Acetylation Of Transcription Factors Research Articles

Glycolysis mediates neuron specific histone acetylation in valproic acid-induced human excitatory neuron differentiation.

Pregnancy exposure of valproic acid (VPA) is widely adopted as a model of environmental factor induced autism spectrum disorder (ASD). Increase of excitatory/inhibitory synaptic transmission ratio has been proposed as the mechanism of VPA induced ASD. How this happened, particularly at the level of excitatory neuron differentiation in human neural progenitor cells (NPCs) remains largely unclear. Here, we report that VPA exposure remarkably inhibited human NPC proliferation and induced excitatory neuronal differentiation without affecting inhibitory neurons. Following VPA treatment, mitochondrial dysfunction was observed before neuronal differentiation, as showed by ultrastructural changes, respiratory complex activity, mitochondrial membrane potential and oxidation levels. Meanwhile, extracellular acidification assay revealed an elevation of glycolysis by VPA stimulation. Interestingly, inhibiting glycolysis by 2-deoxy-d-glucose-6-phosphate (2-DG) efficiently blocked the excitatory neuronal differentiation of human NPCs induced by VPA. Furthermore, 2-DG treatment significantly compromised the VPA-induced expression of H3ac and H3K9ac, and the VPA-induced binding of H3K9ac on the promoter of Ngn2 and Mash1, two key transcription factors of excitatory neuron fate determination. These data, for the first time, demonstrated that VPA biased excitatory neuron differentiation by glycolysis-mediated histone acetylation of neuron specific transcription factors.

In This Issue

Patients with B-lymphoid malignancies are at increased risk of severe COVID-19, but the impact of antineoplastic therapies on COVID-19 outcomes in this population is uncertain. Here Rubinstein et al. compare the outcomes of COVID-19 infection among 995 patients with B-lymphoid malignancies and multiple control populations of patients with cancer. The cohort size enables distinguishing contributions of lymphoid malignancy and of antineoplastic therapy, with adjustment for important prognostic factors. The results indicate that patients recently treated for B-lymphoid malignancies are at increased risk of severe COVID-19.See article, p. 181.Genomic characterization of pediatric acute myeloid leukemia (AML) at relapse identified recurrent somatic tandem duplications of exon 13 of UBTF (upstream binding transcription factor) in nearly 10% of cases. These UBTF tandem duplication (TD) AMLs are associated with adolescence, FLT3 and WT1 cooperating mutations, yet do not occur with other known driver alterations. Extension into additional datasets demonstrates that UBTF-TDs are rare in adults and present in approximately 4% of children with AML at diagnosis. These UBTF-TD AMLs are associated with poor outcome and high rates of minimal residual disease positivity. Collectively, these findings suggest that UBTF-TD represents a new subtype of pediatric AML.See article, p. 194.Bulk DNA sequencing can identify a pool of mutations within a sample. With serial sampling of the same tumor, one can infer clonal evolution: which mutations likely cooccur in the same subclones and how the subclonal frequencies change through time, space, or lineage differentiation. The complex and noisy nature of bulk genomic sequencing data requires considerable computational resources to reconstruct clonal evolution, limiting applications to high-throughput and high-resolution datasets. Wintersinger et al. developed Pairtree, a computational method for building clonal evolution trees from deeply sampled cancer to construct much more detailed and accurate trees than previously possible. In B-cell leukemias, Pairtree used up to 90 samples per cancer to reveal up to 26 distinct cell populations. Increasing data complexity impairs performance of the existing algorithms, whereas Pairtree performs stably and with increased accuracy.See article, p. 208.DNMT3A mutations are recurrent in hematopoietic malignancies and in clonal hematopoiesis (CH), a preneoplastic state characterized by asymptomatic expansion of mutant hematopoietic stem and progenitor cells (HSPC). The expansion is explained by increased competitive fitness of mutant HSPC under specific selection pressure, such as Dnmt3a-mutant HSPC in IFNγ-driven emergency hematopoiesis. However, molecular and functional underpinnings of competitive fitness in CH remain uncharacterized. Zhang et al. identify the Dnmt3a–Txnip–p53–p21 axis as a molecular mechanism of Dnmt3a-mutant clonal advantage. Specifically, activation of this axis boosts quiescence and survival of Dnmt3a-mutant HSPC relative to their wild-type counterparts during IFNγ challenge, enabling the mutant HSPC to prevail.See article, p. 220.ZNF384 fusion oncoproteins define a subtype of lineage ambiguous leukemia. In this article, Dickerson et al. utilize mouse and human models of ZNF384-rearranged leukemia to investigate the mechanisms of leukemogenesis. They show that expression of ZNF384 fusions in mouse and human progenitors skews hematopoietic development and drives lineage aberrancy, and cooccurring Ras mutations promote development of leukemia. This is accompanied by histone acetylation and deregulation of core hematopoietic transcription factors. In addition, ZNF384-fusion leukemia exhibits overexpression of FLT3 with sensitivity to FLT3 inhibition in xenograft models, providing a therapeutic approach in this high-risk subtype of leukemia.See article, p. 240.

