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Phenome-based approach identifies RIC1-linked Mendelian syndrome through zebrafish models, biobank associations and clinical studies.
Unlu G, Qi X, Gamazon ER, Melville DB, Patel N, Rushing AR, Hashem M, Al-Faifi A, Chen R, Li B, Cox NJ, Alkuraya FS, Knapik EW
(2020) Nat Med 26: 98-109
MeSH Terms: Abnormalities, Multiple, Animals, Behavior, Animal, Biological Specimen Banks, Chondrocytes, Disease Models, Animal, Extracellular Matrix, Fibroblasts, Guanine Nucleotide Exchange Factors, Humans, Models, Biological, Musculoskeletal System, Osteogenesis, Phenomics, Phenotype, Procollagen, Protein Transport, Secretory Pathway, Syndrome, Zebrafish, Zebrafish Proteins
Show Abstract · Added January 15, 2020
Discovery of genotype-phenotype relationships remains a major challenge in clinical medicine. Here, we combined three sources of phenotypic data to uncover a new mechanism for rare and common diseases resulting from collagen secretion deficits. Using a zebrafish genetic screen, we identified the ric1 gene as being essential for skeletal biology. Using a gene-based phenome-wide association study (PheWAS) in the EHR-linked BioVU biobank, we show that reduced genetically determined expression of RIC1 is associated with musculoskeletal and dental conditions. Whole-exome sequencing identified individuals homozygous-by-descent for a rare variant in RIC1 and, through a guided clinical re-evaluation, it was discovered that they share signs with the BioVU-associated phenome. We named this new Mendelian syndrome CATIFA (cleft lip, cataract, tooth abnormality, intellectual disability, facial dysmorphism, attention-deficit hyperactivity disorder) and revealed further disease mechanisms. This gene-based, PheWAS-guided approach can accelerate the discovery of clinically relevant disease phenome and associated biological mechanisms.
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21 MeSH Terms
Structures of the AMPA receptor in complex with its auxiliary subunit cornichon.
Nakagawa T
(2019) Science 366: 1259-1263
MeSH Terms: Animals, Brain, Cryoelectron Microscopy, Glutamic Acid, Ion Channel Gating, Protein Structure, Secondary, Protein Transport, Rats, Receptors, AMPA, Receptors, Glutamate, Synaptic Transmission
Show Abstract · Added March 3, 2020
In the brain, AMPA-type glutamate receptors (AMPARs) form complexes with their auxiliary subunits and mediate the majority of fast excitatory neurotransmission. Signals transduced by these complexes are critical for synaptic plasticity, learning, and memory. The two major categories of AMPAR auxiliary subunits are transmembrane AMPAR regulatory proteins (TARPs) and cornichon homologs (CNIHs); these subunits share little homology and play distinct roles in controlling ion channel gating and trafficking of AMPAR. Here, I report high-resolution cryo-electron microscopy structures of AMPAR in complex with CNIH3. Contrary to its predicted membrane topology, CNIH3 lacks an extracellular domain and instead contains four membrane-spanning helices. The protein-protein interaction interface that dictates channel modulation and the lipids surrounding the complex are revealed. These structures provide insights into the molecular mechanism for ion channel modulation and assembly of AMPAR/CNIH3 complexes.
Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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11 MeSH Terms
A missense mutation in SLC6A1 associated with Lennox-Gastaut syndrome impairs GABA transporter 1 protein trafficking and function.
Cai K, Wang J, Eissman J, Wang J, Nwosu G, Shen W, Liang HC, Li XJ, Zhu HX, Yi YH, Song J, Xu D, Delpire E, Liao WP, Shi YW, Kang JQ
(2019) Exp Neurol 320: 112973
MeSH Terms: Adolescent, Animals, GABA Plasma Membrane Transport Proteins, HEK293 Cells, HeLa Cells, Humans, Lennox Gastaut Syndrome, Male, Mutation, Missense, Pedigree, Protein Transport, Rats
Show Abstract · Added March 18, 2020
BACKGROUND - Mutations in SLC6A1 have been associated mainly with myoclonic atonic epilepsy (MAE) and intellectual disability. We identified a novel missense mutation in a patient with Lennox-Gastaut syndrome (LGS) characterized by severe seizures and developmental delay.
METHODS - Exome Sequencing was performed in an epilepsy patient cohort. The impact of the mutation was evaluated by H γ-aminobutyric acid (GABA) uptake, structural modeling, live cell microscopy, cell surface biotinylation and a high-throughput assay flow cytometry in both neurons and non neuronal cells.
