The endoplasmic reticulum (ER) is the membrane-bound organelle characterized by the reticular network of tubules. It is well established that the ER tubules are shaped by ER membrane proteins containing the conserved reticulon-homology domain (RHD). Membrane shaping by the RHD-containing proteins is also involved in regulation of ER-phagy, selective autophagy of the ER. However, it remains unclear whether there exists ER membrane-shaping proteins other than the RHD-containing proteins. In this study, we characterize Arl6IP5, an ER membrane protein containing the conserved PRA1 domain, as an ER membrane-shaping protein. Upon overexpression, Arl6IP5 induces the extensive network of the ER tubules, and constricts the ER membrane as judged by exclusion of a luminal ER enzyme from the ER tubules. The membrane constriction by Arl6IP5 allows the cells to maintain the tubular ER network in the absence of microtubules. siRNA-mediated knockdown of Arl6IP5 impairs the ER morphology, and the phenotype of the Arl6IP5 knockdown cells is rescued by exogenous expression of Arl6IP1, an RHD-containing protein. Furthermore, exogenous expression of Arl6IP5 rescues the phenotype of Arl6IP1 knockdown cells, and the PRA1 domain is sufficient to rescue it. Upon disruption of the possible short hairpin structures of the PRA1 domain, Arl6IP5 abolishes membrane constriction. The siRNA-mediated knockdown of Arl6IP5 impairs flux of the ER-phagy mediated by FAM134B. These results indicate that Arl6IP5 acts as an ER membrane-shaping protein involved in regulation of ER-phagy, implying that the PRA1 domain may serve as a general membrane-shaping unit other than the RHD.

CD4+CD25+ regulatory T cells (Tregs) contribute to the pathogenesis of sepsis-induced immunosuppression. We have identified interleukin (IL)-36β as a critical cytokine regulating CD4+CD25+ Treg activity.

This study aimed to further investigate the underlying mechanism of IL-36β-triggered responses in murine CD4+CD25+ Tregs in presence of lipolysaccharide (LPS) and in a mouse model of sepsis induced by cecal and puncture (CLP).

Following LPS exposure, ER-phagy activity increased, peaked at 12 h, and then markedly declined. Furthermore, we observed that IL-36β could activate ER-phagy of CD4+CD25+ Tregs under LPS challenge. Mechanistic investigations revealed the critical involvement of the endoplasmic reticulum (ER) stress-related protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK)-activating transcription factor 4 (ATF4) signaling axis in IL-36β-induced ER-phagy. Moreover, IL-36β knockout (IL-36β-/-) strongly dampened ER-phagy and PERK-ATF4 signaling under LPS stimulation compared to the wild-type group. IL-36β-elicited effects on CD4+CD25+ Tregs were significantly abrogated by FAM134B (the ER-phagy-specific receptor) knockout or salubrinal (a specific inhibitor of the PERK-ATF4 pathway). In addition, IL-36β was potent in diminishing serum levels of creatinine (Cr), aspartate transaminase (AST), and alanine transaminase (ALT) and attenuated histopathologic alterations in the liver, kidneys, and lungs of CLP mice. Importantly, the absence of IL-36β notably aggravated the survival rate of septic mice, indicating a beneficial role in septic prognosis.

IL-36β can down-regulate the immune activity of CD4+CD25+ Tregs via ER-phagy induction. Our study might provide novel targets for therapeutic strategies to prevent the development of sepsis.

Alcohol-associated liver disease (ALD) is a hepatocyte dysfunction disease caused by chronic or excessive alcohol consumption, which can lead to extensive hepatocyte necrosis and even liver failure. Currently, the pathogenesis of ALD and the anti-ALD mechanisms have not been fully elucidated yet. In this study, we investigated the effects of endoplasmic reticulum autophagy (ER-phagy) in ALD and the role of acid-sensing ion channel 1a (ASIC1a) in ER stress-mediated ER-phagy. A mouse model of ALD was established using the Gao-Binge method and the AML12 cell line treated with alcohol was used as an in vitro model. We showed that ASIC1a expression was significantly increased and ER-phagy was activated in both the in vivo and in vitro models. In alcohol-treated AML12 cells, we showed that blockade of ASIC1a with PcTx-1 or knockdown of ASIC1a reduced alcohol-induced intracellular Ca2+ accumulation and ER stress. In addition, inhibition of ER stress with 4-PBA reduced the level of ER-phagy. Furthermore, knockdown of the ER-phagy receptor family with sequence similarity 134 member B (FAM134B) alleviated alcohol-triggered hepatocyte injury and apoptosis. In conclusion, this study demonstrates that alcohol activates ER stress-induced ER-phagy and liver injury by increasing ASIC1a expression and ASIC1a-mediated Ca2+ influx, providing a novel strategy for the treatment of ALD.

Chinese Tuina has been used to treat skeletal muscle contusion (SMC) for a long time in China, yet its efficacy and mechanisms remain unclear. Previous studies have shown the vital roles of endoplasmic reticulum (ER) stress and autophagy during injured skeletal muscle recovery, we postulated that Chinese Tuina could expedite the healing of SMC by fine-tuning these processes. In this study, we established a rat model of SMC through weight-dropping and divided the rats into three groups: SMC, SMC+Tuina, and SMC+Tuina+ 3-methyladenine (3-MA) groups, while using untreated normal SD rats as a control. We assessed gait and edema via CatWalk gait analysis and swelling measurements, respectively. Tumor necrosis factor-α (TNF-α) expression was determined by immunohistochemistry (IHC). Morphological and ultrastructural alterations in the damaged muscle tissue were examined using hematoxylin and eosin (HE) staining and transmission electron microscopy (TEM), respectively. Expression of GRP78, LC3B and FAM134b was determined by western blot, and Colocalization of LC3B and FAM134b was examined by immunofluorescence. SMC+Tuina exhibited significantly improved gait and reduced edema. SMC+Tuina showed improvements in morphology and ultrastructure of damaged muscles, as well as decreased expression of TNF-α. Additionally, in SMC+Tuina, expression of GRP78 was downregulated, while expressions of FAM134 and LC3B were upregulated, and colocalization of FAM134 and LC3B was also enhanced. However, autophagy inhibitor 3-MA weakened the aforementioned effects of Chinese Tuina. The obtained results indicated that Chinese Tuina has a positive therapeutic effect in rats with SMC, potentially by promoting autophagy to reduce inflammation and ER stress.

