Histone deacetylase 8 regulates cortactin deacetylation and contraction in smooth muscle tissues

HDAC8 as a target in drug discovery: Function, structure and design

Histone deacetylases (HDACs) have emerged as prominent therapeutic targets in drug discovery. Among the members of the HDAC family, HDAC8 exhibits distinct structural and physiological features from other members of the class Ⅰ HDACs. In addition to histones, numerous non-histone substrates such as structural maintenance of chromosomes 3 (SMC3), p53, estrogen-related receptor alpha (ERRα), etc., have been identified for HDAC8, suggesting the involvement of HDAC8 in diverse biological processes. Studies have demonstrated that HDAC8 plays essential roles in certain disease development, e.g., acute myeloid leukemia (AML), neuroblastoma, and X-Linked disorders. Despite several HDAC8 inhibitors have been discovered, only one compound has progressed to clinical studies. Recently, novel strategies targeting HDAC8 have emerged, including identifying innovative zinc-chelating groups (ZBG), developing multi-target drugs, and HDAC8 PROTACs. This review aims to summarize recent progress in developing new HDAC8 inhibitors that incorporate novel strategies and provide an overview of the clinical improvements associated with HDAC8 inhibitors.

Targeting cytoskeletal biomechanics to modulate airway smooth muscle contraction in asthma

To contract, to deform, and remodel, the airway smooth muscle cell relies on dynamic changes in the structure of its mechanical force-bearing cytoskeleton. These alternate between a "fluid-like" (relaxed) state characterized by weak contractile protein-protein interactions within the cytoskeletal apparatus and a "solid-like" (contractile) state promoted by strong and highly organized molecular interactions. In this review, we discuss the roles for actin, myosin, factors promoting actin polymerization and depolymerization, adhesome complexes, and cell-cell junctions in these dynamic processes. We describe the relationship between these cytoskeletal factors, extracellular matrix components of bronchial tissue, and mechanical stretch and other changes within the airway wall in the context of the physical mechanisms of cytoskeletal fluidization-resolidification. We also highlight studies that emphasize the distinct processes of cell shortening and force transmission in airway smooth muscle and previously unrecognized roles for actin in cytoskeletal dynamics. Finally, we discuss the implications of these discoveries for understanding and treating airway obstruction in asthma.

Lysine deacetylase inhibitors have low selectivity in cells and exhibit predominantly off-target effects

Lysine deacetylases (KDACs or HDACs) are metal-dependent enzymes that regulate lysine acetylation, a post-translational modification that is present on thousands of human proteins, essential for many cellular processes, and often misregulated in diseases. The selective inhibition of KDACs would allow for understanding of the biological roles of individual KDACs and therapeutic targeting of individual enzymes. Recent studies have suggested that purportedly specific KDAC inhibitors have significant off-target binding, but the biological consequences of off-target binding were not evaluated. We compared the effects of treatment with two of the reportedly most KDAC-selective inhibitors, Tubastatin A and PCI-34051, in HT1080 cells in which the endogenous KDAC6 or KDAC8 gene has been mutated to inactivate enzyme catalysis while retaining enzyme expression. Genetic inactivation results in much stronger deacetylation defects on known targets compared to inhibitor treatment. Gene expression analysis revealed that both inhibitors have extensive and extensively overlapping off-target effects in cells, even at low inhibitor doses. Furthermore, Tubastatin A treatment led to increased histone acetylation, while inactivation of KDAC6 or KDAC8 did not. Genetic inactivation of KDAC6, but not KDAC8, impaired tumor formation in a xenograft model system, in contrast to previous reports with KDAC inhibitors suggesting the reverse. We conclude that the majority of observed biological effects of treatment with KDAC inhibitors are due to off-target effects rather than the intended KDAC inhibition. Developing a truly specific KDAC6 inhibitor could be a promising therapeutic avenue, but it is imperative to develop new inhibitors that selectively mimic genetic inactivation of individual KDACs.

Inhibition of HDAC8 mitigates AKI by reducing DNA damage and promoting homologous recombination repair

Nephrotoxicity is a major side effect of platinum-based antineoplastic drugs, and there is currently no available therapeutic intervention. Our study suggests that targeting histone deacetylase 8 could be a potential treatment for cisplatin-induced acute kidney injury (AKI). In a murine model of AKI induced by cisplatin, the administration of PCI-34051, a selective inhibitor of HDAC8, resulted in significant improvement in renal function and reduction in renal tubular damage and apoptosis. Pharmacological inhibition of HDAC8 also decreased caspase-3 and PARP1 cleavage, attenuated Bax expression and preserved Bcl-2 levels in the injured kidney. In cultured murine renal epithelial cells (mRTECs) exposed to cisplatin, treatment with PCI-34051 or transfection with HDAC8 siRNA reduced apoptotic cell numbers and diminished expression of cleaved caspase-3 and PARP1; conversely, overexpression of HDAC8 intensified these changes. Additionally, PCI-34051 reduced p53 expression levels along with those for p21, p-CDK2 and γ-H2AX while preserving MRE11 expression in the injured kidney. Similarly, pharmacological and genetic inhibition of HDAC8 reduced γ-H2AX and enhanced MRE11 expression; conversely, HDAC8 overexpression exacerbated these changes in mRTECs exposed to cisplatin. These results support that HDAC8 inhibition attenuates cisplatin-induced AKI through a mechanism associated with reducing DNA damage and promoting its repair.

Effects of Gene Alternative Splicing Events on Resistance to Cryptocaryonosis of Large Yellow Croaker (Larimichthys crocea)

Large yellow croaker (L. crocea) is a productive species in marine aquaculture with great economic value in China. However, the sustainable development of large yellow croaker is hampered by various diseases including cryptocaryonosis caused by Cryptocaryon irritans. The genetic regulation processes for cryptocaryonosis in large yellow croaker are still unclear. In this present study, we analyzed differential alternative splicing events between a C. irritans resistance strain (RS) and a commercial strain (CS). We identified 678 differential alternative splicing (DAS) events from 453 genes in RS and 719 DAS events from 500 genes in CS. A set of genes that are specifically alternatively spliced in RS was identified including mfap5, emp1, and trim33. Further pathway analysis revealed that the specifically alternative spliced genes in RS were involved in innate immune responses through the PRR pathway and the Toll and Imd pathway, suggesting their important roles in the genetic regulation processes for cryptocaryonosis in large yellow croaker. This study would be helpful for the studies of the pathogenesis of cryptocaryonosis and dissection of C. irritans resistance for L. crocea.

Zinc-Dependent Histone Deacetylases in Lung Endothelial Pathobiology

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and, as such, provides a semi-selective barrier between the blood and the interstitial space. Compromise of the lung EC barrier due to inflammatory or toxic events may result in pulmonary edema, which is a cardinal feature of acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS). The EC functions are controlled, at least in part, via epigenetic mechanisms mediated by histone deacetylases (HDACs). Zinc-dependent HDACs represent the largest group of HDACs and are activated by Zn2+. Members of this HDAC group are involved in epigenetic regulation primarily by modifying the structure of chromatin upon removal of acetyl groups from histones. In addition, they can deacetylate many non-histone histone proteins, including those located in extranuclear compartments. Recently, the therapeutic potential of inhibiting zinc-dependent HDACs for EC barrier preservation has gained momentum. However, the role of specific HDAC subtypes in EC barrier regulation remains largely unknown. This review aims to provide an update on the role of zinc-dependent HDACs in endothelial dysfunction and its related diseases. We will broadly focus on biological contributions, signaling pathways and transcriptional roles of HDACs in endothelial pathobiology associated mainly with lung diseases, and we will discuss the potential of their inhibitors for lung injury prevention.

