bims-unfpre 2023-02-12 papers

bims-unfpre

Biomed News

on Unfolded protein response

Issue of 2023–02–12
thirteen papers selected by
Susan Logue, University of Manitoba

A journey in UPR modeling.
Autophagy controls mucus secretion from intestinal goblet cells by alleviating ER stress.
The functional role of Ire1 in regulating autophagy and proteasomal degradation under prolonged proteotoxic stress.
The Activation of Reticulophagy by ER Stress through the ATF4-MAP1LC3A-CCPG1 Pathway in Ovarian Granulosa Cells Is Linked to Apoptosis and Necroptosis.
Scaffold Hopping and Screening for Potent Small Molecule Agonists for GRP94: Implications to Alleviate ER Stress-Associated Pathogenesis.
MANF regulates neuronal survival and UPR through its ER-located receptor IRE1α.
Runx1/3-driven adaptive endoplasmic reticulum stress pathways contribute to neurofibromagenesis.
Inhibition of the Activating Transcription Factor 6 Branch of Endoplasmic Reticulum Stress Ameliorates Brain Injury after Deep Hypothermic Circulatory Arrest.
Negligible role of TRAIL death receptors in cell death upon endoplasmic reticulum stress in B-cell malignancies.
Genomic targets of the IRE1-XBP1s pathway in mediating metabolic adaptation in epithelial plasticity.
Control of immune cell function by the unfolded protein response.
Enhanced IRE1α Phosphorylation/Oligomerization-Triggered XBP1 Splicing Contributes to Parkin-Mediated Prevention of SH-SY5Y Cell Death under Nitrosative Stress.
Shuffled ATG8 interacting motifs form an ancestral bridge between UFMylation and autophagy.

Biol Cell. 2023 Feb 07.

A journey in UPR modeling.

Ilaria Pontisso, Roberto Ornelas Guevara, Laurent Combettes, Geneviève Dupont.

  Protein folding and protein maturation largely occur in the controlled environment of the Endoplasmic Reticulum (ER). Perturbation to the correct functioning of this organelle leads to altered proteostasis and accumulation of misfolded proteins in the ER lumen. This condition is commonly known as ER stress and is appearing as an important contributor in the pathogenesis of several human diseases. Monitoring of the quality control processes is mediated by the Unfolded Protein Response (UPR). This response consists in a complex network of signaling pathways that aim to restore protein folding and ER homeostasis. Conditions in which UPR is not able to overcome ER stress lead to a switch of the UPR signaling program from an adaptive to a pro-apoptotic one, revealing a key role of UPR in modulating cell fate decisions. Because of its high complexity and its involvement in the regulation of different cellular outcomes, UPR has been the center of the development of computational models, which tried to better dissect the role of UPR or of its specific components in several contexts. In this review, we go through the existing mathematical models of UPR. We emphasize how their study contributed to an improved characterization of the role of this intricate response in the modulation of cellular functions. This article is protected by copyright. All rights reserved.

Keywords:  ATF6; ER stress; IRE1; PERK; Unfolded Protein Response; computational model; mathematical model; signaling

DOI:  https://doi.org/10.1111/boc.202200111
Cell Host Microbe. 2023 Jan 31. pii: S1931-3128(23)00031-8. [Epub ahead of print]

Autophagy controls mucus secretion from intestinal goblet cells by alleviating ER stress.

Maria Naama, Shahar Telpaz, Aya Awad, Shira Ben-Simon, Sarina Harshuk-Shabso, Sonia Modilevsky, Elad Rubin, Jasmin Sawaed, Lilach Zelik, Mor Zigdon, Nofar Asulin, Sondra Turjeman, Michal Werbner, Supapit Wongkuna, Rachel Feeney, Bjoern O Schroeder, Abraham Nyska, Meital Nuriel-Ohayon, Shai Bel.

  Colonic goblet cells are specialized epithelial cells that secrete mucus to physically separate the host and its microbiota, thus preventing bacterial invasion and inflammation. How goblet cells control the amount of mucus they secrete is unclear. We found that constitutive activation of autophagy in mice via Beclin 1 enables the production of a thicker and less penetrable mucus layer by reducing endoplasmic reticulum (ER) stress. Accordingly, genetically inhibiting Beclin 1-induced autophagy impairs mucus secretion, while pharmacologically alleviating ER stress results in excessive mucus production. This ER-stress-mediated regulation of mucus secretion is microbiota dependent and requires the Crohn's-disease-risk gene Nod2. Overproduction of mucus alters the gut microbiome, specifically expanding mucus-utilizing bacteria, such as Akkermansia muciniphila, and protects against chemical and microbial-driven intestinal inflammation. Thus, ER stress is a cell-intrinsic switch that limits mucus secretion, whereas autophagy maintains intestinal homeostasis by relieving ER stress.

