Activation of SRF-regulated chromosomal templates by Rho-family GTPases requires a signal that also induces H4 hyperacetylation

Inhibitors of Rho/MRTF/SRF Transcription Pathway Regulate Mitochondrial Function

RhoA-regulated gene transcription by serum response factor (SRF) and its transcriptional cofactor myocardin-related transcription factors (MRTFs) signaling pathway has emerged as a promising therapeutic target for pharmacological intervention in multiple diseases. Altered mitochondrial metabolism is one of the major hallmarks of cancer, therefore, this upregulation is a vulnerability that can be targeted with Rho/MRTF/SRF inhibitors. Recent advances identified a novel series of oxadiazole-thioether compounds that disrupt the SRF transcription, however, the direct molecular target of these compounds is unclear. Herein, we demonstrate the Rho/MRTF/SRF inhibition mechanism of CCG-203971 and CCG-232601 in normal cell lines of human lung fibroblasts and mouse myoblasts. Further studies investigated the role of these molecules in targeting mitochondrial function. We have shown that these molecules hyperacetylate histone H4K12 and H4K16 and regulate the genes involved in mitochondrial function and dynamics. These small molecule inhibitors regulate mitochondrial function as a compensatory mechanism by repressing oxidative phosphorylation and increasing glycolysis. Our data suggest that these CCG molecules are effective in inhibiting all the complexes of mitochondrial electron transport chains and further inducing oxidative stress. Therefore, our present findings highlight the therapeutic potential of CCG-203971 and CCG-232601, which may prove to be a promising approach to target aberrant bioenergetics.

Rho/SRF Inhibitor Modulates Mitochondrial Functions

CCG-1423 is a Rho A pathway inhibitor that has been reported to inhibit Rho/SRF-mediated transcriptional regulation. Serum response factor and its cofactors, which include ternary complex factors and myocardin-related transcription factors, regulate various cellular functions. In this study, we observed that CCG-1423 modulates the mitochondrial functions. The effect of this small molecule drug was determined by measuring mitochondrial function using an XFe96 Analyzer and an Oxygraph 2k (O2k) high-resolution respirometer. CCG-1423 treatment significantly reduced oxidative phosphorylation in a dose-dependent manner. However, CCG-1423 increased the glycolytic rate. We also observed that histone 4 at lysine-16 underwent hyperacetylation with the treatment of this drug. Immunolabeling with F-actin and MitoTracker revealed the alteration in the actin cytoskeleton and mitochondria. Taken together, our findings highlight a critical role of CCG-1423 in inhibiting the transcription of SRF/p49 and PGC-1α, β, resulting in the downregulation of mitochondrial genes, leading to the repression of mitochondrial oxidative phosphorylation and overall ATP reduction. This study provides a better understanding of the effects of CCG-1423 on mitochondria, which may be useful for the assessment of the potential clinical application of CCG-1423 and its derivatives.

Long Noncoding RNA CRYBG3 Blocks Cytokinesis by Directly Binding G-Actin

The dynamic interchange between monomeric globular actin (G-actin) and polymeric filamentous actin filaments (F-actin) is fundamental and essential to many cellular processes, including cytokinesis and maintenance of genomic stability. Here, we report that the long noncoding RNA LNC CRYBG3 directly binds G-actin to inhibit its polymerization and formation of contractile rings, resulting in M-phase cell arrest. Knockdown of LNC CRYBG3 in tumor cells enhanced their malignant phenotypes. Nucleotide sequence 228-237 of the full-length LNC CRYBG3 and the ser14 domain of β-actin is essential for their interaction, and mutation of either of these sites abrogated binding of LNC CRYBG3 to G-actin. Binding of LNC CRYBG3 to G-actin blocked nuclear localization of MAL, which consequently kept serum response factor (SRF) away from the promoter region of several immediate early genes, including JUNB and Arp3, which are necessary for cellular proliferation, tumor growth, adhesion, movement, and metastasis. These findings reveal a novel lncRNA-actin-MAL-SRF pathway and highlight LNC CRYBG3 as a means to block cytokinesis and to treat cancer by targeting the actin cytoskeleton.Significance: Identification of the long noncoding RNA LNC CRYBG3 as a mediator of microfilament disorganization marks it as a novel therapeutic antitumor strategy. Cancer Res; 78(16); 4563-72. ©2018 AACR.

Stimulation of Fas/FasL-mediated apoptosis by luteolin through enhancement of histone H3 acetylation and c-Jun activation in HL-60 leukemia cells

Luteolin (3',4',5,7-tetrahydroxyflavone), which exists in fruits, vegetables, and medicinal herbs, is used in Chinese traditional medicine for treating various diseases, such as hypertension, inflammatory disorders, and cancer. However, the gene-regulatory role of luteolin in cancer prevention and therapy has not been clarified. Herein, we demonstrated that treatment with luteolin resulted in a significant decrease in the viability of human leukemia cells. In the present study, by evaluating fragmentation of DNA and poly (ADP-ribose) polymerase (PARP), we found that luteolin was able to induce PARP cleavage and nuclear fragmentation as well as an increase in the sub-G₀ /G₁ fraction. In addition, luteolin also induced Fas and Fas ligand (FasL) expressions and subsequent activation of caspases-8 and -3, which can trigger the extrinsic apoptosis pathway, while knocking down Fas-associated protein with death domain (FADD) prevented luteolin-induced PARP cleavage. Immunoblot and chromatin immunoprecipitation (ChIP) analyses revealed that luteolin increased acetylation of histone H3, which is involved in the upregulation of Fas and FasL. Moreover, both the extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) pathways are involved in luteolin-induced histone H3 acetylation. Finally, luteolin also activated the c-Jun signaling pathway, which contributes to FasL, but not Fas, gene expression and downregulation of c-Jun expression by small interfering RNA transfection which resulted in a significant decrease in luteolin-induced PARP cleavage. Thus, our results demonstrate that luteolin induced apoptosis of HL-60 cells, and this was associated with c-Jun activation and histone H3 acetylation-mediated Fas/FasL expressions.

