Roles of the Nkx3.1 homeobox gene in prostate organogenesis and carcinogenesis

Metformin Overcomes the Consequences of NKX3.1 Loss to Suppress Prostate Cancer Progression

BACKGROUND

The antidiabetic drug metformin has known anticancer effects related to its antioxidant activity; however, its clinical benefit for prostate cancer (PCa) has thus far been inconclusive. Here, we investigate whether the efficacy of metformin in PCa is related to the expression status of NKX3.1, a prostate-specific homeobox gene that functions in mitochondria to protect the prostate from aberrant oxidative stress.

OBJECTIVE

To investigate the relationship of NKX3.1 expression and metformin efficacy in PCa.

DESIGN, SETTING, AND PARTICIPANTS

Functional studies were performed in vivo and in vitro in genetically engineered mouse models and human LNCaP cells, and organotypic cultures having normal or reduced/absent levels of NKX3.1. Correlative studies were performed using two independent retrospective tissue microarray cohorts of radical prostatectomies and a retrospective cohort of prostate biopsies from patients on active surveillance.

INTERVENTION

Metformin was administered before or after the induction of oxidative stress by treatment with paraquat.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Functional endpoints included analyses of histopathology, tumorigenicity, and mitochondrial function. Correlative endpoints include Kaplan-Meier curves and Cox proportional hazard regression models.

RESULTS AND LIMITATIONS

Metformin reversed the adverse consequences of NKX3.1 deficiency following oxidative stress in vivo and in vitro, as evident by reduced tumorigenicity and restored mitochondrial function. Patients with low NKX3.1 expression showed a significant clinical benefit from taking metformin.

CONCLUSIONS

Metformin can overcome the adverse consequences of NKX3.1 loss for PCa progression by protecting against oxidative stress and promoting normal mitochondrial function. These functional activities and clinical correlates were observed only with low NKX3.1 expression. Thus, the clinical benefit of metformin in PCa may depend on the status of NKX3.1 expression.

PATIENT SUMMARY

Prostate cancer patients with low NKX3.1 are likely to benefit most from metformin treatment to delay disease progression in a precision interception paradigm.

NKX3.1 Localization to Mitochondria Suppresses Prostate Cancer Initiation

Mitochondria provide the first line of defense against the tumor-promoting effects of oxidative stress. Here we show that the prostate-specific homeoprotein NKX3.1 suppresses prostate cancer initiation by protecting mitochondria from oxidative stress. Integrating analyses of genetically engineered mouse models, human prostate cancer cells, and human prostate cancer organotypic cultures, we find that, in response to oxidative stress, NKX3.1 is imported to mitochondria via the chaperone protein HSPA9, where it regulates transcription of mitochondrial-encoded electron transport chain (ETC) genes, thereby restoring oxidative phosphorylation and preventing cancer initiation. Germline polymorphisms of NKX3.1 associated with increased cancer risk fail to protect from oxidative stress or suppress tumorigenicity. Low expression levels of NKX3.1 combined with low expression of mitochondrial ETC genes are associated with adverse clinical outcome, whereas high levels of mitochondrial NKX3.1 protein are associated with favorable outcome. This work reveals an extranuclear role for NKX3.1 in suppression of prostate cancer by protecting mitochondrial function. SIGNIFICANCE: Our findings uncover a nonnuclear function for NKX3.1 that is a key mechanism for suppression of prostate cancer. Analyses of the expression levels and subcellular localization of NKX3.1 in patients at risk of cancer progression may improve risk assessment in a precision prevention paradigm, particularly for men undergoing active surveillance.See related commentary by Finch and Baena, p. 2132.This article is highlighted in the In This Issue feature, p. 2113.

Stromal cell interplay in prostate development, physiology, and pathological conditions

Advances in prostatic stroma studies over the past few decades have demonstrated that the stroma not only supports and nourishes the gland's secretory epithelium but also participates in key aspects of morphogenesis, in the prostate's hormonal metabolism, and in the functionality of the secretory epithelium. Furthermore, the stroma is implicated in the onset and progression of prostate cancer through the formation of the so-called reactive stroma, which corresponds to a tumorigenesis-permissive microenvironment. Prostatic stromal cells are interconnected and exchange paracrine signals among themselves in a gland that is highly sensitive to endocrine hormones. There is a growing body of evidence that telocytes, recently detected interstitial cells that are also present in the prostate, are involved in stromal organization, so that their processes form a network of interconnections with both the epithelium and the other stromal cells. The present review provides an update on the different types of prostate stromal cells, their interrelationships and implications for prostate development, physiology and pathological conditions.

Mapping of m6A and Its Regulatory Targets in Prostate Cancer Reveals a METTL3-Low Induction of Therapy Resistance

Recent evidence has highlighted the role of N 6-methyladenosine (m6A) in the regulation of mRNA expression, stability, and translation, supporting a potential role for posttranscriptional regulation mediated by m6A in cancer. Here, we explore prostate cancer as an exemplar and demonstrate that low levels of N 6-adenosine-methyltransferase (METTL3) is associated with advanced metastatic disease. To investigate this relationship, we generated the first prostate m6A maps, and further examined how METTL3 regulates expression at the level of transcription, translation, and protein. Significantly, transcripts encoding extracellular matrix proteins are consistently upregulated with METTL3 knockdown. We also examined the relationship between METTL3 and androgen signaling and discovered the upregulation of a hepatocyte nuclear factor-driven gene signature that is associated with therapy resistance in prostate cancer. Significantly, METTL3 knockdown rendered the cells resistant to androgen receptor antagonists via an androgen receptor-independent mechanism driven by the upregulation of nuclear receptor NR5A2/LRH-1. IMPLICATIONS: These findings implicate changes in m6A as a mechanism for therapy resistance in metastatic prostate cancer.

NKX6-1 mediates cancer stem-like properties and regulates sonic hedgehog signaling in leiomyosarcoma

Background

Leiomyosarcoma (LMS), the most common soft tissue sarcoma, exhibits heterogeneous and complex genetic karyotypes with severe chromosomal instability and rearrangement and poor prognosis.

Methods

Clinical variables associated with NKX6-1 were obtained from The Cancer Genome Atlas (TCGA). NKX6-1 mRNA expression was examined in 49 human uterine tissues. The in vitro effects of NXK6-1 in LMS cells were determined by reverse transcriptase PCR, western blotting, colony formation, spheroid formation, and cell viability assays. In vivo tumor growth was evaluated in nude mice.

Results

Using The Cancer Genome Atlas (TCGA) and human uterine tissue datasets, we observed that NKX6-1 expression was associated with poor prognosis and malignant potential in LMS. NKX6-1 enhanced in vitro tumor cell aggressiveness via upregulation of cell proliferation and anchorage-independent growth and promoted in vivo tumor growth. Moreover, overexpression and knockdown of NKX6-1 were associated with upregulation and downregulation, respectively, of stem cell transcription factors, including KLF8, MYC, and CD49F, and affected sphere formation, chemoresistance, NOTCH signaling and Sonic hedgehog (SHH) pathways in human sarcoma cells. Importantly, treatment with an SHH inhibitor (RU-SKI 43) but not a NOTCH inhibitor (DAPT) reduced cell survival in NKX6-1-expressing cancer cells, indicating that an SHH inhibitor could be useful in treating LMS. Finally, using the TCGA dataset, we demonstrated that LMS patients with high expression of NKX6-1 and HHAT, an SHH pathway acyltransferase, had poorer survival outcomes compared to those without.

Conclusions

Our findings indicate that NKX6-1 and HHAT play critical roles in the pathogenesis of LMS and could be promising diagnostic and therapeutic targets for LMS patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00726-6.

