Peptones stimulate intestinal cholecystokinin gene transcription via cyclic adenosine monophosphate response element-binding factors

Cholecystokinin (CCK) is a potent intestinal hormone that regulates several digestive functions. Despite the physiological importance of CCK, the cell ular and molecular mechanisms that govern its synthesis and secretion are n ot completely identified. Peptones, which are fair counterparts of the prot ein fraction in the intestinal lumen, are good stimulants of CCK secretion. We have previously shown that peptones activate CCK gene transcription in STC-1 enteroendocrine cells. The DNA element(s) necessary to induce the tra nscriptional stimulation was preliminary, localized in the first 800 bp of the CCK gene promoter. In the present study, we identify a DNA element [pep tone-response element (PepRE)] essential to confer peptone-responsiveness t o the CCK promoter, and we characterize the transcription factors implicate d. Localization of the PepRE between -93 and -70 bp of the promoter was est ablished using serial 5'-3' deletions. Systematic site-directed mutagenesis demonstrated that the core PepRE sequence, spanning from nucleotide -72 to -83, overlapped with the putative AP-1/CRE site. Mutations in the core seq uence dramatically decreased peptone-responsiveness of CCK promoter fragmen ts. The PepRE functioned as a low-aftinity CRE consensus site, binding only transcription factors of the CREB family. Overexpression, in STC-1 cells, of a dominant-negative protein (A-CREB), that prevented the binding of CREB factors to DNA, completely abolished the peptone-induced transcriptional s timulation. Peptone treatment did not modify the nature and the abundance o f proteins bound to the PepRE but led to increased phosphorylation of the C REB factors. In conclusion, the present study first demonstrates that CCK g ene expression is under the control of protein-derived nutrients in the STC -1 enteroendocrine cell line.