Expression of androgen receptor coregulatory proteins in prostate cancer and stromal-cell culture models

Bag-1 Expression in Hyperplastic and Neoplastic Prostate Tissue: Is There Any Relationship with BCL-Related Proteins and Androgen Receptor Status?

Aims and Background

To evaluate the function and distribution of BAG-1 protein in hyperplastic and neoplastic prostate tissue and establish the relationship between this protein and BCL-related proteins (BCL-2 and BAX), androgen receptor (AR) expression and chromogranin A.

Methods

Twenty-eight prostatic adenocarcinomas and 16 prostate hyperplasias were included in this retrospective study. BAG-1, BCL-2, BAX, androgen receptor and chromogranin A immunostaining was performed by means of standard avidin-biotin peroxidase methods. The M30 antibody was used to identify preapoptotic and apoptotic cells. The immunohistochemical histological score (HSCORE) semi-quantative system was used to evaluate immunohistochemical staining.

Results

Statistical analysis showed a significant difference in HSCOREs of BAX, M30 and AR between the carcinoma and hyperplasia groups. Carcinomas expressed higher HSCOREs of these markers than hyperplasias. There were significant differences in nuclear and cytoplasmic BAG-1 positivity between high and low-grade carcinomas. BAG-1 expression was higher in low-grade carcinomas. In the carcinoma group there was a positive correlation (Pearson) between BCL-2 and cytoplasmic/nuclear BAG-1. In the hyperplasia group there was a negative correlation between BAX and BCL-2, and between AR and M30. We also detected a positive correlation between AR and nuclear/cytoplasmic BAG-1 and between nuclear and cytoplasmic BAG-1 in hyperplasias. BAG-1 showed the same specific basal cell localization as BCL-2 in hyperplastic and normal glands.

Conclusions

The BAG-1 protein showed a distinct distribution pattern in hyperplastic and neoplastic prostate. BAG-1 in association with BCL-2 inhibits apoptosis and may prolong the life of neoplastic cells and give them a chance to gain new oncogenic features in early carcinogenesis.

Androgen receptor phosphorylation: biological context and functional consequences

The androgen receptor (AR) is a ligand-regulated transcription factor that belongs to the family of nuclear receptors. In addition to regulation by steroid, the AR is also regulated by post-translational modifications generated by signal transduction pathways. Thus, the AR functions not only as a transcription factor but also as a node that integrates multiple extracellular signals. The AR plays an important role in many diseases, including complete androgen insensitivity syndrome, spinal bulbar muscular atrophy, prostate and breast cancer, etc. In the case of prostate cancer, dependence on AR signaling has been exploited for therapeutic intervention for decades. However, the effectiveness of these therapies is limited in advanced disease due to restoration of AR signaling. Greater understanding of the molecular mechanisms involved in AR action will enable the development of improved therapeutics to treat the wide range of AR-dependent diseases. The AR is subject to regulation by a number of kinases through post-translational modifications on serine, threonine, and tyrosine residues. In this paper, we review the AR phosphorylation sites, the kinases responsible for these phosphorylations, as well as the biological context and the functional consequences of these phosphorylations. Finally, what is known about the state of AR phosphorylation in clinical samples is discussed.

Hic-5 influences genomic and non-genomic actions of the androgen receptor in prostate myofibroblasts

There is extensive knowledge of androgen receptor (AR) signaling in cancer cells, but less regarding androgen action in stromal cells of the tumor microenvironment. We report here the genome-wide effects of a stromal cell specific molecular adapter and AR coregulator, hydrogen peroxide-inducible gene 5 (Hic-5/TGFB1I1), on AR function in prostate myofibroblasts. Following androgen stimulation, Hic-5 rapidly translocates to the nucleus, coincident with increased phosphorylation of focal adhesion kinase. As a coregulator, Hic-5 acted to amplify or inhibit regulation of approximately 50% of AR target genes, affected androgen regulation of growth, cell adhesion, motility and invasion. These data suggest Hic-5 as a transferable adaptor between focal adhesions and the nucleus of prostate myofibroblasts, where it acts a key mediator of the specificity and sensitivity of AR signaling. We propose a model in which Hic-5 coordinates AR signaling with adhesion and extracellular matrix contacts to regulate cell behavior in the tumor microenvironment.

Expression and function of nuclear receptor co-activator 4: evidence of a potential role independent of co-activator activity

Nuclear receptor coactivator 4 (NcoA4), also known as androgen receptor-associated protein 70 (ARA70), was initially discovered as a component of Ret-Fused Gene expressed in a subset of papillary thyroid carcinomas. Subsequent studies have established NcoA4 as a coactivator for a variety of nuclear receptors, including peroxisome proliferator activated receptors α and γ, and receptors for steroid hormones, vitamins D and A, thyroid hormone, and aryl hydrocarbons. While human NcoA4 has both LXXLL and FXXLF motifs that mediate p160 coactivator nuclear receptor interactions, this ubiquitously expressed protein lacks clearly defined functional domains. Several studies indicate that NcoA4 localizes predominantly to the cytoplasm and affects ligand-binding specificity of the androgen receptor, which has important implications for androgen-independent prostate cancer. Two NcoA4 variants, which may exert differential activities, have been identified in humans. Recent studies suggest that NcoA4 may play a role in development, carcinogenesis, inflammation, erythrogenesis, and cell cycle progression that may be independent of its role as a receptor coactivator. This review summarizes what is currently known of the structure, expression, regulation, and potential functions of this unique protein in cancerous and non-cancerous pathologies.

Androgen receptor co-activators in the regulation of cellular events in prostate cancer

OBJECTIVES

Androgen receptor (AR) action in benign and malignant tissue is potentiated by a number of co-regulatory proteins that may interact with one or more receptor domains. With improvement of research methodologies, it became possible to detect a number of co-activators whose expression is increased in prostate cancer tissue.

METHODS

Manuscripts describing prostate cancer-relevant regulation of cellular events by co-activators are selected and summarized.

RESULTS

AR co-activators may regulate histone modification, proteasomal degradation, chaperones, sumoylation, chromatin remodeling, and cytoskeleton. Some of them (TIF-2) are up-regulated by androgens, whereas the expression of others increases during androgen ablation (p300, CBP, and Tip60). Most co-factors are important for the stimulation of cellular proliferation, although in some cases (ART-27), they act as tumor suppressors and are deleted in prostate cancer tissue. In addition to stimulating AR, some co-activators suppress apoptosis in prostate cancer cells that do not express the AR (p300 and SRC-3). It was recently shown that the inhibition of p300 slows down proliferation, stimulates apoptosis, and inhibits migration and invasion.

CONCLUSIONS

Co-factors whose down-regulation results in the alterations of multiple cellular functions may be valid targets for novel therapies in advanced prostate cancer.

