Induction of AP-1 activity by androgen activation of the androgen receptor in LNCaP human prostate carcinoma cells

The Subcutaneous Adipose Microenvironment as a Determinant of Body Fat Development in Polycystic Ovary Syndrome

Context

Adipose steroid metabolism modifies body fat development in polycystic ovary syndrome (PCOS).

Objective

To determine whether subcutaneous (SC) abdominal adipose aldo-keto reductase 1C3 (AKR1C3; a marker of testosterone generation) is increased in normal-weight women with PCOS vs age- and body mass index (BMI)-matched normoandrogenic ovulatory women (controls) and is related to SC abdominal adipose activator protein-1 (AP-1; a marker of adipocyte differentiation) and/or androgen receptor (AR) protein expression in predicting fat accretion.

Design

Prospective cohort study.

Setting

Academic center.

Patients

Eighteen normal-weight PCOS women; 17 age- and BMI-matched controls.

Interventions

Circulating hormone/metabolic determinations, intravenous glucose tolerance testing, total body dual-energy x-ray absorptiometry, SC abdominal fat biopsy, immunohistochemistry.

Main Outcome Measures

Clinical characteristics, hormonal concentrations, body fat distribution, SC adipose AKR1C3, AR, and AP-1 protein expression.

Results

Women with PCOS had significantly higher serum androgen levels and greater android/gynoid fat mass ratios than controls. SC adipose AKR1C3, AR, and AP-1 protein expressions were comparable between the study groups, but groups differed in correlations. In PCOS women vs controls, SC adipose AKR1C3 protein expression correlated positively with android and gynoid fat masses and negatively with SC adipose AP-1 protein expression. SC adipose AR protein expression correlated negatively with fasting serum free fatty acid and high-density lipoprotein levels. In both study groups, SC adipose AKR1C3 protein expression negatively correlated with serum cortisol levels.

Conclusion

In normal-weight PCOS women, SC abdominal adipose AKR1C3 protein expression, in combination with intra-adipose AP-1 and AR-dependent events, predicts fat accretion in the presence of physiological cortisol levels.

Neural Transcription Factors in Disease Progression

Progression to the malignant state is fundamentally dependent on transcriptional regulation in cancer cells. Optimum abundance of cell cycle proteins, angiogenesis factors, immune evasion markers, etc. is needed for proliferation, metastasis or resistance to treatment. Therefore, dysregulation of transcription factors can compromise the normal prostate transcriptional network and contribute to malignant disease progression.The androgen receptor (AR) is considered to be a key transcription factor in prostate cancer (PCa) development and progression. Consequently, androgen pathway inhibitors (APIs) are currently the mainstay in PCa treatment, especially in castration-resistant prostate cancer (CRPC). However, emerging evidence suggests that with increased administration of potent APIs, prostate cancer can progress to a highly aggressive disease that morphologically resembles small cell carcinoma, which is referred to as neuroendocrine prostate cancer (NEPC), treatment-induced or treatment-emergent small cell prostate cancer. This chapter will review how neuronal transcription factors play a part in inducing a plastic stage in prostate cancer cells that eventually progresses to a more aggressive state such as NEPC.

Upgrading well plates using open microfluidic patterning

Cellular communication between multiple cell types is a ubiquitous process that is responsible for vital physiological responses observed in vivo (e.g., immune response, organ function). Many in vitro coculture strategies have been developed, both in traditional culture and microscale systems, and have shown the potential to recreate some of the physiological behaviors of organs or groups of cells. A fundamental limitation of current systems is the difficulty of reconciling the additional engineering requirements for creating soluble factor signaling systems (e.g., segregated cell culture) with the use of well-characterized materials and platforms that have demonstrated successful results and biocompatibility in assays. We present a new open-microfluidic platform, the Monorail Device, that is placed in any existing well plate or Petri dish and enables patterning of segregated coculture regions, thereby allowing the direct upgrade of monoculture experiments into multiculture assays. Our platform patterns biocompatible hydrogel walls via microfluidic spontaneous capillary flow (SCF) along a rail insert set inside commercially available cultureware, creating customized pipette-accessible cell culture chambers that require fewer cells than standard macroscale culture. Importantly, the device allows the use of native surfaces without additional modification or treatments, while creating permeable dividers for the diffusion of soluble factors. Additionally, the ease of patterning afforded by our platform makes reconfiguration of the culture region as simple as changing the rail insert. We demonstrate the ability of the device to pattern flows on a variety of cell culture surfaces and create hydrogel walls in complex and precise shapes. We characterize the physical parameters that enable a reproducible SCF-driven flow and highlight specialized design features that increase the ease of use of the device and control of the open microfluidic flow. Further, we present the performance of our platform according to useful coculture criteria, including permeability and integrity of our hydrogel walls and surface-sensitive cell culture. Lastly, we show the potential of this type of platform to create modular multikingdom culture systems that can be used to study soluble factor signaling between mammalian cells, bacteria, and fungi, as well as the potential for adaptation of this technology by researchers across multiple fields.

