'How can I halt thee?' The puzzles involved in autophagic inhibition

Role of autophagy and proteostasis in neurodegenerative diseases: Exploring the therapeutic interventions

Neurodegenerative disorders are devastating disorders characterized by gradual loss of neurons and cognition or mobility impairment. The common pathological features of these diseases are associated with the accumulation of misfolded or aggregation of proteins. The pivotal roles of autophagy and proteostasis in maintaining cellular health and preventing the accumulation of misfolded proteins, which are associated with neurodegenerative diseases like Huntington's disease (HD), Alzheimer's disease (AD), and Parkinson's disease (PD). This article presents an in-depth examination of the interplay between autophagy and proteostasis, highlighting how these processes cooperatively contribute to cellular homeostasis and prevent pathogenic protein aggregate accumulation. Furthermore, the review emphasises the potential therapeutic implications of targeting autophagy and proteostasis to mitigate neurodegenerative diseases. While advancements in research hold promise for developing novel treatments, the article also addresses the challenges and complexities associated with modulating these intricate cellular pathways. Ultimately, advancing understanding of the underlying mechanism of autophagy and proteostasis in neurodegenerative disorders provides valuable insights into potential therapeutic avenues and future research directions.

Targeting of lysosomal-bound protein mEAK-7 for cancer therapy

mEAK-7 (mammalian EAK-7 or MTOR-associated protein, eak-7 homolog), is an evolutionarily conserved lysosomal membrane protein that is highly expressed in several cancer cells. Multiple recent studies have identified mEAK-7 as a positive activator of mTOR (mammalian/mechanistic target of rapamycin) signaling via an alternative mTOR complex, implying that mEAK-7 plays an important role in the promotion of cancer proliferation and migration. In addition, structural analyses investigating interactions between mEAK-7 and V-ATPase, a protein complex responsible for regulating pH homeostasis in cellular compartments, have suggested that mEAK-7 may contribute to V-ATPase-mediated mTORC1 activation. The C-terminal α-helix of mEAK-7 binds to the D and B subunits of the V-ATPase, creating a pincer-like grip around its B subunit. This binding undergoes partial disruption during ATP hydrolysis, potentially enabling other proteins such as mTOR to bind to the α-helix of mEAK-7. mEAK-7 also promotes chemoresistance and radiation resistance by sustaining DNA damage-mediated mTOR signaling through interactions with DNA-PKcs (DNA-dependent protein kinase catalytic subunit). Taken together, these findings indicate that mEAK-7 may be a promising therapeutic target against tumors. However, the precise molecular mechanisms and signal transduction pathways of mEAK-7 in cancer remain largely unknown, motivating the need for further investigation. Here, we summarize the current known roles of mEAK-7 in normal physiology and cancer development by reviewing the latest studies and discuss potential future developments of mEAK-7 in targeted cancer therapy.

The Golgi stacking protein GRASP55 is targeted by the natural compound prodigiosin

BACKGROUND

The bacterial secondary metabolite prodigiosin has been shown to exert anticancer, antimalarial, antibacterial and immunomodulatory properties. With regard to cancer, it has been reported to affect cancer cells but not non-malignant cells, rendering prodigiosin a promising lead compound for anticancer drug discovery. However, a direct protein target has not yet been experimentally identified.

METHODS

We used mass spectrometry-based thermal proteome profiling in order to identify target proteins of prodigiosin. For target validation, we employed a genetic knockout approach and electron microscopy.

RESULTS

We identified the Golgi stacking protein GRASP55 as target protein of prodigiosin. We show that prodigiosin treatment severely affects Golgi morphology and functionality, and that prodigiosin-dependent cytotoxicity is partially reduced in GRASP55 knockout cells. We also found that prodigiosin treatment results in decreased cathepsin activity and overall blocks autophagic flux, whereas co-localization of the autophagosomal marker LC3 and the lysosomal marker LAMP1 is clearly promoted. Finally, we observed that autophagosomes accumulate at GRASP55-positive structures, pointing towards an involvement of an altered Golgi function in the autophagy-inhibitory effect of this natural compound.

CONCLUSION

Taken together, we propose that prodigiosin affects autophagy and Golgi apparatus integrity in an interlinked mode of action involving the regulation of organelle alkalization and the Golgi stacking protein GRASP55. Video Abstract.

Modulation of Autophagy Direction to Enhance Antitumor Effect of Endoplasmic-Reticulum-Targeted Therapy: Left or Right?

Strategies that induce dysfunction in the endoplasmic reticulum (ER) hold great promise for anticancer therapy, but remain unsatisfactory due to the compensatory autophagy induction after ER disruption. Moreover, as autophagy can either promote or suppress cell survival, which direction of autophagy better suits ER-targeting therapy remains controversial. Here, a targeted nanosystem is constructed, which efficiently escorts anticancer therapeutics into the ER, triggering substantial ER stress and autophagy. Concurrently, an autophagy enhancer or inhibitor is combined into the same nanoparticle, and their impacts on ER-related activities are compared. In the orthotopic breast cancer mouse model, the autophagy enhancer increases the antimetastasis effect of ER-targeting therapy and suppresses over 90% of cancer metastasis, while the autophagy inhibitor has a bare effect. Mechanism studies reveal that further enhancing autophagy accelerates central protein snail family transcriptional repressor 1 (SNAI1) degradation, suppressing downstream epithelial-mesenchymal transition, while inhibiting autophagy does the opposite. With the same trend, ER-targeting therapy combined with an autophagy enhancer provokes stronger immune response and tumor inhibition than the autophagy inhibitor. Mechanism studies reveal that the autophagy enhancer elevates Ca2+ release from the ER and functions as a cascade amplifier of ER dysfunction, which accelerates Ca2+ release, resulting in immunogenic cell death (ICD) induction and eventually triggering immune responses. Together, ER-targeting therapy benefits from the autophagy-enhancing strategy more than the autophagy-inhibiting strategy for antitumor and antimetastasis treatment.

