Post-translational modification of p53 protein in response to DNA damage

grantor: University of Torontop53, the tumour suppressor, has potent growth suppressive functions. It is not normally active in cells. It is activated by damage to DNA, or by the presence of activated oncogenes in cells. The mechanism by which p53 protein is activated to reveal its anti-proliferative functions is of importance, and is the theme of this thesis. Post-translational modifications of proteins often signal their activation or inactivation. p53 is known to have several post-translational modifications--phosphorylation, acetylation, glycosylation, poly(ADP)ribosylation and 5.8S rRNA linkage. One aim of the thesis was to identify molecules that would signal DNA damage to p53, to activate its function. The other aim was to identify post-translational modifications on p53 following DNA damage induced by ionizing radiation. Using non-radioactive techniques, this thesis demonstrates that ionizing radiation causes post-translational modifications on p53, especially in the form of multiple phosphorylations and acetylations. The role of DNA-dependent protein kinase in phosphorylating and regulating p53 function was assessed. Though this kinase is activated by damaged DNA, and can phosphorylate p53 'in vitro', this study did not find any evidence of a functional role for DNA-dependent protein kinase in mouse cells. Evidence is also presented to show that phosphorylation of p53 on the cell cycle-regulated cyclin dependent kinase 1 site is constitutive and is not regulated by ionizing radiation.Ph.D