BAP1 links metabolic regulation of ferroptosis to tumour suppression

CAF secreted miR-522 suppresses ferroptosis and promotes acquired chemo-resistance in gastric cancer

BACKGROUND

Ferroptosis is a novel mode of non-apoptotic cell death induced by build-up of toxic lipid peroxides (lipid-ROS) in an iron dependent manner. Cancer-associated fibroblasts (CAFs) support tumor progression and drug resistance by secreting various bioactive substances, including exosomes. Yet, the role of CAFs in regulating lipid metabolism as well as ferroptosis of cancer cells is still unexplored and remains enigmatic.

METHODS

Ferroptosis-related genes in gastric cancer (GC) were screened by using mass spectrum; exosomes were isolated by ultra-centrifugation and CAF secreted miRNAs were determined by RT-qPCR. Erastin was used to induce ferroptosis, and ferroptosis levels were evaluated by measuring lipid-ROS, cell viability and mitochondrial membrane potential.

RESULTS

Here, we provide clinical evidence to show that arachidonate lipoxygenase 15 (ALOX15) is closely related with lipid-ROS production in gastric cancer, and that exosome-miR-522 serves as a potential inhibitor of ALOX15. By using primary stromal cells and cancer cells, we prove that exosome-miR-522 is mainly derived from CAFs in tumor microenvironment. Moreover, heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) was found to mediate miR-522 packing into exosomes, and ubiquitin-specific protease 7 (USP7) stabilizes hnRNPA1 through de-ubiquitination. Importantly, cisplatin and paclitaxel promote miR-522 secretion from CAFs by activating USP7/hnRNPA1 axis, leading to ALOX15 suppression and decreased lipid-ROS accumulation in cancer cells, and ultimately result in decreased chemo-sensitivity.

CONCLUSIONS

The present study demonstrates that CAFs secrete exosomal miR-522 to inhibit ferroptosis in cancer cells by targeting ALOX15 and blocking lipid-ROS accumulation. The intercellular pathway, comprising USP7, hnRNPA1, exo-miR-522 and ALOX15, reveals new mechanism of acquired chemo-resistance in GC.

The epigenetic regulators and metabolic changes in ferroptosis-associated cancer progression

Ferroptosis, a novel form of regulated cell death, is different from other types of cell death in morphology, genetics and biochemistry. Increasing evidence indicates that ferroptosis has significant implications on cell death linked to cardiomyopathy, tumorigenesis, and cerebral hemorrhage to name a few. Here we summarize current literature on ferroptosis, including organelle dysfunction, signaling transduction pathways, metabolic reprogramming and epigenetic regulators in cancer progression. With regard to organelles, mitochondria-induced cysteine starvation, endoplasmic reticulum-related oxidative stress, lysosome dysfunction and golgi stress-related lipid peroxidation all contribute to induction of ferroptosis. Understanding the underlying mechanism in ferroptosis could provide insight into the treatment of various intractable diseases including cancers.

Aiming at Cancer In Vivo: Ferroptosis-Inducer Delivered by Nanoparticles

Induction of ferroptosis has emerged as a potential cancer therapeutic approach. In this issue of Cell Chemical Biology, Zhang et al. (2019) demonstrate the anticancer efficacy and safety of the ferroptosis inducer imidazole ketone erastin (IKE) in a xenograft model by using a nanoparticle-based delivery system.

Energy-stress-mediated AMPK activation inhibits ferroptosis

Energy stress depletes ATP and induces cell death. Here, we identify an unexpected inhibitory role of energy stress on ferroptosis, a form of regulated cell death induced by iron-dependent lipid peroxidation. We found that ferroptotic cell death and lipid peroxidation can be inhibited by treatments that induce or mimic energy stress. Inactivation of AMP-activated protein kinase (AMPK), a sensor of cellular energy status, largely abolishes the protective effects of energy stress on ferroptosis in vitro and on ferroptosis-associated renal ischemia/reperfusion injury in vivo. Cancer cells with high basal AMPK activation are resistant to ferroptosis, and AMPK inactivation sensitizes these cells to ferroptosis. Functional and lipidomic analyses further link AMPK regulation of ferroptosis to AMPK-mediated phosphorylation of acetyl-CoA carboxylase (ACC) and polyunsaturated fatty acid biosynthesis. Together, our study demonstrates that energy stress inhibits ferroptosis partly through AMPK, and reveals an unexpected coupling between ferroptosis and AMPK-mediated energy stress signaling.

Paclitaxel-Potentiated Photodynamic Theranostics for Synergistic Tumor Ablation and Precise Anticancer Efficacy Monitoring

Photodynamic theranostics that allows for concurrent photodynamic therapy (PDT) and precise therapeutic response report has emerged as an intriguing direction in the development of precision medicine. An ultra-efficient photodynamic theranostics platform was developed here based on combining and potentiating a theranostic photosensitizer, TPCI, with other therapies for synergistic anticancer effect and synchronous self-reporting of therapeutic response. In this study, TPCI and a chemotherapy agent paclitaxel (PTX) were co-encapsulated in liposomes, which exhibited a superb synergistic anticancer effect against a series of tumor cell lines. The potency of both drugs had been boosted for up to 30-fold compared with sole PDT or chemotherapy. More strikingly, the released TPCI lighted up the nuclei of dead cells, triggered either by PDT or chemotherapy, through binding with the chromatin and activating its aggregation-induced emission, therefore self-reporting the anticancer effect of the combined therapy in real time. The in vivo study using a mouse model bearing PC3 prostate tumor cells demonstrated the effective ablation of tumors with initial sizes of 200 mm³ and the precise early tumor response monitoring by TPCI/PTX@Lipo. This PTX-potentiated photodynamic theranostics strategy herein represented a new prototype of self-reporting nanomedicine for precise tumor therapy.

