Histone H3K4 methyltransferase DcATX1 promotes ethylene induced petal senescence in carnation

Petal senescence is controlled by a complex regulatory network. Epigenetic regulation like histone modification influences chromatin state and gene expression. However, involvement of histone methylation in regulating petal senescence is still largely unknown. Here, we found that the trimethylation of histone H3 at Lysine 4 (H3K4me3) is increased during the ethylene induced petal senescence in carnation (Dianthus caryophyllus L.). The H3K4me3 levels are positively associated with the expression of transcription factor DcWRKY75, ethylene biosynthetic genes DcACS1 and DcACO1, and senescence associated genes (SAGs) DcSAG12 and DcSAG29. Further, we identified that carnation DcATX1 (ARABIDOPSIS HOMOLOG OF TRITHORAX1) encodes a histone lysine methyltransferase which can methylate H3K4. Knockdown of DcATX1 delays ethylene induced petal senescence in carnation, which is associated with the downregulated expression of DcWRKY75, DcACO1 and DcSAG12. While overexpression of DcATX1 exhibits the opposite effects. DcATX1 promotes the transcription of DcWRKY75, DcACO1 and DcSAG12 by targeting to their promoters to elevate the H3K4me3 levels. Overall, our results demonstrate that DcATX1 is a H3K4 methyltransferase that promotes the expression of DcWRKY75, DcACO1 and DcSAG12 by regulating H3K4me3 levels, thereby accelerating ethylene induced petal senescence in carnation. This study further indicates that epigenetic regulation is important for plant senescence process.

HAUSP Is a Key Epigenetic Regulator of the Chromatin Effector Proteins

HAUSP (herpes virus-associated ubiquitin-specific protease), also known as Ubiquitin Specific Protease 7, plays critical roles in cellular processes, such as chromatin biology and epigenetics, through the regulation of different signaling pathways. HAUSP is a main partner of the “Epigenetic Code Replication Machinery,” ECREM, a large protein complex that includes several epigenetic players, such as the ubiquitin-like containing plant homeodomain (PHD) and an interesting new gene (RING), finger domains 1 (UHRF1), as well as DNA methyltransferase 1 (DNMT1), histone deacetylase 1 (HDAC1), histone methyltransferase G9a, and histone acetyltransferase TIP60. Due to its deubiquitinase activity and its ability to team up through direct interactions with several epigenetic regulators, mainly UHRF1, DNMT1, TIP60, the histone lysine methyltransferase EZH2, and the lysine-specific histone demethylase LSD1, HAUSP positions itself at the top of the regulatory hierarchies involved in epigenetic silencing of tumor suppressor genes in cancer. This review highlights the increasing role of HAUSP as an epigenetic master regulator that governs a set of epigenetic players involved in both the maintenance of DNA methylation and histone post-translational modifications.

Inference of Rift Valley Fever pathogenesis in Bos taurus using a gene co-expression network

Background: Rift Valley Fever (RVF) is a viral disease caused by the Rift Valley Fever virus and spread mainly by the Aedes and Culex mosquito species. The disease primarily infects domestic animals such as sheep, goats, and cattle, resulting in a spectrum of clinical outcomes including morbidity, massive storm abortions, and neonatal fatalities. RVF outbreaks are closely linked to above-average rainfall and flooding, which create an ideal environment for mosquitos to breed, multiply, and transmit the virus to animals. The outcomes of human RVF infection range from self-limiting febrile illness to potentially fatal hemorrhagic diatheses and miscarriage in pregnant women. Collectively, the economic losses due to the zoonotic RVF disease is immense. Methods: Using the Weighted Gene Co-expression Network Analysis (WGCNA) package, RNA-Seq data generated from five healthy Bos taurus steer calves aged 4-6 months was obtained from the Gene Expression Omnibus (GEO) database (Accession number GSE71417). The data was utilized to construct a gene co-expression network. Enriched modules containing genes potentially involved in RVF infection progression were identified. Moreover, using the Multiple Expectation Maximizations for Motif Elicitation (MEME) suite, consensus regulatory motifs of enriched gene clusters were deciphered and the most abundant putative regulatory motif in each enriched module unveiled by comparative analysis with publicly available motifs using the TOMTOM motif comparison tool. The potential roles of the identified regulatory motifs were inferred by literature mining. Results: The constructed gene co-expression network revealed thirty-three (33) modules, nine of which were enriched for Gene Ontology terms linked to RVF pathogenesis. Functional enrichment in two (red and turquoise) of the nine modules was significant. ASH1-like histone lysine methyltransferase and Astrotactin were the hub genes for the red and turquoise modules respectively. ASH1-like histone lysine methyltransferase gene is involved in chromatin epigenetic modification while Astrotactin is a vertebrate-specific gene that plays an important role in neurodevelopment. Additionally, consensus regulatory motifs located on the 3' end of genes in each enriched module was identified. Conclusions: In this study, we have developed a gene co-expression network that has aided in the unveiling of functionally related genes, intramodular hub genes, and immunity genes potentially involved in RVF pathogenesis. The discovery of functional genes with putative critical roles in the establishment of RVF infection establishment will contribute to the understanding of the molecular mechanism of RVF pathogenesis. Importantly, the putative regulatory motifs identified are plausible targets for RVF drug and vaccine development. Keywords: Rift Valley Fever, Bos taurus, Gene co-expression network, modules, hub genes, Regulatory motifs.

