Protein Quality Control in the Endoplasmic Reticulum and Cancer

GRP78 inhibitor HA15 increases the effect of Bortezomib on eradicating multiple myeloma cells through triggering endoplasmic reticulum stress

Bortezomib (BTZ), a selective proteasome inhibitor, exhibits a significant efficacy in the therapy of multiple myeloma (MM) partly through triggering endoplasmic reticulum (ER) stress-dependent apoptosis. However, sensitivity to BTZ varies greatly among patients. ER stress functions as a double-edged sword in regulating cell survival depending on cell context and ER stress extent. The major aim of this study was to investigate whether GRP78 inhibitor, HA15, increased the therapeutic effect of BTZ on MM to through further increasing ER stress and shifting the balance towards cell apoptosis. The biological role of BTZ and HA15 was assessed using Cell counting kit- (CCK-) 8, colony formation, and Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labelling (TUNEL) assay. We found that BTZ combined with HA15 remarkably decreased MM cell viability more effective than BTZ monotherapy, though low dose of HA15 did not exhibit a significant cytotoxicity to MM cells. BTZ combined with HA15 also repressed colony formation ability of MM cell and accelerated MM cell apoptosis compared with BTZ monotherapy. Mechanistically, HA15 synergized with BTZ to trigger ER stress, as evidence by significantly increased expression of ER stress markers (GRP78, ATF4, CHOP, and XBP1). Importantly, unfolded protein response (UPR) inhibitor significantly damaged the effect of BTZ combined with HA15 on accelerating MM cell death. In vivo, combination treatment with BTZ and HA15 inhibited tumor growth more effective than BTZ alone, whereas these effects were blocked by UPR inhibitor. Taken together, these results demonstrate that ER stress is a critical pathway in regulating MM cell survival, and that combination treatment with BTZ and HA15 may be an effective strategy to treat MM patients that fail to respond to BTZ monotherapy.

Research progress on endoplasmic reticulum homeostasis in kidney diseases

The endoplasmic reticulum (ER) plays important roles in biosynthetic and metabolic processes, including protein and lipid synthesis, Ca²⁺ homeostasis regulation, and subcellular organelle crosstalk. Dysregulation of ER homeostasis can cause toxic protein accumulation, lipid accumulation, and Ca²⁺ homeostasis disturbance, leading to cell injury and even death. Accumulating evidence indicates that the dysregulation of ER homeostasis promotes the onset and progression of kidney diseases. However, maintaining ER homeostasis through unfolded protein response, ER-associated protein degradation, autophagy or ER-phagy, and crosstalk with other organelles may be potential therapeutic strategies for kidney disorders. In this review, we summarize the recent research progress on the relationship and molecular mechanisms of ER dysfunction in kidney pathologies. In addition, the endogenous protective strategies for ER homeostasis and their potential application for kidney diseases have been discussed.

Membrane trafficking in breast cancer progression: protein kinase D comes into play

Protein kinase D (PKD) is a serine/threonine kinase family that controls important cellular functions, most notably playing a key role in the secretory pathway at the trans-Golgi network. Aberrant expression of PKD isoforms has been found mainly in breast cancer, where it promotes various cellular processes such as growth, invasion, survival and stem cell maintenance. In this review, we discuss the isoform-specific functions of PKD in breast cancer progression, with a particular focus on how the PKD controlled cellular processes might be linked to deregulated membrane trafficking and secretion. We further highlight the challenges of a therapeutic approach targeting PKD to prevent breast cancer progression.

O-GlcNAcylation enhances Reticulon 2 protein stability and its promotive effects on gastric cancer progression

Our previous study indicated that Reticulon 2 (RTN2) was upregulated and facilitated the progression of gastric cancer. Protein O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) is a general feature during tumorigenesis, and regulates protein activity and stability through post-translational modification on serine/threonine. However, the relationship between RTN2 and O-GlcNAcylation have never been determined. In this study, we explored the influence of O-GlcNAcylation on RTN2 expression and its promotive role in gastric cancer. We found that RTN2 interacted with O-GlcNAc transferase (OGT) and was modified by O-GlcNAc. O-GlcNAcylation enhanced RTN2 protein stability via attenuating its lysosomal degradation in gastric cancer cells. Furthermore, our results demonstrated that RTN2-induced activation of ERK signalling was dependent on O-GlcNAcylation. Consistently, the stimulative effects of RTN2 on cellular proliferation and migration were abrogated by OGT inhibition. Tissue microarray with immumohistochemical staining also confirmed that the expression of RTN2 was positively correlated with the level of total O-GlcNAcylation as well as the phosphorylation level of ERK. Besides, combined RTN2 and O-GlcNAc staining intensity could improve predictive accuracy for gastric cancer patients' survival compared with each alone. Altogether, these findings suggest that O-GlcNAcylation on RTN2 was pivotal for its oncogenic functions in gastric cancer. Targeting RTN2 O-GlcNAcylation might provide new ideas for gastric cancer therapies.

Novel roles of karyopherin subunit alpha 2 in hepatocellular carcinoma

Hepatocellular carcinoma is the most common type of liver cancer and associated with a high fatality rate. This disease poses a major threat to human health worldwide. A considerable number of genetic and epigenetic factors are involved in the development of hepatocellular carcinoma. However, the molecular mechanism underlying the progression of hepatocellular carcinoma remains unclear. Karyopherin subunit alpha 2 (KPNA2), also termed importin α1, is a member of the nuclear transporter family. In recent years, KPNA2 has been gradually linked to the nuclear transport pathway for a variety of tumor-associated proteins. Furthermore, it promotes tumor development by participating in various pathophysiological processes such as cell proliferation, apoptosis, immune response, and viral infection. In hepatocellular carcinoma, it has been found that KPNA2 expression is significantly higher in liver cancer tissues versus paracancerous tissues. Moreover, it has been identified as a marker of poor prognosis and early recurrence in patients with hepatocellular carcinoma. Nevertheless, the role of KPNA2 in the development of hepatocellular carcinoma remains to be determined. This review summarizes the current knowledge on the pathogenesis and role of KPNA2 in hepatocellular carcinoma, and provides new directions and strategies for the diagnosis, treatment, and prediction of prognosis of this disease.

A meta-analysis and bioinformatics analysis of P4HB expression levels in the prognosis of cancer patients

BACKGROUND

P4HB (prolyl 4-hydroxylase, beta polypeptide) is a human chromosomal gene that encodes an endoplasmic reticulum (ER) molecular chaperone protein with oxidoreductase, chaperone and isomerase activities. Recent studies indicated that P4HB may have clinical significance, with elevated P4HB expression reported in cancer patients, but its impact on tumor prognosis is not yet clear. To our knowledge, this is the first meta-analysis to show an association between P4HB expression and the prognosis of various cancers.

METHODS

We conducted a systematic literature search in the PubMed, PubMed Central, Web of Science, Embase, CNKI, Wanfang and Weipu databases, followed by a quantitative meta-analysis using Stata SE14.0 and R statistics software 4.2.1. The hazard ratio (HR) and relative risk (RR) were analyzed to evaluate the relationships of P4HB expression levels with overall survival (OS), disease-free survival (DFS), and clinicopathological parameters of cancer patients. Subsequently, P4HB expression in various cancer types was validated using the Gene Expression Profiling Interactive Analysis (GEPIA) online database.

RESULTS

Ten articles containing the data of 4121 cancer patients were included in the analysis, and a significant correlation of high P4HB expression with apparently shorter OS was found (HR, 1.90; 95% CI, 1.50-2.40; P < 0.01), while there was no significant correlation with gender (RR, 1.06; 95% CI, 0.91-1.22; P = 0.084), or age. Additionally, GEPIA online analysis revealed significant upregulation of P4HB in 13 types of cancer. Among them, P4HB overexpression was associated with shorter OS in 9 and worse DFS in 11 cancer types.

CONCLUSIONS

Upregulation of P4HB is correlated with worse prognosis in various cancers, which could provide new ideas for the development of P4HB-related diagnostic biomarkers and new therapeutic targets.

