Fig. 1. TTF-1 activation of the Tg and synthetic target promoters is PKA dependent in A126 cells. A, A126 cells were stably transfected with pRSV-TTF1 and pRSV-NEO. A pool of 10 clones expressing TTF1 was analyzed by Western blot analysis, using specific antibodies. Clones expressing TTF1 were further analyzed by transient transfection with pTg-CAT, pCRE-CAT, and C-PKA. B, A126 cells were transiently transfected with pRSV-TTF1, pTg-CAT, and C-PKA expressing vectors. C, A126 cells were transfected with a synthetic TTF1 target promoter (pTgTTF1-CAT) as described in the text with () or without () cotransfection with a C-PKA expression vector. The total amount of transfected DNA was adjusted to 40 µg/ml with salmon sperm DNA. A pRSV-LacZ (2.5 µ g/ml) reporter gene was included to normalize for transfection efficiency. CAT activities were quantified by ß-scope and normalized to ß-galactosidase activities. The activity of pRSV-CAT was taken as 100%. Results are expressed as the percentage of enzymatic activity and represent the means of three independent experiments; bars, SD. Stimulation by PKA of TTF1 activity was inhibited by a PKA-specific inhibitor PKI (see "Materials and Methods").