Repression of androgen receptor transcription through the E2F1/DNMT1 axis

AR loss in prostate cancer stroma mediated by NF-κB and p38-MAPK signaling disrupts stromal morphogen production

Androgen Receptor (AR) activity in prostate stroma is required to maintain prostate homeostasis. This is mediated through androgen-dependent induction and secretion of morphogenic factors that drive epithelial cell differentiation. However, stromal AR expression is lost in aggressive prostate cancer. The mechanisms leading to stromal AR loss and morphogen production are unknown. We identified TGFβ1 and TNFα as tumor-secreted factors capable of suppressing AR mRNA and protein expression in prostate stromal fibroblasts. Pharmacological and RNAi approaches identified NF-κB as the major signaling pathway involved in suppressing AR expression by TNFα. In addition, p38α- and p38δ-MAPK were identified as suppressors of AR expression independent of TNFα. Two regions of the AR promoter were responsible for AR suppression through TNFα. FGF10 and Wnt16 were identified as androgen-induced morphogens, whose expression was lost upon TNFα treatment and enhanced upon p38-MAPK inhibition. Wnt16, through non-canonical Jnk signaling, was required for prostate basal epithelial cell survival. These findings indicate that stromal AR loss is mediated by secreted factors within the TME. We identified TNFα/TGFβ as two possible factors, with TNFα mediating its effects through NF-κB or p38-MAPK to suppress AR mRNA transcription. This leads to loss of androgen-regulated stromal morphogens necessary to maintain normal epithelial homeostasis.

Targeting DNA methylation and B7-H3 in RB1-deficient and neuroendocrine prostate cancer

Aberrant DNA methylation has been implicated as a key driver of prostate cancer lineage plasticity and histologic transformation to neuroendocrine prostate cancer (NEPC). DNA methyltransferases (DNMTs) are highly expressed, and global DNA methylation is dysregulated in NEPC. We identified that deletion of DNMT genes decreases expression of neuroendocrine lineage markers and substantially reduced NEPC tumor development and metastasis in vivo. Decitabine, a pan-DNMT inhibitor, attenuated tumor growth in NEPC patient-derived xenograft models, as well as retinoblastoma gene (RB1)-deficient castration-resistant prostate adenocarcinoma (CRPC) models compared with RB1-proficient CRPC. We further found that DNMT inhibition increased expression of B7 homolog 3 (B7-H3), an emerging druggable target, via demethylation of B7-H3. We tested DS-7300a (i-DXd), an antibody-drug conjugate targeting B7-H3, alone and in combination with decitabine in models of advanced prostate cancer. There was potent single-agent antitumor activity of DS-7300a in both CRPC and NEPC bearing high expression of B7-H3. In B7-H3-low models, combination therapy of decitabine plus DS-7300a resulted in enhanced response. DNMT inhibition may therefore be a promising therapeutic target for NEPC and RB1-deficient CRPC and may sensitize B7-H3-low prostate cancer to DS-7300a through increasing target expression. NEPC and RB1-deficient CRPC represent prostate cancer subgroups with poor prognosis, and the development of biomarker-driven therapeutic strategies for these populations may ultimately help improve patient outcomes.

Novel Insights on the Role of Epigenetics in Androgen Receptor's Expression in Prostate Cancer

The androgens/androgen receptor (AR) axis is the main therapeutic target in prostate cancer (PCa). However, while initially responsive, a subset of tumors loses AR expression through mechanisms putatively associated with epigenetic modifications. In this study, we assessed the link between the presence of CpG methylation in the 5'UTR and promoter regions of AR and loss of AR expression. Hence, we characterized and compared the methylation signature at CpG resolution of these regulatory regions in vitro, both at basal levels and following treatment with 5-aza-2-deoxycytidine (DAC) alone, or in combination with Trichostatin A (TSA). Our results showed heterogeneity in the methylation signature of AR negative cell lines and pinpointed the proximal promoter region as the most consistently methylated site in DU-145. Furthermore, this region was extremely resistant to the demethylating effects of DAC and was only significantly demethylated upon concomitant treatment with TSA. Nevertheless, no AR re-expression was detected at the mRNA or protein level. Importantly, after treatment, there was a significant increase in repressive histone marks at AR region 1 in DU-145 cells. Altogether, our data indicate that AR region 1 genomic availability is crucial for AR expression and that the inhibition of histone methyltransferases might hold promise for AR re-expression.

