Ciglitazone-induced cellular anti-proliferation increases p27kip1 protein levels through both increased transcriptional activity and inhibition of proteasome degradation

Appraisal of the Possible Role of PPARγ Upregulation by CLA of Probiotic Pediococcus pentosaceus GS4 in Colon Cancer Mitigation

The prevalence of colon cancer (CC) is increasing at the endemic scale, which is accompanied by subsequent morbidity and mortality. Although there have been noteworthy achievements in the therapeutic strategies in recent years, the treatment of patients with CC remains a formidable task. The current study focused on to study role of biohydrogenation-derived conjugated linoleic acid (CLA) of probiotic Pediococcus pentosaceus GS4 (CLA_GS4) against CC, which induced peroxisome proliferator-activated receptor gamma (PPARγ) expression in human CC HCT-116 cells. Pre-treatment with PPARγ antagonist bisphenol A diglycidyl ether has significantly reduced the inhibitory efficacy of enhanced cell viability of HCT-116 cells, suggesting the PPARγ-dependent cell death. The cancer cells treated with CLA/CLA_GS4 demonstrated the reduced level of Prostaglandin E2 PGE₂ in association with reduced COX-2 and 5-LOX expressions. Moreover, these consequences were found to be associated with PPARγ-dependent. Furthermore, delineation of mitochondrial dependent apoptosis with the help of molecular docking LigPlot analysis showed that CLA can bind with hexokinase-II (hHK-II) (highly expressed in cancer cells) and that this association underlies voltage dependent anionic channel to open, thereby causing mitochondrial membrane depolarization, a condition that initiates intrinsic apoptotic events. Apoptosis was further confirmed by annexin V staining and elevation of caspase 1p10 expression. Taken all together, it is deduced that, mechanistically, the upregulation of PPARγ by CLA_GS4 of P. pentosaceus GS4 can alter cancer cell metabolism in association with triggering apoptosis in CC.

Pharmacological Strategies for Insulin Sensitivity in Obesity and Cancer: Thiazolidinediones and Metformin

Background:

Chronic diseases, such as obesity and cancer, have high prevalence rates. Both diseases have hyperinsulinemia, hyperglycemia, high levels of IGF-1 and inflammatory cytokines in common. Therefore, these can be considered triggers for cancer development and growth. In addition, low-grade inflammation that modulates the activation of immune cells, cellular metabolism, and production of cytokines and chemokines are common in obesity, cancer, and insulin resistance. Pharmacological strategies are necessary when a change in lifestyle does not improve glycemic homeostasis. In this regard, thiazolidinediones (TZD) possess multiple molecular targets and regulate PPARγ in obesity and cancer related to insulin resistance, while metformin acts through the AMPK pathway.

Objective:

The aim of this study was to review TZD and metformin as pharmacological treatments for insulin resistance associated with obesity and cancer.

Conclusions:

Thiazolidinediones restored adiponectin secretion and leptin sensitivity, reduced lipid droplets in hepatocytes and orexigen peptides in the hypothalamus. In cancer cells, TZD reduced proliferation, production of reactive oxygen species, and inflammation by acting through the mTOR and NFκB pathways. Metformin has similar effects, though these are AMPK-dependent. In addition, both drugs can be efficient against certain side effects caused by chemotherapy.

Hexavalent chromium induces oxidative stress and mitochondria-mediated apoptosis in isolated skin fibroblasts of Indo-Pacific humpback dolphin

The increasing gas emissions and industrial wastewater discharge of anthropogenic hexavalent chromium (Cr(VI)) have been growing health concerns to the high trophic level marine mammals. Our previous studies showed that Indo-Pacific humpback dolphin (Sousa chinensis), stranded on the Pearl River Estuary region, contained exceedingly high levels of Cr in their skin-tissues. Unfortunately, the molecular toxic mechanisms on this mammal are absent, limiting our understanding of the eco-physiological impacts of Cr(VI) on dolphins. Thus, the cytotoxicity effects of Cr(VI) were analyzed on fibroblasts we isolated from the skin of S. chinensis (ScSF). This study showed that Cr(VI) markedly inhibited the viability of ScSF cells via induction of apoptosis accompanied by an increase in the production of reactive oxygen species and the population of G2/M arrest or apoptotic sub-G1 phase cells, up-regulation of p53, and activation of caspase-3. Further investigation on intracellular mechanisms indicated that Cr(VI) induced depletion of mitochondrial membrane potential in cells through regulating the expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) proteins, resulting in decrease of the ATP level, cytochrome c release from mitochondria into cytosol, and the activation of caspase-9. Furthermore, antioxidants N-acetylcysteine and vitamin C displayed chemoprotective activity against Cr(VI) via suppression of p53 expression, indicating that the Cr(VI)-induced cell death may be mediated by oxidative stress. Overall, these results provide insights into the potential mechanisms underlying the cytotoxicity of Cr(VI) in Indo-Pacific humpback dolphin skin cells, offer experimental support for the proposed protective role of antioxidants in Cr(VI)-induced toxicity, and suggest that Cr(VI) contamination is one of key health concern issues for the protection of Indo-Pacific humpback dolphin.

