Systematic analysis of microRNAs targeting the androgen receptor in prostate cancer cells

Stromal Androgen Receptor in Prostate Cancer Development and Progression

Prostate cancer development and progression is the result of complex interactions between epithelia cells and fibroblasts/myofibroblasts, in a series of dynamic process amenable to regulation by hormones. Whilst androgen action through the androgen receptor (AR) is a well-established component of prostate cancer biology, it has been becoming increasingly apparent that changes in AR signalling in the surrounding stroma can dramatically influence tumour cell behavior. This is reflected in the consistent finding of a strong association between stromal AR expression and patient outcomes. In this review, we explore the relationship between AR signalling in fibroblasts/myofibroblasts and prostate cancer cells in the primary site, and detail the known functions, actions, and mechanisms of fibroblast AR signaling. We conclude with an evidence-based summary of how androgen action in stroma dramatically influences disease progression.

Epigenomic Regulation of Androgen Receptor Signaling: Potential Role in Prostate Cancer Therapy

Androgen receptor (AR) signaling remains the major oncogenic pathway in prostate cancer (PCa). Androgen-deprivation therapy (ADT) is the principle treatment for locally advanced and metastatic disease. However, a significant number of patients acquire treatment resistance leading to castration resistant prostate cancer (CRPC). Epigenetics, the study of heritable and reversible changes in gene expression without alterations in DNA sequences, is a crucial regulatory step in AR signaling. We and others, recently described the technological advance Chem-seq, a method to identify the interaction between a drug and the genome. This has permitted better understanding of the underlying regulatory mechanisms of AR during carcinogenesis and revealed the importance of epigenetic modifiers. In screening for new epigenomic modifiying drugs, we identified SD-70, and found that this demethylase inhibitor is effective in CRPC cells in combination with current therapies. The aim of this review is to explore the role of epigenetic modifications as biomarkers for detection, prognosis, and risk evaluation of PCa. Furthermore, we also provide an update of the recent findings on the epigenetic key processes (DNA methylation, chromatin modifications and alterations in noncoding RNA profiles) involved in AR expression and their possible role as therapeutic targets.

Changes in the Level of Circulating hsa-miR-297 and hsa-miR-19b-3p miRNA Are Associated with Generalization of Prostate Cancer

We performed diagnostic classification of plasma specimens from patients with non-metastatic and metastatic prostate cancer based on pairs of miRNA that have no individual diagnostic significance. Of 230 miRNA detected in plasma specimens, 3 pairs were diagnostically significant. The miRNA pair hsa-miR-19b-3p and hsa-miR-297 demonstrated highest sensitivity and specificity. Among common target genes of these miRNA, CFL2 gene associated with cell mobility was detected.

Prognostic value of cross-omics screening for kidney clear cell renal cancer survival

Background

Kidney renal clear cell carcinoma (KIRC) is a type of cancer that is resistant to chemotherapy and radiotherapy and has limited treatment possibilities. Large-scale molecular profiling of KIRC tumors offers a great potential to uncover the genetic and epigenetic changes underlying this disease and to improve the clinical management of KIRC patients. However, in practice the clinicians and researchers typically focus on single-platform molecular data or on a small set of genes. Using molecular and clinical data of over 500 patients, we have systematically studied which type of molecular data is the most informative in predicting the clinical outcome of KIRC patients, as a standalone platform and integrated with clinical data.

Results

We applied different computational approaches to preselect on survival-predictive genomic markers and evaluated the usability of mRNA/miRNA/protein expression data, copy number variation (CNV) data and DNA methylation data in predicting survival of KIRC patients. Our analyses show that expression and methylation data have statistically significant predictive powers compared to a random guess, but do not perform better than predictions on clinical data alone. However, the integration of molecular data with clinical variables resulted in improved predictions. We present a set of survival associated genomic loci that could potentially be employed as clinically useful biomarkers.

Conclusions

Our study evaluates the survival prediction of different large-scale molecular data of KIRC patients and describes the prognostic relevance of such data over clinical-variable-only models. It also demonstrates the survival prognostic importance of methylation alterations in KIRC tumors and points to the potential of epigenetic modulators in KIRC treatment.

Reviewers

An extended abstract of this research paper was selected for the CAMDA Satellite Meeting to ISMB 2015 by the CAMDA Programme Committee. The full research paper then underwent one round of Open Peer Review under a responsible CAMDA Programme Committee member, Djork-Arné Clevert, PhD (Bayer AG, Germany). Open Peer Review was provided by Martin Otava, PhD (Janssen Pharmaceutica, Belgium) and Hendrik Luuk, PhD (The Centre for Disease Models and Biomedical Imaging, University of Tartu, Estonia). The Reviewer comments section shows the full reviews and author responses.

Electronic supplementary material

The online version of this article (doi:10.1186/s13062-016-0170-1) contains supplementary material, which is available to authorized users.

Differential microRNA expression is associated with androgen receptor expression in breast cancer

The androgen receptor (AR) is frequently expressed in breast cancer; however, its prognostic value remains unclear. AR expression in breast cancer has been associated with improved outcomes in estrogen receptor (ER)‑positive breast cancer compared with ER‑negative disease. Eliminating AR function in breast cancer is critically important for breast cancer progression. However, the mechanism underlying AR regulation remains poorly understood. The study of microRNAs (miRNAs) has provided important insights into the pathogenesis of hormone‑dependent cancer. To determine whether miRNAs function in the AR regulation of breast cancer, the present study performed miRNA expression profiling in AR‑positive and ‑negative breast cancer cell lines. A total of 153 miRNAs were differentially expressed in AR‑positive compared with AR‑negative breast cancer cells; 52 were upregulated and 101 were downregulated. A number of these have been extensively associated with breast cancer cell functions, including proliferation, invasion and drug‑resistance. Furthermore, through pathway enrichment analysis, signaling pathways associated with the prediction targets of the miRNAs were characterized, including the vascular endothelial growth factor and mammalian target of rapamycin signaling pathways. In conclusion, the results of the present study indicated that the expression of miRNAs may be involved in the mechanism underlying AR regulation of breast cancer, and may improve understanding of the role of AR in breast cancer.

The Molecular Evolution of Castration-resistant Prostate Cancer

CONTEXT

Androgen deprivation therapy (ADT) is the backbone of treatment for advanced prostate cancer. However, castration-resistant prostate cancer (CRPC) nearly invariably develops through a range of different molecular mechanisms accompanied by progression to a more aggressive phenotype.

OBJECTIVE

To understand the key molecular mechanisms leading to CRPC and the functional implications of this progression. Understanding molecular evolutionary mechanisms in CRPC is essential for the development of novel curative therapeutic approaches.

EVIDENCE ACQUISITION

A systematic literature search to identify relevant original articles was conducted using PubMed. Findings verified in independent studies and supported by in vivo data were prioritised. From the eligible collection, 50 papers were selected.

EVIDENCE SYNTHESIS

The majority of CRPC tumours harbour alterations in the androgen receptor (AR) at the DNA, RNA, and/or protein level, and/or other alterations involving the AR signalling pathway, so this central molecule is the focus of this review. To survive and resume growth despite low levels of circulating androgens, prostate cancer cells can also adapt androgen synthesis or induce alternative pathways.

CONCLUSIONS

Despite more efficient ADT strategies, most evidence points to persistent AR signalling as a major mechanism of progression to CRPC. Resistance due to transdifferentiation or AR independence is also emerging as a mechanism of resistance. The diversity of potential resistance mechanisms supports the need for combination treatment and serial monitoring for adaptive treatment strategies.

PATIENT SUMMARY

In this review, we summarise how prostate cancer cells evade androgen deprivation therapy and become more aggressive. Defining the molecular mechanisms will be critical for the development of new treatment approaches and hence improved survival.

