Elaborate cooperation of poly(rC)-binding proteins 1/2 and glutathione in ferroptosis induced by plasma-activated Ringer's lactate.

Reactive species are involved in various aspects of neoplastic diseases, including carcinogenesis, cancer-specific metabolism and therapeutics. Non-thermal plasma (NTP) can directly provide reactive species, by integrating atmospheric and interjacent molecules as substrates, to represent a handy strategy to load oxidative stress in situ. NTP causes apoptosis and/or ferroptosis specifically in cancer cells of various types. Plasma-activated Ringer's lactate (PAL) is another modality at the preclinical stage as cancer therapeutics, based on more stable reactive species. PAL specifically kills malignant mesothelioma (MM) cells, employing lysosomal ·NO as a switch from autophagy to ferroptosis. However, the entire molecular mechanisms have not been elucidated yet. Here we studied cytosolic iron regulations in MM and other cancer cells in response to PAL exposure. We discovered that cells with higher catalytic Fe(II) are more susceptible to PAL-induced ferroptosis. PAL caused a cytosolic catalytic Fe(II)-associated pathology through iron chaperones, poly (rC)-binding proteins (PCBP)1/2, inducing a disturbance in glutathione-regulated iron homeostasis. PCBP1/NCOA4-mediated ferritinophagy started at a later phase, further increasing cytosolic catalytic Fe(II), ending in ferroptosis. In contrast, PCBP2 after PAL exposure contributed to iron loading to mitochondria, leading to mitochondrial dysfunction. Therapeutic effect of PAL was successfully applied to an orthotopic MM xenograft model in mice. In conclusion, PAL can selectively sensitize MM cells to ferroptosis by remodeling cytoplasmic iron homeostasis, where glutathione and PCBPs play distinct roles, resulting in lethal ferritinophagy and mitochondrial dysfunction. Our findings indicate the clinical application of PAL as a ferroptosis-inducer and the potential of PCBPs as novel targets in cancer therapeutics.

Environmental impact on carcinogenesis under BRCA1 haploinsufficiency.

Cancer is the primary cause of human mortality in Japan since 1981. Although numerous novel therapies have been developed and applied in clinics, the number of deaths from cancer is still increasing worldwide. It is time to consider the strategy of cancer prevention more seriously. Here we propose a hypothesis that cancer can be side effects of long time-use of iron and oxygen and that carcinogenesis is an evolution-like cellular events to obtain "iron addiction with ferroptosis-resistance" where genes and environment interact each other. Among the recognized genetic risk factors for carcinogenesis, we here focus on BRCA1 tumor suppressor gene and how environmental factors, including daily life exposure and diets, may impact toward carcinogenesis under BRCA1 haploinsufficiency. Although mice models of BRCA1 mutants have not been successful for decades in generating phenotype mimicking the human counterparts, a rat model of BRCA1 mutant was recently established that reasonably mimics the human phenotype. Two distinct categories of oxidative stress, one by radiation and one by iron-catalyzed Fenton reaction, promoted carcinogenesis in Brca1 rat mutants. Furthermore, mitochondrial damage followed by alteration of iron metabolism finally resulted in ferroptosis-resistance of target cells in carcinogenesis. These suggest a possibility that cancer prevention by active pharmacological intervention may be possible for BRCA1 mutants to increase the quality of their life rather than preventive mastectomy and/or oophorectomy.

BRCA1 haploinsufficiency impairs iron metabolism to promote chrysotile-induced mesothelioma via ferroptosis resistance.

