A small composite probasin promoter confers high levels of prostate-specific gene expression through regulation by androgens and glucocorticoids in vitro and in vivo

Diverse landscape of genetically engineered mouse models: Genomic and molecular insights into prostate cancer

Prostate cancer (PCa) is a significant health concern for men worldwide and is particularly prevalent in the United States. It is a complex disease presenting different molecular subtypes and varying degrees of aggressiveness. Transgenic/genetically engineered mouse models (GEMMs) greatly enhanced our understanding of the intricate molecular processes that underlie PCa progression and have offered valuable insights into potential therapeutic targets for this disease. The integration of whole-exome and whole-genome sequencing, along with expression profiling, has played a pivotal role in advancing GEMMs by facilitating the identification of genetic alterations driving PCa development. This review focuses on genetically modified mice classified into the first and second generations of PCa models. We summarize whether models created by manipulating the function of specific genes replicate the consequences of genomic alterations observed in human PCa, including early and later disease stages. We discuss cases where GEMMs did not fully exhibit the expected human PCa phenotypes and possible causes of the failure. Here, we summarize the comprehensive understanding, recent advances, strengths and limitations of the GEMMs in advancing our insights into PCa, offering genetic and molecular perspectives for developing novel GEMM models.

FOXP2 confers oncogenic effects in prostate cancer

Identification oncogenes is fundamental to revealing the molecular basis of cancer. Here, we found that FOXP2 is overexpressed in human prostate cancer cells and prostate tumors, but its expression is absent in normal prostate epithelial cells and low in benign prostatic hyperplasia. FOXP2 is a FOX transcription factor family member and tightly associated with vocal development. To date, little is known regarding the link of FOXP2 to prostate cancer. We observed that high FOXP2 expression and frequent amplification are significantly associated with high Gleason score. Ectopic expression of FOXP2 induces malignant transformation of mouse NIH3T3 fibroblasts and human prostate epithelial cell RWPE-1. Conversely, FOXP2 knockdown suppresses the proliferation of prostate cancer cells. Transgenic overexpression of FOXP2 in the mouse prostate causes prostatic intraepithelial neoplasia. Overexpression of FOXP2 aberrantly activates oncogenic MET signaling and inhibition of MET signaling effectively reverts the FOXP2-induced oncogenic phenotype. CUT&Tag assay identified FOXP2-binding sites located in MET and its associated gene HGF. Additionally, the novel recurrent FOXP2-CPED1 fusion identified in prostate tumors results in high expression of truncated FOXP2, which exhibit a similar capacity for malignant transformation. Together, our data indicate that FOXP2 is involved in tumorigenicity of prostate.

Pre-Clinical Models to Study Human Prostate Cancer

Prostate cancer is a common cancer among men and typically progresses slowly for several decades before becoming aggressive and spreading to other organs, leaving few treatment options. While large animals have been studied, the dog's prostate is anatomically similar to humans and has been used to study spontaneous prostate cancer. However, most research currently focuses on the mouse as a model organism due to the ability to genetically modify their prostatic tissues for molecular analysis. One milestone in this research was the identification of the prostate-specific promoter Probasin, which allowed for the prostate-specific expression of transgenes. This has led to the generation of mice with aggressive prostatic tumors through overexpression of the SV40 oncogene. The Probasin promoter is also used to drive Cre expression and has allowed researchers to generate prostate-specific loss-of-function studies. Another landmark moment in the process of modeling prostate cancer in mice was the orthoptic delivery of viral particles. This technology allows the selective overexpression of oncogenes from lentivirus or the use of CRISPR to generate complex loss-of-function studies. These genetically modified models are complemented by classical xenografts of human prostate tumor cells in immune-deficient mice. Overall, pre-clinical models have provided a portfolio of model systems to study and address complex mechanisms in prostate cancer for improved treatment options. This review will focus on the advances in each technique.

Preclinical models and evaluation criteria of prostatitis

Prostatitis is a common urological condition that affects almost half of all men at some point in their life. The prostate gland has a dense nerve supply that contributes to the production of fluid to nourish sperm and the mechanism to switch between urination and ejaculation. Prostatitis can cause frequent urination, pelvic pain, and even infertility. Long-term prostatitis increases the risk of prostate cancer and benign prostate hyperplasia. Chronic non-bacterial prostatitis presents a complex pathogenesis, which has challenged medical research. Experimental studies of prostatitis require appropriate preclinical models. This review aimed to summarize and compare preclinical models of prostatitis based on their methods, success rate, evaluation, and range of application. The objective of this study is to provide a comprehensive understanding of prostatitis and advance basic research.

Pyruvate Kinase M1 Suppresses Development and Progression of Prostate Adenocarcinoma

SIGNIFICANCE

Differential expression of PKM1 and PKM2 impacts prostate tumorigenesis and suggests a potential therapeutic vulnerability in prostate cancer.

Allosteric interactions prime androgen receptor dimerization and activation

The androgen receptor (AR) is a nuclear receptor that governs gene expression programs required for prostate development and male phenotype maintenance. Advanced prostate cancers display AR hyperactivation and transcriptome expansion, in part, through AR amplification and interaction with oncoprotein cofactors. Despite its biological importance, how AR domains and cofactors cooperate to bind DNA has remained elusive. Using single-particle cryo-electron microscopy, we isolated three conformations of AR bound to DNA, showing that AR forms a non-obligate dimer, with the buried dimer interface utilized by ancestral steroid receptors repurposed to facilitate cooperative DNA binding. We identify novel allosteric surfaces which are compromised in androgen insensitivity syndrome and reinforced by AR's oncoprotein cofactor, ERG, and by DNA-binding motifs. Finally, we present evidence that this plastic dimer interface may have been adopted for transactivation at the expense of DNA binding. Our work highlights how fine-tuning AR's cooperative interactions translate to consequences in development and disease.

MYC drives aggressive prostate cancer by disrupting transcriptional pause release at androgen receptor targets

c-MYC (MYC) is a major driver of prostate cancer tumorigenesis and progression. Although MYC is overexpressed in both early and metastatic disease and associated with poor survival, its impact on prostate transcriptional reprogramming remains elusive. We demonstrate that MYC overexpression significantly diminishes the androgen receptor (AR) transcriptional program (the set of genes directly targeted by the AR protein) in luminal prostate cells without altering AR expression. Analyses of clinical specimens reveal that concurrent low AR and high MYC transcriptional programs accelerate prostate cancer progression toward a metastatic, castration-resistant disease. Data integration of single-cell transcriptomics together with ChIP-seq uncover an increase in RNA polymerase II (Pol II) promoter-proximal pausing at AR-dependent genes following MYC overexpression without an accompanying deactivation of AR-bound enhancers. Altogether, our findings suggest that MYC overexpression antagonizes the canonical AR transcriptional program and contributes to prostate tumor initiation and progression by disrupting transcriptional pause release at AR-regulated genes.

Evidence for context-dependent functions of KDM5B in prostate development and prostate cancer

Prostate cancer (PCa) is one of the leading causes of cancer-related deaths worldwide. Prostate tumorigenesis and PCa progression involve numerous genetic as well as epigenetic perturbations. Histone modification represents a fundamental epigenetic mechanism that regulates diverse cellular processes, and H3K4 methylation, one such histone modification associated with active transcription, can be reversed by dedicated histone demethylase KDM5B (JARID1B). Abnormal expression and functions of KDM5B have been implicated in several cancer types including PCa. Consistently, our bioinformatics analysis reveals that the KDM5B mRNA levels are upregulated in PCa compared to benign prostate tissues, and correlate with increased tumor grade and poor patient survival, supporting an oncogenic function of KDM5B in PCa. Surprisingly, however, when we generated prostate-specific conditional Kdm5b knockout mice using probasin (Pb) promoter-driven Cre: loxP system, we observed that Kdm5b deletion did not affect normal prostate development but instead induced mild hyperplasia. These results suggest that KDM5B may possess context-dependent roles in normal prostate development vs. PCa development and progression.