Toxic Effects Induced by Diuron and Its Metabolites in Caenorhabditis elegans

The toxicity of diuron herbicide and its metabolites has been extensively investigated; however, their precise toxic mechanisms have yet to be fully appreciated. In this context, we evaluated the toxic mechanism of diuron, 3,4-dichloroaniline (DCA) and 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU), using Caenorhabditis elegans (C. elegans) in the L1 larval stage. For this purpose, worms were acutely exposed to the test chemicals with a preliminary concentration range of 0.5 to 500 μM and first analyzed for lethality (%). Next, the highest concentration (500 μM) was considered for survival (%), reactive oxygen and nitrogen species (RONS), glutathione (GSH) and ATP levels, autophagy index, behavior, and dopaminergic neurodegeneration parameters. Interestingly, increased lethality (%) was found for all chemicals at the higher concentrations tested (100 and 500 μM), with significant differences at 500 μM DCA (p < 0.05). A decrease in the median survival was observed mainly for DCA. Although no changes were observed in RONS production, GSH levels were significantly increased upon diuron and DCA treatment, likely reflecting an attempt to restore the redox status. Moreover, diuron and its metabolites impaired ATP levels, suggesting an alteration in mitochondrial function. The latter may trigger autophagy as an adaptive survival mechanism, but this was not observed in C. elegans. Dopaminergic neurotoxicity was observed upon treatment with all the tested chemicals, but only diuron induced alterations in the worms' locomotor behavior. Combined, these results indicate that exposure to high concentrations of diuron and its metabolites elicit distinct adverse outcomes in C. elegans, and DCA in particular, plays an important role in the overall toxicity observed in this experimental model.

Tubulin deacetylase NDST3 modulates lysosomal acidification: Implications in neurological diseases

Neurological diseases (NDs), featured by progressive dysfunctions of the nervous system, have become a growing burden for the aging populations. N-Deacetylase and N-sulfotransferase 3 (NDST3) is known to catalyze deacetylation and N-sulfation on disaccharide substrates. Recently, NDST3 is identified as a novel deacetylase for tubulin, and its newly recognized role in modulating microtubule acetylation and lysosomal acidification provides fresh insights into ND therapeutic approaches using NDST3 as a target. Microtubule acetylation and lysosomal acidification have been reported to be critical for activities in neurons, implying that the regulators of these two biological processes, such as the previously known microtubule deacetylases, histone deacetylase 6 (HDAC6) and sirtuin 2 (SIRT2), could play important roles in various NDs. Aberrant NDST3 expression or tubulin acetylation has been observed in an increasing number of NDs, including amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD), schizophrenia and bipolar disorder, Alzheimer's disease (AD), and Parkinson's disease (PD), suggesting that NDST3 is a key player in the pathogenesis of NDs and may serve as a target for development of new treatment of NDs.

Emerging roles of autophagy in the development and treatment of urothelial carcinoma of the bladder

INTRODUCTION

High recurrence rates, frequent surveillance strategies, and current multidisciplinary treatment approaches make urothelial carcinoma of bladder (UCB) one of the most expensive cancers to clinically manage. Recent studies have demonstrated a role for autophagy in bladder tumorigenesis. It serves as a tumor suppressor by maintaining genomic integrity and preventing tumor proliferation during initial stages of tumor development. Nevertheless, once established, cancer cells may utilize protective autophagy to endure cellular stress and survive in the adverse environment. Its excessive stimulation supports cancer cells' resistance to therapeutic modalities.

AREAS COVERED

PubMed and Google Scholar electronic databases were searched for recently published studies. This review summarizes emerging roles of autophagy in development/progression of UCB and treatment resistance and explores novel therapeutic targets for prevention of cancer invasion, metastatic spread', and disease relapse.

EXPERT OPINION

The development of novel therapies via targeting of autophagy may augment current treatment regimens and improve clinical outcomes. Synthetic compounds or plant-based metabolites are reported to enhance cancer therapies by modulating autophagic flux. Successful autophagy-focused therapeutic intervention requires a mechanistic understanding of autophagic effects on tumor initiation and progression and the development of efficient biomarkers to monitor it in tumor tissues.

Autophagy Modulators in Cancer Therapy

Autophagy is a process of self-degradation that plays an important role in removing damaged proteins, organelles or cellular fragments from the cell. Under stressful conditions such as hypoxia, nutrient deficiency or chemotherapy, this process can also become the strategy for cell survival. Autophagy can be nonselective or selective in removing specific organelles, ribosomes, and protein aggregates, although the complete mechanisms that regulate aspects of selective autophagy are not fully understood. This review summarizes the most recent research into understanding the different types and mechanisms of autophagy. The relationship between apoptosis and autophagy on the level of molecular regulation of the expression of selected proteins such as p53, Bcl-2/Beclin 1, p62, Atg proteins, and caspases was discussed. Intensive studies have revealed a whole range of novel compounds with an anticancer activity that inhibit or activate regulatory pathways involved in autophagy. We focused on the presentation of compounds strongly affecting the autophagy process, with particular emphasis on those that are undergoing clinical and preclinical cancer research. Moreover, the target points, adverse effects and therapeutic schemes of autophagy inhibitors and activators are presented.

Broad-Spectrum HDAC Inhibitors Promote Autophagy through FOXO Transcription Factors in Neuroblastoma

Depending on context and tumor stage, deregulation of autophagy can either suppress tumorigenesis or promote chemoresistance and tumor survival. Histone deacetylases (HDACs) can modulate autophagy; however, the exact mechanisms are not fully understood. Here, we analyze the effects of the broad-spectrum HDAC inhibitors (HDACi) panobinostat and vorinostat on the transcriptional regulation of autophagy with respect to autophagy transcription factor activity (Transcription factor EB-TFEB, forkhead boxO-FOXO) and autophagic flux in neuroblastoma cells. In combination with the late-stage autophagic flux inhibitor bafilomycin A1, HDACis increase the number of autophagic vesicles, indicating an increase in autophagic flux. Both HDACi induce nuclear translocation of the transcription factors FOXO1 and FOXO3a, but not TFEB and promote the expression of pro-autophagic FOXO1/3a target genes. Moreover, FOXO1/3a knockdown experiments impaired HDACi treatment mediated expression of autophagy related genes. Combination of panobinostat with the lysosomal inhibitor chloroquine, which blocks autophagic flux, enhances neuroblastoma cell death in culture and hampers tumor growth in vivo in a neuroblastoma zebrafish xenograft model. In conclusion, our results indicate that pan-HDACi treatment induces autophagy in neuroblastoma at a transcriptional level. Combining HDACis with autophagy modulating drugs suppresses tumor growth of high-risk neuroblastoma cells. These experimental data provide novel insights for optimization of treatment strategies in neuroblastoma.

Tau oligomers accumulation sensitizes prostate cancer cells to docetaxel treatment

PURPOSE

Human tau is a highly dynamic, multifunctional protein expressed in different isoforms and conformers, known to modulate microtubule turnover. Tau oligomers are considered pathologic forms of the protein able to initiate specific protein accumulation diseases, called tauopathies. In our study, we investigated the potential association between autophagy and tau oligomers accumulation and its role in the response of prostate cancer cells to docetaxel.

