Activation of JNK and IRE1 is critically involved in tanshinone I-induced p62 dependent autophagy in malignant pleural mesothelioma cells: implication of p62 UBA domain

A Cross-Talk about Radioresistance in Lung Cancer-How to Improve Radiosensitivity According to Chinese Medicine and Medicaments That Commonly Occur in Pharmacies

Lung cancer is one of the most common cancers in the population and is characterized by non-specific symptoms that delay the diagnosis and reduce the effectiveness of oncological treatment. Due to the difficult placement of the tumor, one of the main methods of lung cancer treatment is radiotherapy, which damages the DNA of cancer cells, inducing their apoptosis. However, resistance to ionizing radiation may develop during radiotherapy cycles, leading to an increase in the number of DNA points of control that protect cells from apoptosis. Cancer stem cells are essential for radioresistance, and due to their ability to undergo epithelial-mesenchymal transition, they modify the phenotype, bypassing the genotoxic effect of radiotherapy. It is therefore necessary to search for new methods that could improve the cytotoxic effect of cells through new mechanisms of action. Chinese medicine, with several thousand years of tradition, offers a wide range of possibilities in the search for compounds that could be used in conventional medicine. This review introduces the potential candidates that may present a radiosensitizing effect on lung cancer cells, breaking their radioresistance. Additionally, it includes candidates taken from conventional medicine-drugs commonly available in pharmacies, which may also be significant candidates.

Tanshinone I: Pharmacological activities, molecular mechanisms against diseases and future perspectives

BACKGROUND

Tanshinone I (Tan I) is known as one of the important active components in Salvia miltiorrhiza. In recent years, Tan I has received a substantial amount of attention from the research community for various studies being updated and has been shown to possess favorable activities including anti-oxidative stress, regulation of cell autophagy or apoptosis, inhibition of inflammation, etc. PURPOSE: To summarize the investigation progress on the anti-disease efficacy and effect mechanism of Tan I in recent years, and provide perspectives for future study on the active ingredient.

METHOD

Web of Science and PubMed databases were used to search for articles related to "Tanshinone I" published from 2010 to 2022. Proteins or genes and signaling pathways referring to Tan I against diseases were summarized and classified along with its different therapeutic actions. Protein-protein interaction (PPI) analysis was then performed, followed by molecular docking between proteins with high node degree and Tan I, as well as bioinformactic analysis including GO, KEGG and DO enrichment analysis with the collected proteins or genes.

RESULTS

Tan I shows multiple therapeutic effects, including protection of the cardiovascular system, anti-cancer, anti-inflammatory, anti-neurodegenerative diseases, etc. The targets (proteins or genes) affected by Tan I against diseases involve Bcl-2, Bid, ITGA2, PPAT, AURKA, VEGF, PI3K, AKT, PRK, JNK, MMP9, ABCG2, CASP3, Cleaved-caspase-3, AMPKα, PARP, etc., and the regulatory pathways refer to Akt/Nrf2, SAPK/JNK, PI3K/Akt/mTOR, JAK/STAT3, ATF-2/ERK, etc. What's more, AKT1, CASP3, and STAT3 were predicted as the key action targets for Tan I by PPI analysis combined with molecular docking, and the potential therapeutic effects mechanisms against diseases were also further predicted by bioinformatics analyses based on the reported targets, providing new insights into the future investigation and helping to facilitate the drug development of Tan I.