Crosstalk Between Peroxisome Proliferator-Activated Receptor Gamma and the Canonical WNT/β-Catenin Pathway in Chronic Inflammation and Oxidative Stress During Carcinogenesis

Inflammation and oxidative stress are common and co-substantial pathological processes accompanying, promoting, and even initiating numerous cancers. The canonical WNT/β-catenin pathway and peroxisome proliferator-activated receptor gamma (PPARγ) generally work in opposition. If one of them is upregulated, the other one is downregulated and vice versa. WNT/β-catenin signaling is upregulated in inflammatory processes and oxidative stress and in many cancers, although there are some exceptions for cancers. The opposite is observed with PPARγ, which is generally downregulated during inflammation and oxidative stress and in many cancers. This helps to explain in part the opposite and unidirectional profile of the canonical WNT/β-catenin signaling and PPARγ in these three frequent and morbid processes that potentiate each other and create a vicious circle. Many intracellular pathways commonly involved downstream will help maintain and amplify inflammation, oxidative stress, and cancer. Thus, many WNT/β-catenin target genes such as c-Myc, cyclin D1, and HIF-1α are involved in the development of cancers. Nuclear factor-kappaB (NFκB) can activate many inflammatory factors such as TNF-α, TGF-β, interleukin-6 (IL-6), IL-8, MMP, vascular endothelial growth factor, COX2, Bcl2, and inducible nitric oxide synthase. These factors are often associated with cancerous processes and may even promote them. Reactive oxygen species (ROS), generated by cellular alterations, stimulate the production of inflammatory factors such as NFκB, signal transducer and activator transcription, activator protein-1, and HIF-α. NFκB inhibits glycogen synthase kinase-3β (GSK-3β) and therefore activates the canonical WNT pathway. ROS activates the phosphatidylinositol 3 kinase/protein kinase B (PI3K/Akt) signaling in many cancers. PI3K/Akt also inhibits GSK-3β. Many gene mutations of the canonical WNT/β-catenin pathway giving rise to cancers have been reported (CTNNB1, AXIN, APC). Conversely, a significant reduction in the expression of PPARγ has been observed in many cancers. Moreover, PPARγ agonists promote cell cycle arrest, cell differentiation, and apoptosis and reduce inflammation, angiogenesis, oxidative stress, cell proliferation, invasion, and cell migration. All these complex and opposing interactions between the canonical WNT/β-catenin pathway and PPARγ appear to be fairly common in inflammation, oxidative stress, and cancers.

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.

Combination treatment with proteasome inhibitors and antiestrogens has a synergistic effect mediated by p21WAF1 in estrogen receptor-positive breast cancer

Although antiestrogens significantly improve the survival of patients with ER-positive breast cancer, therapeutic resistance remains a major limitation. The combinatorial use of antiestrogen with other therapies was proposed to increase their efficiency and more importantly, to prevent or delay the resistance phenomenon. In the present study, we addressed their combined effects with proteasome inhibitors (PIs). The effects of antiestrogens (hydroxyl-tamoxifen, raloxifen and fulvestrant) currently used in endocrine therapy were tested in combination with PIs, bortezomib or MG132, on the growth of three ER-positive breast cancer cell lines and in two cellular models of acquired antiestrogen resistance. When compared to single treatments, these combined treatments were significantly more effective in preventing the growth of the cell lines. The regulation of key cell cycle proteins, the cyclin-dependent kinase inhibitors, p21WAF1 and p27KIP1, were also studied. Bortezomib and MG132 drastically increased p21WAF1 expression through elevation of its mRNA concentration. Notably, p27KIP1 regulation was quite different from that of p21WAF1. Furthermore, the effect of bortezomib in combination with antiestrogen was evaluated on antiestrogen-resistant cell lines. The growth of two antiestrogen-resistant cell lines appeared responsive to proteasome inhibition and was strongly decreased by a combined therapy with an antiestrogen. Collectively, these findings provide new perspectives for the use of PIs in combination with endocrine therapies for breast cancer and possibly to overcome acquired hormonal resistance.

