Promotes Prostate Cancer Cell Growth Research Articles

MicroRNA181c inhibits prostate cancer cell growth and invasion by targeting multiple ERK signaling pathway components.

The ERK signaling pathway is frequently deregulated in tumorigenesis, mostly by classical mechanisms such as gene mutation of its components (eg, RAS and RAF). However, whether and how multiple key components of ERK pathway are regulated by microRNAs are not clear. We firstly predicted post-transcriptional regulation of multiple key components of the ERK signaling pathway by miR181c through bioinformatics analysis, and then confirmed the post-transcriptional regulation by dual luciferase reporter gene assays and Western blot analysis. The biological effects of miR181c on prostate cancer cell proliferation, apoptosis, migration, and invasion were measured by CCK-8 assay, flow cytometry, wound scratch assay, transwell cell migration, and invasion assays. miR181c post-transcriptionally regulated multiple key members of the ERK signaling pathway, including extracellular signal-regulated kinase 2 (ERK2), ribosomal S6 kinase 2 (RSK2), serum response factor (SRF), and FBJ murine osteosarcoma viral oncogene homolog (c-Fos). Ectopic expression of miR181c mimics effectively suppressed prostate cancer cell proliferation, migration, and invasion, but promoted cell apoptosis. Furthermore, miR181c treatment combined with the multi-kinase inhibitor sorafenib significantly enhanced these anti-tumor effects. Downregulation of miR181c results in deregulated ERK signaling and promotes prostate cancer cell growth and metastasis.

PrLZ increases prostate cancer docetaxel resistance by inhibiting LKB1/AMPK-mediated autophagy.

Rationale: Docetaxel-mediated chemotherapy is the first-line standard approach and has been determined to show a survival advantage for metastatic castration-resistant prostate cancer (mCRPC) patients. However, a substantial proportion of patients eventually becomes refractory due to drug resistance. The detailed mechanisms remain unclear. We have previously reported that Prostate Leucine Zipper (PrLZ), a specific oncogene of prostate cancer (PCa), promotes PCa cell growth at the castration-resistant stage, thus suggesting a vital role of PrLZ in the progression of CRPC. In this study, we aimed to investigate the role of PrLZ in docetaxel resistance in PCa, focusing on PrLZ-regulating autophagy pathway.Methods: Human PCa PC3, LNCaP and C4-2 cell lines were used as the model system in vitro and PCa xenografts and PrLZ-knockout mice were used as the model system in vivo. Docetaxel-induced cell death and apoptosis in PCa were determined by MTT and flow cytometry assay. The role of PrLZ on the regulation of autophagy and liver kinase B1/AMP-activated protein kinase (LKB1/AMPK) signaling pathway was analyzed using immunoblotting, immunoprecipitation, siRNA silencing and plasmid overexpression.Results: PrLZ increased docetaxel-mediated drug resistance both in vitro and in vivo. Mechanistic dissection revealed that PrLZ interacted with LKB1 and further inhibited the activation of LKB1/AMPK signals, which negatively contributed to the induction of autophagy. Moreover, PrLZ/LKB1-mediated autophagy conferred resistance to docetaxel-induced cell death and apoptosis both in vitro and in vivo.Conclusion: These findings identify a novel role of PrLZ in autophagy manipulation and provide new insight into docetaxel chemoresistance in PCa, suggesting a new strategy for treating mCRPC by targeting this newly identified signaling pathway.

Vitamin D receptor-binding site variants affect prostate cancer progression.

Vitamin D is an important modulator of cellular proliferation through the vitamin D receptor (VDR) that binds to DNA in the regulatory sequences of target genes. We hypothesized that single nucleotide polymorphisms (SNPs) in VDR-binding sites might affect target gene expression and influence the progression of prostate cancer. Using a genome-wide prediction database, 62 SNPs in VDR-binding sites were selected for genotyping in 515 prostate cancer patients and the findings were replicated in an independent cohort of 411 patients. Prognostic significance on prostate cancer progression was assessed by Kaplan-Meier analysis and the Cox regression model. According to multivariate analyses adjusted for known predictors, HFE rs9393682 was found to be associated with disease progression for localized prostate cancer, and TUSC3 rs1378033 was associated with progression for advanced prostate cancer in both cohorts. Vitamin D treatment inhibited HFE mRNA expression, and down-regulation of HFE by transfecting small interfering RNA suppressed PC-3 human prostate cancer cell proliferation and wound healing ability. In contrast, vitamin D treatment induced TUSC3 expression, and silencing TUSC3 promoted prostate cancer cell growth and migration. Further analysis of an independent microarray dataset confirmed that low TUSC3 expression correlated with poor patient prognosis. Our results warrant further studies using larger cohorts. This study identifies common variants in VDR-binding sites as prognostic markers of prostate cancer progression and HFE and TUSC3 as plausible susceptibility genes.

