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104 Transcriptional Regulation of CCR3, an Entry Coreceptor for HIV-1: Evidence for a TATA-Less, Rare Human Promoter Element, Conserved between Drosophila and Humans
S. Vijh*1, D. E. Dayhoff1, C. Wang1, P. K. Ehrenberg1, and N. L. Michael2
1US Military HIV Res. Program and 2Walter Reed Army Inst. of Res., Rockville, MD, USA
Background: CCR3, an entry coreceptor for HIV-1, plays a significant role in HIV-1-infection of the central nervous system and HIV-1-specific cytotoxic T-lymphocyte activity. The antigen-presenting function and chemotaxis of immature dendritic cells have been shown to be blocked via CCR3. Thus, CCR3 also has an important immunoregulatory role. Hence, the CCR3 transcription unit was characterized to determine the factors that regulate it.
Methods: Screening of a lambda library of human peripheral blood mononuclear cell DNA, plasmid human genomic library, 5 RACE, and generation of deletion constructs with luciferase as reporter identified the CCR3 promoter.
Results: Six unique cDNA CCR3 transcripts are formed by alternative splicing of 8 exons and 7 introns that fall into 2 major mRNA size classes of ~1.8 and ~3.0(4.0 kb. Five cDNAs diverge at (11 and 1 cDNA diverges at (772 bp from the translation initiation codon. The uninterrupted CCR3 coding region is separated from the regulatory region by an intron of ~22.54 kb. 5 and 3 deletion mapping identified a TATA-less, 37-bp core promoter region ((3 to +34 relative to the transcription start point) that conforms to the Drosophila downstream promoter element (DPE). Mutations at +1, +24, and +29 to +32 significantly reduce the transcription of the CCR3 core promoter. Altering the distance between the initiator and the DPE by ±3 bp abrogates promoter activity.
Conclusions: CCR3 is the first TATA-less DPE-containing chemokine receptor gene described to date. The DPE has been described previously for 205 Drosophila core promoters and 2 human genes. The human CCR3 DPE provides evidence for a functional rare promoter element conserved between Drosophila and humans. The regulation of DPE-containing CCR3 promoter compared with other TATA-containing alpha- and beta-chemokine receptor genes will provide insight into the factors that control the expression of HIV-1 entry coreceptors.
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