mTORC1 inhibition restricts inflammation-associated gastrointestinal tumorigenesis in mice
Stefan Thiem, … , Andrew Jarnicki, Matthias Ernst
Stefan Thiem, … , Andrew Jarnicki, Matthias Ernst
Published January 16, 2013
Citation Information: J Clin Invest. 2013;123(2):767-781. https://doi.org/10.1172/JCI65086.
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Research Article Oncology

mTORC1 inhibition restricts inflammation-associated gastrointestinal tumorigenesis in mice

Abstract

Gastrointestinal cancers are frequently associated with chronic inflammation and excessive secretion of IL-6 family cytokines, which promote tumorigenesis through persistent activation of the GP130/JAK/STAT3 pathway. Although tumor progression can be prevented by genetic ablation of Stat3 in mice, this transcription factor remains a challenging therapeutic target with a paucity of clinically approved inhibitors. Here, we uncovered parallel and excessive activation of mTOR complex 1 (mTORC1) alongside STAT3 in human intestinal-type gastric cancers (IGCs). Furthermore, in a preclinical mouse model of IGC, GP130 ligand administration simultaneously activated mTORC1/S6 kinase and STAT3 signaling. We therefore investigated whether mTORC1 activation was required for inflammation-associated gastrointestinal tumorigenesis. Strikingly, the mTORC1-specific inhibitor RAD001 potently suppressed initiation and progression of both murine IGC and colitis-associated colon cancer. The therapeutic effect of RAD001 was associated with reduced tumor vascularization and cell proliferation but occurred independently of STAT3 activity. We analyzed the mechanism of GP130-mediated mTORC1 activation in cells and mice and revealed a requirement for JAK and PI3K activity but not for GP130 tyrosine phosphorylation or STAT3. Our results suggest that GP130-dependent activation of the druggable PI3K/mTORC1 pathway is required for inflammation-associated gastrointestinal tumorigenesis. These findings advocate clinical application of PI3K/mTORC1 inhibitors for the treatment of corresponding human malignancies.

Authors

Stefan Thiem, Thomas P. Pierce, Michelle Palmieri, Tracy L. Putoczki, Michael Buchert, Adele Preaudet, Ryan O. Farid, Chris Love, Bruno Catimel, Zhengdeng Lei, Steve Rozen, Veena Gopalakrishnan, Fred Schaper, Michael Hallek, Alex Boussioutas, Patrick Tan, Andrew Jarnicki, Matthias Ernst

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Figure 7

Excessive PIP3 accumulation and mTORC1 activation in cells expressing mutant GP130.

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Excessive PIP3 accumulation and mTORC1 activation in cells expressing mu...
(A–C) Formation of PIP3 at the cell membrane was monitored as an indicator of PI3K activity by immunofluorescent staining using the PIP3-specific GST-GRP1PH probe. The representative images show (A) naive 293T cells or (B) cells transiently expressing the indicated chimeric EpoR/GP130 receptor. Cells were stimulated for the indicated time with hyper–IL-6 (HypIL6; 100 ng/ml) or Epo (50 U/ml). (C) Images were then used for cell segmentation analysis and quantification with MetaMorph software. For each time point a total of 150 to 300 cells was analyzed, and results are depicted as mean ± SEM (*P < 0.05 when compared with unstimulated isogenic cells). Scale bar: 10 μm. Also refer to Supplemental Figure 9. (D and E) Immunoblot analysis of (D) naive 293T cells or (E) cells transiently expressing the EpoR/gp130F2 receptor. Cultures were serum starved and, where indicated, exposed to the PI3K inhibitor LY294002 (25 μM) 60 minutes prior to stimulation with hyper–IL-6 (100 ng/ml) or Epo (50 U/ml) for the indicated period. (F) Immunoblot analysis of 293T cells transiently expressing the indicated mutant EpoR/GP130 receptor. Serum-starved cells were stimulated for 60 minutes with Epo (50 U/ml). The schematic shows the transfected EpoR/GP130 receptors, which encode tyrosine (Y) to phenylalanine (F) substitution or truncation mutations in the cytosolic domain of human GP130. The consensus function of the individual Y residues and their amino acid position are depicted. Also refer to Supplemental Figure 11. Note that the pERK1/2 lanes were run on the same gel but were noncontiguous.