mTOR and HIF-1α-mediated tumor metabolism in an LKB1 mouse model of Peutz-Jeghers syndrome

Dulbecco Center for Cancer Research, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 07/2009; 106(27):11137-11142. DOI: 10.1073/pnas.0900465106

ABSTRACT Peutz-Jeghers syndrome (PJS) is a familial cancer disorder due to inherited loss of function mutations in the LKB1/ STK11
serine/threonine kinase. PJS patients develop gastrointestinal hamartomas with 100% penetrance often in the second decade
of life, and demonstrate an increased predisposition toward the development of a number of additional malignancies. Among
mitogenic signaling pathways, the mammalian-target of rapamycin complex 1 (mTORC1) pathway is hyperactivated in tissues and
tumors derived from LKB1-deficient mice. Consistent with a central role for mTORC1 in these tumors, rapamycin as a single
agent results in a dramatic suppression of preexisting GI polyps in LKB1+/− mice. However, the key targets of mTORC1 in LKB1-deficient
tumors remain unknown. We demonstrate here that these polyps, and LKB1- and AMPK-deficient mouse embryonic fibroblasts, show
dramatic up-regulation of the HIF-1α transcription factor and its downstream transcriptional targets in an rapamycin-suppressible
manner. The HIF-1α targets hexokinase II and Glut1 are up-regulated in these polyps, and using FDG-PET, we demonstrate that
LKB1+/− mice show increased glucose utilization in focal regions of their GI tract corresponding to these gastrointestinal
hamartomas. Importantly, we demonstrate that polyps from human Peutz-Jeghers patients similarly exhibit up-regulated mTORC1
signaling, HIF-1α, and GLUT1 levels. Furthermore, like HIF-1α and its target genes, the FDG-PET signal in the GI tract of
these mice is abolished by rapamycin treatment. These findings suggest a number of therapeutic modalities for the treatment
and detection of hamartomas in PJS patients, and potential for the screening and treatment of the 30% of sporadic human lung
cancers bearing LKB1 mutations.

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