Histone acetyltransferase activity of p300 enhances the activation of IL-12 p40 promoter

IL-10 regulates Il12b expression via histone deacetylation: implications for intestinal macrophage homeostasis

To prevent excessive inflammatory responses to commensal microbes, intestinal macrophages, unlike their systemic counterparts, do not produce inflammatory cytokines in response to enteric bacteria. Consequently, loss of macrophage tolerance to the enteric microbiota plays a central role in the pathogenesis of inflammatory bowel diseases. Therefore, we examined whether the hyporesponsive phenotype of intestinal macrophages is programmed by prior exposure to the microbiota. IL-10, but not in vivo exposure to the microbiota, programs intestinal macrophage tolerance, because wild-type (WT) colonic macrophages from germ-free and specific pathogen-free (SPF)-derived mice produce IL-10, but not IL-12 p40, when activated with enteric bacteria. Basal and activated IL-10 expression is mediated through a MyD88-dependent pathway. Conversely, colonic macrophages from germ-free and SPF-derived colitis-prone Il10(-/-) mice demonstrated robust production of IL-12 p40. Next, mechanisms through which IL-10 inhibits Il12b expression were investigated. Although Il12b mRNA was transiently induced in LPS-activated WT bone marrow-derived macrophages (BMDMs), expression persisted in Il10(-/-) BMDMs. There were no differences in nucleosome remodeling, mRNA stability, NF-κB activation, or MAPK signaling to explain prolonged transcription of Il12b in Il10(-/-) BMDMs. However, acetylated histone H4 transiently associated with the Il12b promoter in WT BMDMs, whereas association of these factors was prolonged in Il10(-/-) BMDMs. Experiments using histone deacetylase (HDAC) inhibitors and HDAC3 short hairpin RNA indicate that HDAC3 is involved in histone deacetylation of the Il12b promoter by IL-10. These results suggest that histone deacetylation on the Il12b promoter by HDAC3 mediates homeostatic effects of IL-10 in macrophages.

A rearranged EP300 gene in the human B-cell lymphoma cell line RC-K8 encodes a disabled transcriptional co-activator that contributes to cell growth and oncogenicity

Human diffuse large B-cell lymphoma cell line RC-K8 has an altered EP300 locus that encodes a C-terminally truncated histone acetyltransferase (HAT) protein (p300ΔC). We now show that p300ΔC contains 1047N-terminal amino acids of p300 fused to 25 amino acids encoded by sequences from chromosome 6. Over-expressed p300ΔC localized to nuclear subdomains and interacted with transcription factor REL. p300ΔC did not function as a co-activator for REL-directed transactivation, and blocked the ability of wild-type p300 to enhance transcriptional activation by REL. Knock down of p300ΔC in RC-K8 cells reduced their growth in both liquid culture and soft agar. Truncations of p300 were not found in eight other B-lymphoma cell lines. These results suggest that p300ΔC contributes to the oncogenic state of RC-K8 cells by acting as a defective co-activator.

IKK and NF-kappaB-mediated regulation of Claspin impacts on ATR checkpoint function

In response to replication stress, Claspin mediates the phosphorylation and activation of Chk1 by ATR. Claspin is not only necessary for the propagation of the DNA-damage signal, but its destruction by the ubiquitin-proteosome pathway is required to allow the cell to continue the cell cycle allowing checkpoint recovery. Here, we demonstrate that both the NF-kappaB family of transcription factors and their upstream kinase IKK can regulate Claspin levels by controlling its mRNA expression. Furthermore, we show that c-Rel directly controls Claspin gene transcription. Disruption of IKK and specific NF-kappaB members impairs ATR-mediated checkpoint function following DNA damage. Importantly, hyperactivation of IKK results in a failure to inactivate Chk1 and impairs the recovery from the DNA checkpoint. These results uncover a novel function for IKK and NF-kappaB modulating the DNA-damage checkpoint response, allowing the cell to integrate different signalling pathways with the DNA-damage response.

