Defining a functional androgen responsive element in the 5' far upstream flanking region of the prostate-specific antigen gene

The Importance of Time to Prostate-Specific Antigen (PSA) Nadir after Primary Androgen Deprivation Therapy in Hormone-Naïve Prostate Cancer Patients

Prostate-specific antigen (PSA) is currently the most useful biomarker for detection of prostate cancer (PCa). The ability to measure serum PSA levels has affected all aspects of PCa management over the past two decades. The standard initial systemic therapy for advanced PCa is androgen-deprivation therapy (ADT). Although PCa patients with metastatic disease initially respond well to ADT, they often progress to castration-resistant prostate cancer (CRPC), which has a high mortality rate. We have demonstrated that time to PSA nadir (TTN) after primary ADT is an important early predictor of overall survival and progression-free survival for advanced PCa patients. In in vivo experiments, we demonstrated that the presence of fibroblasts in the PCa tumor microenvironment can prolong the period for serum PSA decline after ADT, and enhance the efficacy of ADT. Clarification of the mechanisms that affect TTN after ADT could be useful to guide selection of optimal PCa treatment strategies. In this review, we discuss recent in vitro and in vivo findings concerning the involvement of stromal–epithelial interactions in the biological mechanism of TTN after ADT to support the novel concept of “tumor regulating fibroblasts”.

Long terminal repeats act as androgen-responsive enhancers for the PSA-kallikrein locus

The androgen receptor (AR) signaling pathway is a common therapeutic target for prostate cancer, because it is critical for the survival of both hormone-responsive and castrate-resistant tumor cells. Most of the detailed understanding that we have of AR transcriptional activation has been gained by studying classical target genes. For more than two decades, Kallikrein 3 (KLK3) (prostate-specific antigen) has been used as a prototypical AR target gene, because it is highly androgen responsive in prostate cancer cells. Three regions upstream of the KLK3 gene, including the distal enhancer, are known to contain consensus androgen-responsive elements required for AR-mediated transcriptional activation. Here, we show that KLK3 is one of a specific cluster of androgen-regulated genes at the centromeric end of the kallikrein locus with enhancers that evolved from the long terminal repeat (LTR) (LTR40a) of an endogenous retrovirus. Ligand-dependent recruitment of the AR to individual LTR-derived enhancers results in concurrent up-regulation of endogenous KLK2, KLK3, and KLKP1 expression in LNCaP prostate cancer cells. At the molecular level, a kallikrein-specific duplication within the LTR is required for maximal androgen responsiveness. Therefore, KLK3 represents a subset of target genes regulated by repetitive elements but is not typical of the whole spectrum of androgen-responsive transcripts. These data provide a novel and more detailed understanding of AR transcriptional activation and emphasize the importance of repetitive elements as functional regulatory units.

Androgen dependent transcription of a mouse prostatic protein gene, PSP94: involvement of estrogen receptors

Prostatic secretory protein 94 (PSP94) is a prostatic protein found in both humans and rodents. As with other prostatic proteins, expression of this protein is regulated by androgens. In order to understand the androgen-responsive transcriptional regulation mechanisms involved, the present study aimed to identify and characterize the promoter activity of the gene. The 5'flanking (5'f) region of mouse PSP94 (mPSP94) gene was cloned and introduced into a vector upstream of the luciferase reporter gene. A Chinese hamster ovarian cell line, CHO, and a human prostate adenocarcinoma cell line, LNCaP, were transiently transfected with our reporter constructs along with an androgen receptor expression vector, and treated with dihydrotestosterone. Reporter gene assay revealed that the 5'f region of mPSP94 gene was indeed responsible for the androgen-dependent transcription. Subsequent deletion and mutation analysis indicated that the androgen responsive element (ARE)-like sequence at position -93 from the transcription start site was primarily responsible for androgen dependency. Interestingly, when estrogen receptor (ER) α was co-transfected, the androgen-dependent transcription was substantially increased. However, ERα-dependent enhancement of androgen responses was not observed when estrogen responsive element (ERE)-like motifs of the promoter region were deleted. Administration of estrogen did not influence the enhancement associated with ERα, although an anti-estrogen suppressed such effects. Collectively, these data suggest that the androgen-dependent transcription of the mPSP94 gene was co-regulated/modulated by the presence of ERα via ERE-like motifs.

Androgen receptor signaling and mutations in prostate cancer

Normal and neoplastic growth of the prostate gland are dependent on androgen receptor (AR) expression and function. Androgenic activation of the AR, in association with its coregulatory factors, is the classical pathway that leads to transcriptional activity of AR target genes. Alternatively, cytoplasmic signaling crosstalk of AR by growth factors, neurotrophic peptides, cytokines or nonandrogenic hormones may have important roles in prostate carcinogenesis and in metastatic or androgen-independent (AI) progression of the disease. In addition, cross-modulation by various nuclear transcription factors acting through basal transcriptional machinery could positively or negatively affect the AR or AR target genes expression and activity. Androgen ablation leads to an initial favorable response in a significant number of patients; however, almost invariably patients relapse with an aggressive form of the disease known as castration-resistant or hormone-refractory prostate cancer (PCa). Understanding critical molecular events that lead PCa cells to resist androgen-deprivation therapy is essential in developing successful treatments for hormone-refractory disease. In a significant number of hormone-refractory patients, the AR is overexpressed, mutated or genomically amplified. These genetic alterations maintain an active presence for a highly sensitive AR, which is responsive to androgens, antiandrogens or nonandrogenic hormones and collectively confer a selective growth advantage to PCa cells. This review provides a brief synopsis of the AR structure, AR coregulators, posttranslational modifications of AR, duality of AR function in prostate epithelial and stromal cells, AR-dependent signaling, genetic changes in the form of somatic and germline mutations and their known functional significance in PCa cells and tissues.

