Differential cholecystokinin brain/gut transcription initiation in the rat: evidence for brain-specific start sites

Brain/gut cholecystokinin (CCK) has well-established translational and post-translational differences. By contrast, CCK transcription regulation is reported to be the same in brain and gut. Accordingly, the rat CCK gene has been evaluated for differential brain/gut transcription initiation. Using the 5'-flanking region of the rat CCK gene, DNase I protection assays were performed. We evaluated reporter constructs deleted of the conventional transcription start site in cell culture. Finally, brain and gut mRNA was evaluated using both a reverse transcription serial primer polymerase chain reaction assay as well as rapid amplification of cDNA ends (RACE) analysis. TFIID protein protects against DNase I digestion between -177 and -196 bp. In tissue culture, spontaneous 5'-flanking region transcription initiation occurs until deletion proceeds upstream of -140 bp. RACE analysis performed on mRNA from the rat brain identifies heretofore undescribed transcription initiation at -43 bp 5' as well as at +1,212 (in exon II). These alternative transcription initiation sites are utilized in brain, but not gut. The rat CCK gene has alternative 5'-flanking region transcription initiation sites. These alternative sites are utilized only in the brain. These data may provide insights into how brain and gut respond to their differing physiological demands.