Histone deacetylase 6 (HDAC6) is an unique subtype of histone deacetylases with two tandem deacetylase domains and substrate specificity for non-histone proteins. It is involved in many important physiological and pathological processes and has become a promising therapeutic target in recent decades. Different kinds of potent HDAC6-selective inhibitors have been reported around the world. This paper reviews the progress in the study of structure and functions of HDAC6 as well as the development of HDAC6-selective inhibitors.
Histone Deacetylase Inhibitors ; pharmacology ; Histone Deacetylases ; chemistry ; Humans ; Substrate Specificity

BACKGROUNDPlacental multidrug resistance-associated protein 2 (MRP2), encoded by ABCC2 gene in human, plays a significant role in regulating drugs' transplacental transfer rates. Studies on placental MRP2 regulation could provide more therapeutic targets for individualized and safe pharmacotherapy during pregnancy. Currently, the roles of epigenetic mechanisms in regulating placental drug transporters are still unclear. This study aimed to investigate the effect of histone deacetylases (HDACs) inhibition on MRP2 expression in the placental trophoblast cell line and to explore whether HDAC1/2/3 are preliminarily involved in this process.

METHODSThe human choriocarcinoma-derived trophoblast cell line (Bewo cells) was treated with the HDAC inhibitors-trichostatin A (TSA) at different concentration gradients of 0.5, 1.0, 3.0, and 5.0 μmol/L. Cells were harvested after 24 and 48 h treatment. Small interfering RNA (siRNA) specific for HDAC1/HDAC2/HDAC3 or control siRNA was transfected into cells. Total HDAC activity was detected by colorimetric assay kits. HDAC1/2/3/ABCC2 messenger RNA (mRNA) and protein expressions were determined by real-time quantitative polymerase chain reaction and Western-blot analysis, respectively. Immunofluorescence for MRP2 protein expression was visualized and assessed using an immunofluorescence microscopy and ImageJ software, respectively.

RESULTSTSA could inhibit total HDAC activity and HDAC1/2/3 expression in company with increase of MRP2 expression in Bewo cells. Reduction of HDAC1 protein level was noted after 24 h of TSA incubation at 1.0, 3.0, and 5.0 μmol/L (vs. vehicle group, all P < 0.001), accompanied with dose-dependent induction of MRP2 expression (P = 0.045 for 1.0 μmol/L, P = 0.001 for 3.0 μmol/L, and P < 0.001 for 5.0 μmol/L), whereas no significant differences in MRP2 expression were noted after HDAC2/3 silencing. Fluorescent micrograph images of MRP2 protein were expressed on the cell membrane. The fluorescent intensities of MRP2 in the control, HDAC2, and HDAC3 siRNA-transfected cells were week, and no significant differences were noticed among these three groups (all P > 0.05). However, MRP2 expression was remarkably elevated in HDAC1 siRNA-transfected cells, which displayed an almost 3.19-fold changes in comparison with the control siRNA-transfected cells (P < 0.001).

CONCLUSIONSHDACs inhibition could up-regulate placental MRP2 expression in vitro, and HDAC1 was probably to be involved in this process.

Cell Line ; Histone Deacetylase 1 ; metabolism ; Histone Deacetylase 2 ; metabolism ; Histone Deacetylase Inhibitors ; pharmacology ; Histone Deacetylases ; metabolism ; Humans ; Hydroxamic Acids ; pharmacology ; Microscopy, Fluorescence ; Multidrug Resistance-Associated Proteins ; genetics ; metabolism ; RNA, Messenger ; Trophoblasts ; cytology ; metabolism

