Tumor Suppressor In Prostate Cancer Research Articles

Micro-ribonucleic acid 29b inhibits cell proliferation and invasion and enhances cell apoptosis and chemotherapy effects of cisplatin via targeting of DNMT3b and AKT3 in prostate cancer.

BackgroundMicro-ribonucleic acids (miRNAs) are crucial regulators in malignant tumors. miRNA-29b (miR-29b) has been identified as a tumor suppressor in prostate cancer (PCa). However, very few studies have investigated the effects of miR-29b in PCa, especially the mechanism and its association with chemotherapy. Our study aimed to explore the role and mechanism of miR-29b in PCa.Materials and methodsThe expression levels of miR-29b were detected in ten clinical PCa specimens and four different PCa cell lines through quantitative real-time polymerase chain reaction. After miR-29b mimics and inhibitors were successfully transfected into LNCaP, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was then used to investigate cell proliferation and cisplatin sensitivity of PCa cells. Cell cycle, cell apoptosis, and cell invasion were detected via flow cytometry, annexin V–fluorescein isothiocyanate labeling, and transwell assay, respectively. Based on bioinformatic methods, Western blot analysis, and dual-luciferase reporter assay, novel target genes of miR-29b were identified.ResultsmiR-29b was downregulated in PCa tissues compared with matched adjacent nontumor tissues. In the androgen-independent PCa cell line (LNCaP-AI), the expression of miR-29b was much lower than the androgen-dependent PCa cell line (LNCaP). Subsequent studies showed that forced expression of miR-29b inhibited cell proliferation and cell invasion and induced cell apoptosis in PCa. Upregulation of miR-29b also enhanced the chemosensitivity of PCa cells to cisplatin. Moreover, we identified DNMT3b and AKT3 as novel target genes of miR-29b in PCa.ConclusionTaken together, the results showed that miR-29b plays a tumor-suppressive role in PCa. It inhibits cell biological behavior and enhances the chemotherapy effects of cisplatin through its involvement in epigenetic regulation and PI3K/AKT pathway.

MiR-188-5p inhibits tumour growth and metastasis in prostate cancer by repressing LAPTM4B expression.

Elucidation of the molecular targets and pathways regulated by the tumour-suppressive miRNAs can shed light on the oncogenic and metastatic processes in prostate cancer (PCa). Using miRNA profiling analysis, we find that miR-188-5p was significantly down-regulated in metastatic PCa. Down-regulation of miR-188-5p is an independent prognostic factor for poor overall and biochemical recurrence-free survival. Restoration of miR-188-5p in PCa cells (PC-3 and LNCaP) significantly suppresses proliferation, migration and invasion in vitro and inhibits tumour growth and metastasis in vivo. We also find overexpression of miR-188-5p in PC-3 cells can significantly enhance the cells' chemosensitivity to adriamycin. LAPTM4B is subsequently identified as a direct target of miR-188-5p in PCa, and is found to be significantly over-expressed in PCa. Knockdown of LAPTM4B phenotypically copies miR-188-5p-induced phenotypes, whereas ectopic expression of LAPTM4B reverses the effects of miR-188-5p. We also find that restoration of miR-188-5p can inhibit the PI3K/AKT signaling pathway via the suppression of LAPTM4B. Taken together, this is the first report unveils that miR-188-5p acts as a tumour suppressor in PCa and may therefore serve as a useful therapeutic target for the development of new anticancer therapy.

Integrative analysis of FOXP1 function reveals a tumor-suppressive effect in prostate cancer.

