Identification of HDAC10, a novel class II human histone deacetylase containing a leucine-rich domain

Epigenetic tools (The Writers, The Readers and The Erasers) and their implications in cancer therapy

Addition of chemical tags on the DNA and modification of histone proteins impart a distinct feature on chromatin architecture. With the advancement in scientific research, the key players underlying these changes have been identified as epigenetic modifiers of the chromatin. Indeed, the plethora of enzymes catalyzing these modifications, portray the diversity of epigenetic space and the intricacy in regulating gene expression. These epigenetic players are categorized as writers: that introduce various chemical modifications on DNA and histones, readers: the specialized domain containing proteins that identify and interpret those modifications and erasers: the dedicated group of enzymes proficient in removing these chemical tags. Research over the past few decades has established that these epigenetic tools are associated with numerous disease conditions especially cancer. Besides, with the involvement of epigenetics in cancer, these enzymes and protein domains provide new targets for cancer drug development. This is certain from the volume of epigenetic research conducted in universities and R&D sector of pharmaceutical industry. Here we have highlighted the different types of epigenetic enzymes and protein domains with an emphasis on methylation and acetylation. This review also deals with the recent developments in small molecule inhibitors as potential anti-cancer drugs targeting the epigenetic space.

Gene alterations in monocytes are pathogenic factors for immunoglobulin a nephropathy by bioinformatics analysis of microarray data

Background

Immunoglobulin A nephropathy (IgAN) is the most frequent primary glomerulopathy worldwide. The study aimed to provide potential molecular biomarkers for IgAN management.

Methods

The public gene expression profiling GSE58539 was utilized, which contained 17 monocytes samples (8 monocytes samples isolated from IgAN patients and 9 monocytes samples isolated from healthy blood donors). Firstly, differentially expressed genes (DEGs) between the two kinds of samples were identified by limma package. Afterwards, pathway enrichment analysis was implemented. Thereafter, protein-protein interaction (PPI) network was constructed and key nodes in PPI network were predicted using four network centrality analyses. Ultimately, gene functional interaction (FI) was constructed according to expressions in each sample, and then module network was extracted from FI network.

Results

A total of 678 DEGs were screened out, of these, 72 DEGs were identified as crucial nodes in PPI network that could well distinguish IgAN and healthy samples. In particular, IL6, TNF, IL1B, PRKACA and CCL20 were closely related to pathways such as hematopoietic cell lineage, apoptosis and Toll-like receptor (TLR) signaling pathway. Moreover, 12 genes in the FI network belonged to the 72 identified key nodes, such as CCL20, HDAC10, FPR2 and PRKACA, which were also key genes in 4 module networks.

Conclusions

Several crucial genes were identified in monocytes of IgAN patients, such as IL6, TNF, IL1B, CCL20, PRKACA, FPR2 and HDAC10. These genes might co-involve in pathways such as TLR and apoptosis signaling during IgAN progression.

Polyamine Deacetylase Structure and Catalysis: Prokaryotic Acetylpolyamine Amidohydrolase and Eukaryotic HDAC10

Polyamines such as putrescine, spermidine, and spermine are small aliphatic cations that serve myriad biological functions in all forms of life. While polyamine biosynthesis and cellular trafficking pathways are generally well-defined, only recently has the molecular basis of reversible polyamine acetylation been established. In particular, enzymes that catalyze polyamine deacetylation reactions have been identified and structurally characterized: histone deacetylase 10 (HDAC10) from Homo sapiens and Danio rerio (zebrafish) is a highly specific N⁸-acetylspermidine deacetylase, and its prokaryotic counterpart, acetylpolyamine amidohydrolase (APAH) from Mycoplana ramosa, is a broad-specificity polyamine deacetylase. Similar to the greater family of HDACs, which mainly serve as lysine deacetylases, both enzymes adopt the characteristic arginase-deacetylase fold and employ a Zn²⁺-activated water molecule for catalysis. In contrast with HDACs, however, the active sites of HDAC10 and APAH are sterically constricted to enforce specificity for long, slender polyamine substrates and exclude bulky peptides and proteins containing acetyl-l-lysine. Crystal structures of APAH and D. rerio HDAC10 reveal that quaternary structure, i.e., dimer assembly, provides the steric constriction that directs the polyamine substrate specificity of APAH, whereas tertiary structure, a unique 3₁₀ helix defined by the P(E,A)CE motif, provides the steric constriction that directs the polyamine substrate specificity of HDAC10. Given the recent identification of HDAC10 and spermidine as mediators of autophagy, HDAC10 is rapidly emerging as a biomarker and target for the design of isozyme-selective inhibitors that will suppress autophagic responses to cancer chemotherapy, thereby rendering cancer cells more susceptible to cytotoxic drugs.

Lysine Acetylation Goes Global: From Epigenetics to Metabolism and Therapeutics

Post-translational acetylation of lysine residues has emerged as a key regulatory mechanism in all eukaryotic organisms. Originally discovered in 1963 as a unique modification of histones, acetylation marks are now found on thousands of nonhistone proteins located in virtually every cellular compartment. Here we summarize key findings in the field of protein acetylation over the past 20 years with a focus on recent discoveries in nuclear, cytoplasmic, and mitochondrial compartments. Collectively, these findings have elevated protein acetylation as a major post-translational modification, underscoring its physiological relevance in gene regulation, cell signaling, metabolism, and disease.

HDAC10 promotes lung cancer proliferation via AKT phosphorylation

Histone deacetylase 10 (HDAC10) is a member of the class II HDACs, and its role in cancer is emerging. In this study, we found that HDAC10 is highly expressed in lung cancer tissues. It resides mainly in the cytoplasm of lung cancer cells but resides in the nucleus of adjacent normal cells. Further examinations revealed that HDAC10 resides in the cytoplasm in multiple lung cancer cell lines, including the A549, H358 and H460 cell lines, but mainly resides in the nucleus of normal lung epithelial 16HBE cells. A leucine-rich motif, R505L506L507C508V509A510L511, was identified as its nuclear localization signal (NLS), and a mutant (Mut-505-511) featuring mutations to A at each of its original R and L positions was found to be nuclear-localization defective. Functional analysis revealed that HDAC10 promoted lung cancer cell growth and that its knockdown induced cell cycle arrest and apoptosis. Mechanistic studies showed that HDAC10 knockdown significantly decreased the phosphorylation of AKT at Ser473 and that AKT expression significantly rescued the cell cycle arrest and apoptosis elicited by HDAC10 knockdown. A co-immunoprecipitation assay suggested that HDAC10 interacts with AKT and that inhibition of HDAC10 activity decreases its interaction with and phosphorylation of AKT. Finally, we confirmed that HDAC10 promoted lung cancer proliferation in a mouse model. Our study demonstrated that HDAC10 localizes and functions in the cytoplasm of lung cancer cells, thereby underscoring its potential role in the diagnosis and treatment of lung cancer.

