title: Phosphoinositides suppress gamma-secretase in both the detergent-soluble and -insoluble states.
abstract: gamma-Secretase is an aspartic protease that hydrolyzes type I membrane proteins within the hydrophobic environment of the lipid bilayer. Using the CHAPSO-solubilized gamma-secretase assay system, we previously found that gamma-secretase activity was sensitive to the concentrations of detergent and phosphatidylcholine. This strongly suggests that the composition of the lipid bilayer has a significant impact on the activity of gamma-secretase. Recently, level of secreted beta-amyloid protein was reported to be attenuated by increasing levels of phosphatidylinositol 4,5-diphosphate (PI(4,5)P2) in cultured cells. However, it is not clear whether PI(4,5)P2 has a direct effect on gamma-secretase activity. In this study, we found that phosphoinositides directly inhibited CHAPSO-solubilized gamma-secretase activity. Interestingly, neither phosphatidylinositol nor inositol triphosphate altered gamma-secretase activity. PI(4,5)P2 was also found to inhibit gamma-secretase activity in CHAPSO-insoluble membrane microdomains (rafts). Kinetic analysis of beta-amyloid protein production in the presence of PI(4,5)P2 suggested a competitive inhibition. Even though phosphoinositides are minor phospholipids of the membrane, the concentration of PI(4,5)P2 within the intact membrane has been reported to be in the range of 4-8 mm. The presence of PI(4,5)P2-rich rafts in the membrane has been reported in a range of cell types. Furthermore, gamma-secretase is enriched in rafts. Taking these data together, we propose that phosphoinositides potentially regulate gamma-secretase activity by suppressing its association with the substrate.
authors.affiliation: Department of Neuropathology, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan.
authors.forename: Satoko
authors.initials: S
authors.lastname: Osawa
authors.forename: Satoru
authors.initials: S
authors.lastname: Funamoto
authors.forename: Mika
authors.initials: M
authors.lastname: Nobuhara
authors.forename: Satoko
authors.initials: S
authors.lastname: Wada-Kakuda
authors.forename: Masafumi
authors.initials: M
authors.lastname: Shimojo
authors.forename: Sosuke
authors.initials: S
authors.lastname: Yagishita
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ihara
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000737:chemistry / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D002793:Cholic Acids / Q000737:chemistry*; D006224:Cricetinae; D003412:Cricetulus; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D021962:Membrane Microdomains / Q000737:chemistry / Q000201:enzymology*; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000737:chemistry / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D002793:Cholic Acids; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D019269:Phosphatidylinositol 4,5-Diphosphate; C048531:chapso; D053829:Amyloid Precursor Protein Secretases