Androgen-deprived LNCaP Cells Research Articles

CYB561 supports the neuroendocrine phenotype in castration-resistant prostate cancer.

Castration-resistant prostate cancer (CRPC) is associated with resistance to androgen deprivation therapy, and an increase in the population of neuroendocrine (NE) differentiated cells. It is hypothesized that NE differentiated cells secrete neuropeptides that support androgen-independent tumor growth and induce aggressiveness of adjacent proliferating tumor cells through a paracrine mechanism. The cytochrome b561 (CYB561) gene, which codes for a secretory vesicle transmembrane protein, is constitutively expressed in NE cells and highly expressed in CRPC. CYB561 is involved in the α-amidation-dependent activation of neuropeptides, and contributes to regulating iron metabolism which is often dysregulated in cancer. These findings led us to hypothesize that CYB561 may be a key player in the NE differentiation process that drives the progression and maintenance of the highly aggressive NE phenotype in CRPC. In our study, we found that CYB561 expression is upregulated in metastatic and NE prostate cancer (NEPC) tumors and cell lines compared to normal prostate epithelia, and that its expression is independent of androgen regulation. Knockdown of CYB561 in androgen-deprived LNCaP cells dampened NE differentiation potential and transdifferentiation-induced increase in iron levels. In NEPC PC-3 cells, depletion of CYB561 reduced the secretion of growth-promoting factors, lowered intracellular ferrous iron concentration, and mitigated the highly aggressive nature of these cells in complementary assays for cancer hallmarks. These findings demonstrate the role of CYB561 in facilitating transdifferentiation and maintenance of NE phenotype in CRPC through its involvement in neuropeptide biosynthesis and iron metabolism pathways.

Abstract 3394: Participation of molecular iodine and PPARG in prostate cancer progression and neuroendocrine differentiation

Abstract Introduction: Advanced prostate cancer (PCa) therapy is based on androgen deprivation; however, cancerous cells develop resistance, and can develop a highly aggressive neuroendocrine (NE) phenotype. Molecular iodine (I2) has antitumoral effects in breast cancer models, in which PPARG receptors represent the main mechanism of action described. In PCa though, PPARG is considered pro-tumoral and I2 effects have not been fully studied. Hence, the aim of this study was to analyze I2 individual and combined effects with androgen deprivation by using both androgen dependent (AD) and independent (AI), in vitro and in vivo PCa models. Methods: In vitro. I2 effects in cell viability and invasion were analyzed in AD (LNCaP) and AI (DU145, PC3) PCa cells. LNCaP cells were also treated with androgen receptor (AR) antagonists. PPARG participation in I2 effects was assessed with GW9962 (antagonist) and rosiglitazone (agonist). NE phenotype was induced in LNCaP by prolonged culture under androgen-depleted conditions and was assessed by measuring the growth and length of neurite-like projections. RT-qPCR was employed to assess the expression of NE markers (SYP, ENO2), and lipogenic genes (FASN, SREBF1). In vivo. Eighteen weeks-old TRAMP mice were subjected to sham surgery or castration, and were provided or not with I2 (0.025%, drinking water) for four weeks. Prostates were subjected to histopathological analysis (H&E and Masson's trichrome) and IHC (AR, SYP, PPARG). Scoring systems were used to grade the severity of high proliferative intraepithelial lesions (HPIN), and desmoplasia. Results: I2 decreased the cell viability and invasion capacity of all PCa cells tested, and when supplied with AR antagonists further enhanced their antiproliferative effects in LNCaP cells. I2 failed to induce the expression of PPARG target genes, and GW9662 did not prevent I2-induced decrease in cell viability. Like androgen deprivation, I2 also caused NE-like morphology in LNCaP cells, but unlike androgen deprived LNCaP cells, I2 treated cells had decreased expression of NE markers. In TRAMP mice, I2 increased the presence of HPIN, reduced nuclear AR protein detection, and had no effect on PPARG. As expected, castration reduced HPIN, caused epithelial atrophy and desmoplasia; decreased total AR levels and PPARG nuclear levels. However, the number of NE (SYP-positive) cells did not change. The addition of I2 to castration did not modify the score of epithelial lesions but increased the desmoplasia and the presence of NE cells. Conclusions: I2 exhibited in vitro antineoplastic effects over epithelial cells, however, these effects did not translate into the in vivo model. PPARG did not seem to mediate I2 effects. Overall, our data suggest that tumoral microenvironment may interfere with I2 epithelial-specific antitumoral effects. Funding: PAPIIT-UNAM (IN217223, IN202322) and CONAHCYT (774791). Citation Format: Carlos Montes de Oca, Lourdes Álvarez, Carmen Aceves, Brenda Anguiano. Participation of molecular iodine and PPARG in prostate cancer progression and neuroendocrine differentiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3394.

