PERK-mediated Autophagy in Osteosarcoma Cells Resists ER Stress-induced Cell Apoptosis

Bioinformatics analysis identifies potential autophagy key genes and immune infiltration in preeclampsia

BACKGROUND

Preeclampsia (PE) is a disease that seriously threatens maternal and fetal health. Appropriate autophagy can shield the placenta from oxidative stress, but its role in PE is unclear.

OBJECTIVE

To identify potential autophagy-related genes in PE.

METHODS

Microarray datasets from the Gene Expression Omnibus database, compassing the test dataset GSE10588, along with validation datasets GSE4707 and GSE60438 GPL10558, were utilized. Differentially expressed genes (DEGs) were identified using the limma R package, intersected with autophagy-related genes. Hub genes were obtained using the Cytoscape software and analyzed via gene set enrichment analysis (GSEA). The diagnostic capability of hub genes was evaluated using receiver operating characteristic (ROC) curve analysis. Analysis of immune cell infiltration was conducted using single-sample gene set enrichment analysis (ssGSEA) and CIBERSORT methods. Placental tissues were collected from 10 normal pregnant women and 10 preeclamptic pregnant women, and the expression of hub genes was validated through immunohistochemistry and western blot analysis.

RESULTS

Analysis of the microarray data identified 2224 DEGs, among which 26 were autophagy-related DEGs identified through intersection with autophagy genes. Ten hub genes were identified. Immune cell infiltration analysis suggested the potential involvement of T regulatory cells (Tregs), natural killer cells, neutrophils, and T follicular helper cells in the pathogenesis of PE. ROC curve analysis indicated promising diagnostic capabilities for EGFR and TP53. Additionally, levels of EGFR and TP53 were significantly higher in placental tissue from PE pregnancies compared to normal pregnancies.

CONCLUSION

EGFR and TP53 may play a role in PE by influencing autophagy.

Targeting PERK-ATF4-P21 axis enhances the sensitivity of osteosarcoma HOS cells to Mppα-PDT

Osteosarcoma (OS) is the most prevalent type of malignant bone tumor in adolescents. The overall survival of OS patients has reached a plateau recently. Thus, there is an urgent need to develop approaches to improve the sensitivity of OS to therapies. Pyropheophorbide-α methyl ester-mediated photodynamic therapy (MPPα-PDT) is a new type of tumor therapy, and elucidating its mechanism is helpful to improve its anti-tumor efficacy. Here, we investigated how PERK signaling promotes the human OS (HOS) cell survival induced by MPPα-PDT, as overcoming this may enhance sensitivity to MPPα-PDT. We found that MPPα-PDT combined with PERK inhibitor GSK2656157 enhanced HOS cell apoptosis by suppressing autophagy and p21. Autophagy inhibition and p21 depletion enhanced cell death, indicating pro-survival effects in MPPα-PDT. Notably, p21 was found to be an effector of the PERK-Atf4 pathway, which could positively regulate autophagy mediated by MPPα-PDT. In conclusion, we found that the combination of MPPα-PDT and GSK2656157 enhanced apoptosis in HOS cells by inhibiting autophagy. Mechanistically, this autophagy is p21-dependent and can be suppressed by GSK2656157, thereby enhancing sensitivity to MPPα-PDT.

Synergistic apoptosis by combination of metformin and an O-GlcNAcylation inhibitor in colon cancer cells

BACKGROUND

Although autophagy is an important mediator of metformin antitumor activity, the role of metformin in the crosstalk between autophagy and apoptosis remains unclear. The aim was to confirm the anticancer effect by inducing apoptosis by co-treatment with metformin and OSMI-1, an inhibitor of O-GlcNAcylation, in colon cancer cells.

METHODS

Cell viability was measured by MTT in colon cancer cell lines HCT116 and SW620 cells. Co-treatment with metformin and OSMI-1 induced autophagy and apoptosis, which was analyzed using western blot, reverse transcription-polymerase chain reaction (RT-PCR) analysis, and fluorescence-activated cell sorting (FACS). Combined treatment with metformin and OSMI-1 synergistically inhibit the growth of HCT116 was confirmed by xenograft tumors.

RESULTS

We showed that metformin inhibited mammalian target of rapamycin (mTOR) activity by inducing high levels of C/EBP homologous protein (CHOP) expression through endoplasmic reticulum (ER) stress and activating adenosine monophosphate-activated protein kinase (AMPK) to induce autophagy in HCT116 cells. Interestingly, metformin increased O-GlcNAcylation and glutamine:fructose-6-phosphate amidotransferase (GFAT) levels in HCT116 cells. Thus, metformin also blocks autophagy by enhancing O-GlcNAcylation, whereas OSMI-1 increases autophagy via ER stress. In contrast, combined metformin and OSMI-1 treatment resulted in continuous induction of autophagy and disruption of O-GlcNAcylation homeostasis, resulting in excessive autophagic flux, which synergistically induced apoptosis. Downregulation of Bcl2 promoted apoptosis via the activation of c-Jun N-terminal kinase (JNK) and CHOP overexpression, synergistically inducing apoptosis. The activation of IRE1α/JNK signaling by OSMI-1 and PERK/CHOP signaling by metformin combined to inhibit Bcl2 activity, ultimately leading to the upregulation of cytochrome c release and activation of caspase-3.

CONCLUSIONS

In conclusion, combinatorial treatment of HCT116 cells with metformin and OSMI-1 resulted in more synergistic apoptosis being induced by enhancement of signal activation through ER stress-induced signaling rather than the cell protective autophagy function. These results in HCT116 cells were also confirmed in xenograft models, suggesting that this combination strategy could be utilized for colon cancer treatment.

Crosstalk between endoplasmic reticulum stress response and autophagy in human diseases

Cells activate protective mechanisms to overcome stressful conditions that threaten cellular homeostasis, including imbalances in calcium, redox, and nutrient levels. Endoplasmic reticulum (ER) stress activates an intracellular signaling pathway, known as the unfolded protein response (UPR), to mitigate such circumstances and protect cells. Although ER stress is sometimes a negative regulator of autophagy, UPR induced by ER stress typically activates autophagy, a self-degradative pathway that further supports its cytoprotective role. Sustained activation of ER stress and autophagy is known to trigger cell death and is considered a therapeutic target for certain diseases. However, ER stress-induced autophagy can also lead to treatment resistance in cancer and exacerbation of certain diseases. Since the ER stress response and autophagy affect each other, and the degree of their activation is closely related to various diseases, understanding their relationship is very important. In this review, we summarize the current understanding of two fundamental cellular stress responses, the ER stress response and autophagy, and their crosstalk under pathological conditions to help develop therapies for inflammatory diseases, neurodegenerative disorders, and cancer.

