Isolation and androgen regulation of the human homeobox cDNA, NKX3.1

ENO2, a Glycolytic Enzyme, Contributes to Prostate Cancer Metastasis: A Systematic Review of Literature

Prostate cancer (PCa) is the second leading cause of male cancer deaths in the UK and the fifth worldwide. The presence of distant PCa metastasis can reduce the 5-year survival rate from 100% to approximately 30%. Enolase 2 (ENO2), a crucial glycolytic enzyme in cancer metabolism, is associated with the metastasis of multiple cancers and is also used as a marker for neuroendocrine tumours. However, its role in PCa metastasis remains unclear. In this study, we systematically reviewed the current literature to determine the association between ENO2 and metastatic PCa. Medline, Web of Science, and PubMed were searched for eligible studies. The search yielded five studies assessing ENO2 expression in PCa patients or cell lines. The three human studies suggested that ENO2 expression is correlated with late-stage, aggressive PCa, including castrate-resistant PCa (CRPC), metastatic CRPC, and neuroendocrine PCa (NEPC). This was further supported by two in vitro studies indicating that ENO2 expression can be regulated by the tumour microenvironment, such as androgen deprived conditions and the presence of bone-forming osteoblasts. Therefore, ENO2 may functionally contribute to PCa metastasis, possibly due to the unique metabolic features of PCa, which are glycolysis dependent only at the advanced metastatic stage.

NKX3.1 Expression in Non-Prostatic Tumors and Characterizing its Expression in Esophageal/Gastroesophageal Adenocarcinoma

The NKX3.1 immunohistochemical stain is widely recognized as a highly sensitive and specific marker for prostate adenocarcinoma. Nevertheless, its expression has been documented in various nonprostatic tissues and malignancies. This review aims to provide an overview of NKX3.1 expression in diverse tumor types, with a specific focus on its aberrant expression in esophageal/gastroesophageal adenocarcinoma (E/GE-ADC). In our investigation, we explored the expression of NKX3.1 in a series of E/GE-ADC to shed light on its prevalence in this tumor category. A total of 50 samples, comprising primary and metastatic E/GE-ADC specimens from 34 patients, were subjected to immunohistochemical analysis. Stained sections were scored based on the intensity and distribution-categorized as negative, weak, moderate, or strong in either a focal or diffuse pattern. Strong staining corresponds to the intensity observed in normal prostate controls, while focal and diffuse staining denote <50% and ≥50% of tumor nuclei staining positive, respectively. Our semiquantitative scoring revealed that 6 (12%) of the primary and metastatic E/GE-ADC specimens exhibited variable positivity for NKX3.1. This finding suggests that E/GE-ADC can sporadically stain positive for NKX3.1, introducing potential challenges in definitively determining the primary site of origin in certain clinical scenarios. Along with a literature review of NKX3.1 expression in other tumor types, our study provides additional important information about the extent to which this immunostain can be seen in E/GE-ADCs, which, to our knowledge, has not been reported.

Gene expression of male pathway genes sox9 and amh during early sex differentiation in a reptile departs from the classical amniote model

BACKGROUND

Sex determination is the process whereby the bipotential embryonic gonads become committed to differentiate into testes or ovaries. In genetic sex determination (GSD), the sex determining trigger is encoded by a gene on the sex chromosomes, which activates a network of downstream genes; in mammals these include SOX9, AMH and DMRT1 in the male pathway, and FOXL2 in the female pathway. Although mammalian and avian GSD systems have been well studied, few data are available for reptilian GSD systems.

RESULTS

We conducted an unbiased transcriptome-wide analysis of gonad development throughout differentiation in central bearded dragon (Pogona vitticeps) embryos with GSD. We found that sex differentiation of transcriptomic profiles occurs at a very early stage, before the gonad consolidates as a body distinct from the gonad-kidney complex. The male pathway genes dmrt1 and amh and the female pathway gene foxl2 play a key role in early sex differentiation in P. vitticeps, but the central player of the mammalian male trajectory, sox9, is not differentially expressed in P. vitticeps at the bipotential stage. The most striking difference from GSD systems of other amniotes is the high expression of the male pathway genes amh and sox9 in female gonads during development. We propose that a default male trajectory progresses if not repressed by a W-linked dominant gene that tips the balance of gene expression towards the female trajectory. Further, weighted gene expression correlation network analysis revealed novel candidates for male and female sex differentiation.

CONCLUSION

Our data reveal that interpretation of putative mechanisms of GSD in reptiles cannot solely depend on lessons drawn from mammals.

Comparative Transcriptome Analysis Provides Insight into Spatio-Temporal Expression Characteristics and Genetic Regulatory Network in Postnatal Developing Subcutaneous and Visceral Fat of Bama Pig

The depot differences between Subcutaneous Fat (SAF) and Visceral Fat (VAF) are critical for human well-being and disease processes in regard to energy metabolism and endocrine function. Miniature pigs (Sus scrofa) are ideal biomedical models for human energy metabolism and obesity due to the similarity of their lipid metabolism with that of humans. However, the regulation of differences in fat deposition and development remains unclear. In this study, the development of SAF and VAF was characterized and compared in Bama pig during postnatal development (infancy, puberty and adulthood), using RNA sequencing techniques (RNA-Seq). The transcriptome of SAF and VAF was profiled and isolated from 1-, 3- and 6 months-old pigs and identified 23,636 expressed genes, of which 1,165 genes were differentially expressed between the depots and/or developmental stages. Upregulated genes in SAF showed significant function and pathway enrichment in the central nervous system development, lipid metabolism, oxidation-reduction process and cell adhesion, whereas genes involved in the immune system, actin cytoskeleton organization, male gonad development and the hippo signaling pathway were preferentially expressed in VAF. Miner analysis of short time-series expression demonstrated that differentiation in gene expression patterns between the two depots corresponded to their distinct responses in sexual development, hormone signaling pathways, lipid metabolism and the hippo signaling pathway. Transcriptome analysis of SAF and VAF suggested that the depot differences in adipose tissue are not only related to lipid metabolism and endocrine function, but are closely associated with sexual development and organ size regulation.

Metabolic reprogramming in prostate cancer

Although low risk localised prostate cancer has an excellent prognosis owing to effective treatments, such as surgery, radiation, cryosurgery and hormone therapy, metastatic prostate cancer remains incurable. Existing therapeutic regimens prolong life; however, they are beset by problems of resistance, resulting in poor outcomes. Treatment resistance arises primarily from tumour heterogeneity, altered genetic signatures and metabolic reprogramming, all of which enable the tumour to serially adapt to drugs during the course of treatment. In this review, we focus on alterations in the metabolism of prostate cancer, including genetic signatures and molecular pathways associated with metabolic reprogramming. Advances in our understanding of prostate cancer metabolism might help to explain many of the adaptive responses that are induced by therapy, which might, in turn, lead to the attainment of more durable therapeutic responses.