Keywords:  Beclin 1; ER stress; Nod2; autophagy; colitis; goblet cell; inflammatory bowel diseases; microbiota; mucus; unfolded protein response

DOI:  https://doi.org/10.1016/j.chom.2023.01.006
FEBS J. 2023 Feb 09.

The functional role of Ire1 in regulating autophagy and proteasomal degradation under prolonged proteotoxic stress.

Eshita Das, Kiran Kumari Sahu, Ipsita Roy.

  Inhibition of endoribonuclease/kinase Ire1 has shown beneficial effects in many proteotoxicity-induced pathology models. The mechanism by which this occurs has not been elucidated completely. Using a proteotoxic yeast model of Huntington's disease, we show that deletion of Ire1 led to lower protein aggregation at longer time points. The rate of protein degradation was higher in ΔIre1 cells. We monitored the two major protein degradation mechanisms in the cell. The increase in expression of Rpn4, coding for the transcription factor controlling proteasome biogenesis, was higher in ΔIre1 cells. The chymotrypsin-like proteasomal activity was also significantly enhanced in these cells at later time points of aggregation. The gene and protein expression levels of the autophagy gene Atg8 were higher in ΔIre1 than in wild-type cells. Significant increase in autophagy flux was also seen in ΔIre1 cells at later time points of aggregation. The results suggest that deletion of Ire1 activates UPR-independent arms of the proteostasis network, especially under conditions of aggravated stress. Thus, inhibition of Ire1 may regulate UPR-independent cellular stress-response pathways under prolonged stress.

Keywords:  Atg8; Autophagy flux; Proteasome; Protein degradation; Rpn4

DOI:  https://doi.org/10.1111/febs.16747
Int J Mol Sci. 2023 Feb 01. pii: 2749. [Epub ahead of print]24(3):

The Activation of Reticulophagy by ER Stress through the ATF4-MAP1LC3A-CCPG1 Pathway in Ovarian Granulosa Cells Is Linked to Apoptosis and Necroptosis.

Huiduo Li, Yanan Jing, Xiaoya Qu, Jinyi Yang, Pengge Pan, Xinrui Liu, Hui Gao, Xiuying Pei, Cheng Zhang, Yanzhou Yang.

  Female infertility is caused by premature ovarian failure (POF), which is triggered by the endoplasmic reticulum (ER) stress-mediated apoptosis of granulosa cells. The ER unfolded protein response (UPRer) is initiated to promote cell survival by alleviating excessive ER stress, but cellular apoptosis is induced by persistent or strong ER stress. Recent studies have reported that reticulophagy is initiated by ER stress. Whether reticulophagy is activated in the ER stress-mediated apoptosis of granulosa cells and which pathway is initiated to activate reticulophagy during the apoptosis of granulosa cells are unknown. Therefore, the role of reticulophagy in granulosa cell death and the relationship between ER stress and reticulophagy were investigated in this work. Our results suggest that the ER stress inducer tunicamycin causes POF in mice, which is attributed to the apoptosis of granulosa cells and is accompanied by the activation of UPRer and reticulophagy. Furthermore, granulosa cells were treated with tunicamycin, and granulosa cell apoptosis was triggered and increased the expression of UPRer and reticulophagy molecules. The expression of ATF4 was then downregulated by RNAi, which decreased the levels of autophagy and the reticulophagy receptor CCGP1. Furthermore, ATF4 targets MAP1LC3A, as revealed by the ChIP sequencing results, and co-IP results demonstrated that MAP1LC3A interacts with CCPG1. Therefore, reticulophagy was activated by ER stress through the ATF4-MAP1LC3A-CCPG1 pathway to mitigate ER stress. Additionally, the role of reticulophagy in granulosa cells was investigated by the knockdown of CCPG1 with RNAi. Interestingly, only a small number of granulosa cells died by apoptosis, whereas the death of most granulosa cells occurred by necroptosis triggered by STAT1 and STAT3 to impair ER proteostasis and the ER protein quality control system UPRer. Taken together, the results indicate that the necroptosis of granulosa cells is triggered by up- and downregulating the reticulophagy receptor CCPG1 through STAT1/STAT3-(p)RIPK1-(p)RIPK3-(p)MLKL and that reticulophagy is activated by ER stress through the ATF4-MAP1LC3A-CCPG1 pathway.

