Hormone Receptor Superfamily Research Articles

Abstract 1519: Peroxisome proliferator-activated receptor ≤ promotes colonic inflammation and inflammation-associated tumorigenesis

Abstract Although epidemiologic and experimental evidence strongly indicates chronic inflammation as a risk factor for cancer, it remains unclear how chronic inflammation contributes carcinogenesis. Peroxisome proliferator-activated receptor ≤ (PPARδ) is one member of PPAR family that belongs to the nuclear hormone receptor superfamily and is also ligand-dependent transcription factor. Although PPARδ has been shown to be involved in chronic inflammation and the progression of hereditary and sporadic CRC, its role in inflammation-induced carcinogenesis is not defined. The aim of our present study was to determine whether PPARδ contributes to the pathogenesis of colonic inflammation and inflammation-associated carcinogenesis. Here we present genetic evidence demonstrating that deletion of PPARδ diminishes colonic inflammation accompanied with reducing infiltration of immune cells and the expression of pro-inflammatory chemokines and cytokines in a mouse model of colitis. These PPARδ-dependent chemokines are responsible for recruitment of leukocytes from the circulation to local inflammatory sites and the tumor microenvironment. Our results further reveal that activation of PPARδ induces COX-2 expression in colonic epithelial cells. Importantly, COX-2-derived PGE2 stimulates macrophages to produce pro-inflammatory chemokines and cytokines. More intriguingly, loss of PPARδ attenuated colonic chronic inflammation and colitis-associated adenoma growth via PGE2 signaling in two mouse models of colitis-associated tumorigenesis. Collectively, our results demonstrate that PPARδ promotes colonic chronic inflammation and colitis-associated tumor growth via a PGE2 signaling which mediates the crosstalk between tumor epithelial cells and macrophages. Our data further supports the notion that the existence of crosstalk between PPARδ and COX-2 signaling in CRC progression. These findings indicate that PPARδ plays a pivotal role in connecting colonic inflammation to cancer progression and may represent a potential therapeutic target for prevention or treatment of colorectal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1519. doi:1538-7445.AM2012-1519

Abstract 266: Angiotensin I-7 modulates transcriptional (de)activation of multiple members of steroid hormone receptor superfamily: Possible mechanisms underlying inhibited proliferation in (T47D) human breast cancer cells

Abstract Introduction: Renin Angiotensin System (RAS) is correlated to breast cancer and to other types of cancer. Angiotensin I-7 [Ang-(I-7)] is an endogenous 7-amino acid peptide hormone of this system that has anti-proliferative properties. Interestingly, there are increasing evidences that RAS is implicated in the development of breast cancer. Objectives: We aimed to evaluate the expression of steroid hormone receptors (progesterone receptors (PR), estrogen receptors (ER), androgen receptors (AR), apoptosis and proliferation in tumoral (T47D) epithelial mammary cell line, after Ang-(I-7) treatment. Methods: Tumoral (T47D) cultured cell line was treated with angiotensin I-7 peptide and cells were harvested after 2, and 15 days, when expression analysis of steroid hormone receptors was performed by real time PCR. The same treatment was used for the apoptosis and cell cycle analyses, done using the 5HT-GUAVA flow cytometer. Results: Expression of steroid hormone receptors implicated to breast carcinogenesis such as genomic progesterone receptors (PR(A+B) and PRB), estrogen receptors (Era and ERb), androgen receptor (AR) were never investigated together in the sex hormone-sensitive human breast cancer cell T47D after angiotensin I-7 exposure. When T47D cells were treated with angiontensin I-7 peptide were all up-regulated of the control level (PRA+B (1.0-fold), PRB (2.3-fold), Era (7.8-fold), ERb (8.1-fold) and AR (1.9-fold) - p < 0.01) in early treatment (2 days). However, important down-regulation of all receptors was observed after 15 days. T47D responded by down-regulating PRA+B (-3.5-fold), PRB (-3.1-fold), Era (-4.3-fold), ERb (-4.6-fold) and AR (-6.05-fold), all compared to basal conditions (p < 0.001). The functional relevance of steroid hormone receptors inhibition in sensitive human breast cancer cell line was confirmed by flow cytometry, assaying cell viability, apoptosis and proliferation by flow cytometry. Ang-(I-7) 2 day treatment significantly increased cell cycle in all phases (G0/G1, S and G2/M) when compared to control and decreased apoptosis (p < 0.05), but after 15 days there was a significant reduction in all cell cycle phases (p < 0.05) and increased apoptosis indexes were observed (p < 0.001). Conclusion: These results suggest anti-proliferative actions of Ang-(I-7), which has already been demonstrated previously for this peptide by our research group (Alecrim et al, 2011). Moreover, we could also observe a pro-apoptotic effect sustained for 15 days in these cells, and it seems to be correlated to the down-regulated expression of all steroid hormone receptors studied. In summary, Ang-(1-7) drives T47D cells to apoptosis and the use of the peptide as a novel therapeutic compound for breast cancer should be considered. Support: FAPESP Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 266. doi:1538-7445.AM2012-266

