Histone 2B Monoubiquitination Research Articles

Novel protein-truncating variants of a chromatin-modifying gene MSL2 in syndromic neurodevelopmental disorders

Numerous large scale genomic studies have uncovered rare but recurrent pathogenetic variants in a significant number of genes encoding epigenetic machinery in cases with neurodevelopmental disorders (NDD) especially autism spectrum disorder (ASD). These findings provide strong support for the functional importance of epigenetic regulators in neurodevelopment. After the clinical genomics evaluation of the patients using exome sequencing, we have identified, three novel protein-truncating variants (PTVs) in the MSL2 gene (OMIM: 614802) which encodes a chromatin modifying enzyme. MSL2 modifies chromatin through both mono-ubiquitination of histone 2B on lysine 34 (K34) and acetylation of histone H4 on lysine 16 (K16). We reported first time the detailed clinical features associated with 3 MSL2 PTVs. There are 15 PTVs (13 de novo) reported from the large genomics studies (12 cases) or ClinVar (3 cases) of NDD, ASD, and developmental disorders (DD) but the specific clinical features for these cases are not described. Taken together, our descriptions of dysmorphic face and other features support the causal role of MSL2 in a likely syndromic neurodevelopmental disorder and add MSL2 to a growing list of epigenetic genes implicated in ASD.

The diverse roles of histone 2B monoubiquitination in the life of plants.

Covalent modification of histones is an important tool for gene transcriptional control in eukaryotes, which coordinates growth, development, and adaptation to environmental changes. In recent years, an important role for monoubiquitination of histone 2B (H2B) has emerged in plants, where it is associated with transcriptional activation. In this review, we discuss the dynamics of the H2B monoubiquitination system in plants and its role in regulating developmental processes including flowering, circadian rhythm, photomorphogenesis, and the response to abiotic and biotic stress including drought, salinity, and fungal, bacterial, and viral pathogens. Furthermore, we highlight the crosstalk between H2B monoubiquitination and other histone modifications which fine-tunes transcription and ensures developmental plasticity. Finally, we put into perspective how this versatile regulatory mechanism can be developed as a useful tool for crop improvement.

The histone H2B ubiquitin ligase RNF40 is required for HER2-driven mammary tumorigenesis

The HER2-positive breast cancer subtype (HER2+-BC) displays a particularly aggressive behavior. Anti-HER2 therapies have significantly improved the survival of patients with HER2+-BC. However, a large number of patients become refractory to current targeted therapies, necessitating the development of new treatment strategies. Epigenetic regulators are commonly misregulated in cancer and represent attractive molecular therapeutic targets. Monoubiquitination of histone 2B (H2Bub1) by the heterodimeric ubiquitin ligase complex RNF20/RNF40 has been described to have tumor suppressor functions and loss of H2Bub1 has been associated with cancer progression. In this study, we utilized human tumor samples, cell culture models, and a mammary carcinoma mouse model with tissue-specific Rnf40 deletion and identified an unexpected tumor-supportive role of RNF40 in HER2+-BC. We demonstrate that RNF40-driven H2B monoubiquitination is essential for transcriptional activation of RHO/ROCK/LIMK pathway components and proper actin-cytoskeleton dynamics through a trans-histone crosstalk with histone 3 lysine 4 trimethylation (H3K4me3). Collectively, this work demonstrates a previously unknown essential role of RNF40 in HER2+-BC, revealing the H2B monoubiquitination axis as a possible tumor context-dependent therapeutic target in breast cancer.

Ubiquitin E3 Ligase AaBre1 Responsible for H2B Monoubiquitination Is Involved in Hyphal Growth, Conidiation and Pathogenicity in Alternaria alternata.

