Androgen-independent prostate cancer: potential role of androgen and ErbB receptor signal transduction crosstalk

Identification of a novel six autophagy-related genes signature for the prognostic and a miRNA-related autophagy predictor for anti-PD-1 therapy responses in prostate cancer

Background

Autophagy is a highly conserved homeostatic process in the human body that is responsible for the elimination of aggregated proteins and damaged organelles. Several autophagy-related genes (ARGs) contribute to the process of tumorigenesis and metastasis of prostate cancer (PCa). Also, miRNAs have been proven to modulate autophagy by targeting some ARGs. However, their potential role in PCa still remains unclear.

Methods

An univariate Cox proportional regression model was used to identify 17 ARGs associated with the overall survival (OS) of PCa. Then, a multivariate Cox proportional regression model was used to construct a 6 autophagy-related prognostic genes signature. Patients were divided into low-risk group and high-risk group using the median risk score as a cutoff value. High-risk patients had shorter OS than low-risk patients. Furthermore, the signature was validated by ROC curves. Regarding mRNA and miRNA, 12 differentially expressed miRNAs (DEMs) and 1073 differentially expressed genes (DEGs) were detected via the GEO database. We found that miR-205, one of the DEMs, was negatively regulated the expression of ARG (NKX2–3). Based on STRING analysis results, we found that the NKX2–3 was moderately related to the part of genes among the 6 autophagy-related genes prognostic signature. Further, NKX 2–3 was significantly correlated with OS and some clinical parameters of PCa by cBioProtal. By gene set enrichment analysis (GSEA). Lastly, we demonstrated that the association between NKX2–3 and tumor mutation burden (TMB) and PDCD1 (programmed cell death 1) of PCa.

Results

We identified that the six ARGs expression patterns are independent predictors of OS in PCa patients. Furthermore, our results suggest that ARGs and miRNAs are inter-related. MiR-205 was negatively regulated the expression of ARG (NKX2–3). Further analysis demonstrated that NKX2–3 may be a potential biomarker for predicting the efficacy of anti-PD-1 therapy in PCa.

Conclusions

The current study may offer a novel autophagy-related prognostic signature and may identify a promising miRNA-ARG pathway for predicting the efficacy of anti-PD-1 therapy in PCa.

Peptide-Based Therapeutics for Oncology

The development of peptide-based drugs, which are usually synthetic analogues of endogenous peptides, is currently one of the most topical directions in drug development. Among them, antitumor peptide-based drugs are of great interest. Anticancer peptides can be classified into three main groups based on their mechanism of action: inhibitory, necrosis-inducing and pro-apoptotic peptides. As an antitumor therapy, peptides are considered to have at least the same efficacy as chemotherapy or surgical treatment, but offer advantages in terms of safety and tolerability, given that chemotherapy is usually characterized by severe adverse effects, and surgery carries additional risks for patients. Short peptides have a number of benefits over other molecules. First, compared with full-length proteins and antibodies, short peptides are less immunogenic, more stable ex-vivo (prolonged storage at room temperature), and have better tumor or organ permeability. Moreover, the production of such short peptide-based drugs is more cost effective. Second, in comparison with small organic molecules, peptides have higher efficacy and specificity. Finally, due to the fact that the main products of peptide metabolism are amino acids, these drugs are usually characterized by lower toxicity. Short peptides have a highly selective mechanism of action, thereby demonstrating low toxicity. Furthermore, with the addition of different stabilizing structural modifications, as well as novel drug delivery systems, the peptide-based drugs are proving to be promising therapeutics for cancer mono- or polytherapy. However, challenges remain including that endogenous and synthetic peptide molecules can be oncogenic. Therefore, it is important to investigate whether peptides contribute to tumor growth. In order to answer such questions, numerous preclinical and clinical studies of peptide-based therapeutics are currently being conducted.

