Cell-specific expression of the glucose-dependent insulinotropic polypeptide gene functions through a GATA and an ISL-1 motif in a mouse neuroendocrine tumor cell line.

ABSTRACT

BACKGROUND/AIMS: Glucose-dependent insulinotropic polypeptide (GIP) is a 42-amino acid gastrointestinal regulatory peptide that, in the presence of glucose, stimulates insulin secretion from beta-cells. GIP is expressed in gastrointestinal K-cells. Prior analysis of the GIP promoter demonstrated that 193 bases of the promoter are required to direct cell specific expression. Here we sought to identify and characterize the transcription factors involved. RESULTS: By mutational analysis of the GIP promoter in a neuroendocrine cell line (STC-1), we identified two regions located between bases -193 and -182 and bases -156 and -151 that, when independently altered, were responsible for a 90% and 85% reduction in transcription, respectively. When we compared these two regions with known motifs from transcription factor databases, we identified the cis elements as potential GATA and ISL-1 binding sites. With subsequent electrophoretic mobility shift analysis (EMSA) using STC-1 nuclear extracts, we demonstrated the ability of these regions to form specific DNA protein complexes. Furthermore, we utilized antisera to confirm the specific binding of GATA-4 to the upstream site and ISL-1 to the downstream element. CONCLUSION: These findings provide evidence for the involvement of the transcription factors GATA-4 and ISL-1 in the cell-specific expression of the GIP gene.