Increased phosphotyrosine content on withdrawal of STI571 from LAMA84-r cells.

Total cellular protein was harvested from cells grown continuously in the presence of 1 μM STI571 (time zero) and then hourly after thorough washing and reculture in media without STI571. The Western blot membrane was probed with an antiphosphotyrosine antibody (upper panel) and reprobed with an antiactin antisera (lower panel). The densitometric ratio of the phospho-Bcr-Abl (p-p210)/actin bands is shown for each time point and demonstrates a 41-fold increase in Bcr-Abl autophosphorylation after 5 hours of STI571 withdrawal.