Distinct autophagosomal-lysosomal fusion mechanism revealed by thapsigargin-induced autophagy arrest

New mechanistic insights on transferrin synthesis inhibition and release of bound iron mediated by lead loaded ultrafine carbon black

The obstruction of transferrin-mediated Fe3+ transport has been identified as a potential initiator for hepatic ferroptosis. However, the understanding of how environmental pollutants influence the Fe3+ transport of transferrin remains missing. In this study, we firstly developed a combination strategy to evaluate the impairment of conformation and function of transferrin induced by ultrafine carbon black under Pb2+ loading (Pb-UFCB) at cellular and protein molecular levels. Specifically, the exposure of Pb-UFCB led to a notable 46.3 ± 4.2 % reduction in transferrin expression, which can be ascribed to the oxidative DNA damage (203.3 ± 28.0 %) induced by reactive oxygen species and apoptosis mediated via mitochondrial pathway. Flow cytometry analysis revealed a dose-time-dependent increase in intracellular Pb2+ content. This escalation intensified the adverse effects of UFCB. Furthermore, at protein molecular levels, Pb-UFCB triggered a significant release of Fe3+ from transferrin (373.7 ± 25.0 % of control) by inducing the compact skeleton, reorganization of secondary structure and fluorescence sensitization of transferrin. Our results unveil the pathways of Fe3+ transport impairment of transferrin induced by Pb-UFCB, which can provide theoretical support for the prevention and diagnosis of ferroptosis-related diseases.

Mutant p53 upregulates HDAC6 to resist ER stress and facilitates Ku70 deacetylation, which prevents its degradation and mitigates DNA damage in colon cancer cells

Cancer cells employ interconnected mechanisms to withstand intrinsic and extrinsic stress, with mutant p53 (mutp53) playing a key role in bolstering resistance to endoplasmic reticulum (ER) stress. In this study, we further investigated this phenomenon, focusing on the DNA damage triggered by ER stress. Our findings indicate that mutp53 mitigates ER stress-induced DNA damage by sustaining high levels of Ku70, a critical protein in DNA repair via the non-homologous end joining (NHEJ) pathway, which functions alongside Ku80. HDAC6 upregulation emerged as a crucial driver of this response. HDAC6 deacetylates Ku70, promoting its nuclear localization and protecting it from degradation. This mechanism ensures continuous activity of the NHEJ repair pathway, allowing mutp53-expressing cells to better manage DNA damage from ER stress, thus contributing to the genomic instability characteristic of cancer progression. Furthermore, HDAC6 maintains the activation of the ATF6 branch of the unfolded protein response (UPR), enhancing the ability of mutp53 cells to resist ER stress, as ATF6 supports cellular adaptation to misfolded proteins and stressful conditions. Since HDAC6 is central to this enhanced stress resistance and DNA repair, targeting it could disrupt these protective mechanisms, increasing the vulnerability of mutp53 cancer cells to ER stress and inhibiting cancer progression.

Cannabidiol Enhances the Anticancer Activity of Etoposide on Prostate Cancer Cells

Introduction: Cannabis sativa extract has been used as an herbal medicine since ancient times. It is one of the most researched extracts, especially among supportive treatments against cancer. Prostate cancer is one of the most frequently diagnosed cancer types in men worldwide and an estimated 288,300 new cases were diagnosed in 2023. Today, many advanced therapeutic approaches are used for prostate cancer, such as immunotherapy and chemotherapy, but acquired drug resistance, long-term drug usage and differentiation of cancer cells mostly restricted the efficiency of therapies. Therefore, it is thought that the use of natural products to overcome these limitations and improve the effectiveness of existing therapies may offer promising approaches. The present study focused on the investigation of the possible enhancer role of cannabidiol (CBD), which is a potent ingredient compound of Cannabis, on the chemotherapeutic agent etoposide in prostate cancer cells. Methods: Herein, we tested the potentiator role of CBD on etoposide in prostate cancer cells by testing the cytotoxic effect, morphological alterations, apoptotic effects, autophagy, unfolded protein response (UPR) signaling, endoplasmic reticulum-associated degradation mechanism (ERAD), angiogenic and androgenic factors, and epithelial-mesenchymal transition (EMT). In addition, we examined the combined treatment of CBD and etoposide on colonial growth, migrative, invasive capability, 3D tumor formation, and cellular senescence. Results: Our findings demonstrated that cotreatment of etoposide with CBD importantly suppressed autophagic flux and induced ERAD and UPR signaling in LNCaP cells. Also, CBD strongly enhanced the etoposide-mediated suppression of androgenic signaling, angiogenic factor VEGF-A, protooncogene c-Myc, EMT, and also induced apoptosis through activation caspase-3 and PARP-1. Moreover, coadministration markedly decreased tumorigenic properties, such as proliferative capacity, colonial growth, migration, and 3D tumor formation and also induced senescence. Altogether, our data revealed that CBD has a potent enhancer effect on etoposide-associated anticancer activities. Conclusion: The present study suggests that the use of CBD as a supportive therapy in existing chemotherapeutic approaches may be a promising option, but this effectiveness needs to be investigated on a large scale.

Altered Mitochondrial Bioenergetics and Calcium Kinetics in Young-Onset PLA2G6 Parkinson's Disease iPSCs

Parkinson's disease (PD) has emerged as a multisystem disorder affecting multiple cellular and organellar systems in addition to the dopaminergic neurons. Disease-specific induced pluripotent stem cells (iPSCs) model early developmental changes and cellular perturbations that are otherwise inaccessible from clinical settings. Here, we report the early changes in patient-derived iPSCs carrying a homozygous recessive mutation, R741Q, in the PLA2G6 gene. A gene-edited R747W iPSC line mirrored these phenotypes, thus validating our initial findings. Bioenergetic dysfunction and hyperpolarization of mitochondrial membrane potentials were hallmarks of the PD iPSCs. Further, a concomitant increase in glycolytic activity indicated a possible compensation for mitochondrial respiration. Elevated basal reactive oxygen species (ROS) and decreased catalase expression were also observed in the disease iPSCs. No change in autophagy was detected. These inceptive changes could be potential targets for early intervention of prodromal PD in the absence of disease-modifying therapies. However, additional investigations are crucial to delineate the cause-effect relationships of these observations.

CKAP4 in hepatocellular carcinoma: competitive RETREG1/FAM134B binding, reticulophagy regulation, and cancer progression

RETREG1/FAM134B is known for its role as a reticulophagy receptor. Our previous study established that RETREG1 is upregulated in hepatocellular carcinoma (HCC) and contributes to disease progression by activating the AKT signaling pathway. However, the specific mechanisms underlying the elevated expression of RETREG1 in HCC remain unclear. This study unveils the interaction of RETREG1 with CKAP4 and TRIM21. We demonstrated that TRIM21 ubiquitinates RETREG1 at K247 and K252, facilitating its proteasomal degradation. Conversely, CKAP4 shields RETREG1 from degradation by competitively binding to it, revealing a novel post-translational modification mechanism for RETREG1. By modulating RETREG1 expression, CKAP4, and TRIM21 intricately regulate reticulophagy. Additionally, we observed that stress-induced TRIM21 upregulation mitigates the function of RETREG1 to restore ER stress equilibrium. The oncogenic potential of CKAP4 in HCC was demonstrated using various animal models. Clinical sample analyses suggested that CKAP4 is a potential biomarker for HCC prognosis and diagnosis.Abbreviation: AKT: thymoma viral proto-oncogene; aa: amino acid; bp: base pair; CHX: cycloheximide; co-IP: co-Immunoprecipitation; CQ: chloroquine; CKAP4: cytoskeleton-associated protein 4; DKK1: dickkopf WNT signaling pathway inhibitor 1; DUBs: deubiquitinating enzymes; EBSS: Earle's balanced salt solution; EGFP: enhanced green fluorescent protein; ER: endoplasmic reticulum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; HCC: hepatocellular carcinoma; HFD: high-fat diet; HiTV: hyperdynamic tail vein injection; IF: immunofluorescence; IHC: immunohistochemistry; IP-MS: immunoprecipitation-mass spectrometry; LIR: LC3-interacting region; mAbs: monoclonal antibodies; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; mCherry: monomeric cherry; oe: overexpression; PDX: patient-derived tumor xenograft; reticulophagy: endoplasmic reticulum selective autophagy; RETREG1: reticulophagy regulator 1; RHD: reticulon-homology domain; Tg: thapsigargin; Tm: tunicamycin; TRIM21: tripartite motif-containing 21; UB: ubiquitin; WT: wild-type.

A review on phytochemicals as combating weapon for multidrug resistance in cancer

One can recognize multidrug resistance (MDR) and residue as a biggest difficulty in cancer specialist. Chemotherapy-resistant cancer may be successfully treated by combining MDR-reversing phytochemicals with anticancer drugs. Though, clinical application of phytochemicals either alone or in conjunction with chemotherapy is still in its early stages or requires more research to determine their safety and efficacy. In this review we highlighted topics related to MDR in cancer, including an introduction to subject, mechanism of action of efflux pump, specific proteins involved in drug resistance, altered drug targets, increased drug metabolism, and potential role of phytochemicals in overcoming drug resistance.

