CBP and p300: HATs for different occasions

TLR2-dependent inhibition of macrophage responses to IFN-gamma is mediated by distinct, gene-specific mechanisms

Mycobacterium tuberculosis uses multiple mechanisms to avoid elimination by the immune system. We have previously shown that M. tuberculosis can inhibit selected macrophage responses to IFN-γ through TLR2-dependent and -independent mechanisms. To specifically address the role of TLR2 signaling in mediating this inhibition, we stimulated macrophages with the specific TLR2/1 ligand Pam₃CSK₄ and assayed responses to IFN-γ. Pam₃CSK₄ stimulation prior to IFN-γ inhibited transcription of the unrelated IFN-γ-inducible genes, CIITA and CXCL11. Surface expression of MHC class II and secretion of CXCL11 were greatly reduced as well, indicating that the reduction in transcripts had downstream effects. Inhibition of both genes required new protein synthesis. Using chromatin immunoprecipitation, we found that TLR2 stimulation inhibited IFN-γ-induced RNA polymerase II binding to the CIITA and CXCL11 promoters. Furthermore, TATA binding protein was unable to bind the TATA box of the CXCL11 promoter, suggesting that assembly of transcriptional machinery was disrupted. However, TLR2 stimulation affected chromatin modifications differently at each of the inhibited promoters. Histone H3 and H4 acetylation was reduced at the CIITA promoter but unaffected at the CXCL11 promoter. In addition, NF-κB signaling was required for inhibition of CXCL11 transcription, but not for inhibition of CIITA. Taken together, these results indicate that TLR2-dependent inhibition of IFN-γ-induced gene expression is mediated by distinct, gene-specific mechanisms that disrupt binding of the transcriptional machinery to the promoters.

Minireview: role of protein methylation and demethylation in nuclear hormone signaling

Nuclear hormone receptors (NRs) are transcription factors responsible for mediating the biological effects of hormones during development, metabolism, and homeostasis. Induction of NR target genes is accomplished through the assembly of hormone-bound NR complexes at target promoters and coincides with changes in histone modifications that promote transcription. Some coactivators and corepressors of NR can enhance or inhibit NR function by covalently modifying histones. One such modification is methylation, which plays important roles in transcriptional regulation. Histone methylation is catalyzed by histone methyltransferases and reversed by histone demethylases. Recent studies have uncovered the importance of these enzymes in the regulation of NR target genes. In addition to histones, these enzymes have nonhistone substrates and can methylate and demethylate NRs and coregulatory proteins in order to modulate their function. This review discusses recent progress in our understanding of the role of methylation and demethylation of histones, NRs, and their coregulators in NR-mediated transcription.

Expression and significance of androgen receptor coactivators in urothelial carcinoma of the bladder

Urothelial carcinoma (UC) of the bladder is approximately three times more common in men than women. While the etiology for this gender difference in incidence remains unknown, a role for androgen receptor (AR) signaling has been suggested. The mechanisms by which AR activity is regulated in UC cells, however, are largely elusive. Here, we explore the significance of coregulators that are critical for the formation of a functional AR transcriptional complex, in UC cells. Using two AR-positive UC cell lines, TCC-SUP and UMUC3, we demonstrate the expression of the coactivators NCOA1, NCOA2, NCOA3, CREBBP, and EP300 in UC cells. small interfering RNA-mediated knockdown of the AR or any of these coactivators markedly impacted cell viability and abrogated androgen-dependent cell proliferation. Noteworthy, contrary to AR-positive prostate cancer cells, expression of these AR-associated coactivators was not androgen regulated in UC cells. To assess the clinical relevance of coactivator expression, we performed immunohistochemistry on paraffin-embedded sections from 55 patients with UC of the bladder. We found that while 24 out of 55 (44%) of tumors expressed the AR, each of the coactivators was expressed by 85-100% of the bladder cancers. Moreover, we noted a significant downregulation of NCOA1 expression in tumors versus adjacent, non-tumor bladder urothelium, with a mean of 68% (range 0-100) of tumor cells demonstrating NCOA1 staining versus a mean of 81% (range 0-90) of non-tumor cells (P=0.03). Taken together, our data suggest an important role for AR-associated coactivators in UC and point toward differences in the regulation of AR activity between bladder and prostate cancer cells.

Transcription factors in long-term memory and synaptic plasticity

Transcription is a molecular requisite for long-term synaptic plasticity and long-term memory formation. Thus, in the last several years, one main interest of molecular neuroscience has been the identification of families of transcription factors that are involved in both of these processes. Transcription is a highly regulated process that involves the combined interaction and function of chromatin and many other proteins, some of which are essential for the basal process of transcription, while others control the selective activation or repression of specific genes. These regulated interactions ultimately allow a sophisticated response to multiple environmental conditions, as well as control of spatial and temporal differences in gene expression. Evidence based on correlative changes in expression, genetic mutations, and targeted molecular inhibition of gene expression have shed light on the function of transcription in both synaptic plasticity and memory formation. This review provides a brief overview of experimental work showing that several families of transcription factors, including CREB, C/EBP, Egr, AP-1, and Rel, have essential functions in both processes. The results of this work suggest that patterns of transcription regulation represent the molecular signatures of long-term synaptic changes and memory formation.

Spatiotemporal expression of histone acetyltransferases, p300 and CBP, in developing embryonic hearts

Histone acetyltransferases (HATs), p300 and cAMP response element binding protein (CREB)-binding protein (CBP) are two structurally related transcriptional co-activators that activate expression of many eukaryotic genes involved in cellular growth and signaling, muscle differentiation and embryogenesis. However, whether these proteins play important and different roles in mouse cardiogenesis is not clear. Here, we investigate the protein distributions and mRNA expression of the two HATs in embryonic and adult mouse heart during normal heart development by using immunohistochemical and RT-PCR techniques. The data from immunohistochemical experiments revealed that p300 was extensively present in nearly every region of the hearts from embryonic stages to the adulthood. However, no CBP expression was detected in embryonic hearts at day E7.5. CBP expression appeared at the later stages, and the distribution of CBP was less than that of p300. In the developmental hearts after E10.5, both for p300 and CBP, the mRNA expression levels reached a peak on day E10.5, and then were gradually decreased afterwards. These results reveal that both p300 and CBP are related to embryonic heart development. The dynamic expression patterns of these two enzymes during mouse heart development indicate that they may play an important role on heart development. However, there is a difference in spatiotemporal expression patterns between these two enzymes during heart development. The expression of p300 is earlier and more predominate, suggesting that p300 may play a more important role in embryonic heart development especially during cardiac precursor cell induction and interventricular septum formation.

A novel mode of action of YC-1 in HIF inhibition: stimulation of FIH-dependent p300 dissociation from HIF-1{alpha}

Hypoxia-inducible factor (HIF)-1 plays a key role in tumor promotion by inducing approximately 60 genes required for tumor adaptation to hypoxia; thus, it is viewed as a target for cancer therapy. For this reason, YC-1, which down-regulates HIF-1alpha and HIF-2alpha at the post-translational level, is being developed as a novel anticancer drug. We here found that YC-1 acts in a novel manner to inhibit HIF-1. In the Gal4 reporter system, which is not degraded by YC-1, YC-1 was found to significantly inactivate the COOH-terminal transactivation domain (CAD) of HIF-1alpha, whereas it failed to inactivate CAD(N803A) mutant. In coimmunoprecipitation assays, YC-1 stimulated factor inhibiting HIF (FIH) binding to CAD even in hypoxia, whereas it failed to increase the cellular levels of hydroxylated Asn803 of CAD. It was also found that YC-1 prevented p300 recruitment by CAD in mammalian two-hybrid and coimmunoprecipitation assays. The involvement of FIH in YC-1-induced CAD inactivation was confirmed in EPO-enhancer and Gal4 reporter systems using FIH small interfering RNA and dimethyloxalylglycine FIH inhibitor. Indeed, FIH inhibition rescued HIF target gene expressions repressed by YC-1. In cancer cell lines other than Hep3B, YC-1 inhibits HIF-1alpha via the FIH-dependent CAD inactivation as well as via the protein down-regulation. Given these results, we suggest that the functional inactivation of HIF-alpha contributes to the YC-1-induced deregulation of hypoxia-induced genes.

