Hypoxia inhibition of apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)

Treatment with siRNA and antisense oligonucleotides targeted to HIF-1alpha induced apoptosis in human tongue squamous cell carcinomas

Overexpression of hypoxia inducible factor-1alpha (HIF-1alpha) in cancers has been correlated to a more aggressive tumor phenotype. We investigated the effect of HIF-1alpha knockout on the in vitro survival and death of human tongue squamous cell carcinomas (SCC-4 and SCC-9). Under normoxic condition, a basal level of HIF-1alpha protein was constitutively expressed in SCC-9 cells, albeit an undetectable level of HIF-1alpha messages. Exposure to hypoxia induced only a transient increase in mRNA transcript but a prolonged elevation of HIF-1alpha protein and its immediate downstream target gene product, VEGF. Under normoxic or hypoxic conditions, treatment of SCC-9 cells with AS-HIF-1alpha ODN suppressed both constitutive and hypoxia-induced HIF-1alpha expression at both mRNA and protein levels. Knockout of HIF-1alpha gene expression via either AS-HIF-1alpha ODN or siRNA (siRNAHIF-1alpha) treatment resulted in inhibition of cell proliferation and induced apoptosis in SCC-4 and SCC-9 cells. We also demonstrated that exposure of SCC-9 cells to hypoxia led to a time-dependent increase in the expression of bcl-2 and IAP-2, but not p53. The attenuated levels of bcl-2 and IAP-2, and the enhanced activity of caspase-3 after treatment with AS-HIF-1alpha ODN may contribute partly to the effects of HIF-1alpha blockade on SCC-9 cell death. Collectively, our data suggest that a constitutive or hypoxia-induced expression of HIF-1alpha in SCC-9 and SCC-4 cells is sufficient to confer target genes expression essential for tumor proliferation and survival. As a result, interfering with HIF-1alpha pathways by antisense or siRNA strategy may provide a therapeutic target for human tongue squamous cell carcinomas.

Hypoxia inhibits tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by blocking Bax translocation

The hypoxic environment in solid tumors results from oxygen consumption by rapid proliferation of tumor cells. Hypoxia has been shown to facilitate the survival of tumor cells and to be a cause of malignant transformation. Hypoxia also is well known to attenuate the therapeutic activity of various therapies in cancer management. These observations indicate that hypoxia plays a critical role in tumor biology. However, little is known about the effects of hypoxia on apoptosis, especially on apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a potent apoptosis inducer that has been shown to specifically limit tumor growth without damaging normal cells and tissues in vivo. To address the effects of hypoxia on TRAIL-induced apoptosis, HCT116 human colon carcinoma cells were exposed to hypoxic or normoxic conditions and treated with soluble TRAIL protein. Hypoxia dramatically inhibited TRAIL-induced apoptosis in HCT116 cells, which are highly susceptible to TRAIL in normoxia. Hypoxia increased antiapoptotic Bcl-2 family member proteins and inhibitors of apoptosis proteins. Interestingly, these hypoxia-increased antiapoptotic molecules were decreased by TRAIL treatment to the levels lower than those of the untreated conditions, suggesting that hypoxia inhibits TRAIL-induced apoptosis via other mechanisms rather than up-regulation of these antiapoptotic molecules. Additional characterization revealed that hypoxia significantly inhibits TRAIL-induced translocation of Bax from the cytosol to the mitochondria in HCT116 and A549 cells, with the concomitant inhibition of cytochrome c release from the mitochondria. Bax-deficient HCT116 cells were completely resistant to TRAIL regardless of oxygen content, demonstrating a pivotal role of Bax in TRAIL-induced apoptotic signaling. Thus, our data indicate that hypoxia inhibits TRAIL-induced apoptosis by blocking Bax translocation to the mitochondria, thereby converting cells to a Bax-deficient state.

