Multifaceted roles of ATM in autophagy: From nonselective autophagy to selective autophagy

HUWE1-mediated ubiquitination and degradation of oxidative damage repair gene ATM maintains mitochondrial quality control system in lens epithelial cells

Mitochondrial dysfunction, resulting from a diminished oxidative damage repair capacity of mitochondrial DNA (mtDNA) in peripheral lens epithelial cells (LECs), is a key pathogenic mechanism in age-related cortical cataract (ARCC). This study aims to investigate the potential role of the E3 ligase HUWE1 and its ubiquitination substrate, the oxidative damage repair gene ATM, in the pathogenesis of ARCC. Our findings reveal that ATM protein expression is downregulated in human peripheral lens epithelial cells and the turbid cortex, correlating with increased expression of HUWE1. Overexpression of ATM is shown to repair damaged mtDNA, protect mitochondria in LECs from oxidative damage, inhibit mitochondrial fission, enhance mitochondrial biogenesis and mitophagy, and prevent LECs apoptosis. Conversely, overexpression of HUWE1 may negate the protective effects of ATM via the ubiquitination pathway, promote oxidative stress-induced mitochondrial damage, increase the expression of mitochondrial fission proteins Drp1/Fis1, lead to mitochondrial network fragmentation and LECs apoptosis. In a SD rat lens model ex vitro, the ATM inhibitor AZD0156 exacerbated lens opacity, whereas the mitochondrial fission inhibitor Mdivi-1 restored lens transparency. These results suggest that modulating key molecules involved in oxidative damage repair and mitochondrial fission pathways could enhance mitochondrial quality control, paving the way for the development of targeted molecular therapies for the prevention and treatment of ARCC.

PPARβ/δ Activation Improves Corticosterone-Induced Oxidative Stress Damage in Astrocytes by Targeting UBR5/ATM Signaling

Oxidative stress-mediated astrocytic damage contributes to nerve injury and the development of depression, especially under stress conditions. Peroxisomes and pexophagy are essential for balancing oxidative stress and protein degradation products. Our previous findings suggest that peroxisome proliferators-activated receptor β/δ (PPARβ/δ) activation significantly alleviates depressive behaviors by preventing astrocytic injury. However, the underlying mechanisms remain unclear. In the present study, we established oxidative injury by treating astrocytes with corticosterone. Subsequently, PPARβ/δ agonists and antagonists were applied to determine the effects of PPARβ/δ on balancing peroxisomes and pexophagy in astrocytes. The PPARβ/δ agonist (GW0742) significantly improved cell viability and decreased intracellular reactive oxygen species (ROS) production induced by corticosterone, while pretreatment with the PPARβ/δ, antagonist GSK3787 reversed the effects of GW0742. Moreover, activating PPARβ/δ promoted peroxisomal biogenesis factor 5 (PEX5)-mediated pexophagy by enhancing the phosphorylation of ataxia-telangiectasia mutated (ATM) kinase. Conversely, blocking PPARβ/δ with GSK3787 partially abolished the effects of GW0742. Further investigations demonstrated that activation of PPARβ/δ not only induced transcription of the ubiquitin protein ligase E3 component n-recognin 5 (UBR5) but also enhanced the interaction between PPARβ/δ and UBR5, contributing to ATM interactor (ATMIN) degradation, and increased phosphorylated ATM kinase levels. Therefore, this study revealed that activating PPARβ/δ improves corticosterone-induced oxidative damage in astrocytes by enhancing pexophagy. PPARβ/δ directly interacts with UBR5 to facilitate ATMIN degradation and promotes ATM phosphorylation, thereby maintaining the balance between peroxisomes and pexophagy. These findings suggest that PPARβ/δ is a potential target for promoting pexophagy in astrocytes upon stress.

