J Biol Chem. 2018 Apr 18. pii: jbc.RA118.003145. doi: 10.1074/jbc.RA118.003145. [Epub ahead of print]
Lactoferrin is a natural inhibitor of plasminogen activation.
Zwirzitz A1, Reiter M2, Skrabana R3, Ohradanova-Repic A2, Majdic O2, Gutekova M4, Cehlar O3, Petrovčíková E5, Kutejova E5, Stanek G2, Stockinger H6, Leksa V7.
The plasminogen system is essential for dissolution of fibrin clots, and in addition, it is involved in a wide variety of other physiological processes, including proteolytic activation of growth factors, cell migration, and removal of protein aggregates. On the other hand, uncontrolled plasminogen activation contributes to many pathological processes, e.g. tumor cells’ invasion in cancer progression. Moreover, some virulent bacterial species, e.g. Streptococci or Borrelia, bind human plasminogen and hijack the host’s plasminogen system to penetrate tissue barriers. Thus, the conversion of plasminogen to the active serine protease plasmin must be tightly regulated. Here, we show that human lactoferrin, an iron-binding milk glycoprotein, blocks plasminogen activation on the cell surface by direct binding to human plasminogen. We mapped the mutual binding sites to the N-terminal region of lactoferrin, encompassed also in the bioactive peptide lactoferricin, and kringle 5 of plasminogen. Finally, lactoferrin blocked tumor cell invasion in vitro and also plasminogen activation driven by Borrelia. Our results explain many diverse biological properties of lactoferrin, and also suggest that lactoferrin may be useful as a potential tool for therapeutic interventions to prevent both invasive malignant cells and virulent bacteria from penetrating host tissues.