PAGE4 positivity is associated with attenuated AR signaling and predicts patient survival in hormone-naive prostate cancer

Cancer testis antigens: Emerging therapeutic targets leveraging genomic instability in cancer

Cancer care has witnessed remarkable progress in recent decades, with a wide array of targeted therapies and immune-based interventions being added to the traditional treatment options such as surgery, chemotherapy, and radiotherapy. However, despite these advancements, the challenge of achieving high tumor specificity while minimizing adverse side effects continues to dictate the benefit-risk balance of cancer therapy, guiding clinical decision making. As such, the targeting of cancer testis antigens (CTAs) offers exciting new opportunities for therapeutic intervention of cancer since they display highly tumor specific expression patterns, natural immunogenicity and play pivotal roles in various biological processes that are critical for tumor cellular fitness. In this review, we delve deeper into how CTAs contribute to the regulation and maintenance of genomic integrity in cancer, and how these mechanisms can be exploited to specifically target and eradicate tumor cells. We review the current clinical trials targeting aforementioned CTAs, highlight promising pre-clinical data and discuss current challenges and future perspectives for future development of CTA-based strategies that exploit tumor genomic instability.

Single-cell and bulk RNA sequencing reveal cancer-associated fibroblast heterogeneity and a prognostic signature in prostate cancer

Cancer-associated fibroblasts (CAFs), the central players in the tumor microenvironment (TME), can promote tumor progression and metastasis via various functions. However, the properties of CAFs in prostate cancer (PCa) have not been fully assessed. Therefore, we aimed to examine the CAF characteristics in PCa and construct a CAF-derived signature to predict PCa prognosis. CAFs were identified using single-cell RNA sequencing (scRNA-seq) data from 3 studies. We performed the FindAllMarkers function to extract CAF marker genes and constructed a signature to predict the biochemical relapse-free survival (bRFS) of PCa in the Cancer Genome Atlas (TCGA) cohort. Subsequently, different algorithms were applied to reveal the differences of the TME, immune infiltration, treatment responses in the high- and low-risk groups. Additionally, the CAF heterogeneity was assessed in PCa, which were confirmed by the functional enrichment analysis, gene set enrichment analysis (GSEA), and AUCell method. The scRNA-seq analysis identified a CAF cluster with 783 cells and determined 183 CAF marker genes. Cell-cell communication revealed extensive interactions between fibroblasts and immune cells. A CAF-related prognostic model, containing 7 genes (ASPN, AEBP1, ALDH1A1, BGN, COL1A1, PAGE4 and RASD1), was developed to predict bRFS and validated by 4 independent bulk RNA-seq cohorts. Moreover, the high-risk group of the signature score connected with an immunosuppressive TME, such as a higher level of M2 macrophages and lower levels of plasma cells and CD8+ T cells, and a reduced reaction rate for immunotherapy compared with low-risk group. After re-clustering CAFs via unsupervised clustering, we revealed 3 biologically distinct CAF subsets, namely myofibroblast-like CAFs (myCAFs), immune and inflammatory CAFs (iCAFs) and antigen-presenting CAFs (apCAFs). In conclusion, the CAF-derived signature, the first of its kind, can effectively predict PCa prognosis and serve as an indicator for immunotherapy. Furthermore, our study identified 3 CAF subpopulations with distinct functions in PCa.

Tissue-Specific Regulation of the Wnt/β-Catenin Pathway by PAGE4 Inhibition of Tankyrase

Spatiotemporal control of Wnt/β-catenin signaling is critical for organism development and homeostasis. The poly-(ADP)-ribose polymerase Tankyrase (TNKS1) promotes Wnt/β-catenin signaling through PARylation-mediated degradation of AXIN1, a component of the β-catenin destruction complex. Although Wnt/β-catenin is a niche-restricted signaling program, tissue-specific factors that regulate TNKS1 are not known. Here, we report prostate-associated gene 4 (PAGE4) as a tissue-specific TNKS1 inhibitor that robustly represses canonical Wnt/β-catenin signaling in human cells, zebrafish, and mice. Structural and biochemical studies reveal that PAGE4 acts as an optimal substrate decoy that potently hijacks substrate binding sites on TNKS1 to prevent AXIN1 PARylation and degradation. Consistently, transgenic expression of PAGE4 in mice phenocopies TNKS1 knockout. Physiologically, PAGE4 is selectively expressed in stromal prostate fibroblasts and functions to establish a proper Wnt/β-catenin signaling niche through suppression of autocrine signaling. Our findings reveal a non-canonical mechanism for TNKS1 inhibition that functions to establish tissue-specific control of the Wnt/β-catenin pathway.