MicroRNA-455-3p functions as a tumor suppressor by targeting eIF4E in prostate cancer.

MicroRNAs (miRNAs) are strongly implicated in various cancers, including prostate cancer. Recently, microRNA-455-3p (miR-455-3p) has been shown to be aberrantly expressed in many tumor tissues, but its functions in tumorigenesis remain unknown. In this study, we investigated the role of miR-455-3p in prostate cancer. We found that miR-455-3p is markedly downregulated in prostate cancer cell lines and clinical tumor specimens. Gain-of-function and loss-of-function studies showed that miR-455-3p promotes prostate cancer cell growth both invitro and invivo. Bioinformatics analysis and Luciferase reporter assays demonstrated that miR-455-3p directly targets and suppresses eIF4E, the rate-limiting factor for cap-dependent translation, which plays important roles in the initiation and progression of prostate cancers. Further studies demonstrated that miR-455-3p inhibits cap-dependent translation and the proliferation of prostate cancer cells through targeting eIF4E. Taken together, our findings suggest that miR-455-3p functions as a tumor suppressor by directly targeting eIF4E in prostate carcinogenesis and may be used as a potential target for therapeutic intervention in prostate cancer.

Transcriptional regulation of core autophagy and lysosomal genes by the androgen receptor promotes prostate cancer progression

ABSTRACTAR (androgen receptor) signaling is crucial for the development and maintenance of the prostate as well as the initiation and progression of prostate cancer. Despite the AR's central role in prostate cancer progression, it is still unclear which AR-mediated processes drive the disease. Here, we identified 4 core autophagy genes: ATG4B, ATG4D, ULK1, and ULK2, in addition to the transcription factor TFEB, a master regulator of lysosomal biogenesis and function, as transcriptional targets of AR in prostate cancer. These findings were significant in light of our recent observation that androgens promoted prostate cancer cell growth in part through the induction of autophagy. Expression of these 5 genes was essential for maximal androgen-mediated autophagy and cell proliferation. In addition, expression of each of these 5 genes alone or in combination was sufficient to increase prostate cancer cell growth independent of AR activity. Further, bioinformatic analysis demonstrated that the expression of these genes correlated with disease progression in 3 separate clinical cohorts. Collectively, these findings demonstrate a functional role for increased autophagy in prostate cancer progression, provide a mechanism for how autophagy is augmented, and highlight the potential of targeting this process for the treatment of advanced prostate cancer.

NKAIN2 functions as a novel tumor suppressor in prostate cancer.

Recurrent chromosome breakpoints at 6q22.31, leading to truncation and potential loss-of-function of the NKAIN2 gene, in Chinese prostate cancer patients were previously identified. In this study we investigated genomic, methylation and expression changes of NKAIN2 in a large number of prostate cancer samples and determined its functional role in prostate cancer cells. Fluorescence in situ hybridization analysis confirmed that NKAIN2 truncation is specific to Chinese while deletion of the gene is frequent in both Chinese and UK prostate cancers. Significantly reduced expression of NKAIN2 was also detected at both RNA and protein levels. Somatic mutations of NKAIN2 in prostate cancer samples exist but at very low frequency, suggesting that it is a putative tumor suppressor gene (TSG) with haploid insufficiency. Our functional studies showed that overexpression of NKAIN2 in prostate cancer cells inhibits cellular growth by promoting cell apoptosis, and decreasing cell migration and invasion. Conversely, knockdown of NKAIN2 promotes prostate cancer cell growth by inhibiting cell apoptosis, and increasing cell migration and invasion. These data imply that NKAIN2 is a novel TSG whose activity is commonly reduced in prostate cancer. It may restrain the disease development and progression by inducing apoptosis and suppressing cancer cell growth, migration and invasion. This study provides new insights into prostate carcinogenesis and opportunities for development of novel therapies for prostate cancer.

