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Phosphatase inhibition and cell survival after DNA damage induced by radiation

Julie Hamilton1, Anna M Grawenda, Eric J Bernhard

  • 1Gray Institute for Radiation Oncology and Biology, University of Oxford, Oxford, UK.

Cancer Biology & Therapy
|July 3, 2009
PubMed

Insights

Targeting specific phosphatases, like protein phosphatase 1 (PP1) and PHLPPL, can enhance tumor cell radiosensitivity. This offers a potential new strategy for cancer treatment by inhibiting phosphatases instead of kinases.

Area of Science:

  • Oncology
  • Molecular Biology
  • Biochemistry

Background:

  • Kinase activity promotes cell survival post-DNA damage.
  • The role of phosphatases in cell fate determination is less understood.
  • Identifying phosphatase roles in radiation survival is crucial for therapeutic targets.

Purpose of the Study:

  • To define the role of phosphatases in tumor cell radiosensitivity.
  • To identify specific phosphatases as potential targets for enhancing radiation therapy.
  • To investigate the effects of inhibiting serine/threonine phosphatases on tumor cell fate.

Main Methods:

  • Utilized naturally occurring inhibitors and siRNA to assess phosphatase inhibition.
  • Tested four serine/threonine phosphatases: PP1, PP2A, PHLPP, and PHLPPL.
  • Evaluated effects on radiosensitivity in tumor cell lines with ras mutations or EGFR activation.

Main Results:

  • Calyculin A (inhibiting PP1 and PP2A) reduced survival in EGFR-overexpressing SQ20B cells.
  • Okadaic acid (preferentially inhibiting PP2A) had less effect, suggesting PP1's greater role in SQ20B radiosensitivity.
  • Knockdown of PP1 catalytic subunit and PHLPPL increased radiosensitivity across tested cell lines.

Conclusions:

  • Targeted inhibition of specific phosphatases, particularly PP1 and PHLPPL, enhances tumor cell radiosensitivity.
  • Phosphatase inhibition presents a viable alternative to kinase inhibition for improving radiation therapy outcomes.
  • This study identifies novel targets for intervention to overcome radioresistance in cancer.

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