Protein folding in the endoplasmic reticulum

Defective anterograde protein-trafficking contributes to endoplasmic reticulum-stress in a CLN1 disease model

Lysosomal storage disorders (LSDs) represent 70 inherited metabolic diseases, in most of which neurodegeneration is a devastating manifestation. The CLN1 disease is a fatal neurodegenerative LSD, caused by inactivating mutations in the CLN1 gene encoding palmitoyl-protein thioesterase-1 (PPT1). S-palmitoylation, a reversable posttranslational modification by saturated fatty acids (generally palmitate) facilitates endosomal trafficking of many proteins, especially in the brain. While palmitoyl-acyltransferases (called ZDHHCs) catalyze S-palmitoylation, depalmitoylation is mediated by palmitoyl-protein thioesterases (PPTs). We previously reported that in Cln1-/- mice, which mimic human CLN1-disease, endoplasmic reticulum (ER)-stress leads to unfolded protein response (UPR) contributing to neurodegeneration. However, the mechanism underlying ER-stress has remained elusive. The anterograde (ER to Golgi) protein-trafficking is mediated via COPII (coat protein complex II) vesicles, whereas the retrograde transport (Golgi to ER) is mediated by COPI vesicles. We hypothesized that dysregulated anterograde protein-trafficking causing stagnation of proteins in the ER leads to ER-stress in Cln1-/- mice. We found that the levels of five COPII vesicle-associated proteins (i.e. Sar1, Sec23, Sec24, Sec13 and Sec31) are significantly higher in the ER-fractions of cortical tissues from Cln1-/- mice compared with those from their WT littermates. Remarkably, all COPII proteins, except Sec13, undergo S-palmitoylation. Moreover, CLN8, a Batten disease-protein, requires dynamic S-palmitoylation (palmitoylation-depalmitoylation) for ER-Golgi trafficking. Intriguingly, Ppt1-deficiency in Cln1-/- mice impairs ER-Golgi trafficking of Cln8-protein along with several other COPII-associated proteins. We propose that impaired anterograde trafficking causes excessive accumulation of proteins in the ER causing ER-stress and UPR contributing to neurodegeneration in CLN1 disease.

Glycosylation as an intricate post-translational modification process takes part in glycoproteins related immunity

Protein glycosylation, the most ubiquitous and diverse type of post-translational modification in eukaryotic cells, proteins are input into endoplasmic reticulum and Golgi apparatus for sorting and modification with intricate quality control, are then output for diverse functional glycoproteins that are utilized by cells to precisely regulate various biological processes. In order to maintain the precise spatial structure of glycoprotein, misfolded and unfolded glycoproteins are recognized, segregated and degraded to ensure the fidelity of protein folding and maturation. This review enumerates the role of five immune-related glycoproteins and reveals the relevance of glycosylation to their antigen presentation, immune effector function, immune recognition, receptor binding and activation, and cell adhesion and migration. With the knowledgement of glycoproteins in immune responses and etiologies, we propose several relevant therapeutic strategies on targeting glycosylation process for immunotherapy.

Plasmopara viticola Effector PvRXLR10 Targets a Host Phospholipase VvipPLA-IIδ2 to Suppress Plant Immunity in Grapevine

Plasmopara viticola that causes grapevine downy mildew disease in viticulture regions is among the 10 most relevant pathogens worldwide. It secretes a large arsenal of effectors to facilitate colonisation by perturbing host immunity. However, the underlying mechanisms by which P. viticola effectors disturb grapevine defence are still largely unknown. In this study, we report that PvRXLR10, an RXLR effector with a WY domain, promotes P. viticola infection in grapevine and Phytophthora parasitica colonisation in Nicotiana benthamiana. PvRXLR10 interacts with a host patatin-like protein VvipPLA-IIδ2 with phospholipase A2 activity. The WY domain of PvRXLR10 is not responsible for cell death suppression in N. benthamiana but is necessary for PvRXLR10 interaction with VvipPLA-IIδ2. Overexpression and RNAi-mediated suppression of VvipPLA-IIδ2 expression in Vitis vinifera consistently showed that this protein positively regulates plant immunity in response to P. viticola infection. Interestingly, we found that VvipPLA-IIδ2 partially associates with PvRXLR10 at the endoplasmic reticulum (ER). Reverse transcription-quantitative PCR (RT-qPCR) analysis showed that the expression of VvipPLA-IIδ2 was suppressed by PvRXLR10 during P. viticola infection. The overexpression of VvipPLA-IIδ2 in V. vinifera induced higher expression of genes related to jasmonic acid (JA) biosynthesis, signalling pathways and defence response. The evidence indicates the important roles of VvipPLA-IIδ2 in grapevine immunity and P. viticola effector PvRXLR10 targets this protein to promote its infection.

p.Phe508del-CFTR Trafficking: A Protein Quality Control Perspective Through UPR, UPS, and Autophagy

Cystic fibrosis (CF) is a genetic disease due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The most frequent mutation (p.Phe508del) results in a misfolded protein (p.Phe508del-CFTR) with an altered transport to the membrane of the cells via the conventional protein secretion (CPS) pathway. Nevertheless, it can use unconventional protein secretion (UPS). Indeed, p.Phe508del-CFTR forms a complex with GRASP55 to assist its direct trafficking from the endoplasmic reticulum to the plasma membrane. While GRASP55 is a key player of UPS, it is also a key player of stress-induced autophagy. In parallel, the unfolded protein response (UPR), which is activated in the presence of misfolded proteins, is tightly linked to UPS and autophagy through the key effectors IRE1, PERK, and ATF6. A better understanding of how UPS, UPR, and stress-induced autophagy interact to manage protein trafficking in CF and other conditions could lead to novel therapeutic strategies. By enhancing or modulating these pathways, it may be possible to increase p.Phe508del-CFTR surface expression. In summary, this review highlights the critical roles of UPS- and UPR-induced autophagy in managing protein transport, offering new perspectives for therapeutic approaches.

Half a Century of Progress: The Evolution of Wheat Germ-Based In Vitro Translation into a Versatile Protein Production Method

The first demonstration of wheat germ extract (WGE)-based in vitro translation synthesising a protein from exogenously introduced messenger ribonucleic acid (mRNA) was published approximately fifty years ago. Since then, there have been numerous crucial improvements to the WGE-based in vitro translation, resulting in a significant increase in yield and the development of high-throughput protein-producing platforms. These developments have transformed the original setup into a versatile eukaryotic protein production method with broad applications. The present review explores the theoretical background of the implemented modifications and brings a panel of examples for WGE applications in high-throughput protein studies and synthesis of challenging-to-produce proteins such as protein complexes, extracellular proteins, and membrane proteins. It also highlights the unique advantages of in vitro translation as an open system for synthesising radioactively labelled proteins, as illustrated by numerous publications using WGE to meet the protein demands of these studies. This review aims to orientate readers in finding the most appropriate WGE arrangement for their specific needs and demonstrate that a deeper understanding of the system modifications will help them make further adjustments to the reaction conditions for synthesising difficult-to-express proteins.

Mechanical effect of protein glycosylation on BiP-mediated post-translational translocation and folding in the endoplasmic reticulum

About one-third of the proteins synthesized in eukaryotic cells are directed to the secretory pathway, where close to 70% are being N-glycosylated. N-glycosylation is a crucial modification for various cellular processes, including endoplasmic reticulum (ER) glycoprotein folding quality control, lysosome delivery, and cell signaling. The defects in N-glycosylation can lead to severe developmental diseases. For the proteins to be glycosylated, they must be translocated to the ER through the Sec61 translocon channel, either via co-translationally or post-translationally. N-glycosylation not only could accelerate post-translational translocation but may also enhance protein stability, while protein folding can assist in their movement into the ER. However, the precise mechanisms by which N-glycosylation and folding influence translocation remain poorly understood. The chaperone BiP is essential for post-translational translocation, using a "ratchet" mechanism to facilitate protein entry into the ER. Although research has explored how BiP interacts with protein substrates, there has been less focus on its binding to glycosylated substrates. Here, we review the effect of N-glycosylation on protein translocation, employing single-molecule studies and ensembles approaches to clarify the roles of BiP and N-glycosylation in these processes. Our review explores the possibility of a direct relationship between translocation and a ratchet effect of glycosylation and the importance of BiP in binding glycosylated proteins for the ER quality control system.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-025-01313-x.