The transcriptional network of the androgen receptor (AR), a key molecule of prostate cancer, is frequently modulated by interactions with other transcriptional factors such as forkhead box protein A1 (FOXA1). However, global regulatory mechanisms of AR signaling mediated by such factors have not been well investigated. Here we conducted a chromatin immunoprecipitation sequence analysis, which revealed that another FOX family, FOXP1, is specifically regulated by both AR and FOXA1. We also found that FOXP1 acts as a tumor suppressor in prostate cancer through inhibiting cell proliferation and migration. We generated an extensive global map of FOXP1 binding sites and found that FOXP1 is directly involved in AR-mediated transcription. We demonstrated that FOXP1 has a repressive effect on AR-induced transcriptional activity or histone modification in enhancer regions. Moreover, by a global analysis of androgen-mediated transcriptional networks, we observed enrichment of FOXP1 binding genes in the gene cluster negatively regulated by FOXP1. Evaluation of FOXP1 expression in clinical samples indicated that the decreased expression of FOXP1 is another prognostic factor of prostate cancer. Taken together, our results suggest a novel mechanism in which AR-induced FOXP1 functions as a direct modulator of the AR and FOXA1 centric global transcriptional network.

The Role of SIRT1 in Cancer: The Saga Continues

This Commentary highlights the article by Di Sante etal, which presents data supporting the status of SIRT1 as a tumor suppressor in prostate cancer.

Abstract C75: Unique SPOP somatic mutations in African American prostate cancer

Abstract SPOP (Speckle-type POZ protein) is a tumor suppressor in prostate cancer (PCa). Somatic heterozygous missense mutations in SPOP have been reported in up to 15% of PCa in Caucasian American (CA). However, the mutation frequency and the genetic role of SPOP in African American (AA) PCa are currently unknown. We sequenced exons 6 and 7 of the SPOP gene for somatic mutations in 49 AA prostate tumor tissues collected in the Southern Louisiana area and identified five (10%) tumors carrying heterozygous missense mutations and one tumor carrying a novel synonymous variant. Intriguingly, all mutations are clustered in exon 6 and change conserved amino acids. Moreover, three mutations represent novel mutations and unique to AA PCa. To further identify unique SPOP somatic mutations in AA PCa, we expanded mutation screening to all of the other exons of the SPOP gene but no additional coding variant or deletion/insertion was identified. Quantitative RT-PCR analysis indicates that the SPOP mutations in AA prostate tumors reduced SPOP RNA levels in tumors compared with SPOP levels in their adjacent normal prostate tissues; therefore, supporting the notion of SPOP as a tumor suppressor gene. These results indicate that AA prostate tumors carry similar frequency but a unique profile of SPOP somatic mutations as in Caucasian PCa. The clinical relevance and the pathological significance of SPOP mutations in AA PCa will be discussed. Citation Format: Eric L. Buckles, Chiping Qian, Sumana Majumdar, Jovanny Zabaleta, Wanguo Liu. Unique SPOP somatic mutations in African American prostate cancer. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr C75. doi:10.1158/1538-7755.DISP13-C75

A functional variant in miR-143 promoter contributes to prostate cancer risk.

MicroRNAs are important regulators in numerous cellular processes, including cell differentiation, proliferation, and apoptosis. Recently, miR-143 was identified as a tumor suppressor in prostate cancer (PCa). To explore the mechanism of dysregulation and anti-tumor function of miR-143 in PCa, we first found a single-nucleotide polymorphism rs4705342T>C in the promoter region of miR-143 through bioinformatics tools and then performed a case-control study including 608 PCa patients and 709 controls. Results suggested that subjects with TC/CC genotypes had significantly decreased risk of PCa compared with those with TT genotype (adjusted OR 0.68, 95% CI 0.55-0.85). Further functional assays showed that the risk-associated T allele increased the protein-binding affinity and reduced the activity of the promoter compared with C allele. In addition, restoration of miR-143 by mimics in PCa cells significantly inhibited cell proliferation and migration and down-regulated the expression level of kallikrein-related peptidase 2 (KLK2) mRNA and protein. The miR-143-KLK2 axis was also confirmed by luciferase reporter assay in vitro. In conclusion, our findings demonstrate that there is the significant association between the functional promoter variant rs4705342T>C in miR-143 and PCa risk and newly describe the miR-143-KLK2 interaction which provided another potential mechanism for miR-143 anti-tumor function.

