A Pooled RNAi Screening Strategy Reveals Novel Regulators for EpCAM

The cell surface receptor, Epithelial Cell Adhesion Molecule (EpCAM), is overexpressed in a variety of cancers and has been carefully examined for its functional role in carcinogenesis and its potential as a therapeutic target. However, little is known about the upstream molecular pathways that regulate EpCAM expression. To elucidate the mechanisms by which EpCAM expression is controlled, we designed a combinatorial screening strategy that utilized pooled shRNA gene knockdown with magnetically-activated cell separation for selection of cells with reduced EpCAM protein expression on the cell surface. The pooled RNAi screen was analyzed by comparing EpCAM-enriched and EpCAM-depleted cell populations for shRNA abundance using competitive hybridization to microarrays. Our RNAi screen and further validation efforts revealed that at least four genes (GRM1, SLITRK5, EFNA5, and IL23A) are important for EpCAM expression in the ovarian cancer cell line OVCAR8. Further investigations into the ephrin ligand, EFNA5, suggest that its activation by the Eph receptor, EPHA4, contributes to the regulation of EpCAM expression via a reverse signaling mechanism. Our screening strategy revealed novel mechanisms for the regulation of EpCAM expression and provides insight into the biology of this cancer-associated gene. Importantly, this study also demonstrates the utility of pooled RNAi screening in the identification of genes required for the regulation of cell surface protein expression. Two condition experiment; EpCAM-Bound or EpCAM-Unbound OVCAR8 cells vs Reference population of transduced cells without phenotypic selection; biological triplicate