Utility of NKX3.1 immunohistochemistry in the differential diagnosis of seminal vesicles versus prostatic tissue in needle biopsy

NKX3.1 is considered a reliable immunohistochemical marker of prostatic origin with high specificity and sensitivity. However, NKX3.1 positivity has been described in other neoplastic and non-neoplastic tissues, such as mesenchymal chondrosarcoma, sex-cord stromal tumors, rete testis adenocarcinoma, lobular and ductal carcinoma of the breast, salivary glands, peribronchial submucosal glands, and Sertoli cells. We analyzed expression of two antibodies (mono and polyclonal) of NKX3.1 in a total of 63 non-neoplastic seminal vesicles. We used 52 resection materials (12 seminal vesicles without prostatic adenocarcinoma, 26 seminal vesicles with prostatic adenocarcinoma infiltration, and 14 cases of seminal vesicles infiltrated by urothelial carcinoma) and 11 prostatic core needle biopsies with incidentally sampled fragment of seminal vesicles. In all cases, tissues from seminal vesicles were completely negative for NKX3.1, despite using polyclonal and monoclonal NKX3.1 antibodies, and regardless of the detection system utilized (diaminobenzidine (DAB) versus alkaline phosphatase (AF)). However, prostatic adenocarcinoma was negative in several cases (n = 6), when AF detection system was used. Reaction with DAB was strong and robust in all cases. Based on our data, we can recommend NKX3.1 as a negative immunohistochemical marker of seminal vesicles.

A comparison of prostatic development in xenografts of human fetal prostate and human female fetal proximal urethra grown in dihydrotestosterone-treated hosts

The goal of this paper is to explore the ability of the human female urogenital sinus immediately below the bladder (proximal urethra) to undergo prostatic development in response to dihydrotestosterone (DHT). To establish this idea, xenografts of human fetal female proximal urethra were grown in castrated nude mouse hosts receiving a subcutaneous DHT pellet. To verify the prostatic nature of the resultant glands, DHT-treated human fetal female urethral xenografts were compared with human fetal prostatic xenografts (derived from male specimens) grown in untreated and DHT-treated castrated mouse hosts and human fetal female proximal urethral xenografts grown in untreated castrated hosts. The resultant glands observed in DHT-treated human fetal female proximal urethral xenografts expressed 3 prostate-specific markers, NKX3.1, prostate specific antigen and prostatic acid phosphatase as well as the androgen receptor. Glands induced by DHT exhibited a protein expression profile of additional immunohistochemical markers (seven keratins, RUNX1, ESR2, TP63 and FOXA1) consistent with the unique spatial pattern of these proteins in prostatic ducts. Xenografts of human fetal female proximal urethra grown in DHT-treated hosts also expressed one of the salient features of prostatic development, namely androgen responsiveness. The experimental induction of prostatic differentiation from human fetal female proximal urethra makes possible future in-depth analysis of the molecular pathways directly involved in initiation of human prostatic development and subsequent epithelial differentiation, and more important whether the molecular pathways involved in human prostatic development are similar/identical versus different from that in murine prostatic development.

Tissue control of androgen action: The ups and downs of androgen receptor expression

The hormone testosterone plays crucial roles during male development and puberty and throughout life, as an anabolic regulator of muscle and bone structure and function. The actions of testosterone are mediated, primarily, through the androgen receptor, a member of the nuclear receptor superfamily. The androgen receptor gene is located on the X-chromosome and receptor levels are tightly controlled both at the level of transcription of the gene and post-translationally at the protein level. Sp1 has emerged as the major driver of expression of the androgen receptor gene, while auto-regulation by androgens is associated with both positive and negative regulation in a possible cell-selective manner. Research into the networks of positive and negative regulators of the androgen receptor gene are vital in order to understand the temporal and spatial control of receptor levels and the consequences for healthy aging and disease. A clear understanding of the multiple transcription factors participating in regulation of the androgen receptor gene will likely aid in the development and application of hormone therapies to boast or curb receptor activity.

Inhibition of Androgen Receptor Function and Level in Castration-Resistant Prostate Cancer Cells by 2-[(isoxazol-4-ylmethyl)thio]-1-(4-phenylpiperazin-1-yl)ethanone

The androgen receptor (AR) plays a critical role in the development of castration-resistant prostate cancer (CRPC) as well as in the resistance to the second-generation AR antagonist enzalutamide and the selective inhibitor of cytochrome P450 17A1 (CYP17A1) abiraterone. Novel agents targeting AR may inhibit the growth of prostate cancer cells resistant to enzalutamide and/or abiraterone. Through a high-throughput/high-content screening of a 220,000-member small molecule library, we have previously identified 2-[(isoxazol-4-ylmethyl)thio]-1-(4-phenylpiperazin-1-yl)ethanone (IMTPPE) (SID 3712502) as a novel small molecule capable of inhibiting AR transcriptional activity and protein level in C4-2 prostate cancer cells. In this study, we show that IMTPPE inhibits AR-target gene expression using real-time polymerase chain reaction, Western blot, and luciferase assays. IMTPPE inhibited proliferation of AR-positive, but not AR-negative, prostate cancer cells in culture. IMTPPE inhibited the transcriptional activity of a mutant AR lacking the ligand-binding domain (LBD), indicating that IMTPPE inhibition of AR is independent of the LBD. Furthermore, animal studies showed that IMTPPE inhibited the growth of 22Rv1 xenograft tumor, a model for enzalutamide-resistant prostate cancer. These findings suggest that IMTPPE is a potential lead compound for developing clinical candidates for the treatment of CRPC, including those resistant to enzalutamide.

Negative regulation of the androgen receptor gene through a primate-specific androgen response element present in the 5' UTR

The androgen receptor (AR) is a widely expressed ligand-activated transcription factor which mediates androgen signalling by binding to androgen response elements (AREs) in normal tissue and prostate cancer (PCa). Within tumours, the amount of AR plays a crucial role in determining cell growth, resistance to therapy and progression to fatal castrate recurrent PCa in which prostate cells appear to become independent of androgenic steroids. Despite the pivotal role of the AR in male development and fertility and all stages of PCa development, the mechanisms governing AR expression remain poorly understood. In this work, we describe an active nonconsensus androgen response element (ARE) in the 5' UTR of the human AR gene. The ARE represses transcription upon binding of activated AR, and this downregulation is relieved by disruption of the regulatory element through mutation. Also, multiple species comparison of the genomic region reveals that this ARE is specific to primates, leading to the conclusion that care must be exercised when elucidating the operation of the human AR in PCa based upon rodent promoter studies.

