| 1. |
- Ahnström, Josefin, et al.
(författare)
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Activated protein C cofactor function of protein S: a novel role for a gamma-carboxyglutamic acid residue
- 2011
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Ingår i: Blood. - : American Society of Hematology. - 1528-0020 .- 0006-4971. ; 117:24, s. 6685-6693
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Tidskriftsartikel (refereegranskat)abstract
- Protein S has an important anticoagulant function by acting as a cofactor for activated protein C (APC). We recently reported that the EGF1 domain residue Asp95 is critical for APC cofactor function. In the present study, we examined whether additional interaction sites within the Gla domain of protein S might contribute to its APC cofactor function. We examined 4 residues, composing the previously reported "Face1" (N33S/P35T/E36A/Y39V) variant, as single point substitutions. Of these protein S variants, protein S E36A was found to be almost completely inactive using calibrated automated thrombography. In factor Va inactivation assays, protein S E36A had 89% reduced cofactor activity compared with wild-type protein S and was almost completely inactive in factor VIIIa inactivation; phospholipid binding was, however, normal. Glu36 lies outside the omega-loop that mediates Ca2+-dependent phospholipid binding. Using mass spectrometry, it was nevertheless confirmed that Glu36 is gamma-carboxylated. Our finding that Gla36 is important for APC cofactor function, but not for phospholipid binding, defines a novel function (other than Ca2+ coordination/phospholipid binding) for a Gla residue in vitamin K-dependent proteins. It also suggests that residues within the Gla and EGF1 domains of protein S act cooperatively for its APC cofactor function. (Blood. 2011;117(24):6685-6693)
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| 2. |
- Andersson, Helena M., et al.
(författare)
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Activated protein C cofactor function of protein S: a critical role for Asp95 in the EGF1-like domain
- 2010
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Ingår i: Blood. - : American Society of Hematology. - 1528-0020 .- 0006-4971. ; 115:23, s. 4878-4885
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Tidskriftsartikel (refereegranskat)abstract
- Protein S has an established role in the protein C anticoagulant pathway, where it enhances the factor Va (FVa) and factor VIIIa (FVIIIa) inactivating property of activated protein C (APC). Despite its physiological role and clinical importance, the molecular basis of its action is not fully understood. To clarify the mechanism of the protein S interaction with APC, we have constructed and expressed a library of composite or point variants of human protein S, with residue substitutions introduced into the Gla, thrombin-sensitive region (TSR), epidermal growth factor 1 (EGF1), and EGF2 domains. Cofactor activity for APC was evaluated by calibrated automated thrombography (CAT) using protein S-deficient plasma. Of 27 variants tested initially, only one, protein S D95A (within the EGF1 domain), was largely devoid of functional APC cofactor activity. Protein S D95A was, however, gamma-carboxylated and bound phospholipids with an apparent dissociation constant (Kd(app)) similar to that of wildtype (WT) protein S. In a purified assay using FVa R506Q/R679Q, purified protein S D95A was shown to have greatly reduced ability to enhance APC-induced cleavage of FVa Arg306. It is concluded that residue Asp95 within EGF1 is critical forAPC cofactor function of protein S and could define a principal functional interaction site for APC. (Blood. 2010;115(23):4878-4885)
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| 3. |
- Christoffersen, Christina, et al.
(författare)
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Endothelium-protective sphingosine-1-phosphate provided by HDL-associated apolipoprotein M
- 2011
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 108:23, s. 9613-9618
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Tidskriftsartikel (refereegranskat)abstract
- Protection of the endothelium is provided by circulating sphingosine-1-phosphate(S1P), which maintains vascular integrity. We show that HDL-associated S1P is bound specifically to both human and murine apolipoprotein M (apoM). Thus, isolated human ApoM(+) HDL contained S1P, whereas ApoM(-) HDL did not. Moreover, HDL in Apom(-/-) mice contains no S1P, whereas HDL in transgenic mice overexpressing human apoM has an increased S1P content. The 1.7-angstrom structure of the S1P-human apoM complex reveals that S1P interacts specifically with an amphiphilic pocket in the lipocalin fold of apoM. Human ApoM(+) HDL induced S1P(1) receptor internalization, downstream MAPK and Akt activation, endothelial cell migration, and formation of endothelial adherens junctions, whereas apoM(-) HDL did not. Importantly, lack of S1P in the HDL fraction of Apom(-/-) mice decreased basal endothelial barrier function in lung tissue. Our results demonstrate that apoM, by delivering S1P to the S1P(1) receptor on endothelial cells, is a vasculoprotective constituent of HDL.
