Biochemical analysis of distinct activation functions in p300 that enhance transcription initiation with chromatin templates

Novel berberine derivatives as p300 histone acetyltransferase inhibitors in combination treatment for breast cancer

Adenoviral E1A binding protein p300 (EP300 or p300) and its similar paralog, cyclic-AMP response element binding protein (CBP), are important histone acetyltransferases (HAT) and transcriptional co-activators in epigenetics, participating in numerous cellular pathways including proliferation, differentiation and apoptosis. The overexpression or dysregulation of p300/CBP is closely related to oncology-relevant disease. The inhibition of p300 HAT has been found to be a potential drug target. Berberine has been reported to show anticancer activity and synergistic effect in combination with some of the clinical anticancer drugs via modulation of various pathways. Here, the present study sought to discover more chemotypes of berberine derivatives as p300 HAT inhibitors and to examine the combination of these novel analogues with doxorubicin for the treatment of breast cancer. A series of novel berberine derivatives with modifications of A/B/D rings of berberine have been designed, synthesized and screened. Compound 7b was found to exhibit inhibitory potency against p300 HAT with IC50 values of 1.51 μM. Western blotting proved that 7b decreased H3K27Ac and interfered with the expression of oncology-relevant protein in MCF-7 cells. Further bioactive evaluation showed that combination of compound 7b with doxorubicin could significantly inhibit tumor growth and invasion in vitro and in vivo.

Acetylation of nuclear receptors in health and disease: an update

Lysine acetylation is a common reversible post-translational modification of proteins that plays a key role in regulating gene expression. Nuclear receptors (NRs) include ligand-inducible transcription factors and orphan receptors for which the ligand is undetermined, which together regulate the expression of genes involved in development, metabolism, homeostasis, reproduction and human diseases including cancer. Since the original finding that the ERα, AR and HNF4 are acetylated, we now understand that the vast majority of NRs are acetylated and that this modification has profound effects on NR function. Acetylation sites are often conserved and involve both ordered and disordered regions of NRs. The acetylated residues function as part of an intramolecular signalling platform intersecting phosphorylation, methylation and other modifications. Acetylation of NR has been shown to impact recruitment into chromatin, co-repressor and coactivator complex formation, sensitivity and specificity of regulation by ligand and ligand antagonists, DNA binding, subcellular distribution and transcriptional activity. A growing body of evidence in mice indicates a vital role for NR acetylation in metabolism. Additionally, mutations of the NR acetylation site occur in human disease. This review focuses on the role of NR acetylation in coordinating signalling in normal physiology and disease.

Unravelling the Role of P300 and TMPRSS2 in Prostate Cancer: A Literature Review

Prostate cancer is one of the most common malignant diseases in men, and it contributes significantly to the increased mortality rate in men worldwide. This study aimed to review the roles of p300 and TMPRSS2 (transmembrane protease, serine 2) in the AR (androgen receptor) pathway as they are closely related to the development and progression of prostate cancer. This paper represents a library-based study conducted by selecting the most suitable, up-to-date scientific published articles from online journals. We focused on articles that use similar techniques, particularly those that use prostate cancer cell lines and immunohistochemical staining to study the molecular impact of p300 and TMPRSS2 in prostate cancer specimens. The TMPRSS2:ERG fusion is considered relevant to prostate cancer, but its association with the development and progression as well as its clinical significance have not been fully elucidated. On the other hand, high p300 levels in prostate cancer biopsies predict larger tumor volumes, extraprostatic extension of disease, and seminal vesicle involvement at prostatectomy, and may be associated with prostate cancer progression after surgery. The inhibition of p300 has been shown to reduce the proliferation of prostate cancer cells with TMPRSS2:ETS (E26 transformation-specific) fusions, and combining p300 inhibitors with other targeted therapies may increase their efficacy. Overall, the interplay between the p300 and TMPRSS2 pathways is an active area of research.

Structural insights into p300 regulation and acetylation-dependent genome organisation

Histone modifications are deposited by chromatin modifying enzymes and read out by proteins that recognize the modified state. BRD4-NUT is an oncogenic fusion protein of the acetyl lysine reader BRD4 that binds to the acetylase p300 and enables formation of long-range intra- and interchromosomal interactions. We here examine how acetylation reading and writing enable formation of such interactions. We show that NUT contains an acidic transcriptional activation domain that binds to the TAZ2 domain of p300. We use NMR to investigate the structure of the complex and found that the TAZ2 domain has an autoinhibitory role for p300. NUT-TAZ2 interaction or mutations found in cancer that interfere with autoinhibition by TAZ2 allosterically activate p300. p300 activation results in a self-organizing, acetylation-dependent feed-forward reaction that enables long-range interactions by bromodomain multivalent acetyl-lysine binding. We discuss the implications for chromatin organisation, gene regulation and dysregulation in disease.

Structure-activity relationship and antitumor activity of 1,4-pyrazine-containing inhibitors of histone acetyltransferases P300/CBP

Acetylation of histone lysine residues by histone acetyltransferase (HAT) p300 and its paralog CBP play important roles in gene regulation in health and diseases. The HAT domain of p300/CBP has been found to be a potential drug target for cancer. Compound screening followed by structure-activity relationship studies yielded a novel series of 1,4-pyrazine-containing inhibitors of p300/CBP HAT with their IC50s as low as 1.4 μM. Enzyme kinetics and other studies support the most potent compound 29 is a competitive inhibitor of p300 HAT against the substrate histone. It exhibited a high selectivity for p300 and CBP, with negligible activity on other classes of HATs in human. Compound 29 inhibited cellular acetylation of several histone lysine residues and showed strong activity against proliferation of a panel of solid and blood cancer cells. These results indicate it is a novel pharmacological lead for drug development targeting these cancers as well as a useful chemical probe for biological studies of p300/CBP.

Speckles and paraspeckles coordinate to regulate HSV-1 genes transcription

Numbers of nuclear speckles and paraspeckles components have been demonstrated to regulate herpes simplex virus 1 (HSV-1) replication. However, how HSV-1 infection affects the two nuclear bodies, and whether this influence facilitates the expression of viral genes, remains elusive. In the current study, we found that HSV-1 infection leads to a redistribution of speckles and paraspeckles components. Serine/arginine-rich splicing factor 2 (SRSF2), the core component of speckles, was associated with multiple paraspeckles components, including nuclear paraspeckles assembly transcript 1 (NEAT1), PSPC1, and P54nrb, in HSV-1 infected cells. This association coordinates the transcription of viral genes by binding to the promoters of these genes. By association with the enhancer of zeste homolog 2 (EZH2) and P300/CBP complex, NEAT1 and SRSF2 influenced the histone modifications located near viral genes. This study elucidates the interplay between speckles and paraspeckles following HSV-1 infection and provides insight into the mechanisms by which HSV-1 utilizes host cellular nuclear bodies to facilitate its life cycle.

