Lysosome vacuolation disrupts the completion of autophagy during norephedrine exposure in SH-SY5Y human neuroblastoma cells

18β-glycyrrhetinic acid promotes gastric cancer cell autophagy and inhibits proliferation by regulating miR-328-3p/signal transducer and activator of transcription 3

BACKGROUND

Gastric cancer (GC) is one of the most common cancer types worldwide, and its prevention and treatment methods have garnered much attention. As the active ingredient of licorice, 18β-glycyrrhetinic acid (18β-GRA) has a variety of pharmacological effects. The aim of this study was to explore the effective target of 18β-GRA in the treatment of GC, in order to provide effective ideas for the clinical prevention and treatment of GC.

AIM

To investigate the mechanism of 18β-GRA in inhibiting cell proliferation and promoting autophagy flux in GC cells.

METHODS

Whole transcriptomic analyses were used to analyze and screen differentially expressed microRNAs (miRNAs) in GC cells after 18β-GRA intervention. Lentivirus-transfected GC cells and the Cell Counting Kit-8 were used to detect cell proliferation ability, cell colony formation ability was detected by the clone formation assay, and flow cytometry was used to detect the cell cycle and apoptosis. A nude mouse transplantation tumor model of GC cells was constructed to verify the effect of miR-328-3p overexpression on the tumorigenicity of GC cells. Tumor tissue morphology was observed by hematoxylin and eosin staining, and microtubule-associated protein light chain 3 (LC3) expression was detected by immunohistochemistry. TransmiR, STRING, and miRWalk databases were used to predict the relationship between miR-328-3p and signal transducer and activator of transcription 3 (STAT3)-related information. Expression of STAT3 mRNA and miR-328-3p was detected by quantitative polymerase chain reaction (qPCR) and the expression levels of STAT3, phosphorylated STAT3 (p-STAT3), and LC3 were detected by western blot analysis. The targeted relationship between miR-328-3p and STAT3 was detected using the dual-luciferase reporter gene system. AGS cells were infected with monomeric red fluorescent protein-green fluorescent protein-LC3 adenovirus double label. LC3 was labeled and autophagy flow was observed under a confocal laser microscope.

RESULTS

The expression of miR-328-3p was significantly upregulated after 18β-GRA intervention in AGS cells (P = 4.51E-06). Overexpression of miR-328-3p inhibited GC cell proliferation and colony formation ability, arrested the cell cycle in the G0/G1 phase, promoted cell apoptosis, and inhibited the growth of subcutaneous tumors in BALB/c nude mice (P < 0.01). No obvious necrosis was observed in the tumor tissue in the negative control group (no drug intervention or lentivirus transfection) and vector group (the blank vector for lentivirus transfection), and more cells were loose and necrotic in the miR-328-3p group. Bioinformatics tools predicted that miR-328-3p has a targeting relationship with STAT3, and STAT3 was closely related to autophagy markers such as p62. After overexpressing miR-328-3p, the expression level of STAT3 mRNA was significantly decreased (P < 0.01) and p-STAT3 was downregulated (P < 0.05). The dual-luciferase reporter gene assay showed that the luciferase activity of miR-328-3p and STAT3 3’ untranslated regions of the wild-type reporter vector group was significantly decreased (P < 0.001). Overexpressed miR-328-3p combined with bafilomycin A₁ (Baf A₁) was used to detect the expression of LC3 II. Compared with the vector group, the expression level of LC3 II in the overexpressed miR-328-3p group was downregulated (P < 0.05), and compared with the Baf A₁ group, the expression level of LC3 II in the overexpressed miR-328-3p + Baf A₁ group was upregulated (P < 0.01). The expression of LC3 II was detected after intervention of 18β-GRA in GC cells, and the results were consistent with the results of miR-328-3p overexpression (P < 0.05). Additional studies showed that 18β-GRA promoted autophagy flow by promoting autophagosome synthesis (P < 0.001). qPCR showed that the expression of STAT3 mRNA was downregulated after drug intervention (P < 0.05). Western blot analysis showed that the expression levels of STAT3 and p-STAT3 were significantly downregulated after drug intervention (P < 0.05).

