A noncanonical function of EIF4E limits ALDH1B1 activity and increases susceptibility to ferroptosis

Isoliquiritigenin alleviates myocardial ischemia-reperfusion injury by regulating the Nrf2/HO-1/SLC7a11/GPX4 axis in mice

Ischemia-reperfusion (I/R) injury, a multifaceted pathological process, occurs when the prolongation of reperfusion duration triggers ferroptosis-mediated myocardial damage. Isoliquiritigenin (ISL), a single flavonoid from licorice, exhibits a wide range of pharmacological impacts, but its function in ferroptosis caused by myocardial I/R injury remains unclear. This study delved into the protective effect of ISL on myocardial I/R injury-induced ferroptosis and its mechanism. Neonatal mouse cardiomyocytes (NMCM) underwent hypoxia/reoxygenation (H/R) to simulate the pathological process of myocardial I/R. ISL significantly attenuated H/R-triggered production of reactive oxygen species in NMCM, reduced the expression of malondialdehyde and the activity of lactate dehydrogenase, enhanced superoxide dismutase and catalase activity, and increased the expression of nuclear factor E2-related factor 2 (Nrf2) and its downstream heme oxygenase 1 (HO-1), thereby mitigating oxidative stress damage. CCK8 experiment revealed that the ferroptosis inhibitor Ferrostatin-1 significantly improved myocardial cell viability after 24 h of reoxygenation, and ISL treatment showed a similar effect. ISL reduced intracellular free iron accumulation, up-regulated glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 (SLC7A11) expression, and inhibited lipid peroxidation accumulation, thereby alleviating ferroptosis. The Nrf2-specific inhibitor ML385 counteracted ISL's defensive role against H/R-triggered oxidative stress damage and ferroptosis. In vivo experiments further confirmed that by regulating the translocation of Nrf2 into the nucleus, ISL treatment increased the levels of HO-1, GPX4, and SLC7A11, inhibited the expression of ACSL4, Drp1 to exert the antioxidant role, alleviated mitochondrial damage, and ferroptosis, ultimately reducing myocardial infarction area and injury induced by I/R. ML385 nearly abolished ISL's protective impact on the I/R model by inhibiting Nrf2 function. In summary, ISL is capable of mitigating oxidative stress, mitochondrial damage, and cardiomyocyte ferroptosis caused by I/R, thereby reducing myocardial injury. A key mechanism includes triggering the Nrf2/HO-1/SLC7A11/GPX4 pathway to prevent oxidative stress damage and cardiomyocyte ferroptosis caused by I/R.

Protein modification and degradation in ferroptosis

Ferroptosis is a form of iron-related oxidative cell death governed by an integrated redox system, encompassing pro-oxidative proteins and antioxidative proteins. These proteins undergo precise control through diverse post-translational modifications, including ubiquitination, phosphorylation, acetylation, O-GlcNAcylation, SUMOylation, methylation, N-myristoylation, palmitoylation, and oxidative modification. These modifications play pivotal roles in regulating protein stability, activity, localization, and interactions, ultimately influencing both the buildup of iron and lipid peroxidation. In mammalian cells, regulators of ferroptosis typically undergo degradation via two principal pathways: the ubiquitin-proteasome system, which handles the majority of protein degradation, and autophagy, primarily targeting long-lived or aggregated proteins. This comprehensive review aims to summarize recent advances in the post-translational modification and degradation of proteins linked to ferroptosis. It also discusses strategies for modulating ferroptosis through protein modification and degradation systems, providing new insights into potential therapeutic applications for both cancer and non-neoplastic diseases.

Ciprofloxacin is a novel anti-ferroptotic antibiotic

Cancer patients undergoing chemotherapy are susceptible to various bacterial infections, necessitating prompt and precise antimicrobial treatment with antibiotics. Ciprofloxacin is a clinically utilized broad-spectrum antimicrobial agent known for its robust antiseptic activity. While ferroptosis, an oxidative form of cell death, has garnered attention as a promising avenue in cancer therapy, the potential impact of ciprofloxacin on the anticancer effects of ferroptosis remains unclear. This study seeks to investigate the potential influence of antibiotics on ferroptosis in human pancreatic ductal adenocarcinoma (PDAC) cells. Here, we report a previously unrecognized role of ciprofloxacin in inhibiting ferroptosis in human PDAC cells. Mechanistically, ciprofloxacin suppresses erastin-induced endoplasmic reticulum (ER) stress through the activating transcription factor 6 (ATF6) and ER to nucleus signaling 1 (ERN1) pathway. Excessive ER stress activation can trigger glutathione peroxidase 4 (GPX4) degradation through autophagic mechanisms. In contrast, ciprofloxacin enhances the protein stability of GPX4, a crucial regulator that suppresses ferroptosis by inhibiting lipid peroxidation. Thus, our study demonstrates the anti-ferroptotic role of ciprofloxacin, highlighting the importance of careful consideration when contemplating the combination of ciprofloxacin with specific ferroptosis inducers in PDAC patients.

A novel MYC-ZNF706-SLC7A11 regulatory circuit contributes to cancer progression and redox balance in human hepatocellular carcinoma

The oncogenic potential of chromosome 8q22 copy number gain in liver cancer remains to be depicted. Here, we report that ZNF706, encoded by a gene mapped to chromosome 8q22, is a C2H2-type zinc finger protein. However, the biological function and mechanism of ZNF706 have been poorly investigated. Clinically, ZNF706 expression was elevated in hepatocellular carcinoma (HCC), and high ZNF706 expression was associated with unfavorable survival in HCC patients. Functional experiments revealed that ZNF706 knockdown inhibited HCC progression both in vitro and in vivo. RNA sequencing (RNA-seq) and chromatin immunoprecipitation-based deep sequencing (ChIP-seq) revealed that mechanistically, ZNF706 is a crucial ferroptosis regulator and that SLC7A11 is a critical target of ZNF706. In addition, ZNF706 knockdown inhibited SLC7A11 expression, increased lipid peroxidation, and promoted ferroptosis. Further analysis revealed that ZNF706 is a novel direct target transcriptionally activated by MYC in HCC cells. Importantly, MYC depletion reduced SLC7A11-mediated redox homeostasis, and this effect was reversed by ZNF706 reexpression. Collectively, our data demonstrate that ZNF706 is a potential oncogene in liver cancer and functions as a ferroptosis regulator by modulating SLC7A11 expression, constituting a potential therapeutic target for HCC.

Ferroptosis: principles and significance in health and disease

Ferroptosis, an iron-dependent form of cell death characterized by uncontrolled lipid peroxidation, is governed by molecular networks involving diverse molecules and organelles. Since its recognition as a non-apoptotic cell death pathway in 2012, ferroptosis has emerged as a crucial mechanism in numerous physiological and pathological contexts, leading to significant therapeutic advancements across a wide range of diseases. This review summarizes the fundamental molecular mechanisms and regulatory pathways underlying ferroptosis, including both GPX4-dependent and -independent antioxidant mechanisms. Additionally, we examine the involvement of ferroptosis in various pathological conditions, including cancer, neurodegenerative diseases, sepsis, ischemia-reperfusion injury, autoimmune disorders, and metabolic disorders. Specifically, we explore the role of ferroptosis in response to chemotherapy, radiotherapy, immunotherapy, nanotherapy, and targeted therapy. Furthermore, we discuss pharmacological strategies for modulating ferroptosis and potential biomarkers for monitoring this process. Lastly, we elucidate the interplay between ferroptosis and other forms of regulated cell death. Such insights hold promise for advancing our understanding of ferroptosis in the context of human health and disease.

