Biological function and prognostic significance of peroxisome proliferator-activated receptor δ in rectal cancer

Activation of PPARδ in bone marrow endothelial progenitor cells improves their hematopoiesis-supporting ability after myelosuppressive injury

Dysfunctional bone marrow (BM) endothelial progenitor cells (EPCs) with high levels of reactive oxygen species (ROS) are responsible for defective hematopoiesis in poor graft function (PGF) patients with acute leukemia or myelodysplastic neoplasms post-allotransplant. However, the underlying mechanism by which BM EPCs regulate their intracellular ROS levels and the capacity to support hematopoiesis have not been well clarified. Herein, we demonstrated decreased levels of peroxisome proliferator-activated receptor delta (PPARδ), a lipid-activated nuclear receptor, in BM EPCs of PGF patients compared with those with good graft function (GGF). In vitro assays further identified that PPARδ knockdown contributed to reduced and dysfunctional BM EPCs, characterized by the impaired ability to support hematopoiesis, which were restored by PPARδ overexpression. Moreover, GW501516, an agonist of PPARδ, repaired the damaged BM EPCs triggered by 5-fluorouracil (5FU) in vitro and in vivo. Clinically, activation of PPARδ by GW501516 benefited the damaged BM EPCs from PGF patients or acute leukemia patients in complete remission (CR) post-chemotherapy. Mechanistically, we found that increased expression of NADPH oxidases (NOXs), the main ROS-generating enzymes, may lead to elevated ROS level in BM EPCs, and insufficient PPARδ may trigger BM EPC damage via ROS/p53 pathway. Collectively, we found that defective PPARδ contributes to BM EPC dysfunction, whereas activation of PPARδ in BM EPCs improves their hematopoiesis-supporting ability after myelosuppressive therapy, which may provide a potential therapeutic target not only for patients with leukemia but also for those with other cancers.

Loss of CHGA Protein as a Potential Biomarker for Colon Cancer Diagnosis: A Study on Biomarker Discovery by Machine Learning and Confirmation by Immunohistochemistry in Colorectal Cancer Tissue Microarrays

Simple Summary

The identification of effective novel biomarkers is emergently needed in colon cancer patients. In the present study, firstly we predicted that CHGA could be a biomarker for colon cancer based on the protein–protein interaction network of all the reported biomarkers that were collected from our colorectal cancer biomarker database (CBD). Then we verified our results using a diagnostic test in gene expression data and an immunohistochemistry test. The results of this study suggest that a loss of CHGA expression from the normal colon and adjacent mucosa to colon cancer may be used as a valuable biomarker for early diagnosis of colon cancer patients.

Abstract

Background. The incidence of colorectal cancers has been constantly increasing. Although the mortality has slightly decreased, it is far from satisfaction. Precise early diagnosis for colorectal cancer has been a great challenge in order to improve patient survival. Patients and Methods. We started with searching for protein biomarkers based on our colorectal cancer biomarker database (CBD), finding differential expressed genes (GEGs) and non-DEGs from RNA sequencing (RNA-seq) data, and further predicted new biomarkers of protein–protein interaction (PPI) networks by machine learning (ML) methods. The best-selected biomarker was further verified by a receiver operating characteristic (ROC) test from microarray and RNA-seq data, biological network, and functional analysis, and immunohistochemistry in the tissue arrays from 198 specimens. Results. There were twelve proteins (MYO5A, CHGA, MAPK13, VDAC1, CCNA2, YWHAZ, CDK5, GNB3, CAMK2G, MAPK10, SDC2, and ADCY5) which were predicted by ML as colon cancer candidate diagnosis biomarkers. These predicted biomarkers showed close relationships with reported biomarkers of the PPI network and shared some pathways. An ROC test showed the CHGA protein with the best diagnostic accuracy (AUC = 0.9 in microarray data and 0.995 in RNA-seq data) among these candidate protein biomarkers. Furthermore, immunohistochemistry examination on our colon cancer tissue microarray samples further confirmed our bioinformatical prediction, indicating that CHGA may be used as a potential biomarker for early diagnosis of colon cancer patients. Conclusions. CHGA could be a potential candidate biomarker for diagnosing earlier colon cancer in the patients.