Curcumin and PCI-34051 combined treatment ameliorates inflammation and fibrosis by affecting MAP kinase pathway

OBJECTIVE

Bronchoconstriction, along with inflammation and hyperresponsiveness is the characteristic feature associated with asthma, contributing to variable airflow obstruction, which manifests shortness of breath, cough and wheeze, etc. Histone deacetylases 8 (HDAC8) is the member of class I HDAC family and known to regulate microtubule integrity and muscle contraction. Therefore, we aimed to investigate the effects of HDAC8 inhibition in murine model of asthma using Pan-HDAC inhibitor curcumin (CUR) and HDAC8-specific inhibitor PCI-34051 (PCI), alone and in combination.

MATERIALS AND METHODS

To develop asthmatic mouse model, Balb/c mice were sensitized and challenged with ovalbumin (OVA). CUR (10 mg/kg, pre, post, alone and combined treatment) and PCI (0.5 mg/kg), were administered through intranasal (i.n) route, an hour before OVA aerosol challenge. Effects of HDAC8 inhibition by CUR and PCI pretreatments were evaluated in terms of inflammation, oxidative stress and fibrosis markers. Efficacy of curcumin post-treatment (CUR(p)) was also evaluated simultaneously.

RESULTS

Inflammatory cell recruitment, oxidative stress (reactive oxygen species, nitric oxide), histamine and Immunoglobulin E (IgE) levels and expression of fibrosis markers including hydroxyproline, matrix metalloproteinases-9 and alpha smooth muscle actin (MMP-9 and α-SMA) were significantly reduced by CUR, CUR(p), PCI-alone and combined treatments. Protein expressions of HDAC8, Nuclear factor-κB (NF-κB) accompanied by MAPKs (mitogen-activated protein kinases) were significantly reduced by the treatments. Structural alterations were examined by histopathological analysis and linked with the fibrotic changes.

CONCLUSIONS

Present study indicates protective effects of HDAC8 inhibition in asthma using HDAC8 using CUR and PCI alone or in combination, attenuates airway inflammation, fibrosis and remodeling; hence, bronchoconstriction was accompanied through modulation of MAP kinase pathway.

Targeting Histone Deacetylases 6 in Dual-Target Therapy of Cancer

Histone deacetylases (HDACs) are the major regulators of the balance of acetylation of histone and non-histone proteins. In contrast to other HDAC isoforms, HDAC6 is mainly involved in maintaining the acetylation balance of many non-histone proteins. Therefore, the overexpression of HDAC6 is associated with tumorigenesis, invasion, migration, survival, apoptosis and growth of various malignancies. As a result, HDAC6 is considered a promising target for cancer treatment. However, none of selective HDAC6 inhibitors are in clinical use, mainly because of the low efficacy and high concentrations used to show anticancer properties, which may lead to off-target effects. Therefore, HDAC6 inhibitors with dual-target capabilities represent a new trend in cancer treatment, aiming to overcome the above problems. In this review, we summarize the advances in tumor treatment with dual-target HDAC6 inhibitors.

Design, Synthesis, and Biological Evaluation of New Urushiol Derivatives as Potent Class I Histone Deacetylase Inhibitors

In the present study, a novel series of 11 urushiol-based hydroxamic acid histone deacetylase (HDAC) inhibitors was designed, synthesized, and biologically evaluated. Compounds 1-11 exhibited good to excellent inhibitory activities against HDAC1/2/3 (IC50 : 42.09-240.17 nM) and HDAC8 (IC50 : 16.11-41.15 nM) in vitro, with negligible activity against HDAC6 (>1409.59 nM). Considering HDAC8, docking experiments revealed some important features contributing to inhibitory activity. According to Western blot analysis, select compounds could notably enhance the acetylation of histone H3 and SMC3 but not-tubulin, indicating their privileged structure is appropriate for targeting class I HDACs. Furthermore, antiproliferation assays revealed that six compounds exerted greater in vitro antiproliferative activity against four human cancer cell lines (A2780, HT-29, MDA-MB-231, and HepG2, with IC50 values ranging from 2.31-5.13 μM) than suberoylanilide hydroxamic acid; administration of these compounds induced marked apoptosis in MDA-MB-231 cells, with cell cycle arrest in the G2/M phase. Collectively, specific synthesized compounds could be further optimized and biologically explored as antitumor agents.

HDAC8 as an emerging target in drug discovery with special emphasis on medicinal chemistry

HDAC8 catalyzes the deacetylation of both histones and nonhistone proteins. The abnormal expression of HDAC8 is associated with various pathological conditions causing cancer and other diseases like myopathies, Cornelia de Lange syndrome, renal fibrosis, and viral and parasitic infections. The substrates of HDAC8 are involved in diverse molecular mechanisms of cancer such as cell proliferation, invasion, metastasis and drug resistance. Based on the crystal structures and the key residues at the active site, HDAC8 inhibitors have been designed along the canonical pharmacophore. This article details the importance, recent advancements, and the structural and functional aspects of HDAC8 with special emphasis on the medicinal chemistry aspect of HDAC8 inhibitors that will help in developing novel epigenetic therapeutics.

Corroborating evidence for aberrant expression of histone deacetylase 8 in endometriosis

Purpose

The aim of this study was to evaluate the dynamic change in staining of Class I HDACs and Hdac6 in lesions harvested serially from different time points in mice with induced endometriosis. In addition, the effect of Hdac8 activation as well as Hdac8 and Hdac6 inhibition on lesional progression and fibrogenesis was evaluated.

Methods

Immunohistochemistry analysis of Class I HDACs and Hdac6 in serially harvested lesion samples in mouse. Hdac8 activation, as well as Hdac6/8 inhibition, was evaluated in mice with induced endometriosis.

Results

We found a progressive increase in lesional staining of Hdac1, Hdac8, and Hdac6 and gradual decrease in Hdac2 staining and consistently reduced staining of Hdac3 during the course of lesional progression. The stromal Hdac8 staining correlated most prominently with all markers of lesional fibrosis. Hdac8 activation significantly accelerated the progression and fibrogenesis of endometriotic lesions. In contrast, specific inhibition of Hdac8 or Hdac6, especially of Hdac8, significantly hindered lesional progression and fibrogenesis.

Conclusions

Hdac8 is progressively and aberrantly overexpressed as endometriotic lesions progress. This, along with the documented HDAC1 upregulation in endometriosis and the overwhelming evidence for the therapeutic potentials of HDACIs, calls for further and in-depth investigation of epigenetic aberrations of endometriosis in general and of HDACs in particular.

Phage-assisted, active site-directed ligand evolution of a potent and selective histone deacetylase 8 inhibitor

Phage-assisted, active site-directed ligand evolution (PADLE) is a recently developed technique that uses an amber codon-encoded noncanonical amino acid (ncAA) as an anchor to direct phage-displayed peptides to a target for an enhanced ligand identification process. 2-Amino-8-oxodecanoic acid (Aoda) is a ketone-containing ncAA residue in the macrocyclic peptide natural product apicidin that is a pan-inhibitor of Zn2+ -dependent histone deacetylases (HDACs). Its ketone serves as an anchoring point to coordinate the catalytic zinc ion in HDACs. Using a previously evolved N𝜀 -acetyl-lysyl-tRNA synthetase in combination with tRNAPyl , we showed that Aoda was efficiently incorporated into proteins in Escherichia coli by amber suppression. By propagating an amber codon-obligate phagemid library in E. coli encoding Aoda, we generated an Aoda-containing phage-displayed peptide library. Using this library to conduct PADLE against HDAC8 revealed a 7-mer peptide GH8P01F1 with Aoda-flanking amino acid residues that matched existing peptide sequences in identified HDAC8 substrates. Switching Aoda in GH8P01F1 to a more Zn2+ -chelating ncAA S-2-amino-8-hydroxyamino-8-oxooctanoic acid (Asuha) led to an extremely potent compound GH8HA01, which has an HDAC8-inhibition Ki value of 0.67 nM. GH8HA01 and its 5-mer truncation analogue Ac-GH8HA01Δ1Δ7 that has an HDAC8-inhibition Ki value of 0.31 nM are two of the most potent HDAC8 inhibitors that have been developed. Furthermore, both are highly selective against HDAC8 compared with other HDACs tested, demonstrating the great potential of using PADLE to identify highly potent and selective ligands for targets with conserved active sites among homologues.