Gene Expression Signature Predictive of Neuroendocrine Transformation in Prostate Adenocarcinoma

Neuroendocrine prostate cancer (NEPC) can arise de novo, but much more commonly occurs as a consequence of a selective pressure from androgen deprivation therapy or androgen receptor antagonists used for prostate cancer (PCa) treatment. The process is known as neuroendocrine transdifferentiation. There is little molecular characterization of NEPCs and consequently there is no standard treatment for this kind of tumors, characterized by highly metastases rates and poor survival. For this purpose, we profiled 54 PCa samples with more than 10-years follow-up for gene and miRNA expression. We divided samples into two groups (NE-like vs. AdenoPCa), according to their clinical and molecular features. NE-like tumors were characterized by a neuroendocrine fingerprint made of known neuroendocrine markers and novel molecules, including long non-coding RNAs and components of the estrogen receptor signaling. A gene expression signature able to predict NEPC was built and tested on independently published datasets. This study identified molecular features (protein-coding, long non-coding, and microRNAs), at the time of surgery, that may anticipate the NE transformation process of prostate adenocarcinoma. Our results may contribute to improving the diagnosis and treatment of this subgroup of tumors for which traditional therapy regimens do not show beneficial effects.

pathfindR: An R Package for Comprehensive Identification of Enriched Pathways in Omics Data Through Active Subnetworks

Pathway analysis is often the first choice for studying the mechanisms underlying a phenotype. However, conventional methods for pathway analysis do not take into account complex protein-protein interaction information, resulting in incomplete conclusions. Previously, numerous approaches that utilize protein-protein interaction information to enhance pathway analysis yielded superior results compared to conventional methods. Hereby, we present pathfindR, another approach exploiting protein-protein interaction information and the first R package for active-subnetwork-oriented pathway enrichment analyses for class comparison omics experiments. Using the list of genes obtained from an omics experiment comparing two groups of samples, pathfindR identifies active subnetworks in a protein-protein interaction network. It then performs pathway enrichment analyses on these identified subnetworks. To further reduce the complexity, it provides functionality for clustering the resulting pathways. Moreover, through a scoring function, the overall activity of each pathway in each sample can be estimated. We illustrate the capabilities of our pathway analysis method on three gene expression datasets and compare our results with those obtained from three popular pathway analysis tools. The results demonstrate that literature-supported disease-related pathways ranked higher in our approach compared to the others. Moreover, pathfindR identified additional pathways relevant to the conditions that were not identified by other tools, including pathways named after the conditions.

Data analysis algorithm for the development of extracellular miRNA-based diagnostic systems for prostate cancer

Urine of prostate cancer (PCa) carries miRNAs originated from prostate cancer cells as a part of both nucleoprotein complexes and cell-secreted extracellular vesicles. The analysis of such miRNA-markers in urine can be a convenient option for PCa screening. The aims of this study were to reveal miRNA–markers of PCa in urine and design a robust and precise diagnostic test, based on miRNA expression analysis. The expression analysis of the 84 miRNAs in paired urine extracellular vesicles (EVs) and cell free urine supernatant samples from healthy donors, patients with benign and malignant prostate tumours was done using miRCURY LNA miRNA qPCR Panels (Exiqon, Denmark). Sets of miRNAs differentially expressed between the donor groups were found in urine EVs and urine supernatant. Diagnostically significant miRNAs were selected and algorithm of data analysis, based on expression data on 24-miRNA in urine and obtained using 17 analytical systems, was designed. The developed algorithm of data analysis describes a series of steps necessary to define cut-off values and sequentially analyze miRNA expression data according to the cut-offs to facilitate classification of subjects in case/control groups and allows to detect PCa patients with 97.5% accuracy.

