Galectin-4 binds to sulfated glycosphingolipids and CEA in patches on the
Galectin-4, a member of the galectin family, is expressed in the epithelium of the alimentary tract. It has two tandemly-repeated carbohydrate recognition domains (CRDs), and specifically binds to a SO3-3Gal1-3GalNAc pyranoside with high affinity (Ideo et al., Glycobiology 12, 199-208, 2002). In this study, we found that galectin-4 binds to glycosphingolipids carrying 3-O-sulfated Gal residues, such as SB1a, SM3, SM4s, SB2, SM2a, and GM1, but not to glycosphingolipids with 3-O-sialylated Gal, such as sLc4Cer, snLc4Cer, GM3, GM2, and GM4, using both an enzyme-linked immunosorbent assay and a surface plasmon resonance assay. A confocal immunocytochemical assay showed that galectin-4 was colocalized with SB1a, GM1, and carcinoembryonic antigen (CEA) in the patches on the cell surface of human colon adenocarcinoma CCK-81 and LS174T cells. This localization was distinct from caveolin/VIP21 localization. Furthermore, immobilized galectin-4 promoted adhesion of CCK-81 cells through the sulfated glycosphingolipid, SB1a. CEA also bound to galectin-4 with KD value of 2 x 10-8 M by SPR, and co-immunoprecipitated with galectin-4 in LS174T cell lysates. These findings suggest that SB1a and CEA in the patches on the cell surface of human colon adenocarcinoma cells could be biological important ligands for galectin-4.
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