Regulation of a Novel Androgen Receptor Target Gene, the Cyclin B1 Gene, through Androgen-Dependent E2F Family Member Switching

Abstract

The malignant transformation of human prostatic epithelium is associated with the loss of androgen receptor (AR) in the surrounding stroma. However, the function and mechanisms of AR signaling in prostate cancer (PCa) stroma remain elusive. Here we report, by using proteomics pathway array analysis (PPAA), that androgen and its receptor inhibit the proliferation of prostate stromal cells through transcriptional suppression of cyclin B1, and we confirmed our findings at mRNA and protein levels using AR-negative or -positive primary prostate stromal cells. Furthermore, AR showed a negative correlation with cyclin B1 expression in stroma of human PCa samples in vivo. Mechanistically, we identify cyclin B1 as a bona fide AR target gene in prostate stromal cells. The negative regulation of cyclin B1 by AR is mediated through switching between E2F1 and E2F4 on the promoter of cyclin B1. E2F1 binds to the cyclin B1 promoter and maintains its expression and subsequent cell cycle progression in AR-negative stromal cells or AR-positive stromal cells when androgens are depleted. Upon stimulation with androgen in ARpositive stromal cells, E2F1 is displaced from the binding site by AR and replaced with E2F4, leading to the recruitment of the silencing mediator for retinoid and thyroid hormone receptor (SMRT)/histone deacetylase 3 (HDAC3) corepressor complex and repression of cyclin B1 at the chromatin level. The switch between E2F1 and E2F4 at the E2F binding site of the cyclin B1 promoter coincides with an androgen-dependent interaction between AR and E2F1 as well as the cytoplasmic-to-nuclear translocation of E2F4. Thus, we identified a novel mechanism for E2F factors in the regulation of cell cycle gene expression and cell cycle progression under the control of AR signaling. E 2F transcription factors control the expression of key components of the DNA replication machinery as well as the G 1 /S and G 2 /M cell cycle transitions (34,42). Eight members of the E2F family have been characterized (28). E2F1 to E2F6 form heterodimers with either DP-1 or DP-2 protein (3) to bind DNA and activate or repress gene expression. The retinoblastoma (pRB) tumor suppressor and the related p107 and p130 proteins (termed pocket proteins) bind to particular E2Fs in vivo and recruit corepressor complexes that contain histone deacetylases (HDACs), mediating the active repression of E2F-responsive genes (1, 34).E2F proteins are divided into two subcategories with opposing functions in transcriptional activation in vivo. E2F1, E2F2, and E2F3 (termed activator E2Fs) play a key role in promoting the activation of E2F-responsive genes, cell cycle entry, and cell growth. The conditional ablation of E2F3 in mice lacking E2F1 and E2F2 results in mouse embryonic fibroblasts (MEFs) that are unable to proliferate (38). MEFs lacking E2F3 alone display a slow-growth phenotype (11). On the other hand, E2F4 to E2F8 appear to be involved primarily in the transcriptional repression of E2F-responsive genes. The activator E2Fs contain nuclear localization sign...

Androgen Receptor Promotes the Oncogenic Function of Overexpressed Jagged1 in Prostate Cancer by Enhancing Cyclin B1 Expression via Akt Phosphorylation

“…More importantly, cyclin B1 expression level is affected dramatically by the phosphorylation level of Akt, which indicates that p-Akt might be involved in the transcription regulation of cyclin B1. AR has been shown in prostate cancer epithelial cells to influence the expression levels and activities of several cell-cycle genes essential for the G 1 -S and G 2 -M cell-cycle transition (40,47). In addition, Akt regulates the expression and stability of AR at multiple levels, ranging from transcriptional to posttranslational modulation (48).…”

“…Li and colleagues found that transactivation of cyclin B1 in LNCaP cell was increased by androgen and AR (40). We assumed that AR transcription activity for cyclin B1 might be enhanced by overexpressed Jagged1 through Akt phosphorylation.…”

“…To examine how p-Akt affects cyclin B1 expression by Jagged1 and AR, ChIP assays were performed with anti-AR antibody through AREs (40,41) in the cyclin B1 promoter region in AR-positive LNCaP cells with different Jagged1 expression levels. LNCaP cells cultured in androgen-depleted medium were used as a negative control as there was no DHT-induced AR binding.…”

Proto-oncogene Activity of Melanoma Antigen-A11 (MAGE-A11) Regulates Retinoblastoma-related p107 and E2F1 Proteins

“…A threshold model was proposed where genes that regulate cell proliferation or apoptosis are induced by different levels of E2F that act as positive or negative regulators of cell growth (53). Positive and negative cooperation in gene regulation by AR and E2F1 were reported in prostate cancer cells (95)(96)(97). Relative levels of MAGE-A11 and p107 influence AR and E2F1 transcriptional activation or repression.…”

Inhibition of Plk1 and Cyclin B1 Expression Results in Panobinostat-Induced G2 Delay and Mitotic Defects

“…In addition, the PLK1 and Cyclin B1 promoters are positively regulated by E2F family members2829. Therefore, we determined the effect of panobinostat treatment on the expression of E2F family members in synchronised cells (figure 7A).…”