The self-renewal and differentiation of hematopoietic stem cells(HSCs)are highly regulated by epigenetic modification,in which histone acetylation can activate or silence gene transcription.Histone deacetylase inhibitors(HDACIs)can inhibit the activity of histone deacetylase in HSCs to increase histone acetylation.A variety of HDACIs,such as trichostatin A and valproic acid,are used to expand HSCs in vitro,especially cord blood HSCs,combined with cytokines in serum-free culture to obtain more long-term repopulating cells.HDACIs promote the transcription of pluripotent genes related to stem cell self-renewal and inhibit the expression of genes related to differentiation,so as to promote the expansion and inhibit differentiation of HSCs.The expansion of cord blood HSCs by small molecular HDACIs in vitro is expected to improve the quantity of cord blood HSCs.The further research will focus on high-throughput screening for the most powerful HDACIs and the highly selective HDACIs,exploring the combination of epigenetic modifiers of different pathways.
Epigenesis, Genetic ; Fetal Blood ; Hematopoietic Stem Cells ; Histone Deacetylase Inhibitors/pharmacology* ; Valproic Acid/pharmacology*

In order to examine the strong anticancer action and low toxicity of Trichostatin A (TSA), the effect of TSA was examined on the growth inhibition, acetylation of histone H3 and apoptosis in HL-60 cells by employing MTT, immunocytochemical techniques, and Annexin-V-FITC/ PI assay. Our results showed that TSA could inhibit proliferation of HL- 60 cells in a time- and dose-dependent manner, and the IC50 at the 36th h was 100 ng/ml. The apoptosis-inducing effect of TSA on HL-60 cells was also time- and dose-dependent. But it didn't demonstrate apparent apoptosis induction in NPBMNCs within specific dose and time range. Both of the acetylation of histone H3 in HL-60 cells and NPBMNCs increased significantly (P<0.05) after treated with 100 ng/ml TSA for 4 h. However, there was no significant differences between the two groups (P>0.05). It is concluded that TSA can inhibit growth and induce apoptosis of HL-60 cells in a time- and dose-dependent manner, and is able to selectively induce apoptosis in HL-60 cells but does not respond in NPBMNCs under the same conditions. The difference of TSA between HL-60 cells and NPBMNCs can't be explained by the regulation of histone acetylation.
Acetylation ; Antineoplastic Agents ; pharmacology ; Apoptosis ; drug effects ; HL-60 Cells ; Histone Deacetylase Inhibitors ; Histone Deacetylases ; chemistry ; Humans ; Hydroxamic Acids ; pharmacology

OBJECTIVETo investigate the protective effect of histone deacetylase inhibitor NL101 on L-homocysteine (HCA)-induced toxicity in rat neurons, and the toxic effect on normal rat neurons.

METHODSIn the presence of NL101 at various concentrations, HCA (5 mmol/L)-induced changes in cell density, necrosis, and viability were determined in the mixed cultures of rat cortical cells and the primary cultures of rat neurons. The direct effect of NL101 on primary neurons was also observed in the absence of HCA. Histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) was used as the control. After the treatments, cell viability, the density, and morphology of neurons and glial cells, and cell necrosis were determined.

RESULTSIn the mixed cultures of cortical cells, NL101 had no effect on HCA (5 mmol/L)-induced cell number reduction at 0.001-10μmol/L; however, it significantly attenuated necrosis at 1-10 μmol/L, and increased neuronal number at 1 μmol/L. NL101 had no effect on the mixed cortical cells in the absence of HCA. In the primary neurons, NL101 reduced neuronal viability and mildly increased necrosis at 1-10 μmol/L in the absence of HCA, while it significantly attenuated HCA-induced neuronal viability reduction at 0.01-10 μmol/L and reduced neuronal necrosis at 1-10 μmol/L. The effects of NL101 were apparently similar to those of SAHA.

CONCLUSIONNL101 has protective effect on HCA-induced neuronal injury but it is neurotoxic at high concentrations, which is similar to the typical histone deacetylase inhibitor SAHA.