Abstract 1334: Induction of autophagy by ormeloxifene and mevastatin through Protein Kinase D1 in prostate cancer cells

Abstract Objective: Chemotherapy-induced emergence of drug resistance is one of the major limitations to treat prostate cancer. Numerous studies report that autophagic cell death functions as a suppressor of tumorigenesis in prostate cancer. Although chemotherapeutic drugs inhibit growth of cancer cells, they also activate chemokine, CCL2 which protects prostate cancer cells from autophagic cell death. Protein Kinase D1 (PKD1) plays multiple roles in the fundamental biological processes and is known as a tumor suppressor in prostate cancer. Here, we report for the first time that PKD1 inhibits CCL2 expression in prostate cancer cells. Therefore, we also investigated whether PKD1 modulation inhibits CCL2 and potentiates autophagic cell death. We have found a novel combination of mevastatin (MVS) and ormeloxifene (ORM), a non-steroidal, selective estrogen receptor inhibitor, effectively increases PKD1 expression and induces autophagic cell death in prostate cancer cells. Methods: Prostate cancer cells (C4-2) stably overexpressing PKD1 (C4-2-PKD1-GFP) or vector control (C4-2-GFP) were treated with ORM (10µM) and MVS (20µM) and their combination for 48h. Cell viability was performed by CellTiter 96® AQueous One Solution cell proliferation assay. CCL2 expression levels were quantified by ELISA as per the manufacturer's instructions. Cell migration assays were performed with pre-incubation of 3-MA (5mM; 3-Methyladenine, an autophagy inhibitor) for 2h, or exogenously added CCL2 (100ng/mL) in the lower part of a Boyden chamber. The cells were treated with ORM alone or in combination with MVS for 18h for the analysis of proteins expression involved in autophagy. Immmunoblot experiments were performed using an autophagy sampler kit as per the manufacturer's instructions. Results: Our results suggest that a combination of ORM and MVS increases PKD1 and inhibits CCL2 expression in prostate cancer cells. It inhibits cell proliferation, migration and metastasis of prostate cancer cells. Additionally, it was observed that ORM and MVS effectively inhibits CCL2 induced cell motility in PKD1 overexpressing cells, however the effect was not observed in PKD1 null cells. The PKD1 dependent inhibition of CCL2 expression activates autophagy as evidenced by activation of autophagy markers (LC3A, LC3B). It down-regulates survivin-1, Beclin-1 and NFκB-65, inducing autophagy in cancer cells. The cells treated with 3-MA and/or exogenous CCL2 abrogated the effects induced by MVS and ORM. Conclusion: Here, we propose for the first time a link between PKD1 and autophagy. We have found a novel combination of MVS and ORM that effectively increases PKD1 expression and induces autophagic cell death in prostate cancer cells. This study prospects combined therapies targeting PKD1/CCL2 and the PI3K/Akt/mTOR/survivin pathway as a valid strategy to overcome the resistance of prostate cancer cells. Citation Format: Rishi K. Gara, Sonam Kumari, Aditya Ganju, Murali M. Yallapu, Ankita Shah, Sheema Khan, Man M. Singh, Subhash C. Chauhan, Meena Jaggi. Induction of autophagy by ormeloxifene and mevastatin through Protein Kinase D1 in prostate cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1334. doi:10.1158/1538-7445.AM2014-1334