DNA damage response (DDR) via NKX3.1 expression in prostate cells

It has been reported that NKX3.1 an androgen-regulated homeobox gene restricted to prostate and testicular tissues, encodes a homeobox protein, which transcriptionally regulates oxidative damage responses and enhances topoisomerase I re-ligation by a direct interaction with the ATM protein in prostate cells. In this study, we aimed to investigate the role of NKX3.1 in DNA double-strand break (DSB) repair. We demonstrate that the DNA damage induced by CPT-11 (irinotecan, a topo I inhibitor), doxorubicin (a topo II inhibitor), and H2O2 (a mediator of oxidative damage), but not by etoposide (another topo II inhibitor), is negatively influenced by NKX3.1 expression. We also examined γH2AX((S139)) foci formation and observed that the overexpression of NKX3.1 resulted a remarkable decrease in the formation of γH2AX((S139)) foci. Intriguingly, we observed in NKX3.1 silencing studies that the depletion of NKX3.1 correlated with a significant decrease in the levels of p-ATM((S1981)) and γH2AX((S139)). The data imply that the DNA damage response (DDR) can be altered, perhaps via a decrease in the topoisomerase I re-ligation function; this is consistent with the physical association of NKX3.1 with DDR mediators upon treatment of both PC-3 and LNCaP cells with CPT-11. Furthermore, the depletion of NKX3.1 resulted in a G1/S progression via the facilitation of an increase in E2F stabilization concurrent with the suppressed DDR. Thus, the topoisomerase I inhibitor-mediated DNA damage enhanced the physical association of NKX3.1 with γH2AX((S139)) on the chromatin in LNCaP cells, whereas NKX3.1 in the soluble fraction was associated with p-ATM((S1981)) and RAD50 in these cells. Overall, the data suggest that androgens and NKX3.1 expression regulate the progression of the cell cycle and concurrently activate the DDR. Therefore, androgen withdrawal may augment the development of an error-prone phenotype and, subsequently, the loss of DNA damage control during prostate cancer progression.

Comprehensive gene expression analysis reveals multiple signal pathways associated with prostate cancer

Prostate cancer (PC) depends on androgenic signaling for growth and survival. To data, the exact molecular mechanism of hormone controlling proliferation and tumorigenesis in the PC remains unclear. Therefore, in this study, we explored the differentially expressed genes (DEGs) and identified featured genes related to hormone stimulus from PC. Two sets of gene expression data, including PC and normal control sample, were downloaded from Gene Expression Omnibus (GEO) database. The t-test was used to identify DEGs between PC and controls. Gene ontology (GO) functional annotation was applied to analyze the function of DEGs and screen hormone-related DEGs. Then these hormone-related DEGs were further analyzed in constructed cancer network and Human Protein Reference Database to screen important signaling pathways they participated in. A total of 912 DEGs were obtained which included 326 up-regulated genes and 586 down-regulated genes. GO functional enrichment analysis identified 50 hormone-related DEGs associated with PC. After pathway and PPI network analysis, we found these hormone-related DEGs participated in several important signaling pathways including TGF-β (TGFB2, TGFB3 and TGFBR2), MAPK (TGFB2, TGFB3 and TGFBR2), insulin (PIK3R3, SHC1 and EIF4EBP1), and p53 signaling pathways (CCND2 and CDKN1A). In addition, a total of five hormone-related DEGs (SHC1, CAV1, RXRA, CDKN1A and SRF) were located in the center of PPI network and 12 hormone-related DEGs formed six protein modules. These important signal pathways and hormone-related DEGs may provide potential therapeutic targets for PC.

TWIST1, A novel androgen-regulated gene, is a target for NKX3-1 in prostate cancer cells

Background

TWIST1 plays a key role in EMT-mediated tumor invasion and metastasis. Since bone metastasis is a hallmark of advanced prostate cancer and is detected in at least 85% of patients who die of this disease, it is of great importance to understand the regulation of the cellular signaling pathways involved in the metastatic process.

Methods

Prostatic cell lines were analyzed using real time RT-PCR, chromatin immunoprecipitations (ChIP) and transfection of siRNA’s and reporter constructs.

Results

We report in this paper that TWIST1 is an androgen-regulated gene under tight regulation of NKX3-1. Androgens repress the expression of TWIST1 via NKX3-1, which is a prostate–specific tumor suppressor that is down-regulated in the majority of metastatic prostate tumors. We show that NKX3-1 binds to the TWIST1 promoter and that NKX3-1 over-expression reduces the activity of a TWIST1 promoter reporter construct, whereas NKX3-1 siRNA up-regulates endogenous TWIST1 mRNA in prostate cancer cells.

Conclusion

Our finding that NKX3-1 represses TWIST1 expression emphasizes the functional importance of NKX3-1 in regulating TWIST1 expression during prostate cancer progression to metastatic disease.

Proline-mediated proteasomal degradation of the prostate-specific tumor suppressor NKX3.1

Reduced expression of the homeodomain transcription factor NKX3.1 is associated with prostate cancer initiation and progression. NKX3.1 turnover requires post-translational modifications including phosphorylation and ubiquitination. Here, we demonstrate the existence of a non-canonical mechanism for NKX3.1 turnover that does not require ubiquitination. Using a structure-function approach, we have determined that the conserved, C-terminal 21-amino acid domain of NKX3.1 (C21) is required for this novel ubiquitin-independent degradation mechanism. Addition of C21 decreased half-life of enhanced green fluorescence protein (EGFP) by 5-fold, demonstrating that C21 constitutes a portable degron. Point mutational analyses of C21 revealed that a conserved proline residue (Pro-221) is central to degron activity, and mutation to alanine (P221A) increased NKX3.1 half-life >2-fold. Proteasome inhibition and in vivo ubiquitination analyses indicated that degron activity is ubiquitin-independent. Evaluating degron activity in the context of a ubiquitination-resistant, lysine-null NKX3.1 mutant (NKX3.1(KO)) confirmed that P221A mutation conferred additional stability to NKX3.1. Treatment of prostate cancer cell lines with a C21-based peptide specifically increased the level of NKX3.1, suggesting that treatment with degron mimetics may be a viable approach for NKX3.1 restoration.

Retinoic acid and androgen receptors combine to achieve tissue specific control of human prostatic transglutaminase expression: a novel regulatory network with broader significance

In the human prostate, expression of prostate-specific genes is known to be directly regulated by the androgen-induced stimulation of the androgen receptor (AR). However, less is known about the expression control of the prostate-restricted TGM4 (hTGP) gene. In the present study we demonstrate that the regulation of the hTGP gene depends mainly on retinoic acid (RA). We provide evidence that the retinoic acid receptor gamma (RAR-G) plays a major role in the regulation of the hTGP gene and that presence of the AR, but not its transcriptional transactivation activity, is critical for hTGP transcription. RA and androgen responsive elements (RARE and ARE) were mapped to the hTGP promoter by chromatin immunoprecipitation (ChIP), which also indicated that the active ARE and RARE sites were adjacent, suggesting that the antagonistic effect of androgen and RA is related to the relative position of binding sites. Publicly available AR and RAR ChIP-seq data was used to find gene potentially regulated by AR and RAR. Four of these genes (CDCA7L, CDK6, BTG1 and SAMD3) were tested for RAR and AR binding and two of them (CDCA7L and CDK6) proved to be antagonistically regulated by androgens and RA confirming that this regulation is not particular of hTGP.

