ER-resident Protein Research Articles

Defects in autophagy lead to selective in vivo changes in turnover of cytosolic and organelle proteins in Arabidopsis.

Identification of autophagic protein cargo in plants in autophagy-related genes (ATG) mutants is complicated by changes in protein synthesis and protein degradation. To detect autophagic cargo, we measured protein degradation rate in shoots and roots of Arabidopsis (Arabidopsis thaliana) atg5 and atg11 mutants. These data show that less than a quarter of proteins changing in abundance are probable cargo and revealed roles of ATG11 and ATG5 in degradation of specific glycolytic enzymes and of other cytosol, chloroplast, and ER-resident proteins, and a specialized role for ATG11 in degradation of proteins from mitochondria and chloroplasts. Protein localization in transformed protoplasts and degradation assays in the presence of inhibitors confirm a role for autophagy in degrading glycolytic enzymes. Autophagy induction by phosphate (Pi) limitation changed metabolic profiles and the protein synthesis and degradation rates of atg5 and atg11 plants. A general decrease in the abundance of amino acids and increase in secondary metabolites in autophagy mutants was consistent with altered catabolism and changes in energy conversion caused by reduced degradation rate of specific proteins. Combining measures of changes in protein abundance and degradation rates, we also identify ATG11 and ATG5-associated protein cargo of low Pi-induced autophagy in chloroplasts and ER-resident proteins involved in secondary metabolism.

Abstract 517: Protein disulfide isomerase as a predictive biomarker for non-muscle invasive bladder cancer recurrence

Abstract INTRODUCTION AND OBJECTIVE: High recurrence rates found in non-muscle invasive bladder cancer (NMIBC) pose a financial and psychological burden for patients. We demonstrated that bladder cancer (BC) cells release protein disulfide isomerase (PDI), a redox-regulated ER-resident protein, via extracellular vesicles (EVs) when experiencing high levels of ER stress for their own survival. Chronic exposure to PDI-enriched BC EVs induced malignant transformation in recipient non-transformed cells. We hypothesized that the dynamic redox state in BC cells determines PDI cellular localization and tumors with elevated PDI preferentially incorporate PDI into EVs for removal. Furthermore, PDI expression levels and subcellular localization in tumors from NMIBC patients may predict NMIBC recurrence. METHODS: Retrospective chart review identified 122 patients with newly diagnosed low-grade NMIBC classified into 2 groups: recurrent (N=55) and non-recurrent (N=67) during follow-up period. Formalin fixed paraffin embedded tumor specimens from index transurethral resection of bladder tumor (TURBT) were obtained and a tissue microarray (TMA) was constructed. Immunofluorescent staining of TMA sections was conducted using antibodies against PDI and BiP, an ER stress marker. Stained tissues were photographed and tumor regions in each field were manually masked and confirmed by a genitourinary pathologist. Within each tumor region, total antibody labeling was determined by measuring the mean pixel intensity values with NIH ImageJ/Fiji. Manders coefficient was used to assess the colocalization of epitopes using JACoP plugin in ImageJ. RESULTS: Tumor tissues from patients that recurred expressed significantly higher levels of PDI and BiP. Moreover, high PDI and BiP expression predicted worse recurrence-free survival. These data suggest that tissues under higher levels of ER stress—as indicated by higher levels of PDI and BiP expression—have a higher risk of recurrence. Significantly higher levels of PDI were detected in non-ER cytosol in recurrent cohort tumors. CONCLUSIONS: This study provides a novel mechanism for BC recurrence and valuable clinical predictive biomarkers for NMIBC recurrence and progression. Future clinical applications targeting this pathway may be an avenue to prevent NMIBC recurrence. Citation Format: Kit L. Yuen, Chia-Hao Wu, Christopher R. Silvers, Alexis R. Steinmetz, Hiroshi Miyamoto, Edward M. Messing, Yi-Fen Lee. Protein disulfide isomerase as a predictive biomarker for non-muscle invasive bladder cancer recurrence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 517.

