Terminal neuroendocrine differentiation of human prostate carcinoma cells in response to increased intracellular cyclic AMP

A forward genetic screen identifies Sirtuin1 as a driver of neuroendocrine prostate cancer

Although localized prostate cancer is relatively indolent, advanced prostate cancer manifests with aggressive and often lethal variants, including neuroendocrine prostate cancer (NEPC). To identify drivers of aggressive prostate cancer, we leveraged Sleeping Beauty (SB) transposon mutagenesis in a mouse model based on prostate-specific loss-of-function of Pten and Tp53 . Compared with control mice, SB mice developed more aggressive prostate tumors, with increased incidence of metastasis. Notably, a significant percentage of the SB prostate tumors display NEPC phenotypes, and the transcriptomic features of these SB mouse tumors recapitulated those of human NEPC. We identified common SB transposon insertion sites (CIS) and prioritized associated CIS-genes differentially expressed in NEPC versus non-NEPC SB tumors. Integrated analysis of CIS-genes encoding for proteins representing upstream, post-translational modulators of master regulators controlling the transcriptional state of SB -mouse and human NEPC tumors identified sirtuin 1 ( Sirt1 ) as a candidate mechanistic determinant of NEPC. Gain-of-function studies in human prostate cancer cell lines confirmed that SIRT1 promotes NEPC, while its loss-of-function or pharmacological inhibition abrogates NEPC. This integrative analysis is generalizable and can be used to identify novel cancer drivers for other malignancies.

Summary

Using an unbiased forward mutagenesis screen in an autochthonous mouse model, we have investigated mechanistic determinants of aggressive prostate cancer. SIRT1 emerged as a key regulator of neuroendocrine prostate cancer differentiation and a potential target for therapeutic intervention.

Treatment-induced stemness and lineage plasticity in driving prostate cancer therapy resistance

Most human cancers are heterogeneous consisting of cancer cells at different epigenetic and transcriptional states and with distinct phenotypes, functions, and drug sensitivities. This inherent cancer cell heterogeneity contributes to tumor resistance to clinical treatment, especially the molecularly targeted therapies such as tyrosine kinase inhibitors (TKIs) and androgen receptor signaling inhibitors (ARSIs). Therapeutic interventions, in turn, induce lineage plasticity (also called lineage infidelity) in cancer cells that also drives therapy resistance. In this Perspective, we focus our discussions on cancer cell lineage plasticity manifested as treatment-induced switching of epithelial cancer cells to basal/stem-like, mesenchymal, and neural lineages. We employ prostate cancer (PCa) as the prime example to highlight ARSI-induced lineage plasticity during and towards development of castration-resistant PCa (CRPC). We further discuss how the tumor microenvironment (TME) influences therapy-induced lineage plasticity. Finally, we offer an updated summary on the regulators and mechanisms driving cancer cell lineage infidelity, which should be therapeutically targeted to extend the therapeutic window and improve patients' survival.

Regulation of Molecular Biomarkers Associated with the Progression of Prostate Cancer

Androgen receptor signaling regulates the normal and pathological growth of the prostate. In particular, the growth and survival of prostate cancer cells is initially dependent on androgen receptor signaling. Exposure to androgen deprivation therapy leads to the development of castration-resistant prostate cancer. There is a multitude of molecular and cellular changes that occur in prostate tumor cells, including the expression of neuroendocrine features and various biomarkers, which promotes the switch of cancer cells to androgen-independent growth. These biomarkers include transcription factors (TP53, REST, BRN2, INSM1, c-Myc), signaling molecules (PTEN, Aurora kinases, retinoblastoma tumor suppressor, calcium-binding proteins), and receptors (glucocorticoid, androgen receptor-variant 7), among others. It is believed that genetic modifications, therapeutic treatments, and changes in the tumor microenvironment are contributing factors to the progression of prostate cancers with significant heterogeneity in their phenotypic characteristics. However, it is not well understood how these phenotypic characteristics and molecular modifications arise under specific treatment conditions. In this work, we summarize some of the most important molecular changes associated with the progression of prostate cancers and we describe some of the factors involved in these cellular processes.

Glucocorticoid Receptor (GR) Activation Is Associated with Increased cAMP/PKA Signaling in Castration-Resistant Prostate Cancer

In castration-resistant prostate cancer (CRPC), increased glucocorticoid receptor (GR) expression and ensuing transcriptional activity have been proposed as an oncogenic "bypass" mechanism in response to androgen receptor (AR) signaling inhibition (ARSi). Here, we report that GR transcriptional activity acquired following ARSi is associated with the upregulation of cyclic adenosine monophosphate (cAMP)-associated gene expression pathways in both model systems and metastatic prostate cancer patient samples. In the context of ARSi, the expression of GR-mediated genes encoding cAMP signaling pathway-associated proteins can be inhibited by treatment with selective GR modulators (SGRMs). For example, in the context of ARSi, we found that GR activation resulted in upregulation of protein kinase inhibitor beta (PKIB) mRNA and protein levels, leading to nuclear accumulation of the cAMP-dependent protein kinase A catalytic subunit (PKA-c). Increased PKA-c, in turn, is associated with increased cAMP response element-binding protein phosphorylation and activity. Furthermore, enzalutamide and SGRM combination therapy in mice bearing CRPC xenografts delayed CRPC progression compared with enzalutamide therapy alone, and reduced tumor PKIB mRNA expression. Supporting the clinical importance of GR/PKA signaling activation in CRPC, we found a significant enrichment of both cAMP pathway signaling-associated gene expression and high NR3C1 (GR) activity in patient-derived xenograft models and metastatic human CRPC samples. These findings suggest a novel mechanism linking CRPC-induced GR transcriptional activity with increased cAMP signaling in AR-antagonized CRPC. Furthermore, our findings suggest that GR-specific modulation in addition to AR antagonism may delay GR+ CRPC time to recurrence, at least in part, by inhibiting tumor cAMP/PKA pathways.

IL-6 evoked biochemical changes in prostate cancer cells

The pro-inflammatory cytokine IL-6 has been associated with the progression of PCa to a castration-resistant phenotype. In this work, we characterized the biochemical changes evoked by IL-6 in three different models of PCa cells, including LNCaP, C4-2, and PC3. The effect of IL-6 on PCa cells was compared with the effect obtained by co-stimulation with the cAMP-inducing agent forskolin (FSK). Stimulation of LNCaP cells with IL-6 or IL-6 + FSK evoked increased expression of the neuroendocrine marker tubulin IIIβ and Cav3.2 T-type Ca²⁺ channel subunit. PC3 cells, representing a more advanced state of PCa, had high levels of tubulin IIIβ expression without any further changes observed by treatment with IL-6 or IL-6 + FSK. Elevated expression of the glucocorticoid receptor was observed in PC3, but not in LNCaP or C4-2 cells. Glucocorticoid receptor expression was not regulated by IL-6 stimulation of LNCaP or C4-2 cells. IL-6 acting alone or together with FSK evoked a significant reduction in the expression of the transcription factor REST and retinoblastoma tumor suppressor protein Rb1. In LNCaP cells, IL-6 acting alone or together with FSK had no effect on the expression of several biological markers of advanced PCa, including Aurora kinase A, valosin-containing protein, calcium-sensing receptor, calreticulin, S100A protein, and Protein S. In PC3 cells, co-treatment with IL-6 + FSK evoked increased expression of REST and S100A proteins, as well as a reduction in Protein S levels. These findings reveal a complex pattern of biochemical changes in PCa cells under the influence of IL-6.

Focus on the tumor microenvironment: A seedbed for neuroendocrine prostate cancer

The tumor microenvironment (TME) is a microecology consisting of tumor and mesenchymal cells and extracellular matrices. The TME plays important regulatory roles in tumor proliferation, invasion, metastasis, and differentiation. Neuroendocrine differentiation (NED) is a mechanism by which castration resistance develops in advanced prostate cancer (PCa). NED is induced after androgen deprivation therapy and neuroendocrine prostate cancer (NEPC) is established finally. NEPC has poor prognosis and short overall survival and is a major cause of death in patients with PCa. Both the cellular and non-cellular components of the TME regulate and induce NEPC formation through various pathways. Insights into the roles of the TME in NEPC evolution, growth, and progression have increased over the past few years. These novel insights will help refine the NEPC formation model and lay the foundation for the discovery of new NEPC therapies targeting the TME.