Cellular and Molecular Progression of Prostate Cancer: Models for Basic and Preclinical Research

Simple Summary

The molecular progression of prostate cancer is complex and elusive. Biological research relies heavily on in vitro and in vivo models that can be used to examine gene functions and responses to the external agents in laboratory and preclinical settings. Over the years, several models have been developed and found to be very helpful in understanding the biology of prostate cancer. Here we describe these models in the context of available information on the cellular and molecular progression of prostate cancer to suggest their potential utility in basic and preclinical prostate cancer research. The information discussed herein should serve as a hands-on resource for scholars engaged in prostate cancer research or to those who are making a transition to explore the complex biology of prostate cancer.

Abstract

We have witnessed noteworthy progress in our understanding of prostate cancer over the past decades. This basic knowledge has been translated into efficient diagnostic and treatment approaches leading to the improvement in patient survival. However, the molecular pathogenesis of prostate cancer appears to be complex, and histological findings often do not provide an accurate assessment of disease aggressiveness and future course. Moreover, we also witness tremendous racial disparity in prostate cancer incidence and clinical outcomes necessitating a deeper understanding of molecular and mechanistic bases of prostate cancer. Biological research heavily relies on model systems that can be easily manipulated and tested under a controlled experimental environment. Over the years, several cancer cell lines have been developed representing diverse molecular subtypes of prostate cancer. In addition, several animal models have been developed to demonstrate the etiological molecular basis of the prostate cancer. In recent years, patient-derived xenograft and 3-D culture models have also been created and utilized in preclinical research. This review is an attempt to succinctly discuss existing information on the cellular and molecular progression of prostate cancer. We also discuss available model systems and their tested and potential utility in basic and preclinical prostate cancer research.

ETV4 promotes late development of prostatic intraepithelial neoplasia and cell proliferation through direct and p53-mediated downregulation of p21

BACKGROUND

ETV4 is one of the ETS proteins overexpressed in prostate cancer (PC) as a result of recurrent chromosomal translocations. In human prostate cell lines, ETV4 promotes migration, invasion, and proliferation; however, its role in PC has been unclear. In this study, we have explored the effects of ETV4 expression in the prostate in a novel transgenic mouse model.

METHODS

We have created a mouse model with prostate-specific expression of ETV4 (ETV4 mice). By histochemical and molecular analysis, we have investigated in these engineered mice the expression of p21, p27, and p53. The implications of our in vivo findings have been further investigated in human cells lines by chromatin-immunoprecipitation (ChIP) and luciferase assays.

RESULTS

ETV4 mice, from two independent transgenic lines, have increased cell proliferation in their prostate and two-thirds of them, by the age of 10 months, developed mouse prostatic intraepithelial neoplasia (mPIN). In these mice, cdkn1a and its p21 protein product were reduced compared to controls; p27 protein was also reduced. By ChIP assay in human prostate cell lines, we show that ETV4 binds to a specific site (-704/-696 bp upstream of the transcription start) in the CDKN1A promoter that was proven, by luciferase assay, to be functionally competent. ETV4 further controls CDKN1A expression by downregulating p53 protein: this reduction of p53 was confirmed in vivo in ETV4 mice.

CONCLUSIONS

ETV4 overexpression results in the development of mPIN but not in progression to cancer. ETV4 increases prostate cell proliferation through multiple mechanisms, including downregulation of CDKN1A and its p21 protein product: this in turn is mediated through direct binding of ETV4 to the CDKN1A promoter and through the ETV4-mediated decrease of p53. This multi-faceted role of ETV4 in prostate cancer makes it a potential target for novel therapeutic approaches that could be explored in this ETV4 transgenic model.

GRK2 enforces androgen receptor dependence in the prostate and prostate tumors

Metastatic tumors that have become resistant to androgen deprivation therapy represent the major challenge in treating prostate cancer. Although these recurrent tumors typically remain dependent on the androgen receptor (AR), non-AR-driven tumors that also emerge are particularly deadly and becoming more prevalent. Here, we present a new genetically engineered mouse model for non-AR-driven prostate cancer that centers on a negative regulator of G protein-coupled receptors that is downregulated in aggressive human prostate tumors. Thus, prostate-specific expression of a dominant-negative G protein-coupled receptor kinase 2 (GRK2-DN) transgene diminishes AR and AR target gene expression in the prostate, and confers resistance to castration-induced involution. Further, the GRK2-DN transgene dramatically accelerates oncogene-initiated prostate tumorigenesis by increasing primary tumor size, potentiating visceral organ metastasis, suppressing AR, and inducing neuroendocrine marker mRNAs. In summary, GRK2 enforces AR-dependence in the prostate, and the loss of GRK2 function in prostate tumors accelerates disease progression towards the deadliest stage.

Taxane-based Chemotherapy Induced Androgen Receptor Splice Variant 7 in Patients with Castration-Resistant Prostate Cancer: A Tissue-based Analysis

In total, 95 prostate cancer (Pca) patients who underwent transurethral resection of the prostate from 2000 to 2013 were assigned to four groups: Group 1, hormone-naïve and T1a or T1b Pca (n = 17); Group 2, hormone-sensitive and metastatic Pca (n = 33); Group 3, chemo-naïve castration-resistant Pca (CRPC), (n = 18); and Group 4, CRPC with chemotherapy (n = 27). Full-length androgen receptor (ARfl) transcript levels significantly increased from Group 1 through to Group 3 (p = 0.045), but decreased from Group 3 through to Group 4. AR splice variant 7 (ARV7) and glucocorticoid receptor (GR) transcript levels significantly increased from Group 1 through to Group 4 (p = 0.002 and 0.049, respectively). Kaplan-Meier curve revealed that the high transcript level of these three receptors resulted in significantly poorer cancer-specific survival (CSS) than that by low transcript level, although Cox regression analysis revealed that the ARV7 level alone was an independent prognostic factor for CSS in CRPC patients (high vs. low: hazard ratio, 1.897; 95% confidence interval, 1.102-3.625; p = 0.042). In conclusion, ARV7 and GR transcript levels significantly increase as Pca progresses to CRPC.

Genetically Engineered Mouse Models of Prostate Cancer in the Postgenomic Era

Recent genomic sequencing analyses have unveiled the spectrum of genomic alterations that occur in primary and advanced prostate cancer, raising the question of whether the corresponding genes are functionally relevant for prostate tumorigenesis, and whether such functions are associated with particular disease stages. In this review, we describe genetically engineered mouse models (GEMMs) of prostate cancer, focusing on those that model genomic alterations known to occur in human prostate cancer. We consider whether the phenotypes of GEMMs based on gain or loss of function of the relevant genes provide reliable counterparts to study the predicted consequences of the corresponding genomic alterations as occur in human prostate cancer, and we discuss exceptions in which the GEMMs do not fully emulate the expected phenotypes. Last, we highlight future directions for the generation of new GEMMs of prostate cancer and consider how we can use GEMMs most effectively to decipher the biological and molecular mechanisms of disease progression, as well as to tackle clinically relevant questions.

Discovery of Novel Androgen Receptor Ligands by Structure-based Virtual Screening and Bioassays

Androgen receptor (AR) is a ligand-activated transcription factor that plays a pivotal role in the development and progression of many severe diseases such as prostate cancer, muscle atrophy, and osteoporosis. Binding of ligands to AR triggers the conformational changes in AR that may affect the recruitment of coactivators and downstream response of AR signaling pathway. Therefore, AR ligands have great potential to treat these diseases. In this study, we searched for novel AR ligands by performing a docking-based virtual screening (VS) on the basis of the crystal structure of the AR ligand binding domain (LBD) in complex with its agonist. A total of 58 structurally diverse compounds were selected and subjected to LBD affinity assay, with five of them (HBP1-3, HBP1-17, HBP1-38, HBP1-51, and HBP1-58) exhibiting strong binding to AR-LBD. The IC₅₀ values of HBP1-51 and HBP1-58 are 3.96 µM and 4.92 µM, respectively, which are even lower than that of enzalutamide (Enz, IC₅₀ = 13.87 µM), a marketed second-generation AR antagonist. Further bioactivity assays suggest that HBP1-51 is an AR agonist, whereas HBP1-58 is an AR antagonist. In addition, molecular dynamics (MD) simulations and principal components analysis (PCA) were carried out to reveal the binding principle of the newly-identified AR ligands toward AR. Our modeling results indicate that the conformational changes of helix 12 induced by the bindings of antagonist and agonist are visibly different. In summary, the current study provides a highly efficient way to discover novel AR ligands, which could serve as the starting point for development of new therapeutics for AR-related diseases.

