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

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