The position of single-base deletions in the VNTR sequence of the carboxyl ester lipase (CEL) gene determines pathogenicity

ABSTRACTVariable number of tandem repeat (VNTR) sequences present in the genome can have functional consequences that contribute to human disease. This is the case for the CEL gene, which encodes the digestive enzyme carboxyl ester lipase. CEL has a VNTR located in exon 11, and rare single-base deletions (DELs) within this region cause MODY8, an inherited disorder characterized by exocrine pancreatic dysfunction and diabetes. Here, we have studied how the position of single-base deletions within the CEL VNTR affects the protein’s pathogenic properties. We investigated four naturally occurring CEL variants with single-base deletions in different VNTR segments (DEL1, DEL4, DEL9, DEL13), of which only DEL1 and DEL4 have been observed in MODY8 patients. When expressed in a cellular model system, only DEL1 and DEL4 exhibited significantly reduced secretion and increased intracellular aggregation compared to normal CEL. We found that all DEL variants had slightly decreased enzymatic activity and that their level of O-glycosylation was affected. Moreover, only DEL1 and DEL4 significantly increased endoplasmic reticulum (ER) stress. In conclusion, CEL single-base deletion variants have the highest pathogenic potential when the mutational event has taken place in the proximal VNTR part, resulting in the longest aberrant protein tails. Thus, DEL1 and DEL4 are pathogenic CEL variants, whereas we consider DEL13 as benign and DEL9 as likely benign. These findings have implications for our understanding of how CEL mutations cause pancreatic disease through protein misfolding and proteotoxicity, leading to ER stress and activation of the unfolded protein response.

Download Full-text

Endoplasmic Reticulum Stress Regulators: New Drug Targets for Parkinson’s Disease

Journal of Parkinson s Disease ◽

10.3233/jpd-212673 ◽

2021 ◽

pp. 1-10

Author(s):

Vera Kovaleva ◽

Mart Saarma

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Endoplasmic Reticulum ◽

Protein Folding ◽

Er Stress ◽

Protein Misfolding ◽

Drug Targets ◽

Dopamine Neurons ◽

Drug Candidates ◽

The Unfolded Protein Response

Parkinson’s disease (PD) pathology involves progressive degeneration and death of vulnerable dopamine neurons in the substantia nigra. Extensive axonal arborisation and distinct functions make this type of neurons particularly sensitive to homeostatic perturbations, such as protein misfolding and Ca2 + dysregulation. Endoplasmic reticulum (ER) is a cell compartment orchestrating protein synthesis and folding, as well as synthesis of lipids and maintenance of Ca2 +-homeostasis in eukaryotic cells. When misfolded proteins start to accumulate in ER lumen the unfolded protein response (UPR) is activated. UPR is an adaptive signalling machinery aimed at relieving of protein folding load in the ER. When UPR is chronic, it can either boost neurodegeneration and apoptosis or cause neuronal dysfunctions. We have recently discovered that mesencephalic astrocyte-derived neurotrophic factor (MANF) exerts its prosurvival action in dopamine neurons and in animal model of PD through the direct binding to UPR sensor inositol-requiring protein 1 alpha (IRE1α) and attenuation of UPR. In line with this, UPR targeting resulted in neuroprotection and neurorestoration in various preclinical PD animal models. Therefore, growth factors (GFs), possessing both neurorestorative activity and restoration of protein folding capacity are attractive as drug candidates for PD treatment especially their blood-brain barrier penetrating analogs and small molecule mimetics. In this review, we discuss ER stress as a therapeutic target to treat PD; we summarize the existing preclinical data on the regulation of ER stress for PD treatment. In addition, we point out the crucial aspects for successful clinical translation of UPR-regulating GFs and new prospective in GFs-based treatments of PD, focusing on ER stress regulation.

