Differential Effects of Estradiol and Bisphenol A on SET8 and SIRT1 Expression in Ovarian Cancer Cells.

Exposure to estrogenic compounds has been shown to epigenetically reprogram the female reproductive tract and may contribute to ovarian cancer. The goal of this study was to compare the effect of estradiol or bisphenol A (BPA) on the expression of histone-modifying enzymes (HMEs) in ovarian cancer cells. Using 2 human ovarian cancer cell lines, we examined the expression of SET8, a histone methyltransferase, and SIRT1, a histone deacetylase, after exposure to estrogen or BPA. These experiments were carried out in complete media (fetal bovine serum) that contain natural hormones to understand the impact of additional exposure to estrogen or BPA on HME expression. We found differential expression of the HMEs in the different models examined and between the different compounds. Further, we determined that the changes in gene expression occurred via estrogen receptor signaling using the estrogen receptor antagonist, ICI 182,780 (fulvestrant).

Differential effect of estradiol and bisphenol A on Set8 and Sirt1 expression in prostate cancer.

Exposure to estrogenic compounds has been shown to epigenetically reprogram the prostate and may contribute to prostate cancer. The goal of this study was to determine the effect of physiological doses of estradiol and bisphenol A (BPA) on the expression of histone modifying enzymes (HMEs) in prostate cancer. Using two human prostate cancer cell lines we examined the expression of Set8, a histone methyltransferase, and Sirt1, a histone deacetylase, after exposure to estrogen or BPA. These experiments were carried out in the presence of natural hormones to understand the impact of additional exposure to estrogen or BPA on HME expression. We found differential expression of the HMEs in the different models and between the different compounds. Further, we determined that the changes in gene expression occurred via estrogen receptor signaling using the ER antagonist, ICI 182,780 (fulvestrant). Interestingly we found that the combination of ICI with estrogen or BPA greatly affected the expression of Set8, even when the hormone alone had no effect. This study demonstrates that the effects of estrogen and BPA on HME expression vary and that the presence of both the estrogen receptor and androgen receptor may be important for therapeutic intervention.

Neonatal exposure to estradiol/bisphenol A alters promoter methylation and expression of Nsbp1 and Hpcal1 genes and transcriptional programs of Dnmt3a/b and Mbd2/4 in the rat prostate gland throughout life.

Evidence supporting an early origin of prostate cancer is growing. We demonstrated previously that brief exposure of neonatal rats to estradiol or bisphenol A elevated their risk of developing precancerous lesions in the prostate upon androgen-supported treatment with estradiol as adults. Epigenetic reprogramming may be a mechanism underlying this inductive event in early life, because we observed overexpression of phosphodiesterase 4D variant 4 (Pde4d4) through induction of hypomethylation of its promoter. This epigenetic mark was invisible in early life (postnatal d 10), becoming apparent only after sexual maturation. Here, we asked whether other estrogen-reprogrammable epigenetic marks have similar or different patterns in gene methylation changes throughout life. We found that hypomethylation of the promoter of nucleosome binding protein-1 (Nsbp1), unlike Pde4d4, is an early and permanent epigenetic mark of neonatal exposure to estradiol/bisphenol A that persists throughout life, unaffected by events during adulthood. In contrast, hippocalcin-like 1 (Hpcal1) is a highly plastic epigenetic mark whose hypermethylation depends on both type of early-life exposure and adult-life events. Four of the eight genes involved in DNA methylation/demethylation showed early and persistent overexpression that was not a function of DNA methylation at their promoters, including genes encoding de novo DNA methyltransferases (Dnmt3a/b) and methyl-CpG binding domain proteins (Mbd2/4) that have demethylating activities. Their lifelong aberrant expression implicates them in early-life reprogramming and prostate carcinogenesis during adulthood. We speculate that the distinctly different fate of early-life epigenetic marks during adulthood reflects the complex nature of lifelong editing of early-life epigenetic reprogramming.

Retinoblastoma tumor suppressor status is a critical determinant of therapeutic response in prostate cancer cells.

The retinoblastoma tumor suppressor protein (RB), a critical mediator of cell cycle progression, is functionally inactivated in the majority of human cancers, including prostatic adenocarcinoma. The importance of RB tumor suppressor function in this disease is evident because 25% to 50% of prostatic adenocarcinomas harbor aberrations in RB pathway. However, no previous studies challenged the consequence of RB inactivation on tumor cell proliferation or therapeutic response. Here, we show that RB depletion facilitates deregulation of specific E2F target genes, but does not confer a significant proliferative advantage in the presence of androgen. However, RB-deficient cells failed to elicit a cytostatic response (compared with RB proficient isogenic controls) when challenged with androgen ablation, AR antagonist, or combined androgen blockade. These data indicate that RB deficiency can facilitate bypass of first-line hormonal therapies used to treat prostate cancer. Given the established effect of RB on DNA damage checkpoints, these studies were then extended to determine the impact of RB depletion on the response to cytotoxic agents used to treat advanced disease. In this context, RB-deficient prostate cancer cells showed enhanced susceptibility to cell death induced by only a selected subset of cytotoxic agents (antimicrotubule agents and a topoisomerase inhibitor). Combined, these data indicate that RB depletion dramatically alters the cellular response to therapeutic intervention in prostate cancer cells and suggest that RB status could potentially be developed as a marker for effectively directing therapy.

Androgen receptor corepressors and prostate cancer.

The androgen receptor (AR) mediates the effects of male steroid hormones (androgens) and contributes to a wide variety of physiological and pathophysiological conditions. As such, the regulatory mechanisms governing AR activity are of high significance. Concerted effort has been placed on delineating the mechanisms that control AR activity in prostate cancer, as AR is required for survival and proliferation in this tumor type. Moreover, AR is the central therapeutic target for metastatic prostate cancers, and recurrent tumors evade therapy by restoring AR activity. It is increasingly apparent that AR cofactors which modulate receptor activity can contribute to prostate cancer growth or progression, and this has been particularly well established for AR coactivators. The present review is focused on the role of AR corepressors in governing androgen action, with a specific emphasis on their activities in prostate cancer.

Cyclin D1b variant influences prostate cancer growth through aberrant androgen receptor regulation.

Cyclin D1 is a multifaceted regulator of both transcription and cell-cycle progression that exists in two distinct isoforms, cyclin D1a and D1b. In the prostate, cyclin D1a acts through discrete mechanisms to negatively regulate androgen receptor (AR) activity and thus limit androgen-dependent proliferation. Accordingly, cyclin D1a is rarely overexpressed in prostatic adenocarcinoma and holds little prognostic value in this tumor type. However, a common polymorphism (A870) known to facilitate production of cyclin D1b is associated with increased prostate cancer risk. Here we show that cyclin D1b is expressed at high frequency in prostate cancer and is up-regulated in neoplastic disease. Furthermore, our data demonstrate that, although cyclin D1b retains AR association, it is selectively compromised for AR regulation. The altered ability of cyclin D1b to regulate the AR was observed by using both in vitro and in vivo assays and was associated with compromised regulation of AR-dependent proliferation. Consistent with previous reports, expression of cyclin D1a inhibited cell-cycle progression in AR-dependent prostate cancer cells. Strikingly, cyclin D1b significantly stimulated proliferation in this cell type. AR-negative prostate cancer cells were nonresponsive to cyclin D1 (a or b) expression, indicating that defects in AR corepressor function yield a growth advantage specifically in AR-dependent cells. In summary, these studies indicate that the altered AR regulatory capacity of cyclin D1b contributes to its association with increased prostate cancer risk and provide evidence of cyclin D1b-mediated transcriptional regulation.