Stimulation of Cell Surface F1-ATPase Activity by Apolipoprotein A-I Inhibits Endothelial Cell Apoptosis and Promotes Proliferation
Objectives— Several findings argue for a protective effect of high-density lipoproteins (HDLs) against endothelial dysfunction. The molecular mechanisms underlying this protective effect are not fully understood, although recent works suggest that the actions of HDL on the endothelium are initiated by multiple interactions between HDLs (lipid or protein moiety) and cell surface receptors. We previously showed that the mitochondrial related F1-ATPase is a cell surface receptor for HDLs and their main atheroprotective apolipoprotein (apoA-I). Herein we test the hypothesis that the cell surface F1-ATPase may contribute to the ability of apoA-I and HDLs to maintain endothelial cell survival.
Methods and Results— Cell imaging and binding assays confirmed the presence of the F1-ATPase at the surface of human umbilical vein endothelial cells (HUVECs) and its ability to bind apoA-I. Cell surface F1-ATPase activity (ATP hydrolysis into ADP) was stimulated by apoA-I and was inhibited by its specific inhibitor IF1-H49K. Furthermore the antiapoptotic and proliferative effects of apoA-I on HUVECs were totally blocked by the F1-ATPase ligands IF1-H49K, angiostatin and anti-βF1-ATPase antibody, independently of the scavenger receptor SR-BI and ABCA1.
Conclusion— This study suggests an important contribution of cell surface F1-ATPase to apoA-I-mediated endothelial cell survival, which may contribute to the atheroprotective functions of apoA-I.
Elevated plasma levels of high-density lipoproteins (HDLs) are protective against coronary artery diseases.1 In the endothelium, HDLs promote cell proliferation and migration2,3 and protect endothelial cells against apoptosis, which is assumed to be an important early event in the development of cardiovascular diseases. Beside, a low plasma concentration of HDLs is an independent predicting factor of endothelial dysfunction both in healthy individuals or in hyperlipidemic, diabetic, and coronary patients, and endothelial dysfunction has been reported in patients with primary hypoalphalipoproteinemia.4 Altogether, these findings argue for a protective effect of HDLs against the development of endothelial dysfunction, which might well contribute along with the known function of HDLs in reverse cholesterol transport, to protection against cardiovascular diseases.
The molecular mechanisms underlying the protective effects of HDLs on endothelial cell survival are not fully understood. Recent works showed that these effects might depend on lysosphingolipids present in the HDL lipid moiety through the activation of the prosurvival PI3K/Akt pathway.5,6 Nevertheless, other studies have reported that the apolipoprotein moiety of HDLs can partially mimic the effect of HDLs on endothelial cell proliferation and apoptosis inhibition,7–9 suggesting that direct interactions between the apolipoprotein part of HDLs and cell surface receptor(s) might contribute to HDL-mediated endothelial cell survival, independently of the lysosphingolipid components. For instance overexpression of the lipoprotein scavenger receptor SR-BI in endothelial cells was shown to trigger apoptosis via the caspase-8 pathway in a ligand-independent manner, but HDLs could inhibit this apoptotic effect through interaction with SR-BI.10 Beside this effect, HDL receptors other than SR-BI could be involved in HDL-mediated endothelial protection.
A cell surface complex related to the mitochondrial F1-ATPase has been recently reported to be expressed on different cell types. On human hepatocytes, we have shown that the β-chain subunit of the F1-ATPase is a high-affinity receptor for apolipoprotein A-I (apoA-I), the main atheroprotective apolipoprotein of HDLs.11 Other groups have also reported the expression of F1-ATPase at the cell surface of endothelial cells.12 In this cell type, it has been demonstrated that angiostatin, a cleavage-product of plasminogen involved in regulating angiogenesis, binds to the cell surface F1-ATPase.
Based on these results, we have hypothesized that the cell surface F1-ATPase pathway may contribute to the antiapoptotic and proliferative effects mediated by apoA-I and HDLs on endothelial cells. In the present study, we have first confirmed the presence of the F1-ATPase at the cell surface of human umbilical vein endothelial cells (HUVECs) and its ability to bind apoA-I. We have then investigated the regulation of the cell surface F1-ATPase activity on HUVECs and its effects on endothelial cell survival.