TMED9 coordinates the clearance of misfolded GPI-anchored proteins out of the ER and into the Golgi

The p24-family member, TMED9, has recently emerged as a player in secretory pathway protein quality control (PQC) that influences the trafficking and degradation of misfolded proteins. Here, we show that TMED9 plays a central role in the PQC of GPI-anchored proteins (GPI-APs). Typically, upon release from the endoplasmic reticulum (ER)-resident chaperone calnexin, misfolded GPI-APs traffic to the Golgi by an ER-export pathway called Rapid ER stress-induced Export (RESET). From the Golgi, they access the plasma membrane where they are rapidly internalized for lysosomal degradation. We used biochemical and imaging approaches in cultured cells to demonstrate that at steady-state, the majority of misfolded GPI-APs reside in the ER in association with calnexin and TMED9. During RESET, they dissociate from calnexin and increase their association with TMED9. Inhibition of TMED9's function through siRNA-induced depletion or chemical inhibitor, BRD4780, blocked ER-export of misfolded GPI-APs. In contrast, TMED9-inhibition did not prevent ER-export of wild-type GPI-APs, indicating a specific role for TMED9 in GPI-AP PQC. Intriguingly, we discovered that acute treatment with BRD4780 induced a shift in TMED9 localization away from the ER to the downstream Golgi cisternae and blocked the RESET pathway. Upon removal of BRD4780 following acute treatment, TMED9 regained access to the ER where TMED9 was able to associate with the RESET substrate and restore the RESET pathway. These results suggest that TMED9 plays a requisite role in RESET by capturing misfolded GPI-APs that are released by calnexin within the ER and conveying them to the Golgi.

Concept of Future Glycoprotein Drugs: Synthesis of a Thioglycosidically Linked α-N-Acetylgalactosamine-Carrying Cyclic Peptide as a Model of Miniature Macrophage Activating Factor

Glycoproteins are often considered as drug candidates. However, the regulation of post-translational glycan attachment remains an issue. We hypothesized that replacing the oxygen atom in the glycosidic linkage with sulfur atoms would stabilize the labile linkage against glycosidases, resulting in improved pharmacokinetics. In this study, we focused on the macrophage-activating factor (MAF) carrying O-linked N-acetylgalactosamine (GalNAc) and creating a miniature glycopeptide associated with MAF. A partial structure of MAF with a chemical mutation at three amino acid residues was designed in which threonine was replaced with cysteine (Cys), leading to a thioglycosidically linked GalNAc and a conformationally stable cyclic peptide due to the disulfide bond. GalNAc-Cys was used in solid-phase peptide synthesis, and the desired cyclic glycopeptide was synthesized. In the synthesis of GalNAc-Cys, glycosylation reactions were carried out based on the hard and soft acids and bases concept, where glycosyl trichloroacetimidate and fluoride were successfully used to couple with the thiol group in Cys. GalNAc-Cys was also evaluated as a substrate of α-GalNAc-ase and was shown to resist hydrolysis, supporting our concept. The synthesized cyclic miniature MAF induced LPS-assisted IL-12 production and resisted against α-GalNAc-ase.

Skeletal muscle atrophy induced by aging and disuse atrophy are strongly associated with the upregulation of the endoplasmic stress protein CHOP in rats

BACKGROUND

While canonical anabolic and proteolytic pathways have been well examined in the context of skeletal muscle proteostasis, the roles of endoplasmic reticulum stress (ERS) and the induced unfolded protein response (UPR) are underappreciated. Thus, we aimed to determine whether aging and/or disuse atrophy in rats altered skeletal muscle ERS/UPR markers.

METHODS AND RESULTS

Soleus (SOL) and plantaris (PLT) muscles of 3-month-old (mo), 6 mo, 12 mo, 18 mo, and 24 mo rats (9-10 per group, 48 in total) were analyzed for UPR proteins with further analysis performed on the protein CHOP. The gastrocnemius muscles of 4 mo rats that had undergone hindlimb immobilization (HLI, n = 12) or sham casting (CTL, n = 12) were analyzed for similar targets as well as more extensive CHOP-related targets. CHOP protein was greater in the PLT and SOL of 18 and 24 mo rats versus other age groups (P < 0.05). Moreover, negative correlations existed between CHOP expression and normalized PLT (R=-0.702, P < 0.001) and SOL (R=-0.658, P < 0.001) muscle weights in all rats analyzed at different ages. CHOP protein expression was also greater in the gastrocnemius of HLI versus CTL rats (P < 0.001), and a negative correlation existed between CHOP protein expression and normalized muscle weights in these rats (R=-0.814, P < 0.001). Nuclear CHOP protein levels (P < 0.010) and genes transcriptionally regulated by CHOP were also greater in HLI versus CTL rats (P < 0.001) implicating transcriptional activity of CHOP is elevated during disuse atrophy.

CONCLUSIONS

CHOP is operative during aging- and disuse-induced skeletal muscle atrophy in rodents, and more research is needed to determine if CHOP is a key mechanistic driver of these processes.

SEL1L-mediated endoplasmic reticulum associated degradation inhibition suppresses proliferation and migration in Huh7 hepatocellular carcinoma cells

BACKGROUND

Proteins play a central role in regulating biological functions, and various pathways regulate their synthesis and secretion. Endoplasmic reticulum-associated protein degradation (ERAD) is crucial for monitoring protein synthesis and processing unfolded or misfolded proteins in actively growing tumor cells. However, the role of the multiple ERAD complexes in liver cancer remains unclear.

AIM

To elucidate the effects of SEL1L-mediated ERAD on Huh7 and explore the underlying mechanisms in vivo and in vitro.

METHODS

Huh7 cells were treated with ERAD inhibitor to identify ERAD's role. Cell counting kit-8, 5-ethynyl-2'-deoxyuridine and colony formation experiments were performed. Apoptosis level and migration ability were assessed using fluorescence activated cell sorting and Transwell assay, respectively. Huh7 SEL1L knockout cell line was established via clustered regularly interspaced short palindromic repeats, proliferation, apoptosis, and migration were assessed through previous experiments. The role of SEL1L in vivo and the downstream target of SEL1L were identified using Xenograft and mass spectrometry, respectively.

RESULTS

The ERAD inhibitor suppressed cell proliferation and migration and promoted apoptosis. SEL1L-HRD1 significantly influenced Huh7 cell growth. SEL1L knockout suppressed tumor cell proliferation and migration and enhanced apoptosis. Mass spectrometry revealed EXT2 is a primary substrate of ERAD. SEL1L knockout significantly increased the protein expression of EXT2. Furthermore, EXT2 knockdown partially restored the effect of SEL1L knockout.

CONCLUSION

ERAD inhibition suppressed the proliferation and migration of Huh7 and promoted its apoptosis. EXT2 plays an important role and ERAD might be a potential treatment for Huh7 hepatocellular carcinoma.

The interplay between gut microbiota and the unfolded protein response: Implications for intestinal homeostasis preservation and dysbiosis-related diseases

The unfolded protein response (UPR) is a complex intracellular signal transduction system that orchestrates the cellular response during Endoplasmic Reticulum (ER) stress conditions to reestablish cellular proteostasis. If, on one side, prolonged ER stress conditions can lead to programmed cell death and autophagy as a cytoprotective mechanism, on the other, unresolved ER stress and improper UPR activation represent a perilous condition able to trigger or exacerbate inflammatory responses. Notably, intestinal and immune cells experience ER stress physiologically due to their high protein secretory rate. Indeed, there is evidence of UPR's involvement in both physiological and pathological intestinal conditions, while less is known about its bidirectional interaction with gut microbiota. However, gut microbes and their metabolites can influence ER stress and UPR pathways, and, in turn, ER stress conditions can shape gut microbiota composition, with important implications for overall intestinal health. Thus, targeting UPR components is an intriguing strategy for treating ER stress-linked dysbiosis and diseases, particularly intestinal inflammation.

Molecular puzzle of insulin: structural assembly pathways and their role in diabetes

Properly folded proteins are essential for virtually all cellular processes including enzyme catalysis, signal transduction, and structural support. The cells have evolved intricate mechanisms of control, such as the assistance of chaperones and proteostasis networks, to ensure that proteins mature and fold correctly and maintain their functional conformations. Here, we review the mechanisms governing the folding of key hormonal regulators or glucose homeostasis. The insulin synthesis in pancreatic β-cells begins with preproinsulin production. During translation, the insulin precursor involves components of the endoplasmic reticulum (ER) translocation machinery, which are essential for proper orientation, translocation, and cleavage of the signal peptide of preproinsulin. These steps are critical to initiate the correct folding of proinsulin. Proinsulin foldability is optimized in the ER, an environment evolved to support the folding process and the formation of disulfide bonds while minimizing misfolding. This environment is intricately linked to ER stress response pathways, which have both beneficial and potentially harmful effects on pancreatic β-cells. Proinsulin misfolding can result from excessive biosynthetic ER load, proinsulin gene mutations, or genetic predispositions affecting the ER folding environment. Misfolded proinsulin leads to deficient insulin production and contributes to diabetes pathogenesis. Understanding the mechanisms of protein folding is critical for addressing diabetes and other protein misfolding-related diseases.