Lineage plasticity and treatment resistance in prostate cancer: the intersection of genetics, epigenetics, and evolution

Androgen deprivation therapy is a cornerstone of treatment for advanced prostate cancer, and the development of castrate-resistant prostate cancer (CRPC) is the primary cause of prostate cancer-related mortality. While CRPC typically develops through a gain in androgen receptor (AR) signaling, a subset of CRPC will lose reliance on the AR. This process involves genetic, epigenetic, and hormonal changes that promote cellular plasticity, leading to AR-indifferent disease, with neuroendocrine prostate cancer (NEPC) being the quintessential example. NEPC is enriched following treatment with second-generation anti-androgens and exhibits resistance to endocrine therapy. Loss of RB1, TP53, and PTEN expression and MYCN and AURKA amplification appear to be key drivers for NEPC differentiation. Epigenetic modifications also play an important role in the transition to a neuroendocrine phenotype. DNA methylation of specific gene promoters can regulate lineage commitment and differentiation. Histone methylation can suppress AR expression and promote neuroendocrine-specific gene expression. Emerging data suggest that EZH2 is a key regulator of this epigenetic rewiring. Several mechanisms drive AR-dependent castration resistance, notably AR splice variant expression, expression of the adrenal-permissive 3βHSD1 allele, and glucocorticoid receptor expression. Aberrant epigenetic regulation also promotes radioresistance by altering the expression of DNA repair- and cell cycle-related genes. Novel therapies are currently being developed to target these diverse genetic, epigenetic, and hormonal mechanisms promoting lineage plasticity-driven NEPC.

Downregulation of CAMK2N1 due to DNA Hypermethylation Mediated by DNMT1 that Promotes the Progression of Prostate Cancer

Calcium/calmodulin-dependentprotein kinase II inhibitor I (CAMK2N1) as one of the tumor suppressor genes is significantly downregulated in prostate cancer (PCa). Reduced expression of CAMK2N1 is positively correlated with PCa progression. However, the mechanisms of CAMK2N1 downregulation in PCa are still unclear. The promoter region of CAMK2N1 contains a large number of CG loci, providing the possibility for DNA methylation. Consequently, we hypothesized that DNA methylation can result in the reduced expression of CAMK2N1 in PCa. In the presented study, the DNA methylation level of CAMK2N1 in prostate cells and clinical specimens was determined by bisulfite sequencing (BS), pyrosequencing, and in silico analysis. Results showed that CAMK2N1 was highly methylated in PCa cells and tissues compared to normal prostate epithelial cells and nonmalignant prostate tissues, which was associated with the clinicopathological characteristics in PCa patients. Afterwards, we explored the expression of CAMK2N1 and its DNA methylation level by qRT-PCR, western blot, BS, and methylation-specific PCR in PCa cells after 5-Aza-CdR treatment or DNMT1 genetic modification, which demonstrated that the reduced expression of CAMK2N1 can be restored by 5-Aza-CdR treatment via demethylation. Moreover, DNMT1 formed a positive feedback loop with CAMK2N1 in PCa cells. The expression of CAMK2N1 was downregulated by DNMT1-mediated DNA methylation, which reversely induced DNMT1 expression through activating AKT or ERK signaling pathway. Finally, functional assays including wound healing, invasion, and migration assay, as well as the xenograft model in nude mice indicated that CAMK2N1 inhibited the invasion, migration, and proliferation of PCa cells and these effects were reversed by DNMT1 overexpression. In conclusion, DNMT1-mediated hypermethylation of CAMK2N1 not only downregulates the gene expression but also promotes the progression of PCa.