Identifying the Metabolic Signatures of PPARD-Overexpressing Gastric Tumors

Peroxisome proliferator-activated receptor delta (PPARD) is a nuclear receptor known to play an essential role in regulation of cell metabolism, cell proliferation, inflammation, and tumorigenesis in normal and cancer cells. Recently, we found that a newly generated villin-PPARD mouse model, in which PPARD is overexpressed in villin-positive gastric progenitor cells, demonstrated spontaneous development of large, invasive gastric tumors as the mice aged. However, the role of PPARD in regulation of downstream metabolism in normal gastric and tumor cells is elusive. The aim of the present study was to find PPARD-regulated downstream metabolic changes and to determine the potential significance of those changes to gastric tumorigenesis in mice. Hyperpolarized [1-13C] pyruvate magnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, and liquid chromatography-mass spectrometry were employed for metabolic profiling to determine the PPARD-regulated metabolite changes in PPARD mice at different ages during the development of gastric cancer, and the changes were compared to corresponding wild-type mice. Nuclear magnetic resonance spectroscopy-based metabolomic screening results showed higher levels of inosine monophosphate (p = 0.0054), uracil (p = 0.0205), phenylalanine (p = 0.017), glycine (p = 0.014), and isocitrate (p = 0.029) and lower levels of inosine (p = 0.0188) in 55-week-old PPARD mice than in 55-week-old wild-type mice. As the PPARD mice aged from 10 weeks to 35 weeks and 55 weeks, we observed significant changes in levels of the metabolites inosine monophosphate (p = 0.0054), adenosine monophosphate (p = 0.009), UDP-glucose (p = 0.0006), and oxypurinol (p = 0.039). Hyperpolarized [1-13C] pyruvate magnetic resonance spectroscopy performed to measure lactate flux in live 10-week-old PPARD mice with no gastric tumors and 35-week-old PPARD mice with gastric tumors did not reveal a significant difference in the ratio of lactate to total pyruvate plus lactate, indicating that this PPARD-induced spontaneous gastric tumor development does not require glycolysis as the main source of fuel for tumorigenesis. Liquid chromatography-mass spectrometry-based measurement of fatty acid levels showed lower linoleic acid, palmitic acid, oleic acid, and steric acid levels in 55-week-old PPARD mice than in 10-week-old PPARD mice, supporting fatty acid oxidation as a bioenergy source for PPARD-expressing gastric tumors.

Knockdown of PPARδ Induces VEGFA-Mediated Angiogenesis via Interaction With ERO1A in Human Colorectal Cancer

Angiogenesis is an important mechanism underlying the development and metastasis of colorectal cancer (CRC) and has emerged as a therapeutic target for metastatic CRC (mCRC). Our recent studies found that Peroxisome proliferator-activated receptor β/δ/D (PPARδ) regulates vascular endothelial growth factor A(VEGFA) secretion and the sensitivity to bevacizumab in CRC. However, its exact effect and underlying mechanisms remain unidentified. In this study, we showed that PPARδ expression was inversely associated with the microvascular density in human CRC tissues. Knockdown of PPARδ enhanced VEGFA expression in HCT116 cells and HUVEC angiogenesis in vitro; these phenomena were replicated in the experimental in vivo studies. By tandem mass tag (TMT)-labeling proteomics and chromatin immunoprecipitation sequencing (ChIP-seq) analyses, endoplasmic reticulum oxidoreductase 1 alpha (ERO1A) was screened and predicted as a target gene of PPARδ. This was verified by exploring the effect of coregulation of PPARδ and ERO1A on the VEGFA expression in HCT116 cells. The results revealed that PPARδ induced VEGFA by interacting with ERO1A. In conclusion, our results suggest that knockdown of PPARδ can promote CRC angiogenesis by upregulating VEGFA through ERO1A. This pathway may be a potential target for mCRC treatment.

AMPK phosphorylates PPARδ to mediate its stabilization, inhibit glucose and glutamine uptake and colon tumor growth

Peroxisome proliferator-activated receptor δ (PPARδ) is a nuclear receptor transcription factor that plays an important role in the regulation of metabolism, inflammation, and cancer. In addition, the nutrient-sensing kinase 5'AMP-activated protein kinase (AMPK) is a critical regulator of cellular energy in coordination with PPARδ. However, the molecular mechanism of the AMPK/PPARδ pathway on cancer progression is still unclear. Here, we found that activated AMPK induced PPARδ-S50 phosphorylation in cancer cells, whereas the PPARδ/S50A (nonphosphorylation mimic) mutant reversed this event. Further analysis showed that the PPARδ/S50E (phosphorylation mimic) but not the PPARδ/S50A mutant increased PPARδ protein stability, which led to reduced p62/SQSTM1-mediated degradation of misfolded PPARδ. Furthermore, PPARδ-S50 phosphorylation decreased PPARδ transcription activity and alleviated PPARδ-mediated uptake of glucose and glutamine in cancer cells. Soft agar and xenograft tumor model analysis showed that the PPARδ/S50E mutant but not the PPARδ/S50A mutant inhibited colon cancer cell proliferation and tumor growth, which was associated with inhibition of Glut1 and SLC1A5 transporter protein expression. These findings reveal a new mechanism of AMPK-induced PPARδ-S50 phosphorylation, accumulation of misfolded PPARδ protein, and inhibition of PPARδ transcription activity contributing to the suppression of colon tumor formation.

