Truncated Carboxyl-Terminal Fragments of β-Amyloid Precursor Protein Are Processed to Amyloid β-Proteins 40 and 42

Abstract

We previously showed that beta-amyloid precursor protein (APP) is cleaved not only in the middle of the membrane (gamma-cleavage) but also at novel cleavage sites close to the membrane/cytoplasmic boundary (epsilon-cleavage), releasing APP intracellular domains (AICDs) 49-99 and 50-99. To learn more about the relationship between gamma- and epsilon-cleavage, C-terminally truncated carboxyl-terminal fragments (CTFs) of APP, especially CTFs1-48 and 1-49 (the postulated products that are generated by epsilon-cleavage), were transiently expressed in CHO cells. Most importantly, the cells expressing CTF1-49 secreted predominantly amyloid beta-protein (Abeta) 40, while those expressing CTF1-48 secreted preferentially Abeta42. This supports our assumption that epsilon-cleavage precedes Alphabeta production and that preceding epsilon-cleavage determines the preference for the final Abeta species. The gamma-secretase inhibitors, L-685,458 and DAPT, suppressed Abeta production from CTF1-49. Regarding Abeta production from CTF1-48, L-685,458 suppressed it, but DAPT failed to do so. A dominant negative mutant of presenilin 1 suppressed the production of Abeta40 and 42 from both CTFs1-48 and 1-49. These data should shed significant light into the mechanism of Abeta production.

γ-Secretase: Successive Tripeptide and Tetrapeptide Release from the Transmembrane Domain of β-Carboxyl Terminal Fragment

“…Tetrapeptide release is apparently inherent to the A␤ 42 processing, because GGVV, which may have been released to produce A␤ 36 , was undetectable. Relating to the third point, our previous results suggest strongly that the A␤ 40 -producing process is distinct from the A␤ 42 -producing process (Funamoto et al, 2004;Qi-Takahara et al, 2005). The latter process was less sensitive to DFK-167, a difluoro ketone peptidomimetic, than was the former.…”

“…Presumably, a distinct cleavage-sensitive conformation would be required for long A␤s to bind to the ␥-secretase complex. This may relate to the previous observation that longer A␤ species generated by transfection are easily processed, and smaller A␤ species are more difficult to process (Funamoto et al, 2004).…”

“…Using a transfection experiment, we noted an unusual rule: A␤ 51 and A␤ 48 preferentially generated A␤ 42 , whereas other longer A␤s, including A␤ 49 , A␤ 50 , and A␤ 52 , produced predominantly A␤ 40 (Funamoto et al, 2004). Although the exact mechanism remains unknown, these results suggest that this three-residue rule is involved in the preference for the final product, A␤ 40 or A␤ 42 .…”

Amyloid β-Protein Precursor Juxtamembrane Domain Regulates Specificity of γ-Secretase-dependent Cleavages

“…The fact that only longer A␤ but not longer AICD was identified, even after extremely rigorous attempts, suggests that ⑀-cleavage of APP precedes ␥-cleavage. Consistently, it has been shown that A␤40/42 can be generated from heterologously expressed longer A␤ peptides whose C termini end at the ⑀-cleavage site (56). Similarly, Lefranc-Jullien et al (57) demonstrated that APP⑀ (APP with a C-terminal truncation at the ⑀-cleavage site) could undergo normal ␥-cleavage upon ectodomain shedding.…”

Development of 2′-Deoxy-4′-C-Ethynyl-2-Fluoroadenosine (EFdA) which has Supremely High Anti-HIV Activity and Low Toxicity and Prevents the Emergence of Resistant HIV Mutants, and Discovery of Different Substrate Selectivity between Viral and Human Nucleic Acid Polymerases

“…Aβ generation and aggregation as plaques are the hallmark pathology of Alzheimer's Disease (AD; [15,[50][51][52][53]). The peptides have been evidenced to be neurotoxic, as they are reported mediators of inflammation [54,55], and oxidative stress [56].…”