Molecular mechanisms of transformation by the BCR-ABL oncogene.

The BCR-ABL oncogene is generated by the Philadelphia chromosome (Ph) translocation, fusing the BCR gene to the ABL gene. The BCR-ABL fusion protein has elevated ABL tyrosine kinase activity that is critical for transformation of hematopoietic cells. Chronic myelogenous leukemia (CML) cells transformed by BCR-ABL show reduced growth factor requirements and apoptosis, as well as enhanced viability and altered adhesion. The elevated ABL kinase activity leads to chronic activation of signaling pathways that are required for all aspects of transformation. Progression of the disease from chronic phase to blast crisis correlates with additional cytogenetic alterations that are likely to contribute to the failure of traditional therapy. This review describes molecular mechanisms that are thought to be important for transformation by the BCR-ABL oncoprotein and points at pathways for targeted drug development in the treatment of CML.