BIOSYNTHESIS AND REGULATION OF EXPRESSION OF THE HNK-1 EPITOPE ON MYELIN-ASSOCIATED GLYCOPROTEIN IN A TRANSFECTED CELL MODEL SYSTEM

The HNK-1 antibody recognizes a carbohydrate epitope expressed by many cell adhesion molecules in the nervous system that has been proposed to be an important adhesive determinant, This epitope is particularly prominent on the myelin-associated glycoprotein (MAG) and is related t o the antigenic target in an autoimmune mediated demyelinating neuropa thy. Elucidation of the mechanisms underlying the biosynthesis and reg ulation of expression of the HNK-1 epitope is therefore likely to have important functional and clinical implications. In order to investiga te its biosynthesis and the regulation of its expression, we have expr essed both human and rat MAG in several different cell lines by retrov iral infection, These studies indicate that the cellular milieu determ ines whether the HNK-1 epitope is expressed on the MAG polypeptide and provide an explanation for the significant variation in HNK-1 levels that has been noted in different species, Using a transfected human ne uroblastoma line, we have determined that this epitope is present on t he fourth and/or fifth immunoglobulin-like domain of rat MAG and that it is added intracellularly, probably in the trans Golgi, Finally we h ave found that expression of the HNK-1 epitope is increased by activat ion of different second messenger systems, providing direct evidence t hat its expression can be regulated independently from that of the MAG polypeptide, (C) 1995 Wiley-Liss, Inc.