Role of Peroxisome Proliferator-Activated Receptor-γ Coactivator-1α in the Transcriptional Regulation of the Human Uncoupling Protein 2 Gene in INS-1E Cells

Department of Laboratory Medicine, Landeskliniken and Paracelsus Private Medical University Salzburg, Austria.
Endocrinology (Impact Factor: 4.5). 03/2006; 147(2):966-76. DOI: 10.1210/en.2005-0817
Source: PubMed


A role of uncoupling protein 2 (UCP2) as negative modulator of insulin secretion has been suggested, but the transcriptional pathways regulating beta-cell UCP2 gene expression have been established in rodents only. We show here that the underlying sequence motifs are not conserved in the human gene and provide evidence for regulatory mechanisms involving the transcriptional cofactor peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1alpha). PGC-1alpha potentiates thyroid hormone (T(3))-mediated transcriptional activation of the human UCP2 gene in INS-1E cells. Two thyroid hormone response elements (TREs) located at -322/-317 (TRE1) and -170/-165 (TRE2) were identified, and mutation of either TRE1 or TRE2 abrogated the stimulatory effect of T(3) treatment. Furthermore, two E-box motifs at -911/-906 (E1) and -743/-738 (E2) are involved in the regulation of UCP2 gene expression by sterol regulatory element binding protein isoforms (SREBP)-1a, -1c, and -2. Mutational analysis revealed that the presence of either E1 or E2 is sufficient to mediate activation of UCP2 gene transcription by nuclear active SREBPs. PGC-1alpha coactivates liver X receptor-mediated expression of SREBP-1c as well as dexamethasone-stimulated SREBP-2 expression in INS-1E cells. These transcriptional responses are antagonized by orphan nuclear receptor short heterodimer partner overexpression, which might explain its positive effects on glucose-stimulated insulin secretion in beta-cells overexpressing UCP2. We also provide evidence that despite a lack of sequence homology within the regulatory region, the principal mechanisms regulating UCP2 gene expression are similar in rats and humans, being consistent with a role for UCP2 as a modulator of insulin secretion in humans.

