Identification of calcium and integrin-binding protein 1 as a novel regulator of production of amyloid β peptide using CRISPR/Cas9-based screening system.

The aberrant metabolism of amyloid β peptide (Aβ) has been implicated in the etiology of Alzheimer disease (AD). Aβ is produced via the sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretases. However, the precise regulatory mechanism of Aβ generation still remains unclear. To gain a better understanding of the molecular mechanism of Aβ production, we established a genetic screening method based on the CRISPR/Cas9 system to identify novel regulators of Aβ production. We successfully identified calcium and integrin-binding protein 1 (CIB1) as a potential negative regulator of Aβ production. The disruption of Cib1 significantly upregulated Aβ levels. In addition, immunoprecipitation experiments demonstrated that CIB1 interacts with the γ-secretase complex. Moreover, the disruption of Cib1 specifically reduced the cell-surface localization of mature Nicastrin (Nct), which is a component of the γ-secretase complex, without changing the intrinsic activity of γ-secretase. Finally, we confirmed using the single-cell RNA-seq data in human that CIB1 mRNA level in neuron was decreased in the early stage of AD. Taken together, our results indicate that CIB1 regulates Aβ production via controlling the subcellular localization of γ-secretase, suggesting CIB1 is involved in the development of AD.