Coactivator CREB-binding Protein Research Articles

Analysis of tumor biomarkers in patients (pts) with advanced hepatocellular carcinoma (HCC) from a phase 1b study of E7386, a CREB-binding protein/β-catenin interaction inhibitor, in combination with lenvatinib.

535 Background: E7386, a novel oral anticancer agent, inhibits β-catenin binding to its transcriptional co-activator CREB-binding protein, thus modulating Wnt/β-catenin signaling. Lenvatinib is a multikinase inhibitor that targets VEGFR 1–3, FGFR 1–4, PDGFRα, RET, and KIT. We previously reported the safety/tolerability, pharmacokinetics, biomarkers, and preliminary efficacy of E7386 plus lenvatinib in 25 pts with HCC in the dose escalation part of a phase 1b study1 (NCT04008797). Here, we present the results of exploratory tumor biomarker analyses from this study. Methods: Pts with HCC were treated with E7386 10–80 mg QD and 60–120 mg BID plus lenvatinib (bodyweight < 60 kg: 8 mg QD; ≥ 60 kg: 12 mg QD). Archival or fresh tumor samples were collected at baseline and post-treatment; tumor tissue was assessed for genetic alteration, immunohistochemistry (IHC), and gene expression. Gene signature scores of interest were calculated using obtained gene expression data. The preliminary association between biomarker status and efficacy was investigated. Results: Of the 25 pts enrolled, 22 had baseline tumor samples available for the gene mutation analysis. TERT (6 pts: 27%), CTNNB1 (5 pts: 23%), and TP53 (4 pts: 18%) mutations were detected. CTNNB1 mutation was confirmed in 3 of 7 responders and 2 of 13 non-responders. Nuclear β-catenin expression was confirmed by IHC analysis in 5 of 16 pts; it was expressed in 3 of 5 pts with CTNNB1 MUT and 2 of 11 pts with CTNNB1 WT. Pts with expression of nuclear β-catenin had 2 partial responses (PRs) among 5 pts; those without β-catenin expression had 2 PRs among 11 pts. Additionally, IHC analysis of tumor microvessel density (MVD; number of CD31+ vessels) at baseline suggested that greater maximum tumor shrinkage (MTS) tended to be observed in the MVD-high population compared to the MVD-low population. 7 Pts had evaluable baseline and post-baseline tumor samples and were included in the gene signature analysis. Despite the small sample size, preliminary results indicated that MTS may be associated with a decrease in Wnt signaling and angiogenesis gene signature scores (spearman r [r]=0.61 for both) and attenuation of hypoxic induction and glycolysis gene signature scores (r=0.79 and 0.68, respectively). Conclusions: These exploratory tumor biomarker analyses suggest that E7386 in combination with lenvatinib may affect the tumor microenvironment in HCC pts through effects on Wnt signaling, angiogenesis, hypoxic response, and glycolysis pathways. This concept is the basis for treatment with this combination. However, given the small sample size, further investigation is needed to confirm these effects on the tumor microenvironment. Enrollment of pts with HCC to the expansion part of Study 102 is ongoing. 1. Ikeda et al. ASCO 2023. Clinical trial information: NCT04008797 .

Abstract C085: OPN-6602, a dual EP300/CBP bromodomain inhibitor modulates androgen-driven transcription, including MYC, in mCRPC

