Autophagy and the invisible line between life and death. Eur J Cell Biol. 2016;95:598-610. [PMID: 28340912 DOI: 10.1016/j.ejcb.2016.10.005]

Nano-sized polystyrene plastics toxicity: Necroptosis pathway caused by autophagy blockade and lysosomal dysfunction

The persistent detection of nano-sized plastic particles in humans, animals, and animal-derived products underscores the potential impact of these particles on living organisms. Consequently, the toxicology of such particles has emerged as a pivotal research interests in recent years. In this study, NP was synthesized successfully with an average particle size of 100 nm using a emulsion polymerization method as model particles. Following co-incubation of IEC-6 cells with NP for 24-168 h, a notable inhibition of cell viability and proliferation was observed. The significant activation of autophagy and a concomitant blockage of autophagic flux in IEC-6 cells after 24-72 h of co-incubation with NP were unveiled by transmission electron microscopy, western blotting, and double-fluorescent autophagy analysis. A significant increase in the number of lysosomes and an increase in the expression of hydrolase CTSB were detected, indicating dysregulation of lysosomal function. The subsequent transcriptomic and metabolomics analyses, coupled with the observation of activated lysosomes and the RIPK1-RIPK3-MLKL/PYGL pathway, led us to posit that the blockade of autophagy and lysosomal dysfunction, culminating in lysosomal membrane permeabilization (LMP) induced necroptosis, constitutes one of the mechanisms contributing to the cytotoxicity of NP. SYNOPSIS: The cytotoxicity and its related mechanisms of nano-plastic is still unclear. This study found that nano-plastics may induce necroptosis in cells, and autophagy blockade and lysosomal dysfunction are prodromal manifestations.

In Vitro Investigation of Biological and Toxic Effects of 4-Octylphenol on Human Cells

Alkylphenols are byproducts of anthropogenic activities that widely contaminate waters, soils and air; among them, the most represented are 4-nonylphenol (4-NP) and 4-octylphenol (4-OP). These compounds tend to bioaccumulate in animal and plant tissues and also represent a risk to human health. Indeed, humans are constantly exposed to alkylphenols through ingestion of contaminated water and food, inhalation and dermal absorption. In the present work, we characterized the cytotoxic ability of 4-OP towards several human cell lines, representing the potential main targets in the human body, also comparing its effect with that of 4-NP and of a mixture of both 4-OP and 4-NP in a range of concentrations between 1 and 100 μM. Viability assays demonstrated that each cell type had a peculiar sensitivity to 4-OP and that, in some cases, a combination of the two alkylphenols displayed a higher cytotoxic activity with respect to the single compound. Then, we focused our attention on a liver cell line (HepG2) in which we observed that 4-OP increased cell death and also caused interference with protective physiological cell processes, such as the unfolded protein response, autophagy and the antioxidant response. Finally, our experimental data were compared and correlated with ADMET properties originating from an in silico analysis. Altogether, our findings highlight a possible contribution of this pollutant to deregulation of the normal homeostasis in human liver cells.

Autophagy and autophagic cell death in sepsis: friend or foe?

In sepsis, inflammation, and nutrient deficiencies endanger cellular homeostasis and survival. Autophagy is primarily a mechanism of cellular survival under fasting conditions. However, autophagy-dependent cell death, known as autophagic cell death, is proinflammatory and can exacerbate sepsis. Autophagy also regulates various types of non-inflammatory and inflammatory cell deaths. Non-inflammatory apoptosis tends to suppress inflammation, however, inflammatory necroptosis, pyroptosis, ferroptosis, and autophagic cell death lead to the release of inflammatory cytokines and damage-associated molecular patterns (DAMPs) and amplify inflammation. The selection of cell death mechanisms is complex and often involves a mixture of various styles. Similarly, protective autophagy and lethal autophagy may be triggered simultaneously in cells. How cells balance the regulatory mechanisms of these processes is an area of interest that is still under investigation. Therapies aimed at modulating autophagy are considered promising. Enhancing autophagy helps clear and recycle damaged organelles and reduce the burden of inflammatory processes while inhibiting excessive autophagy, which could prevent autophagic cell death. In this review, we introduce recent advances in research and the complex regulatory system of autophagy in sepsis.

Autophagy and Apoptosis in Acute Brain Injuries: From Mechanism to Treatment

Significance: Autophagy and apoptosis are two important cellular mechanisms behind brain injuries, which are severe clinical situations with increasing incidences worldwide. To search for more and better treatments for brain injuries, it is essential to deepen the understanding of autophagy, apoptosis, and their interactions in brain injuries. This article first analyzes how autophagy and apoptosis participate in the pathogenetic processes of brain injuries respectively and mutually, then summarizes some promising treatments targeting autophagy and apoptosis to show the potential clinical applications in personalized medicine and precision medicine in the future. Recent Advances: Most current studies suggest that apoptosis is detrimental to brain recovery. Several studies indicate that autophagy can cause unnecessary death of neurons after brain injuries, while others show that autophagy is beneficial for acute brain injuries (ABIs) by facilitating the removal of damaged proteins and organelles. Whether autophagy is beneficial or detrimental in ABIs depends on many factors, and the results from different research groups are diverse or even controversial, making this topic more appealing to be explored further. Critical Issues: Neuronal autophagy and apoptosis are two primary pathological processes in ABIs. How they interact with each other and how their regulations affect the outcome and prognosis of brain injuries remain uncertain, making these answers more critical. Future Directions: Insights into the interplay between autophagy and apoptosis and the accurate regulations of their balance in ABIs may promote personalized and precise treatments in the field of brain injuries. Antioxid. Redox Signal. 38, 234-257.

