Project description:Background and Aims: Chronic HBV infection is a major cause of liver disease and cancer. Virus-host interactions and the pathogenesis of virus-induced liver disease are only partially understood. Hypoxia has been shown to play a major role in disease biology and carcinogenesis and HBV replicates a naturally hypoxic organ. In this study we aimed to investigate the role of liver hypoxia for HBV infection. Methods: Using cell culture, animal models and human tissues we investigated the impact of hyproxia on the HBV life cycle. Results: Establishing liver cell-based model systems that mimic hepatic oxygen, we uncover a major role of hypoxia in regulating HBV transcription. Hypoxia-inducible factors (HIFs) perturb HBV replication and expression in cell-based and animal models. Conservation of hypoxia responsive elements in the viral basal core promoter uncover an essential role for HIFs in regulating the hepadnaviridae family of hepatotropic viruses. Conclusions: Identifying a role for this conserved oxygen sensors in regulating HBV replication provides a new understanding of virus-host interactions and liver disease biology, improve state-of-the-art HBV model systems and unravels new opportunities for therapeutic targeting of chronic hepatitis B.
Project description:Unscheduled R-loops are a major source of replication stress and DNA damage. R-loop-induced replication defects are sensed and suppressed by ATR kinase, whereas it is not known whether R-loop itself is actively involved in ATR activation and, if so, how this is achieved. Here, we report that the nuclear form of RNA-editing enzyme ADAR1 promotes ATR activation and resolves genome-wide R-loops, a process that requires its double-stranded RNA-binding domains. Mechanistically, ADAR1 interacts with TOPBP1 and facilitates its loading on perturbed replication forks by enhancing the association of TOPBP1 with RAD9 of the 9-1-1 complex. When replication is inhibited, DNA-RNA hybrid competes with TOPBP1 for ADAR1 binding to promote the translocation of ADAR1 from damaged fork to R-loop region. There, ADAR1 recruits RNA helicases DHX9 and DDX21 to unwind R-loops, simultaneously allowing TOPBP1 to stimulate ATR more efficiently. Collectively, we propose that the tempo-spatially regulated assembly of ADAR1-nucleated protein complexes link R-loop clearance and ATR activation, while R-loops crosstalk with blocked replication forks by transposing ADAR1 to finetune ATR activity and safeguard the genome.
Project description:Erguler2013 - Unfolded protein stress response
The model investigates the mechanism by which UPR (unfolded protein response) outcome switches between survival and death.
This model is described in the article:
A mathematical model of the unfolded protein stress response reveals the decision mechanism for recovery, adaptation and apoptosis.
Erguler K, Pieri M, Deltas C.
BMC Syst Biol. 2013 Feb 21;7(1):16.
Abstract:
BACKGROUND: The unfolded protein response (UPR) is a major signalling cascade acting in the quality control ofprotein folding in the endoplasmic reticulum (ER). The cascade is known to play an accessory rolein a range of genetic and environmental disorders including neurodegenerative and cardiovasculardiseases, diabetes and kidney diseases. The three major receptors of the ER stress involved withthe UPR, i.e. IRE1a, PERK and ATF6, signal through a complex web of pathways to convey anappropriate response. The emerging behaviour ranges from adaptive to maladaptive depending on theseverity of unfolded protein accumulation in the ER; however, the decision mechanism for the switchand its timing have so far been poorly understood.
RESULTS:
Here, we propose a mechanism by which the UPR outcome switches between survival and death.We compose a mathematical model integrating the three signalling branches, and perform a comprehensivebifurcation analysis to investigate possible responses to stimuli. The analysis reveals threedistinct states of behaviour, low, high and intermediate activity, associated with stress adaptation, tolerance,and the initiation of apoptosis. The decision to adapt or destruct can, therefore, be understoodas a dynamic process where the balance between the stress and the folding capacity of the ER playsa pivotal role in managing the delivery of the most appropriate response. The model demonstratesfor the first time that the UPR is capable of generating oscillations in translation attenuation and theapoptotic signals, and this is supplemented with a Bayesian sensitivity analysis identifying a set ofparameters controlling this behaviour.
CONCLUSIONS:
This work contributes largely to the understanding of one of the most ubiquitous signalling pathwaysinvolved in protein folding quality control in the metazoan ER. The insights gained have direct consequenceson the management of many UPR-related diseases, revealing, in addition, an extended listof candidate disease modifiers. Demonstration of stress adaptation sheds light to how preconditioningmight be beneficial in manifesting the UPR outcome to prevent untimely apoptosis, and paves the wayto novel approaches for the treatment of many UPR-related conditions.
In the paper, PERKA refers to the amount of phosphorylated PERK monomer. However, it refers to the active complex in the model. The complex with the model parameterization is formed of 4 monomers (n=4). So, the value of PERKA should be multiplied by 4, in order to generate the figures in the paper (eg. Figure 12).