Kallikreins on steroids: structure, function, and hormonal regulation of prostate-specific antigen and the extended kallikrein locus

The 15 members of the kallikrein-related serine peptidase (KLK) family have diverse tissue-specific expression profiles and putative proteolytic functions. The kallikrein family is also emerging as a rich source of disease biomarkers with KLK3, commonly known as prostate-specific antigen, being the current serum biomarker for prostate cancer. The kallikrein locus is also notable because it is extraordinarily responsive to steroids and other hormones. Indeed, at least 14 functional hormone response elements have been identified in the kallikrein locus. A more comprehensive understanding of the transcriptional regulation of kallikreins may help the field make more informed hypotheses about the physiological functions of kallikreins and their effectiveness as biomarkers. In this review, we describe the organization of the kallikrein locus and the structure of kallikrein genes and proteins. We also focus on the transcriptional regulation of kallikreins by androgens, progestins, glucocorticoids, mineralocorticoids, estrogens, and other hormones in animal models and human prostate, breast, and reproductive tract tissues. The interaction of the androgen receptor with androgen response elements in the promoter and enhancer of KLK2 and KLK3 is also summarized in detail. There is evidence that all kallikreins are regulated by multiple nuclear receptors. Yet, apart from KLK2 and KLK3, it is not clear whether all kallikreins are direct transcriptional targets. Therefore, we argue that gaining more detailed information about the mechanisms that regulate kallikrein expression should be a priority of future studies and that the kallikrein locus will continue to be an important model in the era of genome-wide analyses.

Intronic DNA elements regulate androgen-dependent expression of the murine Nkx3.1 gene

Nkx3.1 is a well-conserved homeobox gene that is involved in development, differentiation and maintenance of prostate epithelial cells. Nkx3.1 expression is induced by androgen in prostate epithelia and, as such, our interest is to understand the mechanism(s) for this androgen-dependent expression in normal epithelial cells. In this report, we show that the region of DNA sequence 2.7 kilobases in front of the mouse Nkx3.1 gene drives enhanced transcription in prostate epithelia cells; however, this segment was not capable of androgen-directed regulation. Among the multiple, potential androgen response elements (AREs) identified by scanning sequences near and within the gene, two sequences within the intron of the murine Nkx3.1 gene were demonstrated to confer androgen-dependent transcription in reporter gene transfection experiments. Each of the elements, termed ARE A and ARE B, contained a 6-base pair core sequence, TGTTCT, that has been described as an androgen receptor half-site binding sequence, separated by 498 base pairs of DNA. Both of the intronic half-sites bind activated androgen receptor from a variety of sources, albeit with different apparent affinities. This region of the Nkx3.1 gene demonstrates a high degree of conservation among diverse species and mutagenesis experiments demonstrated that both elements are required for androgen stimulation. Taken together, our study shows that androgen-dependent transcription of the mouse Nkx3.1 gene is conferred through a noncanonical element within the intron of the gene.

Direct progesterone receptor and indirect androgen receptor interactions with the kallikrein-related peptidase 4 gene promoter in breast and prostate cancer

Kallikrein 4 (KLK4) is a member of the human KLK gene family of serine proteases, many of which are implicated in hormone-dependent cancers. Like other KLKs, such as KLK3/PSA and KLK2, KLK4 gene expression is also regulated by steroid hormones in hormone-dependent cancers, although the transcriptional mechanisms are ill defined. Here, we have investigated the mechanisms mediating the hormonal regulation of KLK4 in breast (T47D) and prostate (LNCaP and 22Rv1) cancer cells. We have shown that KLK4 is only expressed in breast and prostate cancers that express the progesterone receptor (PR) and androgen receptor (AR), respectively. Expression analysis in PR- and AR-positive cells showed that the two predominant KLK4 variants that use either TIS1 or TIS2a/b are both up-regulated by progesterone in T47D cells and androgens in LNCaP cells. Two putative hormone response elements, K4.pPRE and K4.pARE at -2419 bp and -1005 bp, respectively, were identified in silico. Electrophoretic mobility shift assays and luciferase reporter experiments suggest that neither K4.pARE nor approximately 2.8 kb of the KLK4 promoter interacts directly with the AR to mediate KLK4 expression in LNCaP and 22Rv1 cells. However, we have shown that K4.pPRE interacts directly with the PR to up-regulate KLK4 gene expression in T47D cells. Further, chromatin immunoprecipitation experiments showed a time-dependent recruitment of the PR to the KLK4 promoter (-2496 to -2283), which harbors K4.pPRE. This is the first study to show that progesterone-regulated KLK4 expression in T47D cells is mediated partly by a hormone response element (K4.pPRE) at -2419 bp.

