Endoplasmic Reticulum Resident Protein Research Articles

Prevalence and Significance of AGR2 Expression in Human Cancer.

Anterior gradient 2 (AGR2) is a resident endoplasmic reticulum (ER) protein with a vital role in embryonal development, mucus maturation, tissue regeneration, and wound healing. To determine the prevalence and clinical significance of AGR2 expression in cancer, a tissue microarray containing 14,966 tumors from 134 different tumor types and subtypes as well as 608 samples of 76 different normal tissue types was analyzed by immunohistochemistry (IHC). AGR2 positivity was found in 103 of 134 tumor categories, and 83 tumor categories contained at least one strongly positive case. AGR2 expression was most frequently seen in tumors of the female genital tract, particularly adenocarcinomas (up to 100%), various breast cancer subtypes (57.1%-100%), urothelial carcinoma (74.6%-100%), adenocarcinomas of the upper and lower gastrointestinal tract (93.6%-99.6%), and pancreaticobiliary cancers (65.2%-98.2%). AGR2 positivity was slightly less common in squamous cell carcinomas (46.4%-77.3%) and mainly absent in mesenchymal and lymphoid tumors. While AGR2 expression was only weak or absent in the normal thyroid, it was moderate to strong in 46.0% of adenomas, 52.8% of follicular carcinomas, and 81.8% of papillary carcinomas of the thyroid. High AGR2 expression was strongly linked to poor ISUP (p < 0.0001), Fuhrman (p < 0.0001), and Thoenes (p < 0.0001) grades as well as advanced pT stage (p = 0.0035) in clear cell renal cell carcinoma (ccRCC). Low AGR2 expression was associated with high BRE grade in breast cancer (p = 0.0049), nodal metastasis (p = 0.0275) and RAS mutation (p = 0.0136) in colorectal cancer, nodal metastasis (p = 0.0482) in endometrioid endometrial carcinoma, high grade in noninvasive urothelial carcinoma (p = 0.0003), and invasive tumor growth in urothelial carcinoma (p < 0.0001). It is concluded that AGR2 expression occurs in a broad range of different tumor entities and that AGR2 assessment may serve as a diagnostic aid for the distinction of thyroidal neoplasms and as a prognostic marker in various cancer types.

Syntaxin11 Deficiency Inhibits CRAC Channel Priming To Suppress Cytotoxicity And Gene Expression In FHLH4 Patient T Lymphocytes.

CRAC channels enable calcium entry from the extracellular space in response to a variety of stimuli and are crucial for gene expression and granule exocytosis in lymphocytes. Here we find that Syntaxin11, a Q-SNARE, associated with FHLH4 disease in human patients, directly binds Orai1, the pore forming subunit of CRAC channels. Syntaxin11 depletion strongly inhibited SOCE, CRAC currents, IL-2 expression and cytotoxicity in cell lines and FHLH4 patient T lymphocytes. Constitutively active H134 Orai1 mutant completely reconstituted calcium entry in Syntaxin11 depleted cells and the defects of granule exocytosis as well as gene expression could be bypassed by ionomycin induced calcium influx in FHLH4 T lymphocytes. Our data reveal a Syntaxin11 induced pre-activation state of Orai which is necessary for its subsequent coupling and gating by the endoplasmic reticulum resident Stim protein. We propose that ion channel regulation by specific SNAREs is a primary and conserved function which may have preceded their role in vesicle fusion.

IER3IP1 mutations cause neonatal diabetes due to impaired proinsulin trafficking.

Immediate early response 3 interacting-protein 1 (IER3IP1) is an endoplasmic reticulum resident protein, highly expressed in pancreatic cells and the developing brain cortex. Homozygous mutations in IER3IP1 have been found in individuals with microcephaly and neonatal diabetes, yet the underlying mechanism causing beta cell failure remains unclear. Here, we utilized differentiation of genome edited-stem cells into pancreatic islet cells to elucidate the molecular basis of IER3IP1 neonatal diabetes. Using CRISPR-Cas9, we generated two distinct IER3IP1-mutant human embryonic stem cell lines: a homozygous knock-in model of a patient mutation (IER3IP1V21G), and a knockout model (IER3IP1-/-). While these mutant stem cell lines differentiated normally into definitive endoderm and pancreatic progenitors, we observed that IER3IP1-KO stem cell derived-islets (SC-islets) presented a significant decrease in beta cell numbers and elevated ER stress. Retention Using Selective Hooks (RUSH) assay revealed three-fold reduction in ER-to-Golgi trafficking of proinsulin in IER3IP1 mutant beta cells. Additionally, IER3IP1 mutant SC-islets implanted into immunocompromised mice displayed defective human insulin secretion, indicating the deleterious impact of IER3IP1 mutations on beta cell function. Our study provides valuable insights into the role of IER3IP1 in human beta cell biology and establishes a useful model to investigate ER-to-Golgi trafficking defects within beta cells.