Identification of miR-30b-3p and miR-30d-5p as direct regulators of androgen receptor signaling in prostate cancer by complementary functional microRNA library screening

The Androgen Receptor (AR) plays a key role in prostate biology and in the progression of prostate cancer (PCa) to castration resistance. The role of microRNAs (miRNAs) in aberrant AR signaling have not been fully characterized. Here we screened a library of 810 miRNA mimics to identify miRNAs that alter AR activity in complementary functional assays including protein lysate microarray (LMA) quantification of AR and PSA protein levels, AR transcriptional reporter activity, and AR-positive PCa cell viability. Candidate AR-regulating miRNAs were verified through AR transcriptional reporter and cell viability assays. MiRNA binding sites were found within the AR 3'-untranslated region (UTR) and within the AR and AR-V7 coding regions. MiRNA activity was characterized by western blotting, 3'-UTR reporter assay, and AR-GFP and AR-V7-GFP reporter assays. Results uncovered miR-30 family members as direct AR inhibitors. Inhibition of endogenous miR-30b-3p and miR-30d-5p enhanced AR expression and androgen-independent cell growth. Droplet digital RT-PCR quantification of miR-30c-5p and miR-30d-5p revealed significantly reduced levels in metastatic castration resistant PCa (CRPC), when compared to healthy prostate tissues. MiR-30d-5p levels were inversely correlated with AR activity, as measured by PSA mRNA, in metastatic CRPC. Collectively, these studies provide a comprehensive evaluation of AR-regulating miRNAs in PCa.

Molecular mechanisms underlying resistance to androgen deprivation therapy in prostate cancer

Prostate cancer (PCa) is the most widely diagnosed male cancer in the Western World and while low- and intermediate-risk PCa patients have a variety of treatment options, metastatic patients are limited to androgen deprivation therapy (ADT). This treatment paradigm has been in place for 75 years due to the unique role of androgens in promoting growth of prostatic epithelial cells via the transcription factor androgen receptor (AR) and downstream signaling pathways. Within 2 to 3 years of ADT, disease recurs-at which time, patients are considered to have castration-recurrent PCa (CR-PCa). A universal mechanism by which PCa becomes resistant to ADT has yet to be discovered. In this review article, we discuss underlying molecular mechanisms by which PCa evades ADT. Several major resistance pathways center on androgen signaling, including intratumoral and adrenal androgen production, AR-overexpression and amplification, expression of AR mutants, and constitutively-active AR splice variants. Other ADT resistance mechanisms, including activation of glucocorticoid receptor and impairment of DNA repair pathways are also discussed. New therapies have been approved for treatment of CR-PCa, but increase median survival by only 2-8 months. We discuss possible mechanisms of resistance to these new ADT agents. Finally, the practicality of the application of "precision oncology" to this continuing challenge of therapy resistance in metastatic or CR-PCa is examined. Empirical validation and clinical-based evidence are definitely needed to prove the superiority of "precision" treatment in providing a more targeted approach and curative therapies over the existing practices that are based on biological "cause-and-effect" relationship.

miR-634 exhibits anti-tumor activities toward hepatocellular carcinoma via Rab1A and DHX33

Deregulation of microRNAs contributes to the aberrant growth of hepatocellular carcinoma (HCC). Here, we showed that miR-634 expression was frequently decreased in HCC. Low miR-634 expression was significantly associated with larger tumor size, poorer tumor differentiation, advanced TNM stage, vascular invasion, absence of tumor capsule and unfavorable overall survival. Overexpression of miR-634 markedly attenuated cell viability, colony formation, tumor growth and metastasis, whereas miR-634 inhibition resulted in the opposite phenotypes. Furthermore, re-introduction of miR-634 induced cell apoptosis in vitro and in vivo. Mechanistically, miR-634 inhibited the expression of Rab1A and DHX33 via directly binding to the 3'-UTR of both genes. In clinical samples, the expression of Rab1A or DHX33 was reversely correlated with miR-634. Re-expression of Rab1A or DHX33 abrogated the miR-634-mediated inhibition of cell proliferation and migration. Collectively, our data suggest a tumor suppressor role of miR-634 in HCC. The newly identified miR-634/Rab1A or miR-634/DHX33 axis serves as a potential therapeutic target for the clinical management.

The expression of microRNA 574-3p as a predictor of postoperative outcome in patients with esophageal squamous cell carcinoma

BACKGROUND

Despite advances in radical esophagectomies and adjuvant therapy, the postoperative prognosis in esophageal squamous cell carcinoma (ESCC) patients remains poor. The aim of this study was to identify a molecular signature to predict postoperative favorable outcomes in patients with ESCC.

METHODS

As a training data set, total RNA was extracted from formalin-fixed paraffin-embedded samples of surgically removed specimens from 19 ESCC patients who underwent curative esophagectomy. The expression of microRNA (miRNA) was detected using a miRNA oligo chip on which 885 genes were mounted. As a validation data set, we obtained frozen samples of surgically resected tumors from 12 independent ESCC patients and the expression of miR-574-3p was detected by quantitative real-time PCR.

RESULTS

Our microarray analysis in the training set patients identified three miRNAs (miR-574-3p, miR-106b, and miR-1303) and five miRNAs (miR-1203, miR-1909, miR-204, miR-371-3p, miR-886-3p) which were differentially expressed between the patients with (n = 14) and without (n = 5) postoperative tumor relapse (p < 0.01 and p < 0.05, respectively). Higher expression of miR-574-3p, which showed the most significant association with non-relapse (p = 0.001), was associated with favorable overall survival (p = 0.016). Real-time PCR experiments on the validation set patients confirmed that higher expression of miR-574-3p was associated with non-tumor relapse (p = 0.029) and better overall survival (p = 0.004).

CONCLUSIONS

Our results suggest that the aberrant expression of the miRNAs identified in this study plays key roles in the progression of ESCC. miR-574-3p was suggested to have a tumor suppressor effect, and thus, to be a predictor of postoperative outcome in patients with ESCC.

Systematic drug screening reveals specific vulnerabilities and co-resistance patterns in endocrine-resistant breast cancer

Background

The estrogen receptor (ER) inhibitor tamoxifen reduces breast cancer mortality by 31 % and has served as the standard treatment for ER-positive breast cancers for decades. However, 50 % of advanced ER-positive cancers display de novo resistance to tamoxifen, and acquired resistance evolves in 40 % of patients who initially respond. Mechanisms underlying resistance development remain poorly understood and new therapeutic opportunities are urgently needed. Here, we report the generation and characterization of seven tamoxifen-resistant breast cancer cell lines from four parental strains.

Methods

Using high throughput drug sensitivity and resistance testing (DSRT) with 279 approved and investigational oncology drugs, exome-sequencing and network analysis, we for the first time, systematically determine the drug response profiles specific to tamoxifen resistance.

Results

We discovered emerging vulnerabilities towards specific drugs, such as ERK1/2-, proteasome- and BCL-family inhibitors as the cells became tamoxifen-resistant. Co-resistance to other drugs such as the survivin inhibitor YM155 and the chemotherapeutic agent paclitaxel also occurred.

Conclusion

This study indicates that multiple molecular mechanisms dictate endocrine resistance, resulting in unexpected vulnerabilities to initially ineffective drugs, as well as in emerging co-resistances. Thus, combatting drug-resistant tumors will require patient-tailored strategies in order to identify new drug vulnerabilities, and to understand the associated co-resistance patterns.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2452-5) contains supplementary material, which is available to authorized users.

Phosphorylated mTOR is associated to androgen receptor expression in early triple-negative breast cancer

The significance of phosphorylated mTOR (p-mTOR) expression is unknown in triple-negative breast carcinoma (TNBC). The aims of the present study were to assess the expression of p-mTOR in early TNBC and to evaluate possible correlations between androgen receptor (AR) expression, clinicopathological parameters and disease outcome. Between January 2009 and December 2013, all consecutive patients who were diagnosed and completed the treatment of invasive TNBC at our institution were eligible for this analysis. Patients with stage IV disease were excluded. The evaluation of p-mTOR immunohistochemical staining was semi-quantitatively considering both the percentage of positive tumor cells (range, 0-100%) and staining intensity (range, 0-3+). Ninety-eight TNBC patients were included. Approximately 33% of cases were p-mTOR positive and there was no association between positive immunostaining for p-mTOR and DFS (p=0.74) and OS (p=0.81). p-mTOR positivity was associated with small tumor size (p=0.03) and AR expression (p=0.04). High expression of p-mTOR may drive tumor proliferation in almost one third of TNBC. The biological association between mTOR activation and AR pathway suggests that there may exist a subgroup of TNBC in which the combination of both AR antagonism and mTOR inhibition should have a synergistic effect on cell growth and tumor progression.