Dexamethasone-stimulated glucocorticoid receptor signaling positively regulates the endoplasmic reticulum-associated degradation (ERAD) mechanism in hepatocellular carcinoma cells

Hepatocellular carcinoma is one of the most common types of primary liver cancer in adults and also it is the third leading cause of cancer-related deaths worldwide. Although there are various treatment options such as surgery, radiation, targeted drug therapy, immunotherapy and chemotherapy, most hepatocellular carcinomas are highly resistant to systemic treatments. Today, the molecular pathogenesis of hepatocellular carcinoma remains largely obscure. Therefore, there is a need for detailed research for the characterization of molecular signaling networks related to the development of hepatocellular carcinoma. Recent studies have attention to the hormonal regulation of hepatocellular carcinoma cells mediated by systemic hormones such as glucocorticoids. However, glucocorticoid-mediated regulation of endoplasmic reticulum-associated degradation (ERAD) and unfolded protein response (UPR), which are known to be important survival mechanisms for cancer cells remains unknown in hepatocellular carcinoma. In the present study, we showed that dexamethasone-induced glucocorticoid receptor signaling mediated advanced regulation of ERAD and UPR signaling in hepatocellular carcinoma cells. Glucocorticoid signaling positively regulates mRNA and protein levels of ERAD components and also protein kinase RNA-like ER Kinase (PERK) and inositol-requiring enzyme 1⍺ (IRE1⍺) branches of UPR signaling are accompanied the glucocorticoid signaling. In addition, putative glucocorticoid response elements (GREs) were determined in the promoter regions of ERAD members in in-silico analyses. Additionally, silencing of ERAD components significantly reduced the tumorigenic features of hepatocellular carcinoma cells, including cell proliferation, metastasis, invasion and 3D tumor formation. Collectively, these results reveal a novel pattern of regulation of ERAD components by glucocorticoid-mediated in human hepatocellular carcinoma cells.

Design, synthesis and biological evaluation of liposome entrapped iridium(III) complexes toward SGC-7901 cells

In this study, two new iridium(III) polypyridyl complexes [Ir(bzq)₂(DIPH)](PF₆) (bzq = deprotonated benzo[h]quinoline, DIPH = 4-(2,5-dibromo-4-(1H-imidazo[4,5-f][1,10]phenanthrolim-2-yl)-4-hydroxybutan-2-one) (Ir1) and [Ir(piq)₂(DIPH)](PF₆) (piq = deprotonated 1-phenylisoquinoline) (Ir2) were synthesized and characterized by elemental analysis, HRMS, ¹H and ¹³C NMR. The cytotoxic activity of Ir1, Ir2, Ir1lipo and Ir2lipo against cancer cells SGC-7901, HepG2, A549, HeLa, B16 and normal NIH3T3 cells in vitro was evaluated using 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) method. Ir1 and Ir2 showed no cytotoxic activity, but their liposome-entrapped Ir1 (Ir1lipo) and Ir2 (Ir2lipo) showed significant cellular activity, especially sensitive to SGC-7901 with IC₅₀ values of 4.7 ± 0.2 and 12.4 ± 0.5 μM, respectively. The cellular uptake, endoplasmic reticulum (ER) localization, autophagy, tubulin polymerization, glutathione (GSH), malondialdehyde (MDA) and release of cytochrome c were investigated to explore the mechanisms of apoptosis. The calreticulin (CRT), heat shock protein 70 (HSP70), high mobility group box 1 (HMGB1) were also explored. Western blotting showed that Ir1lipo and Ir2lipo inhibited PI3K (phosphoinositide-3 kinase), AKT (protein kinase B), p-AKT and activated Bcl-2 (B-cell lymphoma-2) protein and apoptosis-regulated factor caspase 3 (cysteinyl aspartate specific proteinase-3) and cleaving PARP (poly ADP-ribose polymerase). The results demonstrated that Ir1lipo and Ir2lipo induce cell apoptosis through targeting the endoplasmic reticulum (ER), cause oxidative stress damage, inhibiting PI3K/AKT signaling pathway, immunogenic cell death (ICD) and inhibit the cell growth at G2/M phase.

TOLLIP-mediated autophagic degradation pathway links the VCP-TMEM63A-DERL1 signaling axis to triple-negative breast cancer progression

Triple-negative breast cancer (TNBC) is the most challenging breast cancer subtype to treat due to the lack of effective targeted therapies. Transmembrane (TMEM) proteins represent attractive drug targets for cancer therapy, but biological functions of most members of the TMEM family remain unknown. Here, we report for the first time that TMEM63A (transmembrane protein 63A), a poorly characterized TMEM protein with unknown functions in human cancer, functions as a novel oncogene to promote TNBC cell proliferation, migration, and invasion in vitro and xenograft tumor growth and lung metastasis in vivo. Mechanistic investigations revealed that TMEM63A localizes in endoplasmic reticulum (ER) and lysosome membranes, and interacts with VCP (valosin-containing protein) and its cofactor DERL1 (derlin 1). Furthermore, TMEM63A undergoes autophagy receptor TOLLIP-mediated autophagic degradation and is stabilized by VCP through blocking its lysosomal degradation. Strikingly, TMEM63A in turn stabilizes oncoprotein DERL1 through preventing TOLLIP-mediated autophagic degradation. Notably, pharmacological inhibition of VCP by CB-5083 or knockdown of DERL1 partially abolishes the oncogenic effects of TMEM63A on TNBC progression both in vitro and in vivo. Collectively, these findings uncover a previously unknown functional and mechanistic role for TMEM63A in TNBC progression and provide a new clue for targeting TMEM63A-driven TNBC tumors by using a VCP inhibitor.Abbreviations: ATG16L1, autophagy related 16 like 1; ATG5, autophagy related 5; ATP5F1B/ATP5B, ATP synthase F1 subunit beta; Baf-A1, bafilomycin A₁; CALCOCO2/NDP52, calcium binding and coiled-coil domain 2; CANX, calnexin; DERL1, derlin 1; EGFR, epidermal growth factor receptor; ER, endoplasmic reticulum; ERAD, endoplasmic reticulum-associated degradation; HSPA8, heat shock protein family A (Hsp70) member 8; IP, immunoprecipitation; LAMP2A, lysosomal associated membrane protein 2; NBR1, NBR1 autophagy cargo receptor; OPTN, optineurin; RT-qPCR, reverse transcription-quantitative PCR; SQSTM1/p62, sequestosome 1; TAX1BP1, Tax1 binding protein 1; TMEM63A, transmembrane protein 63A; TNBC, triple-negative breast cancer; TOLLIP, toll interacting protein; VCP, valosin containing protein.

Hepatic transcriptome analysis reveals the metabolic strategies of largemouth bass (Micropterus salmoides) under different dissolved oxygen condition

Dissolved oxygen (DO) affects aquatic animals at a fundamental level so that the differences in its metabolic strategies under prolonged hypoxic conditions need an urgent exploration. In this experiment, largemouth bass (Micropterus salmoides) were chronically exposed (6 weeks) to severe hypoxia (S-HYP, DO: 2.0 ± 0.4 mg/L) and mild hypoxia (M-HYP, DO: 5.1 ± 0.4 mg/L). Compared to the control group (CON, DO:8.4 ± 0.4 mg/L), 1196 and 232 differentially expressed genes (DEGs) were obtained in S-HYP and M-HPY groups via transcriptome analysis, respectively. In S-HYP, lipolysis was promoted while anabolism was blocked. Meanwhile, significantly less fat droplet area was observed in the liver histology of S-HYP. Additionally, the cell cycle also responded to hypoxia, being blocked in the G1 phase with the suspension of DNA replication process. In M-HYP, the processing of protein in the endoplasmic reticulum and the synthesis of various aminoacyl t-RNA were inhibited, and a novel balance of the urea cycle might be established in the biosynthesis of arginine. The key DEGs involved in the above metabolic pathways, such as atgl, cpt1, arg1, etc., were validated by Q-PCR yielding results consistent with transcriptome data. This study indicates that the largemouth bass is prone to increase the proportion of lipid as an energy supply to adapt to the reprogramming of energy metabolism, while reducing the rate of cell proliferation to adapt to chronic severe hypoxia. This is also an undescribed observation in fish liver metabolism that largemouth bass may transform the synthesis and processing strategies of protein when exposed to chronic mild hypoxia.

The Role of the Rhomboid Superfamily in ER Protein Quality Control: From Mechanisms and Functions to Diseases

The endoplasmic reticulum (ER) is an essential organelle in eukaryotic cells and is a major site for protein folding, modification, and lipid synthesis. Perturbations within the ER, such as protein misfolding and high demand for protein folding, lead to dysregulation of the ER protein quality control network and ER stress. Recently, the rhomboid superfamily has emerged as a critical player in ER protein quality control because it has diverse cellular functions, including ER-associated degradation (ERAD), endosome Golgi-associated degradation (EGAD), and ER preemptive quality control (ERpQC). This breadth of function both illustrates the importance of the rhomboid superfamily in health and diseases and emphasizes the necessity of understanding their mechanisms of action. Because dysregulation of rhomboid proteins has been implicated in various diseases, such as neurological disorders and cancers, they represent promising potential therapeutic drug targets. This review provides a comprehensive account of the various roles of rhomboid proteins in the context of ER protein quality control and discusses their significance in health and disease.

