A corepressor and chicken ovalbumin upstream promoter transcriptional factor proteins modulate peroxisome proliferator-activated receptor-gamma2/retinoid X receptor alpha-activated transcription from the murine lipoprotein lipase promoter

Chromogranin A and its derived peptides: potential regulators of cholesterol homeostasis

Chromogranin A (CHGA), a member of the granin family of proteins, has been an attractive therapeutic target and candidate biomarker for several cardiovascular, neurological, and inflammatory disorders. The prominence of CHGA stems from the pleiotropic roles of several bioactive peptides (e.g., catestatin, pancreastatin, vasostatins) generated by its proteolytic cleavage and by their wide anatomical distribution. These peptides are emerging as novel modulators of cardiometabolic diseases that are often linked to high blood cholesterol levels. However, their impact on cholesterol homeostasis is poorly understood. The dynamic nature of cholesterol and its multitudinous roles in almost every aspect of normal body function makes it an integral component of metabolic physiology. A tightly regulated coordination of cholesterol homeostasis is imperative for proper functioning of cellular and metabolic processes. The deregulation of cholesterol levels can result in several pathophysiological states. Although studies till date suggest regulatory roles for CHGA and its derived peptides on cholesterol levels, the mechanisms by which this is achieved still remain unclear. This review aims to aggregate and consolidate the available evidence linking CHGA with cholesterol homeostasis in health and disease. In addition, we also look at common molecular regulatory factors (viz., transcription factors and microRNAs) which could govern the expression of CHGA and genes involved in cholesterol homeostasis under basal and pathological conditions. In order to gain further insights into the pathways mediating cholesterol regulation by CHGA/its derived peptides, a few prospective signaling pathways are explored, which could act as primers for future studies.

Multiple roles of COUP-TFII in cancer initiation and progression

Chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an orphan nuclear receptor that acts as a transcriptional activator or repressor in a cell type-dependent manner. Best characterized for its role in the regulation of angiogenesis during mouse development, COUP-TFII also plays important roles in glucose metabolism and cancer. Expression of COUP-TFII is altered in various endocrine conditions. Cell type-specific functions and the regulation of COUP-TFII expression result in its varying physiological and pathological actions in diverse systems. Evidence will be reviewed for oncogenic and tumor-suppressive functions of COUP-TFII, with roles in angiogenesis, metastasis, steroidogenesis, and endocrine sensitivity of breast cancer described. The applicability of current data to our understanding of the role of COUP-TFII in cancer will be discussed.

Chicken adipocyte fatty acid-binding protein knockdown affects expression of peroxisome proliferator-activated receptor γ gene during oleate-induced adipocyte differentiation

Adipocyte fatty acid-binding protein (A-FABP) is expressed in both adipose cells and macrophages. As one of the downstream genes of peroxisome proliferator-activated receptor γ (PPAR-γ), A-FABP plays an important role in the lipid metabolism of adipocytes in mammal and poultry. However, studies in A-FABP null macrophages of mice showed that A-FABP was a critical regulator of PPAR-γ and could affect the expression of PPAR-γ. The current study was designed to investigate whether the same mechanism as that in macrophages exists in chicken adipocytes. After transfection with interference and overexpression plasmids of A-FABP in chicken adipocytes for 24 h, oleate was added to the medium. Then, lipid accumulation, nonesterified fatty acids (NEFA) in the medium, and expression of lipid metabolism-related genes were detected. The results showed that in the A-FABP knockdown adipocytes, lipid accumulation was decreased at 6 h and NEFA in the medium was higher at 1 and 6 h compared with that in the control group. Moreover, gene expression levels of lipoprotein lipase, perilipin, and PPAR-γ were higher than that of the control group (P < 0.05). In the A-FABP overexpression adipocytes, lipid accumulation and expression of lipid metabolism related genes were similar to that of the control group. However, NEFA in the medium was significantly lower in the A-FABP overexpression group 1 h after adding oleate (P < 0.05). The present study suggested that the A-FABP knockdown might lead to decreased lipid accumulation and upregulated expression of PPAR-γ in chicken adipocytes.

