Nuclear respiratory factor 1 controls myocyte enhancer factor 2A transcription to provide a mechanism for coordinate expression of respiratory chain subunits.
ABSTRACT Nuclear respiratory factors NRF1 and NRF2 regulate the expression of nuclear genes encoding heme biosynthetic enzymes, proteins required for mitochondrial genome transcription and protein import, and numerous respiratory chain subunits. NRFs thereby coordinate the expression of nuclear and mitochondrial genes relevant to mitochondrial biogenesis and respiration. Only two of the nuclear-encoded respiratory chain subunits have evolutionarily conserved tissue-specific forms: the cytochrome c oxidase (COX) subunits VIa and VIIa heart/muscle (H) and ubiquitous (L) isoforms. We used genome comparisons to conclude that the promoter regions of COX6A(H) and COX7A(H) lack NRF sites but have conserved myocyte enhancer factor 2 (MEF2) elements. We show that MEF2A mRNA is induced with forced expression of NRF1 and that the MEF2A 5'-regulatory region contains an evolutionarily conserved canonical element that binds endogenous NRF1 in chromatin immunoprecipitation (ChIP) assays. NRF1 regulates MEF2A promoter-reporters according to overexpression, RNA interference underexpression, and promoter element mutation studies. As there are four mammalian MEF2 isotypes, we used an isoform-specific antibody in ChIP to confirm MEF2A binding to the COX6A(H) promoter. These findings support a role for MEF2A as an intermediary in coordinating respiratory chain subunit expression in heart and muscle through a NRF1 --> MEF2A --> COX(H) transcriptional cascade. MEF2A also bound the MEF2A and PPARGC1A promoters in ChIP, placing it within a feedback loop with PGC1alpha in controlling NRF1 activity. Interruption of this cascade and loop may account for striated muscle mitochondrial defects in mef2a null mice. Our findings also account for the previously described indirect regulation by NRF1 of other MEF2 targets in muscle such as GLUT4.
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ABSTRACT: Since gastrointestinal mucosa is constantly exposed to reactive oxygen species from various sources, the presence of antioxidants may contribute to the body's natural defenses against inflammatory diseases. HYPOTHESIS: To define the polyphenols extracted from dried apple peels (DAPP) and determine their antioxidant and anti-inflammatory potential in the intestine. Caco-2/15 cells were used to study the role of DAPP preventive actions against oxidative stress (OxS) and inflammation induced by iron-ascorbate (Fe/Asc) and lipopolysaccharide (LPS), respectively. RESULTS: The combination of HPLC with fluorescence detection, HPLC-ESI-MS TOF and UPLC-ESI-MS/MS QQQ allowed us to characterize the phenolic compounds present in the DAPP (phenolic acids, flavonol glycosides, flavan-3-ols, procyanidins). The addition of Fe/Asc to Caco-2/15 cells induced OxS as demonstrated by the rise in malondialdehyde, depletion of n-3 polyunsaturated fatty acids, and alterations in the activity of endogenous antioxidants (SOD, GPx, G-Red). However, preincubation with DAPP prevented Fe/Asc-mediated lipid peroxidation and counteracted LPS-mediated inflammation as evidenced by the down-regulation of cytokines (TNF-α and IL-6), and prostaglandin E2. The mechanisms of action triggered by DAPP induced also a down-regulation of cyclooxygenase-2 and nuclear factor-κB, respectively. These actions were accompanied by the induction of Nrf2 (orchestrating cellular antioxidant defenses and maintaining redox homeostasis), and PGC-1α (the "master controller" of mitochondrial biogenesis). CONCLUSION: Our findings provide evidence of the capacity of DAPP to reduce OxS and inflammation, two pivotal processes involved in inflammatory bowel diseases.PLoS ONE 01/2013; 8(1):e53725. · 3.73 Impact Factor
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ABSTRACT: The heart is an omnivore organ that requires constant energy production to match its functional demands. In the adult heart, adenosine-5'-triphosphate (ATP) production occurs mainly through mitochondrial fatty acid and glucose oxidation. The heart must constantly adapt its energy production in response to changes in substrate supply and work demands across diverse physiologic and pathophysiologic conditions. The cardiac myocyte maintains a high level of mitochondrial ATP production through a complex transcriptional regulatory network that is orchestrated by the members of the peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family. There is increasing evidence that during the development of cardiac hypertrophy and in the failing heart, the activity of this network, including PGC-1, is altered. This review summarizes our current understanding of the perturbations in the gene regulatory pathways that occur during the development of heart failure. An appreciation of the role this regulatory circuitry serves in the regulation of cardiac energy metabolism may unveil novel therapeutic targets aimed at the metabolic disturbances that presage heart failure. This article is part of a Special Issue entitled:Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.Biochimica et Biophysica Acta 08/2012; · 4.66 Impact Factor
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ABSTRACT: A majority of mammalian promoters are associated with CpG islands. CpG island promoters frequently lack common core promoter elements, such as the TATA box, and often have dispersed transcription start sites. The mechanism through which CpG island promoters are transcriptionally initiated remains unclear. We speculate that some transcription factors can direct transcription initiation by themselves. To test this hypothesis, we screened a variety of transcription factors to see whether they could initiate transcription. Most transcription factors, including specificity protein 1 (Sp1) and nuclear factor Y (NF-Y), showed little transcriptional initiation activity. However, nuclear respiratory factor 1 (NRF-1), the basic helix-loop-helix/leucine zipper (bHLH/ZIP) family of proteins and the E-twenty six (Ets) family of proteins had strong transcriptional activity. We further demonstrated that these transcription factors initiate dispersed transcription. Our studies provide perspectives to the mechanism of transcription initiation from CpG island promoters.Gene 08/2013; · 2.20 Impact Factor