Selenite-induced Apoptosis Research Articles

Selenite selectively kills lung fibroblasts to treat bleomycin-induced pulmonary fibrosis

BackgroundInterstitial lung disease (ILD) treatment is a critical unmet need. Selenium is an essential trace element for human life and an antioxidant that activates glutathione, but the gap between its necessity and its toxicity is small and requires special attention. Whether selenium can be used in the treatment of ILD remains unclear. MethodsWe investigated the prophylactic and therapeutic effects of selenite, a selenium derivative, in ILD using a murine model of bleomycin-induced idiopathic pulmonary fibrosis (IPF). We further elucidated the underlying mechanism using in vitro cell models and examined their relevance in human tissue specimens. The therapeutic effect of selenite in bleomycin-administered mice was assessed by respiratory function and histochemical changes. Selenite-induced apoptosis and reactive oxygen species (ROS) production in murine lung fibroblasts were measured. ResultsSelenite, administered 1 day (inflammation phase) or 8 days (fibrotic phase) after bleomycin, prevented and treated deterioration of lung function and pulmonary fibrosis in mice. Mechanistically, selenite inhibited the proliferation and induced apoptosis of murine lung fibroblasts after bleomycin treatment both in vitro and in vivo. In addition, selenite upregulated glutathione reductase (GR) and thioredoxin reductase (TrxR) in murine lung fibroblasts, but not in lung epithelial cells, upon bleomycin treatment. GR and TrxR inhibition eliminates the therapeutic effects of selenite. Furthermore, we found that GR and TrxR were upregulated in the human lung fibroblasts of IPF patient samples. ConclusionsSelenite induces ROS production and apoptosis in murine lung fibroblasts through GR and TrxR upregulation, thereby providing a therapeutic effect in bleomycin-induced IPF.

Cytosolic JNK-dependent microtubule reassembly protects Jurkat leukemia cells from selenite-induced apoptosis

BackgroundSelenite at high dosage exhibits great potential in curing tumors. It has been shown that selenite inhibits tumor growth through regulation of microtubule dynamics, however, the exact underlying mechanisms remained to be fully elucidated. Methods & resultsWestern blots were carried out to evaluate expression level of different molecules. Our current study discovered that selenite induced microtubule disassembly, cell cycle arrest and finally resulted in apoptosis in Jurkat leukemia cells, while during this process disassembled tubulins were re-organized after long-term exposure to selenite. Furthermore, JNK was activated in the cytoplasm of selenite-treated Jurkat cells, and inhibition of JNK activity successfully prevented the process of microtubule re-assembly. Moreover, inactivation of JNK further enhanced selenite-induced cell cycle arrest and apoptosis. According to the results from cell counting-8 assay, blockage of microtubule re-assembly by colchicine further inhibited Jurkat cell viability after exposure to selenite. Experiments in a xenograft model also proved that selenite could alter JNK activity, destroy microtubule structure and inhibit cell division in vivo. Moreover, TP53, MAPT and YWHAZ were identified to be three most confident interactors that link JNK to microtubule assembly using PPIs analysis. ConclusionOur study indicated that cytosolic JNK-dependent microtubule re-organization took a protective function during selenite-induced apoptosis, while inhibition of this process would finally enhance the anti-tumor effect of selenite.

Selenite-induced ROS/AMPK/FoxO3a/GABARAPL-1 signaling pathway modulates autophagy that antagonize apoptosis in colorectal cancer cells