Do wolframin, P-glycoprotein, and GRP78/BiP cooperate to alter the response of L1210 cells to endoplasmic reticulum stress or drug sensitivity?

In previous research, we revealed that murine leukemia cells L1210 with induced expression of P-glycoprotein (P-gp, a membrane drug transporter, product of the Abcb1 gene) are better able to withstand endoplasmic reticulum (ER) stress (ERS) than their P-gp negative counterparts. This was associated with increased GRP78/BiP expression and modulation of the expression of several other proteins active in the cellular response to ERS (like CHOP, spliced XBP1, 50-kDa ATF6 protein fragment and others) in P-gp positive cells. Wolframin is an ER transmembrane protein, product of the WFS1 gene whose mutations are associated with Wolfram syndrome. However, this protein is frequently overexpressed in cells undergoing ERS and its expression may accompany changes in the above ERS markers. Therefore, our aim in this work was to investigate wolframin expression in P-gp-negative and P-gp-positive murine leukemia L1210 cells in relation to ERS related proteins in normal or ERS condition. We induced ERS in cells either by blocking N-glycosylation in the ER with tunicamycin or by blocking ER Ca2+-ATPase activity with thapsigargin, as known ER stressors. The results of this paper demonstrated increased wolframin expression in P-gp positive cells compared to P-gp negative cells. Immunoprecipitation experiments revealed the formation of complexes between wolframin and ERS related proteins (PERK, ATF6 and GRP78/BiP), the amount of which varied depending on the presence of the above ER stressors.

TMED9 coordinates the clearance of misfolded GPI-anchored proteins out of the endoplasmic reticulum and into the Golgi

The p24-family member, TMED9, has recently emerged as a player in secretory pathway protein quality control (PQC) that influences the trafficking and degradation of misfolded proteins. Here we show that TMED9 plays a central role in the PQC of GPI-anchored proteins (GPI-APs). Typically, upon release from the endoplasmic reticulum (ER)-resident chaperone calnexin, misfolded GPI-APs traffic to the Golgi by an ER-export pathway called Rapid ER stress-induced Export (RESET). From the Golgi, they access the plasma membrane where they are rapidly internalized for lysosomal degradation. We used biochemical and imaging approaches in cultured cells to demonstrate that at steady-state, the majority of misfolded GPI-APs reside in the ER in association with calnexin and TMED9. During RESET, they dissociate from calnexin and increase their association with TMED9. Inhibition of TMED9's function through siRNA-induced depletion or chemical inhibitor, BRD4780, blocked ER-export of misfolded GPI-APs. By contrast, TMED9-inhibition did not prevent ER-export of wild type GPI-APs, indicating a specific role for TMED9 in GPI-AP PQC. Intriguingly, we discovered that acute treatment with BRD4780 induced a shift in TMED9 localization away from the ER to the downstream Golgi cisternae and blocked the RESET pathway. Upon removal of BRD4780 following acute treatment, TMED9 regained access to the ER where TMED9 was able to associate with the RESET substrate and restore the RESET pathway. These results suggest that TMED9 plays a requisite role in RESET by capturing misfolded GPI-APs that are released by calnexin within the ER and conveying them to the Golgi.

Unfolded protein response: An essential element of intestinal homeostasis and a potential therapeutic target for inflammatory bowel disease

Different physiological and pathological situations can produce alterations in the cell's endoplasmic reticulum (ER), leading to a condition known as ER stress, which can trigger an intricate intracellular signal transduction system known as the unfolded protein response (UPR). UPR is primarily tailored to restore proteostasis and ER equilibrium; otherwise, if ER stress persists, it can cause programmed cell death as a cytoprotective mechanism and drive inflammatory processes. Therefore, since intestinal cells strongly rely on UPR for their biological functions and unbalanced UPR has been linked to inflammatory, metabolic, and immune disorders, here we discussed the role of the UPR within the intestinal tract, focusing on the UPR contribution to inflammatory bowel disease development. Importantly, we also highlighted the promising potential of UPR components as therapeutic targets for intestinal inflammatory diseases.

Site-specific analysis and functional characterization of N-linked glycosylation for β-Klotho protein

β-Klotho (KLB), a type I transmembrane protein, serves as an obligate co-receptor determining the tissue-specific actions of endocrine fibroblast growth factors (FGFs). Despite accumulative evidence suggesting the occurrence of N-glycosylation in the KLB protein, the precise N-glycosites, glycoforms, and the impacts of N-glycosylation on the expression and function of the KLB protein remain unexplored. Employing a mass spectrometry-based approach, a total of 12 N-glycosites displaying heterogeneous site occupancy and glycoforms were identified within the extracellular region of the recombinant human KLB protein. Molecular simulation revealed negligible impact of these N-glycans on the overall structure of the KLB protein. However, both pharmacological inhibition of N-glycosylation and mutagenesis targeting N-glycosites reduced mature KLB protein content without impacting KLB mRNA synthesis in cells, underscoring the critical role of N-glycosylation in maintaining the stability of the KLB protein. Further studies revealed that the underglycosylated KLB mutant underwent rapid degradation via both lysosomal and proteasomal pathways and was unable to be efficiently trafficked to the plasma membrane, leading to impaired FGF21 signaling transduction. Collectively, multisite N-glycosylation is essential for the stability and cell surface localization of the KLB protein, representing a novel modulatory mechanism of endocrine FGF signaling.

Multiplex, multimodal mapping of variant effects in secreted proteins

Despite widespread advances in DNA sequencing, the functional consequences of most genetic variants remain poorly understood. Multiplexed Assays of Variant Effect (MAVEs) can measure the function of variants at scale, and are beginning to address this problem. However, MAVEs cannot readily be applied to the ~10% of human genes encoding secreted proteins. We developed a flexible, scalable human cell surface display method, Multiplexed Surface Tethering of Extracellular Proteins (MultiSTEP), to measure secreted protein variant effects. We used MultiSTEP to study the consequences of missense variation in coagulation factor IX (FIX), a serine protease where genetic variation can cause hemophilia B. We combined MultiSTEP with a panel of antibodies to detect FIX secretion and post-translational modification, measuring a total of 44,816 effects for 436 synonymous variants and 8,528 of the 8,759 possible missense variants. 49.6% of possible F9 missense variants impacted secretion, post-translational modification, or both. We also identified functional constraints on secretion within the signal peptide and for nearly all variants that caused gain or loss of cysteine. Secretion scores correlated strongly with FIX levels in hemophilia B and revealed that loss of secretion variants are particularly likely to cause severe disease. Integration of the secretion and post-translational modification scores enabled reclassification of 63.1% of F9 variants of uncertain significance in the My Life, Our Future hemophilia genotyping project. Lastly, we showed that MultiSTEP can be applied to a wide variety of secreted proteins. Thus, MultiSTEP is a multiplexed, multimodal, and generalizable method for systematically assessing variant effects in secreted proteins at scale.

Isoform-specific N-linked glycosylation of NaV channel α-subunits alters β-subunit binding sites

Voltage-gated sodium channel α-subunits (NaV1.1-1.9) initiate and propagate action potentials in neurons and myocytes. The NaV β-subunits (β1-4) have been shown to modulate α-subunit properties. Homo-oligomerization of β-subunits on neighboring or opposing plasma membranes has been suggested to facilitate cis or trans interactions, respectively. The interactions between several NaV channel isoforms and β-subunits have been determined using cryogenic electron microscopy (cryo-EM). Interestingly, the NaV cryo-EM structures reveal the presence of N-linked glycosylation sites. However, only the first glycan moieties are typically resolved at each site due to the flexibility of mature glycan trees. Thus, existing cryo-EM structures may risk de-emphasizing the structural implications of glycans on the NaV channels. Herein, molecular modeling and all-atom molecular dynamics simulations were applied to investigate the conformational landscape of N-linked glycans on NaV channel surfaces. The simulations revealed that negatively charged sialic acid residues of two glycan sites may interact with voltage-sensing domains. Notably, two NaV1.5 isoform-specific glycans extensively cover the α-subunit region that, in other NaV channel α-subunit isoforms, corresponds to the binding site for the β1- (and likely β3-) subunit immunoglobulin (Ig) domain. NaV1.8 contains a unique N-linked glycosylation site that likely prevents its interaction with the β2 and β4-subunit Ig-domain. These isoform-specific glycans may have evolved to facilitate specific functional interactions, for example, by redirecting β-subunit Ig-domains outward to permit cis or trans supraclustering within specialized cellular compartments such as the cardiomyocyte perinexal space. Further experimental work is necessary to validate these predictions.