International consensus guidelines for the definition, detection, and interpretation of autophagy-dependent ferroptosis

Macroautophagy/autophagy is a complex degradation process with a dual role in cell death that is influenced by the cell types that are involved and the stressors they are exposed to. Ferroptosis is an iron-dependent oxidative form of cell death characterized by unrestricted lipid peroxidation in the context of heterogeneous and plastic mechanisms. Recent studies have shed light on the involvement of specific types of autophagy (e.g. ferritinophagy, lipophagy, and clockophagy) in initiating or executing ferroptotic cell death through the selective degradation of anti-injury proteins or organelles. Conversely, other forms of selective autophagy (e.g. reticulophagy and lysophagy) enhance the cellular defense against ferroptotic damage. Dysregulated autophagy-dependent ferroptosis has implications for a diverse range of pathological conditions. This review aims to present an updated definition of autophagy-dependent ferroptosis, discuss influential substrates and receptors, outline experimental methods, and propose guidelines for interpreting the results.Abbreviation: 3-MA:3-methyladenine; 4HNE: 4-hydroxynonenal; ACD: accidentalcell death; ADF: autophagy-dependentferroptosis; ARE: antioxidant response element; BH2:dihydrobiopterin; BH4: tetrahydrobiopterin; BMDMs: bonemarrow-derived macrophages; CMA: chaperone-mediated autophagy; CQ:chloroquine; DAMPs: danger/damage-associated molecular patterns; EMT,epithelial-mesenchymal transition; EPR: electronparamagnetic resonance; ER, endoplasmic reticulum; FRET: Försterresonance energy transfer; GFP: green fluorescent protein;GSH: glutathione;IF: immunofluorescence; IHC: immunohistochemistry; IOP, intraocularpressure; IRI: ischemia-reperfusion injury; LAA: linoleamide alkyne;MDA: malondialdehyde; PGSK: Phen Green™ SK;RCD: regulatedcell death; PUFAs: polyunsaturated fatty acids; RFP: red fluorescentprotein;ROS: reactive oxygen species; TBA: thiobarbituricacid; TBARS: thiobarbituric acid reactive substances; TEM:transmission electron microscopy.

Aldehyde dehydrogenase 1 family: A potential molecule target for diseases

Aldehyde dehydrogenase 1 (ALDH1), a crucial aldehyde metabolizing enzyme, has six family members. The ALDH1 family is expressed in various tissues, with a significant presence in the liver. It plays a momentous role in several pathophysiological processes, including aldehyde detoxification, oxidative stress, and lipid peroxidation. Acetaldehyde detoxification is the fundamental function of the ALDH1 family in participating in vital pathological mechanisms. The ALDH1 family can catalyze retinal to retinoic acid (RA) that is a hormone-signaling molecule and plays a vital role in the development and adult tissues. Furthermore, there is a need for further and broader research on the role of the ALDH1 family as a signaling molecule. The ALDH1 family is widely recognized as a cancer stem cell (CSC) marker and plays a significant role in the proliferation, invasion, metastasis, prognosis, and drug resistance of cancer. The ALDH1 family also participates in other human diseases, such as neurodegenerative diseases, osteoarthritis, diabetes, and atherosclerosis. It can inhibit disease progression by inhibiting/promoting the expression/activity of the ALDH1 family. In this review, we comprehensively analyze the tissue distribution, and functions of the ALDH1 family. Additionally, we review the involvement of the ALDH1 family in diseases, focusing on the underlying pathological mechanisms and briefly talk about the current status and development of ALDH1 family inhibitors. The ALDH1 family presents new possibilities for treating diseases, with both its upstream and downstream pathways serving as promising targets for therapeutic intervention. This offers fresh perspectives for drug development in the field of disease research.

Lipid-derived electrophiles inhibit the function of membrane channels during ferroptosis

The therapeutic targeting of ferroptosis requires full understanding of the molecular mechanism of this regulated cell death pathway. While lipid-derived electrophiles (LDEs), including 4-hydroxy-2-nonenal (4-HNE), are important biomarkers of ferroptosis, a functional role for these highly reactive species in ferroptotic cell death execution has not been established. Here, through mechanistic characterization of LDE-detoxification impairment, we demonstrate that LDEs mediate altered protein function during ferroptosis. Applying live cell fluorescence imaging, we first identified that export of glutathione-LDE-adducts through multidrug resistance-associated protein (MRP) channels is inhibited following exposure to a panel of ferroptosis inducers (FINs) with different modes of action (type I-IV FINs erastin, RSL3, FIN56, and FINO2). This channel inhibition was recreated by both initiation of lipid peroxidation and treatment with 4-HNE. Importantly, treatment with radical-trapping antioxidants prevented impaired LDE-adduct export when working with both FINs and lipid peroxidation initiators but not 4-HNE, pinpointing LDEs as the cause of this inhibited MRP activity observed during ferroptosis. Our findings, when combined with reports of widespread LDE alkylation of key proteins following ferroptosis induction, including MRP1, set a precedent for LDEs as critical mediators of ferroptotic cell damage. Lipid hydroperoxide breakdown to form truncated phospholipids and LDEs may fully explain membrane permeabilization and modified protein function downstream of lipid peroxidation, offering a unified explanation of the molecular cell death mechanism of ferroptosis.

Ferroptotic therapy in cancer: benefits, side effects, and risks

Ferroptosis is a type of regulated cell death characterized by iron accumulation and uncontrolled lipid peroxidation, leading to plasma membrane rupture and intracellular content release. Originally investigated as a targeted therapy for cancer cells carrying oncogenic RAS mutations, ferroptosis induction now exhibits potential to complement chemotherapy, immunotherapy, and radiotherapy in various cancer types. However, it can lead to side effects, including immune cell death, bone marrow impairment, liver and kidney damage, cachexia (severe weight loss and muscle wasting), and secondary tumorigenesis. In this review, we discuss the advantages and offer an overview of the diverse range of documented side effects. Furthermore, we examine the underlying mechanisms and explore potential strategies for side effect mitigation.

Adverse effects of ferroptotic therapy: mechanisms and management

Ferroptosis, a nonapoptotic form of cell death characterized by iron accumulation and uncontrolled lipid peroxidation, holds promise as a therapeutic approach in cancer treatment, alongside established modalities, such as chemotherapy, immunotherapy, and radiotherapy. However, recent research has raised concerns about its side effects, including damage to immune cells, hematopoietic stem cells, liver, and kidneys, the development of cachexia, and the risk of secondary tumor formation. In this review, we provide an overview of these emerging findings, with a specific emphasis on elucidating the underlying mechanisms, and underscore the critical significance of effectively managing side effects associated with targeted ferroptosis-based therapy.