Acetylation of the human T-cell leukemia virus type 1 Tax oncoprotein by p300 promotes activation of the NF-kappaB pathway

The oncogenic potential of the HTLV-1 Tax protein involves activation of the NF-kappaB pathway, which depends on Tax phosphorylation, ubiquitination and sumoylation. We demonstrate that the nuclei of Tax-expressing cells, including HTLV-1 transformed T-lymphocytes, contain a pool of Tax molecules acetylated on lysine residue at amino acid position 346 by the transcriptional coactivator p300. Phosphorylation of Tax on serine residues 300/301 was a prerequisite for Tax localization in the nucleus and correlated with its subsequent acetylation by p300, whereas sumoylation, resulting in the formation of Tax nuclear bodies in which p300 was recruited, favored Tax acetylation. Overexpression of p300 markedly increased Tax acetylation and the ability of a wild type HTLV-1 provirus, but not of a mutant provirus carrying an acetylation deficient Tax gene, to activate gene expression from an integrated NF-kappaB-controlled promoter. Thus, Tax acetylation favors NF-kappaB activation and might play an important role in HTLV-1-induced cell transformation.

Experience-dependent epigenetic modifications in the central nervous system

This mini-review describes recent discoveries demonstrating that experience can drive the production of epigenetic marks in the adult nervous system and that the experience-dependent regulation of epigenetic molecular mechanisms in the mature central nervous system participates in the control of gene transcription underlying the formation of long-term memories. In the mammalian experimental systems investigated thus far, epigenetic mechanisms have been linked to associative fear conditioning, extinction of learned fear, and hippocampus-dependent spatial memory formation. Intriguingly, in one experimental system epigenetic marks at the level of chromatin structure (histone acetylation) have been linked to the recovery of memories that had seemed to be "lost" (i.e., not available for recollection). Environmental enrichment has long been known to have positive effects on memory capacity, and recent studies have suggested that these effects are at least partly due to the recruitment of epigenetic mechanisms by environmental enrichment. Finally, an uncoupling of signal transduction pathways from the regulation of epigenetic mechanisms in the nucleus has been implicated in the closure of developmental critical periods. Taken together, these eclectic findings suggest a new perspective on experience-dependent dynamic regulation of epigenetic mechanisms in the adult nervous system and their relevance to biological psychiatry.

Transcriptional coactivators are not required for herpes simplex virus type 1 immediate-early gene expression in vitro

Virion protein 16 (VP16) of herpes simplex virus type 1 (HSV-1) is a potent transcriptional activator of viral immediate-early (IE) genes. The VP16 activation domain can recruit various transcriptional coactivators to target gene promoters. However, the role of transcriptional coactivators in HSV-1 IE gene expression during lytic infection had not been fully defined. We showed previously that transcriptional coactivators such as the p300 and CBP histone acetyltransferases and the BRM and Brg-1 chromatin remodeling complexes are recruited to viral IE gene promoters in a manner dependent mostly on the presence of the activation domain of VP16. In this study, we tested the hypothesis that these transcriptional coactivators are required for viral IE gene expression during infection of cultured cells. The disrupted expression of the histone acetyltransferases p300, CBP, PCAF, and GCN5 or the BRM and Brg-1 chromatin remodeling complexes did not diminish IE gene expression. Furthermore, IE gene expression was not impaired in cell lines that lack functional p300, or BRM and Brg-1. We also tested whether these coactivators are required for the VP16-dependent induction of IE gene expression from transcriptionally inactive viral genomes associated with high levels of histones in cultured cells. We found that the disruption of coactivators also did not affect IE gene expression in this context. Thus, we conclude that the transcriptional coactivators that can be recruited by VP16 do not contribute significantly to IE gene expression during lytic infection or the induction of IE gene expression from nucleosomal templates in vitro.

Chapter 2. Calcineurin signaling and the slow oxidative skeletal muscle fiber type

Calcineurin, also known as protein phosphatase 2B (PP2B), is a calcium-calmodulin-dependent phosphatase. It couples intracellular calcium to dephosphorylate selected substrates resulting in diverse biological consequences depending on cell type. In mammals, calcineurin's functions include neuronal growth, development of cardiac valves and hypertrophy, activation of lymphocytes, and the regulation of ion channels and enzymes. This chapter focuses on the key roles of calcineurin in skeletal muscle differentiation, regeneration, and fiber type conversion to an oxidative state, all of which are crucial to muscle development, metabolism, and functional adaptations. It seeks to integrate the current knowledge of calcineurin signaling in skeletal muscle and its interactions with other prominent regulatory pathways and their signaling intermediates to form a molecular overview that could provide directions for possible future exploitations in human metabolic health.

p300 expression is induced by oxygen deficiency and protects neuron cells from damage

Low oxygen level or oxygen deficiency (hypoxia) is a major factor causing neuronal damage in many diseases. Inducing cell adaptation to hypoxia is an effective method for neuroprotection that can be achieved by either inhibiting the death effectors or enhancing the survival factors. Transcription coactivator p300 is necessary for hypoxia-induced transcriptional activation and plays an important role in neuron survival. However, the alteration of p300 expression under hypoxia condition and its role in hypoxia-induced neuronal damage remain unclear. In this study, the distribution of p300 in rat brain and the alteration of its expression in rat hippocampus during hypobaric hypoxia exposure were detected. In addition, the role of p300 in neuronal-like PC12 cell damage induced by oxygen deficiency (3% oxygen) was evaluated. Our results showed that p300 protein was mainly expressed in the cells expressed beta-tubulin III in the cerebral cortex, hippocampus, cerebellum cortex, medulla oblongata and hypothalamus. Less or no positive signal of p300 expression was observed in beta-tubulin III negative cells. This indicated that p300 was predominantly expressed in neurons of rat brain. Furthermore, p300 expression was up-regulated in rat hippocampus during hypoxia exposure and in neuronal-like PC12 cells under 3% oxygen condition. Interestingly, neuronal-like PC12 cell damage induced by oxygen deficiency (3% oxygen) was increased by suppression of p300 expression with short hairpin RNA (shRNA). These data indicate that p300 is an important molecule for neuroprotection under hypoxia.

Transcriptional regulation by AIRE: molecular mechanisms of central tolerance

The negative selection of T cells in the thymus is necessary for the maintenance of self tolerance. Medullary thymic epithelial cells have a key function in this process as they express a large number of tissue-specific self antigens that are presented to developing T cells. Mutations in the autoimmune regulator (AIRE) protein cause a breakdown of central tolerance that is associated with decreased expression of self antigens in the thymus. In this Review, we discuss the role of AIRE in the thymus and recent advances in our understanding of how AIRE might function at the molecular level to regulate gene expression.

