Figure 1.
Selective inhibition by TGFβ of the cAMP-dependent stimulation of DNA synthesis. Quiescent 4-day-old dog thyrocytes were stimulated for 48 h with either (A) TSH (1 mU/ml), forskolin (10−5 M), or dibutyryl cAMP (10−4 M), or (B) EGF (25 ng/ml), HGF (40 ng/ml), or TPA (10 ng/ml), or none, in combination or not with different TGFβ1 concentrations. BrdU was present for the last 24 h, and the percentage of BrdU-labeled cells was determined. (C) Iodide uptake was measured in parallel. Four-day-old dog thyrocytes were stimulated for 48 h by TSH (1 mU/ml) with or without various TGFβ1 concentrations or remained in control condition. Cells were then incubated for 2 h with 131I-labeled Na (10−6 M, 2 μCi/ml) and mercaptomethylimidazol (1 mM), and the cell radioactivity was measured as described (Taton et al., 1993).