title: A novel pathway for human endothelial cell activation by antiphospholipid/anti-β2 glycoprotein I antibodies.
abstract: Antiphospholipid Abs (APLAs) are associated with thrombosis and recurrent fetal loss. These Abs are primarily directed against phospholipid-binding proteins, particularly β(2)GPI, and activate endothelial cells (ECs) in a β(2)GPI-dependent manner after binding of β(2)GPI to EC annexin A2. Because annexin A2 is not a transmembrane protein, the mechanisms of APLA/anti-β(2)GPI Ab-mediated EC activation are uncertain, although a role for a TLR4/myeloid differentiation factor 88-dependent pathway leading to activation of NF-κB has been proposed. In the present study, we confirm a critical role for TLR4 in anti-β(2)GPI Ab-mediated EC activation and demonstrate that signaling through TLR4 is mediated through the assembly of a multiprotein signaling complex on the EC surface that includes annexin A2, TLR4, calreticulin, and nucleolin. An essential role for each of these proteins in cell activation is suggested by the fact that inhibiting the expression of each using specific siRNAs blocked EC activation mediated by APLAs/anti-β(2)GPI Abs. These results provide new evidence for novel protein-protein interactions on ECs that may contribute to EC activation and the pathogenesis of APLA/anti-β(2)GPI-associated thrombosis and suggest potential new targets for therapeutic intervention in antiphospholipid syndrome.
authors: Department of Cell Biology, Lerner Research Institute, Cleveland, OH, USA.
authors: Kristi L
authors: KL
authors: Allen
authors: Fabio V
authors: FV
authors: Fonseca
authors: Venkaiah
authors: V
authors: Betapudi
authors: Belinda
authors: B
authors: Willard
authors: Jainwei
authors: J
authors: Zhang
authors: Keith R
authors: KR
authors: McCrae
mesh_terms: D017306:Annexin A2 / Q000235:genetics / Q000378:metabolism*; D017152:Antibodies, Antiphospholipid / Q000494:pharmacology*; D015153:Blotting, Western; D064032:Calbindin 2; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D021962:Membrane Microdomains; D010743:Phospholipids / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D064030:S100 Calcium Binding Protein G / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013927:Thrombosis; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014471:Umbilical Veins / Q000166:cytology / Q000378:metabolism; D053482:beta 2-Glycoprotein I / Q000276:immunology*; D000097796:Nucleolin
chemical_list: D017306:Annexin A2; D017152:Antibodies, Antiphospholipid; D064032:Calbindin 2; D008156:Luciferases; D010743:Phospholipids; D010750:Phosphoproteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D064030:S100 Calcium Binding Protein G; D051197:Toll-Like Receptor 4; D053482:beta 2-Glycoprotein I; D000097796:Nucleolin; C495345:TLR4 protein, human