The Presenilin 1 Protein Is a Component of a High Molecular Weight Intracellular Complex That Contains β-Catenin

Abstract

The presenilin (PS) genes associated with Alzheimer disease encode polytopic transmembrane proteins which undergo physiologic endoproteolytic cleavage to generate stable NH 2 -and COOH-terminal fragments (NTF or CTF) which co-localize in intracellular membranes, but are tightly regulated in their stoichiometry and abundance. We have used linear glycerol velocity and discontinuous sucrose gradient analysis to investigate the distribution and native conformation of PS1 and PS2 during this regulated processing in cultured cells and in brain. The PS1 NTF and CTF co-localize in the endoplasmic reticulum (ER) and in the Golgi apparatus, where they are components of a ϳ250-kDa complex. This complex also contains ␤-catenin but not ␤-amyloid precursor protein (APP). In contrast, the PS1 holoprotein precursor is predominantly localized to the rough ER and smooth ER, where it is a component of a ϳ180-kDa native complex. PS2 forms similar but independent complexes. Restricted incorporation of the presenilin NTF and CTF along with a potentially functional ligand (␤-catenin) into a multimeric complex in the ER and Golgi apparatus may provide an explanation for the regulated accumulation of the NTF and CTF.Mutations in the genes encoding the presenilin (PS) 1 1 (PS1) and presenilin 2 (PS2) account for the majority of early-onset familial Alzheimer's disease (1-3). Both genes encode polytopic transmembrane proteins that are predominantly localized in intracellular membranes, including the nuclear envelope, the endoplasmic reticulum, and the Golgi apparatus (4, 5). Structural studies suggested that these proteins contain either six or eight transmembrane (TM) domains, and that the amino and carboxyl termini as well as a large hydrophilic loop following the sixth TM domain are located in the cytoplasm (5-7). The presenilins undergo physiological endoproteolytic processing within the large cytoplasmic loop following TM6 by an unknown protease that produces heterogeneous ϳ29-kDa aminoterminal and ϳ18 -20-kDa carboxyl-terminal fragments (8, 9). The presenilin holoproteins are maintained at low steady levels both in brain and in other peripheral tissues, probably by proteasome-mediated degradation (10, 11). As a result, the presenilin species most readily detected are the stable NH 2 -and COOH-terminal endoproteolytic fragments, the stoichiometry of which appears to be tightly regulated (8).The functional role of the presenilins is still unknown, although roles in cellular differentiation, in signal transduction, in apoptosis, or in intracellular protein trafficking have been proposed. To better understand the presenilin proteins and their biological functions, we have investigated both the native state of these proteins and their biochemical subcellular localization in membrane fractions derived from cultured cells and from the human brain. Our data suggest that the presenilins form detergent-sensitive high molecular mass complexes. The PS1 holoprotein is a component of a complex of ϳ180 kDa, while the endoproteolytic fragments are ...

Turn‐off, drop‐out: Functional state switching of cadherins

“…Presenilin also stimulates the interaction of E-cadherin with ␤-catenin and the cytoskeleton; the ultimate effect is to enhance adhesion (Baki et al, 2001;Georgakopoulos et al, 1999). The relationship between competition for binding of p120 ctn , enhanced binding of ␤-catenin to cadherin, and the interaction of presenilin with the cytosolic ␤-catenin complex (Murayama et al, 1998;Yu et al, 1998) remains to be clarified. This complex web of p120 ctn interactions and their ramifications, as well as its potential role in transcription (Daniel and Reynolds, 1999;Prokhortchouk et al, 2001), suggests that, like ␤-catenin, p120 ctn is a key regulatory molecule integrating cell adhesion and transcription during development.…”

Random Mutagenesis of Presenilin-1 Identifies Novel Mutants Exclusively Generating Long Amyloid β-Peptides

“…Subcellular Fractionation with Discontinuous Sucrose GradientsSubcellular fractionation was performed according to a previously described method (22). HEK293 cells transfected with PS1 cDNA were homogenized with a Polytron homogenizer in 5 mM HEPES (pH 7.2), 1 mM EDTA, and protease inhibitor mixture.…”

“…Glycerol Velocity Gradient Centrifugation-Glycerol velocity gradient centrifugation was carried out as described previously (22). HEK293 cells transfected with PS1 cDNA were disrupted with a Polytron homogenizer (Kinematica AG, Littau-Lucerne, Switzerland), and nuclei and large cell debris were sedimented by centrifugation at 1500 ϫ g for 10 min.…”

The aspartate-257 of presenilin 1 is indispensable for mouse development and production of β-amyloid peptides through β-catenin-independent mechanisms

“…Overexpression of exogenous PS does not increase the levels of processed fragments and results in the replacement of endogenous NTF and CTF (5). The cleaved fragments are stable and assemble into a high molecular weight (HMW) complex required for PS proteolytic activity (6).…”