Previous studies have shown that selenium possessed chemotherapeutic effect against multiple malignant cancers, inducing diverse stress responses including apoptosis and autophagy. Selenite was previously shown to induce apoptosis and autophagy in colorectal cancer cells. However, the relationship between selenite-induced apoptosis and autophagy was not fully understood. Our results revealed a pro-survival role of selenite-induced autophagy against apoptosis in colorectal cancer cells. Real-time PCR array of autophagy-related genes showed that GABARAPL-1 was significantly upregulated in colorectal cancer cells, which was confirmed by western blot and immunofluorescence results. Knockdown of GABARAPL-1 significantly inhibited selenite-induced autophagy and enhanced apoptosis. Furthermore, we found that selenite-induced upregulation of GABARAPL-1 was caused by upregulated p-AMPK and FoxO3a level. Their interaction was correlated with involved in regulation of GABARAPL-1. We observed that activation and inhibition of AMPK influenced both autophagy and apoptosis level via FoxO3a/ GABARAPL-1 signaling, implying the pro-survival role of autophagy against apoptosis. Importantly, we corroborated these findings in a colorectal cancer xenograft animal model with immunohistochemistry and western blot results. Collectively, these results show that sodium selenite could induce ROS/AMPK/FoxO3a/GABARAPL-1-mediated autophagy and downregulate apoptosis in both colorectal cancer cells and colon xenograft model. These findings help to explore sodium selenite as a potential anti-cancer drug in clinical practices.

Protective Effects of Trimetazidine in Retarding Selenite-Induced Lens Opacification

ABSTRACTPurpose: Cataracts are the leading cause of vision loss worldwide, and the over-production of reactive oxygen species (ROS) is the foremost underlying cause of cataracts. Reducing ROS levels can efficiently prevent lens opacification, as evidenced by many studies. Here, we inhibited ROS overproduction with trimetazidine (TMZ), which is an antioxidant, to explore the therapeutic effects of TMZ and the mechanism of lens opacification.Materials and methods: Sodium selenite-induced cataract formation resulted in a significant loss of lens transparency. This effect could be efficiently rescued by TMZ, which was further found to be an inhibitor of ROS production, as determined by assaying oxidative stress-related parameters (SOD activity, MDA, ·OH and H2O2 levels) during cataract formation. The experimental protocols involving animal research were approved by the Animal Care and Ethics Committee of Wenzhou Medical University and conducted according to the Association for Research in Vision and Ophthalmology under the guidelines of the Animal Welfare Act (SYXK 2015–0009).Results: Our study found that TMZ can retard the onset and progression of lens opacification in vivo in experiments using Sprague-Dawley (SD) suckling rats and can rescue the morphology of HLEB3 cells in vitro. The flow cytometry and DNA fragmentation assays showed that TMZ could prevent sodium selenite-induced apoptosis. The western blot analysing showed that the levels of apoptosis-associated Bcl-2 and Nrf2 were dramatically decreased following the sodium selenite treatment. In addition, the bisulfate DNA sequencing revealed that the demethylation of CpGs in the promoter region of Keap1 was stimulated, and that this demethylation could be inhibited by TMZ by rescuing the Nrf2 expression level.Conclusions: Our findings indicate that the antioxidant TMZ strongly reduces ROS production, which ultimately delays the progression of cataract formation, suggesting that treatment with TMZ represents a novel, promising antioxidant protection to retard cataract formation.

Selenite-induced apoptosis signalling in differentially sensitive mesothelioma cell lines

Selenite-induced apoptosis signalling in differentially sensitive mesothelioma cell lines

Antitumor activity of selenium compounds and its underlying mechanism in human oral squamous cell carcinoma cells: A preliminary study

ObjectiveOral cancer is an aggressive disease that infiltrates the adjacent tissues and frequently metastasizes to lymph nodes in the neck. Currently, no chemotherapy effectively prevents its metastasis. Selenium compounds have been recently scrutinized as chemotherapeutic agents for various cancers. In this study, we aimed to investigate the antitumor activity of selenium compounds and elucidate the underlying inhibitory mechanism of these agents in oral cancer cells. MethodsThe growth inhibitory effects of selenium compounds (sodium selenite, selenomethionine, and Se-methylselenocysteine) on human oral squamous cell carcinoma (HOSCC) cell lines (HSC-3, HSC-4, and SAS) were evaluated by MTT assay. Selenite-induced apoptosis, caspase activity, and endoplasmic reticulum (ER) stress in HSC-3 cells were evaluated by flow cytometry and western blot. Effects of selenite on Akt expression in HSC-3 cells were evaluated by ELISA and western blot. ResultsSelenium compounds significantly inhibited cell growth and induced apoptosis in HOSCC cell lines. HSC-3 cells, in particular, were highly sensitive to selenite. In selenite-treated HSC-3 cells, caspase-3, 8, and 9 were conspicuously activated; pretreatment with pan-caspase inhibitor or caspase-12 inhibitor dramatically reduced selenite-induced apoptosis; ER stress markers, caspase-12 and eIF-2α, were highly activated, but Akt activation in the Akt/phosphoinositide-3-kinase pathway was downregulated. ConclusionOur findings indicate that selenite induces apoptosis in HOSCC cell lines in a caspase-dependent manner through mitochondrial, death-receptor, and ER stress pathways. In addition, selenite could exhibit antitumor activity by downregulating Akt activation, which plays an important role in cell growth and chemotherapy resistance.

