Gastrin promotes intestinal polyposis through cholecystokinin-B receptor-mediated proliferative signaling and fostering tumor microenvironment.

Abstract

Increased serum gastrin concentrations in patients with colorectal cancer suggested the tumorigenic trophic effect of gastrin. Detailed and global molecular mechanisms explaining trophic effect of gastrin had not been revealed. In the current study, intestinal polyposis of APC(Min/⁺) mice was compared between phosphate buffered saline (PBS) injected and gastrin (10 μg/kg, thrice per week) injected group. Total number of intestinal polyposis was counted and immunohistochemical staining with F4/80 and CD3 was done. MTT assay, cell cycle analysis, and Western blot for cyclin D1, CDK4, and β-catenin were performed in Raw 264.7 and HCT116 cells before and after gastrin administration. Experiments were repeated with YM022 or transfection with si-cholecystokinin-B receptor (CCK-B-R). Intraperitoneal gastrin significantly increased intestinal polyposis in APC(Min/⁺) mice (P<0.005), in which significant increases in macrophage were noted on F4/80 immunohistochemical staining (Plt;0.05) as well as Ki-67 staining (Plt;0.05) after gastrin. On comparative cytokine array, gastrin increased interleukin-1β (IL-1β), interleukin 3Rβ (IL-3Rβ), stromal cell-derived factor-1α (SDF-1α), thymus and activation-regulated chemokine (TARC), and thymus-derived chemotactic agent 3 (TCA-3) in macrophage cells, which was further confirmed with real time polymerase chain reaction (RT-PCR) analysis (P<0.05). In addition to increased inflammatory cytokines, gastrin increased macrophage proliferation accompanied with increased cyclin D1 and CDK4. Targeted for HCT116 cells, gastrin significantly increased proliferation as well as increases in synthetic phase of cell cycle. YM022 as gastrin antagonist significantly abolished the trophic actions of gastrin (P<0.05). HCT116 cells transfected with siCCK-B-R, gastrin did not increase either cell cycle or β-catenin in spite of gastrin administration. Conclusively, gastrin promoted intestinal polyposis through either direct gastrin receptor-mediated proliferative signaling or fostering tumor microenvironment such as macrophage activation.