Vitamin B6 regulates mRNA expression of peroxisome proliferator-activated receptor-γ target genes

We previously demonstrated that vitamin B6 suppresses tumorigenesis in the colon of mice and exerts an anti-inflammatory effect through the inhibition of NF-κB activation. As these effects resemble the pharmacological properties of thiazolidinedione (TZD), a synthetic peroxisome proliferator-activated receptor-γ (PPARγ) ligand, this study was designed to examine the effect of vitamin B6 on the activation of PPARγ and adipogenesis in 3T3-L1 adipocyte cells. Pyridoxal 5'-phosphate (PLP), one of the vitamin B6 derivatives, was shown to promote adipogenesis in the 3T3-L1 adipocytes. In addition, PLP specifically induced mRNA expression of PPARγ target genes in the 3T3-L1 adipocytes and enhanced the lipid accumulation and adipocyte fatty acid-binding protein (aP2) mRNA expression in NIH3T3 cells stably expressing PPARγ. Furthermore, the administration of vitamin B6 increased the expression of aP2 mRNA in mouse adipose tissues. Collectively, these observations suggest a novel function of vitamin B6 as an activator for PPARγ, which may contribute to the anti-tumor and anti-inflammatory effects of vitamin B6.

Agonism of Peroxisome Proliferator Receptor-Gamma may have Therapeutic Potential for Neuroinflammation and Parkinson's Disease

Evidence suggests inflammation, mitochondria dysfunction, and oxidative stress play major roles in Parkinson's disease (PD), where the primary pathology is the significant loss of dopaminergic neurons in the substantia nigra (SN). Current methods used to treat PD focus mainly on replacing dopamine in the nigrostriatal system. However, with time these methods fail and worsen the symptoms of the disease. This implies there is more to the treatment of PD than just restoring dopamine or the dopaminergic neurons, and that a broader spectrum of factors must be changed in order to restore environmental homeostasis. Pharmacological agents that can protect against progressive neuronal degeneration, increase the level of dopamine in the nigrostriatal system, or restore the dopaminergic system offer various avenues for the treatment of PD. Drugs that reduce inflammation, restore mitochondrial function, or scavenge free radicals have also been shown to offer neuroprotection in various animal models of PD. The activation of peroxisome proliferator receptor- gamma (PPAR-gamma ) has been associated with altering insulin sensitivity, increasing dopamine, inhibiting inflammation, altering mitochondrial bioenergetics, and reducing oxidative stress - a variety of factors that are altered in PD. Therefore, PPAR-gamma activation may offer a new clinically relevant treatment approach to neuroinflammation and PD related neurodegeneration. This review will summarize the current understanding of the role of PPAR-gamma agonists in neuroinflammation and discuss their potential for the treatment of PD.

Lipoprotein lipase: from gene to obesity

Lipoprotein lipase (LPL) is a multifunctional enzyme produced by many tissues, including adipose tissue, cardiac and skeletal muscle, islets, and macrophages. LPL is the rate-limiting enzyme for the hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins, chylomicrons, and very low-density lipoproteins (VLDL). LPL-catalyzed reaction products, fatty acids, and monoacylglycerol are in part taken up by the tissues locally and processed differentially; e.g., they are stored as neutral lipids in adipose tissue, oxidized, or stored in skeletal and cardiac muscle or as cholesteryl ester and TG in macrophages. LPL is regulated at transcriptional, posttranscriptional, and posttranslational levels in a tissue-specific manner. Nutrient states and hormonal levels all have divergent effects on the regulation of LPL, and a variety of proteins that interact with LPL to regulate its tissue-specific activity have also been identified. To examine this divergent regulation further, transgenic and knockout murine models of tissue-specific LPL expression have been developed. Mice with overexpression of LPL in skeletal muscle accumulate TG in muscle, develop insulin resistance, are protected from excessive weight gain, and increase their metabolic rate in the cold. Mice with LPL deletion in skeletal muscle have reduced TG accumulation and increased insulin action on glucose transport in muscle. Ultimately, this leads to increased lipid partitioning to other tissues, insulin resistance, and obesity. Mice with LPL deletion in the heart develop hypertriglyceridemia and cardiac dysfunction. The fact that the heart depends increasingly on glucose implies that free fatty acids are not a sufficient fuel for optimal cardiac function. Overall, LPL is a fascinating enzyme that contributes in a pronounced way to normal lipoprotein metabolism, tissue-specific substrate delivery and utilization, and the many aspects of obesity and other metabolic disorders that relate to energy balance, insulin action, and body weight regulation.

