A candidate X-linked mental retardation gene is a component of a new family of histone deacetylase-containing complexes

Inhibitors of Protein Methyltransferases and Demethylases

Post-translational modifications of histones by protein methyltransferases (PMTs) and histone demethylases (KDMs) play an important role in the regulation of gene expression and transcription and are implicated in cancer and many other diseases. Many of these enzymes also target various nonhistone proteins impacting numerous crucial biological pathways. Given their key biological functions and implications in human diseases, there has been a growing interest in assessing these enzymes as potential therapeutic targets. Consequently, discovering and developing inhibitors of these enzymes has become a very active and fast-growing research area over the past decade. In this review, we cover the discovery, characterization, and biological application of inhibitors of PMTs and KDMs with emphasis on key advancements in the field. We also discuss challenges, opportunities, and future directions in this emerging, exciting research field.

Constitutive scaffolding of multiple Wnt enhanceosome components by Legless/BCL9

Wnt/β-catenin signaling elicits context-dependent transcription switches that determine normal development and oncogenesis. These are mediated by the Wnt enhanceosome, a multiprotein complex binding to the Pygo chromatin reader and acting through TCF/LEF-responsive enhancers. Pygo renders this complex Wnt-responsive, by capturing β-catenin via the Legless/BCL9 adaptor. We used CRISPR/Cas9 genome engineering of Drosophila legless (lgs) and human BCL9 and B9L to show that the C-terminus downstream of their adaptor elements is crucial for Wnt responses. BioID proximity labeling revealed that BCL9 and B9L, like PYGO2, are constitutive components of the Wnt enhanceosome. Wnt-dependent docking of β-catenin to the enhanceosome apparently causes a rearrangement that apposes the BCL9/B9L C-terminus to TCF. This C-terminus binds to the Groucho/TLE co-repressor, and also to the Chip/LDB1-SSDP enhanceosome core complex via an evolutionary conserved element. An unexpected link between BCL9/B9L, PYGO2 and nuclear co-receptor complexes suggests that these β-catenin co-factors may coordinate Wnt and nuclear hormone responses.

ZMYM3 regulates BRCA1 localization at damaged chromatin to promote DNA repair

In this study, Leung et al. identified ZMYM3 (zinc finger, myeloproliferative, and mental retardation-type 3) as a chromatin-interacting protein that promotes DNA repair by homologous recombination. This work identifies a critical chromatin-binding DNA damage response factor, ZMYM3, which modulates BRCA1 functions within chromatin to ensure the maintenance of genome integrity.

Chromatin connects DNA damage response factors to sites of damaged DNA to promote the signaling and repair of DNA lesions. The histone H2A variants H2AX, H2AZ, and macroH2A represent key chromatin constituents that facilitate DNA repair. Through proteomic screening of these variants, we identified ZMYM3 (zinc finger, myeloproliferative, and mental retardation-type 3) as a chromatin-interacting protein that promotes DNA repair by homologous recombination (HR). ZMYM3 is recruited to DNA double-strand breaks through bivalent interactions with both histone and DNA components of the nucleosome. We show that ZMYM3 links the HR factor BRCA1 to damaged chromatin through specific interactions with components of the BRCA1-A subcomplex, including ABRA1 and RAP80. By regulating ABRA1 recruitment to damaged chromatin, ZMYM3 facilitates the fine-tuning of BRCA1 interactions with DNA damage sites and chromatin. Consistent with a role in regulating BRCA1 function, ZMYM3 deficiency results in impaired HR repair and genome instability. Thus, our work identifies a critical chromatin-binding DNA damage response factor, ZMYM3, which modulates BRCA1 functions within chromatin to ensure the maintenance of genome integrity.

Histone Deacetylase 1 Is Essential for Rod Photoreceptor Differentiation by Regulating Acetylation at Histone H3 Lysine 9 and Histone H4 Lysine 12 in the Mouse Retina

Histone acetylation has a regulatory role in gene expression and is necessary for proper tissue development. To investigate the specific roles of histone deacetylases (HDACs) in rod differentiation in neonatal mouse retinas, we used a pharmacological approach that showed that inhibition of class I but not class IIa HDACs caused the same phenotypic changes seen with broad spectrum HDAC inhibitors, most notably a block in the differentiation of rod photoreceptors. Inhibition of HDAC1 resulted in increase of acetylation of lysine 9 of histone 3 (H3K9) and lysine 12 of histone 4 (H4K12) but not lysine 27 of histone 3 (H3K27) and led to maintained expression of progenitor-specific genes such as Vsx2 and Hes1 with concomitant block of expression of rod-specific genes. ChiP experiments confirmed these changes in the promoters of a group of progenitor genes. Based on our results, we suggest that HDAC1-specific inhibition prevents progenitor cells of the retina from exiting the cell cycle and differentiating. HDAC1 may be an essential epigenetic regulator of the transition from progenitor cells to terminally differentiated photoreceptors.

LSD1: biologic roles and therapeutic targeting

LSD1 (KDM1A; BHC110; AOF2) was the first protein reported to exhibit histone demethylase activity and has since been shown to have multiple essential roles in mammalian biology. Given its enzymatic activity and its high-level expression in many human malignancies, a significant recent focus has been the development of pharmacologic inhibitors. Here we summarize structural and biochemical knowledge of this important epigenetic regulator, with a particular emphasis on the functional and preclinical studies in oncology that have provided justification for the evaluation of tranylcypromine derivative LSD1 inhibitors in early phase clinical trials.

Epigenetic Mechanisms in Developmental Alcohol-Induced Neurobehavioral Deficits

Alcohol consumption during pregnancy and its damaging consequences on the developing infant brain are significant public health, social, and economic issues. The major distinctive features of prenatal alcohol exposure in humans are cognitive and behavioral dysfunction due to damage to the central nervous system (CNS), which results in a continuum of disarray that is collectively called fetal alcohol spectrum disorder (FASD). Many rodent models have been developed to understand the mechanisms of and to reproduce the human FASD phenotypes. These animal FASD studies have provided several molecular pathways that are likely responsible for the neurobehavioral abnormalities that are associated with prenatal alcohol exposure of the developing CNS. Recently, many laboratories have identified several immediate, as well as long-lasting, epigenetic modifications of DNA methylation, DNA-associated histone proteins and microRNA (miRNA) biogenesis by using a variety of epigenetic approaches in rodent FASD models. Because DNA methylation patterns, DNA-associated histone protein modifications and miRNA-regulated gene expression are crucial for synaptic plasticity and learning and memory, they can therefore offer an answer to many of the neurobehavioral abnormalities that are found in FASD. In this review, we briefly discuss the current literature of DNA methylation, DNA-associated histone proteins modification and miRNA and review recent developments concerning epigenetic changes in FASD.

A Novel Interaction between TFII-I and Mdm2 with a Negative Effect on TFII-I Transcriptional Activity

Williams-Beuren syndrome-associated transcription factor TFII-I plays a critical regulatory role in bone and neural tissue development and in immunity, in part by regulating cell proliferation in response to mitogens. Mdm2, a cellular oncogene responsible for the loss of p53 tumor suppressor activity in a significant proportion of human cancers, was identified in this study as a new binding partner for TFII-I and a negative regulator of TFII-I-mediated transcription. These findings suggest a new p53-independent mechanism by which increased Mdm2 levels found in human tumors could influence cancer cells. In addition to that, we present data indicating that TFII-I is an important cellular regulator of transcription from the immediate-early promoter of human cytomegalovirus, a promoter sequence frequently used in mammalian expression vectors, including vectors for gene therapy. Our observation that Mdm2 over-expression can decrease the ability of TFII-I to activate the CMV promoter might have implications for the efficiency of experimental gene therapy based on CMV promoter–derived vectors in cancers with Mdm2 gene amplification.