Bortezomib-mediated downregulation of S-phase kinase protein-2 (SKP2) causes apoptotic cell death in chronic myelogenous leukemia cells

Background

Proteasome inhibitors are attractive cancer therapeutic agents because they can regulate apoptosis-related proteins. Bortezomib also known as Velcade^®, a proteasome inhibitor that has been approved by the food and drug administration for treatment of patients with multiple myeloma, and many clinical trials are ongoing to examine to the efficacy of bortezomib for the treatment of other malignancies. Bortezomib has been shown to induce apoptosis and inhibit cell growth of many cancer cells. In current study, we determine whether bortezomib induces cell death/apoptosis in CML.

Methods

Cell viability was measured using MTT assays. Apoptosis was measured by annexin V/PI dual staining and DNA fragmentation assays. Immunoblotting was performed to examine the expression of proteins. Colony assays were performed using methylcellulose.

Results

Treatment of CML cells with bortezomib results in downregulation of S-phase kinase protein 2 (SKP2) and concomitant stabilization of the expression of p27Kip1. Furthermore, knockdown of SKP2 with small interference RNA specific for SKP2 caused accumulation of p27Kip1. CML cells exposed to bortezomib leads to conformational changes in Bax protein, resulting in loss of mitochondrial membrane potential and leakage of cytochrome c to the cytosol. In the cytosol, cytochrome c causes sequential activation of caspase-9, caspase-3, PARP cleavage and apoptosis. Pretreatment of CML cells with a universal inhibitor of caspases, z-VAD-fmk, prevents bortezomib-mediated apoptosis. Our data also demonstrated that bortezomib treatment of CML downregulates the expression of inhibitor of apoptosis proteins. Finally, inhibition of proteasome pathways by bortezomib suppresses colony formation ability of CML cells.

Conclusions

Altogether, these findings suggest that bortezomib suppresses the cell proliferation via induction of apoptosis in CML cells by downregulation of SKP2 with concomitant accumulation of p27Kip1, suggesting that proteasomal pathway may form novel therapeutic targets for better management of CML.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0823-y) contains supplementary material, which is available to authorized users.

Human Skin Cells Are More Sensitive than Human Lung Cells to the Cytotoxic and Cell Cycle Arresting Impacts of Particulate and Soluble Hexavalent Chromium

Hexavalent chromium Cr(VI) is a known human lung carcinogen, with solubility playing an important role in its carcinogenic potency. Dermal exposure to Cr(VI) is common and has been associated with skin damage; however, no link between chromate exposure and skin cancer has been found. In this study, we compared the cytotoxic and clastogenic effects of Cr(VI) and its impacts on cell cycle progression in human lung and skin fibroblasts. We found human skin cells arrested earlier in their cell cycle and exhibit more cytotoxicity than human lung cells, despite taking up similar amounts of Cr. These outcomes are consistent with a hypothesis that different cellular and molecular responses underlie the differences in carcinogenic outcome in these two tissues.

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.

The role of peroxisome proliferator-activated receptors in colorectal cancer

Colorectal cancer is one of the most common cancers in the world. Dietary fat intake is a major risk factor for colorectal cancer. Some nuclear hormone receptors play an important role in regulating nutrient metabolism and energy homeostasis. Among these receptors, special attention has been focused on the role of peroxisome proliferator-activated receptors (PPARs) in colorectal cancer, because PPARs are involved in regulation of lipid and carbohydrate metabolism. PPARs are ligand-activated intracellular transcription factors. The PPAR subfamily consists of three subtypes encoded by distinct genes named PPARα, PPARβ/δ, and PPARγ. PPARγ is the most extensively studied subtype of PPARs. Even though many investigators have studied the expression and clinical implications of PPARs in colorectal cancer, there are still many controversies about the role of PPARs in colorectal cancer. In this paper, the recent progresses in understanding the role of PPARs in colorectal cancer are summarized.

Roles of estrogen receptor and p21(Waf1) in bortezomib-induced growth inhibition in human breast cancer cells

Proteasome inhibitors such as bortezomib constitute novel therapeutic agents that are currently in clinical use and in clinical trials. In some neoplasms, cyclin-dependent kinase inhibitors (CKI) such as p21(WAF1) have been proposed as key targets of proteasome inhibitors. p21(WAF1) expression can be modulated by p53, a tumor suppressor, and especially in breast cancer cells, by estrogen receptor alpha (ERα), which is highly relevant to cancer growth. We investigated the effects of bortezomib using a panel of six cancer cell lines with variable status of ERα or p53 and found that bortezomib inhibited the growth of all cell lines in the same concentration range irrespective of the ERα expression or the mutational status of p53. Bortezomib treatment significantly enhanced p21(WAF1) protein levels in all cell lines but with different mechanisms according to ERα status. In ERα-positive cells, bortezomib treatment caused a strong increase in p21(WAF1) mRNA, whereas in ERα-negative cells it predominantly enhanced p21(WAF1) protein levels suggesting a posttranslational mechanism of p21(WAF1) regulation in the ERα-negative cells. Moreover, the antiproliferative activity of bortezomib was prevented by ERα silencing or p21(WAF1) knockdown in ERα-positive cells. Collectively, our results highlight the potential roles of ERα and p21(WAF1) in growth inhibition of cancer cells mediated by proteasome inhibitors, such as bortezomib.

