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The Role of Hepatocyte Nuclear Factor-3 (Forkhead Box A1) and Androgen Receptor in Transcriptional Regulation of Prostatic Genes

Department of Cell and Developmental Biology (N.G., J.Z., R.J.M.), Vanderbilt University Medical Center; Department of Urologic Surgery (N.G., J.Z., T.C.C., J.M., Y.W., R.J., A.G., R.J.M.), and the Vanderbilt Prostate Cancer Center, Vanderbilt University; Department of Cancer Biology (T.C.C., J.M., Y.W., R.J., A.G., R.J.M.), and the Vanderbilt Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37232; and The Prostate Centre at Vancouver General Hospital (M.A.R., P.S.R.), Vancouver, British Columbia V6H 3Z6, Canada

Address all correspondence and requests for reprints to: Robert J. Matusik, Ph.D., Department of Urologic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee 37232. E-mail: Robert.matusik{at}vanderbilt.edu.

	ABSTRACT

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
Androgens and mesenchymal factors are essential extracellular signals for the development as well as the functional activity of the prostate epithelium. Little is known of the intraepithelial determinants that are involved in prostatic differentiation. Here we found that hepatocyte nuclear factor-3 (HNF-3), an endoderm developmental factor, is essential for androgen receptor (AR)-mediated prostatic gene activation. Two HNF-3 cis-regulatory elements were identified in the rat probasin (PB) gene promoter, each immediately adjacent to an androgen response element. Remarkably, similar organization of HNF-3 and AR binding sites was observed in the prostate-specific antigen (PSA) gene core enhancer, suggesting a common functional mechanism. Mutations that disrupt these HNF-3 motifs significantly abolished the maximal androgen induction of PB and PSA activities. Overexpressing a mutant HNF-3 deleted in the C-terminal region inhibited the androgen-induced promoter activity in LNCaP cells where endogenous HNF-3 is expressed. Chromatin immunoprecipitation revealed in vivo that the occupancy of HNF-3 on PSA enhancer can occur in an androgen-depleted condition, and before the recruitment of ligand-bound AR. A physical interaction of HNF-3 and AR was detected through immunoprecipitation and confirmed by glutathione-S-transferase pull-down. This interaction is directly mediated through the DNA-binding domain/hinge region of AR and the forkhead domain of HNF-3. In addition, strong HNF-3 expression, but not HNF-3ß or HNF-3, is detected in both human and mouse prostatic epithelial cells where markers (PSA and PB) of differentiation are expressed. Taken together, these data support a model in which regulatory cues from the cell lineage and the extracellular environment coordinately establish the prostatic differentiated response.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
THE PROSTATE IS a male accessory sex organ that is found exclusively in mammals. This organ produces various components found in the semen. Androgens are required to initiate prostatic development, to establish prostatic morphogenesis, and to begin secretory activities. In the mouse, the developing fetal testis begins to produce androgens at embryonic d 12.5–13 (E12.5–13) with peak production at E17–18, during which the earliest signs of prostatic formation are observed (1, 2). Ablation or surgical removal of fetal testes during the ambisexual period inhibits the development of prostate and other male internal sex organs (3). Androgens act directly through androgen receptor (AR) to elicit their effects (4). Testicular feminization mice, which express a nonfunctional AR, never develop a prostate, even though their testes produce adequate amounts of testosterone (3, 5). In addition, prostatic epithelial cells that do not express functional AR, also do not express characteristic secretory markers (6). These observations demonstrated the essential requirement of androgens and AR for prostate development and function. Interestingly, tissue recombination experiments have shown that the urogenital epithelium from testicular feminization mice develops normal prostate gland histology when combined with wild-type urogenital mesenchyme (UGM), although these urogenital epithelium contain a defective AR (7). Also, it has been observed that the induction of prostatic epithelial buds occurs before AR expression in wild-type prostatic epithelial cells (8, 9, 10). These results argue that the epithelial AR is not required for prostatic determination, although it is essential for the production of androgen-dependent secretory proteins at later stages (6).

Extensive tissue recombination studies have proven that mesenchymal-epithelial interactions play a key role in directing prostate development (3, 11). Epithelial cells from other urogenital sinus derivatives (bladder, urethra, and vagina) can be instructively induced by UGM to give rise to prostatic tissue (3, 12, 13, 14, 15). Similar results have been obtained using human bladder epithelial cells (16). The ductal-acinar structures that form in such experiments histologically resemble prostatic epithelium and produce prostate-specific antigen (PSA) (16). Nevertheless, the response of epithelia to inductive mesenchyme is limited by the developmental repertoire of the germ layer origin of the epithelium (17). For example, mesodermally derived seminal vesicle epithelium responds to either urogenital sinus or seminal vesicle mesenchyme by generating seminal vesicle. In contrast, the endodermally derived epithelia of the prostate, bladder, or urethra respond to the same inductive mesenchyme by generating prostatic tissue. Therefore, it is apparent that the cell developmental program is determined by both epithelial and mesenchymal factors. Although androgens and mesenchymal factors are critical for prostatic development, epithelial factors that directly participate in this process are still unknown.

Hepatocyte nuclear factor-3 proteins (newly named as forkhead box A proteins) are a group of endoderm-related developmental factors (HNF-3, HNF-3ß, and HNF-3) that belong to the forkhead box transcription factor family (18, 19, 20). In mice, HNF-3ß is first expressed in the endoderm progenitor during gastrulation (E6.5), immediately followed by the expression of HNF-3 (before organogenesis, E7–8) and HNF-3 (19, 21). The targeted null mutation of HNF-3ß gene results in embryonic lethality due to the absence of endodermal progenitor cells (22), whereas homozygous mutation of HNF-3 gene leads to perinatal death due to pancreatic defects (23). All three HNF-3 genes are restrictively expressed in the endoderm-derived organs in the adult and are involved in endodermal differentiation (19). In vivo footprinting using mouse embryo liver cells showed that HNF-3 factors, among a few of the earliest transcription factors, bind to the enhancer of liver-specific albumin gene before this gene is activated (19, 24). This binding of HNF-3 is believed to provide developmental competence to the target gene, which becomes activated during hepatic induction when additional liver- enriched transcription factors are recruited (19, 25, 26). Although HNF-3 proteins were first discovered in liver (27), the highest HNF-3 mRNA level was detected in the prostate gland by comparison of 16 human tissues (28). A novel expression pattern of HNF-3 in the epithelium of the bladder, urethra, and prostate has also been reported (28, 29). However, in the urogenital system, target genes that are regulated by HNF-3 have not been identified. The role of HNF-3 in the urogenital system remains to be defined.

In the adult prostate, fully differentiated luminal epithelial cells secrete androgen-dependent prostate-specific proteins, such as probasin (PB) in the rat and PSA in the human. Activation of these characteristic genes in the epithelium signifies that prostatic differentiation has occurred. The transcription factors that regulate these genes may also be involved in the process of prostate development. Therefore, a better understanding of the transcriptional regulation of these prostate-specific genes is likely to provide insight into organ development. In the present study, characterization of the PB promoter has led to the identification of two HNF-3 cis-regulatory motifs, which are immediately adjacent to functional AR binding sites (ARBSs). We have observed a similar organization of the androgen response element (ARE) adjacent to HNF-3 sites in the PSA gene enhancer and the prostatic acid phosphatase (PAP) gene promoter/enhancer, suggesting that a common functional mechanism is involved. DNA mutation studies showed that these HNF-3 sites are essential for maximal androgen induction of both PB and PSA gene. Chromatin immunoprecipitation (ChIP) assay confirmed that HNF-3 occupies the PSA enhancer in vivo. In addition, we detected a direct protein-protein interaction between HNF-3 and AR. These data suggest that an endodermal transcription factor HNF-3 and a steriod receptor AR may coordinately participate in the assembly of a nucleoprotein complex, which directs prostatic differentiated function. The regulatory mechanism between HNF-3 and AR may also apply to the transcriptional control of other prostatic epithelial cell-specific genes.