Abstract 4081: Id4 (inhibitor of dna binding 4) crosstalk with pten-akt pathway

Abstract Introduction: Inhibitor of DNA binding/differentiation protein 4 (Id4), acts as a dominant negative regulator of basic helix loop helix (bHLH) family of transcription factors. Id4 shares the homology of HLH domain with other Ids and lack the basic DNA binding region. Previous studies from our lab had shown that unlike Id1, Id2 and Id3, Id4 acts as a tumor suppressor in prostate cancer by attenuating cell proliferation and promoting apoptosis. In this study we investigated whether Id4 acts as a tumor suppressor by regulating the AKT pathway. Experimental procedures: Id4 protein expression was analyzed on human prostate adenocarcinoma samples by Immunohistochemistry. We also performed Immunohistochemistry to determine AKT, pAKT, PTEN protein expression in Id4 knockout mouse prostates. In addition we determined the expression levels of the above mentioned proteins in prostate cancer cell lines with or without Id4 (LNCaP, LNCaP-Id4, DU145, DU145+Id4, PC3). Results: IHC demonstrated decreased Id4 protein expression in human prostate tissue samples whereas higher nuclear Id4 expression was found in normal human and mouse prostate tissues. IHC on Id4 knockout (Id4-/-) mouse prostates demonstrated an increase in pAKT expression, whereas AKT expression did not change significantly when compared to normal mouse prostate. PTEN expression levels decreased ignificantly in Id4 knockout mouse prostates. Similar pattern was observed in prostate cancer cell lines: DU145 cells lacking Id4 had low PTEN as compared to Id4 over-expressing DU145 cells. Id4 expression was also associated with PI3 kinase activity in LNCaP and PC3 cells. These results suggest Id4 regulates AKT-PI3K pathway by attenuating PTEN. Conclusions: Id4 appears as a potential tumor suppressor gene that exerts its tumor suppressor activity by promoting PTEN expression. PTEN in turn regulates AKT phosphorylation that stabilizes p53, AR and NKX3.1 expression in the normal prostate. Acknowledgement: The research was supported by NIH/NCI-RO1CA128914 and in part by NIH/NCRR/RCMI G12RR03062 Citation Format: Shravan Kumar Komaragiri. Id4 (inhibitor of dna binding 4) crosstalk with pten-akt pathway. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4081. doi:10.1158/1538-7445.AM2014-4081

Abstract 5205: CCND1 is a miR-193b target in prostate cancer

Abstract Prostate cancer is the most frequent cancer of men in Western countries and causes second most of the cancer-related deaths. In addition to genetic changes also epigenetic alterations and micro-RNAs (miRNAs) are important in prostate cancer development. Our group has previously shown that miR-193b is hypermethylated in 22Rv1 prostate cancer cell line and that it is putative tumor suppressor in prostate cancer. In melanoma and hepatocellular carcinoma, it has been shown that CCND1, encoding cyclin D1 protein, is among the target genes of miR-193b. The aim of this project was to study if CCND1 is a target of miR-193b in prostate cancer. According to qRT-PCR and microarray analyses, the expression of CCND1 and miR-193b were inversely correlated in prostate cancer cell lines (PC-3, VCaP, 22Rv1, LAPC4, DU145, LNCaP) and in LuCaP xenografts. Using a luciferase reporter gene assay in 22Rv1 cells, we showed that miR-193b targets CCND1 3′UTR. In 22Rv1 cells with low endogenous miR-193b expression, transient pre-miR-193b transfection reduced CCND1 mRNA levels and cyclin D1 and phospho-RB protein levels. By rescue experiment we confirmed that the downregulation of cyclin D1 and phospho-RB proteins is due to miR-193b. When prostate cancer cell lines were treated with cdk4/6 inhibitor, 22Rv1 and VCaP cells with low miR-193b and high CCND1 expression showed significant growth retardation. In contrast, the inhibitor did not have any effect on the growth of PC-3 and DU145 cells with high miR-193b and low CCND1 expression. Furthermore, immunohistochemical analysis of 337 specimens showed that cyclin D1 is expressed significantly higher in castration resistant compared to hormone-naïve prostate cancers. Therefore, we conclude that CCND1 is one of the miR-193b targets in prostate cancer. Citation Format: Kirsi M. Tuppurainen, Hanna E. Rauhala, Mauro Scaravilli, Robert L. Vessella, Tapio Visakorpi. CCND1 is a miR-193b target in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5205. doi:10.1158/1538-7445.AM2014-5205

Abstract 3311: The cholesterol/ 27-hydroxycholesterol axis is a novel therapeutic target in castrate resistant prostate cancer

