Cdk9 signaling promotes megakaryocytic and inhibits erythroid induction. (A) K562 cells transduced with lentiviral shRNA constructs targeting Cdk9 (C9) underwent immunoblotting of whole cell lysates with the indicated antibodies. (B) Cells from panel A were treated 72 hours with 25 nM of TPA before immunoblotting. (C,D) K562 cells transduced with lentiviral shRNA constructs targeting HEXIM1 (H1) were subjected to immunoblot analysis of the whole cell lysates with the indicated antibodies. R1 indicates RUNX1. Where designated, cells received 200 nM of flavopiridol (FP) for 24 hours before harvesting. (E) Cells from panel C treated with 25 nM of TPA underwent immunoblot analysis. Arrows indicate position of αIIb integrin.