Identification of androgen-responsive genes that are alternatively regulated in androgen-dependent and androgen-independent rat prostate tumors

The brominated flame retardants TBECH and DPTE alter prostate growth, histology and gene expression patterns in the mouse

The brominated flame retardants (BFRs), 1,2-dibromo-4-(1,2 dibromoethyl)cyclohexane (TBECH) and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE) bind to the androgen receptor (AR). in vitro bioassays have shown that TBECH is a potent androgen agonist while DPTE is a potent AR antagonist. Both TBECH and DPTE alter gene expression associated with AR regulation. However, it remains to be determined if TBECH and DPTE can affect the prostate. For this reason, we exposed CD1 mice to a 1:1 mixture of TBECH diastereomers α and β, a 1:1 mixture of γ and δ, and to DPTE, and tested their effects on prostate growth, histology and gene expression profiles. Castrated mice were used to study the androgenic effects of TBECHαβ and TBECHγδ while the antagonistic effects of DPTE were studied in non-castrated mice. We observed that testosterone and TBECHγδ increased body and prostate weights while TBECHαβ affected neither of them; and that DPTE had no effect on body weight but reduced prostate weight drastically. Histomorphometric analysis of the prostate revealed epithelial and glandular alterations in the TBECHγδ group comparable to those in testosterone group while alterations in the TBECHαβ group were less pronounced. DPTE displayed androgen antagonist activity reminiscent of castration. The transcription profile of the prostate was altered by castration and exposure to testosterone and to TBECHγδ reversed several of these changes. Testosterone and TBECHγδ also regulated the expression of several androgen responsive genes implicated in prostate growth and cancer. While DPTE resulted in a drastic reduction in prostate weight, it only affected a small number of genes. The results indicate that TBECHγδ and DPTE are of high human health concern as they may contribute to changes in prostate growth, histology and function.

RhoC and guanine nucleotide exchange factor Net1 in androgen-unresponsive mouse mammary carcinoma SC-4 cells and human prostate cancer after short-term endocrine therapy

BACKGROUND

Endocrine resistance is a critical issue in managing patients with prostate cancer. This study is undertaken to search for a potential molecular target connected with this process using a model system of androgen-dependent and androgen-unresponsive SC-3 and SC-4 cells.

METHODS

Expression profiles, actin stress fiber organization, and the levels of activated Rho GTPases were compared between SC-4 and SC-3 cells using an oligonucleotide microarray, phalloidin staining, and a Rho activation assay. The cell viability was analyzed with a Rho inhibitor or by stable transfection with either a dominant-negative (DN) form of RhoC or a mutant form of NET1 (mutNET1). The expressions of RhoC, NET1, and epithelial-mesenchymal transition (EMT) markers were immunohistochemically analyzed in human prostate cancer specimens after short-term endocrine therapy and in an untreated condition.

RESULTS

SC-4 cells exhibited mesenchymal phenotypes with activation of Rho signals. Treatment with a Rho inhibitor suppressed the cell viability in SC-4 cells, but not in SC-3 cells. The cell viability of SC-4 cells stably expressing DN-RhoC and mutNET1 was also attenuated. In the immunohistochemical analysis, NET1 and the EMT marker of N-cadherin were expressed at higher levels in prostate cancers after short-term endocrine therapy than in untreated tumors, and RhoC expression was maintained after short-term endocrine therapy.

CONCLUSIONS

Rho signaling is involved in the cell survival of SC-4 cells. The higher expressions of RhoC and NET1 in human prostate cancers after short-term endocrine therapy suggest that RhoC and NET1 may become therapeutic targets during endocrine therapy.

LNCaP Atlas: gene expression associated with in vivo progression to castration-recurrent prostate cancer

Background

There is no cure for castration-recurrent prostate cancer (CRPC) and the mechanisms underlying this stage of the disease are unknown.

Methods

We analyzed the transcriptome of human LNCaP prostate cancer cells as they progress to CRPC in vivo using replicate LongSAGE libraries. We refer to these libraries as the LNCaP atlas and compared these gene expression profiles with current suggested models of CRPC.

Results

Three million tags were sequenced using in vivo samples at various stages of hormonal progression to reveal 96 novel genes differentially expressed in CRPC. Thirty-one genes encode proteins that are either secreted or are located at the plasma membrane, 21 genes changed levels of expression in response to androgen, and 8 genes have enriched expression in the prostate. Expression of 26, 6, 12, and 15 genes have previously been linked to prostate cancer, Gleason grade, progression, and metastasis, respectively. Expression profiles of genes in CRPC support a role for the transcriptional activity of the androgen receptor (CCNH, CUEDC2, FLNA, PSMA7), steroid synthesis and metabolism (DHCR24, DHRS7, ELOVL5, HSD17B4, OPRK1), neuroendocrine (ENO2, MAOA, OPRK1, S100A10, TRPM8), and proliferation (GAS5, GNB2L1, MT-ND3, NKX3-1, PCGEM1, PTGFR, STEAP1, TMEM30A), but neither supported nor discounted a role for cell survival genes.

Conclusions

The in vivo gene expression atlas for LNCaP was sequenced and support a role for the androgen receptor in CRPC.

Molecular regulation of androgen action in prostate cancer

Androgens are critical regulators of prostate differentiation and function, as well as prostate cancer growth and survival. Therefore, androgen ablation is the preferred systemic treatment for disseminated prostate cancer. Androgen action is exerted in target tissues via binding the androgen receptor (AR), a nuclear receptor transcription factor. Historically, the gene expression program mediated by the AR has been poorly understood. However, recent gene expression profiling and more traditional single-gene characterization studies have revealed many androgen-regulated genes that are important mediators of androgen action in both normal and malignant prostate tissue. This review will focus on the androgen-regulated gene expression program, and examine how recently identified androgen-regulated genes are likely to contribute to the development and progression of prostate cancer. We will also summarize several recent studies that have attempted to unravel how these genes are deregulated in androgen depletion independent prostate cancer.