Inhibition of cellular proliferation through IkappaB kinase-independent and peroxisome proliferator-activated receptor gamma-dependent repression of cyclin D1

Abscisic acid signaling through LANCL2 and PPARγ induces activation of p38MAPK resulting in dormancy of prostate cancer metastatic cells

Prostate cancer (PCa) is one the most common malignancies in men. The high incidence of bone metastasis years after primary therapy suggests that disseminated tumor cells must become dormant, but maintain their ability to proliferate in the bone marrow. Abscisic acid (ABA) is a stress response molecule best known for its regulation of seed germination, stomal opening, root shoot growth and other stress responses in plants. ABA is also synthesized by mammalian cells and has been linked to human disease. The aim of the present study was to examine the role of ABA in regulating tumor dormancy via signaling through lanthionine synthetase C‑like protein 2 (LANCL2) and peroxisome proliferator activated receptor γ (PPARγ) receptors. ABA signaling in human PCa cell lines was studied using targeted gene knockdown (KD), western blotting, quantitative PCR, cell proliferation, migration, invasion and soft agar assays, as well as co‑culture assays with bone marrow stromal cells. The data demonstrated that ABA signaling increased the expression of p21, p27 and p16, while inhibiting viability, migration, invasion and colony size in a reversable manner without toxicity. ABA also induced p38MAPK activation and NR2F1 signaling. Targeted gene KD of LANCL2 and PPARγ abrogated the cellular responses to ABA. Taken together, these data demonstrate that ABA may induce dormancy in PCa cell lines through LANCL2 and PPARγ signaling, and suggest novel targets to manage metastatic PCa growth.

Xianlinglianxiafang Inhibited the growth and metastasis of triple-negative breast cancer via activating PPARγ/AMPK signaling pathway

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer characterized by high invasion and metastasis rates. Xian-Ling-Lian-Xia formula (XLLX) is a traditional Chinese medicine prescription widely used in China for treating TNBC. Clinical studies have shown that XLLX significantly reduces the recurrence and metastasis rate of TNBC and improves disease-free survival. However, the potential molecular mechanisms of XLLX on TNBC are not clear yet. Here, we investigated the effects of XLLX on TNBC using a mouse model and tumor cell lines. The results showed that XLLX significantly inhibited the proliferation, migration, and invasion abilities of TNBC cell lines MDA-MB-231 and 4T1 in vitro, induced apoptosis, and regulated the expression of proliferation, apoptosis, and EMT marker proteins in tumor cells. In in vivo experiments, XLLX treatment significantly reduced the progression of TNBC tumors and lung metastasis. Transcriptomics reveals that XLLX treatment significantly enriched differentially expressed genes in the peroxisome proliferator-activated receptor gamma (PPARγ) and AMP-dependent protein kinase (AMPK) signaling pathways. The western blot results confirmed that XLLX significantly upregulated the protein expression of PPARγ and p-AMPK in TNBC cells, tumors, and lung tissues. It is noteworthy that GW9662 (a PPARγ inhibitor) and Compound C (an AMPK inhibitor) partially reversed the anti-proliferation and anti-metastasis effects of XLLX in TNBC cells. Therefore, XLLX may effectively inhibit the growth and metastasis of TNBC by activating the PPARγ/AMPK signaling pathway.

The Role of Transcription Factor PPAR-γ in the Pathogenesis of Psoriasis, Skin Cells, and Immune Cells

The peroxisome proliferator-activated receptor PPAR-γ is one of three PPAR nuclear receptors that act as ligand-activated transcription factors. In immune cells, the skin, and other organs, PPAR-γ regulates lipid, glucose, and amino acid metabolism. The receptor translates nutritional, pharmacological, and metabolic stimuli into the changes in gene expression. The activation of PPAR-γ promotes cell differentiation, reduces the proliferation rate, and modulates the immune response. In the skin, PPARs also contribute to the functioning of the skin barrier. Since we know that the route from identification to the registration of drugs is long and expensive, PPAR-γ agonists already approved for other diseases may also represent a high interest for psoriasis. In this review, we discuss the role of PPAR-γ in the activation, differentiation, and proliferation of skin and immune cells affected by psoriasis and in contributing to the pathogenesis of the disease. We also evaluate whether the agonists of PPAR-γ may become one of the therapeutic options to suppress the inflammatory response in lesional psoriatic skin and decrease the influence of comorbidities associated with psoriasis.

Impacts of Gum Arabic and Polyvinylpyrrolidone (PVP) with Salicylic Acid on Peach Fruit (Prunus persica) Shelf Life

Peaches are grown in many Egyptian orchards for local and global fresh market sales. The interior fruit tissue breakdown (IFTB), often resulting in decayed peaches, is a severe problem during marketing. Therefore, to minimize FTB of peaches, in this study, gum arabic (GA) and polyvinylpyrrolidone (PVP) were mixed with different concentrations of salicylic acid (SA) (0, 1, and 2 mM) and were applied as edible coating to extend the shelf life of peach fruits. Mature peaches were selected and harvested when peaches reached total soluble solid content (SSC: 8.5%) and fruit firmness of about 47 N. Fruits were coated and stored at room temperature (26 ± 1 °C and air humidity 51 ± 1%) for 10 days during two seasons: 2020 and 2021. Fruit coated with GA/PVP-SA 2 mM showed a significant (p < 0.05) inhibition in degrading enzyme activities (CWDEs), such as lipoxygenase (LOX), cellulase (CEL), and pectinase (PT), compared to uncoated and coated fruits during the shelf-life period. Hence, cell wall compartments were maintained. Consequently, there was a reduction in browning symptoms in fruits by inhibiting polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities. Thus, the fruit skin browning index showed almost no symptoms. The lipid peroxidation process and ionic permeability declined as well. The result suggests that, by applying GA/PVP-SA 2 mM as an edible coating, fruit tissue breakdown can be minimized, and the shelf life of peach can be extended up to 10 days without symptoms of tissue breakdown.

Genome-wide analysis of mRNAs, lncRNAs, and circRNAs during intramuscular adipogenesis in Chinese Guizhou Congjiang pigs

Intramuscular fat content is an important determinant of meat quality, and preadipocyte differentiation plays a critical role in intramuscular fat deposition in pigs. However, many types of RNA differentiation, including messenger RNA (mRNA), long non-coding RNA (lncRNA), and circular RNA (circRNA) remain unreported despite their crucial roles in regulating adipogenesis. Chinese Guizhou Congjiang pigs are raised in the Guizhou province of China for their high-quality meat. Therefore, it is important for breeders to explore the mechanisms of proliferation and differentiation of intramuscular adipocytes from the longissimus dorsi muscle of these pigs. In the present study, a transcriptome analysis of intramuscular preadipocytes from Chinese Guizhou Congjiang pigs, including analyses of mRNAs, lncRNAs, and circRNAs at days 0 (D0), 4 (D4), and 8 (D8) was performed. A total of 1,538, 639, and 445 differentially expressed (DE) mRNAs, 479, 192, and 126 DE lncRNAs, and 360, 439, and 304 DE circRNAs were detected between D4 and D0, D8 and D0, and D8 and D4, respectively. Functional analyses identified many significantly enriched RNAs related to lipid deposition, cell differentiation, metabolism processes, and obesity-related diseases, biological processes, and pathways. We identified two lncRNAs (TCONS_00012086 and TCONS_00007245) closely related to fat deposition according to their target genes and tissue expression profiles. Subcellular distribution analysis using quantitative real-time PCR (qRT-PCR) revealed that both TCONS_00012086 and TCONS_00007245 are cytoplasmic lncRNAs. These data provide a genome-wide resource for mRNAs, lncRNAs, and circRNAs potentially involved in Chinese Guizhou Congjiang pig fat metabolism, thus improving our understanding of their function in adipogenesis.

