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Mechanisms of KCNQ1 channel dysfunction in long QT syndrome involving voltage sensor domain mutations.
Huang H, Kuenze G, Smith JA, Taylor KC, Duran AM, Hadziselimovic A, Meiler J, Vanoye CG, George AL, Sanders CR
(2018) Sci Adv 4: eaar2631
MeSH Terms: Cell Membrane, HEK293 Cells, Humans, KCNQ1 Potassium Channel, Leupeptins, Long QT Syndrome, Loss of Function Mutation, Magnetic Resonance Spectroscopy, Mutant Proteins, Mutation, Proteasome Endopeptidase Complex, Proteasome Inhibitors, Protein Domains, Protein Folding, Protein Structure, Secondary, Proteolysis
Show Abstract · Added March 14, 2018
Mutations that induce loss of function (LOF) or dysfunction of the human KCNQ1 channel are responsible for susceptibility to a life-threatening heart rhythm disorder, the congenital long QT syndrome (LQTS). Hundreds of mutations have been identified, but the molecular mechanisms responsible for impaired function are poorly understood. We investigated the impact of 51 KCNQ1 variants with mutations located within the voltage sensor domain (VSD), with an emphasis on elucidating effects on cell surface expression, protein folding, and structure. For each variant, the efficiency of trafficking to the plasma membrane, the impact of proteasome inhibition, and protein stability were assayed. The results of these experiments combined with channel functional data provided the basis for classifying each mutation into one of six mechanistic categories, highlighting heterogeneity in the mechanisms resulting in channel dysfunction or LOF. More than half of the KCNQ1 LOF mutations examined were seen to destabilize the structure of the VSD, generally accompanied by mistrafficking and degradation by the proteasome, an observation that underscores the growing appreciation that mutation-induced destabilization of membrane proteins may be a common human disease mechanism. Finally, we observed that five of the folding-defective LQTS mutant sites are located in the VSD S0 helix, where they interact with a number of other LOF mutation sites in other segments of the VSD. These observations reveal a critical role for the S0 helix as a central scaffold to help organize and stabilize the KCNQ1 VSD and, most likely, the corresponding domain of many other ion channels.
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16 MeSH Terms
UNC-45a promotes myosin folding and stress fiber assembly.
Lehtimäki JI, Fenix AM, Kotila TM, Balistreri G, Paavolainen L, Varjosalo M, Burnette DT, Lappalainen P
(2017) J Cell Biol 216: 4053-4072
MeSH Terms: Actomyosin, Cell Adhesion, Cell Line, Tumor, Cell Movement, Cell Polarity, Gene Expression, Humans, Intracellular Signaling Peptides and Proteins, Myosin Type II, Osteoblasts, Proteasome Endopeptidase Complex, Protein Folding, Protein Isoforms, Stress Fibers, Tetratricopeptide Repeat
Show Abstract · Added March 14, 2018
Contractile actomyosin bundles, stress fibers, are crucial for adhesion, morphogenesis, and mechanosensing in nonmuscle cells. However, the mechanisms by which nonmuscle myosin II (NM-II) is recruited to those structures and assembled into functional bipolar filaments have remained elusive. We report that UNC-45a is a dynamic component of actin stress fibers and functions as a myosin chaperone in vivo. UNC-45a knockout cells display severe defects in stress fiber assembly and consequent abnormalities in cell morphogenesis, polarity, and migration. Experiments combining structured-illumination microscopy, gradient centrifugation, and proteasome inhibition approaches revealed that a large fraction of NM-II and myosin-1c molecules fail to fold in the absence of UNC-45a. The remaining properly folded NM-II molecules display defects in forming functional bipolar filaments. The C-terminal UNC-45/Cro1/She4p domain of UNC-45a is critical for NM-II folding, whereas the N-terminal tetratricopeptide repeat domain contributes to the assembly of functional stress fibers. Thus, UNC-45a promotes generation of contractile actomyosin bundles through synchronized NM-II folding and filament-assembly activities.
© 2017 Lehtimäki et al.