Hepatocarcinogenesis in FXR−/− Mice Mimics Human HCC Progression That Operates through HNF1α Regulation of FXR Expression

Farnesoid X receptor (FXR) (nuclear receptor subfamily 1, group H, member 4) is a member of nuclear hormone receptor superfamily, which plays essential roles in metabolism of bile acids, lipid, and glucose. We previously showed spontaneously hepatocarcinogenesis in aged FXR(-/-) mice, but its relevance to human hepatocellular carcinoma (HCC) is unclear. Here, we report a systematical analysis of hepatocarcinogenesis in FXR(-/-) mice and FXR expression in human liver cancer. In this study, liver tissues obtained from FXR(-/-) and wild-type mice at different ages were compared by microarray gene profiling, histological staining, chemical analysis, and quantitative real-time PCR. Primary hepatic stellate cells and primary hepatocytes isolated from FXR(-/-) and wild-type mice were also analyzed and compared. The results showed that the altered genes in FXR(-/-) livers were mainly related to metabolism, inflammation, and fibrosis, which suggest that hepatocarcinogenesis in FXR(-/-) mice recapitulated the progression of human liver cancer. Indeed, FXR expression in human HCC was down-regulated compared with normal liver tissues. Furthermore, the proinflammatory cytokines, which were up-regulated in human HCC microenvironment, decreased FXR expression by inhibiting the transactivity of hepatic nuclear factor 1α on FXR gene promoter. Our study thereby demonstrates that the down-regulation of FXR has an important role in human hepatocarcinogenesis and FXR(-/-) mice provide a unique animal model for HCC study.

Peroxisome Proliferator-Activated Receptor Gamma (PPAR-γ) and Neurodegenerative Disorders

As the growth of the aging population continues to accelerate globally, increased prevalence of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and stroke, has generated substantial public concern. Unfortunately, despite of discoveries of common factors underlying these diseases, few drugs are available to effectively treat these diseases. Peroxisome proliferator-activated receptor gamma (PPAR-γ) is a ligand-activated transcriptional factor that belongs to the nuclear hormone receptor superfamily. PPAR-γ has been shown to influence the expression or activity of a large number of genes in a variety of signaling networks, including regulation of insulin sensitivity, glucose homeostasis, fatty acid oxidation, immune responses, redox balance, cardiovascular integrity, and cell fates. Recent epidemiological, preclinical animal, and clinical studies also show that PPAR-γ agonists can lower the incidence of a number of neurological disorders, despite of multiple etiological factors involved in the development of these disorders. In this manuscript, we review current knowledge on mechanisms underlying the beneficial effect of PPAR-γ in different neurodegenerative diseases, in particular, AD, PD, and stroke, and attempt to analyze common and overlapping features among these diseases. Our investigation unveiled information suggesting the ability for PPAR-γ to inhibit NF-κB-mediated inflammatory signaling at multiple sites, and conclude that PPAR-γ agonists represent a novel class of drugs for treating neuroinflammatory diseases.

