Inhibition of mitochondrial complex III or dihydroorotate dehydrogenase (DHODH) triggers formation of poly(A)+ RNA foci adjacent to nuclear speckles following activation of ATM (ataxia telangiectasia mutated)

Intracellular and intercellular signalling networks play an essential role in optimizing cellular homoeostasis and are thought to be partly reflected in nuclear mRNA dynamics. However, the regulation of nuclear mRNA dynamics by intracellular and intercellular signals remains largely unexplored, and research tools are lacking. Through an original screening based on the mRNA metabolic mechanism, we discovered that eight well-known inhibitors cause significant nuclear poly(A)+ RNA accumulation. Among these inhibitors, we discovered a new mRNA metabolic response in which the addition of antimycin A, an inhibitor of mitochondrial respiratory-chain complex III (complex III), resulted in a marked accumulation of poly(A)+ RNA near the nuclear speckles. Furthermore, dihydroorotate dehydrogenase (DHODH) inhibitors, a rate-limiting enzyme in the intracellular de novo pyrimidine synthesis reaction that specifically exchanges electrons with complex III, also caused a remarkable accumulation of nuclear poly(A)+ RNA adjacent to the nuclear speckles, which was abolished by extracellular uridine supply, indicating that the depletion of intracellular pyrimidine affects poly(A)+ RNA metabolism. Further analysis revealed that ataxia telangiectasia mutated (ATM), a serine and threonine kinase and a master regulator of DNA double-strand break (DSB) and nucleolar stress, is required for this poly(A)+ RNA nuclear accumulation phenomenon. This study reports new insights into novel aspects of nuclear poly(A)+ RNA metabolism, especially the relationship between mitochondrial respiratory-chain functions, pyrimidine metabolism, and nuclear RNA metabolism.

细胞内与细胞间信号网络在优化细胞稳态中扮演着至关重要的角色，且据推测，这些网络在一定程度上反映了细胞核mRNA的动态变化。然而，关于细胞内与细胞间信号对细胞核mRNA动态变化的调控机制尚处于探索的初期阶段，且缺乏必要的研究工具。通过基于mRNA代谢机制的原创筛选，我们发现八种已知的抑制剂导致了显著的细胞核poly(A)+RNA积累。在这些抑制剂中，我们发现了一种新的mRNA代谢反应：添加抗霉素A，即抑制线粒体呼吸链复合物III（复合物III）的抑制剂，导致细胞核周围poly(A)+RNA的显著积累。此外，二氢叶酸脱氢酶（DHODH）抑制剂，作为细胞内从头合成嘧啶反应中限速酶，该酶与复合物III特异性交换电子，也引起了细胞核周围poly(A)+RNA的显著积累，这一现象可通过细胞外尿苷的补充而被消除，表明细胞内嘧啶的耗竭影响了poly(A)+RNA的代谢。进一步分析揭示，共济失调毛细血管扩张症突变蛋白（ATM），一种丝氨酸/苏氨酸激酶，同时也是DNA双链断裂（DSB）和核仁应激的主导调节因子，对于这一poly(A)+RNA在细胞核中的积累现象是必需的。本研究报告了对细胞核poly(A)+RNA代谢新领域的洞察，特别是线粒体呼吸链功能、嘧啶代谢与细胞核RNA代谢之间的关系。