The development of chemo-resistance remains a significant hurdle in effective cancer therapy. NRF1 and NRF2, key regulators of redox homeostasis, play crucial roles in the cellular response to oxidative stress, with implications for both tumor growth and resistance to chemotherapy. This study delves into the dualistic role of NRF2, exploring its protective functions in normal cells and its paradoxical support of tumor survival and drug resistance in cancerous cells. We investigate the interplay between the PERK/NRF signaling pathway, ER stress, autophagy, and the unfolded protein response, offering a mechanistic perspective on how these processes contribute to chemoresistance. Our findings suggest that targeting NRF signaling pathways may offer new avenues for overcoming resistance to chemotherapeutic agents, highlighting the importance of a nuanced approach to redox regulation in cancer treatment. This research provides a molecular basis for the development of NRF-targeted therapies, potentially enhancing the efficacy of existing cancer treatments and offering hope for more effective management of resistant tumors.

Protein misfolding and aggregation in the endoplasmic reticulum (ER) have been causally linked to a variety of human diseases. Two key pathways for eliminating misfolded proteins and aggregates in the ER are ER-associated degradation (ERAD) and ER-phagy, respectively. While both pathways have been well characterized biochemically, our understanding of their physiological relevance and significance remains limited. In recent years, significant advances have been made, including the generation and characterization of various knockout and knockin mouse models, the identification of human disease-associated or -causing variants, and insights into the coordination between ERAD and autophagy in physiological contexts. In this review, we summarize these advancements, highlighting the key roles of a highly conserved suppressor of lin-12-like-hydroxymethyl glutaryl-coenzyme A reductase degradation 1 (SEL1L-HRD1) protein complex of ERAD and ER-phagy in health and disease.

Cellular stresses, particularly endoplasmic reticulum (ER) stress induced by ER-to-Golgi transport blockade, trigger Golgi-independent secretion of cytosolic and transmembrane proteins. However, the molecular mechanisms underlying this unconventional protein secretion (UPS) remain largely elusive. Here, we report that an ER tubulovesicular structure (ER tubular body [ER-TB]), shaped by the tubular ER-phagy receptors ATL3 and RTN3L, plays an important role in stress-induced UPS of transmembrane proteins such as cystic fibrosis transmembrane conductance regulator (CFTR) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Correlative light-electron microscopy analyses demonstrate the formation of ER-TB under UPS-inducing conditions in HEK293 and HeLa cells. Individual gene knockdowns of ATL3 and RTN3 inhibit ER-TB formation and the UPS of trafficking-deficient ΔF508-CFTR. Combined supplementation of ATL3 and RTN3L induces ER-TB formation and UPS. ATL3 also participates in the SARS-CoV-2-associated convoluted membrane formation and Golgi-independent trafficking of SARS-CoV-2 spike protein. These findings suggest that ER-TB serves a common function in mediating stress-induced UPS, which participates in various physiological and pathophysiological processes.

Genetic mutations in retinol dehydrogenase 5 (RDH5), a rate-limiting enzyme of the visual cycle, is associated with nyctalopia, age-related macular disease, and stationary congenital fundus albipunctatus (FA). A majority of these mutations impair RDH5 protein expression and intracellular localization. However, the regulatory mechanisms underlying RDH5 metabolism remain unclear. Here, we find that RDH5 undergoes degradation via the autophagy-lysosomal pathway, and its stability is regulated by interacting with HSP90. Deletion of HSP90α or HSP90β by CRISPR-Cas9 or inhibition of HSP90 activity by IPI-504 downregulates RDH5 protein level, but not its mRNA expression, and this downregulation is restored by autophagic inhibitors (3-MA, CQ, and Baf-A1) and siRNA of ATG5 or ATG7, but not by the proteasome inhibitor MG132. RDH5 can physically interact with SQSTM1/P62, and this interaction is enhanced in HSP90-deficient cells as well as in CQ-treated cells. Knocking down SQSTM1/P62 by siRNA induces RDH5 protein accumulation. Moreover, HSP90, RDH5, and Calnexin form a complex through intermolecular interactions. Deficiency of HSP90α or HSP90β dissociates RDH5 from Calnexin and increases RDH5 translocation from the endoplasmic reticulum to the cytosol. Taken together, we propose that dysfunction of HSP90 leads to RDH5 release from Calnexin in the endoplasmic reticulum into the cytosol, where it binds to the adaptor SQSTM1/P62 for degradation in the autolysosome. RDH5 is a novel client candidate of HSP90. The downregulation of RDH5 may be responsible for the nyctalopia side effect noted in cancer patients receiving HSP90 inhibitor treatment currently in the clinical trial.

The synthesis of membrane and secreted proteins is safeguarded by an endoplasmic reticulum-associated ribosome quality control (ER-RQC) that promotes the disposal of defective translation products by the proteasome or via a lysosome-dependent pathway involving the degradation of portions of the ER by macroautophagy (reticulophagy). The UFMylation of RPL26 on ER-stalled ribosomes is essential for activating the ER-RQC and reticulophagy. Here, we report that the viral deubiquitinase (vDUB) encoded in the N-terminal domain of the Epstein-Barr virus (EBV) large tegument protein BPLF1 hinders the UFMylation of RPL26 on ribosomes that stall at the ER, promotes the stabilization of ER-RQC substrates, and inhibits reticulophagy. The vDUB did not act as a de-UFMylase or interfere with the UFMylation of the ER membrane protein CYB5R3 by the UFL1 ligase. Instead, it copurified with ribosomes in sucrose gradients and abrogated a ZNF598- and LTN1-independent ubiquitination event required for RPL26 UFMylation. Physiological levels of BPLF1 impaired the UFMylation of RPL26 in productively EBV-infected cells, pointing to an important role of the enzyme in regulating the translation quality control that allows the efficient synthesis of viral proteins and the production of infectious virus.Abbreviation: BPLF1, BamH1 P fragment left open readingframe-1; CDK5RAP3, CDK5regulatory subunit associated protein 3; ChFP, mCherry fluorescent protein; DDRGK1, DDRGKdomain containing 1; EBV, Epstein-Barr virus; eGFP, enhancedGFP; ER-RQC, endoplasmicreticulum-associated ribosome quality control; LCL, EBV-carryinglymphoblastoid cell line; GFP, green fluorescent protein; RQC, ribosome quality control; SRP, signal recognition particle; UFM1, ubiquitin fold modifier 1; UFL1, UFM1 specific ligase 1.

