Mechanism of Cancer Cell Adaptation to Metabolic Stress PROTEOMICS IDENTIFICATION OF A NOVEL THYROID HORMONE-MEDIATED GASTRIC CARCINOGENIC

Gastric cancer is the second most common cancer world-wide and has a poor prognosis. To determine the mech-anism of adaptation to metabolic stress in cancer cells, we used gastric cancer as a model system to reveal the potential signaling pathways involved. Two-dimensional polyacrylamide gel electrophoresis coupled with ESI-Q-TOF MS/MS analysis was used to identify differentially expressed proteins between gastric tumor tissues and the corresponding noncancerous tissues. In total, 107 spots with significant alteration (over 2-fold, p < 0.05) were positively identified by MS/MS analysis. Altered expression of representative proteins was validated by RT-PCR and Western blotting. Cluster analysis of the changed proteins revealed an interesting group of meta-bolic proteins, which suggested accumulation of triiodo-thyronine (T3; the major functional component of thyroid hormone) and overexpression of hypoxia-induced factor (HIF) in gastric carcinoma. These observations were fur-ther confirmed by electrochemiluminescence immunoas-say and immunohistochemistry. T3-induced expression of HIF1- and vascular endothelial growth factor was further verified using a gastric cancer cell line and in vivo mouse model. Because the early accumulation of HIF1- was found to be independent of de novo transcription, we also found that the cytosolic cascade phosphatidylinositol 3-kinase/Akt pathway sensitive to T3 stimulus was in-volved. Furthermore we demonstrated that T3-induced overexpression of HIF1- was mediated by fumarate ac-cumulation and could be enhanced by fumarate hydratase inactivation but inhibited by 2-oxoglutarate. These results provide evidence for alteration of metabolic proteins and dysfunction of thyroid hormone regulation in gastric tu-mors, and a novel thyroid hormone-mediated tumorigenic signaling pathway is proposed. Our findings are consid-ered a significant step toward a better understanding of adaptations to metabolic stress in gastric carcinogenesis. Molecular & Cellular Proteomics 8