Biology subjects

Smith, G. L.

Publications and source records attributed to Smith, G. L..

25 records · Page 2Linked to original sources

bioRxiv2020

Novel role for ESCRT-III component CHMP4C in the integrity of the endocytic network utilized for herpes simplex virus envelopment

Enveloped viruses exploit cellular trafficking pathways for their morphogenesis, providing potential scope for the development of new antiviral therapies. We have previously shown that herpes simplex virus 1 (HSV1) utilises recycling endocytic membranes as the source of its envelope, in a process involving four Rab GTPases. To identify novel factors involved in HSV1 envelopment, we have screened an siRNA library targeting over eighty human trafficking proteins including coat proteins, adaptor proteins, fusion factors, fission factors and Rab effectors. Depletion of eleven factors reduced virus yield by 20- to 100-fold, including three early secretory pathway proteins; four late secretory pathway proteins; and four endocytic pathway proteins, three of which are membrane fission factors. Five of the eleven targets were chosen for further analysis in virus infection where it was found that the absence of only one, the fission factor CHMP4C, known for its role in the cytokinesis checkpoint, specifically reduced virus production at the final stage of morphogenesis. Ultrastructural and confocal microscopy of CHMP4C-depleted, HSV1-infected cells, showed an accumulation of endocytic membranes; extensive tubulation of recycling, transferrin receptor-positive endosomes indicative of aberrant fission; and a failure in virus envelopment. No effect on the late endocytic pathway was detected, while exogenous CHMP4C was shown to localise to recycling endosomes. Taken together, these data reveal a novel role for the CHMP4C fission factor in the integrity of the recycling endosomal network, which has been unveiled through the dependence of HSV1 on these membranes for the acquisition of their envelopes. ImportanceCellular transport pathways play a fundamental role in secretion and membrane biogenesis. Enveloped viruses exploit these pathways to direct their membrane proteins to sites of envelopment, and as such, are powerful tools for unravelling subtle activities of trafficking factors, potentially pinpointing therapeutic targets. Using the sensitive biological readout of virus production, over eighty trafficking factors involved in diverse and poorly defined cellular processes have been screened for involvement in the complex process of HSV1 envelopment. Out of eleven potential targets, CHMP4C - a key component in the cell-cycle abscission checkpoint - stood out as being required for the physical process of virus wrapping in endocytic tubules, where it was shown to localise. In the absence of CHMP4C, recycling endocytic membranes failed to undergo scission, causing transient tubulation and accumulation of membranes and unwrapped virus. These data reveal a new role for this important cellular factor in the biogenesis of recycling endocytic membranes.

cell biology↗

bioRxiv2020

DDX50 is a viral restriction factor thay enhances TRIF-dependent IRF3 activation

The transcription factors IRF3 and NF-{kappa}B are crucial in innate immune signalling in response to many viral and bacterial pathogens. However, mechanisms leading to their activation remain incompletely understood. Canonical RLR signalling and detection of viral RNA is dependent upon the receptors RIG-I, MDA5 and TLR3. Alternatively, the DExD-Box RNA helicases DDX1-DDX21-DHX36 activate IRF3/NF-{kappa}B in a TRIF-dependent manner independent of RIG-I, MDA5 or TLR3. Here we describe DDX50, which shares 55.6% amino acid identity with DDX21, as a component of the dsRNA sensing machinery and signalling pathway. Deletion of DDX50 in mouse and human cells impaired activation of the IFN{beta} promoter, IRF3-dependent endogenous gene expression and cytokine/chemokine production in response to cytoplasmic dsRNA (polyIC transfection), and infection by RNA and DNA viruses. Mechanistically, DDX50 co-immunoprecipitated with TRIF and DDX1, promoting complex formation upon stimulation. Furthermore, whilst MAVs/TBK1 induced signalling is intact in Ddx50 KO cells, TRIF-dependent signalling was impaired suggesting DDX50 drives TRIF-dependent Ifn{beta} transcription. Importantly, loss of DDX50 resulted in increased replication and dissemination of vaccinia virus, herpes simplex virus and Zika virus highlighting its important role as a viral restriction factor. Author summaryThe detection of viral RNA or DNA by host RNA or DNA sensors and the subsequent antiviral immune response are crucial for the outcome of infection and host survival in response to a multitude of viral pathogens. Detection of viral RNA or DNA culminates in the upregulation of inflammatory cytokines, chemokines and pathogen restriction factors that augment the host innate immune response, restrict viral replication and clear infection. The canonical RNA sensor RIG-I is a member of the large family of DExD/H-box helicases, however the biological role of many DExD/H-box helicases remain unknown. In this report, we describe the DExD-Box helicase DDX50 as a new component of the RNA sensing machinery. In response to DNA and RNA virus infection, DDX50 functions to enhance activation of the transcription factor IRF3, which enhances antiviral signalling. The biological importance of DDX50 is illustrated by its ability to restrict the establishment of viral infection and to diminish the yields of vaccinia virus, herpes simplex virus and Zika virus. These findings increase knowledge of the poorly characterised host protein DDX50 and add another factor to the intricate network of proteins involved in regulating antiviral signalling in response to infection.

