Loss of Cdk5rap2 triggers cellular senescence via β-catenin-mediated downregulation of WIP1

Loss-of-function mutations in Cdk5rap2 is associated with the developmental disorders, primary microcephaly and primordial dwarfism, but the underlying molecular link remains obscure. Here, we show that Cdk5rap2 loss in BJ-5ta human fibroblasts triggers senescence that is associated with proliferation defect, which is manifested as small body size in Cdk5rap2an/an mice. In fibroblasts, Cdk5rap2 loss induces p53 Ser15 phosphorylation that correlates with decreased level of the p53 phosphatase, WIP1. Ectopic WIP1 expression reverses senescence in Cdk5rap2-depleted cells, linking senescence to WIP1 downregulation. Cdk5rap2 interacts with GSK3β, increasing inhibitory Ser9 phosphorylation in GSK3β, which phosphorylates and tags β-catenin for degradation. Thus, Cdk5rap2 loss decreases GSK3β Ser9 phosphorylation and increases GSK3β activity, reducing β-catenin that affects expression of NF-κB target genes, including WIP1. Consequently, Cdk5rap2 or β-catenin depletion downregulates WIP1. GSK3β Inhibition in Cdk5rap2-depleted cells restores β-catenin and WIP1 levels, reducing p53 Ser15 phosphorylation and preventing senescence. Conversely, WIP1 inhibition increases p53 Ser15 phosphorylation and senescence in Cdk5rap2-depleted cells lacking GSK3β activity. Senescence through GSK3β/β-catenin downregulation of WIP1 may contribute to the developmental disorders associated with Cdk5rap2 loss-of-function.