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Flow Cytometry Analysis of Tissue Factor Expression in Human Platelets
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Flow Cytometry Analysis of Tissue Factor Expression in Human Platelets

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Tissue factor pathway inhibitor-2 (TFPI-2) recognizes the complement and kininogen binding protein gC1qR/p33 (gC1qR):

Ellinor I B Peerschke1, Ramona J Petrovan, Berhane Ghebrehiwet

  • 1New York Presbyterian Hospital, Weill-Cornell Center, 525 East 68th Street, Room F715, New York 10021, USA. epeersch@med.cornell.edu

Thrombosis and Haemostasis
|October 7, 2004
PubMed

Insights

Tissue Factor Pathway Inhibitor-2 (TFPI-2) directly binds to gC1qR/p33 (gC1qR), influencing protease activity in vascular inflammation and atherosclerosis. This interaction localizes TFPI-2, potentially modulating tissue remodeling and kininogen activation.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Pathology

Background:

  • Tissue Factor Pathway Inhibitor-2 (TFPI-2) is implicated in physiological and pathological processes, including cancer invasion, vascular inflammation, and atherosclerosis.
  • Immunohistochemical studies revealed overlapping tissue distribution of TFPI-2, High Molecular Weight Kininogen (HK), and gC1qR/p33 (gC1qR) in atherosclerotic lesions.
  • gC1qR is a versatile protein modulating complement, coagulation, and kinin cascades.

Purpose of the Study:

  • To investigate the direct interaction between TFPI-2 and gC1qR.
  • To characterize the binding kinetics and domains involved in the TFPI-2/gC1qR interaction.
  • To assess the functional consequences of TFPI-2/gC1qR binding on protease inhibition.

Main Methods:

  • Immunoprecipitation and solid-phase binding assays to confirm direct TFPI-2/gC1qR interaction.
  • ELISA and surface plasmon resonance (Biacore) to quantify binding affinity (Kd) and specificity.
  • Site-directed mutagenesis and antibody inhibition studies to identify critical binding domains and regions.
  • Fluid-phase chromogenic assays to evaluate TFPI-2's protease inhibitory activity upon gC1qR binding.

Main Results:

  • Direct, specific, and saturable binding between TFPI-2 and gC1qR was demonstrated (Kd ≈ 70 nM).
  • The Kunitz-2 domain of TFPI-2 is crucial for gC1qR binding, with its deletion reducing interaction by ~75%.
  • gC1qR binding to TFPI-2 resulted in modest reductions in TFPI-2's inhibition of plasmin but did not affect kallikrein inhibition.

Conclusions:

  • gC1qR directly binds TFPI-2, primarily through TFPI-2's Kunitz-2 domain.
  • gC1qR may localize TFPI-2 to the pericellular environment in processes like tissue remodeling and inflammation.
  • This localization could modulate local protease activity and regulate High Molecular Weight Kininogen activation.

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