Small interfering RNA (siRNA) decreases MUC1 levels in breast cancer cells. (a) Western blots (IB) of the MUC1 cytoplasmic tail (MUC1-CT) and extracellular domain (MUC1-EX) in untreated (parental), or luciferase siRNA treated (siLuc) or MUC1 siRNA (siMUC1) treated MDA-MB-468 and BT-20 cells. Lysates were analyzed 48 hours post-transfection; tubulin is shown as a loading control. (b) Flow cytometry analysis of the MUC1 extracellular domain in unpermeabilized, siRNA-treated MDA-MB-468 and BT-20 lines. Cells were analyzed at 24 hour intervals beginning 48 hours post-transfection. The black line represents isotype control, the green luciferase siRNA (siLuc), and the red MUC1 siRNA (siMUC1).