Characterization of an influenza virus pseudotyped with Ebolavirus glycoprotein

We have produced a new Ebola virus pseudotype: E-S-FLU, which can be handled in biosafety level-1/2 containment for laboratory analysis. E-S-FLU is a single cycle influenza virus coated with Ebolavirus glycoprotein, and it encodes enhanced green fluorescence protein as a reporter that replaces the influenza haemagglutinin. MDCK-SIAT1 cells were transduced to express Ebolavirus glycoprotein as a stable transmembrane protein for E-S-FLU production. Infection of cells by E-S-FLU was dependent on Niemann-Pick C1 protein, which is the well-characterized receptor for Ebola virus entry at the late endosome/lysosome membrane. E-S-FLU was neutralized specifically by anti-Ebola glycoprotein antibody and a variety of small drug molecules that are known to inhibit entry of wild-type Ebola virus. To demonstrate the application of this new Ebola virus pseudotype, we show that a single laboratory batch was sufficient to screen a library (LOPAC®1280 Sigma) of 1280 pharmacologically active compounds for inhibition of virus entry. 215 compounds inhibited E-S-FLU infection, while only 22 inhibited the control H5-S-FLU virus coated in an H5 haemagglutinin. These inhibitory compounds have very dispersed targets and mechanisms of action e.g. calcium channel blockers, estrogen receptor antagonists, anti-histamines, serotonin uptake inhibitors etc. and this correlates with inhibitor screening results with other pseudotypes or wild-type Ebola virus in the literature. E-S-FLU is a new tool for Ebola virus cell entry studies and is easily applied to high throughput screening assays for small molecule inhibitors or antibodies.Importance Ebola virus is from the Filoviridae family and is a biosafety level 4 pathogen. There are no FDA-approved therapeutics for Ebola virus. These characteristics warrant the development of surrogates of Ebola virus that can be handled in more convenient laboratory containment to study the biology of the virus, and screen for inhibitors. Here we characterized a new surrogate named E-S-FLU, that is based on a disabled influenza virus core coated with the Ebola virus surface protein, but does not contain any genetic information from the Ebola virus itself. We show that E-S-FLU uses the same cell entry pathway as wild-type Ebola virus. As an example of the ease of use of E-S-FLU in biosafety level-1/2 containment, we showed that a single production batch could provide enough surrogate virus to screen a standard small molecule library of 1280 candidates for inhibitors of viral entry

Rer1p competes with APH-1 for binding to nicastrin and regulates γ-secretase complex assembly in the early secretory pathway

The γ-secretase complex, consisting of presenilin, nicastrin, presenilin enhancer-2 (PEN-2), and anterior pharynx defective-1 (APH-1) cleaves type I integral membrane proteins like amyloid precursor protein and Notch in a process of regulated intramembrane proteolysis. The regulatory mechanisms governing the multistep assembly of this “proteasome of the membrane” are unknown. We characterize a new interaction partner of nicastrin, the retrieval receptor Rer1p. Rer1p binds preferentially immature nicastrin via polar residues within its transmembrane domain that are also critical for interaction with APH-1. Absence of APH-1 substantially increased binding of nicastrin to Rer1p, demonstrating the competitive nature of these interactions. Moreover, Rer1p expression levels control the formation of γ-secretase subcomplexes and, concomitantly, total cellular γ-secretase activity. We identify Rer1p as a novel limiting factor that negatively regulates γ-secretase complex assembly by competing with APH-1 during active recycling between the endoplasmic reticulum (ER) and Golgi. We conclude that total cellular γ-secretase activity is restrained by a secondary ER control system that provides a potential therapeutic value

NuSAP, a novel microtubule-associated protein involved in mitotic spindle organization

Here, we report on the identification of nucleolar spindle–associated protein (NuSAP), a novel 55-kD vertebrate protein with selective expression in proliferating cells. Its mRNA and protein levels peak at the transition of G2 to mitosis and abruptly decline after cell division. Microscopic analysis of both fixed and live mammalian cells showed that NuSAP is primarily nucleolar in interphase, and localizes prominently to central spindle microtubules during mitosis. Direct interaction of NuSAP with microtubules was demonstrated in vitro. Overexpression of NuSAP caused profound bundling of cytoplasmic microtubules in interphase cells, and this relied on a COOH-terminal microtubule-binding domain. In contrast, depletion of NuSAP by RNA interference resulted in aberrant mitotic spindles, defective chromosome segregation, and cytokinesis. In addition, many NuSAP-depleted interphase cells had deformed nuclei. Both overexpression and knockdown of NuSAP impaired cell proliferation. These results suggest a crucial role for NuSAP in spindle microtubule organization

Presenilin 1 mediates the turnover of telencephalin in hippocampal neurons via an autophagic degradative pathway

