Three-tiered kinase modules, such as the Raf-MEK (mitogen-activated or extracellular signal-regulated protein kinase kinase)-ERK (extracellular signal-regulated kinase) mitogen-activated protein ...kinase pathway, are widespread in biology, suggesting that this structure conveys evolutionarily advantageous properties. We show that the three-tiered kinase amplifier module combined with negative feedback recapitulates the design principles of a negative feedback amplifier (NFA), which is used in electronic circuits to confer robustness, output stabilization, and linearization of nonlinear signal amplification. We used mathematical modeling and experimental validation to demonstrate that the ERK pathway has properties of an NFA that (i) converts intrinsic switch-like activation kinetics into graded linear responses, (ii) conveys robustness to changes in rates of reactions within the NFA module, and (iii) stabilizes outputs in response to drug-induced perturbations of the amplifier. These properties determine biological behavior, including activation kinetics and the response to drugs.
Influenza A virus (IAV) is a lytic virus in primary cultures of many cell types and in vivo. We report that the kinase RIPK3 is essential for IAV-induced lysis of mammalian fibroblasts and lung ...epithelial cells. Replicating IAV drives assembly of a RIPK3-containing complex that includes the kinase RIPK1, the pseudokinase MLKL, and the adaptor protein FADD, and forms independently of signaling by RNA-sensing innate immune receptors (RLRs, TLRs, PKR), or the cytokines type I interferons and TNF-α. Downstream of RIPK3, IAV activates parallel pathways of MLKL-driven necroptosis and FADD-mediated apoptosis, with the former reliant on RIPK3 kinase activity and neither on RIPK1 activity. Mice deficient in RIPK3 or doubly deficient in MLKL and FADD, but not MLKL alone, are more susceptible to IAV than their wild-type counterparts, revealing an important role for RIPK3-mediated apoptosis in antiviral immunity. Collectively, these results outline RIPK3-activated cytolytic mechanisms essential for controlling respiratory IAV infection.
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•RIPK3-deficient cells are resistant to IAV-induced death•RIPK3 activates both necroptosis and apoptosis upon IAV infection•RIPK3-mediated necroptosis requires MLKL, while apoptosis necessitates FADD•RIPK3-activated apoptosis compensates for loss of necroptosis in vivo
Influenza A viruses (IAV) kill the cells in which they replicate. Nogusa et al. identify a central role for the host kinase RIPK3 in triggering death of IAV-infected cells. They find that RIPK3 activates parallel, redundant pathways of necroptosis and apoptosis to destroy the infected cell and protect the host.
The role of apoptosis inducing factor (AIF) in promoting cell death versus survival remains controversial. We report that the loss of AIF in fibroblasts led to mitochondrial electron transport chain ...defects and loss of proliferation that could be restored by ectopic expression of the yeast NADH dehydrogenase Ndi1. Aif-deficiency in T cells led to decreased peripheral T cell numbers and defective homeostatic proliferation, but thymic T cell development was unaffected. In contrast, Aif-deficient B cells developed and functioned normally. The difference in the dependency of T cells versus B cells on AIF for function and survival correlated with their metabolic requirements. Ectopic Ndi1 expression rescued homeostatic proliferation of Aif-deficient T cells. Despite its reported roles in cell death, fibroblasts, thymocytes and B cells lacking AIF underwent normal death. These studies suggest that the primary role of AIF relates to complex I function, with differential effects on T and B cells.
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•AIF regulates complex I function but not cell death in lymphocytes and MEF•AIF is essential for T cell survival but not for B cell function and development•B cells fulfill their energetic needs via glycolysis and T cells via respiration•Expression of the yeast Ndi1 rescues defects in Aif-deficient T cells and MEF
The role of AIF in cell death versus survival is controversial. Green and colleagues find that Aif deficiency does not affect lymphocyte cell death but instead impairs respiration by reducing complex I levels. Due to differences in their metabolic requirements, Aif deficiency severely reduces T cell survival while B cells remain unaffected.