Abstract Metastatic castration-resistant prostate cancer (mCRPC) remains an urgent unmet medical need despite existing therapies that target androgen receptor (AR) signaling. Disease progression is commonly a result of acquired resistance to existing anti-androgen therapies. Biological models have revealed potential resistance mechanisms of CRPC through the reactivation of the AR pathway. Transcriptional coactivators CREB-binding protein (CBP) and E1A binding protein (EP300) are high value targets in mCRPC as they mediate androgen-dependent and -independent activity of the AR pathway. EP300 and CBP proteins harbor both histone acetyltransferase (HAT)- and bromo-domains, and the HAT activity of EP300 regulates AR function. EP300 bromodomain inhibition partially blocks its HAT activity, reducing AR-mediated gene expression and tumor growth. OPN-6602 and OPN-6742 are potent, selective, and orally active small molecule dual EP300/CBP bromodomain inhibitors which abrogate persistent AR signaling in CRPC by modulating H3K27 acetylation and the recruitment of EP300, AR full length (AR-FL), and AR variant 7 (AR-v7) to AR response elements. OPN-6602 and OPN-6742 obstruct the EP300 bromodomain leading to downregulation of the AR pathway and consequent anti-tumor effects in AR-dependent CRPC. OPN-6602 and OPN-6742 are highly selective (>100-fold) against other bromodomains based on a screening panel of 40 bromodomains. Biochemical screens using AlphaScreen technology show these compounds to be equipotent against EP300 and CBP. OPN-6602 is particularly potent by Surface Plasmon Resonance analysis, displaying a KD of 0.87 nM, with a fast association rate (1.5 E+06/Ms) and a slow dissociation rate (1.3 E-03/s). Consequently, OPN-6602 displays a noteworthy residence time of 13 minutes. Both compounds show an AR-selective mode of action with anti-proliferative activity in AR-dependent prostate cancer cell lines (e.g. VCaP, LNCaP, and 22Rv-1) but are inactive against AR-negative prostate cancer cell lines (e.g. DU145). VCaP and mCRPC patient-derived xenograft (PDX) RNA profiling provides evidence of a marked, dose-dependent, pharmacodynamic response indicative of EP300/CBP inhibition. In the VCaP xenograft model, OPN-6602 and OPN-6742 show dose-dependent tumor growth inhibition and corresponding pharmacodynamic responses with prostate-specific antigen level decreases and decreased H3K27 acetylation. In the QR (AR-v7+) PDX model of CRPC (post-androgen deprivation therapy), a synergistic effect was observed between OPN-6602 and enzalutamide. This combination further modulates the expression of AR-driven transcripts such as MYC compared to single agent treatments. The pharmacokinetic profiles of OPN-6602 and OPN-6742 are favorable for oral single daily dose administration due to a high Cmax and short half-life. Due to its higher potency, OPN-6602 has been chosen as clinical candidate and a first-in-human study will start in 2024. Citation Format: Bernice Matusow, Wayne Spevak, Chao Zhang, Yan Ma, Rafe Shellooe, Peipei Li, James Tsai, Pan- Yu Chen, Parmveer Singh, Jackie Walling, Christine Nichols, Jason Halladay, Kerry Inokuchi, Gaston Habets, Gideon Bollag. OPN-6602, a dual EP300/CBP bromodomain inhibitor modulates androgen-driven transcription, including MYC, in mCRPC [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C085.

The C-terminal transactivation domain of MITF interacts promiscuously with co-activator CBP/p300

The microphthalmia-associated transcription factor (MITF) is one of four closely related members of the MiT/TFE family (TFEB, TFE3, TFEC) that regulate a wide range of cellular processes. MITF is a key regulator of melanocyte-associated genes, and essential to proper development of the melanocyte cell lineage. Abnormal MITF activity can contribute to the onset of several diseases including melanoma, where MITF is an amplified oncogene. To enhance transcription, MITF recruits the co-activator CREB-binding protein (CBP) and its homolog p300 to gene promoters, however the molecular determinants of their interaction are not yet fully understood. Here, we characterize the interactions between the C-terminal MITF transactivation domain and CBP/p300. Using NMR spectroscopy, protein pulldown assays, and isothermal titration calorimetry we determine the C-terminal region of MITF is intrinsically disordered and binds with high-affinity to both TAZ1 and TAZ2 of CBP/p300. Mutagenesis studies revealed two conserved motifs within MITF that are necessary for TAZ2 binding and critical for MITF-dependent transcription of a reporter gene. Finally, we observe the transactivation potential of the MITF C-terminal region is reliant on the N-terminal transactivation domain for function. Taken together, our study helps elucidate the molecular details of how MITF interacts with CBP/p300 through multiple redundant interactions that lend insight into MITF function in melanocytes and melanoma.

Rational peptide design for inhibition of the KIX–MLL interaction

The kinase-inducible domain interacting (KIX) domain is an integral part of the general transcriptional coactivator CREB-binding protein, and has been associated with leukemia, cancer, and various viral diseases. Hence, the KIX domain has attracted considerable attention in drug discovery and development. Here, we rationally designed a KIX inhibitor using a peptide fragment corresponding to the transactivation domain (TAD) of the transcriptional activator, mixed-lineage leukemia protein (MLL). We performed theoretical saturation mutagenesis using the Rosetta software to search for mutants expected to bind KIX more tightly than the wild-type MLL TAD. Mutant peptides with higher helical propensities were selected for experimental characterization. We found that the T2857W mutant of the MLL TAD peptide had the highest binding affinity for KIX compared to the other 12 peptides designed in this study. Moreover, the peptide had a high inhibitory effect on the KIX–MLL interaction with a half-maximal inhibitory concentration close to the dissociation constant for this interaction. To our knowledge, this peptide has the highest affinity for KIX among all previously reported inhibitors that target the MLL site of KIX. Thus, our approach may be useful for rationally developing helical peptides that inhibit protein–protein interactions implicated in the progression of various diseases.

