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Molecular Endocrinology, doi:10.1210/me.2007-0094
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Molecular Endocrinology 21 (12): 2864-2876
Copyright © 2007 by The Endocrine Society

Transcriptional Regulation of the Androgen Receptor Cofactor Androgen Receptor Trapped Clone-27

Jerome C. Nwachukwu1, Wenhui Li1, Inés Pineda-Torra, Hong Ying Huang, Rachel Ruoff, Ellen Shapiro, Samir S. Taneja, Susan K. Logan and Michael J. Garabedian

Departments of Microbiology (J.C.N., W.L., I.P.-T., M.J.G.), Pharmacology (J.C.N., R.R., S.K.L.), and Urology (H.Y.H., R.R., E.S., S.S.T., S.K.L., M.J.G.), New York University Cancer Institute, New York University (NYU) School of Medicine, New York, New York 10016

Address all correspondence and requests for reprints to: Michael J. Garabedian, Department of Microbiology, 550 First Avenue, New York, New York 10016. E-mail: garabm01{at}med.nyu.edu.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
Cofactors modulate nuclear receptor activity and impact human health and disease, yet surprisingly little is known about their transcriptional regulation. Androgen receptor trapped clone-27 (ART-27) is a cofactor that binds to androgen receptor (AR) amino terminus and modulates AR-dependent transcription. Interestingly, ART-27 displays both a cell type- and developmental stage-specific expression pattern. However, the cis-acting elements and trans-acting factors affecting ART-27 gene expression have not been elucidated. We found that ART-27 gene expression is repressed and its promoter is histone H3-K27 tri-methylated in human embryonic kidney cells, but not prostate cells, and the histone deacetylase inhibitor, trichostatin A, relieves this inhibition. The DNA response elements that control the induction of ART-27 gene expression were also characterized. The major cis-acting element corresponds to a consensus cAMP-responsive element (CRE) and binds the CRE-binding protein (CREB) as shown by EMSA and chromatin immunoprecipitation assays. Furthermore, ART-27 promoter activity is induced upon CREB overexpression. Epidermal growth factor, which activates CREB via phosphorylation, also induces ART-27 expression, whereas a reduction in CREB phosphorylation or expression blocks this induction in prostate cells. In human prostate development, both epithelial and stromal cells express CREB; however, active phosphorylated CREB is restricted to epithelial cells where ART-27 is expressed. Based on these findings, we propose a transcriptional regulatory circuit for the developmental expression of ART-27 that includes repression by chromatin modification through a trichostatin A-sensitive factor and activation upon growth factor stimulation via CREB.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
THE NUCLEAR RECEPTOR superfamily consists of evolutionarily conserved, ligand-activated transcription factors that regulate various biological processes. Nuclear receptors typically activate transcription by binding DNA regulatory regions containing hormone-responsive elements, recruiting specific coactivator complexes upon ligand-binding, and directing assembly of transcription-initiation complexes at the promoters of target genes (1, 2). Coactivators are essential to nuclear receptor function (3) by enhancing nuclear receptor activity through multiple mechanisms including posttranscriptional modification of the nuclear receptor and nearby histones and through chromatin remodeling (1).

Recent evidence indicates that transcriptional regulation of coactivators is critical to nuclear receptor function. The E2F family of transcription factors, which control genes involved in cell cycle progression (4), regulates some coactivators. For example, steroid receptor coactivator-3 (SRC-3), which promotes tumor growth in breast cancer, is induced by E2F1 (5). Interestingly, both E2F1 and SRC-3 drive overexpression of SRC-3 in breast cancer (5).

Other coactivators are targeted by the cAMP-responsive element (CRE)-binding protein (CREB), a transcription factor that controls cell differentiation and cell survival (6, 7, 8). For instance, peroxisome proliferator-activated receptor-{gamma} coactivator-1{alpha} (PGC-1{alpha}) is a master regulator of energy metabolism and mitochondrial biogenesis and transducers of regulated CREB-binding proteins (TORCs) stimulate mitochondrial gene expression by activating CREB-mediated transcription of PGC-1{alpha} (9). In addition, mutant huntingtin protein represses CREB-mediated transcription of PGC-1{alpha} and leads to mitochondrial dysfunction and neurodegeneration in mice models for Huntington’s disease (10). However, little is known about transcriptional regulation of most nuclear receptor coactivators.

Androgen receptor trapped clone-27 (ART-27) was identified in our laboratory in a yeast two-hybrid screen for coregulators of the androgen receptor (AR) N terminus. ART-27 binds to AR residues 153–336, which encompasses the entire AF-1a and a part of the AF-1b domain. It enhances transcriptional activity of AR as well as glucocorticoid, estrogen, and thyroid hormone receptors, indicating that ART-27 is a nuclear receptor coactivator (11).

ART-27 (also known as UXT/STAP1) is a component of a large multiprotein complex that contains RNA polymerase II subunit 5, a subunit shared by all three RNA polymerases; unconventional prefoldin RPB5-interactor (URI), which plays a central role in the regulation of nutrient-sensitive; target-of-rapamycin (TOR)-dependent gene expression programs; a pair of prefoldin β-subunits; and the TATA-binding protein-interacting proteins, TIP48 and TIP49, which are ATP-dependent helicases present in various chromatin remodeling complexes (11, 12). Hence, ART-27 associates with key components of the transcriptional machinery and likely serves to link AR to the URI transcription factor complex.

In addition to its transcriptional regulatory properties, ART-27 has also been demonstrated to be a component of the centrosome (13), and its binding partner, URI, is required for DNA stability in Caenorhabditis elegans (14). Therefore, ART-27 may also participate in pathways that are associated with the control of genome integrity.

ART-27 function has been examined in the prostate, where AR is known to play a crucial role in both prostate development and cancer. These studies indicate that ART-27 inhibits androgen-dependent cell proliferation in LNCaP prostate cancer cells (15). Consistent with a growth-inhibitory function, ART-27 protein expression is down-regulated in prostate cancer (15). In normal prostate, ART-27 expression is cell-type specific (15). In both fetal and adult prostate, ART-27 protein expression is restricted to luminal epithelial cells (terminally differentiated secretory cells surrounding the lumen) (15).

