Myc-dependent Mitochondrial Generation of Acetyl-CoA Contributes to Fatty Acid Biosynthesis and Histone Acetylation during Cell Cycle Entry

Cell reprogramming from a quiescent to proliferative state requires coordinate activation of multiple -omic networks. These networks activate histones, increase cellular bioenergetics and the synthesis of macromolecules required for cell proliferation. However, mechanisms that coordinate the regulation of these interconnected networks are not fully understood. The oncogene c-Myc (Myc) activates cellular metabolism and global chromatin remodeling. Here we tested for an interconnection between Myc regulation of metabolism and acetylation of histones. Using [¹³C₆]glucose and a combination of GC/MS and LC/ESI tandem mass spectrometry, we determined the fractional incorporation of ¹³C-labeled 2-carbon fragments into the fatty acid palmitate, and acetyl-lysines at the N-terminal tail of histone H4 in myc^−/− and myc^+/+ Rat1A fibroblasts. Our data demonstrate that Myc increases mitochondrial synthesis of acetyl-CoA, as the de novo synthesis of ¹³C-labeled palmitate was increased 2-fold in Myc-expressing cells. Additionally, Myc induced a forty percent increase in ¹³C-labeled acetyl-CoA on H4-K16. This is linked to the capacity of Myc to increase mitochondrial production of acetyl-CoA, as we show that mitochondria provide 50% of the acetyl groups on H4-K16. These data point to a key role for Myc in directing the interconnection of -omic networks, and in particular, epigenetic modification of proteins in response to proliferative signals.     

Recruitment of cAMP-response Element-binding Protein and Histone Deacetylase Has Opposite Effects on Glucocorticoid Receptor Gene Transcription

Glucocorticoids control the synthesis of the glucocorticoid receptor (GR) in various tissues through a negative feedback regulation of the mRNA. In this study, we have identified feedback regulatory domains in the human GR gene promoter and examined the roles of GR, the cAMP-response element-binding protein (CREB), and HDAC-6 in association with promoter elements of the human GR gene. Using breast cancer T47D and HeLa-GR cells, we identify specific negative glucocorticoid-response elements in the GR gene. The feedback regulatory domains were also involved in interactions with CREB. GR-bound negative glucocorticoid-response elements recruited HDAC-6, and this was dependent on treatment with dexamethasone. Both CREB and HDAC-6 formed complexes with GR-dexamethasone. The HDAC-6 LXXLL motif between amino acids 313 and 418 made direct contact with the GR AF-1 domain. Interestingly enough, although the level of GR decreased in CREB knockdown cells, it was elevated in HDAC-6 knockdown cells. Our results suggest that CREB-P is dephosphorylated and that HDAC-6 is recruited by the GR, and they play opposite roles in the negative feedback regulation of the GR gene.     

Cyclin Cln3p links G1 progression to hyphal and pseudohyphal development in Candida albicans

G1 cyclins coordinate environmental conditions with growth and differentiation in many organisms. In the pathogen Candida albicans, differentiation of hyphae is induced by environmental cues but in a cell cycle-independent manner. Intriguingly, repressing the G1 cyclin Cln3p under yeast growth conditions caused yeast cells to arrest in G1, increase in size, and then develop into hyphae and pseudohyphae, which subsequently resumed the cell cycle. Differentiation was dependent on Efg1p, Cph1p, and Ras1p, but absence of Ras1p was also synthetically lethal with repression of CLN3. In contrast, repressing CLN3 in environment-induced hyphae did not inhibit growth or the cell cycle, suggesting that yeast and hyphal cell cycles may be regulated differently. Therefore, absence of a G1 cyclin can activate developmental pathways in C. albicans and uncouple differentiation from the normal environmental controls. The data suggest that the G1 phase of the cell cycle may therefore play a critical role in regulating hyphal and pseudohyphal development in C. albicans.     

A WD Repeat Protein Controls the Cell Cycle and Differentiation by Negatively Regulating Cdc2/B-Type Cyclin Complexes

In the fission yeast Schizosaccharomyces pombe, p34^cdc2 plays a central role controlling the cell cycle. We recently isolated a new gene named srw1⁺, capable of encoding a WD repeat protein, as a multicopy suppressor of hyperactivated p34^cdc2. Cells lacking srw1⁺ are sterile and defective in cell cycle controls. When starved for nitrogen source, they fail to effectively arrest in G₁ and die of accelerated mitotic catastrophe if regulation of p34^cdc2/Cdc13 by inhibitory tyrosine phosphorylation is compromised by partial inactivation of Wee1 kinase. Fertility is restored to the disruptant by deletion of Cig2 B-type cyclin or slight inactivation of p34^cdc2. srw1⁺ shares functional similarity with rum1⁺, having abilities to induce endoreplication and restore fertility to rum1 disruptants. In the srw1 disruptant, Cdc13 fails to be degraded when cells are starved for nitrogen. We conclude that Srw1 controls differentiation and cell cycling at least by negatively regulating Cig2- and Cdc13-associated p34^cdc2 and that one of its roles is to down-regulate the level of the mitotic cyclin particularly in nitrogen-poor environments.     

The Rice NAD+-Dependent Histone Deacetylase OsSRT1 Targets Preferentially to Stress- and Metabolism-Related Genes and Transposable Elements

Histone acetylation/deacetylation is an important chromatin modification for epigenetic regulation of gene expression. Silent information regulation2 (Sir2)-related sirtuins are nicotinamide-adenine dinucleotide (NAD⁺)-dependent histone deacetylases (HDAC). The mammalian sirtuin family comprises 7 members (SIRT1-7) that act in different cellular compartments to regulate metabolism and aging. The rice genome contains only two Sir2-related genes: OsSRT1 (or SRT701) and OsSRT2 (orSRT702). OsSRT1 is closely related to the mammalian SIRT6, while OsSRT2 is homologous to SIRT4. Previous work has shown that OsSRT1 is required for the safeguard against genome instability and cell damage in rice plant. In this work we investigated the role of OsSRT1 on genome-wide acetylation of histone H3 lysine 9 (H3K9ac) and studied the genome-wide binding targets of OsSRT1. The study reveals that OsSRT1 binds to loci with relatively low levels of H3K9ac and directly regulates H3K9ac and expression of many genes that are related to stress and metabolism, indicating that OsSRT1 is an important site-specific histone deacetylase for gene regulation in rice. In addition, OsSRT1 is found to also target to several families of transposable elements, suggesting that OsSRT1 is directly involved in transposable element repression.     

TFIIIC Binding to Alu Elements Controls Gene Expression via Chromatin Looping and Histone Acetylation

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Repression of the Long Noncoding RNA-LET by Histone Deacetylase 3 Contributes to Hypoxia-Mediated Metastasis

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Highlights? There is low expression of lncRNA-LET in various tumor tissues ? Hypoxia-induced low expression of lncRNA-LET occurred through histone deacetylase 3 ? The lncRNA-LET is bound to NF90, which increases NF90 degradation by the proteasome ? Low lncRNA-LET expression contributes to hypoxia-induced cell invasion