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Human T-cell leukemia virus I tax protein sensitizes p53-mutant cells to DNA damage

Valia T Mihaylova1, Allison M Green, Moshe Khurgel

  • 1Departments of Microbiology, University of Virginia Health System, Charlottesville, Virginia, USA.

Cancer Research
|June 19, 2008
PubMed

Insights

The Tax protein sensitizes cancer cells with p53 mutations to DNA-damaging chemotherapy, while protecting normal cells with wild-type p53. This suggests Tax could enhance cancer treatment efficacy and reduce side effects.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Virology

Background:

  • Mutations in the p53 tumor suppressor gene are linked to cancer chemotherapy resistance and treatment failure.
  • The human T-cell leukemia virus type I (HTLV-I) encoded protein, Tax, is known to cause genomic instability and disrupt cellular processes.
  • Previous studies indicated Tax sensitizes cells to UV treatment, but the extent and mechanism remained unclear.

Purpose of the Study:

  • To investigate the role of Tax in sensitizing cancer cells with p53 mutations to DNA-damaging agents.
  • To elucidate the mechanism by which Tax affects cellular response to DNA damage.
  • To determine if Tax offers differential effects on p53-mutant versus p53 wild-type cells.

Main Methods:

  • Treatment of various cancer cell lines (p53-deleted, p53-mutant, and p53 wild-type) with DNA-damaging agents (mitomycin C, etoposide, UV light, ionizing radiation, vinblastine) in the presence or absence of Tax.
  • Transfection of p53-deleted cell lines with wild-type p53.
  • Analysis of retinoblastoma protein, E2F1, Puma, Noxa, and Bax dimerization expression levels.
  • Assessment of apoptosis induction.

Main Results:

  • Tax sensitized p53-mutant and p53-deleted cells to mitomycin C, etoposide, and UV light, but not ionizing radiation or vinblastine.
  • Tax unexpectedly protected p53 wild-type cells from DNA-damaging agents.
  • Tax-induced sensitization in p53-deleted cells was reversed by wild-type p53 reintroduction.
  • Tax activated a p53-independent proapoptotic pathway via downregulation of retinoblastoma protein and upregulation of E2F1, leading to increased Puma, Noxa, and Bax dimerization.

Conclusions:

  • Tax protein differentially impacts cancer cells based on p53 status, sensitizing p53-mutant cells while protecting p53 wild-type cells.
  • Tax mediates sensitization through a p53-independent apoptotic pathway.
  • These findings suggest Tax as a potential adjunctive therapeutic agent to improve cancer chemotherapy effectiveness and potentially reduce normal tissue toxicity.

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