METHODS

We evaluated in vitro the expression of tau oligomers in prostate cancer cell lines, PC3 and DU145, in presence of autophagy inhibitors and investigated the role of tau oligomers accumulation in resistance to docetaxel treatment.

RESULTS

Tau protein was basally expressed in prostate cancer lines as several monomeric and oligomeric forms. The pharmacologic inhibition of autophagy induced in cancer cells the accumulation of tau protein, with a prevalent expression of oligomeric forms. Immunofluorescence analysis of untreated cells revealed that tau was visible mainly in dividing cells where it was localized on the mitotic spindle. Inhibition of autophagy determined an evident upregulation of tau signal in dividing cells and the presence of aberrant monoastral mitotic spindles. The accumulation of tau oligomers was associated with DNA DSB and increased cytotoxic effect by docetaxel.

CONCLUSIONS

Our data indicate that autophagy could exert a promoting role in cancer growth and during chemotherapy facilitating degradation of tau protein and thus blocking the antimitotic effect of accumulated tau oligomers. Thus, therapeutic strategies aimed at stimulating tau oligomers formation, such as autophagy inhibition, could be an effective adjuvant in cancer therapy.

Small Extracellular Vesicles: A Novel Avenue for Cancer Management

Extracellular vesicles are small membrane particles derived from various cell types. EVs are broadly classified as ectosomes or small extracellular vesicles, depending on their biogenesis and cargoes. Numerous studies have shown that EVs regulate multiple physiological and pathophysiological processes. The roles of small extracellular vesicles in cancer growth and metastasis remain to be fully elucidated. As endogenous products, small extracellular vesicles are an ideal drug delivery platform for anticancer agents. However, several aspects of small extracellular vesicle biology remain unclear, hindering the clinical implementation of small extracellular vesicles as biomarkers or anticancer agents. In this review, we summarize the utility of cancer-related small extracellular vesicles as biomarkers to detect early-stage cancers and predict treatment outcomes. We also review findings from preclinical and clinical studies of small extracellular vesicle-based cancer therapies and summarize interventional clinical trials registered in the United States Food and Drug Administration and the Chinese Clinical Trials Registry. Finally, we discuss the main challenges limiting the clinical implementation of small extracellular vesicles and recommend possible approaches to address these challenges.

The ERK1/2-ATG13-FIP200 signaling cascade is required for autophagy induction to protect renal cells from hypoglycemia-induced cell death

Autophagy, an evolutionarily conserved lysosomal degradation pathway, is known to regulate a variety of physiological and pathological processes. At present, the function and the precise mechanism of autophagy regulation in kidney and renal cells remain elusive. Here, we explored the role of ERK1 and ERK2 (referred as ERK1/2 hereafter) in autophagy regulation in renal cells in response to hypoglycemia. Glucose starvation potently and transiently activated ERK1/2 in renal cells, and this was concomitant with an increase in autophagic flux. Perturbing ERK1/2 activation by treatment with inhibitors of RAF or MEK1/2, via the expression of a dominant-negative mutant form of MEK1/2 or RAS, blocked hypoglycemia-mediated ERK1/2 activation and autophagy induction in renal cells. Glucose starvation also induced the accumulation of reactive oxygen species in renal cells, which was involved in the activation of the ERK1/2 cascade and the induction of autophagy in renal cells. Interestingly, ATG13 and FIP200, the members of the ULK1 complex, contain the ERK consensus phosphorylation sites, and glucose starvation induced an association between ATG13 or FIP200 and ERK1/2. Moreover, the expression of the phospho-defective mutants of ATG13 and FIP200 in renal cells blocked glucose starvation-induced autophagy and rendered cells more susceptible to hypoglycemia-induced cell death. However, the expression of the phospho-mimic mutants of ATG13 and FIP200 induced autophagy and protected renal cells from hypoglycemia-induced cell death. Taken together, our results demonstrate that hypoglycemia activates the ERK1/2 signaling to regulate ATG13 and FIP200, thereby stimulating autophagy to protect the renal cells from hypoglycemia-induced cell death.

Prodigiosin Sensitizes Sensitive and Resistant Urothelial Carcinoma Cells to Cisplatin Treatment

Cisplatin-based treatment is the standard of care therapy for urothelial carcinomas. However, complex cisplatin resistance mechanisms limit the success of this approach. Both apoptosis and autophagy have been shown to contribute to this resistance. Prodigiosin, a secondary metabolite from various bacteria, exerts different biological activities including the modulation of these two cellular stress response pathways. We analyzed the effect of prodigiosin on protein levels of different autophagy- and apoptosis-related proteins in cisplatin-sensitive and -resistant urothelial carcinoma cells (UCCs). Furthermore, we investigated the effect on cell viability of prodigiosin alone or in combination with cisplatin. We made use of four different pairs of cisplatin-sensitive and -resistant UCCs. We found that prodigiosin blocked autophagy in UCCs and re-sensitized cisplatin-resistant cells to apoptotic cell death. Furthermore, we found that prodigiosin is a potent anticancer agent with nanomolar IC50 values in all tested UCCs. In combination studies, we observed that prodigiosin sensitized both cisplatin-sensitive and -resistant urothelial carcinoma cell lines to cisplatin treatment with synergistic effects in most tested cell lines. These effects of prodigiosin are at least partially mediated by altering lysosomal function, since we detected reduced activities of cathepsin B and L. We propose that prodigiosin is a promising candidate for the therapy of cisplatin-resistant urothelial carcinomas, either as a single agent or in combinatory therapeutic approaches.

Extracellular microvesicles promote microglia-mediated pro-inflammatory responses to ethanol

Alcohol use disorder (AUD) pathology features pro-inflammatory gene induction and microglial activation. The underlying cellular processes that promote this activation remain unclear. Previously considered cellular debris, extracellular vesicles (EVs) have emerged as mediators of inflammatory signaling in several disease states. We investigated the role of microvesicles (MVs, 50 nm-100 µm diameter EVs) in pro-inflammatory and microglial functional gene expression using primary organotypic brain slice culture (OBSC). Ethanol caused a unique immune gene signature that featured: temporal induction of pro-inflammatory TNF-α and IL-1β, reduction of homeostatic microglia state gene Tmem119, progressive increases in purinergic receptor P2RY12 and the microglial inhibitory fractalkine receptor CX3CR1, an increase in the microglial presynaptic gene C1q, and a reduction in the phagocytic gene TREM2. MV signaling was implicated in this response as reduction of MV secretion by imipramine blocked pro-inflammatory TNF-α and IL-1β induction by ethanol, and ethanol-conditioned MVs (EtOH-MVs) reproduced the ethanol-associated immune gene signature in naïve OBSC slices. Depletion of microglia prior to ethanol treatment prevented pro-inflammatory activity of EtOH-MVs, as did incubation of EtOH-MVs with the HMGB1 inhibitor glycyrrhizin. Ethanol caused HMGB1 secretion from cultured BV2 microglia in MVs through activation of PI3 kinase. In summary, these studies find MVs modulate pro-inflammatory gene induction and microglial activation changes associated with ethanol. Thus, MVs may represent a novel therapeutic target to reduce neuroinflammation in the setting of alcohol abuse or other diseases that feature a neuroimmune component. [Correction added on 5 April 2021, after first online publication: The copyright line was changed.].