Abstract The most recent estimates indicate that men have a seventeen percent chance of developing invasive prostate cancer (PCa) over their lifetime. This makes PCa the most commonly diagnosed malignancy among men in industrialized countries, accounting for the second leading cause of cancer-related deaths. Although PCa almost always develops resistance to androgen-deprivation therapy, both androgen receptor (AR) itself and the processes downstream of the receptor remain active and are necessary for cancer progression and thus continue to be viable targets for therapeutic intervention. In this regard, it is of significance that several independent studies demonstrate a link between elevated intra-prostatic levels of cholesterol and the presence of malignancy. This puts into context our current finding that 27-hydroxycholesterol (27HC), a primary metabolite of cholesterol, regulates pathways and processes that oppose AR action. For example, AR activation results in a net uptake of cholesterol by PCa cells and enhances denovo lipogenesis, while 27HC down-regulates genes involved in cholesterol uptake and activates those involved in its efflux. More importantly, we show that treatment of PCa cell lines with 27HC inhibits their proliferation, an activity that is reversed upon supplementing the cells with an exogenous source of cholesterol or upon over-expression of low density lipoprotein receptor (LDLR), a membrane protein that mediates the uptake of cholesterol. In prostatic tissues, 27HC is synthesized directly from cholesterol by the cytochrome P450 enzyme, CYP27A1. To further highlight the above axis as a novel therapeutic target, using data mining approaches from clinical databases, we show that (1) transcript levels of CYP27A1 are dramatically down-regulated during PCa progression and (2) patients whose tumors express high levels of CYP27A1transcript exhibit longer disease free survival. Most notably, we were able to show that over-expression of CYP27A1 inhibits the proliferation of PCa cell lines in vitro and delays the growth of xenografts in castrated immune-deficient mice. In summary, our data thus far strongly implicates that CYP27A1 is a potential tumor suppressor in PCa and highlights the cholesterol/27HC axis as a target for the development of novel therapeutics for castrate resistant disease. Citation Format: Mahmoud A. Alfaqih, Erik R. Nelson, Rachid Safi, Jeff Jasper, Ching-yi Chang, Stephen J. Freedland, Donald P. McDonnell. The cholesterol/ 27-hydroxycholesterol axis is a novel therapeutic target in castrate resistant prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3311. doi:10.1158/1538-7445.AM2014-3311

SPDEF inhibits prostate carcinogenesis by disrupting a positive feedback loop in regulation of the Foxm1 oncogene.

SAM-pointed domain-containing ETS transcription factor (SPDEF) is expressed in normal prostate epithelium. While its expression changes during prostate carcinogenesis (PCa), the role of SPDEF in prostate cancer remains controversial due to the lack of genetic mouse models. In present study, we generated transgenic mice with the loss- or gain-of-function of SPDEF in prostate epithelium to demonstrate that SPDEF functions as tumor suppressor in prostate cancer. Loss of SPDEF increased cancer progression and tumor cell proliferation, whereas over-expression of SPDEF in prostate epithelium inhibited carcinogenesis and reduced tumor cell proliferation in vivo and in vitro. Transgenic over-expression of SPDEF inhibited mRNA and protein levels of Foxm1, a transcription factor critical for tumor cell proliferation, and reduced expression of Foxm1 target genes, including Cdc25b, Cyclin B1, Cyclin A2, Plk-1, AuroraB, CKS1 and Topo2alpha. Deletion of SPDEF in transgenic mice and cultures prostate tumor cells increased expression of Foxm1 and its target genes. Furthermore, an inverse correlation between SPDEF and Foxm1 levels was found in human prostate cancers. The two-gene signature of low SPDEF and high FoxM1 predicted poor survival in prostate cancer patients. Mechanistically, SPDEF bound to, and inhibited transcriptional activity of Foxm1 promoter by interfering with the ability of Foxm1 to activate its own promoter through auto-regulatory site located in the −745/−660 bp Foxm1 promoter region. Re-expression of Foxm1 restored cellular proliferation in the SPDEF-positive cancer cells and rescued progression of SPDEF-positive tumors in mouse prostates. Altogether, SPDEF inhibits prostate carcinogenesis by preventing Foxm1-regulated proliferation of prostate tumor cells. The present study identified novel crosstalk between SPDEF tumor suppressor and Foxm1 oncogene and demonstrated that this crosstalk is required for tumor cell proliferation during progression of prostate cancer in vivo.