	RESULTS

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
Two HNF-3 Binding Sites Are Identified on the PB Promoter
The rat PB is a prostate-specific and androgen-regulated gene, which has been extensively characterized (30, 31, 32, 33, 34, 35, 36, 37, 38). It has been shown that a 12-kb fragment of the PB 5'-flanking sequence, a -426/+28-bp fragment as well as an artificial PB promoter, androgen-response region (ARR)₂PB, which contains an extra copy of -244/-96 bp fused in front of the -286/+28-bp region, is able to specifically target genes to transgenic mouse prostate (31, 33, 35, 36, 39, 40, 41). Therefore, the minimal fragment that confers prostate specificity was mapped to the 315-bp region (-286/+28) (36), which contains two functional ARBSs (ARBS-1 at -236/-223 and ARBS-2 at -140/-117) (30). Based on the hypothesis that additional key cis-acting elements remain to be uncovered, an extensive mutation analysis was performed. In this study, we report two critical HNF-3 motifs that are essential for promoter activity.

The first cis-acting element, designated as R1, is located at -253/-237 bp, immediately upstream to ARBS-1. The second element, designated as R2, is located at -126/-107 bp, downstream and slightly overlapping ARBS-2 (Fig. 1A). To identify putative transcription factor (TF)-binding sites, we employed web-based search engines TESS (www.cbil.upenn.edu/tess) and TFSEARCH (www.cbrc.jp/research/db/TFSEARCH.html). The search was restricted to a maximum of 20% mismatch within an element length of six nucleotides (nt) or greater. Either a 9-nt sequence (-252/-244 bp) located in R1 or a 9-nt sequence (-121/-113 bp) located in R2 highly matched with the HNF-3 consensus binding sequence (5'-TRTTTRYTY-3') (20). The first 7-nt 5'-T(A/G)TT(T/G)(G/A)(T/C)-3', extracted from various known HNF-3-regulated gene promoters (20), perfectly matched with the TATTTGT motif in R2 (Fig. 1A). Figure 1B shows a typical EMSA using nuclear extract prepared from LNCaP human prostate cancer cells, which express HNF-3 (Fig. 1C). The TTRs (Fig. 1B) is a strong HNF-3 binding unit on the liver transthyretin (TTR) gene promoter and was originally used to affinity purify HNF-3 proteins (27, 42, 43). Strong complexes were formed when the TTRs consensus HNF-3 binding site was used (Fig. 1B, lane 2), and these complexes were reduced with the addition of antibodies against HNF-3 or HNF-3ß (lanes 3 and 4). RT-PCR using primers specific for HNF-3ß failed to detect the expression of HNF-3ß in LNCaP cells (data not shown), indicating the effect caused by HNF-3ß (M20) antibody may be due to the cross-reactivity of this antibody because HNF-3 and HNF-3ß have highly homologous C termini. Four complexes, designated as a, b, c, and d, were formed with radiolabeled PB-127/-102, which contains R2 (Fig. 1B, lane7). Three complexes, designated as A, B, and C, were formed with PB-257/-232, which contains R1 (Fig. 1B, lane 20). HNF-3 antibody distinctly abolished the binding of two R2 complexes (lane 8, b and c) and R1 complex B (lane 21), whereas mock antibodies had no visible effect (lanes 10–16 and 23). A 200-fold molar excess of cold TTRs oligonucleotide completely competed off the complexes b and c (lane 17), indicating binding specificity. An increasing competitor (400- to 600-fold) further affected complex a (lanes 18 and 19), suggesting that a higher-order HNF-3 complex might be contained in complex a. Because complex a was not affected by HNF-3 antibody (lane 8), it indicates that this complex may have higher stability and the epitope in this complex may not be accessible to HNF-3 antibody. Western blot in Fig. 1C shows that HNF-3 protein was strongly detected in LNCaP and PC3, but weakly detected in DU145 cells in comparison with the positive control HepG2 cells, and the negative control Hela or Cos-1 cells. The expression of HNF-3 mRNA in these three prostatic cell lines (LNCaP, PC3, and DU145) was confirmed by RT-PCR (data not shown). Similar EMSA results in Fig. 1B were obtained when PC3 nuclear extract was used (data not shown).

View larger version (100K): [in this window] [in a new window]   Fig. 1. Identification of Two HNF-3 Binding Sites in the PB Promoter A, Location of HNF-3 motifs. Mutation study revealed two key cis-acting elements R1 and R2 (dashed lines). Each contains a potential HNF-3 binding motif (bold arrows). The direction of the arrow indicates the sense or the antisense strand that matched the consensus sequence. Two adjacent ARBSs (ARBS-1 and ARBS-2) are underlined. Sequences in italic indicate the nucleotide replacements in mutation assays. B, EMSA. LNCaP nuclear extracts were incubated with radiolabeled TTRs (consensus HNF-3 binding sequence), PB-127/-102, or PB-257/-232 probes. Strong complexes formed with TTRs (lane 2). HNF-3 or HNF-3ß antibody reduced the corresponding band (lanes 3 and 4). Four complexes, a, b, c and d, were formed with R2 (lane 7). Complexes b and c were specifically removed by HNF-3 or HNF-3ß antibody (lanes 8 and 9), but not other mock antibodies (lanes 10–16). molar excess (200-fold) of cold TTRs oligonucleotides completely competed off complexes b and c (lane 17), whereas 400- and 600-fold molar excess of TTRs also affected complex a (lanes 18 and 19). Three complexes, A, B, and C, were formed with R1 (lane 18). Complex B was specifically eliminated by HNF-3 antibody (lane 19). C, Western blot. Whole-cell lysates (20 µg) from HepG2, Hela, Cos-1, LNCaP, PC3, and DU145 cells were resolved on SDS-PAGE and probed with HNF-3 antibody. D, A radiolabled oligonucleotide (ARBS2/R2, Table 1) containing both ARBS-2 and R2 was used in EMSA with 10 µg LNCaP nuclear extract. With the presence of an ARBS, two HNF-3 complexes (arrows) still formed with R2, because both complexes were reduced or removed by HNF-3 antibody (lane 1 vs. 2), or eliminated by mutating the HNF-3 motif in ARBS2/R2-M (lane 7, Table 1). Both complexes were not affected by 100-, 200-, and 500-fold molar excess of cold ARBS-2 site (lanes 4–6), whereas several

View larger version (58K): [in this window] [in a new window]   Fig. 1A. Continued other complexes (asterisk) were sensitive to the competition. E, Southwestern blot. Nuclear extracts from LNCaP and PC-3 cells were separated on SDS-PAGE, transblotted to nitrocellulose membranes, and probed with radiolabeled 2xR2 (lanes 1 and 3), 2xmR2 (lanes 2 and 4) or 2xAR-con probes (lane 5). A Western blot using HNF-3 antibody was performed as a parallel control. Arrows indicate migration of proteins bound to the respective probes or antibody.

