Interferon-Inducible ADAR1 p150 Is Essential for the Survival of Oral Squamous Cell Carcinoma

We identified ADAR1 as one of the top essential genes for oral squamous cell carcinoma (OSCC) survival from our genome-wide CRISPR/Cas9 screen in OSCC cell lines. In this study, we confirm that ADAR1-knockout (KO) inhibits cell viability and colony forming ability, and induces apoptosis. We report that IFN-β treatment sensitizes less-dependent cell lines to ADAR1 KO-induced cell lethality. Overexpression of ADAR1-p150, but not ADAR1-p110, rescued cell lethality upon ADAR1 KO, confirming that the IFN-inducible p150 is responsible for OSCC survival. Using a deaminase inactive mutant, we demonstrate that the editing function of ADAR1 is important for OSCC survival. Furthermore, we show that ADAR1 KO-induced cell death is mediated by both PKR and MDA5. We compute gene signatures of ADAR1 dependency in OSCC tumors, and found that those with high ADAR1 dependency score are associated with well or moderate differentiation, likely due to high PKR expression or activation. While a majority of ADAR1-dependent tumors exhibit a low T cell-inflamed gene expression profile, ADAR1 KO upregulates PD-L1, a marker of anti-PD1 response, indicating that ADAR1 inhibition may enhance immunotherapy response in OSCC. Collectively, these findings suggest that targeting ADAR1-p150 not only induces OSCC cell death but could induce a favorable response to anti-PD1.