FANCD2 protects against bone marrow injury from ferroptosis

The HMGB1-AGER-STING1 pathway mediates the sterile inflammatory response to alkaliptosis

Alkaliptosis is a recently discovered form of regulated cell death driven by intracellular alkalization. However, the immune characteristics and mechanisms of alkaliptosis are still poorly understood. Here, we show that HMGB1, a multifunctional alarm protein that drives innate immunity, is necessary for inflammation caused by alkaliptotic damage. During alkaliptosis, HMGB1 translocation and release from the nucleus to the cytoplasm to the extracellular space requires nuclear DNA damage signals, whereas the FANCD2-dependent (but not ATM-mediated) DNA repair pathway inhibits this process. Once released by alkaliptotic cancer cells, extracellular HMGB1 binds to the AGER receptor in macrophages and then activates the STING1 pathway to produce pro-inflammatory cytokines (e.g., TNF and IL6). Consequently, the pharmacological or genetic inhibition of the HMGB1-AGER-STING1 pathway limits cytokine production during alkaliptosis. These findings provide new insight into the sterile inflammatory response to cell death.

STING1 Promotes Ferroptosis Through MFN1/2-Dependent Mitochondrial Fusion

Ferroptosis is a type of iron-dependent regulated cell death caused by the disruption that occurs when oxidative stress and antioxidant defenses interact, and then driven by lipid peroxidation and subsequent plasma membrane ruptures. The regulation of ferroptosis involves many factors, including the crosstalk between subcellular organelles, such as mitochondria, endoplasmic reticulum (ER), lysosomes, lipid droplets, and peroxisomes. Here, we show that the ER protein STING1 (also known as STING or TMEM173) promotes ferroptosis in human pancreatic cancer cell lines by increasing MFN1/2-dependent mitochondrial fusion, but not mitophagy-mediated mitochondrial removal. The classic ferroptosis inducer erastin, but not sulfasalazine, induces the accumulation of STING1 in the mitochondria, where it binds to MFN1/2 to trigger mitochondrial fusion, leading to subsequent reactive oxygen species production and lipid peroxidation. Consequently, in vitro or xenograft mouse models show that the genetic depletion of STING1 or MFN1/2 (but not the mitophagy regulator PINK1 or PRKN) reduces the sensitivity of pancreatic cancer cells to ferroptosis. These findings not only establish a new mitochondrial fusion-dependent cell death mechanism, but also indicate a potential strategy for enhancing ferroptosis-based therapy.

Molecular characterization, expression and functional analysis of yak IFITM3 gene

IFITM3 is interferon-induced transmembrane 3, which plays an extremely key role in anti-proliferation, anti-virus and anti-tumor diseases. In this study, the yak (Bos grunniens) IFITM3 (BgIFITM3) gene contained a 5'-untranslated region (UTR) (25 bp), a coding region (441 bp), and a 3'-UTR (115 bp). The expression of BgIFITM3 gene in liver was significantly higher than that in heart, spleen, lung and kidney (P < 0.01). BgIFITM3 protein was localized on the yak hepatocyte plasma membrane, and its expression was significantly different between 1 day and 15 months of age (P < 0.05). Moreover, the prokaryotic expression vector of BgIFITM3 protein was constructed and expressed successfully, with a molecular weight of 19.5 kDa. The activities of yak hepatocyte were significantly inhibited after treating with BgIFITM3 protein (10 and 20 μg/mL) (P < 0.01). The expression levels of ERBB-2, IRS-1, PI3KR-1, AKT-1 and MAPK-3 were significantly lower after treating with 20 μg/mL BgIFITM3 protein (P < 0.05). Besides, the activities of HepG2 cells were significantly inhibited after treating with BgIFITM3 protein (1, 10 and 20 μg/mL) (P < 0.05). While, the cloning ability and migration ability of HepG2 cells were significantly inhibited after treating with 10 μg/mL BgIFITM3 protein (P < 0.05). Finally, the mitochondria of HepG2 cells was concentrated, cristae widened, and the double film density of mitochondria was increased after treating with 10 μg/mL BgIFITM3 protein. After 10 μg/mL BgIFITM3 protein treating, the expression levels of VDAC-2, VDAC-3 and p53 genes were significantly increased, but the expression level of GPX-4 gene was significantly decreased (P < 0.01). Taken together, the BgIFITM3 protein could inhibit the proliferations of yak hepatocyte and HepG2 cells by regulating the PI3K/Akt pathway or ferroptosis-related genes, respectively. These results benefit for further study of the function of BgIFITM3 protein.

Ferroptosis-Related Gene-Based Prognostic Model and Immune Infiltration in Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is one of the most common tumors in the urinary system. Ferroptosis plays a vital role in ccRCC development and progression. We did an update of ferroptosis-related multigene expression signature for individualized prognosis prediction in patients with ccRCC. Differentially expressed ferroptosis-related genes in ccRCC and normal samples were screened using The Cancer Genome Atlas. Univariate and multivariate Cox regression analyses and machine learning methods were employed to identify optimal prognosis-related genes. CARS1, CD44, FANCD2, HMGCR, NCOA4, SLC7A11, and ACACA were selected to establish a prognostic risk score model. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that these genes were mainly enriched in immune-related pathways; single-sample Gene Set Enrichment Analysis revealed several immune cells potentially related to ferroptosis. Kaplan-Meier survival analysis demonstrated that patients with high-risk scores had significantly poor overall survival (log-rank P = 7.815 × 10^-11). The ferroptosis signature was identified as an independent prognostic factor. Finally, a prognostic nomogram, including the ferroptosis signature, age, histological grade, and stage status, was constructed. Analysis of The Cancer Genome Atlas-based calibration plots, C-index, and decision curve indicated the excellent predictive performance of the nomogram. The ferroptosis-related seven-gene risk score model is useful as a prognostic biomarker and suggests therapeutic targets for ccRCC. The prognostic nomogram may assist in individualized survival prediction and improve treatment strategies.

Construction and External Validation of a Ferroptosis-Related Gene Signature of Predictive Value for the Overall Survival in Bladder Cancer

Purpose: To identify whether ferroptosis-related genes play predictive roles in bladder cancer patients and to develop a ferroptosis-related gene signature to predict overall survival outcomes.

Materials and Methods: We downloaded the mRNA expression files and clinical data of 256 bladder samples (188 bladder tumour and 68 nontumour samples) from the GEO database and 430 bladder samples (411 bladder tumour and 19 nontumour samples) from the TCGA database. A multigene signature based on prognostic ferroptosis-related genes was constructed by least absolute shrinkage and selection operator Cox regression analysis in the GEO cohort. The TCGA cohort was used to validate the ferroptosis-related gene signature. Next, functional enrichment analysis, including both Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analyses, was performed to elucidate the mechanism underlying the signature. The ssGSEA scores of 16 immune cells and 13 immune-related pathway activities between the high-risk and low-risk groups were also analysed in our study.

