Abstract 1704: Interferon inducible ADAR1 is essential for the survival of oral squamous cell carcinoma

Abstract

Abstract Treating oral squamous cell carcinoma (OSCC) remains challenging due to limited knowledge of the critical genes that could affect cell survival in OSCC. We have previously utilized genome-wide CRISPR-Cas9 knockout functional screens to explore the genetic vulnerabilities of OSCC and identified Adenosine deaminase acting on RNA (ADAR1) as one of the top fitness genes. ADAR1 is an interferon-stimulated gene (ISG) that catalyses adenosine-to-inosine (A-to-I) editing of double-stranded RNA (dsRNA), which suppresses dsRNA sensing mechanism from triggering cell death. ADAR1 gene encodes for two isoforms, the constitutively expressed P110 and the interferon-inducible P150. Given that deleting ADAR1 severely impacts OSCC viability, we aimed to elucidate key molecular mechanisms underlying this gene dependency which may provide opportunities for developing better treatment strategies. Here, we validated ADAR1 dependency via competitive co-culture assay using single-guide RNA (sgRNA) knockout in selected OSCC cell lines. We also confirmed that sgRNA-mediated ADAR1 knockout resulted in prominent cell lethality through increased apoptosis and inhibition of colony formation. Cell lethality is evident in ADAR1 KO cells in conjunction with the phosphorylation of a dsRNA sensor, protein kinase R (PKR) which regulates cell death mechanism. In ADAR1-less dependent cells, IFN-β treatment increased the expression of ISGs including ADAR1, and sensitized the cells to ADAR1 KO-induced cell death. Overexpression of ADAR1-P150 but not ADAR1-P110 rescued cell lethality in ADAR1-depleted cells, suggesting that ADAR1-P150 is required for OSCC survival. We also demonstrate that the deaminase function of ADAR1 is important in conferring survival to a subset of OSCC lines. In addition to PKR, the melanoma differentiation-associated protein 5 (MDA5) dsRNA sensor is also important in mediating ADAR1 KO-induced cell lethality OSCC and co-deleting both PKR and MDA5 enabled the partial rescue of cell death compared to when each gene was knocked out individually. Collectively, our results uncover the essentiality of IFN-inducible ADAR1-P150 for OSCC survival, and reveal that the activation of PKR and MDA5 dsRNA sensing pathways underlie the cell lethality caused by ADAR1 deletion. Citation Format: Pei San Yee, Annie Wai Yeeng Chai, Shi Mun Yee, Shi Yin Ooi, Yee Hua Tan, Mathew Garnett, Siew Kit Ng, Sok Ching Cheong. Interferon inducible ADAR1 is essential for the survival of oral squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1704.