title: In vivo clearance of human protein S in a mouse model: influence of C4b-binding protein and the Heerlen polymorphism.
abstract: OBJECTIVE
  To explore the effect of the Heerlen polymorphism and C4b-binding protein (C4BP) on protein S catabolism in vitro and in vivo.
  
  
  RESULTS
  Radiolabeled protein S was efficiently bound and intracellularly degraded by THP-1 macrophages, and both processes were strongly reduced in the presence of the protein S-carrier protein C4BP. To test whether C4BP displays a similar protective effect in vivo, survival experiments were performed in mice. In the absence of C4BP, radiolabeled human protein S disappeared in a biphasic manner (mean residence time [MRT] 2 hours). However, the presence of C4BP resulted in a 4-fold prolonged survival of protein S (MRT 8 hours; P<0.0001). We also applied this experimental model to recombinant protein S-Heerlen, a naturally occurring variant that contains a Ser460Pro substitution. These clearance experiments revealed a strongly decreased survival of recombinant protein S-S460P (MRT 0.6 hours; P=0.021), which could be compensated partially by C4BP (MRT 1.4 hours; P=0.012 compared with protein S-S460P).
  
  
  CONCLUSIONS
  Protein S-S460P has a reduced survival in vivo, which may explain the low levels of free protein S in individuals carrying this polymorphism. Furthermore, C4BP prevents premature clearance of protein S and uses this ability to compensate the increased clearance of protein S-S460P.
authors.affiliation: INSERM U.143, Kremlin-Bicêtre, France.
authors.forename: Cécile V
authors.initials: CV
authors.lastname: Denis
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Roberts
authors.forename: Tilman M
authors.initials: TM
authors.lastname: Hackeng
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lenting
mesh_terms: D000818:Animals; D002460:Cell Line; D050716:Complement C4b-Binding Protein / Q000235:genetics*; D004195:Disease Models, Animal; D006801:Humans; D007457:Iodine Radioisotopes; D008099:Liver / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011110:Polymorphism, Genetic; D017293:Protein S / Q000235:genetics* / Q000493:pharmacokinetics*; D013927:Thrombosis / Q000235:genetics* / Q000378:metabolism*
chemical_list: D050716:Complement C4b-Binding Protein; D007457:Iodine Radioisotopes; D017293:Protein S; C499867:protein S Heerlen