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

Protein Misfolding ◽

Misfolded Proteins ◽

Secretory Proteins ◽

Unfolded Protein ◽

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.

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 ◽

Stress Resistance ◽

Protein Misfolding ◽

Misfolded Proteins ◽

Secretory Proteins ◽

Unfolded Protein ◽

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.

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 ◽

Protein Misfolding ◽

Down Regulation ◽

Unfolded Protein ◽

Activity Loss ◽

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.

The unfolded protein response coordinates the production of endoplasmic reticulum protein and endoplasmic reticulum membrane.

Molecular Biology of the Cell ◽

10.1091/mbc.8.9.1805 ◽

1997 ◽

Vol 8 (9) ◽

pp. 1805-1814 ◽

Cited By ~ 277

Author(s):

J S Cox ◽

R E Chapman ◽

P Walter

Keyword(s):

Endoplasmic Reticulum ◽

Secretory Pathway ◽

Lipid Synthesis ◽

Secretory Proteins ◽

Endoplasmic Reticulum Membrane ◽

Yeast Saccharomyces Cerevisiae ◽

Unfolded Protein ◽

The endoplasmic reticulum (ER) is a multifunctional organelle responsible for production of both lumenal and membrane components of secretory pathway compartments. Secretory proteins are folded, processed, and sorted in the ER lumen and lipid synthesis occurs on the ER membrane itself. In the yeast Saccharomyces cerevisiae, synthesis of ER components is highly regulated: the ER-resident proteins by the unfolded protein response and membrane lipid synthesis by the inositol response. We demonstrate that these two responses are intimately linked, forming different branches of the same pathway. Furthermore, we present evidence indicating that this coordinate regulation plays a role in ER biogenesis.

Proteostasis In The Endoplasmic Reticulum: Road to Cure

Cancers ◽

10.3390/cancers11111793 ◽

2019 ◽

Vol 11 (11) ◽

pp. 1793 ◽

Cited By ~ 7

Author(s):

Nam ◽

Jeon

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Protein Quality ◽

Tumor Development ◽

Therapeutic Interventions ◽

Secretory Proteins ◽

Unfolded Protein ◽

Stress Signals ◽

The endoplasmic reticulum (ER) is an interconnected organelle that is responsible for the biosynthesis, folding, maturation, stabilization, and trafficking of transmembrane and secretory proteins. Therefore, cells evolve protein quality-control equipment of the ER to ensure protein homeostasis, also termed proteostasis. However, disruption in the folding capacity of the ER caused by a large variety of pathophysiological insults leads to the accumulation of unfolded or misfolded proteins in this organelle, known as ER stress. Upon ER stress, unfolded protein response (UPR) of the ER is activated, integrates ER stress signals, and transduces the integrated signals to relive ER stress, thereby leading to the re-establishment of proteostasis. Intriguingly, severe and persistent ER stress and the subsequently sustained unfolded protein response (UPR) are closely associated with tumor development, angiogenesis, aggressiveness, immunosuppression, and therapeutic response of cancer. Additionally, the UPR interconnects various processes in and around the tumor microenvironment. Therefore, it has begun to be delineated that pharmacologically and genetically manipulating strategies directed to target the UPR of the ER might exhibit positive clinical outcome in cancer. In the present review, we summarize recent advances in our understanding of the UPR of the ER and the UPR of the ER–mitochondria interconnection. We also highlight new insights into how the UPR of the ER in response to pathophysiological perturbations is implicated in the pathogenesis of cancer. We provide the concept to target the UPR of the ER, eventually discussing the potential of therapeutic interventions for targeting the UPR of the ER for cancer treatment.

The PGRS Domain of Mycobacterium tuberculosis PE_PGRS Protein Rv0297 Is Involved in Endoplasmic Reticulum Stress-Mediated Apoptosis through Toll-Like Receptor 4

mBio ◽

10.1128/mbio.01017-18 ◽

2018 ◽

Vol 9 (3) ◽

Cited By ~ 19

Author(s):

Sonam Grover ◽

Tarina Sharma ◽

Yadvir Singh ◽

Sakshi Kohli ◽

Manjunath P. ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Mycobacterium Tuberculosis ◽

Er Stress ◽

Toll Like Receptor ◽

Toll Like Receptor 4 ◽

Content Type ◽

Unfolded Protein ◽

ABSTRACT The genome of Mycobacterium tuberculosis , the causal organism of tuberculosis (TB), encodes a unique protein family known as the PE/PPE/PGRS family, present exclusively in the genus Mycobacterium and nowhere else in the living kingdom, with largely unexplored functions. We describe the functional significance of the PGRS domain of Rv0297, a member of this family. In silico analyses revealed the presence of intrinsically disordered stretches and putative endoplasmic reticulum (ER) localization signals in the PGRS domain of Rv0297 (Rv0297PGRS). The PGRS domain aids in ER localization, which was shown by infecting macrophage cells with M. tuberculosis and by overexpressing the protein by transfection in macrophage cells followed by activation of the unfolded protein response, as evident from increased expression of GRP78/GRP94 and CHOP/ATF4, leading to disruption of intracellular Ca 2+ homeostasis and increased nitric oxide (NO) and reactive oxygen species (ROS) production. The consequent activation of the effector caspase-8 resulted in apoptosis of macrophages, which was Toll-like receptor 4 (TLR4) dependent. Administration of recombinant Rv0297PGRS (rRv0297PGRS) also exhibited similar effects. These results implicate a hitherto-unknown role of the PGRS domain of the PE_PGRS protein family in ER stress-mediated cell death through TLR4. Since this protein is already known to be present at later stages of infection in human granulomas it points to the possibility of it being employed by M. tuberculosis for its dissemination via an apoptotic mechanism. IMPORTANCE Apoptosis is generally thought to be a defense mechanism in protecting the host against Mycobacterium tuberculosis in early stages of infection. However, apoptosis during later stages in lung granulomas may favor the bacterium in disseminating the disease. ER stress has been found to induce apoptosis in TB granulomas, in zones where apoptotic macrophages accumulate in mice and humans. In this study, we report ER stress-mediated apoptosis of host cells by the Rv0297-encoded PE_PGRS5 protein of M. tuberculosis exceptionally present in the pathogenic Mycobacterium genus. The PGRS domain of Rv0297 aids the protein in localizing to the ER and induces the unfolded protein response followed by apoptosis of macrophages. The effect of the Rv0297PGRS domain was found to be TLR4 dependent. This study presents novel insights on the strategies employed by M. tuberculosis to disseminate the disease.