The roles of microRNAs in the progression of castration-resistant prostate cancer

Prostate cancer (PCa) is one of the leading causes of cancer-related death in men. PCa is androgen-dependent, and androgen-deprivation therapy is effective for first-line hormonal treatment, but the androgen-independent phenotype of PCa eventually develops, which is difficult to treat and has no effective cure. Recently, microRNAs have been discovered to have important roles in the initiation and progression of PCa, suggesting their use in diagnosis, predicting prognosis and development of treatment for castration-resistant PCa (CRPC). Understanding the networks of microRNAs and their target genes is necessary to ascertain their roles and importance in the development and progression of PCa. This review summarizes the current knowledge about microRNAs regulating PCa progression and elucidates the mechanism of progression to CRPC.

MicroRNA-449a enhances radiosensitivity by downregulation of c-Myc in prostate cancer cells

MicroRNAs (miRNAs) have been reported to be involved in DNA damage response induced by ionizing radiation (IR). c-Myc is reduced when cells treated with IR or other DNA damaging agents. It is unknown whether miRNAs participate in c-Myc downregulation in response to IR. In the present study, we found that miR-449a enhanced radiosensitivity in vitro and in vivo by targeting c-Myc in prostate cancer (LNCaP) cells. MiR-449a was upregulated and c-Myc was downregulated in response to IR in LNCaP cells. Overexpression of miR-449a or knockdown of c-Myc promoted the sensitivity of LNCaP cells to IR. By establishing c-Myc as a direct target of miR-449a, we revealed that miR-449a enhanced radiosensitivity by repressing c-Myc expression in LNCaP cells. Furthermore, we showed that miR-449a enhanced radiation-induced G2/M phase arrest by directly downregulating c-Myc, which controlled the Cdc2/CyclinB1 cell cycle signal by modulating Cdc25A. These results highlight an unrecognized mechanism of miR-449a-mediated c-Myc regulation in response to IR and may provide alternative therapeutic strategies for the treatment of prostate cancer.

Molecular characterization of a novel androgen receptor transgene responsive to MicroRNA mediated post-transcriptional control exerted via 3'-untranslated region

BACKGROUND

Androgen Receptor (AR) gene is associated with Prostate cancer (PCa) and hence targeting androgen-and AR-signaling axis remains the most promising primary therapeutic option to treat the disease. The AR mRNA has a 6.8 kb long 3'-untranslated region (UTR) which harbors several experimentally validated and numerous predicted miRNA binding sites. AR 3'-UTR is likely to positively or negatively regulate AR expression by interacting with miRNAs and possibly other trans-acting auxiliary factors including 3'-UTR RNA binding proteins. In this context, systematic understanding of the regulatory role of AR 3'-UTR in intrinsic post-transcriptional control of AR gene expression is of significance to understand AR related diseases including PCa.

METHODS

In this study, we have constructed a heterologous reporter system in which Firefly luciferase and AR expression is experimentally influenced by the presence of AR 3'-UTR and its interactions with ectopically expressing miRNA.

RESULTS

The expression of AR 3'-UTR containing reporters, including the Firefly luciferase and the AR open reading frame (ORF) were repressed by the overexpression of miR-488* mimics. In addition, the AR expressed from 3'-UTR containing expression vectors was fully functional in its transactivation function as determined by a prostate specific antigen (PSA) reporter assay. Further, by using confocal microscopy we also demonstrate that AR can translocate to the nucleus upon DHT activation confirming the functional ability of AR.

CONCLUSIONS

AR transgenes with AR 3'-UTR fragments closely resemble the endogenous AR expression than any other previously characterized AR expression constructs. The 3'-UTR containing AR expression system is amiable to post-transcriptional manipulations including miRNA mediated repression of AR expression. This AR reporter system has the potential to be used in determining specificity of AR targeting miRNAs and their role in AR functional regulatory networks. Prostate 76:834-844, 2016. © 2016 Wiley Periodicals, Inc.

A dual yet opposite growth-regulating function of miR-204 and its target XRN1 in prostate adenocarcinoma cells and neuroendocrine-like prostate cancer cells

Androgen deprivation therapy in prostate cancer (PCa) causes neuroendocrine differentiation (NED) of prostatic adenocarcinomas (PAC) cells, leading to recurrence of PCa. Androgen-responsive genes involved in PCa progression including NED remain largely unknown. Here we demonstrated the importance of androgen receptor (AR)-microRNA-204 (miR-204)-XRN1 axis in PCa cell lines and the rat ventral prostate. Androgens downregulate miR-204, resulting in induction of XRN1 (5′-3′ exoribonuclease 1), which we identified as a miR-204 target. miR-204 acts as a tumor suppressor in two PAC cell lines (LNCaP and 22Rv1) and as an oncomiR in two neuroendocrine-like prostate cancer (NEPC) cell lines (PC-3 and CL1). Importantly, overexpression of miR-204 and knockdown of XRN1 inhibited AR expression in PCa cells. Repression of miR-34a, a known AR-targeting miRNA, contributes AR expression by XRN1. Thus we revealed the AR-miR-204-XRN1-miR-34a positive feedback loop and a dual function of miR-204/XRN1 axis in prostate cancer.

ASC-J9(®) suppresses castration resistant prostate cancer progression via degrading the enzalutamide-induced androgen receptor mutant AR-F876L

Androgen deprivation therapy (ADT) with the newly developed powerful anti-androgen enzalutamide (Enz, also known as MDV3100) has promising therapeutic effects to suppress castration resistant prostate cancer (CRPC) and extending patients' lives an extra 4.8 months. However, most Enz therapy eventually fails with the development of Enz resistance. The detailed mechanisms how CRPC develops Enz resistance remain unclear and may involve multiple mechanisms. Among them, the induction of the androgen receptor (AR) mutant AR-F876L in some CRPC patients may represent one driving force that confers Enz resistance. Here, we demonstrate that the AR degradation enhancer, ASC-J9(®), not only degrades wild-type AR, but also has the ability to target AR-F876L. The consequence of suppressing AR-F876L may then abrogate AR-F876L mediated CRPC cell proliferation and metastasis. Thus, developing ASC-J9(®) as a new therapeutic approach may represent a novel therapy to better suppress CRPC that has already developed Enz resistance.

MiR-185 attenuates androgen receptor function in prostate cancer indirectly by targeting bromodomain containing 8 isoform 2, an androgen receptor co-activator

OBJECTIVES

Aberrant androgen receptor (AR) signaling functions are implicated in prostate cancer (PCa) pathogenesis. Here, we studied interactions between miR-185 and the bromodomain containing 8 isoform 2 (BRD8 ISO2) to investigate indirect mechanisms of miR-185 with respect to AR function through BRD8 ISO2 in PCa.

METHODS

Putative miRNA response element (MRE) of miR-185 in 3'-untranslated region (3'-UTR) of BRD8 ISO2 mRNA was predicted by software and confirmed using dual-luciferase assays and Ago2 immunoprecipitation. BRD8 and AR expression were determined by qRT-PCR and Western blot in PCa cells and tissues. MMTV-Fluc reporter plasmids and dual-luciferase assays were used to evaluate AR activity.

RESULTS

MRE prediction, dual-luciferase assays and Ago2 immunoprecipitation confirmed that miR-185 is capable of binding the 3'-UTR of BRD8 ISO2 mRNA. QRT-PCR and Western blot indicated that BRD8 ISO2 expression is decreased by miR-185 mimic transfection while increased by miR-185 inhibitor transfection. MMTV-Fluc reporter assays revealed that miR-185 can attenuate AR function by suppressing BRD8 ISO2. Additionally, Pearson's correlation analyses confirmed that BRD8 ISO2 mRNA expression is inversely correlated with miR-185 expression in clinical specimens.

CONCLUSION

In addition to suppression of AR expression, miR-185 can attenuate AR function indirectly by suppressing BRD8 ISO2. MiR-185 and BRD8 ISO2 may be possible therapeutic targets for PCa treatment.