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.

Peroxisome proliferator-activated receptor γ and colorectal cancer

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

Insights on distinct pathways of thiazolidinediones (PPARgamma ligand)-promoted apoptosis in TRAIL-sensitive or -resistant malignant urothelial cells

Thiazolidinediones, including rosiglitazone and troglitazone, are insulin-sensitizing drugs and high-affinity ligands for the peroxisome proliferator-activated receptor gamma (PPARgamma). Apart from their antidiabetic activity, these molecules possess antitumor properties. We investigated their potential apoptotic effects on RT4 (derived from a well-differentiated Grade I papillary tumor) and T24 (derived from an undifferentiated Grade III carcinoma) bladder cancer cells. Rosiglitazone induced G2/M or G0/G1 phase cell cycle arrest in RT4 and T24 cells, respectively. Only troglitazone triggered apoptosis via extrinsic and intrinsic pathways in both cell lines. Interestingly, rosiglitazone amplified TRAIL-induced apoptosis in TRAIL-sensitive RT4 cells or let TRAIL-resistant T24 cells to respond to TRAIL. Thiazolidinediones acted through PPARgamma activation-independent mechanisms. The underlying mechanisms involved for the first time in cancer cells the upregulation of soluble and/or membrane-bound TRAIL. This was associated with increased cell surface death receptor 5 expression and c-FLIP and survivin downregulation, mediated in part through proteasome-dependent degradation in troglitazone-promoted cell death. Therefore, the combination of rosiglitazone and TRAIL could be clinically relevant as chemopreventive or therapeutic agents for the treatment of TRAIL-resistant high-grade urothelial cancers.

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

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

Peroxisome proliferator-activated receptor γ and colorectal cancer

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

Current understanding of the role of PPARγ in gastrointestinal cancers

Numerous studies have indicated that PPARγ plays multiple roles such as in inflammation, cell cycle control, cell proliferation, apoptosis, and carcinogenesis, thus PPARγ contributes to the homeostasis. Many in vitro studies have showed that ligand-induced activation of PPARγ possess antitumor effect in many cancers including CRC. However, the role of PPARγ in gastrointestinal cancers, especially in colorectal cancer, is rather controversial. Nevertheless, some recent studies with the positive results on the possible application of PPARγ ligands, such as Bezafibrate or Rosiglitazone in gastrointestinal cancers, have suggested a potential usefulness of PPARγ agonists in cancer prevention and therapy. In this review, the authors discuss the recent developments in the role of PPARγ in gastrointestinal cancers.

On to the road to degradation: atherosclerosis and the proteasome

Protein metabolism is a central element of every living cell. The ubiquitin-proteasome system (UPS) is an integral part of the protein metabolism machinery mediating post-transcriptional processing and degradation of the majority of intracellular proteins. Over the past few years, remarkable progress has been made in our understanding of the role of the UPS in vascular biology and pathobiology, particularly atherosclerosis. This review reflects on the recent developments from the effects on endothelial cells and the initial stage of atherosclerosis to the effects on vascular smooth muscle and the progression stage of atherosclerosis and finally to the effects on cell viability and the complication stage of atherosclerosis. It will conclude with the integration of the available information in a synoptic view of the involvement of the UPS in atherosclerosis.

Bortezomib-mediated expression of p27Kip1 through S-phase kinase protein 2 degradation in epithelial ovarian cancer