Fatty Acids Metabolism: The Bridge Between Ferroptosis and Ionizing Radiation

Exposure of tumor cells to ionizing radiation (IR) alters the microenvironment, particularly the fatty acid (FA) profile and activity. Moreover, abnormal FA metabolism, either catabolism or anabolism, is essential for synthesizing biological membranes and delivering molecular signals to induce ferroptotic cell death. The current review focuses on the bistable regulation characteristics of FA metabolism and explains how FA catabolism and anabolism pathway crosstalk harmonize different ionizing radiation-regulated ferroptosis responses, resulting in pivotal cell fate decisions. In summary, targeting key molecules involved in lipid metabolism and ferroptosis may amplify the tumor response to IR.

Nuclear receptors: Lipid and hormone sensors with essential roles in the control of cancer development

Nuclear receptors (NRs) are a superfamily of ligand-activated transcription factors that act as biological sensors and use a combination of mechanisms to modulate positively and negatively gene expression in a spatial and temporal manner. The highly orchestrated biological actions of several NRs influence the proliferation, differentiation, and apoptosis of many different cell types. Synthetic ligands for several NRs have been the focus of extensive drug discovery efforts for cancer intervention. This review summarizes the roles in tumour growth and metastasis of several relevant NR family members, namely androgen receptor (AR), estrogen receptor (ER), glucocorticoid receptor (GR), thyroid hormone receptor (TR), retinoic acid receptors (RARs), retinoid X receptors (RXRs), peroxisome proliferator-activated receptors (PPARs), and liver X receptors (LXRs). These studies are key to develop improved therapeutic agents based on novel modes of action with reduced side effects and overcoming resistance.

Expressions of miR-302a, miR-105, and miR-888 Play Critical Roles in Pathogenesis, Radiotherapy, and Prognosis on Rectal Cancer Patients: A Study From Rectal Cancer Patients in a Swedish Rectal Cancer Trial of Preoperative Radiotherapy to Big Database Analyses

Differential expressions and functions of various micoRNAs (miRNAs) have been intensively studied in both colon and rectal cancers. However, the importance of miRNAs on radiotherapy (RT) response and clinical outcome in rectal cancer patients remains unclear. In this study, we used real-time polymerase chain reaction to examine the expressions of miR-302a, miR-105, and miR-888 in normal mucosa and cancer tissue from rectal cancer patients with and without preoperative RT. The biological function of miR-302a, miR-105, and miR-888 expression was further analyzed and identified through the public databases: TCGA (The Cancer Genome Atlas) and GEPIA (Gene Expression Profiling Interactive Analysis). The results showed that the expression of miR-105 in rectal cancer was higher than that in normal mucosa in RT (P = 0.042) and non-RT patients (P = 0.003) and was associated with mucinous histological type (P = 0.004), COX-2 (P = 0.042), and p73 expression (P = 0.030). The expression of miR-302a was shown more frequently in cancers with necrosis (P = 0.033) and with WRAP53 expression (P = 0.015), whereas miR-888 expression occurred more frequently in tumors with protein the expression of survivin (P = 0.015), AEG-1 (astrocyte elevated gene-1) (P = 0.003), and SATB1 (special AT-rich sequence binding protein 1) (P = 0.036). Moreover, TargetScan also predicted AEG-1 and SATB1 as putative targets for miR-888. The miRNA-gene network analysis showed that ABI2 was associated with all the three miRNAs, with lower expression and good diagnostic value in rectal cancers. The TCGA database demonstrated the association of miR-105 expression with high carcinoembryonic antigen level (P = 0.048). RT reduced the expressions of miR-302a, miR-105, and miR-888. Prognostic analysis showed that miR-888 expression was independently associated with worse survival of patients without RT [overall survival, P = 0.001; disease-free survival, P = 0.009]. Analysis of biological function revealed that the protein serine/threonine kinase activity and PI3K-AKT signaling pathway were the most significantly enriched functions and pathways, respectively. Our findings suggest that miR-105 is involved in rectal cancer pathogenesis and miR-888 is associated with prognosis. MiR-302a, miR-105, and miR-888 have potential influence on the pathogenesis, RT, and prognosis of rectal cancer.

Prognostic value of nuclear FBI-1 in patients with rectal cancer with or without preoperative radiotherapy

