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 o f cholecystokinin (CCK) dysfunction. While cloning the human CCK-A rec eptor complementary DNA (cDNA), we found predominance of a 262-base pa ir coding region deletion in a cDNA library prepared from a patient wi th this phenotype. The aim of this study was to determine the abundanc e, functional significance, and mechanism for generating this gene pro duct. Methods: Relative abundance of CCK receptor gene products was de termined using polymerase chain reaction and hybridization analysis. C onstructs were expressed in COS cells and studied for radioligand bind ing and intracellular calcium responses. A human genomic clone for thi s receptor was sequenced, and the critical regions were compared with those of the patient. Results: Ninety-three percent of the patient's C CK 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 Ranking introns were norma l in the patient. Conclusions: Abnormality of processing an apparently normal CCK receptor gene yields the predominant product with an absen t third exon and encoding a nonfunctional receptor, probably reflectin g 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.