Loss of single immunoglobulin interlukin-1 receptor-related molecule leads to enhanced colonic polyposis in Apcmin mice

2010 
Background & Aims Commensal bacteria can activate signaling by the Toll-like and interleukin-1 receptors (TLR and IL-1R) to mediate pathogenesis of inflammatory bowel diseases and colitis-associated cancer. We investigated the role of the single immunoglobulin IL-1 receptor-related (SIGIRR) molecule, a negative regulator of TLR and IL-1R signaling, as a tumor suppressor to determine whether SIGIRR controls cell-cycle progression, genetic instability, and colon tumor initiation by modulating commensal TLR signaling in the gastrointestinal tract. Methods We analyzed adenomatous polyposis coli ( Apc ) min/+/ Sigirr −/− mice for polyps, microadenomas, and anaphase bridge index. Commensal bacteria were depleted from mice with antibiotics. Akt, mammalian target of rapamycin (mTOR), and β-catenin pathways were examined by immunoblotting and immunohistochemistry. Loss of heterozygosity of Apc and expression of cytokines and proinflammatory mediators were measured by nonquantitative or quantitative polymerase chain reaction. Results Apc min/+/ Sigirr −/− mice had increased loss of heterozygosity of Apc and microadenoma formation, resulting in spontaneous colonic polyposis, compared with Apc min/+ /Sigirr +/+ mice. The increased colonic tumorigenesis that occurred in the Apc min/+/ Sigirr −/− mice depended on the presence of commensal bacteria in the gastrointestinal tract. Cell proliferation and chromosomal instability increased in colon crypt cells of the Apc min/+/ Sigirr −/− mice. Akt, mTOR, and their substrates were hyperactivated in colon epithelium of Apc min/+/ Sigirr −/− mice in response to TLR or IL-1R ligands. Inhibition of the mTOR pathway by rapamycin reduced formation of microadenomas and polyps in the Apc min/+/ Sigirr −/− mice. Conclusions SIGIRR acts as a tumor suppressor in the colon by inhibiting TLR-induced, mTOR-mediated cell-cycle progression and genetic instability.
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