Keywords:  CCPG1; ER stress; apoptosis; granulosa cells; necroptosis; reticulophagy; unfolded protein response

DOI:  https://doi.org/10.3390/ijms24032749
Mol Biotechnol. 2023 Feb 10.

Scaffold Hopping and Screening for Potent Small Molecule Agonists for GRP94: Implications to Alleviate ER Stress-Associated Pathogenesis.

Shoufia Jabeen Mubarak, Surabhi Gupta, Hemamalini Vedagiri.

  Disparity in the activity of Endoplasmic reticulum (ER) leads to degenerative diseases, mainly associated with protein misfolding and aggregation leading to cellular dysfunction and damage, ultimately contributing to ER stress. ER stress activates the complex network of Unfolded Protein Response (UPR) signaling pathways mediated by transmembrane proteins IRE1, ATF6, and PERK. In addition to UPR, many ER chaperones have evolved to optimize the output of properly folded secretory and membrane proteins. Glucose-regulated protein 94 (GRP94), an ER chaperone of heat shock protein HSP90 family, directs protein folding through interaction with other components of the ER protein folding machinery and assists in ER-associated degradation (ERAD). Activation of GRP94 would increase the efficacy of protein folding machinery and regulate the UPR pathway toward homeostasis. The present study aims to screen for novel agonists for GRP94 based on Core hopping, pharmacophore hypothesis, 3D-QSAR, and virtual screening with small-molecule compound libraries in order to improve the efficiency of native protein folding by enhancing GRP94 chaperone activity, therefore to reduce protein misfolding and aggregation. In this study, we have employed the strategy of small molecule-dependent ER programming to enhance the chaperone activity of GRP94 through scaffold hopping-based screening approach to identify specific GRP94 agonists. New scaffolds generated by altering the cores of NECA, the known GRP94 agonist, were validated by employing pharmacophore hypothesis testing, 3D-QSAR modeling, and molecular dynamics simulations. This facilitated the identification of small molecules to improve the efficiency of native protein folding by enhancing GRP94 activity. High-throughput virtual screening of the selected pharmacophore hypothesis against Selleckchem and ZINC databases retrieved a total of 2,27,081 compounds. Further analysis on docking and ADMET properties revealed Epimedin A, Narcissoside, Eriocitrin 1,2,3,4,6-O-Pentagalloylglucose, Secoisolariciresinol diglucoside, ZINC92952357, ZINC67650204, and ZINC72457930 as potential lead molecules. The stability and interaction of these small molecules were far better than the known agonist, NECA indicating their efficacy in selectively alleviating ER stress-associated pathogenesis. These results substantiate the fact that small molecule-dependent ER reprogramming would activate the ER chaperones and therefore reduce the protein misfolding as well as aggregation associated with ER stress in order to restore cellular homeostasis.

Keywords:  3D-QSAR; ER stress; GRP94; MD simulations; Pharmacophore modeling; Scaffold hopping; UPR

DOI:  https://doi.org/10.1007/s12033-023-00685-3
Cell Rep. 2023 Feb 03. pii: S2211-1247(23)00077-3. [Epub ahead of print]42(2): 112066

MANF regulates neuronal survival and UPR through its ER-located receptor IRE1α.

Vera Kovaleva, Li-Ying Yu, Larisa Ivanova, Olesya Shpironok, Jinhan Nam, Ave Eesmaa, Esa-Pekka Kumpula, Sven Sakson, Urve Toots, Mart Ustav, Juha T Huiskonen, Merja H Voutilainen, Päivi Lindholm, Mati Karelson, Mart Saarma.

  Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-located protein with cytoprotective effects in neurons and pancreatic β cells in vitro and in models of neurodegeneration and diabetes in vivo. However, the exact mode of MANF action has remained elusive. Here, we show that MANF directly interacts with the ER transmembrane unfolded protein response (UPR) sensor IRE1α, and we identify the binding interface between MANF and IRE1α. The expression of wild-type MANF, but not its IRE1α binding-deficient mutant, attenuates UPR signaling by decreasing IRE1α oligomerization; phosphorylation; splicing of Xbp1, Atf6, and Txnip levels; and protecting neurons from ER stress-induced death. MANF-IRE1α interaction and not MANF-BiP interaction is crucial for MANF pro-survival activity in neurons in vitro and is required to protect dopamine neurons in an animal model of Parkinson's disease. Our data show IRE1α as an intracellular receptor for MANF and regulator of neuronal survival.