Dynamic interplay between sortilin and syndecan-1 contributes to prostate cancer progression

Prostate cancer (PCa) development and progression relies on the programming of glucose and lipid metabolism, and this involves alterations in androgen receptor expression and signalling. Defining the molecular mechanism that underpins this metabolic programming will have direct significance for patients with PCa who have a poor prognosis. Here we show that there is a dynamic balance between sortilin and syndecan-1, that reports on different metabolic phenotypes. Using tissue microarrays, we demonstrated by immunohistochemistry that sortilin was highly expressed in low-grade cancer, while syndecan-1 was upregulated in high-grade disease. Mechanistic studies in prostate cell lines revealed that in androgen-sensitive LNCaP cells, sortilin enhanced glucose metabolism by regulating GLUT1 and GLUT4, while binding progranulin and lipoprotein lipase (LPL) to limit lipid metabolism. In contrast, in androgen-insensitive PC3 cells, syndecan-1 was upregulated, interacted with LPL and colocalised with β3 integrin to promote lipid metabolism. In addition, androgen-deprived LNCaP cells had decreased expression of sortilin and reduced glucose-metabolism, but increased syndecan-1 expression, facilitating interactions with LPL and possibly β3 integrin. We report a hitherto unappreciated molecular mechanism for PCa, which may have significance for disease progression and how androgen-deprivation therapy might promote castration-resistant PCa.

The lncRNA PTTG3P promotes the progression of CRPC via upregulating PTTG1

Overexpression of certain long non-coding RNAs (lncRNAs) promotes the progression of castration-resistant prostate cancer (CRPC). The significance and potential role of the lncRNA designated pituitary tumour-transforming 3, pseudogene (PTTG3P) in CRPC is unknown. We detected PTTG3P expression by qPCR. Upregulated PTTG3P expression was performed to explore the role of PTTG3P in PCa cells resistant to ADT (androgen deprivation therapy). The relationship among PTTG3P, mir-146a-3p and PTTG1 were validated by qPCR, western blot and luciferase assay. PTTG3P levels were significantly increased in the androgen-independent PC cell lines, as well as in CRPC tissues compared with those of the androgen-dependent prostate cancer cell line LNCaP and tumour tissues of patients with hormone-naive prostate cancers. Enforced expression of PTTG3P in androgen-deprived LNCaP cells significantly enhanced survival, clonogenicity, and tumorigenicity. Further, PTTG3P acted as a competing endogenous RNA (ceRNA, natural miRNA sponge) to upregulate PTTG1 expression by competing for mir-146a-3p in the progression to CRPC. Our findings suggest that PTTG3P promotes the resistance of prostate cancer cells to androgen-deprivation therapy via upregulating PTTG1. PTTG3P may therefore represent a potential target for therapy of CRPC.

HASH1 nuclear localization persists in neuroendocrine transdifferentiated prostate cancer cells, even upon reintroduction of androgen

Neuroendocrine prostate cancer (NEPC) is thought to arise as prostate adenocarcinoma cells transdifferentiate into neuroendocrine (NE) cells to escape potent anti-androgen therapies however, the exact molecular events accompanying NE transdifferentiation and their plasticity remain poorly defined. Cell fate regulator ASCL1/hASH1’s expression was markedly induced in androgen deprived (AD) LNCaP cells and prominent nuclear localisation accompanied acquisition of the NE-like morphology and expression of NE markers (NSE). By contrast, androgen-insensitive PC3 and DU145 cells displayed clear nuclear hASH1 localisation under control conditions that was unchanged by AD, suggesting AR signalling negatively regulated hASH1 expression and localisation. Synthetic androgen (R1881) prevented NE transdifferentiation of AD LNCaP cells and markedly suppressed expression of key regulators of lineage commitment and neurogenesis (REST and ASCL1/hASH1). Post-AD, NE LNCaP cells rapidly lost NE-like morphology following R1881 treatment, yet ASCL1/hASH1 expression was resistant to R1881 treatment and hASH1 nuclear localisation remained evident in apparently dedifferentiated LNCaP cells. Consequently, NE cells may not fully revert to an epithelial state and retain key NE-like features, suggesting a “hybrid” phenotype. This could fuel greater NE transdifferentiation, therapeutic resistance and NEPC evolution upon subsequent androgen deprivation. Such knowledge could facilitate CRPC tumour stratification and identify targets for more effective NEPC management.

