Locus-wide chromatin remodeling and enhanced androgen receptor-mediated transcription in recurrent prostate tumor cells

Chromatin and Epigenetic Dysregulation of Prostate Cancer Development, Progression, and Therapeutic Response

The dysregulation of chromatin and epigenetics has been defined as the overarching cancer hallmark. By disrupting transcriptional regulation in normal cells and mediating tumor progression by promoting cancer cell plasticity, this process has the ability to mediate all defined hallmarks of cancer. In this review, we collect and assess evidence on the contribution of chromatin and epigenetic dysregulation in prostate cancer. We highlight important mechanisms leading to prostate carcinogenesis, the emergence of castration-resistance upon treatment with androgen deprivation therapy, and resistance to antiandrogens. We examine in particular the contribution of chromatin structure and epigenetics to cell lineage commitment, which is dysregulated during tumorigenesis, and cell plasticity, which is altered during tumor progression.

The involvement of hsa_circ_0000417 in the development of hypospadias by regulating AR

BACKGROUND

Congenital hypospadias is a common congenital malformation of the urinary system in male children. However, the role of circRNA in congenital hypospadias remains unknown.

METHODS

Differentially expressed circRNAs and mRNAs were identified by RNA sequencing. GO and KEEG analysis were performed to uncover the key function and pathways. The interaction networks were constructed and analyzed by competing endogenous (ce)RNA analysis. Immunohistochemistry (IHC) and qRT-PCR were used to detect the expressions of androgen receptor (AR) and hsa_circ_0000417 in normal and hypospadias tissues. Further, the correlation between hsa_circ_0000417 and other clinical indicators were calculated.

RESULTS

Compared with normal foreskin tissues, 1329 circRNAs and 978 mRNAs were significantly upregulated, 3176 circRNAs and 614 mRNAs were significantly downregulated in hypospadias tissues, respectively. MAPK and PI3K-Akt signaling pathways play important roles in congenital hypospadias. The expression of AR and hsa_circ_0000417 in 68 hypospadias tissues was significantly lower than that in 68 normal foreskin tissues (P < 0.05). The expression of the AR, as analyzed using IHC, was consistent with the qPCR results. A significant correlation was noted between the expression of AR and hsa_circ_0000417 in 68 clinical samples (P < 0.05). Furthermore, the expression level of hsa_circ_0000417 was associated with the incidence of other diseases and the location of the hypospadias site (P < 0.05). Expression of hsa_circ_0000417 was significantly downregulated in hypospadias patients without other diseases (P < 0.05).

CONCLUSION

Hsa_circ_0000417 may regulate the expression of AR, and the expression of hsa_circ_0000417 in normal foreskin tissues is associated with the occurrence of hypospadias.

Chromatin reprogramming as an adaptation mechanism in advanced prostate cancer

Tumor evolution is based on the ability to constantly mutate and activate different pathways under the selective pressure of targeted therapies. Epigenetic alterations including those of the chromatin structure are associated with tumor initiation, progression and drug resistance. Many cancers, including prostate cancer, present enlarged nuclei, and chromatin appears altered and irregular. These phenotypic changes are likely to result from epigenetic dysregulation. High-throughput sequencing applied to bulk samples and now to single cells has made it possible to study these processes in unprecedented detail. It is therefore timely to review the impact of chromatin relaxation and increased DNA accessibility on prostate cancer growth and drug resistance, and their effects on gene expression. In particular, we focus on the contribution of chromatin-associated proteins such as the bromodomain-containing proteins to chromatin relaxation. We discuss the consequence of this for androgen receptor transcriptional activity and briefly summarize wider gain-of-function effects on other oncogenic transcription factors and implications for more effective prostate cancer treatment.

Molecular Mechanisms Related to Hormone Inhibition Resistance in Prostate Cancer

Management of metastatic or advanced prostate cancer has acquired several therapeutic approaches that have drastically changed the course of the disease. In particular due to the high sensitivity of prostate cancer cells to hormone depletion, several agents able to inhibit hormone production or binding to nuclear receptor have been evaluated and adopted in clinical practice. However, despite several hormonal treatments being available nowadays for the management of advanced or metastatic prostate cancer, the natural history of the disease leads inexorably to the development of resistance to hormone inhibition. Findings regarding the mechanisms that drive this process are of particular and increasing interest as these are potentially related to the identification of new targetable pathways and to the development of new drugs able to improve our patients' clinical outcomes.

MRGBP promotes AR-mediated transactivation of KLK3 and TMPRSS2 via acetylation of histone H2A.Z in prostate cancer cells

The androgen receptor (AR) promotes growth of prostate cancer cells by controlling the expression of target genes. This study showed that MRG domain binding protein (MRGBP) accelerated AR-mediated transactivation. We first showed that MRGBP promoted growth of AR-positive prostate cancer cells. MRGBP increased the expression of certain AR target genes, including KLK3 and TMPRSS2, and it associated with AR binding regions of these genes during androgen treatment. Furthermore, MRGBP interacted with MRG15 and TIP60 in prostate cancer cells. Androgen-stimulated AR enhanced histone H3K4me1 or H3K4me3 levels at AR binding regions. MRGBP was recruited to active gene regions through its binding with H3K4me1/3 by MRG15. Then, MRGBP promoted recruitment of TIP60 and acetylation of histone variant H2A.Z at the location of AR binding. Accordingly, AR occupancy of the AR binding regions was increased by MRGBP. Together, these results suggest that MRGBP promotes activation of AR-associated enhancer and promoter regions through an epigenetic mechanism.

Epigenetic Regulation in Prostate Cancer Progression

Purpose of Review

An important number of newly identified molecular alterations in prostate cancer affect gene encoding master regulators of chromatin biology epigenetic regulation. This review will provide an updated view of the key epigenetic mechanisms underlying prostate cancer progression, therapy resistance, and potential actionable mechanisms and biomarkers.

Recent Findings

Key players in chromatin biology and epigenetic master regulators has been recently described to be crucially altered in metastatic CRPC and tumors that progress to AR independency. As such, epigenetic dysregulation represents a driving mechanism in the reprograming of prostate cancer cells as they lose AR-imposed identity.

Summary

Chromatin integrity and accessibility for transcriptional regulation are key features altered in cancer progression, and particularly relevant in nuclear hormone receptor-driven tumors like prostate cancer. Understanding how chromatin remodeling dictates prostate development and how its deregulation contributes to prostate cancer onset and progression may improve risk stratification and treatment selection for prostate cancer patients.

Androgen receptor-mediated downregulation of microRNA-221 and -222 in castration-resistant prostate cancer

MicroRNAs (miRNAs) play important roles in cancer formation and progression by suppressing the production of key functional proteins at the post-transcriptional level in a sequence-specific manner. While differential expression of miRNAs is widely observed in cancers including prostate cancer (PCa), how these miRNAs are transcriptionally regulated is largely unknown. MiRNA-221 and miRNA-222 (miR-221/-222) are well-established oncogenes and overexpressed in breast, liver, pancreas, and lung cancer, but their expression and biological functions in PCa remain controversial. Both up and down regulation have been observed in patient samples. Specifically, studies have demonstrated miR-221/-222 function as oncogenes, and promote PCa cell proliferation and the development of castration-resistant prostate cancer (CRPC). However, the expression level of miR-221/-222 is downregulated in several miRNA expression profiling studies. In this study, we demonstrate miR-221/-222 are androgen receptor (AR)-repressed genes and reside in a long primary transcript (pri-miRNA). Derepression of miR-221/-222 after androgen deprivation therapy (ADT) may enhance PCa cell proliferation potential through promoting G1/S phase transition. This function is likely transient but important in the development of CRPC. Downregulation of miR-221/-222 subsequently occurs once AR activity is restored through AR overexpression in CRPC. Our findings shed light on the complexity of transcriptional regulation of miRNAs in PCa and suggest context-dependent targeting of oncogenic miRNAs.