Malignant mesothelioma (MM) is still a social burden associated with asbestos exposure. Local iron accumulation thereby represents the major pathogenesis, followed by oxidative DNA strand breaks and genomic alterations in the mesothelium. BRCA1 is a critical component of homologous recombination repair directed to DNA double-stranded breaks, whereas BRCA1 germline mutation is an established risk for breast/ovarian cancer, its role in MM development remains to be elucidated. Murine Brca1 mutant models so far have not reproduced human phenotypes. However, a rat Brca1 mutant model (Mut; L63X/+ ) recently reproduced them at least partially. Here we describe the differential induction of MM in Brca1 mutant rats by intraperitoneal injection of chrysotile or crocidolite. Only Mut males injected with chrysotile revealed a promotional effect on mesothelial carcinogenesis in comparison with wild-type and/or females, with all the MMs Brca1 haploinsufficient. Array-based comparative genomic hybridization of MMs disclosed a greater extent of chromosomal deletions in Brca1 mutants, including Cdkn2a/2b accompanied by Tfr2 amplification, in comparison with wild-type tumors. Mutant MMs indicated iron metabolism dysregulation, such as an increase in catalytic Fe(II) and Ki67-index as well as a decrease in Fe(III) and ferritin expression. Simultaneously, mutant MMs revealed ferroptosis resistance by upregulation of Slc7A11 and Gpx4. At an early carcinogenic stage of 4 weeks, induced Brca1 expression in mesothelial cells was significantly suppressed in chrysotile/Mut in comparison with crocidolite/Mut, whereas significant preference to iron with a decrease in Fe(III) has been already established. In conclusion, chrysotile exposure can be a higher risk for MM in BRCA1 mutant males, considering the rat results.

Iron as spirit of life to share under monopoly.

Any independent life requires iron to survive. Whereas iron deficiency causes oxygen insufficiency, excess iron is a risk for cancer, generating a double-edged sword. Iron metabolism is strictly regulated via specific systems, including iron-responsive element (IRE)/iron regulatory proteins (IRPs) and the corresponding ubiquitin ligase FBXL5. Here we briefly reflect the history of bioiron research and describe major recent advancements. Ferroptosis, a newly coined Fe(II)-dependent regulated necrosis, is providing huge impact on science. Carcinogenesis is a process to acquire ferroptosis-resistance and ferroptosis is preferred in cancer therapy due to immunogenicity. Poly(rC)-binding proteins 1/2 (PCBP1/2) were identified as major cytosolic Fe(II) chaperone proteins. The mechanism how cells retrieve stored iron in ferritin cores was unraveled as ferritinophagy, a form of autophagy. Of note, ferroptosis may exploit ferritinophagy during the progression. Recently, we discovered that cellular ferritin secretion is through extracellular vesicles (EVs) escorted by CD63 under the regulation of IRE/IRP system. Furthermore, this process was abused in asbestos-induced mesothelial carcinogenesis. In summary, cellular iron metabolism is tightly regulated by multi-system organizations as surplus iron is shared through ferritin in EVs among neighbor and distant cells in need. However, various noxious stimuli dramatically promote cellular iron uptake/storage, which may result in ferroptosis.

BRCA1 haploinsufficiency promotes chromosomal amplification under Fenton reaction-based carcinogenesis through ferroptosis-resistance.

Germline-mutation in BRCA1 tumor suppressor gene is an established risk for carcinogenesis not only in females but also in males. Deficiency in the repair of DNA double-strand breaks is hypothesized as a responsible mechanism for carcinogenesis. However, supporting data is insufficient both in the mutation spectra of cancers in the patients with BRCA1 germline-mutation and in murine knockout/knock-in models of Brca1 haploinsufficiency. Furthermore, information on the driving force toward carcinogenesis in BRCA1 mutation carriers is lacking. Here we applied Fenton reaction-based renal carcinogenesis to a rat heterozygously knockout model of BRCA1 haploinsufficiency (mutant [MUT] model; L63X/+). Rat MUT model revealed significant promotion of renal cell carcinoma (RCC) induced by ferric nitrilotriacetate (Fe-NTA). Array-based comparative genome hybridization of the RCCs identified significant increase in chromosomal amplification, syntenic to those in breast cancers of BRCA1 mutation carriers, including c-Myc, in comparison to those in the wild-type. Subacute-phase analysis of the kidney after repeated Fe-NTA treatment in the MUT model revealed dysregulated iron metabolism with mitochondrial malfunction assessed by expression microarray and electron microscopy, leading to renal tubular proliferation with iron overload. In conclusion, we for the first time demonstrate that biallelic wild-type BRCA1 provides more robust protection for mitochondrial metabolism under iron-catalyzed oxidative stress, preventing the emergence of neoplastic cells with chromosomal amplification. Our results suggest that oxidative stress via excess iron is a major driving force for carcinogenesis in BRCA1 haploinsufficiency, which can be a target for cancer prevention and therapeutics.