Abstract 400: Functional, structural and binding studies of the atypical ER-resident protein FKBP7, a potential target in chemoresistant prostate cancer

Abstract Background: Metastatic Castration Resistant Prostate Cancer (mCRPC) is the latest stage of Prostate Cancer (PCa). Despite the use of taxane-based chemotherapies Docetaxel and Cabazitaxel, mCRPC remains lethal due to chemoresistance. We recently identified FKBP7 as a potential therapeutic target of interest in PCa. FKBP7 is overexpressed in taxane-resistant PCa cells and impacts both cell proliferation and Docetaxel efficacy in chemoresistant models. We demonstrated FKBP7 affects translation and binds to the translation initiation complex eIF4F. FKBP7 is an ER-resident FKBP, but its properties remain poorly described. Methods: FKBP7 expression upon chemotherapy treatment was assessed by Western Blot and correlation between FKBP7 expression and clinical prognosis was examined on public cancer databases. Subcellular localization of FKBP7 was addressed by digitonin-based fractionation. Finally, FKBP7-predicted structure was obtained with structural modeling servers and sequence alignments were performed on AliView. We then produced and purified the recombinant catalytic domain of FKBP7 and collected high quality 15N HSQC NMR spectra. Afterwards, we examined its interaction with well-known FKBP ligands. Results: Increased FKBP7 expression was observed upon treatment with several cytotoxic chemotherapies in PCa-cell lines, and TCGA data underlined FKBP7 impacts survival in other cancers than PCa. Together, this suggests an enlarged potential involvement of FKBP7 in adaptive resistance. Mechanistically, in taxane-resistant models, FKBP7 overexpression did not result from higher protein stability but rather from a transcriptional regulation. Preliminary results of subcellular fractionation showed FKBP7 is present in the Endoplasmic Reticulum (ER) and seems to localize in the cytosol, independently of proteasomal degradation. We also confirmed FKBP7 is N45-glycosylated and observed that cytosolic-FKBP7 appears mainly glycosylated. This suggests that the ER-resident FKBP7 could be refluxed in the cytosol depending on its glycosylation state to regulate the activity of the cytosolic eIF4F complex. We are currently validating this hypothesis. At last, structural modeling predicted a FKBP-type fold with a potential FKBP7 substrate specificity as its catalytic pocket presents distinct composition for charge and bulkiness compared to other FKBPs. Accordingly, FKBP7 strongly binds Rapamycin and Everolimus, but surprisingly not FK506, confirming a selective binding profile. Conclusion: Our work depicts the recently identified FKBP7/eIF4F pathway in PCa-resistance and points atypical properties for the ER-resident FKBP7. It also indicates FKBP7 could be a druggable target in adaptive resistance of other solid cancers. Besides, we gathered original data on its structure and specificity for future drug-targeting strategies. Citation Format: Luce Dreno, Carolina Tiraboschi, Sofian Lacoste, Sofia Calpe Gomez, Marine F. Garrido, Matthieu Bertrand, Mariana Tannoury, Eric Jacquet, Naima Nhiri, Yohann Loriot, Karim Fizazi, Daniel Compagno, Nadine Assrir, Ewen Lescop, Anne Chauchereau. Functional, structural and binding studies of the atypical ER-resident protein FKBP7, a potential target in chemoresistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 400.

VAP Proteins - From Organelle Tethers to Pathogenic Host Interactors and Their Role in Neuronal Disease.

Vesicle-associated membrane protein (VAMP)-associated proteins (VAPs) are ubiquitous ER-resident tail-anchored membrane proteins in eukaryotic cells. Their N-terminal major sperm protein (MSP) domain faces the cytosol and allows them to interact with a wide variety of cellular proteins. Therefore, VAP proteins are vital to many cellular processes, including organelle membrane tethering, lipid transfer, autophagy, ion homeostasis and viral defence. Here, we provide a timely overview of the increasing number of VAPA/B binding partners and discuss the role of VAPA/B in maintaining organelle-ER interactions and cooperation. Furthermore, we address how viruses and intracellular bacteria hijack VAPs and their binding partners to induce interactions between the host ER and pathogen-containing compartments and support pathogen replication. Finally, we focus on the role of VAP in human disease and discuss how mutated VAPB leads to the disruption of cellular homeostasis and causes amyotrophic lateral sclerosis.

