Summary: Alzheimer’s disease (AD) is a progressive neurodegenerative disease caused by accumulations of Aβ peptides. Production and fibrillation of Aβ are downregulated by BRI2 and BRI3, which are physiological inhibitors of amyloid precursor protein (APP) processing and Aβ oligomerization. Here, we identify nuclear receptor binding protein 1 (NRBP1) as a substrate receptor of a Cullin-RING ubiquitin ligase (CRL) that targets BRI2 and BRI3 for degradation. Moreover, we demonstrate that (1) dimerized NRBP1 assembles into a functional Cul2- and Cul4A-containing heterodimeric CRL through its BC-box and an overlapping cryptic H-box, (2) both Cul2 and Cul4A contribute to NRBP1 CRL function, and (3) formation of the NRBP1 heterodimeric CRL is strongly enhanced by chaperone-like function of TSC22D3 and TSC22D4. NRBP1 knockdown in neuronal cells results in an increase in the abundance of BRI2 and BRI3 and significantly reduces Aβ production. Thus, disrupting interactions between NRBP1 and its substrates BRI2 and BRI3 may provide a useful therapeutic strategy for AD. : Yasukawa et al. demonstrate that BRI2 and BRI3, physiological inhibitors of Aβ production and aggregation, are substrates of NRBP1-ubiquitin ligase. In the presence of TSC22D3 and TSC22D4, a dimer of the substrate receptor NRBP1 assembles into a functional Cul2- and Cul4A-containing heterodimeric CRL through overlapping BC-box and cryptic H-box motifs on NRBP1. Keywords: E3 ubiquitin ligase, CRL, Cullin, ubiquitination, NRBP1, Alzheimer’s disease, amyloid β, amyloid-β precursor protein/APP, BRI2/ITM2B, BRI3/ITM2C
