INTRINSIC SIGNALING FUNCTION OF APP AS A NOVEL TARGET OF 3 V642 MUTATIONS LINKED TO FAMILIAL ALZHEIMERS-DISEASE

APP(695) is a transmembrane precursor of A beta amyloid. In familial A lzheimer's disease (FAD), three mutations V642Y/F/G were discovered in APP(695), which has been suggested by multiple studies to be a cell s urface signaling receptor. We previously reported that normal APP(695) encodes a potential G(o)-linked receptor with ligand-regulated functi on and that expression of the three FAD mutants (FAD-APPs), not normal APP, induces cellular outputs by G(o)-dependent mechanisms. This sugg ests that FAD-APPs are constitutively active G(o)-linked receptors. He re, we provide direct evidence for this notion. Reconstitution of eith er recombinant FAD-APP with G(o) into vesicles induced activation of G (o), which was inhibitable by pertussis toxin, sensitive to Mg2+ and p roportional in quantity to the reconstituted amounts of FAD-APP. Consi stent with the dominant inheritance of this type of FAD, this function was dominant over normal APP, because little activation was observed in APP(695)-G(o) vesicles. Experiments with antibody competition and s equence deletion indicated that His657-Lys676 of FAD-APP, which has be en specified as the ligand-dependent G(o)-coupling domain of normal AP P, was responsible for this constitutive activation, confirming that t he three FAD-APPs are mutationally activated APP(695). This study iden tifies the intrinsic signaling function of APP to be a novel target of hereditary Alzheiner's disease mutations, providing an in vitro syste m for the screening of potential FAD inhibitors.