NKX6.1 Represses Tumorigenesis, Metastasis, and Chemoresistance in Colorectal Cancer

Accumulating evidence suggests that NKX6.1 (NK homeobox 1) plays a role in various types of cancer. In our previous studies, we identified NKX6.1 hypermethylation as a promising marker and demonstrated that the NKX6.1 gene functions as a metastasis suppressor through the epigenetic regulation of the epithelial-to-mesenchymal transition (EMT) in cervical cancer. More recently, we have demonstrated that NKX6.1 methylation is related to the chemotherapy response in colorectal cancer (CRC). Nevertheless, the biological function of NKX6.1 in the tumorigenesis of CRC remains unclear. In this study, we showed that NKX6.1 suppresses tumorigenic and metastatic ability both in vitro and in vivo. NKX6.1 represses cell invasion partly through the modulation of EMT. The overexpression of NKX6.1 enhances chemosensitivity in CRC cells. To further explore how NKX6.1 exerts its tumor-suppressive function, we used RNA sequencing technology for comprehensive analysis. The results showed that differentially expressed genes (DEGs) were mainly related to cell migration, response to drug, transcription factor activity, and growth factor activity, suggesting that these DEGs are involved in the function of NKX6.1 suppressing cancer invasion and metastasis. Our results demonstrated that NKX6.1 functions as a tumor suppressor partly by repressing EMT and enhancing chemosensitivity in CRC, making it a potential therapeutic target.

In Vitro Zika Virus Infection of Human Neural Progenitor Cells: Meta-Analysis of RNA-Seq Assays

The Zika virus (ZIKV) is an emergent arthropod-borne virus (arbovirus) responsible for congenital Zika syndrome (CZS) and a range of other congenital malformations. Evidence shows that ZIKV infects human neural progenitor cells (hNPCs) in the fetal brain, prompting inflammation and tissue damage/loss. Despite recent advances, little is known about the pathways involved in CZS pathogenesis. We performed a meta-analysis, gene ontology (GO), and pathway analysis of whole transcriptome studies with the aim of clarifying the genes and pathways potentially altered during hNPCs infection with ZIKV. We selected three studies (17 samples of infected hPNCs compared to hPNCs uninfected controls) through a systematic search of the Gene Expression Omnibus (GEO) database. The raw reads were trimmed, counted, and normalized. Next, we performed a rank product meta-analysis to detect consistently differentially expressed genes (DEGs) in these independent experiments. We detected 13 statistically significant DEGs. GO ontology and reactome analysis showed an enrichment of interferon, pro-inflammatory, and chemokines signaling and apoptosis pathways in ZIKV-infected cells. Moreover, we detected three possible new candidate genes involved in hNPCs infection: APOL6, XAF1, and TNFRSF1. Our results confirm that interferon (IFN) signaling dominates the ZIKV response, and that a crucial contribution is given by apoptotic pathways, which might elicit the CZS phenotype.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

Frequently rearranged and overexpressed δ-catenin is responsible for low sensitivity of prostate cancer cells to androgen receptor and β-catenin antagonists

The mechanism of prostate cancer (PCa) progression towards the hormone refractory state remains poorly understood. Treatment options for such patients are limited and present a major clinical challenge. Previously, δ-catenin was reported to promote PCa cell growth in vitro and its increased level is associated with PCa progression in vivo. In this study we show that re-arrangements at Catenin Delta 2 (CTNND2) locus, including gene duplications, are very common in clinically significant PCa and may underlie δ-catenin overexpression. We find that δ-catenin in PCa cells exists in a complex with E-cadherin, p120, and α- and β-catenin. Increased expression of δ-catenin leads to its further stabilization as well as upregulation and stabilization of its binding partners. Resistant to degradation and overexpressed δ-catenin isoform activates Wnt signaling pathway by increasing the level of nuclear β-catenin and subsequent stimulation of Tcf/Lef transcription targets. Evaluation of responses to treatments, with androgen receptor (AR) antagonist and β-catenin inhibitors revealed that cells with high levels of δ-catenin are more resistant to killing with single agent treatment than matched control cells. We show that combination treatment targeting both AR and β-catenin networks is more effective in suppressing tumor growth than targeting a single network. In conclusion, targeting clinically significant PCa with high levels of δ–catenin with anti-androgen and anti β-catenin combination therapy may prevent progression of the disease to a castration-resistant state and, thus, represents a promising therapeutic strategy.

Nkx2-3-A Slippery Slope From Development Through Inflammation Toward Hematopoietic Malignancies

The development of peripheral lymphoid tissues from the mesoderm is the result of a complex convergence combining lymphohematopoietic differentiation with the local specification of nonhematopoietic mesenchymal components. Although the various transcriptional regulators with fate-determining effects in diversifying the mobile leukocyte subsets have been thoroughly studied and identified, the tissue-specific determinants promoting the regional differentiation of resident mesenchyme are less understood. Of these factors, various members of the NK-class Nkx paralogues have emerged as key regulators for the organogenesis of spleen and mucosal lymphoid tissues, and recent data have also indicated their involvement in various pathological events, including gut inflammation and hematopoietic malignancies. Here, we summarize available data on the roles of Nkx2-3 in lymphoid tissue development and discuss its possible value as a developmental marker and disease-associated pathogenic trait.

A homeobox protein, NKX6.1, up-regulates interleukin-6 expression for cell growth in basal-like breast cancer cells

Among breast cancer subtypes, basal-like breast cancer is particularly aggressive, and research on the molecules involved in its pathology might contribute to therapy. In this study, we found that expression of NKX6.1, a homeobox transcription factor, is higher in basal-like breast cancer than in other subtypes. In loss-of-function experiments on basal-like breast cancer cell lines, NKX6.1-depleted cells exhibited reduced cell growth. Because cytokine interleukin-6 (IL-6) is expressed in basal-like breast cancer, and increases cell growth, we analyzed expression levels of IL6, an IL-6 gene, and observed reduced IL6 expression in NKX6.1-depleted cells. In a reporter assay, IL6 promoter activity was reduced by loss of NKX6.1 function. A pull-down assay showed that NKX6.1 binds to the proximal region in IL6 promoter. These results indicate that NKX6.1 directly up-regulates IL6 expression. To investigate further, we established cells with forced expression of IL-6. We observed that exogenous IL-6 expression restored the reduced cell growth of NKX6.1-depleted cells. Furthermore, orthotopic xenografts showed that NKX6.1-depleted cells lost the capacity for tumor formation. We therefore conclude that NKX6.1 is a factor for IL-6-regulated growth and tumor formation in basal-like breast cancer. Our findings facilitate profound understanding of basal-like breast cancer, and the development of suitable therapy.

The tumor suppressor ING1b is a novel corepressor for the androgen receptor and induces cellular senescence in prostate cancer cells

The androgen receptor (AR) signaling is critical for prostate cancer (PCa) progression to the castration-resistant stage with poor clinical outcome. Altered function of AR-interacting factors may contribute to castration-resistant PCa (CRPCa). Inhibitor of growth 1 (ING1) is a tumor suppressor that regulates various cellular processes including cell proliferation. Interestingly, ING1 expression is upregulated in senescent primary human prostate cells; however, its role in AR signaling in PCa was unknown. Using a proteomic approach by surface-enhanced laser desorption ionization-mass spectrometry (SELDI-MS) combined with immunological techniques, we provide here evidence that ING1b interacts in vivo with the AR. The interaction was confirmed by co-immunoprecipitation, in vitro GST-pull-down, and quantitative intracellular colocalization analyses. Functionally, ING1b inhibits AR-responsive promoters and endogenous key AR target genes in the human PCa LNCaP cells. Conversely, ING1b knockout (KO) mouse embryonic fibroblasts (MEFs) exhibit enhanced AR activity, suggesting that the interaction with ING1b represses the AR-mediated transcription. Also, data suggest that ING1b expression is downregulated in CRPCa cells compared with androgen-dependent LNCaP cells. Interestingly, its ectopic expression induces cellular senescence and reduces cell migration in both androgen-dependent and CRPCa cells. Intriguingly, ING1b can also inhibit androgen-induced growth in LNCaP cells in a similar manner as AR antagonists. Moreover, ING1b upregulates different cell cycle inhibitors including p27(KIP1), which is a novel target for ING1b. Taken together, our findings reveal a novel corepressor function of ING1b on various AR functions, thereby inhibiting PCa cell growth.