Exploiting Epigenetic Alterations in Prostate Cancer

Prostate cancer affects an increasing number of men worldwide and is a leading cause of cancer-associated deaths. Beside genetic mutations, many epigenetic alterations including DNA and histone modifications have been identified in clinical prostate tumor samples. They have been linked to aberrant activity of enzymes and reader proteins involved in these epigenetic processes, leading to the search for dedicated inhibitory compounds. In the wake of encouraging anti-tumor efficacy results in preclinical models, epigenetic modulators addressing different targets are now being tested in prostate cancer patients. In addition, the assessment of microRNAs as stratification biomarkers, and early clinical trials evaluating suppressor microRNAs as potential prostate cancer treatment are being discussed.

Src promotes castration-recurrent prostate cancer through androgen receptor-dependent canonical and non-canonical transcriptional signatures

Progression of prostate cancer (PC) to castration-recurrent growth (CRPC) remains dependent on sustained expression and transcriptional activity of the androgen receptor (AR). A major mechanism contributing to CRPC progression is through the direct phosphorylation and activation of AR by Src-family (SFK) and ACK1 tyrosine kinases. However, the AR-dependent transcriptional networks activated by Src during CRPC progression have not been elucidated. Here, we show that activated Src (Src527F) induces androgen-independent growth in human LNCaP cells, concomitant with its ability to induce proliferation/survival genes normally induced by dihydrotestosterone (DHT) in androgen-dependent LNCaP and VCaP cells. Src induces additional gene signatures unique to CRPC cell lines, LNCaP-C4-2 and CWR22Rv1, and to CRPC LuCaP35.1 xenografts. By comparing the Src-induced AR-cistrome and/or transcriptome in LNCaP to those in CRPC and LuCaP35.1 tumors, we identified an 11-gene Src-regulated CRPC signature consisting of AR-dependent, AR binding site (ARBS)-associated genes whose expression is altered by DHT in LNCaP[Src527F] but not in LNCaP cells. The differential expression of a subset (DPP4, BCAT1, CNTNAP4, CDH3) correlates with earlier PC metastasis onset and poorer survival, with the expression of BCAT1 required for Src-induced androgen-independent proliferation. Lastly, Src enhances AR binding to non-canonical ARBS enriched for FOXO1, TOP2B and ZNF217 binding motifs; cooperative AR/TOP2B binding to a non-canonical ARBS was both Src- and DHT-sensitive and correlated with increased levels of Src-induced phosphotyrosyl-TOP2B. These data suggest that CRPC progression is facilitated via Src-induced sensitization of AR to intracrine androgen levels, resulting in the engagement of canonical and non-canonical ARBS-dependent gene signatures.

Epigenomic Regulation of Androgen Receptor Signaling: Potential Role in Prostate Cancer Therapy

Androgen receptor (AR) signaling remains the major oncogenic pathway in prostate cancer (PCa). Androgen-deprivation therapy (ADT) is the principle treatment for locally advanced and metastatic disease. However, a significant number of patients acquire treatment resistance leading to castration resistant prostate cancer (CRPC). Epigenetics, the study of heritable and reversible changes in gene expression without alterations in DNA sequences, is a crucial regulatory step in AR signaling. We and others, recently described the technological advance Chem-seq, a method to identify the interaction between a drug and the genome. This has permitted better understanding of the underlying regulatory mechanisms of AR during carcinogenesis and revealed the importance of epigenetic modifiers. In screening for new epigenomic modifiying drugs, we identified SD-70, and found that this demethylase inhibitor is effective in CRPC cells in combination with current therapies. The aim of this review is to explore the role of epigenetic modifications as biomarkers for detection, prognosis, and risk evaluation of PCa. Furthermore, we also provide an update of the recent findings on the epigenetic key processes (DNA methylation, chromatin modifications and alterations in noncoding RNA profiles) involved in AR expression and their possible role as therapeutic targets.

Putative functions of tissue kallikrein-related peptidases in vaginal fluid

Cervical-vaginal fluid (CVF) is a complex biological fluid that hydrates the mucosa of the lower female reproductive system. In-depth proteomic and biochemical studies on CVF have revealed that it contains large amounts of endogenous proteases and protease inhibitors, including an abundance of several members of the tissue kallikrein-related peptidase (KLK) family. Despite their ubiquitous presence in human tissues and fluids, KLK expression levels vary considerably, with maximum expression observed in reproduction-related tissues and fluids. The roles of KLKs in the lower female reproductive system are not fully understood. The activation of KLKs in CVF is dependent on pH and various modes of KLK regulation in the vagina exist. KLKs have been postulated to have roles in physiological functions related to antimicrobial processes, vaginal and cervical epithelial desquamation, sperm transport, and the processing of fetal membranes as observed in preterm premature rupture of membranes. Increased understanding of the functional roles of KLKs in the lower female reproductive system could lead to new diagnostic and therapeutic modalities for conditions such as vaginal infections and vaginal atrophy.

Androgen receptor: acting in the three-dimensional chromatin landscape of prostate cancer cells

Androgen receptor (AR) acts as a hormone-controlled transcription factor that conveys the messages of both natural and synthetic androgens to the level of genes and gene programs. Defective AR signaling leads to a wide array of androgen insensitivity disorders, and deregulated AR function, in particular overexpression of AR, is involved in the growth and progression of prostate cancer. Classic models of AR action view AR-binding sites as upstream regulatory elements in gene promoters or their proximity. However, recent wider genomic screens indicate that AR target genes are commonly activated through very distal chromatin-binding sites. This highlights the importance of long-range chromatin regulation of transcription by the AR, shifting the focus from the linear gene models to three-dimensional models of AR target genes and gene programs. The capability of AR to regulate promoters from long distances in the chromatin is particularly important when evaluating the role of AR in the regulation of genes in malignant prostate cells that frequently show striking genomic aberrations, especially gene fusions. Therefore, in addition to the mechanisms of DNA loop formation between the enhancer bound ARs and the transcription apparatus at the target core promoter, the mechanisms insulating distally bound ARs from promiscuously making contacts and activating other than their normal target gene promoters are critical for proper physiological regulation and thus currently under intense investigation. This review discusses the current knowledge about the AR action in the context of gene aberrations and the three-dimensional chromatin landscape of prostate cancer cells.

REST mediates androgen receptor actions on gene repression and predicts early recurrence of prostate cancer

The androgen receptor (AR) is a key regulator of prostate tumorgenesis through actions that are not fully understood. We identified the repressor element (RE)-1 silencing transcription factor (REST) as a mediator of AR actions on gene repression. Chromatin immunoprecipitation showed that AR binds chromatin regions containing well-characterized cis-elements known to mediate REST transcriptional repression, while cell imaging studies confirmed that REST and AR closely co-localize in vivo. Androgen-induced gene repression also involves modulation of REST protein turnover through actions on the ubiquitin ligase β-TRCP. Androgen deprivation or AR blockage with inhibitor MDV3100 (Enzalutamide) leads to neuroendocrine (NE) differentiation, a phenomenon that is mimicked by REST inactivation. Gene expression profiling revealed that REST not only acts to repress neuronal genes but also genes involved in cell cycle progression, including Aurora Kinase A, that has previously been implicated in the growth of NE-like castration-resistant tumors. The analysis of prostate cancer tissue microarrays revealed that tumors with reduced expression of REST have higher probability of early recurrence, independently of their Gleason score. The demonstration that REST modulates AR actions in prostate epithelia and that REST expression is negatively correlated with disease recurrence after prostatectomy, invite a deeper characterization of its role in prostate carcinogenesis.

