STI 571 inhibits Steel factor (SLF)–dependent phosphorylation of c-kit.

Serum was withheld from M-07e cells overnight before they were pretreated with various concentrations of STI 571 for 90 minutes. Cells were then treated with vehicle (phosphate-buffered saline) or SLF (final concentration, 200 ng/mL) for 15 minutes. Whole cell lysates were immunoblotted by using an antiphosphotyrosine (anti-P-Tyr) antibody. The membrane was stripped and reprobed with a monoclonal antibody specific for human c-kit. The arrow indicates the position of the 145-kd isoform of c-kit. Representative results from 1 of 8 independent experiments are shown.