Eprinomectin, a novel semi-synthetic macrocylic lactone is cytotoxic to PC3 metastatic prostate cancer cells via inducing apoptosis

Prostate Cancer (PCa) is the second most common cancer among men in United States after skin cancer. Conventional chemotherapeutic drugs available for PCa treatment are limited due to toxicity and resistance issues. Therefore, there is an urgent need to develop more effective treatment for advanced PCa. In this current study, we focused on evaluating the anti-cancer efficacy of Eprinomectin (EP), a novel avermectin analog against PC3 metastatic PCa cells. EP displayed robust inhibition of cell viability of PC3 cells in addition to suppressing the colony formation and wound healing capabilities. Our study showed that EP targets PC3 cells via inducing ROS and apoptosis activation. EP treatment enforces cell cycle arrest at G0/G1 phase via targeting cyclin-dependent kinase 4 (CDK4) and subsequent induction of apoptosis in PC3 cells. At the molecular level, EP effectively inhibited the expression of various cancer stem cell markers such as ALDH1, Sox-2, Nanog, Oct3/4 and CD44. Interestingly, EP also inhibited the activity of alkaline phosphatase, a maker of pluripotent stem cells. Of note, EP treatment resulted in the translocation of β-catenin from the nucleus to the cytoplasm indicating that EP antagonizes Wnt/β-catenin signaling pathway. Western blotting analysis revealed that EP downregulated the expression of key cell cycle markers such as cyclin D1, cyclin D3, CDK4, and c-Myc. In addition, EP inhibited the anti-apoptotic markers such as Mcl-1, XIAP, c-IAP1 and survivin in PC3 cells. On the other hand, EP treatment resulted in the activation of pH2A.X, Bad, caspase-9, caspase-3 and cleavage of PARP1. Taken together, our data suggests that EP is a potential agent to treat advanced PCa cells via modulating apoptosis signaling.

Stromal-epithelial interactions in prostate cancer: Overexpression of PAGE4 in stromal cells inhibits the invasive ability of epithelial cells

It is now widely recognized that carcinoma-associated fibroblasts which are believed to be myofibroblasts, promote the transformation of prostate epithelial cells to cancer cells, enhance their proliferation and invasiveness, and induce the acquisition of resistance to cancer therapy and immune evasiveness. Prostate-associated gene 4 (PAGE4) is an intrinsically disordered protein that is remarkably prostate-specific. PAGE4 is also a stress-response protein that functions as a transcriptional regulator and is upregulated in early-stage prostate cancer (PCa) and its precursor lesions. However, PAGE4 is downregulated in high-grade PCa and metastatic disease. Here, we show that PAGE4 is highly expressed in the stromal cells surrounding the cancer-adjacent "normal" glands and low-grade PCa lesions but not in lesions proximal to high-grade PCa. Overexpression of PAGE4 in a stromal cell line inhibits the migration and invasion of PCa epithelial cells in multiple coculture systems. PAGE4 overexpression also inhibits the downregulation of E-cadherin in PCa epithelial cells when cocultured with stromal cells. Furthermore, signaling via tumor necrosis factor-α and transforming growth factor-β pathways is decreased in the stromal cells overexpressing PAGE4 suggesting that PAGE4 appears to play a protective role against disease progression by perturbing interactions between epithelial cells and stromal cells in PCa. Taken together, these findings support previous observations that upregulation of PAGE4 in PCa correlates with a better prognosis and highlight PAGE4 as a novel therapeutic target for early-stage "low-risk" disease.

