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

The relationship between sexual dimorphism and androgen response element proliferation in primate genomes

In the males of many vertebrate species, sexual selection has led to the evolution of sexually dimorphic traits, which often are developmentally controlled by androgen signaling involving androgen response elements (AREs). Evolutionary changes in the number and genomic locations of AREs can modify patterns of receptor regulation and potentially alter gene expression. Here, we use recently sequenced primate genomes to evaluate the hypothesis that the strength of sexual selection is related to the genome-wide number of AREs in a diversifying lineage. In humans, we find a higher incidence of AREs near male-biased genes and androgen-responsive genes when compared to randomly selected genes from the genome. In a set of primates, we find that gains or losses of AREs proximal to genes are correlated with changes in male expression levels and the degree of sex-biased expression of those genes. In a larger set of primates, we find that increases in indicators of sexual selection are correlated with genome-wide ARE counts. Our results suggest that the responsiveness of the genome to androgens in humans and their close relatives has been shaped by sexual selection that arises from competition among males for mating access to females.

Protein Kinase N1 control of androgen-responsive serum response factor action provides rationale for novel prostate cancer treatment strategy

Sustained reliance on androgen receptor (AR) after failure of AR-targeting androgen deprivation therapy (ADT) prevents effective treatment of castration-recurrent (CR) prostate cancer (CaP). Interfering with the molecular machinery by which AR drives CaP progression may be an alternative therapeutic strategy but its feasibility remains to be tested. Here, we explore targeting the mechanism by which AR, via RhoA, conveys androgen-responsiveness to serum response factor (SRF), which controls aggressive CaP behavior and is maintained in CR-CaP. Following a siRNA screen and candidate gene approach, RNA-Seq studies confirmed that the RhoA effector Protein Kinase N1 (PKN1) transduces androgen-responsiveness to SRF. Androgen treatment induced SRF-PKN1 interaction, and PKN1 knockdown or overexpression severely impaired or stimulated, respectively, androgen regulation of SRF target genes. PKN1 overexpression occurred during clinical CR-CaP progression, and hastened CaP growth and shortened CR-CaP survival in orthotopic CaP xenografts. PKN1's effects on SRF relied on its kinase domain. The multikinase inhibitor lestaurtinib inhibited PKN1 action and preferentially affected androgen regulation of SRF over direct AR target genes. In a CR-CaP patient-derived xenograft, expression of SRF target genes was maintained while AR target gene expression declined and proliferative gene expression increased. PKN1 inhibition decreased viability of CaP cells before and after ADT. In patient-derived CaP explants, lestaurtinib increased AR target gene expression but did not significantly alter SRF target gene or proliferative gene expression. These results provide proof-of-principle for selective forms of ADT that preferentially target different fractions of AR's transcriptional output to inhibit CaP growth.

High resolution digital autoradiographic and dosimetric analysis of heterogeneous radioactivity distribution in xenografted prostate tumors

PURPOSE

The first main aim of this study was to illustrate the absorbed dose rate distribution from ¹⁷⁷Lu in sections of xenografted prostate cancer (PCa) tumors using high resolution digital autoradiography (DAR) and compare it with hypothetical identical radioactivity distributions of ⁹⁰Y or 7 MeV alpha-particles. Three dosimetry models based on either dose point kernels or Monte Carlo simulations were used and evaluated. The second and overlapping aim, was to perform DAR imaging and dosimetric analysis of the distribution of radioactivity, and hence the absorbed dose rate, in tumor sections at an early time point after injection during radioimmunotherapy using ¹⁷⁷Lu-h11B6, directed against the human kallikrein 2 antigen.

METHODS

Male immunodeficient BALB/c nude mice, aged 6-8 w, were inoculated by subcutaneous injection of ∼10⁷ LNCaP cells in a 200 μl suspension of a 1:1 mixture of medium and Matrigel. The antibody h11B6 was conjugated with the chelator CHX-A″-DTPA after which conjugated h11B6 was mixed with ¹⁷⁷LuCl₃. The incubation was performed at room temperature for 2 h, after which the labeling was terminated and the solution was purified on a NAP-5 column. About 20 MBq ¹⁷⁷Lu-h11B6 was injected intravenously in the tail vein. At approximately 10 h postinjection (hpi), the mice were sacrificed and one tumor was collected from each of the five animals and cryosectioned into 10 μm thick slices. The tumor slices were measured and imaged using the DAR MicroImager system and the M3Vision software. Then the absorbed dose rate was calculated using a dose point kernel generated with the Monte Carlo code gate v7.0.