The Use of Immunohistochemical Expression of SF-1 and EMA in Distinguishing Adrenocortical Tumors From Renal Neoplasms

Steroidogenic factor -1 (SF-1) is an orphan member of the nuclear hormone receptor superfamily, and is considered to play an important role in the differentiation of steroidogenic tissues. In this study, we compared the immunohistochemical stains of SF-1 and epithelial membrane antigen (EMA) in non-neoplastic adrenal tissue, and adrenal and renal tumors using tissue microarrays (TMAs). The adrenal tissue array included 19 cases of normal adrenal cortex, 22 cases of adrenal adenoma, and 20 cases of adrenal cortical carcinoma. The renal tissue array included 20 cases of each of the following types of renal cell carcinoma: clear cell, papillary, and chromophobe. In addition, 20 cases of renal oncocytoma were also included in the study. SF-1 showed positive staining in all cases (100%) of normal adrenal cortex and adrenal cortical adenoma, and in 18 (90%) cases of adrenocortical carcinoma. In renal tumors, SF-1 showed negative stains in all of oncocytoma, papillary, and chromophobe renal cell carcinoma. Only 3 out of 20 cases of clear cell renal cell carcinoma showed weak positivity in approximately 10% of tumor cells. EMA stained positively in 85%, 95%, 100%, and 95% of clear cell, papillary, chromophobe renal cell carcinomas, and oncocytomas, respectively. EMA was completely negative in the adrenal TMAs. In conclusion, SF-1 and EMA may be helpful in the differentiation of adrenal tumors from renal tumors in difficult cases.

5,7‐Dimethoxyflavone, an activator of PPARα/γ, inhibits UVB‐induced MMP expression in human skin fibroblast cells

Peroxisome proliferator-activated receptors (PPARs), which are members of the nuclear hormone receptor superfamily, are a family of ligand-activated transcription factors that consist of three isotypes (PPAR α, δ and γ). PPAR activity was previously thought to be limited to lipid metabolism and glucose homeostasis; however, intensive studies of PPARα/γ in recent years have revealed their importance in age-related inflammation and photoaging as regulators of cytokines, matrix metalloproteinases (MMPs) and nuclear factor-kappa B (NF-κB). We evaluated the ability of the PPARα/γ activator 5,7-dimethoxyflavone (5,7-DMF) to inhibit ultraviolet B (UVB)-induced MMP expression in Hs68 human skin fibroblasts. Hs68 cells were treated with 5,7-DMF and then exposed to UVB irradiation. MMP expression, production and activity were determined by reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay and gelatin zymography. PPARα/γ expression, catalase expression, and mitogen-activated protein kinase (MAPK), activator protein-1 (AP-1) and NF-κB signalling were evaluated by Western blot analysis. PPARα/γ activity was assessed with the GAL4/PPARα/γ transactivation assay. We found that 5,7-DMF strongly decreased MMP expression, production and activity. In addition, 5,7-DMF significantly increased PPARα/γ activation and catalase expression, thereby downregulating UVB-induced reactive oxygen species (ROS) production, ROS-induced MAPK signalling and downstream transcription factors. Finally, 5,7-DMF reduced IκBα phosphorylation, blocked NF-κB p65 nuclear translocation, strongly suppressed proinflammatory cytokines such as interleukin-6 (IL-6) and IL-8. 5,7-DMF prevents UVB-induced MMP expression by suppressing UVB-induced oxidative stress and age-related inflammation via NF-κB and MAPK/AP-1 pathways. Our findings suggest the usefulness of 5,7-DMF for preventing and treating skin photoaging.