Download Full-text

The Role of Endoplasmic Reticulum Stress in Cardiovascular Disease and Exercise

International Journal of Vascular Medicine ◽

10.1155/2017/2049217 ◽

2017 ◽

Vol 2017 ◽

pp. 1-9 ◽

Cited By ~ 22

Author(s):

Junyoung Hong ◽

Kwangchan Kim ◽

Jong-Hee Kim ◽

Yoonjung Park

Keyword(s):

Cardiovascular Disease ◽

Endoplasmic Reticulum ◽

Er Stress ◽

Signaling Pathways ◽

Protein Misfolding ◽

Unfolded Protein ◽

Activating Transcription Factor ◽

Apoptosis And Inflammation ◽

The Unfolded Protein Response

Endoplasmic reticulum (ER) stress, which is highly associated with cardiovascular disease, is triggered by a disturbance in ER function because of protein misfolding or an increase in protein secretion. Prolonged disruption of ER causes ER stress and activation of the unfolded protein response (UPR) and leads to various diseases. Eukaryotic cells respond to ER stress via three major sensors that are bound to the ER membrane: activating transcription factor 6 (ATF6), inositol-requiring protein 1α (IRE1α), and protein kinase RNA-like ER kinase (PERK). Chronic activation of ER stress causes damage in endothelial cells (EC) via apoptosis, inflammation, and oxidative stress signaling pathways. The alleviation of ER stress has recently been accepted as a potential therapeutic target to treat cardiovascular diseases such as heart failure, hypertension, and atherosclerosis. Exercise training is an effective nonpharmacological approach for preventing and alleviating cardiovascular disease. We here review the recent viewing of ER stress-mediated apoptosis and inflammation signaling pathways in cardiovascular disease and the role of exercise in ER stress-associated diseases.

Download Full-text

ER stress and the unfolded protein response in intestinal inflammation

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00063.2010 ◽

2010 ◽

Vol 298 (6) ◽

pp. G820-G832 ◽

Cited By ~ 107

Author(s):

Michael A. McGuckin ◽

Rajaraman D. Eri ◽

Indrajit Das ◽

Rohan Lourie ◽

Timothy H. Florin

Keyword(s):

Er Stress ◽

Unfolded Protein Response ◽

Protein Misfolding ◽

Intestinal Inflammation ◽

Secretory Cells ◽

Unfolded Protein ◽

Bowel Diseases ◽

Stressed Cells ◽

The Unfolded Protein Response ◽

Protein Response

Endoplasmic reticulum (ER) stress is a phenomenon that occurs when excessive protein misfolding occurs during biosynthesis. ER stress triggers a series of signaling and transcriptional events known as the unfolded protein response (UPR). The UPR attempts to restore homeostasis in the ER but if unsuccessful can trigger apoptosis in the stressed cells and local inflammation. Intestinal secretory cells are susceptible to ER stress because they produce large amounts of complex proteins for secretion, most of which are involved in mucosal defense. This review focuses on ER stress in intestinal secretory cells and describes how increased protein misfolding could occur in these cells, the process of degradation of misfolded proteins, the major molecular elements of the UPR pathway, and links between the UPR and inflammation. Evidence is reviewed from mouse models and human inflammatory bowel diseases that ties ER stress and activation of the UPR with intestinal inflammation, and possible therapeutic approaches to ameliorate ER stress are discussed.

Download Full-text

Human CPA1 mutation causes digestive enzyme misfolding and chronic pancreatitis in mice

Gut ◽

10.1136/gutjnl-2018-315994 ◽

2018 ◽

Vol 68 (2) ◽

pp. 301-312 ◽

Cited By ~ 21

Author(s):

Eszter Hegyi ◽

Miklós Sahin-Tóth

Keyword(s):

Chronic Pancreatitis ◽

Er Stress ◽

Digestive Enzyme ◽

Pancreatic Disease ◽

Mutant Mice ◽

Inflammatory Disorder ◽

Loss Of Function ◽

Stress Markers ◽

Elevated Expression

ObjectiveChronic pancreatitis is a progressive, relapsing inflammatory disorder of the pancreas, which often develops in the background of genetic susceptibility. Recently, loss-of-function mutations in CPA1, which encodes the digestive enzyme carboxypeptidase A1, were described in sporadic early onset cases and in hereditary pancreatitis. Mutation-induced misfolding of CPA1 and associated endoplasmic reticulum (ER) stress was suggested as potential disease mechanism; however, in vivo evidence has been lacking. The objective of the present study was to create a mouse model that recapitulates features of CPA1-associated chronic pancreatitis.DesignWe knocked-in the most frequently occurring p.N256K human CPA1 mutation to the mouse Cpa1 locus. Mutant mice were characterised with respect to pancreas pathology and ER stress and compared with C57BL/6N and CPA1 null control mice.ResultsIn the CPA1 N256K mutant mice, we observed hallmarks of chronic pancreatitis that included progressive acinar cell atrophy, inflammatory cell infiltration, fibrosis and acinar-ductal metaplasia. In contrast, similarly to the C57BL/6N mice, the CPA1 null control strain exhibited no signs of pancreatic disease. Mutation p.N256K induced misfolding of mouse CPA1 and resulted in elevated expression of ER stress markers Hspa5 (BiP) and Ddit3 (CHOP) both in cell culture and mutant mice.ConclusionThe results offer categorical evidence that CPA1 mutations elicit enzyme misfolding and cause chronic pancreatitis via an ER stress-related mechanism.

