MafB repression is required for DC differentiation. (A) MafB expression was monitored by RT-PCR in blood PBMC-derived macrophages (MΦ) and DCs. Data are representative of at least 2 separate experiments; actin RT-PCR was used as a normalization control. (B) MafB expression was monitored by RT-PCR in untreated promyelocytic HL-60 PUER clones (Myel) (lane 1) or differentiated to DC by βE treatment (lane 2), monocytic HL-60 PUER clones (Mo) cultured in the presence of D3 in the absence of βE (lane 3), or redirected to DC fate by βE-induced PU.1 activation (lane 4). Culture conditions were as described for Figure 5. (C-D) Constitutive MafB expression inhibits DC differentiation. FACS analysis of CD1a, CD80, and CD86 DC marker expression in GFP+ and GFP– cells of MFG-MafB-iGFP virus (MafB) or MFG-iGFP control viruses (ctrl) infected HL-60 cells 96 hours after induction of DC differentiation with 200 ng/mL A23187 calcium ionophore (C). Percentages of positive cells per quadrant are indicated. Differential DC marker expression in infected (GFP+, ▪) and uninfected (GFP–, ▦) cells was plotted as ratio of positive-to-negative cells for MafB virus and control virus-infected cultures (D).