Lestaurtinib inhibits histone phosphorylation and androgen-dependent gene expression in prostate cancer cells

Background

Epigenetics is defined as heritable changes in gene expression that are not based on changes in the DNA sequence. Posttranslational modification of histone proteins is a major mechanism of epigenetic regulation. The kinase PRK1 (protein kinase C related kinase 1, also known as PKN1) phosphorylates histone H3 at threonine 11 and is involved in the regulation of androgen receptor signalling. Thus, it has been identified as a novel drug target but little is known about PRK1 inhibitors and consequences of its inhibition.

Methodology/Principal Finding

Using a focused library screening approach, we identified the clinical candidate lestaurtinib (also known as CEP-701) as a new inhibitor of PRK1. Based on a generated 3D model of the PRK1 kinase using the homolog PKC-theta (protein kinase c theta) protein as a template, the key interaction of lestaurtinib with PRK1 was analyzed by means of molecular docking studies. Furthermore, the effects on histone H3 threonine phosphorylation and androgen-dependent gene expression was evaluated in prostate cancer cells.

Conclusions/Significance

Lestaurtinib inhibits PRK1 very potently in vitro and in vivo. Applied to cell culture it inhibits histone H3 threonine phosphorylation and androgen-dependent gene expression, a feature that has not been known yet. Thus our findings have implication both for understanding of the clinical activity of lestaurtinib as well as for future PRK1 inhibitors.

Modeling prostate cancer in mice: limitations and opportunities

The complex dynamics of the tumor microenvironment and prostate cancer heterogeneity have confounded efforts to establish suitable preclinical mouse models to represent human cancer progression from early proliferative phenotypes to aggressive, androgen-independent, and invasive metastatic tumors. Current models have been successful in capitulating individual characteristics of the aggressive tumors. However, none of these models comprehensively mimics human cancer progression, establishing the challenge in their exploitation to study human disease. The ability to tailor phenotypic outcomes in mice by compounding mutations to target specific molecular pathways provides a powerful tool toward disruption of signaling pathways contributing to the initiation and progression of castration-resistant prostate cancer. Each model is characterized by unique features contributing to the understanding of prostate tumorigenesis, as well as limitations challenging our knowledge of the mechanisms of cancer development and progression. Emerging strategies utilize genomic manipulation technology to circumvent these limitations toward the formulation of attractive, physiologically relevant models of prostate cancer progression to advanced disease. This review discusses the current value of the widely used and well-characterized mouse models of prostate cancer progression to metastasis, as well as the opportunities begging exploitation for the development of new models for testing the antitumor efficacy of therapeutic strategies and identifying new biomarkers of disease progression.

Integration of regulatory networks by NKX3-1 promotes androgen-dependent prostate cancer survival

The NKX3-1 gene is a homeobox gene required for prostate tumor progression, but how it functions is unclear. Here, using chromatin immunoprecipitation coupled to massively parallel sequencing (ChIP-seq) we showed that NKX3-1 colocalizes with the androgen receptor (AR) across the prostate cancer genome. We uncovered two distinct mechanisms by which NKX3-1 controls the AR transcriptional network in prostate cancer. First, NKX3-1 and AR directly regulate each other in a feed-forward regulatory loop. Second, NKX3-1 collaborates with AR and FoxA1 to mediate genes in advanced and recurrent prostate carcinoma. NKX3-1- and AR-coregulated genes include those found in the "protein trafficking" process, which integrates oncogenic signaling pathways. Moreover, we demonstrate that NKX3-1, AR, and FoxA1 promote prostate cancer cell survival by directly upregulating RAB3B, a member of the RAB GTPase family. Finally, we show that RAB3B is overexpressed in prostate cancer patients, suggesting that RAB3B together with AR, FoxA1, and NKX3-1 are important regulators of prostate cancer progression. Collectively, our work highlights a novel hierarchical transcriptional regulatory network between NKX3-1, AR, and the RAB GTPase signaling pathway that is critical for the genetic-molecular-phenotypic paradigm in androgen-dependent prostate cancer.

ETS1 regulates NKX3.1 5' promoter activity and expression in prostate cancer cells

BACKGROUND

NKX3.1 controls the differentiation and proliferation of prostatic epithelial cells both during development and in the adult, while its expression is frequently downregulated in prostate cancers. Transcriptional control of NKX3.1 expression and in particular, factors that function via the NKX3.1 5' proximal promoter are poorly characterized.

METHODS

Deletion reporter analyses, bioinformatics, electromobility shift assays (EMSA), chromatin immunoprecipitation (ChIP) and Western blotting were performed to identify and functionally characterize sites of transcription factor binding within the initial 2,062 bp of the NKX3.1 5' promoter.

RESULTS

Deletion reporter studies of the 2,062 bp NKX3.1 5' promoter sequence localized positive transcriptional activity between -1069 and -993. Bioinformatic analyses identified the presence of two overlapping ETS1 binding sites within this region, designated EBS1 and EBS2, which exhibited 82% and 74% homology, respectively, to the ETS consensus binding sequence. EMSA and supershift assays indicated binding of both endogenous ETS1 and a recombinant GST-ETS1 protein solely to EBS1, a result that was confirmed in vivo by ChIP analysis. ETS1 overexpression transactivated NKX3.1 promoter reporter activity and upregulated endogenous NKX3.1 mRNA and protein levels in the LNCaP prostate cancer cell line, demonstrating a functional role for ETS1 in the regulation of NKX3.1 expression.

CONCLUSIONS

ETS1 upregulation of NKX3.1 expression in LNCaP cells is mediated in part via its interaction with an EBS located in the NKX3.1 5' proximal promoter. ETS1 may regulate NKX3.1 during prostate development, with the aberrant ETS1 expression and cellular localization frequently observed in human prostate tumors potentially contributing to the abnormal expression of NKX3.1.