Discovery of circulating microRNAs associated with human prostate cancer using a mouse model of disease

Circulating microRNAs (miRNAs) are emerging as useful non-invasive markers of disease. The objective of this study was to use a mouse model of prostate cancer as a tool to discover serum miRNAs that could be assessed in a clinical setting. Global miRNA profiling identified 46 miRNAs at significantly altered levels (p ≤ 0.05) in the serum of TRansgenic Adenocarcinoma of Mouse Prostate (TRAMP) mice with advanced prostate cancer compared to healthy controls. A subset of these miRNAs with known human homologues were validated in an independent cohort of mice and then measured in serum from men with metastatic castration-resistant prostate cancer (mCRPC; n = 25) or healthy men (n = 25). Four miRNAs altered in mice, mmu-miR-141, mmu-miR-298, mmu-miR-346 and mmu-miR-375, were also found to be at differential levels in the serum of men with mCRPC. Three of these (hsa-miR-141, hsa-miR-298 and hsa-miR-375) were upregulated in prostate tumors compared with normal prostate tissue, suggesting that they are released into the blood as disease progresses. Moreover, the intra-tumoral expression of hsa-miR-141 and hsa-miR-375 were predictors of biochemical relapse after surgery. This study is the first to demonstrate that specific serum miRNAs are common between human prostate cancer and a mouse model of the disease, highlighting the potential of such models for the discovery of novel biomarkers.

Network-based prediction for sources of transcriptional dysregulation using latent pathway identification analysis

Understanding the systemic biological pathways and the key cellular mechanisms that dictate disease states, drug response, and altered cellular function poses a significant challenge. Although high-throughput measurement techniques, such as transcriptional profiling, give some insight into the altered state of a cell, they fall far short of providing by themselves a complete picture. Some improvement can be made by using enrichment-based methods to, for example, organize biological data of this sort into collections of dysregulated pathways. However, such methods arguably are still limited to primarily a transcriptional view of the cell. Augmenting these methods still further with networks and additional -omics data has been found to yield pathways that play more fundamental roles. We propose a previously undescribed method for identification of such pathways that takes a more direct approach to the problem than any published to date. Our method, called latent pathway identification analysis (LPIA), looks for statistically significant evidence of dysregulation in a network of pathways constructed in a manner that implicitly links pathways through their common function in the cell. We describe the LPIA methodology and illustrate its effectiveness through analysis of data on (i) metastatic cancer progression, (ii) drug treatment in human lung carcinoma cells, and (iii) diagnosis of type 2 diabetes. With these analyses, we show that LPIA can successfully identify pathways whose perturbations have latent influences on the transcriptionally altered genes.

Trihydrophobin 1 attenuates androgen signal transduction through promoting androgen receptor degradation

The androgen-signaling pathway plays critical roles in normal prostate development, benign prostatic hyperplasia, established prostate cancer, and in prostate carcinogenesis. In this study, we report that trihydrophobin 1 (TH1) is a potent negative regulator to attenuate the androgen signal-transduction cascade through promoting androgen receptor (AR) degradation. TH1 interacts with AR both in vitro and in vivo, decreases the stability of AR, and promotes AR ubiquitination in a ligand-independent manner. TH1 also associates with AR at the active androgen-responsive prostate-specific antigen (PSA) promoter in the nucleus of LNCaP cells. Decrease of endogenous AR protein by TH1 interferes with androgen-induced luciferase reporter expression and reduces endogenous PSA expression. Taken together, these results indicate that TH1 is a novel regulator to control the duration and magnitude of androgen signal transduction and might be directly involved in androgen-related developmental, physiological, and pathological processes.

Epidermal growth factor receptor expression escapes androgen regulation in prostate cancer: a potential molecular switch for tumour growth

Androgen deprivation therapy reduces prostate cancer (PCa) tumour growth; however, disease relapse often ensues independently of androgen stimulation, producing androgen-refractory tumours with increased invasion, proliferation, and malignancy. Androgens downregulate epidermal growth factor receptor (EGFR) in normal prostate but not in PCa. Thus, loss of EGFR regulation and altered signalling may, in part, explain the transition of prostate tumours from androgen dependent to androgen independent. Studies in animal models, PCa cell lines, and tumour specimens suggest that androgens modulate prostate growth and function through mechanisms that involve ‘cross-talk’ between androgen receptor (AR) and growth factor receptor signalling pathways. The objective of this review is to discuss the paradoxical relationship between androgen regulation of EGFR in normal prostate and PCa. We reviewed the literature from mid-1980s through 2009 to assess the relationship between androgens and EGFR function in modulating the growth of normal prostate and PCa. Loss of androgen regulation of EGFR in PCa may be responsible for increased tumour growth, invasion, and metastasis, with important implications on the clinical management of PCa. We advance the hypothesis that a molecular switch, responsible for downregulating EGFR expression by androgens in the normal prostate, is either lost or modified in PCa.

