Research Article Δ DNMT3B4-del Contributes to Aberrant DNA Methylation Patterns in Lung Tumorigenesis Mark Z. Ma a,b , Ruxian Lin a , José Carrillo c , Manisha Bhutani d , Ashutosh Pathak e , Hening Ren a,b , Yaokun Li f , Jiuzhou Song c , Li Mao a,b, ⁎ a Department of Oncology and Diagnostic Sciences, University of Maryland School of Dentistry, University of Maryland, 650 W Baltimore St, Baltimore, MD 21201, USA b Marlene and Stewart Greenebaum Cancer Center, University of Maryland, 22 S Greene St, Baltimore, MD 21201, USA c Department of Animal and Avian Sciences, University of Maryland, College Park, Silver Spring, MD 20742, USA d Department of Hematologic Oncology and Blood Disorders, Levine Cancer Institute/Carolinas Healthcare System, Charlotte, NC, USA e Teva Pharmaceuticals, 1090 Horsham Rd, North Wales, PA 19454, USA f College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi 712100, PR China abstract article info Article history: Received 23 June 2015 Received in revised form 17 August 2015 Accepted 1 September 2015 Available online 7 September 2015 Keywords: DNMT3B ΔDNMT3B ΔDNMT3B-del DNA methylation Lung cancer Mouse model Tumorigenesis Aberrant DNA methylation is a hallmark of cancer but mechanisms contributing to the abnormality remain elu- sive. We have previously shown that ΔDNMT3B is the predominantly expressed form of DNMT3B. In this study, we found that most of the lung cancer cell lines tested predominantly expressed DNMT3B isoforms without exons 21, 22 or both 21 and 22 (a region corresponding to the enzymatic domain of DNMT3B) termed DNMT3B/ΔDNMT3B-del. In normal bronchial epithelial cells, DNMT3B/ΔDNMT3B and DNMT3B/ΔDNMT3B-del displayed equal levels of expression. In contrast, in patients with non-small cell lung cancer NSCLC), 111 (93%) of the 119 tumors predominantly expressed DNMT3B/ΔDNMT3B-del, including 47 (39%) tumors with no detect- able DNMT3B/ΔDNMT3B. Using a transgenic mouse model, we further demonstrated the biological impact of ΔDNMT3B4-del, the ΔDNMT3B-del isoform most abundantly expressed in NSCLC, in global DNA methylation pat- terns and lung tumorigenesis. Expression of ΔDNMT3B4-del in the mouse lungs resulted in an increased global DNA hypomethylation, focal DNA hypermethylation, epithelial hyperplastia and tumor formation when chal- lenged with a tobacco carcinogen. Our results demonstrate ΔDNMT3B4-del as a critical factor in developing aber- rant DNA methylation patterns during lung tumorigenesis and suggest that ΔDNMT3B4-del may be a target for lung cancer prevention. © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction DNA methylation is a major form of inheritable epigenetic mecha- nism that regulates the genome. It is important in the dosage compen- sation of sex chromosome, the repression of retrotransposons, the maintenance of genome stability, and the coordinated expression of imprinted genes during development and cellular differentiation (Edwards et al., 2010; Hansen et al., 2011; Jones, 2002; Robertson, 2001). These epigenetic modifications direct the establishment of cell lineage through maintenance of inheritable gene expression profile and genomic stability (Messerschmidt et al., 2014). Most sites of DNA methylation occur at cytosine residuals of CpG dinucleotides. In normal adult tissues, the CpG sites at the repetitive regions of the genome are heavily methylated, while most of the CpG islands located at or near the promoter regions are unmethylated. DNA methylation is catalyzed by various DNA methyltransferases. DNMT1 is the enzyme critical for maintaining DNA methylation patterns during DNA replication whereas DNMT3A and DNMT3B can methylate DNA in de novo manner to devel- op new methylation patterns in the genome (Bestor, 2000; Li et al., 1992; Okano et al., 1999). While DNA demethylation may occur in ei- ther a passive or active manner (Chen et al., 2003; Tahiliani et al., 2009), mechanisms of these actions remain largely unclear. In tumorigenesis, the landscape of DNA methylation patterns chang- es dramatically, with the general observation of reduced global DNA methylation and an increase of DNA methylation at certain promoter CpG islands (Jones, 2012). While extensive efforts have been devoted to study promoter DNA hypermethylation as a common epigenetic al- teration in cancers (Jones and Baylin, 2007; Suzuki et al., 2002), global DNA hypomethylation is recognized as an epigenetic abnormality in human tumorigenesis as well (Feinberg and Vogelstein, 1987). It is be- lieved that DNMTs, particularly DNMT3B, are involved in the promoter hypermethylation in tumorigenesis as DNMT3B is often overexpressed in cancer tissues (Van Emburgh and Robertson, 2011). However, EBioMedicine 2 (2015) 1340–1350 ⁎ Corresponding author at: Department of Oncology and Diagnostic Sciences, University of Maryland School of Dentistry, 650 W Baltimore St, Baltimore, MD 21201, USA. E-mail address: lmao@umaryland.edu (L. Mao). http://dx.doi.org/10.1016/j.ebiom.2015.09.002 2352-3964/© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Contents lists available at ScienceDirect EBioMedicine journal homepage: www.ebiomedicine.com