Ubiquitination is one of several post-transcriptional modifications of histone 2B (H2B) which affect the chromatin structure and, hence, influence gene transcription. This study focuses on Alternaria alternata, a fungal pathogen responsible for leaf spot in many plant species. The experiments show that the product of AaBRE1, a gene which encodes H2B monoubiquitination E3 ligase, regulates hyphal growth, conidial formation and pathogenicity. Knockout of AaBRE1 by the homologous recombination strategy leads to the loss of H2B monoubiquitination (H2Bub1), as well as a remarkable decrease in the enrichment of trimethylated lysine 4 on histone 3 (H3K4me3). RNA sequencing assays elucidated that the transcription of genes encoding certain C2H2 zinc-finger family transcription factors, cell wall-degrading enzymes and chitin-binding proteins was suppressed in the AaBRE1 knockout cells. GO enrichment analysis showed that these proteins encoded by the set of genes differentially transcribed between the deletion mutant and wild type were enriched in the functional categories “macramolecular complex”, “cellular metabolic process”, etc. A major conclusion was that the AaBRE1 product, through its effect on histone 2B monoubiquitination and histone 3 lysine 4 trimethylation, makes an important contribution to the fungus’s hyphal growth, conidial formation and pathogenicity.

Correction: The replication initiator protein of a geminivirus interacts with host monoubiquitination machinery and stimulates transcription of the viral genome.

[This corrects the article DOI: 10.1371/journal.ppat.1006587.].

SaRNA-guided Ago2 targets the RITA complex to promoters to stimulate transcription.

Small activating RNAs (saRNAs) targeting specific promoter regions are able to stimulate gene expression at the transcriptional level, a phenomenon known as RNA activation (RNAa). It is known that RNAa depends on Ago2 and is associated with epigenetic changes at the target promoters. However, the precise molecular mechanism of RNAa remains elusive. Using human CDKN1A (p21) as a model gene, we characterized the molecular nature of RNAa. We show that saRNAs guide Ago2 to and associate with target promoters. saRNA-loaded Ago2 facilitates the assembly of an RNA-induced transcriptional activation (RITA) complex, which, in addition to saRNA-Ago2 complex, includes RHA and CTR9, the latter being a component of the PAF1 complex. RITA interacts with RNA polymerase II to stimulate transcription initiation and productive elongation, accompanied by monoubiquitination of histone 2B. Our results establish the existence of a cellular RNA-guided genome-targeting and transcriptional activation mechanism and provide important new mechanistic insights into the RNAa process.

Monoubiquitination of Histone 2B at the Disease Resistance Gene Locus Regulates Its Expression and Impacts Immune Responses in Arabidopsis

Disease resistance (R) genes are key components in plant immunity. Here, we show that Arabidopsis (Arabidopsis thaliana) E3 ubiquitin ligase genes HISTONE MONOUBIQUITINATION1 (HUB1) and HUB2 regulate the expression of R genes SUPPRESSOR OF npr1-1, CONSTITUTIVE1 (SNC1) and RESISTANCE TO PERONOSPORA PARASITICA4. An increase of SNC1 expression induces constitutive immune responses in the bonzai1 (bon1) mutant, and the loss of HUB1 or HUB2 function reduces SNC1 up-regulation and suppresses the bon1 autoimmune phenotypes. HUB1 and HUB2 mediate histone 2B (H2B) monoubiquitination directly at the SNC1 R gene locus to regulate its expression. In addition, SNC1 and HUB1 transcripts are moderately up-regulated by pathogen infection, and H2B monoubiquitination at SNC1 is enhanced by pathogen infection. Together, this study indicates that H2B monoubiquitination at the R gene locus regulates its expression and that this histone modification at the R gene locus has an impact on immune responses in plants.

