ADAR1 Prevents R-loop Accumulation-Driven ATR Pathway Activation in Ovarian Cancer

Abstract

BackgroundAdenosine (A)-to-inosine (I) RNA editing is the most prevalent RNA editing mechanism, in which adenosine deaminases acting on RNA 1 (ADAR1) is a major adenosine deaminase. Increasing evidence suggests that editing dysregulation of ADAR1 plays an important role in human tumorigenesis, while the underlying mechanism remains elusive. MethodsThe clinical relevance of ADAR1 was analyzed by real-time PCR, western blotting and immunohistochemistry of ovarian cancer tissues. ADAR1 function on ovarian cancer cells in vitro were explored by colony formation assay, transwell assay and Brdu-based cell cycle assay in vitro and xenograft models in vivo. Western blotting, immunostaining and DNA/RNA immunoprecipitation-qPCR were conducted to confirm DNA damage and R-loop accumulation in ovarian cancer cells. Co-immunoprecipitation and DNA/RNA immunoprecipitation were performed to detect interaction of DHX9, ADAR1 and R-loop complex in ovarian cancer cells.ResultsWe demonstrated that ADAR1 was highly expressed in ovarian cancer tissues and negatively correlated with progression free survival of ovarian cancer patients. Importantly, silence of ADAR1 repressed ovarian cancer cell growth and colony formation in vitro and inhibited ovarian cancer cell tumorigenesis in vivo. Further cell cycle and transcriptome profile analysis revealed that silence of ADAR1 in ovarian cancer cells induced cell cycle arrest at G1/G0 stage. Mechanically, loss of ADAR1 caused R-loop abnormal accumulation, thereby contributing to single stand DNA break and ATR pathway activation. Additionally, ADAR1 interacted with DHX9 to regulate R-loop complex formation, and A-to-I editing of nascent RNA repressed R-loop formation during co-transcriptional process. ConclusionsOur results identify a novel ADAR1/R-loop/ATR axis critical for ovarian cancer progression and a potential target for ovarian cancer therapy.