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

Glioblastoma (GBM), 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
GBMs, the function and regulation of PTEN in PTEN-intact GSCs are unknown.
Here we found that PTEN directly interacts with MMS19 and competitively
disrupts MMS19-based cytosolic iron-sulfur (Fe-S) cluster assembly (CIA)
machinery in the differentiated glioma cells (DGCs). Interrogation of
GSCs, when compared with their matched DGCs, revealed that PTEN is
specifically succinated at cysteine (C) 211 in GSCs. Isotope tracing
coupled with mass spectrometry analysis confirmed that fumarate, generated
by adenylosuccinate lyase (ADSL) in de novo purine synthesis pathway which
is highly activated in GSCs, promotes PTEN C211 succination. This
modification abrogates the interaction between PTEN and MMS19, thereby
reactivating CIA machinery pathway in GSCs. Functionally, inhibiting PTEN
C211 succination through re-expressing PTEN C211S mutant, depleting ADSL,
or consuming fumarate by N-acetylcysteine (NAC), an FDA-approved
prescription drug, impairs GSC maintenance. Importantly, re-expressing
PTEN C211S or treating with NAC sensitizes GSC-derived brain tumors to
temozolomide and irradiation, the standard-of-care treatments for GBM
patients, by retarding CIA machinery-mediated DNA damage repair. These
findings reveal an immediately practicable strategy to target GSCs for
treating GBMs by combined therapy with repurposing NAC.

胶质母细胞瘤（Glioblastoma, GBM）是致死性最高的原发性脑肿瘤，其病灶内存在胶质瘤干细胞（glioma stem cells, GSCs）——这类细胞不仅可启动并维持肿瘤的恶性表型，还能增强肿瘤的治疗抵抗能力。尽管PTEN（磷酸酶和张力蛋白同源物）在GBM中常发生突变，但在PTEN完整的GSCs中，PTEN的功能与调控机制仍未明确。本研究发现，PTEN可与MMS19直接结合，并在分化型胶质瘤细胞（differentiated glioma cells, DGCs）中竞争性破坏基于MMS19的胞质铁硫簇组装（cytosolic iron-sulfur cluster assembly, CIA）系统。通过对比GSCs与其配对的DGCs，研究人员发现PTEN在GSCs中特异地在半胱氨酸（C）211位点发生琥珀酰化修饰。同位素示踪联合质谱分析证实，在GSCs中高度激活的从头嘌呤合成通路中，腺苷琥珀酸裂解酶（adenylosuccinate lyase, ADSL）催化生成的延胡索酸可促进PTEN C211位点的琥珀酰化。该修饰会阻断PTEN与MMS19的相互作用，进而重新激活GSCs中的CIA通路。功能实验显示，通过过表达PTEN C211S突变体、敲低ADSL，或使用FDA批准的处方药N-乙酰半胱氨酸（N-acetylcysteine, NAC）消耗延胡索酸，均可削弱GSCs的自我维持能力。值得注意的是，过表达PTEN C211S或使用NAC处理，可通过阻滞CIA系统介导的DNA损伤修复，使GSCs来源的脑肿瘤对替莫唑胺与放射治疗（GBM患者的标准治疗方案）更加敏感。本研究揭示了一种可快速落地的GBM治疗策略：通过联合使用老药新用的NAC靶向GSCs。