Endoplasmic reticulum (ER) stress and autophagy (ER-phagy) occurring in nerve cells are crucial physiological processes closely associated with Alzheimer's disease (AD). Visualizing the two processes is paramount to advance our understanding of AD pathologies. Among the biomarkers identified, peroxynitrite (ONOO-) emerges as a key molecule in the initiation and aggravation of ER stress and ER-phagy, highlighting its significance in the underlying mechanisms of the two processes. In this work, we designed and synthesized an innovative ONOO--responsive AIEgen-based fluorescent probe (DHQM) with the ability to monitor ER stress and ER-phagy in AD model cells. DHQM demonstrated excellent aggregation-induced emission (AIE) properties, endowing it with outstanding ability for washing-free intracellular imaging. Meanwhile, it exhibited high sensitivity, remarkable selectivity to ONOO-, and exceptional ER-targeting ability. The probe was successfully applied for fluorescence imaging of ER ONOO- fluctuations to assess the ER stress status in aluminum-induced AD model cells. Our findings revealed that aluminum-induced ferroptosis, a regulated cell death process, was pivotal in the excessive ONOO- production, which in turn activated and exacerbated ER stress. Furthermore, the aluminum-stimulated ER-phagy was observed utilizing DHQM, which might be crucial in inhibiting ferroptosis and mitigating aberrant ER stress. Overall, this study not only offers valuable insights into the pathological mechanisms of AD at the ER level but also opens new potential therapeutic avenues targeting these pathways.

Uncontrollable cancer cell growth is characterized by the maintenance of cellular homeostasis through the continuous accumulation of misfolded proteins and damaged organelles. This review delineates the roles of two complementary and synergistic degradation systems, the ubiquitin-proteasome system (UPS) and the autophagy-lysosome system, in the degradation of misfolded proteins and damaged organelles for intracellular recycling. We emphasize the interconnected decision-making processes of degradation systems in maintaining cellular homeostasis, such as the biophysical state of substrates, receptor oligomerization potentials (e.g., p62), and compartmentalization capacities (e.g., membrane structures). Mitochondria, the cellular hubs for respiration and metabolism, are implicated in tumorigenesis. In the subsequent sections, we thoroughly examine the mechanisms of mitochondrial quality control (MQC) in preserving mitochondrial homeostasis in human cells. Notably, we explored the relationships between mitochondrial dynamics (fusion and fission) and various MQC processes-including the UPS, mitochondrial proteases, and mitophagy-in the context of mitochondrial repair and degradation pathways. Finally, we assessed the potential of targeting MQC (including UPS, mitochondrial molecular chaperones, mitochondrial proteases, mitochondrial dynamics, mitophagy and mitochondrial biogenesis) as cancer therapeutic strategies. Understanding the mechanisms underlying mitochondrial homeostasis may offer novel insights for future cancer therapies.

Photoimmunotherapy represents a novel and promising modality in anti-tumor immunotherapy, offering new hope in the realm of cancer treatment due to its distinctive mechanism and substantial therapeutic efficacy. This innovative approach synergistically integrates photon technology with immunological principles, utilizing photon energy to activate the body's immune response. Photon-driven pyroptosis, a pivotal element of photoimmunotherapy, has significantly revitalized the advancement of this discipline. To support this critical progress, this minireview offers an exhaustive examination of the organic dyes presently employed for photon-driven pyroptosis, alongside an analysis of the prevailing challenges and opportunities in dye molecule design. It is our aspiration that this minireview will contribute to the acceleration of developments in photon-driven pyroptosis dye and the broader field of photoimmunotherapy.

Organellar homeostasis and crosstalks within a cell have emerged as essential regulatory and determining factors for the survival and functions of cells. In response to various stimuli, cells can activate the organellar quality control systems (QCS) to maintain homeostasis. Numerous studies have demonstrated that dysfunction of QCS can lead to various aging-related diseases such as neurodegenerative, pulmonary, cardiometabolic diseases and cancers. However, the interplay between QCS and their potential role in these diseases are poorly understood. In this review, we present an overview of the current findings of QCS and their crosstalk, encompassing mitochondria, endoplasmic reticulum, Golgi apparatus, ribosomes, peroxisomes, lipid droplets, and lysosomes as well as the aberrant interplays among these organelles that contributes to the onset and progression of aging-related disorders. Furthermore, potential therapeutic approaches based on these quality control interactions are discussed. Our perspectives can enhance insights into the regulatory networks underlying QCS and the pathology of aging and aging-related diseases, which may pave the way for the development of novel therapeutic targets.

The endoplasmic reticulum (ER) is a pivotal organelle responsible for protein and lipid synthesis, calcium homeostasis, and protein quality control within eukaryotic cells. To maintain cellular health, damaged or excess portions of the ER must be selectively degraded via a process known as selective autophagy, or ER-phagy. This specificity is driven by a network of protein receptors and regulatory mechanisms. In this review, we explore the molecular mechanisms governing ER-phagy, with a focus on the FAM134 family of ER-resident ER-phagy receptors. We discuss the molecular pathways and Posttranslational modifications that regulate receptor activation and clustering, and how these modifications fine-tune ER-phagy in response to stress. This review provides a concise understanding of how ER-phagy contributes to cellular homeostasis and highlights the need for further studies in models where ER stress and autophagy are dysregulated.

