TCF4 regulates BIRC5 expression. (A) To determine whether TCF transcription activity was present in HTLV-1–infected cells, promoter plasmids containing 3 wild-type (pGL3-OT/Top; ■) or mutant (pGL3-OF/Fop; □) copies of the TCF4 binding site driving luciferase expression were transfected into C8166 or primary cells from an ATL patient (ATL46) using Human T-cell Nucleofection kit (Amaxa). The CMV–β-galactosidase control plasmid was cotransfected to adjust for transfection efficiency. Graphs represent luciferase activity from at least 2 independent experiments. (B) Control (□) plasmid or plasmid expressing a dominant-negative TCF4 protein (DN-TCF4; ■) were transiently transfected into C8166 or ATL46 cells as described in “Methods.” Forty-eight hours after transfection, cells were harvested, total RNA extracted, and RT-PCR performed for BIRC5 and GAPDH mRNA. The graph represents the BIRC5 mRNA levels per GAPDH message done in triplicate. (C) Transfection of C8166 and ATL46 cells was performed as described in “Methods.” Forty-eight hours after transfection, the viability of the cells was determined using trypan blue dye exclusion. The viability of the cells from the vector control (CON) transfection was set at 100%. The graph represents values from at least 3 experiments.