Reactive Oxygen Species Regulate Hypoxia-Inducible Factor 1 Differentially in Cancer and Ischemia

Department of Biomedical Engineering, School of Medicine, Johns Hopkins University, 613 Traylor Bldg, 720 Rutland Ave., Baltimore, MD 21205, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 07/2008; 28(16):5106-19. DOI: 10.1128/MCB.00060-08
Source: PubMed

ABSTRACT In exercise, as well as cancer and ischemia, hypoxia-inducible factor 1 (HIF1) transcriptionally activates hundreds of genes vital for cell homeostasis and angiogenesis. While potentially beneficial in ischemia, upregulation of the HIF1 transcription factor has been linked to inflammation, poor prognosis in many cancers, and decreased susceptibility of tumors to radiotherapy and chemotherapy. Considering HIF1's function, HIF1alpha protein and its hydroxylation cofactors look increasingly attractive as therapeutic targets. Independently, antioxidants have shown promise in lowering the risk of some cancers and improving neurological and cardiac function following ischemia. The mechanism of how different antioxidants and reactive oxygen species influence HIF1alpha expression has drawn interest and intense debate. Here we present an experimentally based computational model of HIF1alpha protein degradation that represents how reactive oxygen species and antioxidants likely affect the HIF1 pathway differentially in cancer and ischemia. We use the model to demonstrate effects on HIF1alpha expression from combined doses of five potential therapeutically targeted compounds (iron, ascorbate, hydrogen peroxide, 2-oxoglutarate, and succinate) influenced by cellular oxidation-reduction and involved in HIF1alpha hydroxylation. Results justify the hypothesis that reactive oxygen species work by two opposite ways on the HIF1 system. We also show how tumor cells and cells under ischemic conditions would differentially respond to reactive oxygen species via changes to HIF1alpha expression over the course of hours to days, dependent on extracellular hydrogen peroxide levels and largely independent of initial intracellular levels, during hypoxia.

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Available from: Aleksander S Popel, Sep 27, 2015
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    • "Thiol groups are one of the members of the antioxidant system as they have been revealed to devastate the reactive oxygen species (ROS) and other free radicals by enzymic and nonenzymic mechanisms [13] [14]. It has been recently advocated that genetic factors may also have an effect on the ROS system activity and ROS production [15]. It has been found that the exposure of proteins to oxidative stress resulted in decrease and functional defects in the thiol groups [16] [17]. "
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    ABSTRACT: Purpose: To investigate the oxidant and antioxidant status of patients with type 2 diabetes mellitus and non-proliferative diabetic retinopathy (DRP), and to compare them with those of age and sex matched patients in the control group. Methods: Forty-four patients who had cataract surgery were enrolled in the study. Patients were classified into two groups. We included 22 patients with DRP in one group and 22 patients in the control group. Samples of aqueous humor and serum were taken from all patients. Serum and aqueous ischemia-modified albumin (IMA), total thiol, total antioxidant capacity (TAC) and total oxidative stress (TOS) levels were compared statistically in two groups. Results: Median serum IMA levels were 44.80 absorbance units in the DRP group and 40.15 absorbance units in the control group (p=0.031). Median serum total thiol levels in the DRP group were statistically significantly less than those in the control group (3051.13 and 3910.12 respectively, p=0.004). Mean TOS levels in the serum were 2.93±0.19 in the DRP group and 2.61±0.26 in the control group (p=0.039). The differences in mean total thiol, TAC and TOS levels in the aqueous humor and mean TAC levels in the serum were not statistically significant. IMA could not be detected in the aqueous humor. Conclusion: IMA, total thiol and TOS levels in the serum might be useful markers in monitoring the risk of DRP development.
    Journal of Ophthalmology 12/2014; 2014. DOI:10.1155/2014/820853 · 1.43 Impact Factor
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    • "Kinetic parameters of these antioxidant enzymes in the model were based on available experimental data on Tpx, Trx, and TR enzymes (see Table S2 in Supplement I). The concentrations of the phenomenological enzymes (Pr, PSH, and Red) were determined as a result of the fitting of experimental data on the basal level of intracellular H 2 O 2 concentration (Qutub and Popel, 2008). In the model we neglected the processes of H 2 O 2 degradation through the oxidation of cellular proteins and the generation of free radicals by H 2 O 2 . "
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    ABSTRACT: Cells are constantly exposed to Reactive Oxygen Species (ROS) produced both endogenously to meet phys- iological requirements and from exogenous sources. While endogenous ROS are considered as important signalling molecules, high uncontrollable ROS are detrimental. It is unclear how cells can achieve a bal- ance between maintaining physiological redox homeostasis and robustly activate the antioxidant system to remove exogenous ROS. We have utilised a Systems Biology approach to understand how this robust adaptive system fulfils homeostatic requirements of maintaining steady-state ROS and growth rate, while undergoing rapid readjustment under challenged conditions. Using a panel of human ovarian and normal cell lines, we experimentally quantified and established interrelationships between key elements of ROS homeostasis. The basal levels of NRF2 and KEAP1 were cell line specific and maintained in tight corre- lation with their growth rates and ROS. Furthermore, perturbation of this balance triggered cell specific kinetics of NRF2 nuclear–cytoplasmic relocalisation and sequestration of exogenous ROS. Our experi- mental data were employed to parameterise a mathematical model of the NRF2 pathway that elucidated key response mechanisms of redox regulation and showed that the dynamics of NRF2-H2O2 regulation defines a relationship between half-life, total and nuclear NRF2 level and endogenous H2O2 that is cell line specific.
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    • "However, Fig. 4 shows that the total intracellular concentration of iron remains unaffected in the presence of extracellular Asc, implying that the cytoprotective effects of iron against Asc-provoked cell death are not related to iron deficiency. Further, it is known that the level of hypoxia inducible factor-1 (HIF-1), a transcription factor that is involved in the regulation of different aspects of cancer cell biology, can be affected by Asc303132, iron3334, and H2O235. Fig. 5 shows characteristic micrographs, intensities and histograms of HIF-1α immunofluorescence. "
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    ABSTRACT: In vitro studies have shown that hydrogen peroxide (H2O2) produced by high-concentration ascorbate and cell culture medium iron efficiently kills cancer cells. This provided the rationale for clinical trials of high-dose intravenous ascorbate-based treatment for cancer. A drawback in all the in vitro studies was their failure to take into account the in vivo concentration of iron to supplement cell culture media which are characterized by low iron content. Here we showed, using two prostate cancer cell lines (LNCaP and PC-3) and primary astrocytes, that the anticancer/cytotoxic effects of ascorbate are completely abolished by iron at physiological concentrations in cell culture medium and human plasma. A detailed examination of mechanisms showed that iron at physiological concentrations promotes both production and decomposition of H2O2. The latter is mediated by Fenton reaction and prevents H2O2 accumulation. The hydroxyl radical, which is produced in the Fenton reaction, is buffered by extracellular proteins, and could not affect intracellular targets like H2O2. These findings show that anticancer effects of ascorbate have been significantly overestimated in previous in vitro studies, and that common cell culture media might be unsuitable for redox research.
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