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15 MeSH Terms
Camptothecin resistance is determined by the regulation of topoisomerase I degradation mediated by ubiquitin proteasome pathway.
Ando K, Shah AK, Sachdev V, Kleinstiver BP, Taylor-Parker J, Welch MM, Hu Y, Salgia R, White FM, Parvin JD, Ozonoff A, Rameh LE, Joung JK, Bharti AK
(2017) Oncotarget 8: 43733-43751
MeSH Terms: BRCA1 Protein, Camptothecin, Cell Line, Tumor, DNA Topoisomerases, Type I, DNA-Binding Proteins, Drug Resistance, Neoplasm, Gene Editing, Humans, Ku Autoantigen, Multiprotein Complexes, PTEN Phosphohydrolase, Phosphorylation, Proteasome Endopeptidase Complex, Protein Binding, Protein Kinase C, Proteolysis, RNA Interference, Topoisomerase I Inhibitors, Ubiquitin
Show Abstract · Added November 26, 2018
Proteasomal degradation of topoisomerase I (topoI) is one of the most remarkable cellular phenomena observed in response to camptothecin (CPT). Importantly, the rate of topoI degradation is linked to CPT resistance. Formation of the topoI-DNA-CPT cleavable complex inhibits DNA re-ligation resulting in DNA-double strand break (DSB). The degradation of topoI marks the first step in the ubiquitin proteasome pathway (UPP) dependent DNA damage response (DDR). Here, we show that the Ku70/Ku80 heterodimer binds with topoI, and that the DNA-dependent protein kinase (DNA-PKcs) phosphorylates topoI on serine 10 (topoI-pS10), which is subsequently ubiquitinated by BRCA1. A higher basal level of topoI-pS10 ensures rapid topoI degradation leading to CPT resistance. Importantly, PTEN regulates DNA-PKcs kinase activity in this pathway and PTEN deletion ensures DNA-PKcs dependent higher topoI-pS10, rapid topoI degradation and CPT resistance.
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MeSH Terms
Bortezomib augments lymphocyte stimulatory cytokine signaling in the tumor microenvironment to sustain CD8+T cell antitumor function.
Pellom ST, Dudimah DF, Thounaojam MC, Uzhachenko RV, Singhal A, Richmond A, Shanker A
(2017) Oncotarget 8: 8604-8621
MeSH Terms: Adenocarcinoma, Animals, Antineoplastic Agents, Bortezomib, Breast Neoplasms, CD8-Positive T-Lymphocytes, Cell Line, Tumor, Cytokines, Female, Fibrosarcoma, Kidney Neoplasms, Lung Neoplasms, Lymphocytes, Tumor-Infiltrating, Mice, Inbred BALB C, Mice, Transgenic, Phosphatidylinositol 3-Kinase, Proteasome Endopeptidase Complex, Proteasome Inhibitors, Proto-Oncogene Proteins c-akt, Receptors, Cytokine, STAT5 Transcription Factor, Signal Transduction, Tumor Escape, Tumor Microenvironment
Show Abstract · Added March 14, 2017
Tumor-induced immune tolerance poses a major challenge for therapeutic interventions aimed to manage cancer. We explored approaches to overcome T-cell suppression in murine breast and kidney adenocarcinomas, and lung fibrosarcoma expressing immunogenic antigens. We observed that treatment with a reversible proteasome inhibitor bortezomib (1 mg/kg body weight) in tumor-bearing mice significantly enhanced the expression of lymphocyte-stimulatory cytokines IL-2, IL-12, and IL-15. Notably, bortezomib administration reduced pulmonary nodules of mammary adenocarcinoma 4T1.2 expressing hemagglutinin (HA) model antigen (4T1HA) in mice. Neutralization of IL-12 and IL-15 cytokines with a regimen of blocking antibodies pre- and post-adoptive transfer of low-avidity HA518-526-specific CD8+T-cells following intravenous injection of 4T1HA cells increased the number of pulmonary tumor nodules. This neutralization effect was counteracted by the tumor metastasis-suppressing action of bortezomib treatments. In bortezomib-treated 4T1HA tumor-bearing mice, CD4+T-cells showed increased IL-2 production, CD11c+ dendritic cells showed increased IL-12 and IL-15 production, and HA-specific activated CD8+T-cells showed enhanced expression of IFNγ, granzyme-B and transcription factor eomesodermin. We also noted a trend of increased expression of IL-2, IL-12 and IL-15 receptors as well as increased phosphorylation of STAT5 in tumor-infiltrating CD8+T-cells following bortezomib treatment. Furthermore, bortezomib-treated CD8+T-cells showed increased phosphorylation of mitogen-activated protein kinase p38, and Akt, which was abrogated by phosphatidylinositide 3-kinase (PI3K) inhibitor. These data support the therapeutic potential of bortezomib in conjunction with other immunotherapies to augment the strength of convergent signals from CD8+T-cell signaling molecules including TCR, cytokine receptors and downstream PI3K/Akt/STAT5 pathways to sustain CD8+T-cell effector function in the tumor microenvironment.