Predictive value of PTEN and AR coexpression of sustained responsiveness to hormonal therapy in prostate cancer--a pilot study

One limitation of current biochemical or histologic analysis of advanced prostate cancer (PC; T(3)/T(4) +/- N(x) M(x)) is the ability to identify on first diagnostic biopsy patients who will make a durable response to hormone ablation therapy. The aim of this study was to assess the predictive value (sustained response to hormonal therapy and clinical outcome (relapse-free and overall survival)) of phosphatase and tensin homolog (PTEN) and the androgen receptor (AR) immunoexpression in the presenting biopsy. Analysis was performed on 47 samples (10 cases of benign prostatic hyperplasia and 37 hormone-naive PCs). Patients selected represented two stages in the natural history of PC: The "clinical metastatic androgen-responsive" (androgen-dependent PC, ADPC) and the "clinical metastatic androgen-resistant" (androgen-independent PC, AIPC). Reduced immunoreactivity (IR) of either or both PTEN/AR in the initial hormone-naive PC samples was observed with increased frequency in AIPCs. In the ADPC group, low PTEN and/or AR-IR was associated with a shorter median relapse-free survival, i.e., at 30 months after surgery, the probability of relapse-free survival for high expressors of PTEN and AR was 85.7% (SEM = 9.3) compared with only 16.6% (SEM = 15.2) in low expressors. At 36 months, only 28.5% (SEM = 9.3) of ADPC high expressors had experienced a biochemical relapse compared with 100% of low expressors (hazard ratio, 4.6; 95% confidence interval, 4.7-146.8). Further studies analyzing the coexpression of PTEN and AR should be undertaken to validate this pilot study and the utility of these biomarkers in routine histopathologic workup of patients with PC.

A functionally significant cross-talk between androgen receptor and ErbB2 pathways in estrogen receptor negative breast cancer

Recent studies have identified novel subgroups in ER-negative breast cancer based on the expression pattern of androgen receptor (AR). One subtype (molecular apocrine) has an over-expression of steroid-response genes and ErbB2. Using breast cancer cell lines with molecular apocrine features, we demonstrate a functional cross-talk between AR and ErbB2 pathways. We show that stimulation of AR and ErbB2 pathways leads to the cross-regulation of gene expression for AR, ErbB2, FOXA1, XBP1, TFF3, and KLK3. As opposed to the physiologic transient phosphorylation of extracellular signal-regulated kinase (ERK1/2) observed with the testosterone treatment, we demonstrate that the addition of ErbB2 inhibition leads to a persistent phosphorylation of ERK1/2, which negatively regulates the downstream signaling and cell growth. This suggests a mechanism for the cross-talk involving the ERK pathway. Moreover, testosterone stimulates the proliferation of molecular apocrine breast cell lines, and this effect can be reversed using antiandrogen flutamide and anti-ErbB2 AG825. Conversely, the growth stimulatory effect of heregulin can also be inhibited with flutamide, suggesting a cross-talk between the AR and ErbB2 pathways affecting cell proliferation. Importantly, there is a synergy with the combined use of flutamide and AG825 on cell proliferation and apoptosis, which indicates a therapeutic advantage in the combined blockage of AR and ErbB2 pathways.

