Proteostatic Signaling & Control of Protein Synthesis

Protein Response ◽

New Protein

The tremendous diversity and complexity of proteins invariably results in protein misfolding, to which cells have evolved numerous mechanisms of mitigating. Degrading misfolded proteins is perhaps the most intuitive strategy, but also critical to managing proteostasis are the elaborate mechanisms of translational control. Attenuated rates of translation ameliorate protein misfolding by downregulating the flux of new protein and conserving ATP. Loss of translational control, particularly in neurons, constitutes a major proteostatic dysfunction capable of causing or exacerbating neurodegeneration, while interventions aimed at downregulating protein synthesis are generally neuroprotective. In this review, I examine the critical neuronal signaling networks employed to control translation with an emphasis on current research. This includes the Unfolded Protein Response (UPR), the mitochondrial UPR (mtUPR), mTORC1 signaling, and stress granule formation.

The Inflammatory Bowel Disease Drug Azathioprine Induces Autophagy via mTORC1 and the Unfolded Protein Response Sensor PERK

Inflammatory Bowel Diseases ◽

10.1093/ibd/izz039 ◽

2019 ◽

Vol 25 (9) ◽

pp. 1481-1496 ◽

Cited By ~ 6

Author(s):

Kirsty M Hooper ◽

Victor Casanova ◽

Sadie Kemp ◽

Katherine A Staines ◽

Jack Satsangi ◽

...

Keyword(s):

Inflammatory Bowel Disease ◽

Flow Cytometry ◽

Bowel Disease ◽

Unfolded Protein ◽

Drug Mechanism ◽

Mtorc1 Signaling ◽

Inflammatory Bowel ◽

Abstract Background Genetic studies have strongly linked autophagy to Crohn’s disease (CD), and stimulating autophagy in CD patients may be therapeutically beneficial. The aim of this study was to evaluate the effect of current inflammatory bowel disease (IBD) drugs on autophagy and investigate molecular mechanisms of action and functional outcomes in relation to this cellular process. Methods Autophagy marker LC3 was evaluated by confocal fluorescence microscopy and flow cytometry. Drug mechanism of action was investigated by polymerase chain reaction (PCR) array with changes in signaling pathways examined by immunoblot and quantitative reverse transcription PCR (RT-qPCR). Clearance of adherent-invasive Escherichia coli (AIEC) and levels of pro-inflammatory cytokine tumor necrosis factor alpha (TNFα) were evaluated by gentamicin protection assays and RT-qPCR, respectively. The marker LC3 was analyzed in peripheral blood mononuclear cells (PBMCs) from pediatric patients by flow cytometry. Results Azathioprine induces autophagy via mechanisms involving modulation of mechanistic target of rapamycin (mTORC1) signaling and stimulation of the unfolded protein response (UPR) sensor PERK. Induction of autophagy with azathioprine correlated with the enhanced clearance of AIEC and dampened AIEC-induced increases in TNFα. Azathioprine induced significant increase in autophagosome bound LC3-II in PBMC populations ex vivo, supporting in vitro findings. In patients, the CD-associated ATG16L1 T300A single-nucleotide polymorphism did not attenuate azathioprine induction of autophagy. Conclusions Modulation of autophagy via mTORC1 and the UPR may contribute to the therapeutic efficacy of azathioprine in IBD.

Beyond the cell factory: Homeostatic regulation of and by the UPRER

Science Advances ◽

10.1126/sciadv.abb9614 ◽

2020 ◽

Vol 6 (29) ◽

pp. eabb9614

Author(s):

Melissa G. Metcalf ◽

Ryo Higuchi-Sanabria ◽

Gilberto Garcia ◽

C. Kimberly Tsui ◽

Andrew Dillin

Keyword(s):

