Quantitative analysis of NRF2 pathway reveals key elements of the regulatory circuits underlying antioxidant response and proliferation of ovarian cancer cells

Cells are constantly exposed to Reactive Oxygen Species (ROS) produced both endogenously to meet physiological 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 balance 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 correlation 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 experimental 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

Glutathione Metabolism in Renal Cell Carcinoma Progression and Implications for Therapies

A significantly increased level of the reactive oxygen species (ROS) scavenger glutathione (GSH) has been identified as a hallmark of renal cell carcinoma (RCC). The proposed mechanism for increased GSH levels is to counteract damaging ROS to sustain the viability and growth of the malignancy. Here, we review the current knowledge about the three main RCC subtypes, namely clear cell RCC (ccRCC), papillary RCC (pRCC), and chromophobe RCC (chRCC), at the genetic, transcript, protein, and metabolite level and highlight their mutual influence on GSH metabolism. A further discussion addresses the question of how the manipulation of GSH levels can be exploited as a potential treatment strategy for RCC

Glucose deprivation activates a metabolic and signaling amplification loop leading to cell death.

The altered metabolism of cancer can render cells dependent on the availability of metabolic substrates for viability. Investigating the signaling mechanisms underlying cell death in cells dependent upon glucose for survival, we demonstrate that glucose withdrawal rapidly induces supra-physiological levels of phospho-tyrosine signaling, even in cells expressing constitutively active tyrosine kinases. Using unbiased mass spectrometry-based phospho-proteomics, we show that glucose withdrawal initiates a unique signature of phospho-tyrosine activation that is associated with focal adhesions. Building upon this observation, we demonstrate that glucose withdrawal activates a positive feedback loop involving generation of reactive oxygen species (ROS) by NADPH oxidase and mitochondria, inhibition of protein tyrosine phosphatases by oxidation, and increased tyrosine kinase signaling. In cells dependent on glucose for survival, glucose withdrawal-induced ROS generation and tyrosine kinase signaling synergize to amplify ROS levels, ultimately resulting in ROS-mediated cell death. Taken together, these findings illustrate the systems-level cross-talk between metabolism and signaling in the maintenance of cancer cell homeostasis

Coordinated transcriptional regulation between a reactive oxygen species-responsive gene network and the circadian clock in Arabidopsis thaliana : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Plant Biology, New Zealand

Most organisms have evolved endogenous biological clocks as internal timekeepers to fine-tune physiological processes to the external environment. Energetic cycles such as photosynthesis and glycolytic cycles are physiological processes that have been shown to be under clock control. This work sought to understand the mechanism of the synchrony between the circadian oscillator and products of energetic cycles. The fact that plants rely on photosynthesis for survival,and that photosynthesis relies on the sun, this would have meant that oxygen levels would have fluctuated across the day. A common by-product of oxygen metabolism and photosynthesis is the Reactive Oxygen Species(ROS). Evidence has proposed ROS as regulators of cellular signaling and plant development. However, if ROS levels are left unmanaged, it may cause oxidative stress in organisms, which could damage cellular components and disrupt normal mechanisms of cellular signaling. Therefore, it is advantageous for plants to be able to anticipate such periodic burst in ROS. My research investigates the role of the circadian clock in regulating ROS homeostasis in the model plant Arabidopsis thaliana. I found that ROS production and scavenging wax and wane in a periodic manner under diurnal and circadian conditions. Not only that, at the transcriptional level, ROS7 responsive genes exhibited time-of-day specific phases under diurnal and circadian conditions,suggesting the role of the circadian clock in ROS signaling. Mutations in the core-clock regulator, CIRCADIAN3 CLOCK3 ASSOCIATED3 1 (CCA1), affect both the transcriptional regulation of ROS genes and ROS homeostasis. Furthermore, mis- expressions of other clock genes such as EARLY3 FLOWERING3 33 (ELF3), LUX3 ARRHYTHMO3 (LUX) and TIMING3 OF3 CAB3 EXPRESSION3 13 (TOC1) also have profound effects on ROS signaling and homeostasis, thus suggesting a global clock effect on ROS networks. Taken together, CCA1 is proposed as a master regulator of ROS signaling where the response to oxidative stress is dependent on the time of CCA1 expression. Plants exhibit the strongest response at dawn, the time when CCA1 peaks. Moreover, CCA1 can associate to the Evening Element or CCA17Binding Site on promoters of ROS genes in vivo to coordinate transcription. A common feature of circadian clocks is the presence of multiple interlocked transcriptional feedback loops. It is shown here that the oscillator incorporates ROS as a component of the loop where ROS signals could feed back to affect circadian behavior by changing CCA1 and TOC1 transcription. The clock regulates a plethora of output pathways; particularly the transcription of an output gene FLAVIN3BINDING3KELCH3REPEAT3FHBOX31(FKF1) is affected by ROS signals. Temporal coordination of ROS signaling by CCA1 and the reciprocal control of circadian behavior by ROS revealed a mechanistic link of which plants match their physiology to the environment to confer fitness.Page v (Acknowledgements) has been removed from the published version at the author's request