MiR-146a functions as a tumor suppressor in prostate cancer by targeting Rac1.

miR-146a (miR-146a-5p) has been reported to be aberrantly expressed in different types of cancers, the current knowledge about the role of miR-146a in prostate cancer is still limited. The expression levels of miR-146a in cell lines and tissues were measured by qRT-PCR and in situ hybridization. Effects of miR-146a on cell growth and migration were evaluated by colony formation assay and RTCA assay, respectively. The dual luciferase assay was used to examine the binding between miR-146a and the 3'UTR of potential targets. We found that enforced over-expression of miR-146a in prostate cancer cells suppressed whereas knockdown of miR-146a increased anchorage-independent growth, migration, and invasion. Mechanistic studies revealed that miR-146a repressed the expression of Rac1 through binding to its 3'UTR. Consistently, knockdown of Rac1 phenocopied the anti-migration effect of overexpressing miR-146a, and knockdown of Rac1 in miR-146a-silencing cells antagonized the increase in cell motility induced by silencing miR-146a. Furthermore, miR-146a was found to be inversely correlated with Rac1 in human prostate cancer tissues. Our data suggest that miR-146a plays a suppressive role in prostate cancer through down-regulation of Rac1. The miR-146a/Rac1 signaling axis may be a potential therapeutic target to prevent prostate cancer progression.

Reciprocal regulation of PCGEM1 and miR-145 promote proliferation of LNCaP prostate cancer cells.

Prostate cancer gene expression marker 1 (PCGEM1) is a long non-coding RNA (lncRNA) overexpressed in prostate cancer (PCa) cells that promotes PCa initiation and progression, and protects against chemotherapy-induced apoptosis. The microRNA miR-145 functions as a tumor suppressor in PCa. We speculate that reciprocal regulation of PCGEM1 and miR-145 promote proliferation of LNCaP prostate cancer cells. To test this hypothesis, the interaction between PCGEM1 and miR-145 was examined using a luciferase reporter assay. Expression levels were selectively altered in LNCaP cells and noncancerous RWPE-1 prostate cells by transfection of miR-145 or small interfering RNA sequences against (siRNA) PCGEM1. Relative expression levels were detected by RT-PCR, tumor cell growth and early apoptosis by the MTT assay and flow cytometry, respectively, and tumor cell migration and invasion properties by transwell assays. The effect of siRNA PCGEM1 and miR-145 transfection on prostate cancer growth in vivo was examined in the (nu/nu) mouse model. PCGEM1 and miR-145 exhibited reciprocal regulation; downregulation of PCGEM1 expression in LNCaP cells increased expression of miR-145, while overexpression of miR-145 decreased PCGEM1 expression. Transfection of the miR-145 expression vector and siRNA PCGEM1 inhibited tumor cell proliferation, migration, and invasion, and induced early apoptosis both in vitro. In contrast, there was no effect on RWPE-1 cells. We demonstrate a reciprocal negative control relationship between PCGEM1 and miR-145 that regulates both LNCaP cell proliferation and nu/nu PCa tumor growth. The results also identify PCGEM1 and associated regulators as possible targets for PCa therapy.

The lncRNA PCAT29 inhibits oncogenic phenotypes in prostate cancer.

Long noncoding RNAs (lncRNA) have recently been associated with the development and progression of a variety of human cancers. However, to date, the interplay between known oncogenic or tumor-suppressive events and lncRNAs has not been well described. Here, the novel lncRNA, prostate cancer-associated transcript 29 (PCAT29), is characterized along with its relationship to the androgen receptor. PCAT29 is suppressed by DHT and upregulated upon castration therapy in a prostate cancer xenograft model. PCAT29 knockdown significantly increased proliferation and migration of prostate cancer cells, whereas PCAT29 overexpression conferred the opposite effect and suppressed growth and metastases of prostate tumors in chick chorioallantoic membrane assays. Finally, in prostate cancer patient specimens, low PCAT29 expression correlated with poor prognostic outcomes. Taken together, these data expose PCAT29 as an androgen-regulated tumor suppressor in prostate cancer. This study identifies PCAT29 as the first androgen receptor-repressed lncRNA that functions as a tumor suppressor and that its loss may identify a subset of patients at higher risk for disease recurrence. Visual Overview: http://mcr.aacrjournals.org/content/early/2014/07/31/1541-7786.MCR-14-0257/F1.large.jpg.

