Sensitivity to TGF-β in ATL cell lines and CTLL-2 cell lines expressing MEL1 or MEL1S gene. (A) Resistance of ATL cell lines to TGF-β. ATL cell lines, ATL-55T and ED, and mouse T-cell line, CTLL-2, were treated with the indicated concentrations of TGF-β for 72 hours. Proliferation of each cell was examined by MTT assay. The results are shown as percentages of the values obtained from control TGF-β-free culture. The experiment was performed at least 3 times. The results are the mean ± SD of 3 experiments. (B) Expression of MEL1 and MEL1S gene in CTLL-2 transfected with vectors expressing MEL1 or MEL1S genes. CTLL-2 was transfected with vectors expressing MEL1 or MEL1S genes, and their expressions were studied by RT-PCR as described in Figure 3. Lane 1 shows 293 cells (control); lane 2, CTLL-2/empty vector; lane 3, CTLL-2/MEL1; and lane 4, CTLL-2/MEL1S. (C) MEL1S expression confers resistance against TGF-β in CTLL-2. MEL1-expressing (▴, MEL1; ▪, MEL1S) and unmodified (•) CTLL-2 were treated with the indicated concentrations of TGF-β for 96 hours. The results are shown as percentages of the values obtained from control TGF-β-free culture. The results are the mean ± SD of 3 experiments.