Protein Misfolding ◽

Lipid Synthesis ◽

Transcriptional Response ◽

Cell Factory ◽

Unfolded Protein ◽

Membrane Bound ◽

Emerging Themes ◽

Protein Response ◽

Cellular Components

The endoplasmic reticulum (ER) is commonly referred to as the factory of the cell, as it is responsible for a large amount of protein and lipid synthesis. As a membrane-bound organelle, the ER has a distinct environment that is ideal for its functions in synthesizing these primary cellular components. Many different quality control machineries exist to maintain ER stability under the stresses associated with synthesizing, folding, and modifying complex proteins and lipids. The best understood of these mechanisms is the unfolded protein response of the ER (UPRER), in which transmembrane proteins serve as sensors, which trigger a coordinated transcriptional response of genes dedicated for mitigating the stress. As the name suggests, the UPRER is most well described as a functional response to protein misfolding stress. Here, we focus on recent findings and emerging themes in additional roles of the UPRER outside of protein homeostasis, including lipid homeostasis, autophagy, apoptosis, and immunity.

Protein Misfolding Induces Hypoxic Preconditioning via a Subset of the Unfolded Protein Response Machinery

Molecular and Cellular Biology ◽

10.1128/mcb.00922-10 ◽

2010 ◽

Vol 30 (21) ◽

pp. 5033-5042 ◽

Cited By ~ 39

Author(s):

Xianrong R. Mao ◽

C. Michael Crowder

Keyword(s):

Protein Misfolding ◽

Transcriptional Response ◽

Hypoxic Preconditioning ◽

Misfolded Proteins ◽

Hypoxic Exposure ◽

Hypoxic Injury ◽

Unfolded Protein ◽

ABSTRACT Prolonged cellular hypoxia results in energy failure and ultimately cell death. However, less-severe hypoxia can induce a cytoprotective response termed hypoxic preconditioning (HP). The unfolded protein response pathway (UPR) has been known for some time to respond to hypoxia and regulate hypoxic sensitivity; however, the role of the UPR, if any, in HP essentially has been unexplored. We have shown previously that a sublethal hypoxic exposure of the nematode Caenorhabditis elegans induces a protein chaperone component of the UPR (L. L. Anderson, X. Mao, B. A. Scott, and C. M. Crowder, Science 323:630-633, 2009). Here, we show that HP induces the UPR and that the pharmacological induction of misfolded proteins is itself sufficient to stimulate a delayed protective response to hypoxic injury that requires the UPR pathway proteins IRE-1, XBP-1, and ATF-6. HP also required IRE-1 but not XBP-1 or ATF-6; instead, GCN-2, which is known to suppress translation and induce an adaptive transcriptional response under conditions of UPR activation or amino acid deprivation, was required for HP. The phosphorylation of the translation factor eIF2α, an established mechanism of GCN-2-mediated translational suppression, was not necessary for HP. These data suggest a model where hypoxia-induced misfolded proteins trigger the activation of IRE-1, which along with GCN-2 controls an adaptive response that is essential to HP.

Suppression of Mouse AApoAII Amyloidosis Progression by Daily Supplementation with Oxidative Stress Inhibitors

Oxidative Medicine and Cellular Longevity ◽

10.1155/2019/1263274 ◽

2019 ◽

Vol 2019 ◽

pp. 1-14

Author(s):

Jian Dai ◽

Xin Ding ◽

Hiroki Miyahara ◽

Zhe Xu ◽

Xiaoran Cui ◽

...

Keyword(s):

