Abstract PR01: Role of mitochondrial folate transporter in metabolism of tumor cells
Authors: Kovalenko Ilya , Schöckel Laura , Glasauer Andrea , Haegebarth Andrea , Christian Sven 
Published: May 2016

The objective of the present study is to identify modulators of cellular metabolism among transportome genes which could potentially be exploited as targets in pancreatic ductal adenocarcinoma (PDAC). Indeed cancer cells have the ability to adapt in order to survive stressful environment where oxygen and nutrients are limited due to the poor vasculature and outgrowth of stromal component. Thus, disrupting mechanisms of metabolic adaptation could inhibit tumor proliferation or sensitize tumor cells to treatment. Ion channels and transporters provide the link between cancer cells, stroma and matrix. Additionally these proteins may redirect metabolic fluxes among the cellular compartments which could provide alternative utilization of available substrates.

We performed a Metabolic Flux Analyzer siRNA-based screen of transportome genes in Mia PaCa-2 cells to find transporters that influence either glycolysis (extracellular acidification rate) or oxidative phosphorylation (oxygen consumption rate). Among the hits SLC25A32 (Mitochondrial Folate Transporter) was identified to significantly increase oxygen consumption. SLC25A32 is poorly characterized in the literature and its function and role in tumorigenesis are currently unknown. The gene was shown to be expressed in the inner mitochondrial membrane and was identified as a bi-directional mitochondrial transporter of tetrahydroxyfolate (THF). Interestingly an inactivating mutation of SLC25A32 leads to glycine auxotrophy in CHO cells. Additionally, amplification of SLC25A32 is found in a large portion of cancers (breast, prostate, ovary and liver). This gene amplification confers poor prognosis in breast cancer patients.

In depth follow-up studies revealed that siRNA-mediated inhibition of SLC25A32 caused an increase in mitochondrial reactive oxygen species (ROS) production, G2/M cell cycle arrest and subsequently cell death. MitoTEMPO, a mitochondrial targeted antioxidant, partially rescues this phenotype, indicating that ROS mediates the death phenotype upon SLC25A32 inhibition. Furthermore, mitochondrial gene expression profiling revealed that downregulation of SLC25A32 decreased the expression of anti-apoptotic genes (BCL2L, SFN), making cells more susceptible to death, and upregulated the mitochondrial uncoupler UCP-1, which explains the increase in oxygen consumption. In agreement with our knockdown studies, overexpression of SLC25A32 in Mia PaCa-2 cell line led to a decrease in oxygen consumption. Furthermore SLC25A32 overexpression augmented cell growth. Both these results confirm the role of SLC25A32 in modulating mitochondrial homeostasis and demonstrate that the amplification of this gene may provide advantage for cancer cell proliferation and survival.

Based on our data, SLC25A32 might be a potential anti-cancer target for PDAC patients.

Citation Format: Ilya Kovalenko, Laura Schöckel, Andrea Glasauer, Andrea Haegebarth, Sven Christian. Role of mitochondrial folate transporter in metabolism of tumor cells. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr PR01.