The Androgen Receptor and Its Crosstalk With the Src Kinase During Castrate-Resistant Prostate Cancer Progression

While the androgen receptor (AR) signalling is the mainstay therapeutic target for metastatic prostate cancers, these tumours will inevitably develop therapy resistance to AR pathway inhibitors suggesting that prostate tumour cells possess the capability to develop mechanisms to bypass their dependency on androgens and/or AR to survive and progress. In many studies, protein kinases such as Src are reported to promote prostate tumour progression. Specifically, the pro-oncogene tyrosine Src kinase regulates prostate cancer cell proliferation, adhesion, invasion, and metastasis. Not only can Src be activated under androgen depletion, low androgen, and supraphysiological androgen conditions, but also through crosstalk with other oncogenic pathways. Reciprocal activations between Src and AR proteins had also been reported. These findings rationalize Src inhibitors to be used to treat castrate-resistant prostate tumours. Although several Src inhibitors had advanced to clinical trials, the failure to observe patient benefits from these studies suggests that further evaluation of the roles of Src in prostate tumours is required. Here, we summarize the interplay between Src and AR signalling during castrate-resistant prostate cancer progression to provide insights on possible approaches to treat prostate cancer patients.

ETS transcription factor ELF3 (ESE-1) is a cell cycle regulator in benign and malignant prostate

This study aimed to elucidate the role of ELF3, an ETS family member in normal prostate growth and prostate cancer. Silencing ELF3 in both benign prostate (BPH-1) and prostate cancer (PC3) cell lines resulted in decreased colony forming ability, inhibition of cell migration and reduced cell viability due to cell cycle arrest, establishing ELF3 as a cell cycle regulator. Increased ELF3 expression in more advanced prostate tumours was shown by immunostaining of tissue microarrays and from analysis of gene expression and genetic alteration studies. This study indicates that ELF3 functions as part of normal prostate epithelial growth but also as a potential oncogene in advanced prostate cancers.

Advances in neuroendocrine prostate cancer research: From model construction to molecular network analyses

Prostate cancer is the most common cancer among men and has a high incidence and associated mortality worldwide. It is an androgen-driven disease in which tumor growth is triggered via ligand-mediated signaling through the androgen receptor (AR). Recent evidence suggests that the widespread use of effective AR pathway inhibitors may increase the occurrence of neuroendocrine prostate cancer (NEPC), an aggressive and treatment-resistant AR-negative variant; however, mechanisms controlling NEPC development remain to be elucidated. Various preclinical models have recently been developed to investigate the mechanisms driving the NEPC differentiation. In the present study, we summarized strategies for the development of NEPC models and proposed a novel method for model evaluation, which will help in the timely and accurate identification of NEPC by virtue of its ability to recapitulate the heterogeneity of prostate cancer. Moreover, we discuss the origin and the mechanism of NEPC. The understanding of the regulatory network mediating neuroendocrine differentiation presented in this review could provide valuable insights into the identification of novel drug targets for NEPC as well as into the causes of antiandrogenic drug resistance.

Role of MicroRNAs in Neuroendocrine Prostate Cancer

Therapy-induced neuroendocrine prostate cancer (t-NEPC/NEPC) is an aggressive variant of prostate cancer (PCa) that frequently emerges in castration-resistant prostate cancer (CRPC) under the selective pressure of androgen receptor (AR)-targeted therapies. This variant is extremely aggressive, metastasizes to visceral organs, tissues, and bones despite low serum PSA, and is associated with poor survival rates. It arises via a reversible trans-differentiation process, referred to as ‘neuroendocrine differentiation’ (NED), wherein PCa cells undergo a lineage switch and exhibit neuroendocrine features, characterized by the expression of neuronal markers such as enolase 2 (ENO2), chromogranin A (CHGA), and synaptophysin (SYP). The molecular and cellular mechanisms underlying NED in PCa are complex and not clearly understood, which contributes to a lack of effective molecular biomarkers for diagnosis and therapy of this variant. NEPC is thought to derive from prostate adenocarcinomas by clonal evolution. A characteristic set of genetic alterations, such as dual loss of retinoblastoma (RB1) and tumor protein (TP53) tumor suppressor genes and amplifications of Aurora kinase A (AURKA), NMYC, and EZH2, has been reported to drive NEPC. Recent evidence suggests that microRNAs (miRNAs) are important epigenetic players in driving NED in advanced PCa. In this review, we highlight the role of miRNAs in NEPC. These studies emphasize the diverse role that miRNAs play as oncogenes and tumor suppressors in driving NEPC. These studies have unveiled the important role of cellular processes such as the EMT and cancer stemness in determining NED in PCa. Furthermore, miRNAs are involved in intercellular communication between tumor cells and stromal cells via extracellular vesicles/exosomes that contribute to lineage switching. Recent studies support the promising potential of miRNAs as novel diagnostic biomarkers and therapeutic targets for NEPC.

Aggressive variants of prostate cancer: underlying mechanisms of neuroendocrine transdifferentiation

Prostate cancer is a hormone-driven disease and its tumor cell growth highly relies on increased androgen receptor (AR) signaling. Therefore, targeted therapy directed against androgen synthesis or AR activation is broadly used and continually improved. However, a subset of patients eventually progresses to castration-resistant disease. To date, various mechanisms of resistance have been identified including the development of AR-independent aggressive variant prostate cancer based on neuroendocrine transdifferentiation (NED). Here, we review the highly complex processes contributing to NED. Genetic, epigenetic, transcriptional aberrations and posttranscriptional modifications are highlighted and the potential interplay of the different factors is discussed. Background Aggressive variant prostate cancer (AVPC) with traits of neuroendocrine differentiation emerges in a rising number of patients in recent years. Among others, advanced therapies targeting the androgen receptor axis have been considered causative for this development. Cell growth of AVPC often occurs completely independent of the androgen receptor signal transduction pathway and cells have mostly lost the typical cellular features of prostate adenocarcinoma. This complicates both diagnosis and treatment of this very aggressive disease. We believe that a deeper understanding of the complex molecular pathological mechanisms contributing to transdifferentiation will help to improve diagnostic procedures and develop effective treatment strategies. Indeed, in recent years, many scientists have made important contributions to unravel possible causes and mechanisms in the context of neuroendocrine transdifferentiation. However, the complexity of the diverse molecular pathways has not been captured completely, yet. This narrative review comprehensively highlights the individual steps of neuroendocrine transdifferentiation and makes an important contribution in bringing together the results found so far.

Narrative review of challenges in the management of advanced neuroendocrine prostate cancer

With wide availability of potent androgen receptor targeted agents (ARTAs), the incidence of treatment-related neuroendocrine prostate cancer (t-NEPC) has been dramatically increasing. However, there is no standard effective treatment for this disease state. Recent advances in genomic and molecular medicine have identified some critical features of NEPC that would help in understanding the biology of the disease. Furthermore, invaluable pre-clinical in vivo and in vitro research models that represent NEPC have been developed. These advances in research have revealed a large heterogeneity of t-NEPC with varying degree of androgen receptor (AR), neuroendocrine (NE) marker, and cell cycle associated gene expressions, which may have clinical implication in terms of prognosis and treatment selection. Based on these studies, some potential drug targets have been identified, and early clinical trials are ongoing. In the future, more precise disease classification and biomarker-driven selection of patients will be critical for optimization of treatment for patients with NEPC. In the present review, we describe up-to-date findings of recent research on this topic and introduce ongoing therapeutic developments that are expected to lead to novel treatment strategies for NEPC in the future.

