Epigenetic regulation of the taxol resistance-associated gene TRAG-3 in human tumors.
TRAG-3, originally identified as a taxol resistance-associated gene from an ovarian carcinoma cell line, is upregulated in many human tumors. Like many tumor antigens, TRAG-3 mRNA is not detectable or is expressed at very low levels in normal fetal and adult human tissues except for testis, where TRAG-3 mRNA transcripts are detected abundantly. TRAG-3 mRNA is frequently overexpressed in tumors but is rarely detected in adjacent normal tissues. To delineate the transcriptional regulation of this tumor antigen, we cloned and sequenced the TRAG-3 promoter. A 539-base pair fragment upstream of the initiation site, which contains two unusual CT repeat stretches, was sufficient to drive the maximum activity of a luciferase reporter gene. Sodium bisulfite sequencing of genomic DNA revealed that the amount of DNA methylation in exon 2 and in the promoter regions is inversely correlated with gene expression. In normal tissues, TRAG-3 is hypermethylated and is thus transcriptionally silenced. In those tumors where TRAG-3 is actively transcribed, the TRAG-3 promoter and exon 2 are hypomethylated. Treatment of a TRAG-3-silenced cell line H23 with the demethylating reagent 5-aza-cytosine reduced DNA methylation and induced TRAG-3 expression in a dose-dependent manner. These results indicate that DNA demethylation is an important epigenetic mechanism that regulates the TRAG-3 tumor antigen in human tumors.
Yao
Xiaoming
X
Medical Service, Veterans Affairs Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94305, USA.
Hu
Ji-Fan
JF
Li
Tao
T
Yang
Youwen
Y
Sun
Zhihong
Z
Ulaner
Gary A
GA
Vu
Thanh H
TH
Hoffman
Andrew R
AR
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001483:Base Sequence; D045744:Cell Line, Tumor; D003596:Cytosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019175:DNA Methylation; D017931:DNA Primers; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D009363:Neoplasm Proteins / Q000235:genetics*; D017239:Paclitaxel / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics
D000972:Antineoplastic Agents, Phytogenic; C118809:CSAG2 protein, human; D017931:DNA Primers; D009363:Neoplasm Proteins; D012333:RNA, Messenger; C039854:5-azacytosine; D003596:Cytosine; D017239:Paclitaxel