Atonal Homolog 1 Is Required for Growth and Differentiation Effects of Notch/γ-Secretase Inhibitors on Normal and Cancerous Intestinal Epithelial Cells

Division of Gastroenterology, Hepatology, and Nutrition, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.
Gastroenterology (Impact Factor: 16.72). 09/2010; 139(3):918-28, 928.e1-6. DOI: 10.1053/j.gastro.2010.05.081
Source: PubMed


The atonal homolog 1 (Atoh1) transcription factor is required for intestinal secretory (goblet, Paneth, enteroendocrine) cell differentiation. Notch/gamma-secretase inhibitors (GSIs) block proliferation and induce secretory cell differentiation in the intestine. We used genetic analyses of mice to determine whether Atoh1 mediates the effects of GSIs in normal and cancerous intestinal epithelia.
We studied mice with intestine-specific disruption of Atoh1 (Atoh1(Deltaintestine)), the adenomatosis polyposis coli (APC)(min) mutation, both mutations (Atoh1(Deltaintestine); APC(min)), or littermate controls; mice were given GSI or vehicle. Colorectal cancer (CRC) cell lines were treated with GSI or vehicle and with small hairpin RNAs to reduce ATOH1. Differentiation and homeostasis were assessed by protein, RNA, and histologic analyses.
GSIs failed to induce secretory cell differentiation or apoptosis or decrease proliferation of Atoh1-null progenitor cells, compared with wild-type cells. Exposure of APC(min) adenomas to GSIs decreased proliferation and increased secretory cell numbers in an Atoh1-dependent manner. In CRC cells treated with GSI, ATOH1 levels were correlated inversely with proliferation. ATOH1 was required for secretory cell gene expression in cell lines and in mice.
ATOH1 is required for all effects of GSIs in intestinal crypts and adenomas; Notch has no unique function in intestinal progenitors and cancer cells other than to regulate ATOH1 expression. Reducing ATOH1 activity might mitigate intestinal toxicity from systemic GSI therapy for nonintestinal diseases. Among gastrointestinal malignancies, ATOH1 mediates the effects of GSIs, so ATOH1 expression levels might predict responses to these inhibitors. We propose that only the subset of CRCs that retain ATOH1 expression will respond to GSIs.

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Available from: Avedis Kazanjian, Mar 03, 2014
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    • "Differentiation Math1/Atoh1, which is negatively regulated by Notch signaling, is the key mediator of secretory metaplasia after Notch loss of function (Kazanjian et al., 2010). In addition to rescuing secretory cell metaplasia, Math1 deletion also restored proliferation after Notch blockade, suggesting that Math1-mediated cell cycle exit is a factor in maintaining crypt homeostasis. "
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    ABSTRACT: Proper organ homeostasis requires tight control of adult stem cells and differentiation through the integration of multiple inputs. In the mouse small intestine, Notch and Wnt signaling are required both for stem cell maintenance and for a proper balance of differentiation between secretory and absorptive cell lineages. In the absence of Notch signaling, stem cells preferentially generate secretory cells at the expense of absorptive cells. Here, we use function-blocking antibodies against Notch receptors to demonstrate that Notch blockade perturbs intestinal stem cell function by causing a derepression of the Wnt signaling pathway, leading to misexpression of prosecretory genes. Importantly, attenuation of the Wnt pathway rescued the phenotype associated with Notch blockade. These studies bring to light a negative regulatory mechanism that maintains stem cell activity and balanced differentiation, and we propose that the interaction between Wnt and Notch signaling described here represents a common theme in adult stem cell biology. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Full-text · Article · Mar 2015 · Cell Reports
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    • "The qRT-PCR measurements (Figure 4A) showed that the changes in secretory cell numbers went with changes in Notch pathway gene expression: expression of Dll4 was increased by 70%, that of Hes1 was decreased by 44%, and that of Atoh1 - a sign of commitment to a secretory fate [28], [29] - was increased by 84%. These effects are all in accord with standard expectations for a system in which Dll1 delivers lateral inhibition via Notch to restrict commitment to a secretory fate, with Hes1 and the Delta genes as main mediators of inhibition. "
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    ABSTRACT: The stem cells of the small intestine are multipotent: they give rise, via transit-amplifying cell divisions, to large numbers of columnar absorptive cells mixed with much smaller numbers of three different classes of secretory cells--mucus-secreting goblet cells, hormone-secreting enteroendocrine cells, and bactericide-secreting Paneth cells. Notch signaling is known to control commitment to a secretory fate, but why are the secretory cells such a small fraction of the population, and how does the diversity of secretory cell types arise? Using the mouse as our model organism, we find that secretory cells, and only secretory cells, pass through a phase of strong expression of the Notch ligand Delta1 (Dll1). Onset of this Dll1 expression coincides with a block to further cell division and is followed in much less than a cell cycle time by expression of Neurog3--a marker of enteroendocrine fate--or Gfi1--a marker of goblet or Paneth cell fate. By conditional knock-out of Dll1, we confirm that Delta-Notch signaling controls secretory commitment through lateral inhibition. We infer that cells stop dividing as they become committed to a secretory fate, while their neighbors continue dividing, explaining the final excess of absorptive over secretory cells. Our data rule out schemes in which cells first become committed to be secretory, and then diversify through subsequent cell divisions. A simple mathematical model shows how, instead, Notch signaling may simultaneously govern the commitment to be secretory and the choice between alternative modes of secretory differentiation.
    Full-text · Article · Sep 2011 · PLoS ONE
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    • "Intestinal cell cycle arrest and secretory cell metaplasia are believed to reflect activation of the transcription factor Math1 (Kazanjian et al., 2010; van Es et al., 2010; Kim and Shivdasani, 2011), which is absent from the stomach (Yang et al., 2001). Thus, stomach Notch signaling probably operates through an alternative factor, which affects cell proliferation less quickly and secretory cells less profoundly than Math1 does in the intestine. "
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    ABSTRACT: The mammalian adult gastric epithelium self-renews continually through the activity of stem cells located in the isthmus of individual gland units. Mechanisms facilitating stomach stem and progenitor cell homeostasis are unknown. Here, we show that Notch signaling occurs in the mouse stomach epithelium during development and becomes restricted mainly to the isthmus in adult glands, akin to its known localization in the proliferative compartment of intestinal villi. Using genetic and chemical inhibition, we demonstrate that Notch signaling is required to maintain the gastric stem cell compartment. Activation of Notch signaling in lineage-committed stomach epithelial cells is sufficient to induce dedifferentiation into stem and/or multipotential progenitors that populate the mucosa with all major cell types. Prolonged Notch activation within dedifferentiated parietal cells eventually enhances cell proliferation and induces adenomas that show focal Wnt signaling. In contrast, Notch activation within native antral stomach stem cells does not affect cell proliferation. These results establish a role for Notch activity in the foregut and highlight the importance of cellular context in gastric tumorigenesis.
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