Hypoxia enhances transcriptional activity of androgen receptor through hypoxia-inducible factor-1α in a low androgen environment

The androgen receptor (AR) acts as a ligand-dependent transcriptional factor controlling development or progression of prostate cancer. Androgen ablation by castration is an effective therapy for prostate cancer, whereas eventually most of the tumors convert from a hormone-sensitive to a hormone-refractory disease state and grow even in a low androgen environment (e.g., 0.1nM 5α-dihydrotestosterone (DHT)) like the castration-resistant stage. Androgen ablation results in hypoxia, and solid tumors possess hypoxic environments. Hypoxia-inducible factor (HIF)-1, which is composed of HIF-1α and HIF-1β/ARNT subunits, functions as a master transcription factor for hypoxia-inducible genes. Here, we report that hypoxia enhances AR transactivation in the presence of 0.05 and 0.1nM DHT in LNCaP prostate cancer cells. siRNA-mediated knockdown of HIF-1α inhibited hypoxia-enhanced AR transactivation. Its inhibition by HIF-1α siRNA was canceled by expression of a siRNA-resistant form of HIF-1α. HIF-1α siRNA repressed hypoxia-stimulated expression of the androgen-responsive NKX3.1 gene in the presence of 0.1nM DHT, but not in the absence of DHT. In hypoxia, HIF-1α siRNA-repressed AR transactivation was restored in mutants in which HIF-1α lacked DNA-binding activity. Furthermore, a dominant negative form of HIF-1α canceled hypoxia-enhanced AR transactivation, and HIF-1β/ARNT siRNAs had no influence on hypoxia-enhanced AR transactivation. These results indicate that hypoxia leads to HIF-1α-mediated AR transactivation independent of HIF-1 activity and that HIF-1β/ARNT is not necessarily required for the transactivation.

Androgen action during prostate carcinogenesis

Androgens are critical for normal prostate development and function, as well as prostate cancer initiation and progression. Androgens function mainly by regulating target gene expression through the androgen receptor (AR). Many studies have shown that androgen-AR signaling exerts actions on key events during prostate carcinogenesis. In this review, androgen action in distinct aspects of prostate carcinogenesis, including (i) cell proliferation, (ii) cell apoptosis, and (iii) prostate cancer metastasis will be discussed.

Mechanism of lymph node metastasis in prostate cancer

Detection of lymph node metastases indicates poor prognosis for prostate cancer patients. Therefore, elucidation of the mechanism(s) of lymph node metastasis is important to understand the progression of prostate cancer and also to develop therapeutic interventions. In this article, the known mechanisms for lymph node metastasis are discussed and the involvement of lymphatic vessels in prostate cancer lymph node metastasis is comprehensively summarized. In addition, contradictory findings regarding the importance of lymphangiogenesis in facilitating lymph node metastasis in prostate cancer are pointed out and reconcilation is attempted.

NKX3.1 potentiates TNF-alpha/CHX-induced apoptosis of prostate cancer cells through increasing caspase-3 expression and its activity

NKX3.1, a prostate-specific homeobox gene, plays an important role in prostate cancer and usually functions as tumor suppressor gene. Previously we have demonstrated that forced expression of NKX3.1 reduced cell growth and invasion in prostate cancer cell line PC-3. Presently, we investigated the effect of NKX3.1 on the sensitivity of the prostate cancer cells to apoptosis inducer tumor necrosis factor-alpha (TNF-alpha) and cycloheximide (CHX). PC-3 cells were transfected with NKX3.1 expression plasmid (pcDNA3.1-NKX3.1) and LNCaP cells were transfected with siRNA expression plasmid (pRNAT-RNAi1) targeting NKX3.1. The cell morphology and apoptotic rate were analyzed by Hoechst 33342 staining and Flow Cytometry in absence or presence of TNF-alpha and CHX. The activity of caspase-3 was determined using DEVD-pNA as substrate. Simultaneously, the effect of NKX3.1 on caspase-3 expression was detected using RT-PCR and Western blot. The results showed that ectopic expression of NKX3.1 promoted TNF-alpha/CHX-induced apoptosis in PC-3 cells, whereas knockdown of NKX3.1 protected LNCaP cells from apoptosis induced by TNF-alpha/CHX. The pro-apoptosis activity of NKX3.1 might partially contribute to its elevation of caspase-3 expression and activity. Manipulating NKX3.1 expression should be a promising therapeutic strategy for treating both androgen-dependent and androgen-independent prostate cancer.

Androgen regulation of the prostatic tumour suppressor NKX3.1 is mediated by its 3' untranslated region

The homeodomain transcription factor NKX3.1 is a prostate-specific tumour suppressor, expression of which is reduced or undetectable in the majority of metastatic prostate tumours. In the normal prostate and in prostate cancer cells, NKX3.1 expression is under tight androgenic control that we have shown to be mediated by its ~2.5 kb 3'UTR (3' untranslated region). Reporter deletion analysis of the NKX3.1 3'UTR identified three regions that were transactivated by DHT (5alpha-dihydrotestosterone) in the AR (androgen receptor)-expressing prostate cancer cell line LNCaP. Reversal of DHT effects by the anti-androgen bicalutamide supported an AR-mediated mechanism, and bioinformatic analysis of the NKX3.1 3'UTR identified canonical AREs (androgen-response elements) in each of the androgen-responsive regions. EMSAs (electrophoretic mobility-shift assays) indicated binding of the AR DNA-binding domain to two of the AREs, a proximal ARE at +2378-2392 from the transcription start site, and a more distal ARE at +3098-3112. ChIP (chromatin immunoprecipitation) analysis provided further evidence of ligand-dependent recruitment of endogenous AR to sequence encompassing each of the two elements, and site-directed mutagenesis and deletion analysis confirmed the contribution of each of the AREs in reporter assays. The present studies have therefore demonstrated that the NKX3.1 3'UTR functions as an androgen-responsive enhancer, with the proximal ARE contributing the majority and the distal ARE providing a smaller, but significant, proportion of the androgen responsiveness of the NKX3.1 3'UTR. Characterization of androgen-responsive regions of the NKX3.1 gene will assist in the identification of transcriptional regulatory mechanisms that lead to the deregulation of NKX3.1 expression in advanced prostate cancers.

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

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

Identification of novel androgen-responsive genes by sequencing of LongSAGE libraries

BACKGROUND

The development and maintenance of the prostate is dependent on androgens and the androgen receptor. The androgen pathway continues to be important in prostate cancer. Here, we evaluated the transcriptome of prostate cancer cells in response to androgen using long serial analysis of gene expression (LongSAGE) libraries.

RESULTS

There were 131 tags (87 genes) that displayed statistically significant (p

CONCLUSION

These processes may represent the molecular mechanisms of androgen-dependency of the prostate. Genes that participate in these pathways may be targets for therapies or biomarkers of prostate cancer.