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    • "PGC-1α overexpression in cultured islets or β-cell lines suppressed glucose-stimulated membrane depolarization, induced glucose-6-phosphatase, and thereby reduced insulin secretion together with changes in expression of genes involved in energy metabolism and control of β-cell function (19). In addition, reduced insulin secretion has been observed after PGC-1α–induced uncoupling protein 2 (UCP2) expression in β-cells (46). An increased respiration uncoupling in islet mitochondria through UCP2 might lead to a lower ATP/ADP ratio, which could explain the impaired insulin secretion described here. "
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    ABSTRACT: Adult β-cell dysfunction, a hallmark of type 2 diabetes, can be programmed by adverse fetal environment. We have shown that fetal glucocorticoids (GCs) participate in this programming through inhibition of β-cell development. Here we have investigated the molecular mechanisms underlying this regulation. We showed that GCs stimulate the expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a coregulator of the GCs receptor (GR), and that the overexpression of PGC-1α represses genes important for β-cell development and function. More precisely, PGC-1α inhibited the expression of the key β-cell transcription factor pancreatic duodenal homeobox 1 (Pdx1). This repression required the GR and was mediated through binding of a GR/PGC-1α complex to the Pdx1 promoter. To explore PGC-1α function, we generated mice with inducible β-cell PGC-1α overexpression. Mice overexpressing PGC-1α exhibited at adult age impaired glucose tolerance associated with reduced insulin secretion, decreased β-cell mass, and β-cell hypotrophy. Interestingly, PGC-1α expression in fetal life only was sufficient to impair adult β-cell function whereas β-cell PGC-1α overexpression from adult age had no consequence on β-cell function. Altogether, our results demonstrate that the GR and PGC-1α participate in the fetal programming of adult β-cell function through inhibition of Pdx1 expression.
    Diabetes 12/2012; 62(4). DOI:10.2337/db12-0314 · 8.10 Impact Factor
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    • "Besides UCP2 activation by superoxide ions and lipid peroxidation products [11], it has been reported that the levels of UCP proteins in tissues and cells is mainly regulated at the transcriptional level [31] [32]. Here, we show that UCP2 mRNA is induced by GEM, although the identification of the precise mechanisms of this induction needs further investigation. "
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    ABSTRACT: Cancer cells exhibit an endogenous constitutive oxidative stress higher than that of normal cells, which renders tumours vulnerable to further reactive oxygen species (ROS) production. Mitochondrial uncoupling protein 2 (UCP2) can mitigate oxidative stress by increasing the influx of protons into the mitochondrial matrix and reducing electron leakage and mitochondrial superoxide generation. Here, we demonstrate that chemical uncouplers or UCP2 over-expression strongly decrease mitochondrial superoxide induction by the anticancer drug gemcitabine (GEM) and protect cancer cells from GEM-induced apoptosis. Moreover, we show that GEM IC(50) values well correlate with the endogenous level of UCP2 mRNA, suggesting a critical role for mitochondrial uncoupling in GEM resistance. Interestingly, GEM treatment stimulates UCP2 mRNA expression suggesting that mitochondrial uncoupling could have a role also in the acquired resistance to GEM. Conversely, UCP2 inhibition by genipin or UCP2 mRNA silencing strongly enhances GEM-induced mitochondrial superoxide generation and apoptosis, synergistically inhibiting cancer cell proliferation. These events are significantly reduced by the addition of the radical scavenger N-acetyl-l-cysteine or MnSOD over-expression, demonstrating a critical role of the oxidative stress. Normal primary fibroblasts are much less sensitive to GEM/genipin combination. Our results demonstrate for the first time that UCP2 has a role in cancer cell resistance to GEM supporting the development of an anti-cancer therapy based on UCP2 inhibition associated to GEM treatment.
    Biochimica et Biophysica Acta 06/2012; 1823(10):1856-63. DOI:10.1016/j.bbamcr.2012.06.007 · 4.66 Impact Factor
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    • "PGC1α is a master regulator of mitochondrial biogenesis, and when upregulated its expression is associated with increased expression of protective genes such as UCP2.30, 43 PGC1α is also a direct transcriptional regulator of UCP2, which is a mitochondrial protein responsible for inhibiting increases in membrane potential under the conditions of low adenosine diphosphate which, in turn, decreases reactive oxygen species production.29 UCP2 has been implicated in the pathogenesis of NASH and non-alcoholic fatty liver disease.20, 21, 28, 29 The phenotype of our Men1 HET mice on a HFD suggest that menin has a role in mediating the expression of these important metabolically related proteins and factors described above. "
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    ABSTRACT: The menin tumor suppressor protein is abundantly expressed in the liver, although no function has been identified because of lack of tumor development in multiple endocrine neoplasia type 1 (Men1) null livers. We examine the phenotype of mice lacking one functional allele of Men1 (consistent with the phenotype in humans with MEN1 syndrome) challenged with high fat diet (HFD) to elucidate a metabolic function for hepatic menin. In this study, we challenged mice harboring a liver-specific hemizygous deletion of Men1 (HETs) alongside wild-type (WT) counterparts with HFD for 3 months and monitored the severity of metabolic changes. We demonstrate that the HET mice challenged with HFD for 3 months show an increased weight gain with decreased glucose tolerance compared with WT counterparts. Along with these changes, there was a more severe serum hormone profile involving increased serum insulin, glucose and glucagon, all hallmarks of the type 2 diabetic phenotype. In concert with increased serum hormones, we found that these mice have significantly increased liver triglycerides coupled with increased liver steatosis and inflammatory markers. Quantitative real-time PCR and western blotting studies show increases in enzymes involved with lipogenesis and hepatic glucose production. We conclude that hepatic menin is required for regulation of diet-induced metabolism, and our studies indicate a protective role for the Men1 gene in the liver when challenged with HFD.
    Nutrition & Diabetes 05/2012; 2(5):e34. DOI:10.1038/nutd.2012.7 · 2.65 Impact Factor
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