Vanadium (V) exposure is known to induce renal toxicity, yet its specific effects on renal cell types and molecular mechanisms remain incompletely understood. We used single nucleus RNA sequencing (snRNA-seq) to characterize the impact of V on duck kidney cells at a cellular resolution. Following a 44-day exposure, immunofluorescence analysis revealed a significant increase in α-SMC expression in the renal interstitium, indicative of fibrotic response. SnRNA-seq identified 12 major cell types organized into 19 clusters within the kidney. Significant changes in cell composition were observed, notably an increase in proximal tubule cells (PT2 subtype), glomerular endothelial cells, principal cells, and alterations in immune cell proportions, while collecting duct intercalated cells (CD-IC) and thick ascending limb showed decreased percentages. Differential gene expression analysis highlighted pathways implicated in V toxicity across different cell types. Changes in drug metabolism-cytochrome P450, butanoate metabolism, and actin cytoskeleton regulation were exhibited by PT cells. Alterations in collecting duct secretion, oxidative phosphorylation, and bicarbonate reclamation pathways were shown in CD-IC cells. Furthermore, immune cells displayed changes in T cell receptor and chemokine signaling pathways, indicative of altered immune responses. Taken together, these findings contribute to a better shedding light on the pathogenic mechanisms of V induced renal injury.

ER-phagy is an evolutionarily conserved mechanism crucial for maintaining cellular homeostasis. However, significant gaps persist in our understanding of how ER-phagy and the ER network vary across cell subtypes, tissues, and organs. Furthermore, the pathophysiological relevance of ER-phagy remains poorly elucidated. Addressing these questions requires developing quantifiable methods to visualize ER-phagy and ER architecture in vivo. We generated two transgenic mouse lines expressing an ER lumen-targeting tandem RFP-GFP (ER-TRG) tag, either constitutively or conditionally. This approach enables precise spatiotemporal measurements of ER-phagy and ER structure at single-cell resolution in vivo. Systemic analysis across diverse organs, tissues, and primary cultures derived from these ER-phagy reporter mice unveiled significant variations in basal ER-phagy, both in vivo and ex vivo. Furthermore, our investigation uncovered substantial remodeling of ER-phagy and the ER network in different tissues under stressed conditions such as starvation, oncogenic transformation, and tissue injury. In summary, both reporter models represent valuable resources with broad applications in fundamental research and translational studies.

Here, we report that the RTN3L-SEC24C endoplasmic reticulum autophagy (ER-phagy) receptor complex, the CUL3KLHL12 E3 ligase that ubiquitinates RTN3L, and the FIP200 autophagy initiating protein, target mutant proinsulin (Akita) condensates for lysosomal delivery at ER tubule junctions. When delivery was blocked, Akita condensates accumulated in the ER. In exploring the role of tubulation in these events, we unexpectedly found that loss of the Parkinson's disease protein, PINK1, reduced peripheral tubule junctions and blocked ER-phagy. Overexpression of the PINK1 kinase substrate, DRP1, increased junctions, reduced Akita condensate accumulation, and restored lysosomal delivery in PINK1-depleted cells. DRP1 is a dual-functioning protein that promotes ER tubulation and severs mitochondria at ER-mitochondria contact sites. DRP1-dependent ER tubulating activity was sufficient for suppression. Supporting these findings, we observed PINK1 associating with ER tubules. Our findings show that PINK1 shapes the ER to target misfolded proinsulin for RTN3L-SEC24C-mediated macro-ER-phagy at defined ER sites called peripheral junctions. These observations may have important implications for understanding Parkinson's disease.

Sepsis represents a significant global health and hygiene challenge. Excessive activation of macrophages in sepsis can result in certain patients displaying characteristics akin to those observed in Macrophage Activation Syndrome (MAS). MAS represents a grave immune system disorder characterized by persistent and severe inflammation within the body. In the context of sepsis, MAS presents atypically, leading some researchers to refer to it as Macrophage Activation-Like Syndrome (MALS). However, there are currently no effective treatment measures for this situation. The purpose of this article is to explore potential treatment methods for sepsis-associated MALS.

The objective of this review is to synthesize the specific pathophysiological mechanisms and treatment strategies of MAS to investigate potential therapeutic approaches for sepsis-associated MALS.

We searched major databases (including PubMed, Web of Science, and Google Scholar etc.) for literature encompassing macrophage activation syndrome and sepsis up to Mar 2024 and combined with studies found in the reference lists of the included studies.

We have synthesized the underlying pathophysiological mechanism of MALS in sepsis, and then summarized the diagnostic criteria and the effects of various treatment modalities utilized in patients with MAS or MALS. In both scenarios, heterogeneous treatment responses resulting from identical treatment approaches were observed. The determination of whether the patient is genuinely experiencing MALS significantly impacts the ultimate outcomes of therapeutic efficacy. In order to tackle this concern, additional clinical trials and research endeavors are imperative.

The development of anticancer drugs that target different organelles has received extensive attention due to the characteristics of cancer recurrence, metastasis, and drug resistance. The endoplasmic reticulum (ER) is an important structure within the cell that is primarily responsible for protein synthesis, folding, modification, and transport and plays a crucial role in cell function and health. ER stress activation induces cancer cell apoptosis. New anticancer drugs with different anticancer mechanisms and selectivity can be designed because of redox activity, composition diversity, and metal complexes structure regulation. Over the past few decades, dozens of metal complexes have killed cancer cells through ER stress, showing powerful tumor-suppressive effects. This review summarizes the progress of research on anticancer metallic drugs that induce ER stress over the past few years, which is expected to bring more breakthroughs in the field of medicine and life science.