ATM facilitates autophagy and protects against oxidative stress and apoptosis in response to ER stress in vitro

The endoplasmic reticulum (ER) responds to cellular stress by initiating an unfolded protein response (UPR) that mitigates misfolded protein accumulation by promoting protein degradation pathways. Chronic ER stress leads to UPR-mediated apoptosis and is a common underlying feature of various diseases, highlighting the modulators of the UPR as attractive targets for therapeutic intervention. Ataxia-telangiectasia mutated protein kinase (ATM) is a stress-responsive kinase that initiates autophagy in response to reactive oxygen species (ROS), and ATM deficiency is associated with increased ER stress markers in vitro. However, whether ATM participates in the UPR remains unclear. In this in vitro study, a novel role for ATM in the ER stress response is described using the well-characterized HEK293 cells treated with the common ER stress-inducing agent, tunicamycin, with and without the potent ATM inhibitor, KU-60019. We show for the first time that ATM is activated in a time-dependent manner downstream of UPR initiation in response to tunicamycin treatment. Furthermore, we demonstrate that ATM is required for p62-bound protein cargo degradation through the autophagy pathway in response to ER stress. Lastly, our data suggest a protective role for ATM in ER stress-mediated oxidative stress and mitochondrial apoptosis. Taken together, we highlight ATM as a potential novel drug target in ER stress-related diseases.

The Chromosome Passenger Complex (CPC) Components and Its Associated Pathways Are Promising Candidates to Differentiate Between Normosensitive and Radiosensitive ATM-Mutated Cells

Background

Sensitivity to ionizing radiation differs between individuals, but there is a limited understanding of the biological mechanisms that account for these variations. One example of such mechanisms are the mutations in the ATM (mutated ataxia telangiectasia) gene, that cause the rare recessively inherited disease Ataxia telangiectasia (AT). Hallmark features include chromosomal instability and increased sensitivity to ionizing radiation (IR).

Objectives

To deepen the molecular understanding of radiosensitivity and to identify potential new markers to predict it, human ATM-mutated and proficient cells were compared on a proteomic level.

Design

In this study, we analyzed 3 cell lines from AT patients, with varying radiosensitivity, and 2 cell lines from healthy volunteers, 24 hours and 72 hours post-10 Gy irradiation.

Methods

We used label-free mass spectrometry to identify differences in signaling pathways after irradiation in normal and radiosensitive individuals. Cell viability was initially determined by water soluble tetrazolium (WST) assay and DNA damage response was analyzed with 53BP1 repair foci formation along with KRAB-associated protein 1 (KAP1) phosphorylation.

Results

Proteomic analysis identified 4028 proteins, which were used in subsequent in silico pathway enrichment analysis to predict affected biological pathways post-IR. In AT cells, networks were heterogeneous at both time points with no common pathway identified. Mitotic cell cycle progress was the most prominent pathway altered after IR in cells from healthy donors. In particular, components of the chromosome passenger complex (INCENP and CDCA8) were significantly downregulated after 72 hours. This could also be verified at the mRNA level.

Conclusion

Altogether, the most striking result was that proteins forming the chromosome passenger complex were downregulated after radiation exposure in healthy normosensitive control cells, but not in radiosensitive ATM-deficient cells. Thus, mitosis-associated proteins form an interesting compound to gain insights into the development and prediction of radiosensitivity.

The Pathogenesis of Pancreatitis and the Role of Autophagy

The pathogenesis of acute and chronic pancreatitis has recently evolved as new findings demonstrate a complex mechanism operating through various pathways. In this review, the current evidence indicating that several mechanisms act in concert to induce and perpetuate pancreatitis were presented. As autophagy is now considered a fundamental mechanism in the pathophysiology of both acute and chronic pancreatitis, the fundamentals of the autophagy pathway were discussed to allow for a better understanding of the pathophysiological mechanisms of pancreatitis. The various aspects of pathogenesis, including trypsinogen activation, ER stress and mitochondrial dysfunction, the implications of inflammation, and macrophage involvement in innate immunity, as well as the significance of pancreatic stellate cells in the development of fibrosis, were also analyzed. Recent findings on exosomes and the miRNA regulatory role were also presented. Finally, the role of autophagy in the protection and aggravation of pancreatitis and possible therapeutic implications were reviewed.

Effects of Ataxia-Telangiectasia Mutated Variants on Radionecrosis and Local Control After Stereotactic Radiation Surgery for Non-Small Cell Lung Cancer Brain Metastases

Purpose

Genetic variants affecting the radiation response protein ataxia-telangiectasia mutated (ATM) have been associated with increased adverse effects of radiation but also with improved local control after conventional radiation therapy. However, it is unknown whether ATM variants affect rates of radionecrosis (RN) and local intracranial progression (LIP) after stereotactic radiosurgery (SRS) for brain metastases.