Circular RNA profiling reveals an abundant circHIPK3 that regulates cell growth by sponging multiple miRNAs

Circular RNAs (circRNAs) represent a class of widespread and diverse endogenous RNAs that may regulate gene expression in eukaryotes. However, the regulation and function of human circRNAs remain largely unknown. Here we generate ribosomal-depleted RNA sequencing data from six normal tissues and seven cancers, and detect at least 27,000 circRNA candidates. Many of these circRNAs are differently expressed between the normal and cancerous tissues. We further characterize one abundant circRNA derived from Exon2 of the HIPK3 gene, termed circHIPK3. The silencing of circHIPK3 but not HIPK3 mRNA significantly inhibits human cell growth. Via a luciferase screening assay, circHIPK3 is observed to sponge to 9 miRNAs with 18 potential binding sites. Specifically, we show that circHIPK3 directly binds to miR-124 and inhibits miR-124 activity. Our results provide evidence that circular RNA produced from precursor mRNA may have a regulatory role in human cells.

Androgen receptor-related diseases: what do we know?

The androgen receptor (AR) and the androgen-AR signaling pathway play a significant role in male sexual differentiation and the development and function of male reproductive and non-reproductive organs. Because of AR's widely varied and important roles, its abnormalities have been identified in various diseases such as androgen insensitivity syndrome, spinal bulbar muscular atrophy, benign prostatic hyperplasia, and prostate cancer. This review provides an overview of the function of androgens and androgen-AR mediated diseases. In addition, the diseases delineated above are discussed with respect to their association with mutations and other post-transcriptional modifications in the AR. Finally, we present an introduction to the potential therapeutic application of most recent pharmaceuticals including miRNAs in prostate cancer that specifically target the transactivation function of the AR at post-transcriptional stages.

Clinical significance of expression of miR-135b, LZTS1 and β-catenin in pancreatic cancer

AIM: To detect the expression of miR-135b, LZTS1 and β-catenin in pancreatic cancer in an attempt to explore their clinical significance.

METHODS: Locked nucleic acid in situ hybridization (ISH) and immunohisto-chemistry were used to detect the expression of miR-135b, LZTS1 and β-catenin proteins in 70 pancreatic cancer tissues and adjacent normal tissues, respectively.

RESULTS: The positive rate of miR-135b in pancreatic cancer was higher than that in adjacent tissues (71.4% vs 42.9%, P = 0.001). The positive rates of LZTS1 and β-catenin proteins in pancreatic cancer were significantly lower than those in adjacent tissues (34.3% vs 68.6%, 34.3% vs 74.3%, P < 0.05). Expression of miR-135b had a negative correlation with that of LZTS1 in pancreatic cancer (r = -0.61, P < 0.05), but miR-135b expression had no significant correlation with β-catenin (r = 0.06, P > 0.05). LZTS1 expression had a positive correlation with that of β-catenin (r = 0.37, P < 0.05). Expression of miR-135b, LZTS1 and β-catenin was closely related with lymph node metastasis and clinical stage (P < 0.05), but had no correlation with patient age, sex, tumor site or histological grade (P > 0.05).

CONCLUSION: miR-135b is highly expressed in pancreatic cancer, while the expression of LZTS1 and β-catenin is decreased. Up-regulated expression of miR-135b may participate in the development of pancreatic cancer by down-regulating the expression of LZTS1 protein.

A transcriptional target of androgen receptor, miR-421 regulates proliferation and metabolism of prostate cancer cells

Prostate cancer is one of the most common malignancies, and microRNAs have been recognized to be involved in tumorigenesis of various kinds of cancer including prostate cancer (PCa). Androgen receptor (AR) plays a core role in prostate cancer progression and is responsible for regulation of numerous downstream targets including microRNAs. This study identified an AR-repressed microRNA, miR-421, in prostate cancer. Expression of miR-421 was significantly suppressed by androgen treatment, and correlated to AR expression in different prostate cancer cell lines. Furthermore, androgen-activated AR could directly bind to androgen responsive element (ARE) of miR-421, as predicted by bioinformatics resources and demonstrated by ChIP and luciferase reporter assays. In addition, over-expression of miR-421 markedly supressed cell viability, delayed cell cycle, reduced glycolysis and inhibited migration in prostate cancer cells. According to the result of miR-421 target genes searching, we focused on 4 genes NRAS, PRAME, CUL4B and PFKFB2 based on their involvement in cell proliferation, cell cycle progression and metabolism. The expression of these 4 downstream targets were significantly repressed by miR-421, and the binding sites were verified by luciferase assay. Additionally, we explored the expression of miR-421 and its target genes in human prostate cancer tissues, both in shared microarray data and in our own cohort. Significant differential expression and inverse correlation were found in PCa patients.

A feed-forward regulatory loop between androgen receptor and PlncRNA-1 promotes prostate cancer progression

We previously reported that PlncRNA-1, a long non-coding RNA that is up-regulated in prostate cancer (PCa), affects the proliferation and apoptosis of PCa cells. However, the molecular mechanisms underlying these effects remain largely unknown. In this study, we demonstrated that long non-coding RNA PlncRNA-1, whose expression is promoted by Androgen Receptor (AR), protects AR from microRNA-mediated suppression in PCa cells. PlncRNA-1 knockdown resulted in the up-regulation of a series of AR-targeting microRNAs, among which miR-34c and miR-297 were found to regulate both AR and PlncRNA-1 expression at the post-transcriptional level. Functional analysis revealed that miR-34c and miR-297 overexpression down-regulated AR expression and inhibited the expression of downstream AR targets and that PlncRNA-1 overexpression rescued these effects. The association of PlncRNA-1 with tumor progression was also evaluated in mouse xenograft models, PCa tissues (16 paired samples), and blood samples (35 biopsy-negative and 37 biopsy-positive). Together, the data generated in this study indicate that PlncRNA-1 sponges AR-targeting microRNAs to protect AR from microRNA-mediated down-regulation and that these events form a regulatory feed-forward loop in the development of PCa. These findings suggest that PlncRNA-1 might potentially serve as a novel biomarker in PCa and that PlncRNA-1 might warrant further investigation to determine its potential role as a promising therapeutic target in PCa.

The Potential of MicroRNAs as Prostate Cancer Biomarkers

CONTEXT

Short noncoding RNAs known as microRNAs (miRNAs) control protein expression through the degradation of RNA or the inhibition of protein translation. The miRNAs influence a wide range of biologic processes and are often deregulated in cancer. This family of small RNAs constitutes potentially valuable markers for the diagnosis, prognosis, and therapeutic choices in prostate cancer (PCa) patients, as well as potential drugs (miRNA mimics) or drug targets (anti-miRNAs) in PCa management.

OBJECTIVE

To review the currently available data on miRNAs as biomarkers in PCa and as possible tools for early detection and prognosis.

EVIDENCE ACQUISITION

A systematic review was performed searching the PubMed database for articles in English using a combination of the following terms: microRNA, miRNA, cancer, prostate cancer, miRNA profiling, diagnosis, prognosis, therapy response, and predictive marker.

EVIDENCE SYNTHESIS

We summarize the existing literature regarding the profiling of miRNA in PCa detection, prognosis, and response to therapy. The articles were reviewed with the main goal of finding a common recommendation that could be translated from bench to bedside in future clinical practice.

CONCLUSIONS

The miRNAs are important regulators of biologic processes in PCa progression. A common expression profile characterizing each tumor subtype and stage has still not been identified for PCa, probably due to molecular heterogeneity as well as differences in study design and patient selection. Large-scale studies that should provide additional important information are still missing. Further studies, based on common clinical parameters and guidelines, are necessary to validate the translational potential of miRNAs in PCa clinical management. Such common signatures are promising in the field and emerge as potential biomarkers.

PATIENT SUMMARY

The literature shows that microRNAs hold potential as novel biomarkers that could aid prostate cancer management, but additional studies with larger patient cohorts and common guidelines are necessary before clinical implementation.