Constant Degradation of the Androgen Receptor by MDM2 Conserves Prostate Cancer Stem Cell Integrity

Prostate cancer stem cells (CSC) are implicated in tumor initiation, cancer progression, metastasis, and the development of therapeutic-resistant disease. It is well known that the bulk of prostate cancer cells express androgen receptor (AR) and that androgens are required for prostate cancer growth, progression, and emergence of castration-resistant disease. In contrast, the small subpopulation of self-renewing CSCs exhibits an AR-negative (AR^-) signature. The mechanisms underlying the absence of AR are unknown. Using CSC-like cell models isolated from clinical biopsy tissues, we identify the E3 ligase MDM2 as a key regulator of prostate CSC integrity. First, unlike what has been reported for the bulk of AR⁺ tumor cells where MDM2 regulates the temporal expression of AR during transcriptional activity, MDM2 in CSCs promoted the constant ubiquitination and degradation of AR, resulting in sustained loss of total AR protein. Second, MDM2 promoted CSC self-renewal, the expression of stem cell factors, and CSC proliferation. Loss of MDM2 reversed these processes and induced expression of full-length AR (and not AR variants), terminal differentiation into luminal cells, and cell death. Selectively blocking MDM2-mediated activity in combination with androgen/AR-targeted therapy may offer a novel strategy for eliminating AR^- CSCs in addition to the bulk of AR⁺ prostate cancer cells, decreasing metastatic tumor burden and inhibiting the emergence of therapeutic resistance.Significance: These findings provide a novel mechanistic aspect of prostate cancer cell stemness that advances our understanding of the diverse transcriptional activity that bypasses AR in contributing to therapeutic resistance, tumor progression, and metastasis.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/6/1124/F1.large.jpg.

Cells of Origin for Prostate Cancer

Comprehensive knowledge of the normal prostate epithelial lineage hierarchy is a prerequisite to investigate the identity of the cells of origin for prostate cancer. The basal and luminal cells constitute most of the prostate epithelium and have been the major focuses of the study on the cells of origin for prostate cancer. Much progress has been made during the past few decades, mainly using mouse models, to understand the inter-lineage relationship and intra-lineage heterogeneity in adults as well as the lineage plasticity during conditions of stress. These studies have concluded that the adult mouse prostate basal and luminal cells are largely independently sustained under physiological conditions, but both types of cells possess the capacity for bipotent differentiation under stress or artificial experimental conditions. However, the existence or the identity of the putative progenitors within each lineage warrants further investigation. Whether the human prostate lineage hierarchy is completely the same as that of the mouse remains uncertain. Experiments from independent groups have demonstrated that both types of cells in mice and humans can serve as targets for transformation. But controversies remain whether the disease from distinct cells of origin display different clinical behaviors. Further investigation of the intra-lineage heterogeneity will provide new insights into this issue. Understanding the identity of the cells of origin for prostate cancer will help identify novel prognostic markers for early detection of aggressive prostate cancers, provide insights into the therapeutic vulnerability of these tumors, and inspire novel therapeutic strategies.

Generation of transgenic mouse line with prostate-specific expression of codon-improved Cre recombinase

Background

Genetically engineered mouse models are useful tools to decipher molecular mechanisms of diseases. As for prostates, a rat probasin promoter has been widely used to drive prostate-specific gene expression. To optimize its codon usage to that of mammals, we used codon-improved Cre recombinase (iCre) for prostate-specific Cre-loxP recombination.

Materials and methods

We generated transgenic mice that express iCre driven by conventional probasin promoter in a prostate-specific manner (PB-iCre). Linearized PB-iCre transgene deoxyribonucleic acids (DNAs) were microinjected into pronuclei of fertilized mouse embryos. The integration of the transgene was confirmed by Southern blot analysis. A line of transgenic mice expressing a sufficient amount of iCre mRNA in its prostate was selected. To test recombinase activity of PB-iCre in vivo, its offspring was crossbred with Pten^flox/flox mice in which murine prostate adenocarcinoma is reported to occur upon excision of loxP-flanked regions.

Results

Eight founder animals were obtained, all of which showed germ line integration of PB-iCre transgene by Southern blot analysis. Among them, the prostate from only one line (line 58) expressed a sufficient amount of iCre mRNA. This line was crossbred with Pten^flox/flox mice to generate PB-iCre58/Pten^flox/flox. As a result, 12-week-old PB-iCre58/Pten^flox/flox mice presented with prostate adenocarcinoma that was histologically similar to human cribriform prostate cancer of Gleason grade 4.

Conclusions

We have successfully established a transgenic mouse line that expresses iCre in a prostate-specific manner.

Histone 2B-GFP Label-Retaining Prostate Luminal Cells Possess Progenitor Cell Properties and Are Intrinsically Resistant to Castration

The existence of slow-cycling luminal cells in the prostate has been suggested, but their identity and functional properties remain unknown. Using a bigenic mouse model to earmark, isolate, and characterize the quiescent stem-like cells, we identify a label-retaining cell (LRC) population in the luminal cell layer as luminal progenitors. Molecular and biological characterizations show that these luminal LRCs are significantly enriched in the mouse proximal prostate, exhibit relative dormancy, display bipotency in both in vitro and in vivo assays, and express a stem/progenitor gene signature with resemblance to aggressive prostate cancer. Importantly, these LRCs, compared with bulk luminal cells, maintain a lower level of androgen receptor (AR) expression and are less androgen dependent and also castration resistant in vivo. Finally, analysis of phenotypic markers reveals heterogeneity within the luminal progenitor cell pool. Our study establishes luminal LRCs as progenitors that may serve as a cellular origin for castration-resistant prostate cancer.

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A bigenic mouse model to study prostatic slow-cycling luminal epithelial cells

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Prostate label-retaining cells (LRCs) exhibit stem/progenitor cell activities

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Luminal LRCs are developmentally bipotent and display a progenitor gene signature

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Luminal LRCs resist castration and molecularly resemble aggressive prostate cancer

The protein kinase C super-family member PKN is regulated by mTOR and influences differentiation during prostate cancer progression

BACKGROUND

Phosphoinositide-3 (PI-3) kinase signaling has a pervasive role in cancer. One of the key effectors of PI-3 kinase signaling is AKT, a kinase that promotes growth and survival in a variety of cancers. Genetically engineered mouse models of prostate cancer have shown that AKT signaling is sufficient to induce prostatic epithelial neoplasia (PIN), but insufficient for progression to adenocarcinoma. This contrasts with the phenotype of mice with prostate-specific deletion of Pten, where excessive PI-3 kinase signaling induces both PIN and locally invasive carcinoma. We reasoned that additional PI-3 kinase effector kinases promote prostate cancer progression via activities that provide biological complementarity to AKT. We focused on the PKN kinase family members, which undergo activation in response to PI-3 kinase signaling, show expression changes in prostate cancer, and contribute to cell motility pathways in cancer cells.

METHODS

PKN kinase activity was measured by incorporation of ³² P into protein substrates. Phosphorylation of the turn-motif (TM) in PKN proteins by mTOR was analyzed using the TORC2-specific inhibitor torin and a PKN1 phospho-TM-specific antibody. Amino acid substitutions in the TM of PKN were engineered and assayed for effects on kinase activity. Cell motility-related functions and PKN localization was analyzed by depletion approaches and immunofluorescence microscopy, respectively. The contribution of PKN proteins to prostate tumorigenesis was characterized in several mouse models that express PKN transgenes. The requirement for PKN activity in prostate cancer initiated by loss of phosphatase and tensin homolog deleted on chromosome 10 (Pten), and the potential redundancy between PKN isoforms, was analyzed by prostate-specific deletion of Pkn1, Pkn2, and Pten.