Intrinsically disordered proteins and phenotypic switching: Implications in cancer

It is now well established that intrinsically disordered proteins (IDPs) that constitute a large part of the proteome across the three kingdoms, play critical roles in several biological processes including phenotypic switching. However, dysregulated expression of IDPs that engage in promiscuous interactions can lead to pathological states. In this chapter, using cancer as a paradigm, we discuss how IDP conformational dynamics and the resultant conformational noise can modulate phenotypic switching. Thus, contrary to the prevailing wisdom that phenotypic switching is highly deterministic (has a genetic underpinning) in cancer, emerging evidence suggests that non-genetic mechanisms, at least in part due to the conformational noise, may also be a confounding factor in phenotypic switching.

PAGE4 promotes prostate cancer cells survive under oxidative stress through modulating MAPK/JNK/ERK pathway

Background

Prostate cancer (PCa) is one of the most common cancers in male worldwide. Oxidative stress has been recognized as one of the driving signals pathologically linked to PCa progression. Nevertheless, the association of oxidative stress with PCa progression remains unclear.

Methods

Western blot, q-RT-PCR and bioinformatics analyses were used to examine PAGE4 expression. Comet assay and Annexin V/ PI dual staining assay were performed to investigate DNA damage and cell death under oxidative stress. Mouse xenograft model of PCa cells was established to verify the role of PAGE4 in vivo. Transcriptomic analysis was performed to investigate the underlying mechanism for the function of PAGE4 under oxidative stress. Western blot assay was conducted to determine the status of MAPK pathway. Immunohistochemistry was used to identify protein expression of PAGE4 in tumor tissues.

Results

In this study, we found that PAGE4 expression was increased in PCa cells under oxidative stress condition. PAGE4 overexpression protected PCa cells from oxidative stress-inducing cell death by reducing DNA damage. PAGE4 overexpression promoted PCa cells growth in vivo. Mechanistically, PAGE4 promoted the survival of prostate cancer cells through regulating MAPK pathway which reflected in decreasing the phosphorylation of MAP2K4, JNK and c-JUN but increasing phosphorylation of ERK1/2.

Conclusion

Our findings indicate that PAGE4 protects PCa cells from DNA damage and apoptosis under oxidative stress by modulating MAPK signalling pathway. PAGE4 expression may serve as a prognostic biomarker for clinical applications.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1032-3) contains supplementary material, which is available to authorized users.

Prostate-Associated Gene 4 (PAGE4): Leveraging the Conformational Dynamics of a Dancing Protein Cloud as a Therapeutic Target

Prostate cancer (PCa) is a leading cause of mortality and morbidity globally. While genomic alterations have been identified in PCa, in contrast to some other cancers, use of such information to personalize treatment is still in its infancy. Here, we discuss how PAGE4, a protein which appears to act both as an oncogenic factor as well as a metastasis suppressor, is a novel therapeutic target for PCa. Inhibiting PAGE4 may be a viable strategy for low-risk PCa where it is highly upregulated. Conversely, PAGE4 expression is downregulated in metastatic PCa and, therefore, reinstituting its sustained expression may be a promising option to subvert or attenuate androgen-resistant PCa. Thus, fine-tuning the levels of PAGE4 may represent a novel approach for personalized medicine in PCa.

Phenotypic Plasticity, Bet-Hedging, and Androgen Independence in Prostate Cancer: Role of Non-Genetic Heterogeneity

It is well known that genetic mutations can drive drug resistance and lead to tumor relapse. Here, we focus on alternate mechanisms-those without mutations, such as phenotypic plasticity and stochastic cell-to-cell variability that can also evade drug attacks by giving rise to drug-tolerant persisters. The phenomenon of persistence has been well-studied in bacteria and has also recently garnered attention in cancer. We draw a parallel between bacterial persistence and resistance against androgen deprivation therapy in prostate cancer (PCa), the primary standard care for metastatic disease. We illustrate how phenotypic plasticity and consequent mutation-independent or non-genetic heterogeneity possibly driven by protein conformational dynamics can stochastically give rise to androgen independence in PCa, and suggest that dynamic phenotypic plasticity should be considered in devising therapeutic dosing strategies designed to treat and manage PCa.