An expended Methods section can be found in the supplemental materials (available online at http://atvb.ahajournals.org).
HUVECs (Cambrex, France) were cultured in EGM-2 medium containing 2% (v/v) fetal bovine serum and growth factors (Cambrex). Cells were seeded in collagen I-coated dishes at a density of 5000 cells/cm2, grown in EGM-2 complete medium until 80% to 90% confluence, and used at the third through sixth passages.
Cells were incubated in serum-free EGM-2 medium without growth factors for 16 hours with or without (control, set at 0) different treatments. Afterward, the pool of floating cells and adherent cells (collected by trypsinization) was incubated for 1 hour at room temperature with FITC-annexin V or with FAM-VAD-FMK poly caspases reagent. Flow cytometry analyses were then performed as described in supplemental materials.
Proliferation analyses were carried out by using 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) reduction reagent kit (ATCC). Briefly, 10 000 cells per well were seeded in 96-well plates and incubated in EGM-2 complete medium for 24 hours. Then, cells were stimulated or not (control) with different treatments in fresh 2% serum EGM-2 medium (without growth factors) for 24 hours. MTT reagent was added, then cells were lysed and plates were read at 570 nm.
Apo-AI Binds to the Cell Surface F1-ATPase on Endothelial Cells
Cell surface expression of the F1-ATPase on HUVECs has been already reported.12 Flow cytometry analysis of the expression of both the α-chain (αF1) and the β-chain (βF1) of F1-ATPase at the cell surface of intact HUVECs (selected as cells excluding propidium iodide) showed a significant staining over the isotypic control (supplemental Figure IA). In addition, streptavidin pull-down of biotinylated cell surface proteins confirmed the presence of the βF1 at the plasma membrane, whereas β-actin and Tom20, a translocase of the outer membrane of the mitochondria, were not detected (supplemental Figure IB). By confocal microscopy, a βF1 labeling revealed patch-like structures on the cell surface which did not colocalize with Mitotracker Red, a specific marker of mitochondria (Figure 1a through 1c) but colocalized with CD31, an established endothelial cell surface marker (Figure 1i through 1k). By contrast, after permeabilization, βF1 labeling showed a mitochondrial distribution that colocalized with Mitotracker Red (Figure 1e through 1g). βF1 staining was specific as isotypic controls did not show fluorescence (Figure 1d, 1h, and 1l).
The ability of apoA-I to bind endothelial cells was investigated at 4°C using lipid-free 125I-apoA-I. HUVECs bind 125I-apoA-I in a saturable manner with a specific maximal binding, Bmax=80 ng apoA-I per mg cell protein (Figure 2A, closed triangles) and a high affinity binding (Kd=1.6 μg/mL) as calculated by the Scatchard method. Nonspecific binding (Figure 2A, open triangles) was determined in the presence of a 100-fold excess of unlabeled apoA-I and varied from 15% to 25% of total binding. Cell association of 125I-apoA-I to HUVECs was investigated at 37°C for 2 hours (Figure 2B). The specific association occurred with a Bmax of 450 ng apoA-I / mg cell protein and the apparent Kd value in the Scatchard plot was 13 μg/mL (Figure 2B, closed square). Furthermore, ABCA1 is an apoA-I receptor expressed on endothelial cells13 and inhibition of ABCA1 expression in HUVECs by siRNA (Figure 2B, open squares) did not significantly change the apparent Kd value (15 μg/mL) but reduced by about 30% the Bmax value (330 ng apoA-I per mg cell protein), indicating that ABCA1 might only partially contribute to the high-affinity apoA-I binding sites on HUVECs. Same values as untransfected cells were obtained after transfection of HUVECs with control siRNA (not shown).