Targeting LIPA independent of its lipase activity is a therapeutic strategy in solid tumors via induction of endoplasmic reticulum stress

Triple-negative breast cancer (TNBC) has a poor clinical outcome, due to a lack of actionable therapeutic targets. Herein we define lysosomal acid lipase A (LIPA) as a viable molecular target in TNBC and identify a stereospecific small molecule (ERX-41) that binds LIPA. ERX-41 induces endoplasmic reticulum (ER) stress resulting in cell death, and this effect is on target as evidenced by specific LIPA mutations providing resistance. Importantly, we demonstrate that ERX-41 activity is independent of LIPA lipase function but dependent on its ER localization. Mechanistically, ERX-41 binding of LIPA decreases expression of multiple ER-resident proteins involved in protein folding. This targeted vulnerability has a large therapeutic window, with no adverse effects either on normal mammary epithelial cells or in mice. Our study implicates a targeted strategy for solid tumors, including breast, brain, pancreatic and ovarian, whereby small, orally bioavailable molecules targeting LIPA block protein folding, induce ER stress and result in tumor cell death.

The Role of Selenoproteins SELENOM and SELENOT in the Regulation of Apoptosis, ER Stress, and Calcium Homeostasis in the A-172 Human Glioblastoma Cell Line.

Simple SummaryIn this work, we present for the first time the effects of the suppression of the activity of poorly studied selenoproteins SELENOM and SELENOT in human glioblastoma cells, which is extremely important for understanding the functions of these proteins in brain cells. It has been shown that despite the structural similarity of these proteins, they affect the viability of these cancer cells in different ways, affecting various molecular mechanisms of regulation of pro-apoptotic genes, ER stress markers, and their physiological partners, as well as the regulation of cytosolic calcium.It is known that seven mammalian selenoproteins are localized in the endoplasmic reticulum: SELENOM, SELENOT, SELENOF, SELENOK, SELENOS, SELENON, and DIO2. Among them, SELENOM and SELENOT are the least studied; therefore, the study of their function using the widespread method of suppressing the expression of genes encoding these proteins and the activity of the enzymes themselves by RNA interference is of great interest. We have shown that a decrease in the expression of SELENOM and SELENOT mRNA in the A-172 human glioblastoma cell line by more than 10 times and the quantitative content of enzymes by more than 3 times leads to ER stress, expressed as a decrease in the ER capacity for storing Ca2+ ions. At the level of regulation of apoptotic processes, SELENOM knockdown leads to an increase in the expression of pro-apoptotic CHOP, GADD34, PUMA, and BIM genes, but a compensatory increase in the levels of SELENOT and antioxidant genes from the group of glutathione peroxidases and thioredoxins did not induce cell death. Knockdown of SELENOT had the opposite effect, reducing the expression of pro-apoptotic proteins and regulating the level of a smaller number of genes encoding antioxidant enzymes, which also did not affect the baseline level of apoptosis in the studied cells. At the same time, ER stress induced by MSA or SeNPs induced a more pronounced pro-apoptotic effect in SELENOT knockdown cells through suppression of the expression of selenium-containing antioxidant proteins. Thus, in this work, for the first time, the mechanisms of fine regulation of the processes of apoptosis, cell proliferation, and ER stress by two ER resident proteins, SELENOM and SELENOT, are touched upon, which is not only fundamental but also applied to clinical importance due to the close relationship between the calcium signaling system of cells, folding proteins-regulators of apoptosis and cell survival pathways.

Mechanisms regulating the sorting of soluble lysosomal proteins.

Lysosomes are key regulators of many fundamental cellular processes such as metabolism, autophagy, immune response, cell signalling and plasma membrane repair. These highly dynamic organelles are composed of various membrane and soluble proteins, which are essential for their proper functioning. The soluble proteins include numerous proteases, glycosidases and other hydrolases, along with activators, required for catabolism. The correct sorting of soluble lysosomal proteins is crucial to ensure the proper functioning of lysosomes and is achieved through the coordinated effort of many sorting receptors, resident ER and Golgi proteins, and several cytosolic components. Mutations in a number of proteins involved in sorting soluble proteins to lysosomes result in human disease. These can range from rare diseases such as lysosome storage disorders, to more prevalent ones, such as Alzheimer’s disease, Parkinson’s disease and others, including rare neurodegenerative diseases that affect children. In this review, we discuss the mechanisms that regulate the sorting of soluble proteins to lysosomes and highlight the effects of mutations in this pathway that cause human disease. More precisely, we will review the route taken by soluble lysosomal proteins from their translation into the ER, their maturation along the Golgi apparatus, and sorting at the trans-Golgi network. We will also highlight the effects of mutations in this pathway that cause human disease.

