Abstract P3-01-06: TIGAR induces two compartment metabolic coupling and tamoxifen resistance
Authors: Ko Y-H , Bombonati A , Martinez-Outschoorn UE 
Published: August 2014

We have previously demonstrated that metabolic coupling occurs in a subgroup of human breast cancers between fibroblasts and carcinoma cells. In metabolically coupled tumors, cancer associated fibroblasts (CAFs) have low Cav-1 protein expression, are highly glycolytic and generate large amounts of lactate which is then released to the extracellular space via increased expression of monocarboxylate transporter 4 (MCT4) compared to normal fibroblasts (NFs). Conversely, in metabolically coupled tumors, carcinoma cells have low glycolysis with high uptake of lactate via monocarboxylate transporter 1 (MCT1) and high mitochondrial oxidative phosphorylation (OXPHOS) using lactate as a substrate compared to non-carcinoma epithelial cells. We have identified two fibroblast markers of metabolically coupled breast cancer: low caveolin-1 (Cav-1) protein expression and high MCT4 protein expression. Low Cav-1 expression and high MCT4 expression in breast cancer fibroblasts are prognostic biomarkers associated with poor outcomes. However, the mechanisms by which carcinoma cells reprogram CAFs to induce loss of fibroblast Cav-1 or increased expression of MCT4 protein are unknown.

TP53 inducible glycolysis and apoptosis regulator (TIGAR) is a p53 regulated protein that inhibits glycolysis and induces OXPHOS. We investigated the role of TIGAR on expression of the fibroblast prognostic biomarkers Cav-1 and MCT4. We immunohistochemically stained 10 human ER+ breast cancer samples for TIGAR. TIGAR protein expression was highest in the carcinoma cells compared to fibroblasts and non-carcinoma epithelial cells in all 10 samples. We then cocultured T47D ER+ breast cancer cells with human fibroblasts (BJ-1) and discovered that the presence of fibroblasts was sufficient to increase TIGAR protein expression in carcinoma cells (1.5 fold, p&lt;0.05). This coculture system was also sufficient to downregulate Cav-1 protein expression in fibroblasts (2.3 fold, p&lt;0.01). We generated fibroblasts with Cav-1 shRNA knockdown and discovered that TIGAR protein expression decreased. We generated TIGAR overexpressing T47D cells and found that they had higher OXPHOS activity. Coculture of TIGAR overexpressing T47D cells with fibroblasts induced further downregulation of Cav-1 protein in fibroblasts (3.2 fold, p&lt;0.05) and increased MCT4 protein in fibroblasts (2 fold, p&lt;0.05) compared to coculture with control T47D cells. Overexpression of TIGAR in T47D cells was sufficient to increase 2-deoxyglucose uptake in fibroblasts by 1.2 fold (p&lt;0.01) and decrease 2-deoxyglucose uptake in T47D cells by 1.3 fold (p&lt;0.05). 2-deoxyglycose uptake is a marker of glycolysis. Finally, resistance to baseline apoptosis (1.6 fold,p&lt;0.001) and with tamoxifen (1.2 fold, p&lt;0.01) was induced by TIGAR overexpression. In summary, TIGAR expression in carcinoma cells is sufficient to induce carcinoma cell resistance to apoptosis, decrease Cav-1 and increase MCT4 protein expression in fibroblasts. TIGAR should be studied as a prognostic and predictive biomarker in breast cancer and a potential drug target.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-01-06.