Results: Thirty-three (67.3%) ferroptosis-related genes were differentially expressed between bladder tumour samples and nontumour samples in the GEO cohort. The intersection of prognostic ferroptosis-related genes and differentially expressed genes identified four prognostic targets, including ALOX5, FANCD2, HMGCR and FADS2. The least absolute shrinkage and selection operator Cox regression successfully built a 4-gene signature: risk score value = e^sum (each gene’s normalized expression * each gene’s coefficient). Univariate and multivariate Cox regression analyses were performed in both the GEO and TCGA cohorts to test the independent prognostic value of the 4-gene risk signature. Multivariate Cox regression analysis in the GEO cohort identified age (p < 0.001), grade (p = 0.129) and risk score (p = 0.016) as independent prognostic predictors for overall survival. Multivariate Cox regression analysis in the TCGA cohort also identified age (p = 0.002), stage (p < 0.001) and risk score (p = 0.006) as independent prognostic predictors for overall survival. The type II IFN response was determined to be significantly weakened in the high-risk group in both the GEO and TCGA cohorts.

Conclusion: We successfully built a ferroptosis-related gene signature of significant predictive value for bladder cancer. These results suggest a novel research direction for targeted therapy of bladder cancer in the future.

Mitochondrial DNA stress triggers autophagy-dependent ferroptotic death

Pancreatic cancer tends to be highly resistant to current therapy and remains one of the great challenges in biomedicine with very low 5-year survival rates. Here, we report that zalcitabine, an antiviral drug for human immunodeficiency virus infection, can suppress the growth of primary and immortalized human pancreatic cancer cells through the induction of ferroptosis, an iron-dependent form of regulated cell death. Mechanically, this effect relies on zalcitabine-induced mitochondrial DNA stress, which activates the STING1/TMEM173-mediated DNA sensing pathway, leading to macroautophagy/autophagy-dependent ferroptotic cell death via lipid peroxidation, but not a type I interferon response. Consequently, the genetic and pharmacological inactivation of the autophagy-dependent ferroptosis pathway diminishes the anticancer effects of zalcitabine in cell culture and animal models. Together, these findings not only provide a new approach for pancreatic cancer therapy but also increase our understanding of the interplay between autophagy and DNA damage response in shaping cell death.Abbreviations: ALOX: arachidonate lipoxygenase; ARNTL/BMAL1: aryl hydrocarbon receptor nuclear translocator-like; ATM: ATM serine/threonine kinase; ATG: autophagy-related; cGAMP: cyclic GMP-AMP; CGAS: cyclic GMP-AMP synthase; ER: endoplasmic reticulum; FANCD2: FA complementation group D2; GPX4: glutathione peroxidase 4; IFNA1/IFNα: interferon alpha 1; IFNB1/IFNβ: interferon beta 1; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; MDA: malondialdehyde; mtDNA: mitochondrial DNA; NCOA4: nuclear receptor coactivator 4; PDAC: pancreatic ductal adenocarcinoma; POLG: DNA polymerase gamma, catalytic subunit; qRT-PCR: quantitative polymerase chain reaction; RCD: regulated cell death; ROS: reactive oxygen species; SLC7A11: solute carrier family 7 member 11; STING1/TMEM173: stimulator of interferon response cGAMP interactor 1; TFAM: transcription factor A, mitochondrial.

Cellular degradation systems in ferroptosis

In eukaryotic cells, macromolecular homeostasis requires selective degradation of damaged units by the ubiquitin-proteasome system (UPS) and autophagy. Thus, dysfunctional degradation systems contribute to multiple pathological processes. Ferroptosis is a type of iron-dependent oxidative cell death driven by lipid peroxidation. Various antioxidant systems, especially the system xc--glutathione-GPX4 axis, play a significant role in preventing lipid peroxidation-mediated ferroptosis. The endosomal sorting complex required for transport-III (ESCRT-III)-dependent membrane fission machinery counteracts ferroptosis by repairing membrane damage. Moreover, cellular degradation systems play a dual role in regulating the ferroptotic response, depending on the cargo they degrade. The key ferroptosis repressors, such as SLC7A11 and GPX4, are degraded by the UPS. In contrast, the overactivation of selective autophagy, including ferritinophagy, lipophagy, clockophagy and chaperone-mediated autophagy, promotes ferroptotic death by degrading ferritin, lipid droplets, circadian proteins, and GPX4, respectively. Autophagy modulators (e.g., BECN1, STING1/TMEM173, CTSB, HMGB1, PEBP1, MTOR, AMPK, and DUSP1) also determine the ferroptotic response in a context-dependent manner. In this review, we provide an updated overview of the signals and mechanisms of the degradation system regulating ferroptosis, opening new horizons for disease treatment strategies.

Emerging mechanisms and targeted therapy of ferroptosis in cancer

Ferroptosis is an iron- and lipid reactive oxygen species (ROS)-dependent form of programmed cell death that is distinct from other forms of regulatory cell death at the morphological, biological, and genetic levels. Emerging evidence suggests critical roles for ferroptosis in cell metabolism, the redox status, and various diseases, such as cancers, nervous system diseases, and ischemia-reperfusion injury, with ferroptosis-related proteins. Ferroptosis is inhibited in diverse cancer types and functions as a dynamic tumor suppressor in cancer development, indicating that the regulation of ferroptosis can be utilized as an interventional target for tumor treatment. Small molecules and nanomaterials that reprogram cancer cells to undergo ferroptosis are considered effective drugs for cancer therapy. Here, we systematically summarize the molecular basis of ferroptosis, the suppressive effect of ferroptosis on tumors, the effect of ferroptosis on cellular metabolism and the tumor microenvironment (TME), and ferroptosis-inducing agents for tumor therapeutics. An understanding of the latest progress in ferroptosis could provide references for proposing new potential targets for the treatment of cancers.

Comparison of Ferroptosis-Inhibitory Mechanisms between Ferrostatin-1 and Dietary Stilbenes (Piceatannol and Astringin)

Synthetic arylamines and dietary phytophenolics could inhibit ferroptosis, a recently discovered regulated cell death process. However, no study indicates whether their inhibitory mechanisms are inherently different. Herein, the ferroptosis-inhibitory mechanisms of selected ferrostatin-1 (Fer-1) and two dietary stilbenes (piceatannol and astringin) were compared. Cellular assays suggested that the ferroptosis-inhibitory and electron-transfer potential levels decreased as follows: Fer-1 >> piceatannol > astringin; however, the hydrogen-donating potential had an order different from that observed by the antioxidant experiments and quantum chemistry calculations. Quantum calculations suggested that Fer-1 has a much lower ionization potential than the two stilbenes, and the aromatic N-atoms were surrounded by the largest electron clouds. By comparison, the C4'O-H groups in the two stilbenes exhibited the lowest bond disassociation enthalpies. Finally, the three were found to produce corresponding dimer peaks through ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry analysis. In conclusion, Fer-1 mainly depends on the electron transfer of aromatic N-atoms to construct a redox recycle. However, piceatannol and astringin preferentially donate hydrogen atoms at the 4'-OH position to mediate the conventional antioxidant mechanism that inhibits ferroptosis, and to ultimately form dimers. These results suggest that dietary phytophenols may be safer ferroptosis inhibitors for balancing normal and ferroptotic cells than arylamines with high electron-transfer potential.