The MON1-CCZ1 complex plays dual roles in autophagic degradation and vacuolar protein transport in rice

Autophagy is a highly conserved cellular program in eukaryotic cells which mediates the degradation of cytoplasmic components through the lysosome, also named the vacuole in plants. However, the molecular mechanisms underlying the fusion of autophagosomes with the vacuole remain unclear. Here, we report the functional characterization of a rice (Oryza sativa) mutant with defects in storage protein transport in endosperm cells and accumulation of numerous autophagosomes in root cells. Cytological and immunocytochemical experiments showed that this mutant exhibits a defect in the fusion between autophagosomes and vacuoles. The mutant harbors a loss-of-function mutation in the rice homolog of Arabidopsis thaliana MONENSIN SENSITIVITY1 (MON1). Biochemical and genetic evidence revealed a synergistic interaction between rice MON1 and AUTOPHAGY-RELATED 8a in maintaining normal growth and development. In addition, the rice mon1 mutant disrupted storage protein sorting to protein storage vacuoles. Furthermore, quantitative proteomics verified that the loss of MON1 function influenced diverse biological pathways including autophagy and vacuolar transport, thus decreasing the transport of autophagic and vacuolar cargoes to vacuoles. Together, our findings establish a molecular link between autophagy and vacuolar protein transport, and offer insights into the dual functions of the MON1-CCZ1 (CAFFEINE ZINC SENSITIVITY1) complex in plants.

Beclin-1 and LC3B expression in canine mast cell tumours: an immuno-ultrastructural and immunohistochemical study of autophagy

Mast cell tumours (MCTs) are common malignant neoplasms in dogs, for which prognosis and therapeutic decisions are based on histological features and proliferation markers. Autophagy is a cellular catabolic process responsible for degrading cytoplasmic components to maintain homeostasis, alterations in which are frequently linked to tumour growth and progression. This study was conducted to investigate the occurrence of autophagy in canine MCTs and to verify its value as a prognostic indicator for dogs with the disease. Beclin-1 and LC3B expressions were investigated using immunohistochemistry, and autophagy was ultrastructurally characterised. The autophagic phenomenon was successfully visualised in neoplastic mast cells under transmission electron and immunoelectron microscopy. MCTs from dogs that died due to the disease showed higher positivity for Beclin-1 and dogs with MCTs presenting a LC3B granular immunohistochemical pattern had a significantly shorter post-surgical survival. The occurrence of autophagy is an indicator of poor prognosis. Future studies are needed to elucidate the specific mechanisms and open new opportunities to treatments targeting this cancer cell advantage.

Thapsigargin and its prodrug derivatives: exploring novel approaches for targeted cancer therapy through calcium signaling disruption

Thapsigargin, a sesquiterpene lactone derived from Thapsia garganica L., has demonstrated mixed potential as an anticancer agent due to its potent ability to disrupt calcium signaling and induce apoptosis. This review evaluates the chemopreventive and chemotherapeutic potential of thapsigargin, focusing on its molecular mechanisms and toxicity. An extensive literature review of studies published since 2015 was conducted using databases such as PubMed/MedLine and Science Direct. Findings indicate that thapsigargin's primary mechanism is the inhibition of sarco/endoplasmic reticulum calcium ATPase, leading to endoplasmic reticulum stress and cell death in various cancer types. Despite these effects, thapsigargin's non-specific cytotoxicity results in significant side effects, including organ damage and histamine-related reactions. Recent advances in targeted delivery, especially with the prodrug mipsagargin, initially suggested promise in minimizing these toxicities by selectively activating in cancer cells expressing prostate-specific membrane antigen (PSMA). However, the completion of clinical trials with no ongoing studies suggests that the viability of mipsagargin and other prodrugs remains uncertain, especially in light of the toxicities observed. While thapsigargin and its derivatives present a potential pathway in cancer treatment, their future role in oncology requires careful re-evaluation.

The phospholamban R14del generates pathogenic aggregates by impairing autophagosome-lysosome fusion

Phospholamban (PLN) plays a crucial role in regulating sarcoplasmic reticulum (SR) Ca2+ cycling and cardiac contractility. Mutations within the PLN gene have been detected in patients with cardiomyopathy, with the heterozygous variant c.40_42delAGA (p.R14del) of PLN being the most prevalent. Investigations into the mechanisms underlying the pathology of PLN-R14del have revealed that cardiac cells from affected patients exhibit pathological aggregates containing PLN. Herein, we performed comprehensive molecular and cellular analyses to delineate the molecular aberrations associated with the formation of these aggregates. We determined that PLN aggregates contain autophagic proteins, indicating inefficient degradation via the autophagy pathway. Our findings demonstrate that the expression of PLN-R14del results in diminished autophagic flux due to impaired fusion between autophagosomes and lysosomes. Mechanistically, this defect is linked to aberrant recruitment of key membrane fusion proteins to autophagosomes, which is mediated in part by changes in Ca2+ homeostasis. Collectively, these results highlight a novel function of PLN-R14del in regulating autophagy, that may contribute to the formation of pathogenic aggregates in patients with cardiomyopathy. Prospective strategies tailored to ameliorate impaired autophagy may hold promise against PLN-R14del disease.

Effects of selegiline on neuronal autophagy involving α-synuclein secretion

Cell-to-cell transmission of α-synuclein (α-syn) pathology underlies the spread of neurodegeneration in Parkinson's disease. α-Syn secretion is an important factor in the transmission of α-syn pathology. However, it is unclear how α-syn secretion is therapeutically modulated. Here, we investigated effects of monoamine oxidase (MAO)-B inhibitor selegiline on α-syn secretion. Treatment with selegiline promoted α-syn secretion in mouse primary cortical neuron cultures, and this increase was kept under glial cell-eliminated condition by Ara-C. Selegiline-induced α-syn secretion was blocked by cytosolic Ca2+ chelator BAPTA-AM in primary neurons. Selegiline-induced α-syn secretion was retained in MAOA siRNA knockdown, whereas it was abrogated by ATG5 knockdown in SH-SY5Y cells. Selegiline increased LC3-II generation with a reduction in intracellular p62/SQSTM1 levels in primary neurons. The increase in LC3-II generation was blocked by co-treatment with BAPTA-AM in primary neurons. Additionally, fractionation experiments showed that selegiline-induced α-syn secretion occurred in non-extracellular vesicle fractions of primary neurons and SH-SY5Y cells. Collectively, these findings show that selegiline promotes neuronal autophagy involving secretion of non-exosomal α-syn via a change of cytosolic Ca2+ levels.

ATF6 supports lysosomal function in tumor cells to enable ER stress-activated macroautophagy and CMA: impact on mutant TP53 expression

The inhibition of the unfolded protein response (UPR), which usually protects cancer cells from stress, may be exploited to potentiate the cytotoxic effect of drugs inducing ER stress. However, in this study, we found that ER stress and UPR activation by thapsigargin or tunicamycin promoted the lysosomal degradation of mutant (MUT) TP53 and that the inhibition of the UPR sensor ATF6, but not of ERN1/IRE1 or EIF2AK3/PERK, counteracted such an effect. ATF6 activation was indeed required to sustain the function of lysosomes, enabling the execution of chaperone-mediated autophagy (CMA) as well as of macroautophagy, processes involved in the degradation of MUT TP53 in stressed cancer cells. At the molecular level, by pharmacological and genetic approaches, we demonstrated that the inhibition of ATF6 correlated with the activation of MTOR and with TFEB and LAMP1 downregulation in thapsigargin-treated MUT TP53 carrying cells. We hypothesize that the rescue of MUT TP53 expression by ATF6 inhibition, could further activate MTOR and maintain lysosomal dysfunction, further inhibiting MUT TP53 degradation, in a vicious circle. The findings of this study suggest that the presence of MUT TP53, which often exerts oncogenic properties, should be considered before approaching treatments combining ER stressors with ATF6 inhibitors against cancer cells, while it could represent a promising strategy against cancer cells that harbor WT TP53.

VMP1: a multifaceted regulator of cellular homeostasis with implications in disease pathology

Vacuole membrane protein 1 (VMP1) is an integral membrane protein that plays a pivotal role in cellular processes, particularly in the regulation of autophagy. Autophagy, a self-degradative mechanism, is essential for maintaining cellular homeostasis by degradation and recycling damaged organelles and proteins. VMP1 involved in the autophagic processes include the formation of autophagosomes and the subsequent fusion with lysosomes. Moreover, VMP1 modulates endoplasmic reticulum (ER) calcium levels, which is significant for various cellular functions, including protein folding and cellular signaling. Recent studies have also linked VMP1 to the cellular response against viral infections and lipid droplet (LD). Dysregulation of VMP1 has been observed in several pathological conditions, including neurodegenerative diseases such as Parkinson's disease (PD), pancreatitis, hepatitis, and tumorogenesis, underscoring its potential as a therapeutic target. This review aims to provide an overview of VMP1's multifaceted roles and its implications in disease pathology.

