesis. miR-130b high-expressing cells develop large, dedifferentiated, and vascularized tumors in mouse xenografts, features that are reverted by intratumor injection of a specific antisense RNA. In contrast, injection of the corresponding mimic in mouse xenografts from miR-130b low-expressing cells increases tumor growth and angiogenic potential while reduces the epithelial hallmarks. These biologic effects are reproduced in human CRC cell lines. We identify peroxisome proliferator-activated receptor γ (PPARγ) as an miR-130b direct target in CRC in vitro and in vivo. Notably, the effects of PPARγ gain- and loss-of-function phenocopy those due to miR-130b down-regulation or up-regulation, respectively, underscoring their biologic relevance. Furthermore, we provide mechanistic evidences that most of the miR-130b-dependent effects are due to PPARγ suppression that in turn deregulates PTEN, E-cadherin, Snail, and vascular endothelial growth factor, key mediators of cell proliferation, EMT, and angiogenesis. Since higher levels of miR-130b are found in advanced tumor stages (III-IV), we propose a novel role of the miR-130b-PPARγ axis in fostering the progression toward more invasive CRCs. Detection of onco-miR-130b and its association with PPARγ may be useful as a prognostic biomarker. Its targeting in vivo should be evaluated as a novel effective therapeutic tool against CRC.

Peroxisome proliferator-activated receptor γ-mediated induction of microRNA-145 opposes tumor phenotype in colorectal cancer

MicroRNAs (miRNAs) regulate diverse biological processes by inhibiting translation or inducing degradation of target mRNAs. miR-145 is a candidate tumor suppressor in colorectal carcinoma (CRC). Colorectal carcinogenesis involves deregulation of cellular processes controlled by a number of intertwined chief transcription factors, such as PPARγ and SOX9. Since PPAR family members are able to modulate complex miRNAs networks, we hypothesized a role of miRNA-145 in the interaction between PPARγ and SOX9 in colorectal carcinogenesis. To address this issue, we evaluated gene expression in tissue specimens of CRC patients and we took advantage of invitro models represented by CRC derived cell lines (CaCo2, SW480, HCT116, and HT-29), employing PPARγ activation and/or miRNA-145 ectopic overexpression to analyze how their interplay impact the expression of SOX9 and the development of a malignant phenotype.

RESULTS

PPARγ regulates the expression of miR-145 by directly binding to a PPAR response element (PPRE) in its promoter at -1207/-1194bp from the transcription start site. The binding is essential for miR-145 upregulation by PPARγ upon rosiglitazone treatment. Ectopic expression of miR-145, in turn, regulates SOX9 expression through the binding to specific seed motifs. The PPARγ-miR-145-SOX9 axis overarches cell cycle progression, invasiveness and differentiation of CRC derived cell lines. Together, these results suggest that miR-145 is a novel target of PPARγ, acts as a tumor suppressor in CRC cell lines and is a key regulator of intestinal cell differentiation by directly targeting SOX9, a marker of undifferentiated progenitors in the colonic crypts.

PPARγ1 phosphorylation enhances proliferation and drug resistance in human fibrosarcoma cells

