Comprehensive In Vivo Analysis of p300 Hematopoietic Tumor Suppressor Functions.

Characterization of chromosomal translocations in leukemias has led to a better understanding of the causes of disease, as well as to new cures. The transcriptional co-activators p300 and CBP are not only targets of translocations, but perturbation of their normal function is central to the transforming effects of most translocation oncogenes in acute myelogenous leukemia. In our prior studies, we demonstrated that genetic inactivation of p300 or CBP function resulted in perturbed hematopoietic differentiation, and the development of hematologic malignancies. However, given the large size and many functional domains of p300/CBP, it has been difficult to determine which specific domains and activities are necessary for them to suppress hematologic tumor formation. We have now developed a novel forward-genetic mouse model that allows us to systematically evaluate p300 structure-function and determine which functional domain mediates hematologic tumor suppression in vivo. By systematically mutating functional domains within p300 and expressing the mutants in embryonic stem (ES) cells, we have been able to generate a series of chimeric mice lines, each expressing a particular mutation in p300. Our current work entails the careful examination of the peripheral blood and bone marrow for each mouse line in order to determine the importance of specific p300 domains for the suppression of hematologic malignancies that arise in the absence of p300. Moreover, this study is helping us gain insight into the mechanisms responsible for the establishment and maintenance of normal, functional stem and progenitor cell populations. This information will be important for elucidating the transcriptional programs that are likely disrupted in leukemias, thus revealing molecular mechanisms that can be used to direct the development of new cures.