Disrupted intricacy of histone H3K4 methylation in neurodevelopmental disorders

Methylation of histone H3 lysine 4 (H3K4me) is an intricately regulated posttranslational modification, which is broadly associated with enhancers and promoters of actively transcribed genomic loci. Recent advances in next-generation sequencing have identified a number of H3K4me regulators mutated in neurodevelopmental disorders including intellectual disabilities, autism spectrum disorders, and schizophrenia. Here, we aim to summarize the molecular function of H3K4me-regulating enzymes in brain development and function. We describe four H3K4me methyltransferases (KMT2A, KMT2C, KMT2D, KMT2F), four demethylases (KDM1A, KDM5A, KDM5B, KDM5C), and two reader proteins (PHF21A, PHF8) mutated in neurodevelopmental disorders. Understanding the role of these chromatin regulators in the development and maintenance of neural connections will advance therapeutic opportunities for prevention and treatment of these lifelong neurodevelopmental disorders.

A microdeletion encompassing PHF21A in an individual with global developmental delay and craniofacial anomalies

In Potocki-Shaffer syndrome (PSS), the full phenotypic spectrum is manifested when deletions are at least 2.1 Mb in size at 11p11.2. The PSS-associated genes EXT2 and ALX4, together with PHF21A, all map to this region flanked by markers D11S1393 and D11S1319. Being proximal to EXT2 and ALX4, a 1.1 Mb region containing 12 annotated genes had been identified by deletion mapping to explain PSS phenotypes except multiple exostoses and parietal foramina. Here, we report a male patient with partial PSS phenotypes including global developmental delay, craniofacial anomalies, minor limb anomalies, and micropenis. Using microarray, qPCR, RT-qPCR, and Western blot analyses, we refined the candidate gene region, which harbors five genes, by excluding two genes, SLC35C1 and CRY2, which resulted in a corroborating role of PHF21A in developmental delay and craniofacial anomalies. This microdeletion contains the least number of genes at 11p11.2 reported to date. Additionally, we also discuss the phenotypes observed in our patient with respect to those of published cases of microdeletions across the Potocki-Shaffer interval.

Screen for multi-SUMO-binding proteins reveals a multi-SIM-binding mechanism for recruitment of the transcriptional regulator ZMYM2 to chromatin

Protein SUMOylation has emerged as an important regulatory event, particularly in nuclear processes such as transcriptional control and DNA repair. In this context, small ubiquitin-like modifier (SUMO) often provides a binding platform for the recruitment of proteins via their SUMO-interacting motifs (SIMs). Recent discoveries point to an important role for multivalent SUMO binding through multiple SIMs in the binding partner as exemplified by poly-SUMOylation acting as a binding platform for ubiquitin E3 ligases such as ring finger protein 4. Here, we have investigated whether other types of protein are recruited through multivalent SUMO interactions. We have identified dozens of proteins that bind to multi-SUMO platforms, thereby uncovering a complex potential regulatory network. Multi-SUMO binding is mediated through multi-SIM modules, and the functional importance of these interactions is demonstrated for the transcriptional corepressor ZMYM2/ZNF198 where its multi-SUMO-binding activity is required for its recruitment to chromatin.

The nuclear localization pattern and interaction partners of GTF2IRD1 demonstrate a role in chromatin regulation

GTF2IRD1 is one of the three members of the GTF2I gene family, clustered on chromosome 7 within a 1.8 Mb region that is prone to duplications and deletions in humans. Hemizygous deletions cause Williams-Beuren syndrome (WBS) and duplications cause WBS duplication syndrome. These copy number variations disturb a variety of developmental systems and neurological functions. Human mapping data and analyses of knockout mice show that GTF2IRD1 and GTF2I underpin the craniofacial abnormalities, mental retardation, visuospatial deficits and hypersociability of WBS. However, the cellular role of the GTF2IRD1 protein is poorly understood due to its very low abundance and a paucity of reagents. Here, for the first time, we show that endogenous GTF2IRD1 has a punctate pattern in the nuclei of cultured human cell lines and neurons. To probe the functional relationships of GTF2IRD1 in an unbiased manner, yeast two-hybrid libraries were screened, isolating 38 novel interaction partners, which were validated in mammalian cell lines. These relationships illustrate GTF2IRD1 function, as the isolated partners are mostly involved in chromatin modification and transcriptional regulation, whilst others indicate an unexpected role in connection with the primary cilium. Mapping of the sites of protein interaction also indicates key features regarding the evolution of the GTF2IRD1 protein. These data provide a visual and molecular basis for GTF2IRD1 nuclear function that will lead to an understanding of its role in brain, behaviour and human disease.

Symmetrical Dose-Dependent DNA-Methylation Profiles in Children with Deletion or Duplication of 7q11.23

Epigenetic dysfunction has been implicated in a growing list of disorders that include cancer, neurodevelopmental disorders, and neurodegeneration. Williams syndrome (WS) and 7q11.23 duplication syndrome (Dup7) are rare neurodevelopmental disorders with broad phenotypic spectra caused by deletion and duplication, respectively, of a 1.5-Mb region that includes several genes with a role in epigenetic regulation. We have identified striking differences in DNA methylation across the genome between blood cells from children with WS or Dup7 and blood cells from typically developing (TD) children. Notably, regions that were differentially methylated in both WS and Dup7 displayed a significant and symmetrical gene-dose-dependent effect, such that WS typically showed increased and Dup7 showed decreased DNA methylation. Differentially methylated genes were significantly enriched with genes in pathways involved in neurodevelopment, autism spectrum disorder (ASD) candidate genes, and imprinted genes. Using alignment with ENCODE data, we also found the differentially methylated regions to be enriched with CCCTC-binding factor (CTCF) binding sites. These findings suggest that gene(s) within 7q11.23 alter DNA methylation at specific sites across the genome and result in dose-dependent DNA-methylation profiles in WS and Dup7. Given the extent of DNA-methylation changes and the potential impact on CTCF binding and chromatin regulation, epigenetic mechanisms most likely contribute to the complex neurological phenotypes of WS and Dup7. Our findings highlight the importance of DNA methylation in the pathogenesis of WS and Dup7 and provide molecular mechanisms that are potentially shared by WS, Dup7, and ASD.

KDM1 class flavin-dependent protein lysine demethylases

Flavin-dependent, lysine-specific protein demethylases (KDM1s) are a subfamily of amine oxidases that catalyze the selective posttranslational oxidative demethylation of methyllysine side chains within protein and peptide substrates. KDM1s participate in the widespread epigenetic regulation of both normal and disease state transcriptional programs. Their activities are central to various cellular functions, such as hematopoietic and neuronal differentiation, cancer proliferation and metastasis, and viral lytic replication and establishment of latency. Interestingly, KDM1s function as catalytic subunits within complexes with coregulatory molecules that modulate enzymatic activity of the demethylases and coordinate their access to specific substrates at distinct sites within the cell and chromatin. Although several classes of KDM1-selective small molecule inhibitors have been recently developed, these pan-active site inhibition strategies lack the ability to selectively discriminate between KDM1 activity in specific, and occasionally opposing, functional contexts within these complexes. Here we review the discovery of this class of demethylases, their structures, chemical mechanisms, and specificity. Additionally, we review inhibition of this class of enzymes as well as emerging interactions with coregulatory molecules that regulate demethylase activity in highly specific functional contexts of biological and potential therapeutic importance.