AGR2 knockdown induces ER stress and mitochondria fission to facilitate pancreatic cancer cell death

Anterior gradient 2 (AGR2) is often overexpressed in many human cancers, including pancreatic ductal adenocarcinoma (PDAC). Elevated AGR2 expression is known to play a critical role in tumor development, progression, and metastasis and positively correlates with poor patient survival. However, the relationship between AGR2 expression and tumor growth is not fully understood. Our study aims to investigate the impact of AGR2 knockdown on the survival of two pancreatic cancer cell lines, HPAF-II and PANC-1, that exhibit high AGR2 expression. This study revealed that the knockdown of AGR2 expression through an inducible shRNA-mediated approach reduced the proliferative ability and colony-forming potential of PDAC cells compared to scramble controls. Significantly, knocking down AGR2 led to the inhibition of multiple protein biosynthesis pathways and induced ER stress through unfolded protein response (UPR) activation. AGR2 knockdown induced ER stress and increased mitochondrial fission, while mitochondrial fusion remained unaffected. Ultimately, apoptotic cell death was heightened in AGR2 knockdown PDAC cells compared to the controls. Overall, these data reveal a new axis involving AGR2-ER stress-associated mitochondrial fission that could be targeted to improve PDAC patient outcomes.

Bioinformatics analysis and alternative polyadenylation in Heat Shock Proteins 70 (HSP70) family members

OBJECTIVE

The Heat Shock Protein 70 (HSP70) family is a highly conserved group of molecular chaperones essential for maintaining cellular homeostasis. These proteins are necessary for protein folding, assembly, and degradation and involve cell recovery from stress conditions. HSP70 proteins are upregulated in response to heat shock, oxidative stress, and pathogenic infections. Their primary role is preventing protein aggregation, refolding misfolded proteins, and targeted degradation of irreparably damaged proteins. Given their involvement in fundamental cellular processes and stress responses, HSP70 proteins are critical for cell survival and modulating disease outcomes in cancer, neurodegeneration, and other pathologies. The present study aims to understand domain architecture, physicochemical properties, phosphorylation, ubiquitination, and alternative polyadenylation site prediction in various HSP70 members.

METHOD

SMART and InterProScan software were used for domain analysis. EXPASY Protparam, NetPhos 3.1 server DTU, and MUbisiDa were used for physicochemical analysis, phosphorylation, and ubiquitination site analysis, respectively. Alternative polyadenylation was studied using the EST database.

RESULT

Domain analysis shows that coiled-coil and nucleotide-binding domains are present in some of the HSP70 members. Five HSP70 family members have alternate polyadenylation sites in their 3'UTR.

CONCLUSION

The present work has provided valuable insights into their structure, functions, interactome, and polyadenylation patterns. Studying their therapeutic potential in diseases like cancer can be helpful.

Exploring the Role of FICD, a New Potential Gene Involved in Borderline Intellectual Functioning, Psychological and Metabolic Disorders

Background/Objectives: AMPylation is a post-translational modification involving the transfer of adenosine monophosphate (AMP) from adenosine triphosphate (ATP) to target proteins, serving as a critical regulatory mechanism in cellular functions. This study aimed to expand the phenotypic spectrum associated with mutations in the FICD gene, which encodes an adenyltransferase enzyme involved in both AMPylation and deAMPylation. Methods: A clinical evaluation was conducted on a patient presenting with a complex clinical profile. Whole-exome sequencing (WES) was performed to identify potential genetic variants contributing to the observed phenotype. Results: The patient exhibited borderline intellectual functioning (BIF), acanthosis, abdominal muscle hypotonia, anxiety, depression, obesity, and optic nerve subatrophy. WES revealed a de novo missense variant, c.1295C>T p.Ala432Val, in the FICD gene. This variant, classified as of uncertain significance, is located in the highly conserved region TLLFATTEY (aa 428-436), suggesting a potential impact on protein function. Conclusions: These findings highlight the importance of the FICD gene in diverse clinical manifestations and emphasize the need for further studies to elucidate the genetic mechanisms underlying these phenotypes. Continued research is essential to improve our understanding of FICD-related conditions.

Biomimetic Folding Strategies for Chemical Synthesis of Disulfide-Bonded Peptides and Proteins

Disulfide-bonded peptides and proteins, including hormones, toxins, growth factors, and others, are abundant in living organisms. These molecules play crucial physiological roles such as regulating cell and organism growth, development, and metabolism. They have also found widespread applications as drugs or tool molecules in biomedical and pharmaceutical research. However, the chemical synthesis of disulfide-bonded proteins is complicated by the challenges associated with their folding. This review focuses on the latest advancements in disulfide-bonded peptide and protein folding technologies. Particularly, it highlights biomimetic folding strategies that emulate the naturally occurring oxidative folding processes in nature. These strategies include chaperone-assisted folding, glycosylation-assisted folding, and organic-based oxidative folding methods. The review also anticipates future directions in folding technology. Such research offers innovative approaches for the chemical synthesis of complex proteins that are otherwise difficult to fold.

Subcellular Localization Guides eNOS Function

Nitric oxide synthases (NOS) are enzymes responsible for the cellular production of nitric oxide (NO), a highly reactive signaling molecule involved in important physiological and pathological processes. Given its remarkable capacity to diffuse across membranes, NO cannot be stored inside cells and thus requires multiple controlling mechanisms to regulate its biological functions. In particular, the regulation of endothelial nitric oxide synthase (eNOS) activity has been shown to be crucial in vascular homeostasis, primarily affecting cardiovascular disease and other pathophysiological processes of importance for human health. Among other factors, the subcellular localization of eNOS plays an important role in regulating its enzymatic activity and the bioavailability of NO. The aim of this review is to summarize pioneering studies and more recent publications, unveiling some of the factors that influence the subcellular compartmentalization of eNOS and discussing their functional implications in health and disease.

Exploring the dual role of endoplasmic reticulum stress in urological cancers: Implications for tumor progression and cell death interactions

The endoplasmic reticulum (ER) is crucial for maintaining calcium balance, lipid biosynthesis, and protein folding. Disruptions in ER homeostasis, often due to the accumulation of misfolded or unfolded proteins, lead to ER stress, which plays a significant role in various diseases, especially cancer. Urological cancers, which account for high male mortality worldwide, pose a persistent challenge due to their incurability and tendency to develop drug resistance. Among the numerous dysregulated biological mechanisms, ER stress is a key factor in the progression and treatment response of these cancers. This review highlights the dual role of aberrant ER stress activation in urologic cancers, affecting both tumor growth and therapeutic outcomes. While ER stress can support tumor growth through pro-survival autophagy, it primarily inhibits cancer progression via apoptosis and pro-death autophagy. Interestingly, ER stress can paradoxically aid cancer progression through mechanisms such as exosome-mediated immune evasion. Additionally, the review examines how pharmacological interventions, particularly with phytochemicals, can stimulate ER stress-mediated tumor suppression. Key regulators, including PERK, IRE1α, and ATF6, are discussed for their roles in upregulating CHOP levels and triggering apoptosis. In conclusion, a deeper understanding of ER stress in urological cancers not only clarifies the complex interactions between cellular stress and cancer progression but also provides new opportunities for innovative therapeutic strategies.

Topology surveillance of the lanosterol demethylase CYP51A1 by signal peptide peptidase

Cleavage of transmembrane segments on target proteins by the aspartyl intramembrane protease signal peptide peptidase (SPP, encoded by HM13) has been linked to immunity, viral infection and protein quality control. How SPP recognizes its various substrates and specifies their fate remains elusive. Here, we identify the lanosterol demethylase CYP51A1 as an SPP substrate and show that SPP-catalysed cleavage triggers CYP51A1 clearance by endoplasmic reticulum-associated degradation (ERAD). We observe that SPP targets only a fraction of CYP51A1 molecules, and we identify an amphipathic helix in the CYP51A1 N terminus as a key determinant for SPP recognition. SPP recognition is remarkably specific to CYP51A1 molecules with the amphipathic helix aberrantly inserted in the membrane with a type II orientation. Thus, our data are consistent with a role for SPP in topology surveillance, triggering the clearance of certain potentially non-functional conformers.