PHD finger of autoimmune regulator: an epigenetic link between the histone modifications and tissue-specific antigen expression in thymus

Methylation of lysine residues on histone H3 tails regulates transcription. A recent addition to the list of known methylated histone binding modules is the plant homeodomain (PHD) finger, which is usually found in nuclear proteins with chromatin-related functions. Autoimmune regulator (AIRE) protein contains two PHD fingers and mutations in AIRE gene cause the monogenic disease autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). AIRE is expressed in thymic medullary epithelial cells where it promotes the expression of tissue-specific antigens. However the mechanism by which AIRE controls gene expression is currently unknown and the function of its domains, in particular of its PHD fingers is still elusive and controversial. In this review we discuss recent works on AIRE PHD finger(s) providing a new link between the status of histone modifications and the regulation of tissue-specific antigen expression in thymus.

Evaluating epigenetic landmarks in the brain of multiple sclerosis patients: a contribution to the current debate on disease pathogenesis

The evidence suggesting a role of epigenetics in the definition of complex trait diseases is rapidly increasing. The gender prevalence of multiple sclerosis, the low level concordance in homozygous twins and the linkage to several genetic loci, suggest an epigenetic component to the definition of this demyelinating disorder. While the immune etio-pathogenetic mechanism of disease progression has been well characterized, still relatively little is known about the initial events contributing to onset and progression of the demyelinating lesion. This article addresses the challenging question of whether loss of the mechanisms of epigenetic regulation of gene expression in the myelinating cells may contribute to the pathogenesis of multiple sclerosis, by affecting the repair process and by modulating the levels of enzymes involved in neo-epitope formation. The role of altered post-translational modifications of nucleosomal histones and DNA methylation in white matter oligodendroglial cells are presented in terms of pathogenetic concepts and the relevance to therapeutic intervention is then discussed.

Genome-wide relationship between histone H3 lysine 4 mono- and tri-methylation and transcription factor binding

We characterized the relationship of H3K4me1 and H3K4me3 at distal and proximal regulatory elements by comparing ChIP-seq profiles for these histone modifications and for two functionally different transcription factors: STAT1 in the immortalized HeLa S3 cell line, with and without interferon-gamma (IFNG) stimulation; and FOXA2 in mouse adult liver tissue. In unstimulated and stimulated HeLa cells, respectively, we determined approximately 270,000 and approximately 301,000 H3K4me1-enriched regions, and approximately 54,500 and approximately 76,100 H3K4me3-enriched regions. In mouse adult liver, we determined approximately 227,000 and approximately 34,800 H3K4me1 and H3K4me3 regions. Seventy-five percent of the approximately 70,300 STAT1 binding sites in stimulated HeLa cells and 87% of the approximately 11,000 FOXA2 sites in mouse liver were distal to known gene TSS; in both cell types, approximately 83% of these distal sites were associated with at least one of the two histone modifications, and H3K4me1 was associated with over 96% of marked distal sites. After filtering against predicted transcription start sites, 50% of approximately 26,800 marked distal IFNG-stimulated STAT1 binding sites, but 95% of approximately 5800 marked distal FOXA2 sites, were associated with H3K4me1 only. Results for HeLa cells generated additional insights into transcriptional regulation involving STAT1. STAT1 binding was associated with 25% of all H3K4me1 regions in stimulated HeLa cells, suggesting that a single transcription factor can interact with an unexpectedly large fraction of regulatory regions. Strikingly, for a large majority of the locations of stimulated STAT1 binding, the dominant H3K4me1/me3 combinations were established before activation, suggesting mechanisms independent of IFNG stimulation and high-affinity STAT1 binding.

Message in a nucleus: signaling to the transcriptional machinery

Tissue differentiation and signal transduction involve dramatic changes in gene expression. These changes can be brought about by the expression or activation of sequence-specific transcription factors. In order to regulate their target genes, such factors must navigate the intricate chromatin environment and engage the complex basal transcriptional machinery. We discuss three mechanisms through which signaling pathways can interact with complexes that alter chromatin structure or recruit RNA polymerase II. Signals that promote differentiation may alter the properties of such transcriptional regulatory complexes by incorporating tissue-specific subunits. Alternatively, adaptor subunits specialized to interact with specific transcription factors may allow a single complex to respond to multiple signals. Finally, individual regulatory proteins may integrate a variety of signals, allowing crosstalk between pathways.

Effects of the SANT domain of tension-induced/inhibited proteins (TIPs), novel partners of the histone acetyltransferase p300, on p300 activity and TIP-6-induced adipogenesis

We previously identified a set of transcription regulators, referred to as TIPs (tension-induced/inhibited proteins), with a role in myogenic versus adipogenic differentiation. Here we report that the TIP family comprises eight isoforms, all bearing a SANT (switching-defective protein 3, adaptor 2, nuclear receptor corepressor, and transcription factor IIIB) domain and some of them presenting S-adenosyl-l-methionine (SAM) and nuclear receptor box (NRB) motifs, all characteristic of histone-modifying enzymatic complexes. TIPs have SANT-dependent, p300-mediated histone acetyltransferase (HAT) activity. Ectopic TIP-6 (SANT(+) SAM(-) NRB(-)) but not TIP-6DeltaSANT induced de novo PPARgamma2-mediated adipogenic gene expression in NIH 3T3 cells and promoted preadipocyte differentiation into fat cells. TIP-6 was also involved in mediating hormonally/biochemically induced adipogenic differentiation of 3T3-L1 cells. Furthermore, TIP-6 was identified in adipose tissue in vivo. TIP-6 bound directly and indirectly to p300 and histone H4 (H4). Deletion of the SANT domain did not abolish TIP-6 interaction with p300 and H4 but eliminated direct TIP-6 binding to p300. Chromatin immunoprecipitation assays showed the recruitment of TIP-6, TIP-6DeltaSANT, and p300 to the PPARgamma2 promoter, but H3/H4 acetylation occurred only when p300 was directly associated with TIP-6. These studies demonstrated the importance of TIPs in the recruitment of p300 to specific promoters and in the regulation of p300 HAT activity through the involvement of the SANT domain. Furthermore, we identified TIP-6 as a new member of the adipogenic cascade.

Genetic and epigenetic defects in mental retardation

Mental retardation (MR) is a highly diverse group of cognitive disorders. The high incidence of MR, 2-3% in most populations, and the high burden for families and society makes this condition one of the major unsolved problems in modern medicine. Gene defects account for about half of all patients and more than 300 genes are known that, when mutated, lead to cognitive dysfunction. A strikingly high number of these MR genes encode regulators of chromatin structure and of chromatin-mediated transcription regulation. Prominent examples of these include the methyl CpG-binding protein MECP2, the H3K4 demethylase JARID1c and the H3K9 histone methyltransferase EHMT1. Moreover, several of these epigenetic MR proteins have been found to directly interact with one another or act in complexes that regulate the local chromatin structure at target genes that are key to normal neuronal activities. Thus, it appears that the function of individual MR genes converges to similar biological processes. More detailed knowledge about the altered DNA methylation and histone marks that are introduced by epigenetic gene mutations as well as more insight into neuronal genes whose expression is disrupted by this will provide a rationale for therapeutic strategies.

Quantitative control of adaptive cardiac hypertrophy by acetyltransferase p300

BACKGROUND

Acetyltransferase p300 is essential for cardiac development and is thought to be involved in cardiac myocyte growth through MEF2- and GATA4-dependent transcription. However, the importance of p300 in the modulation of cardiac growth in vivo is unknown.

METHODS AND RESULTS

Pressure overload induced by transverse aortic coarctation, postnatal physiological growth, and human heart failure were associated with large increases in p300. Minimal transgenic overexpression of p300 (1.5- to 3.5-fold) induced striking myocyte and cardiac hypertrophy. Both mortality and cardiac mass were directly related to p300 protein dosage. Heterozygous loss of a single p300 allele reduced pressure overload-induced hypertrophy by approximately 50% and rescued the hypertrophic phenotype of p300 overexpressers. Increased p300 expression had no effect on total histone deacetylase activity but was associated with proportional increases in p300 acetyltransferase activity and acetylation of the p300 substrates histone 3 and GATA-4. Remarkably, a doubling of p300 levels was associated with the de novo acetylation of MEF2. Consistent with this, genes specifically upregulated in p300 transgenic hearts were highly enriched for MEF2 binding sites.