Li & Wang report that components of nuclear speckles and paraspeckles are redistributed upon HSV-1 infection. They show that the association of Serine/arginine-rich splicing factor 2 (SRSF2) with nuclear paraspeckles assembly transcript 1 (NEAT1) coordinates the transcription of viral genes

Beta-Genus Human Papillomavirus 8 E6 Destabilizes the Host Genome by Promoting p300 Degradation

The beta genus of human papillomaviruses infects cutaneous keratinocytes. Their replication depends on actively proliferating cells and, thus, they conflict with the cellular response to the DNA damage frequently encountered by these cells. This review focus on one of these viruses (HPV8) that counters the cellular response to damaged DNA and mitotic errors by expressing a protein (HPV8 E6) that destabilizes a histone acetyltransferase, p300. The loss of p300 results in broad dysregulation of cell signaling that decreases genome stability. In addition to discussing phenotypes caused by p300 destabilization, the review contains a discussion of the extent to which E6 from other β-HPVs destabilizes p300, and provides a discussion on dissecting HPV8 E6 biology using mutants.

CBP/p300: Critical Co-Activators for Nuclear Steroid Hormone Receptors and Emerging Therapeutic Targets in Prostate and Breast Cancers

The CREB-binding protein (CBP) and p300 are two paralogous lysine acetyltransferases (KATs) that were discovered in the 1980s-1990s. Since their discovery, CBP/p300 have emerged as important regulatory proteins due to their ability to acetylate histone and non-histone proteins to modulate transcription. Work in the last 20 years has firmly established CBP/p300 as critical regulators for nuclear hormone signaling pathways, which drive tumor growth in several cancer types. Indeed, CBP/p300 are critical co-activators for the androgen receptor (AR) and estrogen receptor (ER) signaling in prostate and breast cancer, respectively. The AR and ER are stimulated by sex hormones and function as transcription factors to regulate genes involved in cell cycle progression, metabolism, and other cellular functions that contribute to oncogenesis. Recent structural studies of the AR/p300 and ER/p300 complexes have provided critical insights into the mechanism by which p300 interacts with and activates AR- and ER-mediated transcription. Breast and prostate cancer rank the first and forth respectively in cancer diagnoses worldwide and effective treatments are urgently needed. Recent efforts have identified specific and potent CBP/p300 inhibitors that target the acetyltransferase activity and the acetytllysine-binding bromodomain (BD) of CBP/p300. These compounds inhibit AR signaling and tumor growth in prostate cancer. CBP/p300 inhibitors may also be applicable for treating breast and other hormone-dependent cancers. Here we provide an in-depth account of the critical roles of CBP/p300 in regulating the AR and ER signaling pathways and discuss the potential of CBP/p300 inhibitors for treating prostate and breast cancer.

Endocrine disrupting chemicals may deregulate DNA repair through estrogen receptor mediated seizing of CBP/p300 acetylase

PURPOSE

Environmental pollutants are known to induce DNA breaks, leading to genomic instability. Here, we propose a novel mechanism for the genotoxic effects exerted by environmentally exposed endocrine-disrupting chemicals (EDCs).

METHODS

Bibliographic research and presentation of the analysis.

DISCUSSION

In mammals, nucleotide excision repair, base excision repair, homologous recombination and non-homologous end-joining pathways are some of the major DNA repair pathways. p300 along with CREB-binding protein (CBP) contributes to chromatin remodeling, DNA damage response and repair of both single- and double-stranded DNA breaks. In addition to its role in DNA repair, CBP/p300 also acts as a coactivator to interact with the estrogen receptor and androgen receptor during its estrogen- and androgen-dependent transactivation, respectively. Since activated estrogen receptors (ERs) seize p300 from the repressed genes and redistribute it to the enhancer genes to activate transcription, the cellular functioning may be based on a balance between these pathways and any disturbance in one may alter the other, leading to undesirable physiological effects.

CONCLUSION

In conclusion, CBP/p300 is important for DNA repair and nuclear hormone receptor transactivation. Activated hormone receptors can sequester p300 to regulate the hormonal effects. Hence, we believe that activation of ERs by EDCs results in sequestration of CBP/p300 for ER transactivation and transcription initiation of its target genes, leading to a competition for CBP/P300, resulting in the deregulation of all other pathways involving p300/CBP.

Modulation of SRSF2 expression reverses the exhaustion of TILs via the epigenetic regulation of immune checkpoint molecules

The elevated expression of immune checkpoints by the tumor microenvironment is associated with poor prognosis in several cancers due to the exhaustion of tumor-infiltrating lymphocytes (TILs), and the effective suppression of the expression of these genes is key to reversing the exhaustion of TILs. Herein, we determined that serine/arginine-rich splicing factor 2 (SRSF2) is a target for blocking the tumor microenvironment-associated immunosuppressive effects. We found that the expression of SRSF2 was increased in exhausted T cells and that SRSF2 was involved in multiple immune checkpoint molecules mediating TILs' exhaustion. Furthermore, SRSF2 was revealed to regulate the transcription of these immune checkpoint genes by associating with an acyl-transferases P300/CBP complex and altering the H3K27Ac level near these genes, thereafter influencing the recruitment of signal transducer and activator of transcription 3 (STAT3) to these gene promoters. Collectively, our data indicated that SRSF2 functions as a modulator of the anti-tumor response of T cells and may be a therapeutic target for reversing the exhaustion of TILs.

Discovery, Structure-Activity Relationship, and Biological Activity of Histone-Competitive Inhibitors of Histone Acetyltransferases P300/CBP

Histone acetyltransferase (HAT) p300 and its paralog CBP acetylate histone lysine side chains and play critical roles in regulating gene transcription. The HAT domain of p300/CBP is a potential drug target for cancer. Through compound screening and medicinal chemistry, novel inhibitors of p300/CBP HAT with their IC₅₀ values as low as 620 nM were discovered. The most potent inhibitor is competitive against histone substrates and exhibits a high selectivity for p300/CBP. It inhibited cellular acetylation and had strong activity with EC₅₀ of 1-3 μM against proliferation of several tumor cell lines. Gene expression profiling in estrogen receptor (ER)-positive breast cancer MCF-7 cells showed that inhibitor treatment recapitulated siRNA-mediated p300 knockdown, inhibited ER-mediated gene transcription, and suppressed expression of numerous cancer-related gene signatures. These results demonstrate that the inhibitor is not only a useful probe for biological studies of p300/CBP HAT but also a pharmacological lead for further drug development targeting cancer.

JQ1, a bromodomain inhibitor, suppresses Th17 effectors by blocking p300-mediated acetylation of RORγt

BACKGROUND AND PURPOSE

Th17 cells play critical roles in chronic inflammation, including fibrosis. Histone acetyltransferase p300, a bromodomain-containing protein, acetylates RORγt and promotes Th17 cell development. The bromodomain inhibitor JQ1 was shown to alleviate Th17-mediated pathologies, but the underlying mechanism remains unclear. We hypothesized that JQ1 suppresses the response of Th17 cells by impairing p300-mediated acetylation of RORγt.