ATF4 in cellular stress, ferroptosis, and cancer

Activating transcription factor 4 (ATF4), a member of the ATF/cAMP response element-binding (CREB) family, plays a critical role as a stress-induced transcription factor. It orchestrates cellular responses, particularly in the management of endoplasmic reticulum stress, amino acid deprivation, and oxidative challenges. ATF4's primary function lies in regulating gene expression to ensure cell survival during stressful conditions. However, when considering its involvement in ferroptosis, characterized by severe lipid peroxidation and pronounced endoplasmic reticulum stress, the ATF4 pathway can either inhibit or promote ferroptosis. This intricate relationship underscores the complexity of cellular responses to varying stress levels. Understanding the connections between ATF4, ferroptosis, and endoplasmic reticulum stress holds promise for innovative cancer therapies, especially in addressing apoptosis-resistant cells. In this review, we provide an overview of ATF4, including its structure, modifications, and functions, and delve into its dual role in both ferroptosis and cancer.

Polyamine-mediated ferroptosis amplification acts as a targetable vulnerability in cancer

Targeting ferroptosis, an iron-dependent form of regulated cell death triggered by the lethal overload of lipid peroxides, in cancer therapy is impeded by our limited understanding of the intersection of tumour's metabolic feature and ferroptosis vulnerability. In the present study, arginine is identified as a ferroptotic promoter using a metabolites library. This effect is mainly achieved through arginine's conversion to polyamines, which exerts their potent ferroptosis-promoting property in an H2O2-dependent manner. Notably, the expression of ornithine decarboxylase 1 (ODC1), the critical enzyme catalysing polyamine synthesis, is significantly activated by the ferroptosis signal--iron overload--through WNT/MYC signalling, as well as the subsequent elevated polyamine synthesis, thus forming a ferroptosis-iron overload-WNT/MYC-ODC1-polyamine-H2O2 positive feedback loop that amplifies ferroptosis. Meanwhile, we notice that ferroptotic cells release enhanced polyamine-containing extracellular vesicles into the microenvironment, thereby further sensitizing neighbouring cells to ferroptosis and accelerating the "spread" of ferroptosis in the tumour region. Besides, polyamine supplementation also sensitizes cancer cells or xenograft tumours to radiotherapy or chemotherapy through inducing ferroptosis. Considering that cancer cells are often characterized by elevated intracellular polyamine pools, our results indicate that polyamine metabolism exposes a targetable vulnerability to ferroptosis and represents an exciting opportunity for therapeutic strategies for cancer.

Gut Microbiome Mediates Ferroptosis Resistance for Colorectal Cancer Development

Colorectal cancer is a prevalent cancer type in the United States, affecting both genders and influenced by genetics and environmental factors. The role of the gut microbiome in colorectal cancer development and therapy response is a burgeoning field of study. A recent study uncovered that trans-3-indoleacrylic acid (IDA), a microbial metabolite from P. anaerobius, promotes colorectal cancer by inhibiting ferroptosis, a type of nonapoptotic cell death driven by unrestricted lipid peroxidation and subsequent membrane damage. IDA activates aryl hydrocarbon receptor (AHR), a nuclear transcription factor, leading to the expression of aldehyde dehydrogenase 1 family member A3 (ALDH1A3). ALDH1A3, known for aldehyde detoxification, also contributes to ferroptosis resistance by generating reduced nicotinamide adenine dinucleotide (NADH), critical for the synthesis of reduced coenzyme Q10 (COQH10), by apoptosis-inducing factor mitochondria-associated 2 (AIFM2, also known as FSP1). Knocking out AHR, AIFM2, or ALDH1A3 reverses the inhibitory effect of IDA on ferroptosis and IDA-mediated tumor growth. Significantly, P. anaerobius is enriched in patients with colorectal cancer, and supplementing IDA or P. anaerobius accelerates colorectal cancer progression in spontaneous or orthotopic mouse models. Taken together, these findings suggest that targeting P. anaerobius-mediated ferroptosis resistance emerges as a promising strategy to combat colorectal cancer development.

The lipid basis of cell death and autophagy

ABBREVIATIONS

ACSL: acyl-CoA synthetase long chain family; DISC: death-inducing signaling complex; DAMPs: danger/damage-associated molecular patterns; Dtgn: dispersed trans-Golgi network; FAR1: fatty acyl-CoA reductase 1; GPX4: glutathione peroxidase 4; LPCAT3: lysophosphatidylcholine acyltransferase 3; LPS: lipopolysaccharide; MUFAs: monounsaturated fatty acids; MOMP: mitochondrial outer membrane permeabilization; MLKL, mixed lineage kinase domain like pseudokinase; oxPAPC: oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine; OxPCs: oxidized phosphatidylcholines; PUFAs: polyunsaturated fatty acids; POR: cytochrome p450 oxidoreductase; PUFAs: polyunsaturated fatty acids; RCD: regulated cell death; RIPK1: receptor interacting serine/threonine kinase 1; SPHK1: sphingosine kinase 1; SOAT1: sterol O-acyltransferase 1; SCP2: sterol carrier protein 2; SFAs: saturated fatty acids; SLC47A1: solute carrier family 47 member 1; SCD: stearoyl-CoA desaturase; VLCFA: very long chain fatty acids.

A guideline on the molecular ecosystem regulating ferroptosis

Ferroptosis, an intricately regulated form of cell death characterized by uncontrolled lipid peroxidation, has garnered substantial interest since this term was first coined in 2012. Recent years have witnessed remarkable progress in elucidating the detailed molecular mechanisms that govern ferroptosis induction and defence, with particular emphasis on the roles of heterogeneity and plasticity. In this Review, we discuss the molecular ecosystem of ferroptosis, with implications that may inform and enable safe and effective therapeutic strategies across a broad spectrum of diseases.

Protein translation: biological processes and therapeutic strategies for human diseases

Protein translation is a tightly regulated cellular process that is essential for gene expression and protein synthesis. The deregulation of this process is increasingly recognized as a critical factor in the pathogenesis of various human diseases. In this review, we discuss how deregulated translation can lead to aberrant protein synthesis, altered cellular functions, and disease progression. We explore the key mechanisms contributing to the deregulation of protein translation, including functional alterations in translation factors, tRNA, mRNA, and ribosome function. Deregulated translation leads to abnormal protein expression, disrupted cellular signaling, and perturbed cellular functions- all of which contribute to disease pathogenesis. The development of ribosome profiling techniques along with mass spectrometry-based proteomics, mRNA sequencing and single-cell approaches have opened new avenues for detecting diseases related to translation errors. Importantly, we highlight recent advances in therapies targeting translation-related disorders and their potential applications in neurodegenerative diseases, cancer, infectious diseases, and cardiovascular diseases. Moreover, the growing interest lies in targeted therapies aimed at restoring precise control over translation in diseased cells is discussed. In conclusion, this comprehensive review underscores the critical role of protein translation in disease and its potential as a therapeutic target. Advancements in understanding the molecular mechanisms of protein translation deregulation, coupled with the development of targeted therapies, offer promising avenues for improving disease outcomes in various human diseases. Additionally, it will unlock doors to the possibility of precision medicine by offering personalized therapies and a deeper understanding of the molecular underpinnings of diseases in the future.

