Lysosomal cell death at a glance

Biocapture-Directed Chemical Labeling for Discerning Stressed States of Organelles

Lysosomal rupture engaged in diverse diseases remains poorly discerned from lysosomal membrane permeabilization (LMP). We herein reported biocapture-directed chemical labeling (BCCL) for the discern of lysosomal rupture by tracking the release of optically labeled cathepsins from damaged lysosomes into the cytosol. BCCL entails covalent anchoring of an azide-tagged suicide substrate (Epo-LeuTyr^Az) to the enzyme active site and bioorthogonal ligation of the introduced azide with ^DBCORC, a ratiometric sensor featuring an acidity-reporting red emissive X-rhodamine-lactam (ROX), blue emissive coumarin (CM) inert to pH, and DBCO reactive to azide. Aided with fluorescein isocyanate-labeled sialic acid (FITC-Sia), a probe remained in pH-elevated lysosomes but dissipated from LMP⁺ lysosomes, BCCL enables optical discern of four states of lysosomes: ruptured lysosomes (blue in cytosol), LMP⁺ lysosomes (blue in lysosomes), pH-elevated lysosomes (blue and green in lysosomes), and physiological lysosomes (blue, green and red in lysosomes). This approach could find applicability to study lysosome rupture over LMP in diseases and to evaluate lysosome rupture-inducing drugs.

Bibliometric Analysis of Cathepsin B Research From 2011 to 2021

Cathepsin B (CTSB) is a lysosomal protease implicated in the progression of various diseases. A large number of CTSB-related studies have been conducted to date. However, there is no comprehensive bibliometric analysis on this subject. In our study, we performed quantitative analysis of CTSB-related publications retrieved from the Science Citation Index Expanded (SCIE) of the Web of Science Core Collection (reference period: 2011–2021). A total of 3,062 original articles and reviews were retrieved. The largest number of publications were from USA (n = 847, 27.66%). The research output of each country showed positive correlation with gross domestic product (GDP) (r = 0.9745, P < 0.0001). Active collaborations between countries/regions were also observed. Reinheckel T and Sloane BF were perhaps the most impactful researchers in the research landscape of CTSB. Plos ONE was the most prevalent (119/3,062, 3.89%) and cited journal (3,021 citations). Comprehensive analysis of the top citations, co-citations, and keywords was performed to acquire the theoretical basis and hotspots of CTSB-related research. The main topics included CTSB-related cancers and inflammatory diseases, CTSB-associated cell death pattern, and the applications of CTSB. These results provide comprehensive insights into the current status of global CTSB-related research especially in pancreas, which is worthy of continued follow-up by practitioners and clinicians in this field.

Bacterial Quorum-Sensing Signal DSF Inhibits LPS-Induced Inflammations by Suppressing Toll-like Receptor Signaling and Preventing Lysosome-Mediated Apoptosis in Zebrafish

Bacteria and their eukaryotic hosts have co-evolved for millions of years, and the former can intercept eukaryotic signaling systems for the successful colonization of the host. The diffusible signal factor (DSF) family represents a type of quorum-sensing signals found in diverse Gram-negative bacterial pathogens. Recent evidence shows that the DSF is involved in interkingdom communications between the bacterial pathogen and the host plant. In this study, we explored the anti-inflammatory effect of the DSF and its underlying molecular mechanism in a zebrafish model. We found that the DSF treatment exhibited a strong protective effect on the inflammatory response of zebrafish induced by lipopolysaccharide (LPS). In the LPS-induced inflammation zebrafish model, the DSF could significantly ameliorate the intestinal pathological injury, reduce abnormal migration and the aggregation of inflammatory cells, inhibit the excessive production of inflammatory mediator reactive oxygen species (ROS) content, and prevent apoptosis. Through an RNA-Seq analysis, a total of 938 differentially expressed genes (DEGs) was screened between LPS and LPS + DSF treatment zebrafish embryos. A further bioinformatics analysis and validation revealed that the DSF might inhibit the LPS-induced zebrafish inflammatory response by preventing the activation of signaling in the Toll-like receptor pathway, attenuating the expression of pro-inflammatory cytokines and chemokines, and regulating the activation of the caspase cascade through restoring the expression of lysosomal cathepsins and apoptosis signaling. This study, for the first time, demonstrates the anti-inflammatory role and a potential pharmaceutical application of the bacterial signal DSF. These findings also suggest that the interkingdom communication between DSF-producing bacteria and zebrafish might occur in nature.

Revisiting Regulated Cell Death Responses in Viral Infections

The fate of a viral infection in the host begins with various types of cellular responses, such as abortive, productive, latent, and destructive infections. Apoptosis, necroptosis, and pyroptosis are the three major types of regulated cell death mechanisms that play critical roles in viral infection response. Cell shrinkage, nuclear condensation, bleb formation, and retained membrane integrity are all signs of osmotic imbalance-driven cytoplasmic swelling and early membrane damage in necroptosis and pyroptosis. Caspase-driven apoptotic cell demise is considered in many circumstances as an anti-inflammatory, and some pathogens hijack the cell death signaling routes to initiate a targeted attack against the host. In this review, the selected mechanisms by which viruses interfere with cell death were discussed in-depth and were illustrated by compiling the general principles and cellular signaling mechanisms of virus–host-specific molecule interactions.

Regulation of the lysosome by sphingolipids: potential role in aging

Sphingolipids are a class of bioactive complex lipids that have been closely associated with aging and aging-related diseases. However, the mechanism through which sphingolipids control aging has long been a mystery. Emerging studies reveal that sphingolipids exert tight control over lysosomal homeostasis and function, as evidenced by sphingolipid-related diseases, including but not limited to lysosomal storage disorders. These diseases are defined by primary lysosomal defects and a few secondary defects such as mitochondrial dysfunction. Intriguingly, recent research indicates that the majority of these defects are also associated with aging, implying that sphingolipid-related diseases and aging may share common mechanisms. We propose that the lysosome is a pivotal hub for sphingolipid-mediated aging regulation. This review discusses the critical roles of sphingolipid metabolism in regulating various lysosomal functions, with an emphasis on how such regulation may contribute to aging and aging-related diseases.

Emerging roles of mitotic autophagy

Lysosomes exert pleiotropic functions to maintain cellular homeostasis and degrade autophagy cargo. Despite the great advances that have boosted our understanding of autophagy and lysosomes in both physiology and pathology, their function in mitosis is still controversial. During mitosis, most organelles are reshaped or repurposed to allow the correct distribution of chromosomes. Mitotic entry is accompanied by a reduction in sites of autophagy initiation, supporting the idea of an inhibition of autophagy to protect the genetic material against harmful degradation. However, there is accumulating evidence revealing the requirement of selective autophagy and functional lysosomes for a faithful chromosome segregation. Degradation is the most-studied lysosomal activity, but recently described alternative functions that operate in mitosis highlight the lysosomes as guardians of mitotic progression. Because the involvement of autophagy in mitosis remains controversial, it is important to consider the specific contribution of signalling cascades, the functions of autophagic proteins and the multiple roles of lysosomes, as three entangled, but independent, factors controlling genomic stability. In this Review, we discuss the latest advances in this area and highlight the therapeutic potential of targeting autophagy for drug development.

