Analysis of the CC chemokine receptor 3 gene reveals a complex 5′ exon organization, a functional role for untranslated exon 1, and a broadly active promoter with eosinophil-selective elements

Abstract

To understand the regulation of CC chemokine receptor 3 (CCR3) expression, its gene structure and promoter have been characterized. The CCR3 gene contains 4 exons that give rise to multiple messenger RNA (mRNA) species by alternative splicing. Exon 1 is present in all transcripts, whereas exon 2 or 3 is present at low frequency (< 10%). Exon 4 contains the open reading frame and 11 bp of the 5' untranslated region. Northern analysis revealed 4 species of CCR3 mRNA. Direct sequencing revealed that the first 1 kb of the promoter and exon 1 contained only one mutation in 19 individuals, indicating that the CCR3 promoter and exon 1 are conserved between individuals. The first 1.6 kb of the 5' flanking region of exon 1 contained promoter elements including a TATA box and motifs for myeloid transcription factors and had strong promoter activity in eosinophilic, lymphoid, myeloid, and respiratory epithelial cell lines. Deletion analysis revealed differential regulation of the CCR3 promoter in eosinophilic and epithelial cells suggesting the presence of lineage-specific elements. Interestingly, exon 1 enhanced the activity of the promoter and this effect was especially prominent in eosinophilic cells. Thus, the human CCR3 gene has a complex 5' exon structure, a conserved promoter with strong activity in multiple cell types, and a functional 5' untranslated exon.