NLRC3 Localizes to the Endoplasmic Reticulum via Interactions with a Novel ER-Resident Protein

Abstract Nucleotide binding domain, leucine rich repeat CARD containing protein 3 (NLRC3) is a member of the NLR gene family. Members of this family have been associated with human inflammatory diseases such as Crohn’s disease and cryopyrin-associated periodic syndrome. Although NLRC3 (and others) are not associated with human diseases, it is expressed preferentially in the immune system and functions in pathogen recognition. NLRC3 is an intracellular protein involved in the sensing of lipopolysaccharide and cytosolic nucleic acids. NLRC3 is hypothesized to act as a negative regulator in response to bacterial and viral infection, suggesting that the vertebrate immune system has evolved specific inhibitors to limit the inflammatory response. We performed an unbiased yeast two-hybrid screen using an amino terminal fragment of NLRC3 to identify putative interacting proteins that might help elucidate the mechanism by which NLRC3 might inhibit inflammatory responses. To this end, we identified several interacting proteins. One protein in particular localizes to the endoplasmic reticulum (ER) and might serve as a localization-dependent anchor for NLRC3, thus facilitating its interaction with STING and TBK1. Here we show NLRC3 is distributed to the ER where it can interact with several important signaling molecules involved in type I interferon production. Supported by a grant from the NIH (R15 GM134430)

S‐acylation of STIM1 regulates store‐operated calcium entry

The initiating events happening during store‐operated calcium entry are not completely understood despite the tremendous importance of this process in immune responses. Upon endoplasmic reticulum (ER) calcium depletion, STIM1 and Orai1 form calcium release‐activated calcium (CRAC) channels to allow calcium influx from the extracellular milieu. S‐acylation is a reversible post‐translational modification of cysteine residues that affects protein structure, stability, and targeting to subdomains in the plasma membrane. Previously, we have shown that Orai1 is rapidly S‐acylated following T cell activation in Jurkat cells as well as ER calcium store depletion in HEK293 cells. Here we demonstrate that STIM1 is S‐acylated at C437 residue upon T cell activation and ER calcium store depletion. This is an interesting observation because very little is known about S‐acylation and its consequences in ER‐resident proteins. Upon store depletion, STIM1 adopts an extended conformation that permits binding to Orai1. We hypothesize that S‐acylation of STIM1 promotes and stabilizes the extended conformation of STIM1. Consistent with this hypothesis, we show that substitution of cysteine 437 in the STIM1 Orai1 activating region to a serine decreases calcium entry after store depletion. We further show that the ability of STIM1 to form puncta depends on its S‐acylation at this residue. Together with S‐acylation of Orai1, these data demonstrate that CRAC channel components are rapidly S‐acylated after ER calcium store depletion. In summary, based on our previous published literature on Orai1 S‐acylation, and current discovery of S‐acylation of STIM1, it is evident that S‐acylation recruits Orai1 to specialized membrane subdomains to form puncta with STIM1, whose extended conformation is stabilized by S‐acylation at its 437 residue. Hence, S‐acylation of Orai1 and STIM1 play a crucial role facilitate store‐operated calcium entry.

Phosphorylation at Ser724 of the ER stress sensor IRE1α governs its activation state and limits ER stress–induced hepatosteatosis