Differential expression of AP-1 transcription factors in human prostate LNCaP and PC-3 cells: role of Fra-1 in transition to CRPC status

Androgen receptor (AR) signaling axis plays a vital role in the development of prostate and critical in the progression of prostate cancer. Androgen withdrawal initially regresses tumors but eventually develops into aggressive castration-resistant prostate cancer (CRPC). Activator Protein-1 (AP-1) transcription factors are most likely to be associated with malignant transformation in prostate cancer. Hence, to determine the implication of AR and AP-1 in promoting the transition of prostate cancer to the androgen-independent state, we used AR-positive LNCaP and AR-negative PC-3 cells as an in vitro model system. The effect of dihydrotestosterone or anti-androgen bicalutamide on the cell proliferation and viability was assessed by MTT assay. Expression studies on AR, marker genes-PSA, TMPRSS2, and different AP-1 factors were analyzed by semi-quantitative RT-PCR and expressions of AR and Fra-1 proteins were analyzed by Western blotting. Dihydrotestosterone induced the cell proliferation in LNCaP with no effect on PC-3 cells. Bicalutamide decreased the viability of both LNCaP and PC-3 cells. Dihydrotestosterone induced the expression of AR, PSA, c-Jun, and Fra-1 in LNCaP cells, and it was c-Jun and c-Fos in case of PC-3 cells, while bicalutamide decreased their expression. In addition, constitutive activation and non-regulation of Fra-1 by bicalutamide in PC-3 cells suggested that Fra-1, probably a key component, involved in transition of aggressive androgen-independent PC-3 cells with poor prognosis.

Cell-lineage specificity and role of AP-1 in the prostate fibroblast androgen receptor cistrome

Androgen receptor (AR) signalling in fibroblasts is important in prostate development and carcinogenesis, and is inversely related to prostate cancer mortality. However, the molecular mechanisms of AR action in fibroblasts and other non-epithelial cell types are largely unknown. The genome-wide DNA binding profile of AR in human prostate fibroblasts was identified by chromatin immunoprecipitation sequencing (ChIP-Seq), and found to be common to other fibroblast lines but disparate from AR cistromes of prostate cancer cells and tissue. Although AR binding sites specific to fibroblasts were less well conserved evolutionarily than those shared with cancer epithelia, they were likewise correlated with androgen regulation of fibroblast gene expression. Whereas FOXA1 is the key pioneer factor of AR in cancer epithelia, our data indicated that AP-1 likely plays a more important role in the AR cistrome in fibroblasts. The specificity of AP-1 and FOXA1 to binding in these cells is demonstrated using immunoblot and immunohistochemistry. Importantly, we find the fibroblast cistrome is represented in whole tissue/in vivo ChIP-seq studies at both genomic and resulting protein levels, highlighting the importance of the stroma in whole tissue -omic studies. This is the first nuclear receptor ChIP-seq study in prostatic fibroblasts, and provides novel insight into the action of fibroblast AR in prostate cancer.

GSK-3β/NFAT Signaling Is Involved in Testosterone-Induced Cardiac Myocyte Hypertrophy

Testosterone induces cardiac hypertrophy through a mechanism that involves a concerted crosstalk between cytosolic and nuclear signaling pathways. Nuclear factor of activated T-cells (NFAT) is associated with the promotion of cardiac hypertrophy, glycogen synthase kinase-3β (GSK-3β) is considered to function as a negative regulator, mainly by modulating NFAT activity. However, the role played by calcineurin-NFAT and GSK-3β signaling in testosterone-induced cardiac hypertrophy has remained unknown. Here, we determined that testosterone stimulates cardiac myocyte hypertrophy through NFAT activation and GSK-3β inhibition. Testosterone increased the activity of NFAT-luciferase (NFAT-Luc) in a time- and dose-dependent manner, with the activity peaking after 24 h of stimulation with 100 nM testosterone. NFAT-Luc activity induced by testosterone was blocked by the calcineurin inhibitors FK506 and cyclosporine A and by 11R-VIVIT, a specific peptide inhibitor of NFAT. Conversely, testosterone inhibited GSK-3β activity as determined by increased GSK-3β phosphorylation at Ser9 and β-catenin protein accumulation, and also by reduction in β-catenin phosphorylation at residues Ser33, Ser37, and Thr41. GSK-3β inhibition with 1-azakenpaullone or a GSK-3β-targeting siRNA increased NFAT-Luc activity, whereas overexpression of a constitutively active GSK-3β mutant (GSK-3βS9A) inhibited NFAT-Luc activation mediated by testosterone. Testosterone-induced cardiac myocyte hypertrophy was established by increased cardiac myocyte size and [³H]-leucine incorporation (as a measurement of cellular protein synthesis). Calcineurin-NFAT inhibition abolished and GSK-3β inhibition promoted the hypertrophy stimulated by testosterone. GSK-3β activation by GSK-3βS9A blocked the increase of hypertrophic markers induced by testosterone. Moreover, inhibition of intracellular androgen receptor prevented testosterone-induced NFAT-Luc activation. Collectively, these results suggest that cardiac myocyte hypertrophy induced by testosterone involves a cooperative mechanism that links androgen signaling with the recruitment of NFAT through calcineurin activation and GSK-3β inhibition.

