Reactivating PTEN to impair glioma stem cells by inhibiting cytosolic iron-sulfur assembly.

Glioblastoma, the most lethal primary brain tumor, harbors glioma stem cells (GSCs) that not only initiate and maintain malignant phenotypes but also enhance therapeutic resistance. Although frequently mutated in glioblastomas, the function and regulation of PTEN in PTEN-intact GSCs are unknown. Here, we found that PTEN directly interacted with MMS19 and competitively disrupted MMS19-based cytosolic iron-sulfur (Fe-S) cluster assembly (CIA) machinery in differentiated glioma cells. PTEN was specifically succinated at cysteine (C) 211 in GSCs compared with matched differentiated glioma cells. Isotope tracing coupled with mass spectrometry analysis confirmed that fumarate, generated by adenylosuccinate lyase (ADSL) in the de novo purine synthesis pathway that is highly activated in GSCs, promoted PTEN C211 succination. This modification abrogated the interaction between PTEN and MMS19, reactivating the CIA machinery pathway in GSCs. Functionally, inhibiting PTEN C211 succination by reexpressing a PTEN C211S mutant, depleting ADSL by shRNAs, or consuming fumarate by the US Food and Drug Administration-approved prescription drug N-acetylcysteine (NAC) impaired GSC maintenance. Reexpressing PTEN C211S or treating with NAC sensitized GSC-derived brain tumors to temozolomide and irradiation, the standard-of-care treatments for patients with glioblastoma, by slowing CIA machinery-mediated DNA damage repair. These findings reveal an immediately practicable strategy to target GSCs to treat glioblastoma by combination therapy with repurposed NAC.

Hypoxanthine phosphoribosyl transferase 1 metabolizes temozolomide to activate AMPK for driving chemoresistance of glioblastomas.

Temozolomide (TMZ) is a standard treatment for glioblastoma (GBM) patients. However, TMZ has moderate therapeutic effects due to chemoresistance of GBM cells through less clarified mechanisms. Here, we demonstrate that TMZ-derived 5-aminoimidazole-4-carboxamide (AICA) is converted to AICA ribosyl-5-phosphate (AICAR) in GBM cells. This conversion is catalyzed by hypoxanthine phosphoribosyl transferase 1 (HPRT1), which is highly expressed in human GBMs. As the bona fide activator of AMP-activated protein kinase (AMPK), TMZ-derived AICAR activates AMPK to phosphorylate threonine 52 (T52) of RRM1, the catalytic subunit of ribonucleotide reductase (RNR), leading to RNR activation and increased production of dNTPs to fuel the repairment of TMZ-induced-DNA damage. RRM1 T52A expression, genetic interruption of HPRT1-mediated AICAR production, or administration of 6-mercaptopurine (6-MP), a clinically approved inhibitor of HPRT1, blocks TMZ-induced AMPK activation and sensitizes brain tumor cells to TMZ treatment in mice. In addition, HPRT1 expression levels are positively correlated with poor prognosis in GBM patients who received TMZ treatment. These results uncover a critical bifunctional role of TMZ in GBM treatment that leads to chemoresistance. Our findings underscore the potential of combined administration of clinically available 6-MP to overcome TMZ chemoresistance and improve GBM treatment.

HSP90B1-mediated plasma membrane localization of GLUT1 promotes radioresistance of glioblastomas.

Ionizing radiation is a popular and effective treatment option for glioblastoma (GBM). However, resistance to radiation therapy inevitably occurs during treatment. It is urgent to investigate the mechanisms of radioresistance in GBM and to find ways to improve radiosensitivity. Here, we found that heat shock protein 90 beta family member 1 (HSP90B1) was significantly upregulated in radioresistant GBM cell lines. More importantly, HSP90B1 promoted the localization of glucose transporter type 1, a key rate-limiting factor of glycolysis, on the plasma membrane, which in turn enhanced glycolytic activity and subsequently tumor growth and radioresistance of GBM cells. These findings imply that targeting HSP90B1 may effectively improve the efficacy of radiotherapy for GBM patients, a potential new approach to the treatment of glioblastoma.