Animals ; Cell Survival ; drug effects ; Cells, Cultured ; Histone Deacetylase Inhibitors ; pharmacology ; Neurons ; drug effects ; Rats

There are large knowledge gaps regarding how to control stem cells growth and differentiation. The limitations of currently available technologies, such as growth factors and/or gene therapies has led to the search of alternatives. We explore here how a cell's epigenome influences determination of cell type, and potential applications in tissue engineering. A prevalent epigenetic modification is the acetylation of DNA core histone proteins. Acetylation levels heavily influence gene transcription. Histone deacetylase (HDAC) enzymes can remove these acetyl groups, leading to the formation of a condensed and more transcriptionally silenced chromatin. Histone deacetylase inhibitors (HDACis) can inhibit these enzymes, resulting in the increased acetylation of histones, thereby affecting gene expression. There is strong evidence to suggest that HDACis can be utilised in stem cell therapies and tissue engineering, potentially providing novel tools to control stem cell fate. This review introduces the structure/function of HDAC enzymes and their links to different tissue types (specifically bone, cardiac, neural tissues), including the history, current status and future perspectives of using HDACis for stem cell research and tissue engineering, with particular attention paid to how different HDAC isoforms may be integral to this field.
Acetylation ; drug effects ; Histone Deacetylase Inhibitors ; pharmacology ; Histone Deacetylases ; metabolism ; Histones ; isolation & purification ; metabolism ; Humans ; Tissue Engineering

OBJECTIVETo investigate the effects of two histone deacetylase (HDAC) inhibitors, valproic acid (VPA) and TSA, on the expression of vascular endothelial growth factor (VEGF) and its receptor KDR of the leukemia cell line Kasumi-1 cells, and to explore their potential mechanism in leukemia angiogenesis.

METHODKasumi-1 cells were treated with VPA and TSA at different concentrations for 3 days. The mRNA and protein expression levels of VEGF and KDR were determined by semi-quantitative RT-PCR and Western blot, and the bFGF mRNA by semi-quantitative RT-PCR.

RESULTSAs compared with that of control groups, VPA at 3 mmol/L downregulated the VEGF mRNA expression level for VEGF(121) from 0.632 ± 0.014 to 0.034 ± 0.004 and for VEGF(165) from 0.526 ± 0.021 to 0.015 ± 0.001, for KDR mRNA from 0.258 ± 0.034 to 0.038 ± 0.000, and for bFGF mRNA from 0.228 ± 0.017 to 0.086 ± 0.015. TSA downregulated the VEGF mRNA and KDR mRNA at concentration of 100 nmol/L, but its effect on bFGF mRNA only at higher concentration.

CONCLUSIONHDAC inhibitors might inhibit the leukemia angiogenesis by regulating the expression of VEGF and its recptor.

Angiogenesis Inducing Agents ; Cell Line ; Histone Deacetylase Inhibitors ; pharmacology ; Humans ; RNA, Messenger ; genetics ; Valproic Acid ; pharmacology ; Vascular Endothelial Growth Factor A

To investigate the effect of monoamine oxidase inhibitor tranylcypromine (TCP) on the differentiation of human U251 glioma cells, we treated U251 cells with TCP and/or 100 nmol/L histone deacetylase inhibitor trychostatin A (TSA). The differentiation of U251 cells was observed with inverted microscopy. The cell proliferation and cell cycle distribution were determined by MTT assay and flow cytometry, respectively. Apoptosis was observed by Hoechst 33258 staining. The levels of differentiation-related genes were assessed by real-time PCR and Western blotting. TCP-induced differentiation was characterized by typical morphological changes, inhibition of cellular proliferation, accumulation of cells in the G1 phase of the cell cycle, decreased expression of the pluripotency transcription factors Oct4 and Sox2, and increased expression of glial fibrillary acid protein (GFAP). The combination of TCP and TSA treatment also triggered an over-expression of GFAP. These findings suggest that TCP may induce differentiation of U251 glioma cells, and the differentiation process may be promoted by histone deacetylase inhibitor TSA.
Brain Neoplasms ; pathology ; Cell Line, Tumor ; Cell Transformation, Neoplastic ; drug effects ; Glioma ; pathology ; Histone Deacetylase Inhibitors ; pharmacology ; Humans ; Hydroxamic Acids ; pharmacology ; Monoamine Oxidase Inhibitors ; pharmacology ; Tranylcypromine ; pharmacology

