Figure 4.

Transcriptional activation does not accurately reflect accessibility of a recombination substrate. (A) Transcription of the MMTV LTR is increased by butyrate treatment when the promoter is stably maintained. Cells harboring transiently unmethylated (white), stably unmethylated (gray), or stably methylated (black) pSC1 were assayed for luciferase activity after drug treatment as indicated. The fold activation was calculated by setting the untreated samples to one, and the numerical values are listed above the bars. The average of three experiments is shown. The absolute level of luciferase activity of the untreated stable pSC1 was 1,062 ± 490; stable pSC1 ME was 323 ± 78; and that with no extract was 237 ± 76. (B) Western blot analysis reveals that glucocorticoid receptor (GR) is expressed in 293E cells as compared with U2OS cells that do not express glucocorticoid receptor and HeLa cells known to express glucocorticoid receptor (42, 43). (C) E1a can block glucocorticoid-dependent transactivation of the MMTV LTR. U2OS cells were transfected with glucocorticoid receptor in the presence (black) or absence (white) of E1a and dexamethasone (Dex) and were monitored for luciferase activity.