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 role of ferroptosis in ionizing radiation-induced cell death and tumor suppression

Ferroptosis, a form of regulated cell death caused by lipid peroxidation, was recently identified as a natural tumor suppression mechanism. Here, we show that ionizing radiation (IR) induces ferroptosis in cancer cells. Mechanistically, IR induces not only reactive oxygen species (ROS) but also the expression of ACSL4, a lipid metabolism enzyme required for ferroptosis, resulting in elevated lipid peroxidation and ferroptosis. ACSL4 ablation largely abolishes IR-induced ferroptosis and promotes radioresistance. IR also induces the expression of ferroptosis inhibitors, including SLC7A11 and GPX4, as an adaptive response. IR- or KEAP1 deficiency-induced SLC7A11 expression promotes radioresistance through inhibiting ferroptosis. Inactivating SLC7A11 or GPX4 with ferroptosis inducers (FINs) sensitizes radioresistant cancer cells and xenograft tumors to IR. Furthermore, radiotherapy induces ferroptosis in cancer patients, and increased ferroptosis correlates with better response and longer survival to radiotherapy in cancer patients. Our study reveals a previously unrecognized link between IR and ferroptosis and indicates that further exploration of the combination of radiotherapy and FINs in cancer treatment is warranted.

Energy stress inhibits ferroptosis via AMPK

Energy stress disturbs cellular homeostasis and induces cell death. Our recent study revealed that ferroptosis (a non-apoptotic cell death) is an energy-requiring process, and energy stress-mediated activation of adenosine monophosphate-activated protein kinase (AMPK) inhibits ferroptosis. Mechanistically, AMPK regulates ferroptosis through acetyl-CoA carboxylase (ACC) and polyunsaturated fatty acid (PUFA) biosynthesis.

Artemisinin compounds sensitize cancer cells to ferroptosis by regulating iron homeostasis

The antimalarial drug artemisinin and its derivatives have been explored as potential anticancer agents, but their underlying mechanisms are controversial. In this study, we found that artemisinin compounds can sensitize cancer cells to ferroptosis, a new form of programmed cell death driven by iron-dependent lipid peroxidation. Mechanistically, dihydroartemisinin (DAT) can induce lysosomal degradation of ferritin in an autophagy-independent manner, increasing the cellular free iron level and causing cells to become more sensitive to ferroptosis. Further, by associating with cellular free iron and thus stimulating the binding of iron-regulatory proteins (IRPs) with mRNA molecules containing iron-responsive element (IRE) sequences, DAT impinges on IRP/IRE-controlled iron homeostasis to further increase cellular free iron. Importantly, in both in vitro and a mouse xenograft model in which ferroptosis was triggered in cancer cells by the inducible knockout of GPX4, we found that DAT can augment GPX4 inhibition-induced ferroptosis in a cohort of cancer cells that are otherwise highly resistant to ferroptosis. Collectively, artemisinin compounds can sensitize cells to ferroptosis by regulating cellular iron homeostasis. Our findings can be exploited clinically to enhance the effect of future ferroptosis-inducing cancer therapies.

Novel Germline Mutations in DNA Damage Repair in Patients with Malignant Pleural Mesotheliomas

INTRODUCTION

Although next-generation sequencing (NGS) has brought insight into critical mutations or pathways (e.g., DNA damage sensing and repair) involved in the etiology of many cancers and has directed new screening, prevention, and therapeutic approaches for patients and families, it has only recently been used in malignant pleural mesotheliomas (MPMs).

METHODS

We analyzed the blood samples from patients with MPM using the NGS platform MSK-IMPACT to explore cancer-predisposing genes. The loss-of-function variants or pathogenic entries were identified, and clinicopathologic information was collected.

RESULTS

Of 84 patients with MPM, 12% (10 of 84) had pathogenic variants. Clinical characteristics were similar between cohorts, although patients with germline pathogenic variants were more likely to have more than two first-degree family members with cancer than those without germline mutations (40% versus 12%; Fisher's exact test, p < 0.05). Novel, deleterious variants in mesotheliomas included MutS homolog 3 (1% [one of 84]; 95% confidence interval [CI]: 0%-7%), breast cancer gene 1-associated ring domain 1 (1% [one of 84]; 95% CI: 0%-7%), and RecQ-like helicase 4 (2% [two of 84]; 95% CI: 0%-9%). Pathogenic variants previously reported on germline testing in patients with mesotheliomas were breast cancer gene 1-associated protein 1 (4% [three of 84]; 95% CI: 1%-10%), breast cancer gene 2 (1% [one of 84]; 95% CI: 0%-7%), and MRE11 homolog, double strand break repair nuclease (1% [one of 84]; 95% CI: 0%-7%). One patient (1% [one of 84]; 95% CI: 0%-7%) had a likely pathogenic alteration in SHQ1, H/ACA ribonucleoprotein assembly factor that has not been associated with a heritable susceptibility to cancer.

CONCLUSIONS

Our study lends further support for the role of aberrations in DNA damage repair genes in the pathogenesis of MPMs and suggests that targeting the members of these pathways for screening and treatment warrants further study.

Ferroptosis in Carcinoma: Regulatory Mechanisms and New Method for Cancer Therapy

Ferroptosis is a new form of programmed cell death with characteristic accumulation of reactive oxygen species (ROS) resulting from iron accumulation and lipid peroxidation. Ferroptosis is involved in many diseases, including cancer, and induction of ferroptosis has shown attractive antitumour activities. In this review, we summarize recent findings on the regulatory mechanisms of key regulators of ferroptosis, including the catalytic subunit solute carrier family 7 member 11 (SLC7A11), the glutathione peroxidase 4 (GPX4), p53 and non-coding RNAs, the correlations between ferroptosis and iron homeostasis or autophagy, ferroptosis-inducing agents and nanomaterials and the diagnostic and prognostic value of ferroptosis-associated genes in TCGA data.