Cortactin in Lung Cell Function and Disease

Cortactin (CTTN) is an actin-binding and cytoskeletal protein that is found in abundance in the cell cortex and other peripheral structures of most cell types. It was initially described as a target for Src-mediated phosphorylation at several tyrosine sites within CTTN, and post-translational modifications at these tyrosine sites are a primary regulator of its function. CTTN participates in multiple cellular functions that require cytoskeletal rearrangement, including lamellipodia formation, cell migration, invasion, and various other processes dependent upon the cell type involved. The role of CTTN in vascular endothelial cells is particularly important for promoting barrier integrity and inhibiting vascular permeability and tissue edema. To mediate its functional effects, CTTN undergoes multiple post-translational modifications and interacts with numerous other proteins to alter cytoskeletal structures and signaling mechanisms. In the present review, we briefly describe CTTN structure, post-translational modifications, and protein binding partners and then focus on its role in regulating cellular processes and well-established functional mechanisms, primarily in vascular endothelial cells and disease models. We then provide insights into how CTTN function affects the pathophysiology of multiple lung disorders, including acute lung injury syndromes, COPD, and asthma.

Structure-based prediction of HDAC6 substrates validated by enzymatic assay reveals determinants of promiscuity and detects new potential substrates

Histone deacetylases play important biological roles well beyond the deacetylation of histone tails. In particular, HDAC6 is involved in multiple cellular processes such as apoptosis, cytoskeleton reorganization, and protein folding, affecting substrates such as ɑ-tubulin, Hsp90 and cortactin proteins. We have applied a biochemical enzymatic assay to measure the activity of HDAC6 on a set of candidate unlabeled peptides. These served for the calibration of a structure-based substrate prediction protocol, Rosetta FlexPepBind, previously used for the successful substrate prediction of HDAC8 and other enzymes. A proteome-wide screen of reported acetylation sites using our calibrated protocol together with the enzymatic assay provide new peptide substrates and avenues to novel potential functional regulatory roles of this promiscuous, multi-faceted enzyme. In particular, we propose novel regulatory roles of HDAC6 in tumorigenesis and cancer cell survival via the regulation of EGFR/Akt pathway activation. The calibration process and comparison of the results between HDAC6 and HDAC8 highlight structural differences that explain the established promiscuity of HDAC6.

Modulation of cellular processes by histone and non-histone protein acetylation

Lysine acetylation is a widespread and versatile protein post-translational modification. Lysine acetyltransferases and lysine deacetylases catalyse the addition or removal, respectively, of acetyl groups at both histone and non-histone targets. In this Review, we discuss several features of acetylation and deacetylation, including their diversity of targets, rapid turnover, exquisite sensitivity to the concentrations of the cofactors acetyl-CoA, acyl-CoA and NAD⁺, and tight interplay with metabolism. Histone acetylation and non-histone protein acetylation influence a myriad of cellular and physiological processes, including transcription, phase separation, autophagy, mitosis, differentiation and neural function. The activity of lysine acetyltransferases and lysine deacetylases can, in turn, be regulated by metabolic states, diet and specific small molecules. Histone acetylation has also recently been shown to mediate cellular memory. These features enable acetylation to integrate the cellular state with transcriptional output and cell-fate decisions.

Histone deacetylase 8 interacts with the GTPase SmRho1 in Schistosoma mansoni

Background

Schistosoma mansoni histone deacetylase 8 (SmHDAC8) has elicited considerable interest as a target for drug discovery. Invalidation of its transcripts by RNAi leads to impaired survival of the worms in infected mice and its inhibition causes cell apoptosis and death. To determine why it is a promising therapeutic target the study of the currently unknown cellular signaling pathways involving this enzyme is essential. Protein partners of SmHDAC8 were previously identified by yeast two-hybrid (Y2H) cDNA library screening and by mass spectrometry (MS) analysis. Among these partners we characterized SmRho1, the schistosome orthologue of human RhoA GTPase, which is involved in the regulation of the cytoskeleton. In this work, we validated the interaction between SmHDAC8 and SmRho1 and explored the role of the lysine deacetylase in cytoskeletal regulation.

Methodology/principal findings

We characterized two isoforms of SmRho1, SmRho1.1 and SmRho1.2. Co- immunoprecipitation (Co-IP)/Mass Spectrometry (MS) analysis identified SmRho1 partner proteins and we used two heterologous expression systems (Y2H assay and Xenopus laevis oocytes) to study interactions between SmHDAC8 and SmRho1 isoforms.

To confirm SmHDAC8 and SmRho1 interaction in adult worms and schistosomula, we performed Co-IP experiments and additionally demonstrated SmRho1 acetylation using a Nano LC-MS/MS approach. A major impact of SmHDAC8 in cytoskeleton organization was documented by treating adult worms and schistosomula with a selective SmHDAC8 inhibitor or using RNAi followed by confocal microscopy.

Conclusions/significance

Our results suggest that SmHDAC8 is involved in cytoskeleton organization via its interaction with the SmRho1.1 isoform. The SmRho1.2 isoform failed to interact with SmHDAC8, but did specifically interact with SmDia suggesting the existence of two distinct signaling pathways regulating S. mansoni cytoskeleton organization via the two SmRho1 isoforms. A specific interaction between SmHDAC8 and the C-terminal moiety of SmRho1.1 was demonstrated, and we showed that SmRho1 is acetylated on K136. SmHDAC8 inhibition or knockdown using RNAi caused extensive disruption of schistosomula actin cytoskeleton.

Schistosoma mansoni is the major parasitic platyhelminth species causing intestinal schistosomiasis. Currently one drug, praziquantel, is the treatment of choice but its use in mass treatment programs means that the development of resistance is likely and renders imperative the development of new therapeutic agents. As new potential targets we have focused on lysine deacetylases, and in particular S. mansoni histone deacetylase 8 (SmHDAC8). Previous studies showed that reduction in the level of transcripts of SmHDAC8 by RNAi led to the impaired survival of the worms after the infection of mice. The analysis of the 3D structure of SmHDAC8 by X-ray crystallography showed that the catalytic domain structure diverges significantly from that of human HDAC8 and this was exploited to develop novel potential anti-schistosomal drugs. The biological roles of SmHDAC8 are unknown. For this reason, we previously characterized its protein binding partners and identified the schistosome orthologue of the human RhoA GTPase, suggesting the involvement of SmHDAC8 in the modulation of cytoskeleton organization. Here we investigated the interaction between SmHDAC8 and SmRho1 and identified two SmRho1 isoforms (SmRho1.1 and SmRho1.2). Our study showed that SmHDAC8 is involved in schistosome cytoskeleton organization.

Histone-deacetylase 8 drives the immune response and the growth of glioma

Many epigenetic modifications occur in glioma, in particular the histone-deacetylase class proteins play a pivotal role in glioma development, driving the proliferation rate and the invasiveness of tumor cells, and modulating the tumor microenvironment. In this study, we evaluated the role of the histone deacetylase HDAC8 in the regulation of the immune response in glioma and tumor growth. We found that inhibition of HDAC8 by the specific inhibitor PCI-34051 reduces tumor volume in glioma mouse models. We reported that HDAC8 modulates the viability and the migration of human and murine glioma cells. Interestingly, HDAC8 inhibition increases the acetylation of alpha-tubulin, suggesting this epigenetic modification controls glioma migration. Furthermore, we identify HDAC8 as a key molecule that supports a poorly immunogenic tumor microenvironment, modulating microglial phenotype and regulating the gene transcription of NKG2D ligands that trigger the Natural Killer cell-mediated cytotoxicity of tumor cells. Altogether, these results identify HDAC8 as a key actor in glioma growth and tumor microenvironment, and pave the way to a better knowledge of the molecular mechanisms of immune escape in glioma.