METTL3-mediated m6A modification of LINC00839 maintains glioma stem cells and radiation resistance by activating Wnt/ß-catenin signaling.

Long noncoding RNAs (lncRNAs) are involved in glioma initiation and progression. Glioma stem cells (GSCs) are essential for tumor initiation, maintenance, and therapeutic resistance. However, the biological functions and underlying mechanisms of lncRNAs in GSCs remain poorly understood. Here, we identified that LINC00839 was overexpressed in GSCs. A high level of LINC00839 was associated with GBM progression and radiation resistance. METTL3-mediated m6A modification on LINC00839 enhanced its expression in a YTHDF2-dependent manner. Mechanistically, LINC00839 functioned as a scaffold promoting c-Src-mediated phosphorylation of ß-catenin, thereby inducing Wnt/ß-catenin activation. Combinational use of celecoxib, an inhibitor of Wnt/ß-catenin signaling, greatly sensitized GSCs to radiation. Taken together, our results showed that LINC00839, modified by METTL3-mediated m6A, exerts tumor progression and radiation resistance by activating Wnt/ß-catenin signaling.

PGC1α Degradation Suppresses Mitochondrial Biogenesis to Confer Radiation Resistance in Glioma.

Radiotherapy is a major component of standard-of-care treatment for gliomas, the most prevalent type of brain tumor. However, resistance to radiotherapy remains a major concern. Identification of mechanisms governing radioresistance in gliomas could reveal improved therapeutic strategies for treating patients. Here, we report that mitochondrial metabolic pathways are suppressed in radioresistant gliomas through integrated analyses of transcriptomic data from glioma specimens and cell lines. Decreased expression of peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α), the key regulator of mitochondrial biogenesis and metabolism, correlated with glioma recurrence and predicted poor prognosis and response to radiotherapy of patients with glioma. The subpopulation of glioma cells with low-mitochondrial-mass exhibited reduced expression of PGC1α and enhanced resistance to radiotherapy treatment. Mechanistically, PGC1α was phosphorylated at serine (S) 636 by DNA-dependent protein kinase in response to irradiation. Phosphorylation at S636 promoted the degradation of PGC1α by facilitating its binding to the E3 ligase RNF34. Restoring PGC1α activity with expression of PGC1α S636A, a phosphorylation-resistant mutant, or a small-molecule PGC1α activator ZLN005 increased radiosensitivity of resistant glioma cells by reactivating mitochondria-related reactive oxygen species production and inducing apoptotic effects both in vitro and in vivo. In summary, this study identified a self-protective mechanism in glioma cells in which radiotherapy-induced degradation of PGC1α and suppression of mitochondrial biogenesis play a central role. Targeted activation of PGC1α could help improve response to radiotherapy in patients with glioma. SIGNIFICANCE: Glioma cells reduce mitochondrial biogenesis by promoting PGC1α degradation to promote resistance to radiotherapy, indicating potential therapeutic strategies to enhance radiosensitivity.

Diallyl trisulfide sensitizes radiation therapy on glioblastoma through directly targeting thioredoxin 1.

Radiotherapy is a standard-of-care treatment approach for glioblastoma (GBM) patients, but therapeutic resistance to radiotherapy remains a major challenge. Here we demonstrate that diallyl trisulfide (DATS) directly conjugates with cysteine (C) 32 and C35 (C32/35) residues of thioredoxin 1 (Trx1) through Michael addition reactions. Due to localizing in activity center of Trx1, the conjugation between DATS and C32/35 results in inhibition of Trx1 activity, therefore disturbing thioredoxin system and leading to accumulated levels of reactive oxygen species (ROS). High levels of Trx1 expression are correlated with poor prognosis of glioma patients. Notably, we reveal that DATS synergistically enhances irradiation (IR)-induced ROS accumulation, apoptosis, DNA damage, as well as inhibition of tumor growth of GBM cells. These findings highlight the potential benefits of DATS in sensitizing radiotherapy of GBM patients.