Pin1 promotes human CaV2.1 channel polyubiquitination by RNF138: pathophysiological implication for episodic ataxia type 2

Loss-of-function mutations in the human gene encoding the neuron-specific Ca2+ channel CaV2.1 are linked to the neurological disease episodic ataxia type 2 (EA2), as well as neurodevelopmental disorders such as developmental delay and developmental epileptic encephalopathy. Disease-associated CaV2.1 mutants may exhibit defective proteostasis and promote endoplasmic reticulum (ER)-associated degradation of their wild-type (WT) counterpart in a dominant-negative manner. The E3 ubiquitin ligase RNF138 was previously shown to mediate EA2-related aberrant degradation of CaV2.1 at the ER. Herein we aimed to elucidate the ER proteostasis mechanism of CaV2.1. The peptidyl-prolyl cis/trans isomerase, NIMA-interacting 1 (Pin1) was identified as a novel neuronal CaV2.1 binding partner that promoted polyubiquitination and proteasomal degradation of CaV2.1. Suppression of endogenous Pin1 level with either shRNA knockdown or the Pin1 inhibitor all-trans retinoic acid (ATRA) enhanced endogenous CaV2.1 protein level in neurons, and attenuated ER-associated degradation of CaV2.1 WT and EA2-causing mutants. Detailed mutation analyses suggested that Pin1 interacted with specific phosphorylated serine/threonine-proline motifs in the intracellular II-III loop and the distal carboxy-terminal region of human CaV2.1. We further generated Pin1-insensitive CaV2.1 constructs and demonstrated that, during ER quality control, Pin1 served as an upstream regulator of CaV2.1 polyubiquitination and degradation by RNF138. Pin1 regulation was required for the dominant-negative effect of EA2 missense mutants, but not nonsense mutants, on CaV2.1 WT protein expression. Our data are consistent with the idea that CaV2.1 proteostasis at the ER, as well as dominant-negative suppression of disease-causing loss-of-function mutants on CaV2.1 WT, entail both Pin1/RNF138-dependent and -independent mechanisms.

Inhibition of PA28γ expression can alleviate osteoarthritis by inhibiting endoplasmic reticulum stress and promoting STAT3 phosphorylation

Aims

Osteoarthritis (OA) is a common degenerative disease. PA28γ is a member of the 11S proteasome activator and is involved in the regulation of several important cellular processes, including cell proliferation, apoptosis, and inflammation. This study aimed to explore the role of PA28γ in the occurrence and development of OA and its potential mechanism.

Methods

A total of 120 newborn male mice were employed for the isolation and culture of primary chondrocytes. OA-related indicators such as anabolism, catabolism, inflammation, and apoptosis were detected. Effects and related mechanisms of PA28γ in chondrocyte endoplasmic reticulum (ER) stress were studied using western blotting, real-time polymerase chain reaction (PCR), and immunofluorescence. The OA mouse model was established by destabilized medial meniscus (DMM) surgery, and adenovirus was injected into the knee cavity of 15 12-week-old male mice to reduce the expression of PA28γ. The degree of cartilage destruction was evaluated by haematoxylin and eosin (HE) staining, safranin O/fast green staining, toluidine blue staining, and immunohistochemistry.

Results

We found that PA28γ knockdown in chondrocytes can effectively improve anabolism and catabolism and inhibit inflammation, apoptosis, and ER stress. Moreover, PA28γ knockdown affected the phosphorylation of IRE1α and the expression of TRAF2, thereby affecting the mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) signalling pathways, and finally affecting the inflammatory response of chondrocytes. In addition, we found that PA28γ knockdown can promote the phosphorylation of signal transducer and activator of transcription 3 (STAT3), thereby inhibiting ER stress in chondrocytes. The use of Stattic (an inhibitor of STAT3 phosphorylation) enhanced ER stress. In vivo, we found that PA28γ knockdown effectively reduced cartilage destruction in a mouse model of OA induced by the DMM surgery.

Conclusion

PA28γ knockdown in chondrocytes can inhibit anabolic and catabolic dysregulation, inflammatory response, and apoptosis in OA. Moreover, PA28γ knockdown in chondrocytes can inhibit ER stress by promoting STAT3 phosphorylation.

MiR-204-5p regulates SIRT1 to promote the endoplasmic reticulum stress-induced apoptosis of inner ear cells in C57BL/6 mice with hearing loss

PURPOSE

This study investigated the effect of miR-204-5p-mediated silencing of SIRT1 on the development of deafness in C57BL/6 mice and the roles of miR-204-5p and SIRT1 in deafness.

METHODS

Auditory brainstem response recordings, H&E staining, and immunohistochemistry were used to observe changes in hearing function and cochlear tissue morphology in 2-month-old and 15-month-old C57BL/6 mice. A senescence model was induced using H2O2 in inner ear cells (HEI-OC1). Changes in HEI-OC1 cell proliferation were detected using the CCK-8 assay, whereas flow cytometry was used to detect changes in apoptosis. MiR-204-5p expression was measured via RT‒qPCR. The SIRT1 agonist RSV and a miR-204-5p inhibitor were used to study changes in ER stress (ERS), proliferation, and apoptosis in HEI-OC1 cells. Western blotting was performed to detect changes in ATF4, CHOP, SIRT1, PERK, p-PERK, Bax, and Bcl-2 protein levels. A dual-luciferase reporter gene assay was carried out to assess the ability of miR-204-5p to target SIRT1.

RESULTS

Relative miR-204-5p expression levels in the cochleae of aged C57BL/6 mice increased, whereas SIRT1 expression levels decreased, and miR-204-5p and SIRT1 expression levels were negatively correlated. ERS and increased 8-OHDG levels were observed in aged C57BL/6 mice. In a model of inner ear cell aging, H2O2 treatment induced increases in miR-204-5p expression and ERS-mediated apoptosis. MiR-204-5p was found to target SIRT1 and inhibit its expression. SIRT1 activation and a miR-204-5p inhibitor promoted HEI-OC1 cell proliferation and reduced apoptosis. The miR-204-5p inhibitor regulated expression of the ERS proteins PERK, ATF4, and CHOP to upregulate Bcl-2 and downregulate Bax.

CONCLUSION

This study identified the roles of miR-204-5p and SIRT1 in deafness in C57BL/6 mice and investigated the loss of cochlear outer hair cells and the involvement of apoptosis and ERS in deafness.

Self-Assembly at Curved Biointerfaces

Most of the biological interfaces are curved. Understanding the organizational structures and interaction patterns at such curved biointerfaces is therefore crucial not only for deepening our comprehension of the principles that govern life processes but also for designing and developing targeted drugs aimed at diseased cells and tissues. Despite the considerable efforts dedicated to this area of research, our understanding of curved biological interfaces is still limited. Many aspects of these interfaces remain elusive, presenting both challenges and opportunities for further exploration. In this review, we summarize the structural characteristics of biological interfaces found in nature, the current research status of materials associated with curved biointerfaces, and the theoretical advancements achieved to date. Finally, we outline future trends and challenges in the theoretical and technological development of curved biointerfaces. By addressing these challenges, people could bridge the knowledge gap and unlock the full potential of curved biointerfaces for scientific and technological advancements, ultimately benefiting various fields and improving human health and well-being.

Cotton Bollworm (H. armigera) Effector PPI5 Targets FKBP17-2 to Inhibit ER Immunity and JA/SA Responses, Enhancing Insect Feeding

The cotton bollworm causes severe mechanical damage to plants during feeding and leaves oral secretions (OSs) at the mechanical wounds. The role these OSs play in the invasion of plants is still largely unknown. Here, a novel H. armigera effector peptidyl prolyl trans-isomerase 5 (PPI5) was isolated and characterized. PPI5 induces the programmed cell death (PCD) due to the unfolded protein response (UPR) in tobacco leaf. We reveal that PPI5 is important for the growth and development of cotton bollworm on plants, as it renders plants more susceptible to feeding. The GhFKBP17-2, was identified as a host target for PPI5 with peptidyl-prolyl isomerase (PPIase) activity. CRISPR/Cas9 knock-out cotton mutant (CR-GhFKBP17-1/3), VIGS (TRV: GhFKBP17-2) and overexpression lines (OE-GhFKBP17-1/3) were created and the data indicate that GhFKBP17-2 positively regulates endoplasmic reticulum (ER) stress-mediated plant immunity in response to cotton bollworm infestation. We further confirm that PPI5 represses JA and SA levels by downregulating the expression of JA- and SA-associated genes, including JAZ3/9, MYC2/3, JAR4, PR4, LSD1, PAD4, ICS1 and PR1/5. Taken together, our results reveal that PPI5 reduces plant defense responses and makes plants more susceptible to cotton bollworm infection by targeting and suppressing GhFKBP17-2 -mediated plant immunity.

Kinesin-1 mediates proper ER folding of the CaV1.2 channel and maintains mouse glucose homeostasis

Glucose-stimulated insulin secretion (GSIS) from pancreatic beta cells is a principal mechanism for systemic glucose homeostasis, of which regulatory mechanisms are still unclear. Here we show that kinesin molecular motor KIF5B is essential for GSIS through maintaining the voltage-gated calcium channel CaV1.2 levels, by facilitating an Hsp70-to-Hsp90 chaperone exchange to pass through the quality control in the endoplasmic reticulum (ER). Phenotypic analyses of KIF5B conditional knockout (cKO) mouse beta cells revealed significant abolishment of glucose-stimulated calcium transients, which altered the behaviors of insulin granules via abnormally stabilized cortical F-actin. KIF5B and Hsp90 colocalize to microdroplets on ER sheets, where CaV1.2 but not Kir6.2 is accumulated. In the absence of KIF5B, CaV1.2 fails to be transferred from Hsp70 to Hsp90 via STIP1, and is likely degraded via the proteasomal pathway. KIF5B and Hsc70 overexpression increased CaV1.2 expression via enhancing its chaperone binding. Thus, ER sheets may serve as the place of KIF5B- and Hsp90-dependent chaperone exchange, which predominantly facilitates CaV1.2 production in beta cells and properly enterprises GSIS against diabetes.