RESULTS

The DAR system produced high resolution images of the radioactivity distribution, close to the resolution of single PCa cells. The DAR images revealed a pronounced heterogeneous radioactivity distribution, i.e., count rate per area, in the tumors, indicated by the normalized intensity variations along cross sections as mean ± SD: 0.15 ± 0.15, 0.20 ± 0.18, 0.12 ± 0.17, 0.15 ± 0.16, and 0.23 ± 0.22, for each tumor section, respectively. The absorbed dose rate distribution for ¹⁷⁷Lu at the time of dissection 10 hpi showed a maximum value of 2.9 ± 0.4 Gy/h (mean ± SD), compared to 6.0 ± 0.9 and 159 ± 25 Gy/h for the hypothetical ⁹⁰Y and 7 MeV alpha-particle cases assuming the same count rate densities. Mean absorbed dose rate values were 0.13, 0.53, and 6.43 Gy/h for ¹⁷⁷Lu, ⁹⁰Y, and alpha-particles, respectively.

CONCLUSIONS

The initial uptake of ¹⁷⁷Lu-h11B6 produces a high absorbed dose rate, which is important for a successful therapeutic outcome. The hypothetical ⁹⁰Y case indicates a less heterogeneous absorbed dose rate distribution and a higher mean absorbed dose rate compared to ¹⁷⁷Lu, although with a potentially increased irradiation of surrounding healthy tissue. The hypothetical alpha-particle case indicates the possibility of a higher maximum absorbed dose rate, although with a more heterogeneous absorbed dose rate distribution.

Expression profiles and functional associations of endogenous androgen receptor and caveolin-1 in prostate cancer cell lines

BACKGROUND

In prostate cancer (PCa) patients, the protein target for androgen deprivation and blockade therapies is androgen receptor (AR). AR interacts with many proteins that function to either co-activate or co-repress its activity. Caveolin-1 (Cav-1) is not found in normal prostatic epithelium, but is found in PCa, and may be an AR co-regulator protein.

METHODS

We investigated cell line-specific signatures and associations of endogenous AR and Cav-1 in six PCa cell lines of known androgen sensitivity: LNCaP (androgen sensitive); 22Rv1 (androgen responsive); PC3, DU145, and ALVA41 (androgen non-reliant); and RWPE1 (non-malignant). Protein and mRNA expression profiles were compared and electron microscopy used to identify cells with caveolar structures. For cell lines expressing both AR and Cav-1, knockdown techniques using small interfering RNA against AR or Cav-1 were used to test whether diminished expression of one affected the other. Co-sedimentation of AR and Cav-1 was used to test their association. A reporter assay for AR genomic activity was utilized following Cav-1 knockdown.

RESULTS

AR-expressing LNCaP and 22Rv1 cells had low endogenous Cav-1 mRNA and protein. Cell lines that expressed little or no AR (DU145, PC3, ALVA41, and RWPE1) expressed high endogenous levels of Cav-1. AR knockdown in LNCaP cells had little effect on Cav-1, but Cav-1 knockdown inhibited AR expression and genomic activity.

CONCLUSIONS

These data show endogenous AR and Cav-1 mRNA and protein expression is inversely related in PCa cells, with Cav-1 acting on the androgen/AR signaling axis possibly as an AR co-activator, demonstrated by diminished AR genomic activity following Cav-1 knockdown.

Androgen response element of the glycine N-methyltransferase gene is located in the coding region of its first exon

Androgen plays an important role in the pathogenesis of PCa (prostate cancer). Previously, we identified GNMT (glycine N-methyltransferase) as a tumour susceptibility gene and characterized its promoter region. Besides, its enzymatic product-sarcosine has been recognized as a marker for prognosis of PCa. The goals of this study were to determine whether GNMT is regulated by androgen and to map its AREs (androgen response elements). Real-time PCR analyses showed that R1881, a synthetic AR (androgen receptor) agonist induced GNMT expression in AR-positive LNCaP cells, but not in AR-negative DU145 cells. In silico prediction showed that there are four putative AREs in GNMT-ARE1, ARE2 and ARE3 are located in the intron 1 and ARE4 is in the intron 2. Consensus ARE motif deduced from published AREs was used to identify the fifth ARE-ARE5 in the coding region of exon 1. Luciferase reporter assay found that only ARE5 mediated the transcriptional activation of R1881. ARE3 overlaps with a YY1 [Yin and Yang 1 (motif (CaCCATGTT, +1118/+1126)] that was further confirmed by antibody supershift and ChIP (chromatin immunoprecipitation) assays. EMSA (electrophoretic mobility shift assay) and ChIP assay confirmed that AR interacts with ARE5 in vitro and in vivo. In summary, GNMT is an AR-targeted gene with its functional ARE located at +19/+33 of the first exon. These results are valuable for the study of the influence of androgen on the gene expression of GNMT especially in the pathogenesis of cancer.

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.

