CD24, A GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED MOLECULE, IS TRANSIENTLY EXPRESSED DURING THE DEVELOPMENT OF HUMAN CENTRAL-NERVOUS-SYSTEM ANDIS A MARKER OF HUMAN NEURAL CELL LINEAGE TUMORS

CD24 is a glycoprotein with an unusual structure consisting of a small protein core extensively glycosylated and linked to the outer surface of the plasma membrane by a glycosylphosphatidylinositol (GPI) lipid anchor. Its murine homolog mCD24 is transiently expressed during the d evelopment and differentiation of the hematopoietic and neural cell li neages. We have searched for the expression of CD24 in the developing and in the mature human brain as well as in a wide range of neuroectod ermal tumors. Neuroblastomas, a subgroup of tumors able to maturate fr om undifferentiated features towards mature ganglioneuromas, were more extensively studied. Immunohistochemical studies demonstrated that CD 24 is transiently expressed by neurons during human brain development. In neuroectodermal tumors, CD24 is a marker of neuronal tumors. Furth ermore, in neuroblastomas, CD24 expression decreases as tumors differe ntiate. In non-neuronal neuroectodermal tumors, CD24 expression is mos tly absent. When present, it correlates with the emergence of anaplast ic histological features. Reverse transcriptase-polymerase chain react ion (RT-PCR) demonstrated the presence of an unique transcript identic al in both hematopoietic, developing and tumoral nervous tissue. RT-PC R and in situ hydridization techniques showed that CD24 expression is transcriptionally regulated. Interestingly, Western blot analysis demo nstrated differential CD24 isoforms according to the tissue (hematopoi etic versus nervous), the differentiation status, and the origin of ne uroblastomas likely reflecting variations in the extent of glycosylati on. This indicates an additional level of regulation of CD24 involving post-translational modifications.