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MESH Headings

• Androgens/metabolism
• Animals
• Cell Line, Tumor
• Gene Expression Profiling/methods
• Gene Expression Regulation, Neoplastic
• Genes, Neoplasm
• Humans
• Male
• Mice
• Mice, Inbred BALB C
• Mice, Nude
• Prostatic Neoplasms/genetics
• RNA, Neoplasm/genetics

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Grants

• R01 CA105304 NCI NIH HHS
• CA105304 NCI NIH HHS

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Affiliation(s)

Tammy L Romanuik Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
Gang Wang Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
Robert A Holt Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
Steven JM Jones Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
Marco A Marra Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, British Columbia, Canada
Marianne D Sadar Genome Sciences Centre, British Columbia Cancer Agency, Vancouver, British Columbia, Canada

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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.

Transcriptional regulation of the TGF-beta1 promoter by androgen receptor

TGF (transforming growth factor)-beta1 is a multifunctional cytokine that influences homoeostatic processes of various tissues. TGF-beta1 expression is inhibited by androgens in the prostate gland, whereas its expression is enhanced by androgens in highly metastatic prostate cancer cells. Here, we examined regulation of human TGF-beta1 promoter activity by androgen in prostate cancer cells. The full-length (-3363 to +110) promoter showed a high level of activity in response to androgen in PC3mm2 cells expressing AR (androgen receptor). Further deletion analysis revealed three distal and three proximal AREs (androgen-response elements) in the promoter. Gel-shift and footprint assays show that these AREs physically interact with the DNA-binding domain of AR. Chromatin immunoprecipitation assays revealed the androgen-dependent recruitment of AR to the ARE-containing regions of the TGF-beta1 gene. More importantly, a negative ARE was detected in the TGF-beta1 promoter. Both positive and negative AREs are functional in the androgen-regulated transcription of the TGF-beta1 promoter. These findings imply that androgen signalling may positively or negatively regulate TGF-beta1 expression in response to various signals or under different environmental conditions.

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.

Tissue prostate-specific antigen facilitates refractory prostate tumor progression via enhancing ARA70-regulated androgen receptor transactivation

Despite being well recognized as the best biomarker for prostate cancer, pathophysiologic roles of prostate-specific antigen (PSA) remain unclear. We report here that tissue PSA may be involved in the hormone-refractory prostate cancer progression. Histologic analyses show that the increased tissue PSA levels are correlated with lower cell apoptosis index and higher cell proliferation rate in hormone-refractory tumor specimens. By stably transfecting PSA cDNA into various prostate cancer cell lines, we found that PSA could promote the growth of androgen receptor (AR)-positive CWR22rv1 and high-passage LNCaP (hormone-refractory prostate cancer cells) but not that of AR-negative PC-3 and DU145 cells. Surprisingly, the protease activity of PSA is not crucial for PSA to stimulate growth and promote AR transactivation. We further showed that increased PSA could enhance ARA70-induced AR transactivation via modulating the p53 pathway that results in the decreased apoptosis and increased cell proliferation in prostate cancer cells. Knockdown of PSA in LNCaP and CWR22rv1 cells causes cell apoptosis and cell growth arrest at the G(1) phase. In vitro colony formation assay and in vivo xenografted tumor results showed the suppression of prostate cancer growth via targeting PSA expression. Collectively, our findings suggest that, in addition to being a biomarker, PSA may also become a new potential therapeutic target for prostate cancer. PSA small interfering RNA or smaller molecules that can degrade PSA protein may be developed as alternative approaches to treat the prostate cancer.

Splicing of a novel androgen receptor exon generates a constitutively active androgen receptor that mediates prostate cancer therapy resistance

The standard systemic treatment for prostate cancer (PCa) is androgen ablation, which causes tumor regression by inhibiting activity of the androgen receptor (AR). Invariably, PCa recurs with a fatal androgen-refractory phenotype. Importantly, the growth of androgen-refractory PCa remains dependent on the AR through various mechanisms of aberrant AR activation. Here, we studied the 22Rv1 PCa cell line, which was derived from a CWR22 xenograft that relapsed during androgen ablation. Three AR isoforms are expressed in 22Rv1 cells: a full-length version with duplicated exon 3 and two truncated versions lacking the COOH terminal domain (CTD). We found that CTD-truncated AR isoforms are encoded by mRNAs that have a novel exon 2b at their 3' end. Functionally, these AR isoforms are constitutively active and promote the expression of endogenous AR-dependent genes, as well as the proliferation of 22Rv1 cells in a ligand-independent manner. AR mRNAs containing exon 2b and their protein products are expressed in commonly studied PCa cell lines. Moreover, exon 2b-derived species are enriched in xenograft-based models of therapy-resistant PCa. Together, our data describe a simple and effective mechanism by which PCa cells can synthesize a constitutively active AR and thus circumvent androgen ablation.

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.

Integrating differentiation and cancer: the Nkx3.1 homeobox gene in prostate organogenesis and carcinogenesis

Several tissue-specific regulatory genes have been found to play essential roles in both organogenesis and carcinogenesis. In the prostate, the Nkx3.1 homeobox gene plays an important role in normal differentiation of the prostatic epithelium while its loss of function is an initiating event in prostate carcinogenesis in both mouse models and human patients. Thus, the Nkx3.1 homeobox gene provides a paradigm for understanding the relationship between normal differentiation and cancer, as well as studying the roles of homeobox genes in these processes. Here, we review recent findings concerning the roles of Nkx3.1 in development and discuss how its normal function is disrupted in processes of early prostate carcinogenesis.

Androgen-dependent gene expression of prostate-specific antigen is enhanced synergistically by hypoxia in human prostate cancer cells

The androgen receptor (AR) is implicated in prostate cancer growth, progression, and angiogenesis. Hypoxia-inducible factor-1 (HIF-1), which transcriptionally regulates hypoxia-inducible angiogenic factors, is up-regulated in prostate cancers compared with adjacent normal tissues. HIF-1 may be involved in prostate cancer as well as the AR, but the involvement of HIF-1 in prostate cancer angiogenesis and progression has not been fully elucidated. In the present study, we found that in prostate cancer LNCaP cells dihydrotestosterone enhanced the expression of GLUT-1, one of the HIF-1 target genes, and also that hypoxia enhanced the expression of prostate-specific antigen (PSA) that is one of the AR target genes and is involved in tumor invasion. Small interfering RNA that specifically inhibits HIF-1 reduced the expression levels of PSA as well as GLUT-1. Reporter gene analysis showed that dihydrotestosterone activated the HIF-1-mediated gene expression and hypoxia enhanced the AR-induced promoter activity of human PSA gene. Deletion and site-directed mutation of the 5'-flanking region of human PSA gene revealed that the sequence ACGTG between -3951 and -3947 was essential in the response to hypoxia. Furthermore, chromatin immunoprecipitation assay indicated that HIF-1 interacts with the AR on the human PSA gene promoter. These results indicated that in prostate cancers, HIF-1 might cooperate with the AR to activate the expression of several genes related to tumor angiogenesis, invasion, and progression.

