Expression of RUNX1 correlates with megakaryocytic induction of K562 cells. (A) Immunoblottting of whole cell lysates with rabbit anti-RUNX1. K562 cells were grown for 48 hours with or without TPA and with or without a bone marrow stromal monolayer. Immunoblotting with mouse antitubulin was performed to control for lane loading. (B) Immunoblotting of whole cell lysates with rabbit anti-RUNX1, rabbit anti–phospho-ERK, and mouse antitubulin. K562 cells were grown for 48 hours with or without TPA and with or without the MKK1/2 inhibitor U0126.