The MAPK (mitogen-activated protein kinase) pathway is one of the most important and intensively studied signalling pathways. It is at the heart of a molecular-signalling network that governs the ...growth, proliferation, differentiation and survival of many, if not all, cell types. It is de-regulated in various diseases, ranging from cancer to immunological, inflammatory and degenerative syndromes, and thus represents an important drug target. Over recent years, the computational or mathematical modelling of biological systems has become increasingly valuable, and there is now a wide variety of mathematical models of the MAPK pathway which have led to some novel insights and predictions as to how this system functions. In the present review we give an overview of the processes involved in modelling a biological system using the popular approach of ordinary differential equations. Focusing on the MAPK pathway, we introduce the features and functions of the pathway itself before comparing the available models and describing what new biological insights they have led to.
Sexual function is crucial for the quality of life and can be highly affected by preoperative therapy and surgery. The aim of this study was to identify potential risk factors for poor sexual ...function and quality of life.
Female patients were asked to complete the Female Sexual Function Index (FSFI-6). Male patients were demanded to answer the International Index of Erectile Function (IIEF-5).
In total, 79 patients filled in the questionary, yielding a response rate of 41.57%. The proportion of women was represented by 32.91%, and the median age was 76.0 years (66.0-81.0). Sexual dysfunction appeared in 88.46% of female patients. Severe erectile dysfunction occurred in 52.83% of male patients. Univariate analysis showed female patients (OR: 0.17, 95%CI: 0.05-0.64,
= 0.01), older age (OR: 0.34, 95%CI 0.11-1.01,
= 0.05), tumor localization under 6cm from the anal verge (OR: 4.43, 95%CI: 1.44-13.67,
= 0.01) and extension of operation (APR and ISR) (OR: 0.13, 95%CI: 0.03-0.59,
= 0.01) as significant risk factors for poor outcome. Female patients (OR: 0.12, 95%CI: 0.03-0.62,
= 0.01) and tumors below 6 cm from the anal verge (OR: 4.64, 95%CI: 1.18-18.29,
= 0.03) were shown to be independent risk factors for sexual dysfunction after multimodal therapy in the multivariate analysis. Quality of life was only affected in the case of extensive surgery (
= 0.02).
Higher Age, female sex, distal tumors and extensive surgery (APR, ISR) are revealed risk factors for SD in this study. Quality of life was only affected in the case of APR or ISR.
The Epidermal Growth Factor Receptor (EGFR) activated Extracellular-signal Regulated Kinase (ERK) pathway is a critical cell signalling pathway that relays the signal for a cell to proliferate from ...the plasma membrane to the nucleus. Deregulation of the EGFR/ERK pathway due to alterations affecting the expression or function of a number of pathway components has long been associated with numerous forms of cancer. Under normal conditions, Epidermal Growth Factor (EGF) stimulates a rapid but transient activation of ERK as the signal is rapidly shutdown. Whereas, under cancerous mutation conditions the ERK signal cannot be shutdown and is sustained resulting in the constitutive activation of ERK and continual cell proliferation. In this study, we have used computational modelling techniques to investigate what effects various cancerous alterations have on the signalling flow through the ERK pathway.
We have generated a new model of the EGFR activated ERK pathway, which was verified by our own experimental data. We then altered our model to represent various cancerous situations such as Ras, B-Raf and EGFR mutations, as well as EGFR overexpression. Analysis of the models showed that different cancerous situations resulted in different signalling patterns through the ERK pathway, especially when compared to the normal EGF signal pattern. Our model predicts that cancerous EGFR mutation and overexpression signals almost exclusively via the Rap1 pathway, predicting that this pathway is the best target for drugs. Furthermore, our model also highlights the importance of receptor degradation in normal and cancerous EGFR signalling, and suggests that receptor degradation is a key difference between the signalling from the EGF and Nerve Growth Factor (NGF) receptors.
