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Intracellular Degradation of Helicobacter pylori VacA Toxin as a Determinant of Gastric Epithelial Cell Viability.
Foegeding NJ, Raghunathan K, Campbell AM, Kim SW, Lau KS, Kenworthy AK, Cover TL, Ohi MD
(2019) Infect Immun 87:
MeSH Terms: Autophagy, Bacterial Proteins, Cell Line, Cell Survival, Epithelial Cells, Gastric Mucosa, Helicobacter Infections, Helicobacter pylori, Humans, Hydrogen-Ion Concentration, Muramidase, Protein Stability, Protein Transport, Proteolysis
Show Abstract · Added February 7, 2019
VacA is a secreted pore-forming toxin that induces cell vacuolation and contributes to the pathogenesis of gastric cancer and peptic ulcer disease. We observed that purified VacA has relatively little effect on the viability of AGS gastric epithelial cells, but the presence of exogenous weak bases such as ammonium chloride (NHCl) enhances the susceptibility of these cells to VacA-induced vacuolation and cell death. Therefore, we tested the hypothesis that NHCl augments VacA toxicity by altering the intracellular trafficking of VacA or inhibiting intracellular VacA degradation. We observed VacA colocalization with LAMP1- and LC3-positive vesicles in both the presence and absence of NHCl, indicating that NHCl does not alter VacA trafficking to lysosomes or autophagosomes. Conversely, we found that supplemental NHCl significantly increases the intracellular stability of VacA. By conducting experiments using chemical inhibitors, stable ATG5 knockdown cell lines, and ATG16L1 knockout cells (generated using CRISPR/Cas9), we show that VacA degradation is independent of autophagy and proteasome activity but dependent on lysosomal acidification. We conclude that weak bases like ammonia, potentially generated during infection by urease and other enzymes, enhance VacA toxicity by inhibiting toxin degradation.
Copyright © 2019 American Society for Microbiology.
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14 MeSH Terms
An alternative N-terminal fold of the intestine-specific annexin A13a induces dimerization and regulates membrane-binding.
McCulloch KM, Yamakawa I, Shifrin DA, McConnell RE, Foegeding NJ, Singh PK, Mao S, Tyska MJ, Iverson TM
(2019) J Biol Chem 294: 3454-3463
MeSH Terms: Animals, Annexins, Cell Membrane, Epithelial Cells, Humans, Hydrogen-Ion Concentration, Intestinal Mucosa, Intestines, Liposomes, Mice, Models, Molecular, Organ Specificity, Protein Binding, Protein Conformation, alpha-Helical, Protein Multimerization, Protein Structure, Quaternary, Protein Transport
Show Abstract · Added April 1, 2019
Annexin proteins function as Ca-dependent regulators of membrane trafficking and repair that may also modulate membrane curvature. Here, using high-resolution confocal imaging, we report that the intestine-specific annexin A13 (ANX A13) localizes to the tips of intestinal microvilli and determined the crystal structure of the ANX A13a isoform to 2.6 Å resolution. The structure revealed that the N terminus exhibits an alternative fold that converts the first two helices and the associated helix-loop-helix motif into a continuous α-helix, as stabilized by a domain-swapped dimer. We also found that the dimer is present in solution and partially occludes the membrane-binding surfaces of annexin, suggesting that dimerization may function as a means for regulating membrane binding. Accordingly, as revealed by binding and cellular localization assays, ANX A13a variants that favor a monomeric state exhibited increased membrane association relative to variants that favor the dimeric form. Together, our findings support a mechanism for how the association of the ANX A13a isoform with the membrane is regulated.
© 2019 McCulloch et al.
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17 MeSH Terms
Loss of MYO5B Leads to Reductions in Na Absorption With Maintenance of CFTR-Dependent Cl Secretion in Enterocytes.
Engevik AC, Kaji I, Engevik MA, Meyer AR, Weis VG, Goldstein A, Hess MW, Müller T, Koepsell H, Dudeja PK, Tyska M, Huber LA, Shub MD, Ameen N, Goldenring JR
(2018) Gastroenterology 155: 1883-1897.e10
MeSH Terms: Animals, Aquaporins, Chlorides, Cystic Fibrosis Transmembrane Conductance Regulator, Duodenum, Enterocytes, Gene Silencing, Humans, Intestinal Mucosa, Intestines, Malabsorption Syndromes, Mice, Mice, Knockout, Microvilli, Mucolipidoses, Myosin Type V, Protein Transport, Sodium-Glucose Transporter 1, Sodium-Hydrogen Exchanger 3, Sodium-Hydrogen Exchangers, Sucrase-Isomaltase Complex, Tamoxifen
Show Abstract · Added February 7, 2019
BACKGROUND & AIMS - Inactivating mutations in MYO5B cause microvillus inclusion disease (MVID), but the physiological cause of the diarrhea associated with this disease is unclear. We investigated whether loss of MYO5B results in aberrant expression of apical enterocyte transporters.