Community structure analysis of transcriptional networks reveals distinct molecular pathways for early- and late-onset temporal lobe epilepsy with childhood febrile seizures

Age at epilepsy onset has a broad impact on brain plasticity and epilepsy pathomechanisms. Prolonged febrile seizures in early childhood (FS) constitute an initial precipitating insult (IPI) commonly associated with mesial temporal lobe epilepsy (MTLE). FS-MTLE patients may have early disease onset, i.e. just after the IPI, in early childhood, or late-onset, ranging from mid-adolescence to early adult life. The mechanisms governing early (E) or late (L) disease onset are largely unknown. In order to unveil the molecular pathways underlying E and L subtypes of FS-MTLE we investigated global gene expression in hippocampal CA3 explants of FS-MTLE patients submitted to hippocampectomy. Gene coexpression networks (GCNs) were obtained for the E and L patient groups. A network-based approach for GCN analysis was employed allowing: i) the visualization and analysis of differentially expressed (DE) and complete (CO) - all valid GO annotated transcripts - GCNs for the E and L groups; ii) the study of interactions between all the system's constituents based on community detection and coarse-grained community structure methods. We found that the E-DE communities with strongest connection weights harbor highly connected genes mainly related to neural excitability and febrile seizures, whereas in L-DE communities these genes are not only involved in network excitability but also playing roles in other epilepsy-related processes. Inversely, in E-CO the strongly connected communities are related to compensatory pathways (seizure inhibition, neuronal survival and responses to stress conditions) while in L-CO these communities harbor several genes related to pro-epileptic effects, seizure-related mechanisms and vulnerability to epilepsy. These results fit the concept, based on fMRI and behavioral studies, that early onset epilepsies, although impacting more severely the hippocampus, are associated to compensatory mechanisms, while in late MTLE development the brain is less able to generate adaptive mechanisms, what has implications for epilepsy management and drug discovery.

Assembly and interrogation of Alzheimer's disease genetic networks reveal novel regulators of progression

Alzheimer's disease (AD) is a complex multifactorial disorder with poorly characterized pathogenesis. Our understanding of this disease would thus benefit from an approach that addresses this complexity by elucidating the regulatory networks that are dysregulated in the neural compartment of AD patients, across distinct brain regions. Here, we use a Systems Biology (SB) approach, which has been highly successful in the dissection of cancer related phenotypes, to reverse engineer the transcriptional regulation layer of human neuronal cells and interrogate it to infer candidate Master Regulators (MRs) responsible for disease progression. Analysis of gene expression profiles from laser-captured neurons from AD and controls subjects, using the Algorithm for the Reconstruction of Accurate Cellular Networks (ARACNe), yielded an interactome consisting of 488,353 transcription-factor/target interactions. Interrogation of this interactome, using the Master Regulator INference algorithm (MARINa), identified an unbiased set of candidate MRs causally responsible for regulating the transcriptional signature of AD progression. Experimental assays in autopsy-derived human brain tissue showed that three of the top candidate MRs (YY1, p300 and ZMYM3) are indeed biochemically and histopathologically dysregulated in AD brains compared to controls. Our results additionally implicate p53 and loss of acetylation homeostasis in the neurodegenerative process. This study suggests that an integrative, SB approach can be applied to AD and other neurodegenerative diseases, and provide significant novel insight on the disease progression.

KDM1 histone lysine demethylases as targets for treatments of oncological and neurodegenerative disease

Histone methylation and demethylation are important processes associated with the regulation of gene transcription, and alterations in histone methylation status have been linked to a large number of human diseases. Initially thought to be an irreversible process, histone methylation is now known to be reversed by two families of proteins containing over 30 members that act to remove methyl groups from specific lysine residues present in the tails of histone H3 and histone H4. A rapidly growing number of reports have implicated the FAD-dependent lysine specific demethylase (KDM1) family in cancer, and several small-molecule inhibitors are in development for the treatment of cancer. An additional role has emerged for KDM1 in brain function, offering additional opportunities for the development of novel therapeutic strategies in neurodegenerative disease. A decade after the identification of KDM1A as a histone demethylase, the first selective inhibitors have now reached the clinic.

7q11.23 dosage-dependent dysregulation in human pluripotent stem cells affects transcriptional programs in disease-relevant lineages

Cell reprogramming promises to make characterization of the impact of human genetic variation on health and disease experimentally tractable by enabling the bridging of genotypes to phenotypes in developmentally relevant human cell lineages. Here we apply this paradigm to two disorders caused by symmetrical copy number variations of 7q11.23, which display a striking combination of shared and symmetrically opposite phenotypes--Williams-Beuren syndrome and 7q-microduplication syndrome. Through analysis of transgene-free patient-derived induced pluripotent stem cells and their differentiated derivatives, we find that 7q11.23 dosage imbalance disrupts transcriptional circuits in disease-relevant pathways beginning in the pluripotent state. These alterations are then selectively amplified upon differentiation of the pluripotent cells into disease-relevant lineages. A considerable proportion of this transcriptional dysregulation is specifically caused by dosage imbalances in GTF2I, which encodes a key transcription factor at 7q11.23 that is associated with the LSD1 repressive chromatin complex and silences its dosage-sensitive targets.

Characterization of the SUMO-binding activity of the myeloproliferative and mental retardation (MYM)-type zinc fingers in ZNF261 and ZNF198

SUMO-binding proteins interact with SUMO modified proteins to mediate a wide range of functional consequences. Here, we report the identification of a new SUMO-binding protein, ZNF261. Four human proteins including ZNF261, ZNF198, ZNF262, and ZNF258 contain a stretch of tandem zinc fingers called myeloproliferative and mental retardation (MYM)-type zinc fingers. We demonstrated that MYM-type zinc fingers from ZNF261 and ZNF198 are necessary and sufficient for SUMO-binding and that individual MYM-type zinc fingers function as SUMO-interacting motifs (SIMs). Our binding studies revealed that the MYM-type zinc fingers from ZNF261 and ZNF198 interact with the same surface on SUMO-2 recognized by the archetypal consensus SIM. We also present evidence that MYM-type zinc fingers in ZNF261 contain zinc, but that zinc is not required for SUMO-binding. Immunofluorescence microscopy studies using truncated fragments of ZNF198 revealed that MYM-type zinc fingers of ZNF198 are necessary for localization to PML-nuclear bodies (PML-NBs). In summary, our studies have identified and characterized the SUMO-binding activity of the MYM-type zinc fingers in ZNF261 and ZNF198.

A selective phenelzine analogue inhibitor of histone demethylase LSD1

Lysine-specific demethylase 1 (LSD1) is an epigenetic enzyme that oxidatively cleaves methyl groups from monomethyl and dimethyl Lys4 of histone H3 (H3K4Me1, H3K4Me2) and can contribute to gene silencing. This study describes the design and synthesis of analogues of a monoamine oxidase antidepressant, phenelzine, and their LSD1 inhibitory properties. A novel phenelzine analogue (bizine) containing a phenyl-butyrylamide appendage was shown to be a potent LSD1 inhibitor in vitro and was selective versus monoamine oxidases A/B and the LSD1 homologue, LSD2. Bizine was found to be effective at modulating bulk histone methylation in cancer cells, and ChIP-seq experiments revealed a statistically significant overlap in the H3K4 methylation pattern of genes affected by bizine and those altered in LSD1–/– cells. Treatment of two cancer cell lines, LNCaP and H460, with bizine conferred a reduction in proliferation rate, and bizine showed additive to synergistic effects on cell growth when used in combination with two out of five HDAC inhibitors tested. Moreover, neurons exposed to oxidative stress were protected by the presence of bizine, suggesting potential applications in neurodegenerative disease.

