Increased expression of the histone H3 lysine 4 methyltransferase MLL4 and the histone H3 lysine 27 demethylase UTX prolonging the overall survival of patients with glioblastoma and a methylated MGMT promoter

Abstract

OBJECTIVE The purpose of the present study was to investigate the epigenetic and prognostic roles of an H3K4 methyltransferase (mixed lineage leukemia 4 [MLL4]) and H3K27 demethylase (ubiquitously transcribed tetratricopeptide repeat gene on X chromosome [UTX]) in progression-free survival (PFS) and overall survival (OS) of patients with glioblastoma (GBM) who were treated with radiotherapy, chemotherapy, or both after resection. In addition, the authors examined methylation at the promoter of the O-6-methylguanine-DNA methyltransferase ( MGMT) gene and other prognostic factors predicting length of PFS and OS in these patients. METHODS The medical records of 76 patients having a new diagnosis of histologically ascertained GBM in the period of January 2002 to December 2013 at the authors' institution were retrospectively reviewed. Immunohistochemical staining for MLL4 and UTX was performed on archived paraffin-embedded tissues obtained by biopsy or resection. The methylation status of the MGMT promoter in these tissues was determined by methylation-specific PCR analysis. RESULTS During the follow-up period (mean length 18.1 months, range 4.1-43.5 months), 68 (89.5%) of the patients died. The MGMT promoter was methylated in 49 patients (64.5%) and unmethylated in 27 (35.5%). The immunoreactivity pattern of UTX was identical to that of MLL4; increased expression of these 2 proteins was observed in samples from 34 patients (44.7%) and decreased expression in 42 patients (55.3%). The mean length of PFS was 9.2 months (95% CI 6.8-11.6 months). Extent of surgery, recursive partitioning analysis (RPA) class, and methylation status of the MGMT promoter were all associated with increased PFS in the multivariate analysis of factors predicting PFS. The mean length of OS was 18.6 months (95% CI 14.3-22.9 months). Patient age (p = 0.004), WHO performance status score (p = 0.019), extent of surgery (p = 0.007), RPA class (p = 0.036), methylation status of the MGMT promoter (p = 0.010), and increased expression of UTX-MLL4 (p = 0.001) were significantly associated with increased OS in multivariate analysis. Interestingly, in patients with an unmethylated MGMT promoter, immunoreactivity of UTX-MLL4 was not associated with changes in OS (p = 0.350). However, in the patients with a methylated MGMT promoter, increased UTX-MLL4 expression was strongly associated with increased OS (p < 0.001). CONCLUSIONS The results of this study suggest that increased expression of UTX-MLL4 positively influences the outcome of patients with GBM having a methylated MGMT promoter. Therefore, UTX-MLL4 immunoreactivity could be a useful predictor of the response to conventional treatment with radiotherapy or chemotherapy among GBM patients whose tumors have a methylated MGMT promoter.

Keywords: CpG = cytosine-phosphate-guanine; FFPE = formalin-fixed, paraffin-embedded; GBM = glioblastoma; MGMT = O-6-methylguanine DNA methyltransferase; MLL4 = mixed lineage leukemia 4; MSP = methylation-specific PCR; O-6-methyl guanine methyltransferase; OS = overall survival; PFS = progression-free survival; PSQ = pyrosequencing; ROC = receiver operating characteristic; RPA = recursive partitioning analysis; UTX = ubiquitously transcribed tetratricopeptide repeat gene on X chromosome; UTX–MLL4 complex; epigenome; glioblastoma; oncology; prognosis; survival.