Oxidative Stress ◽

Protein Misfolding ◽

Amyloid Fibrils ◽

Treatment Strategies ◽

Amyloid Deposition ◽

Unfolded Protein ◽

Antioxidative Effects ◽

Protein Misfolding And Aggregation

Protein Response ◽

Amyloidosis is a group of diseases characterized by protein misfolding and aggregation to form amyloid fibrils and subsequent deposition within various tissues. Previous studies have indicated that amyloidosis is often associated with oxidative stress. However, it is not clear whether oxidative stress is involved in the progression of amyloidosis. We administered the oxidative stress inhibitors tempol and apocynin via drinking water to the R1.P1-Apoa2c mouse strain induced to develop mouse apolipoprotein A-II (AApoAII) amyloidosis and found that treatment with oxidative stress inhibitors led to reduction in AApoAII amyloidosis progression compared to an untreated group after 12 weeks, especially in the skin, stomach, and liver. There was no effect on ApoA-II plasma levels or expression of Apoa2 mRNA. Detection of the lipid peroxidation markers 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA) revealed that the antioxidative effects of the treatments were most obvious in the skin, stomach, and liver, which contained higher levels of basal oxidative stress. Moreover, the unfolded protein response was reduced in the liver and was associated with a decrease in oxidative stress and amyloid deposition. These results suggest that antioxidants can suppress the progression of AApoAII amyloid deposition in the improved microenvironment of tissues and that the effect may be related to the levels of oxidative stress in local tissues. This finding provides insights for antioxidative stress treatment strategies for amyloidosis.

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 ◽

Protein Misfolding ◽

Intestinal Inflammation ◽

Secretory Cells ◽

Unfolded Protein ◽

Bowel Diseases ◽

Stressed Cells ◽

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.

Complementary Roles of GADD34- and CReP-Containing Eukaryotic Initiation Factor 2α Phosphatases during the Unfolded Protein Response

Molecular and Cellular Biology ◽

10.1128/mcb.00190-16 ◽

2016 ◽

Vol 36 (13) ◽

pp. 1868-1880 ◽

Cited By ~ 21

Author(s):

David W. Reid ◽

Angeline S. L. Tay ◽

Jeyapriya R. Sundaram ◽

Irene C. J. Lee ◽

Qiang Chen ◽

...

Keyword(s):

Protein Synthesis ◽

Control Cell ◽

Mrna Translation ◽

Initiation Factor ◽

Current View ◽

Eukaryotic Initiation Factor ◽

Unfolded Protein ◽

Phosphorylation of eukaryotic initiation factor 2α (eIF2α) controls transcriptome-wide changes in mRNA translation in stressed cells. While phosphorylated eIF2α (P-eIF2α) attenuates global protein synthesis, mRNAs encoding stress proteins are more efficiently translated. Two eIF2α phosphatases, containing GADD34 and CReP, catalyze P-eIF2α dephosphorylation. The current view of GADD34, whose transcription is stress induced, is that it functions in a feedback loop to resolve cell stress. In contrast, CReP, which is constitutively expressed, controls basal P-eIF2α levels in unstressed cells. Our studies show that GADD34 drives substantial changes in mRNA translation in unstressed cells, particularly targeting the secretome. Following activation of the unfolded protein response (UPR), rapid translation ofGADD34mRNA occurs and GADD34 is essential for UPR progression. In the absence of GADD34, eIF2α phosphorylation is persistently enhanced and the UPR translational program is significantly attenuated. This “stalled” UPR is relieved by the subsequent activation of compensatory mechanisms that include AKT-mediated suppression of PKR-like kinase (PERK) and increased expression ofCRePmRNA, partially restoring protein synthesis. Our studies highlight the coordinate regulation of UPR by the GADD34- and CReP-containing eIF2α phosphatases to control cell viability.

The unfolded protein response is triggered following a single, unaccustomed resistance-exercise bout

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00511.2013 ◽

2014 ◽

Vol 307 (6) ◽

pp. R664-R669 ◽

Cited By ~ 33

Author(s):

Daniel I. Ogborn ◽

Bryon R. McKay ◽

Justin D. Crane ◽

Gianni Parise ◽

Mark A. Tarnopolsky

Keyword(s):

