BRCA1delC, but not siRNA, inhibits cell cycle progression in human breast cancer cell lines. (a) Decreased bromodeoxyuridine (BrdU) incorporation in T47D and MDA-MB-468 BRCA1delC (del) clones. Neomycin-resistant clones were used as controls. Separate cultures were transiently transfected with BRCA1 siRNA. Clones were treated with etoposide (E) as described in Materials and Methods. These experiments were performed three times with similar results. Error bars indicate SEM. (b) T47D and MDA-MB-468 BRCA1delC and neomycin-resistant control (neo) clones were treated with etoposide (etopo) or vehicle prior to western blotting with the anti-cell-cycle-regulatory antibodies indicated at the left. Blots were stripped and incubated with anti-β-actin antibody to determine the relative amounts of protein in each lane. Representative blots are shown.