Department of Medicine, Division of Molecular Oncology, Washington University School of Medicine, St. Louis, Missouri.
ICCE Institute, Washington University School of Medicine, St. Louis, Missouri.
Cancer Res Commun. 2024 Apr 4;4(4):986-1003. doi: 10.1158/2767-9764.CRC-23-0488.
Detection of viral double-stranded RNA (dsRNA) is an important component of innate immunity. However, many endogenous RNAs containing double-stranded regions can be misrecognized and activate innate immunity. The IFN-inducible ADAR1-p150 suppresses dsRNA sensing, an essential function for adenosine deaminase acting on RNA 1 (ADAR1) in many cancers, including breast. Although ADAR1-p150 has been well established in this role, the functions of the constitutively expressed ADAR1-p110 isoform are less understood. We used proximity labeling to identify putative ADAR1-p110-interacting proteins in breast cancer cell lines. Of the proteins identified, the RNA helicase DHX9 was of particular interest. Knockdown of DHX9 in ADAR1-dependent cell lines caused cell death and activation of the dsRNA sensor PKR. In ADAR1-independent cell lines, combined knockdown of DHX9 and ADAR1, but neither alone, caused activation of multiple dsRNA sensing pathways leading to a viral mimicry phenotype. Together, these results reveal an important role for DHX9 in suppressing dsRNA sensing by multiple pathways.
These findings implicate DHX9 as a suppressor of dsRNA sensing. In some cell lines, loss of DHX9 alone is sufficient to cause activation of dsRNA sensing pathways, while in other cell lines DHX9 functions redundantly with ADAR1 to suppress pathway activation.
检测病毒双链 RNA（dsRNA）是先天免疫的一个重要组成部分。然而，许多含有双链区域的内源性 RNA 可能会被错误识别并激活先天免疫。IFN 诱导的 ADAR1-p150 抑制 dsRNA 感应，这是许多癌症（包括乳腺癌）中 RNA 腺苷脱氨酶 1（ADAR1）的一个重要功能。尽管 ADAR1-p150 在这一作用中已得到充分证实，但组成型表达的 ADAR1-p110 同工型的功能则知之甚少。我们使用邻近标记法鉴定了乳腺癌细胞系中 ADAR1-p110 相互作用蛋白的假定蛋白。在所鉴定的蛋白质中，RNA 解旋酶 DHX9 特别引人注目。在 ADAR1 依赖性细胞系中敲低 DHX9 会导致细胞死亡和 dsRNA 传感器 PKR 的激活。在 ADAR1 非依赖性细胞系中，DHX9 和 ADAR1 的联合敲低，但两者单独敲低均不会导致多种 dsRNA 感应途径的激活，从而导致病毒模拟表型。总之，这些结果揭示了 DHX9 在抑制多种途径的 dsRNA 感应中的重要作用。这些发现表明 DHX9 是 dsRNA 感应的抑制剂。在一些细胞系中，单独缺失 DHX9 就足以激活 dsRNA 感应途径，而在其他细胞系中，DHX9 与 ADAR1 冗余以抑制途径激活。
