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Amyloidogenic processing of the Alzheimer beta-amyloid precursor protein depends on lipid rafts.

Ehehalt R, Keller P, Haass C, Thiele C, Simons K - J. Cell Biol. (2003)

Bottom Line: A beta generation was dependent on endocytosis and was reduced after expression of the dynamin mutant K44A and the Rab5 GTPase-activating protein, RN-tre.Although APP inside raft clusters seems to be cleaved by beta-secretase, APP outside rafts undergoes cleavage by alpha-secretase.Thus, access of alpha- and beta-secretase to APP, and therefore A beta generation, may be determined by dynamic interactions of APP with lipid rafts.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, D-01307 Dresden, Germany.

ABSTRACT
Formation of senile plaques containing the beta-amyloid peptide (A beta) derived from the amyloid precursor protein (APP) is an invariant feature of Alzheimer's disease (AD). APP is cleaved either by beta-secretase or by alpha-secretase to initiate amyloidogenic (release of A beta) or nonamyloidogenic processing of APP, respectively. A key to understanding AD is to unravel how access of these enzymes to APP is regulated. Here, we demonstrate that lipid rafts are critically involved in regulating A beta generation. Reducing cholesterol levels in N2a cells decreased A beta production. APP and the beta-site APP cleavage enzyme (BACE1) could be induced to copatch at the plasma membrane upon cross-linking with antibodies and to segregate away from nonraft markers. Antibody cross-linking dramatically increased production of A beta in a cholesterol-dependent manner. A beta generation was dependent on endocytosis and was reduced after expression of the dynamin mutant K44A and the Rab5 GTPase-activating protein, RN-tre. This inhibition could be overcome by antibody cross-linking. These observations suggest the existence of two APP pools. Although APP inside raft clusters seems to be cleaved by beta-secretase, APP outside rafts undergoes cleavage by alpha-secretase. Thus, access of alpha- and beta-secretase to APP, and therefore A beta generation, may be determined by dynamic interactions of APP with lipid rafts.

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Related in: MedlinePlus

Copatching of YFP-wtAPP and BACE1A-VSVG at the cell surface. (A) Immunofluorescence of BACE1A-VSVG using polyclonal antiserum 7523 against the NH2-terminal part of BACE1 (green) and YFP-wtAPP using mAb 3E6 against the FP (red). Both proteins were randomly distributed at the cell surface when the antibody was added after fixation. (B) Colocalization of YFP-wtAPP (red) and BACE1A-VSVG (green) after antibody induced patching with the same antibodies as above. Bar, 10 μm.
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fig3: Copatching of YFP-wtAPP and BACE1A-VSVG at the cell surface. (A) Immunofluorescence of BACE1A-VSVG using polyclonal antiserum 7523 against the NH2-terminal part of BACE1 (green) and YFP-wtAPP using mAb 3E6 against the FP (red). Both proteins were randomly distributed at the cell surface when the antibody was added after fixation. (B) Colocalization of YFP-wtAPP (red) and BACE1A-VSVG (green) after antibody induced patching with the same antibodies as above. Bar, 10 μm.

Mentions: Both BACE1 and wtAPP colocalized with PLAP at the plasma membrane in the majority of cells, but they clearly segregated from TfR del 5–41 (Fig. 2). BACE1 and wtAPP could also be localized to the same patches upon cross-linking (Fig. 3). For quantitative analyses of the extent of copatching, images of 10 randomly selected cells on one coverslip were taken and assigned into four categories: (1) coclustering (>80% overlap); (2) partial coclustering (clearly overlapping spots 30–80%); (3) random distribution, and (4) segregation. The data from five independent experiments (Fig. 4) indicate that cross-linked wtAPP and BACE1 copatched with the raft protein PLAP and segregated from the nonraft protein TfR del 5–41.


Amyloidogenic processing of the Alzheimer beta-amyloid precursor protein depends on lipid rafts.

Ehehalt R, Keller P, Haass C, Thiele C, Simons K - J. Cell Biol. (2003)

Copatching of YFP-wtAPP and BACE1A-VSVG at the cell surface. (A) Immunofluorescence of BACE1A-VSVG using polyclonal antiserum 7523 against the NH2-terminal part of BACE1 (green) and YFP-wtAPP using mAb 3E6 against the FP (red). Both proteins were randomly distributed at the cell surface when the antibody was added after fixation. (B) Colocalization of YFP-wtAPP (red) and BACE1A-VSVG (green) after antibody induced patching with the same antibodies as above. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172747&req=5

fig3: Copatching of YFP-wtAPP and BACE1A-VSVG at the cell surface. (A) Immunofluorescence of BACE1A-VSVG using polyclonal antiserum 7523 against the NH2-terminal part of BACE1 (green) and YFP-wtAPP using mAb 3E6 against the FP (red). Both proteins were randomly distributed at the cell surface when the antibody was added after fixation. (B) Colocalization of YFP-wtAPP (red) and BACE1A-VSVG (green) after antibody induced patching with the same antibodies as above. Bar, 10 μm.
Mentions: Both BACE1 and wtAPP colocalized with PLAP at the plasma membrane in the majority of cells, but they clearly segregated from TfR del 5–41 (Fig. 2). BACE1 and wtAPP could also be localized to the same patches upon cross-linking (Fig. 3). For quantitative analyses of the extent of copatching, images of 10 randomly selected cells on one coverslip were taken and assigned into four categories: (1) coclustering (>80% overlap); (2) partial coclustering (clearly overlapping spots 30–80%); (3) random distribution, and (4) segregation. The data from five independent experiments (Fig. 4) indicate that cross-linked wtAPP and BACE1 copatched with the raft protein PLAP and segregated from the nonraft protein TfR del 5–41.

Bottom Line: A beta generation was dependent on endocytosis and was reduced after expression of the dynamin mutant K44A and the Rab5 GTPase-activating protein, RN-tre.Although APP inside raft clusters seems to be cleaved by beta-secretase, APP outside rafts undergoes cleavage by alpha-secretase.Thus, access of alpha- and beta-secretase to APP, and therefore A beta generation, may be determined by dynamic interactions of APP with lipid rafts.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, D-01307 Dresden, Germany.

ABSTRACT
Formation of senile plaques containing the beta-amyloid peptide (A beta) derived from the amyloid precursor protein (APP) is an invariant feature of Alzheimer's disease (AD). APP is cleaved either by beta-secretase or by alpha-secretase to initiate amyloidogenic (release of A beta) or nonamyloidogenic processing of APP, respectively. A key to understanding AD is to unravel how access of these enzymes to APP is regulated. Here, we demonstrate that lipid rafts are critically involved in regulating A beta generation. Reducing cholesterol levels in N2a cells decreased A beta production. APP and the beta-site APP cleavage enzyme (BACE1) could be induced to copatch at the plasma membrane upon cross-linking with antibodies and to segregate away from nonraft markers. Antibody cross-linking dramatically increased production of A beta in a cholesterol-dependent manner. A beta generation was dependent on endocytosis and was reduced after expression of the dynamin mutant K44A and the Rab5 GTPase-activating protein, RN-tre. This inhibition could be overcome by antibody cross-linking. These observations suggest the existence of two APP pools. Although APP inside raft clusters seems to be cleaved by beta-secretase, APP outside rafts undergoes cleavage by alpha-secretase. Thus, access of alpha- and beta-secretase to APP, and therefore A beta generation, may be determined by dynamic interactions of APP with lipid rafts.

Show MeSH
Related in: MedlinePlus