Clinical relevance of the transcriptional signature regulated by CDC42 in colorectal cancer

CDC42 is an oncogenic Rho GTPase overexpressed in colorectal cancer (CRC). Although CDC42 has been shown to regulate gene transcription, the specific molecular mechanisms regulating the oncogenic ability of CDC42 remain unknown. Here, we have characterized the transcriptional networks governed by CDC42 in the CRC SW620 cell line using gene expression analysis. Our results establish that several cancer-related signaling pathways, including cell migration and cell proliferation, are regulated by CDC42. This transcriptional signature was validated in two large cohorts of CRC patients and its clinical relevance was also studied. We demonstrate that three CDC42-regulated genes offered a better prognostic value when combined with CDC42 compared to CDC42 alone. In particular, the concordant overexpression of CDC42 and silencing of the putative tumor suppressor gene CACNA2D2 dramatically improved the prognostic value. The CACNA2D2/CDC42 prognostic classifier was further validated in a third CRC cohort as well as in vitro and in vivo CRC models. Altogether, we show that CDC42 has an active oncogenic role in CRC via the transcriptional regulation of multiple cancer-related pathways and that CDC42-mediated silencing of CACNA2D2 is clinically relevant. Our results further support the use of CDC42 specific inhibitors for the treatment of the most aggressive types of CRC.

Epigenetic Regulation of Viral Biological Processes

It is increasingly clear that DNA viruses exploit cellular epigenetic processes to control their life cycles during infection. This review will address epigenetic regulation in members of the polyomaviruses, adenoviruses, human papillomaviruses, hepatitis B, and herpes viruses. For each type of virus, what is known about the roles of DNA methylation, histone modifications, nucleosome positioning, and regulatory RNA in epigenetic regulation of the virus infection will be discussed. The mechanisms used by certain viruses to dysregulate the host cell through manipulation of epigenetic processes and the role of cellular cofactors such as BRD4 that are known to be involved in epigenetic regulation of host cell pathways will also be covered. Specifically, this review will focus on the role of epigenetic regulation in maintaining viral episomes through the generation of chromatin, temporally controlling transcription from viral genes during the course of an infection, regulating latency and the switch to a lytic infection, and global dysregulation of cellular function.

The cell- and tissue-specific transcription mechanism of the TATA-less syntaxin 1A gene

Syntaxin 1A (Stx1a) plays an important role in regulation of neuronal synaptic function. To clarify the mechanism of basic transcriptional regulation and neuron-specific transcription of Stx1a we cloned the Stx1a gene from rat, in which knowledge of the expression profile was accumulated, and elucidated that Stx1a consisting of 10 exons, possesses multiple transcription initiation sites and a 204-bp core promoter region (CPR) essential for transcription in PC12 cells. The TATA-less, conserved, GC-rich CPR has 2 specific protein (SP) sites that bind SP1 and are responsible for 65% of promoter activity. The endogenous CPR, including 23 CpG sites, is not methylated in PC12 cells, which express Stx1a and fetal rat skin keratinocyte (FRSK) cells, which do not, although an exogenous methylated CPR suppresses reporter activity in both lines. Trichostatin A (TSA) and class I histone deacetylase (HDAC) inhibitors, but not 5-azacytidine, induce Stx1a in FRSK cells. Acetylated histone H3 only associates to the CPR in FRSK cells after TSA addition, whereas the high acetylated histone H3-CPR association in PC12 cells was unchanged following treatment. HDAC inhibitor induction of Stx1a was negated by mithramycin A and deletion/mutation of 2 SP sites. HDAC1, HDAC2, and HDAC8 detach from the CPR when treated with TSA in FRSK cells and are associated with the CPR in lungs, and acetylated histone H3 associates to this region in the brain. In the first study characterizing a syntaxin promoter, we show that association of SP1 and acetylated histone H3 to CPR is important for Stx1a transcription and that HDAC1, HDAC2, and HDAC8 decide cell/tissue specificity in a suppressive manner.

Small-molecule agonists of mammalian Diaphanous-related (mDia) formins reveal an effective glioblastoma anti-invasion strategy

Formin agonists impede the most dangerous aspect of glioblastoma—tumor spread into surrounding healthy tissue. Formin activation impairs a novel aspect of the transformed cell and informs the development of antitumor strategies for a cancer needing a more effective therapy.