Dynamic nucleosome-depleted regions at androgen receptor enhancers in the absence of ligand in prostate cancer cells

Nucleosome positioning at transcription start sites is known to regulate gene expression by altering DNA accessibility to transcription factors; however, its role at enhancers is poorly understood. We investigated nucleosome positioning at the androgen receptor (AR) enhancers of TMPRSS2, KLK2, and KLK3/PSA in prostate cancer cells. Surprisingly, a population of enhancer modules in androgen-deprived cultures showed nucleosome-depleted regions (NDRs) in all three loci. Under androgen-deprived conditions, NDRs at the TMPRSS2 enhancer were maintained by the pioneer AR transcriptional collaborator GATA-2. Androgen treatment resulted in AR occupancy, an increased number of enhancer modules with NDRs without changes in footprint width, increased levels of histone H3 acetylation (AcH3), and dimethylation (H3K4me2) at nucleosomes flanking the NDRs. Our data suggest that, in the absence of ligand, AR enhancers exist in an equilibrium in which a percentage of modules are occupied by nucleosomes while others display NDRs. We propose that androgen treatment leads to the disruption of the equilibrium toward a nucleosome-depleted state, rather than to enhancer de novo "remodeling." This allows the recruitment of histone modifiers, chromatin remodelers, and ultimately gene activation. The "receptive" state described here could help explain AR signaling activation under very low ligand concentrations.

Sesquiterpenoids from myrrh inhibit androgen receptor expression and function in human prostate cancer cells

AIM

To examine whether two naturally occurring sesquiterpenoids (ST1 and ST2) with anti-proliferative activity in prostate cancer cells inhibit androgen receptor (AR) signaling.

METHODS

Human prostate cancer cell lines LNCaP and PC3 were used. The expression of AR, AR translocation into the nucleus, and expression levels of AR coactivators ARA70 and steroid receptor coactivator-1 (SRC-1) in LNCaP cells were examined using real-time PCR and Western blot. Changes in prostate-specific antigen (PSA) protein levels, PSA promoter activity, and androgen response element (ARE)-mediated reporter gene activity were examined using enzyme-linked immunoabsorbent assay (ELISA) and transient transfection assays. Co-immunoprecipitation was performed to analyze the interaction between AR and the AR coactivators in ST1- and ST2-treated cells.

RESULTS

In LNCaP cells, ST1 and ST2 (40 μmol/L) led to a significant decrease in the expression of AR as well as a reduction of AR translocation into the nucleus, but had no effect on AR protein translation. ST1 and ST2 treatment also resulted in a significant decrease in the level of PSA protein secreted into the medium and was able to suppress PSA promoter-dependent and ARE-dependent luciferase activity. Furthermore, decreased expression of ARA70 and SRC-1 was observed when LNCaP cells were exposed to ST1 and ST2, which interfered with their ability to interact with AR.

CONCLUSION

The observations suggest that suppression of AR transactivation by ST1 and ST2 may be mediated, in part, by inhibiting AR nuclear translocation and/or interfering with the interaction between AR and its coactivators ARA70 and SRC-1. Therefore, sesquiterpenoids could be developed as novel therapeutic agents for treating prostate cancer.

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.

The rules of DNA recognition by the androgen receptor

The androgen receptor (AR) and glucocorticoid, progestagen, and mineralocorticoid receptors all recognize classical DNA response elements that are organized as inverted repeats of 5'-AGAACA-3'-like motifs with a three-nucleotide spacer. Next to such elements, the AR also recognizes a second type of androgen response element (ARE), the so-called selective AREs, which resemble more the direct repeats of the same hexamer. In this work, we show that not only the AR but also the progestagen receptor can recognize the selective AREs, whereas neither glucocorticoid nor mineralocorticoid receptor can. Recently, genomic AR-binding fragments have been postulated to contain AR-binding sites that diverge considerably from the classical ARE consensus. Extensive mutational analyses of these candidate motifs, however, reinstalls the values of the consensus sequence for the AREs as mentioned above, the importance of their dimeric nature and the presence of exactly three-nucleotide spacing. We developed a position-specific probability matrix that was used to predict with higher accuracy new AREs in different AR-binding regions. So far, all AR-binding genomic fragments that were analyzed contain AREs defined as receptor-dimer binding motifs with the ability to confer responsiveness to a reporter 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.

Androgen modulation of coregulator expression in prostate cancer cells

Aberrant coregulator expression that occurs during prostate cancer (PCa) progression correlates with poor prognosis and aggressive disease. This has been attributed to the ability to regulate androgen receptor-mediated transcription. We have shown previously that the androgenic milieu regulates the expression of the coactivators p300 and FHL2, with severe consequences for PCa cell proliferation and androgen receptor transcriptional activity. To determine the extent of androgen dependency of coregulator genes, we designed a cDNA-mediated annealing, selection, extension, and ligation RNA profiling array that probes the expression of 186 coregulators. Using this assay, we demonstrated androgen control over approximately 30% of coregulator genes in PCa cells. For a subset of 15 functionally diverse coregulators, androgen regulation was confirmed using real-time RT-PCR and immunoblotting. The extent, dose dependency, and kinetics by which androgens affect coregulator expression differed widely, indicating diverse molecular mechanisms underlying these effects. Moreover, differences in coregulator expression were observed between isogenic androgen-dependent and castration-recurrent PCa cells. Small interfering RNA-mediated changes in coregulator expression had profound effects on cell proliferation, which were most pronounced in castration-recurrent cells. Taken together, our integrated approach combining expression profiling, characterization of androgen-dependent coregulator expression, and validation of the importance of altered coregulator expression for cell proliferation identified several potential novel therapeutic targets for PCa treatment.