Flaviviruses strategically utilize the endoplasmic reticulum (ER) in their replication cycles. However, the role of ER autophagy (ER-phagy) in viral replication process remains poorly understood. Here, we reveal that prolonged Zika virus (ZIKV) infection results from the degradation of ER-phagy receptor FAM134B, facilitated by viral NS2A protein. Mechanistically, ER-localized NS2A undergoes K48-linked polyubiquitination at lysine (K) 56 by E3 ligase AMFR. Ubiquitinated NS2A binds to FAM134B and AMFR orchestrates the degradation of NS2A-FAM134B complexes. AMFR-catalyzed NS2A ubiquitination not only targets FAM134B degradation but also hinders the FAM134B-AMFR axis. Notably, a recombinant ZIKV mutant (ZIKV-NS2AK56R), lacking ubiquitination and ER-phagy inhibition, exhibits attenuation in ZIKV-induced microcephalic phenotypes in human brain organoids and replicates less efficiently, resulting in weakened pathogenesis in mouse models. In this work, our mechanistic insights propose that flaviviruses manipulate ER-phagy to modulate ER turnover, driving viral infection. Furthermore, AMFR-mediated flavivirus NS2A ubiquitination emerges as a potential determinant of viral pathogenecity.

To investigate the protective mechanisms of hydrogen sulfide (H2S) in sepsis-induced acute kidney injury (SAKI), we conducted an in vivo study using a SAKI mouse model induced by intraperitoneal lipopolysaccharide (LPS) injection. Following 6 h of LPS injection, levels of tumor necrosis factor-alpha (TNF-α) and blood urea nitrogen (Bun) were significantly elevated in mouse plasma. In the kidneys of SAKI mice, expression of H2S-generating enzymes cysteinyl-tRNA synthetase (CARS), cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) was markedly downregulated, while glucose-regulated protein 78 (GRP78), activating transcription factor 6 (ATF6), phosphorylated protein kinase R-like endoplasmic reticulum kinase/protein kinase R-like endoplasmic reticulum kinase (p-PERK/PERK), and B-cell lymphoma-2 recombinant protein X/B-cell lymphoma-2 (Bax/Bcl2) expression was significantly upregulated. H2S improved renal function and attenuated renal histopathological changes in SAKI mice, thereby alleviating LPS-induced endoplasmic reticulum stress (ERS). Additionally, it inhibited the expression of p-PERK/PERK and Bax/Bcl2. After inhibiting CSE activity with dl-propargylglycine (PPG i. p.), the renal tissue pathology in LPS-induced AKI mice was further exacerbated, leading to enhanced activation of the PERK/Bax-Bcl2 pathway. Our findings suggest that endogenous H2S influences the pathogenesis of SAKI, while exogenous H2S protects against LPS-induced AKI by inhibiting the PERK/Bax-Bcl2 pathway involved in ERS.

ER-phagy, a selective form of autophagic degradation of endoplasmic reticulum (ER) fragments, plays an essential role in governing ER homeostasis. Dysregulation of ER-phagy is associated with the unfolded protein response (UPR), which is a major clue for evoking inflammatory diseases. However, the molecular mechanism underpinning the connection between ER-phagy and disease remains poorly defined. Here, we identified ubiquitin-associated domain-containing protein 2 (UBAC2) as a receptor for ER-phagy, while at the same time being a negative regulator of inflammatory responses. UBAC2 harbors a canonical LC3-interacting region (LIR) in its cytoplasmic domain, which binds to autophagosomal GABARAP. Upon ER-stress or autophagy activation, microtubule affinity-regulating kinase 2 (MARK2) phosphorylates UBAC2 at serine (S) 223, promoting its dimerization. Dimerized UBAC2 interacts more strongly with GABARAP, thus facilitating selective degradation of the ER. Moreover, by affecting ER-phagy, UBAC2 restrains inflammatory responses and acute ulcerative colitis (UC) in mice. Our findings indicate that ER-phagy directed by a MARK2-UBAC2 axis may provide targets for the treatment of inflammatory disease.

Intrinsically disordered regions (IDRs) play a pivotal role in organellar remodeling. They transduce signals across membranes, scaffold signaling complexes, and mediate vesicular traffic. Their functions are regulated by constraining conformational ensembles through specific intra- and intermolecular interactions, physical tethering, and posttranslational modifications. The endoplasmic reticulum (ER)-phagy receptor FAM134B/RETREG1, known for its reticulon homology domain (RHD), includes a substantial C-terminal IDR housing the LC3 interacting motif. Beyond engaging the autophagic machinery, the function of the FAM134B-IDR is unclear. Here, we investigate the characteristics of the FAM134B-IDR by extensive modeling and molecular dynamics simulations. We present detailed structural models for the IDR, mapping its conformational landscape in solution and membrane-anchored configurations. Our analysis reveals that depending on the membrane anchor, the IDRs collapse onto the membrane and induce positive membrane curvature to varying degrees. The charge patterns underlying this Janus-like behavior are conserved across other ER-phagy receptors. We found that IDRs alone are sufficient to sense curvature. When combined with RHDs, they intensify membrane remodeling and drive efficient protein clustering, leading to faster budding, thereby amplifying RHD remodeling functions. Our simulations provide a perspective on IDRs of FAM134B, their Janus-like membrane interactions, and the resulting modulatory functions during large-scale ER remodeling.

Autophagy is a conservative catabolic process that typically serves a cell-protective function. Under stress conditions, when the cellular environment becomes unstable, autophagy is activated as an adaptive response for self-protection. Autophagy delivers damaged cellular components to lysosomes for degradation and recycling, thereby providing essential nutrients for cell survival. However, this function of promoting cell survival under stress conditions often leads to malignant progression and chemotherapy resistance in cancer. Consequently, autophagy is considered a potential target for cancer therapy. Herein, we aim to review how natural products act as key modulators of autophagy by regulating cellular stress conditions. We revisit various stressors, including starvation, hypoxia, endoplasmic reticulum stress, and oxidative stress, and their regulatory relationship with autophagy, focusing on recent advances in ovarian cancer research. Additionally, we explore how polyphenolic compounds, flavonoids, alkaloids, terpenoids, and other natural products modulate autophagy mediated by stress responses, affecting the malignant biological behavior of cancer. Furthermore, we discuss their roles in ovarian cancer therapy. This review emphasizes the importance of natural products as valuable resources in cancer therapeutics, highlighting the need for further exploration of their potential in regulating autophagy. Moreover, it provides novel insights and potential therapeutic strategies in ovarian cancer by utilizing natural products to modulate autophagy.