The unfolded protein response (UPR) pathway: the unsung hero in breast cancer management

Tumor cells always have the need to produce an increased amount of proteins in the cells. This elevated amount of proteins increases the pressure on the organelles of the cell such as the endoplasmic reticulum and compels it to increase its protein folding efficiency. However, it is by a matter of fact, that the amount of proteins synthesized outweighs the protein folding capacity of the ER which in turn switches on the UPR pathway by activating the three major molecular sensors and other signaling cascades, which helps in cell survival instead of instant death. However, if this pathway is active for a prolonged period of time the tumor cells heads toward apoptosis. Again, interestingly this is not the same as in case of non- tumorogenic cells. This exhibit a straight natural pathway for tumor cells-specific destruction which has a great implication in today's world where hormone therapies and chemo-therapies are non-effective for various types of breast cancer, a major type being Triple Negative Breast Cancer. Thus a detailed elucidation of the molecular involvement of the UPR pathway in breast cancer may open new avenues for management and attract novel chemotherapeutic targets providing better hopes to patients worldwide.

Multiple Mechanisms Converging on Transcription Factor EB Activation by the Natural Phenol Pterostilbene

Pterostilbene (Pt) is a potentially beneficial plant phenol. In contrast to many other natural compounds (including the more celebrated resveratrol), Pt concentrations producing significant effects in vitro can also be reached with relative ease in vivo. Here we focus on some of the mechanisms underlying its activity, those involved in the activation of transcription factor EB (TFEB). A set of processes leading to this outcome starts with the generation of ROS, attributed to the interaction of Pt with complex I of the mitochondrial respiratory chain, and spreads to involve Ca²⁺ mobilization from the ER/mitochondria pool, activation of CREB and AMPK, and inhibition of mTORC1. TFEB migration to the nucleus results in the upregulation of autophagy and lysosomal and mitochondrial biogenesis. Cells exposed to several μM levels of Pt experience a mitochondrial crisis, an indication for using low doses in therapeutic or nutraceutical applications. Pt afforded significant functional improvements in a zebrafish embryo model of ColVI-related myopathy, a pathology which also involves defective autophagy. Furthermore, long-term supplementation with Pt reduced body weight gain and increased transcription levels of Ppargc1a and Tfeb in a mouse model of diet-induced obesity. These in vivo findings strengthen the in vitro observations and highlight the therapeutic potential of this natural compound.

[Lack of GAGA protein in Trl mutants causes massive cell death in Drosophila spermatogenesis and oogenesis]

Белок дрозофилы GAGA (GAF) является фактором эпигенетической регуляции транскрипции большой группы генов с широким разнообразием клеточных функций. GAF кодируется геном Trithorax-like (Trl), который экспрессируется в различных органах и тканях на всех стадиях онтогенеза дрозофилы. Мутации этого гена вызывают множественные нарушения развития. В предыдущих работах мы показали, что этот белок необходим для развития половой системы как самцов, так и самок дрозофилы. Снижение экспрессии гена Trl приводило ко множественным нарушениям спермато- и оогенеза. Одно из значительных нарушений было связано с массовой деградацией и потерей клеток зародышевого пути, что позволило предположить, что этот белок вовлечен в регуляцию клеточной гибели. В представленной работе мы провели более детальное цитологическое исследование, чтобы определить, какой тип гибели клеток зародышевого пути характерен для Trl-мутантов, и происходят ли нарушения или изменения этого процесса по сравнению с нормой. Полученные результаты показали, что недостаток белка GAF вызывает массовую гибель клеток зародышевого пути как у самок, так и самцов дрозофилы, но проявляется эта гибель в зависимости от пола по-разному. У самок, мутантных по гену Trl, фенотипически этот процесс не отличается от нормы и в гибнущих яйцевых камерах выявлены признаки апоптоза и аутофагии клеток зародышевого пути. У самцов, мутантных по гену Trl, в отличие от самок, не обнаружены признаки апоптоза. У самцов мутации Trl индуцируют массовую гибель клеток через аутофагию, что не характерно для сперматогенеза дрозофилы и не описано ранее ни в норме, ни у мутаций по другим генам. Таким образом, недостаток GAF у мутантов Trl приводит к усилению апоптотической и аутофагической гибели клеток зародышевого пути. Эктопическая клеточная гибель и атрофия зародышевой линии, вероятно, связаны с нарушением экспрессии генов-мишеней GAGAфактора, среди которых есть гены, регулирующие как апоптоз, так и аутофагию.