Methods and Materials

Patients undergoing an initial course of SRS for non-small cell lung cancer (NSCLC) brain metastases at a single institution were retrospectively identified. Kaplan-Meier estimates were calculated and Cox proportional hazards testing was performed based on ATM variant status.

Results

A total of 541 patients completed SRS for brain metastasis secondary to NSCLC, of whom 260 completed molecular profiling. Variants of ATM were identified in 36 cases (13.8%). Among patients who completed molecular profiling, RN incidence was 4.9% (95% CI, 1.6%-8.2%) at 6 months and 9.9% (95% CI, 4.8%-15.0%) at 12 months. Incidence of RN was not significantly increased among patients with ATM variants, with an RN incidence of 5.3% (95% CI, 0.0%-15.3%) at both 6 and 12 months (P = .46). For all patients who completed genomic profiling, LIP was 5.4% (95% CI, 2.4%-8.4%) at 6 months and 9.8% (5.5%-14.1%) at 12 months. A significant improvement in LIP was not detected among patients with ATM variants, with an LIP incidence of 3.1% (0.0%-9.1%) at both 6 and 12 months (P = .26). Although differences according to ATM variant type (pathologic variant or variant of unknown significance) did not reach significance, no patients with ATM pathologic variants experienced LIP.

Conclusions

We did not detect significant associations between ATM variant status and RN or LIP after SRS for NSCLC brain metastases. The current data set allows estimation of patient cohort sizes needed to power future investigations to identify genetic variants that associate with significant differences in outcomes after SRS.

Ataxia-Telangiectasia Mutated Is Involved in Autolysosome Formation

Ataxia-telangiectasia mutated (ATM), a master kinase of the DNA damage response (DDR), phosphorylates a multitude of substrates to activate signaling pathways after DNA double-strand breaks (DSBs). ATM inhibitors have been evaluated as anticancer drugs to potentiate the cytotoxicity of DNA damage-based cancer therapy. ATM is also involved in autophagy, a conserved cellular process that maintains homeostasis by degrading unnecessary proteins and dysfunctional organelles. In this study, we report that ATM inhibitors (KU-55933 and KU-60019) provoked accumulation of autophagosomes and p62 and restrained autolysosome formation. Under autophagy-inducing conditions, the ATM inhibitors caused excessive autophagosome accumulation and cell death. This new function of ATM in autophagy was also observed in numerous cell lines. Repression of ATM expression using an siRNA inhibited autophagic flux at the autolysosome formation step and induced cell death under autophagy-inducing conditions. Taken together, our results suggest that ATM is involved in autolysosome formation and that the use of ATM inhibitors in cancer therapy may be expanded.

CircHULC accelerates the growth of human liver cancer stem cells by enhancing chromatin reprogramming and chromosomal instability via autophagy

BACKGROUND

Although CircHULC was overexpressed in several cancers, the role of CircHULC in malignancies has yet to be elucidated.

METHODS

Gene infection, tumorigenesis test in vitro and in vivo and the signaling pathway analysis were performed.

RESULTS

our results indicate that CircHULC promotes growth of human liver cancer stem cells and the malignant differentiation of hepatocyte-like cells. Mechanistically, CircHULC enhances the methylation modification of PKM2 via CARM1 and the deacetylase Sirt1. Moreover, CircHULC enhances the binding ability of TP53INP2/DOR with LC3 and LC3 with ATG4, ATG3, ATG5, ATG12. Therefore, CircHULC promotes the formation of autophagosomes. In particular, the binding ability of phosphorylated Beclin1 (Ser14) to Vps15, Vps34, ATG14L were significantly increased after CircHULC was overexpressed. Strikingly, CircHULC affects the expression of chromatin reprogramming factors and oncogenes through autophagy. Thereafter, Oct4, Sox2, KLF4, Nanog, and GADD45 were significantly decreased and C-myc was increased after CircHULC was overexpressed. Thus, CircHULC promotes the expression of H-Ras, SGK, P70S6K, 4E-BP1, Jun, and AKT. Interestingly, both CARM1 and Sirt1 determine the cancerous function of CircHULC dependent on autophagy.