Hypoxia-mediated down-regulation of Bid and Bax in tumors occurs via hypoxia-inducible factor 1-dependent and -independent mechanisms and contributes to drug resistance

Solid tumors with disorganized, insufficient blood supply contain hypoxic cells that are resistant to radiotherapy and chemotherapy. Drug resistance, an obstacle to curative treatment of solid tumors, can occur via suppression of apoptosis, a process controlled by pro- and antiapoptotic members of the Bcl-2 protein family. Oxygen deprivation of human colon cancer cells in vitro provoked decreased mRNA and protein levels of proapoptotic Bid and Bad. Hypoxia-inducible factor 1 (HIF-1) was dispensable for the down-regulation of Bad but required for that of Bid, consistent with the binding of HIF-1alpha to a hypoxia-responsive element (positions -8484 to -8475) in the bid promoter. Oxygen deprivation resulted in proteosome-independent decreased expression of Bax in vitro, consistent with a reduction in global translation efficiency. The physiological relevance of Bid and Bax down-regulation was confirmed in tumors in vivo. Oxygen deprivation resulted in decreased drug-induced apoptosis and clonogenic resistance to agents with different mechanisms of action. The contribution of Bid and/or Bax down-regulation to drug responsiveness was demonstrated by the relative resistance of normoxic cells that had no or reduced expression of Bid and/or Bax and by the finding that forced expression of Bid in hypoxic cells resulted in increased sensitivity to the topoisomerase II inhibitor etoposide.

Influence of hypoxia on TRAIL-induced apoptosis in tumor cells

PURPOSE

Tumor hypoxia reduces the efficacy of radiotherapy, many types of chemotherapy, and tumor necrosis factor-alpha (TNF-alpha). TRAIL (TNF-alpha-related apoptosis-inducing ligand) is a ligand for death receptors of the TNF superfamily shown to be selectively toxic for tumor cells and thereby a promising antineoplastic tool. The impact of hypoxia on TRAIL-induced apoptosis was examined in this study.

METHODS AND MATERIALS

Apoptosis induction and growth rates of various tumor cell lines under hypoxia were evaluated in vitro. Biologically effective induction of hypoxia was verified by determination of hypoxia-inducible factor-1 (HIF-1) activation. The efficacy of TRAIL- and radiation-induced apoptosis under different oxygen conditions was quantified in vitro. The impact of Bcl-2 on TRAIL-induced apoptosis under hypoxia or normoxia was evaluated by comparing cells expressing Bcl-2 with a vector control.

RESULTS

Moderate hypoxia caused no growth retardation or apoptosis, but led to activation of HIF-1 as a prerequisite of hypoxic gene induction. Cellular responses to TRAIL differed considerably among the cell lines tested. Hypoxia reduced radiation-induced, but not TRAIL-induced, apoptosis in the tested cell lines. Hypoxia did not induce Bcl-2 expression. Bcl-2 had a minor impact on the efficacy of TRAIL-induced apoptosis.

CONCLUSION

Taken together, the data indicate that TRAIL is clearly effective under conditions of proven hypoxia.

The release of tumor necrosis factor-alpha is associated with ischemic tolerance in human stroke

Tumor necrosis factor (TNF)-alpha overexpression has been related to experimental ischemic tolerance when transient ischemia precedes cerebral infarction. We investigated TNF-alpha and interleukin (IL)-6 plasma concentrations in 283 patients with an acute stroke within 24 hours after symptom onset. An ipsilateral transient ischemic attack (TIA) within 72 hours before stroke was recorded in 38 patients. The infarct volume measured on computed tomography on days 4 to 7 and the frequency of poor outcome (Barthel Index score < 85) at 3 months were significantly lower in patients with prior TIA. Plasma concentrations of TNF-alpha were higher (42.5 +/- 9.9 vs 13.1 +/- 6.4pg/ml, p < 0.0001) and IL-6 levels were lower (10.1 +/- 6.2 vs 28.3 +/- 17.3pg/ml, p < 0.0001) in patients with prior TIA. A new variable termed TNF-alpha/IL-6 index was considered positive when TNF-alpha was greater than 30pg/ml and IL-6 was less than 30pg/ml. Positive TNF-alpha/IL-6 index was found in 92% of patients with prior TIA and in 1% of those without. TNF-alpha/IL-6 index (p = 0.0003) and TIA (p = 0.0001) were associated with good outcome in logistic regression analysis after adjusting for potential confounding factors. Ischemic tolerance in acute stroke is associated with increased plasma levels of TNF-alpha in the presence of reduced concentrations of IL-6.