The myth of cobra venom cytotoxin: More than just direct cytolytic actions

Cobra venom cytotoxin (CTX) is a non-enzymatic three-finger toxin that constitutes 40-60% of cobra venom. Thus, it plays an important role in the pathophysiology of cobra envenomation, especially in local dermonecrosis. The three-finger hydrophobic loops of CTX determine the cytotoxicity. Nevertheless, the actual mechanisms of cytotoxicity are not fully elucidated as they involve not only cytolytic actions but also intracellular signalling-mediated cell death pathways. Furthermore, the possible transition cell death pattern remains to be explored. The actual molecular mechanisms require further studies to unveil the relationship between different CTXs from different cobra species and cell types which may result in differential cell death patterns. Here, we discuss the biophysical interaction of CTX with the cell membrane involving four binding modes: electrostatic interaction, hydrophobic partitioning, isotropic phase, and oligomerisation. Oligomerisation of CTX causes pore formation in the membrane lipid bilayer. Additionally, the CTX-induced apoptotic pathway can be executed via death receptor-mediated extrinsic pathways and mitochondrial-mediated intrinsic pathways. We also discuss lysosomal-mediated necrosis and the occurrence of necroptosis following CTX action. Collectively, we provided an insight into concentration-dependent transition of cell death pattern which involves different mechanistic actions. This contributes a new direction for further investigation of cytotoxic pathways activated by the CTXs for future development of biotherapeutics targeting pathological effects caused by CTX.

Trehalose Suppresses Lysosomal Anomalies in Supporting Cells of Oocytes and Maintains Female Fertility

Supporting cells of oocytes, i.e., cumulus cells, control oocyte quality, which determines fertilization success. Therefore, the transformation of mature and immature cumulus cells (MCCs and ICCs, respectively) into dysmature cumulus cells (DCCs) with dead characteristics deteriorates oocyte quality. However, the molecular basis for this transformation remains unclear. Here, we explored the link between autophagic decline and cumulus transformation using cumulus cells from patients with infertility, female mice, and human granulosa cell-derived KGN cell lines. When human cumulus cells were labeled with LysoTracker probes, fluorescence corresponding to lysosomes was enhanced in DCCs compared to that in MCCs and ICCs. Similarly, treatment with the autophagy inhibitor chloroquine elevated LysoTracker fluorescence in both mouse cumulus cells and KGN cells, subsequently suppressing ovulation in female mice. Electron microscopy analysis revealed the proliferation of abnormal lysosomes in chloroquine-treated KGN cells. Conversely, the addition of an autophagy inducer, trehalose, suppressed chloroquine-driven problematic lysosomal anomalies and ameliorated ovulation problems. Our results suggest that autophagy maintains the healthy state of the supporting cells of human oocytes by suppressing the formation of lysosomes. Thus, our results provide insights into the therapeutic effects of trehalose on female fertility.

The Lysosome in Malignant Melanoma: Biology, Function and Therapeutic Applications

Lysosomes are membrane-bound vesicles that play roles in the degradation and recycling of cellular waste and homeostasis maintenance within cells. False alterations of lysosomal functions can lead to broad detrimental effects and cause various diseases, including cancers. Cancer cells that are rapidly proliferative and invasive are highly dependent on effective lysosomal function. Malignant melanoma is the most lethal form of skin cancer, with high metastasis characteristics, drug resistance, and aggressiveness. It is critical to understand the role of lysosomes in melanoma pathogenesis in order to improve the outcomes of melanoma patients. In this mini-review, we compile our current knowledge of lysosomes' role in tumorigenesis, progression, therapy resistance, and the current treatment strategies related to lysosomes in melanoma.

Imatinib disturbs lysosomal function and morphology and impairs the activity of mTORC1 in human hepatocyte cell lines

The tyrosine kinase inhibitors (TKIs) imatinib and lapatinib are associated with severe hepatotoxicity, whose mechanisms are currently under investigation. As amphiphilic drugs, imatinib and lapatinib enrich in lysosomes. In the present study, we investigated their effects on lysosomal morphology and function in HepG2 and HuH-7 cells and explored possible links between lysosomal dysfunction and hepatotoxicity. Both TKIs increased the lysosomal volume time and concentration-dependently in HepG2 and HuH-7 cells. In HepG2 cells, lapatinib and imatinib raised the lysosomal pH and destabilized the lysosomal membrane, thereby impairing lysosomal proteolytic activity such as cathepsin B processing. Imatinib activated the transcription factor EB (TFEB), a regulator of lysosomal biogenesis and function, as demonstrated by nuclear TFEB accumulation and increased expression of TFEB-target genes. Because of lysosomal dysfunction, imatinib impaired mTORC1 activation, a protein complex activated on the lysosomal surface, which explained TFEB activation. HepG2 cells treated with imatinib showed increased levels of MAP1LC3A/B-II and of ATG13 (S318) phosphorylation, indicating induction of autophagy due to TFEB activation. Finally, imatinib induced apoptosis in HepG2 cells in a time and concentration-dependent manner, explained by lysosomal and mitochondrial toxicity. Our findings provide a new lysosome-centered mechanism for imatinib-induced hepatotoxicity that could be extended to other lysosomotropic drugs.

Non-apoptotic cell death-based cancer therapy: Molecular mechanism, pharmacological modulators, and nanomedicine

As an emerging cancer therapeutic target, non-apoptotic cell death such as ferroptosis, necroptosis and pyroptosis, etc., has revealed significant potential in cancer treatment for bypassing apoptosis to enhance the undermined therapeutic efficacy triggered by apoptosis resistance. A variety of anticancer drugs, synthesized compounds and natural products have been proven recently to induce non-apoptotic cell death and exhibit excellent anti-tumor effects. Moreover, the convergence of nanotechnology with functional materials and biomedicine science has provided tremendous opportunities to construct non-apoptotic cell death-based nanomedicine for innovative cancer therapy. Nanocarriers are not only employed in targeted delivery of non-apoptotic inducers, but also used as therapeutic components to induce non-apoptotic cell death to achieve efficient tumor treatment. This review first introduces the main characteristics, the mechanism and various pharmacological modulators of different non-apoptotic cell death forms, including ferroptosis, necroptosis, pyroptosis, autophagy, paraptosis, lysosomal-dependent cell death, and oncosis. Second, we comprehensively review the latest progresses of nanomedicine that induces various forms of non-apoptotic cell death and focus on the nanomedicine targeting different pathways and components. Furthermore, the combination therapies of non-apoptotic cell death with photothermal therapy, photodynamic therapy, immunotherapy and other modalities are summarized. Finally, the challenges and future perspectives in this regard are also discussed.

Lysosomes in Stem Cell Quiescence: A Potential Therapeutic Target in Acute Myeloid Leukemia

Lysosomes are cellular organelles that regulate essential biological processes such as cellular homeostasis, development, and aging. They are primarily connected to the degradation/recycling of cellular macromolecules and participate in cellular trafficking, nutritional signaling, energy metabolism, and immune regulation. Therefore, lysosomes connect cellular metabolism and signaling pathways. Lysosome's involvement in the critical biological processes has rekindled clinical interest towards this organelle for treating various diseases, including cancer. Recent research advancements have demonstrated that lysosomes also regulate the maintenance and hemostasis of hematopoietic stem cells (HSCs), which play a critical role in the progression of acute myeloid leukemia (AML) and other types of cancer. Lysosomes regulate both HSCs' metabolic networks and identity transition. AML is a lethal type of blood cancer with a poor prognosis that is particularly associated with aging. Although the genetic landscape of AML has been extensively described, only a few targeted therapies have been produced, warranting the need for further research. This review summarizes the functions and importance of targeting lysosomes in AML, while highlighting the significance of lysosomes in HSCs maintenance.