Glucose-stimulated PGC-1α couples with CBP and Runx2 to mediate intervertebral disc degeneration through transactivation of ADAMTS4/5 in diet-induced obesity mice.

Emerging evidence suggests that type 2 diabetes mellitus (T2DM) is associated with the pathogenesis of intervertebral disc degeneration (IDD). However, it is still unclear how T2DM contributes to IDD. Herein, we observed the accumulation of blood glucose and degenerative lumbar discs in mice fed a high-fat diet. Detection of differentially expressed genes in degenerative lumbar discs revealed that ADAMTS4 (A Disintegrin and Metalloproteinase with Thrombospondin motifs) and ADAMTS5 genes were significantly increased. In vitro analyses demonstrated that Runt-Related Transcription Factor 2 (Runx2) recruited both PPARgamma Coactivator 1alpha (PGC-1α) and CREB-Binding Protein (CBP) to transactivate the expression of ADAMTS4/5. Glucose stimulation could dose-dependently induce the accumulation of PGC-1α and promoted the binding of the CBP-PGC-1α-Runx2 complex to the promoters of ADAMTS4/5. Depletion of CBP-PGC-1α-Runx2 complex members and treatment with either PGC-1α inhibitor SR-18292 or CBP inhibitor EML425 in vitro could dramatically inhibit the glucose-induced expression of ADAMTS4/5. Administration of SR-18292 and EML425 in diabetic mice could prevent the degeneration of lumbar discs. Collectively, our results revealed a molecular mechanism by which the hyperglycemia-dependent CBP-PGC-1α-Runx2 complex was required for the transactivation of ADAMTS4/5. The blockage of this complex in diabetic mice may help prevent IDD.

Differential Regulation of the BDNF Gene in Cortical and Hippocampal Neurons.

Brain-derived neurotrophic factor (BDNF) is a widely expressed neurotrophin that supports the survival, differentiation, and signaling of various neuronal populations. Although it has been well described that expression of BDNF is strongly regulated by neuronal activity, little is known whether regulation of BDNF expression is similar in different brain regions. Here, we focused on this fundamental question using neuronal populations obtained from rat cerebral cortices and hippocampi of both sexes. First, we thoroughly characterized the role of the best-described regulators of BDNF gene - cAMP response element binding protein (CREB) family transcription factors, and show that activity-dependent BDNF expression depends more on CREB and the coactivators CREB binding protein (CBP) and CREB-regulated transcriptional coactivator 1 (CRTC1) in cortical than in hippocampal neurons. Our data also reveal an important role of CREB in the early induction of BDNF mRNA expression after neuronal activity and only modest contribution after prolonged neuronal activity. We further corroborated our findings at BDNF protein level. To determine the transcription factors regulating BDNF expression in these rat brain regions in addition to CREB family, we used in vitro DNA pulldown assay coupled with mass spectrometry, chromatin immunoprecipitation (ChIP), and bioinformatics, and propose a number of neurodevelopmentally important transcription factors, such as FOXP1, SATB2, RAI1, BCL11A, and TCF4 as brain region-specific regulators of BDNF expression. Together, our data reveal complicated brain region-specific fine-tuning of BDNF expression.SIGNIFICANCE STATEMENT To date, majority of the research has focused on the regulation of brain-derived neurotrophic factor (BDNF) in the brain but much less is known whether the regulation of BDNF expression is universal in different brain regions and neuronal populations. Here, we report that the best described regulators of BDNF gene from the cAMP-response element binding protein (CREB) transcription factor family have a more profound role in the activity-dependent regulation of BDNF in cortex than in hippocampus. Our results indicate a brain region-specific fine tuning of BDNF expression. Moreover, we have used unbiased determination of novel regulators of the BDNF gene and report a number of neurodevelopmentally important transcription factors as novel potential regulators of the BDNF expression.