We then investigated the contribution of cell surface F1-ATPase to the binding of apoA-I onto endothelial cells. ApoA-I binding to endothelial cells was specific as an excess of unlabeled apoA-I displaced 125I-apoA-I binding by about 85% (Figure 3A), whereas an excess of lipid-free ovalbumin did not (not shown). We observed that the F1-ATPase inhibitor (IF1-H49K) and an anti-β-chain of F1-ATPase antibody (anti-βF1) both inhibited by about 70% the specific binding of 125I-apoA-I on HUVECs, whereas no inhibition was observed with isotypic IgG1 (Figure 3A). Interestingly, after inhibition of ABCA1 expression, IF1-H49K could compete 125I-apoA-I binding to the same extent as an excess of unlabeled apoA-I, confirming that ABCA1 is partly involved in specific apoA-I binding to HUVECs. The specificity of IF1-H49K binding on the cell surface F1-ATPase was confirmed because 125I-IF1-H49K binding could be totally abolished with an excess of unlabeled IF1-H49K, as well as an excess of apoA-I or anti-βF1 antibody (Figure 3B). Finally, we excluded any contribution of SR-BI to lipid-free apoA-I binding because an anti-SR-BI antibody, previously shown to inhibit HDL binding and cholesteryl ester uptake on human hepatocytes,11,14 did not compete for the binding of apoA-I on endothelial cells (Figure 3A).
Cell Surface F1-ATPase Activity Is Stimulated by ApoA-I on Endothelial Cells
Our previous studies performed on human hepatocytes reported that the 9.6-kDa basic protein IF1, a natural inhibitor of the hydrolytic activity of mitochondrial F1-ATPase,15 decreased extracellular ADP level by inhibiting cell surface F1-ATPase activity.11 Conversely, apoA-I binding to cell surface F1-ATPase increased extracellular ADP production by stimulating ATP hydrolysis, a process also inhibited by IF1.11 We therefore have investigated whether cell surface F1-ATPase was regulated in the same way on HUVECs. The ability of IF1 to inhibit F1-ATPase activity depends on pH with a better efficiency at pH below 6.5. To perform experiments at neutral pH, we used a mutated form of IF1 (histidine 49 replaced by lysine, referred to as IF1-H49K), designed to be active at all pH values.15 Extracellular ATP hydrolysis activity on HUVECs was analyzed by measuring the generation of [α-32P]ADP from [α-32P]ATP in the cell medium. We observed a basal hydrolytic activity after 10 minutes (not shown), which was markedly increased (+62%±13) in the presence of apoA-I (supplemental Figure II). In these conditions, the purified IF1-H49K protein could reduce both the basal (−35%±3) and the apoA-I-stimulated hydrolysis activity (supplemental Figure II). Interestingly, dual-label assay with [3H]ADP and 32Pi demonstrated that the [3H]ATP generated from [3H]ADP on the surface of HUVECs was not 32P-labeled (data not shown), indicating that, in our conditions, cell surface F1-ATPase did not contribute to extracellular ATP production, as previously reported on hepatocytes and endothelial cells.16,17
Cell Surface F1-ATPase Activity Stimulates Endothelial Cell Survival
To measure the contribution of cell surface F1-ATPase on endothelial cell survival, apoptosis and proliferation assays were performed on HUVECs (Figures 4 and 5⇓, respectively). Regarding apoptosis, lipid-free apoA-I treatment prevented HUVEC apoptosis in a dose dependent manner, a 50% inhibition being obtained at 3.6 μmol/L (100 μg/mL) apoA-I (Figure 4A). Conversely, the F1-ATPase inhibitor IF1-H49K caused a dose-dependent increase of cellular apoptosis (Figure 4A). In parallel, apoA-I treatment could induce cellular proliferation in a dose-dependent way (+25% at 100 μg/mL, Figure 5A), whereas IF1-H49K showed a dose-response antiproliferative effect reaching 30% at 1 μmol/L (Figure 5A). Interestingly the antiapoptotic and proliferative effects of apoA-I were completely abolished when the cells were cotreated with equimolar concentrations of IF1-H49K (Figure 4B and 5⇓B) and IF1-H49K proapoptotic and antiproliferative effects were conserved when coincubated in 10-fold excess as compared to apoA-I (data not shown), indicating that effects of apoA-I on cell survival are lost when the F1-ATPase is inhibited. Conversely, apoA-I effects on cell survival were conserved when coincubated in 10-fold excess as compared to IF1-H49K (data not shown), which is consistent with experiments suggesting a competition between apoA-I and IF1-H49K on F1-ATPase binding sites (Figure 3). To confirm the