Regulates Prostate Cancer Research Articles

Abstract 979: Identification of a novel long noncoding RNA within the LCK gene locus that regulates prostate cancer cell growth

Abstract Prostate cancer remains the second most common type of cancer and frequent cause of cancer-related mortality in American men. Even though many patients with metastatic prostate cancer will initially respond to androgen deprivation therapy, virtually all patients will relapse and develop lethal castration-resistant prostate cancer. Long noncoding RNAs (lncRNAs) are emerging as critical regulatory elements of many cellular biological processes, and there is increasing evidence demonstrating that dysregulation of lncRNAs is associated with many human cancers, including cancers of the prostate, breast, and lung. We have discovered in a high-throughput RNAi screen identifying regulators of prostate cancer cell growth that knockdown of lymphocyte-specific protein tyrosine kinase (LCK) significantly decreases growth of prostate cancer cells in the presence and absence of androgen. Surprisingly, immunoprecipitation and western blot analyses show that LCK is not expressed at the protein level in prostate cancer cells. Rapid amplification of cDNA ends (RACE) and sequencing have revealed that a previously unannotated lncRNA lies within exon six and the 3’UTR of the LCK gene. While short hairpin RNAs (shRNAs) targeting the carboxy-terminus of the LCK gene decreases cell growth, expression of shRNAs specific for the amino-terminus has no effect on growth. Furthermore, only quantitative polymerase chain reaction (qPCR) primers directed toward the 3’ section of the LCK gene yield detectable levels of transcript. These data provide further validation for the existence of a lncRNA within the LCK gene locus. Remarkably, the lncRNA situated within the LCK gene is dramatically upregulated in response to androgen. Therefore, we have labeled this lncRNA “HULLK” for Hormone-upregulated lncRNA within LCK. Cellular fractionation and qPCR show that HULLK predominantly localizes to the cytoplasm. In addition to the effects on prostate cancer cell growth, we have data that alludes to the increase in transcript levels of several Src family members following depletion of HULLK. Thus, these studies indicate that the LCK gene contains a lncRNA involved in the regulation of prostate cancer cell growth and perhaps transcription. While additional analyses will be required to fully characterize HULLK, our data suggest that it may serve as a novel regulator of prostate cancer proliferation. Citation Format: Huy Q. Ta, Samuel R. Jackson, Hilary Whitworth, Shriti Bhadel, Daniel Gioeli. Identification of a novel long noncoding RNA within the LCK gene locus that regulates prostate cancer cell growth. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 979.

Abstract 1091: miR-125 family of miRNAs mediates prostate cancer cell proliferation and migration

Abstract Background: Prostate cancer is the second most common malignancy in American men and causes ∼27540 deaths per annum. microRNAs (miRNAs) are a class of short non-coding RNAs that regulate the expression of protein-coding genes via either mRNA degradation or translational repression. These small molecules are known to be aberrantly expressed in prostate cancer (PCa) and possess both tumor suppressive and oncogenic properties. miR-125 is a highly conserved miRNA family comprised of three homolog members hsa-miR-125a, hsa-miR-125b-1, and hsa-miR-125b-2. Members of this family have been attributed both disease suppressing and promoting functions in certain contexts however their role in PCa has yet to be fully elucidated. Methods: miRNA expression was evaluated in a publicly available dataset (GSE21032) comprised of 28 normal, 98 primary PCa and 13 metastasis samples. miR-125 expression was assessed in a panel of 8 prostate cell lines comprising PrEC prostate epithelial cells, RWPE-1, BPH1, DU145, LNCaP, C4-2B, PC3, and PC3-2M cell lines using the Qiagen miScript system. MirWalk was used to identify predicted targets of the miRNAs. miR-125 expression was transiently inhibited in LNCaP, C4-2B, PC3, and PC3-2M cell lines using miScript miRNA inhibitors and miRNA and target mRNA expression, cell proliferation and migration were measured post-transfection. Results: Analysis of human data revealed miR-125a-3p was significantly up-regulated in metastasis samples compared to both primary PCa and normal tissues (log fold change (FC) 1.743, p-value 9.01E-08 logFC = 1.536 p-value = 8.80E-08 respectively). Next, we validated miR-125 family member expression in prostate cancer cell lines compared to PrEC and RWPE-1 prostate epithelial cells. Most notably, we observed that miR-125b-2 expression was significantly higher in all prostate cancer cell lines. Inhibition of miR-125b-2, significantly reduced the proliferation of the LNCaP, C4-2B, and PC3-2M cell lines. Moreover, inhibition of this miRNA significantly impaired prostate cancer cell migration by 43.8% (p-value = 0.003). Using MirWalk, we examined potential targets for regulation by miR-125b-2 and identified the potent tumor suppressor Quaking family as top hit. Our results show that inhibition of miR-125b-2 significantly enhanced the expression of Quaking family members (1.79 fold). Conclusions: Our results demonstrate that the miR-125 family of miRNAs plays a role in regulating prostate cancer cell proliferation and migration, potentially by mitigating Quaking activity. Citation Format: Sinead T. Aherne, Fiona O’Neill, Stephen F. Madden, Martin Clynes, Conor C. Lynch. miR-125 family of miRNAs mediates prostate cancer cell proliferation and migration. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1091.