Acetylation of Abelson interactor 1 at K416 regulates actin cytoskeleton and smooth muscle contraction

Actin cytoskeletal reorganization plays an important role in regulating smooth muscle contraction, which is essential for the modulation of various physiological functions including airway tone. The adapter protein Abi1 (Abelson interactor 1) participates in the control of smooth muscle contraction. The mechanisms by which Abi1 coordinates smooth muscle function are not fully understood. Here, we found that contractile stimulation elicited Abi1 acetylation in human airway smooth muscle (HASM) cells. Mutagenesis analysis identified lysine‐416 (K416) as a major acetylation site. Replacement of K416 with Q (glutamine) enhanced the interaction of Abi1 with neuronal Wiskott‐Aldrich syndrome protein (N‐WASP), an important actin‐regulatory protein. Moreover, the expression of K416Q Abi1 promoted actin polymerization and smooth muscle contraction without affecting myosin light chain phosphorylation at Ser‐19 and vimentin phosphorylation at Ser‐56. Furthermore, p300 is a lysine acetyltransferase that catalyzes acetylation of histone and non‐histone proteins in various cell types. Here, we discovered that a portion of p300 was localized in the cytoplasm of HASM cells. Knockdown of p300 reduced the agonist‐induced Abi1 acetylation in HASM cells and in mouse airway smooth muscle tissues. Smooth muscle conditional knockout of p300 inhibited actin polymerization and the contraction of airway smooth muscle tissues without affecting myosin light chain phosphorylation and vimentin phosphorylation. Together, our results suggest that contractile stimulation induces Abi1 acetylation via p300 in smooth muscle. Acetylation at K416 promotes the coupling of Abi1 with N‐WASP, which facilitates actin polymerization and smooth muscle contraction. This is a novel acetylation‐dependent regulation of the actin cytoskeleton in smooth muscle.

Targeting HDAC8 to ameliorate skeletal muscle differentiation in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) causes progressive skeletal muscle degeneration and currently there are few therapeutic options. The identification of new drug targets and their validation in model systems of DMD could be a promising approach to make progress in finding new treatments for this lethal disease. Histone deacetylases (HDACs) play key roles in myogenesis and the therapeutic approach targeting HDACs in DMD is in an advanced phase of clinical trial. Here, we show that the expression of HDAC8, one of the members of the HDAC family, is increased in DMD patients and dystrophic zebrafish. The selective inhibition of HDAC8 with the PCI-34051 inhibitor rescues skeletal muscle defects, similarly to the treatment with the pan-HDAC inhibitor Givinostat. Through acetylation profile of zebrafish with HDAC8 dysregulation, we identified new HDAC8 targets involved in cytoskeleton organization such as tubulin that, when acetylated, is a marker of stable microtubules. Our work provides evidence of HDAC8 overexpression in DMD patients and zebrafish and supports its specific inhibition as a new valuable therapeutic approach in the treatment of this pathology.

Antisense Oligonucleotide-Mediated Reduction of HDAC6 Does Not Reduce Tau Pathology in P301S Tau Transgenic Mice

Acetylation of tau protein is dysregulated in Alzheimer's Disease (AD). It has been proposed that acetylation of specific sites in the KXGS motif of tau can regulate phosphorylation of nearby residues and reduce the propensity of tau to aggregate. Histone deacetylase 6 (HDAC6) is a cytoplasmic enzyme involved in deacetylation of multiple targets, including tau, and it has been suggested that inhibition of HDAC6 would increase tau acetylation at the KXGS motifs and thus may present a viable therapeutic approach to treat AD. To directly test the contribution of HDAC6 to tau pathology, we intracerebroventricularly injected an antisense oligonucleotide (ASO) directed against HDAC6 mRNA into brains of P301S tau mice (PS19 model), which resulted in a 70% knockdown of HDAC6 protein in the brain. Despite a robust decrease in levels of HDAC6, no increase in tau acetylation was observed. Additionally, no change of tau phosphorylation or tau aggregation was detected upon the knockdown of HDAC6. We conclude that HDAC6 does not impact tau pathology in PS19 mice.

NBM-BMX, an HDAC8 Inhibitor, Overcomes Temozolomide Resistance in Glioblastoma Multiforme by Downregulating the β-Catenin/c-Myc/SOX2 Pathway and Upregulating p53-Mediated MGMT Inhibition

Although histone deacetylase 8 (HDAC8) plays a role in glioblastoma multiforme (GBM), whether its inhibition facilitates the treatment of temozolomide (TMZ)-resistant GBM (GBM-R) remains unclear. By assessing the gene expression profiles from short hairpin RNA of HDAC8 in the new version of Connectivity Map (CLUE) and cells treated by NBM-BMX (BMX)-, an HDAC8 inhibitor, data analysis reveals that the Wnt signaling pathway and apoptosis might be the underlying mechanisms in BMX-elicited treatment. This study evaluated the efficacy of cotreatment with BMX and TMZ in GBM-R cells. We observed that cotreatment with BMX and TMZ could overcome resistance in GBM-R cells and inhibit cell viability, markedly inhibit cell proliferation, and then induce cell cycle arrest and apoptosis. In addition, the expression level of β-catenin was reversed by proteasome inhibitor via the β-catenin/ GSK3β signaling pathway to reduce the expression level of c-Myc and cyclin D1 in GBM-R cells. BMX and TMZ cotreatment also upregulated WT-p53 mediated MGMT inhibition, thereby triggering the activation of caspase-3 and eventually leading to apoptosis in GBM-R cells. Moreover, BMX and TMZ attenuated the expression of CD133, CD44, and SOX2 in GBM-R cells. In conclusion, BMX overcomes TMZ resistance by enhancing TMZ-mediated cytotoxic effect by downregulating the β-catenin/c-Myc/SOX2 signaling pathway and upregulating WT-p53 mediated MGMT inhibition. These findings indicate a promising drug combination for precision personal treating of TMZ-resistant WT-p53 GBM cells.

Selective HDAC8 Inhibition Attenuates Isoproterenol-Induced Cardiac Hypertrophy and Fibrosis via p38 MAPK Pathway

Histone deacetylase (HDAC) expression and enzymatic activity are dysregulated in cardiovascular diseases. Among Class I HDACs, HDAC2 has been reported to play a key role in cardiac hypertrophy; however, the exact function of HDAC8 remains unknown. Here we investigated the role of HDAC8 in cardiac hypertrophy and fibrosis using the isoproterenol-induced cardiac hypertrophy model system.Isoproterenol-infused mice were injected with the HDAC8 selective inhibitor PCI34051 (30 mg kg⁻¹ body weight). Enlarged hearts were assessed by HW/BW ratio, cross-sectional area, and echocardiography. RT-PCR, western blotting, histological analysis, and cell size measurements were performed. To elucidate the role of HDAC8 in cardiac hypertrophy, HDAC8 knockdown and HDAC8 overexpression were also used. Isoproterenol induced HDAC8 mRNA and protein expression in mice and H9c2 cells, while PCI34051 treatment decreased cardiac hypertrophy in isoproterenol-treated mice and H9c2 cells. PCI34051 treatment also reduced the expression of cardiac hypertrophic markers (Nppa, Nppb, and Myh7), transcription factors (Sp1, Gata4, and Gata6), and fibrosis markers (collagen type I, fibronectin, and Ctgf) in isoproterenol-treated mice. HDAC8 overexpression stimulated cardiac hypertrophy in cells, whereas HDAC8 knockdown reversed those effects. HDAC8 selective inhibitor and HDAC8 knockdown reduced the isoproterenol-induced activation of p38 MAPK, whereas HDAC8 overexpression promoted p38 MAPK phosphorylation. Furthermore, p38 MAPK inhibitor SB203580 significantly decreased the levels of p38 MAPK phosphorylation, as well as ANP and BNP protein expression, induced by HDAC8 overexpression.Here we show that inhibition of HDAC8 activity or expression suppresses cardiac hypertrophy and fibrosis. These findings suggest that HDAC8 could be a promising target to treat cardiac hypertrophy and fibrosis by regulating p38 MAPK.

