Inhibition Of Lysosomal Function Research Articles

Noncanonical autophagy is a new strategy to inhibit HSV-1 through STING1 activation

ABSTRACT STING1 (stimulator of interferon response cGAMP interactor 1) plays an essential role in immune responses for virus inhibition via inducing the production of type I interferon, inflammatory factors and macroautophagy/autophagy. In this study, we found that STING1 activation could induce not only canonical autophagy but also non-canonical autophagy (NCA) which is independent of the ULK1 or BECN1 complexes to form MAP1LC3/LC3-positive structures. Whether STING1-induced NCA has similar characters and physiological functions to canonical autophagy is totally unknown. Different from canonical autophagy, NCA could increase single-membrane structures and failed to degrade long-lived proteins, and could be strongly suppressed by interrupting vacuolar-type H+-translocating ATPase (V-ATPase) activity. Importantly, STING1-induced NCA could effectively inhibit DNA virus HSV-1 in cell model. Moreover, STING1 [1–340], a STING1 mutant lacking immunity and inflammatory response due to deletion of the tail end of STING1, could degrade virus through NCA alone, suggesting that the antiviral effect of activated STING1 could be separately mediated by inherent immunity, canonical autophagy, and NCA. In addition, the translocation and dimerization of STING1 do not rely on its immunity function and autophagy pathway. Similar to canonical autophagy, LC3-positive structures of NCA induced by STING1 could finally fuse with lysosomes, and the degradation of HSV-1 could be reverted by inhibition of lysosome function, suggesting that the elimination of DNA virus via NCA still requires the lysosome pathway. Collectively, we proved that besides its classical immunity function and canonical autophagy pathway, STING1-induced NCA is also an efficient antiviral pathway for the host cell. Abbreviations: ATG: autophagy related; Baf: bafilomycin A1; CASM: conjugation of LC3 to a single membrane; CGAS: cyclic GMP-AMP synthase; cGAMP: cyclic GMP-AMP; CQ: chloroquine; CTD: C-terminal domain; CTT: C-terminal tail; ER: endoplasmic reticulum; ERGIC: ER-Golgi intermediate compartment; HSV-1: herpes simplex virus 1; IRF3: interferon regulatory factor 3; IFNs: interferons; LAMP1: lysosomal associated membrane protein 1; LAP: LC3-associated phagocytosis; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; RB1CC1/FIP200: RB1 inducible coiled-coil 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK binding kinase 1; TGOLN2/TGN46: trans-golgi network protein 2; ULK1: unc-51 like autophagy activating kinase 1; V-ATPase: vacuolar-type H+-translocating ATPase; VSV: vesicular stomatitis virus

San-wei-tan-xiang capsule attenuates atherosclerosis by increasing lysosomal activity in adipose tissue macrophages

Ethnopharmacological relevanceDyslipidemia is the leading risk factor of atherosclerosis (AS). Adipose tissue macrophages (ATMs) can regulate postprandial cholesterol levels via uptake and hydrolyzation of lipids and regulation of macrophage cholesterol efflux (MCE). San-wei-tan-xiang (SWTX) capsule, a Traditional Chinese medicine, exerts clinical benefits in patients with atherosclerotic cardiovascular diseases. Aim of the studyThis work is aimed to evaluate the chemical ingredients and mechanisms of SWTX in anti-AS. Materials and methodsThe chemical ingredients of SWTX identified by liquid chromatography coupled with tandem mass spectrometry were used for network pharmacological analysis. The atheroprotective function of SWTX was evaluated in ApoE−/− mice fed a cholesterol-enriched diet. ResultsThe chemical ingredients identified in SWTX were predicated to be important for lipid metabolism and AS. Animals studies suggested that SWTX effectively attenuated the atherosclerotic plaque growth, elevated postprandial HDL cholesterol levels, elevated the proportion of Tim4 and CD36-expressed ATMs, and upregulated the uptake of lipid and lysosomal activity in ATMs. SWTX-induced elevation of postprandial HDL cholesterol levels was dependent on increased lysosomal activity, since chloroquine, an inhibitor of lysosomal function, blocked the effect of SWTX. Lastly, some predicated bioactive compounds in SWTX can elevate lysosomal activity in vitro. ConclusionSWTX could attenuate atherosclerotic plaque formation by elevating lysosomal activity and enhancing MCE in ATMs.