Recent advances of tanshinone in regulating autophagy for medicinal research

Initially described as an ancient and highly conserved catabolic biofunction, autophagy plays a significant role in disease pathogenesis and progression. As the bioactive ingredient of Salvia miltiorrhiza, tanshinone has recently shown profound effects in alleviating and treating various diseases by regulating autophagy. However, compared to the remarkable achievements in the known pharmacological effects of this traditional Chinese medicine, there is a lack of a concise and comprehensive review deciphering the mechanism by which tanshinone regulates autophagy for medicinal research. In this context, we concisely review the advances of tanshinone in regulating autophagy for medicinal research, including human cancer, the nervous system, and cardiovascular diseases. The pharmacological effects of tanshinone targeting autophagy involve the regulation of autophagy-related proteins, such as Beclin-1, LC3-II, P62, ULK1, Bax, ATG3, ATG5, ATG7, ATG9, and ATG12; the regulation of the PI3K/Akt/mTOR, MEK/ERK/mTOR, Beclin-1-related, and AMPK-related signaling pathways; the accumulation of reactive oxygen species (ROS); and the activation of AMPK. Notably, we found that tanshinone played a dual role in human cancers in an autophagic manner, which may provide a new avenue for potential clinical application. In brief, these findings on autophagic tanshinone and its derivatives provide a new clue for expediting medicinal research related to tanshinone compounds and autophagy.

Neuronal IRE-1 coordinates an organism-wide cold stress response by regulating fat metabolism

Cold affects many aspects of biology, medicine, agriculture, and industry. Here, we identify a conserved endoplasmic reticulum (ER) stress response, distinct from the canonical unfolded protein response, that maintains lipid homeostasis during extreme cold. We establish that the ER stress sensor IRE-1 is critical for resistance to extreme cold and activated by cold temperature. Specifically, neuronal IRE-1 signals through JNK-1 and neuropeptide signaling to regulate lipid composition within the animal. This cold-response pathway can be bypassed by dietary supplementation with unsaturated fatty acids. Altogether, our findings define an ER-centric conserved organism-wide cold stress response, consisting of molecular neuronal sensors, effectors, and signaling moieties, which control adaptation to cold conditions in the organism. Better understanding of the molecular basis of this stress response is crucial for the optimal use of cold conditions on live organisms and manipulation of lipid saturation homeostasis, which is perturbed in human pathologies.

Tanshinone I regulates autophagic signaling via the activation of AMP-activated protein kinase in cancer cells

Tanshinone I, one of the components of Salvia miltiorrhiza Bunge, exhibits anti-tumor ability and induces autophagy. But the mechanisms are not fully understood. This study aims to investigate whether AMP-activated protein kinase dependent pathway is involved in the autophagic signaling regulation and its relationship with tumor suppression. Breast cancer cells (MDA-MB-231, MCF-7) and hepatocellular carcinoma cells (HepG2) were treated with Tanshinone I or vehicle. Acridine orange dyeing and transmission electron microscopy were employed to evaluate autophagic cells. MTT and Cell Counting Kit-8 assays were used to detect the effect of Tanshinone I combined with autophagy inhibitors on cell proliferation. Western blot was used to detect the expression levels of Beclin1 and LC3-I/II, as well as the phosphorylation of AMPKα and ULK1. Our results showed that Tanshinone I suppressed proliferation of HepG2, MDA-MB-231 and MCF-7 cancer cell lines. LC3-II and P62 were induced by Tanshinone I in all three cancer cell lines. But autophagic flux analysis showed that Tanshinone I treatment induced autophagy only in MDA-MB-231, which was also proved by transmission electron microscopy. Tanshinone I upregulated the phosphorylation of AMPKα and its downstream ULK1. AMP-activated protein kinase inhibitor compound C attenuated Beclin 1 and LC3-II expression induced by Tanshinone I in HepG2. In MDA-MB-231, compound C surprisingly induced LC3-II upregulation which is independent of AMPKα activation. Under this circumstance, treatment of Tanshinone I combined with compound C significantly inhibited MDA-MB-231 proliferation, compared with Tanshinone I treatment alone. This study demonstrates that Tanshinone I could induce cancer cell death and regulate autophagy signaling in breast cancer and hepatic carcinoma cells. Activation of AMPKα was found to be involved in autophagic signaling regulation by Tanshinone I.