immunology↗

bioRxiv2019

Golgi anti-apoptotic proteins are evolutionarily conserved ion channels that regulate cell death in plants

Programmed cell death regulates developmental and stress responses in eukaryotes. Golgi anti-apoptotic proteins (GAAPs) are evolutionarily conserved cell death regulators. Human and viral GAAPs inhibit apoptosis and modulate intracellular Ca2+ fluxes, and viral GAAPs form cation-selective channels. Although most mammalian cell death regulators are not conserved at the sequence level in plants, the GAAP gene family shows expansion, with five paralogues (AtGAAP1-5) in the Arabidopsis genome. We pursued molecular and physiological characterization of AtGAAPs making use of the advanced knowledge of their human and viral counterparts. Structural modeling of AtGAAPs predicted the presence of a channel-like pore, and electrophysiological recordings from purified AtGAAP3 reconstituted into lipid bilayers confirmed that plant GAAPs can function as ion channels. AtGAAP1 and AtGAAP4 localized exclusively to the Golgi within the plant cell, while AtGAAP2, AtGAAP3 and AtGAAP5 also showed tonoplastic localization. Gene expression analysis revealed differential spatial expression and abundance of transcript for AtGAAP paralogues in Arabidopsis tissues. We demonstrate that AtGAAP1-5 inhibit Bax-induced cell death in yeast. However, overexpression of AtGAAP1 induces cell death in Nicotiana benthamiana leaves and lesion mimic phenotype in Arabidopsis. We propose that AtGAAPs function as Golgi-localized ion channels that regulate cell death by affecting ionic homeostasis within the cell. HighlightArabidopsis Golgi anti-apoptotic proteins (GAAPs) share functional conservation with their human and viral counterparts in cell death regulation and ion channel activity AbbreviationsAtGAAP, Arabidopsis thaliana GAAP; BI-1, Bax inhibitor-1; CFP, cyan fluorescent protein; CMLV, camelpox virus; ER, Endoplasmic reticulum; GAAP, Golgi anti-apoptotic protein; GFP, green fluorescent protein; hGAAP, human GAAP; LFG, Lifeguard; LMM, lesion mimic mutant; PCD, programmed cell death; TMBIM, transmembrane Bax inhibitor-1 motif-containing; TMDs, transmembrane domains; vGAAP, viral GAAP; YFP, yellow fluorescent protein

plant biology↗

bioRxiv2019

Enhanced efficacy of vaccination with vaccinia virus in old versus young mice

Immunosenescence is believed to be responsible for poor vaccine efficacy in the elderly. To overcome this difficulty, research into vaccination strategies and the mechanisms of immune responses to vaccination is required. By analyzing the innate and adaptive immune responses to vaccination with vaccinia virus (VACV) in mice of different age groups, we found that immune cell recruitment, production of cytokines/chemokines and control of viral replication at the site of intradermal vaccination were preserved in aged mice and were comparable with younger groups. Analysis of cervical draining lymph nodes (dLN) collected after vaccination showed that numbers of germinal center B cells and follicular T helper cells were similar across different age groups. The number of VACV-specific CD8 T cells in the spleen and the levels of serum neutralizing antibodies 1 month after vaccination were also comparable across all age groups. However, following intranasal challenge of vaccinated mice, body weight loss was lower and virus was cleared more rapidly in aged mice than in younger animals. In conclusion, vaccination with VACV can induce an effective immune response and stronger protection in elderly animals. Thus, the development of recombinant VACV-based vaccines against different infectious diseases should be considered as a strategy for improving vaccine immunogenicity and efficacy in the elderly.

