Abstract

BackgroundIn mammalian intestines, Notch signaling plays a critical role in mediating cell fate decisions; it promotes the absorptive (or enterocyte) cell fate, while concomitantly inhibiting the secretory cell fate (i.e. goblet, Paneth and enteroendocrine cells). We recently reported that intestinal-specific Kaiso overexpressing mice (KaisoTg) exhibited chronic intestinal inflammation and had increased numbers of all three secretory cell types, hinting that Kaiso might regulate Notch signaling in the gut. However, Kaiso’s precise role in Notch signaling and whether the KaisoTg secretory cell fate phenotype was linked to Kaiso-induced inflammation had yet to be elucidated.MethodsIntestines from 3-month old Non-transgenic and KaisoTg mice were “Swiss” rolled and analysed for the expression of Notch1, Dll-1, Jagged-1, and secretory cell markers by immunohistochemistry and immunofluorescence. To evaluate inflammation, morphological analyses and myeloperoxidase assays were performed on intestines from 3-month old KaisoTg and control mice. Notch1, Dll-1 and Jagged-1 expression were also assessed in stable Kaiso-depleted colon cancer cells and isolated intestinal epithelial cells using real time PCR and western blotting. To assess Kaiso binding to the DLL1, JAG1 and NOTCH1 promoter regions, chromatin immunoprecipitation was performed on three colon cancer cell lines.ResultsHere we demonstrate that Kaiso promotes secretory cell hyperplasia independently of Kaiso-induced inflammation. Moreover, Kaiso regulates several components of the Notch signaling pathway in intestinal cells, namely, Dll-1, Jagged-1 and Notch1. Notably, we found that in KaisoTg mice intestines, Notch1 and Dll-1 expression are significantly reduced while Jagged-1 expression is increased. Chromatin immunoprecipitation experiments revealed that Kaiso associates with the DLL1 and JAG1 promoter regions in a methylation-dependent manner in colon carcinoma cell lines, suggesting that these Notch ligands are putative Kaiso target genes.ConclusionHere, we provide evidence that Kaiso’s effects on intestinal secretory cell fates precede the development of intestinal inflammation in KaisoTg mice. We also demonstrate that Kaiso inhibits the expression of Dll-1, which likely contributes to the secretory cell phenotype observed in our transgenic mice. In contrast, Kaiso promotes Jagged-1 expression, which may have implications in Notch-mediated colon cancer progression.

Highlights

  • In mammalian intestines, Notch signaling plays a critical role in mediating cell fate decisions; it promotes the absorptive cell fate, while concomitantly inhibiting the secretory cell fate

  • We demonstrate that Kaiso inhibits the expression of Delta-like ligand (Dll)-1, which likely contributes to the secretory cell phenotype observed in our transgenic mice

  • We recently reported that ectopic expression of the poxvirus and zinc finger (POZ)-zinc finger transcription factor Kaiso in the intestines of 12-month old mice (KaisoTg) resulted in chronic intestinal inflammation and a significant increase in secretory cell types compared to nontransgenic (NonTg) mice

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Summary

Introduction

Notch signaling plays a critical role in mediating cell fate decisions; it promotes the absorptive (or enterocyte) cell fate, while concomitantly inhibiting the secretory cell fate (i.e. goblet, Paneth and enteroendocrine cells). Methods: Intestines from 3-month old Non-transgenic and KaisoTg mice were “Swiss” rolled and analysed for the expression of Notch, Dll-1, Jagged-1, and secretory cell markers by immunohistochemistry and immunofluorescence. Unlike most terminally differentiated IECs, Paneth cells migrate downward toward the base of intervillar crypts, where intestinal stem and progenitor cell populations reside [3, 6, 7]. The constant turnover of cells within the intestinal epithelium requires strict regulation of the signaling pathways that govern stem and progenitor cell proliferation and differentiation. While several pathways are critical for intestinal homeostasis, the Notch signaling pathway is indispensible for dictating intestinal cell fate decisions [8,9,10,11,12,13]

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