Adhesion of human Meg-01 leukemia cells to fibronectin is unresponsive to tyrosine kinase attenuation by STI571.

(A) Meg-01 cells were treated in triplicate with 10 μM STI571 (▴) or an equal volume of PBS used as the delivery vehicle (○) and were allowed to proliferate in Meg-01 media. Cell viability was determined by trypan blue exclusion. (B) Western blots of whole cell lysates were run to show expression of P210^BCR-ABL and tyrosine-phosphorylated proteins in Meg-01 cells treated with 10 μM STI571 or PBS for 3 hours. The P210^BCR-ABL–specific band is indicated by an asterisk. Expression of grb2 was used as a loading control. (C) τ₅₀ was determined for spins with Meg-01 cells treated with 10 μM STI571 for 3.5 hours (n = 11) or an equal volume of PBS for 1.5 hours or 3.5 hours (n = 12). No difference in adhesion was observed between 1.5 hours and 3.5 hours for control Meg-01 cells treated with only PBS (data not shown). The magnitude of binding was not significantly affected when the kinase activity was arrested by STI571 (P = .81); however, decreased adhesion could be measured by blocking α₅β₁integrins with a soluble RGD fragment (n = 4) that prevents binding to fibronectin. Meg-01 cells treated with STI571 or PBS were assayed on BSA only (no FN), which represents nonspecific binding and is very small, at or below the minimum detection threshold of the device (≤ 5 dyne/cm²). At times, profiles could not be determined because of the small number of cells remaining after a spin in the absence of fibronectin.