The Role of Post-Translational Acetylation and Deacetylation of Signaling Proteins and Transcription Factors after Cerebral Ischemia: Facts and Hypotheses

Histone deacetylase (HDAC) and histone acetyltransferase (HAT) regulate transcription and the most important functions of cells by acetylating/deacetylating histones and non-histone proteins. These proteins are involved in cell survival and death, replication, DNA repair, the cell cycle, and cell responses to stress and aging. HDAC/HAT balance in cells affects gene expression and cell signaling. There are very few studies on the effects of stroke on non-histone protein acetylation/deacetylation in brain cells. HDAC inhibitors have been shown to be effective in protecting the brain from ischemic damage. However, the role of different HDAC isoforms in the survival and death of brain cells after stroke is still controversial. HAT/HDAC activity depends on the acetylation site and the acetylation/deacetylation of the main proteins (c-Myc, E2F1, p53, ERK1/2, Akt) considered in this review, that are involved in the regulation of cell fate decisions. Our review aims to analyze the possible role of the acetylation/deacetylation of transcription factors and signaling proteins involved in the regulation of survival and death in cerebral ischemia.

Inhibition of p300 by Garcinol Protects against Cisplatin-Induced Acute Kidney Injury through Suppression of Oxidative Stress, Inflammation, and Tubular Cell Death in Mice.

Emerging evidence suggests that epigenetic mechanisms such as histone modification are crucially involved in the pathophysiology of acute kidney injury (AKI). The histone acetyltransferase p300 regulates several biological processes through the acetylation of histones or transcription factors. However, the role of p300 in cisplatin-induced AKI remains poorly understood. Therefore, we investigated the effects of garcinol, a potent p300 inhibitor, on cisplatin-induced AKI and explored the mechanisms. Administration of garcinol significantly reversed the upregulation of p300 and increased acetylation of histone H3, along with amelioration of renal dysfunction and histopathological injury in the kidneys of cisplatin-injected mice. Garcinol also attenuated oxidative stress and reduced expression of pro-oxidant enzymes. In addition, garcinol reduced the elevated production of cytokines and chemokines and suppressed immune cell accumulation together with downregulation of vascular adhesion molecules. These beneficial effects of garcinol were associated with a reduction in acetylation of the p65 subunit of nuclear factor kappa-B. Further, garcinol significantly inhibited apoptosis and caspase-3 activation, with a decrease in p53 acetylation in cisplatin-injected mice. Taken together, we demonstrated that the inhibition of p300 by garcinol ameliorated cisplatin-induced renal injury, presumably through epigenetic mechanisms. These results suggest that garcinol might be a potential preventive agent for cisplatin-induced AKI.