Tumor Heterogeneity-Based Sscr-Score Predicts Prognosis and Reveals Mechanism of SORL1 in Restraining CLL Progression

Introduction Complex heterogeneity is a hallmark of chronic lymphocytic leukemia (CLL) that challenges oncological research and optimal treatment regimens. Although genetic markers with prognostic values have been developed for risk assessment in CLL, the existing prognostic models are far from satisfaction. Single-cell RNA sequencing (scRNA-seq) technologies have made it possible to illustrate the genetic heterogeneity and cell differentiation status at the single-cell level. A prognostic model associated with CLL cell differentiation status was established to refine the risk assessment of CLL patients. Methods Primary CLL cells from 90 patients and CD19+ B cells from 20 healthy donors were collected with informed consents according to the Declaration of Helsinki. Expression levels of SORL1 mRNA and protein in CLL cells were determined by quantitative RT-PCR and western blotting. Cell viability was measured by the CCK-8 assay. Cell cycle and apoptosis were analyzed by PI and Annexin V-PE/7AAD staining. Fatty acid oxidation rate was assessed with Fatty Acid Oxidation Complete Assay Kit. Red oil O staining was performed to evaluate the lipid deposition in CLL cells. Single cell sequencing data were analyzed by the Seurat package and Monocle package in R4.0.5. Results The scRNA-seq profile revealed remarkable intra- and inter-tumoral heterogeneity of CLL. According to the differentiation status, this study reconstructed the evolutionary history of CLL cells, which reflected the molecular classification and risk subgroups of CLL. At the key point of cell differentiation, CLL cells were divided into two subsets with progressive and indolent genetic signatures respectively. Genes differentially expressed between aggressive and indolent subsets were identified. Through univariate and multivariate analysis, four genes (SORL1, SGK1, CYBB, RPL22L1) with significant prognostic values were selected to construct a risk model named SSCR-Score. The risk score was calculated and validated in two independent validation cohorts (Fig 1A). SSCR-Score has revealed the positive prognostic value of SORL1 in CLL. Increased expression of SORL1 was associated with prolonged overall survival and improved time to first treatment in CLL. Among patients with ZAP70 (-) or IGHV mutated status, the expression levels of SORL1 were up-regulated. Although increased expression of SORL1 was associated with favorable prognosis, the biological mechanism of SORL1 still remained ill-defined. This study demonstrated that overexpression of SORL1 restrained cell proliferation, induced cell apoptosis and G2/M cell cycle arrest in CLL cells. In accordance with the RNA sequencing profile, overexpression of SORL1 suppressed abnormal lipid reposition and fatty acid oxidation in CLL cells. On a molecular level, SORL1 down-regulated the expression of lipid-metabolism related genes, including lipoprotein lipase (LPL), carnitine palmitoyltransferase 1A (CPT1A) and carnitine palmitoyltransferase 2 (CPT2). To illustrate the SORL1-mediated regulation of LPL, immunofluorescence staining was performed. Results showed that SORL1 accelerated the degradation of LPL. After the inhibition of lysosome function, accelerated degradation of LPL was not observed in CLL cells overexpressing SORL1. Rescue experiments substantiated that SORL1 impeded progression of CLL through downregulating the activity of LPL which promoted lipid metabolism. Immuno-coprecipitation experiment showed that anti-SORL1 antibody precipitated LPL protein. Additionally, 6-Shohaol induced overexpression of SORL1 in CLL cells. It exhibited potent anti-CLL efficacy by suppressing cell proliferation, promoting cell apoptosis and G2/M cell cycle arrest in CLL cells (Fig 1B). Conclusion CLL presented remarkable heterogeneity which reflected different biological subclasses and risk groups. Through identifying genes differentially expressed between aggressive and indolent cell subsets, a novel prognostic model named SSCR-Score was developed to optimize risk stratification of CLL patients. Moreover, SORL1 restrained progression of CLL by inhibiting lipid metabolism regulated by LPL in CLL cells. SORL1 may serve as a potential strategy for the development of novel therapeutic target in CLL. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Paraoxonase 2 is an ER chaperone that regulates the epithelial Na+ channel.