Propofol Regulates ER Stress to Inhibit Tumour Growth and Sensitize Osteosarcoma to Doxorubicin

Osteosarcoma is the most common malignant bone tumour affecting children and young adults. The antitumour role of propofol, a widely used intravenous sedative-hypnotic agent, has been recently reported in different cancer types. In this study, we aimed to assess the role of propofol on osteosarcoma and explore the possible mechanisms. Propofol of increasing concentrations (2.5, 5, 10, and 20 μg/ml) was used to treat the MG63 and 143B cells for 72 hours, and the CCK8 assay was applied to evaluate the tumour cell proliferation. Tumour cell migration and invasion were assessed with the transwell assay. The tumour cells were also treated with doxorubicin single agent or in combination with propofol to explore their synergic role. Differential expressed genes after propofol treatment were obtained and functionally assessed with bioinformatic tools. Expression of ER stress markers CHOP, p-eIF2α, and XBP1s was evaluated to validate the activation of ER stress response with western blot and qRT-PCR. The statistical analyses were performed with R v4.2.1. Propofol treatment led to significant growth inhibition in MG63 and 143B cells in a dose-dependent manner (p < 0.05). Osteosarcoma migration (MG63 91.4 (82-102) vs. 56.8 (49-65), p < 0.05; 143B 96.6 (77-104) vs. 45.4 (28-54), p < 0.05) and invasion (MG63 68.6 (61-80) vs. 32 (25-39), p < 0.05; 143B 90.6 (72-100) vs. 39.2 (26-55), p < 0.05) were reduced after propofol treatment. Doxorubicin sensitivity was increased after propofol treatment compared with the control group (p < 0.05). Bioinformatic analysis showed significant functional enrichment in ER stress response after propofol treatment. Upregulation of CHOP, p-eIF2α, and XBP1s was detected in MG63 and 143B secondary to propofol treatment. In conclusion, we found that propofol treatment suppressed osteosarcoma proliferation and invasion and had a synergic role with doxorubicin by inducing ER stress. Our findings provided a novel option in osteosarcoma therapy.

Mechanism and Role of Endoplasmic Reticulum Stress in Osteosarcoma

Osteosarcoma is the most common malignant bone tumor, often occurring in children and adolescents. The etiology of most patients is unclear, and the current conventional treatment methods are chemotherapy, radiotherapy, and surgical resection. However, the sensitivity of osteosarcoma to radiotherapy and chemotherapy is low, and the prognosis is poor. The development of new and useful treatment strategies for improving patient survival is an urgent need. It has been found that endoplasmic reticulum (ER) stress (ERS) affects tumor angiogenesis, invasion, etc. By summarizing the literature related to osteosarcoma and ERS, we found that the unfolded protein response (UPR) pathway activated by ERS has a regulatory role in osteosarcoma proliferation, apoptosis, and chemoresistance. In osteosarcoma, the UPR pathway plays an important role by crosstalk with autophagy, oxidative stress, and other pathways. Overall, this article focuses on the relationship between ERS and osteosarcoma and reviews the potential of drugs or gene targets associated with ERS for the treatment of osteosarcoma.

Canonical and Noncanonical ER Stress-Mediated Autophagy Is a Bite the Bullet in View of Cancer Therapy

Cancer cells adapt multiple mechanisms to counter intense stress on their way to growth. Tumor microenvironment stress leads to canonical and noncanonical endoplasmic stress (ER) responses, which mediate autophagy and are engaged during proteotoxic challenges to clear unfolded or misfolded proteins and damaged organelles to mitigate stress. In these conditions, autophagy functions as a cytoprotective mechanism in which malignant tumor cells reuse degraded materials to generate energy under adverse growing conditions. However, cellular protection by autophagy is thought to be complicated, contentious, and context-dependent; the stress response to autophagy is suggested to support tumorigenesis and drug resistance, which must be adequately addressed. This review describes significant findings that suggest accelerated autophagy in cancer, a novel obstacle for anticancer therapy, and discusses the UPR components that have been suggested to be untreatable. Thus, addressing the UPR or noncanonical ER stress components is the most effective approach to suppressing cytoprotective autophagy for better and more effective cancer treatment.

Unfolded Protein Response-Related Signature Associates With the Immune Microenvironment and Prognostic Prediction in Osteosarcoma

Background: Osteosarcoma is a highly malignant bone tumor commonly occurring in adolescents with a poor 5-year survival rate. The unfolded protein response (UPR) can alleviate the accumulation of misfolded proteins to maintain homeostasis under endoplasmic reticulum stress. The UPR is linked to the occurrence, progression, and drug resistance of tumors. However, the function of UPR-related genes (UPRRGs) in disease progression and prognosis of osteosarcoma remains unclear.

Methods: The mRNA expression profiling and corresponding clinical features of osteosarcoma were acquired from TARGET and GEO databases. Consensus clustering was conducted to confirm different UPRRG subtypes. Subsequently, we evaluated the prognosis and immune status of the different subtypes. Functional analysis of GO, GSEA, and GSVA was used to reveal the molecular mechanism between the subtypes. Finally, four genes (STC2, PREB, TSPYL2, and ATP6V0D1) were screened to construct and validate a risk signature to predict the prognosis of patients with osteosarcoma.

Result: We identified two subtypes according to the UPRRG expression patterns. The subgroup with higher immune scores, lower tumor purity, and active immune status was linked to a better prognosis. Meanwhile, functional enrichment revealed that immune-related signaling pathways varied markedly in the two subtypes, suggesting that the UPR might influence the prognosis of osteosarcoma via influencing the immune microenvironment. Moreover, prognostic signature and nomogram models were developed based on UPRRGs, and the results showed that our model has an excellent performance in predicting the prognosis of osteosarcoma. qPCR analysis was also conducted to verify the expression levels of the four genes.