Like most transcription cofactors, little is known about the regulation of ART-27 expression. Previous studies have used chromatin immunoprecipitation (ChIP) assays to show that ART-27 is an E2F target gene (16, 17). Some E2F family members, such as E2F6, function as a transcriptional repressor through the recruitment of a polycomb repressive complex (PRC) (18, 19, 20). Consistent with the role of E2F in repression, deletion of two E2F binding sites in the ART-27 upstream regulatory region results in activation of the promoter in human embryonic kidney 293 cells. Moreover, ART-27 mRNA levels were increased upon reduction of E2F6 by small interfering RNA (siRNA) in 293 cells (16). ART-27 is likely subject to both positive and negative regulation during development in that ART-27 protein is detected only when the developing prostate gland has proceeded from a solid mass of undifferentiated cells to a stage where differentiated luminal epithelial cells are evident (15).

Here we report the analysis of the cis-acting DNA response elements and trans-acting factors that control ART-27 gene expression. We find that transcriptional regulation of ART-27 involves cell-specific repression that is relieved by the histone deacetylase inhibitor trichostatin A (TSA) as well as CREB-mediated activation of the ART-27 promoter.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
Cell-Specific Regulation of ART-27 by TSA and Growth Factors
ART-27 protein is expressed at high levels in differentiated prostate luminal epithelial cells, but its expression is not detectable in undifferentiated precursors and stromal cells (15). The mechanism by which ART-27 expression is restricted to luminal cells remains largely unknown. Previous studies in 293 cells have shown that E2F transcription factors bind the ART-27 promoter and that the ART-27 mRNA level is increased by reducing expression of E2F6 by siRNA (16, 17). We hypothesize that ART-27 will not be repressed in a cell type in which it is ordinarily expressed in vivo, such as prostate epithelial cells. To test this idea, we examined the regulation of ART-27 in the LNCaP prostate epithelial cancer cell line, because LNCaP cells retain most of their luminal characteristics in culture, including AR expression (21).

We treated 293 and LNCaP cells with TSA, a histone deacetylase inhibitor, or dimethylsulfoxide (DMSO) vehicle control for 4 h and examined ART-27 mRNA levels. TSA increases ART-27 mRNA levels in 293 cells but does not affect ART-27 mRNA levels in LNCaP cells (Fig. 1AGo). ART-27 insensitivity to TSA is not restricted to LNCaP cells, because it is also observed in DU145 cells, an AR-negative prostate cancer line (data not shown). These results suggest that ART-27 gene expression is suppressed by a TSA-sensitive factor in 293 but not in LNCaP cells.


Figure 1
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  		Fig. 1. Cell-Specific Regulation of ART-27 mRNA

A, Effect of TSA on ART-27 mRNA levels. 293 or LNCaP cells were deprived of serum for 24 h and treated with DMSO vehicle or 100 ng/ml TSA for 4 h. Total RNA was isolated and analyzed by RT-QPCR. Relative ART-27 mRNA levels are normalized to RPL19 and calibrated to untreated samples in each cell line, which were arbitrarily set to 1. B, Effect of Serum on ART-27 mRNA levels. 293 or LNCaP cells were serum starved for 24 h and then stimulated with serum for 3 h. Relative mRNA levels were determined as indicated in A.

 
To examine positive regulation of ART-27, we determined ART-27 expression levels in response to extracellular signals. We observed a dose-dependent increase in ART-27 mRNA levels after stimulation of LNCaP cells with serum (Fig. 1BGo). By contrast, 293 cells do not induce ART-27 mRNA upon serum stimulation (Fig. 1BGo). These results indicate that ART-27 mRNA expression is serum responsive in LNCaP but not 293 cells. Thus, ART-27 gene expression is repressed by TSA-susceptible factors and can be induced by extracellular signals in cells not subject to this negative regulation.

The 5'-Regulatory Region of ART-27 Contains Positive cis-Acting Elements
To determine the regulatory elements that govern transcription of ART-27, about 2 kb of the ART-27 5'-regulatory region was placed upstream of a promoterless luciferase reporter gene. The ART-27-luciferase reporters containing –2065/+124, –965/+124, –533/+124, –383/+124, –154/ +124, and +16/+124 were transfected into HeLa cells and assayed for luciferase activity (Fig. 2AGo). HeLa cells were used in these studies because they are easily transfected, unlike LNCaP cells. However, like LNCaP cells, ART-27 gene expression in HeLa cells is largely insensitive to negative regulation by E2F6 as it is in 293 cells (16). Few regulatory elements appear to lie within the –2065/–383 region of the ART-27 promoter, because constructs ending at different points within this region show equivalent activity (Fig. 2AGo). By comparison, an ART-27-luciferase reporter encompassing –154/+124 shows a 40% increase in activity, suggesting the presence of a weak inhibitory element between –383 and –154 bp (Fig. 2AGo). This observation is consistent with the reported location of an E2F transcription factor-binding site that is important for repression of ART-27 (16, 17). In contrast, decreased ART-27-luciferase reporter activity is observed with 5'-deletions from –154 to +16, suggesting that key regulatory elements required for ART-27 promoter activity have been deleted (Fig. 2AGo).


Figure 2
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  		Fig. 2. Mapping the ART-27 Promoter

A, Large-scale deletion analysis of the ART-27 5'-regulatory region. HeLa cells were transfected with a series of human ART-27-luciferase reporter constructs or the empty pGL3 vector (VO), along with Lac-Z to control for transfection efficiency for 24 h. The locations of previously identified E2F-binding sites are indicated. Relative luciferase units (RLU) normalized to β-galactosidase activity are shown. B, Fine-scale analysis of the ART-27 –154/+19-bp region. Luciferase assay was performed as described in A. RLU normalized to β-galactosidase activity are shown. The locations of consensus Sp1-binding site and CRE are indicated, in addition to the E2F-binding site.