Directed mutational scanning reveals a balance between acidic and hydrophobic residues in strong human activation domains.

SUMMARYAcidic activation domains are intrinsically disordered regions of the transcription factors that bind coactivators. The intrinsic disorder and low evolutionary conservation of activation domains have made it difficult to identify the sequence features that control activity. To address this problem, we designed thousands of variants in seven acidic activation domains and measured their activities with a high-throughput assay in human cell culture. We found that strong activation domain activity requires a balance between the number of acidic residues and aromatic and leucine residues. These findings motivated a predictor of acidic activation domains that scans the human proteome for clusters of aromatic and leucine residues embedded in regions of high acidity. This predictor identifies known activation domains and accurately predicts previously unidentified ones. Our results support a flexible acidic exposure model of activation domains in which the acidic residues solubilize hydrophobic motifs so that they can interact with coactivators. A record of this paper’s transparent peer review process is included in the supplemental information.

Multivalency enables unidirectional switch-like competition between intrinsically disordered proteins

Intrinsically disordered proteins must compete for binding to common regulatory targets to carry out their biological functions. Previously, we showed that the activation domains of two disordered proteins, the transcription factor HIF-1α and its negative regulator CITED2, function as a unidirectional, allosteric molecular switch to control transcription of critical adaptive genes under conditions of oxygen deprivation. These proteins achieve transcriptional control by competing for binding to the TAZ1 domain of the transcriptional coactivators CREB-binding protein (CBP) and p300 (CREB: cyclic-AMP response element binding protein). To characterize the mechanistic details behind this molecular switch, we used solution NMR spectroscopy and complementary biophysical methods to determine the contributions of individual binding motifs in CITED2 to the overall competition process. An N-terminal region of the CITED2 activation domain, which forms a helix when bound to TAZ1, plays a critical role in initiating competition with HIF-1α by enabling formation of a ternary complex in a process that is highly dependent on the dynamics and disorder of the competing partners. Two other conserved binding motifs in CITED2, the LPEL motif and an aromatic/hydrophobic motif that we term ϕC, function synergistically to enhance binding of CITED2 and inhibit rebinding of HIF-1α. The apparent unidirectionality of competition between HIF-1α and CITED2 is lost when one or more of these binding regions is altered by truncation or mutation of the CITED2 peptide. Our findings illustrate the complexity of molecular interactions involving disordered proteins containing multivalent interaction motifs and provide insight into the unique mechanisms by which disordered proteins compete for occupancy of common molecular targets within the cell.

Molecular mimicry of NF-κB by vaccinia virus protein enables selective inhibition of antiviral responses.

Infection of mammalian cells with viruses activates NF-κB to induce the expression of cytokines and chemokines and initiate an antiviral response. Here, we show that a vaccinia virus protein mimics the transactivation domain of the p65 subunit of NF-κB to inhibit selectively the expression of NF-κB-regulated genes. Using co-immunoprecipitation assays, we found that the vaccinia virus protein F14 associates with NF-κB co-activator CREB-binding protein (CBP) and disrupts the interaction between p65 and CBP. This abrogates CBP-mediated acetylation of p65, after which it reduces promoter recruitment of the transcriptional regulator BRD4 and diminishes stimulation of NF-κB-regulated genes CXCL10 and CCL2. Recruitment of BRD4 to the promoters of NFKBIA and CXCL8 remains unaffected by either F14 or JQ1 (a competitive inhibitor of BRD4 bromodomains), indicating that BRD4 recruitment is acetylation-independent. Unlike other viral proteins that are general antagonists of NF-κB, F14 is a selective inhibitor of NF-κB-dependent gene expression. An in vivo model of infection demonstrated that F14 promotes virulence. Molecular mimicry of NF-κB may be conserved because other orthopoxviruses, including variola, monkeypox and cowpox viruses, encode orthologues of F14.

Characterization of the High-Affinity Fuzzy Complex between the Disordered Domain of the E7 Oncoprotein from High-Risk HPV and the TAZ2 Domain of CBP.

