Heterodi-(oligo)merization of STAT5A and STAT5B in TonB cells.

<p>TonB cells were cultured in the presence of IL-3, BCR-ABL, and IL-3 plus BCR-ABL. Aliquots were starved overnight by withdrawal of IL-3 (Starvation) and re-stimulated with IL-3 for 30 minutes (Restimulation) or were treated with 1 µM imatinib mesylate (BCR-ABL+IM). Cells were lysed and STAT5A (left) and STAT5B (right) were immunoprecipitated with isoform-specific anti-STAT5 antibodies. Overall tyrosine phosphorylation of precipitated proteins (upper panel), co-precipitation of the other STAT5 isoform (middle panel), and the amount of precipitated STAT5 as a loading control (lower panel) were analyzed by western blotting.