Hypoxia enhances the expression of prostate-specific antigen by modifying the quantity and catalytic activity of Jumonji C domain-containing histone demethylases

Oxygen concentration in prostate cancer tissue is significantly low, i.e. ~0.3% O2. This study showed that pathological hypoxia (<0.5% O2) increased the expression of androgen receptor (AR) target genes such as prostate-specific antigen (PSA) and kallikrein-related peptidase 2 in LNCaP human prostate cancer cells by modifying the quantity and activity of related Jumonji C domain-containing histone demethylases (JMJDs). Under pathological hypoxia, the catalytic activities of JMJD2A, JMJD2C and Jumonji/ARID domain-containing protein 1B (JARID1B) were blocked due to the lack of their substrate, i.e. oxygen. Chromatin immunoprecipitation analyses showed that hypoxia increased the appearance of H3K9me3 and H3K4me3, substrates of JMJD2s and JARID1B, respectively, in the PSA enhancer. In contrast, JMJD1A, which demethylates both H3K9me2 and H3K9me1, maintained its catalytic activity even under severe hypoxia. Furthermore, hypoxia increased the expression of JMJD1A. Hypoxia and androgen additively increased the recruitment of JMJD1A and p300 on the enhancer region of PSA through interaction with the hypoxia-inducible factor-1α and AR, both of which bind the PSA enhancer. Thus, hypoxia enhanced the demethylation of H3K9me2 and H3K9me1, leading to provide unmethylated H3K9 residues that are substrates for histone acetyltransferase, p300. Consequently, hypoxia increased the acetylation of histones of the PSA enhancer, which facilitates its transcription.

Integrated transcriptomic and epigenomic analysis of primary human lung epithelial cell differentiation

Elucidation of the epigenetic basis for cell-type specific gene regulation is key to gaining a full understanding of how the distinct phenotypes of differentiated cells are achieved and maintained. Here we examined how epigenetic changes are integrated with transcriptional activation to determine cell phenotype during differentiation. We performed epigenomic profiling in conjunction with transcriptomic profiling using in vitro differentiation of human primary alveolar epithelial cells (AEC). This model recapitulates an in vivo process in which AEC transition from one differentiated cell type to another during regeneration following lung injury. Interrogation of histone marks over time revealed enrichment of specific transcription factor binding motifs within regions of changing chromatin structure. Cross-referencing of these motifs with pathways showing transcriptional changes revealed known regulatory pathways of distal alveolar differentiation, such as the WNT and transforming growth factor beta (TGFB) pathways, and putative novel regulators of adult AEC differentiation including hepatocyte nuclear factor 4 alpha (HNF4A), and the retinoid X receptor (RXR) signaling pathways. Inhibition of the RXR pathway confirmed its functional relevance for alveolar differentiation. Our incorporation of epigenetic data allowed specific identification of transcription factors that are potential direct upstream regulators of the differentiation process, demonstrating the power of this approach. Integration of epigenomic data with transcriptomic profiling has broad application for the identification of regulatory pathways in other models of differentiation.

Understanding the role of epigenetic control of gene expression is critical to the full description of biological processes, such as development and regeneration. Herein we utilize the differentiation of cells from the distal lung to gain insight into the correlation between the epigenetic landscape, molecular signaling events, and eventual changes in transcription and phenotype. We found that by integrating epigenetic profiling with whole genome transcriptomic data we were able to determine which molecular signaling events were activated and repressed during adult alveolar epithelial cell differentiation, and we identified epigenetic changes that contributed to these changes. Furthermore, we validated the role of one of these predicted but not previously identified pathways, retinoid X receptor signaling, in this process.

Genome-wide DNA methylation profiling of CpG islands in hypospadias

PURPOSE

Hypospadias is one of the most frequent genital malformations in the male newborn, and results from abnormal penile and urethral development. The etiology of hypospadias remains largely unknown despite intensive investigations. Fetal androgens have a crucial role in genital differentiation. Recent studies have suggested that molecular mechanisms that underlie the effects of androgens on the fetus may involve disruption of epigenetic programming of gene expression during development. We assessed whether epigenetic modification of DNA methylation is associated with hypospadias in a case-control study of 12 hypospadias and 8 control subjects.

MATERIALS AND METHODS

Genome-wide DNA methylation profiling was performed on the study subjects using the Illumina Infinium® HumanMethylation450 BeadChip, which enables the direct investigation of methylation status of more than 485,000 individual CpG sites throughout the genome. The methylation level at each CpG site was compared between cases and controls using the t test and logistic regression.

RESULTS

We identified 14 CpG sites that were associated with hypospadias with p <0.00001. These CpG sites were in or near the SCARB1, MYBPH, SORBS1, LAMA4, HOXD11, MYO1D, EGFL7, C10orf41, LMAN1L and SULF1 genes. Two CpG sites in SCARB1 and MYBPH genes remained statistically significant after correction for multiple testing (p = 2.61 × 10(-09), p(corrected) = 0.008; p = 3.06 × 10(-08), p(corrected) = 0.02, respectively).

CONCLUSIONS

To our knowledge this is the first study to investigate hypospadias using a unique and novel epigenetic approach. Our findings suggest DNA methylation patterns are useful in identifying new genes such as SCARB1 and MYBPH that may be involved in the etiology of hypospadias.

Persistent androgen receptor-mediated transcription in castration-resistant prostate cancer under androgen-deprived conditions

The androgen receptor (AR) is a ligand-inducible transcription factor that mediates androgen action in target tissues. Upon ligand binding, the AR binds to thousands of genomic loci and activates a cell-type specific gene program. Prostate cancer growth and progression depend on androgen-induced AR signaling. Treatment of advanced prostate cancer through medical or surgical castration leads to initial response and durable remission, but resistance inevitably develops. In castration-resistant prostate cancer (CRPC), AR activity remains critical for tumor growth despite androgen deprivation. Although previous studies have focused on ligand-dependent AR signaling, in this study we explore AR function under the androgen-deprived conditions characteristic of CRPC. Our data demonstrate that AR persistently occupies a distinct set of genomic loci after androgen deprivation in CRPC. These androgen-independent AR occupied regions have constitutively open chromatin structures that lack the canonical androgen response element and are independent of FoxA1, a transcription factor involved in ligand-dependent AR targeting. Many AR binding events occur at proximal promoters, which can act as enhancers to augment transcriptional activities of other promoters through DNA looping. We further show that androgen-independent AR binding directs a gene expression program in CRPC, which is necessary for the growth of CRPC after androgen withdrawal.