The intrinsically disordered N-terminal region of the E7 protein from high-risk human papillomavirus (HPV) strains is responsible for oncogenic transformation of host cells through its interaction with a number of cellular factors, including the TAZ2 domain of the transcriptional coactivator CREB-binding protein. Using a variety of spectroscopic and biochemical tools, we find that despite its nanomolar affinity, the HPV16 E7 complex with TAZ2 is disordered and highly dynamic. The disordered domain of HPV16 E7 protein does not adopt a single conformation on the surface of TAZ2 but engages promiscuously with its target through multiple interactions involving two conserved motifs, termed CR1 and CR2, that occupy an extensive binding surface on TAZ2. The fuzzy nature of the complex is a reflection of the promiscuous binding repertoire of viral proteins, which must efficiently dysregulate host cell processes by binding to a variety of host factors in the cellular environment.

Nucleosome assembly protein 1 is a regulator of histone H1 acetylation.

Acetylation of histone H1 is generally considered to activate transcription, whereas deacetylation of H1 represses transcription. However, the precise mechanism of the acetylation is unknown. Here, using chromatography, we identified nucleosome assembly protein 1 (NAP-1) as having inhibitory activity against histone H1 acetylation by acetyltransferase p300. We found that native NAP-1 interacts with H1 in a Drosophila crude extract. We also found that it inhibits the deacetylation of histone H1 by histone deacetylase 1. The core histones in nucleosomes were acetylated in a GAL4-VP16 transcriptional activator-dependent manner in vitro. This acetylation was strongly repressed by hypoacetylated H1 but to a lesser extent by hyperacetylated H1. Consistent with these findings, a micrococcal nuclease assay indicated that hypoacetylated H1, which represses activator-dependent acetylation, was incorporated into chromatin, whereas hyperacetylated H1 was not. To determine the contribution of NAP-1 to transcriptional regulation in vivo, we compared NAP-1 knockdown (KD) with coactivator CREB-binding protein (CBP) KD using RNA sequencing in Drosophila Schneider 2 cells. Most genes were downregulated rather than upregulated by NAP-1 KD, and those downregulated genes were also downregulated by CBP KD. Our results suggest that NAP-1 plays a role in transcriptional regulation by fine-tuning the acetylation of histone H1. Graphical Abstract.

The molecular basis of allostery in a facilitated dissociation process

Facilitated dissociation provides a mechanism by which high-affinity complexes can be rapidly disassembled. The negative feedback regulator CITED2 efficiently downregulates the hypoxic response by displacing the hypoxia-inducible transcription factor HIF-1α from the TAZ1 domain of the transcriptional coactivators CREB-binding protein (CBP) and p300. Displacement occurs by a facilitated dissociation mechanism involving a transient ternary intermediate formed by binding of the intrinsically disordered CITED2 activation domain to the TAZ1:HIF-1α complex. The short lifetime of the intermediate precludes straightforward structural investigations. To obtain insights into the molecular determinants of facilitated dissociation, we model the ternary intermediate by generating a fusion peptide composed of the primary CITED2 and HIF-1α binding motifs. X-ray crystallographic and NMR studies of the fusion peptide complex reveal TAZ1-mediated negative cooperativity that results in nearly mutually exclusive binding of specific CITED2 and HIF-1α interaction motifs, providing molecular-level insights into the allosteric switch that terminates the hypoxic response.

Grap2 cyclin D interacting protein negatively regulates CREB‑binding protein, inhibiting fibroblast‑like synoviocyte growth.

Rheumatoid arthritis(RA) is one of the most critical articular diseases, which is characterized by synovial hyperplasia and impaired quality of life. The clinical features of RA include chronic inflammation of the joints associated with synovial cell overgrowth. However, the mechanism regulating the outgrowth of fibroblast‑like synoviocytes(FLS) is not fully understood. The present study reported that grap2 cyclinD interacting protein(GCIP), an inhibitor of DNA binding/differentiation(ID)‑like helix‑loop‑helix protein, interacted with cAMP‑response element‑binding protein (CREB)‑binding protein(CBP). Furthermore, GCIP repressed CREB‑ and NF‑κB‑dependent gene expression by inhibiting CBP binding to RNA polymerase II complexes. GCIP depletion via small interfering RNA enhanced FLS growth, whereas stable GCIP expression suppressed the growth of 293cells. In addition, GCIP depletion in FLS induced the expression of cyclinD1, a CREB target gene. The present study identified a novel inhibitory mechanism in which an ID protein may functionally target the transcriptional coactivator CBP. These results suggested that GCIP downregulation may be pivotal in FLS outgrowth.