The mammalian paraoxonases (PONs) have been linked to protection against oxidative stress. However, the physiological roles of members in this family (PON1, PON2, and PON3) are still being characterized. PON2 and PON3 are expressed in the aldosterone-sensitive distal nephron of the kidney and have been shown to negatively regulate expression of the epithelial sodium channel (ENaC), a trimeric ion channel that orchestrates salt and water homeostasis. To date, the nature of this phenomenon has not been explored. Therefore, to investigate the mechanism by which PON2 regulates ENaC, we expressed PON2 along with the ENaC subunits in fisher rat thyroid (FRT) cells, a system that is amenable to biochemical analyses of ENaC assembly and trafficking. We found that PON2 primarily resides in the endoplasmic reticulum (ER) in FRT cells, and its expression reduces the abundance of each ENaC subunit, reflecting enhanced subunit turnover. In contrast, no effect on the levels of mRNAs encoding the ENaC subunits was evident. Inhibition of lysosome function with chloroquine or NH4Cl did not alter the inhibitory effect of PON2 on ENaC expression. In contrast, PON2 accelerates ENaC degradation in a proteasome-dependent manner and acts before ENaC subunit ubiquitination. As a result of enhanced ENaC subunit ubiquitination and degradation, both channel surface expression and ENaC-mediated Na+ transport in FRT cells were reduced by PON2. Together, our data suggest that PON2 functions as an ER chaperone to monitor ENaC biogenesis and redirects the channel for ER-associated degradation.

Role of Tim4 in the regulation of ABCA1+ adipose tissue macrophages and post-prandial cholesterol levels

Dyslipidemia is a main driver of cardiovascular diseases. The ability of macrophages to scavenge excess lipids implicate them as mediators in this process and understanding the mechanisms underlying macrophage lipid metabolism is key to the development of new treatments. Here, we investigated how adipose tissue macrophages regulate post-prandial cholesterol transport. Single-cell RNA sequencing and protected bone marrow chimeras demonstrated that ingestion of lipids led to specific transcriptional activation of a population of resident macrophages expressing Lyve1, Tim4, and ABCA1. Blocking the phosphatidylserine receptor Tim4 inhibited lysosomal activation and the release of post-prandial high density lipoprotein cholesterol following a high fat meal. Both effects were recapitulated by chloroquine, an inhibitor of lysosomal function. Moreover, clodronate-mediated cell-depletion implicated Tim4+ resident adipose tissue macrophages in this process. Thus, these data indicate that Tim4 is a key regulator of post-prandial cholesterol transport and adipose tissue macrophage function and may represent a novel pathway to treat dyslipidemia.

Inhibiting SARS‐CoV‐2 infection with lysosomal alkalizers

Understanding the SARS‐CoV‐2 virus’ routes of infection, virus–host–protein interactions, and mechanisms of virus‐induced cytopathic effects will greatly aid in the discovery and design of new therapeutics to treat COVID‐19. Chloroquine and hydroxychloroquine, extensively explored as clinical agents for COVID‐19, have multiple cellular effects including alkalizing lysosomes and blocking autophagy as well as exhibiting dose‐limiting toxicities in patients. To identify an alternative lysosome‐based drug repurposing opportunity we evaluated additional lysosomotropic compounds . We found that six of these compounds blocked the cytopathic effect of SARS‐CoV‐2 in Vero E6 cells with half‐maximal effective concentration (EC50) values ranging from 2.0 to 13 μM and selectivity indices (SIs; SI = CC50/EC50) ranging from 1.5‐ to >10‐fold. We demonstrate how the compounds (1) blocked lysosome functioning and autophagy, (2) prevented pseudotyped particle entry, (3) increased lysosomal pH, and (4) that ROC‐325 reduced viral titers in the EpiAirway 3D tissue model. Consistent with these findings, the siRNA knockdown of ATP6V0D1 blocked the HCoV‐NL63 cytopathic effect in LLC‐MK2 cells. Moreover, an analysis of SARS‐CoV‐2 infected Vero E6 cell lysate revealed significant dysregulation of autophagy and lysosomal function, suggesting a contribution of the lysosome to the life cycle of SARS‐CoV‐2. Our findings support targeting the lysosome to combat SARS‐CoV‐2 infections and inhibitors of lysosomal function could become an important component of drug combination therapies aimed at improving treatment and outcomes for COVID‐19.

Jia-Ji Electro-Acupuncture Improves Locomotor Function With Spinal Cord Injury by Regulation of Autophagy Flux and Inhibition of Necroptosis.