Directed Differentiation of Human Embryonic Stem Cells into Prostate Organoids In Vitro and its Perturbation by Low-Dose Bisphenol A Exposure

Studies using rodent and adult human prostate stem-progenitor cell models suggest that developmental exposure to the endocrine disruptor Bisphenol-A (BPA) can predispose to prostate carcinogenesis with aging. Unknown at present is whether the embryonic human prostate is equally susceptible to BPA during its natural developmental window. To address this unmet need, we herein report the construction of a pioneer in vitro human prostate developmental model to study the effects of BPA. The directed differentiation of human embryonic stem cells (hESC) into prostatic organoids in a spatial system was accomplished with precise temporal control of growth factors and steroids. Activin-induced definitive endoderm was driven to prostate specification by combined exposure to WNT10B and FGF10. Matrigel culture for 20–30 days in medium containing R-Spondin-1, Noggin, EGF, retinoic acid and testosterone was sufficient for mature prostate organoid development. Immunofluorescence and gene expression analysis confirmed that organoids exhibited cytodifferentiation and functional properties of the human prostate. Exposure to 1 nM or 10 nM BPA throughout differentiation culture disturbed early morphogenesis in a dose-dependent manner with 1 nM BPA increasing and 10 nM BPA reducing the number of branched structures formed. While differentiation of branched structures to mature organoids seemed largely unaffected by BPA exposure, the stem-like cell population increased, appearing as focal stem cell nests that have not properly entered lineage commitment rather than the rare isolated stem cells found in normally differentiated structures. These findings provide the first direct evidence that low-dose BPA exposure targets hESC and perturbs morphogenesis as the embryonic cells differentiate towards human prostate organoids, suggesting that the developing human prostate may be susceptible to disruption by in utero BPA exposures.

Prostate Sphere-forming Stem Cells Are Derived from the P63-expressing Basal Compartment

Prostate stem cells (P-SCs) are capable of giving rise to all three lineages of prostate epithelial cells, including basal, luminal, and neuroendocrine cells. Multiple methods have been used to identify P-SCs in adult prostates. These include in vivo renal capsule implantation of a single epithelial cell with urogenital mesenchymal cells, in vitro prostasphere and organoid cultures, and lineage tracing with castration-resistant Nkx3.1 expression (CARN), in conjunction with expression of cell type-specific markers. Both organoid culture and CARN tracing show the existence of P-SCs in the luminal compartment. Although prostasphere cells predominantly express basal cell-specific cytokeratin and P63, the lineage of prostasphere-forming cells in the P-SC hierarchy remains to be determined. Using lineage tracing with P63(CreERT2), we show here that the sphere-forming P-SCs are P63-expressing cells and reside in the basal compartment. Therefore we designate them as basal P-SCs (P-bSCs). P-bSCs are capable of differentiating into AR(+) and CK18(+) organoid cells, but organoid cells cannot form spheres. We also report that prostaspheres contain quiescent stem cells. Therefore, the results show that P-bSCs represent stem cells that are early in the hierarchy of overall prostate tissue stem cells. Understanding the contribution of the two types of P-SCs to prostate development and prostate cancer stem cells and how to manipulate them may open new avenues for control of prostate cancer progression and relapse.

Exploring prostate cancer genome reveals simultaneous losses of PTEN, FAS and PAPSS2 in patients with PSA recurrence after radical prostatectomy

The multifocal nature of prostate cancer (PCa) creates a challenge to patients' outcome prediction and their clinical management. An approach that scrutinizes every cancer focus is needed in order to generate a comprehensive evaluation of the disease, and by correlating to patients' clinico-pathological information, specific prognostic biomarker can be identified. Our study utilized the Affymetrix SNP 6.0 Genome-wide assay to investigate forty-three fresh frozen PCa tissue foci from twenty-three patients. With a long clinical follow-up period that ranged from 2.0-9.7 (mean 5.4) years, copy number variation (CNV) data was evaluated for association with patients' PSA status during follow-up. From our results, the loss of unique genes on 10q23.31 and 10q23.2-10q23.31 were identified to be significantly associated to PSA recurrence (p < 0.05). The implication of PTEN and FAS loss (10q23.31) support previous reports due to their critical roles in prostate carcinogenesis. Furthermore, we hypothesize that the PAPSS2 gene (10q23.2-10q23.31) may be functionally relevant in post-operative PSA recurrence because of its reported role in androgen biosynthesis. It is suggestive that the loss of the susceptible region on chromosome 10q, which implicates PTEN, FAS and PAPSS2 may serve as genetic predictors of PSA recurrence after radical prostatectomy.

The role of Nkx3.2 in chondrogenesis

Transcription factor, Nkx3.2, is a member of the NK family of developmental genes and is expressed during embryogenesis in a variety of mammalian model organisms, including chicken and mouse. It was first identified in Drosophila as the Bagpipe (bap) gene, where it has been demonstrated to be essential during formation of the midgut musculature. However, mammalian homolog Nkx3.2 has been shown to play a significant role in axial and limb skeletogenesis; in particular, the human skeletal disease, spondylo-megaepiphyseal-metaphyseal dysplasia (SMMD), is associated with mutations of the Nkx3.2 gene. In this review, we highlight the role of Nkx3.2 during musculoskeletal development, with an emphasis on the factor's role in determining chondrogenic cell fate and its subsequent role in endochondral ossification and chondrocyte survival.

Systems analysis of the prostate tumor suppressor NKX3.1 supports roles in DNA repair and luminal cell differentiation

NKX3.1 is a homeobox transcription factor whose function as a prostate tumor suppressor remains insufficiently understood because neither the transcriptional program governed by NKX3.1, nor its interacting proteins have been fully revealed. Using affinity purification and mass spectrometry, we have established an extensive NKX3.1 interactome which contains the DNA repair proteins Ku70, Ku80, and PARP, thus providing a molecular underpinning to previous reports implicating NKX3.1 in DNA repair. Transcriptomic profiling of NKX3.1-negative prostate epithelial cells acutely expressing NKX3.1 revealed a rapid and complex response that is a near mirror image of the gene expression signature of human prostatic intraepithelial neoplasia (PIN). Pathway and network analyses suggested that NKX3.1 actuates a cellular reprogramming toward luminal cell differentiation characterized by suppression of pro-oncogenic c-MYC and interferon-STAT signaling and activation of tumor suppressor pathways. Consistently, ectopic expression of NKX3.1 conferred a growth arrest depending on TNFα and JNK signaling. We propose that the tumor suppressor function of NKX3.1 entails a transcriptional program that maintains the differentiation state of secretory luminal cells and that disruption of NKX3.1 contributes to prostate tumorigenesis by permitting luminal cell de-differentiation potentially augmented by defects in DNA repair.

Structural analysis of microRNA-target interaction by sequential seed mutagenesis and stem-loop 3' RACE

Background

As a consequence of recent RNAseq efforts, miRNAomes of diverse tissues and species are available. However, most interactions between microRNAs and regulated mRNAs are still to be deciphered. While in silico analysis of microRNAs results in prediction of hundreds of potential targets, bona-fide interactions have to be verified e.g. by luciferase reporter assays using fused target sites as well as controls incorporating mutated seed sequences. The aim of this study was the development of a straightforward approach for sequential mutation of multiple target sites within a given 3’ UTR.

Methodology/Principal Findings

The established protocol is based on Seed Mutagenesis Assembly PCR (SMAP) allowing for rapid identification of microRNA target sites. Based on the presented approach, we were able to determine the transcription factor NKX3.1 as a genuine target of miR-155. The sequential mutagenesis of multiple microRNA target sites was examined by miR-29a mediated CASP7 regulation, which revealed one of two predicted target sites as the predominant site of interaction. Since 3’ UTR sequences of non-model organisms are either lacking in databases or computationally predicted, we developed a Stem-Loop 3’ UTR RACE PCR (SLURP) for efficient generation of required 3’ UTR sequence data. The stem-loop primer allows for first strand cDNA synthesis by nested PCR amplification of the 3’ UTR. Besides other applications, the SLURP method was used to gain data on porcine CASP7 3’UTR evaluating evolutionary conservation of the studied interaction.

Conclusions/Significance

Sequential seed mutation of microRNA targets based on the SMAP approach allows for rapid structural analysis of several target sites within a given 3’ UTR. The combination of both methods (SMAP and SLURP) enables targeted analysis of microRNA binding sites in hitherto unknown mRNA 3’ UTRs within a few days.