Abstract A29: Loss of histone H2B monoubiquitination in ovarian cancer – new therapeutic targeting opportunities based on chromatin relaxation

Abstract Post-translational modifications of histones are involved in diverse functions, including gene transcription and the DNA damage response. Targeting elements of the DNA damage response pathway is of increasing interest for the treatment of epithelial ovarian cancer (EOC). Monoubiquitination of histone H2B at lysine 120 (H2Bub1) is present at the coding region of highly expressed genes such as the gene encoding p21, CDKN1A, under conditions of DNA damage. Addition of this histone mark relies on the E3 ubiquitin ligase ring finger protein complex RNF20-RNF40 that we, and others, have previously shown interacts with members of the PAF1 complex necessary for RNA polymerase II-based transcriptional elongation. At 8.5 kDa, ubiquitin constitutes a bulky addition likely sufficient to interfere with condensed chromatin fibres, leading to a more open fibre conformation with greater accessibility for transcription factors and DNA repair proteins. H2Bub1 has been described as a master switch for mammalian gene regulation, with roles in histone cross-talk. Furthermore, H2Bub1 has recently been linked to the cellular DNA damage response, with the protein kinase ATM phosphorylating RNF20-RNF40 to induce H2Bub1 at sites of double strand breaks, leading to a more open chromatin structure for optimal repair. Global H2Bub1 loss has been reported in breast, colon, lung and parathyroid tumors1, and in some of these tumor types has been associated with advancing stage. We have undertaken immunohistochemical analyses of global H2Bub1 and total histone H2B using tissue microarrays of EOC sourced from the Australian Ovarian Cancer Study and the Gynaecological Oncology Biobank at Westmead. Expression of total histone H2B was high and consistent across all tumors, whereas over 70% of tumors showed total loss of global H2Bub1. Contrary to reports that global H2Bub1 levels decreased with advanced stage in breast cancer, we did not observe this for ovarian cancer. This may be related to the fact that cohorts of EOC are skewed towards tumors of advanced stage, as most women present with Stage III-IV disease. The mechanism of H2Bub1 loss in ovarian cancer is currently unknown, but is likely to involve genetic or epigenetic regulation of genes encoding proteins that function as components of E3 ubiquitin ligase machinery. We have previously shown that loss-of-function mutations in the tumor suppressor CDC73, a PAF1 complex member, lead to loss of H2Bub1 in parathyroid cancer1; however, we observed consistent staining of CDC73 in ovarian tumors. We are currently analysing EOCs for expression of RNF20 given that the RNF20 promoter is hypermethylated in breast cancer and TCGA-ovarian reports RNF20 missense mutations with neutral to medium predicted impact scores. This data will be presented. Given the apparent fundamental role of H2Bub1 in determining the accessibility of chromatin for molecules such as DNA repair proteins, H2Bub1 and/or its associated ubiquitin ligase machinery, may be considered as potential therapeutic targets for the treatment of EOC. 1Hahn MA, Dickson K-A, Jackson S, Clarkson A, Gill AJ and Marsh DJ. The tumor suppressor CDC73 interacts with the ring finger proteins RNF20 and RNF40 and is required for the maintenance of histone 2B monoubiquitination Human Molecular Genetics 2012; 21(3):559-568. Citation Format: Deborah J. Marsh, Anna deFazio, Adele Clarkson, Catherine Kennedy, Gregory G. Gard, Anthony J. Gill. Loss of histone H2B monoubiquitination in ovarian cancer – new therapeutic targeting opportunities based on chromatin relaxation. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A29.

Adenovirus Evasion of Interferon-Mediated Innate Immunity by Direct Antagonism of a Cellular Histone Posttranslational Modification

Overcoming the cellular type I interferon (IFN) host defense response is critical for a virus to ensure successful infection. Investigating the effects of human adenovirus (HAdV) infection on global cellular histone posttranslational modification (hPTM), we discovered that virus infection-induced activation of IFN signaling triggers a global increase in the monoubiquitination of histone 2B (H2B) at lysine 120, which is a mark for transcriptionally active chromatin. This hPTM, catalyzed by the hBre1/RNF20 complex, is necessary for activation of the cellular IFN-stimulated gene (ISG) expression program in response to viruses. To establish effective infection, the HAdV E1A protein binds to and dissociates thehBre1 complex to block IFN-induced H2B monoubiquitination and associated ISG expression. Together, these data uncover a key role for H2B monoubiquitination in the type I IFN response and a viral mechanism of antagonizing this hPTM to evade the IFN response.