The Tissue Kallikrein Family of Serine Proteases: Functional Roles in Human Disease and Potential as Clinical Biomarkers

Prostate specific antigen (PSA) or human kallikrein 3 (hK3) has long been an effective biomarker for prostate cancer. Now, other members of the tissue kallikrein (KLK) gene family are fast becoming of clinical interest due to their potential as prognostic biomarkers. particularly for hormone dependent cancers. The tissue kallikreins are serine proteases that are encoded by highly conserved multi-gene family clusters in rodents and humans. The rat and mouse loci contain 10 and 25 functional genes, respectively, while the human locus at 19q 13.4 contains 15 genes. The structural organization and size of these genes are similar across species; all genes have 5 coding exons that encode a prepro-enzyme. Although the physiological activators of these zymogens have not been described, in vitro biochemical studies show that some kallikreins can auto-activate and others can activate each other, suggesting that the kallikreins may participate in an enzymatic cascade similar to that of the coagulation cascade. These genes are expressed, to varying degrees, in a wide range of tissues suggesting a functional involvement in a diverse range of physiological and pathophysiological processes. These include roles in normal skin desquamation and psoriatic lesions, tooth development, neural plasticity, and Alzheimer's disease (AD). Of particular interest is the expression of many kallikreins in prostate, ovarian, and breast cancers where they are emerging as useful prognostic indicators of disease progression.

Antisense-MDM2 sensitizes LNCaP prostate cancer cells to androgen deprivation, radiation, and the combination in vivo

PURPOSE

To test the effects of antisense (AS)-MDM2 alone and with androgen deprivation (AD), radiotherapy (RT), and AD + RT on wild-type LNCaP cells in an orthotopic in vivo model.

METHODS

Androgen-sensitive LNCaP cells were grown in the prostates of nude mice. Magnetic resonance imaging-based tumor volume and serum prostate-specific antigen (PSA) measurements were used to assess effects on tumor response. Tumor response was measured by biochemical and tumor volume failure definitions and doubling time estimates from fitted PSA and tumor volume growth curves. Expression of MDM2, p53, p21, and Ki-67 was quantified using immunohistochemical staining and image analysis of formalin-fixed tissue, analogous to methods used clinically.

RESULTS

Antisense-MDM2 significantly inhibited the growth of LNCaP tumors over the mismatch controls. The most significant increase in tumor growth delay and tumor doubling time was from AS-MDM2 + AD + RT, although the effect of AS-MDM2 + AD was substantial. Expression of MDM2 was significantly reduced by AS-MDM2 in the setting of RT.

CONCLUSIONS

This is the first in vivo investigation of the effects of AS-MDM2 in an orthotopic model and the first to demonstrate incremental sensitization when added to AD and AD + RT. The results with AD underscore the potential to affect micrometastatic disease, which is probably responsible for treatment failure in 30-40% of men with high-risk disease.

Androgen regulation of the human hair follicle: the type I hair keratin hHa7 is a direct target gene in trichocytes

Previous work had shown that most members of the complex human hair keratin family were expressed in terminal scalp hairs. An exception to this rule was the type I hair keratin hHa7, which was only detected in some but not all vellus hairs of the human scalp (Langbein et al, 1999). Here we show that hHa7 exhibits constitutive expression in medullary cells of all types of male and female sexual hairs. Medullated beard, axillary, and pubic hairs arise during puberty from small, unmedullated vellus hairs under the influence of circulating androgens. This suggested an androgen-controlled expression of the hHa7 gene. Further evidence for this assumption was provided by the demonstration of androgen receptor (AR) expression in the nuclei of medullary cells of beard hairs. Moreover, homology search for the semipalindromic androgen receptor-binding element (ARE) consensus sequence GG(A)/(T)ACAnnnTGTTCT in the proximal hHa7 promoter revealed three putative ARE motifs. Electrophoretic mobility shift assays demonstrated the specific binding of AR to all three hHa7 AREs. Their function as AR-responsive elements, either individually or in concert within the hHa7 promoter, could be further confirmed by transfection studies with or without an AR expression vector in PtK2 and prostate PC3-Arwt cells, respectively in the presence or absence of a synthetic androgen. Our study detected hHa7 as the first gene in hair follicle trichocytes whose expression appears to be directly regulated by androgens. As such, hHa7 represents a marker for androgen action on hair follicles and might be a suitable tool for investigations of androgen-dependent hair disorders.

Tip110, the Human Immunodeficiency Virus Type 1 (HIV-1) Tat-interacting Protein of 110 kDa as a Negative Regulator of Androgen Receptor (AR) Transcriptional Activation

Upon binding to androgen, androgen receptor (AR) can activate expression of target genes through its direct binding to the androgen-responsive elements (AREs), which are located within the target gene promoters and/or enhancers. A number of cellular proteins have been identified as co-regulators to regulate this transactivation process. One common structural feature among these co-regulators is the presence of the LXXLL motif (X, any amino acid), the so-called nuclear receptor (NR) box, through which binding of these regulatory proteins to AR occurs. We have recently shown that Tip110 functions to potentiate the transactivation activity of human immunodeficiency virus type I (HIV-1) Tat protein. In this study, we report that Tip110 is a potent AR-binding protein that can suppress AR activity. Tip110 bound to AR in an NR box-dependent manner and inhibited AREs-mediated reporter gene expression. The inhibitory effects were abolished by removal of the NR box. Moreover, knock-down of the constitutive Tip110 expression significantly augmented AR transcriptional activation. In agreement with these findings, Tip110 overexpression blocked the prostate-specific antigen (PSA) gene, a well characterized target gene of AR from expression in LNCaP cells. Further analysis revealed that Tip110 prevented the complex formation between AR and AREs. Taken together, these results indicate that Tip110 is a negative regulator of AR transcriptional activation, and may be directly involved in AR-related developmental, physiological, and pathological processes.