Dysregulation of mitochondrial dynamics and the muscle transcriptome in ICU patients suffering from sepsis induced multiple organ failure

Background

Septic patients treated in the intensive care unit (ICU) often develop multiple organ failure including persistent skeletal muscle dysfunction which results in the patient's protracted recovery process. We have demonstrated that muscle mitochondrial enzyme activities are impaired in septic ICU patients impairing cellular energy balance, which will interfere with muscle function and metabolism. Here we use detailed phenotyping and genomics to elucidate mechanisms leading to these impairments and the molecular consequences.

Methodology/Principal Findings

Utilising biopsy material from seventeen patients and ten age-matched controls we demonstrate that neither mitochondrial in vivo protein synthesis nor expression of mitochondrial genes are compromised. Indeed, there was partial activation of the mitochondrial biogenesis pathway involving NRF2α/GABP and its target genes TFAM, TFB1M and TFB2M yet clearly this failed to maintain mitochondrial function. We therefore utilised transcript profiling and pathway analysis of ICU patient skeletal muscle to generate insight into the molecular defects driving loss of muscle function and metabolic homeostasis. Gene ontology analysis of Affymetrix analysis demonstrated substantial loss of muscle specific genes, a global oxidative stress response related to most probably cytokine signalling, altered insulin related signalling and a substantial overlap between patients and muscle wasting/inflammatory animal models. MicroRNA 21 processing appeared defective suggesting that post-transcriptional protein synthesis regulation is altered by disruption of tissue microRNA expression. Finally, we were able to demonstrate that the phenotype of skeletal muscle in ICU patients is not merely one of inactivity, it appears to be an actively remodelling tissue, influenced by several mediators, all of which may be open to manipulation with the aim to improve clinical outcome.

Conclusions/Significance

This first combined protein and transcriptome based analysis of human skeletal muscle obtained from septic patients demonstrated that losses of mitochondria and muscle mass are accompanied by sustained protein synthesis (anabolic process) while dysregulation of transcription programmes appears to fail to compensate for increased damage and proteolysis. Our analysis identified both validated and novel clinically tractable targets to manipulate these failing processes and pursuit of these could lead to new potential treatments.

Chicken ovalbumin upstream promoter transcription factor II regulates uncoupling protein 3 gene transcription in Phodopus sungorus

BACKGROUND

Ucp3 is an integral protein of the inner mitochondrial membrane with a role in lipid metabolism preventing deleterious effects of fatty acids in states of high lipid oxidation. Ucp3 is expressed in brown adipose tissue and skeletal muscle and controlled by a transcription factor complex including PPARalpha, MyoD and the histone acetyltransferase p300. Several studies have demonstrated interaction of these factors with chicken ovalbumin upstream promoter transcription factor II (Coup-TFII). This nuclear receptor is involved in organogenesis and other developmental processes including skeletal muscle development, but also co-regulates a number of metabolic genes. In this study we in silico analyzed the upstream region of Ucp3 of the Djungarian hamster Phodopus sungorus and identified several putative response elements for Coup-TFII. We therefore investigated whether Coup-TFII is a further player in the transcriptional control of the Ucp3 gene in rodents.