The hepatic P450 hemoproteins CYPs 4A are typical N-terminally anchored Type I endoplasmic reticulum (ER)-proteins, that are inducible by hypolipidemic drugs and other "peroxisome proliferators". They are engaged in the ω-/ω-1-oxidation of various fatty acids including arachidonic acid, prostaglandins and leukotrienes and in the biotransformation of some therapeutic drugs. Herein we report that of the mammalian liver CYPs 4A, human CYP4A11 and mouse Cyp4a12a are preferential targets of the ER-lysosome-associated degradation (ERLAD). Consequently, these proteins are stabilized both as 1%Triton X100-soluble and -insoluble species in mouse hepatocytes and HepG2-cells deficient in the autophagic initiation ATG5-gene. Although these proteins exhibit surface LC3-interacting regions (LIRs) that would target them directly to the autophagosome, they nevertheless interact intimately with the autophagic receptor SQSTM1/p62. Through structural deletion analyses and site-directed mutagenesis, we have identified the Cyp4A-interacting p62 subdomain to lie between residues 170 and 233, which include its Traf6-binding and LIM-binding subdomains. Mice carrying a liver-specific genetic deletion of p62 residues 69-251 (p62Mut) that includes the CYP4A-interacting subdomain also exhibit Cyp4a-protein stabilization both as Triton X100-soluble and -insoluble species. Consistently, p62Mut mouse liver microsomes exhibit enhanced ω- and ω-1-hydroxylation of arachidonic acid to its physiologically active metabolites 19- and 20-HETEs relative to the corresponding wild-type mouse liver microsomes. Collectively, our findings suggest that any disruption of CYP4A ERLAD results in functionally active P450 protein and consequent production of proinflammatory metabolites on one hand, and insoluble aggregates on the other, which may contribute to pathological aggregates i.e. Mallory-Denk bodies/inclusions, hallmarks of many liver diseases.

Lysosomal compartments control the clearance of cell-own material (autophagy) or of material that cells endocytose from the external environment (heterophagy) to warrant supply of nutrients, to eliminate macromolecules or parts of organelles present in excess, aged, or containing toxic material. Inherited or sporadic mutations in lysosomal proteins and enzymes may hamper their folding in the endoplasmic reticulum (ER) and their lysosomal transport via the Golgi compartment, resulting in lysosomal dysfunction and storage disorders. Defective cargo delivery to lysosomal compartments is harmful to cells and organs since it causes accumulation of toxic compounds and defective organellar homeostasis. Assessment of resident proteins and cargo fluxes to the lysosomal compartments is crucial for the mechanistic dissection of intracellular transport and catabolic events. It might be combined with high-throughput screenings to identify cellular, chemical, or pharmacological modulators of these events that may find therapeutic use for autophagy-related and lysosomal storage disorders. Here, discuss qualitative, quantitative and chronologic monitoring of autophagic, heterophagic and lysosomal protein trafficking in fixed and live cells, which relies on fluorescent single and tandem reporters used in combination with biochemical, flow cytometry, light and electron microscopy approaches implemented by artificial intelligence-based technology.

Plasma lipids are mainly carried in apolipoprotein B (apoB) containing lipoproteins. High levels of these lipoproteins are associated with several metabolic diseases and lowering their plasma levels is associated with reduced incidence of atherosclerotic cardiovascular disease. MicroRNAs (miRs) are small non-coding RNAs that reduce the protein expression of their target mRNAs and are potential therapeutic agents. Here, we identified a novel miR-615-3p that interacts with human 3'-UTR of apoB mRNA, induces post-transcriptional mRNA degradation, and reduces cellular and secreted apoB100 in human hepatoma Huh-7 cells. Reducing cellular miR-615-3p levels by CRISPR-sgRNA increased cellular and secreted apoB100 indicating endogenous miR regulates apoB expression. Overexpression of miR-615-3p along with or without palmitic acid treatment decreased cellular and media apoB and increased cellular triglyceride levels without inducing endoplasmic reticulum stress. These studies have identified miR-615-3p as a negative regulator of apoB expression in human liver-derived cells. It is likely that there are more miRs that regulate apoB-containing lipoprotein assembly and secretion. Discovery of additional miRs may uncover novel mechanisms that control lipoprotein assembly and secretion.

Cells routinely utilize the unfolded protein response (UPR) to alleviate endoplasmic reticulum (ER)-stress or trigger about apoptotic death under extreme ER-stress conditions. Tumor cells are subjected to persistent ER-stress due to their crowded microenvironment, but can maintain hyperactive proliferation under most stressful conditions. Therefore, understanding strategies employed by cancer cells to escape from UPR-related apoptosis has important medical implications. SEC24 homolog C (SEC24C) was found decreased in later colorectal cancer (CRC) stages, but its exact role in response to ER-stress and activation of UPR in hepatocellular carcinoma (HCC) remains to be elucidated. Here, we have identified the downregulation of SEC24C in human HCC sample and its suppressive role in regulating HCC proliferation and chemoresistance. Mechanistically, SEC24C was found to interact with eukaryotic translation initiation factor 2 alpha kinase 3 (EIF2AK3 or PERK) and activate the downstream UPR-related apoptosis. During this process, SEC24C was observed to be anchored in nucleus under normal condition but responded immediately to ER-stress and could subsequently translocate to the ER. Furthermore, overexpression of SEC24C significantly augmented the efficacy of bortezomib in HCC treatment. In conclusion, our findings revealed a novel role of SEC24C in regulating HCC proliferation and chemoresistance by modulating UPR activation.