The heterogeneity of prostate cancers lacking AR activity will require diverse treatment approaches

The use of androgen deprivation therapy and second-line anti-androgens in prostate cancer has led to the emergence of tumors employing multiple androgen receptor (AR)-dependent and AR-independent mechanisms to resist AR-targeted therapies in castration-resistant prostate cancer (CRPC). While the AR signaling axis remains the cornerstone for therapeutic development in CRPC, a clearer understanding of the heterogeneous biology of CRPC tumors is needed for innovative treatment strategies. In this review, we discuss the characteristics of CRPC tumors that lack AR activity and the temporal and spatial considerations for the conversion of an AR-dependent to an AR-independent tumor type. We describe the more prevalent treatment-emergent phenotypes arising in the CRPC disease continuum, including amphicrine, AR-low, double-negative, neuroendocrine and small cell phenotypes. We discuss the association between the loss of AR activity and tumor plasticity with a focus on the roles of transcription factors like SOX2, DNA methylation, alternative splicing, and the activity of epigenetic modifiers like EZH2, BRD4, LSD1, and the nBAF complex in conversion to a neuroendocrine or small cell phenotype in CRPC. We hypothesize that only a subset of CRPC tumors have the propensity for tumor plasticity and conversion to the neuroendocrine phenotype and outline how we might target these plastic and emergent phenotypes in CRPC. In conclusion, we assess the current and future avenues for treatment and determine that the heterogeneity of CRPCs lacking AR activity will require diverse treatment approaches.

Resistance to androgen receptor signaling inhibition does not necessitate development of neuroendocrine prostate cancer

Resistance to AR signaling inhibitors (ARSis) in a subset of metastatic castration-resistant prostate cancers (mCRPCs) occurs with the emergence of AR^– neuroendocrine prostate cancer (NEPC) coupled with mutations/deletions in PTEN, TP53, and RB1 and the overexpression of DNMTs, EZH2, and/or SOX2. To resolve whether the lack of AR is the driving factor for the emergence of the NE phenotype, molecular, cell, and tumor biology analyses were performed on 23 xenografts derived from patients with PC, recapitulating the full spectrum of genetic alterations proposed to drive NE differentiation. Additionally, phenotypic response to CRISPR/Cas9-mediated AR KO in AR⁺ CRPC cells was evaluated. These analyses document that (a) ARSi-resistant NEPC developed without androgen deprivation treatment; (b) ARS in ARSi-resistant AR⁺/NE⁺ double-positive “amphicrine” mCRPCs did not suppress NE differentiation; (c) the lack of AR expression did not necessitate acquiring a NE phenotype, despite concomitant mutations/deletions in PTEN and TP53, and the loss of RB1 but occurred via emergence of an AR^–/NE^– double-negative PC (DNPC); (d) despite DNPC cells having homogeneous genetic driver mutations, they were phenotypically heterogeneous, expressing basal lineage markers alone or in combination with luminal lineage markers; and (e) AR loss was associated with AR promoter hypermethylation in NEPCs but not in DNPCs.

The inhibitory effect of melatonin on human prostate cancer

Prostate cancer (PCa) is one of the most commonly diagnosed human cancers in males. Nearly 191,930 new cases and 33,330 new deaths of PCa are estimated in 2020. Androgen and androgen receptor pathways played essential roles in the pathogenesis of PCa. Androgen depletion therapy is the most used therapies for primary PCa patients. However, due to the high relapse and mortality of PCa, developing novel noninvasive therapies have become the focus of research. Melatonin is an indole-like neurohormone mainly produced in the human pineal gland with a prominent anti-oxidant property. The anti-tumor ability of melatonin has been substantially confirmed and several related articles have also reported the inhibitory effect of melatonin on PCa, while reviews of this inhibitory effect of melatonin on PCa in recent 10 years are absent. Therefore, we systematically discuss the relationship between melatonin disruption and the risk of PCa, the mechanism of how melatonin inhibited PCa, and the synergistic benefits of melatonin and other drugs to summarize current understandings about the function of melatonin in suppressing human prostate cancer. We also raise several unsolved issues that need to be resolved to translate currently non-clinical trials of melatonin for clinic use. We hope this literature review could provide a solid theoretical basis for the future utilization of melatonin in preventing, diagnosing and treating human prostate cancer.

Neuroendocrine cells of the prostate: Histology, biological functions, and molecular mechanisms

Prostate cancer (PCa) is a common cause of cancer-related mortality in men worldwide. Although most men are diagnosed with low grade, indolent tumors that are potentially curable, a significant subset develops advanced disease where hormone therapy is required to target the androgen receptor (AR). Despite its initial effect, hormone therapy eventually fails and the tumor progresses to lethal stages even through continued inhibition of AR. This review article focuses on the role of PCa cellular heterogeneity in therapy resistance and disease progression. Although AR-positive luminal-type cells represent the vast majority of PCa cells, there exists a minor component of AR-negative neuroendocrine (NE) cells that are resistant to hormonal therapy and are enriched by the treatment. In addition, it is now well accepted that a significant subset of hormonally treated tumors recur as small cell neuroendocrine carcinoma (SCNC), further highlighting the importance of targeting NE cells in addition to the more abundant luminal-type cancer cells. Although it has been long recognized that NE cells are present in PCa, their underlying function in benign prostate and molecular mechanisms contributing to PCa progression remains poorly understood. In this article, we review the morphology and function of NE cells in benign prostate and PCa as well as underlying molecular mechanisms. In addition, we review the major reported mechanisms for transformation from common adenocarcinoma histology to the highly lethal SCNC, a significant clinical challenge in the management of advanced PCa.

A novel miRNA inhibits metastasis of prostate cancer via decreasing CREBBP-mediated histone acetylation

BACKGROUND

To identify novel miRNAs implicated in prostate cancer metastasis.

METHODS

Sixty-five prostate cancer tissues and paired pan-cancer tissues were sequenced. Novel miRNAs were re-analyzed by MIREAP program. Biological functions of miR-N5 were transwell experiment and colony formation. Target genes of miR-N5 were analyzed by bioinformatic analysis. Downstream of target gene was analyzed by The Cancer Genome Atlas (TCGA) and Memorial Sloan Kettering Cancer Center (MSKCC) databases and confirmed by CHIP experiment.

RESULTS

We identified a novel miRNA-miR-N5, which was downregulated in PCa cells, PCa tissue, and in the serum of patients with PCa. Knockout of miR-N5 enhanced migration and invasiveness in vitro. miR-N5 specified targeted CREBBP 3'-UTR and inhibited CREBBP expression, which mediated H3K56 acetylation at the promoter of EGFR, β-catenin and CDH1.

CONCLUSION

This study may shed the light on miR-N5 which influences metastasis via histone acetylation.

Cell Stress Induced Stressome Release Including Damaged Membrane Vesicles and Extracellular HSP90 by Prostate Cancer Cells

Tumor cells exhibit therapeutic stress resistance-associated secretory phenotype involving extracellular vesicles (EVs) such as oncosomes and heat shock proteins (HSPs). Such a secretory phenotype occurs in response to cell stress and cancer therapeutics. HSPs are stress-responsive molecular chaperones promoting proper protein folding, while also being released from cells with EVs as well as a soluble form known as alarmins. We have here investigated the secretory phenotype of castration-resistant prostate cancer (CRPC) cells using proteome analysis. We have also examined the roles of the key co-chaperone CDC37 in the release of EV proteins including CD9 and epithelial-to-mesenchymal transition (EMT), a key event in tumor progression. EVs derived from CRPC cells promoted EMT in normal prostate epithelial cells. Some HSP family members and their potential receptor CD91/LRP1 were enriched at high levels in CRPC cell-derived EVs among over 700 other protein types found by mass spectrometry. The small EVs (30-200 nm in size) were released even in a non-heated condition from the prostate cancer cells, whereas the EMT-coupled release of EVs (200-500 nm) and damaged membrane vesicles with associated HSP90α was increased after heat shock stress (HSS). GAPDH and lactate dehydrogenase, a marker of membrane leakage/damage, were also found in conditioned media upon HSS. During this stress response, the intracellular chaperone CDC37 was transcriptionally induced by heat shock factor 1 (HSF1), which activated the CDC37 core promoter, containing an interspecies conserved heat shock element. In contrast, knockdown of CDC37 decreased EMT-coupled release of CD9-containing vesicles. Triple siRNA targeting CDC37, HSP90α, and HSP90β was required for efficient reduction of this chaperone trio and to reduce tumorigenicity of the CRPC cells in vivo. Taken together, we define "stressome" as cellular stress-induced all secretion products, including EVs (200-500 nm), membrane-damaged vesicles and remnants, and extracellular HSP90 and GAPDH. Our data also indicated that CDC37 is crucial for the release of vesicular proteins and tumor progression in prostate cancer.