EXPERIMENTAL APPROACH

The effect of JQ1 on p300-mediated acetylation of RORγt was investigated in HEK293T (overexpressing Flag-p300 and Myc-RORγt) and human Th17 cells through immunoprecipitation and western blotting. To determine the regions of p300 responsible for JQ1-mediated suppression of HAT activity, we performed HAT assays on recombinant p300 fragments with/without the bromodomain, after exposure to JQ1. Additionally, the effect of JQ1 on p300-mediated acetylation of RORγt and Th17 cell function was verified in vivo, using murine Schistosoma-induced fibrosis models. Liver injury was assessed by histopathological examination and measurement of serum enzyme levels. Expression of Th17 effectors was detected by qRT-PCR, whereas IL-17- and RORγt-positive granuloma cells were detected by FACS.

KEY RESULTS

JQ1 impaired p300-mediated RORγt acetylation in human Th17 and HEK293T cells. JQ1 failed to suppress the acetyltransferase activity of p300 fragments lacking the bromodomain. JQ1 treatment attenuated Schistosoma-induced fibrosis in mice, by inhibiting RORγt acetylation and IL-17 expression.

CONCLUSIONS AND IMPLICATIONS

JQ1 impairs p300-mediated RORγt acetylation, thus reducing the expression of RORγt target genes, including Th17-specific cytokines. JQ1-mediated inhibition of p300 acetylase activity requires the p300 bromodomain. Strategies targeting p300 may provide new therapeutic approaches for controlling Th17-related diseases.

p300 mediates the histone acetylation of ORMDL3 to affect airway inflammation and remodeling in asthma

BACKGROUND

Bronchial asthma is affected by both environmental and genetic factors. The orosomucoid 1-like protein 3 (ORMDL3) gene is related to childhood asthma and is involved in airway inflammation and airway remodeling. The ORMDL3 promoter contains binding sites for the histone acetylase p300. Gene expression can be affected by epigenetic modifications. This study aimed to investigate whether the p300-mediated histone acetylation (HAT) of ORMDL3 gene affects airway inflammation and remodeling in asthma.

METHODS

16HBE14o- cells were transfected with various concentrations of a wild-type p300 plasmid or p300HAT-deletion plasmids. A dual luciferase reporter assay was used to examine the effect of p300-mediated HAT on the ORMDL3 promoter. Thirty BALB/c mice were randomly divided into a control group, an ovalbumin (OVA)-induced asthma group and an asthma + C646 (a selective inhibitor of p300) group. Noninvasive lung function tests were conducted to examine airway hyperreactivity (AHR) in the different groups. HE and Masson's trichrome staining was performed to examine airway remodeling and inflammation. Immunohistochemistry, western blotting and real-time PCR were used to analyze ORMDL3 expression in lung tissues. ELISA and western blotting were used to evaluate the HAT status in lung tissue. The ChIP assay was used to determine the relationship of the ORMDL3 promoter to p300 or acetylated histone H3 (aceH3).

RESULTS

p300 activated transcription from the ORMDL3 promoter, resulting in an increase in endogenous ORMDL3 mRNA levels. ORMDL3 promoter activity was reduced when the HAT activity of p300 was lost. ORMDL3 expression was elevated, and HAT activity was high in the lung tissues of asthmatic mice. p300 and aceH3 bound to the promoter region of ORMDL3. In the asthma group, the amounts of p300 and aceH3 recruited to the ORMDL3 promoter were increased. C646 inhibited p300 expression and reduced HAT activity and aceH3 levels in asthmatic mice, thereby reducing ORMDL3 expression and relieving AHR and airway remodeling.

CONCLUSION

p300-mediated HAT modulates the expression of the asthma susceptibility gene ORMDL3, thereby improving the process of airway inflammation and remodeling in asthma.

CAGI SickKids challenges: Assessment of phenotype and variant predictions derived from clinical and genomic data of children with undiagnosed diseases

Whole-genome sequencing (WGS) holds great potential as a diagnostic test. However, the majority of patients currently undergoing WGS lack a molecular diagnosis, largely due to the vast number of undiscovered disease genes and our inability to assess the pathogenicity of most genomic variants. The CAGI SickKids challenges attempted to address this knowledge gap by assessing state-of-the-art methods for clinical phenotype prediction from genomes. CAGI4 and CAGI5 participants were provided with WGS data and clinical descriptions of 25 and 24 undiagnosed patients from the SickKids Genome Clinic Project, respectively. Predictors were asked to identify primary and secondary causal variants. In addition, for CAGI5, groups had to match each genome to one of three disorder categories (neurologic, ophthalmologic, and connective), and separately to each patient. The performance of matching genomes to categories was no better than random but two groups performed significantly better than chance in matching genomes to patients. Two of the ten variants proposed by two groups in CAGI4 were deemed to be diagnostic, and several proposed pathogenic variants in CAGI5 are good candidates for phenotype expansion. We discuss implications for improving in silico assessment of genomic variants and identifying new disease genes.

NEAT1 regulates neuroglial cell mediating Aβ clearance via the epigenetic regulation of endocytosis-related genes expression

The accumulation of intracellular β-amyloid peptide (Aβ) is important pathological characteristic of Alzheimer's disease (AD). However, the exact underlying molecular mechanism remains to be elucidated. Here, we reported that Nuclear Paraspeckle Assembly Transcript 1 (NEAT1), a long n on-coding RNA, exhibits repressed expression in the early stage of AD and its down-regulation declines neuroglial cell mediating Aβ clearance via inhibiting expression of endocytosis-related genes. We find that NEAT1 is associated with P300/CBP complex and its inhibition affects H3K27 acetylation (H3K27Ac) and H3K27 crotonylation (H3K27Cro) located nearby to the transcription start site of many genes, including endocytosis-related genes. Interestingly, NEAT1 inhibition down-regulates H3K27Ac but up-regulates H3K27Cro through repression of acetyl-CoA generation. NEAT1 also mediates the binding between STAT3 and H3K27Ac but not H3K27Cro. Therefore, the decrease of H3K27Ac and/or the increase of H3K27Cro declines expression of multiple related genes. Collectively, this study first reveals the different roles of H3K27Ac and H3K27Cro in regulation of gene expression and provides the insight of the epigenetic regulatory mechanism of NEAT1 in gene expression and AD pathology.

Comparative genomics provides new insights into the remarkable adaptations of the African wild dog (Lycaon pictus)

Within the Canidae, the African wild dog (Lycaon pictus) is the most specialized with regards to cursorial adaptations (specialized for running), having only four digits on their forefeet. In addition, this species is one of the few canids considered to be an obligate meat-eater, possessing a robust dentition for taking down large prey, and displays one of the most variable coat colorations amongst mammals. Here, we used comparative genomic analysis to investigate the evolutionary history and genetic basis for adaptations associated with cursoriality, hypercanivory, and coat color variation in African wild dogs. Genome-wide scans revealed unique amino acid deletions that suggest a mode of evolutionary digit loss through expanded apoptosis in the developing first digit. African wild dog-specific signals of positive selection also uncovered a putative mechanism of molar cusp modification through changes in genes associated with the sonic hedgehog (SHH) signaling pathway, required for spatial patterning of teeth, and three genes associated with pigmentation. Divergence time analyses suggest the suite of genomic changes we identified evolved ~1.7 Mya, coinciding with the diversification of large-bodied ungulates. Our results show that comparative genomics is a powerful tool for identifying the genetic basis of evolutionary changes in Canidae.