Tuning Transcription Factor Availability through Acetylation-Mediated Genomic Redistribution

SummaryIt is widely assumed that decreasing transcription factor DNA-binding affinity reduces transcription initiation by diminishing occupancy of sequence-specific regulatory elements. However, in vivo transcription factors find their binding sites while confronted with a large excess of low-affinity degenerate motifs. Here, using the melanoma lineage survival oncogene MITF as a model, we show that low-affinity binding sites act as a competitive reservoir in vivo from which transcription factors are released by mitogen-activated protein kinase (MAPK)-stimulated acetylation to promote increased occupancy of their regulatory elements. Consequently, a low-DNA-binding-affinity acetylation-mimetic MITF mutation supports melanocyte development and drives tumorigenesis, whereas a high-affinity non-acetylatable mutant does not. The results reveal a paradoxical acetylation-mediated molecular clutch that tunes transcription factor availability via genome-wide redistribution and couples BRAF to tumorigenesis. Our results further suggest that p300/CREB-binding protein-mediated transcription factor acetylation may represent a common mechanism to control transcription factor availability.

Deficiency of ATP-citrate lyase (ACLY) in chondrocytes limits cartilage damage induced by obesity via high-fat diet in mice

Purpose: ATP-citrate lyase (ACLY) is an enzyme located in the cytosol and nucleus that generates acetyl-CoA from mitochondrial-derived citrate. Altered ACLY activity is observed in metabolic disorders, and several core features of metabolic syndrome such as dyslipidemia, obesity and insulin resistance have been linked to OA. Our recent study revealed that ACLY is upregulated in human knee OA chondrocytes. This could cause accumulation of nucleocytosolic acetyl-CoA, leading to increased matrix catabolism via dysregulated histone and transcription factor acetylation.

PGRN exerts inflammatory effects via SIRT1-NF-κB in adipose insulin resistance

Progranulin (PGRN), a multifunctional protein implicated in embryonic development and immune response, was recently introduced as a novel marker of chronic inflammation related with insulin resistance in obesity and type 2 diabetes mellitus. However, the potential mechanisms of PGRN on insulin signaling pathways are poorly understood. In this study, PGRN mediated the chemotaxis of RAW264.7, impaired insulin action and stimulated production of inflammatory factors in adipocytes, which was accompanied by increased c-Jun N-terminal kinase (JNK) activation and serine phosphorylation of insulin receptor substrate-1. PGRN knockdown partially led to an increase in insulin action as well as a decrease in the JNK activation and extracellular signal-regulated kinase phosphorylation in cells exposed to tumor-necrosis factor-α (TNF-α). Meanwhile, PGRN treatment resulted in an elevation of transcription factor nuclear factor κB (NF-κB) nuclear translocation and acetylation, and increased Il-1b, Il6, Tnf-a expression, whereas NF-κB inhibition reversed PGRN-induced insulin action impairment and inflammatory gene expression. Finally, we showed that sirtuin 1 (SIRT1) expression was downregulated by PGRN treatment, whereas SIRT1 overexpression improved PGRN-induced insulin resistance, NF-κB activation, and inflammatory gene expression. Our results suggest that PGRN regulates adipose tissue inflammation possibly by controlling the gain of proinflammatory transcription in a SIRT1-NF-κB dependent manner in response to inducers such as fatty acids and endoplasmic reticulum stress.

Ky-2, a hybrid compound histone deacetylase inhibitor, regulated inflammatory response in LPS-driven human macrophages.

