Dimeric Transmembrane Orientations of APP/C99 Regulate γ-Secretase Processing Line Impacting Signaling and Oligomerization
Amyloid precursor protein (APP) cleavage by the {beta} secretase produces the C99 transmembrane (TM) protein, which contains three dimerization-inducing Gly-x-x-x-Gly motifs. We demonstrate that dimeric C99 TM orientations regulate the precise cleavage lines by {gamma}-secretase. Of all possible dimeric orientations imposed by a coiled coil to the C99 TM-cytosolic domain, the dimer (cc-del7) containing 33Gly-x-x-x-Gly37 in the interface promoted A{beta}42 processing line and AICD (APP Intracellular Domain)-dependent gene transcription, including BACE1 mRNA induction, enhancing amyloidogenic signaling. Another orientation exhibiting 25Gly-x-x-x-Gly29 in the interface (cc-del6) favored processing to A{beta}43/40, induced significantly less gene transcription, while promoting formation of SDS-resistant "A{beta}-like" oligomers, reminiscent of A{beta} peptide oligomers. These required both Val24 of a pro-{beta} motif and the 25Gly-x-x-x-Gly29 interface. Thus, crossing angles imposed by dimeric orientations give access to {gamma}-secretase at A{beta}48 or A{beta}49, linking the former to enhanced signaling and A{beta}42. We discuss avenues of blocking amyloidogenic processing.