Loss of ATRX suppresses ATM dependent DNA damage repair by modulating H3K9me3 to enhance temozolomide sensitivity in glioma.

Mutations in ATRX constitute the most prevalent genetic abnormalities in gliomas. The presence of ATRX mutations in glioma serves as a marker of better prognosis with longer patient survival although the underlying mechanisms are poorly understood. In the present study, we found that ATRX biological function was significantly involved in DNA replication and repair. CRISPR/Cas9-mediated genetic inactivation of ATRX induced inhibition of cell proliferation, invasion and vasculogenic mimicry. In addition, temozolomide (TMZ) treatment induced greater DNA damage and apoptotic changes in ATRX knockout glioma cells. Moreover, we confirmed that ATRX knockout resulted in a failure to trigger ATM phosphorylation and finally restrained the activation of downstream proteins of the ATM pathway. The ATM-associated DNA repair pathway was extensively compromised in ATRX knockout cells owing to decreased histone H3K9me3 availability. Public databases also showed that patients with low ATRX expression exhibited preferable overall survival and profited more from TMZ treatment. These data suggest that ATRX is involved in DNA damage repair by regulating the ATM pathway and might serve as a prognostic maker in predicting TMZ chemosensitivity.

Han B ，Cai J ，Gao W ，Meng X ，Gao F ，Wu P ，Duan C ，Wang R ，Dinislam M ，Lin L ，Kang C ，Jiang C ... -  《-》

ATRX/EZH2 complex epigenetically regulates FADD/PARP1 axis, contributing to TMZ resistance in glioma.

Rationale: Glioma is the most common primary malignant brain tumor in adults. Chemoresistance of temozolomide (TMZ), the first-line chemotherapeutic agent, is a major issue in the management of patients with glioma. Alterations of alpha thalassemia/mental retardation syndrome X-linked (ATRX) gene constitute one of the most prevalent genetic abnormalities in gliomas. Therefore, elucidation of the role of ATRX contributing to TMZ resistance in glioma is urgently needed. Methods: We performed the bioinformatics analysis of gene expression, and DNA methylation profiling, as well as RNA and ChIP-seq data sets. CRISPR-Cas9 gene editing system was used to achieve the ATRX knockout in TMZ resistant cells. In vitro and in vivo experiments were carried out to investigate the role of ATRX contributing to TMZ resistance in glioma. Results: We found that ATRX expression was upregulated via DNA demethylation mediated by STAT5b/TET2 complex and strengthened DNA damage repair by stabilizing PARP1 protein in TMZ resistant cells. ATRX elicited PARP1 stabilization by the down-regulating of FADD expression via the H3K27me3 enrichment, which was dependent on ATRX/EZH2 complex in TMZ resistant cells. Magnetic resonance imaging (MRI) revealed that the PARP inhibitor together with TMZ inhibited glioma growth in ATRX wild type TMZ resistant intracranial xenograft models. Conclusions: The present study further illustrated the novel mechanism of the ATRX/PARP1 axis contributing to TMZ resistance. Our results provided substantial new evidence that PARP inhibitor might be a potential adjuvant agent in overcoming ATRX mediated TMZ resistance in glioma.

Han B ，Meng X ，Wu P ，Li Z ，Li S ，Zhang Y ，Zha C ，Ye Q ，Jiang C ，Cai J ，Jiang T ... -  《Theranostics》

Mutant IDH1 Enhances Temozolomide Sensitivity via Regulation of the ATM/CHK2 Pathway in Glioma.

Lin L ，Cai J ，Tan Z ，Meng X ，Li R ，Li Y ，Jiang C ... -  《-》

Estrogen receptor beta enhances chemotherapy response of GBM cells by down regulating DNA damage response pathways.

Zhou M ，Sareddy GR ，Li M ，Liu J ，Luo Y ，Venkata PP ，Viswanadhapalli S ，Tekmal RR ，Brenner A ，Vadlamudi RK ... -  《Scientific Reports》

IDH1-R132H acts as a tumor suppressor in glioma via epigenetic up-regulation of the DNA damage response.

Patients with glioma whose tumors carry a mutation in isocitrate dehydrogenase 1 (IDH1R132H) are younger at diagnosis and live longer. IDH1 mutations co-occur with other molecular lesions, such as 1p/19q codeletion, inactivating mutations in the tumor suppressor protein 53 (TP53) gene, and loss-of-function mutations in alpha thalassemia/mental retardation syndrome X-linked gene (ATRX). All adult low-grade gliomas (LGGs) harboring ATRX loss also express the IDH1R132H mutation. The current molecular classification of LGGs is based, partly, on the distribution of these mutations. We developed a genetically engineered mouse model harboring IDH1R132H, TP53 and ATRX inactivating mutations, and activated NRAS G12V. Previously, we established that ATRX deficiency, in the context of wild-type IDH1, induces genomic instability, impairs nonhomologous end-joining DNA repair, and increases sensitivity to DNA-damaging therapies. In this study, using our mouse model and primary patient-derived glioma cultures with IDH1 mutations, we investigated the function of IDH1R132H in the context of TP53 and ATRX loss. We discovered that IDH1R132H expression in the genetic context of ATRX and TP53 gene inactivation (i) increases median survival in the absence of treatment, (ii) enhances DNA damage response (DDR) via epigenetic up-regulation of the ataxia-telangiectasia-mutated (ATM) signaling pathway, and (iii) elicits tumor radioresistance. Accordingly, pharmacological inhibition of ATM or checkpoint kinases 1 and 2, essential kinases in the DDR, restored the tumors' radiosensitivity. Translation of these findings to patients with IDH1132H glioma harboring TP53 and ATRX loss could improve the therapeutic efficacy of radiotherapy and, consequently, patient survival.

Núñez FJ ，Mendez FM ，Kadiyala P ，Alghamri MS ，Savelieff MG ，Garcia-Fabiani MB ，Haase S ，Koschmann C ，Calinescu AA ，Kamran N ，Saxena M ，Patel R ，Carney S ，Guo MZ ，Edwards M ，Ljungman M ，Qin T ，Sartor MA ，Tagett R ，Venneti S ，Brosnan-Cashman J ，Meeker A ，Gorbunova V ，Zhao L ，Kremer DM ，Zhang L ，Lyssiotis CA ，Jones L ，Herting CJ ，Ross JL ，Hambardzumyan D ，Hervey-Jumper S ，Figueroa ME ，Lowenstein PR ，Castro MG ... -  《-》