 
To further map this regulatory region, a series of ART-27 5'-truncations from –154 to +19 bp were made and assayed for luciferase activity (Fig. 2BGo). Deletions from –154 to –53 bp did not compromise ART-27 promoter activity. In comparison, deletions from –53 to –14 bp reduce ART-27 promoter activity, suggesting that elements required for ART-27 expression lie between –53 and –14 bp upstream of the ART-27 start site of transcription.

A cis-Acting CRE Is Important for ART-27 Promoter Activity
To identify putative transcription factor-binding sites located between –53 and –14 bp, the DNA sequence of this region was analyzed using MatInspector software (22, 23, 24). The binding sites identified include a consensus CRE (–23 to –14), an Sp1 transcription factor-binding site (–41 to –31), and a CCAAT/enhancer-binding protein-{alpha} (C/EBP{alpha})-binding site (–51 to –42). To test the functional relevance of these binding sites, we coexpressed CREB and Sp1 with various reporters containing or lacking their respective binding sites. Overexpression of CREB activated ART-27-luciferase reporter constructs containing the CRE (Fig. 3AGo). Overexpression of Sp1 also activates the ART-27 luciferase reporter (Fig. 3BGo). These findings suggest that basal factors, such as Sp1, and inducible factors, such as CREB, are important for induction of ART-27 expression.


Figure 3
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  		Fig. 3. CREB and Sp1 Enhance ART-27 Promoter Activity

A, CREB activates ART-27-luciferase reporter constructs. HeLa cells were seeded in 24-well plates and transfected for 24 h with either the 0.1 µg empty pGL3 vector (VO) or ART-27-luciferase reporter, with 10 ng Lac-Z and 0.1 µg empty vector (EV) or CREB. Relative luciferase units (RLU) normalized to β-galactosidase activity are shown. B, Sp1 also activates ART-27-luciferase reporter. Cells were seeded as above and transfected with 0.1 µg empty pGL3 vector (VO) or ART-27-luciferase reporter, 10 ng of Lac-Z plasmids, and 0.1 µg empty vector (EV) or Sp1 for 24 h. RLU were normalized to β-galactosidase activity from three independent experiments. Error bars represent SD.

 
The importance of the C/EBP{alpha}-binding site and the CRE for ART-27 promoter activity was assessed using ART-27-luciferase reporter constructs deleted of their respective DNA-binding elements (Fig. 4Go). ART-27 promoter activity was not reduced by deletion of the C/EBP{alpha}-binding site ({Delta}1) (Fig. 4BGo). In contrast, deletion of the CRE ({Delta}2) compromised ART-27 promoter activity by more than 50%, suggesting that the CRE but not the C/EBP{alpha}-binding site is important for ART-27 promoter activity.


Figure 4
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  		Fig. 4. Fine-Structure Analysis of the ART-27 Regulatory Region

A, Sequence of the ART-27 5'-regulatory regions responsible for mediating transcriptional activation. Below the sequence are the predicted transcription factors binding sites. The consensus C/EBP{alpha}-binding site ({Delta}1) or CRE ({Delta}2) within the –146/+19-Luc reporter were deleted. In addition, trinucleotide substitutions (S1–S8) were introduced at the indicated regions. B,Functional analysis of regulatory regions controlling ART-27 expression. HeLa cells were transfected with the indicated ART-27-luciferase reporter constructs as described in Fig. 2Go. C, A CREB family member binds the functional response element in the ART-27 gene regulatory region. EMSA was performed using an oligonucleotide containing sequences derived from –28/–7 of the wild type (WT) 5'-regulatory region of the ART-27 gene (probe) incubated with HeLa cell nuclear extracts. Binding to the probe was competed with the indicated molar excess of unlabeled WT, consensus transcription factor-binding sites (left), or mutant (S3–S7) sequences (middle). The binding mixtures were also incubated with the indicated antibodies before resolution on polyacrylamide gel (right).

 
We also investigated the requirement of the CRE sequence for ART-27 promoter activity by introducing a series of trinucleotide substitutions (S1–S8) spanning the CRE site and measuring the activities of the resulting ART-27-luciferase reporter constructs (Fig. 4BGo). ART-27 promoter activity was largely unaffected by nucleotide substitutions flanking the CRE (S1–S3, S7, and S8; Fig. 4BGo). However, mutations within the CRE (S4–S6) compromise promoter activity, indicating that this sequence is important for ART-27 expression. This result suggests that a sequence-specific transcription factor binding the CRE element, such as CREB, is important for the induction of ART-27 gene expression.

A CREB Family Member Binds to the CRE in Vitro
We next sought to determine whether this CRE serves as a binding site for CREB or another factor by EMSA. Upon incubation with HeLa cell nuclear extracts, we observed a shift in mobility of the labeled oligonucleotide probe spanning the CRE (–28/–7). This binding is competed by an excess of unlabeled probe (lane 2 vs. 3) and can also be competed with a consensus sequence for CREB binding (lane 6) but not consensus C/EBP{alpha}- and Sp1-binding sites (lanes 4–5) (Fig. 4CGo). Although probes containing substitutions S3 or S7, which fall outside the CRE, still compete, probes containing substitutions S4–S6 within the CRE fail to compete with the wild-type-labeled probe for protein binding (lanes 7–14), indicating sequence-dependent recognition of the CRE by the bound protein (Fig. 4CGo).

Upon incubation with CREB antibody, but not C/EBP{alpha} antibody, a supershift in probe mobility is also observed (lanes 15–17) (Fig. 4CGo). Because the CREB antibody used in this experiment also reacts with activating transcription factor-1 (ATF-1) and cAMP-responsive element modulator, we are unable to exclude association of these two factors with the CRE at this point. These results indicate that CREB or a related family member associates with the ART-27 CRE in a sequence-specific manner.