Potential roles of the endoplasmic reticulum stress pathway in amyotrophic lateral sclerosis

The endoplasmic reticulum (ER) is a major organelle involved in protein quality control and cellular homeostasis. ER stress results from structural and functional dysfunction of the organelle, along with the accumulation of misfolded proteins and changes in calcium homeostasis, it leads to ER stress response pathway such as unfolded protein response (UPR). Neurons are particularly sensitive to the accumulation of misfolded proteins. Thus, the ER stress is involved in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, prion disease and motor neuron disease (MND). Recently, the complex involvement of ER stress pathways has been demonstrated in experimental models of amyotrophic lateral sclerosis (ALS)/MND using pharmacological and genetic manipulation of the unfolded protein response (UPR), an adaptive response to ER stress. Here, we aim to provide recent evidence demonstrating that the ER stress pathway is an essential pathological mechanism of ALS. In addition, we also provide therapeutic strategies that can help treat diseases by targeting the ER stress pathway.

Endoplasmic Reticulum Stress in Chronic Obstructive Pulmonary Disease: Mechanisms and Future Perspectives

The endoplasmic reticulum (ER) is an integral organelle for maintaining protein homeostasis. Multiple factors can disrupt protein folding in the lumen of the ER, triggering ER stress and activating the unfolded protein response (UPR), which interrelates with various damage mechanisms, such as inflammation, apoptosis, and autophagy. Numerous studies have linked ER stress and UPR to the progression of chronic obstructive pulmonary disease (COPD). This review focuses on the mechanisms of other cellular processes triggered by UPR and summarizes drug intervention strategies targeting the UPR pathway in COPD to explore new therapeutic approaches and preventive measures for COPD.

Diagnostic Potential of microRNAs in Extracellular Vesicles Derived from Bronchoalveolar Lavage Fluid for Pneumonia—A Preliminary Report

Current clinical needs require the development and use of rapid and effective diagnostic indicators to accelerate the identification of pneumonia and the process of microbiological diagnosis. MicroRNAs (miRNAs) in extracellular vesicles (EVs) have become attractive candidates for novel biomarkers to evaluate the presence and progress of many diseases. We assessed their performance as biomarkers of pneumonia. Patients were divided into the pneumonia group (with pneumonia) and the control group (without pneumonia). We identified and compared two upregulated miRNAs in EVs derived from bronchoalveolar lavage fluid (BALF-EVs) between the two groups (P_{miR–17–5p} = 0.009; P_{miR–193a–5p} = 0.031). Interestingly, in cell-debris pellets and EVs-free supernatants derived from bronchoalveolar lavage fluid (BALF-cell-debris pellets and BALF-EVs-free supernatants), total plasma, and EVs derived from plasma (plasma-EVs), the expression of miR–17–5p and miR–193a–5p showed no difference between pneumonia group and control group. In vitro experiments revealed that miR–17–5p and miR–193a–5p were strikingly upregulated in EVs derived from macrophages stimulated by lipopolysaccharide. MiR–17–5p (area under the curve, AUC: 0.753) and miR–193a–5p (AUC: 0.692) in BALF-EVs are not inferior to procalcitonin (AUC: 0.685) in the diagnosis of pneumonia. Furthermore, miR–17–5p and miR–193a–5p in BALF-EVs had a significantly higher specificity compared to procalcitonin and could be served as a potential diagnostic marker. MiR–17–5p and miR–193a–5p in EVs may be involved in lung inflammation by influencing the forkhead box O (FoxO) signaling pathway and protein processing in endoplasmic reticulum. This study is one of the few studies which focused on the potential diagnostic role of miRNAs in BALF-EVs for pneumonia and the possibility to use them as new biomarkers for a rapid and early diagnosis.

Molecular interaction between small nuclear ribonucleoprotein polypeptide G and heat shock protein 70.14: a microscale thermophoresis exposition towards developing anti-cancer drugs

BACKGROUND

Targeting protein-protein interactions (PPIs) linked to protein quality control (PQC) pathways as potential anti-cancer drug targets have unanimously widened biological insights and the therapeutic potential of PPIs as smart-drug discovery tools in cancer. PPIs between disease-relevant proteins associated with protein homeostasis in PQC pathways have been linked to improved mechanistic understanding associated with conformational abnormalities and impairment, cellular proteotoxicity, induced apoptosis, and pathogenesis in different types of cancers. In this context, PPIs between small nuclear ribonucleoprotein polypeptide G (SNRPG) and heat shock protein 70.14 (Hsp70.14) have attracted attention as potential smart drug discovery tools in cancer diagnostics and therapeutics. Validated evidence of high-quality biological data has shown the presence of the two proteins in different types of cancers including breast cancer. The links between SNRPG and Hsp70.14 in cancer-cell networks remain elusive, overlooked, and uncharacterized.

METHODOLOGY

In this study, we explored the interaction between the two oncogenic proteins using the MST-based assays.

RESULTS

The results revealed a low K_D in the nanomolar concentration range of 2.4673 × 10^-7 demonstrating a great affinity for SNRPG binding to Hsp70.14.

CONCLUSIONS

The results suggest a possible involvement between the two proteins in hostile tumour microenvironments. Furthermore, these findings offer a different therapeutic perspective that could pave the way for the creation of novel small molecule inhibitors as drugs for the treatment of cancer.

Identifying a Novel Endoplasmic Reticulum-Related Prognostic Model for Hepatocellular Carcinomas

From the standpoint of the ER (endoplasmic reticulum), we were interested in identifying hub genes that impact clinical prognosis for HCC (hepatocellular carcinoma) patients and developing an ER-related prognostic model. Using TCGA-LIHC (The Cancer Genome Atlas-Liver Hepatocellular Carcinoma) and GSE14520 datasets, we conducted a series of analyses, which included differential gene screening, clinical prognostic analysis, Lasso regression, nomogram prediction, tumour clustering, gene functional enrichment, and tumour infiltration of immune cells. Following our screening for ER-related genes ( $n=1975$ ), we conducted a Lasso regression model to obtain five hub genes, KPNA2, FMO3, SPP1, KIF2C, and LPCAT1, using TCGA-LIHC as a training set. According to risk scores, HCC samples within either the TCGG-LIHC or GSE14520 cohort were categorized into high- and low-risk groups. Compared to the high-risk group of HCC patients, patients in the low-risk group had a better prognosis of OS (overall survival) or RFS (relapse-free survival). For TCGA-LIHC training set, with the factors of risk score, stage, age, and sex, we plotted a nomogram for 1-, 3-, and 5-year survival predictions. Our model demonstrated better clinical validity in both TCGA-LIHC and GSE14520 cohorts. Additionally, events related to biological enzyme activity, biological metabolic processes, or the cell cycle were associated with the prognostic risk of ER. Furthermore, two HCC prognosis-associated tumour clusters were identified by ER hub gene-based consensus clustering. Our findings indicated a link between ER prognostic signature-related high/low risk and tumour infiltration levels of several immune cells, such as “macrophages M2/M0” and “regulatory T cells (Tregs).” Overall, we developed a novel ER-related clinical prognostic model for HCC patients.

PDIA2 Bridges Endoplasmic Reticulum Stress and Metabolic Reprogramming During Malignant Transformation of Chronic Colitis

Background

Chronic inflammation contributes to approximately 20% of cancers; the underlying mechanisms are still elusive. Here, using an animal model of colitis to colon-cancerous transformation, we demonstrated that endoplasmic reticulum (ER) stress couples with metabolic reprogramming to promote a malignant transformation of chronic inflammation.

Methods

The animal model for chronic colitis to colon-cancerous transformation was established in C57BL/6N mice by azoxymethane (AOM) and dextran sodium sulfate (DSS) treatments. The differential proteins in control and AOM/DSS-treated colon mucosa were determined using proteomic analysis; the kinetics of metabolic modifications were monitored by mitochondrial oxygen flux, extracellular acidification, and targeted metabolomics; the molecule linker between ER stress and metabolic modifications were identified by coimmunoprecipitation, KEGG pathway analysis, and the subcutaneous tumor model using gene-specific knockdown colon cancer cells. Tissue array analysis were used to evaluate the differential protein in cancer and cancer-adjacent tissues.