A Novel Ferroptosis-Associated Gene Signature to Predict Prognosis in Patients with Uveal Melanoma

Background: Uveal melanoma (UM) is the most common intraocular tumor in adults. Ferroptosis is a newly recognized process of cell death, which is different from other forms of cell death in terms of morphology, biochemistry and genetics, and has played a vital role in cancer biology. The present research aimed to construct a gene signature from ferroptosis-related genes that have the prognostic capacity of UM. Methods: UM patients from The Cancer Genome Atlas (TCGA) were taken as the training cohort, and GSE22138 from Gene Expression Omnibus (GEO) was treated as the validation cohort. A total of 103 ferroptosis-related genes were retrieved from the GeneCards. We performed Kaplan–Meier and univariate Cox analysis for preliminary screening of ferroptosis-related genes with potential prognostic capacity in the training cohort. These genes were then applied into an overall survival-based LASSO Cox regression model, constructing a gene signature. The discovered gene signature was then evaluated via Kaplan–Meier (KM), Cox, and ROC analyses in both cohorts. The Pearson correlation coefficient examined the correlations between risk score and UM common mutations and autophagy. The analyses of GSEA and immune infiltrating were performed to better study the functional annotation of the gene signature and the character of each kind of immune cell in the tumor microenvironment. Results: A seven-gene signature was found from the training cohort and validated in all cohorts by Kaplan–Meier and Cox regression analyses, revealing its independent prognosis value in UM. Moreover, ROC analysis was conducted, confirming the strong predictive ability that this signature had for UM prognosis. A total of 52.24% (256/490) autophagy-related genes were significantly correlated with risk scores. Analyses of GSEA and immune infiltrating detailed exhibited specific pathways associated with the seven-gene signature, also confirming the crucial role that Mast cells resting played in the prognosis of the seven-gene signature. Conclusions: In this study, a novel ferroptosis-related seven-gene signature (ALOX12, CD44, MAP1LC3C, STEAP3, HMOX1, ITGA6, and AIFM2/FSP1) was built. It could accurately predict UM prognosis and was related to Mast cells resting, which provides the potential for personalized outcome prediction and the development of new therapies in the UM population.

Tetrachlorobenzoquinone exposure triggers ferroptosis contributing to its neurotoxicity

Halogenated quinones are representative metabolites of persistent organic pollutants. Tetrachlorobenzoquinone (TCBQ) is a reactive metabolite of the widely used fungicide hexachlorobenzene (HCB) and wood preservative pentachlorophenol (PCP). Our previous studies have demonstrated that TCBQ induced neuron-like cell apoptosis in a reactive oxygen species (ROS)-dependent manner. Here, we found that TCBQ caused lipid peroxidation and cellular morphological changes including shrinked mitochondrial size, suggesting the involvement of a recently uncovered form of programmed cell death (PCD), ferroptosis. Indeed, we then identified that ferroptosis is a novel PCD driven by TCBQ, which was correlated with a decrease in glutathione peroxidase 4 (GPX4) level and iron accumulation by altering iron metabolism. Notably, nuclear factor erythroid-derived 2-like 2 (Nrf2) is a negative regulator in modulating the outcomes of ferroptosis as an adaptive cellular defense response. Nrf2 activation enhanced iron storage capacity and GPX4 activity by elevating ferritin heavy chain 1 (FTH1) expression and glutathione (GSH) level, respectively. On the contrary, Nfe2l2 (Nrf2) deficiency enhanced PC12 cells susceptibility to ferroptosis.

Ferroptosis: molecular mechanisms and health implications

Cell death can be executed through different subroutines. Since the description of ferroptosis as an iron-dependent form of non-apoptotic cell death in 2012, there has been mounting interest in the process and function of ferroptosis. Ferroptosis can occur through two major pathways, the extrinsic or transporter-dependent pathway and the intrinsic or enzyme-regulated pathway. Ferroptosis is caused by a redox imbalance between the production of oxidants and antioxidants, which is driven by the abnormal expression and activity of multiple redox-active enzymes that produce or detoxify free radicals and lipid oxidation products. Accordingly, ferroptosis is precisely regulated at multiple levels, including epigenetic, transcriptional, posttranscriptional and posttranslational layers. The transcription factor NFE2L2 plays a central role in upregulating anti-ferroptotic defense, whereas selective autophagy may promote ferroptotic death. Here, we review current knowledge on the integrated molecular machinery of ferroptosis and describe how dysregulated ferroptosis is involved in cancer, neurodegeneration, tissue injury, inflammation, and infection.

Broadening horizons: the role of ferroptosis in cancer

The discovery of regulated cell death processes has enabled advances in cancer treatment. In the past decade, ferroptosis, an iron-dependent form of regulated cell death driven by excessive lipid peroxidation, has been implicated in the development and therapeutic responses of various types of tumours. Experimental reagents (such as erastin and RSL3), approved drugs (for example, sorafenib, sulfasalazine, statins and artemisinin), ionizing radiation and cytokines (such as IFNγ and TGFβ1) can induce ferroptosis and suppress tumour growth. However, ferroptotic damage can trigger inflammation-associated immunosuppression in the tumour microenvironment, thus favouring tumour growth. The extent to which ferroptosis affects tumour biology is unclear, although several studies have found important correlations between mutations in cancer-relevant genes (for example, RAS and TP53), in genes encoding proteins involved in stress response pathways (such as NFE2L2 signalling, autophagy and hypoxia) and the epithelial-to-mesenchymal transition, and responses to treatments that activate ferroptosis. Herein, we present the key molecular mechanisms of ferroptosis, describe the crosstalk between ferroptosis and tumour-associated signalling pathways, and discuss the potential applications of ferroptosis in the context of systemic therapy, radiotherapy and immunotherapy.