Histone acetyltransferase p300 is a coactivator for transcription factor REL and is C-terminally truncated in the human diffuse large B-cell lymphoma cell line RC-K8

Human c-Rel (REL) is a member of the NF-kappaB family of transcription factors. REL's normal physiological role is in the regulation of B-cell proliferation and survival. The REL gene is amplified in many human B-cell lymphomas and overexpression of REL can transform chicken lymphoid cells. In this report, histone acetyltransferase p300 enhanced REL-induced transactivation and interacted with REL both in vitro and in REL-transformed chicken spleen cells and the B-lymphoma cell line RC-K8, in which REL is constitutively active and required for proliferation. However, due to a deletion in the EP300 locus, only a C-terminally truncated form of p300 is expressed in RC-K8 cells. These results suggest a role for p300 in REL-mediated oncogenic activity in B lymphoma.

Aging-dependent upregulation of IL-23p19 gene expression in dendritic cells is associated with differential transcription factor binding and histone modifications

Age-associated changes in immune response increase the risk of infection and promote inflammation and autoimmunity in older adults. The newly discovered cytokine IL-23 contributes to the maintenance and expansion of Th-17 cells, which promote proinflammatory responses. Our preliminary findings suggested that Th-17 responses are increased in aged mice. IL-23 consists of p40 and p19 subunits. Expression of the p19 subunit is regulated at the transcriptional level by NF-kappaB p65 and c-Rel transcription factors. Using bone-marrow-derived dendritic cells (DCs) from C57BL/6 mice, we show that IL-23 protein production and p19 subunit mRNA levels are significantly increased in DCs from aged mice after activation with TLR ligands (LPS + R848) when compared with DCs of young adult mice. We found that the increase in p19 expression in aged cells is associated with chromatin remodeling characterized by di- and tri-methylation of histone H3K4 and binding of mainly c-Rel at the p19 promoter. In young DCs, the promoter is tri-methylated only at H3K4 and bound by both p65 and c-Rel. C-Rel knockdown restores p65 binding in aged cells but does not activate p19 expression, suggesting that c-Rel is critical for p19 expression. In addition, p65 knockdown significantly increases c-Rel binding and p19 expression in young DCs to levels close to those detected in old cells. Furthermore, the decrease in p65 binding at the p19 promoter in old DCs was specific to the p19 gene since p65 binding to the IL-12p40 promoter was not significantly different between old and young DCs. Our results demonstrate that selective changes in H3K4 methylation, and c-Rel and p65 binding at the p19 promoter occur in DCs and contribute to the upregulation of the p19 subunit expression and IL-23 protein production observed in aged mice. This suggests epigenetic and transcriptional mechanisms contribute to dysregulated inflammatory and autoimmune responses associated with aging.

Histone deacetylase inhibitors decrease Toll-like receptor-mediated activation of proinflammatory gene expression by impairing transcription factor recruitment

Post-translational modifications of histone proteins are major mechanisms that modify chromatin structure and regulate gene expression in eukaryotes. Activation of histone acetyltransferases or inhibition of histone deacetylases (HDACs) is generally believed to allow chromatin to assume a more open state, permitting transcriptional activity. We report here the surprising observation that treatment of murine dendritic cells with the HDAC inhibitors trichostatin A (TSA) or suberoylanilide hydroxamic acid (SAHA) in non-apoptotic concentrations strongly inhibited induction of both interleukin-12 protein p40 (IL-12p40) mRNA and protein upon stimulation of Toll-like receptors (TLRs). Moreover, TLR-mediated up-regulation of costimulatory molecules was also inhibited. Up-regulation of tumour necrosis factor-alpha mRNA and protein in response to TLR agonists was only affected upon prolonged exposure to HDAC inhibitors and regulation of IL-1 beta was not affected. Similar effects were apparent in murine and human macrophages. Regarding the mode of action, HDAC inhibition increased the acetylation status at the IL-12p40 locus. Nevertheless, IL-12p40 chromatin remodelling, binding of Rel-A and IRF1 to the IL-12p40 promoter and transcriptional activation were abrogated. In contrast, HDAC inhibitors had no effects on upstream nuclear factor-kappaB and mitogen-activated protein kinase activation. Thus HDACs positively regulate the expression of a subset of cytokine genes by enabling transcription factor recruitment.