CONCLUSIONS

Small increments in p300 are necessary and sufficient to drive myocardial hypertrophy, possibly through acetylation of MEF2 and upstream of signals promoting phosphorylation or nuclear export of histone deacetylases. We propose that induction of myocardial p300 content is a primary rate-limiting event in the response to hemodynamic loading in vivo and that p300 availability drives and constrains adaptive myocardial growth. Specific reduction of p300 content or activity may diminish stress-induced hypertrophy and forestall the development of heart failure.

Histone acetylation and flagellin are essential for Legionella pneumophila-induced cytokine expression

Legionella pneumophila causes severe pneumonia. Acetylation of histones is thought to be an important regulator of gene transcription, but its impact on L. pneumophila-induced expression of proinflammatory cytokines is unknown. L. pneumophila strain 130b induced the expression of the important chemoattractant IL-8 and genome-wide histone modifications in human lung epithelial A549 cells. We analyzed the IL-8-promoter and found that histone H4 was acetylated and H3 was phosphorylated at Ser(10) and acetylated at Lys(14), followed by transcription factor NF-kappaB. Recruitment of RNA polymerase II to the IL-8 promoter corresponded with increases in gene transcription. Histone modification and IL-8 release were dependent on p38 kinase and NF-kappaB pathways. Legionella-induced IL-8 expression was decreased by histone acetylase (HAT) inhibitor anacardic acid and enhanced by histone deacetylase (HDAC) inhibitor trichostatin A. After Legionella infection, HATs p300 and CREB-binding protein were time-dependently recruited to the IL-8 promoter, whereas HDAC1 and HDAC5 first decreased and later reappeared at the promoter. Legionella specifically induced expression of HDAC5 but not of other HDACs in lung epithelial cells, but knockdown of HDAC1 or 5 did not alter IL-8 release. Furthermore, Legionella-induced cytokine release, promoter-specific histone modifications, and RNA polymerase II recruitment were reduced in infection with flagellin-deletion mutants. Legionella-induced histone modification as well as HAT-/HDAC-dependent IL-8 release could also be shown in primary lung epithelial cells. In summary, histone acetylation seems to be important for the regulation of proinflammatory gene expression in L. pneumophila infected lung epithelial cells. These pathways may contribute to the host response in Legionnaires' disease.

Histone modifying enzymes: structures, mechanisms, and specificities

Histone modifying enzymes catalyze the addition or removal of an array of covalent modifications in histone and non-histone proteins. Within the context of chromatin, these modifications regulate gene expression as well as other genomic functions and have been implicated in establishing and maintaining a heritable epigenetic code that contributes to defining cell identity and fate. Biochemical and structural characterization of histone modifying enzymes has yielded important insights into their respective catalytic mechanisms, substrate specificities, and regulation. In this review, we summarize recent advances in understanding these enzymes, highlighting studies of the histone acetyltransferases (HATs) p300 (also now known as KAT3B) and Rtt109 (KAT11) and the histone lysine demethylases (HDMs) LSD1 (KDM1) and JMJD2A (KDM4A), present overriding themes that derive from these studies, and pose remaining questions concerning their regulatory roles in mediating DNA transactions.

PIASy represses CCAAT/enhancer-binding protein delta (C/EBPdelta) transcriptional activity by sequestering C/EBPdelta to the nuclear periphery

CCAAT/enhancer binding proteindelta (C/EBPdelta) plays a key role in mammary epithelial cell G(0) growth arrest, and "loss of function" alterations in C/EBPdelta have been reported in breast cancer and acute myeloid leukemia. C/EBPdelta is regulated at the transcriptional, post-transcriptional, and post-translational levels, suggesting tight control of C/EBPdelta content and function. Protein inhibitors of activated STATs (PIASs) regulate a growing number of transcription factors, including C/EBPs. HC11 nontransformed mammary epithelial cells express PIAS3, PIASxbeta, and PIASy, and all three PIAS family members repress C/EBPdelta transcriptional activity. PIASy is the most potent, however, repressing C/EBPdelta transcriptional activity by >80%. PIASy repression of C/EBPdelta transcriptional activity is dependent upon interaction between the highly conserved PIASy N-terminal nuclear matrix binding domain (SAPD) and the C/EBPdelta transactivation domain (TAD). PIASy repression of C/EBPdelta transcriptional activity is independent of histone deacetylase activity, PIASy E3 SUMO ligase activity, and C/EBPdelta sumoylation status. PIASy expression is associated with C/EBPdelta translocation from nuclear foci, where C/EBPdelta co-localizes with p300, to the nuclear periphery. PIASy-mediated translocation of C/EBPdelta is dependent upon the PIASy SAPD and C/EBPdelta TAD. PIASy reduces the expression of C/EBPdelta adhesion-related target genes and enhances repopulation of open areas within a cell monolayer in the in vitro "scratch" assay. These results demonstrate that PIASy represses C/EBPdelta by a mechanism that requires interaction between the PIASy SAPD and C/EBPdelta TAD and does not require PIASy SUMO ligase activity or C/EBPdelta sumoylation. PIASy alters C/EBPdelta nuclear localization, reduces C/EBPdelta transcriptional activity, and enhances cell proliferation/migration.

The C/H3 domain of p300 is required to protect VRK1 and VRK2 from their downregulation induced by p53

Background

The vaccinia-related kinase 1 (VRK1) protein, an activator of p53, can be proteolytically downregulated by an indirect mechanism, which requires p53-dependent transcription.

Principal Findings

In this work we have biochemically characterized the contribution of several p53 transcriptional cofactors with acetyl transferase activity to the induction of VRK1 downregulation that was used as a functional assay. Downregulation of VRK1 induced by p53 is prevented in a dose dependent manner by either p300 or CBP, but not by PCAF, used as transcriptional co-activators, suggesting that p53 has a different specificity depending on the relative level of these transcriptional cofactors. This inhibition does not require p53 acetylation, since a p53 acetylation mutant also induces VRK1 downregulation. PCAF can not revert the VRK1 protection effect of p300, indicating that these two proteins do not compete for a common factor needed to induce VRK1 downregulation. The protective effect is also induced by the C/H3 domain of p300, a region implicated in binding to several transcription factors and SV40 large T antigen; but the protective effect is lost when a mutant C/H3Del33 is used. The protective effect is a consequence of direct binding of the C/H3 domain to the transactivation domain of p53. A similar downregulatory effect can also be detected with VRK2 protein.

Conclusions/Significance

Specific p53-dependent effects are determined by the availability and ratios of its transcriptional cofactors. Specifically, the downregulation of VRK1/VRK2 protein levels, as a consequence of p53 accumulation, is thus dependent on the levels of the p300/CBP protein available for transcriptional complexes, since in this context this cofactor functions as a repressor of the effect. These observations point to the relevance of knowing the cofactor levels in order to determine one effect or another.

PARP activation and the alteration of vasoactive factors and extracellular matrix protein in retina and kidney in diabetes

AIMS

The development of diabetic complications is associated with increased oxidative stress which may damage DNA leading to the activation of nuclear enzyme poly (ADP-ribose) polymerase (PARP). PARP overactivation may further exacerbate the oxidative state of the cell through its consumption of nicotinamide adenine dinucleotide. In diabetic retinopathy and nephropathy, early characteristic features include increased production of vasoactive factors such as endothelin 1 (ET-1) and increased synthesis of extracellular matrix (ECM) proteins such as fibronectin (FN) and its splice variant extra domain B containing (EDB(+)) FN. We investigated the role of PARP in the development of diabetic retinopathy and nephropathy.