Protein arginine methyltransferase 5 functions as an epigenetic activator of the androgen receptor to promote prostate cancer cell growth

Protein arginine methyltransferase 5 (PRMT5) is an emerging epigenetic enzyme that mainly represses transcription of target genes via symmetric dimethylation of arginine residues on histones H4R3, H3R8 and H2AR3. Accumulating evidence suggests that PRMT5 may function as an oncogene to drive cancer cell growth by epigenetic inactivation of several tumor suppressors. Here, we provide evidence that PRMT5 promotes prostate cancer cell growth by epigenetically activating transcription of the androgen receptor (AR) in prostate cancer cells. Knockdown of PRMT5 or inhibition of PRMT5 by a specific inhibitor reduces the expression of AR and suppresses the growth of multiple AR-positive, but not AR-negative, prostate cancer cells. Significantly, knockdown of PRMT5 in AR-positive LNCaP cells completely suppresses the growth of xenograft tumors in mice. Molecular analysis reveals that PRMT5 binds to the proximal promoter region of the AR gene and contributes mainly to the enriched symmetric dimethylation of H4R3 in the same region. Mechanistically, PRMT5 is recruited to the AR promoter by its interaction with Sp1, the major transcription factor responsible for AR transcription, and forms a complex with Brg1, an ATP-dependent chromatin remodeler, on the proximal promoter region of the AR gene. Furthermore, PRMT5 expression in prostate cancer tissues is significantly higher than that in benign prostatic hyperplasia tissues, and PRMT5 expression correlates positively with AR expression at both the protein and mRNA levels. Taken together, our results identify PRMT5 as a novel epigenetic activator of AR in prostate cancer. Given that inhibiting AR transcriptional activity or androgen synthesis remains the major mechanism of action for most existing anti-androgen agents, our findings also raise an interesting possibility that targeting PRMT5 may represent a novel approach for prostate cancer treatment by eliminating AR expression.

Platelet-activating factor receptor activation promotes prostate cancer cell growth, invasion and metastasis via ERK1/2 pathway.

Platelet-activating factor (PAF) and its receptor (PAFR), have been reported to participate in many cellular processes of cancer. However, little is known about their function in prostate cancer. In the present study, we found that PAFR was overexpressed in prostate cancer cells. PAF stimulation dose-dependently promoted the invasion, migration and growth of prostate cancer cells invitro, while knockdown of PAFR inhibited the effect of PAF on prostate cancer cells. We further found that PAFR promoted prostate cancer cell growth and metastasis invivo. Moreover, we found that PAFR activation increased MMP-3 expression and decreased E-cadherin expression of prostate cancer cells invitro and invivo. Finally, we found that PAFR time-dependently induced activation of ERK1/2, and ERK1/2 pathway contributed to PAFR-mediated prostate cancer cell invasion, migration and growth. Together, our findings demonstrate that PAFR can activate ERK1/2 pathway, and subsequently increase MMP-3 expression and decrease E-cadherin expression, which finally promote prostate cancer cell growth, invasion and metastasis. Thus, PAFR may act as a potential target for therapeutic use of prostate cancer.

Upregulation of miR-556-5p promoted prostate cancer cell proliferation by suppressing PPP2R2A expression.

The prognosis and survival rate of prostate cancer are very poor. Previous studies have shown that miR-556-5p have emerged as important regulators in cancer cell biological processes. The role of miR-556-5p in prostate cancer remains unclear. In this study, expression of miR-556-5p in prostate cancer cell lines and tissues was upregulated. Result of MTT assays, colony formation and anchorage-independent growth assays demonstrated that overexpression of miR-556-5p promoted prostate cancer cell growth. Additionally, PPP2R2A was identified as a direct target of miR-556-5p. Ectopic expression of miR-556-5p led to downregulation of PPP2R2A protein, which resulted in the downregulation of p27, upregulation of cyclin D1. Taken together, our data provide compelling evidence that miR-556-5p functions as an onco-miRNA and participates in prostate cancer carcinogenesis by suppressing PPP2R2A expression.

The histone demethylase PHF8 promotes prostate cancer cell growth by activating the oncomiR miR-125b.