Histone deacetylase inhibitor trichostatin a potentiates doxorubicin-induced apoptosis by up-regulating PTEN expression

BACKGROUND

The tumor suppressor gene PTEN is a major negative regulator of the PI3K/Akt cellular survival pathway. Overexpression of PTEN by adenoviral transfection increases doxorubicin-induced apoptosis. Whereas doxorubicin-induced apoptosis can be potentiated by the histone deacetylase (HDAC) inhibitor Trichostatin A (TSA), the mechanisms underlying this process remain unclear. The aim of this work was to investigate whether changes in PTEN expression are involved in TSA/doxorubicin-induced apoptosis.

METHODS

We treated 293 T cells with TSA and doxorubicin, detected apoptosis by using Hoechst 33342 staining, and examined changes of PTEN and Egr-1 expression by quantitative real-time polymerase chain reaction (PCR). Luciferase reporter assay was used to evaluate the promoter activity of PTEN and Western blot and enzyme-linked immunosorbent assay (ELISA) were used to confirm changes in the expression of PTEN. The chromatin immunoprecipitation (ChIP) assay was performed to estimate the acetylation level of PTEN promoter.

RESULTS

Doxorubicin-induced apoptosis was enhanced by TSA, whereas small interfering RNA (siRNA) targeting PTEN inhibited TSA/doxorubicin-induced apoptosis. Also, TSA promoted Egr-1 expression, which is the main transcription factor of PTEN, and this resulted in up-regulation of PTEN expression, which consequently potentiated apoptosis. Moreover, histone acetyltransferase p300 was able to synergistically activate PTEN transcription with Egr-1, implicating the role of histone acetylation in the regulation of PTEN expression.

CONCLUSIONS

TSA promoted doxorubicin-induced apoptosis through a mechanism that involved the stimulation of Egr-1 expression, acetylation of core histones at the PTEN promoter, and consequently induction of PTEN transcription. These findings provide a theoretical basis for the therapeutic application of combined treatment of TSA/doxorubicin for cancer.

The proximal GC-rich region of p16INK4a gene promoter plays a role in its transcriptional regulation

p16(INK4a) plays a key role in control of cell cycle progression by negatively regulating the CDK4/6 activity. This study establishes that the p16(INK4a) minimal promoter region required for the transcription factor Sp1 function is mapped at 62 bp upstream of the translation initiation codon. This region is GC-rich and shown to interact specifically with Sp1. siRNA-induced Sp1 silencing resulted in the inhibition of the p16(INK4a) minimal promoter activity. Additionally, by using a promoter sequence-directed siRNA method, we demonstrate that the histone H3 at the GC-rich region in the minimal promoter of p16(INK4a) is hypermethylated, with a concurrent reduction of both the activity of p16(INK4a) promoter and the level of endogenous p16(INK4a) mRNA. Moreover, we show that the specific mutation of the GC-rich region of the minimal promoter resulted in the complete loss of its regulatory activities. We conclude that the region spanning -62 to +1 bp of p16(INK4a) promoter plays a role in p16(INK4a) transcription regulation.

Hepatitis C virus core protein recruits nucleolar phosphoprotein B23 and coactivator p300 to relieve the repression effect of transcriptional factor YY1 on B23 gene expression

Hepatitis C virus (HCV) core has a pleiotropic effect on various promoters. In this study, we found that the expression of nucleolar phosphoprotein B23 was enhanced in HCV core-expressing cells and, moreover, HCV core interacts directly with the C-terminal end of B23. Using sucrose gradient centrifugation analysis and immunoprecipitation assays, HCV core was found in a large complex containing B23 and its interacting partner transcription factor YY1. Both B23 and HCV core associated with YY1 in the central GA/GK-rich and C-terminal zinc finger domain. These physical interactions between core, B23, and YY1 led to ternary complex formation that was bound to the YY1 response element. In a transient cotransfection experiment, relief of the trans-suppression activity of YY1 on the YY1-response element-driven reporter by core and B23 was found. This is also true when examining the effects of these three constructs on the B23 promoter-driven reporter. Additionally, chromatin immunoprecipitation assays indicated that a transcriptional activation complex consisting of core, together with B23, p300, and YY1, was recruited to the YY1 response element of B23 promoter, and this probably occurred through complex formation between core and these three cellular transcription regulators. This is different from the situation in the absence of core, where YY1 and histone deacetylase 1, but not B23 and p300, were associated on the YY1 element as the transcription repression complex. Together, our results indicate that HCV core can recruit B23 and p300 to relieve the repression effect of YY1 on B23 promoter activity, a property that requires the intrinsic histone acetyltransferase activity of p300. Thus, because these three core-associated cellular transcription regulators have a multitude of cellular interacting proteins and are involved in a versatility of cellular processes, the complex formation described here may partially account for the pleiotropic effects of core protein on gene expression and cellular function in HCV-infected cells.