METHODS - We studied alterations in apical membrane transporters in MYO5B-knockout mice, as well as mice with tamoxifen-inducible, intestine-specific disruption of Myo5b (VilCre;Myo5b mice) or those not given tamoxifen (controls). Intestinal tissues were collected from mice and analyzed by immunostaining, immunoelectron microscopy, or cultured enteroids were derived. Functions of brush border transporters in intestinal mucosa were measured in Ussing chambers. We obtained duodenal biopsy specimens from individuals with MVID and individuals without MVID (controls) and compared transporter distribution by immunocytochemistry.
RESULTS - Compared to intestinal tissues from littermate controls, intestinal tissues from MYO5B-knockout mice had decreased apical localization of SLC9A3 (also called NHE3), SLC5A1 (also called SGLT1), aquaporin (AQP) 7, and sucrase isomaltase, and subapical localization of intestinal alkaline phosphatase and CDC42. However, CFTR was present on apical membranes of enterocytes from MYO5B knockout and control mice. Intestinal biopsies from patients with MVID had subapical localization of NHE3, SGLT1, and AQP7, but maintained apical CFTR. After tamoxifen administration, VilCre;Myo5b mice lost apical NHE3, SGLT1, DRA, and AQP7, similar to germline MYO5B knockout mice. Intestinal tissues from VilCre;Myo5b mice had increased CFTR in crypts and CFTR localized to the apical membranes of enterocytes. Intestinal mucosa from VilCre;Myo5b mice given tamoxifen did not have an intestinal barrier defect, based on Ussing chamber analysis, but did have decreased SGLT1 activity and increased CFTR activity.
CONCLUSIONS - Although trafficking of many apical transporters is regulated by MYO5B, trafficking of CFTR is largely independent of MYO5B. Decreased apical localization of NHE3, SGLT1, DRA, and AQP7 might be responsible for dysfunctional water absorption in enterocytes of patients with MVID. Maintenance of apical CFTR might exacerbate water loss by active secretion of chloride into the intestinal lumen.
Copyright © 2018 AGA Institute. Published by Elsevier Inc. All rights reserved.
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Functional features of the "finger" domain of the DEG/ENaC channels MEC-4 and UNC-8.
Matthewman C, Johnson CK, Miller DM, Bianchi L
(2018) Am J Physiol Cell Physiol 315: C155-C163
MeSH Terms: Amino Acid Sequence, Animals, Calcium, Cell Death, Cell Membrane Permeability, Epithelial Sodium Channels, Magnesium, Membrane Proteins, Mutation, Oocytes, Protein Transport, Sodium, Xenopus laevis
Show Abstract · Added March 26, 2019
UNC-8 and MEC-4 are two members of the degenerin/epithelial Na channel (DEG/ENaC) family of voltage-independent Na channels that share a high degree of sequence homology and functional similarity. For example, both can be hyperactivated by genetic mutations [UNC-8(d) and MEC-4(d)] that induce neuronal death by necrosis. Both depend in vivo on chaperone protein MEC-6 for function, as demonstrated by the finding that neuronal death induced by hyperactive UNC-8 and MEC-4 channels is prevented by null mutations in mec-6. UNC-8 and MEC-4 differ functionally in three major ways: 1) MEC-4 is calcium permeable, whereas UNC-8 is not; 2) UNC-8, but not MEC-4, is blocked by extracellular calcium and magnesium in the micromolar range; and 3) MEC-6 increases the number of MEC-4 channels at the cell surface in oocytes but does not have this effect on UNC-8. We previously reported that Capermeability of MEC-4 is conferred by the second transmembrane domain. We show here that the extracellular "finger" domain of UNC-8 is sufficient to mediate inhibition by divalent cations and that regulation by MEC-6 also depends on this region. Thus, our work confirms that the finger domain houses residues involved in gating of this channel class and shows for the first time that the finger domain also mediates regulation by chaperone protein MEC-6. Given that the finger domain is the most divergent region across the DEG/ENaC family, we speculate that it influences channel trafficking and function in a unique manner depending on the channel subunit.