contribution of apoA-I to F1-ATPase-mediated cell survival pathway, experiments were also performed with the anti-βF1-ATPase blocking antibody (anti-βF1), which was shown to inhibit apoA-I binding to cell surface F1-ATPase (Figure 3A). As reported in Figures 4B and 5⇓B, anti-βF1 antibody could abrogate apoA-I-mediated cell survival effects to the same extent as IF1-H49K. Interestingly, the anti-βF1 antibody alone has a slight apoptotic effect (Figure 4B) and a potent antiproliferative effect (Figure 5B) on HUVECs, suggesting that it may work in a similar manner as IF1-H49K on endothelial cell survival by inhibiting the F1-ATPase. Finally, to confirm the ability of apoA-I to specifically activate a F1-ATPase-mediated cell survival pathway, we also used angiostatin, another ligand of the cell surface F1-ATPase which, contrary to apoA-I, inhibits endothelial cell proliferation.12 By treating endothelial cells with angiostatin in a similar concentration range as used in other studies,12 we confirmed its ability to induce apoptosis and inhibit cell proliferation (Figures 4B and 5⇓B). Furthermore, apoA-I effects on cell survival were abolished under angiostatin treatment, in a similar way as IF1-H49K and the anti-βF1 antibody (Figures 4B and 5⇓B).
Both apoptotic and proliferative effects of lipid-free apoA-I were fully maintained under treatment with the inhibitory SR-BI antibody (Figures 4C and 5⇑C). For comparison, the antiapoptotic and proliferative effects of whole HDL particles were inhibited by 30% when coincubated with this antibody (Figures 4C and 5⇑C), strengthening the idea that the effects of lipid-free apoA-I are independent of SR-BI whereas part of the effects of HDLs would be mediated by this receptor. Furthermore, inhibition of ABCA1 expression in HUVECs by siRNA (Figure 4D, inset), which is another apoA-I receptor also expressed on endothelial cells,13 did not change apoA-I and IF1-H49K effects on endothelial cell survival (Figures 4D and 5⇑D), indicating that ABCA1 is not involved in these processes.
Altogether these results support the interpretation that cell surface F1-ATPase is responsible for the effect of lipid-free apoA-I on endothelial cell survival.
ADP and ADP Analogues Mimic the Effect of ApoA-I on Endothelial Cell Survival
To investigate the role of the cell surface F1-ATPase activity (ie, generation of ADP) on endothelial cell survival, we tested the effect of ADP and different ADP analogues on HUVEC apoptosis (supplemental Figure III). 2-MeSADP dramatically inhibited HUVEC apoptosis in a dose-dependent manner, with a maximal effect at 0.1 nmol/L. Identical results were obtained with ADPβS, a more stable analogue.18 The product of cell surface F1-ATPase activity, ADP, could also inhibit HUVEC apoptosis but at higher concentration (10 nmol/L) probably because of the high degradation of ADP at the cell surface.16 These effects were specific for ADP because neither hydrolysis products (AMP and adenosine) nor its precursor (ATP) could protect cells against apoptosis at the same concentration (data not shown).
Until recently, F1Fo ATP synthase expression was believed to be strictly confined to the inner membrane of mitochondria where it generates most of the cellular ATP. An important recent finding is that some components of the F1 catalytic part of the ATP synthase (also called F1-ATPase) are expressed as cell surface receptors for apparently unrelated ligands found in the course of studies carried out on cholesterol metabolism, immune mechanisms and angiogenesis.19 For instance, our group identified on human hepatocytes this cell surface F1-ATPase as a high-affinity receptor for HDLs and its major atheroprotective apolipoprotein, apoA-I.11 In parallel, a complex containing the α- and β-subunits of the F1-ATPase has been described at the cell surface of endothelial cells as a receptor for angiostatin.12 This proteolytic cleavage fragment from plasminogen displays a potent antiangiogenic effect by limiting cell proliferation. Based on these results, we hypothesized that apoA-I might also interact with the endothelial cell surface F1-ATPase to initiate a signaling pathway contributing to the antiapoptotic and proliferative effects mediated by HDLs and apoA-I on endothelial cells.4 We first confirmed the cell surface expression of the α- and β-subunits of the ATP synthase, suggesting that at least the F1-ATPase catalytic domain of the ATP synthase is expressed there.