Ferroptosis resistance determines high susceptibility of murine A/J strain to iron-induced renal carcinogenesis.

Cancer susceptibility is a critical factor in the understanding of carcinogenesis. Intraperitoneal (i.p.) injection of an iron chelate, ferric nitrilotriacetate (Fe-NTA), produces hydroxyl radicals via Fenton reaction to induce ferroptosis in renal proximal tubules. Rats or mice subjected to repeated i.p. injections of Fe-NTA develop renal cell carcinoma (RCC). To elucidate the molecular mechanisms that cause susceptibility to renal carcinogenesis, we first established an inter-strain difference in the susceptibility to Fe-NTA-induced renal carcinogenesis in mice. Based on a previous observation of a low incidence of RCC with this model in C57BL/6J strain mice, we investigated A/J strain mice here, which demonstrated significantly higher susceptibility to Fe-NTA-induced renal carcinogenesis. Homozygous deletion of the Cdkn2a/2b tumor suppressor locus was detected for the first time in A/J strain mice. Focusing on ferroptosis and iron metabolism, we explored the mechanisms involved that lead to the difference in RCC development. We compared the protective responses in the kidney of A/J and C57BL/6J strains after Fe-NTA treatment. After 3-week Fe-NTA treatment, A/J mice maintained higher levels of expression of glutathione peroxidase 4 and xCT (SLC7A11), leading to a lower level of lipid peroxidation. Simultaneously, A/J mice had decreased expression of transferrin receptor and increased expression of ferritin to greater degrees than C57BL/6 mice. After a single Fe-NTA injection, higher levels of oxidative cell damage and cytosolic catalytic Fe(II) were observed in C57BL/6J mice, accompanied by a greater increase in lipocalin-2. Lipocalin-2 deficiency significantly decreased oxidative renal damage. Our results suggest that a genetic trait favoring ferroptosis resistance contributes to high susceptibility to Fe-NTA-induced RCC in A/J strain.

Prognostic significance of the MDM2/HMGA2 ratio and histological tumor grade in dedifferentiated liposarcoma.

Dedifferentiated liposarcoma (DDLPS) is a relatively common soft tissue sarcoma that results from the progression of well-differentiated liposarcoma (WDLPS). This study aimed to investigate the progression process and to clarify the pathological and genetic factors related to poor prognosis in DDLPS. In 32 DDLPS cases and five WDLPS cases, genetic factors were analyzed by custom comparative genomic hybridization (CGH) array, which was designed to densely cover gene regions known to be frequently amplified in WD/DDLPS. The analyses comparing primary and metastatic lesions and those comparing histologically different areas in the same tumor revealed intra-tumoral genetic heterogeneity and progression. According to a prognostic analysis comparing the good-prognosis and the poor-prognosis groups, we selected MDM2 and HMGA2 as candidate genes associated with poor and good prognosis, respectively. The ratios of the amplification or gain levels of MDM2 and HMGA2 expressed in log ratios (log[MDM2/HMGA2] = log[MDM2]-log[HMGA2]) were significantly associated with prognosis. An amplification or gain level of MDM2 that was more than twice that of HMGA2 (MDM2/HMGA2 > 2, log[MDM2/HMGA2] > 1) was strongly related to poor OS (P < .001) and poor distant metastasis-free survival (DMFS) (P < .001). In the pathological analysis of 44 cases of DDLPS, histological tumor grade, cellular atypia, and MDM2 immunoreactivity were related to overall survival (OS), while HMGA2 immunoreactivity tended to be associated with OS. Cellular atypia was also associated with DMFS. In conclusion, histological grade and MDM2 expression were determined to be prognostically important, and the MDM2/HMGA2 amplification or gain ratio was found to have significant prognostic value by the custom CGH array analysis.