Dietary agents in the chemoprevention of prostate cancer

Nutritional factors have been estimated to contribute 20-60% of cancers around the globe, and almost one-third of deaths are being reported in Western countries. According to estimates by the American Cancer Society, during the year 2005 about 232,090 new cases of prostate cancer will be diagnosed alone in the United States and 30,350 men will die of this disease. The high incidence and long latency period of prostate cancer offer plenty of time to pursue strategies toward prevention and/or treatment to suppress or revert this disease. Epidemiological evidence suggests that plant-based dietary agents decrease the risk of some types of human cancer, including prostate cancer. Intake of 400-600 g/day of fruits and vegetables is associated with reduced risk of several cancers. The use of micronutrients and/or other phenolic agents in the diet or synthetic exogenous supplements to prevent neoplastic transformation of normal cells or to slow the progression of established malignant changes in cancer cells is termed "chemoprevention." Considerable attention has been devoted to identify plant-based dietary agents that may serve as natural inhibitors of prostate carcinogenesis. Much progress has been made in the last decade in this area of investigation through identification of pathways that play important roles in prostate tumorigenesis. This article summarizes epidemiological, clinical, and mechanistic studies and the significance of plant-derived dietary agents such as flavonoids, indoles, isothiocyanates, phenolics, monoterpenes, and complementary and alternative agents in the management of prostate cancer with recommendations for future studies to advance this area of research.

EGFR and Her-2 regulate the constitutive activation of NF-kappaB in PC-3 prostate cancer cells

BACKGROUND

The mechanism through which NF-kappaB (NF-kappaB) is constitutively activated in prostate cancer cells remains unclear. We investigated whether members of the ErbB family of epidermal growth factor receptors (EGFR) are involved in the constitutive activation of NF-kappaB in prostate cancer cell lines.

METHODS AND RESULTS

EGFR, Her-2, and ErbB3 are expressed and constitutively activated in PC-3, DU145, and LNCaP prostate cancer cells lines. Using several pharmacological ErbB inhibitors, we demonstrate that EGFR and Her-2 are involved in the constitutive activation of NF-kappaB in PC-3 cells through two different mechanisms. EGFR activates NF-kappaB through the phosphorylation of IkappaBalpha on serines 32/36 thereby influencing the nuclear translocation of the p65 subunit. In contrast, Her-2 activates NF-kappaB independently of IkappaBalpha phosphorylation on serines 32/36.

CONCLUSION

This study directly implicates ErbB receptors in the activation of NF-kappaB in PC-3 prostate cancer cells.

Heregulin-induced activation of HER2 and HER3 increases androgen receptor transactivation and CWR-R1 human recurrent prostate cancer cell growth

PURPOSE

The androgen receptor (AR) is a ligand-dependent transcription factor that mediates gene expression and growth of normal and malignant prostate cells. In prostate tumors that recur after androgen withdrawal, the AR is highly expressed and transcriptionally active in the absence of testicular androgens. In these "androgen-independent" tumors, alternative means of AR activation have been invoked, including regulation by growth factors and their receptors in prostate cancer recurrence.

EXPERIMENTAL DESIGN AND RESULTS

In this report, we show that HER receptor tyrosine kinases 1 through 4 are expressed in the CWR-R1 recurrent prostate cancer cell line; their stimulation by epidermal growth factor (EGF) and heregulin activates downstream signaling, including mitogen-activated protein kinase and phosphatidylinositol-3 kinase and Akt pathways. We show that heregulin activates HER2 and HER3 and increases androgen-dependent AR transactivation of reporter genes in CWR-R1 cells. Tyrosine phosphorylation of HER2 and HER3, AR transactivation, and cell proliferation induced by heregulin were more potently inhibited by the EGFR/HER2 dual tyrosine kinase inhibitor GW572016 (lapatinib) than the EGFR-specific inhibitor ZD1839 (gefitinib). Basal proliferation in the absence of growth factors was also inhibited by GW572016 to a greater extent than ZD1839, suggesting that low level HER2/HER3 activation perhaps by an autocrine pathway contributes to the proliferation signal.

CONCLUSIONS

These data indicate that heregulin signaling through HER2 and HER3 increases AR transactivation and alters growth in a recurrent prostate cancer cell line. Therefore, inhibition of low-level HER2 signaling may be a potential novel therapeutic strategy in prostate cancer.