The low-complexity domains of the KMT2D protein regulate histone monomethylation transcription to facilitate pancreatic cancer progression

Background Liquid–liquid phase separation (LLPS) within the nucleus is directly linked to driving gene expression through transcriptional complexes. Histone lysine methyltransferase 2D (KMT2D) is widely present in many cancers. It is known to epigenetically stimulate the expression of genes associated with tumorigenesis and metastasis. Our analyses show that KMT2D possesses two distinct low-complexity domains (LCDs) capable of driving the assembly of membrane-less condensates. The dependence of the mechanisms underlying monomethylation of H3K4 on the LLPS microenvironment derived from KMT2D LCDs is unclear in tumor. Methods KMT2D LCD-depletion cells were used to investigate tumor cell proliferation, apoptosis, and migration. We identified some core proteins, including WDR5, RBBP5, and ASH2L, which are involved in the KMT2D-associated catalytic complex in KMT2D LCD-deficient cells to further elucidate the mechanism that decreases monomethylation of H3K4. We also evaluated the viability of KMT2D LCD-deficient cells in vivo. Finally, using 1,6-hexanediol (HD), an inhibitor of LLPS, we determined cell activities associated with KMT2D function in wild-type PANC-1 cells. Results Without the LLPS microenvironment in KMT2D LCD-deficient cells or wild-type PANC-1 cells treated with HD, the WDR5 protein was significantly less stable and the protein–protein interactions between the components of the KMT2D–enzyme complex were attenuated, impairing the formation of the complex. Moreover, with the decrease in H3K4me1 level at enhancers, transcription factors such as LIFR and KLF4 were markedly downregulated, effectively inhibiting tumor progression. In xenograft tumor models, PANC-1 cells lacking the KMT2D LCDs showed effectively suppressed tumor growth compared to normal cells. Conclusions Our data indicate that the two low-complexity domains of the KMT2D protein could form a stable LLPS microenvironment, promoting the KMT2D catalysis of H3K4 monomethylation through stabilization of the WDR5 protein and KMT2D–enzyme complex. Therefore, finding ways to regulate the LLPS microenvironment will be benefitial for new cancer treatment strategies.

EHMT2/G9a as an Epigenetic Target in Pediatric and Adult Brain Tumors

Epigenetic mechanisms, including post-translational modifications of DNA and histones that influence chromatin structure, regulate gene expression during normal development and are also involved in carcinogenesis and cancer progression. The histone methyltransferase G9a (euchromatic histone lysine methyltransferase 2, EHMT2), which mostly mediates mono- and dimethylation by histone H3 lysine 9 (H3K9), influences gene expression involved in embryonic development and tissue differentiation. Overexpression of G9a has been observed in several cancer types, and different classes of G9a inhibitors have been developed as potential anticancer agents. Here, we review the emerging evidence suggesting the involvement of changes in G9a activity in brain tumors, namely glioblastoma (GBM), the main type of primary malignant brain cancer in adults, and medulloblastoma (MB), the most common type of malignant brain cancer in children. We also discuss the role of G9a in neuroblastoma (NB) and the drug development of G9a inhibitors.