METHODS

Two models of diabetic complications were used. PARP-1 knockout mice and their respective wild type controls were fed a 30% galactose diet for 2 months. The rats were given injections of PARP inhibitor 3-aminobenzamide (30 mg/kg/day).

RESULTS

Analysis of the retinal and kidney tissues showed hyperhexosemia-induced oxidative stress and increased expression of ET-1, FN and EDB(+) FN in association with increased transcriptional co-activator p300 along with p300-dependent transcription factors, myocyte enhancing factors 2A and 2C. Furthermore, we showed increased PARP expression in the kidneys and retina of the diabetic rats. PARP blockade in both animal models prevented these hyperhexosemia-induced effects.

CONCLUSIONS

These findings suggests that hyperhexosemia and diabetes causes upregulation of ET-1, FN and EDB(+) FN at the transcriptional level in the retina and kidney via a signaling pathway mediated by PARP and an epigenetic mechanism involving p300 and MEF2 transcription factors. Understanding these mechanisms is important in identifying novel treatment targets.

Beyond transcription factors: the role of chromatin modifying enzymes in regulating transcription required for memory

One of the alluring aspects of examining chromatin modifications in the role of modulating transcription required for long-term memory processes is that these modifications may provide transient and potentially stable epigenetic marks in the service of activating and/or maintaining transcriptional processes. These, in turn, may ultimately participate in the molecular mechanisms required for neuronal changes subserving long-lasting changes in behavior. As an epigenetic mechanism of transcriptional control, chromatin modification has been shown to participate in maintaining cellular memory (e.g., cell fate) and may underlie the strengthening and maintenance of synaptic connections required for long-term changes in behavior. Epigenetics has become central to several fields of neurobiology, where researchers have found that regulation of chromatin modification has a significant role in epilepsy, drug addiction, depression, neurodegenerative diseases, and memory. In this review, we will discuss the role of chromatin modifying enzymes in memory processes, as well as how recent studies in yeast genetics and cancer biology may impact the way we think about how chromatin modification and chromatin remodeling regulate neuronal function.

Dysregulation of CREB binding protein triggers thrombin-induced proliferation of vascular smooth muscle cells

Thrombin is a potent mitogen for vascular smooth muscle cells (VSMCs). CBP has been regarded as a potential therapeutic target on the basis of its ability to affect cell growth. Therefore we hypothesized that CBP mediates thrombin-induced proliferation of VSMCs. We constructed recombinant adenoviral vector that expresses four short hairpin RNA (shRNA) targeting rat CBP mRNA (CBP-shRNA/Ad). VSMCs were infected with CBP-shRNA/Ad and treated with thrombin. CBP level were analyzed by quantitative real-time PCR and Western blot. To evaluate VSMC proliferation, the cell cycle and DNA synthesis were analyzed by flow cytometry and (3)H-thymidine incorporation, respectively. CBP-shRNA/Ad infection inhibited thrombin-induced CBP expression in a dose-dependent manner concomitant with a decrease in the percentage of cells in the S phase and in DNA synthesis. These findings suggest that CBP plays a pivotal role in the S phase progression of VSMCs.

Transcription factor YY1 and its associated acetyltransferases CBP and p300 interact with hepatitis delta antigens and modulate hepatitis delta virus RNA replication

Hepatitis delta virus (HDV) is a pathogenic RNA virus with a plant viroid-like genome structure. HDV encodes two isoforms of delta antigen (HDAg), the small and large forms of HDAg (SHDAg and LHDAg), which are essential for HDV RNA replication and virion assembly, respectively. Replication of HDV RNA depends on host cellular transcription machinery, and the exact molecular mechanism for HDV RNA replication is still unclear. In this study, we demonstrated that both isoforms of HDAg interact with transcription factor YY1 (Yin Yang 1) in vivo and in vitro. Their interaction domains were identified as the middle region encompassing the RNA binding domain of HDAg and the middle GA/GK-rich region and the C-terminal zinc-finger region of YY1. Results of sucrose gradient centrifugation analysis indicated the cosedimentation of the majority of SHDAg and a portion of the LHDAg with YY1 and its associated acetyltransferases CBP (CREB-binding protein) and p300 as a large nuclear complex in vivo. Furthermore, exogenous expression of YY1 or CBP/p300 in HDV RNA replication system showed an enhancement of HDV RNA replication. Interestingly, the acetyltransferase activity of p300 is important for this enhancement. Moreover, SHDAg could be acetylated in vivo, and treatment with cellular deacetylase inhibitor elevated the replication of HDV RNA and acetylation of SHDAg. All together, our results reveal that HDAg interacts with cellular transcription factor YY1 and its associated acetyltransferases CBP and p300 in a large nuclear complex, which in turn modulates the replication of HDV RNA.

Molecular basis of nuclear factor-kappaB activation by astrocyte elevated gene-1

Malignant glioma is a consistently fatal brain cancer. The tumor invades the surrounding tissue, limiting complete surgical removal and thereby initiating recurrence. Identifying molecules critical for glioma invasion is essential to develop targeted, effective therapies. The expression of astrocyte elevated gene-1 (AEG-1) increases in malignant glioma and AEG-1 regulates in vitro invasion and migration of malignant glioma cells by activating the nuclear factor-kappaB (NF-kappaB) signaling pathway. The present studies elucidate the domains of AEG-1 important for mediating its function. Serial NH(2)-terminal and COOH-terminal deletion mutants were constructed and functional analysis revealed that the NH(2)-terminal 71 amino acids were essential for invasion, migration, and NF-kappaB-activating properties of AEG-1. The p65-interaction domain was identified between amino acids 101 to 205, indicating that p65 interaction alone is not sufficient to mediate AEG-1 function. Coimmunoprecipitation assays revealed that AEG-1 interacts with cyclic AMP-responsive element binding protein-binding protein (CBP), indicating that it might act as a bridging factor between NF-kappaB, CBP, and the basal transcription machinery. Chromatin immunoprecipitation assays showed that AEG-1 is associated with the NF-kappaB binding element in the interleukin-8 promoter. Thus, AEG-1 might function as a coactivator for NF-kappaB, consequently augmenting expression of genes necessary for invasion of glioma cells. In these contexts, AEG-1 represents a viable potential target for the therapy of malignant glioma.

Cellular signaling and potential new treatment targets in diabetic retinopathy

Dysfunction and death of microvascular cells and imbalance between the production and the degradation of extracellular matrix (ECM) proteins are a characteristic feature of diabetic retinopathy (DR). Glucose-induced biochemical alterations in the vascular endothelial cells may activate a cascade of signaling pathways leading to increased production of ECM proteins and cellular dysfunction/death. Chronic diabetes leads to the activation of a number of signaling proteins including protein kinase C, protein kinase B, and mitogen-activated protein kinases. These signaling cascades are activated in response to hyperglycemia-induced oxidative stress, polyol pathway, and advanced glycation end product formation among others. The aberrant signaling pathways ultimately lead to activation of transcription factors such as nuclear factor-κB and activating protein-1. The activity of these transcription factors is also regulated by epigenetic mechanisms through transcriptional coactivator p300. These complex signaling pathways may be involved in glucose-induced alterations of endothelial cell phenotype leading to the production of increased ECM proteins and vasoactive effector molecules causing functional and structural changes in the microvasculature. Understanding of such mechanistic pathways will help to develop future adjuvant therapies for diabetic retinopathy.