Conclusion: We revealed the crucial contribution of UPRRGs in the immune microenvironment and prognostic prediction of osteosarcoma patients and provided new insights for targeted therapy and prognostic assessment of the disease.

Deciphering the Pharmacological Mechanisms of Qidan Dihuang Decoction in Ameliorating Renal Fibrosis in Diabetic Nephropathy through Experimental Validation In Vitro and In Vivo

OBJECTIVE

QiDan DiHuang decoction (QDD) has been proven to have good efficacy in decreasing albuminuria levels, improving renal function, and inhibiting renal fibrosis in diabetic nephropathy (DN). However, the potential mechanism remains unclear. The purpose of this study was to explore the underlying mechanism of QDD for treating DN in vitro and in vivo.

METHODS

Db/db mice were treated with QDD or saline intragastrically for 12 weeks. Non-diabetic db/m mice were used as controls. Rat renal tubular epithelial cells (NRK-52E) were cultured in high glucose conditions. ATF4 siRNA was transfected into NRK-52E cells. Different indicators were detected via UPLC, RT-PCR, western blotting, cell viability assays and apoptosis, transmission electron microscopy, histology, and immunofluorescence staining.

RESULTS

Db/db mice experienced severe kidney damage and fibrosis, increased levels of PERK, eIF2α, and ATF4, and suppression of renal autophagy compared with db/m mice. The results showed a significant improvement in glucose intolerance, blood urea nitrogen, urine albumin, serum creatinine, and renal fibrosis in db/db mice with QDD treatment. Meanwhile, the application of QDD resulted in the downregulation of PERK, eIF2α, and ATF4 and the upregulation of autophagy in diabetic kidneys. In vitro, the exposure of NRK-52E cells to high glucose resulted in downregulation of the ratio of LC3-II/LC3-I and upregulation of P62, a reduction in the number of autophagosomes and upregulation of fibronectin (FN), collagen IV and TGF-β1 protein, which was reversed by QDD treatment through inhibiting ATF4 expression.

CONCLUSIONS

Taken together, our results suggest that QDD effectively alleviates diabetic renal injuries and fibrosis by inhibiting the PERK-eIF2α-ATF4 pathway and promoting autophagy in diabetic nephropathy.

Chondrocyte-derived Exosomal miR-195 Inhibits Osteosarcoma Cell Proliferation and Anti-Apoptotic by Targeting KIF4A in vitro and in vivo

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Osteosarcoma (OS) chemoresistance and distant metastasis are directly associated with OS recurrence and dismal patient prognosis, which are serious concerns for the medical community.

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However, current knowledge on OS pathogenesis and treatment remains limited. We found that kinesin superfamily protein 4A (KIF4A) acts as a potential OS biomarker.

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KIF4A promoted OS cell proliferation and anti-apoptotic in vitro and enhanced tumor growth in vivo. Our results indicate that miR-195 inhibits the expression of KIF4A by directly targeting its 3’-untranslated region

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Hence, targeting KIF4A could be a novel therapeutic strategy for OS and miR-195 may be a potential KIF4A-targeting drug. Furthermore, this study demonstrates that normal human chondrocytes can be used to produce miR-195-carrying exosomes to successfully deliver miR-195 into OS cells.

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Thus, our results suggest that chondrocyte-derived exosomal miR-195 may be developed into a potential adjuvant chemotherapeutic drug.

Background

Osteosarcoma (OS) is a primary malignant tumor of the bone that occurs in adolescents and is characterized by a young age at onset, high malignancy, high rate of metastasis, and poor prognosis. However, the factors influencing disease progression and prognosis remain unclear.

Methods

In this study, we aimed to investigate the role of chondrocyte-derived exosomal miR-195 in OS. We used normal human chondrocytes to form miR-195-carrying exosomes to deliver miR-195 into OS cells. Xenograft tumor experiments were performed in mice intratumorally injected with exosomal miR-195. We found that kinesin superfamily protein 4A (KIF4A) promoted OS tumor progression and anti-apoptotic.

Resules

We demonstrated that miR-195 inhibited the expression of KIF4A by directly targeting its 3’-untranslated region. Moreover, we observed that exosomal miR-195 successfully inhibited OS cell tumor growth and antiapoptotic in vitro and suppressed tumor growth in vivo.

Conclusion

Collectively, these results demonstrate that normal human chondrocyte-derived exosomal miR-195 can be internalized by OS cells and inhibit tumor growth and antiapoptotic by targeting KIF4A, providing a new direction for clarifying the molecular mechanism underlying OS development.

Reciprocal regulation between ER stress and autophagy in renal tubular fibrosis and apoptosis

Both endoplasmic reticulum (ER) stress and autophagy have been implicated in chronic kidney injury and renal fibrosis. However, the relationship and regulatory mechanisms between ER stress and autophagy under this condition remain largely unknown. In this study, we first established a mouse model of ER stress-induced chronic kidney injury by 2 weekly injections of a low dose of tunicamycin (TM), a classical ER stress inducer. This model showed the induction of ER stress, autophagy, fibrosis and apoptosis in kidney tissues. In vitro, TM also induced ER stress, autophagy, fibrosis and apoptosis in HK-2 human kidney proximal tubular cells and BUMPT-306 mouse kidney proximal tubular cells. In these cells, autophagy inhibitor suppressed TM-induced fibrotic changes and apoptosis, suggesting an involvement of autophagy in ER stress-associated chronic kidney injury. PERK inhibitor ameliorated autophagy, fibrotic protein expression and apoptosis in TM-treated cells, indicating a role of the PERK/eIF2α pathway in autophagy activation during ER stress. Similar results were shown in TGF-β1-treated HK-2 cells. Interestingly, in both TM- or TGF-β1-treated kidney proximal tubular cells, inhibition of autophagy exaggerated ER stress, suggesting that autophagy induced by ER stress provides a negative feedback mechanism to reduce the stress. Together, these results unveil a reciprocal regulation between ER stress and autophagy in chronic kidney injury and fibrosis.