In Vitro Synthesized HNF-3 Binds R1 and R2
Because crude nuclear extracts were used in EMSA and Southwestern experiments, it was necessary to confirm the results with HNF-3 synthesized by in vitro transcription/translation (TNT). Figure 2 shows that synthesized HNF-3 specifically bound to the radiolabeled R2 in EMSA (Fig. 2A, lane 3), in contrast to the TNT blank control (lane 2), which only formed a nonspecific band. Three mutant HNF-3 proteins deleted in the N-terminal (N), C-terminal (C), or both terminal regions [FH (forkhead)] still showed binding activities (lanes 4–6), because all mutants still contain the FH DNA-binding domain (DBD). The binding of HNF-3 was completely removed by an antibody against the HNF-3 C terminus (Fig. 2B, lane 2 vs. 3). The same antibody could not eliminate the complex formed by the mutant HNF-3 deleted in the C terminus (lane 5 vs. 6). In addition, a mutant probe (mPB-127/-102 bp) containing a mutated HNF-3 motif also affected the specific binding (lane 2 vs. 4). Similar results were observed when using R1 (PB-257/-232 bp) sequence. As shown in Fig. 2C, HNF-3/R1 interaction is relatively weaker in contrast to HNF-3/R2 (Fig. 2C, lane 2 vs. 4), because R1 has a 1-bp mismatch with HNF-3 cognate binding site, whereas R2 is a perfect match. The presence of multiple HNF-3 sites with different affinities has been proposed to be relevant for transcriptional modulation (44). These in vitro experiments confirmed the identification of two HNF-3 cis-regulatory elements adjacent to ARBSs in the PB proximal promoter.

View larger version (43K): [in this window] [in a new window]   Fig. 2. In Vitro Synthesized HNF-3 Binds R1 and R2 A, Wild-type HNF-3 and three mutant proteins (N, FH, and C) were synthesized by in vitro TNT, and incubated with radiolabeled PB-127/-102 probe. In contrast to a nonspecific band (arrowhead) formed with the TNT blank control (lane 2), wild- type HNF-3 and HNF-3C formed a strong complex (lanes 3 and 6), whereas N and FH (arrowhead) showed weak binding ability (lanes 4 and 5, overexposure). B, The binding of HNF-3 with PB-127/-102 was eliminated by an antibody raised against the HNF-3 C terminus (lane 3 vs. 2). The same antibody did not affect the complex formed by HNF-3C, which has a deletion in the C terminus (lane 6 vs. 5). The HNF-3 binding was also affected by mutating the TRTTTGY motif (lane 4 vs. 2). C, Similar results but weaker binding affinity was observed when PB-257/-232 was used as a probe (lane 4 vs. 2).

HNF-3 Is Expressed in Prostate Epithelial Cells

View larger version (114K): [in this window] [in a new window]   Fig. 3. HNF-3 Protein Is Expressed in Mouse and Human Prostate A–D, Immunohistochemistry. Nuclear staining of HNF-3 protein was restrictively detected in both mouse (A and B) and human luminal epithelial cells (C and D). E, Western blot. Fresh mouse prostate tissue lysates from different lobes (VP, ventral prostate; DLP, dorsal-lateral prostate; AP, anterior prostate; NP, whole normal prostate) were separated by SDS-PAGE and detected with HNF-3 (C20), HNF-3ß (P19), and HNF-3 (N19) antibodies.

HNF-3 Binding Sites Are Essential for Maximum Androgenic Induction

View larger version (59K): [in this window] [in a new window]   Fig. 4. Two HNF-3 Motifs Are Essential for Maximum Androgenic Induction in PB A, Wild-type PB promoter sequences containing boxed HNF-3 motifs were mutated (underlined lowercase characters) as indicated in M1–M3. B, EMSA was conducted using 10 µg LNCaP cell extracts incubated with either wild-type PB-127/-102 or mutant R2 probes (lanes 1–3). M1 disrupted the binding of three complexes (lane 2, a, b, and c), whereas only the higher-order complex a was eliminated by M2 (lane 3). Addition of HNF-3 antibody further removed complexes b and c (lane 4). C, LNCaP cells were transiently transfected with luciferase reporter constructs (0.2 µg/well) containing either wild-type or mutant (M1–M3) PB promoters. Each well also received 0.0125 µg of Renilla vector. Cells were treated with or without 10-8 M DHT for 24 h before harvest. Background activities of cell lysates with no DNA transfection were subtracted from the data obtained in the experimental group, before the normalization with Renilla activities. Results are presented as relative luciferase activity. Data shown here are a representative from at least six independent experiments in triplicate. Error bars indicate SD values. Asterisk indicates where P < 0.01 as compared with the androgen-induced activity in wild-type (WT) reporter. D, Probes (ARBS2/R2-M1, -M2, and ARBS1/R1-M3, Table 1) containing mutant HNF-3 motifs were used in EMSA to determine their interactions with a purified GST-AR-DBD protein described in Materials and Methods.

Overexpressing a Mutant HNF-3 Inhibits PB Activity

View larger version (22K): [in this window] [in a new window]   Fig. 5. Overexpressing a Mutant HNF-3 Inhibits PB Activity A, An empty vector as well as expression vectors corresponding to wild-type HNF-3, N141-466, or C1-294 (0.2 µg per well) were cotransfected with a PB luciferase reporter into LNCaP cells. Cells were treated with or without 10-8 M R1881 for 24 h followed by luciferase assays. B, Different amounts of C1-294 (0.05 µg, 0.15 µg, or 0.25 µg per well) were cotransfected into LNCaP cells with PB reporter. Luciferase activities were determined after 24 h incubation in the presence or absence of androgen. C, In contrast to panel B, C1-294 (0.05 µg, 0.15 µg, or 0.25 µg per well) was cotransfected into LNCaP cells with a mutant PB reporter (M1, in Fig. 4). Error bars indicate SD values. Asterisk indicates P < 0.01 in comparison with androgen-induced activities in control wells, which were transfected with empty vector. D, No significant change in AR protein level was detected by Western blot in cells transiently transfected with wild-type HNF-3, N141-466, or C1-294.

Identification of Two Functional HNF-3 Binding Sites in PSA Core Enhancer

View larger version (54K): [in this window] [in a new window]   Fig. 6. Identification of HNF-3 Binding Motifs in the PSA Core Enhancer A, Two HNF-3 binding sequences (bold arrow) were identified in the PSA core enhancer (-4.2/-3.9 kb) region. The first element (-4122/-4109), designated as PSA1, is adjacent to ARE III (underlined). The second one (-4028/-4005), designated as PSA2, is located in the middle of ARE IIIA and ARE IIIB (underlined). B, EMSA. In vitro synthesized wild-type HNF-3 and mutant proteins (N, FH, and C) were able to bind PSA1 (lanes 3–6) as compared with the TNT blank control (lane 2). The HNF-3 binding was supershifted by the HNF-3 antibody (lane 3 vs. 7). C, Concomitant DNA binding of AR and HNF-3. Radiolabeled oligonucleotide containing both ARE III and PSA1 was incubated with a constant amount (0.1 µg) of a purified GST AR-DBD protein. A slow migrating ternary complex (AR/HNF-3/DNA) (lanes 5–8) was formed as addition of increasing amounts (1, 2, 3, and 4 µl) of in vitro synthesized HNF-3, in contrast to HNF-3 alone (lane 3) or AR alone (lane 4), indicating that HNF-3 and AR can occupy DNA concomitantly. The ternary complex was disrupted by addition of HNF-3 antibody (lane 9). D, EMSA using LNCaP nuclear extract shows the formation of HNF-3/PSA1 complexes (lane 2), which were disrupted by HNF-3 antibody (lane 3). The probe PSA1 (see Table 1 for sequence) contains binding sites for both AR and HNF-3. E, In vitro synthesized wild-type HNF-3 also interacts with PSA2 (lane 4).