CONCLUSION

18β-GRA promotes the synthesis of autophagosomes and inhibits GC cell proliferation by regulating the miR-328-3p/STAT3 signaling pathway.

Aristolochic acid induces an inflammatory response with prostaglandin E2 production and apoptosis in NRK-52E proximal tubular cells

Aristolochic acid nephropathy (AAN) is a type of drug-induced nephropathy in which ingestion of aristolochic acid (AA) causes acute kidney injury, with progressive renal fibrosis and upper urothelial carcinoma. Although the pathological features of AAN have been reported to involve significant cell degeneration and loss in the proximal tubules, the details of the toxic mechanism in the acute phase of the disease remain unclear. This study investigates the cell death pathway and intracellular metabolic kinetics of AA exposure in rat NRK-52E proximal tubular cells. AA exposure induces dose- and time-dependent apoptotic cell death in NRK-52E cells. We examined the inflammatory response to further investigate the mechanism of AA-induced toxicity. AA exposure increased the gene expression of inflammatory cytokines IL-6 and TNF-α, suggesting that AA exposure induces inflammation. Furthermore, analysis of lipid mediators by LC-MS revealed increases in intra- and extra-cellular arachidonic acid and prostaglandin E2 (PGE2). To investigate the relationship between the AA-induced increase in PGE2 production and cell death, celecoxib, an inhibitor of cyclooxygenase-2 (COX-2), which is involved in the production of PGE2, was administered, and a marked inhibition of AA-induced cell death was observed. These results suggest that exposure to AA induces concentration- and time-dependent apoptosis in NRK-52E cells, which is attributed to inflammatory responses mediated by COX-2 and PGE2.

HMGB1/RAGE axis mediates stress-induced RVLM neuroinflammation in mice via impairing mitophagy flux in microglia

Background

Microglial mediated neuroinflammation in the rostral ventrolateral medulla (RVLM) plays roles in the etiology of stress-induced hypertension (SIH). It was reported that autophagy influenced inflammation via immunophenotypic switching of microglia. High-mobility group box 1 (HMGB1) acts as a regulator of autophagy and initiates the production of proinflammatory cytokines (PICs), but the underlying mechanisms remain unclear.

Methods

The stressed mice were subjected to intermittent electric foot shocks plus noises administered for 2 h twice daily for 15 consecutive days. In mice, blood pressure (BP) and renal sympathetic nerve activity (RSNA) were monitored by noninvasive tail-cuff method and platinum-iridium electrodes placed respectively. Microinjection of siRNA-HMGB1 (siHMGB1) into the RVLM of mice to study the effect of HMGB1 on microglia M1 activation was done. mRFP-GFP-tandem fluorescent LC3 (tf-LC3) vectors were transfected into the RVLM to evaluate the process of autolysosome formation/autophagy flux. The expression of RAB7, lysosomal-associated membrane protein 1 (LAMP1), and lysosomal pH change were used to evaluate lysosomal function in microglia. Mitophagy was identified by transmission electron microscopic observation or by checking LC3 and MitoTracker colocalization under a confocal microscope.

Results

We showed chronic stress increased cytoplasmic translocations of HMGB1 and upregulation of its receptor RAGE expression in microglia. The mitochondria injury, oxidative stress, and M1 polarization were attenuated in the RVLM of stressed Cre-CX3CR1/RAGE^fl/fl mice. The HMGB1/RAGE axis increased at the early stage of stress-induced mitophagy flux while impairing the late stages of mitophagy flux in microglia, as revealed by decreased GFP fluorescence quenching of GFP-RFP-LC3-II puncta and decreased colocalization of lysosomes with mitochondria. The expressions of RAB7 and LAMP1 were decreased in the stressed microglia, while knockout of RAGE reversed these effects and caused an increase in acidity of lysosomes. siHMGB1 in the RVLM resulted in BP lowering and RSNA decreasing in SIH mice. When the autophagy inducer, rapamycin, is used to facilitate the mitophagy flux, this treatment results in attenuated NF-κB activation and reduced PIC release in exogenous disulfide HMGB1 (ds-HMGB1)-stimulated microglia.