CONCLUSIONS

we shed light on the fact that the targeted attenuation of deregulated functioning of CircHULC could be a viable approach for cancer treatment, and CircHULC may acts as the potential biomarker and therapeutic target for liver cancer.

Effect of Autophagy Inhibitors on Radiosensitivity in DNA Repair-Proficient and -Deficient Glioma Cells

Background and Objectives: The development of radioresistance is a fundamental barrier to successful glioblastoma therapy. Autophagy is thought to play a role in facilitating the DNA repair of DNA damage foci in radiation-exposed tumor cells, thus, potentially contributing to their restoration of proliferative capacity and development of resistance in vitro. However, the effect of autophagy inhibitors on DNA damage repair is not fully clear and requires further investigation. Materials and Methods: In this work, we utilized M059K (DNA-PKcs proficient) and M059J (DNA-PKcs deficient) glioma cell lines to investigate the role of autophagy inhibitors in the DNA repair of radiation-induced DNA damage. Cell viability following radiation was determined by trypan blue exclusion in both cell lines. Cell death and autophagy assays were performed to evaluate radiation-induced cell stress responses. DNA damage was measured as based on the intensity of phosphorylated γ-H2AX, a DNA double-stranded breaks (DSBs) marker, in the presence or absence of autophagy inhibitors. Results: The cell viability assay showed that M059J cells were more sensitive to the same dose of radiation (4 Gy) than M059K cells. This observation was accompanied by an elevation in γ-H2AX formation in M059J but not in M059K cells. In addition, the DAPI/TUNEL and Senescence-associated β-galactosidase (SA-β-gal) staining assays did not reveal significant differences in apoptosis and/or senescence induction in response to radiation, respectively, in either cell line. However, acridine orange staining demonstrated clear promotion of acidic vesicular organelles (AVOs) in both cell lines in response to 4 Gy radiation. Moreover, DNA damage marker levels were found to be elevated 72 h post-radiation when autophagy was inhibited by the lysosomotropic agent bafilomycin A1 (BafA1) or the PI3K inhibitor 3-methyl adenine (3-MA) in M059K cells. Conclusions: The extent of the DNA damage response remained high in the DNA-PKcs deficient cells following exposure to radiation, indicating their inability to repair the newly formed DNA-DSBs. On the other hand, radioresistant M059K cells showed more DNA damage response only when autophagy inhibitors were used with radiation, suggesting that the combination of autophagy inhibitors with radiation may interfere with DNA repair efficiency.

Autophagy Induced by Muscarinic Acetylcholine Receptor 1 Mediates Migration and Invasion Targeting Atg5 via AMPK/mTOR Pathway in Prostate Cancer

Increasing numbers of researchers discovered the expression of muscarinic acetylcholine receptor 1 in human cancers, while its function in human prostate cancer is still unclear. Our present study focused on CHRM1 to clarify its role in mediating autophagy in prostate cancer. We used immunohistochemistry, western blotting, and immunofluorescence experiments to observe the expression of muscarinic acetylcholine receptor 1 both in nude mice with subcutaneous tumors and in prostate cancer cells. The autophagy was observed through transmission electron microscopy, western blotting, quantitative real-time PCR, and immunofluorescence. After that, we used lentivirus to establish CHRM1 and Atg5 knockdown models. Then, the migration and invasion abilities after knocking down muscarinic acetylcholine receptor 1 and Atg5 were detected by transwell assays. In addition, the AMPK/mTOR pathway-related targets were detected by western blotting. We found that muscarinic acetylcholine receptor 1 was abundantly expressed both in vitro and in vivo in prostate cancer. The overexpression of muscarinic acetylcholine receptor 1 positively regulated migration and invasion in tumor cells as well as the activation of autophagy. Muscarinic acetylcholine receptor 1 was highly correlated with Atg5 and activated the AMPK/mTOR signaling pathway. Downregulation of Atg5 inhibited cell autophagy in prostate cancer cells and the migration and invasion of prostate cancer cells. Meanwhile, abnormal expressions of AMPK/mTOR pathway-related proteins were found. In conclusion, the present findings indicated that muscarinic acetylcholine receptor 1 is highly expressed in prostate cancer cells and promotes cell invasion and migration of prostate cancer. Autophagy is activated in prostate cancer cells and the activation of muscarinic acetylcholine receptor 1 positively regulates autophagy in prostate cancer cells. Moreover, muscarinic acetylcholine receptor 1 induces autophagy-mediated cell migration and invasion by targeting Atg5 in prostate cancer cells via AMPK/mTOR pathway, which uncovered that regulating muscarinic acetylcholine receptor 1, identified in this study, can be a promising solution for treating prostate cancer.