Knockdown of the inducible nitric oxide synthase (NOS2) splicing variant S3 promotes autophagic cell death from nitrosative stress in SW480 human colon cancer cells

Low levels of nitric oxide (NO) produced by constitutively expressed inducible NO synthase (NOS2) in tumor cells may be an important factor in their development. NOS2 expression is associated with high mortality rates for various cancers. Alternative splicing of NOS2 down-regulates its enzymatic activity, resulting in decreased intracellular NO concentrations. Specific probes to detect alternative splicing of NOS2 were used in two isogenic human colon cancer cell lines derived either from the primary tumor (SW480) or from a lymph node metastasis (SW620). Splicing variant of NOS2 S3, lacking exons 9, 10, and 11, was overexpressed in SW480 cells. NOS2 S3 was silenced in SW480 cells. Flow-cytometry analysis was used to estimate the intracellular NO levels and to analyze the cell cycle of the studied cell lines. Western blot analysis and quantitative real-time polymerase chain reaction (qRT-PCR) were used to determine apoptosis and autophagy markers. SW480 and SW620 cells expressed NOS2 S3. Overexpression of the NOS2 S3 in SW480 cells downregulated intracellular NO levels. SW480 cells with knocked down NOS2 S3 (referred to as S3C9 cells) had higher intracellular levels of NO compared to the wild-type SW480 cells under serum restriction. Higher NO levels resulted in the loss of viability of S3C9 cells, which was associated with autophagy. Induction of autophagy by elevated intracellular NO levels in S3C9 cells under serum restriction, suggests that autophagy operates as a cytotoxic response to nitrosative stress. The expression of NOS2 S3 plays an important role in regulating intracellular NO production and maintaining viability in SW480 cells under serum restriction. These findings may prove significant in the design of NOS2/NO-based therapies for colon cancer.

Eupatilin Impacts on the Progression of Colon Cancer by Mitochondria Dysfunction and Oxidative Stress

Colon cancer is one of the most frequently diagnosed cancer types. Some colon cancer cases resist standard anticancer drugs. Therefore, many studies have focused on developing therapeutic supplements using natural products with low side effects and broad physiological activity. Eupatilin is a flavonoid that is mainly extracted from artemisia and promotes apoptosis in numerous cancer types. However, since the current understanding of its physiological mechanisms on colon cancer cells is insufficient, we investigated how eupatilin affects the growth of two colon cancer cell lines, namely HCT116 and HT29. Our results showed that eupatilin inhibits cell viability and induces apoptosis accompanied by mitochondrial depolarization. It also induces oxidative stress in colon cancer cells and regulates the expression of proteins involved in the endoplasmic reticulum stress and autophagic process. Moreover, eupatilin may target the PI3K/AKT and mitogen-activated protein kinase (MAPK) signaling pathways in colon cancer cells. It also prevents colon cancer cell invasion. Furthermore, eupatilin has a synergistic effect with 5-fluorouracil (5-FU; a standard anticancer drug) on 5-FU-resistant HCT116 cells. These results suggest that eupatilin can be developed as an adjuvant to enhance traditional anticancer drugs in colon cancer.

Autophagy in Viral Development and Progression of Cancer

Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases. Although this catabolic process can be triggered by a great variety of stimuli, action in cells varies according to cellular context. Autophagy has been previously linked to disease development modulation, including cancer. Autophagy helps suppress cancer cell advancement in tumor transformation early stages, while promoting proliferation and metastasis in advanced settings. Oncoviruses are a particular type of virus that directly contribute to cell transformation and tumor development. Extensive molecular studies have revealed complex ways in which autophagy can suppress or improve oncovirus fitness while still regulating viral replication and determining host cell fate. This review includes recent advances in autophagic cellular function and emphasizes its antagonistic role in cancer cells.

Autophagy in Viral Development and Progression of Cancer

Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases. Although this catabolic process can be triggered by a great variety of stimuli, action in cells varies according to cellular context. Autophagy has been previously linked to disease development modulation, including cancer. Autophagy helps suppress cancer cell advancement in tumor transformation early stages, while promoting proliferation and metastasis in advanced settings. Oncoviruses are a particular type of virus that directly contribute to cell transformation and tumor development. Extensive molecular studies have revealed complex ways in which autophagy can suppress or improve oncovirus fitness while still regulating viral replication and determining host cell fate. This review includes recent advances in autophagic cellular function and emphasizes its antagonistic role in cancer cells.

