Carcinogenesis Advance Access originally published online on October 24, 2008
Carcinogenesis 2009 30(1):28-34; doi:10.1093/carcin/bgn240
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Specific association between the methyl-CpG-binding domain protein 2 and the hypermethylated region of the human telomerase reverse transcriptase promoter in cancer cells
1 INSERM U590, Lyon F-69008, France
2 Institut de Pathologie, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne CH-1011, Switzerland
3 ProfileXpert/Neurobiotec Service, INSERM U842, Bron F-69676, France
* To whom correspondence should be addressed. INSERM U590, Oncogenèse et Progression Tumorale, Centre Léon Bérard, 28 rue Laënnec, 69373 Lyon Cedex 08, France. Tel: +33 4 78 78 59 22; Fax: +33 4 78 78 27 20; Email: dante{at}univ-lyon1.fr
Human telomerase reverse transcriptase (hTERT) is expressed in most cancer cells. Paradoxically, its promoter is embedded in a hypermethylated CpG island. A short region escapes to this alteration, allowing a basal level of transcription. However, the methylation of adjacent regions may play a role in the maintenance of low hTERT expression. It is now well established that methyl-CpG binding domain proteins mediate the transcriptional silencing of hypermethylated genes. The potential involvement of these proteins in the control of hTERT expression was firstly investigated in HeLa cells. Chromatin immunoprecipitation assays showed that only methyl-CpG-binding domain protein 2 (MBD2) associated the hypermethylated hTERT promoter. In MBD2 knockdown HeLa cells, constitutively depleted in MBD2, neither methyl CpG binding protein 2 (MeCP2) nor MBD1 acted as substitutes for MBD2. MBD2 depletion by transient or constitutive RNA interference led to an upregulation of hTERT transcription that can be downregulated by expressing mouse Mbd2 protein. Our results indicate that MBD2 is specifically and directly involved in the transcriptional repression of hTERT in HeLa cells. This specific transcriptional repression was also observed in breast, liver and neuroblastoma cancer cell lines. Thus, MBD2 seems to be a general repressor of hTERT in hTERT-methylated telomerase-positive cells.
Abbreviations: ChIP, chromatin immunoprecipitation; hTERT, human telomerase reverse transcriptase; KD, knockdown; MBD, methyl-CpG-binding domain; mRNA, messenger RNA; nt, nucleotide; PCR, polymerase chain reaction; RT, reverse transcription
These authors contributed equally to this work. Received August 20, 2008; revised October 3, 2008; accepted October 11, 2008.