FIG. 2.

Cell-type-specific activation of bcl-2 promoter by RB. (A) Effects of RB on the activity of Bcl-2 P1P2 and Bcl-2 P1 promoters in MDCK epithelial cells. One microgram of each Bcl-2 CAT construct was transfected with 5 μg of pSV-RB expression vector (black bars) or the pSV-RBΔ vector as a control (white bars). The results shown are averages of values obtained in three independent experiments expressed as fold activation of CAT activity relative to the basal promoter activity, which is assigned a value of 1. Error bars indicate standard deviation. (B) Dose-dependent effect of RB on transcriptional activity of the Bcl-2 P1P2 promoter in MDCK epithelial cells and in NIH 3T3 fibroblasts. One microgram of Bcl-2 P1P2 CAT construct was cotransfected with increasing amounts of pSV-RB expression vector (solid lines, filled circles) or the pSV-RBΔ vector as a control (stippled lines, triangles). Each value is expressed as fold activation of CAT activity relative to the baseline value obtained by cotransfecting the Bcl-2 P1P2 CAT vector with the empty expression vector. The results shown are the averages of values obtained in three independent experiments performed in duplicate. Error bars indicate standard deviations. (C) Effects of RB on the activity of Bcl-2 P2 (−1093) promoter in MDCK epithelial cells, in two stably transformed cell lines: fibroblast-like MDCK(1-6) transformed by wild-type LT and epithelial-cell-like MDCK(2a5) transformed by mutated LT(K1) and in MCF7 cells. Cells were transfected with 1 μg of the Bcl-2 P2 (−1093) CAT construct and 5 μg of the pSV-RB expression vector (black bars) or the empty expression vector (white bars). The results are averages of values obtained in three independent experiments performed in duplicate and are expressed as in panel A.