ABSTRACT
Ribosome biosynthesis is a major intracellular energy-consuming process. We previously identified a nucleolar factor, nucleomethylin (NML), which regulates intracellular energy consumption by limiting rRNA transcription. Here, we show that, in livers of obese mice, the recruitment of NML to rRNA gene loci is increased to repress rRNA transcription. To clarify the relationship between obesity and rRNA transcription, we generated NML-null (NML-KO) mice. NML-KO mice show elevated rRNA level, reduced ATP concentration, and reduced lipid accumulation in the liver. Furthermore, in high-fat-diet (HFD)-fed NML-KO mice, hepatic rRNA levels are not decreased. Both weight gain and fat accumulation in HFD-fed NML-KO mice are significantly lower than those in HFD-fed wild-type mice. These findings indicate that rRNA transcriptional activation promotes hepatic energy consumption, which alters hepatic lipid metabolism. Namely, hepatic rRNA transcriptional repression by HFD feeding is essential for energy storage.
Subject(s)
Diet, High-Fat , Liver/metabolism , RNA, Ribosomal/metabolism , Adenosine Triphosphate/metabolism , Animals , Energy Metabolism , Fatty Acids/biosynthesis , Gene Expression , Lipid Metabolism/genetics , Liver/diagnostic imaging , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Obese , Nuclear Proteins/deficiency , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Obesity/etiology , Obesity/metabolism , Obesity/pathology , RNA, Ribosomal/genetics , Sirtuin 1/metabolism , Tomography, X-Ray Computed , Transcription, GeneticABSTRACT
We previously identified a novel protein complex, eNoSC, which senses intracellular energy status and epigenetically regulates the rDNA locus by changing the ratio between the numbers of active and silent gene clusters. eNoSC contains a novel nucleolar protein, Nucleomethylin (NML), which has a methyltransferase-like domain and binds to Lys9-dimethylated histone H3 at the rDNA locus, along with the NAD(+)-dependent deacetylase SIRT1 and the histone methyltransferase SUV39H. The aim of this study was to determine the role of NML in liver after partial hepatectomy (PHx). We assessed liver regeneration and lipid metabolism after PHx in wild-type (WT) and NML transgenic (NML-TG) mice. Survival rates of NML-TG mice were reduced after PHx. We found that hepatic triglyceride content in NML-TG mice remained elevated 48h after PHx, but not delayed liver regeneration. Moreover, hepatic ATP levels in NML-TG mice were higher than that in WT 48h after PHx. These observations suggest that NML may regulate consumption of hepatic triglyceride in liver regeneration after PHx due to storage of excess ATP. The delayed consumption of hepatic triglyceride may be the cause of reduced survival rate in NML-TG mice.
Subject(s)
Adenosine Triphosphate/metabolism , Liver Regeneration , Liver/physiology , Methyltransferases/metabolism , Nuclear Proteins/metabolism , Animals , Animals, Genetically Modified , Female , Gene Expression Regulation , Genes, rRNA , Hepatectomy , Liver/enzymology , Liver/surgery , Methyltransferases/genetics , Mice , Nuclear Proteins/genetics , RNA-Binding Proteins , Transcription, Genetic , Triglycerides/metabolismABSTRACT
Intracellular energy balance is important for cell survival. In eukaryotic cells, the most energy-consuming process is ribosome biosynthesis, which adapts to changes in intracellular energy status. However, the mechanism that links energy status and ribosome biosynthesis is largely unknown. Here, we describe eNoSC, a protein complex that senses energy status and controls rRNA transcription. eNoSC contains Nucleomethylin, which binds histone H3 dimethylated Lys9 in the rDNA locus, in a complex with SIRT1 and SUV39H1. Both SIRT1 and SUV39H1 are required for energy-dependent transcriptional repression, suggesting that a change in the NAD(+)/NADH ratio induced by reduction of energy status could activate SIRT1, leading to deacetylation of histone H3 and dimethylation at Lys9 by SUV39H1, thus establishing silent chromatin in the rDNA locus. Furthermore, eNoSC promotes restoration of energy balance by limiting rRNA transcription, thus protecting cells from energy deprivation-dependent apoptosis. These findings provide key insight into the mechanisms of energy homeostasis in cells.
Subject(s)
DNA, Ribosomal/genetics , Energy Metabolism , Gene Silencing , Transcription, Genetic , Cell Death , Cell Line , Cell Nucleolus/metabolism , Glucose/metabolism , Histone Methyltransferases , Histone-Lysine N-Methyltransferase/chemistry , Histone-Lysine N-Methyltransferase/metabolism , Histones/metabolism , Humans , Methyltransferases/chemistry , Methyltransferases/metabolism , Models, Molecular , Molecular Sequence Data , Multiprotein Complexes/chemistry , Multiprotein Complexes/metabolism , NAD/metabolism , Nuclear Proteins/chemistry , Nuclear Proteins/metabolism , Protein Methyltransferases , Protein Structure, Tertiary , RNA-Binding Proteins , Repressor Proteins/metabolism , Sirtuin 1 , Sirtuins/metabolismABSTRACT
DNA demethylation plays a critical role in transcriptional regulation in differentiated somatic cells. However, there is no experimental evidence that CpG methylation in a small region of a genome restricts gene expression. Here, we show that the anti-CD3repsilon/CD28 antibody stimulation of human CD4+ T cells induces IL2 expression following epigenetic changes, including active demethylation of a specific CpG site, recruitment of Oct-1, and changes in histone modifications. When the stimulatory signal is withdrawn, Oct-1 remains on the enhancer region as a stable marker of the stimulation, causing the second induction to be faster and stronger. Our observations indicate that Oct-1-binding followed by CpG demethylation are key events in the epigenetic regulation of IL2 expression and may act as a memory of the regulatory event.
