A Natural Androgen Receptor Antagonist Induces Cellular Senescence in Prostate Cancer Cells

Abstract

We have previously identified a natural occurring, androgen receptor-specific antagonist. Atraric acid (AA) inhibits the transactivation of the androgen receptor (AR) and androgen-mediated growth of AR-expressing human prostate cancer (PCa) cell lines. Here we show that AA treatment of living cells provokes molecular changes of AR signaling. In addition to a deceleration of nuclear translocation a block of the intramolecular amino/carboxy (N/C)-terminal interaction of the AR was observed. Furthermore, using high-resolution confocal fluorescence microscopy, a reduced speckle formation of the AR was observed in line with an increased intranuclear mobility of the receptor. This suggests decreased DNA binding of the AR, which is further indicated by an impaired chromatin recruitment of the AR to the prostate-specific antigen promoter and enhancer shown by chromatin immunoprecipitation experiments. Using inhibitors of the non-receptor tyrosine kinase Src or Akt, known interaction partners of AR, reduced the level of androgen-induced cellular senescence suggesting a partly non-genomic pathway to induce cellular senescence by AA. Using PP2 (4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) pyrimidine or Akt inhibitors, inhibitors of the nonreceptor tyrosine kinase Src or Akt, known interaction partners of AR, reduced the level of androgen-induced cellular senescence, suggesting a partly nongenomic pathway to induce cellular senescence by AA. Treatment of LNCaP cells with AA is associated with hypophosphorylation of the retinoblastoma tumor suppressor and an increase of p16 expression, whereas the p53-p21 signaling pathway seems not be affected by AA treatment. Analyzing human PCa tissue samples treated with AA ex vivo also indicates an induction of cellular senescence associated with an increase of p16 expression but not p21. Taken together, these data indicate that AA exhibits novel features to inhibit AR amino/carboxy-terminal interaction, the AR-mediated nuclear activities and growth of PCa cells.

The activation of OR51E1 causes growth suppression of human prostate cancer cells

“…qRT-PCR and primers used for the detection of E2F transcription factor 1 (E2F1), cyclin-dependent kinase inhibitor 2A (CDKN2A; p16) and cyclin-dependent kinase inhibitor 1A (CDKN1A; p21) were previously described [9, 54]. NK3 homeobox 1 (NKX3-1) and PSA (KLK3) were also analyzed.…”

“…A high concentration of the AR agonist R1881 was used as a positive control for the induction of cellular senescence in LNCaP cells [9]. The senescence-associated β-galactosidase (SA β-Gal) staining was performed as previously described [9, 54, 62]. …”

Senolytic compounds control a distinct fate of androgen receptor agonist- and antagonist-induced cellular senescent LNCaP prostate cancer cells

“…In order to analyze the activity of senolytic agents in senescent LNCaP cells, first, cellular senescence was induced in the PCa cell line LNCaP cells by treating with AR agonist at SAL or antagonist for 72 h as described earlier [9,13] (Fig. 1a, b).…”

“…We have previously described that cellular senescence can be induced by AR-signaling in PCa. On the one hand, several AR antagonists such as atraric acid, compound C28, or aminosteroids have been shown to induce cellular senescence in PCa cells [9][10][11]. On the other hand, induction of cellular senescence by supraphysiological level of AR agonists, the natural androgen dihydrotestosterone (DHT) or the less metabolized synthetic androgen methyltrienolone (R1881), were also described [12,13].…”

A novel crosstalk between the tumor suppressors ING1 and ING2 regulates androgen receptor signaling

“…The effect of androgens and the AR on the invasion and proliferation of PCa cells have been well established [5,6]. On the other hand, AR antagonists and the AR have also been reported to be involved in the induction of apoptosis and cellular senescence of PCa cells [7,8]. However, the possibility to inhibit the androgen-activated AR by cellular tumor suppressors that act as AR corepressors is not fully understood.…”