As₂O₃ induces down-regulation of Bcr-Abl protein in overexpressing (AR230-r1, Baf3/BCR-ABL-r1) and mutant (Ba/F3p210^T315I) Bcr-Abl–expressing cells resistant to imatinib. (A) Exponentially growing cells were exposed to increasing doses of As₂O₃. After 48 hours, cells were harvested and protein expression levels were determined by Western blot analysis using equal amount of protein. Blots were probed with antiabl (top panel) and antiactin antibodies (bottom panel). (B) Baf3/BCR-ABL-r1 cells were exposed to 1 or 2 μM imatinib ± 1 μMAs₂O₃ for 48 hours. Phosphotyrosine content and protein expression of p210^Bcr-Abl were analyzed using α-pY and α-abl antibodies. Protein loading was controlled by probing for actin.