title: Differential responses to doxorubicin-induced phosphorylation and activation of Akt in human breast cancer cells.
abstract: BACKGROUND
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. xinquli@mdanderson.org
authors.forename: Xinqun
authors.initials: X
authors.lastname: Li
authors.forename: Yang
authors.initials: Y
authors.lastname: Lu
authors.forename: Ke
authors.initials: K
authors.lastname: Liang
authors.forename: Bolin
authors.initials: B
authors.lastname: Liu
authors.forename: Zhen
authors.initials: Z
authors.lastname: Fan
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology*; D045744:Cell Line, Tumor; D018076:DNA, Complementary / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics; D004317:Doxorubicin / Q000494:pharmacology*; D004789:Enzyme Activation; D005260:Female; D005720:Gamma Rays; D018734:Genes, erbB-2; D006706:Homeostasis; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D000903:Antibiotics, Antineoplastic; D018076:DNA, Complementary; D004273:DNA, Neoplasm; D004317:Doxorubicin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt