title: Tissue factor activation: is disulfide bond switching a regulatory mechanism?
abstract: A majority of tissue factor (TF) on cell surfaces exists in a cryptic form (ie, coagulation function inactive) but retains its functionality in cell signaling. Recent studies have suggested that cryptic TF contains unpaired cysteine thiols and that activation involves the formation of the disulfide bond Cys186-Cys 209 and that protein disulfide isomerase (PDI) regulates TF coagulant and signaling activities by targeting this disulfide bond. This study was carried out to investigate the validity of this novel concept. Although treatment of MDA 231 tumor cells, fibroblasts, and stimulated endothelial cells with the oxidizing agent HgCl(2) markedly increased the cell-surface TF coagulant activity, the increase is associated with increased anionic phospholipids at the cell surface. Annexin V, which binds to anionic phospholipids, attenuated the increased TF coagulant activity. It is noteworthy that treatment of cells with reducing agents also increased the cell surface TF activity. No evidence was found for either detectable expression of PDI at the cell surface or association of TF with PDI. Furthermore, reduction of PDI with the gene silencing had no effect on either TF coagulant or cell signaling functions. Overall, the present data undermine the recently proposed hypothesis that PDI-mediated disulfide exchange plays a role in regulating TF procoagulant and cell signaling functions.
authors.affiliation: Biomedical Research Division, University of Texas Health Science Center at Tyler, TX 75708, USA. usha.pendurthi@uthct.edu
authors.forename: Usha R
authors.initials: UR
authors.lastname: Pendurthi
authors.forename: Samit
authors.initials: S
authors.lastname: Ghosh
authors.forename: Samir K
authors.initials: SK
authors.lastname: Mandal
authors.forename: L Vijaya Mohan
authors.initials: LV
authors.lastname: Rao
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology; D004202:Disinfectants / Q000494:pharmacology; D004220:Disulfides / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D008627:Mercuric Chloride / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D019704:Protein Disulfide-Isomerases / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D013925:Thromboplastin / Q000378:metabolism*
chemical_list: D017304:Annexin A5; D004202:Disinfectants; D004220:Disulfides; D016877:Oxidants; D010743:Phospholipids; D008627:Mercuric Chloride; D013925:Thromboplastin; D019704:Protein Disulfide-Isomerases