The interplay between autophagy and ferroptosis presents a novel conceptual therapeutic framework for neuroendocrine prostate cancer

In American men, the incidence of prostate cancer (PC) is the highest among all types of cancer, making it the second leading cause of mortality associated with cancer. For advanced or metastatic PC, antiandrogen therapies are standard treatment options. The administration of these treatments unfortunately carries the potential risk of inducing neuroendocrine prostate cancer (NEPC). Neuroendocrine differentiation (NED) serves as a crucial indicator of prostate cancer development, encompassing various factors such as phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR), Yes-associated protein 1 (YAP1), AMP-activated protein kinase (AMPK), miRNA. The processes of autophagy and ferroptosis (an iron-dependent form of programmed cell death) play pivotal roles in the regulation of various types of cancers. Clinical trials and preclinical investigations have been conducted on many signaling pathways during the development of NEPC, with the deepening of research, autophagy and ferroptosis appear to be the potential target for regulating NEPC. Due to the dual nature of autophagy and ferroptosis in cancer, gaining a deeper understanding of the developmental programs associated with achieving autophagy and ferroptosis may enhance risk stratification and treatment efficacy for patients with NEPC.

Autophagy supports PDGFRA-dependent brain tumor development by enhancing oncogenic signaling

Autophagy is a conserved cellular degradation process. While autophagy-related proteins were shown to influence the signaling and trafficking of some receptor tyrosine kinases, the relevance of this during cancer development is unclear. Here, we identify a role for autophagy in regulating platelet-derived growth factor receptor alpha (PDGFRA) signaling and levels. We find that PDGFRA can be targeted for autophagic degradation through the activity of the autophagy cargo receptor p62. As a result, short-term autophagy inhibition leads to elevated levels of PDGFRA but an unexpected defect in PDGFA-mediated signaling due to perturbed receptor trafficking. Defective PDGFRA signaling led to its reduced levels during prolonged autophagy inhibition, suggesting a mechanism of adaptation. Importantly, PDGFA-driven gliomagenesis in mice was disrupted when autophagy was inhibited in a manner dependent on Pten status, thus highlighting a genotype-specific role for autophagy during tumorigenesis. In summary, our data provide a mechanism by which cells require autophagy to drive tumor formation.

C9orf72-catalyzed GTP loading of Rab39A enables HOPS-mediated membrane tethering and fusion in mammalian autophagy

The multi-subunit homotypic fusion and vacuole protein sorting (HOPS) membrane-tethering complex is required for autophagosome-lysosome fusion in mammals, yet reconstituting the mammalian HOPS complex remains a challenge. Here we propose a "hook-up" model for mammalian HOPS complex assembly, which requires two HOPS sub-complexes docking on membranes via membrane-associated Rabs. We identify Rab39A as a key small GTPase that recruits HOPS onto autophagic vesicles. Proper pairing with Rab2 and Rab39A enables HOPS complex assembly between proteoliposomes for its tethering function, facilitating efficient membrane fusion. GTP loading of Rab39A is important for the recruitment of HOPS to autophagic membranes. Activation of Rab39A is catalyzed by C9orf72, a guanine exchange factor associated with amyotrophic lateral sclerosis and familial frontotemporal dementia. Constitutive activation of Rab39A can rescue autophagy defects caused by C9orf72 depletion. These results therefore reveal a crucial role for the C9orf72-Rab39A-HOPS axis in autophagosome-lysosome fusion.

Expanded polyQ aggregates interact with sarco-endoplasmic reticulum calcium ATPase and Drosophila inhibitor of apoptosis protein1 to regulate polyQ mediated neurodegeneration in Drosophila

Polyglutamine (polyQ) induced neurodegeneration is one of the leading causes of progressive neurodegenerative disorders characterized clinically by deteriorating movement defects, psychiatric disability, and dementia. Calcium [Ca2+] homeostasis, which is essential for the functioning of neuronal cells, is disrupted under these pathological conditions. In this paper, we simulated Huntington's disease phenotype in the neuronal cells of the Drosophila eye and identified [Ca2+] pump, sarco-endoplasmic reticulum calcium ATPase (SERCA), as one of the genetic modifiers of the neurodegenerative phenotype. This paper shows genetic and molecular interaction between polyglutamine (polyQ) aggregates, SERCA and DIAP1. We present evidence that polyQ aggregates interact with SERCA and alter its dynamics, resulting in a decrease in cytosolic [Ca2+] and an increase in ER [Ca2+], and thus toxicity. Downregulating SERCA lowers the enhanced calcium levels in the ER and rescues, morphological and functional defects caused due to expanded polyQ repeats. Cell proliferation markers such as Yorkie (Yki), Scalloped (Sd), and phosphatidylinositol 3 kinases/protein kinase B (PI3K/Akt), also respond to varying levels of calcium due to genetic manipulations, adding to the amelioration of degeneration. These results imply that neurodegeneration due to expanded polyQ repeats is sensitive to SERCA activity, and its manipulation can be an important step toward its therapeutic measures.

4-PBA inhibits endoplasmic reticulum stress to improve autophagic flux in the treatment of protamine/lipopolysaccharide-induced interstitial cystitis in rats

Interstitial cystitis (IC) has severe clinical symptoms with unclear mechanism. The continuous inflammatory response of the bladder is the basis of its pathogenesis. Endoplasmic reticulum stress (ERS) is involved in the regulation and development of various inflammatory diseases. And autophagy plays an important role in IC. In this study, we mainly focus on the therapeutic effect of endoplasmic reticulum stress and autophagy on protamine/lipopolysaccharide-induced interstitial cystitis. Female Sprague-Dawley rats were randomized into three experimental groups as follows: sham controls(N), IC alone, and IC+4-PBA.Rats in group IC received 10 mg/ml PS in the urinary bladder, followed by 2 mg/ml LPS instillation after 30 min, IC+4-PBA group SD rats received 4-PBA solution administered intragastrically once a day for 5 days. ERS biomarker (GRP78), autophagy-related proteins (LC3I/II, and Beclin1), autophagic flux biomarker (P62), inflammatory biomarkers (IL-6, TNF-a, NF-κB), apoptotic biomarkers (Caspase 3, Bax) were highest in the IC group compared to IC+4-PBA group and N group and the biomarkers expression in IC+4-PBA group were lower than in the IC group, anti-apoptotic biomarker (Bcl-2) was highest in the N group compared to the IC group and IC+4-PBA group and lower in the IC group than in the IC+4-PBA group, oxidative stress biomarkers (HO-1, NQO-1) were remarkably lower in the control group than in the IC and IC+4-PBA groups and notably lower in the IC group than in the IC+4-PBA group. The histological score and mast cell count demonstrated most severe in the IC group than those in the IC+4-PBA group. TUNEL assay examined the level of apoptosis in IC group was higher than in the IC+4-PBA group. The bladder micturition function was significantly improved with 4-PBA treatment. 4-PBA inhibits ERS to recover autophagic flux, and then to suppress the bladder oxidative stress, the inflammatory reaction and apoptosis, finally improve the bladder urinary function in Protamine/Lipopolysaccharide (PS/LPS) induced IC.

TRPML3/BK complex promotes autophagy and bacterial clearance by providing a positive feedback regulation of mTOR via PI3P

TRPML3 is a Ca2+/Na+ release channel residing in both phagophores and endolysosomal membranes. It is activated by PI3P and PI3,5P2. Its activity can be enhanced by high luminal pH and by replacing luminal Na+ with K+. Here, we report that big-conductance Ca2+-activated potassium (BK) channels form a positive feedback loop with TRPML3. Ca2+ release via TRPML3 activates BK, which in turn facilitates TRPML3-mediated Ca2+ release, potentially through removing luminal Na+ inhibition. We further show that TRPML3/BK and mammalian target of rapamycin (mTOR) form another positive feedback loop to facilitate autophagy induction in response to nutrient starvation, i.e., mTOR inhibition upon nutrient starvation activates TRPML3/BK, and this further reduces mTOR activity, thereby increasing autophagy induction. Mechanistically, the feedback regulation between TRPML3/BK and mTOR is mediated by PI3P, an endogenous TRPML3 activator that is enriched in phagophores and is up-regulated by mTOR reduction. Importantly, bacterial infection activates TRPML3 in a BK-dependent manner, and both TRPML3 and BK are required for mTOR suppression and autophagy induction responding to bacterial infection. Suppressing either TRPML3 or BK helps bacteria survival whereas increasing either TRPML3 or BK favors bacterial clearance. Considering that TRPML3/BK is inhibited by low luminal pH but activated by high luminal pH and PI3P in phagophores, we suggest that TRPML3/BK and mTOR form a positive feedback loop via PI3P to ensure efficient autophagy induction in response to nutrient deprivation and bacterial infection. Our study reveals a role of TRPML3-BK coupling in controlling cellular homeostasis and intracellular bacterial clearance via regulating mTOR signaling.

