ABSTRACT
Alzheimer's disease (AD) is a progressive neurodegenerative disease caused by accumulations of Aß peptides. Production and fibrillation of Aß are downregulated by BRI2 and BRI3, which are physiological inhibitors of amyloid precursor protein (APP) processing and Aß 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 Aß production. Thus, disrupting interactions between NRBP1 and its substrates BRI2 and BRI3 may provide a useful therapeutic strategy for AD.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Amyloid beta-Peptides/biosynthesis , Cullin Proteins/metabolism , Membrane Proteins/metabolism , Nerve Tissue Proteins/metabolism , Proteolysis , Receptors, Cytoplasmic and Nuclear/metabolism , Ubiquitin-Protein Ligases/metabolism , Vesicular Transport Proteins/metabolism , Amino Acid Sequence , Amyloid beta-Peptides/metabolism , Animals , Female , HEK293 Cells , HeLa Cells , Humans , Male , Mice, Inbred ICR , Protein Binding , Protein Multimerization , Receptors, Cytoplasmic and Nuclear/chemistry , Substrate Specificity , Transcription Factors/metabolism , Ubiquitination , Vesicular Transport Proteins/chemistryABSTRACT
Elongin A increases the rate of RNA polymerase II (pol II) transcript elongation by suppressing transient pausing by the enzyme. Elongin A also acts as a component of a cullin-RING ligase that can target stalled pol II for ubiquitylation and proteasome-dependent degradation. It is not known whether these activities of Elongin A are functionally interdependent in vivo. Here, we demonstrate that Elongin A-deficient (Elongin A(-/-)) embryos exhibit abnormalities in the formation of both cranial and spinal nerves and that Elongin A(-/-) embryonic stem cells (ESCs) show a markedly decreased capacity to differentiate into neurons. Moreover, we identify Elongin A mutations that selectively inactivate one or the other of the aforementioned activities and show that mutants that retain the elongation stimulatory, but not pol II ubiquitylation, activity of Elongin A rescue neuronal differentiation and support retinoic acid-induced upregulation of a subset of neurogenesis-related genes in Elongin A(-/-) ESCs.