Jia-Ji electro-acupuncture (EA) has been widely applied in clinic to exhibit curative effects on spinal cord injury (SCI). However, its underlying mechanisms leading to improvement of motor function after SCI remain unclear. Allen’s method was made by NYU Impactor M-III equipment to create the SCI rats model. Rats were randomly divided into four groups: Sham (only laminectomy), Model (SCI group), EA (SCI + Jia-Ji EA treatment), EA + CQ (SCI + Jia-Ji EA treatment + inhibitor chloroquine). Basso-Beattie-Bresnahan assessment showed improvement of hind limb motor function after Jia-Ji electro-acupuncture treatment. Histological change of injured spinal cord tissue was alleviated after treatment, observed by hematoxylin-eosin and Nissl staining. The mRNA and protein expression levels of RIPK1, RIPK3 and MLKL were decreased in EA group. Besides, the increased expression of LC3 and reduced expression of P62 after treatment compared with Model group, confirmed that Jia-Ji electro-acupuncture could enhance the autophagy flux. Electron microscopy imaging showed increasing the number of lysosomes, autophagosomes, and autolysosomes after Jia-Ji electro-acupuncture treatment. Furthermore, inhibition of lysosome function with CQ led to partly eliminate the effect of EA on reducing necroptosis. These data make the case that Jia-Ji electro-acupuncture treatment may improve locomotor function by promoting autophagy flux and inhibiting necroptosis.

Exosomes induce endolysosomal permeabilization as a gateway by which exosomal tau seeds escape into the cytosol

The microtubule-associated protein tau has a critical role in Alzheimer’s disease and other tauopathies. A proposed pathomechanism in the progression of tauopathies is the trans-synaptic spreading of tau seeds, with a role for exosomes which are secretory nanovesicles generated by late endosomes. Our previous work demonstrated that brain-derived exosomes isolated from tau transgenic rTg4510 mice encapsulate tau seeds with the ability to induce tau aggregation in recipient cells. We had also shown that exosomes can hijack the endosomal pathway to spread through interconnected neurons. Here, we reveal how tau seeds contained within internalized exosomes exploit mechanisms of lysosomal degradation to escape the endosome and induce tau aggregation in the cytosol of HEK293T-derived ‘tau biosensor cells’. We found that the majority of the exosome-containing endosomes fused with lysosomes to form endolysosomes. Exosomes induced their permeabilization, irrespective of the presence of tau seeds, or whether the exosomal preparations originated from mouse brains or HEK293T cells. We also found that permeabilization is a conserved mechanism, operating in both non-neuronal tau biosensor cells and primary neurons. However, permeabilization of endolysosomes only occurred in a small fraction of cells, which supports the notion that permeabilization occurs by a thresholded mechanism. Interestingly, tau aggregation was only induced in cells that exhibited permeabilization, presenting this as an escape route of exosomal tau seeds into the cytosol. Overexpression of RAB7, which is required for the formation of endolysosomes, strongly increased tau aggregation. Conversely, inhibition of lysosomal function with alkalinizing agents, or by knocking-down RAB7, decreased tau aggregation. Together, we conclude that the enzymatic activities of lysosomes permeabilize exosomal and endosomal membranes, thereby facilitating access of exosomal tau seeds to cytosolic tau to induce its aggregation. Our data underscore the importance of endosomal membrane integrity in mechanisms of cellular invasion by misfolded proteins that are resistant to lysosomal degradation.

The SARS-CoV-2 Cytopathic Effect Is Blocked by Lysosome Alkalizing Small Molecules

Understanding the SARS-CoV-2 virus’ pathways of infection, virus–host–protein interactions, and mechanisms of virus-induced cytopathic effects will greatly aid in the discovery and design of new therapeutics to treat COVID-19. Chloroquine and hydroxychloroquine, extensively explored as clinical agents for COVID-19, have multiple cellular effects including alkalizing lysosomes and blocking autophagy as well as exhibiting dose-limiting toxicities in patients. Therefore, we evaluated additional lysosomotropic compounds to identify an alternative lysosome-based drug repurposing opportunity. We found that six of these compounds blocked the cytopathic effect of SARS-CoV-2 in Vero E6 cells with half-maximal effective concentration (EC50) values ranging from 2.0 to 13 μM and selectivity indices (SIs; SI = CC50/EC50) ranging from 1.5- to >10-fold. The compounds (1) blocked lysosome functioning and autophagy, (2) prevented pseudotyped particle entry, (3) increased lysosomal pH, and (4) reduced (ROC-325) viral titers in the EpiAirway 3D tissue model. Consistent with these findings, the siRNA knockdown of ATP6V0D1 blocked the HCoV-NL63 cytopathic effect in LLC-MK2 cells. Moreover, an analysis of SARS-CoV-2 infected Vero E6 cell lysate revealed significant dysregulation of autophagy and lysosomal function, suggesting a contribution of the lysosome to the life cycle of SARS-CoV-2. Our findings suggest the lysosome as a potential host cell target to combat SARS-CoV-2 infections and inhibitors of lysosomal function could become an important component of drug combination therapies aimed at improving treatment and outcomes for COVID-19.