Prognostic value of infiltrating immune cells in clear cell renal cell carcinoma (ccRCC)

In this study, we attempted to evaluate the prognostic value of infiltrating immune/stromal cells in clear cell renal cell carcinoma (ccRCC), by using the immune scores and stromal scores based on the "Estimation of STromal and Immune cells in MAlignant Tumours using Expression data" algorithm to represent the levels of infiltrating immune cells and stromal cells. We found that the infiltrating immune cells were associated with poor prognosis of ccRCC. To assess the role of infiltrating immune cells in ccRCC cells, first, we performed differentially expressed genes analysis and functional analysis for validation. The results showed that the underlying mechanism by which infiltrating immune cells promoted cancer progression involved in regulating the nuclear division, angiogenesis, and immune response. Next, we investigated the relationship between infiltrating immune cells and mutations in ccRCC cells. We found that the infiltrating immune cells have certain effects on genetic mutations. In conclusion, infiltrating immune cells within the tumor microenvironment can be used to predict prognosis in ccRCC.

Recent Progress in Ferroptosis Inducers for Cancer Therapy

Ferroptosis is a newly discovered form of regulated cell death that is the nexus between metabolism, redox biology, and human health. Emerging evidence shows the potential of triggering ferroptosis for cancer therapy, particularly for eradicating aggressive malignancies that are resistant to traditional therapies. Recently, there has been a great deal of effort to design and develop anticancer drugs based on ferroptosis induction. Recent advances of ferroptosis-inducing agents at the intersection of chemistry, materials science, and cancer biology are presented. The basis of ferroptosis is summarized first to highlight the feasibility and characteristics of triggering ferroptosis for cancer therapy. A literature review of ferroptosis inducers (including small molecules and nanomaterials) is then presented to delineate their design, action mechanisms, and anticancer applications. Finally, some considerations for research on ferroptosis inducers are spotlighted, followed by a discussion on the challenges and future development directions of this burgeoning field.

Aldo-keto reductases protect metastatic melanoma from ER stress-independent ferroptosis

The incidence of melanoma is increasing over the years with a still poor prognosis and the lack of a cure able to guarantee an adequate survival of patients. Although the new immuno-based coupled to target therapeutic strategy is encouraging, the appearance of targeted/cross-resistance and/or side effects such as autoimmune disorders could limit its clinical use. Alternative therapeutic strategies are therefore urgently needed to efficiently kill melanoma cells. Ferroptosis induction and execution were evaluated in metastasis-derived wild-type and oncogenic BRAF melanoma cells, and the process responsible for the resistance has been dissected at molecular level. Although efficiently induced in all cells, in an oncogenic BRAF- and ER stress-independent way, most cells were resistant to ferroptosis execution. At molecular level we found that: resistant cells efficiently activate NRF2 which in turn upregulates the early ferroptotic marker CHAC1, in an ER stress-independent manner, and the aldo-keto reductases AKR1C1 ÷ 3 which degrades the 12/15-LOX-generated lipid peroxides thus resulting in ferroptotic cell death resistance. However, inhibiting AKRs activity/expression completely resensitizes resistant melanoma cells to ferroptosis execution. Finally, we found that the ferroptotic susceptibility associated with the differentiation of melanoma cells cannot be applied to metastatic-derived cells, due to the EMT-associated gene expression reprogramming process. However, we identified SCL7A11 as a valuable marker to predict the susceptibility of metastatic melanoma cells to ferroptosis. Our results identify the use of pro-ferroptotic drugs coupled to AKRs inhibitors as a new valuable strategy to efficiently kill human skin melanoma cells.

Pleural mesothelioma and lung cancer: the role of asbestos exposure and genetic variants in selected iron metabolism and inflammation genes

Two of the major cancerous diseases associated with asbestos exposure are malignant pleural mesothelioma (MPM) and lung cancer (LC). In addition to asbestos exposure, genetic factors have been suggested to be associated with asbestos-related carcinogenesis and lung genotoxicity. While genetic factors involved in the susceptibility to MPM were reported, to date the influence of individual genetic variations on asbestos-related lung cancer risk is still poorly understood. Since inflammation and disruption of iron (Fe) homeostasis are hallmarks of asbestos exposure affecting the pulmonary tissue, this study aimed at investigating the association between Fe-metabolism and inflammasome gene variants and susceptibility to develop LC or MPM, by comparing an asbestos-exposed population affected by LC with an "asbestos-resistant exposed population". A retrospective approach similar to our previous autopsy-based pilot study was employed in a novel cohort of autoptic samples, thus giving us the possibility to corroborate previous findings obtained on MPM by repeating the analysis in a novel cohort of autoptic samples. The protective role of HEPH coding SNP was further confirmed. In addition, the two non-coding SNPs, either in FTH1 or in TF, emerged to exert a similar protective role in a new cohort of LC exposed individuals from the same geographic area of MPM subjects. No association was found between NLRP1 and NLRP3 polymorphisms with susceptibility to develop MPM and LC. Further research into a specific MPM and LC "genetic signature" may be needed to broaden our knowledge of the genetic landscape attributed to result in MPM and LC.

The chemical basis of ferroptosis

Lipid peroxidation underlies the mechanism of oxidative cell death now known as ferroptosis. This modality, distinct from other forms of cell death, has been intensely researched in recent years owing to its relevance in both degenerative disease and cancer. The demonstration that it can be modulated by small molecules in multiple pathophysiological contexts offers exciting opportunities for novel pharmacological interventions. Herein, we introduce the salient features of lipid peroxidation, how it can be modulated by small molecules and what principal aspects require urgent investigation by researchers in the field. The central role of non-enzymatic reactions in the execution of ferroptosis will be emphasized, as these processes have hitherto not been generally considered 'druggable'. Moreover, we provide a critical perspective on the biochemical mechanisms that contribute to cell vulnerability to ferroptosis and discuss how they can be exploited in the design of novel therapeutics.