The extensive invasive capacity of glioblastoma (GBM) makes it resistant to surgery, radiotherapy, and chemotherapy and thus makes it lethal. In vivo, GBM invasion is mediated by Rho GTPases through unidentified downstream effectors. Mammalian Diaphanous (mDia) family formins are Rho-directed effectors that regulate the F-actin cytoskeleton to support tumor cell motility. Historically, anti-invasion strategies focused upon mDia inhibition, whereas activation remained unexplored. The recent development of small molecules directly inhibiting or activating mDia-driven F-actin assembly that supports motility allows for exploration of their role in GBM. We used the formin inhibitor SMIFH2 and mDia agonists IMM-01/-02 and mDia2-DAD peptides, which disrupt autoinhibition, to examine the roles of mDia inactivation versus activation in GBM cell migration and invasion in vitro and in an ex vivo brain slice invasion model. Inhibiting mDia suppressed directional migration and spheroid invasion while preserving intrinsic random migration. mDia agonism abrogated both random intrinsic and directional migration and halted U87 spheroid invasion in ex vivo brain slices. Thus mDia agonism is a superior GBM anti-invasion strategy. We conclude that formin agonism impedes the most dangerous GBM component—tumor spread into surrounding healthy tissue. Formin activation impairs novel aspects of transformed cells and informs the development of anti-GBM invasion strategies.

Repression of SRF target genes is critical for Myc-dependent apoptosis of epithelial cells

Oncogenic levels of Myc expression sensitize cells to multiple apoptotic stimuli, and this protects long-lived organisms from cancer development. How cells discriminate physiological from supraphysiological levels of Myc is largely unknown. Here, we show that induction of apoptosis by Myc in breast epithelial cells requires association of Myc with Miz1. Gene expression and ChIP-Sequencing experiments show that high levels of Myc invade target sites that lack consensus E-boxes in a complex with Miz1 and repress transcription. Myc/Miz1-repressed genes encode proteins involved in cell adhesion and migration and include several integrins. Promoters of repressed genes are enriched for binding sites of the serum-response factor (SRF). Restoring SRF activity antagonizes Myc repression of SRF target genes, attenuates Myc-induced apoptosis, and reverts a Myc-dependent decrease in Akt phosphorylation and activity, a well-characterized suppressor of Myc-induced apoptosis. We propose that high levels of Myc engage Miz1 in repressive DNA binding complexes and suppress an SRF-dependent transcriptional program that supports survival of epithelial cells.

Regulated localization is sufficient for hormonal control of regulator of G protein signaling homology Rho guanine nucleotide exchange factors (RH-RhoGEFs)

The regulator of G protein signaling homology (RH) Rho guanine nucleotide exchange factors (RhoGEFs) (p115RhoGEF, leukemia-associated RhoGEF, and PDZ-RhoGEF) contain an RH domain and are specific GEFs for the monomeric GTPase RhoA. The RH domains interact specifically with the α subunits of G12 heterotrimeric GTPases. Activated Gα13 modestly stimulates the exchange activity of both p115RhoGEF and leukemia-associated RhoGEF but not PDZ-RhoGEF. Because all three RH-RhoGEFs can localize to the plasma membrane upon expression of activated Gα13, cellular localization of these RhoGEFs has been proposed as a mechanism for controlling their activity. We use a small molecule-regulated heterodimerization system to rapidly control the localization of RH-RhoGEFs. Acute localization of the proteins to the plasma membrane activates RhoA within minutes and to levels that are comparable with activation of RhoA by hormonal stimulation of G protein-coupled receptors. The catalytic activity of membrane-localized RhoGEFs is not dependent on activated Gα13. We further show that the conserved RH domains can rewire two different RacGEFs to activate Rac1 in response to a traditional activator of RhoA. Thus, RH domains act as independent detectors for activated Gα13 and are sufficient to modulate the activity of RhoGEFs by hormones via mediating their localization to substrate, membrane-associated RhoA.

Cell density impacts epigenetic regulation of cytokine-induced E-selectin gene expression in vascular endothelium

Growing evidence suggests that the phenotype of endothelial cells during angiogenesis differs from that of quiescent endothelial cells, although little is known regarding the difference in the susceptibility to inflammation between both the conditions. Here, we assessed the inflammatory response in sparse and confluent endothelial cell monolayers. To obtain sparse and confluent monolayers, human umbilical vein endothelial cells were seeded at a density of 7.3 × 10(3) cells/cm(2) and 29.2 × 10(3) cells/cm(2), respectively, followed by culturing for 36 h and stimulation with tumor necrosis factor α. The levels of tumor necrosis factor α-induced E-selectin protein and mRNA expression were higher in the confluent monolayer than in the sparse monolayer. The phosphorylation of c-jun N-terminal kinase and p38 mitogen-activated protein kinase or nuclear factor-κB activation was not involved in this phenomenon. A chromatin immunoprecipitation assay of the E-selectin promoter using an anti-acetyl-histone H3 antibody showed that the E-selectin promoter was highly and specifically acetylated in the confluent monolayer after tumor necrosis factor α activation. Furthermore, chromatin accessibility real-time PCR showed that the chromatin accessibility at the E-selectin promoter was higher in the confluent monolayer than in the sparse monolayer. Our data suggest that the inflammatory response may change during blood vessel maturation via epigenetic mechanisms that affect the accessibility of chromatin.