Carcinogenesis as Side Effects of Iron and Oxygen Utilization: From the Unveiled Truth toward Ultimate Bioengineering.

Evolution from the first life on earth to humans took ~3.8 billion years. During the time there have been countless struggles among the species. Mycobacterium tuberculosis was the last major uncontrollable species against the human public health worldwide. After the victory with antibiotics, cancer has become the leading cause of death since 1981 in Japan. Considering that life inevitably depends on ceaseless electron transfers through iron and oxygen, we believe that carcinogenesis is intrinsically unavoidable side effects of using iron and oxygen. Many animal models unequivocally revealed that excess iron is a risk for carcinogenesis. This is supported by a variety of human epidemiological data on cancer risk and prognosis. Cancer is basically a disease of the genome with persistently activated oncogenes and inactivated tumor suppressor genes through which iron addiction with ferroptosis-resistance is maintained. Engineering has made a great advance in the past 50 years. In particular, nanotechnology is distinct in that the size of the engineered molecules is similar to that of our biomolecules. While some nano-molecules are found carcinogenic, there are principles to avoid such carcinogenicity with a smart possibility to use nano-molecules to specifically kill cancer cells. Non-thermal plasma is another modality to fight against cancer.

Novel ovarian endometriosis model causes infertility via iron-mediated oxidative stress in mice.

Ovarian endometriosis (OE) provides women of reproductive age with not only severe menstrual pain but also infertility and an increased risk for ovarian carcinogenesis. Whereas peritoneal endometriosis models have been developed with syngeneic implantation of minced uterine tissue and oncogenic K-ras allele with conditional Pten deletion within ovarian surface epithelium generated preneoplastic endometrial glandular morphology, followed by endometrioid adenocarcinoma, there has been no mouse model of OE similar to human counterparts, applicable to preclinical studies. Here we for the first time established a murine OE model that reveals infertility, and evaluated the involvement of iron catalyzed oxidative stress in the pathogenesis. Minced uterine tissue from female mice was implanted on ovarian surface of syngeneic mice after bursectomy to induce OE. Ectopic growth of endometrium was observed in association with ovary 4 weeks after implantation in 85.7% (12/14) of the operated mice with our protocol. Endometriotic lesions involved intestine, pancreas and peritoneal wall. Fibrosis around the ovary was prominent and increased time-dependently in the OE group. Iron accumulation was significantly increased in the OE group, leading to oxidative stress in each stage of the follicles as evaluated by 4-hydroxy-2-nonenal-modified proteins and 8-hydroxy-2'-deoxyguanosine. Expression of follicle stimulating hormone receptor in the follicles revealed a significant decrease during pre-antral, antral and pre-ovulatory phases in the OE group. Finally, the number of pups was significantly reduced in the OE group in comparison to the controls. This model affords an opportunity to evaluate agents or procedures to counteract ovarian endometriosis in the preclinical settings.

Asbestos conceives Fe(II)-dependent mutagenic stromal milieu through ceaseless macrophage ferroptosis and ß-catenin induction in mesothelium.

Asbestos is still a social burden worldwide as a carcinogen causing malignant mesothelioma. Whereas recent studies suggest that local iron reduction is a preventive strategy against carcinogenesis, little is known regarding the cellular and molecular mechanisms surrounding excess iron. Here by differentially using high-risk and low-risk asbestos fibers (crocidolite and anthophyllite, respectively), we identified asbestos-induced mutagenic milieu for mesothelial cells. Rat and cell experiments revealed that phagocytosis of asbestos by macrophages results in their distinctive necrotic death; initially lysosome-depenent cell death and later ferroptosis, which increase intra- and extra-cellular catalytic Fe(II). DNA damage in mesothelial cells, as assessed by 8-hydroxy-2'-deoxyguanosine and γ-H2AX, increased after crocidolite exposure during regeneration accompanied by ß-catenin activation. Conversely, ß-catenin overexpression in mesothelial cells induced higher intracellular catalytic Fe(II) with increased G2/M cell-cycle fraction, when p16INK4A genomic loci localized more peripherally in the nucleus. Mesothelial cells after challenge of H2O2 under ß-catenin overexpression presented low p16INK4A expression with a high incidence of deletion in p16INK4A locus. Thus, crocidolite generated catalytic Fe(II)-rich mutagenic environment for mesothelial cells by necrotizing macrophages with lysosomal cell death and ferroptosis. These results suggest novel molecular strategies to prevent mesothelial carcinogenesis after asbestos exposure.