Androgen deprivation modulates gene expression profile along prostate cancer progression

Androgen deprivation therapy (ADT) is the standard of care for metastatic prostate cancer and initially induces tumor regression, but invariably results in castration-resistant prostate cancer through various mechanisms, incompletely discovered. Our aim was to analyze the dynamic modulation, determined by ADT, of the expression of selected genes involved in the pathogenesis and progression of prostate cancer (TMPRSS2:ERG, WNT11, SPINK1, CHGA, AR, and SPDEF) using real-time polymerase chain reaction in a series of 59 surgical samples of prostate carcinomas, including 37 cases preoperatively treated with ADT and 22 untreated cases, and in 43 corresponding biopsies. The same genes were analyzed in androgen-deprived and control LNCaP cells. Three genes were significantly up-modulated (WNT11 and AR) or down-modulated (SPDEF) in patients treated with ADT versus untreated cases, as well as in androgen-deprived LNCaP cells. The effect of ADT on CHGA gene up-modulation was almost exclusively detected in cases positive for the TMPRSS2:ERG fusion. The correlation between biopsy and surgical samples was poor for most of the tested genes. Gene expression analysis of separate tumor areas from the same patient showed an extremely heterogeneous profile in the 6 tested cases (all untreated). In conclusion, our results strengthened the implication of ADT in promoting a prostate cancer aggressive phenotype and identified potential biomarkers, with special reference to the TMPRSS2:ERG fusion, which might favor the development of neuroendocrine differentiation in hormone-treated patients. However, intratumoral heterogeneity limits the use of gene expression analysis as a potential prognostic or predictive biomarker in patients treated with ADT.

Effect of cabazitaxel on the growth of human castration-refractory prostate cancer cells in vitro compared to docetaxel and on the anti-tumor properties of the angio-inhibitor PEDF in vivo.

205 Background: Docetaxel/DTX and cabazitaxel/CBZ have shown promise in the treatment of metastatic Castration-Refractory Prostate Cancer/mCPRC however, comparative studies are missing. Toxicities of these drugs are significant, urging the need to modify taxane regimens. Recently, low-dose metronomic/LDM treatments using conventional chemotherapeutic drugs have shown benefits in CPRC in improving the effect of anti-angiogenic agents. Previously, we have demonstrated that LDM-DTX in combination with PEDF curbs significantly CRPC growth, limits metastases formation and prolongs survival in vivo. In this study, we intended to compare the cytotoxic effect of CBZ and DTX on CRPC cells in vitro and CL1 tumors in vivo. Methods: PC3, DU145 cell lines were from ATCC.CL1 cells were obtained from androgen-deprived LNCaP cells. Cell proliferation was assessed by crystal violet staining and cell cycle analyses. In vitro cytotoxicity assays were performed on CL1 cells/RAW264.7 macrophages co-cultures treated with PEDF and increasing doses of taxanes. For the in vivo studies, CL1 cells were engineered to stably express the DsRed Express protein +/- PEDF. PEDF anti-tumor effects were assessed on s.c. xenografts treated with DTX (5mg/kg ip ev. 4 day) as reference, CBZ (5mg/kg ip ev. 4 days, 1mg/kg for 10 days, 0.5mg/kg q.a.d. and 0.1mg/kg daily) or placebo. Results: CBZ limits cell proliferation with a greater efficacy than DTX in all CRPC cell lines tested. DU145 presented the largest difference. High doses of taxane blocked tumor cells in mitosis, whereas LDM increased the SubG1 population. This effect was significantly higher in DU145 cells treated with CBZ. In vivo, 5mg/kg CBZ delayed tumor growth more efficiently than 5mg/kg DTX. PEDF/5mg/kg CBZ markedly delayed tumor growth compared to all treatments. Finally, engulfment of tumor cells by macrophages was higher in combined treatments suggesting an inflammation-related process. Conclusions: CBZ is more efficient than DTX both in vitro and in vivo.The data also reinforce PEDF as a promising anti-neoplasic agent in combination with LDM taxane chemotherapies.