Our results suggest that different routes to ERK activation are being utilised in different cancerous situations which therefore has interesting implications for drug selection strategies. We also conducted a comparison of the critical differences between signalling from different growth factor receptors (namely EGFR, mutated EGFR, NGF, and Insulin) with our results suggesting the difference between the systems are large scale and can be attributed to the presence/absence of entire pathways rather than subtle difference in individual rate constants between the systems.
Abstract
Viral infection can activate cytokine expression and trigger cell death. Programmed necrosis, like apoptosis, eliminates pathogen-infected cells as a component of host defense while also ...regulating the function and survival of professional immune cells, including T cells. Receptor-interacting protein kinase (RIPK3) has been shown to mediate programmed necrosis induced by certain viral infections. Deficiency of RIPK3 results in compromised elimination of pathogen-infected cells and increased viral burdens. We present evidence for this effect in mice acutely infected with influenza A virus (IAV). RIPK3-deficient (RKO) mice have significantly increased body weight loss after both mild IAV x31 infection and severe IAV PR8 infections, with decreased survival in the latter case and significantly increased viral loads in the lungs compared to littermate controls. However these effects were primarily observed after day 7 post infection, indicating that regulation of death in the virally-targeted epithelial cell was not the cause of the observed pathogenic phenotype. Indeed, ex-vivo tetramer and ICCS assays showed significantly diminished virus-specific CD8 T cell responses with a reduced frequency of bifunctional IFNγ+ and TNFα+ cells and a lower MFI of IFNγ production by RKO CD8 T cells suggesting that the increased viral loads and weight loss in RKO animals may be a result of reduced T cell activity. Current studies are addressing the role of RIPK3 in regulating T cell function.
Abstract
One important feature of T-cell memory formation is the process of cell death during the contraction phase of the immune response. CD8 T-cell contraction after acute infections is mediated ...by the intrinsic apoptosis pathway, regulated by the interaction of anti-apoptotic BCL2 with pro-apoptotic Bim. In a murine model of influenza A virus infection, we found that Bim-deficient animals experienced a total ablation of the CD8+ T cell contraction phase leading to the significant accumulation of antigen-specific cells. While these cells displayed typical memory phenotypes, in vivo adoptive transfer and in vitro functional studies show that Bim-deficient memory CD8 T cells are non-responsive to stimulation by antigenic peptides and fail to expand properly on secondary challenge, indicating an intrinsic defect of this spent effector population. These functional deficiencies begin to emerge even at the peak of the primary response. Taken together, these results demonstrate that efficient memory generation entails the generation of a distinct, productive memory lineage that is capable of evading Bim-mediated apoptosis.
Abstract
Apoptosis can play a central role in the response to intracellular infections, both in the regulation of innate and adaptive immune responses and in the survival of the pathogen-infected ...cell. We investigated the effect of apoptosis in the response to influenza in various apoptosis deficient mouse models (Bim-/-, Bcl-2 and Akt tg) in vivo. Quantification of CD8 T-cells specific for immunodominant influenza epitopes (DbNP366, Db PA244, KbPB1703) revealed an increase in percentage and absolute CD8+ T cell numbers in the Akt tg, Bcl2 tg and Bim-/- primary, memory and secondary CD8+ T cell responses. The most striking effect was found in the Bim-/- model: a total ablation of the contraction phase after the CD8+ T cell response, leaving the number of flu specific memory CD8+ T cells abnormally high. Surprisingly, the immunodominance hierarchy in the memory Bim-/- response resembles that of a recall response (NP>>PA≈PB1). Their recall potential seemed blunted on a per cell basis compared to recall infections in wildtype mice, but after competitive adoptive transfer, the intrinsic recall division potential between the two memory cell populations was identical. However, Bim-/- CD8 T cells proved to be functionally deficient by cytokine production and effector activity, indicating a defect in the quality of memory. Thus, Bim-/- mediated contraction plays a role in selecting a memory precursor population with effector, rather than division, potential.
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