Molecular Links Between Angiogenesis and Neuroendocrine Phenotypes in Prostate Cancer Progression

As a common therapy for prostate cancer, androgen deprivation therapy (ADT) is effective for the majority of patients. However, prolonged ADT promotes drug resistance and progression to an aggressive variant with reduced androgen receptor signaling, so called neuroendocrine prostate cancer (NEPC). Until present, NEPC is still poorly understood, and lethal with no effective treatments. Elevated expression of neuroendocrine related markers and increased angiogenesis are two prominent phenotypes of NEPC, and both of them are positively associated with cancers progression. However, direct molecular links between the two phenotypes in NEPC and their mechanisms remain largely unclear. Their elucidation should substantially expand our knowledge in NEPC. This knowledge, in turn, would facilitate the development of effective NEPC treatments. We recently showed that a single critical pathway regulates both ADT-enhanced angiogenesis and elevated expression of neuroendocrine markers. This pathway consists of CREB1, EZH2, and TSP1. Here, we seek new insights to identify molecules common to pathways promoting angiogenesis and neuroendocrine phenotypes in prostate cancer. To this end, our focus is to summarize the literature on proteins reported to regulate both neuroendocrine marker expression and angiogenesis as potential molecular links. These proteins, often described in separate biological contexts or diseases, include AURKA and AURKB, CHGA, CREB1, EZH2, FOXA2, GRK3, HIF1, IL-6, MYCN, ONECUT2, p53, RET, and RB1. We also present the current efforts in prostate cancer or other diseases to target some of these proteins, which warrants testing for NEPC, given the urgent unmet need in treating this aggressive variant of prostate cancer.

Valproic Acid Addresses Neuroendocrine Differentiation of LNCaP Cells and Maintains Cell Survival

Purpose

Neuroendocrine differentiation of prostate cancer, induced by androgen deprivation therapy, is mainly related to advanced disease and poor clinical outcome. Genetic and epigenetic alterations are the key elements of the prostate carcinogenesis. A group of compounds able to induce changes in this sense is inhibitors of histone deacetylase, to which it belongs valproic acid (VPA). In the present paper, we evaluated the role of this molecule on the neuroendocrine differentiation of LNCaP cells together with the effect on proliferation and survival signals.

Methods

Cell growth was analyzed by MTT and flow cytometry, while expression of proteins through Western blot analysis.

Results

Our results have documented that VPA in LNCaP cells reduces cell proliferation, decreases the S phase and Cyclin A, and up-regulates the cyclin-dependent kinase inhibitors p21waf and p27. The acquisition of androgen-independent condition is consistent with an induction of β-III Tubulin and gamma Enolase, both markers of neuroendocrine phenotype. However, all these features cease with the removal of valproate from the culture medium, demonstrating the transitory nature of the epigenetic event. The VPA treatment does not compromise the survival phosphorylated signals of Akt, ERK1/2 and mTOR/p70S6K that remain up-regulated. Consistently, there is an increase of phospho-FOXO3a, to which corresponds the decreased expression of the corresponding oncosuppressor protein.

Conclusion

Overall, our findings indicate that VPA in LNCaP prostate tumor cells, although it reduces cell proliferation, is able to drive neuroendocrine phenotype and to maintain the survival of these cells. Keeping in mind that neuroendocrine differentiation of prostate cancer appears to be associated with a poor prognosis, it is necessary to develop new treatments that do not induce neurodifferentiation but able to counteract cell survival.

Neuroendocrine Differentiation of Prostate Cancer-An Intriguing Example of Tumor Evolution at Play

Our understanding of neuroendocrine prostate cancer (NEPC) has assumed a new perspective in light of the recent advances in research. Although classical NEPC is rarely seen in the clinic, focal neuroendocrine trans-differentiation of prostate adenocarcinoma occurs in about 30% of advanced prostate cancer (PCa) cases, and represents a therapeutic challenge. Even though our knowledge of the mechanisms that mediate neuroendocrine differentiation (NED) is still evolving, the role of androgen deprivation therapy (ADT) as a key driver of this phenomenon is increasingly becoming evident. In this review, we discuss the molecular, cellular, and therapeutic mediators of NED, and emphasize the role of the tumor microenvironment (TME) in orchestrating the phenotype. Understanding the role of the TME in mediating NED could provide us with valuable insights into the plasticity associated with the phenotype, and reveal potential therapeutic targets against this aggressive form of PCa.

RNA Splicing of the BHC80 Gene Contributes to Neuroendocrine Prostate Cancer Progression

BACKGROUND

Prostate adenocarcinoma (AdPC) progression to treatment-induced neuroendocrine prostate cancer (t-NEPC) is associated with poor patient survival. While AdPC and t-NEPC share similar genomes, they possess distinct transcriptomes, suggesting that RNA splicing and epigenetic mechanisms may regulate t-NEPC development.

OBJECTIVE

To characterize the role of alternative RNA splicing of the histone demethylase BHC80 during t-NEPC progression.

DESIGN, SETTING, AND PARTICIPANTS

The expression of BHC80 splice variants (BHC80-1 and BHC80-2) were compared between AdPC and t-NEPC patient tumors. Regulatory mechanisms of RNA splicing of the BHC80 gene were studied, and the signal pathways mediated by BHC80 splice variants were investigated in t-NEPC cell and xenograft models.

RESULTS

Global transcriptome analyses identified that the BHC80-2 variant is highly expressed in t-NEPC. Compared with the known histone demethylation activities of the BHC80 gene, we discovered a novel nonepigenetic action of BHC80-2, whereby BHC80-2 is localized in the cytoplasm to trigger the MyD88-p38-TTP pathway, which results in increased RNA stability of multiple tumor-promoting cytokines. While BHC80-2 does not induce neuroendocrine differentiation of cancer cells, it stimulates cell proliferation and tumor progression independent of androgen receptor signaling. Blockade of BHC80-2-regulated MyD88 signaling suppresses growth of several t-NEPC cell spheroid and xenograft models.

CONCLUSIONS

Gain of function of BHC80-2 through alternative RNA splicing activates immune responses of cancer cells to promote t-NEPC development.

PATIENT SUMMARY

The main obstacle to develop effective therapies for patients with t-NEPC is the lack of understanding on how t-NEPC is developed. Our study not only identifies a previously unknown BHC80-2-MyD88 signaling pathway that plays an important role during t-NEPC development, but also provides a proof of principle that targeting this signal pathway may offer an avenue to treat t-NEPC.

PEG10 is associated with treatment-induced neuroendocrine prostate cancer

Neuroendocrine (NE) differentiation of advanced prostate adenocarcinoma following androgen receptor (AR) axis-directed therapy is becoming increasingly recognized. Several models of this transdifferentiation provide insight into its molecular pathogenesis and have highlighted the placental gene PEG10 for further study. Using our unique model of enzalutamide resistance (ENZR) and NE differentiation, we studied PEG10/AR interplay in enzalutamide treatment-resistant cell lines 42DENZR and 42FENZR compared to LNCaP and castration-resistant 16DCRPC cells. ENZR cell lines with positive terminal NE marker status also displayed higher baseline expression of PEG10 compared to LNCaP and 16DCRPC. Antagonism of AR activity increased PEG10 expression followed by an increase in terminal NE markers. Conversely, stimulating AR activity via androgen supplementation reversed PEG10 and NE marker expression in a time and dose-dependent manner. These results were supported by human data showing that PEG10 expression is highest in NEPC and that AR-dependent gene, PSA, is negatively correlated with PEG10 in adenocarcinoma. Further, ChIP assay confirmed binding of activated AR to the PEG10 enhancer, decreasing PEG10 expression. While PEG10 did not drive NEPC, its knockdown reduced NE markers in our cell lines. Moreover, PEG10 knockdown in vitro- and in vivo-attenuated tumor growth. Overall, these observations indicate that PEG10 is an AR-repressed gene which modulates NE markers in ENZR cells and targeting PEG10 in advanced prostate cancer with NE features is a rational and viable option.