2 Communities
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24 MeSH Terms
Tyrosine phosphorylation modulates mitochondrial chaperonin Hsp60 and delays rotavirus NSP4-mediated apoptotic signaling in host cells.
Chattopadhyay S, Mukherjee A, Patra U, Bhowmick R, Basak T, Sengupta S, Chawla-Sarkar M
(2017) Cell Microbiol 19:
MeSH Terms: Apoptosis, Cell Line, Chaperonin 60, Glycoproteins, Host-Pathogen Interactions, Humans, Phosphorylation, Proteasome Endopeptidase Complex, Protein Processing, Post-Translational, Proteolysis, Rotavirus, Signal Transduction, Time Factors, Toxins, Biological, Tyrosine, Viral Nonstructural Proteins
Show Abstract · Added November 3, 2017
Phosphoproteomics-based platforms have been widely used to identify post translational dynamics of cellular proteins in response to viral infection. The present study was undertaken to assess differential tyrosine phosphorylation during early hours of rotavirus (RV) SA11 infection. Heat shock proteins (Hsp60) were found to be enriched in the data set of RV-SA11 induced differentially tyrosine-phosphorylated proteins at 2 hr post infection (hpi). Hsp60 was further found to be phosphorylated by an activated form of Src kinase on 227th tyrosine residue, and tyrosine phosphorylation of mitochondrial chaperonin Hsp60 correlated with its proteasomal degradation at 2-2.5hpi. Interestingly, mitochondrial Hsp60 positively influenced translocation of the rotaviral nonstructural protein 4 to mitochondria during RV infections. Phosphorylation and subsequent transient degradation of mitochondrial Hsp60 during early hours of RV-SA11 infection resulted in inhibition of premature import of nonstructural protein 4 into mitochondria, thereby delaying early apoptosis. Overall, the study highlighted one of the many strategies rotavirus undertakes to prevent early apoptosis and subsequent reduced viral progeny yield.
© 2016 John Wiley & Sons Ltd.
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16 MeSH Terms
Interaction of Gcn4 with target gene chromatin is modulated by proteasome function.
Howard GC, Tansey WP
(2016) Mol Biol Cell 27: 2735-41
MeSH Terms: Adenosine Triphosphatases, Basic-Leucine Zipper Transcription Factors, Cell Cycle Proteins, Chromatin, DNA-Binding Proteins, Molecular Chaperones, Proteasome Endopeptidase Complex, Proteolysis, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Transcription Factors, Transcriptional Activation, Ubiquitin, Ubiquitination, Valosin Containing Protein
Show Abstract · Added March 26, 2019
The ubiquitin-proteasome system (UPS) influences gene transcription in multiple ways. One way in which the UPS affects transcription centers on transcriptional activators, the function of which can be stimulated by components of the UPS that also trigger their destruction. Activation of transcription by the yeast activator Gcn4, for example, is attenuated by mutations in the ubiquitin ligase that mediates Gcn4 ubiquitylation or by inhibition of the proteasome, leading to the idea that ubiquitin-mediated proteolysis of Gcn4 is required for its activity. Here we probe the steps in Gcn4 activity that are perturbed by disruption of the UPS. We show that the ubiquitylation machinery and the proteasome control different steps in Gcn4 function and that proteasome activity is required for the ability of Gcn4 to bind to its target genes in the context of chromatin. Curiously, the effect of proteasome inhibition on Gcn4 activity is suppressed by mutations in the ubiquitin-selective chaperone Cdc48, revealing that proteolysis per se is not required for Gcn4 activity. Our data highlight the role of Cdc48 in controlling promoter occupancy by Gcn4 and support a model in which ubiquitylation of activators-not their destruction-is important for function.
