Expression of DNA methyltransferases DNMT1,3A, and 3B in normal hematopoiesis and in acute and chronic myelogenous leukemia

Abstract

Aberrant hypermethylation of tumor suppressor genes plays an important role in the development of many tumors. Recently identified new DNA methyltransferase (DNMT) genes, DNMT3A and DNMT3B, code for de novo methyltransferases. To determine the roles of DNMT3A, DNMT3B, as well as DNMT1, in the development of leukemia, competitive polymerase chain reaction (PCR) assays were performed and the expression levels of DNMTs were measured in normal hematopoiesis, 33 cases of acute myelogenous leukemia (AML), and 17 cases of chronic myelogenous leukemia (CML). All genes were constitutively expressed, although at different levels, in T lymphocytes, monocytes, neutrophils, and normal bone marrow cells. Interestingly, DNMT3B was expressed at high levels in CD34 ؉ bone marrow cells but down-regulated in differentiated cells. In AML, 5.3-, 4.4-, and 11.7-fold mean increases were seen in the levels of DNMT1, 3A, and 3B, respectively, compared with the control bone marrow cells. Although CML cells in the chronic phase did not show significant changes, cells in the acute phase showed 3.2-, 4.5-, and 3.4-fold mean increases in the levels of DNMT1, 3A, and 3B, respectively. Using methylation-specific PCR, it was observed that the p15 INAK4B IntroductionDNA methylation plays an important role in tissue-and stagespecific gene regulation, 1,2 genomic imprinting, 3,4 and X-chromosome inactivation, 5 and has been shown to be essential for normal mammalian development. 6 Recent studies have revealed that both global DNA hypomethylation and regional hypermethylation occur in tumorigenesis. [7][8][9] Such aberrant DNA methylation is observed in a nonrandom, tumor type-specific manner. 10 In particular, certain types of tumors show regional hypermethylation of CpG islands associated with the promoter regions of tumor suppressor genes, such as RB, 11 VHL, 12 p16 INAK4A , 13 and hMLH1. 14 Furthermore, the regional hypermethylation is often associated with the inactivation of the tumor suppressor genes. 15 These data suggest that this epigenetic process has a pathogenetic role in the clonal evolution of cancer. 9 In hematologic malignancies, aberrant DNA hypermethylation is thought to have relevance to leukemogenesis. 16 For example, during the progression of chronic myelogenous leukemia (CML), the ABL1 promoter of the BCR-ABL fusion gene becomes significantly hypermethylated. 17,18 Also, aberrant hypermethylation of the p15 INAK4B tumor suppressor gene is associated with its inactivation in at least half of the patients with acute lymphoblastic leukemia (ALL) and acute myelogenous leukemia (AML). 19,20 Furthermore, hypermethylation of p15 INAK4B is observed concomitant with the disease progression in myelodysplastic syndrome (MDS). 21 In addition to these tumor-related genes, a number of other genes are concurrently hypermethylated in AML, 22 suggesting that there might be a dysregulation in the normal DNA methylation mechanism, by which the leukemic cells become predisposed to hypermethylation.Until recently, only one mammalian DNA methyl...

Polymorphisms of the DNMT3B gene and risk of squamous cell carcinoma of the head and neck: A case–control study

“…Over-expression of DNMT3B has been observed in some cancer types, and it contributes to the generation of aberrant methylation in cancer [19][20][21][22][23][24][25][26]. As we previously reported, the DNMT3B contains a C-T transition polymorphism (C46359T) at a novel alternative promoter region, -149 base pairs from the transcription start site, which in in vitro assays confers a 30% increase in the promoter activity of DNMT3B [13].…”

Expression levels of DNA methyltransferase genes do not correlate with p15INK4B gene methylation in myelodysplastic syndromes

“…Furthermore, the expression levels of DNMTs are higher in AML patients with, than without methylated p15 INK4B . 9 The present study uses real-time quantitative RT-PCR to determine whether individual expression levels of DNMTs correlate with aberrant methylation of the p15 INK4B gene in patients with MDS.…”

MTSS1, a novel target of DNA methyltransferase 3B, functions as a tumor suppressor in hepatocellular carcinoma

“…Mouse studies have shown that both Dnmt3a and Dnmt3b are required for the establishment and maintenance of genomic methylation patterns and proper murine development (Bachman et al, 2001;Gowher and Jeltsch, 2002;Kaneda et al, 2004). DNMT3A and DNMT3B are upregulated in certain types of hematological malignancies and solid tumors, including leukocythemia (Mizuno et al, 2001;Claus and Lubbert, 2003), colorectal cancer Takeshima et al, 2006), lung cancer, breast cancer (Girault et al, 2003;Shafiei et al, 2008) and HCC (Saito et al, 2002;Choi et al, 2003). Specifically, DNMT3B contributes to oncogenic phenotypes (Linhart et al, 2007) and tumorigenesis in vivo by gene-specific de novo methylation and transcriptional silencing (Wang et al, 2007).…”