Association between genetic polymorphisms in the prostate-specific antigen gene promoter and serum prostate-specific antigen levels

BACKGROUND

Recent evidence suggests that genetic variation in the promoter of the prostate-specific antigen (PSA) gene may contribute to individual variation in serum PSA levels. However, polymorphisms associated with variations in PSA levels have not been identified.

METHODS

We used the polymerase chain reaction to amplify the promoter region of the PSA genes (nucleotide positions -3873 to -5749 with respect to the start of transcription) of 409 healthy white men at risk for lung disease. Polymerase chain reaction products were sequenced to identify polymorphisms in the PSA gene promoter and to genotype the men for common single nucleotide polymorphisms (SNPs) and were cloned into luciferase reporter constructs to assay PSA promoter activity in human LNCaP prostate cancer cells. Analysis of variance was used to test the association of polymorphism frequencies with mean serum PSA levels. All statistical tests were two-sided.

RESULTS

The -4643G/A SNP (G allele) had a 21.2% prevalence and was associated with increases in serum PSA levels (P =.017) and PSA promoter activity (P<.001). The -5412C/T SNP (C allele) had a 22.0% prevalence and was associated with an increase in serum PSA levels (P =.0015). The -5429T/G SNP (G allele) had a 23.0% prevalence, was associated with an increase in serum PSA levels (P =.021), and was in linkage disequilibrium with the -5412C/T SNP. The promoter activity of the -5412 C/-5429 G haplotype was higher than that of the -5412 T/-5429 T haplotype (P<.001).

CONCLUSIONS

Genetic variations in the PSA promoter are associated with serum PSA levels in men without prostatic disease. PSA promoter genotype information may help to refine models of PSA cutoff values.

Biology of prostate-specific antigen

Prostate-specific antigen (PSA) is an androgen-regulated serine protease produced by both prostate epithelial cells and prostate cancer (PCa) and is the most commonly used serum marker for cancer. It is a member of the tissue kallikrein family, some of the members of which are also prostate specific. PSA is a major protein in semen, where its function is to cleave semenogelins in the seminal coagulum. PSA is secreted into prostatic ducts as an inactive 244-amino acid proenzyme (proPSA) that is activated by cleavage of seven N-terminal amino acids. PSA that enters the circulation intact is rapidly bound by protease inhibitors, primarily alpha1-antichymotrypsin, although a fraction is inactivated in the lumen by proteolysis and circulates as free PSA. This proteolytic inactivation, as well as the cleavage of proPSA to PSA, is less efficient in PCa. Serum total PSA levels are increased in PCa, and PSA screening has dramatically altered PCa presentation and management. Unfortunately, although high PSA levels are predictive of advanced PCa, a large fraction of organ-confined cancers present with much lower total PSA values that overlap those levels found in men without PCa. Measurement of free versus total PSA can increase specificity for PCa, and tests under development to measure forms of proPSA may further enhance the ability to detect early-stage PCa. PSA is also widely used to monitor responses to therapy and is under investigation as a therapeutic target. Finally, recent data indicate that there may be additional roles for PSA in the pathogenesis of PCa.

Novel prostate-specific promoter derived from PSA and PSMA enhancers

The expression of prostate-specific membrane antigen (PSMA) and prostate-specific antigen (PSA), two well characterized marker proteins, remains highly active in the hormone refractory stage of prostate cancer. In this study, an artificial chimeric enhancer (PSES) composed of two modified regulatory elements controlling the expression of PSA and PSMA genes was tested for its promoter activity and tissue specificity using the reporter system. As a result, this novel PSES promoter remained silent in PSA- and PSMA-negative prostate and non-prostate cancer cell lines, but mediated high levels of luciferase in PSA- and PSMA-expressing prostate cancer cell lines in the presence and absence of androgen. To determine whether PSES could be used for in vivo gene therapy of prostate cancer, a recombinant adenovirus, Ad-PSES-luc, was constructed. Luciferase activity in prostate cancer cell lines mediated by Ad-PSES-luc was 400- to 1000-fold higher than in several other non-prostate cell lines, suggesting the high tissue-specificity of the PSES promoter in an adenoviral vector. Finally, recombinant virus Ad-PSES-luc was injected into mice to evaluate the tissue-discriminatory promoter activity in an experimental animal. Unlike Ad-CMV-luc, the luciferase activity from systemic injection of Ad-PSES-luc was fairly low in all major organs. However, when injected into prostate, Ad-PSES-luc drove high luciferase activity almost exclusively in prostate and not in other tissues. Our results demonstrated the potential use of PSES for the treatment of androgen-independent prostate cancer patients.

