Galectin-1 binds mucin in human trophoblast

Abstract

Mucins are multifunctional highly glycosylated proteins expressed by the female reproductive tract. Differential expression of MUC1 and MUC15 has been shown in trophoblast. This study was undertaken to establish the distribution of mucin(s) in cytotrophoblast cell cultures using anti-bovine submaxillary mucin (BSM) and to investigate the possibility of MUC1/mucin(s) being a binding partner of trophoblast galectin-1. MUC1 is demonstrated here using immunocytochemistry on isolated cytotrophoblast and the HTR-8/SVneo extravillous trophoblast cell line but detection of additional trophoblast mucins cannot be excluded. Western blot analysis showed similar bands ranging from 30 to >200 kDa with anti-BSM and the well-known mucin antibodies HMFG1 and B72.3. Immunocytochemistry and cell-based ELISA data were found to support that all of the antibodies used are reactive with BSM, suggesting the presence of shared epitopes between BSM and trophoblast mucin(s). Binding of galectin-1 to trophoblast MUC1/mucin(s) was analyzed using a solid-phase assay and co-immunoprecipitation. Recombinant galectin-1 binding to isolated trophoblast mucin in solid-phase assay was sensitive to lactose, a carbohydrate inhibitor of galectin binding. In whole HTR-8/SVneo lysates, ~200 kDa mucin was detected in galectin-1 immunoprecipitates, while endogenous galectin-1 was present in BSM-immunoprecipitates. Furthermore, double fluorescence immunocytochemistry showed overlap of galectin-1 and trophoblast mucins at the plasma membrane of HTR-8/SVneo cells. These results suggest that trophoblast mucin(s) could act as binding partners of galectin-1, in a carbohydrate-dependent manner.

Interaction of extravillous trophoblast galectin-1 and mucin(s)—Is there a functional relevance?

“…37 Expression of MUC1 has also been observed in isolated trophoblast cells, as well as in JAr and BeWo choriocarcinoma cells. 2,37 The MUC1 staining pattern is consistent with plasma membrane/cytoplasmic localization in rhesus monkey trophoblast cells and in freshly isolated trophoblast. 2,28 Strong membrane staining was obtained using either antibodies specific for the cytoplasmic MUC1 domain or for carbohydrate MUC1 epitopes.…”

“…2,37 The MUC1 staining pattern is consistent with plasma membrane/cytoplasmic localization in rhesus monkey trophoblast cells and in freshly isolated trophoblast. 2,28 Strong membrane staining was obtained using either antibodies specific for the cytoplasmic MUC1 domain or for carbohydrate MUC1 epitopes. 2 Kumar et al recently detected the MUC1 extracellular domain in nuclear speckles and in spliceosomes in rhesus monkey trophoblast cells using 3 different antibodies specific for MUC1 VNTR.…”

“…In contrast, using polyclonal anti-bovine submaxillar mucin antibodies (anti-BSM) we recently demonstrated moderate to strong MUC1/mucin(s) staining of first trimester placental villi ( Fig. 1), 2 while Jeschke et al reported strong MUC1 expression in human first and second trimester placenta. 37 Expression of MUC1 has also been observed in isolated trophoblast cells, as well as in JAr and BeWo choriocarcinoma cells.…”

“…2,28 Strong membrane staining was obtained using either antibodies specific for the cytoplasmic MUC1 domain or for carbohydrate MUC1 epitopes. 2 Kumar et al recently detected the MUC1 extracellular domain in nuclear speckles and in spliceosomes in rhesus monkey trophoblast cells using 3 different antibodies specific for MUC1 VNTR. 39 Nucleus associated staining was also seen in JAr choriocarcinoma cells and in MCF7 breast cancer cells.…”

“…1 Expression of mucins has also been recorded on human trophoblast cells of fetal origin, from which they can be coisolated with the endogenous lectin, gal-1. 2 On the other hand, gal-1 has been shown to influence adhesive, migratory and invasive behavior of trophoblast cells in vitro, 3 through interactions with glycoconjugates. This review is aimed at deliberating the possibility that mucins, as heavily glycosylated proteins, might be among the functionally relevant galectin ligands in human trophoblast.…”