BMI1 reprogrammes histone acetylation and enhances c-fos pathway via directly binding to Zmym3 in malignant myeloid progression

The polycomb group BMI1 is proved to be crucial in malignant myeloid progression. However, the underlying mechanism of the action of BMI1 in myeloid malignant progression was not well characterized. In this study, we found that the patients of both myelodysplastic syndromes and chronic myeloid leukaemia with BMI1 overexpression had a higher risk in malignant myeloid progression. In vitro gene transfection studies showed that BMI1 inhibited cell myeloid and erythroid differentiation induced by 12-O-tetradecanoyl phorbol-13-acetate (TPA) and histone deacetylase inhibitor sodium butyrate respectively. BMI1 also resisted apoptosis induced by arsenic trioxide. Moreover, the transcript levels of Runx1 and Pten were down-regulated in Bmi1-transfected cells in company with histone deacetylation modification. By using chromatin immunoprecipitation (ChIP) collaborated with secondary generation sequencing and verified by ChIP-PCR, we found that BMI1 directly bound to the promoter region of Zmym3, which encodes a component of histone deacetylase-containing complexes. In addition, as one of the downstream target genes of this complex, c-fos was activated with increasing histone acetylation when ZMYM3 was suppressed in the Bmi1-transfected cells. These results suggested that BMI1 may reprogramme the histone acetylation profile in multiple genes through either indirect or direct binding effects which probably contributes to the malignant progression of myeloid progenitor cells.

The histone demethylase LSD1/KDM1A promotes the DNA damage response

Histone demethylation is known to regulate transcription, but its role in other processes is largely unknown. We report a role for the histone demethylase LSD1/KDM1A in the DNA damage response (DDR). We show that LSD1 is recruited directly to sites of DNA damage. H3K4 dimethylation, a major substrate for LSD1, is reduced at sites of DNA damage in an LSD1-dependent manner. The E3 ubiquitin ligase RNF168 physically interacts with LSD1 and we find this interaction to be important for LSD1 recruitment to DNA damage sites. Although loss of LSD1 did not affect the initial formation of pH2A.X foci, 53BP1 and BRCA1 complex recruitment were reduced upon LSD1 knockdown. Mechanistically, this was likely a result of compromised histone ubiquitylation preferentially in late S/G2. Consistent with a role in the DDR, knockdown of LSD1 resulted in moderate hypersensitivity to γ-irradiation and increased homologous recombination. Our findings uncover a direct role for LSD1 in the DDR and place LSD1 downstream of RNF168 in the DDR pathway.

Expanding the druggable space of the LSD1/CoREST epigenetic target: new potential binding regions for drug-like molecules, peptides, protein partners, and chromatin

Lysine specific demethylase-1 (LSD1/KDM1A) in complex with its corepressor protein CoREST is a promising target for epigenetic drugs. No therapeutic that targets LSD1/CoREST, however, has been reported to date. Recently, extended molecular dynamics (MD) simulations indicated that LSD1/CoREST nanoscale clamp dynamics is regulated by substrate binding and highlighted key hinge points of this large-scale motion as well as the relevance of local residue dynamics. Prompted by the urgent need for new molecular probes and inhibitors to understand LSD1/CoREST interactions with small-molecules, peptides, protein partners, and chromatin, we undertake here a configurational ensemble approach to expand LSD1/CoREST druggability. The independent algorithms FTMap and SiteMap and our newly developed Druggable Site Visualizer (DSV) software tool were used to predict and inspect favorable binding sites. We find that the hinge points revealed by MD simulations at the SANT2/Tower interface, at the SWIRM/AOD interface, and at the AOD/Tower interface are new targets for the discovery of molecular probes to block association of LSD1/CoREST with chromatin or protein partners. A fourth region was also predicted from simulated configurational ensembles and was experimentally validated to have strong binding propensity. The observation that this prediction would be prevented when using only the X-ray structures available (including the X-ray structure bound to the same peptide) underscores the relevance of protein dynamics in protein interactions. A fifth region was highlighted corresponding to a small pocket on the AOD domain. This study sets the basis for future virtual screening campaigns targeting the five novel regions reported herein and for the design of LSD1/CoREST mutants to probe LSD1/CoREST binding with chromatin and various protein partners.

SUMOylation of GTF2IRD1 regulates protein partner interactions and ubiquitin-mediated degradation

GTF2IRD1 is one of the genes implicated in Williams-Beuren syndrome, a disease caused by haploinsufficiency of certain dosage-sensitive genes within a hemizygous microdeletion of chromosome 7. GTF2IRD1 is a prime candidate for some of the major features of the disease, presumably caused by abnormally reduced abundance of this putative transcriptional repressor protein. GTF2IRD1 has been shown to interact with the E3 SUMO ligase PIASxβ, but the significance of this relationship is largely unexplored. Here, we demonstrate that GTF2IRD1 can be SUMOylated by the SUMO E2 ligase UBC9 and the level of SUMOylation is enhanced by PIASxβ. A major SUMOylation site was mapped to lysine 495 within a conserved SUMO consensus motif. SUMOylation of GTF2IRD1 alters the affinity of the protein for binding partners that contain SUMO-interacting motifs, including a novel family member of the HDAC repressor complex, ZMYM5, and PIASxβ itself. In addition, we show that GTF2IRD1 is targeted for ubiquitination and proteasomal degradation. Cross regulation by SUMOylation modulates this process, thus potentially regulating the level of GTF2IRD1 protein in the cell. These findings, concerning post-translational control over the activity and stability of GTF2IRD1, together with previous work showing how GTF2IRD1 directly regulates its own transcription levels suggest an evolutionary requirement for fine control over GTF2IRD1 activity in the cell.

LSD1 inhibition: a therapeutic strategy in cancer?

INTRODUCTION

The role of epigenetic dysfunction in cancer is increasingly appreciated. This has raised the question as to whether enzymes that regulate the structure and function of chromatin might represent novel therapeutic targets. The histone demethylase LSD1 is one such candidate and novel, potent inhibitors are under development.

AREAS COVERED

The literature on LSD1 (also known as KDM1A, AOF2, BHC110 or KIAA0601) was identified in Pubmed and is herein discussed. Areas covered include the structure and enzymatic activity of LSD1, its role in chromatin regulatory complexes, its functional roles in normal and malignant tissue, pharmacological inhibitors of its activity and their putative therapeutic roles.

EXPERT OPINION

Pre-clinical data supporting a therapeutic role for LSD1 inhibitors are most encouraging in acute myeloid leukaemia, although optimal dosing strategies and beneficial combinations with other agents remain unclear. Studies making use of potent, selective LSD1 inhibitors active in the nanomolar range are required to establish therapeutic indications in other subtypes of haematological malignancy, and in solid tumours.

Searching for Hif1-α interacting proteins in renal cell carcinoma

INTRODUCTION

Kidney tumours are frequently characterised by hypoxic conditions due to a local imbalance between oxygen (O2) supply and consumption. Hif1-α regulates angiogenesis, tumour growth, tumour progression, metastatic spread, and glucose metabolism by acting as a transcription factor for relevant genes. Here, we describe an immunohistochemical study of Hif1-α, a comprehensive computational study of Hif1-α interacting proteins (HIPs), an analysis correlating expression levels of Hif1-α with upstream and downstream proteins, and an analysis of the utility of Hif1-α for prognosis in a cohort of patients with renal cell carcinoma.

MATERIALS AND METHODS

The patient cohort included 80 patients. For immunohistochemistry evaluation, tissue microarrays were constructed. The IntAct, MINT, and BOND databases were used for the HIP approach. The Kruskal-Wallis test was used for comparing protein expression with pathology measurements. Correlation was expressed as the Pearson coefficient.