HOXC8 inhibits androgen receptor signaling in human prostate cancer cells by inhibiting SRC-3 recruitment to direct androgen target genes

HOX (homeobox) genes encode homeodomain-containing transcription factors critical to development, differentiation, and homeostasis. Their dysregulation has been implicated in a variety of cancers. Previously, we showed that a subset of genes of the HOXC cluster is upregulated in primary prostate tumors, lymph node metastases, and malignant prostate cell lines. In the present study, we show that HOXC8 inhibits androgen receptor (AR)-mediated gene induction in LNCaP prostate cancer cells and HPr-1 AR, a nontumorigenic prostate epithelial cell line. Mechanistically, HOXC8 blocks the AR-dependent recruitment of the steroid receptor coactivators steroid receptor coactivator-3 (SRC-3), and CREB binding protein to the androgen-regulated prostate-specific antigen gene enhancer and inhibits histone acetylation of androgen-regulated genes. Inhibition of androgen induction by HOXC8 is reversed upon expression of SRC-3, a member of the SRC/p160 steroid receptor cofactor family. Coimmunoprecipitation studies show that HOXC8 expression inhibits the hormone-dependent interaction of AR and SRC-3. Finally, HOXC8 expression increases invasion in HPr-1 AR nontumorigenic cells. These data suggest a complex role for HOXC8 in prostate cancer, promoting invasiveness while inhibiting AR-mediated gene induction at androgen response element-regulated genes associated with differentiated function of the prostate. A greater understanding of HOXC8 actions in the prostate and its interactions with androgen signaling pathways may elucidate mechanisms driving the onset and progression of prostate cancer.

Cancer biomarker discovery: the entropic hallmark

Background

It is a commonly accepted belief that cancer cells modify their transcriptional state during the progression of the disease. We propose that the progression of cancer cells towards malignant phenotypes can be efficiently tracked using high-throughput technologies that follow the gradual changes observed in the gene expression profiles by employing Shannon's mathematical theory of communication. Methods based on Information Theory can then quantify the divergence of cancer cells' transcriptional profiles from those of normally appearing cells of the originating tissues. The relevance of the proposed methods can be evaluated using microarray datasets available in the public domain but the method is in principle applicable to other high-throughput methods.

Methodology/Principal Findings

Using melanoma and prostate cancer datasets we illustrate how it is possible to employ Shannon Entropy and the Jensen-Shannon divergence to trace the transcriptional changes progression of the disease. We establish how the variations of these two measures correlate with established biomarkers of cancer progression. The Information Theory measures allow us to identify novel biomarkers for both progressive and relatively more sudden transcriptional changes leading to malignant phenotypes. At the same time, the methodology was able to validate a large number of genes and processes that seem to be implicated in the progression of melanoma and prostate cancer.

Conclusions/Significance

We thus present a quantitative guiding rule, a new unifying hallmark of cancer: the cancer cell's transcriptome changes lead to measurable observed transitions of Normalized Shannon Entropy values (as measured by high-througput technologies). At the same time, tumor cells increment their divergence from the normal tissue profile increasing their disorder via creation of states that we might not directly measure. This unifying hallmark allows, via the the Jensen-Shannon divergence, to identify the arrow of time of the processes from the gene expression profiles, and helps to map the phenotypical and molecular hallmarks of specific cancer subtypes. The deep mathematical basis of the approach allows us to suggest that this principle is, hopefully, of general applicability for other diseases.

Modulation of aryl hydrocarbon receptor activity by four and a half LIM domain 2

The aryl hydrocarbon receptor (AhR) mediates transcriptional effects of a diverse array of ligands including environmental contaminants that have been linked to various cancers. The transcriptional activity of the AhR is modulated by different coregulators such as the p160 family members of coactivators and nuclear receptor coactivator 4 (NcoA4). In this study, we provide novel evidence that four and a half LIM only protein 2 (FHL2) interacts with and differentially modulates the transcriptional activity of AhR. Co-immunoprecipitation studies indicate that FHL2 interacts with AhR in a ligand-independent manner but not with its heterodimeric partner, AhR nuclear translocator (ARNT). Overexpression of FHL2 enhanced AhR-mediated expression of a luciferase reporter gene in a dose- and ligand-dependent manner in COS cells. Furthermore, FHL2 cooperated with NcoA4 to synergistically enhance AhR transcriptional activity in these cells. However, the impact of FHL2 on AhR transcriptional activity was cell-specific: FHL2 facilitated AhR action in MCF-7 and PC-3 cells, whereas it suppressed AhR activity in T47D and LNCaP cells. These results of reporter gene studies were corroborated by the impact of FHL2 overexpression on, an established target gene of AhR, cytochrome P450 (CYP1A1) expression. We also demonstrated a potential competition of AhR and androgen receptor (AR) for FHL2 availability in COS cells, as FHL2-facilitation was significantly decreased in the presence of liganded AR. These findings indicate a functional interaction between AhR and FHL2 that modulates the activity of AhR and therefore could affect its role in cancer progression or development.

Ubiquitylation of epsilon-COP by PIRH2 and regulation of the secretion of PSA

Ubiquitylation appears to be involved in the membrane trafficking system including endocytosis, exocytosis, and ER-to-Golgi transport. We found that PIRH2, which was identified as an interacting protein for androgen receptor or p53, interacts with and ubiquitylates the epsilon-subunit of coatmer complex, epsilon-COP. PIRH2 promotes the ubiquitylation of epsilon-COP in vitro and in vivo and consequently promotes the degradation of epsilon-COP. The interaction between PIRH2 and epsilon-COP is affected by the presence of androgen, and PIRH2 in the presence of androgen promotes ubiquitylation of epsilon-COP in vivo. Furthermore, overexpression of the wild type of PIRH2 in prostate cancer cells causes downregulation of the secretion of prostate-specific antigen (PSA), a secretory protein in prostate epithelial cells and one of diagnostic markers for prostate cancer. Our results indicate that PIRH2 functions as a regulator for COP I complex.

Androgen receptor coregulators and their involvement in the development and progression of prostate cancer

The androgen receptor signaling axis plays an essential role in the development, function and homeostasis of male urogenital structures including the prostate gland although the mechanism by which the AR axis contributes to the initiation, progression and metastatic spread of prostate cancer remains somewhat enigmatic. A number of molecular events have been proposed to act at the level of the AR and associated coregulators to influence the natural history of prostate cancer including deregulated expression, somatic mutation, and post-translational modification. The purpose of this article is to review the evidence for deregulated expression and function of the AR and associated coactivators and corepressors and how such events might contribute to the progression of prostate cancer by controlling the selection and expression of AR targets.