Effects of matcha tea extract on cell viability and peroxisome proliferator-activated receptor γ expression on T47D breast cancer cells

PURPOSE

In the following work, we investigated the nuclear peroxisome proliferator-activated receptor gamma (PPARγ)-dependent proliferation behavior of breast cancer cells after stimulation with matcha green tea extract (MTE).

METHODS

T47D cells were stimulated with MTE at concentrations of 5, 10 and 50 µg/ml. Cell viability was assessed using a WST-1 assay after an incubation time of 72 h. PPARγ expression was quantified at the gene level by real-time polymerase chain reaction (PCR). A western blot (WB) was carried out for the qualitative assessment of the expression behavior of on a protein level.

RESULTS

The WST-1 test showed a significant inhibition of viability in T47D cells after 72 h at 5, 10 and 50 µg/ml. The PCR showed an overexpression of PPARγ in T47D cells in all concentrations. At the concentration of 50 µg/ml the expression was significantly increased (p < 0.05). The WB demonstrated a significant quantitative increase of PPARγ at protein level with MTE concentrations of 10 and 50 µg/ml. In addition, there was a negative correlation between the overexpression of PPAR γ and the inhibition of proliferation.

CONCLUSION

MTE decreases the cell viability of T47D cells and furthermore leads to an overexpression of PPARγ on protein and mRNA level.

Mechanisms Governing Metabolic Heterogeneity in Breast Cancer and Other Tumors

Reprogramming of metabolic priorities promotes tumor progression. Our understanding of the Warburg effect, based on studies of cultured cancer cells, has evolved to a more complex understanding of tumor metabolism within an ecosystem that provides and catabolizes diverse nutrients provided by the local tumor microenvironment. Recent studies have illustrated that heterogeneous metabolic changes occur at the level of tumor type, tumor subtype, within the tumor itself, and within the tumor microenvironment. Thus, altered metabolism occurs in cancer cells and in the tumor microenvironment (fibroblasts, immune cells and fat cells). Herein we describe how these growth advantages are obtained through either “convergent” genetic changes, in which common metabolic properties are induced as a final common pathway induced by diverse oncogene factors, or “divergent” genetic changes, in which distinct factors lead to subtype-selective phenotypes and thereby tumor heterogeneity. Metabolic heterogeneity allows subtyping of cancers and further metabolic heterogeneity occurs within the same tumor mass thought of as “microenvironmental metabolic nesting”. Furthermore, recent findings show that mutations of metabolic genes arise in the majority of tumors providing an opportunity for the development of more robust metabolic models of an individual patient’s tumor. The focus of this review is on the mechanisms governing this metabolic heterogeneity in breast cancer.

PPARgamma: A Potential Intrinsic and Extrinsic Molecular Target for Breast Cancer Therapy

Over the last decades, the breast tumor microenvironment (TME) has been increasingly recognized as a key player in tumor development and progression and as a promising prognostic and therapeutic target for breast cancer patients. The breast TME, representing a complex network of cellular signaling—deriving from different stromal cell types as well as extracellular matrix components, extracellular vesicles, and soluble growth factors—establishes a crosstalk with cancer cells sustaining tumor progression. A significant emphasis derives from the tumor surrounding inflammation responsible for the failure of the immune system to effectively restrain breast cancer growth. Thus, effective therapeutic strategies require a deeper understanding of the interplay between tumor and stroma, aimed at targeting both the intrinsic neoplastic cells and the extrinsic surrounding stroma. In this scenario, peroxisome proliferator-activated receptor (PPAR) γ, primarily known as a metabolic regulator, emerged as a potential target for breast cancer treatment since it functions in breast cancer cells and several components of the breast TME. In particular, the activation of PPARγ by natural and synthetic ligands inhibits breast cancer cell growth, motility, and invasiveness. Moreover, activated PPARγ may educate altered stromal cells, counteracting the pro-inflammatory milieu that drive breast cancer progression. Interestingly, using Kaplan–Meier survival curves, PPARγ also emerges as a prognostically favorable factor in breast cancer patients. In this perspective, we briefly discuss the mechanisms by which PPARγ is implicated in tumor biology as well as in the complex regulatory networks within the breast TME. This may help to profile approaches that provide a simultaneous inhibition of epithelial cells and TME components, offering a more efficient way to treat breast cancer.

PPARγ and Diabetes: Beyond the Genome and Towards Personalized Medicine

PURPOSE OF REVIEW

Full and partial synthetic agonists targeting the transcription factor PPARγ are contained in FDA-approved insulin-sensitizing drugs and used for the treatment of metabolic syndrome-related dysfunctions. Here, we discuss the association between PPARG genetic variants and drug efficacy, as well as the role of alternative splicing and post-translational modifications as contributors to the complexity of PPARγ signaling and to the effects of synthetic PPARγ ligands.

RECENT FINDINGS

PPARγ regulates the transcription of several target genes governing adipocyte differentiation and glucose and lipid metabolism, as well as insulin sensitivity and inflammatory pathways. These pleiotropic functions confer great relevance to PPARγ in physiological regulation of whole-body metabolism, as well as in the etiology of metabolic disorders. Accordingly, PPARG gene mutations, nucleotide variations, and post-translational modifications have been associated with adipose tissue disorders and the related risk of insulin resistance and type 2 diabetes (T2D). Moreover, PPARγ alternative splicing isoforms-generating dominant-negative isoforms mainly expressed in human adipose tissue-have been related to impaired PPARγ activity and adipose tissue dysfunctions. Thus, multiple regulatory levels that contribute to PPARγ signaling complexity may account for the beneficial as well as adverse effects of PPARγ agonists. Further targeted analyses, taking into account all these aspects, are needed for better deciphering the role of PPARγ in human pathophysiology, especially in insulin resistance and T2D. The therapeutic potential of full and partial PPARγ synthetic agonists underlines the clinical significance of this nuclear receptor. PPARG mutations, polymorphisms, alternative splicing isoforms, and post-translational modifications may contribute to the pathogenesis of metabolic disorders, also influencing the responsiveness of pharmacological therapy. Therefore, in the context of the current evidence-based trend to personalized diabetes management, we highlight the need to decipher the intricate regulation of PPARγ signaling to pave the way to tailored therapies in patients with insulin resistance and T2D.

Natural and Synthetic PPARγ Ligands in Tumor Microenvironment: A New Potential Strategy against Breast Cancer

Multiple lines of evidence indicate that activation of the peroxisome proliferator-activated receptor γ (PPARγ) by natural or synthetic ligands exerts tumor suppressive effects in different types of cancer, including breast carcinoma. Over the past decades a new picture of breast cancer as a complex disease consisting of neoplastic epithelial cells and surrounding stroma named the tumor microenvironment (TME) has emerged. Indeed, TME is now recognized as a pivotal element for breast cancer development and progression. Novel strategies targeting both epithelial and stromal components are under development or undergoing clinical trials. In this context, the aim of the present review is to summarize PPARγ activity in breast TME focusing on the role of this receptor on both epithelial/stromal cells and extracellular matrix components of the breast cancer microenvironment. The information provided from the in vitro and in vivo research indicates PPARγ ligands as potential agents with regards to the battle against breast cancer.

