Structure of the murine macrophage scavenger receptor gene and evaluation of sequences that regulate expression in the macrophage cell line, P388D.

The structure of the entire murine scavenger receptor gene was determined; it consists of eleven exons spanning more than 60 kilobases. Primer extension showed that transcription initiates at a cluster of sites unassociated with a TATAA element. DNA sequences adjacent to these transcription start sites are highly conserved in murine, human, and bovine genes. When transcriptional activity was tested using a luciferase reporter gene, a promoter fragment (-124 to +20) stimulated luciferase production in P388D1 macrophage-like cells but not in non-macrophage COS-7 or 3T3 cells. A longer promoter fragment (approximately 5 kb) stimulated luciferase activity a further 10-fold in P388D1 cells. However, using a series of fragments from -67 to -1500 bp, a 127 bp fragment (-67 to +50) was as active as a 1500 bp fragment in these assays. Mutation of a putative AP-1 element in the -67 to +50 promoter fragment reduced luciferase activity by 40%; mutation of a putative GATA factor element to TATA increased luciferase activity nearly 2-fold while mutation to AATA had no effect and deletion of the GATA sequence inhibited activity by about 50%. The results suggest that a scavenger receptor promoter fragment can confer cell-specific transcription and that the activity may be mediated in part by factors that recognize the AP-1 and GATA elements.