Keywords:  BiP; CP: Molecular biology; CP: Neuroscience; ER stress; IRE1α; MANF; PD; Parkinson’s disease; UPR; mesencephalic astrocyte-derived neurotrophic factor; neuronal survival; unfolded protein response

DOI:  https://doi.org/10.1016/j.celrep.2023.112066
Oncogene. 2023 Feb 09.

Runx1/3-driven adaptive endoplasmic reticulum stress pathways contribute to neurofibromagenesis.

Youjin Na, Ashley Hall, Yanan Yu, Liang Hu, Kwangmin Choi, Jake A Burgard, Sara Szabo, Gang Huang, Nancy Ratner, Jianqiang Wu.

Neurofibromatosis type 1 (NF1) patients are predisposed to develop plexiform neurofibromas (PNFs). Three endoplasmic reticulum (ER) stress response pathways restore cellular homeostasis. The unfolded protein response (UPR) sensors contribute to tumor initiation in many cancers. We found that all three UPR pathways were activated in mouse and human PNFs, with protein kinase RNA [PKR]-like ER kinase (PERK) the most highly expressed. We tested if neurofibroma cells adapt to ER stress, leading to their growth. Pharmacological or genetic inhibition of PERK reduced mouse neurofibroma-sphere number, and genetic inhibition in PERK in Schwann cell precursors (SCPs) decreased tumor-like lesion numbers in a cell transplantation model. Further, in a PNF mouse model, deletion of PERK in Schwann cells (SCs) and SCPs reduced tumor size, number, and increased survival. Mechanistically, loss of Nf1 activated PERK-eIF2α-ATF4 signaling and increased ATF4 downstream target gene p21 translocation from nucleus to cytoplasm. This nucleus-cytoplasm translocation was mediated by exportin-1. Runx transcriptionally activated ribosome gene expression and increased protein synthesis to allow SCs to adapt to ER stress and tumor formation. We propose that targeting proteostasis might provide cytotoxic and/or potentially durable novel therapy for PNFs.

DOI: https://doi.org/10.1038/s41388-023-02620-x
J Clin Med. 2023 Jan 19. pii: 814. [Epub ahead of print]12(3):

Inhibition of the Activating Transcription Factor 6 Branch of Endoplasmic Reticulum Stress Ameliorates Brain Injury after Deep Hypothermic Circulatory Arrest.

You-Peng Zhang, Qin Yang, Yi-Ai Li, Ming-Huan Yu, Guo-Wei He, Yu-Xiang Zhu, Zhi-Gang Liu, Xiao-Cheng Liu.

  Neurological dysfunction is a common complication of deep hypothermic circulatory arrest (DHCA). Endoplasmic reticulum (ER) stress plays a role in neuronal ischemia-reperfusion injury; however, it is unknown whether it contributes to DHCA-induced brain injury. Here, we aimed to investigate the role of ER stress in a rat DHCA model and cell hypothermic oxygen-glucose deprivation reoxygenation (OGD/R) model. ER stress and apoptosis-related protein expression were identified using Western blot analysis. Cell counting assay-8 and flow cytometry were used to determine cell viability and apoptosis, respectively. Brain injury was evaluated using modified neurological severity scores, whereas brain injury markers were detected through histological examinations and immunoassays. We observed significant ER stress molecule upregulation in the DHCA rat hippocampus and in hypothermic OGD/R PC-12 cells. In vivo and in vitro experiments showed that ER stress or activating transcription factor 6 (ATF6) inhibition alleviated rat DHCA-induced brain injury, increased cell viability, and decreased apoptosis accompanied by C/EBP homologous protein (CHOP). ER stress is involved in DHCA-induced brain injury, and the inhibition of the ATF6 branch of ER stress may ameliorate this injury by inhibiting CHOP-mediated apoptosis. This study establishes a scientific foundation for identifying new therapeutic targets for perioperative brain protection in clinical DHCA.

Keywords:  ATF6; apoptosis; brain injury; deep hypothermic circulatory arrest; endoplasmic reticulum stress

DOI:  https://doi.org/10.3390/jcm12030814
Oncogenesis. 2023 Feb 08. 12(1): 6

Negligible role of TRAIL death receptors in cell death upon endoplasmic reticulum stress in B-cell malignancies.