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13 MeSH Terms
Chronic kidney disease alters lipid trafficking and inflammatory responses in macrophages: effects of liver X receptor agonism.
Kaseda R, Tsuchida Y, Yang HC, Yancey PG, Zhong J, Tao H, Bian A, Fogo AB, Linton MRF, Fazio S, Ikizler TA, Kon V
(2018) BMC Nephrol 19: 17
MeSH Terms: Adult, Aged, Biological Transport, Female, Humans, Hydrocarbons, Fluorinated, Inflammation Mediators, Lipoproteins, HDL, Lipoproteins, LDL, Liver X Receptors, Macrophages, Male, Middle Aged, Protein Transport, Renal Insufficiency, Chronic, Sulfonamides, THP-1 Cells
Show Abstract · Added April 10, 2018
BACKGROUND - Our aim was to evaluate lipid trafficking and inflammatory response of macrophages exposed to lipoproteins from subjects with moderate to severe chronic kidney disease (CKD), and to investigate the potential benefits of activating cellular cholesterol transporters via liver X receptor (LXR) agonism.
METHODS - LDL and HDL were isolated by sequential density gradient ultracentrifugation of plasma from patients with stage 3-4 CKD and individuals without kidney disease (HDL and HDL, respectively). Uptake of LDL, cholesterol efflux to HDL, and cellular inflammatory responses were assessed in human THP-1 cells. HDL effects on inflammatory markers (MCP-1, TNF-α, IL-1β), Toll-like receptors-2 (TLR-2) and - 4 (TLR-4), ATP-binding cassette class A transporter (ABCA1), NF-κB, extracellular signal regulated protein kinases 1/2 (ERK1/2) were assessed by RT-PCR and western blot before and after in vitro treatment with an LXR agonist.
RESULTS - There was no difference in macrophage uptake of LDL isolated from CKD versus controls. By contrast, HD was significantly less effective than HDL in accepting cholesterol from cholesterol-enriched macrophages (median 20.8% [IQR 16.1-23.7] vs control (26.5% [IQR 19.6-28.5]; p = 0.008). LXR agonist upregulated ABCA1 expression and increased cholesterol efflux to HDL of both normal and CKD subjects, although the latter continued to show lower efflux capacity. HDL increased macrophage cytokine response (TNF-α, MCP-1, IL-1β, and NF-κB) versus HDL. The heightened cytokine response to HDL was further amplified in cells treated with LXR agonist. The LXR-augmentation of inflammation was associated with increased TLR-2 and TLR-4 and ERK1/2.
CONCLUSIONS - Moderate to severe impairment in kidney function promotes foam cell formation that reflects impairment in cholesterol acceptor function of HDL. Activation of cellular cholesterol transporters by LXR agonism improves but does not normalize efflux to HDL. However, LXR agonism actually increases the pro-inflammatory effects of HDL through activation of TLRs and ERK1/2 pathways.
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17 MeSH Terms
Dynamic Glycosylation Governs the Vertebrate COPII Protein Trafficking Pathway.
Cox NJ, Unlu G, Bisnett BJ, Meister TR, Condon BM, Luo PM, Smith TJ, Hanna M, Chhetri A, Soderblom EJ, Audhya A, Knapik EW, Boyce M
(2018) Biochemistry 57: 91-107
MeSH Terms: Acetylglucosamine, Acylation, Animals, COP-Coated Vesicles, Cell Line, Collagen, Craniofacial Abnormalities, Disease Models, Animal, Glycosylation, Humans, Organelles, Protein Conformation, Protein Processing, Post-Translational, Protein Transport, Vertebrates, Vesicular Transport Proteins, Zebrafish
Show Abstract · Added March 15, 2018
The COPII coat complex, which mediates secretory cargo trafficking from the endoplasmic reticulum, is a key control point for subcellular protein targeting. Because misdirected proteins cannot function, protein sorting by COPII is critical for establishing and maintaining normal cell and tissue homeostasis. Indeed, mutations in COPII genes cause a range of human pathologies, including cranio-lenticulo-sutural dysplasia (CLSD), which is characterized by collagen trafficking defects, craniofacial abnormalities, and skeletal dysmorphology. Detailed knowledge of the COPII pathway is required to understand its role in normal cell physiology and to devise new treatments for disorders in which it is disrupted. However, little is known about how vertebrates dynamically regulate COPII activity in response to developmental, metabolic, or pathological cues. Several COPII proteins are modified by O-linked β-N-acetylglucosamine (O-GlcNAc), a dynamic form of intracellular protein glycosylation, but the biochemical and functional effects of these modifications remain unclear. Here, we use a combination of chemical, biochemical, cellular, and genetic approaches to demonstrate that site-specific O-GlcNAcylation of COPII proteins mediates their protein-protein interactions and modulates cargo secretion. In particular, we show that individual O-GlcNAcylation sites of SEC23A, an essential COPII component, are required for its function in human cells and vertebrate development, because mutation of these sites impairs SEC23A-dependent in vivo collagen trafficking and skeletogenesis in a zebrafish model of CLSD. Our results indicate that O-GlcNAc is a conserved and critical regulatory modification in the vertebrate COPII-dependent trafficking pathway.
