The molecular basis for retention of integral membrane proteins in the endoplasmic reticulum (ER) is not well understood. We recently discovered a novel ER molecular chaperone termed Cosmc, which is essential for folding and normal activity of the Golgi enzyme T-synthase. Cosmc, a type II single-pass transmembrane protein, lacks any known ER retrieval/retention motifs. To explore specific ER localization determinants in Cosmc we generated a series of Cosmc mutants along with chimeras of Cosmc with a non-ER resident type II protein, the human transferrin receptor. Here we show that the 18 amino acid transmembrane domain (TMD) of Cosmc is essential for ER localization and confers ER retention to select chimeras. Moreover, mutations of a single Cys residue within the TMD of Cosmc prevent formation of disulfide-bonded dimers of Cosmc and eliminate ER retention. These studies reveal that Cosmc has a unique ER-retention motif within its TMD and provide new insights into the molecular mechanisms by which TMDs of resident ER proteins contribute to ER localization.
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Thomas Kukar;
Thomas B. Ladd;
Paul Robertson;
Sean A. Pintchovski;
Brenda Moore;
Maralyssa A. Bann;
Zhao Ren;
Karen Jansen-West;
Kim Malphrus;
Simone Eggert;
Hiroko Maruyama;
Barbara A. Cottrell;
Pritam Das;
Guriqbal S. Basi;
Edward H. Koo;
Todd E. Golde
Background: γ-Secretase modulators (GSMs) bind APP near lysine 624.
Results: Mutation of lysine 624 shifts cleavage toward smaller Aβ with no effect on ϵ cleavage.
Conclusion: The amino acid at 624 in substrates affects the final γ-secretase cut.
Significance: γ-Secretase cleavage likely begins at ϵ and proceeds up the transmembrane until Aβ is released, and GSMs may modulate this process through lysine 624.
Hepatitis C virus (HCV) entry into permissive cells is a complex process that involves interactions with at least four co-factors followed by endocytosis and low pH-dependent fusion with endosomes. The precise sequence of receptor engagement and their roles in promoting HCV E1E2 glycoprotein-mediated fusion are poorly characterized. Because cell-free HCV tolerates an acidic environment, we hypothesized that binding to one or more receptors on the cell surface renders E1E2 competent to undergo low pH-induced conformational changes and promote fusion with endosomes. To test this hypothesis, we examined the effects of low pH and of the second extracellular loop (ECL2) of CD81, one of the four entry factors, on HCV infectivity. Pretreatment with an acidic buffer or with ECL2 enhanced infection through changing the E1E2 conformation, as evidenced by the altered reactivity of these proteins with conformation-specific antibodies and stable association with liposomes. However, neither of the two treatments alone permitted direct fusion with the cell plasma membrane. Sequential HCV preincubation with ECL2 and acidic buffer in the absence of target cells resulted in a marked loss of infectivity, implying that the receptor-bound HCV is primed for low pH-dependent conformational changes. Indeed, soluble receptor-pretreated HCV fused with the cell plasma membrane at low pH under conditions blocking an endocytic entry pathway. These findings suggest that CD81 primes HCV for low pH-dependent fusion early in the entry process. The simple triggering paradigm and intermediate conformations of E1E2 identified in this study could help guide future vaccine and therapeutic efforts to block HCV infection.
Background: Plasmodium knowlesi is one of five Plasmodium species known to cause malaria in humans and can result in severe illness and death. While a zoonosis in humans, this simian malaria parasite species infects macaque monkeys and serves as an experimental model for in vivo, ex vivo and in vitro studies. It has underpinned malaria discoveries relating to host-pathogen interactions, the immune response and immune evasion strategies. This study investigated differences in P. knowlesi gene expression in samples from ex vivo and in vitro cultures. Methods: Gene expression profiles were generated using microarrays to compare the stage-specific transcripts detected for a clone of P. knowlesi propagated in the blood of a rhesus macaque host and then grown in an ex-vivo culture, and the same clone adapted to long-term in vitro culture. Parasite samples covering one blood-stage cycle were analysed at four-hour intervals. cDNA was generated and hybridized to an oligoarray representing the P. knowlesi genome. Two replicate experiments were developed from in vitro cultures. Expression values were filtered, normalized, and analysed using R and Perl language and applied to a sine wave model to determine changes in equilibrium and amplitude. Differentially expressed genes from ex vivo and in vitro time points were detected using limma R/Bioconductor and gene set enrichment analysis (GSEA). Results: Major differences were noted between the ex vivo and in vitro time courses in overall gene expression and the length of the cycle (25.5 hours ex vivo; 33.5 hours in vitro). GSEA of genes up-regulated ex vivo showed an enrichment of various genes including SICAvar, ribosomal- associated and histone acetylation pathway genes. In contrast, certain genes involved in metabolism and cell growth, such as porphobilinogen deaminase and tyrosine phosphatase, and one SICAvar gene, were significantly up-regulated in vitro. Conclusions: This study demonstrates how gene expression in P. knowlesi blood-stage parasites can differ dramatically depending on whether the parasites are grown in vivo, with only one cycle of development ex vivo, or as an adapted isolate in long-term in vitro culture. These data bring emphasis to the importance of studying the parasite, its biology and disease manifestations in the context of the host.
Background: Cargo proteins recruit Arf-dependent adaptors for packaging.
Results: Cargo presence at the Golgi/endosomes leads to specific adaptor recruitment.
Conclusion: Arf activation is more closely coupled to cargo than previously appreciated, and we interpret the specificity in adaptor recruitment as evidence of the lack of freely diffusible activated Arfs.
Significance: Cargos play a role in the activation of Arfs and recruitment of specific adaptors.