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| 4. |
- Christoffersen, Christina, et al.
(författare)
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The plasma concentration of HDL-associated apoM is influenced by LDL receptor-mediated clearance of apoB-containing particles
- 2012
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Ingår i: Journal of Lipid Research. - 1539-7262. ; 53:10, s. 2198-2204
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Tidskriftsartikel (refereegranskat)abstract
- ApoM is mainly associated with HDL. Nevertheless, we have consistently observed positive correlations of apoM with plasma LDL cholesterol in humans. Moreover, LDL receptor deficiency is associated with increased plasma apoM in mice. Here, we tested the idea that plasma apoM concentrations are affected by the rate of LDL receptor-mediated clearance of apoB-containing particles. We measured apoM in humans each carrying one of three different LDL receptor mutations (n = 9) or the apoB3500 mutation (n = 12). These carriers had increased plasma apoM (1.34 +/- 0.13 mu M, P = 0.003, and 1.23 +/- 0.10 mu M, P = 0.02, respectively) as compared with noncarriers (0.93 +/- 0.04 mu M). When we injected human apoM-containing HDL into Wt (n = 6) or LDL receptor-deficient mice (n = 6), the removal of HDL-associated human apoM was delayed in the LDL receptor-deficient mice. After 2 h, 54 +/- 5% versus 90 +/- 8% (P < 0.005) of the initial amounts of human apoM remained in the plasma of Wt and LDL receptor-deficient mice, respectively. Finally, we compared the turnover of radio-iodinated LDL and plasma apoM concentrations in 45 normocholesterolemic humans. There was a negative correlation between plasma apoM and the fractional catabolic rate of LDL (r = -0.38, P = 0.009). These data suggest that the plasma clearance of apoM, despite apoM primarily being associated with HDL, is influenced by LDL receptor-mediated clearance of apoB-containing particles.-Christoffersen, C., M. Benn, P. M. Christensen, P. L. S. M. Gordts, A. J. M. Roebroek, R. Frikke-Schmidt, A. Tybjaerg-Hansen, B. Dahlback, and L. B. Nielsen. The plasma concentration of HDL-associated apoM is influenced by LDL receptor-mediated clearance of apoB-containing particles. J. Lipid Res. 2012. 53: 2198-2204.
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| 5. |
- Elsoe, Sara, et al.
(författare)
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Apolipoprotein M binds oxidized phospholipids and increases the antioxidant effect of HDL
- 2012
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Ingår i: Atherosclerosis. - : Elsevier BV. - 1879-1484 .- 0021-9150. ; 221:1, s. 91-97
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Oxidation of LDL plays a key role in the development of atherosclerosis. HDL may, in part, protect against atherosclerosis by inhibiting LDL oxidation. Overexpression of HDL-associated apolipoprotein M (apoM) protects mice against atherosclerosis through a not yet clarified mechanism. Being a lipocalin, apoM contains a binding pocket for small lipophilic molecules. Here, we report that apoM likely serves as an antioxidant in HDL by binding oxidized phospholipids, thus enhancing the antioxidant potential of HDL. Methods and results: HDL was isolated from wild type mice, apoM-deficient mice, and two lines of apoM-Tg mice with similar to 2-fold and similar to 10-fold increased plasma apoM, respectively. Increasing amounts of HDL-associated apoM were associated with an increase in the resistance of HDL to oxidation with Cu2+ or 2,2'-azobis 2-methyl-propanimidamide, dihydrochloride (AAPH) and to an increased ability of HDL to protect human LDL against oxidation. Oxidized phospholipids, but not native phospholipids, quenched the intrinsic fluorescence of recombinant human apoM and the quenching could be competed with myristic acid suggesting selective binding of oxidized phospholipid in the lipocalin-binding pocket of apoM. Conclusions: The results suggest that apoM can bind oxidized phospholipids and that it increases the antioxidant effect of HDL. This new mechanism may explain at least part of the antiatherogenic potential of apoM. (C) 2011 Elsevier Ireland Ltd. All rights reserved.