HDAC11 is a regulator of diverse immune functions

Histone deacetylases deacetylate histone and non-histone protein targets. Aberrant HDAC expression and function have been observed in several diseases, which make these enzymes attractive treatment targets. Here, we summarize recent literature that addresses the roles of HDAC11 on the regulation of different immune cells including neutrophils, myeloid derived suppressor cells and T-cells. HDAC11 was initially identified as a negative regulator of the well-known anti-inflammatory cytokine IL-10. Hence, antagonizing HDAC11 activity may have anti-tumor potential, whereas activating HDAC11 may be useful to treat chronic inflammation or autoimmunity. However, to anticipate biological side-effects of HDAC11 modulators, more molecular insights will be required.

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.

HDAC10 promotes angiogenesis in endothelial cells through the PTPN22/ERK axis

Angiogenesis is crucially involved in many physiological and pathological processes including tumor growth, but the molecular mechanisms regulating angiogenesis are incompletely understood. In this study, we investigated the functions and mechanism of histone deacetylase 10 (HDAC10), a member of the HDAC II family, in regulation of angiogenesis. HDAC10 overexpression in human umbilical vein endothelial cells (HUVECs) promoted tube formation, whereas depletion of HDAC10 from HUVECs inhibited tube formation in vitro and in vivo. Mechanistically, HDAC10 overexpression increased extracellular-regulated kinase 1/2 (ERK1/2) activation, whereas depletion of HDAC10 inhibited ERK1/2 activation. Finally, HDAC10 promoted ERK1/2 phosphorylation by deacetylating the promoter of protein tyrosine phosphatase, non-receptor type 22 (PTPN22) and inhibiting the expression of PTPN22, which is a negative regulator of ERK phosphorylation. Collectively, our results identify HDAC10 as a key regulator of angiogenesis and reveal that HDAC10 functions in this process by binding and deacetylating the PTPN22 promoter and subsequently inhibiting PTPN22 expression, which in turn increases ERK1/2 phosphorylation. Our studies suggest that HDAC10 is a potential target for therapeutic intervention to inhibit angiogenesis and tumor growth.

Histone deacetylase 10 structure and molecular function as a polyamine deacetylase

Cationic polyamines such as spermidine and spermine are critical in all forms of life, as they regulate the function of biological macromolecules. Intracellular polyamine metabolism is regulated by reversible acetylation and dysregulated polyamine metabolism is associated with neoplastic diseases such as colon cancer, prostate cancer and neuroblastoma. Here we report that histone deacetylase 10 (HDAC10) is a robust polyamine deacetylase, using recombinant enzymes from Homo sapiens (human) and Danio rerio (zebrafish). The 2.85 Å-resolution crystal structure of zebrafish HDAC10 complexed with a transition-state analogue inhibitor reveals that a glutamate gatekeeper and a sterically constricted active site confer specificity for N⁸-acetylspermidine hydrolysis and disfavour acetyllysine hydrolysis. Both HDAC10 and spermidine are known to promote cellular survival through autophagy. Accordingly, this work sets a foundation for studying the chemical biology of autophagy through the structure-based design of inhibitors that may also serve as new leads for cancer chemotherapy.

Polyamines bind to nucleic acids and their function is regulated by reversible acetylation. Here, the authors show that histone deacetylase 10 is a polyamine deacetylase and present its crystal structure with a bound polyamine transition state analogue inhibitor.

Exercise Training and Epigenetic Regulation: Multilevel Modification and Regulation of Gene Expression

Exercise training elicits acute and adaptive long term changes in human physiology that mediate the improvement of performance and health state. The responses are integrative and orchestrated by several mechanisms, as gene expression. Gene expression is essential to construct the adaptation of the biological system to exercise training, since there are molecular processes mediating oxidative and non-oxidative metabolism, angiogenesis, cardiac and skeletal myofiber hypertrophy, and other processes that leads to a greater physiological status. Epigenetic is the field that studies about gene expression changes heritable by meiosis and mitosis, by changes in chromatin and DNA conformation, but not in DNA sequence, that studies the regulation on gene expression that is independent of genotype. The field approaches mechanisms of DNA and chromatin conformational changes that inhibit or increase gene expression and determine tissue specific pattern. The three major studied epigenetic mechanisms are DNA methylation, Histone modification, and regulation of noncoding RNA-associated genes. This review elucidates these mechanisms, focusing on the relationship between them and their relationship with exercise training, physical performance and the enhancement of health status. On this chapter, we clarified the relationship of epigenetic modulations and their intimal relationship with acute and chronic effect of exercise training, concentrating our effort on skeletal muscle, heart and vascular responses, that are the most responsive systems against to exercise training and play crucial role on physical performance and improvement of health state.

A class of their own: exploring the nondeacetylase roles of class IIa HDACs in cardiovascular disease

Histone deacetylases (HDACs) play integral roles in many cardiovascular biological processes ranging from transcriptional and translational regulation to protein stabilization and localization. There are 18 known HDACs categorized into 4 classes that can differ on the basis of substrate targets, subcellular localization, and regulatory binding partners. HDACs are classically known for their ability to remove acetyl groups from histone and nonhistone proteins that have lysine residues. However, despite their nomenclature and classical functions, discoveries from many research groups over the past decade have suggested that nondeacetylase roles exist for class IIa HDACs. This is not surprising given that class IIa HDACs have, for example, relatively poor deacetylase capabilities and are often shuttled in and out of nuclei upon specific pathological and nonpathological cardiac events. This review aims to consolidate and elucidate putative nondeacetylase roles for class IIa HDACs and, where possible, highlight studies that provide evidence for their noncanonical roles, especially in the context of cardiovascular maladies. There has been great interest recently in exploring the pharmacological regulators of HDACs for use in therapeutic interventions for treating cardiovascular diseases and inflammation. Thus it is of interest to earnestly consider nonenzymatic and or nondeacetylase roles of HDACs that might be key in potentiating or abrogating pathologies. These noncanonical HDAC functions may possibly yield new mechanisms and targets for drug discovery.