Autophagy is a pro-survival adaptive response to heat shock in bovine cumulus-oocyte complexes

Autophagy is a physiological mechanism that can be activated under stress conditions. However, the role of autophagy during oocyte maturation has been poorly investigated. Therefore, this study characterized the role of autophagy on developmental competence and gene expression of bovine oocytes exposed to heat shock (HS). Cumulus-oocyte-complexes (COCs) were matured at Control (38.5 °C) and HS (41 °C) temperatures in the presence of 0 and 10 mM 3-methyladenine (3MA; autophagy inhibitor). Western blotting analysis revealed that HS increased autophagy marker LC3-II/LC3-I ratio in oocytes. However, there was no effect of temperature for oocytes matured with 3MA. On cumulus cells, 3MA reduced LC3-II/LC3-I ratio regardless of temperature. Inhibition of autophagy during IVM of heat-shocked oocytes (3MA-41 °C) reduced cleavage and blastocyst rates compared to standard in vitro matured heat-shocked oocytes (IVM-41 °C). Therefore, the magnitude of HS detrimental effects was greater in the presence of autophagy inhibitor. Oocyte maturation under 3MA-41 °C reduced mRNA abundance for genes related to energy metabolism (MTIF3), heat shock response (HSF1), and oocyte maturation (HAS2 and GREM1). In conclusion, autophagy is a stress response induced on heat shocked oocytes. Inhibition of autophagy modulated key functional processes rendering the oocyte more susceptible to the deleterious effects of heat shock.

Exocytosis of Progeny Infectious Varicella-Zoster Virus Particles via a Mannose-6-Phosphate Receptor Pathway without Xenophagy following Secondary Envelopment

The literature on the egress of different herpesviruses after secondary envelopment is contradictory. In this report, we investigated varicella-zoster virus (VZV) egress in a cell line from a child with Pompe disease, a glycogen storage disease caused by a defect in the enzyme required for glycogen digestion. In Pompe cells, both the late autophagy pathway and the mannose-6-phosphate receptor (M6PR) pathway are interrupted. We have postulated that intact autophagic flux is required for higher recoveries of VZV infectivity. To test that hypothesis, we infected Pompe cells and then assessed the VZV infectious cycle. We discovered that the infectious cycle in Pompe cells was remarkably different from that of either fibroblasts or melanoma cells. No large late endosomes filled with VZV particles were observed in Pompe cells; only individual viral particles in small vacuoles were seen. The distribution of the M6PR pathway (trans-Golgi network to late endosomes) was constrained in infected Pompe cells. When cells were analyzed with two different anti-M6PR antibodies, extensive colocalization of the major VZV glycoprotein gE (known to contain M6P residues) and the M6P receptor (M6PR) was documented in the viral highways at the surfaces of non-Pompe cells after maximum-intensity projection of confocal z-stacks, but neither gE nor the M6PR was seen in abundance at the surfaces of infected Pompe cells. Taken together, our results suggested that (i) Pompe cells lack a VZV trafficking pathway within M6PR-positive large endosomes and (ii) most infectious VZV particles in conventional cell substrates are transported via large M6PR-positive vacuoles without degradative xenophagy to the plasma membrane.IMPORTANCE The long-term goal of this research has been to determine why VZV, when grown in cultured cells, invariably is more cell associated and has a lower titer than other alphaherpesviruses, such as herpes simplex virus 1 (HSV1) or pseudorabies virus (PRV). Data from both HSV1 and PRV laboratories have identified a Rab6 secretory pathway for the transport of single enveloped viral particles from the trans-Golgi network within small vacuoles to the plasma membrane. In contrast, after secondary envelopment in fibroblasts or melanoma cells, multiple infectious VZV particles accumulated within large M6PR-positive late endosomes that were not degraded en route to the plasma membrane. We propose that this M6PR pathway is most utilized in VZV infection and least utilized in HSV1 infection, with PRV's usage being closer to HSV1's usage. Supportive data from other VZV, PRV, and HSV1 laboratories about evidence for two egress pathways are included.

The Second Generation Antibody-Drug Conjugate SYD985 Overcomes Resistances to T-DM1

Trastuzumab-emtansine (T-DM1) is an antibody-drug conjugate (ADC) approved for the treatment of HER2 (human epidermal growth factor receptor 2)-positive breast cancer. T-DM1 consists of trastuzumab covalently linked to the cytotoxic maytansinoid DM1 via a non-cleavable linker. Despite its efficacy, primary or acquired resistance frequently develops, particularly in advanced stages of the disease. Second generation ADCs targeting HER2 are meant to supersede T-DM1 by using a cleavable linker and a more potent payload with a different mechanism of action. To determine the effect of one of these novel ADCs, SYD985, on tumors resistant to T-DM1, we developed several patient-derived models of resistance to T-DM1. Characterization of these models showed that previously described mechanisms-HER2 downmodulation, impairment of lysosomal function and upregulation of drug efflux pumps-account for the resistances observed, arguing that mechanisms of resistance to T-DM1 are limited, and most of them have already been described. Importantly, SYD985 was effective in these models, showing that the resistance to first generation ADCs can be overcome with an improved design.