NUPR1 is a critical repressor of ferroptosis

Ferroptosis is a type of iron-dependent regulated cell death, representing an emerging disease-modulatory mechanism. Transcription factors play multiple roles in ferroptosis, although the key regulator for ferroptosis in iron metabolism remains elusive. Using NanoString technology, we identify NUPR1, a stress-inducible transcription factor, as a driver of ferroptosis resistance. Mechanistically, NUPR1-mediated LCN2 expression blocks ferroptotic cell death through diminishing iron accumulation and subsequent oxidative damage. Consequently, LCN2 depletion mimics NUPR1 deficiency with respect to ferroptosis induction, whereas transfection-enforced re-expression of LCN2 restores resistance to ferroptosis in NUPR1-deficient cells. Pharmacological or genetic blockade of the NUPR1-LCN2 pathway (using NUPR1 shRNA, LCN2 shRNA, pancreas-specific Lcn2 conditional knockout mice, or the small molecule ZZW-115) increases the activity of the ferroptosis inducer erastin and worsens pancreatitis, in suitable mouse models. These findings suggest a link between NUPR1-regulated iron metabolism and ferroptosis susceptibility.

Characteristics and Biomarkers of Ferroptosis

The induction and consequences of regulated cell death (RCD) are accompanied by changes in gene and protein expression, biochemical pathways, as well as cell morphology and size. Such RCDs have a significant impact on development, tissue homeostasis, and the occurrence and progression of disease. Among different forms of RCD, ferroptosis appears to be the main cause of tissue damage driven by iron overload and lipid peroxidation. In fact, the dysfunctional ferroptotic response is implicated in a variety of pathological conditions and diseases, such as neurodegenerative diseases, tissue ischemia-reperfusion injury, tumorigenesis, infections, and immune diseases. Ferroptotic response can be fine-tuned through various oxidative stress and antioxidant defense pathways, coupling with metabolism, gene transcription, and protein degradation machinery. Accordingly, a series of ferroptosis inducers or inhibitors targeting redox- or iron metabolism-related proteins or signal transduction have been developed. Although this kind of RCD has recently attracted great interest in basic and clinical research, detecting and monitoring a ferroptotic response still faces challenges. In this mini-review, we not only summarize the latest knowledge about the characteristics of ferroptosis in vitro and in vivo, but also discuss the specificity and limitations of current biomarkers of ferroptosis.

Pirin is a nuclear redox-sensitive modulator of autophagy-dependent ferroptosis

In regulated cell death, genetically encoded molecular machinery destroys cells. This process is not only essential for organ development and homeostasis, but also leads to pathological diseases. One form of regulated cell death is ferroptosis, which is an iron-dependent oxidative cell death caused by lipid peroxidation. Although inducing ferroptosis is an emerging anticancer strategy, the molecular mechanism underlying tumor resistance to ferroptotic cell death is still unclear. Here, we show that pirin (PIR), an iron-binding nuclear protein, plays a previously unrecognized role in mediating ferroptosis resistance in human pancreatic cancer cells. The transcription factor NFE2L2 mediates the upregulation of PIR during ferroptosis caused by small-molecule compounds (e.g., erastin or RSL3). PIR is a nuclear redox sensor and regulator, and increasing it limits the oxidative damage of DNA and the subsequent cytoplasmic transport and extracellular release of HMGB1. In contrast, the depletion of PIR initiates HMGB1-dependent autophagy by binding to BECN1, and subsequently promotes ferroptosis by activating ACSL4. Consequently, in cell cultures and xenograft mouse models, blocking PIR signaling enhances ferroptosis-mediated tumor growth suppression. Together, these findings provide new insights into the molecular mechanisms of autophagy-dependent ferroptosis.

A ferroptosis-related gene signature predicts overall survival in patients with lung adenocarcinoma

Aims: To elucidate the association between ferroptosis-related genes and prognosis in patients with lung adenocarcinoma (LUAD). Materials & methods: A ferroptosis-related gene signature was made by lasso regression analysis through the LUAD datasets of the Cancer Genome Atlas. The prognostic value of the multigene signature was externally validated in the GSE72094 dataset from the Gene Expression Omnibus database. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis were used to explore underlying mechanisms. Results & conclusion: We established a novel ferroptosis-related gene signature for overall survival in LUAD that was predictive in both the training and validation cohorts. Immune-related pathways were significantly enriched, and immune status differed between the high- and low-risk groups. Targeting ferroptosis is a potential therapeutic option in LUAD. These results still need to be confirmed by more studies.

Cathepsin B is a mediator of organelle-specific initiation of ferroptosis

Ferroptosis is a type of non-apoptotic regulated cell death that involves excessive iron accumulation and subsequent lipid peroxidation. Although the antioxidant mechanisms of ferroptosis have been extensively studied recently, little is known about the interactions between the different organelles that control ferroptosis. Here, we show that the translocation of lysosomal cysteine protease cathepsin B (CTSB) into the nucleus is an important molecular event that mediates organelle-specific initiation of ferroptosis in human pancreatic cancer cells. Iron-dependent lysosomal membrane permeability triggers the release of CTSB from the lysosome to nucleus during ferroptosis. Mechanistically, nuclear CTSB accumulation causes DNA damage and subsequent activation of the stimulator of interferon response CGAMP interactor 1 (STING1/STING)-dependent DNA sensor pathway, which ultimately leads to autophagy-dependent ferroptosis. Consequently, the genetic inhibition of CTSB-dependent STING1 activation by RNAi prevents ferroptosis in cell culture and animal models. These new findings not only enhance our understanding of the mechanism by which organelles specifically trigger ferroptosis, but also may provide a potential way to enhance the anticancer activity of ferroptosis therapy.

Osteocyte apoptosis: the roles and key molecular mechanisms in resorption-related bone diseases

Vital osteocytes have been well known to function as an important orchestrator in the preservation of robustness and fidelity of the bone remodeling process. Nevertheless, some key pathological factors, such as sex steroid deficiency and excess glucocorticoids, and so on, are implicated in inducing a bulk of apoptotic osteocytes, subsequently resulting in resorption-related bone loss. As much, osteocyte apoptosis, under homeostatic conditions, is in an optimal state of balance tightly controlled by pro- and anti-apoptotic mechanism pathways. Importantly, there exist many essential signaling proteins in the process of osteocyte apoptosis, which has a crucial role in maintaining a homeostatic environment. While increasing in vitro and in vivo studies have established, in part, key signaling pathways and cross-talk mechanism on osteocyte apoptosis, intrinsic and complex mechanism underlying osteocyte apoptosis occurs in various states of pathologies remains ill-defined. In this review, we discuss not only essential pro- and anti-apoptotic signaling pathways and key biomarkers involved in these key mechanisms under different pathological agents, but also the pivotal role of apoptotic osteocytes in osteoclastogenesis-triggered bone loss, hopefully shedding new light on the attractive and proper actions of pharmacotherapeutics of targeting apoptosis and ensuing resorption-related bone diseases such as osteoporosis and fragility fractures.