Leptin regulates estrogen receptor gene expression in ATDC5 cells through the extracellular signal regulated kinase signaling pathway

Both estrogen and leptin play an important role in the regulation of physiological processes of endochondral bone formation in linear growth. Estrogen receptors (ERα and ERβ) are known as members of the superfamily of nuclear steroid hormone receptors and are detected in all zones of growth plate chondrocytes. They can be regulated in a ligand-independent manner. Whether leptin regulates ERs in the growth plate is still not clear. To explore this issue, chondrogenic ATDC5 cells were used in the present study. Messenger RNA and protein analyses were performed by quantitative PCR and Western blotting. We found that both ERα and ERβ were dynamically expressed during the ATDC5 cell differentiation for 21 days. Leptin (50 ng/ml) significantly upregulated ERα and ERβ mRNA and protein levels 48 h after leptin stimulation (P<0.05) at day 14. The up-regulation of ERα and ERβ mRNA by leptin was shown in a dose-dependent manner, but the most effective dose of leptin was different (100 and 1,000 ng/ml, respectively). Furthermore, we confirmed that leptin augmented the phosphorylation of ERK1/2 in a time-dependent manner. A maximum eightfold change was observed at 15 min. Finally, a specific ERK1/2 inhibitor, UO126, blocked leptin-induced ERs regulation in ATDC5 cells, indicating that ERK1/2 mediates, partly, the effects of leptin on ERs. These data demonstrate, for the first time, that leptin regulates the expression of ERs in growth plate chondrocytes via ERK signaling pathway, thereby suggesting a crosstalk between leptin and estrogen receptors in the regulation of bone formation.

Farnesoid X receptor expression is reduced in human hepatocellular carcinoma

Farnesoid X receptor (FXR, NR1H4) is a member of nuclear hormone receptor superfamily. Previously studies showed that FXR−/− mice spontaneously developed liver tumors when they aged, however, the relevance of which to human hepatocellular carcinoma (HCC) is unclear. The aim of this study is to observe whether FXR expression is also downregulated in HCC and discuss the mechanism of the reduced FXR expression in HCC. Expression of FXR and small heterodimer partner (SHP) was measured by real-time PCR and immunohistochemical technique. Effect of pro-inflammatory cytokines on expression of FXR and its promoter activity were determined in primary hepatocytes or HepG2 and Huh7 cell lines. Our results showed that expression of FXR and its target gene SHP in human HCC was strongly downregulated compared to the normal liver tissues. In addition, pro-inflammatory cytokines were able to decrease FXR expression by inhibiting the FXR promoter activity. In conclusion this work demonstrates FXR expression is strongly downregulated in human HCC, which may be caused by decreased FXR promoter activity, suggesting a potential role of FXR in human HCC development.

Liganded Thyroid Hormone Receptor Inhibits Phorbol 12-O-Tetradecanoate-13-Acetate-Induced Enhancer Activity via Firefly Luciferase cDNA

Thyroid hormone receptor (TR) belongs to the nuclear hormone receptor (NHR) superfamily and regulates the transcription of its target genes in a thyroid hormone (T3)-dependent manner. While the detail of transcriptional activation by T3 (positive regulation) has been clarified, the mechanism of T3-dependent repression (negative regulation) remains to be determined. In addition to naturally occurring negative regulations typically found for the thyrotropin β gene, T3-bound TR (T3/TR) is known to cause artificial negative regulation in reporter assays with cultured cells. For example, T3/TR inhibits the transcriptional activity of the reporter plasmids harboring AP-1 site derived from pUC/pBR322-related plasmid (pUC/AP-1). Artificial negative regulation has also been suggested in the reporter assay with firefly luciferase (FFL) gene. However, identification of the DNA sequence of the FFL gene using deletion analysis was not performed because negative regulation was evaluated by measuring the enzymatic activity of FFL protein. Thus, there remains the possibility that the inhibition by T3 is mediated via a DNA sequence other than FFL cDNA, for instance, pUC/AP-1 site in plasmid backbone. To investigate the function of FFL cDNA as a transcriptional regulatory sequence, we generated pBL-FFL-CAT5 by ligating FFL cDNA in the 5' upstream region to heterologous thymidine kinase promoter in pBL-CAT5, a chloramphenicol acetyl transferase (CAT)-based reporter gene, which lacks pUC/AP-1 site. In kidney-derived CV1 and choriocarcinoma-derived JEG3 cells, pBL-FFL-CAT5, but not pBL-CAT5, was strongly activated by a protein kinase C activator, phorbol 12-O-tetradecanoate-13-acetate (TPA). TPA-induced activity of pBL-FFL-CAT5 was negatively regulated by T3/TR. Mutation of nt. 626/640 in FFL cDNA attenuated the TPA-induced activation and concomitantly abolished the T3-dependent repression. Our data demonstrate that FFL cDNA sequence mediates the TPA-induced transcriptional activity, which is inhibited by T3/TR.