Phosphorylation of EIF2S1 (eukaryotic translation initiation factor 2 subunit alpha) is indispensable for nuclear translocation of TFEB and TFE3 during ER stress

There are diverse links between macroautophagy/autophagy pathways and unfolded protein response (UPR) pathways under endoplasmic reticulum (ER) stress conditions to restore ER homeostasis. Phosphorylation of EIF2S1/eIF2α is an important mechanism that can regulate all three UPR pathways through transcriptional and translational reprogramming to maintain cellular homeostasis and overcome cellular stresses. In this study, to investigate the roles of EIF2S1 phosphorylation in regulation of autophagy during ER stress, we used EIF2S1 phosphorylation-deficient (A/A) cells in which residue 51 was mutated from serine to alanine. A/A cells exhibited defects in several steps of autophagic processes (such as autophagosome and autolysosome formation) that are regulated by the transcriptional activities of the autophagy master transcription factors TFEB and TFE3 under ER stress conditions. EIF2S1 phosphorylation was required for nuclear translocation of TFEB and TFE3 during ER stress. In addition, EIF2AK3/PERK, PPP3/calcineurin-mediated dephosphorylation of TFEB and TFE3, and YWHA/14-3-3 dissociation were required for their nuclear translocation, but were insufficient to induce their nuclear retention during ER stress. Overexpression of the activated ATF6/ATF6α form, XBP1s, and ATF4 differentially rescued defects of TFEB and TFE3 nuclear translocation in A/A cells during ER stress. Consequently, overexpression of the activated ATF6 or TFEB form more efficiently rescued autophagic defects, although XBP1s and ATF4 also displayed an ability to restore autophagy in A/A cells during ER stress. Our results suggest that EIF2S1 phosphorylation is important for autophagy and UPR pathways, to restore ER homeostasis and reveal how EIF2S1 phosphorylation connects UPR pathways to autophagy.Abbreviations: A/A: EIF2S1 phosphorylation-deficient; ACTB: actin beta; Ad-: adenovirus-; ATF6: activating transcription factor 6; ATZ: SERPINA1/α1-antitrypsin with an E342K (Z) mutation; Baf A1: bafilomycin A1; BSA: bovine serum albumin; CDK4: cyclin dependent kinase 4; CDK6: cyclin dependent kinase 6; CHX: cycloheximide; CLEAR: coordinated lysosomal expression and regulation; Co-IP: coimmunoprecipitation; CTSB: cathepsin B; CTSD: cathepsin D; CTSL: cathepsin L; DAPI: 4',6-diamidino-2-phenylindole dihydrochloride; DMEM: Dulbecco's modified Eagle's medium; DMSO: dimethyl sulfoxide; DTT: dithiothreitol; EBSS: Earle's Balanced Salt Solution; EGFP: enhanced green fluorescent protein; EIF2S1/eIF2α: eukaryotic translation initiation factor 2 subunit alpha; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; ERAD: endoplasmic reticulum-associated degradation; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; FBS: fetal bovine serum; gRNA: guide RNA; GSK3B/GSK3β: glycogen synthase kinase 3 beta; HA: hemagglutinin; Hep: immortalized hepatocyte; IF: immunofluorescence; IRES: internal ribosome entry site; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LMB: leptomycin B; LPS: lipopolysaccharide; MAP1LC3A/B/LC3A/B: microtubule associated protein 1 light chain 3 alpha/beta; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MEFs: mouse embryonic fibroblasts; MFI: mean fluorescence intensity; MTORC1: mechanistic target of rapamycin kinase complex 1; NES: nuclear export signal; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; OE: overexpression; PBS: phosphate-buffered saline; PLA: proximity ligation assay; PPP3/calcineurin: protein phosphatase 3; PTM: post-translational modification; SDS: sodium dodecyl sulfate; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SEM: standard error of the mean; TEM: transmission electron microscopy; TFE3: transcription factor E3; TFEB: transcription factor EB; TFs: transcription factors; Tg: thapsigargin; Tm: tunicamycin; UPR: unfolded protein response; WB: western blot; WT: wild-type; Xbp1s: spliced Xbp1; XPO1/CRM1: exportin 1.

CLEC18A Impairs Phagocytosis by Reducing FcγRIIA Expression and Arresting Autophagosome-Lysosome Fusion

Mixed cryoglobulinemia (MC) is a hepatitis C virus (HCV)-related extrahepatic manifestation that is characterized by the abnormal presence of immune complexes (ICs). This may be due to the reduced uptake and clearance of ICs. The C-type lectin member 18A (CLEC18A) is a secretory protein that is expressed abundantly in hepatocytes. We previously observed that CLEC18A increased significantly in the phagocytes and sera of patients with HCV, particularly those with MC. Herein, we explored the biological functions of CLEC18A in the MC syndrome development of patients with HCV by using an in vitro cell-based assay with quantitative reverse transcription-PCR, immunoblotting, immunofluorescence, flow cytometry, and enzyme-linked immunosorbent assays. HCV infection or Toll-like receptor 3/7/8 activation could induce CLEC18A expression in Huh7.5 cells. Upregulated CLEC18A interacts with Rab5 and Rab7 and enhances type I/III interferon production to inhibit HCV replication in hepatocytes. However, overexpressed CLEC18A suppressed phagocytic activity in phagocytes. Significantly decreased levels of the Fc gamma receptor (FcγR) IIA were found in the neutrophils of HCV patients, particularly in those with MC (P < 0.005). We demonstrated that CLEC18A could inhibit FcγRIIA expression in a dose-dependent manner through the production of NOX-2-dependent reactive oxygen species to impair the uptake of ICs. Additionally, CLEC18A suppresses the Rab7 expression that is induced by starvation. Overexpressed CLEC18A does not affect autophagosome formation but does reduce the recruitment of Rab7 to autophagosomes, thereby retarding the maturation of autophagosomes and affecting autophagosome-lysosome fusion. We offer a novel molecular machinery with which to understand the association of HCV infection with autoimmunity and propose that CLEC18A may act as a candidate biomarker for HCV-associated MC. IMPORTANCE During infection, the host immune system produces cellular factors to protect against pathogen invasion. However, when the immune response overreacts and there is dysregulated cytokine homeostasis, autoimmunity occurs following an infection. We identified a cellular factor that is involved in HCV-related extrahepatic manifestation, namely, CLEC18A, which is expressed abundantly in hepatocytes and phagocytes. It inhibits HCV replication in hepatocytes by interacting with Rab5/7 and enhancing type I/III IFN expression. However, overexpressed CLEC18A inhibited FcγRIIA expression in phagocytes to impair phagocytosis. Furthermore, the interaction between CLEC18A and Rab5/7 may reduce the recruitment of Rab7 to autophagosomes and thereby retard autophagosome maturation and cause immune complex accumulation. A decreasing trend in CLEC18A levels that was accompanied by reduced HCV RNA titers and diminished cryoglobulin was observed in the sera of HCV-MC patients after direct-acting antiviral therapy. CLEC18A may be used for the evaluation of anti-HCV therapeutic drug effects and could be a potential predisposing factor for the development of MC syndrome.

Porcine Reproductive and Respiratory Syndrome Virus nsp5 Induces Incomplete Autophagy by Impairing the Interaction of STX17 and SNAP29

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen that has devastated the worldwide swine industry for over 30 years. Autophagy is an evolutionarily conserved intracellular lysosomal degradation pathway, and previous studies have documented that PRRSV infection prompts autophagosome accumulation. However, whether PRRSV induces complete or incomplete autophagy remains controversial. Here, we demonstrated that overexpression of PRRSV nonstructural protein 5 (nsp5) induced the accumulation of autophagosomes, and a similar scenario was observed in PRRSV-infected cells. Moreover, both PRRSV infection and nsp5 overexpression activated incomplete autophagy, as evidenced by the blockage of autophagosome-lysosome fusion. Mechanistically, nsp5 overexpression, as well as PRRSV infection, inhibited the interaction of syntaxin 17 (STX17) with synaptosomal-associated protein 29 (SNAP29), two SNARE proteins that mediate autophagosome fusion with lysosomes, to impair the formation of autolysosomes. We further confirmed that nsp5 interacted with STX17, rather than SANP29, and the interacting domains of STX17 were the N-terminal motif and SNARE motif. Taken together, the findings of our study suggest a mechanism by which PRRSV induces incomplete autophagy by blocking autophagosome degradation and provide insights into the development of new therapeutics to combat PRRSV infection. IMPORTANCE A substantial number of viruses have been demonstrated to utilize or hijack autophagy to benefit their replication. In the case of porcine reproductive and respiratory syndrome virus (PRRSV), previous studies have demonstrated the proviral effects of autophagy on PRRSV proliferation. Thus, an investigation of the mechanism by which PRRSV regulates the autophagy processes can provide new insight into viral pathogenesis. Autophagic flux is a dynamic process that consists of autophagosome formation and subsequent lysosomal degradation. However, the exact effect of PRRSV infection on the autophagic flux remains disputed. In this study, we demonstrated that PRRSV infection, as well as PRRSV nsp5 overexpression, inhibited the interaction of STX17 with SNAP29 to impair the fusion of autophagosomes with lysosomes, thereby blocking autophagic flux. This information will help us to understand PRRSV-host interactions and unravel new targets for PRRS prevention and control.

Impaired hepatic autophagy exacerbates hepatotoxin induced liver injury

Hepatotoxins activate the hepatic survival pathway, but it is unclear whether impaired survival pathways contribute to liver injury caused by hepatotoxins. We investigated the role of hepatic autophagy, a cellular survival pathway, in cholestatic liver injury driven by a hepatotoxin. Here we demonstrate that hepatotoxin contained DDC diet impaired autophagic flux, resulting in the accumulation of p62-Ub-intrahyaline bodies (IHBs) but not the Mallory Denk-Bodies (MDBs). An impaired autophagic flux was associated with a deregulated hepatic protein-chaperonin system and significant decline in Rab family proteins. Additionally, p62-Ub-IHB accumulation activated the NRF2 pathway rather than the proteostasis-related ER stress signaling pathway and suppressed the FXR nuclear receptor. Moreover, we demonstrate that heterozygous deletion of Atg7, a key autophagy gene, aggravated the IHB accumulation and cholestatic liver injury. Conclusion: Impaired autophagy exacerbates hepatotoxin-induced cholestatic liver injury. The promotion of autophagy may represent a new therapeutic approach for hepatotoxin-induced liver damage.

