CCK-B/gastrin receptors in human colorectal cancer

Background Mature amidated gastrin (G17 amide) mediates its effects in the gastrointestinal tract by activating G protein-coupled CCK-B/gastrin recept ors. Although trophic actions of gastrin on the gastric mucosa have been we ll-established, the effect of G17 amide, progastrin and intermediates to co lon neoplasia in humans is controversial. While epidemiological evidence fr om patients with elevated serum gastrin levels related to pernicious anaemi a. does not support an increased risk for, colon cancer [1], a recent study suggests that prolonged hypergastrinaemia is associated with an increased risk for colon cancer [2]. The extent to which trophic actions of gastrin i n colorectal cancer are mediated by functional gastrin receptors remains to be defined. The aim of the present study was to determine CCK-B/gastrin re ceptor expression, structure, and function in 79 patients with, colon cance r. Materials and methods CCK-B/gastrin receptor cDNAs were isolated from 79 hu man colorectal. cancer specimens and 15 control tissues, subcloned into the eukaryotic expression vector pCR3.1 and subjected to DNA sequence analysis . Wild-type and mutant cDNAs were transiently expressed in COS-7 cells to d etermine ligand affinities by I-125-labelled CCK-8S competition binding. Ac tivation of the MAP kinase signalling cascade by G17 amide was determined i n transfected Colo 320 cells expressing the wild-type or mutant CCK-B/gastr in receptors. Clonal expansion of single cells was quantified in transfecte d Colo 320 cells. Results Gastrin mRNA is expressed in 44% of colorectal cancers and in 13% o f control tissues. CCK-B/gastrin receptor mRNA is expressed in 38% of color ectal cancers and 13% of normal colonic tissue. Co-expression of gastrin an d CCK-B/gastrin receptor message is significantly increased in colorectal. cancer specimens (32% vs. 0%). There is no correlation between CCK-B/ gastr in receptor expression and disease stage or histological grading. DNA seque nce analysis revealed one spontaneous CCK-B/gastrin receptor mutation withi n the third intracellular loop with an exchange of valine-287 for phenylala nine. Pharmacological characterisation of the V-287 --> F CCK-B/gastrin rec eptor reveals wild-type affinities for G17 amide, glycine-extended gastrin, CCK-8S and L,365,260. Mutation V-287 --> F is associated with a loss of ga strin-induced MAPK p44/p42 signalling in Colo 320 cells while clonal expans ion from single cells is increased by 53.1 +/- 15.9% when compared to Colo 320 cells expressing wild-Me CCK-B/gastrin receptors. Conclusions Structural alterations of CCK-B/gastrin receptors may account f or increased growth-promoting effects of amidated gastrins, in colorectal c ancer.