CREB Is Recruited to the ART-27 Promoter
To determine whether CREB is specifically recruited to the CRE of the ART-27 gene, ChIP assays were performed (Fig. 5Go). LNCaP cells were cross-linked with formaldehyde, chromatin was prepared and sheared, and the cross-linked protein-DNA complexes were precipitated with antibodies against CREB or control IgG. PCR was then performed on the precipitated DNA fragments to amplify the CRE-binding site 23 bp upstream of the start site of transcription. A region approximately 5 kb upstream of the ART-27 promoter [upstream region (UPS)] was amplified as a control for ChIP specificity. We observed an 8-fold enrichment of CREB at the CRE relative to the UPS in LNCaP cells (Fig. 5BGo).


Figure 5
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  		Fig. 5. CREB Recruitment and Chromatin Modification at the ART-27 Promoter

A, Schematic illustration of the ART-27 5'-regulatory region. CREB and E2F binding sites are shown as hatched and white boxes, respectively, whereas the black box upstream represents a region that serves as negative control for the ChIP assays. PCR primers (arrows) spanning a control UPS (–4966 bp) or the CRE (–23 bp) were used to amplify input and precipitated DNA. B, CREB recruitment to ART-27. ChIPs were performed on 293 and LNCaP cells with antibody against CREB. C, Histone H3 modifications at the ART-27. ChIP assays were performed on 293 and LNCaP cells with antibodies against Ac-H3K9/14 (activating mark) and 3Me-H3K27 (repressive mark). Recruitment was normalized to input and shown as fold recruitment relative to UPS, which was arbitrarily set as 1. Data were averaged from three independent experiments. The error bars represent SD.

 
We also examined whether CREB could occupy the ART-27 regulatory region in 293 cells by ChIP. Recall that ART-27 displays basal mRNA expression in 293 cells that is not induced by serum but can be further elevated by TSA. We found a 3-fold enrichment of CREB at the CRE relative to the UPS in 293 cells (Fig. 5BGo). Thus, CREB binds the ART-27 CRE in vitro, activates the ART-27 promoter in reporter assays (Figs. 3AGo and 4CGo), and occupies the CRE region of the ART-27 promoter in LNCaP and, to a lesser extent, in 293 cells.

Histone Modifications at the ART-27 Promoter
To determine whether there are cell-specific differences in chromatin modification near the ART-27 CRE, we compared the levels of repressive and active histone marks, trimethylated (3Me)-H3K27 and acetylated (Ac)-H3K9/14, respectively, at the ART-27 promoter in 293 and LNCaP cells by ChIP. We detected higher levels of the active histone H3 modification Ac-H3K9/14 at the ART-27 regulatory region in LNCaP than in 293 cells (Fig. 5CGo). This suggests that in LNCaP cells the ART-27 promoter is in a chromatin context permissive for activation and is consistent with the robust induction of ART-27 expression by CREB observed in LNCaP as compared with 293 cells.

By contrast, a greater amount of the repressive chromatin mark 3Me-H3K27 was observed at the ART-27 CRE in 293 relative to LNCaP cells (Fig. 5CGo), suggesting that the ART-27 promoter is in a repressive chromatin environment in 293. These results indicate that cell-specific regulation of ART-27 mRNA is associated with differences in histone modification at the ART-27 promoter.

Epidermal Growth Factor (EGF) Induces ART-27
To mediate transcription, CREB is activated by phosphorylation at serine 133 (S133). This phosphorylation is mediated by several kinases including protein kinase A in response to increased cAMP levels, protein kinase B/Akt upon activation of the phosphatidylinositol 3-kinase pathway, and the 90-kDa ribosomal protein S6 kinases (RSKs and MSKs) upon activation of the MAPK pathway (25, 26, 27, 28, 29). Although many peptide growth factors can activate these pathways, we examined the role of CREB activation in ART-27 gene expression by EGF, because EGF plays an important role in prostate development and cancer, and expression of its receptor, EGFR/ErbB1 is androgen sensitive in LNCaP cells (30, 31, 32).

EGF stimulation leads to S133 phosphorylation of CREB in both 293 and LNCaP cells (Fig. 6AGo), suggesting that EGF activates CREB in both cell types. However, EGF-dependent phosphorylation of CREB was much more robust in LNCaP compared with 293 cells. For example, after 10 min of EGF stimulation, CREB phosphorylation is enhanced only 2-fold in 293 cells but nearly 10-fold in LNCaP cell (Fig. 6AGo). In addition, 293 cells show constitutive phosphorylation of ATF-1 compared with LNCaP cells (Fig. 6AGo).


Figure 6
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  		Fig. 6. EGF-Dependent Recruitment of CREB and Induction of ART-27

A, Activation of CREB by EGF. Western blot analysis for pCREB, pATF-1, and CREB in whole-cell lysates of 293 and LNCaP cells serum starved for 24 h and then treated with 100 ng/ml EGF for 0, 5, 10, and 15 min. The numbers below the blots represent the ratio of pCREB to total CREB levels. B, EGF-dependent recruitment of CREB to ART-27. 293 and LNCaP cells were serum starved for 24 h and stimulated with 100 ng/ml EGF for 20 min. ChIP assays were performed as described in Fig. 5Go using CREB and p300 antibodies. C, Effect of EGF on ART-27 gene expression. Cells were deprived of serum for 24 h, treated with DMSO or 100 ng/ml TSA for 1 h, and then stimulated with PBS vehicle or 100 ng/ml EGF for 3 h. Total RNA was isolated and analyzed by RT-QPCR. Relative ART-27 mRNA levels normalized to RPL19 are shown.

 
We next examined EGF-dependent recruitment of CREB to ART-27 and found that CREB and its coactivator p300 are recruited to the ART-27 promoter in an EGF-dependent manner in LNCaP but not 293 cells (Fig. 6BGo). Consistent with this finding, LNCaP cells up-regulate ART-27 mRNA when stimulated with EGF (Fig. 6CGo), whereas 293 cells do not. And although TSA increases ART-27 mRNA level in 293 cells, treatment with EGF does not further enhance the expression of ART-27 (Fig. 6CGo).