The Role of PPARγ Ligands in Breast Cancer: From Basic Research to Clinical Studies

Peroxisome proliferator-activated receptor gamma (PPARγ), belonging to the nuclear receptor superfamily, is a ligand-dependent transcription factor involved in a variety of pathophysiological conditions such as inflammation, metabolic disorders, cardiovascular disease, and cancers. In this latter context, PPARγ is expressed in many tumors including breast cancer, and its function upon binding of ligands has been linked to the tumor development, progression, and metastasis. Over the last decade, much research has focused on the potential of natural agonists for PPARγ including fatty acids and prostanoids that act as weak ligands compared to the strong and synthetic PPARγ agonists such as thiazolidinedione drugs. Both natural and synthetic compounds have been implicated in the negative regulation of breast cancer growth and progression. The aim of the present review is to summarize the role of PPARγ activation in breast cancer focusing on the underlying cellular and molecular mechanisms involved in the regulation of cell proliferation, cell cycle, and cell death, in the modulation of motility and invasion as well as in the cross-talk with other different signaling pathways. Besides, we also provide an overview of the in vivo breast cancer models and clinical studies. The therapeutic effects of natural and synthetic PPARγ ligands, as antineoplastic agents, represent a fascinating and clinically a potential translatable area of research with regards to the battle against cancer.

Flow cytometry-based FRET identifies binding intensities in PPARγ1 protein-protein interactions in living cells

PPARγ is a pharmacological target in inflammatory and metabolic diseases. Upon agonistic treatment or following antagonism, binding of co-factors is altered, which consequently affects PPARγ-dependent transactivation as well as its DNA-independent properties. Therefore, establishing techniques to characterize these interactions is an important issue in living cells. Methods: Using the FRET pair Clover/mRuby2, we set up a flow cytometry-based FRET assay by analyzing PPARγ1 binding to its heterodimerization partner RXRα. Analyses of PPARγ-reporter and co-localization studies by laser-scanning microscopy validated this system. Refining the system, we created a new readout to distinguish strong from weak interactions, focusing on PPARγ-binding to the co-repressor N-CoR2. Results: We observed high FRET in cells expressing Clover-PPARγ1 and mRuby2-RXRα, but no FRET when cells express a mRuby2-RXRα deletion mutant, lacking the PPARγ interaction domain. Focusing on the co-repressor N-CoR2, we identified in HEK293T cells the new splice variant N-CoR2-ΔID1-exon. Overexpressing this isoform tagged with mRuby2, revealed no binding to Clover-PPARγ1, nor in murine J774A.1 macrophages. In HEK293T cells, binding was even lower in comparison to N-CoR2 constructs in which domains established to mediate interaction with PPARγ binding are deleted. These data suggest a possible role of N-CoR2-ΔID1-exon as a dominant negative variant. Because binding to N-CoR2-mRuby2 was not altered following activation or antagonism of Clover-PPARγ1, we determined the effect of pharmacological treatment on FRET intensity. Therefore, we calculated flow cytometry-based FRET efficiencies based on our flow cytometry data. As with PPARγ antagonism, PPARγ agonist treatment did not prevent binding of N-CoR2. Conclusion: Our system allows the close determination of protein-protein interactions with a special focus on binding intensity, allowing this system to characterize the role of protein domains as well as the effect of pharmacological agents on protein-protein interactions.

Interleukin-33 / Cyclin D1 imbalance in severe liver steatosis predicts susceptibility to ischemia reperfusion injury

Transplanting donor livers with severe macrosteatosis is associated with increased risk of primary non-function (PNF). The purpose of this study was to identify steatosis-driven biomarkers as a predisposition to severe liver damage and delayed recovery following ischemia reperfusion injury. Wistar rats were fed a methionine- and choline-deficient (MCD) diet for up to three weeks to achieve severe macrosteatosis (>90%). Animals underwent diet withdrawal to control chow and/or underwent ischemia reperfusion and partial hepatectomy injury (I/R-PHx) and reperfused out to 7 days on control chow. For animals with severe macrosteatosis, hepatic levels of IL-33 decreased while Cyclin D1 levels increased in the absence of NF-κB p65 phosphorylation. Animals with high levels of nuclear Cyclin D1 prior to I/R-PHx either did not survive or had persistent macrosteatosis after 7 days on control chow. Survival 7 days after I/R-PHx fell to 57% which correlated with increased Cyclin D1 and decreased liver IL-33 levels. In the absence of I/R-PHx, withdrawing the MCD diet normalized IL-33, Cyclin D1 levels, and I/R-PHx survival back to baseline. In transplanted grafts with macrosteatosis, higher Cyclin D1 mRNA expression was observed. Shifts in Cyclin D1 and IL-33 expression may identify severely macrosteatotic livers with increased failure risk if subjected to I/R injury. Clinical validation of the panel in donor grafts with macrosteatosis revealed increased Cyclin D1 expression corresponding to delayed graft function. This pre-surgical biomarker panel may identify the subset of livers with increased susceptibility to PNF.

Expression of NR1H3 in endometrial carcinoma and its effect on the proliferation of Ishikawa cells in vitro

Purpose

Our study aimed to investigate the expression of NR1H3 in endometrial carcinoma, its effect on the proliferation of endometrial carcinoma cells in vitro, and the underlying mechanism of this effect.

Materials and methods

Immunohistochemistry of paraffin-embedded, sectioned specimens and of a tissue microarray was conducted to estimate the expression of NR1H3 (liver X receptors α: LXRα) and NR1H2 (liver X receptors β: LXRβ) in endometrial carcinoma tissues. The subcellular localization of NR1H3 in the endometrial carcinoma cell line Ishikawa was determined by immunofluorescence. An agonist of NR1H3, TO901317, was then administered to activate the expression of NR1H3, and cell viability and cell-cycle progression were investigated through MTT and flow cytometric assays, respectively. The gene and protein expression levels of NR1H3, cyclin D1 (CCND1), and cyclin E (CCNE) in cells pretreated with different concentrations of TO901317 for different periods of time were also detected by real-time RT-PCR and Western blot, respectively.

Results

The results showed that, in contrast to NR1H2, which was expressed at low levels in endometrial tissues, NR1H3 was upregulated in endometrial adenocarcinoma tissues compared to levels in normal endometrial tissues and endometrial polyps. Moreover, NR1H3 was mainly expressed in the cytoplasm of Ishikawa cells. TO901317 significantly decreased cell viability and arrested the cell cycle in Ishikawa cells in a dose- and time-dependent manner. Furthermore, the administration of TO901317 not only promoted the expression of NR1H3 but also inhibited the expression of CCND1 and CCNE in Ishikawa cells.

Conclusion

We demonstrated that NR1H3 is upregulated in endometrial adenocarcinoma and that it inhibits cell viability by inhibiting the expression of CCND1 and CCNE in endometrial carcinoma cells. Our study indicates that NR1H3 may play a role in the development of endometrial cancer and may emerge as a promising therapeutic target.