Analysis of randomly mutated AlSRKb genes reveals that most loss-of-function mutations cause defects in plasma membrane localization

Only very limited information is available on why some nonsynonymous variants severely alter gene function while others have no effect. To identify the characteristic features of mutations that strongly influence gene function, this study focused on SRK which encodes a highly polymorphic receptor kinase expressed in stigma papillary cells that underlies a female determinant of self-incompatibility in Brassicaceae. A set of 300 Arabidopsis thaliana transformants expressing mutated SRKb from A. lyrata was constructed using error-prone PCR and the genotype and self-incompatibility phenotype of each transformant were determined. Almost all the transformants showing the self-incompatibility defect contained mutations in AlSRKb that altered localization to the plasma membrane. The observed mutations occurred in amino acid residues that were highly conserved across S haplotypes and whose predicted locations were in the interior of the protein. Our findings suggested that mutations causing the self-incompatibility defect were more likely to result from changes to AlSRKb biosynthesis than from loss of AlSRKb function. In addition, we examined whether the RandomForest and Extreme Gradient Boosting methods could predict the self-incompatibility phenotypes of SRK mutants.

The prolyl isomerase FKBP11 is a secretory translocon accessory factor

Eukaryotic cells encode thousands of secretory and membrane proteins, many of which are cotranslationally translocated into the endoplasmic reticulum (ER). Nascent polypeptides entering the ER encounter a network of molecular chaperones and enzymes that facilitate their folding. A rate-limiting step for some proteins is the trans-to-cis isomerization of the peptide bond between proline and the residue preceding it. The human ER contains six prolyl isomerases, but the function, organization, and substrate range of these proteins is not clear. Here we show that the metazoan-specific, prolyl isomerase FKBP11 binds to ribosome-translocon complexes (RTCs) in the ER membrane, dependent on its single transmembrane domain and a conserved, positively charged region at its cytosolic C-terminus. High-throughput mRNA sequencing shows selective engagement with ribosomes synthesizing secretory and membrane proteins with long translocated segments, and functional analysis shows reduced stability of two such proteins, EpCAM and PTTG1IP, in cells depleted of FKBP11. We propose that FKBP11 is a translocon accessory factor that acts on a broad range of soluble secretory and transmembrane proteins during their synthesis at the ER.

Endoplasmic Reticulum Stress in Bronchopulmonary Dysplasia: Contributor or Consequence?

Bronchopulmonary dysplasia (BPD) is the most common complication of prematurity. Oxidative stress (OS) and inflammation are the major contributors to BPD. Despite aggressive treatments, BPD prevalence remains unchanged, which underscores the urgent need to explore more potential therapies. The endoplasmic reticulum (ER) plays crucial roles in surfactant and protein synthesis, assisting mitochondrial function, and maintaining metabolic homeostasis. Under OS, disturbed metabolism and protein folding transform the ER structure to refold proteins and help degrade non-essential proteins to resume cell homeostasis. When OS becomes excessive, the endogenous chaperone will leave the three ER stress sensors to allow subsequent changes, including cell death and senescence, impairing the growth potential of organs. The contributing role of ER stress in BPD is confirmed by reproducing the BPD phenotype in rat pups by ER stress inducers. Although chemical chaperones attenuate BPD, ER stress is still associated with cellular senescence. N-acetyl-lysyltyrosylcysteine amide (KYC) is a myeloperoxidase inhibitor that attenuates ER stress and senescence as a systems pharmacology agent. In this review, we describe the role of ER stress in BPD and discuss the therapeutic potentials of chemical chaperones and KYC, highlighting their promising role in future therapeutic interventions.

Megakaryocyte maturation involves activation of the adaptive unfolded protein response

Endoplasmic reticulum stress triggers the unfolded protein response (UPR) to promote cell survival or apoptosis. Transient endoplasmic reticulum stress activation has been reported to trigger megakaryocyte production, and UPR activation has been reported as a feature of megakaryocytic cancers. However, the role of UPR signaling in megakaryocyte biology is not fully understood. We studied the involvement of UPR in human megakaryocytic differentiation using PMA (phorbol 12-myristate 13-acetate)-induced maturation of megakaryoblastic cell lines and thrombopoietin-induced differentiation of human peripheral blood-derived progenitors. Our results demonstrate that an adaptive UPR is a feature of megakaryocytic differentiation and that this response is not associated with ER stress-induced apoptosis. Differentiation did not alter the response to the canonical endoplasmic reticulum stressors DTT or thapsigargin. However, thapsigargin, but not DTT, inhibited differentiation, consistent with the involvement of Ca2+ signaling in megakaryocyte differentiation.

Endoplasmic reticulum stress alters myelin associated protein expression and extracellular vesicle composition in human oligodendrocytes

Myelination of the central nervous system is mediated by specialized glial cells called oligodendrocytes (OLs). Multiple sclerosis (MS) is characterized by loss of myelination and subsequent clinical symptoms that can severely impact the quality of life and mobility of those affected by the disease. The major protein components of myelin sheaths are synthesized in the endoplasmic reticulum (ER), and ER stress has been observed in patients with MS. Extracellular vesicles (EVs) have been shown to carry bioactive cargo and have the potential to be utilized as noninvasive biomarkers for various diseases. In the current study, we sought to determine how ER stress in OLs affected the production of key myelination proteins and EV release and composition. To achieve this, tunicamycin was used to induce ER stress in a human oligodendroglioma cell line and changes in myelination protein expression and markers of autophagy were assessed. EVs were also separated from the conditioned cell culture media through size exclusion chromatography and characterized. Significant reductions in the expression of myelination proteins and alterations to autophagosome formation were observed in cells undergoing ER stress. EVs released from these cells were slightly smaller relative to controls, and had strong expression of LC3B. We also observed significant upregulation of miR-29a-3p in ER stress EVs when compared to controls. Taken together, these data suggest that ER stress negatively impacts production of key myelination proteins and induces cells to release EVs that may function to preemptively activate autophagic pathways in neighboring cells.

PKD regulates mitophagy to prevent oxidative stress and mitochondrial dysfunction during mouse oocyte maturation

Mitochondria play dominant roles in various cellular processes such as energy production, apoptosis, calcium homeostasis, and oxidation-reduction balance. Maintaining mitochondrial quality through mitophagy is essential, especially as its impairment leads to the accumulation of dysfunctional mitochondria in aging oocytes. Our previous research revealed that PKD expression decreases in aging oocytes, and its inhibition negatively impacts oocyte quality. Given PKD's role in autophagy mechanisms, this study investigates whether PKD regulates mitophagy to maintain mitochondrial function and support oocyte maturation. When fully grown oocytes were treated with CID755673, a potent PKD inhibitor, we observed meiosis arrest at the metaphase I stage, along with decreased spindle stability. Our results demonstrate an association with mitochondrial dysfunction, including reduced ATP production and fluctuations in Ca2+ homeostasis, which ultimately lead to increased ROS accumulation, stimulating oxidative stress-induced apoptosis and DNA damage. Further research has revealed that these phenomena result from PKD inhibition, which affects the phosphorylation of ULK, thereby reducing autophagy levels. Additionally, PKD inhibition leads to decreased Parkin expression, which directly and negatively affects mitophagy. These defects result in the accumulation of damaged mitochondria in oocytes, which is the primary cause of mitochondrial dysfunction. Taken together, these findings suggest that PKD regulates mitophagy to support mitochondrial function and mouse oocyte maturation, offering insights into potential targets for improving oocyte quality and addressing mitochondrial-related diseases in aging females.

The complexity of extracellular vesicles: Bridging the gap between cellular communication and neuropathology

Brain-derived extracellular vesicles (EVs) serve a prominent role in maintaining homeostasis and contributing to pathology in health and disease. This review establishes a crucial link between physiological processes leading to EV biogenesis and their impacts on disease. EVs are involved in the clearance and transport of proteins and nucleic acids, responding to changes in cellular processes associated with neurodegeneration, including autophagic disruption, organellar dysfunction, aging, and other cell stresses. In neurodegenerative disorders (e.g., Alzheimer's disease, Parkinson's disease, etc.), EVs contribute to the spread of pathological proteins like amyloid β, tau, ɑ-synuclein, prions, and TDP-43, exacerbating neurodegeneration and accelerating disease progression. Despite evidence for both neuropathological and neuroprotective effects of EVs, the mechanistic switch between their physiological and pathological functions remains elusive, warranting further research into their involvement in neurodegenerative disease. Moreover, owing to their innate ability to traverse the blood-brain barrier and their ubiquitous nature, EVs emerge as promising candidates for novel diagnostic and therapeutic strategies. The review uniquely positions itself at the intersection of EV cell biology, neurophysiology, and neuropathology, offering insights into the diverse biological roles of EVs in health and disease.