© 2016 Howard and Tansey. 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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MeSH Terms
Promotion of BRCA2-Dependent Homologous Recombination by DSS1 via RPA Targeting and DNA Mimicry.
Zhao W, Vaithiyalingam S, San Filippo J, Maranon DG, Jimenez-Sainz J, Fontenay GV, Kwon Y, Leung SG, Lu L, Jensen RB, Chazin WJ, Wiese C, Sung P
(2015) Mol Cell 59: 176-87
MeSH Terms: Amino Acid Substitution, BRCA2 Protein, Breast Neoplasms, Cell Line, Female, HeLa Cells, Homologous Recombination, Humans, Models, Biological, Molecular Mimicry, Mutagenesis, Site-Directed, Nuclear Magnetic Resonance, Biomolecular, Proteasome Endopeptidase Complex, Protein Subunits, Rad51 Recombinase, Recombinant Proteins, Replication Protein A
Show Abstract · Added February 5, 2016
The tumor suppressor BRCA2 is thought to facilitate the handoff of ssDNA from replication protein A (RPA) to the RAD51 recombinase during DNA break and replication fork repair by homologous recombination. However, we find that RPA-RAD51 exchange requires the BRCA2 partner DSS1. Biochemical, structural, and in vivo analyses reveal that DSS1 allows the BRCA2-DSS1 complex to physically and functionally interact with RPA. Mechanistically, DSS1 acts as a DNA mimic to attenuate the affinity of RPA for ssDNA. A mutation in the solvent-exposed acidic domain of DSS1 compromises the efficacy of RPA-RAD51 exchange. Thus, by targeting RPA and mimicking DNA, DSS1 functions with BRCA2 in a two-component homologous recombination mediator complex in genome maintenance and tumor suppression. Our findings may provide a paradigm for understanding the roles of DSS1 in other biological processes.
Copyright © 2015 Elsevier Inc. All rights reserved.
1 Communities
2 Members
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17 MeSH Terms
Functions of the proteasome on chromatin.
McCann TS, Tansey WP
(2014) Biomolecules 4: 1026-44
MeSH Terms: Animals, Chromatin, Humans, Proteasome Endopeptidase Complex, RNA, Messenger, Transcription, Genetic
Show Abstract · Added February 12, 2015
The proteasome is a large self-compartmentalized protease complex that recognizes, unfolds, and destroys ubiquitylated substrates. Proteasome activities are required for a host of cellular functions, and it has become clear in recent years that one set of critical actions of the proteasome occur on chromatin. In this review, we discuss some of the ways in which proteasomes directly regulate the structure and function of chromatin and chromatin regulatory proteins, and how this influences gene transcription. We discuss lingering controversies in the field, the relative importance of proteolytic versus non-proteolytic proteasome activities in this process, and highlight areas that require further investigation. Our intention is to show that proteasomes are involved in major steps controlling the expression of the genetic information, that proteasomes use both proteolytic mechanisms and ATP-dependent protein remodeling to accomplish this task, and that much is yet to be learned about the full spectrum of ways that proteasomes influence the genome.
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6 MeSH Terms
Loss of Fbw7 reprograms adult pancreatic ductal cells into α, δ, and β cells.