Suppression of androgen receptor transactivation and prostate cancer cell growth by heterogeneous nuclear ribonucleoprotein A1 via interaction with androgen receptor coregulator ARA54

The androgen receptor (AR) requires coregulators for its optimal transactivation. Whether AR coregulators also need interacting proteins to modulate their function remains unclear. Here we describe heterogeneous nuclear ribonucleoprotein (hnRNP) A1 as an associated negative modulator for the AR coregulator ARA54. hnRNP A1 selectively suppressed ARA54-enhanced wild-type and mutant AR transactivation via interruption of AR-ARA54 interaction and ARA54 homodimerization. Stable transfection of hnRNP A1 in the LNCaP cells suppressed AR-mediated cell growth and the expression of prostate-specific antigen, and this suppressive effect was abolished by the addition of ARA54-small interfering RNA. Small interfering RNA knockdown of endogenous hnRNP A1 enhanced cell growth and prostate-specific antigen expression in LNCaP cells. These results not only suggest that the loss of hnRNP A1 expression might activate the ARA54-enhanced cell growth and contribute to the prostate cancer progression, but also demonstrate the dual functional roles for ARA54 as an AR coregulator directly and as a mediator for the suppressive effect of hnRNP A1 indirectly. The novel finding that a protein can modulate AR function without direct interaction with AR might provide a new therapeutic approach to battle prostate cancer by targeting AR indirectly with fewer side effects.

Functional interaction of nuclear receptor coactivator 4 with aryl hydrocarbon receptor

Aryl hydrocarbon receptor (AhR) transcriptional activity is enhanced by interaction with p160 coactivators. We demonstrate here that NcoA4, a nuclear receptor coactivator, interacts with and amplifies AhR action. NcoA4-AhR and NcoA4-ARNT interactions were demonstrated by immunoprecipitation in T47D breast cancer and COS cells and was independent of ligand. Overexpression of NcoA4 enhanced AhR transcriptional activity 3.2-fold in the presence of dioxin, whereas overexpression of a splice variant, NcoA4beta, as well as a variant lacking the C-terminal region enhanced AhR transcriptional activity by only 1.6-fold. Enhanced AhR signaling by NcoA4 was independent of the LXXLL and FXXLF motifs or of the activation domain. NcoA4 protein localized to cytoplasm in the absence of dioxin and in both the cytoplasm and nucleus following dioxin treatment. NcoA4-facilitation of AhR activity was abolished by overexpression of androgen receptor, suggesting a potential competition of AhR and androgen receptor for NcoA4. These findings thus demonstrate a functional interaction between NcoA4 and AhR that may alter AhR activity to affect disease development and progression.

Expression of BAG-1 protein correlates with aggressive behavior of prostate cancers

BACKGROUND

Differences in tumor behavior, ranging from indolent to aggressive, create a need for novel prognostic biomarkers. BAG-1 is a co-chaperone that regulates the activity of Hsp70, Bcl-2, Raf-1, growth factor, and steroid receptors (e.g., the Androgen Receptor).

METHODS

Using immunohistochemical method, we explored BAG-1 expression in prostate cancers and its association with clinicopathological parameters.

RESULTS

BAG-1 immunostaining was elevated in prostate cancer compared to normal prostatic epithelium. Higher nuclear BAG-1 in hormone-refractory (n = 34) compared to localized untreated tumors (n = 58) (P < 0.0001) suggested that upregulation of the nuclear isoform may contribute to disease progression. In 64 early-stage patients (T2N0M0) treated with external-beam irradiation, cytosolic BAG-1 correlated with higher pretreatment levels of serum Prostate specific antigen (P = 0.04) and shorter time to disease progression (P = 0.00004).

CONCLUSIONS

Increased cytosolic and nuclear BAG-1 expression may denote more aggressive variants of prostate cancer.

Expression and function of human steroid receptor RNA activator in prostate cancer cells: role of endogenous hSRA protein in androgen receptor-mediated transcription

Steroid receptor RNA activator (SRA) was first isolated as a steroid receptor co-activator that functioned as an RNA transcript. Later, we demonstrated that SRA needs to be translated in order to co-activate androgen receptor (AR). Here, we showed that three isoforms of human SRA enhanced AR activities. Small interfering RNA against SRA suppressed AR activities in PC-3 cells transfected with pSG5AR and in LNCaP cells that have an endogenous mutated-AR. Western blot showed that SRA protein was expressed at a higher level in PC-3 than in LNCaP cells, suggesting that SRA may be related to hormone-independent growth of prostate cancer.

Evaluation of steroid receptors, coregulators, and molecules associated with uterine receptivity in secretory endometria from untreated women with polycystic ovary syndrome

OBJECTIVE

To evaluate gene and protein expression of steroid receptors, nuclear receptor coregulators, and uterine receptivity markers in midsecretory phase endometria from untreated women with polycystic ovary syndrome (PCOS).

DESIGN

Case-control study.

SETTING

Hospital research unit.

PATIENT(S)

Eight patients with PCOS and eight fertile women of similar age to those with PCOS.

INTERVENTION(S)

Endometrial samples were obtained from women with PCOS (PCOSE) and normal (NE) women during the midsecretory phase of the menstrual cycle.

MAIN OUTCOME MEASURE(S)

Expression studies (immunohistochemistry, reverse transcription-polymerase chain reaction [RT-PCR] and Western blot).

RESULT(S)

Endometria from PCOS exhibit higher levels of messenger RNA (mRNA) and protein for estrogen receptor alpha and coactivators than NE. Epithelial cells had a greater expression of progesterone receptor in PCOSE, whereas, no differences were observed in gene and protein expression of the nuclear corepressor (NcoR) and the antiadhesion molecule mucin type-1 (MUC-1) between PCOSE and NE. Immunodetection for the coactivator ARA70 was higher in PCOSE than in NE; in contrast, expression of beta3-integrin in epithelia was lower in PCOSE than in control endometria.

CONCLUSION(S)

The higher response to steroid hormones of endometria from untreated PCOS-women induces diminished expression of beta3 integrin, which partially explain implantation failure in PCOS patients.

EXPRESSION OF ANDROGEN RECEPTOR ASSOCIATED PROTEIN 55 (ARA55) IN THE DEVELOPING HUMAN FETAL PROSTATE

PURPOSE

Development and differentiation of the human fetal prostate are androgen dependent and follow a specific pattern of solid bud-ductal morphogenesis, which involves stromal-epithelial interactions. Androgen receptor associated protein 55 (ARA55) an androgen receptor coactivator localized in stromal cells, binds to androgen receptor (AR) and regulates androgen receptor translocation and transcriptional activity. We investigated whether ARA55 has a role in human prostate development.