Epigenetic regulation of kallikrein-related peptidases: there is a whole new world out there

The human kallikreins are a cluster of 15 kallikreins and kallikrein-related peptidases (KLKs). Evidence shows the involvement of KLKs in a wide range of pathophysiological processes, and underscores their potential contribution to cancer, skin and neurodegenerative disorders. The control of KLK expression is not fully elucidated. Understanding the mechanisms controlling KLK expression is an essential step towards exploring the pathogenesis of several diseases and the use of KLKs as disease biomarkers and/or therapeutic targets. Recently, epigenetic changes (including methylation, histone modification and microRNAs [miRNAs]) have drawn attention as a new dimension for controlling KLK expression. Reports showed the effect of methylation on the expression of KLK genes. This was also shown to have potential utility as a prognostic marker in cancer. miRNAs are small RNAs that control the expression of their targets at the post-transcriptional level. Target prediction showed that KLKs are potential targets of miRNAs that are dysregulated in tumors, including prostate, kidney and ovarian cancers, with downstream effect on tumor proliferation. Experimental validation remains an essential step to confirm the KLK-miRNA interaction. Epigenetic regulation of KLKs holds promise for an array of therapeutic applications in many diseases including cancer.

Androgen receptor overexpression alters binding dynamics of the receptor to chromatin and chromatin structure

BACKGROUND

Castration-resistant prostate cancers (CRPCs) overexpress often androgen receptor (AR). Here, we investigated the effect of AR overexpression on the dynamics of AR loading and RNA polymerase II (RNA Pol II) recruitment to chromatin. Acetylation of histone 3 (AcH3) on lysines 9 and 14 (K9 and K14) was also studied.

METHODS

We used an LNCaP-based AR overexpression cell line model that includes a control line and two sublines, LNCaP-ARmo and LNCaP-ARhi, which overexpress AR twofold to threefold and fourfold to fivefold, respectively. Cells were exposed to 1 or 100 nM of dihydrotestosterone (DHT). Chromatin immunoprecipitation (ChIP) on the promoters and enhancers of prostate specific antigen (PSA) and transmembrane protease, serine 2 (TMPRSS2) genes was performed. qRT-PCR was used to measure the levels of PSA and TMPRSS2 transcripts.

RESULTS

Upon stimulation with 1 nM DHT, AR and RNA Pol II were recruited onto PSA and TMPRSS2 enhancer regions to a greater extent (P < 0.05) in AR-overexpressing cells compared to control cells. The difference in AR loading between the control and AR-overexpressing cells was abolished by a higher DHT concentration. The ratio of AcH3/H3 was increased in AR-overexpressing cells. The induction of transcription of PSA and TMPRSS2 occurred earlier in the AR-overexpressing cells.

CONCLUSIONS

Our findings suggest that the levels of AR potentiate the recruitment of the AR, as well as components of the basic transcription machinery, to chromatin and affect the acetylation of histones in the presence of low levels of androgens. These changes result in enhanced gene transcription of AR target genes.

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.

The CXCL12/CXCR4 axis promotes ligand-independent activation of the androgen receptor

The molecular mechanisms responsible for the transition of some prostate cancers from androgen ligand-dependent to androgen ligand-independent are incompletely established. Molecules that are ligands for G protein coupled receptors (GPCRs) have been implicated in ligand-independent androgen receptor (AR) activation. The purpose of this study was to examine whether CXCL12, the ligand for the GPCR, CXCR4, might mediate prostate cancer cell proliferation through AR-dependent mechanisms involving functional transactivation of the AR in the absence of androgen. The results of these studies showed that activation of the CXCL12/CXCR4 axis promoted: The nuclear accumulation of both wild-type and mutant AR in several prostate epithelial cell lines; AR-dependent proliferative responses; nuclear accumulation of the AR co-regulator SRC-1 protein; SRC-1:AR protein:protein association; co-localization of AR and SRC-1 on the promoters of AR-regulated genes; AR- and SRC-1 dependent transcription of AR-regulated genes; AR-dependent secretion of the AR-regulated PSA protein; P13K-dependent phosphorylation of AR; MAPK-dependent phosphorylation of SRC-1, and both MAPK- and P13K-dependent secretion of the PSA protein, in the absence of androgen. Taken together, these studies identify CXCL12 as a novel, non-steroidal growth factor that promotes the growth of prostate epithelial cells through AR-dependent mechanisms in the absence of steroid hormones. These findings support the development of novel therapeutics targeting the CXCL12/CXCR4 axis as an ancillary to those targeting the androgen/AR axis to effectively treat castration resistant/recurrent prostate tumors.

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.

Mechanisms of prostate cancer initiation and progression

Prostate cancer is a major health problem as it continues to be the most frequently diagnosed cancer in men in the Western world. While improved early detection significantly decreased mortality, prostate cancer still remains the second leading cause of cancer-related death in Western men. Understanding the mechanisms of prostate cancer initiation and progression should have a significant impact on development of novel therapeutic approaches that can help to combat this disease. The recent explosion of novel high-throughput genetic technologies together with studies in animal models and human tissues allowed a comprehensive analysis and functional validation of the molecular changes. This chapter will summarize and discuss recently identified critical genetic and epigenetic changes that drive prostate cancer initiation and progression. These discoveries should help concentrate the efforts of drug development on key pathways and molecules, and finally translate the knowledge that is gained from mechanistic studies into effective treatments.

Androgen receptor mutations are associated with altered epigenomic programming as evidenced by HOXA5 methylation

Male external genital differentiation is accompanied by implementation of a long-term, male-specific gene expression pattern indicating androgen programming in cultured genital fibroblasts. We hypothesized the existence of an epigenetic background contributing to this phenomenon. DNA methylation levels in 2 normal scrotal fibroblast strains from 46,XY males compared to 2 labia majora fibroblast strains from 46,XY females with complete androgen insensitivity syndrome (AIS) due to androgen receptor (AR) mutations were analyzed by Illumina GoldenGate methylation arrays®. Results were validated with pyrosequencing in labia majora fibroblast strains from fifteen 46,XY patients and compared to nine normal male scrotal fibroblast strains. HOXA5 showed a significantly higher methylation level in complete AIS. This finding was confirmed by bisulfite pyrosequencing of 14 CpG positions within the HOXA5 promoter in the same strains. Extension of the 2 groups revealed a constant low HOXA5 methylation pattern in the controls in contrast to a highly variable methylation pattern in the AIS patients. HOXA5 represents a candidate gene of androgen-mediated promoter methylation. The constantly low HOXA5 DNA methylation level of normal male scrotal fibroblast strains and the frequently high methylation levels in labia majora fibroblast strains in AIS indicate for the first time that androgen programming in sexual differentiation is not restricted to global gene transcription but also occurs at the epigenetic level.

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.

A systematic approach to understand the functional consequences of non-protein coding risk regions

A primary goal of genetic association studies is to elucidate genes and novel biological mechanisms involved in disease. Recently, genome-wide association studies have identified many common genetic variants that are significantly associated with complex diseases such as cancer. In contrast to Mendelian disorders, a sizable fraction of the variants lies outside known protein-coding regions; therefore, understanding their biological consequences presents a major challenge in human genetics. Here we describe an integrated framework to allow non-protein coding loci to be annotated with respect to regulatory functions. This will facilitate identification of target genes as well as prioritize variants for functional testing.

Functional enhancers at the gene-poor 8q24 cancer-linked locus

Multiple discrete regions at 8q24 were recently shown to contain alleles that predispose to many cancers including prostate, breast, and colon. These regions are far from any annotated gene and their biological activities have been unknown. Here we profiled a 5-megabase chromatin segment encompassing all the risk regions for RNA expression, histone modifications, and locations occupied by RNA polymerase II and androgen receptor (AR). This led to the identification of several transcriptional enhancers, which were verified using reporter assays. Two enhancers in one risk region were occupied by AR and responded to androgen treatment; one contained a single nucleotide polymorphism (rs11986220) that resides within a FoxA1 binding site, with the prostate cancer risk allele facilitating both stronger FoxA1 binding and stronger androgen responsiveness. The study reported here exemplifies an approach that may be applied to any risk-associated allele in non-protein coding regions as it emerges from genome-wide association studies to better understand the genetic predisposition of complex diseases.