The Genomics of Prostate Cancer: A Historic Perspective

The genomics of prostate cancer (PCA) has been difficult to study compared with some other cancer types for a multitude of reasons, despite significant efforts since the early 1980s. Overcoming some of these obstacles has paved the way for greater insight into the genomics of PCA. The advent of high-throughput technologies coming from the initial use of microsatellite and oligonucleotide probes gave rise to techniques like comparative genomic hybridization (CGH). With the introduction of massively parallel genomic sequencing, referred to as next-generation sequencing (NGS), a deeper understanding of cancer genomics in general has occurred. Along with these technologic advances, there has been the development of computational biology and statistical approaches to address novel large data sets characterized by single base resolution. This review will provide a historic perspective of PCA genomics with an emphasis on the cardinal mutations and alterations observed to be consistently seen in PCA for both hormone-naïve localized PCA and castration-resistant prostate cancer (CRPC). There will be a focus on alterations that have the greatest potential to play a role in disease progression and therapy management.

RETRACTED: Neuroendocrine differentiation contributes to radioresistance development and metastatic potential increase in non-small cell lung cancer

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the authors and their institute. The BBA Editor-in-Chief has agreed to retract the paper. In this paper, there were two errors identified to the journal by the authors: The first error was in Western blot gel band images of Fig. 4A (p-MAPK, MAPK, p-Erk, and Stat3) and the 8 gel band images of Fig. 4G. The second error was in the cell culture images of Figures 3F, 3J, and 4E. The authors state that these errors were due to uploading mistakes in the preparation of the manuscript. The authors apologize for these errors and any inconvenience caused. The Editor-in-Chief initially agreed to retract the paper based on the identification of these two errors. Readers are able to see further discussion of the paper on the PubPeer site here: https://pubpeer.com/publications/569EB2CE7A7335D7F3F8F3FF310936

EMT, stemness and tumor plasticity in aggressive variant neuroendocrine prostate cancers

Neuroendocrine/Aggressive Variant Prostate Cancers are lethal variants of the disease, with an aggressive clinical course and very short responses to conventional therapy. The age-adjusted incidence rate for this tumor sub-type has steadily increased over the past 20 years in the United States, with no reduction in the associated mortality rate. The molecular networks fueling its emergence and sustenance are still obscure; however, many factors have been associated with the onset and progression of neuroendocrine differentiation in clinically typical adenocarcinomas including loss of androgen-receptor expression and/or signaling, conventional therapy, and dysregulated cytokine function. "Tumor-plasticity" and the ability to dedifferentiate into alternate cell lineages are central to this process. Epithelial-to-mesenchymal (EMT) signaling pathways are major promoters of stem-cell properties in prostate tumor cells. In this review, we examine the contributions of EMT-induced cellular-plasticity and stem-cell signaling pathways to the progression of Neuroendocrine/Aggressive Variant Prostate Cancers in the light of potential therapeutic opportunities.

Roles of Alternative RNA Splicing of the Bif-1 Gene by SRRM4 During the Development of Treatment-induced Neuroendocrine Prostate Cancer

Treatment-induced neuroendocrine prostate cancer (t-NEPC) is an aggressive subtype of prostate cancer (PCa) that becomes more prevalent when hormonal therapy, chemotherapy, or radiation therapy is applied to patients with metastatic prostate adenocarcinoma (AdPC). How AdPC cells survive these anti-cancer therapies and progress into t-NEPC remains unclear. By comparing the whole transcriptomes between AdPC and t-NEPC, we identified Bif-1, an apoptosis-associated gene, which undergoes alternative RNA splicing in t-NEPC. We found that while Bif-1a is the predominant variant of the Bif-1 gene in AdPC, two neural-specific variants, Bif-1b and Bif-1c, are highly expressed in t-NEPC patients, patient derived xenografts, and cell models. The neural-specific RNA splicing factor, SRRM4, promotes Bif-1b and Bif-1c splicing, and the expression of SRRM4 in tumors is strongly associated with Bif-1b/-1c levels. Furthermore, we showed that Bif-1a is pro-apoptotic, while Bif-1b and Bif-1c are anti-apoptotic in PCa cells under camptothecin and UV light irritation treatments. Taken together, our data indicate that SRRM4 regulates alternative RNA splicing of the Bif-1 gene that enables PCa cells resistant to apoptotic stimuli under anti-cancer therapies, and may contribute to AdPC progression into t-NEPC.

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Alternative RNA splicing of the apoptosis-related gene, Bif-1, is associated with the development of t-NEPC.

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SRRM4 regulates alternative RNA splicing of the Bif-1 gene.

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Bif-1a in AdPC cells is pro-apoptotic, while neural Bif-1 variants, Bif-1b/-1c, enable tumor cells resistant to apoptosis.

Treatment-induced neuroendocrine prostate cancer (t-NEPC) is an aggressive subtype of castration-resistant prostate cancer. It becomes more prevalent when more potent androgen receptor inhibitors are applied to patients. However, mechanisms by which t-NEPC develops remain unclear. Here we report alternative RNA splicing of the apoptosis-related gene, Bif-1, may contribute to t-NEPC establishment. We show that the expression of neural Bif-1 variants is upregulated in t-NEPC, and confers tumor cells resistance to apoptotic stimuli. We propose that tumor cells have to first develop mechanisms to counteract therapy-induced cell death before they can undergo neuroendocrine differentiation for t-NEPC.

Effect of A549 neuroendocrine differentiation on cytotoxic immune response

The present study was designed to determine the effects of factors secreted by the lung adenocarcinoma cell line with the neuroendocrine phenotype, A549NED, on cytotoxic T lymphocytes (CTLs) activity in vitro A perspective that integrates the nervous, endocrine and immune system in cancer research is essential to understand the complexity of dynamic interactions in tumours. Extensive clinical research suggests that neuroendocrine differentiation (NED) is correlated with worse patient outcomes; however, little is known regarding the effects of neuroendocrine factors on the communication between the immune system and neoplastic cells. The human lung cancer cell line A549 was induced to NED (A549NED) using cAMP-elevating agents. The A549NED cells showed changes in cell morphology, an inhibition of proliferation, an overexpression of chromogranin and a differential pattern of biogenic amine production (decreased dopamine and increased serotonin [5-HT] levels). Using co-cultures to determine the cytolytic CTLs activity on target cells, we showed that the acquisition of NED inhibits the decrease in the viability of the target cells and release of fluorescence. Additionally, the conditioned medium of A549NED and 5-HT considerably decreased the viability and proliferation of the Jurkat cells after 24 h. Thus, our study successfully generated a neuroendocrine phenotype from the A549 cell line. In co-cultures with CTLs, the pattern of secretion by A549NED impaired the proliferation and cytotoxic activity of CTLs, which might be partly explained by the increased release of 5-HT.

CXCL12γ Promotes Metastatic Castration-Resistant Prostate Cancer by Inducing Cancer Stem Cell and Neuroendocrine Phenotypes

There is evidence that cancer stem-like cells (CSC) and neuroendocrine behavior play critical roles in the pathogenesis and clinical course of metastatic castration-resistant prostate cancer (m-CRPC). However, there is limited mechanistic understanding of how CSC and neuroendocrine phenotypes impact the development of m-CRPC. In this study, we explored the role of the intracellular chemokine CXCL12γ in CSC induction and neuroendocrine differentiation and its impact on m-CRPC. CXCL12γ expression was detected in small-cell carcinoma of metastatic tissues and circulating tumor cells from m-CRPC patients and in prostate cancer cells displaying an neuroendocrine phenotype. Mechanistic investigations demonstrated that overexpression of CXCL12γ induced CSC and neuroendocrine phenotypes in prostate cancer cells through CXCR4-mediated PKCα/NFκB signaling, which promoted prostate tumor outgrowth, metastasis, and chemoresistance in vivo Together, our results establish a significant function for CXCL12γ in m-CRPC development and suggest it as a candidate therapeutic target to control aggressive disease.Significance: Expression of CXCL12γ induces the expression of a cancer stem cell and neuroendocrine phenotypes, resulting in the development of aggressive m-CRPC. Cancer Res; 78(8); 2026-39. ©2018 AACR.