A similar mutation assay was performed to determine the biological relevance of these HNF-3 motifs in PSA enhancer. Figure 7A shows two mutant PSA reporter constructs, mPSA1-EP and mPSA2-EP, which were generated by PCR and transfected into LNCaP cells. Primers used for PCR are shown in Table 1. Luciferase activities were measured and compared with wild-type construct. Figure 7B shows that point mutations that abolish HNF-3 binding in either PSA1 (Fig. 6C, lane 2) or PSA2 (lane 4) significantly affected the maximal androgen-induced PSA activities (Fig. 7B, P < 0.01). A 95% reduction of activity in the PSA enhancer has been reported previously by deleting the region corresponding to PSA1 (53). Similarly, the direct interaction between AR and ARE III remained intact when mutant oligonucleotide (Table 1, mPSA1), containing both ARE III and mutant HNF-3 motif, was used in EMSA (Fig. 7D), indicating that the loss of PSA activity is not directly due to the loss of AR/ARE III binding. These results suggest that both HNF-3 motifs are essential for maximal PSA induction by androgen.

View larger version (33K): [in this window] [in a new window]   Fig. 7. Mutations in HNF-3 Sites Inhibited Maximal Androgen Induction of PSA A, Two mutant PSA reporters (mPSA1-EP and mPSA2-EP) were generated by introducing point mutations to HNF-3 motifs in PSA1 and PSA2, individually. B, LNCaP cells were transiently transfected with wild-type and mutant PSA-EP luciferase constructs. Luciferase activities were determined after 24 h incubation in the presence or absence of 10-8 M R1881. Three independent experiments were performed in triplicate. Background activity of untransfected cell lysate was subtracted from the results before normalization with Renilla activities. Error bars indicate SD values. Asterisk indicates where P < 0.01 in comparison with the androgen-induced activity in wild-type reporter. C, Oligonucleotides containing mutant HNF-3 sites (mPSA1 and mPSA2, Table 1) were used in EMSA to determine the HNF-3 binding. D, An oligonucleotide (mPSA1, Table 1 for sequence) containing both ARE III and a mutant HNF-3 motif shows similar binding intensity with a purified GST AR-DBD protein in EMSA.

HNF-3 Binds PSA Enhancer in Vivo

View larger version (73K): [in this window] [in a new window]   Fig. 8. HNF-3 Occupies PSA Enhancer in Vivo A, Schematic diagram of PSA gene 5'-upstream region. Six DNA fragments corresponding to the distal, ARE III, middle, ARE II, and ARE (2 ) regions were amplified in ChIP assays using primers described previously (56 ). B, LNCaP cells were initially grown in RPMI 1640 with 5% charcoal/dextran-treated fetal bovine serum for 3 d. Cells were then incubated for another 48 h with or without 10-8 M DHT treatment. Western blot was performed to determine the expression levels of PSA and HNF-3. C, Formaldehyde-cross-linked chromatins were sheared by sonication into an average size of 0.5–1.0 kb. D, After an overnight IP with AR or HNF-3 antibodies, formaldehyde cross-linking was reversed, and DNA fragments were extracted, followed by PCR amplification (Materials and Methods).

HNF-3 Interacts with AR

View larger version (48K): [in this window] [in a new window]   Fig. 9. HNF-3 Directly Interacts with AR A, AR-Hela cells, with stably integrated flag-AR, were transfected with an HNF-3 expression vector (pcDNA3.1D/V5-HNF-3) and a control LacZ expression vector (pcDNA3.1D/V5-LacZ). Western blot using anti-V5 antibody detected the V5-labeled LacZ (lane 3) and HNF-3 (lane 4) proteins in transfected cells, but not in nontransfected cells (lanes 1 and 2). All cell lysates were immunoprecipitated by an anti-flag M2 affinity gel in the presence of EB. The gel was washed before Western blot analysis. Anti-flag detected flag-AR in all AR-Hela cell precipitates but not in normal Hela cells (lanes 5 vs. 6–10). Anti-V5 detected HNF-3 (lanes 14–16) but not LacZ (lane 13) in AR-Hela precipitates. The AR/HNF-3 interaction was not affected in the presence of 25 µg/ml (lane 15) and 100 µg/ml (lane 16) EB. B, LNCaP cell lysates (1 mg per IP) from DHT-treated or untreated cells were immunoprecipitated with HNF-3 or AR antibody in the presence of EB (0–100 µg/ml) as indicated. Western blot was performed using individual antibodies as indicated. C, A schematic diagram showing a series of AR and HNF-3 subdomains used in in vitro GST pull-down assays. The AR DBD/hinge region and the HNF-3 FH domain are highlighted in black. Two conserved HNF-3

View larger version (41K): [in this window] [in a new window]   Fig. 9A. Continued C-terminal domains designated as region 2 and 3 are in striped boxes. D, Five purified GST-AR fusion proteins (20 µg for each) were bound to glutathione agarose beads, followed by incubation with V5-labled HNF-3 protein synthesized in vitro. Western blot was performed to determine the HNF-3-interacting domain in AR. E, The GST AR fusion proteins DBD/Hinge (50 ng), NT/DBD (250 ng), and DBD/LBD (150 ng) were used in EMSA to determine their DNA binding activities with ARBS-1 on a molar basis. F, The expression of eight V5-labeled HNF-3 subdomains as well as a LacZ protein was confirmed in Western blot (lanes 1–9). These proteins were in vitro synthesized and incubated with the GST-bound AR NT/DBD, DBD/Hinge, and DBD/LBD to determine the AR-interacting region in HNF-3. G, The interaction of AR-DBD/Hinge and HNF-3 FH domain was resistant to the presence of 25–150 µg/ml of EB. LBD, Ligand-binding domain; NT, N-terminal domain.

Responsible Domains for AR/HNF-3 Interaction

	DISCUSSION

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
In this study, we report that an extracellular signal mediator, AR, and a tissue-restricted FH protein, HNF-3, coordinately participate in prostatic gene regulation. HNF-3/FH proteins are a group of transcription factors that share remarkable sequence similarity over their DBD, termed a FH or winged-helix domain (19, 20, 67, 68). The HNF-3/FH proteins are involved in the differentiation of endoderm-derived tissues. This feature has been strikingly conserved among the metazoans (19). The Drosophila homeotic protein, FH, which is equivalent to HNF-3, was found to be essential for the development of the terminal region including the foregut and hindgut (67); the PHA-4 protein, which is a Caenorhabditis elegans HNF-3 equivalent protein, is also required for the formation of terminal gut structures in the worm (44). In mammals, HNF-3 proteins (HNF-3, HNF-3ß, and HNF-3) were originally discovered as liver-enriched factors, because of their ability to bind to the TTR gene promoter (27, 42). In early embryo development, HNF-3 proteins are believed to provide developmental competence to numerous liver-specific genes through their high-affinity DNA elements. This mechanism is essential for the activation of these target genes in later stages (19, 26). The role that HNF-3 and some other developmental factors play in organ differentiation has been proposed as genetic potentiation (19, 26, 69).

