Inhibition of dynamin-dependent endocytosis increases shedding of the amyloid precursor protein ectodomain and reduces generation of amyloid β protein

Carey, Robyn M; Balcz, Brigitte A; López-Coviella, Ignacio; Slack, Barbara E.

doi:10.1186/1471-2121-6-30

Cited by 120 publications

(66 citation statements)

References 47 publications

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“…Because we also observed that UBQLN1 knockdown also increased levels of secreted A␤ in HEK293 cells, it is unlikely that accumulation of APP on the cell surface is a consequence of the decreased rate of endocytosis. In support of this, it has recently been shown that the overexpression of dynamin I dominant negative mutant (K44A) increases shedding of the APP ectodomain (sAPP␣) while significantly reducing the release of A␤ in HEK293 cells consistent with the premise that APP internalization is necessary for A␤ generation in HEK293 cells (36). In this context, however, it should be noted that, in HeLa cells, the dynamin I mutant (K44A) not only increased sAPP␣ levels, but also increased endogenous A␤ secretion suggesting that A␤ can be produced directly at the plasma membrane (37).…”

Section: Discussionmentioning

confidence: 78%

Ubiquilin 1 Modulates Amyloid Precursor Protein Trafficking and Aβ Secretion

Hiltunen

Thomas

et al. 2006

Journal of Biological Chemistry

118

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Ubiquilin 1 (UBQLN1) is a ubiquitin-like protein, which has been shown to play a central role in regulating the proteasomal degradation of various proteins, including the presenilins. We recently reported that DNA variants in UBQLN1 increase the risk for Alzheimer disease, by influencing expression of this gene in brain. Here we present the first assessment of the effects of UBQLN1 on the metabolism of the amyloid precursor protein (APP). For this purpose, we employed RNA interference to down-regulate UBQLN1 in a variety of neuronal and non-neuronal cell lines. We demonstrate that down-regulation of UBQLN1 accelerates the maturation and intracellular trafficking of APP, while not interfering with ␣-, ␤-, or ␥-secretase levels or activity. UBQLN1 knockdown increased the ratio of APP mature/immature, increased levels of full-length APP on the cell surface, and enhanced the secretion of sAPP (␣-and ␤-forms). Moreover, UBQLN1 knockdown increased levels of secreted A␤40 and A␤42. Finally, employing a fluorescence resonance energy transfer-based assay, we show that UBQLN1 and APP come into close proximity in intact cells, independently of the presence of the presenilins. Collectively, our findings suggest that UBQLN1 may normally serve as a cytoplasmic "gatekeeper" that may control APP trafficking from intracellular compartments to the cell surface. These findings suggest that changes in UBQLN1 steady-state levels affect APP trafficking and processing, thereby influencing the generation of A␤. Alzheimer disease (AD)3 is the most common cause of progressive neurological disorder leading to dementia. It is neuropathologically characterized by extracellular deposits of amyloid beta (A␤) peptide and by the generation of intracellular neurofibrillary tangles. Mutations in the amyloid precursor protein (APP), presenilin-1 (PSEN1), and presenilin-2 (PSEN2) genes are responsible for roughly half of the rare autosomal dominant, early-onset forms of the disease, which usually occur before the age of 60 (1-4). Meanwhile, apolipoprotein E (APOE) is the only commonly accepted susceptibility factor for late-onset AD (5, 6). Most mutations in APP, PSEN1, and PSEN2 genes lead to the increased production of A␤42 (relative to A␤40). A␤ is released from APP via sequential proteolytic cleavage by the ␤-and ␥-secretases (7). In addition to APP, the presenilins, and APOE, it is evident that additional AD susceptibility genes exist; successfully identifying these novel risk genes is an extremely important task that will not only facilitate prediction and diagnosis of AD but can also elucidate novel therapeutic approaches to treating and preventing AD.We have recently shown that genetic variants in the ubiquilin 1 (UBQLN1) gene, located on chromosome 9q22, increase the risk for AD, possibly by altering the expression and alternative splicing of this gene in brain (8). As is often the case with gene variants exerting modest effects on disease risk, subsequent genetic studies have both supported (9, 10) and not supported (11, 12) the initial g...