The Role of Epigenetic Change in Therapy-Induced Neuroendocrine Prostate Cancer Lineage Plasticity

The androgen receptor (AR) signaling pathway is critical for growth and differentiation of prostate cancer cells. For that reason, androgen deprivation therapy with medical or surgical castration is the principal treatment for metastatic prostate cancer. More recently, new potent AR signaling inhibitors (ARSIs) have been developed. These drugs improve survival for men with metastatic castration-resistant prostate cancer (CRPC), the lethal form of the disease. However, ARSI resistance is nearly universal. One recently appreciated resistance mechanism is lineage plasticity or switch from an AR-driven, luminal differentiation program to an alternate differentiation program. Importantly, lineage plasticity appears to be increasing in incidence in the era of new ARSIs, strongly implicating AR suppression in this process. Lineage plasticity and shift from AR-driven tumors occur on a continuum, ranging from AR-expressing tumors with low AR activity to AR-null tumors that have activation of alternate differentiation programs versus the canonical luminal program found in AR-driven tumors. In many cases, AR loss coincides with the activation of a neuronal program, most commonly exemplified as therapy-induced neuroendocrine prostate cancer (t-NEPC). While genetic events clearly contribute to prostate cancer lineage plasticity, it is also clear that epigenetic events-including chromatin modifications and DNA methylation-play a major role. Many epigenetic factors are now targetable with drugs, establishing the importance of clarifying critical epigenetic factors that promote lineage plasticity. Furthermore, epigenetic marks are readily measurable, demonstrating the importance of clarifying which measurements will help to identify tumors that have undergone or are at risk of undergoing lineage plasticity. In this review, we discuss the role of AR pathway loss and activation of a neuronal differentiation program as key contributors to t-NEPC lineage plasticity. We also discuss new epigenetic therapeutic strategies to reverse lineage plasticity, including those that have recently entered clinical trials.

Roles of Key Epigenetic Regulators in the Gene Transcription and Progression of Prostate Cancer

Prostate cancer (PCa) is a top-incidence malignancy, and the second most common cause of death amongst American men and the fifth leading cause of cancer death in men around the world. Androgen receptor (AR), the key transcription factor, is critical for the progression of PCa by regulating a series of target genes by androgen stimulation. A number of co-regulators of AR, including co-activators or co-repressors, have been implicated in AR-mediated gene transcription and PCa progression. Epigenetic regulators, by modifying chromatin integrity and accessibility for transcription regulation without altering DNA sequences, influence the transcriptional activity of AR and further regulate the gene expression of AR target genes in determining cell fate, PCa progression and therapeutic response. In this review, we summarized the structural interaction of AR and epigenetic regulators including histone or DNA methylation, histone acetylation or non-coding RNA, and functional synergy in PCa progression. Importantly, epigenetic regulators have been validated as diagnostic markers and therapeutic targets. A series of epigenetic target drugs have been developed, and have demonstrated the potential to treat PCa alone or in combination with antiandrogens.

Lifetime Impact of Cow's Milk on Overactivation of mTORC1: From Fetal to Childhood Overgrowth, Acne, Diabetes, Cancers, and Neurodegeneration

The consumption of cow's milk is a part of the basic nutritional habits of Western industrialized countries. Recent epidemiological studies associate the intake of cow's milk with an increased risk of diseases, which are associated with overactivated mechanistic target of rapamycin complex 1 (mTORC1) signaling. This review presents current epidemiological and translational evidence linking milk consumption to the regulation of mTORC1, the master-switch for eukaryotic cell growth. Epidemiological studies confirm a correlation between cow's milk consumption and birthweight, body mass index, onset of menarche, linear growth during childhood, acne vulgaris, type 2 diabetes mellitus, prostate cancer, breast cancer, hepatocellular carcinoma, diffuse large B-cell lymphoma, neurodegenerative diseases, and all-cause mortality. Thus, long-term persistent consumption of cow's milk increases the risk of mTORC1-driven diseases of civilization. Milk is a highly conserved, lactation genome-controlled signaling system that functions as a maternal-neonatal relay for optimized species-specific activation of mTORC1, the nexus for regulation of eukaryotic cell growth, and control of autophagy. A deeper understanding of milk´s impact on mTORC1 signaling is of critical importance for the prevention of common diseases of civilization.