Ferroptosis: A Frontier in Osteoporosis

Reduced bone mass and degeneration of the microarchitecture of bone tissue are the hallmarks of osteoporosis, a bone metabolic disease that increases skeletal fragility and fracture susceptibility. Osteoporosis is primarily caused by unbalanced bone remodeling, in which bone synthesis is outpaced by bone resorption caused by osteoclasts. Along with the bone-building vitamins calcium and vitamin D, typical medications for treating osteoporosis include bisphosphonates and calcitonin. The present therapies effectively stop osteoclast activation that is too high, however they come with varying degrees of negative effects. Numerous factors can contribute to osteoporosis, which is characterized by a loss of bone mass and density due to the deterioration of the bone's microstructure, which makes the bone more fragile. As a result, it is a systemic bone condition that makes patients more likely to fracture. Interest in the function of ferroptosis in the pathophysiology of osteoporosis is developing. In this review, we go through the shape of the cell, the fundamental mechanisms of ferroptosis, the relationship between osteoclasts and osteoblasts, the association between ferroptosis and diabetic osteoporosis, steroid-induced osteoporosis, and the relationship between ferroptosis and postmenopausal osteoporosis. The functions of ferroptosis and osteoporosis in cellular function, signaling cascades, pharmacological inhibition, and gene silencing have been better understood thanks to recent advances in biomedical research.

Design, synthesis, and biological evaluation of 2-amino-6-methyl-phenol derivatives targeting lipid peroxidation with potent anti-ferroptotic activities

The suppression of ferroptosis is emerging as a promising therapeutic strategy for effectively treating a wide range of diseases, including neurodegenerative disorders, organ ischemia-reperfusion injury, and inflammatory conditions. However, the clinical utility of ferroptosis inhibitors is significantly impeded by the limited availability of rational drug designs. In our previous study, we successfully unraveled the efficacy of ferrostatin-1 (Fer-1) attributed to the synergistic effect of its ortho-diamine (-NH) moiety. In this study, we present the discovery of the ortho-hydroxyl-amino moiety as a novel scaffold for ferroptosis inhibitors, employing quantum chemistry as well as in vitro and in vivo assays. 2-amino-6-methylphenol derivatives demonstrated remarkable inhibition of RSL3-induced ferroptosis, exhibiting EC50 values ranging from 25 nM to 207 nM. These compounds do not appear to modulate iron homeostasis or lipid reactive oxygen species (ROS) generation pathways. Nevertheless, they effectively prevent the accumulation of lipid peroxides in living cells. Furthermore, compound 13 exhibits good in vivo activities as it effectively protect mice from kidney ischemia-reperfusion injury. In summary, compound 13 has been identified as a potent ferroptosis inhibitor, warranting further investigation as a promising lead compound.

The aldehyde dehydrogenase ALDH1B1 exerts antiviral effects through the aggregation of the adaptor MAVS

Type I interferons (IFNs) are produced by almost all cell types and play a vital role in host defense against viral infection. Infection with an RNA virus activates receptors such as RIG-I, resulting in the recruitment of the adaptor protein MAVS to the RIG-I-like receptor (RLR) signalosome and the formation of prion-like functional aggregates of MAVS, which leads to IFN-β production. Here, we identified the aldehyde dehydrogenase 1B1 (ALDH1B1) as a previously uncharacterized IFN-stimulated gene (ISG) product with critical roles in the antiviral response. Knockout of ALDH1B1 increased, whereas overexpression of ALDH1B1 restricted, the replication of RNA viruses, such as vesicular stomatitis virus (VSV), Zika virus (ZIKV), dengue virus (DENV), and influenza A virus (IAV). We found that ALDH1B1 localized to mitochondria, where it interacted with the transmembrane domain of MAVS to promote MAVS aggregation. ALDH1B1 was recruited to MAVS aggregates. In addition, ALDH1B1 also enhanced the interaction between activated RIG-I and MAVS, thus increasing IFN-β production and the antiviral response. Furthermore, Aldh1b1-/- mice developed more severe symptoms than did wild-type mice upon IAV infection. Together, these data identify an aldehyde dehydrogenase in mitochondria that functionally regulates MAVS-mediated signaling and the antiviral response.

Ferroptosis in immunostimulation and immunosuppression

Ferroptosis is a form of iron-dependent regulated cell death characterized by the accumulation of toxic lipid peroxides, particularly in the plasma membrane, leading to lytic cell death. While it plays a crucial role in maintaining the overall health and proper functioning of multicellular organisms, it can also contribute to tissue damage and pathological conditions. Although ferroptotic damage is generally recognized as an immunostimulatory process associated with the release of damage-associated molecular patterns (DAMPs), the occurrence of ferroptosis in immune cells or the release of immunosuppressive molecules can result in immune tolerance. Consequently, there is ongoing exploration of targeting the upstream signals or the machinery of ferroptosis to therapeutically enhance or inhibit the immune response. In addition to introducing the core molecular mechanisms of ferroptosis, we will focus on the immune characteristics of ferroptosis in pathological conditions, particularly in the context of infection, sterile inflammation, and tumor immunity.

TXNDC12 inhibits lipid peroxidation and ferroptosis

Ferroptosis is a type of regulated cell death characterized by lipid peroxidation and subsequent damage to the plasma membrane. Here, we report a ferroptosis resistance mechanism involving the upregulation of TXNDC12, a thioredoxin domain-containing protein located in the endoplasmic reticulum. The inducible expression of TXNDC12 during ferroptosis in leukemia cells is inhibited by the knockdown of the transcription factor ATF4, rather than NFE2L2. Mechanistically, TXNDC12 acts to inhibit lipid peroxidation without affecting iron accumulation during ferroptosis. When TXNDC12 is overexpressed, it restores the sensitivity of ATF4-knockdown cells to ferroptosis. Moreover, TXNDC12 plays a GPX4-independent role in inhibiting lipid peroxidation. The absence of TXNDC12 enhances the tumor-suppressive effects of ferroptosis induction in both cell culture and animal models. Collectively, these findings demonstrate an endoplasmic reticulum-based anti-ferroptosis pathway in cancer cells with potential translational applications.

SMURF2 predisposes cancer cell toward ferroptosis in GPX4-independent manners by promoting GSTP1 degradation

Ferroptosis is a non-apoptotic form of regulated cell death. Glutathione (GSH) peroxidase 4 (GPX4) and GSH-independent ferroptosis suppressor protein 1 (FSP1) have been identified as major defenses. Here, we uncover a protective mechanism mediated by GSH S-transferase P1 (GSTP1) by monitoring proteinomic dynamics during ferroptosis. Dramatic downregulation of GSTP1 is caused by SMURF2-mediated GSTP1 ubiquitination and degradation at early stages of ferroptosis. Intriguingly, GSTP1 acts in GPX4- and FSP1-independent manners by catalyzing GSH conjugation of 4-hydroxynonenal and detoxifying lipid hydroperoxides via selenium-independent GSH peroxidase activity. Genetic modulation of the SMURF2/GSTP1 axis or the pharmacological inhibition of GSTP1's catalytic activity sensitized tumor responses to Food and Drug Administration (FDA)-approved ferroptosis-inducing drugs both in vitro and in vivo. GSTP1 expression also confers resistance to immune checkpoint inhibitors by blunting ferroptosis. Collectively, these findings demonstrate a GPX4/FSP1-independent cellular defense mechanism against ferroptosis and suggest that targeting SMURF2/GSTP1 to sensitize cancer cells to ferroptosis has potential as an anticancer therapy.