Small-molecule intramimics of formin autoinhibition: a new strategy to target the cytoskeletal remodeling machinery in cancer cells

Although the cancer cell cytoskeleton is a clinically validated target, few new strategies have emerged for selectively targeting cell division by modulating the cytoskeletal structure, particularly ways that could avoid the cardiotoxic and neurotoxic effects of current agents such as taxanes. We address this gap by describing a novel class of small-molecule agonists of the mammalian Diaphanous (mDia)-related formins, which act downstream of Rho GTPases to assemble actin filaments, and their organization with microfilaments to establish and maintain cell polarity during migration and asymmetric division. GTP-bound Rho activates mDia family members by disrupting the interaction between the DID and DAD autoregulatory domains, which releases the FH2 domain to modulate actin and microtubule dynamics. In screening for DID-DAD disruptors that activate mDia, we identified two molecules called intramimics (IMM-01 and -02) that were sufficient to trigger actin assembly and microtubule stabilization, serum response factor-mediated gene expression, cell-cycle arrest, and apoptosis. In vivo analysis of IMM-01 and -02 established their ability to slow tumor growth in a mouse xenograft model of colon cancer. Taken together, our work establishes the use of intramimics and mDia-related formins as a new general strategy for therapeutic targeting of the cytoskeletal remodeling machinery of cancer cells.

Cellular mechanisms of somatic stem cell aging

Tissue homeostasis and regenerative capacity rely on rare populations of somatic stem cells endowed with the potential to self-renew and differentiate. During aging, many tissues show a decline in regenerative potential coupled with a loss of stem cell function. Cells including somatic stem cells have evolved a series of checks and balances to sense and repair cellular damage to maximize tissue function. However, during aging the mechanisms that protect normal cell function begin to fail. In this review, we will discuss how common cellular mechanisms that maintain tissue fidelity and organismal lifespan impact somatic stem cell function. We will highlight context-dependent changes and commonalities that define aging, by focusing on three age-sensitive stem cell compartments: blood, neural, and muscle. Understanding the interaction between extrinsic regulators and intrinsic effectors that operate within different stem cell compartments is likely to have important implications for identifying strategies to improve health span and treat age-related degenerative diseases.

Mechanobiology and developmental control

Morphogenesis is the remarkable process by which cells self-assemble into complex tissues and organs that exhibit specialized form and function during embryological development. Many of the genes and chemical cues that mediate tissue and organ formation have been identified; however, these signals alone are not sufficient to explain how tissues and organs are constructed that exhibit their unique material properties and three-dimensional forms. Here, we review work that has revealed the central role that physical forces and extracellular matrix mechanics play in the control of cell fate switching, pattern formation, and tissue development in the embryo and how these same mechanical signals contribute to tissue homeostasis and developmental control throughout adult life.

Expression of neuroepithelial transforming gene 1 is enhanced in oesophageal cancer and mediates an invasive tumour cell phenotype

INTRODUCTION

Neuroepithelial Transforming Gene 1 (NET1) is a well characterised oncoprotein and a proven marker of an aggressive phenotype in a number of cancers, including gastric adenocarcinoma. We aimed to investigate whether NET1 plays a functional role in oesophageal cancer (OAC) and its pre-malignant phenotype Barrett's oesophagus.

METHODS

Baseline NET1 mRNA levels were determined by qPCR across a panel of six cell lines, including normal oesophageal, Barrett's and OAC derived cells. Quantification of NET1 protein in OAC cells was performed using Western blot and immunofluorescence. NET1 expression was modulated by treating with lysophosphatidic acid (LPA) and NET1-specific siRNA. The functional effects of NET1 knockdown were assessed in vitro using proliferation, migration and invasion assays.

RESULTS

NET1 expression was increased in Barrett's and in OAC-derived cells in comparison to normal oesophageal cells. The highest expression was observed in OE33 a Barrett's-related OAC cell line. NET1 protein and mRNA expression was enhanced by LPA treatment in OAC and furthermore LPA treatment caused increased proliferation, migration and invasion in a NET1-dependent manner. NET1 knockdown resulted in reduced OAC cell proliferation and invasion.

CONCLUSIONS

As found in other malignancies, NET1 expression is elevated in OAC and its pre-malignant phenotype, Barrett's oesophagus. NET1 promotes OAC cell invasion and proliferation and it mediates LPA-induced OAC cell migration.

Histone deacetylase inhibition promotes osteoblast maturation by altering the histone H4 epigenome and reduces Akt phosphorylation

Bone has remarkable regenerative capacity, but this ability diminishes during aging. Histone deacetylase inhibitors (HDIs) promote terminal osteoblast differentiation and extracellular matrix production in culture. The epigenetic events altered by HDIs in osteoblasts may hold clues for the development of new anabolic treatments for osteoporosis and other conditions of low bone mass. To assess how HDIs affect the epigenome of committed osteoblasts, MC3T3 cells were treated with suberoylanilide hydroxamic acid (SAHA) and subjected to microarray gene expression profiling and high-throughput ChIP-Seq analysis. As expected, SAHA induced differentiation and matrix calcification of osteoblasts in vitro. ChIP-Seq analysis revealed that SAHA increased histone H4 acetylation genome-wide and in differentially regulated genes, except for the 500 bp upstream of transcriptional start sites. Pathway analysis indicated that SAHA increased the expression of insulin signaling modulators, including Slc9a3r1. SAHA decreased phosphorylation of insulin receptor β, Akt, and the Akt substrate FoxO1, resulting in FoxO1 stabilization. Thus, SAHA induces genome-wide H4 acetylation and modulates the insulin/Akt/FoxO1 signaling axis, whereas it promotes terminal osteoblast differentiation in vitro.

