The publication data currently available has been vetted by Vanderbilt faculty, staff, administrators and trainees. The data itself is retrieved directly from NCBI's PubMed and is automatically updated on a weekly basis to ensure accuracy and completeness.
If you have any questions or comments, please contact us.
Subversion of endoplasmic reticulum (ER) function is a feature shared by multiple intracellular bacteria and viruses, and in many cases this disruption of cellular function activates pathways of the unfolded protein response (UPR). In the case of infection with , the etiologic agent of brucellosis, the unfolded protein response in the infected placenta contributes to placentitis and abortion, leading to pathogen transmission. Here we show that infection of pregnant mice led to death of infected placental trophoblasts in a manner that depended on the VirB type IV secretion system (T4SS) and its effector VceC. The trophoblast death program required the ER stress-induced transcription factor CHOP. While NOD1/NOD2 expression in macrophages contributed to ER stress-induced inflammation, these receptors did not play a role in trophoblast death. Both placentitis and abortion were independent of apoptosis-associated Speck-like protein containing a caspase activation and recruitment domain (ASC). These studies show that uses its T4SS to induce cell-type-specific responses to ER stress in trophoblasts that trigger placental inflammation and abortion. Our results suggest further that in the T4SS and its effectors are under selection as bacterial transmission factors. infects the placenta of pregnant cows, where it replicates to high levels and triggers abortion of the calf. The aborted material is highly infectious and transmits infection to both cows and humans, but very little is known about how causes abortion. By studying this infection in pregnant mice, we discovered that kills trophoblasts, which are important cells for maintaining pregnancy. This killing required an injected bacterial protein (VceC) that triggered an endoplasmic reticulum (ER) stress response in the trophoblast. By inhibiting ER stress or infecting mice that lack CHOP, a protein induced by ER stress, we could prevent death of trophoblasts, reduce inflammation, and increase the viability of the pups. Our results suggest that injects VceC into placental trophoblasts to promote its transmission by abortion.
Copyright © 2019 Byndloss et al.
The unfolded protein response (UPR) detects and restores deficits in the endoplasmic reticulum (ER) protein folding capacity. Ceapins specifically inhibit the UPR sensor ATF6α, an ER-tethered transcription factor, by retaining it at the ER through an unknown mechanism. Our genome-wide CRISPR interference (CRISPRi) screen reveals that Ceapins function is completely dependent on the ABCD3 peroxisomal transporter. Proteomics studies establish that ABCD3 physically associates with ER-resident ATF6α in cells and in vitro in a Ceapin-dependent manner. Ceapins induce the neomorphic association of ER and peroxisomes by directly tethering the cytosolic domain of ATF6α to ABCD3's transmembrane regions without inhibiting or depending on ABCD3 transporter activity. Thus, our studies reveal that Ceapins function by chemical-induced misdirection which explains their remarkable specificity and opens up new mechanistic routes for drug development and synthetic biology.
© 2019, Torres et al.
The mitochondrial antiviral signaling protein (MAVS) orchestrates host antiviral innate immune response to RNA virus infection. However, how MAVS signaling is controlled to eradicate virus while preventing self-destructive inflammation remains obscure. Here, we show that protein geranylgeranylation, a posttranslational lipid modification of proteins, limits MAVS-mediated immune signaling by targeting Rho family small guanosine triphosphatase Rac1 into the mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) at the mitochondria-ER junction. Protein geranylgeranylation and subsequent palmitoylation promote Rac1 translocation into MAMs upon viral infection. MAM-localized Rac1 limits MAVS' interaction with E3 ligase Trim31 and hence inhibits MAVS ubiquitination, aggregation, and activation. Rac1 also facilitates the recruitment of caspase-8 and cFLIP to the MAVS signalosome and the subsequent cleavage of Ripk1 that terminates MAVS signaling. Consistently, mice with myeloid deficiency of protein geranylgeranylation showed improved survival upon influenza A virus infection. Our work revealed a critical role of protein geranylgeranylation in regulating antiviral innate immune response.
