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The Function of Ectopic ATP Synthase in Extracellular Vesicles.

ABSTRACT: Ectopic adenosine triphosphate synthase (eATP synthase) was found on the cell surface to generate extracellular ATP in various cancer cells. Recently using proteomics approach, several reports identified ATP synthase in extracellular vesicles (EVs) which are important in cell-cell communications. However, the functions of ATP synthase in EVs are still unclear. Here we increased the expression of eATP synthase on the plasma membrane of lung cancer A549 cells via 0.1% FBS starvation and collected EVs including microvesicles and exosomes from the culture medium using serial centrifugation. Both of them were assuredly isolated and confirmed by transmission electron microscopy, nano tracking analysis, and specific EV markers. We also used western blot to demonstrate the presence of ATP synthase in EVs. Besides, dot blot experiment revealed that the F1 portion faced towards extracellular space using anti-ATP beta subunit antibody. Under starvation, the expression of eATP synthase was enhanced on cell surface and exosomes as well as increased EV secretion. To further investigate the functions, we first elucidated whether eATP synthase on EV membrane produced ATP by ATP luciferase analysis. Our data showed that there was no significant ATP production. Moreover, we performed proteomic analysis using dimethyl labeling and LC-MS/MS to compare the difference between EVs released by A549 control and starvation. We identified a total of 1504 and 869 proteins in microvesicles and exosomes, respectively. Using 1.5- and 0.67-fold change as the thresholds, there were 171 and 46 differential expressed proteins in microvesicles and exosomes, respectively. Seven ATP synthase subunits in microvesicles and five in exosomes were identified. The proteomic data were further analyzed using gene set enrichment analysis (GSEA) within the C2 (curated gene sets) subclasses and setting 0.25 as FDR cutoff to find out biological functions related to eATP synthase. Among these up-regulated terms, metabolism, cell cycle and apoptosis were enriched, which indicating that starvation influences cell behavior. Additionally, the immune response is upregulated strikingly in exosomes within C2 gene set. One of these immune response pathways, MHC-1 antigen presentation, was previously proved to interact with eATP synthase which could be recognized by several immune cells.

INSTRUMENT(S): LTQ Orbitrap Elite

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Epithelial Cell, Cell Culture

SUBMITTER: Chang Nai-Wen

LAB HEAD: Hsueh-Fen Juan

PROVIDER: PXD014995 | Pride | 2023-05-22

REPOSITORIES: Pride

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Project description:Adenosine triphosphate (ATP) synthase is located on the inner membrane of mitochondria which generate ATP for various cellular processes. Our previous studies showed that ATP synthases existed on plasma membrane of several types of cancer cells, which was defined as ectopic ATP synthase. However, the trafficking pathway of ectopic ATP synthase is still unclear. To investigate how ATP synthase subunits are involved in the trafficking process, we performed shot-gun proteomic analysis to reveal the plasma membrane proteins of A549 lung cancer cells and identified four subunits of ATP synthases, ATP5A1, ATP5B, ATP5H, and MT-ATP6. With the results of gene set enrichment analysis, we inferred that ectopic ATP synthase subunits are assembled as complex consistently and then translocated to cell surface through the trafficking of mitochondria. On the other hand, microtubules are involved in many intracellular transport. During protein trafficking, mitochondria and vesicles are transported to their final destination along microtubules by motor proteins such as kinesins and dyneins. To explore the function of microtubules in the trafficking of ectopic ATP synthase, we treated MCF-7 breast and A549 lung cancer cells with nocodazole, a microtubule depolymerization agent, and found that the expression level of ectopic ATP synthase decreased using both immunocytochemistry and flow cytometry. Besides, since kinesin family member 5B (KIF5B) is an important motor proteins involved in the transport of mitochondria, we further performed the immunoprecipitation of KIF5B followed by liquid chromatography−tandem mass spectrometry (LC−MS/MS). The result revealed that one of the mitochondrial outer membrane proteins, dynamin-1 like proteins (Drp1), was able to associate to KIF5B. From our recent research results and other reports show that Drp1 is a mediator of mitochondrial dynamic through regulation of mitochondrial fission. Taken together, our findings suggested that Drp1-KIF5B complex-mediated mitochondrial trafficking along microtubules may play a critical role in the transport of ectopic ATP synthase

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The Function of Ectopic ATP Synthase in Extracellular Vesicles.

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