Artemisia annua L. Polyphenol-Induced Cell Death Is ROS-Independently Enhanced by Inhibition of JNK in HCT116 Colorectal Cancer Cells

c-Jun N-terminal kinase (JNK) is activated by chemotherapeutic reagents including natural plant polyphenols, and cell fate is determined by activated phospho-JNK as survival or death depending on stimuli and cell types. The purpose of this study was to elucidate the role of JNK on the anticancer effects of the Korean plant Artemisia annua L. (pKAL) polyphenols in p53 wild-type HCT116 human colorectal cancer cells. Cell morphology, protein expression levels, apoptosis/necrosis, reactive oxygen species (ROS), acidic vesicles, and granularity/DNA content were analyzed by phase-contrast microscopy; Western blot; and flow cytometry of annexin V/propidium iodide (PI)-, dichlorofluorescein (DCF)-, acridine orange (AO)-, and side scatter pulse height (SSC-H)/DNA content (PI)-stained cells. The results showed that pKAL induced morphological changes and necrosis or late apoptosis, which were associated with loss of plasma membrane/Golgi integrity, increased acidic vesicles and intracellular granularity, and decreased DNA content through downregulation of protein kinase B (Akt)/β-catenin/cyclophilin A/Golgi matrix protein 130 (GM130) and upregulation of phosphorylation of H2AX at Ser-139 (γ-H2AX)/p53/p21/Bak cleavage/phospho-JNK/p62/microtubule-associated protein 1 light chain 3B (LC3B)-I. Moreover, JNK inhibition by SP600125 enhanced ROS-independently pKAL-induced cell death through downregulation of p62 and upregulation of p53/p21/Bak cleavage despite a reduced state of DNA damage marker γ-H2AX. These findings indicate that phospho-JNK activated by pKAL inhibits p53-dependent cell death signaling and enhances DNA damage signaling, but cell fate is determined by phospho-JNK as survival rather than death in p53 wild-type HCT116 cells.

Tanshinone I induces cell apoptosis by reactive oxygen species-mediated endoplasmic reticulum stress and by suppressing p53/DRAM-mediated autophagy in human hepatocellular carcinoma

Human hepatocellular carcinoma (HCC) is the most common type of liver cancer, and it has a high mortality rate. Despite surgical treatments, radiotherapy, and chemotherapy, the median survival of patients with advanced HCC is low. Evidence has shown that tanshinone (TA) I exhibits anti-proliferative activity against numerous cancers. However, the role of TA I and its mechanism in HCC remain unknown. Here, we determined the anti-cancer potential of TA I against HCC cell lines HepG2 and Huh7. Cell viability was analyzed using a Cell Counting Kit-8 assay. Flow cytometry was used to analyze cell cycles and apoptosis. Western blotting was used to detect protein expression and phosphorylation levels. TA I was found to inhibit cell proliferation, induce G0/G1 phase arrest, and trigger apoptosis in HepG2 and Huh7 cells. We further explored the molecular mechanism of TA I-mediated apoptosis. Our results showed that TA I induced G0/G1 phase arrest through downregulation of cyclin D1 expression and upregulation of p21 expression. TA I induced cell apoptosis via reactive oxygen species-mediated endoplasmic reticulum stress and by inhibiting p53/damage-regulated autophagy modulator (DRAM)-mediated autophagy in HepG2 and Huh7 cells. Therefore, TA I may be an anti-cancer drug candidate in the treatment of HCC.

New vistas in malignant mesothelioma: MicroRNA architecture and NRF2/MAPK signal transduction

Malignant mesothelioma (MM) is a cancer of the mesothelial lining of the pleura, peritoneum, pericardium and testes. The most common form is asbestos-linked MM that is etiologically linked to repeated asbestos exposure with a long latency period, although non-asbestos MM has also been reported. Late diagnosis, poor survival rates, lack of diagnostic and prognostic markers act as major impediments in the clinical management of MM. Despite advances in immune checkpoint inhibition and CAR T-cell-based therapies, MM which is of different histologic subtypes remains challenging to treat. We review microRNAs (miRNAs) and the miRNA interactome implicated in MM which can be useful as circulating miRNA biomarkers for early diagnosis of MM and as biomarkers for prognostication in MM. Further, we underscore the relevance of the NRF2/MAPK signal transduction pathway that has been implicated in MM which may be useful as druggable targets or as biomarkers of predictive response. In addition, since MM is driven partly by inflammation, we elucidate chemopreventive phytochemicals that are beneficial in MM, either via crosstalk with the NRF2/MAPK pathway or via concerted anticancer mechanisms, and may be of benefit as adjuvants in chemotherapy. Taken together, a multifactorial approach comprising identification of miRNA target hubs and NRF2/MAPK biomarkers along with appropriately designed clinical trials may enable early detection and faster intervention in MM translating into better patient outcomes for this aggressive cancer.