MATERIALS AND METHODS

ARA55 expression was examined in 25 human prostates from fetuses at gestational ages 10 to 40 weeks and compared to the expression of 34betaE12 (a basal cell marker), smooth muscle actin, desmin (a smooth muscle marker), vimentin (a mesenchymal marker) and Ki-67 (a proliferation marker) by immunohistochemistry.

RESULTS

Prostatic epithelium appeared as solid epithelial buds from the urogenital sinus. It underwent arborization and ductal differentiation from the center to the periphery. ARA55 was expressed in stromal cells with a zonal pattern, primarily in the peripheral zone surrounding the noncanalized acini. Most cells in solid buds were positive for 34betaE12, while only basal layer cells in the centrally located epithelial ducts stained with 34betaE12. Solid buds also had a higher proliferation index than ducts. In addition, ARA55 expressing stromal cells but not ARA55 negative stromal cells showed smooth muscle differentiation.

CONCLUSIONS

The intimate relationship between ARA55 expressing stromal cells and mitotically active, noncanalized acini suggests that ARA55 has a role in the stromal-epithelial interaction involved in fetal prostate development.

Signal transduction in prostate cancer progression

Prostate cancer is the most frequently diagnosed cancer among men and the second leading cause of male cancer deaths in the United States. When prostate cancer initially presents in the clinic, the tumour is dependent on androgen for growth and, therefore, responsive to the surgical or pharmacological ablation of circulating androgens. However, there is a high rate of treatment failure because the disease often recurs as androgen-independent metastases. Surprisingly, this late-stage androgen-independent prostate cancer almost always retains expression of the AR (androgen receptor), despite the near absence of circulating androgens. Although late-stage prostate cancer is androgen-independent, the AR still seems to play a role in cancer cell growth at this stage of disease. Therefore a key to understanding hormone-independent prostate cancer is to determine the mechanism(s) by which the AR can function even in the absence of physiological levels of circulating androgen. This review will focus on the role of growth factor signalling in prostate cancer progression to androgen independence and thus outline potential molecular areas of intervention to treat prostate cancer progression.

Role of TGF-beta2 in the human hair cycle

Male pattern baldness is the result of premature entry into catagen due to androgens. In order to prevent hair loss, it is important to understand two critical steps, i.e., the induction mechanism of premature entry and the regression process of catagen. At the initiation, dihydrotestosterone (DHT) stimulates synthesis of transforming growth factor-beta2 (TGF-beta2) in dermal papilla cells. TGF-beta2 suppresses proliferation of epithelial cells and stimulates synthesis of certain caspases. Then TGF-beta2 triggers the intrinsic caspase network and subsequently epithelial cells are eliminated through apoptotic cell death. TGF-beta antagonists are effective in preventing catagen-like morphological changes and in promoting elongation of hair follicles in vivo and in vitro. These lines of evidence strongly suggest the presence of a "catagen cascade" in male pattern baldness, involving: (1) the conversion of testosterone to DHT by type II 5-alpha-reductase; (2) the synthesis of TGF-beta2 in dermal papilla cells; and (3) the activation of the intrinsic caspase network. These sequential events contribute to the shortening of the human hair cycle.

Novel Function of Androgen Receptor-associated Protein 55/Hic-5 as a Negative Regulator of Smad3 Signaling

Androgen receptor-associated protein 55 (ARA55/Hic-5) belongs to the LIM protein superfamily and is featured by three or four N-terminal LD motifs and four C-terminal zinc finger-like LIM domains. Both LD motifs and LIM domains can serve as protein-protein interaction interfaces. Recently, we found that enforced expression of ARA55 inhibits transforming growth factor-beta-mediated up-regulation of Smad binding element-luciferase reporter activity in NRP-154 and NRP-152 rat prostate and LNCaP human prostate cell lines. Moreover, ARA55 also inhibits the induction of Smad-binding element 4-luciferase and 3TP-luciferase (a plasminogen activator inhibitor-1 (PAI-1) promoter construct) reporters by constitutively active (CA)-Smad3 in these cell lines. Co-immunoprecipitation studies suggest an interaction between ARA55 and either CA-Smad3 or wild-type Smad3 in HEK293 cells that occurs through the MH2 domain of Smad3 and the C terminus of ARA55 with wild-type Smad3 having stronger affinity than CA-Smad3 to ARA55. Glutathione S-transferase pull-down assays demonstrate that this interaction can occur in a cell-free system. These results are consistent with the luciferase data showing that the C terminus of ARA55 is critical for suppression of Smad3 activity. Furthermore, using a mammalian two-hybrid system, we confirmed that ARA55 interacts with the MH2 domain of Smad3 and suppresses CA-Smad3-induced transcriptional responses. In conclusion, these results support that ARA55 selectively intercepts transforming growth factor-beta signaling through an interaction of the LIM domain of ARA55 with the MH2 domain of Smad3.

Expression and function of androgen receptor coactivators in prostate cancer

Human androgen receptor (AR) associates with coactivator or corepressor proteins that modulate its activation in the presence of ligand. Early studies on AR coactivators in carcinoma of the prostate were hampered because of lack of respective antibodies. Investigations at mRNA level revealed that most benign and malignant prostate cells express common coactivators. AR coactivators SRC-1 and TIF-2 are up-regulated in tissue specimens obtained from patients who failed prostate cancer endocrine therapy. Increased expression of these coactivators is associated with enhanced activation of the AR by the adrenal androgen dehydroepiandrosterone. Similar association between AR coactivator expression and high prostate cancer grade and stage was reported for RAC-3 (SRC-3). The transcriptional integrator CBP was detected in clinical specimens representing organ-confined prostate cancer, lymph node metastases and tumour cell lines. Agonistic effect of the nonsteroidal antiandrogen hydroxyflutamide was strongly potentiated in prostate cells transfected with CBP cDNA. A functional homologue of CBP, p300, is implicated in ligand-independent AR activation by interleukin-6. The AR coactivator Tip60, which is up-regulated by androgen ablation, is recruited to the promoter of the prostate-specific antigen gene in the absence of androgen in androgen-independent prostate cancer sublines. It was proposed that the cofactor ARA70 is a specific enhancer of AR action. However, research from other laboratories has demonstrated interaction between ARA70 and other steroid receptors. Although in some cases dominant-negative coactivator mutants inhibited proliferation of prostate cancer cells in vitro, confirmation from in vivo tumour models is missing. In summary, several abnormalities in AR coactivator expression and function are associated with prostate cancer progression.

