Handling Editor: Jennifer Lippincott-Schwartz
ABSTRACT
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.
Footnotes
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: S.C., Y.C., S.B., S.G., S.N.B.; Methodology: S.C., Y.C., S.B., S.N.B.; Software: Y.C., S.B., S.G.; Validation: Y.C., S.G.; Formal analysis: S.G., S.N.B.; Investigation: S.C., Y.C., S.B., S.G.; Data curation: S.C., S.N.B.; Writing - original draft: S.N.B.; Visualization: S.N.B.; Supervision: S.N.B.; Project administration: S.N.B.; Funding acquisition: S.N.B.
Funding
S.N.B. is supported by The Swarnajayanti Fellowship (SJF/LS-03/2014-15) from Department of Scientific and Industrial Research, Ministry of Science and Technology, India, while Y.C., S.B., S.C. and S.G. received their support from Council of Scientific and Industrial Research, India (CSIR). We are supported by funds from High Risk High Reward Project Grant (HRR/2016/00093), Science and Engineering Research Board, Dept. of Science and Technology, Govt. of India and an Indo-French Centre for the Promotion of Advanced Research (CEFIPRA) Project Grant (6003-J).
Supplementary information
Supplementary information available online at https://jcs.biologists.org/lookup/doi/10.1242/jcs.250241.supplemental
- Received June 16, 2020.
- Accepted November 17, 2020.
- © 2020. Published by The Company of Biologists Ltd
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