High-altitude deer mouse hypoxia-inducible factor-2α shows defective interaction with CREB-binding protein

Numerous mammalian species have adapted to the chronic hypoxia of high altitude. Recent genomic studies have identified evidence for natural selection of genes and associated genetic changes in these species. A major gap in our knowledge is an understanding of the functional significance, if any, of these changes. Deer mice (Peromyscus maniculatus) live at both low and high altitudes in North America, providing an opportunity to identify functionally important genetic changes. High-altitude deer mice show evidence of natural selection on the Epas1 gene, which encodes for hypoxia-inducible factor-2α (Hif-2α), a central transcription factor of the hypoxia-inducible factor pathway. An SNP encoding for a T755M change in the Hif-2α protein is highly enriched in high-altitude deer mice, but its functional significance is unknown. Here, using coimmunoprecipitation and transcriptional activity assays, we show that the T755M mutation produces a defect in the interaction of Hif-2α with the transcriptional coactivator CREB-binding protein. This results in a loss of function because of decreased transcriptional activity. Intriguingly, the effect of this mutation depends on the amino acid context. Interchanges between methionine and threonine at the corresponding position in house mouse (Mus musculus) Hif-2α are without effects on CREB-binding protein binding. Furthermore, transfer of a set of deer mouse–specific Hif-2α amino acids to house mouse Hif-2α is sufficient to confer sensitivity of house mouse Hif-2α to the T755M substitution. These findings provide insight into high-altitude adaptation in deer mice and evolution at the Epas1 locus.

Enhancer RNAs predict enhancer-gene regulatory links and are critical for enhancer function in neuronal systems.

Genomic enhancer elements regulate gene expression programs important for neuronal fate and function and are implicated in brain disease states. Enhancers undergo bidirectional transcription to generate non-coding enhancer RNAs (eRNAs). However, eRNA function remains controversial. Here, we combined Assay for Transposase-Accessible Chromatin using Sequencing (ATAC-Seq) and RNA-Seq datasets from three distinct neuronal culture systems in two activity states, enabling genome-wide enhancer identification and prediction of putative enhancer–gene pairs based on correlation of transcriptional output. Notably, stimulus-dependent enhancer transcription preceded mRNA induction, and CRISPR-based activation of eRNA synthesis increased mRNA at paired genes, functionally validating enhancer–gene predictions. Focusing on enhancers surrounding the Fos gene, we report that targeted eRNA manipulation bidirectionally modulates Fos mRNA, and that Fos eRNAs directly interact with the histone acetyltransferase domain of the enhancer-linked transcriptional co-activator CREB-binding protein (CBP). Together, these results highlight the unique role of eRNAs in neuronal gene regulation and demonstrate that eRNAs can be used to identify putative target genes.

Differential contribution of p300 and CBP to regulatory element acetylation in mESCs

BackgroundThe transcription coactivators CREB binding protein (CBP) and p300 are highly homologous acetyltransferases that mediate histone 3 lysine 27 acetylation (H3K27ac) at regulatory elements such as enhancers and promoters. Although in most cases, CBP and p300 are considered to be functionally identical, both proteins are indispensable for development and there is evidence of tissue-specific nonredundancy. However, characterization of chromatin and transcription states regulated by each protein is lacking.ResultsIn this study we analyze the individual contribution of p300 and CBP to the H3K27ac landscape, chromatin accessibility, and transcription in mouse embryonic stem cells (mESC). We demonstrate that p300 is the predominant H3K27 acetyltransferase in mESCs and that loss of acetylation in p300KD mESCs is more pronounced at enhancers compared to promoters. While loss of either CBP or p300 has little effect on the open state of chromatin, we observe that distinct gene sets are transcriptionally dysregulated upon depletion of p300 or CBP. Transcriptional dysregulation is generally correlated with dysregulation of promoter acetylation upon depletion of p300 (but not CBP) and appears to be relatively independent of dysregulated enhancer acetylation. Interestingly, both our transcriptional and genomic analyses demonstrate that targets of the p53 pathway are stabilized upon depletion of p300, suggesting an unappreciated view of the relationship between p300 and p53 in mESCs.ConclusionsThis genomic study sheds light on distinct functions of two important transcriptional regulators in the context of a developmentally relevant cell type. Given the links to both developmental disorders and cancer, we believe that our study may promote new ways of thinking about how these proteins function in settings that lead to disease.