Ectopic expression of homeobox gene NKX2-1 in diffuse large B-cell lymphoma is mediated by aberrant chromatin modifications

Homeobox genes encode transcription factors ubiquitously involved in basic developmental processes, deregulation of which promotes cell transformation in multiple cancers including hematopoietic malignancies. In particular, NKL-family homeobox genes TLX1, TLX3 and NKX2-5 are ectopically activated by chromosomal rearrangements in T-cell neoplasias. Here, using transcriptional microarray profiling and RQ-PCR we identified ectopic expression of NKL-family member NKX2-1, in a diffuse large B-cell lymphoma (DLBCL) cell line SU-DHL-5. Moreover, in silico analysis demonstrated NKX2-1 overexpression in 5% of examined DLBCL patient samples. NKX2-1 is physiologically expressed in lung and thyroid tissues where it regulates differentiation. Chromosomal and genomic analyses excluded rearrangements at the NKX2-1 locus in SU-DHL-5, implying alternative activation. Comparative expression profiling implicated several candidate genes in NKX2-1 regulation, variously encoding transcription factors, chromatin modifiers and signaling components. Accordingly, siRNA-mediated knockdown and overexpression studies confirmed involvement of transcription factor HEY1, histone methyltransferase MLL and ubiquitinated histone H2B in NKX2-1 deregulation. Chromosomal aberrations targeting MLL at 11q23 and the histone gene cluster HIST1 at 6p22 which we observed in SU-DHL-5 may, therefore, represent fundamental mutations mediating an aberrant chromatin structure at NKX2-1. Taken together, we identified ectopic expression of NKX2-1 in DLBCL cells, representing the central player in an oncogenic regulative network compromising B-cell differentiation. Thus, our data extend the paradigm of NKL homeobox gene deregulation in lymphoid malignancies.

Dose-related estrogen effects on gene expression in fetal mouse prostate mesenchymal cells

Developmental exposure of mouse fetuses to estrogens results in dose-dependent permanent effects on prostate morphology and function. Fetal prostatic mesenchyme cells express estrogen receptor alpha (ERα) and androgen receptors and convert stimuli from circulating estrogens and androgens into paracrine signaling to regulate epithelial cell proliferation and differentiation. To obtain mechanistic insight into the role of different doses of estradiol (E2) in regulating mesenchymal cells, we examined E2-induced transcriptomal changes in primary cultures of fetal mouse prostate mesenchymal cells. Urogenital sinus mesenchyme cells were obtained from male mouse fetuses at gestation day 17 and exposed to 10 pM, 100 pM or 100 nM E2 in the presence of a physiological concentration of dihydrotestosterone (0.69 nM) for four days. Gene ontology studies suggested that low doses of E2 (10 pM and 100 pM) induce genes involved in morphological tissue development and sterol biosynthesis but suppress genes involved in growth factor signaling. Genes involved in cell adhesion were enriched among both up-regulated and down-regulated genes. Genes showing inverted-U-shape dose responses (enhanced by E2 at 10 pM E2 but suppressed at 100 pM) were enriched in the glycolytic pathway. At the highest dose (100 nM), E2 induced genes enriched for cell adhesion, steroid hormone signaling and metabolism, cytokines and their receptors, cell-to-cell communication, Wnt signaling, and TGF- β signaling. These results suggest that prostate mesenchymal cells may regulate epithelial cells through direct cell contacts when estrogen level is low whereas secreted growth factors and cytokines might play significant roles when estrogen level is high.

Transcriptional activation of prostate specific homeobox gene NKX3-1 in subsets of T-cell lymphoblastic leukemia (T-ALL)

Homeobox genes encode transcription factors impacting key developmental processes including embryogenesis, organogenesis, and cell differentiation. Reflecting their tight transcriptional control, homeobox genes are often embedded in large non-coding, cis-regulatory regions, containing tissue specific elements. In T-cell acute lymphoblastic leukemia (T-ALL) homeobox genes are frequently deregulated by chromosomal aberrations, notably translocations adding T-cell specific activatory elements. NKX3-1 is a prostate specific homeobox gene activated in T-ALL patients expressing oncogenic TAL1 or displaying immature T-cell characteristics. After investigating regulation of NKX3-1 in primary cells and cell lines, we report its ectopic expression in T-ALL cells independent of chromosomal rearrangements. Using siRNAs and expression profiling, we exploited NKX3-1 positive T-ALL cell lines as tools to investigate aberrant activatory mechanisms. Our data confirmed NKX3-1 activation by TAL1/GATA3/LMO and identified LYL1 as an alternative activator in immature T-ALL cells devoid of GATA3. Moreover, we showed that NKX3-1 is directly activated by early T-cell homeodomain factor MSX2. These activators were regulated by MLL and/or by IL7-, BMP4- and IGF2-signalling. Finally, we demonstrated homeobox gene SIX6 as a direct leukemic target of NKX3-1 in T-ALL. In conclusion, we identified three major mechanisms of NKX3-1 regulation in T-ALL cell lines which are represented by activators TAL1, LYL1 and MSX2, corresponding to particular T-ALL subtypes described in patients. These results may contribute to the understanding of leukemic transcriptional networks underlying disturbed T-cell differentiation in T-ALL.

Nkx3.1 functions as para-transcription factor to regulate gene expression and cell proliferation in non-cell autonomous manner

Nkx3.1 is a homeoprotein transcription factor (TF) that inhibits proliferation of prostate epithelial cells (PECs) and acts as a tumor suppressor for prostate cancer (PCa). Because TFs classically function within the cells that produce them, Nkx3.1-induced growth inhibition was considered to occur in a cell-autonomous manner. We, however, found that Nkx3.1 protein can be secreted from cultured PECs and is detectable in the prostatic fluid and urine. A PCa-related point mutation (T164A) abolished Nkx3.1 secretion. Amazingly, secreted Nkx3.1 protein can translocate into adjacent cells, bind to the regulatory sequence of Nkx3.1 target genes and impact the expression of these genes in these adjacent cells. Expression of Nkx3.1 in PECs can also affect gene expression in adjacent cells, and this effect is abolished by the T164A mutation. Nkx3.1 protein inhibits cell proliferation when added to the culture. Expression of Nkx3.1, not the T164A mutant, also inhibits the proliferation of co-cultured cells. These results indicate that Nkx3.1 functions as a "para-transcription factor (PTF)," with the ability to regulate genes and inhibit cell proliferation in a non-cell autonomous manner. We also demonstrate that Nkx3.1 contains an evolutionarily conserved protein transduction domain essential for its PTF function, implicating potentially common PTF function among homeoproteins. In addition to the PCa-related T164A mutant, the secreted Nkx3.1 is reduced drastically in the prostatic fluid and urine of mice with PCa. These results indicate that Nkx3.1 can function as a PTF to suppress PCa and the urinary Nkx3.1 may be a potential biomarker for PCa diagnosis.

Estrogenic environmental chemicals and drugs: mechanisms for effects on the developing male urogenital system

Development and differentiation of the prostate from the fetal urogenital sinus (UGS) is dependent on androgen action via androgen receptors (AR) in the UGS mesenchyme. Estrogens are not required for prostate differentiation but do act to modulate androgen action. In mice exposure to exogenous estrogen during development results in permanent effects on adult prostate size and function, which is mediated through mesenchymal estrogen receptor (ER) alpha. For many years estrogens were thought to inhibit prostate growth because estrogenic drugs studied were administered at very high concentrations that interfered with normal prostate development. There is now extensive evidence that exposure to estrogen at very low concentrations during the early stages of prostate differentiation can stimulate fetal/neonatal prostate growth and lead to prostate disease in adulthood. Bisphenol A (BPA) is an environmental endocrine disrupting chemical that binds to both ER receptor subtypes as well as to AR. Interest in BPA has increased because of its prevalence in the environment and its detection in over 90% of people in the USA. In tissue culture of fetal mouse UGS mesenchymal cells, BPA and estradiol stimulated changes in the expression of several genes. We discuss here the potential involvement of estrogen in regulating signaling pathways affecting cellular functions relevant to steroid hormone signaling and metabolism and to inter- and intra-cellular communications that promote cell growth. The findings presented here provide additional evidence that BPA and the estrogenic drug ethinylestradiol disrupt prostate development in male mice at administered doses relevant to human exposures.

