Effect of 9-cis retinoic acid (9-cis–RA) and vitamin D analog (KH1060) on C/EBPε protein expression in NB4 cells. NB4 cells were cultured with 9-cis-RA (10⁻⁷ mol/L), KH1060 (10⁻⁷ mol/L) and 9-cis–RA + KH1060 (10⁻⁷ mol/L). Rat-1 cell transfected with either C/EBPε expression vector or empty vector were used as positive (+) and negative (−) controls, respectively. Cells were harvested for protein extraction on days 0, 2, and 4 of culture and analyzed by Western blotting.