title: Inhibition of tumor cell surface ATP synthesis by pigment epithelium-derived factor: implications for antitumor activity.
abstract: Recently, we have shown that the antiangiogenic pigment epithelium-derived             factor (PEDF) can bind the catalytic β-subunit of F1-ATP synthase and inhibit             endothelial cell surface ATP synthase activity. This factor can additionally restrict             tumor growth, invasion and metastasis, and can directly induce death on several             tumor cell types. Active cell surface ATP synthase is also present in certain             tumor cells and its ATP product is considered a stimulus for tumor growth. The             present study aimed to elucidate the biological implications of the interactions             between the extracellular PEDF and tumor cell surface ATP synthase. Incubation             of T24 human urinary bladder carcinoma cells in media containing human recombinant             PEDF protein for 48-96 h dramatically decreased cell viability in a concentration-dependent             fashion as monitored by real-time cell impedance with a microelectronic system,             microscopic imaging and biomarkers of live cells. Intact tumor cells exhibited             cell surface ATP synthesis activity, which was inhibited by piceatannol, a specific             inhibitor of F1/F0-ATP synthase. Immunoblotting revealed that the β subunit of             F1-ATP synthase was present in plasma membrane fractions of these cells. Interestingly,             pre-incubation of tumor cells with PEDF inhibited the activity of cell surface             ATP synthase in a concentration-dependent fashion. The PEDF-derived peptide 34-mer             decreased tumor cell viability and inhibited extracellular ATP synthesis to the             same extent as full-length PEDF. Moreover, ATP additions attenuated both the PEDF-mediated             decrease in tumor cell viability and the inhibition of endothelial cell tube formation.             The results lead to conclude that PEDF is a novel inhibitor of tumor cell surface             ATP synthase activity that exhibits a cytotoxic effect on tumor cells, and that             the structural determinants for these properties are within the peptide region             34-mer of the PEDF polypeptide. The data strongly suggest a role for the interaction             between the 34-mer region of PEDF and tumor cell-surface ATP synthase in promoting             tumor cell death.
authors.affiliation: Section of Protein Structure and Function, Laboratory of Retinal                     Cell and Molecular Biology, NEI-NIH, Bethesda, MD, USA.
authors.forename: Monika
authors.initials: M
authors.lastname: Deshpande
authors.forename: Luigi
authors.initials: L
authors.lastname: Notari
authors.forename: Preeti
authors.initials: P
authors.lastname: Subramanian
authors.forename: Vicente
authors.initials: V
authors.lastname: Notario
authors.forename: S Patricia
authors.initials: SP
authors.lastname: Becerra
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D005136:Eye Proteins / Q000494:pharmacology*; D006801:Humans; D025261:Mitochondrial Proton-Translocating ATPases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009414:Nerve Growth Factors / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D021122:Protein Subunits / Q000378:metabolism; D015843:Serpins / Q000494:pharmacology*; D013267:Stilbenes / Q000494:pharmacology; D000099174:Pigment Epithelium-Derived Factor
chemical_list: D000255:Adenosine Triphosphate; D020533:Angiogenesis Inhibitors; D005136:Eye Proteins; D025261:Mitochondrial Proton-Translocating ATPases; D009414:Nerve Growth Factors; D010446:Peptide Fragments; D021122:Protein Subunits; D015843:Serpins; D013267:Stilbenes; D000099174:Pigment Epithelium-Derived Factor; C041525:3,3',4,5'-tetrahydroxystilbene; C474451:F1F0-ATP synthase