Notch signaling regulates transcriptional level of Runx1 and modulates the function of Runx1 protein through the effector protein, Hes1. (A) COS7 cells were transfected with HA-tagged Runx1 and 3xFLAG-tagged Hes1. Whole-cell extracts were immunoprecipitated (IP) with anti-FLAG antibody or anti-HA antibody followed by immunoblotting (blot) using anti-HA antibody or anti-FLAG antibody. (B) Relative luciferase activity in HeLa cells transfected with Runx1 (200 ng) and Runx1-dependent macrophage colony-stimulating factor receptor (pM-CSF-R) luciferase reporter (300 ng) with or without cotransfection of Hes1 (60, 200, or 600 ng). Data are means ± standard errors of duplicate wells in a representative experiment. Reproducible results were obtained in 3 independent experiments.