453 - Protein kinase CK2 regulates prostate cancer cell migration and proliferation through phosphorylation of PRH/HHEX

453 - Protein kinase CK2 regulates prostate cancer cell migration and proliferation through phosphorylation of PRH/HHEX

The AR/NCOA1 axis regulates prostate cancer migration by involvement of PRKD1.

Due to the urgent need for new prostate cancer (PCa) therapies, the role of androgen receptor (AR)-interacting proteins should be investigated. In this study we aimed to address whether the AR coactivator nuclear receptor coactivator 1 (NCOA1) is involved in PCa progression. Therefore, we tested the effect of long-term NCOA1 knockdown on processes relevant to metastasis formation. [(3)H]-thymidine incorporation assays revealed a reduced proliferation rate in AR-positive MDA PCa 2b and LNCaP cells upon knockdown of NCOA1, whereas AR-negative PC3 cells were not affected. Furthermore, Boyden chamber assays showed a strong decrease in migration and invasion upon NCOA1 knockdown, independently of the cell line's AR status. In order to understand the mechanistic reasons for these changes, transcriptome analysis using cDNA microarrays was performed. Protein kinase D1 (PRKD1) was found to be prominently up-regulated by NCOA1 knockdown in MDA PCa 2b, but not in PC3 cells. Inhibition of PRKD1 reverted the reduced migratory potential caused by NCOA1 knockdown. Furthermore, PRKD1 was negatively regulated by AR. Immunohistochemical staining of PCa patient samples revealed a strong increase in NCOA1 expression in primary tumors compared with normal prostate tissue, while no final conclusion could be drawn for PRKD1 expression in tumor specimens. Thus, our findings directly associate the AR/NCOA1 complex with PRKD1 regulation and cellular migration and support the concept of therapeutic inhibition of NCOA1 in PCa.

Lymphatic endothelial cells actively regulate prostate cancer cell invasion.

Lymphatic vessels serve as the primary route for metastatic spread to lymph nodes. However, it is not clear how interactions between cancer cells and lymphatic endothelial cells (LECs), especially within hypoxic microenvironments, affect the invasion of cancer cells. Here, using an MR compatible cell perfusion assay, we investigated the role of LEC-prostate cancer (PCa) cell interaction in the invasion and degradation of the extracellular matrix (ECM) by two human PCa cell lines, PC-3 and DU-145, under normoxia and hypoxia, and determined the metabolic changes that occurred under these conditions. We observed a significant increase in the invasion of ECM by invasive PC-3 cells, but not poorly invasive DU-145 cells when human dermal lymphatic microvascular endothelial cells (HMVEC-dlys) were present. Enhanced degradation of ECM by PC-3 cells in the presence of HMVEC-dlys identified interactions between HMVEC-dlys and PCa cells influencing cancer cell invasion. The enhanced ECM degradation was partly attributed to increased MMP-9 enzymatic activity in PC-3 cells when HMVEC-dlys were in close proximity. Significantly higher uPAR and MMP-9 expression levels observed in PC-3 cells compared to DU-145 cells may be one mechanism for increased invasion and degradation of matrigel by these cells irrespective of the presence of HMVEC-dlys. Hypoxia significantly decreased invasion by PC-3 cells, but this decrease was significantly attenuated when HMVEC-dlys were present. Significantly higher phosphocholine was observed in invasive PC-3 cells, while higher glycerophosphocholine was observed in DU-145 cells. These metabolites were not altered in the presence of HMVEC-dlys. Significantly increased lipid levels and lipid droplets were observed in PC-3 and DU-145 cells under hypoxia reflecting an adaptive survival response to oxidative stress. These results suggest that in vivo, invasive cells in or near lymphatic endothelial cells are likely to be more invasive and degrade the ECM to influence the metastatic cascade. Copyright © 2016 John Wiley & Sons, Ltd.