Testing weighted splitting schemes on a one-column transport-chemistry model

In many transport-chemistry models, a huge system of ODE’s of the advection-diffusion-reaction type has to be integrated in time. Typically, this is done with the help of operator splitting. Rosenbrock schemes combined with approximate matrix factorization (ROS-AMF) are an alternative to operator splitting which does not suffer from splitting errors. However, implementation of ROS-AMF schemes often requires serious changes in the code. In this paper we test another classical second order splitting introduced by Strang in 1963, which, unlike the popular Strang splitting, seemed to be forgotten and rediscovered recently (partially due to its intrinsic parallellism). This splitting, called symmetrically weighted sequential (SWS) splitting, is simple and straightforward to apply, independent of the order of the operators and has an operator-level parallelism. In the experiments, the SWS scheme compares favorably to the Strang splitting, but is less accurate than ROS-AMF

Role of surface charge and oxidative stress in cytotoxicity of organic monolayer-coated silicon nanoparticles towards macrophage NR8383 cells

Background - Surface charge and oxidative stress are often hypothesized to be important factors in cytotoxicity of nanoparticles. However, the role of these factors is not well understood. Hence, the aim of this study was to systematically investigate the role of surface charge, oxidative stress and possible involvement of mitochondria in the production of intracellular reactive oxygen species (ROS) upon exposure of rat macrophage NR8383 cells to silicon nanoparticles. For this aim highly monodisperse (size 1.6 ± 0.2 nm) and well-characterized Si core nanoparticles (Si NP) were used with a surface charge that depends on the specific covalently bound organic monolayers: positively charged Si NP-NH2, neutral Si NP-N3 and negatively charged Si NP-COOH. Results - Positively charged Si NP-NH2 proved to be more cytotoxic in terms of reducing mitochondrial metabolic activity and effects on phagocytosis than neutral Si NP-N3, while negatively charged Si NP-COOH showed very little or no cytotoxicity. Si NP-NH2 produced the highest level of intracellular ROS, followed by Si NP-N3 and Si NP-COOH; the latter did not induce any intracellular ROS production. A similar trend in ROS production was observed in incubations with an isolated mitochondrial fraction from rat liver tissue in the presence of Si NP. Finally, vitamin E and vitamin C induced protection against the cytotoxicity of the Si NP-NH2 and Si NP-N3, corroborating the role of oxidative stress in the mechanism underlying the cytotoxicity of these Si NP. Conclusion - Surface charge of Si-core nanoparticles plays an important role in determining their cytotoxicity. Production of intracellular ROS, with probable involvement of mitochondria, is an important mechanism for this cytotoxicit

Primary and secondary oxidative stress in Bacillus

Coping with oxidative stress originating from oxidizing compounds or reactive oxygen species (ROS), associated with the exposure to agents that cause environmental stresses, is one of the prerequisites for an aerobic lifestyle of Bacillus spp. such as B. subtilis, B. cereus and B. anthracis. This minireview highlights novel insights in the primary oxidative stress response caused by oxidizing compounds including hydrogen peroxide and the secondary oxidative stress responses apparent upon exposure to a range of agents and conditions leading to environmental stresses such as antibiotics, heat and acid. Insights in the pathways and damaging radicals involved have been compiled based among others on transcriptome studies, network analyses and fluorescence techniques for detection of ROS at single cell level. Exploitation of the current knowledge for the control of spoilage and pathogenic bacteria is discussed

Oxidasi Biologi, Radikal Bebas, dan Antioxidant

Introductions : Aerobic metabolism process induces production of free radicals (ROS) 2.5% of oxygen consumption or about 3.4 kg/24 hours.  Content : Stressor likes ultraviolet radiation, hypoxia, hyperoxia, pollutant, and other chemical substances could induce ROS production. Stressor also stimulates secretion of antioxidant enzymatic such as catalase, hydropheroxidase, and superoxide dismutase. The ROS produced will disturb homeostasis or stimulate cell growth, dependent on the level of ROS. When the ROS level is overwhelm the antioxidant capacity, cell leading to undergo oxidative stress. If the ROS level and antioxidant capacities are equilibrium, it leading to cell growth. Other resources of ROS result from biologic oxidation reaction particularly from mitochondria. To scavenge ROS, cell has provided several antioxidants water and lipid soluble both enzymatic and non-enzymatic.Conclusion : The ROS is produced in aerobically life resulted from oxidative phosphorilations chain reaction. Cell provides the antioxidant both enzymatic and non-enzymatic in order to scavenge it.         Â