Protein Synthesis ◽

Protein Kinase ◽

Resistance Exercise ◽

Initiation Factor ◽

Knee Extensors ◽

Leg Extension ◽

Unfolded Protein ◽

Endoplasmic reticulum (ER) stress results from an imbalance between the abundance of synthesized proteins and the folding capacity of the ER. In response, the unfolded protein response (UPR) attempts to restore ER function by attenuating protein synthesis and inducing chaperone expression. Resistance exercise (RE) stimulates protein synthesis; however, a postexercise accumulation of unfolded proteins may activate the UPR. Aging may impair protein folding, and the accumulation of oxidized and misfolded proteins may stimulate the UPR at rest in aged muscle. Eighteen younger ( n = 9; 21 ± 3 yr) and older ( n = 9; 70 ± 4 yr) untrained men completed a single, unilateral bout of RE using the knee extensors (four sets of 10 repetitions at 75% of one repetition maximum on the leg press and leg extension) to determine whether the UPR is increased in resting, aged muscle and whether RE stimulates the UPR. Muscle biopsies were taken from the nonexercised and exercised vastus lateralis at 3, 24, and 48 h postexercise. Age did not affect any of the proteins and transcripts related to the UPR. Glucose-regulated protein 78 (GRP78) and protein kinase R-like ER protein kinase (PERK) proteins were increased at 48 h postexercise, whereas inositol-requiring enzyme 1 alpha (IRE1α) was elevated at 24 h and 48 h. Despite elevated protein, GRP78 and PERK mRNA was unchanged; however, IRE1α mRNA was increased at 24 h postexercise. Activating transcription factor 6 (ATF6) mRNA increased at 24 h and 48 h, whereas ATF4, CCAAT/enhancer-binding protein homologous protein (CHOP), and growth arrest and DNA damage protein 34 mRNA were unchanged. These data suggest that RE activates specific pathways of the UPR (ATF6/IRE1α), whereas PERK/eukaryotic initiation factor 2 alpha/CHOP does not. In conclusion, acute RE results in UPR activation, irrespective of age.

The Unfolded Protein Response and Chemical Chaperones Reduce Protein Misfolding and Colitis in Mice

Gastroenterology ◽

10.1053/j.gastro.2013.01.023 ◽

2013 ◽

Vol 144 (5) ◽

pp. 989-1000.e6 ◽

Cited By ~ 111

Author(s):

Stewart Siyan Cao ◽

Ellen M. Zimmermann ◽

Brandy–Mengchieh Chuang ◽

Benbo Song ◽

Anosike Nwokoye ◽

...

Keyword(s):

Protein Misfolding ◽

Chemical Chaperones ◽

Unfolded Protein ◽

Age-related decline of the unfolded protein response in the heart promotes protein misfolding and cardiac pathology

10.1101/2021.06.16.448596 ◽

2021 ◽

Author(s):

Christoph Hofmann ◽

Erik A Blackwood ◽

Tobias Jakobi ◽

Clara Sandmann ◽

Julia Groß ◽

...

Keyword(s):

Heart Failure ◽

Cardiac Myocytes ◽

Protein Misfolding ◽

Cardiac Myocyte ◽

Myocardial Dysfunction ◽

Disease Process ◽

Unfolded Protein ◽

Cardiac myocyte death during heart failure is particularly detrimental, given that cardiac muscle exhibits limited regenerative potential. Protein aggregation was previously observed in end-stage heart failure, suggesting protein-misfolding in cardiac myocytes as a contributor to the disease process. However, the relationship between protein-misfolding, cardiac myocyte death, and myocardial dysfunction is yet to be clearly established. Here, we showed that protein synthesis and the unfolded protein response (UPR) declined as a function of mammalian postnatal development, especially in tissues with low mitotic activity, such as the heart. A deeper examination in animals models showed that compared to neonatal cardiac myocytes, adult cardiac myocytes expressed lower levels of the adaptive UPR transcription factor, ATF6, as well as lower levels of numerous ATF6-regulated genes, which was associated with susceptibility to ER stress-induced cell death. Further reduction of the ATF6-dependent gene program in ATF6 knock-out mice led to the accumulation of misfolded proteins in the myocardium and impaired myocardial function in response to cardiac stress, indicating that ATF6 plays a critical adaptive role in the setting of cardiac disease. Thus, strategies to increase ATF6 aimed at balancing proteostasis in cardiac myocytes might be a fruitful avenue for the development of novel therapies for heart disease and other age-associated diseases.