title: TFPIβ is the GPI-anchored TFPI isoform on human endothelial cells and placental microsomes.
abstract: Tissue factor pathway inhibitor (TFPI) produces factor Xa-dependent feedback inhibition of factor VIIa/tissue factor-induced coagulation. Messages for 2 isoforms of TFPI have been identified. TFPIα mRNA encodes a protein with an acidic N-terminus, 3 Kunitz-type protease inhibitor domains and a basic C-terminus that has been purified from plasma and culture media. TFPIβ mRNA encodes a form in which the Kunitz-3 and C-terminal domains of TFPIα are replaced with an alternative C-terminus that directs the attachment of a glycosylphosphatidylinositol (GPI) anchor, but whether TFPIβ protein is actually expressed is not clear. Moreover, previous studies have suggested that the predominant form of TFPI released from cells by phosphatidylinositol-specific phospholipase C (PIPLC) treatment is TFPIα, implying it is bound at cell surfaces to a separate GPI-anchored coreceptor. Our studies show that the form of TFPI released by PIPLC treatment of cultured endothelial cells and placental microsomes is actually TFPIβ based on (1) migration on SDS-PAGE before and after deglycosylation, (2) the lack of a Kunitz-3 domain, and (3) it contains a GPI anchor. Immunoassays demonstrate that, although endothelial cells secrete TFPIα, greater than 95% of the TFPI released by PIPLC treatment from the surface of endothelial cells and from placental microsomes is TFPIβ.
authors.affiliation: Division of Hematology, Washington University School of Medicine, 660 SEuclid Ave, St Louis, MO 63110, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Girard
authors.forename: Elodee
authors.initials: E
authors.lastname: Tuley
authors.forename: George J
authors.initials: GJ
authors.lastname: Broze
mesh_terms: D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D058851:GPI-Linked Proteins / Q000378:metabolism / Q000502:physiology*; D061307:Human Umbilical Vein Endothelial Cells / Q000378:metabolism*; D006801:Humans; D008074:Lipoproteins / Q000378:metabolism / Q000502:physiology*; D008861:Microsomes / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism* / Q000648:ultrastructure; D011247:Pregnancy; D020033:Protein Isoforms / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D058851:GPI-Linked Proteins; D008074:Lipoproteins; D020033:Protein Isoforms; C051928:lipoprotein-associated coagulation inhibitor