Smooth muscle cell-specific knockout of androgen receptor: a new model for prostatic disease

Androgen-driven stromal-epithelial interactions play a key role in normal prostate development and function as well as in the progression of common prostatic diseases such as benign prostatic hyperplasia and prostate cancer. However, exactly how, and via which cell type, androgens mediate their effects in the adult prostate remains unclear. This study investigated the role for smooth muscle (SM) androgen signaling in normal adult prostate homeostasis and function using mice in which androgen receptor was selectively ablated from prostatic SM cells. In adulthood the knockout (KO) mice displayed a 44% reduction in prostate weight and exhibited histological abnormalities such as hyperplasia, inflammation, fibrosis, and reduced expression of epithelial, SM, and stem cell identify markers (e.g. p63 reduced by 27% and Pten by 31%). These changes emerged beyond puberty and were not explained by changes in serum hormones. Furthermore, in response to exogenous estradiol, adult KO mice displayed an 8.5-fold greater increase in prostate weight than controls and developed urinary retention. KO mice also demonstrated a reduced response to castration compared with controls. Together these results demonstrate that prostate SM cells are vital in mediating androgen-driven stromal-epithelial interactions in adult mouse prostates, determining cell identity and function and limiting hormone-dependent epithelial cell proliferation. This novel mouse model provides new insight into the possible role for SM androgen action in prostate disease.

Activation of Paired-homeobox gene PITX1 by del(5)(q31) in T-cell acute lymphoblastic leukemia

In T-cell acute lymphoblasic leukemia (T-ALL), neoplastic chromosomal rearrangements are known to deregulate members of the homeobox gene families NKL and HOXA. Here, analysis of T-ALL cell lines and primary cells identified aberrant expression of a third homeobox gene group, the Paired (PRD) class. LOUCY cells revealed chromosomal deletion at 5q31, which targets the downstream regulatory region of the PRD homeobox gene PITX1, removing a STAT1 binding site. STAT1 mediates repressive interleukin 2 (IL2)-STAT1 signaling, implicating IL2 pathway avoidance as a possible activation mechanism. Among primary T-ALL samples, 2/22 (9%) aberrantly expressed PITX1, highlighting the importance of this gene. Forced expression of PITX1 in JURKAT cells and subsequent target gene analysis prompted deregulation of genes involved in T-cell development including HES1, JUN, NKX3-1, RUNX1, RUNX2, and TRIB2. Taken together, our data show leukemic activation of PITX1, a novice PRD-class homeobox gene in a subset of early-staged T-ALL, which may promote leukemogenesis by inhibiting T-cell development.

HOXC8 inhibits androgen receptor signaling in human prostate cancer cells by inhibiting SRC-3 recruitment to direct androgen target genes

HOX (homeobox) genes encode homeodomain-containing transcription factors critical to development, differentiation, and homeostasis. Their dysregulation has been implicated in a variety of cancers. Previously, we showed that a subset of genes of the HOXC cluster is upregulated in primary prostate tumors, lymph node metastases, and malignant prostate cell lines. In the present study, we show that HOXC8 inhibits androgen receptor (AR)-mediated gene induction in LNCaP prostate cancer cells and HPr-1 AR, a nontumorigenic prostate epithelial cell line. Mechanistically, HOXC8 blocks the AR-dependent recruitment of the steroid receptor coactivators steroid receptor coactivator-3 (SRC-3), and CREB binding protein to the androgen-regulated prostate-specific antigen gene enhancer and inhibits histone acetylation of androgen-regulated genes. Inhibition of androgen induction by HOXC8 is reversed upon expression of SRC-3, a member of the SRC/p160 steroid receptor cofactor family. Coimmunoprecipitation studies show that HOXC8 expression inhibits the hormone-dependent interaction of AR and SRC-3. Finally, HOXC8 expression increases invasion in HPr-1 AR nontumorigenic cells. These data suggest a complex role for HOXC8 in prostate cancer, promoting invasiveness while inhibiting AR-mediated gene induction at androgen response element-regulated genes associated with differentiated function of the prostate. A greater understanding of HOXC8 actions in the prostate and its interactions with androgen signaling pathways may elucidate mechanisms driving the onset and progression of prostate cancer.

NKX3.1 is a direct TAL1 target gene that mediates proliferation of TAL1-expressing human T cell acute lymphoblastic leukemia

TAL1 (also known as SCL) is expressed in >40% of human T cell acute lymphoblastic leukemias (T-ALLs). TAL1 encodes a basic helix-loop-helix transcription factor that can interfere with the transcriptional activity of E2A and HEB during T cell leukemogenesis; however, the oncogenic pathways directly activated by TAL1 are not characterized. In this study, we show that, in human TAL1–expressing T-ALL cell lines, TAL1 directly activates NKX3.1, a tumor suppressor gene required for prostate stem cell maintenance. In human T-ALL cell lines, NKX3.1 gene activation is mediated by a TAL1–LMO–Ldb1 complex that is recruited by GATA-3 bound to an NKX3.1 gene promoter regulatory sequence. TAL1-induced NKX3.1 activation is associated with suppression of HP1-α (heterochromatin protein 1 α) binding and opening of chromatin on the NKX3.1 gene promoter. NKX3.1 is necessary for T-ALL proliferation, can partially restore proliferation in TAL1 knockdown cells, and directly regulates miR-17-92. In primary human TAL1-expressing leukemic cells, the NKX3.1 gene is expressed independently of the Notch pathway, and its inactivation impairs proliferation. Finally, TAL1 or NKX3.1 knockdown abrogates the ability of human T-ALL cells to efficiently induce leukemia development in mice. These results suggest that tumor suppressor or oncogenic activity of NKX3.1 depends on tissue expression.

FGF signalling in prostate development, tissue homoeostasis and tumorigenesis

The FGFs (fibroblast growth factors) regulate a broad spectrum of biological activities by activating transmembrane FGFR (FGF receptor) tyrosine kinases and their coupled intracellular signalling pathways. In the prostate, the mesenchymal-epithelial interactions mediated by androgen signalling and paracrine factors are essential for gland organogenesis, homoeostasis and tumorigenesis. FGFs mediate these mesenchymal-epithelial interactions in the prostate by paracrinal crosstalk through a diverse set of ligands and receptors. Gain- and loss-of-function studies in mouse models have demonstrated the requirement for the FGF signalling axis in prostate development and homoeostasis. The aberrant induction of this axis in either compartment of the prostate results in developmental disorders, disrupts the homoeostatic balance and leads to prostate carcinogenesis. FGFs are also implicated in mediating androgen signalling in the prostate between mesenchymal and epithelial compartments. Therefore studying FGF signalling in the prostate will help us to better understand the underlying molecular mechanisms by which the gland develops, maintains homoeostasis and undergoes carcinogenesis; as well as yield clues on how androgens mediate these processes and how advanced-tumour prostate cells escape strict androgen regulations.

MYC overexpression induces prostatic intraepithelial neoplasia and loss of Nkx3.1 in mouse luminal epithelial cells

Lo-MYC and Hi-MYC mice develop prostatic intraepithelial neoplasia (PIN) and prostatic adenocarcinoma as a result of MYC overexpression in the mouse prostate. However, prior studies have not determined precisely when, and in which cell types, MYC is induced. Using immunohistochemistry (IHC) to localize MYC expression in Lo-MYC transgenic mice, we show that morphological and molecular alterations characteristic of high grade PIN arise in luminal epithelial cells as soon as MYC overexpression is detected. These changes include increased nuclear and nucleolar size and large scale chromatin remodeling. Mouse PIN cells retained a columnar architecture and abundant cytoplasm and appeared as either a single layer of neoplastic cells or as pseudo-stratified/multilayered structures with open glandular lumina-features highly analogous to human high grade PIN. Also using IHC, we show that the onset of MYC overexpression and PIN development coincided precisely with decreased expression of the homeodomain transcription factor and tumor suppressor, Nkx3.1. Virtually all normal appearing prostate luminal cells expressed high levels of Nkx3.1, but all cells expressing MYC in PIN lesions showed marked reductions in Nkx3.1, implicating MYC as a key factor that represses Nkx3.1 in PIN lesions. To determine the effects of less pronounced overexpression of MYC we generated a new line of mice expressing MYC in the prostate under the transcriptional control of the mouse Nkx3.1 control region. These "Super-Lo-MYC" mice also developed PIN, albeit a less aggressive form. We also identified a histologically defined intermediate step in the progression of mouse PIN into invasive adenocarcinoma. These lesions are characterized by a loss of cell polarity, multi-layering, and cribriform formation, and by a "paradoxical" increase in Nkx3.1 protein. Similar histopathological changes occurred in Hi-MYC mice, albeit with accelerated kinetics. Our results using IHC provide novel insights that support the contention that MYC overexpression is sufficient to transform prostate luminal epithelial cells into PIN cells in vivo. We also identified a novel histopathologically identifiable intermediate step prior to invasion that should facilitate studies of molecular pathway alterations occurring during early progression of prostatic adenocarcinomas.