Overexpression of miR-199/214 is a distinctive feature of iron-induced and asbestos-induced sarcomatoid mesothelioma in rats.

Malignant mesothelioma (MM) is one of the most lethal tumors in humans. The onset of MM is linked to exposure to asbestos, which generates reactive oxygen species (ROS). ROS are believed to be derived from the frustrated phagocytosis and the iron in asbestos. To explore the pathogenesis of MM, peritoneal MM was induced in rats by the repeated intraperitoneal injection of iron saccharate and nitrilotriacetate. In the present study, we used microarray techniques to screen the microRNA (miR) expression profiles of these MM. We observed that the histological subtype impacted the hierarchical clustering of miR expression profiles and determined that miR-199/214 is a distinctive feature of iron saccharate-induced sarcomatoid mesothelioma (SM). Twist1, a transcriptional regulator of the epithelial-mesenchymal transition, has been shown to activate miR-199/214 transcription; thus, the expression level of Twist1 was examined in iron-induced and asbestos-induced mesotheliomas in rats. Twist1 was exclusively expressed in iron saccharate-induced SM but not in the epithelioid subtype. The Twist1-miR-199/214 axis is activated in iron saccharate-induced and asbestos-induced SM. The expression levels of miR-214 and Twist1 were correlated in an asbestos-induced MM cell line, suggesting that the Twist1-miR-199/214 axis is preserved. MeT5A, an immortalized human mesothelial cell line, was used for the functional analysis of miR. The overexpression of miR-199/214 promoted cellular proliferation, mobility and phosphorylation of Akt and ERK in MeT5A cells. These results indicate that miR-199/214 may affect the aggressive biological behavior of SM.

Mth1 deficiency provides longer survival upon intraperitoneal crocidolite injection in female mice.

Exposure to asbestos fiber is central to mesothelial carcinogenesis. Recent sequencing studies on human and rodent malignant mesothelioma (MM) revealed frequently mutated genes, including CDKN2A, BAP1 and NF2. Crocidolite directly or indirectly catalyses the generation of hydroxyl radicals, which appears to be the major driving force for mesothelial mutations. DNA base modification is an oxidative DNA damage mechanism, where 8-hydroxy-2'-deoxyguanosine (8-OHdG) is the most abundant modification both physiologically and pathologically. Multiple distinct mechanisms work together to decrease the genomic level of 8-OHdG through the enzymatic activities of Mutyh, Ogg1 and Mth1. Knockout of one or multiple enzymes is not lethal but increases the incidence of tumors. Here, we used single knockout (KO) mice to test whether the deficiency of these three genes affects the incidence and prognosis of asbestos-induced MM. Intraperitoneal injection of 3 mg crocidolite induced MM at a fraction of 14.8% (4/27) in Mth1 KO, 41.4% (12/29) in Mutyh KO and 24.0% (6/25) in Ogg1 KO mice, whereas 31.7% (20/63) induction was observed in C57BL/6 wild-type (Wt) mice. The lifespan of female Mth1 KO mice was longer than that of female Wt mice (p = 0.0468). Whole genome scanning of MM with array-based comparative genomic hybridization revealed rare genomic alterations compared to MM in rats and humans. These results indicate that neither Mutyh deficiency nor Ogg1 deficiency promotes crocidolite-induced MM in mice, but the sanitizing nucleotide pool with Mth1 is advantageous in crocidolite-induced mesothelial carcinogenesis.