S-phase kinase protein 2 (SKP2), an F-box protein, targets cell-cycle regulators including cyclin-dependent kinase inhibitor p27Kip1 through ubiquitin-mediated degradation. SKP2 is frequently overexpressed in variety of cancers. We investigated the function of SKP2 and its ubiquitin-proteasome pathway in a large series (156) of epithelial ovarian cancer (EOC) patient samples, using a panel of cell lines, and nude mouse model. Using immunohistochemistry, we detected SKP2 in 13.2% tumor samples and found that it was inversely associated with p27Kip1. EOC subset with high level of SKP2 and low level of p27Kip1 showed a strong association with proliferative marker Ki167 (P<0.0014). Treatment of EOC cell lines with bortezomib or expression of siRNA of SKP2 causes downregulation of SKP2 and accumulation of p27Kip1. In addition, co-treatment of EOC with bortezomib and cisplatin causes more pronounced effect on cell proliferation, apoptosis and downregulation of SKP2 leading to accumulation of p27kip1. Bortezomib treatment of EOC cells causes apoptosis by involving mitochondrial pathway, activation of caspases and downregulation of XIAP, and survivin. Finally, treatment of EOC cell line xenografts with bortezomib resulted in growth inhibition of tumors in nude mice through downregulation of SKP2 and accumulation of p27Kip1. Altogether, our results suggest that SKP2 and ubiquitin-proteasome pathway may be a potential target for therapeutic intervention for treatment of EOC.

Proteasome inhibitor MG-132 mediated expression of p27Kip1 via S-phase kinase protein 2 degradation induces cell cycle coupled apoptosis in primary effusion lymphoma cells

Primary effusion lymphoma (PEL) is an incurable, aggressive B-cell malignancy that develops rapid resistance to conventional chemotherapy. MG-132, a proteasome inhibitor, suppresses cell proliferation and induces apoptosis in several PEL cell lines. Treatment of PEL cells with MG-132 results in downregulation of S-phase kinase protein 2 (SKP2) and accumulation of p27Kip1. Furthermore, MG-132 treatment of PEL cells causes Bax conformational changes, leading to loss of mitochondrial membrane potential and release of cytochrome c to the cytosole. Such cytochrome c release results in sequential activation of caspases and apoptosis, while pretreatment of PEL cells with universal inhibitor of caspases, z-VAD-fmk prevents cell death induced by MG-132. Finally, our data demonstrated in PEL cells that MG-132 downregulates the expression of inhibitor of apoptosis proteins XIAP, cIAP1 and survivin. Altogether, these findings suggest that MG-132 is a potent inducer of apoptosis of PEL cells via downregulation of SKP2 leading to accumulation of p27Kip1, resulting in cell cycle arrest and apoptosis and strongly suggest that targeting the proteasomal pathway may provide a novel therapeutic approach for the treatment of PEL.

PPAR-γ agonists and their effects on IGF-I receptor signaling: Implications for cancer

It is now well established that the development and progression of a variety of human malignancies are associated with dysregulated activity of the insulin-like growth factor (IGF) system. In this regard, promising drugs have been developed to target the IGF-I receptor or its ligands. These therapies are limited by the development of insulin resistance and compensatory hyperinsulinemia, which in turn, may stimulate cancer growth. Novel therapeutic approaches are, therefore, required. Synthetic PPAR-γ agonists, such as thiazolidinediones (TZDs), are drugs universally used as antidiabetic agents in patients with type 2 diabetes. In addition of acting as insulin sensitizers, PPAR-γ agonists mediate in vitro and in vivo pleiotropic anticancer effects. At least some of these effects appear to be linked with the downregulation of the IGF system, which is induced by the cross-talk of PPAR-γ agonists with multiple components of the IGF system signaling. As hyperinsulinemia is an emerging cancer risk factor, the insulin lowering action of PPAR-γ agonists may be expected to be also beneficial to reduce cancer development and/or progression. In light of these evidences, TZDs or other PPAR-γ agonists may be exploited in those tumors "addicted" to the IGF signaling and/or in tumors occurring in hyperinsulinemic patients.

Bortezomib (Velcade) induces p27Kip1 expression through S-phase kinase protein 2 degradation in colorectal cancer

S-phase kinase protein 2 (SKP2), an F-box protein, targets cell cycle regulators including cycle-dependent kinase inhibitor p27Kip1 via ubiquitin-mediated degradation. SKP2 is frequently overexpressed in a variety of cancers. We investigated the role of SKP2 and its ubiquitin-proteasome pathway in colorectal carcinoma using a panel of cell lines, clinical samples, and the NUDE mouse model. Using immunohistochemical analysis on a large tissue microarray of 448 samples, an inverse association of SKP2 expression with p27Kip1 protein levels was seen. A colorectal cancer (CRC) subset with high level of SKP2 and low level of p27Kip1 showed a decreased overall survival (P = 0.0057). Treatment of CRC cell lines with bortezomib or expression of small interfering RNA of SKP2 causes down-regulation of SKP2 and accumulation of p27Kip1. Furthermore, treatment of CRC cells with bortezomib causes apoptosis by involving the mitochondrial pathway and activation of caspases. In addition, treatment of CRC cells with bortezomib down-regulated the expression of XIAP, cIAP1, and survivin. Finally, treatment of CRC cell line xenografts with bortezomib resulted in growth inhibition of tumors in NUDE mice via down-regulation of SKP2 and accumulation of p27Kip1. Altogether, our results suggest that SKP2 and the ubiquitin-proteasome pathway may be potential targets for therapeutic intervention for treatment of CRC.