Dysregulation of Glutamate Transport Enhances Treg Function That Promotes VEGF Blockade Resistance in Glioblastoma

Anti-VEGF therapy prolongs recurrence-free survival in patients with glioblastoma but does not improve overall survival. To address this discrepancy, we investigated immunologic resistance mechanisms to anti-VEGF therapy in glioma models. A screening of immune-associated alterations in tumors after anti-VEGF treatment revealed a dose-dependent upregulation of regulatory T-cell (Treg) signature genes. Enhanced numbers of Tregs were observed in spleens of tumor-bearing mice and later in tumors after anti-VEGF treatment. Elimination of Tregs with CD25 blockade before anti-VEGF treatment restored IFNγ production from CD8⁺ T cells and improved antitumor response from anti-VEGF therapy. The treated tumors overexpressed the glutamate/cystine antiporter SLC7A11/xCT that led to elevated extracellular glutamate in these tumors. Glutamate promoted Treg proliferation, activation, suppressive function, and metabotropic glutamate receptor 1 (mGlutR1) expression. We propose that VEGF blockade coupled with glioma-derived glutamate induces systemic and intratumoral immunosuppression by promoting Treg overrepresentation and function, which can be pre-emptively overcome through Treg depletion for enhanced antitumor effects. SIGNIFICANCE: Resistance to VEGF therapy in glioblastoma is driven by upregulation of Tregs, combined blockade of VEGF, and Tregs may provide an additive antitumor effect for treating glioblastoma.

BAP1 Missense Mutations in Cancer: Friend or Foe?

BRCA-associated protein-1 (BAP1) is mutated in several cancers and a few therapies targeting BAP1 loss-of-function mutations have been proposed, some of them being already tested in clinical trials. However, most of the missense mutations have not been functionally characterized, although such information is essential for successful patient stratification.

Functional Genomic Screen in Mesothelioma Reveals that Loss of Function of BRCA1-Associated Protein 1 Induces Chemoresistance to Ribonucleotide Reductase Inhibition

Loss of function of BRCA1-associated protein 1 (BAP1) is observed in about 50% of malignant pleural mesothelioma (MPM) cases. The aim of this study was to investigate whether this aspect could be exploited for targeted therapy. A genetically engineered model was established expressing either functional or nonfunctional BAP1, and whole-genome siRNA synthetic lethality screens were performed assessing differentially impaired survival between the two cell lines. The whole-genome siRNA screen unexpectedly revealed 11 hits (FDR < 0.05) that were more cytotoxic to BAP1-proficient cells. Two actionable targets, ribonucleotide reductase (RNR) catalytic subunit M1 (RRM1) and RNR regulatory subunit M2 (RRM2), were validated. In line with the screen results, primary mesothelioma (BAP1 ^+/-) overexpressing BAP1 C91A (catalytically dead mutant) was more resistant to RNR inhibition, while BAP1 knockdown in the BAP1-proficient cell lines rescued the cells from their vulnerability to RNR depletion. Gemcitabine and hydroxyurea were more cytotoxic in BAP1-proficient cell line-derived spheroids compared with BAP1 deficient. Upregulation of RRM2 upon gemcitabine and hydroxyurea treatment was more profound in BAP1 mut/del cell lines. Increased lethality mediated by RNR inhibition was observed in NCI-H2452 cells reconstituted with BAP1-WT but not with BAP1 C91A. Upregulation of RRM2 in NCI-H2452-BAP1 WT spheroids was modest compared with control or C91A mutant. Together, we found that BAP1 is involved in the regulation of RNR levels during replication stress. Our observations reveal a potential clinical application where BAP1 status could serve as predictive or stratification biomarker for RNR inhibition-based therapy in MPM.

Ferroptosis caused by cysteine insufficiency and oxidative insult

Free iron has long been assumed to be a deteriorating factor in an oxidative insult and was recently found to be directly associated with ferroptosis, a specific type of cell death. The free iron-involved production of lipid peroxides activates the fatal pathway, resulting in nonapoptotic, programed cell death. Lipid peroxides appear to destroy membrane integrity, leading to cell rupture. Glutathione (GSH) is a major redox molecule that functions to protect against ferroptosis by its ability to donate an electron to glutathione peroxidase 4 (GPX4), the sole enzyme that reduces phospholipid hydroperoxides. The availability of free cysteine (Cys) determines the levels of GSH synthesis, and, hence, its deprivation causes ferroptosis. Free iron is provided via ferritinophagy, the chaperone-mediated autophagic degradation of ferritin, but GPX4 also undergoes degradation via chaperone-mediated autophagy. Activated Nrf2 and ATF4 induce the expression of the cystine transporter xCT to cope with ferroptosis. To the contrary, the excessive activation of p53 induces ferroptosis by suppressing the expression of xCT in genetic and nongenetic manners. It therefore appears that xCT functions as the gatekeeper for determining cellular survival by regulating the availability of Cys in the cell. The issue of the extent of involvement of ferroptosis in an in vivo situation largely remains ambiguous. Establishing tools for specifying ferroptotic cells in situ would facilitate our understanding of its roles in pathogenesis.

