Identification and Molecular Characterization of a Novel Member of the Siglec Family (SIGLEC9)

Abstract

Using the positional cloning approach, we have identified siglec-9 (HGMW-approved symbol SIGLEC9) a novel member of the sialic acid-binding Ig-like lectin (Siglec) family, which belongs to the immunoglobulin superfamily (IgSF). We characterized the genomic structure of this gene and determined its chromosomal localization, its homology to other members of the siglec family, and its tissue expression profile. The siglec-9 gene is composed of seven exons, with six intervening introns. The coding region consists of 1392 nucleotides and produces a 463-amino-acid protein. Furthermore, we have localized this gene to 19q13.4, 43.19 kb more telomeric than KLK14 (a member of the kallikrein gene family) through genomic sequencing data and restriction mapping with EcoRI. This novel siglec shows a high degree of homology to many members of the siglec family, including siglec-7 (80%), siglec-8 (72%), siglec-5 (65%), and CD33 (64%). This high degree of homology is also conserved in the extracellular Ig-like domains. Through RT-PCR, we have examined the expression of siglec-9 in a large number of tissues and have found relatively high-level expression in bone marrow, placenta, spleen, and fetal liver. Based on its homology to CD33, we speculate that this gene may also have some utility as a target for immunological antineoplastic therapy.