Induction of JAML mRNA in RA-treated cells. (A) Time-response to ATRA in NB4 cells. Cells were treated for different times using 5 × 10^-7 M ATRA. (B) JAML expression correlates with the capacity of NB4 cells to differentiate. NB4 and NB4.306 cells were cultured with 10^-6 M ATRA and harvested after 0, 24, and 48 hours. Viable cells (i) and percent of NBT-positive cells (ii) were counted each day and JAML mRNA expression was analyzed (iii). (C) JAML mRNA is induced in ATRA-treated primary APL cells. Cells were purified from 3 untreated patients cultivated in the absence (–) or presence (+) of 10^-7 M ATRA for 5 (APL no. 2)or6(APL no. 1 and APL no. 3) days. Northern blots were performed using 8 μg (A,Biii) or 2 μg (C) total RNA. Hybridization with a glyceraldehyde phosphate dehydrogenase (GAPDH) probe controlled for RNA quantities in each lane.