We observed strong nuclear staining of HNF-3 in both human and mouse prostate epithelial cells (Fig. 3, C–F). The prostate epithelium, like the epithelium of other urogenital sinus derivatives (bladder and urethra), is derived from the endodermal layer of the embryo. In contrast, Wolffian duct derivatives (epididymis, ductus, deferens, and seminal vesicle) are derived from the mesoderm (17, 70). Understanding the role of HNF-3 in the prostate may provide an insight into the differences in epithelial patterning and developmental programs among prostate and Wolffian-derived organs, which are all androgen dependent (3, 70). The cell type-dependent expression of HNF-3 and other endodermal factors could easily provide an explanation why prostatic differentiation markers such as PSA can be instructively induced in bladder epithelial cells under proper extracellular signals (16), whereas such differentiation, under the same signals, cannot occur in a mesoderm-derived context (3).

Using in vitro gel shift and mutation assays, functional HNF-3 sites were identified in both PSA and PB gene-regulatory regions (Figs. 1, 2, and 6). ChIP assay unambiguously demonstrated that HNF-3 binds to PSA enhancer in vivo (Fig. 8). In our experiments, HNF-3 binding sites were further identified in other prostate-specific gene-regulatory regions. As shown in Fig. 10A, the proximal promoter of the rat prostatic acid phosphatase gene (rPAP) contains an HNF-3 binding sequence at -113/-103 bp. This sequence, as well as an upstream ARE, is well conserved in its human homolog hPAP gene promoter (71). In the hPAP upstream enhancer (-1258/-779 bp), a G/T-rich region (-1183/-1151 bp) contains two HNF-3 binding sites with a putative ARE in the middle. This region also exists in the rPAP enhancer (Fig. 10A), except that only one HNF-3 binding site was found. Importantly, the hPAP enhancer (-1258/-779 bp) is related to the cell-specific expression of hPAP gene (48). In addition, two HNF-3 motifs (at -184/-173 bp and -141/126 bp, Fig. 10A) were found in the rat prostatic steroid-binding protein C1 (PBP C1) gene promoter (72). We confirmed all of these HNF-3 sites experimentally by EMSA (data not shown). The sequences used in EMSA are shown in Table 1. Figure 10B is a schematic diagram showing a striking similarity in the organization of binding motifs for HNF-3 and AR in these highly prostate-specific genes, which suggests that a common functional mechanism may apply.

View larger version (38K): [in this window] [in a new window]   Fig. 10. Similar Organization of HNF-3 and AR Binding Motifs in Prostate Gene-Regulatory Regions A, A summary of HNF-3 binding motifs identified in this study. B, Schematic diagram showing remarkable similarity in the organization of AR and HNF-3 binding motifs in different prostate gene regulatory regions.

X-ray crystallography revealed that the structure of the HNF-3 FH domain resembles the globular domain of linker histone H1 (77). In vitro nucleosome assembly experiments further showed that HNF-3 is able to open compacted chromatin by displacing linker histone in an ATP-independent manner (24, 45). This mechanism of HNF-3 action is mediated through its high-affinity DNA-binding sites as well as the binding of its C terminus to histones H3 and H4 (24). We used transient transfection experiments to examine the role of HNF-3 in prostatic gene regulation. Although transiently transfected DNA does not appear to assemble the same higher-order chromatin structure observed with genomic DNA, certain aspects of nucleosome-mediated regulation can be observed on transiently expressed DNA (46, 47). This has been shown by the studies of Crowe et al. (47), who demonstrated that HNF-3 relieves nucleosome-mediated transcription repression of a liver-specific gene in transient transfection experiments. In our study, mutations of these HNF-3 binding motifs significantly abolished PB and PSA gene activities (Figs. 4 and 7). Overexpression of a mutant HNF-3 protein (C_1-294) suppressed PB promoter activity in a dose-responsive and binding site-dependent manner (Fig. 5). These results are consistent with the assumption that some level of nucleosome assembly occurs on the introduced plasmid. Also, these data are in agreement with previous studies showing that overproduction of mutant HNF-3 proteins deleted in a similar region suppressed multiple liver gene expressions (78, 79). However, in contrast to AR, which binds to ARE in a ligand-dependent manner, HNF-3 occupies the PSA enhancer in the absence of androgen (Fig. 8). The DNA binding of HNF-3 does not seem to be directly associated with PSA activation, which eventually requires the recruitment of ligand-bound AR onto the multiple AREs (Fig. 8). Thus, HNF-3, by itself, is not a strong transactivator; however, the occupancy of HNF-3 in the regulatory region may confer certain transcriptional potential to target prostatic genes that is required for the later recruitment of additional factors as well as activation by a strong and rate-limiting activator (ligand-bound AR) during prostatic differentiation.

Transcriptional regulation depends not only on the interactions between DNA-binding proteins and their respective cis-regulatory elements but also on the interactions among these proteins and with other components of the transactivation machinery. In addition to interacting with various type I or type II coregulators, steroid receptors also make contact with other DNA binding proteins, resulting in modulation of transcriptional activity (80). In the present work, AR was found to directly interact with HNF-3 (Fig. 9), because such interaction was resistant to the presence of a DNA intercalator, EB (Fig. 9, A, B, and G), which serves as a good indicator of DNA-dependent and DNA-independent protein associations (65). In fact, AR has been found to interact with a number of DNA binding transcription factors including activator protein 1 (AP-1) (81), Sma- and mad-related protein 3 (82, 83), nuclear factor B (NFB) (84), sex-determining region Y (SRY) (85), prostate-derived ets factor (86), and other steroid receptors (80). The phenomenon of interactions of AR and these distinct transcription factors was called cross-modulation, which was illustrated by well documented AR interactions with AP-1 and NF B (81, 84). Such cross-talks between different signaling pathways may increase regulatory diversity and provide opportunities for cell-specific response. For example, a testis-expressed protein encoded by the SRY interacts with AR and plays a role in germ cell development (85); a newly discovered prostatic epithelium-specific Ets transcription factor PDEF directly contacts AR and activates PSA gene expression. Here, the adjacent binding of HNF-3 and a direct contact with AR may establish an efficient molecular mechanism for ligand-bound AR to rapidly target correct gene sequences. Crystallographic study of HNF-3/DNA revealed a bend of DNA of about 13° upon HNF-3 binding (77), which may provide favorable DNA conformation for adjacent factors, because chromatin-associated proteins such as high-mobility group box-containing proteins have been well demonstrated for their ability to enhance DNA binding of steroid receptors by generating a sharp bend in DNA (87). A similar mechanism may apply to the current model. It has been shown dynamically that the physical binding of GR to a glucocorticoid response element (GRE) was facilitated by the adjacent HNF-3ß binding (58). This appears to be true for several other liver-specific genes (57, 61). In addition, HNF-3 proteins cooperate with ER to activate vitellogenin B1 gene transcription (88). Thus, cooperation between steroid receptors and HNF-3 proteins may be a general mechanism for the control of various tissue-specific genes.