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17 MeSH Terms
COPI mediates recycling of an exocytic SNARE by recognition of a ubiquitin sorting signal.
Xu P, Hankins HM, MacDonald C, Erlinger SJ, Frazier MN, Diab NS, Piper RC, Jackson LP, MacGurn JA, Graham TR
(2017) Elife 6:
MeSH Terms: Coat Protein Complex I, Exosomes, Protein Transport, R-SNARE Proteins, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Ubiquitin
Show Abstract · Added March 14, 2018
The COPI coat forms transport vesicles from the Golgi complex and plays a poorly defined role in endocytic trafficking. Here we show that COPI binds K63-linked polyubiquitin and this interaction is crucial for trafficking of a ubiquitinated yeast SNARE (Snc1). Snc1 is a v-SNARE that drives fusion of exocytic vesicles with the plasma membrane, and then recycles through the endocytic pathway to the Golgi for reuse in exocytosis. Removal of ubiquitin from Snc1, or deletion of a β'-COP subunit propeller domain that binds K63-linked polyubiquitin, disrupts Snc1 recycling causing aberrant accumulation in internal compartments. Moreover, replacement of the β'-COP propeller domain with unrelated ubiquitin-binding domains restores Snc1 recycling. These results indicate that ubiquitination, a modification well known to target membrane proteins to the lysosome or vacuole for degradation, can also function as recycling signal to sort a SNARE into COPI vesicles in a non-degradative pathway.
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7 MeSH Terms
A disease-associated frameshift mutation in caveolin-1 disrupts caveolae formation and function through introduction of a de novo ER retention signal.
Copeland CA, Han B, Tiwari A, Austin ED, Loyd JE, West JD, Kenworthy AK
(2017) Mol Biol Cell 28: 3095-3111
MeSH Terms: Caveolae, Caveolin 1, Endocytosis, Endoplasmic Reticulum, Fibroblasts, Frameshift Mutation, Humans, Hypertension, Pulmonary, Mutation, Protein Transport
Show Abstract · Added April 2, 2019
Caveolin-1 (CAV1) is an essential component of caveolae and is implicated in numerous physiological processes. Recent studies have identified heterozygous mutations in the gene in patients with pulmonary arterial hypertension (PAH), but the mechanisms by which these mutations impact caveolae assembly and contribute to disease remain unclear. To address this question, we examined the consequences of a familial PAH-associated frameshift mutation in , P158PfsX22, on caveolae assembly and function. We show that C-terminus of the CAV1 P158 protein contains a functional ER-retention signal that inhibits ER exit and caveolae formation and accelerates CAV1 turnover in MEFs. Moreover, when coexpressed with wild-type (WT) CAV1 in MEFs, CAV1-P158 functions as a dominant negative by partially disrupting WT CAV1 trafficking. In patient skin fibroblasts, CAV1 and caveolar accessory protein levels are reduced, fewer caveolae are observed, and CAV1 complexes exhibit biochemical abnormalities. Patient fibroblasts also exhibit decreased resistance to a hypo-osmotic challenge, suggesting the function of caveolae as membrane reservoir is compromised. We conclude that the P158PfsX22 frameshift introduces a gain of function that gives rise to a dominant negative form of CAV1, defining a new mechanism by which disease-associated mutations in CAV1 impair caveolae assembly.
© 2017 Copeland, Han, et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).
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Association of FGFR1 with ERα Maintains Ligand-Independent ER Transcription and Mediates Resistance to Estrogen Deprivation in ER Breast Cancer.