Bicalutamide functions as an androgen receptor antagonist by assembly of a transcriptionally inactive receptor

Prostate cancers (PCa) that relapse after androgen deprivation therapy invariably express high levels of androgen receptor (AR) and AR-regulated genes. Most do not respond to secondary hormonal therapies, including AR antagonists, and the mechanisms of AR activation in these clinically androgen-independent tumors are unclear. Bicalutamide, the most widely used AR antagonist, is a competitive antagonist shown previously to stabilize AR association with cytosolic heat shock protein complexes. This study found nuclear AR expression in bicalutamide-treated androgen-independent PCa and found that bicalutamide could stimulate AR nuclear translocation. Moreover, specific DNA binding by the bicalutamide-liganded AR was demonstrated in vivo using a VP16-AR fusion protein and was confirmed by chromatin immunoprecipitation showing binding to the prostate-specific antigen enhancer in LNCaP PCa cells. Nonetheless, bicalutamide could not stimulate interactions between the AR N and C termini or recruitment of steroid receptor coactivator proteins (SRC-1 or -2), although SRC transfection augmented AR activity in the presence of dihydrotestosterone and inhibitory concentrations of bicalutamide. These results demonstrate that bicalutamide stimulates the assembly of a transcriptionally inactive AR on DNA and support altered coactivator (or corepressor) expression as a mechanism of bicalutamide-resistant androgen-independent PCa.

Androgen and retinoic acid interaction in LNCaP cells, effects on cell proliferation and expression of retinoic acid receptors and epidermal growth factor receptor

BACKGROUND

Modulation of the expression of retinoic acid receptors (RAR) alpha and gamma in adult rat prostate by testosterone (T) suggests that RAR signaling events might mediate some of the androgen effects on prostate cells.

METHOD

In this study, we examined the interactions between T and retinoic acid (RA) in cell growth of human prostate carcinoma cells, LNCaP, and their relationship with the expression of RAR and epidermal growth factor receptor (EGF-R).

RESULTS

Both T and RA, when administered alone, stimulated 3H-thymidine incorporation in LNCaP cells in a dose-dependent manner; the effect of each agent was reciprocally attenuated by the other agent. Testosterone treatment of LNCaP cells also resulted in dose dependent, biphasic increases in RAR alpha and gamma mRNAs; increases paralleled that of 3H-thymidine incorporation and were attenuated by the presence of 100 nM RA. These results suggest a link between RAR signaling and the effect of T on LNCaP cell growth. Gel electrophoretic mobility shift assays revealed the presence of putative androgen responsive element (ARE) in the promoter region of RAR alpha gene, suggesting that a direct AR-DNA interaction might mediate the effects of T on RAR alpha gene. Furthermore, treatment of LNCaP cells with 20 nM T resulted in an increase in EGF-R. In contrast, EGF-R was suppressed by 100 nM RA that also suppressed the effect of T.

CONCLUSIONS

Current results demonstrate interactions between T and RA in the expression of RARs and cell growth in LNCaP cells. The presence of putative ARE in the promoter of the RAR alpha gene suggests that AR-DNA interaction might mediate the effects of T on RAR alpha gene. The opposite effects of T and RA on the expression of RAR and EGF-R suggest that signal events of these receptors might be involved in the interaction between T and RA in the control of LNCaP cell growth.

Transcription-targeted gene therapy for androgen-independent prostate cancer

The Escherichia coli enzyme (purine nucleoside phosphorylase, PNP) gene is delivered directly into PC3 tumors by one injection of replication-deficient human type-5 adenovirus (Ad5). Expressed PNP converts the systemically administered prodrug, 6MPDR, to a toxic purine, 6MP, causing cell death. We sought to increase the specificity of recombinant Ad vectors by controlling PNP expression with the promoter region from the androgen-dependent, prostate-specific rat probasin (Pb) gene. To increase its activity, the promoter was combined with the SV40 enhancer (SVPb). Cell lines were transfected with plasmids containing both a reporter gene, under SVPb control, and a reference gene cassette to allow normalization of expression levels. Plasmids expressed approximately 20-fold more reporter in prostate cancer than in other cells, but surprisingly, the SVPb element was both androgen-independent and retained substantial prostate specificity. Killing by Ad5-SVPb-PNP vector of cell lines cultured with 6MPDR for 6 days was 5- to 10-fold greater in prostate cancer than in liver or lung cells. In vivo, a single intratumoral injection of Ad5-SVPb-PNP (4 x 10(8) pfu), followed by 6MPDR administration twice daily for 6 days, significantly suppressed the growth of human prostate tumors in nude mice and increased their survival compared to control animals. Thus, the androgen-independent, prostate-targeting Ad5 vector reduces human prostate cancer growth significantly in vitro and in vivo. This first example of an androgen-independent vector points the way toward treatment of emerging androgen-independent prostate cancer in conjunction with hormone ablation therapy at a time when the tumor burden is low.

Formation of the androgen receptor transcription complex

Androgen receptor (AR) is required for sexual differentiation and is implicated in the development of prostate cancer. Here we describe distinct functions for cofactor proteins and gene regulatory elements in the assembly of AR-mediated transcription complexes. The formation of an activation complex involves AR, coactivators, and RNA polymerase II recruitment to both the enhancer and promoter, whereas the formation of a repression complex involves factors bound only at the promoter and not the enhancer. These results suggest a model for the functional coordination between the promoter and enhancer in which communication between these elements is established through shared coactivators in the AR transcription complex.

