title: Androgen Receptor Splice Variants Are Not Substrates of Nonsense-Mediated Decay.
abstract: BACKGROUND
  Androgen receptor (AR) splice variants have been clinically associated with progressive cancer, castration-resistance, and resistance to AR antagonists and androgen synthesis inhibitors. AR variants can be generated by genomic alterations and alternative splicing, and their expression is androgen-regulated. There has been a suggestion that AR variants bearing premature termination codons and coding for truncated proteins should be regulated by the nonsense-mediated decay (NMD) mRNA surveillance pathway, suggesting that either the NMD pathway is dysfunctional in variant-expressing cell lines or that variants are somehow able to evade degradation by NMD.
  
  
  METHODS
  We first used siRNA knockdown of the NMD regulator, UPF1, in an NMD reporter assay to determine if this surveillance pathway is functioning normally in AR variant-expressing cell lines. We then used UPF1 knockdown to determine if expression of the AR variants ARV3 and ARV7 is affected by inhibition of NMD. Next, we analyzed androgen regulation of UPF1 and used transcript expression analysis to determine if there is any association between UPF1 expression, resistance, and ARV3 or ARV7 expression.
  
  
  RESULTS
  We found that the NMD pathway functions normally in the AR variant-expressing cell line 22Rv1 and that inhibition of NMD does not increase expression of ARV3 or ARV7. Furthermore, we found that expression of UPF1 is not androgen-regulated. We also found that UFP1 expression levels do not differentiate castration-sensitive from resistant cell line and that UPF1 expression does not correlate with expression of ARV3 or ARV7 in cells in which these variants are highly expressed.
  
  
  CONCLUSIONS
  This study eliminates a possible mechanism of regulation of certain AR variants. Future research into the regulation of AR variants should focus on other mechanisms to better understand the origin of these variants and to possibly inhibit their expression for the resensitization of resistant cancers. Prostate 77:829-837, 2017. © 2017 Wiley Periodicals, Inc.
authors.affiliation: Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland.
authors.forename: Atinuke S
authors.initials: AS
authors.lastname: Ajiboye
authors.affiliation: Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, Maryland.
authors.forename: David
authors.initials: D
authors.lastname: Esopi
authors.affiliation: Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland.|Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Yegnasubramanian
authors.affiliation: Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland.|Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Denmeade
mesh_terms: D017398:Alternative Splicing; D059002:Androgen Receptor Antagonists / Q000378:metabolism; D000728:Androgens / Q000378:metabolism; D045744:Cell Line, Tumor; D018389:Codon, Nonsense; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D064129:Prostatic Neoplasms, Castration-Resistant / Q000235:genetics; D012333:RNA, Messenger; D011944:Receptors, Androgen / Q000235:genetics*
chemical_list: D059002:Androgen Receptor Antagonists; D000728:Androgens; D018389:Codon, Nonsense; D012333:RNA, Messenger; D011944:Receptors, Androgen
keywords: UPF1; androgen receptor; nonsense-mediated decay; prostate cancer; splice variants