Assessing the bioavailability and biotoxicity of spiromesifen and its main metabolite spiromesifen-enol (M01) reveals the defense mechanisms of earthworms (Eisenia fetida)

As a promising acaricide and potentially hazardous material, the defense mechanisms of non-target organisms to its exposure are unknown. This study investigates the bioavailability and biotoxicity of spiromesifen and spiromesifen-enol (M01), its main metabolite, in Eisenia fetida. The results showed that M01 was more persistent in the soil environment and E. fetida than spiromesifen. Transcriptome analysis indicated that the spiromesifen- and M01-induced differentially expressed genes (DEGs) were mainly enriched in lysosomal and phagosomal pathways. Analysis of the key common DEGs showed that both spiromesifen and M01 significantly influenced the lysosomes, phagosomes, antioxidant systems, and detoxification systems. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that spiromesifen and M01 damaged E. fetida epidermis and enhanced lysosomal and phagosomal activities. Significant oxidative stress effects were observed at the end of exposure. The hydroxyl free radical (·OH^-) content and neutral red retention time (NRRT) could serve as sensitive early biomarkers to predict their pollution. These results revealed the synergistic effects of the epidermis, lysosomes, phagosomes, antioxidant systems, and detoxification system in resisting spiromesifen- and M01-induced damage, which could contribute to the defense mechanisms of non-target organisms against these pollutants.

Lysosome-mediated chemoresistance in acute myeloid leukemia

Despite the outstanding advances in understanding the biology underlying the pathophysiology of acute myeloid leukemia (AML) and the promising preclinical data published lastly, AML treatment still relies on a classic chemotherapy regimen largely unchanged for the past five decades. Recently, new drugs have been approved for AML, but the real clinical benefit is still under evaluation. Nevertheless, primary refractory and relapse AML continue to represent the main clinical challenge, as the majority of AML patients will succumb to the disease despite achieving a complete remission during the induction phase. As such, treatments for chemoresistant AML represent an unmet need in this disease. Although great efforts have been made to decipher the biological basis for leukemogenesis, the mechanism by which AML cells become resistant to chemotherapy is largely unknown. The identification of the signaling pathways involved in resistance may lead to new combinatory therapies or new therapeutic approaches suitable for this subset of patients. Several mechanisms of chemoresistance have been identified, including drug transporters, key secondary messengers, and metabolic regulators. However, no therapeutic approach targeting chemoresistance has succeeded in clinical trials, especially due to broad secondary effects in healthy cells. Recent research has highlighted the importance of lysosomes in this phenomenon. Lysosomes' key role in resistance to chemotherapy includes the potential to sequester drugs, central metabolic signaling role, and gene expression regulation. These results provide further evidence to support the development of new therapeutic approaches that target lysosomes in AML.

Annexins A1 and A2 are recruited to larger lysosomal injuries independently of ESCRTs to promote repair

Damaged lysosomes can be repaired by calcium release-dependent recruitment of the ESCRT machinery. However, the involvement of annexins, another group of calcium-responding membrane repair proteins, has not been fully addressed. Here, we show that although all ubiquitously expressed annexins (ANXA1, A2, A4, A5, A6, A7, and A11) localize to damaged lysosomes, only ANXA1 and ANXA2 are important for repair. Their recruitment is calcium-dependent, ESCRT-independent, and selective towards lysosomes with large injuries. Lysosomal leakage was more severe when ANXA1 or ANXA2 was depleted compared to that of ESCRT components. These findings suggest that ANXA1 and ANXA2 constitute an additional repair mechanism that serves to minimize leakage from damaged lysosomes.

Lysosomal ATP Transporter SLC17A9 Controls Cell Viability via Regulating Cathepsin D

SLC17A9 (solute carrier family 17 member 9) functions as an ATP transporter in lysosomes as well as other secretory vesicles. SLC17A9 inhibition or silence leads to cell death. However, the molecular mechanisms causing cell death are unclear. In this study, we report that cell death induced by SLC17A9 deficiency is rescued by the transcription factor EB (TFEB), a master gene for lysosomal protein expression, suggesting that SLC17A9 deficiency may be the main cause of lysosome dysfunction, subsequently leading to cell death. Interestingly, Cathepsin D, a lysosomal aspartic protease, is inhibited by SLC17A9 deficiency. Heterologous expression of Cathepsin D successfully rescues lysosomal dysfunction and cell death induced by SLC17A9 deficiency. On the other hand, the activity of Cathepsin B, a lysosomal cysteine protease, is not altered by SLC17A9 deficiency, and Cathepsin B overexpression does not rescue lysosomal dysfunction and cell death induced by SLC17A9 deficiency. Our data suggest that lysosomal ATP and SLC17A9 play critical roles in lysosomal function and cell viability by regulating Cathepsin D activity.

Lysosomal Changes in Mitosis

The recent discovery demonstrating that the leakage of cathepsin B from mitotic lysosomes assists mitotic chromosome segregation indicates that lysosomal membrane integrity can be spatiotemporally regulated. Unlike many other organelles, structural and functional alterations of lysosomes during mitosis remain, however, largely uncharted. Here, we demonstrate substantial differences in lysosomal proteome, lipidome, size, and pH between lysosomes that were isolated from human U2OS osteosarcoma cells either in mitosis or in interphase. The combination of pharmacological synchronization and mitotic shake-off yielded ~68% of cells in mitosis allowing us to investigate mitosis-specific lysosomal changes by comparing cell populations that were highly enriched in mitotic cells to those mainly in the G1 or G2 phases of the cell cycle. Mitotic cells had significantly reduced levels of lysosomal-associated membrane protein (LAMP) 1 and the active forms of lysosomal cathepsin B protease. Similar trends were observed in levels of acid sphingomyelinase and most other lysosomal proteins that were studied. The altered protein content was accompanied by increases in the size and pH of LAMP2-positive vesicles. Moreover, mass spectrometry-based shotgun lipidomics of purified lysosomes revealed elevated levels of sphingolipids, especially sphingomyelin and hexocylceramide, and lysoglyserophospholipids in mitotic lysosomes. Interestingly, LAMPs and acid sphingomyelinase have been reported to stabilize lysosomal membranes, whereas sphingomyelin and lysoglyserophospholipids have an opposite effect. Thus, the observed lysosomal changes during the cell cycle may partially explain the reduced lysosomal membrane integrity in mitotic cells.