An additional parameter (tmr=10)) is used in the model. This parameter is not mentioned in the paper. The model values of kf(=10) and kr(=1) are not consistent with that of the paper (kf=100, kr=10, in the paper). However, this is corrected by the introduction of "tmr" in the model, which is multiplied with kf and kr to get the resulting values.
The term "tmr" was missing in the kinetic laws of the reactions reu7 and reu8, in the original model. This has been corrected as per the author's request.
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Project description:All mammalian cells need oxygen. Inadequate oxygen (hypoxia) triggers cellular responses for survival and the maintenance of homeostasis. A transcription factor, hypoxia-inducible factor (HIF), plays a central role in the hypoxia response; its activity is regulated by the oxygen-dependent degradation of the HIF-1a protein. Despite the ubiquity and importance of hypoxia responses, very little is known about the variation in the global transcriptional response to hypoxia among different cell types and its links to tissue and cell-specific diseases. We analyzed the temporal changes in global transcript levels in response to hypoxia in primary renal proximal tubule epithelial cells (RPTECs), breast epithelial cells, smooth muscle (SMs), and endothelial cells (ECs) with DNA microarrays. The extent of the transcriptional response to hypoxia was greatest in the renal tubule cells. This exaggerated response was associated with a uniquely high level of HIF-1a RNA in renal cells and could be diminished by reducing HIF-1a expression via RNA interference (RNAi). A gene-expression signature of the hypoxia response, derived from our studies of cultured mammary and renal tubular epithelial cells, showed coordinated variation in several human cancers, and was a strong predictor of clinical outcomes in both breast and ovarian cancers. In an analysis of a large, published gene-expression dataset from breast cancers, we found that the prognostic information in the hypoxia signature was virtually independent of that provided by the previously reported wound signature and more predictive of outcomes than any of the clinical parameters in current use. A stimulus or stress experiment design type is where that tests response of an organism(s) to stress/stimulus. e.g. osmotic stress, behavioral treatment Using regression correlation
Project description:DNA replication during S-phase is accompanied by establishment of sister chromatid cohesion to ensure faithful chromosome segregation. The Eco1 acetyltransferase, helped by factors including Ctf4 and Chl1, concomitantly acetylates the chromosomal cohesin complex to stabilize its cohesive links. Here we show that Ctf4 recruits the Chl1 helicase to the replisome via a conserved interaction motif that Chl1 shares with GINS and polymerase α. We visualize recruitment by EM analysis of a reconstituted Chl1-Ctf4-GINS assembly. The Chl1 helicase facilitates replication fork progression under conditions of nucleotide depletion, however this function does not require Ctf4 interaction. Conversely, Ctf4 interaction, but not helicase activity, is required for Chl1’s role in sister chromatid cohesion. A physical interaction between Chl1 and the cohesin complex during S-phase suggests that Chl1 contacts cohesin to facilitate its acetylation. Our results reveal how Ctf4 forms a replisomal interaction hub that coordinates replication fork progression and sister chromatid cohesion establishment.
Project description:The purpose of this study was to understand how expression of the ER stress sensor ERN2/IRE1b affects the unfolded protein response to ER stress
Project description:All mammalian cells need oxygen. Inadequate oxygen (hypoxia) triggers cellular responses for survival and the maintenance of homeostasis. A transcription factor, hypoxia-inducible factor (HIF), plays a central role in the hypoxia response; its activity is regulated by the oxygen-dependent degradation of the HIF-1a protein. Despite the ubiquity and importance of hypoxia responses, very little is known about the variation in the global transcriptional response to hypoxia among different cell types and its links to tissue and cell-specific diseases. We analyzed the temporal changes in global transcript levels in response to hypoxia in primary renal proximal tubule epithelial cells (RPTECs), breast epithelial cells, smooth muscle (SMs), and endothelial cells (ECs) with DNA microarrays. The extent of the transcriptional response to hypoxia was greatest in the renal tubule cells. This exaggerated response was associated with a uniquely high level of HIF-1a RNA in renal cells and could be diminished by reducing HIF-1a expression via RNA interference (RNAi). A gene-expression signature of the hypoxia response, derived from our studies of cultured mammary and renal tubular epithelial cells, showed coordinated variation in several human cancers, and was a strong predictor of clinical outcomes in both breast and ovarian cancers. In an analysis of a large, published gene-expression dataset from breast cancers, we found that the prognostic information in the hypoxia signature was virtually independent of that provided by the previously reported wound signature and more predictive of outcomes than any of the clinical parameters in current use. A stimulus or stress experiment design type is where that tests response of an organism(s) to stress/stimulus. e.g. osmotic stress, behavioral treatment Keywords: stimulus_or_stress_design