Results

AOM/DSS treatment induced 38 tumors in 10 mice at the 14th week with the mean tumor size 9.35 ± 3.87 mm², which was significantly decreased to 5.85 ± 0.95 mm² by the ER stress inhibitor 4-phenylbutyric acid (4PBA). Seven differential proteins were determined from control (1,067 ± 48) and AOM/DSS-treated mucosa (1,077 ± 59); the level of ER protein PDIA2 (protein disulfide isomerase-associated 2) was increased over 7-fold in response to AOM/DSS treatment. PDIA2 interacted with 420 proteins that were involved in 8 signaling pathways, in particular with 53 proteins in metabolic pathways. PDIA2 translocated from ER to mitochondria and interacted with the components of complexes I and II to inhibit oxophosphorylation but increase glycolysis. Knockdown PDIA2 in colon cancer cells restored the metabolic imbalance and significantly repressed tumor growth in the xenograft animal model. 4PBA therapy inhibited the AOM/DSS-mediated overexpression of PDIA2 and metabolic modifications and suppressed colon cancer growth. In clinic, PDIA2 was overexpressed in colon cancer tissues rather than cancer-adjacent tissues and was related with the late stages and lymph node metastasis of colon cancer.

Conclusions

Persistent ER stress reprograms the metabolism to promote the malignant transformation of chronic colitis; PDIA2 serves as a molecule linker between ER stress and metabolic reprogramming. The inhibition of ER stress restores metabolic homeostasis and attenuates the cancerous transformation of chronic inflammation.

Identification and Validation of an Endoplasmic Reticulum Stress-Related lncRNA Signature for Colon Adenocarcinoma Patients

Purpose

Methods

Results

Conclusion

Ubiquitination-Proteasome System (UPS) and Autophagy Two Main Protein Degradation Machineries in Response to Cell Stress

In response to environmental stimuli, cells make a series of adaptive changes to combat the injury, repair the damage, and increase the tolerance to the stress. However, once the damage is too serious to repair, the cells will undergo apoptosis to protect the overall cells through suicidal behavior. Upon external stimulation, some intracellular proteins turn into unfolded or misfolded protein, exposing their hydrophobic regions to form protein aggregation, which may ultimately produce serious damage to the cells. Ubiquitin plays an important role in the degradation of these unnatural proteins by tagging with ubiquitin chains in the ubiquitin-proteasome or autophagy system. If the two processes fail to eliminate the abnormal protein aggregates, the cells will move to apoptosis and death. Dysregulation of ubiquitin-proteasome system (UPS) and autophagy may result in the development of numerous diseases. This review focuses on the molecular mechanisms of UPS and autophagy in clearance of intracellular protein aggregates, and the relationship between dysregulation of ubiquitin network and diseases.

Protein Aggregation in the ER: Calm behind the Storm

As one of the largest organelles in eukaryotic cells, the endoplasmic reticulum (ER) plays a vital role in the synthesis, folding, and assembly of secretory and membrane proteins. To maintain its homeostasis, the ER is equipped with an elaborate network of protein folding chaperones and multiple quality control pathways whose cooperative actions safeguard the fidelity of protein biogenesis. However, due to genetic abnormalities, the error-prone nature of protein folding and assembly, and/or defects or limited capacities of the protein quality control systems, nascent proteins may become misfolded and fail to exit the ER. If not cleared efficiently, the progressive accumulation of misfolded proteins within the ER may result in the formation of toxic protein aggregates, leading to the so-called “ER storage diseases”. In this review, we first summarize our current understanding of the protein folding and quality control networks in the ER, including chaperones, unfolded protein response (UPR), ER-associated protein degradation (ERAD), and ER-selective autophagy (ER-phagy). We then survey recent research progress on a few ER storage diseases, with a focus on the role of ER quality control in the disease etiology, followed by a discussion on outstanding questions and emerging concepts in the field.

Reticulon 3-mediated Chk2/p53 activation suppresses hepatocellular carcinogenesis and is blocked by hepatitis B virus

OBJECTIVE

Dysfunction of endoplasmic reticulum (ER) proteins is closely related to homeostasis disturbance and malignant transformation of hepatocellular carcinoma (HCC). Reticulons (RTN) are a family of ER-resident proteins critical for maintaining ER function. Nevertheless, the precise roles of RTN in HCC remain largely unclear. The aim of the study is to examine the effect of reticulon family member RTN3 on HCC development and explore the underlying mechanisms.

DESIGN

Clinical HCC samples were collected to assess the relationship between RTN3 expression and patients' outcome. HCC cell lines were employed to examine the effects of RTN3 on cellular proliferation, apoptosis and signal transduction in vitro. Nude mice model was used to detect the role of RTN3 in modulating tumour growth in vivo.

RESULTS

We found that RTN3 was highly expressed in normal hepatocytes but frequently downregulated in HCC. Low RTN3 expression predicted poor outcome in patients with HCC in TP53 gene mutation and HBV infection status-dependent manner. RTN3 restrained HCC growth and induced apoptosis by activating p53. Mechanism studies indicated that RTN3 facilitated p53 Ser392 phosphorylation via Chk2 and enhanced subsequent p53 nuclear localisation. RTN3 interacted with Chk2, recruited it to ER and promoted its activation in an ER calcium-dependent manner. Nevertheless, the tumour suppressive effects of RTN3 were abrogated in HBV-positive cells. HBV surface antigen competed with Chk2 for RTN3 binding and blocked RTN3-mediated Chk2/p53 activation.

CONCLUSION

The findings suggest that RTN3 functions as a novel suppressor of HCC by activating Chk2/p53 pathway and provide more clues to better understand the oncogenic effects of HBV.

ER-Phagy: A New Regulator of ER Homeostasis

The endoplasmic reticulum (ER) is one of the most important cellular organelles and is essential for cell homeostasis. Upon external stimulation, ER stress induces the unfolded protein response (UPR) and ER-associated degradation (ERAD) to maintain ER homeostasis. However, persistent ER stress can lead to cell damage. ER-phagy is a selective form of autophagy that ensures the timely removal of damaged ER, thereby protecting cells from damage caused by excessive ER stress. As ER-phagy is a newly identified form of autophagy, many receptor-mediated ER-phagy pathways have been discovered in recent years. In this review, we summarize our understanding of the maintenance of ER homeostasis and describe the receptors identified to date. Finally, the relationships between ER-phagy and diseases are also discussed.

Network Pharmacology and Bioinformatics Methods Reveal the Mechanism of Zao-Jiao-Ci in the Treatment of LSCC

Objective

Zao-Jiao-Ci (ZJC), a traditional Chinese medicine, is considered as a promising candidate to treat laryngeal squamous cell carcinoma (LSCC). However, the underlying molecular mechanism remains unclear.

Methods

Gene expression profiles of GSE36668 were available from the GEO database, and differentially expressed genes (DEGs) of LSCC were obtained by R package; subsequently, enrichment analysis on KEGG and GO of DEGs was performed. The active ingredients of ZJC were screened from the TCMSP database, and the matched candidate targets were obtained by PharmMapper. Furthermore, we constructed protein-protein interaction (PPI) networks of DEGs and candidate targets, respectively, and we screened the core network from the merged network through combining the two PPI networks using Cytoscape 3.7.2. The key targets derived from the core network were analyzed to find out the associated KEGG signal enrichment pathway. By the GEPIA online website, Kaplan–Meier analysis was used to complete the overall survival and disease-free survival of the selected genes in the core module.

Results

We identified 96 candidate targets of ZJC and 86 DEGs of LSCC, the latter including 50 upregulated genes and 36 downregulated genes. DEGs were obviously enriched in the following biological functions: extracellular structure organization, the extracellular matrix organization, and endodermal cell differentiation. The 60 key targets from the core network were enriched in the signal pathways including transcriptional misregulation cancer, cell cycle, and so on. We found that LSCC patients with high expression of HIST1H3J, HIST1H3F, and ITGA4 had worse overall survival, while higher expression of NTRK1, COPS5, HIST1H3A, and HIST1H3G had significantly worse disease-free survival.

Conclusion

It suggested that the interaction between ZJC and LSCC was related to the signal pathways of transcriptional misregulation cancer and cell cycle, revealing that it may be the mechanism of ZJC in the treatment of LSCC.