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.

Suppression of androgen receptor-mediated gene expression by a sequence-specific DNA-binding polyamide

Androgen receptor (AR) is essential for the growth and progression of prostate cancer in both hormone-sensitive and hormone-refractory disease. A DNA-binding polyamide that targets the consensus androgen response element binds the prostate-specific antigen (PSA) promoter androgen response element, inhibits androgen-induced expression of PSA and several other AR-regulated genes in cultured prostate cancer cells, and reduces AR occupancy at the PSA promoter and enhancer. Down-regulation of PSA by this polyamide was comparable to that produced by the synthetic antiandrogen bicalutamide (Casodex) at the same concentration. Genome-wide expression analysis reveals that a similar number of transcripts are affected by treatment with the polyamide and with bicalutamide. Direct inhibition of the AR-DNA interface by sequence-specific DNA binding small molecules could offer an alternative approach to antagonizing AR activity.

Advances in preclinical investigation of prostate cancer gene therapy

Treating recurrent prostate cancer poses a great challenge to clinicians. Research efforts in the last decade have shown that adenoviral vector-based gene therapy is a promising approach that could expand the arsenal against prostate cancer. This maturing field is at the stage of being able to translate many preclinical discoveries into clinical practices. At this juncture, it is important to highlight the promising strategies including prostate-targeted gene expression, the use of oncolytic vectors, therapy coupled to reporter gene imaging, and combined treatment modalities. In fact, the early stages of clinical investigation employing combined, multimodal gene therapy focused on loco-regional tumor eradication and showed promising results. Clinicians and scientists should seize the momentum of progress to push forward to improve the therapeutic outcome for the patients.

Sodium selenite inhibits interleukin-6-mediated androgen receptor activation in prostate cancer cells via upregulation of c-Jun

BACKGROUND

It has been suggested that interleukin-6 (IL-6) may modulate androgen receptor (AR) action to accelerate prostate cancer (PCa) progression. Selenium compounds are highly recommended as a promising chemopreventive agent for PCa. This study was to determine if selenium can repress IL-6 mediated AR action in PCa progression.

METHODS

Cell proliferation, prostate-specific antigen, gene transfer, and Western blot assays were used to study the effects of sodium selenite and methylseleninic acid on IL-6 mediated AR action on an AR expressing human prostate cancer cell line, LNCaP.

RESULTS

We found that sodium selenite, but not methylseleninic acid, significantly (p<0.05) inhibited IL-6-induced trans-activating activity of AR and cell proliferation in LNCaP cells. Interestingly, although sodium selenite did not show effect on activation of both STAT3 and ERK1/2 in the presence of IL-6, an increased expression of c-Jun was detected in cells after treatment with sodium selenite. Indeed, we showed overexpression of c-Jun blocked IL-6-induced AR activation.

CONCLUSIONS

Taken together, our results suggest that sodium selenite not methylseleninic acid can inhibit IL-6-mediated AR activation by increased c-Jun in LNCaP cells. Sodium selenite may be a proper selenium form for further testing its potency on intervening IL-6-mediated PCa progression.

Specific targeting of gene therapy to prostate cancer using a two-step transcriptional amplification system

Significant advances in gene therapy have been made as a result of the improvement of gene delivery systems, discovery of new therapeutic genes, better understanding of mechanisms of disease progression, exploration and improvement of tissue-specific gene regulatory sequences, and development of better prodrug/enzyme systems. This review discusses adenoviral-based and prostate-specific cancer gene therapy--emphasizing tissue-specific promoter choices to increase gene therapy safety and specificity--and the development of prostate-targeted vectors, with a focus on the two-step transactivation system for amplifying gene expression, specifically in prostate cancer cells. Several examples will be discussed for the scientific basis and therapeutic applications. In addition, prostate cancer gene therapy clinical trials and future directions in this field will also be described briefly.

Gum mastic inhibits the expression and function of the androgen receptor in prostate cancer cells

Accumulating evidence suggests that the androgen receptor (AR) may play an important role in the development and progression of prostate cancer. To find new, useful compounds that effectively may attenuate the function of AR in prostate cancer cells, the authors investigated the effect of gum mastic, a natural resin, on AR activity. An androgen-responsive prostate cancer cell line LNCaP was used as a model for this study. Gene transfer, reverse transcriptase-polymerase chain reaction analysis, electrophoretic mobility shift assay, and Western blot analysis were used to test the effect of gum mastic on the expression and function of the AR. To demonstrate the inhibitory effect of gum mastic on the function of the AR, the expression of androgen-regulated genes, including prostate-specific antigen (PSA), human kallikrein 2 (hK2), and NKX3.1 were measured. In addition, transient transfection assays with the PSA promoter and the AR promoter also were used to test the effects of mastic. The results showed that gum mastic inhibited the expression of the AR at the transcriptional level, resulting in the down-regulation of both AR messenger RNA and protein levels. Therefore, the function of the AR was inhibited, as reflected by the reduced expression of NKX3.1 and PSA and by androgen-stimulated growth. Because gum mastic exhibited a strong in vitro potency to attenuate the expression and function of the AR, further investigation will be required to determine whether this naturally occurring substance has in vivo potency to inhibit prostate cancer development.