Sancho R, Gruber R, Gu G, Behrens A
(2014) Cell Stem Cell 15: 139-53
MeSH Terms: Animals, Basic Helix-Loop-Helix Transcription Factors, Cell Differentiation, Cell Line, Tumor, Cell Lineage, F-Box Proteins, F-Box-WD Repeat-Containing Protein 7, Gene Deletion, Gene Expression Profiling, Gene Expression Regulation, Developmental, Glucagon-Secreting Cells, Glucose, HEK293 Cells, Humans, Insulin, Insulin Secretion, Insulin-Secreting Cells, Mice, Multipotent Stem Cells, Nerve Tissue Proteins, Pancreatic Ducts, Proteasome Endopeptidase Complex, Regeneration, Somatostatin-Secreting Cells, Ubiquitin-Protein Ligases, Ubiquitination
Show Abstract · Added January 23, 2015
The adult pancreas is capable of limited regeneration after injury but has no defined stem cell population. The cell types and molecular signals that govern the production of new pancreatic tissue are not well understood. Here, we show that inactivation of the SCF-type E3 ubiquitin ligase substrate recognition component Fbw7 induces pancreatic ductal cells to reprogram into α, δ, and β cells. Loss of Fbw7 stabilized the transcription factor Ngn3, a key regulator of endocrine cell differentiation. The induced β cells resemble islet β cells in morphology and histology, express genes essential for β cell function, and release insulin after glucose challenge. Thus, loss of Fbw7 appears to reawaken an endocrine developmental differentiation program in adult pancreatic ductal cells. Our study highlights the plasticity of seemingly differentiated adult cells, identifies Fbw7 as a master regulator of cell fate decisions in the pancreas, and reveals adult pancreatic duct cells as a latent multipotent cell type.
Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.
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26 MeSH Terms
Disruption of N-linked glycosylation promotes proteasomal degradation of the human ATP-binding cassette transporter ABCA3.
Beers MF, Zhao M, Tomer Y, Russo SJ, Zhang P, Gonzales LW, Guttentag SH, Mulugeta S
(2013) Am J Physiol Lung Cell Mol Physiol 305: L970-80
MeSH Terms: ATP-Binding Cassette Transporters, Cells, Cultured, Endoplasmic Reticulum, Glycosylation, Humans, Mutation, Proteasome Endopeptidase Complex, Protein Transport, Tunicamycin
Show Abstract · Added January 20, 2015
The lipid transport protein, ABCA3, expressed in alveolar type 2 (AT2) cells, is critical for surfactant homeostasis. The first luminal loop of ABCA3 contains three putative N-linked glycosylation sites at residues 53, 124, and 140. A common cotranslational modification, N-linked glycosylation, is critical for the proper expression of glycoproteins by enhancing folding, trafficking, and stability through augmentation of the endoplasmic reticulum (ER) folding cycle. To understand its role in ABCA3 biosynthesis, we utilized EGFP-tagged fusion constructs with either wild-type or mutant ABCA3 cDNAs that contained glutamine for asparagine substitutions at the putative glycosylation motifs. In A549 cells, inhibition of glycosylation by tunicamycin increased the electrophoretic mobility (Mr) and reduced the expression level of wild-type ABCA3 in a dose-dependent manner. Fluorescence imaging of transiently transfected A549 or primary human AT2 cells showed that although single motif mutants exhibited a vesicular distribution pattern similar to wild-type ABCA3, mutation of N124 and N140 residues resulted in a shift toward an ER-predominant distribution. By immunoblotting, the N53 mutation exhibited no effect on either the Mr or ABCA3 expression level. In contrast, substitutions at N124 or N140, as well a N124/N140 double mutation, resulted in increased electrophoretic mobility indicative of a glycosylation deficiency accompanied by reduced overall expression levels. Diminished steady-state levels of glycan-deficient ABCA3 isoforms were rescued by treatment with the proteasome inhibitor MG132. These results suggest that cotranslational N-linked glycosylation at N124 and N140 is critical for ABCA3 stability, and its disruption results in protein destabilization and proteasomal degradation.
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9 MeSH Terms