Studies of human chronic myelogenous leukemia in a mouse model

CML is a stem cell disease and is characterized by the Philadelphia (Ph) chromosome and its product, Bcr-Abl. Despite the extensive studies on Bcr-Abl over the years, the understanding of Bcr-Abl mediated leukemogenesis has been hampered by the inability to develop a proper animal model for CML. The major obstacles in developing an efficient animal model using retroviral transduction and bone marrow transplantation techniques have been finding the conditions with which to infect the right target cells, and directing and maintaining Bcr-Abl expression in the cells. By using different conditions and a retrovirus vector, I found that Bcr-Abl reproducibly induced CML-like myeloproliferative disorder (MPD) in mice with 100% efficiency and a latency of 3-to-4 weeks. These features made this model ideal for the investigation on the functions and importance of the domains, binding proteins, and signal pathways of Bcr-Abl in Bcr-Abl mediated leukemogenesis. I found that Interleukin (IL)-3 and Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) were overproduced in leukemic bone marrow cells. Structure-function analysis revealed that the SH2 domain of Bcr-Abl was not required for the induction of MPD in mice. However, in contrast to the mono-phasic disease of wild type Bcr-Abl mice, SH2 mutant Bcr-Abl mice manifested a bi-phasic disease: an early B-lymphoproliferative disorder followed by a delayed, but similar MPD, as induced by wild type Bcr-Abl. Furthermore, I showed that the B-lymphoproliferative disorder induced by SH2 mutant Bcr-Abl could be suppressed by MPD induced by wild type Bcr-Abl. I found that the tyrosine kinase activity of Bcr-Abl was essential for the induction of MPD (or any disease) in mice. However, we also found that the Abl tyrosine kinase activity alone was not sufficient to induce CML, suggesting that the Bcr sequences in Bcr-Abl played an important role(s) in CML induction. I found that the coiled-coil domain of Bcr sequences was necessary and sufficient to activate Abl to induce CML. Deletion of the Src Homology (SH)-3 domains rescued the ability of the coiled-coil domain deleted Bcr-Abl to induce MPD, suggesting that both the coiled-coil domain and the rest of the Bcr sequences have determinants for MPD induction.