DNMT3A inhibits E2F1-induced arterial marker expression and impairs angiogenesis in human umbilical artery endothelial cells

Arterial marker genes EphrinB2 and HEY2 are essential for cardiovascular development and postnatal neovascularization. Our previous study confirmed that E2F1 could activate the transcription of EphrinB2 and HEY2 in human mesenchymal stem cells; however, the detailed mechanism has not been resolved yet. In this study, we focused on the interaction between E2F1 and DNMT3A, a de novo DNA methyltransferase, on regulating the expression of EphrinB2 and HEY2, and explored the potential mechanisms. Gain- and loss-of-function experiments implicated the positive effect of E2F1 on the expression of EphrinB2 and HEY2 and tube formation in human umbilical artery endothelial cells. Accumulation of DNMT3A decreased the levels of EphrinB2 and HEY2, and impaired tube formation induced by E2F1, while inhibiting DNMT3A by RNA interference augmented their expression and angiogenesis in E2F1-trasfected cells. We then asked whether the low expressions of EphrinB2 and HEY2 induced by DNMT3A are related to the methylation status of their promoters. Surprisingly, the methylation status of the CpG islands in the promoter region was not significantly affected by overexpression of exogenous DNMT3A. Furthermore, the interaction between E2F1 and DNMT3A was confirmed by co-immunoprecipitation. DNMT3A could inhibit the transcription of EphrinB2 and HEY2 promoters by affecting the binding of E2F1 to its recognition sequences as revealed by luciferase reporter assay and chromatin immunoprecipitation. These results identified a novel mechanism underlying the cooperation of DNMT3A with E2F1 on regulating target gene expression, and revealed their roles in the angiogenic process.

The Role of Crosstalk between AR3 and E2F1 in Drug Resistance in Prostate Cancer Cells

Background: Drug resistance is one of the most prevalent causes of death in advanced prostate cancer patients. Combination therapies that target cancer cells via different mechanisms to overcome resistance have gained increased attention in recent years. However, the optimal drug combinations and the underlying mechanisms are yet to be fully explored. Aim and methods: The aim of this study is to investigate drug combinations that inhibit the growth of drug-resistant cells and determine the underlying mechanisms of their actions. In addition, we also established cell lines that are resistant to combination treatments and tested new compounds to overcome the phenomenon of double drug-resistance. Results: Our results show that the combination of enzalutamide (ENZ) and docetaxel (DTX) effectively inhibit the growth of prostate cancer cells that are resistant to either drug alone. The downregulation of transcription factor E2F1 plays a crucial role in cellular inhibition in response to the combined therapy. Notably, we found that the androgen receptor (AR) variant AR3 (a.k.a. AR-V7), but not AR full length (AR-FL), positively regulates E2F1 expression in these cells. E2F1 in turn regulates AR3 and forms a positive regulatory feedforward loop. We also established double drug-resistant cell lines that are resistant to ENZ+DTX combination therapy and found that the expression of both AR3 and E2F1 was restored in these cells. Furthermore, we identified that auranofin, an FDA-approved drug for the treatment of rheumatoid arthritis, overcame drug resistance and inhibited the growth of drug-resistant prostate cancer cells both in vitro and in vivo. Conclusion and significance: This proof-of-principle study demonstrates that targeting the E2F1/AR3 feedforward loop via a combination therapy or a multi-targeting drug could circumvent castration resistance in prostate cancer.