AimsProstate cancer (PCa) is the most frequently diagnosed malignancy in men. However, the underlying mechanism is not fully understood. In this study, we aim to research the molecular mechanisms underlying the initiation and progression of PCa.ResultsPlant homeodomain finger protein 8 (PHF8) is upregulated in human PCa tissues and cell lines. PHF8 knockdown attenuates growth and cellular transformation of PCa cells. PHF8 depletion induces PCa cell apoptosis by activating proapoptotic proteins and inactivating antiapoptotic proteins. Furthermore, miR-125b is a target of PHF8, and miR-125b seems to be essential for the hyper proliferation of PCa cells in the presence of PHF8.ConclusionIn conclusion, we identify the histone demethylase PHF8 as an oncogenic protein in human PCa. These findings indicate PHF8 as a potential candidate for clinical intervention.

Abstract 2450: CaMKK2-AMPK signaling facilitates androgen-mediated prostate cancer cell metabolism

Abstract Prostate cancer is the most commonly diagnosed malignancy among men in industrialized countries, accounting for the second leading cause of cancer-related deaths. While we now know that the androgen receptor (AR) is important for progression to the deadly advanced stages of the disease, it is poorly understood what AR-regulated processes drive this pathology. Previous work from several independent laboratories has suggested AR signaling promotes prostate cancer through a Ca2+/calmodulin-dependent protein kinase kinase beta (CaMKK2)-dependent signaling mechanism. Further, it was demonstrated this enzymatic cascade promotes the use of sugars for cellular energy, a common trait for many cancers. Given CaMKK2's known role as a regulator of various aspects of metabolism, we hypothesized that CaMKK2 could promote prostate cancer cell growth through additional mechanisms beyond glycolysis. To test our hypothesis, we used clinical samples to track the activation of downstream signaling components of CaMKK2 in prostate cancer. The mechanistic role of these components was then identified using a variety of cell-based assays and xenograft mouse models of prostate cancer. Here, we demonstrate that AR-mediated CaMKK2 signaling regulates prostate cancer cell growth via the metabolic sensor 5′-AMP-activated protein kinase (AMPK), a kinase that classically regulates cellular energy homeostasis. In patients, activation of AMPK correlated with prostate cancer progression. Using a combination of radiolabeled assays and emerging metabolomic approaches, we also show that prostate cancer cells respond to androgen treatment by increasing not only rates of glycolysis, as is commonly seen in many cancers, but also glucose and fatty acid oxidation. Importantly, this effect was dependent on androgen-mediated AMPK activity. Our results further indicate that the AMPK-mediated metabolic changes increased intracellular ATP levels and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)-mediated mitochondrial biogenesis, affording distinct growth advantages to the prostate cancer cells. Correspondingly, we used outlier analysis to determine that PGC-1α is overexpressed in a subpopulation of clinical cancer samples. This was in contrast to what was observed in immortalized benign human prostate cells and a testosterone-induced rat model of benign prostatic hyperplasia. Taken together, our findings converge to demonstrate that androgens can co-opt the CaMKK2-AMPK-PGC-1α signaling cascade, a known homeostatic mechanism, to increase prostate cancer cell growth. The current study points to the potential utility of developing metabolic-targeted therapies directed towards the CaMKK2-AMPK-PGC-1α signaling axis for the treatment of prostate cancer. Citation Format: Daniel E. Frigo, Yan Shi, Jenny J. Han, Efrosini Tsouko, Michael M. Ittmann. CaMKK2-AMPK signaling facilitates androgen-mediated prostate cancer cell metabolism. [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 2450. doi:10.1158/1538-7445.AM2014-2450

Abstract 2121: Resveratrol regulates phospho-serine 81 androgen receptor and its stability to inhibit growth of prostate cancer cells