RESULTS

Hif1-α expression correlates significantly with the "clear" histological subtype of renal cell carcinoma (p < 0.01). The samples with the worst prognoses related to the pathological variables analysed showed the highest levels of Hif1-α expression. Significant correlations were found with Bcl-2, CAIX, C-kit, EGFR, TGF-β, proteins of the VEGF family, proteins related to differentiation (such as Notch1 and Notch3) and certain metabolic enzymes. Bioinformatic analysis suggested 45 evidence-based HIPs and 4 complexes involving protein Hif1-α.

CONCLUSIONS

This work summarises the multifaceted role of Hif1-α in the pathology of renal cell carcinomas, and it identifies HIPs that could help provide mechanistic explanations for the different behaviours seen in tumours.

Translocations disrupting PHF21A in the Potocki-Shaffer-syndrome region are associated with intellectual disability and craniofacial anomalies

Potocki-Shaffer syndrome (PSS) is a contiguous gene disorder due to the interstitial deletion of band p11.2 of chromosome 11 and is characterized by multiple exostoses, parietal foramina, intellectual disability (ID), and craniofacial anomalies (CFAs). Despite the identification of individual genes responsible for multiple exostoses and parietal foramina in PSS, the identity of the gene(s) associated with the ID and CFA phenotypes has remained elusive. Through characterization of independent subjects with balanced translocations and supportive comparative deletion mapping of PSS subjects, we have uncovered evidence that the ID and CFA phenotypes are both caused by haploinsufficiency of a single gene, PHF21A, at 11p11.2. PHF21A encodes a plant homeodomain finger protein whose murine and zebrafish orthologs are both expressed in a manner consistent with a function in neurofacial and craniofacial development, and suppression of the latter led to both craniofacial abnormalities and neuronal apoptosis. Along with lysine-specific demethylase 1 (LSD1), PHF21A, also known as BHC80, is a component of the BRAF-histone deacetylase complex that represses target-gene transcription. In lymphoblastoid cell lines from two translocation subjects in whom PHF21A was directly disrupted by the respective breakpoints, we observed derepression of the neuronal gene SCN3A and reduced LSD1 occupancy at the SCN3A promoter, supporting a direct functional consequence of PHF21A haploinsufficiency on transcriptional regulation. Our finding that disruption of PHF21A by translocations in the PSS region is associated with ID adds to the growing list of ID-associated genes that emphasize the critical role of transcriptional regulation and chromatin remodeling in normal brain development and cognitive function.

Role of H3K4 demethylases in complex neurodevelopmental diseases

Significant neurological disorders can result from subtle perturbations of gene regulation that are often linked to epigenetic regulation. Proteins that regulate the methylation of lysine 4 of histone H3 (H3K4) and play a central role in epigenetic regulation, and mutations in genes encoding these enzymes have been identified in both autism and Rett syndrome. The H3K4 demethylases remove methyl groups from lysine 4 leading to loss of RNA polymerase binding and transcriptional repression. When these proteins are mutated, brain development is altered. Currently, little is known regarding how these gene regulators function at the genomic level. In this article, we will discuss findings that link H3K4 demethylases to neurodevelopment and neurological disease.

Targeting protein lysine methylation and demethylation in cancers

During the last decade, we saw an explosion of studies investigating the role of lysine methylation/demethylation of histones and non-histone proteins, such as p53, NF-kappaB, and E2F1. These 'Ying-Yang' post-translational modifications are important to fine-tuning the activity of these proteins. Lysine methylation and demethylation are catalyzed by protein lysine methyltransferases (PKMTs) and protein lysine demethylases (PKDMs). PKMTs, PKDMs, and their substrates have been shown to play important roles in cancers. Although the underlying mechanisms of tumorigenesis are still largely unknown, growing evidence is starting to link aberrant regulation of methylation to tumorigenesis. This review focuses on summarizing the recent progress in understanding of the function of protein lysine methylation, and in the discovery of small molecule inhibitors for PKMTs and PKDMs. We also discuss the potential and the caveats of targeting protein lysine methylation for the treatment of cancer.

Arabidopsis homologs of retinoblastoma-associated protein 46/48 associate with a histone deacetylase to act redundantly in chromatin silencing

RNA molecules such as small-interfering RNAs (siRNAs) and antisense RNAs (asRNAs) trigger chromatin silencing of target loci. In the model plant Arabidopsis, RNA–triggered chromatin silencing involves repressive histone modifications such as histone deacetylation, histone H3 lysine-9 methylation, and H3 lysine-27 monomethylation. Here, we report that two Arabidopsis homologs of the human histone-binding proteins Retinoblastoma-Associated Protein 46/48 (RbAp46/48), known as MSI4 (or FVE) and MSI5, function in partial redundancy in chromatin silencing of various loci targeted by siRNAs or asRNAs. We show that MSI5 acts in partial redundancy with FVE to silence FLOWERING LOCUS C (FLC), which is a crucial floral repressor subject to asRNA–mediated silencing, FLC homologs, and other loci including transposable and repetitive elements which are targets of siRNA–directed DNA Methylation (RdDM). Both FVE and MSI5 associate with HISTONE DEACETYLASE 6 (HDA6) to form complexes and directly interact with the target loci, leading to histone deacetylation and transcriptional silencing. In addition, these two genes function in de novo CHH (H = A, T, or C) methylation and maintenance of symmetric cytosine methylation (mainly CHG methylation) at endogenous RdDM target loci, and they are also required for establishment of cytosine methylation in the previously unmethylated sequences directed by the RdDM pathway. This reveals an important functional divergence of the plant RbAp46/48 relatives from animal counterparts.

Chromatin, made of histones and DNA, is often covalently modified in the nucleus, and modifications can regulate gene transcription. RNA molecules such as small-interfering or silencing RNAs (siRNAs) and antisense RNAs (asRNAs) can trigger silencing of gene expression in eukaryotes. We have found that in the flowering plant Arabidopsis, two homologous putative histone-binding proteins associate with a histone deacetylase and function in partial redundancy in chromatin-based silencing of various loci targeted by siRNAs or asRNAs. They act in partial redundancy to silence a development-regulatory gene that controls the transition to flowering and whose silencing is triggered by asRNAs, and genomic loci containing transposable and repetitive elements whose silencing is triggered by siRNAs via the siRNA–directed DNA Methylation (RdDM) pathway. In addition, these two genes function in maintenance of DNA methylation at RdDM loci and are also required for establishment of DNA methylation in the previously unmethylated sequences, revealing that histone modifications are partly required for DNA methylation. Our findings implicate that RNA–triggered transcriptional silencing involves repressive histone modifications such as deacetylation at a target locus.

Biochemistry and biology of the inducible multifunctional transcription factor TFII-I: 10 years later

Exactly twenty years ago TFII-I was discovered as a biochemical entity that was able to bind to and function via a core promoter element called the Initiator (Inr). Since then several different properties of this signal-induced multifunctional factor were discovered. Here I update these ever expanding functions of TFII-I--focusing primarily on the last ten years since the first review appeared in this journal.

Crypton transposons: identification of new diverse families and ancient domestication events

Background

"Domestication" of transposable elements (TEs) led to evolutionary breakthroughs such as the origin of telomerase and the vertebrate adaptive immune system. These breakthroughs were accomplished by the adaptation of molecular functions essential for TEs, such as reverse transcription, DNA cutting and ligation or DNA binding. Cryptons represent a unique class of DNA transposons using tyrosine recombinase (YR) to cut and rejoin the recombining DNA molecules. Cryptons were originally identified in fungi and later in the sea anemone, sea urchin and insects.

