GSK3α negatively regulates GSK3β by decreasing its protein levels and enzymatic activity in mouse embryonic stem cells.

Glycogen synthase kinase 3 (GSK3) is a crucial regulator of cellular processes, including stem cell maintenance and differentiation. Although the roles of the two GSK3 isozymes, GSK3α and GSK3β, are well documented, their specific interactions remain less understood. In this study, we explored the regulatory interplay between GSK3α and GSK3β in mouse embryonic stem cells (mESCs). Using genetic manipulation, small-molecule inhibitors, and biochemical analysis, we found that inhibition of GSK3α kinase activity increases GSK3β protein levels and activity, whereas overexpression of GSK3α reduces GSK3β protein levels and activity. Domain-swapping experiments between the two isozymes identified the glycine-rich region at the N terminus of GSK3α as the key sequence responsible for downregulating GSK3β protein levels. Our findings reveal a novel interaction between GSK3 isozymes, with GSK3α modulating GSK3β activity to maintain the balance between stem cell pluripotency and neural differentiation. This insight may open new pathways for understanding stem cell fate mechanisms and developing GSK3-targeted therapeutic strategies in regenerative medicine.