Transcription factor EB‑mediated autophagy promotes dermal fibroblast differentiation and collagen production by regulating endoplasmic reticulum stress and autophagy‑dependent secretion

Autophagy is reported to be involved in the formation of skin hypertrophic scar (HTS). However, the role of autophagy in the process of fibrosis remains unclear, therefore an improved understanding of the molecular mechanisms associated with autophagy may accelerate the development of effective therapeutic strategies against HTS. The present study evaluated the roles of autophagy mediated by transcription factor EB (TFEB), a pivotal regulator of lysosome biogenesis and autophagy, in transforming growth factor-β1 (TGF-β1)-induced fibroblast differentiation and collagen production. Fibroblasts were treated with TGF-β1, TGF-β1 + tauroursodeoxycholic acid (TUDCA) or TGF-β1 + TFEB-small interfering RNA (siRNA). TGF-β1 induced phenotypic transformation of fibro-blasts, as well as collagen synthesis and secretion in fibroblasts in a dose-dependent manner. Western blotting and immuno-fluorescence analyses demonstrated that TGF-β1 upregulated the expression of autophagy-related proteins through the endoplasmic reticulum (ER) stress pathway, whereas TUDCA reversed TGF-β1-induced changes. Reverse transcription-quantitative PCR (RT-qPCR), western blotting and RFP-GFP-LC3 double fluorescence analyses demonstrated that knockdown of TFEB by TFEB-siRNA decreased autophagic flux, upregulated the expression of proteins involved in the apoptotic pathway, such as phosphorylated-α subunit of eukaryotic initiation factor 2, C/EBP homologous protein and cysteinyl aspartate specific proteinase 3, and also downregulated the expression of α-smooth muscle actin and collagen I (COL I) in fibroblasts. Immunofluorescence confocal analyses and enzyme-linked immunosorbent assay indicated that TGF-β1 increased the colocalization of COL I with lysosomal-associated membrane protein 1 and Ras-related protein Rab-8A, a marker of secretory vesicles, in fibroblasts, as well as the secretion of pro-COL Iα1 in culture supernatants. Meanwhile, these effects were abolished by TFEB knockdown. The present results suggested that autophagy reduced ER stress, decreased cell apoptosis and maintained fibroblast activation not only through degradation of misfolded or unfolded proteins, but also through promotion of COL I release from the autolysosome to the extracellular environment.

Autophagy protein ATG7 is a critical regulator of endothelial cell inflammation and permeability

Endothelial cell (EC) inflammation and permeability are critical pathogenic mechanisms in many inflammatory conditions including acute lung injury. In this study, we investigated the role of ATG7, an essential autophagy regulator with no autophagy-unrelated functions, in the mechanism of EC inflammation and permeability. Knockdown of ATG7 using si-RNA significantly attenuated thrombin-induced expression of proinflammatory molecules such as IL-6, MCP-1, ICAM-1 and VCAM-1. Mechanistic study implicated reduced NF-κB activity in the inhibition of EC inflammation in ATG7-silenced cells. Moreover, depletion of ATG7 markedly reduced the binding of RelA/p65 to DNA in the nucleus. Surprisingly, the thrombin-induced degradation of IκBα in the cytosol was not affected in ATG7-depleted cells, suggesting a defect in the translocation of released RelA/p65 to the nucleus in these cells. This is likely due to suppression of thrombin-induced phosphorylation and thereby inactivation of Cofilin1, an actin-depolymerizing protein, in ATG7-depleted cells. Actin stress fiber dynamics are required for thrombin-induced translocation of RelA/p65 to the nucleus, and indeed our results showed that ATG7 silencing inhibited this response via inactivation of Cofilin1. ATG7 silencing also reduced thrombin-mediated EC permeability by inhibiting the disassembly of VE-cadherin at adherens junctions. Together, these data uncover a novel function of ATG7 in mediating EC inflammation and permeability, and provide a mechanistic basis for the linkage between autophagy and EC dysfunction.

Myricetin induces apoptosis and autophagy by inhibiting PI3K/Akt/mTOR signalling in human colon cancer cells

BACKGROUND

The compound 3,3',4',5,5',7-hexahydroxyflavone (myricetin) is a natural flavonoid with antitumour activity. Most of the studies on myricetin have focused on the induction of tumour cell apoptosis, and little is known about the regulatory effects of myricetin on autophagy in colorectal cancer.

METHODS

Here, we studied the effects of myricetin on colon cancer cell proliferation, apoptosis and autophagy. We detected colon cancer cell apoptosis induced by myricetin via flow cytometry and Hoechst 33258 staining. Transmission electron microscopy was performed to observe the morphological changes associated with autophagy. The expression levels of apoptosis-, autophagy- and PI3K/Akt/mTOR signalling-related proteins were measured by Western blot analysis.

RESULTS

This study confirmed that myricetin inhibits the proliferation of 4 kinds of colon cancer cell lines. Myricetin induced cell apoptosis and autophagy by inhibiting PI3K/Akt/mTOR signalling pathway. In addition, the inhibition of autophagy with 3-methyladenine (3-MA) promoted the apoptosis of myricetin-treated colon cancer cells.

CONCLUSIONS

Considering that myricetin induces apoptosis and autophagy in colon cancer cells, myricetin may become a viable candidate for chemotherapy; it could be used to exert tumour inhibitory effects alone or as adjuvant chemotherapy to inhibit autophagy. These studies may provide further evidence for the potential use of myricetin in the treatment of colon cancer.