Mesothelioma: Scientific clues for prevention, diagnosis, and therapy

Mesothelioma affects mostly older individuals who have been occupationally exposed to asbestos. The global mesothelioma incidence and mortality rates are unknown, because data are not available from developing countries that continue to use large amounts of asbestos. The incidence rate of mesothelioma has decreased in Australia, the United States, and Western Europe, where the use of asbestos was banned or strictly regulated in the 1970s and 1980s, demonstrating the value of these preventive measures. However, in these same countries, the overall number of deaths from mesothelioma has not decreased as the size of the population and the percentage of old people have increased. Moreover, hotspots of mesothelioma may occur when carcinogenic fibers that are present in the environment are disturbed as rural areas are being developed. Novel immunohistochemical and molecular markers have improved the accuracy of diagnosis; however, about 14% (high-resource countries) to 50% (developing countries) of mesothelioma diagnoses are incorrect, resulting in inadequate treatment and complicating epidemiological studies. The discovery that germline BRCA1-asssociated protein 1 (BAP1) mutations cause mesothelioma and other cancers (BAP1 cancer syndrome) elucidated some of the key pathogenic mechanisms, and treatments targeting these molecular mechanisms and/or modulating the immune response are being tested. The role of surgery in pleural mesothelioma is controversial as it is difficult to predict who will benefit from aggressive management, even when local therapies are added to existing or novel systemic treatments. Treatment outcomes are improving, however, for peritoneal mesothelioma. Multidisciplinary international collaboration will be necessary to improve prevention, early detection, and treatment.

Toward a genome-based treatment landscape for renal cell carcinoma

Knowledge about molecular mechanisms driving development and progression of renal cell carcinoma has been elucidated by different studies. In few years we discovered a large difference between genomic landscapes of clear cell and non-clear cell carcinoma. Moreover, tumor heterogeneity and different acquisition of gene mutations during tumor progression are issues of particular interest. In this review we focalized our attention on principal genomic alterations identified among RCC subtypes. Acquired gene mutations may be an adaptive response to several external pressure including metabolic, treatment, genomic and immune-related external pressure. Thus we correlated and discussed principal genomic alterations adopted by tumor to escape from each external pressures. The aim of the present work is to summarize current knowledge about genomic alterations in RCC with special interest of treatment strategies tailored on the basis of disease mutations assessment.

Intercellular interaction dictates cancer cell ferroptosis via NF2-YAP signalling

Ferroptosis, a cell death process driven by cellular metabolism and iron-dependent lipid peroxidation, is implicated in various diseases such as ischemic organ damage and cancer^1,2. As a central regulator of ferroptosis, the enzyme glutathione peroxidase 4 (GPX4) protects cells from ferroptosis by neutralizing lipid peroxides, which are byproducts of cellular metabolism; as such, inhibiting GPX4 directly, or indirectly by depriving its substrate glutathione or building blocks of glutathione (such as cysteine), can trigger ferroptosis³. Ferroptosis contributes to the antitumour function of multiple tumour suppressors including p53, BAP1, and fumarase^4-7. Counterintuitively, mesenchymal cancer cells, which are prone to metastasis and often resistant to various treatments, have shown to be highly susceptible to ferroptosis^8,9. Here, we demonstrate that ferroptosis can be regulated non-cell autonomously by cadherin-mediated intercellular contacts. In epithelial cells, E-cadherin-mediated intercellular interaction suppresses ferroptosis through intracellular Merlin-Hippo signalling. Antagonizing this signalling axis unleashes the activity of the proto-oncogenic transcriptional co-activator YAP to promote ferroptosis through upregulation of multiple ferroptosis modulators, including acyl-CoA synthetase long chain family member 4 (ACSL4) and transferrin receptor. This finding provides mechanistic insights into the observations that epithelial mesenchymal transition (EMT)/metastasis-prone cancer cells are highly sensitive to ferroptosis⁸. Importantly, the regulation of ferroptosis by cell-cell contact and Merlin-YAP signalling is not limited to epithelial cells; a similar mechanism also modulates ferroptosis in some non-epithelial cells. Finally, we found that genetic inactivation of the tumour suppressor Merlin, a frequent tumourigenic event in mesothelioma^10,11, renders cancer cells more sensitive to ferroptosis in an orthotopic mouse model of malignant mesothelioma. Together, this study unveils the role of intercellular interaction and intracellular Merlin-YAP signalling in dictating ferroptotic death; it also suggests that malignant mutations in Merlin-YAP signalling can serve as biomarkers predicting cancer cell responsiveness to future ferroptosis-inducing therapies.

ATF3 promotes erastin-induced ferroptosis by suppressing system Xc

The amino acid antiporter system Xc⁻ is important for the synthesis of glutathione (GSH) that functions to prevent lipid peroxidation and protect cells from nonapoptotic, iron-dependent death (i.e., ferroptosis). While the activity of system Xc⁻ often positively correlates with the expression level of its light chain encoded by SLC7A11, inhibition of system Xc⁻ activity by small molecules (e.g., erastin) causes a decrease in the intracellular GSH level, leading to ferroptotic cell death. How system Xc⁻ is regulated during ferroptosis remains largely unknown. Here we report that activating transcription factor 3 (ATF3), a common stress sensor, can promote ferroptosis induced by erastin. ATF3 suppressed system Xc⁻, depleted intracellular GSH, and thereby promoted lipid peroxidation induced by erastin. ATF3 achieved this activity through binding to the SLC7A11 promoter and repressing SLC7A11 expression in a p53-independent manner. These findings thus add ATF3 to a short list of proteins that can regulate system Xc⁻ and promote ferroptosis repressed by this antiporter.