High Glucose with Insulin Induces Cell Cycle Progression and Activation of Oncogenic Signaling of Bladder Epithelial Cells Cotreated with Metformin and Pioglitazone

Metformin and pioglitazone are two commonly prescribed oral hypoglycemic agents for diabetes. Recent evidence suggests that these drugs may contribute to bladder cancer. This study investigated molecular mechanism underlying effects of metformin and pioglitazone in bladder epithelial carcinogenesis in type 2 diabetes. The cells derived from human bladder epithelial cells (HBlEpCs) were treated with metformin or pioglitazone with high glucose and insulin. Cell viability and proliferation were evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and a bromodeoxyuridine incorporation assay, respectively, while cell cycle regulatory factors and oncogene expression were analyzed using western blotting. Metformin or pioglitazone suppressed cell viability concentration and time dependently, which was reversed by exposure to high glucose with or without insulin. Prolonged exposure to high glucose and insulin enhanced cyclin D, cyclin-dependent kinase 4 (Cdk4), and Cdk2 expression and suppressed cyclin-dependent kinase inhibitors p21 and p15/16 in HBlEpC cotreated with pioglitazone and metformin. Levels of tumor suppressor proteins p53 and cav-1 were downregulated while those of the oncogenic protein as c-Myc were upregulated under high glucose and insulin supplementation in HBlEpC cotreated with pioglitazone and metformin. Prolonged exposure to high glucose with or without insulin downregulated B cell lymphoma 2-associated X (Bax) and failed to enhance the expression of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38MAPK) in drug-treated cells. These results suggest that hyperglycemic and insulinemic conditions promote cell cycle progression and oncogenic signaling in drug-treated bladder epithelial cells and uncontrolled hyperglycemia and hyperinsulinemia are probably greater cancer risk factors than diabetes drugs.

A genome-wide landscape of mRNAs, lncRNAs, and circRNAs during subcutaneous adipogenesis in pigs

Background

Preadipocyte differentiation plays a critical role in subcutaneous fat deposition in pigs. However, the roles of different RNAs, such as messenger RNAs (mRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) in the differentiation process of subcutaneous preadipocytes, are still largely unclear. In the present study, a transcriptome analysis, including the analysis of mRNAs, lncRNAs, and circRNAs, during different differentiation stages, namely, day 0 (D0), day 2 (D2), day 4 (D4), and day 8 (D8), of subcutaneous preadipocytes from Chinese Erhualian pigs was performed.

Results

A total of 1554, 470, 1344, 1777, and 676 differentially expressed (DE) mRNAs, 112, 58, 95, 136, and 93 DE lncRNAs, and 902, 787, 710, 932, and 850 DE circRNAs were identified between D2 and D0, between D4 and D2, between D8 and D4, between D4 and D0, and between D8 and D0, respectively. Furthermore, functional enrichment analysis showed that the common DE mRNAs during the entire differentiation process were mainly involved in lipid metabolic and cell differentiation processes. Additionally, co-expression network analysis identified the potential lncRNAs related to adipogenesis, e.g., MSTRG.131380 and MSTRG.62128.

Conclusions

Our study provides new insights of the expression changes of RNAs during adipogenic differentiation, which might contribute to the phenotype of subcutaneous adipogenesis. These results greatly improve our understanding of the molecular mechanisms regulating subcutaneous fat deposition in pigs.

Electronic supplementary material

The online version of this article (10.1186/s40104-018-0292-7) contains supplementary material, which is available to authorized users.

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.

Roles of p21, p53, cyclin D1, CDK-4, estrogen receptor α in aflatoxin B1-induced cytotoxicity in testicular tissue of mice

This study was done in order to investigate time-dependent effect of AFB1 on expression of genes involving in cell cycle check point machinery at G, S, and M phases. For this purpose, 24 mature male Swiss albino mice were randomly divided into control and test groups. The animals in test group subdivided into three groups, which received the AFB1 at a daily dose of 20 µg/kg body weight, through intraperitoneal (i.p.) route, for 7, 14, and 21 days. The p21, p53, cyclin D1, CDK4, and ERα expressions at both mRNA and protein level were analyzed by using reverse transcription PCR (RT-PCR) and immunohistochemistry, respectively. Moreover, the tubular differentiation (TDI) and spermiogenesis (SPI) indices were analyzed. Finally, the testicular DNA fragmentation was assessed by using DNA Ladder test. Observations revealed that the AFB1 remarkably (P < .05) reduced cyclin D1, Cdk4, and ERα expression at both mRNA and protein levels. Up-regulated p21 and p53 expression was revealed in AFB1-received animals, which developed time dependently. Histological examinations exhibited a significant reduction in TDI and SPI indices. Finally, the AFB1 resulted in severe DNA fragmentation. Our data showed that the AFB1 by down-regulating the cyclin D1, Cdk4, and ERα expression adversely affects cyclin D1/Cdk4 and cyclin D1/ERα interactions. Moreover, the AFB1-induced overexpression of p21 (as a kinase inhibitor), in turn results in cell cycle arrest via inhibiting the Cdk4 interaction with cyclin D1. Finally, the AFB1-induced DNA damage triggers the p53-dependent apoptosis pathway independent to p21 overexpression.

PPARγ activation by troglitazone enhances human lung cancer cells to TRAIL-induced apoptosis via autophagy flux

Members of the tumor necrosis factor (TNF) transmembrane cytokine superfamily, such as TNFα and Fas ligand (FasL), play crucial roles in inflammation and immunity. TRAIL is a member of this superfamily with the ability to selectively trigger cancer cell death but does not motive cytotoxicity to most normal cells. Troglitazone are used in the cure of type II diabetes to reduce blood glucose levels and improve the sensitivity of an amount of tissues to insulin. In this study, we revealed that troglitazone could trigger TRAIL-mediated apoptotic cell death in human lung adenocarcinoma cells. Pretreatment of troglitazone induced activation of PPARγ in a dose-dependent manner. In addition conversion of LC3-I to LC3-II and PPARγ was suppressed in the presence of GW9662, a well-characterized PPARγ antagonist. Treatment with troglitazone resulted in a slight increase in conversion rate of LC3-I to LC3-II and significantly decreased p62 expression levels in a dose-dependent manner. This indicates that troglitazone induced autophagy flux activation in human lung cancer cells. Inhibition of autophagy flux applying a specific inhibitor and genetically modified ATG5 siRNA enclosed troglitazone-mediated enhancing effect of TRAIL. These data demonstrated that activation of PPARγ mediated by troglitazone enhances human lung cancer cells to TRAIL-induced apoptosis via autophagy flux and also suggest that troglitazone may be a combination therapeutic target with TRAIL protein in TRAIL-resistant cancer cells.

Prostaglandin D2-Mediated DP2 and AKT Signal Regulate the Activation of Androgen Receptors in Human Dermal Papilla Cells

Prostaglandin D2 (PGD2) and prostaglandin D2 receptor 2 (DP2) is known to be an important factor in androgenetic alopecia (AGA). However, the effect of PGD2 in human dermal papilla cells (hDPCs) is not fully understood. The function of PGD2-induced expression of the androgen receptor (AR), DP2, and AKT (protein kinase B) signal were examined by using real time-PCR (qRT-PCR), western blot analysis, immunocytochemistry (ICC), and siRNA transfection system. PGD2 stimulated AR expression and AKT signaling through DP2. PGD2 stimulated AR related factors (transforming growth factor beta 1 (TGFβ1), Creb, lymphoid enhancer binding factor 1 (LEF1), and insulin-like growth factor 1, (IGF-1)) and AKT signaling (GSK3β and Creb) on the AR expression in hDPCs. However, these factors were down-regulated by DP2 antagonist (TM30089) and AKT inhibitor (LY294002) as well as DP2 knockdown in hDPCs decreased AR expression and AKT signaling. Finally, we confirmed that PGD2 stimulates the expression of AR related target genes, and that AKT and its downstream substrates are involved in AR expression on hDPCs. Taken together, our data suggest that PGD2 promotes AR and AKT signal via DP2 in hDPCs, thus, PGD2 and DP2 signal plays a critical role in AR expression. These findings support the additional explanation for the development of AGA involving PGD2-DP2 in hDPCs.