Francesca Favaro, Demi Both, Ingrid A M Derks, Marcel Spaargaren, Cristina Muñoz-Pinedo, Eric Eldering.

Impairments in protein folding in the endoplasmic reticulum (ER) lead to a condition called ER stress, which can trigger apoptosis via the mitochondrial or the death receptor (extrinsic) pathway. There is controversy concerning involvement of the death receptor (DR)4 and DR5-Caspase-8 -Bid pathway in ER stress-mediated cell death, and this axis has not been fully studied in B-cell malignancies. Using three B-cell lines from Mantle Cell Lymphoma, Waldenström's macroglobulinemia and Multiple Myeloma origins, we engineered a set of CRISPR KOs of key components of these cell death pathways to address this controversy. We demonstrate that DR4 and/or DR5 are essential for killing via TRAIL, however, they were dispensable for ER-stress induced-cell death, by Thapsigargin, Brefeldin A or Bortezomib, as were Caspase-8 and Bid. In contrast, the deficiency of Bax and Bak fully protected from ER stressors. Caspase-8 and Bid were cleaved upon ER-stress stimulation, but this was DR4/5 independent and rather a result of mitochondrial-induced feedback loop subsequent to Bax/Bak activation. Finally, combined activation of the ER-stress and TRAIL cell-death pathways was synergistic with putative clinical relevance for B-cell malignancies.

DOI: https://doi.org/10.1038/s41389-023-00450-w
Nucleic Acids Res. 2023 Feb 11. pii: gkad077. [Epub ahead of print]

Genomic targets of the IRE1-XBP1s pathway in mediating metabolic adaptation in epithelial plasticity.

Dianhua Qiao, Melissa Skibba, Xiaofang Xu, Allan R Brasier.

Epithelial mesenchymal plasticity (EMP) is a complex cellular reprogramming event that plays a major role in tissue homeostasis. Recently we observed the unfolded protein response (UPR) triggers EMP through the inositol-requiring protein 1 (IRE1α)-X-box-binding protein 1 spliced (XBP1s) axis, enhancing glucose shunting to protein N glycosylation. To better understand the genomic targets of XBP1s, we identified its genomic targets using Cleavage Under Targets and Release Using Nuclease (CUT&RUN) of a FLAG-epitope tagged XBP1s in RSV infection. CUT&RUN identified 7086 binding sites in chromatin that were enriched in AP-1 motifs and GC-sequences. Of these binding sites, XBP1s peaks mapped to 4827 genes controlling Rho-GTPase signaling, N-linked glycosylation and ER-Golgi transport. Strikingly, XBP1s peaks were within 1 kb of transcription start sites of 2119 promoters. In addition to binding core mesenchymal transcription factors SNAI1 and ZEB1, we observed that hexosamine biosynthetic pathway (HBP) enzymes were induced and contained proximal XBP1s peaks. We demonstrate that IRE1α -XBP1s signaling is necessary and sufficient to activate core enzymes by recruiting elongation-competent phospho-Ser2 CTD modified RNA Pol II. We conclude that the IRE1α-XBP1s pathway coordinately regulates mesenchymal transcription factors and hexosamine biosynthesis in EMP by a mechanism involving recruitment of activated pSer2-Pol II to GC-rich promoters.

DOI: https://doi.org/10.1093/nar/gkad077
Nat Rev Immunol. 2023 Feb 08.

Control of immune cell function by the unfolded protein response.

Giusy Di Conza, Ping-Chih Ho, Juan R Cubillos-Ruiz, Stanley Ching-Cheng Huang.

Initiating and maintaining optimal immune responses requires high levels of protein synthesis, folding, modification and trafficking in leukocytes, which are processes orchestrated by the endoplasmic reticulum. Importantly, diverse extracellular and intracellular conditions can compromise the protein-handling capacity of this organelle, inducing a state of 'endoplasmic reticulum stress' that activates the unfolded protein response (UPR). Emerging evidence shows that physiological or pathological activation of the UPR can have effects on immune cell survival, metabolism, function and fate. In this Review, we discuss the canonical role of the adaptive UPR in immune cells and how dysregulation of this pathway in leukocytes contributes to diverse pathologies such as cancer, autoimmunity and metabolic disorders. Furthermore, we provide an overview as to how pharmacological approaches that modulate the UPR could be harnessed to control or activate immune cell function in disease.

