Regulation of mammalian gastrin/CCK receptor (CCK2R) expression in vitro and in vivo

The gastrin/CCK receptor (CCK2R) mediates the physiological functions of gastrin in the stomach, including stimulation of acid secretion and cellular proliferation and migration, but little is known about the factors that regulate its expression. We identified endogenous CCK2R expression in several cell lines and used luciferase promoter-reporter constructs to define the minimal promoter required for transcription in human gastric adenocarcinoma, AGS, and rat gastric mucosa, RGM1, cells. Consensus binding sites for SP1, C/EBP and GATA were essential for activity. Following serum withdrawal from RGM1 and AR42J cells, endogenous CCK2R mRNA abundance and the activity of a CCK2R promoter-reporter construct were significantly elevated. Transcription of CCK2R was also increased in AGS-G(R) and RGM1 cells by gastrin through mechanisms partly dependent upon protein kinase C (PKC) and mitogen/extracellular signal-regulated kinase (MEK). Gastrin significantly increased endogenous CCK2R expression in RGM1 cells, and CCK2R protein expression was elevated in the stomach of hypergastrinaemic animals. In mice with cryoulcers in the acid-secreting mucosa, CCK2R expression increased progressively in the regenerating mucosa adjacent to the ulcer repair margin, evident at 6 days postinjury and maximal at 13 days. De novo expression of CCK2R was observed in the submucosa beneath the repairing ulcer crater 6-9 days postinjury. Many of the cells in mucosa and submucosa that expressed CCK2R in response to cryoinjury were identified as myofibroblasts, since they coexpressed vimentin and smooth muscle alpha-actin but not desmin. The data suggest that increased CCK2R expression might influence the outcome of epithelial inflammation or injury and that the response may be mediated in part by myofibroblasts.