The lack of EGF-dependent recruitment of CREB and regulation of ART-27 mRNA in 293 cells is consistent with repressive histone modifications detected at the ART-27 promoter (Figs. 5Go and 6Go). TSA does not affect CREB recruitment or Ac-H3K9/14 levels at the ART-27 promoter in 293 cells (supplemental Fig. S2A, published as supplemental data on The Endocrine Society’s Journals Online web site at http://mend.endojournals.org), suggesting that repression of ART-27 expression is dominant over activation.

Induction of ART-27 by EGF in LNCaP cells is also observed in DU145 cells, which like LNCaP cells show strong EGF-dependent phosphorylation of CREB (data not shown). These results indicate that EGF leads to robust S133 phosphorylation of CREB, enhances recruitment of CREB and p300 to the ART-27 promoter, and increases expression of ART-27 mRNA in LNCaP but not 293 cells.

CREB Mediates Induction of ART-27 by EGF
To determine whether CREB is required for EGF-dependent induction of ART-27, we depleted CREB expression in LNCaP cells using RNA interference (RNA-i) and assessed the effect of EGF on ART-27 gene expression. LNCaP cells transfected with CREB siRNA express approximately 70% less CREB protein than control cells (Fig. 7AGo). Not only are CREB levels reduced, but the active S133 phosphorylated form of CREB is also decreased, whereas EGF-dependent phosphorylation of ATF-1 and ERK1/2 as well as total ERK1/2 protein levels are unaffected (Fig. 7AGo). Importantly, EGF fails to induce ART-27 expression if CREB expression is reduced in LNCaP cells (Fig. 7BGo), indicating that CREB is required for EGF-induction of ART-27.


Figure 7
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  		Fig. 7. CREB Mediates Induction of ART-27 by EGF

A, Transient depletion of CREB via RNA-i. LNCaP cells were transfected with nonsilencing siRNA (control) or siRNA against CREB. After 48 h, cells were serum starved for 24 h and then stimulated with 100 ng/ml EGF for 5 min. Whole-cell lysates were analyzed by Western blot. Relative pCREB and CREB levels are indicated as numbers below the blots. B, Effect of CREB depletion on ART-27 mRNA level. LNCaP cells were transfected and serum starved as described above and then stimulated with EGF for 3 h. Total RNA was analyzed by RT-QPCR. Relative ART-27 mRNA levels normalized to RPL19 are shown.

 
To further investigate the function of CREB activation in ART-27 gene expression, 293 and LNCaP cells were treated with the MAPK kinase inhibitor U0126. In 293 cells, U0126 treatment abolished ERK1/2 phosphorylation but had no effect on CREB phosphorylation (supplemental Fig. S2B). Likewise, U0126 did not affect ART-27 mRNA expression or induction by TSA in 293 cells (data not shown; supplemental Fig. S2C). These results suggest that CREB phosphorylation and TSA induction of ART-27 occurs through an ERK-independent mechanism in 293 cells.

In contrast, U0126-treated LNCaP cells showed reduced CREB and ERK1/2 phosphorylation upon EGF stimulation (Fig. 8AGo). Notably, LNCaP cells treated with U0126 fail to induce ART-27 mRNA in response to EGF (Fig. 8BGo). The effect of EGF activation on ART-27 expression is also observed at the protein level. LNCaP cells stimulated with EGF up-regulate ART-27 protein in a dose-dependent manner (Fig. 8CGo), and U0126 blocks this induction (Fig. 8DGo). These results indicate that ERK activation in LNCaP cells is associated with CREB phosphorylation and induction of ART-27 gene expression in response to EGF.


Figure 8
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  		Fig. 8. The MAPK Kinase Inhibitor U0126 Blocks Induction of ART-27 by EGF

A, Effect of U0126 on CREB activation by EGF. LNCaP cells were serum starved for 24 h, pretreated with DMSO vehicle or 10 µM U0126 for 1 h, and then stimulated with PBS vehicle (–) or 100 ng/ml EGF for 5 min. Whole-cell lysates were analyzed by western blot. B, Effect of U0126 on ART-27 mRNA levels. LNCaP cells were deprived of serum for 24 h, pretreated with DMSO vehicle or 10 µM U0126 for 1 h, and then stimulated with PBS vehicle or 100 ng/ml EGF for 3 h. Total RNA was analyzed by RT-QPCR. Relative ART-27 mRNA levels normalized to RPL19 are shown. C, LNCaP cells up-regulate ART-27 protein in response to EGF. LNCaP cells were seeded equally in a 24-well dish, deprived of serum for 24 h, and treated with PBS vehicle (0) or 2, 20, or 100 ng/ml EGF for 3 h. Whole-cell lysates were analyzed by Western blot. D, U0126 inhibits EGF induction of ART-27 protein. LNCaP cells were deprived of serum for 24 h, pretreated with DMSO vehicle or 10 µM U0126 for 1 h, and then stimulated with PBS vehicle or EGF for 3 h. Whole-cell lysates were analyzed by Western blot.

 
Expression and S133 Phosphorylation of CREB during Prostate Development
We have previously shown that ART-27 is regulated during human prostate development (15). Early in development, ART-27 is not detected in the undifferentiated prostatic buds that lack a defined lumen, whereas later in development, ART-27 is detected when the buds differentiate and contain a well-defined lumen (15). Moreover, in the developing urogenital sinus from which the prostate develops, and in adult prostate, ART-27 protein is undetectable in smooth muscle and other stromal cells (15).