Peroxisome proliferator-activated receptor subtypes in mammary gland development and breast cancer

Introduction Peroxisome proliferator-activated receptors (PPARs) are ligand activated transcription factors that are members of the nuclear hormone receptor superfamily [1]. There are three members of this subfamily, PPARα, PPARβ/δ and PPARγ with each subtype having overlapping but distinct tissue distribution [1]. PPARα is primarily expressed in tissues involved with fatty acid

The role of PPAR in myocardial response to ischemia in normal and diseased heart

Peroxisome proliferator-activated receptors (PPAR), ligand-activated transcription factors, belong to the nuclear hormone receptor superfamily regulating expression of genes involved in different aspects of lipid metabolism, inflammation and cardiac energy production. Activation of PPAR-α isoform by its natural ligands, fatty acids (FA) and eicosanoids, promotes mitochondrial FA oxidation as the primary ATP-generating pathway. On the other hand, PPAR-γ regulates lipid anabolism or storage, while, until recently, the function of PPAR-β/δ has been less explored. Under conditions associated with acute or chronic oxygen deprivation, PPAR-α modulates expression of genes that determine substrate switch (FA vs. glucose) aimed at maintenance of basic cardiac function. Although PPAR-α and PPAR-γ synthetic agonists, hypolipidemic and antidiabetic drugs, have been reported to protect the heart against ischemia/reperfusion injury, it is still a matter of debate whether PPAR activation plays a beneficial or detrimental role in myocardial response to ischemia, in particular, in pathological conditions. This article reviews some findings demonstrating the impact of PPAR activation on cardiac resistance to ischemia in normal and pathologically altered heart. Specifically, it addresses the issue of susceptibility to ischemia in the diabetic myocardium, with particular regards to the role of PPAR. Finally, involvement of PPAR in the mechanisms of lipid-independent cardioprotective effects of some hypolipidemic drugs is also discussed.

Ligand-Specific Structural Changes in the Vitamin D Receptor in Solution

Vitamin D receptor (VDR) is a member of the nuclear hormone receptor superfamily. When bound to a variety of vitamin D analogues, VDR manifests a wide diversity of physiological actions. The molecular mechanism by which different vitamin D analogues cause specific responses is not understood. The published crystallographic structures of the ligand binding domain of VDR (VDR-LBD) complexed with ligands that have differential biological activities have exhibited identical protein conformations. Here we report that rat VDR-LBD (rVDR-LBD) in solution exhibits differential chemical shifts when bound to three ligands that cause diverse responses: the natural hormone, 1,25-dihydroxyvitamin D(3) [1,25(OH)₂D₃], a potent agonist analogue, 2-methylene-19-nor-(20S)-1,25-dihydroxyvitamin D₃ [2MD], and an antagonist, 2-methylene-(22E)-(24R)-25-carbobutoxy-26,27-cyclo-22-dehydro-1α,24-dihydroxy-19-norvitamin D₃ [OU-72]. Ligand-specific chemical shifts mapped not only to residues at or near the binding pocket but also to residues remote from the ligand binding site. The complexes of rVDR-LBD with native hormone and the potent agonist 2MD exhibited chemical shift differences in signals from helix-12, which is part of the AF2 transactivation domain that appears to play a role in the selective recruitment of coactivators. By contrast, formation of the complex of rVDR-LBD with the antagonist OU-72 led to disappearance of signals from residues in helices-11 and -12. We present evidence that disorder in this region of the receptor in the antagonist complex prevents the attachment of coactivators.