FSH and testosterone signaling in Sertoli cells

Testosterone and follicle-stimulating hormone (FSH) are required to obtain full reproductive potential. In the testis, somatic Sertoli cells transduce signals from testosterone and FSH into the production of factors that are required by germ cells as they mature into spermatozoa. Recent advances in identifying new signaling pathways that are regulated by FSH and testosterone have allowed for refinement in the understanding of the independent, overlapping and synergistic actions of these hormones. In this review, we discuss the signaling pathways that are regulated by FSH and testosterone as well as the resulting metabolic and gene expression changes that occur as related to Sertoli cell proliferation, differentiation and the support of spermatogenesis.

Perillyl alcohol inhibits the expression and function of the androgen receptor in human prostate cancer cells

Perillyl alcohol is a hydroxylated monocyclic monoterpene. In animal study, monoterpene has shown to have an anti-tumor effect. The aim of this study is to evaluate whether POH plays an important role in the development and progression of prostate cancer (pCa). We treated LNCaP cells with different concentrations of perillyl alcohol (POH). First of all, we performed cell proliferation assay and prostate-specific antigen (PSA) and human glandular kallikrein (hK2) quantification assays. LNCaP cells were treated with or without POH for Western blot analysis of androgen receptor (AR) and c-Jun. Finally, we performed transient transfection assay by transfecting LNCaP cells-which were treated with or without POH-with pGL-3 luciferase vector containing PSA promoter and AR promoter. We observed inhibition of the expression and function of the AR by POH, through inhibition of androgen-induced cell growth and androgen-stimulated secretion of prostate-specific antigen and hK2, in human pCa cell line LNCaP. In addition, we demonstrated, for the first time, that POH inhibits the transcription activities of the AR gene promoter by over-expression of c-Jun protein. These novel properties of POH strongly suggest that POH could be highly useful for intervention of pCa.

The evolution of the glandular kallikrein locus: identification of orthologs and pseudogenes in the cotton-top tamarin

Comparisons of the glandular kallikreins loci in human, mouse and rat revealed remarkable differences. For example, the mouse and the rat lack the genes encoding prostate-specific antigen (PSA) and human glandular kallikrein 2 (hK2). In contrast, the intergenic region between KLK1 and KLK15 is devoid of genes and spans only 1.5 kb in humans, but encompasses 23 KLK1-like genes spanning 290 kb in the mouse. To further elucidate the evolution of glandular kallikrein genes, we investigated the structure and organization of these genes in the cotton-top tamarin (Saguinus oedipus), a New World monkey. We conclude that this species has no PSA gene. Moreover, the ortholog of the hK2 gene is a pseudogene, as it contains several mutations that preclude formation of a functional serine protease. The expression of this gene was probably silenced by a 15-bp deletion observed in an androgen response element in the upstream promoter region. Replacing the deleted base pairs in vitro with nucleotides from the human counterpart dramatically restored the transcriptional activity to a level that even surpassed that of the human ortholog. We also determined the nucleotide sequence of KLK15 and the intergenic region between this gene and KLK1 in the cotton-top tamarin. The region between KLK1 and KLK15 is conserved between the cotton-top tamarin and humans, and there are no signs of the extension seen in the mouse. KLK15 appeared to be functional, thus, we predict that it generates a protease with specificity similar to that of the human ortholog.

HER2/neu kinase-dependent modulation of androgen receptor function through effects on DNA binding and stability

Given the role of the EGFR/HER2 family of tyrosine kinases in breast cancer, we dissected the molecular basis of EGFR/HER2 kinase signaling in prostate cancer. Using the small molecule dual EGFR/HER2 inhibitor PKI-166, we show that the biologic effects of EGFR/HER-2 pathway inhibition are caused by reduced AR transcriptional activity. Additional genetic and pharmacologic experiments show that this modulation of AR function is mediated by the HER2/ERBB3 pathway, not by EGFR. This HER2/ERBB3 signal stabilizes AR protein levels and optimizes binding of AR to promoter/enhancer regions of androgen-regulated genes. Surprisingly, the downstream signaling pathway responsible for these effects appears to involve kinases other than Akt. These data suggest that the HER2/ERBB3 pathway is a critical target in hormone-refractory prostate cancer.

IDENTIFYING THE COMBINATION OF THE TRANSCRIPTIONAL REGULATORY SEQUENCES ON PROSTATE SPECIFIC ANTIGEN AND HUMAN GLANDULAR KALLIKREIN GENES

PURPOSE

The combination of prostate specific antigen (PSA) and human glandular kallikrein (KLK2) promoters and/or enhancers was used to establish a new model to determine the feasibility of tissue specific expression for prostate cancer.

