FIG. 3.

Activation of p21 promoter by E12 and E47 independent of p53. (A) Transcriptional activation of p21 promoter by E12 and E47. MG63 cells were cotransfected with 2.0 μg of the p21-luc reporter plasmid in combination with pCMV-E12, pCMV-E47, or pCMV-del E12 (Δ1-507). The cells were cultured in DMEM containing 2% FBS for 48 h and collected for luciferase assay. Luciferase activity mediated by pcDNA3 is arbitrarily set at 1. (B) Schematic diagram of luc reporter constructs. The 2.4-kb promoter sequence of the p21 gene (solid line) was cloned at the site upstream of the luciferase gene in p21-luc. Possible binding sites for E2A (inverted triangles) and p53 (boxes) in the promoter are shown. Dashed lines, internal deletions. (C) Two micrograms of p21 promoter deletion mutant reporter plasmids with or without the E12 or E47 expression plasmid (2 μg) along with the pCMV-β-gal plasmid was transfected into MG63 cells. The cells were cultured in DMEM containing 2% FBS for 48 h and collected for luciferase assay. Luciferase activities were normalized against β-Gal activities. Activities relative to that mediated by the empty pcDNA3 are shown.