The C-terminal fragment of the Alzheimer's disease amyloid protein precursor is degraded by a proteasome-dependent mechanism distinct from gamma-secretase

Eur J Biochem. 2001 Oct;268(20):5329-36. doi: 10.1046/j.0014-2956.2001.02465.x.


The beta-amyloid protein (Abeta) is derived by proteolytic processing of the amyloid protein precursor (APP). Cleavage of APP by beta-secretase generates a C-terminal fragment (APP-CTFbeta), which is subsequently cleaved by gamma-secretase to produce Abeta. The aim of this study was to examine the cleavage of APP-CTFbeta by gamma-secretase in primary cortical neurons from transgenic mice engineered to express the human APP-CTFbeta sequence. Neurons were prepared from transgenic mouse cortex and proteins labelled by incubation with [35S]methionine and [35S]cysteine. Labelled APP-CTFbeta and Abeta were then immunoprecipitated with a monoclonal antibody (WO2) specific for the transgene sequences. Approximately 30% of the human APP-CTFbeta (hAPP-CTFbeta) was converted to human Abeta (hAbeta), which was rapidly secreted. The remaining 70% of the hAPP-CTFbeta was degraded by an alternative pathway. The cleavage of hAPP-CTFbeta to produce hAbeta was inhibited by specific gamma-secretase inhibitors. However, treatment with proteasome inhibitors caused an increase in both hAPP-CTFbeta and hAbeta levels, suggesting that the alternative pathway was proteasome-dependent. A preparation of recombinant 20S proteasome was found to cleave a recombinant cytoplasmic domain fragment of APP (APPcyt) directly. The study suggests that in primary cortical neurons, APP-CTFbeta is degraded by two distinct pathways, one involving gamma-secretase, which produces Abeta, and a second major pathway involving direct cleavage of APP-CTFbeta within the cytoplasmic domain by the proteasome. These results raise the possibility that defective proteasome function could lead to an increase in Abeta production in the AD brain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alzheimer Disease / enzymology
  • Alzheimer Disease / metabolism*
  • Amyloid Precursor Protein Secretases
  • Amyloid beta-Protein Precursor / chemistry*
  • Amyloid beta-Protein Precursor / metabolism*
  • Animals
  • Aspartic Acid Endopeptidases
  • Blotting, Western
  • Cells, Cultured
  • Cysteine Endopeptidases / metabolism*
  • Endopeptidases / metabolism*
  • Humans
  • Mice
  • Mice, Transgenic
  • Models, Biological
  • Multienzyme Complexes / antagonists & inhibitors
  • Multienzyme Complexes / metabolism*
  • Neurons / metabolism
  • Peptide Fragments / chemistry*
  • Peptide Fragments / metabolism*
  • Protease Inhibitors / metabolism
  • Proteasome Endopeptidase Complex
  • Recombinant Proteins / metabolism
  • Time Factors


  • Amyloid beta-Protein Precursor
  • Multienzyme Complexes
  • Peptide Fragments
  • Protease Inhibitors
  • Recombinant Proteins
  • Amyloid Precursor Protein Secretases
  • Endopeptidases
  • Cysteine Endopeptidases
  • Aspartic Acid Endopeptidases
  • BACE1 protein, human
  • Bace1 protein, mouse
  • Proteasome Endopeptidase Complex