An Antidepressant Drug Increased TRAIL Receptor-2 Expression and Sensitized Lung Cancer Cells to TRAIL-induced Apoptosis

BACKGROUND

TRAIL has emerged as a promising therapeutic target due to its ability to selectively induce apoptosis in cancer cells while sparing normal cells. Autophagy, a highly regulated cellular recycling mechanism, is known to play a cell survival role by providing a required environment for the cell. Recent studies suggest that autophagy plays a significant role in increasing TRAIL resistance in certain cancer cells. Thus, regulating autophagy in TRAIL-mediated cancer therapy is crucial for its role in cancer treatment.

OBJECTIVE

Our study explored whether the antidepressant drug desipramine could enhance the ability of TRAIL to kill cancer cells by inhibiting autophagy.

METHODS

The effect of desipramine on TRAIL sensitivity was examined in various lung cancer cell lines. Cell viability was measured by morphological analysis, trypan blue exclusion, and crystal violet staining. Flow cytometry analysis was carried out to measure apoptosis with annexin V-PI stained cells. Western blotting, rtPCR, and immunocytochemistry were carried out to measure autophagy and death receptor expression. TEM was carried out to detect autophagy inhibition.

RESULTS

Desipramine treatment increased the TRAIL sensitivity in all lung cancer cell lines. Mechanistically, desipramine treatment induced death receptor expression to increase TRAIL sensitivity. This effect was confirmed when the genetic blockade of DR5 reduced the effect of desipramine in enhanced TRAIL-mediated cell death. Further investigation revealed that desipramine treatment increased the LC3 and p62 levels, indicating the inhibition of lysosomal degradation of autophagy. Notably, TRAIL, in combination with either desipramine or the autophagy inhibitor chloroquine, exhibited enhanced cytotoxicity compared to TRAIL treatment alone.

CONCLUSION

Our findings revealed the potential of desipramine to induce TRAIL-mediated cell death by autophagy impairment. This discovery suggests its therapeutic potential for inducing TRAIL-mediated cell death by increasing the expression of death receptors, which is caused by impairing autophagy.

Hydroalcoholic extract of Buxus sempervirens shows antiproliferative effect on melanoma, colorectal carcinoma and prostate cancer cells by affecting the autophagic flow

Buxus sempervirens (European Box, Buxaceae, boxwood) has been used in folk medicine to treat rheumatism, arthritis, fever, malaria and skin ulceration while, in recent years, interest has grown on possible employment of boxwood extracts in cancer therapy. We studied the effect of hydroalcoholic extract from dried leaves of Buxus sempervirens (BSHE) on four human cell lines (BMel melanoma cells, HCT116 colorectal carcinoma cells, PC3 prostate cancer cells, and HS27 skin fibroblasts) to ascertain its possible antineoplastic activity. This extract inhibited proliferation of all cell lines in different degree as shown, after 48 h-exposure and MTS assay, by the values of GR₅₀ (normalized growth rate inhibition₅₀) that were 72, 48, 38, and 32 μg/mL for HS27, HCT116, PC3 and BMel cells, respectively. At the above GR₅₀ concentrations, 99% of all studied cells remained vital showing accumulation of acidic vesicles in the cytoplasm, mainly around nuclei, whereas a higher extract concentration (125 μg/mL) was cytotoxic causing, after 48 h-exposure, death of all BMel and HCT116 cells. Immunofluorescence showed microtubule-associated light chain three protein (LC3, a marker for autophagy) to be localized on the above acidic vesicles when cells were treated for 48 h with BSHE (GR₅₀ concentrations). Western blot analysis revealed, in all treated cells, a significant increase (2.2-3.3 times at 24 h) of LC3II, i.e., the phosphatidylethanolamine conjugate of the cytoplasmic form LC3I that is recruited in autophagosome membranes during autophagy. Such increase was accompanied, in all cell lines treated for 24 h or 48 h with BSHE, by a significant increment (2.5-3.4 times at 24 h) of p62, an autophagic cargo protein undergoing degradation during the autophagic process. Therefore, BSHE appeared to promote autophagic flow with its following blockade and consequent accumulation of autophagosome or autolysosomes. The antiproliferative effects of BSHE also involved cell cycle regulators such as p21 (HS27, BMel and HCT116 cells) and cyclin B1 (HCT116, BMel and PC3 cells) whereas, among apoptosis markers, BSHE only decreased (30%-40% at 48 h) the expression of the antiapoptotic protein survivin. It was concluded that BSHE impairs autophagic flow with arrest of proliferation and death in both fibroblasts and cancer cells, being the latter much more sensitive to these effects.

Glutamine Produces Ammonium to Tune Lysosomal pH and Regulate Lysosomal Function

Glutamine is one of the most abundant amino acids in the cell. In mitochondria, glutaminases 1 and 2 (GLS1/2) hydrolyze glutamine to glutamate, which serves as the precursor of multiple metabolites. Here, we show that ammonium generated during GLS1/2-mediated glutaminolysis regulates lysosomal pH and in turn lysosomal degradation. In primary human skin fibroblasts BJ cells and mouse embryonic fibroblasts, deprivation of total amino acids for 1 h increased lysosomal degradation capacity as shown by the increased turnover of lipidated microtubule-associated proteins 1A/1B light chain 3B (LC3-II), several autophagic receptors, and endocytosed DQ-BSA. Removal of glutamine but not any other amino acids from the culture medium enhanced lysosomal degradation similarly as total amino acid starvation. The presence of glutamine in regular culture media increased lysosomal pH by >0.5 pH unit and the removal of glutamine caused lysosomal acidification. GLS1/2 knockdown, GLS1 antagonist, or ammonium scavengers reduced lysosomal pH in the presence of glutamine. The addition of glutamine or NH4Cl prevented the increase in lysosomal degradation and curtailed the extension of mTORC1 function during the early time period of amino acid starvation. Our findings suggest that glutamine tunes lysosomal pH by producing ammonium, which regulates lysosomal degradation to meet the demands of cellular activities. During the early stage of amino acid starvation, the glutamine-dependent mechanism allows more efficient use of internal reserves and endocytosed proteins to extend mTORC1 activation such that the normal anabolism is not easily interrupted by a brief disruption of the amino acid supply.

Highly expressed SERCA2 triggers tumor cell autophagy and is a druggable vulnerability in triple-negative breast cancer

Chemoresistance remains a major obstacle to successful treatment of triple negative breast cancer (TNBC). Identification of druggable vulnerabilities is an important aim for TNBC therapy. Here, we report that SERCA2 expression correlates with TNBC progression in human patients, which promotes TNBC cell proliferation, migration and chemoresistance. Mechanistically, SERCA2 interacts with LC3B via LIR motif, facilitating WIPI2-independent autophagosome formation to induce autophagy. Autophagy-mediated SERCA2 degradation induces SERCA2 transactivation through a Ca²⁺/CaMKK/CREB-1 feedback. Moreover, we found that SERCA2-targeting small molecule RL71 enhances SERCA2-LC3B interaction and induces excessive autophagic cell death. The increase in SERCA2 expression predisposes TNBC cells to RL71-induced autophagic cell death in vitro and in vivo. This study elucidates a mechanism by which TNBC cells maintain their high autophagy activity to induce chemoresistance, and suggests increased SERCA2 expression as a druggable vulnerability for TNBC.

Intracellular cholesterol transport inhibition Impairs autophagy flux by decreasing autophagosome-lysosome fusion

BACKGROUND

Autophagy is an intracellular degradation process crucial for homeostasis. During autophagy, a double-membrane autophagosome fuses with lysosome through SNARE machinery STX17 to form autolysosome for degradation of damaged organelle. Whereas defective autophagy enhances cholesterol accumulation in the lysosome and impaired autophagic flux that results Niemann-Pick type C1 (NPC1) disease. However, exact interconnection between NPC1 and autophagic flux remain obscure due to the existence of controversial reports.

RESULTS

This study aimed at a comparison of the effects of three autophagic inhibitor drugs, including chloroquine, U18666A, and bafilomycin A1, on the intracellular cholesterol transport and autophagy flux. Chloroquine, an autophagic flux inhibitor; U1866A, a NPC1 inhibitor, and bafilomycin A, a lysosomotropic agent are well known to inhibit autophagy by different mechanism. Here we showed that treatment with U1866A and bafilomycin A induces lysosomal cholesterol accumulation that prevented autophagic flux by decreasing autophagosome-lysosome fusion. We also demonstrated that accumulation of cholesterol within the lysosome did not affect lysosomal pH. Although the clearance of accumulated cholesterol by cyclodextrin restored the defective autophagosome-lysosome fusion, the autophagy flux restoration was possible only when lysosomal acidification was not altered. In addition, a failure of STX17 trafficking to autophagosomes plays a key role in prevention of autophagy flux caused by intracellular cholesterol transport inhibitors.

