Regulation of telomerase reverse transcriptase gene activity by upstream stimulatory factor

Area of Science:

• Molecular Biology
• Cancer Biology
• Epigenetics

Background:

• Human telomerase reverse transcriptase (hTERT) upregulation drives cancer cell immortalization.
• The precise mechanisms controlling hTERT transcription remain incompletely understood.
• Previous models implicating Myc/Max in hTERT promoter activation are being re-evaluated.

Purpose of the Study:

• To investigate the role of alternative E-box-binding proteins in regulating hTERT transcription.
• To elucidate the mechanism of hTERT promoter activation in cancer cells.
• To identify key factors involved in cellular immortalization.

Main Methods:

• In vitro and in vivo binding assays to assess protein-DNA interactions.
• Reporter gene assays to measure hTERT promoter activity.
• Co-transfection experiments with coactivators and kinase inhibitors.

Main Results:

• Upstream stimulatory factor (USF) 1 and 2 heterodimers bind strongly to E-boxes in the hTERT promoter.
• Myc/Max complexes do not significantly bind these E-boxes.
• USF1/2 binding is observed in both hTERT-positive and -negative cells, but activation occurs only in hTERT-positive cells.
• hTERT promoter activation by USF1/2 is enhanced by p300 and inhibited by p38-MAP kinase inhibition.

Conclusions:

• USF1/2 plays a critical role in activating hTERT transcription in immortalized cancer cells.
• USF binding to the hTERT promoter is context-dependent, acting as a stimulator in cancer cells and potentially neutral or repressive in normal somatic cells.
• USF1/2 is a key contributor to the acquisition and maintenance of cancer cell immortality.