Inositol-requiring enzyme 1 (IRE1) is an evolutionarily conserved sensor of endoplasmic reticulum (ER) stress and mediates a key branch of the unfolded protein response in eukaryotic cells. It is an ER-resident transmembrane protein that possesses Ser/Thr protein kinase and endoribonuclease (RNase) activities in its cytoplasmic region. IRE1 is activated through dimerization/oligomerization and autophosphorylation at multiple sites, acting through its RNase activity to restore the functional capacity of the ER. However, it remains poorly defined in vivo how the autophosphorylation events of endogenous IRE1 govern its dynamic activation and functional output. Here, we generated a mouse model harboring a S724A knock-in mutation (Ern1S724A/S724A) and investigated the importance of phosphorylation at Ser724 within the kinase activation loop of murine IRE1α. We found that in mouse embryonic fibroblast cells and in primary hepatocytes, S724A mutation resulted in markedly reduced IRE1α autophosphorylation in parallel with blunted activation of its RNase activity to catalyze X-box binding protein 1 (Xbp1) mRNA splicing. Furthermore, ablation of IRE1α phosphorylation at Ser724 exacerbated ER stress–induced hepatic steatosis in tunicamycin-treated Ern1S724A/S724A mice. This was accompanied by significantly decreased hepatic production of spliced XBP1 protein but increased CCAAT-enhancer–binding protein homologous protein (CHOP) level, along with suppressed expression of key metabolic regulators of fatty acid β-oxidation and lipid secretion. These results demonstrate a critical role of phosphorylation at Ser724 of IRE1α in dynamically controlling its kinase activity, and thus its autophosphorylation state, which is coupled to activation of its RNase activity in counteracting hepatic steatosis under ER stress conditions.

Targeting WEE1/AKT Restores p53-Dependent Natural Killer-Cell Activation to Induce Immune Checkpoint Blockade Responses in "Cold" Melanoma.

Immunotherapy has revolutionized cancer treatment. Unfortunately, most tumor types do not respond to immunotherapy due to a lack of immune infiltration or "cold" tumor microenvironment (TME), a contributing factor in treatment failure. Activation of the p53 pathway can increase apoptosis of cancer cells, leading to enhanced antigen presentation, and can stimulate natural killer (NK) cells through expression of stress ligands. Therefore, modulation of the p53 pathway in cancer cells with wild-type TP53 has the potential to enhance tumor immunogenicity to NK cells, produce an inflammatory TME, and ultimately lead to tumor regression. In this study, we report simultaneous targeting of the AKT/WEE1 pathways is a novel and tolerable approach to synergistically induce p53 activation to inhibit tumor development. This approach reduced the growth of melanoma cells and induced plasma membrane surface localization of the ER-resident protein calreticulin, an indicator of immunogenic cell death (ICD). Increase in ICD led to enhanced expression of stress ligands recognized by the activating NK-cell receptor NKG2D, promoting tumor lysis. WEE1/AKT inhibition resulted in recruitment and activation of immune cells, including NK cells, in the TME, triggering an inflammatory cascade that transformed the "cold" TME of B16F10 melanoma into a "hot" TME that responded to anti-programmed cell death protein 1 (anti-PD-1), resulting in complete regression of established tumors. These results suggest that AKT/WEE1 pathway inhibition is a potential approach to broaden the utility of class-leading anti-PD-1 therapies by enhancing p53-mediated, NK cell-dependent tumor inflammation and supports the translation of this novel approach to further improve response rates for metastatic melanoma.

Hyperosmotic Stress Induces Phosphorylation of CERT and Enhances Its Tethering throughout the Endoplasmic Reticulum

The ceramide transport protein (CERT) delivers ceramide from the endoplasmic reticulum (ER) to the Golgi apparatus, where ceramide is converted to sphingomyelin (SM). The function of CERT is regulated in two distinct phosphorylation-dependent events: multiple phosphorylations in a serine-repeat motif (SRM) and phosphorylation of serine 315 residue (S315). Pharmacological inhibition of SM biosynthesis results in an increase in SRM-dephosphorylated CERT, which serves as an activated form, and an enhanced phosphorylation of S315, which augments the binding of CERT to ER-resident VAMP-associated protein (VAP), inducing the full activation of CERT to operate at the ER–Golgi membrane contact sites (MCSs). However, it remains unclear whether the two phosphorylation-dependent regulatory events always occur coordinately. Here, we describe that hyperosmotic stress induces S315 phosphorylation without affecting the SRM-phosphorylation state. Under hyperosmotic conditions, the binding of CERT with VAP-A is enhanced in an S315 phosphorylation-dependent manner, and this increased binding occurs throughout the ER rather than restrictedly at the ER–Golgi MCSs. Moreover, we found that de novo synthesis of SM with very-long acyl chains preferentially increases via a CERT-independent mechanism under hyperosmotic-stressed cells, providing an insight into a CERT-independent ceramide transport pathway for de novo synthesis of SM.