AKT upregulates B-Raf Ser445 phosphorylation and ERK1/2 activation in prostate cancer cells in response to androgen depletion

Upregulated ERK1/2 activity is often correlated with AKT activation during prostate cancer (PCa) progression, yet their functional relation needs elucidation. Using androgen-deprived LNCaP cells, in which ERK1/2 activation occurs in strong correlation with AKT activation, we found that AKT-mediated B-Raf regulation is necessary for ERK1/2 activation. Specifically, in response to androgen deprivation, AKT upregulated B-Raf phosphorylation at Ser445 without affecting A-Raf or C-Raf-1. This effect of AKT was abolished by Arg25 to Ala mutation or truncating (∆4-129) the pleckstrin homology domain of AKT, indicating that the canonical AKT regulation is important for this signaling. Intriguingly, although a constitutively active AKT containing N-terminal myristoylation signal could sufficiently upregulate B-Raf phosphorylation at Ser445 in LNCaP cells, subsequent MEK/ERK activation still required hormone deprivation. In contrast, AKT activity was sufficient to induce not only B-Raf phosphorylation but also MEK/ERK activation in the hormone refractory LNCaP variant, C4-2. These data indicate that androgen depletion may induce MEK/ERK activation through a synergy between AKT-dependent and -independent mechanisms and that the latter may become deregulated in association with castration resistance. In support, consistent AKT-mediated B-Raf regulation was also detected in a panel of PCa lines derived from the cPten−/−L mice before and after castration. Our results also demonstrate that AKT regulates androgen receptor levels partly via the Raf/MEK/ERK pathway. This study reveals a novel crosstalk between ERK1/2 and AKT in PCa cells.

TAK-441, a novel investigational smoothened antagonist, delays castration-resistant progression in prostate cancer by disrupting paracrine hedgehog signaling

Hedgehog (Hh) signaling is a highly conserved intercellular and intracellular communication mechanism that governs organogenesis and is dysregulated in cancers of numerous tissues, including prostate. Up-regulated expression of the Hh ligands, Sonic (Shh) and Desert (Dhh), has been reported in androgen-deprived and castration-resistant prostate cancer (CRPC). In a cohort of therapy naive, short- and long-term neoadjuvant hormone therapy-treated (NHT), and CRPC specimens, we observed elevated Dhh expression predominantly in long-term NHT specimens and elevated Shh expression predominantly in CRPC specimens. Together with previously demonstrated reciprocal signaling between Shh-producing prostate cancer (PCa) cells and urogenital mesenchymal fibroblasts, these results suggest that castration-induced Hh expression promotes CRPC progression through reciprocal paracrine signaling within the tumor microenvironment. We tested whether the orally available Smoothened (Smo) antagonist, TAK-441, could impair castration-resistant progression of LNCaP PCa xenografts by disrupting paracrine Hh signaling. Although TAK-441 or cyclopamine did not affect androgen withdrawal-induced Shh up-regulation or viability of LNCaP cells, castration-resistant progression of LNCaP xenografts was significantly delayed in animals treated with TAK-441. In TAK-441-treated xenografts, expression of murine orthologs of the Hh-activated genes, Gli1, Gli2 and Ptch1, was substantially suppressed, while expression of the corresponding human orthologs was unaffected. As androgen-deprived LNCaP cells up-regulate Shh expression, but are not sensitive to Smo antagonists, these studies indicate that TAK-441 leads to delayed castration-resistant progression of LNCaP xenografts by disrupting paracrine Hh signaling with the tumor stroma. Thus, paracrine Hh signaling may offer unique opportunities for prognostic biomarker development, drug targeting and therapeutic response monitoring of PCa progression.

Abstract 4952: A novel smoothened antagonist, TAK-441, delays castration-resistant progression in prostate cancer by disrupting paracrine hedgehog signaling.