MATERIALS AND METHODS

In vitro studies used the construction of PSA and KLK2 promoters/enhancers vectors to elucidate the link between the promoter/enhancer of PSA and KLK2. Reverse transcriptase-polymerase chain reaction assays were used to determine cell specific expression. Therefore, an attractive tissue specific expression vector for PSA and KLK2 gene was identified.

RESULTS

The reporter vectors driven by KLK2 promoter had much lower luciferase activities than those of the reporter vectors driven by PSA promoter in LNCaP cells. Furthermore, the most efficient and cell specific reporter activity after 5alpha-androstan-17beta-ol-3-one treatment among the reporter vectors constructed in this study was that of pKLK2EPSABHE, which was driven by KLK2 enhancer and PSA promoter/enhancer. The pKLK2EPSABHE reporter vector could induce 800-fold higher than the KLK2 basic promoter and its reporter activity was 16 times that of the enhancer/promoter element of KLK2 following induction by androgen.

CONCLUSIONS

The results verify that the PSA promoter/enhancer must be combined with KLK2 to ensure the full activity and cell specificity of the gene. These expressions coupled with mechanic target validation yield valuable clues regarding the model of action of complex mixtures. This model is a potentially useful tool in gene therapy for metastatic prostate cancer.

Steroid hormone regulation of the human kallikrein 10 (KLK10) gene in cancer cell lines and functional characterization of the KLK10 gene promoter

BACKGROUND

The human kallikrein 10 (KLK10) gene is a new member of the human tissue kallikrein gene family. It encodes for a secreted serine protease (hK10) with predicted trypsin-like enzymatic activity. KLK10 is highly expressed in the sex organs and its expression level changes in malignancy.

METHODS

To determine the role of steroid hormones in KLK10 gene expression, we investigated its modulation by 17beta-estradiol, 5alpha-dihydrotestosterone, norgestrel, dexamethasone and aldosterone, at both the transcription and translation level, in a panel of cancer cell lines. After steroid hormone stimulation, the change of KLK10 mRNA was monitored with reverse transcriptase polymerase chain reaction and hK10 protein levels in the culture supernatant were quantified with an hK10-specific immunoassay. The presence of hormone response elements in the KLK10 gene promoter was examined with the chloramphenicol acetyltransferase reporter gene system.

RESULTS

The KLK10 expression was mainly up-regulated by estrogens, androgens and progestins, and to a lesser extent by dexamethasone and aldosterone in the breast cancer cell lines BT-474, MCF-7 and T-47D, both at the mRNA and protein levels. The effect of stimulation of these steroids on KLK10 expression varied among the cell lines. Estrogens, androgens and progestins were most potent in the BT-474, T-47D and MCF-7 cells, respectively. The up-regulation effect of estrogens, androgens, and progestins on KLK10 expression can be blocked by their antagonists ICI-182, 780, RU-56,187, and mifepristone, respectively. Time course studies showed that hK10 protein started to increase 1 day after steroid hormone stimulation and this increase persisted for 7 days. These data suggest that steroid hormones up-regulate KLK10 gene expression through direct interaction between hormone-receptor complexes and their cognate hormone response elements. To search for hormone response elements, we functionally characterized the KLK10 promoter by placing it upstream of the chloramphenicol acetyltransferase reporter gene. We found that KLK10 promoter activity did not rely on the presence of functional estrogen and androgen receptors. Also, the presence of functional estrogen and androgen receptors did not increase its constitutive activity. We suggest that the hormone response elements that mediate the transcriptional regulation of KLK10 are unlikely to locate in the KLK10 promoter.

CONCLUSIONS

Estrogens, androgens and progestins modulate KLK10 expression through their own receptors but this regulation is not mediated by steroid hormone response elements in the promoter of the KLK10 gene.

Gene expression changes following androgen receptor elimination in LNCaP prostate cancer cells

We have shown recently that inhibition of androgen receptor (AR) expression with an antisense AR oligonucleotide (ODN) inhibits LNCaP prostate tumor cells in vitro as well as in vivo. In this study, we investigated gene expression changes that occur after AR signaling blockade, either through AR elimination by antisense treatment or through complete androgen receptor inhibition by androgen deprivation combined with the antiandrogen bicalutamide, in order to search for genes that are directly or indirectly regulated through the AR. Gene expression changes were investigated with cDNA NIH 10K gene microarrays in response to treatment over 48 h. Expression of selected genes was further analyzed by real-time reverse transcriptase (RT)-polymerase chain reaction (PCR), Western blotting, and radioimmunoassay. A comparison of antisense-treated and androgen-deprived cells revealed several concordances such as significant downregulation of prostate-specific genes, cell-cycle regulatory genes, genes of the cholesterol biosynthesis pathway, and several cytoskeletal genes. However, there were also several genes that were differentially regulated. Among the genes that were exclusively changed by treatment with the antisense AR ODN were the insulin-like growth factor binding protein 2 (IGFBP2) and the phosphatidylinositol-4-phosphate 5-kinase type I alpha (PIP5KIA). On the other hand, complete androgen receptor blockade induced changes in the expression of the prostate overexpressed gene 1 and the S100 calcium binding protein P. In summary, we identified a cohort of interesting genes whose expression was highly affected by elimination of the AR in LNCaP prostate cancer cells. Further investigations are warranted to clarify their role in the AR signaling pathway and their susceptibility as a target for the treatment of prostate cancer.