Frequent homozygous deletion of Cdkn2a/2b in tremolite-induced malignant mesothelioma in rats.

The onset of malignant mesothelioma (MM) is linked to exposure to asbestos fibers. Asbestos fibers are classified as serpentine (chrysotile) or amphibole, which includes the crocidolite, amosite, anthophyllite, tremolite, and actinolite types. Although few studies have been undertaken, anthophyllite has been shown to be associated with mesothelioma, and tremolite, a contaminant in talc and chrysotile, is a risk factor for carcinogenicity. Here, after characterizing the length and width of these fibers by scanning electron microscopy, we explored the cytotoxicity induced by tremolite and anthophyllite in cells from an immortalized human mesothelial cell line (MeT5A), murine macrophages (RAW264.7), and in a rat model. Tremolite and short anthophyllite fibers were phagocytosed and localized to vacuoles, whereas the long anthophyllite fibers were caught on the pseudopod of the MeT5A and Raw 264.7 cells, according to transmission electron microscopy. The results from a 2-day time-lapse study revealed that tremolite was engulfed and damaged the MeT5A and RAW264.7 cells, but anthophyllite was not cytotoxic to these cells. Intraperitoneal injection of tremolite in rats induced diffuse serosal thickening, whereas anthophyllite formed focal fibrosis and granulomas on peritoneal serosal surfaces. Furthermore, the loss of Cdkn2a/2b, which are the most frequently lost foci in human MM, were observed in 8 cases of rat MM (homozygous deletion [5/8] and loss of heterozygosity [3/8]) by array-based comparative genomic hybridization techniques. These results indicate that tremolite initiates mesothelial injury and persistently frustrates phagocytes, causing subsequent peritoneal fibrosis and MM. The possible mechanisms of carcinogenicity based on fiber diameter/length are discussed.

Expression of P-REX2a is associated with poor prognosis in endometrial malignancies.

P-REX2a is a PTEN inhibitor that also activates Rac 1. No associations with P-REX2a and human endometrial cancers have been reported to date. In this study, we immunohistochemically analyzed 155 uterine endometrial malignancies for P-REX2a expression. The P-REX2a-positive tumors displayed worse prognosis independent of PTEN expression. Then, we transduced either P-REX2a expression vector or short hairpin RNAs targeting P-REX2a into 2 uterine endometrioid carcinoma cell lines, OMC-2 and JHUEM-14. Ectopic expression of P-REX2a led to increased cell proliferation only in the PTEN-expressing OMC-2 cells but did not show any change in the PTEN-negative JHUEM-14 cells or the P-REX2a-knockdown cells. Induction of P-REX2a increased and knockdown of P-REX2a decreased cell migration in both cell lines. Then, we performed expression microarray analysis using these cells, and pathway analysis revealed that the expression of members of the GPCR downstream pathway displayed the most significant changes induced by the knockdown of P-REX2a. Immunohistochemical analysis revealed that Vav1, a member of the GPCR downstream pathway, was expressed in 139 of the 155 endometrial tumors, and the expression levels of Vav1 and P-REX2a showed a positive correlation (r = 0.44, p < 0.001). In conclusion, P-REX2a enhanced cell motility via the GPCR downstream pathway independently of PTEN leading to progression of uterine endometrioid malignancies and poor prognosis of the patients.

Superiority of rat over murine model for studies on the evolution of cancer genome.