Restoring function to inactivating G protein-coupled receptor variants in the hypothalamic-pituitary-gonadal axis1

G protein-coupled receptors (GPCRs) are central to the functioning of the hypothalamic-pituitary-gonadal axis (HPG axis) and include the rhodopsin-like GPCR family members, neurokinin 3 receptor, kappa-opioid receptor, kisspeptin 1 receptor, gonadotropin-releasing hormone receptor, and the gonadotropin receptors, luteinizing hormone/choriogonadotropin receptor and follicle-stimulating hormone receptor. Unsurprisingly, inactivating variants of these receptors have been implicated in a spectrum of reproductive phenotypes, including failure to undergo puberty, and infertility. Clinical induction of puberty in patients harbouring such variants is possible, but restoration of fertility is not always a realisable outcome, particularly for those patients suffering from primary hypogonadism. Thus, novel pharmaceuticals and/or a fundamental change in approach to treating these patients are required. The increasing wealth of data describing the effects of coding-region genetic variants on GPCR function has highlighted that the majority appear to be dysfunctional as a result of misfolding of the encoded receptor protein, which, in turn, results in impaired receptor trafficking through the secretory pathway to the cell surface. As such, these intracellularly retained receptors may be amenable to 'rescue' using a pharmacological chaperone (PC)-based approach. PCs are small, cell permeant molecules hypothesised to interact with misfolded intracellularly retained proteins, stabilising their folding and promoting their trafficking through the secretory pathway. In support of the use of this approach as a viable therapeutic option, it has been observed that many rescued variant GPCRs retain at least a degree of functionality when 'rescued' to the cell surface. In this review, we examine the GPCR PC research landscape, focussing on the rescue of inactivating variant GPCRs with important roles in the HPG axis, and describe what is known regarding the mechanisms by which PCs restore trafficking and function. We also discuss some of the merits and obstacles associated with taking this approach forward into a clinical setting.

Time-resolved interactome profiling deconvolutes secretory protein quality control dynamics

Many cellular processes are governed by protein-protein interactions that require tight spatial and temporal regulation. Accordingly, it is necessary to understand the dynamics of these interactions to fully comprehend and elucidate cellular processes and pathological disease states. To map de novo protein-protein interactions with time resolution at an organelle-wide scale, we developed a quantitative mass spectrometry method, time-resolved interactome profiling (TRIP). We apply TRIP to elucidate aberrant protein interaction dynamics that lead to the protein misfolding disease congenital hypothyroidism. We deconvolute altered temporal interactions of the thyroid hormone precursor thyroglobulin with pathways implicated in hypothyroidism pathophysiology, such as Hsp70-/90-assisted folding, disulfide/redox processing, and N-glycosylation. Functional siRNA screening identified VCP and TEX264 as key protein degradation components whose inhibition selectively rescues mutant prohormone secretion. Ultimately, our results provide novel insight into the temporal coordination of protein homeostasis, and our TRIP method should find broad applications in investigating protein-folding diseases and cellular processes.

Exosomal misfolded proteins released by cancer stem cells: dual functions in balancing protein homeostasis and orchestrating tumor progression

Cancer stem cells (CSCs), the master regulators of tumor heterogeneity and progression, exert profound influence on cancer metastasis, via various secretory vesicles. Emerging from CSCs, the exosomes serve as pivotal mediators of intercellular communication within the tumor microenvironment, modulating invasion, angiogenesis, and immune responses. Moreover, CSC-derived exosomes play a central role in sculpting a dynamic landscape, contributing to the malignant phenotype. Amidst several exosomal cargoes, misfolded proteins have recently gained attention for their dual functions in maintaining protein homeostasis and promoting tumor progression. Disrupting these communication pathways could potentially prevent the maintenance and expansion of CSCs, overcome treatment resistance, and inhibit the supportive environment created by the tumor microenvironment, thereby improving the effectiveness of cancer therapies and reducing the risk of tumor recurrence and metastasis. Additionally, exosomes have also shown potential therapeutic applications, such as in drug delivery or as biomarkers for cancer diagnosis and prognosis. Therefore, comprehending the biology of exosomes derived from CSCs is a multifaceted area of research with implications in both basic sciences and clinical applications. This review explores the intricate interplay between exosomal misfolded proteins released by CSCs, the potent contributor in tumor heterogeneity, and their impact on cellular processes, shedding light on their role in cancer progression.

Gp93 inhibits unfolded protein response-mediated c-Jun N-terminal kinase activation and cell invasion

In eukaryotes, Hsp90B1 serves as a vital chaperonin, facilitating the accurate folding of proteins. Interestingly, Hsp90B1 exhibits contrasting roles in the development of various types of cancers, although the underlying reasons for this duality remain enigmatic. Through the utilization of the Drosophila model, this study unveils the functional significance of Gp93, the Drosophila ortholog of Hsp90B1, which hitherto had limited reported developmental functions. Employing the Drosophila cell invasion model, we elucidated the pivotal role of Gp93 in regulating cell invasion and modulating c-Jun N-terminal kinase (JNK) activation. Furthermore, our investigation highlights the involvement of the unfolded protein response-associated IRE1/XBP1 pathway in governing Gp93 depletion-induced, JNK-dependent cell invasion. Collectively, these findings not only uncover a novel molecular function of Gp93 in Drosophila, but also underscore a significant consideration pertaining to the testing of Hsp90B1 inhibitors in cancer therapy.

Critical role of endoplasmic reticulum stress on bisphenol A-induced cytotoxicity in human keratinocyte HaCaT cells

Bisphenol A (BPA) is widely used in plastic and paper products, and its exposure can occur through skin contact or oral ingestion. The hazardous effects of BPA absorbed through the skin may be more severe; however, few studies have investigated the skin toxicity of BPA. This study investigated the effects of BPA on human epidermal keratinocyte cell lines, which is relevant for skin exposure. BPA treatment reduced cell viability in a time- and concentration-dependent manner and elevated oxidative and endoplasmic reticulum (ER) stress. N-acetylcysteine (NAC), an oxidative stress inhibitor, reduced BPA-induced reactive oxygen species (ROS) levels. However, only 10% of the decreased cell viability was restored at the highest NAC concentration. Treatment with tauroursodeoxycholic acid (TUDCA), which is an ER stress inhibitor, effectively countered the increase in ER stress-related proteins induced by BPA. Moreover, TUDCA treatment led to a reduction in oxidative stress, as demonstrated by the decrease in ROS levels, maintenance of mitochondrial membrane potential, and modulation of stress signaling proteins. Consequently, TUDCA significantly improved BPA-induced cytotoxicity in a concentration-dependent manner. Notably, combined treatment using TUDCA and NAC further reduced the BPA-induced ROS levels; however, no significant difference in cell viability was observed compared with that for TUDCA treatment alone. These findings indicated that the oxidative stress observed following BPA exposure was exacerbated by ER stress. Moreover, the principal factor driving BPA-induced cytotoxicity was indeed ER stress, which has potential implications for developing therapeutic strategies for diseases associated with similar stress responses.

Comparative RNA-Seq of Ten Phaeodactylum tricornutum Accessions: Unravelling Criteria for Robust Strain Selection from a Bioproduction Point of View

The production of biologics in mammalian cells is hindered by some limitations including high production costs, prompting the exploration of other alternative expression systems that are cheaper and sustainable like microalgae. Successful productions of biologics such as monoclonal antibodies have already been demonstrated in the diatom Phaeodactylum tricornutum; however, limited production yields still remain compared to mammalian cells. Therefore, efforts are needed to make this microalga more competitive as a cell biofactory. Among the seventeen reported accessions of P. tricornutum, ten have been mainly studied so far. Among them, some have already been used to produce high-value-added molecules such as biologics. The use of "omics" is increasingly being described as useful for the improvement of both upstream and downstream steps in bioprocesses using mammalian cells. Therefore, in this context, we performed an RNA-Seq analysis of the ten most used P. tricornutum accessions (Pt1 to Pt10) and deciphered the differential gene expression in pathways that could affect bioproduction of biologics in P. tricornutum. Our results highlighted the benefits of certain accessions such as Pt9 or Pt4 for the production of biologics. Indeed, these accessions seem to be more advantageous. Moreover, these results contribute to a better understanding of the molecular and cellular biology of P. tricornutum.