Endogenous GAS6 and Mer receptor signaling regulate prostate cancer stem cells in bone marrow.

GAS6 and its receptors (Tryo 3, Axl, Mer or “TAM”) are known to play a role in regulating tumor progression in a number of settings. Previously we have demonstrated that GAS6 signaling regulates invasion, proliferation, chemotherapy-induced apoptosis of prostate cancer (PCa) cells. We have also demonstrated that GAS6 secreted from osteoblasts in the bone marrow environment plays a critical role in establishing prostate tumor cell dormancy. Here we investigated the role that endogenous GAS6 and Mer receptor signaling plays in establishing prostate cancer stem cells in the bone marrow microenvironment.We first observed that high levels of endogenous GAS6 are expressed by disseminated tumor cells (DTCs) in the bone marrow, whereas relatively low levels of endogenous GAS6 are expressed in PCa tumors grown in a s.c. setting. Interestingly, elevated levels of endogenous GAS6 were identified in putative cancer stem cells (CSCs, CD133+/CD44+) compared to non-CSCs (CD133–/CD44–) isolated from PCa/osteoblast cocultures in vitro and in DTCs isolated from the bone marrow 24 hours after intracardiac injection. Moreover, we found that endogenous GAS6 expression is associated with Mer receptor expression in growth arrested (G1) PCa cells, which correlates with the increase of the CSC populations. Importantly, we found that overexpression of GAS6 activates phosphorylation of Mer receptor signaling and subsequent induction of the CSC phenotype in vitro and in vivo.Together these data suggest that endogenous GAS6 and Mer receptor signaling contribute to the establishment of PCa CSCs in the bone marrow microenvironment, which may have important implications for targeting metastatic disease.

249 Cell surface branching glycan regulates prostate cancer invasiveness by enhancing α5β1 integrin signaling

249 Cell surface branching glycan regulates prostate cancer invasiveness by enhancing α5β1 integrin signaling

MicroRNA 338-3p exhibits tumor suppressor role and its down-regulation is associated with adverse clinical outcome in prostate cancer patients

MicroRNAs (miRNAs) are small non-coding RNAs that function in transcriptional and post-transcriptional regulation of gene expression. Several miRNAs have been implicated in regulating prostate cancer (PCa) progression. Deregulations of miRNA regulatory networks have been reported in ERG positive PCa, which accounts for ~50% of PCa and have been suggested to affect tumor aggressiveness. The function of miR338-3p, its prognostic significance, and its association with ERG positive PCa has not been fully investigated. Using microarray expression profiling, we identified miRNA338-3p as among the top deregulated miRNAs associated with ERG status in PCa. We investigated miR338-3p function using in vitro and in vivo experimental models and its expression was assessed and validated in clinical samples and a public cohort of localized and metastatic prostate cancer. miR338-3p was significantly down-regulated with disease progression from benign prostate tissue to primary and metastatic lesions. In localized disease, patients with lower miR338-3p expression levels showed increased association to biochemical recurrence and several adverse pathological parameters compared to patients with higher miRNA338-3p tissue expression levels. Using in vitro PCa cell models, overexpression of miR338-3p resulted in a decrease in cell invasion and expression of chemokine signalling genes CXCL12, CXCR4, and CXCR7. In vivo, orthotropic implantation of PC3 cells stably expressing miR338-3p was associated with a significant decrease in tumor weights compared to control cells. miR338-3p has anti-proliferative and anti-invasive properties. It affects CXCR4 axis, and its down-regulation is associated with adverse clinical outcomes in PCa patients.

