Figure 2.

Estrogen signaling enhances luminal progenitor proliferation. (A) Luminal progenitors were examined using CFC assays and were either treated with E₂, EtOH, E₂ plus ICI, or EtOH plus ICI at the indicated concentrations. The CFC cultures were fixed and stained, and the colony numbers were quantified (n=3). As shown, in the presence of E₂, the colony-forming capacity of luminal progenitors was increased (1.48-fold as compared to EtOH), and blocking ERα significantly attenuated this induction. (B) Luminal progenitors were treated as in (A), and colony size (i.e., the ability of the luminal progenitors to form mature luminal cells) was determined by counting the number of cells in each colony. As shown, ICI treatment significantly reduced colony size in a dose-dependent manner. Images show representative colonies from each treatment. (C) Luminal progenitors were placed in matrigel cultures with or without irradiated fibroblasts (i3T3) in complete medium for 7 days and were then treated with E₂, E₂ plus ICI, or EtOH for an additional 7 days. Thereafter, the frequency of progenitors was assessed via CFC assay. In matrigels without i3T3, E₂ significantly increased luminal progenitor frequency, which was circumvented with ICI. Interestingly, the addition of i3T3 alone increased progenitor cell numbers, and the addition of E₂ had a small but statistically significant effect. Aliquots from the same samples were placed in the CFC assays before the matrigel cultures to give the starting luminal progenitor frequency. *P<0.05, **P<0.005, ***P<0.0001, ****P<0.00001.