PPAR gamma regulates MITF and beta-catenin expression and promotes a differentiated phenotype in mouse melanoma S91

Melanoma represents one of the most rapidly metastasizing, hence deadly tumors due to its high proliferation rate and invasiveness, characteristics of undifferentiated embryonic tissues. Given the absence of effective therapy for metastatic melanoma, understanding more fully the molecular mechanisms underlying melanocyte differentiation may provide opportunities for novel therapeutic intervention. Here we show that in mouse melanoma S91 cells activation of the peroxisome proliferator activated receptor (PPAR) gamma induces events resembling differentiation, such as growth arrest accompanied by apoptosis, spindle morphology and enhanced tyrosinase expression. These events are preceded by an initial transient increase in expression from the Microphthalmia-associated transcription factor gene, (MITF) promoter, whereas exposure to a PPAR gamma ligand- ciglitazone that exceeds 8 h, causes a gradual decrease of MITF, until by 48 h MITF expression is substantially reduced. Beta-catenin, an MITF transcriptional activator, shows a similar pattern of decline during ciglitazone treatment, consistent with previous reports that activated PPAR gamma inhibits the Wnt/beta-catenin pathway through induction of beta-catenin proteasomal degradation. We suggest that the PPAR gamma-mediated beta-catenin down-regulation is likely to be responsible for changes in MITF levels. The data suggest that PPAR gamma, besides its well-established role in mesenchymal cell differentiation towards adipocytes, might regulate differentiation in the melanocytic lineage.

Expression of peroxisome proliferator-activated receptor-gamma in colon cancer: correlation with histopathological parameters, cell cycle-related molecules, and patients' survival

Peroxisome proliferator-activated receptor gamma (PPAR-gamma), a ligand-activated transcription factor, is a key regulator of adipogenic differentiation and glucose homeostasis. PPAR-gamma ligands have recently been demonstrated to affect proliferation and differentiation in cancer cells lines. The aim of the present work was to examine PPAR-gamma expression in colon cancer cases. PPAR-gamma expression was examined immunohistochemically in 86 colon cancer cases and was correlated with clinicopathological parameters, tumor proliferative capacity, cell cycle-related molecule expression, and patient survival. Positive PPAR-gamma immunostaining was prominent in 48 of 86 cases (56%). PPAR-gamma positivity was not correlated with Dukes' stage, histological grade of differentiation, lymph node and liver metastasis, venous invasion, tumor proliferative capacity, or patient survival. A statistically significant correlation was found between PPAR-gamma and the expression of cell cycle-related molecules pRb (P < 0.016), cyclin D1 (P <0.009), p16 (P<0.032), and p21 (P<0.033), while a positive trend for cyclin E was also noted (P<0.057). The pattern, intensity, and extent of PPAR-gamma expression in positive cases were not correlated with any of the examined variables. Our findings support evidence for participation of this protein in the biological mechanisms underlying carcinogenic evolution in the colon, also suggesting the importance of specific PPAR-gamma ligands as cell cycle modulators for a future therapeutic approach in colon cancer.

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

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

Effects of Thiazolidinediones on Differentiation, Proliferation, and Apoptosis

Thiazolidinediones induce adipocyte differentiation and thereby limit proliferative potential; hence, early investigations focused on their ability to modulate cellular proliferation and apoptosis. Several lines of evidence indicate significant thiazolidinedione-mediated antitumor activity. An emerging view is that some antitumor effects are totally or partially peroxisome proliferator-activated receptor-γ (PPARγ) dependent, whereas others are PPARγ independent. The aim of this review is to examine the current evidence about the molecular mechanisms by which thiazolidinediones augment cellular differentiation, inhibit cellular proliferation, and induce apoptosis. We first address the role of thiazolidinediones and/or PPARγ on Wnt/β-catenin signaling pathway as it affects cellular differentiation and then discuss other pathways that are also involved in differentiation as well as proliferation and apoptosis. (Mol Cancer Res 2007;5(6):523–30)

The potential of antidiabetic thiazolidinediones for anticancer therapy

The thiazolidinediones (TZDs) are a class of synthetic compounds for treatment of insulin-resistant Type 2 diabetes mellitus. TZDs are known activators of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma), and exert their antidiabetic action largely through this nuclear receptor family. Moreover, increasing experimental evidences of PPAR-gamma-independent effects are accumulating. Apart from the established metabolic actions, TZD treatment exerts additional biological effect such as control of cell growth, differentiation, motility and programmed cell death. In this context, considerable interest has focused on TZDs as potential chemopreventive agents in oncology; however, despite encouraging observation on the potential anticancer effect of these drugs in several in vitro experimental models, controversial results have been obtained with animal models and in pilot clinical trials. This review summarises the molecular mechanisms of the antineoplastic actions of TZDs and the relevance of these findings in human pathology and therapy.