Conclusions

Collectively, we demonstrated that inhibition of the HMGB1/RAGE axis activation led to increased stress-induced mitophagy flux, hence reducing the activity of microglia-mediated neuroinflammation and consequently reduced the sympathetic vasoconstriction drive in the RVLM.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1673-3) contains supplementary material, which is available to authorized users.

Adrenergic modulation of AMPK‑dependent autophagy by chronic stress enhances cell proliferation and survival in gastric cancer

Epidemiological data show that chronic stress has adverse effects on the incidence and progression of cancer. As a critical target organ for stress hormones, the stomach is frequently subjected to stress-related injury. However, few reports regarding the association between stress and gastric cancer (GC) have been published. The present study aimed to investigate the effect of chronic stress on the growth and survival of GC, and the role of the autophagy process. A restraint-stress procedure over 21 days was used to establish a chronic stress mouse model. Subcutaneous xenografts and gastric orthotopic xenografts were established in BALB/c nude mice. Alzet osmotic minipumps containing either PBS or propranolol hydrochloride was inserted on the nape of the neck 7 days prior to the initiation of restraint stress. The presence of autophagosomes and autolysosomes were examined by electron microscopy. The stress hormone norepinephrine significantly enhanced the proliferation of GC cells. By inhibiting adrenoreceptor expression, it was demonstrated that β2-adrenergic receptor (ADRB2) was the specific β-adrenergic receptor subtype responsible for catecholamine release. In addition, it was demonstrated that the induction of autophagy was a novel consequence of β2-adrenergic activation in GC cells. This was demonstrated by the appearance of double-membrane vesicles, punctuate GFP-RFP-microtubule-associated protein 1 light chain 3 distribution in the cytoplasm and a corresponding increase in autophagic flux. Notably, norepinephrine-induced autophagy was shown to have a tumor-promoting role under conditions of chronic stress in vitro and in vivo. It was further demonstrated that, upon activation of cAMP-response element binding protein, chronic stress promoted autophagic flux through the adenosine 5′-monophosphate-activated protein kinase-unc-51 like autophagy activating kinase 1 (AMPK-ULK1) pathway. Tissue microarray analysis revealed a negative correlation between the expression of ADRB2 and autophagic marker p62/sequestosome-1 in GC tumor samples. Additionally, high protein levels of ADRB2 correlated positively with tumor, node, metastasis stage and poor prognosis in patients with GC. These results establish a novel pathway that chronic stress activates tumor-promoting autophagy to accelerate the progression of GC. The present study is the first, to the best of our knowledge, providing preclinical evidence that chronic stress serves a role in the progression of GC.

Corynoxine B ameliorates HMGB1-dependent autophagy dysfunction during manganese exposure in SH-SY5Y human neuroblastoma cells

Manganese (Mn) has recently come into the limelight as an important environmental risk factor for neurodegenerative disorders. Although multiple neurotoxicity of Mn have been extensively studied, the exact mechanism of Mn-induced autophagic dysregulation is still poorly understood. The main aim of this study was to explore the role of cytosolic high-mobility group box 1 (HMGB1)-dependent autophagy in Mn-induced autophagic dysregulation and neurotoxicity. SH-SY5Y cells were treated with culture solution (control) and three different concentrations of Mn (50, 100, and 200 μM) for 24 h to detect the effect of Mn on HMGB1-dependent autophagy. We found Mn could increase the HMGB1 mRNA level and its cytosolic translocation and dysregulate autophagy, and Mn-induced alpha-synuclein overexpression interfered with the interaction of HMGB1 and Beclin1, to subsequently promote Beclin1 binding to Bcl2. Another important finding was the neuroprotective role of corynoxine B (Cory B) in Mn-induced autophagic dysregulation and neurotoxicity. We set up six experimental groups: control (culture solution); 200 μM Mn treatment; 100 μM Cory B-alone treatment; and three different pretreated concentrations of Cory B (25, 50, and 100 μM). Our results showed that Cory B ameliorated Mn-induced autophagic dysregulation and neurotoxicity partly by dissociating HMGB1 from alpha-synuclein and inhibiting mTOR signaling.

