Spatiotemporal processing of neural cell adhesion molecules 1 and 2 by BACE1 in vivo

Abstract

Neural cell adhesion molecules 1 (NCAM1) and 2 (NCAM2) belong to the cell adhesion molecules of the immunoglobulin superfamily and have been shown to regulate formation, maturation, and maintenance of synapses. NCAM1 and NCAM2 undergo proteolysis, but the identity of all the proteases involved and how proteolysis is used to regulate their functions are not known. We report here that NCAM1 and NCAM2 are BACE1 substrates in vivo . NCAM1 and NCAM2 overexpressed in HEK cells were both cleaved by metalloproteinases or BACE1, and NCAM2 was also processed by γ-secretase. We identified the BACE1 cleavage site of NCAM1 (at Glu 671) and NCAM2 (at Glu 663) using mass spectrometry and site-directed mutagenesis. Next, we assessed BACE1-mediated processing of NCAM1 and NCAM2 in the mouse brain during aging. NCAM1 and NCAM2 were cleaved in the olfactory bulb of BACE1+/+ but not BACE1−/− mice at postnatal day 10 (P10), 4 and 12 months of age. In the hippocampus, a BACE1-specific soluble fragment of NCAM1 (sNCAM1β) was only detected at P10. However, we observed an accumulation of full-length NCAM1 in hippocampal synaptosomes in 4-month-old BACE1−/− mice. We also found that polysialylated NCAM1 (PSA-NCAM1) levels were increased in BACE1−/− mice at P10 and demonstrated that BACE1 cleaves both NCAM1 and PSA-NCAM1 in vitro . In contrast, we did not find evidence for BACE1-dependent NCAM2 processing in the hippocampus at any age analyzed. In summary, our data demonstrate that BACE1 differentially processes NCAM1 and NCAM2 depending on the region of brain, subcellular localization, and age in vivo .

The Hidden Side of NCAM Family: NCAM2, a Key Cytoskeleton Organization Molecule Regulating Multiple Neural Functions

“…Many proteins with these domains are involved in cell signaling through the activation of tyrosine kinases, such us Tyrosine-protein kinase Fyn or focal adhesion kinase, FAK. Thirdly, both NCAM2 isoforms present a proteolytic site between amino acids 682 and 701; proteolysis at this site causes the extracellular fragment to be released [ 75 , 76 ]. Fourthly, the extracellular region has eight N-glycosylation sites which are HNK-1 sequences.…”

“…In particular, different metalloproteases cleave adhesion molecules in order to remove the physical bond between presynaptic and postsynaptic membranes and thus reshape synapses. Cleavage has been described in several proteins of the immunoglobulin superfamily, such as NCAM1, L1CAM and NCAM2 [ 75 , 161 ]. In vivo, NCAM2 is cleaved by ADAM10 and BACE-1 and could participate in synapses plasticity and remodeling.…”

Re-Expression of Poly/Oligo-Sialylated Adhesion Molecules on the Surface of Tumor Cells Disrupts Their Interaction with Immune-Effector Cells and Contributes to Pathophysiological Immune Escape

“…There are three isoforms of NCAM2 located on the membrane, with molecular weights of 90, 115, and 125 kDa, respectively, the smallest isoform of which is attached to glycosylphosphatidylinositol (GPI) on membranes [79][80][81][82][83]. NCAM-2 has a high sequence identity with NCAM-1 [84,85]. The sequence identity between NCAM-1 and NCAM-2 is highest at the Ig1, Ig2, and Ig5 modules and in the cytoplasmic region.…”

“…Regarding the latter diseases, only a short hint to a vast array of publications seems appropriate in the context of this review. In fact, numerous publications have described that imbalances in sialic acid distribution and the degree of sialylated glycoproteins in conjunction with their co-partners are causal factors for certain neuronal diseases, such as Alzheimer's disease [85,188,189,247,254], Parkinson's disease [255,256], multiple sclerosis [257][258][259], and schizophrenia [260]. It is well known that the absence of sialic acid and galactose residues or the upregulation of certain lectins, e.g., siglec-1 in body cells, leads to various autoimmune diseases and tissue inflammation by activation of immune effector cells [261].…”

“…The degree of glycosylation in the Ig5 module probably determines a possible modulation and function of NCAM-2 [282]. Similar to NCAM-2 [283,284], NCAM-1 (except its 180 kDa isoform) carries a HNK-1 carbohydrate structure at the Ig5 module [59,85] (see below).…”