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Plasminogen-dependent internalization of soluble melanotransferrin involves the low-density lipoprotein

Jonathan Michaud-Levesque1, Michel Demeule, Richard Béliveau

  • 1Laboratoire de Médecine Moléculaire, Service d'Hémato-Oncologie, Hôpital Ste-Justine, Université du Québec à Montréal, Montréal, Québec, Canada.

Biological Chemistry
|June 16, 2007
PubMed

Insights

Plasminogen (Plg) enhances soluble melanotransferrin (sMTf) cell uptake, particularly via lysine-Plg interacting with low-density lipoprotein receptor-related protein (LRP) and annexin II. This suggests a novel Plg-mediated internalization pathway for sMTf clearance.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Molecular Medicine

Background:

  • Soluble melanotransferrin (sMTf) is a transferrin family protein involved in iron transport.
  • The cellular uptake mechanisms of sMTf are not fully elucidated.
  • Plasminogen (Plg) is a key protein in the fibrinolytic system with known interactions with cell surface receptors.

Purpose of the Study:

  • To investigate the role of plasminogen (Plg) in the cellular internalization of recombinant soluble melanotransferrin (sMTf).
  • To identify the specific forms of Plg and cell surface receptors involved in sMTf uptake.
  • To elucidate the mechanism of Plg-mediated sMTf internalization.

Main Methods:

  • Biospecific interaction analysis to study sMTf and Plg binding.
  • Cellular uptake assays using U87 glioblastoma cells and LRP-deficient MEF cells.
  • Inhibition studies using receptor-associated proteins, antibodies, and varying experimental conditions.

Main Results:

  • Both Glu- and Lys-Plg bind to sMTf.
  • Lysine-Plg significantly enhances sMTf cell surface binding and uptake in a saturable, temperature-dependent manner.
  • Low-density lipoprotein receptor-related protein (LRP) and annexin II are implicated in Lys-Plg-dependent sMTf internalization.

Conclusions:

  • Plasminogen, particularly Lys-Plg, mediates the internalization of sMTf.
  • The uptake process involves LRP and annexin II, suggesting a novel clearance pathway.
  • This finding provides insights into the biological function and potential therapeutic targeting of sMTf.

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