Evolution of the species and carcinogenesis are similar in that genomic alterations are the key events. Oxidative stress derived from various etiologies is one of the major causes of carcinogenesis by inducing mutations in the genome. Persistent oxidative stress in the renal proximal tubules through Fenton reaction catalysed by ferric nitrilotriacetate (Fe-NTA) generates renal cell carcinoma (RCC) in mice and rats. Here, in order to observe the species difference in oxidative stress-induced carcinogenesis and to obtain an insight regarding the characteristics of each species, we compared the genomic alterations using array-based comparative genome hybridisation among RCCs in Mutyh knockout/wild-type mice (C57BL/6 background) induced by Fe-NTA, RCCs in F1 hybrids of Brown-Norway/Fischer-344 wild-type rats and clear cell renal cell carcinoma (CCRCC)/papillary renal cell carcinoma (PRCC) of humans. The average deviated fraction of genomic segments, either loss or gain, from the standard biallelic position was 0.220 (N = 4), 0.304 (N = 11), 0.283 (N = 12), and 0.261 (N = 5), respectively, for murine RCC, rat RCC, human CCRCC, and human PRCC. Notably, gain/loss ratio was remarkably different as indicated by 0.0820, 0.161, 0.821, and 4.44, respectively. These data suggest that higher species require more genomic alterations with amplification preference for renal carcinogenesis. Further studies are necessary to identify the molecular mechanisms whether the present results depend on cellular functional differences, etiology of carcinogenesis or the target cells in carcinogenesis.

Fenton reaction-induced renal carcinogenesis in Mutyh-deficient mice exhibits less chromosomal aberrations than the rat model.

Oxidative stress including iron excess has been associated with carcinogenesis. The level of 8-oxoguanine, a major oxidatively modified base in DNA, is maintained very low by three distinct enzymes, encoded by OGG1, MUTYH and MTH1. Germline biallelic inactivation of MUTYH represents a familial cancer syndrome called MUTYH-associated polyposis. Here, we used Mutyh-deficient mice to evaluate renal carcinogenesis induced by ferric nitrilotriacetate (Fe-NTA). Although the C57BL/6 background is cancer-resistant, a repeated intraperitoneal administration of Fe-NTA induced a high incidence of renal cell carcinoma (RCC; 26.7%) in Mutyh-deficient mice in comparison to wild-type mice (7.1%). Fe-NTA treatment also induced renal malignant lymphoma, which did not occur without the Fe-NTA treatment in both the genotypes. Renal tumor-free survival after Fe-NTA treatment was marginally different (P = 0.157) between the two genotypes. Array-based comparative genome hybridization analyses revealed, in RCC, the loss of heterozygosity in chromosomes 4 and 12 without p16INKA inactivation; these results were confirmed by a methylation analysis and showed no significant difference between the genotypes. Lymphomas showed a preference for genomic amplifications. Dlk1 inactivation by promoter methylation may be involved in carcinogenesis in both tumors. Fe-NTA-induced murine RCCs revealed significantly less genomic aberrations than those in rats, demonstrating a marked species difference.

Iron and thiol redox signaling in cancer: An exquisite balance to escape ferroptosis.

Epidemiological data indicate a constant worldwide increase in cancer mortality, although the age of onset is increasing. Recent accumulation of genomic data on human cancer via next-generation sequencing confirmed that cancer is a disease of genome alteration. In many cancers, the Nrf2 transcription system is activated via mutations either in Nrf2 or Keap1 ubiquitin ligase, leading to persistent activation of the genes with antioxidative functions. Furthermore, deep sequencing of passenger mutations is clarifying responsible cancer causative agent(s) in each case, including aging, APOBEC activation, smoking and UV. Therefore, it is most likely that oxidative stress is the principal initiating factor in carcinogenesis, with the involvement of two essential molecules for life, iron and oxygen. There is evidence based on epidemiological and animal studies that excess iron is a major risk for carcinogenesis, suggesting the importance of ferroptosis-resistance. Microscopic visualization of catalytic Fe(II) has recently become available. Although catalytic Fe(II) is largely present in lysosomes, proliferating cells harbor catalytic Fe(II) also in the cytosol and mitochondria. Oxidative stress catalyzed by Fe(II) is counteracted by thiol systems at different functional levels. Nitric oxide, carbon monoxide and hydrogen (per)sulfide modulate these reactions. Mitochondria generate not only energy but also heme/iron sulfur cluster cofactors and remain mostly dysfunctional in cancer cells, leading to Warburg effects. Cancer cells are under persistent oxidative stress with a delicate balance between catalytic iron and thiols, thereby escaping ferroptosis. Thus, high-dose L-ascorbate and non-thermal plasma as well as glucose/glutamine deprivation may provide additional benefits as cancer therapies over preexisting therapeutics.

