Integrin-associated protein (IAP or CD47) is expressed in a variety of tissues, including the nervous system and immune system. To understand how cells control the expression of the IAP gene, we cloned the 5′-proximal region of the human IAP gone and investigated IAP promoter activity by transient transfection. RT-PCR confirmed the expression of IAP transcripts in human neuroblastoma IMR-32 and hepatoma HepG2 cells. Deletion analysis identified a core promoter of the human IAP gene located between nucleotide positions -232 and -12 relative to the translation initiation codon in these two cell lines. Site-directed mutagenesis and gel electrophoretic mobility shift assay identified a α-Pal/NRF-1 binding element within the IAP core promoter. Supershift assays using the α-Pal/NRF-1 antiserum confirmed the binding of this transcription factor on the α-Pal/NRF-1 site. Overexpression of the DNA binding domain of α-Pal/NRF-1 in cells enhanced DNA-α-Pal/NRF-1 binding in vitro. Furthermore, overexpression of full-length α-Pal/NRF-1 significantly enhanced IAP promoter activity while overexpression of dominant-negative mutant reduced promoter activity both in the cultured human cell lines and primary mouse cortical cells. These results revealed that α-Pal/NRF-1 is an essential transcription factor in the regulation of human IAP gene expression.
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