Transcriptional suppression of androgen receptor by 18β-glycyrrhetinic acid in LNCaP human prostate cancer cells

Androgen receptor (AR) plays a pivotal role as a target for amplification/mutation in pathogenesis and tumor progression in prostate, and thus, controlling AR activity or expression might be a feasible therapeutic approach for the treatment of prostate cancer. Here, we report the novel mechanisms by which 18β-glycyrrhetinic acid (GA) targets AR to stimulate cell death in both hormone-responsive and -refractory prostate cancer cells. We found that miR-488, a tumor suppressive microRNA, was markedly induced by GA treatment, resulting in the down-regulation of AR expression and inhibition of cellular responses mediated by androgens. Moreover, GA not only suppressed the expression of androgen target genes (TMPRSS2, PSA, and NKX3.1), but also enhanced the suppressive effect of anti-androgens (bicalutamide and flutamide) on LNCaP cell growth. Our data further provides evidence that down-regulation of AR expression by GA may occur through transcriptional suppression at AR promoter region between - 1014 and - 829. Ectopic expression of SFR and E2F3α reversed the inhibitory effect of GA on AR promoter activity as well as protein expression, suggesting that GA may target transcription factors SRF and E2F3α to regulate AR expression. Taken together, our study provides new insights on AR regulation and GA as a potential therapeutic candidate for human prostate cancer.

Epigenetics and prostate cancer: defining the timing of DNA methyltransferase deregulation during prostate cancer progression

DNA methyltransferases (DNMTs) regulate gene expression by methylating cytosine residues within CpG dinucleotides. Aberrant methylation patterns have been shown in a variety of human tumours including prostate cancer. However, the expression of DNMTs in clinical samples across the spectrum of prostate cancer progression has not been studied before. Tissue microarrays were constructed from the prostatectomy specimens of 309 patients across the spectrum of prostate cancer progression: hormone-naïve low-grade prostate cancer (n=49), hormone-naïve high-grade prostate cancer (n=151), hormonally treated high-grade prostate cancer (n=65), and castrate-resistant prostate cancer (CRPC) including neuroendocrine carcinoma (n=44). Adjacent non-neoplastic parenchyma was also available in 100 patients. In 71 patients with high-grade carcinoma and lymph node metastasis, tissue from the metastasis was also available for analysis. Immunohistochemical staining was performed with antibodies against DNMT1, DNMT2, DNMT3A, DNMT3B, and DNMT3L. Our results showed that DNMT1 and DNMT3L were upregulated early in prostate cancer progression, whereas DNMT2 was upregulated as a response to androgen ablation. DNMT1, DNMT3A, and DNMT3B were higher in the late stages of prostate cancer progression, i.e., the emergence of castrate resistance and androgen-independent growth. Lastly, DNMT1, DNMT2, and DNMT3L were upregulated in lymph node metastases compared to primary carcinomas. Our results highlight a cascade of epigenetic events in prostate cancer progression.

DNMT1 Regulates Epithelial-Mesenchymal Transition and Cancer Stem Cells, Which Promotes Prostate Cancer Metastasis

Cancer metastasis is a multistep process associated with the induction of an epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs). Although significant progress has been made in understanding the molecular mechanisms regulating EMT and the CSC phenotype, little is known of how these processes are regulated by epigenetics. Here we demonstrate that reduced expression of DNA methyltransferase 1 (DNMT1) plays an important role in the induction of EMT and the CSC phenotype by prostate cancer (PCa) cells, with enhanced tumorigenesis and metastasis. First, we observed that reduction of DNMT1 by 5-azacitidine (5-Aza) promotes EMT induction as well as CSCs and sphere formation in vitro. Reduced expression of DNMT1 significantly increased PCa migratory potential. We showed that the increase of EMT and CSC activities by reduction of DNMT1 is associated with the increase of protein kinase C. Furthermore, we confirmed that silencing DNMT1 is correlated with enhancement of the induction of EMT and the CSC phenotype in PCa cells. Additionally, chromatin immunoprecipitation assay reveals that reduction of DNMT1 promotes the suppression of H3K9me3 and H3K27me3 on the Zeb2 and KLF4 promoter region in PCa cells. Critically, we found in an animal model that significant tumor growth and more disseminated tumor cells in most osseous tissues were observed following injection of 5-Aza pretreated-PCa cells compared with vehicle-pretreated PCa cells. Our results suggest that epigenetic alteration of histone demethylation regulated by reduction of DNMT1 may control induction of EMT and the CSC phenotype, which facilitates tumorigenesis in PCa cells and has important therapeutic implications in targeting epigenetic regulation.