Co-delivery of doxorubicin and paclitaxel by reduction/pH dual responsive nanocarriers for osteosarcoma therapy

Nanoparticle-based drug delivery system offers a promising platform for combination cancer therapy. However, the inefficient drug release in cells reduces the therapeutic efficacy of cancer nanomedicines. Herein, a PEGylated poly(α-lipoic acid) copolymer (mPEG-PαLA) was prepared and used as a reduction/pH dual responsive nanocarrier to simultaneously deliver paclitaxel (PTX) and doxorubicin (DOX) for osteosarcoma therapy. The amphiphilic mPEG-PαLA could efficiently encapsulate both PTX and DOX during its self-assembly into micelles in aqueous solution to generate PTX and DOX co-loaded nanoparticles (NP-PTX-DOX). The as-prepared NP-PTX-DOX showed enhanced PTX and DOX release in response to reductive and acidic stimuli. Moreover, the dual-drug loaded nanoparticles were efficiently internalized by K7 osteosarcoma cells and released drugs intracellularly, as confirmed by flow cytometry analysis and confocal laser scanning microscopy. Consequently, NP-PTX-DOX exhibited synergistic therapeutic effects and induced enhanced cell apoptosis in K7 cells. Furthermore, NP-PTX-DOX presented improved biodistribution and higher tumor growth inhibition efficacy compared to the control groups in a murine osteosarcoma model. Altogether, the results of this work indicate that the proposed strategy is promising for osteosarcoma therapy using mPEG-PαLA copolymer as a dual-responsive nanocarrier to co-deliver anticancer drugs.

ER Stress-Sensor Proteins and ER-Mitochondrial Crosstalk-Signaling Beyond (ER) Stress Response

Recent studies undoubtedly show the importance of inter organellar connections to maintain cellular homeostasis. In normal physiological conditions or in the presence of cellular and environmental stress, each organelle responds alone or in coordination to maintain cellular function. The Endoplasmic reticulum (ER) and mitochondria are two important organelles with very specialized structural and functional properties. These two organelles are physically connected through very specialized proteins in the region called the mitochondria-associated ER membrane (MAM). The molecular foundation of this relationship is complex and involves not only ion homeostasis through the shuttling of calcium but also many structural and apoptotic proteins. IRE1alpha and PERK are known for their canonical function as an ER stress sensor controlling unfolded protein response during ER stress. The presence of these transmembrane proteins at the MAM indicates its potential involvement in other biological functions beyond ER stress signaling. Many recent studies have now focused on the non-canonical function of these sensors. In this review, we will focus on ER mitochondrial interdependence with special emphasis on the non-canonical role of ER stress sensors beyond ER stress.

Autophagy Regulation by the Translation Machinery and Its Implications in Cancer

Various metabolic pathways and molecular processes in the cell act intertwined, and dysregulating the interplay between some of them may lead to cancer. It is only recently that defects in the translation process, i.e., the synthesis of proteins by the ribosome using a messenger (m)RNA as a template and translation factors, have begun to gain strong attention as a cause of autophagy dysregulation with effects in different maladies, including cancer. Autophagy is an evolutionarily conserved catabolic process that degrades cytoplasmic elements in lysosomes. It maintains cellular homeostasis and preserves cell viability under various stress conditions, which is crucial for all eukaryotic cells. In this review, we discuss recent advances shedding light on the crosstalk between the translation and the autophagy machineries and its impact on tumorigenesis. We also summarize how this interaction is being the target for novel therapies to treat cancer.

Manganese activates autophagy to alleviate endoplasmic reticulum stress-induced apoptosis via PERK pathway

Overexposure to manganese (Mn) is neurotoxic. Our previous research has demonstrated that the interaction of endoplasmic reticulum (ER) stress and autophagy participates in the early stage of Mn‐mediated neurotoxicity in mouse. However, the mechanisms of ER stress signalling pathways in the initiation of autophagy remain confused. In the current study, we first validated that ER stress–mediated cell apoptosis is accompanied by autophagy in SH‐SY5Y cells. Then, we found that inhibiting ER stress with 4‐phenylbutyrate (4‐PBA) decreased ER stress–related protein expression and reduced cell apoptosis, whereas blocking autophagy with 3‐methyladenine (3‐MA) increased cell apoptosis. These data indicate that protective autophagy was activated to alleviate ER stress–mediated apoptosis. Knockdown of the protein kinase RNA‐like ER kinase (PERK) gene inhibited Mn‐induced autophagy and weakened the interaction between ATF4 and the LC3 promoter. Our results reveal a novel molecular mechanism in which ER stress may regulate autophagy via the PERK/eIF2α/ATF4 signalling pathway. Additionally, Mn may activate protective autophagy to alleviate ER stress–mediated apoptosis via the PERK/eIF2α/ATF4 signalling pathway in SH‐SY5Y cells.

The Inflammatory Bowel Disease Drug Azathioprine Induces Autophagy via mTORC1 and the Unfolded Protein Response Sensor PERK

BACKGROUND

Genetic studies have strongly linked autophagy to Crohn's disease (CD), and stimulating autophagy in CD patients may be therapeutically beneficial. The aim of this study was to evaluate the effect of current inflammatory bowel disease (IBD) drugs on autophagy and investigate molecular mechanisms of action and functional outcomes in relation to this cellular process.

METHODS

Autophagy marker LC3 was evaluated by confocal fluorescence microscopy and flow cytometry. Drug mechanism of action was investigated by polymerase chain reaction (PCR) array with changes in signaling pathways examined by immunoblot and quantitative reverse transcription PCR (RT-qPCR). Clearance of adherent-invasive Escherichia coli (AIEC) and levels of pro-inflammatory cytokine tumor necrosis factor alpha (TNFα) were evaluated by gentamicin protection assays and RT-qPCR, respectively. The marker LC3 was analyzed in peripheral blood mononuclear cells (PBMCs) from pediatric patients by flow cytometry.

RESULTS

Azathioprine induces autophagy via mechanisms involving modulation of mechanistic target of rapamycin (mTORC1) signaling and stimulation of the unfolded protein response (UPR) sensor PERK. Induction of autophagy with azathioprine correlated with the enhanced clearance of AIEC and dampened AIEC-induced increases in TNFα. Azathioprine induced significant increase in autophagosome bound LC3-II in PBMC populations ex vivo, supporting in vitro findings. In patients, the CD-associated ATG16L1 T300A single-nucleotide polymorphism did not attenuate azathioprine induction of autophagy.