Targeting proteasomal deubiquitinases USP14 and UCHL5 with b-AP15 reduces 5-fluorouracil resistance in colorectal cancer cells

5-Fluorouracil (5-FU) is the first-line treatment for colorectal cancer (CRC) patients, but the development of acquired resistance to 5-FU remains a big challenge. Deubiquitinases play a key role in the protein degradation pathway, which is involved in cancer development and chemotherapy resistance. In this study, we investigated the effects of targeted inhibition of the proteasomal deubiquitinases USP14 and UCHL5 on the development of CRC and resistance to 5-FU. By analyzing GEO datasets, we found that the mRNA expression levels of USP14 and UCHL5 in CRC tissues were significantly increased, and negatively correlated with the survival of CRC patients. Knockdown of both USP14 and UCHL5 led to increased 5-FU sensitivity in 5-FU-resistant CRC cell lines (RKO-R and HCT-15R), whereas overexpression of USP14 and UCHL5 in 5-FU-sensitive CRC cells decreased 5-FU sensitivity. B-AP15, a specific inhibitor of USP14 and UCHL5, (1-5 μM) dose-dependently inhibited the viability of RKO, RKO-R, HCT-15, and HCT-15R cells. Furthermore, treatment with b-AP15 reduced the malignant phenotype of CRC cells including cell proliferation and migration, and induced cell death in both 5-FU-sensitive and 5-FU-resistant CRC cells by impairing proteasome function and increasing reactive oxygen species (ROS) production. In addition, b-AP15 inhibited the activation of NF-κB pathway, suppressing cell proliferation. In 5-FU-sensitive and 5-FU-resistant CRC xenografts nude mice, administration of b-AP15 (8 mg·kg-1·d-1, intraperitoneal injection) effectively suppressed the growth of both types of tumors. These results demonstrate that USP14 and UCHL5 play an important role in the development of CRC and resistance to 5-FU. Targeting USP14 and UCHL5 with b-AP15 may represent a promising therapeutic strategy for the treatment of CRC.

Ferroptosis Signaling Pathways: Alzheimer's Disease

The involvements of iron metabolism, lipid peroxidation, and oxidative stress in Alzheimer's disease (AD) development have recently received a lot of attention. We also observe that these pathogenic occurrences play a key role in regulating ferroptosis, a unique regulatory cell death that is iron-dependent, oxidative, and non-apoptotic. Iron is a crucial component that makes up a subunit of the oxidase responsible for lipid peroxidation. A family of non-heme iron enzymes known as lipoxygenases (LOXs) can cause ferroptosis by oxidising polyunsaturated fatty acids in cellular membranes (PUFAs). Toxic lipid hydroperoxides are produced in large part by the iron in LOX active sites. Deferoxamine and deferiprone, two iron chelators, could also treat ferroptosis by eliminating the crucial catalytic iron from LOXs. Phospholipids containing polyunsaturated fatty acids are the main substrates of lipid peroxidation in ferroptosis, which is favourably controlled by enzymes like ACSL4, LPCAT3, ALOXs, or POR. Selective stimulation of autophagic degradation pathways leads to an increase in iron accumulation and lipid peroxidation, which promotes ferroptosis. We highlighted recent advancements in our understanding of ferroptosis signaling routes in this study. One form of regulated necrotic cell death known as ferroptosis has been linked to a number of diseases, including cancer, neurological disorders, and ischemia/reperfusion injury. Cerebrospinal fluid (CSF) ferritin may be a good indicator of the amount of iron in the brain because it is the main protein that stores iron.

Evoking Ferroptosis by Synergistic Enhancement of a Cyclopentadienyl Iridium-Betulin Immune Agonist

Ferroptosis is a form of programmed cell death driven by iron-dependent lipid peroxidation (LPO) with the potential for antitumor immunity activation. In this study, a nonferrous cyclopentadienyl metal-based ferroptosis inducer [Ir(Cp*)(Bet)Cl]Cl (Ir-Bet) was developed by a metal-ligand synergistic enhancement (MLSE) strategy involving the reaction of [Ir(Cp*)Cl]2 Cl2 with the natural product Betulin. The fusion of Betulin with iridium cyclopentadienyl (Ir-Cp*) species as Ir-Bet not only tremendously enhanced the antiproliferative activity toward cancer cells, but also activated ferritinophagy for iron homeostasis regulation by PI3K/Akt/mTOR cascade inhibition with a lower dosage of Betulin, and then evoked an immune response by nuclear factor kappa-B (NF-κB) activation of Ir-Cp* species. Further immunogenic cell death (ICD) occurred by remarkable ferroptosis through glutathione (GSH) depletion, glutathione peroxidase 4 (GPX4) deactivation and ferritinophagy. An in vivo vaccination experiment demonstrated desirable antitumor and immunogenic effects of Ir-Bet by increasing the ratio of cytotoxic T cells (CTLs)/regulatory T cells (Tregs).

Autophagy: Regulator of cell death

Autophagy is the process by which cells degrade and recycle proteins and organelles to maintain intracellular homeostasis. Generally, autophagy plays a protective role in cells, but disruption of autophagy mechanisms or excessive autophagic flux usually leads to cell death. Despite recent progress in the study of the regulation and underlying molecular mechanisms of autophagy, numerous questions remain to be answered. How does autophagy regulate cell death? What are the fine-tuned regulatory mechanisms underlying autophagy-dependent cell death (ADCD) and autophagy-mediated cell death (AMCD)? In this article, we highlight the different roles of autophagy in cell death and discuss six of the main autophagy-related cell death modalities, with a focus on the metabolic changes caused by excessive endoplasmic reticulum-phagy (ER-phagy)-induced cell death and the role of mitophagy in autophagy-mediated ferroptosis. Finally, we discuss autophagy enhancement in the treatment of diseases and offer a new perspective based on the use of autophagy for different functional conversions (including the conversion of autophagy and that of different autophagy-mediated cell death modalities) for the clinical treatment of tumors.