Catalase is required for peroxisome maintenance during adipogenesis

Although obesity contributes to the onset and pathogenesis of metabolic diseases, it has been repeatedly demonstrated that being overweight or mildly obese carries a survival advantage compared with being thin or normal-weight. This relationship is called the obesity paradox. Hence, it is necessary to clarify the underlying mechanism of obesity onset for the prevention and treatment of these diseases. Catalase is distributed in peroxisomes under normal redox conditions and catalase activity is increased during the differentiation of 3T3-L1 preadipocytes to adipocytes. Although peroxisomes are responsible for lipid metabolism, the role of peroxisomal catalase in the process of lipid accumulation remains unclear. The present study aimed to investigate the relationships among catalase activity, peroxisome content, and lipid accumulation during the differentiation of 3T3-L1 preadipocytes to adipocytes. Increased catalase activity and lipid accumulation were observed during the differentiation of preadipocytes. Silencing of catalase by small interfering RNA or treatment with 3-amino-1,2,4-triazole (3-AT), a catalase inhibitor, resulted in reduced lipid accumulation. Inhibition of catalase activity in peroxisomes increases hydrogen peroxide (H₂O₂) levels, which results in a reduction of peroxisome content. Extracellular H₂O₂ had no influence on lipid accumulation during differentiation. The occurrence of autophagy was clearly enhanced in cells treated with 3-AT. Spautin-1, an inhibitor of autophagy flux, protected against a reduction in lipid accumulation by treatment with 3-AT. Our data provide evidence that catalase protects against the degradation of peroxisomes via the occurrence of autophagy triggered by the generation of H₂O₂ in peroxisomes. These results suggest that catalase in peroxisomes is crucial to adipogenesis.

MTMR3 is upregulated in patients with breast cancer and regulates proliferation, cell cycle progression and autophagy in breast cancer cells

As a member of the myotubularin family, myotubularin related protein 3 (MTMR3) has been demonstrated to participate in tumor development, including oral and colon cancer. However, little is known about its functional roles in breast cancer. In the present study, the expression of MTMR3 in breast cancer was evaluated by immunohistochemical staining of tumor tissues from 172 patients. Online data was then used for survival analysis from the PROGgeneV2 database. In vitro, MTMR3 expression was silenced in MDA-MB-231 cells via lentiviral shRNA transduction. MTT, colony formation and flow cytometry assays were performed in the control and MTMR3-silenced cells to evaluate the cell growth, proliferation and cell cycle phase distribution, respectively. Western blotting was used to evaluate the protein expression levels of autophagy-related markers. The results demonstrated that the expression of MTMR3 in breast cancer tissues was significantly increased compared with adjacent normal tissues. MTMR3 was highly expressed in triple-negative breast cancer and was associated with disease recurrence. MTMR3 knockdown in MDA-MB-231 cells inhibited cell proliferation and induced cell cycle arrest and autophagy. The present results indicated that MTMR3 may have an important role in promoting the progression of breast cancer, and its inhibition may serve as a promising therapeutic target for breast cancer treatment.

Endoplasmic Reticulum Stress and Unfolded Protein Response in Breast Cancer: The Balance between Apoptosis and Autophagy and Its Role in Drug Resistance

The unfolded protein response (UPR) is a stress response activated by the accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum (ER) and its uncontrolled activation is mechanistically responsible for several human pathologies, including metabolic, neurodegenerative, and inflammatory diseases, and cancer. Indeed, ER stress and the downstream UPR activation lead to changes in the levels and activities of key regulators of cell survival and autophagy and this is physiologically finalized to restore metabolic homeostasis with the integration of pro-death or/and pro-survival signals. By contrast, the chronic activation of UPR in cancer cells is widely considered a mechanism of tumor progression. In this review, we focus on the relationship between ER stress, apoptosis, and autophagy in human breast cancer and the interplay between the activation of UPR and resistance to anticancer therapies with the aim to disclose novel therapeutic scenarios. The hypothesis that autophagy and UPR may provide novel molecular targets in human malignancies is discussed.

Sodium butyrate induces autophagy in colorectal cancer cells through LKB1/AMPK signaling

Butyrate is produced by the fermentation of undigested dietary fibers and acts as the promising candidate for cancer treatment. However, the mechanism underlying sodium butyrate (NaB)-induced autophagy in colorectal cancer is not yet completely understood. The expressions of LC3-II protein and mRNA were detected by western blot and quantitative RT-PCR in colorectal cancer (CRC) cell lines HCT-116 and HT-29, respectively. Autolysosome formation was observed by transmission electron microscope. AMPK and LKB1 were inhibited by chemical inhibitor or siRNAs and confirmed by western blot. NaB elevated the protein and mRNA expressions of LC3 in a dose-dependent manner. NaB treatment increased the formation of autolysosome and expression of phosphorylated liver kinase B1 (LKB1), AMP-activated protein kinase (AMPK), and acetyl-CoA carboxylase (ACC). Treatment with compound C (an inhibitor of AMPK) and siRNA-mediated knockdown of AMPK and LKB1 significantly attenuated NaB-induced autophagy in CRC cells. Collectively, these findings indicated that LKB1 and AMPK are critical for NaB-mediated autophagy and may act as the novel targets for colorectal cancer therapy in the future.