Selective phosphorylations of the SRC-3/AIB1 coactivator integrate genomic reponses to multiple cellular signaling pathways

Although several lines of evidence have indicated that the activity of SRC-3/AIB1/ACTR/pCIP/RAC3/TRAM1 could be regulated by phosphorylation, an important question remained as to how different signaling pathways can act through limiting concentrations of the same SRC-3 molecule to exert different physiological functions. Herein, we report the successful identification of six functional in vivo SRC-3 phosphorylation sites. Interestingly, all phosphorylation sites are required for coactivation of estrogen and androgen receptors, but not all sites are required for coactivation of NF-kappaB. Different combinations of site-specific phosphorylations of SRC-3 are required for induction of IL-6 gene expression by TNF-alpha as compared to oncogenic transformation of MEFs. Mechanisms of pathway selectivity involve protein-protein interactions of differentially phosphorylated SRC-3 with downstream transcriptional activators and coactivators. Our results uncovered an additional level of transcriptional regulation whereby specific modulations of SRC-3 phosphorylation allow this coactivator to function as a regulatable integrator for diverse signaling pathways in cells.

Expression of androgen receptor coregulators in prostate cancer

PURPOSE

The androgen receptor (AR)-mediated signaling pathway seems to be essentially involved in the development and progression of prostate cancer. In vitro studies have shown that altered expression of AR coregulators may significantly modify transcriptional activity of AR, suggesting that these coregulators could also contribute to the progression of prostate cancer. Here, our goal was to assess alterations in the expression of the AR coregulators in prostate cancer in vivo.

EXPERIMENTAL DESIGN

The expression of 16 AR coactivators and corepressors (SRC1, beta-catenin, TIF2, PIAS1, PIASx, ARIP4, BRCA1, AIB1, AIB3, CBP, STAT1, NCoR1, AES, cyclin D1, p300, and ARA24) was measured in prostate cancer cell lines, xenografts, and clinical prostate tumor specimens by using real-time quantitative reverse transcription-PCR. In addition, gene copy number of SRC1 was analyzed by fluorescence in situ hybridization.

RESULTS

Both AR-positive and AR-negative cell lines and xenografts expressed the coregulators. Most of the coregulators studied were expressed at equal levels in benign prostatic hyperplasia and untreated and hormone-refractory carcinomas. However, the expression of PIAS1 and SRC1 was significantly (P = 0.048 and 0.017, respectively) lower in hormone-refractory prostate tumors than in untreated prostate tumors. No overexpression of the coregulators was found in the clinical material. Paradoxically, the SRC1 gene was found to be amplified and highly expressed in a LuCaP 70 prostate cancer xenograft.

CONCLUSIONS

These findings suggest that the decreased expression of PIAS1 and SRC1 could be involved in the progression of prostate cancer. In addition, gene amplification of SRC1 in one of the xenografts implies that, in some tumors, genetic alteration of SRC1 may provide a growth advantage.

Specific block of androgen receptor activity by antisense oligonucleotides

Claims about molecular mechanisms underlying the resistance to anti-hormones of prostate cancer cells find support in biological experiments, which involve hormone-independent activation of the androgen receptor's (AR) transcriptional activity. In order to test this hypothesis, we attempted to shut down the expression of AR by the means of target-directed antisense oligonucleotides. A set of 49 oligonucleotides matching sequences of the AR mRNA either in the coding sequence or in the 3' and 5' untranslated regions were synthesized and examined in a cellular AR-dependent reporter system. Five antisense oligonucleotides were identified as highly potent inhibitors of AR-driven gene expression in a cellular reporter assay. These five were further profiled using point-mutated control sequences for the assessment of AR inhibition. In addition the expression of another AR-driven gene, the modulator of PSA expression (gene for inhibition of prostate specific antigen, an endogenous, AR-driven gene) was examined. Finally, we observed that the hormone-independent but AR-mediated transactivation by IGF-1 could also be specifically shut-down by these antisense oligonucleotides. The selection of highly target-restricted antisense oligonucleotides in the prostate cancer cell line LNCaP provided tools to study a central role of the androgen receptor in growth regulation of prostatic cancer cell lines and could be of utility in cancer situations in vivo.

Expression of AR associated protein 55 (ARA55) and androgen receptor in prostate cancer

BACKGROUND

Androgen receptor (AR) transcription is modulated by several cofactors such as AR associated proteins (ARA) including ARA70, ARA54, and ARA55. ARA55 increases AR transcription and alters ligand specificity. We hypothesized that ARA55 might play an important role in prostate cancer development or progression. We evaluated the messenger RNA (mRNA) expression of ARA55 in prostate cancer tissues, and analyzed the relation between ARA55 expression and clinical characteristics.

METHODS

A total of 30 prostate cancer specimens (20 previously untreated prostate cancers and 10 recurrent, hormone-refractory prostate cancers (HRPC)) and 5 benign prostatic hypertrophy (BPH) tissue samples were examined. mRNA expression of ARA55 and AR were analyzed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) using real time PCR.

RESULTS

ARA55 expression was identified in all tissue samples of previously untreated prostate cancer, HRPC and BPH. ARA55 expression level in HRPC specimens was significantly lower than that in previously untreated prostate cancer (P = 0.02) or BPH (P = 0.005) samples using quantitative PCR. On the other hand, higher ARA55 expression was associated with shorter recurrence-free survival (P = 0.02) and overall survival (P = 0.01) in HRPC patients. AR expression was also revealed in all specimens of both prostate cancer and BPH. AR expression level in HRPC samples was significantly higher than that in previously untreated prostate cancer (P = 0.001) and BPH (P = 0.01) samples.

CONCLUSIONS

ARA55 may be associated with prostate cancer development and progression. ARA55 expression level in HRPC specimens was significantly lower than that in previously untreated prostate cancer or BPH specimens. On the contrary, our results suggested that a higher ARA55 expression level may result in unfavorable recurrence-free survival and overall survival in HRPC patients. The role of ARA55 may differ between prostate cancer development and the process of progression to a hormone-refractory state. These data not only help to understand the molecular mechanism of prostate cancer development or recurrence, but may also lead to a therapeutic strategy for recurrent prostate cancer that is refractory to hormonal treatment.

Expression of androgen receptor coactivators in normal and cancer prostate tissues and cultured cell lines

BACKGROUND

In prostate cancer cell lines, androgen receptor (AR) coactivators modulate the transcriptional activity of AR. However, very little is known about their expression in normal prostate tissue and during progression to cancer.

METHODS

AR and coactivators ARA54, ARA55, ARA70, and SRC1 RNA were analyzed by RT-PCR in normal and tumoral tissues of the same prostate, in prostate cell lines, and after hormonal treatments of prostate epithelial cells.

RESULTS

AR-coactivators were expressed in normal and tumoral tissues and in cultured prostate cells; only ARA55 expression was decreased in tumoral relative to normal tissue of all seven prostates analyzed. It was not expressed in LNCaP and DU145 cancer cells and low in PNT2 immortalized cells in which all coactivator's expression were down regulated by DHT and up regulated by E2. In addition, coactivator's expression was increased in hyperplastic relative to normal prostate fibroblasts.