Mineralocorticoid Receptor (MR) trans-Activation of Inflammatory AP-1 Signaling: DEPENDENCE ON DNA SEQUENCE, MR CONFORMATION, AND AP-1 FAMILY MEMBER EXPRESSION

Glucocorticoids are commonly used to treat inflammatory disorders. The glucocorticoid receptor (GR) can tether to inflammatory transcription factor complexes, such as NFκB and AP-1, and trans-repress the transcription of cytokines, chemokines, and adhesion molecules. In contrast, aldosterone and the mineralocorticoid receptor (MR) primarily promote cardiovascular inflammation by incompletely understood mechanisms. Although MR has been shown to weakly repress NFκB, its role in modulating AP-1 has not been established. Here, the effects of GR and MR on NFκB and AP-1 signaling were directly compared using a variety of ligands, two different AP-1 consensus sequences, GR and MR DNA-binding domain mutants, and siRNA knockdown or overexpression of core AP-1 family members. Both GR and MR repressed an NFκB reporter without influencing p65 or p50 binding to DNA. Likewise, neither GR nor MR affected AP-1 binding, but repression or activation of AP-1 reporters occurred in a ligand-, AP-1 consensus sequence-, and AP-1 family member-specific manner. Notably, aldosterone interactions with both GR and MR demonstrated a potential to activate AP-1. DNA-binding domain mutations that eliminated the ability of GR and MR to cis-activate a hormone response element-driven reporter variably affected the strength and polarity of these responses. Importantly, MR modulation of NFκB and AP-1 signaling was consistent with a trans-mechanism, and AP-1 effects were confirmed for specific gene targets in primary human cells. Steroid nuclear receptor trans-effects on inflammatory signaling are context-dependent and influenced by nuclear receptor conformation, DNA sequence, and the expression of heterologous binding partners. Aldosterone activation of AP-1 may contribute to its proinflammatory effects in the vasculature.

JunD Is Required for Proliferation of Prostate Cancer Cells and Plays a Role in Transforming Growth Factor-β (TGF-β)-induced Inhibition of Cell Proliferation

TGF-β inhibits proliferation of prostate epithelial cells. However, prostate cancer cells in advanced stages become resistant to inhibitory effects of TGF-β. The intracellular signaling mechanisms involved in differential effects of TGF-β during different stages are largely unknown. Using cell line models, we have shown that TGF-β inhibits proliferation in normal (RWPE-1) and prostate cancer (DU145) cells but does not have any effect on proliferation of prostate cancer (PC3) cells. We have investigated the role of Jun family proteins (c-Jun, JunB, and JunD) in TGF-β effects on cell proliferation. Jun family members were expressed at different levels and responded differentially to TGF-β treatment. TGF-β effects on JunD protein levels, but not mRNA levels, correlated with its effects on cell proliferation. TGF-β induced significant reduction in JunD protein in RWPE-1 and DU145 cells but not in PC3 cells. Selective knockdown of JunD expression using siRNA in DU145 and PC3 cells resulted in significant reduction in cell proliferation, and forced overexpression of JunD increased the proliferation rate. On the other hand, knockdown of c-Jun or JunB had little, if any, effect on cell proliferation; overexpression of c-Jun and JunB decreased the proliferation rate in DU145 cells. Further studies showed that down-regulation of JunD in response to TGF-β treatment is mediated via the proteasomal degradation pathway. In conclusion, we show that specific Jun family members exert differential effects on proliferation in prostate cancer cells in response to TGF-β, and inhibition of cell proliferation by TGF-β requires degradation of JunD protein.

Inhibitor of p52 NF-κB subunit and androgen receptor (AR) interaction reduces growth of human prostate cancer cells by abrogating nuclear translocation of p52 and phosphorylated AR(ser81)

