Gastroenterology

Gastroenterology

Volume 138, Issue 1, January 2010, Pages 241-254
Gastroenterology

Basic—Alimentary Tract
The Hormone Receptor GUCY2C Suppresses Intestinal Tumor Formation by Inhibiting AKT Signaling

https://doi.org/10.1053/j.gastro.2009.08.064Get rights and content

Background & Aims

GUCY2C is the intestinal receptor for the paracrine hormones guanylin and uroguanylin that converts guanosine-5′-triphosphate to cyclic guanosine monophosphate (cGMP). It functions as a tumor suppressor; its loss disrupts intestinal homeostasis and promotes tumorigenesis. We investigated the effects of GUCY2C loss on intestinal cell proliferation, metabolism, signaling, and tumorigenesis in mice.

Methods

Intestinal cell proliferation and metabolism were examined in Gucy2c−/− and colon cancer cells by microscopy, immunoblot, and functional analyses. Microarray analyses compared gene expression profiles of intestine cell from Gucy2c−/− and wild-type mice. v akt murine thymoma viral oncogene homolog (AKT) regulation and signaling were examined, and the role of AKT in GUCY2C-dependent tumorigenesis was defined in Gucy2c−/−Akt1−/− mice.

Results

The size and number of intestinal crypts increased in Gucy2c−/− mice; the associated epithelial cells showed accelerated proliferation, increased glycolysis, and reduced oxidative phosphorylation, which was reversed by oral administration of cGMP. Conversely, activating guanylyl cyclase C in human colon cancer cells delayed cell-cycle progression, decreased DNA synthesis and colony formation, reduced glycolysis, and increased mitochondrial adenosine triphosphate production. AKT signaling pathways were activated in intestines of Gucy2c−/− mice, associated with increased AKT phosphorylation. Disruption of AKT activity, pharmacologically or genetically, reduced DNA synthesis, proliferation, and glycolysis, and increased mitochondrial biogenesis. Intestinal tumorigenesis increased after administration of azoxymethane to Gucy2c−/− mice, compared with wild-type mice, but was eliminated in Gucy2c−/−Akt1−/− mice.

Conclusions

GUCY2C is a tumor suppressor that controls proliferation and metabolism of intestinal epithelial cells by inactivating AKT signaling. This receptor and its ligands, which are paracrine hormones, might be novel candidates for anticolorectal cancer therapy.

Section snippets

Materials and Methods

For further details, please see the Supplementary Experimental Procedures section.

GUCY2C Signaling Coordinates Proliferation and Metabolism in Intestinal Epithelial Cells

Elimination of GUCY2C signaling in mice (Gucy2c−/−) expanded the size (Figure 1A) and number (Figure 1B) of crypts, associated with an increase in proteins promoting the cell-cycle transition, including cyclin D1, cyclin-dependent kinase (CDK4), phosphorylated retinoblastoma, and β-catenin, while decreasing the cyclin-dependent kinase inhibitor p27 (Figure 1C). Expansion of the proliferating compartment was coupled with epithelial bioenergetic reprogramming, with increased glycolytic metabolism

Discussion

There is a common process for transformation in all cells involving the evolution of autonomous growth and survival through deregulation of homeostatic processes underlying proliferation and metabolism.1, 22 This evolution is rooted in the genetic basis of cancer, in which the graded progression of the malignant phenotype reflects accumulation of sequential mutations.34, 35 In turn, this genetic instability reflects self-reinforcing cycles of proliferation uncoupled from normal DNA damage

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    Conflicts of interest The authors disclose the following: Scott Arthur Waldman is a paid consultant to Merck, and the Chair (uncompensated) of the Scientific Advisory Board of Targeted Diagnostics and Therapeutics, Inc, which provided research funding that, in part, supported this work and has a license to commercialize inventions related to this work; Giovanni Mario Pitari receives research salary support from Merck, he is an inventor on patents that include information contained in this manuscript. The remaining authors disclose no conflicts.

    Funding These studies were supported by grants from the National Institutes of Health (CA75123, CA95026) and Targeted Diagnostic and Therapeutics Inc. (S.A.W.), and the National Institutes of Health (CA133950), the Pennsylvania Department of Health, and the Prevent Cancer Foundation (G.M.P.).

    The Pennsylvania Department of Health and the National Institutes of Health specifically disclaim responsibility for any analyses, interpretations, or conclusions.

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