Peroxisome proliferator-activated receptor γ coactivator-1α is a predictor of lymph node metastasis and poor prognosis in human colorectal cancer

Peroxisome proliferator-activated receptor γ (PPARγ) and PPARγ coactivator-1α (PGC-1α) expression levels are correlated with clinical outcome in breast cancer. However, the potential biological and clinical significance of PPARγ and PGC-1α in colorectal cancer remains unknown. Here we investigated PPARγ and PGC-1α expression in colorectal cancer, and the associations of these expression levels with clinicopathological features. We also evaluated the roles of PPARγ and PGC-1α as prognostic factors in colorectal cancer. We performed immunohistochemical analysis to investigate PPARγ and PGC-1α expression in human colorectal cancer tissues and adjacent normal tissues from 108 primary colorectal cancer patients. We then examined how these expression levels correlated with clinicopathological features. Using the Kaplan-Meier method, we evaluated 3-year disease-free survival (DFS) and overall survival (OS) in patients with tumors expressing different levels of PPARγ and PGC-1α. Our results revealed that PPARγ expression was not significantly correlated with age at surgery, gender, differentiation, depth of infiltration, relapse, or TNM stage. Additionally, PGC-1α expression was not significantly correlated with age at surgery, differentiation, depth of infiltration, relapse, or TNM stage. However, PGC-1α expression was significantly correlated with nodal metastasis (p=0.020). Survival analysis demonstrated reduced OS in the PGC-1α-positive group compared to the PGC-1α-negative group (p=0.03). Our present findings suggest that PGC-1α may be useful for predicting nodal metastasis, and may represent a biomarker for poor prognosis in colorectal cancer.

Crosstalk between the Androgen Receptor and PPAR Gamma Signaling Pathways in the Prostate

Nuclear receptors are a superfamily of ligand-activated transcription factors that play critical roles in the regulation of normal biological processes and several disease states. Of the nuclear receptors expressed within the prostate, the androgen receptor (AR) promotes the differentiation of prostatic epithelial cells and stimulates production of enzymes needed for liquefaction of semen. Multiple forms of AR also promote the growth of both early and late stage prostate cancers. As a result, drugs that target the AR signaling pathway are routinely used to treat patients with advanced forms of prostate cancer. Data also suggest that a second member of the nuclear receptor superfamily, the peroxisome proliferator activated receptor gamma (PPARγ), is a tumor suppressor that regulates growth of normal prostate and prostate cancers. Recent studies indicate there is a bidirectional interaction between AR and PPARγ, with each receptor influencing the expression and/or activity of the other within prostatic tissues. In this review, we examine how AR and PPARγ each regulate the growth and development of normal prostatic epithelial cells and prostate cancers. We also discuss interactions between the AR and PPARγ signaling pathways and how those interactions may influence prostate biology.

Nck2, an unexpected regulator of adipogenesis

The regulation of adipose tissue expansion by adipocyte hypertrophy and/or hyperplasia is the topic of extensive investigations given the potential differential contribution of the 2 processes to the development of numerous chronic diseases associated with obesity. We recently discovered that the loss-of-function of the Src homology domain-containing protein Nck2 in mice promotes adiposity accompanied with adipocyte hypertrophy and impaired function, and enhanced adipocyte differentiation in vitro. Moreover, in severely-obese human's adipose tissue, we found that Nck2 expression is markedly downregulated. In this commentary, our goal is to expand upon additional findings providing further evidence for a unique Nck2-dependent mechanism regulating adipogenesis. We propose that Nck2 should be further investigated as a regulator of the reliance of white adipose tissue on hyperplasia versus hypertrophy during adipose tissue expansion, and hence, as a potential novel molecular target in obesity.

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.

Fatty Acids and Breast Cancer: Make Them on Site or Have Them Delivered

Brisk fatty acid (FA) production by cancer cells is accommodated by the Warburg effect. Most breast and other cancer cell types are addicted to fatty acids (FA), which they require for membrane phospholipid synthesis, signaling purposes, and energy production. Expression of the enzymes required for FA synthesis is closely linked to each of the major classes of signaling molecules that stimulate BC cell proliferation. This review focuses on the regulation of FA synthesis in BC cells, and the impact of FA, or the lack thereof, on the tumor cell phenotype. Given growing awareness of the impact of dietary fat and obesity on BC biology, we will also examine the less-frequently considered notion that, in addition to de novo FA synthesis, the lipolytic uptake of preformed FA may also be an important mechanism of lipid acquisition. Indeed, it appears that cancer cells may exist at different points along a "lipogenic-lipolytic axis," and FA uptake could thwart attempts to exploit the strict requirement for FA focused solely on inhibition of de novo FA synthesis. Strategies for clinically targeting FA metabolism will be discussed, and the current status of the medicinal chemistry in this area will be assessed. J. Cell. Physiol. 231: 2128-2141, 2016. © 2016 Wiley Periodicals, Inc.

Aberrant expression of cyclin D1 in cancer

Cyclin D1 binds and activates cyclin-dependent kinases 4/6 (Cdk4/6) to phosphorylate the retinoblastoma (RB) family proteins, relieving E2F/DPs from the negative restraint of RB proteins and histone deacetylases. The cyclin D-Cdk4/6 complexes activate cyclin E/Cdk2 through titration of the Cdk inhibitors p21^Cip1/p27^Kip1. Cyclin E/Cdk2 further phosphorylates RBs, thereby activating E2F/DPs, and cells enter the S phase of the cell cycle. Cyclin D-Cdk4/6 also phosphorylates MEP50 subunit of the protein arginine methyltransferase 5 (PRMT5), which cooperates with cyclin D1 to drive lymphomagenesis in vivo. Activated PRMPT5 causes arginine methylation of p53 to suppress expression of pro-apoptotic and anti-proliferative target genes, explaining the molecular mechanism for tumorigenesis. Cyclin D1 physically interacts with transcription factors such as estrogen receptor, androgen receptor, and Myb family proteins to regulate gene expression in Cdk-independent fashion. Dmp1 is a Myb-like protein that quenches the oncogenic signals from activated Ras or HER2 by inducing Arf/p53-dependent cell cycle arrest. Cyclin D1 binds to Dmp1α to activate both Arf and Ink4a promoters to induce cell cycle arrest or apoptosis in non-transformed cells to prevent them from neoplastic transformation. Dmp1-deficiency significantly accelerates mouse mammary tumorigenesis with reduced apoptosis and increased metastasis. Cyclin D1 interferes with ligand activation of PPARγ involved in cellular differentiation; it also physically interacts with histone deacetylases (HDACs) and p300 to repress gene expression. It has also been shown that cyclin D1 accelerates tumorigenesis through transcriptional activation of miR-17/20 and Dicer1 which, in turn, represses cyclin D1 expression. Identification of cyclin D1-binding proteins/promoters will be essential for further clarification of its biological activities.