Combination Targeting of the Bromodomain and Acetyltransferase Active Site of p300/CBP

p300 and CBP are highly related histone acetyltransferase (HAT) enzymes that regulate gene expression, and their dysregulation has been linked to cancer and other diseases. p300/CBP is composed of a number of domains including a HAT domain, which is inhibited by the small molecule A-485, and an acetyl-lysine binding bromodomain, which was recently found to be selectively antagonized by the small molecule I-CBP112. Here we show that the combination of I-CBP112 and A-485 can synergize to inhibit prostate cancer cell proliferation. We find that the combination confers a dramatic reduction in p300 chromatin occupancy compared to the individual effects of blocking either domain alone. Accompanying this loss of p300 on chromatin, combination treatment leads to the reduction of specific mRNAs including androgen-dependent and pro-oncogenic prostate genes such as KLK3 (PSA) and c-Myc. Consistent with p300 directly affecting gene expression, mRNAs that are significantly reduced by combination treatment also exhibit a strong reduction in p300 chromatin occupancy at their gene promoters. The relatively few mRNAs that are up-regulated upon combination treatment show no correlation with p300 occupancy. These studies provide support for the pharmacologic advantage of concurrent targeting of two domains within one key epigenetic modification enzyme.

The ZZ domain of p300 mediates specificity of the adjacent HAT domain for histone H3

Human p300 is a transcriptional co-activator and a major acetyltransferase that acetylates histones and other proteins facilitating gene transcription. The activity of p300 relies on the fine-tuned interactome that involves a dozen p300 domains and hundreds of binding partners and links p300 to a wide range of vital signaling events. Here, we report on a novel function of the ZZ-type zinc finger (ZZ) of p300 as a reader of histone H3. We show that the ZZ domain and acetyllysine recognizing bromodomain (BD) of p300 play critical roles in modulating p300 enzymatic activity and its association with chromatin. Acetyllysine binding of BD is essential for acetylation of histones H3 and H4, whereas interaction of the ZZ domain with H3 promotes selective acetylation of histone H3K27 and H3K18.

Mono-ADP-ribosylation of histone 3 at arginine-117 promotes proliferation through its interaction with P300

Relatively little attention has been paid to ADP-ribosylated modifications of histones, especially to mono-ADP-ribosylation. As an increasing number of mono-ADP-ribosyltransferases have been identified in recent studies, the functions of mono-ADP-ribosylated proteins have aroused research interest. In particular, histones are substrates of some mono-ADP-ribosyltransferases and mono-ADP-ribosylated histone have been detected in physiological or pathological processes. In this research, arginine-117 (Arg-117; R-117) of hsitone3(H3) is identified as the a site of mono-ADP-ribosylation in colon carcinoma(the first such site to be identified); this posttranslational modification may promote the proliferation of colon carcinoma cells in vitro and in vivo. Using a point-mutant lentivirus transfection and using an activator of P300 allowed us to observe the mono-ADP-ribosylation at H3R117 and enhancement of the activity of P300 to up-regulate the level of acetylated β-catenin, which could increase the expression of c-myc and cyclin D1.

Role of the CBP catalytic core in intramolecular SUMOylation and control of histone H3 acetylation

The histone acetyl transferases CREB-binding protein (CBP) and its paralog p300 play a critical role in numerous cellular processes. Dysregulation of their catalytic activity is associated with several human diseases. Previous work has elucidated the regulatory mechanisms of p300 acetyltransferase activity, but it is not known whether CBP activity is controlled similarly. Here, we present the crystal structure of the CBP catalytic core encompassing the bromodomain (BRD), CH2 (comprising PHD and RING), HAT, and ZZ domains at 2.4-Å resolution. The BRD, PHD, and HAT domains form an integral structural unit to which the RING and ZZ domains are flexibly attached. The structure of the apo-CBP HAT domain is similar to that of acyl-CoA-bound p300 HAT complexes and shows that the acetyl-CoA binding site is stably formed in the absence of cofactor. The BRD, PHD, and ZZ domains interact with small ubiquitin-like modifier 1 (SUMO-1) and Ubc9, and function as an intramolecular E3 ligase for SUMOylation of the cell cycle regulatory domain 1 (CRD1) of CBP, which is located adjacent to the BRD. In vitro HAT assays suggest that the RING domain, the autoregulatory loop (AL) within the HAT domain, and the ZZ domain do not directly influence catalytic activity, whereas the BRD is essential for histone H3 acetylation in nucleosomal substrates. Several lysine residues in the intrinsically disordered AL are autoacetylated by the HAT domain. Upon autoacetylation, acetyl-K1596 (Ac-K1596) binds intramolecularly to the BRD, competing with histones for binding to the BRD and acting as a negative regulator that inhibits histone H3 acetylation.

A course-based undergraduate research experience investigating p300 bromodomain mutations

Course-based undergraduate research experiences (CUREs) provide an opportunity for students to engage in experiments with outcomes that are unknown to both the instructor and students. These experiences allow students and instructors to collaboratively bridge the research laboratory and classroom, and provide research experiences for a large number of students relative to traditional individual mentored research. Here, we describe a molecular biology CURE investigating the impact of clinically relevant mutations found in the bromodomain of the p300 transcriptional regulator on acetylated histone interaction. In the CURE, students identified missense mutations in the p300 bromodomain using the Catalogue of Somatic Mutations in Cancer (COSMIC) database and hypothesized the effects of the mutation on the acetyl-binding function of the domain. They cloned and purified the mutated bromodomain and performed peptide pulldown assays to define its potential to bind to acetylated histones. Upon completion of the course, students showed increased confidence performing molecular techniques and reported positively on doing a research project in class. In addition, results generated in the classroom were further validated in the research laboratory setting thereby providing a new model for faculty to engage in both course-based and individual undergraduate research experiences.

Drosophila Eye Model to Study Neuroprotective Role of CREB Binding Protein (CBP) in Alzheimer's Disease

BACKGROUND

The progressive neurodegenerative disorder Alzheimer's disease (AD) manifests as loss of cognitive functions, and finally leads to death of the affected individual. AD may result from accumulation of amyloid plaques. These amyloid plaques comprising of amyloid-beta 42 (Aβ42) polypeptides results from the improper cleavage of amyloid precursor protein (APP) in the brain. The Aβ42 plaques have been shown to disrupt the normal cellular processes and thereby trigger abnormal signaling which results in the death of neurons. However, the molecular-genetic mechanism(s) responsible for Aβ42 mediated neurodegeneration is yet to be fully understood.

