Differentiation of NB4 cells, a maturation inducible cell line isolated from human acute promyelocytic leukemia, requires RAF1/MEK/ERK signaling involved in ATRA-induced differentiation in APL cells through enhancing the protein level of C/EBPβ, C/EBPε and PU.1 [94]. The gene discussed is CEBPE; the disease is acute promyelocytic leukemia.