Regulation of the human telomerase reverse transcriptase gene

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• Most somatic human cells lack telomerase activity due to silenced telomerase reverse transcriptase (hTERT) gene expression.
• Conversely, most cancer cells exhibit telomerase positivity, suggesting hTERT gene reactivation during tumorigenesis.
• The origin of hTERT expression in tumors, whether from telomerase-positive stem cells or gene reactivation, is not fully understood.

Purpose of the Study:

• To investigate the regulatory mechanisms underlying tumor-specific hTERT gene expression.
• To identify potential repressors and cis-acting elements involved in hTERT gene silencing in normal cells.
• To elucidate the reasons for the differential expression of hTERT between normal and cancer cells.

Main Methods:

• Analysis of hTERT transcript levels in telomerase-negative and telomerase-positive cells.
• Investigating hTERT expression as a recessive trait in tumor cell lines.
• Utilizing monochromosomal hybrids to identify chromosomes potentially coding for hTERT repressors.

Main Results:

• Telomerase-negative cells lack detectable hTERT transcripts, while telomerase-positive cells show low levels (0.2-6 mRNA molecules/cell).
• hTERT expression in tumor cell lines behaves as a recessive trait, suggesting the presence of repressors in normal cells.
• Studies indicate that multiple chromosomes may harbor genes encoding these repressors.

Conclusions:

• hTERT gene expression is tightly regulated, likely at the transcriptional level.
• The tumor-specific expression of hTERT is potentially mediated by the absence or inactivation of cellular repressors.
• Further research is needed to identify the specific cis-acting elements targeted by repression and the factors controlling hTERT expression in tumors.