Association of the interferon-β gene with pericentromeric heterochromatin is dynamically regulated during virus infection through a YY1-dependent mechanism

The role of non-enzymatic glycation on Tau-DNA interactions: Kinetic and mechanistic approaches

Despite the regulatory role of Tau protein in the stabilization and assembly of microtubules, this protein has an important function in the protection and stabilizing of DNA molecules in the cell nucleus. In the present study, it has been indicated that glycation of lysine residues (Lys-267, Lys-274, and Lys-280) in the microtubule-binding domain (MBD) can considerably decrease its binding affinity to DNA molecules. The structural analysis also confirmed that the decreased glycated tau-DNA complex's stability was due to structural modification of this protein after the glycation process. The study of hippocampal cells under hyperglycemic conditions showed that near to 70% of Tau proteins glycated in these cells, although the expression of Tau remained unaffected. The assessment of H3K9me2, as a marker for binding of Tau to pericentromeric heterochromatin (PCH), indicated that localization of Tau protein on PCH was remarkably decreased at high glucose conditions relative to the controls. It is suggested that increasing the structural stability of Tau protein limits the ability of this protein for DNA binding, while the molecular and physical barrier of glycated Lys residues should not be neglected.

Tau Oligomers Neurotoxicity

Although the mechanisms of toxic activity of tau are not fully recognized, it is supposed that the tau toxicity is related rather not to insoluble tau aggregates but to its intermediate forms. It seems that neurofibrillar tangles (NFTs) themselves, despite being composed of toxic tau, are probably neither necessary nor sufficient for tau-induced neuronal dysfunction and toxicity. Tau oligomers (TauOs) formed during the early stages of tau aggregation are the pathological forms that play a key role in eliciting the loss of neurons and behavioral impairments in several neurodegenerative disorders called tauopathies. They can be found in tauopathic diseases, the most common of which is Alzheimer's disease (AD). Evidence of co-occurrence of b-amyloid, α-synuclein, and tau into their most toxic forms, i.e., oligomers, suggests that these species interact and influence each other's aggregation in several tauopathies. The mechanism responsible for oligomeric tau neurotoxicity is a subject of intensive investigation. In this review, we summarize the most recent literature on the damaging effect of TauOs on the stability of the genome and the function of the nucleus, energy production and mitochondrial function, cell signaling and synaptic plasticity, the microtubule assembly, neuronal cytoskeleton and axonal transport, and the effectiveness of the protein degradation system.

A genetic variant controls interferon-β gene expression in human myeloid cells by preventing C/EBP-β binding on a conserved enhancer

Interferon β (IFN-β) is a cytokine that induces a global antiviral proteome, and regulates the adaptive immune response to infections and tumors. Its effects strongly depend on its level and timing of expression. Therefore, the transcription of its coding gene IFNB1 is strictly controlled. We have previously shown that in mice, the TRIM33 protein restrains Ifnb1 transcription in activated myeloid cells through an upstream inhibitory sequence called ICE. Here, we show that the deregulation of Ifnb1 expression observed in murine Trim33^-/- macrophages correlates with abnormal looping of both ICE and the Ifnb1 gene to a 100 kb downstream region overlapping the Ptplad2/Hacd4 gene. This region is a predicted myeloid super-enhancer in which we could characterize 3 myeloid-specific active enhancers, one of which (E5) increases the response of the Ifnb1 promoter to activation. In humans, the orthologous region contains several single nucleotide polymorphisms (SNPs) known to be associated with decreased expression of IFNB1 in activated monocytes, and loops to the IFNB1 gene. The strongest association is found for the rs12553564 SNP, located in the E5 orthologous region. The minor allele of rs12553564 disrupts a conserved C/EBP-β binding motif, prevents binding of C/EBP-β, and abolishes the activation-induced enhancer activity of E5. Altogether, these results establish a link between a genetic variant preventing binding of a transcription factor and a higher order phenotype, and suggest that the frequent minor allele (around 30% worldwide) might be associated with phenotypes regulated by IFN-β expression in myeloid cells.

Genome-wide association studies identify multiple genetic variants associated with higher order phenotypes. Pinpointing the causative variant and understanding its molecular mode of action is a complex task. Using a murine model of interferon-β transcriptional deregulation, we characterize a super-enhancer controlling Ifnb1 expression in myeloid cells. The most active enhancer of this locus is conserved in humans, but presents a frequent variant found in around 30% of the population worldwide. This variant prevents binding of the C/EBP-β transcription factor, and is associated with decreased expression of IFNB1 in activated monocytes. When mimicked in the murine enhancer, it abolishes its inducible enhancer activity. Our results describe the molecular link between a point mutation and a cellular phenotype that could influence clinical situations.

Of Keeping and Tipping the Balance: Host Regulation and Viral Modulation of IRF3-Dependent IFNB1 Expression

The type I interferon (IFN) response is a principal component of our immune system that allows to counter a viral attack immediately upon viral entry into host cells. Upon engagement of aberrantly localised nucleic acids, germline-encoded pattern recognition receptors convey their find via a signalling cascade to prompt kinase-mediated activation of a specific set of five transcription factors. Within the nucleus, the coordinated interaction of these dimeric transcription factors with coactivators and the basal RNA transcription machinery is required to access the gene encoding the type I IFN IFNβ (IFNB1). Virus-induced release of IFNβ then induces the antiviral state of the system and mediates further mechanisms for defence. Due to its key role during the induction of the initial IFN response, the activity of the transcription factor interferon regulatory factor 3 (IRF3) is tightly regulated by the host and fiercely targeted by viral proteins at all conceivable levels. In this review, we will revisit the steps enabling the trans-activating potential of IRF3 after its activation and the subsequent assembly of the multi-protein complex at the IFNβ enhancer that controls gene expression. Further, we will inspect the regulatory mechanisms of these steps imposed by the host cell and present the manifold strategies viruses have evolved to intervene with IFNβ transcription downstream of IRF3 activation in order to secure establishment of a productive infection.

