HB-EGF mRNA expression by ML-3 cell line in basal conditions and after different stimuli. (A) After 24 hours, HB-EGF mRNA was strongly induced by ATRA, 1,25-(OH)₂D₃(vitamin D₃), DMSO, and PMA. (B) After 96 hours, ATRA- and 1,25-(OH)₂D₃-induced bands were still present.