HDAC inhibitor prevents LPS mediated inhibition of CYP19A1 expression and 17β-estradiol production in granulosa cells

LPS inhibits CYP19A1 expression and 17β-estradiol (E2) production in granulosa cells (GCs). This is one of the major causes of infertility underlying postpartum uterine infections. However, the precise molecular mechanism is not well elucidated. Recently we have shown, buffalo GCs exposed to LPS (1.0 μg/ml) in serum free culture, transiently increased the pro-inflammatory cytokine genes (IL-1β, TNF-α, IL-6) expression, followed by the inhibition of CYP19A1 expression and E2 production. The present study showed that transient increase in pro-inflammatory cytokines was associated with HDACs (gene expression and nuclear activity). Therefore, we tested the hypothesis if Trichostatin A (TSA), a HDAC inhibitor, can attenuate LPS induced pro-inflammatory cytokine gene expression and can prevent LPS mediated down-regulation of CYP19A1 expression and E2 in GCs. Results showed that TSA pre-treatment significantly attenuated LPS induced pro-inflammatory cytokine gene expressions, HDACs (both gene expression and enzyme activity in nucleus) and NF-κB nuclear translocation. Additionally, TSA pre-treatment reversed the inhibitory effect of LPS on CYP19A1 expression and E2 production. CHIP analyses of H3 (Lys 9/14) acetylation of ovary specific CYP19A1 proximal promoter (PII) showed that TSA pre-treatment prevented the LPS mediated H3 deacetylation, thereby increased the acetylation of PII and restored CYP19A1 expression and E2 production. The present study demonstrated that TSA pre-treatment attenuated- LPS induced immune response involving NF-κB and HDACs, and thus prevented inhibition of CYP19A1 expression and E2 production through chromatin remodeling. Our study suggests that HDAC inhibitors could be a potential therapeutic strategy to treat infertility underlying postpartum uterine infections.

Growth attenuation is associated with histone deacetylase 10-induced autophagy in the liver

Our previous data suggested that the histone deacetylase (HDAC) SIRT1 is involved in mediating the effect of nutrition on growth. The aim of the present research was to study the mechanism by which additional HDACs may be involved in nutrition-induced linear growth. The in vivo studies were performed in young male Sprague-Dawley rats that were either fed ad libitum (AL) or subjected to 10days of 40% food restriction (RES) and then refed (CU). For in vitro studies, Huh7 hepatoma cells were used. Food restriction led to significant reduction in liver weight, concomitant with increased autophagy (i.e., a decrease in the level of P62 and an increase in the expression level of Ambra1 and Atg16L2 genes in the RES group). At the same time, we found that the level of HDAC10 was significantly increased. Overexpression of HDAC10 in Huh7 hepatoma cells led to reduced cell viability and increased autophagy as shown by increased conversion of LC3-I to LC3-II. An increase in the level of HDAC10 was also obtained when mTOR was inhibited by Rapamycin. siRNA directed against HDAC10 abolished the effect of Rapamycin on cell viability and Ambra1 and Atg16L2 increased expression. These results suggest that increased levels of HDAC10 may mediate the effect of malnutrition on growth attenuation and autophagy. Deciphering the role of epigenetic regulation in the nutrition-growth connection may pave the way for the development of new forms of treatment for children with growth disorders.

Histone Deacetylase 10 Regulates the Cell Cycle G2/M Phase Transition via a Novel Let-7-HMGA2-Cyclin A2 Pathway

Histone deacetylase (HDAC) inhibition leads to cell cycle arrest in G1 and G2, suggesting HDACs as therapeutic targets for cancer and diseases linked to abnormal cell growth and proliferation. Many HDACs are transcriptional repressors. Some may alter cell cycle progression by deacetylating histones and repressing transcription of key cell cycle regulatory genes. Here, we report that HDAC10 regulates the cell cycle via modulation of cyclin A2 expression, and cyclin A2 overexpression rescues HDAC10 knockdown-induced G2/M transition arrest. HDAC10 regulates cyclin A2 expression by deacetylating histones near the let-7 promoter, thereby repressing transcription. In HDAC10 knockdown cells, let-7f and microRNA 98 (miR-98) were upregulated and the let-7 family target, HMGA2, was downregulated. HMGA2 loss resulted in enrichment of the transcriptional repressor E4F at the cyclin A2 promoter. These findings support a role for HDACs in cell cycle regulation, reveal a novel mechanism of HDAC10 action, and extend the potential of HDACs as targets in diseases of cell cycle dysregulation.

HDAC Family Members Intertwined in the Regulation of Autophagy: A Druggable Vulnerability in Aggressive Tumor Entities

The exploitation of autophagy by some cancer entities to support survival and dodge death has been well-described. Though its role as a constitutive process is important in normal, healthy cells, in the milieu of malignantly transformed and highly proliferative cells, autophagy is critical for escaping metabolic and genetic stressors. In recent years, the importance of histone deacetylases (HDACs) in cancer biology has been heavily investigated, and the enzyme family has been shown to play a role in autophagy, too. HDAC inhibitors (HDACi) are being integrated into cancer therapy and clinical trials are ongoing. The effect of HDACi on autophagy and, conversely, the effect of autophagy on HDACi efficacy are currently under investigation. With the development of HDACi that are able to selectively target individual HDAC isozymes, there is great potential for specific therapy that has more well-defined effects on cancer biology and also minimizes toxicity. Here, the role of autophagy in the context of cancer and the interplay of this process with HDACs will be summarized. Identification of key HDAC isozymes involved in autophagy and the ability to target specific isozymes yields the potential to cripple and ultimately eliminate malignant cells depending on autophagy as a survival mechanism.

Histone deacetylase 10 suppresses proliferation and invasion by inhibiting the phosphorylation of β-catenin and serves as an independent prognostic factor for human clear cell renal cell carcinoma

OBJECTIVE

Histone deacetylase (HDAC) is a tumor suppressor gene in various carcinomas; however, the effect of HDAC10 on human renal cell carcinoma (RCC) remains unknown. In the current study we analyzed the expression and function of HDAC10 in human clear cell RCC.

