Figure 2.

Effect of cAMP on STAR levels and promoter activity in TG cells. A, TG cells were extracted for Western blot analysis either immediately after isolation (time zero), or after 24 and 48 h in culture. Twenty-four h after plating, the TG cells were treated with 0.5 mm 8-Br-cAMP, and the levels of STAR were examined (15 μg protein/lane) at time 0.5 and 6 h after the addition of cAMP. β-Actin served as loading marker. B, A series of promoter truncations subcloned into a CAT reporter gene (14) were used to transfect E9.5 mouse TG cells (see Materials and Methods). Twenty-four hours after transfection, cells were treated with 8-Br-cAMP (0.5 mm), and 24 h later all monolayers were harvested for CAT assays. CAT activity was determined using 2 μg protein for a 7-h assay. Promoter activity is presented as the mean ± sd of ¹⁴C-chloramphenicol converted to the acetylated products. Activity levels were statistically significant when compared with the respective values obtained for the −152/+6 construct treated with cAMP: a, P < 0.05; b, P < 0.005; c, P < 0.001; d, P > 0.1.