Differential Responses to Doxorubicin-Induced Phosphorylation and Activation of Akt in Human Breast Cancer Cells

Breast Cancer Res. 2005;7(5):R589-97. doi: 10.1186/bcr1259. Epub 2005 May 24.

Abstract

Introduction: We have shown previously that overexpression of constitutively active Akt or activation of Akt caused by constitutively active Ras or human epidermal growth factor receptor-2 (HER2) confers on breast cancer cells resistance to chemotherapy or radiotherapy. As an expanded study we here report differential responses in terms of phosphorylation and activation of Akt as a result of treatment with doxorubicin in a panel of breast cancer cell lines.

Methods: The levels of Akt phosphorylation and activity were measured by Western blot analysis with an anti-Ser473-phosphorylated Akt antibody and by in vitro Akt kinase assay using glycogen synthase kinase-3 as a substrate.

Results: Within 24 hours after exposure to doxorubicin, MCF7, MDA468 and T47D cells showed a drug-dose-dependent increase in the levels of phosphorylated Akt; in contrast, SKBR3 and MDA231 cells showed a decrease in the levels of phosphorylated Akt, and minimal or no changes were detected in MDA361, MDA157 and BT474 cells. The doxorubicin-induced Akt phosphorylation was correlated with increased kinase activity and was dependent on phosphoinositide 3-kinase (PI3-K). An increased baseline level of Akt was also found in MCF7 cells treated with ionizing radiation. The cellular responses to doxorubicin-induced Akt phosphorylation were potentiated after the expression of Akt upstream activators including HER2, HER3 and focal adhesion kinase.

Conclusion: Taken together with our recent published results showing that constitutive Akt mediates resistance to chemotherapy or radiotherapy, our present data suggest that the doxorubicin-induced phosphorylation and activation of Akt might reflect a cellular defensive mechanism of cancer cells to overcome doxorubicin-induced cytotoxic effects, which further supports the current efforts of targeting PI3-K/Akt for enhancing the therapeutic responses of breast cancer cells to chemotherapy and radiotherapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibiotics, Antineoplastic / pharmacology
  • Blotting, Western
  • Breast Neoplasms / enzymology*
  • Cell Line, Tumor
  • DNA, Complementary / genetics
  • DNA, Neoplasm / genetics
  • Doxorubicin / pharmacology*
  • Enzyme Activation
  • Female
  • Gamma Rays
  • Genes, erbB-2
  • Homeostasis
  • Humans
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphorylation
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Proto-Oncogene Proteins c-akt / radiation effects

Substances

  • Antibiotics, Antineoplastic
  • DNA, Complementary
  • DNA, Neoplasm
  • Doxorubicin
  • Phosphatidylinositol 3-Kinases
  • Proto-Oncogene Proteins c-akt