Zebrafish C-reactive protein isoforms inhibit SVCV replication by blocking autophagy through interactions with cell membrane cholesterol

In the present work, the mechanisms involved in the recently reported antiviral activity of zebrafish C-reactive protein-like protein (CRP1-7) against the spring viraemia of carp rhabdovirus (SVCV) in fish are explored. The results neither indicate blocking of the attachment or the binding step of the viral replication cycle nor suggest the direct inhibition of G protein fusion activity or the stimulation of the host’s interferon system. However, an antiviral state in the host is induced. Further results showed that the antiviral protection conferred by CRP1-7 was mainly due to the inhibition of autophagic processes. Thus, given the high affinity of CRPs for cholesterol and the recently described influence of the cholesterol balance in lipid rafts on autophagy, both methyl-β-cyclodextrin (a cholesterol-complexing agent) and 25-hydroxycholesterol (a cholesterol molecule with antiviral properties) were used to further describe CRP activity. All the tested compounds exerted antiviral activity by affecting autophagy in a similar manner. Further assays indicate that CRP reduces autophagy activity by initially disturbing the cholesterol ratios in the host cellular membranes, which in turn negatively affects the intracellular regulation of reactive oxygen species (ROS) and increases lysosomal pH as a consequence. Ultimately, here we propose that such pH changes exert an inhibitory direct effect on SVCV replication by disrupting the pH-dependent membrane-fusogenic ability of the viral glycoprotein G, which allows the release of the virus from endosomes into cytoplasm during its entry phase.

Autophagy modulators for the treatment of oral and esophageal squamous cell carcinomas

Oral squamous cell carcinomas (OSCC) and esophageal squamous cell carcinomas (ESCC) exhibit a survival rate of less than 60% and 40%, respectively. Late-stage diagnosis and lack of effective treatment strategies make both OSCC and ESCC a significant health burden. Autophagy, a lysosome-dependent catabolic process, involves the degradation of intracellular components to maintain cell homeostasis. Targeting autophagy has been highlighted as a feasible therapeutic strategy with clinical utility in cancer treatment, although its associated regulatory mechanisms remain elusive. The detection of relevant biomarkers in biological fluids has been anticipated to facilitate early diagnosis and/or prognosis for these tumors. In this context, recent studies have indicated the presence of specific proteins and small RNAs, detectable in circulating plasma and serum, as biomarkers. Interestingly, the interplay between biomarkers (eg, exosomal microRNAs) and autophagic processes could be exploited in the quest for targeted and more effective therapies for OSCC and ESCC. In this review, we give an overview of the available biomarkers and innovative targeted therapeutic strategies, including the application of autophagy modulators in OSCC and ESCC. Additionally, we provide a viewpoint on the state of the art and on future therapeutic perspectives combining the early detection of relevant biomarkers with drug discovery for the treatment of OSCC and ESCC.

Anti-Tumor Potential of a 5-HT3 Receptor Antagonist as a Novel Autophagy Inducer in Lung Cancer: A Retrospective Clinical Study with In Vitro Confirmation

Unlike 5-hydroxytryptamine (5-HT, serotonin) 1 and 5-HT2, the effect of 5-HT3 receptors on tumor cells is poorly understood. We conducted this study to determine whether the perioperative use of 5-HT3 receptor antagonists, which are widely used antiemetics, impacts the recurrence and mortality after lung cancer surgery and related anti-tumor mechanisms. From data on 411 patients, propensity score matching was used to produce 60 1:2 matched pairs of patients, and variables associated with the prognosis after open lung cancer surgery were analyzed. Additionally, the effects of 5-HT3 receptor antagonists were confirmed in vitro on A549 human lung adenocarcinoma cells. Cancer recurrence occurred in 10 (8.2%) and 14 (22.95%) patients (p = 0.005), treated or untreated, with palonosetron or ramosetron. Perioperative usage of palonosetron or ramosetron was also associated with lower recurrence rate after lung cancer surgery (hazard ratio (HR), 0.293; 95% confidence interval (CI) 0.110-0.780, p = 0.0141). Our in vitro experiments also showed that palonosetron and ramosetron inhibited cell proliferation and colony formation and reduced migration, which was associated with autophagic cell death via the extracellular signal-regulated kinase (ERK) pathway. Palonosetron and ramosetron may have anti-tumor potential against lung cancer cells, suggesting the need to consider these drugs as first-choice antiemetics in patients undergoing lung cancer surgery.

Pro-survival autophagy: An emerging candidate of tumor progression through maintaining hallmarks of cancer

Autophagy is an evolutionary conserved catabolic process that regulates the cellular homeostasis by targeting damaged cellular contents and organelles for lysosomal degradation and sustains genomic integrity, cellular metabolism, and cell survival during diverse stress and adverse conditions. Recently, the role of autophagy is extremely debated in the regulation of cancer initiation and progression. Although autophagy has a dichotomous role in the regulation of cancer, growing numbers of studies largely indicate the pro-survival role of autophagy in cancer progression and metastasis. In this review, we discuss the detailed mechanisms of autophagy, the role of pro-survival autophagy that positively drives several classical as well as emerging hallmarks of cancer for tumorigenic progression, and also we address various autophagy inhibitors that could be harnessed against pro-survival autophagy for effective cancer therapeutics. Finally, we highlight some outstanding problems that need to be deciphered extensively in the future to unravel the role of autophagy in tumor progression.

Cytotoxic and Antitumor Activity of Lactaptin in Combination with Autophagy Inducers and Inhibitors

Autophagy is a degradative process in which cellular organelles and proteins are recycled to restore homeostasis and cellular metabolism. Autophagy can be either a prosurvival or a prodeath process and remains one of the most fundamental processes for cell vitality. Thus autophagy modulation is an important approach for reinforcement anticancer therapeutics. Earlier we have demonstrated that recombinant analog of human milk protein lactaptin (RL2) induced apoptosis of various cultured cancer cells and activated lipidation of microtubule-associated protein 1 light chain 3 (LC3). In this study we investigated whether autophagy inhibitors-chloroquine (CQ), Ku55933 (Ku), and 3-methyladenine (3MA)-or inducer-rapamycin (Rap)-can enhance cytotoxic activity of lactaptin analog in cancer cells and its anticancer activity in the mice model. Western Blot analysis revealed that RL2 induced short-term autophagy in MDA-MB-231 and MCF-7 cells at early stages of incubation and that these data were confirmed by the transmission electron microscopy of autophagosome/autophagolysosome formation. RL2 stimulates reactive oxygen species (ROS) production, autophagosomes accumulation, upregulation of ATG5 with processing of LC3I to LC3II, and downregulation of p62/sequestosome 1 (p62). We have shown that autophagy modulators, CQ, Ku, and Rap, synergistically increased cytotoxicity of RL2, and RL2 with CQ induced autophagic cell death. In addition, CQ, Ku, and Rap in combination with RL2 decreased activity of lysosomal protease Cathepsin D. More importantly, combining RL2 with CQ, we improved antitumor effect in mice. Detected synergistic cytotoxic effects of both types of autophagy regulators, inhibitors, and inducers with RL2 against cancer cells allow us to believe that these combinations can be a basis for the new anticancer approach. Finally, we suppose that CQ and Rap promoting of short-term RL2-induced autophagy interlinks with final autophagic cell death.