RESULTS AND CONCLUSIONS

PKN1 and PKN2 contribute to motility pathways in human prostate cancer cells. PKN1 and PKN2 kinase activity is regulated by TORC2-dependent phosphorylation of the TM, which together with published data indicates that PKN proteins receive multiple PI-3 kinase-dependent inputs. Transgenic expression of active AKT and PKN1 is not sufficient for progression beyond PIN. Moreover, Pkn1 is not required for tumorigenesis initiated by loss of Pten. Triple knockout of Pten, Pkn1, and Pkn2 in mouse prostate results in squamous cell carcinoma, an uncommon but therapy-resistant form of prostate cancer.

Novel galeterone analogs act independently of AR and AR-V7 for the activation of the unfolded protein response and induction of apoptosis in the CWR22Rv1 prostate cancer cell model

The androgen receptor (AR) has long been the primary target for the treatment of prostate cancer (PC). Despite continuous efforts to block AR activity through ligand depletion, AR antagonism, AR depletion and combinations thereof, advanced PC tumors remain resilient. Herein, we evaluate two galeterone analogs, VNPT-178 and VNLG-74A, in PC cell models of diverse androgen and AR dependence attempting to delineate their mechanisms of action and potential clinical utility. Employing basic biochemical techniques, we determined that both analogs have improved antiproliferative and anti-AR activities compared to FDA-approved abiraterone and enzalutamide. However, induction of apoptosis in these models is independent of the AR and its truncated variant, AR-V7, and instead likely results from sustained endoplasmic reticulum stress and deregulated calcium homeostasis. Using in silico molecular docking, we predict VNPT-178 and VNLG-74A bind the ATPase domain of BiP/Grp78 and Hsp70-1A with greater affinity than the AR. Disruption of 70 kDa heat shock protein function may be the underlying mechanism of action for these galeterone analogs. Therefore, despite simultaneously antagonizing AR activity, AR and/or AR-V7 expression alone may inadequately predict a patient's response to treatment with VNPT-178 or VNLG-74A. Future studies evaluating the context-specific limitations of these compounds may provide clarity for their clinical application.

Transgenic overexpression of NanogP8 in the mouse prostate is insufficient to initiate tumorigenesis but weakly promotes tumor development in the Hi-Myc mouse model

This project was undertaken to address a critical cancer biology question: Is overexpression of the pluripotency molecule Nanog sufficient to initiate tumor development in a somatic tissue? Nanog1 is critical for the self-renewal and pluripotency of ES cells, and its retrotransposed homolog, NanogP8 is preferentially expressed in somatic cancer cells. Our work has shown that shRNA-mediated knockdown of NanogP8 in prostate, breast, and colon cancer cells inhibits tumor regeneration whereas inducible overexpression of NanogP8 promotes cancer stem cell phenotypes and properties. To address the key unanswered question whether tissue-specific overexpression of NanogP8 is sufficient to promote tumor development in vivo, we generated a NanogP8 transgenic mouse model, in which the ARR₂PB promoter was used to drive NanogP8 cDNA. Surprisingly, the ARR₂PB-NanogP8 transgenic mice were viable, developed normally, and did not form spontaneous tumors in >2 years. Also, both wild type and ARR₂PB-NanogP8 transgenic mice responded similarly to castration and regeneration and castrated ARR₂PB-NanogP8 transgenic mice also did not develop tumors. By crossing the ARR₂PB-NanogP8 transgenic mice with ARR₂PB-Myc (i.e., Hi-Myc) mice, we found that the double transgenic (i.e., ARR₂PB-NanogP8; Hi-Myc) mice showed similar tumor incidence and histology to the Hi-Myc mice. Interestingly, however, we observed white dots in the ventral lobes of the double transgenic prostates, which were characterized as overgrown ductules/buds featured by crowded atypical Nanog-expressing luminal cells. Taken together, our present work demonstrates that transgenic overexpression of NanogP8 in the mouse prostate is insufficient to initiate tumorigenesis but weakly promotes tumor development in the Hi-Myc mouse model.

Systematic and functional characterization of novel androgen receptor variants arising from alternative splicing in the ligand-binding domain

The presence of intact ligand-binding domain (LBD) ensures the strict androgen-dependent regulation of androgen receptor (AR): binding of androgen induces structural reorganization of LBD resulting in release of AR from HSP90, suppression of nuclear export which otherwise dominates over import and nuclear translocation of AR as a transcription factor. Thus, loss or defects of the LBD abolish constraint from un-liganded LBD as exemplified by constitutively active AR variants (AR-Vs), which are associated with emerging resistance mechanism to anti-AR therapy in castration-resistant prostate cancer (mCRPC). Recent analysis of the AR splicing landscapes revealed mCRPC harboring multiple AR-Vs with diverse patterns of inclusion/exclusion of exons (exons 4–8) corresponding to LBD to produce namely exon-skipping variants. In silico construction for these AR-Vs revealed four novel AR-Vs having unique features: Exclusion of specified exons introduces a frameshift in variants v5es, v6es and v7es. ARv56es maintains the reading frame resulting in the inclusion of the C-terminal half of the LBD. We systematically characterized these AR-Vs regarding their subcellular localization, affinity for HSP90 and transactivation capability. Notably, ARv5es was free from HSP90, exclusively nuclear, and constitutively active similarly as previously reported for v567es. In contrast, v6es and v7es were similar in that they are cytoplasmic, transcriptionally inactive and bind HSP90, ARv56es was present in both nucleus and cytoplasm, does not bind HSP90 and is transcriptionally inactive. Converting these transcriptionally inactive AR-Vs into active forms, we identified the two separate elements that allosterically suppress otherwise constitutively active AR-Vs; one in exon 5 for v6es and v7es and the other in exon 8 for v56es. Our findings identify a novel constitutively active AR-V, ARv5es and establish a method to predict potential activities of AR-Vs carrying impaired LBD.

Oncolytic virotherapy for urological cancers

Oncolytic virotherapy is a cancer treatment in which replication-competent viruses are used that specifically infect, replicate in and lyse malignant tumour cells, while minimizing harm to normal cells. Anecdotal evidence of the effectiveness of this strategy has existed since the late nineteenth century, but advances and innovations in biotechnological methods in the 1980s and 1990s led to a renewed interest in this type of therapy. Multiple clinical trials investigating the use of agents constructed from a wide range of viruses have since been performed, and several of these enrolled patients with urological malignancies. Data from these clinical trials and from preclinical studies revealed a number of challenges to the effectiveness of oncolytic virotherapy that have prompted the development of further sophisticated strategies. Urological cancers have a range of distinctive features, such as specific genetic mutations and cell surface markers, which enable improving both effectiveness and safety of oncolytic virus treatments. The strategies employed in creating advanced oncolytic agents include alteration of the virus tropism, regulating transcription and translation of viral genes, combination with chemotherapy, radiotherapy or gene therapy, arming viruses with factors that stimulate the immune response against tumour cells and delivery technologies to ensure that the viral agent reaches its target tissue.

Tbx18 Regulates the Differentiation of Periductal Smooth Muscle Stroma and the Maintenance of Epithelial Integrity in the Prostate

The T-box transcription factor TBX18 is essential to mesenchymal cell differentiation in several tissues and Tbx18 loss-of-function results in dramatic organ malformations and perinatal lethality. Here we demonstrate for the first time that Tbx18 is required for the normal development of periductal smooth muscle stromal cells in prostate, particularly in the anterior lobe, with a clear impact on prostate health in adult mice. Prostate abnormalities are only subtly apparent in Tbx18 mutants at birth; to examine postnatal prostate development we utilized a relatively long-lived hypomorphic mutant and a novel conditional Tbx18 allele. Similar to the ureter, cells that fail to express Tbx18 do not condense normally into smooth muscle cells of the periductal prostatic stroma. However, in contrast to ureter, the periductal stromal cells in mutant prostate assume a hypertrophic, myofibroblastic state and the adjacent epithelium becomes grossly disorganized. To identify molecular events preceding the onset of this pathology, we compared gene expression in the urogenital sinus (UGS), from which the prostate develops, in Tbx18-null and wild type littermates at two embryonic stages. Genes that regulate cell proliferation, smooth muscle differentiation, prostate epithelium development, and inflammatory response were significantly dysregulated in the mutant urogenital sinus around the time that Tbx18 is first expressed in the wild type UGS, suggesting a direct role in regulating those genes. Together, these results argue that Tbx18 is essential to the differentiation and maintenance of the prostate periurethral mesenchyme and that it indirectly regulates epithelial differentiation through control of stromal-epithelial signaling.

