TGF-β1 responsiveness in various leukemia cell lines with the up- or down-regulation of TCF8 expression. (A,B) The down-regulation of the TCF8 protein by TCF8 siRNA. The CTLL2 (A) and MOLT4 (B) cell lines were transfected with either TCF8 or the AllStars Negative Control (ANC) siRNAs and then were incubated for 24 hours. The levels of TCF8 protein were examined in each cell line by Western blotting (left panel). After transfection with siRNAs, the cells were treated with the indicated concentrations of TGF-β1 for 72 hours. The degree of proliferation of each cell line was examined by MTT assay. The results are shown as percentages of the values obtained from the control TGF-β1–free culture (right panel). A ◇ represents parental cells, □ represents cells treated with ANC siRNA, and ▴ represents cells treated with TCF8 siRNA. Student t test (P < .05) was used for the statistical analysis. (C,D) The enforced expression of TCF8 in HTLV-1–infected cell lines. The TCF8 protein levels were examined in each MT-2 (C) and HUT102 (D) cell transfected with a mock or TCF8 expression plasmid after 24 hours by Western blotting (left panel). The cells were treated with the indicated concentrations of TGF-β1 for 72 hours and the proliferation of each was examined by MTT assay. The results are shown as percentages of the values obtained from the control TGF-β1–free culture (right panel). Parental cells (◇), mock vector-transfected cells (□), and TCF8 expression plasmid-transfected cells (▴). All data are the means plus or minus standard deviation in a duplicate assay. Student t test (P < .05) was used for the statistical analysis.