The Inhibitory Role of Rab11b in Osteoclastogenesis through Triggering Lysosome-Induced Degradation of c-Fms and RANK Surface Receptors.

Rab11b, abundantly enriched in endocytic recycling compartments, is required for the establishment of the machinery of vesicle trafficking. Yet, no report has so far characterized the biological function of Rab11b in osteoclastogenesis. Using in vitro model of osteoclasts differentiated from murine macrophages like RAW-D cells or bone marrow-derived macrophages, we elucidated that Rab11b served as an inhibitory regulator of osteoclast differentiation sequentially via (i) abolishing surface abundance of RANK and c-Fms receptors; and (ii) attenuating nuclear factor of activated T-cells c1 (NFATc-1) upstream signaling cascades, following RANKL stimulation. Rab11b was localized in early and late endosomes, Golgi complex, and endoplasmic reticulum; moreover, its overexpression enlarged early and late endosomes. Upon inhibition of lysosomal function by a specific blocker, chloroquine (CLQ), we comprehensively clarified a novel function of lysosomes on mediating proteolytic degradation of c-Fms and RANK surface receptors, drastically ameliorated by Rab11b overexpression in RAW-D cell-derived osteoclasts. These findings highlight the key role of Rab11b as an inhibitor of osteoclastogenesis by directing the transport of c-Fms and RANK surface receptors to lysosomes for degradation via the axis of early endosomes-late endosomes-lysosomes, thereby contributing towards the systemic equilibrium of the bone resorption phase.

Inhibition of Lysosomal Function Mitigates Protective Mitophagy and Augments Ceramide Nanoliposome-Induced Cell Death in Head and Neck Squamous Cell Carcinoma.

Therapies for head and neck squamous cell carcinoma (HNSCC) are, at best, moderately effective, underscoring the need for new therapeutic strategies. Ceramide treatment leads to cell death as a consequence of mitochondrial damage by generating oxidative stress and causing mitochondrial permeability. However, HNSCC cells are able to resist cell death through mitochondria repair via mitophagy. Through the use of the C6-ceramide nanoliposome (CNL) to deliver therapeutic levels of bioactive ceramide, we demonstrate that the effects of CNL are mitigated in drug-resistant HNSCC via an autophagic/mitophagic response. We also demonstrate that inhibitors of lysosomal function, including chloroquine (CQ), significantly augment CNL-induced death in HNSCC cell lines. Mechanistically, the combination of CQ and CNL results in dysfunctional lysosomal processing of damaged mitochondria. We further demonstrate that exogenous addition of methyl pyruvate rescues cells from CNL + CQ-dependent cell death by restoring mitochondrial functionality via the reduction of CNL- and CQ-induced generation of reactive oxygen species and mitochondria permeability. Taken together, inhibition of late-stage protective autophagy/mitophagy augments the efficacy of CNL through preventing mitochondrial repair. Moreover, the combination of inhibitors of lysosomal function with CNL may provide an efficacious treatment modality for HNSCC.

Lysosomal dysfunction in osteoarthritis and aged cartilage triggers apoptosis in chondrocytes through BAX mediated release of Cytochrome c