The mouse C/EBPdelta gene promoter is regulated by STAT3 and Sp1 transcriptional activators, chromatin remodeling and c-Myc repression

CCAAT/enhancer binding proteindelta (C/EBPdelta) gene transcription is highly induced in G(0) growth arrested mammary epithelial cells and "loss of function" alterations in C/EBPdelta have been reported in human breast cancer. To gain a better understanding of the positive and negative factors that control C/EBPdelta gene expression we investigated the role of transcriptional activators, coactivators, repressors, histone modifications, chromatin remodeling and basal transcriptional machinery components in growing and growth arrested HC11 mouse mammary epithelial cells. Growth arrest treatments result in increased STAT3 activation (pSTAT3) and increased C/EBPdelta expression. Co-immunoprecipitation and chromatin immunoprecipitation (ChIP) assays demonstrated that pSTAT3 and Sp1 interact and bind to the transcriptionally active C/EBPdelta promoter. ChIP assays performed under exponentially growing (C/EBPdelta non-expressing) conditions demonstrated that the C/EBPdelta promoter is preloaded with transcriptional activators (Sp1 and CREB) and transcriptional machinery components (TBP and RNA Pol II). In contrast, under G(0) growth arrest (C/EBPdelta expressing) conditions ChIP analysis detected pSTAT3, Sp1, NCoA/SRC1, CBP/p300, pCREB, TBP, and serine 2 phosphorylated Pol II (pPol II) in association with the C/EBPdelta proximal promoter. C/EBPdelta promoter-associated histone post-translational modification analysis revealed histone H3 and H4 acetylation and methylation patterns consistent with a constitutively "open" chromatin conformation. Chromatin remodeling experiments demonstrated that BRG1, the ATPase component of the SWI/SNF chromatin remodeling complex, is required for C/EBPdelta transcription. Finally, C/EBPdelta expression is repressed in proliferating mammary epithelial cells by c-Myc via a mechanism that involves the binding of c-Myc:Max dimers to C/EBPdelta promoter-bound Miz-1. These results provide a molecular model of C/EBPdelta transcriptional regulation under G(0) growth arrest conditions.

Differential binding modes of the bromodomains of CREB-binding protein (CBP) and p300 with acetylated MyoD

The recruitment of the bromodomains of CREB-binding protein (CBP) and p300 by the acetylated myogenic transcription factor MyoD was previously shown to be critical for the enhanced MyoD transcriptional activity following acetylation at its Lys99 and Lys102 positions. However, the modes of binding interactions of the bromodomains of CBP and p300 with acetylated MyoD have not been well-characterized. In the current study, by employing a panel of MyoD peptides encompassing the 99 and 102 positions, we showed that Lys99 monoacetylation and Lys99/Lys102 double acetylation defined the critical binding interfaces with the bromodomains of CBP and p300, respectively. This also represented the first identification of a recognition motif for the p300 bromodomain and revelation of the differential recognition motifs for the bromodomains of CBP and p300. This information could be exploited for developing novel tools for structural and functional studies of the highly homologous CBP and p300 transcriptional coactivators.

The role of the transcriptional coactivator p300 in prostate cancer progression

Although the factors contributing to the progression of prostate cancer (PC) remain incompletely understood, androgens have long been recognized to play a central role in this process. Upon entering PC cells, androgens bind to a cognate nuclear receptor, the androgen receptor (AR). The activated AR translocates to the nucleus, binds as a dimer to androgen response elements (AREs) in the promoter of target genes, where it recruits the coactivator proteins necessary for the formation of a productive transcriptional complex, an event crucial for PC cell viability. For many decades, the androgen dependency of PCs has been exploited therapeutically by androgen ablation strategies. Although initially successful, these forms of therapy almost inevitably fail eventually, and an androgen depletion independent (ADI) disease emerges, for which currently no cure is available. Studies from our laboratory and others demonstrate that despite low circulating levels of functional androgens, the AR is critical for the proliferation and survival of ADI PC cells. Recent data indicate that alterations in the expression and/or activity of AR coactivator proteins occur during PC progression that can foster ADI activation of the AR. Here, we have investigated the role of the coactivator p300 in AR transcriptional activity and progression of PC.

Vasoactive intestinal peptide inhibits cyclooxygenase-2 expression in activated macrophages, microglia, and dendritic cells

Prostaglandin E2 (PGE2) is a potent lipid mediator produced by the inducible form of the enzyme cyclooxygenase (COX-2) in inflammatory cells. PGE2 and COX-2 are critical mediators in the pathogenesis of several inflammatory and degenerative diseases, and have therefore emerged as therapeutic targets for the treatment of such disorders. Vasoactive intestinal peptide (VIP) is a well-known anti-inflammatory neuropeptide that protects against several immune disorders by regulating a wide panel of inflammatory mediators. In this work we show the inhibitory effect of VIP on COX-2 expression and subsequent production of PGE2 by macrophages, dendritic cells, and microglia activated with different inflammatory stimuli. This inhibitory effect is exerted at the transcriptional level and mediated through the VIP receptor VPAC1. VIP downregulates NFkappaB-dependent gene activation of the COX-2 promoter. These findings demonstrate a novel property of VIP that might contribute to their anti-inflammatory effects in vivo, i.e., the inhibition of the inducible COX-2/PGE2 system.

Lithium inhibits Smad3/4 transactivation via increased CREB activity induced by enhanced PKA and AKT signaling

Smad proteins are intracellular transducers for transforming growth factor-beta (TGF-beta) signaling and play a critical role in differentiation, tissue repair and apoptosis of the central nervous system. Both TGF-beta and its regulated gene, plasminogen activator inhibitor type-1 (PAI-1), have been implicated in the etiology and progression of neurodegenerative diseases and mood disorders. We previously reported that GSK-3beta protein depletion suppresses Smad3/4-dependent gene transcription and causes a reduction in PAI-1 expression. Here, we provide evidence that lithium, the drug for the treatment and prophylaxis of bipolar disorder, inhibits Smad-dependent signaling by regulating cAMP-protein kinase A (PKA), AKT-glycogen synthase kinase-3beta (GSK-3beta), and CRE-dependent signaling pathways in neuron-enriched cerebral cortical cultures of rats. We demonstrate that lithium-induced activation of these pathways inhibits Smad3/4-dependent gene transcription through an increase in pCREB(Ser133) protein levels, an enhanced interaction between pCREB(Ser133) and p300/CBP, which causes Smad3/4-p300/CBP complex disruption and transcriptional suppression of Smad3/4-dependent genes. Therapeutic implications of our findings are discussed.

In vitro specificities of Arabidopsis co-activator histone acetyltransferases: implications for histone hyperacetylation in gene activation

In genetic hybrids displaying nucleolar dominance, acetylation of lysines 5, 8, 12 and 16 of histone H4 (H4K5, H4K8, H4K12, H4K16) and acetylation of histone H3 on lysines 9 and 14 (H3K9, H3K14) occurs at the promoters of active ribosomal RNA (rRNA) genes, whereas silenced rRNA genes are deacetylated. Likewise, histone hyperacetylation correlates with the active state of transgenes and of endogenous plant genes involved in physiological processes, including cold tolerance, light-responsiveness and flowering. To investigate histone hyperacetylation dynamics we used sodium butyrate, a histone deacetylase inhibitor known to switch silent rRNA genes on, in order to enrich the pool of acetylated histones. Mass spectrometric analyses revealed unique mono- (K16Ac), di- (K12Ac, K16Ac), tri- (K8Ac, K12Ac, K16Ac), and tetra-acetylated (K5Ac, K8Ac, K12Ac, K16Ac) histone H4 isoforms, suggesting that H4 hyperacetylation occurs in a processive fashion, beginning with lysine 16 and ending with lysine 5. Using a combination of molecular and mass spectrometric assays we then determined the specificities of seven of the nine functional co-activator type histone acetyltransferases (HATs) in Arabidopsis thaliana: specifically HATs of the CBP (HAC1, HAC5, HAC12), GNAT (HAG1, HAG2), and MYST families (HAM1, HAM2). Specific HATs acetylate histone H4K5 (HAM1, HAM2), H4K12 (HAG2), and H3K14 (HAG1), suggesting that acetylation of these lysines may have special regulatory significance. Other acetylation events, including histone H3K9 acetylation, are likely to result from the activities of the broad-specificity HAC1, HAC5, and HAC12 histone acetyltransferases.