Fas-associating death domain protein overexpression induces apoptosis in lung cancer cells

OBJECTIVES

Non-small cell lung cancers commonly develop resistance to radiation and chemotherapy, and they often present at stages beyond surgical resectability. Because current treatment modalities are inadequate, novel therapies are necessary to reduce the effects of the increasing incidence in pulmonary neoplasms. Fas-associating death domain protein is a central mediator of death receptor-initiated apoptosis that directly activates the caspase-8 protease. We hypothesized that overexpression of Fas-associating death domain protein would effectively eradicate lung cancer cells by induction of apoptosis.

METHODS

Cultured A549 alveolar carcinoma and NCI-H226 squamous carcinoma cells were exposed to increasing multiplicities of infection of a replication-deficient, adenoviral vector that expresses the wild-type murine Fas-associating death domain protein gene or control virus for 4 hours. Twenty-four hours later, cells were assessed for viability by crystal violet staining and caspase activation by microscopic analysis. Protein lysates were examined by Western blotting for expression of Fas-associating death domain protein and activated caspase-8.

RESULTS

Adenoviral infection with the wild-type murine Fas-associating death domain protein gene in A549 cells resulted in a dose-dependent expression of Fas-associating death domain protein and the appearance of cleaved, activated caspase-8. Increasing multiplicities of infection of the wild-type murine Fas-associating death domain protein gene, but not control adenovirus, was associated with increased cell death in A549 and NCI-H226 cells. The wild-type murine Fas-associating death domain protein gene infection of A549 cells at multiplicities of infection of 50 induced at least 10-fold increase in Fas-associating death domain protein levels and decreased viability by > 50% (n = 3; P <.001).

CONCLUSION

Overexpression of Fas-associating death domain protein induced dose-dependent cell death in A549 and NCI-H226 lung epithelial cancer cells. Expression of Fas-associating death domain protein results in activation of caspases, a hallmark of apoptosis. Delivery of the wild-type murine Fas-associating death domain protein gene to drug- and radiation-resistant lung cancer may be a novel method for therapy of non-small cell lung cancer.

Natural cellular inhibitors of caspases

The crucial role of cell death in many diseases is obvious and has spurred intense research to understand the regulation of apoptotic pathways. Caspase activation is central to many of the apoptotic pathways. In recent years, the study of the regulation of caspase activation and activity in various cell lines and in diseases has revealed highly complex mechanisms regulating cell survival or cell death. In this review, the major natural cellular anticaspase factors are described with particular attention to the inhibitors that prevent active caspases from committing the cell to irreversible destruction. The major group of caspase inhibitors known is the inhibitor of apoptosis proteins (IAP) and this review describes the characteristics of IAP, regulation of IAP expression, and mechanisms of action of IAP. However, other proteins including Bcl-2 family members, heat shock proteins, caspase-like decoy, calpains and proteases, and lipid moieties in the form of phosphoinositides also can function as caspase inhibitors. The current knowledge of the inhibition of these non-IAP factors is described herein.

