Activation of the glutathione peroxidase 2 (GPx2) promoter by beta-catenin

GPx2, formerly named gastrointestinal glutathione peroxidase, is highly expressed in the proliferative area of the intestinal crypt-to-villus axis and in Paneth cells. Additionally, GPx2 is transiently up-regulated during development of gastrointestinal adenocarcinomas. Because both normal proliferation and differentiation of intestinal epithelial cells as well as carcinogenesis are regulated by the Wnt pathway, it was tested whether GPx2 may be a target of the beta-catenin/TCF complex which transfers Wnt signals. The GPx2 promoter contains five putative beta-catenin/TCF binding sites. Accordingly, the promoter was active in two cell lines with a constitutively active Wnt pathway, HepG2 and SW480, but not in BHK-21 cells in which the pathway is silent. Overexpression of beta-catenin/TCF activated the GPx2 promoter in all three cell lines. Overexpression of wild-type adenomatous polyposis coli (APC) in SW480 cells which harbor a mutated APC gene decreased basal GPx2 promoter activity. Truncation of the promoter identified one beta-catenin/TCF binding site that was sufficient for activation. Mutation of this site reduced the response to beta-catenin/TCF by more than 50%. These findings suggest a function of GPx2 in the maintenance of normal renewal of the intestinal epithelium. Whether up-regulation of GPx2 during carcinogenesis supports tumor growth or can rather be considered as a counteracting effect remains to be investigated.     

(−)-Epicatechin mitigates radiation-induced intestinal injury and promotes intestinal regeneration via suppressing oxidative stress

Abstract

The high radiosensitivity of the intestinal epithelium limits the survival of victims by nuclear accidents or terrorism and limits effective radiotherapy against abdominal malignancies. Recently, we reported that (?)-epicatechin (EC) modulates oxidative stress and exerts neuroprotection. Here, we investigate the protective effects of EC against intestinal damage induced by radiation. The established model is acute moderate but reversible intestinal injury damage. We also set up the injured model of “minigut” ex vivo, which mimic the process of intestinal regeneration in vivo. We found that EC can repress oxidative stress by regulating SOD and MDA levels in serum and intestine tissue. Correspondingly, EC can decrease apoptosis of crypt cells in Lgr5-EGFP-IRES-creERT2 mice after radiation. Further studies demonstrated that EC can promote Nrf2 translocation from cytoplasm to nuclear and then activate the expression of HO1 and NQO1. Interestingly, EC can enhance the activity of intestine stem cells labelled by Lgr5 and promote intestinal epithelium regeneration determined by HE and immunofluorescence staining in vivo and in vitro. We also found that EC can activate the Wnt/β-catenin signal pathway confirmed by TCF/LEF luciferase reporter assay. Together, EC can provide the protective effect on intestine and promote intestinal regeneration after radiation through Nrf2 and Wnt/β-catenin signal pathway.