Insights Into Ferroptosis, a Novel Target for the Therapy of Cancer

Ferroptosis is a new form of programmed cell death (PCD) characterized by an excess iron accumulation and subsequent unbalanced redox states. Ferroptosis is different from the already reported PCD and has unique morphological features and biochemical processes. Ferroptosis was first elaborated by Brent R. Stockwell’s lab in 2012, in which small molecules erastin and RSL-3 induce PCD in Ras mutant cell lines. Ferroptosis involves various physiological processes and occurrence of disease and especially shows strong potential in cancer treatment. Development of small molecule compounds based on Stockwell’s research was found to kill cancer cells, and some FDA-approved drugs were discovered to result in ferroptosis of cancer cells. Radiotherapy and checkpoint therapy have been widely used as a treatment for many types of cancer. Recently, some papers have reported that chemotherapy, radiotherapy, and checkpoint therapy induce ferroptosis of cancer cells, which provides new strategies for cancer treatment. Nevertheless, the limitless proliferation of tumor cells and the lack of cell death mechanisms are important reasons for drug resistance for tumor therapy. Therefore, we reviewed the molecular mechanism of ferroptosis and sensitivity to ferroptosis of different cancer cells and tumor treatment strategy.

Lysosomes: Multifunctional compartments ruled by a complex regulatory network

More than 50 years have passed since Nobel laureate Cristian de Duve described for the first time the presence of tiny subcellular compartments filled with hydrolytic enzymes: the lysosome. For a long time, lysosomes were deemed simple waste bags exerting a plethora of hydrolytic activities involved in the recycling of biopolymers, and lysosomal genes were considered to just be simple housekeeping genes, transcribed in a constitutive fashion. However, lysosomes are emerging as multifunctional signalling hubs involved in multiple aspects of cell biology, both under homeostatic and pathological conditions. Lysosomes are involved in the regulation of cell metabolism through the mTOR/TFEB axis. They are also key players in the regulation and onset of the immune response. Furthermore, it is becoming clear that lysosomal hydrolases can regulate several biological processes outside of the lysosome. They are also implicated in a complex communication network among subcellular compartments that involves intimate organelle‐to‐organelle contacts. Furthermore, lysosomal dysfunction is nowadays accepted as the causative event behind several human pathologies: low frequency inherited diseases, cancer, or neurodegenerative, metabolic, inflammatory, and autoimmune diseases. Recent advances in our knowledge of the complex biology of lysosomes have established them as promising therapeutic targets for the treatment of different pathologies. Although recent discoveries have started to highlight that lysosomes are controlled by a complex web of regulatory networks, which in some cases seem to be cell‐ and stimuli‐dependent, to harness the full potential of lysosomes as therapeutic targets, we need a deeper understanding of the little‐known signalling pathways regulating this subcellular compartment and its functions.

Low level lysosomal membrane permeabilization for limited release and sub-lethal functions of cathepsin proteases in the cytosol and nucleus

For a long time, lysosomes were purely seen as organelles in charge of garbage disposal within the cell. They destroy any cargo delivered into their lumen with a plethora of highly potent hydrolytic enzymes, including various proteases. In case of damage to their limiting membranes, the lysosomes release their soluble content with detrimental outcomes for the cell. In recent years however, this view of the lysosome changed towards acknowledging it as a platform for integration of manifold intra- and extracellular signals. Even impaired lysosomal membrane integrity is no longer considered to be a one-way street to cell death. Increasing evidence suggests that lysosomal enzymes, mainly cathepsin proteases, can be released in a spatially and temporarily restricted manner that is compatible with cellular survival. This way, cathepsins can act in the cytosol and the nucleus, where they affect important cellular processes such as cell division. Here, we review this evidence and discuss the routes and molecular mechanisms by which the cathepsins may reach their unusual destination.

The Complex Mechanisms by Which Neurons Die Following DNA Damage in Neurodegenerative Diseases

Human cells are exposed to numerous exogenous and endogenous insults every day. Unlike other molecules, DNA cannot be replaced by resynthesis, hence damage to DNA can have major consequences for the cell. The DNA damage response contains overlapping signalling networks that repair DNA and hence maintain genomic integrity, and aberrant DNA damage responses are increasingly described in neurodegenerative diseases. Furthermore, DNA repair declines during aging, which is the biggest risk factor for these conditions. If unrepaired, the accumulation of DNA damage results in death to eliminate cells with defective genomes. This is particularly important for postmitotic neurons because they have a limited capacity to proliferate, thus they must be maintained for life. Neuronal death is thus an important process in neurodegenerative disorders. In addition, the inability of neurons to divide renders them susceptible to senescence or re-entry to the cell cycle. The field of cell death has expanded significantly in recent years, and many new mechanisms have been described in various cell types, including neurons. Several of these mechanisms are linked to DNA damage. In this review, we provide an overview of the cell death pathways induced by DNA damage that are relevant to neurons and discuss the possible involvement of these mechanisms in neurodegenerative conditions.

The Cationic Amphiphilic Drug Hexamethylene Amiloride Eradicates Bulk Breast Cancer Cells and Therapy-Resistant Subpopulations with Similar Efficiencies

The resistance of cancer cell subpopulations, including cancer stem cell (CSC) populations, to apoptosis-inducing chemotherapeutic agents is a key barrier to improved outcomes for cancer patients. The cationic amphiphilic drug hexamethylene amiloride (HMA) has been previously demonstrated to efficiently kill bulk breast cancer cells independent of tumor subtype or species but acts poorly toward non-transformed cells derived from multiple tissues. Here, we demonstrate that HMA is similarly cytotoxic toward breast CSC-related subpopulations that are resistant to conventional chemotherapeutic agents, but poorly cytotoxic toward normal mammary stem cells. HMA inhibits the sphere-forming capacity of FACS-sorted human and mouse mammary CSC-related cells in vitro, specifically kills tumor but not normal mammary organoids ex vivo, and inhibits metastatic outgrowth in vivo, consistent with CSC suppression. Moreover, HMA inhibits viability and sphere formation by lung, colon, pancreatic, brain, liver, prostate, and bladder tumor cell lines, suggesting that its effects may be applicable to multiple malignancies. Our observations expose a key vulnerability intrinsic to cancer stem cells and point to novel strategies for the exploitation of cationic amphiphilic drugs in cancer treatment.

Cytotoxic mechanisms of doxorubicin at clinically relevant concentrations in breast cancer cells

Doxorubicin (DOX) is a chemotherapeutic agent frequently used for the treatment of a variety of tumor types, such as breast cancer. Despite the long history of DOX, the mechanistic details of its cytotoxic action remain controversial. Rather than one key mechanism of cytotoxic action, DOX is characterized by multiple mechanisms, such as (1) DNA intercalation and adduct formation, (2) topoisomerase II (TopII) poisoning, (3) the generation of free radicals and oxidative stress, and (4) membrane damage through altered sphingolipid metabolism. Many past reviews of DOX cytotoxicity are based on supraclinical concentrations, and several have addressed the concentration dependence of these mechanisms. In addition, most reviews lack a focus on the time dependence of these processes. We aim to update the concentration and time-dependent trends of DOX mechanisms at representative clinical concentrations. Furthermore, attention is placed on DOX behavior in breast cancer cells due to the frequent use of DOX to treat this disease. This review provides insight into the mechanistic pathway(s) of DOX at levels found within patients and establishes the magnitude of effect for each mechanism.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

Intracellular inflammatory signalling cascades in human monocytic cells on challenge with phytohemagglutinin and 2,4,6-trinitrophenol

Phytohemagglutinin (PHA) is a plant mitogen that can agglutinate human leukocytes and erythrocytes. PHA is mainly derived from red kidney beans and can act as an exogenous pyrogen. When entering into the blood circulation, exogenous pyrogens principally interact with monocytes and macrophages and induce the release of pro-inflammatory cytokines. Monocytes and macrophages are the cells that fight against foreign invaders and acts as a primary line of immune defence. Similar to PHA, the chemical 2,4,6-trinitrophenol (TNP) also acts as an exogenous pyrogen. The study focused on the in vitro interaction of PHA and TNP with the human monocyte/macrophage cell model THP-1. The exposure and associated change in cellular morphology, organelle function, mechanism of cell death, inflammatory signalling and expression of inflammation-related genes were analyzed in different time periods. It was observed that PHA and TNP induce dose and time-dependent toxicity to monocytes/macrophages where the mechanism of cell death was different for PHA and TNP. Both PHA and TNP can evoke immune signalling with increased expression of inflammatory genes and associated activation of intracellular signalling cascades.