Genome-wide scans of inherited genetic variation in the normal population have recently identified many sites (loci) associated with the predisposition to complex diseases such as cancer. Some of these cancer-associated loci, however, are devoid of genes (situated in so-called “gene deserts”) and the mechanism(s) of the association are not readily apparent. In the work reported here, we show that loci associated with several cancers in a gene desert found at chromosomal area 8q24 have embedded regulatory sequences affecting gene expression as enhancers, and in one case this activity is modulated by genetic variation. The results provide insight into the mechanism(s) governing genetic cancer risk.

Hyperacetylation in prostate cancer induces cell cycle aberrations, chromatin reorganization and altered gene expression profiles

Histone acetylation is a fundamental mechanism in the regulation of local chromatin conformation and gene expression. Research has focused on the impact of altered epigenetic environments on the expression of specific genes and their pathways. However, changes in histone acetylation also have a global impact on the cell. In this study we used digital texture analysis to assess global chromatin patterns following treatment with trichostatin A (TSA) and have observed significant alterations in the condensation and distribution of higher-order chromatin, which were associated with altered gene expression profiles in both immortalised normal PNT1A prostate cell line and androgen-dependent prostate cancer cell line LNCaP. Furthermore, the extent of TSA-induced disruption was both cell cycle and cell line dependent. This was illustrated by the identification of sub-populations of prostate cancer cells expressing high levels of H3K9 acetylation in the G(2)/M phase of the cell cycle that were absent in normal cell populations. In addition, the analysis of enriched populations of G(1) cells showed a global decondensation of chromatin exclusively in normal cells.

Long-range activation of FKBP51 transcription by the androgen receptor via distal intronic enhancers

Androgen receptor (AR) is a ligand-controlled transcription factor frequently deregulated in prostate carcinomas. Since there is scarce information on the action of AR on the chromatin level, we have elucidated the molecular mechanisms underlying the androgen-dependent regulation of immunophilin FKBP51 in prostate cancer cells. In comparison to the canonical AR target PSA, FKBP51 is more rapidly and strongly induced by androgen, with the regulation occurring merely at the transcriptional level. FKBP51 locus harbors 13 in silico-predicted androgen response elements (AREs), with most of them located downstream from transcription start site (TSS) and capable of binding AR in vitro. Chromatin immunoprecipitation assays in VCaP and LNCaP prostate cancer cells indicate that activation of the locus by the AR relies on four major intronic sites, with the compound ARE-containing sites ≥90 kb downstream from the TSS playing critical roles. Binding of agonist-loaded AR onto these sites in vivo was accompanied with significant recruitment of RNA polymerase II and BRM-containing chromatin remodeling complexes to the FKBP51 locus, which resulted in changes in the histone density of the locus. Our results indicate that very distal AREs act as genuine and robust enhancers, highlighting the importance of long-range regulation of transcription by the AR.

Repression of Runx2 by androgen receptor (AR) in osteoblasts and prostate cancer cells: AR binds Runx2 and abrogates its recruitment to DNA

Runx2 and androgen receptor (AR) are master transcription factors with pivotal roles in bone metabolism and prostate cancer (PCa). We dissected AR-mediated repression of Runx2 in dihydrotestosterone (DHT)-treated osteoblastic and PCa cells using reporter assays and endogenous Runx2 target genes. Repression required DHT, but not AR's transactivation function, and was associated with nuclear colocalization of the two proteins. Runx2 and AR coimmunoprecipitated and interacted directly in glutathione-S-transferase pull-down assays. Interaction was ionic in nature. Intact AR DNA-binding domain (DBD) was necessary and sufficient for both interaction with Runx2 and its repression. Runx2 sequences required for interaction were the C-terminal 132 amino acid residues together with the Runt DBD. Runx2 DNA binding was abrogated by endogenous AR in chromatin immunoprecipitation assays and by recombinant AR-DBD in gel shift assays. Furthermore, AR caused increased nuclear mobility of Runx2 as indicated by faster fluorescence recovery after photobleaching. Thus, AR binds Runx2 and abrogates its binding to DNA and possibly to other nuclear components. Clinical relevance of our results was suggested by an inverse correlation between expression of AR-responsive prostate-specific antigen and osteocalcin genes in PCa biopsies. Given the tumor suppressor properties of Runx2, its repression by AR may constitute a mechanism of hormone carcinogenesis. Attenuation of Runx2 by AR in osteoblasts may play a role in skeletal metabolism: the bone-sparing effect of androgens is attributable, in part, to keeping Runx2 activity in check and preventing high-turnover bone disease such as seen after castration and in transgenic mice overexpressing Runx2 in osteoblasts.

Androgen-induced coactivator ANCCA mediates specific androgen receptor signaling in prostate cancer

Androgen receptor (AR) plays a pivotal role in prostate cancer, primarily by regulating different gene expression programs elicited by androgen, which is important for cancer cell proliferation, survival, and differentiation. It is believed that the transcriptional function of AR is mediated largely by distinct nuclear coregulators. We report here the identification of ANCCA (also known as ATAD2), a new member of the AAA+ ATPase family proteins, as a novel AR coactivator. ANCCA interacts directly with AR and enhances its transcriptional activity, and is required for androgen-stimulated expression of a specific subgroup of genes including IGF1R, IRS-2, SGK1, and survivin. Upon androgen stimulation, ANCCA together with AR is recruited to the specific AR target genes. Suppression of ANCCA expression strongly inhibited the proliferation of androgen-responsive or androgen-independent, AR-positive prostate cancer cells and caused a significant increase of cellular apoptosis. Strikingly, the ANCCA gene itself, located at chromosome 8q24, is highly induced by androgen in androgen-dependent prostate cancer cells and xenograft tumors. Although ANCCA is hardly detected in normal human prostate tissue, high levels of ANCCA are found in hormone-independent prostate cancer cell lines, xenograft tumor, and a subset of prostate cancers with high Gleason scores. Together, these findings suggest that ANCCA plays an important role in prostate cancer by mediating specific AR functions in cancer cell survival and proliferation. The possession of ATPase and bromodomain by ANCCA makes it an attractive target for the development of therapeutics for the disease.

Inhibition of AR-mediated transcription by binding of Oct1 to a motif enriched in AR-occupied regions

BACKGROUND

The androgen receptor (AR) plays roles in prostate development and cancer (PCa). In response to androgens, the AR binds to androgen-response elements (AREs) to modulate gene transcription. The responses of such genes are dependent on the cellular milieu and on sequences around the AREs, which attract other transcription factors. Previously, bioinformatic analysis of 62 AR-occupied regions (ARORs) in PCa cells revealed enrichment for both AREs and a TTGGCAAATA-like motif. We undertook the present study to investigate the significance of the TTGGCAAATA-like motif.

METHODS

Prostate cancer cell lines, LNCaP and C4-2B, were analyzed by transient transfections of wild-type and mutant reporter constructs, electro-mobility shift assays (EMSAs), and RT-qPCR analysis of endogenous genes.