METHODOLOGY/PRINCIPAL FINDINGS

We have utilized Gal4/UAS system to develop a transgenic fruit fly model for Aβ42 mediated neurodegeneration. Targeted misexpression of human Aβ42 in the differentiating photoreceptor neurons of the developing eye of transgenic fly triggers neurodegeneration. This progressive neurodegenerative phenotype resembles Alzheimer's like neuropathology. We identified a histone acetylase, CREB Binding Protein (CBP), as a genetic modifier of Aβ42 mediated neurodegeneration. Targeted misexpression of CBP along with Aβ42 in the differentiating retina can significantly rescue neurodegeneration. We found that gain-of-function of CBP rescues Aβ42 mediated neurodegeneration by blocking cell death. Misexpression of Aβ42 affects the targeting of axons from retina to the brain but misexpression of full length CBP along with Aβ42 can restore this defect. The CBP protein has multiple domains and is known to interact with many different proteins. Our structure function analysis using truncated constructs lacking one or more domains of CBP protein, in transgenic flies revealed that Bromo, HAT and polyglutamine (BHQ) domains together are required for the neuroprotective function of CBP. This BHQ domain of CBP has not been attributed to promote survival in any other neurodegenerative disorders.

CONCLUSIONS/SIGNIFICANCE

We have identified CBP as a genetic modifier of Aβ42 mediated neurodegeneration. Furthermore, we have identified BHQ domain of CBP is responsible for its neuroprotective function. These studies may have significant bearing on our understanding of genetic basis of AD.

A synthetic lethal screen identifies the Vitamin D receptor as a novel gemcitabine sensitizer in pancreatic cancer cells

Overcoming chemoresistance of pancreatic cancer (PCa) cells should significantly extend patient survival. The current treatment modalities rely on a variety of DNA damaging agents including gemcitabine, FOLFIRINOX, and Abraxane that activate cell cycle checkpoints, which allows cells to survive these drug treaments. Indeed, these treatment regimens have only extended patient survival by a few months. The complex microenvironment of PCa tumors has been shown to complicate drug delivery thus decreasing the sensitivity of PCa tumors to chemotherapy. In this study, a genome-wide siRNA library was used to conduct a synthetic lethal screen of Panc1 cells that was treated with gemcitabine. A sublethal dose (50 nM) of the drug was used to model situations of limiting drug availability to PCa tumors in vivo. Twenty-seven validated sensitizer genes were identified from the screen including the Vitamin D receptor (VDR). Gemcitabine sensitivity was shown to be VDR dependent in multiple PCa cell lines in clonogenic survival assays. Sensitization was not achieved through checkpoint override but rather through disrupting DNA repair. VDR knockdown disrupted the cells' ability to form phospho-γH2AX and Rad51 foci in response to gemcitabine treatment. Disruption of Rad51 foci formation, which compromises homologous recombination, was consistent with increased sensitivity of PCa cells to the PARP inhibitor Rucaparib. Thus inhibition of VDR in PCa cells provides a new way to enhance the efficacy of genotoxic drugs.

All in the family: a portrait of a nuclear receptor co-activator complex

In this issue of Molecular Cell, Yi et al. (2015) use biochemical assays and cryo-EM to determine the molecular architecture of an estrogen receptor (ERα) co-activator complex bound to DNA.

"Nuclear FGF receptor-1 and CREB binding protein: an integrative signaling module"

In this review we summarize the current understanding of a novel integrative function of Fibroblast Growth Factor Receptor-1 (FGFR1) and its partner CREB Binding Protein (CBP) acting as a nuclear regulatory complex. Nuclear FGFR1 and CBP interact with and regulate numerous genes on various chromosomes. FGFR1 dynamic oscillatory interactions with chromatin and with specific genes, underwrites gene regulation mediated by diverse developmental signals. Integrative Nuclear FGFR1 Signaling (INFS) effects the differentiation of stem cells and neural progenitor cells via the gene-controlling Feed-Forward-And-Gate mechanism. Nuclear accumulation of FGFR1 occurs in numerous cell types and disruption of INFS may play an important role in developmental disorders such as schizophrenia, and in metastatic diseases such as cancer. Enhancement of INFS may be used to coordinate the gene regulation needed to activate cell differentiation for regenerative purposes or to provide interruption of cancer stem cell proliferation.

Structure of a biologically active estrogen receptor-coactivator complex on DNA

Estrogen receptor (ER/ESR1) is a transcription factor critical for development, reproduction, metabolism, and cancer. ER function hinges on its ability to recruit primary and secondary coactivators, yet structural information on the full-length receptor-coactivator complex to complement preexisting and sometimes controversial biochemical information is lacking. Here, we use cryoelectron microscopy (cryo-EM) to determine the quaternary structure of an active complex of DNA-bound ERα, steroid receptor coactivator 3 (SRC-3/NCOA3), and a secondary coactivator (p300/EP300). Our structural model suggests the following assembly mechanism for the complex: each of the two ligand-bound ERα monomers independently recruits one SRC-3 protein via the transactivation domain of ERα; the two SRC-3s in turn bind to different regions of one p300 protein through multiple contacts. We also present structural evidence for the location of activation function 1 (AF-1) in a full-length nuclear receptor, which supports a role for AF-1 in SRC-3 recruitment.

Coactivators p300 and CBP maintain the identity of mouse embryonic stem cells by mediating long-range chromatin structure

Master transcription factors Oct4, Sox2, and Nanog are required to maintain the pluripotency and self-renewal of embryonic stem cells (ESCs) by regulating a specific transcriptional network. A few other transcription factors have been shown to be important in ESCs by interacting with these master transcription factors; however, little is known about the transcriptional mechanisms regulated by coregulators (coactivators and corepressors). In this study, we examined the function of two highly homologous coactivators, p300 and CREB-binding protein (CBP), in ESCs. We find that these two coactivators play redundant roles in maintaining the undifferentiated state of ESCs. They are recruited by Nanog through physical interaction to Nanog binding loci, mediating the formation of long-range chromatin looping structures, which is essential to maintain ESC-specific gene expression. Further functional studies reveal that the p300/CBP binding looping fragments contain enhancer activities, suggesting that the formation of p300/CBP-mediated looping structures may recruit distal enhancers to create a concentration of factors for the transcription activation of genes that are involved in self-renewal and pluripotency. Overall, these results provide a total new insight into the transcriptional regulation mechanism of coactivators p300 and CBP in ESCs, which is important in maintaining self-renewal and pluripotency, by mediating the formation of higher order chromosome structures.

Adenovirus small E1A employs the lysine acetylases p300/CBP and tumor suppressor Rb to repress select host genes and promote productive virus infection

Oncogenic transformation by adenovirus small e1a depends on simultaneous interactions with the host lysine acetylases p300/CBP and the tumor suppressor RB. How these interactions influence cellular gene expression remains unclear. We find that e1a displaces RBs from E2F transcription factors and promotes p300 acetylation of RB1 K873/K874 to lock it into a repressing conformation that interacts with repressive chromatin-modifying enzymes. These repressing p300-e1a-RB1 complexes specifically interact with host genes that have unusually high p300 association within the gene body. The TGF-β, TNF-, and interleukin-signaling pathway components are enriched among such p300-targeted genes. The p300-e1a-RB1 complex condenses chromatin in a manner dependent on HDAC activity, p300 lysine acetylase activity, the p300 bromodomain, and RB K873/K874 and e1a K239 acetylation to repress host genes that would otherwise inhibit productive virus infection. Thus, adenovirus employs e1a to repress host genes that interfere with viral replication.

