• Increasing biochemical and genetic evidence indicates that the amyloid-β (Aβ) peptide derived from amyloid precursor protein (APP) plays a central role in Alzheimer's disease (AD) pathogenesis. We previously reported that RanBP9 promotes Aβ generation by scaffolding APP/BACE1/LRP complexes together. Interestingly, the RanBP9-Δ1/N60 (residues 1-392) deletion mutant interacted much more strongly with APP/BACE1/LRP than full-length RanBP9. In this study, we found that RanBP9-N60, a processed form of RanBP9 virtually identical to the RanBP9-Δ1/N60 mutant, was strongly increased in AD brains compared with controls. To evaluate the potential pathogenic consequences of this phenotype, we studied the differential biological properties of fulllength RanBP9 vs. RanBP9-Δ1/N60 in HEK293T and Neuro-2A cells. The RanBP9-Δ1/N60 fragment, which lacks a nuclear localization signal, displayed enhanced cytoplasmic vs. nuclear localization and >3-fold enhanced stability than full-length RanBP9. Importantly, RanBP9-Δ1/N60, which contains the LisH dimerization domain, retained the capacity to form self-interacting multimeric complexes and increased Aβ generation by -5-fold over vector controls, more potent than the -3-fold increase seen by full-length RanBP9. Taken together, these data indicate that RanBP9-N60 may further drive the amyloid cascade in AD and that the proteolytic processing of RanBP9 may be an attractive therapeutic target. - Lakshmana, M. K., Chung, J. Y., Wickramarachchi, S., Tak, E., Bianchi, E., Koo, E. H., Kang, D. E. A fragment of the scaffolding protein RanBP9 is increased in Alzheimer's disease brains and strongly potentiates amyloid β peptide generation. © FASEB.

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