METTL3 Increases Temozolomide Resistance in MGMT-Negative Glioblastoma by Enhancing CBX5 mRNA Stability in an m6A-IGF2BP2-Dependent Manner.

AIMS: We examined whether chromobox protein 5 (CBX5) contributes to temozolomide (TMZ) resistance in O6-methylguanine-DNA methyltransferase (MGMT)-negative glioblastoma (GBM) and whether it is regulated by methyltransferase-like 3 (METTL3)-dependent N6-methyladenosine (m6A) and insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2).

METHODS

Public datasets, clinical specimens, MGMT-negative cells, and subcutaneous xenografts were examined using functional, mechanistic, and rescue assays.

RESULTS

In the CGGA693 cohort of the Chinese Glioma Genome Atlas, higher CBX5 expression remained associated with shorter survival after multivariable adjustment (hazard ratio 1.178, 95% confidence interval 1.050-1.322; p = 0.005). CBX5 depletion increased TMZ sensitivity, apoptosis, and DNA damage, reduced ATM phosphorylation and RAD51 abundance, and restricted TMZ-treated xenograft growth; overexpression produced reciprocal effects in vitro. METTL3 depletion reduced CBX5 expression, mRNA stability, m6A enrichment, and wild-type reporter activity but did not significantly affect the m6A motif-mutant reporter. IGF2BP2 depletion reduced CBX5 protein and mRNA stability, whereas RNA immunoprecipitation supported an IGF2BP2-CBX5 mRNA association. CBX5 re-expression partially reversed METTL3 depletion-induced effects on viability and DNA damage.

CONCLUSION

METTL3-dependent m6A modification and IGF2BP2-associated stabilization help maintain CBX5 expression, contributing to TMZ resistance and ATM-RAD51-associated signaling in MGMT-negative GBM models.