Abstract Resveratrol, a polyphenol, has been reported as a cell growth inhibitor of various types of cancer. The molecular mechanisms of resveratrol are involved in different cellular signal transductions such as anti-inflammation and anti-oxidation. Resveratrol inhibits growth of prostate cancer cells through regulating cyclin-dependent kinases, anti-apoptotic proteins, and pro-apoptotic proteins. Notably, resveratrol may down-regulate androgen receptor (AR) and its downstream gene to inhibit prostate cancer cell growth. In previous study, serine 81 phosphorylation of AR increases its protein stability and transcriptional activity, which promotes prostate cancer cell growth. The aim of this study is to investigate whether AR serine 81 phosphorylation would be a target of resveratrol in prostate cancer cells. Our data indicate that resveratrol inhibited the growth of prostate cancer cell line, LNCaP, with the decrease of AR phospho-serine 81 levels. Moreover, AR protein stability was declined by resveratrol without affecting AR mRNA expression. Indeed, resveratrol inhibited AR transcriptional activity in results of AR reporter assay and PSA level in LNCaP cells. In summary, the results suggest that resveratrol might inhibit growth of LNCaP cells, at least, via decreasing phospho-serine 81 of AR, AR protein stability, and AR transcriptional activity. Citation Format: Yu-Ting Peng, Tzu-Yin Chen, Mei-Chih Chen, Eugene Lin, Ho Lin. Resveratrol regulates phospho-serine 81 androgen receptor and its stability to inhibit growth of 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 2121. doi:10.1158/1538-7445.AM2014-2121

Abstract 3309: Castration-resistant prostate cancer (CRPC) growth is mediated through gamma-aminobutyric acid a receptor (GABAAR)

Abstract The GABAergic signaling and growth factor pathways have been implicated in neuroendocrine differentiation and CRPC progression. We hypothesized that the GABAergic signaling and epidermal growth factor receptor (EGFR) pathway worked together to promote prostate cancer (PCa) progression. Using androgen receptor (AR)-negative PC-3 cells and AR-positive LNCaP cells derived from human PCa patients, we demonstrated that both cell lines responded to GABA(10-7M - 10-14M) and isoguvacine [a GABAAR antagonist] (10-7M - 10-11M) treatments over two days with elevated growth in a concentration-dependent manner (n=3 for each). Both GABA and isoguvacine also significantly (p<0.05) stimulated expressions of EGFR ligands (EGF, HB-EGF, and TGF-α) (n=3 for each) in both PCa cell lines as determined by real-time quantitative PCR. Immunoblot analyses indicated significant (p<0.05, n=3) elevation of phosphorylation levels of EGFR (Tyr1068) and downstream signal component Src (Tyr416) after GABA and isoguvacine treatments in both cell types with the same temporal changes as those observed with EGFR ligand expressions. Further involvement of GABAAR and EGFR signaling pathway in GABA and isoguvacine-stimulated PCa cell growth and signal transduction was studied using picrotoxin (a GABAAR antagonist) (10-6M ) and gefitinib (an EGFR inhibitor)( 10-6M). Both picrotoxin and gefitinib significantly (p<0.05, n=3) suppressed the GABA and isoguvacine-stimulated cell growth, as well as EGFR (Tyr1068) and Src (Tyr416) phosphorylation. Immunohistochemical studies of GABAAR α1 and phospho-Src (Tyr416) demonstrated that the presence of these molecules was largely limited to prostate carcinomatous glands, but the levels were extremely low or absent in the normal prostate. In addition, GABAAR α1 and phosphor-Src (Tyr416) were co-localized within the cancerous prostate. Our results demonstrate for the first time, that the GABAergic signaling in CRPC cells is mediated through the EGFR pathway, suggesting that GABA may work as autocrine or paracine to promote PCa progression. The clinical implications of this pathway in CRPC may be of significance by therapeutically targeting the GABAAR pathway. Citation Format: Weijuan Wu. Castration-resistant prostate cancer (CRPC) growth is mediated through gamma-aminobutyric acid a receptor (GABAAR). [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 3309. doi:10.1158/1538-7445.AM2014-3309

MP31-09 IDENTIFICATION OF A RETRO-TRANSPOSON DERIVED GENE ASSOCIATED WITH PROGRESSION TO NEUROENDOCRINE PROSTATE CANCER.