Post-translational regulation plays a critical role in the control of cell growth and proliferation. The phosphorylation of peroxisome proliferator-activated receptor γ (PPARγ) is the most important post-translational modification. The function of PPARγ phosphorylation has been studied extensively in the past. However, the relationship between phosphorylated PPARγ1 and tumors remains unclear. Here we investigated the role of PPARγ1 phosphorylation in human fibrosarcoma HT1080 cell line. Using the nonphosphorylation (Ser84 to alanine, S84A) and phosphorylation (Ser84 to aspartic acid, S84D) mutant of PPARγ1, the results suggested that phosphorylation attenuated PPARγ1 transcriptional activity. Meanwhile, we demonstrated that phosphorylated PPARγ1 promoted HT1080 cell proliferation and this effect was dependent on the regulation of cell cycle arrest. The mRNA levels of cyclin-dependent kinase inhibitor (CKI) p21(Waf1/Cip1) and p27(Kip1) descended in PPARγ1(S84D) stable HT1080 cell, whereas the expression of p18(INK4C) was not changed. Moreover, compared to the PPARγ1(S84A), PPARγ1(S84D) up-regulated the expression levels of cyclin D1 and cyclin A. Finally, PPARγ1 phosphorylation reduced sensitivity to agonist rosiglitazone and increased resistance to anticancer drug 5-fluorouracil (5-FU) in HT1080 cell. Our findings establish PPARγ1 phosphorylation as a critical event in human fibrosarcoma growth. These findings raise the possibility that chemical compounds that prevent the phosphorylation of PPARγ1 could act as anticancer drugs.

Small molecule agonists of PPAR-γ exert therapeutic effects in esophageal cancer

The transcription factor PPAR-γ plays various roles in lipid metabolism, inflammation, cellular differentiation, and apoptosis. PPAR-γ agonists used to treat diabetes may have utility in cancer treatment. Efatutazone is a novel later generation PPAR-γ agonist that selectively activates PPAR-γ target genes and has antiproliferative effects in a range of malignancies. In this study, we investigated PPAR-γ status in esophageal squamous cell carcinoma (ESCC) and investigated the antiproliferative effects of efatutazone. PPAR-γ was expressed heterogeneously in ESCC, in which it exhibited an inverse relationship with Ki-67 expression. PPAR-γ expression was associated independently with good prognosis in ESCC. Efatutazone, but not the conventional PPAR-γ agonist troglitazone, inhibited ESCC cell proliferation in vitro and in vivo. Mechanistic investigations suggested that efatutazone acted by upregulating p21Cip1 protein in the nucleus through inactivation of the Akt pathway and dephosphorylation of p21Cip1 at Thr145 without affecting the transcriptional activity of p21Cip1. We also found that treatment with efatutazone led to phosphorylation of the EGF receptor and activation of the mitogen-activated protein kinase (MAPK) pathway. Accordingly, the combination of efatutazone with the antiepithelial growth factor receptor antibody cetuximab synergized to negatively regulate the phosphoinositide 3-kinase-Akt and MAPK pathways. Together, our results suggest that efatutazone, alone or in combination with cetuximab, may offer therapeutic effects in ESCC.

Tumour-infiltrating CD68+ and CD57+ cells predict patient outcome in stage II-III colorectal cancer

Background:

The aim of our study was to evaluate the prognostic role of immunological microenvironnement in stage II–III CRC patients.

Methods:

We constructed a tissue microarray from 196 consecutive patients with stage II–III CRC and compared CD3, CD4, CD8, CD57, CD68, CXCL9/MIG, CXCL13, and PPARγ immunoreactivity in tumour samples and their matched non-tumour tissue. We assessed their association with relapse-free survival (RFS; primary endpoint) and overall survival (OS) in multivariate Cox models.

Results:

Low densities of CD57+ and CD68+ tumour-infiltrating cells (TIC) independently predicted worse outcomes. A prognostic score combining CD57 (+, > vs −, ⩽2 cells per spot) and CD68 (+, >0 vs −, =0 cells per spot) TIC density discriminated CRC patients at low (CD68+/CD57+), intermediate (CD68+/CD57−), or high (CD68−/CD57−) risk, with hazard ratios for the intermediate-risk and high-risk groups of 2.7 (95% confidence interval (CI): 1.3–5.8) and 9.0 (3.2–25.4) for RFS, and 2.5 (1.2–5.1) and 10.6 (3.8–29.2) for OS, respectively, as compared with the low-risk group. Corresponding 5-year survival rates (95% CI) in the low-, moderate- and high-risk groups were 84% (71–91), 65% (54–74), and 12% (2–47), respectively, for RFS, and 91% (80–96), 76% (66–84), and 25% (7–59), respectively, for OS.

