CD24 HSA (heat stable antigen), BA-1
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
GPI anchor
B Cell
Leukemia cell
Epithelial Cell
Lung
Thymocyte
Pancreas
Ovary
Prostate
Granulocyte
Breast
Monocyte
Langerhans Cell
Erythrocyte
35 / 35
70 / 70

Expression
CD24 is expressed throughout B cell lineage development, on mature granulocytes, non-T cell acute lymphoblastic leukemia (ALL) and on a variety of epithelial cell types but not on downregulated plasma cells.  The antigen is also present on 2% of thymocytes and normal epithelium.  In humans a high level of expression is found in pancreatic, ovarian, breast, prostate and small cell lung cancer.  Mouse CD24 is present at all stages of B cell development and on most thymocytes.  The absence of expression from mature T cells is closely associated with their maturation from CD4+CD8+CD24+ thymocytes to either CD4+CD8-CD24- or CD4-CD8+CD24- T cells.  The antigen is also expressed on mouse monocytes, granulocytes, Langerhans cells and erythrocytes.  Rat CD24 expression has been detected, using in situ hybridization, in the developing central nervous system and in the epithelium of developing nonneural tissues.
 

Structure
MOLECULAR FAMILY NAME:  Belongs to the sialoglycoprotein family.

CD24 is a single-pass GPI-anchored 27 aa glycoprotein.  It contains an extracellular domain which contains a 48% content of Ser and Thr residues that are potential O-linked glycosylation sites.  Extensive N- and O-linked glyclosylation gives rise to molecules of varying molecular weight and the extent of glycosylation is cell-type dependent.  Three different CD24 mAbs recognize epitopes that are of a carbohydrate nature and are dependent on sialic acid.  The precursor forms of mouse and rat CD24 show a 62.5% and 65% aa identity to the human sequence.  However, the mature form of the molecule shows only 33% in the mouse/human and 42% in the rat/human sequence identity.  The CD24a gene has a single intron and encodes the CD24 mRNA.  Both the CD24b and CD24c genes lack the intron, are not expressed in adult mouse tissues and may have arisen by retropositioning.

MOLECULAR MASS
Cell Type Unreduced Reduced
B-lymphocytes 35-70 kDa

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION

CD24 shows a displacement of C terminal 19 aa-23 aa by GPI-anchor, an extensive N-linked glycosylation and an extensive O-linked glycosylation.

Ligands
CD24 has been reported to be a P-selectin ligand (see CD62P).

LIGANDS AND MOLECULES ASSOCIATED WITH CD24
Molecule Comment
P-selectin In mouse and on human carcinomas

Homotypic binding has been reported for murine CD24.  Low CD24 expression on B memory cells may represent a separate lineage of B cells.  While this issue is quite controversial, the point that memory B cells in mice are low in CD24 has been replicated by several labs. 




Function
CD24 is involved in regulating the binding capacity of CD49d/CD29 (VLA-4).  It may play a role in B-cell differentiation as pre-treatment of B cells with mAb blocks this process and knockout mice have mildely affected B cell maturation.  The function is unknown for human CD24 but crosslinking of murine CD24 can induce a rapid rise in calcium levels and on early murine B cells can trigger apoptosis.  Murine CD24 may serve as a co-stimulatory molecule for CD4+ T cells and affect B cell adhesion directly as an adhesion molecule or by modifying the specificity and/or avidity of other adhesive interactions.  CD62P (P-selectin ligand) binds a carbohydrate of CD24.  CD24 has a signal transduction role in granulocytes as some antibodies (VIBE3) induce an oxidative burst response and costimulate B cells to proliferate with PMA.

BIOCHEMICAL ACTIVITY

Crosslinking of CD24 can induce increased intracellular Ca+2 in mature B lymphocytes.

DISEASE RELEVANCE AND FUNCTION OF CD24 IN INTACT ANIMAL

CD24 is a marker in staging B cell development.  It is a diagnostic and prognostic marker in acute myelogenous leukemia B-cell malignancies and Sezary syndrome.  CD24 presence correlates with aggressive progression of breast, ovarian and is expressed at high levels in small lung carcinomas. The CD62 P-selectin ligand on human carcinomas are involved in carcinoma binding to platelets.  CD24 may play a role in memory cell formation and is thought to be involved in the adhesion and spread of metastatic tumors.

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD24: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD24: No information.

ADDITIONAL INSIGHTS

Multiple CD24 genes have been identified and mapped in both human and mouse.

Recent studies in the murine model provide intriguing evidence of a role for murine CD24 in early lymphoid development and provide further impetus to determine whether CD24 shares parallel functions in human B lymphocyte biology.

Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 934P25063
MouseP24807M58661
RatQ07490Z11663
Antibodies
ML5   View Reactivity

Revised June 25, 2008


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