Antibody-mediated rejection (AMR) is one of the major causes of graft loss after transplantation. Recently, the regulation of B cell differentiation and the prevention of donor-specific antibody (DSA) production have gained increased attention in transplant research. Herein, we established a secondary allogeneic in vivo skin transplant model to study the effects of romidepsin (FK228) on DSA. The survival of grafted skins was monitored daily. The serum levels of DSA and the number of relevant immunocytes in the recipient spleens were evaluated by flow cytometry. Then, we isolated and purified B cells from B6 mouse spleens in vitro by magnetic bead sorting. The B cells were cultured with interleukin-4 (IL-4) and anti-clusters of differentiation 40 (CD40) antibody with or without FK228 treatment. The immunoglobulin G1 (IgG1) and IgM levels in the supernatant were evaluated by enzyme-linked immunosorbent assay (ELISA). Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and western blotting were conducted to determine the corresponding levels of messenger RNA (mRNA) and protein expression in cultured cells and the recipient spleens. The results showed that FK228 significantly improved the survival of allogeneic skin grafts. Moreover, FK228 inhibited DSA production in the serum along with the suppression of histone deacetylase 1 (HADC1) and HDAC2 and the upregulation of the acetylation of histones H2A and H3. It also inhibited the differentiation of B cells to plasma cells, decreased the transcription of positive regulatory domain-containing 1 (Prdm1) and X-box-binding protein 1 (Xbp1), and decreased the expression of phosphorylated inositol-requiring enzyme 1 α (p-IRE1α), XBP1, and B lymphocyte-induced maturation protein-1 (Blimp-1). In conclusion, FK228 could decrease the production of antibodies by B cells via inhibition of the IRE1α-XBP1 signaling pathway. Thus, FK228 is considered as a promising therapeutic agent for the clinical treatment of AMR.
Animals ; Depsipeptides ; Endoribonucleases ; Hematopoietic Stem Cell Transplantation ; Histone Deacetylase Inhibitors/pharmacology* ; Mice ; Protein Serine-Threonine Kinases ; Skin Transplantation

The aim of the study was to explore the synergistic effect of the proteasome inhibitor bortezomib (bor) and the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) on apoptosis of T lymphoma cell lines Jurkat and Hut78, and on the formation of aggresome. Jurkat and Hut78 cells were treated with bor (10 nmol/L) or bor (10 nmol/L) combined with SAHA (2 micromol/L) respectively. Cell growth inhibition was estimated by trypan blue dye exclusion test. Cell morphology was evaluated by light microscopy with Wright's staining of cytocentrifuge preparations. Cell apoptosis was analyzed by flow cytometry. Ultrastructure of cell apoptosis and aggresome were observed by transmission electron microscopy. The results showed that proliferation of both Jurkat and Hut78 cells was significantly inhibited in the bor+SAHA group, as compared with the control group and the bor alone group. Flow cytometric analysis confirmed that the percentage of apoptosis in Jurkat and Hut78 cells in the bor+SAHA group (41.8+/-4.7% and 72.7+/-11.7% respectively) was remarkably higher than those in the control group (3.6+/-1.3% and 7.0+/-1.9% respectively) and the bor alone group (6.3+/-2.3% and 18.7+/-9.2% respectively) (p<0.01). Ultrastructure examination revealed that typical aggresomes in cells could be observed in bor alone group. The combination of bor and SAHA diminished both the amount and density of aggresomes, or even eliminated them, accompanied by the increased rate of apoptosis. It is concluded that proteasome inhibitor combined with histone deacetylase inhibitor synergically induces T lymphoma cell apoptosis. Bortezomib stimulates the formation of aggresome, while SAHA destroys this aggresome structure, which may be one of the mechanisms underlying the enhancement of bortezomib-induced apoptosis.
Apoptosis ; drug effects ; Boronic Acids ; pharmacology ; Bortezomib ; Drug Synergism ; Histone Deacetylase Inhibitors ; pharmacology ; Humans ; Jurkat Cells ; Lymphoma, T-Cell ; drug therapy ; Proteasome Inhibitors ; Pyrazines ; pharmacology