METHODS

RCC tissues from 145 patients who underwent radical nephrectomies were evaluated. HDAC10 protein and mRNA expression was examined by immunohistochemistry and quantitative RT-PCR, respectively. HDAC10 expression was increased by stable transfection with a vector containing full-length cDNA of HDAC10, and HDAC10 expression was decreased by siRNA in two RCC cell lines. Proliferation analysis of RCC cells in vitro was investigated using the WST-1 assay, and the invasion assay was performed using a 24-well Transwell chamber. The phosphorylation of β-catenin induced by HDAC10 was evaluated by Western blot.

RESULTS

HDAC10 expression in RCC tissues was significantly down-regulated compared to normal kidney tissues. Moreover, the low level of HDAC10 expression was uniformly associated with advanced clinical stage, larger tumor diameter, higher pathologic grade, and metastatic RCC. In addition, decreased expression of HDAC10 significantly prompted the proliferation and invasion of RCC cells in vitro. Although HDAC10 did not regulate the expression of β-catenin, HDAC10 suppressed the phosphorylation of β-catenin in RCC cells.

CONCLUSIONS

HDAC10 expression is suppressed in human clear cell RCC and is involved in development and metastasis of RCC. The findings herein suggest that HDAC10 is an independent predictive factor for RCC prognosis, and restoring HDAC10 expression may be a new therapeutic strategy for advanced RCC.

Targeting histone deacetylases: a novel approach in Parkinson's disease

The worldwide prevalence of movement disorders is increasing day by day. Parkinson's disease (PD) is the most common movement disorder. In general, the clinical manifestations of PD result from dysfunction of the basal ganglia. Although the exact underlying mechanisms leading to neural cell death in this disease remains unknown, the genetic causes are often established. Indeed, it is becoming increasingly evident that chromatin acetylation status can be impaired during the neurological disease conditions. The acetylation and deacetylation of histone proteins are carried out by opposing actions of histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. In the recent past, studies with HDAC inhibitors result in beneficial effects in both in vivo and in vitro models of PD. Various clinical trials have also been initiated to investigate the possible therapeutic potential of HDAC inhibitors in patients suffering from PD. The possible mechanisms assigned for these neuroprotective actions of HDAC inhibitors involve transcriptional activation of neuronal survival genes and maintenance of histone acetylation homeostasis, both of which have been shown to be dysregulated in PD. In this review, the authors have discussed the putative role of HDAC inhibitors in PD and associated abnormalities and suggest new directions for future research in PD.

How the flexibility of human histone deacetylases influences ligand binding: an overview

Over the past decade, human histone deacetylases (HDACs) have become interesting as therapeutic targets because of the benefits that their modulation might provide in aging-related disorders. Recently, studies using crystallography and computational chemistry have provided information on the structure and conformational changes related to HDAC-mediated recognition events. Through the description of the key mass and one-off movements observed in metal-dependent HDACs, here we highlight the impact of flexibility on drug-binding affinity and specificity. The collected information will be useful for not only a better understanding of the biological functions of HDACs, but also the conception of new selective binders.

50 years of protein acetylation: from gene regulation to epigenetics, metabolism and beyond

In 1964, Vincent Allfrey and colleagues reported the identification of histone acetylation and with deep insight proposed a regulatory role for this protein modification in transcription regulation. Subsequently, histone acetyltransferases (HATs), histone deacetylases (HDACs) and acetyl-Lys-binding proteins were identified as transcription regulators, thereby providing compelling evidence for his daring hypothesis. During the past 15 years, reversible protein acetylation and its modifying enzymes have been implicated in many cellular functions beyond transcription regulation. Here, we review the progress accomplished during the past 50 years and discuss the future of protein acetylation.

Towards selective inhibition of histone deacetylase isoforms: what has been achieved, where we are and what will be next

Histone deacetylases (HDACs) are widely studied targets for the treatment of cancer and other diseases. Up to now, over twenty HDAC inhibitors have entered clinical studies and two of them have already reached the market, namely the hydroxamic acid derivative SAHA (vorinostat, Zolinza) and the cyclic depsipeptide FK228 (romidepsin, Istodax) that have been approved for the treatment of cutaneous T-cell lymphoma (CTCL). A common aspect of the first HDAC inhibitors is the absence of any particular selectivity towards specific isozymes. Some of molecules resulted to be “pan”-HDAC inhibitors, while others are class I selective. In the meantime, the knowledge of HDAC biology has continuously progressed. Key advances in the structural biology of various isozymes, reliable molecular homology models as well as suitable biological assays have provided new tools for drug discovery activities. This Minireview aims at surveying these recent developments as well as the design, synthesis and biological characterization of isoform-selective derivatives.

Differential effects of binge methamphetamine injections on the mRNA expression of histone deacetylases (HDACs) in the rat striatum

Methamphetamine use disorder is characterized by recurrent binge episodes. Humans addicted to methamphetamine experience various degrees of cognitive deficits and show evidence of neurodegenerative processes in the brain. Binge injections of METH to rodents also cause significant toxic changes in the brain. In addition, this pattern of METH injections can alter gene expression in the dorsal striatum. Gene expression is regulated, in part, by histone deacetylation. We thus tested the possibility that METH toxic doses might cause changes in the mRNA levels of histone deacetylases (HDACs). We found that METH did produce significant decreases in the mRNA expression of HDAC8, which is a class I HDAC. METH also decreased expression of HDAC6, HDAC9, and HDAC10 that are class II HDACs. The expression of the class IV HDAC, HDAC11, was also suppressed by METH. The expression of Sirt2, Sirt5, and Sirt6 that are members of class III HDACs was also downregulated by METH injections. Our findings implicate changes in HDAC expression may be an early indicator of impending METH-induced neurotoxicity in the striatum. This idea is consistent with the accumulated evidence that some HDACs are involved in neurodegenerative processes in the brain.

