A role of heparan sulphate proteoglycan in the cellular uptake of lipocalins ß-lactoglobulin and allergen Fel d 4

Abstract

Lipocalins, small extracellular hydrophobic molecule carriers, can be internalized by a variety of different cells. However, to date receptors have only been identified for human lipocalins. Here, we specifically investigated uptake mechanisms for lipocalins ß-lactoglobulin and Fel d 4 in HeLa and Chinese hamster ovary (CHO) cells. We provide evidence that cell surface heparan sulphate proteoglycan is essential for internalization of these lipocalins. In HeLa cells, lipocalin uptake was inhibited by competition with soluble heparin, enzymatic digestion of cellular heparan sulphate by heparinase and inhibition of its biosynthesis by sodium chlorate. Biochemical studies by heparin affinity chromatography and colocalization studies further supported a role of heparan sulphate proteoglycan in lipocalin uptake. Finally, lipocalin uptake was blocked in CHO mutant cells defective in glycosaminoglycan biosynthesis whereas in wild-type cells it was clearly detectable. Thus, cell surface heparan sulphate proteoglycan represents a novel component absolutely participating in the cellular uptake of some lipocalins.

Inhalant Mammal-Derived Lipocalin Allergens and the Innate Immunity

“…Another characteristic feature of lipocalin proteins is their capacity to bind to specific cell-surface receptors ( 39 , 42 ). In humans, three groups of lipocalin receptors can be recognized ( 42 , 43 ). The group taking up the lipocalin-ligand complex in an endocytic manner includes megalin ( 44 ), the lipocalin 1-interacting membrane receptor (LIMR) ( 41 , 45 ), the lipocalin-2 receptor NGalR/24p3R ( 46 ) and basigin ( 47 ).…”

“…For example, food allergen β-lactoglobulin (Bos d 5) was reported to be taken up by LIMR ( 206 ) which was not, however, confirmed in another study ( 207 ). Instead, β-lactoglobulin, as well as cat Fel d 4, were recently found to be internalized by the cell-surface heparan sulfate proteoglycan-mediated endocytosis in HeLa and CHO cells ( 43 ). Although these studies did not assess the allergenic capacity of lipocalins, obviously the active uptake of allergens through binding to cell-surface receptors can facilitate their access to the immune system.…”

Ameliorating Atopy by Compensating Micronutritional Deficiencies in Immune Cells: A Double-Blind Placebo-Controlled Pilot Study

“…13,14 We previously showed that the whey protein b-lactoglobulin (BLG), which is known to be a major allergen in cow's milk, loses its allergenic properties when it carries micronutrients such as flavonoid-bound iron, 15,16 vitamin A, 17 and vitamin D. 18 Dietary uptake of digestion-and protease-resistant BLG occurs through the lymphatic vessels 19,20 and is receptor-mediated. [21][22][23] Different receptors have been described as binding to it, [24][25][26][27][28][29] and there are probably also clathrin-dependent 30 mechanisms involved. Upon ingestion, BLG is associated with immune cells in the lamina propria of the intestine within minutes.…”