DUBbing Ferroptosis in Cancer Cells

Ferroptosis, a form of iron-dependent, nonapoptotic cell death that is induced by excessive lipid peroxidation, has been recently identified as a new tumor suppression mechanism. In this issue of Cancer Research, Liu and colleagues demonstrate that the deubiquitinase (DUB) OTUB1 is frequently overexpressed in human cancers, and functions to "dub" (trim) the ferroptosis process in cancer cells and promotes tumor development by stabilizing the cystine transporter, SLC7A11. This study not only reveals a hitherto unappreciated regulatory mechanism of ferroptosis but also identifies potential therapeutic targets for cancer treatment.See related article by Liu et al., p. 1913.

Stearoyl-CoA Desaturase 1 Protects Ovarian Cancer Cells from Ferroptotic Cell Death

Activation of ferroptosis, a recently described mechanism of regulated cell death, dramatically inhibits growth of ovarian cancer cells. Given the importance of lipid metabolism in ferroptosis and the key role of lipids in ovarian cancer, we examined the contribution to ferroptosis of stearoyl-CoA desaturase (SCD1, SCD), an enzyme that catalyzes the rate-limiting step in monounsaturated fatty acid synthesis in ovarian cancer cells. SCD1 was highly expressed in ovarian cancer tissue, cell lines, and a genetic model of ovarian cancer stem cells. Inhibition of SCD1 induced lipid oxidation and cell death. Conversely, overexpression of SCD or exogenous administration of its C16:1 and C18:1 products, palmitoleic acid or oleate, protected cells from death. Inhibition of SCD1 induced both ferroptosis and apoptosis. Inhibition of SCD1 decreased CoQ₁₀, an endogenous membrane antioxidant whose depletion has been linked to ferroptosis, while concomitantly decreasing unsaturated fatty acyl chains in membrane phospholipids and increasing long-chain saturated ceramides, changes previously linked to apoptosis. Simultaneous triggering of two death pathways suggests SCD1 inhibition may be an effective component of antitumor therapy, because overcoming this dual mechanism of cell death may present a significant barrier to the emergence of drug resistance. Supporting this concept, we observed that inhibition of SCD1 significantly potentiated the antitumor effect of ferroptosis inducers in both ovarian cancer cell lines and a mouse orthotopic xenograft model. Our results suggest that the use of combined treatment with SCD1 inhibitors and ferroptosis inducers may provide a new therapeutic strategy for patients with ovarian cancer. SIGNIFICANCE: The combination of SCD1 inhibitors and ferroptosis inducers may provide a new therapeutic strategy for the treatment of ovarian cancer patients.See related commentary by Carbone and Melino, p. 5149.

Ferroptosis at the crossroads of cancer-acquired drug resistance and immune evasion

Ferroptosis is a recently recognized cell death modality that is morphologically, biochemically and genetically distinct from other forms of cell death and that has emerged to play an important role in cancer biology. Recent discoveries have highlighted the metabolic plasticity of cancer cells and have provided intriguing insights into how metabolic rewiring is a critical event for the persistence, dedifferentiation and expansion of cancer cells. In some cases, this metabolic reprogramming has been linked to an acquired sensitivity to ferroptosis, thus opening up new opportunities to treat therapy-insensitive tumours. However, it is not yet clear what metabolic determinants are critical for therapeutic resistance and evasion of immune surveillance. Therefore, a better understanding of the processes that regulate ferroptosis sensitivity should ultimately aid in the discovery of novel therapeutic strategies to improve cancer treatment. In this Perspectives article, we provide an overview of the known mechanisms that regulate sensitivity to ferroptosis in cancer cells and how the modulation of metabolic pathways controlling ferroptosis might reshape the tumour niche, leading to an immunosuppressive microenvironment that promotes tumour growth and progression.

Epigenetic regulation of ferroptosis by H2B monoubiquitination and p53

Monoubiquitination of histone H2B on lysine 120 (H2Bub1) is an epigenetic mark generally associated with transcriptional activation, yet the global functions of H2Bub1 remain poorly understood. Ferroptosis is a form of non-apoptotic cell death characterized by the iron-dependent overproduction of lipid hydroperoxides, which can be inhibited by the antioxidant activity of the solute carrier family member 11 (SLC7A11/xCT), a component of the cystine/glutamate antiporter. Whether nuclear events participate in the regulation of ferroptosis is largely unknown. Here, we show that the levels of H2Bub1 are decreased during erastin-induced ferroptosis and that loss of H2Bub1 increases the cellular sensitivity to ferroptosis. H2Bub1 epigenetically activates the expression of SLC7A11. Additionally, we show that the tumor suppressor p53 negatively regulates H2Bub1 levels independently of p53's transcription factor activity by promoting the nuclear translocation of the deubiquitinase USP7. Moreover, our studies reveal that p53 decreases H2Bub1 occupancy on the SLC7A11 gene regulatory region and represses the expression of SLC7A11 during erastin treatment. These data not only suggest a noncanonical role of p53 in chromatin regulation but also link p53 to ferroptosis via an H2Bub1-mediated epigenetic pathway. Overall, our work uncovers a previously unappreciated epigenetic mechanism for the regulation of ferroptosis.

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.

BAP1 in solid tumors

One of the most attractive cancer-related genes under investigation is BAP1. Reasons of this growing interest are related to the wide spectrum of pathways directly or indirectly modulated by this gene and shared by several solid tumors. Programmed cell-death, cell metabolisms, immune cells development, ferroptosis and defects in DNA damage response are only some of the multitude of processes depending on BAP1. Loss of this gene seems to occur in different times of tumor history. Moreover, times of BAP1 loss strongly diverge among primary tumors suggesting the presence of several and different triggering factors. Regardless of when it happens, BAP1 loss usually results in prognosis worsening and in the acquisition of more aggressive clinical features by cancer cells.