Decreased expression of histone deacetylase 10 predicts poor prognosis of gastric cancer patients

Aberrant expression of histone deacetylase (HDACs) was associated with carcinogenesis and progression of various tumors. However, the association of HDAC10 with clinical outcomes in gastric cancer patients is unclear. Thus, the objective of the current study was to evaluate the association of expression level of HDAC10 with clinicopathologic factors and prognosis of patients with gastric cancer. The expression level of HDAC10 in 179 paraffin-embedded gastric cancer tissue specimens was examined by immunohistochemistry (IHC). As a result, we found that expression of HDAC10 in gastric cancer was significantly decreased in gastric cancer tissues as compared with adjacent tissues (51.4% vs. 87.3%, P < 0.001). HDAC10 expression was significantly correlated with gender (P = 0.023), tumor size (P = 0.015), histological grade (P = 0.009), tumor invasion (P = 0.033), lymph node metastatic status (P = 0.019) and tumor stage (P = 0.004), but not correlated with age and lauren classification (all P > 0.05). Kaplan-Meier survival curves showed that the overall survival rate was significantly lower in the patients with low expression of HDAC10 compared with those patients with high HDAC10 (P < 0.001). Moreover, multivariate analysis revealed that HDAC10 expression was an independent prognostic factor for gastric cancer patients (P = 0.001). These results suggest that HDAC10 expression could see as a prognosis marker for gastric cancer patients.

Targeting histone deacetylases for cancer therapy: from molecular mechanisms to clinical implications

Genetic abnormalities have been conventionally considered as hallmarks of cancer. However, studies over the past decades have demonstrated that epigenetic regulation also participates in the development of cancer. The fundamental patterns of epigenetic components, such as DNA methylation and histone modifications, are frequently altered in tumor cells. Acetylation is one of the best characterized modifications of histones, which is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDACs). HDACs are a group of enzymes which catalyze the removal of the acetyl groups of both histones and non-histone proteins. HDACs are involved in modulating most key cellular processes, including transcriptional regulation, apoptosis, DNA damage repair, cell cycle control, autophagy, metabolism, senescence and chaperone function. Because HDACs have been found to function incorrectly in cancer, various HDAC inhibitors are being investigated to act as cancer chemotherapeutics. The primary purpose of this paper is to summarize recent studies of the links between HDACs and cancer, and further discuss the underlying mechanisms of anti-tumor activities of HDAC inhibitors and clinical implications.

Histone deacetylase (HDAC) 10 suppresses cervical cancer metastasis through inhibition of matrix metalloproteinase (MMP) 2 and 9 expression

Aberrant expression of histone deacetylases (HDACs) is associated with carcinogenesis. Some HDAC inhibitors are widely considered as promising anticancer therapeutics. A major obstacle for development of HDAC inhibitors as highly safe and effective anticancer therapeutics is that our current knowledge on the contributions of different HDACs in various cancer types remains scant. Here we report that the expression level of HDAC10 was significantly lower in patients exhibiting lymph node metastasis compared with that in patients lacking lymph node metastasis in human cervical squamous cell carcinoma. Forced expression of HDAC10 in cervical cancer cells significantly inhibited cell motility and invasiveness in vitro and metastasis in vivo. Mechanistically, HDAC10 suppresses expression of matrix metalloproteinase (MMP) 2 and 9 genes, which are known to be critical for cancer cell invasion and metastasis. At the molecular level, HDAC10 binds to MMP2 and -9 promoter regions, reduces the histone acetylation level, and inhibits the binding of RNA polymerase II to these regions. Furthermore, an HDAC10 mutant lacking histone deacetylase activity failed to mimic the functions of full-length protein. These results identify a critical role of HDAC10 in suppression of cervical cancer metastasis, underscoring the importance of developing isoform-specific HDAC inhibitors for treatment of certain cancer types such as cervical squamous cell carcinoma.

Metabolic reprogramming by class I and II histone deacetylases

Accumulating evidence suggests that protein acetylation plays a major regulatory role in many facets of transcriptional control of metabolism. The enzymes that catalyze the addition and removal of acetyl moieties are the histone acetyl transferases (HATs) and histone deacetylases (HDACs), respectively. Several recent studies have uncovered novel mechanisms and contexts in which different HDACs play crucial roles in metabolic control. Understanding the role of class I and II HDACs in different metabolic programs during development, as well as in the physiology and pathology of the adult organism, will lead to novel therapeutics for metabolic disease. Here, we review the current understanding of how class I and class II HDACs contribute to metabolic control.

Screening of selective histone deacetylase inhibitors by proteochemometric modeling

BACKGROUND

Histone deacetylase (HDAC) is a novel target for the treatment of cancer and it can be classified into three classes, i.e., classes I, II, and IV. The inhibitors selectively targeting individual HDAC have been proved to be the better candidate antitumor drugs. To screen selective HDAC inhibitors, several proteochemometric (PCM) models based on different combinations of three kinds of protein descriptors, two kinds of ligand descriptors and multiplication cross-terms were constructed in our study.

RESULTS

The results show that structure similarity descriptors are better than sequence similarity descriptors and geometry descriptors in the leftacterization of HDACs. Furthermore, the predictive ability was not improved by introducing the cross-terms in our models. Finally, a best PCM model based on protein structure similarity descriptors and 32-dimensional general descriptors was derived (R2 = 0.9897, Qtest2 = 0.7542), which shows a powerful ability to screen selective HDAC inhibitors.

CONCLUSIONS

Our best model not only predict the activities of inhibitors for each HDAC isoform, but also screen and distinguish class-selective inhibitors and even more isoform-selective inhibitors, thus it provides a potential way to discover or design novel candidate antitumor drugs with reduced side effect.

HDAC6 at the Intersection of Neuroprotection and Neurodegeneration

Histone deacetylase 6 (HDAC6) catalyzes multiple reactions. We summarize the current knowledge on HDAC6, its targets and functions. Among others, HDAC6 recognizes damaged proteins and assures that these proteins are destroyed by autophagy. On the other hand, HDAC6 also modifies the tracks used by the clearance mechanism so that axonal transport becomes less efficient. We hypothesize that a disturbance in the equilibrium between the different functions of HDAC6 could play an important role in neurodegeneration.