Roles of AML1/RUNX1 in T-cell malignancy induced by loss of p53

AML1/RUNX1 is a frequent target of chromosome translocations and mutations in myeloid and B-cell leukemias, and upregulation of AML1 is also observed in some cases of T-cell leukemias and lymphomas. This study shows that the incidence of thymic lymphoma in p53-null mice is less frequent in the Aml1(+/-) than in the Aml1(+/+) background. AML1 is upregulated in p53-null mouse bone-marrow cells and embryonic fibroblasts. In the steady state, p53 binds to and inhibits the distal AML1 promoter. When the cells are exposed to stresses, p53 is released from the distal AML1 promoter, resulting in upregulation of AML1. Overexpression of AML1 stimulates T-lymphocyte proliferation. These results suggest that upregulation of AML1 induced by loss of p53 promotes lymphoid-cell proliferation, thereby inducing lymphoma development.

Epstein - Barr virus transforming protein LMP-1 alters B cells gene expression by promoting accumulation of the oncoprotein ΔNp73α

Many studies have proved that oncogenic viruses develop redundant mechanisms to alter the functions of the tumor suppressor p53. Here we show that Epstein-Barr virus (EBV), via the oncoprotein LMP-1, induces the expression of ΔNp73α, a strong antagonist of p53. This phenomenon is mediated by the LMP-1 dependent activation of c-Jun NH2-terminal kinase 1 (JNK-1) which in turn favours the recruitment of p73 to ΔNp73α promoter. A specific chemical inhibitor of JNK-1 or silencing JNK-1 expression strongly down-regulated ΔNp73α mRNA levels in LMP-1-containing cells. Accordingly, LMP-1 mutants deficient to activate JNK-1 did not induce ΔNp73α accumulation. The recruitment of p73 to the ΔNp73α promoter correlated with the displacement of the histone-lysine N-methyltransferase EZH2 which is part of the transcriptional repressive polycomb 2 complex. Inhibition of ΔNp73α expression in lymphoblastoid cells (LCLs) led to the stimulation of apoptosis and up-regulation of a large number of cellular genes as determined by whole transcriptome shotgun sequencing (RNA-seq). In particular, the expression of genes encoding products known to play anti-proliferative/pro-apoptotic functions, as well as genes known to be deregulated in different B cells malignancy, was altered by ΔNp73α down-regulation. Together, these findings reveal a novel EBV mechanism that appears to play an important role in the transformation of primary B cells.

Approximately 20% of worldwide human cancers have been associated with viral infections. Many oncogenic viruses exert their transforming properties by inactivating the products of tumour suppressor genes. One of the best characterized events induced by ongocenic viruses is the inactivation of the transcriptional factors p53. The mucosal high-risk HPV types, EBV, HTLV-1 and KSHV, via their viral proteins, are able to target p53 by distinct mechanisms. We have recently described a novel p53 inactivation mechanism of some cutaneous beta HPV types which have been suggested to be associated with skin carcinogenesis. Beta HPV38 induces accumulation of the p53 antagonist, ΔNp73α which in turn silences the expression of the p53-regulated genes. Here we report that also EBV, via the oncoprotein LMP-1, induces the expression of ΔNp73α which is dependent on the recruitment of p73 on ΔNp73 promoter and the activation of JNK-1. The recruitment of p73 to the ΔNp73 promoter correlated with the displacement of the histone-lysine N-methyltransferase EZH2 which is part of a transcriptional repressive polycomb 2 complex. We also show that ΔNp73α plays an important role in transformation of primary human B cells and regulates the expression of a large number of cellular genes that encode proteins linked to cancer development, including lymphomagenesis.

Restoring cell polarity: an HSC fountain of youth

Until recently, aging was viewed as a fixed and irreversible process. However, in this issue of Cell Stem Cell, Florian et al. (2012) reveal a link between increased activity of the RhoGTPase Cdc42, hematopoietic stem cell polarity, and aging that can be regulated by pharmacological inhibition of Cdc42.

Oct-1 cooperates with the TATA binding initiation complex to control rapid transcription of human iNOS

Expression of the human inducible nitric oxide synthase (hiNOS) is generally undetectable in resting cells, but stimulation by a variety of signals including cytokines induces transcription in most cell types. The tight transcriptional regulation of the enzyme is a complex mechanism many aspects of which remain unknown. Here, we describe an octamer (Oct) element in hiNOS proximal promoter, located close to the TATA box. This site constitutively binds Oct-1 and its deletion abrogates cytokine-induced transcription, showing that it is indispensable though not sufficient for transcription. Increasing the distance between Oct and the TATA box by inserting inert DNA sequence inhibits transcription, and footprinting of this region shows no other protein binding in resting cells, suggesting an interaction between the two complexes. Chromatin immunoprecipitation assays detect the presence of Oct-1, RNA polymerase II and trimethyl K4 histone H3 on the proximal promoter in resting cells, confirming that the gene is primed for transcription before stimulation. RT-PCR of various fragments along the hiNOS gene shows that transcription is initiated in resting cells and this is inhibited by interference with Oct-1 binding to the proximal site of the promoter. We propose that, through interaction with the initiation complex, Oct-1 regulates hiNOS transcription by priming the gene for the rapid response required in an immune response.

