Regulation of human telomerase activity: repression by normal chromosome 3 abolishes nuclear telomerase reverse...

Area of Science:

• Molecular Biology
• Cancer Biology
• Genetics

Background:

• Telomerase is essential for replicating chromosome ends and is upregulated in tumors, enabling unlimited cell proliferation.
• The human telomerase reverse transcriptase subunit (hTERT) is the key component responsible for telomerase activity.
• Understanding hTERT regulation is critical for targeting cancer cell proliferation.

Purpose of the Study:

• To investigate the transcriptional regulation of hTERT.
• To identify the role of chromosome 3 in controlling telomerase activity.
• To determine if c-Myc is involved in chromosome 3-mediated hTERT repression.

Main Methods:

• Quantitative reverse transcription PCR (RT-PCR) to measure hTERT RNA levels.
• Microcell transfer of chromosome 3 into a human breast carcinoma cell line (21NT).
• Analysis of hTERT transcripts, reporter gene constructs, and expression of c-Myc and its target genes.

Main Results:

• Telomerase-positive cells contain 0.2-6 molecules of spliced hTERT RNA; negative cells have <0.004 molecules/cell.
• Microcell transfer of chromosome 3 into 21NT cells abolished telomerase activity and induced senescence.
• Chromosome 3 transfer reduced immature hTERT RNA by >30-fold without affecting c-Myc or its target genes, and did not alter reporter gene expression from the hTERT promoter region.

Conclusions:

• hTERT RNA levels are primarily regulated at the transcriptional level.
• A repressor on chromosome 3 significantly reduces hTERT transcription.
• The chromosome 3-mediated repression of hTERT does not involve c-Myc or regulatory elements near the hTERT 5' flanking region.