Transcription factor binding to the ISREs and CRE sites in the CCR5 promoter. (A) EMSA showing binding of complexes to the ISREs of CCR5 (ISRE-1 through ISRE-3) and the ISRE of human β2m as a consensus probe (cons) using nuclear extracts of U251 cells either unstimulated or stimulated with 500 U/mL of IFN-γ for 2 hours. IFN-γ stimulation induced formation of 1 major () and 2 minor (→) complexes to CCR5-ISRE-1 and CCR5-ISRE-3 and weak binding of these complexes to CCR5-ISRE-2, specific for the ISRE in the probes. (B) Using specific antibodies, the proteins binding to the β2m-ISRE on IFN-γ treatment were identified as IRF-1 and IRF-2, whereas the complexes binding to ISRE-1 and ISRE-3 contained only IRF-1. (C) EMSA showing binding of complexes to the CRE sites located in the CCR5 upstream promoter (CRE-1 through CRE-3) and a CRE consensus probe (cons) using nuclear extracts of U251 cells. Binding of 3 complexes () to CCR5-CRE-2 and, to a lesser extent, CCR5-CRE-3, specific for the CRE in the probes, was detected. (D) Using specific antibodies, the proteins binding to CCR5-CRE-2 and CCR5-CRE-3 were identified as CREB-1 and ATF-1. In addition, the CCR5-CRE-2 binding complex was revealed to also contain CREM-1. *Supershifted complexes. Shown are representatives of 2 independent experiments.