Probing the Tumor Suppressor Function of BAP1 in CRISPR-Engineered Human Liver Organoids

The deubiquitinating enzyme BAP1 is a tumor suppressor, among others involved in cholangiocarcinoma. BAP1 has many proposed molecular targets, while its Drosophila homolog is known to deubiquitinate histone H2AK119. We introduce BAP1 loss-of-function by CRISPR/Cas9 in normal human cholangiocyte organoids. We find that BAP1 controls the expression of junctional and cytoskeleton components by regulating chromatin accessibility. Consequently, we observe loss of multiple epithelial characteristics while motility increases. Importantly, restoring the catalytic activity of BAP1 in the nucleus rescues these cellular and molecular changes. We engineer human liver organoids to combine four common cholangiocarcinoma mutations (TP53, PTEN, SMAD4, and NF1). In this genetic background, BAP1 loss results in acquisition of malignant features upon xenotransplantation. Thus, control of epithelial identity through the regulation of chromatin accessibility appears to be a key aspect of BAP1's tumor suppressor function. Organoid technology combined with CRISPR/Cas9 provides an experimental platform for mechanistic studies of cancer gene function in a human context.

The Non-Essential Amino Acid Cysteine Becomes Essential for Tumor Proliferation and Survival

The non-essential amino acid cysteine is used within cells for multiple processes that rely on the chemistry of its thiol group. Under physiological conditions, many non-transformed tissues rely on glutathione, circulating cysteine, and the de novo cysteine synthesis (transsulfuration) pathway as sources of intracellular cysteine to support cellular processes. In contrast, many cancers require exogeneous cystine for proliferation and viability. Herein, we review how the cystine transporter, xCT, and exogenous cystine fuel cancer cell proliferation and the mechanisms that regulate xCT expression and activity. Further, we discuss the potential contribution of additional sources of cysteine to the cysteine pool and what is known about the essentiality of these processes in cancer cells. Finally, we discuss whether cyst(e)ine dependency and associated metabolic alterations represent therapeutically targetable metabolic vulnerabilities.

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.

Cystine/glutamate antiporter xCT (SLC7A11) facilitates oncogenic RAS transformation by preserving intracellular redox balance

RAS genes are among the most mutated proto-oncogenes in human cancer. The mechanisms supporting RAS transformation are not fully understood, particularly regarding the relative contributions of oxidant versus antioxidant pathways. Here, we report that the cystine/glutamate transporter xCT is essential for RAS-induced tumorigenicity by enhancing antioxidant glutathione synthesis. Our findings uncover that RAS controls xCT transcription by downstream activation of ETS-1 to synergize with ATF4. This has clinical relevance since xCT expression is upregulated in human cancers exhibiting an activated RAS pathway. Therefore, oncogenic RAS transformation is supported by induction of an antioxidant program, highlighting xCT as a potential vulnerability for therapeutic targeting.

The RAS family of proto-oncogenes are among the most commonly mutated genes in human cancers and predict poor clinical outcome. Several mechanisms underlying oncogenic RAS transformation are well documented, including constitutive signaling through the RAF-MEK-ERK proproliferative pathway as well as the PI3K-AKT prosurvival pathway. Notably, control of redox balance has also been proposed to contribute to RAS transformation. However, how homeostasis between reactive oxygen species (ROS) and antioxidants, which have opposing effects in the cell, ultimately influence RAS-mediated transformation and tumor progression is still a matter of debate and the mechanisms involved have not been fully elucidated. Here, we show that oncogenic KRAS protects fibroblasts from oxidative stress by enhancing intracellular GSH levels. Using a whole transcriptome approach, we discovered that this is attributable to transcriptional up-regulation of xCT, the gene encoding the cystine/glutamate antiporter. This is in line with the function of xCT, which mediates the uptake of cystine, a precursor for GSH biosynthesis. Moreover, our results reveal that the ETS-1 transcription factor downstream of the RAS-RAF-MEK-ERK signaling cascade directly transactivates the xCT promoter in synergy with the ATF4 endoplasmic reticulum stress-associated transcription factor. Strikingly, xCT was found to be essential for oncogenic KRAS-mediated transformation in vitro and in vivo by mitigating oxidative stress, as knockdown of xCT strongly impaired growth of tumor xenografts established from KRAS-transformed cells. Overall, this study uncovers a mechanism by which oncogenic RAS preserves intracellular redox balance and identifies an unexpected role for xCT in supporting RAS-induced transformation and tumorigenicity.

Ferritinophagy is required for the induction of ferroptosis by the bromodomain protein BRD4 inhibitor (+)-JQ1 in cancer cells

(+)-JQ1 is an inhibitor of the tumor-driver bromodomain protein BRD4 and produces satisfactory effects because it efficiently increases apoptosis. Ferroptosis is an oxidative cell death program differing from apoptosis. Ferroptosis is characterized by high levels of iron and reactive oxygen species and has been confirmed to suppress tumor growth. In this study, BRD4 expression in cancer and its influence on the prognosis of cancer patients were analyzed using data from public databases. In addition, the effect of the BRD4 inhibitor (+)-JQ1 on ferroptosis was investigated via a series of in vitro assays. A nude mouse model was used to evaluate the function of (+)-JQ1 in ferroptosis in vivo. The potential mechanisms by which (+)-JQ1 regulates ferroptosis were explored. The results showed that BRD4 expression levels were higher in cancer tissues than in normal tissues and were related to poor prognosis in cancer patients. Furthermore, ferroptosis was induced under (+)-JQ1 treatment and BRD4 knockdown, indicating that (+)-JQ1 induces ferroptosis via BRD4 inhibition. Moreover, the anticancer effect of (+)-JQ1 was enhanced by ferroptosis inducers. Further studies confirmed that (+)-JQ1 induced ferroptosis via ferritinophagy, which featured autophagy enhancement by (+)-JQ1 and increased iron levels. Subsequently, the reactive oxygen species levels were increased by iron via the Fenton reaction, leading to ferroptosis. In addition, expression of the ferroptosis-associated genes GPX4, SLC7A11, and SLC3A2 was downregulated under (+)-JQ1 treatment and BRD4 knockdown, indicating that (+)-JQ1 may regulate ferroptosis by controlling the expression of ferroptosis-associated genes regulated by BRD4. Finally, (+)-JQ1 regulated ferritinophagy and the expression of ferroptosis-associated genes via epigenetic inhibition of BRD4 by suppressing the expression of the histone methyltransferase G9a or enhancing the expression of the histone deacetylase SIRT1. In summary, the BRD4 inhibitor (+)-JQ1 induces ferroptosis via ferritinophagy or the regulation of ferroptosis-associated genes through epigenetic repression of BRD4.