Forced expression of miR-143 and -145 in cardiomyocytes induces cardiomyopathy with a reductive redox shift

BACKGROUND

Animal model studies show that reductive stress is involved in cardiomyopathy and myopathy, but the exact physiological relevance remains unknown. In addition, the microRNAs miR-143 and miR-145 have been shown to be upregulated in cardiac diseases, but the underlying mechanisms associated with these regulators have yet to be explored.

METHODS

We developed transgenic mouse lines expressing exogenous miR-143 and miR-145 under the control of the alpha-myosin heavy chain (αMHC) promoter/enhancer.

RESULTS

The two transgenic lines showed dilated cardiomyopathy-like characteristics and early lethality with markedly increased expression of miR-143. The expression of hexokinase 2 (HK2), a cardioprotective gene that is a target of miR-143, was strongly suppressed in the transgenic hearts, but the in vitro HK activity and adenosine triphosphate (ATP) content were comparable to those observed in wild-type mice. In addition, transgenic complementation of HK2 expression did not reduce mortality rates. Although HK2 is crucial for the pentose phosphate pathway (PPP) and glycolysis, the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) was unexpectedly higher in the hearts of transgenic mice. The expression of gamma-glutamylcysteine synthetase heavy subunit (γ-GCSc) and the in vitro activity of glutathione reductase (GR) were also higher, suggesting that the recycling of GSH and its de novo biosynthesis were augmented in transgenic hearts. Furthermore, the expression levels of glucose-6-phosphate dehydrogenase (G6PD, a rate-limiting enzyme for the PPP) and p62/SQSTM1 (a potent inducer of glycolysis and glutathione production) were elevated, while p62/SQSTM1 was upregulated at the mRNA level rather than as a result of autophagy inhibition. Consistent with this observation, nuclear factor erythroid-2 related factor 2 (Nrf2), Jun N-terminal kinase (JNK) and inositol-requiring enzyme 1 alpha (IRE1α) were activated, all of which are known to induce p62/SQSTM1 expression.

CONCLUSIONS

Overexpression of miR-143 and miR-145 leads to a unique dilated cardiomyopathy phenotype with a reductive redox shift despite marked downregulation of HK2 expression. Reductive stress may be involved in a wider range of cardiomyopathies than previously thought.

Inhibition on JNK Mimics Silencing of Wnt-11 Mediated Cellular Response in Androgen-Independent Prostate Cancer Cells

Prostate cancer (PCa) is one of the most common cancers among men, and one of the leading causes of cancer death for men. The c-Jun N-terminal kinase (JNK) pathway is required for several cellular functions, such as survival, proliferation, differentiation, and migration. Wnt-11, a member of the Wnt family, has been identified for its upregulation in PCa; however, downstream signalling of Wnt-11 remains to be fully characterized. In this study, we investigated the role of the JNK pathway as a potential downstream factor for Wnt-11 signalling. For this purpose, LNCaP, DU145, and PC-3 PCa cells and normal epithelial PNT1A cells were treated with a specific JNK kinase inhibitor: JNKVIII. Our results showed that JNK inhibition decreased mitochondrial membrane potential and promoted cell death in a cell type-dependent manner. We found that JNK inhibition led to an increase in autophagy and prevented epithelial–mesenchymal transition (EMT) in independently growing androgen cells. JNK inhibition and the silencing of Wnt-11 showed similar responses in DU145 and PC-3 cells and decreased metastasis-related biomarkers, cell migration, and invasion. Overall, our results suggest that JNK signalling plays a significant role in the pathophysiology of PCa by mediating Wnt-11 induced signals. Our data highlights that both the JNK pathway and Wnt-11 could be a useful therapeutic target for the combinatory application of current PCa.