The LEF1/CYLD axis and cIAPs regulate RIP1 deubiquitination and trigger apoptosis in selenite-treated colorectal cancer cells

Inhibitor-of-apoptosis protein (IAP) inhibitors have been reported to synergistically reduce cell viability in combination with a variety of chemotherapeutic drugs via targeted cellular IAP (cIAP) depletion. Here, we found that cIAP silencing sensitised colorectal cancer (CRC) cells to selenite-induced apoptosis. Upon selenite treatment, the K63-linked ubiquitin chains on receptor-interacting protein 1 (RIP1) were removed, leading to the formation of the death-inducing complex and subsequent caspase-8 activation. Although the ubiquitinases cIAP1 and cIAP2 were significantly downregulated after a 24-h selenite treatment, cylindromatosis (CYLD) deubiquitinase protein levels were marginally upregulated. Chromatin immunoprecipitation assays revealed that lymphoid enhancer factor-1 (LEF1) dissociated from the CYLD promoter upon selenite treatment, thus abolishing suppression of CYLD gene expression. We corroborated these findings in a CRC xenograft animal model using immunohistochemistry. Collectively, our findings demonstrate that selenite caused CYLD upregulation via LEF1 and cIAP downregulation, both of which contribute to the degradation of ubiquitin chains on RIP1 and subsequent caspase-8 activation and apoptosis. Importantly, our results identify a LEF1-binding site in the CYLD promoter as a potential target for combinational therapy as an alternative to cIAPs.

RhoA modulates functional and physical interaction between ROCK1 and Erk1/2 in selenite-induced apoptosis of leukaemia cells

RhoA GTPase dysregulation is frequently reported in various tumours and haematologic malignancies. RhoA, regulating Rho-associated coiled-coil-forming kinase 1 (ROCK1), modulates multiple cell functions, including malignant transformation, metastasis and cell death. Therefore, RhoA/ROCK1 could be an ideal candidate target in cancer treatment. However, the roles of RhoA/ROCK1 axis in apoptosis of leukaemia cells remain elusive. In this study, we explored the effects of RhoA/ROCK1 cascade on selenite-induced apoptosis of leukaemia cells and the underlying mechanism. We found selenite deactivated RhoA/ROCK1 and decreased the association between RhoA and ROCK1 in leukaemia NB4 and Jurkat cells. The inhibited RhoA/ROCK1 signalling enhanced the phosphorylation of Erk1/2 in a Mek1/2-independent manner. Erk1/2 promoted apoptosis of leukaemia cells after it was activated. Intriguingly, it was shown that both RhoA and ROCK1 were present in the multimolecular complex containing Erk1/2. GST pull-down analysis showed ROCK1 had a direct interaction with GST-Erk2. In addition, selenite-induced apoptosis in an NB4 xenograft model was also found to be associated with the RhoA/ROCK1/Erk1/2 pathway. Our data demonstrate that the RhoA/ROCK1 signalling pathway has important roles in the determination of cell fates and the modulation of Erk1/2 activity at the Mek–Erk interplay level.