Farnesoid X receptor inhibits LNcaP cell proliferation via the upregulation of PTEN.

Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. In the present study, the activation of the farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, was demonstrated to inhibit cell proliferation in LNcaP cells. Using clinical samples, mRNA and protein levels of FXR were found to be significantly decreased by quantitative PCR and western blot analysis in prostate cancer tissues. In vitro studies identified further that activation or overexpression of FXR suppressed prostate cancer cell proliferation as measured by BrdU incorporation assays. At the molecular level, the results further revealed that the expression of the tumor suppressor gene, PTEN, was upregulated by FXR activation. Therefore, the observations indicated that FXR functions as a tumor suppressor in prostate cancer, which may provide a novel method for molecular targeting cancer treatment.

The microRNA-23b/27b/24-1 cluster is a disease progression marker and tumor suppressor in prostate cancer.

Our recent study of microRNA (miRNA) expression signatures in prostate cancer (PCa) has revealed that all members of the miR-23b/27b/24-1 cluster are significantly downregulated in PCa tissues. The aim of this study was to investigate the effectiveness of these clustered miRNAs as a disease progression marker and to determine the functional significance of these clustered miRNAs in PCa. Expression of the miR-23b/27b/24-1 cluster was significantly reduced in PCa tissues. Kaplan-Meier survival curves showed that low expression of miR-27b predicted a short duration of progression to castration-resistant PCa. Gain-of-function studies using mature miR-23b, miR-27b,and miR-24-1 significantly inhibited cell proliferation, migration and invasion in PCa cells (PC3 and DU145). To identify the molecular targets of these miRNAs, we carried out gene expression and in silico database analyses. GOLM1 was directly regulated by miR-27b in PCa cells. Elucidation of the molecular targets and pathways regulated by the tumor-suppressive microRNAs should shed light on the oncogenic and metastatic processes in PCa.

MiR-26a inhibits prostate cancer progression by repression of Wnt5a.

MicroRNAs (miRNAs) are small noncoding RNAs that are involved in different biological processes by suppressing target gene expression. miRNA microarray analysis revealed a significant decrease of miR-26a in prostate cancer tissues versus their normal counterparts, but the role of miR-26a is needed to investigate. In the present study, we found that miR-26a expression was lower in prostate cancer tissues compared with their normal controls, so did the prostate cancer cells. Next, by lentivirus-mediated gain-of-function studies, it was showed that stable miR-26a inhibited cell proliferation, metastasis, and epithelial mesenchymal transition and induced G1 phase arrest in prostate cancer. It was predicted that Wnt5a was a potential target gene of miR-26a by bioinformatics analysis. Then, luciferase assay and Western blot analysis identified that Wnt5a was a new direct target gene of miR-26a and miR-26a inhibited prostate cancer progression via Wnt5a. Altogether, the findings suggested that miR-26a may function as a tumor suppressor in prostate cancer by targeting Wnt5a.

Inhibitor of differentiation 4 (ID4) inactivation promotes de novo steroidogenesis and castration-resistant prostate cancer.