Histone deacetylase has attracted much attention as an epigenetic factor, and the modulation of histone and transcription factor acetylation status is important for regulating gene expression. Moreover, histone deacetylase inhibitors are involved in cellular growth and differentiation. In the present study, we examined the effects of Ky-2, a hybrid-compound HDAC inhibitor, on inflammatory reactions and the polarization of macrophages in vitro. Human monocyte-like THP-1 cells were polarized to macrophage-like cells using phorbol 12-myristate 13-acetate, and then polarized to M1 macrophages with LPS. Ky-2 inhibited HDAC2 expression and enhanced the acetylation of histone H3 in THP-1 cells. It also downregulated the expression of the IL-1β-encoding gene and the LPS-induced phosphorylation of p38 mitogen-activated protein kinases in THP-1 cells. Moreover, the expression of nod-like receptor protein 3 and cleaved caspase-1 p20 was downregulated in Ky-2-treated THP-1 cells. In contrast, this agent upregulated the expression of IL-1ra in LPS-treated THP-1 cells. These results indicate that Ky-2-treatment downregulates the expression of the inflammatory cytokine, IL-1β, in LPS-treated THP-1 cells, suggesting that Ky-2 might regulate M1 macrophage polarization through the suppression of inflammatory responses such as NLRP3 inflammasome activation.

Modulation of matrix metabolism by ATP-citrate lyase in articular chondrocytes

Certain dysregulated chondrocyte metabolic adaptive responses such as decreased activity of the master regulator of energy metabolism AMP-activated protein kinase (AMPK) promote osteoarthritis (OA). Metabolism intersects with epigenetic and transcriptional responses. Hence, we studied chondrocyte ATP-citrate lyase (ACLY), which generates acetyl-CoA from mitochondrial-derived citrate, and modulates acetylation of histones and transcription factors. We assessed ACLY in normal and OA human knee chondrocytes and cartilages by Western blotting and immunohistochemistry, and quantified acetyl-CoA fluorometrically. We examined histone and transcription factor lysine acetylation by Western blotting, and assessed histone H3K9 and H3K27 occupancy of iNOS, MMP3, and MMP13 promoters by chromatin immunoprecipitation (ChIP) and quantitative PCR (qPCR). We analyzed iNOS, MMP3, MMP13, aggrecan (ACAN), and Col2a1 gene expression by RT-qPCR. Glucose availability regulated ACLY expression and function, nucleocytosolic acetyl-CoA, and histone acetylation. Human knee OA chondrocytes exhibited increased ACLY activation (assessed by Ser-455 phosphorylation), associated with increased H3K9 and H3K27 acetylation. Inhibition of ACLY attenuated IL-1β-induced transcription of iNOS, MMP3, and MMP13 by suppressing acetylation of p65 NF-κB, H3K9, and H3K27, blunted release of NO, MMP3, and MMP13, and also reduced SOX9 acetylation that promoted SOX9 nuclear translocation, leading to increased aggrecan and Col2a1 mRNA expression. ACLY is a novel player involved in regulation of cartilage matrix metabolism. Increased ACLY activity in OA chondrocytes increased nucleocytosolic acetyl-CoA, leading to increased matrix catabolism via dysregulated histone and transcription factor acetylation. Pharmacologic ACLY inhibition in OA chondrocytes globally reverses these changes and stimulates matrix gene expression and AMPK activation, supporting translational investigation in OA.

Acetyl-CoA Carboxylase 1-Dependent Protein Acetylation Controls Breast Cancer Metastasis and Recurrence

Breast tumor recurrence and metastasis represent the main causes of cancer-related death in women, and treatments are still lacking. Here, we define thelipogenic enzyme acetyl-CoA carboxylase (ACC) 1 as a key player in breast cancer metastasis. ACC1 phosphorylation was increased in invading cells both in murine and human breast cancer, serving as a point of convergence for leptin and transforming growth factor (TGF) β signaling. ACC1 phosphorylation was mediated by TGFβ-activated kinase (TAK)1, and ACC1 inhibition was indispensable for the elevation of cellular acetyl-CoA, the subsequent increase in Smad2 transcription factor acetylation and activation, and ultimately epithelial-mesenchymal transition and metastasis induction. ACC1 deficiency worsened tumor recurrence upon primary tumor resection in mice, and ACC1 phosphorylation levels correlated with metastatic potential in breast and lung cancer patients. Given the demonstrated effectiveness of anti-leptin receptor antibody treatment in halting ACC1-dependent tumor invasiveness, our work defines a "metabolocentric" approach in metastatic breast cancer therapy.

