beta-Catenin stabilization imparts crypt progenitor phenotype to hyperproliferating colonic epithelia

Utilizing the Citrobacter rodentium (CR)-induced transmissible murine colonic hyperplasia (TMCH) model, we provide mechanistic basis of changes in [beta-catenin/APC/CKI epsilon leading to progression and/or regression of hyperplasia in vivo. In response to CR-induced TMCH, crypt lengths increased significantly between days 6-27 post-infection, followed by a steep decline by day 34. beta-Ca-45/total beta-catenin were elevated on day 1 post-infection, preceding changes in crypt length, and persisted for 27 days before declining by day 34. Importantly, cellular CKle and beta-catenin coimmunoprecipitated and exhibited remarkable parallel changes in kinetics during hyperplasia/regression phases. beta-catenin, phosphorylated at Ser33,37 and Thr41 (beta-cat(33,37/41)), was low till day 12, followed by gradual increase until day 27 before declining by day 34. GSK-3 beta exhibited significant Se-9-phosphorylation/inactivation at days 6-12 with partial recovery at days 27-34. Wild type (wt) APC (p312) levels increased at day 6 with transient proteolysis/truncation to p130 form between days 12 and 15; p312 reappeared by day 19 and returned to baseline by day 34. The kinetics of beta-Cat(45)/beta-catenin nuclear accumulation and acetylation (Ac-beta-Cat(Ly49)) from days 6 to 27, followed by loss of phosphorylation/acetylation by day 34 was almost identical: Tcf-4 coimmunoprecipitated with beta-Cat(45)/beta-catenin and localized immunohistochernically to beta-Cat(45)/beta-cateninpositive regions leading to elevated cyclin D1 expression, during the hyperproliferative, but not regression phases of TMCH. CKle mediated phosphorylation of beta-Cat(45), resulting in stabilization/nuclear translocation of beta-Cat(45) may be critical for maintaining proliferation at days 6-27. Reversal of GSK-3 beta phosphorylation and APC changes may be equally critical during the regression phase from days 27 to 34. (C) 2008 Elsevier Inc. All rights reserved.