Fatty acids in component of milk enhance the expression of the cAMP-response-element-binding-protein-binding protein (CBP)/p300 gene in developing rats

Fatty acids in milk are thought to play an important role in intestinal maturation and gene expression in the rat small intestine during the suckling-weaning period. In the present study, we determined the jejunal mRNA level of the cAMP-response-element-binding-protein-binding protein (CBP)/p300, which is one of the chromatin remodelling factors and regulates histone acetylation, during the postnatal period in rats. The mRNA level of CBP/p300 was high during the suckling and middle of the weaning period (day 5 to 20) and then declined sharply to a low level at the end of the weaning period and after weaning. In situ hybridisation also showed that CBP/p300 mRNA levels in the villus as well as the basal membrane clearly decreased after weaning. Rat pups at age 17 d, weaned to a high-fat diet, showed higher levels of CBP/p300 mRNA than those weaned to a low-fat diet. Oral administration of caprylic acid, oleic acid and linoleic acid, which are major fatty acid components in milk, induced jejunal CBP/p300 gene expression. The present results suggest that fatty acids in components of milk enhance expression of the CBP/p300 genes in the small intestine.

Roles of CREB-binding protein (CBP)/p300 in respiratory epithelium tumorigenesis

CREB-binding protein (CBP) and its homologue p300 are transcriptional co-activators of various sequence-specific transcription factors that are involved in a wide array of cellular activities, such as DNA repair, cell growth, differentiation and apoptosis. Several studies have suggested that CBP and p300 might be considered as tumour suppressors, with their prominent role being the cross-coupling of distinct gene expression patterns in response to various stimuli. They exert their actions mainly via acetylation of histones and other regulatory proteins (e.g. p53). A major paradox in CBP/p300 function is that they seem capable of contributing to various opposed cellular processes. Respiratory epithelium tumorigenesis represents a complex process of multi-step accumulations of a gamut of genetic and epigenetic aberrations. Transcription modulation through the alternate formation of activating and repressive complexes is the ultimate converging point of these derangements, and CBP/p300 represents key participants in this interplay. Thus, illumination of their molecular actions and interactions could reveal new potential targets for pharmacological interventions in respiratory epithelium carcinogenesis.

Nuclear expression of E2F4 induces cell death via multiple pathways in normal human intestinal epithelial crypt cells but not in colon cancer cells

E2F transcription factors control cell cycle progression. The localization of E2F4 in intestinal epithelial cells is cell cycle dependent, being cytoplasmic in quiescent differentiated cells but nuclear in proliferative cells. However, whether nuclear translocation of E2F4 alone is sufficient to trigger intestinal epithelial cell proliferation remains to be established. Adenoviruses expressing fusion proteins between green fluorescent protein (GFP) and wild-type (wt)E2F4 or GFP and nuclear localization signal (NLS)-tagged E2F4 were used to infect normal human intestinal epithelial crypt cells (HIEC). In contrast to expression of wtE2F4, persistent expression of E2F4 into the nucleus of HIEC triggered phosphatidylserine exposure, cytoplasmic shrinkage, zeiosis, formation of apoptotic bodies, and activation of caspase 9 and caspase 3. Inhibition of caspase activities by zVAD-fmk partially inhibited cell death induced by E2F4-NLS. An induction of p53, phosphorylated Ser15-p53, PUMA, FAS, BAX, RIP, and phosphorylated JNK1 was also observed in HIEC expressing E2F4-NLS compared with wtE2F4-expressing cells. E2F1 and p14ARF expression remained unaltered. Downregulation of p53 expression by RNA interference attenuated cell death induced by E2F4-NLS. By contrast, the level of cell death was negligible in colon cancer cells despite the strong expression of E2F4 into the nucleus. In conclusion, deregulated nuclear E2F4 expression induces apoptosis via multiple pathways in normal intestinal epithelial cells but not in colon cancer cells. Hence, mutations that deregulate E2F4 localization may provide an initial proliferative advantage but at the same time accelerate cell death. However, intestinal cells acquiring mutations (e.g., p53, Bax loci, etc.) may escape apoptosis, thereby revealing the full mitogenic potential of the E2F4 transcription factor.

Progesterone: Therapeutic opportunities for neuroprotection and myelin repair

Progesterone and its metabolites promote the viability of neurons in the brain and spinal cord. Their neuroprotective effects have been documented in different lesion models, including traumatic brain injury (TBI), experimentally induced ischemia, spinal cord lesions and a genetic model of motoneuron disease. Progesterone plays an important role in developmental myelination and in myelin repair, and the aging nervous system appears to remain sensitive to some of progesterone's beneficial effects. Thus, the hormone may promote neuroregeneration by several different actions by reducing inflammation, swelling and apoptosis, thereby increasing the survival of neurons, and by promoting the formation of new myelin sheaths. Recognition of the important pleiotropic effects of progesterone opens novel perspectives for the treatment of brain lesions and diseases of the nervous system. Over the last decade, there have been a growing number of studies showing that exogenous administration of progesterone or some of its metabolites can be successfully used to treat traumatic brain and spinal cord injury, as well as ischemic stroke. Progesterone can also be synthesized by neurons and by glial cells within the nervous system. This finding opens the way for a promising therapeutic strategy, the use of pharmacological agents, such as ligands of the translocator protein (18 kDa) (TSPO; the former peripheral benzodiazepine receptor or PBR), to locally increase the synthesis of steroids with neuroprotective and neuroregenerative properties. A concept is emerging that progesterone may exert different actions and use different signaling mechanisms in normal and injured neural tissue.

Synergistic activation of human involucrin gene expression by Fra-1 and p300--evidence for the presence of a multiprotein complex

Involucrin is expressed in the differentiated suprabasal epidermal layers, and an AP1 transcription factor-binding site present in the involucrin promoter distal regulatory region is required for this regulation. This site binds Fra-1, but cofactor interaction at this site has not been adequately characterized. We show that Fra-1 and p300 histone acetyltransferase are present at the AP1 site, as detected by chromatin immunoprecipitation. This interaction is functional, as treating p300 expressing keratinocytes with calcium or 12-O-tetradeconylphorbol-13-acetate, results in a synergistic increase in hINV expression, and this enhanced activation can be reproduced by coexpression of Fra-1 and p300. p300 also co-precipitates with Fra-1, but protein fractionation studies suggest that this interaction requires an additional protein. Fra-1 also interacts with other proteins that interact at the AP1-5 site, including JunD, JunB, Sp1, and P/CAF. Contrary to results in some other systems, Fra-1 functions as a positive transcriptional regulator in human keratinocytes. These studies suggest that a large multiprotein complex, which includes Fra-1, p300, P/CAF, junD, junB, and Sp1 acts at the AP1-5 site to produce a synergistic increase in hINV gene expression.

