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Dependence on vitamin K-dependent protein S for eukaryotic cell secretion of the beta-chain of C4b-binding protein.

ABSTRACT: The anticoagulant vitamin K-dependent protein S (PS) circulates in plasma in two forms, 30% free and 70% being bound to the complement regulatory protein C4b-binding protein (C4BP). The major C4BP isoform consists of 7 ?-chains and 1 ?-chain (C4BP?(+)), the chains being linked by disulfide bridges. PS binds to the ?-chain with high affinity. In plasma, PS is in molar excess over C4BP?(+) and due to the high affinity, all C4BP?(+) molecules contain a bound PS. Taken together with the observation that PS-deficient patients have decreased levels of C4BP?(+), this raises the question of whether PS is important for secretion of the ?-chain from the cell. To test this hypothesis, HEK293 cells were stably and transiently transfected with ?-chain cDNA in combinations with cDNAs for PS and/or the ?-chain. The concentration of ?-chains in the medium increased after co-transfection with PS cDNA, but not by ?-chain cDNA, suggesting secretion of the ?-chains from the cells to be dependent on concomitant synthesis of PS, but not of the ?-chains. Thus, ?-chains that were not disulfide-linked to the ?-chains were secreted in complex with PS, either as monomers or dimers. Pulse-chase demonstrated that the complexes between PS and ?-chain were formed intracellularly, in the endoplasmic reticulum. In conclusion, our results demonstrate that successful secretion of ?-chains depends on intracellular complex formation with PS, but not on the ?-chains. This provides an explanation for the decreased ?-chain levels observed in PS-deficient patients.

SUBMITTER: Carlsson S

PROVIDER: S-EPMC2952205 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

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Dependence on vitamin K-dependent protein S for eukaryotic cell secretion of the beta-chain of C4b-binding protein.

Carlsson Sofia S Dahlbäck Björn B

The Journal of biological chemistry 20100806 42

The anticoagulant vitamin K-dependent protein S (PS) circulates in plasma in two forms, 30% free and 70% being bound to the complement regulatory protein C4b-binding protein (C4BP). The major C4BP isoform consists of 7 α-chains and 1 β-chain (C4BPβ(+)), the chains being linked by disulfide bridges. PS binds to the β-chain with high affinity. In plasma, PS is in molar excess over C4BPβ(+) and due to the high affinity, all C4BPβ(+) molecules contain a bound PS. Taken together with the observation ...[more]

PMID: 20693287

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Dataset Information

Dependence on vitamin K-dependent protein S for eukaryotic cell secretion of the beta-chain of C4b-binding protein.

Publications

Dependence on vitamin K-dependent protein S for eukaryotic cell secretion of the beta-chain of C4b-binding protein.

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