I-branching N-acetylglucosaminyltransferase regulates prostate cancer invasiveness by enhancing α5β1 integrin signaling.

Cell surface carbohydrates are important for cell migration and invasion of prostate cancer (PCa). Accordingly, the I‐branching N‐acetylglucosaminyltransferase (GCNT2) converts linear i‐antigen to I‐branching glycan, and its expression is associated with breast cancer progression. In the present study, we identified relationships between GCNT2 expression and clinicopathological parameters in patients with PCa. Paraffin‐embedded PCa specimens were immunohistochemically tested for GCNT2 expression, and the roles of GCNT2 in PCa progression were investigated using cell lines with high GCNT2 expression and low GCNT2 expression. GCNT2‐positive cells were significantly lesser in organ‐confined disease than in that with extra‐capsular extensions, and GCNT2‐negative tumors were associated with significantly better prostate‐specific antigen‐free survival compared with GCNT2‐positive tumors. Subsequent functional studies revealed that knockdown of GCNT2 expression in PCa cell lines significantly inhibited cell migration and invasion. GCNT2 regulated the expression of cell surface I‐antigen on the O‐glycan and glycolipid. Moreover, I‐antigen‐bearing glycolipids were subject to α5β1 integrin–fibronectin mediated protein kinase B phosphorylation. In conclusion, GCNT2 expression is closely associated with invasive potential of PCa.

Estrogen Exhibits a Biphasic Effect on Prostate Tumor Growth through the Estrogen Receptor β-KLF5 Pathway.

Estrogens are effective in the treatment of prostate cancer; however, the effects of estrogens on prostate cancer are enigmatic. In this study, we demonstrated that estrogen (17β-estradiol [E2]) has biphasic effects on prostate tumor growth. A lower dose of E2 increased tumor growth in mouse xenograft models using DU145 and PC-3 human prostate cancer cells, whereas a higher dose significantly decreased tumor growth. We found that anchorage-independent apoptosis in these cells was inhibited by E2 treatment. Similarly, in vivo angiogenesis was suppressed by E2. Interestingly, these effects of E2 were abolished by knockdown of either estrogen receptor β (ERβ) or Krüppel-like zinc finger transcription factor 5 (KLF5). Ιn addition, E2 suppressed KLF5-mediated transcription through ERβ, which inhibits proapoptotic FOXO1 and proangiogenic PDGFA expression. Furthermore, we revealed that a nonagonistic ER ligand GS-1405 inhibited FOXO1 and PDGFA expression through the ERβ-KLF5 pathway and regulated prostate tumor growth without ERβ transactivation. Therefore, these results suggest that E2 biphasically modulates prostate tumor formation by regulating KLF5-dependent transcription through ERβ and provide a new strategy for designing ER modulators, which will be able to regulate prostate cancer progression with minimal adverse effects due to ER transactivation.

Differential Roles of Carboxylated and Uncarboxylated Osteocalcin in Prostate Cancer Growth.

Serum levels of osteocalcin (OC), a bone matrix non-collagenous protein secreted by osteoblasts, are correlated with pathological bone remodeling such as the bone metastasis of cancer, as well as physiological bone turnover. The pathological roles in prostate cancer growth of the two existing types of serum OC, γ-carboxylated (GlaOC) and lower- (or un-) carboxylated (GluOC), have not yet been discriminatively examined. In the present study, we demonstrate that normal prostate epithelial cell growth was promoted by both types of OC, while growth of cancer cells in the prostate was accelerated by GlaOC but suppressed by GluOC. We suggest that OC regulates prostate cancer growth depending on the γ-carboxylation, in part by triggering reduced phosphorylation of receptor tyrosine kinases.

Metabolic and molecular regulation of dietary polyunsaturated fatty acids on prostate cancer.

