Abstract
Adenomatous polyposis coli (APC) is a tumor suppressor gene inactivated in familial adenomatous polyposis and sporadic colorectal cancer. Mice carrying a loss-of-function mutation in the apc gene (apc(Min/+)) spontaneously develop gastrointestinal tumors. APC fosters degradation of beta-catenin, which in turn upregulates the serum-and glucocorticoid-inducible kinase SGK1. SGK1 stimulates KCNQ1, which is required for luminal K+ recycling and thus for gastric acid secretion. BCECF-fluorescence was utilized to determine gastric acid secretion in isolated gastric glands from apc(Min/+) mice and their wild type littermates (apc(+/+)). Western blotting was employed to analyse beta-catenin and SGK1 expression and immunohistochemistry to determine KCNQ1 protein abundance. beta-catenin and SGK1 expression were enhanced in apc(Min/+) mice. Cytosolic pH was similar in apc(Min/+) mice and apc(+/+) mice. Na+-independent pH recovery following an ammonium pulse (Delta pH/min), which reflects H+/K+ ATPase activity, was, however, significantly faster in apc(Min/+) mice than in apc(+/+) mice. In both genotypes Delta pH/min was abolished in the presence of H+/K+ ATPase inhibitor omeprazole (100 mu M). Treatment of apc(Min/+) and apc(+/+) mice with 5 mu M forskolin 15 minutes prior to the experiment or increase in local K+-concentrations to 35 mM (replacing Na+/NMDG) significantly increased Delta pH/min and abrogated the differences between genotypes. The increase of Delta pH/min in apc(Min/+) mice required SGK1, as it was abolished by additional knockout of SGK1 (apc(Min/+)/sgk1(-/-)). In conclusion, basal gastric acid secretion is significantly enhanced in apc(Min/+) mice, pointing to a role of APC in the regulation of gastric acid secretion. The effect of APC requires H+/K+ ATPase activity and is at least partially due to SGK1-dependent upregulation of KCNQ1. Copyright (C) 2009 S. Karger AG, Basel