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Internalization of exogenously added memapsin 2 (beta-secretase) ectodomain by cells is mediated by amyloid precursor

Xiang-Ping Huang1, Wan-Pin Chang, Gerald Koelsch

  • 1Protein Studies Program, Oklahoma Medical Research Foundation, University of Oklahoma Health Science Center, Oklahoma City, Oklahoma 73104, USA.

The Journal of Biological Chemistry
|June 16, 2004
PubMed

Insights

Exogenously added memapsin 2 ectodomain (M2(ED)) enters cells via amyloid precursor protein (APP) endocytosis, increasing amyloid-beta (Abeta) production. This interaction is APP-dependent and occurs independently of memapsin 2

Area of Science:

  • Neuroscience
  • Cell Biology
  • Biochemistry

Background:

  • Alzheimer's disease pathogenesis involves amyloid precursor protein (APP) cleavage by memapsin 2 (beta-secretase) into amyloid-beta (Abeta) peptides.
  • Both APP and memapsin 2 are Type I transmembrane proteins that undergo endocytosis into endosomes.
  • Specific endocytic signals reside within the cytosolic domains of APP and memapsin 2.

Purpose of the Study:

  • To investigate the interaction between exogenously added memapsin 2 ectodomain (M2(ED)) and cells expressing APP.
  • To determine the mechanism and functional consequences of M2(ED) internalization.
  • To elucidate the role of APP's endocytic machinery in mediating M2(ED) uptake.

Main Methods:

  • Cell transfection with native APP and APP Swedish mutant (APPsw).
  • Treatment with M2(ED) and glycosylphosphatidylinositol-specific phospholipase C.
  • Fluorescence resonance energy transfer (FRET) experiments and immunoprecipitation assays.

Main Results:

  • M2(ED) internalization into endosomes was observed in cells expressing APP, leading to increased Abeta production.
  • M2(ED) uptake was dependent on APP's endocytosis signal and reduced by phospholipase C treatment.
  • Interaction was independent of memapsin 2 active site binding and APP's beta-secretase site.

Conclusions:

  • Exogenous M2(ED) interacts with cell surface APP, facilitating its own internalization via APP-mediated endocytosis.
  • This interaction enhances Abeta production, suggesting a novel mechanism influencing Alzheimer's disease pathology.
  • The findings highlight a potential interplay between extracellular memapsin 2 fragments and APP processing in vivo.

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