Clustered PHD domains in mixed lineage leukaemia proteins are attracted by acetylation-rich active promoters and enhancers

Histone lysine methyltransferase (KMT2) proteins form the core of COMPASS and COMPASS-like complexes that mediate transcriptional memory by methylating H3K4 at promoters and enhancers. KMT2A-D proteins, alternatively called mixed lineage leukaemia proteins (MLL1-4), contain highly conserved unique triplet and quartet of plant homeodomains (PHDs). Here, we show that clustered PHDs, expressed in isolation in HeLa cells, localize to well-defined loci of acetylation-rich active promoters and enhancers. Binding sites overlap with targets of full-length KMT2A (MLL1) and the COMPASS-like subunit WDR5, RbBP5 and with cell cycle and cancer-related genes. COSMIC data identify frequent variations in the PHDs of KMT2 proteins, particularly KMT2C, in a wide spectrum of malignancies. Changes are enriched at conserved positions within the PHDs, indicating that they cause loss-of-function mutations. Taken together, the biochemical and cancer data suggest that the PHDs contribute to KMT2A-D targeting to active promoters and enhancers.

SETDB1 Fuels the Lung Cancer Phenotype by Modulating Epigenome, 3D Genome Organization and Chromatin Mechanical Properties

Imbalance in the finely orchestrated system of chromatin-modifying enzymes is a hallmark of many pathologies such as cancers, since causing the affection of the epigenome and transcriptional reprogramming. Here, we demonstrate that a loss-of-function mutation (LOF) of the major histone lysine methyltransferase SETDB1 possessing oncogenic activity in lung cancer cells leads to broad changes in the overall architecture and mechanical properties of the nucleus through genome-wide redistribution of heterochromatin, which perturbs chromatin spatial compartmentalization. Together with the enforced activation of the epithelial expression program, cytoskeleton remodeling, reduced proliferation rate and restricted cellular migration, this leads to the reversed oncogenic potential of lung adenocarcinoma cells. These results emphasize an essential role of chromatin architecture in the determination of oncogenic programs and illustrate a relationship between gene expression, epigenome, 3D genome and nuclear mechanics.

Abstract P340: Histone Methyltransferase Smyd1a Protects Heart From Ischemic Injury By Regulating Mitochondrial Respiration

SMYD1a, a myosin-specific histone lysine methyltransferase, plays a major role in regulating disease-induced remodeling in the adult heart. Previously, we demonstrated that the inducible loss of this chromatin-bound enzyme is sufficient to induce cardiac hypertrophy and failure in vivo , which is preceded by downregulation of mitochondrial proteins involved in oxidative phosphorylation (OXPHOS), and reduction of mitochondrial respiration capacity. However, our most recent data in transgenic mice (TG) displaying inducible, cardiomyocyte-specific overexpression of SMYD1a show that these mice are protected from ischemic injury after permanent occlusion (PO) of the LAD manifested by reduced infarct size and cardiac dysfunction compared to littermate controls (WT), suggesting that SMYD1 plays a protective role in the heart and mitigates disease-induced remodeling. Additionally, global proteomic evaluation of cardiac tissue from TG mice showed unique expression of metabolic enzymes, including proteins from the electron transport chain, and our high-resolution mitochondrial respirometry analysis showed that overexpression of SMYD1a leads to increased oxygen consumption rates through Complex I and II. To further asses OXPHOS efficiency in TG mice we subjected them to permanent occlusion of the LAD and evaluated ATP production rates in isolated mitochondria from TG and WT mice, by measuring the molar amount of ATP produced per mole of atomic oxygen consumed (known as ATP:O ratio). Interestingly, we observed a significant increase in ATP:O ratio in TG mice 24h after PO suggesting that they are much more efficient at producing ATP. Finally, we show that the global regulation of mitochondrial respiration in TG mice occurs through transcriptional control of Ppargc1α . Our results confirm that cardiac expression of Ppargc1α was significantly reduced in WT mice (48h after PO) but maintained at basal levels in TG mice, which also corroborated with our ChIP-qPCR data showing SMYD1a binding to the Ppargc1α promoter and regulating its expression. Overall, these results show that SMYD1a can mitigate ischemic injury and adverse remodeling in the adult myocardium, which occurs through Ppargc1α expression and regulation of cardiac energetics and metabolism.

Computational systems analysis of differential gene expression in brain metastatic breast cancer.

We utilized readily available computational tools (1-5) and published microarray data (6-9) to understand in an unbiased fashion the most distinguishing molecular features of differentially expressed genes in brain metastatic tissues from humans with metastatic breast cancer, and their genomic sites. We present our findings here, which reveal enrichment for function at the Golgi apparatus, an overlap of molecular signatures with development of the lip and the craniofacial structure, and demonstrate that the genomic sites of the most differentially expressed genes in metastasis to the brain in human breast cancer are enriched for binding sites for Barx2 and IKZF1, may be occupied by Aebp2 and the histone lysine methyltransferase KMT2H, and marked at the chromatin at H3K79me2 and H3K4me3.