Formisano L, Stauffer KM, Young CD, Bhola NE, Guerrero-Zotano AL, Jansen VM, Estrada MM, Hutchinson KE, Giltnane JM, Schwarz LJ, Lu Y, Balko JM, Deas O, Cairo S, Judde JG, Mayer IA, Sanders M, Dugger TC, Bianco R, Stricker T, Arteaga CL
(2017) Clin Cancer Res 23: 6138-6150
MeSH Terms: Animals, Breast Neoplasms, Cell Line, Tumor, Disease Models, Animal, Drug Resistance, Neoplasm, Estrogen Receptor Modulators, Estrogen Receptor alpha, Female, Fibroblast Growth Factors, Gene Amplification, Gene Expression Regulation, Neoplastic, Humans, Mice, Molecular Targeted Therapy, Neoplasm Staging, Protein Kinase Inhibitors, Protein Transport, Receptor, Fibroblast Growth Factor, Type 1, Signal Transduction, Transcription, Genetic
Show Abstract · Added March 14, 2018
amplification occurs in approximately 15% of estrogen receptor-positive (ER) human breast cancers. We investigated mechanisms by which amplification confers antiestrogen resistance to ER breast cancer. ER tumors from patients treated with letrozole before surgery were subjected to Ki67 IHC, FGFR1 FISH, and RNA sequencing (RNA-seq). ER/-amplified breast cancer cells, and patient-derived xenografts (PDX) were treated with FGFR1 siRNA or the FGFR tyrosine kinase inhibitor lucitanib. Endpoints were cell/xenograft growth, FGFR1/ERα association by coimmunoprecipitation and proximity ligation, ER genomic activity by ChIP sequencing, and gene expression by RT-PCR. ER/-amplified tumors in patients treated with letrozole maintained cell proliferation (Ki67). Estrogen deprivation increased total and nuclear FGFR1 and FGF ligands expression in ER/amplified primary tumors and breast cancer cells. In estrogen-free conditions, FGFR1 associated with ERα in tumor cell nuclei and regulated the transcription of ER-dependent genes. This association was inhibited by a kinase-dead FGFR1 mutant and by treatment with lucitanib. ChIP-seq analysis of estrogen-deprived ER/-amplified cells showed binding of FGFR1 and ERα to DNA. Treatment with fulvestrant and/or lucitanib reduced FGFR1 and ERα binding to DNA. RNA-seq data from -amplified patients' tumors treated with letrozole showed enrichment of estrogen response and E2F target genes. Finally, growth of ER/amplified cells and PDXs was more potently inhibited by fulvestrant and lucitanib combined than each drug alone.s These data suggest the ERα pathway remains active in estrogen-deprived ER/-amplified breast cancers. Therefore, these tumors are endocrine resistant and should be candidates for treatment with combinations of ER and FGFR antagonists. .
©2017 American Association for Cancer Research.
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20 MeSH Terms
A Chimeric Egfr Protein Reporter Mouse Reveals Egfr Localization and Trafficking In Vivo.
Yang YP, Ma H, Starchenko A, Huh WJ, Li W, Hickman FE, Zhang Q, Franklin JL, Mortlock DP, Fuhrmann S, Carter BD, Ihrie RA, Coffey RJ
(2017) Cell Rep 19: 1257-1267
MeSH Terms: Adult Stem Cells, Amphiregulin, Animals, Embryo, Mammalian, ErbB Receptors, Genes, Reporter, Green Fluorescent Proteins, Hepatocytes, Intestinal Mucosa, Mice, Microscopy, Fluorescence, Protein Transport, Recombinant Proteins, Transgenes
Show Abstract · Added June 21, 2017
EGF receptor (EGFR) is a critical signaling node throughout life. However, it has not been possible to directly visualize endogenous Egfr in mice. Using CRISPR/Cas9 genome editing, we appended a fluorescent reporter to the C terminus of the Egfr. Homozygous reporter mice appear normal and EGFR signaling is intact in vitro and in vivo. We detect distinct patterns of Egfr expression in progenitor and differentiated compartments in embryonic and adult mice. Systemic delivery of EGF or amphiregulin results in markedly different patterns of Egfr internalization and trafficking in hepatocytes. In the normal intestine, Egfr localizes to the crypt rather than villus compartment, expression is higher in adjacent epithelium than in intestinal tumors, and following colonic injury expression appears in distinct cell populations in the stroma. This reporter, under control of its endogenous regulatory elements, enables in vivo monitoring of the dynamics of Egfr localization and trafficking in normal and disease states.
Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.
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14 MeSH Terms