Iron Metabolism in Ferroptosis

Ferroptosis is a form of regulated cell death that is characterized by iron-dependent oxidative damage and subsequent plasma membrane ruptures and the release of damage-associated molecular patterns. Due to the role of iron in mediating the production of reactive oxygen species and enzyme activity in lipid peroxidation, ferroptosis is strictly controlled by regulators involved in many aspects of iron metabolism, such as iron uptake, storage, utilization, and efflux. Translational and transcriptional regulation of iron homeostasis provide an integrated network to determine the sensitivity of ferroptosis. Impaired ferroptosis is implicated in various iron-related pathological conditions or diseases, such as cancer, neurodegenerative diseases, and ischemia-reperfusion injury. Understanding the molecular mechanisms underlying the regulation of iron metabolism during ferroptosis may provide effective strategies for the treatment of ferroptosis-associated diseases. Indeed, iron chelators effectively prevent the occurrence of ferroptosis, which may provide new approaches for the treatment of iron-related disorders. In this review, we summarize recent advances in the theoretical modeling of iron-dependent ferroptosis, and highlight the therapeutic implications of iron chelators in diseases.

Emerging mechanisms and applications of ferroptosis in the treatment of resistant cancers

The development of chemotherapy drugs has promoted anticancer treatment, but the effect on tumours is not clear because of treatment resistance; thus, it is necessary to further understand the mechanism of cell death to explore new therapeutic targets. As a new type of programmed cell death, ferroptosis is increasingly being targeted in the treatment of many cancers with clinical drugs and experimental compounds. Ferroptosis is stimulated in tumours with inherently high levels of ferrous ions by a reaction with abundant polyunsaturated fatty acids and the inhibition of antioxidant enzymes, which can overcome treatment resistance in cancers mainly through GPX4. In this review, we focus on the intrinsic cellular regulators against ferroptosis in cancer resistance, such as GPX4, NRF2 and the thioredoxin system. We summarize the application of novel compounds and drugs to circumvent treatment resistance. We also introduce the application of nanoparticles for the treatment of resistant cancers. In conclusion, targeting ferroptosis represents a considerable strategy for resistant cancer treatment.

Molecular characteristics associated with ferroptosis in hepatocellular carcinoma progression

The aim of this study was to investigate the genes associated with ferroptosis and the progression of hepatocellular carcinoma (HCC). The RNA sequencing data of erastin-induced ferroptosis in HCC cells were downloaded from the Sequence Read Archive database with accession number SRP119173. The microarray dataset GSE89377 of HCC progression was downloaded from the Gene Expression Omnibus database. The ferroptosis-related genes were screened by differential analysis and HCC progression-related genes were screened by cluster analysis using Mfuzz. Then, the genes associated with ferroptosis and HCC progression were screened by Venn analysis, followed by functional enrichment, protein-protein interaction (PPI) analysis, and transcription factor (TF) prediction. Finally, survival analysis was performed using data from the Cancer Genome Atlas database. A total of 33 upregulated and 52 downregulated genes associated with HCC progression and ferroptosis were obtained, and these genes were significantly involved in the negative regulation of ERK1 and ERK2 cascades; the NAD biosynthetic process; alanine, aspartate, and glutamate metabolism; and other pathways. The PPI network contained 52 genes and 78 interactions, of which, cell division cycle 20 (CDC20) and heat shock protein family B (small) member 1 (HSPB1) were hub genes found in higher degrees. Among the 85 genes associated with HCC progression and ferroptosis, two TFs (activating TF 3 (ATF3) and HLF) were predicted, with HSPB1 targeted by ATF3. In addition, 26 genes that were found to be significantly correlated with the overall survival of HCC patients were screened, including CDC20 and thyroid hormone receptor interactor 13. Several genes associated with HCC progression and ferroptosis were screened based on a comprehensive bioinformatics analysis. These genes played roles in HCC progression and ferroptosis via the negative regulation of the ERK1 and ERK2 cascades; the NAD biosynthetic process; and alanine, aspartate, and glutamate metabolism. ATF3 and HSPB1 played important roles in HCC progression and ferroptosis, with HSPB1 possibly regulated by ATF3.

Structure-activity relationship and mechanism of four monostilbenes with respect to ferroptosis inhibition

Erastin-treated bone marrow-derived mesenchymal stem cells (bmMSCs) were prepared and used to compare the ferroptosis inhibitory bioactivities of four monostilbenes, including rhapontigenin (1a), isorhapontigenin (1b), piceatannol-3'-O-glucoside (1c), and rhapontin (1d). Their relative levels were 1c ≈ 1b > 1a ≈ 1d in 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid (C11-BODIPY), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and flow cytometric assays. The comparison highlighted two 4'-OH-containing monostilbenes (1c and 1b) in ferroptosis inhibitory bioactivity. Similar structure-activity relationships were also observed in antioxidant assays, including 1,1-diphenyl-2-picryl-hydrazl radical (DPPH˙)-trapping, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO˙)-trapping, and Fe3+-reducing assays. UPLC-ESI-Q-TOF-MS analysis of the DPPH˙-trapping reaction of the monostilbenes revealed that they can inhibit ferroptosis in erastin-treated bmMSCs through a hydrogen donation-based antioxidant pathway. After hydrogen donation, these monostilbenes usually produce the corresponding stable dimers; additionally, the hydrogen donation potential was enhanced by the 4'-OH. The enhancement by 4'-OH can be attributed to the transannular resonance effect. This effect can be used to predict the inhibition potential of other π-π conjugative phenolics.

The Mechanism of Ferroptosis and Applications in Tumor Treatment

Iron-dependent ferroptosis is a new form of cell death in recent years, which is driven by lipid peroxidation. The lethal lipid accumulation caused by glutathione depletion or inactivation of glutathione peroxidase 4 (GPX4) is characteristic of the ferroptosis process. In recent years, with the in-depth study of ferroptosis, various types of diseases have been reported to be related to ferroptosis. In other words, ferroptosis, which has attracted widespread attention in the fields of biochemistry, oncology, and especially materials science, can undoubtedly provide a new way for patients. This review introduces the relevant mechanisms of ferroptosis, the relationship between ferroptosis and various cancers, as well as the application of ferroptosis in tumor treatment. We also sorted out the genes and drugs that regulate ferroptosis. Moreover, small molecule compound-induced ferroptosis has a strong inhibitory effect on tumor growth in a drug-resistant environment, which can enhance the sensitivity of chemotherapeutic drugs, suggesting that ferroptosis is very important in the treatment of tumor drug resistance, but the details are still unclear. How to use ferroptosis to fight cancer, and how to prevent drug-resistant tumor cells have become the focus and direction of research. At the end of the article, some existing problems related to ferroptosis are summarized for future research.