Identification of novel genes that regulate androgen receptor signaling and growth of androgen-deprived prostate cancer cells

Prostate cancer progression to castration refractory disease is associated with anomalous transcriptional activity of the androgen receptor (AR) in an androgen-depleted milieu. To identify novel gene products whose downregulation transactivates AR in prostate cancer cells, we performed a screen of enzymatically-generated shRNA lenti-libraries selecting for transduced LNCaP cells with elevated expression of a fluorescent reporter gene under the control of an AR-responsive promoter. The shRNAs present in selected populations were analyzed using high-throughput sequencing to identify target genes. Highly enriched gene targets were then validated with siRNAs against selected genes, testing first for increased expression of luciferase from an AR-responsive promoter and then for altered expression of endogenous androgen-regulated genes in LNCaP cells. We identified 20 human genes whose silencing affected the expression of exogenous and endogenous androgen-responsive genes in prostate cancer cells grown in androgen-depleted medium. Knockdown of four of these genes upregulated the expression of endogenous AR targets and siRNAs targeting two of these genes (IGSF8 and RTN1) enabled androgen-independent proliferation of androgen-dependent cells. The effects of IGSF8 appear to be mediated through its interaction with a tetraspanin protein, CD9, previously implicated in prostate cancer progression. Remarkably, homozygous deletions of IGSF8 are found almost exclusively in prostate cancers but not in other cancer types. Our study shows that androgen independence can be achieved through the inhibition of specific genes and reveals a novel set of genes that regulate AR signaling in prostate cancers.

NF-κB and androgen receptor variant expression correlate with human BPH progression

BACKGROUND

Benign prostatic hyperplasia (BPH) is a common, chronic progressive disease. Inflammation is associated with prostatic enlargement and resistance to 5α-reductase inhibitor (5ARI) therapy. Activation of the nuclear factor-kappa B (NF-κB) pathway is linked to both inflammation and ligand-independent prostate cancer progression.

METHODS

NF-κB activation and androgen receptor variant (AR-V) expression were quantified in transition zone tissue samples from patients with a wide range of AUASS from incidental BPH in patients treated for low grade, localized peripheral zone prostate cancer to advanced disease requiring surgical intervention. To further investigate these pathways, human prostatic stromal and epithelial cell lines were transduced with constitutively active or kinase dead forms of IKK2 to regulate canonical NF-κB activity. The effects on AR full length (AR-FL) and androgen-independent AR-V expression as well as cellular growth and differentiation were assessed.

RESULTS

Canonical NF-κB signaling was found to be upregulated in late versus early stage BPH, and to be strongly associated with non-insulin dependent diabetes mellitus. Elevated expression of AR-variant 7 (AR-V7), but not other AR variants, was found in advanced BPH samples. Expression of AR-V7 significantly correlated with the patient AUASS and TRUS volume. Forced activation of canonical NF-κB in human prostatic epithelial and stromal cells resulted in elevated expression of both AR-FL and AR-V7, with concomitant ligand-independent activation of AR reporters. Activation of NF-κB and over expression of AR-V7 in human prostatic epithelial cells maintained cell viability in the face of 5ARI treatment.

CONCLUSION

Activation of NF-κB and AR-V7 in the prostate is associated with increased disease severity. AR-V7 expression is inducible in human prostate cells by forced activation of NF-κB resulting in resistance to 5ARI treatment, suggesting a potential mechanism by which patients may become resistant to 5ARI therapy.

CUDC-101, a Novel Inhibitor of Full-Length Androgen Receptor (flAR) and Androgen Receptor Variant 7 (AR-V7) Activity: Mechanism of Action and In Vivo Efficacy

Castration-resistant prostate cancer (CRPC) is an androgen receptor (AR)-dependent disease expected to cause the death of more than 27,000 Americans in 2015. There are only a few available treatments for CRPC, making the discovery of new drugs an urgent need. We report that CUDC-101 (an inhibitor od HER2/NEU, EGFR and HDAC) inhibits both the full length AR (flAR) and the AR variant AR-V7. This observation prompted experiments to discover which of the known activities of CUDC-101 is responsible for the inhibition of flAR/AR-V7 signaling. We used pharmacologic and genetic approaches, and found that the effect of CUDC-101 on flAR and AR-V7 was duplicated only by other HDAC inhibitors, or by silencing the HDAC isoforms HDAC5 and HDAC10. We observed that CUDC-101 treatment or AR-V7 silencing by RNAi equally reduced transcription of the AR-V7 target gene, PSA, without affecting viability of 22Rv1 cells. However, when cellular proliferation was used as an end point, CUDC-101 was more effective than AR-V7 silencing, raising the prospect that CUDC-101 has additional targets beside AR-V7. In support of this, we found that CUDC-101 increased the expression of the cyclin-dependent kinase inhibitor p21, and decreased that of the oncogene HER2/NEU. To determine if CUDC-101 reduces growth in a xenograft model of prostate cancer, this drug was given for 14 days to castrated male SCID mice inoculated with 22Rv1 cells. Compared to vehicle, CUDC-101 reduced xenograft growth in a statistically significant way, and without macroscopic side effects. These studies demonstrate that CUDC-101 inhibits wtAR and AR-V7 activity and growth of 22Rv1 cells in vitro and in vivo. These effects result from the ability of CUDC-101 to target not only HDAC signaling, which was associated with decreased flAR and AR-V7 activity, but multiple additional oncogenic pathways. These observations raise the possibility that treatment of CRPC may be achieved by using similarly multi-targeted approaches.

Histone demethylase JMJD2A drives prostate tumorigenesis through transcription factor ETV1

Histone demethylase upregulation has been observed in human cancers, yet it is unknown whether this is a bystander event or a driver of tumorigenesis. We found that overexpression of lysine-specific demethylase 4A (KDM4A, also known as JMJD2A) was positively correlated with Gleason score and metastasis in human prostate tumors. Overexpression of JMJD2A resulted in the development of prostatic intraepithelial neoplasia in mice, demonstrating that JMJD2A can initiate prostate cancer development. Moreover, combined overexpression of JMJD2A and the ETS transcription factor ETV1, a JMJD2A-binding protein, resulted in prostate carcinoma formation in mice haplodeficient for the phosphatase and tensin homolog (Pten) tumor-suppressor gene. Additionally, JMJD2A cooperated with ETV1 to increase expression of yes associated protein 1 (YAP1), a Hippo pathway component that itself was associated with prostate tumor aggressiveness. ETV1 facilitated the recruitment of JMJD2A to the YAP1 promoter, leading to changes in histone lysine methylation in a human prostate cancer cell line. Further, YAP1 expression largely rescued the growth inhibitory effects of JMJD2A depletion in prostate cancer cells, indicating that YAP1 is a downstream effector of JMJD2A. Taken together, these data reveal a JMJD2A/ETV1/YAP1 axis that promotes prostate cancer initiation and that may be a suitable target for therapeutic inhibition.

Oxidative stress promotes benign prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) is characterized by increased tissue mass in the transition zone of the prostate, which leads to obstruction of urine outflow and significant morbidity in the majority of older men. Plasma markers of oxidative stress are increased in men with BPH but it is unclear whether oxidative stress and/or oxidative DNA damage are causal in the pathogenesis of BPH.

METHODS

Levels of 8-OH deoxyguanosine (8-OH dG), a marker of oxidative stress, were measured in prostate tissues from normal transition zone and BPH by ELISA. 8-OH dG was also detected in tissues by immunohistochemistry and staining quantitated by image analysis. Nox4 promotes the formation of reactive oxygen species. We therefore created and characterized transgenic mice with prostate specific expression of Nox4 under the control of the prostate specific ARR2PB promoter.

RESULTS

Human BPH tissues contained significantly higher levels of 8-OH dG than control transition zone tissues and the levels of 8-OH dG were correlated with prostate weight. Cells with 8-OH dG staining were predominantly in the epithelium and were present in a patchy distribution. The total fraction of epithelial staining with 8-OH dG was significantly increased in BPH tissues by image analysis. The ARR2PB-Nox4 mice had increased oxidative DNA damage in the prostate, increased prostate weight, increased epithelial proliferation, and histological changes including epithelial proliferation, stromal thickening, and fibrosis when compared to wild type controls.