Role of Phosphorylated HDAC4 in Stroke-Induced Angiogenesis

Acetylation or deacetylation of chromatin proteins and transcription factors is part of a complex signaling system that is involved in the control of neurological disorders. Recent studies have demonstrated that histone deacetylases (HDACs) exert protective effects in attenuating neuronal injury after ischemic insults. Class IIa HDAC4 is highly expressed in the brain, and neuronal activity depends on the nucleocytoplasmic shuttling of HDAC4. However, little is known about HDAC4 and its roles in ischemic stroke. In this study, we report that phosphorylation of HDAC4 was remarkably upregulated after stroke and blockade of HDAC4 phosphorylation with GÖ6976 repressed stroke-induced angiogenesis. Phosphorylation of HDAC4 was also increased in endothelial cells hypoxia model and suppression of HDAC4 phosphorylation inhibited the tube formation and migration of endothelial cells in vitro. Furthermore, in addition to the inhibition of angiogenesis, blockade of HDAC4 phosphorylation suppressed the expression of genes downstream of HIF-VEGF signaling in vitro and in vivo. These data indicate that phosphorylated HDAC4 may serve as an important regulator in stroke-induced angiogenesis. The protective mechanism of phosphorylated HDAC4 is associated with HIF-VEGF signaling, implicating a novel therapeutic target in stroke.

From HDACi to KDACi: we need to revisit non-epigenetic pathways affected by inhibiting lysine deacetylases in therapy.

Various human maladies during aging are associated with substantial transcriptomic deregulation. Such widespread alterations of gene expression are thought to be mediated, at least partially, by changes in histone modifications. Large amount of data suggest that changes in histone acetylation levels are associated with severe diseases as well as aging [1]. Drugs that target and reverse the deregulated histone acetylation sites have therefore attracted considerable attention in recent years as an efficient approach for epigenetic therapy [1], [2]. Indeed, previous studies suggested that administrating histone deacetylase inhibitors could serve as a therapeutic avenue in age‐associated maladies by transcriptional reprogramming [ …

Abstract 825: Myc-nick promotes efferocytosis through M2 macrophage polarization

Abstract Resolution of inflammation is an active process which is important for maintaining or restoring homeostasis in response to inflammatory insult. Failure in resolution results in persistent and chronic inflammation which increases the risk of cancer development. Efferocytosis, an essential part of resolution of inflammation, is defined as phagocytic removal of apoptotic cells, especially neutrophils, at the inflamed site, thereby preventing exposure of tissue to toxic intracellular components. It is carried out by a distinct group of phagocytes including anti-inflammatory macrophages (M2 type). Therefore, M2 macrophages represent a key component of the cellular proresolving mechanism and a potential factor for prevention of inflammation-associated cancer. Dysregulation, often overexpression, of c-Myc drives dedifferentiation of cancer cells to acquire capacity for self-renewal and metastasis, which accounts for poor prognosis in cancer patients. A cytoplasmic N-terminal part of full length c-Myc, termed Myc-nick, has been reported to promote differentiation of myoblasts. In the present study, we investigated whether Myc-nick is involved in M2 macrophage polarization and promotion of efferocytosis. We found that ectopic expression of Myc-nick in mouse bone marrow derived macrophages (BMDM) promoted the M2 macrophage polarization through upregulation of interleukin 10 (IL-10) and peroxisome proliferator activated receptor gamma (PPARγ). Furthermore, overexpression of exogenous Myc-nick in BMDM increased capture of apoptotic cells by BMDM through upregulation of a class of phosphatidyl serine (PS) receptors including T-cell immunoglobulin and mucin domain containing 4 (Timd4). PS constitutes one of ‘eat-me’ signals carried by apoptotic cells. PS receptors present on the surface of macrophages are important to recognize, engulf and finally clear apoptotic cells via phagocytosis. In addition, Myc-nick-induced efferocytosis was found to be tightly associated with K (lysine) acetyltransferase 2A (Kat2a/Gcn5). This may lead to the acetylation of transcription factors that regulate expression of PS receptor proteins. In conclusion, activation of M2 macrophages by Myc-nick facilitates efferocytosis and hence resolution of inflammation, and this may suppress inflammation-associated cancer progression. Citation Format: Xiancai Zhong, Ha-Na Lee, Young-Joon Surh. Myc-nick promotes efferocytosis through M2 macrophage polarization. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 825.

