Link between Mitochondria and NADPH Oxidase 1 Isozyme for the Sustained Production of Reactive Oxygen Species and Cell Death

Abstract

Although mitochondria and the Nox family of NADPH oxidase are major sources of reactive oxygen species (ROS) induced by external stimuli, there is limited information on their functional relationship. This study has shown that serum withdrawal promotes the production of ROS in human 293T cells by stimulating both the mitochondria and Nox1. An analysis of their relationship revealed that the mitochondria respond to serum withdrawal within a few minutes, and the ROS produced by the mitochondria trigger Nox1 action by stimulating phosphoinositide 3-kinase (PI3K) and Rac1. Activation of the PI3K/ Rac1/Nox1 pathway was evident 4 -8 h after but not earlier than serum withdrawal initiation, and this time lag was found to be required for an additional activator of the pathway, Lyn, to be expressed. Functional analysis suggested that, although the mitochondria contribute to the early (0 -4 h) accumulation of ROS, the maintenance of the induced ROS levels to the later (4 -8 h) phase required the action of the PI3K/Rac1/Nox1 pathway. Serum withdrawal-treated cells eventually lost their viability, which was reversed by blocking either the mitochondria-dependent induction of ROS using rotenone or KCN or the PI3K/ Rac1/Nox1 pathway using the dominant negative mutants or small interfering RNAs. This suggests that mitochondrial ROS are essential but not enough to promote cell death, which requires the sustained accumulation of ROS by the subsequent action of Nox1. Overall, this study shows a signaling link between the mitochondria and Nox1, which is crucial for the sustained accumulation of ROS and cell death in serum withdrawal-induced signaling. Reactive oxygen species (ROS)2 such as H 2 O 2 and O 2 . act as key mediators of the cellular signaling induced by the ligation of the cell surface receptors as well as by many classes of environmental agents (1-3). Cell stimulation by such agents has been shown to increase the cellular ROS levels, which regulate various cellular functions such as growth, differentiation, migration, and viability. Therefore, to better understand the regulatory mechanisms of diverse cell functions, it is essential that the cellular processes that lead to the induction of ROS be identified. The mitochondria and the Nox family of NADPH oxidase have emerged as major sources of ROS induction (4, 5). The mitochondria generate ROS as byproducts of respiration, and inhibitors of the mitochondrial respiratory chain, such as rotenone and KCN, have been shown to attenuate the ability of hormones and cytokines to promote the production of ROS in various cell types (6, 7). Confocal microscopy has consistently shown increased mitochondrial ROS levels as a response to cell stimulation (7,8). NADPH oxidase is a membrane enzyme that is responsible for the oxidative burst induced in activated phagocytes (9, 10). The proposed model suggests that phagocyte stimulation by fMLP results in the activation of phosphoinositide 3-kinase (PI3K), which then triggers the translocation of Rho GTPase Rac from the cytosol to the plas...

Intracellular reactive oxygen species are essential for PI3K/Akt/mTOR-dependent IL-7-mediated viability of T-cell acute lymphoblastic leukemia cells

“…Interestingly, the fact that both apocynin and rotenone alone were sufficient to completely prevent IL-7-mediated ROS upregulation and T-ALL cell viability suggests that NADPH complex and mitochondrial respiration may be intertwined in the context of IL-7 signaling, a possibility that is not unprecedented. [38][39][40] Glucose metabolism is regulated by glucose uptake, and in hematopoietic cells Glut1 is the primary source for intracellular glucose. 41 We previously reported that IL-7 induces Glut1 upregulation and glucose uptake in a PI3K-dependent manner in T-ALL cells.…”

Vascular endothelial growth factor in eye disease

“…All of these events have been suggested to be initiated by superoxide overproduction by the mitochondrial electron-transport chain (Brownlee, 2005). However, while mitochondrial-derived ROS are important for the initiation of oxidative stress responses in models of hyperglycemia, studies in other models indicate that activity of NADPH oxidase is required in order to sustain sufficient levels of ROS formation for the transduction of specific cellular responses (Kimura et al, 2005;Lee et al, 2006b;Schafer et al, 2003). Data showing increased activity of NAD(P)H oxidase in retinas and vascular tissues of diabetic patients and animals and in high glucose-treated endothelial cells suggest that NAD(P)H oxidase is an important source of ROS in the diabetic milieu (Al-Shabrawey et al, In Pressa; Al-Shabrawey et al, In Press-b; Al-Shabrawey et al, 2006;Ellis et al, 1998;Griendling et al, 2000;Inoguchi et al, 2003b;Sonta et al, 2004).…”

The mitochondria mediate the induction of NOX1 gene expression by aldosterone in an ATF-1-dependent manner

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