CD242 ICAM-4 (intracellular adhesion molecule 4), LW (Landsteiner-Wiener blood group)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Lineage Restricted Molecule
Type 1 glycoprotein
Erythrocyte
Red Cell
42 / 42

Expression
CD242 is expressed as part of the Rh membrane complex.  The antigens are relatively poorly expressed when the CD240D (RhD) polypeptide is absent as in the RhD-negative phenotype.  CD242 seems to be erythroid specific although there are conflicting results on the reactivity with a subset of lymphocytes.  Expression is on erythrocytes and red blood cells.

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

CD242 is a single-pass type-1 249 aa glycoprotein.  It contains a 218 aa extracellular domain which contains 2 Ig-like C2-type domains and has 4 potential N-linked glycosylation sites, a 21 aa transmembrane domain and a 10 aa cytoplasmic domain which has a shared similarity with the ICAM protein family which is a relatively low abundance membrane protein.  CD242 binds to the leukocyte adhesion LFA-1 protein, (CD11a/CD18).  CD242 is a carrier of the Landsteiner Wiener (LW) blood group system.

MOLECULAR MASS
Cell Type Unreduced Reduced
37-43 kDa


POST-TRANSCRIPTIONAL MODIFICATION

CD242 consists of 3 exons and alternative splicing yields 2 transcript variants.

POST-TRANSLATIONAL MODIFICATION
 
CD242 is N- and O-glycosylated.

Ligands
LIGANDS AND MOLECULES ASSOCIATED WITH CD242

CD242 binds CD11a/CD18, CD11b/CD18, β1 and β5 integrins, platelets fibrinogen receptor and endothelial cell vitronectin receptor.

Function
CD242 is a member of the intracellular adhesion molecule (ICAM) family and is a carrier of the LW blood group.  It is an adhesion molecule that plays a role in the interaction of macrophages, neutrophils, platelets and may be involved in differentiation of erythroblasts.  Expression is relatively early during erythropoiesis which suggests that on erythroblasts it may interact with VLA-4 on macrophages to stabilize erythroblastic islands in normal bone marrow.  Recombinant CD242 chimeric proteins binds LFA-1 and Mac-1 (CD11b/CD18) binds to the 1st Ig-like domain whereas the Mac-1 binding site encompasses both the 1st and 2nd Ig-like domains.  CD242 binds the integrin very late antigen-4 (VLA-4, a4b1) and aV-containing integrins.  CD242 may be involved in red cell senescence and splenic macrophages which could remove senescent red cells through the interaction of b2 integrins with CD242. 
 
BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD242 IN INTACT ANIMAL

Levels of CD242 expression on sickle red cells are higher than on normal red cells so that CD242 molecules may contribute to adhesion to endothelium and potentiate episodes of vaso-occlusive events associated with episodes of acute pain in sickle cell disease.  Rare LW null individuals have been described but this does not lead to clinical syndrome or red cell dysfunction.  CD242 antigens may be depressed in pregnancy and some malignancies.

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD242: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD242: No information.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 3386Q14773
Antibodies

Revised June 25, 2008


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