The antidepressant fluoxetine normalizes the nuclear glucocorticoid receptor evoked by psychosocial stress

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has been implicated in the pathophysiology of depression and stress disorders. Glucocorticoids, key regulators of the stress response, exert diverse effects on cellular processes in the hippocampus. Beside non-genomic pathways, glucocorticoid effects are mediated through activation of the glucocorticoid receptor (GR), a ligand activated transcriptional factor that belongs to the nuclear hormone receptor superfamily. We analysed the GR protein levels both in the cytoplasmic and nuclear compartments of the hippocampus of Wistar rats exposed to chronic psychosocial isolation stress upon chronic fluoxetine (FLU) treatment. Under chronic stress, corticosterone levels (CORT) were decreased compared to the control, and treatment with FLU did not change its level in the stressed rats. At the molecular level, FLU normalized the level of nuclear GR protein in the hippocampus of the stressed rats. Discrepancy between normalization of nuclear GR in the hippocampus and lack of normalization of HPA axis activity judged by CORT, suggests that other brain structures such as the amygdale and prefrontal cortex that also regulate HPA axis activity, seem not to be normalized by the FLU treatment used in our study.

Farnesoic acid and methyl farnesoate production during lobster reproduction: Possible functional correlation with retinoid X receptor expression

Farnesoic acid (FA) and methyl farnesoate (MF) are juvenile hormone-related compounds secreted by the mandibular organ (MO) of crustaceans and play an important role in stimulation of ovarian maturation. To better understand how the MO activity influences female reproduction by secretion of FA and MF, the biosynthesis and release of these two compounds were measured in vitro by the incorporation of l-[ 3H-methyl]methionine into MF and [2- 14C]acetate into FA by the MO of Homarus americanus. The production of FA is 7.5 times that of MF, and most FA and MF synthesized remained within the gland, and was not released into the surrounding medium. Most FA and MF were synthesized in the anterior fan-fold region of the MO. The rates of biosynthesis of FA and MF were stage-related, with maximal production occurring during secondary vitellogenesis (i.e. stages 4 and 5). A potential juvenoid receptor, retinoid X receptor (RXR), HaRXR, was characterized using PCR cloning techniques. HaRXR belongs to the nuclear hormone receptor superfamily and its deduced amino acid sequence shares a high homology to other RXRs of crustaceans, insects, and vertebrates. Transcripts of HaRXR can be detected in many tissues, and significant high expression level was detected in the MO, especially in the anterior fan-fold region. Expression of HaRXR was also related to reproductive stage, and maximal level of expression was observed at stage 4, in which secondary vitellogenesis is occurring. Changes in transcript level of HaRXR and the rates of FA/MF biosynthesis in the female reproductive cycle indicate that HaRXR and FA/MF may play important roles in crustacean reproduction.

Osteoblast-Specific Transcription Factor Osterix Increases Vitamin D Receptor Gene Expression in Osteoblasts

Osterix (Osx) is an osteoblast-specific transcription factor required for osteoblast differentiation from mesenchymal stem cells. In Osx knock-out mice, no bone formation occurs. The vitamin D receptor (VDR) is a member of the nuclear hormone receptor superfamily that regulates target gene transcription to ensure appropriate control of calcium homeostasis and bone development. Here, we provide several lines of evidence that show that the VDR gene is a target for transcriptional regulation by Osx in osteoblasts. For example, calvaria obtained from Osx-null embryos displayed dramatic reductions in VDR expression compared to wild-type calvaria. Stable overexpression of Osx stimulated VDR expression in C2C12 mesenchymal cells. Inhibition of Osx expression by siRNA led to downregulation of VDR. In contrast, Osx levels remained unchanged in osteoblasts in VDR-null mice. Mechanistic approaches using transient transfection assays showed that Osx directly activated a 1 kb fragment of the VDR promoter in a dose-dependent manner. To define the region of the VDR promoter that was responsive to Osx, a series of VDR promoter deletion mutants were examined and the minimal Osx-responsive region was refined to the proximal 120 bp of the VDR promoter. Additional point mutants were used to identify two GC-rich regions that were responsible for VDR promoter activation by Osx. Chromatin immunoprecipitation assays demonstrated that endogenous Osx was associated with the native VDR promoter in primary osteoblasts in vivo. Cumulatively, these data strongly support a direct regulatory role for Osx in VDR gene expression. They further provide new insight into potential mechanisms and pathways that Osx controls in osteoblasts and during the process of osteoblastic cell differentiation.

