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Trafficking and processing of APP b -secretase. Intracellular trafficking of APP: relation to its physiological function?. APP. TMD. 5A3/1G7. NH 2. APP localizes to the plasma membrane, Golgi and endosomes. Pastorino, unpublished data. APP. TMD. C-term APP Ab. NH 2.
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Trafficking and processing of APP b-secretase
Intracellular trafficking of APP: relation to its physiological function?
APP TMD 5A3/1G7 NH2 APP localizes to the plasma membrane, Golgi and endosomes Pastorino, unpublished data
APP TMD C-term APP Ab NH2 Staining for C-term domain of APP is detected also in the nucleus Pastorino, unpublished data
APP TMD 5A3/1G7 NH2 APP internalizes from the plasma membrane into intracellular compartments, endosomes and Golgi COOH Koo and Squazzo, 1994
APP co-localizes with the endosomes Pastorino et al., 2006
Why we want to study the trafficking of APP? Because, the intracellular localization of APP INFLUENCES the production of b-Amyloid peptide
Processing of APP a-secretase g-secretase b-secretase APP TMD NH2 COOH b-secretase a-secretase saAPPs C99 C83 sbAPPs g-secretase g-secretase Ab p3 AICD AICD Pathogenic amyloidogenic pathway Protective non-amyloidogenic pathway
Intracellular compartments and processing of APP a-secretase activity: in the plasma membrane (where metalloproteases, known to have like TACE and ADAM10/ADAM17, reside). b-secretase activity: mostly in the endosomes, possible also in the ER and Golgi g-secretase activity: mostly in the ER, also in lysosomes and possible at the plasma membrane (still under debate).
Trafficking of APP aAPP APP a-secretase activity APP C83 C99 b-secretase activity bAPPs AICD C99 Ab g-secretase activity
GOOD!! APP retained @ plasma membrane = Internalization of full length APP = Protective non-amyloidogenic processing BAD!!! pathogenic amyloidogenic processing
Products dowstream of non-amyloidogenic processing: aAPPs: soluble stub of APP deriving from the a-secretase cleavage : possible neurotrophic function p3: c-terminal truncated portion of the sequence of b-amyloid, deriving from the subsequent action of a- and g-secretase. DOES NOT aggregate. Unknown function. AICD: APP Intra Cellular Domain, deriving from the cleavage of g-secretase. Known regulation of transcriptional activity.
Products downstream of the amyloidogenic processing: bAPPs: soluble stub of APP deriving from the b-secretase cleavage : unknown function C99: c-terminal stub containing the entire intact sequence of the b-amyloid peptide, deriving from the action of b-secretase. It is the substrate from where b-amyloid peptides derive. b-Amyloid peptides: generated by the subsequent action of b- and g-secretases. At very low concentration could be neurotrophic, however, when forming aggregates they are VERY TOXIC and lead to the formation of the core of the b-amyloid plaque in AD AICD:APP Intra Cellular Domain, deriving from the cleavage of g-secretase. Known regulation of transcriptional activity.
Loss of non-amyloidogenic activity as a possible way to develop AD?
Selective Serotonin reuptake inhibitors (SSRI) reduce ISF Abeta…
Chronic SSRI treatment reduces the load of Abeta plaques in AD mice
Chronic SSRI treatment reduces the load of Abeta peptides in AD mice…
Use of antidepressant associates to reduced PIB uptake in humans
Activation of serotoninergic receptors leads to increased non-amyloidogenic pathway
Activation of non-amyloidogenic pathway as protective from AD?
Sirtuins levels are reduced in aging Is sirtuins activity lost in AD? Could their activity be protective?
Sirt1 expression regulates non-amyloidogenic processing of APP in AD mice
Sirt1 expression regulates levels of the a-secretase ADAM10 in AD mice both as protein….
SIRT1 regulates ADAM10 expression by deacetylating Retinoic Acid Receptor beta (RARb)
Levels of the transcription factor HES1 are regulated by SIRT1
The aspartyl protease BACE b-Amyloid cleaving enzyme
BACE is expressed mostly in the brain Vassar et al., 1999
In the cell, BACE localizes to Golgi apparatus and Endosomes Vassar et al., 1999
BACE activity 1-In vitro, BACE is mostly active at an acidic pH range between 4.5-5.5. 2-BACE is supposed to be mostly active in the endosomes, due to BACE co-localization and to the acidic pH of these organelles. Although in vivo, interaction between BACE and APP was observed at the plasma membrane and in the endosomes, in cell culture, BACE was active also in the ER and in the Golgi apparatus.
It was previously reported that BACE interacts with GGAs in yeast two hybrid system GGA1, 2 and 3 are monomeric adaptors that are recruited to the trans-Golgi network. GGAs’ function relates to regulation of the trafficking and degradation of proteins GGA consists of 4 distinct domains: VHS domain that binds DxxxLL residue in proteins GAT domain which binds Arf:GTP Hinge region to recruit clathrin A gamma adapton ear homology domain Tesco et al., Neuron. 2007 Jun 7;54(5):721-37.
BACE co-localizes and is degraded within lysosomes Koh et al., 2005
APP contains caspase cleavage sites in its sequence Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. However, although apoptosis increases C99 and Ab levels, this effects do not depend on caspase-mediated cleavage of APP (Tesco et al., 2003).
Does apoptosis lead to increased amyloidogenic processing of APP up-regulating BACE?
In this paper: Apoptosis increases levels of BACE and C99 in different cell lines These effects are reverted by the apoptosis inhibitor zVAD. Apoptosis regulates levels of BACE affecting its degradation not its synthesis, suggesting a post-translational mechanism. During apoptosis GGA3 is cleaved generating a Dominant Negative fragment that further affects BACE trafficking and degradation.
Apoptosis increases levels of C99….. Tesco et al., Neuron. 2007 Jun 7;54(5):721-37.
…and BACE Tesco et al., Neuron. 2007 Jun 7;54(5):721-37.
Apoptosis regulates levels of BACE affecting its degradation not its synthesis The BACE trafficking molecule GGA3 is cleaved during apoptosis A dominant negative truncated form of GGA3 is generated under apoptotic stimuli, increasing levels of Ab and BACE