Strong evidence suggests that HNF-3, like AP-1 (81), SRY (85), and PDEF (86), is another AR-DBD-interacting transcription factor (Fig. 9, D and F). Even though the DBDs of steroid receptors appear to be mainly involved in DNA binding and homodimerization of receptor monomers, mounting evidence suggests that this domain also serves as an interaction interface for other proteins. Among these interacting partners are coactivators (89, 90, 91, 92), factors of basal transcription machinery (93), and other transcription factors (81, 85, 86). Most of these interactions are biologically relevant and result in transcriptional activation or repression. In the present work, IP experiments in LNCaP cells demonstrated that the interaction of endogenous AR and HNF-3 occurs in the presence of androgen (Fig. 9B), which suggests the physical relevance of this interaction. In vitro DNA binding experiments showed that both proteins can adjacently and concomitantly bind respective cis-regulatory elements (Figs. 1D and 6, C and D); these results suggest that such AR/HNF-3 interaction does not inhibit the DNA binding of either protein and that these interaction events are mediated through separate motifs in AR-DBD. The identification of an AR/HNF-3 interaction may extend our understanding of the role of DBD in androgen action and provide a general insight into the regulatory mechanism between HNF-3 proteins and steroid receptors.

In summary, we report multiple HNF-3 cis-acting motifs in prostatic gene regulatory regions and provide evidence that HNF-3 is essential for maximal gene activation by AR. The interaction of HNF-3 and AR on closely positioned regulatory sequences may be a part of a complex that is important for prostate gene transactivation. The expression of HNF-3 in bladder (and urethra) epithelium (28, 29) and the emergence of AR expression in bladder epithelium in tissue recombination (with UGM) (16, 17) further support the involvement of these two factors in prostatic differentiation. We predict that the cooperation between AR and HNF-3 may be an extensive mechanism involving the establishment of the prostatic lineage and differentiated function.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 
Cell Culture and Transfection Assays
The human prostate carcinoma cell lines DU145, LNCaP, and PC-3, the human cervical adenocarcinoma cell line Hela, the human hepatocellular carcinoma cell line HepG2, and the monkey kidney cell line COS-1 were obtained from American Type Culture Collection (Manassas, VA). All cell lines were cultured as recommended by American Type Culture Collection. The AR-Hela cells expressing stably integrated flag-tagged full-length AR were acquired from Dr. Michael Carey (UCLA School of Medicine, Los Angeles, CA) (55). Transient transfection assays were performed using lipofectin reagent (4 µl/well) for LNCaP cells and lipofectamine 2000 for other cell lines. The pRL-CMV containing the Renilla luciferase reporter gene (Promega Corp., Madison, WI) was used to optimize transfection efficiencies for each cell line. Optimal volumes of liposome and transfection durations were obtained and used to get the highest transfection efficiencies. Briefly, cells were seeded at an initial density of 8–10 x 10⁴ per well in 24-well plates 1 d before transfection. The following morning, cells were transfected with plasmid DNA and lipofectin or lipofectamine 2000 in Opti-MEM I-reduced serum medium (31985; Life Technologies, Inc., Gaithersburg, MD). In transfection experiments where AR expression was required, 0.2 µg of rat AR expression vector was transfected for each well. The total amount of plasmid DNA was normalized to 0.8–1 µg/well by the addition of pVZ-1 plasmid. In addition, all samples received 12.5 ng/well of pRL-CMV reporter plasmid. After 4–6 h of transfection, the medium was replaced by MEM (11090; Life Technologies, Inc.) with 5% charcoal/dextran-treated fetal bovine serum (HyClone, Logan, UT) in the presence or absence of 10^-8 M R1881 or DHT. Cells were harvested and lysed with 80 µl passive lysis buffers after 24 h of incubation. The luciferase activity was determined using the dual luciferase reporter assay system (E1960; Promega Corp.) and LUMIstar (BMG Lab. Technologies, Inc., Durham, NC). Background activity of the cell lysate with no DNA transfection was subtracted from the activities obtained from the experimental group. All values were normalized by Renilla activity to correct for the transfection efficiency. Results are presented as relative luciferase activities. Each experiment was repeated at least three separate times in triplicate. In promoter mutagenesis experiments, mean normalized values from samples showing the highest inhibition of promoter activity were compared with those from samples transfected with the wild-type promoter by using Student’s paired t test.

Reporter Plasmids and Expression Vectors
ARR₂PBLuc reporter contains an additional androgen- response region (-244 to -96 nt) fused upstream of the -286/+28-bp PB promoter to enhance the androgen response (36). A 621-bp fragment of PSA minimal promoter (-610 to +11 nt) was amplified by PCR and cloned at the SmaI and XhoI sites of pGL3-basic luciferase vector (Promega Corp.), after which an 823-bp upstream enhancer fragment (-4758 to -3935 bp) containing the -4.1/-3.9 kb PSA core enhancer region was obtained by PCR and inserted upstream of the PSA promoter at SacI and SmaI sites, resulting in PSA-EPLuc reporter construct (EP stands for enhancer/promoter). For promoter mutagenesis studies, three mutant PB promoter fragments and two mutant PSA enhancer fragments were generated using PCR-based site-directed mutagenesis. All mutant and wild-type fragments were cloned into pGL3-basic vector. The primers used for PCR are listed in Table 1.

Mammalian HNF-3 expression vector pRB-HNF-3 (25) was kindly provided by Dr. Kenneth S. Zaret (Fox Chase Cancer Center, Philadelphia, PA). Full-length wild-type HNF-3 cDNA and eight cDNAs encoding differently truncated HNF-3 fragments were PCR amplified and directionally cloned into pcDNA3.1D/V5/His-TOPO expression vector (K4900; Invitrogen, San Diego, CA) in frame with the carboxy-terminal V5 epitope and 6xHis tag. The resulting expression vectors were pHNF-3-WT_1-466, pHNF-3-NT_141-466, pHNF-3-FH_141-294, pHNF-3-CT_1-294, pHNF-3-23_1-385, pHNF-3-3_1-420, pHNF-3-NT_1-180, pHNF-3-CT_295-466, and pHNF-3-DN_59-345. The pcDNA3.1D/V5/His/lacZ is an expression control vector included in the pcDNA3.1 Directional TOPO Expression Kit. The rat AR expression vector (36) and GST-AR_NT/DBD, GST-AR_DBD, and GST-AR_DBD/LBD vectors (66) have been described previously. GST-AR_NT was amplified by PCR and cloned into pRC/CMV (Invitrogen) as a BamHI fragment and subcloned into the BamHI site of pGEX-3X vector (Pharmacia Biotech, Piscataway, NJ) in frame with the GST fusion. GST-AR_LBD was cloned using pCMV/AR6 as the template (66), and the PCR product was digested with BamHI and cloned into the BamHI site of pGEX-3X vector. All reporter and expression constructs were confirmed by sequencing.