Androgen receptor signaling regulates T-type Ca2+ channel expression and neuroendocrine differentiation in prostate cancer cells

Therapies designed to reduce androgen production or receptor activation are effective in limiting prostate tumor growth. However, prolonged treatment with anti-androgen therapies results in the progression of prostate cancers into an androgen refractory state. Neuroendocrine differentiation (NED) has been associated with the progression of prostate cancers to an androgen resistant phenotype. In this work we investigated the effect of disrupting androgen receptor signaling in promoting NED of prostate carcinoma cells and whether it is accompanied by an increase in T-type Ca2+ channel expression. The effect of disrupting androgen signaling was assessed in LNCaP and 22Rv1 prostate cancer cells following treatment with the androgen receptor blocker, bicalutamide, or hormone-depleted media. Treatment of LNCaP cells with bicalutamide or hormone-depleted media for 4-10 d evoked considerable morphological and biochemical changes consistent with NED including the development of long neurite-like processes and the expression of the neuronal marker, tubulin IIIβ. PCR analysis of bicalutamide-stimulated cells revealed no significant changes in Cav3.2 mRNA. However, stimulation of LNCaP cells with bicalutamide or hormone-depleted media for 10 d evoked a significant increase in Cav3.2 protein expression and the appearance of functional T-type Ca2+ channels. Inhibition of T-type Ca2+ channel function with various pharmacological blockers disrupted the morphological differentiation of LNCaP cells. Bicalutamide-evoked expression of functional T-type Ca2+ channels in LNCaP cells promoted chemoresistance to docetaxel. These findings indicate that disruption of androgen receptor signaling in prostate cancer cells evokes increased expression of functional T-type Ca2+ channels, which may result in significant morphological and biochemical changes.

Alternative RNA splicing of the MEAF6 gene facilitates neuroendocrine prostate cancer progression

Although potent androgen receptor pathway inhibitors (ARPI) improve overall survival of metastatic prostate cancer patients, treatment-induced neuroendocrine prostate cancer (t-NEPC) as a consequence of the selection pressures of ARPI is becoming a more common clinical issue. Improved understanding of the molecular biology of t-NEPC is essential for the development of new effective management approaches for t-NEPC. In this study, we identify a splice variant of the MYST/Esa1-associated factor 6 (MEAF6) gene, MEAF6-1, that is highly expressed in both t-NEPC tumor biopsies and neuroendocrine cell lines of prostate and lung cancers. We show that MEAF6-1 splicing is stimulated by neuronal RNA splicing factor SRRM4. Rather than inducing neuroendocrine trans-differentiation of cells in prostate adenocarcinoma, MEAF6-1 upregulation stimulates cell proliferation, anchorage-independent cell growth, invasion and xenograft tumor growth. Gene microarray identifies that these MEAF6-1 actions are in part mediated by the ID1 and ID3 genes. These findings suggest that the MEAF6-1 variant does not induce neuroendocrine differentiation of prostate cancer cells, but rather facilitates t-NEPC progression by increasing the proliferation rate of cells that have acquired neuroendocrine phenotypes.

Organoids with cancer stem cell-like properties secrete exosomes and HSP90 in a 3D nanoenvironment

Ability to form cellular aggregations such as tumorspheres and spheroids have been used as a morphological marker of malignant cancer cells and in particular cancer stem cells (CSC). However, the common definition of the types of cellular aggregation formed by cancer cells has not been available. We examined morphologies of 67 cell lines cultured on three dimensional morphology enhancing NanoCulture Plates (NCP) and classified the types of cellular aggregates that form. Among the 67 cell lines, 49 cell lines formed spheres or spheroids, 8 cell lines formed grape-like aggregation (GLA), 8 cell lines formed other types of aggregation, and 3 cell lines formed monolayer sheets. Seven GLA-forming cell lines were derived from adenocarcinoma among the 8 lines. A neuroendocrine adenocarcinoma cell line PC-3 formed asymmetric GLA with ductal structures on the NCPs and rapidly growing asymmetric tumors that metastasized to lymph nodes in immunocompromised mice. In contrast, another adenocarcinoma cell line DU-145 formed spheroids in vitro and spheroid-like tumors in vivo that did not metastasize to lymph nodes until day 50 after transplantation. Culture in the 3D nanoenvironment and in a defined stem cell medium enabled the neuroendocrine adenocarcinoma cells to form slowly growing large organoids that expressed multiple stem cell markers, neuroendocrine markers, intercellular adhesion molecules, and oncogenes in vitro. In contrast, the more commonly used 2D serum-contained environment reduced intercellular adhesion and induced mesenchymal transition and promoted rapid growth of the cells. In addition, the 3D stemness nanoenvironment promoted secretion of HSP90 and EpCAM-exosomes, a marker of CSC phenotype, from the neuroendocrine organoids. These findings indicate that the NCP-based 3D environment enables cells to form stem cell tumoroids with multipotency and model more accurately the in vivo tumor status at the levels of morphology and gene expression.

Clinical and molecular features of treatment-related neuroendocrine prostate cancer

Treatment-related neuroendocrine prostate cancer is a lethal form of prostate cancer that emerges in the later stages of castration-resistant prostate cancer treatment. Treatment-related neuroendocrine prostate cancer transdifferentiates from adenocarcinoma as an adaptive response to androgen receptor pathway inhibition. The incidence of treatment-related neuroendocrine prostate cancer has been rising due to the increasing use of potent androgen receptor pathway inhibitors. Typically, treatment-related neuroendocrine prostate cancer is characterized by either low or absent androgen receptor expression, small cell carcinoma morphology and expression of neuroendocrine markers. Clinically, it manifests with predominantly visceral or lytic bone metastases, bulky tumor masses, low prostate-specific antigen levels or a short response duration to androgen deprivation therapy. Furthermore, although the tumor initially responds to platinum-based chemotherapy, the duration of the response is short. Based on the poor prognosis, it is imperative to identify novel molecular targets for treatment-related neuroendocrine prostate cancer. Recent advances in genomic and molecular research, supported by novel in vivo models, have identified some of the key molecular characteristics of treatment-related neuroendocrine prostate cancer. The gain of MYCN and AURKA oncogenes, along with the loss of tumor suppressor genes TP53 and RB1 are key genomic alterations associated with treatment-related neuroendocrine prostate cancer. Androgen receptor repressed genes, such as BRN2 and PEG10, are also necessary for treatment-related neuroendocrine prostate cancer. These genetic changes converge on pathways upregulating genes, such as SOX2 and EZH2, that facilitate lineage plasticity and neuroendocrine differentiation. As a result, on potent androgen receptor pathway inhibition, castration-resistant prostate cancer transdifferentiates to treatment-related neuroendocrine prostate cancer in a clonally divergent manner. Further understanding of the disease biology is required to develop novel drugs and biomarkers that would help treat this aggressive prostate cancer variant.

Reduction of two histone marks, H3k9me3 and H3k27me3 by epidrug induces neuroendocrine differentiation in prostate cancer

Neuroendocrine prostate cancer (NE PCa) is an aggressive malignancy, often presenting with advanced metastasis. We previously reported that reduction of histone marks regulated by DNMT1 following epidrug (5-Azacitidine, 5-Aza) treatment controls induction of epithelial to mesenchymal (EMT) and a cancer stem cell (CSC) phenotype, which facilitates tumorigenesis in PCa cells. Here, we use the epidrug 5-Aza as a model for how histone marks may regulate the reprogramming of prostate adenocarcinoma into NE phenotypic cells. First, we observed that 5-Aza treatment of PCa cells in vitro induces a neuron-like phenotype. In addition, significant increases in the expression of the NE markers N-Myc downstream regulated gene 1 (NDRG1), enolase-2 (ENO2), and synaptophysin were observed. Critically, a high density of NE cells with synaptophysin expression was found in tumors generated by 5-Aza pretreatment of PCa cells. Importantly, induction of NE differentiation of PCa cells was associated with an enhancement of NDRG1 expression by reduction of two histone marks, H3K9me3 and H3K27me3. Further, more NDRG1 expression was detected in the subset of PCa cells with reduced expression of H3K9me3 or H3K27me3 in the tumors generated by 5-Aza pretreated PCa cells and critically, these biological differences are also observed in small cell carcinoma in advanced stage of human primary PCa tumors. Our results suggest that reduction of histone marks regulated by the epidrug 5-Aza may control induction of a NE phenotype, which facilitates PCa progression. These studies suggest a strong rationale for developing therapeutics, which target epigenetic regulation.