RESULTS

By quantitative PCR we demonstrated a positive correlation of Coup-TFII and Ucp3 mRNA expression in skeletal muscle and brown adipose tissue in response to food deprivation and cold exposure, respectively. In reporter gene assays Coup-TFII enhanced transactivation of the Ucp3 promoter conveyed by MyoD, PPARalpha, RXRalpha and/or p300. Using deletions and mutated constructs, we identified a Coup-TFII enhancer element 816-840 bp upstream of the transcriptional start site. Binding of Coup-TFII to this upstream enhancer was confirmed in electrophoretic mobility shift and supershift assays.

CONCLUSION

Transcriptional regulation of the Coup-TFII gene in response to starvation and cold exposure seems to be the regulatory mechanism of Ucp3 mRNA expression in brown adipose and skeletal muscle tissue determining the final appropriate rate of transcript synthesis. These findings add a crucial component to the complex transcriptional machinery controlling expression of Ucp3. Given the substantial evidence for a function of Ucp3 in lipid metabolism, Coup-TFII may not only be a negative regulator of glucose responsive genes but also transactivate genes involved in lipid metabolism.

Opposite Smad and chicken ovalbumin upstream promoter transcription factor inputs in the regulation of the collagen VII gene promoter by transforming growth factor-beta

A critical component of the epidermal basement membrane, collagen type VII, is produced by keratinocytes and fibroblasts, and its production is stimulated by the cytokine transforming growth factor-beta (TGF-beta). The gene, COL7A1, is activated by TGF-beta via Smad transcription factors in cooperation with AP1. Here we report a previously unsuspected level of complexity in this regulatory process. We provide evidence that TGF-beta may activate the COL7A1 promoter by two distinct inputs operating through a common region of the promoter. One input is provided by TGF-beta-induced Smad complexes via two Smad binding elements that function redundantly depending on the cell type. The second input is provided by relieving the COL7A1 promoter from chicken ovalbumin upstream promoter transcription factor (COUP-TF)-mediated transcriptional repression. We identified COUP-TFI and -TFII as factors that bind to the TGF-beta-responsive region of the COL7A1 promoter in an expression library screening. COUP-TFs bind to a site between the two Smad binding elements independently of Smad or AP1 and repress the basal and TGF-beta-stimulated activities of this promoter. We provide evidence that endogenous COUP-TF activity represses the COL7A1 promoter. Furthermore, we show that TGF-beta addition causes a rapid and profound down-regulation of COUP-TF expression in keratinocytes and fibroblasts. The results suggest that TGF-beta signaling may exert tight control over COL7A1 by offsetting the balance between opposing Smad and COUP-TFs.

Peroxisome proliferator-activated receptors (PPARS): regulators of gene expression in heart and skeletal muscle

The peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. The three isoforms (PPARalpha, beta/delta and gamma) have been implicated in the regulation of the expression of genes involved in lipid metabolism. Although their prominent role in lipid homeostasis is well established, the way in which the activity of each of the PPAR isoforms is regulated under physiological and pathological conditions is still subject of intensive research. In skeletal as well as cardiac muscle cells it has been demonstrated that the expression of a large panel of proteins involved in the transport and metabolic conversion of fatty acids is under control of PPARs. The pivotal role of the PPARalpha isoform in cardiac fatty acid metabolism has been confirmed in PPARalpha-null mice. The exact role of PPARbeta/delta in the regulation of muscle metabolism is still a matter of debate. Whereas several studies provided evidence to support the notion that PPARalpha and PPARbeta/delta have redundant roles, other studies suggest that PPARalpha activity is counteracted by PPARbeta/delta. Marked effects of bona fide PPARgamma ligands (the anti-diabetic thiazolidinediones) on skeletal and cardiac muscle function and phenotype, have also been reported. However, next to activating PPARgamma, the thiazolidinediones do affect other cellular processes as well. To date it is being realized that the control of the trans-activating capacity of each of the PPAR isoforms is multi-factorial and, in addition to ligand availability, depends on such factors as isoform-specific phosphorylation and selective interaction with various proteins acting either as co-activator or co-repressor.