Gene expression profiles in the PC-3 human prostate cancer cells induced by NKX3.1

NKX3.1, a prostate-specific gene, plays an important role in prostate development and carcinogenesis. However, its precise function has not been established. In present study, we transfected the NKX3.1 eukaryotic expression plasmid (pcDNA3.1-NKX3.1) into human prostate cancer cells PC-3, which lack of NKX3.1 expression, and established stable transfectants. Then, we investigated the influence of NKX3.1 on the cell growth, cell migration and colony formation efficiency. The results showed that restoration of NKX3.1 expression inhibited proliferation and invasion activities of PC-3 cells. Further, a cDNA microarray containing 22,000 human genes was used to identify the gene expression differences. The results showed that there were 1,953 genes showing more than a two-fold difference in expression. Subsequent ontological analysis revealed that a large proportion of the classified genes were related to cell growth, cell signal and cell invasion. Finally, the expression of Caspase-3, Bcl-2, P27, Cdk6 and AMACR, randomly selected genes from microarray data, was validated by RT-PCR and western blot. Collectively, our results first analyzed the gene expression profile in PC-3 cells induced by NKX3.1 and indicated that NKX3.1 might exert its function by regulating the expression of relative genes.

Nkx3.1 and p27(KIP1) cooperate in proliferation inhibition and apoptosis induction in human androgen-independent prostate cancer cells

Prostate cancer (PC), which responds well to androgen ablation initially, invariably progresses to treatment resistance. The so-called androgen-independent PC is also a concern, since there is no effective therapy so far. Nkx3.1 is a putative prostate tumor suppressor that is expressed exclusively in the prostate under the regulation of androgen, and p27(KIP1) functions as a cell proliferation inhibitor and apoptosis trigger by disrupting the cyclin-dependent kinase (CDK)-cyclin complex. Lack of expressions of Nkx3.1 and/or p27(KIP1) have been detected in most advanced PC and is associated with poor clinical progression. Here, we show that endogenous expressions of both Nkx3.1 and p27(KIP1) are lost in the androgen-independent PC3 PC cells, while remaining intact in LNCaP PC cells, which contain functional androgen receptor (AR) and are hormone-responsive. Ectopic restoration of either Nkx3.1 or p27(KIP1) in PC3 cells results in reduced cell proliferation, and increased cell death. Both effects are synergistically enhanced when the two molecules are coexpressed. p27(KIP1) overexpression in PC3 results in increased cell population ceased at the G0/G1 phase, and this cell-cycle-arresting effect is significantly enhanced by the coexpression of Nkx3.1. Flow cytometry further revealed that Nkx3.1 and p27(KIP1) also cooperatively render more PC3 cells undergoing apoptosis. Consistently, the coexpression of Nkx3.1 and p27(KIP1) leads to the decreased expression of Bcl-2 oncogene and a concomitantly upregulated Bax expression. It also activates caspase 3 and leads to increased cleavage of PARP. Our findings thus reveal the crucial relevance of the combined antiproliferative and proapoptotic activities of Nkx3.1 and p27(KIP1) in androgen-independent PC cells, and further suggest that a combined, rather than single gene manipulation may be of clinical value for hormone-refractory PC.

Loss of NKX3.1 favors vascular endothelial growth factor-C expression in prostate cancer

Decreased levels of the prostate-specific homeobox protein NKX3.1 are correlated with hormone-refractory and metastatic prostate cancer. Thus, it is compelling to define the NKX3.1-regulated genes that may be important for the progression of the advanced stage of the disease. In this study, we showed that vascular endothelial growth factor-C (VEGF-C) is one such target gene of NKX3.1. NKX3.1 inhibited VEGF-C expression in prostate cancer, and the loss of NKX3.1 led to increased VEGF-C expression. Histone deacetylase 1 acted as a corepressor of VEGF-C expression along with NKX3.1. Activated RalA acted in synergy with the loss of NKX3.1 for VEGF-C transcription. Patients with deletions at chromosome 8p21.1-p21.2 as a sole deletion developed lymph node metastasis. Interestingly, the higher expression of VEGF-C in prostate cancer is also correlated with lymph node metastasis. Therefore, regulation of VEGF-C expression by NKX3.1 provides a possible mechanism by which the loss of NKX3.1 protein level leads to lymphangiogenesis in the late stages of advanced prostate cancer.

Generation of a prostate from a single adult stem cell

The existence of prostate stem cells (PSCs) was first postulated from the observation that normal prostate regeneration can occur after repeated cycles of androgen deprivation and replacement in rodents. Given the critical role of PSCs in maintaining prostate tissue integrity and their potential involvement in prostate tumorigenesis, it is important to define specific markers for normal PSCs. Several cell-surface markers have been reported to identify candidate PSCs, including stem cell antigen-1 (Sca-1, also known as Ly6a), CD133 (Prom1) and CD44 (refs 3-10). However, many non-PSCs in the mouse prostate also express these markers and thus identification of a more defined PSC population remains elusive. Here we identify CD117 (c-kit, stem cell factor receptor) as a new marker of a rare adult mouse PSC population, and demonstrate that a single stem cell defined by the phenotype Lin(-)Sca-1(+)CD133(+)CD44(+)CD117(+) can generate a prostate after transplantation in vivo. CD117 expression is predominantly localized to the region of the mouse prostate proximal to the urethra and is upregulated after castration-induced prostate involution-two characteristics consistent with that of a PSC marker. CD117(+) PSCs can generate functional, secretion-producing prostates when transplanted in vivo. Moreover, CD117(+) PSCs have long-term self-renewal capacity, as evidenced by serial isolation and transplantation in vivo. Our data establish that single cells in the adult mouse prostate with multipotent, self-renewal capacity are defined by a Lin(-)Sca-1(+)CD133(+)CD44(+)CD117(+) phenotype.

Mouse Fem1b interacts with the Nkx3.1 homeoprotein and is required for proper male secondary sexual development

Previous studies of epithelial cell growth and differentiation in the prostate gland have identified the homeodomain protein Nkx3.1 as a central regulator of prostate development and carcinogenesis. To understand the molecular mechanisms of Nkx3.1 function, we have used yeast two-hybrid analysis to identify Nkx3.1 interacting proteins, and have isolated Fem1b, a mammalian homolog of the C. elegans sex-determining gene Fem-1. In mice, the Fem1b and Nkx3.1 genes encode proteins that interact in glutathione-S-transferase (GST) pull-down and co-immunoprecipitation assays, and are co-expressed in the prostate and testis of neonatal mice. Null mutants for Fem1b generated by gene targeting display defects in prostate ductal morphogenesis and secretory protein expression, similar to phenotypes found in Nkx3.1 mutants. We propose that Fem1b may have a conserved role in the generation of sexual dimorphism through its interaction with Nkx3.1 in the developing prostate gland.

A feedback loop between the androgen receptor and a NEDD4-binding protein, PMEPA1, in prostate cancer cells

PMEPA1 was identified originally as a highly androgen-inducible gene with prostate-abundant expression that was restricted to prostatic epithelial cells. PMEPA1 protein is a NEDD4 (ubiquitin-protein isopeptide ligase)-binding protein, which negatively regulates prostate cancer cell growth. In this study we establish that PMEPA1 is a direct transcriptional target of the androgen receptor (AR). We also demonstrate that PMEPA1 negatively regulates AR protein levels in different cell culture models. Transient expression of PMEPA1 down-regulates AR protein levels and AR transcriptional targets in prostate cancer cells. Conversely, knockdown of PMEPA1 leads to elevated levels of AR protein, AR transcriptional targets (prostate-specific antigen), and increased cell cycle S phase. We define that the PMEPA1-dependent down-regulation of AR is because of AR ubiquitination and proteasome-mediated degradation. The mutant PMEPA1 (PY1/2 motif mutation) that is impaired in NEDD4 recruitment shows attenuated AR ubiquitination and AR protein down-regulation. These data support the hypothesis that PMEPA1 negatively regulates the stability of AR protein by enhancing AR ubiquitination and proteasome-mediated degradation through NEDD4. The effect of PMEPA1 on AR ubiquitination and degradation appears to be MDM2-independent. Thus, the PMEPA1-AR degradation pathway may represent a new androgen-dependent mechanism for regulating AR levels in prostate epithelial cells. These findings underscore that the decreased PMEPA1 expression frequently noted in prostate cancers may lead to increased AR functions and strengthen the biological role of PMEPA1 in prostate cancers.