Cisplatin enhances NK cells immunotherapy efficacy to suppress HCC progression via altering the androgen receptor (AR)-ULBP2 signals

The aim of this study is to investigate the influence of cisplatin on the efficacy of natural killer (NK) cells immunotherapy to suppress HCC progression, and provide valuable information on better application of cisplatin in clinical settings. By using in vitro cell cytotoxicity test and in vivo liver orthotopic xenograft mice model, we identified the role of cisplatin in modulating NK cells cytotoxicity. Luciferase report assay and chromatin immunoprecipitation assay were applied for mechanism dissection. Immunohistochemistry is performed for sample staining. We found cisplatin could enhance the efficacy of NK cells immunotherapy to better suppress HCC progression via altering the androgen receptor (AR)-UL16-binding protein 2 (ULBP2) signals both in vitro and in vivo. Mechanism dissection revealed that cisplatin could suppress AR expression via two distinct ways: increasing miR-34a-5p to suppress AR expression and altering the ubiquitination to accelerate the AR protein degradation. The suppressed AR might then function through up-regulating ULBP2, a natural-killer group 2 member D ligand, to enhance the cytotoxicity of NK cells. Together, these results indicated an unrecognized favoring effect of cisplatin in HCC treatment. By suppressing AR in HCC, cisplatin could up-regulate cytotoxicity of NK cells to better target HCC. This finding may provide a potential new approach to control HCC by combining traditional chemotherapy with immunotherapy.

Moving Beyond the Androgen Receptor (AR): Targeting AR-Interacting Proteins to Treat Prostate Cancer

Medical or surgical castration serves as the backbone of systemic therapy for advanced and metastatic prostate cancer, taking advantage of the importance of androgen signaling in this disease. Unfortunately, resistance to castration emerges almost universally. Despite the development and approval of new and more potent androgen synthesis inhibitors and androgen receptor (AR) antagonists, prostate cancers continue to develop resistance to these therapeutics, while often maintaining their dependence on the AR signaling axis. This highlights the need for innovative therapeutic approaches that aim to continue disrupting AR downstream signaling but are orthogonal to directly targeting the AR itself. In this review, we discuss the preclinical research that has been done, as well as clinical trials for prostate cancer, on inhibiting several important families of AR-interacting proteins, including chaperones (such as heat shock protein 90 (HSP90) and FKBP52), pioneer factors (including forkhead box protein A1 (FOXA1) and GATA-2), and AR transcriptional coregulators such as the p160 steroid receptor coactivators (SRCs) SRC-1, SRC-2, SRC-3, as well as lysine deacetylases (KDACs) and lysine acetyltransferases (KATs). Researching the effect of-and developing new therapeutic agents that target-the AR signaling axis is critical to advancing our understanding of prostate cancer biology, to continue to improve treatments for prostate cancer and for overcoming castration resistance.

Non-coding RNAs in Prostate Cancer: From Discovery to Clinical Applications

Prostate cancer is a heterogeneous disease for which the molecular mechanisms are still not fully elucidated. Prostate cancer research has traditionally focused on genomic and epigenetic alterations affecting the proteome, but over the last decade non-coding RNAs, especially microRNAs, have been recognized to play a key role in prostate cancer progression. A considerable number of individual microRNAs have been found to be deregulated in prostate cancer and their biological significance elucidated in functional studies. This review will delineate the current advances regarding the involvement of microRNAs and their targets in prostate cancer biology as well as their potential usage in the clinical management of the disease. The main focus will be on microRNAs contributing to initiation and progression of prostate cancer, including androgen signalling, cellular plasticity, stem cells biology and metastatic processes. To conclude, implications on potential future microRNA-based therapeutics based on the recent advances regarding the interplay between microRNAs and their targets are discussed.

Non-Coding RNAs in Castration-Resistant Prostate Cancer: Regulation of Androgen Receptor Signaling and Cancer Metabolism

Hormone-refractory prostate cancer frequently relapses from therapy and inevitably progresses to a bone-metastatic status with no cure. Understanding of the molecular mechanisms conferring resistance to androgen deprivation therapy has the potential to lead to the discovery of novel therapeutic targets for type of prostate cancer with poor prognosis. Progression to castration-resistant prostate cancer (CRPC) is characterized by aberrant androgen receptor (AR) expression and persistent AR signaling activity. Alterations in metabolic activity regulated by oncogenic pathways, such as c-Myc, were found to promote prostate cancer growth during the development of CRPC. Non-coding RNAs represent a diverse family of regulatory transcripts that drive tumorigenesis of prostate cancer and various other cancers by their hyperactivity or diminished function. A number of studies have examined differentially expressed non-coding RNAs in each stage of prostate cancer. Herein, we highlight the emerging impacts of microRNAs and long non-coding RNAs linked to reactivation of the AR signaling axis and reprogramming of the cellular metabolism in prostate cancer. The translational implications of non-coding RNA research for developing new biomarkers and therapeutic strategies for CRPC are also discussed.

Epithelial–mesenchymal transition in prostatic disease

A fully differentiated epithelium of the normal prostate gland allows epithelial cells to de-differentiate into mesenchymal-like derivatives via the process of epithelial–mesenchymal transition (EMT) and redifferentiate via the reverse process, mesenchymal–epithelial transition. This review discusses the phenotypic changes associated with EMT and its programming in the development of the two growth disorders of the aging prostate gland, benign prostatic hyperplasia and prostate adenocarcinoma. Considering the cellular heterogeneity that characterizes both conditions, identifying the transcriptional programming of the phenotypic framework defining EMT and its reverse process mesenchymal–epithelial transition in their pathological landscape will enable novel platforms for biomarker-driven therapeutics and their implementation in benign prostatic hyperplasia and prostate cancer.

miR-135b inhibits tumour metastasis in prostate cancer by targeting STAT6

MicroRNAs (miRNAs) are small non-coding RNAs that participate in several cellular functions and tumour progression. A previous microarray study demonstrated that miR-135b is downregulated in prostate cancer (PCa) cells, but the role and molecular mechanism of miR-135b in the regulation of tumour metastasis remain to be elucidated. In the present study, significant downregulation of miR-135b in PCa tissues, compared with noncancerous tissues, was detected by reverse transcription-quantitative polymerase chain reaction. Furthermore, the expression of miR-135b was demonstrated to be associated with the pathological stage and the levels of total and free prostate-specific antigen (PSA) in PCa cells. In addition, signal transducer and activator of transcription 6 (STAT6) was identified as a target of miR-135b in PCa cells by luciferase activity and western blot assays. The upregulation of miR-135b in PCa cells led to reduced expression of STAT6 in the cytoplasm and nucleus of these cells, while the overexpression of miR-135b and knockdown of STAT6 were able to inhibit the migration and invasion abilities of PCa cells in vitro. Therefore, the results of the present study indicate that miR-135b suppresses tumour metastasis by targeting STAT6.

miR-634 restores drug sensitivity in resistant ovarian cancer cells by targeting the Ras-MAPK pathway

Background

Drug resistance hampers the efficient treatment of malignancies, including advanced stage ovarian cancer, which has a 5-year survival rate of only 30 %. The molecular processes underlying resistance have been extensively studied, however, not much is known about the involvement of microRNAs.

Methods

Differentially expressed microRNAs between cisplatin sensitive and resistant cancer cell line pairs were determined using microarrays. Mimics were used to study the role of microRNAs in drug sensitivity of ovarian cancer cell lines and patient derived tumor cells. Luciferase reporter constructs were used to establish regulation of target genes by microRNAs.

Results

MiR-634 downregulation was associated with cisplatin resistance. Overexpression of miR-634 affected cell cycle progression and enhanced apoptosis in ovarian cancer cells. miR-634 resensitized resistant ovarian cancer cell lines and patient derived drug resistant tumor cells to cisplatin. Similarly, miR-634 enhanced the response to carboplatin and doxorubicin, but not to paclitaxel. The cell cycle regulator CCND1, and Ras-MAPK pathway components GRB2, ERK2 and RSK2 were directly repressed by miR-634 overexpression. Repression of the Ras-MAPK pathway using a MEK inhibitor phenocopied the miR-634 effects on viability and chemosensitivity.

