Abstract 768: The ATP6V1C2 (a vacuolar-ATPase gene) is a novel early prognosticator for colorectal cancer

Background: Vacuolar (v) -ATPases are expressed in certain tissues and cell types, and hypothesized to detoxify intracellular environments by expelling protons across plasma membranes, thereby contributing to acidified extracellular environments of solid tumors. Acidic microenvironments suppress anti-cancer cytotoxic T-cells and activate metalloproteinases, promoting tumor cell survival, motility and invasion. Scarce nutrients, hypoxia, and accelerated metabolism that favor pathways that produce excess intracellular protons by promoting glycolysis and lactic acid fermentation, lead to selection of tumor cells that adapted to and countered toxic/acidic cytoplasm. It is unclear whether colorectal cancers (CRCs) upregulate proton-expelling mechanisms, and whether associated genes are prognostic biomarkers. Aim: We hypothesized that adaptations through upregulation of proton transporting genes is prognostic for CRC. This study aims to identify transcriptional adaptations that CRCs undergo in response to acidic microenvironments and evaluate their prognostic value in multiple cohorts of CRC patients. Methods: Comprehensive microarray data from 222 CRCs obtained from The Cancer Genome Atlas were used to screen for genes upregulated in CRCs vs. normal mucosae, and stage III and IV vs. early staged tumors. Filtered genes involved in metabolite transport were tested for their ability to predict survival using Kaplan-Meier survival analysis with a stringent median cutoff. A second cohort was used to corroborate initial findings. A third cohort of matching polyps and adenomas was used to determine if candidate gene upregulation can be detected in pre-cancerous lesions. Functional analysis was performed using siRNA knockdown to determine if the candidate gene is critical for CRC proliferation. Results: Progressive upregulation of ATP6V1C2 from early to late stage CRCs was detected in two separate multinational patient cohorts, where its high expression was correlated with shorter overall survival. Receiver operating characteristic (ROC) curve analysis confirmed that ATP6V1C2 expression successfully discriminated between cancerous and non-cancer tissues. Fisher's exact test confirmed that high ATP6V1C2 expression correlated with advanced depth of invasion (T stage), and distant and liver metastasis. ATP6V1C2 expression was increased in pre-cancerous polyps. SiRNA knockdown of ATP6V1C2 inhibited cell proliferation in high expressing cell lines (HCT116 and HCT15) but not in low expressing RKO and HT29. Citation Format: Timothy J. Zumwalt, Kunitoshi Shigeyasu, Wenhao Weng, Yoshinaga Okugawa, Jinsei Miyoshi, Ajay Goel. The ATP6V1C2 (a vacuolar-ATPase gene) is a novel early prognosticator for colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 768.