Results

Herein we report new Cryptons from animals, fungi, oomycetes and diatom, as well as widely conserved genes derived from ancient Crypton domestication events. Phylogenetic analysis based on the YR sequences supports four deep divisions of Crypton elements. We found that the domain of unknown function 3504 (DUF3504) in eukaryotes is derived from Crypton YR. DUF3504 is similar to YR but lacks most of the residues of the catalytic tetrad (R-H-R-Y). Genes containing the DUF3504 domain are potassium channel tetramerization domain containing 1 (KCTD1), KIAA1958, zinc finger MYM type 2 (ZMYM2), ZMYM3, ZMYM4, glutamine-rich protein 1 (QRICH1) and "without children" (WOC). The DUF3504 genes are highly conserved and are found in almost all jawed vertebrates. The sequence, domain structure, intron positions and synteny blocks support the view that ZMYM2, ZMYM3, ZMYM4, and possibly QRICH1, were derived from WOC through two rounds of genome duplication in early vertebrate evolution. WOC is observed widely among bilaterians. There could be four independent events of Crypton domestication, and one of them, generating WOC/ZMYM, predated the birth of bilaterian animals. This is the third-oldest domestication event known to date, following the domestication generating telomerase reverse transcriptase (TERT) and Prp8. Many Crypton-derived genes are transcriptional regulators with additional DNA-binding domains, and the acquisition of the DUF3504 domain could have added new regulatory pathways via protein-DNA or protein-protein interactions.

Conclusions

Cryptons have contributed to animal evolution through domestication of their YR sequences. The DUF3504 domains are domesticated YRs of animal Crypton elements.

Activation of HIV transcription by the viral Tat protein requires a demethylation step mediated by lysine-specific demethylase 1 (LSD1/KDM1)

The essential transactivator function of the HIV Tat protein is regulated by multiple posttranslational modifications. Although individual modifications are well characterized, their crosstalk and dynamics of occurrence during the HIV transcription cycle remain unclear.We examine interactions between two critical modifications within the RNA-binding domain of Tat: monomethylation of lysine 51 (K51) mediated by Set7/9/KMT7, an early event in the Tat transactivation cycle that strengthens the interaction of Tat with TAR RNA, and acetylation of lysine 50 (K50) mediated by p300/KAT3B, a later process that dissociates the complex formed by Tat, TAR RNA and the cyclin T1 subunit of the positive transcription elongation factor b (P-TEFb). We find K51 monomethylation inhibited in synthetic Tat peptides carrying an acetyl group at K50 while acetylation can occur in methylated peptides, albeit at a reduced rate. To examine whether Tat is subject to sequential monomethylation and acetylation in cells, we performed mass spectrometry on immunoprecipitated Tat proteins and generated new modification-specific Tat antibodies against monomethylated/acetylated Tat. No bimodified Tat protein was detected in cells pointing to a demethylation step during the Tat transactivation cycle. We identify lysine-specific demethylase 1 (LSD1/KDM1) as a Tat K51-specific demethylase, which is required for the activation of HIV transcription in latently infected T cells. LSD1/KDM1 and its cofactor CoREST associates with the HIV promoter in vivo and activate Tat transcriptional activity in a K51-dependent manner. In addition, small hairpin RNAs directed against LSD1/KDM1 or inhibition of its activity with the monoamine oxidase inhibitor phenelzine suppresses the activation of HIV transcription in latently infected T cells.Our data support the model that a LSD1/KDM1/CoREST complex, normally known as a transcriptional suppressor, acts as a novel activator of HIV transcription through demethylation of K51 in Tat. Small molecule inhibitors of LSD1/KDM1 show therapeutic promise by enforcing HIV latency in infected T cells.

Role for transcription factor TFII-I in the suppression of SSeCKS/Gravin/Akap12 transcription by Src

The SSeCKS/Gravin/AKAP12 gene, encoding a kinase scaffolding protein with metastasis-suppressing activity, is transcriptionally downregulated in Src-transformed cells through the recruitment of HDAC1 to a Src-responsive proximal promoter site charged with Sp1, Sp3 and USF1. However, the ectopic expression of these proteins formed a suppressive complex in Src-transformed but not in parental NIH3T3 cells, suggesting the involvement of additional repressor factors. Transcription factor II-I (TFII-I) [general transcription factor 2i (Gtf2i)] was identified by mass spectrometry as being associated with the SSeCKS promoter complex in NIH3T3/Src cells, and moreover, the Src-induced tyrosine phosphorylation of TFII-I significantly increased its binding to the SSeCKS proximal promoter. siRNA-mediated knockdown of TFII-I or the expression of TFII-I(Y248/249F) caused the derepression of SSeCKS in NIH3T3/Src cells. Taken with previous data showing that the tyrosine phosphorylation of TFII-I facilitates its nuclear translocation, these data suggest that Src-family kinase-mediated phosphorylation converts a portion of TFII-I into a transcriptional repressor.

Role of helix-loop-helix proteins during differentiation of erythroid cells

Helix-loop-helix (HLH) proteins play a profound role in the process of development and cellular differentiation. Among the HLH proteins expressed in differentiating erythroid cells are the ubiquitous proteins Myc, USF1, USF2, and TFII-I, as well as the hematopoiesis-specific transcription factor Tal1/SCL. All of these HLH proteins exhibit distinct functions during the differentiation of erythroid cells. For example, Myc stimulates the proliferation of erythroid progenitor cells, while the USF proteins and Tal1 regulate genes that specify the differentiated phenotype. This minireview summarizes the known activities of Myc, USF, TFII-I, and Tal11/SCL and discusses how they may function sequentially, cooperatively, or antagonistically in regulating expression programs during the differentiation of erythroid cells.

Molecular Basis of Williams-Beuren Syndrome: TFII-I Regulated Targets Involved in Craniofacial Development

Objective

The aim of this study is to identify gene targets of TFII-I transcription factors involved in craniofacial development.

Design

Recent findings in individuals with Williams-Beuren syndrome who show facial dysmorphism and cognitive defects have pointed to TFII-I genes ( GTF2I and GTF2IRD1) as the prime candidates responsible for these clinical features. However, TFII-I proteins are multifunctional transcriptional factors regulating a number of genes during development, and how their haploinsufficiency leads to the Williams-Beuren syndrome phenotype is currently unknown.

Results

Here we report the identification of three genes with a well-established relevance to craniofacial development as direct TFII-I targets. These genes, craniofacial development protein 1 ( Cfdp1), Sec23 homolog A ( Sec23a), and nuclear receptor binding SET domain protein 1 ( Nsd1), contain consensus TFII-I binding sites in their proximal promoters; the chromatin immunoprecipitation analysis showed that TFII-I transcription factors are recruited to these sites in vivo.

Conclusions

The results suggest that transcriptional regulation of these genes by TFII-I proteins could provide a possible genotype-phenotype link in Williams-Beuren syndrome.

Structural insights into histone lysine demethylation

Posttranslational modifications of histone tails are crucial epigenetic marks that regulate diverse cellular processes. Histone lysine methylation activates or represses transcription, depending on the site and degree of these modifications. Two classes of histone lysine demethylases remove histone methylation. Lysine demethylase 1 (KDM1, also known as LSD1) is a flavin adenine dinucleotide (FAD)-containing enzyme that removes mono-/di-methylation. The Jumonji C-terminal domain (JmjC) family of histone demethylases uses Fe(2+) and α-ketoglutarate as cofactors to remove all methylation states. Structural studies have provided insights into the overall architecture, the catalytic mechanism, and the substrate specificity of histone demethylases. Here, we review these exciting advances in the structure biology of histone demethylases and discuss the general principles applicable to other histone-modifying enzymes.