Establishment of prostate cancer spheres from a prostate cancer cell line after phenethyl isothiocyanate treatment and discovery of androgen-dependent reversible differentiation between sphere and neuroendocrine cells

Prostate cancer can transform from androgen-responsive to an androgen-independent phenotype. The mechanism responsible for the transformation remains unclear. We studied the effects of an epigenetic modulator, phenethyl isothiocyanate (PEITC), on the androgen-responsive LNCaP cells. After treatment with PEITC, floating spheres were formed with characteristics of prostate cancer stem cells (PCSC). These spheres were capable of self-renewal in media with and without androgen. They have been maintained in both types of media as long term cultures. Upon androgen deprivation, the adherent spheres differentiated to neuroendocrine cells (NEC) with decreased proliferation, expression of androgen receptor, and PSA. NEC reverse differentiated to spheres when androgen was replenished. The sphere cells expressed surface marker CD44 and had enhanced histone H3K4 acetylation, DNMT1 down-regulation and GSTP1 activation. We hypothesize that PEITC-mediated alteration in epigenomics of LNCaP cells may give rise to sphere cells, whereas reversible androgenomic alterations govern the shuttling between sphere PCSC and progeny NEC. Our findings identify unrecognized properties of prostate cancer sphere cells with multi-potential plasticity. This system will facilitate development of novel therapeutic agents and allow further exploration into epigenomics and androgenomics governing the transformation to hormone refractory prostate cancer.

The Genomics of Prostate Cancer: emerging understanding with technologic advances

With the advent of next-generation sequencing technologies and large whole-exome and genome studies in prostate and other cancers, our understanding of the landscape of genomic alterations has dramatically been refined. In additional to well-known alterations in genomic regions involving 8p, 8q, 10q23, common ETS translocations and androgen receptor amplifications, newer technology have uncovered recurrent mutations in SPOP, FOXA1, MED12, IDH and complex large scale genomic alterations (eg, chromoplexy). This review surveys the enhanced landscape of genomic alterations in clinically localized and advanced prostate cancer.

Hyperactive mTOR induces neuroendocrine differentiation in prostate cancer cell with concurrent up-regulation of IRF1

BACKGROUND

Neuroendocrine-differentiated prostate cancer (NEPCa) is refractory to androgen deprivation therapy and shows a poor prognosis. The underlying mechanisms responsible for neuroendocrine differentiation (NED) are yet to be clarified. In this study, we investigated the role of mammalian target of rapamycin (mTOR) in NEPCa.

METHODS

We utilized a gain-of-function analysis by establishing a human PCa LNCaP stable line that expresses hyperactive mTOR (LNCaP-mTOR). Then, we employed a comprehensive mass spectrometric analysis to identify a key transcription factor in LNCaP-mTOR, followed by a loss-of-function analysis using CRISPR/Cas system.

RESULTS

The activation of mTOR induced NED. We observed significant cell growth arrest in NED of LNCaP-mTOR, which accompanied increased expression of p21^WAF1/CIP1 . A comprehensive mass spectrometric analysis identified interferon regulatory factor 1 (IRF1) as a key transcription factor in growth arrest of LNCaP-mTOR. The disruption of IRF1 gene in LNCaP-mTOR reversed cell growth arrest along with the suppression of its target p21^WAF1/CIP1 . These results indicate that the growth arrest in NED is at least in part dependent on IRF1 through the induction of p21^WAF1/CIP1 .

CONCLUSIONS

We identified active mTOR as a novel inducer of NED, and elucidated a mechanism underlying the malignant transformation of NEPCa by recapitulating NED in vitro.

Establishment of a neuroendocrine prostate cancer model driven by the RNA splicing factor SRRM4

Neuroendocrine prostate cancer (NEPC) is becoming more prevalent as more potent androgen receptor (AR) pathway inhibitors are applied to patients with metastatic tumors. However, there are limited cell and xenograft models currently available, hindering the investigation of signal pathways involved in regulating NEPC progression and the design of high throughput screening assays for inhibitors to treat NEPC patients. Here, we report an NEPC model, LnNE, that is derived from prostate adenocarcinoma cells and has global similarity in transcription and RNA splicing to tumors from NEPC patients. LnNE xenografts are castrate-resistant and highly aggressive. Its tumor take is ∼3-5 weeks and tumor doubling time is ∼2-3 weeks. LnNE expresses multiple neuroendocrine markers, preserves AR expression, but is PSA negative. Its neuroendocrine phenotype cannot be reversed by androgen treatment. LnNE cells grow as multi-cellular spheroids under 2-dimensional culture conditions similar to the NEPC cell line NCI-H660, but have higher proliferation rate and are easier to be transfected. LnNE cells can also adapt to 3-dimensional culture conditions in a 96-plate format, allowing high throughput screening assays. In summary, the LnNE model is useful to study the mechanisms of NEPC progression and to discover potential therapies for NEPC.

Biology and evolution of poorly differentiated neuroendocrine tumors

Neuroendocrine (NE) cancers are a diverse group of neoplasms typically diagnosed and treated on the basis of their site of origin. This Perspective focuses on advances in our understanding of the tumorigenesis and treatment of poorly differentiated neuroendocrine tumors. Recent evidence from sequencing indicates that, although neuroendocrine tumors can arise de novo, they can also develop as a result of lineage plasticity in response to pressure from targeted therapies. We discuss the shared genomic alterations of these tumors independently of their site of origin, and we explore potential therapeutic strategies on the basis of recent biological findings.

Neural Stem Cells, Neural Progenitors, and Neurotrophic Factors

Neural stem cells (NSCs) have been proposed as a promising cellular source for the treatment of diseases in nervous systems. NSCs can self-renew and generate major cell types of the mammalian central nervous system throughout adulthood. NSCs exist not only in the embryo, but also in the adult brain neurogenic region: the subventricular zone (SVZ) of the lateral ventricle. Embryonic stem (ES) cells acquire NSC identity with a default mechanism. Under the regulations of leukemia inhibitory factor (LIF) and fibroblast growth factors, the NSCs then become neural progenitors. Neurotrophic and differentiation factors that regulate gene expression for controlling neural cell fate and function determine the differentiation of neural progenitors in the developing mammalian brain. For clinical application of NSCs in neurodegenerative disorders and damaged neurons, there are several critical problems that remain to be resolved: 1) how to obtain enough NSCs from reliable sources for autologous transplantation; 2) how to regulate neural plasticity of different adult stem cells; 3) how to control differentiation of NSCs in the adult nervous system. In order to understand the mechanisms that control NSC differentiation and behavior, we review the ontogeny of NSCs and other stem cell plasticity of neuronal differentiation. The role of NSCs and their regulation by neurotrophic factors in CNS development are also reviewed.

Induction of Neuroendocrine Differentiation in Prostate Cancer Cells by Dovitinib (TKI-258) and its Therapeutic Implications

Prostate cancer (PCa) remains the second-leading cause of cancer-related deaths in American men with an estimated mortality of more than 26,000 in 2016 alone. Aggressive and metastatic tumors are treated with androgen deprivation therapies (ADT); however, the tumors acquire resistance and develop into lethal castration resistant prostate cancer (CRPC). With the advent of better therapeutics, the incidences of a more aggressive neuroendocrine prostate cancer (NEPC) variant continue to emerge. Although de novo occurrences of NEPC are rare, more than 25% of the therapy-resistant patients on highly potent new-generation anti-androgen therapies end up with NEPC. This, along with previous observations of an increase in the number of such NE cells in aggressive tumors, has been suggested as a mechanism of resistance development during prostate cancer progression. Dovitinib (TKI-258/CHIR-258) is a pan receptor tyrosine kinase (RTK) inhibitor that targets VEGFR, FGFR, PDGFR, and KIT. It has shown efficacy in mouse-model of PCa bone metastasis, and is presently in clinical trials for several cancers. We observed that both androgen receptor (AR) positive and AR-negative PCa cells differentiate into a NE phenotype upon treatment with Dovitinib. The NE differentiation was also observed when mice harboring PC3-xenografted tumors were systemically treated with Dovitinib. The mechanistic underpinnings of this differentiation are unclear, but seem to be supported through MAPK-, PI3K-, and Wnt-signaling pathways. Further elucidation of the differentiation process will enable the identification of alternative salvage or combination therapies to overcome the potential resistance development.