Download Full-text

Translational and posttranslational regulation of XIAP by eIF2α and ATF4 promotes ER stress–induced cell death during the unfolded protein response

Molecular Biology of the Cell ◽

10.1091/mbc.e13-11-0664 ◽

2014 ◽

Vol 25 (9) ◽

pp. 1411-1420 ◽

Cited By ~ 65

Author(s):

Nobuhiko Hiramatsu ◽

Carissa Messah ◽

Jaeseok Han ◽

Matthew M. LaVail ◽

Randal J. Kaufman ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Cell Death ◽

Er Stress ◽

Unfolded Protein Response ◽

Protein Misfolding ◽

Down Regulation ◽

Unfolded Protein ◽

Activity Loss ◽

The Unfolded Protein Response ◽

Protein Response

Endoplasmic reticulum (ER) protein misfolding activates the unfolded protein response (UPR) to help cells cope with ER stress. If ER homeostasis is not restored, UPR promotes cell death. The mechanisms of UPR-mediated cell death are poorly understood. The PKR-like endoplasmic reticulum kinase (PERK) arm of the UPR is implicated in ER stress–induced cell death, in part through up-regulation of proapoptotic CCAAT/enhancer binding protein homologous protein (CHOP). Chop−/− cells are partially resistant to ER stress–induced cell death, and CHOP overexpression alone does not induce cell death. These findings suggest that additional mechanisms regulate cell death downstream of PERK. Here we find dramatic suppression of antiapoptosis XIAP proteins in response to chronic ER stress. We find that PERK down-regulates XIAP synthesis through eIF2α and promotes XIAP degradation through ATF4. Of interest, PERK's down-regulation of XIAP occurs independently of CHOP activity. Loss of XIAP leads to increased cell death, whereas XIAP overexpression significantly enhances resistance to ER stress–induced cell death, even in the absence of CHOP. Our findings define a novel signaling circuit between PERK and XIAP that operates in parallel with PERK to CHOP induction to influence cell survival during ER stress. We propose a “two-hit” model of ER stress–induced cell death involving concomitant CHOP up-regulation and XIAP down-regulation both induced by PERK.

Download Full-text

BiP Availability Distinguishes States of Homeostasis and Stress in the Endoplasmic Reticulum of Living Cells

Molecular Biology of the Cell ◽

10.1091/mbc.e09-12-1066 ◽

2010 ◽

Vol 21 (12) ◽

pp. 1909-1921 ◽

Cited By ~ 50

Author(s):

Chun Wei Lai ◽

Deborah E. Aronson ◽

Erik Lee Snapp

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Protein Misfolding ◽

Single Cells ◽

Cell Types ◽

Secretory Protein ◽

Misfolded Proteins ◽

Secretory Proteins ◽

Molecular Events ◽

The Unfolded Protein Response

Accumulation of misfolded secretory proteins causes cellular stress and induces the endoplasmic reticulum (ER) stress pathway, the unfolded protein response (UPR). Although the UPR has been extensively studied, little is known about the molecular changes that distinguish the homeostatic and stressed ER. The increase in levels of misfolded proteins and formation of complexes with chaperones during ER stress are predicted to further crowd the already crowded ER lumen. Surprisingly, using live cell fluorescence microscopy and an inert ER reporter, we find the crowdedness of stressed ER, treated acutely with tunicamycin or DTT, either is comparable to homeostasis or significantly decreases in multiple cell types. In contrast, photobleaching experiments revealed a GFP-tagged variant of the ER chaperone BiP rapidly undergoes a reversible quantitative decrease in diffusion as misfolded proteins accumulate. BiP mobility is sensitive to exceptionally low levels of misfolded protein stressors and can detect intermediate states of BiP availability. Decreased BiP availability temporally correlates with UPR markers, but restoration of BiP availability correlates less well. Thus, BiP availability represents a novel and powerful tool for reporting global secretory protein misfolding levels and investigating the molecular events of ER stress in single cells, independent of traditional UPR markers.