Because we have shown that CREB mediates induction of ART-27 in cultured prostate cells, we examined CREB and phospho-CREB (pCREB) expression in human prostate development. Sections of early (15-wk) and late (21 wk) urogenital sinus were stained using CREB and pCREB (S133) antibodies. Early in development, both the stromal and epithelial cells surrounding the urethra and prostatic buds stain for CREB (Fig. 9AGo). In contrast, stromal cells do not stain for pCREB, whereas pCREB antibody stains a majority of epithelial cells (Fig. 9BGo). Later in development, there is still virtually no pCREB immunoreactivity in stromal cells (Fig. 9DGo), but pCREB staining remains detectable in luminal epithelial cells (Fig. 9DGo). These results are consistent with CREB activation preceding epithelial cell-specific induction of ART-27 and suggest that activated CREB mediates ART-27 induction in prostate epithelial cells.


Figure 9
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  		Fig. 9. Expression of CREB and pCREB in Human Prostate Development

Paraffin-embedded sections of 15-wk-old (A and B) and 21-wk-old (C and D) human fetal urogenital sinus were stained with CREB (A and C) and pCREB (S133) (B and D) antibodies. A and C show that cells in the stroma (str) and epithelial cells surrounding the lumen of the urethra (U) and prostatic buds (PB) express CREB. B and D show that CREB is phosphorylated at S133 in epithelial cells but not in most stromal cells.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
MATERIALS AND METHODS
 REFERENCES
 
ART-27 is an epithelial cell-specific AR cofactor that is regulated in both prostate development and cancer (11, 15). In this study, we define the cis-acting DNA regulatory elements and trans-acting factors controlling ART-27 gene expression. We show that ART-27 expression is regulated through cell type-specific transcriptional mechanisms. E2F transcription factors have previously been shown to repress ART-27 mRNA expression in 293 cells (16, 17). E2Fs are not only transcriptional activators, but certain family members, such as E2F6 are also repressors that recruit EZH2-containing PRCs (19, 20, 33). PRC2 contains class I histone deacetylase (HDAC) activity and thus are sensitive to inhibition by TSA (34). TSA induces ART-27 mRNA in 293 but not LNCaP cells (Fig. 1AGo), suggesting that transcriptional repression of the ART-27 gene involves cell-specific factors such as E2F6 and EZH2. This effect is specific for type 1 but not type 3 HDAC because inhibition of type 3 NAD+-dependent HDACs by nicotinamide does not induce ART-27 expression (data not shown). EZH2 specifically trimethylates histone H3 on lysine 27 (3Me-H3K27), and this modification is associated with gene repression by EZH2/PRC2 (35, 36). Consistent with this idea, a 3Me-H3K27 mark is detected at the ART-27 promoter in 293 cells but not LNCaP cells (Fig. 5CGo), and E2F6 mRNA levels are higher in 293 and a prostate stromal cell line as compared with LNCaP cells (supplemental Fig. S1). Our results indicate that a type 1 HDAC is involved in repression of ART-27 expression.

CREB is constitutively active, relatively insensitive to EGF stimulation, and occupies the ART-27 regulatory region in 293 cells, and this likely results in the basal ART-27 mRNA expression and lack of EGF induction observed in this cell type. In contrast, in LNCaP cells, CREB is activated in response to EGF and is recruited to the ART-27 promoter to induce ART-27 gene expression (Figs. 5–7GoGoGo). Our data suggest that the pattern of ART-27 gene expression is a result of E2F/EZH2/PRC2-mediated repression in undifferentiated epithelial precursors and CREB-mediated activation of the ART-27 promoter in differentiated luminal cells (Fig. 10Go).


Figure 10
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  		Fig. 10. Model for Regulation of ART-27 Gene Expression in Prostate Epithelial Cells

We propose that in undifferentiated cells (left), ART-27 is repressed by an E2F6/EZH2/PRC2 complex that trimethylates histone H3K27 (3Me-H3K27). PRC2 contains a type 1 HDAC that accounts for enhanced ART-27 gene expression in 293 cells upon TSA treatment. In differentiated cells (right), the level or activity of the E2F6/EZH2/PRC2 complex is reduced, and ART-27 gene expression is no longer repressed. TSA has no effect on ART-27 mRNA, and 3Me-H3K27 is not detected at the ART-27 promoter. In response to EGF or other growth factors, CREB increasingly occupies the ART-27 promoter, recruits coactivators (e.g. p300) that acetylates histone H3K9/14 (Ac-H3K9/14), and results in activation of ART-27 gene expression.

 
The activation of CREB and induction of ART-27 in epithelial cells during prostate development is likely mediated by EGFR signaling. It is likely that stromal cells secrete paracrine factors, such as EGF and keratinocyte growth factor, whose receptors (EGFR/ErbB1 and KGFR/FGFR2, respectively) are expressed exclusively by epithelial cells (37, 38) and induce ART-27 mRNA expression. Therefore, EGFR signaling is a good candidate pathway to govern CREB activation and ART-27 expression during prostate development.

What is the mechanism underlying diminished ART-27 expression in prostate cancer? Although up-regulation of the E2F/EZH2/PRC2 transcriptional repression complex or reduced phosphorylation and recruitment of CREB to the ART-27 promoter are attractive mechanisms for reduced ART-27 expression, it is not clear that the down-regulation of ART-27 protein observed in prostate cancer occurs at the level of transcription. It is conceivable that changes in ART-27 translation and/or degradation could also affect its expression. Indeed, expression profiling studies suggest that ART-27 mRNA is present at roughly similar levels throughout the stages of prostate cancer (39, 40), despite clear indications that ART-27 protein levels are reduced in human prostate cancer (15). In addition, we have recently shown that a somatic alteration in AR associated with prostate cancer (AR-P340L) shows a diminished transcriptional response to ART-27 and may bypass the need for of ART-27 in AR-dependent cell growth suppression (41). Therefore, it is likely that multiple mechanisms underlie reduced ART-27 function in prostate cancer.