Activation of the unfolded protein response (UPR)-associated transcription factor ATF6 has emerged as a promising strategy to reduce the secretion and subsequent toxic aggregation of destabilized, amyloidogenic proteins implicated in systemic amyloid diseases. However, the molecular mechanism by which ATF6 activation reduces the secretion of amyloidogenic proteins remains poorly defined. We employ a quantitative interactomics platform to define how ATF6 activation reduces secretion of a destabilized, amyloidogenic immunoglobulin light chain (LC) associated with light-chain amyloidosis (AL). Using this platform, we show that ATF6 activation increases the targeting of this destabilized LC to a subset of pro-folding ER proteostasis factors that retains the amyloidogenic LC within the ER, preventing its secretion. Our results define a molecular basis for the ATF6-dependent reduction in destabilized LC secretion and highlight the advantage for targeting this UPR-associated transcription factor to reduce secretion of destabilized, amyloidogenic proteins implicated in AL and related systemic amyloid diseases.
Copyright © 2019 Elsevier Ltd. All rights reserved.
Pancreatic α-cells exhibit oscillations in cytosolic Ca (Ca), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca oscillations have not been elucidated. As β-cell Ca oscillations are regulated in part by Ca-activated K (K) currents, this work investigated the role of K in α-cell Ca handling and GCG secretion. α-Cells displayed K currents that were dependent on Ca influx through L- and P/Q-type voltage-dependent Ca channels (VDCCs) as well as Ca released from endoplasmic reticulum stores. α-Cell K was decreased by small-conductance Ca-activated K (SK) channel inhibitors apamin and UCL 1684, large-conductance Ca-activated K (BK) channel inhibitor iberiotoxin (IbTx), and intermediate-conductance Ca-activated K (IK) channel inhibitor TRAM 34. Moreover, partial inhibition of α-cell K with apamin depolarized membrane potential ( V) (3.8 ± 0.7 mV) and reduced action potential (AP) amplitude (10.4 ± 1.9 mV). Although apamin transiently increased Ca influx into α-cells at low glucose (42.9 ± 10.6%), sustained SK (38.5 ± 10.4%) or BK channel inhibition (31.0 ± 11.7%) decreased α-cell Ca influx. Total α-cell Ca was similarly reduced (28.3 ± 11.1%) following prolonged treatment with high glucose, but it was not decreased further by SK or BK channel inhibition. Consistent with reduced α-cell Ca following prolonged K inhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that K activation provides a hyperpolarizing influence on α-cell V that sustains Ca entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca is elevated during secretagogue stimulation, K activation helps to preserve GCG secretion.
Pharmacologic activation of stress-responsive signaling pathways provides a promising approach for ameliorating imbalances in proteostasis associated with diverse diseases. However, this approach has not been employed in vivo. Here we show, using a mouse model of myocardial ischemia/reperfusion, that selective pharmacologic activation of the ATF6 arm of the unfolded protein response (UPR) during reperfusion, a typical clinical intervention point after myocardial infarction, transcriptionally reprograms proteostasis, ameliorates damage and preserves heart function. These effects were lost upon cardiac myocyte-specific Atf6 deletion in the heart, demonstrating the critical role played by ATF6 in mediating pharmacologically activated proteostasis-based protection of the heart. Pharmacological activation of ATF6 is also protective in renal and cerebral ischemia/reperfusion models, demonstrating its widespread utility. Thus, pharmacologic activation of ATF6 represents a proteostasis-based therapeutic strategy for ameliorating ischemia/reperfusion damage, underscoring its unique translational potential for treating a wide range of pathologies caused by imbalanced proteostasis.
Pharmacologic arm-selective unfolded protein response (UPR) signaling pathway activation is emerging as a promising strategy to ameliorate imbalances in endoplasmic reticulum (ER) proteostasis implicated in diverse diseases. The small molecule (2-hydroxy-5-methylphenyl)-3-phenylpropanamide () was previously identified (
Plate et al., 2016) to preferentially activate the ATF6 arm of the UPR, promoting protective remodeling of the ER proteostasis network. Here we show that -dependent ATF6 activation requires metabolic oxidation to form an electrophile that preferentially reacts with ER proteins. Proteins covalently modified by include protein disulfide isomerases (PDIs), known to regulate ATF6 activation. Genetic depletion of PDIs perturbs -dependent induction of the ATF6-target gene, , implicating covalent modifications of PDIs in the preferential activation of ATF6 afforded by treatment with . Thus, is a pro-drug that preferentially activates ATF6 signaling through a mechanism involving localized metabolic activation and selective covalent modification of ER resident proteins that regulate ATF6 activity.
