Abstract
Galectin-3 is a lectin important in animal development and regulatory processes and is found selectively localized at the implantation site of the mouse embryo. To better understand the role of galectin-3 at the maternal-fetal interface, a binding partner was isolated and characterized. Homogenates of uteroplacental tissue were incubated with immobilized recombinant galectin-3, and specifically bound proteins were eluted using lactose. The principal protein, p400, had an M(r) of 400,000 in SDS-PAGE. Physical properties of p400 and amino acid sequences of seven tryptic peptides were similar to cubilin from rats, humans, and dogs, identifying p400 as the murine ortholog of cubilin. This was further supported by the tissue distribution observed only in yolk sac, kidney, and ileum with monospecific antiserum for p400. Cubilin occurred in yolk sac epithelium throughout pregnancy, but galectin-3 was there only during the last week. Unexpectedly, cubilin was found only in perforin-containing granules of uterine natural killer (uNK) cells, although galectin-3 occurred throughout the cell cytoplasm. In situ hybridization revealed cubilin mRNA in yolk sac epithelium but not uNK cells, implying that yolk sac-derived cubilin is endocytosed by uNK cells via galectin-3. This is consistent with cubilin being an endogenous partner of galectin-3 at the maternal-fetal interface and suggests an important role for cubilin in uNK cell function.
Highlights
Galectin-31 is one of at least 10 members of a lectin family, which share a conserved carbohydrate recognition domain and which exert their varied biological effects through interaction with complementary -galactoside ligands of glycoprotein or glycolipid “counterreceptors.” Since galectins are divalent and are able to form multivalent aggregates, they can cross-link counterreceptors, effecting cell-cell, cell-matrix, or matrix-matrix interactions, possibly initiating signal
Isolation of several membrane or matrix counterreceptors by affinity chromatography has revealed that galectins are linked to a variety of important processes including neoplastic transformation, cell adhesion, tumor invasiveness and metastasis, cellular proliferation, and localized immunomodulation. gal-3 and its mRNA are expressed in trophoblast cells of placenta as well as in the granular uterine natural killer (uNK) cells of the metrial gland and decidualized endometrium of the murine implantation site [2,3,4]
To determine if p400 is present in uNK cells associated with artificially stimulated deciduomata, which do not have an adjacent yolk sac, deciduomata sections were probed with anti-perforin and anti-p400
Summary
Galectin-3 (gal-3)1 is one of at least 10 members of a lectin family, which share a conserved carbohydrate recognition domain and which exert their varied biological effects through interaction with complementary -galactoside ligands of glycoprotein or glycolipid “counterreceptors.” Since galectins are divalent and are able to form multivalent aggregates, they can cross-link counterreceptors, effecting cell-cell, cell-matrix, or matrix-matrix interactions, possibly initiating signal. The specificity of anti-p400 was examined as follows: gal-3-binding proteins and placentalfetal membrane extracts were subjected to PAGE, blotted to nitrocellulose, and probed with anti-p400 (Fig. 3); an immunoreactive band (lane 1) extrapolating to about Mr 400,000 is found, with a slower moving band extrapolating to about Mr 800,000.
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