Functional switching of TGF-beta1 signaling in liver cancer via epigenetic modulation of a single CpG site in TTP promoter.
OBJECTIVE
Acquisition of resistance to the antiproliferative effect of transforming growth factor (TGF)-beta1 is crucial for the malignant progression of cancers. In this study, we sought to determine whether deregulated expression of tristetrapolin (TTP), a negative posttranscriptional regulator of c-Myc, confers resistance to the antiproliferative effects of TGF-beta1 on liver cancer cells.


METHODS
The epigenetics of TTP promoter regulation and its effects on TGF-beta1 signaling were examined in hepatocellular carcinoma (HCC) cell lines and patient tissues.


RESULTS
TTP was down-regulated in HCC cell lines (10/11), compared with normal liver, as well as in tumor tissues (19/24) from paired HCC specimens. Methylation of a specific single CpG site located within the TGF-beta1-responsive region (TRR) of the TTP promoter was significantly associated with TTP down-regulation in both HCC cell lines and tumor tissues (r = -0.606383, P < .001). The singly methylated CpG site was specifically bound by a transcriptional repressor complex consisting of MECP2/c-Ski/DNMT3A and abolished the TGF-beta1-induced as well as basal-level expression of TTP. The epigenetic inactivation of TTP led to an increased half-life of c-Myc mRNA and blocked the cytostatic effect of TGF-beta1. Statistically significant correlations were observed between the single CpG site methylation and expression levels of TTP or c-Myc in clinical samples of HCC.


CONCLUSIONS
Abrogation of the post-transcriptional regulation of c-Myc via methylation of a specific single CpG site in the TTP promoter presents a novel mechanism for the gain of selective resistance to the antiproliferative signaling of TGF-beta1 in HCC.
Sohn
Bo Hwa
BH
Medical Genomics Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Korea.
Park
In Young
IY
Lee
Jung Ju
JJ
Yang
Suk-Jin
SJ
Jang
Ye Jin
YJ
Park
Kyung Chan
KC
Kim
Dong Joon
DJ
Lee
Dong Chul
DC
Sohn
Hyun Ahm
HA
Kim
Tae Woo
TW
Yoo
Hyang-Sook
HS
Choi
Jong Young
JY
Bae
Yun Soo
YS
Yeom
Young Il
YI
D001483:Base Sequence; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D018899:CpG Islands; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D004268:DNA-Binding Proteins / Q000378:metabolism; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051783:Methyl-CpG-Binding Protein 2 / Q000378:metabolism; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D012323:RNA Processing, Post-Transcriptional; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D051816:Tristetraprolin / Q000235:genetics* / Q000378:metabolism
D004268:DNA-Binding Proteins; C000717967:DNMT3A protein, human; C497392:MECP2 protein, human; C489427:MYC protein, human; D051783:Methyl-CpG-Binding Protein 2; D046912:Multiprotein Complexes; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D053773:Transforming Growth Factor beta1; D051816:Tristetraprolin; C497552:ZFP36 protein, human; C060614:SKI protein, human; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A