The same γ‐secretase accounts for the multiple intramembrane cleavages of APP

Abstract

It has been hypothesized that different C-terminus of bamyloid peptide (Ab) may be generated by different c-secretase activities. Recently, we have identified a new f-cleavage site at Ab46, leading to an important finding that the C-terminus of Ab is produced by a series of sequential cleavages. This finding prompted us to examine the effects of the known c-secretase inhibitors on different steps of the c-secretase-mediated sequential cleavages and specifically their effects on the formation and turnover of the intermediate Ab 46 . Our results demonstrate that some of the known inhibitors, such as L-685,458 and III-31C as well as inhibitors IV and V, inhibit the formation of secreted Ab 40/42 by inhibiting the formation of the intermediate Ab 46 . However, most of the other inhibitors show no inhibitory effect on the formation of the intermediate Ab 46 , but rather inhibit the turnover of Ab 46 , resulting in its accumulation. In addition, the non-steroidal anti-inflammatory drugs (NSAIDs) ibuprofen and sulindac sulfide have no effect on the formation and turnover of Ab 46 , but rather modulate the ratio of secreted Ab at a step after the formation of Ab 40 and Ab 42 . Thus, our data strongly suggest that the multi-sequential intramembrane cleavages of amyloid precursor protein C (APP) are likely catalyzed by the same c-secretase.

Aβ46 Is Processed to Aβ40 and Aβ43, but Not to Aβ42, in the Low Density Membrane Domains

“…Inconsistency between their results and ours may have arisen from the differences in the assay systems for ␥-secretase; Zhao et al (26) used either cell culture or a cell-free system using the total membrane fraction, whereas we used a cell-free system using the LDM domains. Most importantly, the pH (7.0) of our cell-free system differed from that of the system used by Zhao et al (26) (pH 6.4). We found that A␤ processing at lower pH (pH 6.5) proceeds in a ␥-secretase-independent manner by another protease, presumably involving cathepsin D, whose activity localized to fraction 4.…”

“…This again points to the possibility that the A␤42-producing process is separate from the A␤40-producing process. However, Zhao et al (26) recently reported that A␤46 is an intermediate precursor of both A␤40 and A␤42. Inconsistency between their results and ours may have arisen from the differences in the assay systems for ␥-secretase; Zhao et al (26) used either cell culture or a cell-free system using the total membrane fraction, whereas we used a cell-free system using the LDM domains.…”

“…However, Zhao et al (26) recently reported that A␤46 is an intermediate precursor of both A␤40 and A␤42. Inconsistency between their results and ours may have arisen from the differences in the assay systems for ␥-secretase; Zhao et al (26) used either cell culture or a cell-free system using the total membrane fraction, whereas we used a cell-free system using the LDM domains. Most importantly, the pH (7.0) of our cell-free system differed from that of the system used by Zhao et al (26) (pH 6.4).…”

Ex Vivo Occupancy of γ-Secretase Inhibitors Correlates with Brain β-Amyloid Peptide Reduction in Tg2576 Mice

“…We extended these findings to ␥-secretase in brains of Tg2576 mice to which 1996; Blanchard et al, 1997;Kim et al, 1997;Siman and Salidas, 2004 belong to the azepinone class of ␥-secretase inhibitors (R. Olson and C. Albright, in preparation). All three of these ␥-secretase inhibitors belong to the nontransition state class of molecules that are proposed to bind to an allosteric binding site on the presenilin subunit of ␥-secretase (Kornilova et al, 2003;Tian et al, 2003;Clarke et al, 2006;Morohashi et al, 2006), and that exert their effect through inhibition of the turnover of ␥-secretase processing intermediates (Qi-Takahara et al, 2005;Zhao et al, 2007 (Yan et al, 2004) and rhesus cortex homogenates (Patel et al, 2006) in the presence of unlabeled ␥-secretase inhibitors indicates that [ 3 H]IN973 is binding specifically to ␥-secretase. Furthermore, previous studies have shown that binding to mouse embryos is greatly reduced in embryos from presenilin-1 knockouts compared with wild-type embryos (Yan et al, 2004 (Iben et al, manuscript in preparation), very similar to the IC 50 values for inhibition of A␤40 in human embryonic kidney cells overexpressing the Swedish mutation of APP of 7.4 and 0.8 nM, respectively, and for inhibition of A␤42 of 7.9 and 0.4 nM, respectively (data not shown).…”

Down-regulation of APLP1 mRNA expression in hippocampus of pilocarpine-induced epileptic rats

“…APP family include multifunctional proteins related to Alzheimer's disease, nervous system lesions and epilepsy [17,18] . The three proteins of the APP family (APP, APLP1 and APLP2) share a high degree of similarity in their sequences, but may have different functions [19] , since alterations in ei- ther fragments or protein splicing could lead to various pathological changes [20] .…”