The Folding Pathway of ABC Transporter CFTR: Effective and Robust

De novo protein folding into a native three-dimensional structure is indispensable for biological function, is instructed by its amino acid sequence, and occurs along a vectorial trajectory. The human proteome contains thousands of membrane-spanning proteins, whose biosynthesis begins on endoplasmic reticulum-associated ribosomes. Nearly half of all membrane proteins traverse the membrane more than once, including therapeutically important protein families such as solute carriers, G-protein-coupled receptors, and ABC transporters. These mediate a variety of functions like signal transduction and solute transport and are often of vital importance for cell function and tissue homeostasis. Missense mutations in multispan membrane proteins can lead to misfolding and cause disease; an example is the ABC transporter Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Even though our understanding of multispan membrane-protein folding still is rather rudimental, the cumulative knowledge of 20 years of basic research on CFTR folding has led to development of drugs that modulate the misfolded protein. This has provided the prospect of a life without CF to the vast majority of patients. In this review we describe our understanding of the folding pathway of CFTR in cells, which is modular and tolerates many defects, making it effective and robust. We address how modulator drugs affect folding and function of CFTR, and distinguish protein stability from its folding process. Since the domain architecture of (mammalian) ABC transporters are highly conserved, we anticipate that the insights we discuss here for folding of CFTR may lay the groundwork for understanding the general rules of ABC-transporter folding.

Shrimp shapes a resistance trait against vibriosis by memorizing the colonization resistance of intestinal microbiota

Vibriosis is one of the most serious diseases that commonly occurs in aquatic animals, thus, shaping a steady inherited resistance trait in organisms has received the highest priority in aquaculture. Whereas, the mechanisms underlying the development of such a resistance trait are mostly elusive. In this study, we constructed vibriosis-resistant and susceptible families of the Pacific white shrimp Litopenaeus vannamei after four generations of artificial selection. Microbiome sequencing indicated that shrimp can successfully develop a colonization resistance trait against Vibrio infections. This trait was characterized by a microbial community structure with specific enrichment of a single probiotic species (namely Shewanella algae), and notably, its formation was inheritable and might be memorized by host epigenetic remodeling. Regardless of the infection status, a group of genes was specifically activated in the resistant family through disruption of complete methylation. Specifically, hypo-methylation and hyper-expression of genes related to lactate dehydrogenase (LDH) and iron homeostasis might provide rich sources of specific carbon (lactate) and ions for the colonization of S. algae, which directly results in the reduction of Vibrio load in shrimp. Lactate feeding increased the survival of shrimp, while knockdown of LDH gene decreased the survival when shrimp was infected by Vibrio pathogens. In addition, treatment of shrimp with the methyltransferase inhibitor 5-azacytidine resulted in upregulations of LDH and some protein processing genes, significant enrichment of S. algae, and simultaneous reduction of Vibrio in shrimp. Our results suggest that the colonization resistance can be memorized as epigenetic information by the host, which has played a pivotal role in vibriosis resistance. The findings of this study will aid in disease control and the selection of superior lines of shrimp with high disease resistance.

Genome-wide identification and characterization of DIRIGENT gene family (CcDIR) in pigeonpea (Cajanus cajan L.) provide insights on their spatial expression pattern and relevance to stress response

This study is a thorough characterization of pigeonpea dirigent gene (CcDIR) family, an important component of the lignin biosynthesis pathway. Genome-wide analysis identified 25 CcDIR genes followed by a range of analytical approaches employed to unravel their structural and functional characteristics. Structural examination revealed a classic single exon and no intron arrangement in CcDIRs contributing to our understanding on evolutionary dynamics. Phylogenetic analysis elucidated evolutionary relationships among CcDIR genes with six DIR sub-families, while motif distribution analysis displayed and highlighted ten conserved protein motifs in CcDIRs. Promoter analyses of all the dirigent genes detected 18 stress responsive cis-acting elements offering insights into transcriptional regulation. While spatial expression analyses across six plant tissues showed preferential expression of CcDIR genes, exposure to salt (CcDIR2 and CcDIR9) and herbivory (CcDIR1, CcDIR2, CcDIR3 and CcDIR11), demonstrated potential roles of specific DIRs in plant defense. Interestingly, increased gene expression during herbivory, also correlated with increased lignin content authenticating the specific response. Furthermore, exogenous application of stress hormones, SA and MeJA on leaves significantly induced the expression of CcDIRs that responded to herbivory. Taken together, these findings contribute to a comprehensive understanding of CcDIR genes impacting development and stress response in the important legume pigeonpea.

The biogenesis of potassium transporters: implications of disease-associated mutations

The concentration of intracellular and extracellular potassium is tightly regulated due to the action of various ion transporters, channels, and pumps, which reside primarily in the kidney. Yet, potassium transporters and cotransporters play vital roles in all organs and cell types. Perhaps not surprisingly, defects in the biogenesis, function, and/or regulation of these proteins are linked to range of catastrophic human diseases, but to date, few drugs have been approved to treat these maladies. In this review, we discuss the structure, function, and activity of a group of potassium-chloride cotransporters, the KCCs, as well as the related sodium-potassium-chloride cotransporters, the NKCCs. Diseases associated with each of the four KCCs and two NKCCs are also discussed. Particular emphasis is placed on how these complex membrane proteins fold and mature in the endoplasmic reticulum, how non-native forms of the cotransporters are destroyed in the cell, and which cellular factors oversee their maturation and transport to the cell surface. When known, we also outline how the levels and activities of each cotransporter are regulated. Open questions in the field and avenues for future investigations are further outlined.

VCP/p97 mediates nuclear targeting of non-ER-imported prion protein to maintain proteostasis

Mistargeting of secretory proteins in the cytosol can trigger their aggregation and subsequent proteostasis decline. We have identified a VCP/p97-dependent pathway that directs non-ER-imported prion protein (PrP) into the nucleus to prevent the formation of toxic aggregates in the cytosol. Upon impaired translocation into the ER, PrP interacts with VCP/p97, which facilitates nuclear import mediated by importin-ß. Notably, the cytosolic interaction of PrP with VCP/p97 and its nuclear import are independent of ubiquitination. In vitro experiments revealed that VCP/p97 binds non-ubiquitinated PrP and prevents its aggregation. Inhibiting binding of PrP to VCP/p97, or transient proteotoxic stress, promotes the formation of self-perpetuating and partially proteinase resistant PrP aggregates in the cytosol, which compromised cellular proteostasis and disrupted further nuclear targeting of PrP. In the nucleus, RNAs keep PrP in a soluble and non-toxic conformation. Our study revealed a novel ubiquitin-independent role of VCP/p97 in the nuclear targeting of non-imported secretory proteins and highlights the impact of the chemical milieu in triggering protein misfolding.

Mitigating candidiasis with acarbose by targeting Candida albicans α-glucosidase: in-silico, in-vitro and transcriptomic approaches

Biofilm-associated candidiasis poses a significant challenge in clinical settings due to the limited effectiveness of existing antifungal treatments. The challenges include increased pathogen virulence, multi-drug resistance, and inadequate penetration of antimicrobials into biofilm structures. One potential solution to this problem involves the development of novel drugs that can modulate fungal virulence and biofilm formation, which is essential for pathogenesis. Resistance in Candida albicans is initiated by morphological changes from yeast to hyphal form. This transition triggers a series of events such as cell wall elongation, increased adhesion, invasion of host tissues, pathogenicity, biofilm formation, and the initiation of an immune response. The cell wall is a critical interface for interactions with host cells, primarily through various cell wall proteins, particularly mannoproteins. Thus, cell wall proteins and enzymes are considered potential antifungal targets. In this regard, we explored α-glucosidase as our potential target which plays a crucial role in processing mannoproteins. Previous studies have shown that inhibition of α-glucosidase leads to defects in cell wall integrity, reduced adhesion, diminished secretion of hydrolytic enzymes, alterations in immune recognition, and reduced pathogenicity. Since α-glucosidase, primarily converts carbohydrates, our study focuses on FDA-approved carbohydrate mimic drugs (Glycomimetics) with well-documented applications in various biological contexts. Through virtual screening of 114 FDA-approved carbohydrate-based drugs, a pseudo-sugar Acarbose, emerged as a top hit. Acarbose is known for its pharmacological potential in managing type 2 diabetes mellitus by targeting α-glucosidase. Our preliminary investigations indicate that Acarbose effectively inhibits C. albicans biofilm formation, reduces virulence, impairs morphological switching, and hinders the adhesion and invasion of host cells, all at very low concentrations in the nanomolar range. Furthermore, transcriptomic analysis reveals the mechanism of action of Acarbose, highlighting its role in targeting α-glucosidase.