Conclusion

miR-634 levels determine chemosensitivity in ovarian cancer cells. We identify miR-634 as a therapeutic candidate to resensitize chemotherapy resistant ovarian tumors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0464-4) contains supplementary material, which is available to authorized users.

Adaptive responses of androgen receptor signaling in castration-resistant prostate cancer

Prostate Cancer (PCa) is an important age-related disease being the most common cancer malignancy and the second leading cause of cancer mortality in men in Western countries. Initially, PCa progression is androgen receptor (AR)- and androgen-dependent. Eventually advanced PCa reaches the stage of Castration-Resistant Prostate Cancer (CRPC), but remains dependent on AR, which indicates the importance of AR activity also for CRPC. Here, we discuss various pathways that influence the AR activity in CRPC, which indicates an adaptation of the AR signaling in PCa to overcome the treatment of PCa. The adaptation pathways include interferences of the normal regulation of the AR protein level, the expression of AR variants, the crosstalk of the AR with cytokine tyrosine kinases, the Src-Akt-, the MAPK-signaling pathways and AR corepressors. Furthermore, we summarize the current treatment options with regard to the underlying molecular basis of the common adaptation processes of AR signaling that may arise after the treatment with AR antagonists, androgen deprivation therapy (ADT) as well as for CRPC, and point towards novel therapeutic strategies. The understanding of individualized adaptation processes in PCa will lead to individualized treatment options in the future.

Role of BioResponse 3,3'-Diindolylmethane in the Treatment of Human Prostate Cancer: Clinical Experience

Castration-resistant prostate cancer (CRPC) progression after androgen deprivation therapy shows upregulated expression of androgen receptor (AR) splice variants, induced epithelial-to-mesenchymal transition phenotypes and enhanced stem cell characteristics, all of which are associated with resistance to enzalutamide. Since there is no curative treatment for CRPC, innovative treatments are urgently needed. In our recent study, we found that resistance to enzalutamide was partly due to deregulated expression of microRNAs such as miR-34a, miR-124, miR-27b, miR-320 and let-7, which play important roles in regulating AR and stem cell marker gene expression that appears to be linked with resistance to enzalutamide. Importantly, we found that BioResponse 3,3'-diindolylmethane (BR-DIM) treatment in vitro and in vivo caused downregulation in the expression of wild-type AR. The AR splice variants, Lin28B and EZH2, appear to be deregulated through the re-expression of let-7, miR-27b, miR-320 and miR-34a in human prostate cancer (PCa). BR-DIM administered in clinical trials was well tolerated, and 93% of patients had detectable prostatic DIM levels. The inhibitory effects of BR-DIM on AR and AR target gene such as prostate-specific antigen were also observed in the clinical trial. Our preclinical and clinical studies provide the scientific basis for a 'proof-of-concept' clinical trial in CRPC patients treated with enzalutamide in combination with BR-DIM. This strategy could be expanded in future clinical trials in patients with PCa to determine whether or not they could achieve a better treatment outcome which could be partly mediated by delaying or preventing the development of CRPC.

Systematic Identification of MicroRNAs That Impact on Proliferation of Prostate Cancer Cells and Display Changed Expression in Tumor Tissue

BACKGROUND

Systematic approaches to functionally identify key players in microRNA (miRNA)-target networks regulating prostate cancer (PCa) proliferation are still missing.

OBJECTIVE

To comprehensively map miRNA regulation of genes relevant for PCa proliferation through phenotypic screening and tumor expression data.

DESIGN, SETTING, AND PARTICIPANTS

Gain-of-function screening with 1129 miRNA molecules was performed in five PCa cell lines, measuring proliferation, viability, and apoptosis. These results were integrated with changes in miRNA expression from two cohorts of human PCa (188 tumors in total). For resulting miRNAs, the predicted targets were collected and analyzed for patterns with gene set enrichment analysis, and for their association with biochemical recurrence free survival.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Rank product statistical analysis was used to evaluate miRNA effects in phenotypic screening and for expression differences in the prostate tumor cohorts. Expression data were analyzed using the significance analysis of microarrays (SAM) method and the patient material was subjected to Kaplan-Meier statistics.

RESULTS AND LIMITATIONS

Functional screening identified 25 miRNAs increasing and 48 miRNAs decreasing cell viability. Data integration resulted in 14 miRNAs, with aberrant expression and effect on proliferation. These miRNAs are predicted to regulate >3700 genes, of which 28 were found up-regulated and 127 down-regulated in PCa compared with benign tissue. Seven genes, FLNC, MSRB3, PARVA, PCDH7, PRNP, RAB34, and SORBS1, showed an inverse association to their predicted miRNA, and were identified to significantly correlate with biochemical recurrence free survival in PCa patients.

CONCLUSIONS

A systematic in vitro screening approach combined with in vivo expression and gene set enrichment analysis provide unbiased means for revealing novel miRNA-target links, possibly driving the oncogenic processes in PCa.

PATIENT SUMMARY

This study identified novel regulatory molecules, which impact on PCa proliferation and are aberrantly expressed in clinical tumors. Thus, our study reveals regulatory nodes with potential for therapy.

MiR-449a suppresses the epithelial-mesenchymal transition and metastasis of hepatocellular carcinoma by multiple targets

Background

Increasing evidence indicates that Epithelial–mesenchymal transition (EMT) can be regulated by microRNAs (miRNAs). MiR-449a is a liver abundant miRNA. However, the role of miR-449a in the metastasis of hepatocellular carcinoma (HCC) remains largely unknown.

Methods

The expression levels of miR-449a were first examined in HCC cell lines and tumour tissues by real-time PCR. The in vitro and in vivo functional effect and underlying molecular mechanisms of miR-449a were examined further.

Results

In the present study, we found that miR-449a was significantly decreased in HCC cells and tissues, especially in those with the portal vein tumor thrombus. In HCC cell lines, stable overexpression of miR-449a was sufficient to inhibit cell motility in vitro, and pulmonary metastasis in vivo. In addition, ectopic overexpression of miR-449a in HCC cells promoted the expression of epithelial markers and reduced the levels of mesenchymal markers. Further studies revealed that the reintroduction of miR-449a attenuated the downstream signaling of Met, and consequently reduced the accumulation of Snail in cell nucleus by targeting the 3’-untranslated regions (3’-UTR) of FOS and Met.

Conclusions

Our data highlight an important role of miR-449a in the molecular etiology of HCC, and implicate the potential application of miR-449a in cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1738-3) contains supplementary material, which is available to authorized users.

Downregulation of miR-185 and upregulation of miR-218 expression may be potential diagnostic and prognostic biomarkers of human chondrosarcoma

Increasing evidence has confirmed that dysregulation of microRNAs (miRNAs) can contribute to the progression and metastasis of human tumors. Chondrosarcoma is the most common primary malignant bone tumor in adults and has no effective systemic treatment, and patients with this disease have poor survival. Thus, it is important to find new diagnostic markers and improve treatment options. In the current study, we are interested to examine the role of miR-185 and miR-218 expression in patients with chondrosarcoma using real-time PCR. Moreover, the association of the two miRNAs with clinicopathological features and prognosis was evaluated. Survival and Cox proportional hazards analyses were performed to find the association of miR-185 expression and miR-218 levels with prognosis in the patients. Our results indicated that the miR-185 expression was significantly downexpressed in clinical chondrosarcoma bone tissues compared with adjacent normal tissues (P = 0.001). MiR-218 expression level was increased in clinical chondrosarcoma bone tissue than those adjacent normal tissues (P = 0.001). Decreased expression of miR-185 showed remarkable correlation with advanced tumor stage (P = 0.019), tumor grade (P < 0.001), and distant metastasis (P = 0.001). Moreover, high expression of miR-218 was strongly correlated with advanced tumor stage (P = 0.014), tumor grade (P < 0.001), and distant metastasis (P = 0.002). Kaplan-Meier survival analysis revealed that the low miR-185 expression group and the high miR-218 expression group had remarkably shorter overall survival (log-rank test P = 0.007, P = 0.004). The multivariate Cox proportional hazards model indicated that decreased expression of miR-185 and increased expression of miR-218 (P = 0.017, P = 0.012), advanced tumor stage (P = 0.006, P = 0.012), tumor grade (P = 0.032, P = 0.016), and distant metastasis (P = 0.004, P = 0.015) were independently related to overall survival in patients with chondrosarcoma. In conclusion, downregulation of miR-185 and upregulation of miR-218 can be associated with progression of chondrosarcoma and also both of them may act as tumor suppressor genes in chondrosarcoma.