Based on these findings, we propose that developmental regulation of ART-27 expression is important in restraining AR-mediated prostate epithelial cell proliferation by regulating a subset of AR-responsive genes important to prostate growth inhibition and differentiation. This implies that alterations in the level of ART-27 modulate AR target gene selectivity, which, in turn, affects AR-dependent cell growth regulation, a hypothesis we are currently testing.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
REFERENCES
 
Cell Culture
LNCaP cells were cultured in RPMI 1640 medium (Invitrogen, Carlsbad, CA) supplemented with 10% fetal bovine serum (FBS) (Hyclone, Logan, UT) and 1% penicillin-streptomycin (PS) (Mediatech/Cellgro, Herndon, VA). HEK-293T (293) cells were cultured in DMEM (Cellgro) supplemented with 10% FBS and 1% PS. HeLa cells were cultured in DMEM supplemented with 10% FBS and 2 mM L-glutamine (Invitrogen) and 1% PS. Cells were maintained at 5% CO2 in a 37 C incubator. The prostate stromal cells immortalized with hTERT, were a kind gift from Dr. Peng Lee (NYU School of Medicine) and were maintained in RPMI 1640 medium plus 10% FBS and 1% PS.

Real-Time Quantitative PCR (QPCR)
Total RNA was isolated using the RNeasy kit with on-column DNase digest (QIAGEN Inc., Valencia, CA). Total RNA was reverse transcribed at 55 C for 1 h, using Superscript III reverse transcriptase and oligo-(dT)20 primers (Invitrogen). Real-time PCR was performed using specific primers to ART-27 (forward 5'-CAACAGCCTCACCAAGGACT-3' and reverse 5'-TCTGCAGGCCTTGTAGTTCTC-3' or forward 5'-CTGGAGTTGACACTGGCAGA-3' and reverse 5'-AGTCCTTGGTGAGGCTGTTG-3') or ribosomal protein L19 (RPL19, forward 5'-CACAAGCTGAAGGCAGACAA-3' and reverse 5'-GCGTGCTTCCTTGGTCTTAG-3') and 2x SYBR green Taq-ready mix (Sigma-Aldrich, St. Louis, MO) according to the manufacturer’s directions. Amplifications were performed at 60 C in a Roche Lightcycler (Roche, Indianapolis, IN). No signal was detected in reactions performed without prior reverse transcription. Reactions with dissociation curves that do not show a single, sharp peak were excluded from analysis. Relative mRNA levels were determined as previously described, using RPL19 as control (42). Error bars represent SD between replicates.

Cloning and Construction of ART-27 Promoter Reporter Plasmids
Genomic sequences between –2060 and +346 bp from the ART-27 transcription-initiation site (+1 bp) were retrieved from the human genome database and amplified from normal human genomic DNA by PCR using oligonucleotides 5'-GCATGGT(G)A(G)CCTCACGCCTGTAATC-3' and 5'-GCAAGCT(G)CGAGGTTCAGCCTTC-3'. Bases in parentheses were changed to the underlined bases to generate KpnI restriction sites for subcloning. The resulting product was cloned into the EcoRV site of pBluescript SK+ (Stratagene, La Jolla, CA). ART-27-regulatory regions were cloned into a pGL3 basic plasmid (Promega, Madison, WI) to generate the reporter constructs. All constructs were verified by restriction digest and sequenced. Transcription factor analysis of the promoter was performed using MatInspector (22). Deletions {Delta}1 and {Delta}2 and mutations S1–S8 in the ART-27 regulatory region were generated using the QuikChange site-directed mutagenesis kit (Stratagene) and oligonucleotides listed in Supplemental Table 1 according to the manufacturer’s recommendations.

Luciferase Assay
HeLa and 293 cells were seeded in a 24-well plate at a density of 3 x 104 or in a six-well plate at a density of 1.5 x 105 in phenol red-free DMEM supplemented with 10% charcoal-stripped FBS. Transfection was performed using Lipofectamine Plus (Invitrogen) reagent according to the manufacturer’s instructions. For transfection of cells in 24-well plates, each well received 100 ng of the control pGL3 or ART-27 regulatory region-luciferase reporter plasmid, and 10 ng of CMV-LacZ. After 4 h, transfection mixtures were removed, and the cells were refed with phenol red-free medium plus 10% FBS. After 24 h, the transfectants were washed with PBS and lysed in 1x luciferase cell culture lysis reagent (Promega). The cell extracts were analyzed for luciferase activity, and the values were normalized to β-galactosidase activity, except where indicated. Luciferase activity was quantified in a reaction mixture containing 15 µl lysate and 100 µl luciferase assay reagent [25 mM glycylglycine (pH 7.8), 10 mM MgSO4, 1 mM ATP, 0.1 mg/ml BSA, 1 mM dithiothreitol], using an LMax microplate reader luminometer and 1 mM D-luciferin as substrate.

EMSA
Double-stranded oligonucleotides were end-labeled with [32P{gamma}]ATP by using T4-polynucleotide kinase. HeLa cell nuclear extracts (10 µg) was added to the radiolabeled double-stranded oligonucleotides in a total volume of 20 µl with 2.5 µg poly (dI-dC) and 1 µg herring sperm DNA in binding buffer [10 mM Tris (pH 8.0), 40 mM KCl, 0.05% Nonidet P-40, 6% glycerol, and 1 mM dithiothreitol] and incubated for 30 min at room temperature. C/EBP{alpha} consensus was 5'-TGCAGATTGCGCAATCTGCA-3' (Santa Cruz sc-2525; Santa Cruz Biotechnology, Santa Cruz, CA); CREB consensus was 5'-AGAGATTGCCTGACGTCAGAGAGCTAG-3' (Santa Cruz sc-2504); and Sp1 consensus was 5'-ATTCGATCGGGGCGGGGCGAGC-3' (Santa Cruz sc-2502). Binding reactions were resolved on 6% nondenaturing polyacrylamide gels in 0.25x Tris-borate-EDTA buffer at room temperature. Gels were dried before autoradiography. Antibodies against CREB (Sc-186X) and C/EBP{alpha} (Sc-9314X) were purchased from Santa Cruz Biotechnology.