Role of PPARg2 transcription factor in thiazolidinedione-induced insulin sensitization

Adipose tissue is the key regulator of energy balance, playing an active role in lipid storage and metabolism and may be a dynamic buffer to control fatty acid flux. Peroxisome proliferator-activated receptor gamma isoform-2 (PPARg2), an isoform of the nuclear hormone receptor superfamily, has been implicated in almost all aspects of human metabolic alterations such as obesity, insulin resistance, type-2 diabetes and dyslipidaemia. The PPARg2 isoform is highly present in adipose tissue where it functions as a thrifty phenotype, which promotes adipocyte differentiation and triglyceride storage. Thiazolidinediones, antidiabetic drugs, induce insulin sensitivity by controlling adipokines. The thiazolidinediones bind with PPARg2 in adipocytes and exert an agonist effect by enhancing adipogenesis and fatty acid uptake. Thiazolidinediones stimulate PPARg2, by which they down-regulate tumour necrosis factor-α, leptin, interleukin-6 and plasminogen and also enhance insulin sensitivity. The aim of this work is to define role of PPARg2 transcription factor in thiazolidinedione-induced insulin sensitization. The PPARg2 alters the transcription of the target gene. This altered gene transcription results in the up-regulation of insulin-sensitizing factors and down-regulation of insulin-resistant factors. The variant Pro12Ala of the PPARg2 gene is an important modulator in metabolic control in the body. Thiazolidinediones stimulate PPARg2 transcription factor by which PPARg2 binds to responsive elements located in the promoter regions of many genes and modulates their transcriptive activity. There is a strong mutual relationship between receptor binding and agonism, which is evidence of the insulin-sensitizing target of thiazolidinediones in PPARg2. This evidently increases the biological potency of the glucose-lowering effect of thiazolidinediones in vivo as well as their antidiabetic activity. PPARg2 transcription factor plays an important role in treatment of type-2 diabetes with thiazolidindiones. The variant Pro12Ala of the PPARg2 gene promotes the activity of thiazolidinediones in minimizing insulin resistance. Transcriptional activity of Pro12Ala variant improves the activity of insulin. Thus thiazolidinediones promote the phosphorylation of PPARg2 to induce insulin sensitivity.

Transcriptional Regulation of S Phase Kinase-associated Protein 2 by NR4A Orphan Nuclear Receptor NOR1 in Vascular Smooth Muscle Cells

Members of the NR4A subgroup of the nuclear hormone receptor superfamily have emerged as key transcriptional regulators of proliferation and inflammation. NOR1 constitutes a ligand-independent transcription factor of this subgroup and induces cell proliferation; however, the transcriptional mechanisms underlying this mitogenic role remain to be defined. Here, we demonstrate that the F-box protein SKP2 (S phase kinase-associated protein 2), the substrate-specific receptor of the ubiquitin ligase responsible for the degradation of p27(KIP1) through the proteasome pathway, constitutes a direct transcriptional target for NOR1. Mitogen-induced Skp2 expression is silenced in vascular smooth muscle cells (VSMC) isolated from Nor1-deficient mice or transfected with Nor1 siRNA. Conversely, adenovirus-mediated overexpression of NOR1 induces Skp2 expression in VSMC and decreases protein abundance of its target p27. Transient transfection experiments establish that NOR1 transactivates the Skp2 promoter through a nerve growth factor-induced clone B response element (NBRE). Electrophoretic mobility shift and chromatin immunoprecipitation assays further revealed that NOR1 is recruited to this NBRE site in the Skp2 promoter in response to mitogenic stimulation. In vivo Skp2 expression is increased during the proliferative response underlying neointima formation, and this transcriptional induction depends on the expression of NOR1. Finally, we demonstrate that overexpression of Skp2 rescues the proliferative arrest of Nor1-deficient VSMC. Collectively, these results characterize Skp2 as a novel NOR1-regulated target gene and detail a previously unrecognized transcriptional cascade regulating mitogen-induced VSMC proliferation.

