The α5β1 fibronectin receptor: Characterization of the α5 gene promoter

A genomic clone containing the gene for the α5 subunit of the human α5β1 integrin complex was isolated by screening a human genomic library with the previously described α5 cDNA (Argraves, W. S., Suzuki, S., Arai, H., Thompson, K., Pierschbacher, M. D., and Ruoslahti, E. (1987) J. Cell Biol 105, 1183-1190). The α5 gene 5'-flanking region lacks both TATA and CCAAT boxes, and it is located in a CpG island. This region was an active promoter in transfection assays using the HT-1080 cell line (fibrosarcoma), which expresses α5, but was inactive in the Raji cell line (B cell), which does not express α5. These results indicate that the α5 gene 5'-flanking region acts as a promoter that exhibits the expected cell-type specificity. Deletion of α5 promoter sequences from position -657 to -178 caused transcription stimulation, suggesting that a silencer is located between these sites. Successive 5' deletions from position -178 decreased promoter activity until activity was essentially eliminated on deletion to position -27. Isolation of a functional promoter for the α5 gene is a first step in understanding how expression of this gene is controlled at the molecular level.