The endocytic receptor megalin binds the iron transporting neutrophil-gelatinase-associated lipocalin with high affinity and mediates its cellular uptake

Neutrophil-gelatinase-associated lipocalin (NGAL) is a prominent protein of specific granules of human neutrophils also synthesized by epithelial cells during inflammation. NGAL binds bacterial siderophores preventing bacteria from retrieving iron from this source. Also, NGAL may be important in delivering iron to cells during formation of the tubular epithelial cells of the primordial kidney. No cellular receptor for NGAL has been described. We show here that megalin, a member of the low-density lipoprotein receptor family expressed in polarized epithelia, binds NGAL with high affinity, as shown by surface plasmon resonance analysis. Furthermore, a rat yolk sac cell line known to express high levels of megalin, endocytosed NGAL by a mechanism completely blocked by an antibody against megalin.