Factor that binds to the inducer of short transcripts of the human immunodeficiency virus-1 (FBI-1) represents as a crucial gene regulator in colorectal cancer; however, the correlation between FBI-1 and preoperative radiotherapy (RT) in rectal cancer (RC) has not yet been reported. The aim was to detect FBI-1 expression in patients with RC with or without RT, by immunohistochemistry and quantitative polymerase chain reaction, and to analyze its association with clinicopathological features and response to RT. The results from immunohistochemistry analysis (n=139) and reverse transcription-quantitative polymerase chain reaction (n=55) demonstrated that FBI-1 was overexpressed in patients with RC, whether they had received preoperative RT or not. Subsequently, the association between FBI-1 expression, and the clinicopathological features and response to RT in patients with RC was analyzed. Cytoplasmic FBI-1 was upregulated in non-RT (n=77) and RT (n=62) groups (17.7 vs. 74.0%, P<0.001; 41.1 vs. 69.4%, P=0.002, respectively) of patients with RC compared with normal mucosa. However, nuclear FBI-1 was downregulated (75.8 vs. 22.1%, P<0.001; 83.9 vs. 35.5%, P<0.001, respectively) in both groups. RT had no significant effect on FBI-1 expression in RC tissues. Furthermore, nuclear FBI-1 was positively associated with tumor-node-metastasis stage and distant recurrence (P=0.003 and P=0.010, respectively). In patients with stage I, II or III RC, higher nuclear FBI-1 expression was associated with poorer disease-free survival [hazard ratio (HR)=1.934, 95% confidence interval (CI): 1.055-3.579, P=0.033] and overall survival (HR=2.174, 95% CI: 1.102-4.290, P=0.025), independently of sex, age, growth pattern, differentiation and RT. In addition, FBI-1 was positively correlated with numerous biological factors, including p73 [Spearman's correlation coefficient (r_s)=0.332, P=0.007], lysyl oxidase (r_s=0.234, P=0.043), Wrap53 (r_s=-0.425, P=0.0002) and peroxisome proliferator-activated receptor δ (r_s=-0.294, P=0.026). In conclusion, the present study demonstrated that nuclear FBI-1 was an independent prognostic factor in patients with RC and correlated with numerous biological factors, which indicated that it may have multiple roles in RC.

Unraveling the role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) expression in colon carcinogenesis

The peroxisome proliferator-activated-β/δ (PPARβ/δ) was identified in 1994, but not until 1999 was PPARβ/δ suggested to be involved in carcinogenesis. Initially, it was hypothesized that expression of PPARβ/δ was increased during colon cancer progression, which led to increased transcription of yet-to-be confirmed target genes that promote cell proliferation and tumorigenesis. It was also hypothesized at this time that lipid-metabolizing enzymes generated lipid metabolites that served as ligands for PPARβ/δ. These hypothetical mechanisms were attractive because they potentially explained how non-steroidal anti-inflammatory drugs inhibited tumorigenesis by potentially limiting the concentration of endogenous PPARβ/δ ligands that could activate this receptor that was increased in cancer cells. However, during the last 20 years, considerable research was undertaken describing expression of PPARβ/δ in normal and cancer cells that has led to a significant impact on the mechanisms by which PPARβ/δ functions in carcinogenesis. Whereas results from earlier studies led to much uncertainty about the role of PPARβ/δ in cancer, more recent analyses of large databases have revealed a more consistent understanding. The focus of this review is on the fundamental level of PPARβ/δ expression in normal tissues and cancerous tissue as described by studies during the past two decades and what has been delineated during this timeframe about how PPARβ/δ expression influences carcinogenesis, with an emphasis on colon cancer.

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.

Peroxisome proliferator-activated receptors (PPARs) are potential drug targets for cancer therapy

Peroxisome-proliferator-activated receptors (PPARs) are nuclear hormone receptors including PPARα, PPARδ and PPARγ, which play an important role in regulating cancer cell proliferation, survival, apoptosis, and tumor growth. Activation of PPARs by endogenous or synthetic compounds regulates tumor progression in various tissues. Although each PPAR isotype suppresses or promotes tumor development depending on the specific tissues or ligands, the mechanism is still unclear. In this review, we summarized the regulative mechanism of PPARs on cancer progression.

PPAR Agonists for the Prevention and Treatment of Lung Cancer

Lung cancer is the most common and most fatal of all malignancies worldwide. Furthermore, with more than half of all lung cancer patients presenting with distant metastases at the time of initial diagnosis, the overall prognosis for the disease is poor. There is thus a desperate need for new prevention and treatment strategies. Recently, a family of nuclear hormone receptors, the peroxisome proliferator-activated receptors (PPARs), has attracted significant attention for its role in various malignancies including lung cancer. Three PPARs, PPARα, PPARβ/δ, and PPARγ, display distinct biological activities and varied influences on lung cancer biology. PPARα activation generally inhibits tumorigenesis through its antiangiogenic and anti-inflammatory effects. Activated PPARγ is also antitumorigenic and antimetastatic, regulating several functions of cancer cells and controlling the tumor microenvironment. Unlike PPARα and PPARγ, whether PPARβ/δ activation is anti- or protumorigenic or even inconsequential currently remains an open question that requires additional investigation. This review of current literature emphasizes the multifaceted effects of PPAR agonists in lung cancer and discusses how they may be applied as novel therapeutic strategies for the disease.

Metastasis regulation by PPARD expression in cancer cells

Peroxisome proliferator-activated receptor-δ (PPARD) is upregulated in many major human cancers, but the role that its expression in cancer cells has in metastasis remains poorly understood. Here, we show that specific PPARD downregulation or genetic deletion of PPARD in cancer cells significantly repressed metastasis in various cancer models in vivo. Mechanistically, PPARD promoted angiogenesis via interleukin 8 in vivo and in vitro. Analysis of transcriptome profiling of HCT116 colon cancer cells with or without genetic deletion of PPARD and gene expression patterns in The Cancer Genome Atlas colorectal adenocarcinoma database identified novel pro-metastatic genes (GJA1, VIM, SPARC, STC1, SNCG) as PPARD targets. PPARD expression in cancer cells drastically affected epithelial-mesenchymal transition, migration, and invasion, further underscoring its necessity for metastasis. Clinically, high PPARD expression in various major human cancers (e.g., colorectal, lung, breast) was associated with significantly reduced metastasis-free survival. Our results demonstrate that PPARD, a druggable protein, is an important molecular target in metastatic cancer.