EMSAs
Nuclear extract for PC-3 cells was prepared as described previously. Nuclear extract for LNCaP cells was purchased from Geneka Biotechnology, Inc. (Montreal, Quebec, Canada). Recombinant wild-type and truncated HNF-3 proteins were synthesized in vitro using the TNT T7 Quick Coupled Transcription/Translation System (L1170; Promega Corp.). GST-AR fusion proteins were purified as described previously (66). All nuclear extracts and purified proteins were stored in buffers containing 1x concentration of complete protease inhibitor cocktail (Roche Molecular Biochemicals, Mannheim, Germany). All oligonucleotides for EMSAs were synthesized by Integrated DNA Technologies, Inc. (Coralville, IA). The probes were end labeled with T4 polynucleotide kinase (New England Biolabs, Beverly, MA), [-³²P]ATP and purified by 15% PAGE. A typical binding reaction involved a 10-min preincubation with 10 µg of nuclear extract, 1 µg of the nonspecific competitor poly (dI-dC), and buffer D [20 mM HEPES-NaOH (pH 7.9); 100 mM KCl; 0.2 mM EDTA; 1.5 mM MgCl₂; 1 mM dithiothreitol; 20% glycerol; and 1 mM phenylmethylsulfonyl fluoride (PMSF)], followed by a 15-min incubation with 200,000 cpm of radiolabeled probe in a total volume of 20 µl. In oligonucleotide competitions, 200- to 600-fold molar excess of cold, double-stranded oligonucleotide was added to the preincubation mix. In experiments where in vitro synthesized HNF-3 proteins were used, 1–5 µl of 50 µl products from the TNT reaction system were added to the preincubation mix. In supershift analyses, antibodies were added after the binding reaction and incubated for an additional 20 min on ice before electrophoresis. All supershift antibodies (AR, C-19: sc-815X; AR, N-20: sc-816X; HNF-3, C-20: sc-6553X; HNF-3ß, M-20: sc-6554X; HNF3-, N-19: sc-5361X; p-c-Jun: sc-822X; c-Fos: sc-447X; NF-1, H-300: sc-5567X; Oct-1: sc-8024X) were purchased from Santa Cruz Biotechnology, Inc. (Santa Cruz, CA). The concentration of antibody in each EMSA reaction was 0.2 µg/µl. Complexes were resolved by electrophoresis for 2.5 h at 160 V on a 5% native polyacrylamide gel, which was later dried and processed for autoradiography.

Southwestern and Western Blot Analysis
An oligonucleotide containing two tandem copies of wild-type -124/-109 bp (2xR2: 5'-ACCTATTTGTATACTAACCTATTTGTATACTAGATGACA-3'), and another oligonucleotide containing two mutant sites (2xmR2: 5'-ACCTAgaaGTATACTAACCTAgaaGTATACTAGATGACA-3') were radiolabeled by extension of an annealed 10-bp primer, 5'-TGTCATCTAG-3'. (Underscored letters represent the nucleotide replacements in the wild-type TATTTGTAT motif.) The primed oligonucleotide probes were radiolabeled with the Klenow fragment of Escherichia coli DNA polymerase, deoxynucleotide triphosphates, [-³²P]dATP, and [-³²P]dTTP. An oligonucleotide containing two copies of consensus ARBS (see Table 1) was radiolabeled in the same condition and used for a positive control. Nuclear extracts (30 µ g) of PC-3 and LNCaP cells were heated at 70 C for 10 min in 1x lithium dodecyl sulfate loading buffer (Invitrogen), resolved on 4% stacking, 12% resolving SDS-polyacrylamide gel, and electrophoretically transferred to nitrocellulose membranes (Bio-Rad, Hercules, CA). Membranes were soaked in PBS for 15 min, blocked for 4 h at room temperature with buffer A [20 mM HEPES-NaOH (pH 7.8), 50 mM NaCl, 12.5 mg/ml skim milk, 2.5 mg/ml BSA, 200 µg/ml native salmon sperm DNA, 5 µg/ml poly dI-dC, and 50 ng/ml single-stranded DNA], and incubated overnight at room temperature in 2.5 ml of buffer A plus 10⁷ cpm of radiolabeled probe. Membranes were washed three times for 15 min each at room temperature in a washing buffer containing 20 mM HEPES-NaOH, 50 mM NaCl, 1 mg/ml of skim milk, and 0.025% Nonidet P-40. Membranes were dried completely at room temperature before autoradiography.

For Western blot analysis, cell pellets and freshly dissected mouse tissues were collected, sonicated, and centrifuged in cold RIPA buffer [1x PBS (pH 7.4), 1% Nonidet P-40, 0.5% sodium deoxycholate, 0.1% SDS, 1 mM PMSF, and 1x concentration of complete protease inhibitor cocktail]. After the transfer to polyvinylidine difluoride membrane (Invitrogen), membranes were blocked in Tris-buffered saline containing 0.1% Tween 20 and 5% skim milk, and incubated with primary antibody (1:1000 dilution: anti-HNF-3, anti-HNF-3ß, anti-HNF-3, anti-AR, anti-PSA and anti-flag) for 1 h with shaking at room temperature. Anti-flag M2 monoclonal antibody (F3165) was purchased from Sigma (St. Louis, MO). In cases where anti-V5-horseradish peroxidase antibody (R96125; Invitrogen) was used to detect the recombinant V5-tagged HNF-3 proteins, a dilution of 1:5000 was used according to the protocol of the manufacturer. The signal was visualized by enhanced chemiluminescence assay (Amersham Pharmacia Biotech, Arlington Heights, IL).

Immunohistochemical Assays
The individual prostate lobes (anterior prostate, dorsal prostate, lateral prostate, and ventral prostate) were dissected from 10-wk-old CD-1 mice and fixed in 10% buffered formalin. Human prostate tissues were obtained from the Department of Pathology of Vanderbilt University Medical Center (Nashville, TN). After processing and embedding in paraffin, 5-µm sections were cut for immunohistochemical detection of HNF-3 proteins. Sections were deparaffinized, rehydrated, and placed in 1 M urea. Antigenic sites were exposed by microwaving the sections for 30 min at 95-99 C before the removal of endogenous peroxidase activity with DAKO peroxidase blocking reagent (DAKO Corp., Carpinteria, CA). Nonspecific binding was blocked by incubating the sections with Vectastain rabbit normal serum (Vectastain ABC Kit, PK-6105, Vector Laboratories, Inc., Burlingame, CA) for 30 min. The sections were incubated with anti-HNF-3 (C-20) antibody overnight at 4 C (1:1500 dilution), washed in PBS (pH 7.4), and incubated with Vectastain biotinylated antigoat IgG at room temperature for 30 min. The sections were washed with PBS and incubated for 30 min with Vectastain streptavidin. After additional washes with PBS, peroxidase activity was detected using 3',3'-diaminobenzidine tetrahydrochlorate (Liquid DAB Substrate-Chromagen System, DAKO Corp.). The reaction was terminated in distilled water, and the sections were counterstained with Harris hematoxylin (Surgipath, Richmond, VA), dehydrated, and permanently mounted with cytoseal XYL (Stephens Scientific, Kalamazoo, MI).