Expression of prostate specific antigen (PSA) is negatively regulated by p53

Although prostate-specific antigen (PSA) is considered a uniquely important tumor marker and is broadly used for early detection of prostate cancer, the molecular mechanisms underlying its elevated expression in tumors have been unknown. By using cDNA microarray gene expression profiling, we found a fourfold increase in the PSA mRNA level in prostatic carcinoma cell line LNCaP, in which the p53 pathway was suppressed by a dominant negative p53 mutant. Consistently, p53 suppression caused a 4-8-fold increase in secretion of PSA protein in culture medium, suggesting that PSA gene expression is under negative control of p53. While wild type p53 strongly repressed, dominant negative p53 mutants stimulated PSA promoter-driven transcription and secretion of PSA in transient transfection experiments. The inhibitory effect of wild type p53 was undetectable in the presence of trichostatin A, suggesting the involvement of histone deacetylation in negative regulation of PSA promoter activity. Thus, PSA is likely to be a tissue specific indicator of transformation-associated p53 suppression in prostate cells. This finding provides a plausible explanation for a frequent increase of PSA levels in advanced prostate cancer.

SRY interacts with and negatively regulates androgen receptor transcriptional activity

This study investigated interactions between SRY, the Y chromosome encoded male sex determining factor, and the androgen receptor (AR). Coexpression of AR and SRY caused marked repression of AR transcriptional activity on a series of androgen-responsive reporter genes. Mammalian one- and two-hybrid experiments demonstrated an AR-SRY interaction mediated by the AR DNA binding domain. Precipitations with glutathione S-transferase fusion proteins indicated that AR-SRY interactions were direct and mediated by the AR DNA binding domain and the SRY high mobility group box DNA binding domain. Transient expression of SRY in LNCaP prostate cancer cells repressed expression of an androgen-dependent prostate-specific antigen (PSA) reporter gene and stable SRY expression repressed the endogenous PSA gene. SRY protein expression was increased by proteosome inhibitors and by the androgen-liganded AR in transient and stable transfectants. AR transcriptional activity was also repressed by DAX1, and the effects of SRY and DAX1 on the AR were additive. These findings indicate that interactions between the AR, SRY, and DAX1 contribute to normal male development and function and suggest a general role for protein-protein interactions between high mobility group box proteins and steroid hormone receptors in regulating tissue-specific gene expression.

Testosterone acts directly on CD4+ T lymphocytes to increase IL-10 production

Males are less susceptible than females to experimental autoimmune encephalomyelitis and many other autoimmune diseases. Gender differences in cytokine production have been observed in splenocytes of experimental autoimmune encephalomyelitis mice stimulated with myelin proteins and may underlie gender differences in susceptibility. As these differences should not be limited to responses specific for myelin proteins, gender differences in cytokine production upon stimulation with Ab to CD3 were examined, and the mechanisms were delineated. Splenocytes from male mice stimulated with Ab to CD3 produced more IL-10 and IL-4 and less IL-12 than those from female mice. Furthermore, splenocytes from dihydrotestosterone (DHT)-treated female mice produced more IL-10 and less IL-12 than those from placebo-treated female mice, whereas there was no difference in IL-4. IL-12 knockout mice were then used to determine whether changes in IL-10 production were mediated directly by testosterone vs indirectly by changes in IL-12. The results of these experiments favored the first hypothesis, because DHT treatment of female IL-12 knockout mice increased IL-10 production. To begin to delineate the mechanism by which DHT may be acting, the cellular source of IL-10 was determined. At both the RNA and protein levels, IL-10 was produced primarily by CD4+ T lymphocytes. CD4+ T lymphocytes were then shown to express the androgen receptor, raising the possibility that testosterone acts directly on CD4+ T lymphocytes to increase IL-10 production. In vitro experiments demonstrated increased IL-10 production following treatment of CD4+ T lymphocytes with DHT. Thus, testosterone can act directly via androgen receptors on CD4+ T lymphocytes to increase IL-10 gene expression.

Regions of prostate-specific antigen (PSA) promoter confer androgen-independent expression of PSA in prostate cancer cells

Prostate-specific antigen (PSA) is expressed primarily by both normal prostate epithelium and the vast majority of prostate cancers. Increases in serum PSA during endocrine therapy are generally considered as evidence for prostate cancer recurrence or progression to androgen independence. The mechanisms by which PSA up-regulation occurs in androgen-refractory prostate cancer cells are unknown. In this study, by using LNCaP and its lineage-derived androgen-independent PSA-producing subline, C4-2, we identified two cis-elements within the 5.8-kilobase pair PSA promoter that are essential for the androgen-independent activity of PSA promoter in prostate cancer cells. First, a previously reported 440-bp androgen-responsive element enhancer core (AREc) was found to be important for the high basal PSA promoter activity in C4-2 cells. Both mutation analysis and supershift experiments demonstrated that androgen receptor (AR) binds to the AREs within the AREc and activate the basal PSA promoter activity in C4-2 cells under androgen-deprived conditions. Second, a 150-bp pN/H region was demonstrated to be a strong AR-independent positive-regulatory element of the PSA promoter in both LNCaP and C4-2 cells. Through DNase I footprinting and linker scan mutagenesis, a 17-bp RI site was identified as the key cis-element within the pN/H region. Data from electrophoretic mobility shift analysis and UV cross-linking experiments further indicated that a 45-kDa (p45) cell-specific transcription factor associates with RI in prostate cancer cells and may be responsible for driving the PSA promoter activity independent of androgen and AR. Furthermore, by juxtaposing AREc and pN/H, we produced a chimeric PSA promoter (supra-PSA) that exhibits 2-3-fold higher activity than the wild type PSA promoter in both LNCaP and C4-2 cells.