Cancer/Testis Antigens: "Smart" Biomarkers for Diagnosis and Prognosis of Prostate and Other Cancers

A clinical dilemma in the management of prostate cancer (PCa) is to distinguish men with aggressive disease who need definitive treatment from men who may not require immediate intervention. Accurate prediction of disease behavior is critical because radical treatment is associated with high morbidity. Here, we highlight the cancer/testis antigens (CTAs) as potential PCa biomarkers. The CTAs are a group of proteins that are typically restricted to the testis in the normal adult but are aberrantly expressed in several types of cancers. Interestingly, >90% of CTAs are predicted to belong to the realm of intrinsically disordered proteins (IDPs), which do not have unique structures and exist as highly dynamic conformational ensembles, but are known to play important roles in several biological processes. Using prostate-associated gene 4 (PAGE4) as an example of a disordered CTA, we highlight how IDP conformational dynamics may regulate phenotypic heterogeneity in PCa cells, and how it may be exploited both as a potential biomarker as well as a promising therapeutic target in PCa. We also discuss how in addition to intrinsic disorder and post-translational modifications, structural and functional variability induced in the CTAs by alternate splicing represents an important feature that might have different roles in different cancers. Although it is clear that significant additional work needs to be done in the outlined direction, this novel concept emphasizing (multi)functionality as an important trait in selecting a biomarker underscoring the theranostic potential of CTAs that is latent in their structure (or, more appropriately, the lack thereof), and casts them as next generation or “smart” biomarker candidates.

Prostate-associated gene 4 (PAGE4), an intrinsically disordered cancer/testis antigen, is a novel therapeutic target for prostate cancer

Prostate-associated gene 4 (PAGE4) is a remarkably prostate-specific Cancer/Testis Antigen that is highly upregulated in the human fetal prostate and its diseased states but not in the adult normal gland. PAGE4 is an intrinsically disordered protein (IDP) that functions as a stress-response protein to suppress reactive oxygen species as well as prevent DNA damage. In addition, PAGE4 is also a transcriptional regulator that potentiates transactivation by the oncogene c-Jun. c-Jun forms the AP-1 complex by heterodimerizing with members of the Fos family and plays an important role in the development and pathology of the prostate gland, underscoring the importance of the PAGE4/c-Jun interaction. HIPK1, also a component of the stress-response pathway, phosphorylates PAGE4 at T51 which is critical for its transcriptional activity. Phosphorylation induces conformational and dynamic switching in the PAGE4 ensemble leading to a new cellular function. Finally, bioinformatics evidence suggests that the PAGE4 mRNA could be alternatively spliced resulting in four potential isoforms of the polypeptide alluding to the possibility of a range of conformational ensembles with latent functions. Considered together, the data suggest that PAGE4 may represent the first molecular link between stress and prostate cancer (PCa). Thus, pharmacologically targeting PAGE4 may be a novel opportunity for treating and managing patients with PCa, especially patients with low-risk disease.

Phosphorylation-induced conformational dynamics in an intrinsically disordered protein and potential role in phenotypic heterogeneity

Intrinsically disordered proteins (IDPs) that lack a unique 3D structure and comprise a large fraction of the human proteome play important roles in numerous cellular functions. Prostate-Associated Gene 4 (PAGE4) is an IDP that acts as a potentiator of the Activator Protein-1 (AP-1) transcription factor. Homeodomain-Interacting Protein Kinase 1 (HIPK1) phosphorylates PAGE4 at S9 and T51, but only T51 is critical for its activity. Here, we identify a second kinase, CDC-Like Kinase 2 (CLK2), which acts on PAGE4 and hyperphosphorylates it at multiple S/T residues, including S9 and T51. We demonstrate that HIPK1 is expressed in both androgen-dependent and androgen-independent prostate cancer (PCa) cells, whereas CLK2 and PAGE4 are expressed only in androgen-dependent cells. Cell-based studies indicate that PAGE4 interaction with the two kinases leads to opposing functions. HIPK1-phosphorylated PAGE4 (HIPK1-PAGE4) potentiates c-Jun, whereas CLK2-phosphorylated PAGE4 (CLK2-PAGE4) attenuates c-Jun activity. Consistent with the cellular data, biophysical measurements (small-angle X-ray scattering, single-molecule fluorescence resonance energy transfer, and NMR) indicate that HIPK1-PAGE4 exhibits a relatively compact conformational ensemble that binds AP-1, whereas CLK2-PAGE4 is more expanded and resembles a random coil with diminished affinity for AP-1. Taken together, the results suggest that the phosphorylation-induced conformational dynamics of PAGE4 may play a role in modulating changes between PCa cell phenotypes. A mathematical model based on our experimental data demonstrates how differential phosphorylation of PAGE4 can lead to transitions between androgen-dependent and androgen-independent phenotypes by altering the AP-1/androgen receptor regulatory circuit in PCa cells.