CONCLUSIONS

ARA55 is both an AR coactivator and a focal adhesion protein (Hic-5). Its role in the progression of prostate carcinoma may therefore involve these two different functions. Its decrease in cancer tissue suggests that it plays a different role than that expected, namely, facilitate cell proliferation and therefore mobility and metastasis.

Secretion of endogenous kallikreins 2 and 3 by androgen receptor-transfected PC-3 prostate cancer cells

Androgen independent PC-3 cells lack androgen receptor (AR) expression and do not produce kallikrein 2 (hK2) or 3 (prostate-specific antigen, PSA). In this paper, we examined the ability of androgens to stimulate PSA and hK2 production in AR transfected PC-3 cells (PC-3(AR)) and compared this to LNCaP cells. PSA and hK2 were measured in the culture medium and cell lysates using an ELISA-based immunofluorometric assay. Only androgens were able to induce PSA and hK2 secretion in PC-3(AR) cells in a dose- and time-dependent manner depending on the level of AR present. The level of androgen-induced PSA and hK2 secretion in PC-3(AR) cells was approximately 1.5 and 0.9% that induced in LNCaP cells, respectively. Insulin-like growth factor-I (IGF-I), which has been shown to activate AR in the absence of ligand, did not activate PSA secretion in the absence of androgen, but further increased the dihydrotestosterone-induced PSA secretion in PC-3(AR) cells. The lack of PSA and hK2 production in parental PC-3 cells is thus a result of their lack of AR expression. PSA and/or hK2 production in PC-3(AR) cells can thus serve as an endogenous reporter system to investigate AR action or to screen putative endocrine disrupters.

The transcriptional co-activator cAMP response element-binding protein-binding protein is expressed in prostate cancer and enhances androgen- and anti-androgen-induced androgen receptor function

Progression of human prostate cancer toward therapy resistance occurs in the presence of wild-type or mutated androgen receptors (ARs) that, in some cases, exhibit aberrant activation by various steroid hormones and anti-androgens. The AR associates with a number of co-activators that possess histone acetylase activity and act as bridging molecules to components of the transcription initiation complex. In previous reports, it was shown that the transcriptional co-activator CREB (cAMP response element-binding protein)-binding protein (CBP) enhances AR activity in a ligand-dependent manner. In the present study, we have investigated whether CBP modifies antagonist/agonist balance of the nonsteroidal anti-androgens hydroxyflutamide and bicalutamide. In prostate cancer DU-145 cells, which were transiently transfected with CBP cDNA, hydroxyflutamide enhanced AR activity to a greater extent than bicalutamide in the presence of either wild-type or the mutated AR 730 val-->met. In two sublines of LNCaP cells that contain the mutated AR 877 thr-->ala and overexpressed CBP, increase in AR activity was observed after treatment with hydroxyflutamide but not with bicalutamide. Anti-androgens did not influence AR expression in cells transfected with CBP cDNA, as judged by Western blot analysis. Endogenous CBP protein was detected by Western blot in nuclear extracts from the three prostate cancer cell lines, LNCaP, PC-3, and DU-145, all derived from therapy-resistant prostate cancer. In addition, CBP was expressed in both basal and secretory cells of benign prostate epithelium, high-grade prostate intraepithelial neoplasia, and prostate cancer clinical specimens, as evidenced by immunohistochemical staining. Taken together, our findings demonstrate the selective enhancement of agonistic action of the anti-androgen hydroxyflutamide by the transcriptional co-activator CBP, which is a new, potentially relevant mechanism contributing to the acquisition of therapy resistance in prostate cancer.

Ras signaling in prostate cancer progression

When prostate cancer is first detected it generally is dependent on the presence of androgens for growth, and responds to androgen ablation therapies. However, the disease often recurs in a disseminated and apparently androgen independent (AI) form, and in this state is almost invariably fatal. Considerable evidence indicates that the Androgen receptor (AR) continues to be required even in androgen independent (AI) disease. Thus, a key to understanding hormone independent prostate cancer is to determine the mechanism(s) by which the AR can function even in the absence of physiologic levels of androgen. In this article, we argue that growth factors and receptors that utilize Ras family members drive prostate cancer progression to a state of androgen hypersensitivity; and that post-translational modifications (e.g., phosphorylations) of transcriptional cofactors might be responsible for modulating the function of the AR so that it is active even at low concentrations of androgen.

A novel steroid receptor co-activator protein (SRAP) as an alternative form of steroid receptor RNA-activator gene: expression in prostate cancer cells and enhancement of androgen receptor activity

We have cloned a cDNA coding for a novel steroid receptor co-activator protein termed SRAP from a rat prostate library. Although the nucleotide sequence of the SRAP has 78.2% identity to that of the human steroid receptor RNA activator (SRA), a novel RNA molecule which was reported to act as an RNA transcript without being translated into protein [Lanz, McKenna, Onate, Albrecht, Wong, Tsai, Tsai and O'Malley (1999) Cell 97, 17-27], the cDNA of SRAP is capable of generating a functional protein. Glutathione S-transferase pull-down assays showed that SRAP associates with the partial androgen receptor (AR) protein composed of a DNA-binding domain and an activation function 2. Luciferase assays demonstrated that SRAP enhances the transactivation activity of the AR, the glucocorticoid receptor and the peroxisome proliferator-activated receptor gamma(1) in a ligand-dependent manner. Using a green fluorescent protein (GFP) fusion-protein construct, we demonstrated in vivo translation of the GFP-SRAP fusion protein in HeLa cells co-transfected with pSG5AR and reporter gene in the presence of 5 alpha-dihydrotestosterone (DHT). Co-transfection of the GFP-SRAP fusion protein expression plasmid enhanced the transactivation activity of AR whereas incorporation of mutations in SRAP of the fusion protein resulted in loss of enhancement of the transactivation activity. Northern blot analysis and reverse transcriptase PCR assays showed that SRAP and SRA are expressed in rat and human prostate cancer cell lines respectively. In HeLa cells and the human prostate cancer cells line DU-145, co-transfected with SRAP, the DHT-dependent transactivation activities of AR were not completely inhibited by the anti-androgen flutamide, but the transactivation activities still remained high even in the presence of 5 microM flutamide, suggesting that SRAP may play an important role in enhancing AR activity in prostate cancer.