Revealing the global mechanism related to carnosine synthesis in the pectoralis major of slow-growing Korat chickens using a proteomic approach.

This study aimed to find global mechanisms related to carnosine synthesis in slow-growing Korat chickens (KRC) using a proteomic approach. M. pectoralis major samples were collected from 10-week-old female KRC including low-carnosine (LC, 2,756.6±82.88 μg/g; n = 5) and high-carnosine (HC, 4,212.5 ±82.88 μg/g; n = 5). We identified 152 common proteins, and 8 of these proteins showed differential expression between the LC and HC groups (p<0.05). Heat shock 70 kDa protein 8, Heat shock 70 kDa protein 2, protein disulfide isomerase family A, member 6, and endoplasmic reticulum resident protein 29 were significantly involved in protein processing in the endoplasmic reticulum pathway (false discovery rate<0.05), suggesting that the pathway is related to differential carnosine concentration in the M. pectoralis major of KRC. A high concentration of carnosine in the meat is mainly involved in low abundances of Titin isoform Ch12 and Connectin and high abundances of M-protein to maintain homeostasis during muscle contraction. These consequences improve meat characteristics, which were confirmed by the principal component analysis. Carnosine synthesis may occur when muscle cells need to recover homeostasis after being interfered with carnosine synthesis precursors, leading to improved muscle function. To the best of our knowledge, this is the first study to describe in detail the global molecular mechanisms in divergent carnosine contents in meat based on the proteomic approach.

TMCO1 is upregulated in breast cancer and regulates the response to pro-apoptotic agents in breast cancer cells

AbstractThe release of Ca2+ ions from endoplasmic reticulum calcium stores is a key event in a variety of cellular processes, including gene transcription, migration and proliferation. This release of Ca2+ often occurs through inositol 1,4,5-triphosphate receptors and the activity of these channels and the levels of stored Ca2+ in the endoplasmic reticulum are important regulators of cell death in cancer cells. A recently identified Ca2+ channel of the endoplasmic reticulum is transmembrane and coiled-coil domains 1 (TMCO1). In this study, we link the overexpression of TMCO1 with prognosis in node-positive basal breast cancer patients. We also identify interacting proteins of TMCO1, which include endoplasmic reticulum-resident proteins involved in Ca2+ regulation and proteins directly involved in nucleocytoplasmic transport. Interacting proteins included nuclear transport proteins and TMCO1 was shown to have both nuclear and endoplasmic reticulum localisation in MDA-MB-231 basal breast cancer cells. These studies also define a role for TMCO1 in the regulation of breast cancer cells in their sensitivity to BCL-2/MCL-1 inhibitors, analogous to the role of inositol 1,4,5-triphosphate receptors in the regulation of cell death pathways activated by these agents.

Characterizing interactions of endoplasmic reticulum resident proteins in situ through the YST-PPI method.

The mutual interactions of endoplasmic reticulum (ER) resident proteins in the ER maintain its functions, prompting the protein folding, modification, and transportation. Here, a new method, named YST-PPI (YESS-based Split fast TEV protease system for Protein-Protein Interaction) was developed, targeting the characterization of protein interactions in ER. YST-PPI method integrated the YESS system, split-TEV technology, and endoplasmic reticulum retention signal peptide (ERS) to provide an effective strategy for studying ER in situ PPIs in a fast and quantitative manner. The interactions among 15 ER-resident proteins, most being identified molecular chaperones, of S. cerevisiae were explored using the YST-PPI system, and their interaction network map was constructed, in which more than 74 interacting resident protein pairs were identified. Our studies also showed that Lhs1p plays a critical role in regulating the interactions of most of the ER-resident proteins, except the Sil1p, indicating its potential role in controlling the ER molecular chaperones. Moreover, the mutual interaction revealed by our studies further confirmed that the ER-resident proteins perform their functions in a cooperative way and a multimer complex might be formed during the process.