How Is the Fidelity of Proteins Ensured in Terms of Both Quality and Quantity at the Endoplasmic Reticulum? Mechanistic Insights into E3 Ubiquitin Ligases

The endoplasmic reticulum (ER) is an interconnected organelle that plays fundamental roles in the biosynthesis, folding, stabilization, maturation, and trafficking of secretory and transmembrane proteins. It is the largest organelle and critically modulates nearly all aspects of life. Therefore, in the endoplasmic reticulum, an enormous investment of resources, including chaperones and protein folding facilitators, is dedicated to adequate protein maturation and delivery to final destinations. Unfortunately, the folding and assembly of proteins can be quite error-prone, which leads to the generation of misfolded proteins. Notably, protein homeostasis, referred to as proteostasis, is constantly exposed to danger by flows of misfolded proteins and subsequent protein aggregates. To maintain proteostasis, the ER triages and eliminates terminally misfolded proteins by delivering substrates to the ubiquitin–proteasome system (UPS) or to the lysosome, which is termed ER-associated degradation (ERAD) or ER-phagy, respectively. ERAD not only eliminates misfolded or unassembled proteins via protein quality control but also fine-tunes correctly folded proteins via protein quantity control. Intriguingly, the diversity and distinctive nature of E3 ubiquitin ligases determine efficiency, complexity, and specificity of ubiquitination during ERAD. ER-phagy utilizes the core autophagy machinery and eliminates ERAD-resistant misfolded proteins. Here, we conceptually outline not only ubiquitination machinery but also catalytic mechanisms of E3 ubiquitin ligases. Further, we discuss the mechanistic insights into E3 ubiquitin ligases involved in the two guardian pathways in the ER, ERAD and ER-phagy. Finally, we provide the molecular mechanisms by which ERAD and ER-phagy conduct not only protein quality control but also protein quantity control to ensure proteostasis and subsequent organismal homeostasis.

Whole transcriptome sequencing and integrated network analysis elucidates the effects of 3,8-Di-O-methylellagic acid 2-O-glucoside derived from Sanguisorba offcinalis L., a novel differentiation inducer on erythroleukemia cells

Acute erythroid leukemia (AEL) is a rare and aggressive hematologic malignancy with no specific treatment. Sanguisorba officinalis L. (S. officinalis), a well-known traditional Chinese medicine, possesses potent anticancer activity. However, the active components of S. officinalis against AEL and the associated molecular mechanisms remain unknown. In this study, we predicted the anti-AML effect of S. officinalis based on network pharmacology. Through the identification of active components of S. officinalis, we found that 3,8-Di-O-methylellagic acid 2-O-glucoside (DMAG) not only significantly inhibited the proliferation of erythroleukemic cell line HEL, but also induced their differentiation to megakaryocytes. Furthermore, we demonstrated that DMAG could prolong the survival of AEL mice model. Whole-transcriptome sequencing was performed to elucidate the underlying molecular mechanisms associated with anti-AEL effect of DMAG. The results showed that the total of 68 miRNAs, 595 lncRNAs, 4030 mRNAs and 35 circRNAs were significantly differentially expressed during DMAG induced proliferation inhibition and differentiation of HEL cells. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that the differentially expressed miRNAs, lncRNAs, mRNAs and circRNAs were mainly involved in metabolic, HIF-1, MAPK, Notch pathway and apoptosis. The co-expression networks showed that miR-23a-5p, miR-92a-1-5p, miR-146b and miR-760 regulatory networks were crucial for megakaryocyte differentiation induced by DMAG. In conclusion, our results suggest that DMAG, derived from S. officinalis might be a potent differentiation inducer of AEL cells and provide important information on the underlying mechanisms associated with its anti-AEL activity.

Tandem Mass Tag-Based Proteomic Analysis of Potential Biomarkers for Hepatocellular Carcinoma Differentiation

Purpose

The poor prognosis of hepatocellular carcinoma (HCC) urgent us to discover early and effective biomarkers. In this study, we applied tandem mass tag (TMT)-based proteomic analysis to discover potential protein markers for HCC identification and differentiation.

Patients and Methods

Fifteen patients, well-differentiated (G1, N = 5), moderate-differentiated (G2, N = 5), and poorly differentiated (G3, N = 5), with 30 matched pair tissues (both tumor and adjacent non-tumor tissues derived from the same patient) were enrolled. All samples were subjected to TMT labeling and LC−MS/MS analysis. The identified proteins were subsequently assigned to GO and KEGG for predicting function. The identified protein candidates were validated using immunohistochemistry (IHC).

Results

A total of 1010 proteins were identified. Of these, 154 differentially expressed proteins (DEPs), 100 up-regulated and 54 down-regulated, were found between tumor and adjacent non-tumor tissues; 12 DEPs, 9 up-regulated and 3 down-regulated, were found between G1 and G3 tissues; 8 DEPs, 5 up-regulated and 3 down-regulated, were found between G1 and G2 tissues; 11 DEPs, 8 up-regulated and 3 down-regulated, were found between G2 and G3 tissues. Among them, ASS1 and CPS1 were significantly up-regulated while UROD and HBB were significantly down-regulated in G3 compared with G1 and G2 tumors. Three proteins, CYB5A, FKBP11 and YBX1, were significantly up-regulated in G1 compared with both G2 and G3 tumors. The 7 biomarker candidates were further verified by IHC.

Conclusion

A variety of DEPs related to the histological differentiation of HCC were identified, among which ASS1, CPS1, URPD and HBB proteins were potential biomarkers for distinguishing poorly differentiated HCC, while CYB5A, FKBP11 and YBX1 were potential biomarkers for distinguishing well-differentiated HCC. Our findings may further provide a new insight facilitating the diagnosis and prognosis of HCC.

Regulation of the proteostasis network during enterovirus infection: A feedforward mechanism for EV-A71 and EV-D68

The proteostasis network guarantees successful protein synthesis, folding, transportation, and degradation. Mounting evidence has revealed that this network maintains proteome integrity and is linked to cellular physiology, pathology, and virus infection. Human enterovirus A71 (EV-A71) and EV-D68 are suspected causative agents of acute flaccid myelitis, a severe poliomyelitis-like neurologic syndrome with no known cure. In this context, further clarification of the molecular mechanisms underlying EV-A71 and EV-D68 infection is paramount. Here, we summarize the components of the proteostasis network that are intercepted by EV-A71 and EV-D68, as well as antivirals that target this network and may help develop improved antiviral drugs.

P4HB: A novel diagnostic and prognostic biomarker for bladder carcinoma

Prolyl 4-hydroxylase, beta polypeptide (P4HB) protein is an endoplasmic reticulum (ER) molecular chaperone protein and has been reported to be overexpressed in multiple tumor types. However, the role of P4HB in bladder cancer (BLCA) has not yet been elucidated. The aim of the present study was to investigate the prognostic value of P4HB and the association between clinicopathological characteristics and P4HB in BLCA. P4HB expression levels were assessed through The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases, and validated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis in BLCA tissues and cells. A total of 69 pairs of tumor and normal samples were used to analyze the expression of P4HB via immunohistochemical staining. A co-expression network and functional enrichment analyses were conducted to investigate the biological function of P4HB in BLCA. The protein-protein interaction (PPI) network was constructed by Search Tool for the Retrieval of Interacting Genes. The results showed that P4HB was highly expressed in BLCA cells and tissues. The area under the curve value for P4HB expression to discriminate between tumor and normal tissues was up to 0.888 (95% CI: 0.801–0.975; P<0.001) and 0.881 (95% CI: 0.825–0.937; P<0.001) in TCGA database and our database, respectively. Furthermore, the expression level of P4HB was an independent risk factor for overall survival (OS) and recurrence-free survival (RFS) by univariate and multivariate analyses. Kaplan-Meier survival analysis demonstrated that high P4HB expression was associated with low OS and RFS. Pathway enrichment analysis suggested that P4HB was involved in protein processing in the endoplasmic reticulum (ER), including N-glycan modification and protein metabolic processes responding to ER stress. PPI analysis revealed that the potential targets of P4HB were mainly involved in posttranslational protein modification and response to ER stress. In conclusion, the expression level of P4HB aid in identifying patients with early-stage BLCA and predicting the prognosis of BLCA. Therefore, P4HB may be a novel diagnostic and prognostic biomarker for BLCA.

ERAD deficiency promotes mitochondrial dysfunction and transcriptional rewiring in human hepatic cells

Mitochondrial dysfunction is associated with a variety of human diseases including neurodegeneration, diabetes, nonalcohol fatty liver disease (NAFLD), and cancer, but its underlying causes are incompletely understood. Using the human hepatic cell line HepG2 as a model, we show here that endoplasmic reticulum-associated degradation (ERAD), an ER protein quality control process, is critically required for mitochondrial function in mammalian cells. Pharmacological inhibition or genetic ablation of key proteins involved in ERAD increased cell death under both basal conditions and in response to proinflammatory cytokines, a situation frequently found in NAFLD. Decreased viability of ERAD-deficient HepG2 cells was traced to impaired mitochondrial functions including reduced ATP production, enhanced reactive oxygen species (ROS) accumulation, and increased mitochondrial outer membrane permeability. Transcriptome profiling revealed widespread down-regulation of genes underpinning mitochondrial functions, and up-regulation of genes associated with tumor growth and aggression. These results highlight a critical role for ERAD in maintaining mitochondrial functional and structural integrity and raise the possibility of improving cellular and organismal mitochondrial function via enhancing cellular ERAD capacity.