Epigenetic mechanisms regulate stem cell expressed genes Pou5f1 and Gfra1 in a male germ cell line

Male fertility is declining and an underlying cause may be due to environment-epigenetic interactions in developing sperm, yet nothing is known of how the epigenome controls gene expression in sperm development. Histone methylation and acetylation are dynamically regulated in spermatogenesis and are sensitive to the environment. Our objectives were to determine how histone H3 methylation and acetylation contribute to the regulation of key genes in spermatogenesis. A germ cell line, GC-1, was exposed to either the control, or the chromatin modifying drugs tranylcypromine (T), an inhibitor of the histone H3 demethylase KDM1 (lysine specific demethylase 1), or trichostatin (TSA), an inhibitor of histone deacetylases, (HDAC). Quantitative PCR (qPCR) was used to identify genes that were sensitive to treatment. As a control for specificity the Myod1 (myogenic differentiation 1) gene was analyzed. Chromatin immunoprecipitation (ChIP) followed by qPCR was used to measure histone H3 methylation and acetylation at the promoters of target genes and the control, Myod1. Remarkably, the chromatin modifying treatment specifically induced the expression of spermatogonia expressed genes Pou5f1 and Gfra1. ChIP-qPCR revealed that induction of gene expression was associated with a gain in gene activating histone H3 methylation and acetylation in Pou5f1 and Gfra1 promoters, whereas CpG DNA methylation was not affected. Our data implicate a critical role for histone H3 methylation and acetylation in the regulation of genes expressed by spermatogonia – here, predominantly mediated by HDAC-containing protein complexes.

Reversal of histone methylation: biochemical and molecular mechanisms of histone demethylases

The importance of histone methylation in gene regulation was suggested over 40 years ago. Yet, the dynamic nature of this histone modification was recognized only recently, with the discovery of the first histone demethylase nearly five years ago. Since then, our insight into the mechanisms, structures, and macromolecular complexes of these enzymes has grown exponentially. Overall, the evidence strongly supports a key role for histone demethylases in eukaryotic transcription and other chromatin-dependent processes. Here, we examine these and related facets of histone demethylases discovered to date, focusing on their biochemistry, structure, and enzymology.

DNA copy numbers profiles in affinity-purified ovarian clear cell carcinoma

PURPOSE

Advanced ovarian clear cell carcinoma (CCC) is one of the most aggressive ovarian malignancies, in part because it tends to be resistant to platinum-based chemotherapy. At present, little is known about the molecular genetic alterations in CCCs except that there are frequent activating mutations in PIK3CA. The purpose of this study is to comprehensively define the genomic changes in CCC based on DNA copy number alterations.

EXPERIMENTAL DESIGN

We performed 250K high-density single nucleotide polymorphism array analysis in 12 affinity-purified CCCs and 10 CCC cell lines. Discrete regions of amplification and deletion were also analyzed in additional 21 affinity-purified CCCs using quantitative real-time PCR.

RESULTS

The level of chromosomal instability in CCC as defined by the extent of DNA copy number changes is similar to those previously reported in low-grade ovarian serous carcinoma but much less than those in high-grade serous carcinoma. The most remarkable region with DNA copy number gain is at chr20, which harbors a potential oncogene, ZNF217. This discrete amplicon is observed in 36% of CCCs but rarely detected in serous carcinomas regardless of grade. In addition, homozygous deletions are detected at the CDKN2A/2B and LZTS1 loci. Interestingly, the DNA copy number changes observed in fresh CCC tissues are rarely detected in the established CCC cell lines.

CONCLUSIONS

This study provides the first high resolution, genome-wide view of DNA copy number alterations in ovarian CCC. The findings provide a genomic landscape for future studies aimed at elucidating the pathogenesis and developing new target-based therapies for CCCs.

Comparative analysis of small molecules and histone substrate analogues as LSD1 lysine demethylase inhibitors

LSD1 is a flavin-dependent histone demethylase that oxidatively removes methyl groups from Lys-4 of histone H3. LSD1 belongs to the amine oxidase enzyme superfamily which utilize molecular oxygen to transform amines to imines that are hydrolytically cleaved to formaldehyde. In prior studies, it has been shown that monoamine oxidase inhibitory scaffolds such as propargylamines and cyclopropylamines can serve as mechanism-based inactivators of LSD1. Propargylamine-histone H3 peptide analogues are potent LSD1 inhibitors, whereas small molecule antidepressant MAO acetylenic inhibitors like pargyline do not inhibit LSD1. In contrast, the small molecule MAO cyclopropylamine inhibitor tranylcypromine is a time-dependent LSD1 inhibitor but exo-cyclopropylamine-peptide substrate analogue is not. To provide further insight into small molecule versus peptide relationships in LSD1 inhibition, herein we further our analysis of warheads in peptide scaffolds to include the chlorovinyl, endo-cyclopropylamine, and hydrazine-functionalities as LSD1 inactivators. We find that chlorovinyl-H3 is a mechanism-based LSD1 inactivator whereas endo-cyclopropylamine-H3 does not show time-dependent inactivation. The hydrazine-H3 was shown to be the most potent LSD1 suicide inhibitor yet reported, more than 20-fold more efficient in inhibiting demethylation than propargylamine-H3 derivatives. We re-explored MAO antidepressant agent phenelzine (phenethylhydrazine), previously reported to be a weak LSD1 inhibitor, and found that it is far more potent than previously appreciated. We show that phenelzine can block histone H3K4Me demethylation in cells, validating it as a pharmacologic tool and potential lead structure for anticancer therapy.

The role of histone modifications and variants in regulating gene expression in breast cancer

The role of epigenetic phenomena in cancer biology is increasingly being recognized. Here we focus on the mechanisms and enzymes involved in regulating histone methylation and acetylation, and the modulation of histone variant expression and deposition. Implications of these epigenetic marks for tumor development, progression and invasiveness are discussed with a particular emphasis on breast cancer progression.

In vitro nuclear interactome of the HIV-1 Tat protein

BACKGROUND

One facet of the complexity underlying the biology of HIV-1 resides not only in its limited number of viral proteins, but in the extensive repertoire of cellular proteins they interact with and their higher-order assembly. HIV-1 encodes the regulatory protein Tat (86-101aa), which is essential for HIV-1 replication and primarily orchestrates HIV-1 provirus transcriptional regulation. Previous studies have demonstrated that Tat function is highly dependent on specific interactions with a range of cellular proteins. However they can only partially account for the intricate molecular mechanisms underlying the dynamics of proviral gene expression. To obtain a comprehensive nuclear interaction map of Tat in T-cells, we have designed a proteomic strategy based on affinity chromatography coupled with mass spectrometry.

RESULTS

Our approach resulted in the identification of a total of 183 candidates as Tat nuclear partners, 90% of which have not been previously characterised. Subsequently we applied in silico analysis, to validate and characterise our dataset which revealed that the Tat nuclear interactome exhibits unique signature(s). First, motif composition analysis highlighted that our dataset is enriched for domains mediating protein, RNA and DNA interactions, and helicase and ATPase activities. Secondly, functional classification and network reconstruction clearly depicted Tat as a polyvalent protein adaptor and positioned Tat at the nexus of a densely interconnected interaction network involved in a range of biological processes which included gene expression regulation, RNA biogenesis, chromatin structure, chromosome organisation, DNA replication and nuclear architecture.

CONCLUSION

We have completed the in vitro Tat nuclear interactome and have highlighted its modular network properties and particularly those involved in the coordination of gene expression by Tat. Ultimately, the highly specialised set of molecular interactions identified will provide a framework to further advance our understanding of the mechanisms of HIV-1 proviral gene silencing and activation.