RESULTS

In two of six tested ARORs, point mutations in the TTGGCAAATA-like motif resulted in inhibition of DHT-mediated enhancer activity. EMSA revealed that Oct1 bound the motif, and that the mutations that abolished DHT responsiveness in the transfection assays augmented Oct1 binding. These results suggest a role for Oct1 as a context-dependent negative coregulator of AR. Consistent with this, siRNA knockdown of Oct1 increased the DHT-mediated enhancer activity of transfected reporters as well as an endogenous AR target gene, transglutaminase 2.

CONCLUSIONS

Oct1 negatively regulates DHT-mediated enhancer activity in a subset of ARORs. The enrichment of ARORs for the Oct-binding, TTGGCAAATA-like motif may reflect a mechanism that utilizes Oct1 to keep AR activity in check at some ARORs, while augmenting AR activity in other ARORs. Therefore, Oct1 may have regulatory functions in prostate development and cancer progression.

Histone deacetylases are required for androgen receptor function in hormone-sensitive and castrate-resistant prostate cancer

Transcriptional activity of the androgen receptor (AR) is crucial for growth and survival of prostate cancer even upon development of resistance to androgen ablation and antiandrogen therapies. Therefore, novel therapies that can suppress AR transcriptional activity when conventional hormone therapies fail are needed. Here, we show that histone deacetylase (HDAC) inhibitors, including SAHA (vorinostat) and LBH589, which are currently being tested in clinic, could be such a therapy. HDAC inhibitors block the AR-mediated transcriptional activation of many genes, including the TMPRSS2 gene involved in fusion with ETS family members in a majority of prostate cancers. Genetic knockdown of either HDAC1 or HDAC3 can also suppress expression of AR-regulated genes, recapitulating the effect of HDAC inhibitor treatment. Whereas HDAC inhibitor treatment can lower androgen receptor protein levels in prostate cancer cells, we show that independent of AR protein levels, HDAC inhibitors block AR activity through inhibiting the assembly of coactivator/RNA polymerase II complex after AR binds to the enhancers of target genes. Failed complex assembly is associated with a phase shift in the cyclical wave of AR recruitment that typically occurs in response to ligand treatment. HDAC inhibitors retain the ability to block AR activity in castration-resistant prostate cancer models and, therefore, merit clinical investigation in this setting. The HDAC-regulated AR target genes defined here can serve as biomarkers to ensure sufficient levels of HDAC inhibition.

Germline competent embryonic stem cells derived from rat blastocysts

Rats have important advantages over mice as an experimental system for physiological and pharmacological investigations. The lack of rat embryonic stem (ES) cells has restricted the availability of transgenic technologies to create genetic models in this species. Here, we show that rat ES cells can be efficiently derived, propagated, and genetically manipulated in the presence of small molecules that specifically inhibit GSK3, MEK, and FGF receptor tyrosine kinases. These rat ES cells express pluripotency markers and retain the capacity to differentiate into derivatives of all three germ layers. Most importantly, they can produce high rates of chimerism when reintroduced into early stage embryos and can transmit through the germline. Establishment of authentic rat ES cells will make possible sophisticated genetic manipulation to create models for the study of human diseases.

Prolonged androgen receptor loading onto chromatin and the efficient recruitment of p160 coactivators contribute to androgen-independent growth of prostate cancer cells

BACKGROUND

Growth of most ablation-resistant prostate cancers (CaPs) is dependent on androgen receptor (AR) activity in chromatin, but cancer cells in these tumors have acquired altered AR activation. It is unclear how the aberrantly activated AR loads onto regulatory regions of AR-targeted genes. The purpose of this study was to assess the AR chromatin loading in an androgen-depleted environment.

METHODS

The expression of PSA in androgen-resistant CaP cells was determined using RT-PCR and Western blot analysis. In order to investigate the binding of the AR to the PSA gene regulatory regions, chromatin immunoprecipitation (ChIP) was performed in the androgen-independent cds2 cell line in the presence or absence of androgens. In addition, we examined the involvement of p160 coactivators in the chromatin loading of the AR.

RESULTS

It was found that constitutive activation of PSA expression was the result of sustained occupancy by the AR at the regulatory region of this gene. This stable AR loading was not blocked by the AR antagonist bicalutamide. Furthermore, androgen-resistant CaP cells highly expressed both AR and the p160 coactivators and the AR was able to recruit TIF2. Downregulation of TIF2 using short hairpin RNA disrupted the AR loading to the PSA enhancer and subsequently inhibited AR activity.

CONCLUSION

Prolonged AR localization to the regulatory regions of AR targeted genes and the recruitment of p160 coactivators are a potential mechanism leading to androgen-independent activation of the AR. Disruption of AR chromatin loading could therefore become an important therapeutic target for this disease.

Calpain-mediated androgen receptor breakdown in apoptotic prostate cancer cells

Since androgen receptor (AR) plays an important role in prostate cancer development and progression, androgen-ablation has been the frontline therapy for treatment of advanced prostate cancer even though it is rarely curative. A curative strategy should involve functional and structural elimination of AR from prostate cancer cells. We have previously reported that apoptosis induced by medicinal proteasome-inhibitory compound celastrol is associated with a decrease in AR protein levels. However celastrol-stimulated events contributing to this AR decrease have not been elucidated. Here, we report that a variety of chemotherapeutic agents, including proteasome inhibitors, a topoisomerase inhibitor, DNA-damaging agents and docetaxel that cause cell death, decrease AR levels in LNCaP prostate cancer cells. This decrease in AR protein levels was not due to the suppression of AR mRNA expression in these cells. We observed that a proteolytic activity residing in cytosol of prostate cancer cells is responsible for AR breakdown and that this proteolytic activity was stimulated upon induction of apoptosis. Interestingly, proteasome inhibitor celastrol- and chemotherapeutic drug VP-16-stimulated AR breakdown was attenuated by calpain inhibitors calpastatin and N-acetyl-L-leucyl-L-leucyl-L-methioninal. Furthermore, AR proteolytic activity pulled down by calmodulin-agarose beads from celastrol-treated PC-3 cells showed immunoreactivity to a calpain antibody. Taken together, these results demonstrate calpain involvement in proteasome inhibitor-induced AR breakdown, and suggest that AR degradation is intrinsic to the induction of apoptosis in prostate cancer cells.

Genomic androgen receptor-occupied regions with different functions, defined by histone acetylation, coregulators and transcriptional capacity

BACKGROUND

The androgen receptor (AR) is a steroid-activated transcription factor that binds at specific DNA locations and plays a key role in the etiology of prostate cancer. While numerous studies have identified a clear connection between AR binding and expression of target genes for a limited number of loci, high-throughput elucidation of these sites allows for a deeper understanding of the complexities of this process.

METHODOLOGY/PRINCIPAL FINDINGS

We have mapped 189 AR occupied regions (ARORs) and 1,388 histone H3 acetylation (AcH3) loci to a 3% continuous stretch of human genomic DNA using chromatin immunoprecipitation (ChIP) microarray analysis. Of 62 highly reproducible ARORs, 32 (52%) were also marked by AcH3. While the number of ARORs detected in prostate cancer cells exceeded the number of nearby DHT-responsive genes, the AcH3 mark defined a subclass of ARORs much more highly associated with such genes -- 12% of the genes flanking AcH3+ARORs were DHT-responsive, compared to only 1% of genes flanking AcH3-ARORs. Most ARORs contained enhancer activities as detected in luciferase reporter assays. Analysis of the AROR sequences, followed by site-directed ChIP, identified binding sites for AR transcriptional coregulators FoxA1, CEBPbeta, NFI and GATA2, which had diverse effects on endogenous AR target gene expression levels in siRNA knockout experiments.