Cisplatin is a common anticancer drug, but its frequent nephrotoxicity limits its clinical use. Small GTP-binding protein GDP dissociation stimulator (smgGDS), a small GTPase chaperone protein, was considerably downregulated during cisplatin-induced acute kidney injury (CDDP-AKI), especially in renal tubular epithelial cells. SmgGDS-knockdown mice was established and found that smgGDS knockdown promoted CDDP-AKI, as demonstrated by an increase in serum creatine, blood urea nitrogen levels and the appearance of tubular patterns. RNA sequencing suggested that protein kinase RNA-like ER kinase (PERK), which bridges mitochondria-associated ER membranes, was involved in smgGDS knockdown following CDDP-AKI, and then identified that smgGDS knockdown increased phosphorylated-PERK in vivo and in vitro. Furthermore, we confirmed that smgGDS deficiency aggravated apoptosis and ER stress in vivo and in vitro. And the ER stress inhibitor 4-Phenylbutyric acid and the inhibition of PERK phosphorylation mitigated smgGDS deficiency-induced ER stress related apoptosis following cisplatin treatment, while the eIF2α phosphorylation inhibitor could not reverse the smgGDS deficiency accelerated cell death. Furthermore, the over-expression of smgGDS could reverse the ER stress and apoptosis caused by CDDP. Overall, smgGDS regulated PERK-dependent ER stress and apoptosis, thereby influencing renal damage. This study identified a target for diagnosing and treating cisplatin-induced acute kidney injury.

Reticulophagy is mediated by autophagy receptors that function in one of the two domains of the ER, tubules or flat sheets. Three different conserved mammalian receptors mediate autophagy in ER tubules: RTN3L, ATL3 and CALCOCO1. Previous studies have shown that RTN3L maintains proteostasis by targeting mutant aggregation-prone proteins for autophagy at distinct foci in ER tubules that we named ERPHS (ER-reticulophagy sites). The role for ATL3 and CALCOCO1 in proteostasis has not been addressed. Here we analyzed three different misfolded disease-causing RTN3L substrates and show that ATL3 and CALCOCO1 target the same cargoes for autophagy. Colocalization and knock down studies revealed that RTN3L and ATL3 are both required for the formation of RTN3L-containing ERPHS, while CALCOCO1 is not. We propose that RTN3L, ATL3 and CALCOCO1 work in parallel to maintain proteostasis within the ER network by targeting cargoes at different sites in the tubules.Abbreviation ATL3: atlastin GTPase 3; Baf: bafilomycin A1; CALCOCO1: calcium binding and coiled-coil domain 1; Epr1: ER-phagy receptor 1; ER: endoplasmic reticulum; ERAD: ER-associated protein degradation; ERPHS: ER-reticulophagy sites; LAMP1: lysosomal associated membrane protein 1; PGRMC1: progesterone receptor membrane component 1; POMC: proopiomelanocortin; Pro-AVP: pro-arginine vasopressin; RETREG1: reticulophagy regulator 1; reticulophagy: endoplasmic reticulum selective autophagy; RTN3L: reticulon 3 long isoform; VAPA: VAMP associated protein A.

Protein biogenesis within the endoplasmic reticulum (ER) is crucial for organismal function. Errors during protein folding necessitate the removal of faulty products. ER-associated protein degradation and ER-phagy target misfolded proteins for proteasomal and lysosomal degradation. The mechanisms initiating ER-phagy in response to ER proteostasis defects are not well understood. By studying mouse primary cells and patient samples as a model of ER storage disorders (ERSDs), we show that accumulation of faulty products within the ER triggers a response involving SESTRIN2, a nutrient sensor controlling mTORC1 signaling. SESTRIN2 induction by XBP1 inhibits mTORC1's phosphorylation of TFEB/TFE3, allowing these transcription factors to enter the nucleus and upregulate the ER-phagy receptor FAM134B along with lysosomal genes. This response promotes ER-phagy of misfolded proteins via FAM134B-Calnexin complex. Pharmacological induction of FAM134B improves clearance of misfolded proteins in ERSDs. Our study identifies the interplay between nutrient signaling and ER quality control, suggesting therapeutic strategies for ERSDs.

The endoplasmic reticulum (ER) comprises an array of structurally distinct subdomains, each with characteristic functions. While altered ER-associated processes are linked to age-onset pathogenesis, whether shifts in ER morphology underlie these functional changes is unclear. We report that ER remodeling is a conserved feature of the aging process in models ranging from yeast to C. elegans and mammals. Focusing on C. elegans as an exemplar of metazoan aging, we find that as animals age, ER mass declines in virtually all tissues and ER morphology shifts from rough sheets to tubular ER. The accompanying large-scale shifts in proteomic composition correspond to the ER turning from protein synthesis to lipid metabolism. To drive this substantial remodeling, ER-phagy is activated early in adulthood, promoting turnover of rough ER in response to rises in luminal protein-folding burden and reduced global protein synthesis. Surprisingly, ER remodeling is a pro-active and protective response during aging, as ER-phagy impairment limits lifespan in yeast and diverse lifespan-extending paradigms promote profound remodeling of ER morphology even in young animals. Altogether our results reveal ER-phagy and ER morphological dynamics as pronounced, underappreciated mechanisms of both normal aging and enhanced longevity.