An overview of the anti-cancer actions of Tanshinones, derived from Salvia miltiorrhiza (Danshen)

Tanshinone is a herbal medicinal compound described in Chinese medicine, extracted from the roots of Salvia miltiorrhiza (Danshen). This family of compounds, including Tanshinone IIA and Tanshinone I, have shown remarkable potential as anti-cancer molecules, especially against breast, cervical, colorectal, gastric, lung, and prostate cancer cell lines, as well as leukaemia, melanoma, and hepatocellular carcinoma among others. Recent data has indicated that Tanshinones can modulate multiple molecular pathways such as PI3K/Akt, MAPK and JAK/STAT3, and exert their pharmacological effects against different malignancies. In addition, preclinical and clinical data, together with the safety profile of Tanshinones, encourage further applications of these compounds in cancer therapeutics. In this review article, the effect of Tanshinones on different cancers, challenges in their pharmacological development, and opportunities to harness their clinical potential have been documented.

L-Ascorbic Acid Inhibits Breast Cancer Growth by Inducing IRE/JNK/CHOP-Related Endoplasmic Reticulum Stress-Mediated p62/SQSTM1 Accumulation in the Nucleus

Anticancer effects of L-ascorbic acid (Vitamin C, L-AA) have been reported in various types of cancers. L-AA intake reduces breast cancer recurrence and mortality; however, the role of L-AA in the treatment of breast cancer remains poorly understood. In this study, we investigated the effect and mechanism action of L-AA on breast cancer growth. L-AA inhibited the growth of breast cancer cells by inducing apoptotic cell death at the evaluated treatment concentrations without affecting normal cells. Moreover, L-AA induces autophagosome formation via regulation of mammalian target of rapamycin (mTOR), Beclin1, and autophagy-related genes (ATGs) and increased autophagic flux. Notably, we observed that L-AA increased p62/SQSTM1 (sequestosome 1) protein levels. Accumulation of p62 protein in cancer cells in response to stress has been reported, but its role in cancer regulation remains controversial. Here, we demonstrated that L-AA-induced p62 accumulation is related to L-AA-induced breast cancer growth inhibition. Furthermore, L-AA induced endoplasmic reticulum (ER) stress via the IRE–JNK–CHOP (inositol-requiring endonuclease–c-Jun N-terminal kinase–C/EBP homologous protein) signaling pathways, which increased the nuclear levels of p62/SQSTM1. These findings provide evidence that L-AA-induced ER stress could be crucial for p62 accumulation-dependent cell death, and L-AA can be useful in breast cancer treatment.

Naturally occurring anti-cancer compounds: shining from Chinese herbal medicine

Numerous natural products originated from Chinese herbal medicine exhibit anti-cancer activities, including anti-proliferative, pro-apoptotic, anti-metastatic, anti-angiogenic effects, as well as regulate autophagy, reverse multidrug resistance, balance immunity, and enhance chemotherapy in vitro and in vivo. To provide new insights into the critical path ahead, we systemically reviewed the most recent advances (reported since 2011) on the key compounds with anti-cancer effects derived from Chinese herbal medicine (curcumin, epigallocatechin gallate, berberine, artemisinin, ginsenoside Rg3, ursolic acid, silibinin, emodin, triptolide, cucurbitacin B, tanshinone I, oridonin, shikonin, gambogic acid, artesunate, wogonin, β-elemene, and cepharanthine) in scientific databases (PubMed, Web of Science, Medline, Scopus, and Clinical Trials). With a broader perspective, we focused on their recently discovered and/or investigated pharmacological effects, novel mechanism of action, relevant clinical studies, and their innovative applications in combined therapy and immunomodulation. In addition, the present review has extended to describe other promising compounds including dihydroartemisinin, ginsenoside Rh2, compound K, cucurbitacins D, E, I, tanshinone IIA and cryptotanshinone in view of their potentials in cancer therapy. Up to now, the evidence about the immunomodulatory effects and clinical trials of natural anti-cancer compounds from Chinese herbal medicine is very limited, and further research is needed to monitor their immunoregulatory effects and explore their mechanisms of action as modulators of immune checkpoints.