P-290 Isolation and characterization of extracellular vesicles from human endometrial organoids

Abstract Study question Do human endometrial organoids produce extracellular vesicles (EVs)? Summary answer Endometrial organoids release EVs (ORG-EVs) that we successfully and comprehensively characterize according to guidelines. What is known already EVs play a crucial role in cellular communication, garnering increasing attention in physiological and pathological processes. Although the enormous potential of EVs has been extensively demonstrated across a large variety of research fields, the promise held by EVs derived from human endometrial organoids is still largely unexplored. Indeed, nowadays there is limited research available on the presence, role, and function of EVs derived from organoids of female reproductive tissue samples. This underscores the importance of adopting standardized methods for isolating, characterizing, and reporting findings, which is crucial for advancing in this promising and innovative, yet challenging, research field. Study design, size, duration This study involved establishing organoid cultures from endometrial biopsies of healthy women (n = 10) of reproductive age, who underwent ovarian surgery between January and October 2023. ORG-EVs were isolated using differential ultracentrifugation. Characterization of ORG-EVs, including assessment of their biophysical and biochemical properties, adhered to guidelines established by the International Society for Extracellular Vesicles (ISEV). Participants/materials, setting, methods Endometrial specimens from 10 women were employed to establish organoid cultures. ORG-EVs were isolated from spent medium through differential ultracentrifugation. Morphology, size distribution and concentration analysis were performed using Transmission Electron Microscopy (TEM) and Nanoparticle Tracking Analysis (NTA). Western blotting was used to confirm the presence of EVs markers. Main results and the role of chance TEM analysis confirmed the presence of isolated ORG-EVs, elucidating their morphology and structural integrity. NTA revealed that ORG-EVs had an average size of 160.4 ± 6.2 nm (mean ± SD) and a mean concentration of 5.2E+11 ± 2.1E+10 particles/ml (mean ± SD). Western blot analysis further confirmed the vesicular nature of the assessed particles, demonstrating positivity for standard EV markers such as tetraspanins (CD63 and CD9), and soluble proteins (ALIX and TSG101), while excluding the endoplasmic reticulum-resident protein calnexin (negative control). Additionally, ORG-EVs exhibited a positive signal for mucin1 (MUC1), a glycoprotein present on the surface of endometrial epithelial cells, thereby confirming their cellular origin. Limitations, reasons for caution This is a pilot study, characterized by a small sample size requiring larger cohorts to validate results and, at the same time, to undertake deeper exploration of ORG-EVs’ molecular cargo. Emphasizing the critical need for standardized isolation and characterization methods is paramount. Wider implications of the findings Endometrial organoids enhance EVs production, providing a powerful tool for reproductive aspects studies, and improving regenerative medicine and artificial reproductive technology. These initial findings propel further exploration, unveiling of ORG-EVs’ molecular cargo aiming to elucidate their potential role in human female reproductive tissues and mechanism related to embryo implantation process. Trial registration number not applicable

IRE1α determines ferroptosis sensitivity through regulation of glutathione synthesis

Cellular sensitivity to ferroptosis is primarily regulated by mechanisms mediating lipid hydroperoxide detoxification. We show that inositol-requiring enzyme 1 (IRE1α), an endoplasmic reticulum (ER) resident protein critical for the unfolded protein response (UPR), also determines cellular sensitivity to ferroptosis. Cancer and normal cells depleted of IRE1α gain resistance to ferroptosis, while enhanced IRE1α expression promotes sensitivity to ferroptosis. Mechanistically, IRE1α’s endoribonuclease activity cleaves and down-regulates the mRNA of key glutathione biosynthesis regulators glutamate-cysteine ligase catalytic subunit (GCLC) and solute carrier family 7 member 11 (SLC7A11). This activity of IRE1α is independent of its role in regulating the UPR and is evolutionarily conserved. Genetic deficiency and pharmacological inhibition of IRE1α have similar effects in inhibiting ferroptosis and reducing renal ischemia–reperfusion injury in mice. Our findings reveal a previously unidentified role of IRE1α to regulate ferroptosis and suggests inhibition of IRE1α as a promising therapeutic strategy to mitigate ferroptosis-associated pathological conditions.