Lysine acetylation of cytoskeletal proteins: Emergence of an actin code

Reversible lysine acetylation of nuclear proteins such as histones is a long-established important regulatory mechanism for chromatin remodeling and transcription. In the cytoplasm, acetylation of a number of cytoskeletal proteins, including tubulin, cortactin, and the formin mDia2, regulates both cytoskeletal assembly and stability. More recently, acetylation of actin itself was revealed to regulate cytoplasmic actin polymerization through the formin INF2, with downstream effects on ER-to-mitochondrial calcium transfer, mitochondrial fission, and vesicle transport. This finding raises the possibility that actin acetylation, along with other post-translational modifications to actin, might constitute an "actin code," similar to the "histone code" or "tubulin code," controlling functional shifts to these central cellular proteins. Given the multiple roles of actin in nuclear functions, its modifications might also have important roles in gene expression.

HDAC8: A Promising Therapeutic Target for Acute Myeloid Leukemia

Histone deacetylase 8 (HDAC8), a class I HDAC that modifies non-histone proteins such as p53, is highly expressed in different hematological neoplasms including a subtype of acute myeloid leukemia (AML) bearing inversion of chromosome 16 [inv(16)]. To investigate HDAC8 contribution to hematopoietic stem cell maintenance and myeloid leukemic transformation, we generated a zebrafish model with Hdac8 overexpression and observed an increase in hematopoietic stem/progenitor cells, a phenotype that could be reverted using a specific HDAC8 inhibitor, PCI-34051 (PCI). In addition, we demonstrated that AML cell lines respond differently to PCI treatment: HDAC8 inhibition elicits cytotoxic effect with cell cycle arrest followed by apoptosis in THP-1 cells, and cytostatic effect in HL60 cells that lack p53. A combination of cytarabine, a standard anti-AML chemotherapeutic, with PCI resulted in a synergistic effect in all the cell lines tested. We, then, searched for a mechanism behind cell cycle arrest caused by HDAC8 inhibition in the absence of functional p53 and demonstrated an involvement of the canonical WNT signaling in zebrafish and in cell lines. Together, we provide the evidence for the role of HDAC8 in hematopoietic stem cell differentiation in zebrafish and AML cell lines, suggesting HDAC8 inhibition as a therapeutic target in hematological malignancies. Accordingly, we demonstrated the utility of a highly specific HDAC8 inhibition as a therapeutic strategy in combination with standard chemotherapy.

Effect of sodium butyrate on HDAC8 mRNA expression in colorectal cancer cell lines and molecular docking study of LHX1 - sodium butyrate interaction

Colorectal cancer (CRC) is the third most common type of cancer and the fourth leading cause of cancer related deaths worldwide. The Histone Deacetylase 8 (HDAC8) gene is a gene with unique features which can be used as a potential target for drug design. The LHX1 transcription factor is an important transcription factor for this gene. The aim of this study was to investigate the effect of sodium butyrate (NaB) as a histone deacetylase inhibitor (HDACi) on the expression of the HDAC8 gene in the colorectal cancer cell line, and the molecular docking of the LHX1 transcription factor with NaB. For this purpose, HCT-116 and HT-29 cell lines were treated with different concentrations of NaB (6.25 mM to 150 mM) at 24, 48 and 72 hours. Subsequently, RNA was extracted from the treated and untreated cells and cDNA was synthesized. Quantitative Real-Time-PCR was done to investigate the mRNA expression of HDAC8. Molecular docking was also performed to investigate the interaction between NaB and LHX1. Based on Real-time-PCR results, the concentration of 150 mM of NaB after 24 hours in HT-29 and HCT-116 cell lines caused a significant reduction in mRNA expression of HDAC8 (P<0.05). After 48 hours of treatment, there was a significant decrease in the mRNA expression of HDAC8 at all concentrations (P<0.05). The docking results showed that LHX1 and NaB interacted best at the lowest energy levels. Our results also showed that NaB bonded strongly to LHX1. In addition, our results demonstrated that NaB bound to the LHX1 transcription factor and inhibited the function of this factor and consequently decreased the transcription from the HDAC8 gene which resulted in cell death. Future studies are needed to assess the likely molecular mechanisms of NaB action on gene expression.

Design, synthesis, and biological evaluation of dual targeting inhibitors of histone deacetylase 6/8 and bromodomain BRPF1

Histone modifying proteins, specifically histone deacetylases (HDACs) and bromodomains, have emerged as novel promising targets for anticancer therapy. In the current work, based on available crystal structures and docking studies, we designed dual inhibitors of both HDAC6/8 and the bromodomain and PHD finger containing protein 1 (BRPF1). Biochemical and biophysical tests showed that compounds 23a,b and 37 are nanomolar inhibitors of both target proteins. Detailed structure-activity relationships were deduced for the synthesized inhibitors which were supported by extensive docking and molecular dynamics studies. Cellular testing in acute myeloid leukemia (AML) cells showed only a weak effect, most probably because of the poor permeability of the inhibitors. We also aimed to analyse the target engagement and the cellular activity of the novel inhibitors by determining the protein acetylation levels in cells by western blotting (tubulin vs histone acetylation), and by assessing their effects on various cancer cell lines.

Histone Deacetylases (HDACs): Evolution, Specificity, Role in Transcriptional Complexes, and Pharmacological Actionability

Histone deacetylases (HDACs) are evolutionary conserved enzymes which operate by removing acetyl groups from histones and other protein regulatory factors, with functional consequences on chromatin remodeling and gene expression profiles. We provide here a review on the recent knowledge accrued on the zinc-dependent HDAC protein family across different species, tissues, and human pathologies, specifically focusing on the role of HDAC inhibitors as anti-cancer agents. We will investigate the chemical specificity of different HDACs and discuss their role in the human interactome as members of chromatin-binding and regulatory complexes.

Inhibiting Airway Smooth Muscle Contraction Using Pitavastatin: A Role for the Mevalonate Pathway in Regulating Cytoskeletal Proteins

Despite maximal use of currently available therapies, a significant number of asthma patients continue to experience severe, and sometimes life-threatening bronchoconstriction. To fill this therapeutic gap, we examined a potential role for the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) inhibitor, pitavastatin. Using human airway smooth muscle (ASM) cells and murine precision-cut lung slices, we discovered that pitavastatin significantly inhibited basal-, histamine-, and methacholine (MCh)-induced ASM contraction. This occurred via reduction of myosin light chain 2 (MLC2) phosphorylation, and F-actin stress fiber density and distribution, in a mevalonate (MA)- and geranylgeranyl pyrophosphate (GGPP)-dependent manner. Pitavastatin also potentiated the ASM relaxing effect of a simulated deep breath, a beneficial effect that is notably absent with the β2-agonist, isoproterenol. Finally, pitavastatin attenuated ASM pro-inflammatory cytokine production in a GGPP-dependent manner. By targeting all three hallmark features of ASM dysfunction in asthma—contraction, failure to adequately relax in response to a deep breath, and inflammation—pitavastatin may represent a unique asthma therapeutic.

HDAC3 and HDAC8 are required for cilia assembly and elongation

Cilia are extended from mother centrioles in quiescent G0/G1 cells and retracted in dividing cells. Diverse post-translational modifications play roles in the assembly and disassembly of the cilium. Here, we examined class I histone deacetylases (HDACs) as positive regulators of cilia assembly in serum-deprived RPE1 and HK2 cells. We observed that the number of cells with cilia was significantly reduced in HDAC3- and HDAC8-depleted cells. The ciliary length also decreased in HDAC3- and HDAC8-depleted cells compared to that in control cells. A knockdown-rescue experiment showed that wild-type HDAC3 and HDAC8 rescued the cilia assembly and ciliary length in HDAC3- and HDAC8-depleted cells, respectively; however, deacetylase-dead HDAC3 and HDAC8 mutants did not. This suggests that deacetylase activity is critical for both HDAC3 and HDAC8 function in cilia assembly and ciliary length control. This is the first study to report that HDACs are required for the assembly and elongation of the primary cilia.