Lysoptosis is an evolutionarily conserved cell death pathway moderated by intracellular serpins

Lysosomal membrane permeabilization (LMP) and cathepsin release typifies lysosome-dependent cell death (LDCD). However, LMP occurs in most regulated cell death programs suggesting LDCD is not an independent cell death pathway, but is conscripted to facilitate the final cellular demise by other cell death routines. Previously, we demonstrated that Caenorhabditis elegans (C. elegans) null for a cysteine protease inhibitor, srp-6, undergo a specific LDCD pathway characterized by LMP and cathepsin-dependent cytoplasmic proteolysis. We designated this cell death routine, lysoptosis, to distinguish it from other pathways employing LMP. In this study, mouse and human epithelial cells lacking srp-6 homologues, mSerpinb3a and SERPINB3, respectively, demonstrated a lysoptosis phenotype distinct from other cell death pathways. Like in C. elegans, this pathway depended on LMP and released cathepsins, predominantly cathepsin L. These studies suggested that lysoptosis is an evolutionarily-conserved eukaryotic LDCD that predominates in the absence of neutralizing endogenous inhibitors.

STAT3 Enhances Sensitivity of Glioblastoma to Drug-Induced Autophagy-Dependent Cell Death

Simple Summary

Glioblastoma is the most common primary brain cancer in adults. One reason for the development and malignancy of this tumor is the misregulation of certain cellular proteins. The oncoprotein STAT3 that is frequently overactive in glioblastoma cells is associated with more aggressive disease and decreased patient survival. Autophagy is a form of cellular self digestion that normally maintains cell integrity and provides nutrients and basic building blocks required for growth. While glioblastoma is known to be particularly resistant to conventional therapies, recent research has suggested that these tumors are more sensitive to excessive overactivation of autophagy, leading to autophagy-dependent tumor cell death. Here, we show a hitherto unknown role of STAT3 in sensitizing glioblastoma cells to excessive autophagy induced with the repurposed drug pimozide. These findings provide the basis for future research aimed at determining whether STAT3 can serve as a predictor for autophagy-proficient tumors and further support the notion of overactivating autophagy for cancer therapy.

Abstract

Glioblastoma (GBM) is a devastating disease and the most common primary brain malignancy of adults with a median survival barely exceeding one year. Recent findings suggest that the antipsychotic drug pimozide triggers an autophagy-dependent, lysosomal type of cell death in GBM cells with possible implications for GBM therapy. One oncoprotein that is often overactivated in these tumors and associated with a particularly dismal prognosis is Signal Transducer and Activator of Transcription 3 (STAT3). Here, we used isogenic human and murine GBM knockout cell lines, advanced fluorescence microscopy, transcriptomic analysis and FACS-based assessment of cell viability to show that STAT3 has an underappreciated, context-dependent role in drug-induced cell death. Specifically, we demonstrate that depletion of STAT3 significantly enhances cell survival after treatment with Pimozide, suggesting that STAT3 confers a particular vulnerability to GBM. Furthermore, we show that active STAT3 has no major influence on the early steps of the autophagy pathway, but exacerbates drug-induced lysosomal membrane permeabilization (LMP) and release of cathepsins into the cytosol. Collectively, our findings support the concept of exploiting the pro-death functions of autophagy and LMP for GBM therapy and to further determine whether STAT3 can be employed as a treatment predictor for highly apoptosis-resistant, but autophagy-proficient cancers.

Roles of N-Methyl-D-Aspartate Receptors (NMDARs) in Epilepsy

Epilepsy is one of the most common neurological disorders characterized by recurrent seizures. The mechanism of epilepsy remains unclear and previous studies suggest that N-methyl-D-aspartate receptors (NMDARs) play an important role in abnormal discharges, nerve conduction, neuron injury and inflammation, thereby they may participate in epileptogenesis. NMDARs belong to a family of ionotropic glutamate receptors that play essential roles in excitatory neurotransmission and synaptic plasticity in the mammalian CNS. Despite numerous studies focusing on the role of NMDAR in epilepsy, the relationship appeared to be elusive. In this article, we reviewed the regulation of NMDAR and possible mechanisms of NMDAR in epilepsy and in respect of onset, development, and treatment, trying to provide more evidence for future studies.

The V-ATPases in cancer and cell death

Transmembrane ATPases are membrane-bound enzyme complexes and ion transporters that can be divided into F-, V-, and A-ATPases according to their structure. The V-ATPases, also known as H⁺-ATPases, are large multi-subunit protein complexes composed of a peripheral domain (V1) responsible for the hydrolysis of ATP and a membrane-integrated domain (V0) that transports protons across plasma membrane or organelle membrane. V-ATPases play a fundamental role in maintaining pH homeostasis through lysosomal acidification and are involved in modulating various physiological and pathological processes, such as macropinocytosis, autophagy, cell invasion, and cell death (e.g., apoptosis, anoikis, alkaliptosis, ferroptosis, and lysosome-dependent cell death). In addition to participating in embryonic development, V-ATPase pathways, when dysfunctional, are implicated in human diseases, such as neurodegenerative diseases, osteopetrosis, distal renal tubular acidosis, and cancer. In this review, we summarize the structure and regulation of isoforms of V-ATPase subunits and discuss their context-dependent roles in cancer biology and cell death. Updated knowledge about V-ATPases may enable us to design new anticancer drugs or strategies.

Lysosome‑targeted drug combination induces multiple organelle dysfunctions and non‑canonical death in pancreatic cancer cells

Pancreatic cancer is one of the leading causes of cancer-related mortality and has the lowest 5-year survival rate. Therefore, novel strategies are urgently required to treat pancreatic cancer. Pancreatic ductal adenocarcinoma (PDAC) cells rely on enhanced lysosomal function for survival and proliferation to facilitate the degradation of contents accumulated via autophagy and macropinocytosis. Previously, we have reported that the combination of epidermal growth factor receptor/HER2 inhibitor lapatinib and sphingosine analog fingolimod (FTY720) confers a significant cytostatic effect in lung cancer cells. In the present study, the combined effects of these drugs on PDAC cell lines, BxPC-3, KP-4, PANC-1 and MIA PaCa-2, were examined. It was observed that FTY720 enhanced the lapatinib-induced cytotoxic effect and caused non-canonical and lysosome-dependent death in PDAC cells. Lapatinib and FTY720 induced lysosomal swelling and inhibited lysosomal acidification. Combination treatment with lapatinib and FTY720 increased lysosomal membrane permeability, induced mitochondrial depolarization, induced endoplasmic reticulum stress and disturbed intracellular calcium homeostasis. Additionally, the cytotoxic effect of lapatinib was enhanced by hydroxychloroquine or the CDK4/6 inhibitor abemaciclib, both of which induce lysosomal dysfunction. Collectively, these results indicated that the lysosome-targeted drug combination induces multiple organelle dysfunction and exerts a marked cytotoxic effect in PDAC cells.

