Cereblon-mediated degradation of the amyloid precursor protein via the ubiquitin-proteasome pathway

Cereblon (CRBN) was identified as a gene that causes intellectual disabilities. The encoded CRBN protein, containing 442 amino acids, is located in several organs. Cytosolic CRBN was reported to mainly act as a component of the E3 ubiquitin ligase complex. CRBN is one of the substrate receptors of the E3 ubiquitin ligase complex and promotes the degradation of targeted proteins. Studies have reported that CRBN recognizes the C-terminal region of the amyloid precursor protein (APP), a protein known for its involvement in the development of Alzheimer's disease. Although CRBN may interact with the C-terminal region of APP in mice, the CRBN-mediated degradation mechanism of human APP remains unclear. Here, we analyzed the CRBN-mediated degradation mechanism of human APP via the ubiquitin-proteasome system. Immunoprecipitation experiments showed that CRBN interacts with human full-length APP via its C-terminal region. Next, we examined CRBN-mediated degradation of APP in the ubiquitin-proteasome system. CRBN recognizes Lys⁷⁵¹ in human APP and ubiquitinates it in SH-SY5Y cells. Overexpression of CRBN decreased wild-type APP expression levels. In contrast, the expression level of K751R APP remained unchanged by CRBN overexpression, while knockdown of endogenous CRBN increased APP levels. As such, our results suggest that CRBN ubiquitinates Lys⁷⁵¹ of human APP thereby degrading it via the ubiquitin-proteasome system.