We also provide evidence that the cell surface F1-ATPase on HUVECs is a high-affinity receptor for lipid-free apoA-I. Binding parameters for lipid-free apoA-I on HUVECs are very similar to those obtained earlier on bovine aortic endothelial cells (BAECs),20 suggesting the presence of the same receptor(s) in the endothelium of different origin with a high affinity of about 5.10−8 mol/L. Interestingly, the apparent Kd value was 8-fold increased at 37°C as compared to the value measured at 4°C (Figure 2). This lower affinity of apoA-I at 37°C might be attributable to conformational changes in its binding sites, as previously reported.21 Also, the Bmax of the cell association was more than 5-fold higher at 37°C than at 4°C, suggesting that apoA-I is internalized at 37°C by endothelial cells, potentially through ABCA1 because this transporter has been previously reported to contribute to ≈40% of lipid-free apoA-I binding on aortic endothelial cells and to modulate apoA-I trancytosis through these cells.13 Indeed our data confirm that ABCA1 partially contributes to lipid-free apoA-I high affinity binding sites on HUVECs because ≈30% decrease in the Bmax value was observed after inactivation of ABCA1 expression. However, beside ABCA1, cell surface F1-ATPase represents ≈60% to 70% of the lipid-free apoA-I binding as shown by competition experiments with antibody against the β-chain of F1-ATPase (anti-βF1) or with the F1-ATPase inhibitor protein IF1-H49K.22 When ABCA1 expression is inhibited, the apparent Kd did not significantly change as compared to cell expressing ABCA1, which indicates a similar affinity of ABCA1 and F1-ATPAse for lipid-free apoA-I. Conversely, we evidenced that SR-BI was not involved in lipid-free apoA-I binding sites, consistently with previous results obtained on hepatocytes14 and BAECs.13 It is more likely that the lipid moiety associated to apoA-I within HDL particles is essential for interaction with SR-BI.1
The ability of IF1 to specifically bind and inhibit the mitochondrial F1-ATPase is well documented22 but has never been investigated regarding its cell surface localization. In this study we evidenced that IF1-H49K binding on HUVECs was totally abolished under incubation with an anti-βF1 antibody, and we also observed a cross-competition between IF1-H49K and apoA-I binding. Taken together these results confirm the ability of IF1-H49K to specifically bind to the cell surface F1-ATPase on HUVECs and to compete with apoA-I.
Our results establish that proliferative and antiapoptotic effects of lipid-free apoA-I are abolished with the F1-ATPase specific inhibitor protein IF1-H49K. Furthermore, both anti-βF1 inhibitory antibody and angiostatin could also abrogate apoA-I effects to the same extent as IF1-H49K. Altogether our results argue that F1-ATPase is responsible for the effect of lipid-free apoA-I on endothelial cell survival. Interestingly, effects of apoA-I and IF1-H49K on endothelial cell survival were fully maintained after reduction of ABCA1 expression, which indicates that ABCA1 is not involved in apoA-I-mediated prosurvival effects on endothelial cells.
