INSULIN UPSTREAM FACTOR-1 AND A NOVEL UBIQUITOUS FACTOR BIND TO THE HUMAN ISLET AMYLOID-POLYPEPTIDE AMYLIN GENE PROMOTER

The islet amyloid polypeptide (IAPP) gene is expressed primarily in th e islet beta-cell and the peptide is co-secreted with insulin. To inve stigate mechanisms important in its regulation, we have used the elect rophoretic mobility-shift assay and methylation interference to determ ine systematically sites of DNA-protein interactions in the human IAPP promoter. We identified beta-cell-specific DNA-protein complexes at t hree sites, each of which contained a consensus binding site for insul in upstream factor 1 (IUF-1). This complex was displaced with an antis erum to IUF-1, confirming that IUF-1 binds to the human IAPP promoter in vitro. We have also identified a DNA-protein complex within the reg ion -220/-250 in both beta- and non-beta-cell lines. This region conta ins a motif with partial identity with the binding site for the ubiqui tous transcription factor upstream stimulatory factor (USF), which bin ds to the human insulin promoter. However, purified USF was not able t o bind to this putative site in the IAPP promoter and an oligonucleoti de containing a functional USF-binding site was unable to displace bin ding from the IAPP oligonucleotide. Methylation interference revealed that the DNA-protein complex binds to a sequence that overlaps the USF -like sequence, and may therefore be a novel helix-loop-helix protein. These results suggest that, although both IAPP and insulin are beta-c ell peptides, IAPP contains regulatory regions both common to and dist inct from insulin.