Accumulating evidence shows that androgen receptor (AR) activation and signaling plays a key role in growth and progression in all stages of prostate cancer, even under low androgen levels or in the absence of androgen in the castration-resistant prostate cancer. Sustained activation of AR under androgen-deprived conditions may be due to its interaction with co-activators, such as p52 NF-κB subunit, and/or an increase in its stability by phosphorylation that delays its degradation. Here we identified a specific inhibitor of AR/p52 interaction, AR/p52-02, via a high throughput screen based on the reconstitution of Gaussia Luciferase. We found that AR/p52-02 markedly inhibited growth of both castration-resistant C4-2 (IC50 ∼6 μM) and parental androgen-dependent LNCaP (IC50 ∼4 μM) human prostate cancer cells under low androgen conditions. Growth inhibition was associated with significantly reduced nuclear p52 levels and DNA binding activity, as well as decreased phosphorylation of AR at serine 81, increased AR ubiquitination, and decreased AR transcriptional activity as indicated by decreased prostate-specific antigen (PSA) mRNA levels in both cell lines. AR/p52-02 also caused a reduction in levels of p21(WAF/CIP1), which is a direct AR targeted gene in that its expression correlates with androgen stimulation and mitogenic proliferation in prostate cancer under physiologic levels of androgen, likely by disrupting the AR signaling axis. The reduced level of cyclinD1 reported previously for this compound may be due to the reduction in nuclear presence and activity of p52, which directly regulates cyclinD1 expression, as well as the reduction in p21(WAF/CIP1), since p21(WAF/CIP1) is reported to stabilize nuclear cyclinD1 in prostate cancer. Overall, the data suggest that specifically inhibiting the interaction of AR with p52 and blocking activity of p52 and pARser81 may be an effective means of reducing castration-resistant prostate cancer cell growth.

Expression of spermidine/spermine N(1) -acetyl transferase (SSAT) in human prostate tissues is related to prostate cancer progression and metastasis

INTRODUCTION

Prostate cancer (PCa) in many patients remains indolent for the rest of their lives, but in some patients, it progresses to lethal metastatic disease. Gleason score is the current clinical method for PCa prognosis. It cannot reliably identify aggressive PCa, when GS is ≤ 7. It is shown that oxidative stress plays a key role in PCa progression. We have shown that in cultured human PCa cells, an activation of spermidine/spermine N(1) -acetyl transferase (SSAT; EC 2.3.1.57) enzyme initiates a polyamine oxidation pathway and generates copious amounts of reactive oxygen species in polyamine-rich PCa cells.

METHOD

We used RNA in situ hybridization and immunohistochemistry methods to detect SSAT mRNA and protein expression in two tissue microarrays (TMA) created from patient's prostate tissues. We analyzed 423 patient's prostate tissues in the two TMAs.

RESULTS

Our data show that there is a significant increase in both SSAT mRNA and the enzyme protein in the PCa cells as compared to their benign counterpart. This increase is even more pronounced in metastatic PCa tissues as compared to the PCa localized in the prostate. In the prostatectomy tissues from early-stage patients, the SSAT protein level is also high in the tissues obtained from the patients who ultimately progress to advanced metastatic disease.

DISCUSSION

Based on these results combined with published data from our and other laboratories, we propose an activation of an autocrine feed-forward loop of PCa cell proliferation in the absence of androgen as a possible mechanism of castrate-resistant prostate cancer growth.

A microfluidic coculture and multiphoton FAD analysis assay provides insight into the influence of the bone microenvironment on prostate cancer cells

In prostate cancer, bone is a frequent site of metastasis; however, the molecular mechanisms of this tumor tropism remain unclear. Here, we integrate a microfluidic coculture platform with multi-photon imaging based techniques to assess both phenotypic cell behavior and FAD fluorescence intensity and fluorescence lifetime in the same cell. This platform combines two independent assays normally performed with two different cell populations into a single device, allowing us to simultaneously assess both phenotypic cell behavior and enzyme activity. We observed that the osteotropic prostate cancer cell line (C4-2B), when in a coculture with bone marrow stromal cells (MC3T3-E1), has increased protrusive phenotype and increased total and protein-bound FAD compared to its parent cell line (LNCaP). We hypothesized that an increase in ROS-generating APAO activity may be responsible for these effects, and found that the effects were decreased in the presence of the antioxidant N-Acetyl Cysteine (NAC). This suggests that an ROS-related signaling mechanism at the bone metastatic site may be correlated with and play a role in increased invasion of metastasizing prostate cancer cells. The studies performed using this combined platform will lead to new insights into the mechanisms that drive prostate cancer metastasis.

Targeting androgen receptor and JunD interaction for prevention of prostate cancer progression

BACKGROUND

Multiple studies show that reactive oxygen species (ROS) play a major role in prostate cancer (PCa) development and progression. Previously, we reported an induction of Spermidine/Spermine N(1) -Acetyl Transferase (SSAT) by androgen-activated androgen receptor (AR)-JunD protein complex that leads to over-production of ROS in PCa cells. In our current research, we identify small molecules that specifically block AR-JunD in this ROS-generating metabolic pathway.

METHODS

A high throughput assay based on Gaussia Luciferase reconstitution was used to identify inhibitors of the AR-JunD interaction. Selected hits were further screened using a fluorescence polarization competitor assay to eliminate those that bind to the AR Ligand Binding Domain (LBD), in order to identify molecules that specifically target events downstream to androgen activation of AR. Eleven molecules were selected for studies on their efficacy against ROS generation and growth of cultured human PCa cells by DCFH dye-oxidation assay and DNA fluorescence assay, respectively. In situ Proximity Ligation Assay (PLA), SSAT promoter-luciferase reporter assay, and western blotting of apoptosis and cell cycle markers were used to study mechanism of action of the lead compound.