Background: Regulation of virus entry by host lipids is poorly understood.
Results: Imaging of low pH-mediated fusion between single vesicular stomatitis pseudoviruses and lipid bilayers revealed a striking reliance on anionic lipids.
Conclusion: The dependence of fusion on late endosome-resident anionic lipids suggests a new means for regulating the virus entry sites.
Significance: Reliance on specific lipids for fusion may shed light on future antiviral strategies.
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David T. Selewski;
David J. Askenazi;
Brian C. Bridges;
David S. Cooper;
Geoffrey M. Fleming;
Matthew Paden;
Mark Verway;
Rashmi Sahay;
Eileen King;
Michael Zappitelli
Objective: To characterize the epidemiology of fluid overload and its association with mortality and duration of extracorporeal membrane oxygenation in children treated with extracorporeal membrane oxygenation. Design: Retrospective cohort study. Setting: Six tertiary children's hospital ICUs. Patients: Seven hundred fifty-six children younger than 18 years old treated with extracorporeal membrane oxygenation for greater than or equal to 24 hours from January 1, 2007, to December 31, 2011. Interventions: None. Measurements and Main Results: Overall survival to extracorporeal membrane oxygenation decannulation and hospital discharge was 74.9% (n = 566) and 57.7% (n = 436), respectively. Median fluid overload at extracorporeal membrane oxygenation initiation was 8.8% (interquartile range, 0.3-19.2), and it differed between hospital survivors and non survival, though not between extracorporeal membrane oxygenation survivors and non survivors. Median peak fluid overload on extracorporeal membrane oxygenation was 30.9% (interquartile range, 15.4-54.8). During extracorporeal membrane oxygenation, 84.8% had a peak fluid overload greater than or equal to 10%; 67.2% of patients had a peak fluid overload of greater than or equal to 20% and 29% of patients had a peak fluid overload of greater than or equal to 50%. The median peak fluid overload was lower in patients who survived on extracorporeal membrane oxygenation (27.2% vs 44.4%; p < 0.0001) and survived to hospital discharge (24.8% vs 43.3%; p < 0.0001). After adjusting for acute kidney injury, pH at extracorporeal membrane oxygenation initiation, nonrenal complications, extracorporeal membrane oxygenation mode, support type, center and patient age, the degree of fluid overload at extracorporeal membrane oxygenation initiation (p = 0.05), and the peak fluid overload on extracorporeal membrane oxygenation (p < 0.0001) predicted duration of extracorporeal membrane oxygenation in survivors. Multivariable analysis showed that peak fluid overload on extracorporeal membrane oxygenation (adjusted odds ratio, 1.09; 95% CI, 1.04-1.15) predicted mortality on extracorporeal membrane oxygenation; fluid overload at extracorporeal membrane oxygenation initiation (adjusted odds ratio, 1.13; 95% CI, 1.05-1.22) and peak fluid overload (adjusted odds ratio, 1.18; 95% CI, 1.12-1.24) both predicted hospital morality. Conclusions: Fluid overload occurs commonly and is independently associated with adverse outcomes including increased mortality and increased duration of extracorporeal membrane oxygenation in a broad pediatric extracorporeal membrane oxygenation population. These results suggest that fluid overload is a potential target for intervention to improve outcomes in children on extracorporeal membrane oxygenation.
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Vera Rocha-Perugini;
Henar Suarez;
Susana Alvarez;
Soraya Lopez-Martin;
Gina M. Lenzi;
Felipe Vences-Catalan;
Shoshana Levy;
Baek Kim;
María A. Munoz-Fernandez;
Francisco Sanchez-Madrid;
Maria Yanez-Mo
In this study, we report that the tetraspanin CD81 enhances human immunodeficiency virus (HIV)-1 reverse transcription in HIV-1-infected cells. This is enabled by the direct interaction of CD81 with the deoxynucleoside triphosphate phosphohydrolase SAMHD1. This interaction prevents endosomal accumulation and favours the proteasome-dependent degradation of SAMHD1. Consequently, CD81 depletion results in SAMHD1 increased expression, decreasing the availability of deoxynucleoside triphosphates (dNTP) and thus HIV-1 reverse transcription. Conversely, CD81 overexpression, but not the expression of a CD81 carboxy (C)-terminal deletion mutant, increases cellular dNTP content and HIV-1 reverse transcription. Our results demonstrate that the interaction of CD81 with SAMHD1 controls the metabolic rate of HIV-1 replication by tuning the availability of building blocks for reverse transcription, namely dNTPs. Together with its role in HIV-1 entry and budding into host cells, the data herein indicate that HIV-1 uses CD81 as a rheostat that controls different stages of the infection.
Patch-clamp recording has enabled single-cell electrical, morphological and genetic studies at unparalleled resolution. Yet it remains a laborious and low-throughput technique, making it largely impractical for large-scale measurements such as cell type and connectivity characterization of neurons in the brain. Specifically, the technique is critically limited by the ubiquitous practice of manually replacing patch-clamp pipettes after each recording. To circumvent this limitation, we developed a simple, fast, and automated method for cleaning glass pipette electrodes that enables their reuse within one minute. By immersing pipette tips into Alconox, a commercially-available detergent, followed by rinsing, we were able to reuse pipettes 10 times with no degradation in signal fidelity, in experimental preparations ranging from human embryonic kidney cells to neurons in culture, slices, and in vivo. Undetectable trace amounts of Alconox remaining in the pipette after cleaning did not affect ion channel pharmacology. We demonstrate the utility of pipette cleaning by developing the first robot to perform sequential patch-clamp recordings in cell culture and in vivo without a human operator.