Direct binding of CoREST1 to SUMO-2/3 contributes to gene-specific repression by the LSD1/CoREST1/HDAC complex

Posttranslational modification of transcription factors by the small ubiquitin-related modifier SUMO is associated with transcriptional repression, but the underlying mechanisms remain incompletely described. We have identified binding of the LSD1/CoREST1/HDAC corepressor complex to SUMO-2. Here we show that CoREST1 binds directly and noncovalently to SUMO-2, but not SUMO-1, and CoREST1 bridges binding of the histone demethylase LSD1 to SUMO-2. Depletion of SUMO-2/3 conjugates led to transcriptional derepression, reduced occupancy of CoREST1 and LSD1, and changes in histone methylation and acetylation at some, but not all, LSD1/CoREST1/HDAC target genes. We have identified a nonconsensus SUMO-interaction motif (SIM) in CoREST1 required for SUMO-2 binding, and we show that mutation of the CoREST1 SIM disrupted SUMO-2 binding and transcriptional repression of some neuronal-specific genes in nonneuronal cells. Our results reveal that direct interactions between CoREST1 and SUMO-2 mediate SUMO-dependent changes in chromatin structure and transcription that are important for cell-type-specific gene expression.

The ZNF217 oncogene is a candidate organizer of repressive histone modifiers

The zinc finger protein 217 (ZNF217) is an important oncogene based on the high frequency of amplification and overexpression in many cancer types, but its molecular mode of gene regulation is poorly understood. We purified a complex of nuclear ZNF217-binding proteins by affinity chromatography and identified its components by mass spectrometry as Jarid1b/Plu-1, G9a, LSD1, CoREST and CtBP1. Individual binding of these with ZNF217 was confirmed by co-immunoprecipiation (IP). Known activities of these proteins suggested a role of the ZNF217 complex in histone modification. Using in vitro assays the following activities were demonstrated: Histone H3 lysine 4 trimethyl (H3K4me3) demethylase activity, which co-fractionated with Jarid1b/Plu-1 in anion-exchange chromatography; H3K9 methylation, the known principal activity of G9a; and H3K27 methylation. The latter suggested EZH2 as another ZNF217 binding candidate, which could be confirmed by co-IP. Taken together, these findings suggest that ZNF217 assembles a distinct set of histone modifying proteins at target DNA sites that act synergistically in transcriptional repression.

Fruit flies and intellectual disability

Mental retardation--known more commonly nowadays as intellectual disability--is a severe neurological condition affecting up to 3% of the general population. As a result of the analysis of familial cases and recent advances in clinical genetic testing, great strides have been made in our understanding of the genetic etiologies of mental retardation. Nonetheless, no treatment is currently clinically available to patients suffering from intellectual disability. Several animal models have been used in the study of memory and cognition. Established paradigms in Drosophila have recently captured cognitive defects in fly mutants for orthologs of genes involved in human intellectual disability. We review here three protocols designed to understand the molecular genetic basis of learning and memory in Drosophila and the genes identified so far with relation to mental retardation. In addition, we explore the mental retardation genes for which evidence of neuronal dysfunction other than memory has been established in Drosophila. Finally, we summarize the findings in Drosophila for mental retardation genes for which no neuronal information is yet available. All in all, this review illustrates the impressive overlap between genes identified in human mental retardation and genes involved in physiological learning and memory.

The STAGA subunit ADA2b is an important regulator of human GCN5 catalysis

Human STAGA is a multisubunit transcriptional coactivator containing the histone acetyltransferase GCN5L. Previous studies of the related yeast SAGA complex have shown that the yeast Gcn5, Ada2, and Ada3 components form a heterotrimer that is important for the enzymatic function of SAGA. Here, we report that ADA2a and ADA2b, two human homologues of yeast Ada2, each have the ability to form a heterotrimer with ADA3 and GCN5L but that only the ADA2b homologue is found in STAGA. By comparing the patterns of acetylation of several substrates, we found context-dependent requirements for ADA2b and ADA3 for the efficient acetylation of histone tails by GCN5. With human proteins, unlike yeast proteins, the acetylation of free core histones by GCN5 is unaffected by ADA2b or ADA3. In contrast, the acetylation of mononucleosomal substrates by GCN5 is enhanced by ADA2b, with no significant additional effect of ADA3, and the efficient acetylation of nucleosomal arrays (chromatin) by GCN5 requires both ADA2b and ADA3. Thus, ADA2b and ADA3 appear to act at two different levels of histone organization within chromatin to facilitate GCN5 function. Interestingly, although ADA2a forms a complex(es) with GCN5 and ADA3 both in vitro and in vivo, ADA2a-containing complexes are unable to acetylate nucleosomal H3. We have also shown the preferential recruitment of ADA2b, relative to ADA2a, to p53-dependent genes. This finding indicates that the previously demonstrated presence and function of GCN5 on these promoters reflect the action of STAGA and that the ADA2a and ADA2b paralogues have nonredundant functional roles.

NF-Y substitutes H2A-H2B on active cell-cycle promoters: recruitment of CoREST-KDM1 and fine-tuning of H3 methylations

The CCAAT box is a frequent promoter element, as illustrated by bioinformatic analysis, and it is bound by NF-Y, a trimer with H2A-H2B-like subunits. We developed a MNase I-based ChIP protocol on homogeneous cell populations to study cell-cycle promoters at the single nucleosome level. We analyzed histone methylations and the association of enzymatic activities. Two novel results emerged: (i) H3-H4 are present on core promoters under active conditions, with the expected cohort of ‘positive’ modifications; H2A-H2B are removed and substituted by NF-Y. Through the use of a dominant negative mutant we show that NF-Y is important for H3K36me3 deposition and for elongation, not recruitment of Pol II; (ii) H3K4 methylations are highly dynamic and H3K4me1 is a crucial positive mark. Functional siRNA inactivation and treatment with Tranylcypromine determined that KDM1 (LSD1) plays a positive role in transcription, specifically of G2/M genes. It requires CoREST, which is recruited on active promoters through direct interactions with NF-Y. These data are the first in vivo indication of a crucial interplay between core histones and ‘deviant’ histone-fold such as NF-Y, leading to fine-tuning of histone methylations.

ZNF198 stabilizes the LSD1-CoREST-HDAC1 complex on chromatin through its MYM-type zinc fingers

Histone modifications in chromatin regulate gene expression. A transcriptional co-repressor complex containing LSD1–CoREST–HDAC1 (termed LCH hereafter for simplicity) represses transcription by coordinately removing histone modifications associated with transcriptional activation. RE1-silencing transcription factor (REST) recruits LCH to the promoters of neuron-specific genes, thereby silencing their transcription in non-neuronal tissues. ZNF198 is a member of a family of MYM-type zinc finger proteins that associate with LCH. Here, we show that ZNF198-like proteins are required for the repression of E-cadherin (a gene known to be repressed by LSD1), but not REST-responsive genes. ZNF198 binds preferentially to the intact LCH ternary complex, but not its individual subunits. ZNF198- and REST-binding to the LCH complex are mutually exclusive. ZNF198 associates with chromatin independently of LCH. Furthermore, modification of HDAC1 by small ubiquitin-like modifier (SUMO) in vitro weakens its interaction with CoREST whereas sumoylation of HDAC1 stimulates its binding to ZNF198. Finally, we mapped the LCH- and HDAC1–SUMO-binding domains of ZNF198 to tandem repeats of MYM-type zinc fingers. Therefore, our results suggest that ZNF198, through its multiple protein-protein interaction interfaces, helps to maintain the intact LCH complex on specific, non-REST-responsive promoters and may also prevent SUMO-dependent dissociation of HDAC1.