Ferroptosis and Cancer: Mitochondria Meet the "Iron Maiden" Cell Death

Ferroptosis is a new type of oxidative regulated cell death (RCD) driven by iron-dependent lipid peroxidation. As major sites of iron utilization and master regulators of oxidative metabolism, mitochondria are the main source of reactive oxygen species (ROS) and, thus, play a role in this type of RCD. Ferroptosis is, indeed, associated with severe damage in mitochondrial morphology, bioenergetics, and metabolism. Furthermore, dysregulation of mitochondrial metabolism is considered a biochemical feature of neurodegenerative diseases linked to ferroptosis. Whether mitochondrial dysfunction can, per se, initiate ferroptosis and whether mitochondrial function in ferroptosis is context-dependent are still under debate. Cancer cells accumulate high levels of iron and ROS to promote their metabolic activity and growth. Of note, cancer cell metabolic rewiring is often associated with acquired sensitivity to ferroptosis. This strongly suggests that ferroptosis may act as an adaptive response to metabolic imbalance and, thus, may constitute a new promising way to eradicate malignant cells. Here, we review the current literature on the role of mitochondria in ferroptosis, and we discuss opportunities to potentially use mitochondria-mediated ferroptosis as a new strategy for cancer therapy.

Ferroptosis was more initial in cell death caused by iron overload and its underlying mechanism in Parkinson's disease

Ferroptosis, an iron-dependent nonapoptotic cell death, was referred in neurodegenerative diseases, but its role in Parkinson's disease remains unclear. Here, we used ferric ammonium citrate (FAC) to treat dopaminergic cell to mimic the iron overload during the progression of Parkinson's disease (PD). We found that the cell death types of iron-overloaded dopaminergic cells induced by concentrations of FAC were different. Ferroptosis firstly occurred in a relatively low concentration of FAC-treated group, and then apoptosis appeared in response to the increased iron doses. Moreover, both ferroptosis and apoptosis caused by iron overload could be rescued by inhibitors of ferroptosis, but inhibitors of apoptosis did not prevent the occurrence of ferroptosis. We verified that ferroptosis occurred before apoptosis in α-SynA53T homozygous PD mice model. The underlying mechanism might be associated with the p53 signaling pathway, but not MAPK signaling pathway. Collectively, our results revealed a previously unappreciated role of ferroptosis in the early stages of PD and indicated that ferroptosis could elicit apoptosis in cell death caused by iron overload.

miR-194-5p inhibits SLC40A1 expression to induce cisplatin resistance in ovarian cancer

BACKGROUND

miR-194-5p has been associated with drug resistance in many cancers. However, the role of miR-194-5p in cisplatin resistance in ovarian cancer is still unclear.

MATERIALS AND METHODS

To study the role and mechanism of miR-194-5p in cisplatin resistance, qRT-PCR was performed to determine the expression of miR-194-5p and SLC40A1 in ovarian cancer. Cell Counting Kit-8 (CCK8) assay was used to analyse cell viability after cisplatin treatment. Dual-luciferase reporter gene assay was performed to examine the relationship between miR-194-5p and SLC40A1. The genes downstream of SLC40A1 were investigated through bioinformatics analysis.

RESULTS

Compared to cisplatin-sensitive ovarian cancer cells, higher miR-194-5p expression and lower SLC40A1 expression were found in cisplatin-resistant ovarian cancer cells. Moreover, this study demonstrated that over-expression of miR-194-5p inhibited SLC40A1 expression, and knockdown of miR-194-5p promoted SLC40A1 expression. In addition, dual-luciferase reporter gene assay further confirmed the negative correlation between miR-194-5p and SLC40A1. Furthermore, we found that over-expression of miR-194-5p resulted in cisplatin resistance. When miR-194-5p and SLC40A1 were simultaneously up-regulated, cisplatin sensitivity increased, while down-regulation of miR-194-5p sensitised ovarian cancer cells to cisplatin. However, when miR-194-5p and SLC40A1 were simultaneously down-regulated, cisplatin sensitivity was decreased. These data suggested that miR-194-5p inhibited SLC40A1 expression to induce cisplatin resistance. In addition, bioinformatics analysis indicated a positive correlation of SLC40A1 with hephaestin (HEPH), and homeostatic iron regulator (HFE). However, we found that HEPH and HFE were associated with cisplatin resistance, suggesting that their role in drug resistance is induced by miR-194-5p/SLC40A1.

CONCLUSION

In conclusion, we found that miR-194-5p inhibited SLC40A1 expression to induce cisplatin resistance in ovarian cancer. This study suggests that miR-194-5p could be a potential therapeutic target and a prognostic biomarker for ovarian cancer, with important implications for future research.

Inhibitory Effect and Mechanism of Action of Quercetin and Quercetin Diels-Alder anti-Dimer on Erastin-Induced Ferroptosis in Bone Marrow-Derived Mesenchymal Stem Cells

In this study, the anti-ferroptosis effects of catecholic flavonol quercetin and its metabolite quercetin Diels-Alder anti-dimer (QDAD) were studied using an erastin-treated bone marrow-derived mesenchymal stem cell (bmMSCs) model. Quercetin exhibited higher anti-ferroptosis levels than QDAD, as indicated by 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid (C11-BODIPY), 2',7'-dichlorodihydrofluoroscein diacetate (H2DCFDA), lactate dehydrogenase (LDH) release, cell counting kit-8 (CCK-8), and flow cytometric assays. To understand the possible pathways involved, the reaction product of quercetin with the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH^●) was measured using ultra-performance liquid-chromatography coupled with electrospray-ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC-ESI-Q-TOF-MS). Quercetin was found to produce the same clusters of molecular ion peaks and fragments as standard QDAD. Furthermore, the antioxidant effects of quercetin and QDAD were compared by determining their 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical-scavenging, Cu²⁺-reducing, Fe³⁺-reducing, lipid peroxidation-scavenging, and DPPH^●-scavenging activities. Quercetin consistently showed lower IC₅₀ values than QDAD. These findings indicate that quercetin and QDAD can protect bmMSCs from erastin-induced ferroptosis, possibly through the antioxidant pathway. The antioxidant pathway can convert quercetin into QDAD-an inferior ferroptosis-inhibitor and antioxidant. The weakening has highlighted a rule for predicting the relative anti-ferroptosis and antioxidant effects of catecholic flavonols and their Diels-Alder dimer metabolites.