PTEN-regulated AKT/FoxO3a/Bim signaling contributes to reactive oxygen species-mediated apoptosis in selenite-treated colorectal cancer cells

Mounting evidence shows that selenium possesses chemotherapeutic potential against tumor cells, including leukemia, prostate cancer and colorectal cancer (CRC) cells. However, the detailed mechanism by which sodium selenite specifically kills tumor cells remains unclear. Herein, we demonstrated that supranutritional doses of selenite-induced apoptosis in CRC cells through reactive oxygen species (ROS)-dependent modulation of the PI3K/AKT/FoxO3a signaling pathway. First, we found that selenite treatment in HCT116 and SW480 CRC cells caused inhibition of AKT and the nuclear accumulation of FoxO3a by western blot and immunofluorescence analyses, respectively, thereby facilitating transcription of the target genes bim and PTEN. Modulation of the AKT/FoxO3a/Bim signaling pathway by chemical inhibitors or RNA interference revealed that these events were critical for selenite-induced apoptosis in CRC cells. Additionally, we discovered that FoxO3a-mediated upregulation of PTEN exerted a further inhibitory effect on the AKT survival pathway. We also corroborated our findings in vivo by performing immunohistochemistry experiments. In summary, our results show that selenite could induce ROS-dependent FoxO3a-mediated apoptosis in CRC cells and xenograft tumors through PTEN-mediated inhibition of the PI3K/AKT survival axis. These results help to elucidate the molecular mechanisms underlying selenite-induced cell death in tumor cells and provide a theoretical basis for translational applications of selenium.

Comparative proteomics analysis of sodium selenite-induced apoptosis in human prostate cancer cells

Selenium is an important trace mineral necessary for human health. Clinical trials have shown potential inhibitory effects of selenium in advanced or aggressive prostate cancer. However, its mechanism of action remains unclear. This study investigated the mechanism of action of sodium selenite in human prostate cancer PC-3 cells using proteomics. CCK-8 assays were used to detect cell viability and the inhibitory rate. Cell apoptosis was detected by annexin V-FITC and propidium iodide double staining using flow cytometry. Selenite inhibited the growth of PC-3 cells causing them to display morphological changes typical of apoptosis. The rate of cell apoptosis also increased. Proteomics identified a variety of differentially expressed proteins in PC-3 cells exposed to selenite. Eighteen protein spots were identified by MALDI-TOF mass spectrometry. These proteins were separated into those involved in redox balance, protein degradation and cellular energy metabolism. Three differently expressed proteins (SOD1, Stathmin and Erp29) were chosen for Western blot verification, together with several apoptosis-related proteins. Western blot analyses showed that selenite-induced apoptosis was accompanied by activation of caspase-8 and specific proteolytic cleavage of PARP. This led to an increase in the pro-apoptotic protein Bax, and to a decrease in the anti-apoptotic protein Bcl-2 and in hypoxia inducible factor-1α. Increased ROS generation and decreased mitochondrial membrane potential were consistent with reduced expression of antioxidative proteins identified by comparative proteomics. We therefore propose that sodium selenite induces the apoptosis of PC-3 cells mainly through the mitochondrial pathway, but also via ER stress and HIF-1α mediated pathways.

Induction of apoptosis and autophagy by sodium selenite in A549 human lung carcinoma cells through generation of reactive oxygen species

Selenium in the form of sodium selenite has been reported to exert anti-tumor effects in several cancer cell types by inducing autophagic cell death and apoptosis mediated by reactive oxygen species (ROS). However, the exact molecular pathways underlying these effects have not been fully established. The present study used A549 human lung carcinoma cells for further investigation of the anti-cancer mechanism of sodium selenite. We showed that sodium selenite modulated both the extrinsic and intrinsic apoptotic pathways, which were interconnected by Bid truncation. We used z-VAD-fmk, a pan-caspase inhibitor, to demonstrate that sodium selenite-induced apoptosis was dependent on the activation of caspases. Sodium selenite also increased autophagy, as indicated by an increase in microtubule-associated protein light chain-3 (LC3) puncta, accumulation of LC3II, and elevation of autophagic flux. Pretreatment with bafilomycin A1 enhanced sodium selenite-induced apoptosis, indicating that sodium selenite-induced autophagy functioned as a survival mechanism. Sodium selenite treatment also resulted in generation of ROS, which abrogated mitochondrial membrane potential (MMP) and regulated both apoptosis and autophagy. Phospho-nuclear factor erythroid 2-related factor 2 (p-Nrf2) showed a ROS-dependent translocation to the nucleus, which suggested that Nrf2 might increase cell survival by suppressing ROS accumulation and apoptosis mediated by oxidative stress. Sodium selenite treatment of A549 cells therefore appeared to trigger both apoptosis and cytoprotective autophagy, which were both mediated by ROS. The data suggest that regulation of ROS generation and autophagy can be a potential strategy for treating lung cancer that is resistant to pro-apoptotic therapeutics.

