SRCL/CL-P1 recognizes GalNAc and a carcinoma-associated antigen, Tn antigen

SRCL /CL-P1 was recently identified as a scavenger receptor with a C-type lectin domain, which was expressed in vascular endothelial cells and could bind to Gram-positive and Gram-negative bacteria, yeast and oxidized LDL. We found that SRCL was expressed in some but not all nurse-like cells examined. Furthermore, to characterize the C-type lectin domain of SRCL, the secreted form of the C-type lectin domain (LEC-AP) of SRCL, which was fused to the signal sequence of IgG and Alkaline Phosphatase, was expressed in 293/EBNA-1 cells and the culture medium was used for the in vitro binding assay. LEC-AP specifically bound to GalNAc-conjugated gel in a Ca(2+)-dependent manner, and this binding was inhibited by free GalNAc, L-, D-fucose, D-galactose, lactose, and especially T antigen and Tn antigen. Furthermore, we examined whether or not SRCL could take up saccharide-conjugated particles. 293/EBNA-1 cells stably expressing SRCL were found to take up GalNAc but not mannose-conjugated particles on confocal microscopy. The binding of GalNAc-conjugated particles to these cells was quantitatively measured by comparing the x-means of individual cell populations. An approximately 2.1-fold increase in immunofluorescence intensity was observed for the SRCL transfectants compared to control vector transfectants. Our results provide a basis for understanding the scavenger function of SRCL as to carbohydrate-containing ligands.