CONCLUSIONS

Oxidative stress and oxidative DNA damage are important in the pathogenesis of BPH.

Analysis of TMEFF2 allografts and transgenic mouse models reveals roles in prostate regeneration and cancer

BACKGROUND

Previous results from our lab indicate a tumor suppressor role for the transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2) in prostate cancer (PCa). Here, we further characterize this role and uncover new functions for TMEFF2 in cancer and adult prostate regeneration.

METHODS

The role of TMEFF2 was examined in PCa cells using Matrigel(TM) cultures and allograft models of PCa cells. In addition, we developed a transgenic mouse model that expresses TMEFF2 from a prostate specific promoter. Anatomical, histological, and metabolic characterizations of the transgenic mouse prostate were conducted. The effect of TMEFF2 in prostate regeneration was studied by analyzing branching morphogenesis in the TMEFF2-expressing mouse lobes and alterations in branching morphogenesis were correlated with the metabolomic profiles of the mouse lobes. The role of TMEFF2 in prostate tumorigenesis in whole animals was investigated by crossing the TMEFF2 transgenic mice with the TRAMP mouse model of PCa and analyzing the histopathological changes in the progeny.

RESULTS

Ectopic expression of TMEFF2 impairs growth of PCa cells in Matrigel or allograft models. Surprisingly, while TMEFF2 expression in the TRAMP mouse did not have a significant effect on the glandular prostate epithelial lesions, the double TRAMP/TMEFF2 transgenic mice displayed an increased incidence of neuroendocrine type tumors. In addition, TMEFF2 promoted increased branching specifically in the dorsal lobe of the prostate suggesting a potential role in developmental processes. These results correlated with data indicating an alteration in the metabolic profile of the dorsal lobe of the transgenic TMEFF2 mice.

CONCLUSIONS

Collectively, our results confirm the tumor suppressor role of TMEFF2 and suggest that ectopic expression of TMEFF2 in mouse prostate leads to additional lobe-specific effects in prostate regeneration and tumorigenesis. This points to a complex and multifunctional role for TMEFF2 during PCa progression.

Sequence-function correlations and dynamics of ERG isoforms. ERG8 is the black sheep of the family

The transcription factor ERG is known to have divergent roles. On one hand, it acts as differentiation factor of endothelial cells. On the other hand, it has pathological roles in various cancers. Genomic analyses of the ERG gene show that it gives rise to several isoforms. However, functional differences between these isoforms, representing potential reasons for distinct effects in diverse cell types have not been addressed in detail so far. We set out to investigate the major protein isoforms and found that ERG8 contains a unique C-terminus. This isoform, when expressed as GFP-fusion protein, localized mainly to the cytosol, whereas the other major isoforms (ERG1-4) were predominantly nuclear. Using site directed mutagenesis and laser scanning microscopy of live cells, we could identify nuclear localization (NLS) and nuclear export sequences (NES). These analyses indicated that ERG8 lacks a classical NLS and the DNA-binding domain, but holds an additional NES within its distinctive C-terminus. All the tested isoforms were shuttling between nucleus and cytosol and showed a high degree of mobility. ERG’s 1 to 4 were transcriptionally active on ERG-promoter elements whereas ERG8 was inactive, which is in line with the absence of a DNA-binding domain. Fluorescence resonance energy transfer (FRET) microscopy revealed that ERG8 can bind to the transcriptionally active ERG’s. Knockdown of ERG8 in endothelial cells resulted in upregulation of endogenous ERG-transcriptional activity implying ERG8 as an inhibitor of the active ERG isoforms. Quantitative PCR revealed a different ratio of active ERG’s to ERG8 in cancer- versus non-transformed cells.

Characterization of autoimmune inflammation induced prostate stem cell expansion

BACKGROUND

The presence of inflammation in prostate cancer (PCa) and benign prostate hyperplasia (BPH) has been well described but the cellular mechanisms by which inflammation modulates the prostate are currently unclear. Prostate stem cells (PSC) not only maintain prostate homeostasis but also are considered to be the cell of origin of PCa and an important contributor to BPH. However, the impact of inflammation on PSC is not well understood. Therefore, we initiated studies to evaluate the effect of inflammation on PSC.

METHOD

Ovalbumin specific CD8(+) T cells were intravenously delivered to intact and castrated prostate ovalbumin expressing transgenic-3 (POET-3) mice to induce inflammation. Lin (CD45/CD31)(-) Sca1(+) CD49f(+) cells (LSC) and progenitor cells within LSC were determined by flow cytometry. Sorted LSC were subjected to a prostate sphere forming assay to evaluate PSC clonal propagation, proliferation, immediate differentiation, and self-renewal ability. Density of individual spheres was measured by a cantilever-based resonator weighing system. Morphology and characterization of prostate spheres was determined by hematoxylin and eosin (H&E) staining and immunohistochemistry (IHC). Finally, immediate PSC differentiation in sphere formation was determined by immunofluorescence for epithelial cytokeratin markers cytokeratin (CK) 5 and CK8.

RESULT

Data presented here demonstrate a significant expansion of the proliferative (BrdU(+) ) LSC population, including CK5(+) , p63(+) , CK18(+) cells, as well as intermediate cells (CK5(+) /CK8(+) ) in inflamed prostates. Histological images reveal that PSC from inflamed prostates produce significantly larger spheres, indicating that the enhanced proliferation observed in LSC is sustained in vitro in the absence of inflammatory mediators. In addition, cultures from inflamed PSC yielded increased number of tubule-like spheres. These tube-like spheres grown from PSCs isolated from inflamed mice exhibited stratification of a CK8(+) luminal-like layer and a CK5(+) basal-like layer. Notably, the numbers of spheres formed by inflamed and non-inflamed PSC were equal, suggesting that even though proliferation is enhanced by inflammation, the homeostatic level of PSC is maintained.

CONCLUSION

Induction of inflammation promotes PSC expansion and immediate differentiation through highly proliferative progenitor cells while the homeostasis of PSC is maintained.

Targeted polymeric nanoparticles for cancer gene therapy

In this article, advances in designing polymeric nanoparticles for targeted cancer gene therapy are reviewed. Characterization and evaluation of biomaterials, targeting ligands, and transcriptional elements are each discussed. Advances in biomaterials have driven improvements to nanoparticle stability and tissue targeting, conjugation of ligands to the surface of polymeric nanoparticles enable binding to specific cancer cells, and the design of transcriptional elements has enabled selective DNA expression specific to the cancer cells. Together, these features have improved the performance of polymeric nanoparticles as targeted non-viral gene delivery vectors to treat cancer. As polymeric nanoparticles can be designed to be biodegradable, non-toxic, and to have reduced immunogenicity and tumorigenicity compared to viral platforms, they have significant potential for clinical use. Results of polymeric gene therapy in clinical trials and future directions for the engineering of nanoparticle systems for targeted cancer gene therapy are also presented.

Mouse models of prostate cancer: picking the best model for the question

When the National Institutes of Health Mouse Models of Human Cancer Consortium initiated the Prostate Steering Committee 15 years ago, there were no genetically engineered mouse (GEM) models of prostate cancer (PCa). Today, a PubMed search for "prostate cancer mouse model" yields 3,200 publications and this list continues to grow. The first generation of GEM utilized the newly discovered and characterized probasin promoter driving viral oncogenes such as Simian virus 40 large T antigen to yield the LADY and TRAMP models. As the PCa research field has matured, the second generation of models has incorporated the single and multiple molecular changes observed in human disease, such as loss of PTEN and overexpression of Myc. Application of these models has revealed that mice are particularly resistant to developing invasive PCa, and once they achieve invasive disease, the PCa rarely resembles human disease. Nevertheless, these models and their application have provided vital information on human PCa progression. The aim of this review is to provide a brief primer on mouse and human prostate histology and pathology, provide descriptions of mouse models, as well as attempt to answer the age old question: Which GEM model of PCa is the best for my research question?