Molecular structure and biological function of the cancer-amplified nuclear receptor coactivator SRC-3/AIB1

Nuclear hormone receptors are ligand-dependent transcription factors that require coactivators to regulate target gene expression. The steroid receptor coactivator-3 (SRC-3), also known as p/CIP, RAC3, AIB1, ACTR and TRAM-1, is a cancer-amplified coactivator in the SRC gene family that also contains SRC-1 and TIF2/GRIP1. SRC-3 interacts with nuclear receptors and certain other transcription factors, recruits histone acetyltransferases and methyltransferases for chromatin remodeling and facilitates target gene transcription. Accumulated results from both ex vivo and animal model studies indicate that SRC-3 plays important roles in many biological processes involving cell proliferation, cell migration, cell differentiation, somatic growth, sexual maturation, female reproductive function, vasoprotection and breast cancer. This article summarizes our current knowledge about SRC-3 under the following topics: molecular cloning and characterization; molecular structure and functional mechanisms; SRC-3 as a molecular target of growth factors and cytokines; organization and expression of the SRC-3 gene; generation and characterization of SRC-3 knockout mice; role of SRC-3 in the vasoprotective effects of estrogen; role of SRC-3 in cell migration, proliferation and cancers.

The roles of sex steroid receptor coregulators in cancer

Sex steroid hormones, estrogen, progesterone and androgen, play pivotal roles in sex differentiation and development, and in reproductive functions and sexual behavior. Studies have shown that sex steroid hormones are the key regulators in the development and progression of endocrine-related cancers, especially the cancers of the reproductive tissues. The actions of estrogen, progesterone and androgen are mediated through their cognate intracellular receptor proteins, the estrogen receptors (ER), the progesterone receptors (PR) and the androgen receptor (AR), respectively. These receptors are members of the nuclear receptor (NR) superfamily, which function as transcription factors that regulate their target gene expression. Proper functioning of these steroid receptors maintains the normal responsiveness of the target tissues to the stimulations of the steroid hormones. This permits the normal development and function of reproductive tissues. It can be inferred that factors influencing the expression or function of steroid receptors will interfere with the normal development and function of the target tissues, and may induce pathological conditions, including cancers. In addition to the direct contact with the basal transcription machinery, nuclear receptors enhance or suppress transcription by recruiting an array of coactivators and corepressors, collectively named coregulators. Therefore, the mutation or aberrant expression of sex steroid receptor coregulators will affect the normal function of the sex steroid receptors and hence may participate in the development and progression of the cancers.

Heterogeneous expression and functions of androgen receptor co-factors in primary prostate cancer

The androgen receptor (AR), a ligand-activated transcription factor of the steroid receptor superfamily, plays an important role in normal prostate growth and in prostate cancer. The recent identification of various AR co-factors prompted us to evaluate their possible roles in prostate tumorigenesis. To this end, we analyzed the expression of AR and eight of its co-factors by quantitative in situ RNA hybridization in 43 primary prostate cancers with different degrees of differentiation. Our results revealed nearly constant expression of AR and heterogeneous expression of AR co-factors, with increased expression of PIAS1 and Ran/ARA24, decreased expression of ELE1/ARA70, and no change in TMF1/ARA160, ARA54, SRC1, or TRAP220. Interestingly, whereas TMF1/ARA160, ELE1/ARA70, ARA54, RAN/ARA24, and PIAS1 were preferentially expressed in epithelial cells, another co-factor, ARA55, was preferentially expressed in stromal cells. Although the changes in levels of these co-activators did not correlate with Gleason score, their occurrence in high-grade prostatic intraepithelial neoplasia, suggests their involvement in initiation (or an early stage) of cancer. In addition, human prostate tumor cell proliferation and colony formation were markedly reduced by ELE1/ATRA70. Together, these findings indicate that changes in levels of expression of AR co-factors may play important, yet different, roles in prostate tumorigenesis.

Regulation of the expression of protein kinase C isoenzymes in rat ventral prostate: effects of age, castration and flutamide treatment

Protein kinase C (PKC) isoenzymes are involved in cell function, growth, apoptosis and neoplastic transformation in the prostate gland. We detected by means of Western blot the expression of the classical alpha and beta1, the novel epsilon and the atypical zeta isoforms of PKC in ventral prostates from rats with different extents of plasma testosterone levels and/or androgen imprinting on the gland. The expression of the four isoforms decreased in 5-day castrated rats showing apoptotical regression of the gland and a drastic reduction of circulating testosterone. However, the expression of PKC isoenzymes (alpha, beta1, epsilon ) increased in prostates from pubertal (35-days old) rats that are characterized by relatively low but extremely bioactive testosterone plasma levels. Treatment of adult rats for 14 days with flutamide (daily s.c. injection of 15 mg/Kg B.W.) resulted in increased expression of the four isoenzymes; it occurred in the presence of increased (normal rats) or drastically reduced (rats castrated after 9 days of flutamide administration) levels of plasma testosterone conceivably through a direct effect of this nonsteroidal antiandrogen on prostate cells. Measurements of PKC(alpha) activity were in agreement with the observations on protein expression and showed that flutamide (that is extensively used in the treatment of advanced prostate cancer) elicits some impairment in the mechanisms of translocation of this isoform from the cytosol to the membrane. Thus, in addition to the possibility of direct effects of flutamide upon the rat prostate, we present evidence that the levels of circulating androgens and/or their bioactivity in the gland regulate the expression of various important PKC isoforms.

Age-related changes in nuclear receptor coactivator immunoreactivity in motoneurons of the spinal nucleus of the bulbocavernosus of male rats

Immunoreactivity of phosphorylated cAMP response element binding protein-binding protein/p300 (CBP/p300) and steroid receptor coactivator-1 (SRC-1) was examined in motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in young and old male rats by immunohistochemistry. In young animals, intense immunoreactive CBP/p300 and SRC-1 proteins were confined to the nuclei, but not in the nucleolus of SNB motoneurons. In old animals, both the intensity of CBP/p300 and SRC-1 immunoreactivity in the nuclei and number of CBP/p300 and SRC-1 immunoreactive nuclei of the SNB motoneurons were significantly reduced. A marked decline in the expression of CBP/p300 and SRC-1 in the aged SNB motoneurons suggests down-regulation of androgen receptor coactivator-mediated gene expression in the SNB system with advancing age.

Estrogen receptor-mediated effects of tamoxifen on human endometrial cancer cells

Tamoxifen is an estrogen receptor (ER)-antagonist that is widely used for the treatment of breast cancer, although it increases the risk of endometrial cancer. The mechanism mediating the stimulatory effect of tamoxifen on endometrial cancer is presently unknown. In this study we examined the effects of tamoxifen on Ishikawa 3H-12 endometrial cancer cells and MCF-7 breast cancer cells. Ishikawa cell growth was stimulated by 4-hydroxytamoxifen and accompanied by increased transcriptional activity of the endogenous ER. These stimulatory effects did not occur in MCF-7 cells. The relative transcriptional activity of the activation function (AF) 1 domain of ERalpha compared with that of the AF2 domain was 4-fold higher in Ishikawa cells than in MCF-7 cells. Mitogen-activated protein (MAP) kinase, which stimulates the transcriptional activity of AF1, was constitutively activated in Ishikawa cells, but not in MCF-7 cells. These observations suggest that the constitutively activated MAP kinase-signaling pathway in Ishikawa cells enhances the transcriptional activity of ERalpha via the AF1 domain. This ERalpha activation pathway may be involved in the stimulatory effect of tamoxifen on the development and/or progression of endometrial cancer.