Abstract Hedgehog (Hh) signaling is a highly conserved inter- and intracellular communication mechanism that governs organogenesis and is dysregulated in cancers of numerous tissues, including prostate. Up-regulated expression of the Hh ligands, Sonic (Shh) and Desert (Dhh), has been reported in androgen-deprived and castration-resistant prostate cancer (CRPC). In a cohort of therapy naive, short- and long-term neoadjuvant hormone therapy-treated (NHT), and CRPC specimens, we observed elevated Dhh expression predominantly in long-term NHT specimens and elevated Shh expression predominantly in CRPC specimens. Together with previously demonstrated reciprocal signaling between Shh-producing prostate cancer (PCa) cells and urogenital mesenchymal fibroblasts, these results suggest that castration-induced Hh expression promotes CRPC progression through reciprocal paracrine signaling within the tumor microenvironment. We tested whether the orally available Smoothened (Smo) antagonist, TAK-441, could impair castration-resistant progression of LNCaP PCa xenografts by disrupting paracrine Hh signaling. While TAK-441 or cyclopamine did not affect androgen withdrawal-induced Shh up-regulation or viability of LNCaP cells, castration-resistant progression of LNCaP xenografts was significantly delayed in animals treated with TAK-441. In TAK-441-treated xenografts, expression of murine orthologues of the Hh-activated genes, Gli1, Gli2, and Ptch1, was substantially suppressed, while expression of the corresponding human orthologues was unaffected. Since androgen-deprived LNCaP cells up-regulate Shh expression, but are not sensitive to Smo antagonists, these studies indicate that TAK-441 leads to delayed castration-resistant progression of LNCaP xenografts by disrupting paracrine Hh signaling with the tumor stroma. Thus, paracrine Hh signaling may offer unique opportunities for prognostic biomarker development, drug targeting and therapeutic response monitoring of PCa progression. Citation Format: Mazyar Ghaffari, Naokazu Ibuki, Irene Iu, Mitali Pandey, Ladan Fazli, Masahide Kashiwagi, Hideaki Tojo, Osamu Nakanishi, Martin E. Gleave, Michael E. Cox. A novel smoothened antagonist, TAK-441, delays castration-resistant progression in prostate cancer by disrupting paracrine hedgehog signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4952. doi:10.1158/1538-7445.AM2013-4952

Abstract 1294: Identification of the binding domains that allow ligand-independent co-activation of androgen receptor by Gli2.

Abstract Gli proteins are transcription factors that mediate the cellular response to Hedgehog signaling. Gli activity guides cell fate decisions during development and is required for the proper morphogenesis of embryonic tissues, including the prostate gland. Previously, we showed that exogenous overexpression of Gli1 or Gli2 in androgen-deprived LNCaP cells increased the expressions of androgen-dependent genes in prostate cancer (PCa) cells and conferred androgen-independent growth behavior to them (Chen et al., Mol Cancer, 9: 89-101, 2010). We also showed that Gli1 or Gli2 proteins co-immunoprecipitate with AR, suggesting that AR interacts with Gli proteins to mediate these effects. Based upon this data, we proposed that Gli1/2 proteins are ligand-independent co-activators of AR in PCa. To better understand the Gli2-AR interaction and its effects on PCa responsiveness to androgen ablation, we fine mapped the specific interaction domains between Gli2 and AR. Complete or partial recombinant Gli2 cDNAs were tagged with GST and the GST-tagged proteins were purified on glutathione beads prior to incubation with in vitro translated human AR protein fragments. GST pulldown assays showed that GLI2 specifically recognizes and binds the Tau5 region within the AR N-terminal domain (AA 391-555). Likewise, AR binds to Gli2 within an extended C-terminal domain (AA 628-1091) that may involve two distinct AR binding sites. AR co-activation studies in 293T cells shows that the presence of binding site(s) and the Gli2 activation domain are required for Gli2 co-activation of AR. Gli2 was tested for its ability to co-activate natural truncated variants of the AR. The interaction of Gli2 with the Tau4 domain of AR was consistent with the ability of Gli2 to co-activate truncated variants of the AR that lack the DNA binding domain. Our work demonstrates that Gli2 co-activation of AR requires direct interaction between the tau5 domain in the AR N-terminus and the AR binding domains in the Gli2 C-terminus as well as the Gli2 activation domain. Gli2 binding at tau5 supports co-activation of the wildtype AR (in both the presence and absence of androgen) as well as co-activation of truncated receptors that do not bind androgens. As such, the evidence that Gli2 expression is increased in PCa by androgen ablation suggests that it may be a factor in progression to castration resistant PCa. Supported by the DOD PCRP (W81XH-10-1-0493, to RB). Citation Format: Na Li, Mengqian Chen, Ralph Buttyan. Identification of the binding domains that allow ligand-independent co-activation of androgen receptor by Gli2. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1294. doi:10.1158/1538-7445.AM2013-1294

