BACE Is Degraded via the Lysosomal Pathway

Young Ho Koh,Christine A.F Von Arnim,Bradley T Hyman,Rudolph E Tanzi,Giuseppina Tesco

doi:10.1074/jbc.m506199200

Young Ho Koh, Christine A.F Von Arnim + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m506199200

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Abstract

Amyloid plaques are formed by aggregates of amyloid-beta-peptide, a 37-43-amino acid fragment (primarily Abeta(40) and Abeta(42)) generated by proteolytic processing of the amyloid precursor protein (APP) by beta- and gamma-secretases. A type I transmembrane aspartyl protease, BACE (beta-site APP cleaving enzyme), has been identified to be the beta-secretase. BACE is targeted through the secretory pathway to the plasma membrane where it can be internalized to endosomes. The carboxyl terminus of BACE contains a di-leucine-based signal for sorting of transmembrane proteins to endosomes and lysosomes. In this study, we set out to determine whether BACE is degraded by the lysosomal pathway and whether the di-leucine motif is necessary for targeting BACE to the lysosomes. Here we show that lysosomal inhibitors, chloroquine and NH(4)Cl, lead to accumulation of endogenous and ectopically expressed BACE in a variety of cell types, including primary neurons. Furthermore, the inhibition of lysosomal hydrolases results in the redistribution and accumulation of BACE in the late endosomal/lysosomal compartments (lysosome-associated membrane protein 2 (LAMP2)-positive). In contrast, the BACE-LL/AA mutant, in which Leu(499) and Leu(500) in the COOH-terminal sequence (DDISLLK) were replaced by alanines, only partially co-localized with LAMP2-positive compartments following inhibition of lysosomal hydrolases. Collectively, our data indicate that BACE is transported to the late endosomal/lysosomal compartments where it is degraded via the lysosomal pathway and that the di-leucine motif plays a role in sorting BACE to lysosomes.

Highlights

Transmembrane aspartyl protease, ␤-site amyloid precursor protein (APP) cleaving enzyme (BACE), has been identified to be the ␤-secretase [3, 4]
We have found that lysosomal inhibitors, but not proteasomal inhibitors lead to the accumulation of both endogenous and ectopically expressed BACE in a variety of cell types, including primary cortical neurons
These data are somewhat discrepant but reconcilable with a previous report [15] of an increase in BACE protein levels following treatment with proteasomal inhibitors in SH-SY5Y cells overexpressing BACE. It is not clear from this study that endogenous BACE would normally be degraded by the proteasome

Summary

BACE Is Degraded via the Lysosomal Pathway*

Amyloid plaques are formed by aggregates of amyloid-␤-peptide, a 37– 43-amino acid fragment (primarily A␤40 and A␤42) generated by proteolytic processing of the amyloid precursor protein (APP) by ␤- and ␥-secretases. The inhibition of lysosomal hydrolases results in the redistribution and accumulation of BACE in the late endosomal/lysosomal compartments (lysosomeassociated membrane protein 2 (LAMP2)-positive). Amyloid plaques are formed by aggregates of A␤, a 37– 43-amino acid peptide (primarily A␤40 and A␤42) generated by proteolytic processing of the amyloid precursor protein (APP), a large type I integral transmembrane protein. Eukaryotic cells contain two major systems for protein degradation: the lysosomal apparatus, a membrane-enclosed vacuole containing multiple acid proteases (cathepsins and other hydrolases), and the proteasome, an ATP-dependent proteolytic complex that mostly degrades ubiquitinated proteins. We set out to determine whether BACE is degraded by the lysosomal pathway, and whether the di-leucine motif is necessary for targeting of BACE to lysosomes

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DISCUSSION