Attachment of stem leukemic cells to the bone marrow extracellular matrix increases their resistance to chemotherapy and contributes to the disease persistence. In chronic myelogenous leukemia (CML), the activity of the fusion BCR-ABL kinase affects adhesion signaling. Using real-time monitoring of microimpedance, we studied in detail the kinetics of interaction of human CML cells (JURL-MK1, MOLM-7) and of control BCR-ABL-negative leukemia cells (HEL, JURKAT) with fibronectin-coated surface. The effect of two clinically used kinase inhibitors, imatinib (a relatively specific c-ABL inhibitor) and dasatinib (dual ABL/SRC family kinase inhibitor), on cell binding to fibronectin is described. Both imatinib and low-dose (several nM) dasatinib reinforced CML cell interaction with fibronectin while no significant change was induced in BCR-ABL-negative cells. On the other hand, clinically relevant doses of dasatinib (100 nM) had almost no effect in CML cells. The efficiency of the inhibitors in blocking the activity of BCR-ABL and SRC-family kinases was assessed from the extent of phosphorylation at autophosphorylation sites. In both CML cell lines, SRC kinases were found to be transactivated by BCR-ABL. In the intracellular context, EC50 for BCR-ABL inhibition was in subnanomolar range for dasatinib and in submicromolar one for imatinib. EC50 for direct inhibition of LYN kinase was found to be about 20 nM for dasatinib and more than 10 µM for imatinib. Cells pretreated with 100 nM dasatinib were still able to bind to fibronectin and SRC kinases are thus not necessary for the formation of cell-matrix contacts. However, a minimal activity of SRC kinases might be required to mediate the increase in cell adhesivity induced by BCR-ABL inhibition. Indeed, active (autophosphorylated) LYN was found to localize in cell adhesive structures which were visualized using interference reflection microscopy.

Department of Cell Biology Faculty of Science Charles University Prague Prague Czech Republic

Department of Cellular Biochemistry Institute of Hematology and Blood Transfusion Prague Czech Republic

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