An androgen response element mediates LNCaP cell dependent androgen induction of the hK2 gene

Human glandular kallikrein (hK2) is an androgen regulated protein primarily expressed in the prostate and recently identified as a novel prostate cancer marker. A 5 kb 5' flanking region of the hK2 gene was isolated and sequenced to characterize the regulatory mechanisms for the expression of hK2 in the androgen responsive prostate cell line, LNCaP. Using gene transfer, gel shift, and mutagenesis assays we have identified an ARE in the 5' far upstream promoter region of the hK2 gene that is crucial for its regulation in LNCaP cells. This study further demonstrated that the hK2 upstream ARE plays a predominant role in androgenic response. More interestingly, previously identified AREs in the prostate specific antigen promoter and the hK2 proximal promoter exert little activity in LNCaP cells. This study for the first time identifies a unique ARE that alone mediates the function of the androgen receptor in LNCaP cells in a cell dependent manner. This study also examines the activity of this ARE with 1alpha, 25 dihydroxy-vitamin D3 on the expression of the hK2 gene in LNCaP cells.

A role for GATA transcription factors in the androgen regulation of the prostate-specific antigen gene enhancer

The transgenic mouse line Ggamma/T-15 containing the fetal globin promoter linked to SV40 T antigen unexpectedly results in androgen-independent prostate carcinomas. Given the key role of GATA-1 transcription factor in fetal globin gene promoter activity, we investigated whether specific GATA family members are expressed in the prostate and whether they can regulate prostate-specific genes. We found that GATA-2 and -3 are the predominant GATA family members expressed in human and mouse prostate and that GATA mRNA levels are not regulated by androgen. We identified six GATA sites flanking an androgen-response element located in the far-upstream enhancer of the prostate-specific antigen (PSA) gene. These GATA sites are targets for GATA factors and are essential for optimal androgen induction of transfected PSA enhancer/promoter plasmids in LNCaP, a PSA and androgen receptor expressing human prostate cancer cell line. Our results suggest that prostatic GATA-2 and -3 are involved in the androgen regulation of the PSA gene.

Tea polyphenols down-regulate the expression of the androgen receptor in LNCaP prostate cancer cells

Androgens via their cognate receptor may be involved in the development and progression of prostate cancer. The aim of this study was to determine whether tea polyphenols have inhibitory effects on androgen action in an androgen-responsive, prostate cancer cell line, LNCaP. The tea polyphenol, EGCG, inhibited LNCaP cell growth and the expression of androgen regulated PSA and hK2 genes. Moreover, EGCG had a significant inhibitory effect on the androgenic inducibility of the PSA promoter. Immunoblotting detected a decrease in androgen receptor protein with treatments of the tea polyphenols EGCG, GCG and theaflavins. Northern blot analysis showed decreased levels of androgen receptor mRNA by EGCG. Transient transfections demonstrated that EGCG and theaflavins could repress the transcriptional activities of the androgen receptor promoter region. An Sp1 binding site in the androgen receptor gene promoter is an important regulatory component for its expression. This study suggests Sp1 is the target for the tea polyphenols because treatments of EGCG decreased the expression, DNA binding activity and transactivation activity of Sp1 protein. In conclusion, we have described a new property of tea polyphenols that inhibits androgen action by repressing the transcription of the androgen receptor gene.

PDEF, a novel prostate epithelium-specific ets transcription factor, interacts with the androgen receptor and activates prostate-specific antigen gene expression

Prostate cancer, the most frequent solid cancer in older men, is a leading cause of cancer deaths. Although proliferation and differentiation of normal prostate epithelia and the initial growth of prostate cancer cells are androgen-dependent, prostate cancers ultimately become androgen-independent and refractory to hormone therapy. The prostate-specific antigen (PSA) gene has been widely used as a diagnostic indicator for androgen-dependent and -independent prostate cancer. Androgen-induced and prostate epithelium-specific PSA expression is regulated by a proximal promoter and an upstream enhancer via several androgen receptor binding sites. However, little progress has been made in identifying androgen-independent regulatory elements involved in PSA gene regulation. We report the isolation of a novel, prostate epithelium-specific Ets transcription factor, PDEF (prostate-derived Ets factor), that among the Ets family uniquely prefers binding to a GGAT rather than a GGAA core. PDEF acts as an androgen-independent transcriptional activator of the PSA promoter. PDEF also directly interacts with the DNA binding domain of androgen receptor and enhances androgen-mediated activation of the PSA promoter. Our results, as well as the critical roles of other Ets factors in cellular differentiation and tumorigenesis, strongly suggest that PDEF is an important regulator of prostate gland and/or prostate cancer development.

Cooperative assembly of androgen receptor into a nucleoprotein complex that regulates the prostate-specific antigen enhancer

Prostate cancer is characterized by elevated serum levels of prostate-specific antigen (PSA). PSA gene expression is controlled by an androgen-responsive transcriptional enhancer. Our study suggests that formation of a nucleoprotein complex, encompassing 170 base pairs of enhancer DNA, mediates androgen-responsive PSA enhancer activity. The complex is assembled by cooperative binding of androgen receptor to at least four tandem, nonconsensus androgen response elements (AREs). Systematic mutagenesis of the AREs demonstrated that they act synergistically to stimulate androgen receptor-responsive gene expression. We discuss a mechanism whereby a combination of high androgen receptor levels in the prostate and low affinity AREs contribute to the cell type specificity and activity of the enhancer.