Loss of ERdj5 exacerbates oxidative stress in mice with alcoholic liver disease via suppressing Nrf2

Alcoholic liver disease is the major cause of chronic liver diseases. Excessive alcohol intake results in endoplasmic reticulum (ER) stress. ERdj5, a member of DNAJ family, is an ER-resident chaperone protein, whose role in alcoholic liver disease remains to be investigated. In this study, we aim to address the effect of ERdj5 on alcoholic liver disease and the underlying mechanism. Hepatic Dnajc10 (ERdj5) mRNA expression was elevated in both human and mouse alcoholic hepatitis. In mice subjected to chronic and binge ethanol feeding, ERdj5 levels were also markedly increased. Hepatic Dnajc10 correlated with Xbp1s mRNA. Tunicamycin, an ER stress inducer, increased ERdj5 levels. Dnajc10 knockout mice exhibited exacerbated alcohol-induced liver injury and hepatic steatosis. However, the macrophage numbers and chemokine levels were similar to those in wild-type mice. Depletion of Dnajc10 promoted oxidative stress. Ethanol feeding increased hepatic H2O2 levels, and these were further increased in Dnajc10 knockout mice. Additionally, Dnajc10-deficient hepatocytes produced large amounts of reactive oxygen species. Notably, Nrf2, a central regulator of oxidative stress, was decreased by depletion of Dnajc10 in the nuclear fraction of ethanol-treated mouse liver. Consistently, liver tissues from ethanol-fed Dnajc10 knockout mice had reduced expression of downstream antioxidant genes. Furthermore, hepatic glutathione content in the liver of knockout mice declined compared to wild-type mice. In conclusion, our results demonstrate that ethanol-induced ERdj5 may regulate the Nrf2 pathway and glutathione contents, and have protective effects on liver damage and alcohol-mediated oxidative stress in mice. These suggest that ERdj5 has the potential to protect against alcoholic liver disease.

Caffeine and MDMA (Ecstasy) Exacerbate ER Stress Triggered by Hyperthermia.

Drugs of abuse can cause local and systemic hyperthermia, a known trigger of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). Another trigger of ER stress and UPR is ER calcium depletion, which causes ER exodosis, the secretion of ER-resident proteins. In rodent models, club drugs such as 3,4-methylenedioxymethamphetamine (MDMA, ‘ecstasy’) can create hyperthermic conditions in the brain and cause toxicity that is affected by the environmental temperature and the presence of other drugs, such as caffeine. In human studies, MDMA stimulated an acute, dose-dependent increase in core body temperature, but an examination of caffeine and MDMA in combination remains a topic for clinical research. Here we examine the secretion of ER-resident proteins and activation of the UPR under combined exposure to MDMA and caffeine in a cellular model of hyperthermia. We show that hyperthermia triggers the secretion of normally ER-resident proteins, and that this aberrant protein secretion is potentiated by the presence of MDMA, caffeine, or a combination of the two drugs. Hyperthermia activates the UPR but the addition of MDMA or caffeine does not alter the canonical UPR gene expression despite the drug effects on ER exodosis of UPR-related proteins. One exception was increased BiP/GRP78 mRNA levels in MDMA-treated cells exposed to hyperthermia. These findings suggest that club drug use under hyperthermic conditions exacerbates disruption of ER proteostasis, contributing to cellular toxicity.

Activation of the sigma-1 receptor chaperone alleviates symptoms of Wolfram syndrome in preclinical models.

The Wolfram syndrome is a rare autosomal recessive disease affecting many organs with life-threatening consequences; currently, no treatment is available. The disease is caused by mutations in the WSF1 gene, coding for the protein wolframin, an endoplasmic reticulum (ER) transmembrane protein involved in contacts between ER and mitochondria termed as mitochondria-associated ER membranes (MAMs). Inherited mutations usually reduce the protein's stability, altering its homeostasis and ultimately reducing ER to mitochondria calcium ion transfer, leading to mitochondrial dysfunction and cell death. In this study, we found that activation of the sigma-1 receptor (S1R), an ER-resident protein involved in calcium ion transfer, could counteract the functional alterations of MAMs due to wolframin deficiency. The S1R agonist PRE-084 restored calcium ion transfer and mitochondrial respiration in vitro, corrected the associated increased autophagy and mitophagy, and was able to alleviate the behavioral symptoms observed in zebrafish and mouse models of the disease. Our findings provide a potential therapeutic strategy for treating Wolfram syndrome by efficiently boosting MAM function using the ligand-operated S1R chaperone. Moreover, such strategy might also be relevant for other degenerative and mitochondrial diseases involving MAM dysfunction.

