Figure 4. Ability of MCF-7 cells to form colonies after stimulation with E2 or RA under normal or inhibited IKKα activity. (A) Cells were treated as detailed in the Material and Methods section prior to be analyzed for ability to form colonies. Colonies of more than 40 cells were visible. To count also smaller colonies, a replica was obtained on transparent plastic with a black marker (as shown on the right). (B) Specific fields (two for each treatment) as examined by light microscopy (10×) revealing that addition of any or the other ligand to IKKα-inhibited cells further diminished the number of the smaller colonies induced by addition of BAY11-7082. The reported experiment has been confirmed by two different assays that originated very similar results.