Global DNA hypomethylation, in particular that of the gene promoter sequence in gene hypermethylation, is a well-known characteristic of human cancer. Subtelomeres are enriched CpG islands; methylation is believed to be a potential epigenetic regulator. However, regulation on the telomere length remains largely unknown. To demonstrate this correlation, four nasopharyngeal carcinoma cell lines (CNE, CNE1, CNE2, 5–8F) were treated for 72 hours with 0, 1, or 2.5 μM of the demethylating agent 5-aza-2′-deoxycytidine (5-aza-dC). Subtelomeric (D4Z4) level methylation was evaluated with a bisulfite assay, the human telomerase catalytic subunit (hTERT) expression was assayed by reverse transcription–polymerase chain reaction, the telomerase activity was detected using a telomeric repeat amplification protocol assay, and the telomere length was measured by Southern blot terminal restriction fragment analysis. There was significant demethylation following 5-aza-dC treatment, and a strongly repressed hTERT expression decreased the telomerase activity and remarkably shortened telomeres. Thus, partial subtelomeric methylation does not repress hTERT expression; conversely, demethylation may downregulate hTERT expression and shorten telomeres.
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