Knockdown Of GCN5 Research Articles

H3K14ac facilitates the reinstallation of constitutive heterochromatin in Drosophila early embryos by engaging Eggless/SetDB1

Constitutive heterochromatin, a fundamental feature of eukaryotic nucleus essential for transposon silencing and genome stability, is rebuilt on various types of repetitive DNA in the zygotic genome during early embryogenesis. However, the molecular program underlying this process remains poorly understood. Here, we show that histone H3 lysine 14 acetylation (H3K14ac) is engaged in the reinstallation of constitutive heterochromatin in Drosophila early embryos. H3K14ac partially colocalizes with H3 lysine 9 trimethylation (H3K9me3) and its methyltransferase Eggless/SetDB1 around the mid-blastula transition. Concealing H3K14ac by either antibody injection or maternal knockdown of Gcn5 diminishes Eggless/SetDB1 nuclear foci and reduces the deposition of H3K9me3. Structural analysis reveals that Eggless/SetDB1 recognizes H3K14ac via its tandem Tudor domains, and disrupting the binding interface causes defects in Eggless/SetDB1 distribution and derepression of a subset of transposons. Therefore, H3K14ac, a histone modification normally associated with active transcription, is a crucial component of the early embryonic machinery that introduces constitutive heterochromatic features to the newly formed zygotic genome.

Inhibition of ACLY Leads to Suppression of Osteoclast Differentiation and Function Via Regulation of Histone Acetylation.

ATP-citrate lyase (ACLY), generating most of the nucleocytosolic acetyl coenzyme A (acetyl-CoA) for histone acetylation, links cell metabolism to epigenetic regulation. Recent investigations demonstrated that ACLY activated by metabolic reprogramming played an essential role in both M1 and M2 macrophage activation via histone acetylation. Previous studies also revealed that histone methylation and acetylation were critical for transcriptional regulation of osteoclast-specific genes. Considering that osteoclast differentiation also undergoes metabolic reprogramming and the activity of ACLY is always Akt-dependent, we inferred that receptor activator of NF-κB (RANK) activation might enhance the activity of ACLY through downstream pathways and ACLY might play a role in osteoclast formation. In the current study, we found that ACLY was gradually activated during RANK ligand (RANKL)-induced osteoclast differentiation from bone marrow-derived macrophages (BMMs). Both ACLY knock-down and small molecular ACLY inhibitor BMS-303141 significantly decreased nucleocytosolic acetyl-CoA in BMMs and osteoclasts and suppressed osteoclast formation in vitro. BMS-303141 also suppressed osteoclast formation in vivo and prevents ovariectomy (OVX)-induced bone loss. Further investigations showed that RANKL triggered ACLY translocation into nucleus, consistent with increasing histone H3 acetylation, which was correlated to ACLY. The H3 lysine residues influenced by ACLY were in accordance with GCN5 targets. Using GCN5 knock-down and overexpression, we showed that ACLY and GCN5 functioned in the same pathway for histone H3 acetylation. Analysis of pathways downstream of RANK activation revealed that ACLY was Akt-dependent and predominately affected Akt pathway. With the help of RNA-sequencing, we discovered Rac1 as a downstream regulator of ACLY, which was involved in shACLY-mediated suppression of osteoclast differentiation, cytoskeleton organization, and signal transduction and was transcriptionally regulated by ACLY via histone H3 acetylation. To summarize, our results proved that inhibition of ATP-citrate lyase led to suppression of osteoclast differentiation and function via regulation of histone acetylation. Rac1 could be a downstream regulator of ACLY. © 2021 American Society for Bone and Mineral Research (ASBMR).

Function of GCN5 in the TGF-β1-induced epithelial-to-mesenchymal transition in breast cancer.

