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Physiologically generated presenilin 1 lacking exon 8 fails to rescue brain PS1-/- phenotype and forms complexes with wildtype PS1 and nicastrin.

ABSTRACT: The presenilin 1 (PSEN1) L271V mutation causes early-onset familial Alzheimer's disease by disrupting the alternative splicing of the PSEN1 gene, producing some transcripts harboring the L271V point mutation and other transcripts lacking exon 8 (PS1(?exon8)). We previously reported that PS1 L271V increased amyloid beta (A?) 42/40 ratios, while PS1(?exon8) reduced A?42/40 ratios, indicating that the former and not the exon 8 deletion transcript is amyloidogenic. Also, PS1(?exon8) did not rescue A? generation in PS1/2 double knockout cells indicating its identity as a severe loss-of-function splice form. PS1(?exon8) is generated physiologically raising the possibility that we had identified the first physiological inactive PS1 isoform. We studied PS1(?exon8) in vivo by crossing PS1(?exon8) transgenics with either PS1-null or Dutch APP(E693Q) mice. As a control, we crossed APP(E693Q) with mice expressing a deletion in an adjacent exon (PS1(?exon9)). PS1(?exon8) did not rescue embryonic lethality or Notch-deficient phenotypes of PS1-null mice displaying severe loss of function in vivo. We also demonstrate that this splice form can interact with wildtype PS1 using cultured cells and co-immunoprecipitation (co-IP)/bimolecular fluorescence complementation. Further co-IP demonstrates that PS1(?exon8) interacts with nicastrin, participating in the ?-secretase complex formation. These data support that catalytically inactive PS1(?exon8) is generated physiologically and participates in protein-protein interactions.

SUBMITTER: Brautigam H

PROVIDER: S-EPMC4660297 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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Physiologically generated presenilin 1 lacking exon 8 fails to rescue brain PS1-/- phenotype and forms complexes with wildtype PS1 and nicastrin.

Brautigam Hannah H Moreno Cesar L CL Steele John W JW Bogush Alexey A Dickstein Dara L DL Kwok John B J JB Schofield Peter R PR Thinakaran Gopal G Mathews Paul M PM Hof Patrick R PR Gandy Sam S Ehrlich Michelle E ME

Scientific reports 20151126

The presenilin 1 (PSEN1) L271V mutation causes early-onset familial Alzheimer's disease by disrupting the alternative splicing of the PSEN1 gene, producing some transcripts harboring the L271V point mutation and other transcripts lacking exon 8 (PS1(∆exon8)). We previously reported that PS1 L271V increased amyloid beta (Aβ) 42/40 ratios, while PS1(∆exon8) reduced Aβ42/40 ratios, indicating that the former and not the exon 8 deletion transcript is amyloidogenic. Also, PS1(∆exon8) did not rescue A ...[more]

PMID: 26608390

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Project description:Mutations in presenilin proteins (PS1 and PS2) lead to early-onset Alzheimer's disease. PS proteins are endoproteolytically cleaved into two main fragments: the NTF (PS N-terminal fragment) and the CTF (PS C-terminal fragment). The two fragments are believed to constitute the core catalytic enzyme activity called gamma-secretase, which is responsible for cleaving beta-amyloid precursor protein to release Abeta. Thus, studying factors that modulate PS fragment levels could provide important information about gamma-secretase. Previously, we demonstrated that the protein, ubiquilin-1, interacts both in vivo and in vitro with PS and that overexpression of ubiquilin-1 or -2 leads to increased accumulation of full-length PS proteins. Using wild-type HEK-293 cells (human embryonic kidney 293 cells) and PS-inducible cells, we now show that overexpression of either ubiquilin-1 or -2 decreases the PS NTF and CTF levels. Conversely, siRNA (small interfering RNA)-mediated knockdown of ubiquilin-1 and -2 proteins increased the PS NTF and CTF levels. We considered that ubiquilin might alter PS fragment accumulation by acting as a shuttle factor escorting PS fragments to the proteasome for degradation. However, through proteasome inhibition studies, we show that this does not occur. Instead, our results suggest that ubiquilin regulates PS fragment production. We also examined whether other components of the gamma-secretase complex are affected by ubiquilin expression. Interestingly, overexpression of ubiquilin resulted in a decrease in Pen-2 and nicastrin levels, two essential components of the gamma-secretase complex. In contrast, knockdown of ubiquilin-1 and -2 protein expression by RNAi (RNA interference) increased Pen-2 and nicastrin levels. Finally, we show that inhibition of the proteasome results in decreased PS fragment production and that reversal of proteasome inhibition restores PS fragment production, suggesting that the proteasome may be involved in PS endoproteolysis. These studies implicate ubiquilin as an important factor in regulating PS biogenesis and metabolism.

Dataset Information

Physiologically generated presenilin 1 lacking exon 8 fails to rescue brain PS1-/- phenotype and forms complexes with wildtype PS1 and nicastrin.

Publications

Physiologically generated presenilin 1 lacking exon 8 fails to rescue brain PS1-/- phenotype and forms complexes with wildtype PS1 and nicastrin.

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