Sestrin2 protects against bavachin induced ER stress through AMPK/mTORC1 signaling pathway in HepG2 cells

Bavachin (BV), a natural flavonoid compound derived from Psoralea corylifolia L, has been reported to be a potential hepatotoxin. Our previous studies have found that BV can induce endoplasmic reticulum (ER) stress-related cell apoptosis, but the molecular mechanism underlying BV-induced ER stress remains obscure. Sestrin2, a highly conserved stress-inducible protein, is involved in the cellular responses of various stress conditions and homeostatic regulation. However, whether Sestrin2 participated in the ER stress related hepatotoxicity against BV is still elusive. In the present study, we aim to investigate the role of BV on liver injury of mice and the impact of Sestrin2 on BV-induced ER stress in HepG2 cells. The results in mice showed that BV induced ER stress related liver injury with increased Sestrin2 expression involvement. Knockdown of Sestrin2 with siRNA aggravated BV-induced ER stress significantly in HepG2 cells. Further mechanistic study uncovered that inhibition of mTORC1 with rapamycin blocked BV-induced ER stress, and treatment with Sestrin2 siRNA blocked the inhibition effect of AMPK to mTORC1. Therefore, constant mTORC1 would lead to accumulation of misfolded or unfolded proteins and aggravated ER stress. Collectively, our study indicates that Sestrin2 confers protection against BV-induced ER stress via activating of the AMPK/mTORC1 pathway.

Recombinant Treponema pallidum protein Tp0768 promotes proinflammatory cytokine secretion of macrophages through ER stress and ROS/NF-κB pathway

In response to danger signals, macrophages rapidly produce many inflammatory cytokines that trigger the cascade release of inflammatory mediators, leading to tissue damage, which is an important cause of clinical manifestations of syphilis at all stages. However, we still know very little about the specific mechanism of this process. Tp0768 is an infection-stage-dependent antigen that plays an important role in the infection of Treponema pallidum. In this study, we demonstrated that Tp0768 stimulation of macrophages can cause IL-1β, IL-6, and IL-8 mRNA expression levels to increase in a dose- and time-dependent manner. Further research showed that Tp0768 activated ER stress and the ROS/NF-κB pathway in macrophages. Inhibition of ER stress and the ROS/NF-κB pathway inhibited the expression of IL-1β, IL-6, and IL-8 induced by Tp0768. In addition, pretreatment with a PERK pathway inhibitor significantly reduced the expression of the NF-κB and JNK pathways, while also downregulating the expression of IL-1β, IL-6, and IL-8. Tp0768 stimulation can activate IRE1α/XBP-1 signaling and participate in the induction of inflammatory cytokines through the JNK pathway. These findings indicate that Tp0768 promotes the secretion of proinflammatory cytokines IL-1β, IL-6, and IL-8 by macrophages through ER stress and the ROS/NF-κB pathway, which are also involved in the activation of the NF-κB and JNK pathways that are induced by the PERK pathway and activation of IRE1α/XBP-1 signaling. KEY POINTS: • This study found for the first time that the recombinant Treponema pallidum protein Tp0768 promotes the production of IL-1β, IL-6, and IL-8 by macrophages through ER stress. • Recombinant Treponema pallidum protein Tp0768 regulates the ROS/NF-κB pathway through ER stress. • ER stress-related pathway PERK induces the expression of IL-1β, IL-6, and IL-8 by activating the NF-κB pathway and the JNK pathway. • IRE1α can induce the splicing of XBP-1mRNA and activate the JNK pathway.

Cellular Protein Quality Control in Diabetic Cardiomyopathy: From Bench to Bedside

Heart failure is a serious comorbidity and the most common cause of mortality in diabetes patients. Diabetic cardiomyopathy (DCM) features impaired cellular structure and function, culminating in heart failure; however, there is a dearth of specific clinical therapy for treating DCM. Protein homeostasis is pivotal for the maintenance of cellular viability under physiological and pathological conditions, particularly in the irreplaceable cardiomyocytes; therefore, it is tightly regulated by a protein quality control (PQC) system. Three evolutionarily conserved molecular processes, the unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), and autophagy, enhance protein turnover and preserve protein homeostasis by suppressing protein translation, degrading misfolded or unfolded proteins in cytosol or organelles, disposing of damaged and toxic proteins, recycling essential amino acids, and eliminating insoluble protein aggregates. In response to increased cellular protein demand under pathological insults, including the diabetic condition, a coordinated PQC system retains cardiac protein homeostasis and heart performance, on the contrary, inappropriate PQC function exaggerates cardiac proteotoxicity with subsequent heart dysfunction. Further investigation of the PQC mechanisms in diabetes propels a more comprehensive understanding of the molecular pathogenesis of DCM and opens new prospective treatment strategies for heart disease and heart failure in diabetes patients. In this review, the function and regulation of cardiac PQC machinery in diabetes mellitus, and the therapeutic potential for the diabetic heart are discussed.

Mechanism of Action of Novel Pyrazole Carboxamide Containing a Diarylamine Scaffold against Rhizoctonia solani

In the last few decades, Rhizoctonia solani causing rice sheath blight has resulted in a lot of economic losses in the world. Therefore, many novel pyrazole carboxamide fungicides have been intensively researched and employed to fight against it. In this regard, in recent years, our group reported a novel pyrazole carboxamide containing a diarylamine scaffold with good antifungal activity against rice sheath blight in the pot test and field trial. Following this project, the antifungal mechanism of action of the pyrazole carboxamide has been elucidated in this work. The antifungal result showed that compound SCU2028, N-[2-[(3-chlorophenyl)amino]-phenyl]-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, was equivalent to the commercial fungicide thifluzamide and its EC₅₀ value was 0.022 mg/L against R. solani. Also, the observation results by scanning electron microscopy and transmission electron microscopy showed that it could destroy the fungus' cell walls or membranes and result in the leakage of contents and increase of the number of mitochondria and abnormal morphology. Meanwhile, the result on the mitochondrial membrane potential (MMP) showed that it could decrease R. solani's MMP. Furthermore, the results by label-free quantitative proteomic analysis showed that 1153 proteins were found after R. solani was treated with compound SCU2028, including 212 proteins in the control group and 257 proteins in the treatment group. A total of 142 differential proteins were obtained, of which 92 proteins were upregulated and 50 proteins were downregulated. The differentially expressed proteins affected a series of physiological and biochemical pathways in the mitochondria, endoplasmic reticulum, ribosome, and other related GO and KEGG pathways. In particular, the inhibition of the respiratory chain caused by the TCA cycle and oxidative phosphorylation KEGG pathway indicated that complex II (succinate dehydrogenase) and complex IV (cytochrome oxidase) might be compound SCU2028's main action targets. In addition, multiple experiments of qRT-PCR, enzyme activity detection, and molecular docking confirmed complex II and complex IV as targets. It could be seen that these findings provided a theoretical support for further research and development of the pyrazole carboxamide fungicides.

Role of Autophagy in Cancer Cell Response to Nucleolar and Endoplasmic Reticulum Stress

Eukaryotic cells are exposed to many internal and external stimuli that affect their fate. In particular, the exposure to some of these stimuli induces stress triggering a variety of stress responses aimed to re-establish cellular homeostasis. It is now established that the deregulation of stress response pathways plays a central role in cancer initiation and progression, allowing the adaptation of cells to an altered state in the new environment. Autophagy is a tightly regulated pathway which exerts “housekeeping” role in physiological processes. Recently, a growing amount of evidence highlighted the crucial role of autophagy in the regulation of integrated stress responses, including nucleolar and endoplasmic reticulum. In this review, we attempt to afford an overview of the complex role of nucleolar and endoplasmic reticulum stress-response mechanisms in the regulation of autophagy in cancer and cancer treatment.

Targeted Inhibition of P4HB Promotes Cell Sensitivity to Gemcitabine in Urothelial Carcinoma of the Bladder

Background

Bladder cancer (BC) is a common malignancy worldwide that accounts for 3% of global cancer diagnoses. Chemotherapy resistance limits the therapeutic effect of chemotherapeutic agents in patients with BC. Prolyl 4-hydroxylase, beta polypeptide (P4HB) is an endoplasmic reticulum (ER) chaperone that is upregulated in bladder cancer tissues (The Cancer Genome Atlas, TCGA datasets). Knockdown or suppression of P4HB exerts anticancer activity and sensitizes cells to chemotherapy in various types of cancer.