Roles of cancer/testis antigens (CTAs) in breast cancer

Breast cancer is the most common cancer diagnosed and is the second leading cause of cancer death among women in the US. For breast cancer, early diagnosis and efficient therapy remains a significant clinical challenge. Therefore, it is necessary to identify novel tumor associated molecules to target for biomarker development and immunotherapy. In this regard, cancer testis antigens (CTAs) have emerged as a potential clinical biomarker targeting immunotherapy for various malignancies due to the nature of its characteristics. CTAs are a group of tumor associated antigens (TAAs) that display normal expression in immune-privileged organs, but display aberrant expression in several types of cancers, particularly in advanced cancers. Investigation of CTAs for the clinical management of breast malignancies indicates that these TAAs have potential roles as novel biomarkers, with increased specificity and sensitivity compared to those currently used in the clinic. Moreover, TAAs could be therapeutic targets for cancer immunotherapy. This review is an attempt to address the promising CTAs in breast cancer and their possible clinical implications as biomarkers and immunotherapeutic targets with particular focus on challenges and future interventions.

Functional networks inference from rule-based machine learning models

BACKGROUND

Functional networks play an important role in the analysis of biological processes and systems. The inference of these networks from high-throughput (-omics) data is an area of intense research. So far, the similarity-based inference paradigm (e.g. gene co-expression) has been the most popular approach. It assumes a functional relationship between genes which are expressed at similar levels across different samples. An alternative to this paradigm is the inference of relationships from the structure of machine learning models. These models are able to capture complex relationships between variables, that often are different/complementary to the similarity-based methods.

RESULTS

We propose a protocol to infer functional networks from machine learning models, called FuNeL. It assumes, that genes used together within a rule-based machine learning model to classify the samples, might also be functionally related at a biological level. The protocol is first tested on synthetic datasets and then evaluated on a test suite of 8 real-world datasets related to human cancer. The networks inferred from the real-world data are compared against gene co-expression networks of equal size, generated with 3 different methods. The comparison is performed from two different points of view. We analyse the enriched biological terms in the set of network nodes and the relationships between known disease-associated genes in a context of the network topology. The comparison confirms both the biological relevance and the complementary character of the knowledge captured by the FuNeL networks in relation to similarity-based methods and demonstrates its potential to identify known disease associations as core elements of the network. Finally, using a prostate cancer dataset as a case study, we confirm that the biological knowledge captured by our method is relevant to the disease and consistent with the specialised literature and with an independent dataset not used in the inference process.

AVAILABILITY

The implementation of our network inference protocol is available at: http://ico2s.org/software/funel.html.

Disorder, Promiscuous Interactions, and Stochasticity Regulate State Switching in the Unstable Prostate

A causal link between benign prostatic hyperplasia (BPH) and prostate cancer has long been suspected but not widely accepted. A new model is proposed that supports such a connection. In contrast to the prevailing wisdom, our model, that draws on dynamical systems theory, suggests that in response to stress, epithelial cells in the unstable gland can give rise to both types of diseases via a phenotypic switching mechanism. The central idea is that phenotypic switching is a stochastic process which exploits the plasticity of the epithelial cell. It is driven by 'noise' contributed by the conformational dynamics of proteins that are intrinsically disordered. In a system that is noisy when stressed, disorder promotes promiscuity, unmasks latent information, and rewires the network to cause phenotypic switching. Cells with newly acquired phenotypes can transcend the traditional zonal boundaries to give rise to BPH or prostate cancer depending on the microenvironment. Establishing causality between the two diseases may provide us with an opportunity to better understand their etiology and guide prevention and treatment strategies. J. Cell. Biochem. 117: 2235-2240, 2016. © 2016 Wiley Periodicals, Inc.