DOI: https://doi.org/10.1038/s41577-023-00838-0
Int J Mol Sci. 2023 Jan 19. pii: 2017. [Epub ahead of print]24(3):

Enhanced IRE1α Phosphorylation/Oligomerization-Triggered XBP1 Splicing Contributes to Parkin-Mediated Prevention of SH-SY5Y Cell Death under Nitrosative Stress.

Tsung-Lang Chiu, Hsin-Yi Huang, Hui-Fen Chang, Hsin-Rong Wu, Mei-Jen Wang.

  Mutations in parkin, a neuroprotective protein, are the predominant cause of autosomal recessive juvenile Parkinson's disease. Neuroinflammation-derived nitrosative stress has been implicated in the etiology of the chronic neurodegeneration. However, the interactions between genetic predisposition and nitrosative stress contributing to the degeneration of dopaminergic (DA) neurons remain incompletely understood. Here, we used the SH-SY5Y neuroblastoma cells to investigate the function of parkin and its pathogenic mutants in relation to cell survival under nitric oxide (NO) exposure. The results showed that overexpression of wild-type parkin protected SH-SY5Y cells from NO-induced apoptosis in a reactive oxygen species-dependent manner. Under nitrosative stress conditions, parkin selectively upregulated the inositol-requiring enzyme 1α/X-box binding protein 1 (IRE1α/XBP1) signaling axis, an unfolded protein response signal through the sensor IRE1α, which controls the splicing of XBP1 mRNA. Inhibition of XBP1 mRNA splicing either by pharmacologically inhibiting IRE1α endoribonuclease activity or by genetically knocking down XBP1 interfered with the protective activity of parkin. Furthermore, pathogenic parkin mutants with a defective protective capacity showed a lower ability to activate the IRE1α/XBP1 signaling. Finally, we demonstrated that IRE1α activity augmented by parkin was possibly mediated through interacting with IRE1α to regulate its phosphorylation/oligomerization processes, whereas mutant parkin diminished its binding to and activation of IRE1α. Thus, these results support a direct link between the protective activity of parkin and the IRE1α/XBP1 pathway in response to nitrosative stress, and mutant parkin disrupts this function.

Keywords:  IRE1α; Parkinson’s disease; XBP1; neuroinflammation; nitric oxide; nitrosative stress; oligomerization; parkin

DOI:  https://doi.org/10.3390/ijms24032017
EMBO J. 2023 Feb 10. e112053

Shuffled ATG8 interacting motifs form an ancestral bridge between UFMylation and autophagy.

Lorenzo Picchianti, Víctor Sánchez de Medina Hernández, Ni Zhan, Nicholas At Irwin, Roan Groh, Madlen Stephani, Harald Hornegger, Rebecca Beveridge, Justyna Sawa-Makarska, Thomas Lendl, Nenad Grujic, Christin Naumann, Sascha Martens, Thomas A Richards, Tim Clausen, Silvia Ramundo, G Elif Karagöz, Yasin Dagdas.

  UFMylation involves the covalent modification of substrate proteins with UFM1 (Ubiquitin-fold modifier 1) and is important for maintaining ER homeostasis. Stalled translation triggers the UFMylation of ER-bound ribosomes and activates C53-mediated autophagy to clear toxic polypeptides. C53 contains noncanonical shuffled ATG8-interacting motifs (sAIMs) that are essential for ATG8 interaction and autophagy initiation. However, the mechanistic basis of sAIM-mediated ATG8 interaction remains unknown. Here, we show that C53 and sAIMs are conserved across eukaryotes but secondarily lost in fungi and various algal lineages. Biochemical assays showed that the unicellular alga Chlamydomonas reinhardtii has a functional UFMylation pathway, refuting the assumption that UFMylation is linked to multicellularity. Comparative structural analyses revealed that both UFM1 and ATG8 bind sAIMs in C53, but in a distinct way. Conversion of sAIMs into canonical AIMs impaired binding of C53 to UFM1, while strengthening ATG8 binding. Increased ATG8 binding led to the autoactivation of the C53 pathway and sensitization of Arabidopsis thaliana to ER stress. Altogether, our findings reveal an ancestral role of sAIMs in UFMylation-dependent fine-tuning of C53-mediated autophagy activation.

Keywords:  ER-phagy; UFMylation; phylogenomics; ribosome stalling; selective autophagy

DOI:  https://doi.org/10.15252/embj.2022112053