F₁F_OATP Synthase Is Expressed at the Surface of Embryonic Rat Heart-Derived H9c2 Cells and Is Affected by Cardiac-Like Differentiation

Abstract

Taking advantage from the peculiar features of the embryonic rat heart-derived myoblast cell line H9c2, the present study is the first to provide evidence for the expression of F1FO ATP synthase and of ATPase Inhibitory Factor 1 (IF1) on the surface of cells of cardiac origin, together documenting that they were affected through cardiac-like differentiation. Subunits of both the catalytic F1 sector of the complex (ATP synthase-β) and of the peripheral stalk, responsible for the correct F1-FO assembly/coupling, (OSCP, b, F6) were detected by immunofluorescence, together with IF1. The expression of ATP synthase-β, ATP synthase-b and F6 were similar for parental and differentiated H9c2, while the levels of OSCP increased noticeably in differentiated cells, where the results of in situ Proximity Ligation Assay were consistent with OSCP interaction within ecto-F1FO complexes. An opposite trend was shown by IF1 whose ectopic expression appeared greater in the parental H9c2. Here, evidence for the IF1 interaction with ecto-F1FO complexes was provided. Functional analyses corroborate both sets of data. i) An F1FO ATP synthase contribution to the exATP production by differentiated cells suggests an augmented expression of holo-F1FO ATP synthase on plasma membrane, in line with the increase of OSCP expression and interaction considered as a requirement for favoring the F1-FO coupling. ii) The absence of exATP generation by the enzyme, and the finding that exATP hydrolysis was largely oligomycin-insensitive, are in line in parental cells with the deficit of OSCP and suggest the occurrence of sub-assemblies together evoking more regulation by IF1.

The mitochondrial stress-induced protein carboxyl-terminal alanine and threonine tailing (msiCAT-tailing) promotes glioblastoma tumorigenesis by modulating mitochondrial functions

“…In carcinogenesis, ATP synthase is often found re-localized to the plasma membrane and is known as the ectopic ATP synthase complex (eATP synthase). These eATP synthases have catalytic activity and can promote the generation of ATP in the extracellular environment to establish a suitable tumor microenvironment (55). eATP synthase was shown to be first assembled in mitochondria and then delivered to the cell surface via microtubules (46).…”

Spatial and temporal dynamics of ATP synthase from mitochondria toward the cell surface

“…Based on its ectopic location, this type of ATP synthase is referred to as ectopic ATP (eATP) synthase. Similar to the ATP synthase located on mitochondria, this cell-surface eATP synthase possesses catalytic activity that facilitates the generation of ATP in the extracellular environment to establish a suitable microenvironment 4 , 9 . For instance, cancer cells under hypoxic conditions increase the catalytic activity of their eATP synthase to adapt to this unfavorable environment 10 – 12 .…”

DJ-1 interacts with the ectopic ATP-synthase in endothelial cells during acute ischemia and reperfusion

“…The F O F 1 ATP-synthase is the enzyme responsible for the formation of ATP from ADP and inorganic phosphate, driven by the electrochemical gradient established through the electron transport chain in the mitochondria. Despite it was originally believed to exclusively locate in the inner mitochondrial membrane, its ectopic expression in the cell surface have been proven for a wide spectrum of cell types, including vascular ECs 5 – 7 , hepatocytes 8 , 9 , adipocytes 10 , lymphocytes 11 , keratinocytes 12 , muscle 13 , and neural cells 14 , 15 , in both tumour and normal conditions 16 . It is known to act as a receptor for angiostatin 6 , and apolipoprotein A-I 7 , 8 , and to promote tumour-recognition by the immune system 16 – 18 .…”