Histone deacetylase modulators provided by Mother Nature

Protein acetylation status results from a balance between histone acetyltransferase and histone deacetylase (HDAC) activities. Alteration of this balance leads to a disruption of cellular integrity and participates in the development of numerous diseases, including cancer. Therefore, modulation of these activities appears to be a promising approach for anticancer therapy. Histone deacetylase inhibitors (HDACi) are epigenetically active drugs that induce the hyperacetylation of lysine residues within histone and non-histone proteins, thus affecting gene expression and cellular processes such as protein-protein interactions, protein stability, DNA binding and protein sub-cellular localization. Therefore, HDACi are promising anti-tumor agents as they may affect the cell cycle, inhibit proliferation, stimulate differentiation and induce apoptotic cell death. Over the last 30 years, numerous synthetic and natural products, including a broad range of dietary compounds, have been identified as HDACi. This review focuses on molecules from natural origins modulating HDAC activities and presenting promising anticancer activities.

Overview of the Classical Histone Deacetylase Enzymes and Histone Deacetylase Inhibitors

The important role of histone deacetylase enzymes in regulating gene expression, cellular proliferation, and survival has made them attractive targets for the development of histone deacetylase inhibitors as anticancer drugs. Suberoylanilide hydroxamic acid (Vorinostat, Zolinza), a structural analogue of the prototypical Trichostatin A, was approved by the US Food and Drug Administration for the treatment of advanced cutaneous T-cell lymphoma in 2006. This was followed by approval of the cyclic peptide, depsipeptide (Romidepsin, Istodax) for the same disease in 2009. Currently numerous histone deacetylase inhibitors are undergoing preclinical and clinical trials for the treatment of hematological and solid malignancies. Most of these studies are focused on combinations of histone deacetylase inhibitors with other therapeutic modalities, particularly conventional chemotherapeutics and radiotherapy. The aim of this paper is to provide an overview of the classical histone deacetylase enzymes and histone deacetylase inhibitors with an emphasis on potential combination therapies.

Histone deacetylase cytoplasmic trapping by a novel fluorescent HDAC inhibitor

Inhibitors of histone deacetylases (HDAC) are an important emerging class of drugs for the treatment of cancers. HDAC inhibitors are currently under evaluation in clinical trials as single agents and as sensitizers in combinations with chemotherapies and radiation therapy. Although these drugs have important effects on cancer cell growth and functions, the mechanisms underlying HDAC inhibitor activities remain to be fully defined. By using rational drug design, compound 2, a fluorescent class II HDAC targeting inhibitor, was synthesized and observed to accumulate in the cytoplasmic compartments of treated cells, but not in the nuclei. Furthermore, immunostaining of inhibitor exposed cells for HDAC4 showed accumulation of this enzyme in the cytoplasmic compartment with concomitant increased acetylation of tubulin and nuclear histones. These observations support a mechanism by which nuclear histone acetylation is increased as a result of HDAC4 trapping and sequestration in the cytoplasm after binding to compound 2. The HDAC inhibitor offers potential as a novel theranostic agent, combining diagnostic and therapeutic properties in the same molecule.

HDAC3 and the molecular brake pad hypothesis

Successful transcription of specific genes required for long-term memory processes involves the orchestrated effort of not only transcription factors, but also very specific enzymatic protein complexes that modify chromatin structure. Chromatin modification has been identified as a pivotal molecular mechanism underlying certain forms of synaptic plasticity and memory. The best-studied form of chromatin modification in the learning and memory field is histone acetylation, which is regulated by histone acetyltransferases and histone deacetylases (HDACs). HDAC inhibitors have been shown to strongly enhance long-term memory processes, and recent work has aimed to identify contributions of individual HDACs. In this review, we focus on HDAC3 and discuss its recently defined role as a negative regulator of long-term memory formation. HDAC3 is part of a corepressor complex and has direct interactions with Class II HDACs that may be important for its molecular and behavioral consequences. And last, we propose the "molecular brake pad" hypothesis of HDAC function. The HDACs and associated corepressor complexes may function in neurons, in part, as "molecular brake pads." HDACs are localized to promoters of active genes and act as a persistent clamp that requires strong activity-dependent signaling to temporarily release these complexes (or brake pads) to activate gene expression required for long-term memory formation. Thus, HDAC inhibition removes the "molecular brake pads" constraining the processes necessary for long-term memory and results in strong, persistent memory formation.

Structure of prokaryotic polyamine deacetylase reveals evolutionary functional relationships with eukaryotic histone deacetylases

Polyamines are a ubiquitous class of polycationic small molecules that can influence gene expression by binding to nucleic acids. Reversible polyamine acetylation regulates nucleic acid binding and is required for normal cell cycle progression and proliferation. Here, we report the structures of Mycoplana ramosa acetylpolyamine amidohydrolase (APAH) complexed with a transition state analogue and a hydroxamate inhibitor and an inactive mutant complexed with two acetylpolyamine substrates. The structure of APAH is the first of a histone deacetylase-like oligomer and reveals that an 18-residue insert in the L2 loop promotes dimerization and the formation of an 18 Å long "L"-shaped active site tunnel at the dimer interface, accessible only to narrow and flexible substrates. The importance of dimerization for polyamine deacetylase function leads to the suggestion that a comparable dimeric or double-domain histone deacetylase could catalyze polyamine deacetylation reactions in eukaryotes.

The tale of protein lysine acetylation in the cytoplasm

Reversible posttranslational modification of internal lysines in many cellular or viral proteins is now emerging as part of critical signalling processes controlling a variety of cellular functions beyond chromatin and transcription. This paper aims at demonstrating the role of lysine acetylation in the cytoplasm driving and coordinating key events such as cytoskeleton dynamics, intracellular trafficking, vesicle fusion, metabolism, and stress response.

Inhibition of histone deacetylase 10 induces thioredoxin-interacting protein and causes accumulation of reactive oxygen species in SNU-620 human gastric cancer cells

Histone deacetylase (HDAC)10, a novel class IIb histone deacetylase, is the most similar to HDAC6, since both contain a unique second catalytic domain. Unlike HDAC6, which is located in the cytoplasm, HDAC10 resides in both the nucleus and cytoplasm. The transcriptional targets of HDAC10 that are associated with HDAC10 gene regulation have not been identified. In the present study, we found that knockdown of HDAC10 significantly increased the mRNA expression levels of thioredoxin-interacting protein (TXNIP) in SNU-620 human gastric cancer cells; whereas inhibition of HDAC1, HDAC2, and HDAC6 did not affect TXNIP expression. TXNIP is the endogenous inhibitor of thioredoxin (TRX), which acts as a cellular antioxidant. Real-time PCR and immunoblot analysis confirmed that inhibition of HDAC10 induced TXNIP expression. Compared to class I only HDAC inhibitors, inhibitors targeting both class I and II upregulated TXNIP, indicating that TXNIP is regulated by class II HDACs such as HDAC10. We further verified that inhibition of HDAC10 induced release of cytochrome c and activated apoptotic signaling molecules through accumulation of reactive oxygen species (ROS). Taken together, our results demonstrate that HDAC10 is involved in transcriptional downregulation of TXNIP, leading to altered ROS signaling in human gastric cancer cells. How TXNIP is preferentially regulated by HDAC10 needs further investigation.