Endoplasmic Reticulum Stress and Unfolded Protein Response in Breast Cancer: The Balance between Apoptosis and Autophagy and Its Role in Drug Resistance

International Journal of Molecular Sciences ◽

10.3390/ijms20040857 ◽

2019 ◽

Vol 20 (4) ◽

pp. 857 ◽

Cited By ~ 20

Author(s):

Lorenza Sisinni ◽

Michele Pietrafesa ◽

Silvia Lepore ◽

Francesca Maddalena ◽

Valentina Condelli ◽

...

Keyword(s):

Breast Cancer ◽

Endoplasmic Reticulum ◽

Er Stress ◽

Inflammatory Diseases ◽

Unfolded Protein ◽

Chronic Activation ◽

Protein Response ◽

The Relationship

The unfolded protein response (UPR) is a stress response activated by the accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum (ER) and its uncontrolled activation is mechanistically responsible for several human pathologies, including metabolic, neurodegenerative, and inflammatory diseases, and cancer. Indeed, ER stress and the downstream UPR activation lead to changes in the levels and activities of key regulators of cell survival and autophagy and this is physiologically finalized to restore metabolic homeostasis with the integration of pro-death or/and pro-survival signals. By contrast, the chronic activation of UPR in cancer cells is widely considered a mechanism of tumor progression. In this review, we focus on the relationship between ER stress, apoptosis, and autophagy in human breast cancer and the interplay between the activation of UPR and resistance to anticancer therapies with the aim to disclose novel therapeutic scenarios. The hypothesis that autophagy and UPR may provide novel molecular targets in human malignancies is discussed.

Endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation

Journal of Molecular Endocrinology ◽

10.1530/jme-15-0306 ◽

2016 ◽

Vol 57 (1) ◽

pp. R1-R17 ◽

Cited By ~ 31

Author(s):

Kira Meyerovich ◽

Fernanda Ortis ◽

Florent Allagnat ◽

Alessandra K Cardozo

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Diabetic Patients ◽

Β Cells ◽

Β Cell ◽

Unfolded Protein ◽

Islet Inflammation ◽

Insulin-secreting pancreatic β-cells are extremely dependent on their endoplasmic reticulum (ER) to cope with the oscillatory requirement of secreted insulin to maintain normoglycemia. Insulin translation and folding rely greatly on the unfolded protein response (UPR), an array of three main signaling pathways designed to maintain ER homeostasis and limit ER stress. However, prolonged or excessive UPR activation triggers alternative molecular pathways that can lead to β-cell dysfunction and apoptosis. An increasing number of studies suggest a role of these pro-apoptotic UPR pathways in the downfall of β-cells observed in diabetic patients. Particularly, the past few years highlighted a cross talk between the UPR and inflammation in the context of both type 1 (T1D) and type 2 diabetes (T2D). In this article, we describe the recent advances in research regarding the interplay between ER stress, the UPR, and inflammation in the context of β-cell apoptosis leading to diabetes.

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.

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.

Ratiometric sensing of BiP-client versus BiP levels by the unfolded protein response determines its signaling amplitude

eLife ◽

10.7554/elife.27518 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 26

Author(s):

Anush Bakunts ◽

Andrea Orsi ◽

Milena Vitale ◽

Angela Cattaneo ◽

Federica Lari ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Heavy Chain ◽

Immunoglobulin M ◽

Unfolded Protein ◽

Er Chaperone ◽

Ideal System ◽

Insufficient folding capacity of the endoplasmic reticulum (ER) activates the unfolded protein response (UPR) to restore homeostasis. Yet, how the UPR achieves ER homeostatic readjustment is poorly investigated, as in most studies the ER stress that is elicited cannot be overcome. Here we show that a proteostatic insult, provoked by persistent expression of the secretory heavy chain of immunoglobulin M (µs), is well-tolerated in HeLa cells. Upon µs expression, its levels temporarily eclipse those of the ER chaperone BiP, leading to acute, full-geared UPR activation. Once BiP is in excess again, the UPR transitions to chronic, submaximal activation, indicating that the UPR senses ER stress in a ratiometric fashion. In this process, the ER expands about three-fold and becomes dominated by BiP. As the UPR is essential for successful ER homeostatic readjustment in the HeLa-µs model, it provides an ideal system for dissecting the intricacies of how the UPR evaluates and alleviates ER stress.