SP600125 enhances C-2-induced cell death by the switch from autophagy to apoptosis in bladder cancer cells

BACKGROUND

A natural compound Jaspine B and its derivative possess potential anti-cancer activities; However, little is known about the underlying mechanism. Here, the role of a new autophagy inducer Jaspine B derivative C-2 in suppressing bladder cancer cells was researched in vitro and in vivo.

METHODS

The underlying mechanisms and anticancer effect of C-2 in bladder cancer cells were investigated by MTT, western blotting, immunoprecipitation and immunofluorescence assays. The key signaling components were investigated by using pharmacological inhibitors or specific siRNAs. In vivo, we designed a C-2 and SP600125 combination experiment to verify the effectiveness of compound.

RESULTS

C-2 exhibits cytotoxic effect on bladder cancer cells, and JNK activated by C-2 triggers autophagy and up-regulates SQSTM1/p62 proteins, contributing to activation of Nrf2 pathway. Utilization of JNK inhibitor SP600125 or knockdown of JNK by siRNA potentiate the cytotoxicity of C-2 through down-regulation of p62 and LC3II proteins and up-regulation of active-Caspase3 proteins, enhance the cell death effect, facilitating the switch from autophagy to apoptosis. In vivo study, C-2 suppresses tumor growth in a xenograft mouse model of EJ cells without observed toxicity. Combined treatment with SP600125 further enhances tumor inhibition of C-2 associated with enhanced activation of caspase3 and reduction of autophagy.

CONCLUSIONS

It reveals a series of molecular mechanisms about SP600125 potentiate the cytotoxicity and tumor inhibition of C-2 in bladder cancer cells through promoting C-2-induced apoptosis, expecting it provides research basis and theoretical support for new drugs development.

Cadmium-mediated miR-30a-GRP78 leads to JNK-dependent autophagy in chicken kidney

Cadmium-mediated microRNAs have become a heavily researched topic. Few studies mention the regulation of autophagy by cadmium through microRNAs, especially regarding poultry. The kidney is one of the organs most severely affected by cadmium, as it is involved in the accumulation of metal ions; causing such types of damage as apoptosis, necrosis and autophagy to the body. However, the relationship between miR-30a and GRP78 in the chicken kidney during ER stress and autophagy via JNK has not been thoroughly elucidated to date. In our research, we randomly assigned 128 Hy-Line Brown laying chickens to four groups with different diet treatments. The four groups consisted of the control group (0.2 mg Se kg-1), the Se group (2 mg kg-1 of Na₂SeO₃), the Se + Cd group (150 mg kg-1 of CdCl₂ and 2 mg kg-1 of Na₂SeO₃) and the Cd group (150 mg kg-1 of CdCl₂). On the 90th day, we detected the expression of miR-30a, GRP78, ER stress-related genes, IRE-1-JNK and autophagy-related genes. Compared with the control group, the mRNA levels of IRE-1-JNK, ER stress-related genes, autophagy-related genes and GRP78 were significantly increased (P < 0.05), while the expression of miR-30a was significantly decreased (p < 0.05) in the Cd group. However, those changes were clearly alleviated in the Se + Cd group (p < 0.05). In summary, we demonstrated that Cd triggered an miR-30a-GRP78 signaling axis disorder, increasing ER stress and activating the IRE-1-JNK pathway, thereby promoting autophagy in the chicken kidney. Moreover, Se could antagonize the negative impact of Cd.

