GPX8 Regulation of the EMT Program is Mediated by IL-6 Production

Tumor-dependent metabolic remodeling is mainly associated with the production of the building blocks needed to meet the replicating cell’s demand for macromolecule biosynthesis. In contrast, our interest is in unique metabolic processes that do not fall under this category but instead are more likely to present a regulatory role in cell fate determination. Epithelial-mesenchymal transition (EMT) is a cellular program during which cancers, such as breast cancer, gain mesenchymal-like properties, resulting in increased malignant aggressiveness. Despite the extensive study of cancer-related EMT, the role of cellular metabolism in this program is poorly understood. To methodically identify the metabolic genes that play roles in tumor progression, we created Metabolic gEne RApid Visualizer (MERAV, http://merav.wi.mit.edu), a web-based tool for the analysis of human gene expression in normal tissues, primary tumors, and cancer cell lines. This bioinformatics framework resulted in the identification of 44 metabolic genes that are upregulated in high-grade tumors with mesenchymal markers and thus designated by us as the “mesenchymal metabolic signature” (MMS). In order to systematically determine the role of MMS, we developed a FACS-based shRNA screen that identified 16 genes as essential for the EMT program. One of these MMS genes - glutathione peroxidase 8 (GPX8), is a member of the glutathione peroxidase family whose cellular role is still unclear and was not previously connected with cancer. Here, we demonstrate that GPX8 plays a key role in the progression of tumors to a more aggressive state. GPX8 expression is upregulated upon EMT induction and analysis of publicly available databases identified that high levels of GPX8 are correlated with poor patient prognosis in tumors derived from various tissues. We found GPX8 to be necessary for cells to acquire mesenchymal characteristics. The GPX8 knockout (KO) basal B breast cancer MDA-MB-231 cell line demonstrates gaining epithelial-like morphology, reduction in mesenchymal marker expression, and poorer migration. Moreover, GPX8 loss results in the downregulation of IL-6 secretion, a key cytokine that induces the aggressive features of breast cancer cells. Thus we identified a metabolic gene that is essential to the EMT program through the induction of key autocrine cytokines. This role of GPX8 in cancer aggressiveness suggests an unknown cellular mechanism essential for cancer progression and cell fate determination. GPX8 expression could also be exploited for potential therapeutic applications and as a biomarker for breast cancer progression.