CONCLUSIONS

Modulation of autophagy via mTORC1 and the UPR may contribute to the therapeutic efficacy of azathioprine in IBD.

Regulation of PERK expression by FOXO3: a vulnerability of drug-resistant cancer cells

The major impediment to effective cancer therapy has been the development of drug resistance. The tumour suppressive transcription factor FOXO3 promotes cell cycle arrest, senescence and cell death, and mediates the cytotoxic and cytostatic functions of cancer therapeutics. In consequence, FOXO3 is often downregulated as an adaptive response in cancer and particularly in chemotherapeutic drug-resistant cells. Consistently, we find that FOXO3 expression is attenuated in the drug-resistant MCF-7-Epi^R and MCF-7-Tax^R compared to the parental MCF-7 breast cancer cells. Using ChIP, short-interfering RNA (siRNA) knockdown, and overexpression assays as well as Foxo^1/3/4-/- MEFs, we establish the endoplasmic reticulum (ER)-stress defence modulator PERK (eIF2AK3) as a direct downstream transcriptional target of FOXO3. In agreement, there is also a positive correlation between FOXO3 and PERK expression at the protein and RNA levels in breast cancer patient samples. We uncover that PERK expression is downregulated but its activity constitutively elevated in the drug-resistant cells. With this in mind, we exploit this adaptive response of low FOXO3 and PERK expression, and high PERK activity in drug-resistant breast cancer cells and show that these drug-resistant cells are specifically sensitive to PERK inhibition. In support of this finding, we show that ectopic overexpression of FOXO3 can reduce the sensitivity of the resistant cells to the PERK inhibitor GSK2606414, while the Foxo^1/3/4-/- MEFs expressing lower levels of PERK are more sensitive to PERK inhibition compared to wild-type MEFs. PERK inhibitor-titration and -time course experiments showed that the drug-resistant cells, which express lower expression and higher activity levels of PERK, are more sensitive to the increasing concentrations of PERK inhibitor compared to parental MCF-7 cells. Our present work thus reveals a chemotherapeutic drug-resistant cancer cell vulnerability in PERK and suggests PERK as a potential target for cancer therapy, specifically in the context of drug-resistant cancers.

ATF6α Activation Enhances Survival against Chemotherapy and Serves as a Prognostic Indicator in Osteosarcoma

Patients with metastatic or relapsed/refractory osteosarcoma (OS) have a 5-year survival rate of <30%. This has remained unchanged over several decades. One of the factors contributing to lack of improvement in survival is the development of chemoresistance. Hence, elucidating and targeting the mechanisms that promote survival against chemotherapy and lead to chemoresistance is pivotal to improving outcomes for these patients. We identified that endoplasmic reticulum (ER) stress-activated transcription factor, ATF6α, is essential for the survival of OS cells against chemotherapy induced cell death. ATF6α cleavage and activity were enhanced in OS cells compared to normal osteoblasts and knockdown of ATF6α expression enhanced sensitivity of OS cells against chemotherapy induced cell death. This was in part due to increased Bax activation. Pharmacologic inhibition or knock-down of downstream targets of ATF6α, protein disulfide isomerases (PDI) and ERO1β, a thiol oxidase that is involved in the re-oxidation of PDIs also independently induced pronounced killing of OS cells following chemotherapy. Analysis of primary tumors from OS patients reveals that patients with high levels of nuclear ATF6α: (1) also had increased expression of its downstream targets the chaperone BiP and enzyme PDI, (2) had a significant likelihood of developing metastasis at diagnosis, (3) had significantly poorer overall and progression free survival, and (4) had poorer response to chemotherapy. These findings suggest that targeting survival signaling by the ATF6α pathway in OS cells may favor eradication of refractory OS tumor cells and ATF6α could be a useful predictor for chemo-responsiveness and prognosis.

Interactions Between Autophagy and the Unfolded Protein Response: Implications for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis, is characterized by chronic inflammation of the gastrointestinal tract. The etiology involves a combination of genetic and environmental factors resulting in abnormal immune responses to intestinal microbiota. Genetic studies have strongly linked genes involved in autophagy to CD, and genes involved in the unfolded protein response (UPR) to IBD. The UPR is triggered in response to accumulation of misfolded proteins in the endoplasmic reticulum (ER), and autophagy plays a key role in relieving ER stress and restoring homeostasis. This review summarizes the known interactions between autophagy and the UPR and discusses the impact of these converging pathways on IBD pathogenesis. With a paucity of effective long-term treatments for IBD, targeting of synergistic pathways may provide novel and more effective therapeutic options.

Activation of PERK-eIF2α-ATF4-CHOP axis triggered by excessive ER stress contributes to lead-induced nephrotoxicity

Lead (Pb) is a known nephrotoxicant that causes damage to proximal tubular cells. PERK pathway plays an important role in the pathogenesis of renal diseases, but its role in Pb-induced nephrotoxicity remains largely unknown. In this study, data showed that Pb could induce ER stress as shown by increased phosphorylation of PERK with subsequent activation of the eIF2α-ATF4-CHOP axis in primary rat proximal tubular (rPT) cells, indicating the activation of PERK-eIF2α-ATF4-CHOP pathway due to excessive ER stress. Pb-activated PERK pathway can be effectively inhibited by 4-phenylbutyric acid and PERK gene silencing, respectively; whereas continuously up-regulated by tunicamycin (TM) treatment. Moreover, Pb-induced apoptosis and inhibition of autophagic flux in rPT cells were significantly augmented and aggravated by co-treatment with TM, respectively. Pharmacological or genetic inhibition of the PERK pathway results in alleviation of apoptosis and restoration of autophagy inhibition in Pb-exposed rPT cells. Mechanistically, activation of PERK-eIF2α-ATF4-CHOP axis triggered by excessive ER stress in rPT cells leads to Pb-induced apoptosis and blockage of autophagic flux, resulting in nephrotoxicity.