Loss of Tau protein affects the structure, transcription and repair of neuronal pericentromeric heterochromatin

Pericentromeric heterochromatin (PCH) gives rise to highly dense chromatin sub-structures rich in the epigenetic mark corresponding to the trimethylated form of lysine 9 of histone H3 (H3K9me3) and in heterochromatin protein 1α (HP1α), which regulate genome expression and stability. We demonstrate that Tau, a protein involved in a number of neurodegenerative diseases including Alzheimer's disease (AD), binds to and localizes within or next to neuronal PCH in primary neuronal cultures from wild-type mice. Concomitantly, we show that the clustered distribution of H3K9me3 and HP1α, two hallmarks of PCH, is disrupted in neurons from Tau-deficient mice (KOTau). Such altered distribution of H3K9me3 that could be rescued by overexpressing nuclear Tau protein was also observed in neurons from AD brains. Moreover, the expression of PCH non-coding RNAs, involved in PCH organization, was disrupted in KOTau neurons that displayed an abnormal accumulation of stress-induced PCH DNA breaks. Altogether, our results demonstrate a new physiological function of Tau in directly regulating neuronal PCH integrity that appears disrupted in AD neurons.

TRIM33 switches off Ifnb1 gene transcription during the late phase of macrophage activation

Despite its importance during viral or bacterial infections, transcriptional regulation of the interferon-β gene (Ifnb1) in activated macrophages is only partially understood. Here we report that TRIM33 deficiency results in high, sustained expression of Ifnb1 at late stages of toll-like receptor-mediated activation in macrophages but not in fibroblasts. In macrophages, TRIM33 is recruited by PU.1 to a conserved region, the Ifnb1 Control Element (ICE), located 15 kb upstream of the Ifnb1 transcription start site. ICE constitutively interacts with Ifnb1 through a TRIM33-independent chromatin loop. At late phases of lipopolysaccharide activation of macrophages, TRIM33 is bound to ICE, regulates Ifnb1 enhanceosome loading, controls Ifnb1 chromatin structure and represses Ifnb1 gene transcription by preventing recruitment of CBP/p300. These results characterize a previously unknown mechanism of macrophage-specific regulation of Ifnb1 transcription whereby TRIM33 is critical for Ifnb1 gene transcription shutdown.

Transcriptional regulation of the interferon-β gene (Ifnb1) in macrophages is a critical immune event. Here, Ferri et al. show that, at late phases of macrophages activation, TRIM33 bound to a distal repressor element suppresses Ifnb1 transcription by preventing recruitment of CBP/p300.

β-Catenin Upregulates the Constitutive and Virus-Induced Transcriptional Capacity of the Interferon Beta Promoter through T-Cell Factor Binding Sites

Rapid upregulation of interferon beta (IFN-β) expression following virus infection is essential to set up an efficient innate antiviral response. Biological roles related to the antiviral and immune response have also been associated with the constitutive production of IFN-β in naive cells. However, the mechanisms capable of modulating constitutive IFN-β expression in the absence of infection remain largely unknown. In this work, we demonstrate that inhibition of the kinase glycogen synthase kinase 3 (GSK-3) leads to the upregulation of the constitutive level of IFN-β expression in noninfected cells, provided that GSK-3 inhibition is correlated with the binding of β-catenin to the IFN-β promoter. Under these conditions, IFN-β expression occurred through the T-cell factor (TCF) binding sites present on the IFN-β promoter independently of interferon regulatory factor 3 (IRF3). Enhancement of the constitutive level of IFN-β per se was able to confer an efficient antiviral state to naive cells and acted in synergy with virus infection to stimulate virus-induced IFN-β expression. Further emphasizing the role of β-catenin in the innate antiviral response, we show here that highly pathogenic Rift Valley fever virus (RVFV) targets the Wnt/β-catenin pathway and the formation of active TCF/β-catenin complexes at the transcriptional and protein level in RVFV-infected cells and mice.

Directed targeting of chromatin to the nuclear lamina is mediated by chromatin state and A-type lamins

Nuclear organization has been implicated in regulating gene activity. Recently, large developmentally regulated regions of the genome dynamically associated with the nuclear lamina have been identified. However, little is known about how these lamina-associated domains (LADs) are directed to the nuclear lamina. We use our tagged chromosomal insertion site system to identify small sequences from borders of fibroblast-specific variable LADs that are sufficient to target these ectopic sites to the nuclear periphery. We identify YY1 (Ying-Yang1) binding sites as enriched in relocating sequences. Knockdown of YY1 or lamin A/C, but not lamin A, led to a loss of lamina association. In addition, targeted recruitment of YY1 proteins facilitated ectopic LAD formation dependent on histone H3 lysine 27 trimethylation and histone H3 lysine di- and trimethylation. Our results also reveal that endogenous loci appear to be dependent on lamin A/C, YY1, H3K27me3, and H3K9me2/3 for maintenance of lamina-proximal positioning.