Two lectin-like receptors for α1-acid glycoprotein in mouse testis

Abstract

Three glycoforms of alpha 1-acid glycoprotein (AGP) were biotinylated to examine their binding in mouse testis by light microscopy. The transition from one stage to another in the spermatogenic cycle is marked with an appearance of a receptor for the Concanavalin A (Con A) non-reactive glycoform AGP-A in the cytoplasm of spermatocytes, young spermatids and Sertoli cells. This receptor disappears in the late stages of the spermatids. The Con-A intermediately reactive and the Con-A reactive glycoforms, AGP-B and AGP-C, showed weak reaction in the cytoplasm of spermatocytes, spermatids and Sertoli cells and, at the last stages in the spermatogenic cycle, a very strong reaction in the late elongated spermatids and the apical extensions of Sertoli cells. The interactions are lectin-like as confirmed by inhibition with simple sugars. In addition, the bindings were inhibited by steroid hormones. AGP-A was inhibited by testosterone, oestradiol and progesterone, while AGP-B and AGP-C were inhibited by mannose, GlcNAc, cortisone, aldosterone, oestradiol and progesterone. The receptors and the corresponding AGP glycoforms may be adhesion molecules between Sertoli cells and the spermatogenic cells and may have a function as a regulatory factor for spermatozoa development.

Molecular Cloning of a Novel Lipocalin-1 Interacting Human Cell Membrane Receptor Using Phage Display

“…An example for the first group seems to be the receptor for ␣1-acid glycoprotein, a highly sialylated serum lipocalin. Inhibition of ␣1-acid glycoprotein binding to several cells could be inhibited by simple sugars, like mannose and GlcNAc, suggesting that this interaction is mediated by carbohydrates and that the receptor is of a lectin-type (43). Our investigations clearly show that LIMR is an example for a receptor-type binding via direct protein interaction, because it was isolated by means of prokaryotic expression, and a recombinant LIMR produced in E. coli interacts in vitro with Lcn-1.…”

Characterization of the Hepatic Cellular Uptake of α1-Acid Glycoprotein (AGP), Part 1: A Peptide Moiety of Human AGP Is Recognized by the Hemoglobin β-Chain on Mouse Liver Parenchymal Cells

“…17 These findings lead to the hypothesis that a specific uptake route, that recognizes the peptide moiety of AGP, is operative in hepatocytes. To date, receptors for AGP have been proposed in hepatocytes, the human adrenal cortex, the human intestinal epithelial cell line, HepG2 cells, rodent testis, and cultured microvascular endothelium, [18][19][20][21] but all appear to recognize the glycan portion of AGP such as the lectin-like receptor and ASGPR. In addition, there is no experimental evidence for the existence of proteins that recognize the peptide moiety of AGP in the liver.…”

“…14 As mentioned in the introduction section, it has been proposed that a cell surface protein interacts with AGP in several cells, including hepatocytes, but, so far, all recognize the glycan chains of AGP such as ASGPR, [18][19][20][21] and there is no experimental evidence in support of the existence of In-AGP, and (c) western blotting analysis using anti-AGP antibody. A crude membrane fraction of mice hepatocytes was subjected to 2D SDS-PAGE and then transferred to a PVDF membrane.…”

Antisense Down-regulation of Lipocalin-interacting Membrane Receptor Expression Inhibits Cellular Internalization of Lipocalin-1 in Human NT2 Cells

“…There is increasing evidence that many lipocalins bind to specific cell receptors. Receptor binding has been demonstrated for ␣-1-microglobulin (25,26), glycodelin (27), insecticyanin (28), ␣-1-acid glycoprotein (29,30), ␤-lactoglobulin (31,32), and odorant-binding protein (33). Although this is still a controversial area, there is considerable evidence that retinol-binding protein (RBP) binds to its target cells via specific surface receptors (34,35).…”