Chemopreventive effect of apple and berry fruits against colon cancer

Colon cancer arises due to the conversion of precancerous polyps (benign) found in the inner lining of the colon. Prevention is better than cure, and this is very true with respect to colon cancer. Various epidemiologic studies have linked colorectal cancer with food intake. Apple and berry juices are widely consumed among various ethnicities because of their nutritious values. In this review article, chemopreventive effects of these fruit juices against colon cancer are discussed. Studies dealing with bioavailability, in vitro and in vivo effects of apple and berry juices are emphasized in this article. A thorough literature survey indicated that various phenolic phytochemicals present in these fruit juices have the innate potential to inhibit colon cancer cell lines. This review proposes the need for more preclinical evidence for the effects of fruit juices against different colon cancer cells, and also strives to facilitate clinical studies using these juices in humans in large trials. The conclusion of the review is that these apple and berry juices will be possible candidates in the campaign against colon cancer.

Acetylation-defective mutant of Pparγ is associated with decreased lipid synthesis in breast cancer cells

In our prior publications we characterized a conserved acetylation motif (K(R)xxKK) of evolutionarily related nuclear receptors. Recent reports showed that peroxisome proliferator activated receptor gamma (PPARγ) deacetylation by SIRT1 is involved in delaying cellular senescence and maintaining the brown remodeling of white adipose tissue. However, it still remains unknown whether lysyl residues 154 and 155 (K154/155) of the conserved acetylation motif (RIHKK) in Pparγ1 are acetylated. Herein, we demonstrate that Pparγ1 is acetylated and regulated by both endogenous TSA-sensitive and NAD-dependent deacetylases. Acetylation of lysine 154 was identified by mass spectrometry (MS) while deacetylation of lysine 155 by SIRT1 was confirmed by in vitro deacetylation assay. An in vivo labeling assay revealed K154/K155 as bona fide acetylation sites. The conserved acetylation sites of Pparγ1 and the catalytic domain of SIRT1 are both required for the interaction between Pparγ1 and SIRT1. Sirt1 and Pparγ1 converge to govern lipid metabolism in vivo. Acetylation-defective mutants of Pparγ1 were associated with reduced lipid synthesis in ErbB2 overexpressing breast cancer cells. Together, these results suggest that the conserved lysyl residues K154/K155 of Pparγ1 are acetylated and play an important role in lipid synthesis in ErbB2-positive breast cancer cells.

Curcumin inhibits proliferation of breast cancer cells through Nrf2-mediated down-regulation of Fen1 expression

Curcumin can inhibit cell proliferation of breast cancer, but the mechanism for this inhibition remains unclear. Over-expression of Flap endonuclease 1 (Fen1), a DNA repair-specific nuclease, is involved in the development of breast cancer. Nrf2 is a master regulator of cellular antioxidant defense systems. Curcumin can induce the expression of Nrf2 in both non-breast cancer cells and breast cancer cells. However, whether curcumin-induced inhibition of breast cancer cell proliferation may involve Nrf2-mediated Fen1 expression is not yet understood. In this study, we demonstrated that curcumin inhibited Fen1-dependent proliferation of MCF-7 cells and significantly induced Nrf2 protein expression while inhibiting Fen1 protein expression. Curcumin could down-regulate Fen1 gene expression in a Nrf2-dependent manner. Further investigation revealed that curcumin could lead to Nrf2 translocation from the cytoplasm to the nucleus and decrease Fen1 promoter activity by decreasing the recruitment of Nrf2 to the Fen1 promoter. These data suggest that curcumin may inhibit the proliferation of breast cancer cells through Nrf2-mediated down-regulation of Fen1 expression, which may be a new mechanism of curcumin-induced tumor growth inhibition.

Differential roles of PPARγ vs TR4 in prostate cancer and metabolic diseases

Peroxisome proliferator-activated receptor γ (PPARγ, NR1C3) and testicular receptor 4 nuclear receptor (TR4, NR2C2) are two members of the nuclear receptor (NR) superfamily that can be activated by several similar ligands/activators including polyunsaturated fatty acid metabolites, such as 13-hydroxyoctadecadienoic acid and 15-hydroxyeicosatetraenoic acid, as well as some anti-diabetic drugs such as thiazolidinediones (TZDs). However, the consequences of the transactivation of these ligands/activators via these two NRs are different, with at least three distinct phenotypes. First, activation of PPARγ increases insulin sensitivity yet activation of TR4 decreases insulin sensitivity. Second, PPARγ attenuates atherosclerosis but TR4 might increase the risk of atherosclerosis. Third, PPARγ suppresses prostate cancer (PCa) development and TR4 suppresses prostate carcinogenesis yet promotes PCa metastasis. Importantly, the deregulation of either PPARγ or TR4 in PCa alone might then alter the other receptor's influences on PCa progression. Knocking out PPARγ altered the ability of TR4 to promote prostate carcinogenesis and knocking down TR4 also resulted in TZD treatment promoting PCa development, indicating that both PPARγ and TR4 might coordinate with each other to regulate PCa initiation, and the loss of either one of them might switch the other one from a tumor suppressor to a tumor promoter. These results indicate that further and detailed studies of both receptors at the same time in the same cells/organs may help us to better dissect their distinct physiological roles and develop better drug(s) with fewer side effects to battle PPARγ- and TR4-related diseases including tumor and cardiovascular diseases as well as metabolic disorders.

Loss of PPARγ expression in mammary secretory epithelial cells creates a pro-breast tumorigenic environment

Breast cancer is the leading cause of new cancer diagnoses among women. Using peroxisome proliferator-activated receptor (PPAR)γ((+/-)) mice, we showed normal expression of PPARγ was critical to stop 7,12-dimethylbenz[a]anthracene (DMBA)-induced breast tumorigenesis. PPARγ is expressed in many breast cell types including mammary secretory epithelial (MSE) cells. MSEs proliferate as required during pregnancy, and undergo apoptosis or reversible transdifferentiation during involution once lactation is complete. Thus, MSE-specific loss of PPARγ was hypothesized to enhance DMBA-mediated breast tumorigenesis. To test this, MSE cell-specific PPARγ knockout (PPARγ-MSE KO) and control (PPARγ-WT) mice were generated, mated and allowed to nurse for three days. One week after involution, dams were treated with DMBA to initiate breast tumors, and randomized on week 7 to continue receiving a normal chow diet (DMBA Only: PPARγ-WT, n = 15; PPARγ-MSE KO, n = 25) or one supplemented with a PPARγ activating drug (DMBA + ROSI: PPARγ-WT, n = 17; PPARγ-MSE KO, n = 24), and monitored for changes in breast tumor outcomes. PPARγ-MSE KOs had significantly lower overall survival and decreased mammary tumor latency as compared to PPARγ-WT controls. PPARγ activation significantly reduced DMBA-mediated malignant mammary tumor volumes irrespective of genotype. MSE-specific PPARγ loss resulted in decreased mammary gland expression of PTEN and Bax, increased superoxide anion production, and elevated serum eotaxin and RANTES, creating a protumorigenic environment. Moreover, PPARγ activation in MSEs delayed mammary tumor growth in part by down-regulating Cox-1, Cox-2 and cyclin D1. Collectively, these studies highlight a protective role of MSE-specific PPARγ during breast tumorigenesis, and support a novel chemotherapeutic role of PPARγ activation in breast cancer.

