A TRUNCATED ISOFORM OF HUMAN CCK-B GASTRIN RECEPTOR GENERATED BY ALTERNATIVE USAGE OF A NOVEL EXON/

An isoform cDNA of CCK-B/gastrin receptor was isolated from human stom ach. This cDNA differed from initially cloned cDNA only in the 5'-end region and encoded a truncated isoform (Delta CCK-B) in which the puta tive N-terminal extracellular domain of the CCK-B/gastrin receptor was completely lost. Isolation of genomic CCK-B/gastrin receptor DNA reve aled that this transcript is generated by alternative usage of a novel exon, termed exon 1b. Human stomach expressed both transcripts of Del ta CCK-B and entire CCK-B/gastrin receptor (CCK-BR), whereas human sto mach cancer cell line AGS exclusively expressed Delta CCK-B transcript s. Transfection of COS-7 with Delta CCK-B cDNA led to the appearance o f binding sites for I-125-CCK-8. Its ligand selectivity was different from that of CCK-BR. These results suggest the molecular diversity in CCK-B/gastrin receptor subtypes. (C) 1995 Academic Press, Inc.