title: Methyl selenium metabolites decrease prostate-specific antigen expression by inducing protein degradation and suppressing androgen-stimulated transcription.
abstract: Prostate-specific antigen (PSA) is widely used clinically for prostate cancer diagnostics and as an indicator of therapeutic efficacy and recurrence. Several human chemoprevention trials are being conducted to validate the prostate cancer prevention efficacy of selenium and PSA is used in these trials as a biomarker of response. A better understanding of the effects of selenium metabolites on the kinetics of PSA turnover and secretion in prostate cancer cells treated with selenium at concentrations which are achievable physiologically will be important for interpreting the results of these trials. This study addresses whether the putative active anticancer selenium metabolite methylselenol or its precursor methylseleninic acid (MSeA) specifically inhibits PSA expression in the androgen-responsive LNCaP prostate cancer cell model. The results show that exposure to sub-apoptotic concentrations of MSeA and methylselenol inhibited PSA protein expression and secretion, whereas sodium selenite and selenomethionine lacked inhibitory effect. The inhibition was detectable at 3 h of exposure and required a threshold level of MSeA to sustain. Turnover experiments showed that MSeA caused rapid PSA degradation, which was partially blocked by lysosomal inhibitors, but not by a proteasomal inhibitor. Furthermore, MSeA treatment reduced PSA mRNA level, down-regulated androgen receptor protein expression, and inhibited androgen-stimulated PSA promoter transcription. In summary, methylselenol or MSeA specifically and rapidly inhibited PSA expression through two mechanisms of action: inducing PSA protein degradation and suppressing androgen-stimulated PSA transcription. These findings may have important mechanistic implications for the prostate specific cancer chemopreventive action of selenium.
authors.affiliation: Hormel Institute, University of Minnesota, Austin 55912, USA.
authors.forename: Sung Dae
authors.initials: SD
authors.lastname: Cho
authors.forename: Cheng
authors.initials: C
authors.lastname: Jiang
authors.forename: Barbara
authors.initials: B
authors.lastname: Malewicz
authors.forename: Yan
authors.initials: Y
authors.lastname: Dong
authors.forename: Charles Y F
authors.initials: CY
authors.lastname: Young
authors.forename: Kyung-Sun
authors.initials: KS
authors.lastname: Kang
authors.forename: Yong-Soon
authors.initials: YS
authors.lastname: Lee
authors.forename: Clement
authors.initials: C
authors.lastname: Ip
authors.forename: Junxuan
authors.initials: J
authors.lastname: Lü
mesh_terms: D000728:Androgens / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D006801:Humans; D008297:Male; D016566:Organoselenium Compounds / Q000378:metabolism* / Q000494:pharmacology*; D017430:Prostate-Specific Antigen / Q000235:genetics* / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011944:Receptors, Androgen / Q000378:metabolism; D012645:Selenomethionine / Q000378:metabolism; D018038:Sodium Selenite / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D000728:Androgens; D016566:Organoselenium Compounds; D012333:RNA, Messenger; D011944:Receptors, Androgen; D012645:Selenomethionine; C008493:methylselenic acid; D017430:Prostate-Specific Antigen; D018038:Sodium Selenite