Different functions of the histone acetyltransferase HAC1 gene traced in the model species Medicago truncatula, Lotus japonicus and Arabidopsis thaliana.

In eukaryotes, histone acetyltransferases regulate the acetylation of histones and transcription factors, affecting chromatin structural organization, transcriptional regulation, and gene activation. To assess the role of HAC1, a gene encoding for a histone acetyltransferase in Medicago truncatula, stable transgenic lines with modified HAC1 expression in the model plants M. truncatula, Lotus japonicus, and Arabidopsis thaliana were generated by Agrobacterium-mediated transformation and used for functional analyses. Histochemical, transcriptional, flow cytometric, and morphological analyses demonstrated the involvement of HAC1 in plant growth and development, responses to internal stimuli, and cell cycle progression. Expression patterns of a reporter gene encoding beta-glucuronidase (GUS) fused to the HAC1 promoter sequence were associated with young tissues comprised of actively dividing cells in different plant organs. The green fluorescent protein (GFP) signal, driven by the HAC1 promoter, was detected in the nuclei and cytoplasm of root cells. Transgenic lines with HAC1 overexpression and knockdown showed a wide range of phenotypic deviations and developmental abnormalities, which provided lines of evidence for the role of HAC1 in plant development. Synchronization of A. thaliana root tips in a line with HAC1 knockdown showed the involvement of this gene in the acetylation of two core histones during S phase of the plant cell cycle.

Role of transcription factor acetylation in the regulation of metabolic homeostasis.

Post-translational modifications (PTMs) of transcription factors play a crucial role in regulating metabolic homeostasis. These modifications include phosphorylation, methylation, acetylation, ubiquitination, SUMOylation, and O-GlcNAcylation. Recent studies have shed light on the importance of lysine acetylation at nonhistone proteins including transcription factors. Acetylation of transcription factors affects subcellular distribution, DNA affinity, stability, transcriptional activity, and current investigations are aiming to further expand our understanding of the role of lysine acetylation of transcription factors. In this review, we summarize recent studies that provide new insights into the role of protein lysine-acetylation in the transcriptional regulation of metabolic homeostasis.

Mutagenesis Study Reveals the Rim of Catalytic Entry Site of HDAC4 and -5 as the Major Binding Surface of SMRT Corepressor.