CONCLUSIONS/SIGNIFICANCE

We suggest that only some ARORs function under the given physiological conditions, utilizing diverse mechanisms. This diversity points to differential regulation of gene expression by the same transcription factor related to the chromatin structure.

What goes on behind closed doors: physiological versus pharmacological steroid hormone actions

Steroid-hormone-activated receptor proteins are among the best-understood class of factors for altering gene transcription in cells. Steroid receptors are of major importance in maintaining normal human physiology by responding to circulating concentrations of steroid in the nM range. Nonetheless, most studies of steroid receptor action have been conducted using the supra-physiological conditions of saturating concentrations (> or =100 nM) of potent synthetic steroid agonists. Here we summarize the recent developments arising from experiments using two clinically relevant conditions: subsaturating concentrations of agonist (to mimic the circulating concentrations in mammals) and saturating concentrations of antagonists (which are employed in endocrine therapies to block the actions of endogenous steroids). These studies have revealed new facets of steroid hormone action that could not be uncovered by conventional experiments with saturating concentrations of agonist steroids, such as a plethora of factors/conditions for the differential control of gene expression by physiological levels of steroid, a rational approach for examining the gene-specific variations in partial agonist activity of antisteroids, and a dissociation of steroid potency and efficacy that implies the existence of separate, and possibly novel, mechanistic steps and cofactors.

Interleukin-8 signaling promotes androgen-independent proliferation of prostate cancer cells via induction of androgen receptor expression and activation

The aim of our study was to assess the importance of the CXC chemokine and interleukin (IL)-8 in promoting the transition of prostate cancer (CaP) to the androgen-independent state. Stimulation of the androgen-dependent cell lines, LNCaP and 22Rv1, with exogenous recombinant human interleukin-8 (rh-IL-8) increased androgen receptor (AR) gene expression at the messenger RNA (mRNA) and protein level, assessed by quantitative polymerase chain reaction and immunoblotting, respectively. Using an androgen response element-luciferase construct, we demonstrated that rh-IL-8 treatment also resulted in increased AR transcriptional activity in both these cell lines, and a subsequent upregulation of prostate-specific antigen and cyclin-dependent kinase 2 mRNA transcript levels in LNCaP cells. Blockade of CXC chemokine receptor-2 signaling using a small molecule antagonist (AZ10397767) attenuated the IL-8-induced increases in AR expression and transcriptional activity. Furthermore, in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, coadministration of AZ10397767 reduced the viability of LNCaP and 22Rv1 cells exposed to bicalutamide. Our data show that IL-8 signaling increases AR expression and promotes ligand-independent activation of this receptor in two androgen-dependent cell lines, describing two mechanisms by which this chemokine may assist in promoting the transition of CaP to the androgen-independent state. In addition, our data show that IL-8-promoted regulation of the AR attenuates the effectiveness of the AR antagonist bicalutamide in reducing CaP cell viability.

Selective role of an NH2-terminal WxxLF motif for aberrant androgen receptor activation in androgen depletion independent prostate cancer cells

Systemic prostate cancer therapy requires androgen ablation, which inhibits the production or action of androgens. Prostate cancer ultimately relapses during androgen ablation, and an androgen depletion-independent (ADI) phenotype emerges. Aberrant androgen receptor (AR) activation underlies therapy resistance at this stage of the disease, and mounting evidence implicates the large and highly disordered AR NH2-terminal domain (NTD) as a key mediator of this activity. In this study, we investigated the role of the NTD transactivation unit 5 (TAU5) domain in mediating AR transcriptional activity in cell-based models of prostate cancer progression. AR replacement and Gal4-based promoter tethering experiments revealed that AR TAU5 had a dichotomous function, inhibiting ligand-dependent AR activity in androgen-dependent prostate cancer cells, while enhancing ligand-independent AR activity in ADI prostate cancer cells. Molecular dissection of TAU5 showed that a WxxLF motif was fully responsible for its ligand-independent activity. Mechanistically, WxxLF did not rely on an interaction with the AR ligand-binding domain to mediate ligand-independent AR activity. Rather, WxxLF functioned as an autonomous transactivation domain. These data show that ligand-dependent and ligand-independent AR activation rely on fundamentally distinct mechanisms, and define WxxLF as the major transactivation motif within the AR TAU5 domain.

UDP-glucuronosyltransferase 2B15 (UGT2B15) and UGT2B17 Enzymes Are Major Determinants of the Androgen Response in Prostate Cancer LNCaP Cells

Uridine diphosphate-glucuronosyltransferase 2 (UGT2)B15 and B17 enzymes conjugate dihydrotestosterone (DHT) and its metabolites androstane-3alpha, 17beta-diol (3alpha-DIOL) and androsterone (ADT). The presence of UGT2B15/B17 in the epithelial cells of the human prostate has been clearly demonstrated, and significant 3alpha-DIOL glucuronide and ADT-glucuronide concentrations have been detected in this tissue. The human androgen-dependent cancer cell line, LNCaP, expresses UGT2B15 and -B17 and is also capable of conjugating androgens. To assess the impact of these two genes in the inactivation of androgens in LNCaP cells, their expression was inhibited using RNA interference. The efficient inhibitory effects of a UGT2B15/B17 small interfering RNA (siRNA) probe was established by the 70% reduction of these UGT mRNA levels, which was further confirmed at the protein levels. The glucuronidation of dihydrotestosterone (DHT), 3alpha-DIOL, and ADT by LNCaP cell homogenates was reduced by more than 75% in UGT2B15/B17 siRNA-transfected LNCaP cells when compared with cells transfected with a non-target probe. In UGT2B15/B17-deficient LNCaP cells, we observe a stronger response to DHT than in control cells, as determined by cell proliferation and expression of eight known androgen-sensitive genes. As expected, the amounts of DHT in cell culture media from control cells were significantly lower than that from UGT2B15/B17 siRNA-treated cells, which was caused by a higher conversion to its corresponding glucuronide derivative. Taken together these data support the idea that UGT2B15 and -B17 are critical enzymes for the local inactivation of androgens and that glucuronidation is a major determinant of androgen action in prostate cells.

Evidence for calpain-mediated androgen receptor cleavage as a mechanism for androgen independence

Prostate carcinoma is the most commonly diagnosed cancer in men and the second leading cause of death due to cancer in Western civilization. Androgen ablation therapy is effective in treating androgen-dependent tumors, but eventually, androgen-independent tumors recur and are refractory to conventional chemotherapeutics. Hence, the emergence of androgen independence is the most challenging problem in managing prostate tumors. We report a novel mechanism of androgen independence: calpain cleaves the androgen receptor (AR) into an androgen-independent isoform. In vitro and in vivo analyses show that calpain removes the COOH-terminal ligand binding domain generating a constitutively active molecule. Analysis of human prostate tumors indicates that several tumors express higher levels of this truncated AR than noncancerous prostate tissue. In transient transfection studies, the truncated AR is three to five times more potent than the full-length receptor in transactivating transcription. The androgen-independent Rv1 cells express high levels of the truncated AR, and treatment of these cells with a calpain inhibitor reduces truncated AR expression. In the absence of androgen, inhibition of calpain activity induces apoptosis. The HIV protease inhibitor amprenavir inhibits calpain activity and is also effective in inducing apoptosis in the Rv1 cell line. The cell culture studies were reproduced in a mouse xenograft model, where, in the absence of androgens, amprenavir significantly reduces tumor growth. Together, these studies indicate that calpain-dependent proteolysis of the AR may be a mechanism of androgen independence. The calpain inhibition studies suggest that inhibiting this activity may be a potential treatment for some androgen-independent prostate tumors.

