CD24

Heat-stable antigen

Gene: the gene from which the CD24 mRNA is transcribed appears to map to 6q21 (Hough M.R. et al., 1994).
mRNA: size: kb
Protein: CD24 consists of a small protein core comprising 27 amino acids which is extensively glycosylated and is bound to the cell membrane via a glycosyl phosphatidylinositol (GPI) anchor. Nearly half of the amino acids in CD24 are composed of Ser and Thr residues which are potential sites for O-linked glycans indicating that it is a mucin-type protein. CD24 is glycosylated in a cell-type dependent fashion. Several reports have shown that CD24 can be expressed on several solid (non-hematopoietic) tumors such as small cell lung carcinoma, neuroblastoma, rhabdomyosarcoma, and renal cell carcinoma (Fogel M. et al., 1999).
CD24 can act as a specific ligand for P-selectin. P-selectin (CD62P) plays an important role in the initial rolling of leukocytes on activated endothelia as well as in the binding of leukocytes to activated platelets. The main ligand for P-selectin on leukocytes appears to be the cell surface mucin P-selectin glycoprotein ligand-1 (PSGL-1). The CD24/P-selectin binding pathway could be important in the dissemination of tumor cells by facilitating the interaction with platelets or endothelial cells.

Cell lines:
- Using the KS breast cancer cell (BCC) line, which is negative for PSGL-1 (see above) but positive for CD24, it was demonstrated that CD24 could substitute for PSGL-1 and support the binding of tumor cells to activated platelets as well as the rolling of these cells on P-selectin. Therefore, on BCC, CD24 could be an important ligand for P-selectin which could facilitate their binding to platelets or endothelia and thereby favour the metastasis of these tumors (Aigner S. et al., 1998).

- CD24 was detected in KS, AR, MCF-7, and SK-BR-3, but not in MDA-MB-435 and -436 BCC lines (Fogel M. et al., 1999).

- CD24 mRNA was poorly detected in MCF-10 cells, a benign human breast epithelial cell line. In MCF-7 BCC, CD24 mRNA expression was found to be upregulated upon amino acid starvation (Liu W. and Vadgama J.V., 2000).

Tumors:
- On frozen sections of breast carcinomas, CD24 overexpression was found in all 31 ductal carcinomas examined. In low grade intraductal carcinomas, CD24 was found mainly along the apical borders and weakly throughout the cells. High grade intraductal carcinoma stained strongly in the cytoplasm and along the apical borders whereas infiltrating duct carcinoma revealed a strong diffuse cytoplasmic staining (Fogel M. et al., 1999).

Aigner S. et al. (1998) CD24 mediates rolling of breast carcinoma cells on P-selectin. FASEB J. 12, 1241-1251.
Fogel M. et al. (1999) CD24 is a marker for human breast carcinoma. Cancer Lett. 143, 87-94.
Hough M.R. et al. (1994) Mapping of CD24 and homologous sequences to multiple chromosomal loci. Genomics 22, 154-161.
Huang L.R. and Hsu H.C. (1995) Cloning and expression od CD24 gene in human hepatocellular carcinoma: a potential early tumor marker gene correlates with p53 mutation and tumor differentiation. Cancer Res. 55, 4717-4721.
Liu W. and Vadgama J.V. (2000) Identification and characterization of amino acid starvation-induced CD24 gene in MCF-7 human breast cancer cells. Int. J. Oncol. 16, 1049-1054.
Pass M. et al. (1998) The 5'-flanking region of human CD24 gene has cell-type-specific promoter activity in small-cell lung cancer. Int. J. Cancer 78, 496-502.

Under construction