Androgen regulation of prostate morphoregulatory gene expression: Fgf10-dependent and -independent pathways

Androgens are essential and sufficient for prostate gland morphogenesis; however, the downstream gene targets that mediate this action are unclear. To identify androgen-regulated genes involved in prostate development, we used short-term organ culture and examined the effect of testosterone on the expression of several critical prostate morphoregulatory genes. Rat ventral prostates (VP) and lateral prostates (LP) were collected at birth, and contralateral lobes were cultured for 18 h in the presence or absence of 10 nM testosterone with or without OH-flutamide to block residual androgens. Gene expression was quantitated using real-time RT-PCR. Although expression of Fgf10, Nkx3.1, and Ptc was increased in both prostate lobes, other genes were regulated by testosterone in a lobe-specific manner. This included up-regulation of epithelial genes FgfR2iiib, Shh, Hoxb13, and Bmp7 in the VP specifically and down-regulation of mesenchymal genes Wnt5a (VP) and Bmp4 (LP). Thus, in addition to stimulation of homeobox genes and paracrine-acting growth factors, androgens may positively regulate prostatic development through suppression of growth inhibitory genes. Because previous studies revealed a similar gene regulation pattern in response to exogenous Fgf10, experiments were performed to identify androgen-regulated genes mediated through Fgf10 signaling. Short-term VP and LP cultures with FgfR antagonist PD173074 and Mek inhibitor U0126 identified epithelial Shh and Hoxb13 up-regulation by androgens to be Fgf10-dependent. We propose that androgen regulation of prostate development is mediated through positive and negative regulation of multiple morphoregulatory genes acting in combination through complex gene networks. Lobe-specific responses may provide a developmental basis for prostate gland heterogeneity.

Curcumin downregulates homeobox gene NKX3.1 in prostate cancer cell LNCaP

AIM

To elucidate the effect and the mechanisms of curcumin on the expression of the human homeobox gene NKX3.1 in the prostate cancer cell LNCaP.

METHODS

The expression change of NKX3.1 in cells incubated with varying concentrations of curcumin was observed by Western blotting and RT-PCR. A dual luciferase reporter assay was used to test the effect of curcumin on the activity of the NKX3.1 1040 bp promoter. Curcumin-treated cells disposed to a designated amount of androgen analog R1881 and the androgen receptor (AR) antagonist flutamide, then the expression of NKX3.1 or the activity of the NKX3.1 promoter were investigated by Western blotting or reporter gene assay, respectively. Finally, Western blotting and electrophoretic mobility shift assay were performed to demonstrate the effect of curcumin on the expression of AR and its binding activity to the androgen response element (ARE).

RESULTS

Curcumin downregulated the expression of NKX3.1 and the activity of the NKX3.1 1040 bp promoter in LNCaP cells. R1881 increased the expression of NKX3.1, and the AR antagonist flutamide decreased the expression of NKX3.1 in LNCaP cells, while curcumin could inhibit androgen-AR mediated induction of NKX3.1 expression. Curcumin decreased the expression of AR and the binding activity to ARE directly.

CONCLUSION

Curcumin could downregulate NKX3.1 expression in LNCaP cells. It could also inhibit the androgen-AR mediated induction of NKX3.1 expression by downregulating AR expression and blocking its DNA binding activity.

A novel function of caspase-8 in the regulation of androgen-receptor-driven gene expression

Transcriptional regulation by the androgen receptor (AR) is critical for male sexual development and prostate cancer. In this study, we used an expression cloning strategy to identify molecules that regulate AR-driven transcription. Screening of a human cDNA library resulted in isolation of caspase-8 (Casp8), an initiator caspase that mediates death-receptor-induced apoptosis. Casp8 repressed AR-dependent gene expression independently of its apoptotic protease activity by disrupting AR amino-terminal and carboxy-terminal (N/C) interaction and inhibiting androgen-induced AR nuclear localization. Protein-protein interaction analysis revealed that three motifs in Casp8 specifically interacted with the motifs that are known to be involved in AR N/C interaction. Substitutions of the amino-acid residues critical for AR-Casp8 interactions abolished the Casp8-mediated inhibition of AR transactivation. In addition, knockdown of Casp8 by RNA interference specifically affected the androgen-dependent expression of AR-targeting genes in LNCaP cells. These results indicate that Casp8 has a novel function beyond its known role in the mediation of apoptosis.

TRP proteins and cancer

Cancer is the second most common cause of death in western countries. It is therefore of fundamental importance to improve the treatment of patients with malignant tumors. This goal can only be achieved if we get closer insight in the various mechanisms leading to tumor formation. Significant progress in the understanding of carcinogenesis has been made during the last couple of years. Ion channels contribute to the regulation of cell proliferation which has initially been shown for K+ channels. Meanwhile, other ion channels such as Cl-, Na+ and Ca2+ channels seem to influence cellular function like growth, migration and invasion. In addition, cation channels of the transient receptor potential (TRP) superfamily are implicated in cancer formation. Most recent data concerning TRP vanilloid (TRPV) type 6, TRP melastatin (TRPM) type 1 and 8 channels and their relevance for common human cancer types will be highlighted in this review. Furthermore, TRP channel structure and function will be discussed in the light of their possible importance as prognostic markers and targets for drug discovery.

Effects of 9-cis retinoic acid on human homeobox gene NKX3.1 expression in prostate cancer cell line LNCaP

AIM

To study the regulatory effects of 9-cis retinoic acid (RA) on the expression of human homeobox gene NKX3.1 in prostate cancer cell line LNCaP.

METHODS

Flow cytometry, reverse transcriptase polymerase chain reaction and Western blotting were performed to evaluate the effects of 9-cis RA on NKX3.1 expression and cell cycle of LNCaP cells. To identify a regulatory region within the NKX3.1 promoter contributing to the regulation induced by 9-cis RA, we have constructed an NKX3.1 promoter-reporter plasmid, pGL3-1040bp, and its 5'-deletion mutants, which were transfected into LNCaP cells with treatment of 9-cis RA in indicated concentrations.

RESULTS

With the treatment of 9-cis RA, the NKX3.1 promoter activity was increased in reporter gene assay and NKX3.1 expression was enhanced at both mRNA and protein levels in LNCaP cells. We found that the region between -936 and -921 in the upstream of NKX3.1 gene involved the inducible regulation by 9-cis RA treatment. In flow cytometry, 9-cis RA treatment caused accumulation of cells in the G(1) phase of the cell cycle and a fewer cells pass through to G(2)/M.

CONCLUSION

Our results demonstrated that 9-cis RA as a differentiating agent can arrest prostate cancer cells in G(1) phase and reduce cell mitosis, and upregulate the expression of human homeobox gene NKX3.1, which is thought to play an important role in prostate differentiation and to act as a tumor suppressor gene in the prostate.

