Chemotherapy-Activated GSK3β-DNMT1 Signaling Upregulates CD47 to Evade Macrophage Phagocytosis and Drive Temozolomide Resistance in Glioblastoma.

Temozolomide (TMZ) remains the first-line therapy for glioblastoma (GBM) patients. However, the mechanisms underlying the emergence of acquired TMZ resistance after treatment are unclear. Here, we reveal the critical role of macrophage phagocytosis in GBM recurrence and acquired TMZ resistance. Mechanistically, TMZ treatment sustained GSK3β activation and promoted its interaction with DNMT1. This led to the phosphorylation of DNMT1 at the previously unrecognized S977 site for its K981-dependent ubiquitination and destabilization. The downregulation of DNMT1 leads to hypomethylation of the CD47 promoter and increases the expression of CD47, a key inhibitor of macrophage phagocytosis. Elevated CD47 expression suppresses macrophage phagocytosis and promotes the survival of TMZ-treated GBM cells. The small molecule WIN 51708 disrupts the p-GSK3β-Y216-DNMT1 interaction, which stabilizes DNMT1, decreases CD47 expression, restores phagocytosis in vivo, and resensitizes tumors to TMZ. The GSK3β-DNMT1-CD47 axis was found to be conserved in a TMZ-resistant PDX model and in samples from patients with recurrent GBM, supporting its clinical translational value. Our findings underscore the potential of the combined administration of WIN 51708 and TMZ as a strategy to resensitize GBM tumors.