STI571 inhibits Sp transcription factors binding and transactivation capacities. (A) EMSAs with nuclear extracts of untreated (-) or STI571 treated (+) K562 cells in the absence (Ctrl) or the presence of 0.2 μg Sp1- or Sp3-specific antibodies. Formation of specific complexes is indicated on the left (a, B, c, and D) according to the nomenclature already described.7 In the presence of the Sp1 or Sp3 antibodies, migration of specific complexes is retarded as indicated in the text, demonstrating that the complex contains Sp1 or Sp3. The position of supershifted complexes is indicated by black ovals. *Positions of the complexes that have disappeared or the intensity of which has been reduced in the presence of the antibodies. Note that the intensity of supershifted complexes decreased in the presence of STI571. (B) Relative luciferase activity measured 24 hours after the transfection of 20 μg control empty vector or Gal4/Sp1 in the absence (-) or in the presence (+) of 5 μM STI571. These results are representative of 4 independent experiments performed in duplicate ± SE.