The aim of this study is to investigate the role of n-3 and n-9 fatty acids in crucial processes involved in prostate cancer cell growth through a large-scale proteomic analysis. We used a label-free protein quantification method to profile global protein expression of fish oil and oleic acid treated PCa cells and validated a panel of differentially expressed proteins by either Western blot or multiple reaction monitoring. Bioinformatic analysis was also performed to uncover the pathways involved in fatty acid metabolism. Fish oil, not oleic acid, suppresses prostate cancer cell viability. Assessment of fatty acid synthesis pathway activity also shows that oleic acid is a more potent inhibitor than fish oil on de novo fatty acid synthesis. Although fatty acid synthase activity decreases with fish oil treatment, the inhibition of its activity occurs over time while reduction in viability occurs within 24 h. Bioinformatic analysis revealed the pathways altered by these fatty acid treatments. This study suggests that suppression of cell viability by fish oil is independent of fatty acid synthase and fish oil regulates prostate cancer cells through activation of other pathways depending upon length of exposure to fish oil.

Muscarinic Receptor Type-1 Regulates Centrally Hematopoietic Stem Cell Mobilization By Granulocyte-Colony Stimulating Factor Via the Hypothalamic-Pituitary Axis

Hematopoietic stem cells (HSCs) give rise to the cellular constituents of the blood throughout the lifetime. Transplantation of healthy HSCs is the only curative therapy for many hematologic disorders. Collection of these cells is most commonly achieved by administration of granulocyte colony stimulating factor (G-CSF), which mobilizes HSCs from specialized niches within the bone marrow (BM) to peripheral blood for collection. The mechanisms behind G-CSF-induced mobilization remains incompletely understood and may have broad implications about how healthy or cancer cells migrate. We have previously identified a role of signals from the sympathetic nervous system in regulating HSC mobilization (Katayama et al. Cell, 2006) and more recent studies have revealed cholinergic nerves from the parasympathetic nervous system regulated prostate cancer metastasis via the muscarinic receptor type-1 (Chrm1; Magnon et al. Science, 2013). This led us to explore whether Chrm1 could also regulate the migration of HSCs during enforced mobilization. Although steady-state HSC numbers are not altered in the BM of Chrm1−/− mice, G-CSF-induced mobilization of HSPCs to the blood was reduced by ~54% (p=0.008) compared to wild-type (WT) mice. Competitive transplantation of WT and Chrm1−/− blood revealed reduced long-term (16 weeks) repopulating capacity in mutant mice, confirming that the mobilization of functional HSCs was impaired. Although Chrm1 was robustly expressed in the prostate, we did not detect Chrm1 expression by qPCR in HSCs or sorted putative cellular niche constituents (Nestin+ cells, osteoblasts, endothelial cells, and macrophages), suggesting that cholinergic activity was located outside the BM. We thus tested the hypothesis that Chrm1 expression in the brain alters HSC behavior in the BM. To this end, we inhibited Chrm1 with pirenzepine, a specific antagonist that does not cross the blood-brain barrier. Whereas intra-peritoneal pirenzepine administration did not affect HSC mobilization, intra-cerebral pirenzepine administration significantly reduced mobilization (by ~45%, p=0.003), to a similar extent as the knockout mouse. These results suggest that cholinergic signals from the central nervous system (CNS), rather than the peripheral nervous system were required for robust mobilization of HSCs. To investigate the mechanisms by which CNS signals were relayed to HSCs within the BM, we generated chimeric parabions in which WT and Chrm1−/− mice were surgically joined and subsequently mobilized with G-CSF. We found that a paired WT rescued the mobilization defect of Chrm1−/− mice, suggesting that the CNS to BM relay was mediated by a circulating factor. Chrm1 was highly expressed in the hypothalamus of WT brains by qPCR and immunofluorescence. Chemical denervation of the hypothalamus by neonatal monosodium glutamate treatment reduced HSC mobilization (by ~32%, p=0.003), identifying a role for hypothalamic signals in G-CSF mobilization of HSCs. Since the hypothalamus regulates pituitary hormone release, we evaluated their levels. We found that plasma ACTH levels were modestly reduced, combined with a significant reduction in circulating corticosterone (by ~50%, p=0.002) and a dramatic reduction of corticosterone in BM extracellular fluid (by ~98%, p=0.007), suggesting a deficiency in glucocorticoids (GC). Treatment of WT mice with metyrapone, an inhibitor of GC synthesis, significantly reduced HSC mobilization (by ~25%, p<0.05). Furthermore, GC administration rescued the HSC mobilization deficit of Chrm1−/− mice. However, administration of GC above the physiological levels inhibited G-CSF mobilization efficiency. Immunofluorescence analyses revealed reductions in nuclear translocation of the GC receptor (Nr3c1) in HSCs derived from Chrm1−/− mice, a hallmark of nuclear receptor activity. In addition, GC enhanced the migration (by ~2 fold, p<0.05) of WT colony forming progenitors in vitro, suggesting cell-autonomous signaling of GC with their receptor may be necessary during G-CSF mobilization. Ongoing studies are evaluating whether the niche or hematopoietic cells requires GC receptors using Nr3c1-floxed mice. These data are to our knowledge the first direct demonstration of CNS regulation of HSC mobilization and uncover a critical function for physiological levels of GC in enabling HSC migration. DisclosuresNo relevant conflicts of interest to declare.