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Section: Discussionmentioning

confidence: 78%

Ubiquilin 1 Modulates Amyloid Precursor Protein Trafficking and Aβ Secretion

Hiltunen

Thomas

et al. 2006

Journal of Biological Chemistry

118

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“…Uptake of Transferrin-The mutant DynK44A, which inhibits APP endocytosis (12,13,32,45), had a similar stimulatory effect on APP shedding (Fig. 1B) and on APP ␣-and ␤-secretase cleavage (Fig.…”

Section: Snx33 Expression Reduces Endocytosis Of App and Thementioning

confidence: 94%

“…Dyn⌬NT increased AP-APP shedding 5-fold and had an even stronger effect than the well characterized dynamin-1 K44A mutant (Fig. 1B), which was previously shown to inhibit APP endocytosis and increase APP shedding (12,13). As a control, expression of wild-type dynamin, which does not inhibit endocytosis, did not affect APP shedding (Fig.…”

Section: Identification Of Snx33 In An Expression Cloning Screen Formentioning

confidence: 95%

“…Formation of this complex is required for the normal rate of APP endocytosis. Two previous studies used the well characterized dominant-negative dynamin-1 K44A mutant and also reported an increase in APP ␣-secretase cleavage (12,13). The only study that did not report an increase in APP ␣-secretase cleavage upon dynamin K44A expression did not use wild-type APP but rather the Swedish mutant APP (45), which is known to be mainly cleaved in the secretory pathway and seems to depend to a different extent on endocytosis for its ␤-secretase cleavage compared with wild-type APP (52).…”

Section: Discussionmentioning

confidence: 99%

“…Likewise, expression of the dynamin K44A mutant, which interferes with dynamin-dependent endocytosis in a dominant-negative manner, inhibits APP internalization from the plasma membrane and alters APP shedding. However, conflicting results have been reported as to whether this mainly affects the ␣-or the ␤-secretase cleavage or both of them (12,13). Moreover, expression of Rab5, a key regulator of endocytosis, increases APP internalization from the plasma membrane and enhances APP cleavage by ␤-secretase, leading to increased A␤ levels (14).…”

mentioning

confidence: 97%

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A Novel Sorting Nexin Modulates Endocytic Trafficking and α-Secretase Cleavage of the Amyloid Precursor Protein

Schöbel

Neumann

Hertweck³

et al. 2008

Journal of Biological Chemistry

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Ectodomain shedding of the amyloid precursor protein (APP) by the two proteases ␣-and ␤-secretase is a key regulatory event in the generation of the Alzheimer disease amyloid ␤ peptide (A␤). ␤-Secretase catalyzes the first step in A␤ generation, whereas ␣-secretase cleaves within the A␤ domain, prevents A␤ generation, and generates a secreted form of APP with neuroprotective properties. At present, little is known about the cellular mechanisms that control APP ␣-secretase cleavage and A␤ generation. To explore the contributory pathways, we carried out an expression cloning screen. We identified a novel member of the sorting nexin (SNX) family of endosomal trafficking proteins, called SNX33, as a new activator of APP ␣-secretase cleavage. SNX33 is a homolog of SNX9 and was found to be a ubiquitously expressed phosphoprotein. Exogenous expression of SNX33 in cultured cells increased APP ␣-secretase cleavage 4-fold but surprisingly had little effect on ␤-secretase cleavage. This effect was similar to the expression of the dominant negative dynamin-1 mutant K44A. SNX33 bound the endocytic GTPase dynamin and reduced the rate of APP endocytosis in a dynamin-dependent manner. This led to an increase of APP at the plasma membrane, where ␣-secretase cleavage mostly occurs. In summary, our study identifies SNX33 as a new endocytic protein, which modulates APP endocytosis and APP ␣-secretase cleavage, and demonstrates that the rate of APP endocytosis is a major control factor for APP ␣-secretase cleavage.

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