Gene expression meta-analysis reveals the up-regulation of CREB1 and CREBBP in Brodmann Area 10 of patients with schizophrenia

Cognitive impairments characterize individuals with schizophrenia, and are correlated to the patients’ functional outcome. The transcription factor Cyclic AMP-responsive element-binding protein-1 (CREB1) is involved in learning and memory processes. CREB1 and both CREB-binding protein (CREBBP) and E1A Binding Protein P300 (EP300), co-activators of CREB1, have been associated with schizophrenia. We performed a systematic meta-analysis of CREB1, CREBBP and EP300 differential expression in post mortem Brodmann Area 10 (BA10) samples of patients with schizophrenia vs. healthy controls, following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Two microarray datasets met the inclusion criteria (overall 41 schizophrenia samples and 38 controls were analyzed). We detect up-regulation of CREB1 and CREBBP in BA10 samples of patients with schizophrenia, while EP300 wasn't differentially expressed. The integration of two independent datasets and the positive correlation between the expression patterns of CREB1 and CREBBP increase the validity of the results. The up-regulation of CREB1 and its co-activator CREBBP might relate to BA10 altered activation that has been shown in schizophrenia. As BA10 was shown to be involved in the cognitive impairments associated with schizophrenia, this suggests involvement of CREB1 and CREBBP in the cognitive symptoms that characterize the disease.

Abstract B26: Prometastatic effect of ICG-001, a β-catenin/CBP dependent transcription inhibitor, in osteosarcoma

Abstract Osteosarcoma is the most common malignant bone tumor in the pediatric population, representing around 4 cases per million people per year in the world. Patient survival is closely related to the response of tumor cells to chemotherapy, reaching 70% at 5 years for patients with localized disease, but only 25% for high-risk patients with relapsed or metastatic disease. In 20% of cases, patients have detectable metastases at diagnosis, preferentially in the lungs, which is a sign of poor prognosis. However, it is estimated that around 80% of patients have pulmonary micrometastases, sometimes undetectable at diagnosis by imaging techniques. This makes metastatic dissemination a significant issue in the management of osteosarcoma. In addition, the survival rate has not evolved since the past decades and there is no current efficient therapy for these patients. Therefore, it is necessary to develop new therapeutic strategies. In this context, a dysregulation of the canonical Wnt signaling pathway (Wnt/β-catenin) has been reported in many osteosarcoma cases, but its implication in the development of primary and metastatic osteosarcoma is still controversial. An increase in β-catenin expression has been described in human osteosarcoma tissues compared to normal bones. Thus, we evaluated the antitumor potential of ICG-001, a small molecule that specifically binds to the transcriptional co-activator CREB-Binding Protein (CBP), disrupting its interaction with β-catenin and thus suppressing the Wnt/β-catenin target gene expression. First, we demonstrated that ICG-001 inhibits β-catenin/CBP-dependent transcription as evaluated by TCF-LEF reporter assay and RT-qPCR on β-catenin target genes in three human osteosarcoma cell lines, KHOS, MG63, and SJSA1. Moreover, ICG-001 decreases proliferation of osteosarcoma cells in a dose- and time-dependent manner, associated with a cell cycle blockade in G0/G1 phase after 24h of treatment, but without any effect on cell death. However, surprisingly, ICG-001 promotes KHOS, MG63, and SJSA1 cell migration in vitro and the development of pulmonary metastases in a murine xenograft model of osteosarcoma induced by injection of KHOS cells in a paratibial site. This study therefore raises new questions about the role of the Wnt/β-catenin pathway in the metastatic development of osteosarcoma. Thus, it is necessary to identify the different signatures of the signaling pathways potentially activated after disruption of the β-catenin and CBP interaction in osteosarcoma cells and responsible for the prometastatic effect of this drug. Citation Format: Geoffroy Danieau, Sarah Morice, Sarah Renault, Kevin Biteau, Régis Brion, Jérôme Amiaud, Frédéric Lezot, Franck Verrecchia, Françoise Rédini, Bénédicte Brounais-Le Royer. Prometastatic effect of ICG-001, a β-catenin/CBP dependent transcription inhibitor, in osteosarcoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B26.

