The amyloid precursor protein (APP), a large glycoprotein highly expressed in neurons, is cleaved in its intramembranous domain by γ secretase to generate amyloid-β and a free carboxyl-terminal intracellular fragment (APP-CT), which has previously been suggested to interact with the adapter protein Fe65 and the histone acetyltransferase Tip60. An identical γ secretase activity mediates cleavage of Notch, releasing an intracellular signaling domain that translocates to the nucleus. We examined the effect of an ectopically expressed 58-amino acid APP-CT fragment (APP-C58) on human H4 neuroglioma cells. We demonstrate by confocal microscopy and fluorescence resonance energy transfer analysis that APP-C58 translocates to the nucleus and forms a complex in the nucleus with the Tip60, independent of interactions with Fe65. APP-C58 transfected H4 cells undergo apoptosis within 48–72 h, marked by nuclear blebbing, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining, and blockade by a caspase inhibitor. When nuclear access of APP-C58 is prevented by fusing with a strong membrane-targeting farnesylation domain, apoptosis is blocked. APP-C58-induced apoptosis was markedly enhanced by co-transfection with wild type Tip60 and decreased by mutant Tip60 lacking histone acetyltransferase activity, suggesting that Tip60 mediates APP-CT-induced cell death. Thus, γ secretase cleavage of APP may contribute to Alzheimer's disease-related neurodegeneration in two ways: release of amyloid-β and liberation of a bioactive carboxyl-terminal domain from membrane-bound APP.
Cited by (0)
Published, JBC Papers in Press, May 24, 2002, DOI 10.1074/jbc.M203372200
This work was supported by National Institutes of Health Grants P01 AG15379 and AG12406.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.