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Early endocytotic events associated with lactoferrin and its receptor in trophoblast cells.
Author(s) -
Lopez Veronica,
Lonnerdal Bo
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a62-b
Subject(s) - internalization , lactoferrin , endosome , endocytosis , microbiology and biotechnology , cycloheximide , biology , trophoblast , filipin , exocytosis , intracellular , receptor , chemistry , biochemistry , secretion , placenta , protein biosynthesis , cholesterol , pregnancy , fetus , genetics
Preeclampsia is a consequence of impaired trophoblast cell function. Lactoferrin (Lf) is found in amniotic fluid and secreted by the uterine endothelium; however, the significance of this in relation to the pathogenesis of preeclampsia remains unknown. Lf reversibly binds iron (Fe) and modulates diverse cellular functions, such as mitogenesis; however, the processes by which Lf mediates this via its receptor (LfR) remain largely unknown. We hypothesize that in human trophoblast cells, Lf internalization by LfR will result in distinct intracellular compartmentalization, potentially mediating cell function. For siRNA, mastoporan and cycloheximide studies, 125 I‐apo‐(Fe‐free) and 125 I‐holo‐Lf (Fe‐saturated) uptake was measured. Plasma membrane (PM) proteins were biotinylated and LfR abundance was assessed by SDS‐PAGE. For confocal studies, cells were incubated with antibodies against EEA1, Lamp1, TfR and LfR. Knockdown of LfR protein significantly decreased 125 I‐apo‐Lf uptake compared to controls. Cell surface abundance of LfR significantly increased in the presence of apo‐Lf by 10 min but decreased thereafter. Mastoparan significantly decreased and cycloheximide increased 125 I‐apo‐Lf uptake, compared to controls. When stimulated with apo‐Lf, internalized LfR co‐localized with EEA1 and TfR by 10 min and minimally with Lamp1 by 20 min. In summary, LfR mediated apo‐Lf uptake in a clathrin‐dependent manner. Subsequently, LfR enters early endosomes and is recycled back to the PM, while a fraction of LfR undergoes degradation. Our data suggest that apo‐Lf internalized by LfR undergoes sub‐cellular compartmentalization, which may regulate cellular responses. Supported by NIH HD43240.