© 2018, Paxman et al.
Voltage-gated ion channels are critical for neuronal integration. Some of these channels, however, are misregulated in several neurological disorders, causing both gain- and loss-of-function channelopathies in neurons. Using several transgenic mouse models of Alzheimer's disease (AD), we find that sub-threshold voltage signals strongly influenced by hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels progressively deteriorate over chronological aging in hippocampal CA1 pyramidal neurons. The degraded signaling via HCN channels in the transgenic mice is accompanied by an age-related global loss of their non-uniform dendritic expression. Both the aberrant signaling via HCN channels and their mislocalization could be restored using a variety of pharmacological agents that target the endoplasmic reticulum (ER). Our rescue of the HCN channelopathy helps provide molecular details into the favorable outcomes of ER-targeting drugs on the pathogenesis and synaptic/cognitive deficits in AD mouse models, and implies that they might have beneficial effects on neurological disorders linked to HCN channelopathies.
Copyright © 2018. Published by Elsevier Inc.
encodes a transcription factor that is anchored in the endoplasmic reticulum (ER) and activated during the unfolded protein response (UPR) to protect cells from ER stress. Deletion of the isoform activating transcription factor 6α (ATF6α) and its paralog ATF6β results in embryonic lethality and notochord dysgenesis in nonhuman vertebrates, and loss-of-function mutations in ATF6α are associated with malformed neuroretina and congenital vision loss in humans. These phenotypes implicate an essential role for ATF6 during vertebrate development. We investigated this hypothesis using human stem cells undergoing differentiation into multipotent germ layers, nascent tissues, and organs. We artificially activated ATF6 in stem cells with a small-molecule ATF6 agonist and, conversely, inhibited ATF6 using induced pluripotent stem cells from patients with mutations. We found that ATF6 suppressed pluripotency, enhanced differentiation, and unexpectedly directed mesodermal cell fate. Our findings reveal a role for ATF6 during differentiation and identify a new strategy to generate mesodermal tissues through the modulation of the ATF6 arm of the UPR.
Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
OBJECTIVE - Single-cell RNA sequencing studies have revealed that the type-2 diabetes associated two-pore domain K (K2P) channel TALK-1 is abundantly expressed in somatostatin-secreting δ-cells. However, a physiological role for TALK-1 in δ-cells remains unknown. We previously determined that in β-cells, K flux through endoplasmic reticulum (ER)-localized TALK-1 channels enhances ER Ca leak, modulating Ca handling and insulin secretion. As glucose amplification of islet somatostatin release relies on Ca-induced Ca release (CICR) from the δ-cell ER, we investigated whether TALK-1 modulates δ-cell Ca handling and somatostatin secretion.
METHODS - To define the functions of islet δ-cell TALK-1 channels, we generated control and TALK-1 channel-deficient (TALK-1 KO) mice expressing fluorescent reporters specifically in δ- and α-cells to facilitate cell type identification. Using immunofluorescence, patch clamp electrophysiology, Ca imaging, and hormone secretion assays, we assessed how TALK-1 channel activity impacts δ- and α-cell function.
RESULTS - TALK-1 channels are expressed in both mouse and human δ-cells, where they modulate glucose-stimulated changes in cytosolic Ca and somatostatin secretion. Measurement of cytosolic Ca levels in response to membrane potential depolarization revealed enhanced CICR in TALK-1 KO δ-cells that could be abolished by depleting ER Ca with sarco/endoplasmic reticulum Ca ATPase (SERCA) inhibitors. Consistent with elevated somatostatin inhibitory tone, we observed significantly reduced glucagon secretion and α-cell Ca oscillations in TALK-1 KO islets, and found that blockade of α-cell somatostatin signaling with a somatostatin receptor 2 (SSTR2) antagonist restored glucagon secretion in TALK-1 KO islets.
CONCLUSIONS - These data indicate that TALK-1 reduces δ-cell cytosolic Ca elevations and somatostatin release by limiting δ-cell CICR, modulating the intraislet paracrine signaling mechanisms that control glucagon secretion.
Copyright © 2018 The Authors. Published by Elsevier GmbH.. All rights reserved.