Dynamic sieving capillary electrophoresis analysis of xylitol selenite-induced apoptosis in SMMC-7221 cells

DNA ladder fragments, regarded as a biochemical hallmark of apoptosis, have been separated quickly and successfully by capillary electrophoresis. Inter-nucleosomal DNA fragmentations induced by xylitol selenite were determined for the first time, while hydroxypropylmethylcellulose (HPMC) was served as the sieving matrix in dynamic sieving capillary electrophoresis. The calibration curve (r(2) = 0.991) was established and multiples of two different nucleosomes (140 and 180 bp) were formed in the presence of xylitol selenite. Selenium compounds inhibited carcinogenesis in animal models, SMMC-7221 cells and several other cells by increasing apoptosis. The described method was useful in elucidating the anticancer activities of xylitol selenite and other selenium compounds, which was more effective to detect small fragments than slab gel electrophoresis.

Selenite-induced apoptosis and autophagy in colon cancer cells

Sodium selenite (Se) is known to induce diverse stress responses in malignant cells which may lead to various types of cell death including apoptosis and/or autophagy. In colon cancer cells, Se activates several signaling pathways whose interactions and ultimate endpoints may vary in individual study models. In our previous work we showed differences in Se-dependent growth inhibition, cell cycle alterations and apoptosis in colon cancer cells with functional (HCT-116) and deleted (HCT-116-p53KO) p53. Moreover, detailed morphological and biochemical analyses revealed the presence of autophagy in Se-treated cells. Thus the aim of this study was to investigate in detail mechanisms, relationship and crosstalk between apoptosis and autophagy in Se-treated HCT-116 cancer cells differing in p53 status since p53 has been shown to play a well-known role in apoptosis but dichotomous role in autophagy. We report that the absence of p53 in malignant colonocytes changes patterns of response to Se-induced stress which include differential activation of MAP kinases (p38 – HCT-116 and JNK – HCT-116 p53KO) including their respective roles in the process of apoptosis and autophagy as well as the involvement of mTOR or PI3K signaling. Our results seem to suggest that deletion of p53 inevitably leads to a higher level of instability and delays in an individual cell decision in the face of stress whether to activate apoptosis or autophagy which may consequently occur simultaneously with mutual dichotomous relationship.

Selenite induces apoptosis in colorectal cancer cells via AKT-mediated inhibition of β-catenin survival axis

Mounting evidence reveals that selenium possesses chemotherapeutic potential against cancer cells. However, the molecular mechanisms underlying the anti-cancer effect of selenium remain elusive. In this study, with the aim to explore the detailed mechanisms how selenite induces apoptosis in colorectal cancer cells, we investigated the role of AKT/β-catenin signaling, a critical regulator of cell proliferation, survival and tumorigenesis, in selenite-induced apoptosis of colorectal cancer cells and xenograft tumors. We showed that selenite exerted a remarkable inhibitory effect on activation of AKT, leading to suppression of β-catenin activity and expression of its targets: cyclin D1 and survivin. Further experiments by transient expression of AKT and β-catenin revealed that inhibition of AKT/β-catenin was closely correlated with selenite-triggered apoptosis. Importantly, MnTMPyP pretreatment implied reactive oxygen species (ROS) was a crucial upstream signal for selenite-triggered inhibition of AKT/β-catenin. Overall, these observations demonstrate that selenite could induce apoptosis through ROS-dependent inhibition of AKT/β-catenin signaling in colorectal cancer cells in vitro and in vivo, and our findings yield novel insights into elucidating the mechanisms involved in the anti-cancer effect of selenium.