Targeted inhibition of cell-surface serine protease Hepsin blocks prostate cancer bone metastasis

The development of effective therapies inhibiting prostate cancer progression and metastasis may substantially impact prostate cancer mortality and potentially reduce the rates of invasive treatments by enhancing the safety of active surveillance strategies. Hepsin (HPN) is a cell surface serine protease amplified in a subset of human sarcomas (7.2%), as well as in ovarian (10%), lung adeno (5.4%), lung squamous cell (4.5%), adenoid cystic (5%), breast (2.6%), uterine (1.7%) and colon (1.4%) carcinomas. While HPN is not amplified in prostate cancer, it is one of the most prominently overexpressed genes in the majority of human prostate tumors and genetic experiments in mice indicate that Hepsin promotes prostate cancer metastasis, particularly metastasis to the bone marrow. We report here the development, analysis and animal trial of the small-molecule Hepsin inhibitor HepIn-13. Long-term exposure to HepIn-13 inhibited bone, liver and lung metastasis in a murine model of metastatic prostate cancer. These findings indicate that inhibition of Hepsin with small-molecule compounds could provide an effective tool for attenuation of prostate cancer progression and metastasis.

A novel method for somatic transgenesis of the mouse prostate using the Sleeping Beauty transposon system

BACKGROUND

In vivo ectopic gene expression is a common approach for prostate research through the use of transgenes in germline transgenic mice. For some other organs, somatic transgenesis with the Sleeping Beauty transposon system has allowed in vivo ectopic gene expression with higher throughput and lower cost than germline transgenic approaches.

METHODS

Mouse e16 urogenital sinuses (UGSs) were co-injected with plasmids expressing the Sleeping Beauty transposase and plasmids with control or activated BRAF expressing transposons. Following electroporation, the transduced UGSs were grown as allografts in mouse hosts for 8 weeks, and the resulting allografts were evaluated for several endpoints.

RESULTS

Transposon-transduced UGS allografts developed into prostatic tissue with normal tissue structure and cellular differentiation. Integration of transposon vectors into the genomes of transduced allografts was confirmed using linker-mediated PCR, sequencing, and in situ PCR. Transduction of UGS allografts with transposons expressing activated BRAF resulted in ectopic BRAF expression that was detectable at both the mRNA and protein levels. Prostatic ducts over-expressing activated BRAF also had ectopic activation of the ERK1/2 mitogen activated kinases and increased epithelial cell proliferation.

CONCLUSIONS

The Sleeping Beauty transposon system can be used to achieve somatic transgenesis of prostatic allografts. This new method for achieving ectopic gene expression in the prostate will complement other existing approaches such as ectopic gene expression in cell lines and in germline transgenic mice. Advantages of this new approach include preservation of stromal-epithelial interactions not possible with cell lines, and higher throughput and lower cost than traditional germline transgenic approaches.

Tumor-suppressive functions of 15-Lipoxygenase-2 and RB1CC1 in prostate cancer

15-Lipoxygenase-2 (15-LOX2) is a human-specific lipid-peroxidizing enzyme most prominently expressed in epithelial cells of normal human prostate but downregulated or completely lost in>70% of prostate cancer (PCa) cases. Transgenic expression of 15-LOX2 in the mouse prostate surprisingly causes hyperplasia. Here we first provide evidence that 15-LOX2-induced prostatic hyperplasia does not progress to PCa even in p53(+/-) or p53(-/-) background. More important, by generating 15-LOX2; Hi-Myc double transgenic (dTg) mice, we show that 15-LOX2 expression inhibits Myc-induced PCa development, such that in the 3-month- and 6-month-old dTg mice, there is a significant reduction in prostate intraneoplasia (PIN) and PCa prevalent in age-matched Hi-Myc prostates. The dTg prostates show increased cell senescence and expression of several senescence-associated molecules, including p27, phosphorylated Rb, and Rb1cc1. We further show that in HPCa, 15-LOX2 and c-Myc manifest reciprocal protein expression patterns. Moreover, RB1CC1 accumulates in senescing normal human prostate (NHP) cells, and in both NHP and RWPE-1 cells, the 15-LOX2 metabolic products 15(S)-HPETE and 15(S)-HETE induce RB1CC1. We finally show that unlike 15-LOX2, RB1CC1 is not lost but rather frequently overexpressed in PCa samples. RB1CC1 knockdown in PC3 cells enhances clonal growth in vitro and tumor growth in vivo. Together, our present studies provide evidence for tumor-suppressive functions for both 15-LOX2 and RB1CC1.

Molecular-genetic imaging of cancer

Molecular-genetic imaging of cancer using nonviral delivery systems has great potential for clinical application as a safe, efficient, noninvasive tool for visualization of various cellular processes including detection of cancer, and its attendant metastases. In recent years, significant effort has been expended in overcoming technical hurdles to enable clinical adoption of molecular-genetic imaging. This chapter will provide an introduction to the components of molecular-genetic imaging and recent advances on each component leading to safe, efficient clinical applications for detecting cancer. Combination with therapy, namely, generating molecular-genetic theranostic constructs, will provide further impetus for clinical translation of this promising technology.

FGFR1-WNT-TGF-β signaling in prostate cancer mouse models recapitulates human reactive stroma

The reactive stroma surrounding tumor lesions performs critical roles ranging from supporting tumor cell proliferation to inducing tumorigenesis and metastasis. Therefore, it is critical to understand the cellular components and signaling control mechanisms that underlie the etiology of reactive stroma. Previous studies have individually implicated fibroblast growth factor receptor 1 (FGFR1) and canonical WNT/β-catenin signaling in prostate cancer progression and the initiation and maintenance of a reactive stroma; however, both pathways are frequently found to be coactivated in cancer tissue. Using autochthonous transgenic mouse models for inducible FGFR1 (JOCK1) and prostate-specific and ubiquitously expressed inducible β-catenin (Pro-Cat and Ubi-Cat, respectively) and bigenic crosses between these lines (Pro-Cat × JOCK1 and Ubi-Cat × JOCK1), we describe WNT-induced synergistic acceleration of FGFR1-driven adenocarcinoma, associated with a pronounced fibroblastic reactive stroma activation surrounding prostatic intraepithelial neoplasia (mPIN) lesions found both in in situ and reconstitution assays. Both mouse and human reactive stroma exhibited increased transforming growth factor-β (TGF-β) signaling adjacent to pathologic lesions likely contributing to invasion. Furthermore, elevated stromal TGF-β signaling was associated with higher Gleason scores in archived human biopsies, mirroring murine patterns. Our findings establish the importance of the FGFR1-WNT-TGF-β signaling axes as driving forces behind reactive stroma in aggressive prostate adenocarcinomas, deepening their relevance as therapeutic targets.

Androgen receptor splice variant AR3 promotes prostate cancer via modulating expression of autocrine/paracrine factors

Deregulation of androgen receptor (AR) splice variants has been implicated to play a role in prostate cancer development and progression. To understand their functions in prostate, we established a transgenic mouse model (AR3Tg) with targeted expression of the constitutively active and androgen-independent AR splice variant AR3 (a.k.a. AR-V7) in prostate epithelium. We found that overexpression of AR3 modulates expression of a number of tumor-promoting autocrine/paracrine growth factors (including Tgfβ2 and Igf1) and expands prostatic progenitor cell population, leading to development of prostatic intraepithelial neoplasia. In addition, we showed that some epithelial-mesenchymal transition-associated genes are up-regulated in AR3Tg prostates, suggesting that AR3 may antagonize AR activity and halt the differentiation process driven by AR and androgen. This notion is supported by our observations that the number of Ck5(+)/Ck8(+) intermediate cells is increased in AR3Tg prostates after castration, and expression of AR3 transgene in these intermediate cells compromises prostate epithelium regeneration upon androgen replacement. Our results demonstrate that AR3 is a driver of prostate cancer, at least in part, through modulating multiple tumor-promoting autocrine/paracrine factors.