Molecular Pathways: Dietary Regulation of Stemness and Tumor Initiation by the PPAR-δ Pathway

Peroxisome proliferator-activated receptor delta (PPAR-δ) is a nuclear receptor transcription factor that regulates gene expression during development and disease states, such as cancer. However, the precise role of PPAR-δ during tumorigenesis is not well understood. Recent data suggest that PPAR-δ may have context-specific oncogenic and tumor-suppressive roles depending on the tissue, cell-type, or diet-induced physiology in question. For example, in the intestine, pro-obesity diets, such as a high-fat diet (HFD), are associated with increased colorectal cancer incidence. Interestingly, many of the effects of an HFD in the stem and progenitor cell compartment are driven by a robust PPAR-δ program and contribute to the early steps of intestinal tumorigenesis. Importantly, the PPAR-δ pathway or its downstream mediators may serve as therapeutic intervention points or biomarkers in colon cancer that arise in patients who are obese. Although potent PPAR-δ agonists and antagonists exist, their clinical utility may be enhanced by uncovering how PPAR-δ mediates tumorigenesis in diverse tissues and cell types as well as in response to diet. Clin Cancer Res; 22(23); 5636-41. ©2016 AACR.

Establishing the Role of PPARβ/δ in Carcinogenesis

The role of the nuclear hormone receptor peroxisome proliferator-activated receptor β/δ (PPARβ/δ) in carcinogenesis is controversial because conflicting studies indicate that it both inhibits and promotes tumorigenesis. In this review, we focus on recent studies on PPARβ/δ including the significance of increased or decreased PPARβ/δ expression in cancers; a range of opposing mechanisms describing how PPARβ/δ agonists, antagonists, and inverse agonists regulate tumorigenesis and/or whether there may be cell context-specific mechanisms; and whether activating or inhibiting PPARβ/δ is feasible for cancer chemoprevention and/or therapy. Research questions that need to be addressed are highlighted to establish whether PPARβ/δ can be effectively targeted for cancer chemoprevention.

Hematopoietic knockdown of PPARδ reduces atherosclerosis in LDLR-/- mice

PPARδ (peroxisome proliferator-activated receptor δ) mediates inflammation in response to lipid accumulation. Systemic administration of a PPARδ agonist can ameliorate atherosclerosis. Paradoxically, genetic deletion of PPARδ in hematopoietic cells led to a reduction of atherosclerosis in murine models, suggesting that downregulation of PPARδ expression in these cells may mitigate atherogenesis. To advance this finding forward to potential clinical translation through hematopoietic stem cell transplantation-based gene therapy, we employed a microRNA (miRNA) approach to knock down PPARδ expression in bone marrow cells followed by transplantation of the cells into LDLR-/- mice. We found that knockdown of PPARδ expression in the hematopoietic system caused a dramatic reduction in aortic atherosclerotic lesions. In macrophages, a key component in atherogenesis, knockdown of PPARδ led to decreased expression of multiple pro-inflammatory factors, including monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-1β and IL-6. Expression of CCR2, a receptor for MCP-1, was also decreased. The downregulation of pro-inflammatory factors is consistent with significant reduction of macrophage presence in the lesions, which may also be attributable to elevation of ABCA1 (ATP-binding cassette, subfamily A, member 1) and depression of adipocyte differentiate-related protein. Furthermore, the abundance of both MCP-1 and matrix metalloproteinase-9 proteins was reduced in plaque areas. Our results demonstrate that miRNA-mediated PPARδ knockdown in hematopoietic cells is able to ameliorate atherosclerosis.

The prognostic factors and multiple biomarkers in young patients with colorectal cancer

The incidence of colorectal cancer (CRC) in young patients (≤50 years of age) appears to be increasing. However, their clinicopathological characteristics and survival are controversial. Likewise, the biomarkers are unclear. We used the West China (2008-2013, China), Surveillance, Epidemiology, and End Results program (1973-2011, United States) and Linköping Cancer (1972-2009, Sweden) databases to analyse clinicopathological characteristics, survival and multiple biomarkers of young CRC patients. A total of 509,934 CRC patients were included from the three databases. The young CRC patients tended to have more distal location tumours, fewer tumour numbers, later stage, more mucinous carcinoma and poorer differentiation. The cancer-specific survival (CSS) of young patients was significantly better. The PRL (HR = 12.341, 95% CI = 1.615-94.276, P = 0.010), RBM3 (HR = 0.093, 95% CI = 0.012-0.712, P = 0.018), Wrap53 (HR = 1.952, 95% CI = 0.452-6.342, P = 0.031), p53 (HR = 5.549, 95% CI = 1.176-26.178, P = 0.045) and DNA status (HR = 17.602, 95% CI = 2.551-121.448, P = 0.001) were associated with CSS of the young patients. In conclusion, this study suggests that young CRC patients present advanced tumours and more malignant pathological features, while they have a better prognosis. The PRL, RBM3, Wrap53, p53 and DNA status are potential prognostic biomarkers for the young CRC patients.

