GSK3β activity is essential for senescence-associated heterochromatin foci (SAHF) formation induced by HMGA2 in WI38 cells.

Cellular senescence is an irreversible form of cell cycle arrest, which is often characterized by domains of facultative heterochromatin substructures also known as senescence-associated heterochromatin foci (SAHF). SAHF assembly is likely mediated through the downregulation of the Wnt pathway, which inhibits Glycogen Synthase Kinase 3 Beta (GSK3β) in cells undergoing replicative senescence. Alternatively, High Mobility Group AT-Hook 2 (HMGA2) can also induce SAHF formation in primary cells, through a process in which the involved cell signaling pathway is unknown. Accordingly, it is important to determine whether GSK3β and the Wnt pathway are necessary during HMGA2-induced SAHF formation. In this study, we developed a senescence model for SAHF assembly in WI38 cell through ectopic expression of HMGA2. In this model, typical senescent features were identified, including elevated SA-β-galactosidase staining and the downregulation of the Wnt pathway. We also showed that the GSK3β inhibitor LiCl can partly disable SAHF formation through the HMGA2 overexpression in WI38 cells. However, the disabled SAHF formation resulting from the inactivity of GSK3β in our senescence model cannot be restored through ectopic overexpression of Catenin Beta 1 (CTNNB1), a downstream transcription factor of the Wnt pathway. This indicates that the GSK3β activity alone, and not those of downstream target genes, is crucial for the HMGA2-induced SAHF formation following the downregulation of the Wnt pathway.