MicroRNA-125a-5p regulates cancer cell proliferation and migration through NAIF1 in prostate carcinoma.

BackgroundWe investigated the functional roles of microRNA-125a-5p in regulating human prostate carcinoma.MethodsQuantitative reverse transcription-polymerase chain reaction (qRT-PCR) was conducted to evaluate the gene expression levels of miR-125a-5p in eight prostate cancer cell lines and nine biopsy specimens from patients with prostate cancer. miR-125a-5p was genetically knocked down in prostate cancer cell lines, DU145 and VCaP cells by lentiviral transduction. The effects of miR-125a-5p downregulation on prostate cancer cell proliferation and migration were evaluated by MTT assay and transwell assay, respectively. Direct regulation of miR-125a-5p on its downstream targets, NAIF1, and apoptotic gene caspase-3 were evaluated through dual-luciferase reporter assay, qRT-PCR, and Western blot, respectively. NAIF1 was then ectopically overexpressed in DU145 and VCaP cells to modulate prostate cancer cell proliferation and migration. Finally, the effects of miR-125a-5p downregulation or NAIF1 overexpression on the growth of in vivo prostate cancer xenograft were evaluated.ResultsmiR-125a-5p was upregulated in prostate cancer cell lines and human prostate carcinomas. Lentivirus induced miR-125a-5p downregulation in DU145 and VCaP cells inhibited prostate cancer cell proliferation or migration. NAIF1 was the direct target of miR-125a-5p, as both gene and protein expression levels of NAIF1, as well as caspase-3 were upregulated by miR-125a-5p. Forced overexpression of NAIF1 had similar antitumor effects as miR-125a-5p downregulation on prostate cancer cell proliferation and migration. In vivo prostate xenograft assay confirmed the tumor-suppressive effect of miR-125a-5p downregulation or NAIF1 overexpression.ConclusionmiR-125a-5p regulates prostate cancer cell proliferation and migration through NAIF1.

Protein phosphatase 1 suppresses androgen receptor ubiquitylation and degradation.

The phosphoprotein phosphatases are emerging as important androgen receptor (AR) regulators in prostate cancer (PCa). We reported previously that the protein phosphatase 1 catalytic subunit (PP1α) can enhance AR activity by dephosphorylating a site in the AR hinge region (Ser650) and thereby decrease AR nuclear export. In this study we show that PP1α increases the expression of wildtype as well as an S650A mutant AR, indicating that it is acting through one or more additional mechanisms. We next show that PP1α binds primarily to the AR ligand binding domain and decreases its ubiquitylation and degradation. Moreover, we find that the PP1α inhibitor tautomycin increases phosphorylation of AR ubiquitin ligases including SKP2 and MDM2 at sites that enhance their activity, providing a mechanism by which PP1α may suppress AR degradation. Significantly, the tautomycin mediated decrease in AR expression was most pronounced at low androgen levels or in the presence of the AR antagonist enzalutamide. Consistent with this finding, the sensitivity of LNCaP and C4-2 PCa cells to tautomycin, as assessed by PSA synthesis and proliferation, was enhanced at low androgen levels or by treatment with enzalutamide. Together these results indicate that PP1α may contribute to stabilizing AR protein after androgen deprivation therapies, and that targeting PP1α or the AR-PP1α interaction may be effective in castration-resistant prostate cancer (CRPC).