Cell Signaling and Translational Developmental Therapeutics

The relationships between drug pharmacodynamics and subsequent changes in cellular signaling processes are complex. Many in vitro cell signaling studies often use drug concentrations above physiologically safe drug levels achievable in a patient's plasma. Drug companies develop agents to inhibit or modify the activities of specific target enzymes, often without a full consideration that their compounds have additional unknown targets. These two negative sequelae, when published together, become impediments against successful developmental therapeutics and translation because this data distorts our understanding of signaling mechanisms and reduces the probability of successfully translating drug-based concepts from the bench to the bedside. This article will discuss cellular signaling in isolation and as it relates to extant single and combined therapeutic drug interventions. This will lead to a hypothetical series standardized sequential approaches describing a rigorous concept to drug development and clinical translation.

Hypoxia-stimulated ATM activation regulates autophagy-associated exosome release from cancer-associated fibroblasts to promote cancer cell invasion

Cancer-associated fibroblasts (CAFs) as a predominant cell component in the tumour microenvironment (TME) play an essential role in tumour progression. Our earlier studies revealed oxidized ATM activation in breast CAFs, which is independent of DNA double-strand breaks (DSBs). Oxidized ATM has been found to serve as a redox sensor to maintain cellular redox homeostasis. However, whether and how oxidized ATM in breast CAFs regulates breast cancer progression remains poorly understood. In this study, we found that oxidized ATM phosphorylates BNIP3 to induce autophagosome accumulation and exosome release from hypoxic breast CAFs. Inhibition of oxidized ATM kinase by KU60019 (a small-molecule inhibitor of activated ATM) or shRNA-mediated knockdown of endogenous ATM or BNIP3 blocks autophagy and exosome release from hypoxic CAFs. We also show that oxidized ATM phosphorylates ATP6V1G1, a core proton pump in maintaining lysosomal acidification, leading to lysosomal dysfunction and autophagosome fusion with multi-vesicular bodies (MVB) but not lysosomes to facilitate exosome release. Furthermore, autophagy-associated GPR64 is enriched in hypoxic CAFs-derived exosomes, which stimulates the non-canonical NF-κB signalling to upregulate MMP9 and IL-8 in recipient breast cancer cells, enabling cancer cells to acquire enhanced invasive abilities. Collectively, these results provide novel insights into the role of stromal CAFs in promoting tumour progression and reveal a new function of oxidized ATM in regulating autophagy and exosome release.

DNA damage and regulation of protein homeostasis

The accumulation of unrepaired DNA lesions is associated with many pathological outcomes in humans, particularly in neurodegenerative diseases and in normal aging. Evidence supporting a causal role for DNA damage in the onset and progression of neurodegenerative disease has come from rare human patients with mutations in DNA damage response genes as well as from model organisms; however, the generality of this relationship in the normal population is unclear. In addition, the relevance of DNA damage in the context of proteotoxic stress-the widely accepted paradigm for pathology during neurodegeneration-is not well understood. Here, observations supporting intertwined roles of DNA damage and proteotoxicity in aging-related neurological outcomes are reviewed, with particular emphasis on recent insights into the relationships between DNA repair and autophagy, the ubiquitin proteasome system, formation of protein aggregates, poly-ADP-ribose polymerization, and transcription-driven DNA lesions.