Download Full-text

The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote resistance to endoplasmic reticulum stress

10.1101/457077 ◽

2018 ◽

Author(s):

Rolf M. Schmidt ◽

Sebastian Schuck

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Unfolded Protein Response ◽

Protein Misfolding ◽

Misfolded Proteins ◽

Secretory Proteins ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response ◽

Multiple Signaling

ABSTRACTMisfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (UPR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress.

Download Full-text

Aggregated and hyperstable damage-associated molecular patterns are released during ER stress to modulate immune function

10.1101/652990 ◽

2019 ◽

Author(s):

Alexander Andersohn ◽

M. Iveth Garcia ◽

Ying Fan ◽

Max C. Thompson ◽

Askar M. Akimzhanov ◽

...

Keyword(s):

Er Stress ◽

Systemic Inflammation ◽

Protein Misfolding ◽

Inflammatory Responses ◽

Traumatic Injury ◽

Adverse Outcomes ◽

The Unfolded Protein Response ◽

Molecular Patterns ◽

Damage Associated Molecular Patterns

AbstractChronic ER stress occurs when protein misfolding in the ER lumen remains unresolved despite activation of the unfolded protein response. We have shown that traumatic injury such as a severe burn leads to chronic ER stressin vivoleading to systemic inflammation which can last for more than a year. The mechanisms linking chronic ER stress to systemic inflammatory responses is not clear. Here we show that induction of chronic ER stress leads to the release of known and novel damage-associated molecular patterns (DAMPs). The secreted DAMPs are aggregated and markedly protease resistant. ER stress-derived DAMPs activate dendritic cells which are then capable of polarizing naïve T cells. Our findings indicate that induction of chronic ER stress may lead to the release of hyperstable DAMPs into the circulation resulting in persistent systemic inflammation and adverse outcomes.

Download Full-text

The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote ER stress resistance

eLife ◽

10.7554/elife.43244 ◽

2019 ◽

Vol 8 ◽

Cited By ~ 13

Author(s):

Rolf M Schmidt ◽

Julia P Schessner ◽

Georg HH Borner ◽

Sebastian Schuck

Keyword(s):

Er Stress ◽

Unfolded Protein Response ◽

Stress Resistance ◽

Protein Misfolding ◽

Misfolded Proteins ◽

Secretory Proteins ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response ◽

Multiple Signaling

Misfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (UPR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress.

Download Full-text

Activation of the unfolded protein response is associated with impaired granulopoiesis in transgenic mice expressing mutant Elane

Blood ◽

10.1182/blood-2010-10-311704 ◽

2011 ◽

Vol 117 (13) ◽

pp. 3539-3547 ◽

Cited By ~ 45

Author(s):

Suparna Nanua ◽

Mark Murakami ◽

Jun Xia ◽

David S. Grenda ◽

Jill Woloszynek ◽

...

Keyword(s):

Transgenic Mice ◽

Er Stress ◽

Unfolded Protein Response ◽

Protein Misfolding ◽

Strong Support ◽

Chemical Induction ◽

Granulocytic Differentiation ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response

Abstract Severe congenital neutropenia (SCN) is an inborn disorder of granulopoiesis that in many cases is caused by mutations of the ELANE gene, which encodes neutrophil elastase (NE). Recent data suggest a model in which ELANE mutations result in NE protein misfolding, induction of endoplasmic reticulum (ER) stress, activation of the unfolded protein response (UPR), and ultimately a block in granulocytic differentiation. To test this model, we generated transgenic mice carrying a targeted mutation of Elane (G193X) reproducing a mutation found in SCN. The G193X Elane allele produces a truncated NE protein that is rapidly degraded. Granulocytic precursors from G193X Elane mice, though without significant basal UPR activation, are sensitive to chemical induction of ER stress. Basal and stress granulopoiesis after myeloablative therapy are normal in these mice. Moreover, inaction of protein kinase RNA-like ER kinase (Perk), one of the major sensors of ER stress, either alone or in combination with G193X Elane, had no effect on basal granulopoiesis. However, inhibition of the ER-associated degradation (ERAD) pathway using a proteosome inhibitor resulted in marked neutropenia in G193X Elane. The selective sensitivity of G913X Elane granulocytic cells to ER stress provides new and strong support for the UPR model of disease patho-genesis in SCN.

Download Full-text