Simultaneous Study of Anti-Ferroptosis and Antioxidant Mechanisms of Butein and (S)-Butin

To elucidate the mechanism of anti-ferroptosis and examine structural optimization in natural phenolics, cellular and chemical assays were performed with 2'-hydroxy chalcone butein and dihydroflavone (S)-butin. C11-BODIPY staining and flow cytometric assays suggest that butein more effectively inhibits ferroptosis in erastin-treated bone marrow-derived mesenchymal stem cells than (S)-butin. Butein also exhibited higher antioxidant percentages than (S)-butin in five antioxidant assays: linoleic acid emulsion assay, Fe3+-reducing antioxidant power assay, Cu2+-reducing antioxidant power assay, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO•)-trapping assay, and α,α-diphenyl-β-picrylhydrazyl radical (DPPH•)-trapping assay. Their reaction products with DPPH• were further analyzed using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS). Butein and (S)-butin produced a butein 5,5-dimer (m/z 542, 271, 253, 225, 135, and 91) and a (S)-butin 5',5'-dimer (m/z 542, 389, 269, 253, and 151), respectively. Interestingly, butein forms a cross dimer with (S)-butin (m/z 542, 523, 433, 419, 415, 406, and 375). Therefore, we conclude that butein and (S)-butin exert anti-ferroptotic action via an antioxidant pathway (especially the hydrogen atom transfer pathway). Following this pathway, butein and (S)-butin yield both self-dimers and cross dimers. Butein displays superior antioxidant or anti-ferroptosis action to (S)-butin. This can be attributed the decrease in π-π conjugation in butein due to saturation of its α,β-double bond and loss of its 2'-hydroxy group upon biocatalytical isomerization.

Immunological impact of cell death signaling driven by radiation on the tumor microenvironment

Therapeutic irradiation of the tumor microenvironment causes differential activation of pro-survival and pro-death pathways in malignant, stromal, endothelial and immune cells, hence causing a profound cellular and biological reconfiguration via multiple, non-redundant mechanisms. Such mechanisms include the selective elimination of particularly radiosensitive cell types and consequent loss of specific cellular functions, the local release of cytokines and danger signals by dying radiosensitive cells, and altered cytokine secretion by surviving radioresistant cells. Altogether, these processes create chemotactic and immunomodulatory cues for incoming and resident immune cells. Here we discuss how cytoprotective and cytotoxic signaling modules activated by radiation in specific cell populations reshape the immunological tumor microenvironment.

The Tumor Suppressive Roles and Prognostic Values of STEAP Family Members in Breast Cancer

OBJECTIVE

To investigate the expression patterns and prognostic values of STEAP family members in the occurrence and development of breast cancer.

MATERIALS AND METHODS

The Human Protein Atlas was used to analyze the expression level of STEAPs in human normal tissues and malignant tumors. ONCOMINE datasets were analyzed for the comparison of the STEAPs levels between malignant cancers and corresponding normal tissues. Kaplan-Meier plotter was used to analyze the prognostic value of STEAPs in breast cancer patients.

RESULTS

STEAPs were widely distributed in human normal tissues with diverse levels. Normally, it is predicted that STEAP1 and STEAP2 were involved in the mineral absorption process, while STEAP3 participated in the TP53 signaling pathway and iron apoptosis. The results from ONCOMINE showed downregulation of STEAP1, STEAP2, and STEAP4 in breast cancers. Survival analysis revealed that breast cancer patients with high levels of STEAP1, STEAP2, and STEAP4 had a good prognosis, while those with low expression had high overall mortality.

CONCLUSION

STEAP1, STEAP2, and STEAP4 are predicted to be the potential prognostic biomarkers for breast cancer patients, providing novel therapeutic strategies for them.

Chronic iron exposure and c-Myc/H-ras-mediated transformation in fallopian tube cells alter the expression of EVI1, amplified at 3q26.2 in ovarian cancer

Mechanisms underlying the pathogenesis of high-grade serous epithelial ovarian cancers (HGSOC) are not yet well defined although key precursor cells have been identified (including fimbriated fallopian tube epithelium, FTSECs). Since iron is elevated in endometriotic cysts and the pelvic cavity, it is suggested that this source of redox-active iron may contribute to ovarian cancer pathogenesis. Specifically, sources of nontransferrin-bound iron (NTBI) within the pelvic cavity could arise from ovulation, retrograde menstruation, follicular fluid, or iron overload conditions (i.e., hemochromatosis). Herein, we investigated the cellular response of p53-inactivated and telomerase-expressing (immortalized) FTSECs (Pax8⁺/FoxJ1⁻) to NTBI (presented as ferric ammonium citrate (FAC), supplemented in media for >2 months) in order to assess its ability to promote the transition to a tumor-like phenotype; this cellular response was compared with immortalized FTSECs transformed with H-Ras^V12A and c-Myc^T58A. Both approaches resulted in increased cell numbers and expression of the oncogenic transcriptional regulator, ecotropic virus integration site 1 (EVI1, a gene most frequently amplified at 3q26.2 in HGSOC, represented by multiple variants), along with other oncogenic gene products. In contrast to the transformed cells, FAC-exposed FTSECs elicited elevated migratory capacity (and epithelial–mesenchymal transition mRNA profile) along with increased expression of DNA damage response proteins (i.e., FANCD2) and hTERT mRNA relative to controls. Interestingly, in FAC-exposed FTSECs, EVI1 siRNA attenuated hTERT mRNA expression, whereas siRNAs targeting β-catenin and BMI1 (both elevated with chronic iron exposure) reduced Myc and Cyclin D1 proteins. Collectively, our novel findings provide strong foundational evidence for potential iron-induced initiation events, including EVI1 alterations, in the pathogenesis of HGSOC, warranting further in depth investigations. Thus, these findings will substantially advance our understanding of the contribution of iron enriched within the pelvic cavity, which may identify patients at risk of developing this deadly disease.

Molecular mechanisms of ferroptosis and its role in cancer therapy

Ferroptosis is a newly defined programmed cell death process with the hallmark of the accumulation of iron‐dependent lipid peroxides. The term was first coined in 2012 by the Stockwell Lab, who described a unique type of cell death induced by the small molecules erastin or RSL3. Ferroptosis is distinct from other already established programmed cell death and has unique morphological and bioenergetic features. The physiological role of ferroptosis during development has not been well characterized. However, ferroptosis shows great potentials during the cancer therapy. Great progress has been made in exploring the mechanisms of ferroptosis. In this review, we focus on the molecular mechanisms of ferroptosis, the small molecules functioning in ferroptosis initiation and ferroptosis sensitivity in different cancers. We are also concerned with the new arising questions in this particular research area that remains unanswered.

Targeting Ferroptosis to Iron Out Cancer

One of the key challenges in cancer research is how to effectively kill cancer cells while leaving the healthy cells intact. Cancer cells often have defects in cell death executioner mechanisms, which is one of the main reasons for therapy resistance. To enable growth, cancer cells exhibit an increased iron demand compared with normal, non-cancer cells. This iron dependency can make cancer cells more vulnerable to iron-catalyzed necrosis, referred to as ferroptosis. The identification of FDA-approved drugs as ferroptosis inducers creates high expectations for the potential of ferroptosis to be a new promising way to kill therapy-resistant cancers.

