SUBCELLULAR-LOCALIZATION OF THE ALZHEIMERS-DISEASE AMYLOID PRECURSOR PROTEIN AND DERIVED POLYPEPTIDES EXPRESSED IN A RECOMBINANT YEAST SYSTEM

Different isoforms and derived polypeptides of the Alzheimer's disease amyloid protein precursor (A beta PP) have been expressed in the yeas t Pichia pastoris. The expression characteristics of the different A b eta PP polypeptides were studied by post-embedding immunogold electron microscopy with various A beta PP antibodies. The site of intracellul ar expression could be readily identified with specific antibodies. Fu ll length A beta PP was expressed in association with the nuclear memb rane and the endoplasmic reticulum. Secretory derivatives of A beta PP were localized in membrane-bound secretory vesicles. A construct enco ding two copies of beta A4[1-42] linked head-to-tail (beta A4duplex) a ccumulated as irregular dense cytoplasmic and intranuclear inclusions which reacted with all beta A4 antibodies tested A beta A4-C-terminal construct accumulated into membranous structures in the cytoplasm and nucleus and reacted with most antibodies to beta A4 and the cytoplasmi c domain of A beta PP. The two shorter constructs containing the beta A4 sequence formed similar intranuclear aggregates to those reported f or intranuclear inclusions of polyglutamine peptides from huntingtin ( in Huntington's disease) and ataxin protein fragments (in spinocerebel lar ataxia). This is of interest because intracellular aggregation of the polyglutamine and beta A4 peptides may affect cells by similar tox ic mechanisms. These studies demonstrate clear differences in the expr ession properties of different A beta PP polypeptides.