c-Jun in Schwann cells promotes axonal regeneration and motoneuron survival via paracrine signaling

The AP-1 transcription factor c-Jun is a master regulator of the axonal response in neurons. c-Jun also functions as a negative regulator of myelination in Schwann cells (SCs) and is strongly reactivated in SCs upon axonal injury. We demonstrate here that, after injury, the absence of c-Jun specifically in SCs caused impaired axonal regeneration and severely increased neuronal cell death. c-Jun deficiency resulted in decreased expression of several neurotrophic factors, and GDNF and Artemin, both of which encode ligands for the Ret receptor tyrosine kinase, were identified as novel direct c-Jun target genes. Genetic inactivation of Ret specifically in neurons resulted in regeneration defects without affecting motoneuron survival and, conversely, administration of recombinant GDNF and Artemin protein substantially ameliorated impaired regeneration caused by c-Jun deficiency. These results reveal an unexpected function for c-Jun in SCs in response to axonal injury, and identify paracrine Ret signaling as an important mediator of c-Jun function in SCs during regeneration.

Lysophosphatidic acid induces early growth response-1 (Egr-1) protein expression via protein kinase Cδ-regulated extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) activation in vascular smooth muscle cells

Lysophosphatidic acid (LPA) modulates vascular cell function in vitro and in vivo via regulating the expression of specific genes. Previously, we reported that a transcriptional mechanism controls LPA-induced expression of Egr-1 in vascular smooth muscle cells. Egr-1 is a master transcription factor mediating the expression of various genes that have been implied to modulate a broad spectrum of vascular pathologies. In this study, we determined the essential intracellular signaling pathway leading to LPA-induced Egr-1 expression. Our data demonstrate that activation of ERK1/2 and JNK, but not p38 MAPK, is required for LPA-induced Egr-1 expression in smooth muscle cells. We provide the first evidence that MEK-mediated JNK activation leads to LPA-induced gene expression. JNK2 is required for Egr-1 induction. Examining the upstream kinases that mediate ERK and JNK activation, leading to Egr-1 expression, we found that LPA-induced activation of MAPKs and expression of Egr-1 are dependent on PKC activation. We observed that LPA rapidly activates PKCδ and PKCθ. Overexpression of dominant-negative PKCδ, but not dominant-negative PKCθ, diminished activation of ERK and JNK and blocked LPA-induced expression of Egr-1 mRNA and protein. We also evaluated LPA receptor involvement. Our data reveal an intracellular regulatory mechanism: LPA induction of Egr-1 expression is via LPA cognate receptor (LPA receptor 1)-dependent and PKCδ-mediated ERK and JNK activation. This study provides the first evidence that PKCδ mediates ERK and JNK activation in the LPA signaling pathway and that this pathway is required for LPA-induced gene regulation as evidenced by Egr-1 expression.

Cdc42 activity regulates hematopoietic stem cell aging and rejuvenation

The decline in hematopoietic function seen during aging involves a progressive reduction in the immune response and an increased incidence of myeloid malignancy, and has been linked to aging of hematopoietic stem cells (HSCs). The molecular mechanisms underlying HSC aging remain unclear. Here we demonstrate that elevated activity of the small RhoGTPase Cdc42 in aged HSCs is causally linked to HSC aging and correlates with a loss of polarity in aged HSCs. Pharmacological inhibition of Cdc42 activity functionally rejuvenates aged HSCs, increases the percentage of polarized cells in an aged HSC population, and restores the level and spatial distribution of histone H4 lysine 16 acetylation to a status similar to that seen in young HSCs. Our data therefore suggest a mechanistic role for Cdc42 activity in HSC biology and epigenetic regulation, and identify Cdc42 activity as a pharmacological target for ameliorating stem cell aging.

Higher-order chromatin regulation and differential gene expression in the human tumor necrosis factor/lymphotoxin locus in hepatocellular carcinoma cells

The three-dimensional context of endogenous chromosomal regions may contribute to the regulation of gene clusters by influencing interactions between transcriptional regulatory elements. In this study, we investigated the effects of tumor necrosis factor (TNF) signaling on spatiotemporal enhancer-promoter interactions in the human tumor necrosis factor (TNF)/lymphotoxin (LT) gene locus, mediated by CCCTC-binding factor (CTCF)-dependent chromatin insulators. The cytokine genes LTα, TNF, and LTβ are differentially regulated by NF-κB signaling in inflammatory and oncogenic responses. We identified at least four CTCF-enriched sites with enhancer-blocking activities and a TNF-responsive TE2 enhancer in the TNF/LT locus. One of the CTCF-enriched sites is located between the early-inducible LTα/TNF promoters and the late-inducible LTβ promoter. Depletion of CTCF reduced TNF expression and accelerated LTβ induction. After TNF stimulation, via intrachromosomal dynamics, these insulators mediated interactions between the enhancer and the LTα/TNF promoters, followed by interaction with the LTβ promoter. These results suggest that insulators mediate the spatiotemporal control of enhancer-promoter associations in the TNF/LT gene cluster.

Signaling mechanisms that regulate smooth muscle cell differentiation

Extensive studies over the last 30 years have demonstrated that vascular smooth muscle cell (SMC) differentiation and phenotypic modulation is controlled by a dynamic array of environmental cues. The identification of the signaling mechanisms by which these environmental cues regulate SMC phenotype has been more difficult because of our incomplete knowledge of the transcription mechanisms that regulate SMC-specific gene expression. However, recent advances in this area have provided significant insight, and the goal of this review is to summarize the signaling mechanisms by which extrinsic cues control SMC differentiation.

