title: PI3K inhibition causes the accumulation of ubiquitinated presenilin 1 without affecting the proteasome activity.
abstract: gamma-Secretase is an enzymatic complex, composed of presenilin 1 (PS1), nicastrin, pen-2, and aph-1, and is responsible for the intramembranous cleavage of various type-I membrane proteins. The level of each component is tightly regulated in a cell via proteasomal degradation. On the other hand, it has previously been reported that PS1/gamma-secretase is involved in the activation of phosphatidylinositol-3 kinase/Akt (PI3K/Akt) pathway. PI3K is inhibited in Alzheimer's disease (AD) brain, whereas the effects of PI3K inhibition on the metabolism of PS1/gamma-secretase have not been elucidated. Here, we demonstrate that the treatment of neurons with PI3K inhibitors leads to increased levels of PS1/gamma-secretase components through an inhibitory effect on their degradation. Moreover, PI3K inhibition accelerated ubiquitination of PS1. We further show the evidence that the PS1 ubiquitination after PI3K inhibition is represented by the multiple mono-ubiquitination, instead of poly-ubiquitination. Accordingly, treatment of cells with PI3K inhibitor led to a differential intracellular redistribution of PS1 from the one observed after the proteasomal inhibition. These results suggest that PI3K inhibition may trigger the multiple mono-ubiquitination of PS1, which precludes the degradation of PS1/gamma-secretase through the proteasomal pathway. Since PS1/gamma-secretase is deeply involved in the production of Abeta protein, a deeper knowledge into its metabolism could contribute to a better elucidation of AD pathogenesis.
authors.affiliation: Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
authors.forename: Nobuhisa
authors.initials: N
authors.lastname: Aoyagi
authors.forename: Kengo
authors.initials: K
authors.lastname: Uemura
authors.forename: Akira
authors.initials: A
authors.lastname: Kuzuya
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kihara
authors.forename: Jun
authors.initials: J
authors.lastname: Kawamata
authors.forename: Shun
authors.initials: S
authors.lastname: Shimohama
authors.forename: Ayae
authors.initials: A
authors.lastname: Kinoshita
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Takahashi
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D053764:Presenilin-1 / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D053829:Amyloid Precursor Protein Secretases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D053764:Presenilin-1; D046988:Proteasome Endopeptidase Complex; D025801:Ubiquitin