Potential role of endocrine gastrin in the colonic adenoma carcinoma sequence

Abstract

The role of hyper-gastrinaemia in the incidence of colonic cancer remains to be clarified. The aim of this study was to determine whether cholecystokinin-2 (CCK-2) receptor expression predicts the sensitivity of human colonic adenomas to the proliferative effects of serum hyper-gastrinaemia. Gene expression of the classical (74 kDa) CCK-2 receptor in human colonic adenoma specimens and cell lines, was quantified by real-time PCR. Western blotting, using a CCK-2 receptor antiserum, confirmed protein expression. A transformed human colonic adenoma was grown in SCID mice, with hyper-gastrinaemia induced by proton pump inhibitors. CCK-2 receptor blockade was achieved by using neutralising antiserum. Both human colonic adenoma cell lines and biopsies expressed CCK-2 receptor mRNA at levels comparable with CCK-2 receptor transfected fibroblasts and oxyntic mucosa. Western blotting confirmed immunoreactive CCK-2 receptor bands localised to 45, 74 and 82.5 kDa. Omeprazole and lansoprazole-induced hyper-gastrinaemia (resulting in serum gastrin levels of 34.0 and 153.0 pM, respectively) significantly increased the weight of the human adenoma grafts (43% (P=0.016) and 70% (P=0.014), respectively). The effect of hypergastrinaemia on tumour growth was reversed by use of antiserum directed against the CCK-2 receptor. Hyper-gastrinaemia may promote proliferation of human colonic adenomas that express CCK-2 receptor isoforms.

Figure 1

Gene expression of CCK-2 wild type (74 kDa) receptors in a panel of colonic adenoma and adenocarcinoma specimens and cell lines as determined by real time PCR. Mean expression of 2 to 3 separate PCR reactions per sample are shown together with the standard deviations of the mean.

Figure 2

Western blot analysis showing CCK-2 receptor isoform immuno-reactivity of human colonic adenoma specimens and human colonic adenoma cell lines. (A) Human colonic adenoma cell lines. (B) Human colonic adenoma specimens. Resection margin normal (N), adenoma (A) and adenocarcinoma (C) specimens from individual patients. (C) Human colonic adenocarcinoma specimens. Resection margin normal (N) and adenocarcinoma (C) specimens from individual patients.

Figure 3

Western blot analysis showing CCK-2 receptor immuno-reactivity of human colonic adenoma xenografts. (A) Western blots (±omeprazole treatment). (B) Densitometry scans of the immunoreactive bands generated from the Western blots. Red line: imunoreactive bands from grafts obtained from omeprazole-treated mice. Blue line: immuno reactive bands from grafts obtained from vehicle-treated mice.

Figure 4

Final adenoma weights of mice treated with lansoprazole to generate hyper-gastrinaemia and co-administered with a polyclonal affinity purified antiserum, GRE1, directed against the CCK-2 receptor. Group 1: Oral vehicle (phosphate buffered saline (PBS), pH 7.2) + Protein A purified normal rabbit serum (n=11 mice). Group 2: Lansoprazole (orally dosed daily, 0.75 mg/mouse) + normal rabbit serum (n=10 mice). Group 3: Oral vehicle + GRE1 antiserum (n=12 mice). Group 4: Lansoprazole + GRE1 antiserum (n=11 mice).