Deubiquitinase OTUD5 as a Novel Protector against 4-HNE-Triggered Ferroptosis in Myocardial Ischemia/Reperfusion Injury

Despite the development of advanced technologies for interventional coronary reperfusion after myocardial infarction, a substantial number of patients experience high mortality due to myocardial ischemia-reperfusion (MI/R) injury. An in-depth understanding of the mechanisms underlying MI/R injury can provide crucial strategies for mitigating myocardial damage and improving patient survival. Here, it is discovered that the 4-hydroxy-2-nonenal (4-HNE) accumulates during MI/R, accompanied by high rates of myocardial ferroptosis. The loss-of-function of aldehyde dehydrogenase 2 (ALDH2), which dissipates 4-HNE, aggravates myocardial ferroptosis, whereas the activation of ALDH2 mitigates ferroptosis. Mechanistically, 4-HNE targets glutathione peroxidase 4 (GPX4) for K48-linked polyubiquitin-related degradation, which 4-HNE-GPX4 axis commits to myocyte ferroptosis and forms a positive feedback circuit. 4-HNE blocks the interaction between GPX4 and ovarian tumor (OTU) deubiquitinase 5 (OTUD5) by directly carbonylating their cysteine residues at C93 of GPX4 and C247 of OTUD5, identifying OTUD5 as the novel deubiquitinase for GPX4. Consequently, the elevation of OTUD5 deubiquitinates and stabilizes GPX4 to reverse 4-HNE-induced ferroptosis and alleviate MI/R injury. The data unravel the mechanism of 4-HNE in GPX4-dependent ferroptosis and identify OTUD5 as a novel therapeutic target for the treatment of MI/R injury.

GPX4 in cell death, autophagy, and disease

Selenoprotein GPX4 (glutathione peroxidase 4), originally known as PHGPX (phospholipid hydroperoxide glutathione peroxidase), is the main oxidoreductase in the use of glutathione as a reducing agent in scavenging lipid peroxidation products. There are three GPX4 isoforms: cytosolic (cGPX4), mitochondrial (mGPX4), and nuclear (nGPX4), with distinct spatiotemporal expression patterns during embryonic development and adult life. In addition to inducing the main phenotype of ferroptosis, the loss of GPX4 can in some cells trigger apoptosis, necroptosis, pyroptosis, or parthanatos, which mediates or accelerates developmental defects, tissue damage, and sterile inflammation. The interaction of GPX4 with the autophagic degradation pathway further modulates cell fate in response to oxidative stress. Impaired GPX4 function is implicated in tumorigenesis, neurodegeneration, infertility, inflammation, immune disorders, and ischemia-reperfusion injury. Additionally, the R152H mutation in GPX4 can promote the development of Sedaghatian-type spinal metaphyseal dysplasia, a rare and fatal disease in newborns. Here, we discuss the roles of classical GPX4 functions as well as emerging GPX4-regulated processes in cell death, autophagy, and disease.Abbreviations: AA: arachidonic acid; cGPX4: cytosolic GPX4; CMA: chaperone-mediated autophagy; DAMPs: danger/damage-associated molecular patterns; mGPX4: mitochondrial GPX4; nGPX4: nuclear GPX4; GSDMD-N: N-terminal fragment of GSDMD; I/R: ischemia-reperfusion; PLOOH: phospholipid hydroperoxide; PUFAs: polyunsaturated fatty acids; RCD: regulated cell death; ROS: reactive oxygen species; Se: selenium; SSMD: Sedaghatian-type spondylometaphyseal dysplasia; UPS: ubiquitin-proteasome system.

Identification of a Novel Hypoxia-induced Inflammatory Cell Death Pathway

Hypoxic cancer cells resist many anti-neoplastic therapies and can seed recurrence. We found previously that PTP1B deficiency promotes HER2+ breast cancer cell death in hypoxia by activating RNF213, an ∼600kDa protein containing AAA-ATPase domains and two ubiquitin ligase domains (RING and RZ) that also is implicated in Moyamoya disease (MMD), lipotoxicity, and innate immunity. Here we report that PTP1B and ABL1/2 reciprocally control RNF213 phosphorylation on tyrosine-1275. This phosphorylation promotes RNF213 oligomerization and RZ domain activation. The RZ domain ubiquitylates CYLD/SPATA2, and together with the LUBAC complex, induces their degradation. Decreased CYLD/SPATA2 causes NF-κB activation, which together with hypoxia-induced ER-stress triggers GDSMD-dependent pyroptosis. Mutagenesis experiments show that the RING domain negatively regulates the RZ domain. CYLD -deleted HER2+ cell-derived xenografts phenocopy the effects of PTP1B deficiency, and reconstituting RNF213 knockout lines with RNF213 mutants shows that the RZ domain mediates PTP1B-dependent tumor cell death. Our results identify a novel, potentially targetable PTP1B/RNF213/CYCLD/SPATA pathway critical for controlling inflammatory cell death in hypoxic tumors that could be exploited to target hypoxic tumor cells, potentially turning "cold" tumors "hot". Our findings also reveal new insights into RNF213 regulation, and have potentially important implications for the pathogenesis of MMD, atherosclerosis, and inflammatory and auto-immune disorders.

Stiff Substrate Induces Nucleus Pulposus Cell Ferroptosis via YAP and N-Cadherin Mediated Mechanotransduction

Increased tissue stiffness is associated with various pathological processes, such as fibrosis, inflammation, and aging. The matrix stiffness of the nucleus pulposus (NP) tissues increases gradually during intervertebral disc degeneration (IDD), while the mechanism through which NP cells sense and react to matrix stiffness remains unclear. In this study, the results indicate that ferroptosis is involved in stiff substrate-induced NP cell death. The expression of acyl-CoA synthetase long-chain family member 4 (ACSL4) increases in NP cells of the stiff group, which mediates lipid peroxidation and ferroptosis in NP cells. In addition, stiff substrate activates the hippo signaling cascade and induces the nuclear translocation of yes-associated protein (YAP). Interestingly, inhibition of YAP is efficient to reverse the increase of ACSL4 expression caused by matrix stiffness. Furthermore, stiff substrate suppresses the expression of N-cadherin in NP cells. N-cadherin overexpression can inhibit YAP nuclear translocation via the formation of the N-cadherin/β-catenin/YAP complex, and reverse matrix stiffness-induced ferroptosis in NP cells. Finally, the effects of YAP inhibition and N-cadherin overexpression on IDD progression are further illustrated in animal models. These findings reveal a new mechanism of mechanotransduction in NP cells, providing novel insights into the development of therapies for the treatment of IDD.