Rheostatic CD44 isoform expression and its association with oxidative stress in human malignant mesothelioma.

CD44 exists as a standard (CD44s) isoform and different variant isoforms (CD44v) due to alternative splicing. While the complex nature of these different isoforms has not been fully elucidated, CD44v expression has been shown to exert oncogenic effects by promoting tumor progression, metastasis and resistance of tumor cells to chemotherapy. One of the CD44v isoforms, CD44v8-10, was recently shown to protect cancer cells from oxidative stress by increasing the synthesis of glutathione (GSH). However, data regarding CD44 isoform expression in malignant mesothelioma (MM) are still lacking. Here, we show that most of the MM cell lines express both the CD44s and CD44v isoforms, in contrast to non-tumorigenic mesothelial cells, which express only CD44s. Moreover, we show here that these MM cell lines are positive for CD44 variable exon 9, with CD44v8-10 among the variant isoforms expressed. The expression of CD44 variable exon 9 was found to be statistically associated with NF2 inactivation, a common occurrence in MM. Knockdown of CD44 reduced the protein level of xCT, a cystine transporter, and increased oxidative stress. However, an increase in GSH was also observed and was associated with enhanced chemoresistance in CD44-knockdown cells. Increased GSH was mediated by the Nrf2/AP-1-induced upregulation of GCLC, a subunit of the enzyme catalyzing GSH synthesis. Our results thus suggest that the response to CD44 depletion is cell type-dependent and, in cases such as MM cells, compensatory pathway(s) might be activated rheostatically to account for the loss of CD44 and counteract enhanced oxidative stress.

Urokinase-type plasminogen activator receptor promotes proliferation and invasion with reduced cisplatin sensitivity in malignant mesothelioma.

Malignant mesothelioma (MM) is a rare neoplasm associated with asbestos exposure. The prognosis of MM is poor because it is aggressive and highly resistant to chemotherapy. Using a rat model of asbestos-induced MM, we found elevated urokinase-type plasminogen activator receptor (uPAR; Plaur) expression in rat tissues, which was associated with poor prognosis. The proliferation, migration and invasion of MM cells were suppressed by uPAR knockdown and increased by overexpression experiments, irrespective of urokinase-type plasminogen activator (uPA; Plau) levels. More importantly, we found that uPAR expression is associated with sensitivity to cisplatin in MM through the PI3K/AKT pathway, which was demonstrated with specific inhibitors, LY294002 and Akti-1/2. uPAR knockdown significantly increased sensitivity to cisplatin whereas its overexpression significantly decreased cisplatin sensitivity. Furthermore, sera and tissues from MM patients showed significantly high uPAR levels, which suggested the pathogenic role of uPAR in the tumor biology of human MM. In conclusion, our findings indicate that uPAR levels are associated with malignant characteristics and cisplatin sensitivity of MM. In addition to the potential use of uPAR as a prognostic marker, the combination of uPAR abrogation and cisplatin may reveal a promising therapeutic approach for MM.

[Iron function and carcinogenesis].

Though iron is an essential micronutrient for humans, the excess state is acknowledged to be associated with oncogenesis. For example, iron overload in the liver of the patients with hereditary hemocromatosis highly increases the risk of hepatocellular carcinoma. Also, as to asbestos-related mesothelioma, such kinds of asbestos with a higher iron content are considered to be more carcinogenic. Iron is a useful element, which enables fundamental functions for life such as oxygen carrying and electron transport. However, in the situation where organisms are unable to have good control of it, iron turns into a dangerous element which catalyzes generation of reactive oxygen. In this review, I first outline the relationships between iron and cancer in general, then give an explanation about iron-related animal carcinogenesis models.