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| 6. |
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| 7. |
- Ooi, Esther M. M., et al.
(författare)
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Association of apolipoprotein M with high-density lipoprotein kinetics in overweight-obese men
- 2010
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Ingår i: Atherosclerosis. - : Elsevier BV. - 1879-1484 .- 0021-9150. ; 210:1, s. 326-330
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The aim of this study was to investigate associations between plasma apoM concentration and HDL apoA-I and apoA-II kinetics in 60 overweight-obese, insulin resistant men. Methods: Plasma apoM concentration was determined using a sandwich ELISA with two monoclonal antibodies (CV < 5%). The kinetics of HDL apoA-I and apoA-II were measured using intravenous administration of D-3-leucine, gas chromatography-mass spectrometry and multi-compartmental modeling. Results: Plasma apoM was inversely associated with body mass index and positively associated with plasma total cholesterol, LDL cholesterol and HDL cholesterol (p < 0.05). There were no associations between plasma apoM and plasma triglyceride, NEFA, insulin, glucose, HOMA score or adiponectin concentrations. Plasma apoM was positively associated with both apoA-I and apoA-II concentrations (r = 0.406, p < 0.01 and r = 0.510, p < 0.01, respectively) and negatively associated with HDL apoA-I and apoA-II fractional catabolic rate (FCR) (r = -0.291, p = 0.03 and r = -0.291, p = 0.026, respectively). No significant associations were observed between plasma apoM and HDL apoA-I and apoA-II production rate. In multivariate regression models, both plasma apoM and triglycerides were significant, independent predictors of HDL apoA-I FCR (adjusted R-2 = 16%, p < 0.01) and HDL apoA-II FCR (adjusted R-2 = 14%, p < 0.01). Conclusion: ApoM may be a significant, independent predictor of HDL apoA-I and apoA-II catabolism in overweight-obese, insulin resistant men. Crown Copyright (C) 2009 Published by Elsevier Ireland Ltd. All rights reserved.
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| 8. |
- Reglinska-Matveyev, Natalia, et al.
(författare)
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TFPI cofactor function of protein S: essential role of the protein S SHBG-like domain
- 2014
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Ingår i: Blood. - : American Society of Hematology. - 1528-0020 .- 0006-4971. ; 123:25, s. 3979-3987
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Tidskriftsartikel (refereegranskat)abstract
- Protein S is a cofactor for tissue factor pathway inhibitor (TFPI), accelerating the inhibition of activated factor X (FXa). TFPI Kunitz domain 3 residue Glu226 is essential for enhancement of TFPI by protein S. To investigate the complementary functional interaction site on protein S, we screened 44 protein S point, composite or domain swap variants spanning the whole protein S molecule for their TFPI cofactor function using a thrombin generation assay. Of these variants, two protein S/growth arrest-specific 6 chimeras, with either the whole sex hormone-binding globulin (SHBG)-like domain (Val243-Ser635; chimera III) or the SHBG laminin G-type 1 subunit (Ser283-Val459; chimera I), respectively, substituted by the corresponding domain in growth arrest-specific 6, were unable to enhance TFPI. The importance of the protein S SHBG-like domain (and its laminin G-type 1 subunit) for binding and enhancement of TFPI was confirmed in FXa inhibition assays and using surface plasmon resonance. In addition, protein S bound to C4b binding protein showed greatly reduced enhancement of TFPI-mediated inhibition of FXa compared with free protein S. We show that binding of TFPI to the protein S SHBG-like domain enables TFPI to interact optimally with FXa on a phospholipid membrane.
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