Loss of 5-hydroxymethylcytosine is accompanied with malignant cellular transformation.
Dysregulated DNA methylation followed by abnormal gene expression is an epigenetic hallmark in cancer. DNA methylation is catalyzed by DNA methyltransferases, and the aberrant expression or mutations of DNA methyltransferase genes are found in human neoplasm. The enzymes for demethylating 5-methylcytosine were recently identified, and the biological significance of DNA demethylation is a current focus of scientific attention in various research fields. Ten-eleven translocation (TET) proteins have an enzymatic activity for the conversion from 5-methylcytosine to 5-hydroxymethylcytosine (5-hmC), which is an intermediate of DNA demethylation. The loss-of-function mutations of TET2 gene were reported in myeloid malignancies, suggesting that impaired TET-mediated DNA demethylation could play a crucial role in tumorigenesis. It is still unknown, however, whether DNA demethylation is involved in biological properties in solid cancers. Here, we show the loss of 5-hmC in a broad spectrum of solid tumors: for example, a significant reduction of 5-hmC was found in 72.7% of colorectal cancers (CRCs) and 75% of gastric cancers compared to background tissues. TET1 expression was decreased in half of CRCs, and a large part of them was followed by the loss of 5-hmC. These findings suggest that the amount of 5-hmC in tumors is often reduced via various mechanisms, including the downregulation of TET1. Consistently, in the in vitro experiments, the downregulation of TET1 was clearly induced by oncogene-dependent cellular transformation, and loss of 5-hmC was seen in the transformed cells. These results suggest the critical roles of aberrant DNA demethylation for oncogenic processes in solid tissues.
Department of Gastroenterology, Graduate School of Medicine, Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan.
Yotaro
Y
Kudo
Keisuke
K
Tateishi
Keisuke
K
Yamamoto
Shinzo
S
Yamamoto
Yoshinari
Y
Asaoka
Hideaki
H
Ijichi
Genta
G
Nagae
Haruhiko
H
Yoshida
Hiroyuki
H
Aburatani
Kazuhiko
K
Koike
D044503:5-Methylcytosine / Q000378:metabolism* / Q000031:analogs & derivatives; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000235:genetics; D003596:Cytosine / Q000031:analogs & derivatives* / Q000378:metabolism; D019175:DNA Methylation / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics*; D055785:Gene Knockdown Techniques; D006801:Humans; D006899:Mixed Function Oxygenases; D009154:Mutation; D009369:Neoplasms / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D013274:Stomach Neoplasms / Q000235:genetics
D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; C011865:5-hydroxymethylcytosine; D044503:5-Methylcytosine; D003596:Cytosine; D006899:Mixed Function Oxygenases; C462539:TET1 protein, human