The same gamma-secretase accounts for the multiple intramembrane cleavages of APP

It has been hypothesized that different C-terminus of beta-amyloid peptide (Abeta) may be generated by different gamma-secretase activities. Recently, we have identified a new zeta-cleavage site at Abeta46, leading to an important finding that the C-terminus of Abeta is produced by a series of sequential cleavages. This finding prompted us to examine the effects of the known gamma-secretase inhibitors on different steps of the gamma-secretase-mediated sequential cleavages and specifically their effects on the formation and turnover of the intermediate Abeta(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 Abeta(40/42) by inhibiting the formation of the intermediate Abeta(46). However, most of the other inhibitors show no inhibitory effect on the formation of the intermediate Abeta(46), but rather inhibit the turnover of Abeta(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 Abeta(46), but rather modulate the ratio of secreted Abeta at a step after the formation of Abeta(40) and Abeta(42). Thus, our data strongly suggest that the multi-sequential intramembrane cleavages of amyloid precursor protein C (APP) are likely catalyzed by the same gamma-secretase.