FOXA1 inhibits prostate cancer neuroendocrine differentiation

Neuroendocrine prostate cancer (NEPC) has increasingly become a clinical challenge. The mechanisms by which neuroendocrine (NE) cells arises from prostate adenocarcinoma cells are poorly understood. FOXA1 is a transcription factor of the forkhead family that is required for prostate epithelial differentiation. In this study, we demonstrated that FOXA1 loss drives NE differentiation, demarcated by phenotypical changes and NEPC marker expressions. Mechanistically, this is mediated by FOXA1 binding to the promoter of interleukin 8 (IL-8), a chemokine previously shown elevated in NEPC, to directly inhibit its expression. Further, IL-8 upregulation activates the MAPK/ERK pathway, leading to ERK phosphorylation and enolase 2 (ENO2) expression. IL-8 knockdown or ERK inhibition, on the other hand, abolished FOXA1 loss-induced NE differentiation. Analysis of xenograft mouse models confirmed FOXA1 loss in NEPC tumors relative to its adenocarcinoma counterparts. Importantly, FOXA1 is downregulated in human NEPC tumors compared to primary and castration-resistant prostate cancers, and its expression is negatively correlated with that of ENO2. These findings indicate that FOXA1 transcriptionally suppresses IL-8, the expression of which would otherwise stimulate the MAPK/ERK pathway to promote NE differentiation of prostate cancer cells. Our data strongly suggest that FOXA1 loss may play a significant role in enabling prostate cancer progression to NEPC, whereas IL-8 and MAPK/ERK pathways may be promising targets for therapeutic intervention.

Neuronal Trans-Differentiation in Prostate Cancer Cells

BACKGROUND

Neuroendocrine (NE) differentiation in prostate cancer (PCa) is an aggressive phenotype associated with therapy resistance. The complete phenotype of these cells is poorly understood. Clinical classification is based predominantly on the expression of standard NE markers.

METHODS

We analyzed the phenotype of NE carcinoma of the prostate utilizing in vitro methods, in silico, and immunohistochemical analyses of human disease.

RESULTS

LNCaP cells, subjected to a variety of stressors (0.1% [v/v] fetal bovine serum, cyclic AMP) induced a reproducible phenotype consistent with neuronal trans-differentiation. Cells developed long cytoplasmic processes resembling neurons. As expected, serum deprived cells had decreased expression in androgen receptor and prostate specific antigen. A significant increase in neuronal markers also was observed. Gene array analysis demonstrated that LNCaP cells subjected to low serum or cAMP showed statistically significant manifestation of a human brain gene expression signature. In an in silico experiment using human data, we identified that only hormone resistant metastatic prostate cancer showed enrichment of the "brain profile." Gene ontology analysis demonstrated categories involved in neuronal differentiation. Three neuronal markers were validated in a large human tissue cohort.

CONCLUSION

This study proposes that the later stages of PCa evolution involves neuronal trans-differentiation, which would enable PCa cells to acquire independence from the neural axis, critical in primary tumors. Prostate 76:1312-1325, 2016. © 2016 Wiley Periodicals, Inc.

Up-Regulated Expression of LAMP2 and Autophagy Activity during Neuroendocrine Differentiation of Prostate Cancer LNCaP Cells

Neuroendocrine (NE) prostate cancer (PCa) is a highly aggressive subtype of prostate cancer associated with resistance to androgen ablation therapy. In this study, we used LNCaP prostate cancer cells cultured in a serum-free medium for 6 days as a NE model of prostate cancer. Serum deprivation increased the expression of NE markers such as neuron-specific enolase (NSE) and βIII tubulin (βIII tub) and decreased the expression of the androgen receptor protein in LNCaP cells. Using cDNA microarrays, we compared gene expression profiles of NE cells and non-differentiated LNCaP cells. We identified up-regulation of 155 genes, among them LAMP2, a lysosomal membrane protein involved in lysosomal stability and autophagy. We then confirmed up-regulation of LAMP2 in NE cells by qRT-PCR, Western blot and confocal microscopy assays, showing that mRNA up-regulation correlated with increased levels of LAMP2 protein. Subsequently, we determined autophagy activity in NE cells by assessing the protein levels of SQSTM/p62 and LC3 by Western blot and LC3 and Atg5 mRNAs content by qRT-PCR. The decreased levels of SQSTM/p62 was accompanied by an enhanced expression of LC3 and ATG5, suggesting activation of autophagy in NE cells. Blockage of autophagy with 1μM AKT inhibitor IV, or by silencing Beclin 1 and Atg5, prevented NE cell differentiation, as revealed by decreased levels of the NE markers. In addition, AKT inhibitor IV as well as Beclin1 and Atg5 kwockdown attenuated LAMP2 expression in NE cells. On the other hand, LAMP2 knockdown by siRNA led to a marked blockage of autophagy, prevention of NE differentiation and decrease of cell survival. Taken together, these results suggest that LAMP2 overexpression assists NE differentiation of LNCaP cells induced by serum deprivation and facilitates autophagy activity in order to attain the NE phenotype and cell survival. LAMP2 could thus be a potential biomarker and potential target for NE prostate cancer.

Expression of PDE11A in Normal and Malignant Human Tissues

Cyclic nucleotide phosphodiesterase 11A (PDE11A) is the newest member in the PDE family. Although the tissue distribution of PDE11A mRNA has been shown, its protein expression pattern has not been well studied. The goal of this report is to investigate the distribution of PDE11A proteins in a wide range of normal and malignant human tissues. We utilized a polyclonal antibody that recognized all four PDE11A isoforms. Its specificity was demonstrated by Western blot analysis on a recombinant human PDE11A protein and native PDE11A proteins in various human tissues. Immunohistochemistry showed that PDE11A is widely expressed. Various degrees of immunoreactivity were observed in the epithelial cells, endothelial cells, and smooth muscle cells of all tissues examined. The highest expression was in the epithelial, endothelial, and smooth muscle cells of the prostate, Leydig, and spermatogenic cells of the testis, the tubule epithelial cells in the kidney, the epithelial and endothelial cells in the adrenal, the epithelial cells and macrophages in the colon, and the epidermis in the skin. Furthermore, PDE11A expression was also detected in several human carcinomas. Our results suggest that PDE11A might be involved in multiple physiological processes in various organs via its ability to modulate intracellular cAMP and cGMP levels.

SRRM4 Drives Neuroendocrine Transdifferentiation of Prostate Adenocarcinoma Under Androgen Receptor Pathway Inhibition

BACKGROUND

Neuroendocrine prostate cancer (NEPC) is an aggressive subtype of castration-resistant prostate cancer that typically does not respond to androgen receptor pathway inhibition (ARPI), and its diagnosis is increasing.

OBJECTIVE

To understand how NEPC develops and to identify driver genes to inform therapy for NEPC prevention.

DESIGN, SETTING, AND PARTICIPANTS

Whole-transcriptome sequencing data were extracted from prostate tumors from two independent cohorts: The Beltran cohort contained 27 adenocarcinoma and five NEPC patient samples, and the Vancouver Prostate Centre cohort contained three patient samples and nine patient-derived xenografts.

INTERVENTION

A novel bioinformatics tool, comparative alternative splicing detection (COMPAS), was invented to analyze alternative RNA splicing on RNA-sequencing data.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

COMPAS identified potential driver genes for NEPC development. Biochemical and biological validations were performed in both prostate cell and tumor models.

RESULTS AND LIMITATION

More than 66% of the splice events were predicted to be regulated by the RNA splicing factor serine/arginine repetitive matrix 4 (SRRM4). In vitro and in vivo evidence confirmed that one SRRM4 target gene was the RE1 silencing transcription factor (REST), a master regulator of neurogenesis. Moreover, SRRM4 strongly stimulated adenocarcinoma cells to express NEPC biomarkers, and this effect was exacerbated by ARPI. ARPI combined with a gain of SRRM4-induced adenocarcinoma cells to assume multicellular spheroid morphology and was essential in establishing progressive NEPC xenografts. These SRRM4 actions were further enhanced by loss of function of TP53.

CONCLUSIONS

SRRM4 drives NEPC progression. This knowledge may guide the development of novel therapeutics aimed at NEPC.

PATIENT SUMMARY

Using next-generation RNA sequencing and our newly developed bioinformatics tool, we identified a neuroendocrine prostate cancer (NEPC)-specific RNA splicing signature that is predominantly controlled by serine/arginine repetitive matrix 4 (SRRM4). We confirmed that SRRM4 drives NEPC progression, and we propose SRRM4 as a potential therapeutic target for NEPC.