Comprehensive proteomic profiling identifies the androgen receptor axis and other signaling pathways as targets of microRNAs suppressed in metastatic prostate cancer

MicroRNAs are important epigenetic regulators of protein expression by triggering degradation of target mRNAs and/or inhibiting their translation. Dysregulation of microRNA expression has been reported in several cancers, including prostate cancer (PC). We comprehensively characterized the proteomic footprint of a panel of 12 microRNAs that are potently suppressed in metastatic PC (SiM-miRNAs: miR-1, miR-133a, miR-133b, miR-135a, miR-143-3p, miR-145-3p, miR-205, miR-221-3p, miR-221-5p, miR-222-3p, miR-24-1-5p, and miR-31) using reverse-phase proteomic arrays. Re-expression of these SiM-miRNAs in PC cells suppressed cell proliferation and targeted key oncogenic pathways, including cell cycle, apoptosis, Akt/mammalian target of rapamycin signaling, metastasis and the androgen receptor (AR) axis. However, only 12%, at most, of these observed protein expression changes could be explained by predicted direct binding of miRNAs to corresponding mRNAs, suggesting that the majority of these proteomic effects result indirectly. AR and its steroid receptor coactivators (SRCs; SRC-1, -2 and -3) were recurrently affected by these SiM-miRNAs. In agreement, we identified inverse correlations between expression of these SiM-miRNAs and early clinical recurrence, as well as with AR transcriptional activity in human PC tissues. We also identified robust induction of miR-135a by androgen and strong direct binding of AR to the miR-135a locus. As miR-135a potently suppresses AR expression, this results in a negative feedback loop that suppresses AR protein expression in an androgen-dependent manner, while de-repressing AR expression upon androgen deprivation. Our results demonstrate that epigenetic silencing of these SiM-miRNAs can result in increased AR axis activity and cell proliferation, thus contributing to disease progression. We further demonstrate that a negative feedback loop involving miR-135a can restore AR expression under androgen-deprivation conditions, thus contributing to the upregulation of AR protein expression in castration-resistant PC. Finally, our unbiased proteomic profiling demonstrates that the majority of actual protein expression changes induced by SiM-miRNAs cannot be explained based on predicted direct interactions.

MiR-634 decreases cell proliferation and induces apoptosis by targeting mTOR signaling pathway in cervical cancer cells

Taking the emergence of continuous resistance to chemotherapy and the evidence that miRNAs are associated with chemoresistance in cancers into consideration, it is of significant importance to reveal the miRNAs functions for the treatment of cancer. As a novel tumor suppressor, MiR-634 is known to induce apoptosis in tumor cell which is essential for tumorigenesis. Herein, we elucidated the regulation effects of miR-634 in gene expression and discovery of its target gene in cell proliferation and invasion that would aid therapeutic apoptosis. As a result, by targeting mTOR signal pathway, miR-634 inhibited cell proliferation, migration and invasiveness in cervical cancer cells and the block of miR-634 enhances the mTOR expression at both the mRNA and protein levels which regulated the expression of mTOR negatively. Taken together, these results further indicated that miR-634 is an effective target for cancer treatment, and the findings provided in this work might lead to the better understanding of the malignant behavior of cervical carcinoma.

Gene interference strategies as a new tool for the treatment of prostate cancer

Prostate cancer (PCa) is one of the most common cancer in men. It affects older men and the incidence increases with age; the median age at diagnosis is 67 years. The diagnosis of PCa is essentially based on three tools: digital rectal exam, serum concentration of prostate specific antigen, and transrectal ultrasound-guided biopsy. Currently, the therapeutic treatments of this cancer are different and range from the prostatectomy to hormonal therapy, to radiation therapy, to immunotherapy, and to chemotherapy. However, additional efforts are required in order to find new weapons for the treatment of metastatic setting of disease. The purpose of this review is to highlight new therapeutic strategies based on gene interference; in fact, numerous siRNA and miRNA in the therapeutic treatment of PCa are reported below.

miR-634 Activates the Mitochondrial Apoptosis Pathway and Enhances Chemotherapy-Induced Cytotoxicity

Some tumor-suppressing miRNAs target multiple oncogenes concurrently and therefore may be useful as cancer therapeutic agents. Further, such miRNAs may be useful to address chemotherapeutic resistance in cancer, which remains a primary clinical challenge in need of solutions. Thus, cytoprotective processes upregulated in cancer cells that are resistant to chemotherapy are a logical target for investigation. Here, we report that overexpression of miR-634 activates the mitochondrial apoptotic pathway by direct concurrent targeting of genes associated with mitochondrial homeostasis, antiapoptosis, antioxidant ability, and autophagy. In particular, we show how enforced expression of miR-634 enhanced chemotherapy-induced cytotoxicity in a model of esophageal squamous cell carcinoma, where resistance to chemotherapy remains clinically problematic. Our findings illustrate how reversing miR-634-mediated cytoprotective processes may offer a broadly useful approach to improving cancer therapy.

Capsaicin causes inactivation and degradation of the androgen receptor by inducing the restoration of miR-449a in prostate cancer

Capsaicin, a novel antitumor agent extracted from chili peppers, has been proven to induce growth inhibition in various types of cancer including prostate cancer. However, the detailed mechanisms remain largely undiscovered. In the present study, we explored the regulation of the androgen receptor (AR) by capsaicin and further researched the mechanisms of their interaction in AR-positive prostate cancer cells. In the present study, cell viability was assessed by MTT assay. Cell cycle distribution was determined using flow cytometry. Expression levels of cyclin D1, miR-449a, AR and prostate-specific antigen (PSA) were assessed by quantitative real-time polymerase chain reaction or western blot analysis. To further confirm the relationship among miR-449a, AR and prostate cancer proliferation, miR-449a was overexpressed by a lentivirus in prostate cancer cells. We discovered that capsaicin prevented tumor proliferation and cell cycle progression through inactivation and degradation of AR. We also found that restoration of miR-449a induced by capsaicin treatment resulted in the inhibition of AR signaling. Finally, we demonstrated that increased expression of miR-449a sensitized prostate cancer to capsaicin treatment. Finally, our experimental results indicated that capsaicin negatively modulates the activity of AR at the mRNA and protein levels by restoring miR-449a profiling in prostate cancer. In addition, increased expression of miR-449a may facilitate the sensitivity of prostate cancer to capsaicin treatment. Thus, capsaicin may be developed as a novel anti-AR drug for the therapy of prostate cancer.

Regulation of MET-mediated proliferation of thyroid carcinoma cells by miR-449b

Thyroid carcinoma (TC) is a lethal cancer worldwide, whereas its carcinogenesis is not fully understood. Although growing evidence has demonstrated that dysregulation of microRNAs (miRNAs) contributes to the development of various cancers, the role of miRNAs in the pathogenesis of TC is poorly characterized. Here, we analyzed the levels of miR-449b in TC tissues and detected significantly lower miR-449b levels in TC tissues. Moreover, the low miR-449b levels were associated with poor survival. We then overexpressed miR-449b by miRNA mimic transfection and inhibited miR-449b by miRNA antisense transfection. Cell growth was analyzed by CCK-8 assay and MTT assay, and apoptosis and cell proliferation were analyzed by flow cytometry. Overexpression of miR-449b significantly inhibited cell growth, while depletion of miR-449b increased cell growth. Moreover, the effects of miR-449b on cell growth were through modulation of cell proliferation rather than through modulation of cell apoptosis. Targeted genes were predicted by a bioinformatics algorithm and confirmed by a dual luciferase reporter assay, showing that miR-449b binds to the 3'-UTR of MET (hepatocyte growth factor receptor) mRNA, to inhibit its expression in TC cells. MET levels were regulated by miR-449b in TT cells. Together, we show that reduced miR-449b levels in TT tissues may promote TC growth, through MET-mediated cell proliferation.

