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Title: Role of reactive oxygen species in ras-mediated leukaemogenesis
Author: Hole, Paul Spencer
ISNI:       0000 0004 2750 1729
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2010
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Mutations of Ras and activation of the Ras pathway are amongst the most common abnormalities detected in human cancer (-20%), and in myeloid neoplasia. In addition, excessive production of reactive oxygen species (ROS) is a common feature of human malignancy and is often triggered by activation of Ras oncogenes. ROS act as second messengers and can influence a variety of cellular process including growth factor responses and cell survival. This study examined the contribution of ROS production to the phenotype of mutationally-activated Ras in normal human CD34+ haematopoietic progenitor cells. For the first time, this study demonstrated that Ras strongly upregulated the production of both superoxide and hydrogen peroxide (H2O2) in these cells, through the stimulation of NOX oxidase activity, without affecting the expression of endogenous antioxidants or the production of mitochondrial ROS. Ras also promoted both the survival and the growth factor independent proliferation of CD34+ cells. Using oxidase inhibitors and antioxidants, it was found that excessive ROS production by these cells did not contribute to their enhanced survival rather, this study presents the first data demonstrating that ROS promoted their growth factor-independent proliferation. While Ras-induced ROS production specifically activated the p38MAPK oxidative stress response, this failed to induce expression of the cell cycle inhibitor pl6INK4A instead, ROS promoted the expression of cyclin Dl and D3. Expression of activated Ras in human haematopoietic progenitors drives hyperphosphorylation of PKC family members, which mediates several phenotypes of mutant Ras in haematopoietic cells including dysregulated development. This study demonstrated that endogenous H2O2 production contributes to hyperphosphorylation of PKC in this model, and that exogenous H2O2 can drive phosphorylation of PKC in a similar manner. Finally, this study presents preliminary data obtained by kinomic PepChip analysis suggesting that endogenous ROS production driven by mutant Ras can influence the kinase activity of these cells, consistent with the hypothesis that ROS may promote protein phosphorylation via phosphatase inhibition. In summary, this study presents novel data showing endogenous ROS production makes a significant contribution to the phenotype of human haematopoietic progenitor cells expressing mutant Ras and suggests that targeting ROS may be a valid approach in acute myeloid leukaemia therapy.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available