title: A hormone-dependent feedback-loop controls androgen receptor levels by limiting MID1, a novel translation enhancer and promoter of oncogenic signaling.
abstract: BACKGROUND
  High androgen receptor (AR) level in primary tumour predicts increased prostate cancer (PCa)-specific mortality. Furthermore, activations of the AR, PI3K, mTOR, NFκB and Hedgehog (Hh) signaling pathways are involved in the fatal development of castration-resistant prostate cancer during androgen ablation therapy. MID1, a negative regulator of the tumor-suppressor PP2A, is known to promote PI3K, mTOR, NFκB and Hh signaling. Here we investigate the interaction of MID1 and AR.
  
  
  METHODS
  AR and MID1 mRNA and protein levels were measured by qPCR, Western blot and immunohistochemistry. Co-immunoprecipitation followed by PCR and RNA-pull-down followed by Western blot was used to investigate protein-mRNA interaction, chromatin-immunoprecipitation followed by next-generation sequencing for identification of AR chromatin binding sites. AR transcriptional activity and activity of promoter binding sites for AR were analyzed by reporter gene assays. For knockdown or overexpression of proteins of interest prostate cancer cells were transfected with siRNA or expression plasmids, respectively.
  
  
  RESULTS
  The microtubule-associated MID1 protein complex associates with AR mRNA via purine-rich trinucleotide repeats, expansions of which are known to correlate with ataxia and cancer. The level of MID1 directly correlates with the AR protein level in PCa cells. Overexpression of MID1 results in a several fold increase in AR protein and activity without major changes in mRNA-levels, whereas siRNA-triggered knockdown of MID1 mRNA reduces AR-protein levels significantly. Upregulation of AR protein by MID1 occurs via increased translation as no major changes in AR protein stability could be observed. AR on the other hand, regulates MID1 via several functional AR binding sites in the MID1 gene, and, in the presence of androgens, exerts a negative feedback loop on MID1 transcription. Thus, androgen withdrawal increases MID1 and concomitantly AR-protein levels. In line with this, MID1 is significantly over-expressed in PCa in a stage-dependent manner.
  
  
  CONCLUSIONS
  Promotion of AR, in addition to enhancement of the Akt-, NFκB-, and Hh-pathways by sustained MID1-upregulation during androgen deprivation therapy provides a powerful proliferative scenario for PCa progression into castration resistance. Thus MID1 represents a novel, multi-faceted player in PCa and a promising target to treat castration resistant prostate cancer.
authors.forename: Andrea
authors.initials: A
authors.lastname: Köhler
authors.forename: Ummühan
authors.initials: U
authors.lastname: Demir
authors.forename: Eva
authors.initials: E
authors.lastname: Kickstein
authors.forename: Sybille
authors.initials: S
authors.lastname: Krauss
authors.forename: Johanna
authors.initials: J
authors.lastname: Aigner
authors.forename: Beatriz
authors.initials: B
authors.lastname: Aranda-Orgillés
authors.forename: Antonios I
authors.initials: AI
authors.lastname: Karagiannidis
authors.forename: Clemens
authors.initials: C
authors.lastname: Achmüller
authors.forename: Huajie
authors.initials: H
authors.lastname: Bu
authors.forename: Andrea
authors.initials: A
authors.lastname: Wunderlich
authors.forename: Michal-Ruth
authors.initials: MR
authors.lastname: Schweiger
authors.forename: Georg
authors.initials: G
authors.lastname: Schaefer
authors.forename: Susann
authors.initials: S
authors.lastname: Schweiger
authors.forename: Helmut
authors.initials: H
authors.lastname: Klocker
authors.affiliation: Institute of Biochemistry, Center of Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, 6020 Innsbruck, Austria. Rainer.Schneider@uibk.ac.at.
authors.forename: Rainer
authors.initials: R
authors.lastname: Schneider
mesh_terms: D000728:Androgens / Q000378:metabolism; D045744:Cell Line, Tumor; D025461:Feedback, Physiological; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D008868:Microtubule Proteins / Q000096:biosynthesis / Q000235:genetics*; D009376:Neoplasms, Hormone-Dependent / Q000235:genetics* / Q000473:pathology; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011401:Promoter Regions, Genetic; D064129:Prostatic Neoplasms, Castration-Resistant / Q000235:genetics* / Q000473:pathology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011944:Receptors, Androgen / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D044767:Ubiquitin-Protein Ligases
chemical_list: D000728:Androgens; D008868:Microtubule Proteins; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D011944:Receptors, Androgen; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; C109052:MID1 protein, human