Defective intracellular trafficking and export of microRNAs (miRNAs) have been observed in growth-retarded mammalian cells having impaired mitochondrial potential and dynamics. Here, we found that uncoupling protein 2 (Ucp2)-mediated depolarization of mitochondrial membrane also results in progressive sequestration of miRNAs within polysomes and lowers their release via extracellular vesicles. Interestingly, the impaired miRNA-trafficking process in growth-retarded human cells could be reversed in the presence of Genipin, an inhibitor of Ucp2. Mitochondrial detethering of endoplasmic reticulum (ER), observed in cells with depolarized mitochondria, was found to be responsible for defective compartmentalization of translation initiation factor eIF4E to polysomes attached to ER. This caused a retarded translation process accompanied by enhanced retention of miRNAs and target mRNAs within ER-attached polysomes to restrict extracellular export of miRNAs. Reduced compartment-specific activity of the mammalian target of rapamycin complex 1 (mTORC1), the master regulator of protein synthesis, in cells with defective mitochondria or detethered ER, caused reduced phosphorylation of eIF4E-BP1 and prevented eIF4E targeting to ER-attached polysomes and miRNA export. These data suggest how mitochondrial membrane potential and dynamics, by affecting mTORC1 activity and compartmentalization, determine the subcellular localization and export of miRNAs.

在线粒体电位和动力学受损的生长迟缓的哺乳动物细胞中观察到 microRNA (miRNA) 的细胞内运输和输出缺陷。在这里，我们发现解偶联蛋白 2 (Ucp2) 介导的线粒体膜去极化也会导致 miRNA 逐渐隔离在多核糖体内，并减少它们通过细胞外囊泡的释放。有趣的是，在 Ucp2 抑制剂京尼平的存在下，生长迟缓的人类细胞中受损的 miRNA 运输过程可以被逆转。在具有去极化线粒体的细胞中观察到的内质网 (ER) 的线粒体脱链被发现是导致翻译起始因子 eIF4E 与附着于 ER 的多核糖体的缺陷区隔的原因。这导致了翻译过程的延迟，同时增强了 miRNA 和靶 mRNA 在 ER 附着的多核糖体中的保留，从而限制了 miRNA 的细胞外输出。在线粒体有缺陷或 ER 脱链的细胞中，哺乳动物雷帕霉素靶标复合物 1 (mTORC1)（蛋白质合成的主要调节因子）的区室特异性活性降低，导致 eIF4E-BP1 磷酸化降低，并阻止 eIF4E 靶向 ER 附着的多核糖体， miRNA 导出。这些数据表明线粒体膜电位和动力学如何通过影响 mTORC1 活性和区室化来决定 miRNA 的亚细胞定位和输出。