Accelerated chromatin biochemistry using DNA-barcoded nucleosome libraries

Elucidating the molecular details of how chromatin-associated factors deposit, remove and recognize histone post-translational modification (PTM) signatures remains a daunting task in the epigenetics field. We introduce a versatile platform that greatly accelerates biochemical investigations into chromatin recognition and signaling. This technology is based on the streamlined semisynthesis of DNA-barcoded nucleosome libraries with distinct combinations of PTMs. Chromatin immunoprecipitation of these libraries, once they have been treated with purified chromatin effectors or the combined chromatin recognizing and modifying activities of the nuclear proteome, is followed by multiplexed DNA-barcode sequencing. This ultrasensitive workflow allowed us to collect thousands of biochemical data points revealing the binding preferences of various nuclear factors for PTM patterns and how preexisting PTMs, alone or synergistically, affect further PTM deposition via cross-talk mechanisms. We anticipate that the high throughput and sensitivity of the technology will help accelerate the decryption of the diverse molecular controls that operate at the level of chromatin.

Synthetic chromatin approaches to probe the writing and erasing of histone modifications

Posttranslational modifications (PTMs) of chromatin are involved in gene regulation, thereby contributing to cell differentiation, lineage determination, and organism development. Discrete chromatin states are established by the action of a large set of enzymes that catalyze the deposition, propagation, and removal of histone PTMs, thereby modulating gene expression. Given their central role in determining and maintaining cellular phenotype, as well as in controlling chromatin processes such as DNA repair, the dysregulation of these enzymes can have serious consequences, and can result in cancer and neurodegenerative diseases. Thus, such chromatin regulator proteins are promising drug targets. However, they are often present in large, modular protein complexes that specifically recognize target chromatin regions and exhibit intricate regulation through preexisting histone marks. This renders the study of their enzymatic mechanisms complex. Recent developments in the chemical production of defined chromatin substrates show great promise for improving our understanding of the activity of chromatin regulator complexes at the molecular level. Herein I discuss examples highlighting the application of synthetic chromatin to study the enzymatic mechanisms and regulatory pathways of these crucial protein complexes in detail, with potential implications for assay development in pharmacological research.

Acetylation of RNA polymerase II regulates growth-factor-induced gene transcription in mammalian cells

Lysine acetylation regulates transcription by targeting histones and nonhistone proteins. Here we report that the central regulator of transcription, RNA polymerase II, is subject to acetylation in mammalian cells. Acetylation occurs at eight lysines within the C-terminal domain (CTD) of the largest polymerase subunit and is mediated by p300/KAT3B. CTD acetylation is specifically enriched downstream of the transcription start sites of polymerase-occupied genes genome-wide, indicating a role in early stages of transcription initiation or elongation. Mutation of lysines or p300 inhibitor treatment causes the loss of epidermal growth-factor-induced expression of c-Fos and Egr2, immediate-early genes with promoter-proximally paused polymerases, but does not affect expression or polymerase occupancy at housekeeping genes. Our studies identify acetylation as a new modification of the mammalian RNA polymerase II required for the induction of growth factor response genes.

SET1 and p300 act synergistically, through coupled histone modifications, in transcriptional activation by p53

The H3K4me3 mark in chromatin is closely correlated with actively transcribed genes, although the mechanisms involved in its generation and function are not fully understood. In vitro studies with recombinant chromatin and purified human factors demonstrate a robust SET1 complex (SET1C)-mediated H3K4 trimethylation that is dependent upon p53- and p300-mediated H3 acetylation, a corresponding SET1C-mediated enhancement of p53- and p300-dependent transcription that reflects a primary effect of SET1C through H3K4 trimethylation, and direct SET1C-p53 and SET1C-p300 interactions indicative of a targeted recruitment mechanism. Complementary cell-based assays demonstrate a DNA-damage-induced p53-SET1C interaction, a corresponding enrichment of SET1C and H3K4me3 on a p53 target gene (p21/WAF1), and a corresponding codependency of H3K4 trimethylation and transcription upon p300 and SET1C. These results establish a mechanism in which SET1C and p300 act cooperatively, through direct interactions and coupled histone modifications, to facilitate the function of p53.

Genome-wide analysis of FOXO3 mediated transcription regulation through RNA polymerase II profiling

Forkhead box O (FOXO) transcription factors are key players in diverse cellular processes affecting tumorigenesis, stem cell maintenance and lifespan. To gain insight into the mechanisms of FOXO-regulated target gene expression, we studied genome-wide effects of FOXO3 activation. Profiling RNA polymerase II changes shows that FOXO3 regulates gene expression through transcription initiation. Correlative analysis of FOXO3 and RNA polymerase II ChIP-seq profiles demonstrates FOXO3 to act as a transcriptional activator. Furthermore, this analysis reveals a significant part of FOXO3 gene regulation proceeds through enhancer regions. FOXO3 binds to pre-existing enhancers and further activates these enhancers as shown by changes in histone acetylation and RNA polymerase II recruitment. In addition, FOXO3-mediated enhancer activation correlates with regulation of adjacent genes and pre-existence of chromatin loops between FOXO3 bound enhancers and target genes. Combined, our data elucidate how FOXOs regulate gene transcription and provide insight into mechanisms by which FOXOs can induce different gene expression programs depending on chromatin architecture.

BRMS1 suppresses lung cancer metastases through an E3 ligase function on histone acetyltransferase p300

The mechanisms through which the metastasis suppressor gene BRMS1 functions are poorly understood. Herein, we report the identification of a previously undescribed E3 ligase function of BRMS1 on the histone acetyltransferase p300. BRMS1 induces polyubiquitination of p300, resulting in its proteasome-mediated degradation. We identify BRMS1 as the first eukaryote structural mimic of the bacterial IpaH E3 ligase family and establish that the evolutionarily conserved CXD motif located in BRMS1 is responsible for its E3 ligase function. Mutation of this E3 ligase motif not only abolishes BRMS1-induced p300 polyubiquitination and degradation, but importantly, dramatically reduces the metastasis suppressor function of BRMS1 in both in vitro and in vivo models of lung cancer metastasis.

Maxacalcitol ameliorates tubulointerstitial fibrosis in obstructed kidneys by recruiting PPM1A/VDR complex to pSmad3

Tubulointerstitial fibrosis (TIF) is one of the major problems in nephrology because satisfactory therapeutic strategies have not been established. Here, we demonstrate that maxacalcitol (22-oxacalcitriol (OCT)), an analog of active vitamin D, protects the kidney from TIF by suppressing the autoinduction of transforming growth factor-β1 (TGF-β1). OCT suppressed the tubular injury index, interstitial volume index, collagen I positive area, and mRNA levels of extracellular matrix genes in unilateral ureteral-obstructed kidneys in rats. Although the renoprotective mechanism of active vitamin D in previous studies has been mainly attributed to the suppression of renin, OCT did not affect renal levels of renin or angiotensin II. We found that TGF-β1 itself induces its expression in a phospho-Smad3 (pSmad3)-dependent manner, and that OCT ameliorated TIF by abrogating this 'autoinduction'. Under the stimulation of TGF-β1, pSmad3 bound to the proximal promoter region of the TGF-β1 gene. Both OCT and SIS3, a Smad3 inhibitor, abrogated the binding of pSmad3 to the promoter and consequently attenuated the autoinduction. TGF-β1 increased both the nuclear levels of protein phosphatase Mg(2+)/Mn(2+)-dependent 1A (PPM1A), a pSmad3 phosphatase, and the interaction levels between the vitamin D receptor (VDR) and PPM1A. In the absence of OCT, however, the interaction between pSmad3 and PPM1A was weak; therefore, it was insufficient to dephosphorylate pSmad3. The PPM1A/VDR complex was recruited to pSmad3 in the presence of both TGF-β1 and OCT. This recruitment promoted the dephosphorylation of pSmad3 and attenuated the pSmad3-dependent production of TGF-β1. Our findings provide a novel approach to inhibit the TGF-β pathway in fibrotic diseases.

