Characterization of a Novel Member of the Macrophage Mannose Receptor Type C Lectin Family*

Abstract

The recognition of a diversity of carbohydrates by the various calcium dependent (type C) lectin family members has been shown to be critical for a variety of processes ranging from cell adhesion to antigen presentation. Examination of the expressed sequence tag (EST) data base for novel type C lectins using E-selectin as a probe resulted in the identification of a distantly related short polypeptide sequence containing many of the conserved residues found in these carbohydrate-binding proteins. Cloning of the full-length murine cDNA containing this region revealed that this protein is a novel member of the family that includes the macrophage mannose, the phospholipase A₂, and the DEC 205 receptors, with a cysteine-rich domain, a fibronectin type 2 domain, eight type C lectin domains, a transmembrane domain, and a short cytoplasmic carboxyl terminus. Genomic Southern analysis suggests that this is a conserved protein, and examination of a human homologue revealed a high degree of sequence homology with the murine form. Northern blot analysis revealed expression of a large transcript in a number of different human and murine tissues and tumor cells and an alternatively spliced smaller transcript with a divergent 5′ sequence was expressed specifically in the human fetal liver. Analysis of the genomic structure revealed that the gene encoding this lectin was interrupted by a large number of introns, and the intron structure was similar to the macrophage mannose receptor gene. Finally, in situ hybridization analysis demonstrated that the transcript encoding this lectin was found in a number of highly endothelialized sites as well as in chondrocytes in cartilaginous regions of the embryo.