BCR-ABL-induced adhesion defects are tyrosine kinase-independent

The t(9;22) chromosomal translocation results in expression of P210^BCR-ABL a fusion protein necessary for the development of chronic myelogenous leukemia (CML). The constitutive activation of the P210^BCR-ABL tyrosine kinase results in phosphorylation of multiple signaling pathways leading to the transformed phenotype. Additionally, extracellular interactions between P210^BCR-ABL-expressing progenitor cells and bone marrow stroma may provide external signals that facilitate CML development. In contrast to the intracellular signaling pathways involved in CML, little is known about how P210^BCR-ABL expression modifies cell-cell and cell-substratum interactions. To investigate the role of P210^BCR-ABL in modulating cellular adhesion, we used a highly sensitive and quantitative cell detachment apparatus that measures the strength of association between a population of cells and an adhesive matrix. Our findings show that P210^BCR-ABL expression increased adhesion nearly 2-fold between the myeloblastic cell line, 32D, and fibronectin compared to a control vector. We then investigated whether abnormal adhesion due to P210^BCR-ABL expression was caused by its tyrosine kinase activity. A quantitative analysis of cell-fibronectin adhesion found that neither expression of a kinase-inactive P210^BCR-ABL mutant in 32D cells or attenuation of kinase activity by STI571 (imatinib mesylate) in 32D cells transduced with wild-type P210^BCR-ABL could correct the nearly 2-fold increase in cell-fibronectin adhesion. Similarly, STI571 treatment of Meg-01 cells, a P210^BCR-ABL- expressing cell line derived from a patient in blast crisis, failed to inhibit adhesion to fibronectin. Together, our results indicate that changes in adhesion induced by P210^BCR-ABL are independent of its tyrosine kinase activity.