Sequential proteolysis of the amyloid precursor protein (APP) by औ- and γ-secretase activities yields the amyloid औ peptide that is widely deposited in the brains of individuals with Alzheimer's disease. The membrane-anchored aspartyl protease औ-siteAPP-cleaving enzyme (BACE) exhibits all of the characteristics of a औ-secretase and has been shown to cleave APP at its औ-site in vitro and in vivo. We found that BACE undergoes cleavage on a surface-exposed α-helix between amino acid residues Leu-228 and Ala-229, generating stable N- and C-terminal fragments that remain covalently associated via a disulfide bond. The efficiency of BACE endoproteolysis was observed to depend heavily on cell and tissue type. In contrast to brain where holoprotein was predominant, BACE was found primarily as endoproteolyzed fragments in pancreas, liver, and muscle. In addition, we observed a marked up-regulation of BACE endoproteolysis in C2 myoblasts upon differentiation into multinucleated myotubes, a well established model system of muscle tissue specification. As in liver, BACE exists as endoproteolyzed fragments in the hepatic cell line, HepG2. We found that HepG2 cells are capable of generating amyloid औ peptide, suggesting that endoproteolyzed BACE retains measurable औ-secretase activity. We also found that BACE endoproteolysis occurs only after export from the endoplasmic reticulum, is enhanced in the trans-Golgi network, and is sensitive to inhibitors of vesicular acidification. The membrane-bound proteases tumor necrosis factor α-converting enzyme and furin were not found to be responsible for this cleavage nor was BACE observed to mediate its own endoproteolysis by an autocatalytic mechanism. Thus, we characterize a specific processing event that may serve to regulate the enzymatic activity of BACE on a post-translational level.
Cited by (0)
Published, JBC Papers in Press, January 27, 2003, DOI 10.1074/jbc.M213303200
This work was supported by National Institutes of Health Grant PO1 AG11542 (to R. W. D.), a Howard Hughes Medical Institute predoctoral fellowship (to J. T. H.), National Institutes of Health Grant NIA-R01 AG11762 (to G. Schellenberg), a Veterans Affairs Merit Award (to D. G. C.), and National Institute on Aging Grant AG05136 Alzheimer's Disease Research Center/Project (to D. G. C.).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.
