THE CHONDROITIN SULFATE ATTACHMENT SITE OF APPICAN IS FORMED BY SPLICING OUT EXON-15 OF THE AMYLOID PRECURSOR GENE

Appicans are secreted and cell-associated chondroitin sulfate proteogl ycans containing Alzheimer amyloid precursor (APP) as their core prote in, Appicans are found in brain tissue, and in cell cultures their exp ression depends on both cell type and growth conditions. Here we repor t that the core protein of appicans derives from an APP mRNA lacking e xon 15. Splicing out of this exon creates a new consensus sequence for the attachment of a chondroitin sulfate chain in the resulting APP pr oduct. Transfection of C6 glioma or 293 kidney fibroblast cells with A PP cDNAs containing exon 15 produced no appican, while transfection wi th an APP cDNA lacking this exon induced high levels of appican produc tion. Polymerase chain reactions indicated that appican-producing cell s contained an APP mRNA species without exon 15, whereas cells without this mRNA produced no appican. Site directed mutagenesis combined wit h immunoreactivity experiments showed that the chondroitin sulfate cha in is attached to a serine residue 16 amino acids upstream of the amin o terminus of the A beta sequence of APP. The attachment of a glycosam inoglycan chain close to the A beta sequence of APP may affect the pro teolytic processing of APP and production of A beta. The proteoglycan nature of APP suggests that addition of the chondroitin sulfate glycos aminoglycan is important for the implementation of the biological func tion of these proteins.