Histone deacetylases (HDACs) play a pivotal role in eukaryotic gene expression by modulating the levels of acetylation of chromatin and related transcription factors. In contrast to class I HDACs (HDAC1, -2, -3 and -8), the class IIa HDACs (HDAC4, -5, -7 and -9) harbor cryptic deacetylases activity and recruit the SMRT-HDAC3 complex to repress target genes in vivo. In this regard, the specific interaction between the HDAC domain of class IIa HDACs and the C-terminal region of SMRT repression domain 3 (SRD3c) is known to be critical, but the molecular basis of this interaction has not yet been addressed. Here, we used an extensive mutant screening system, named the “partitioned one- plus two-hybrid system”, to isolate SRD3c interaction-defective (SRID) mutants over the entire catalytic domains of HDAC4 (HDAC4c) and -5. The surface presentation of the SRID mutations on the HDAC4c structure revealed that most of the mutations were mapped to the rim surface of the catalytic entry site, strongly suggesting this mutational hot-spot region as the major binding surface of SRD3c. Notably, among the HDAC4c surface residues required for SRD3c binding, some residues (C667, C669, C751, D759, T760 and F871) are present only in class IIa HDACs, providing the molecular basis for the specific interactions between SRD3c and class IIa enzymes. To investigate the functional consequence of SRID mutation, the in vitro HDAC activities of HDAC4 mutants immuno-purified from HEK293 cells were measured. The levels of HDAC activity of the HDAC4c mutants were substantially decreased compared to wild-type. Consistent with this, SRID mutations of HDAC4c prevented the association of HDAC4c with the SMRT-HDAC3 complex in vivo. Our findings may provide structural insight into the binding interface of HDAC4 and -5 with SRD3c, as a novel target to design modulators specific to these enzymes.

Comparative Study between Valproic Acid Combined with Conventional Chemotherapy Versus Conventional Chemotherapy Alone in Egyptian Acute Myeloid Leukemia Patients

It has been postulated that inhibition of Histone Deacetylase (HDAC) can restore normal acetylation of histone proteins and transcription factors, and to be of benefit in the treatment of cancer. So, this study aimed at assessing the response to histone deacetylase inhibitor valproic acid combined with conventional chemotherapy versus conventional chemotherapy alone in Egyptian Acute Myeloid Leukemia (AML) patients. Thirty newly diagnosed AML patients were divided into 2 groups. Group 1 consisted of 15 AML patients received conventional chemotherapy while group 2 consisted of 15 AML patients received valproic acid 40 mg/kg for 7 days and conventional chemotherapy. Ten healthy persons of matched age and sex were considered group 3 (controls). Serum histone deacetylase activity, vascular endothelial growth factor, basic fibroblast growth factor, tumor necrosis factor α, glutathione S transferase and nuclear factor κB in nuclear extract before and after chemotherapy were measured in all patients and controls. Results revealed better clinical response with no side effects with valproic acid than conventional chemotherapy alone (p=0.021). This was associated with statistically significant decrease in histone deacetylase activity in patients receiving valproic acid compared to the other AML group (p=0.00019). There was significant negative correlation between age and HDAC activity at initial presentation in patients receiving valproic acid (p=0.039) while no significant correlation was detected with the other studied laboratory parameters. Our results revealed that valproic acid in the tested dose was safe and associated with better therapeutic response when used in combination with conventional chemotherapy.

Role of Transcription Factor Acetylation in Diabetic Kidney Disease

Nuclear factor (NF)-κB and signal transducer and activator of transcription 3 (STAT3) play a critical role in diabetic nephropathy (DN). Sirtuin-1 (SIRT1) regulates transcriptional activation of target genes through protein deacetylation. Here, we determined the roles of Sirt1 and the effect of NF-κB (p65) and STAT3 acetylation in DN. We found that acetylation of p65 and STAT3 was increased in both mouse and human diabetic kidneys. In human podocytes, advanced glycation end products (AGEs) induced p65 and STAT3 acetylation and overexpression of acetylation-incompetent mutants of p65 and STAT3 abrogated AGE-induced expression of NF-κB and STAT3 target genes. Inhibition of AGE formation in db/db mice by pyridoxamine treatment attenuated proteinuria and podocyte injury, restored SIRT1 expression, and reduced p65 and STAT3 acetylation. Diabetic db/db mice with conditional deletion of SIRT1 in podocytes developed more proteinuria, kidney injury, and acetylation of p65 and STAT3 compared with db/db mice without SIRT1 deletion. Treatment of db/db mice with a bromodomain and extraterminal (BET)-specific bromodomain inhibitor (MS417) which blocks acetylation-mediated association of p65 and STAT3 with BET proteins, attenuated proteinuria, and kidney injury. Our findings strongly support a critical role for p65 and STAT3 acetylation in DN. Targeting protein acetylation could be a potential new therapy for DN.