CONCLUSIONS

Our data provide a new insight that the impaired autophagy flux does not necessarily result in lysosomal cholesterol accumulation even though it prevents autophagosome-lysosome fusion. Video abstract.

Looking into Endoplasmic Reticulum Stress: The Key to Drug-Resistance of Multiple Myeloma?

Multiple myeloma (MM) is the second most common hematologic malignancy, resulting from the clonal proliferation of malignant plasma cells within the bone marrow. Despite significant advances that have been made with novel drugs over the past two decades, MM patients often develop therapy resistance, especially to bortezomib, the first-in-class proteasome inhibitor that was approved for treatment of MM. As highly secretory monoclonal protein-producing cells, MM cells are characterized by uploaded endoplasmic reticulum stress (ERS), and rely heavily on the ERS response for survival. Great efforts have been made to illustrate how MM cells adapt to therapeutic stresses through modulating the ERS response. In this review, we summarize current knowledge on the mechanisms by which ERS response pathways influence MM cell fate and response to treatment. Moreover, based on promising results obtained in preclinical studies, we discuss the prospect of applying ERS modulators to overcome drug resistance in MM.

The marine natural product, dicitrinone B, induces apoptosis through autophagy blockade in breast cancer

Being a highly conserved catabolic process, autophagy is induced by various forms of cellular stress, and its modulation has considerable potential as a cancer therapeutic approach. In the present study, it was demonstrated that dicitrinone B (DB), a rare carbon-bridged citrinin dimer, may exert anticancer effects by blocking autophagy at a late stage, without disrupting lysosomal function in MCF7 breast cancer and MDA-MB-231 triple-negative breast cancer cells. Furthermore, it was discovered that DB significantly enhanced intracellular reactive oxygen species (ROS) production and that the removal of ROS was followed by the attenuation of autophagy inhibition. In addition, DB exerted notable inhibitory effects on the proliferation and promoting effects on the apoptosis of MCF7 and MDA-MB-231 cells. In combination with conventional chemotherapeutic drugs, DB exhibited a further enhanced synergistic effect than when used as a single agent. Overall, the data of the present study demonstrate that DB may prove to be a promising autophagy inhibitor with anticancer activity against breast cancer.

Cancer stem cell plasticity and its implications in the development of new clinical approaches for oral squamous cell carcinoma

Oral squamous cell carcinoma (SCC) represents a major worldwide disease burden, with high rates of recurrence and metastatic spread following existing treatment methods. Populations of treatment resistant cancer stem cells (CSCs) are well characterised in oral SCC. These populations of CSCs engage the cellular programme known as epithelial mesenchymal transition (EMT) to enhance metastatic spread and therapeutic resistance. EMT is characterised by specific morphological changes and the expression of certain cell surface markers that represent a transition from an epithelial phenotype to a mesenchymal phenotype. This process is regulated by several cellular pathways that interact both horizontally and hierarchically. The cellular changes in EMT occur along a spectrum, with sub-populations of cells displaying both epithelial and mesenchymal features. The unique features of these CSCs in terms of their EMT state, cell surface markers and metabolism may offer new druggable targets. In addition, these features could be used to identify more aggressive disease states and the opportunity to personalise therapy depending on the presence of certain CSC sub-populations.

α-synuclein build-up is alleviated via ESCRT-dependent endosomal degradation brought about by p38MAPK inhibition in cells expressing p25α

α-synucleinopathy is driven by an imbalance of synthesis and degradation of α-synuclein (αSyn), causing a build up of αSyn aggregates and post-translationally modified species, which not only interfere with normal cellular metabolism but also by their secretion propagates the disease. Therefore, a better understanding of αSyn degradation pathways is needed to address α-synucleinopathy. Here, we used the nerve growth factor–differentiated catecholaminergic PC12 neuronal cell line, which was conferred α-synucleinopathy by inducible expression of αSyn and tubulin polymerization-promoting protein p25α. p25α aggregates αSyn, and imposes a partial autophagosome–lysosome block to mimic aspects of lysosomal deficiency common in neurodegenerative disease. Under basal conditions, αSyn was degraded by multiple pathways but most prominently by macroautophagy and Nedd4/Ndfip1-mediated degradation. We found that expression of p25α induced strong p38MAPK activity. Remarkably, when opposed by inhibitor SB203580 or p38MAPK shRNA knockdown, endolysosomal localization and degradation of αSyn increased, and αSyn secretion and cytotoxicity decreased. This effect was specifically dependent on Hsc70 and the endosomal sorting complex required for transport machinery, but different from classical microautophagy, as the αSyn Hsc70 binding motif was unnecessary. Furthermore, in a primary neuronal (h)-αSyn seeding model, p38MAPK inhibition decreased pathological accumulation of phosphorylated serine-129-αSyn and cytotoxicity. In conclusion, p38MAPK inhibition shifts αSyn degradation from various forms of autophagy to an endosomal sorting complex required for transport–dependent uptake mechanism, resulting in increased αSyn turnover and cell viability in p25α-expressing cells. More generally, our results suggest that under conditions of autophagolysosomal malfunction, the uninterrupted endosomal pathway offers a possibility to achieve disease-associated protein degradation.

Autophagy in health and disease: From molecular mechanisms to therapeutic target

Macroautophagy/autophagy is an evolutionally conserved catabolic process in which cytosolic contents, such as aggregated proteins, dysfunctional organelle, or invading pathogens, are sequestered by the double-membrane structure termed autophagosome and delivered to lysosome for degradation. Over the past two decades, autophagy has been extensively studied, from the molecular mechanisms, biological functions, implications in various human diseases, to development of autophagy-related therapeutics. This review will focus on the latest development of autophagy research, covering molecular mechanisms in control of autophagosome biogenesis and autophagosome-lysosome fusion, and the upstream regulatory pathways including the AMPK and MTORC1 pathways. We will also provide a systematic discussion on the implication of autophagy in various human diseases, including cancer, neurodegenerative disorders (Alzheimer disease, Parkinson disease, Huntington's disease, and Amyotrophic lateral sclerosis), metabolic diseases (obesity and diabetes), viral infection especially SARS-Cov-2 and COVID-19, cardiovascular diseases (cardiac ischemia/reperfusion and cardiomyopathy), and aging. Finally, we will also summarize the development of pharmacological agents that have therapeutic potential for clinical applications via targeting the autophagy pathway. It is believed that decades of hard work on autophagy research is eventually to bring real and tangible benefits for improvement of human health and control of human diseases.

The neuroprotective effects of glucagon-like peptide 1 in Alzheimer's and Parkinson's disease: An in-depth review

Currently, there is no disease-modifying treatment available for Alzheimer's and Parkinson's disease (AD and PD) and that includes the highly controversial approval of the Aβ-targeting antibody aducanumab for the treatment of AD. Hence, there is still an unmet need for a neuroprotective drug treatment in both AD and PD. Type 2 diabetes is a risk factor for both AD and PD. Glucagon-like peptide 1 (GLP-1) is a peptide hormone and growth factor that has shown neuroprotective effects in preclinical studies, and the success of GLP-1 mimetics in phase II clinical trials in AD and PD has raised new hope. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. GLP-1 analogs are safe, well tolerated, resistant to desensitization and well characterized in the clinic. Herein, we review the existing evidence and illustrate the neuroprotective pathways that are induced following GLP-1R activation in neurons, microglia and astrocytes. The latter include synaptic protection, improvements in cognition, learning and motor function, amyloid pathology-ameliorating properties (Aβ, Tau, and α-synuclein), the suppression of Ca2+ deregulation and ER stress, potent anti-inflammatory effects, the blockage of oxidative stress, mitochondrial dysfunction and apoptosis pathways, enhancements in the neuronal insulin sensitivity and energy metabolism, functional improvements in autophagy and mitophagy, elevated BDNF and glial cell line-derived neurotrophic factor (GDNF) synthesis as well as neurogenesis. The many beneficial features of GLP-1R and GLP-1/GIPR dual agonists encourage the development of novel drug treatments for AD and PD.

Integrated regulation of stress responses, autophagy and survival by altered intracellular iron stores

Iron is a mineral essential for blood production and a variety of critical cellular functions. Altered iron metabolism has been increasingly observed in many diseases and disorders, but a comprehensive and mechanistic understanding of the cellular impact of impaired iron metabolism is still lacking. We examined the effects of iron overload or iron deficiency on cellular stress responses and autophagy which collectively regulate cell homeostasis and survival. Acute iron loading led to increased mitochondrial ROS (mtROS) production and damage, lipid peroxidation, impaired autophagic flux, and ferroptosis. Iron-induced mtROS overproduction is the mechanism of increased lipid peroxidation, impaired autophagy, and the induction of ferroptosis. Iron excess-induced ferroptosis was cell-type dependent and regulated by activating transcription factor 4 (ATF4). Upregulation of ATF4 mitigated iron-induced autophagic dysfunction and ferroptosis, whereas silencing of ATF4 expression impaired autophagy and resulted in increased mtROS production and ferroptosis. Employing autophagy-deficient hepatocytes and different autophagy inhibitors, we further showed that autophagic impairment sensitized cells to iron-induced ferroptosis. In contrast, iron deficiency activated the endoplasmic reticulum (ER) stress response, decreased autophagy, and induced apoptosis. Decreased autophagy associated with iron deficiency was due to ER stress, as reduction of ER stress by 4-phenylbutyric acid (4-PBA) improved autophagic flux. The mechanism of decreased autophagy in iron deficiency is a disruption in lysosomal biogenesis due to impaired posttranslational maturation of lysosomal membrane proteins. In conclusion, iron excess and iron deficiency cause different forms of cell stress and death in part through the common mechanism of impaired autophagic function.