The molecular machinery of regulated cell death

Cells may die from accidental cell death (ACD) or regulated cell death (RCD). ACD is a biologically uncontrolled process, whereas RCD involves tightly structured signaling cascades and molecularly defined effector mechanisms. A growing number of novel non-apoptotic forms of RCD have been identified and are increasingly being implicated in various human pathologies. Here, we critically review the current state of the art regarding non-apoptotic types of RCD, including necroptosis, pyroptosis, ferroptosis, entotic cell death, netotic cell death, parthanatos, lysosome-dependent cell death, autophagy-dependent cell death, alkaliptosis and oxeiptosis. The in-depth comprehension of each of these lethal subroutines and their intercellular consequences may uncover novel therapeutic targets for the avoidance of pathogenic cell loss.

Ferroptosis is a type of autophagy-dependent cell death

Macroautophagy (hereafter referred to as autophagy) involves an intracellular degradation and recycling system that, in a context-dependent manner, can either promote cell survival or accelerate cellular demise. Ferroptosis was originally defined in 2012 as an iron-dependent form of cancer cell death different from apoptosis, necrosis, and autophagy. However, this latter assumption came into question because, in response to ferroptosis activators (e.g., erastin and RSL3), autophagosomes accumulate, and because components of the autophagy machinery (e.g., ATG3, ATG5, ATG4B, ATG7, ATG13, and BECN1) contribute to ferroptotic cell death. In particular, NCOA4-facilitated ferritinophagy, RAB7A-dependent lipophagy, BECN1-mediated system x_c^- inhibition, STAT3-induced lysosomal membrane permeabilization, and HSP90-associated chaperone-mediated autophagy can promote ferroptosis. In this review, we summarize current knowledge on the signaling pathways involved in ferroptosis, while focusing on the regulation of autophagy-dependent ferroptotic cell death. The molecular comprehension of these phenomena may lead to the development of novel anticancer therapies.

The Roles of NRF2 in Modulating Cellular Iron Homeostasis

SIGNIFICANCE

Iron and oxygen are intimately linked: iron is an essential nutrient utilized as a cofactor in enzymes for oxygen transport, oxidative phosphorylation, and metabolite oxidation. However, excess labile iron facilitates the formation of oxygen-derived free radicals capable of damaging biomolecules. Therefore, biological utilization of iron is a tightly regulated process. The nuclear factor (erythroid-derived 2)-like 2 (NRF2) transcription factor, which can respond to oxidative and electrophilic stress, regulates several genes involved in iron metabolism. Recent Advances: The bulk of NRF2 transcription factor research has focused on its roles in detoxification and cancer prevention. Recent works have identified that several genes involved in heme synthesis, hemoglobin catabolism, iron storage, and iron export are under the control of NRF2. Constitutive NRF2 activation and subsequent deregulation of iron metabolism have been implicated in cancer development: NRF2-mediated upregulation of the iron storage protein ferritin or heme oxygenase 1 can lead to enhanced proliferation and therapy resistance. Of note, NRF2 activation and alterations to iron signaling in cancers may hinder efforts to induce the iron-dependent cell death process known as ferroptosis.

CRITICAL ISSUES

Despite growing recognition of NRF2 as a modulator of iron signaling, exactly how iron metabolism is altered due to NRF2 activation in normal physiology and in pathologic conditions remains imprecise; moreover, the roles of NRF2-mediated iron signaling changes in disease progression are only beginning to be uncovered.

FUTURE DIRECTIONS

Further studies are necessary to connect NRF2 activation with physiological and pathological changes to iron signaling and oxidative stress. Antioxid. Redox Signal. 00, 000-000.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Ferroptosis: A Regulated Cell Death Nexus Linking Metabolism, Redox Biology, and Disease

Ferroptosis is a form of regulated cell death characterized by the iron-dependent accumulation of lipid hydroperoxides to lethal levels. Emerging evidence suggests that ferroptosis represents an ancient vulnerability caused by the incorporation of polyunsaturated fatty acids into cellular membranes, and cells have developed complex systems that exploit and defend against this vulnerability in different contexts. The sensitivity to ferroptosis is tightly linked to numerous biological processes, including amino acid, iron, and polyunsaturated fatty acid metabolism, and the biosynthesis of glutathione, phospholipids, NADPH, and coenzyme Q10. Ferroptosis has been implicated in the pathological cell death associated with degenerative diseases (i.e., Alzheimer's, Huntington's, and Parkinson's diseases), carcinogenesis, stroke, intracerebral hemorrhage, traumatic brain injury, ischemia-reperfusion injury, and kidney degeneration in mammals and is also implicated in heat stress in plants. Ferroptosis may also have a tumor-suppressor function that could be harnessed for cancer therapy. This Primer reviews the mechanisms underlying ferroptosis, highlights connections to other areas of biology and medicine, and recommends tools and guidelines for studying this emerging form of regulated cell death.

Autophagy and Ferroptosis - What's the Connection?

PURPOSE OF REVIEW

Autophagy is a conserved intracellular degradation system and plays a dual role in cell death, depending on context and phase. Ferroptosis is a new form of regulated cell death that mainly depends on iron accumulation and lipid peroxidation. In this review, we summarize the processes of autophagy and ferroptosis and discuss their crosstalk mechanisms at the molecular level.

RECENT FINDINGS

The original study shows that ferroptosis is morphologically, biochemically, and genetically distinct from autophagy and other types of cell death. However, recent studies demonstrate that activation of ferroptosis is indeed dependent on the induction of autophagy. Additionally, many ferroptosis regulators such as SLC7A11, GPX4, NRF2, p53, HSPB1, CISD1, FANCD2, and ACSL4 have been identified as potential regulators of autophagy.

SUMMARY

This review not only highlights the importance of autophagy as an emerging mechanism of ferroptosis, but also raises new insights regarding regulated cell death.

Antiferroptotic activity of non-oxidative dopamine

Dopamine is a neurotransmitter that has many functions in the nervous and immune systems. Ferroptosis is a non-apoptotic form of regulated cell death that is involved in cancer and neurodegenerative diseases. However, the role of dopamine in ferroptosis remains unidentified. Here, we show that the non-oxidative form of dopamine is a strong inhibitor of ferroptotic cell death. Dopamine dose-dependently blocked ferroptosis in cancer (PANC1 and HEY) and non-cancer (MEF and HEK293) cells following treatment with erastin, a small molecule ferroptosis inducer. Notably, dopamine reduced erastin-induced ferrous iron accumulation, glutathione depletion, and malondialdehyde production. Mechanically, dopamine increased the protein stability of glutathione peroxidase 4, a phospholipid hydroperoxidase that protects cells against membrane lipid peroxidation. Moreover, dopamine suppressed dopamine receptor D4 protein degradation and promoted dopamine receptor D5 gene expression. Thus, our findings uncover a novel function of dopamine in cell death and provide new insight into the regulation of iron metabolism and lipid peroxidation by neurotransmitters.