The Amyloid Precursor Protein Interacts with GoHeterotrimeric Protein within a Cell Compartment Specialized in Signal Transduction

Abstract

The function of the β-amyloid protein precursor (βAPP), a transmembrane molecule involved in Alzheimer pathologies, is poorly understood. We recently reported the presence of a fraction of βAPP in cholesterol and sphingoglycolipid-enriched microdomains (CSEM), a caveolae-like compartment specialized in signal transduction. To investigate whether βAPP actually interferes with cell signaling, we reexamined the interaction between βAPP and G_oGTPase. In strong contrast with results obtained with reconstituted phospholipid vesicles (Okamoto et al., 1995), we find that incubating total neuronal membranes with 22C11, an antibody that recognizes an N-terminal βAPP epitope, reduces high-affinity G_oGTPase activity. This inhibition is specific of G_αoand is reproduced, in the absence of 22C11, by the addition of the βAPP C-terminal domain but not by two distinct mutated βAPP C-terminal domains that do not bind G_αo. This inhibition of G_αoGTPase activity by either 22C11 or wild-type βAPP cytoplasmic domain suggests that intracellular interactions between βAPP and G_αocould be regulated by extracellular signals. To verify whether this interaction is preserved in CSEM, we first used biochemical, immunocytochemical, and ultrastructural techniques to unambiguously confirm the colocalization of G_αoand βAPP in CSEM. We show that inhibition of basal G_αoGTPase activity also occurs within CSEM and correlates with the coimmunoprecipitation of G_αoand βAPP. The regulation of G_αoGTPase activity by βAPP in a compartment specialized in signaling may have important consequences for our understanding of the physiopathological functions of βAPP.