Presenilin 1 (PS1) interacts with telencephalin (TLN) and the amyloid precursor protein via their transmembrane domain (Annaert, W.G., C. Esselens, V. Baert, C. Boeve, G. Snellings, P. Cupers, K. Craessaerts, and B. De Strooper. 2001. Neuron. 32:579–589). Here, we demonstrate that TLN is not a substrate for γ-secretase cleavage, but displays a prolonged half-life in PS1−/− hippocampal neurons. TLN accumulates in intracellular structures bearing characteristics of autophagic vacuoles including the presence of Apg12p and LC3. Importantly, the TLN accumulations are suppressed by adenoviral expression of wild-type, FAD-linked and D257A mutant PS1, indicating that this phenotype is independent from γ-secretase activity. Cathepsin D deficiency also results in the localization of TLN to autophagic vacuoles. TLN mediates the uptake of microbeads concomitant with actin and PIP2 recruitment, indicating a phagocytic origin of TLN accumulations. Absence of endosomal/lysosomal proteins suggests that the TLN-positive vacuoles fail to fuse with endosomes/lysosomes, preventing their acidification and further degradation. Collectively, PS1 deficiency affects in a γ-secretase–independent fashion the turnover of TLN through autophagic vacuoles, most likely by an impaired capability to fuse with lysosomes

The PIKfyve complex regulates the early melanosome homeostasis required for physiological amyloid formation

International audienceThe metabolism of PI(3,5)P2 is regulated by the PIKfyve, VAC14 and FIG4 complex,whose mutations are associated with hypopigmentation in mice. These pigmentationdefects indicate a key but yet unexplored physiological relevance of this complex inthe biogenesis of melanosomes. Here we show that PIKfyve activity regulatesformation of amyloid matrix composed of PMEL protein within early endosomes,called stage I melanosomes. PIKfyve activity controls the membrane remodeling ofstage I melanosomes that increases PMEL abundance and impairs its sorting andprocessing. PIKfyve activity also affects stage I melanosome kiss-and-runinteractions with lysosomes that is required for PMEL amyloidogenesis andestablishment of melanosome identity. Mechanistically, PIKfyve activity promotes theformation and membrane tubules from stage I melanosomes and their release bymodulating endosomal actin branching. Together our data indicate that PIKfyveactivity is a key regulator of the melanosomal import-export machinery that fine tunesthe formation of functional amyloid fibrils in melanosomes and the maintenance ofmelanosome identity

A novel strategy for the comprehensive analysis of the biomolecular composition of isolated plasma membranes

A methodology for rapid, high-purity isolation of plasma membranes using superparamagnetic nanoparticles is described. The method is illustrated with high-resolution proteomic, glycomic and lipidomic analyses of presenilin-deficient cells

ATP13A3 is a major component of the enigmatic mammalian polyamine transport system

Polyamines, such as putrescine, spermidine, and spermine, are physiologically important polycations, but the transporters responsible for their uptake in mammalian cells remain poorly characterized. Here, we reveal a new component of the mammalian polyamine transport system using CHO-MG cells, a widely used model to study alternative polyamine uptake routes and characterize polyamine transport inhibitors for therapy. CHO-MG cells present polyamine uptake deficiency and resistance to a toxic polyamine biosynthesis inhibitor methylglyoxal bis-(guanylhydrazone) (MGBG), but the molecular defects responsible for these cellular characteristics remain unknown. By genome sequencing of CHO-MG cells, we identified mutations in an unexplored gene, ATP13A3, and found disturbed mRNA and protein expression. ATP13A3 encodes for an orphan P5B-ATPase (ATP13A3), a P-type transport ATPase that represents a candidate polyamine transporter. Interestingly, ATP13A3 complemented the putrescine transport deficiency and MGBG resistance of CHO-MG cells, whereas its knockdown in WT cells induced a CHO-MG phenotype demonstrated as a decrease in putrescine uptake and MGBG sensitivity. Taken together, our findings identify ATP13A3, which has been previously genetically linked with pulmonary arterial hypertension, as a major component of the mammalian polyamine transport system that confers sensitivity to MGBG

A novel approach to analyze lysosomal dysfunctions through subcellular proteomics and lipidomics : the case of NPC1 deficiency

Superparamagnetic iron oxide nanoparticles (SPIONs) have mainly been used as cellular carriers for genes and therapeutic products, while their use in subcellular organelle isolation remains underexploited. We engineered SPIONs targeting distinct subcellular compartments. Dimercaptosuccinic acid-coated SPIONs are internalized and accumulate in late endosomes/lysosomes, while aminolipid-SPIONs reside at the plasma membrane. These features allowed us to establish standardized magnetic isolation procedures for these membrane compartments with a yield and purity permitting proteomic and lipidomic profiling. We validated our approach by comparing the biomolecular compositions of lysosomes and plasma membranes isolated from wild-type and Niemann-Pick disease type C1 (NPC1) deficient cells. While the accumulation of cholesterol and glycosphingolipids is seen as a primary hallmark of NPC1 deficiency, our lipidomics analysis revealed the buildup of several species of glycerophospholipids and other storage lipids in selectively late endosomes/lysosomes of NPC1-KO cells. While the plasma membrane proteome remained largely invariable, we observed pronounced alterations in several proteins linked to autophagy and lysosomal catabolism reflecting vesicular transport obstruction and defective lysosomal turnover resulting from NPC1 deficiency. Thus the use of SPIONs provides a major advancement in fingerprinting subcellular compartments, with an increased potential to identify disease-related alterations in their biomolecular compositions