PPARγ agonists target aromatase via both PGE2 and BRCA1

Obesity is a well-recognized risk factor for postmenopausal breast cancer. Although the underlying mechanisms are not clearly defined, aromatase is thought to play a pivotal role in connecting obesity-associated inflammation with postmenopausal breast cancer. It has been well established that both the proinflammatory prostaglandin E(2) (PGE(2)) and the BRCA1 tumor-suppressor gene regulate aromatase expression. In this issue of the journal (beginning on p. 1183), Subbaramaiah and colleagues improve our understanding of the molecular mechanisms by which PPARγ inhibits aromatase expression. They found that pioglitazone, a PPARγ agonist, inhibited aromatase expression by inhibition of PGE(2) signaling and upregulation of BRCA1. Their findings provide potential targets for preventing or treating obesity-related breast cancer.

Tumor-suppressive effects of CDK8 in endometrial cancer cells

CDK8 is either amplified or mutated in a variety of human cancers, and CDK8 functions as an oncoprotein in melanoma and colorectal cancers. Previously, we reported that loss or reduction of CDK8 results in aberrant fat accumulation in Drosophila and mammals, suggesting that CDK8 plays an important role in inhibiting lipogenesis. Epidemiological studies have identified obesity and overweight as the major risk factors of endometrial cancer, thus we examined whether CDK8 regulates endometrial cancer cell growth by using several endometrial cancer cell lines, including KLE, which express low levels of CDK8, as well as AN3 CA and HEC-1A cells, which have high levels of endogenous CDK8. We observed that ectopic expression of CDK8 in KLE cells inhibited cell proliferation and potently blocked tumor growth in an in vivo mouse model. In addition, gain of CDK8 in KLE cells blocked cell migration and invasion in transwell, wound healing and persistence of migratory directionality assays. Conversely, we observed the opposite effects in all of the aforementioned assays when CDK8 was depleted in AN3 CA cells. Similar to AN3 CA cells, depletion of CDK8 in HEC-1A cells strongly enhanced cell migration in transwell assays, while overexpression of CDK8 in HEC-1A cells blocked cell migration. Furthermore, gene profiling of KLE cells overexpressing CDK8 revealed genes whose protein products are involved in lipid metabolism, cell cycle and cell movement pathways. Finally, depletion of CDK8 increased the expression of lipogenic genes in endometrial cancer cells. Taken together, these results show a reverse correlation between CDK8 levels and several key features of the endometrial cancer cells, including cell proliferation, migration and invasion as well as tumor formation in vivo. Therefore, in contrast to the oncogenic effects of CDK8 in melanoma and colorectal cancers, our results suggest that CDK8 plays a tumor-suppressive role in endometrial cancers.

Linking αMSH with PPARγ in B16-F10 melanoma

We have discovered a new α-melanocyte stimulating hormone (α-MSH)/peroxisome proliferator activated receptor-γ (PPAR-γ) connection in B16-F10 cells. Both PPAR-γ up-regulation and its induction as an active transcription factor were observed in response to α-MSH. The α-MSH/PPAR-γ connection influenced both pigmentation and proliferation. The forskolin-stimulated cAMP/PKA pathway was not able to induce either PPAR-γ translocation into the nucleus or PPAR-γ transcriptional activity. As the melanocortin-1 receptor, the specific receptor for the α-MSH, is a G-protein coupled receptor, we wondered whether the phosphatidylinositol [PI(4,5)P(2) /PLC(β) ] signal pathway was involved in mediating the α-MSH-dependent PPAR-γ activation. Employing inhibitors of PI(4,5)P(2) /PLC(β) pathway, the results of our experiments suggested that this pathway was promoted by α-MSH and that α-MSH played a role in mediating PPAR-γ activation. We have demonstrated, for the first time, that α-MSH induces the PI(4,5)P(2) /PLC(β) pathway, through analysis of the basic steps of the pathway. The α-MSH effect on PPAR-γ was independent of animal species and was not correlated with the physio-pathological status.

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.

PPARγ and NF-κB regulate the gene promoter activity of their shared repressor, TNIP1

Human TNFAIP3 interacting protein 1 (TNIP1) has diverse functions including support of HIV replication through its interaction with viral Nef and matrix proteins, reduction of TNFα-induced signaling through its interaction with NF-κB pathway proteins, and corepression of agonist-bound retinoic acid receptors and peroxisome proliferator-activated receptors (PPAR). The wide tissue distribution of TNIP1 provides the opportunity to influence numerous cellular responses in these roles and defining control of TNIP1 expression would be central to improved understanding of its impact on cell function. We cloned 6kb of the human TNIP1 promoter and performed predictive and functional analyses to identify regulatory elements. The promoter region proximal to the transcription start site is GC-rich without a recognizable TATA box. In contrast to this proximal ~500bp region, 6kb of the promoter increased reporter construct constitutive activity over five-fold. Throughout the 6kb length, in silico analysis identified several potential binding sites for both constitutive and inducible transcription factors; among the latter were candidate NF-κB binding sequences and peroxisome proliferator response elements (PPREs). We tested NF-κB and PPAR regulation of the endogenous TNIP1 gene and cloned promoter by expression studies, electrophoretic mobility shift assays, and chromatin immunoprecipitations. We validated NF-κB sites in the TNIP1 promoter proximal and distal regions as well as one PPRE in the distal region. The ultimate control of the TNIP1 promoter is likely to be a combination of constitutive transcription factors and those subject to activation such as NF-κB and PPAR.

Caffeic acid phenethyl ester inhibits proliferation and migration, and induces apoptosis in platelet-derived growth factor-BB-stimulated human coronary smooth muscle cells

BACKGROUND/AIMS

Restenosis after a percutaneous coronary intervention (PCI) during treatment for coronary artery disease is closely related to smooth muscle cell (SMC) proliferation and migration. In this study, we investigated the effects of caffeic acid phenethyl ester (CAPE) and its underlying mechanism on human coronary SMCs (HCSMCs) after platelet-derived growth factor-BB (PDGF-BB) stimulation in vitro.

METHODS AND RESULTS

The results showed that CAPE inhibited proliferation and migration, and induced apoptosis. Concomitantly, CAPE inhibited activation of AKT1, MEK1 and ERK1/2 signaling molecules at 10-60 min after CAPE treatment. As revealed by flow cytometry, DNA fragmentation and TUNEL assay, the cells accumulated at the sub-G(1) phase, and cell apoptosis was observed after 30 and 90 μM CAPE treatment for 72 h. CAPE triggered the release of cytochrome c from mitochondria to cytosol, upregulated the proapoptotic gene Bax and downregulated the antiapoptotic gene Bcl-2. Upregulation of caspase-9 and caspase-3 indicated that CAPE precipitated the mitochondrion-dependent apoptotic signaling pathway.

CONCLUSIONS

These results provide a molecular explanation for the antiproliferation, antimigration and proapoptotic effects of CAPE on HCSMCs after PDGF-BB stimulation.

Role of Peoxisome Proliferator Activator Receptor gamma on Blood Retinal Barrier Breakdown

The retinal vessels have two barriers: the retinal pigment epithelium and the retinal vascular endothelium. Each barrier exhibits increased permeability under various pathological conditions. This condition is referred to as blood retinal barrier (BRB) breakdown. Clinically, the most frequently encountered condition causing BRB breakdown is diabetic retinopathy. In recent studies, inflammation has been linked to BRB breakdown and vascular leakage in diabetic retinopathy. Biological support for the role of inflammation in early diabetes is the adhesion of leukocytes to the retinal vasculature (leukostasis) observed in diabetic retinopathy. PPARγ is a member of a ligand-activated nuclear receptor superfamily and plays a critical role in a variety of biological processes, including adipogenesis, glucose metabolism, angiogenesis, and inflammation. There is now strong experimental evidence to support the theory that PPARγ inhibits diabetes-induced retinal leukostasis and leakage, playing an important role in the pathogenesis of diabetic retinopathy. Therapeutic targeting of PPARγ may be beneficial to diabetic retinopathy.

