Serum suppresses myeloid progenitor apoptosis by regulating iron homeostasis

Iron starvation induces apoptosis in Rhizopus oryzae in vitro

Mortality associated with mucormycosis remains high despite current antifungals. Iron-starvation strategies have been shown to have promising activity against Mucorales. We hypothesized that iron starvation enhances apoptosis in Rhizopus oryzae. Apoptosis was characterized in R. oryzae transformed with RNAi plasmid targeting FTR1 expression (iron permease mutant) or empty plasmid grown in iron rich (0.125% FeCl3) and iron depleted media (YNB+1mM ferrozine and 1 mM ascorbic acid). Increased apoptosis was observed with dihydrorhodamine-123 and rhodamine-123 staining in the iron starved mutant FTR1 when compared to empty plasmid, followed by increased extracellular ATP levels. In addition, DNA fragmentation and metacaspase activity were prominent in FTR1. In contrast, Rhizopus strains grown in iron-rich medium displayed minimal apoptosis. Our results demonstrate a metacaspase dependent apoptotic process in iron deprived condition and further support the role of iron starvation strategies as an adjunct treatment for mucormycosis, a mechanism by which iron starvation affects R. oryzae.

The effects of iron deficiency on neutrophil/monocyte apoptosis in children

OBJECTIVES

Iron is essential for DNA synthesis; its deficiency may lead to impaired DNA synthesis and subsequent alterations in levels of apoptosis. Here, we have aimed to investigate effects of iron deficiency anaemia (IDA) on apoptotic response of phagocytic cells and to understand whether the effect is reversible after iron supplementation.

MATERIALS AND METHODS

Forty-nine IDA patients and 26 healthy controls, aged between 6 months and 12 years with similar demographic status, were considered. Neutrophil- and monocyte-apoptotic responses of IDA patients and the control group were compared by flow cytometry. Then, IDA patients were provided with oral iron supplementation. On day 15 of iron therapy, neutrophil- and monocyte-apoptotic responses of IDA patients were rechecked and were compared to those of control group.

RESULTS

Neutrophil- and monocyte-apoptotic responses in terms of early and late percentages of apoptosis, and percentages of necrotic cells, were significantly less in IDA patients compared to the control group. The significantly low apoptotic responses of IDA patients rose to levels of the control group by day 15 of iron therapy. Besides, the effect of IDA on apoptotic responses was found to be more enhanced in severe IDA patients that those of mild IDA patients.

CONCLUSION

Correction of differences after iron supplementation therapy implies that IDA might be a cause for changes in neutophil- and monocyte-apoptotic responses. The impact of this diminution of apoptotic cellular function in IDA should be further investigated, with longitudinal studies, in order to document the impact of any severe and/or long-lasting IDA on autoimmunity and malignancy.

The in vitro antitumor effect and in vivo tumor-specificity distribution of human-mouse chimeric antibody against transferrin receptor

Transferrin receptor (TfR/CD71) deserves attention as a selective target for cancer therapy due to its higher expression in tumors versus normal tissues. Also, it has been shown the mouse-derived monoclonal antibody against TfR can significantly inhibit the proliferation of tumor cells. Through constructing the chimeric antibody against TfR, the antigenicity of antibody can be weakened, and most importantly, the antitumor effect of antibody can be strengthened by the introduction of the human Fc fragment. In previous studies, we successfully constructed the human-mouse chimeric antibody against TfR (D2C) and demonstrated that its Fab fragment could specially recognize the TfR on the surface of target cells. In this study, through labeling the chimeric antibody D2C with 125I, we calculated the affinity constant (Ka) of 9.34-9.62x10(9) l/mol for this antibody according to the Scatchard drawing method. Moreover, in vivo studies in nude mice-bearing human liver cancer (SMMC-7721) xenografts have shown that the radioactivity distribution ratio of 131I-D2C on T/NT was 2-14:1 or 3-21:1 on the seventh day after intraperitoneal or intratumoral injection of 131I-labeled D2C (131I-D2C). These evidences indicated that the in vivo distribution of D2C display the characteristics of certain tumor-specificity localization. In vitro studies, D2C can induce the apoptosis of K562 through the mitochondria death pathway and arrest the cell at G1 phase, as determined by cell cycle analysis. Using the human tumor cells (K562, CEM, and SMMC-7721) expressing TfR as target cells, and normal human PBMC as effector cells, Fc fragment of D2C can perform both the antibody-dependent cell-mediated cytotoxicity and the complement-dependent cytotoxicity. Together, it was demonstrated that the D2C display a tumor-specificity distribution, and has a strong antitumor effect. Thus, it has the potential therapeutic significance.

Molecular events contributing to cell death in malignant human hematopoietic cells elicited by an IgG3-avidin fusion protein targeting the transferrin receptor

We have previously reported that an anti-human transferrin receptor IgG3-avidin fusion protein (anti-hTfR IgG3-Av) inhibits the proliferation of an erythroleukemia-cell line. We have now found that anti-hTfR IgG3-Av also inhibits the proliferation of additional human malignant B and plasma cells. Anti-hTfR IgG3-Av induces internalization and rapid degradation of the TfR. These events can be reproduced in cells treated with anti-hTfR IgG3 cross-linked with a secondary Ab, suggesting that they result from increased TfR cross-linking. Confocal microscopy of cells treated with anti-hTfR IgG3-Av shows that the TfR is directed to an intracellular compartment expressing the lysosomal marker LAMP-1. The degradation of TfR is partially blocked by cysteine protease inhibitors. Furthermore, cells treated with anti-hTfR IgG3-Av exhibit mitochondrial depolarization and activation of caspases 9, 8, and 3. The mitochondrial damage and cell death can be prevented by iron supplementation, but cannot be fully blocked by a pan-caspase inhibitor. These results suggest that anti-hTfR IgG3-Av induces lethal iron deprivation, but the resulting cell death does not solely depend on caspase activation. This report provides insights into the mechanism of cell death induced by anti-TfR Abs such as anti-hTfR IgG3-Av, a molecule that may be useful in the treatment of B-cell malignancies such as multiple myeloma.