Interaction of Liberibacter Solanacearum with Host Psyllid Vitellogenin and Its Association with Autophagy

Candidatus Liberibacter solanacearum (CLso) haplotype D, transmitted by the carrot psyllid Bactericera trigonica, is a major constraint for carrot production in Israel. Unveiling the molecular interactions between the psyllid vector and CLso can facilitate the development of nonchemical approaches for controlling the disease caused by CLso. Bacterial surface proteins are often known to be involved in adhesion and virulence; however, interactions of CLso with carrot psyllid proteins that have a role in the transmission process has remained unexplored. In this study, we used CLso outer membrane protein (OmpA) and flagellin as baits to screen for psyllid interacting proteins in a yeast two-hybrid system assay. We identified psyllid vitellogenin (Vg) to interact with both OmpA and flagellin of CLso. As Vg and autophagy are often tightly linked, we also studied the expression of autophagy-related genes to further elucidate this interaction. We used the juvenile hormone (JH-III) to induce the expression of Vg, thapsigargin for suppressing autophagy, and rapamycin for inducing autophagy. The results revealed that Vg negatively regulates autophagy. Induced Vg expression significantly suppressed autophagy-related gene expression and the levels of CLso significantly increased, resulting in a significant mortality of the insect. Although the specific role of Vg remains obscure, the findings presented here identify Vg as an important component in the insect immune responses against CLso and may help in understanding the initial molecular response in the vector against Liberibacter. IMPORTANCE Pathogen transmission by vectors involves multiple levels of interactions, and for the transmission of liberibacter species by psyllid vectors, much of these interactions are yet to be explored. Candidatus Liberibacter solanacearum (CLso) haplotype D inflicts severe economic losses to the carrot industry. Understanding the specific interactions at different stages of infection is hence fundamental and could lead to the development of better management strategies to disrupt the transmission of the bacteria to new host plants. Here, we show that two liberibacter membrane proteins interact with psyllid vitellogenin and also induce autophagy. Altering vitellogenin expression directly influences autophagy and CLso abundance in the psyllid vector. Although the exact mechanism underlying this interaction remains unclear, this study highlights the importance of immune responses in the transmission of this disease agent.

Activated Endolysosomal Cation Channel TRPML1 Facilitates Maturation of α-Synuclein-Containing Autophagosomes

Background: Protein aggregates are degraded via the autophagy-lysosome pathway and alterations in the lysosomal system leading to the accumulation of pathogenic proteins, including aggregates of α-synuclein in Parkinson’s disease (PD). The importance of the endolysosomal transient receptor potential cation channel, mucolipin subfamily 1 (TRPML1) for the lysosomal function is highlighted by the fact that TRPML1 mutations cause the lysosomal storage disease mucolipidosis type IV. In this study, we investigated the mechanism by which activation of TRPML1 affects the degradation of α-synuclein.

Methods: As a model of α-synuclein pathology, we expressed the pathogenic A53Tα-synuclein mutant in HEK293T cells. These cells were treated with the synthetic TRPML1 agonist ML-SA1. The amount of α-synuclein protein was determined by immunoblots. The abundance of aggregates and autolysosomal vesicles was determined by fluorescence microscopy and immunocytochemistry. Findings were confirmed by life-cell imaging and by application of ML-SA1 and the TRPML1 antagonist ML-SI3 to human dopaminergic neurons and human stem cell-derived neurons.

Results: ML-SA1 reduced the percentage of HEK293T cells with α-synuclein aggregates and the amount of α-synuclein protein. The effect of ML-SA1 was blocked by pharmacological and genetic inhibition of autophagy. Consistent with TRPML function, it required the membrane lipid PI(3,5)P_2, and cytosolic calcium. ML-SA1 shifted the composition of autophagosomes towards a higher fraction of mature autolysosomes, also in presence of α-synuclein. In neurons, inhibition of TRPML1 by its antagonist ML-SI3 blocked autophagosomal clearance, whereas the agonist ML-SA1 shifted the composition of a-synuclein particles towards a higher fraction of acidified particles. ML-SA1 was able to override the effect of Bafilomycin A1, which blocks the fusion of the autophagosome and lysosome and its acidification.

Conclusion: These findings suggest, that activating TRPML1 with ML-SA1 facilitates clearance of α-synuclein aggregates primarily by affecting the late steps of the autophagy, i.e., by promoting autophagosome maturation. In agreement with recent work by others, our findings indicate that TRPML1 might constitute a plausible therapeutic target for PD, that warrants further validation in rodent models of α-synuclein pathology.

Fine-tuning cell organelle dynamics during mitosis by small GTPases

During mitosis, the allocation of genetic material concurs with organelle transformation and distribution. The coordination of genetic material inheritance with organelle dynamics directs accurate mitotic progression, cell fate determination, and organismal homeostasis. Small GTPases belonging to the Ras superfamily regulate various cell organelles during division. Being the key regulators of membrane dynamics, the dysregulation of small GTPases is widely associated with cell organelle disruption in neoplastic and non-neoplastic diseases, such as cancer and Alzheimer's disease. Recent discoveries shed light on the molecular properties of small GTPases as sophisticated modulators of a remarkably complex and perfect adaptors for rapid structure reformation. This review collects current knowledge on small GTPases in the regulation of cell organelles during mitosis and highlights the mediator role of small GTPase in transducing cell cycle signaling to organelle dynamics during mitosis.

Hydroxychloroquine Causes Early Inner Retinal Toxicity and Affects Autophagosome-Lysosomal Pathway and Sphingolipid Metabolism in the Retina

Hydroxychloroquine (HCQ) is an anti-malarial drug but also widely used to treat autoimmune diseases like arthritis and lupus. Although there have been multiple reports of the adverse effect of prolonged HCQ usage on the outer retina, leading to bull's-eye maculopathy, the effect of HCQ toxicity on the inner retina as well as on overall visual functions has not been explored in detail. Furthermore, lack of an established animal model of HCQ toxicity hinders our understanding of the underlying molecular mechanisms. Here, using a small clinical study, we confirmed the effect of HCQ toxicity on the inner retina, in particular the reduction in central inner retinal thickness, and established a mouse model of chronic HCQ toxicity that recapitulates the effects observed in human retina. Using the mouse model, we demonstrated that chronic HCQ toxicity results in loss of inner retinal neurons and retinal ganglion cells (RGC) and compromises visual functions. We further established that HCQ treatment prevents autophagosome-lysosome fusion and alters the sphingolipid homeostasis in mouse retina. Our results affirm the notion that HCQ treatment causes early damage to the inner retina and affects visual functions before leading to characteristic toxicity in the macular region of the outer retina, 'bull's-eye maculopathy.' We also provide insights into the underlying molecular mechanisms of HCQ retinal toxicity that may involve autophagy-lysosomal defects and alterations in sphingolipid metabolism.

A Review on Mechanistic Insight of Plant Derived Anticancer Bioactive Phytocompounds and Their Structure Activity Relationship

Cancer is a disorder that rigorously affects the human population worldwide. There is a steady demand for new remedies to both treat and prevent this life-threatening sickness due to toxicities, drug resistance and therapeutic failures in current conventional therapies. Researchers around the world are drawing their attention towards compounds of natural origin. For decades, human beings have been using the flora of the world as a source of cancer chemotherapeutic agents. Currently, clinically approved anticancer compounds are vincristine, vinblastine, taxanes, and podophyllotoxin, all of which come from natural sources. With the triumph of these compounds that have been developed into staple drug products for most cancer therapies, new technologies are now appearing to search for novel biomolecules with anticancer activities. Ellipticine, camptothecin, combretastatin, curcumin, homoharringtonine and others are plant derived bioactive phytocompounds with potential anticancer properties. Researchers have improved the field further through the use of advanced analytical chemistry and computational tools of analysis. The investigation of new strategies for administration such as nanotechnology may enable the development of the phytocompounds as drug products. These technologies have enhanced the anticancer potential of plant-derived drugs with the aim of site-directed drug delivery, enhanced bioavailability, and reduced toxicity. This review discusses mechanistic insights into anticancer compounds of natural origins and their structural activity relationships that make them targets for anticancer treatments.