You have accessJournal of UrologyProstate Cancer: Basic Research II1 Apr 2014MP31-09 IDENTIFICATION OF A RETRO-TRANSPOSON DERIVED GENE ASSOCIATED WITH PROGRESSION TO NEUROENDOCRINE PROSTATE CANCER. Shusuke Akamatsu, Alexander Wyatt, Dong Lin, Summer Lysakowski, Fan Zhang, Soojin Kim, Ladan Fazli, Himisha Beltran, Mark Rubin, Amina Zoubeidi, Yuzhuo Wang, Colin Collins, and Martin Gleave Shusuke AkamatsuShusuke Akamatsu More articles by this author , Alexander WyattAlexander Wyatt More articles by this author , Dong LinDong Lin More articles by this author , Summer LysakowskiSummer Lysakowski More articles by this author , Fan ZhangFan Zhang More articles by this author , Soojin KimSoojin Kim More articles by this author , Ladan FazliLadan Fazli More articles by this author , Himisha BeltranHimisha Beltran More articles by this author , Mark RubinMark Rubin More articles by this author , Amina ZoubeidiAmina Zoubeidi More articles by this author , Yuzhuo WangYuzhuo Wang More articles by this author , Colin CollinsColin Collins More articles by this author , and Martin GleaveMartin Gleave More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2014.02.918AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The treatment of castration resistant prostate cancer has dramatically improved with the recent development of potent androgen receptor (AR) pathway inhibitors. However, stronger AR pathway inhibition appears to be driving resistance mechanisms that are independent of the AR axis, the most recognized of which is neuroendocrine prostate cancer (NEPC). To date, few genes have been associated with progression to NEPC. We developed a patient-derived xenograft model of NEPC trans-differentiation: a hormone-naïve adenocarcinoma that upon AR-blockade initially regresses, but rapidly relapses as NEPC. In this study, we carried out longitudinal expression profiling of xenograft tumors during the trans-differentiation process to identify genes associated with tumor cell survival post-castration and the development NEPC. METHODS Gene profiling of xenografts collected at different time points during the trans-differentiation were compared to data sets of human NEPC. Immunohistochemistry was performed using clinical NEPC samples. Loss of function studies were carried out using siRNA and shRNA in cell growth (WST-8), invasion (Boyden chamber) and migration (scratch) assays. RESULTS We identified a retro-transposon derived gene, Paternally Expressed 10 (PEG10), to be highly expressed during the early trans-differentiation stage and also in clinical NEPC. We confirmed at the protein level that PEG10 is up-regulated post-castration and further significantly elevated in terminal NEPC. PEG10 was highly expressed within NEPC foci of clinical samples. Knockdown of PEG10 in prostate cancer (PC) cells induced apoptosis and G0/G1 arrest, and also attenuated invasion and migration. We found PEG10 knockdown inhibited invasion and migration induced by TGF-β, and modulated response of the cells to TGF-β, resulting in decreased phosphorylation of Smad2 and Smad3, decrease in SBE4 luciferase reporter activity, and inhibition of Snail and Zeb1 induction. Collectively, these data show that PEG10 promotes PC cell growth, and also cooperates with TGF-β to promote invasion and migration of PC cells, conferring aggressive phenotype to these cells. CONCLUSIONS PEG10 is a gene associated both with growth and invasion of NEPC, and is a potential novel therapeutic target for the treatment of NEPC. © 2014FiguresReferencesRelatedDetails Volume 191Issue 4SApril 2014Page: e325 Advertisement Copyright & Permissions© 2014MetricsAuthor Information Shusuke Akamatsu More articles by this author Alexander Wyatt More articles by this author Dong Lin More articles by this author Summer Lysakowski More articles by this author Fan Zhang More articles by this author Soojin Kim More articles by this author Ladan Fazli More articles by this author Himisha Beltran More articles by this author Mark Rubin More articles by this author Amina Zoubeidi More articles by this author Yuzhuo Wang More articles by this author Colin Collins More articles by this author Martin Gleave More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Activation of the Wnt Pathway through AR79, a GSK3β Inhibitor, Promotes Prostate Cancer Growth in Soft Tissue and Bone