Chaperone-Mediated Autophagy Promotes Beclin1 Degradation in Persistently Infected Hepatitis C Virus Cell Culture

Liver cirrhosis is an independent risk factor for hepatocellular carcinoma (HCC). The mechanisms that contribute to HCC development in the cirrhotic microenvironment are unknown. We found that HCC grown in the highly stressed cirrhotic microenvironment undergoes autophagy switching from a protective state characterized by high macroautophagy with low chaperone-mediated autophagy (CMA) to an HCC-promoting state characterized by low macroautophagy with high CMA. This study examined how the stress response executes oncogenic cell programming through autophagy switching using hepatitis C virus cell culture. Protein kinase R-like endoplasmic reticulum kinase expression increased to high levels in hepatitis C virus culture. Protein kinase R-like endoplasmic reticulum kinase-dependent activation of nuclear factor erythroid 2-related factor (Nrf2) led to increased transcription of the cytoprotective genes: heat shock cognate 70 kDa protein and lysosome-associated membrane protein 2A (LAMP2A) and precipitated the induction of CMA. CMA selectively targeted beclin1 degradation, leading to accumulation of the autophagy flux protein p62 due to impaired autophagosome-endosome fusion. This impaired autophagosome-endosome fusion due to beclin1 degradation inhibited endocytosis and degradation of epidermal growth factor receptor. Silencing Nrf2 and LAMP2A reduced cell viability, suggesting that the stress response activates CMA as a compensatory mechanism of cell survival. We report a novel mechanism through which stress response triggers oncogenic Nrf2 signaling that promotes autophagy switching to favor cell survival.

Panobinostat mediated cell death: a novel therapeutic approach for osteosarcoma

Osteosarcoma is an aggressive cancer with a poor long term prognosis. Neo-adjuvant poly-chemotherapy followed by surgical resection remains the standard treatment, which is restricted by multi-drug resistance. If first-line therapy fails, disease control and patient survival rate drop dramatically. We aimed to identify alternative apoptotic mechanisms induced by the histone deacetylase inhibitor panobinostat in osteosarcoma cells. Saos-2, MG63 and U2-OS osteosarcoma cell lines, the immortalized human osteoblast line hFOB and the mouse embryo osteoblasts (MC3T3-E1) were treated with panobinostat. Real time viability and FACS confirmed the cytotoxicity of panobinostat. Cell stress/death related factors were analysed by RT-qPCR and western blot. Cell morphology was assessed by electron microscopy. 10 nM panobinostat caused cell viability arrest and death in all osteosarcoma and osteoblast cells. P21 up-regulation was observed in osteosarcoma cells, while over-expression of p73 was restricted to Saos-2 (TP53^-/-). Survivin and Bcl-2 were suppressed by panobinostat. Endoplasmic reticulum (ER) stress markers BiP, CHOP, ATF4 and ATF6 were induced in osteosarcoma cells. The un-spliced Xbp was no further detectable after treatment. Autophagy players Beclin1, Map1LC3B and UVRAG transcripts over-expressed after 6 hours. Protein levels of Beclin1, Map1LC3B and p62 were up-regulated at 72 hours. DRAM1 was stable. Electron micrographs revealed the fragmentation and the disappearance of the ER and the statistically significant increase of autophagosome vesiculation after treatment. Panobinostat showed a synergistic suppression of survival and promotion of cell death in osteosarcoma cells. Panobinostat offers new perspectives for the treatment of osteosarcoma and other malignant bone tumours.

Trichostatin A reverses the chemoresistance of lung cancer with high IGFBP2 expression through enhancing autophagy

Insulin-like growth factor (IGF) signaling plays an important role in tumorigenesis and metastasis. Here, we analyzed insulin-like growth factor (IGF) binding protein-2 (IGFBP2) expression in 81 lung cancer patients and 36 controls consisting of healthy and benign pulmonary lesion participants for comparison, then validated the IGFBP2 expression in additional 84 lung cancer patients, and evaluated the prognostic and chemoresistant significance of IGFBP2 in two cohorts respectively. Next we detected the reversal effect of trichostatin A (TSA) on chemoresistance in cell lines with high IGFBP2 expression. As a result, the mean expression of IGFBP2 in lung cancer patients was significantly higher than that in controls and increased with lung cancer progressed to advanced stage. In addition, high IGFBP2 expression was independently predictive for chemoresistance; over-expressed IGFBP2 enhances cell activity and TSA can reverse the chemoresistance induced by high IGFBP2 expression through enhancing autophagy. Furthermore, multivariate analysis showed that lung cancer patients whose blood IGFBP2 was higher had a poor survival outcome, with a hazard ratio of 8.22 (95%CI 1.78–37.92, P = 0.007) after adjustment for stage, histopathology, EGFR mutation, age, smoking and surgery.

Induction of ER and mitochondrial stress by the alkylphosphocholine erufosine in oral squamous cell carcinoma cells

Endoplasmic reticulum (ER) plays an essential role in cell function and survival. Accumulation of unfolded or misfolded proteins in the lumen of the ER activates the unfolded protein response (UPR), resulting in ER stress and subsequent apoptosis. The alkylphosphocholine erufosine is a known Akt-mTOR inhibitor in oral squamous cell carcinoma (OSCC). In the present study, we evaluate erufosine’s role to induce ER and mitochondrial stress leading to autophagy, apoptosis, and ROS induction. The cellular toxicity of erufosine was determined in two OSCC cell lines and gene expression and enrichment analyses were performed. A positive enrichment of ER stress upon erufosine exposure was observed, which was verified at protein levels for the ER stress sensors and their downstream mediators. Knockdown and pharmacological inhibition of the ER stress sensors PERK and XBP1 revealed their involvement into erufosine’s cellular effects, including proliferation, apoptosis, and autophagy induction. Autophagy was confirmed by increased acidic vacuoles and LC3-B levels. Upon erufosine exposure, calcium influx into the cytoplasm of the two OSCC cell lines was seen. Apoptosis was confirmed by nuclear staining, Annexin-V, and immunoblotting of caspases. The induction of mitochondrial stress upon erufosine exposure was predicted by gene set enrichment analysis (GSEA) and shown by erufosine’s effect on mitochondrial membrane potential, ATP, and ROS production in OSCC cells. These data show that ER and mitochondrial targeting by erufosine represents a new facet of its mechanism of action as well as a promising new framework in the treatment of head and neck cancers.

