E2F1 increases the transcriptional activity of p19INK4d.

<p><b>A</b>. BHK-ER-E2F1 cells were treated with 4-OHT for 8 h and subjected to nuclear run-on assay. Transcription rates of the indicated genes were normalized to that of β-tubulin. Results are representative of two independent experiments. <b>B–D</b>. Indicated cells were cotransfected with p19CAT (4.4 µg) and pCEFL-β-galactosidase (5 µg) reporter plasmids. CAT activity was determined 48 h after transfection and normalized to β-galactosidase activity. BHK-21 cells were transfected with reporter plasmids and 1 or 3 µg of E2F1 expression vector and grown in medium containing 10% or 1% FBS (<b>B</b>). BHK-ER-E2F1 cells were transfected with reporter plasmids, grown in medium containing 10% or 1% FBS, and treated with 4-OHT as indicated (<b>C</b>). BHK-ER-E2F1 were transfected with wild-type or mutant pRB expression vectors (6 µg) or wild-type or mutant E2F DO (100 nM) for 24 h. Cells were transfected with reporter plasmids for another 24 h before 4-OHT treatment (<b>D</b>). In panels <b>B</b>, <b>C</b> and <b>D</b> values are the average ± SD of three independent experiments, each performed in triplicates.