Purpose

We aimed to investigate whether the inhibition of P4HB enhances the anticancer efficacy of gemcitabine (GEM) in BC cells and to study the underlying molecular mechanisms.

Patients and Methods

The P4HB mRNA expression levels of 411 BC patients from the TCGA database and P4HB expression level of eighty BC paraffin-embedded samples detected by immunohistochemistry (IHC) staining were used for clinical feature and prognostic analyses. Bioinformatics analysis was utilized for the mechanistic investigation. Highly P4HB-expressed BC cell lines (T24 and 5637) treated with P4HB inhibitor (Bacitracin, BAC) were used to study the effects of BAC on the sensitivity of BC cells to GEM and the potential mechanism. P4HB inhibition experiments were performed in highly P4HB-expressed BC cells, and cell viability, colony formation, cell cycle, reactive oxygen species (ROS), apoptosis and pathway proteins were assessed in T24 and 5637 cells.

Results

Western blot analysis showed that P4HB expression was significantly higher in BC tissues than in paired normal tissues. IHC showed that patients with high P4HB expression had a poorer overall survival (OS) rate than those with low P4HB expression. Furthermore, increased P4HB expression was demonstrated to be an independent prognostic marker for BC. Functionally, P4HB inhibition by BAC decreased the cell proliferation ability in vitro. Moreover, BAC treatment sensitized BC cells to GEM. Molecular mechanism analysis indicated that inhibition of P4HB by BAC treatment enhanced the anticancer effects of GEM through increasing cellular ROS content and promoting cell apoptosis and PERK/eIF2α/ATF4/CHOP signaling.

Conclusion

High P4HB expression was significantly correlated with poor prognosis in BC patients. Inhibition of P4HB by BAC decreased the cell proliferation ability and sensitized BC cells to GEM by activating apoptosis and the PERK/eIF2α/ATF4/CHOP pathways.

Stage-specific expression patterns of ER stress-related molecules in mice molars: Implications for tooth development

The endoplasmic reticulum (ER) is a site where protein folding and posttranslational modifications occur, but when unfolded or misfolded proteins accumulate in the ER lumen, an unfolded protein response (UPR) occurs. A UPR activates ER-stress signalling genes, including inositol-requiring enzyme-1 (Ire1), activating transcription factor 6 (Atf6), and double-stranded RNA-activated protein kinase-like endoplasmic reticulum kinase (Perk), to maintain homeostasis. The involvement of ER stress molecules in metabolic disease and hard tissue matrix formation has been established; however, an understanding of the role of ER-stress signalling molecules in tooth development is lacking. The aims of this study are to define the stage-specific expression patterns of ER stress-related molecules and to elucidate their putative functions in the organogenesis of teeth. This study leverages knowledge of the tissue morphology and expression patterns of a range of signalling molecules during tooth development. RT-qPCR, in situ hybridization, and immunohistochemistry analyses were performed to determine the stage-specific expression patterns of ER-stress-related signalling molecules at important stages of tooth development. RT-qPCR analyses showed that Atf6 and Perk have similar expression levels during all stages of tooth development; however, the expression levels of Ire1 and its downstream target X-box binding protein (Xbp1) increased significantly from the cap to the secretory stage of tooth development. In situ hybridization results revealed that Atf6 and Xbp1 were expressed in cells that form the enamel knot at cap stage and ameloblasts and odontoblasts at secretory stage in stage-specific patterns. In addition, Atf6, Ire1, and Xbp1 expression exhibited distinct localization patterns in secretory odontoblasts and ameloblasts of PN0 molars. Overall, our results strongly suggest that ER-stress molecules are involved in tooth development in response to protein overload that occurs during signaling modulations from enamel knots at cap stage and extracellular matrix secretion at secretory stage.

Unraveling the regulatory role of endoplasmic-reticulum-associated degradation in tumor immunity

During malignant transformation and cancer progression, tumor cells face both intrinsic and extrinsic stress, endoplasmic reticulum (ER) stress in particular. To survive and proliferate, tumor cells use multiple stress response pathways to mitigate ER stress, promoting disease aggression and treatment resistance. Among the stress response pathways is ER-associated degradation (ERAD), which consists of multiple components and steps working together to ensure protein quality and quantity. In addition to its established role in stress responses and tumor cell survival, ERAD has recently been shown to regulate tumor immunity. Here we summarize current knowledge on how ERAD promotes protein degradation, regulates immune cell development and function, participates in antigen presentation, exerts paradoxical roles on tumorigenesis and immunity, and thus impacts current cancer therapy. Collectively, ERAD is a critical protein homeostasis pathway intertwined with cancer development and tumor immunity. Of particular importance is the need to further unveil ERAD's enigmatic roles in tumor immunity to develop effective targeted and combination therapy for successful treatment of cancer.

Synthetic Lethality Screening Identifies FDA-Approved Drugs that Overcome ATP7B-Mediated Tolerance of Tumor Cells to Cisplatin

Tumor resistance to chemotherapy represents an important challenge in modern oncology. Although platinum (Pt)-based drugs have demonstrated excellent therapeutic potential, their effectiveness in a wide range of tumors is limited by the development of resistance mechanisms. One of these mechanisms includes increased cisplatin sequestration/efflux by the copper-transporting ATPase, ATP7B. However, targeting ATP7B to reduce Pt tolerance in tumors could represent a serious risk because suppression of ATP7B might compromise copper homeostasis, as happens in Wilson disease. To circumvent ATP7B-mediated Pt tolerance we employed a high-throughput screen (HTS) of an FDA/EMA-approved drug library to detect safe therapeutic molecules that promote cisplatin toxicity in the IGROV-CP20 ovarian carcinoma cells, whose resistance significantly relies on ATP7B. Using a synthetic lethality approach, we identified and validated three hits (Tranilast, Telmisartan, and Amphotericin B) that reduced cisplatin resistance. All three drugs induced Pt-mediated DNA damage and inhibited either expression or trafficking of ATP7B in a tumor-specific manner. Global transcriptome analyses showed that Tranilast and Amphotericin B affect expression of genes operating in several pathways that confer tolerance to cisplatin. In the case of Tranilast, these comprised key Pt-transporting proteins, including ATOX1, whose suppression affected ability of ATP7B to traffic in response to cisplatin. In summary, our findings reveal Tranilast, Telmisartan, and Amphotericin B as effective drugs that selectively promote cisplatin toxicity in Pt-resistant ovarian cancer cells and underscore the efficiency of HTS strategy for identification of biosafe compounds, which might be rapidly repurposed to overcome resistance of tumors to Pt-based chemotherapy.

CSFV protein NS5A activates the unfolded protein response to promote viral replication

Classical swine fever is a world organization for animal health listed disease and is caused by classical swine fever virus (CSFV). CSFV can induced unfolded protein response (UPR) and whether NS5A protein plays a role in this process remains unknown. Here, we demonstrate that CSFV induced all the three signal pathways ATF6, IRE1 and PERK of UPR. Furthermore, this phenomenon may be mediated by the NS5A protein since expression of NS5A alone can achieve the same effect. In the current study, we show that NS5A can interact with GRP78 as measured by using the CO-IP and GST pulldown assays. This interaction plays a positive role in the promotion of CSFV replication. Overexpression or knockdown of GRP78 mediated by lentivirus can enhance or decrease viral replication, respectively. Our findings provide the evidence that CSFV infection can activate the cellular UPRs, in which NS5A and GRP78 play key roles in the process.

Tauroursodeoxycholic acid mediates endoplasmic reticulum stress and autophagy in adrenocortical carcinoma cells

Adrenocortical carcinoma (ACC) is an invasive tumor that occurs in the endocrine system. Increasing evidence has shown that endoplasmic reticulum (ER) stress and autophagy play an important role in tumor formation. Tauroursodeoxycholic acid (TUDCA) is an ER chemical chaperone that can alleviate ER stress. In the present study, TUDCA promoted the proliferation, migration and invasion of ACC SW-13 and NCI-H295R cells. Reverse transcription-quantitative PCR and western blot analysis showed that the expression of glucose-regulated protein 78, a promoter of ER stress, was decreased. The expression levels of protein kinase R (PKR)-like ER kinase and activating transcription factor 6 were correspondingly decreased, and the downstream proteins, C/EBP homologous protein and JNK, were also decreased. The expression levels of the autophagy factor microtubule-associated protein light chain 3-II/I and the anti-apoptotic factor Bcl-2 increased following TUDCA treatment, while the expression of the pro-apoptotic factor Bax decreased. TUDCA alleviated ER stress in ACC SW-13 and NCI-H295R cells and induced autophagy, thereby inhibiting ACC cell apoptosis. ER stress- and autophagy-related signaling pathways are involved in the occurrence of ACC, which may provide potential therapeutic targets for ACC treatment.