Loss of the SSeCKS/Gravin/AKAP12 gene results in prostatic hyperplasia

SSeCKS/Gravin/AKAP12 (SSeCKS) is a kinase scaffolding protein that encodes metastasis-suppressor activity through the suppression of Src-mediated oncogenic signaling and vascular endothelial growth factor expression. SSeCKS expression is down-regulated in Src- and Ras-transformed fibroblasts, in human cancer cell lines and in several types of human cancer, including prostate. Normal human and mouse prostates express abundant SSeCKS in secretory epithelial cells and, to a lesser extent, in the surrounding mesenchyme. Here, we show that the loss of SSeCKS results in prostatic hyperplasia in the anterior and ventral lobes as well as increased levels of apoptosis throughout the prostate. Dysplastic foci were observed less frequently but were associated with the loss of E-cadherin staining and the loss of high molecular weight cytokeratin-positive basal epithelial cells. SSeCKS-null prostate tissues expressed significantly higher relative levels of AKT(poS473) compared with wild-type controls, suggesting that SSeCKS attenuates phosphatidylinositol-3-OH kinase signaling. The data suggest that SSeCKS-null mice have increased susceptibility for oncogenic transformation in the prostate.

Haploinsufficiency of the maspin tumor suppressor gene leads to hyperplastic lesions in prostate

Maspin is a key tumor suppressor gene in prostate and breast cancers with diverse biological functions. However, how maspin regulates prostate tumor progression is not fully understood. In this study, we have used maspin heterozygous knockout mice to determine the effect of maspin haploinsufficiency on prostate development and tumor progression. We report that loss of one copy of maspin gene in Mp(+/-) heterozygous knockout mice leads to the development of prostate hyperplastic lesions, and this effect was mediated through decreased level of cyclin-dependent kinase inhibitors p21 and p27. Prostate hyperplastic lesions in Mp(+/-) mice also induced stromal reaction, which occurred in both aged prostate tissues and in neonatal prostates during early ductal morphogenesis. We showed that maspin was also expressed in prostate smooth muscle cells (PSMC), and recombinant maspin increased PSMC cell adhesion but inhibited cell proliferation. We also observed a defective interaction between epithelial cells and basement membrane in the prostate of Mp(+/-) mice, which was accompanied with a changed pattern of matrix deposition and a loss of epithelial cell polarity. Therefore, we have identified a novel property of maspin, which involves the control of the proliferation in prostate epithelial and smooth muscle cells. This is the first report that a partial loss of maspin caused an early developmental defect of the prostate and prostate hyperplastic lesions in mouse.

Increased expression of NKX3.1 in benign prostatic hyperplasia

OBJECTIVES

To establish the role of the NKX3.1 gene in the development of benign prostatic hyperplasia by comparing the expression of NKX3.1 in messenger ribonucleic acid (mRNA) and protein levels in young adult prostate and BPH tissues.

METHODS

Normal prostate tissue samples (n = 4) were obtained from prostate biopsies of patients less than 40 years of age who underwent diagnostic cystoscopy for microscopic hematuria. Benign prostatic hyperplasia tissues (n = 12) were obtained from patients who underwent transurethral prostate resection for bladder outlet obstruction. The RNAs isolated from these tissue samples were analyzed with quantitative reverse transcriptase polymerase chain reaction; the proteins were analyzed with Western blotting and immunohistochemistry.

RESULTS

The mean NKX3.1 mRNA transcript expression was 19.17 +/- 3.05 vs 1.24 +/- 1.32 in BPH and normal tissues, respectively, and NKX3.1 protein expression of BPH was approximately 2.4-fold higher than in normal prostate tissue. Reverse transcriptase polymerase chain reaction and Western blot analyses revealed that NKX3.1 gene expression in BPH patient tissues were higher compared with normal prostate tissues. Immunohistochemistry results indicated that most of the BPH tissues stained diffusely, and there was no BPH tissue that lacked NKX3.1 expression.

CONCLUSIONS

NKX3.1 expression is elevated in BPH tissues when compared with normal tissues, which may be important in the development of BPH.

Molecular signaling pathways that regulate prostate gland development

Prostate gland development is a complex process that involves coordination of multiple signaling pathways including endocrine, paracrine, autocrine, juxtacrine and transcription factors. To put this into proper context, the present manuscript will begin with a brief overview of the stages of prostate development and a summary of androgenic signaling in the developing prostate, which is essential for prostate formation. This will be followed by a detailed description of other transcription factors and secreted morphogens directly involved in prostate formation and branching morphogenesis. Except where otherwise indicated, results from rodent models will be presented since studies that examine molecular signaling in the developing human prostate gland are sparse at the present time.

Prostate epithelial cell fate

Androgen receptor (AR) within prostatic mesenchymal cells, with the absence of AR in the epithelium, is still sufficient to induce prostate development. AR in the luminal epithelium is required to express the secretory markers associated with differentiation. Nkx3.1 is expressed in the epithelium in early prostatic embryonic development and expression is maintained in the adult. Induction of the mouse prostate gland by the embryonic mesenchymal cells results in the organization of a sparse basal layer below the luminal epithelium with rare neuroendocrine cells that are interdispersed within this basal layer. The human prostate shows similar glandular organization; however, the basal layer is continuous. The strong inductive nature of embryonic prostatic and bladder mesenchymal cells is demonstrated in grafts where embryonic stem (ES) cells are induced to differentiate and organize as a prostate and bladder, respectively. Further, the ES cells can be driven by the correct embryonic mesenchymal cells to form epithelium that differentiates into secretory prostate glands and differentiated bladders that produce uroplakin. This requires the ES cells to mature into endoderm that gives rise to differentiated epithelium. This process is control by transcription factors in both the inductive mesenchymal cells (AR) and the responding epithelium (FoxA1 and Nkx3.1) that allows for organ development and differentiation. In this review, we explore a molecular mechanism where the pattern of transcription factor expression controls cell determination, where the cell is assigned a developmental fate and subsequently cell differentiation, and where the assigned cell now emerges with it's own unique character.

Activator protein-1 transcription factors are associated with progression and recurrence of prostate cancer

To identify biomarkers that discriminate the aggressive forms of prostate cancer, we performed gene expression profiling of prostate tumors using a genetically engineered mouse model that recapitulates the stages of human prostate cancer, namely Nkx3.1; Pten mutant mice. We observed a significant deregulation of the epidermal growth factor and mitogen-activated protein kinase (MAPK) signaling pathways, as well as their major downstream effectors--the activator protein-1 transcription factors c-Fos and c-Jun. Forced expression of c-Fos and c-Jun in prostate cancer cells promotes tumorigenicity and results in activation of extracellular signal-regulated kinase (Erk) MAPK signaling. In human prostate cancer, up-regulation of c-Fos and c-Jun proteins occurs in advanced disease and is correlated with Erk MAPK pathway activation, whereas high levels of c-Jun expression are associated with disease recurrence. Our analyses reveal a hitherto unappreciated role for AP-1 transcription factors in prostate cancer progression and identify c-Jun as a marker of high-risk prostate cancer. This study provides a striking example of how accurate mouse models can provide insights on molecular processes involved in progression and recurrence of human cancer.