RESULTS

Selected lead compound GWARJD10 with EC(50) 10 μM against ROS production was shown to block AR-JunD interaction in situ as well as block androgen-induced SSAT gene expression at IC(50) 5 μM. This compound had no effect on apoptosis markers, but reduced cyclin D1 protein level.

CONCLUSIONS

Inhibitor of AR-JunD interaction, GWARJD10 shows promise for prevention of progression of PCa at an early stage of the disease by blocking growth and ROS production.

Androgen receptor requires JunD as a coactivator to switch on an oxidative stress generation pathway in prostate cancer cells

Relatively high oxidative stress levels in the prostate are postulated to be a major factor for prostate carcinogenesis and prostate cancer (CaP) progression. We focused on elucidating metabolic pathways of oxidative stress generation in CaP cells. Previously, we showed that the transcription factor JunD is essential for androgen-induced reactive oxygen species (ROS) production in androgen-dependent human CaP cells. We also recently showed that androgen induces the first and regulatory enzyme spermidine/spermine N1-acetyltransferase (SSAT) in a polyamine catabolic pathway that produces copious amounts of metabolic ROS. Here, we present coimmunoprecipitation and Gaussia luciferase reconstitution assay data that show that JunD forms a complex with androgen-activated androgen receptor (AR) in situ. Our chromatin immunoprecipitation assay data show that JunD binds directly to a specific SSAT promoter sequence only in androgen-treated LNCaP cells. Using a vector containing a luciferase reporter gene connected to the SSAT promoter and a JunD-silenced LNCaP cell line, we show that JunD is essential for androgen-induced SSAT gene expression. The elucidation of JunD-AR complex inducing SSAT expression leading to polyamine oxidation establishes the mechanistic basis of androgen-induced ROS production in CaP cells and opens up a new prostate-specific target for CaP chemopreventive/chemotherapeutic drug development.

A small molecule polyamine oxidase inhibitor blocks androgen-induced oxidative stress and delays prostate cancer progression in the transgenic adenocarcinoma of the mouse prostate model

High levels of reactive oxygen species (ROS) present in human prostate epithelia are an important etiologic factor in prostate cancer (CaP) occurrence, recurrence, and progression. Androgen induces ROS production in the prostate by a yet unknown mechanism. Here, to the best of our knowledge, we report for the first time that androgen induces an overexpression of spermidine/spermine N1-acetyltransferase, the rate-limiting enzyme in the polyamine oxidation pathway. As prostatic epithelia produce a large excess of polyamines, the androgen-induced polyamine oxidation that produces H2O2 could be a major reason for the high ROS levels in the prostate epithelia. A small molecule polyamine oxidase inhibitor N,N'-butanedienyl butanediamine (MDL 72,527 or CPC-200) effectively blocks androgen-induced ROS production in human CaP cells, as well as significantly delays CaP progression and death in animals developing spontaneous CaP. These data show that polyamine oxidation is not only a major pathway for ROS production in prostate, but inhibiting this pathway also successfully delays CaP progression.

Induction of Kruppel-like factor 5 expression by androgens results in increased CXCR4-dependent migration of prostate cancer cells in vitro

Advanced prostate cancers preferentially metastasize to bone, suggesting that this tissue produces factors that provide a suitable microenvironment for prostate cancer cells. Recently, it has become clear that even in antiandrogen-resistant cancers, the androgen receptor (AR)-signaling axis is required for prostate cancer progression. Therefore, we hypothesized that AR may be involved in the regulation of pathways that are responsible for the homing of prostate cancer cells to select microenvironments. In support of this hypothesis, we have determined that chemokine (C-X-C motif) receptor 4 (CXCR4), the receptor for the chemokine CXCL12, is up-regulated in prostate cancer cells in response to androgens. Given that the levels of CXCL12 are elevated at sites of known prostate cancer metastases such as bone, these results suggest that androgens may influence prostate cancer metastasis. Specifically, we demonstrate that androgens increase the levels of both CXCR4 mRNA and functional protein in LNCaP prostate cancer cells. Importantly, androgens enhanced the migration of LNCaP cells toward a CXCL12 gradient, an effect that could be blocked by the specific CXCR4 antagonist AMD3100. Interestingly, CXCR4 is not directly regulated by androgens but rather is positively up-regulated by Krüppel-like factor 5 (KLF5), a transcription factor that we have shown to be an early, direct target of AR. Further, KLF5 is both required and sufficient for androgen-mediated CXCR4 expression and migration toward CXCL12. Taken together, these findings demonstrate that AR can utilize the CXCL12/CXCR4 axis through induction of KLF5 expression to promote prostate cancer progression and highlight the potential utility of CXCR4 antagonists as prostate cancer therapeutics.

