ABSTRACT
Biochemical and genetic studies have revealed that the presenilins interact with several proteins and are involved in the regulated intramembrane proteolysis of numerous type 1 membrane proteins, thereby linking presenilins to a range of cellular processes. In this study, we report the characterization of a highly conserved tumor necrosis factor receptor-associated factor-6 (TRAF6) consensus-binding site within the hydrophilic loop domain of presenilin-1 (PS-1). In coimmunoprecipitation studies we indicate that presenilin-1 interacts with TRAF6 and interleukin-1 receptor-associated kinase 2. Substitution of presenilin-1 residues Pro-374 and Glu-376 by site-directed mutagenesis greatly reduces the ability of PS1 to associate with TRAF6. By studying these interactions, we also demonstrate that the interleukin-1 receptor type 1 (IL-1R1) undergoes intramembrane proteolytic processing, mediated by presenilin-dependent gamma-secretase activity. A metalloprotease-dependent proteolytic event liberates soluble IL-1R1 ectodomain and produces an approximately 32-kDa C-terminal domain. This IL-1R1 C-terminal domain is a substrate for subsequent gamma-secretase cleavage, which generates an approximately 26-kDa intracellular domain. Specific pharmacological gamma-secretase inhibitors, expression of dominant negative presenilin-1, or presenilin deficiency independently inhibit generation of the IL-1R1 intracellular domain. Attenuation of gamma-secretase activity also impairs responsiveness to IL-1beta-stimulated activation of the MAPKs and cytokine secretion. Thus, TRAF6 and interleukin receptor-associated kinase 2 are novel binding partners for PS1, and IL-1R1 is a new substrate for presenilin-dependent gamma-secretase cleavage. These findings also suggest that regulated intramembrane proteolysis may be a control mechanism for IL-1R1-mediated signaling.
Subject(s)
Amyloid Precursor Protein Secretases/metabolism , Interleukin-1 Receptor-Associated Kinases/metabolism , Presenilin-1/metabolism , Receptors, Interleukin-1 Type I/metabolism , TNF Receptor-Associated Factor 6/metabolism , Amyloid Precursor Protein Secretases/antagonists & inhibitors , Amyloid Precursor Protein Secretases/genetics , Animals , Cell Line , Cytokines/genetics , Cytokines/metabolism , Humans , Interleukin-1 Receptor-Associated Kinases/genetics , MAP Kinase Signaling System/drug effects , MAP Kinase Signaling System/physiology , Mice , Mitogen-Activated Protein Kinase Kinases/genetics , Mitogen-Activated Protein Kinase Kinases/metabolism , Presenilin-1/genetics , Protease Inhibitors/pharmacology , Protein Structure, Secondary/physiology , Protein Structure, Tertiary/physiology , Rats , Receptors, Interleukin-1 Type I/genetics , TNF Receptor-Associated Factor 6/geneticsABSTRACT
This study aimed to determine whether sustained (i.e. dietary) use of caffeine has net effects on performance and mood compared with sustained abstinence, and whether dietary caffeine restores performance and mood adversely affected by sleep restriction. Participants (n = 96) alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for 4 consecutive weeks, while either rested or sleep restricted. Performance involved either a single task requiring sustained vigilance or a varied battery of brief psychomotor and cognitive tasks, and mood was assessed using the Profile of Mood States. Caffeine had no significant net enhancing effects for either performance or mood when participants were rested, and produced no net restorative effects when performance and mood were degraded by sleep restriction.