ATM: Main Features, Signaling Pathways, and Its Diverse Roles in DNA Damage Response, Tumor Suppression, and Cancer Development

ATM is among of the most critical initiators and coordinators of the DNA-damage response. ATM canonical and non-canonical signaling pathways involve hundreds of downstream targets that control many important cellular processes such as DNA damage repair, apoptosis, cell cycle arrest, metabolism, proliferation, oxidative sensing, among others. Of note, ATM is often considered a major tumor suppressor because of its ability to induce apoptosis and cell cycle arrest. However, in some advanced stage tumor cells, ATM signaling is increased and confers remarkable advantages for cancer cell survival, resistance to radiation and chemotherapy, biosynthesis, proliferation, and metastasis. This review focuses on addressing major characteristics, signaling pathways and especially the diverse roles of ATM in cellular homeostasis and cancer development.

ATM Kinase-Dependent Regulation of Autophagy: A Key Player in Senescence?

Increasing evidence suggests a strong interplay between autophagy and genomic stability. Recently, several papers have demonstrated a molecular connection between the DNA Damage Response (DDR) and autophagy and have explored how this link influences cell fate and the choice between apoptosis and senescence in response to different stimuli. The aberrant deregulation of this interplay is linked to the development of pathologies, including cancer and neurodegeneration. Ataxia-telangiectasia mutated kinase (ATM) is the product of a gene that is lost in Ataxia-Telangiectasia (A-T), a rare genetic disorder characterized by ataxia and cerebellar neurodegeneration, defects in the immune response, higher incidence of lymphoma development, and premature aging. Importantly, ATM kinase plays a central role in the DDR, and it can finely tune the balance between senescence and apoptosis: activated ATM promotes autophagy and in particular sustains the lysosomal-mitochondrial axis, which in turn promotes senescence and inhibits apoptosis. Therefore, ATM is the key factor that enables cells to escape apoptosis by entering senescence through modulation of autophagy. Importantly, unlike apoptotic cells, senescent cells are viable and have the ability to secrete proinflammatory and mitogenic factors, thus influencing the cellular environment. In this review we aim to summarize recent advances in the understanding of molecular mechanisms linking DDR and autophagy to senescence, pointing out the role of ATM kinase in these cellular responses. The significance of this regulation in the pathogenesis of Ataxia-Telangiectasia will be discussed.

The role of cell signaling in the crosstalk between autophagy and apoptosis in the regulation of tumor cell survival in response to sorafenib and neratinib

The molecular mechanisms by which tumor cells survive or die following therapeutic interventions are complex. There are three broadly defined categories of cell death processes: apoptosis (Type I), autophagic cell death (Type II), and necrosis (Type III). In hematopoietic tumor cells, the majority of toxic stimuli cause these cells to undergo a death process called apoptosis; apoptosis specifically involves the cleavage of DNA into large defined pieces and their subsequent localization in vesicles. Thus, 'pure' apoptosis largely lacks inflammatory potential. In carcinomas, however, the mechanisms by which tumor cells ultimately die are considerably more complex. Although the machinery of apoptosis is engaged by toxic stimuli, other processes such as autophagy ("self-eating") and replicative cell death can lead to observations that do not simplistically correspond to any of the individual Type I-III formalized death categories. The 'hybrid' forms of cell death observed in carcinoma cells result in cellular materials being released into the extracellular space without packaging, which promotes inflammation, potentially leading to the accelerated re-growth of surviving tumor cells by macrophages. Drugs as single agents or in combinations can simultaneously initiate signaling via both apoptotic and autophagic pathways. Based on the tumor type and its oncogene drivers, as well as the drug(s) being used and the duration and intensity of the autophagosome signal, apoptosis and autophagy have the potential to act in concert to kill or alternatively that the actions of either pathway can act to suppress signaling by the other pathway. And, there also is evidence that autophagic flux, by causing lysosomal protease activation, with their subsequent release into the cytosol, can directly mediate killing. This review will discuss the interactive biology between apoptosis and autophagy in carcinoma cells. Finally, the molecular actions of the FDA-approved drugs neratinib and sorafenib, and how they enhance both apoptotic and toxic autophagic processes, alone or in combination with other agents, is discussed in a bench-to-bedside manner.