Dissecting the roles of the androgen receptor in prostate cancer from molecular perspectives

Androgen receptor plays a pivotal role in prostate cancer progression, and androgen deprivation therapy to intercept androgen receptor signal pathway is an indispensable treatment for most advanced prostate cancer patients to delay cancer progression. However, the emerging of castration-resistant prostate cancer reminds us the alteration of androgen receptor, which includes androgen receptor mutation, the formation of androgen receptor variants, and androgen receptor distribution in cancer cells. In this review, we introduce the process of androgen receptor and also its variants' formation, translocation, and function alteration by protein modification or interaction with other pathways. We dissect the roles of androgen receptor in prostate cancer from molecular perspective to provide clues for battling prostate cancer, especially castration-resistant prostate cancer.

Micro-RNA-204 Participates in TMPRSS2/ERG Regulation and Androgen Receptor Reprogramming in Prostate Cancer

Cancer progression is driven by genome instability incurred rearrangements such as transmembrane protease, serine 2 (TMPRSS2)/v-ets erythroblastosis virus E26 oncogene (ERG) that could possibly turn some of the tumor suppressor micro-RNAs into pro-oncogenic ones. Previously, we found dualistic miR-204 effects, acting either as a tumor suppressor or as an oncomiR in ERG fusion-dependent manner. Here, we provided further evidence for an important role of miR-204 for TMPRSS2/ERG and androgen receptor (AR) signaling modulation and fine tuning that prevents TMPRSS2/ERG overexpression in prostate cancer. Based on proximity-based ligation assay, we designed a novel method for detection of TMPRSS2/ERG protein products. We found that miR-204 is TMPRSS2/ERG oncofusion negative regulator, and this was mediated by DNA methylation of TMPRSS2 promoter. Transcriptional factors runt-related transcription factor 2 (RUNX2) and ETS proto-oncogene 1 (ETS1) were positive regulators of TMPRSS2/ERG expression and promoter hypo-methylation. Clustering of patients' sera for fusion protein, transcript expression, and wild-type ERG transcript isoforms, demonstrated not all patients harboring fusion transcripts had fusion protein products, and only few fusion positive ones exhibited increased wild-type ERG transcripts. miR-204 upregulated AR through direct promoter hypo-methylation, potentiated by the presence of ERG fusion and RUNX2 and ETS1. Proteomics studies provided evidence that miR-204 has dualistic role in AR cancer-related reprogramming, promoting prostate cancer-related androgen-responsive genes and AR target genes, as well as AR co-regulatory molecules. miR-204 methylation regulation was supported by changes in molecules responsible for chromatin remodeling, DNA methylation, and its regulation. In summary, miR-204 is a mild regulator of the AR function during the phase of preserved AR sensitivity as the latter one is required for ERG-fusion translocation.