A comprehensive overview of recent developments on the mechanisms and pathways of ferroptosis in cancer: the potential implications for therapeutic strategies in ovarian cancer

Cancer cells adapt to environmental changes and alter their metabolic pathways to promote survival and proliferation. Metabolic reprogramming not only allows tumor cells to maintain a reduction-oxidation balance by rewiring resources for survival, but also causes nutrient addiction or metabolic vulnerability. Ferroptosis is a form of regulated cell death characterized by the iron-dependent accumulation of lipid peroxides. Excess iron in ovarian cancer amplifies free oxidative radicals and drives the Fenton reaction, thereby inducing ferroptosis. However, ovarian cancer is characterized by ferroptosis resistance. Therefore, the induction of ferroptosis is an exciting new targeted therapy for ovarian cancer. In this review, potential metabolic pathways targeting ferroptosis were summarized to promote anticancer effects, and current knowledge and future perspectives on ferroptosis for ovarian cancer therapy were discussed. Two therapeutic strategies were highlighted in this review: directly inducing the ferroptosis pathway and targeting metabolic vulnerabilities that affect ferroptosis. The overexpression of SLC7A11, a cystine/glutamate antiporter SLC7A11 (also known as xCT), is involved in the suppression of ferroptosis. xCT inhibition by ferroptosis inducers (e.g., erastin) can promote cell death when carbon as an energy source of glucose, glutamine, or fatty acids is abundant. On the contrary, xCT regulation has been reported to be highly dependent on the metabolic vulnerability. Drugs that target intrinsic metabolic vulnerabilities (e.g., GLUT1 inhibitors, PDK4 inhibitors, or glutaminase inhibitors) predispose cancer cells to death, which is triggered by decreased nicotinamide adenine dinucleotide phosphate generation or increased reactive oxygen species accumulation. Therefore, therapeutic approaches that either directly inhibit the xCT pathway or target metabolic vulnerabilities may be effective in overcoming ferroptosis resistance. Real-time monitoring of changes in metabolic pathways may aid in selecting personalized treatment modalities. Despite the rapid development of ferroptosis-inducing agents, therapeutic strategies targeting metabolic vulnerability remain in their infancy. Thus, further studies must be conducted to comprehensively understand the precise mechanism linking metabolic rewiring with ferroptosis.

VANGL2 inhibits antiviral IFN-I signaling by targeting TBK1 for autophagic degradation

Stringent control of type I interferon (IFN-I) signaling is critical to potent innate immune responses against viral infection, yet the underlying molecular mechanisms are still elusive. Here, we found that Van Gogh-like 2 (VANGL2) acts as an IFN-inducible negative feedback regulator to suppress IFN-I signaling during vesicular stomatitis virus (VSV) infection. Mechanistically, VANGL2 interacted with TBK1 and promoted the selective autophagic degradation of TBK1 via K48-linked polyubiquitination at Lys372 by the E3 ligase TRIP, which serves as a recognition signal for the cargo receptor OPTN. Furthermore, myeloid-specific deletion of VANGL2 in mice showed enhanced IFN-I production against VSV infection and improved survival. In general, these findings revealed a negative feedback loop of IFN-I signaling through the VANGL2-TRIP-TBK1-OPTN axis and highlighted the cross-talk between IFN-I and autophagy in preventing viral infection. VANGL2 could be a potential clinical therapeutic target for viral infectious diseases, including COVID-19.

Extracellular SQSTM1 exacerbates acute pancreatitis by activating autophagy-dependent ferroptosis

ABBREVIATIONS

5-HETE, 5-hydroxyeicosatetraenoic acid; ACSL4, acyl-CoA synthetase long chain family member 4; AP, acute pancreatitis; ATG, autophagy related; AGER, advanced glycosylation end-product specific receptor; DAMPs, danger/damage-associated molecular patterns; FTH1, ferritin heavy chain 1; GPX4, glutathione peroxidase 4; IL, interleukin; INSR, insulin receptor; MAP1LC3B, microtubule associated protein 1 light chain 3 beta; MDA, malondialdehyde; MPO, myeloperoxidase; PRRs, pattern recognition receptors; PUFA, polyunsaturated fatty acid; RNAi, RNA interference; SQSTM1, sequestosome 1; TNF, tumor necrosis factor; TLR, toll like receptor.

Ferroptosis in hepatocellular carcinoma: from bench to bedside

The most widespread type of liver cancer, HCC, is associated with disabled cellular death pathways. Despite therapeutic advancements, resistance to current systemic treatments (including sorafenib) compromises the prognosis of patients with HCC, driving the search for agents that might target novel cell death pathways. Ferroptosis, a form of iron-mediated nonapoptotic cell death, has gained considerable attention as a potential target for cancer therapy, especially in HCC. The role of ferroptosis in HCC is complex and diverse. On one hand, ferroptosis can contribute to the progression of HCC through its involvement in both acute and chronic liver conditions. In contrast, having ferroptosis affect HCC cells might be desirable. This review examines the role of ferroptosis in HCC from cellular, animal, and human perspectives while examining its mechanisms, regulation, biomarkers, and clinical implications.

The 4-Hydroxynonenal–Protein Adducts and Their Biological Relevance: Are Some Proteins Preferred Targets?

It is well known that oxidative stress and lipid peroxidation (LPO) play a role in physiology and pathology. The most studied LPO product with pleiotropic capabilities is 4-hydroxynonenal (4-HNE). It is considered as an important mediator of cellular signaling processes and a second messenger of reactive oxygen species. The effects of 4-HNE are mainly attributed to its adduction with proteins. Whereas the Michael adducts thus formed are preferred in an order of potency of cysteine > histidine > lysine over Schiff base formation, it is not known which proteins are the preferred targets for 4-HNE under what physiological or pathological conditions. In this review, we briefly discuss the methods used to identify 4-HNE–protein adducts, the progress of mass spectrometry in deciphering the specific protein targets, and their biological relevance, focusing on the role of 4-HNE protein adducts in the adaptive response through modulation of the NRF2/KEAP1 pathway and ferroptosis.

Plumbagin is a novel GPX4 protein degrader that induces apoptosis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC), the most common type of primary liver cancer, remains a global health challenge requiring novel and effective therapeutic agents and approaches. Here, we found that a natural product plumbagin can inhibit the growth of HCC cells by inducing the downregulation of GPX4, but not other antioxidant enzymes such as CAT, SOD1, and TXN. Functionally, genetic silence of GPX4 enhances, whereas the overexpression of GPX4 inhibits plumbagin-induced apoptosis (rather than ferroptosis) in HCC cells. Furthermore, GPX4 protein specifically binds the deubiquitinase USP31, but not other deubiquitinases such as CYLD, USP1, USP14, USP20, USP30, USP38, UCHL1, UCHL3, and UCHL5. As an inhibitor of deubiquitinating enzymes, especially USP31, plumbagin induces ubiquitination of GPX4 and subsequent proteasomal degradation of GPX4 in HCC cells. Accordingly, plumbagin-mediated tumor suppression is also associated with the downregulation of GPX4 and the upregulation of apoptosis in a subcutaneous xenograft tumor model. Taken together, these findings demonstrate a novel anticancer mechanism of plumbagin by inducing GPX4 protein degradation.

Autophagy-Dependent Ferroptosis in Cancer

Significance: Autophagy is a self-degrading process that determines cell fate in response to various environmental stresses. In contrast to autophagy-mediated cell survival, the signals, mechanisms, and effects of autophagy-dependent cell death remain obscure. The discovery of autophagy-dependent ferroptosis provides a paradigm for understanding the relationship between aberrant degradation pathways and excessive lipid peroxidation in driving regulated cell death. Recent Advances: Ferroptosis was originally described as an autophagy-independent and iron-mediated nonapoptotic cell death. Current studies reveal that the level of intracellular autophagy is positively correlated with ferroptosis sensitivity. Selective autophagic degradation of proteins (e.g., ferritin, SLC40A1, ARNTL, GPX4, and CDH2) or organelles (e.g., lipid droplets or mitochondria) promotes ferroptosis by inducing iron overload and/or lipid peroxidation. Several upstream autophagosome regulators (e.g., TMEM164), downstream autophagy receptors (e.g., HPCAL1), or danger signals (e.g., DCN) are selectively required for ferroptosis-related autophagy, but not for starvation-induced autophagy. The induction of autophagy-dependent ferroptosis is an effective approach to eliminate drug-resistant cancer cells. Critical Issues: How different organelles selectively activate autophagy to modulate ferroptosis sensitivity is not fully understood. Identifying direct protein effectors of ferroptotic cell death remains a challenge. Future Directions: Further understanding of the molecular mechanics and immune consequences of autophagy-dependent ferroptosis is critical for the development of precision antitumor therapies.