Conclusion:

Tumour CD57+ and CD68+ TIC density assessment independently predicts survival in patients with stage II–III CRC. If validated, our score based on a quick, inexpensive, and well-established method such as point counting on diagnostic tissue sections could be used routinely as a prognostic tool in CRC patients.

PPARγ is an E3 ligase that induces the degradation of NFκB/p65

Nuclear factor-κB (NFκB) and peroxisome proliferator activated receptor-γ (PPARγ) are both transcription factors that perform distinct but overlapping roles in cellular regulation. Here we report that PPARγ acts as an E3 ubiquitin ligase, physically interacting with p65 to induce its ubiquitination and degradation. The ligand-binding domain of PPARγ interacts with the Rel Homology Domain region of NFκB/p65 to undergo robust ubiquitination and degradation that was independent of PPARγ transcriptional activity. Moreover, the ligand-binding domain of PPARγ delivered Lys48-linked polyubiquitin, resulting in the ubiquitination and degradation of p65. Lys28 was found to be critically important for PPARγ-mediated ubiquitination and degradation of p65, as it terminated both NFκB/p65-mediated pro-inflammatory responses and xenograft tumours. These findings demonstrate that PPARγ E3 ubiquitin ligase activity induces Lys48-linked ubiquitination and degradation of p65, and that this function is critical to terminate NFκB signalling pathway-elicited inflammation and cancer.

SERPINA3K induces apoptosis in human colorectal cancer cells via activating the Fas/FasL/caspase-8 signaling pathway

SERPINA3K, also known as kallikrein-binding protein (KBP), is a serine proteinase inhibitor with anti-inflammatory and anti-angiogenic activities. Our previous studies showed that SERPINA3K inhibited proliferation in a dose-dependent manner and induced apoptosis of endothelial cells but had no influence on SGC-7901 gastric carcinoma cells or HepG2 hepatocarcinoma cells. However, it is unknown whether SERPINA3K has a direct impact on other carcinoma cells and which mechanisms are involved. In this study, we report for the first time that SERPINA3K not only decreased cell viability but also induced apoptosis in the colorectal carcinoma cell lines SW480 and HT-29. SERPINA3K-induced apoptosis of SW480 and HT-29 was rescued by interference with Fas ligand (FasL) small hairpin RNA. Moreover, SERPINA3K increased the expression of FasL and activated caspase-8. Peroxisome proliferator-activated receptor γ (PPARγ), a transcription factor of FasL, was also upregulated by SERPINA3K in a dose-dependent manner. The upregulation effect of FasL induced by SERPINA3K was reversed after interference with PPARγ small interfering RNA. These results demonstrated that SERPINA3K-induced SW480 and HT-29 cell apoptosis was mediated by the PPARγ/Fas/FasL signaling pathway. Therefore, our study provides additional insight into the direct anti-tumor function by inducing tumor cell apoptosis of SERPINA3K in colorectal tumors.

Deficiency of caveolin-1 in Apc(min/+) mice promotes colorectal tumorigenesis

Caveolin-1 (Cav1), a scaffold protein of membrane caveolae and coactivator of peroxisome proliferator-activated receptor gamma (PPARg), inhibits oncogenic signaling through Ras and wingless. However, the in vivo role of Cav1 in colorectal cancer (CRC) remained unknown. To test whether loss of Cav1 accelerates tumorigenesis, we generated a novel mouse model of CRC by crossing C57BL/6 Apc(min/+) with B6129 Cav1 knockout (Cav1-/-) mice. Apc(min/+) Cav1-/- mice developed large, microinvasive and vascularized intraepithelial adenocarcinomas in the distal colon and rectum with higher incidence than Apc(min/+) Cav1+/- and Apc(min/+) Cav1+/+ littermates. Intratumoral gene signatures related to Ras and wingless signaling were elevated, nuclear localization of PPARg protein and expression of PPARg-target genes were reduced independently of Cav1. The PPARg-agonist rosiglitazone prevented tumor formation in mice irrespectively of the Cav1 status and upregulated expression of the Ras-inhibitory protein docking protein-1. Thus, codeficiency of Cav1 and adenomatous polyposis coli facilitated formation of CRC, and activation of PPARg may offer novel strategies for treatment of CRC.