JunD mediates androgen-induced oxidative stress in androgen dependent LNCaP human prostate cancer cells

BACKGROUND

Numerous and compelling evidence shows that high level of reactive oxygen species (ROS) plays a key role in prostate cancer occurrence, recurrence and progression. The molecular mechanism of ROS overproduction in the prostate gland, however, remains mostly unknown. Unique AP-1 transcription factor JunD has been shown to inhibit cell proliferation, promote differentiation and mediate stress responses in a variety of eukaryotic cells. We previously reported that androgen-androgen receptor induced ROS production in androgen-dependent LNCaP human prostate cancer cells is associated with increased JunD level/AP-1 transcriptional activity.

METHODS

LNCaP cells constitutively overexpressing a functionally inactive form of JunD (JunDDeltaTA) or stably transfected with JunD siRNA (siJunD) to suppress JunD protein expression were established. Overexpression of JunD in LNCaP cells using transient transfection method was applied to assess the induction of ROS production in LNCaP cells. DCF assay was used to measure the ROS concentrations in the transfected as well as non-transfected control cells. RT-PCR and Western blot analyses were used to confirm silencing or overexpression of JunD in the transfected cells.

RESULTS

In the absence of androgen, LNCaP cells transiently transfected with a JunD overexpressing vector have relatively enhanced cellular ROS levels as compared to LNCaP cells transfected with a vector control. LNCaP cells that fail to express functional JunD (JunDDeltaTA or siJunD) do not exhibit any increase in ROS production in response to androgen.

CONCLUSION

Based on these data, we conclude that JunD is an essential mediator of the androgen-induced increase in ROS levels in LNCaP cells.

Activator protein-1 transcription factors are associated with progression and recurrence of prostate cancer

To identify biomarkers that discriminate the aggressive forms of prostate cancer, we performed gene expression profiling of prostate tumors using a genetically engineered mouse model that recapitulates the stages of human prostate cancer, namely Nkx3.1; Pten mutant mice. We observed a significant deregulation of the epidermal growth factor and mitogen-activated protein kinase (MAPK) signaling pathways, as well as their major downstream effectors--the activator protein-1 transcription factors c-Fos and c-Jun. Forced expression of c-Fos and c-Jun in prostate cancer cells promotes tumorigenicity and results in activation of extracellular signal-regulated kinase (Erk) MAPK signaling. In human prostate cancer, up-regulation of c-Fos and c-Jun proteins occurs in advanced disease and is correlated with Erk MAPK pathway activation, whereas high levels of c-Jun expression are associated with disease recurrence. Our analyses reveal a hitherto unappreciated role for AP-1 transcription factors in prostate cancer progression and identify c-Jun as a marker of high-risk prostate cancer. This study provides a striking example of how accurate mouse models can provide insights on molecular processes involved in progression and recurrence of human cancer.

Integration of progesterone receptor action with rapid signaling events in breast cancer models

Recent discoveries suggest that several protein kinases are rapidly activated in response to ligand binding to cytoplasmic steroid hormone receptors (SRs), including progesterone receptors (PRs). Thus, PRs act as ligand-activated transcription factor "sensors" for growth factor-initiated signaling pathways in hormonally regulated tissues, such as the breast. Induction of rapid signaling upon progestin binding to PR-B provides a means to ensure that receptors and co-regulators are appropriately phosphorylated as part of optimal transcription complexes. Alternatively, PR-B activated kinase cascades provide additional avenues for progestin-regulated gene expression independent of PR nuclear action. Herein, an overview of progesterone/PR and signaling cross-talk in breast cancer models is provided. Kinases are emerging as key mediators of PR action. Cross-talk between SR and membrane-initiated signaling events suggests a mechanism for coordinate regulation of gene subsets by mitogenic stimuli in hormonally responsive normal tissues, and is suspected to contribute to cancer biology.

The role of insulin-like growth factor binding protein-3 in the growth inhibitory actions of androgens in LNCaP human prostate cancer cells

Insulin-like growth factor binding protein-3 (IGFBP-3), an antiproliferative and proapoptotic protein, has been shown to be upregulated by growth inhibitory concentrations of androgens in LNCaP human prostate cancer (PCa) cells, but the mechanism of regulation and the role of IGFBP-3 in the modulation of PCa cell proliferation are unknown. In this study, we have examined the effects of a range of concentrations of the synthetic androgen R1881 on IGFBP-3 expression and cell growth in LNCaP cells. We have also investigated the role of androgen-stimulated IGFBP-3 in androgen-induced growth inhibition. We show that low doses of R1881 stimulate LNCaP cell proliferation, but do not induce IGFBP-3 expression, whereas high doses of R1881 that inhibit cell growth, significantly increase expression of IGFBP-3. Importantly, we demonstrate that the combination of calcitriol and androgens not only synergistically upregulates IGFBP-3 expression but also inhibits cell growth better than either hormone alone. siRNA knockdown of IGFBP-3 expression partially reverses the growth inhibition by calcitriol and by androgens. Furthermore, we find that the growth inhibitory dose of R1881 leads to increases in the cyclin dependent kinase inhibitors (CDKIs), p21 and p27 as well as to G1 arrest. These changes can be blocked or partially reversed by IGFBP-3 siRNA, indicating that the induction of CDKIs is downstream of IGFBP-3. Our data suggest, for the first time, that IGFBP-3 is involved in the antiproliferative action of high doses of androgens partly through p21 and p27 pathways and that IGFBP-3 may contribute significantly to androgen-induced changes in LNCaP cell growth.