Ecdysone- and NO-Mediated Gene Regulation by Competing EcR/Usp and E75A Nuclear Receptors during Drosophila Development

The Drosophila ecdysone receptor (EcR/Usp) is thought to activate or repress gene transcription depending on the presence or absence, respectively, of the hormone ecdysone. Unexpectedly, we found an alternative mechanism at work in salivary glands during the ecdysone-dependent transition from larvae to pupae. In the absense of ecdysone, both ecdysone receptor subunits localize to the cytoplasm, and the heme-binding nuclear receptor E75A replaces EcR/Usp at common target sequences in several genes. During the larval-pupal transition, a switch from gene activation by EcR/Usp to gene repression by E75A is triggered by a decrease in ecdysone concentration and by direct repression of the EcR gene by E75A. Additional control is provided by developmentally timed modulation of E75A activity by NO, which inhibits recruitment of the corepressor SMRTER. These results suggest a mechanism for sequential modulation of gene expression during development by competing nuclear receptors and their effector molecules, ecdysone and NO.

Efficacy of Combined Peroxisome Proliferator-Activated Receptor-α Ligand and Glucocorticoid Therapy in a Murine Model of Atopic Dermatitis

Although topical glucocorticoids (GCs) display potent anti-inflammatory activity in inflamed skin, they also can exert numerous harmful effects on epidermal structure and function. In contrast, topical applications of ligands of peroxisome proliferator-activated receptor-α (PPARα) not only reduce inflammation, and also improve cutaneous barrier homeostasis. Therefore, we examined whether sequential topical GCs followed by topical Wy14643 (a ligand of PPARα) might be more effective than either alone for atopic dermatitis (AD) in a hapten (oxazolone)-induced, murine model with multiple features of AD (Ox-AD). Despite expected anti-inflammatory benefits, topical GC alone induced: i) epidermal thinning; ii) reduced expression of involucrin, loricrin and filaggrin; and iii) allowed outside-to-inside penetration of an epicutaneous tracer. While Wy14643 alone yielded significant therapeutic benefits in mice with mild or moderate Ox-AD, it was less effective in severe Ox-AD. Yet, topical applications of Wy14643 after GC was not only significantly effective comparable to GC alone, but it also prevented GC-induced structural and functional abnormalities in permeability barrier homeostasis. Moreover, rebound flares were largely absent after sequential treatment with GC and Wy14643. Together, these results show that GC and PPARα ligand therapy together is not only effective but also prevents development of GC-induced side effects, including rebound flares, in murine AD.

Peroxisome Proliferator Receptor (PPAR) β/δ in psoriatic patients before and after two conventional therapeutic modalities: methotrexate and PUVA

Peroxisome proliferator-activated receptor β/δ is a member of the nuclear hormone receptor superfamily suggested to contribute to psoriasis pathogenesis. Methotrexate and PUVA mainly target the T cell-mediated immunopathology of psoriasis. Our work aimed at estimating PPARβ/δ in psoriatic patients and investigating whether the standard therapeutic modalities (methotrexate and PUVA) exert their anti-psoriatic activity partially through altering PPARβ/δ levels. RT-PCR was used to measure PPAR β/δ mRNA levels in twenty four chronic plaque psoriasis patients. Patients were divided into two groups (12 patients each); group A received intramuscular methotrexate and group B was treated by PUVA 3 times/week in a PUVA 1000 cabin for ten weeks each, followed by measurement of PPAR β/δ mRNA levels. Twelve healthy volunteers served as controls. PPAR β/δ mRNA levels were significantly elevated in all patients and significantly decreased ten weeks after treatment, however, post treatment levels were still significantly elevated in comparison with those of controls. PPAR β/δ mRNA levels showed a significant positive correlation with disease duration.