Rearrangements of minisatellites in the human telomerase reverse transcriptase gene are not correlated with its expression in colon carcinomas

Abstract

Telomerase activation is crucial in human carcinogenesis. The limiting component of telomerase, the catalytic subunit (hTERT), is undetectable in normal somatic cells but present in most tumor cells, including the earliest stages of colon carcinoma. The mechanisms involved in the dierential expression in normal and tumor cells are not understood. In normal cells hTERT expression is shut down by a repressor, and upregulation could be a consequence of cis-acting changes in the hTERT gene, making it resistant to repression. We have identi®ed a polymorphic and a monomorphic minisatellite in the second intron of the hTERT gene, and polymorphic one in intron 6. The polymorphic minisatellite in intron 2 contains binding sites for c-Myc, which has been shown to upregulate hTERT transcription. Screening colon carcinoma DNAs for rearrangements of hTERT minisatellites we detected no changes in 33 samples from tumors, most of which express hTERT. This indicates that size rearrangements of the hTERT minisatellites are not required for telomerase expression in colon carcinomas. Minor changes and one LOH were seen in ®ve tumors. Oncogene (2001) 20, 2600 ± 2605.

The human telomerase gene: complete genomic sequence and analysis of tandem repeat polymorphisms in intronic regions

“…No polymorphism was found for the minisatellite in intron 12 (data not shown). However, contrary to a previous report (Szutorisz et al, 2001), the 61 bp repeat in intron 2 was found to be polymorphic (Figure 3). Four alleles of hTERT-VNTR 2-2nd were found, ranging from 40 to 44 repeats with 44 repeats for the most common allele, with a corresponding degree of heterozygosity of 0.476.…”

hTERT gene copy number is not associated with hTERT RNA expression or telomerase activity in colorectal cancer

“…This is in accordance with a previous study of a small set of breast cancers. 17 We could also demonstrate a significant correlation between increased hTERT gene copy number and aneuploidy. The relationship in colorectal cancer between p53 abnormalities and aneuploidy is well known 30,31 and aneuploidy and gene amplification is closely related.…”

“…17 Interestingly, amplification (or increase in gene copy number) of the hTERT gene at chromosome 5p15.33 has been demonstrated in a significant fraction of established cell lines and malignant tumors of different origin using FISH or differential PCR. [18][19][20] Whether this increased gene dosage also results in an increased hTERT RNA expression followed by upregulation of telomerase activity has not been clarified.…”

Regulation of the human telomerase reverse transcriptase gene

“…The second intron of the hTERT gene contains a meiotically unstable minisatellite with several putative binding sites for c-Myc (Szutorisz et al, 2001;Wu et al, 1999). Size rearrangements of that minisatellite are not required for telomerase expression in colon carcinomas (Szutorisz et al, 2001). In 31 of 33 colon carcinomas that were heterozygous for the polymorphic minisatellite the 1 : 1 ratio of hTERT alleles was maintained, indicating that there had been no gene ampli®cation in these tumors.…”

“…We have found no evidence for rearrangements in the 5' flanking region and the 5' half of the gene (710 to +25 kb) screening a number of cell lines of divers origin. The second intron of the hTERT gene contains a meiotically unstable minisatellite with several putative binding sites for c-Myc (Szutorisz et al, 2001;Wu et al, 1999). Size rearrangements of that minisatellite are not required for telomerase expression in colon carcinomas (Szutorisz et al, 2001).…”