Histone acetyltransferase GCN5 is a critical component of the TGF-β/Smad signaling pathway in breast cancer cells; however, it remains unknown whether it is involved in the development and progression of breast cancer. The present study investigated the role of GCN5 in the induction of the EMT by TGF-β1 in breast cancer cells and its underlying molecular mechanism of action. GCN5 activity was elevated and GCN5 mRNA expression and protein expression were increased in MDA-MB231 cells following stimulation with TGF-β1. Furthermore, TGF-β1 stimulation decreased expression of the epithelial cell marker E-cadherin and increased expression of the mesenchymal cell markers, N-cadherin and vimentin, as well as the expression of other EMT markers, including snail and slug. However, these changes were reversed following GCN5 knockdown leading to the downregulation of GCN5 expression. GCN5 knockdown also inhibited the viability, migration and invasion of MDA-MB231 cells, decreased the expression of p-STAT3, p-AKT, MMP9 and E2F1, and increased the expression of p21 in MDA-MB231 cells compared with cells stimulated with TGF-β1 alone. Therefore, GCN5 may work downstream of TGF-β/Smad signaling pathway to regulate the EMT in breast cancer.

Differential Effects of Histone Acetyltransferase GCN5 or PCAF Knockdown on Urothelial Carcinoma Cells.

Disturbances in histone acetyltransferases (HATs) are common in cancers. In urothelial carcinoma (UC), p300 and CBP are often mutated, whereas the GNAT family HATs GCN5 and PCAF (General Control Nonderepressible 5, p300/CBP-Associated Factor) are often upregulated. Here, we explored the effects of specific siRNA-mediated knockdown of GCN5, PCAF or both in four UC cell lines (UCCs). Expression of various HATs and marker proteins was measured by qRT-PCR and western blot. Cellular effects of knockdowns were analyzed by flow cytometry and ATP-, caspase-, and colony forming-assays. GCN5 was regularly upregulated in UCCs, whereas PCAF was variable. Knockdown of GCN5 or both GNATs, but not of PCAF alone, diminished viability and inhibited clonogenic growth in 2/4 UCCs, inducing cell cycle changes and caspase-3/7 activity. PCAF knockdown elicited GCN5 mRNA upregulation. Double knockdown increased c-MYC and MDM2 (Mouse Double Minute 2) in most cell lines. In conclusion, GCN5 upregulation is especially common in UCCs. GCN5 knockdown impeded growth of specific UCCs, whereas PCAF knockdown elicited minor effects. The limited sensitivity towards GNAT knockdown and its variation between the cell lines might be due to compensatory effects including HAT, c-MYC and MDM2 upregulation. Our results predict that developing drugs targeting individual HATs for UC treatment may be challenging.

GCN5 modulates osteogenic differentiation of periodontal ligament stem cells through DKK1 acetylation in inflammatory microenvironment.

Periodontal ligament stem cells (PDLSCs) from periodontitis patients showed defective osteogenic differentiation. However, the mechanism of impaired osteogenic differentiation of PDLSCs in inflammatory microenvironments is still unclear. In this study, we found that inflammation in the microenvironment resulted in downregulation of histone acetyltransferase GCN5 expression and lack of GCN5 caused decreased osteogenic differentiation of PDLSCs. Previous study showed activated Wnt/β-cateinin pathway of PDLSCs resulted in defective osteogenic differentiation. Here we found knockdown of GCN5 decreased the expression of DKK1, an inhibitor of Wnt/β-cateinin pathway, thus activated Wnt/β-catenin pathway of PDLSCs. Mechanistically, GCN5 regulated DKK1 expression by acetylation of Histone H3 lysine 9 (H3K9) and Histone H3 lysine 14 (H3K14) at its promoter region. Interestingly, we found that in vivo injection of aspirin rescued the periodontitis of rats through inhibiting inflammation and upregulating GCN5 expression. Furthermore, aspirin treatment of PDLSCs upregulated GCN5 expression and increased osteogenic differentiation of PDLSCs. In conclusion, GCN5 plays a protective role in periodontitis through acetylation of DKK1 and applying drugs targeting GCN5, such as aspirin, could be a new approach for periodontitis treatment.