Activation of endoplasmic reticulum stress promotes autophagy and apoptosis and reverses chemoresistance of human small cell lung cancer cells by inhibiting the PI3K/AKT/mTOR signaling pathway

OBJECTIVE

This study aims to investigate the effects of endoplasmic reticulum stress (ERS) on autophagy, apoptosis and chemoresistance of human small cell lung cancer (SCLC) cells via the PI3K/AKT/mTOR signaling pathway.

RESULTS

The expressions of ERS-related proteins (PEAK, eIF2α and CHOP) up-regulated, autophagy-related proteins (LC3, LC3-II and Beclin1) and apoptosis-related proteins (Bax and procaspase-3) down-regulated in NCI-H446 and H69 cells after tunicamycin treatment for 24 h. Compared with the blank group, the tunicamycin, BEZ235 and tunicamycin + BEZ235 groups exhibited decreased expressions of p-PI3K, p-AKT and p-mTOR, and increased expressions of autophagy-related proteins (LC3, LC3-II and Beclin1) and apoptosis proteins (Bax and procaspase-3), and the most obvious changes were observed in the tunicamycin + BEZ235 group.

MATERIALS AND METHODS

CCK-8 assay was applied to select the best cell line from five SCLC cell lines (NCI-H446, H69, H526, H146 and H209). Finally, NCI-H446 and H69 cells were selected for further experiments. NCI-H446/CDDP and H69/CDDP were selected and divided into the blank group, tunicamycin (an ESR inducer) group, BEZ235 (inhibitors of PI3K/AKT/mTOR pathway) group and tunicamycin + BEZ235 group. Cell apoptosis was detected by flow cytometry. Autophagy was observed by fluorescence microscopy and flow cytometry. Western blotting was used to detect the expressions of ERS-related proteins, autophagy-related proteins, apoptosis-related proteins and PI3K/AKT/mTOR pathway-related proteins.

CONCLUSIONS

Our findings provide evidence that the activation of ERS could promote autophagy and apoptosis and reverse chemoresistance of human SCLC cells by inhibiting the PI3K/AKT/mTOR pathway.

The protective autophagy activated by GANT-61 in MYCN amplified neuroblastoma cells is mediated by PERK

The proto-oncogene MYC can trigger the unfolded protein response (UPR). The double-stranded RNA-activated protein kinase-like endoplasmic reticulum kinase (PERK), one of three primary branches of the UPR, is a key regulator of autophagy, promoting tumorigenesis. Upon activation of PERK, there is an increase in phosphorylation of the eukaryotic initiation factor-2 alpha (eIF2α), which in turn, activates the transcription factor-4 (ATF4), responsible for an increased expression of LC3, a common autophagy marker. PERK is repressed upon GLI1 and GLI2 induction. GANT-61 is an inhibitor of GLI1 and GLI2, known to reduce autophagy in MYCN non-amplified, but not in MYCN amplified neuroblastoma (NB) cells. In our study, we tested the effect of the joint administration of a PERK inhibitor (GSK2606414) and the GLI inhibitor GANT-61 to MYCN amplified and MYCN non-amplified NB cells. Our results suggest that inhibition of PERK impairs GANT-61 induced autophagy in NB cells with MYCN amplification, but had no effect on the MYCN non-amplified NB cells. In summary, PERK seems to be a good therapeutic target for NB. Inhibition of PERK reduces autophagy in MYCN amplified NB cells, thus amplifying the efficacy of the GLI inhibitor GANT-61 in reducing proliferation of this type of cancer cells.

Ctenopharyngodon idella PERK (EIF2AK3) decreases cell viability by phosphorylating eIF2α under ER stress

As an upstream kinase of eIF2α, protein kinase RNA-like ER (endoplasmic reticulum) kinase (PERK) is a type I transmembrane protein located in ER in eukaryotic cells. PERK is mainly composed of two domains, the intracavitary domain for BIP protein combination and the dissociative C-terminal region containing a typical serine/threonine kinase domain which promotes the phosphorylation of eIF2α. In this study, we cloned a PERK (also known as EIF2AK3) gene from grass carp (Ctenopharyngodon idella). The full-length cDNA of grass carp PERK (CiPERK) is 5192 bp including a 176 bp of 5' untranslated region, a 1719 bp of 3' untranslated region and a 3297 bp of the longest open reading frame (ORF) encoding 1098 amino acids. Phylogenetic analysis exhibits that CiPERK shares a high degree of sequence homology to the counterparts in other teleosts. RT-PCR indicated that CiPERK expression was significantly up-regulated following the stimulation with TM (tunicamycin). To study the function of CiPERK, the N-terminal sequence of CiPERK and CiGRP78 sequence were separately subcloned into the expression vectors pCMV-HA and pCMV-Flag for co-immunoprecipitation and GST-Pulldown assays. The assays indicated that CiPERK and CiGRP78 can combine with each other in normal conditions. However, under ER stress (TM stimulation) CiPERK can improve the eIF2α phosphorylation level. In addition, CCK assay showed the overexpression of CiPERK in CIK cells decreases the cell viability.

Identification of 4-arylidene curcumin analogues as novel proteasome inhibitors for potential anticancer agents targeting 19S regulatory particle associated deubiquitinase

The proteasomal 19S regulatory particle (RP) associated deubiquitinases (DUBs) have attracted much attention owing to their potential as a therapeutic target for cancer therapy. Identification of new entities against 19S RP associated DUBs and illustration of the underlying mechanisms is crucial for discovery of novel proteasome blockers. In this study, a series of 4-arylidene curcumin analogues were identified as potent proteasome inhibitor by preferentially blocking deubiquitinase function of proteasomal 19S RP with moderate 20S CP inhibition. The most active compound 33 exhibited a major inhibitory effect on 19S RP-associated ubiquitin-specific proteases 14, along with a minor effect on ubiquitin C-terminal hydrolase 5, which resulted in dysfunction of proteasome, and subsequently accumulated ubiquitinated proteins (such as IκB) in several cancer cells. Remarkably, though both 19S RP and 20S CP inhibition induced significantly endoplasmic reticulum stress and triggered caspase-12/9 pathway activation to promote cancer cell apoptosis, the 19S RP inhibition by 33 avoided slow onset time, Bcl-2 overexpression, and PERK-phosphorylation, which contribute to the deficiencies of clinical drug Bortezomib. These systematic studies provided insights in the development of novel proteasome inhibitors for cancer treatment.