Interplay between SOX9, β-catenin and PPARγ activation in colorectal cancer

Colorectal carcinogenesis relies on loss of homeostasic mechanisms regulating cell proliferation, differentiation and survival. These cell processes have been reported to be influenced independently by transcription factors activated downstream of the Wnt pathway, such as SOX9 and β-catenin, and by the nuclear receptor PPARγ. The purpose of this study was to explore the expression levels and functional link between SOX9, β-catenin and PPARγ in the pathogenesis of colorectal cancer (CRC). We evaluated SOX9, β-catenin and PPARγ expression levels on human CRC specimens by qPCR and immunoblot detection. We tested the hypothesis that PPARγ activation might affect SOX9 and β-catenin expression using four colon cancer cell lines (CaCo2, SW480, HCT116, and HT29 cells). In CRC tissues SOX9 resulted up-regulated at both mRNA and protein levels when compared to matched normal mucosa, β-catenin resulted up-regulated at protein levels, while PPARG mRNA and PPARγ protein levels were down-regulated. A significant relationship was observed between high PPARG and SOX9 expression levels in the tumor tissue and female gender (p=0.005 and p=0.04, respectively), and between high SOX9 expression in the tumor tissue and age (p=0.04) and microsatellite instability (MSI), in particular with MSI-H (p=0.0002). Moreover, treatment with the synthetic PPARγ ligand rosiglitazone induced different changes of SOX9 and β-catenin expression and subcellular localization in the colon cancer cell lines examined. In conclusion, SOX9, β-catenin and PPARγ expression levels are deregulated in the CRC tissue, and in colon cancer cell lines ligand-dependent PPARγ activation unevenly influences SOX9 and β-catenin expression and subcellular localization, suggesting a variable mechanistic role in colon carcinogenesis.

Peroxisome proliferator-activated receptor-γ activation inhibits hepatocellular carcinoma cell invasion by upregulating plasminogen activator inhibitor-1

The peroxisome proliferator-activated receptor-γ (PPARγ) is a ligand-activated transcription factor belonging to the nuclear receptor superfamily. Peroxisome proliferator-activated receptor-γ ligands can inhibit cell growth and increase apoptosis of cancer cell lines, suggesting a potential role for PPARγ as a tumor suppressor. Whereas the related studies between PPARγ and cancer cell invasion are still poor. Our previous study indicates that β-estradiol (E2) suppresses hepatocellular carcinoma (HCC) cell invasion. We report here that E2 can activate PPARγ of HCC cells, and activated PPARγ suppresses cell invasion by upregulating the expression level of plasminogen activator inhibitor-1 (PAI-1). We found that PPARγ plays an important role in the E2-induced HCC cell invasion process. Using PPARγ agonist GW1929, a reduced invasion effect was found in HCC cell lines, and this inhibition of cell invasion was dosage-dependent. However, cell invasion was restored by treatment with PPARγ antagonist GW9662. The activated PPARγ upregulated the expression of cell migration-related protein PAI-1. Furthermore, knockdown of PPARγ in HCC cells decreased the level of PAI-1 and advanced cell invasion in response to GW1929. On the contrary, overexpression of PPARγ in HCC cells elevated the level of PAI-1 and inhibited cell invasion. These findings suggest that PPARγ activation inhibits HCC cell invasion via the upregulation of PAI-1 and implicate that PPARγ is a target for the treatment and prevention of HCC cell invasion.