CXCR4 and breast cancer: Because the expression of CXCL12 and CXCR4 are regulated by estrogenic signals in breast cancer cells [23], we investigated the impact of COUP-TFI on the estrogenic regulation of the CXCL12 and CXCR4 genes by treating the MCF-7 clones with 10−8 M E2, 10−6 M ICI, or both for 48 h.As expected, treatment of the control MCF-7 cells with E2 for 48 h resulted in the enhanced expression of CXCL12 (~11-fold induction, Figure 3A) and CXCR4 (~2-fold induction, Figure 3B) in comparison to the untreated and ICI-treated cells.