From Apoptosis to Necroptosis: The Death Wishes to Cancer

DNA mutation is a common event in the human body, but in most situations, it is fixed right away by the DNA damage response program. In case the damage is too severe to repair, the programmed cell death system will be activated to get rid of the cell. However, if the damage affects some critical components of this system, the genetic scars are kept and multiply through mitosis, possibly leading to cancer someday. There are many forms of programmed cell death, but apoptosis and necroptosis represent the default and backup strategy, respectively, in the maintenance of optimal cell population as well as in cancer prevention. For the same reason, the ideal approach for cancer treatment is to induce apoptosis in the cancer cells because it proceeds 20 times faster than tumor cell proliferation and leaves no mess behind. Induction of necroptosis can be the second choice in case apoptosis becomes hard to achieve, however, necroptosis finishes the job at a cost-inflammation.

A Compendium of Information on the Lysosome

For a long time, lysosomes were considered as mere waste bags for cellular constituents. Thankfully, studies carried out in the past 15 years were brimming with elegant and crucial breakthroughs in lysosome research, uncovering their complex roles as nutrient sensors and characterizing them as crucial multifaceted signaling organelles. This review presents the scientific knowledge on lysosome physiology and functions, starting with their discovery and reviewing up to date ground-breaking discoveries highlighting their heterogeneous functions as well as pending questions that remain to be answered. We also review the roles of lysosomes in anti-cancer drug resistance and how they undergo a series of molecular and functional changes during malignant transformation which lead to tumor aggression, angiogenesis, and metastases. Finally, we discuss the strategy of targeting lysosomes in cancer which could lead to the development of new and effective targeted therapies.

The lysosome as an imperative regulator of autophagy and cell death

Lysosomes are single membrane-bound organelles containing acid hydrolases responsible for the degradation of cellular cargo and maintenance of cellular homeostasis. Lysosomes could originate from pre-existing endolysosomes or autolysosomes, acting as a critical juncture between autophagy and endocytosis. Stress that triggers lysosomal membrane permeabilization can be altered by ESCRT complexes; however, irreparable damage to the membrane results in the induction of a selective lysosomal degradation pathway, specifically lysophagy. Lysosomes play an indispensable role in different types of autophagy, including microautophagy, macroautophagy, and chaperone-mediated autophagy, and various cell death pathways such as lysosomal cell death, apoptotic cell death, and autophagic cell death. In this review, we discuss lysosomal reformation, maintenance, and degradation pathways following the involvement of the lysosome in autophagy and cell death, which are related to several pathophysiological conditions observed in humans.

Keeping the host alive - lessons from obligate intracellular bacterial pathogens

Mammals have evolved sophisticated host cell death signaling pathways as an important immune mechanism to recognize and eliminate cell intruders before they establish their replicative niche. However, intracellular bacterial pathogens that have co-evolved with their host have developed a multitude of tactics to counteract this defense strategy to facilitate their survival and replication. This requires manipulation of pro-death and pro-survival host signaling pathways during infection. Obligate intracellular bacterial pathogens are organisms that absolutely require an eukaryotic host to survive and replicate, and therefore they have developed virulence factors to prevent diverse forms of host cell death and conserve their replicative niche. This review encapsulates our current understanding of these host-pathogen interactions by exploring the most relevant findings of Anaplasma spp., Chlamydia spp., Rickettsia spp. and Coxiella burnetii modulating host cell death pathways. A detailed comprehension of the molecular mechanisms through which these obligate intracellular pathogens manipulate regulated host cell death will not only increase the current understanding of these difficult-to-study pathogens but also provide insights into new tools to study regulated cell death and the development of new therapeutic approaches to control infection.

GNS561, a clinical-stage PPT1 inhibitor, is efficient against hepatocellular carcinoma via modulation of lysosomal functions

Hepatocellular carcinoma is the most frequent primary liver cancer. Macroautophagy/autophagy inhibitors have been extensively studied in cancer but, to date, none has reached efficacy in clinical trials. In this study, we demonstrated that GNS561, a new autophagy inhibitor, whose anticancer activity was previously linked to lysosomal cell death, displayed high liver tropism and potent antitumor activity against a panel of human cancer cell lines and in two hepatocellular carcinoma in vivo models. We showed that due to its lysosomotropic properties, GNS561 could reach and specifically inhibited its enzyme target, PPT1 (palmitoyl-protein thioesterase 1), resulting in lysosomal unbound Zn²⁺ accumulation, impairment of cathepsin activity, blockage of autophagic flux, altered location of MTOR (mechanistic target of rapamycin kinase), lysosomal membrane permeabilization, caspase activation and cell death. Accordingly, GNS561, for which a global phase 1b clinical trial in liver cancers was just successfully achieved, represents a promising new drug candidate and a hopeful therapeutic strategy in cancer treatment.

Abbreviations: ANXA5:annexin A5; ATCC: American type culture collection; BafA1: bafilomycin A₁; BSA: bovine serum albumin; CASP3: caspase 3; CASP7: caspase 7; CASP8: caspase 8; CCND1: cyclin D1; CTSB: cathepsin B; CTSD: cathepsin D; CTSL: cathepsin L; CQ: chloroquine; iCCA: intrahepatic cholangiocarcinoma; DEN: diethylnitrosamine; DMEM: Dulbelcco’s modified Eagle medium; FBS: fetal bovine serum; FITC: fluorescein isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HCC: hepatocellular carcinoma; HCQ: hydroxychloroquine; HDSF: hexadecylsulfonylfluoride; IC₅₀: mean half-maximal inhibitory concentration; LAMP: lysosomal associated membrane protein; LC3-II: phosphatidylethanolamine-conjugated form of MAP1LC3; LMP: lysosomal membrane permeabilization; MALDI: matrix assisted laser desorption ionization; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MKI67: marker of proliferation Ki-67; MTOR: mechanistic target of rapamycin kinase; MRI: magnetic resonance imaging; NH₄Cl: ammonium chloride; NtBuHA: N-tert-butylhydroxylamine; PARP: poly(ADP-ribose) polymerase; PBS: phosphate-buffered saline; PPT1: palmitoyl-protein thioesterase 1; SD: standard deviation; SEM: standard error mean; vs, versus; Zn²⁺: zinc ion; Z-Phe: Z-Phe-Tyt(tBu)-diazomethylketone; Z-VAD-FMK: carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]- fluoromethylketone.

