Interaction of the cytosolic domains of sorLA/LR11 with the amyloid precursor protein (APP) and beta-secretase beta-site APP-cleaving enzyme.
sorLA is a recently identified neuronal receptor for amyloid precursor protein (APP) that is known to interact with APP and affect its intracellular transport and processing. Decreased levels of sorLA in the brain of Alzheimer's disease (AD) patients and elevated levels of amyloid-beta peptide (Abeta) in sorLA-deficient mice point to the importance of the receptor in this neurodegenerative disorder. We analyzed APP cleavage in an APP-shedding assay and found that both sorLA and, surprisingly, a sorLA tail construct inhibited APP cleavage in a beta-site APP-cleaving enzyme (BACE)-dependent manner. In line with this finding, sorLA and the sorLA tail significantly reduced secreted Abeta levels when BACE was overexpressed, suggesting that sorLA influences beta-cleavage. To understand the effect of sorLA on APP cleavage by BACE, we analyzed whether sorLA interacts with APP and/or BACE. Because both full-length sorLA and sorLA C-terminal tail constructs were functionally relevant for APP processing, we analyzed sorLA-APP for a potential cytoplasmatic interaction domain. sorLA and C99 coimmunoprecipitated, pointing toward the existence of a new cytoplasmatic interaction site between sorLA and APP. Moreover, sorLA and BACE also coimmunoprecipitate. Thus, sorLA interacts both with BACE and APP and might therefore directly affect BACE-APP complex formation. To test whether sorLA impacts BACE-APP interactions, we used a fluorescence resonance energy transfer assay to evaluate BACE-APP interactions in cells. We discovered that sorLA significantly reduced BACE-APP interactions in Golgi. We postulate that sorLA acts as a trafficking receptor that prevents BACE-APP interactions and hence BACE cleavage of APP.
Spoelgen
Robert
R
Alzheimer's Disease Research Laboratory, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
von Arnim
Christine A F
CA
Thomas
Anne V
AV
Peltan
Ithan D
ID
Koker
Mirjam
M
Deng
Amy
A
Irizarry
Michael C
MC
Andersen
Olav M
OM
Willnow
Thomas E
TE
Hyman
Bradley T
BT
D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases; D019921:Biotinylation; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D003600:Cytosol; D004705:Endocytosis; D010450:Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D007668:Kidney; D026502:LDL-Receptor Related Proteins; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D046912:Multiprotein Complexes; D016297:Mutagenesis, Site-Directed; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011973:Receptors, LDL / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D014162:Transfection
D016564:Amyloid beta-Protein Precursor; D026502:LDL-Receptor Related Proteins; D026901:Membrane Transport Proteins; D046912:Multiprotein Complexes; D011973:Receptors, LDL; D011993:Recombinant Fusion Proteins; C102582:SORL1 protein, human; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human