title: PSA regulates androgen receptor expression in prostate cancer cells.
abstract: BACKGROUND
  Prostate-specific antigen (PSA) is a pivotal downstream target gene of the androgen receptor (AR), and a serum biomarker to monitor prostate cancer (PrCa) progression. It has been reported that PSA transactivates AR, but the mechanistic requirements of this response have not been investigated.
  
  
  METHODS
  We studied the localization of PSA, AR, and Src in intracellular compartments of synthetic androgen (R1881)-stimulated LNCaP and C4-2B PrCa cells, using immunofluorescence and subcellular fractionation approaches. We also investigated the effect of downregulation of PSA on AR expression by immunoblotting and real-time PCR using short hairpin RNA (shRNA) and small interfering RNA (siRNA). Src activity was analyzed by immunoblotting.
  
  
  RESULTS
  R1881 stimulation induced nuclear localization of both PSA and AR in LNCaP and C4-2B PrCa cells as well as increased phosphorylation of Src. Stable shRNA or transient siRNA knockdown of PSA resulted in reduced AR protein levels as well as AR mRNA levels in C4-2B cells. Similar to C4-2B cells, ablation of AR levels upon silencing of PSA was also confirmed in VCaP cells, another androgen-independent cell line. Silencing of PSA did not cause significant changes in Src activation; besides, Src regulation by integrins did not appear to affect AR transcriptional activity.
  
  
  CONCLUSIONS
  PSA localizes to nuclei of androgen-stimulated PrCa cells, and controls AR mRNA and protein levels. This regulatory loop is specific for PSA, does not involve known AR activators such as Src and AKT, and may contribute to AR signaling under conditions of increasing PSA levels in patients.
authors.affiliation: Department of Cancer Biology, Prostate Cancer Discovery and Development Program, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
authors.forename: Parmita
authors.initials: P
authors.lastname: Saxena
authors.forename: Marco
authors.initials: M
authors.lastname: Trerotola
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Aejaz
authors.initials: A
authors.lastname: Sayeed
authors.forename: Jennifer
authors.initials: J
authors.lastname: Vanoudenhove
authors.forename: Dave S
authors.initials: DS
authors.lastname: Adams
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Fitzgerald
authors.forename: Dario C
authors.initials: DC
authors.lastname: Altieri
authors.forename: Lucia R
authors.initials: LR
authors.lastname: Languino
mesh_terms: D045744:Cell Line, Tumor; D015536:Down-Regulation; D006801:Humans; D008297:Male; D015741:Metribolone / Q000494:pharmacology; D009376:Neoplasms, Hormone-Dependent / Q000378:metabolism; D010766:Phosphorylation; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D011944:Receptors, Androgen / Q000096:biosynthesis*
chemical_list: C410798:AR protein, human; D011944:Receptors, Androgen; D015741:Metribolone; D016392:Proto-Oncogene Proteins pp60(c-src); D017430:Prostate-Specific Antigen