ADAR1 RNA editing enzyme regulates R-loop formation and genome stability at telomeres in cancer cells

Yusuke Shiromoto,Kentaro Ariyoshi,Masayuki Sakurai,Kazuko Nishikura,Moeko Minakuchi

doi:10.1038/s41467-021-21921-x

Yusuke Shiromoto, Kentaro Ariyoshi + Show 3 more

Open Access

https://doi.org/10.1038/s41467-021-21921-x

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Abstract

ADAR1 is involved in adenosine-to-inosine RNA editing. The cytoplasmic ADAR1p150 edits 3’UTR double-stranded RNAs and thereby suppresses induction of interferons. Loss of this ADAR1p150 function underlies the embryonic lethality of Adar1 null mice, pathogenesis of the severe autoimmune disease Aicardi-Goutières syndrome, and the resistance developed in cancers to immune checkpoint blockade. In contrast, the biological functions of the nuclear-localized ADAR1p110 remain largely unknown. Here, we report that ADAR1p110 regulates R-loop formation and genome stability at telomeres in cancer cells carrying non-canonical variants of telomeric repeats. ADAR1p110 edits the A-C mismatches within RNA:DNA hybrids formed between canonical and non-canonical variant repeats. Editing of A-C mismatches to I:C matched pairs facilitates resolution of telomeric R-loops by RNase H2. This ADAR1p110-dependent control of telomeric R-loops is required for continued proliferation of telomerase-reactivated cancer cells, revealing the pro-oncogenic nature of ADAR1p110 and identifying ADAR1 as a promising therapeutic target of telomerase positive cancers.

Highlights

ADAR1 is involved in adenosine-to-inosine RNA editing
Adenosine deaminase acting on RNA (ADAR) is the enzyme involved in adenosine-to-inosine RNA editing (A-to-I RNA editing), and three ADAR gene family members (ADAR1, ADAR2, and ADAR3) have been identified in vertebrates[1,2,3,4,5]
Chromosome orientation fluorescence in situ hybridization (CO-FISH) analysis revealed significantly increased involvement of leading strands in telomere fusions detected in Adar1-null mouse embryonic fibroblast (MEF) cells (Supplementary Fig. 1d), indicating that ADAR1 is involved in the mechanism that maintains the integrity of the telomere leading strands

Summary

Results

Depletion of ADAR1 results in telomere DNA damage, telomere abnormalities, and mitotic arrest. Telomere FISH and immunostaining for γH2AX revealed significantly increased telomere dysfunction-induced foci (TIF, indicated by yellow arrowheads), suggesting the causative relevance of the telomeric repeat DNA damage to chromosome abnormality detected in ADAR1-depleted HeLa cells. Accumulation of R-loops at telomeres could explain the increased TIFs, various telomere abnormalities observed in Adar1-null MEF cells (Supplementary Fig. 1), and mitotic arrest detected in ADAR1-depleted HeLa cells (Fig. 1c, d). We prepared telomeric repeat duplex substrates (RNA:RNA and RNA:DNA hybrid) consisting of perfectly complementary sense and antisense strands (Fig. 4b, c) and tested them for in vitro editing with ADAR1p110, the ADAR1 isoform relevant to R-loop regulation (Fig. 2e). ADAR1p110 editing of the completely matched telomeric repeat RNA:DNA hybrids (Fig. 4c, top and bottom for G-strand RNA and C-strand DNA, respectively) was very inefficient, only at the background level, that is,

Telomere

Discussion

HEK293T

Methods