Prostate cancer (PCa) is the most commonly diagnosed cancer in men in the Western world. The transition of androgen-dependent PCa to castration-resistant (CRPC) is a major clinical manifestation during disease progression and presents a therapeutic challenge. Our studies have shown that genetic ablation of inhibitor of differentiation 4 (Id4), a dominant-negative helix loop helix protein, in mice results in prostatic intraepithelial neoplasia lesions and decreased Nkx3.1 expression without the loss of androgen receptor (Ar) expression. ID4 is also epigenetically silenced in the majority of PCa. However, the clinical relevance and molecular pathways altered by ID4 inactivation in PCa are not known. This study investigates the effect of loss of ID4 in PCa cell lines on tumorigenicity and addresses the underlying mechanism. Stable silencing of ID4 in LNCaP cells (L-ID4) resulted in increased proliferation, migration, invasion, and anchorage-independent growth. An increase in the rate of tumor growth, weight, and volume was observed in L-ID4 xenografts compared with that in the LNCaP cells transfected with nonspecific short hairpin RNA (L+ns) in noncastrated mice. Interestingly, tumors were also observed in castrated mice, suggesting that loss of ID4 promotes CRPC. RNA sequence analysis revealed a gene signature mimicking that of constitutively active AR in L-ID4, which was consistent with gain of de novo steroidogenesis. Prostate-specific antigen expression as a result of persistent AR activation was observed in L-ID4 cells but not in L+ns cells. The results demonstrate that ID4 acts as a tumor suppressor in PCa, and its loss, frequently observed in PCa, promotes CRPC through constitutive AR activation.

MicroRNA-296-5p (miR-296-5p) functions as a tumor suppressor in prostate cancer by directly targeting Pin1

Upregulation of Pin1 was shown to advance the functioning of several oncogenic pathways. It was recently shown that Pin1 is potentially an excellent prognostic marker and can also serve as a novel therapeutic target for prostate cancer. However, the molecular mechanism of Pin1 overexpression in prostate cancer is still unclear. In the present study, we showed that the mRNA expression levels of Pin1 were not correlated with Pin1 protein levels in prostate cell lines which indicated that Pin1 may be regulated at the post-transcriptional level. A key player in post-transcriptional regulation is represented by microRNAs (miRNAs) that negatively regulate expressions of protein-coding genes at the post-transcriptional level. A bioinformatics analysis revealed that miR-296-5p has a conserved binding site in the Pin1 3′-untranslated region (UTR). A luciferase reporter assay demonstrated that the seed region of miR-296-5p directly interacts with the 3′-UTR of Pin1 mRNA. Moreover, miR-296-5p expression was found to be inversely correlated with Pin1 expression in prostate cancer cell lines and prostate cancer tissues. Furthermore, restoration of miR-296-5p or the knockdown of Pin1 had the same effect on the inhibition of the ability of cell proliferation and anchorage-independent growth of prostate cancer cell lines. Our results support miR-296-5p playing a tumor-suppressive role by targeting Pin1 and implicate potential effects of miR-296-5p on the prognosis and clinical application to prostate cancer therapy.

Overexpression of HepaCAM inhibits cell viability and motility through suppressing nucleus translocation of androgen receptor and ERK signaling in prostate cancer.

HepaCAM is suppressed in a variety of human cancers, and involved in cell adhesion, growth, migration, invasion, and survival. However, the expression and function of HepaCAM in prostate cancer are still unknown. HepaCAM expression has been detected by RT-PCR, Western blotting and immunohistochemistry staining in prostate cell lines RWPE-1, LNCap, DU145, PC3, and in 75 human prostate tissue specimens, respectively. Meanwhile, the cell proliferation ability was detected by WST-8 assay. The role of HepaCAM in prostate cancer cell migration and invasion was examined by wound healing and transwell assay. And flow cytometry was used to observe the apoptosis of prostate cancer cells. Then we detected changes of Androgen Receptor translocation and ERK signaling using immunofluorescence staining and western blot after overexpression of HepaCAM. The HepaCAM expression was significantly down-regulated in prostate cancer tissues and undetected in prostate cancer cells. However, the low HepaCAM expression was not statistically associated with clinicopathological characteristics of prostate cancer. Overexpression of HepaCAM in prostate cancer cells decreased the cell proliferation, migration and invasion, and induced the cell apoptosis. Meanwhile, HepaCAM prevented the androgen receptor translocation from the cytoplasm to the nucleus and down-regulated the MAPK/ERK signaling. Our results suggested that HepaCAM acted as a tumor suppressor in prostate cancer. HepaCAM inhibited cell viability and motility which might be through suppressing the nuclear translocation of Androgen Receptor and down-regulating the ERK signaling. Therefore, it was indicated that HepaCAM may be a potential therapeutic target for prostate cancer.