Role of GADD45A expression in CEBPB-dependent proliferation inhibition of 32D-BCR/ABL cells. (A) Left: Northern blot analysis on total RNA from 32D-BCR/ABL cells transduced with MigRI GFP ΔuORF-C/EBPβ-ER^TAM (lanes 1-5) or with MigRI GFP (lanes 6-9) before (lanes 1 and 6) or after (lanes 2-5 and 7-9) 4-HT treatment (250 nM). The full-length coding sequence of GADD45A was used as probe; the GAPDH probe was used to control equal loading. Right: Western blot analysis of GADD45A expression in STI571-treated CML-BC mononuclear cells. (B) Left: methylcellulose colony formation (as ratio on plated cells) from 32D-BCR/ABL cells transduced with the MigRI GFP or the MigRI GFP GADD45α-HA retrovirus. Right: proliferation of MigRI GFP or MigRI GFP GADD45α-HA-transduced 32D-BCR/ABL cells; values reported in both panels correspond to the mean plus SD of 3 different experiments. (C) Left: GADD45A expression in ΔuORF C/EBPβ-ER^TAM 32D-BCR/ABL cells transduced with GADD45A or a control shRNA retrovirus before (lanes 1, 3, 5, 7, 9) and after (lanes 2, 4, 6, 8, 10) 4-HT treatment (250 nM). Right: proliferation of 4-HT treated ΔuORF C/EBPβ-ER^TAM 32D-BCR/ABL cells (untransduced, transduced with pSRP GADD45ARNAi2 and pSRP GADD45α-RNAi3 together, or with a control shRNA). Representative of 3 different experiments; percentage of viable over untreated cells (y-axis) after 1, 2, or 3 days of 4-HT treatment (x-axis).