Androgen receptor-mediated repression of novel target genes

BACKGROUND

The androgen receptor (AR) plays a pivotal role in prostate cancer (PCa) initiation and progression. To date, studies have focused disproportionately on androgen-stimulated genes such as prostate-specific antigen (PSA), while repressed genes have gained little attention, even though they too may be involved in regulating cell growth, differentiation, and apoptosis.

METHODS

ChIP Display was used to identify putative AR target genes in the ablation-resistant human PCa cell line, C4-2B. Quantitative real-time reverse transcription-PCR analysis was used to measure gene expression in cells subjected to dihydrotestosterone (DHT) timecourse and dose-response, as well as AR knock-down and bicalutamide-treatments.

RESULTS

We report on three genes, KIAA1217, CHRM1, and WBSCR28, which were newly identified in a screen for AR-occupied regions in C4-2B PCa cells, and which were repressed by treatment with DHT. AR knock-down resulted in increased KIAA1217, CHRM1, and WBSCR28 mRNA, indicating that, like PSA stimulation, AR represses these three genes even in the absence of added ligand. DHT decreased KIAA1217 and CHRM1 pre-mRNA levels, suggesting AR-mediated transcriptional inhibition. Cycloheximide attenuated DHT-mediated repression of CHRM1, suggesting the requirement of new protein synthesis. Furthermore, bicalutamide treatment did not mimic, but rather antagonized DHT-mediated KIAA1217 repression. Unlike the handful of androgen-repressed genes studied thus far, AR occupancy at KIAA1217, CHRM1, and WBSCR28 was mapped outside their respective 5'-promoter regions.

CONCLUSIONS

Many more genes likely share AR-mediated gene repression through distal regulatory elements. Further study of such targets and their transcriptional regulation may help explain the receptor's tumorigenicity in PCa.

Distinct GCN5/PCAF-containing complexes function as co-activators and are involved in transcription factor and global histone acetylation

Transcription in eukaryotes is a tightly regulated, multistep process. Gene-specific transcriptional activators, several different co-activators and general transcription factors are necessary to access specific loci to allow precise initiation of RNA polymerase II transcription. As the dense chromatin folding of the genome does not allow the access of these sites by the huge multiprotein transcription machinery, remodelling is required to loosen up the chromatin structure for successful transcription initiation. In the present review, we summarize the recent evolution of our understanding of the function of two histone acetyl transferases (ATs) from metazoan organisms: GCN5 and PCAF. Their overall structure and the multiprotein complexes in which they are carrying out their activities are discussed. Metazoan GCN5 and PCAF are subunits of at least two types of multiprotein complexes, one having a molecular weight of 2 MDa (SPT3-TAF9-GCN5 acetyl transferase/TATA binding protein (TBP)-free-TAF complex/PCAF complexes) and a second type with about a size of 700 kDa (ATAC complex). These complexes possess global histone acetylation activity and locus-specific co-activator functions together with AT activity on non-histone substrates. Thus, their biological functions cover a wide range of tasks and render them indispensable for the normal function of cells. That deregulation of the global and/or specific AT activities of these complexes leads to the cancerous transformation of the cells highlights their importance in cellular processes. The possible effects of GCN5 and PCAF in tumorigenesis are also discussed.

Tissue kallikrein proteolytic cascade pathways in normal physiology and cancer

Human tissue kallikreins (KLKs or kallikrein-related peptidases) are a subgroup of extracellular serine proteases that act on a wide variety of physiological substrates, while they display aberrant expression patterns in certain types of cancer. Differential expression patterns lead to the exploitation of these proteins as new cancer biomarkers for hormone-dependent malignancies, in particular. The prostate-specific antigen or kallikrein-related peptidase 3 (PSA/KLK3) is an established tumor marker for the diagnosis and monitoring of prostate cancer. It is well documented that specific KLK genes are co-expressed in tissues and in various pathologies suggesting their participation in complex proteolytic cascades. Here, we review the currently established knowledge on the involvement of KLK proteolytic cascades in the regulation of physiological and pathological processes in prostate tissue and in skin. It is well established that the activity of KLKs is often regulated by auto-activation and subsequent autolytic internal cleavage leading to enzymatic inactivation, as well as by inhibitory serpins or by allosteric inhibition by zinc ions. Redistribution of zinc ions and alterations in their concentration due to physiological or pathological reasons activates specific KLKs initiating the kallikrein cascade(s). Recent studies on kallikrein substrate specificity allowed for the construction of a kallikrein interaction network involved in semen liquefaction and prostate cancer, as well as in skin pathologies, such as skin desquamation, psoriasis and cancer. Furthermore, we discuss the crosstalks between known proteolytic pathways and the kallikrein cascades, with emphasis on the activation of plasmin and its implications in prostate cancer. These findings may have clinical implications for the underlying molecular mechanism and management of cancer and other disorders in which KLK activity is elevated.

Identification of novel androgen receptor target genes in prostate cancer

BACKGROUND

The androgen receptor (AR) plays critical roles in both androgen-dependent and castrate-resistant prostate cancer (PCa). However, little is known about AR target genes that mediate the receptor's roles in disease progression.

RESULTS

Using Chromatin Immunoprecipitation (ChIP) Display, we discovered 19 novel loci occupied by the AR in castrate resistant C4-2B PCa cells. Only four of the 19 AR-occupied regions were within 10-kb 5'-flanking regulatory sequences. Three were located up to 4-kb 3' of the nearest gene, eight were intragenic and four were in gene deserts. Whereas the AR occupied the same loci in C4-2B (castrate resistant) and LNCaP (androgen-dependent) PCa cells, differences between the two cell lines were observed in the response of nearby genes to androgens. Among the genes strongly stimulated by DHT in C4-2B cells--D-dopachrome tautomerase (DDT), Protein kinase C delta (PRKCD), Glutathione S- transferase theta 2 (GSTT2), Transient receptor potential cation channel subfamily V member 3 (TRPV3), and Pyrroline-5-carboxylate reductase 1 (PYCR1)--most were less strongly or hardly stimulated in LNCaP cells. Another AR target gene, ornithine aminotransferase (OAT), was AR-stimulated in a ligand-independent manner, since it was repressed by AR siRNA knockdown, but not stimulated by DHT. We also present evidence for in vivo AR-mediated regulation of several genes identified by ChIP Display. For example, PRKCD and PYCR1, which may contribute to PCa cell growth and survival, are expressed in PCa biopsies from primary tumors before and after ablation and in metastatic lesions in a manner consistent with AR-mediated stimulation.

CONCLUSION

AR genomic occupancy is similar between LNCaP and C4-2B cells and is not biased towards 5' gene flanking sequences. The AR transcriptionally regulates less than half the genes nearby AR-occupied regions, usually but not always, in a ligand-dependent manner. Most are stimulated and a few are repressed. In general, response is stronger in C4-2B compared to LNCaP cells. Some of the genes near AR-occupied regions appear to be regulated by the AR in vivo as evidenced by their expression levels in prostate cancer tumors of various stages. Several AR target genes discovered in the present study, for example PRKCD and PYCR1, may open avenues in PCa research and aid the development of new approaches for disease management.