title: Activated protein C modulates inflammation, apoptosis and tissue factor procoagulant activity by regulating endoplasmic reticulum calcium depletion in blood monocytes.
abstract: BACKGROUND
  The endoplasmic reticulum (ER) is responsible for the synthesis and folding of secretory, transmembrane and ER-resident proteins. Conditions that impair protein folding or overwhelm its protein folding capacity disrupt ER homeostasis, thereby causing ER stress. ER stress-induced apoptosis and inflammation are involved in the pathogenesis of inflammatory diseases. Activated protein C (APC) inhibits inflammation and apoptosis in monocytes, and this may partly explain the protective effects of APC treatment in severe sepsis. However, the precise molecular pathways by which APC modulates these effects remain unknown.
  
  
  OBJECTIVE
  To investigate whether APC modulates the ER stress response in human monocytes.
  
  
  METHODS
  We treated monocytes with ER stress-inducing agents in the presence or absence of APC to determine the effect on this response. Protein and mRNA levels were determined by immunoblotting and real-time PCR, respectively. Enzyme assays and flow cytometry were used to determine the role of APC in this model.
  
  
  RESULTS
  In thapsigargin (Tg)-treated cells, APC dampened unfolded protein response activation, as indicated by reduced levels of the 78-kDa glucose-regulated protein (GRP78), in an endothelial protein C receptor-independent and protease-activated receptor-1-independent manner. Consistent with this, APC decreased phosphorylated eukaryotic translational initiation factor 2α and C/EBP homologous protein levels induced by Tg. APC inhibited Tg-induced ER Ca(2+) flux and reactive oxygen species generation. Functionally, APC diminished Tg-induced caspase-3 activity and degradation of the nuclear factor kappaB inhibitor IκBα. Furthermore, APC dampened the induction of tissue factor procoagulant activity facilitated by Tg.
  
  
  CONCLUSIONS
  These studies suggest that APC modulates the adverse effects of ER Ca(2+) depletion in human monocytes.
authors.affiliation: Department of Medical Sciences, McMaster University, Hamilton, ON, Canada.
authors.forename: L J
authors.initials: LJ
authors.lastname: Toltl
authors.forename: R C
authors.initials: RC
authors.lastname: Austin
authors.forename: P C
authors.initials: PC
authors.lastname: Liaw
mesh_terms: D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D002118:Calcium / Q000097:blood*; D020013:Calcium Signaling / Q000187:drug effects; D053148:Caspase 3 / Q000097:blood; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D015870:Gene Expression / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000097:blood / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D009000:Monocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D016328:NF-kappa B / Q000097:blood; D011486:Protein C / Q000494:pharmacology*; D012333:RNA, Messenger / Q000097:blood / Q000235:genetics; D017382:Reactive Oxygen Species / Q000097:blood; D011994:Recombinant Proteins / Q000494:pharmacology; D018805:Sepsis / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D013312:Stress, Physiological / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology; D013925:Thromboplastin / Q000378:metabolism*
chemical_list: D000893:Anti-Inflammatory Agents; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D016328:NF-kappa B; D011486:Protein C; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D019284:Thapsigargin; D013925:Thromboplastin; C505407:CASP3 protein, human; D053148:Caspase 3; C421124:drotrecogin alfa activated; D002118:Calcium