Abstract
Gamma-secretase is a multi-component enzyme complex that performs an intramembranous cleavage, releasing amyloid-beta (Abeta) peptides from processing intermediates of the beta-amyloid precursor protein. Because Abeta peptides are thought to be causative for Alzheimer's disease, inhibiting gamma-secretase represents a potential treatment for this neurodegenerative condition. Whereas inhibitors directed at the active center of gamma-secretase inhibit the cleavage of all its substrates, certain non-steroidal antiinflammatory drugs (NSAIDs) have been shown to selectively reduce the production of the more amyloidogenic Abeta(1-42) peptide without inhibiting alternative cleavages. In contrast to the majority of previous studies, however, we demonstrate that in cell-free systems the mode of action of selected NSAIDs and their derivatives, depending on the concentrations used, can either be classified as modulatory or inhibitory. At modulatory concentrations, a selective and, with respect to the substrate, noncompetitive inhibition of Abeta(1-42) production was observed. At inhibitory concentrations, on the other hand, biochemical readouts reminiscent of a nonselective gamma-secretase inhibition were obtained. When these compounds were analyzed for their ability to displace a radiolabeled, transition-state analog inhibitor from solubilized enzyme, noncompetitive antagonism was observed. The allosteric nature of radioligand displacement suggests that NSAID-like inhibitors change the conformation of the gamma-secretase enzyme complex by binding to a novel site, which is discrete from the binding site for transition-state analogs and therefore distinct from the catalytic center. Consequently, drug discovery efforts aimed at this site may identify novel allosteric inhibitors that could benefit from a wider window for inhibition of gamma (42)-cleavage over alternative cleavages in the beta-amyloid precursor protein and, more importantly, alternative substrates.
Highlights
␥-Secretase is a multi-component enzyme complex that performs an intramembranous cleavage, releasing amyloid- (A) peptides from processing intermediates of the -amyloid precursor protein
Whereas inhibitors directed at the active center of ␥-secretase inhibit the cleavage of all its substrates, certain non-steroidal antiinflammatory drugs (NSAIDs) have been shown to selectively reduce the production of the more amyloidogenic A(1– 42) peptide without inhibiting alternative cleavages
The allosteric nature of radioligand displacement suggests that NSAID-like inhibitors change the conformation of the ␥-secretase enzyme complex by binding to a novel site, which is discrete from the binding site for transition-state analogs and distinct from the catalytic center
Summary
A, amyloid-; AD, Alzheimer’s distides is thought to be the cause of Alzheimer’s disease (AD) (1). A common denominator (reviewed by Hardy (4)) for mutations causative of familial AD (FAD) has been revealed, being abnormalities in the metabolism of APP that appear to lead to an elevation of the production of the A(1– 42) peptide species. This C-terminally elongated A peptide is more prone to aggregation than the shorter and more abundant A(1– 40) species. Considerable effort has been put into the development of potent ␥-secretase inhibitors for the treatment of AD because they have the potential to block the generation of all amyloidogenic peptides from APP-derived substrates (10) This class of compound suffers from the disadvantage that it does not ease; APP, -amyloid precursor protein; NSAID, non-steroidal antiinflammatory drug; CHAPSO, 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate; AICD, APP intracellular domain. Our results indicate that NSAID-like compounds can act as allosteric inhibitors by directly targeting the presenilin-dependent ␥-secretase complex at a novel site discrete from the binding site for transition-state analog ␥-secretase inhibitors
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