Mitochondria Associate with P-bodies and Modulate MicroRNA-mediated RNA Interference

Abstract

P-bodies are cytoplasmic granules that are linked to mRNA decay, mRNA storage, and RNA interference (RNAi). They are known to interact with stress granules in stressed cells, and with late endosomes. Here, we report that P-bodies also interact with mitochondria, as previously described for P-body-related granules in germ cells. The interaction is dynamic, as a large majority of P-bodies contacts mitochondria at least once within a 3-min interval, and for about 18 s. This association requires an intact microtubule network. The depletion of P-bodies does not seem to affect mitochondria, nor the mitochondrial activity to be required for their contacts with P-bodies. However, inactivation of mitochondria leads to a strong decrease of miRNAmediated RNAi efficiency, and to a lesser extent of siRNA-mediated RNAi. The defect occurs during the assembly of active RISC and is associated with a specific delocalization of endogeneous Ago2 from P-bodies. Our study reveals the possible involvement of RNAi defect in pathologies involving mitochondrial deficiencies. P-bodies are ribonucleoprotein granules present in the cytoplasm of eukaryotic cells. They contain all proteins involved in the 5Ј to 3Ј mRNA degradation pathway, such as the decapping enzyme Dcp2, its enhancers Dcp1, Lsm1-7, Edc3, Hedls/Ge1, and the exonuclease Xrn1. This list extends to factors involved in specific degradation pathways, such as RNAi, NMD, and NGD (1, 2). They also contain proteins involved in translational repression, such as eIF4ET, Rck/p54/Dhh1, CPEB1, and the RISC complex. Some of the latter proteins also play a role in mRNA degradation, in particular Rck/p54/Dhh1, which is known as an enhancer of decapping, and the RISC complex when it is guided by a siRNA. Such catalogue of components indicates that P-bodies participate in these two aspects of mRNA metabolism. In addition, P-bodies increase in number and size when free untranslated mRNA accumulates. In mammals, this is observed when degradation is compromised by XrnI silencing (3) or when polysomes are disrupted with puromycin or arsenite (4). Taken together, these data support a role of P-bodies in mRNA degradation, mRNA storage, and RNA interference. Yet, their exact participation is unclear, as none of these functions is markedly affected in cells where P-bodies have been depleted (5-9).Live cell observations show that the number of P-bodies is quite stable over hours, although occasional formation of new P-bodies or fusions of pre-existing ones are observed (10).

Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

“…Mitochondria elicit dynamic relationships with cytosolic P bodies involved in mRNA decay through miRNAs. The inactivation of mitochondria by CCCP leads to a strong decrease of miRNA efficiency [351].…”

The Dual Organization of P-bodies Revealed by Immunoelectron Microscopy and Electron Tomography

“…38 It has also been recently shown a close association between P-bodies and mitochondria in arsenitetreated cells and that mitochondria are required for the miRNA pathway, suggesting that mitochondria serve as a reservoir of miRNA that can be transferred to adjacent P-bodies. 39 Further studies will be necessary to understand the exact link between these two structures during the regulation of mRNA expression.…”

Intracellular and extracellular microRNA: An update on localization and biological role

“…Therefore, mechanisms of AGO-miRNA delivery into mitochondria remains to be further clarified. Notably, the association of mitochondria with P-bodies (Huang et al, 2011) and the existence of contact sites between mitochondrial and ER membranes has been reported (Kornmann, 2013). One could hypothesize that both P-bodies and ER, which have high local RISC concentrations, stay in close vicinity to mitochondrial membranes and facilitate AGO and miRNAs import into the mitochondria.…”