Mitochondrial F1Fo-ATP synthase translocates to cell surface in hepatocytes and has high activity in tumor-like acidic and hypoxic environment.
F1Fo-ATP synthase was originally thought to exclusively locate in the inner membrane of the mitochondria. However, recent studies prove the existence of ectopic F1Fo-ATP synthase on the outside of the cell membrane. Ectopic ATP synthase was proposed as a marker for tumor target therapy. Nevertheless, the protein transport mechanism of the ectopic ATP synthase is still unclear. The specificity of the ectopic ATP synthase, with regard to tumors, is questioned because of its widespread expression. In the current study, we constructed green fluorescent protein-ATP5B fusion protein and introduced it into HepG2 cells to study the localization of the ATP synthase. The expression of ATP5B was analyzed in six cell lines with different 'malignancies'. These cells were cultured in both normal and tumor-like acidic and hypoxic conditions. The results suggested that the ectopic expression of ATP synthase is a consequence of translocation from the mitochondria. The expression and catalytic activity of ectopic ATP synthase were similar on the surface of malignant cells as on the surface of less malignant cells. Interestingly, the expression of ectopic ATP synthase was not up-regulated in tumor-like acidic and hypoxic microenvironments. However, the catalytic activity of ectopic ATP synthase was up-regulated in tumor-like microenvironments. Therefore, the specificity of ectopic ATP synthase for tumor target therapy relies on the high level of catalytic activity that is observed in acidic and hypoxic microenvironments in tumor tissues.
Ma
Zhan
Z
Department of Molecular Biology Laboratory, Shanghai Sixth People's Hospital Affiliated Shanghai Jiao Tong University School of Medicine, China.
Cao
Manlin
M
Liu
Yiwen
Y
He
Yiqing
Y
Wang
Yingzhi
Y
Yang
Cuixia
C
Wang
Wenjuan
W
Du
Yan
Y
Zhou
Muqing
M
Gao
Feng
F
D000255:Adenosine Triphosphate / Q000378:metabolism; D055162:Biocatalysis; D015687:Cell Hypoxia; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology*; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000201:enzymology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000201:enzymology*; D025261:Mitochondrial Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D009369:Neoplasms / Q000201:enzymology / Q000473:pathology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
C506526:ATP5F1B protein, human; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000255:Adenosine Triphosphate; D025261:Mitochondrial Proton-Translocating ATPases