The endoplasmic reticulum (ER) serves as a hub for various cellular processes, and maintaining ER homeostasis is essential for cell function. Reticulophagy is a selective process that removes impaired ER subdomains through autophagy-mediatedlysosomal degradation. While the involvement of ubiquitination in autophagy regulation is well-established, its role in reticulophagy remains unclear. In this study, we screened deubiquitinating enzymes (DUBs) involved in reticulophagy and identified USP20 (ubiquitin specific peptidase 20) as a key regulator of reticulophagy under starvation conditions. USP20 specifically cleaves K48- and K63-linked ubiquitin chains on the reticulophagy receptor RETREG1/FAM134B (reticulophagy regulator 1), thereby stabilizing the substrate and promoting reticulophagy. Remarkably, despite lacking a transmembrane domain, USP20 is recruited to the ER through its interaction with VAPs (VAMP associated proteins). VAPs facilitate the recruitment of early autophagy proteins, including WIPI2 (WD repeat domain, phosphoinositide interacting 2), to specific ER subdomains, where USP20 and RETREG1 are enriched. The recruitment of WIPI2 and other proteins in this process plays a crucial role in facilitating RETREG1-mediated reticulophagy in response to nutrient deprivation. These findings highlight the critical role of USP20 in maintaining ER homeostasis by deubiquitinating and stabilizing RETREG1 at distinct ER subdomains, where USP20 further recruits VAPs and promotes efficient reticulophagy.Abbreviations: ACTB actin beta; ADRB2 adrenoceptor beta 2; AMFR/gp78 autocrine motility factor receptor; ATG autophagy related; ATL3 atlastin GTPase 3; BafA1 bafilomycin A1; BECN1 beclin 1; CALCOCO1 calcium binding and coiled-coil domain 1; CCPG1 cell cycle progression 1; DAPI 4',6-diamidino-2-phenylindole; DTT dithiothreitol; DUB deubiquitinating enzyme; EBSS Earle's Balanced Salt Solution; FFAT two phenylalanines (FF) in an acidic tract; GABARAP GABA type A receptor-associated protein; GFP green fluorescent protein; HMGCR 3-hydroxy-3-methylglutaryl-CoA reductase; IL1B interleukin 1 beta; LIR LC3-interacting region; MAP1LC3/LC3 microtubule associated protein 1 light chain 3; PIK3C3/Vps34 phosphatidylinositol 3-kinase catalytic subunit type 3; RB1CC1/FIP200 RB1 inducible coiled-coil 1; RETREG1/FAM134B reticulophagy regulator 1; RFP red fluorescent protein; RHD reticulon homology domain; RIPK1 receptor interacting serine/threonine kinase 1; RTN3L reticulon 3 long isoform; SEC61B SEC61 translocon subunit beta; SEC62 SEC62 homolog, preprotein translocation factor; SIM super-resolution structured illumination microscopy; SNAI2 snail family transcriptional repressor 2; SQSTM1/p62 sequestosome 1; STING1/MITA stimulator of interferon response cGAMP interactor 1; STX17 syntaxin 17; TEX264 testis expressed 264, ER-phagy receptor; TNF tumor necrosis factor; UB ubiquitin; ULK1 unc-51 like autophagy activating kinase 1; USP20 ubiquitin specific peptidase 20; USP33 ubiquitin specific peptidase 33; VAMP8 vesicle associated membrane protein 8; VAPs VAMP associated proteins; VMP1 vacuole membrane protein 1; WIPI2 WD repeat domain, phosphoinositide interacting 2; ZFYVE1/DFCP1 zinc finger FYVE-type containing 1.

Autophagy, vital for removing cellular waste, is triggered differently by small molecules and nanoparticles. Small molecules, like rapamycin, non-selectively activate autophagy by inhibiting the mTOR pathway, which is essential for cell regulation. This can clear damaged components but may cause cytotoxicity with prolonged use. Nanoparticles, however, induce autophagy, often causing oxidative stress, through broader cellular interactions and can lead to a targeted form known as "xenophagy." Their impact varies with their properties but can be harnessed therapeutically. In this review, the autophagy induced by nanoparticles is explored and small molecules across four dimensions: the mechanisms behind autophagy induction, the outcomes of such induction, the toxicological effects on cellular autophagy, and the therapeutic potential of employing autophagy triggered by nanoparticles or small molecules. Although small molecules and nanoparticles each induce autophagy through different pathways and lead to diverse effects, both represent invaluable tools in cell biology, nanomedicine, and drug discovery, offering unique insights and therapeutic opportunities.

It has been estimated that up to one-third of the proteins encoded by the human genome enter the endoplasmic reticulum (ER) as extended polypeptide chains where they undergo covalent modifications, fold into their native structures, and assemble into oligomeric protein complexes. The fidelity of these processes is critical to support organellar, cellular, and organismal health, and is perhaps best underscored by the growing number of disease-causing mutations that reduce the fidelity of protein biogenesis in the ER. To meet demands encountered by the diverse protein clientele that mature in the ER, this organelle is populated with a cadre of molecular chaperones that prevent protein aggregation, facilitate protein disulfide isomerization, and lower the activation energy barrier of cis-trans prolyl isomerization. Components of the lectin (glycan-binding) chaperone system also reside within the ER and play numerous roles during protein biogenesis. In addition, the ER houses multiple homologs of select chaperones that can recognize and act upon diverse peptide signatures. Moreover, redundancy helps ensure that folding-compromised substrates are unable to overwhelm essential ER-resident chaperones and enzymes. In contrast, the ER in higher eukaryotic cells possesses a single member of the Hsp70, Hsp90, and Hsp110 chaperone families, even though several homologs of these molecules reside in the cytoplasm. In this review, we discuss specific functions of the many factors that maintain ER quality control, highlight some of their interactions, and describe the vulnerabilities that arise from the absence of multiple members of some chaperone families.

Protein homeostasis (proteostasis) deficiency is an important contributing factor to neurological and metabolic diseases. However, how the proteostasis network orchestrates the folding and assembly of multi-subunit membrane proteins is poorly understood. Previous proteomics studies identified Hsp47 (Gene: SERPINH1), a heat shock protein in the endoplasmic reticulum lumen, as the most enriched interacting chaperone for gamma-aminobutyric acid type A (GABAA) receptors. Here, we show that Hsp47 enhances the functional surface expression of GABAA receptors in rat neurons and human HEK293T cells. Furthermore, molecular mechanism study demonstrates that Hsp47 acts after BiP (Gene: HSPA5) and preferentially binds the folded conformation of GABAA receptors without inducing the unfolded protein response in HEK293T cells. Therefore, Hsp47 promotes the subunit-subunit interaction, the receptor assembly process, and the anterograde trafficking of GABAA receptors. Overexpressing Hsp47 is sufficient to correct the surface expression and function of epilepsy-associated GABAA receptor variants in HEK293T cells. Hsp47 also promotes the surface trafficking of other Cys-loop receptors, including nicotinic acetylcholine receptors and serotonin type 3 receptors in HEK293T cells. Therefore, in addition to its known function as a collagen chaperone, this work establishes that Hsp47 plays a critical and general role in the maturation of multi-subunit Cys-loop neuroreceptors.