Lysosomes are the major catabolic organelle of the cell and regulate the macromolecular and organelle turnover and programmed cell death. Here, we investigated the lysosome dysfunction in cartilage and its role in chondrocytes apoptosis and the associated mechanism. Lysosomal acidification in Osteoarthritis (OA) and aged cartilage was determined by LysoSensor staining. Lysosomal function in chondrocytes was blocked by siRNA mediated depletion of Lysosomal Associated Membrane Protein 2 (LAMP2) or with lysosome inhibitors. Chondrocyte apoptosis was determined by LDH release, Caspase-3/7 activation, TUNEL and PI uptake assays. Loss of mitochondrial membrane potential (MMP/ΔΨM) and mitochondrial superoxide level was determined by JC-1 and MitoSOX staining, respectively. Colocalization of mitochondria with BCL2 associated X (BAX) and Cytochrome c was determined by immunostaining. Destabilization of medial meniscus (DMM) was performed to induce OA in mice. Lysosomal acidification was found to be significantly decreased in aged mouse and human and mouse OA cartilage which also showed increased chondrocyte apoptosis. Inhibition of lysosomal function resulted in increased oxidative stress, accumulation of dysfunctional mitochondria and apoptosis in chondrocytes in monolayer and in cartilage explant cultures. Depletion of LAMP2 expression or treatment of chondrocytes with lysosomal function inhibitors increased the expression and mitochondrial translocation of BAX leading to Cytochrome c release. Lysosomal dysfunction-induced apoptosis in chondrocytes was not blocked by antioxidants MitoTempo or Diphenyleneiodonium (DPI) but was abrogated by inhibiting BAX. Lysosomal dysfunction induce apoptosis in chondrocytes through BAX-mediated mitochondrial damage and release of Cytochrome c. Our data points to lysosomal function restoration and/or BAX inhibition in chondrocytes as a therapeutic approach for OA.

Abstract A01: Vps34 promotes macropinocytosis in Tsc2-deficient cells

Abstract Purpose: The mechanistic/mammalian target of rapamycin complex 1 (mTORC1) is constitutively active in many human cancers and in tuberous sclerosis complex (TSC). mTORC1 hyperactivation drives extensive metabolic reprogramming via several interconnected mechanisms, including glucose and glutamine utilization, nucleic acid synthesis, and lipid synthesis. We recently found that treatment with chloroquine (CQ), a lysosomal/autophagy inhibitor, upregulates the uptake and endosomal processing of cholesterol selectively in TSC2-deficient cells, creating a TSC2-specific dependence on exogenous cholesterol. This dependence on exogenous nutrients and the mechanisms of nutrient uptake may be therapeutically targetable. Our central hypothesis is that Tsc2-deficient cells depend on the uptake of exogenous nutrients via macropinocytosis to maintain cellular metabolic homeostasis and proliferation. Methods and Results: To investigate the role of macropinocytosis-mediated nutrient uptake in Tsc2-deficient cells, we measured the uptake of dextran, a polysaccharide taken up via macropinocytosis. Tsc2-deficient cells showed a striking increase in both dextran (3.6-fold, p<0.001) and exogenous protein uptake (~2-fold, p<0.001) relative to Tsc2-expressing cells. Interestingly, mTOR inhibition using Torin1 decreased dextran uptake (3-fold, p<0.001). Pharmacologic and genetic inhibition of the lipid kinase Vps34 markedly abrogated uptake of dextran in Tsc2-deficient cells (~50%, p<0.0001). Macropinocytosis was further increased in Tsc2-deficient cells that lack autophagic mechanisms (25%, p<0.001), suggesting that autophagy inhibition leads to dependence on exogenous nutrient uptake in Tsc2-deficient cells. Additionally, exogenous protein activates mTORC1 signaling of Tsc2-deficient cells grown in amino acid-free media. Treatment with ethylisopropylamiloride (EIPA) resulted in selective growth inhibition of Atg5-deficient, Tsc2-deficient cells (50%, p<0.0001). Genetic inhibition of autophagy (Atg5-/- MEFs) sensitized cells with Tsc2 downregulation to the Vps34 inhibitor, SAR405, resulting in growth inhibition (75%, p<0.0001). Finally, pharmacologic inhibition of lysosomal function with CQ and macropinocytosis with SAR405 inhibited tumor growth and increased tumor latency in an in vivo xenograft model of TSC. Conclusions: These data suggest that macropinocytosis is upregulated in Tsc2-deficient cells via a Vps34-dependent mechanism to support tumorigenesis. Macropinocytosis-mediated nutrient uptake represents an unexplored opportunity for therapeutic intervention in TSC and may also be relevant to other diseases characterized by mTORC1 hyperactivation. Citation Format: Charilaos Filippakis, Amine Belaid, Brian Siroky, Constance Wu, Nicola Alesi, Thomas Alesi, Julie Nijmeh, Hilaire Colletta Lam, Ellizabeth Henske. Vps34 promotes macropinocytosis in Tsc2-deficient cells [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr A01.