Histone deacetylase 10 relieves repression on the melanogenic program by maintaining the deacetylation status of repressors

HDAC10 belongs to the class II histone deacetylase family; however, its functions remain enigmatic. We report here that the HDAC10 protein complex contained deacetylated chaperone protein hsc70, and HDAC10 relieved repression of melanogenesis by decreasing the repressional activity of two transcriptional regulators, paired box protein 3 (Pax3) and KRAB-associated protein 1 (KAP1). HDAC10 physically interacted with Pax3 and KAP1 in a ternary complex and maintained Pax3 and KAP1 in a deacetylated state. Deacetylated Pax3 and KAP1 derepressed promoters of microphthalmia-associated transcription factor (MITF) and melanocyte-specific tyrosinase-related protein 1 and 2 (TRP-1 and TRP-2), three genes of the melanogenesis cascade, in a trichostatin A-sensitive manner. Co-occupancy of melanogenic promoters by HDAC10, Pax3, and KAP1 only happened in cells of the melanocyte lineage, and KAP1 facilitated nuclear enrichment of HDAC10. Finally, cellular melanin content correlated directly with the expression level and activity of HDAC10. Our results not only show that HDAC10 regulates melanogenesis but also demonstrate that the transcriptional activities of Pax3 and KAP1 are intimately linked to their acetylation status.

Histone deacetylase inhibitors induce apoptosis in human eosinophils and neutrophils

Background

Granulocytes are important in the pathogenesis of several inflammatory diseases. Apoptosis is pivotal in the resolution of inflammation. Apoptosis in malignant cells is induced by histone deacetylase (HDAC) inhibitors, whereas HDAC inhibitors do not usually induce apoptosis in non-malignant cells. The aim of the present study was to explore the effects of HDAC inhibitors on apoptosis in human eosinophils and neutrophils.

Methods

Apoptosis was assessed by relative DNA fragmentation assay, annexin-V binding, and morphologic analysis. HDAC activity in nuclear extracts was measured with a nonisotopic assay. HDAC expression was measured by real-time PCR.

Results

A HDAC inhibitor Trichostatin A (TSA) induced apoptosis in the presence of survival-prolonging cytokines interleukin-5 and granulocyte-macrophage colony stimulating factor (GM-CSF) in eosinophils and neutrophils. TSA enhanced constitutive eosinophil and neutrophil apoptosis. Similar effects were seen with a structurally dissimilar HDAC inhibitor apicidin. TSA showed additive effect on the glucocorticoid-induced eosinophil apoptosis, but antagonized glucocorticoid-induced neutrophil survival. Eosinophils and neutrophils expressed all HDACs at the mRNA level except that HDAC5 and HDAC11 mRNA expression was very low in both cell types, HDAC8 mRNA was very low in neutrophils and HDAC9 mRNA low in eosinophils. TSA reduced eosinophil and neutrophil nuclear HDAC activities by ~50-60%, suggesting a non-histone target. However, TSA did not increase the acetylation of a non-histone target NF-κB p65. c-jun-N-terminal kinase and caspases 3 and 6 may be involved in the mechanism of TSA-induced apoptosis, whereas PI3-kinase and caspase 8 are not.

Conclusions

HDAC inhibitors enhance apoptosis in human eosinophils and neutrophils in the absence and presence of survival-prolonging cytokines and glucocorticoids.

Alcohol-induced protein hyperacetylation: Mechanisms and consequences

Although the clinical manifestations of alcoholic liver disease are well-described, little is known about the molecular basis of liver injury. Recent studies have indicated that ethanol exposure induces global protein hyperacetylation. This reversible, post-translational modification on the epsilon-amino groups of lysine residues has been shown to modulate multiple, diverse cellular processes ranging from transcriptional activation to microtubule stability. Thus, alcohol-induced protein hyperacetylation likely leads to major physiological consequences that contribute to alcohol-induced hepatotoxicity. Lysine acetylation is controlled by the activities of two opposing enzymes, histone acetyltransferases and histone deacetylases. Currently, efforts are aimed at determining which enzymes are responsible for the increased acetylation of specific substrates. However, the greater challenge will be to determine the physiological ramifications of protein hyperacetylation and how they might contribute to the progression of liver disease. In this review, we will first list and discuss the proteins known to be hyperacetylated in the presence of ethanol. We will then describe what is known about the mechanisms leading to increased protein acetylation and how hyperacetylation may perturb hepatic function.

Therapeutic application of histone deacetylase inhibitors for central nervous system disorders

Histone deacetylases (HDACs)--enzymes that affect the acetylation status of histones and other important cellular proteins--have been recognized as potentially useful therapeutic targets for a broad range of human disorders. Pharmacological manipulations using small-molecule HDAC inhibitors--which may restore transcriptional balance to neurons, modulate cytoskeletal function, affect immune responses and enhance protein degradation pathways--have been beneficial in various experimental models of brain diseases. Although mounting data predict a therapeutic benefit for HDAC-based therapy, drug discovery and development of clinical candidates face significant challenges. Here, we summarize the current state of development of HDAC therapeutics and their application for the treatment of human brain disorders such as Rubinstein-Taybi syndrome, Rett syndrome, Friedreich's ataxia, Huntington's disease and multiple sclerosis.