Targeting Peroxisome Proliferator-Activated Receptor-β/δ (PPARβ/δ) for Cancer Chemoprevention

The role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in cancer remains contentious due in large part to divergent publications indicating opposing effects in different rodent and human cell culture models. During the past 10 years, some facts regarding PPARβ/δ in cancer have become clearer, while others remain uncertain. For example, it is now well accepted that (1) expression of PPARβ/δ is relatively lower in most human tumors as compared to the corresponding non-transformed tissue, (2) PPARβ/δ promotes terminal differentiation, and (3) PPARβ/δ inhibits pro-inflammatory signaling in multiple in vivo models. However, whether PPARβ/δ is suitable to target with natural and/or synthetic agonists or antagonists for cancer chemoprevention is hindered because of the uncertainty in the mechanism of action and role in carcinogenesis. Recent findings that shed new insight into the possibility of targeting this nuclear receptor to improve human health will be discussed.

Physiological functions of peroxisome proliferator-activated receptor β

The peroxisome proliferator-activated receptors, PPARα, PPARβ, and PPARγ, are a family of transcription factors activated by a diversity of molecules including fatty acids and fatty acid metabolites. PPARs regulate the transcription of a large variety of genes implicated in metabolism, inflammation, proliferation, and differentiation in different cell types. These transcriptional regulations involve both direct transactivation and interaction with other transcriptional regulatory pathways. The functions of PPARα and PPARγ have been extensively documented mainly because these isoforms are activated by molecules clinically used as hypolipidemic and antidiabetic compounds. The physiological functions of PPARβ remained for a while less investigated, but the finding that specific synthetic agonists exert beneficial actions in obese subjects uplifted the studies aimed to elucidate the roles of this PPAR isoform. Intensive work based on pharmacological and genetic approaches and on the use of both in vitro and in vivo models has considerably improved our knowledge on the physiological roles of PPARβ in various cell types. This review will summarize the accumulated evidence for the implication of PPARβ in the regulation of development, metabolism, and inflammation in several tissues, including skeletal muscle, heart, skin, and intestine. Some of these findings indicate that pharmacological activation of PPARβ could be envisioned as a therapeutic option for the correction of metabolic disorders and a variety of inflammatory conditions. However, other experimental data suggesting that activation of PPARβ could result in serious adverse effects, such as carcinogenesis and psoriasis, raise concerns about the clinical use of potent PPARβ agonists.

The prognostic significance of peroxisome proliferator-activated receptor β expression in the vascular endothelial cells of colorectal cancer

OBJECTIVE

Currently, little is known regarding the role of peroxisome proliferator-activated receptor-β (PPAR β) in the vascular endothelial cells (VECs) of colorectal cancers (CRCs). The aim of this study was to investigate the relationship of PPAR β expression in the VECs of CRCs in terms of the prognosis and clinicopathological features of CRC patients.

DESIGN

The expression and localization of PPAR β in the primary cancers and the matched normal mucosal samples of 141 Swedish CRC patients were analyzed in terms of its correlation with clinicopathological features and the expression of angiogenesis-related genes. This study also included 92 Chinese CRC patients.

RESULTS

PPAR β was predominantly localized in the cytoplasm and was significantly downregulated in the VECs of CRC compared to that of the normal mucosa. The low expression levels of PPAR β in the VECs of CRC were statistically correlated with enhanced differentiation, early staging and favorable overall survival and were associated with the increased expression of VEGF and D2-40. The patients exhibiting elevated expression of PPAR β in CRC cells but reduced expression in VECs exhibited more favorable survival compared with the other patients, whereas the patients with reduced expression of PPAR β in CRC cells but increased expression in VECs exhibited less favorable prognosis.

CONCLUSIONS

PPAR β might play a tumor suppressor role in CRC cells in contrast to a tumor promoter role in the VECs of CRCs.

Variants of the PPARD gene and their clinicopathological significance in colorectal cancer

Background

Peroxisome proliferator-activated receptor delta (PPARD) is nuclear hormone receptor involved in colorectal cancer (CRC) differentiation and progression. The purpose of this study was to determine prevalence and spectrum of variants in the PPARD gene in CRC, and their contribution to clinicopathological endpoints.