5alpha-Androstane-3alpha,17beta-diol activates pathway that resembles the epidermal growth factor responsive pathways in stimulating human prostate cancer LNCaP cell proliferation

5alpha-Androstane-3alpha,17beta-diol (3alpha-diol) is considered to have no androgenic effects in androgen target organs unless it is oxidized to 5alpha-dihydrotestosterone (5alpha-DHT). We used microarray and bioinformatics to identify and compare 3alpha-diol and 5alpha-DHT responsive gene in human prostate LNCaP cells. Through a procedure called 'hypervariable determination', a similar set of 30 responsive genes involving signal transduction, transcription regulation, and cell proliferation were selected in 5alpha-DHT-, 3alpha-diol-, and epidermal growth factor (EGF)-treated samples. F-means cluster and networking procedures showed that the responsive pattern of these genes was more closely related between 3alpha-diol and EGF than between 5alpha-DHT and 3alpha-diol treatments. We conclude that 3alpha-diol is capable of stimulating prostate cell proliferation by eliciting EGF-like pathway in conjunction with androgen receptor pathway.

Specificity and heregulin regulation of Ebp1 (ErbB3 binding protein 1) mediated repression of androgen receptor signalling

Although ErbB receptors have been implicated in the progression of prostate cancer, little is known about proteins that may mediate their interactions with the androgen receptor (AR). Ebp1, a protein cloned via its association with the ErbB3 receptor, binds the AR and inhibits androgen-regulated transactivation of wild-type AR in COS cells. As the complement of coregulators in different cells are important for AR activity, we determined the effect of Ebp1 on AR function in prostate cancer cell lines. In addition, we examined the regulation of Ebp1 function by the ErbB3/4 ligand heregulin (HRG). In this study, we demonstrate, using several natural AR-regulated promoters, that Ebp1 repressed transcriptional activation of wild-type AR in prostate cancer cell lines. Downregulation of Ebp1 expression in LNCaP cells using siRNA resulted in activation of AR in the absence of androgen. Ebp1 associated with ErbB3 in LNCaP cells in the absence of HRG, but HRG induced the dissociation of Ebp1 from ErbB3. In contrast, HRG treatment enhanced both the association of Ebp1 with AR and also the ability of Ebp1 to repress AR transactivation. These studies suggest that Ebp1 is an AR corepressor whose biological activity can be regulated by the ErbB3 ligand, HRG.

Prevention of Hormone-Related Cancers: Prostate Cancer

Androgens are known to play an important role in normal prostate development, benign prostatic hyperplasia, established prostate cancer, and in prostate carcinogenesis. However, despite convincing experimental and clinical evidence, the epidemiologic data correlating sex steroid levels with disease risk is inconsistent. More recent work has focused on studies of polymorphisms in germ-line DNA in an effort to develop polygenic models of prostate cancer susceptibility and prognosis. Such models have the potential to aid in the selection of men for specific chemopreventive interventions and to help determine which men with localized prostate cancer are most likely to benefit from aggressive therapy. In this review, we will provide a brief summary of androgen metabolic pathways followed by an assessment of the epidemiology literature addressing the relationship between androgens and prostate cancer. Finally, we will address the two major questions that have arisen in response to the recently published results from the Prostate Cancer Prevention Trial: Who are the best candidates for finasteride chemoprevention, and what are the clinical implications of the high prevalence of prostate cancer that was detected in men with prostate-specific antigen levels in the so-called “normal” range?

Lycopene: modes of action to promote prostate health

Epidemiological evidence strongly suggests that lycopene consumption contributes to prostate cancer risk reduction. Preclinical studies show that lycopene acts via different mechanisms, which have the potential to cooperate in reducing the proliferation of normal and cancerous prostate epithelial cells, in reducing DNA damage, and in improving oxidative stress defense. The mechanisms include inhibition of prostatic IGF-I signaling, IL-6 expression, and androgen signaling. Moreover, lycopene improves gap-junctional communication and induces phase II drug metabolizing enzymes as well as oxidative defense genes. These findings provide plausible explanations for the epidemiological findings how lycopene can contribute to reduced prostate cancer risk. The novel finding that lycopene reduces local androgen signaling in the prostate suggests also efficacy in prevention of benign prostate hyperplasia. Intervention trials in humans are required to finally prove clinical efficacy of the lycopene molecule in prostate health.

