MCUB restricts mitochondrial calcium to support metabolic adaptation and homeostasis in glioblastoma.

The refractory nature of glioblastoma (GBM) is largely attributed to metabolic plasticity and stress adaptation. However, the role of precise mitochondrial calcium (mCa2+) flux gating in this context remains elusive. Here, we identify MCUB as a key gatekeeper upregulated in GBM, establishing a restricted mCa2+ threshold associated with malignancy. Mechanistically, MCUB limits mCa2+ uptake, attenuating pyruvate dehydrogenase activity and enforcing a glycolytic shift. MCUB deficiency triggers mCa2+ overload and reactive oxygen species bursts, sensitizing GBM cells to oxidative stress and radiotherapy. Moreover, hypoxia drives this adaptation via HIF-1α, which upregulates MCUB and reinforces its interaction with MCU to tune mCa2+ flux. Through high-throughput screening, we identify TF-PPAO as a compound interfering with the MCUB-MCU interaction. TF-PPAO exerts antitumor and radiosensitizing effects in xenografts, patient-derived xenografts (PDXs), and GBM organoids. Our findings reveal MCUB-mediated mCa2+ restriction as a mechanism of GBM metabolic adaptation and mitochondrial homeostasis, highlighting MCUB as a therapeutic target.