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ADAR1 controls apoptosis of stressed cells by inhibiting Staufen-mediated mRNA decay

ABSTRACT: Both p150 and p110 isoforms of ADAR1 convert adenosine to inosine in double-stranded RNA (dsRNA). The p150 isoform suppresses the dsRNA sensing mechanism that activates the interferon induction mediated by the MDA5-MAVS signaling. In contrast, the biological function of the p110 isoform localized in the nucleus remains largely unknown. Here we show that stress-activated phosphorylation of ADAR1p110 by MKK6/p38 MAP kinases promotes its binding to Exportin-5 and nuclear export to the cytoplasm. Once translocated to the cytoplasmic, ADAR1p110 suppresses apoptosis of stressed cells by protecting many anti-apoptotic gene transcripts that contain 3’UTR dsRNA structures such as those consisting of inverted Alu repeats. ADAR1p110 competitively inhibits binding of Staufen1 to the 3’UTR dsRNAs and antagonizes the Staufen1-mediated mRNA decay mechanism. Our studies revealed a new stress response mechanism regulated by MAP kinases, in which ADAR1p110 translocates to the cytoplasm and regulates a class of mRNAs required for survival of stressed cells.

ORGANISM(S): Homo sapiens

PROVIDER: GSE85455 | GEO | 2017/03/21

SECONDARY ACCESSION(S): PRJNA338496

REPOSITORIES: GEO

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Project description:Sensing of double-stranded RNA (dsRNA) is an important component of innate immunity. Proteins like PKR and MDA5 recognize dsRNA and activate various pathways to fight viral infection. In addition to viral dsRNA, many endogenous RNAs containing double-stranded regions can be misrecognized as immunogenic. The RNA editing enzyme ADAR1, specifically its p150 isoform, has been shown to suppress activation of PKR and MDA5 through its A-to-I editing activity. While the cytoplasmic ADAR1-p150 isoform has been well established within this role, the functions of the nuclear ADAR1-p110 isoform are less understood. To address this knowledge gap, we utilized proximity labeling by APEX2 to identify putative ADAR1-p110 interacting proteins. We identified 110 proteins across three breast cancer cell lines that either interact with p110 or are within close proximity. Many of these proteins have known roles in RNA metabolism. Nine of the identified proteins belong to the DEAD or DEAH box families of RNA helicases, including DHX9. DHX9 is overexpressed in breast cancer, with expression closely correlated with that of p110. By co-immunoprecipitation we confirmed that p110 interacts with DHX9. Knockdown of DHX9 in several triple-negative breast cancer cell lines caused cell death and activation of the dsRNA sensor PKR. In two cell lines that are refractory to knockdown of ADAR1, the combined knockdown of DHX9 and ADAR1 caused a substantial increase in PKR activity, where knockdown of either alone had no effect. Knockdown of DHX9 and ADAR1 caused activation of the type I IFN pathway, RNase L and NF-KB signaling. Activation of these proteins and pathways was not seen with individual knockdown of ADAR1 or DHX9. Activation of PKR following combined knockdown of ADAR1 and DHX9 could be rescued by expression of p110, p150, DHX9, and catalytically inactive DHX9. Additionally PKR activation could be rescued by the dsRBM of DHX9, revealing an important role for dsRBMs in suppressing PKR activation. Together these results reveal an important role for DHX9 in suppressing dsRNA sensing by multiple pathways.

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ADAR1 controls apoptosis of stressed cells by inhibiting Staufen-mediated mRNA decay

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