The Grb2 binding site is required for the induction of chronic myeloid leukemia-like disease in mice by the Bcr/Abl tyrosine kinase.

The BCR/ABL oncogene results from a balanced translocation between chromosomes 9 and 22 and is found in patients with chronic myeloid leukemia (CML) and in some patients with acute B-lymphoid leukemia. The Bcr/Abl fusion protein is a constitutively active tyrosine kinase that stimulates several intracellular signaling pathways, including activation of Ras through direct binding of the SH2-containing adapter protein Grb2 to Bcr tyrosine 177. A tyrosine-to-phenylalanine mutation (Y177F) at this site blocks the co-association of Bcr/Abl and Grb2 in vivo and impairs focus formation by Bcr/Abl in fibroblasts. However, the Bcr/Abl Y177F mutant can transform hematopoietic cell lines and primary bone marrow cells in vitro, so the importance of the Bcr/Abl-Grb2 interaction to myeloid and lymphoid leukemogenesis in vivo is unclear. We have recently demonstrated the efficient induction of CML-like myeloproliferative disease by BCR/ABL in a murine bone marrow transduction/transplantation model system. The Y177F mutation greatly attenuates the myeloproliferative disease induced by BCR/ABL, with mice developing B- and T-lymphoid leukemias of longer latency. In addition, the v-abl oncogene of Abelson murine leukemia virus, whose protein product lacks interaction with Grb2, is completely defective for the induction of CML-like disease. These results suggest that direct binding of Grb2 is required for the efficient induction of CML-like myeloproliferative disease by oncogenic Abl proteins. (Blood. 2000;96:664-670)

The P190, P210, and P230 forms of the BCR/ABL oncogene induce a similar chronic myeloid leukemia-like syndrome in mice but have different lymphoid leukemogenic activity.

The product of the Philadelphia chromosome (Ph) translocation, the BCR/ABL oncogene, exists in three principal forms (P190, P210, and P230 BCR/ABL) that are found in distinct forms of Ph-positive leukemia, suggesting the three proteins have different leukemogenic activity. We have directly compared the tyrosine kinase activity, in vitro transformation properties, and in vivo leukemogenic activity of the P190, P210, and P230 forms of BCR/ABL. P230 exhibited lower intrinsic tyrosine kinase activity than P210 and P190. Although all three oncogenes transformed both myeloid (32D cl3) and lymphoid (Ba/F3) interleukin (IL)-3-dependent cell lines to become independent of IL-3 for survival and growth, their ability to stimulate proliferation of Ba/F3 lymphoid cells differed and correlated directly with tyrosine kinase activity. In a murine bone marrow transduction/transplantation model, the three forms of BCR/ABL were equally potent in the induction of a chronic myeloid leukemia (CML)-like myeloproliferative syndrome in recipient mice when 5-fluorouracil (5-FU)-treated donors were used. Analysis of proviral integration showed the CML-like disease to be polyclonal and to involve multiple myeloid and B lymphoid lineages, implicating a primitive multipotential target cell. Secondary transplantation revealed that only certain minor clones gave rise to day 12 spleen colonies and induced disease in secondary recipients, suggesting heterogeneity among the target cell population. In contrast, when marrow from non- 5-FU-treated donors was used, a mixture of CML-like disease, B lymphoid acute leukemia, and macrophage tumors was observed in recipients. P190 BCR/ABL induced lymphoid leukemia with shorter latency than P210 or P230. The lymphoid leukemias and macrophage tumors had provirus integration patterns that were oligo- or monoclonal and limited to the tumor cells, suggesting a lineage-restricted target cell with a requirement for additional events in addition to BCR/ABL transduction for full malignant transformation. These results do not support the hypothesis that P230 BCR/ABL induces a distinct and less aggressive form of CML in humans, and suggest that the rarity of P190 BCR/ABL in human CML may reflect infrequent BCR intron 1 breakpoints during the genesis of the Ph chromosome in stem cells, rather than intrinsic differences in myeloid leukemogenicity between P190 and P210.