The amyloid precursor protein interacts with G(o) heterotrimeric protein within a cell compartment specialized in signal transduction

The function of the beta-amyloid protein precursor (beta APP), a transmembr ane molecule involved in Alzheimer pathologies, is poorly understood. We re cently reported the presence of a fraction of beta APP in cholesterol and s phingoglycolipid-enriched microdomains (CSEM), a caveolae-like compartment specialized in signal transduction. To investigate whether beta APP actuall y interferes with cell signaling, we reexamined the interaction between bet a APP and G(o) GTPase. In strong contrast with results obtained with recons tituted phospholipid vesicles (Okamoto et al., 1995), we find that incubati ng total neuronal membranes with 22C11, an antibody that recognizes an N-te rminal beta APP epitope, reduces high-affinity G(o) GTPase activity. This i nhibition is specific of G(alpha o) and is reproduced, in the absence of 22 C11, by the addition of the beta APP C-terminal domain but not by two disti nct mutated beta APP C-terminal domains that do not bind G(alpha o). This i nhibition of G(alpha o) GTPase activity by either 22C11 or wild-type beta A PP cytoplasmic domain suggests that intracellular interactions between beta APP and G(alpha o) could be regulated by extracellular signals. To verify whether this interaction is preserved in CSEM, we first used biochemical, i mmunocytochemical, and ultrastructural techniques to unambiguously confirm the colocalization of G(alpha o) and beta APP in CSEM. We show that inhibit ion of basal G(alpha o) GTPase activity also occurs within CSEM and correla tes with the coimmunoprecipitation of G(alpha o) and beta APP. The regulati on of G(alpha o) GTPase activity by beta APP in a compartment specialized i n signaling may have important consequences for our understanding of the ph ysiopathological functions of beta APP.