Conserved and Diversified Mechanism of Autophagy between Plants and Animals upon Various Stresses

Autophagy is a highly conserved degradation mechanism in eukaryotes, executing the breakdown of unwanted cell components and subsequent recycling of cellular material for stress relief through vacuole-dependence in plants and yeast while it is lysosome-dependent in animal manner. Upon stress, different types of autophagy are stimulated to operate certain biological processes by employing specific selective autophagy receptors (SARs), which hijack the cargo proteins or organelles to the autophagy machinery for subsequent destruction in the vacuole/lysosome. Despite recent advances in autophagy, the conserved and diversified mechanism of autophagy in response to various stresses between plants and animals still remain a mystery. In this review, we intend to summarize and discuss the characterization of the SARs and their corresponding processes, expectantly advancing the scope and perspective of the evolutionary fate of autophagy between plants and animals.

The molecular mosaic of regulated cell death in the cardiovascular system

Cell death is now understood to be a highly regulated process that contributes to normal development and tissue homeostasis, alongside its role in the etiology of various pathological conditions. Through detailed molecular analysis, we have come to know that all cells do not always die in the same way, and that there are at least 7 processes involved, including: apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, and autophagy-mediated cell death. These processes act as pieces in the mosaic of cardiomyocyte cell death, which come together depending on context and stimulus. This review details each individual process, as well as highlights how they come together to produce various cardiac pathologies. By knowing how the pieces go together we can aim towards the development of efficacious therapeutics, which will enable us to prevent cardiomyocyte loss in the face of stress, both reducing mortality and improving quality of life.

3-Acetyldeoxynivalenol induces cell death through endoplasmic reticulum stress in mouse liver

Ingestion of food or cereal products contaminated by deoxynivalenol (DON) and related derivatives poses a threat to the health of humans and animals. However, the toxicity and underlying mechanisms of 3-acetyldeoxynivalenol (3-Ac-DON), an acetylated form of deoxynivalenol, have not been fully elucidated. In the present study, we showed that 3-Ac-DON caused significant oxidative damage, as shown by elevated aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactic dehydrogenase (LDH) in serum, increased lipid peroxidation products, such as hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), decreased activities of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). In addition, 3-Ac-DON exposure led to elevated infiltrations of immune cell, increased apoptosis and autophagy in the liver. Interestingly, 3-Ac-DON-resulted apoptosis and liver injury were partially reduced by autophagy inhibitors. Further study showed that 3-Ac-DON-treated mice had altered ultrastructural changes of endoplasmic reticulum (ER), as well as enhanced protein levels of p-IRE1α, p-PERK, and downstream targets, indicating activation of unfolded protein response (UPR) in the liver. Importantly, 3-Ac-DON induced ER stress, oxidative damage, cell death, infiltration of immune cells, and increased mRNA levels of inflammatory cytokines were significantly abolished by 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, indicating a critical role of UPR signaling for the cellular damage of the liver in response to 3-Ac-DON exposure. In conclusion, using mice as an animal model, we showed that 3-Ac-DON exposure impaired the function of liver, as shown by oxidative damage, cell death, and infiltration of immune cell, in which ER stress played an important role. Restoration of the ER function might be a preventive strategy to reduce the deleterious effect of 3-Ac-DON on the liver of animals.

STING Signaling and Sterile Inflammation

Innate immunity is regulated by a broad set of evolutionary conserved receptors to finely probe the local environment and maintain host integrity. Besides pathogen recognition through conserved motifs, several of these receptors also sense aberrant or misplaced self-molecules as a sign of perturbed homeostasis. Among them, self-nucleic acid sensing by the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway alerts on the presence of both exogenous and endogenous DNA in the cytoplasm. We review recent literature demonstrating that self-nucleic acid detection through the STING pathway is central to numerous processes, from cell physiology to sterile injury, auto-immunity and cancer. We address the role of STING in autoimmune diseases linked to dysfunctional DNAse or related to mutations in DNA sensing pathways. We expose the role of the cGAS/STING pathway in inflammatory diseases, neurodegenerative conditions and cancer. Connections between STING in various cell processes including autophagy and cell death are developed. Finally, we review proposed mechanisms to explain the sources of cytoplasmic DNA.

Bone morphogenetic protein receptor 2 inhibition destabilizes microtubules promoting the activation of lysosomes and cell death of lung cancer cells

Background

Recent studies have shown that bone morphogenetic protein receptor 2 (BMPR2) regulates cell survival signaling events in cancer cells independent of the BMP type 1 receptor (BMPR1) or the Smad-1/5 transcription factor. Mutations in BMPR2 trafficking proteins leads to overactive BMP signaling, which leads to neurological diseases caused by BMPR2 stabilization of the microtubules. It is not known whether BMPR2 regulates the microtubules in cancer cells and what effect this has on cell survival. It is also not known whether alterations in BMPR2 trafficking effects activity and response to BMPR2 inhibitors.

Methods

We utilized BMPR2 siRNA and the BMP receptor inhibitors JL5 and Ym155, which decrease BMPR2 signaling and cause its mislocalization to the cytoplasm. Using the JL5 resistant MDA-MD-468 cell line and sensitive lung cancer cell lines, we examined the effects of BMPR2 inhibition on BMPR2 mislocalization to the cytoplasm, microtubule destabilization, lysosome activation and cell survival.

Results

We show that the inhibition of BMPR2 destabilizes the microtubules. Destabilization of the microtubules leads to the activation of the lysosomes. Activated lysosomes further decreases BMPR2 signaling by causing it to mislocalizated to the cytoplasm and/or lysosome for degradation. Inhibition of the lysosomes with chloroquine attenuates BMPR2 trafficking to the lysosome and cell death induced by BMPR2 inhibitors. Furthermore, in MDA-MD-468 cells that are resistant to JL5 induced cell death, BMPR2 was predominately located in the cytoplasm. BMPR2 failed to localize to the cytoplasm and/or lysosome following treatment with JL5 and did not destabilize the microtubules or activate the lysosomes.

Conclusions

These studies reveal that the inhibition of BMPR2 destabilizes the microtubules promoting cell death of cancer cells that involves the activation of the lysosomes. Resistance to small molecules targeting BMPR2 may occur if the BMPR2 is localized predominantly to the cytoplasm and/or fails to localize to the lysosome for degradation.

Gene expression profile analysis of gallic acid-induced cell death process

Gallic acid is a natural phenolic compound that displays anti-cancer properties in clinically relevant cell culture and rodent models. To date, the molecular mechanism governing the gallic acid-induced cancer cell death process is largely unclear, thus hindering development of novel therapeutics. Therefore, we performed time-course RNA-sequencing to reveal the gene expression profiles at the early (2nd hour), middle (4th and 6th hour), and late (9th hour) stages of the gallic acid-induced cell death process in HeLa cells. By Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, we found significant changes in transcription of the genes in different types of cell death pathways. This involved the ferroptotic cell death pathway at the early stage, apoptotic pathway at the middle stage, and necroptotic pathway at the late stage. Metabolic pathways were identified at all the stages, indicating that this is an active cell death process. Interestingly, the initiation and execution of gallic acid-induced cell death were mediated by multiple biological processes, including iron and amino acid metabolism, and the biosynthesis of glutathione, as targeting on these pathways suppressed cell death. In summary, our work provides a dataset with differentially expressed genes across different stages of cell death process during the gallic acid induction, which is important for further study on the control of this cell death mechanism.