Effect of ligand troglitazone on peroxisome proliferator-activated receptor γ expression and cellular growth in human colon cancer cells

AIM: To investigate the effect of troglitazone on pe-roxisome proliferator-activated receptor γ (PPARγ) expression and cellular growth in human colon cancer HCT-116 and HCT-15 cells and to explore the related molecular mechanism.

METHODS: Human colon cancer HCT-116 and HCT-15 cells cultured in vitro were treated with troglitazone. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were employed to detect the effect of troglitazone on PPARγ expression. The proliferative activity was determined by MTT assay, cell cycle and apoptosis were detected by flow cytometry. Apoptosis-related genes, cell cycle regulatory genes and p53 were examined by RT-PCR and Western blot respectively.

RESULTS: The expression of PPARγ in colon cancer HCT-116 and HCT-15 cells was up-regulated by troglitazone. Troglitazone inhibited proliferation, induced apoptosis and cell cycle G1 arrest in colon cancer cells. Troglitazone induced p53 expression in HCT-116 cells, but not in HCT-15 cells. The down-regulation of survivin and bcl-2 was found in both cell lines and up-regulation of bax was found only in HCT-116 cells, being consistent with growth inhibition in HCT-116 cells but not in HCT-15 cells. Troglitazone increased expression of p21^WAF1/CIP1 (p21), p27^KIP1 (p27) and reduced cyclin D1 in HCT-116 cells while only a minor decrease of cyclin D1 was found in HCT-15 cells.

CONCLUSION: Troglitazone is an inductor of PPARγ in colon cancer cells and inhibits PPARγ-dependently proliferation, which may attribute to cell cycle G1 arrest and apoptosis in colon cancer cells. Troglitazone may induce p53-independent apoptosis and p53-dependent expression of p21 and p27. Depending on cell background, different activation pathways may exist in colon cancer cells.

Arachidonic acid suppresses growth of human lung tumor A549 cells through down-regulation of ALDH3A1 expression

Expression of aldehyde dehydrogenase 3A1 (ALDH3A1) in certain normal and tumor cells is associated with protection against the growth inhibitory effect of reactive aldehydes generated during membrane lipid peroxidation. We found that human lung tumor (A549) cells, which express high levels of ALDH3A1 protein, were significantly less susceptible to the antiproliferative effects of 4-hydroxynonenal compared to human hepatoma HepG2 or SK-HEP-1 cells that lack ALDH3A1 expression. However, A549 cells became susceptible to lipid peroxidation products when they were treated with arachidonic acid. The growth suppression of A549 cells induced by arachidonic acid was associated with increased levels of lipid peroxidation and with reduced ALDH3A1 enzymatic activity, protein, and mRNA levels. Furthermore, arachidonic acid treatment of the A549 cells resulted in an increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma), whereas NF-kappaB binding activity was inhibited. Blocking PPARgamma using a selective antagonist, GW9662, prevented the arachidonic acid-mediated reduction of ALDH3A1 expression as well as the growth inhibition of A549 cells, suggesting the central role of PPARgamma in these phenomena. The increase in PPARgamma and the reduction in ALDH3A1 were also prevented by exposing cells to vitamin E concomitant with arachidonic acid treatment. In conclusion, our data show that the arachidonic acid-induced suppression of A549 cell growth is associated with increased lipid peroxidation and decreased ALDH3A1 expression, which may be due to activation of PPARgamma.

Novel high-affinity PPARgamma agonist alone and in combination with paclitaxel inhibits human anaplastic thyroid carcinoma tumor growth via p21WAF1/CIP1

Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists demonstrate antitumor activity likely through transactivating genes that regulate cell proliferation, apoptosis, and differentiation. The PAX8/PPARgamma fusion oncogene, which is common in human follicular thyroid carcinomas appears to act via dominant negative suppression of wild-type PPARgamma, suggesting that it may be a tumor suppressor gene in thyroid cells. We have identified a novel high-affinity PPARgamma agonist (RS5444) that is dependent upon PPARgamma for its biological activity. This is the first report of this molecule and its antitumor activity. In vitro, the IC50 for growth inhibition is approximately 0.8 nM while anaplastic thyroid carcinoma (ATC) tumor growth was inhibited three- to fourfold in nude mice. siRNA against PPARgamma and a pharmacological antagonist demonstrated that functional PPARgamma was required for growth inhibitory activity of RS5444. RS5444 upregulated the cell cycle kinase inhibitor, p21WAF1/CIP1. Silencing p21WAF1/CIP1 rendered cells insensitive to RS5444. RS5444 plus paclitaxel demonstrated additive antiproliferative activity in cell culture and minimal ATC tumor growth in vivo. RS5444 did not induce apoptosis but combined with paclitaxel, doubled the apoptotic index compared to that of paclitaxel. Our data indicate that functional PPARgamma is a molecular target for therapy in ATC. We demonstrated that RS5444, a thiazolidinedione (Tzd) derivative, alone or in combination with paclitaxel, may provide therapeutic benefit to patients diagnosed with ATC.

Shp-1 mediates the antiproliferative activity of tissue inhibitor of metalloproteinase-2 in human microvascular endothelial cells

The tissue inhibitors of metalloproteinases (TIMPs) regulate matrix metalloproteinase activity required for cell migration/invasion associated with cancer progression and angiogenesis. TIMPs also modulate cell proliferation in vitro and angiogenesis in vivo independent of their matrix metalloproteinase inhibitory activity. Here, we show that TIMP-2 mediates G1 growth arrest in human endothelial cells through de novo synthesis of the cyclin-dependent kinase inhibitor p27Kip1. TIMP-2-mediated inhibition of Cdk4 and Cdk2 activity is associated with increased binding of p27Kip1 to these complexes in vivo. Protein-tyrosine phosphatase inhibitors or expression of a dominant negative Shp-1 mutant ablates TIMP-2 induction of p27Kip1. Finally, angiogenic responses to fibroblast growth factor-2 and vascular endothelial growth factor-A in "motheaten viable" Shp-1-deficient mice are resistant to TIMP-2 inhibition, demonstrating that Shp-1 is an important negative regulator of angiogenesis in vivo.

Ciglitazone-induced p27 gene transcriptional activity is mediated through Sp1 and is negatively regulated by the MAPK signaling pathway

We have previously demonstrated that the PPARgamma ligand, ciglitazone, increases p27kip1 protein levels in HT-29 colon cancer cells through both inhibition of proteasome associated degradation and activation of transcriptional activity. [F. Chen, L.E. Harrison, Cell Signal. 17 (2005) 809] The purpose of this investigation was to further elucidate the mechanism of ciglitazone-induced activation of p27 gene transcription. We observed that the region -774/-462 of the p27 promoter plays a key role in ciglitazone-induced gene transcriptional activity and this region contains two Sp1 binding sites. When the p27PF-luc reporter was co-transfected with Sp1 expression plasmids, ciglitazone-induced p27PF-luc activity significantly increased, while mithramycin A, a Sp1 inhibitor, was able to abrogate its effects. Ciglitazone exposure increased both Sp1 protein expression and Sp1-DNA binding, which was also associated with a decrease of Erk1/2 phosphorylation. A similar increase of Sp1-DNA binding was observed when phosphorylation of Erk1/2 was inhibited by pretreatment with the MAP kinase inhibitor, U0126. In addition, a significant increase of p27PF-luc reporter luciferase activity was noted after MAP kinase inhibition, which could be abolished with co-treatment with mithramycin A. Based on these data, we postulate that ciglitazone induces p27 gene transcription through increased Sp1 binding to its promoter region, which in turn is mediated through increased Sp1 protein levels and decreased inhibitory regulation by the MAP kinase pathway.

Nano neodymium oxide induces massive vacuolization and autophagic cell death in non-small cell lung cancer NCI-H460 cells

Neodymium, a rare earth element, was known to exhibit cytotoxic effects and induce apoptosis in certain cancer cells. Here we show that nano-sized neodymium oxide (Nano Nd2O3) induced massive vacuolization and cell death in non-small cell lung cancer NCI-H460 cells at micromolar equivalent concentration range. Cell death elicited by Nano Nd2O3 was not due to apoptosis and caspases were not involved. Electron microscopy and acridine orange staining revealed extensive autophagy in the cytoplasm of the cells treated by Nano Nd2O3. Autophagy induced by Nano Nd2O3 was accompanied by S-phase cell cycle arrest, mild disruption of mitochondrial membrane potential, and inhibition of proteasome activity. Bafilomycin A1, but not 3-MA, induced apoptosis while inhibiting autophagy. Our results revealed a novel biological function for Nano Nd2O3 and may have implications for the therapy of non-small cell lung cancer.