ATM loss disrupts the autophagy-lysosomal pathway

ATM (ataxia telangiectasia mutated) protein is found associated with multiple organelles including synaptic vesicles, endosomes and lysosomes, often in cooperation with ATR (ataxia telangiectasia and Rad3 related). Mutation of the ATM gene results in ataxia-telangiectasia (A-T), an autosomal recessive disorder with defects in multiple organs including the nervous system. Precisely how ATM deficiency leads to the complex phenotypes of A-T, however, remains elusive. Here, we reported that part of the connection may lie in autophagy and lysosomal abnormalities. We found that ATM was degraded through the autophagy pathway, while ATR was processed by the proteasome. Autophagy and lysosomal trafficking were both abnormal in atm^-/- neurons and the deficits impacted cellular functions such as synapse maintenance, neuronal survival and glucose uptake. Upregulated autophagic flux was observed in atm^-/- lysosomes, associated with a more acidic pH. Significantly, we found that the ATP6V1A (ATPase, H+ transporting, lysosomal V1 subunit A) proton pump was an ATM kinase target. In atm^-/- neurons, lysosomes showed enhanced retrograde transport and accumulated in the perinuclear regions. We attributed this change to an unexpected physical interaction between ATM and the retrograde transport motor protein, dynein. As a consequence, SLC2A4/GLUT4 (solute carrier family 4 [facilitated glucose transporter], member 4) translocation to the plasma membrane was inhibited and trafficking to the lysosomes was increased, leading to impaired glucose uptake capacity. Together, these data underscored the involvement of ATM in a variety of neuronal vesicular trafficking processes, offering new and therapeutically useful insights into the pathogenesis of A-T.Abbreviations: 3-MA: 3-methyladenine; A-T: ataxia-telangiectasia; ALG2: asparagine-linked glycosylation 2 (alpha-1,3-mannosyltransferase); AMPK: adenosine 5'-monophosphate (AMP)-activated protein kinase; ATG5: autophagy related 5; ATM: ataxia telangiectasia mutated; ATP6V1A: ATPase, H+ transporting, lysosomal V1 subunit A; ATR: ataxia-telangiectasia and Rad3 related; BFA1: bafilomycin A₁; CC3: cleaved-CASP3; CGN: cerebellar granule neuron; CLQ: chloroquine; CN: neocortical neuron; CTSB: cathepsin B; CTSD: cathepsin D; DYNLL1: the light chain1 of dynein; EIF4EBP1/4E-BP1: eukaryotic translation initiation factor 4E binding protein 1; Etop: etoposide; FBS: fetal bovine serum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HBS: HEPES-buffered saline; HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; HOMER1: homer protein homolog 1; KU: KU-60019; LAMP1: lysosomal-associated membrane protein 1; LC3B-II: LC3-phosphatidylethanolamine conjugate; Lyso: lysosome; LysopH-GFP: lysopHluorin-GFP; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MAP2: microtubule associated protein 2; MAPK14: mitogen-activated protein kinase 14; MAPK8/JNK1: mitogen-activated protein kinase 8; MCOLN1/TRPML1: mucolipin 1; OSBPL1A: oxysterol binding protein like 1A; PIKK: phosphatidylinositol 3 kinase related kinase; Rapa: rapamycin; RILP: rab interacting lysosomal protein; ROS: reactive oxygen species; SEM: standard error of mean; SLC2A4/GLUT4: solute carrier family 2 (facilitated glucose transporter), member 4; TSC2/tuberin: TSC complex subunit 2; ULK1: unc-51 like kinase 1; UPS: ubiquitin-proteasome system; VE: VE-822; WCL: whole-cell lysate; WT: wild type.

Iron Promotes Dihydroartemisinin Cytotoxicity via ROS Production and Blockade of Autophagic Flux via Lysosomal Damage in Osteosarcoma

Osteosarcoma cellular iron concentration is higher than that in normal bone cells and other cell types. High levels of cellular iron help catalyze the Fenton reaction to produce reactive oxygen species (ROS), which promotes cancer cell proliferation. Dihydroartemisinin (DHA), a classic anti-malarial drug, kills plasmodium through iron-dependent ROS generation. In this research, we observed the anti-osteosarcoma effects and mechanisms of DHA. We found that DHA induced ROS production, caused mitochondrial damage, and activated autophagy via stimulation of the ROS/Erk1/2 pathway. As the storage site for a pool of ferrous iron, lysosomes are often the key organelles affected by drugs targeting iron. In this study, we observed that DHA induced lysosomal superoxide production, leading lysosomal membrane permeabilization (LMP), and autophagic flux blockage. By reducing or increasing cellular iron using deferoxamine (DFO) or ferric ammonium citrate (FAC), respectively, we found that DHA inhibited osteosarcoma in an iron-dependent manner. Therefore, iron may be a potential adjuvant for DHA in osteosarcoma treatment.