Molecular analysis and characterization of PrEC, commercially available prostate epithelial cells

Adenocarcinoma of the prostate comprises 95% of all prostate cancer. Commercially available primary cultures of "normal" prostate epithelial cells, PrECs, have been used as a convenient model to investigate neoplastic transformation. Here PrECs were characterized for the expression of lineage- and developmental-specific markers cytokeratin (CK) 8 and 18, p63, chromogranin A, TMEPAI, S100P, NKX 3.1, ANKH, and FN 1 as well as androgen receptor and prostate-specific antigen by Western blot and Northern blot analyses, immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR), and quantitative real-time PCR. Immunohistochemical staining detected PrECs positive in varying degrees for p63, CK 8, and CK 18, with only the rare cell being positive for chromogranin A. The PrECs also tested positive for p63 protein by Western blot analysis. RT-PCR with PrEC cDNA showed products for FN 1 and S100P but not for ANKH and androgen receptor or prostate-specific antigen. This profile of markers in PrEC cells is consistent with that expected for pubertal prostate epithelial cells.

Physical and functional interactions between the prostate suppressor homeoprotein NKX3.1 and serum response factor

The NKX3.1 transcription factor is an NK family homeodomain protein and a tumor suppressor gene that is haploinsufficient and down-regulated in the early phases of prostate cancer. Like its cardiac homolog, NKX2.5, NKX3.1 acts synergistically with serum response factor (SRF) to activate expression from the smooth muscle gamma-actin (SMGA) gene promoter. Using NMR spectroscopy, three conserved motifs in a construct containing the N-terminal region and homeodomain of NKX3.1 were observed to interact with the MADS box domain of SRF. These motifs interacted both in the absence of DNA and when both proteins were bound to a SMGA promoter DNA sequence. No significant interaction was seen between the homeodomain and SRF MADS box. One of the SRF-interacting regions was the tinman (TN) or engrailed homology-1 motif (EH-1), residues 29-35 (FLIQDIL), which for other NK proteins is the site of interaction with the repressor protein Groucho. A second hydrophobic interacting region was designated the SRF-interacting (SI) motif and included residues 99-105 (LGSYLLD). A third interacting motif was the acidic region adjacent to the SI motif including residues 88-96 (ETLAETEPE). The acidic domain (AD) motif signals also showed strengthening upon the NKX3.1 homeodomain binding to DNA in the absence of SRF, consistent with the acidic region weakly interacting with the homeodomain in the unbound state. The importance of these linear motifs in the transcriptional interaction of NKX3.1 and SRF was demonstrated by targeted mutagenesis of an NKX3.1 expression vector in a SMGA reporter assay. The results implicate the NKX3.1 N-terminal region in regulation of transcriptional activity of this tumor suppressor.

NKX3.1 stabilizes p53, inhibits AKT activation, and blocks prostate cancer initiation caused by PTEN loss

We demonstrate that PTEN loss causes reduced NKX3.1 expression in both murine and human prostate cancers. Restoration of Nkx3.1 expression in vivo in Pten null epithelium leads to decreased cell proliferation, increased cell death, and prevention of tumor initiation. Whereas androgen receptor (AR) positively regulates NKX3.1 expression, NKX3.1 negatively modulates AR transcription and consequently the AR-associated signaling events. Consistent with its tumor suppressor functions, NKX3.1 engages cell cycle and cell death machinery via association with HDAC1, leading to increased p53 acetylation and half-life through MDM2-dependent mechanisms. Importantly, overexpression of Nkx3.1 has little effect on Pten wild-type epithelium, suggesting that PTEN plays a predominant role in PTEN-NKX3.1 interplay. Manipulating NKX3.1 expression may serve as a therapeutic strategy for treating PTEN-deficient prostate cancers.

NKX3.1 is regulated by protein kinase CK2 in prostate tumor cells

Diminished expression of NKX3.1 is associated with prostate cancer progression in humans, and in mice, loss of nkx3.1 leads to epithelial cell proliferation and altered gene expression patterns. The NKX3.1 amino acid sequence includes multiple potential phosphoacceptor sites for protein kinase CK2. To investigate posttranslational regulation of NKX3.1, phosphorylation of NKX3.1 by CK2 was studied. In vitro kinase assays followed by mass spectrometric analyses demonstrated that CK2 phosphorylated recombinant NKX3.1 on Thr89 and Thr93. Blocking CK2 activity in LNCaP cells with apigenin or 5,6-dichlorobenzimidazole riboside led to a rapid decrease in NKX3.1 accumulation that was rescued by proteasome inhibition. Replacing Thr89 and Thr93 with alanines decreased NKX3.1 stability in vivo. Small interfering RNA knockdown of CK2alpha' but not CK2alpha also led to a decrease in NKX3.1 steady-state level. In-gel kinase assays and Western blot analyses using fractionated extracts of LNCaP cells demonstrated that free CK2alpha' could phosphorylate recombinant human and mouse NKX3.1, whereas CK2alpha' liberated from the holoenzyme could not. These data establish CK2 as a regulator of NKX3.1 in prostate tumor cells and provide evidence for functionally distinct pools of CK2alpha' in LNCaP cells.

Analysis of NKX3.1 expression in prostate cancer tissues and correlation with clinicopathologic features

This study aimed to analyze NKX3.1 expression in tissue samples of benign prostate hyperplasia (BPH) and in three different prostate cancer categories. The correlation of NKX3.1 expression with clinical and pathologic features of patients having undergone radical prostatectomy also was investigated. NKX3.1 expression was determined in tissue samples obtained from four different histopathological categories: (1) from patients treated with transurethral prostatectomy for BPH (n = 26), (2) localized prostate cancer patients subjected to radical prostatectomy (n = 38), (3) biopsy samples from prostate cancer patients who were metastatic at the initial admission (n = 10), and (4) tissue samples of prostate cancer patients administered antiandrogens, but who had undergone transurethral prostatectomy for infravesical obstruction (n = 11). Standard immunohistochemical staining was performed using an antiserum raised against recombinant human NKX3.1. Staining was seen in all categories of prostatic tissues. Immunohistochemistry staining scores were lower in prostate cancer patients. The staining scores were significantly higher in patients with BPH compared to metastatic or localized prostate cancer patients. Staining scores of patients with BPH and of those under antiandrogen therapy were similar. No significant correlation was found between NKX3.1 expression and tumor volume, Gleason sum scores, the presence of extraprostatic extension, tumor stage, or serum PSA. NKX3.1 expression is significantly decreased in prostate cancer patients when compared to BPH. However, the decline of NKX3.1 expression was not correlated with prostate cancer progression and was not associated with advanced stage. Thus, NKX3.1 expression is not a clinically valuable prognostic factor.