HCMV US2 co-opts TRC8 to degrade the endoplasmic reticulum-resident protein LMAN2L.

The human cytomegalovirus (HCMV) pUS2 glycoprotein exploits the host's endoplasmic reticulum (ER)-associated degradation (ERAD) pathway to degrade major histocompatibility complex class I (MHC-I) and prevent antigen presentation. Beyond MHC-I, pUS2 has been shown to target a range of cellular proteins for degradation, preventing their cell surface expression. Here we have identified a novel pUS2 target, ER-resident protein lectin mannose binding 2 like (LMAN2L). pUS2 expression was both necessary and sufficient for the downregulation of LMAN2L, which was dependent on the cellular E3 ligase TRC8. Given the hypothesized role of LMAN2L in the trafficking of glycoproteins, we employed proteomic plasma membrane profiling to measure LMAN2L-dependent changes at the cell surface. A known pUS2 target, integrin alpha-6 (ITGA6), was downregulated from the surface of LMAN2L-deficient cells, but not other integrins. Overall, these results suggest a novel strategy of pUS2-mediated protein degradation whereby pUS2 targets LMAN2L to impair trafficking of ITGA6. Given that pUS2 can directly target other integrins, we propose that this single viral protein may exhibit both direct and indirect mechanisms to downregulate key cell surface molecules.

The fatty liver disease–causing protein PNPLA3-I148M alters lipid droplet–Golgi dynamics

Nonalcoholic fatty liver disease, recently renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a progressive metabolic disorder that begins with aberrant triglyceride accumulation in the liver and can lead to cirrhosis and cancer. A common variant in the gene PNPLA3, encoding the protein PNPLA3-I148M, is the strongest known genetic risk factor for MASLD. Despite its discovery 20 y ago, the function of PNPLA3, and now the role of PNPLA3-I148M, remain unclear. In this study, we sought to dissect the biogenesis of PNPLA3 and PNPLA3-I148M and characterize changes induced by endogenous expression of the disease-causing variant. Contrary to bioinformatic predictions and prior studies with overexpressed proteins, we demonstrate here that PNPLA3 and PNPLA3-I148M are not endoplasmic reticulum-resident transmembrane proteins. To identify their intracellular associations, we generated a paired set of isogenic human hepatoma cells expressing PNPLA3 and PNPLA3-I148M at endogenous levels. Both proteins were enriched in lipid droplet, Golgi, and endosomal fractions. Purified PNPLA3 and PNPLA3-I148M proteins associated with phosphoinositides commonly found in these compartments. Despite a similar fractionation pattern as the wild-type variant, PNPLA3-I148M induced morphological changes in the Golgi apparatus, including increased lipid droplet-Golgi contact sites, which were also observed in I148M-expressing primary human patient hepatocytes. In addition to lipid droplet accumulation, PNPLA3-I148M expression caused significant proteomic and transcriptomic changes that resembled all stages of liver disease. Cumulatively, we validate an endogenous human cellular system for investigating PNPLA3-I148M biology and identify the Golgi apparatus as a central hub of PNPLA3-I148M-driven cellular change.

Simultaneous deletion of ORMDL1 and ORMDL3 proteins disrupts immune cell homeostasis.

ORMDL3 is a prominent member of a family of highly conserved endoplasmic reticulum resident proteins, ORMs (ORM1 and ORM2) in yeast, dORMDL in Drosophila and ORMDLs (ORMDL1, ORMDL2, and ORMDL3) in mammals. ORMDL3 mediates feedback inhibition of de novo sphingolipid synthesis. Expression levels of ORMDL3 are associated with the development of inflammatory and autoimmune diseases including asthma, systemic lupus erythematosus, type 1 diabetes mellitus and others. It has been shown that simultaneous deletions of other ORMDL family members could potentiate ORMDL3-induced phenotypes. To understand the complex function of ORMDL proteins in immunity in vivo, we analyzed mice with single or double deletions of Ormdl genes. In contrast to other single and double knockouts, simultaneous deletion of ORMDL1 and ORMDL3 proteins disrupted blood homeostasis and reduced immune cell content in peripheral blood and spleens of mice. The reduced number of splenocytes was not caused by aberrant immune cell homing. A competitive bone marrow transplantation assay showed that the development of Ormdl1-/-/Ormdl3-/- B cells was dependent on lymphocyte intrinsic factors. Highly increased sphingolipid production was observed in the spleens and bone marrow of Ormdl1-/-/Ormdl3-/- mice. Slight, yet significant, increase in some sphingolipid species was also observed in the spleens of Ormdl3-/- mice and in the bone marrow of both, Ormdl1-/- and Ormdl3-/- single knockout mice. Taken together, our results demonstrate that the physiological expression of ORMDL proteins is critical for the proper development and circulation of lymphocytes. We also show cell-type specific roles of individual ORMDL family members in the production of different sphingolipid species.