Effects of vitamin C on androgen receptor mediated actions in human prostate adenocarcinoma cell line LAPC-4

OBJECTIVES

To examine the effects of vitamin C (VC) on androgen receptor (AR)-mediated functions in a human prostate cancer cell line, Los Angeles prostate cancer (LAPC-4). VC is an essential dietary substance in the maintenance and preservation of vital functions in humans. However, the role of VC in prostate cancer remains to be elucidated.

METHODS

Cell proliferation and the expression of two well-known androgen regulated proteins, prostate-specific antigen and human glandular kallikrein-2, were studied in the presence of VC.

RESULTS

In the presence of androgen and VC, both cell growth and the expression of prostate-specific antigen and human glandular kallikrein-2 proteins were decreased. Moreover, AR-mediated transcription activity of the prostate-specific antigen gene was suppressed with VC, similar to the phenomenon observed when cells were treated with hydrogen peroxide. These effects were reversed with catalase. However, additional studies did not reveal changes in the expression level of AR protein or its androgen-binding activity with the addition of VC.

CONCLUSIONS

The results of our study suggest that the pro-oxidant property of VC might be one of the mechanisms by which it modulates AR-mediated function in LAPC-4 cells.

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

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

Involvement of proteasome in the dynamic assembly of the androgen receptor transcription complex

We have used the chromatin immunoprecipitation technique to analyze the formation of the androgen receptor (AR) transcription complex onto prostate-specific antigen (PSA) and kallikrein 2 promoters in LNCaP cells. Our results show that loading of holo-AR and recruitment of RNA polymerase II to the promoters occur transiently. The cyclic nature of AR transcription complex assembly is also illustrated by transient association of coactivators GRIP1 and CREB-binding protein and acetylated histone H3 with the PSA promoter. Treatment of cells with the pure antiandrogen bicalutamide also elicits occupancy of the promoter by AR. In contrast to the agonist-liganded AR, bicalutamide-bound receptor is not capable of recruiting polymerase II, GRIP1, or CREB-binding protein, indicating that the conformation of AR bound to anti-androgen is not competent to assemble transcription complexes. Proteasome is involved in the regulation of AR-dependent transcription, as a proteasome inhibitor, MG-132, prevents the release of the receptor from the PSA promoter, and it also blocks the androgen-induced PSA mRNA accumulation. Furthermore, occupancy of the PSA promoter by the 19 S proteasome subcomplex parallels that by AR. Collectively, formation of the AR transcription complex, encompassing AR, polymerase II, and coactivators, on a regulated promoter is a cyclic process involving proteasome function.

Identification of an androgen-dependent enhancer within the prostate stem cell antigen gene

Prostate stem cell antigen (PSCA) is emerging as an important diagnostic marker and therapeutic target in prostate cancer. Previous studies indicated that PSCA was directly regulated by androgens, but the mechanism has not been elucidated. Here we describe the identification of a compact cell-specific and androgen-responsive enhancer between 2.7 and 3 kb upstream of the transcription start site. The enhancer functions autonomously when positioned immediately adjacent to a minimal promoter. Deoxyribonuclease I footprinting analysis with recombinant androgen receptor (AR) reveals that the enhancer contains two AR binding sites at one end. Mutational analysis of the AR binding sites revealed the importance of the higher affinity one. The dissociation constant of the high affinity binding site (androgen response element I) was determined to be approximately 87 nM. The remainder of the enhancer contains elements that function synergistically with the AR. We discuss the structural organization of the PSCA enhancer and compare it with that found in other AR-regulated genes.

Identification of human male germ cell-associated kinase, a kinase transcriptionally activated by androgen in prostate cancer cells

Androgen is involved in both normal development and malignant transformation of prostate cells. The signal transduction pathways associated with these processes are not well understood. Using a novel kinase display approach, we have identified a protein kinase, human male germ cell-associated kinase (hMAK), which is transcriptionally induced by the androgenic hormone 5alpha-dihydrotestosterone (DHT). The kinetics of induction is rapid and dose-dependent, and the induction is not blocked by cycloheximide treatment. Real time reverse transcription-PCR studies demonstrated a 9-fold induction of hMAK by 10 nm DHT at 24 h post-stimulation. The expression levels of hMAK in prostate cancer cell lines are in general higher than those of normal prostate epithelial cells. A reverse transcription-PCR product encompassing the entire hMAK open reading frame was isolated. The results from sequencing analysis showed that the hMAK protein is 623 amino acids in length and contains a kinase catalytic domain at its N terminus, followed by a proline/glutamine-rich domain. The catalytic domain of this kinase contains sequence motifs related to both the cyclin-dependent kinase and the mitogen-activated protein kinase families. When expressed in COS1 cells, hMAK is kinase-active as demonstrated by autophosphorylation and phosphorylation of exogenous substrate and is localized in the nucleus. A 3.7-kilobase pair promoter of the hMAK locus was isolated from a human genomic DNA bacterial artificial chromosome clone and was shown to be activated by DHT. This activation can be blocked by an anti-androgen drug bicalutamide (Casodex), implicating the involvement of androgen receptor in this process. Taken together, these data suggest that hMAK is a protein kinase targeted by androgen that may participate in androgen-mediated signaling in prostate cancer cells.