Sicilian Litchi Fruit Extracts Induce Autophagy versus Apoptosis Switch in Human Colon Cancer Cells

Litchi chinensis Sonnerat is a tropical tree whose fruits contain significant amounts of bioactive polyphenols. Litchi cultivation has recently spread in Sicily where the climate conditions are particularly favorable for this crop. Recent findings have shown that Litchi extracts display anti-tumor and pro-apoptotic effects in vitro, but the precise underlying mechanisms have not been fully elucidated. In this study, we report for the first time the effects of Sicilian litchi fruit extracts on colon cancer cells. The results indicated that litchi exocarp, mesocarp and endocarp fractions reduce the viability and clonogenic growth of HT29 cells. These effects were due to cell cycle arrest in the G2/M phase followed by caspase-dependent cell death. Interestingly, litchi exocarp and endocarp triggered a precocious autophagic response (16–24 h), which was accompanied by an increase in the level of autophagy related 1/autophagy activating kinase 1 (ATG1/ULK1), beclin-1, microtubule associated protein 1 light chain 3 (LC3)-II and p62 proteins. Autophagy inhibition by bafilomycin A1 or beclin-1 silencing increased cell death, thus suggesting that autophagy was initially triggered as a pro-survival response. Significant effects of Litchi extracts were also observed in other colon cancer cells, including HCT116 and Caco-2 cells. On the other hand, differentiated Caco-2 cells, a model of human enterocytes, appeared to be insensitive to the extracts at the same treatment conditions. High-Performance Liquid Chromatography–Electrospray Ionization-Quadrupole-Time-Of-Flight HPLC/ESI/Q-TOF evidenced the presence of some polyphenolic compounds, specifically in exocarp and endocarp extracts, that can account for the observed biological effects. The results obtained suggest a potential therapeutic efficacy of polyphenolic compounds purified from Sicilian Litchi fractions for the treatment of colon cancer. Moreover, our findings indicate that modulation of autophagy can represent a tool to improve the effectiveness of these agents and potentiate the anti-tumor response of colon cancer cells.

AT 101 induces early mitochondrial dysfunction and HMOX1 (heme oxygenase 1) to trigger mitophagic cell death in glioma cells

In most cases, macroautophagy/autophagy serves to alleviate cellular stress and acts in a pro-survival manner. However, the effects of autophagy are highly contextual, and autophagic cell death (ACD) is emerging as an alternative paradigm of (stress- and drug-induced) cell demise. AT 101 ([-]-gossypol), a natural compound from cotton seeds, induces ACD in glioma cells as confirmed here by CRISPR/Cas9 knockout of ATG5 that partially, but significantly rescued cell survival following AT 101 treatment. Global proteomic analysis of AT 101-treated U87MG and U343 glioma cells revealed a robust decrease in mitochondrial protein clusters, whereas HMOX1 (heme oxygenase 1) was strongly upregulated. AT 101 rapidly triggered mitochondrial membrane depolarization, engulfment of mitochondria within autophagosomes and a significant reduction of mitochondrial mass and proteins that did not depend on the presence of BAX and BAK1. Conversely, AT 101-induced reduction of mitochondrial mass could be reversed by inhibiting autophagy with wortmannin, bafilomycin A₁ and chloroquine. Silencing of HMOX1 and the mitophagy receptors BNIP3 (BCL2 interacting protein 3) and BNIP3L (BCL2 interacting protein 3 like) significantly attenuated AT 101-dependent mitophagy and cell death. Collectively, these data suggest that early mitochondrial dysfunction and HMOX1 overactivation synergize to trigger lethal mitophagy, which contributes to the cell killing effects of AT 101 in glioma cells.

ABBREVIATIONS

ACD, autophagic cell death; ACN, acetonitrile; AT 101, (-)-gossypol; BAF, bafilomycin A₁; BAK1, BCL2-antagonist/killer 1; BAX, BCL2-associated X protein; BH3, BCL2 homology region 3; BNIP3, BCL2 interacting protein 3; BNIP3L, BCL2 interacting protein 3 like; BP, Biological Process; CCCP, carbonyl cyanide m-chlorophenyl hydrazone; CC, Cellular Component; Con, control; CQ, chloroquine; CRISPR, clustered regularly interspaced short palindromic repeats; DMEM, Dulbecco's Modified Eagle Medium; DTT, 1,4-dithiothreitol; EM, electron microscopy; ER, endoplasmatic reticulum; FACS, fluorescence-activated cell sorting; FBS, fetal bovine serum; FCCP, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; GO, Gene Ontology; HAcO, acetic acid; HMOX1, heme oxygenase 1; DKO, double knockout; LC-MS/MS, liquid chromatography coupled to tandem mass spectrometry; LPL, lipoprotein lipase, MEFs, mouse embryonic fibroblasts; mPTP, mitochondrial permeability transition pore; MTG, MitoTracker Green FM; mt-mKeima, mito-mKeima; MT-ND1, mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 1; PBS, phosphate-buffered saline; PE, phosphatidylethanolamine; PI, propidium iodide; PRKN, parkin RBR E3 ubiquitin protein ligase; SDS, sodium dodecyl sulfate; SQSTM1/p62, sequestome 1; STS, staurosporine; sgRNA, single guide RNA; SILAC, stable isotope labeling with amino acids in cell culture; TFA, trifluoroacetic acid, TMRM, tetramethylrhodamine methyl ester perchlorate; WM, wortmannin; WT, wild-type.

