Expression levels of C/EBPα, C/EBPβ, RUNX1, RUNX3, and CBFβ in differentiating U937 and THP-1 myeloid cells. Nuclear extracts (A,C) and whole cell extracts (B,C) were obtained from U937 (A-C) and THP-1 (A) cells at the indicated time points along PMA-induced differentiation; 10 μg from each extract was subjected to Western blot using polyclonal antisera specific for C/EBPα, C/EBPβ (Santa Cruz Biotechnology), RUNX1, CBFβ (Oncogene Research), and RUNX3.⁴⁷  The position of each protein is indicated.