Inhibition of tumor cell surface ATP synthesis by pigment epithelium-derived factor: implications for antitumor activity. Int J Oncol

Section of Protein Structure and Function, Laboratory of Retinal Cell and Molecular Biology, NEI-NIH, Bethesda, MD, USA.
International Journal of Oncology (Impact Factor: 3.03). 04/2012; 41(1):219-27. DOI: 10.3892/ijo.2012.1431
Source: PubMed


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.

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    • "On bovine retinal endothelial cells, membrane-bound ATP synthase binds PEDF with high affinity, resulting in decreased production of extracellular ATP (Notari et al. 2010). Cell surface ATP synthase activity of human bladder carcinoma cells was also inhibited by PEDF leading to reduced tumor cell viability (Deshpande et al. 2012). PEDF has been shown to bind LRP6 to block activation of the wnt signaling pathway (Park et al. 2011). "
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    ABSTRACT: Angiogenesis, or the formation of new blood vessels, is stimulated by angiogenic factors such as vascular endothelial growth factor (VEGF). Pigment epithelium-derived factor (PEDF) is a potent inhibitor of angiogenesis. To explore the mechanism by which PEDF acts, recombinant PEDF was expressed with a 6x-His tag (for purification) and a green fluorescent protein (GFP) tag. The PEDF fusion protein was confirmed to be active in inhibition of endothelial cell proliferation and migration. Direct binding of PEDF to both vascular endothelial growth factor receptor-1 (VEGFR-1) and VEGFR-2 was demonstrated in an in vitro assay similar to an enzyme-linked immunosorbent assay (ELISA). PEDF was shown by immune-confocal microscopy to be localized within treated endothelial cells. When VEGF-stimulated endothelial cells were incubated with PEDF the VEGF receptors showed intracellular localization. These data suggest that the interaction between PEDF and VEGFR-1 or VEGFR-2 may be a possible mechanism for inhibiting angiogenesis. PEDF may be binding to the VEGF receptors to promote their internalization and/or degradation to limit VEGF responses in treated cells.
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    ABSTRACT: The potent actions of pigment epithelium-derived factor (PEDF) on tumour-associated cells, and its extracellular localization and secretion, stimulated research on this multifunctional serpin. Such studies have identified several PEDF receptors and downstream signalling pathways. Known cellular PEDF responses have expanded from the initial discovery that PEDF induces retinoblastoma cell differentiation to its anti-angiogenic, antitumorigenic and antimetastatic properties. Although the diversity of PEDF activities seems to be complex, they are consistent with the varied mechanisms that regulate this multimodal factor. If PEDF is to be used for cancer management, a deeper appreciation of its many functions and mechanisms of action is needed.
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    ABSTRACT: Metabolic syndrome is closely related to erectile dysfunction (ED), and hyperlipidaemia is considered a major risk factor for ED. Adenosine triphosphate (ATP) synthase is believed to play an important role in metabolic syndrome; it has been hypothesised that ATP synthase contributes to ED development. We have verified this hypothesis using primary cultured human corpus cavernosum smooth muscle (HCCSM) cells treated with excessive free fat acid (FFA) and a high-fat diet (HFD) mouse model. Our results showed that high fatty factors could cause lipid accumulation in HCCSM cells, which could result in abnormal lipid metabolism, such as high levels of triglycerides, cholesterol and glucose in the HFD mice. There was a remarkable down-regulation of ATP synthase and p-Akt after in vivo and in vitro excessive FFA treatments. These results indicated that abnormal lipid metabolism could induce ATP synthase down-regulation via the Akt phosphorylation pathway and that ATP synthase may be a target of lipotoxicity in corpus cavernosum smooth muscle cells.
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