Muscle Wasting in Fasting Requires Activation of NF-κB and Inhibition of AKT/Mechanistic Target of Rapamycin (mTOR) by the Protein Acetylase, GCN5

NF-κB is best known for its pro-inflammatory and anti-apoptotic actions, but in skeletal muscle, NF-κB activation is important for atrophy upon denervation or cancer. Here, we show that also upon fasting, NF-κB becomes activated in muscle and is critical for the subsequent atrophy. Following food deprivation, the expression and acetylation of the p65 of NF-κB on lysine 310 increase markedly in muscles. NF-κB inhibition in mouse muscles by overexpression of the IκBα superrepressor (IκBα-SR) or of p65 mutated at Lys-310 prevented atrophy. Knockdown of GCN5 with shRNA or a dominant-negative GCN5 or overexpression of SIRT1 decreased p65K310 acetylation and muscle wasting upon starvation. In addition to reducing atrogene expression, surprisingly inhibiting NF-κB with IκBα-SR or by GCN5 knockdown in these muscles also enhanced AKT and mechanistic target of rapamycin (mTOR) activities, which also contributed to the reduction in atrophy. These new roles of NF-κB and GCN5 in regulating muscle proteolysis and AKT/mTOR signaling suggest novel approaches to combat muscle wasting.

GCN5 Potentiates Glioma Proliferation and Invasion via STAT3 and AKT Signaling Pathways.

The general control of nucleotide synthesis 5 (GCN5), which is one kind of lysine acetyltransferases, regulates a number of cellular processes, such as cell proliferation, differentiation, cell cycle and DNA damage repair. However, its biological role in human glioma development remains elusive. In the present study, we firstly reported that GCN5 was frequently overexpressed in human glioma tissues and GCN5 was positively correlated with proliferation of cell nuclear antigen PCNA and matrix metallopeptidase MMP9. Meanwhile, down-regulation of GCN5 by siRNA interfering inhibited glioma cell proliferation and invasion. In addition, GCN5 knockdown reduced expression of p-STAT3, p-AKT, PCNA and MMP9 and increased the expression of p21 in glioma cells. In conclusion, GCN5 exhibited critical roles in glioma development by regulating cell proliferation and invasion, which suggested that GCN5 might be a potential molecular target for glioma treatment.

Gcn5 Modulates the Cellular Response to Oxidative Stress and Histone Deacetylase Inhibition.

To identify chemical genetic interactions underlying the mechanism of action of histone deacetylase inhibitors (HDACi) a yeast deletion library was screened for hypersensitive deletion mutants that confer increased sensitivity to the HDACi, CG-1521. The screen demonstrated that loss of GCN5 or deletion of components of the Gcn5 histone acetyltransferase (HAT) complex, SAGA, sensitizes yeast to CG-1521-induced cell death. Expression profiling after CG-1521 treatment reveals increased expression of genes involved in metabolism and oxidative stress response, and oxidative stress response mutants are hypersensitive to CG-1521 treatment. Accumulation of reactive oxygen species and increased cell death are enhanced in the gcn5Δ deletion mutant, and are abrogated by anti-oxidants, indicating a central role of oxidative stress in CG-1521-induced cell death. In human cell lines, siRNA mediated knockdown of GCN5 or PCAF, or chemical inhibition of GCN5 enzymatic activity, increases the sensitivity to CG-1521 and SAHA. These data suggest that the combination of HDAC and GCN5/PCAF inhibitors can be used for cancer treatment.

Abstract 427: Upregulation of KLF4 and inhibition of HDAC activity by methylseleninic acid in human esophageal squamous cells

