THE ROLE OF GLYCOSYLATION IN SYNTHESIS AND SECRETION OF BETA-AMYLOID PRECURSOR PROTEIN BY CHINESE-HAMSTER OVARY CELLS

Alzheimer's disease is characterized by P-amyloid deposition in the br ain. This peptide is derived by proteolytic cleavage from P-amyloid pr ecursor protein (APP), a highly glycosylated membrane glycoprotein con taining both N- and O-glycans. There are three major isoforms of APP, which are derived by alternative splicing and contain 695, 751, or 770 amino acids. Since glycosylation can affect many properties of glycop roteins, we studied the role of N- and O-glycosylation in the synthesi s and secretion of APP. APP expression was examined in untransfected w ild-type, Leed mutant, and ldlD mutant Chinese hamster ovary (CHO) cel ls and in analogous clonal cell lines expressing either the transfecte d human wild-type 695-amino-acid form of APP (APP695-WT) or a form mut ated to delete N-glycosylation sites (APP695-XX). These studies showed that maturation of APP in CHO cells is accompanied by the addition of multiple short O-glycans with the following structures: Neu5Ac alpha 2-3Gal beta 1-3GalNAc, Neu5Ac alpha 2-3Gal beta 1-3[Neu5Ac alpha 2-6]G alNAc, and GalNAc. Using glycosylation-defective mutant CHO cell lines and soluble inhibitors of glycosylation, we found that APP secretion was diminished when core N-glycosylation or N-glycan processing was bl ocked, Surprisingly, similar results were found when synthesis and sec retion of either APP695-WT or APP695-XX were analyzed. These results i ndicate that defective N-glycosylation of other cellular proteins, but not of APP itself, affects the metabolism of APP, Interestingly, inhi bition of O-glycosylation did not affect the biosynthesis or secretion of APP, The results of these studies may shed some light on the role that protein glycosylation may play in the pathogenesis of Alzheimer's disease. (C) 1996 Academic Press,Inc.