Novel molecular aspects of prostate carcinogenesis

Prostate adenocarcinoma is one of the most frequently diagnosed forms of cancer in the male population of the Western world. The pivotal role of androgen and its receptor in this disease has been abundantly documented and indeed, chemical castration and treatment with antiandrogens are now standard therapies. However, relapse is often observed after 18-24 months, due to the remarkable ability of prostate tumour cells to adapt to low or undetectable androgen levels. Amplification and mutations of the androgen receptor (AR) gene have been described as well as alterations in cofactor expression and crosstalk with other signalling pathways. Another recent line of research focused on the re-programming of gene expression taking place in prostate tumours. Global expression profiling of normal and cancerous prostate tissues led to the identification of tumour-distinctive patterns. Validation studies are currently underway to identify novel drug targets as well as diagnostic and outcome prediction markers.

Proteomic identification of 14-3-3 sigma as a common component of the androgen receptor and the epidermal growth factor receptor signaling pathways of the human prostate epithelial cell line M12

The epidermal growth factor receptor and androgen receptor (AR) both play major roles in the control of prostate growth. Our hypothesis is that shared downstream components of these two signaling pathways are significant participants in androgen-independent growth. Our first objective was to identify proteins whose activation and/or expression in AR-positive prostate epithelial cells are induced by both epidermal growth factor (EGF) and dihydrotestosterone (DHT). AR expression was induced in a tumorigenic, metastatic subline of the SV40 large T-antigen immortalized human prostate epithelial subline M12 by stable transfection with human wild-type AR cDNA. These M12AR (+) cells with functional AR were treated in parallel with EGF (10 ng/ml) or DHT (10(-8) M) for 24 h before 2D gel electrophoresis and Western immunoblotting with antiphosphotyrosine monoclonal antibody. Coomassie blue-stained spots on a 2D gel run in parallel were aligned with the phosphoproteins on the Western immunoblot, and identified by matrix-assisted laser desorption ionization/time-of-flight mass spectroscopy. The most interesting of the seven proteins that appeared to be phosphorylated by these criteria was 14-3-3 protein sigma. Protein extracted after either EGF or DHT treatment, immunoprecipitated with antiphosphotyrosine monoclonal antibody, and immunoblotted by anti-14-3-3 sigma confirmed phosphorylation of 14-3-3 sigma. Addition of either DHT or EGF to the M12AR(+) cells induced subcellular migration of 14-3-3 sigma and activated a 14-3-3 sigma reporter construct. Immunohistochemical analysis revealed nuclear localization of 14-3-3 sigma in higher Gleason grade prostate cancers relative to benign glands. These findings implicate 14-3-3 sigma in the development of human prostate cancer cells and could provide a new target for intervention in prostate cancer.

Molecular alterations associated with LNCaP cell progression to androgen independence

BACKGROUND

There is no effective therapy currently available for androgen-independent (AI) prostate cancer (CaP). This is largely due to lack of information about the molecular mechanisms by which androgen-dependent tumor cells progress to androgen independence. In this study, we investigated molecular alterations occurring in AI LNCaP cells.

METHODS

We established and characterized three AI LNCaP sublines that exhibited a wide range of cytogenetic alterations. In order to understand why androgen-sensitive LNCaP cells can survive in an androgen-deprived environment, we analyzed the expression of signaling proteins associated with proliferation and survival of AI cells. In addition, gene expression profiling was performed to gain insight into molecular alterations in these LNCaP sublines.

RESULTS

These LNCaP sublines exhibited heightened levels of androgen receptor (AR), HER2, MAPK, serine 473-phosphorylated Akt, and Bcl-2, implicating these proteins as mediators of AI growth. Gene expression profiling identified a common set of 66 genes that were differentially expressed in all three sublines compared to the parental LNCaP cells. Of these, 32 were apparently androgen regulated, while the remainder comprised an expression signature specific for androgen independence.

CONCLUSION

We have developed AI LNCaP cell models and identified several genes that are specifically expressed in these models. Elucidating the relative importance of these genetic changes will help define the molecular mechanism by which CaP progresses to androgen independence.