Due to its bone anabolic activity, methods to increase Wnt activity, such as inhibitors of dickkopf-1 and sclerostin, are being clinically explored. Glycogen synthase kinase (GSK3β) inhibits Wnt signaling by inducing β-catenin degradation, and a GSK3β inhibitor, AR79, is being evaluated as an osteoanabolic agent. However, Wnt activation has the potential to promote tumor growth; therefore, the goal of this study was to determine if AR79 has an impact on the progression of prostate cancer. Prostate cancer tumors were established in subcutaneous and bone sites of mice followed by AR79 administration, and tumor growth, β-catenin activation, proliferation, and apoptosis were assessed. Additionally, prostate cancer and osteoblast cell lines were treated with AR79, and β-catenin status, proliferation (with β-catenin knockdown in some cases), and proportion of ALDH(+)CD133(+) stem-like cells were determined. AR79 promoted prostate cancer tumor growth, decreased phospho-β-catenin, increased total and nuclear β-catenin, and increased tumor-induced bone remodeling. Additionally, AR79 treatment decreased caspase-3 and increased Ki67 expression in tumors and increased bone formation in normal mouse tibiae. Similarly, AR79 inhibited β-catenin phosphorylation, increased nuclear β-catenin accumulation in prostate cancer and osteoblast cell lines, and increased proliferation of prostate cancer cells in vitro through β-catenin. Furthermore, AR79 increased the ALDH(+)CD133(+) cancer stem cell-like proportion of the prostate cancer cell lines. In conclusion, AR79, while being bone anabolic, promotes prostate cancer cell growth through Wnt pathway activation. These data suggest that clinical application of pharmaceuticals that promote Wnt pathway activation should be used with caution as they may enhance tumor growth.

Human kallikrein 2 (KLK2) promotes prostate cancer cell growth via function as a modulator to promote the ARA70-enhanced androgen receptor transactivation

Recent data suggested that tissue human kallikrein 2 (KLK2) might be involved in the carcinogenesis and tumor metastasis of prostate cancer (PCa). However, the detailed pathophysiological roles of KLK2 in PCa remain unclear. We report here that KLK2 may be treated as a potential therapeutic target in castration-resistant PCa (CRPC). Histologic analyses show that the increased KLK2 expression is correlated with higher cell proliferation rate and lower cell apoptosis index in CRPC specimens. Adding functional KLK2 cDNA into high passage LNCaP cells led to increased cell growth, and knockdown of KLK2 expression with KLK2-siRNA in LNCaP cells resulted in increased cell apoptosis with cell growth arrest at the G1 phase. Results from in vitro colony formation assay and in vivo xenografted PCa tissues also demonstrated that targeting KLK2 led to suppressed growth of PCa in the castration-resistant stage. Further mechanism dissection shows that KLK2 may cooperate with the AR coregulator, ARA70, to enhance AR transactivation that may result in alteration of PCa formation. Together, these results suggested KLK2 might become a new therapeutic target to battle the CRPC and KLK2-siRNA may be developed as an alternative approach to suppress PCa growth.

The transcriptional co-activator SND1 is a novel regulator of alternative splicing in prostate cancer cells.

Splicing abnormalities have profound impact in human cancer. Several splicing factors, including SAM68, have pro-oncogenic functions, and their increased expression often correlates with human cancer development and progression. Herein, we have identified using mass spectrometry proteins that interact with endogenous SAM68 in prostate cancer (PCa) cells. Among other interesting proteins, we have characterized the interaction of SAM68 with SND1, a transcriptional co-activator that binds spliceosome components, thus coupling transcription and splicing. We found that both SAM68 and SND1 are upregulated in PCa cells with respect to benign prostate cells. Upregulation of SND1 exerts a synergic effect with SAM68 on exon v5 inclusion in the CD44 mRNA. The effect of SND1 on CD44 splicing required SAM68, as it was compromised after knockdown of this protein or mutation of the SAM68-binding sites in the CD44 pre-mRNA. More generally, we found that SND1 promotes the inclusion of CD44 variable exons by recruiting SAM68 and spliceosomal components on CD44 pre-mRNA. Inclusion of the variable exons in CD44 correlates with increased proliferation, motility and invasiveness of cancer cells. Strikingly, we found that knockdown of SND1, or SAM68, reduced proliferation and migration of PCa cells. Thus, our findings strongly suggest that SND1 is a novel regulator of alternative splicing that promotes PCa cell growth and survival.

