Cloning of the murine CD5 promoter and its tissue-specific regulation

A genomic clone containing 1700 bp of the 5'-flanking region and first exon of the murine CD5 gene was isolated by screening a NIH 3T3 fibroblast genomic library with the previously characterized murine CD5 cDNA. The CD5 5'-flanking region lacks a consensus TATA box but contains Sp1, AP-1, IgH muE2, SV40 enhancer core, CCAAT, TCF2 alpha/PEA3/ets, and C/EBP motifs. Transcription is initiated from multiple sites upstream of an Inr-like sequence. When linked to the CAT reporter gene, the CD5 5'-flanking region was an active promoter in transient transfection assays using the EL4 (T), PD36 (pre-B) and M12 (B) cell lines, but was inactive in NIH 3T3 fibroblasts. This pattern of lymphoid-specific expression reflects the pattern of in vivo CD5 expression. Successive 5' to 3' deletions of the CD5 promoter/CAT reporter construct were transfected into T and B cells revealing a succession of positive and negative regulatory elements until promoter activity was eliminated at position -27. This result identified sequences from -125 to -27 (which contain the Inr, IgH muE2, SV40 enhancer core, and AP-1 sites) as sufficient for tissue-specific promotion. Isolation and characterization of the CD5 promoter represents an initial step in elucidating the control over tissue-specific expression of the murine CD5 gene.