Signaling inhibitors in the treatment of prostate cancer

Inhibiting androgen receptor (AR) activation through medical or surgical castration and blockade of AR-androgen binding is the cornerstone of treatment for advanced prostate cancer. However, in most cases tumor growth eventually becomes androgen independent. Alternative mechanisms of AR activation, some of which involve growth factor receptor signaling, have been demonstrated in prostate cancer models, and it is likely that a number of autocrine and paracrine growth factor ligand-receptor interactions such as those of epidermal growth factors, fibroblast growth factors, and insulin-like growth factors contribute to the androgen independent phenotype by promoting cell proliferation and survival. Blocking activation and signaling through growth factor receptors and upstream signaling proteins has emerged as a credible approach to cancer treatment. Successful application of this approach in prostate cancer using a growing array of small molecule kinase inhibitors, antibodies, and antisense oligonucleotides will be greatly accelerated by elucidation of the key signaling pathways that maintain the androgen independent phenotype.

Androgen receptor (AR) coregulators: an overview

The biological action of androgens is mediated through the androgen receptor (AR). Androgen-bound AR functions as a transcription factor to regulate genes involved in an array of physiological processes, most notably male sexual differentiation and maturation, and the maintenance of spermatogenesis. The transcriptional activity of AR is affected by coregulators that influence a number of functional properties of AR, including ligand selectivity and DNA binding capacity. As the promoter of target genes, coregulators participate in DNA modification, either directly through modification of histones or indirectly by the recruitment of chromatin-modifying complexes, as well as functioning in the recruitment of the basal transcriptional machinery. Aberrant coregulator activity due to mutation or altered expression levels may be a contributing factor in the progression of diseases related to AR activity, such as prostate cancer. AR demonstrates distinct differences in its interaction with coregulators from other steroid receptors due to differences in the functional interaction between AR domains, possibly resulting in alterations in the dynamic interactions between coregulator complexes.

The smooth muscle gamma-actin gene is androgen responsive in prostate epithelia

Nkx 3.1 is an evolutionarily conserved vertebrate homolog of the Drosophila Nk-3 homeodomain gene bagpipe that is expressed by a variety of cells during early mammalian development and has been shown to be a critical factor for prostate development and function. Previous studies utilizing a heterologous cell transfection strategy from our laboratory identified the smooth muscle gamma-actin (SMGA) gene as a novel molecular target of Nkx 3.1 regulatory activity. In the studies presented here, SMGA gene activity and regulation were evaluated in normal and cancerous prostate epithelial cells. SMGA transcripts were demonstrated in prostate epithelia and SMGA mRNA levels were increased in androgen-responsive LNCaP cancer and normal prostate epithelial cells. SMGA gene transcriptional activity was androgen responsive in these cells and required a segment of the human SMGA promoter containing NKE and SRF (serum response factor) binding elements. This region of the human SMGA proximal promoter is well conserved across species and is synergistically activated by coexpression of Nkx 3.1 and SRF in heterologous CV-1 cells. SMGA transcription was not responsive to steroid in PC-3 prostate epithelial cancer cells, which do not express Nkx 3.1. However, SMGA transcription was influenced by expression of androgen receptor in these cells, a situation that allows the androgen-dependent expression of Nkx 3.1. Furthermore, SMGA gene activity was influenced by direct Nkx 3.1 expression in the PC-3 cells. Thus, SMGA gene activity in prostate epithelia is due, in part, to the androgen-dependent expression of Nkx 3.1. As such, our studies provide the initial description of Nkx 3.1 target gene regulatory activity in the prostate.

Expression of RAC 3, a steroid hormone receptor co-activator in prostate cancer

RAC 3, one of the p160 family of co-activators is known to enhance the transcriptional activity of a number of steroid receptors. As co-activators are also known to enhance androgen receptor (AR) activity, we investigated the role of RAC 3 in the context of prostate cancer. In prostate cancer cell lines, we found variable levels of the RAC 3 protein with highest expression seen in AR-positive LNCaP cells, moderate expression in AR-negative PC 3 cells and low-level expression in AR-negative DU 145 cells. Immuno-precipitation studies showed that endogenous RAC 3 interacted with the AR in vivo and transfection assays confirmed that RAC 3 enhanced AR transcriptional activity. In clinical prostate tissue, we found strong RAC 3 mRNA expression and immuno-histochemistry demonstrated that in benign tissue, the protein was expressed predominantly in luminal cells, while in primary malignant epithelium it was more homogeneously expressed. In a series of 37 patients, the levels of RAC 3 expression correlated significantly with tumour grade (P = 0.01) and stage of disease (P = 0.03) but not with serum PSA levels. In addition moderate or high RAC 3 expression was associated with poorer disease-specific survival (P = 0.03). We conclude that RAC 3 is an important co-activator of the AR in the prostate and may have an important role in the progression of prostate cancer.

Different expression of androgen receptor coactivators in human prostate

OBJECTIVES

To investigate the expression of androgen receptor (AR) coactivators in the human prostate for a better understanding of androgen action in prostate cancer.

METHODS

Using reverse transcriptase-polymerase chain reaction, we examined the expression levels of AR coactivators (ARA55, SRC1, ARA54, TIF2, RAC3) in four prostate cancer cell lines (DU145, PC3, LNCaP, and LN-TR2), nine benign prostatic tissue samples, and 21 prostate cancer tissue specimens.

RESULTS

In the cell lines, SRC1 was expressed ubiquitously at almost equal amounts. Contrary to this, ARA55, ARA54, TIF2, and RAC3 displayed cell line-specific expression. In the LN-TR2 cells, established from LNCaP cells by long-term treatment with tumor necrosis factor-alpha, the expression levels of ARA55 and TIF2 were much higher than those in the LNCaP cells. In every prostatic tissue specimen, the expression levels of TIF2 and RAC3 were very low. The expression levels of ARA55 and SRC1 were higher in the cancer specimens with a higher grade or poor response to endocrine therapy than in those with a lower grade or good response to endocrine therapy.

CONCLUSIONS

Prostate cancer cells express AR coactivators. Long-term stimulation by tumor necrosis factor-alpha could increase ARA55 and TIF2 expression in LNCaP cells. The different expression of coactivators may contribute to the different response of prostate cancer to androgenic stimulation or endocrine therapy.