LABORATORY INVESTIGATION - HUMAN/ANIMAL TISSUE Epigenetic regulation of DNA methyltransferases: DNMT1 and DNMT3B in gliomas Ganeshkumar Rajendran • Karthik Shanmuganandam • Ameya Bendre • Dattatreya Mujumdar • Abhay Goel • Anjali Shiras Received: 30 July 2010 / Accepted: 21 December 2010 / Published online: 13 January 2011 Ó Springer Science+Business Media, LLC. 2011 Abstract The role of epigenetics and significance of aberrant gene regulation in etiology of cancer is a well- established phenomenon. The hallmark of cancer epige- netics is aberrant DNA methylation consisting of global hypomethylation and regional hypermethylation of tumor suppressor genes (TSGs) by DNA methyltransferases (DNMTs). In mammals, DNA methylation is catalyzed by DNMTs encoded by DNMT1, DNMT3A, and DNMT3B. Interestingly, little is known about variation in the meth- ylation status of epigenetic regulators themselves in glio- mas. Here, we report significant overexpression of DNMT1 and DNMT3B. A study of the methylation status and his- tone modifications at the promoter region of DNA meth- yltransferase I (DNMT1) gene revealed an unmethylated DNA promoter, similar to that detected in normal brain tissues. However, a differential histone code with distinct euchromatin marks—AcH3, AcH4, and H3k4me2—was specifically detected in tumors, unlike in normal brain tissues, which were found predominantly enriched with heterochromatin marks such as H3K9me2 and H3K27me3. In contrast, a differential methylation pattern of DNMT3B gene promoter occurred in glioma tumors, wherein it was found hypomethylated. Transcriptional silencing by CpG island methylation is a prevalent mechanism for inactiva- tion of TSGs. Inhibiting DNMTs by 5-azacytidine (DNMT inhibitor) treatment led to significant inhibition of expres- sion of DNMT1 and DNMT3B and enhanced expression of TSGs such as PTEN and p21 analyzed in this study. Our studies have identified effects of increased presence of DNMTs on inhibition of tumor suppressors that are epi- genetically silenced in gliomas, thereby leading to aberrant regulation of cell cycle progression and failure to maintain genomic stability. Keywords Tumor suppressor genes Á Histone modifications Á Acetylation Á DNA methylation Á MS-PCR Á ChIP assay Introduction Human gliomas are the most common tumors of the central nervous system (CNS), classified into grades I–IV depending on their extent of malignancy [1]. Glioblastoma multiforme (GBM), the most aggressive of all gliomas, is a highly heterogeneous tumor with most of the cases dis- playing an average survival period of less than 1 year [2]. Several studies have identified that glioma tumor growth is driven by a small subpopulation of cells known as cancer stem cells (CSC), and these cells contribute to the high level of chemo- and radioresistance of gliomas [3–5]. DNA methylation and posttranslational histone modifi- cations are major mechanisms that govern epigenetic reg- ulation of the genome. Aberrant epigenetic inactivation of TSGs leads to gene silencing in various human malignan- cies. This is characterized by DNA hypermethylation of promoter regions and acquisition of histone modifica- tions that are characteristic of repressed chromatin [6, 7]. Electronic supplementary material The online version of this article (doi:10.1007/s11060-010-0520-2) contains supplementary material, which is available to authorized users. The first two authors contributed equally to this work. G. Rajendran Á K. Shanmuganandam Á A. Bendre Á A. Shiras (&) National Centre for Cell Science (NCCS), Pune, India e-mail: anjalishiras@nccs.res.in D. Mujumdar Á A. Goel Seth GS Medical College and KEM Hospital, Mumbai, India 123 J Neurooncol (2011) 104:483–494 DOI 10.1007/s11060-010-0520-2