Enhanced Stim1 expression is associated with acquired chemo-resistance of cisplatin in osteosarcoma cells

Osteosarcoma is the most common primary malignant bone tumor. Although cisplatin is the primary chemotherapy used in osteosarcoma treatment, the cisplatin resistance remains a big challenge for improving overall survival. The store-operated calcium (Ca²⁺) entry (SOCE) and its major mediator Stim1 have been shown to be implicated in a number of pathological processes typical for cancer. In this study, we showed that Stim1 expression was significantly increased in chemo-resistant osteosarcoma tissues compared with chemo-sensitivity tissues. Patients with Sitm1 expression exhibited poorer overall survival than Stim1-negative patients. Moreover, un-regulation of Stim1 expression and SOCE were also observed in cisplatin-resistant MG63/CDDP cells compared with their parental cells. Cisplatin treatment obviously reduced Stim1 expression and SOCE in cisplatin-sensitivity MG63 cells, but had no effects on MG63/CDDP cells. In addition, cisplatin resulted in a more pronounced increase of endoplasmic reticulum (ER) stress in MG63 cells than in their resistant variants, which was evidenced by the activation of molecular markers of ER stress, GRP78, CHOP and ATF4. Knockdown of Stim1 using siRNA remarkably enhanced cisplatin-induced apoptosis and ER stress in MG63/CDDP cells, thereby sensitizing cancer cells to cisplatin. On the other hand, overexpression of Stim1 markedly reversed apoptosis and ER stress following cisplatin treatment. Taken together, these results demonstrate that Stim1 as well as Ca²⁺ entry contributes cisplatin resistance via inhibition of ER stress-mediated apoptosis, and provide important clues to the mechanisms involved in cisplatin resistance for osteosarcoma treatment. Stim1 represents as a target of cisplatin and blockade of Stim1-mediated Ca²⁺ entry may be a useful strategy to improve the efficacy of cisplatin to treat osteosarcoma.

Defective autophagy leads to the suppression of stem-like features of CD271+ osteosarcoma cells

Background

As an important stress-response mechanism, autophagy plays crucial role in the tumor formation and drug resistance of cancer cells including osteosarcoma (OS). OS cancer stem cells (CSCs) also are considered a key factor of tumorigenesis, drug resistance and tumor recurrence. However, the relationship between autophagy and OS CSCs still remains unclear.

Methods

CD271+ OS CSCs and CD271- OS cells were isolated by magnetic activated cell sorting. The autophagy level was evaluated by the mRNA expression of autophagy genes, the protein level of LC3II and p62, and the mean number of GFP-LC3 dot per cell. Lentivirus-delivered specific shRNA was utilized to inhibit the corresponding gene expression. The cell viability was examined with CCK8 assay. The cell proliferation level was detected with BrdU staining assay. Cell death was determined by Annexin V/PI double staining of fluorescence activated cell sorting, lactate dehydrogenase release and caspase-3 activity. Tumorigenicity ability was evaluated by colony and sphere formation assay, the protein expression of stemness markers and tumor formation in nude mice.

Results

Our data indicated that CD271+ OS CSCs had a similar basic autophagy level with CD271- OS cells. Autophagy deficiency had no observable effects on the levels of cell proliferation and death both in CD271+ and CD271- OS cells under normal condition. However, CD271+ OS cells showed a higher autophagy activity than CD271- OS cells under hypoxia and low nutrient (LH) condition. Moreover, autophagy-deficient CD271+ OS cells lost the advantage of tolerance to LH condition compared to CD271- OS cells. Meanwhile, autophagy deficiency enhanced the sensitivity to chemotherapeutics in the CD271+ cells to the comparable level in the CD271- cells. More importantly, deficient-autophagy decreased the protein expression of stemness markers and caused the disappearance of the superiority in tumorigenicity in vitro and vivo in CD271+ OS cells.

Conclusion

The results above demonstrated that autophagy contributes to the stem-like features of CD271+ OS CSCs. Inhibition of autophagy is a promising strategy in the CSCs-targeting OS therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-016-0297-5) contains supplementary material, which is available to authorized users.

Cell apoptosis, autophagy and necroptosis in osteosarcoma treatment

Osteosarcoma is the most common primary bone tumor in children and adolescents. Although combined therapy including surgery and multi-agent chemotherapy have resulted in great improvements in the overall survival of patients, chemoresistance remains an obstacle for the treatment of osteosarcoma. Molecular targets or effective agents that are actively involved in cell death including apoptosis, autophagy and necroptosis have been studied. We summarized how these agents (novel compounds, miRNAs, or proteins) regulate apoptotic, autophagic and necroptotic pathways; and discussed the current knowledge on the role of these new agents in chemotherapy resistance in osteosarcoma.

A novel mechanism of mTORC1-mediated serine/glycine metabolism in osteosarcoma development

Osteosarcoma is the major malignant primary bone cancer in children and adolescents, which is highly aggressive with frequent acquisition of chemoresistance phenotypes. Although much progress has been made, mechanisms of osteosarcoma rapid growth and chemoresistance are still not well elucidated. Generally, alternated metabolic characterization has been proposed to be a hallmark of cancer, yet it is lack of a systematic characterization of cancer metabolic networks. In the present study, we aim to characterize osteosarcoma metabolism and key regulators to reveal mechanisms of how osteosarcoma grows and resists apoptosis under stress conditions. The results demonstrate that mTORC1 pathway is hyperactivated in clinical osteosarcoma samples. However, inhibition of mTORC1 may not be enough to induce significant death of osteosarcoma cells. Results of GC-TOFMS suggested that inhibition of mTORC1 reduce one-carbon amino acids, serine and glycine, in osteosarcoma cells. Moreover, mTORC1 regulates serine/glycine de novo synthesis via modulating glycolysis and serine/glycine synthesis gene expressions. Further, mTORC1/serine/glycine metabolic axis promotes osteosarcoma proliferation and antioxidant ability to environmental stress, which finally leads to cell survival. Our results identify a novel mechanism of mTORC1-mediated serine/glycine metabolism as a significant protective system in osteosarcoma cells.