The effect of COUP-TFI on the CXCL12/CXCR4 axis is mediated by EGF/EGFR activation. (A) The relative expression of EGF and EGFR mRNA was monitored by a real-time PCR analysis using MCF-7 control (Cont.) and COUP clones. The results were normalized against GAPDH as the internal control and are expressed as the mean EGF or EGFR mRNA/GAPDH mRNA ratio ± SEM of at least three independent experiments. The asterisks indicate significant differences (p < 0.05) between the control and COUP clones. (B) ERK activation was examined in the MCF-7 control (Cont.) and COUP clones after a 5- or 10-min stimulation with EGF (10−9 M) or CXCL12 (200 ng/mL). Western blots were performed using antibodies against phospho-ERK (P-ERK) and total ERK (ERK1/2); a representative western blot is presented. The importance of EGFR-specific signaling and general ERK signaling on CXCL12 (C) and CXCR4 (D) regulation was assayed by treating the cells with EGF (10−9 M), AG1478 (25 μM), or U0126 (25 μM) for 48 h. The CXCL12 and CXCR4 relative mRNA levels were monitored by the real-time PCR analysis, normalized to GAPDH mRNA as the internal control, and were expressed as the relative mRNA expression of CXCL12 or CXCR4. Data are the mean ± SEM of at least three independent experiments. The asterisks indicate significant differences (p < 0.05) between the untreated and treated control clones. The pound sign indicates significant differences (p < 0.05) between the untreated and treated COUP clones.