EXPRESSION OF THE AMYLOID PRECURSOR PROTEIN OF ALZHEIMERS-DISEASE ON THE SURFACE OF TRANSFECTED HELA-CELLS

The principal component of the amyloid which accumulates in Alzheimer' s Disease brain is a 4-kDa beta A4 fragment of the amyloid precursor p rotein (APP). Although APP has the structural features of an integral transmembrane receptor, there has been limited evidence for expression of APP at the plasma membrane. The function of APP and related molecu les is unknown. Using rabbit antisera to purified human brain APP, sur face labeling of APP is demonstrable in HeLa cells transfected with th e APP(695) isoform. indirect immunofluorescence indicates the presence of APP at the surface of unfixed or aldehyde-fixed cells; preembeddin g immunoelectron microscopy using 5- or 1-nm gold particles and silver enhancement confirms plasma membrane labeling as well as labeling wit hin intracellular membrane vesicles. Immunolabeling of unfixed cells a t 4 degrees C followed by incubation at 37 degrees C shows APP within endocytic vesicles. Transfected HeLa cells with prominent surface APP were larger with more extensive microvilli than nonimmunoreactive HeLa cells. This is consistent with the postulated role of APP as a mediat or of cell surface adhesion and membrane-matrix stabilization. (C) Aca demic Press, Inc.