title: Honokiol inhibits androgen receptor activity in prostate cancer cells.
abstract: BACKGROUND
  We have shown previously that honokiol (HNK), a bioactive component of the medicinal plant Magnolia officinalis, inhibits growth of human prostate cancer cells in vitro and in vivo. However, the effect of HNK on androgen receptor (AR) signaling has not been studied.
  
  
  METHODS
  LNCaP, C4-2, and TRAMP-C1 cells were used for various assays. Trypan blue dye exclusion assay or clonogenic assay was performed for determination of cell viability. The effects of HNK and/or its analogs on protein levels of AR and its target gene product prostate specific antigen (PSA) were determined by western blotting. RNA interference of p53 was achieved by transient transfection. Reverse transcription-polymerase chain reaction was performed for mRNA expression of AR. Nuclear level of AR was visualized by microscopy. Apoptosis was quantified by DNA fragmentation assay or flow cytometry after Annexin V-propidium iodide staining.
  
  
  RESULTS
  HNK and its dichloroacetate analog (HDCA) were relatively more effective in suppressing cell viability and AR protein level than honokiol epoxide or biseugenol. Nuclear translocation of AR stimulated by a synthetic androgen (R1881) was markedly suppressed in the presence of HNK. Downregulation of AR protein resulting from HNK exposure was attributable to transcriptional repression as well as proteasomal degradation. HNK-mediated suppression of AR protein was maintained in LNCaP cells after knockdown of p53 protein. HNK-induced apoptosis was not affected by R1881 treatment.
  
  
  CONCLUSIONS
  The present study demonstrates, for the first time, that HNK inhibits activity of AR in prostate cancer cells regardless of the p53 status.
authors: Department of Pharmacology & Chemical Biology, and University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
authors: Eun-Ryeong
authors: ER
authors: Hahm
authors: A Isabella
authors: AI
authors: Karlsson
authors: Michael Y
authors: MY
authors: Bonner
authors: Jack L
authors: JL
authors: Arbiser
authors: Shivendra V
authors: SV
authors: Singh
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001713:Biphenyl Compounds / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects*; D006801:Humans; D017705:Lignans / Q000494:pharmacology*; D008297:Male; D011471:Prostatic Neoplasms / Q000378:metabolism*; D011944:Receptors, Androgen / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D000498:Allyl Compounds; D010636:Phenols
chemical_list: D001713:Biphenyl Compounds; D017705:Lignans; D011944:Receptors, Androgen; C005499:honokiol; D000498:Allyl Compounds; D010636:Phenols
keywords: alternative medicine; androgen receptor; honokiol; prostate cancer