Methods and Findings

Direct sequencing of the PPARD gene was performed in 303 primary tumors, in blood samples from 50 patients with ≥3 affected first-degree relatives, 50 patients with 2 affected first-degree relatives, 50 sporadic patients, 360 healthy controls, and in 6 colon cancer cell lines. Mutation analysis revealed 22 different transversions, 7 of them were novel. Three of all variants were somatic (c.548A>G, p.Y183C, c.425-9C>T, and c.628-16G>A). Two missense mutations (p.Y183C and p.R258Q) were pathogenic using in silico predictive program. Five recurrent variants were detected in/adjacent to the exons 4 (c.1-87T>C, c.1-67G>A, c.130+3G>A, and c.1-101-8C>T) and exon 7 (c.489T>C). Variant c.489C/C detected in tumors was correlated to worse differentiation (P = 0.0397).

Conclusions

We found 7 novel variants among 22 inherited or acquired PPARD variants. Somatic and/or missense variants detected in CRC patients are rare but indicate the clinical importance of the PPARD gene.

PPARβ/δ promotes HRAS-induced senescence and tumor suppression by potentiating p-ERK and repressing p-AKT signaling

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) inhibits skin tumorigenesis through mechanisms that may be dependent on HRAS signaling. The present study examined the hypothesis that PPARβ/δ promotes HRAS-induced senescence resulting in suppression of tumorigenesis. PPARβ/δ expression increased p-ERK and decreased p-AKT activity. Increased p-ERK activity results from the dampened HRAS-induced negative feedback response mediated in part through transcriptional upregulation of RAS guanyl-releasing protein 1 (RASGRP1) by PPARβ/δ. Decreased p-AKT activity results from repression of integrin-linked kinase (ILK) and phosphoinositide-dependent protein kinase-1 (PDPK1) expression. Decreased p-AKT activity in turn promotes cellular senescence through upregulation of p53 and p27 expression. Both over-expression of RASGRP1 and shRNA-mediated knockdown of ILK partially restore cellular senescence in Pparβ/δ-null cells. Higher PPARβ/δ expression is also correlated with increased senescence observed in human benign neurofibromas and colon adenoma lesions in vivo. These results demonstrate that PPARβ/δ promotes senescence to inhibit tumorigenesis and provide new mechanistic insights into HRAS-induced cellular senescence.

Knockdown of PPAR δ gene promotes the growth of colon cancer and reduces the sensitivity to bevacizumab in nude mice model

The role of peroxisome proliferator – activated receptor- δ (PPAR δ) gene in colon carcinogenesis remains highly controversial. Here, we established nude mice xenograft model using a human colon cancer cell line KM12C either with PPAR δ silenced or normal. The xenografts in PPAR δ-silenced group grew significantly larger and heavier with less differentiation, promoted cell proliferation, increased expression of vascular endothelial growth factor (VEGF) and similar apoptosis index compared with those of PPAR δ-normal group. After treated with the specific VEGF inhibitor bevacizumab, the capacities of growth and proliferation of xenografts were decreased in both groups while still significantly higher in PPAR δ-silenced group than in PPAR δ-normal group. Administration of PPAR δ agonist significantly decreased VEGF expression in PPAR δ-normal KM12C cells but not in PPAR δ-silenced cells. These findings demonstrate that, knockdown of PPAR δ promotes the growth of colon cancer by inducing less differentiation, accelerating the proliferation and VEGF expression of tumor cells in vivo, and reduces tumor sensitivity to bevacizumab. This study indicates that PPAR δ attenuates colon carcinogenesis.

Targeting peroxisome proliferator-activated receptor-β/δ in colon cancer: how to aim?

Peroxisome proliferator-activated receptor-β/δ (PPARδ) is a ubiquitously expressed, ligand-activated transcriptional factor that performs diverse critical functions in normal cells (e.g., fatty acid metabolism, obesity, apoptosis, and inflammation). Various studies in humans have found that PPARδ is upregulated in primary colorectal cancers; however, these findings have been challenged by those of other reports. Similarly, various in vitro and in vivo mechanistic pre-clinical models have yielded data demonstrating that PPARδ promotes colonic tumorigenesis, but other models have yielded data that contradicts this notion. Definitive studies are therefore needed to establish the exact role of PPARδ in human colorectal tumorigenesis and to provide a theoretical basis for PPARδ therapeutic targeting.

PPARs Signaling and Cancer in the Gastrointestinal System

Nowadays, the study of the peroxisome proliferators activated receptors (PPARs) as potential targets for cancer prevention and therapy has gained a strong interest. From a biological point of view, the overall responsibility of PPARs in cancer development and progression is still controversial since several studies report both antiproliferative and tumor-promoting actions for these signaling molecules in human cancer cells and animal models. In this paper, we discuss PPARs functions in the context of different types of gastrointestinal cancer.

Peroxisome proliferator-activated receptor β/δ cross talks with E2F and attenuates mitosis in HRAS-expressing cells

The role of peroxisome proliferator-activated receptor β/δ (PPARβ/δ) in Harvey sarcoma ras (Hras)-expressing cells was examined. Ligand activation of PPARβ/δ caused a negative selection with respect to cells expressing higher levels of the Hras oncogene by inducing a mitotic block. Mitosis-related genes that are predominantly regulated by E2F were induced to a higher level in HRAS-expressing Pparβ/δ-null keratinocytes compared to HRAS-expressing wild-type keratinocytes. Ligand-activated PPARβ/δ repressed expression of these genes by direct binding with p130/p107, facilitating nuclear translocation and increasing promoter recruitment of p130/p107. These results demonstrate a novel mechanism of PPARβ/δ cross talk with E2F signaling. Since cotreatment with a PPARβ/δ ligand and various mitosis inhibitors increases the efficacy of increasing G₂/M arrest, targeting PPARβ/δ in conjunction with mitosis inhibitors could become a suitable option for development of new multitarget strategies for inhibiting RAS-dependent tumorigenesis.

Dissecting the role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in colon, breast, and lung carcinogenesis

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is a promising drug target since its agonists increase serum high-density lipoprotein; decrease low-density lipoprotein, triglycerides, and insulin associated with metabolic syndrome; improve insulin sensitivity; and decrease high fat diet-induced obesity. PPARβ/δ agonists also promote terminal differentiation and elicit anti-inflammatory activities in many cell types. However, it remains to be determined whether PPARβ/δ agonists can be developed as therapeutics because there are reports showing either pro- or anti-carcinogenic effects of PPARβ/δ in cancer models. This review examines studies reporting the role of PPARβ/δ in colon, breast, and lung cancers. The prevailing evidence would suggest that targeting PPARβ/δ is not only safe but could have anti-carcinogenic protective effects.

The role of peroxisome proliferator-activated receptors in carcinogenesis and chemoprevention

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that are involved in regulating glucose and lipid homeostasis, inflammation, proliferation and differentiation. Although all of these functions might contribute to the influence of PPARs in carcinogenesis, there is a distinct need for a review of the literature and additional experimentation to determine the potential for targeting PPARs for cancer therapy and cancer chemoprevention. As PPAR agonists include drugs that are used for the treatment of metabolic diseases, a more complete understanding of the roles of PPARs in cancer will aid in determining any increased cancer risk for patients undergoing therapy with PPAR agonists.

Immunomodulatory action of dietary fish oil and targeted deletion of intestinal epithelial cell PPARδ in inflammation-induced colon carcinogenesis

The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR)-δ is highly expressed in colonic epithelial cells; however, the role of PPARδ ligands, such as fatty acids, in mucosal inflammation and malignant transformation has not been clarified. Recent evidence suggests that the anti-inflammatory/chemoprotective properties of fish oil (FO)-derived n-3 polyunsaturated fatty acids (PUFAs) may be partly mediated by PPARδ. Therefore, we assessed the role of PPARδ in modulating the effects of dietary n-3 PUFAs by targeted deletion of intestinal epithelial cell PPARδ (PPARδ(ΔIEpC)). Subsequently, we documented changes in colon tumorigenesis and the inflammatory microenvironment, i.e., local [mesenteric lymph node (MLN)] and systemic (spleen) T cell activation. Animals were fed chemopromotive [corn oil (CO)] or chemoprotective (FO) diets during the induction of chronic inflammation/carcinogenesis. Tumor incidence was similar in control and PPARδ(ΔIEpC) mice. FO reduced mucosal injury, tumor incidence, colonic STAT3 activation, and inflammatory cytokine gene expression, independent of PPARδ genotype. CD8(+) T cell recruitment into MLNs was suppressed in PPARδ(ΔIEpC) mice. Similarly, FO reduced CD8(+) T cell numbers in the MLN. Dietary FO independently modulated MLN CD4(+) T cell activation status by decreasing CD44 expression. CD11a expression by MLN CD4(+) T cells was downregulated in PPARδ(ΔIEpC) mice. Lastly, splenic CD62L expression was downregulated in PPARδ(ΔIEpC) CD4(+) and CD8(+) T cells. These data demonstrate that expression of intestinal epithelial cell PPARδ does not influence azoxymethane/dextran sodium sulfate-induced colon tumor incidence. Moreover, we provide new evidence that dietary n-3 PUFAs attenuate intestinal inflammation in an intestinal epithelial cell PPARδ-independent manner.

Modulation of gastrointestinal inflammation and colorectal tumorigenesis by peroxisome proliferator-activated receptor-β/δ (PPARβ/δ)

Critical physiological roles of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) include the regulation glucose and lipid homeostasis, cellular differentiation, and modulation of inflammation. The potential for targeting PPARβ/δ for the prevention and treatment of metabolic diseases or cancer, is compromised because of major inconsistencies in the literature. This is due primarily to uncertainty regarding the effect of PPARβ/δ and its activation on cell proliferation, apoptosis and cell survival. This review summarizes both the confirmed and conflicting mechanisms that have been described for PPARβ/δ and the potential for targeting this nuclear receptor for the prevention and treatment of colon cancer.