ChIP
The procedure and PCR primers used in this study were described previously (56). LNCaP cells were initially grown in RPMI 1640 with 5% charcoal/dextran-treated fetal bovine serum (HyClone). After 3 d of cultivation, cells were either treated with 10^-8 M DHT or continued to grow in the androgen-depleted medium. After 48 h of treatment, cells were washed with PBS and cross-linked with 1% formaldehyde at 37 C for 10 min. Cells were scraped into conical tube, pelleted for 4 min at 2000 rpm at 4 C, resuspended in SDS lysis buffer [1% SDS, 10 mM EDTA, 50 mM Tris-HCl (pH 8.1), 1x proteinase inhibitor cocktail] for 200 µl per 10⁶ cells, and sonicated with four to five sets of 10-sec pulses at an 80% maximum power (Fisher Sonic Dismembrator, model 50; Fisher Scientific, Pittsburgh, PA). After centrifugation for 10 min, supernatants were collected and diluted 1:10 in ChIP dilution buffer [0.01% SDS, 1.1% Triton X-100, 1.2 mM EDTA, 16.7 mM Tris-HCl (pH 8.1), 167 mM NaCl], followed by preclearing for 30 min with 3 µg of sonicated salmon sperm DNA with protein A agarose (80 µl of 50% slurry in 10 mM Tris-HCl, 1 mM EDTA). IP was performed overnight at 4 C with specific antibodies. Protein A agarose (60 µl) with salmon sperm DNA was added for 1 h with rotation to collect the complex. Beads were sequentially washed for 5 min each with low-salt wash buffer (0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl, 150 mM NaCl), high-salt wash buffer (0.1% SDS, 1% Triton X-100, 2 mM EDTA, 20 mM Tris-HCl, 500 mM NaCl), LiCl wash buffer (0.25 M LiCl, 1% Nonidet P-40, 1% deoxycholate, 1 mM EDTA, 10 mM Tris-HCl) and twice with TE buffer (10 mM Tris-HCl, 1 mM EDTA). The complex was eluted twice with 250 µl of elution buffer (1% SDS, 0.1 M NaHCO₃) and eluates were pooled. The formaldehyde cross-linking was reversed by adding 20 µl 5 M NaCl and incubating for 6–8 h at 65 C. Eluates were incubated for an additional 1 h at 45 C with 2 µl of 10 mg/ml Proteinase K. DNA was extracted using QIAquick Spin Column (Qiagen) and 3–5 µl of extracted DNA was used in each PCR amplification.

IP Analysis
DHT-treated or untreated LNCaP cells (0.5–1x10⁷) were washed three times with cold PBS and lysed with 1 ml of nondenaturing lysis buffer (50 mM Tris, 150 mM NaCl, 10 mM EDTA, 0.02% NaN₃, 50 mM NaF, 1 mM Na₃VO₄, 1% NP-40, 1 mM PMSF, 0.5 mM dithiothreitol, and 1x concentration of complete protease inhibitor cocktail). After sonication and centrifugation, 1 mg of total cell lysate for each reaction was incubated at 4 C for 3 h with 20 µl (dry volume) protein G-Sepharose beads (Amersham Biotech), which were conjugated with 1 µg experimental antibody or mock antibody. BSA (1 mg) was added to quench the nonspecific binding. IPs were performed in the presence of EB (0–100 µg/ml as indicated in Results) to disrupt DNA-protein interaction (65). Beads were washed four times with lysis buffer and once with PBS for 5 min each with rotation, which was followed by Western blot. The anti-AR (441) mouse monoclonal IgG (sc-7305; Santa Cruz Biotechnology, Inc.) was used for immunoprecipitate AR, and the anti-HNF-3 (C-20) goat polyclonal IgG (sc-6553; Santa Cruz Biotechnology, Inc.) was used to immunoprecipitate HNF-3. For IP experiments in AR-Hela cells, anti-Flag M2 affinity gel was used to immunoprecipitate the flag-tagged AR, according to the protocol provided in the Flag Tagged Protein Immunoprecipitation Kit (FLAGIPT-1; Sigma).

In Vitro Translation of HNF-3 Proteins and GST Pull-Down Assay
HNF-3 expression vectors with a T7 promoter were transcribed and translated in vitro using the TNT T7 Quick Coupled Transcription/Translation System (L1170; Promega Corp.). A standard reaction involved a 90-min incubation at 30 C with 40 µl of TNT Quick Master, 2 µl of cold 2 mM methionine, and 2 µg of plasmid DNA in a final volume of 50 µl. A LacZ expression vector was translated using the same conditions as a control. In vitro translated recombinant HNF-3 and LacZ proteins were labeled with a C-terminal V5-epitope and were used immediately for in vitro binding reactions.

GST-AR fusion proteins were purified as described previously (66). For GST pull-down assays, 50 µl swelled glutathione agarose beads (G-4510; Sigma) were incubated with 20 µg GST or GST-AR fusion proteins for each reaction. GST-bound beads were equilibrated with PBS-T binding buffer [1x PBS (pH 7.4), 1% Tween 20, and protease inhibitors] and incubated for 2 h at 4 C with 5–10 µl products from the TNT reactions. Complexes were washed four times with 1.5 ml of cold binding buffer, heated for 10 min at 70 C in 1x LDS loading buffer, and separated by SDS-PAGE, after which V5-horseradish peroxidase antibody was used in a standard Western blot to detect proteins that interact with AR in vitro.

	ACKNOWLEDGMENTS

 
We thank Dr. Michael Carey for providing the AR-Hela cells, Dr. Scott Shappell for providing human prostate tissues, and Dr. Kenneth S. Zaret for providing the HNF-3 expression vector. We are grateful to Dr. Marie-Claire Orgebin-Crist, Dr. Susan Kasper, and Dr. Simon W. Hayward for reading the manuscript. We thank Manik Paul for technical assistance. We are also indebted to Dr. Sunil K. Halder, Dr. Chaitanya Nirodi, and Dr. William Tu for their experimental advice.

	FOOTNOTES

 
This work was supported by NIH Grants R01-DK-55748 and R01-CA76142, the Frances Williams Preston Laboratories of the T. J. Martell Foundation and the grant from the Terry Fox Foundation (to P.S.R.).

Abbreviations: AP-1, Activator protein 1; AR, androgen receptor; ARBS, AR binding site; ARE, androgen response element; ARR, androgen response region; ChIP, chromatin immunoprecipitation; DBD, DNA-binding domain; DHT, dihydrotestosterone; E12.5, embryonic d 12.5; EB, ethidium bromide; ER, estrogen receptor; FH, forkhead; GR, glucocorticoid receptor; GST, glutathione-S-transferase; HNF-3, hepatocyte nuclear factor-3; hPAP, human prostatic acid phosphatase; IP, immunoprecipitation; mPSA, mutant PSA; 2xmR2, two copies of mutant R2; nt, nucleotide; PAP, prostatic acid phosphatase; PB, probasin; PMSF, phenylmethylsulfonic fluoride; PSA, prostate-specific antigen; PSA-EP, PSA-enhancer/promoter; 2xR2, two copies of R2; rPAP, rat PAP; SDS, sodium dodecyl sulfate; SRY, sex-determining region Y; TF, transcription factor; TNT, transcription/translation; TTR, transthyretin; UGM, urogenital sinus mesenchyme; VP, ventral prostate.

Received for publication January 20, 2003. Accepted for publication May 6, 2003.

	REFERENCES

TOP ABSTRACT INTRODUCTION RESULTS DISCUSSION MATERIALS AND METHODS REFERENCES

 

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Nuclear Receptors:   AR

Ligands:   Dihydrotestosterone  |  R1881

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