Progesterone receptor action: translating studies in breast cancer models to clinical insights

Progesterone receptors (PR) are useful prognostic indicators of breast cancers likely to respond to anti-estrogen receptor (ER) therapies. However, the role of progesterone, therapeutic progestins, or unliganded or liganded PRin breast cancer development or progression remains controversial. PR are ligand-activated transcription factors that act in concert with intracellular signaling pathways as "sensors" of multiple growth factor inputs to hormonally regulated tissues, such as the breast. The recently defined induction of rapid signaling events upon progestin-binding to PR-B provides a means to ensure that receptors and coregulators are appropriately phosphorylated as part of optimal transcription complexes. PR-activated kinase cascades may provide additional avenues for progestin-regulated gene expression independent of PR nuclear action. Herein, we present an overview ofprogesterone/PR and signaling cross-talk in breast cancer models and discuss the potential significance ofprogestin/PR action in breast cancer biology using examples from both in vitro and in vivo models, as well as limited clinical data. Kinases are emerging as key mediators of PR action. Cross-talk between PR and membrane-initiated signaling events suggests a mechanism for coordinated regulation ofgene subsets by mitogenic stimuli in hormonally responsive normal tissues. Dysregulation of this cross-talk mechanism may contribute to breast cancer biology; further studies are needed to address the potential for targeting PR in addition to ER and selected protein kinases as part of more effective breast cancer therapies.

Integration of Rapid Signaling Events with Steroid Hormone Receptor Action in Breast and Prostate Cancer

Steroid hormone receptors (SRs) are ligand-activated transcription factors and sensors for growth factor-initiated signaling pathways in hormonally regulated tissues, such as the breast or prostate. Recent discoveries suggest that several protein kinases are rapidly activated in response to steroid hormone binding to cytoplasmic SRs. Induction of rapid signaling upon SR ligand binding ensures that receptors and coregulators are appropriately phosphorylated as part of optimal transcription complexes. Alternatively, SR-activated kinase cascades provide additional avenues for SR-regulated gene expression independent of SR nuclear action. We provide an overview of SR and signaling cross talk in breast and prostate cancers, using the human progesterone receptor (PR) and androgen receptor (AR) as models. Kinases are emerging as key mediators of SR action. Cross talk between SR and membrane-initiated signaling events suggests a mechanism for coordinate regulation of gene subsets by mitogenic stimuli in hormonally responsive normal tissues; such cross talk is suspected to contribute to cancer biology.

A conditionally immortalized cell line model for the study of human prostatic epithelial cell differentiation

In the normal human prostate, undifferentiated proliferative cells reside in the basal layer and give rise to luminal secretory cells. There are, however, few epithelial cell lines that have a basal cell phenotype and are able to differentiate. We set out to develop a cell line with these characteristics that would be suitable for the study of the early stages of prostate epithelial cell differentiation. We produced a matched pair of conditionally immortalized prostate epithelial and stromal cell lines derived from the same patient. The growth of these cells is temperature dependent and differentiation can be induced following a rise in culture temperature. Three-dimensional co-cultures of these cell lines elicited gland-like structures reminiscent of prostatic acini. cDNA microarray analysis of the epithelial line demonstrated changes in gene expression consistent with epithelial differentiation. These genes may prove useful as markers for different prostate cell types. The cell lines provide a model system with which to study the process of prostatic epithelial differentiation and stromal-epithelial interactions. This may prove to be useful in the development of differentiation-targeted prostate cancer therapies.

Mitogen-Activated Protein Kinase Signaling is Activated in Prostate Tumors but not Mediated by B-RAF Mutations

OBJECTIVES

A dysregulated mitogen-activated protein kinase (MAPK) pathway plays an important role in various malignancies and is often mediated by mutations in several oncogenes (eg, RAF, RAS). B-RAF mutations, predominantly the specific V600E mutation and additional alterations in exons 11 and 15, were frequently detected in malignant melanomas, papillary thyroid tumors, and colorectal cancers with microsatellite instability (MSI). The present study investigated B-RAF mutations, MSI status, and activation of MAPK signaling in prostate tumors.