ALOX12 is required for p53-mediated tumour suppression through a distinct ferroptosis pathway

It is well established that ferroptosis is primarily controlled by glutathione peroxidase 4 (GPX4). Surprisingly, we observed that p53 activation modulates ferroptotic responses without apparent effects on GPX4 function. Instead, ALOX12 inactivation diminishes p53-mediated ferroptosis induced by ROS stress and abrogates p53-dependent inhibition of tumor growth in xenograft models, suggesting that ALOX12 is critical for p53-mediated ferroptosis. The ALOX12 gene resides on human chromosome 17p13.1, a hot spot of monoallelic deletion in human cancers. Loss of one ALOX12 allele is sufficient to accelerate tumorigenesis in Eμ-Myc lymphoma models. Moreover, ALOX12 missense mutations from human cancers abrogate its ability to oxygenate polyunsaturated fatty acids and to induce p53-mediated ferroptosis. Notably, ALOX12 is dispensable for ferroptosis induced by erastin or GPX4 inhibitors; conversely, ACSL4 is required for ferroptosis upon GPX4 inhibition but dispensable for p53-mediated ferroptosis. Thus, our study identifies an ALOX12-mediated, ACSL4-independent ferroptosis pathway that is critical for p53-dependent tumor suppression.

Regulation of H2A ubiquitination and SLC7A11 expression by BAP1 and PRC1

SLC7A11 (or xCT) imports extracellular cystine into cells to promote glutathione synthesis, thus inhibiting ferroptosis. SLC7A11 expression is tightly controlled in normal cells and its dysregulation results in aberrant expression of SLC7A11 in human cancers. We recently discovered that tumor suppressor BAP1, a H2A deubiquitinase, represses SLC7A11 expression by reducing H2A ubiquitination (H2Aub) on the SLC7A11 promoter. BAP1 inactivation in cancer cells leads to SLC7A11 de-repression, ferroptosis resistance, and tumor development. Here we show that BAP1 promotes ferroptosis induced by class I ferroptosis inducer (FIN) erastin but not by class II FIN RSL3, further supporting that BAP1 regulates ferroptosis through SLC7A11. In addition, we studied how BAP1 coordinates with other transcription factors to regulate SLC7A11 expression and show that BAP1-mediated SLC7A11 repression does not require NRF2 and ATF4 transcription factors. Finally, we show that, while BAP1 decreases whereas PRC1 (a major H2Aub ubiquitin ligase) increases H2Aub binding on the SLC7A11 promoter, both BAP1 and PRC1 represses SLC7A11 expression, suggesting that a dynamic regulation of H2Aub is important for SLC7A11 repression. Together, our data provide additional insights on epigenetic regulation of SLC7A11 expression in cancer cells.

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 Deubiquitylase OTUB1 Mediates Ferroptosis via Stabilization of SLC7A11

Although cell-cycle arrest, senescence, and apoptosis are established mechanisms of tumor suppression, accumulating evidence reveals that ferroptosis, an iron-dependent, nonapoptotic form of cell death, represents a new regulatory pathway in suppressing tumor development. Ferroptosis is triggered by lipid peroxidation and is tightly regulated by SLC7A11, a key component of the cystine-glutamate antiporter. Although many studies demonstrate the importance of transcriptional regulation of SLC7A11 in ferroptotic responses, it remains largely unknown how the stability of SLC7A11 is controlled in human cancers. In this study, we utilized biochemial purification to identify the ubiquitin hydrolase OTUB1 as a key factor in modulating SLC7A11 stability. OTUB1 directly interacted with and stabilized SLC7A11; conversely, OTUB1 knockdown diminished SLC7A11 levels in cancer cells. OTUB1 was overexpressed in human cancers, and inactivation of OTUB1 destabilized SLC7A11 and led to growth suppression of tumor xenografts in mice, which was associated with reduced activation of ferroptosis. Notably, overexpression of the cancer stem cell marker CD44 enhanced the stability of SLC7A11 by promoting the interaction between SLC7A11 and OTUB1; depletion of CD44 partially abrogated this interaction. CD44 expression suppressed ferroptosis in cancer cells in an OTUB1-dependent manner. Together, these results show that OTUB1 plays an essential role in controlling the stability of SLC7A11 and the CD44-mediated effects on ferroptosis in human cancers. SIGNIFICANCE: This study identifies OTUB1 as a key regulator of ferroptosis and implicates it as a potential target in cancer therapy.See related commentary by Gan, p. 1749.

BAP1 suppresses tumor development by inducing ferroptosis upon SLC7A11 repression

The tumor suppressor BRCA1-associated protein 1 (BAP1) is a deubiquitinase that removes histone 2A ubiquitination. How BAP1 suppresses tumor development remains elusive. Our recent study identified the cystine transporter solute carrier family 7 member 11 (SLC7A11) as a critical BAP1 target, and showed that BAP1 promotes ferroptosis (a non-apoptotic cell death) through repressing SLC7A11 expression, resulting in tumor suppression.