Titanium Dioxide Induces Apoptosis under UVA Irradiation via the Generation of Lysosomal Membrane Permeabilization-Dependent Reactive Oxygen Species in HaCat Cells

Titanium dioxide nanoparticles (TiO₂ NPs) have wide commercial applications, owing to their small size; however, the biosafety of TiO₂ NPs should be evaluated further. In this study, we aimed to investigate the cytotoxicity of TiO₂ NPs in the presence and absence of ultraviolet A (UVA) irradiation in human keratinocyte HaCaT cells. TiO₂ NPs did not significantly affect cell viability in the absence of UVA irradiation. Nonetheless, UVA-irradiated TiO₂ NPs induced caspase-dependent apoptosis of HaCaT cells. Exposure of HaCaT cells to TiO₂ NPs and UVA resulted in reactive oxygen species (ROS) generation and lysosomal membrane permeabilization (LMP); both effects were not observed in the absence of UVA irradiation. An analysis of the relationship between LMP and ROS, using CA-074 as a cathepsin inhibitor or NAC as an antioxidant, showed that LMP stimulates ROS generation under these conditions. These results imply that LMP-dependent oxidative stress plays a critical role in the UVA phototoxicity of TiO₂ NPs in HaCaT cells.

Anticancer Mechanisms of Salinomycin in Breast Cancer and Its Clinical Applications

Breast cancer (BC) is the most frequent cancer among women worldwide and is the leading cause of cancer-related deaths in women. Cancer cells with stem cell-like features and tumor-initiating potential contribute to drug resistance, tumor recurrence, and metastasis. To achieve better clinical outcomes, it is crucial to eradicate both bulk BC cells and breast cancer stem cells (BCSCs). Salinomycin, a monocarboxylic polyether antibiotic isolated from Streptomyces albus, can precisely kill cancer stem cells (CSCs), particularly BCSCs, by various mechanisms, including apoptosis, autophagy, and necrosis. There is increasing evidence that salinomycin can inhibit cell proliferation, invasion, and migration in BC and reverse the immune-inhibitory microenvironment to prevent tumor growth and metastasis. Therefore, salinomycin is a promising therapeutic drug for BC. In this review, we summarize established mechanisms by which salinomycin protects against BC and discuss its future clinical applications.

Genomic signatures supporting the symbiosis and formation of chitinous tube in the deep-sea tubeworm Paraescarpia echinospica

Vestimentiferan tubeworms are iconic animals that present as large habitat-forming chitinized tube bushes in deep-sea chemosynthetic ecosystems. They are gutless and depend entirely on their endosymbiotic sulfide-oxidizing chemoautotrophic bacteria for nutrition. Information on the genomes of several siboglinid endosymbionts has improved our understanding of their nutritional supplies. However, the interactions between tubeworms and their endosymbionts remain largely unclear due to a paucity of host genomes. Here, we report the chromosome-level genome of the vestimentiferan tubeworm Paraescarpia echinospica. We found that the genome has been remodeled to facilitate symbiosis through the expansion of gene families related to substrate transfer and innate immunity, suppression of apoptosis, regulation of lysosomal digestion, and protection against oxidative stress. Furthermore, the genome encodes a programmed cell death pathway that potentially controls the endosymbiont population. Our integrated genomic, transcriptomic, and proteomic analyses uncovered matrix proteins required for the formation of the chitinous tube and revealed gene family expansion and co-option as evolutionary mechanisms driving the acquisition of this unique supporting structure for deep-sea tubeworms. Overall, our study provides novel insights into the host’s support system that has enabled tubeworms to establish symbiosis, thrive in deep-sea hot vents and cold seeps, and produce the unique chitinous tubes in the deep sea.

Accumulation of saposin in dystrophic neurites is linked to impaired lysosomal functions in Alzheimer's disease brains

Neuritic plaques in Alzheimer's disease (AD) brains refer to β-amyloid (Aβ) plaques surrounded by dystrophic neurites (DNs), activated microglia and reactive astrocytes. Most recently, we showed that DNs form sequentially in three layers during plaque growth. Although lysosomal proteins such as LAMP1 are found in DNs, it is not clear how many and how early lysosomal proteins are involved in forming neuritic plaques. To answer this unmet question, we examined APP knock-in (APPNL-G-F), 5xFAD and APP/PS1ΔE9 mouse brains and found that the lysosomal activator proteins saposins (SAPs) and LAMP1 were accumulated to surround Aβ plaques at the earliest stage, namely the 1st layer of DNs. Noticeably, lysosomal hydrolases were not detectable in these early DNs, suggesting that DNs at this early stage likely enrich dysfunctional lysosomes. In old AD mouse brains and in the later stage of human AD brains, SAP-C+-DNs and LAMP1+-DNs were gradually reduced in concomitant with the growth of amyloid plaques. Remarkably, the observed LAMP1 immunoreactivity near plaques in aged AD mouse and human brains were actually associated with disease-associated microglia rather than neuronal sources, likely reflecting more severely impaired lysosomal functions in neurons. Western blot analyses showed increased levels of SAP-C in AD mouse brains, and Aβ oligomers induced elevated levels of SAP-C in cellular assays. The elevated protein levels of SAP-C in AD mouse brains during plaque growth potentially contributed lysosomal membrane leakage and loss of hydrolases. Together, our study indicates that lysosomal functions are impaired by being entrapped in DNs early during plaque growth, and this may viciously facilitate growth of amyloid plaques.

Anti-carcinogenic Effect of Cathepsin K Inhibitor, Odanacatib with a Low Dose of Cisplatin Against Human Breast Carcinoma MCF-7 and MDA-MB231 Cells

Background:

A cross-linking agent commonly used for cancer chemotherapy is a platinum compound such as cisplatin. However, with the acquisition of cellular drug resistance and adverse side effects, the potency of cisplatin is, therefore, often tempered. To overcome these issues, the present study has established the use of cathepsin k (CTSK) inhibitor as a potent chemosensitizer.

Methods:

The cytotoxic effect of cisplatin and odanacatib (ODN) on two different breast cancer patient- derived cell lines, MDA-MB-231 and MCF-7, was assessed by MTT-based colorimetric assay. The drug interaction coefficient CDI was used to evaluate the synergistically inhibitory impact of the drug combination and immunoblot was used to examine the expression of certain proteins responsible for cell survival and the mechanism of apoptosis.

Results:

In this study, we found that IC50 of ODN in combination with cisplatin (half of IC25) induced a synergistic cytotoxic effect in different breast cancer cells. Diminished expression of Bcl-2 and increased expression of Bax aroused the cytochrome release, that triggered caspase-9 and -3 activation in the combinatorial group. ODN with a lower dose of cisplatin significantly inhibited the protein expression of novel chemoresistant factors such as STAT3, NFκB and IL-6.

Conclusion:

This study highlights the potential effects of the combination of ODN with a reduced dose of cisplatin on improving the growth inhibition and apoptosis-inducing effect on breast cancer cells via combined inhibition of NF-κB-induced IL-6 and STAT3 activation. The study result suggests that the further development of this novel inhibitor in combination with a low dose of standard cisplatin-based chemotherapy may contribute to an alternative treatment option for certain cancers.

Autophagy Modulators in Cancer Therapy

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