CHEK1 and Alzheimer disease: Apart from CDK4, Aβ1–42 also stimulates the protein expression of CDK1, CDK5, and Cdc25B and lowers the protein levels of 14-3-3, Cdc34, Chk1, cyclin D1, and Rb in SH-SY5Y cells (Hoerndli et al., 2007), which potentially contributes to the cell cycle re-entry of neurons during the course of AD development and progression.