Identification of CCK-B/gastrin receptor splice variants in human peripheral blood mononuclear cells

There is increasing evidence for a direct interaction of the enteric nervou s and immune system. Receptors for neuropeptides such as VIP, somatostatin, and substance P have been characterised in human immuno-haematopoietic cel ls but little is known about the functional significance and expression of receptors for cholecystokinin (CCK) on cells of the immune system. There ar e only few studies that describe the expression of CCK receptors on human l eukaemia-derived cell lines but the receptor structure and function in norm al leukocytes have not been clearly established. We therefore sought to det ermine CCK receptor expression. structure. and function in nontransformed h uman peripheral blood mononuclear cells. Full-length cDNA clones encoding the human CCK-A and CCK-B/gastrin receptor are expressed in peripheral blood mononuclear cells from healthy volunteer s without haematopoietic malignancy. In addition to wild-type CCK-B/gastrin receptor cDNAs, we isolated a splice variant with an in frame insertion of 69 amino acids within its putative third intracellular receptor loop. Dide oxy sequence analysis revealed that the cDNA of this splice variant compris es exons 1-4 but retains intron 4 (207 bp) in the absence of mutations with in the splice donor sites. Transient expression of this splice variant in C OS-7 cells reveals wild-type affinity for CCK-8. Gastrin-17, and antagonist L-365,260. Affinity for glycine-extended gastrin-17 was not increased when compared to the wild-type CCK-B/gastrin receptor. In vitro, gastrin decrea sed H-3-thymidine labelling in phytohaemagglutinin-pretreated mononuclear c ells at a half-maximally effective concentration of 1.5 nM. We also isolate d a cDNA encoding another splice variant of the CCK-B/gastrin receptor with a 158 bp deletion of the entire exon 4 sequence. We conclude that wild-type transcripts of both CCK receptor subtypes and sp lice variants of the CCK-B/gastrin receptor are expressed in nontransformed human mononuclear cells and that gastrin exhibits anti proliferative effec ts. (C) 2001 Elsevier Science B.V. All rights reserved.