title: PI3K-AKT-mTOR pathway is dominant over androgen receptor signaling in prostate cancer cells.
abstract: BACKGROUND
  Androgen receptor (AR) and the phosphatidylinositol-3 kinase (PI3K) signaling are two of the most important pathways implicated in prostate cancer. Previous work has shown that there is crosstalk between these two pathways; however, there are conflicting findings and the molecular mechanisms are not clear. Here we studied the AR-PI3K pathway crosstalk in prostate cancer cells in vitro as well as in vivo.
  
  
  METHODS
  Quantitative PCR, Western analysis, reporter assays, and proliferation analyses in vitro and in vivo were used to evaluate the effect of PI3K pathway inhibition on AR signaling and cell growth.
  
  
  RESULTS
  Transcriptional activity of AR was increased when the PI3K pathway was inhibited at different levels. In the androgen responsive prostate cancer cell line LNCaP, androgen and the mTOR inhibitor rapamycin synergistically activated androgen target genes. Despite increased androgen signaling, rapamycin treatment reduced LNCaP cell growth; the AR antagonist bicalutamide potentiated this effect. Furthermore, the rapamycin derivative CCI-779 reduced the growth of CWR22 prostate cancer xenografts while increasing AR target gene expression.
  
  
  CONCLUSIONS
  These findings suggest that inhibition of the PI3K pathway activates AR signaling. Despite the increase in AR signaling which has proliferative effects, the result of PI3K pathway inhibition is antiproliferative. These findings suggest that the PI3K pathway is dominant over AR signaling in prostate cancer cells which should be considered in developing novel therapeutic strategies for prostate cancer.
authors.affiliation: Department of Molecular Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Mari
authors.initials: M
authors.lastname: Kaarbø
authors.forename: Oyvind Løveseter
authors.initials: OL
authors.lastname: Mikkelsen
authors.forename: Lene
authors.initials: L
authors.lastname: Malerød
authors.forename: Su
authors.initials: S
authors.lastname: Qu
authors.forename: Viola H
authors.initials: VH
authors.lastname: Lobert
authors.forename: Gulcan
authors.initials: G
authors.lastname: Akgul
authors.forename: Thomas
authors.initials: T
authors.lastname: Halvorsen
authors.forename: Gunhild M
authors.initials: GM
authors.lastname: Maelandsmo
authors.forename: Fahri
authors.initials: F
authors.lastname: Saatcioglu
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D015533:Transcriptional Activation
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011944:Receptors, Androgen; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse