E3 ligase LMO7 promotes ALKBH2 ubiquitination to sensitize MGMT-deficient glioblastoma to temozolomide.

Temozolomide (TMZ) resistance in glioblastoma (GBM) is often linked to high MGMT protein levels, but MGMT-deficient tumors can still acquire resistance, implicating MGMT-independent repair pathways. Here, we identify an oxidative stress-responsive LMO7-ALKBH2 ubiquitination mechanism that regulates ALKBH2 stability and modulates alkylation damage tolerance in GBM. The E3 ligase LMO7 directly binds ALKBH2 and promotes K48-linked polyubiquitination and proteasomal degradation of ALKBH2, with Lys7 serving as a major ubiquitin acceptor site. Oxidative stress enhances LMO7-dependent ALKBH2 ubiquitination through NEDD8-dependent cullin neddylation, reducing TMZ-induced ALKBH2 accumulation and increasing TMZ sensitivity. The K7R substitution attenuates LMO7- and oxidative stress-induced ALKBH2 polyubiquitination and degradation and weakens LMO7-dependent TMZ sensitization. Functionally, ALKBH2 depletion sensitizes MGMT-deficient GBM cells to TMZ and methyl methanesulfonate, whereas ALKBH2 re-expression restores alkylator tolerance. In patient datasets, ALKBH2 protein levels are elevated in GBM and inversely associated with MGMT protein levels, an association not detected at the mRNA level. High ALKBH2 expression in chemotherapy-treated IDH-wild-type glioma and low LMO7 expression in the CGGA astrocytoma cohort are each associated with shorter overall survival. Together, these results indicate that oxidative stress-coupled LMO7-dependent polyubiquitination of ALKBH2 modulates TMZ sensitivity in GBM, particularly in MGMT-deficient tumors.