Sodium Selenite-Induced Apoptosis Mediated by ROS Attack in Human Osteosarcoma U2OS Cells

Sodium selenite (Na(2)SeO(3), SSE) is an inorganic Se compound that is widely used in cancer chemoprevention studies. SSE has been shown to have anti-proliferative effects on several types of human cancer cells, but its effect on osteosarcoma cells has thus far not been reported. In this study, the cytotoxic effect of SSE on osteosarcoma cells U2OS was investigated in vitro and found to be higher than on comparable non-cancer cell lines 293 and L6. Treatment with SSE decreased cell growth in a dose- and time-dependent manner and altered cellular morphology. SSE also inhibited cell viability by inducing apoptosis, as evidenced by the formation of apoptotic bodies, generation of reactive oxygen species (ROS), and accumulation of cells during the advanced phase of apoptosis. SSE-induced apoptosis correlated with the activation of CASP 3, downregulation of BCL-2, and upregulation of P53 and PTEN in U2OS cells. These results indicated that SSE induces apoptosis in U2OS cells mainly through an ROS-mediated caspase pathway. This is the first report to show a possible mechanism of the anti-proliferative effect of SSE for the prevention of osteosarcoma in cell culture models.

Superoxide Flashes: EARLY MITOCHONDRIAL SIGNALS FOR OXIDATIVE STRESS-INDUCED APOPTOSIS

Irreversible mitochondrial permeability transition and the resultant cytochrome c release signify the commitment of a cell to apoptotic death. However, the role of transient MPT (tMPT) because of flickering opening of the mitochondrial permeability transition pore remains elusive. Here we show that tMPT and the associated superoxide flashes (i.e. tMPT/superoxide flashes) constitute early mitochondrial signals during oxidative stress-induced apoptosis. Selenite (a ROS-dependent insult) but not staurosporine (a ROS-independent insult) stimulated an early and persistent increase in tMPT/superoxide flash activity prior to mitochondrial fragmentation and a global ROS rise, independently of Bax translocation and cytochrome c release. Selectively targeting tMPT/superoxide flash activity by manipulating cyclophilin D expression or scavenging mitochondrial ROS markedly impacted the progression of selenite-induced apoptosis while exerting little effect on the global ROS response. Furthermore, the tMPT/superoxide flash served as a convergence point for pro- and anti-apoptotic regulation mediated by cyclophilin D and Bcl-2 proteins. These results indicate that tMPT/superoxide flashes act as early mitochondrial signals mediating the apoptotic response during oxidative stress, and provide the first demonstration of highly efficacious local mitochondrial ROS signaling in deciding cell fate.

Proteomic study on sodium selenite-induced apoptosis of human cervical cancer HeLa cells

Sodium selenite can induce the apoptosis of cancer cells, however its mechanism has seldom been studied via proteomics. In this paper, human cervical cancer HeLa cells were investigated by MTT assay and morphological observation to get appropriate selenite concentrations for proteomic study. Results showed that selenite at concentrations larger than 10 μmol/L significantly inhibited the viability of HeLa cells. 40 μmol/L selenite was in the appropriate range for proteomic study. After 24 h treatment with 40 μmol/L selenite, total proteins were extracted from the cells and applied to two-dimensional gel electrophoresis (2DE). Those proteins with their expression levels altered at least 2-fold comparing to the control were picked up for protein identification via MALDI-TOF mass spectrometry and further confirmed by Western blot analysis. About 1000 spots were detected by the software in each 2DE gel, among which 13 differentially expressed proteins were identified by mass spectrometry and most of them are relevant to oxidative stress, such as peroxiredoxins, superoxide dismutase, quinolinate phosphoribosyl transferase, and D-dopachrome tautomerase. Meanwhile, reactive oxygen species (ROS) and mitochondrial membrane potential were also detected by flow cytometry and laser confocal scanning microscope. An increase in ROS generation and a decrease in mitochondrial membrane potential were detected in the selenite-treated cells compared with the control, which are consistent with the down-expression of antioxidative proteins in proteomics. Those results indicate that selenite induces the apoptosis of HeLa cells via ROS-mediated mitochondrial pathway. The present study also implies the potentiality of selenium in cervical cancer treatment.