Endoplasmic reticulum proteins Meigo and Gp93 govern dendrite targeting by regulating Toll-6 localization

Neuronal target recognition is performed by numerous cell-surface transmembrane proteins. Correct folding of these proteins occurs in the endoplasmic reticulum (ER) lumen of the neuronal cells before being transported to the plasma membrane of axons or dendrites. Disturbance in this protein folding process in the ER leads to dysfunction of neuronal cell surface molecules, resulting in abnormal neuronal targeting. In this study, we report that the ER-resident protein Meigo in Drosophila, governs the dendrite targeting of olfactory projection neurons (PNs) along the mediolateral axis of the antennal lobe by regulating Toll-6 localization. Loss of Meigo causes Toll-6 mislocalization in the PNs and mediolateral dendrite targeting defects, which are suppressed by Toll-6 overexpression. Furthermore, we found that the ER-chaperone protein, Gp93, also regulates the mediolateral targeting of PN dendrites by localization of the Toll-6 protein. Gp93 overexpression in the PN homozygous for the meigo mutation, partially rescued the dendrite targeting defect, while meigo knockdown decreased Gp93 expression levels in cultured cells. These results indicate that the ER-proteins Meigo and Gp93 regulate dendrite targeting by attenuating the amount and localization of cell surface receptors, including Toll-6, implying the unexpected but active involvement of ER proteins in neural wiring.

SIDT1 plays a key role in type I IFN responses to nucleic acids in plasmacytoid dendritic cells and mediates the pathogenesis of an imiquimod-induced psoriasis model.

SummaryBackgroundType I IFN (IFN-I) is a family of cytokines involved in the pathogenesis of autoimmune and autoinflammatory diseases such as psoriasis. SIDT1 is an ER-resident protein expressed in the lymphoid lineage, and involved in anti-viral IFN-I responses in vivo, through an unclear mechanism. Herein we have dissected the role of SIDT1 in the natural IFN-producing cells, the plasmacytoid dendritic cells (pDC).MethodsThe function of SIDT1 in pDC was determined by silencing its expression in human primary pDC and GEN2.2 cell line. SIDT1 role in vivo was assessed using the imiquimod-induced psoriasis model in the SIDT1-deficient mice (sidt1−/−).FindingsSilencing of SIDT1 in GEN2.2 led to a blockade of the IFN-I response after stimulation of TLR7 and TLR9, without affecting the pro-inflammatory responses or upregulation of maturation markers. We found that SIDT1 migrates from the ER to the endosomal and lysosomal compartments together with TLR9 after CpG stimulation, participating in the access of the TLR9-CpG complex to lysosome-related vesicles, and therefore mediating the activation of TBK1 and the nuclear migration of IRF7, but not of NF-κB. sidt1−/− mice showed a significant decrease in severity parameters of the imiquimod-induced acute psoriasis-like model, associated with a decrease in the production of IFN-I and IFN-dependent chemokines.InterpretationOur findings indicate that SIDT1 is at the cross-road between the IFN-I and the proinflammatory pathways and constitutes a promising drug target for psoriasis and other diseases mediated by IFN-I responses.FundingThis work was supported by the Consejería de Salud y Familias de la Junta de Andalucía (PIER_S1149 and C2_S0050) and Instituto de Salud Carlos III (PI18/00082 and PI21/01151), partly supported by European FEDER funds, and prior funding to MEAR from the Alliance for Lupus Research and the Swedish Research Council.

Regulating peroxisome-ER contacts via the ACBD5-VAPB tether by FFAT motif phosphorylation and GSK3β.

