Epigenetic silencing of XAF1 in high-grade gliomas is associated with IDH1 status and improved clinical outcome

Abstract

// Thomas R. Reich 1 , Olivier J. Switzeny 1 , Mirjam Renovanz 2 , Clemens Sommer 3 , Bernd Kaina 1 , Markus Christmann 1 , Maja T. Tomicic 1 1 Department of Toxicology, University Medical Center, D-55131 Mainz, Germany 2 Department of Neurosurgery, University Medical Center, D-55131 Mainz, Germany 3 Department of Neuropathology, University Medical Center, D-55131 Mainz, Germany Correspondence to: Maja T. Tomicic, email: tomicic@uni-mainz.de Markus Christmann, email: mchristm@uni-mainz.de Keywords: high-grade glioma, glioblastoma, temozolomide, XAF1 promoter methylation, IDH1 Received: July 22, 2016      Accepted: January 10, 2017      Published: January 19, 2017 ABSTRACT XAF1 (X-linked inhibitor of apoptosis (XIAP)-associated factor 1) is a tumor suppressor that counteracts the anti-apoptotic effects of XIAP and can sensitize cells to cell death triggering events. XAF1 knockdown abrogated the temozolomide (TMZ)-induced G2-arrest and prevented TMZ-induced apoptosis in the glioblastoma (GB) cell line LN229. Promoter methylation of XAF1 was found to be inversely correlated with mRNA expression in GB cells. We analyzed XAF1 methylation in a panel of 16 GB cell lines and 80 patients with first-diagnosed WHO grade III/IV high-grade gliomas using methylation-sensitive high-resolution melt (MS-HRM) analysis. In those patients, XAF1 promoter methylation was strongly associated with enhanced progression free and overall survival. Interestingly, XAF1 promoter methylation was strictly correlated with the occurrence of IDH1 mutations, indicating a causal link to the IDH1 mutant phenotype. XAF1 methylation was observed in 18 grade III tumors all of which showed heterozygous mutations in the IDH1 gene. 17 harbored a mutation leading to an arginine > histidine (R132H) and one carried a mutation causing an arginine > glycine (R132G) substitution. Furthermore, six out of six recurrent and IDH1 mutated grade III tumors also showed XAF1 promoter methylation. The data demonstrate that XAF1 promoter methylation determined by MS-HRM is a robust and precise indicator of IDH1 mutations in grade III gliomas. It is useful for complementing the immunohistochemistry-based detection of mutant IDH, uncovering rare 2-HG-producing IDH1 and potentially IDH2 mutations. The MS-HRM-based detection of XAF1 methylation could therefore be a reliable tool in assisting the sub-classification of high-grade gliomas.