Transcription factors Ets2 and Sp1 act synergistically with histone acetyltransferase p300 in activating human interleukin-12 p40 promoter

There has been considerable interest in researching the regulatory mechanisms that control the synthesis of interleukin (IL)-12, which plays a central role in the differentiation of T-helper-1 cells. In this study, we performed a series of transient transfection experiments designed to elucidate the functional relationship between the IL-12 promoter-specific transcription factors (Ets2 and Sp1) and histone acetylation modification in IL-12 regulation mediated by p300 and various histone deacetylases (HDACs). Results presented in this report demonstrated that the transcription factors Ets2 and Sp1 acted synergistically with p300 to activate the human IL-12 promoter. The histone acetyltransferase (HAT) activity of p300 was required for this synergic effect, because the adenovirus E1A protein inhibited the synergy. Conversely, HDACs repressed the synergic effect of transcription factors and histone acetylation on the activation of IL-12, while p300 was able to rectify it. These data indicated that Ets2 and Sp1 worked concertedly and synergistically with p300 in the regulation of human IL-12 expression.

Interleukin-12 p40 promoter activity is regulated by the reversible acetylation mediated by HDAC1 and p300

Interleukin-12 (IL-12) is a heterodimeric cytokine produced by macrophages in response to intracellular pathogens. The importance of IL-12 in generation of Th1 response against human pathogens has been characterized. The coactivator p300 is an important histone acetyltransferase (HAT) and has been implicated in the regulation of many genes. Histone deacetylases (HDACs) regulate gene transcription through deacetylation of histones. Whether the reversible histone acetylation/deacetylation modification participates in the regulation of IL-12 p40 transcription expression has not been investigated before. In this study, we analyzed the roles of HDAC1 and p300 in the regulation of human IL-12 p40. Co-transfection studies showed that HDAC1 had a repressing effect on the activity of IL-12 p40 promoter. Contrarily, p300 was able to reinforce the C/EBPbeta-mediated activation of IL-12 p40 and it counteracted the HDAC1-mediated repression of the IL-12 promoter. Chromatin immunoprecipitation tests (ChIP) revealed that p300 had a stimulating effect on the acetylation of the histone H3 at IL-12 p40 promoter. In addition, we showed that p300 had a physical interaction with C/EBPbeta and can enhance acetylation of C/EBPbeta. Data presented in this paper indicate that the reversible histone acetylation/deacetylation modification plays an important role in the transcriptional regulation of IL-12.

Histone acetyltransferase p300 promotes the activation of human WT1 promoter and intronic enhancer

The Wilms' tumor gene-1 (WT1) encodes a zinc finger protein involved in gene regulation during kidney, gonad, and heart development. In addition to its promoter, a 258 bp intronic enhancer is required for tissue-specific expression of WT1 gene. p300 is a histone acetyltransferase (HAT) and exerts essential functions in gene regulation. Here, we show that p300 increased the expression of endogenous WT1 mRNA and promoted the activation of the WT1 promoter and intronic enhancer. The results also revealed that the adenovirus E1A repressed the p300 function, while the p300-binding defective E1A delta 2-36 did not, and p300 HAT activity was important for its function since p300 mutant with the HAT domain deleted partially abrogated its ability to activate the WT1 promoter and intronic enhancer. Furthermore, p300 and c-Myb synergistically activated the expression of WT1 gene. This study revealed that p300 and its HAT activity were involved in regulation of WT1 transcription.