Abnormal processing of the human cholecystokinin receptor gene in association with gallstones and obesity

Background & Aims: Cholesterol gallstone disease and obesity are often associated and share the potential, yet unreported, common etiology of cholecystokinin (CCK) dysfunction. While cloning the human CCK-A receptor complementary DNA (cDNA), we found predominance of a 262-base pair coding region deletion in a cDNA library prepared from a patient with this phenotype. The aim of this study was to determine the abundance, functional significance, and mechanism for generating this gene product. Methods: Relative abundance of CCK receptor gene products was determined using polymerase chain reaction and hybridization analysis. Constructs were expressed in COS cells and studied for radioligand binding and intracellular calcium responses. A human genomic clone for this receptor was sequenced, and the critical regions were compared with those of the patient. Results: Ninety-three percent of the patient's CCK receptor transcripts contained the 262-base pair deletion, whereas only 1.5% ± 0.9% of control patients had the deletion. This encoded a receptor that did not bind or signal. The deletion corresponded with the third exon; however, this sequence and flanking introns were normal in the patient. Conclusions: Abnormality of processing an apparently normal CCK receptor gene yields the predominant product with an absent third exon and encoding a nonfunctional receptor, probably reflecting a defective trans-acting splicing factor. An atypical lariat region in the third intron may explain the presence of small amounts of this product in control patients.