Chrysin Attenuates Cell Viability of Human Colorectal Cancer Cells through Autophagy Induction Unlike 5-Fluorouracil/Oxaliplatin

Chemotherapeutic 5-fluorouracil (5-FU) combined with oxaliplatin is often used as the standard treatment for colorectal cancer (CRC). The disturbing side effects and drug resistance commonly observed in chemotherapy motivate us to develop alternative optimal therapeutic options for CRC treatment. Chrysin, a natural and biologically active flavonoid abundant in propolis, is reported to have antitumor effects on a few CRCs. However, whether and how chrysin achieves similar effectiveness to the 5-FU combination is not clear. In this study, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), western blotting, fluorescence microscopy, and reactive oxygen species (ROS) production were assayed. We found that chrysin exhibited similar inhibition of cell viability as the 5-FU combination in a panel of human CRC cells. Furthermore, the results showed that chrysin significantly increased the levels of LC3-II, an autophagy-related marker, in CRC cells, which was not observed with the 5-FU combination. More importantly, blockage of autophagy induction restored chrysin-attenuated CRC cell viability. Further mechanistic analysis revealed that chrysin, not the 5-FU combination, induced ROS generation, and in turn, inhibited the phosphorylation of protein kinase B (Akt) and mammalian target of rapamycin (mTOR). Collectively, these results imply that chrysin may be a potential replacement for the 5-FU and oxaliplatin combination to achieve antitumor activity through autophagy for CRC treatment in the future.

Prucalopride inhibits the glioma cells proliferation and induces autophagy via AKT-mTOR pathway

Backgrounds

Glioma is the most fatal primary brain glioma in central nervous system mainly attributed to its high invasion. Prucalopride, a Serotonin-4 (5-HT4) receptor agonist, has been reported to regulate neurodevelopment. This study aimed to investigate the influence of the Prucalopride on glioma cells and unveil underlying mechanism.

Methods

In this study, glioma cells proliferation was evaluated by Cell counting kit-8 (CCK8). Wound healing and transwell assay were used to test cellular migration and invasion. Flow cytometry was utilized to determine cellular apoptosis rate. Apoptosis related markers, autophagy markers, and protein kinase B (AKT)-mammalian target of rapamycin (mTOR) pathway key molecules were detected using western blot assay.

Results

As a result, the proliferation, migration and invasiveness of glioma cells were impaired by Prucalopride treatment, the apoptosis rate of glioma cells was enhanced by Prucalopride stimulation, accompanied by the increased pro-apoptosis proteins Bax and Cleaved caspase-3 and decreased anti-apoptosis protein Bcl-2. Prucalopride significantly promoted autophagy by increased expression level of Beclin 1 and LC3-II, while decreased expression level of p62. Prucalopride administration resulted in obvious inhibitions of key molecules of AKT-mTOR pathway, including phosphorylated- (p-) AKT, p-mTOR and phosphorylated-ribosomal p70S6 kinase (p-P70S6K).

Conclusions

Taking together, these results indicate that Prucalopride may be likely to play an anti-tumor role in glioma cells, which suggests potential implications for glioma promising therapy alternation in the further clinics.

The change of nuclear LC3 distribution in acute myeloid leukemia cells

Making sure the change of nuclear LC3 distribution in the autophagy of acute myeloid leukemia (AML) cell and finding out the regulation mechanism may lead to a breakthrough for killing AML cells. Western blots were performed to assess the expression of autophagy proteins. Changes in the LC3 distribution were monitored by immunofluorescence assays together with western blots, and the expression levels of Sirt1, DOR, Beclin1, HMGB1, and AMPK mRNA were detected via fluorescent quantitative PCR. The effects of Sirt1 and DOR on cell proliferation and survival were analyzed by MTT, flow cytometry, and western blotting assays. We found that treating AML cells with Ara-c or Sorafenib resulted in autophagy enhancement, and when autophagy was enhanced, nuclear LC3 moved into the cytoplasm. Notably, when autophagy was inhibited by blocking the nuclear LC3 shift, the cytotoxicity of drugs was enhanced. Our results also identified Sirt1 and DOR as regulatory molecules for the observed nuclear LC3 shift, and these molecules further affected the expression of Beclin1, HMGB1, and AMPK. Our results suggest the distribution of nuclear LC3 can be a novel way for further studying death of AML cells,and the regulatory molecules may be new targets for treating AML.

