Nuclear peroxisome proliferator activators

Thiazolidinediones are the newer agents that favourably influence insulin sensitivity and possibly also pancreatic fS-cell function. The biological response of thiazolidinediones is mediated by binding to the nuclear peroxisome proliferator-activated receptor-y (PPAR)... 

Some effects of prostaglandins are mediated through cell surface G-protein coupled receptors (see Chapter ll).306 Some other prostanoids bind to and activate nuclear peroxisome proliferator-activated receptors.306 PGJ2 may inhibit fatty acid synthesis and fat deposition in adipose tissue through these receptors. Some of the prostanoid derivatives enter membranes and may become incorporated into phospholipids and exert their effects there. 

Fig. 2. Summary of the mode of action of peroxisome proliferators (PP) through the nuclear peroxisome proliferator-activated receptor (PPAR). The activation of PPAR requires the retinoic X receptor (RXR). The receptors are found in the cytoplasm and once the ligands bind (1) they undergo a conformational change (2) that allows the complex to enter the nucleus (3). The complex then binds to the peroxisome proliferator response element (PPRE) in the promoter region of target genes to alter transcription (4). Modified from Gervois et alP...

Bind to nuclear peroxisome proliferator-activating receptors (PPARs) involved in transcription of insulin-responsive genes —> sensitization of tissues to insulin, plus 4- hepatic gluconeogenesis and triglycerides and t insulin receptor numbers (Figure VII-2-2). 

Wang D, Wang H, Shi Q, Katkuri S, Walhi W, Desvergne B, Das SK, Dey SK, DuBois RN. Prostaglandin E(2) promotes colorectal adenoma growth via transactivation of the nuclear peroxisome proliferator-activated receptor delta. Cancer Cell. 6 (2004) 285-295. 

Fig. 5.3. Schematic model of the mechanism of formation and action of J-series prostaglandins (PGJ) in the activation of nuclear peroxisome proliferator-activated receptor-y (PPARy).

The thiazolidinediones have also been reported to act as inhibitors of the respiratory chain at high concentrations, and this appears to account for their ability to activate AMGPK in cultured cells. However, the primary target of the thiazolidinediones appears to be the peroxisome proliferator-activated receptor-y ( PPAR-y), a member of the nuclear receptor superfamily expressed in adipocytes. One of the major effects of stimulation of PPAR-y in adipocytes is the release ofthe... 

Finally, it has to be mentioned that LPA also has an intracellular target site, which is the nuclear transcription factor, peroxisome proliferator-activated receptor-y (PPARy). LPA competes for thiazolidinedione binding and activates PPARy-dependent gene transcription. Thereby, LPA induced neointima formation in a rat carotid artery model. 

Peroxisome Proliferator-Activated Receptors (PPARs) P450 Mono-oxygenase System Nuclear Receptors Orphan Receptors... 

Peroxisome Proliferator-Activated Receptors. Figure 1 Common structural and functional features of nuclear receptor transcription factors. Consistent with other members of the nuclear receptor superfamily, the PPARs have a modular domain structure consisting of domains A/B, C, D, and E. Each domain is associated with specific functions. 

The retinoid X receptor (RXR) is a nuclear receptor that binds and is activated by certain endogenous retinoids, such as 9-cis-retinoic acid. RXR is the obligatory heterodimerization partner for a large number of nonclassic steroid nuclear receptors, such as thyroid hoimone receptor, vitamin D3 receptor, peroxisome proliferator-activated receptor and pregnane X receptor. 

Fibrates work by reducing apolipoproteins B, C-III (an inhibitor of LPL), and E, and increasing apolipoproteins A-I and A-II through activation of peroxisome proliferator-activated receptors-alpha (PPAR-a), a nuclear receptor involved in cellular function. The changes in these apolipoproteins result in a reduction in triglyceride-rich lipoproteins (VLDL and IDL) and an increase in HDL. 

NSAID use is also implicated in disease flares in patients with UC. NSAIDs may affect production of both nuclear factor kP and peroxisome proliferator activated receptors (e.g., PPAR-y), both of which are involved in regulating the intestinal responses.11... 

TF transcription factor, R receptor, Fur ferric uptake regulation protein, NF-kB nuclear factor-kB, AP-1 activator protein-1, Egr-1 early growth response-1, VDR la,25-dihydroxy-vitamin D3 receptor, RXR retinoid X receptor, PPARy peroxisome proliferator-activated receptor y NFAT nuclear factor of activated T-cells, HSF heat shock factor, p53 tumor suppressor p53, HIF-1 hypoxia inducible factor-1. ... 

In addition to PXR, the expression of UGT1A1 and several other UGT isoforms have also been reported to be regulated by several other nuclear receptors, including constitutive androstane receptor (CAR) [25,27,28] and peroxisome proliferator activated receptor a (PPARa) [29,30],... 

Desvergne, B., and Wahli, W. (1999). Peroxisome proliferator-activated receptors Nuclear control of metabolism. Endocrine Rev. 20, 649-688. 

ASBT has a complex regulatory system reflecting the importance of this transporter to bile-acid pool size and bile-acid synthesis rates. Hepatic nuclear factor la (HNF-la) is necessary for expression of ASBT as knockout mice showed no expression and had defective bile-acid transport.Conversely, FXR-null mice showed no difference in expression of ASBT, showing that FXR plays no part in regulation of ASBT. In man, HNF-la controls baseline promoter activity of the ASBT gene as the minimal construct with full promoter activity was found to have 3 HNF-la binding sites. These authors also showed that the promoter construct bound peroxisome proliferator activated receptor a (PPARa)/9 cis retinoic acid receptor heterodimer, demonstrating a link between bile-acid absorption and hepatic lipid metabolism mediated by PPARa. 

The farnesoid X receptor is a member of the class of nuclear hormone receptors, which have key roles in development and homeostasis, as well as in many diseases like obesity, diabetes and cancer. The farnesoid X receptor shows structural similarity to the estrogen receptor (ER ), which mediates a broad spectrum of physiological functions such as regulation of reproduction, modulation of bone density, cholesterol transport and breast cancer. The farnesoid X receptor also shows similarity with the peroxisome proliferation-activated receptor y (PPARy), which is involved in fat metabolism, inflammatory and immune responses. The estrogen receptor (ER ), the peroxisome proliferation-activated receptor y (PPARy) and the farnesoid X receptor (FXR) can be clustered in a... 

Sundvold H, Lien S 2001 Identification of a novel peroxisome proliferator-activated receptor (PPAR) gamma promoter in man and transactivation by the nuclear receptor RORalphal. Biochem Biophys Res Commun 287 383-390... 

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