Figure 6.

Cyclin D1b overexpression in MCF-7 cells imparts resistance to antiestrogen therapy. A, MCF-7 cells were infected with adenovirus encoding cyclin D1b and cyclin D1, GFP (control) for 24 h. Next, cells were cultured in complete medium, CDT/Tam (left), or CDT/ICI (right) for another 36 h. Cells were harvested and analyzed by immunoblotting with antibodies to RB, cyclin A, cyclin D1, cyclin D1b, and p27Kip1. Lamin B was used as a loading control. B, MCF-7 cells were treated as described in A of the same figure. Bivariate flow cytometry was performed. Representative histograms of 20,000 gated events from two independent experiments. Quantitation of the percentage of BrdUrd-positive cells are from two independent bivariate flow cytometry experiments; *, P < 0.05; ***, P < 0.001 compared with GFP. C, MCF-7 cells infected with adenoviruses encoding either cyclin D1 or cyclin D1b were plated and cultured in FBS, CDT/Tam, or CDT/ICI for the indicated time and then processed for MTT analyses. Four replicates were performed, and the SD in the data are shown.