E2F1 enhances glycolysis through suppressing Sirt6 transcription in cancer cells

The fast proliferation of cancer cells requires reprogramming of its energy metabolism with aerobic glycolysis as a major energy source. Sirt6, a class III histone deacetylase, has been shown to down regulate glycolysis by inhibiting the expression of several key glycolytic genes. Based on the published study on the metabolic phenotype of E2F1 −/− mice and SIRT6 −/− mice, we hypothesize that E2F1 enhances glycolysis and inhibits the expression of Sirt6. Indeed, over-expressing of E2F1, but not its DNA binding deficient mutant, significantly enhanced glucose uptake and lactate production in bladder and prostate cancer cell lines. E2F1 over-expression also suppressed Sirt6 expression and function. Moreover, E2F1 directly bound to Sirt6 promoter and suppressed Sirt6 promoter activity under both normoxic and hypoxic culture conditions. E2F1 siRNA blocked the up-regulation of E2F1 under hypoxia, increased Sirt6 expression and decreased glycolysis compared to those of scrambled siRNA transected cells. Furthermore, HDAC1 deacetylated E2F1 and diminished its transcription suppression of Sirt6 promoter. Treatment with the HDAC inhibitor, trichostatin A (TSA), suppressed Sirt6 promoter activity with increased binding of acetylated E2F1 to Sirt6 promoter. Mutating the E2F1 binding site on the proximal Sirt6 promoter abolished the suppression of Sirt6 transcription by TSA. These data indicate a novel oncogenic role of E2F1, i.e. enhancing glycolysis by suppressing Sirt6 transcription.

E2F1 Transcription Factor Regulates O-linked N-acetylglucosamine (O-GlcNAc) Transferase and O-GlcNAcase Expression

Protein O-GlcNAcylation, which is controlled by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), has emerged as an important posttranslational modification that may factor in multiple diseases. Until recently, it was assumed that OGT/OGA protein expression was relatively constant. Several groups, including ours, have shown that OGT and/or OGA expression changes in several pathologic contexts, yet the cis and trans elements that regulate the expression of these enzymes remain essentially unexplored. Here, we used a reporter-based assay to analyze minimal promoters and leveraged in silico modeling to nominate several candidate transcription factor binding sites in both Ogt (i.e. the gene for OGT protein) and Mgea5 (i.e. the gene for OGA protein). We noted multiple E2F binding site consensus sequences in both promoters. We performed chromatin immunoprecipitation in both human and mouse cells and found that E2F1 bound to candidate E2F binding sites in both promoters. In HEK293 cells, we overexpressed E2F1, which significantly reduced OGT and MGEA5 expression. Conversely, E2F1-deficient mouse fibroblasts had increased Ogt and Mgea5 expression. Of the known binding partners for E2F1, we queried whether retinoblastoma 1 (Rb1) might be involved. Rb1-deficient mouse embryonic fibroblasts showed increased levels of Ogt and Mgea5 expression, yet overexpression of E2F1 in the Rb1-deficient cells did not alter Ogt and Mgea5 expression, suggesting that Rb1 is required for E2F1-mediated suppression. In conclusion, this work identifies and validates some of the promoter elements for mouse Ogt and Mgea5 genes. Specifically, E2F1 negatively regulates both Ogt and Mgea5 expression in an Rb1 protein-dependent manner.

Osteopontin-c mediates the upregulation of androgen responsive genes in LNCaP cells through PI3K/Akt and androgen receptor signaling

Androgen receptor (AR) signaling is a key pathway modulating prostate cancer (PCa) progression. Several steps in this pathway have been investigated in order to propose novel treatment strategies for advanced PCa. Total osteopontin (OPN) has been described as a biomarker for PCa, in addition to its role in activating the progression of this tumor. Based on the known effects of the OPNc splice variant on PCa progression, the present study investigated whether this isoform can also modulate AR signaling. In order to test this, an in vitro model was used in which LNCaP cells were cultured in the presence of conditioned medium (CM) secreted by PCa cells overexpressing OPNc (OPNc-CM). The activation of AR signaling was evaluated by measuring the expression levels of AR-responsive genes (ARGs) using quantitative polymerase chain reaction and specific oligonucleotides. The data demonstrated that all nine tested ARGs (Fgf8, TMPRSS2, Greb1, Cdk2, Ndrg1, Cdk1, Pmepa1, Psa and Ar) are significantly upregulated in response to OPNc-CM compared with LNCaP cells cultured in CM secreted by control cells transfected with empty expression vector. The specific involvement of OPNc was demonstrated by depleting OPNc from OPNc-CM using an anti-OPNc neutralizing antibody. In addition, by using a phosphoinositide 3-kinase (PI3K)-specific inhibitor and AR antagonists, such as flutamide and bicalutamide, it was also observed that upregulation of ARGs in response to OPNc-CM involves PI3K signaling and depends on the AR. In conclusion, these data indicated that OPNc is able to activate AR signaling through the PI3K pathway and the AR. These data further corroborate our previous data, revealing the OPNc splice variant to be a key molecule that is able to modulate key signaling pathways involved in PCa progression.