Transcriptome profiling analysis reveals that ATP6V0E2 is involved in the lysosomal activation by anlotinib

Anlotinib is a receptor tyrosine kinase inhibitor with potential anti-neoplastic and anti-angiogenic activities. It has been approved for the treatment of non-small-cell lung cancer. Lysosomes are acidic organelles and have been implicated in various mechanisms of cancer therapeutics. However, the effect of anlotinib on lysosomal function has not been investigated. In the present study, anlotinib induces apoptosis in human colon cancer cells. Through transcriptome sequencing, we found for the first time that anlotinib treatment upregulates ATP6V0E2 (ATPase H+ Transporting V0 Subunit E2) and other lysosome-related genes expression in human colon cancer. In human colon cancer, we validated that anlotinib activates lysosomal function and enhances the fusion of autophagosomes and lysosomes. Moreover, anlotinib treatment is shown to inhibit mTOR (mammalian target of rapamycin) signaling and the activation of lysosomal function by anlotinib is mTOR dependent. Furthermore, anlotinib treatment activates TFEB, a key nuclear transcription factor that controls lysosome biogenesis and function. We found that anlotinib treatment promotes TFEB nuclear translocation and enhances its transcriptional activity. When TFEB or ATP6V0E2 are knocked down, the enhanced lysosomal function and autophagy by anlotinib are attenuated. Finally, inhibition of lysosomal function enhances anlotinib-induced cell death and tumor suppression, which may be attributed to high levels of ROS (reactive oxygen species). These findings suggest that the activation of lysosomal function protects against anlotinib-mediated cell apoptosis via regulating the cellular redox status. Taken together, our results provide novel insights into the regulatory mechanisms of anlotinib on lysosomes, and this information could facilitate the development of potential novel cancer therapeutic agents that inhibit lysosomal function.

Enhanced lysosomal function is critical for paclitaxel resistance in cancer cells: reversed by artesunate.

The mechanism underlying the resistance of cancer cells to chemotherapeutic drug varies with different cancer cells. Recent evidence shows that lysosomal function is associated with drug resistance of cancer cells. Artesunate, a derivative of artemisinin, displays broad antitumor activity and direct cytotoxicity on various tumor cells. Our previous study shows that artesunate increases autophagosome accumulation, while significantly decreases autolysosome number in cancer cells, suggesting that artesunate might impair the lysosomal function. In this study, we investigated the effects of artesunate on lysosomal function and its relationship with chemotherapeutic drug resistance in cancer cells. We found that the lysosomal function was significantly enhanced in two drug-resistant (A549/TAX and A549/DDP) cells. Furthermore, we showed that the enhanced lysosomal function by overexpression of transcription factor EB (TFEB) significantly increased MCF-7 cells resistance to doxorubicin (DOX), whereas the decreased lysosomal function by TFEB-knockdown or lysosome inhibitor chloroquine increased MCF-7 cells sensitivity to DOX. Treatment of A549/TAX cells with artesunate (2.5-50 μM) dose-dependently inhibited lysosomal function and the clearance of dysfunctional mitochondria, and induced cell apoptosis. Moreover, we demonstrated that artesunate exerted more potent inhibition on the resistant (A549/TAX and MCF-7/ADR) cells with higher activity of lysosomal function. Our results suggest that artesunate or other inhibitors of lysosomal function would be potential in the treatment of cancer cells with drug resistance caused by the enhanced lysosomal function.

Acidic Compartment Size, Positioning, and Function during Myogenesis and Their Modulation by the Wnt/Beta-Catenin Pathway.

Lysosomes and acidic compartments are involved in breaking down of macromolecules, membrane recycling, and regulation of signaling pathways. Here, we analyzed the role of acidic compartments during muscle differentiation and the involvement of the Wnt/beta-catenin pathway in lysosomal function during myogenesis. Acridine orange was used to localize and quantify acidic cellular compartments in primary cultures of embryonic muscle cells from Gallus gallus. Our results show an increase in acidic compartment size and area, as well as changes in their positioning during the initial steps of myogenesis. The inhibition of lysosomal function by either the chloroquine Lys05 or the downregulation of LAMP-2 with siRNA impaired chick myogenesis, by inhibiting myoblast fusion. Two activators of the Wnt/beta-catenin pathway, BIO and Wnt3a, were able to rescue the inhibitory effects of Lys05 in myogenesis. These results suggest a new role for the Wnt/beta-catenin pathway in the regulation of acidic compartment size, positioning, and function in muscle cells.