Strontium promotes osteogenic differentiation by activating autophagy via the the AMPK/mTOR signaling pathway in MC3T3‑E1 cells

Strontium (Sr) is an alkaline earth metal that exerts the dual effect of improving bone formation and suppressing bone resorption, resulting in increased bone apposition rates and bone mineral density. However, the mechanisms through which Sr exerts these beneficial effects on bone have yet to be fully elucidated. The present study aimed to reveal the underlying molecular mechanisms associated with Sr‑induced osteogenic differentiation. The effects of Sr on cell proliferation and osteogenic differentiation were analyzed by MTT assay, RT‑qPCR, western blot analysis, alkaline phosphatase (ALP) and Alizarin red staining assays. The extent of autophagy was determined by monodansylcadaverine (MDC) staining and western blot analysis of two markers of cellular autophagic activity, the steatosis‑associated protein, sequestosome‑1 (SQSTM1/p62), and the two isoforms of microtubule‑associated protein 1 light chain 3 (LC3), LC‑3‑I/II. The expression levels of AMP‑activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) were also detected by western blot analysis. Sr at a concentration of 3 mM exerted the most pronounced effect on osteogenic differentiation, without any apparent cell toxicity. At the same time, cellular autophagy was active during this process. Subsequently, autophagy was blocked by 3‑methyladenine, and the enhancement of osteogenic differentiation in response to Sr was abrogated. Additionally, the phosphorylation level of AMPK was significantly increased, whereas that of mTOR was significantly decreased, in the Sr‑treated group. Taken together, the findings of the present study demonstrate that Sr stimulates AMPK‑activated autophagy to induce the osteogenic differentiation of MC3T3‑E1 cells.

Autophagy preserves the osteogenic ability of periodontal ligament stem cells under high glucose conditions in rats

OBJECTIVE

To investigate how a high glucose environment influences the osteogenic ability of periodontal ligament stem cells (PDLSCs) and the function of autophagy in this process, we explored whether the osteogenic ability of PDLSCs could be protected by autophagy.

DESIGN

PDLSC proliferation and osteogenesis were evaluated by CCK-8 and western blotting under gradient glucose conditions. The Autophagy RT² Profiler PCR Array was used to screen autophagy-related mRNA expression during PDLSC osteoblastic differentiation on 5.5 mM + osteogenic induction (OI) medium or 25 mM + OI medium on day 3. Autophagy was regulated by an inducer (rapamycin) and inhibitor (bafilomycin) to investigate its protective effects on PDLSCs. A periodontal trauma model was established in diabetic rats to verify the effects of enhanced autophagy activity on PDLSCs.

RESULTS

A high glucose concentration (25 mM) impeded PDLSC proliferation on day 1, and compared with the control condition, high glucose also decreased the osteogenic ability of PDLSCs. The Autophagy RT² Profiler PCR Array showed obvious fluctuations in many autophagy-related genes, such as ULK1 (9.27), MTOR (3.15), MAP1LC3B (4.22), GABARAPL1 (7.09), ATG10 (6.5), AMPK14 (4.47), WIPI1 (3.29), and IGF1 (24.65). Compared with the control condition, an autophagy inducer or inhibitor markedly impaired or enhanced osteogenic differentiation in cells. The diabetic rat periodontal trauma model demonstrated that periodontium tissue partly recovered in the autophagy-enhanced cell injection diabetic rat group.

CONCLUSIONS

High glucose inhibited the activity of PDLSCs, and regulating autophagy protected cell function. Upregulating autophagy partially reversed the adverse effect of high glucose conditions on PDLSCs.

Autophagy in Zika Virus Infection: A Possible Therapeutic Target to Counteract Viral Replication

Zika virus (ZIKV) still constitutes a public health concern, however, no vaccines or therapies are currently approved for treatment. A fundamental process involved in ZIKV infection is autophagy, a cellular catabolic pathway delivering cytoplasmic cargo to the lysosome for degradation—considered as a primordial form of innate immunity against invading microorganisms. ZIKV is thought to inhibit the Akt-mTOR signaling pathway, which causes aberrant activation of autophagy promoting viral replication and propagation. It is therefore appealing to study the role of autophagic molecular effectors during viral infection to identify potential targets for anti-ZIKV therapeutic intervention.

Antiproliferative activities of the second-generation antipsychotic drug sertindole against breast cancers with a potential application for treatment of breast-to-brain metastases

Epidemiological observations have shown that schizophrenia patients after long-term drug treatment exhibited reduced tumor incidences. The potential anticancer effects of antipsychotic drugs are subsequently demonstrated. These drugs are of great interest as agents against untreatable brain metastases because of their ability to traverse the blood-brain barrier (BBB). Most drugs tested thus far are the first-generation antipsychotics (FGAs). But their clinical application may be limited due to high risks of deaths in elderly patients. There is an urgent need to find additional BBB-traversing anticancer agents with lower risks of deaths. In this work, we investigated antitumor activities of eight second-generation-antipsychotic (SGA) drugs, since they exhibit lower mortality rates than FGAs. We discovered that sertindole showed broad antiproliferative activities against seven cancer types including 29 cell-lines and exhibited potent effects toward breast cancer cell-lines, with half maximal concentration to inhibit proliferation by 50% (IC₅₀) as low as 800 nM. We further found that sertindole caused cell death through autophagy-associated apoptosis and its directly-binding inhibition of 5-HT6 involved in this process. In xenotransplant mice, sertindole administration approaching maximal therapeutic dose attenuated breast-tumor growth by 22.7%. Therefore, our study reveals promising anticancer potentials of sertindole against breast cancers, with probable applications for breast-to-brain metastases.