LMO7 mediates cell-specific activation of the Rho-myocardin-related transcription factor-serum response factor pathway and plays an important role in breast cancer cell migration

Serum response factor (SRF) is a ubiquitously expressed transcription factor that regulates cell-specific functions such as muscle development and breast cancer metastasis. The myocardin-related transcription factors (MRTFs), which are transcriptional coactivators mediating cell-specific functions of SRF, are also ubiquitously expressed. How MRTFs and SRF drive cell-specific transcription is still not fully understood. Here we show that LIM domain only 7 (LMO7) is a cell-specific regulator of MRTFs and plays an important role in breast cancer cell migration. LMO7 activates MRTFs by relieving actin-mediated inhibition in a manner that requires, and is synergistic with, Rho GTPase. Whereas Rho is required for LMO7 to activate full-length MRTFs that have three RPEL actin-binding motifs, the disruption of individual actin-RPEL interactions is sufficient to eliminate the Rho dependency and to allow the strong Rho-independent function of LMO7. Mechanistically, we show that LMO7 colocalizes with F-actin and reduces the G-actin/F-actin ratio via a Rho-independent mechanism. The knockdown of LMO7 in HeLa and MDA-MB-231 cells compromises both basal and Rho-stimulated MRTF activities and impairs the migration of MDA-MB-231 breast cancer cells. We also show that LMO7 is upregulated in the stroma of invasive breast carcinoma in a manner that correlates with the increased expression of SRF target genes that regulate muscle and actin cytoskeleton functions. Together, this study reveals a novel cell-specific mechanism regulating Rho-MRTF-SRF signaling and breast cancer cell migration and identifies a role for actin-RPEL interactions in integrating Rho and cell-specific signals to achieve both the synergistic and Rho-dependent activation of MRTFs.

Decoding the histone H4 lysine 20 methylation mark

The molecular biology of histone H4 lysine 20 (H4K20) methylation, like many other post-translational modifications of histones, has been the subject of intensive interest in recent years. While there is an emerging consensus linking H4K20me1, H4K20me2, and H4K20me3 to transcription, repair, and constitutive heterochromatin, respectively, the specific details of these associations and the biological mechanisms by which the methylated histones are introduced and function are now the subject of active investigation. Although a large number of methylases capable of methylating H4K20 have been identified and characterized; there is no known demethylase of H4K20, though the search is ongoing. Additionally, many recent studies have been directed at understanding the role of methylated H4K20 and other histone modifications associated with different biological processes in the context of a combinatorial histone code. It seems likely that continued study of the methylation of H4K20 will yield extremely valuable insights concerning the regulation of histone modifications before and during cell division and the impact of these modifications on subsequent gene expression.

Differing contributions of LIMK and ROCK to TGFβ-induced transcription, motility and invasion

The ability of transforming growth factor β (TGFβ) to induce epithelial-mesenchymal transition (EMT) is mediated by SMAD-dependent and SMAD-independent pathways such as the activation of Rho GTPase signalling. Upon activation, GTP-bound Rho stimulates the ROCK kinases, which in turn phosphorylate numerous substrates including the LIM kinases (LIMK). The net result of ROCK activation is increased actin-myosin contractile force generation, with a contribution from LIMK-induced actin filament stabilisation. In this study, we made use of siRNA-mediated knockdown and selective inhibitors to determine the contributions of ROCK and LIMK to TGFβ-induced responses. We find that both ROCK and LIMK are required for TGFβ stimulation of serum-response factor (SRF) transcriptional activity and actin stress fibre formation during EMT. In contrast, although LIMK inhibition had little effect on cell motility in scratch wound and Transwell migration assays, ROCK inhibition actually promoted TGFβ-induced cell motility by helping individual cells to break free from the epithelial sheet. Furthermore, we demonstrate that selective inhibition of LIMK, but not ROCK, effectively blocked TGFβ driven invasion through a layer of matrigel extracellular matrix protein. These results indicate that the roles of LIMK and ROCK in the Rho signalling pathway downstream of TGFβ are not identical and suggest that LIMK represents an attractive therapeutic target in TGFβ driven organ fibrosis and metastatic cancer spread.

Nucleocytoplasmic translocation of HDAC9 regulates gene expression and dendritic growth in developing cortical neurons

Transcriptional regulation of gene expression is thought to play a pivotal role in activity-dependent neuronal differentiation and circuit formation. Here, we investigated the role of histone deacetylase 9 (HDAC9), which regulates transcription by histone modification, in the development of neocortical neurons. The translocation of HDAC9 from nucleus to cytoplasm was induced by an increase of spontaneous firing activity in cultured mouse cortical neurons. This nucleocytoplasmic translocation was also observed in postnatal development in vivo. The translocation-induced gene expression and cellular morphology was further examined by introducing an HDAC9 mutant that disrupts the nucleocytoplasmic translocation. Expression of c-fos, an immediately-early gene, was suppressed in the mutant-transfected cells regardless of neural activity. Moreover, the introduction of the mutant decreased the total length of dendritic branches, whereas knockdown of HDAC9 promoted dendritic growth. These findings indicate that chromatin remodeling with nucleocytoplasmic translocation of HDAC9 regulates activity-dependent gene expression and dendritic growth in developing cortical neurons.