Phosphorylation-induced Conformational Ensemble Switching in an Intrinsically Disordered Cancer/Testis Antigen

Prostate-associated gene 4 (PAGE4) is an intrinsically disordered cancer/testis antigen that is up-regulated in the fetal and diseased human prostate. Knocking down PAGE4 expression results in cell death, whereas its overexpression leads to a growth advantage of prostate cancer cells (Zeng, Y., He, Y., Yang, F., Mooney, S. M., Getzenberg, R. H., Orban, J., and Kulkarni, P. (2011) The cancer/testis antigen prostate-associated gene 4 (PAGE4) is a highly intrinsically disordered protein. J. Biol. Chem. 286, 13985-13994). Phosphorylation of PAGE4 at Thr-51 is critical for potentiating c-Jun transactivation, an important factor in controlling cell growth, apoptosis, and stress response. Using NMR spectroscopy, we show that the PAGE4 polypeptide chain has local and long-range conformational preferences that are perturbed by site-specific phosphorylation at Thr-51. The population of transient turn-like structures increases upon phosphorylation in an ∼20-residue acidic region centered on Thr-51. This central region therefore becomes more compact and more negatively charged, with increasing intramolecular contacts to basic sequence motifs near the N and C termini. Although flexibility is decreased in the central region of phospho-PAGE4, the polypeptide chain remains highly dynamic overall. PAGE4 utilizes a transient helical structure adjacent to the central acidic region to bind c-Jun with low affinity in vitro. The binding interaction is attenuated by phosphorylation at Thr-51, most likely because of masking the effects of the more compact phosphorylated state. Therefore, phosphorylation of PAGE4 leads to conformational shifts in the dynamic ensemble, with large functional consequences. The changes in the structural ensemble induced by posttranslational modifications are similar conceptually to the conformational switching events seen in some marginally stable ("metamorphic") folded proteins in response to mutation or environmental triggers.

Cancer/testis antigen PAGE4, a regulator of c-Jun transactivation, is phosphorylated by homeodomain-interacting protein kinase 1, a component of the stress-response pathway

Prostate-associated gene 4 (PAGE4) is a cancer/testis antigen that is typically restricted to the testicular germ cells but is aberrantly expressed in cancer. Furthermore, PAGE4 is developmentally regulated with dynamic expression patterns in the developing prostate and is also a stress-response protein that is upregulated in response to cellular stress. PAGE4 interacts with c-Jun, which is activated by the stress-response kinase JNK1, and plays an important role in the development and pathology of the prostate gland. Here, we have identified homeodomain-interacting protein kinase 1 (HIPK1), also a component of the stress-response pathway, as a kinase that phosphorylates PAGE4 at T51. We show that phosphorylation of PAGE4 is critical for its transcriptional activity since mutating this T residue abolishes its ability to potentiate c-Jun transactivation. In vitro single molecule FRET indicates phosphorylation results in compaction of (still) intrinsically disordered PAGE4. Interestingly, however, while our previous observations indicated that the wild-type nonphosphorylated PAGE4 protein interacted with c-Jun [RajagopalanK. et al. (2014) Biochim, Biophys. Acta1842, 154−16324263171], here we show that phosphorylation of PAGE4 weakens its interaction with c-Jun in vitro. These data suggest that phosphorylation induces conformational changes in natively disordered PAGE4 resulting in its decreased affinity for c-Jun to promote interaction of c-Jun with another, unidentified, partner. Alternatively, phosphorylated PAGE4 may induce transcription of a novel partner, which then potentiates c-Jun transactivation. Regardless, the present results clearly implicate PAGE4 as a component of the stress-response pathway and uncover a novel link between components of this pathway and prostatic development and disease.