Ethanol-induced cardiomyocyte toxicity implicit autophagy and NFkB transcription factor

Chronic ethanol (EtOH) consumption causes early detrimental consequences in many tissues including the myocardium, though the molecular mechanisms leading to the alcoholic cardiomyopathy (ACM) still remain to be elucidated. Here, we studied several biomolecular changes occurring in cardiomyoblasts after their exposure to sublethal concentrations of EtOH and the potential synergistic effect with methylmercury (MM) or doxorubicin (DOXO), which are known to produce direct myocardial dysfunction. In addition, the possible role of autophagic responses and Nuclear Factor kappa-B (NFkB) modulation in early post-alcoholic myocardial damage has been investigated. H9c2 rat cardiomyoblasts were incubated for fifteen days with a sub-lethal concentrations of EtOH (1-1000 μM). In particular, treatment of H9c2 cells with EtOH produced an increase of reactive oxygen species (ROS) and the activation of autophagy. Furthermore, chronic exposure to EtOH, was accompanied by a translocation of NFkB into the nucleus dose-dependently. Finally, co-incubation of EtOH (1-1000 μM) with sublethal concentrations of MM or DOXO showed a prominent apoptotic death of cardiomyoblasts accompanied by ROS overproduction, autophagy activation and by an increased nuclear translocation of NFkB as compared to untreated cells. Thus, EtOH produces early changes in cardiomyoblasts characterized by oxidative stress, reactive autophagy and NFkB modulation at concentrations unable to produce direct cell death. Combination of EtOH with cardiotoxic pollutants or drugs makes the cardiomyocyte vulnerable to exogenous insults leading to apoptosis. These data contribute to better identify molecular mechanisms underlying early stages of alcoholic cardiomyopathy and suggest novel strategies to counteract integrated risk of cardiotoxicity in chronic alcohol consumption.

Design of Small Molecule Autophagy Modulators: A Promising Druggable Strategy

Autophagy is a lysosome-dependent mechanism of intracellular degradation for maintaining cellular homeostasis. Dysregulation of autophagy has been verified to be closely linked to a number of human diseases. Consequently, targeting autophagy has been highlighted as a novel therapeutic strategy for clinical utility. Mounting efforts have been done in recent years to elucidate the mechanisms of autophagy regulation and to identify potential modulators of autophagy. However, most of the compounds target complex and multifaceted pathway and proteins, which may limit the evaluation of therapeutic value and in depth studies as chemical tools. Therefore, the development of specific and active autophagy modulators becomes most desirable. Here, we briefly review the regulation of autophagy and then summarize the recent development of small molecules targeting the core autophagic machinery. Finally, we put forward our viewpoints on the current problems, with the aim to provide reference for future drug discovery and potential therapeutic perspectives on novel, potent, selective autophagy modulators.

pH Alkalinization by Chloroquine Suppresses Pathogenic Burkholderia Type 6 Secretion System 1 and Multinucleated Giant Cells

Burkholderia mallei and B. pseudomallei cause glanders and melioidosis, respectively, in humans and animals. A hallmark of pathogenesis is the formation of granulomas containing multinucleated giant cells (MNGCs) and cell death. These processes depend on type 6 secretion system 1 (T6SS-1), which is required for virulence in animals. We examined the cell biology of MNGC formation and cell death. We found that chloroquine diphosphate (CLQ), an antimalarial drug, inhibits Burkholderia growth, phagosomal escape, and subsequent MNGC formation. This depends on CLQ's ability to neutralize the acid pH because other alkalinizing compounds similarly inhibit escape and MNGC formation. CLQ inhibits bacterial virulence protein expression because T6SS-1 and some effectors of type 3 secretion system 3 (T3SS-3), which is also required for virulence, are expressed at acid pH. We show that acid pH upregulates the expression of Hcp1 of T6SS-1 and TssM, a protein coregulated with T6SS-1. Finally, we demonstrate that CLQ treatment of Burkholderia-infected Madagascar hissing cockroaches (HCs) increases their survival. This study highlights the multiple mechanisms by which CLQ inhibits growth and virulence and suggests that CLQ be further tested and considered, in conjunction with antibiotic use, for the treatment of diseases caused by Burkholderia.

Promotion of Proapoptotic Signals by Lysosomal Photodamage: Mechanistic Aspects and Influence of Autophagy

Prior studies demonstrated that a low level (LD10-15 ) of lysosomal photodamage can sensitize cells to the apoptotic death that results from subsequent mitochondrial photodamage. We have proposed that this process occurs via a calpain-catalyzed cleavage of the autophagy-associated protein ATG5 to form a proapoptotic fragment. In this report, we provide evidence for the postulated ATG5 cleavage and show that the sequential photodynamic therapy (PDT) protocol can also partly overcome the adverse effect of hypoxia on the initiation of apoptosis. While autophagy can offer cytoprotection after mitochondrial photodamage, this does not appear to apply when lysosomes are the target. This may account for the ability of very low PDT doses directed at lysosomes to evoke ATG5 cleavage. The resulting proapoptotic effect overcomes intrinsic cytoprotection from mitochondrial photodamage along with a further stimulation of phototoxicity.

Autophagy inhibitors

Autophagy is a lysosome-dependent mechanism of intracellular degradation. The cellular and molecular mechanisms underlying this process are highly complex and involve multiple proteins, including the kinases ULK1 and Vps34. The main function of autophagy is the maintenance of cell survival when modifications occur in the cellular environment. During the past decade, extensive studies have greatly improved our knowledge and autophagy has exploded as a research field. This process is now widely implicated in pathophysiological processes such as cancer, metabolic, and neurodegenerative disorders, making it an attractive target for drug discovery. In this review, we will summarize the different types of inhibitors that affect the autophagy machinery and provide some potential therapeutic perspectives.

Expression analysis of BECN1 in acute myeloid leukemia: association with distinct cytogenetic and molecular abnormalities

INTRODUCTION

In acute myeloid leukemia (AML), it has been shown that AML-derived cells often remain sensitive to autophagy-inducing stimuli, leading to the idea that harnessing the autophagy can be pertinent to AML cytotoxic therapy. Despite this promising notion, to date, there is no comprehensive study addressing autophagy-related genes expression status in AML. As a critical mediator, BECN1 influences the onset and advance of autophagy and several studies have pointed to the BECN1 recurrent allelic deletion and expression variation in a broad range of tumors. To explore this caveat, we chose this alteration-prone gene to investigate in our study.

METHODS

We have analyzed the expression status of BECN1 in a series of 128 de novo AML patients using real-time quantitative polymerase chain reaction (qRT-PCR).

RESULTS

In our favorable subgroup, BECN1 expression did not alter (P = 0.301), but in intermediate and unfavorable patients, we have had BECN1 low expression compared to the normal controls (P = 0.008 and P < 0.001, respectively). We found evidence for the association of reduced expression of BECN1 with FLT3-ITD mutation (19 of 27 patients), monosomal karyotype (all of 11 patients), higher age, and WBC count.

CONCLUSION

Overall, remarkable association of reduced expression of BECN1 with FLT3-ITD mutation and monosomal karyotype and their functional relationship is interesting which should be addressed and verified in future studies.

