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Dependence on Vitamin K-dependent Protein S for Eukaryotic Cell Secretion of the beta-Chain of C4b-binding Protein

Somajo, Sofia LU and Dahlbäck, Björn LU (2010) In Journal of Biological Chemistry 285(42). p.32038-32046
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 alpha-chains and 1 beta-chain (C4BP beta(+)), the chains being linked by disulfide bridges. PS binds to the beta-chain with high affinity. In plasma, PS is in molar excess over C4BP beta(+) and due to the high affinity, all C4BP beta(+) molecules contain a bound PS. Taken together with the observation that PS-deficient patients have decreased levels of C4BP beta(+), this raises the question of whether PS is important for secretion of the beta-chain from the cell. To test this hypothesis, HEK293 cells were stably and... (More)
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 alpha-chains and 1 beta-chain (C4BP beta(+)), the chains being linked by disulfide bridges. PS binds to the beta-chain with high affinity. In plasma, PS is in molar excess over C4BP beta(+) and due to the high affinity, all C4BP beta(+) molecules contain a bound PS. Taken together with the observation that PS-deficient patients have decreased levels of C4BP beta(+), this raises the question of whether PS is important for secretion of the beta-chain from the cell. To test this hypothesis, HEK293 cells were stably and transiently transfected with beta-chain cDNA in combinations with cDNAs for PS and/or the alpha-chain. The concentration of beta-chains in the medium increased after co-transfection with PS cDNA, but not by alpha-chain cDNA, suggesting secretion of the beta-chains from the cells to be dependent on concomitant synthesis of PS, but not of the alpha-chains. Thus, beta-chains that were not disulfide-linked to the alpha-chains were secreted in complex with PS, either as monomers or dimers. Pulse-chase demonstrated that the complexes between PS and beta-chain were formed intracellularly, in the endoplasmic reticulum. In conclusion, our results demonstrate that successful secretion of beta-chains depends on intracellular complex formation with PS, but not on the alpha-chains. This provides an explanation for the decreased beta-chain levels observed in PS-deficient patients. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Biological Chemistry
volume
285
issue
42
pages
32038 - 32046
publisher
ASBMB
external identifiers
  • wos:000282683000017
  • pmid:20693287
  • scopus:77957808702
ISSN
1083-351X
DOI
10.1074/jbc.M110.148452
language
English
LU publication?
yes
id
bd6eef3c-492e-4590-8111-331d0f3abdca (old id 1727049)
alternative location
http://www.ncbi.nlm.nih.gov/pubmed/20693287?dopt=Abstract
date added to LUP
2010-11-23 09:49:37
date last changed
2018-05-29 11:59:06
@article{bd6eef3c-492e-4590-8111-331d0f3abdca,
  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 alpha-chains and 1 beta-chain (C4BP beta(+)), the chains being linked by disulfide bridges. PS binds to the beta-chain with high affinity. In plasma, PS is in molar excess over C4BP beta(+) and due to the high affinity, all C4BP beta(+) molecules contain a bound PS. Taken together with the observation that PS-deficient patients have decreased levels of C4BP beta(+), this raises the question of whether PS is important for secretion of the beta-chain from the cell. To test this hypothesis, HEK293 cells were stably and transiently transfected with beta-chain cDNA in combinations with cDNAs for PS and/or the alpha-chain. The concentration of beta-chains in the medium increased after co-transfection with PS cDNA, but not by alpha-chain cDNA, suggesting secretion of the beta-chains from the cells to be dependent on concomitant synthesis of PS, but not of the alpha-chains. Thus, beta-chains that were not disulfide-linked to the alpha-chains were secreted in complex with PS, either as monomers or dimers. Pulse-chase demonstrated that the complexes between PS and beta-chain were formed intracellularly, in the endoplasmic reticulum. In conclusion, our results demonstrate that successful secretion of beta-chains depends on intracellular complex formation with PS, but not on the alpha-chains. This provides an explanation for the decreased beta-chain levels observed in PS-deficient patients.},
  author       = {Somajo, Sofia and Dahlbäck, Björn},
  issn         = {1083-351X},
  language     = {eng},
  number       = {42},
  pages        = {32038--32046},
  publisher    = {ASBMB},
  series       = {Journal of Biological Chemistry},
  title        = {Dependence on Vitamin K-dependent Protein S for Eukaryotic Cell Secretion of the beta-Chain of C4b-binding Protein},
  url          = {http://dx.doi.org/10.1074/jbc.M110.148452},
  volume       = {285},
  year         = {2010},
}