FBXL4 deficiency increases mitochondrial removal by autophagy

Pathogenic variants in FBXL4 cause a severe encephalopathic syndrome associated with mtDNA depletion and deficient oxidative phosphorylation. To gain further insight into the enigmatic pathophysiology caused by FBXL4 deficiency, we generated homozygous Fbxl4 knockout mice and found that they display a predominant perinatal lethality. Surprisingly, the few surviving animals are apparently normal until the age of 8–12 months when they gradually develop signs of mitochondrial dysfunction and weight loss. One‐year‐old Fbxl4 knockouts show a global reduction in a variety of mitochondrial proteins and mtDNA depletion, whereas lysosomal proteins are upregulated. Fibroblasts from patients with FBXL4 deficiency and human FBXL4 knockout cells also have reduced steady‐state levels of mitochondrial proteins that can be attributed to increased mitochondrial turnover. Inhibition of lysosomal function in these cells reverses the mitochondrial phenotype, whereas proteasomal inhibition has no effect. Taken together, the results we present here show that FBXL4 prevents mitochondrial removal via autophagy and that loss of FBXL4 leads to decreased mitochondrial content and mitochondrial disease.

Correction: Inhibitors of lysosomal function or serum starvation in control or LAMP2 deficient cells do not modify the cellular levels of Parkinson disease-associated DJ-1/PARK 7 protein.

[This corrects the article DOI: 10.1371/journal.pone.0201152.].

Rapid changes in the ATG5-ATG16L1 complex following nutrient deprivation measured using NanoLuc Binary Technology (NanoBIT).

Autophagy plays a role in several human diseases, but each of the current methods to measure autophagy has significant drawbacks. ATG5 and ATG16L1 are regulators necessary for autophagy; therefore, drugs that inhibit the interaction of these proteins may be therapeutically useful. To evaluate the interaction of ATG5 and ATG16L1 in cells, their cDNAs were fused to the coding sequences of SmBIT and LgBIT, two components of NanoLuc luciferase. This generated a luminescent signal when SmBIT and LgBIT interacted to form a functional luciferase as a result of their colocalization that was brought about by the binding of ATG5 and ATG16L1. The assay measures the interaction in real time and can be used in microplate format to allow for multiple experimental conditions to be assessed. The interaction of ATG5 and ATG16L1 is not significantly altered by inhibition of lysosomal function, or inhibitors of Ulk1, Vps34 or mTORC1. However, there was a constitutive interaction of ATG5 and ATG16L1 and luminescence was stimulated within 3min, by up to 500%, when the cells were deprived of nutrients. When the nutrients are returned, the complex returns to its basal status equally rapidly. Sphingosine-1-phosphate and CYM-5541 partially repressed the effects of nutrient starvation. Furthermore, we identified a small-molecule inhibitor that interferes with the interaction of ATG5 and ATG16L1 in cells. This assay provides a novel tool for researchers to measure autophagy and can be potentially applied to many cell types. DATABASE: Replicate data are available in Figshare database https://doi.org/10.6084/m9.figshare.11798946.

GL-V9 exerts anti-T cell malignancies effects via promoting lysosome-dependent AKT1 degradation and activating AKT1/FOXO3A/BIM axis

T-cell malignancies are characterized by the excessive proliferation of hematopoietic precursor cells of T-cell lineage lymphocytes in the bone marrow. Previous studies suggest that T-cell malignancies are usually accompanied by highly activated PI3K/AKT signaling which confers the ability of cancer cells to proliferate and survive. Here, we found that GL-V9, a newly synthesized flavonoid compound, had a potent to inhibit the activation of AKT1 and induce the cell apoptosis in T-cell malignancies including cell lines and primary lymphoblastic leukemia. Results showed that GL-V9-induced degradation of AKT1 blocked PI3K/AKT1 signaling and the degradation of AKT1 could be reversed by NH4Cl, an inhibitor of lysosomal function. Inhibiting AKT1 promoted dephosphorylation of FOXO3A and its nuclear translocation. We further demonstrated that GL-V9-induced apoptosis effects were dependent on the binding of FOXO3A to the BIM promoter, resulting in the production of BH3-only protein BIM. Moreover, GL-V9 showed a more persistent and stronger apoptosis induction effects than pharmacologic PI3K inhibitor. The in vivo studies also verified that GL-V9 possessed the anti-tumor effects by reducing the leukemic burden in T-ALL-bearing BALB/c nude mice. In conclusion, our study provides a new insight into the mechanism of GL-V9-induced apoptosis, suggesting the potency of GL-V9 to be a promising agent against T-cell malignancies.