Structural and functional analysis of domains mediating interaction between the bagpipe homologue, Nkx3.1 and serum response factor

Nkx3.1 is a member of the NK2 class of homeodomain proteins and is expressed in development, being an early marker of the sclerotome and prostate gland. It has been shown to be a critical factor for prostate differentiation and function. Previous studies suggested that Nkx3.1 interacts with Serum Response Factor (SRF) to transactivate the Smooth Muscle gamma-Actin (SMGA) promoter. In studies presented here, we examined the molecular mechanisms underlying the functional synergy of these factors upon SMGA transcription. We demonstrate that full length Nkx3.1 physically interacts with SRF in the absence of DNA and that these factors are able to co-associate in cellular context using a mammalian two-hybrid system. The segment of SRF responsible for Nkx3.1 interaction was mapped to a approximately 30 amino acid region (AAs 142-171) at the N-terminal segment of the MADS box. Two separate regions of Nkx3.1 were found to mediate interactions with SRF. Interestingly, recognized domains of NK2 proteins, namely the TN, homeodomain DNA binding segment, and the NK2-SD do not participate in SRF interactions. One of the Nkx3.1 SRF binding domains was mapped to the N-terminal of the protein consistent with recent studies of these proteins using NMR spectroscopy by Gelmann and colleagues (1). A second SRF binding region was mapped to amino acids C-terminal to the homeodomain. Structural predictions indicate that both of the SRF interacting segments are largely hydrophobic in character and beta-strand in structure. With co-transfection transcriptional analyses we found that interaction between SRF and Nkx3.1 as well as DNA binding by both factors was required for the observed transcriptional synergy. Thus our studies have identified novel protein-protein interacting domains within Nkx3.1 and SRF that operate in concert with their respective DNA binding domains to mediate functional transcriptional synergy of these factors to regulate SMGA gene activation.

Sox9 is required for prostate development

The mammalian prostate arises from the urogenital sinus and few factors have been identified to be important in the early stages of prostate development. In this study we show that the transcription factor Sox9 is expressed in the epithelia of all mouse prostatic lobes from the initial stages of their development. We used a conditional approach with mice expressing Cre recombinase under the control of Nkx3.1 regulatory sequences to delete Sox9 from the developing prostate. Mice with a prostate specific deletion of Sox9 showed a lack of ventral prostate development and abnormal anterior prostate differentiation. Analysis of these mutant animals revealed an early loss of expression of genes specific to the prostate epithelia such as Nkx3.1 and Shh and a marked reduction in proliferation in the ventral prostate but not in other lobes. Fgf signalling, through the MAPK pathway, has been shown to be important in prostate development and a lobe specific phenotype was reported for a prostate specific Fgfr2 mutant mouse model. Here we show that the levels of Fgfr2 and Sprouty2, a downstream target of Fgf signalling, were severely reduced in the ventral prostate of Sox9 mutant animals but not in other lobes. Prostate organ culture studies with a Mek inhibitor, U0126, and a Fgf receptor inhibitor, SU5402, indicate that the timing of expression of Cre in the mutant animals could account for the lobe specific phenotype in the Sox9 and Fgfr2 mutants. These studies imply that Sox9 is required for the early differentiation of the prostate bud epithelia.

Androgen receptor variants and prostate cancer in humanized AR mice

Androgen, acting via the androgen receptor (AR), is central to male development, differentiation and hormone-dependent diseases such as prostate cancer. AR is actively involved in the initiation of prostate cancer, the transition to androgen independence, and many mechanisms of resistance to therapy. To examine genetic variation of AR in cancer, we created mice by germ-line gene targeting in which human AR sequence replaces that of the mouse. Since shorter length of a polymorphic N-terminal glutamine (Q) tract has been linked to prostate cancer risk, we introduced alleles with 12, 21 or 48 Qs to test this association. The three "humanized" AR mouse strains (h/mAR) are normal physiologically, as well as by cellular and molecular criteria, although slight differences are detected in AR target gene expression, correlating inversely with Q tract length. However, distinct allele-dependent differences in tumorigenesis are evident when these mice are crossed to a transgenic prostate cancer model. Remarkably, Q tract variation also differentially impacts disease progression following androgen depletion. This finding emphasizes the importance of AR function in androgen-independent as well as androgen-dependent disease. These mice provide a novel genetic paradigm in which to dissect opposing functions of AR in tumor suppression versus oncogenesis.

Ubiquitination by TOPORS regulates the prostate tumor suppressor NKX3.1

The NKX3.1 gene located at 8p21.2 encodes a homeodomain-containing transcription factor that acts as a haploinsufficient tumor suppressor in prostate cancer. Diminished protein expression of NKX3.1 has been observed in prostate cancer precursors and carcinomas. TOPORS is a ubiquitously expressed E3 ubiquitin ligase that can ubiquitinate tumor suppressor p53. Here we report interaction between NKX3.1 and TOPORS. NKX3.1 can be ubiquitinated by TOPORS in vitro and in vivo, and overexpression of TOPORS leads to NKX3.1 proteasomal degradation in prostate cancer cells. Conversely, small interfering RNA-mediated knockdown of TOPORS leads to an increased steady-state level and prolonged half-life of NKX3.1. These data establish TOPORS as a negative regulator of NKX3.1 and implicate TOPORS in prostate cancer progression.

Loss of Nkx3.1 expression in the transgenic adenocarcinoma of mouse prostate model

BACKGROUND

The transgenic adenocarcinoma of mouse prostate (TRAMP) model has been extensively characterized at the histological and molecular levels, and has been shown to mimic significant features of human prostate cancer. However, the status of Nkx3.1 expression in the TRAMP model has not been elucidated.

METHODS

Immunohistochemical analyses were performed using dorsal, lateral, and ventral prostate (VP) lobes from ages 6 to 30 weeks. Quantitative RT-PCR analyses were performed to determine relative mRNA expression.

RESULTS

Heterogeneous loss of Nkx3.1 was observed in hyperplastic lesions of the ventral, dorsal, and lateral lobes. At 6 weeks of age, the ventral lobe displayed profound loss of Nkx3.1. Diminished Nkx3.1 protein was observed in well- to moderately-differentiated cancer lesions of all lobes. Poorly differentiated (PD) tumors stained negatively for Nkx3.1. Quantitative RT-PCR analyses revealed the presence of Nkx3.1 mRNA in each lobe at all ages, albeit reduced to variable levels.

CONCLUSIONS

These data suggest that disease progression in the TRAMP model may be driven by loss of function of Nkx3.1, in addition to p53 and Rb. Lobe-specific disease progression in the TRAMP model correlates with the reduction of Nkx3.1 protein. Regulation of Nkx3.1 expression during tumorigenesis appears to occur by post-transcriptional and post-translational mechanisms.

Emergence of androgen independence at early stages of prostate cancer progression in Nkx3.1; Pten mice

Although androgen deprivation therapy is a widely used treatment for patients with advanced prostate cancer, it ultimately results in the emergence of a hormone-refractory disease that is invariably fatal. To provide insights into the genesis of this disease, we have employed an in vivo model to investigate how and when prostate epithelial cells can acquire the ability to survive and proliferate in the absence of androgens. In particular, we have been studying the evolution of androgen independence in Nkx3.1; Pten mutant mice, which develop prostatic intraepithelial neoplasia and adenocarcinoma as a consequence of aging, as well as androgen-independent phenotypes following castration. We now find that the prostate epithelial cells from these Nkx3.1; Pten mutant mice are capable of surviving and proliferating in the absence of androgens and that they develop androgen-independent phenotypes well before they display overt prostatic intraepithelial neoplasia or cancer phenotypes. Our findings in this mouse model show that acquisition of androgen independence can be uncoupled from overt cancer progression and raise the possibility that hormone-refractory disease can arise at early stages of prostate carcinogenesis.

Prolonged exposure to reduced levels of androgen accelerates prostate cancer progression in Nkx3.1; Pten mutant mice

In this report, we have investigated the relationship between androgen levels and prostate tumorigenesis in Nkx3.1; Pten mutant mice, a genetically engineered mouse model of human prostate cancer. By experimentally manipulating serum levels of testosterone in these mice for an extended period (i.e., 7 months), we have found that prolonged exposure of Nkx3.1; Pten mutant mice to androgen levels that are 10-fold lower than normal (the "Low-T" group) resulted in a marked acceleration of prostate tumorigenesis compared with those exposed to androgen levels within the reference range (the "Normal-T" group). We found that prostate tumors from the Low-T mutant mice share a similar gene expression profile as androgen-independent prostate tumors from these mutant mice, which includes the deregulated expression of several genes that are up-regulated in human hormone-refractory prostate cancer, such as Vav3 and Runx1. We propose that exposure to reduced androgens may promote prostate tumorigenesis by selecting for molecular events that promote more aggressive, hormone-refractory tumors.