A Novel C-Type Lectin Receptor DCL-1 (CD302) Is a Potential Endocytic Receptor for Tumor Antigen Loading into Antigen Presenting Cells.

Abstract

DCL-1 (CD302) is a novel C-type lectin receptor, discovered as a genetic fusion partner of DEC-205 (CD205), a C-type lectin that delivers antigen from the surface into DC antigen processing pathway (J. Biol. Chem. 2003. 278:34035). We have now examined the molecular nature and expression of DCL-1. DCL-1 contains an external single C-type lectin-like domain followed by a transmembrane and cytoplasmic domain with putative signaling and endocytic motifs. The DCL-1 gene, consisting of 6 exons, was mapped to chromosome 2q24, approximately 5 kb downstream of the DEC-205 gene. Human DCL-1 has 76% protein identity to the mouse ortholog, suggesting its highly conserved function. Northern blot analysis showed that the 4.2 kb DCL-1 mRNA was present in myeloid cell lines, but not in T and B cell lines. Specialized phagocytic cells (i.e. monocytes, macrophages, granulocytes), monocyte-derived DC (MoDC) and blood DC (BDC) expressed DCL-1 mRNA, detected by RT-PCR. Immunoprecipitation/ Western blot (IP/WB) analysis using FLAG-tagged DCL-1 transfectants detected a broad band (modal size 35 kDa), which became a single 26 kDa band after N-glycosidase F digestion, indicating that DCL-1 is N-glycosylated. Flow cytometry studies with DCL-1 mAb (MMRI-20, developed in house) detected moderate levels of DCL-1 expression on granulocytes, monocytes, macrophages, MoDC and BDC, but not on lymphoid cells. Concomitant WB/IP analysis using the DCL-1 mAb detected 26 and 33 kDa doublets in monocytes, macrophages and MoDC. DCL-1 transfectants, macrophages, MoDC and BDC endocytosed cell surface DCL-1 after crosslinking with the DCL-1 mAb. DCL-1-Ig fusion protein bound to GlcNAc- and Man-conjugated beads, but not to GalNAc-, Fuc- and mannan-conjugated beads in a calcium-dependent manner. Thus, DCL-1 is expressed by phagocytes and DC, behaves as a C-type lectin, and is likely to be involved in endocytosis/phagocytosis of microbes. We are exploiting DCL-1 as a potential antigen-loading receptor for DC tumor immunotherapy.