Cell-specific expression of the glucose-dependent insulinotropic polypeptide gene in a mouse neuroendocrine tumor...

Glucose-dependent insulinotropic polypeptide (GIP) is a 42-amino acid gastrointestinal regulatory peptide that, in the presence of glucose, stimulates insulin secretion. GIP is expressed in K cells of the small intestine and in cells of the submandibular salivary gland. Using a rat GIP cDNA as a specific probe, we screened a number of established cell lines for the expression of GIP mRNA. STC-1 cells, a cell line derived from a mouse neuroendocrine tumor, were found to express high levels of GIP mRNA. GIP-specific transcripts were not detected in other cell lines tested, which included cells of intestinal, salivary, and endocrine origin. Analysis of GIP-luciferase fusions identified two promoters, a distal and a proximal promoter, upstream of the translation initiation codon for GIP. The distal promoter, located upstream of position +1, corresponds to the principal promoter of the GIP gene and can promote cell-specific transcription. Sequential deletion and site-directed mutational analysis of the distal promoter demonstrated that the sequence between -193 and -182 determines cell-specific expression of GIP. Contained in this region is a consensus GATA motif, suggesting that a member of the GATA family of DNA-binding proteins is involved in the cell-specific regulation of the GIP gene.