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The low density lipoprotein receptor-related protein mediates the cellular degradation of tissue factor pathway

I Warshawsky1, G J Broze, A L Schwartz

  • 1Edward Mallinckrodt Department of Pediatrics, Jewish Hospital at Washington University School of Medicine, St. Louis, MO 63110.

Proceedings of the National Academy of Sciences of the United States of America
|July 5, 1994
PubMed

Insights

The low density lipoprotein receptor-related protein (LRP) mediates the degradation of tissue factor pathway inhibitor (TFPI). This process involves TFPI binding to an unknown cell surface molecule before LRP-mediated cellular degradation.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Molecular Medicine

Background:

  • The low density lipoprotein receptor-related protein (LRP) is a key hepatic endocytosis receptor.
  • LRP facilitates the clearance of various plasma proteins, including lipoprotein complexes and protease complexes.
  • Tissue factor pathway inhibitor (TFPI) is a critical regulator of the extrinsic pathway of blood coagulation.

Purpose of the Study:

  • To investigate the role of LRP in the cellular degradation of tissue factor pathway inhibitor (TFPI).
  • To characterize the binding kinetics and mechanism of TFPI interaction with cell surface receptors.

Main Methods:

  • Utilized human and rat hepatoma cell lines for in vitro studies.
  • Employed radiolabeled 125I-TFPI to assess binding and degradation.
  • Investigated the effects of anti-LRP antibodies and an LRP-associated 39-kDa protein on TFPI degradation and binding.

Main Results:

  • LRP was demonstrated to mediate the cellular degradation of TFPI.
  • Degradation of 125I-TFPI was significantly inhibited (>80%) by anti-LRP antibodies and the 39-kDa protein.
  • TFPI binding to rat hepatoma cells occurred at approximately 2 x 10^6 sites/cell with a Kd of ~30 nM at 4°C.
  • TFPI cell surface binding was not inhibited by the 39-kDa protein, suggesting an initial interaction with a distinct molecule.

Conclusions:

  • LRP plays a crucial role in the cellular processing and degradation of TFPI.
  • TFPI likely binds initially to an unidentified cell surface receptor before LRP-mediated internalization and degradation.
  • These findings elucidate a novel pathway for TFPI regulation within the hepatic system.

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