It is possible that β′-CTF is generated via cleavage of β-CTF by BACE1, since Vetrivel et al. (2011) showed that BACE1 readily processes β-CTF into β′-CTF in COS cells. In BACE1-expressing cell medium, soluble as well as full-length

BACE1 are detected. We showed previously that treatment with a metalloprotease inhibitor TAPI-1 reduces BACE1 shedding but increases full-length BACE1 release, suggesting that these two events are interrelated physiological processes (Murayama et al. 2005). In the present study, we showed that the FL-BACE1/sol-BACE1 ratio was significantly increased in the media of SH-SY5Y cells and primary neurons expressing BACE1-CA4, compared to those expressing Inhibitors,research,lifescience,medical BACE1-WT. These results Inhibitors,research,lifescience,medical suggest that BACE1 shedding is reduced in the absence of BACE1 palmitoylation, although the underlying mechanism is yet to be established. It is unlikely that lack of raft localization of BACE1 is related to reduced shedding because metalloproteases responsible for BACE1 shedding, such as ADAM10, are predominantly distributed in nonraft fractions (Kojro et al. 2001). Palmitoylation Inhibitors,research,lifescience,medical of BACE1 may affect the physical interactions between

BACE1 and its sheddases and promote BACE1 shedding. BACE1 exists as a homodimer under native conditions. Dimer formation could be influenced by BACE1 posttranslational modifications such as palmitoylation. Previous studies have indicated that dimerization of BACE1 is inhibited in bHEK cells treated with cerulenin, which has an inhibitory effect on palmitoylation (Parsons and Austen 2005), implying a role of palmitoylation in BACE1 dimerization. However, BN-PAGE analysis disclosed no differences in dimer formation between BACE1-WT and BACE1-CA4 proteins. Thus, it Inhibitors,research,lifescience,medical appears that palmitoylation of BACE1 does not directly influence dimerization. It is likely that BACE1 in lipid rafts has functional roles other than processing of APP. BACE1 cleaves a number of substrates, including neuregulins, p-selectin glycoprotein ligand-1, β-subunits

of voltage-gated sodium Inhibitors,research,lifescience,medical channels, and lipo-protein receptor-related protein (Lichtenthaler et al. 2003; von Arnim whatever et al. 2005; Wong et al. 2005; Hu et al. 2006; Pictilisib manufacturer Willem et al. 2006; Kim et al. 2007). It is plausible that BACE1 functions to cleave these membrane proteins that are localized in lipid rafts. In our immunocytochemical analysis of BACE1-expressing neurons, BACE1 immunoreactivity was observed throughout neuronal processes, implying activity in the metabolism of specific synaptic proteins. The mechanisms underlying regulation of BACE1 activity in neurons are complex (Stockley and O’Neill 2008). We and others have demonstrated that reticulon (RTN) proteins such as RTN3 and RTN4-B/C interact with BACE1 and inhibit its β-cleavage activity (He et al. 2004; Murayama et al. 2006). Our preliminary data indicate that RTN3 and RTN4-B/C mostly distributed in nonraft domains (data not shown) where they appear to regulate BACE1.