Effect and Mechanism of Tanshinone I on the Radiosensitivity of Lung Cancer Cells

BACKGROUND

Resistance to radiotherapy is one of the main obstacles to improving cancer prognoses. To effectively destroy cancer cells, novel radiation sensitizers are needed. Recently, several natural products have been shown to exhibit promising tumor-killing properties. However, little is known about the specific mechanisms of these natural compounds on cancer treatment. In this study, after screening a high-throughput natural product library, we identified tanshinone I (Tan I) as a potential radiation sensitizer in lung cancer cells.

METHODS

Lung cancer radioresistant cell lines, H358-IR and H157-IR, were first established to confirm the radioresistant phenotypes. After that, a natural product library was used to screen the potential radiation sensitizer. We further examined the inhibition functions of Tan I on radioresistant cancer cells via a series of experiments.

RESULTS

Tan I significantly inhibited cell proliferation and clone formation, consequently enhancing radiosensitivity in radioresistant lung cancer cells, H358-IR and H157-IR. Stable isotope labeling of amino acids in cell culture (SILAC)-based quantitative proteomics indicated that Tan I downregulates expression of pro-oncogenic protein phosphoribosyl pyrophosphate aminotransferase (PPAT) in both H358-IR and H157-IR cells. Further analysis of molecular docking showed that Tan I is well-docked into the active pocket of the structure of PPAT, serving as a potential PPAT inhibitor.

CONCLUSIONS

Taken together, these findings suggest that inhibition of the tumor promoter PPAT by Tan I exerts marked inhibitory effects on radioresistant lung cancer cells, improving radiation efficacy.

Glucocorticoid-activated IRE1α/XBP-1s signaling: an autophagy-associated protective pathway against endotheliocyte damage

Glucocorticoid-induced endothelial injury has been reported in several diseases. Although there are several theories, the exact mechanism underlying the role of glucocorticoids in this process remains unclear. Autophagy has been reported to occur as a response to different stimuli and can affect cell survival and function. In this study, we found that glucocorticoids induced apoptosis and endoplasmic reticulum (ER) stress in endotheliocytes. Furthermore, we discovered that glucocorticoids induced autophagy in these cells and the inositol requiring protein 1 (IRE1α)/X-box binding protein 1s (XBP-1s) axis, one of the downstream signaling pathways of ER stress, was associated with the glucocorticoid-induced autophagy. The autophagy partly protected endotheliocytes from glucocorticoid-induced apoptosis and inhibition of proliferation. In conclusion, glucocorticoid-induced endoplasmic reticulum stress activated the IRE1α/XBP-1s signaling and induced autophagy, which, in turn, played a protective role in endotheliocyte survival and proliferation, avoiding further cellular damage caused by glucocorticoids.

Monitoring autophagic flux using p62/SQSTM1 based luciferase reporters in glioma cells

Autophagy is a highly dynamic process characterized with the term of autophagic flux. In the present study, we developed a quantifiable luciferase reporter system to measure the capacity as well as the dynamics of autophagic flux. Briefly, a luciferase variant of Luc2p was fused with p62/SQSTM1 or its UBA domain deletion mutant (p62ΔU) and transfected into cells. The expressed Luc2p-p62 fusion protein was primarily degraded via autophagy, while Luc2p-p62ΔU was employed as a normalization control due to its resistance to autophagic degradation. The luciferase activity of the lysates from two parallel populations of glioma cells expressing either Luc2p-p62 or Luc2p-p62ΔU was determined and the ratio of Luc2p-p62ΔU/Luc2p-p62 was used to assay the autophagic flux. By this approach, the induction of autophagy was manifested as an increased Luc2p-p62ΔU/Luc2p-p62 ratio, which could be neutralized by autophagy inhibitors or knockdown of ATG5. The performance of our autophagic flux detection system was comparable to a recently reported GFP-LC3-RFP-LC3ΔG probe. We tested the system in TMZ treated glioma cells, and found that coadministration of chloroquine to attenuate cellular autophagic flux significantly improved the TMZ efficacy by triggering more early apoptosis. Collectively, our luciferase-based autophagic flux assay may serve as a useful alternative yet sensitive method for autophagic flux detection in tumor cells.