Summary: We identified that HDAC3 and HDAC8 are required for the assembly and elongation of the primary cilia.

Promoter conservation in HDACs points to functional implications

Background

Histone deacetylases (HDACs) are the proteins responsible for removing the acetyl group from lysine residues of core histones in chromosomes, a crucial component of gene regulation. Eleven known HDACs exist in humans and most other vertebrates. While the basic function of HDACs has been well characterized and new discoveries are still being made, the transcriptional regulation of their corresponding genes is still poorly understood.

Results

Here, we conducted a computational analysis of the eleven HDAC promoter sequences in 25 vertebrate species to determine whether transcription factor binding sites (TFBSs) are conserved in HDAC evolution, and if so, whether they provide useful information about HDAC expression and function. Furthermore, we used tissue-specific information of transcription factors to investigate the potential expression patterns of HDACs in different human tissues based on their transcription factor binding sites. We found that the TFBS profiles of most of the HDACs were well conserved in closely related species for all HDAC promoters except HDAC7 and HDAC10. HDAC5 had particularly strong conservation across over half of the species studied, with nearly identical profiles in the primate species. Our comparisons of TFBSs with the tissue specific gene expression profiles of their corresponding TFs showed that most HDACs had the ability to be ubiquitously expressed. A few HDAC promoters exhibited the potential for preferential expression in certain tissues, most notably HDAC11 in gall bladder, while HDAC9 seemed to have less propensity for expression in the nervous system.

Conclusions

In general, we found evolutionary conservation in HDAC promoters that seems to be more prominent for the ubiquitously expressed HDACs. In turn, when conservation did not follow usual phylogeny, human TFBS patterns indicated possible functional relevance. While we found that HDACs appear to uniformly expressed, we confirm that the functional differences in HDACs may be less a matter of location of activity than a question of which proteins and which acetyl groups they may be acting on.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5973-x) contains supplementary material, which is available to authorized users.

Acetylome profiling reveals extensive involvement of lysine acetylation in the conversion of muscle to meat

Protein lysine acetylation is an post-translational modification that regulates gene expression, metabolism, cell signaling, and diseases, but its implication in the postmortem (PM) meat quality development is basically unclear. In the present study, a quantitative proteomic analysis was conducted to profile acetylome in porcine muscle within 24 h PM. In total 595 acetylation sites assigned to 163 proteins were identified in porcine muscle, of which 460 sites distributing to 110 proteins significantly changed in acetylation levels in the conversion of muscle to meat. The dynamic acetylation/deacetylaion of muscle proteins was closely associated with critical chemical-biophysical changes in PM muscle. Bioinformatic analysis revealed that protein lysine acetylation likely regulated postmortem meat quality development by regulating glycolysis and muscle pH, cell stress reponse and apoptosis, muscle contraction and rigor mortis, calcium signaling and proteolysis, IMP synthesis and meat flavor development, and even the stability of pigment proteins and meat color. This study provided the first overview of protein lysine acetylation in PM muscle and revealed its significance in the conversion of muscle to meat. Future exploration of the exact role of protein lysine acetylation at specific sites will further our understanding regarding the underlying mechanisms and be helpful for meat quality control. SIGNIFICANCE: This is the first analysis of acetylome in farm animal and postmortem muscle. Our data showed that the dynamic acetylation/deacetylation of muscle proteins was closely related to the postmortem changes of muscle that affect the final quality of raw meat. Proteins related to glucose metabolism and muscle contraction were the two largest clusters of acetylproteins identified in postmortem porcine muscle. Networks of acetylproteins involved in apoptosis, calcium signaling and IMP synthesis were identified in postmortem porcine muscle at the same time. Our results revealed that protein lysine acetylation regulated the conversion of muscle to meat. It likely regulated meat quality development by regulating postmortem glycolysis, mitochondrion initiated cell apoptosis, calcium signaling, rigor mortis, meat flavor compound sysnthesis and meat tenderization. Our study broadened our understanding of the biochemistry regulating the postmortem conversion of muscle to meat and final meat quality development, which may be helpful for future meat quality control.

Extracellular regulation of airway smooth muscle contraction

The molecular mechanisms governing the contraction of airway smooth muscle have always been at the forefront of asthma research. New extracellular molecules affecting the contraction of airway smooth muscle are steadily being discovered. Although interesting, this is disconcerting for researchers trying to find a mend for the significant part of asthma symptoms caused by contraction. Additional efforts are being deployed to understand the intracellular signaling pathways leading to contraction. The goal being to find common pathways that are essential to convey the contractile signal emanating from any single or combination of extracellular molecules. Not only these pathways exist and their details are being slowly unveiled, but some carry the signal inside-out to interact back with extracellular molecules. These latter represent targets with promising therapeutic potential, not only because they are molecules downstream of pathways essential for contraction but also because their extracellular location makes them readily accessible by inhaled drugs.

HDAC8 Regulates a Stress Response Pathway in Melanoma to Mediate Escape from BRAF Inhibitor Therapy

Melanoma cells have the ability to switch to a dedifferentiated, invasive phenotype in response to multiple stimuli. Here, we show that exposure of melanomas to multiple stresses including BRAF-MEK inhibitor therapy, hypoxia, and UV irradiation leads to an increase in histone deacetylase 8 (HDAC8) activity and the adoption of a drug-resistant phenotype. Mass spectrometry-based phosphoproteomics implicated HDAC8 in the regulation of MAPK and AP-1 signaling. Introduction of HDAC8 into drug-naïve melanoma cells conveyed resistance both in vitro and in vivo. HDAC8-mediated BRAF inhibitor resistance was mediated via receptor tyrosine kinase activation, leading to MAPK signaling. Although HDACs function at the histone level, they also regulate nonhistone substrates, and introduction of HDAC8 decreased the acetylation of c-Jun, increasing its transcriptional activity and enriching for an AP-1 gene signature. Mutation of the putative c-Jun acetylation site at lysine 273 increased transcriptional activation of c-Jun in melanoma cells and conveyed resistance to BRAF inhibition. In vivo xenograft studies confirmed the key role of HDAC8 in therapeutic adaptation, with both nonselective and HDAC8-specific inhibitors enhancing the durability of BRAF inhibitor therapy. Our studies demonstrate that HDAC8-specific inhibitors limit the adaptation of melanoma cells to multiple stresses including BRAF-MEK inhibition. SIGNIFICANCE: This study provides evidence that HDAC8 drives transcriptional plasticity in melanoma cells in response to a range of stresses through direct deacetylation of c-Jun.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/11/2947/F1.large.jpg.

