Cloning and analysis of the promoter region of CXCR4, a coreceptor for HIV-1 entry.

The chemokine receptor CXCR4 (also designated fusin and LESTR) is a cofactor for fusion and entry of T cell-tropic strains of HIV-1. CXCR4 is expressed in various cell types; however, the mechanisms involved in the regulation of its expression remain unknown. To delineate these mechanisms, approximately 1.2 kb of DNA from the immediate 5' upstream region of CXCR4 gene was cloned, sequenced, and characterized. Transient expression assays using CXCR4 promoter/luciferase gene reporter constructs revealed that stimulation with PMA plus ionomycin up-regulates the CXCR4 promoter activity in the A3.01 CD4+ T cell line and PBL and that a DNA fragment from -93 to +59 relative to the transcription start site contributes markedly to the basal and induced activity. This fragment contains a consensus TATA box, two potential GC boxes, and a potential nuclear respiratory factor (NRF)-1 binding site, which were confirmed by gel mobility shift assays and footprinting analysis. Mutagenesis studies revealed that a NRF-1 site is especially important for the basal and induced activity of the CXCR4 promoter. Transient expression assays further revealed that stimulation of PBL with either IL-2 or Abs to CD3 and CD28 enhances the CXCR4 promoter activity. Inducibility of the CXCR4 promoter activity by T cell stimulation suggests that overexpression of CXCR4 may be one of the mechanisms whereby immune activation and/or perturbation of the cytokine network up-regulate HIV expression and replication and thus contribute to the progression of HIV disease.