"Sticki-ER": Functions of the Platelet Endoplasmic Reticulum.

Significance: The primary role of platelets is to generate a thrombus by platelet activation. Platelet activation relies on calcium mobilization from the endoplasmic reticulum (ER). ER resident proteins, which are externalized upon platelet activation, are essential for the function of platelet surface receptors and intercellular interactions. Recent Advances: The platelet ER is a conduit for changes in cellular function in response to the extracellular milieu. ER homeostasis is maintained by an appropriate redox balance, regulated calcium stores and normal protein folding. Alterations in ER function and ER stress results in ER proteins externalizing to the cell surface, including members of the protein disulfide isomerase family (PDIs) and chaperones. Critical Issues: The platelet ER is central to platelet function, but our understanding of its regulation is incomplete. Previous studies have focused on the function of PDIs in the extracellular space, and much less on their intracellular role. How platelets maintain ER homeostasis and how they direct ER chaperone proteins to facilitate intercellular signalling is unknown. Future Directions: An understanding of ER functions in the platelet is essential as these may determine critical platelet activities such as secretion and adhesion. Studies are necessary to understand the redox reactions of PDIs in the intracellular versus extracellular space, as these differentially affect platelet function. An unresolved question is how platelet ER proteins control calcium release. Regulation of protein folding in the platelet and downstream pathways of ER stress require further evaluation. Targeting the platelet ER may have therapeutic application in metabolic and neoplastic disease.

Excitotoxic glutamate levels cause the secretion of resident endoplasmic reticulum proteins.

Dysregulation of synaptic glutamate levels can lead to excitotoxicity such as that observed in stroke, traumatic brain injury, and epilepsy. The role of increased intracellular calcium (Ca2+) in the development of excitotoxicity is well established. However, less is known regarding the impact of glutamate on endoplasmic reticulum (ER)-Ca2+-mediated processes such as proteostasis. To investigate this, we expressed a secreted ER Ca2+ modulated protein (SERCaMP) in primary cortical neurons to monitor exodosis, a phenomenon whereby ER calcium depletion causes the secretion of ER-resident proteins that perform essential functions to the ER and the cell. Activation of glutamatergic receptors (GluRs) led to an increase in SERCaMP secretion indicating that normally ER-resident proteins are being secreted in a manner consistent with ER Ca2+ depletion. Antagonism of ER Ca2+ channels attenuated the effects of glutamate and GluR agonists on SERCaMP release. We also demonstrate that endogenous proteins containing an ER retention/retrieval sequence (ERS) are secreted in response to GluR activation supporting that neuronal activation by glutamate promotes ER exodosis. Ectopic expression of KDEL receptors attenuated the secretion of ERS-containing proteins caused by GluR agonists. Taken together, our data indicate that excessive GluR activation causes disruption of neuronal proteostasis by triggering the secretion of ER-resident proteins through ER Ca2+ depletion and describes a new facet of excitotoxicity.

Genome-wide screens identify SEL1L as an intracellular rheostat controlling collagen turnover

Accumulating evidence has implicated impaired extracellular matrix (ECM) clearance as a key factor in fibrotic disease. Despite decades of research elucidating the effectors of ECM clearance, relatively little is understood regarding the upstream regulation of this process. Collagen is the most abundant constituent of normal and fibrotic ECM in mammalian tissues. Its catabolism occurs through extracellular proteolysis and cell-mediated uptake of collagen fragments for intracellular degradation. Given the paucity of information regarding the regulation of this latter process, here we execute unbiased genome-wide screens to understand the molecular underpinnings of cell-mediated collagen clearance. Using this approach, we discover a mechanism through which collagen biosynthesis is sensed by cells internally and directly regulates clearance of extracellular collagen. The sensing mechanism appears to be dependent on endoplasmic reticulum-resident protein SEL1L and occurs via a noncanonical function of this protein. This pathway functions as a homeostatic negative feedback loop that limits collagen accumulation in tissues. In human fibrotic lung disease, the induction of this collagen clearance pathway by collagen synthesis is impaired, thereby contributing to the pathological accumulation of collagen in lung tissue. Thus, we describe cell-autonomous, rheostatic collagen clearance as an important pathway of tissue homeostasis.

