Molecular Cloning and Functional Expression of a Human Intestinal Lactoferrin Receptor

Abstract

Lactoferrin (Lf), a major iron-binding protein in human milk, has been suggested to have multiple biological roles such as facilitating iron absorption, modulating the immune system, embryonic development, and cell proliferation. Our previous binding studies suggested the presence of a specific receptor for Lf (LfR) in the small intestine of newborn infants, which may facilitate iron absorption. We here report the cloning and the functional expression of the human intestinal LfR and the evidence of its involvement in iron metabolism. The entire coding region of the LfR cDNA was cloned by PCR based on amino acid sequences of the purified native LfR (nLfR). The recombinant LfR (rLfR) was then expressed in a baculovirus-insect cell system and purified by immobilized human Lf (hLf) affinity chromatography where binding of hLf to the rLfR was partially Ca(2+) dependent. The apparent molecular mass was 136 kDa under nonreducing conditions and 34 kDa under reducing conditions. 125I-hLf bound to the rLfR with an apparent K(d) of approximately 360 nM. These biochemical properties of the rLfR are similar to those of the nLfR. RT-PCR revealed that the gene was expressed at high levels in fetal small intestine and in adult heart and at lower levels in Caco-2 cells. PI-PLC treatment of Caco-2 cells indicated that the LfR is GPI anchored. In Caco-2 cells transfected with the LfR gene, 125I-hLf binding and 59Fe-hLf uptake were increased by 1.7 and 3.4 times, respectively, compared to those in mock-transfected cells. Our findings demonstrate the presence of a unique receptor-mediated mechanism for nutrient uptake by the newborn.

Identification of proteins in activated human neutrophils susceptible to tyrosyl radical attack. A proteomic study using a tyrosylating fluorophore

“…Given that activation triggers the secretion of the basic lactoferrin [40] the tyrosylation reaction may have occurred in the medium. Binding to lactoferrin receptors may explain why the tyrosylated form also occurs in the soluble fraction [41]. In agreement with our findings it was recently shown that three lactoferrin isoforms of 75, 80, and 85 kDa were constitutively expressed in the plasma membrane and secondary granules of resting neutrophils [42].…”

Nippostrongylus brasiliensis: Identification of intelectin-1 and -2 as Stat6-dependent genes expressed in lung and intestine during infection

“…Among the Stat6-dependent genes that were induced in lung and intestine during infection were IgA, calcium activated chloride channel 3, small proline rich proteins 2 and intelectin-2, which has recently been identified as a gene induced by nematode infection in the small intestine (Table 1) (Komiya, 1998;Pemberton, 2004b). Two intelectin genes have been described in mouse and man with high homology to a Xenopus oocyte granule lectin (Lee, 2001;Pemberton, 2004a;Suzuki, 2001b). Since human intelectin has been described to bind galactofuranose sugars present in cell walls of bacteria, fungi and protozoan parasites and therefore might play a role in immune defense, its mouse homolog was chosen here for further investigation (Daffe, 1990;Latge, 1994;Suzuki, 2001a;Suzuki, 2002;Tsuji, 2001).…”

“…Human intelectin-1 has independently been cloned as lactoferrin receptor from samples of human fetal intestine (Suzuki, 2001b). Lactoferrin is involved in antibacterial responses by either agglutinating bacteria or binding of iron, which lowers the available iron critically required for bacterial growth (Otto, 1992;Teraguchi, 1996).…”

Omentin Plasma Levels and Gene Expression Are Decreased in Obesity

“…Omentin has been identified in other tissues at lower expression levels and named intelectin (14), intestinal lactoferrin receptor (15), or endothelial lectin (16). It is expressed in intestinal Paneth cells (17), endothelial cells (16), and visceral adipose stromal-vascular cells (11).…”