ZSTK474, a specific class I phosphatidylinositol 3-kinase inhibitor, induces G1 arrest and autophagy in human breast cancer MCF-7 cells

Multifaceted activities of class I phosphatidylinositol 3-kinase (PI3K) inhibitor ZSTK474 were investigated on human breast cancer cell MCF-7. ZSTK474 inhibited proliferation of MCF-7 cells potently. Flow cytometric analysis indicated that ZSTK474 induced cell cycle arrest at G1 phase, but no obvious apoptosis occurred. Western blot analysis suggested that blockade of PI3K/Akt/GSK-3β/cyclin D1/p-Rb pathway might contribute to the G1 arrest induced. Moreover, we demonstrated that ZSTK474 induced autophagy in MCF-7 cells by use of various assays including monodansylcadaverine (MDC) staining, transmission electron microscopy (TEM), tandem mRFP-GFP-LC3 fluorescence microscopy, and western blot detection of the autophagy protein markers of LC3B II, p62 and Atg 5. Inhibition of class I PI3K and the downstream mTOR might be involved in the autophagy-inducing effect. Combinational use of ZSTK474 and autophagy inhibitors enhanced cell viability, suggesting ZSTK474-induced autophagy might contribute to the antitumor activity. Our report supports the application of ZSTK474, which is being evaluated in clinical trials, for breast cancer therapy.

Neuroinflammation contributes to autophagy flux blockage in the neurons of rostral ventrolateral medulla in stress-induced hypertension rats

BACKGROUND

Neuroinflammation plays hypertensive roles in the uninjured autonomic nuclei of the central nervous system, while its mechanisms remain unclear. The present study is to investigate the effect of neuroinflammation on autophagy in the neurons of the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of vasomotor tone reside.

METHODS

Stress-induced hypertension (SIH) was induced by electric foot-shock stressors with noise interventions in rats. Systolic blood pressure (SBP) and the power density of the low frequency (LF) component of the SAP spectrum were measured to reflect sympathetic vasomotor activity. Microglia activation and pro-inflammatory cytokines (PICs (IL-1β, TNF-α)) expression in the RVLM were measured by immunoblotting and immunostaining. Autophagy and autophagic vacuoles (AVs) were examined by autophagic marker (LC3 and p62) expression and transmission electron microscopy (TEM) image, respectively. Autophagy flux was evaluated by RFP-GFP-tandem fluorescent LC3 (tf-LC3) vectors transfected into the RVLM. Tissue levels of glutamate, gamma aminobutyric acid (GABA), and plasma levels of norepinephrine (NE) were measured by using high-performance liquid chromatography (HPLC) with electrochemical detection. The effects of the cisterna magna infused minocycline, a microglia activation inhibitor, on the abovementioned parameters were analyzed.

RESULTS

SIH rats showed increased SBP, plasma NE accompanied by an increase in LF component of the SBP spectrum. Microglia activation and PICs expression was increased in SIH rats. TEM demonstrated that stress led to the accumulation of AVs in the RVLM of SIH rats. In addition to the Tf-LC3 assay, the concurrent increased level of LC3-II and p62 suggested the impairment of autophagic flux in SIH rats. To the contrary, minocycline facilitated autophagic flux and induced a hypotensive effect with attenuated microglia activation and decreased PICs in the RVLM of SIH rats. Furthermore, SIH rats showed higher levels of glutamate and lower level of GABA in the RVLM, while minocycline attenuated the decrease in GABA and the increase in glutamate of SIH rats.

CONCLUSIONS

Collectively, we concluded that the neuroinflammation might impair autophagic flux and induced neural excitotoxicity in the RVLM neurons following SIH, which is involved in the development of SIH.