Chondrosarcoma and peroxisome proliferator-activated receptor

Induction of differentiation and apoptosis in cancer cells by ligands of PPARγ is a novel therapeutic approach to malignant tumors. Chondrosarcoma (malignant cartilage tumor) and OUMS-27 cells (cell line established from grade III human chondrosarcoma) express PPARγ. PPARγ ligands inhibited cell proliferation in a dose-dependent manner, and induced apoptosis of OUMS-27. The higher-grade chondrosarcoma expressed a higher amount of antiapoptotic Bcl-xL in vivo. The treatment of OUMS-27 by 15d-PGJ₂, the most potent endogenous ligand for PPARγ, downregulated expression of Bcl-xL and induced transient upregulation of proapoptotic Bax, which could accelerate cytochrome c release from mitochondria to the cytosol, followed by induction of caspase-dependent apoptosis. 15d-PGJ₂ induced the expression of CDK inhibitor p21 protein in human chondrosarcoma cells, which appears to be involved in the mechanism of inhibition of cell proliferation. These findings suggest that targeted therapy with PPARγ ligands could be a novel strategy against chondrosarcoma.

Mechanisms by which thiazolidinediones induce anti-cancer effects in cancers in digestive organs

Increasing evidence suggests that thiazolidinediones (TZDs) could have a therapeutic potential for patients with cancers. Here, the evidence on the mechanisms by which TZDs could contribute to different steps of cancer biology in the digestive system is summarized. According to studies, TZDs induce anti-cancer actions through 3 main pathways: (1) cell growth arrest, (2) induction of apoptosis, and (3) inhibition of cell invasion. Cell growth arrest is induced by an increased level of p27(Kip1). p27(Kip1) accumulation results from the inhibition of the ubiquitin-proteasome system and/or inhibition of MEK-ERK signaling. TZDs induce apoptosis through increased levels of apoptotic molecules, such as p53 and PTEN and/or decreased level of anti-apoptotic molecules, such as Bcl-2 and survivin. Inhibition of MEK-ERK signaling-mediated up-regulation of E-cadherin and claudin-4, and/or decreased expression of matrix metalloproteinases (MMPs) such as MMP-2 and MMP-9, play a role in the TZD-induced inhibition of cancer cell invasion. Thus, TZDs are capable of inducing anti-tumor action in a variety of ways in gastrointestinal cancers.

Transcription elongation regulator 1 is a co-integrator of the cell fate determination factor Dachshund homolog 1

DACH1 (Dachshund homolog 1) is a key component of the retinal determination gene network and regulates gene expression either indirectly as a co-integrator or through direct DNA binding. The current studies were conducted to understand, at a higher level of resolution, the mechanisms governing DACH1-mediated transcriptional repression via DNA sequence-specific binding. DACH1 repressed gene transcription driven by the DACH1-responsive element (DRE). Recent genome-wide ChIP-Seq analysis demonstrated DACH1 binding sites co-localized with Forkhead protein (FOX) binding sites. Herein, DACH1 repressed, whereas FOX proteins enhanced, both DRE and FOXA-responsive element-driven gene expression. Reduced DACH1 expression using a shRNA approach enhanced FOX protein activity. As DACH1 antagonized FOX target gene expression and attenuated FOX signaling, we sought to identify limiting co-integrator proteins governing DACH1 signaling. Proteomic analysis identified transcription elongation regulator 1 (TCERG1) as the transcriptional co-regulator of DACH1 activity. The FF2 domain of TCERG1 was required for DACH1 binding, and the deletion of FF2 abolished DACH1 trans-repression function. The carboxyl terminus of DACH1 was necessary and sufficient for TCERG1 binding. Thus, DACH1 represses gene transcription through direct DNA binding to the promoter region of target genes by recruiting the transcriptional co-regulator, TCERG1.

Alternative cyclin D1 splice forms differentially regulate the DNA damage response

The DNA damage response (DDR) activates downstream pathways including cell cycle checkpoints. The cyclin D1 gene is overexpressed or amplified in many human cancers and is required for gastrointestinal, breast, and skin tumors in murine models. A common polymorphism in the human cyclin D1 gene is alternatively spliced, resulting in cyclin D1a and D1b proteins that differ in their carboxyl terminus. Cyclin D1 overexpression enhances DNA damage-induced apoptosis. The role of cyclin D1 and the alternative splice form in regulating the DDR is not well understood. Herein cyclin D1a overexpression enhanced the DDR as characterized by induction of γH2AX phosphorylation, the assembly of DNA repair foci, specific recruitment of DNA repair factors to chromatin, and G(2)-M arrest. Cyclin D1 deletion in fibroblasts or small interfering RNA-mediated reduction of endogenous cyclin D1 in colon cancer cells reduced the 5-fluorouracil-mediated DDR. Mechanistic studies showed that cyclin D1a, like DNA repair factors, elicited the DDR when stably associated with chromatin.

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.

Attenuation of Forkhead signaling by the retinal determination factor DACH1

The Drosophila Dachshund (Dac) gene, cloned as a dominant inhibitor of the hyperactive growth factor mutant ellipse, encodes a key component of the retinal determination gene network that governs cell fate. Herein, cyclic amplification and selection of targets identified a DACH1 DNA-binding sequence that resembles the FOX (Forkhead box-containing protein) binding site. Genome-wide in silico promoter analysis of DACH1 binding sites identified gene clusters populating cellular pathways associated with the cell cycle and growth factor signaling. ChIP coupled with high-throughput sequencing mapped DACH1 binding sites to corresponding gene clusters predicted in silico and identified as weight matrix resembling the cyclic amplification and selection of targets-defined sequence. DACH1 antagonized FOXM1 target gene expression, promoter occupancy in the context of local chromatin, and contact-independent growth. Attenuation of FOX function by the cell fate determination pathway has broad implications given the diverse role of FOX proteins in cellular biology and tumorigenesis.

Repression of beta-catenin signaling by PPAR gamma ligands

Aberrant activation of the Wnt/beta-catenin signaling pathway plays a crucial role in oncogenesis of various human malignancies. It has been demonstrated that there is a direct interaction between beta-catenin and PPAR gamma. Here we examined the effects of fifteen reported PPAR ligands in a reporter gene assay that is dependent on beta-catenin activation of TCF/LEF transcription factors; only the thiazolidinedione PPAR gamma agonists troglitazone, rosiglitazone and pioglitazone, and a non-thiazolidinedione PPAR gamma activator GW1929 inhibited beta-catenin-induced transcription in a PPAR gamma dependent fashion. The results from mammalian one-hybrid experiments showed that functional PPAR gamma was necessary for ligand-dependent inhibition of beta-catenin transactivation. However, a PPAR gamma activator Fmoc-Leu could not repress beta-catenin-mediated signaling and its transactivation activity. These results indicate that activation of PPAR gamma is necessary, but not sufficient, for the beta-catenin antagonistic activity of a PPAR gamma agonist, and that the inhibitory compounds interfere directly with beta-catenin transactivation activity.