Bone marrow mesenchymal stem cells conditioned medium protects VSC4.1 cells against 2,5-hexanedione-induced autophagy via NGF-PI3K/Akt/mTOR signaling pathway

We aimed to investigate the effects of bone marrow mesenchymal stem cell conditioned medium (BMSC-CM) in preventing 2,5-hexanedione (HD)-induced damage to motoneurons, and examined the molecular mechanisms that mediate these effects. VSC4.1 cells were exposed to 25 mM HD for 24 h followed by incubation with DMEM for 24 h. HD-treated cells were incubated with BMSC-CM at varied concentrations. Incubation with BMSC-CM ameliorated the decreased cell viability and reduced LDH release from cells exposed to HD. BMSC-CM suppressed the elevated number of autophagic vacuoles, cells with LC3 puncta, increased LC3-II/LC3-I ratio, and decreased p62 caused by HD exposure. BMSC-CM elevated NGF and p-TrkA expressions in HD-treated cells. Administration of NGF inhibited autophagy, an effect that was similar to that observed after BMSC-CM treatment; this effect was abolished by the addition of NGF-neutralizing antibodies. BMSC-CM or NGF elevated p-protein kinase B (Akt) and p-mammalian target of rapamycin (mTOR) in HD-exposed cells, which was interrupted by TrkA inhibitor, K252a and mTOR inhibitor, rapamycin. BMSC-CM prevented HD-induced autophagic cell damage in VSC4.1 cells. The neuroprotective effect of BMSC-CM appeared to be at least partly associated with its ability to trigger the NGF-phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR signaling pathway.

High Mobility Group Box-1 (HMGb1): Current Wisdom and Advancement as a Potential Drug Target

High mobility group box-1 (HMGb1) protein, a nuclear non-histone protein that is released or secreted from the cell in response to damage or stress, is a sentinel for the immune system that plays a critical role in cell survival/death pathways. This review highlights key features of the endogenous danger-associated molecular pattern (DAMP) protein, HMGb1 in the innate inflammatory response along with various cofactors and receptors that regulate its downstream effects. The evidence demonstrating increased levels of HMGb1 in human inflammatory diseases and conditions is presented, along with a summary of current small molecule or peptide-like antagonists proven to specifically target HMGb1. Additionally, we delineate the measures needed toward validating this protein as a clinically relevant biomarker or bioindicator and as a relevant drug target.

Mechanisms of autophagy activation in endothelial cell and their targeting during normothermic machine liver perfusion

Ischaemia-reperfusion injury (IRI) is the leading cause of injury seen in the liver following transplantation. IRI also causes injury following liver surgery and haemodynamic shock. The first cells within the liver to be injured by IRI are the liver sinusoidal endothelial cells (LSEC). Recent evidence suggests that LSEC co-ordinate and regulates the livers response to a variety of injuries. It is becoming increasingly apparent that the cyto-protective cellular process of autophagy is a key regulator of IRI. In particular LSEC autophagy may be an essential gatekeeper to the development of IRI. The recent availability of liver perfusion devices has allowed for the therapeutic targeting of autophagy to reduce IRI. In particular normothermic machine liver perfusion (NMP-L) allow the delivery of pharmacological agents to donor livers whilst maintaining physiological temperature and hepatic flow rates. In this review we summarise the current understanding of endothelial autophagy and how this may be manipulated during NMP-L to reduce liver IRI.

Autophagy-mediated neuroprotection induced by octreotide in an ex vivo model of early diabetic retinopathy

Neuronal injury plays a major role in diabetic retinopathy (DR). Our hypothesis was that the balance between neuronal death and survival may depend on a similar equilibrium between apoptosis and autophagy and that a neuroprotectant may act by influencing this equilibrium. Ex vivo mouse retinal explants were treated with high glucose (HG) for 10days and the somatostatin analog octreotide (OCT) was used as a neuroprotectant. Chloroquine (CQ) was used as an autophagy inhibitor. Apoptotic and autophagic markers were evaluated using western blot and immunohistochemistry. HG-treated explants displayed a significant increase of apoptosis paralleled by a significant decrease of the autophagic flux, which was likely to be due to increased activity of the autophagy regulator mTOR (mammalian target of rapamycin). Treatment with OCT rescued HG-treated retinal explants from apoptosis and determined an increase of autophagic activity with concomitant mTOR inhibition. Blocking the autophagic flux with CQ completely abolished the anti-apoptotic effect of OCT. Immunohistochemical observations showed that OCT-induced autophagy is localized to populations of bipolar and amacrine cells and to ganglion cells. These observations revealed the antithetic role of apoptosis and autophagy, highlighting their equilibrium from which neuronal survival is likely to depend. These data suggest the crucial role covered by autophagy, which could be considered as a molecular target for DR neuroprotective treatment strategies.