NUPR1 promotes the proliferation and metastasis of oral squamous cell carcinoma cells by activating TFE3-dependent autophagy

Oral squamous cell carcinoma (OSCC) is the most common type of oral malignancy, and metastasis accounts for the poor prognosis of OSCC. Autophagy is considered to facilitate OSCC development by mitigating various cellular stresses; nevertheless, the mechanisms of autophagy in OSCC cell proliferation and metastasis remain unknown. In our study, high-sensitivity label-free quantitative proteomics analysis revealed nuclear protein 1 (NUPR1) as the most significantly upregulated protein in formalin-fixed paraffin-embedded tumour samples derived from OSCC patients with or without lymphatic metastasis. Moreover, NUPR1 is aberrantly expressed in the OSCC tissues and predicts low overall survival rates for OSCC patients. Notably, based on tandem mass tag-based quantitative proteomic analysis between stable NUPR1 knockdown OSCC cells and scrambled control OSCC cells, we confirmed that NUPR1 maintained autophagic flux and lysosomal functions by directly increasing transcription factor E3 (TFE3) activity, which promoted OSCC cell proliferation and metastasis in vitro and in vivo. Collectively, our data revealed that the NUPR1–TFE3 axis is a critical regulator of the autophagic machinery in OSCC progression, and this study may provide a potential therapeutic target for the treatment of OSCC.

Thapsigargin: key to new host-directed coronavirus antivirals?

Despite the great success of vaccines that protect against RNA virus infections, and the development and clinical use of a limited number of RNA virus-specific drugs, there is still an urgent need for new classes of antiviral drugs against circulating or emerging RNA viruses. To date, it has proved difficult to efficiently suppress RNA virus replication by targeting host cell functions, and there are no approved drugs of this type. This opinion article discusses the recent discovery of a pronounced and sustained antiviral activity of the plant-derived natural compound thapsigargin against enveloped RNA viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Middle East respiratory syndrome coronavirus (MERS-CoV), and influenza A virus. Based on its mechanisms of action, thapsigargin represents a new prototype of compounds with multimodal host-directed antiviral activity.

The different autophagy degradation pathways and neurodegeneration

The term autophagy encompasses different pathways that route cytoplasmic material to lysosomes for degradation and includes macroautophagy, chaperone-mediated autophagy, and microautophagy. Since these pathways are crucial for degradation of aggregate-prone proteins and dysfunctional organelles such as mitochondria, they help to maintain cellular homeostasis. As post-mitotic neurons cannot dilute unwanted protein and organelle accumulation by cell division, the nervous system is particularly dependent on autophagic pathways. This dependence may be a vulnerability as people age and these processes become less effective in the brain. Here, we will review how the different autophagic pathways may protect against neurodegeneration, giving examples of both polygenic and monogenic diseases. We have considered how autophagy may have roles in normal CNS functions and the relationships between these degradative pathways and different types of programmed cell death. Finally, we will provide an overview of recently described strategies for upregulating autophagic pathways for therapeutic purposes.

Raman and fluorescence imaging of phospholipidosis induced by cationic amphiphilic drugs in endothelial cells

Cationic amphiphilic drugs (CADs) are known from lysosomotropism, drug-induced phospholipidosis (DIPL), activation of autophagy, and decreased cell viability, but the relationship between these events is not clear and little is known about DIPL in the endothelium. In this work, the effects of fluoxetine, amiodarone, clozapine, and risperidone on human microvascular endothelial cells (HMEC-1) were studied using a combined methodology of label-free Raman imaging and fluorescence staining. Raman spectroscopy was applied to characterize biochemical changes in lipid profile and their distribution in the cellular compartments, while fluorescence staining (LysoTracker, LipidTOX, LC3B, and JC-1) was used to analyze lysosome volume expansion, activation of autophagy, lipid accumulation, and mitochondrial membrane depolarization. We demonstrated that fluoxetine, amiodarone, and clozapine, but not risperidone, at non-toxic concentrations induced lipid accumulations in the perinuclear and cytoplasmic regions of endothelial cells. Spectroscopic markers of DIPL included a robust increase in the ratio (lipid/(protein + lipid)), an increase in choline-containing lipid, fatty acids, and the presence of cholesterol esters, while starvation-induced activated autophagy revealed a spectroscopic signature associated with subtle changes in the lipid profile only. Interestingly, lysosomal volume expansion, occurrence of DIPL, and activation of autophagy induced by selected CADs all depended on drug-accumulation in acidic pH of lysosome cellular compartments whereas reduced endothelial viability did not, and was attributed to mitochondrial mechanisms as evidenced by a decreased mitochondrial transmembrane potential. In conclusion, drug-induced phospholipidosis in the endothelium did not reduce endothelial viability per se and can be efficiently assayed by Raman imaging.

The MicroRNA-Based Strategies to Combat Cancer Chemoresistance via Regulating Autophagy

Chemoresistance frequently occurs in cancer treatment, which results in chemotherapy failure and is one of the most leading causes of cancer-related death worldwide. Understanding the mechanism of chemoresistance and exploring strategies to overcome chemoresistance have become an urgent need. Autophagy is a highly conserved self-degraded process in cells. The dual roles of autophagy (pro-death or pro-survival) have been implicated in cancers and chemotherapy. MicroRNA (miRNA) is a class of small non-coding molecules that regulate autophagy at the post-transcriptional level in cancer cells. The association between miRNAs and autophagy in cancer chemoresistance has been emphasized. In this review, we focus on the dual roles of miRNA-mediated autophagy in facilitating or combating chemoresistance, aiming to shed lights on the potential role of miRNAs as targets to overcome chemoresistance.

Molecular Basis of Resveratrol-Induced Resensitization of Acquired Drug-Resistant Cancer Cells

Multidrug resistance (MDR) to anticancer drugs remains a serious obstacle to the success of cancer chemotherapy. Resveratrol, a polyphenol, present in natural products exerts anticancer activity and acts as a potential MDR inhibitor in various drug-resistant cancer cells. In the process of resensitization of drug-resistant cancer cells, resveratrol has been shown to interfere with ABC transporters and drug-metabolizing enzymes, increase DNA damage, inhibit cell cycle progression, and induce apoptosis and autophagy, as well as prevent the induction of epithelial to mesenchymal transition (EMT) and cancer stem cells (CSCs). This review summarizes the mechanisms by which resveratrol counteracts MDR in acquired drug-resistant cancer cell lines and provides a critical basis for understanding the regulation of MDR as well as the development of MDR-inhibiting drugs.

Regulation of ER-derived membrane dynamics by the DedA domain-containing proteins VMP1 and TMEM41B

The endoplasmic reticulum (ER) is a central hub for the biogenesis of various organelles and lipid-containing structures. Recent studies suggest that vacuole membrane protein 1 (VMP1) and transmembrane protein 41B (TMEM41B), multispanning ER membrane proteins, regulate the formation of many of these ER-derived structures, including autophagosomes, lipid droplets, lipoproteins, and double-membrane structures for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication. VMP1 and TMEM41B possess a DedA domain that is widely distributed not only in eukaryotes but also in prokaryotes and predicted to adopt a characteristic structure containing two reentrant loops. Furthermore, recent studies show that both proteins have lipid scrambling activity. Based on these findings, the potential roles of VMP1 and TMEM41B in the dynamic remodeling of ER membranes and the biogenesis of ER-derived structures are discussed.

Autophagy and Lysosomal Functionality in CMT2B Fibroblasts Carrying the RAB7K126R Mutation

Charcot-Marie-Tooth type 2B (CMT2B) disease is a dominant axonal peripheral neuropathy caused by five mutations in the RAB7A gene. Autophagy and late endocytic trafficking were already characterized in CMT2B. Indeed, impairment of autophagy and an increase in lysosomal degradative activity were found in cells expressing the mutant proteins. Recently, we described a novel RAB7 mutation associated with predominantly motor CMT2 and impaired EGFR trafficking. With the aim to analyze the autophagy process and lysosomal activity in CMT2B fibroblasts carrying the p.K126R RAB7 novel mutation and to investigate further the causes of the different phenotype, we have performed Western blot, immunofluorescence and cytometric analyses monitoring autophagic markers and endocytic proteins. Moreover, we investigated lipophagy by analyzing accumulation of lipid droplets and their co-localization with endolysosomal degradative compartments. We found that cells expressing the RAB7^K126R mutant protein were characterized by impairment of autophagy and lipophagy processes and by a moderate increase in lysosomal activity compared to the previously studied cells carrying the RAB7^V162M mutation. Thus, we concluded that EGFR trafficking alterations and a moderate increase in lysosomal activity with concomitant impairment of autophagy could induce the specific predominantly motor phenotype observed in K126R patients.

Multidrug Resistance (MDR): A Widespread Phenomenon in Pharmacological Therapies

Multidrug resistance is a leading concern in public health. It describes a complex phenotype whose predominant feature is resistance to a wide range of structurally unrelated cytotoxic compounds, many of which are anticancer agents. Multidrug resistance may be also related to antimicrobial drugs, and is known to be one of the most serious global public health threats of this century. Indeed, this phenomenon has increased both mortality and morbidity as a consequence of treatment failures and its incidence in healthcare costs. The large amounts of antibiotics used in human therapies, as well as for farm animals and even for fishes in aquaculture, resulted in the selection of pathogenic bacteria resistant to multiple drugs. It is not negligible that the ongoing COVID-19 pandemic may further contribute to antimicrobial resistance. In this paper, multidrug resistance and antimicrobial resistance are underlined, focusing on the therapeutic options to overcome these obstacles in drug treatments. Lastly, some recent studies on nanodrug delivery systems have been reviewed since they may represent a significant approach for overcoming resistance.