Proteostasis In The Endoplasmic Reticulum: Road to Cure

The endoplasmic reticulum (ER) is an interconnected organelle that is responsible for the biosynthesis, folding, maturation, stabilization, and trafficking of transmembrane and secretory proteins. Therefore, cells evolve protein quality-control equipment of the ER to ensure protein homeostasis, also termed proteostasis. However, disruption in the folding capacity of the ER caused by a large variety of pathophysiological insults leads to the accumulation of unfolded or misfolded proteins in this organelle, known as ER stress. Upon ER stress, unfolded protein response (UPR) of the ER is activated, integrates ER stress signals, and transduces the integrated signals to relive ER stress, thereby leading to the re-establishment of proteostasis. Intriguingly, severe and persistent ER stress and the subsequently sustained unfolded protein response (UPR) are closely associated with tumor development, angiogenesis, aggressiveness, immunosuppression, and therapeutic response of cancer. Additionally, the UPR interconnects various processes in and around the tumor microenvironment. Therefore, it has begun to be delineated that pharmacologically and genetically manipulating strategies directed to target the UPR of the ER might exhibit positive clinical outcome in cancer. In the present review, we summarize recent advances in our understanding of the UPR of the ER and the UPR of the ER-mitochondria interconnection. We also highlight new insights into how the UPR of the ER in response to pathophysiological perturbations is implicated in the pathogenesis of cancer. We provide the concept to target the UPR of the ER, eventually discussing the potential of therapeutic interventions for targeting the UPR of the ER for cancer treatment.

Mechanisms by which PE21, an extract from the white willow Salix alba, delays chronological aging in budding yeast

We have recently found that PE21, an extract from the white willow Salix alba, slows chronological aging and prolongs longevity of the yeast Saccharomyces cerevisiae more efficiently than any of the previously known pharmacological interventions. Here, we investigated mechanisms through which PE21 delays yeast chronological aging and extends yeast longevity. We show that PE21 causes a remodeling of lipid metabolism in chronologically aging yeast, thereby instigating changes in the concentrations of several lipid classes. We demonstrate that such changes in the cellular lipidome initiate three mechanisms of aging delay and longevity extension. The first mechanism through which PE21 slows aging and prolongs longevity consists in its ability to decrease the intracellular concentration of free fatty acids. This postpones an age-related onset of liponecrotic cell death promoted by excessive concentrations of free fatty acids. The second mechanism of aging delay and longevity extension by PE21 consists in its ability to decrease the concentrations of triacylglycerols and to increase the concentrations of glycerophospholipids within the endoplasmic reticulum membrane. This activates the unfolded protein response system in the endoplasmic reticulum, which then decelerates an age-related decline in protein and lipid homeostasis and slows down an aging-associated deterioration of cell resistance to stress. The third mechanisms underlying aging delay and longevity extension by PE21 consists in its ability to change lipid concentrations in the mitochondrial membranes. This alters certain catabolic and anabolic processes in mitochondria, thus amending the pattern of aging-associated changes in several key aspects of mitochondrial functionality.

SEL1L plays a major role in human malignant gliomas

Suppressor of Lin-12-like (C. elegans) (SEL1L) participates in the endoplasmic reticulum-associated protein degradation pathway, malignant transformation and stem cell biology. We explored the role of SEL1L in 110 adult gliomas, of different molecular subtype and grade, in relation to cell proliferation, stemness, glioma-associated microglia/macrophages (GAMs), prognostic markers and clinical outcome. SEL1L protein expression was assessed by immunohistochemistry and Western blotting. Genetic and epigenetic alterations were detected by molecular genetics techniques. SEL1L was overexpressed in anaplastic gliomas (World Health Organization [WHO] grade III) and in glioblastoma (GB, WHO grade IV) with the highest labelling index (LI) in the latter. Immunoreactivity was significantly associated with histological grade (p = 0.002) and cell proliferation index Ki-67/MIB-1 (p = 0.0001). In GB, SEL1L co-localised with stemness markers Nestin and Sox2. Endothelial cells and vascular pericytes of proliferative tumour blood vessels expressed SEL1L suggesting a role in tumour neo-vasculature. GAMs consistently expressed SEL1L. SEL1L overexpression was significantly associated with TERT promoter mutations (p = 0.0001), EGFR gene amplification (p = 0.0013), LOH on 10q (p = 0.0012) but was mutually exclusive with IDH1/2 mutations (p = 0.0001). SEL1L immunoreactivity correlated with tumour progression and cell proliferation, conditioning poor patient survival and response to therapy. This study emphasises SEL1L as a potential biomarker for the most common subgroup of TERT mutant/EGFR amplified/IDH-WT GBs.

Endoplasmic Reticulum Stress Signaling Pathways: Activation and Diseases

Secretory and membrane proteins are folded in the endoplasmic reticulum (ER) prior to their exit. When ER function is disturbed by exogenous and endogenous factors, such as heat shock, ultraviolet radiation, hypoxia, or hypoglycemia, the misfolded proteins may accumulate, promoting ER stress. To rescue this unfavorable situation, the unfolded protein response is activated to reduce misfolded proteins within the ER. Upon ER stress, the ER transmembrane sensor molecules inositol-requiring enzyme 1 (IRE1), RNA-dependent protein kinase (PKR)-like ER kinase (PERK), and activating transcription factor 6, are activated. Here, we discuss the mechanisms of PERK and IRE1 activation and describe two working models for ER stress initiation: the BiP-dependent model and the ligand-driven model. ER stress activation has been linked to multiple diseases, including cancers, Alzheimer's disease, and diabetes. Thus, the regulation of ER stress may provide potential therapeutic targets for these diseases.

Control of Translation at the Initiation Phase During Glucose Starvation in Yeast

Glucose is one of the most important sources of carbon across all life. Glucose starvation is a key stress relevant to all eukaryotic cells. Glucose starvation responses have important implications in diseases, such as diabetes and cancer. In yeast, glucose starvation causes rapid and dramatic effects on the synthesis of proteins (mRNA translation). Response to glucose deficiency targets the initiation phase of translation by different mechanisms and with diverse dynamics. Concomitantly, translationally repressed mRNAs and components of the protein synthesis machinery may enter a variety of cytoplasmic foci, which also form with variable kinetics and may store or degrade mRNA. Much progress has been made in understanding these processes in the last decade, including with the use of high-throughput/omics methods of RNA and RNA:protein detection. This review dissects the current knowledge of yeast reactions to glucose starvation systematized by the stage of translation initiation, with the focus on rapid responses. We provide parallels to mechanisms found in higher eukaryotes, such as metazoans, for the most critical responses, and point out major remaining gaps in knowledge and possible future directions of research on translational responses to glucose starvation.

Cellular and Molecular Mechanisms in the Pathogenesis of Classical, Vascular, and Hypermobile Ehlers‒Danlos Syndromes

The Ehlers‒Danlos syndromes (EDS) constitute a heterogenous group of connective tissue disorders characterized by joint hypermobility, skin abnormalities, and vascular fragility. The latest nosology recognizes 13 types caused by pathogenic variants in genes encoding collagens and other molecules involved in collagen processing and extracellular matrix (ECM) biology. Classical (cEDS), vascular (vEDS), and hypermobile (hEDS) EDS are the most frequent types. cEDS and vEDS are caused respectively by defects in collagen V and collagen III, whereas the molecular basis of hEDS is unknown. For these disorders, the molecular pathology remains poorly studied. Herein, we review, expand, and compare our previous transcriptome and protein studies on dermal fibroblasts from cEDS, vEDS, and hEDS patients, offering insights and perspectives in their molecular mechanisms. These cells, though sharing a pathological ECM remodeling, show differences in the underlying pathomechanisms. In cEDS and vEDS fibroblasts, key processes such as collagen biosynthesis/processing, protein folding quality control, endoplasmic reticulum homeostasis, autophagy, and wound healing are perturbed. In hEDS cells, gene expression changes related to cell-matrix interactions, inflammatory/pain responses, and acquisition of an in vitro pro-inflammatory myofibroblast-like phenotype may contribute to the complex pathogenesis of the disorder. Finally, emerging findings from miRNA profiling of hEDS fibroblasts are discussed to add some novel biological aspects about hEDS etiopathogenesis.