The role of bromodomain proteins in regulating gene expression

Histone modifications are important in regulating gene expression in eukaryotes. Of the numerous histone modifications which have been identified, acetylation is one of the best characterised and is generally associated with active genes. Histone acetylation can directly affect chromatin structure by neutralising charges on the histone tail, and can also function as a binding site for proteins which can directly or indirectly regulate transcription. Bromodomains specifically bind to acetylated lysine residues on histone tails, and bromodomain proteins play an important role in anchoring the complexes of which they are a part to acetylated chromatin. Bromodomain proteins are involved in a diverse range of functions, such as acetylating histones, remodeling chromatin, and recruiting other factors necessary for transcription. These proteins thus play a critical role in the regulation of transcription.

The function of steroid receptor coactivator-1 in normal tissues and cancer

In 1995, the steroid receptor coactivator-1 (SRC-1) was identified as the first authentic steroid receptor coactivator. Since then, the SRC proteins have remained at the epicenter of coregulator biology, molecular endocrinology and endocrine-related cancer. Cumulative works on SRC-1 have shown that it is primarily a nuclear receptor coregulator and functions to construct highly specific enzymatic protein complexes which can execute efficient and successful transcriptional activation of designated target genes. The versatile nature of SRC-1 enables it to respond to steroid dependent and steroid independent stimulation, allowing it to bind across many families of transcription factors to orchestrate and regulate complex physiological reactions. This review highlights the multiple functions of SRC-1 in the development and maintenance of normal tissue functions as well as its major role in mediating hormone receptor responsiveness. Insights from genetically manipulated mouse models and clinical data suggest SRC-1 is significantly overexpressed in many cancers, in particular, cancers of the reproductive tissues. SRC-1 has been associated with cellular proliferation and tumor growth but its major tumorigenic contributions are promotion and execution of breast cancer metastasis and mediation of resistance to endocrine therapies. The ability of SRC-1 to coordinate multiple signaling pathways makes it an important player in tumor cells' escape of targeted therapy.

E2A proteins enhance the histone acetyltransferase activity of the transcriptional co-activators CBP and p300

The E2A gene encodes the E-protein transcription factors E12 and E47 that play critical roles in B-lymphopoiesis. A somatic chromosomal translocation detectable in 5% of cases of acute lymphoblastic leukemia (ALL) involves E2A and results in expression of the oncogenic transcription factor E2A-PBX1. CREB binding protein (CBP) and its close paralog p300 are transcriptional co-activators with intrinsic histone acetyltransferase (HAT) activity. We and others have shown that direct binding of an N-terminal transcriptional activation domain present in E12/E47 and E2A-PBX1 to the KIX domain of CBP/p300 contributes to E2A protein function. In the current work we show for the first time that the catalytic HAT activity of CBP/p300 is increased in the presence of residues 1-483 of E2A (i.e., the portion present in E2A-PBX1). The addition of purified, recombinant E2A protein to in vitro assays results in a two-fold augmentation of CBP/p300 HAT activity, whereas in vivo assays show a ten-fold augmentation of HAT-dependent transcriptional induction and a five-fold augmentation of acetylation of reporter plasmid-associated histone by CBP in response to co-transfected E2A. Our results indicate that the HAT-enhancing effect is independent of the well-documented E2A-CBP interaction involving the KIX domain and suggest a role for direct, perhaps low affinity binding of E2A to a portion of CBP that includes the HAT domain and flanking elements. Our findings add to a growing body of literature indicating that interactions between CBP/p300 and transcription factors can function in a specific manner to modulate HAT catalytic activity.

Steroid receptor coactivators 1, 2, and 3: critical regulators of nuclear receptor activity and steroid receptor modulator (SRM)-based cancer therapy

Coactivators are a diverse group of non-DNA binding proteins that induce structural changes in agonist-bound nuclear receptors (NRs) that are essential for NR-mediated transcriptional activation. Once bound, coactivators function to bridge enhancer binding proteins to the general transcription machinery, as well as to recruit secondary coactivators that modify promoter and enhancer chromatin in a manner permissive for transcriptional activation. In the following review article, we focus on one of the most in-depth studied families of coactivators, the steroid receptor coactivators (SRC) 1, 2, and 3. SRCs are widely implicated in NR-mediated diseases, especially in cancers, with the majority of studies focused on their roles in breast cancer. We highlight the relevant literature supporting the oncogenic activity of SRCs and their future as diagnostic and prognostic indicators. With much interest in the development of selective receptor modulators (SRMs), we focus on how these coactivators regulate the interactions between SRMs and their respective NRs; and, importantly, the influence that coactivators have on the functional output of SRMs. Furthermore, we speculate that coactivator-specific inhibitors could provide powerful, all-encompassing treatments that target multiple modes of oncogenic regulation in cancers resistant to typical anti-endocrine treatments.

Inhibition of bromodomain-mediated protein–protein interactions as a novel therapeutic strategy

Small molecule inhibitors of acetyl lysine–bromodomain interactions emerge as novel epigenetic tools with potential for therapeutic approaches.

Mapping acetylation sites in E2A identifies a conserved lysine residue in activation domain 1 that promotes CBP/p300 recruitment and transcriptional activation

E-proteins are basic helix-loop-helix transcription factors that function in cell type specification. The gene E2A encodes two E-proteins, E12 and E47, which are required in B-lymphopoiesis. E2A proteins can interact directly with the transcriptional co-activators and lysine acetyltranferases (KATs) CBP, p300 and PCAF to induce target gene transcription. Prior investigations have shown that the E2A-encoded isoform E2-5 is acetylated by CBP, p300 or PCAF in vitro or in vivo. However, E2-5 lacks the important N-terminal activation domain AD1. Furthermore, the acetylated residues in E-proteins have not been mapped, and the functional consequences of acetylation are largely unknown. Here, we use mutagenesis to show that a lysine residue at position 34 within AD1 of E12/E47 is acetylated by CBP/p300 and PCAF. Lys34 lies adjacent to a conserved helical LXXLL motif that interacts directly with the KIX domain of CBP/p300. We show that acetylation at Lys34 increases the affinity of AD1 for the KIX domain and enhances AD1-driven transcriptional induction. Our results illustrate for the first time that AD1 can both recruit, and be acetylated by, KATs and that KAT recruitment may promote transcriptional induction in part through acetylation of AD1 itself.