Vitamin D and cancer

Vitamin D, a steroid hormone and exerts its biological effects through its active metabolite 1alpha, 25 dihydroxyvitamin D3 [1,25(OH)2D3]. Like steroid hormones, 1,25(OH)2D3 is efficacious at very low concentrations and serves as a ligand for vitamin D receptors (VDR), associating with VDR very high affinity. Despite its potent property as a differentiating agent, its use in the clinical practice is hampered by the induction of hypercalcemia at a concentration required to suppress cancer cell proliferation. Therefore nearly 400 structural analogs of vitamin D3 have been synthesized and evaluated for their efficacy and toxicity. Among these analogs, relatively less toxic but highly efficacious analogs, EB1089, RO24-5531, 1alpha-hydroxyvitamin D5 and a few others have been evaluated in a preclinical toxicity and in Phase I clinical trials for dose tolerance in advanced cancer patients. Clinical trials using vitamin D analogs for prevention or therapy of cancer patients are still in their infancy. Vitamin D mediates its action by two independent pathways. Genomic pathway involves nuclear VDR and induces biological effects by interactions with hormone response elements and modulation of differential gene expressions. Evidence also suggests that vitamin D analogs also interact with steroid hormone(s) inducible genes. The non-genomic pathway is characterized by rapid actions of vitamin D. It involves interactions with membrane-VDR interactions and its interactions with protein kinase C and by altering intracellular calcium channels. Thus, the development of nontoxic analogs of vitamin D analogs and understanding of their molecular mechanism(s) of action are of significant importance in the prevention and treatment of cancer by vitamin D.

Androgen-selective gene regulation in the prostate

Androgens are essential for normal prostate growth and function but are also intimately associated with prostate cancer, an important cause of mortality in the ageing male population. The effects of androgens are mediated via a specific androgen receptor (AR) belonging to the nuclear receptor family and acting as a ligand-dependent transcription factor. The AR is built in a modular fashion and composed of a long N-terminal region with transactivation functions, a central DNA-binding domain, an intermediate hinge region and a C-terminal ligand-binding domain with additional transactivation functions. In its inactive form, the AR is complexed to heat-shock proteins, and mainly cytoplasmic. Following activation, the AR enters the nucleus, binds to its cognate DNA response elements as a homodimer and stimulates gene transcription. Various cofactors directly interact with the AR to modulate gene transcription. In addition, cross-talk between the AR and other signalling pathways has been proven for several prostate-expressed genes. Understanding the intricate networks underlying androgen-selective gene regulation represents a formidable challenge but might also offer the chance to identify new drug targets for the treatment of prostate carcinoma.

Effect of geldanamycin on androgen receptor function and stability

In the ligand-binding inactive state, the steroid receptor heterocomplex contains Hsp90, Hsp70, high-molecular weight immunophilins, and other proteins. Hsp90 acts in association with co-chaperones to maintain the native state of the receptor within the cells. It was reported earlier that Hsp90 might not be as important for the androgen receptor (AR) activity as for the glucocorticoid receptor (GR) and the progesterone receptor (PR) activities. We used the Hsp90 inhibitor geldanamycin (GA) to explore the role of Hsp90 in the function of the AR heterocomplex. GA selectively binds to Hsp90 and inhibits its activity, leading to the loss of steroid receptor activity, and frequently, its degradation. In our study, LNCaP prostate cancer cells were treated with GA for 30 minutes or 24 hours, in the presence of mibolerone, a synthetic androgen. GA reduced the androgen-induced AR protein levels to 15% after 24 hours of treatment. Several androgen up-regulated genes, including immunophilin FKBP51 and prostate specific antigen (PSA), were reduced by GA treatment. In cells treated with GA after transfection with a PSA promoter or an androgen response element-driven reporter gene, AR-mediated transactivation of reporter gene expression was reversibly inhibited by GA. Loss of androgen-binding ability and AR levels was attributed to reduced transcription of AR-regulated gene expression. Degradation rate of 35S-labeled AR was significantly increased by GA in the presence or absence of mibolerone. GA induced the degradation of AR through the proteasomal pathway. AR in cells treated with proteasomal inhibitor lactacystin, was insoluble in Nonidet P-40 (NP40)-based buffer and could not restore the androgen-binding ability. We report here that GA treatment disrupted both hormone-binding activity and receptor protein stability, resulting in a dramatic loss of androgen-induced gene activation. These results show that Hsp90 activity is important for both the chaperone-mediated folding of the AR into a high-affinity ligand-binding conformation and the functional activity of the AR.

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.