Checkpoint Kinase 2 Negatively Regulates Androgen Sensitivity and Prostate Cancer Cell Growth.

Prostate cancer is the second leading cause of cancer death in American men, and curing metastatic disease remains a significant challenge. Nearly all patients with disseminated prostate cancer initially respond to androgen deprivation therapy (ADT), but virtually all patients will relapse and develop incurable castration-resistant prostate cancer (CRPC). A high-throughput RNAi screen to identify signaling pathways regulating prostate cancer cell growth led to our discovery that checkpoint kinase 2 (CHK2) knockdown dramatically increased prostate cancer growth and hypersensitized cells to low androgen levels. Mechanistic investigations revealed that the effects of CHK2 were dependent on the downstream signaling proteins CDC25C and CDK1. Moreover, CHK2 depletion increased androgen receptor (AR) transcriptional activity on androgen-regulated genes, substantiating the finding that CHK2 affects prostate cancer proliferation, partly, through the AR. Remarkably, we further show that CHK2 is a novel AR-repressed gene, suggestive of a negative feedback loop between CHK2 and AR. In addition, we provide evidence that CHK2 physically associates with the AR and that cell-cycle inhibition increased this association. Finally, IHC analysis of CHK2 in prostate cancer patient samples demonstrated a decrease in CHK2 expression in high-grade tumors. In conclusion, we propose that CHK2 is a negative regulator of androgen sensitivity and prostate cancer growth, and that CHK2 signaling is lost during prostate cancer progression to castration resistance. Thus, perturbing CHK2 signaling may offer a new therapeutic approach for sensitizing CRPC to ADT and radiation.

MicroRNA-340 inhibits prostate cancer cell proliferation and metastasis by targeting the MDM2-p53 pathway.

An increasing number of studies have demonstrated the important role of microRNAs (miRNAs) in modulating cancer progression and metastasis, but the mechanisms by which miRNAs regulate prostate cancer (PCa) tumorigenesis remain poorly understood. In the present study, we found that miR-340 may act as a tumor suppressor based on our finding that it was significantly downregulated in PCa tumor tissues and cell lines. Moreover, the expression of miR-340 was found to be correlated with the inhibition of cell proliferation, migration and invasion in vitro, and had a suppressive effect on tumor growth in a xenograft mouse model as well. The suppressive effect of miR-340 overexpression was observed in cell lines DU145 and BPH-1 which express wild-type (WT) p53. However, in the p53-null PC-3 cell line, the suppressive effect was not found, indicating that miR-340 may play a critical role in the p53 pathway. Further investigation revealed that mouse double minute 2 (MDM2), an important regulator of p53, was targeted by miR-340 through the direct binding to the 3'UTR of MDM2, which inhibited MDM2 translation. In addition, miR-340 expression stabilized p53 protein levels which caused an increase in p21 expression but a decrease in the anti‑apoptotic protein, BCL-2, in the p53 WT cell lines. Moreover, the miR-340-mediated inhibition of cell progression was mitigated by re-expressing MDM2 in the stable miR‑340-overexpressing PCa cell line, which harbors WT p53. Our findings suggest that miR-340 may function as a novel tumor suppressor in PCa through the MDM2-p53 pathway by directly targeting MDM2, which may be a promising miRNA-targeted therapy for PCa.

