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Dissociation of activated protein C functions by elimination of protein S cofactor enhancement.
PRESTON, ROGER; HARMON, SHONA; NI AINLE, FIONNUALA; JOHNSON, JENNIFER; O'DONNELL, JAMES
Activated protein C (APC) plays a critical anticoagulant role in vivo by inactivating procoagulant factor Va and factor VIIIa and thus down-regulating thrombin generation. In addition, APC bound to the endothelial cell protein C receptor can initiate protease-activated receptor-1 (PAR-1)-mediated cytoprotective signaling. Protein S constitutes a critical cofactor for the anticoagulant function of APC but is not known to be involved in regulating APC-mediated protective PAR-1 signaling. In this study we utilized a site-directed mutagenesis strategy to characterize a putative protein S binding region within the APC Gla domain. Three single amino acid substitutions within the APC Gla domain (D35T, D36A, and A39V) were found to mildly impair protein S-dependent anticoagulant activity (<2-fold) but retained entirely normal cytoprotective activity. However, a single amino acid substitution (L38D) ablated the ability of protein S to function as a cofactor for this APC variant. Consequently, in assays of protein S-dependent factor Va proteolysis using purified proteins or in the plasma milieu, APC-L38D variant exhibited minimal residual anticoagulant activity compared with wild type APC. Despite the location of Leu-38 in the Gla domain, APC-L38D interacted normally with endothelial cell protein C receptor and retained its ability to trigger PAR-1 mediated cytoprotective signaling in a manner indistinguishable from that of wild type APC. Consequently, elimination of protein S cofactor enhancement of APC anticoagulant function represents a novel and effective strategy by which to separate the anticoagulant and cytoprotective functions of APC for potential therapeutic gain.
Keyword(s): Clinical medicine; Hematology; anticoagulant function
Publication Date:
2008
Type: Journal article
Peer-Reviewed: Yes
Language(s): English
Institution: Trinity College Dublin
Citation(s): Harmon, S, Preston, RJ, Ainle, FN, Johnson, JA, Cunningham, MS, Smith, OP, White, B, O'Donnell, JS, Dissociation of activated protein C functions by elimination of protein S cofactor enhancement., The Journal of Biological Chemistry, 283, 45, 2008, 30531 - 30539
First Indexed: 2014-05-13 05:39:16 Last Updated: 2015-07-15 05:42:22