Different pathways regulating endothelial cell survival by HDLs have been described, mediated by scavenger receptor SR-BI or ABCG1 through interactions with HDLs23,24 or by sphingosine 1-phosphate (S1P) receptors through HDL-associated S1P and other lysosphingolipids.5,6 However, our study bypasses these 2 lipid-linked pathways by using lipid-free apoA-I rather than HDL particles. Moreover, we demonstrated that the apoA-I/F1-ATPase-mediated endothelial cell protection occurs independently of SR-BI. Physiologically, both the intimal fluid of arteries and the lymph present a relative concentration of lipid-free or lipid-poor HDL precursors (preβ-HDL) higher than that of mature and fully lipidated HDLs.25,26 These lipid-free or lipid-poor HDL precursors are continuously generated in the plasma compartment during lypolysis of triglyceride-rich HDLs and interconversion of HDL subclasses by lipid transfer proteins, lipoprotein lipase, hepatic lipase, or endothelial lipase.26 However a contribution of mature HDLs to the F1-ATPase-mediated endothelial protection cannot be excluded because IF1-H49K partially inhibits HDL antiapoptotic and proliferative effect on HUVECs, independently of SR-BI (data not shown). Therefore it is possible that these different pathways (F1-ATPase, SR-BI, ABCA1/G1, or S1P/lysophingolipids) contribute to HDL-mediated cell survival and protection against apoptosis, but the relative contributions of each one in normal and pathophysiological conditions will require further investigations.
ApoA-I could stimulate extracellular ADP production by stimulating extracellular ATP hydrolysis on HUVECs, a process also inhibited by IF1-H49K (supplemental Figure II and11). It is likely that ABCA1 ATPase activity is not involved in this process because apoA-I had no effect on the ATP hydrolysis mediated by purified ABCA1.27 Furthermore, the 2 nucleotide binding domains of ABCA1 are localized in the cytosolic side of the membrane. Consequently, contrary to cell surface F1-ATPase, ATP hydrolysis by ABCA1 would produce ADP in the cytoplasm. Altogether these data strongly suggest that apoA-I-mediated extracellular ADP production only occurs through cell surface F1-ATPase activity. Interestingly, we observed that addition of ADP and its analogues protect endothelial cells against apoptosis (supplemental Figure III), suggesting that the ADP generated through activation of the cell surface F1-ATPase by apoA-I could contribute to endothelial cell survival through the implication of ADP-sensitive purinergic receptor(s). Differences of molar concentrations to reach the maximal efficiencies of ADP and ADP analogues (supplemental Figure III) might be attributable to the resistance of ADP analogues to hydrolysis and metabolization28 or differences in affinities for ADP-sensitive purinergic receptor(s). We have recently shown on human hepatocytes that cell surface activation of F1-ATPase by lipid-free apoA-I stimulates the ADP-sensitive P2Y13 receptor, which activates specifically RhoA and its effector ROCK I, leading to stimulation of HDL endocytosis through cytosqueleton reorganization.29 Here, we describe a new role for apoA-I/F1-ATPase pathway on endothelial cell survival, a primary factor in the protection against cardiovascular diseases, but whether ADP-sensitive purinergic receptor(s) are involved in this process and determination of downstream signaling event(s) need further investigations. We can hypothesize that, depending on the cell types, distinct pathway(s) are involved downstream F1-ATPase activation by apoA-I and inducing distinct cellular events such as stimulation of HDL uptake by hepatocytes or endothelial cells survival.
We are grateful to F. L'Faqihi and S. Allart (IFR150) for their assistance in flow cytometry and confocal microscopy analysis; Muriel Laffargue, Ronald Barbaras, and Pierre Vantourout for helpful discussion; Christine Peres for technical assistance; and Pr J.E. Walker (MRC Dunn Human Nutrition Unit, Cambridge, UK) for providing purified IF1-H49K preparations.
Sources of Funding
This work was supported by a grant from INSERM (Avenir), the Association pour la Recherche sur le Cancer (ARC, grant #3711-3913-4847), and the Ligue Nationale Contre le Cancer (#R07002BBA). C. Radojkovic was a recipient of a fellowship from the #UCO O2O2 MECESUP project (Chile) and CONICYT/ambassade de France.
Received January 29, 2009; revision accepted April 7, 2009.
Murugesan G, Sa G, Fox PL. High-density lipoprotein stimulates endothelial cell movement by a mechanism distinct from basic fibroblast growth factor. Circ Res. 1994; 74: 1149–1156.
Calabresi L, Gomaraschi M, Franceschini G. Endothelial protection by high-density lipoproteins: from bench to bedside. Arterioscler Thromb Vasc Biol. 2003; 23: 1724–1731.