ChIP Assay
LNCaP and 293 cells cultured in medium supplemented with 10% FBS for 96 h were cross-linked in 50 mM HEPES (pH 8.0), 1 mM EDTA (pH 8.0), 100 mM NaCl, 11% formaldehyde at room temperature for 10 min. Cross-linking was stopped upon incubation in 0.1 M glycine for 5 min. The fixed cells were washed twice, lifted in cold PBS, and then centrifuged for 5 min. Chromatin was prepared as previously described (43), with some modifications. Nuclei were washed and resuspended in 3 ml modified RIPA buffer [1% Triton X-100, 0.1% deoxycholate, 1 mM EDTA, 0.5 mM EGTA, 10 mM Tris-HCl (pH 8.0), 140 mM NaCl, and 1x protease inhibitor cocktail (Sigma)], sonicated, and centrifuged for 10 min at 4 C. The supernatant was precleared with a protein A-agarose, sheared salmon sperm DNA slurry (Upstate USA, Inc., Lake Placid, NY), centrifuged, and incubated with CREB (48H2) (Cell Signaling Technology, Danvers, MA), p300 (C-20) (Santa Cruz), acetylated histone H3K9/14 (Abcam, Cambridge, MA), or trimethylated histone H3K27 (Abcam) antibodies overnight at 4 C. Protein A-agarose plus sheared salmon sperm DNA slurry was then added, and incubation was continued for 1–2 h. The beads were subject to three sequential 10-min washes with buffers I [0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl (pH 8.1), 150 mM NaCl], II [0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl (pH 8.1), 500 mM NaCl], and III [0.25 M LiCl, 1% Nonidet P-40, 1% deoxycholate, 1 mM EDTA, 10 mM Tris-HCl (pH 8.1)], and rinsed twice in Tris-EDTA buffer. Samples were resuspended in 100 µl proteinase K-SDS (0.5% SDS, 200 µg/ml Proteinase K in Tris-EDTA buffer) and incubated at 55 C for 3 h and then at 65 C overnight to reverse the cross-link. DNA was purified using QIAquick PCR purification kit (QIAGEN). Real-time PCR was performed at 60 C using 2 µl of the DNA. The PCR primers used are as follows: –5 kb UPS, forward 5'-CTTGAAAGCAGGAGGAAACG-3' and reverse 5'-TTCTGGCTTCCATGTTTTCC-3', and CRE, forward 5'-TGCCACTTACGTCATTCACC-3' and reverse 5'-CCAGCAATAAGAAC GGTTGG-3'.

RNA-i
CREB-1 SMARTpool siRNA was purchased from Dharmacon (Lafayette, CO). LNCaP cells were transfected for 4 h with 100 nM nonsilencing or CREB-1 siRNA using Lipofectamine 2000 (Invitrogen). The cells were then allowed to recover for 48 h. Subsequently, the medium was changed to phenol red- and serum-free RPMI 1640 for an additional 24 h before EGF treatment.

Western Blot
Whole cells were lysed in the presence of 1% protease-inhibitors cocktail and 1 mM Na3VO4. Samples were subject to SDS-PAGE, transferred onto Immobilon (Millipore, Billerica, MA), and probed with rabbit affinity-purified ART-27 (15), tubulin (Covance, Princeton, NJ), and ERK1/2 (9102), phospho-ERK1/2 (Thr202/ Tyr204) (9101S), pCREB (S133) (9191), and CREB (48H2) antibodies (Cell Signaling Technology). Membranes were then washed and incubated with antimouse or antirabbit, horseradish peroxidase-conjugated secondary antibodies (KPL, Gaithersburg, MD) for 1 h. After washing, signals were detected on x-ray film using the ECL chemiluminescent detection kit (GE Health Sciences, Boston, MA). Quantitation was performed using a GS-800 calibrated imaging densitometer (Bio-Rad, Hercules, CA).

Immunohistochemistry
The NYU School of Medicine Institutional Review Board approved the use of all human samples. Paraffin-embedded human fetal prostate tissues and immunohistochemistry procedures used in this study have been previously reported (15). CREB and pCREB antibodies were purchased from Cell Signaling Technology.


   ACKNOWLEDGMENTS
 
We thank Susan Ha and Inez Rogatsky for evaluating the manuscript, Dr. Jiri Zavadil and NYU Cancer Institute Genomics Facility for technical help, and Dr. Gregory David for advice and reagents.


   FOOTNOTES
 
This work was supported by Ruth L. Kirschstein National Research Service Award F31 CA113285 (J.C.N.), The Chemotherapy Foundation (S.S.T.), The Concern Foundation (S.K.L.), The American Cancer Society (S.K.L.), the U.S. Department of Defense (W81XWH-04-1-0914 to S.K.L. and W81XWH-06-1-0068 to S.S.T.) and National Institutes of Health grant DK058024 (M.J.G.).

Disclosure Statement: The authors have nothing to disclose.

First Published Online August 30, 2007

1 J.C.N. and W.L. contributed equally to this work. Back

Abbreviations: Ac, Acetylated; AR, androgen receptor; ART-27, androgen receptor trapped clone-27; ATF-1, activating transcription factor-1; C/EBP{alpha}, CCAAT/enhancer-binding protein-{alpha}; ChIP, chromatin immunoprecipitation; CRE, cAMP-responsive element; CREB, CRE-binding protein; DMSO, dimethylsulfoxide; EGF, epidermal growth factor; EGFR, EGF receptor; FBS, fetal bovine serum; HDAC, histone deacetylase; 3Me, trimethylated; pCREB, phosphorylated CREB; PGC-1{alpha}, PRC, peroxisome proliferator-activated receptor-{gamma} coactivator-1{alpha}; polycomb repressive complex; PS, penicillin-streptomycin; QPCR, quantitative PCR; RPL19, ribosomal protein L19; RNA-i, RNA interference; siRNA, small interfering RNA; SRC-3, steroid receptor coactivator-3; TSA, trichostatin A; UPS, upstream region; URI, unconventional prefoldin RPB5-interactor.

Received for publication February 19, 2007. Accepted for publication August 22, 2007.


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