Heat shock protein 90-mediated inactivation of nuclear factor-κB switches autophagy to apoptosis through becn1 transcriptional inhibition in selenite-induced NB4 cells.

Autophagy can protect cells while also contributing to cell damage, but the precise interplay between apoptosis and autophagy and the contribution of autophagy to cell death are still not clear. Previous studies have shown that supranutritional doses of sodium selenite promote apoptosis in human leukemia NB4 cells. Here, we report that selenite treatment triggers opposite patterns of autophagy in the NB4, HL60, and Jurkat leukemia cell lines during apoptosis and provide evidence that the suppressive effect of selenite on autophagy in NB4 cells is due to the decreased expression of the chaperone protein Hsp90 (heat shock protein 90), suggesting a novel regulatory function of Hsp90 in apoptosis and autophagy. Excessive or insufficient expression indicates that Hsp90 protects NB4 cells from selenite-induced apoptosis, and selenite-induced decreases in the expression of Hsp90, especially in NB4 cells, inhibit the activities of the IκB kinase/nuclear factor-κB (IKK/NF-κB) signaling pathway, leading to less nuclear translocation and inactivation of NF-κB and the subsequent weak binding of the becn1 promoter, which facilitates the transition from autophagy to apoptosis. Taken together, our observations provide novel insights into the mechanisms underlying the balance between apoptosis and autophagy, and we also identified Hsp90-NF-κB-Beclin1 as a potential biological pathway for signaling the switch from autophagy to apoptosis in selenite-treated NB4 cells.

Selenite-induced cell death in Saccharomyces cerevisiae: protective role of glutaredoxins

Unlike in higher organisms, selenium is not essential for growth in Saccharomyces cerevisiae. In this species, it causes toxic effects at high concentrations. In the present study, we show that when supplied as selenite to yeast cultures growing under fermentative metabolism, its effects can be dissected into two death phases. From the time of initial treatment, it causes loss of membrane integrity and genotoxicity. Both effects occur at higher levels in mutants lacking Grx1p and Grx2p than in wild-type cells, and are reversed by expression of a cytosolic version of the membrane-associated Grx7p glutaredoxin. Grx7p can also rescue the high levels of protein carbonylation damage that occur in selenite-treated cultures of the grx1 grx2 mutant. After longer incubation times, selenite causes abnormal nuclear morphology and the appearance of TUNEL-positive cells, which are considered apoptotic markers in yeast cells. This effect is independent of Grx1p and Grx2p. Therefore, the protective role of the two glutaredoxins is restricted to the initial stages of selenite treatment. Lack of Yca1p metacaspase or of a functional mitochondrial electron transport chain only moderately diminishes apoptotic-like death by selenite. In contrast, selenite-induced apoptosis is dependent on the apoptosis-inducing factor Aif1p. In the absence of the latter, intracellular protein carbonylation is reduced after prolonged selenite treatment, supporting the supposition that part of the oxidative damage is contributed by apoptotic cells.

ROS leads to MnSOD upregulation through ERK2 translocation and p53 activation in selenite-induced apoptosis of NB4 cells

Following our previous finding that sodium selenite induces apoptosis in human leukemia NB4 cells, we now show that the expression of the critical antioxidant enzyme manganese superoxide dismutase (MnSOD) is remarkably elevated during this process. We further reveal that reactive oxygen species (ROS), especially superoxide radicals, play a crucial role in selenite-induced MnSOD upregulation, with extracellular regulated kinase (ERK) and p53 closely implicated. Specifically, ERK2 translocates into the nucleus driven by ROS, where it directly phosphorylates p53, leading to dissociation of p53 from its inhibitory protein mouse double minute 2 (MDM2). Active p53 directly mediates the expression of MnSOD, serving as the link between ERK2 translocation and MnSOD upregulation.