Peroxisomes and the endoplasmic reticulum (ER) cooperate in cellular lipid metabolism. They form membrane contacts through interaction of the peroxisomal membrane protein ACBD5 (acyl-coenzyme A-binding domain protein 5) and the ER-resident protein VAPB (vesicle-associated membrane protein-associated protein B). ACBD5 binds to the major sperm protein domain of VAPB via its FFAT-like (two phenylalanines [FF] in an acidic tract) motif. However, molecular mechanisms, which regulate formation of these membrane contact sites, are unknown. Here, we reveal that peroxisome-ER associations via the ACBD5-VAPB tether are regulated by phosphorylation. We show that ACBD5-VAPB binding is phosphatase-sensitive and identify phosphorylation sites in the flanking regions and core of the FFAT-like motif, which alter interaction with VAPB-and thus peroxisome-ER contact sites-differently. Moreover, we demonstrate that GSK3β (glycogen synthase kinase-3 β) regulates this interaction. Our findings reveal for the first time a molecular mechanism for the regulation of peroxisome-ER contacts in mammalian cells and expand the current model of FFAT motifs and VAP interaction.

Inhibition of high-fat diet–induced obesity via reduction of ER-resident protein Nogo occurs through multiple mechanisms

Obesity is a risk factor for insulin resistance, type 2 diabetes, and cardiovascular diseases. Reticulon-4 (Nogo) is an endoplasmic reticulum–resident protein with unclear functions in obesity. Herein, we investigated the effect of Nogo on obesity and associated metabolic disorders. Human serum samples were collected to explore the relationship between circulating Nogo-B and body mass index value. Nogo-deficient and WT littermate control mice were fed normal chow or high-fat diet (HFD) for 14 weeks, and HFD-induced obese C57BL/6J mice were injected scrambled or Nogo siRNA for 2 weeks. We found that in human and mouse serum, Nogo-B was positively correlated to body mass index/bodyweight and lipid profiles. Reduced Nogo (by genetic deletion or siRNA transfection) protected mice against HFD-induced obesity and related metabolic disorders. We demonstrate that Nogo deficiency reversed HFD-induced whitening of brown adipose tissue, thereby increasing thermogenesis. It also ameliorated lipid accumulation in tissues by activating the adiponectin–adiponectin receptor 1–AMP-activated kinase α signaling axis. Finally, Nogo deficiency potently reduced HFD-induced serum proinflammatory cytokines and infiltration of macrophages into metabolic organs, which is related to enhanced NF-κB p65 degradation via the lysosome pathway. Collectively, our study suggests that reduced levels of Nogo protect mice against HFD-induced obesity by increasing thermogenesis and energy metabolism while inhibiting NF-κB-mediated inflammation. Our results indicate that inhibition of Nogo may be a potential strategy for obesity treatment.

E3 ubiquitin ligase Nedd4-2 exerts neuroprotective effects during endoplasmic reticulum stress.

The neural precursor cell expressed developmentally down-regulated protein 4-like (Nedd4-2) is an E3 ubiquitin ligase critical for neurodevelopment and homeostasis of neural circuit excitability. While dysregulation of Nedd4-2 has been linked to elevated seizure susceptibility through impaired ubiquitination of multiple direct substrates, it remains largely unclear whether Nedd4-2 interconnects other cellular pathways that affect neuronal activity and seizure susceptibility. Here, we first showed that Nedd4-2 associates with the endoplasmic reticulum (ER) and regulates the expression of multiple ER-resident proteins. Furthermore, utilizing Nedd4-2 conditional knockout mice, we showed that Nedd4-2 is required for the maintenance of spontaneous neural activity and excitatory synapses following the induction of ER stress. When analyzing activation of the canonical pathways of ER stress response, we found that Nedd4-2 is required for phosphorylation of eIF2α. While phosphorylation of eIF2α has been shown to reduce seizure susceptibility, attempts to facilitate phosphorylation of eIF2α in Nedd4-2 conditional knockout mice failed to produce such a beneficial function, suggesting a role for Nedd4-2 in integrating the ER stress response to modulate seizure susceptibility. Altogether, our study demonstrates neuroprotective functions of Nedd4-2 during ER stress in neurons and could provide insight into neurological diseases in which the expression or activity of Nedd4-2 is impaired.