Reporter gene technology: the future looks bright

Reporter gene technology is widely used to monitor the cellular events associated with signal transduction and gene expression. Based upon the splicing of transcriptional control elements to a variety of reporter genes (with easily measurable phenotypes), it "reports" the effects of a cascade of signalling events on gene expression inside cells. The principal advantage of these assays is their high sensitivity, reliability, convenience, and adaptability to large-scale measurements. This review summarises the current status of reporter gene technology including its role in monitoring gene transfer and expression and its development as a biological screen. With the advances in this technology and in detection methods, it is likely that luciferase and green fluorescent protein will become increasingly popular for the non-invasive monitoring of gene expression in living tissues and cells. Such techniques will be important in defining the molecular events associated with gene transcription, which has implications for our understanding of the molecular basis of disease and will influence our approach to gene therapy and drug development.

Interactive effects of triiodothyronine and androgens on prostate cell growth and gene expression

T3 plays an important role in the regulation of cell growth and differentiation. In this study, we show the interactive effects of T3 and androgens on the growth response and expression of the prostate-specific genes, PSA (prostate-specific antigen) and hK2 (human glandular kallikrein), in the human prostate cancer cell line, LNCaP. T3 alone showed pronounced growth enhancement in a dose-dependent fashion. However, in the presence of androgens, higher concentrations of T3 were required to produce additional proliferative effects. T3, androgens, or a combination of the two up-regulated PSA protein production in a dose-dependent fashion, but T3 had little stimulatory effect on hK2 protein expression, regardless of the presence or absence of androgens. Using gene transfer assays, T3 alone showed no effect on transcriptional activation of a reporter gene mediated by the PSA or hK2 enhancer/promoters. T3 potentiated the androgen-mediated transcription of the PSA gene but not that of the hK2 gene. A previous study suggested that the T3 effect on PSA protein expression was caused by an up-regulation of the androgen receptor (AR) protein by T3. Our results contradict these. Although AR expression was increased by T3 alone, Western blot analysis showed that the total cellular AR level was not further increased by T3 in the presence of androgens, in comparison with cells stimulated by androgens alone. Both Western blot analysis and a gel DNA band shift assay revealed that nuclear AR was not increased by T3. This study suggests that transcription factor(s) other than the AR may mediate T3 enhancement of androgenic induction of PSA expression.

Human Kallikrein 2 (hK2) and prostate-specific antigen (PSA): two closely related, but distinct, kallikreins in the prostate

Recent studies on human kallikrein 2 (hK2) have revealed striking similarities and significant differences with the closely related kallikrein PSA. Both PSA and hK2 are primarily localized to the prostate and share close structural similarities. Although both kallikreins are produced by the same secretory epithelial cells in the prostate, hK2 is associated more with prostate tumors than PSA and is highly expressed in poorly differentiated cancer cells. The potent trypsin-like activity of hK2 contrasts with the weak chymotrypsin-like activity of PSA. The inactive precursor form of PSA, proPSA, is converted rapidly to active PSA by hK2, suggesting an important in vivo regulatory function by hK2 on PSA activity. The high homology between hK2 and PSA results in significant cross-reactivity to hK2 by polyclonal and some monoclonal antibodies to PSA. Future studies on both PSA and hK2 need to take into account this potential for cross-reactivity. Specific monoclonal antibodies to hK2 have now demonstrated that serum levels of hK2, like PSA, are correlated with prostate cancer. The production of hK2 protein in active protease form and specific monoclonal antibodies to the hK2 antigen will allow extensive future studies delineating the physiological and clinical utility of this new prostate antigen.

In vivo gene therapy for prostate cancer: preclinical evaluation of two different enzyme-directed prodrug therapy systems delivered by identical adenovirus vectors

Advanced prostate cancer is invariably lethal once it becomes androgen independent (AI). With the aim of developing a new treatment we have used the human androgen-independent prostate cancer cell line, PC-3, to evaluate the effectiveness of two enzyme-directed prodrug therapy (EPT) systems as a novel means for promoting tumor cell destruction in vivo. We have confined our study to the use of a PSA promoter, in a preliminary attempt to achieve prostate specificity. The two EPT systems used were the HSVTK/GCV and PNP/6MPDR systems. These were chosen for their differential dependence on DNA replication for their mechanism of action. In the present work, either the HSVTK or PNP gene, each controlled by a PSA promoter fragment, was delivered by an E1-, replication-deficient human adenovirus (Ad5) into PC-3 tumors growing subcutaneously in BALB/c nude mice. Tumors were injected with a single dose of recombinant Ad5 and mice were treated intraperitoneally with the appropriate prodrug, twice daily, for 6 days thereafter. The growth of established PC-3 tumors was significantly suppressed and host survival increased with a single course of HSVTK/GCV or PNP/6MPDR treatment. HSVTK/GCV-treated PC-3 tumor growth was 80% less than that of control treatments on day 33, while PNP/6MPDR-treated tumor growth was approximately 75% less than that of control treatments on day 52. Survival data showed that 20% of HSVTK/GCV- or PNP/6MPDR-treated animals lived >45 and >448 days, respectively, longer than control animals. These results demonstrate that both HSVTK/GCV and PNP/6MPDR therapies interrupt the growth of an aggressive human prostate cancer cell line in vivo.