Necroptosis-like Neuronal Cell Death Caused by Cellular Cholesterol Accumulation

Aberrant cellular accumulation of cholesterol is associated with neuronal lysosomal storage disorders such as Niemann-Pick disease Type C (NPC). We have shown previously that l-norephedrine (l-Nor), a sympathomimetic amine, induces necrotic cell death associated with massive cytoplasmic vacuolation in SH-SY5Y human neuroblastoma cells. To reveal the molecular mechanism underling necrotic neuronal cell death caused by l-Nor, we examined alterations in the gene expression profile of cells during l-Nor exposure. DNA microarray analysis revealed that the gene levels for cholesterol transport (LDL receptor and NPC2) as well as cholesterol biosynthesis (mevalonate pathway enzymes) are increased after exposure to 3 mm l-Nor for ∼6 h. Concomitant with this observation, the master transcriptional regulator of cholesterol homeostasis, SREBP-2, is activated by l-Nor. The increase in cholesterol uptake as well as biosynthesis is not accompanied by an increase in cholesterol in the plasma membrane, but rather by aberrant accumulation in cytoplasmic compartments. We also found that cell death by l-Nor can be suppressed by nec-1s, an inhibitor of a regulated form of necrosis, necroptosis. Abrogation of SREBP-2 activation by the small molecule inhibitor betulin or by overexpression of dominant-negative SREBP-2 efficiently reduces cell death by l-Nor. The mobilization of cellular cholesterol in the presence of cyclodextrin also suppresses cell death. These results were also observed in primary culture of striatum neurons. Taken together, our results indicate that the excessive uptake as well as synthesis of cholesterol should underlie neuronal cell death by l-Nor exposure, and suggest a possible link between lysosomal cholesterol storage disorders and the regulated form of necrosis in neuronal cells.

Stellettin B Induces G1 Arrest, Apoptosis and Autophagy in Human Non-small Cell Lung Cancer A549 Cells via Blocking PI3K/Akt/mTOR Pathway

Until now, there is not yet antitumor drug with dramatically improved efficacy on non-small cell lung cancer (NSCLC). Marine organisms are rich source of novel compounds with various activities. We isolated stellettin B (Stel B) from marine sponge Jaspis stellifera, and demonstrated that it induced G1 arrest, apoptosis and autophagy at low concentrations in human NSCLC A549 cells. G1 arrest by Stel B might be attributed to the reduction of cyclin D1 and enhancement of p27 expression. The apoptosis induction might be related to the cleavage of PARP and increase of ROS generation. Moreover, we demonstrated that Stel B induced autophagy in A549 cells by use of various assays including monodansylcadaverine (MDC) staining, transmission electron microscopy (TEM), tandem mRFP-GFP-LC3 fluorescence microscopy, and western blot detection of the autophagy markers of LC3B, p62 and Atg5. Meanwhile, Stel B inhibited the expression of PI3K-p110, and the phosphorylation of PDK1, Akt, mTOR, p70S6K as well as GSK-3β, suggesting the correlation of blocking PI3K/Akt/mTOR pathway with the above antitumor activities. Together, our findings indicate the antitumor potential of Stel B for NSCLC by targeting PI3K/Akt/mTOR pathway.

Autophagic flux inhibition and lysosomogenesis ensuing cellular capture and retention of the cationic drug quinacrine in murine models