Epigenetic control of the immune escape mechanisms in malignant carcinomas

Downregulation of the transporter associated with antigen processing 1 (TAP-1) has been observed in many tumors and is closely associated with tumor immunoevasion mechanisms, growth, and metastatic ability. The molecular mechanisms underlying the relatively low level of transcription of the tap-1 gene in cancer cells are largely unexplained. In this study, we tested the hypothesis that epigenetic regulation plays a fundamental role in controlling tumor antigen processing and immune escape mechanisms. We found that the lack of TAP-1 transcription in TAP-deficient cells correlated with low levels of recruitment of the histone acetyltransferase, CBP, to the TAP-1 promoter. This results in lower levels of histone H3 acetylation at the TAP-1 promoter, leading to a decrease in accessibility of the RNA polymerase II complex to the TAP-1 promoter. These observations suggest that CBP-mediated histone H3 acetylation normally relaxes the chromatin structure around the TAP-1 promoter region, allowing transcription. In addition, we found a hitherto-unknown mechanism wherein interferon gamma up-regulates TAP-1 expression by increasing histone H3 acetylation at the TAP-1 promoter locus. These findings lie at the heart of understanding immune escape mechanisms in tumors and suggest that the reversal of epigenetic codes may provide novel immunotherapeutic paradigms for intervention in cancer.

Transgenic mice expressing an inhibitory truncated form of p300 exhibit long-term memory deficits

The formation of many forms of long-term memory requires several molecular mechanisms including regulation of gene expression. The mechanisms directing transcription require not only activation of individual transcription factors but also recruitment of transcriptional coactivators. CBP and p300 are transcriptional coactivators that interact with a large number of transcription factors and regulate transcription through multiple mechanisms, including an intrinsic histone acetyltransferase (HAT) activity. HAT activity mediates acetylation of lysine residues on the amino-terminal tails of histone proteins, thereby increasing DNA accessibility for transcription factors to activate gene expression. CBP has been shown to play an important role in long-term memory formation. We have investigated whether p300 is also required for certain forms of memory. p300 shares a high degree of homology with CBP and has been shown to interact with transcription factors known to be critical for long-term memory formation. Here we demonstrate that conditional transgenic mice expressing an inhibitory truncated form of p300 (p300Delta1), which lacks the carboxy-terminal HAT and activation domains, have impaired long-term recognition memory and contextual fear memory. Thus, our study demonstrates that p300 is required for certain forms of memory and that the HAT and carboxy-terminal domains play a critical role.

Expression of HDAC1 and CBP/p300 in human colorectal carcinomas

BACKGROUND

The histone-modifying enzymes histone deacetylase (HDAC) and histone acetyltransferase (HAT) control gene transcriptional activation and repression in human malignancies.

AIMS

To analyse the expression of HDAC/HAT-associated molecules such as HDAC1, CREB-binding protein (CBP) and p300 in human colorectal carcinomas, and investigate the relationship between their expression levels and clinicopathological parameters.

METHODS

Expression levels of HDAC1, CBP, and p300 in human colorectal cancer were investigated by immunohistochemistry. In situ hybridisation (ISH) and reverse transcription (RT)-PCR analyses were also carried out to confirm mRNA expression levels of these genes. Immunoreactivity was evaluated semi-quantitatively using a staining index (SI). The relationships between the SIs and clinicopathological findings were analysed and survival curves were calculated using the Kaplan-Meier method and log-rank tests.

RESULTS

The mean SIs for HDAC1, CBP, and p300 in this series of tumours were much higher than those in normal colonic mucosa. The presence of HDAC1 and CBP mRNAs on colorectal carcinoma cells as well as normal epithelial cells was confirmed by ISH analysis. A marked increase in p300 mRNA levels was detected in a majority of cases by RT-PCR. Among the patients with colorectal cancer, overexpression of p300 (SI>11.9) correlated with a poor prognosis, whereas high CBP expression levels (SI>16.6) indicated long-term survival.

CONCLUSION

Results showed the up-regulation of these three histone-modifying molecules in this series of colorectal cancers and suggested that monitoring of CBP and p300 may assist prediction of the prognosis in patients with colorectal adenocarcinoma.

Rubinstein-Taybi syndrome: clinical and molecular overview

Rubinstein-Taybi syndrome is characterised by mental retardation, growth retardation and a particular dysmorphology. The syndrome is rare, with a frequency of approximately one affected individual in 100,000 newborns. Mutations in two genes - CREBBP and EP300 - have been identified to cause the syndrome. These two genes show strong homology and encode histone acetyltransferases (HATs), which are transcriptional co-activators involved in many signalling pathways. Loss of HAT activity is sufficient to account for the phenomena seen in Rubinstein-Taybi patients. Although some mutations found in CREBBP are translocations, inversions and large deletions, most are point mutations or small deletions and insertions. Mutations in EP300 are comparatively rare. Extensive screening of patients has revealed mutations in CREBBP and EP300 in around 50% of cases. The cause of the syndrome in the remaining patients remains to be identified, but other genes could also be involved. Here, we describe the clinical presentation of Rubinstein-Taybi syndrome, review the mutation spectrum and discuss the current understanding of causative molecular mechanisms.

Signaling pathways mediating cardiac myocyte gene expression in physiological and stress responses

The contractile cells in the heart (the cardiac myocytes) are terminally differentiated. In response to pathophysiological stresses, cardiac myocytes undergo hypertrophic growth or apoptosis, responses associated with the development of cardiac pathologies. There has been much effort expended in gaining an understanding of the stimuli which promote these responses, and in identifying the intracellular signaling pathways which are activated and potentially involved. These signaling pathways presumably modulate gene and protein expression to elicit the end-stage response. For the regulation of gene expression, the signal may traverse the cytoplasm to modulate nuclear-localized transcription factors as occurs with the mitogen-activated protein kinase or protein kinase B/Akt cascades. Alternatively, the signal may promote translocation of transcription factors from the cytoplasm to the nucleus as is seen with the calcineurin/NFAT and JAK/STAT systems. We present an overview of the principal signaling pathways implicated in the regulation of gene expression in cardiac myocyte pathophysiology, and summarize the current understanding of these pathways, the transcription factors they regulate and the changes in gene expression associated with the development of cardiac pathologies. Finally, we discuss how intracellular signaling and gene expression may be integrated to elicit the overall change in cellular phenotype.

Crx activates opsin transcription by recruiting HAT-containing co-activators and promoting histone acetylation

The homeodomain transcription factor Crx is required for expression of many photoreceptor genes in the mammalian retina. The mechanism by which Crx activates transcription remains to be determined. Using protein-protein interaction assays, Crx was found to interact with three co-activator proteins (complexes): STAGA, Cbp and p300, all of which possess histone acetyl-transferase (HAT) activity. To determine the role of Crx-HAT interactions in target gene chromatin modification and transcriptional activation, quantitative RT-PCR and chromatin immunoprecipitation were performed on Crx target genes, rod and cone opsins, in developing mouse retina. Although cone opsins are transcribed earlier than rhodopsin during development, the transcription of each gene is preceded by the same sequence of events in their promoter and enhancer regions: (i) binding of Crx, followed by (ii) binding of HATs, (iii) the acetylation of histone H3, then (iv) binding of other photoreceptor transcription factors (Nrl and Nr2e3) and RNA polymerase II. In Crx knockout mice (Crx(-/-)), the association of HATs and AcH3 with target promoter/enhancer regions was significantly decreased, which correlates with aberrant opsin transcription and photoreceptor dysfunction in these mice. Similar changes to the opsin chromatin were seen in Y79 retinoblastoma cells, where opsin genes are barely transcribed. These defects in Y79 cells can be reversed by expressing a recombinant Crx or applying histone deacetylase inhibitors. Altogether, these results suggest that one mechanism for Crx-mediated transcriptional activation is to recruit HATs to photoreceptor gene chromatin for histone acetylation, thereby inducing and maintaining appropriate chromatin configurations for transcription.