miR-145 suppress the androgen receptor in prostate cancer cells and correlates to prostate cancer prognosis

Androgen signalling through the androgen receptor (AR) is essential for prostate cancer initiation, progression and transformation to the lethal castration-resistant state. The aim of this study was to characterize the mechanisms by which miR-145 deregulation contribute to prostate cancer progression. The miR-145 levels, measured by quantitative reverse transcription-polymerase chain reaction, were found to inversely correlate with occurrence of metastases, survival and androgen deprivation therapy response in a well-characterized prostate cancer cohort. Introduction of ectopic miR-145 in prostate cancer cells generated an inhibitory effect on the AR at both transcript and protein levels as well as its activity and downstream targets prostate-specific antigen (PSA), kallikrein-related peptidase 2 and TMPRSS2. The regulation was shown to be mediated by direct binding using Ago2-specific immunoprecipitation, but there was also indication of synergetic AR activation. These findings were verified in clinical prostate specimens by demonstrating inverse correlations between miR-145 and AR expression as well as serum PSA levels. In addition, miR-145 was found to regulate androgen-dependent cell growth in vitro. Our findings put forward novel possibilities of therapeutic intervention, as miR-145 potentially could decrease both the stem cells and the AR expressing bulk of the tumour and hence reduce the transformation to the deadly castration-resistant form of prostate cancer.

The role of microRNAs 371 and 34a in androgen receptor control influencing prostate cancer behavior

BACKGROUND

The molecular mechanisms involved in androgen receptor (AR) signaling pathways are not completely understood, and deregulation of microRNAs (miRNAs) expression may play a role in prostate cancer (PC) development and progression.

METHODS

The expression levels of miRNA and AR were evaluated with quantitative real-time polymerase chain reaction using frozen tissue from the surgical specimens of 83 patients submitted to radical prostatectomy. The expression level of miRNAs was correlated with prognostic factors and biochemical recurrence during a follow-up period of 45 months. In vitro and in vivo experiments were performed to understand the effect of miRNAs over AR in the context of that seen in a PC model.

RESULTS

MiR-371 underexpression correlated with non-organ-confined (pT3) disease (P = 0.009). In vitro transfection of miR-371 reduced the levels of AR by 22% and 28% in LNCaP and PC3 cell lines, respectively, and in kallikrein 3, it was reduced by 51%. PC was induced in Balb/c mice using PC-3M-luc-C6 cells, and animals were treated with 3 local doses of miR-371. Tumor growth evaluated by in vivo imaging after luciferase injection was slower in animals treated with miR-371. To explore further the possible role of miRNAs in the AR pathway, LNCaP cell line was treated with 5α-dihydrotestosterone and flutamide showing alteration in miRNAs expression, especially miR-34a, which was significantly underexpressed after treatment with high doses of 5α-dihydrotestosterone.

CONCLUSION

Our data support a role for miRNAs, especially miR-371 and miR-34a, in the complex disarrangement of AR signaling pathway and in the behavior of PC.

Effects of treatment with androgen receptor ligands on microRNA expression of prostate cancer cells

Post-transcriptional regulation by microRNA (miRNA) is an important aspect of androgen receptor (AR) signalling in prostate cancer cells. However, the global profiling of miRNA expression in prostate cancer cells following treatment with AR ligands has not been reported so far. In this study we examined the effect of treatment with two AR agonists (mibolerone (MIB) and dihydrotestosterone (DHT)) and an AR antagonist (bicalutamide (BIC)) on miRNA expression in the human androgen-dependent LNCaP prostate cancer cell line using microarray technology and verification of selected miRNA using quantitative real-time PCR (qRT-PCR). No miRNA was identified as differentially expressed following treatment with the AR antagonist BIC. In contrast, a number of common and compound-specific alterations in miRNA expression were observed following treatment with AR agonists. Unexpectedly it was found that treatment with the AR agonists resulted in the repression of miR-221, a miRNA previously established to be involved with prostate cancer development. This observation indicates that this miRNA may have a more complex role in prostate cancer development than considered previously. Treatment with MIB led to an induction of miR-210 expression, a hypoxia-related miRNA. This miRNA is reported to be involved in cell adaptation to hypoxia and thus induction in conditions of normoxia may be important in driving metabolic changes observed in prostate cancer. Thus examining the effect of AR agonists and antagonists on miRNA expression can provide novel insights into the response of cells to AR ligands and subsequent downstream events.

Androgen receptor signaling in prostate cancer

The androgen receptor (AR), ligand-induced transcription factor, is expressed in primary prostate cancer and in metastases. AR regulates multiple cellular events, proliferation, apoptosis, migration, invasion, and differentiation. Its expression in prostate cancer cells is regulated by steroid and peptide hormones. AR downregulation by various compounds which are contained in fruits and vegetables is considered a chemopreventive strategy for prostate cancer. There is a bidirectional interaction between the AR and micro-RNA (miRNA) in prostate cancer; androgens may upregulate or downregulate the selected miRNA, whereas the AR itself is a target of miRNA. AR mutations have been discovered in prostate cancer, and their incidence may increase with tumor progression. AR mutations and increased expression of selected coactivators contribute to the acquisition of agonistic properties of anti-androgens. Expression of some of the coactivators is enhanced during androgen ablation. AR activity is regulated by peptides such as cytokines or growth factors which reduce the concentration of androgen required for maximal stimulation of the receptor. In prostate cancer, variant ARs which exhibit constitutive activity were detected. Novel therapies which interfere with intracrine synthesis of androgens or inhibit nuclear translocation of the AR have been introduced in the clinic.

MicroRNA-135b regulates ERα, AR and HIF1AN and affects breast and prostate cancer cell growth

MicroRNAs (miRNAs) regulate a wide range of cellular signaling pathways and biological processes in both physiological and pathological states such as cancer. We have previously identified miR-135b as a direct regulator of androgen receptor (AR) protein level in prostate cancer (PCa). We wanted to further explore the relationship of miR-135b to hormonal receptors, particularly estrogen receptor α (ERα). Here we show that miR-135b expression is lower in ERα-positive breast tumors as compared to ERα-negative samples in two independent breast cancer (BCa) patient cohorts (101 and 1302 samples). Additionally, the miR-135b expression is higher in AR-low PCa patient samples (47 samples). We identify ERα as a novel miR-135b target by demonstrating miR-135b binding to the 3'UTR of the ERα and decreased ERα protein and mRNA level upon miR-135b overexpression in BCa cells. MiR-135b reduces proliferation of ERα-positive BCa cells MCF-7 and BT-474 as well as AR-positive PCa cells LNCaP and 22Rv1 when grown in 2D. To identify other genes regulated by miR-135b we performed gene expression studies and found a link to the hypoxia inducible factor 1α (HIF1α) pathway. We show that miR-135b influences the protein level of the inhibitor for hypoxia inducible factor 1α (HIF1AN) and is able to bind to HIF1AN 3'UTR. Our study demonstrates that miR-135b regulates ERα, AR and HIF1AN protein levels through interaction with their 3'UTR regions, and proliferation in ERα-positive BCa and AR-positive PCa cells.

Microdissecting the role of microRNAs in the pathogenesis of prostate cancer

MicroRNAs (miRNAs) are naturally occurring, small, non-coding RNA molecules that post-transcriptionally regulate the expression of a large number of genes involved in various biological processes, either through mRNA degradation or through translation inhibition. Since the discovery of miRNAs, a vast amount of research has implicated the deregulated expression of miRNAs in different malignancies, including prostate cancer (PCa). Different miRNA expression profiles are reportedly associated with the development, progression, and emergence of castration-resistant PCa (CRPC), suggesting their use in the diagnosis, prognosis, and development of anti-cancer treatment models directed against this disease. However, before their exploitation in terms of therapeutics, a thorough understanding and in-depth mechanistic studies of these miRNAs and the gene networks they orchestrate are necessary for ascertaining their definitive role in the development and progression of PCa. This review attempts to extensively summarize the current knowledge of aberrantly expressed miRNAs and their mode of action in PCa, while highlighting the existing discrepancies and future research warranted.