Highlights of This Issue

Accumulation of reactive oxygen species (ROS) causes injury to cell structures, ultimately leading to cancer development. The antioxidant enzyme heme oxygenase 1 (HMOX1/HO-1) is responsible for the maintenance of the cellular homeostasis, playing a critical role in the oxidative stress and the regulation of prostate cancer (PCa) development and progression. Labanca and colleagues demonstrate that activation of BRCA1-NRF2/HO-1 axis defines a new molecular mechanism for the maintenance of the cellular homeostasis in PCa.Recent evidence indicates that the cytotoxicity of PARP inhibitors is due in part to trapping of PARP onto single-strand breaks. It has been proposed that a subset of PARP inhibitors trap allosterically; however, direct evidence of this has not been reported. The study by Hopkins and colleagues reveals that trapping is not allosteric and is instead due to catalytic inhibition. Additionally, trapping is associated with reduced tolerability in vivo, and PARP inhibitors spanning a broad range of trapping potency elicit comparable efficacy at MTD in xenograft models. These results have implications for the suitability of different PARP inhibitors for inclusion in different combination regimens.The tumor microenvironment (TME) is involved in promoting tumor survival and progression. The current study investigates intercellular communication within the TME between colorectal cancer and immune cells using in vitro co-culture systems. Interestingly, immune cell IL6 secretion promotes cancer cell invasion and release of miR-21 and miR-29b, which stimulates further IL6 production by surrounding immune cells. These findings offer a deeper understanding of how cells communicate within the TME and demonstrate that miRNAs are important mediators of this process. Identifying these key signals is crucial for the development of novel therapies targeting the TME.The tumor suppressive actions proposed for vitamin D include its capacity to inhibit Wnt signaling. Identifying a subset of vitamin D receptor (VDR)-expressing pancreatic cancer cells responsive to calcipotriol, a vitamin D analog, Arensman and coworkers describe a novel biochemical mechanism through which vitamin D inhibits Wnt signaling. Calcipotriol increased LDLR-adaptor protein 1 (LDLRAP1) expression resulting in rapid reduction in protein levels of LDLR-related protein 6 (LRP6), a requisite co-receptor for canonical Wnt signaling. Inhibition of Wnt signaling decreased VDR expression; thus, revealing a reciprocal feedback loop between Wnt and vitamin D signaling. In summary, calcipotriol or other vitamin D analogs may be particularly efficacious against tumors with intact VDR and Wnt signaling activity.

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

BackgroundSystematic approaches to functionally identify key players in microRNA (miRNA)-target networks regulating prostate cancer (PCa) proliferation are still missing. ObjectiveTo comprehensively map miRNA regulation of genes relevant for PCa proliferation through phenotypic screening and tumor expression data. Design, setting, and participantsGain-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 analysisRank 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 limitationsFunctional 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. ConclusionsA 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 summaryThis 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.

Autocrine Activation of CHRM3 Promotes Prostate Cancer Growth and Castration Resistance via CaM/CaMKK-Mediated Phosphorylation of Akt.

Although a previous study reported nerve ending-derived acetylcholine promoted prostate cancer invasion and metastasis by regulating the microenvironment of cancer cells, the present study aims to determine whether there is autocrine cholinergic signaling in prostate epithelial cells that promotes prostate cancer growth and castration resistance. In this study, IHC was performed to detect protein expression in mouse prostate tissue sections and human prostate cancer tissue sections. Subcutaneously and orthotopically xenografted tumor models were established to evaluate the functions of autocrine cholinergic signaling in regulating prostate cancer growth and castration resistance. Western blotting analysis was performed to assess the autocrine cholinergic signaling-induced signaling pathway. We found the expression of choline acetyltransferase (ChAT), the secretion of acetylcholine and the expression of CHRM3 in prostate epithelial cells, supporting the presence of autocrine cholinergic signaling in the prostate epithelium. In addition, we found that CHRM3 was upregulated in clinical prostate cancer tissues compared with adjacent non-cancer tissues. Overexpression of CHRM3 or activation of CHRM3 by carbachol promoted cell proliferation, migration, and castration resistance. On the contrary, blockading CHRM3 by shRNA or treatment with darifenacin inhibited prostate cancer growth and castration resistance both in vitro and in vivo. Furthermore, we found that autocrine cholinergic signaling caused calmodulin/calmodulin-dependent protein kinase kinase (CaM/CaMKK)-mediated phosphorylation of Akt. These findings suggest that blockade of CHRM3 may represent a novel adjuvant therapy for castration-resistant prostate cancer.