The E2F1/DNMT1 axis is associated with the development of AR negative castration resistant prostate cancer

BACKGROUND

Research on castration resistant prostate cancer (CRPC) has focused primarily on functional alterations of the androgen receptor (AR). However, little is known about the loss of AR gene expression itself and the possible contribution of AR negative cells to CRPC.

METHODS

Human and murine prostate cancer tissue microarrays (TMAs) were evaluated with antibodies specific for E2F1, DNA methyltransferase 1 or AR. The human prostate cancer TMA consisted of clinical samples ranging from normal tissue to samples of metastatic disease. The murine TMA was comprised of benign, localized or metastatic prostate cancer acquired from TRAMP mice treated with castration and/or 5'-Aza-2'-deoxycytidine (5Aza).

RESULTS

Immunohistochemical analysis revealed increased nuclear DNMT1 staining in localized PCa (P < 0.0001) and metastatic PCa (P < 0.0001) compared to normal tissue. Examination of specific diagnoses revealed that Gleason seven tumors exhibited greater nuclear DNMT1 staining than Gleason six tumors (P < 0.05) and that metastatic tissue exhibited greater levels of nuclear DNMT1 than Gleason seven tumors (P < 0.01). Evaluation of the murine tissue cores revealed that 8.2% and 8.1% of benign tissue cores stained positive for E2F1 and DNMT1 respectively, while 97.0% were AR positive. Conversely, 81% and 100% of tumors were positive for E2F1 and DNMT1 respectively. This was in stark contrast to only 18% of tumors positive for AR. Treatment of mice with 5Aza reduced DNMT1 staining by 30%, while AR increased by 27%.

CONCLUSIONS

These findings demonstrate that the E2F1/DNMT1 inhibitory axis of AR transcription is activated during the emergence of CRPC.

Retinoblastoma tumor suppressor protein in pancreatic progenitors controls α- and β-cell fate

Pancreatic endocrine cells expand rapidly during embryogenesis by neogenesis and proliferation, but during adulthood, islet cells have a very slow turnover. Disruption of murine retinoblastoma tumor suppressor protein (Rb) in mature pancreatic β-cells has a limited effect on cell proliferation. Here we show that deletion of Rb during embryogenesis in islet progenitors leads to an increase in the neurogenin 3-expressing precursor cell population, which persists in the postnatal period and is associated with increased β-cell mass in adults. In contrast, Rb-deficient islet precursors, through repression of the cell fate factor aristaless related homeobox, result in decreased α-cell mass. The opposing effect on survival of Rb-deficient α- and β-cells was a result of opposing effects on p53 in these cell types. As a consequence, loss of Rb in islet precursors led to a reduced α- to β-cell ratio, leading to improved glucose homeostasis and protection against diabetes.

DNMT1 represses p53 to maintain progenitor cell survival during pancreatic organogenesis

In the developing pancreas, self-renewal of progenitors and patterning of cell fates are coordinated to ensure the correct size and cellular makeup of the organ. How this coordination is achieved, however, is not clear. We report that deletion of DNA methyltransferase 1 (Dnmt1) in pancreatic progenitors results in agenesis of the pancreas due to apoptosis of progenitor cells. We show that DNMT1 is bound to the p53 regulatory region and that loss of Dnmt1 results in derepression of the p53 locus. Haploinsufficiency of p53 rescues progenitor cell survival and cellular makeup of the Dnmt1-deleted pancreas.