Copper-dependent autophagic degradation of GPX4 drives ferroptosis

Ferroptosis is a type of iron-dependent regulated cell death characterized by unrestricted lipid peroxidation and membrane damage. Although GPX4 (glutathione peroxidase 4) plays a master role in blocking ferroptosis by eliminating phospholipid hydroperoxides, the regulation of GPX4 remains poorly understood. Here, we report an unexpected role for copper in promoting ferroptotic cell death, but not cuproptosis, by inducing macroautophagic/autophagic degradation of GPX4. Copper chelators reduce ferroptosis sensitivity but do not inhibit other types of cell death, such as apoptosis, necroptosis, and alkaliptosis. Conversely, exogenous copper increases GPX4 ubiquitination and the formation of GPX4 aggregates by directly binding to GPX4 protein cysteines C107 and C148. TAX1BP1 (Tax1 binding protein 1) then acts as an autophagic receptor for GPX4 degradation and subsequent ferroptosis in response to copper stress. Consequently, copper enhances ferroptosis-mediated tumor suppression in a mouse model of pancreatic cancer tumor, whereas copper chelators attenuate experimental acute pancreatitis associated with ferroptosis. Taken together, these findings provide new insights into the link between metal stress and autophagy-dependent cell death.Abbreviations: CALCOCO2, calcium binding and coiled-coil domain 2; GPX4, glutathione peroxidase 4; MAP1LC3A/B, microtubule associated protein 1 light chain 3 alpha/beta; MPO, myeloperoxidase; NCOA4, nuclear receptor coactivator 4; OPTN, optineurin; PDAC, pancreatic ductal adenocarcinoma; RIPK1, receptor interacting serine/threonine kinase 1; ROS, reactive oxygen species; SLC40A1, solute carrier family 40 member 1; SQSTM1, sequestosome 1; TAX1BP1, Tax1 binding protein 1; TEPA, tetraethylenepentamine; TM, tetrathiomolybdate.

The Concept of Cancer Stem Cells: Elaborating on ALDH1B1 as an Emerging Marker of Cancer Progression

Cancer is a multifactorial, complex disease exhibiting extraordinary phenotypic plasticity and diversity. One of the greatest challenges in cancer treatment is intratumoral heterogeneity, which obstructs the efficient eradication of the tumor. Tumor heterogeneity is often associated with the presence of cancer stem cells (CSCs), a cancer cell sub-population possessing a panel of stem-like properties, such as a self-renewal ability and multipotency potential. CSCs are associated with enhanced chemoresistance due to the enhanced efflux of chemotherapeutic agents and the existence of powerful antioxidant and DNA damage repair mechanisms. The distinctive characteristics of CSCs make them ideal targets for clinical therapeutic approaches, and the identification of efficient and specific CSCs biomarkers is of utmost importance. Aldehyde dehydrogenases (ALDHs) comprise a wide superfamily of metabolic enzymes that, over the last years, have gained increasing attention due to their association with stem-related features in a wide panel of hematopoietic malignancies and solid cancers. Aldehyde dehydrogenase 1B1 (ALDH1B1) is an isoform that has been characterized as a marker of colon cancer progression, while various studies suggest its importance in additional malignancies. Here, we review the basic concepts related to CSCs and discuss the potential role of ALDH1B1 in cancer development and its contribution to the CSC phenotype.

Monitoring Mitochondria Function in Ferroptosis

Ferroptosis is a type of regulated necrosis driven by uncontrolled membrane lipid peroxidation. Mitochondria, which are membrane-bound organelles present in almost all eukaryotic cells and play a central role in energy metabolism and various types of cell death, have a complicated role in ferroptosis. On one hand, mitochondrial-derived iron metabolism and reactive oxygen species (ROS) production may promote ferroptosis. On the other hand, mitochondria also possess a dihydroorotate dehydrogenase (DHODH)-dependent antioxidant system that detoxifies lipid peroxides. This chapter summarizes several methods, such as western blotting, immunofluorescence, cell viability assays, mitochondrial fluorescent probes, adenosine 5'-triphosphate (ATP) assay kits, mitochondrial respiration, and mitophagy tests, that may enable researchers to gain a deeper understanding of the dual role of mitochondria in ferroptosis.

Thermal Shift Assay in Ferroptosis

Ferroptosis is a recently described process of cell death that is dependent on unregulated cellular iron accumulation with induction of oxidative stress. Ferroptosis has been linked to several human diseases; therefore, investigations aimed at better understanding the pathway and elucidating avenues for future drug development are warranted. Current assays that target ferroptosis/oxidative stress in cells is limited to western blotting and imaging techniques, and unfortunately provide only a broad understanding that is insufficient to effectively assess novel drugs (ligands). Specifically, these assays do not provide insights about ligand interactions with specific proteins associated with these processes. Herein, we discuss a cell-based thermal shift assay that enables screening of ligands under specific cellular conditions for targeting ferroptosis and/or oxidative stress pathways. These data would provide detailed preliminary evidence required for drug development that targets this pathway.

The lipid flippase SLC47A1 blocks metabolic vulnerability to ferroptosis

Ferroptosis is a type of regulated necrosis caused by unrestricted lipid peroxidation and subsequent plasma membrane rupture. However, the lipid remodeling mechanism that determines sensitivity to ferroptosis remains poorly understood. Here, we report a previously unrecognized role for the lipid flippase solute carrier family 47 member 1 (SLC47A1) as a regulator of lipid remodeling and survival during ferroptosis. Among 49 phospholipid scramblases, flippases, and floppases we analyzed, only SLC47A1 had mRNA that was selectively upregulated in multiple cancer cells exposed to ferroptotic inducers. Large-scale lipidomics and functional analyses revealed that the silencing of SLC47A1 increased RSL3- or erastin-induced ferroptosis by favoring ACSL4-SOAT1-mediated production of polyunsaturated fatty acid cholesterol esters. We identified peroxisome proliferator activated receptor alpha (PPARA) as a transcription factor that transactivates SLC47A1. The depletion of PPARA and SLC47A1 similarly sensitized cells to ferroptosis induction, whereas transfection-enforced re-expression of SLC47A1 restored resistance to ferroptosis in PPARA-deficient cells. Pharmacological or genetic blockade of the PPARA-SLC47A1 pathway increased the anticancer activity of a ferroptosis inducer in mice. These findings establish a direct molecular link between ferroptosis and lipid transporters, which may provide metabolic targets for overcoming drug resistance.