title: Skp2 regulates androgen receptor through ubiquitin-mediated degradation independent of Akt/mTOR pathways in prostate cancer.
abstract: BACKGROUND
  The intervention of advanced prostate cancer (PCa) in patients has been commonly depending on androgen deprivation therapy. Despite of tremendous research efforts, however, molecular mechanisms on AR regulation remain poorly understood, particularly for castration resistant prostate cancer (CRPC). Targeting AR and associated factors is considered an effective strategy in PCa treatment.
  
  
  METHODS
  Human prostate cancer cells were used in this study. Manipulations of Skp2 expression were achieved by Skp2 shRNA/siRNA or overexpression of plasmids. Dual luciferase reporter assay was applied for AR activity assessment. Western blot, ubiquitination assay, immunoprecipitation, and immunofluorescence were applied to detect the proteins.
  
  
  RESULTS
  Our results demonstrated that Skp2 directly involves the regulation of AR expression through ubiquitination-mediated degradation. Skp2 interacted with AR protein in PCa cells, and enforced expression of Skp2 resulted in a decreased level and activity of AR. By contrast, Skp2 knockdown increased the protein accumulation and activity of AR. Importantly, changes of AR contributed by Skp2 led to subsequent alterations of PSA level in PCa cells. AR ubiquitination was significantly increased upon Skp2 overexpression but greatly reduced upon Skp2 knockdown. AR mutant at K847R abrogated Skp2-mediated ubiquitination of AR. NVP-BEZ235, a dual PI3K/mTOR inhibitor, remarkably inhibited Skp2 level with a striking elevation of AR.
  
  
  CONCLUSIONS
  The results indicate that Skp2 is an E3 ligase for proteasome-dependent AR degradation, and K847 on AR is the recognition site for Skp2-mediated ubiquitination. Our findings reveal an essential role of Skp2 in AR signaling.
authors.affiliation: Department of Biochemistry and Cancer Biology, Meharry Medical College, Nashville, Tennessee.
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.forename: Wenfu
authors.initials: W
authors.lastname: Lu
authors.forename: Qing
authors.initials: Q
authors.lastname: Yang
authors.forename: Xiuping
authors.initials: X
authors.lastname: Yu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Matusik
authors.forename: Zhenbang
authors.initials: Z
authors.lastname: Chen
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011804:Quinolines / Q000494:pharmacology; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D007093:Imidazoles; D011804:Quinolines; D011944:Receptors, Androgen; D044786:S-Phase Kinase-Associated Proteins; D025801:Ubiquitin; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; C531198:dactolisib
keywords: Skp2; androgen receptor (AR); prostate cancer (PCa); ubiquitination