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BACE1 activity regulates cell surface contactin-2 levels.

ABSTRACT: Although BACE1 is a major therapeutic target for Alzheimer's disease (AD), potential side effects of BACE1 inhibition are not well characterized. BACE1 cleaves over 60 putative substrates, however the majority of these cleavages have not been characterized. Here we investigated BACE1-mediated cleavage of human contactin-2, a GPI-anchored cell adhesion molecule.Our initial protein sequence analysis showed that contactin-2 harbors a strong putative BACE1 cleavage site close to its GPI membrane linker domain. When we overexpressed BACE1 in CHO cells stably transfected with human contactin-2, we found increased release of soluble contactin-2 in the conditioned media. Conversely, pharmacological inhibition of BACE1 in CHO cells expressing human contactin-2 and mouse primary neurons decreased soluble contactin-2 secretion. The BACE1 cleavage site mutation 1008MM/AA dramatically impaired soluble contactin-2 release. We then asked whether contactin-2 release induced by BACE1 expression would concomitantly decrease cell surface levels of contactin-2. Using immunofluorescence and surface-biotinylation assays, we showed that BACE1 activity tightly regulates contactin-2 surface levels in CHO cells as well as in mouse primary neurons. Finally, contactin-2 levels were decreased in Alzheimer's disease brain samples correlating inversely with elevated BACE1 levels in the same samples.Our results clearly demonstrate that mouse and human contactin-2 are physiological substrates for BACE1. BACE1-mediated contactin-2 cleavage tightly regulates the surface expression of contactin-2 in neuronal cells. Given the role of contactin-2 in cell adhesion, neurite outgrowth and axon guidance, our data suggest that BACE1 may play an important role in these physiological processes by regulating contactin-2 surface levels.

SUBMITTER: Gautam V

PROVIDER: S-EPMC3899608 | biostudies-literature | 2014 Jan

REPOSITORIES: biostudies-literature

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BACE1 activity regulates cell surface contactin-2 levels.

Gautam Vivek V D'Avanzo Carla C Hebisch Matthias M Kovacs Dora M DM Kim Doo Yeon DY

Molecular neurodegeneration 20140109

<h4>Background</h4>Although BACE1 is a major therapeutic target for Alzheimer's disease (AD), potential side effects of BACE1 inhibition are not well characterized. BACE1 cleaves over 60 putative substrates, however the majority of these cleavages have not been characterized. Here we investigated BACE1-mediated cleavage of human contactin-2, a GPI-anchored cell adhesion molecule.<h4>Results</h4>Our initial protein sequence analysis showed that contactin-2 harbors a strong putative BACE1 cleavage ...[more]

PMID: 24405708

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Project description:Amyloid precursor protein (APP) was originally identified as the source of ?-amyloid peptides that accumulate in Alzheimer's disease (AD), but it also has been implicated in the control of multiple aspects of neuronal motility. APP belongs to an evolutionarily conserved family of transmembrane proteins that can interact with a variety of adapter and signaling molecules. Recently, we showed that both APP and its insect ortholog [APPL (APP-Like)] directly bind the heterotrimeric G-protein Go?, supporting the model that APP can function as an unconventional Go?-coupled receptor. We also adapted a well characterized assay of neuronal migration in the hawkmoth, Manduca sexta, to show that APPL-Go? signaling restricts ectopic growth within the developing nervous system, analogous to the role postulated for APP family proteins in controlling migration within the mammalian cortex. Using this assay, we have now identified Manduca Contactin (MsContactin) as an endogenous ligand for APPL, consistent with previous work showing that Contactins interact with APP family proteins in other systems. Using antisense-based knockdown protocols and fusion proteins targeting both proteins, we have shown that MsContactin is selectively expressed by glial cells that ensheath the migratory neurons (expressing APPL), and that MsContactin-APPL interactions normally prevent inappropriate migration and outgrowth. These results provide new evidence that Contactins can function as authentic ligands for APP family proteins that regulate APP-dependent responses in the developing nervous system. They also support the model that misregulated Contactin-APP interactions might provoke aberrant activation of Go? and its effectors, thereby contributing to the neurodegenerative sequelae that typify AD.Members of the amyloid precursor protein (APP) family participate in many aspects of neuronal development, but the ligands that normally activate APP signaling have remained controversial. This research provides new evidence that members of the Contactin family function as authentic ligands for APP and its orthologs, and that this evolutionarily conserved class of membrane-attached proteins regulates key aspects of APP-dependent migration and outgrowth in the embryonic nervous system. By defining the normal role of Contactin-APP signaling during development, these studies also provide the framework for investigating how the misregulation of Contactin-APP interactions might contribute to neuronal dysfunction in the context of both normal aging and neurodegenerative conditions, including Alzheimer's disease.

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BACE1 activity regulates cell surface contactin-2 levels.

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BACE1 activity regulates cell surface contactin-2 levels.

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