Histone deacetylase 7 promotes PML sumoylation and is essential for PML nuclear body formation

Promyelocytic leukemia protein (PML) sumoylation has been proposed to control the formation of PML nuclear bodies (NBs) and is crucial for PML-dependent cellular processes, including apoptosis and transcriptional regulation. However, the regulatory mechanisms of PML sumoylation and its specific roles in the formation of PML NBs remain largely unknown. Here, we show that histone deacetylase 7 (HDAC7) knockdown reduces the size and the number of the PML NBs in human umbilical vein endothelial cells (HUVECs). HDAC7 coexpression stimulates PML sumoylation independent of its HDAC activity. Furthermore, HDAC7 associates with the E2 SUMO ligase, Ubc9, and stimulates PML sumoylation in vitro, suggesting that it possesses a SUMO E3 ligase-like activity to promote PML sumoylation. Importantly, HDAC7 knockdown inhibits tumor necrosis factor alpha-induced PML sumoylation and the formation of PML NBs in HUVECs. These results demonstrate a novel function of HDAC7 and provide a regulatory mechanism of PML sumoylation.

Evolution of the arginase fold and functional diversity

Novel structural superfamilies can be identified among the large number of protein structures deposited in the Protein Data Bank based on conservation of fold in addition to conservation of amino acid sequence. Since sequence diverges more rapidly than fold in protein Evolution, proteins with little or no significant sequence identity are occasionally observed to adopt similar folds, thereby reflecting unanticipated evolutionary relationships. Here, we review the unique alpha/beta fold first observed in the manganese metalloenzyme rat liver arginase, consisting of a parallel eight-stranded beta-sheet surrounded by several helices, and its evolutionary relationship with the zinc-requiring and/or iron-requiring histone deacetylases and acetylpolyamine amidohydrolases. Structural comparisons reveal key features of the core alpha/beta fold that contribute to the divergent metal ion specificity and stoichiometry required for the chemical and biological functions of these enzymes.

The use of diversity profiling to characterize chemical modulators of the histone deacetylases

Target specificity and off-target liabilities are routinely monitored during the early phases of drug discovery for most kinase projects. Typically these criteria are evaluated using a profiling panel comprised of a diverse collection of in vitro kinase assays and relates compound structure to potency and selectivity. The success of these efforts has led to the design of similar panels for phosphatase, protease, and epigenetic targets. Here the implementation of an epigenetic profiling panel, comprised of eleven histone deacetylases (HDACs) and one histone acetyltransferase (HAT), was used to evaluate chemical modulators of these enzymes. HDAC inhibitors (HDACi) such as sodium butyrate and trichostatin A demonstrate diverse biological effects which have led to broad speculation about their therapeutic potential in multiple disease states. Some HDACi have demonstrated tumor suppression in vivo and recently Zolinza was the first HDACi approved by the FDA for the treatment of cutaneous T-cell lymphoma. While HDACi have demonstrated therapeutic utility, many of the first generation compounds are pan-inhibitors. Thus, use of an HDAC profiling panel will be essential in achieving isoform specificity of the next generation of inhibitors. To this end, twenty-one compounds, twelve of which are known to have activities against the HDACs, were tested to evaluate the utility of the epigenetic panel. Additionally, these compounds were tested against a larger 72 member enzyme panel comprised of kinase, phosphatase and protease activities. This effort represents the first time these compounds have been profiled with such a broad range of biochemical activities.

HDAC10 promoter polymorphism associated with development of HCC among chronic HBV patients

Histone deacetylases (HDACs) are key enzymes responsible for the removal of acetyl groups from acetylated histone and non-histone proteins, and play important roles in various biological processes including transcription regulation and DNA repair. In this study, we identified 22 sequence variants by direct DNA sequencing in 24 individuals and five common variant were selected for genotyping in larger-scale subjects (n=1095). Statistical analysis revealed that HDAC10-589C>T was significantly associated with HCC occurrence among chronic HBV patients (OR=2.39, P(cor)=0.04) as well as HCC acceleration among chronic HBV patients (RH=1.97, Pcor=0.002). Functional assay also revealed that luciferase activity of "T" allele was significantly higher than that of "C" allele of HDAC10-589C>T (P=0.023). These results suggest that the "T" allele of HDAC10-589C>T affect on the increased transcription activity, and might accelerate HCC development through increased expression of HDAC10.

Class IIa histone deacetylases: regulating the regulators

In the last decade, the identification of enzymes that regulate acetylation of histones and nonhistone proteins has revealed the key role of dynamic acetylation and deacetylation in various cellular processes. Mammalian histone deacetylases (HDACs), which catalyse the removal of acetyl groups from lysine residues, are grouped into three classes, on the basis of similarity to yeast counterparts. An abundance of experimental evidence has established class IIa HDACs as crucial transcriptional regulators of various developmental and differentiation processes. In the past 5 years, a tremendous effort has been dedicated to characterizing the regulation of these enzymes. In this review, we summarize the latest discoveries in the field and discuss the molecular and structural determinants of class IIa HDACs regulation. Finally, we emphasize that comprehension of the mechanisms underlying class IIa HDAC functions is essential for potential therapeutic applications.

HDAC6, at the crossroads between cytoskeleton and cell signaling by acetylation and ubiquitination

Histone deacetylase 6 (HDAC6) is a unique enzyme with specific structural and functional features. It is actively or stably maintained in the cytoplasm and is the only member, within the histone deacetylase family, that harbors a full duplication of its deacetylase homology region followed by a specific ubiquitin-binding domain at the C-terminus end. Accordingly, this deacetylase functions at the heart of a cellular regulatory mechanism capable of coordinating various cellular functions largely relying on the microtubule network. Moreover, HDAC6 action as a regulator of the HSP90 chaperone activity adds to the multifunctionality of the protein, and allows us to propose a critical role for HDAC6 in mediating and coordinating various cellular events in response to different stressful stimuli.

Histone deacetylase inhibitors in APL and beyond

In recent years the study of chemical modifications to chromatin and their effects on cellular processes has become increasingly important in the field of cancer research. Disruptions to the normal epigenetic pattern of the cell can serve as biomarkers and are important determinants of cancer progression. Accordingly, drugs that inhibit the enzymes responsible for modulating these epigenetic markers, in particular histone deacetylases, are the focus of intense research and development. In this chapter we provide an overview of class I and II histone deacetylases as well as a guide to the diverse types of histone deacetylase inhibitors and their activities in the context of APL. We also discuss the rationale for the use of histone deacetylase inhibitors in combination therapy for the treatment of cancer and the current status of clinical trials.