p53 protein biosignatures in acute myeloid leukemia

Abstract

p53 is a tumor suppressor protein often regarded as the guardian of the genome. It is a highly connected protein involved in many signaling processes in the cell. The inactivation of p53 through genetic mutations in TP53 is common in human cancers and can be detected in more than 50% of malignant tumors. In acute leukemia however, p53 inactivation is not normally a part of leukemogenesis and TP53 is found to be wild-type in >90% of the cases. This thesis has sought to elucidate the nature of the p53 protein regulation in acute myeloid leukemia to increase our understanding of disease development. The experiments have proposed that p53 is wild type, expressed and capable of transactivation of target genes. However, p53 phosphorylation could be correlated to expression of the anti-apoptotic protein Bcl-2 suggesting that Bcl-2 can function as a downstream block to p53-mediated apoptosis. Furthermore, Bcl-2 levels could be associated to a specific mutation in the receptor tyrosine kinase Flt3. Flt3 mutation has been found to be a strong predictor of disease relapse in AML, and driving Bcl-2 expression, thereby inhibiting the p53 pathway, may propose a new important event in leukemogenesis. This thesis has further shown that p53 exists as two main isoforms in patient material from acute myeloid leukemia. The expression of these was influenced by chemotherapy in vivo and induction of one specific form correlated to induction of known p53 target genes. The p53 protein has many known sites for post-translational modifications and serves as a substrate for many enzymes. The p53 protein may thus be a central node in a large network of proteins whose activities are critical for cell life and death. This may suggest that specific p53 signatures could serve as a ‘read-out’ for the p53 network. The expression of the described p53 isoforms were, using a novel correlation algorithm, found to be correlated to several clinical parameters including survival, remission and Flt3 mutation. This could imply that p53 may be used as a possible biomarker for clinical stratification of leukemia patients.