Downregulation of high mobility group box 1 modulates telomere homeostasis and increases the radiosensitivity of human breast cancer cells

Int J Oncol. 2015 Mar;46(3):1051-8. doi: 10.3892/ijo.2014.2793. Epub 2014 Dec 10.

Abstract

The functions of the high mobility group box 1 (HMGB1) in tumor cells include replenishing telomeric DNA and maintaining cell immortality. There is a negative correlation between human telomerase reverse transcriptase (hTERT) and radiosensitivity in tumor cells. Our aim was to elucidate the relationship among HMGB1, telomere homeostasis and radiosensitivity in MCF-7 cells. In this study, we established stably transfected control (MCF-7-NC) and HMGB1 knockdown (MCF-7-shHMGB1) cell lines. The expression of HMGB1 mRNA and the relative telomere length were examined by real-time PCR. Radiosensitivity was detected by clonogenic assay. The protein expressions were determined by western blot analysis. The telomerase activity was detected by PCR-ELISA. Proliferation ability was examined by CCK-8 assay. Cell cycle and apoptosis were examined by flow cytometry. DNA damage foci were detected by immunofluorescence. ShRNA-mediated downregulation of HMGB1 expression increased the radiosensitivity of MCF-7 cells, and reduced the accumulation of hTERT and cyclin D1. Moreover, knockdown of HMGB1 in MCF-7 cells inhibited telomerase activity and cell proliferation, while increasing the extent of apoptosis. Downregulation of HMGB1 modulated telomere homeostasis by changing the level of telomere-binding proteins, such as TPP1 (PTOP), TRF1 and TRF2. This downregulation also inhibited the ATM and ATR signaling pathways. The current data demonstrate that knockdown of HMGB1 breaks telomere homeostasis, enhances radiosensitivity, and suppresses the repair of DNA damage in human breast cancer cells. These results suggested that HMGB1 might be a potential radiotherapy target in human breast cancer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminopeptidases / genetics
  • Aminopeptidases / metabolism
  • Apoptosis / genetics
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / radiotherapy*
  • Cell Cycle / genetics
  • Cell Proliferation / genetics
  • DNA Damage / genetics
  • DNA Damage / radiation effects
  • DNA Repair / genetics
  • Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / genetics
  • Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / metabolism
  • Down-Regulation
  • Female
  • Gene Knockdown Techniques
  • HMGB1 Protein / genetics*
  • HMGB1 Protein / metabolism
  • Humans
  • MCF-7 Cells / radiation effects
  • Radiation Tolerance / genetics
  • Radiation, Ionizing
  • Serine Proteases / genetics
  • Serine Proteases / metabolism
  • Telomerase / genetics
  • Telomerase / metabolism
  • Telomere Homeostasis / physiology*
  • Telomeric Repeat Binding Protein 1 / genetics
  • Telomeric Repeat Binding Protein 1 / metabolism
  • Telomeric Repeat Binding Protein 2 / genetics
  • Telomeric Repeat Binding Protein 2 / metabolism

Substances

  • HMGB1 Protein
  • HMGB1 protein, human
  • TERF2 protein, human
  • Telomeric Repeat Binding Protein 1
  • Telomeric Repeat Binding Protein 2
  • TERT protein, human
  • Telomerase
  • Serine Proteases
  • Aminopeptidases
  • Dipeptidyl-Peptidases and Tripeptidyl-Peptidases
  • tripeptidyl-peptidase 1