Iron-induced mitochondrial permeability transition in cultured hepatocytes

BACKGROUND/AIMS

We previously described that the cold-induced apoptosis of cultured hepatocytes and liver endothelial cells is mediated by an increase in the cellular chelatable iron pool-in the absence of any increase in O(2)(.-)/H(2)O(2) formation. As this is an unusual mechanism, we here set out to assess whether an increase in cellular chelatable iron per se is sufficient to trigger cell injury/apoptosis.

METHODS

Cultured rat hepatocytes were acutely loaded with iron using the membrane-permeable complex Fe(III)/8-hydroxyquinoline and incubated under otherwise 'physiological' conditions.

RESULTS

Incubation with Fe(III)/8-hydroxyquinoline (15 microM/30 microM) increased the cellular chelatable iron and induced strong hepatocellular injury with morphological features of apoptosis, but also of necrosis. The iron-induced cell injury was oxygen-dependent, and although it was not inhibitable by extracellular catalase, it was strongly inhibited by the novel membrane-permeable catalase mimic TAA-1/Fe. The experimentally induced increase in cellular chelatable iron triggered a mitochondrial permeability transition (MPT) as assessed using double-staining with calcein and tetramethylrhodamine methyl ester. The MPT inhibitor cyclosporine A partially and the well-known inhibitor combination trifluoperazine+fructose completely inhibited the iron-induced cell injury/apoptosis.

CONCLUSIONS

These results show that iron per se can induce cell injury/apoptosis and that this injury is mediated via an MPT.

c-Myc augments gamma irradiation-induced apoptosis by suppressing Bcl-XL

Alterations in MYC and p53 are hallmarks of cancer. p53 coordinates the response to gamma irradiation (gamma-IR) by either triggering apoptosis or cell cycle arrest. c-Myc activates the p53 apoptotic checkpoint, and thus tumors overexpressing MYC often harbor p53 mutations. Nonetheless, many of these cancers are responsive to therapy, suggesting that Myc may sensitize cells to gamma-IR independent of p53. In mouse embryo fibroblasts (MEFs) and in E micro -myc transgenic B cells in vivo, c-Myc acts in synergy with gamma-IR to trigger apoptosis, but alone, when cultured in growth medium, it does not induce a DNA damage response. Surprisingly, c-Myc also sensitizes p53-deficient MEFs to gamma-IR-induced apoptosis. In normal cells, and in precancerous B cells of E micro -myc transgenic mice, this apoptotic response is associated with the suppression of the antiapoptotic regulators Bcl-2 and Bcl-X(L) and with the concomitant induction of Puma, a proapoptotic BH3-only protein. However, in p53-null MEFs only Bcl-X(L) expression was suppressed, suggesting levels of Bcl-X(L) regulate the response to gamma-IR. Indeed, Bcl-X(L) overexpression blocked this apoptotic response, whereas bcl-X-deficient MEFs were inherently and selectively sensitive to gamma-IR-induced apoptosis. Therefore, MYC may sensitize tumor cells to DNA damage by suppressing Bcl-X.

Transferrin ensures survival of ovarian carcinoma cells when apoptosis is induced by TNFα, FasL, TRAIL, or Myc

The activation of Myc induces apoptosis of human ovarian adenocarcinoma N.1 cells when serum factors are limited. However, the downstream mechanism that is triggered by Myc is unknown. Myc-activation and treatment with the proapoptotic ligands TNFalpha, FasL, and TRAIL induced H-ferritin expression under serum-deprived conditions. H-ferritin chelates intracellular iron and also intracellular iron sequestration by deferoxamine-induced apoptosis of N.1 cells. Supplementation of serum-free medium with holo-transferrin blocked apoptosis of N.1 cells that was induced by Myc-activation or by treatment with TNFalpha, FasL, and TRAIL, whereas apotransferrin did not prevent apoptosis. This suggests that intracellular iron depletion was a trigger for apoptosis and that transferrin-bound iron rescued N.1 cells. Furthermore, apoptosis of primary human ovarian carcinoma cells, which was induced by TNFalpha, FasL, and TRAIL, was also inhibited by holo-transferrin. The data suggest that Myc-activation, FasL, TNFalpha, and TRAIL disturbed cellular iron homeostasis, which triggered apoptosis of ovarian carcinoma cells and that transferrin iron ensured survival by re-establishing this homeostasis.

Significance of endothelial cell survival programs for renal transplantation

Initial and longer term kidney transplant function is determined in part by the renal allograft microcirculation because it provides a thromboresistant surface, regulates cellular infiltration, and elaborates paracrine and autocrine growth and survival factors. Loss of endothelial-derived signaling mediators accelerates vascular injury and endothelial cell (EC) death. EC apoptosis is implicated in accelerated allograft vasculopathy and premature loss of organ function. Renal allograft EC injury and replacement by recipient-derived repair mechanisms has long been proposed to influence allograft acceptance and function. Repair of cellular injury in allografts is linked with cell-survival mechanisms, but few precise indicators exist to predict recovery and repair in organ transplants. The significance of the growth phenotype of the microvascular endothelium for acute and longer term renal allograft survival is presented.