Role of peroxisome proliferator-activated receptor-gamma coactivator-1alpha 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: 4.64). 03/2006; 147(2):966-76. DOI: 10.1210/en.2005-0817
Source: PubMed

ABSTRACT 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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    • "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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    • "and the opposite expression pattern, suggest that it has a negative influence on UCP2 mRNA expression in vivo. This contrasts with the effect of PPARGC1A on UCP2 gene expression in a rat insulinoma cell line (Oberkofler et al. 2006). However, there is still much debate about the precise function and the tissue-dependent regulation of UCP2 by many genes, and various contradictory results have been reported (Fleury and Sanchis 1999; Villarroya et al. 2007). "
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    ABSTRACT: Knowledge of in vivo relationship between the coactivator PPARGC1A and its target genes is very limited, especially in the pig. In this study, a real-time PCR experiment was performed on longissimus dorsi muscle (MLD) and backfat with 10 presumed PPARGC1A downstream target genes, involved in energy and fat metabolism, to identify possible relationships with PPARGC1A mRNA expression in vivo in the pig (n = 20). Except for UCP3 and LPL, a very significant difference in expression was found between MLD and backfat for all genes (P < 0.01). Hierarchical cluster analysis and the significant pairing of mRNA expression data between sampling locations suggested a genetic regulation of the expression of several target genes. A positive correlation with PPARGC1A was found for CPT1B, GLUT4, PDK4, and TFAM (P < 0.0001). A negative correlation was found for UCP2, FABP4, LEP (P < 0.0001), and TNF (P = 0.0071). No significant correlation was detected for UCP3 and LPL. This study provides evidence for a clear difference in mRNA expression of crucial genes in fat and energy metabolism between 2 important tissues. Our data suggest a clear impact of PPARGC1A on energy and lipid metabolism in vivo in the pig, through several of these downstream target genes.
    Journal of applied genetics 12/2009; 50(4):361-9. DOI:10.1007/BF03195694 · 1.90 Impact Factor
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    • "Various environmental factors modulate Ucp2 transcription: message levels are increased when beta cells are exposed to cold [17], elevated glucose or non-esterified fatty acid levels [15] and hydrogen peroxide [21], whilst it is decreased upon exposure to interleukin-1ß [22]. Most of this information on transcriptional regulation has been obtained from research on rodents, but it is becoming clear that the principal molecular mechanisms are similar in humans, despite a lack of sequence homology within the regulatory region of the respective genes [18]. It is important to realise that UCP2 mRNA and protein levels are not necessarily proportional in beta cells: a low in vivo protein content contrasts for example with a high amount of message, and protein increases may occur without changes in mRNA [23]. "
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    ABSTRACT: Pancreatic beta cells secrete insulin when blood glucose levels are high. Dysfunction of this glucose-stimulated insulin secretion (GSIS) is partly responsible for the manifestation of type 2 diabetes, a metabolic disorder that is rapidly becoming a global pandemic. Mitochondria play a central role in GSIS by coupling glucose oxidation to production of ATP, a signal that triggers a series of events that ultimately leads to insulin release. Beta cells express a mitochondrial uncoupling protein, UCP2, which is rather surprising as activity of such a protein is anticipated to lower the efficiency of oxidative phosphorylation, and hence to impair GSIS. The mounting evidence demonstrating that insulin secretion is indeed blunted by UCP2 agrees with this prediction, and has provoked the idea that UCP2 activity contributes to beta cell pathogenesis and development of type 2 diabetes. Although this notion may be correct, the evolved function of UCP2 remains unclear. With this paper we aim to provide a brief account of the present state of affairs in this field, suggest a physiological role for UCP2, and highlight some of our own recent results.
    Biochimica et Biophysica Acta 07/2008; 1777(7-8):973-9. DOI:10.1016/j.bbabio.2008.03.022 · 4.66 Impact Factor
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