Linear motifs regulating protein secretion, sorting and autophagy in Leishmania parasites are diverged with respect to their host equivalents.

The pathogenic, tropical Leishmania flagellates belong to an early-branching eukaryotic lineage (Kinetoplastida) with several unique features. Unfortunately, they are poorly understood from a molecular biology perspective, making development of mechanistically novel and selective drugs difficult. Here, we explore three functionally critical targeting short linear motif systems as well as their receptors in depth, using a combination of structural modeling, evolutionary sequence divergence and deep learning. Secretory signal peptides, endoplasmic reticulum (ER) retention motifs (KDEL motifs), and autophagy signals (motifs interacting with ATG8 family members) are ancient and essential components of cellular life. Although expected to be conserved amongst the kinetoplastids, we observe that all three systems show a varying degree of divergence from their better studied equivalents in animals, plants, or fungi. We not only describe their behaviour, but also build models that allow the prediction of localization and potential functions for several uncharacterized Leishmania proteins. The unusually Ala/Val-rich secretory signal peptides, endoplasmic reticulum resident proteins ending in Asp-Leu-COOH and atypical ATG8-like proteins are all unique molecular features of kinetoplastid parasites. Several of their critical protein-protein interactions could serve as targets of selective antimicrobial agents against Leishmaniasis due to their systematic divergence from the host.

The nonvesicular sterol transporter Aster-C plays a minor role in whole body cholesterol balance.

The Aster-C protein (encoded by the Gramd1c gene) is an endoplasmic reticulum (ER) resident protein that has been reported to transport cholesterol from the plasma membrane to the ER. Although there is a clear role for the closely-related Aster-B protein in cholesterol transport and downstream esterification in the adrenal gland, the specific role for Aster-C in cholesterol homeostasis is not well understood. Here, we have examined whole body cholesterol balance in mice globally lacking Aster-C under low or high dietary cholesterol conditions. Age-matched Gramd1c +/+ and Gramd1c -/- mice were fed either low (0.02%, wt/wt) or high (0.2%, wt/wt) dietarycholesterol and levels of sterol-derived metabolites were assessed in the feces, liver, and plasma. Compared to wild type controls (Gramd1c +/+) mice, mice lackingGramd1c (Gramd1c -/-) have no significant alterations in fecal, liver, or plasma cholesterol. Given the potential role for Aster C in modulating cholesterol metabolism in diverse tissues, we quantified levels of cholesterol metabolites such as bile acids, oxysterols, and steroid hormones. Compared to Gramd1c +/+ controls, Gramd1c -/- mice had modestly reduced levels of select bile acid species and elevated cortisol levels, only under low dietary cholesterol conditions. However, the vast majority of bile acids, oxysterols, and steroid hormones were unaltered in Gramd1c -/- mice. Bulk RNA sequencing in the liver showed that Gramd1c -/- mice did not exhibit alterations in sterol-sensitive genes, but instead showed altered expression of genes in major urinary protein and cytochrome P450 (CYP) families only under low dietary cholesterol conditions. Collectively, these data indicate nominal effects of Aster-C on whole body cholesterol transport and metabolism under divergent dietary cholesterol conditions. These results strongly suggest that Aster-C alone is not sufficient to control whole body cholesterol balance, but can modestly impact circulating cortisol and bile acid levels when dietary cholesterol is limited.

The role of lipase maturation factor 1 in hypertriglyceridaemia and atherosclerosis: An update.