METHODS

The V600E mutation of the B-RAF gene was analyzed using allele-specific polymerase chain reaction in 79 archival prostatic adenocarcinomas (pT1aG1 to pT3cG3, median Gleason score 6); exons 11 and 15 were sequenced. MSI status was determined using the National Cancer Institute consensus panel for hereditary nonpolyposis colorectal carcinoma (HNPCC) detection. Active MAPK signaling was investigated using immunohistochemistry for p44/ERK1 and p42/ERK2.

RESULTS

No B-RAF mutations could be detected. Six of 79 tumors showed MSI positivity. Active MAPK signaling was detected in 51% of the analyzed tumors. No correlation was found between MAPK activity and histopathologic/clinical characteristics.

CONCLUSION

The most frequent B-RAF gene alterations are not involved in prostate carcinogenesis. MSI is infrequent in prostate cancer and is not linked to B-RAF mutations. MAPK signaling is frequently activated in prostate tumors and might be suitable for a therapeutic approach.

ACTR/AIB1/SRC-3 and androgen receptor control prostate cancer cell proliferation and tumor growth through direct control of cell cycle genes

BACKGROUND

Co-factor ACTR is frequently overexpressed and/or amplified in multiple types of tumors. The mechanism of its function in prostate cancer (CaP) is still unclear.

METHODS

The effects of ACTR and androgen receptor (AR) depletion on cell proliferation and gene expression and their functions were analyzed in a panel of androgen-dependent and -independent CaP cells and CWR22 xenograft.

RESULTS

ACTR and AR, but not TIF2, are required for proliferation of androgen-dependent and -independent cells, and for tumor growth. While AR depletion inhibited the expression of cyclin D1, cyclin B, and cdc2, ACTR depletion reduced the expression of cyclin E and cdk2. In response to serum stimulation, AR and ACTR are recruited to the corresponding target gene promoters to activate their expression in androgen-independent manner.

CONCLUSION

These findings suggest that AR and ACTR may play important roles in androgen ablation resistance by controlling key cell cycle gene expression.

Unraveling androgen receptor interactomes by an array-based method: discovery of proto-oncoprotein c-Rel as a negative regulator of androgen receptor

The androgen receptor (AR) plays a key role in the development and function of male reproductive organs. Using a high-throughput transcription factor-transcription factor (TF-TF) interaction array method, we captured the AR interactomes in androgen-responsive LNCaP cells. Several known and unknown partners of AR, including AP-2, Pax 3/5 (BSAP), c-Rel, RREB-1, LIII BP, and NPAS2 were identified. We investigated one unreported AR-associated transcription factor, the proto-oncoprotein c-Rel, in detail. C-Rel belongs to the NF-kB/Rel families and is persistently active in a number of diseases, including cancer. The presence of c-Rel transcript, protein, and its in vitro and in vivo association with AR was determined. Co-localization of c-Rel with AR both in cytoplasm and nucleus was confirmed by indirect immunofluorescence analysis. Chromatin immunoprecipitation data indicated that c-Rel, like AR, is a part of the nucleoprotein complex regulating the androgen-responsive prostate-specific antigen (PSA) promoter. Overexpression of c-Rel downregulated the promoter activity of both PSA and GRE4-TATA-Luc plasmids in LNCaP and COS cells. Analysis of AR and c-Rel protein levels indicated that the promoter downregulation was not due to reciprocal decrease in the amounts of AR or c-Rel. In summary, we have identified several new partners of AR by using the TF-TF array method and have provided the first evidence of a functional role for c-Rel in androgen-responsive human prostate cancer cells.

Notch signaling is required for normal prostatic epithelial cell proliferation and differentiation

Notch pathway is crucial for stem/progenitor cell maintenance, growth and differentiation in a variety of tissues. Using a transgenic cell ablation approach, we found in our previous study that cells expressing Notch1 are crucial for prostate early development and re-growth. Here, we further define the role of Notch signaling in regulating prostatic epithelial cell growth and differentiation using biochemical and genetic approaches in ex vivo or in vivo systems. Treatment of developing prostate grown in culture with inhibitors of gamma-secretase/presenilin, which is required for Notch cleavage and activation, caused a robust increase in proliferation of epithelial cells co-expressing cytokeratin 8 and 14, lack of luminal/basal layer segregation and dramatically reduced branching morphogenesis. Using conditional Notch1 gene deletion mouse models, we found that inactivation of Notch1 signaling resulted in profound prostatic alterations, including increased tufting, bridging and enhanced epithelial proliferation. Cells within these lesions co-expressed both luminal and basal cell markers, a feature of prostatic epithelial cells in predifferentiation developmental stages. Microarray analysis revealed that the gene expression in a number of genetic networks was altered following Notch1 gene deletion in prostate. Furthermore, expression of Notch1 and its effector Hey-1 gene in human prostate adenocarcinomas were found significantly down-regulated compared to normal control tissues. Taken together, these data suggest that Notch signaling is critical for normal cell proliferation and differentiation in the prostate, and deregulation of this pathway may facilitate prostatic tumorigenesis.