Biochemical and biological analysis of the leukemogenic potential of BCR/ABL

Chronic Myelogenous leukemia (CML) is a biphasic myeloproliferative disease resulting from the neoplastic transformation of the hematopoietic stem cell. The initial phase is an overexpansion of mostly granulocytes, while the blast phase is an accumulation of either myeloid or lymphoid blast cells. BCR/ABL plays a critical role in the pathogenesis of CML, and BCR/ABL contains multiple domains and motifs that can disrupt many signal transduction pathways and cellular functions. Although many binding proteins and affected pathways have been identified, the exact biologically relevant mechanisms used by BCR/ABL to cause a specific expansion of myeloid cells in CML have remained poorly understood. Murine CML models have allowed us to directly test the biological function of specific domains in BCR/ABL leukemogenesis, while techniques such as sensitive microsequencing of protein complexes aided the process of elucidating biochemical mechanisms. In this thesis I have dissected the leukemogenic potential of BCR/ABL from a biological and biochemical perspective. It has been previously shown that expression of BCR/ABL in bone marrow cells by retroviral transduction efficiently induces a myeloproliferative disorder (MPD) in mice. I demonstrate that mutation of a tyrosine containing motif within the BCR region can alter the disease specificity of p185BCR/ABL by inducing both a myeloproliferative disease and an acute B-lymphocytic leukemia (B-ALL) simultaneously in mice. Presence of this region limits the leukemogenic potential of p185BCR/ABL to the myeloid lineage, possibly through the Ras pathway. I also identify a region of BCR/ABL that mediates the interaction and phosphorylation of p62dok that may be involved in efficient expansion of myeloid cells. Finally, through purification of a protein complex mediated by adapter protein NCKbeta, I have isolated a previously unknown substrate of BCR/ABL called Eps8 that may link BCR/ABL to alteration of cytoskeletal signaling pathways. By studying from a biochemical and biological perspective, a more complete story of BCR/ABL mediated leukemogenesis can be told.