MicroRNA-185 and 342 Inhibit Tumorigenicity and Induce Apoptosis through Blockade of the SREBP Metabolic Pathway in Prostate Cancer Cells

MicroRNA (miRNA or miR) inhibition of oncogenic related pathways has been shown to be a promising therapeutic approach for cancer. Aberrant lipid and cholesterol metabolism is involved in prostate cancer development and progression to end-stage disease. We recently demonstrated that a key transcription factor for lipogenesis, sterol regulatory element-binding protein-1 (SREBP-1), induced fatty acid and lipid accumulation and androgen receptor (AR) transcriptional activity, and also promoted prostate cancer cell growth and castration resistance. SREBP-1 was overexpressed in human prostate cancer and castration-resistant patient specimens. These experimental and clinical results indicate that SREBP-1 is a potential oncogenic transcription factor in prostate cancer. In this study, we identified two miRNAs, miR-185 and 342, that control lipogenesis and cholesterogenesis in prostate cancer cells by inhibiting SREBP-1 and 2 expression and down-regulating their targeted genes, including fatty acid synthase (FASN) and 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR). Both miR-185 and 342 inhibited tumorigenicity, cell growth, migration and invasion in prostate cancer cell culture and xenograft models coincident with their blockade of lipogenesis and cholesterogenesis. Intrinsic miR-185 and 342 expression was significantly decreased in prostate cancer cells compared to non-cancerous epithelial cells. Restoration of miR-185 and 342 led to caspase-dependent apoptotic death in prostate cancer cells. The newly identified miRNAs, miR-185 and 342, represent a novel targeting mechanism for prostate cancer therapy.

Proto-oncogene Activity of Melanoma Antigen-A11 (MAGE-A11) Regulates Retinoblastoma-related p107 and E2F1 Proteins

Melanoma antigen-A11 (MAGE-A11) is a low-abundance, primate-specific steroid receptor coregulator in normal tissues of the human reproductive tract that is expressed at higher levels in prostate cancer. Increased expression of MAGE-A11 enhances androgen receptor transcriptional activity and promotes prostate cancer cell growth. Further investigation into the mechanisms of MAGE-A11 function in prostate cancer demonstrated interactions with the retinoblastoma-related protein p107 and Rb tumor suppressor but no interaction with p130 of the Rb family. MAGE-A11 interaction with p107 was associated with transcriptional repression in cells with low MAGE-A11 and transcriptional activation in cells with higher MAGE-A11. Selective interaction of MAGE-A11 with retinoblastoma family members suggested the regulation of E2F transcription factors. MAGE-A11 stabilized p107 by inhibition of ubiquitination and linked p107 to hypophosphorylated E2F1 in association with the stabilization and activation of E2F1. The androgen receptor and MAGE-A11 modulated endogenous expression of the E2F1-regulated cyclin-dependent kinase inhibitor p27(Kip1). The ability of MAGE-A11 to increase E2F1 transcriptional activity was similar to the activity of adenovirus early oncoprotein E1A and depended on MAGE-A11 interactions with p107 and p300. The immunoreactivity of p107 and MAGE-A11 was greater in advanced prostate cancer than in benign prostate, and knockdown with small inhibitory RNA showed that p107 is a transcriptional activator in prostate cancer cells. These results suggest that MAGE-A11 is a proto-oncogene whose increased expression in prostate cancer reverses retinoblastoma-related protein p107 from a transcriptional repressor to a transcriptional activator of the androgen receptor and E2F1.

SATB1 is overexpressed in metastatic prostate cancer and promotes prostate cancer cell growth and invasion

BackgroundSpecial AT-rich sequence binding protein 1 (SATB1) is a nuclear factor that functions as the global chromatin organizer to regulate chromatin structure and gene expression gene expression. SATB1 has been shown to be abnormally expressed in various types of cancer. However, the expression and role of SATB1 in prostate cancer remain unclear.Methods120 cases of prostatic carcinoma and 60 cases of benign prostate hyperplasia were analyzed for SATB1 expression by immunohistochemistry. LNCaP, DU-145, and PC3 prostate cancer cells were examined for SATB1 expression by Western blot analysis. Cell proliferation and invasion was evaluated by CCK8 and transwell invasion assay, respectively.ResultsSATB1 staining was stronger in prostatic carcinomas with metastasis than in those without metastasis, but was absent in benign prostate hyperplasia. Furthermore, SATB1 expression was positively correlated with bone metastasis and the Gleason score. SATB1 overexpression promoted the proliferation and invasion of LNCaP cells while SATB1 knockdown inhibited the proliferation and invasion of DU-145 cells.ConclusionsThese findings provide novel insight into oncogenic role of SATB1 in prostate cancer, suggesting that SATB1 is a promising biomarker and therapeutic target for prostate cancer.