Signaling through Cdk2, importin-alpha and NuMA is required for H2O2-induced mitosis in primary type II pneumocytes

AKT as locus of cancer multidrug resistance and fragility

Complexity and robustness of cancer hypoxic microenvironment are supported by the robust signaling networks of autocrine and paracrine elements creating powerful interactome for multidrug resistance. These elements generate a positive feedback loops responsible for the extreme robustness and multidrug resistance in solid cancer, leukemia, myeloma, and lymphoma. Phosphorylated AKT is a cancer multidrug resistance locus. Targeting that locus by oxidant/antioxidant balance modulation, positive feedback loops are converted into negative feedback loops, leading to disappearance of multidrug resistance. This is a new principle for targeting cancer multidrug resistance by the locus chemotherapy inducing a phenomenon of loops conversion.

AKT as locus of cancer positive feedback loops and extreme robustness

A positive feedback loops induce extreme robustness in metastatic cancer, relapsed leukemia, myeloma or lymphoma. The loops are generated by the signaling interactome networks of autocrine and paracrine elements from cancer hypoxic microenvironment. The elements of the networks are signaling proteins synthesized in hypoxic microenvironment such as the vascular endothelial growth factor, HIF-1α, hepatocyte growth factor, and molecules nitric oxide and H(2)O(2). The signals from upstream or rebound downstream pathways are amplified by the short or wide positive feedback loops, hyperstimulating AKT-inducing cancer extreme robustness. Targeting the phosphorylated AKT locus by an oxidant/antioxidant modulation induces collapse of positive feedback loops and establishment of negative feedback loops leading to stability of the system and disappearance of cancer extreme robustness. This is a new principle for the conversion of cancer positive loops into negative feedback loops by the locus chemotherapy.

AKT as locus of cancer angiogenic robustness and fragility

Angiogenesis get full robustness in metastatic cancer, relapsed leukemia or lymphoma when complex positive feedback loop signaling systems become integrative. A cancer hypoxic microenvironment generates positive loops inducing formation of the vascular functional shunts. AKT is an upstream angiogenic locus of integrative robustness and fragility activated by the positive loops. AKT controls two downstream nodes the mTOR and NOS in nodal organization of the signaling genes. AKT phosphorylation is regulated by a balance of an oxidant/antioxidant. Targeting AKT locus represents new principle to control integrative angiogenic robustness by the locus chemotherapy.

Hydrogen peroxide: a signaling messenger

Hydrogen peroxide (H2O2) is a well-documented component of living cells. It plays important roles in host defense and oxidative biosynthetic reactions. In addition there is growing evidence that at low levels, H2O2 also functions as a signaling agent, particularly in higher organisms. This review evaluates the evidence that H2O2 functions as a signaling agent in higher organisms in light of the known biology and biochemistry of H2O2. All aerobic organisms studied to date from prokaryotes to humans appear to tightly regulate their intracellular H2O2 concentrations at relatively similar levels. Multiple biochemical strategies for rapidly reacting with these low endogenous levels of H2O2 have been elucidated from the study of peroxidases and catalases. Well-defined biochemical pathways involved in the response to exogenous H2O2 have been described in both prokaryotes and yeast. In animals and plants, regulated enzymatic systems for generating H2O2 have been described. In addition oxidation-dependent steps in signal transduction pathways are being uncovered, and evidence is accumulating regarding the nature of the specific reactive oxygen species involved in each of these pathways. Application of physiologic levels of H2O2 to mammalian cells has been shown to stimulate biological responses and to activate specific biochemical pathways in these cells.

Cyclic stretch attenuates effects of hyperoxia on cell proliferation and viability in human alveolar epithelial cells

The treatment of severe lung disease often requires the use of high concentrations of oxygen coupled with the need for assisted ventilation, potentially exposing the pulmonary epithelium to both reactive oxygen species and nonphysiological cyclic stretch. Whereas prolonged hyperoxia is known to cause increased cell injury, cyclic stretch may result in either cell proliferation or injury depending on the pattern and degree of exposure to mechanical deformation. How hyperoxia and cyclic stretch interact to affect the pulmonary epithelium in vitro has not been previously investigated. This study was performed using human alveolar epithelial A549 cells to explore the combined effects of cyclic stretch and hyperoxia on cell proliferation and viability. Under room air conditions, cyclic stretch did not alter cell viability at any time point and increased cell number after 48 h compared with unstretched controls. After exposure to prolonged hyperoxia, cell number and [(3)H]thymidine incorporation markedly decreased, whereas evidence of oxidative stress and nonapoptotic cell death increased. The combination of cyclic stretch with hyperoxia significantly mitigated the negative effects of prolonged hyperoxia alone on measures of cell proliferation and viability. In addition, cyclic stretch resulted in decreased levels of oxidative stress over time in hyperoxia-exposed cells. Our results suggest that cyclic stretch, as applied in this study, can minimize the detrimental effects of hyperoxia on alveolar epithelial A549 cells.