RESULTS - We discovered a heterozygous missense mutation (c700G to A [pG234S) in the SLC6A1 encoding GABA transporter 1 (GAT-1). Structural modeling suggests the mutation destabilizes the global protein conformation. With transient expression of enhanced yellow fluorescence protein (YFP) tagged rat GAT-1 cDNAs, we demonstrated that the mutant GAT-1(G234S) transporter had reduced total protein expression in both rat cortical neurons and HEK 293 T cells. With a high-throughput flow cytometry assay and live cell surface biotinylation, we demonstrated that the mutant GAT-1(G234S) had reduced cell surface expression. H radioactive labeling GABA uptake assay in HeLa cells indicated a reduced function of the mutant GAT-1(G234S).
CONCLUSIONS - This mutation caused instability of the mutant transporter protein, which resulted in reduced cell surface and total protein levels. The mutation also caused reduced GABA uptake in addition to reduced protein expression, leading to reduced GABA clearance, and altered GABAergic signaling in the brain. The impaired trafficking and reduced GABA uptake function may explain the epilepsy phenotype in the patient.
Copyright © 2019. Published by Elsevier Inc.
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MeSH Terms
A dileucine motif in the COOH-terminal domain of NKCC1 targets the cotransporter to the plasma membrane.
Koumangoye R, Omer S, Delpire E
(2019) Am J Physiol Cell Physiol 316: C545-C558
MeSH Terms: Animals, Cell Membrane, Dogs, Leucine, Madin Darby Canine Kidney Cells, Peptide Fragments, Protein Transport, Solute Carrier Family 12, Member 2
Show Abstract · Added April 2, 2019
Na-K-2Cl cotransporter-1 (NKCC1) mediates the electroneutral transport of Na, K, and Cl and is normally localized to the basolateral membrane of polarized epithelial cells. We recently reported the first known solute carrier family 12 member 2 ( SLC12A2) mutation (we call NKCC1-DFX) that causes epithelial dysfunction in an undiagnosed disease program case. The heterozygous mutation leads to truncation of the COOH-terminal tail of the cotransporter, resulting in both mutant and wild-type cotransporters being mistrafficked to the apical membrane of polarized epithelial cells. Here we demonstrate by using consecutive truncations and site-directed mutagenesis of the COOH-terminal domain of NKCC1 that truncation of NKCC1 COOH domain uncouples the cotransporter from the lateral membrane. We identify a dileucine motif that, when mutated, leads to cotransporter accumulation in the cytoplasm and mistrafficking to the apical/subapical region of epithelial cells, thereby recapitulating the phenotype observed with the patient mutation. We show that truncation deletion and LL substitution mutants are trafficked out of the endoplasmic reticulum and trans-Golgi network but accumulate in early and late endosomes where they are degraded.
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8 MeSH Terms
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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MeSH Terms
Matrix stiffness regulates vascular integrity through focal adhesion kinase activity.
Wang W, Lollis EM, Bordeleau F, Reinhart-King CA
(2019) FASEB J 33: 1199-1208
MeSH Terms: Adherens Junctions, Animals, Antigens, CD, Cadherins, Capillary Permeability, Chick Embryo, Endothelium, Vascular, Enzyme Activation, Extracellular Matrix, Female, Focal Adhesion Protein-Tyrosine Kinases, Human Umbilical Vein Endothelial Cells, Humans, Mice, Mice, Transgenic, Phosphorylation, Protein Transport, Tyrosine, src-Family Kinases
Show Abstract · Added April 10, 2019
Tumor vasculature is known to be more permeable than the vasculature found in healthy tissue, which in turn can lead to a more aggressive tumor phenotype and impair drug delivery into tumors. While the stiffening of the stroma surrounding solid tumors has been reported to increase vascular permeability, the mechanism of this process remains unclear. Here, we utilize an in vitro model of tumor stiffening, ex ovo culture, and a mouse model to investigate the molecular mechanism by which matrix stiffening alters endothelial barrier function. Our data indicate that the increased endothelial permeability caused by heightened matrix stiffness can be prevented by pharmaceutical inhibition of focal adhesion kinase (FAK) both in vitro and ex ovo. Matrix stiffness-mediated FAK activation determines Src localization to cell-cell junctions, which then induces increased vascular endothelial cadherin phosphorylation both in vitro and in vivo. Endothelial cells in stiff tumors have more activated Src and higher levels of phosphorylated vascular endothelial cadherin at adherens junctions compared to endothelial cells in more compliant tumors. Altogether, our data indicate that matrix stiffness regulates endothelial barrier integrity through FAK activity, providing one mechanism by which extracellular matrix stiffness regulates endothelial barrier function. Additionally, our work also provides further evidence that FAK is a promising potential target for cancer therapy because FAK plays a critical role in the regulation of endothelial barrier integrity.-Wang, W., Lollis, E. M., Bordeleau, F., Reinhart-King, C. A. Matrix stiffness regulates vascular integrity through focal adhesion kinase activity.
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19 MeSH Terms
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