Identification of a co-activator that links growth factor signalling to c-Jun/AP-1 activation

The AP-1 transcription factor c-Jun is essential for cellular proliferation in many cell types, but the molecular link between growth factors and c-Jun activation has been enigmatic. In this study we identify a previously uncharacterized RING-domain-containing protein, RACO-1 (RING domain AP-1 co-activator-1), as a c-Jun co-activator that is regulated by growth factor signalling. RACO-1 interacted with c-Jun independently of amino-terminal phosphorylation, and was both necessary and sufficient for c-Jun/AP-1 activation. Growth factor-mediated stimulation of AP-1 was attributable to MEK/ERK-dependent stabilization of RACO-1 protein. Stimulation of the MEK/ERK pathway strongly promoted Lys 63-linked ubiquitylation of RACO-1, which antagonized Lys 48-linked degradative auto-ubiquitylation of the same Lys residues. RACO-1 depletion reduced cellular proliferation and decreased expression of several growth-associated AP-1 target genes, such as cdc2, cyclinD1 and hb-egf. Moreover, transgenic overexpression of RACO-1 augmented intestinal tumour formation triggered by aberrant Wnt signalling and cooperated with oncogenic Ras in colonic hyperproliferation. Thus RACO-1 is a co-activator that links c-Jun to growth factor signalling and is essential for AP-1 function in proliferation.

Bag1-L is a phosphorylation-dependent coactivator of c-Jun during neuronal apoptosis

In the nervous system, cell death by apoptosis plays a critical role during normal development and pathological neurodegeneration. Jun N-terminal kinases (JNKs) are essential regulators of neuronal apoptosis. The AP-1 transcription factor c-Jun is phosphorylated at multiple sites within its transactivation domain by the JNKs, and c-Jun phosphorylation is required for JNK-induced neurotoxicity. While the importance of c-Jun as a mediator of apoptotic JNK signaling in neurons is firmly established, the molecular mechanism underlying the requirement for c-Jun N-terminal phosphorylation is enigmatic. Here we identify the multifunctional protein Bag1-L as a coactivator of phosphorylated c-Jun. Bag1-L preferentially interacts with N-terminally phosphorylated c-Jun, and Bag1-L greatly augments transcriptional activation by phosphorylated c-Jun. Chromatin immunoprecipitation experiments revealed binding of Bag1-L to the promoters of proapoptotic AP-1 target genes, and overexpression of Bag1-L augmented cell death in primary neurons. Therefore, Bag1-L functions as a coactivator regulating neurotoxicity mediated by phosphorylated c-Jun.

Subcellular localization of cyclic AMP-responsive element binding protein-regulated transcription coactivator 2 provides a link between obesity and breast cancer in postmenopausal women

Epidemiologic evidence supports a correlation between obesity and breast cancer in women. AMP-activated protein kinase plays an important role in energy homeostasis and inhibits the actions of cyclic AMP-responsive element binding protein-regulated transcription coactivator 2 (CRTC2). In postmenopausal women, the cyclic AMP-responsive element binding protein-dependent regulation of aromatase is a determinant of breast tumor formation through local production of estrogens. The present work aimed to examine the effect of adipokines on aromatase expression and identify additional mechanisms by which prostaglandin E(2) causes increased aromatase expression in human breast adipose stromal cells. Treatment of human adipose stromal cells with forskolin and phorbol 12-myristate 13-acetate (PMA), to mimic prostaglandin E(2), resulted in nuclear translocation of CRTC2. Aromatase promoter II (PII) activity assays showed that CRTC2 in addition to forskolin/PMA treatment significantly increased PII-induced activity. CRTC2 binding to PII was examined by chromatin immunoprecipitation, and forskolin/PMA treatment was associated with increased binding to PII. Treatment of human adipose stromal cells with leptin significantly up-regulated aromatase expression associated with nuclear translocation of CRTC2 and increased binding of CRTC2 to PII. Adiponectin treatment significantly decreased forskolin/PMA-stimulated aromatase expression, consistent with the decreased nuclear translocation of CRTC2 and the decreased binding of CRTC2 to PII. The expression and activity of the AMP-activated protein kinase LKB1 was examined and found to be significantly decreased following either forskolin/PMA or leptin treatment. In contrast, adiponectin significantly increased LKB1 expression and activity. In conclusion, the regulation of aromatase by CRTC2, in response to the altered hormonal milieu associated with menopause and obesity, provides a critical link between obesity and breast cancer.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-citrate lyase links cellular metabolism to histone acetylation

Histone acetylation in single-cell eukaryotes relies on acetyl coenzyme A (acetyl-CoA) synthetase enzymes that use acetate to produce acetyl-CoA. Metazoans, however, use glucose as their main carbon source and have exposure only to low concentrations of extracellular acetate. We have shown that histone acetylation in mammalian cells is dependent on adenosine triphosphate (ATP)-citrate lyase (ACL), the enzyme that converts glucose-derived citrate into acetyl-CoA. We found that ACL is required for increases in histone acetylation in response to growth factor stimulation and during differentiation, and that glucose availability can affect histone acetylation in an ACL-dependent manner. Together, these findings suggest that ACL activity is required to link growth factor-induced increases in nutrient metabolism to the regulation of histone acetylation and gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.