SiRNA library screening to define esophageal adenocarcinoma cell survival factors.

Abstract

70 Background: There is a pressing need to identify new therapeutic targets for esophageal adenocarcinoma (EAC). Hence, we utilized siRNA-screening libraries to identify genes impacting on EAC cancer cell growth to identify potential therapeutic targets. Methods: A “druggable genome” library (6,022 individual siRNAs) was utilized to examine EAC cell survival using the MTT assay. Statistical analysis combined the use of Z-factor, t-test and SSMD. EAC cell lines GohTRT, SKGT4 and OE33 were utilized. Functional validation of the resulting siRNAs utilized RT-PCR, Western Blot, ELISA and TOPFLASH assays. Results: siRNA library screening resulted in positive quality metrics (Z-factor>0.5) confirming its validity and further identifying 118 high confidence gene targets affecting EAC cell growth. Verification of these siRNA targets in multiple cell lines indicated a good level of concordance with the primary screening data. Bioinformatic and pathway mapping approaches of these targets emphasized links between EAC cell proliferation and regulators of inflammation and “immune cell processes” (LIF, C1Qa, C1r, C1s, GDF15, IL9R and TREM2). Pathological and transcriptomic studies demonstrated that LIF (FC=96.7; P<0.0001), GDF15 (EAC: FC=74; P<0.0001), C1Qa and TREM2 may be up-regulated in EAC biopsies. In functional work, exposure of EAC cell lines to recombinant or native proteins of C1q, LIF and GDF15 rescued the observed effects of their respective silencing in EAC cells (>90%,p0.001) and acted as potential growth promoters (>40%, p0.01). Auto-regulatory feedback loops were discovered in response to treatment with exogenous C1q and LIF in EAC cells. Signal transduction could be induced through b-catenin stabilization and STAT3 pathways in response to C1q and LIF treatment respectively. GDF15 was observed to act in a similar fashion to TGFb in scratch wound assays and additionally regulate Th17 type T-cell differentiation. Conclusions: Genes regulating EAC proliferation have been defined by siRNA library screening. We have identified secreted immune factors, not previously associated with EAC biology, capable of regulating EAC cell survival.