Effects of transgene expression of superoxide dismutase and glutathione peroxidase on pulmonary epithelial cell growth in hyperoxia

Prolonged exposure to supraphysiological oxygen concentrations results in the generation of reactive oxygen species, which can cause significant lung injury in critically ill patients. Supplementation with human recombinant antioxidant enzymes (AOE) may mitigate hyperoxic lung injury, but it is unclear which combination and concentration will optimally protect pulmonary epithelial cells. First, stable cell lines were generated in alveolar epithelial cells (MLE12) overexpressing one or more of the following AOE: Mn superoxide dismutase (MnSOD), CuZnSOD, or glutathione peroxidase 1. Next, A549 cells were transduced with 50–300 particles/cell of recombinant adenovirus containing either LacZ or each of the three AOE (alone or in combination). Cells were then exposed to 95% O2 for up to 3 days, with cell number and viability determined daily. Overexpression of either MnSOD (primarily mitochondrial) or CuZnSOD (primarily cytosolic) reversed the growth inhibitory effects of hyperoxia within the first 48 h of exposure, resulting in a significant increase in viable cells ( P < 0.05), with 1.5- to 3-fold increases in activity providing optimal protection. Protection from mitochondrial oxidation was confirmed by assessing aconitase activity, which was significantly improved in cells overexpressing MnSOD ( P < 0.05). Data indicate that optimal protection from hyperoxic injury occurs in cells coexpressing MnSOD and glutathione peroxidase 1, with prevention of mitochondrial oxidation being a critical factor. This has important implications for clinical trials in preterm infants receiving SOD supplementation to prevent acute and chronic lung injury.

H2O2-induced proliferation of primary alveolar epithelial cells is mediated by MAP kinases

Exposure to supraphysiological oxygen concentrations during ventilatory oxygen therapy often causes tissue damage. Alveolar type II (AT II) cells are a major target for oxidant injury, and their ability to proliferate plays a critical role during the repair phase following injury. We hypothesized that reactive oxygen species (ROS), which are produced during hyperoxia, not only cause cellular damage, but may also play a role in the repair process by promoting AT II cell proliferation. We have tested the ability of ROS to induce proliferation in primary cultures of AT II cells by using a wide range of chronic and acute hydrogen peroxide (H2O2) exposures to mimic different types of oxidative stress. We found that chronic exposure to an extracellular flux of 10 microM H2O2/h can significantly increase the intracellular concentration of oxidants, DNA synthesis, and cell proliferation. H2O2-induced AT II cell proliferation was preceded by activation of the mitogen-activated protein kinase ERK (extracellular signal-regulated kinase). Inhibition of ERK and p38 activation prevented H2O2-induced proliferation. These results show that changes in intracellular oxidant concentrations can modulate downstream signaling pathways controlling AT II cell proliferation. This mechanism could be important in the repair process following hyperoxia-induced injury.

TOR kinase and Ran are downstream from PI3K/Akt in H2O2-induced mitosis

Hydrogen peroxide (H2O2) activates signaling cascades essential for cell proliferation via phosphatidylinositol-3-kinase (PI3K) and Akt. Here we show that induction of mitogenic signaling by H2O2 activates sequentially PI3K, Akt, mammalian target of rapamycin (mTOR), and Ran protein. Akt activation is followed by signaling through the mTOR kinase and upregulation of Ran in primary type II pneumocytes, a cell type implicated in the development of lung adenocarcinoma. Pretreatment of the cells with wortmannin, a specific inhibitor of PI3K, or rapamycin, a specific inhibitor of mTOR kinase, prevented H2O2-increased mitosis. H2O2-induced Akt ser-473 phosphorylation and upregulation of Ran protein were prevented by wortmannin but not by rapamycin, indicating that PI3K is upstream of Akt and mTOR is downstream from Akt. Overexpression of myr-Akt or Ran-wt in type II pneumocytes increased Akt ser-473 phosphorylation and mitosis in a catalase-dependent manner, indicating that H2O2 is essential for Akt and Ran signaling. These results indicate that H2O2-induced mitogenic signaling in primary type II pneumocytes is mediated by PI3K, Akt, mTOR-kinase, and Ran protein.