HDAC8 inhibition ameliorates pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fibroproliferative lung disease, and fibroblast-myofibroblast differentiation (FMD) is thought to be a key event in the pathogenesis of IPF. Histone deacetylase-8 (HDAC8) has been shown to associate with α-smooth muscle actin (α-SMA; a marker of FMD) and regulates cell contractility in vascular smooth muscle cells. However, the role of HDAC8 in FMD or pulmonary fibrosis has never been reported. This study investigated the role of HDAC8 in pulmonary fibrosis with a focus on FMD. We observed that HDAC8 expression was increased in IPF lung tissue as well as transforming growth factor (TGF)β1-treated normal human lung fibroblasts (NHLFs). Immunoprecipitation experiments revealed that HDAC8 was associated with α-SMA in TGFβ1-treated NHLFs. HDAC8 inhibition with NCC170 (HDAC8-selective inhibitor) repressed TGFβ1-induced fibroblast contraction and α-SMA protein expression in NHLFs cultured in collagen gels. HDAC8 inhibition with HDAC8 siRNA also repressed TGFβ1-induced expression of profibrotic molecules such as fibronectin and increased expression of antifibrotic molecules such as peroxisome proliferator-activated receptor-γ (PPARγ). Chromatin immunoprecipitation quantitative PCR using an antibody against H3K27ac (histone H3 acetylated at lysine 27; a known HDAC8 substrate and a marker for active enhancers) suggested that HDAC8 inhibition with NCC170 ameliorated TGFβ1-induced loss of H3K27ac at the PPARγ gene enhancer. Furthermore, NCC170 treatment significantly decreased fibrosis measured by Ashcroft score as well as expression of type 1 collagen and fibronectin in bleomycin-treated mouse lungs. These data suggest that HDAC8 contributes to pulmonary fibrosis and that there is a therapeutic potential for HDAC8 inhibitors to treat IPF as well as other fibrotic lung diseases.

Histone deacetylase 8 triggers the migration of triple negative breast cancer cells via regulation of YAP signals

Triple-negative breast cancer (TNBC) shows highly aggressive clinical behaviors and poor prognosis compared to other breast cancer subtypes. Histone deacetylases (HDACs) can regulate the progression of various cancers, but the role of HDAC8 in TNBC remains unexplored. Here, we found that HDAC8 enhanced the in vitro migration abilities of breast cancer cells. Targeted inhibition of HDAC8 via si-HDAC8 and its selective inhibitor PCI34051 could suppress the migration of cells. In TNBC cells, HDAC8 stabilized the expression and increased the nuclear localization of YAP, a major downstream effector of Hippo pathway. While silencing YAP could attenuate HDAC8 triggered migration of TNBC cells. Mechanistically, HDAC8 suppressed the phosphorylation of YAP^Ser127, which was related to its cytoplasmic sequestration degradation. Our data revealed that HDAC8 could trigger the migration of TNBC cells via regulation of Hippo-YAP signals, suggesting that HDAC8 might be a potential target for TNBC therapy.

Novel histone deacetylase 8-selective inhibitor 1,3,4-oxadiazole-alanine hybrid induces apoptosis in breast cancer cells

Identification of isoform-specific histone deacetylase inhibitors (HDACi) is a significant advantage to overcome the adverse side effects of pan-HDACi for the treatment of various diseases, including cancer. We have designed, and synthesized novel 1,3,4 oxadiazole with glycine/alanine hybrids as HDAC8-specific inhibitors and preliminary evaluation has indicated that 1,3,4 oxadiazole with alanine hybrid [(R)-2-amino-N-((5-phenyl-1,3,4-oxadiazol-2-yl)methyl)propanamide (10b)] to be a potent HDAC8 inhibitor. In the present study, the in vitro efficacy of the molecule in inhibiting the cancer cell proliferation and the underlying molecular mechanism was studied. 10b inhibited the growth of MDA-MB-231 and MCF7 breast cancer cells, with a lower IC₅₀ of 230 and 1000 nM, respectively, compared to K562, COLO-205 and HepG2 cells and was not cytotoxic to normal breast epithelial cells, MCF10A. 10b was specific to HDAC8 and did not affect the expression of other class I HDACs. Further, a dose-dependent increase in H3K9 acetylation levels demonstrated the HDAC-inhibitory activity of 10b in MDA-MB-231 cells. Flow cytometric analysis indicated a dose-dependent increase and decrease in the percent apoptotic cells and mitochondrial membrane potential, respectively, when treated with 10b. Immunoblot analysis showed a modulation of Bax/Bcl2 ratio with a decrease in Bcl2 expression and no change in Bax expression. 10b treatment resulted in induction of p21 and inhibition of CDK1 proteins along with cytochrome c release from mitochondria, activation of caspases-3 and -9 and cleavage of poly ADP-ribose polymerase leading to apoptotic death of MDA-MB-231 and MCF7 cells. In conclusion, our results clearly demonstrated the efficacy of 10b as an anticancer agent against breast cancer.

Overexpressed HDAC8 in cervical cancer cells shows functional redundancy of tubulin deacetylation with HDAC6

BACKGROUND

Histone deacetylases (HDACs) are involved in epigenetic gene regulation via deacetylation of acetylated lysine residues of both histone and non-histone proteins. Among the 18 HDACs identified in humans, HDAC8, a class I HDAC, is best understood structurally and enzymatically. However, its precise subcellular location, function in normal cellular physiology, its protein partners and substrates still remain elusive.

METHODS

The subcellular localization of HDAC8 was studied using immunofluorescence and confocal imaging. The binding parterns were identified employing immunoprecipitation (IP) followed by MALDI-TOF analysis and confirmed using in-silico protein-protein interaction studies, HPLC-based in vitro deacetylation assay, intrinsic fluorescence spectrophotometric analysis, Circular dichroism (CD) and Surface Plasmon Resonance (SPR). Functional characterization of the binding was carried out using immunoblot and knockdown by siRNA. Using one way ANOVA statistical significance (n = 3) was determined.

RESULTS

Here, we show that HDAC8 and its phosphorylated form (pHDAC8) localized predominantly in the cytoplasm in cancerous, HeLa, and non-cancerous (normal), HEK293T, cells, although nucleolar localization was observed in HeLa cells. The study identified Alpha tubulin as a novel interacting partner of HDAC8. Further, the results indicated binding and deacetylation of tubulin at ac-lys40 by HDAC8. Knockdown of HDAC8 by siRNA, inhibition of HDAC8 and/or HDAC6 by PCI-34051 and tubastatin respectively, cell-migration, cell morphology and cell cycle analysis clearly explained HDAC8 as tubulin deacetylase in HeLa cells and HDAC6 in HEK 293 T cells.

CONCLUSIONS

HDAC8 shows functional redundancy with HDAC6 when overexpressed in cervical cancer cells, HeLa, and deacetylaes ac-lys40 of alpha tubulin leading to cervical cancer proliferation and progression.

Structure–activity relationships of hydroxamate-based histone deacetylase-8 inhibitors: reality behind anticancer drug discovery

The pan-histone deacetylase (HDAC) inhibitors comprise a fish-like structural orientation where hydrophobic aryl- and zinc-binding groups act as head and tail, respectively of a fish. The linker moiety correlates the body of the fish linking head and tail groups. Despite these pan-HDAC inhibitors, selective HDAC-8 inhibitors are still in demand as a safe remedy. HDAC-8 is involved in invasion and metastasis in cancer. This review deals with the rationale behind HDAC-8 inhibitory activity and selectivity along with detailed structure–activity relationships of diverse hydroxamate-based HDAC-8 inhibitors. HDAC-8 inhibitory potency may be increased by modifying the fish-like pharmacophoric features of such type of pan-HDAC inhibitors. This review may provide a preliminary basis to design and optimize new lead molecules with higher HDAC-8 inhibitory activity. This work may surely enlighten in providing useful information in the field of target-specific anticancer therapy.

Analysis of the interactome of Schistosoma mansoni histone deacetylase 8

BACKGROUND

Histone deacetylase 8 from Schistosoma mansoni (SmHDAC8) is essential to parasite growth and development within the mammalian host and is under investigation as a target for the development of selective inhibitors as novel schistosomicidal drugs. Although some protein substrates and protein partners of human HDAC8 have been characterized, notably indicating a role in the function of the cohesin complex, nothing is known of the partners and biological function of SmHDAC8.

METHODOLOGY/PRINCIPAL FINDINGS

We therefore employed two strategies to characterize the SmHDAC8 interactome. We first used SmHDAC8 as a bait protein in yeast two-hybrid (Y2H) screening of an S. mansoni cDNA library. This allowed the identification of 49 different sequences encoding proteins. We next performed co-immunoprecipitation (Co-IP) experiments on parasite extracts with an anti-SmHDAC8 antibody. Mass spectrometry (MS) analysis allowed the identification of 160 different proteins.

