Methylation status and expression of human telomerase reverse transcriptase mRNA in relation to hypermethylation of the p16 gene in colorectal cancers as analyzed by bisulfite PCR-SSCP.

Abstract

The expression level of human telomerase reverse transcriptase (hTERT) is correlated with telomerase activity and is expressed at high levels in malignant tumors. It is of interest whether expression of hTERT is regulated by methylation of the CpG island in the promoter of the hTERT gene. We examined hTERT expression and methylation status of the hTERT and other genes including p16. We analyzed methylation status by bisulfite treatment and polymerase chain reaction with single-strand conformation polymorphism analysis (PCR-SSCP) and expression of the hTERT by RT-PCR, in 13 cancer cell lines, eight white blood cell samples and 24 colorectal cancer tissues. In the cancer cell lines, hTERT was expressed and the CpG island of the hTERT promoter was methylated. Most colorectal cancer tissues showed similar results. The promoter of hTERT was methylated in six cases, partially methylated in 17 cases and unmethylated in one case. All cases with methylation of hMLH1 or p16 also showed methylation of hTERT; however, some of the cases lacking p16 methylation also had hTERT methylation. Increased expression of hTERT is related to hypermethylation of hTERT in colorectal cancerous tissues as well as some cancer cell lines and disconcordant with hypermethylation of p16.