Lipase maturation factor 1 is an endoplasmic reticulum-resident transmembrane protein, which acts as a critical chaperone necessary for the folding, dimerisation, and secretion of lipases. In this review, we summarise data about the recently revealed role of lipase maturation factor 1 in endoplasmic reticulum redox homeostasis, its novel interaction partners among oxidoreductases and lectin chaperones, and the identification of fibronectin and the low-density lipoprotein receptor as novel non-lipase client proteins of lipase maturation factor 1. Additionally, the role of lipase maturation factor 1-derived circular RNA in atherosclerosis progression via the miR-125a-3p/vascular endothelial growth factor A\Fibroblast Growth Factor 1 axis is discussed. Finally, we focus on the causative role of lipase maturation factor 1 variants in the development of hypertriglyceridaemia - a type of dyslipidaemia that significantly contributes to the development of atherosclerosis and other cardiovascular diseases via different mechanisms.

Inducing Melanoma Cell Apoptosis by ERp57/PDIA3 Antibody in the Presence of CPI-613 and Hydroxychloroquine.

The combination of the cancer mitochondrial metabolic inhibitor CPI-613 and hydroxychloroquine has tumor-suppressive effects on clear cell sarcoma, which shares pathobiological properties with melanoma. Therefore, we intended to examine the effects of a combination of CPI-613 and hydroxychloroquine on the growth of melanoma cells in the present study. However, cell death was not induced in melanoma cells. Therefore, a monoclonal antibody, ICT, that induced apoptosis in melanoma cells in combination with CPI-613 and hydroxychloroquine was developed. Immunoprecipitation, mass spectrometry, and small interfering RNA (siRNA)-mediated gene silencing demonstrated that ICT targeted Endoplasmic Reticulum Resident Protein 57/ Protein Disulfide Isomerase Family A Member 3 (ERp57/PDIA3), which was first identified as being upregulated by metabolic depletion stress and is localized on the cell surface during immunogenic cell death. The combination of CPI-613 and hydroxychloroquine enhanced the localization of ERp57/PDIA3 to the surface of melanoma cells. siRNA-mediated downregulation of ERp57/PDIA3 did not significantly induce ICT-mediated apoptosis in melanoma cells in the presence of CPI-613 and hydroxychloroquine. Therefore, the ICT antibody acts as a tumor suppressor in melanoma cells by targeting the cell membrane ERp57/PDIA3, expression of which was enhanced by the combination of CPI-613 and hydroxychloroquine.

Targeting ER Acetylation to Rescue Proteotoxicity

Transient acetylation within the endoplasmic reticulum (ER) lumen has emerged as a novel mechanism that regulates proteostasis and dynamics of the secretory pathway. The ER acetylation machinery includes AT-1, a membrane transporter that imports acetyl-CoA from the cytosol into the ER lumen, and two acetyltrasferases, ATase1 and ATase2, which acetylate ER cargo and resident proteins. Loss-of-function mutations or gene duplication events that affect ER acetylation are linked to developmental delay and premature death (homozygous mutation), hereditary forms of peripheral neuropathy (homozygous mutation), and autism spectrum disorder with intellectual disability and progeria (gene duplication). Mouse models of dysfunctional ER acetylation mimic associated human phenotypes.

Phytaspase Is Capable of Detaching the Endoplasmic Reticulum Retrieval Signal from Tobacco Calreticulin-3.

Soluble chaperones residing in the endoplasmic reticulum (ER) play vitally important roles in folding and quality control of newly synthesized proteins that transiently pass through the ER en route to their final destinations. These soluble residents of the ER are themselves endowed with an ER retrieval signal that enables the cell to bring the escaped residents back from the Golgi. Here, by using purified proteins, we showed that Nicotiana tabacum phytaspase, a plant aspartate-specific protease, introduces two breaks at the C-terminus of the N. tabacum ER resident calreticulin-3. These cleavages resulted in removal of either a dipeptide or a hexapeptide from the C-terminus of calreticulin-3 encompassing part or all of the ER retrieval signal. Consistently, expression of the calreticulin-3 derivative mimicking the phytaspase cleavage product in Nicotiana benthamiana cells demonstrated loss of the ER accumulation of the protein. Notably, upon its escape from the ER, calreticulin-3 was further processed by an unknown protease(s) to generate the free N-terminal (N) domain of calreticulin-3, which was ultimately secreted into the apoplast. Our study thus identified a specific proteolytic enzyme capable of precise detachment of the ER retrieval signal from a plant ER resident protein, with implications for the further fate of the escaped resident.