Cyclin-dependent Kinase 5 Promotes Myc Stabilization Through Inhibitory Phosphorylation of GSK-3β in Ewing Sarcoma

These findings suggest that functional impairment of GSK-3β and subsequent upregulation of Myc may promote the proliferation of Ewing sarcoma cells. Myc is normally phosphorylated by GSK-3β, which triggers its ubiquitination and proteasomal degradation. Although CDK5 is recognized as a cell-cycle-related kinase, our results demonstrate that CDK5 is associated with increased inhibitory phosphorylation of GSK-3β, resulting in functional suppression of its activity. As a result, GSK-3β-mediated phosphorylation of Myc is attenuated, leading to reduced ubiquitination and accumulation of Myc. Regulation of Myc expression through CDK5-mediated modulation of GSK-3β plays a critical role in controlling Ewing sarcoma cell proliferation and may represent a promising therapeutic target.