Transcriptional regulation of CXCR4 in prostate cancer: significance of TMPRSS2-ERG fusions

CXCR4 is a chemokine receptor that mediates invasion and metastasis. CXCR4 expression is transcriptionally regulated in cancer cells and is associated with aggressive prostate cancer phenotypes. Previously, we and others have shown that the transcription factor ERG regulates CXCR4 expression in prostate cancer cells and that androgens modulate CXCR4 expression via increasing ERG expression. Herein, the molecular mechanisms of ERG-mediated CXCR4 promoter activation, phosphorylation of ERG by intracellular kinases and subsequent CXCR4 expression, as well as the status of ERG and CXCR4 in human prostate cancer specimens were investigated. Using multiple molecular strategies, it was demonstrated that (i) ERG expressed in TMPRSS2-ERG fusion positive VCaP cells selectively binds to specific ERG/Ets bindings sites in the CXCR4 promoter; (ii) distal binding sites mediate promoter activation; (iii) exogenously expressed ERG promotes CXCR4 expression; (iv) ERG is phosphorylated at Serine-81 and -215, by both IKK and Akt kinases, and Akt mediates CXCR4 expression; (v) ERG-induced CXCR4 drives CXCL12-dependent adhesion to fibronectin; and (vi) ERG and CXCR4 were coexpressed in human prostate cancer tissue, consistent with ERG-mediated transcriptional activation of CXCR4. These data demonstrate that ERG activates CXCR4 expression by binding to specific ERG/Ets responsive elements and via intracellular kinases that phosphorylate ERG at discrete serine residues.

IMPLICATIONS

These findings provide a mechanistic link between TMPRSS2-ERG translocations and intracellular kinase-mediated phosphorylation of ERG on enhanced metastasis of tumor cells via CXCR4 expression and function in prostate cancer cells.

Current mouse and cell models in prostate cancer research

Mouse models of prostate cancer (PCa) are critical for understanding the biology of PCa initiation, progression, and treatment modalities. Here, we summarize recent advances in PCa mouse models that led to new insights into specific gene functions in PCa. For example, the study of transgenic mice with TMPRSS2/ERG, an androgen-regulated fusion protein, revealed its role in developing PCa precursor lesions, prostate intraepithelial neoplasia; however, it is not sufficient for PCa development. Double deficiency of Pten and Smad4 leads to a high incidence of metastatic PCa. Targeted deletion of Pten in castration-resistant Nkx3-1-expressing cells results in rapid carcinoma formation after androgen-mediated regeneration, indicating that progenitor cells with luminal characteristics can play a role in initiation of PCa. Transgenic mice with activated oncogenes, growth factors, and steroid hormone receptors or inactivated tumor suppressors continue to provide insights into disease progression from initiation to metastasis. Further development of new PCa models with spatial and temporal regulation of candidate gene expression will probably enhance our understanding of the complex events that lead to PCa initiation and progression, thereby invoking novel strategies to combat this common disease in men.

Loss of survivin in the prostate epithelium impedes carcinogenesis in a mouse model of prostate adenocarcinoma

The inhibitor of apoptosis protein survivin is expressed in most cancers. Using the conditional PTEN deletion mouse model, we previously reported that survivin levels increase with prostate tumor growth. Here we evaluated the functional role of survivin in prostate tumor growth. First, we demonstrated that mice lacking the survivin gene in prostate epithelium were fertile and had normal prostate growth and development. We then serially, from about 10-56 weeks of age, evaluated histopathologic changes in the prostate of mice with PTEN deletion combined with survivin mono- or bi-allelic gene deletion. While within this time period most of the animals with wild-type or monoallelic survivin deletion developed adenocarcinomas, the most severe lesions in the biallelic survivin deleted mice were high-grade prostatic intra-epithelial neoplasia with distinct histopathology. Many atypical cells contained large hypertrophic cytoplasm and desmoplastic reaction in the prostatic intra-epithelial neoplasia lesions of this group was minimal until the late ages. A reduced proliferation index as well as apoptotic and senescent cells were detected in the lesions of mice with compound PTEN/survivin deficiency throughout the time points examined. Survivin deletion was also associated with reduced tumor expression of another inhibitor of apoptosis member, the X-linked inhibitor of apoptosis. Our findings suggest that survivin participates in the progression of prostatic intraepithelial neoplasia to adenocarcinoma, and that survivin interference at the prostatic intraepithelial neoplasia stages may be a potential therapeutic strategy to halt or delay further progression.

Modeling prostate cancer in mice: something old, something new, something premalignant, something metastatic

More than 15 years ago, the first generation of genetically engineered mouse (GEM) models of prostate cancer was introduced. These transgenic models utilized prostate-specific promoters to express SV40 oncogenes specifically in prostate epithelium. Since the description of these initial models, there have been a plethora of GEM models of prostate cancer representing various perturbations of oncogenes or tumor suppressors, either alone or in combination. This review describes these GEM models, focusing on their relevance for human prostate cancer and highlighting their strengths and limitations, as well as opportunities for the future.

Genetically engineered mouse models of prostate cancer

Despite major improvement in treatment of early stage localised prostate cancer, the distinction between indolent tumors and those that will become aggressive, as well as the lack of efficient therapies of advanced prostate cancer, remain major health problems. Genetically engineered mice (GEM) have been extensively used to investigate the molecular and cellular mechanisms underlying prostate tumor initiation and progression, and to evaluate new therapies. Moreover, the recent development of conditional somatic mutagenesis in the mouse prostate offers the possibility to generate new models that more faithfully reproduce the human disease, and thus should contribute to improve diagnosis and treatments. The strengths and weaknesses of various models will be discussed, as well as future opportunities.

Use of PB-Cre4 mice for mosaic gene deletion

Transgene expression from short promoters in transgenic animals can lead to unwanted transgene expression patterns, often as a byproduct of random integration of the expression cassette into the host genome. Here I demonstrate that the often used PB-Cre4 line (also referred to as “Probasin-Cre”), although expressing exclusively in the male prostate epithelium when transmitted through male mice, can lead to recombination of loxP-flanked alleles in a large variety of tissues when transmitted through female mice. This aberrant Cre activity due to Cre expression in the oocytes leads to different outcomes for maternally or paternally transmitted loxP-flanked alleles: Maternally inherited loxP-flanked alleles undergo recombination very efficiently, making female PB-Cre4 mice an efficient monoallelic “Cre deleter line”. However, paternally inherited loxP-flanked alleles are inefficiently recombined by maternal PB-Cre4, giving rise to mosaic expression patterns in the offspring. This mosaic recombination is difficult to detect with standard genotyping approaches of many mouse lines and should therefore caution researchers using PB-Cre4 to use additional approaches to exclude the presence of recombined alleles. However, mosaic recombination should also be useful in transgenic “knockout” approaches for mosaic gene deletion experiments.

Characterization of infectivity-enhanced conditionally replicating adenovectors for prostate cancer radiovirotherapy

Prostate cancer (PCa) is the second most commonly diagnosed and sixth leading cause of cancer death in American men and one for which no curative therapy exists after metastasis. To meet this need for novel therapies, our laboratory has previously generated conditionally replicating adenovirus (CRAd) vectors expressing the sodium iodide symporter (hNIS). This virus transduced PCa cells and induced functional NIS expression, allowing for noninvasive tumor imaging and combination therapy with radioiodide, referred to as radiovirotherapy. We have now generated two new modified vectors to further improve efficacy. Ad5/3PB-ADP-hNIS and Ad5/3PB-hNIS include a hybrid Ad5/3 fiber knob to improve transduction efficiency, and express NIS from the endogenous major late promoter to restrict NIS expression to target cells. Additionally, Ad5/3PB-ADP-hNIS includes the adenovirus death protein (ADP), which hastens the release of viral particles after assembly. These two vectors specifically induce radioisotope uptake, cytopathic effect, and viral replication in androgen receptor-expressing PCa cell lines with Ad5/3PB-ADP-hNIS showing earlier (131)I uptake and cytolysis at low multiplicity of infection. SPECT-CT imaging of xenograft tumors infected with Ad5/3PB-hNIS showed steady uptake, whereas infection with Ad5/3PB-ADP-hNIS led to increasing uptake, indicating viral spread. Radiovirotherapy of xenograft LNCaP tumors with Ad5/3PB-ADP-hNIS showed the most significant survival extension versus control tumors (p=0.001), but the benefit of radiovirotherapy was not statistically significant compared with virotherapy alone in this model. These results show the potential of Ad5/3PB-ADP-hNIS as a vector for treatment of prostate cancer.