immunology↗

bioRxiv2019

GLUT4 expression and glucose transport in human induced pluripotent stem cell-derived cardiomyocytes

Induced pluripotent stem cell derived cardiomyocytes (iPSC-CM) have the potential to transform regenerative cardiac medicine and the modelling of cardiac disease. This is of particular importance in the context of diabetic cardiomyopathy where diabetic individuals exhibit reduced cardiac diastolic contractile performance in the absence of vascular disease, significantly contributing towards high cardiovascular morbidity. In this study, the capacity of iPSC-CM to act as a novel cellular model of cardiomyocytes was assessed. The diabetic phenotype is characterised by insulin resistance, therefore there was a specific focus upon metabolic parameters. Despite expressing crucial insulin signalling intermediates and relevant trafficking proteins, it was identified that iPSC-CM do not exhibit insulin-stimulated glucose uptake. iPSC-CM are spontaneously contractile however contraction mediated uptake was not found to mask any insulin response. The fundamental limitation identified in these cells was a critical lack of expression of the insulin sensitive glucose transporter GLUT4. Using comparative immunoblot analysis and the GLUT-selective inhibitor BAY-876 to quantify expression of these transporters, we show that iPSC-CM express high levels of GLUT1 and low levels of GLUT4 compared to primary cardiomyocytes and cultured adipocytes. Interventions to overcome this limitation were unsuccessful. We suggest that the utility of iPSC-CMs to study cardiac metabolic disorders may be limited by their apparent foetal-like phenotype.

biochemistry↗

bioRxiv2018

Molecular basis of Cul3 ubiquitin ligase subversion by vaccinia virus protein A55

BTB-Kelch proteins are substrate-specific adaptors for cullin-3 (Cul3) RING-box based E3 ubiquitin ligases, which mediate protein ubiquitylation leading to proteasomal degradation. Vaccinia virus encodes three BTB-Kelch proteins, namely A55, C2 and F3. Viruses lacking A55 or C2 demonstrate altered cytopathic effect in cultured cells and altered pathology in vivo. Previous studies show that the ectromelia virus orthologue of A55, EVM150, interacts with Cul3 in cells. We show that A55 binds directly to Cul3 via its N-terminal BTB-BACK domain, and together they form a 2:2 complex in solution. The crystal structure of the A55/Cul3 complex was solved to 2.8 [A] resolution. The overall conformation and binding interfaces resemble those of the cellular BTB-BACK/Cul3 complex structures, despite low sequence similarity of A55 to cellular BTB-BACK proteins. Surprisingly, despite this structural similarity the affinity of Cul3 for A55 is significantly higher than for reported cellular BTB-BACK proteins. Detailed analysis of the binding interface suggests that I48 from A55 at the BTB/Cul3 interface is important for this high-affinity interaction and mutation at this site reduced the affinity by several orders of magnitude. I48 is conserved only in close orthologues of A55 from poxviruses, but not in C2, F3, or other poxvirus or cellular BTB-Kelch proteins. The high affinity interaction between A55 and Cul3 suggests that, in addition to directing the Cul3-RING E3 ligase complex to degrade cellular/viral target proteins that are normally unaffected, A55 may also sequester Cul3 from cellular adaptor proteins and thus protect substrates of these cellular adaptors from ubiquitination and degradation.

biochemistry↗

bioRxiv2017

Versatile open software to quantify cardiomyocyte and cardiac muscle contraction in vitro and in vivo

Contraction of muscle reflects its physiological state. Methods to quantify contraction are often complex, expensive and tailored to specific models or recording conditions, or require specialist knowledge for data extraction. Here we describe an automated, open-source software tool (MUSCLEMOTION) adaptable for use with standard laboratory and clinical imaging equipment that enables quantitative analysis of normal cardiac contraction, disease phenotypes and pharmacological responses. MUSCLEMOTION allowed rapid and easy measurement of contractility in (i) single cardiomyocytes from primary adult heart and human pluripotent stem cells, (ii) multicellular 2D-cardiomyocyte cultures, 3D engineered heart tissues and cardiac organoids/microtissues in vitro and (iii) intact hearts of zebrafish and humans in vivo. Good correlation was found with conventional measures of contraction in each system. Thus, using a single method for processing video recordings, we obtained reliable pharmacological data and measures of cardiac disease phenotype in experimental cell- and animal models and human echocardiograms.

physiology↗