Upregulation of TACE/ADAM17 after ischemic preconditioning is involved in brain tolerance

A short ischemic event (ischemic preconditioning [IPC]) can result in a subsequent resistance to severe ischemic injury (ischemic tolerance [IT]). Although tumor necrosis factor-alpha (TNF-alpha) contributes to the brain damage, its expression and neuroprotective role in models of IPC have also been described. However, the role of TNF-alpha convertase (TACE) in IPC and IT is not known. Using in vitro models, the authors previously demonstrated that TACE is upregulated after ischemic brain damage. In the present study, the authors used a rat model of transient middle cerebral artery occlusion as IPC to investigate TACE expression, its involvement in TNF-alpha release, and its role in IT. Western blot analysis showed that TACE expression is increased after IPC. Ischemic preconditioning caused TNF-alpha release, an effect that was blocked by the selective TACE inhibitor BB-1101 (10 mg. kg(-1). day(-1); SHAM, 1,050 +/- 180; IPC, 1,870 +/- 290; IPC + BB, 1,320 +/- 260 ng/mg; n = 4, < 0.05). Finally, IPC produced a reduction in infarct volume, which was inhibited by treatment with BB-1101 and with anti-TNF-alpha (10 microg/5 doses; SHAM + permanent middle cerebral artery occlusion [pMCAO], 335 +/- 20; IPC + pMCAO, 244 +/- 14; IPC + BB + pMCAO, 300 +/- 6; IPC + anti-TNF + pMCAO, 348 +/- 22 mm3; n = 6-10, < 0.05). Taken together, these data demonstrate that TACE is upregulated after IPC, plays a major role in TNF-alpha shedding in IPC, and has a neuroprotective role in IT.

Regulation of Akt by EGF-R inhibitors, a possible mechanism of EGF-R inhibitor-enhanced TRAIL-induced apoptosis

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a type II transmembrane cytokine and a potent inducer of apoptosis. Epidermal growth factor (EGF) signaling is well known to involve in tumor survival and overexpression of EGF receptor (EGF-R) attributes to decreased responsiveness to many available therapies in cancer treatment. We investigated whether EGF-R inhibitors enhance TRAIL-induced apoptosis. We exposed A549 cells to Genistein, PD153035, and PD158780 for 12h and then treated with recombinant TRAIL protein. TRAIL alone induced 25% cell death after a 3-h treatment, but in cells pretreated with EGF-R inhibitors, TRAIL induced cell death to more than 70% after 3h treatment. Genistein enhanced TRAIL-induced apoptosis in a time- and dose-dependent manner. Western blot analyses showed that pretreatment with Genistein down-regulated the protein levels of total Akt and phosphorylated active Akt. Genistein also decreased the protein level of Bcl-XL that is regulated by Akt. These molecules are well characterized to act against induction of apoptotic cell death. Therefore, our data suggest that EGF-R inhibitor may sensitize A549 cells to TRAIL-induced apoptosis by regulating expression of these proteins. EGF-R inhibitors may play an important role in the anti-cancer activity of TRAIL protein, especially in TRAIL-resistant tumors that arise by expressing constitutively active Akt.

Antagonism between interleukin 3 and erythropoietin in mice with azidothymidine-induced anemia and in bone marrow endothelial cells

Azidothymidine (AZT)-induced anemia in mice can be reversed by the administration of IGF-IL-3 (fusion protein of insulin-like growth factor II (IGF II) and interleukin 3). Although interleukin 3 (IL-3) and erythropoietin (EPO) are known to act synergistically on hematopoietic cell proliferation in vitro, injection of IGF-IL-3 and EPO in AZT-treated mice resulted in a reduction of red cells and an increase of plasma EPO levels as compared to animals treated with IGF-IL-3 or EPO alone. We tested the hypothesis that the antagonistic effect of IL-3 and EPO on erythroid cells may be mediated by endothelial cells. Bovine liver erythroid cells were cultured on monolayers of human bone marrow endothelial cells previously treated with EPO and IGF-IL-3. There was a significant reduction of thymidine incorporation into both erythroid and endothelial cells in cultures pre-treated with IGF-IL-3 and EPO. Endothelial cell culture supernatants separated by ultrafiltration and ultracentrifugation from cells treated with EPO and IL-3 significantly reduced thymidine incorporation into erythroid cells as compared to identical fractions obtained from the media of cells cultured with EPO alone. These results suggest that endothelial cells treated simultaneously with EPO and IL-3 have a negative effect on erythroid cell production.