The emerging role of acid sphingomyelinase in autophagy

Autophagy, the main intracellular process of cytoplasmic material degradation, is involved in cell survival and death. Autophagy is regulated at various levels and novel modulators of its function are being continuously identified. An intriguing recent observation is that among these modulators is the sphingolipid metabolising enzyme, Acid Sphingomyelinase (A-SMase), already known to play a fundamental role in apoptotic cell death participating in several pathophysiological conditions. In this review we analyse and discuss the relationship between autophagy and A-SMase describing how A-SMase may regulate it and defining, for the first time, the existence of an A-SMase-autophagy axis. The imbalance of this axis plays a role in cancer, nervous system, cardiovascular, and hepatic disorders.

A Novel Role of Proline Oxidase in HIV-1 Envelope Glycoprotein-induced Neuronal Autophagy

Proline oxidase (POX) catalytically converts proline to pyrroline-5-carboxylate. This catabolic conversion generates reactive oxygen species (ROS) that triggers cellular signaling cascades including autophagy and apoptosis. This study for the first time demonstrates a role of POX in HIV-1 envelope glycoprotein (gp120)-induced neuronal autophagy. HIV-1 gp120 is a neurotoxic factor and is involved in HIV-1-associated neurological disorders. However, the mechanism of gp120-mediated neurotoxicity remains unclear. Using SH-SY5Y neuroblastoma cells as a model, this study demonstrates that gp120 treatment induced POX expression and catalytic activity. Concurrently, gp120 also increased intracellular ROS levels. However, increased ROS had a minimal effect on neuronal apoptosis. Further investigation indicated that the immediate cellular response to increased ROS paralleled with induction of autophagy markers, beclin-1 and LC3-II. These data lead to the hypothesis that neuronal autophagy is activated as a cellular protective response to the toxic effects of gp120. A direct and functional role of POX in gp120-mediated neuronal autophagy was examined by inhibition and overexpression studies. Inhibition of POX activity by a competitive inhibitor "dehydroproline" decreased ROS levels concomitant with reduced neuronal autophagy. Conversely, overexpression of POX in neuronal cells increased ROS levels and activated ROS-dependent autophagy. Mechanistic studies suggest that gp120 induces POX by targeting p53. Luciferase reporter assays confirm that p53 drives POX transcription. Furthermore, data demonstrate that gp120 induces p53 via binding to the CXCR4 co-receptor. Collectively, these results demonstrate a novel role of POX as a stress response metabolic regulator in HIV-1 gp120-associated neuronal autophagy.

The mammalian target of rapamycin modulates the immunoproteasome system in the heart

The mammalian target of rapamycin (mTOR) plays an important role in cardiac development and function. Inhibition of mTOR by rapamycin has been shown to attenuate pathological cardiac hypertrophy and improve the function of aging heart, accompanied by an inhibition of the cardiac proteasome activity. The current study aimed to determine the potential mechanism(s) by which mTOR inhibition modulates cardiac proteasome. Inhibition of mTOR by rapamycin was found to reduce primarily the immunoproteasome in both H9c2 cells in vitro and mouse heart in vivo, without significant effect on the constitutive proteasome and protein ubiquitination. Concurrent with the reduction of the immunoproteasome, rapamycin reduced two important inflammatory response pathways, the NF-κB and Stat3 signaling. In addition, rapamycin attenuated the induction of the immunoproteasome in H9c2 cells by inflammatory cytokines, including INFγ and TNFα, by suppressing NF-κB signaling. These data indicate that rapamycin indirectly modulated immunoproteasome through the suppression of inflammatory response pathways. Lastly, the role of the immunoproteasome during the development of cardiac hypertrophy was investigated. Administration of a specific inhibitor of the immunoproteasome ONX 0914 attenuated isoproterenol-induced cardiac hypertrophy, suggesting that the immunoproteasome may be involved in the development of cardiac hypertrophy and therefore could be a therapeutic target. In conclusion, rapamycin inhibits the immunoproteasome through its effect on the inflammatory signaling pathways and the immunoproteasome could be a potential therapeutic target for pathological cardiac hypertrophy.

High expression of PI3K core complex genes is associated with poor prognosis in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common leukemia among adults in the Western world. Autophagy is a highly conserved process in eukaryotic cells. In CLL autophagy is involved in mediating the effect of chemotherapy but the role of autophagy in CLL pathogenesis remains unknown. In the present study, we used real-time RT-PCR to analyze expression of the PIK3C3, PIK3R4, and BECN1 genes. These genes encode the components of the PI3K core complex, which is central to initiation of autophagy. A consecutive series of 149 well-characterized CLL cases from Region of Southern Denmark were included in the study. All three genes were observed to be independent markers of prognosis in CLL with high expression being associated with more aggressive disease. With this clear association with outcome in CLL, these genes thereby represent promising candidates for future functional studies on the role of autophagy in CLL, and they may further represent targets of treatment.

Autophagy in cancer

Autophagy is a catabolic degradation process in which cellular proteins and organelles are engulfed by double-membrane autophagosomes and degraded in lysosomes. Autophagy has emerged as a critical pathway in tumor development and cancer therapy, although its precise function remains a conundrum. The current consensus is that autophagy has a dual role in cancer. On the one hand, autophagy functions as a tumor suppressor mechanism by preventing the accumulation of damaged organelles and aggregated proteins. On the other hand, autophagy is a key cell survival mechanism for established tumors; therefore autophagy inhibition suppresses tumor progression. Here, we summarize recent progress on the role of autophagy in tumorigenesis and cancer therapy.

Caspases: a molecular switch node in the crosstalk between autophagy and apoptosis

Autophagy and apoptosis are two important catabolic processes contributing to the maintenance of cellular and tissue homeostasis. Autophagy controls the turnover of protein aggregates and damaged organelles within cells, while apoptosis is the principal mechanism by which unwanted cells are dismantled and eliminated from organisms. Despite marked differences between these two pathways, they are highly interconnected in determining the fate of cells. Intriguingly, caspases, the primary drivers of apoptotic cell death, play a critical role in mediating the complex crosstalk between autophagy and apoptosis. Pro-apoptotic signals can converge to activate caspases to execute apoptotic cell death. In addition, activated caspases can degrade autophagy proteins (i.e., Beclin-1, Atg5, and Atg7) to shut down the autophagic response. Moreover, caspases can convert pro-autophagic proteins into pro-apoptotic proteints to trigger apoptotic cell death instead. It is clear that caspases are important in both apoptosis and autophagy, thus a detailed deciphering of the role of caspases in these two processes is still required to clarify the functional relationship between them. In this article, we provide a current overview of caspases in its interplay between autophagy and apoptosis. We emphasized that defining the role of caspases in autophagy-apoptosis crosstalk will provide a framework for more precise manipulation of these two processes during cell death.