Mechanisms of action of hydroxychloroquine and chloroquine: implications for rheumatology

Despite widespread clinical use of antimalarial drugs such as hydroxychloroquine and chloroquine in the treatment of rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and other inflammatory rheumatic diseases, insights into the mechanism of action of these drugs are still emerging. Hydroxychloroquine and chloroquine are weak bases and have a characteristic 'deep' volume of distribution and a half-life of around 50 days. These drugs interfere with lysosomal activity and autophagy, interact with membrane stability and alter signalling pathways and transcriptional activity, which can result in inhibition of cytokine production and modulation of certain co-stimulatory molecules. These modes of action, together with the drug's chemical properties, might explain the clinical efficacy and well-known adverse effects (such as retinopathy) of these drugs. The unknown dose-response relationships of these drugs and the lack of definitions of the minimum dose needed for clinical efficacy and what doses are toxic pose challenges to clinical practice. Further challenges include patient non-adherence and possible context-dependent variations in blood drug levels. Available mechanistic data give insights into the immunomodulatory potency of hydroxychloroquine and provide the rationale to search for more potent and/or selective inhibitors.

miR-18a promotes Mycobacterial survival in macrophages via inhibiting autophagy by down-regulation of ATM

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is one of leading causes of global deaths. This study aimed to explore the role of miR-18a in RAW264.7 cells response to Mtb infection. Exosomes derived from Mtb-infected cells were isolated and further validated by size, transmission electron microscopy and Western blot. RT-PCR was utilized to measure miR-18a expression. Cell viability and ultrastructure were examined by CFU counting, CCK-8 and electron microscope, respectively. Potential target genes of miR-18a were predicted with bioinformatics and further confirmed using RT-PCR, Western blot and laser confocal microscope analysis, respectively. LC3, AMPK and mTOR were measured using Western blot. We found that miR-18a was induced both in Mtb-infected RAW264.7 cells and its derived exosomes compared with the controls. In addition, up-regulation of miR-18a promoted intracellular Mtb survival, attenuated cell viability and reduced LC3-II level, while its down-regulation had the opposite effect. miR-18a overexpression suppressed level of ATM, one possible target of miR-18a, while its underexpression enhanced ATM. We also found that inhibition of ATM induced LC3-II decrease in Mtb-infected cells and could reverse the increase of LC3-II caused by inhibition of miR-18a. Moreover, down-regulation of miR-18a increased p-AMPK level while reduction of ATM could reverse the change. Taken together, our results suggest that miR-18a is up-regulated in macrophages response to Mtb infection, and it promotes intracellular Mtb survival through repressing autophagic process by down-regulation of ATM pathway. This provides new thought for TB pathogenesis, diagnosis and treatment.

Signaling alterations caused by drugs and autophagy

Autophagy is an evolutionary conserved process that recycles cellular materials in times of nutrient restriction to maintain viability. In cancer therapeutics, the role of autophagy in response to multi-kinase inhibitors, alone or when combined with histone deacetylase (HDAC) inhibitors acts, generally, to facilitate the killing of tumor cells. Furthermore, the formation of autophagosomes and subsequent degradation of their contents can reduce the expression of HDAC proteins themselves as well as of other signaling regulatory molecules such as protein chaperones and mutated RAS proteins. Reduced levels of HDAC6 causes the acetylation and inactivation of heat shock protein 90, and, together with reduced expression of the chaperones HSP70 and GRP78, generates a strong endoplasmic reticulum (ER) stress response. Prolonged intense ER stress signaling causes tumor cell death. Reduced expression of HDACs 1, 2 and 3 causes the levels of programed death ligand 1 (PD-L1) to decline and the expression of Class I MHCA to increase which correlates with elevated immunogenicity of the tumor cells in vivo. This review will specifically focus on the downstream implications that result from autophagic-degradation of HDACs, RAS and protein chaperones.