Anti-Epileptic Drug Targets Ewing Sarcoma.

Ewing Sarcoma (ES) is a rare form of bone cancer that most commonly affects children and adolescents. Chromosomal translocations are fundamental to the development of Ewing Sarcoma, linked to the changes in gene expression affecting transcription factors. Histone acetyl transferases (HATs) and histone deacetylases (HDACs) regulate transcription by modifying acetylation of both histones and transcription factors. Despite the use of multimodal therapeutic approaches current therapies are associated with significant short and long-term side effects. Hence, new therapeutic approaches are needed. In this study, we show that ERG/EWS-ERG, inhibits transcriptional activation properties of RXRα. These results suggest that ERG/EWS-ERG/EWS-Fli-1 may target transcriptional co-activators and transcriptional repressors and thereby regulate RXRα transcriptional activity. To understand the molecular mechanism of action, how the fusion protein targets nuclear receptor function, and to provide a clue for the cancer health disparity seen in Ewing Sarcoma, we hypothesized that the aberrant fusion protein, EWS-ERG/EWS-Fli-1 regulates HDACs-mediated repressor complex and inhibits the binding of transcriptional activator complex causing transcriptional repression of RXRα activity. Since it is known that HDACs regulate nuclear receptors, we proposed that HDAC inhibitor, valproic acid (VPA), an anti-epileptic drug, may reverse the inhibitory properties of EWS-ERG/EWS-Fli-1 oncoprotein on RXRα transcriptional activity and might therefore be used as therapeutic agent in ES. We demonstrate that VPA reverses the inhibitory effect of EWSERG/EWS-Fli-1 on RXRα transcriptional activity and also inhibits the cell growth. Furthermore, VPA induces apoptosis and restored the expression of RXRα target genes RARβ, CRABPII and p21 activity and repressed the expression of aberrant fusion proteins, EWS-ERG and EWS-Fli-1 in Ewing Sarcoma cells. Thus, therapeutic regulation of transcriptional repressor properties of EWS-ERG/EWS-Fli-1 with an anti-epileptic drug with a promising new potential might have a profound impact on prevention, management and treatment of Ewing Sarcoma. Therapeutic use of VPA in minority patients may help reduce the health disparity.

Mechanisms of Histone Deacetylase Inhibitor-Regulated Gene Expression in Cancer Cells

Class I and II histone deacetylase inhibitors (HDACis) are approved for the treatment of cutaneous T-cell lymphoma and are undergoing clinical trials as single agents, and in combination, for other hematological and solid tumors. Understanding their mechanisms of action is essential for their more effective clinical use, and broadening their clinical potential. HDACi induce extensive transcriptional changes in tumor cells by activating and repressing similar numbers of genes. These transcriptional changes mediate, at least in part, HDACi-mediated growth inhibition, apoptosis, and differentiation. Here, we highlight two fundamental mechanisms by which HDACi regulate gene expression—histone and transcription factor acetylation. We also review the transcriptional responses invoked by HDACi, and compare these effects within and across tumor types. The mechanistic basis for how HDACi activate, and in particular repress gene expression, is not well understood. In addition, whether subsets of genes are reproducibly regulated by these agents both within and across tumor types has not been systematically addressed. A detailed understanding of the transcriptional changes elicited by HDACi in various tumor types, and the mechanistic basis for these effects, may provide insights into the specificity of these drugs for transformed cells and specific tumor types. Understanding the mechanisms by which HDACi regulate gene expression and an appreciation of their transcriptional targets could facilitate the ongoing clinical development of these emerging therapeutics. In particular, this knowledge could inform the design of rational drug combinations involving HDACi, and facilitate the identification of mechanism-based biomarkers of response.