The BCR-ABL oncogene is a fusion gene formed by the t(9,22) Philadelphia chromosome found in the chronic and acute phases of chronic myelogenous leukemia. The acute phase is also characterized by additional genetic changes which may be responsible for the transition to acute leukemia. One of these changes is the loss or mutation of the recessive oncogene p53, but the significance of these alterations is unknown. The objective of this research proposal is to determine if alterations in the p53 gene can enhance the transforming potential of the BCR-ABL oncogene in vitro. Patient samples will then be examined for analogous mutations. Unlike the recessive retinoblastoma oncogene, mutations in the p53 gene can act as a dominant negative oncogene. I will study the effect of mutant p53 genes on the growth of fibroblast and hematopoietic cells containing the BCR-ABL gene. Our laboratory has already demonstrated cooperativity between the BCR-ABL and v-myc genes for transformation of rat fibroblast cells. Because of its speed and simplicity I will use this fibroblast model to identify p53 mutations that cooperate with the BCR-ABL gene for transformation. Assays for transformation will include morphology in liquid culture, growth in soft agar, and tumor formation in nude mice. p53 mutations which are transforming in the fibroblast system will be tested for specificity in hematopoietic cells expressing the BCR-ABL gene using mouse bone marrow culture systems already in place in our laboratory. Based on transforming p53 mutations identified in vitro, I will examine blood and bone marrow samples from patients with chronic myelogenous leukemia for analogous p53 mutations. These experiments will use polymerase chain reaction technology to amplify targeted regions of the p53 cDNA from patient samples to study for mutations. The functional significance of any mutation identified in clinical Samples can be tested in the in vitro model. This research will increase our understanding of the acute phase of chronic myelogenous leukemia.