The Stress-response protein prostate-associated gene 4, interacts with c-Jun and potentiates its transactivation

The Cancer/Testis Antigen (CTA), Prostate-associated Gene 4 (PAGE4), is a stress-response protein that is upregulated in prostate cancer (PCa) especially in precursor lesions that result from inflammatory stress. In cells under stress, translocation of PAGE4 to mitochondria increases while production of reactive oxygen species decreases. Furthermore, PAGE4 is also upregulated in human fetal prostate, underscoring its potential role in development. However, the proteins that interact with PAGE4 and the mechanisms underlying its pleiotropic functions in prostatic development and disease remain unknown. Here, we identified c-Jun as a PAGE4 interacting partner. We show that both PAGE4 and c-Jun are overexpressed in the human fetal prostate; and in cell-based assays, PAGE4 robustly potentiates c-Jun transactivation. Single-molecule Förster resonance energy transfer experiments indicate that upon binding to c-Jun, PAGE4 undergoes conformational changes. However, no interaction is observed in presence of BSA or unilamellar vesicles containing the mitochondrial inner membrane diphosphatidylglycerol lipid marker cardiolipin. Together, our data indicate that PAGE4 specifically interacts with c-Jun and that, conformational dynamics may account for its observed pleiotropic functions. To our knowledge, this is the first report demonstrating crosstalk between a CTA and a proto-oncogene. Disrupting PAGE4/c-Jun interactions using small molecules may represent a novel therapeutic strategy for PCa.

Stromal insulin-like growth factor binding protein 3 (IGFBP3) is elevated in the diseased human prostate and promotes ex vivo fibroblast-to-myofibroblast differentiation

Dysregulation of the IGF axis is implicated in the development of benign prostatic hyperplasia (BPH) and prostate cancer (PCa), 2 of the most common diseases affecting elderly males. PCa is the second leading cause of male-related cancer death in Western societies. Although distinct pathologies, BPH and PCa are both characterized by extensive stromal remodeling, in particular fibroblast-to-myofibroblast differentiation, thought to be induced by elevated local production of TGFβ1. We previously showed that TGFβ1-mediated fibroblast-to-myofibroblast differentiation of primary human prostatic stromal cells resulted in the dsyregulation of several components of the IGF axis, including the induction of IGF binding protein 3 (IGFBP3). Using isoform-specific lentiviral-mediated knockdown, we demonstrate herein that IGFBP3 is essential for TGFβ1-mediated differentiation. Although recombinant human IGFBP3 alone was not sufficient to induce differentiation, IGFBP3 synergistically potentiated TGFβ1-mediated stromal remodeling predominantly via an IGF-independent mechanism. Consistent with these in vitro findings, IGFBP3 immunohistochemistry revealed elevated levels of IGFBP3 in the hyperplastic fibromuscular stroma of BPH specimens and in the tumor-adjacent stroma of high-grade PCa. Collectively these data indicate that the dysregulation of the stromal IGF axis, in particular elevated IGFBP3, plays a crucial role in fibroblast-to-myofibroblast differentiation in the diseased prostatic stroma and indicate the therapeutic potential of inhibiting stromal remodeling and the resulting dysregulation of the stromal IGF axis as a novel strategy for the treatment of advanced PCa and BPH.

In vitro model systems to study androgen receptor signaling in prostate cancer

Prostate cancer (PCa) is one of the most common causes of male cancer-related death in Western nations. The cellular response to androgens is mediated via the androgen receptor (AR), a ligand-inducible transcription factor whose dysregulation plays a key role during PCa development and progression following androgen deprivation therapy, the current mainstay systemic treatment for advanced PCa. Thus, a better understanding of AR signaling and new strategies to abrogate AR activity are essential for improved therapeutic intervention. Consequently, a large number of experimental cell culture models have been established to facilitate in vitro investigations into the role of AR signaling in PCa development and progression. These different model systems mimic distinct stages of this heterogeneous disease and exhibit differences with respect to AR expression/status and androgen responsiveness. Technological advances have facilitated the development of in vitro systems that more closely reflect the physiological setting, for example via the use of three-dimensional coculture to study the interaction of prostate epithelial cells with the stroma, endothelium, immune system and tissue matrix environment. This review provides an overview of the most commonly used in vitro cell models currently available to study AR signaling with particular focus on their use in addressing key questions relating to the development and progression of PCa. It is hoped that the continued development of in vitro models will provide more biologically relevant platforms for mechanistic studies, drug discovery and design ensuring a more rapid transfer of knowledge from the laboratory to the clinic.