Cellular prion protein regulates β-secretase cleavage of the Alzheimer's amyloid precursor protein

doi:10.1073/pnas.0609621104

Cellular prion protein regulates β-secretase cleavage of the Alzheimer's amyloid precursor protein

*Proteolysis Research Group, Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, and
^†Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT, United Kingdom;
^§Neurodegeneration Research, Neurology and Gastrointestinal Centre of Excellence for Drug Discovery, GlaxoSmithKline Research and Development Limited, Third Avenue, Harlow, Essex CM19 5AW, United Kingdom;
^¶Mayo Clinic, Jacksonville, FL 32224; and
^‖Roslin Institute, Neuropathogenesis Unit, Edinburgh EH9 3JF, United Kingdom

Edited by Stanley B. Prusiner, University of California, San Francisco, CA, and approved May 10, 2007 (received for review October 30, 2006)

Abstract

Proteolytic processing of the amyloid precursor protein (APP) by β-secretase, β-site APP cleaving enzyme (BACE1), is the initial step in the production of the amyloid β (Aβ) peptide, which is involved in the pathogenesis of Alzheimer's disease. The normal cellular function of the prion protein (PrP^C), the causative agent of the transmissible spongiform encephalopathies such as Creutzfeldt–Jakob disease in humans, remains enigmatic. Because both APP and PrP^C are subject to proteolytic processing by the same zinc metalloproteases, we tested the involvement of PrP^C in the proteolytic processing of APP. Cellular overexpression of PrP^C inhibited the β-secretase cleavage of APP and reduced Aβ formation. Conversely, depletion of PrP^C in mouse N2a cells by siRNA led to an increase in Aβ peptides secreted into the medium. In the brains of PrP knockout mice and in the brains from two strains of scrapie-infected mice, Aβ levels were significantly increased. Two mutants of PrP, PG14 and A116V, that are associated with familial human prion diseases failed to inhibit the β-secretase cleavage of APP. Using constructs of PrP, we show that this regulatory effect of PrP^C on the β-secretase cleavage of APP required the localization of PrP^C to cholesterol-rich lipid rafts and was mediated by the N-terminal polybasic region of PrP^C via interaction with glycosaminoglycans. In conclusion, this is a mechanism by which the cellular production of the neurotoxic Aβ is regulated by PrP^C and may have implications for both Alzheimer's and prion diseases.

Footnotes

**To whom correspondence should be addressed. E-mail: n.m.hooper{at}leeds.ac.uk
Author contributions: E.T.P., J.C.M., and N.M.H. designed research; E.T.P., N.T.W., I.H., E.A.E., C.B.E., and H.N.B. performed research; E.T.P., N.T.W., E.A.E., C.B.E., and N.M.H. analyzed data; I.H., E.A.E., and C.B.E. contributed new reagents/analytic tools; and E.T.P., J.C.M., A.J.T., and N.M.H. wrote the paper.
↵ ^‡Present address: Department of Biological Sciences, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0609621104/DC1.
Abbreviations:

Aβ,

amyloid β;

AD,

Alzheimer's disease;

APP,

amyloid precursor protein;

BACE1,

β-site APP cleaving enzyme;

CJD,

Creutzfeldt–Jakob disease;

GAG,

glycosaminoglycan;

GSS,

Gerstmann–Scheinker–Straussler;

LMW,

low molecular weight;

PrP,

prion protein;

PrPC,

cellular form of PrP;

PrPSc,

infectious form of PrP;

sAPPα,

soluble ectodomain of APP after α-cleavage;

sAPPβ,

soluble ectodomain of APP after β-cleavage;

TSE,

transmissible spongiform encephalopathy.