CONCLUSIONS/SIGNIFICANCE

SmHDAC8 partners are involved in about 40 different processes, included expected functions such as the cohesin complex, cytoskeleton organization, transcriptional and translational regulation, metabolism, DNA repair, the cell cycle, protein dephosphorylation, proteolysis, protein transport, but also some proteasome and ribosome components were detected. Our results show that SmHDAC8 is a versatile deacetylase, potentially involved in both cytosolic and nuclear processes.

HDAC8 functions in spindle assembly during mouse oocyte meiosis

HDAC8 is a class I histone deacetylase that functions in a variety of biological processes through its non-histone substrates. However, its roles during oocyte meiosis remain elusive. Here, we document that HDAC8 localizes at spindle poles and positively participates in the regulation of microtubule organization and spindle assembly in mouse oocytes. Depletion of HDAC8 by siRNA-based gene silencing results in various spindle defects and chromosome misalignment during oocyte meiotic maturation, accompanied by impaired kinetochore-microtubule attachments. Consequently, a higher incidence of aneuploidy is generated in HDAC8-depleted MII eggs. In addition, inhibition of HDAC8 activity with its selective inhibitor PCI-34051 phenocopies the spindle/chromosome defects resulting from HDAC8 depletion by siRNA injection. Finally, we find that HDAC8 is required for the correct localization of ϕ-tubulin to spindle poles. Collectively, these data reveal that HDAC8 plays a significant role in regulating spindle assembly and thus ensuring the euploidy in mouse eggs.

The Dynamic Actin Cytoskeleton in Smooth Muscle

Smooth muscle contraction requires both myosin activation and actin cytoskeletal remodeling. Actin cytoskeletal reorganization facilitates smooth muscle contraction by promoting force transmission between the contractile unit and the extracellular matrix (ECM), and by enhancing intercellular mechanical transduction. Myosin may be viewed to serve as an "engine" for smooth muscle contraction whereas the actin cytoskeleton may function as a "transmission system" in smooth muscle. The actin cytoskeleton in smooth muscle also undergoes restructuring upon activation with growth factors or the ECM, which controls smooth muscle cell proliferation and migration. Abnormal smooth muscle contraction, cell proliferation, and motility contribute to the development of vascular and pulmonary diseases. A number of actin-regulatory proteins including protein kinases have been discovered to orchestrate actin dynamics in smooth muscle. In particular, Abelson tyrosine kinase (c-Abl) is an important molecule that controls actin dynamics, contraction, growth, and motility in smooth muscle. Moreover, c-Abl coordinates the regulation of blood pressure and contributes to the pathogenesis of airway hyperresponsiveness and vascular/airway remodeling in vivo. Thus, c-Abl may be a novel pharmacological target for the development of new therapy to treat smooth muscle diseases such as hypertension and asthma.

Targeting histone deacetylase 8 as a therapeutic approach to cancer and neurodegenerative diseases

Histone deacetylase 8 (HDAC8), a unique class I zinc-dependent HDAC, is an emerging target in cancer and other diseases. Its substrate repertoire extends beyond histones to many nonhistone proteins. Besides being a deacetylase, HDAC8 also mediates signaling via scaffolding functions. Aberrant expression or deregulated interactions with transcription factors are critical in HDAC8-dependent cancers. Many potent HDAC8-selective inhibitors with cellular activity and anticancer effects have been reported. We present HDAC8 as a druggable target and discuss inhibitors of different chemical scaffolds with cellular effects. Furthermore, we review HDAC8 activators that revert activity of mutant enzymes. Isotype-selective HDAC8 targeting in patients with HDAC8-relevant cancers is challenging, however, is promising to avoid adverse side effects as observed with pan-HDAC inhibitors.

Vimentin dephosphorylation at ser-56 is regulated by type 1 protein phosphatase in smooth muscle

Background

The intermediate filament protein vimentin undergoes reversible phosphorylation and dephosphorylation at Ser-56, which plays an important role in regulating the contraction-relaxation cycles of smooth muscle. The protein phosphatases that mediate vimentin dephosphorylation in smooth muscle have not been previously investigated.

Methods

The associations of protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A) with vimentin in mouse tracheal rings was evaluated by co-immunoprecipitation. Lentivirus-mediated shRNA against PP1 was used to assess the role of PP1 in vimentin dephosphorylation and the vimentin-associated process in smooth muscle.

Results

Co-immunoprecipitation analysis showed that vimentin interacted with PP1, but barely with PP2A, in airway smooth muscle. Knockdown of PP1 by lentivirus-mediated shRNA increased the acetylcholine-induced vimentin phosphorylation and smooth muscle contraction. Because vimentin phosphorylation is able to modulate p130 Crk-associated substrate (p130CAS) and actin polymerization, we also evaluated the role of PP1 in the biological processes. Silencing of PP1 also enhanced the agonist-induced the dissociation of p130CAS from vimentin and F/G-actin ratios (an index of actin polymerization). However, PP1 knockdown did not affect c-Abl tyrosine phosphorylation, an important molecule that controls actin dynamics.

Conclusions

Taken together, these findings suggest that PP1 is a key protein serine/threonine phosphatase that controls vimentin Ser-56 dephosphorylation in smooth muscle. PP1 regulates actin polymerization by modulating the dissociation of p130CAS from vimentin, but not by affecting c-Abl tyrosine kinase.

Novel role of cortactin in G protein-coupled receptor agonist-induced nuclear export and degradation of p21Cip1

Monocyte chemotactic protein 1 (MCP1) stimulates phosphorylation of cortactin on Y421 and Y446 residues in a time-dependent manner and phosphorylation at Y446 but not Y421 residue is required for MCP1-induced CDK-interacting protein 1 (p21Cip1) nuclear export and degradation in facilitating human aortic smooth muscle cell (HASMC) proliferation. In addition, MCP1-induced cortactin tyrosine phosphorylation, p21Cip1 degradation and HASMC proliferation are dependent on Fyn activation. Upstream to Fyn, MCP1 stimulated C-C chemokine receptor type 2 (CCR2) and Gi/o and inhibition of either one of these molecules using their specific antagonists or inhibitors attenuated MCP1-induced cortactin tyrosine phosphorylation, p21Cip1 degradation and HASMC proliferation. Cortactin phosphorylation at Y446 residue is also required for another G protein-coupled receptor (GPCR) agonist, thrombin-induced p21Cip1 nuclear export and its degradation in promoting HASMC proliferation. Quite interestingly, the receptor tyrosine kinase (RTK) agonist, platelet-derived growth factor-BB (PDGF-BB)-induced p21Cip1 degradation and HASMC proliferation do not require cortactin tyrosine phosphorylation. Together, these findings demonstrate that tyrosine phosphorylation of cortactin at Y446 residue is selective for only GPCR but not RTK agonist-induced nuclear export and proteolytic degradation of p21Cip1 in HASMC proliferation.

Regulation of RhoA activation and cytoskeletal organization by acetylation

Rho GTPases regulate cell motility in a large part through control of actin cytoskeletal organization. The activation state of Rho proteins is regulated by a wide variety of guanine nucleotide exchange factors (GEFs) and GTPase activating proteins that are differentially expressed among cell types and disease states. The RhoA specific GEF neuroepithelial transforming gene 1 (Net1) is highly expressed in many cancer cells and stimulates cell motility, invasion and cell spreading in response to a variety of ligands. A key feature of Net1 proteins is that they are sequestered in the nucleus in the absence of a motility stimulus. We have recently found that accumulation of the Net1A isoform outside the nucleus, which is the primary Net1 isoform controlling cell motility, is regulated by its acetylation status. Here, we describe acetylation as a novel mechanism of RhoGEF regulation in cell motility that can be targeted in cancer and metastasis.