Gastroenterology

Gastroenterology

Volume 145, Issue 2, August 2013, Pages 416-425.e4
Gastroenterology

Original Research
Full Report: Basic and Translational—Alimentary Tract
IDO1 Metabolites Activate β-catenin Signaling to Promote Cancer Cell Proliferation and Colon Tumorigenesis in Mice

https://doi.org/10.1053/j.gastro.2013.05.002Get rights and content

Background & Aims

Indoleamine 2,3 dioxygenase-1 (IDO1) catabolizes tryptophan along the kynurenine pathway. Although IDO1 is expressed in inflamed and neoplastic epithelial cells of the colon, its role in colon tumorigenesis is not well understood. We used genetic and pharmacologic approaches to manipulate IDO1 activity in mice with colitis-associated cancer and human colon cancer cell lines.

Methods

C57Bl6 wild-type (control), IDO1-/-, Rag1-/-, and Rag1/IDO1 double-knockout mice were exposed to azoxymethane and dextran sodium sulfate to induce colitis and tumorigenesis. Colitis severity was assessed by measurements of disease activity, cytokine levels, and histologic analysis. In vitro experiments were conducted using HCT 116 and HT-29 human colon cancer cells. 1-methyl tryptophan and small interfering RNA were used to inhibit IDO1. Kynurenine pathway metabolites were used to simulate IDO1 activity.

Results

C57Bl6 mice given pharmacologic inhibitors of IDO1 and IDO1-/- mice had lower tumor burdens and reduced proliferation in the neoplastic epithelium after administration of dextran sodium sulfate and azoxymethane than control mice. These reductions also were observed in Rag1/IDO1 double-knockout mice compared with Rag1-/- mice (which lack mature adaptive immunity). In human colon cancer cells, blockade of IDO1 activity reduced nuclear and activated β-catenin, transcription of its target genes (cyclin D1 and Axin2), and, ultimately, proliferation. Exogenous administration of IDO1 pathway metabolites kynurenine and quinolinic acid led to activation of β-catenin and proliferation of human colon cancer cells, and increased tumor growth in mice.

Conclusions

IDO1, which catabolizes tryptophan, promotes colitis-associated tumorigenesis in mice, independent of its ability to limit T-cell–mediated immune surveillance. The epithelial cell–autonomous survival advantage provided by IDO1 to colon epithelial cells indicate its potential as a therapeutic target.

Section snippets

Mice

Wild type (WT), IDO1 knock-out (IDO1-/-), and Rag1-/-, all on the C57BL/6J, originally were purchased from The Jackson Laboratory (Bar Harbor, ME) and then bred in-house to generate comparator groups. IDO1/Rag1 double knock-out (DbKO) mice were generated from these strains. At the start of experiments all mice were 6–12 weeks old and weighed 16–22 g. Age-matched female mice were used preferentially in experiments. Animals were maintained in a specific pathogen-free facility and all comparator

IDO1 Expression in Colitis-Associated Tumors

Expression levels of IDO1 and cytokines recognized as IDO1 inducers were measured in tumors and adjacent inflamed tissue and compared with noncolitis control mice. Levels of IFNγ, tumor necrosis factor α, and IDO1 mRNA and IDO1 protein were significantly higher in tumor tissue than in inflamed tissue adjacent to the tumors or control (noncolitis) specimens (Figure 1A and B). IFN-alfa, a cytokine known to induce IDO1 in plasmacytoid dendritic cells, was not increased significantly in either

Discussion

Inflammation and immune cell infiltration are present in both sporadic and colitis-associated colon cancers. To support continued growth and progression, it is advantageous for tumors to develop adaptive strategies to combat ongoing inflammation and immune assault. By using a murine model of colitis-associated tumorigenesis and human cell lines, we established a role for IDO1 as an adaptive mechanism promoting colon cancer epithelial proliferation.

The most striking finding of this study was

Acknowledgments

Matthew Ciorba extends his most sincere gratitude to Nicholas O. Davidson MD, Thaddeus Stappenbeck MD, PhD, and George Predergast who serve as advisors in career development and on award DK089016.

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    Authors names in bold designate shared first authorship.

    Conflicts of interest The authors disclose no conflicts.

    Funding Supported in part by National Institutes of Health grants DK089016 (M.A.C.), DK064798 (R.D.N.), DK075713 (W.F.S.), and P30-DK52574 (Washington University Digestive Diseases Research Cores Center). Ameet Thaker was a medical student research fellow of the Howard Hughes Medical Institute, and Matthew Ciorba received a Central Society for Clinical Research Early Career Development Award.

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