Regulation of retinoic acid-induced inhibition of AP-1 activity by orphan receptor chicken ovalbumin upstream promoter-transcription factor

Retinoids are therapeutically effective in the treatment of various cancers, and some of the therapeutic action of retinoids can be ascribed to their potent inhibition of AP-1 activity that regulates transcription of genes associated with cell growth. We recently reported that the expression of orphan receptor chicken ovalbumin upstream promoter-transcription factor (COUP-TF) plays a role in mediating the growth inhibitory effect of trans-retinoic acid (trans-RA) in cancer cells. To gain insight into the molecular mechanism by which COUP-TF regulates trans-RA activity, we evaluated the effect of COUP-TF on antagonism of AP-1 activity by trans-RA. Our results demonstrated a positive correlation between COUP-TF expression and the ability of trans-RA to inhibit AP-1 activity in various cancer cell lines. In transient transfection assay, expression of COUP-TF strongly inhibited tumor promoter 12-O-tetradecanoylphorbol-13-acetate-induced AP-1 transactivation activity and transactivation of c-Jun/c-Fos in both a trans-RA-dependent and -independent manner. In vitro studies demonstrated that the addition of COUP-TF inhibited c-Jun DNA binding through a direct protein-protein interaction that is mediated by the DNA binding domain of COUP-TF and the leucine zipper of c-Jun. Stable expression of COUP-TF in COUP-TF-negative MDA-MB231 breast cancer cells restored the ability of trans-RA to inhibit 12-O-tetradecanoylphorbol-13-acetate-induced c-Jun expression. The effect of COUP-TF in enhancing the trans-RA-induced antagonism of AP-1 activity required expression of retinoic acid receptors (RARs), since stable expression of COUP-TF in COUP-TF-negative HT-1376 bladder cancer cells, which do not express RARalpha and RARbeta, failed to restore trans-RA-induced AP-1 repression. Thus, COUP-TF, through its physical interaction with AP-1, promotes anticancer effects of retinoids by potentiating their anti-AP-1 activity.

Peroxisome proliferator-activated receptor gamma and chicken ovalbumin upstream promoter transcription factor II negatively regulate the phosphoenolpyruvate carboxykinase promoter via a common element

A heterodimer of peroxisome proliferator-activated receptor gamma (PPARgamma) and retinoid X receptor (RXR) is required for adipocyte differentiation. The gene encoding cytosolic phosphoenolpyruvate carboxykinase (PEPCK) is a PPARgamma/RXR target gene in adipose tissue. Of the two PPARgamma response elements, gAF1/PCK1 and PCK2, only PCK2 is required for PEPCK expression and responsiveness to the PPARgamma agonist, rosiglitazone, in adipose tissue even though both elements bind PPARgamma/RXR in vitro. In contrast, gAF1/PCK1 is essential for glucocorticoid inhibition of PPARgamma-induced PEPCK gene expression in adipocytes. We report that chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is the predominant nuclear receptor bound to gAF1/PCK1 in preadipocytes. COUP-TFII declines during adipogenesis in reciprocal fashion to PPARgamma. In transiently transfected fibroblasts COUP-TFII acts at gAF1/PCK1 to inhibit PPARgamma/RXR activation via PCK2. In contrast COUP-TFs are transcriptional activators of PEPCK in hepatocytes. PPARgamma/RXR occupies gAF1/PCK1 in adipocytes, and mutation of gAF1/PCK1 enhances PEPCK promoter transactivation by PPARgamma/RXR in fibroblasts, suggesting that this element is also a negative PPARgamma response element. These results indicate that gAF1/PCK1 is a pleiotropic element through which COUP-TFII inhibits premature PEPCK expression, and perhaps adipogenesis in general, and PPARgamma/RXR uses this same element in adipocytes to participate in PEPCK modulation by glucocorticoids.