LINE-1 ORF1p Mimics Viral Innate Immune Evasion Mechanisms in Pancreatic Ductal Adenocarcinoma

Abstract Repeat element viral mimicry is a common feature in pancreatic ductal adenocarcinoma (PDAC) that require mechanisms to manage this repeat “viral” load and attenuate innate immune responses. Here, we show that the LINE-1 ORF1 protein (ORF1p) in PDAC cells plays a role in shielding repeat RNAs from activating a pathogen recognition receptor (PRR)-mediated antiviral response that is independent of retrotransposition. Suppression of ORF1p using short hairpin RNA induces innate immune responses through the dsRNA sensors RIG-I and MAVS. Low ORF1p PDAC cell lines have suppressed expression of PRRs demonstrating convergent mechanisms to suppress innate immune signaling. Localization of ORF1p in processing bodies (PBs) with the dsRNA helicase MOV10 were found important for these antiviral responses. Loss of ORF1p resulted in significant growth reduction in tumorspheres and mouse xenografts with an enriched epithelial cell state, and high ORF1p expression was associated with worsened survival in a cohort of human PDAC patients.