CD170 SIGLEC-5 (sialic-acid binding Ig-like lectin 5)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Monocyte
Neutrophil
Macrophage
Dendritic Cell
Leukocyte
Spleen
Myeloid Cell
Bone Marrow
140 / 140

Expression
CD170 is expressed on dendritic cells, macrophages activated during bacterial and viral infections, neutrophils and monocytic/myeloid lineage cells.  Expression is absent from leukemia cell lines representing early stages of myelomonocytic differenciation.  High levels are found in peripheral leukocytes, spleen, bone marrow and at lower levels in lymph node, lung, appendix, placenta, pancreas and thymus.  Aberrant expression of CD170 by CD34+ progenitor cells is often present in acute myeloid leukemias.

Structure
MOLECULAR FAMILY NAME: Belongs to the immunoglobulin gene superfamily.

CD170 is a single-pass type-1 551 aa glycoprotein.  It contains a signal peptide, an extracellular domain which contains 1 V-type N-terminal domain  and 3 C2-type domains which mediates binding to sialic acid residues, a transmembrane and a cytoplasmic domain which contains 2 ITIM-like motifs and 8 N-linked glycosylation sites.  CD170 is an adhesion molecule, a member of the Siglec family and highly similar to CD33 antigen-like proteins.  By comparison with equivaqlent motifs of CD33, the membrane proximal ITIM is likely to interact with both SHP-1 and SHP-2 tyrosine phosphatases, whereas the membrane distal ITIM may selectively interacts with SHP-1 only.

MOLECULAR MASS
Cell Type Unreduced Reduced
140 kDa

POST-TRANSCRIPTIONAL MODIFICATION

Alternative splicing yields 4 different isoforms.

POST-TRANSLATIONAL MODIFICATION: No information.


Ligands
LIGANDS AND MOLECULES ASSOCIATED WITH CD170

CD170 binds α2,3- and α2,6-linked sialic acid with equal avidity and glycophorin A on human erythrocytes.

Function
CD170 acts as an inhibitory receptor able to downregulate cell activation and is a adhesion molecule that medates sialic-acid dependent binding to cells.  It suppresses its own sialic cell activity in vitro.  Binding to terminal sialic acid residues are carried on as yet unidentified counter-receptors.  It may function as a pattern of self/non-self recognition receptor and mediate negative signals into the cell.  It contains 1 copy of a cytoplasmic motif that is referred to as immunoreceptor tyrosine-based inhibitor motif (ITIM).  This motif is involved in modulation of cellular responses.  The phosphorylated ITIM motif can bind the SH2 domain of several SH2-containing phosphatases.

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD170 IN INTACT ANIMAL

Selective binding of CD170 to sialic acids on Neisseria meningitidis has been shown in vitro to enhance bacterial phagocytosis by macrophages implying a role for CD170 in host defences.


Comments
MOLECULAR INTERACTION -
PROTEIN AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD170: No information.

SUBSTRATES: No information

ENZYMES WHICH MODIFY CD170: No information.
 

Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 8778O15389
Antibodies

Revised June 25, 2008


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