hTERT regulation by NF-κB and c-myc in irradiated HER2-positive breast cancer cells

Abstract

Purpose: Telomerase activity (TA), frequently observed in cancer, compensates for telomere shortening thus preventing cell senescence and conferring resistance to therapy. In the present study, we investigated the expression of human telomerase reverse transcriptase (hTERT) and TA and their regulation, as well as apoptotic rates and correlation with the presence of human epidermal growth factor receptor 2 (HER2), in irradiated tumour-derived breast cancer cells.

Materials and methods: In 50 breast cancer tissue samples hTERT mRNA expression and TA were correlated with cell features (HER2, Estrogen and Progesterone Receptor status). Cells from six samples were then irradiated with 10 and 20 Gy; apoptotic rates were measured by flow cytometry, hTERT mRNA expression by real-time polymerase chain reaction and TA by telomeric repeat amplification protocol assay, at 24–144 h post-irradiation. Chromatin immunoprecipitation was performed to investigate hTERT and cellular-myelocytomatosis (c-myc) promoters' activity. HER2 gene knockdown was performed using small interfering RNA technology.

Results: hTERT/TA were found increased only in irradiated HER2-positive cells, which were found to be more radioresistant, while HER2 knockdown led to hTERT/TA downregulation. HER2 was found to mediate hTERT expression through activation of Nuclear Factor-kappa B (NF-κB) and c-myc.

Conclusions: The present study suggests that following irradiation, HER2 receptor activates hTERT/telomerase, increasing the breast cancer cells' survival potential, through sequential induction of transcription factors NF-κΒ and c-myc.

Keywords:

• HER2
• ionising radiation
• breast cancer
• telomerase
• c-myc
• NF-κB

Acknowledgements

The authors would like to thank Professor George K. Koukoulis from the Department of Pathology, University Hospital of Larissa, for the kind provision of histological analysis of breast cancer tissues. Also, the authors thank Dr Ioannis Tsougos, Department of Medical Physics, for his valuable assistance during irradiation. The present work was supported by the Jennie Kotroni (ID 394) fund donated to BIOMED.

Declaration of interest:

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.