Acquisition of sexual receptivity: roles of chromatin acetylation, estrogen receptor-alpha, and ovarian hormones

Sexually naïve, hormone-primed, C57BL/6J female mice are not receptive to mating attempts by conspecific males. Repeated experience with sexually active males and concurrent treatment with estradiol and progesterone gradually increases female receptivity over the course of five trials to maximal levels. Ovarian hormones activate their cognate nuclear steroid receptors estrogen receptor-α and progesterone receptor to induce female sexual receptivity. Nuclear receptors recruit coactivators of transcription that include histone acetyltransferases to hormone responsive genes. In this set of studies, we found that the histone deacetylase inhibitor sodium butyrate enhances the experiential acquisition of receptivity. Evidence is provided that the actions of sodium butyrate on receptivity require activated estrogen receptor-α and progesterone.

CBP/p300 and SIRT1 are involved in transcriptional regulation of S-phase specific histone genes

BACKGROUND

Histones constitute a type of essential nuclear proteins important for chromatin structure and functions. The expression of major histones is strictly confined to the S phase of a cell cycle and tightly coupled to DNA replication.

METHODOLOGY/PRINCIPAL FINDINGS

With RT-qPCR and ChIP assays, we investigated transcriptional regulation of the S-phase specific histone genes and found that the acetylation level of histones on core histone gene promoters fluctuated during cell cycle in a pattern similar to RNA polymerase II association. Further, we showed that CBP/p300 and SIRT1 were recruited to histone gene promoters in an NPAT-dependent manner, knockdown of which affected histone acetylation on histone gene promoters and histone gene transcription.

SIGNIFICANCE

These observations contribute to further understanding of the mechanism by which the expression of canonical histone genes is regulated, and also implicate a link between histone expression and DNA damage repair and cell metabolism.

HTLV-1 HBZ protein deregulates interactions between cellular factors and the KIX domain of p300/CBP

The complex retrovirus human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia. Deregulation of cellular transcription is thought to be an important step for T-cell transformation caused by viral infection. HTLV-1 basic leucine zipper factor (HBZ) is one of the viral proteins believed to be involved in this process, as it deregulates the expression of numerous cellular genes. In the context of the provirus, HBZ represses HTLV-1 transcription, in part, by binding to the homologous cellular coactivators p300 and CBP. These coactivators play a central role in transcriptional regulation. In this study, we determined that HBZ binds with high affinity to the KIX domain of p300/CBP. This domain contains two binding surfaces that are differentially targeted by multiple cellular factors. We show that two φXXφφ motifs in the activation domain of HBZ mediate binding to a single surface of the KIX domain, the mixed-lineage leukemia (MLL) binding surface. Formation of this interaction inhibits binding of MLL to the KIX domain while enhancing the binding of the transcription factor c-Myb to the opposite surface of KIX. Consequently, HBZ inhibits transcriptional activation mediated by MLL and enhances activation mediated by c-Myb. CREB, which binds the same surface of KIX as c-Myb, also exhibited an increase in activity through HBZ. These results indicate that HBZ is able to alter gene expression by competing with transcription factors for the occupancy of one surface of KIX while enhancing the binding of factors to the other surface.

Tegument protein control of latent herpesvirus establishment and animation

Herpesviruses are successful pathogens that infect most vertebrates as well as at least one invertebrate species. Six of the eight human herpesviruses are widely distributed in the population. Herpesviral infections persist for the life of the infected host due in large part to the ability of these viruses to enter a non-productive, latent state in which viral gene expression is limited and immune detection and clearance is avoided. Periodically, the virus will reactivate and enter the lytic cycle, producing progeny virus that can spread within or to new hosts. Latency has been classically divided into establishment, maintenance, and reactivation phases. Here we focus on demonstrated and postulated molecular mechanisms leading to the establishment of latency for representative members of each human herpesvirus family. Maintenance and reactivation are also briefly discussed. In particular, the roles that tegument proteins may play during latency are highlighted. Finally, we introduce the term animation to describe the initiation of lytic phase gene expression from a latent herpesvirus genome, and discuss why this step should be separated, both molecularly and theoretically, from reactivation.

Distinct roles of GCN5/PCAF-mediated H3K9ac and CBP/p300-mediated H3K18/27ac in nuclear receptor transactivation

Histone acetyltransferases (HATs) GCN5 and PCAF (GCN5/PCAF) and CBP and p300 (CBP/p300) are transcription co-activators. However, how these two distinct families of HATs regulate gene activation remains unclear. Here, we show deletion of GCN5/PCAF in cells specifically and dramatically reduces acetylation on histone H3K9 (H3K9ac) while deletion of CBP/p300 specifically and dramatically reduces acetylations on H3K18 and H3K27 (H3K18/27ac). A ligand for nuclear receptor (NR) PPARδ induces sequential enrichment of H3K18/27ac, RNA polymerase II (Pol II) and H3K9ac on PPARδ target gene Angptl4 promoter, which correlates with a robust Angptl4 expression. Inhibiting transcription elongation blocks ligand-induced H3K9ac, but not H3K18/27ac, on the Angptl4 promoter. Finally, we show GCN5/PCAF and GCN5/PCAF-mediated H3K9ac correlate with, but are surprisingly dispensable for, NR target gene activation. In contrast, CBP/p300 and their HAT activities are essential for ligand-induced Pol II recruitment on, and activation of, NR target genes. These results highlight the substrate and site specificities of HATs in cells, demonstrate the distinct roles of GCN5/PCAF- and CBP/p300-mediated histone acetylations in gene activation, and suggest an important role of CBP/p300-mediated H3K18/27ac in NR-dependent transcription.

Effective formation of the segregation-competent complex determines successful partitioning of the bovine papillomavirus genome during cell division

Effective segregation of the bovine papillomavirus type 1 (BPV1), Epstein-Barr virus (EBV), and Kaposi's sarcoma-associated human herpesvirus type 8 (KSHV) genomes into daughter cells is mediated by a single viral protein that tethers viral genomes to host mitotic chromosomes. The linker proteins that mediate BPV1, EBV, and KSHV segregation are E2, LANA1, and EBNA1, respectively. The N-terminal transactivation domain of BPV1 E2 is responsible for chromatin attachment and subsequent viral genome segregation. Because E2 transcriptional activation and chromatin attachment functions are not mutually exclusive, we aimed to determine the requirement of these activities during segregation by analyzing chimeric E2 proteins. This approach allowed us to separate the two activities. Our data showed that attachment of the segregation protein to chromatin is not sufficient for proper segregation. Rather, formation of a segregation-competent complex which carries multiple copies of the segregation protein is required. Complementation studies of E2 functional domains indicated that chromatin attachment and transactivation functions must act in concert to ensure proper plasmid segregation. These data indicate that there are specific interactions between linker molecules and transcription factors/complexes that greatly increase segregation-competent complex formation. We also showed, using hybrid E2 molecules, that restored segregation function does not involve interactions with Brd4.