The proton pump vacuolar (V)-ATPase is the driving force that mediates the concentration of cationic drugs (weak bases) in the late endosome-lysosome continuum; secondary cell reactions include the protracted transformation of enlarged vacuoles into autophagosomes. We used the inherently fluorescent tertiary amine quinacrine in murine models to further assess the accumulation and signaling associated with cation trapping. Primary fibroblasts concentrate quinacrine ∼5,000-fold from their culture medium (K_M 9.8 µM; transport studies). The drug is present in perinuclear granules that are mostly positive for Rab7 and LAMP1 (microscopy). Both drug uptake and retention are extensively inhibited by treatments with the V-ATPase inhibitor bafilomycin A1. The H⁺ ionophore monensin also prevented quinacrine concentration by fibroblasts. However, inhibition of plasma membrane transporters or of the autophagic process with spautin-1 did not alter quinacrine transport parameters. Ancillary experiments did not support that low micromolar concentrations of quinacrine are substrates for organic cation transporters-1 to -3 or P-glycoprotein. The secondary autophagy induced by quinacrine in cells may derive from the accumulation of incompetent autophagolysosomes, as judged from the accumulation of p62/SQSTM1 and LC3 II (immunoblots). Accordingly, protracted lysosomogenesis is evidenced by increased expression of LAMP1 and LAMP2 in quinacrine-treated fibroblasts (48 h, immunoblots), a response that follows the nuclear translocation of the lysosomal genesis transcription factor TFEB and upregulation of LAMP1 and −2 mRNAs (24 h). Quinacrine administration to live mice evidenced variable distribution to various organs and heterogeneous accumulation within the lung (stereo-microscopy, extraction). Dose-dependent in vivo autophagic and lysosomal accumulation was observed in the lung (immunoblots). No evidence has been found for transport or extrusion mechanisms modulating the cellular uptake of micromolar quinacrine at the plasma membrane level. As shown in vitro and in vivo, V-ATPase-mediated cation sequestration is associated, above a certain threshold, to autophagic flux inhibition and feed-back lysosomogenesis.

Protease 3C of hepatitis A virus induces vacuolization of lysosomal/endosomal organelles and caspase-independent cell death

BACKGROUND

3C proteases, the main proteases of picornaviruses, play the key role in viral life cycle by processing polyproteins. In addition, 3C proteases digest certain host cell proteins to suppress antiviral defense, transcription, and translation. The activity of 3C proteases per se induces host cell death, which makes them critical factors of viral cytotoxicity. To date, cytotoxic effects have been studied for several 3C proteases, all of which induce apoptosis. This study for the first time describes the cytotoxic effect of 3C protease of human hepatitis A virus (3Cpro), the only proteolytic enzyme of the virus.

RESULTS

Individual expression of 3Cpro induced catalytic activity-dependent cell death, which was not abrogated by the pan-caspase inhibitor (z-VAD-fmk) and was not accompanied by phosphatidylserine externalization in contrast to other picornaviral 3C proteases. The cell survival was also not affected by the inhibitors of cysteine proteases (z-FA-fmk) and RIP1 kinase (necrostatin-1), critical enzymes involved in non-apoptotic cell death. A substantial fraction of dying cells demonstrated numerous non-acidic cytoplasmic vacuoles with not previously described features and originating from several types of endosomal/lysosomal organelles. The lysosomal protein Lamp1 and GTPases Rab5, Rab7, Rab9, and Rab11 were associated with the vacuolar membranes. The vacuolization was completely blocked by the vacuolar ATPase inhibitor (bafilomycin A1) and did not depend on the activity of the principal factors of endosomal transport, GTPases Rab5 and Rab7, as well as on autophagy and macropinocytosis.

CONCLUSIONS

3Cpro, apart from other picornaviral 3C proteases, induces caspase-independent cell death, accompanying by cytoplasmic vacuolization. 3Cpro-induced vacuoles have unique properties and are formed from several organelle types of the endosomal/lysosomal compartment. The data obtained demonstrate previously undocumented morphological characters of the 3Cpro-induced cell death, which can reflect unknown aspects of the human hepatitis A virus-host cell interaction.

The suppressive role of p38 MAPK in cellular vacuole formation

Vacuolization of the cytoplasm is one of the dramatic and frequently observed phenomena in various cell types. Cellular vacuoles occur spontaneously or via a wide range of inductive stimuli, but the molecular mechanism involved in this process remains largely unknown. In this study, we investigated the role of the p38 and JNK pathways in the formation of cytoplasmic vacuoles. We found that p38 and JNK agonist anisomycin abolishes spontaneous cytoplasmic vacuolization of HepG2 cells through p38 activation, but not through JNK activation. Importantly, blocking the activity of p38 or suppression the expression of p38 elicits cytoplasmic vacuoles formation in various cancer cells. Furthermore, cytoplasmic vacuoles induced by p38 blocking are derived from the perinuclear region. These observations provide direct evidence for a role of p38 signaling in regulating the formation of cytoplasmic vacuoles.