Investigating the Binding Mechanisms of Intrinsically Disordered Transactivation Domains to the TAZ1 Domain of CBP via Molecular Dynamics Simulation

Intrinsically disordered proteins play important functions in various biological processes. A number of intrinsically disordered transactivation domains (TADs) interact with the TAZ1 domain of the transcriptional coactivator CREB binding protein. In this work, we focus on five disordered TADs whose structures in complex with the TAZ1 domain have been determined via solution NMR. They are CITED2, HIF-1α, p53, STAT2, and RelA. Upon binding to TAZ1, these five TADs wrap around TAZ1 and undergo partial disorder-to-order transitions. A comparison of the TAD/TAZ1 complexes shows that the five TADs wrap around TAZ1 with different orientations and occupy the four TAZ1 binding sites with various orders. To elucidate the microscopic molecular details of the heterogeneous binding processes of TADs with TAZ1, we carried out molecular dynamics simulations using a coarse-grained topology-based model. Free energy analysis showed that intramolecular native contacts increased gradually with intermolecular native contacts for the five TADs. Φ-value analysis showed that only a small fraction of native contacts were formed in the transition state. Kinetics analysis revealed distinct features for the five TADs. HIF-1α and STAT2 bind to TAZ1 with low binding rates, slow transition kinetics, and low evolving probability. CITED2 and RelA bind to TAZ1 with high binding rates, medium transition kinetics, and high evolving probability. p53 binds to TAZ1 with high binding rates, high transition kinetics, and low evolving probability. As the five TADs have low sequence similarity and bind to TAZ1 with different binding poses, the similar and different binding features should reflect the roles that TADs and TAZ1 played in the binding process. Analysis of the binding mechanisms suggests that binding of TADs to TAZ1 is encoded by the TADs as well as templated by the TAZ1.

Pharmacological Modulation of the Wnt/β-Catenin Pathway Inhibits Proliferation and Promotes Differentiation of Long-Lived Memory CD4+ T Cells in Antiretroviral Therapy-Suppressed Simian Immunodeficiency Virus-Infected Macaques.

The major obstacle to human immunodeficiency type 1 virus (HIV-1) eradication is a reservoir of latently infected cells that persists despite long-term antiretroviral therapy (ART) and is maintained through cellular proliferation. Long-lived memory CD4+ T cells with high self-renewal capacity, such as central memory (CM) T cells and stem cell memory (SCM) T cells, are major contributors to the viral reservoir in HIV-infected individuals on ART. The Wnt/β-catenin signaling pathway regulates the balance between self-renewal and differentiation of SCM and CM T cells, and pharmacological manipulation of this pathway offers an opportunity to interfere with the proliferation of latently infected cells. Here, we evaluated in vivo a novel approach to inhibit self-renewal of SCM and CM CD4+ T cells in the rhesus macaque (RM) model of simian immunodeficiency (SIV) infection. We used an inhibitor of the Wnt/β-catenin pathway, PRI-724, that blocks the interaction between the coactivator CREB-binding protein (CBP) and β-catenin, resulting in the cell fate decision to differentiate rather than proliferate. Our study shows that PRI-724 treatment of ART-suppressed SIVmac251-infected RMs resulted in decreased proliferation of SCM and CM T cells and modified the SCM and CM CD4+ T cell transcriptome toward a profile of more differentiated memory T cells. However, short-term treatment with PRI-724 alone did not significantly reduce the size of the viral reservoir. This work demonstrates for the first time that stemness pathways of long-lived memory CD4+ T cells can be pharmacologically modulated in vivo, thus establishing a novel strategy to target HIV persistence.IMPORTANCE Long-lasting CD4+ T cell subsets, such as central memory and stem cell memory CD4+ T cells, represent critical reservoirs for human immunodeficiency virus (HIV) persistence despite suppressive antiretroviral therapy. These cells possess stem cell-like properties of enhanced self-renewal/proliferation, and proliferation of latently infected memory CD4+ T cells plays a key role in maintaining the reservoir over time. Here, we evaluated an innovative strategy targeting the proliferation of long-lived memory CD4+ T cells to reduce viral reservoir stability. Using the rhesus macaque model, we tested a pharmacological inhibitor of the Wnt/β-catenin signaling pathway that regulates T cell proliferation. Our study shows that administration of the inhibitor PRI-724 decreased the proliferation of SCM and CM CD4+ T cells and promoted a transcriptome enriched in differentiation genes. Although the viral reservoir size was not significantly reduced by PRI-724 treatment alone, we demonstrate the potential to pharmacologically modulate the proliferation of memory CD4+ T cells as a strategy to limit HIV persistence.