Genome-wide RNAi screen identifies PMPCB as a therapeutic vulnerability in EpCAM+ hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a genetically heterogeneous disease for which a dominant actionable molecular driver has not been identified. Patients with the stem cell- like EpCAM+AFP+ HCC subtype have poor prognosis. Here, we performed a genome-wide RNAi screen to identify genes with a synthetic lethal interaction with EpCAM as a potential therapeutic target for the EpCAM+AFP+ HCC subtype. We identified 26 candidate genes linked to EpCAM/Wnt/ b-catenin signaling and HCC cell growth. We further characterized the top candidate PMPCB, which plays a role in mitochondrial protein processing, as a bona fide target for EpCAM+ HCC. PMPCB blockage suppressed EpCAM expression and Wnt/b-catenin signaling via mitochondria-related reactive oxygen species production and FOXO activities, resulting in apoptosis and tumor suppression. These results indicate that a synthetic lethality screen is a viable strategy to identify actionable drivers of HCC and identify PMPCB as a therapeutically vulnerable gene in EpCAM+ HCC subpopulations. Significance: This study identifies PMPCB as critical to mitochondrial homeostasis and a synthetic lethal candidate that selectively kills highly resistant EpCAM+ HCC tumors by inactivating the Wnt/b-catenin signaling pathway.