Abstract In the present study, we investigated the potential mechanisms of the inhibition of cell growths induced by methylseleninic acid, MSA. Our result showed that MSA could induce cell growth inhibition and apoptosis in esophageal squamous cell carcinoma (ESCC) cells and inhibit tumor growth measured by xenograft volume in nude mice. Upon treated with MSA, HDACs activity was decreased and GCN5, one of histone acetyltransferases, upregulated as well in human esophageal squamous cell lines. Meanwhile a significant increase of H3K9 acetylation (H3K9ac) was detected. Notably,upregulation of KLF4, which has been wildly reported usually downregulated expression in cell lines and tumor tissues of ESCC, was also observed after MSA treatment. Additionally the acetylated histone H3 could locate more at KLF4 promoter region than non-acetylated one did, showed by chromatin immunoprecipitation assay. Moreover knockdown of GCN5 reduced the protein levels of both H3K9ac and KLF4, along with less cell growth inhibition. Taken all, our result indicates that MSA can exert its anti-tumor effects, at least in part, by up-regulation KLF4, probably via inhibiting the HDAC activity and up-regulation GCN5. By our best of knowledge, this is the first report of selenium-induced selective, post-translational acetylation of histone H3 at Lys9, which may depend on the activities of and the balance between HDACs and HATs. Note: This abstract was not presented at the meeting. Citation Format: Chenfei Hu, Wei Zhang, Qing Xu, Lechuang Chen, Kai Ma, Mei Liu, Hongxia Zhu, Ningzhi Xu. Upregulation of KLF4 and inhibition of HDAC activity by methylseleninic acid in human esophageal squamous cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 427. doi:10.1158/1538-7445.AM2014-427

GCN5-dependent acetylation of HIV-1 integrase enhances viral integration

BackgroundAn essential event during the replication cycle of HIV-1 is the integration of the reverse transcribed viral DNA into the host cellular genome. Our former report revealed that HIV-1 integrase (IN), the enzyme that catalyzes the integration reaction, is positively regulated by acetylation mediated by the histone acetyltransferase (HAT) p300.ResultsIn this study we demonstrate that another cellular HAT, GCN5, acetylates IN leading to enhanced 3'-end processing and strand transfer activities. GCN5 participates in the integration step of HIV-1 replication cycle as demonstrated by the reduced infectivity, due to inefficient provirus formation, in GCN5 knockdown cells. Within the C-terminal domain of IN, four lysines (K258, K264, K266, and K273) are targeted by GCN5 acetylation, three of which (K264, K266, and K273) are also modified by p300. Replication analysis of HIV-1 clones carrying substitutions at the IN lysines acetylated by both GCN5 and p300, or exclusively by GCN5, demonstrated that these residues are required for efficient viral integration. In addition, a comparative analysis of the replication efficiencies of the IN triple- and quadruple-mutant viruses revealed that even though the lysines targeted by both GCN5 and p300 are required for efficient virus integration, the residue exclusively modified by GCN5 (K258) does not affect this process.ConclusionsThe results presented here further demonstrate the relevance of IN post-translational modification by acetylation, which results from the catalytic activities of multiple HATs during the viral replication cycle. Finally, this study contributes to clarifying the recent debate raised on the role of IN acetylated lysines during HIV-1 infection.

GCN5-mediated Transcriptional Control of the Metabolic Coactivator PGC-1β through Lysine Acetylation

Changes in expression levels of genes encoding for proteins that control metabolic pathways are essential to maintain nutrient and energy homeostasis in individual cells as well as in organisms. An important regulated step in this process is accomplished through covalent chemical modifications of proteins that form complexes with the chromatin of gene promoters. The peroxisome proliferators gamma co-activator 1 (PGC-1) family of transcriptional co-activators comprises important components of a number of these complexes and participates in a large array of glucose and lipid metabolic adaptations. Here, we show that PGC-1beta is acetylated on at least 10 lysine residues distributed along the length of the protein by the acetyl transferase general control of amino-acid synthesis (GCN5) and that this acetylation reaction is reversed by the deacetylase sirtuin 1 (SIRT1). GCN5 strongly interacts with PGC-1beta and represses its transcriptional activity associated with transcription factors such as ERRalpha, NRF-1, and HNF4alpha, however acetylation and transcriptional repression do not occur when a catalytically inactive GCN5 is co-expressed. Transcriptional repression coincides with PGC-1beta redistribution to nuclear foci where it co-localizes with GCN5. Furthermore, knockdown of GCN5 ablates PGC-1beta acetylation and increases transcriptional activity. In primary skeletal muscle cells, PGC-1beta induction of endogenous target genes, including MCAD and GLUT4, is largely repressed by GCN5. Functionally, this translates to a blunted response to PGC-1beta-induced insulin-mediated glucose transport. These results suggest that PGC-1beta acetylation by GCN5 might be an important step in the control of glucose and lipid pathways and its dysregulation could contribute to metabolic diseases.