Abstract 5448: Malignant RNA editing by inflammation-responsive RNA editase ADAR1 drives T-cell leukemia relapse via attenuating dsRNA sensing
Authors: Rivera Maria Dolores , Zhang Haoran , Zhou Qingchen , Pham Jessica , Isquith Jane , Sasik Roman , Mark Adam , Enlund Sabina , Holm Frida , Wenxue Ma , Fisch Kathleen , Kuo Dennis , Jamieson Catriona , Jiang Qingfei 
Published: March 2024

Abstract
Leukemia-initiating cells (LICs) play a crucial role in leukemia research and treatment, being considered the source of relapse and resistance, posing a substantial challenge for successful management of the disease. It's crucial to identify the key factors that drive LIC self-renewal to develop targeted methods for eliminating LICs and preventing relapse. In this study, we demonstrate that the RNA editing enzyme ADAR1 plays a vital role as a determinant of stemness, promoting LIC self-renewal by reducing the detection of abnormal double-stranded RNA (dsRNA). As a result, ADAR1-knockdown significantly impairs the ability of LICs to self-renew and extends survival in T-ALL PDX models. We performed RNA-seq studies on enriched T-ALL LICs (CD34+Lin-). The lentivirus-to-cell ratio was optimized to achieve a 50% reduction in ADAR1, resulting in differential expression of 661 genes, with downregulation of critical self-renewal genes in ADAR1-deficient leukemia-initiating cells. Importantly, additional data indicated that ADAR1 likely influences self-renewal gene expression independently of A-to-I RNA editing, revealing novel regulatory mechanisms in leukemia. Knockdown of MDA5 and ADAR1 in patient-derived xenograft (PDX) T-ALL leukemia-initiating cells (LICs) revealed diverse rescue effects on self-renewal in different PDX models. The differential response was associated with variations in gene expression patterns in Rig-I-Like signaling and cytosolic sensing pathways, suggesting intrinsic differences in IFN signaling properties among patients. Moreover, the study proposes a patient-specific reliance on the ADAR1 p150-MDA5 axis for promoting self-renewal, as evidenced by differential rescue effects and varying expression levels of ADAR1 isoforms and MDA5 in T-ALL patient samples and cell lines. ADAR1, beyond its role in RNA editing, acts as a dsRNA binding protein, exerting RNA editing-independent functions to suppress aberrant IFN signaling and promote cancer progression. Using Jurkat cells with high intrinsic MDA5 levels, an ADAR1 knockout (KO) was generated, revealing that ADAR1 is upregulated by IFN treatment, predominantly the p150 isoform. We explored the dual roles of ADAR1—RNA editing-dependent and -independent—in suppressing IFN-induced apoptosis, demonstrating the necessity of both for optimal function. Additionally, ADAR1 was found to suppress cytoplasmic dsRNA sensing pathways, such as RIG-I and PKR, and its RNA editing-independent activity contributes significantly to the suppression of interferon-stimulated gene (ISG) expression in T-ALL. In summary, our findings reveal that ADAR1 acts as a factor that promotes self-renewal while limiting the recognition of naturally occurring dsRNA. Therefore, targeting ADAR1 emerges as a safe and effective therapeutic approach for eradicating LICs in T-ALL.
Citation Format: Maria Dolores Rivera, Haoran Zhang, Qingchen Zhou, Jessica Pham, Jane Isquith, Roman Sasik, Adam Mark, Sabina Enlund, Frida Holm, Ma Wenxue, Kathleen Fisch, Dennis Kuo, Catriona Jamieson, Qingfei Jiang. Malignant RNA editing by inflammation-responsive RNA editase ADAR1 drives T-cell leukemia relapse via attenuating dsRNA sensing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5448.