Nofer JR, Levkau B, Wolinska I, Junker R, Fobker M, von Eckardstein A, Seedorf U, Assmann G. Suppression of endothelial cell apoptosis by high density lipoproteins (HDL) and HDL-associated lysosphingolipids. J Biol Chem. 2001; 276: 34480–34485.
Kimura T, Sato K, Malchinkhuu E, Tomura H, Tamama K, Kuwabara A, Murakami M, Okajima F. High-density lipoprotein stimulates endothelial cell migration and survival through sphingosine 1-phosphate and its receptors. Arterioscler Thromb Vasc Biol. 2003; 23: 1283–1288.
Darbon JM, Tournier JF, Tauber JP, Bayard F. Possible role of protein phosphorylation in the mitogenic effect of high density lipoproteins on cultured vascular endothelial cells. J Biol Chem. 1986; 261: 8002–8008.
Suc I, Escargueil-Blanc I, Troly M, Salvayre R, Negre-Salvayre A. HDL and ApoA prevent cell death of endothelial cells induced by oxidized LDL. Arterioscler Thromb Vasc Biol. 1997; 17: 2158–2166.
Li XA, Guo L, Dressman JL, Asmis R, Smart EJ. A novel ligand-independent apoptotic pathway induced by scavenger receptor class B, type I and suppressed by endothelial nitric-oxide synthase and high density lipoprotein. J Biol Chem. 2005; 280: 19087–19096.
Moser TL, Stack MS, Asplin I, Enghild JJ, Hojrup P, Everitt L, Hubchak S, Schnaper HW, Pizzo SV. Angiostatin binds ATP synthase on the surface of human endothelial cells. Proc Natl Acad Sci U S A. 1999; 96: 2811–2816.
Cavelier C, Rohrer L, von Eckardstein A. ATP-Binding cassette transporter A1 modulates apolipoprotein A-I transcytosis through aortic endothelial cells. Circ Res. 2006; 99: 1060–1066.
Martinez LO, Georgeaud V, Rolland C, Collet X, Tercé F, Perret B, Barbaras R. Characterization of two high-density lipoprotein binding sites on porcine hepatocyte plasma membranes: contribution of scavenger receptor class B type I (SR-BI) to the low-affinity component. Biochemistry. 2000; 39: 1076–1082.
Cabezon E, Butler PJ, Runswick MJ, Walker JE. Modulation of the oligomerization state of the bovine F1-ATPase inhibitor protein, IF1, by pH. J Biol Chem. 2000; 275: 25460–25464.
Yegutkin GG, Henttinen T, Jalkanen S. Extracellular ATP formation on vascular endothelial cells is mediated by ecto-nucleotide kinase activities via phosphotransfer reactions. Faseb J. 2001; 15: 251–260.
Seetharam D, Mineo C, Gormley AK, Gibson LL, Vongpatanasin W, Chambliss KL, Hahner LD, Cummings ML, Kitchens RL, Marcel YL, Rader DJ, Shaul PW. High-density lipoprotein promotes endothelial cell migration and reendothelialization via scavenger receptor-B type I. Circ Res. 2006; 98: 63–72.
Jaspard B, Fournier N, Vieitez G, Atger V, Barbaras R, Vieu C, Manent J, Chap H, Perret B, Collet X. Structural and functional comparison of HDL from homologous human plasma and follicular fluid. A model for extravascular fluid. Arterioscler Thromb Vasc Biol. 1997; 17: 1605–1613.
Rye KA, Barter PJ. Formation and metabolism of prebeta-migrating, lipid-poor apolipoprotein A-I. Arterioscler Thromb Vasc Biol. 2004; 24: 421–428.
Takahashi K, Kimura Y, Kioka N, Matsuo M, Ueda K. Purification and ATPase activity of human ABCA1. J Biol Chem. 2006; 281: 10760–10768.
Abbracchio MP, Burnstock G, Boeynaems JM, Barnard EA, Boyer JL, Kennedy C, Knight GE, Fumagalli M, Gachet C, Jacobson KA, Weisman GA. International Union of Pharmacology LVIII: update on the P2Y G protein-coupled nucleotide receptors: from molecular mechanisms and pathophysiology to therapy. Pharmacol Rev. 2006; 58: 281–341.