Synergistic killing effect of chloroquine and androgen deprivation in LNCaP cells

Modulation of autophagy is a new paradigm in cancer therapeutics. Recently a novel function of chloroquine (CLQ) in inhibiting degradation of autophagic vesicles has been revealed, which raises the question whether CLQ can be used as an adjuvant in targeting autophagic pro-survival mechanism in prostate cancer (PCa). We previously showed that autophagy played a protective role during hormone ablation therapy, in part, by consuming lipid droplets in PCa cells. In addition, blocking autophagy by genetic and pharmacological means in the presence of androgen deprivation caused cell death in PCa cells. To further investigate the importance of autophagy in PCa survival and dissect the role of CLQ in PCa death, we treated hormone responsive LNCaP cells with CLQ in combination with androgen deprivation. We observed that CLQ synergistically killed LNCaP cells during androgen deprivation in a dose- and time-dependent manner. We further confirmed that CLQ inhibited the maturation of autophagic vesicles and decreased the cytosolic ATP. Moreover, CLQ induced nuclear condensation and DNA fragmentation, a hallmark of apoptosis, in androgen deprived LNCaP cells. Taken together, our finding suggests that CLQ may be an useful adjuvant in hormone ablation therapy to improve the therapeutic efficacy.

Neuregulin Promotes Incomplete Autophagy of Prostate Cancer Cells That Is Independent of mTOR Pathway Inhibition

BackgroundGrowth factors activating the ErbB receptors have been described in prostate tumors. The androgen dependent prostate cancer cell line, LNCaP, expresses the ErbB-1, ErbB-2 and ErbB-3 receptor tyrosine kinases. Previously, it was demonstrated that NRG activates ErbB-2/ErbB-3 heterodimers to induce LNCaP cell death, whereas, EGF activates ErbB-1/ErbB-1 or ErbB-1/ErbB-2 dimers to induce cell growth and survival. It was also demonstrated that PI3K inhibitors repressed this cell death suggesting that in androgen deprived LNCaP cells, NRG activates a PI3K-dependent pathway associated with cell death.Methodology/Principal FindingsIn the present study we demonstrate that NRG induces autophagy in LNCaP cells, using LC3 as a marker. However, the autophagy induced by NRG may be incomplete since p62 levels elevate. We also demonstrated that NRG- induced autophagy is independent of mammalian target of rapamycin (mTOR) inhibition since NRG induces Akt and S6K activation. Interestingly, inhibition of reactive oxygen species (ROS) by N-acetylcysteine (NAC), inhibited NRG-induced autophagy and cell death. Our study also identified JNK and Beclin 1 as important components in NRG-induced autophagy and cell death. NRG induced elevation in JNK phosphorylation that was inhibited by NAC. Moreover, inhibitor of JNK inhibited NRG-induced autophagy and cell death. Also, in cells overexpressing Bcl-2 or cells expressing sh-RNA against Beclin 1, the effects of NRG, namely induction of autophagy and cell death, were inhibited.Conclusions/SignificanceThus, in LNCaP cells, NRG-induces incomplete autophagy and cell death that depend on ROS levels. These effects of NRG are mediated by signaling pathway that activates JNK and Beclin 1, but is independent of mTOR inhibition.

Sphingosine Kinase-1 Is Central to Androgen-Regulated Prostate Cancer Growth and Survival

BackgroundSphingosine kinase-1 (SphK1) is an oncogenic lipid kinase notably involved in response to anticancer therapies in prostate cancer. Androgens regulate prostate cancer cell proliferation, and androgen deprivation therapy is the standard of care in the management of patients with advanced disease. Here, we explored the role of SphK1 in the regulation of androgen-dependent prostate cancer cell growth and survival.Methodology/Principal FindingsShort-term androgen removal induced a rapid and transient SphK1 inhibition associated with a reduced cell growth in vitro and in vivo, an event that was not observed in the hormono-insensitive PC-3 cells. Supporting the critical role of SphK1 inhibition in the rapid effect of androgen depletion, its overexpression could impair the cell growth decrease. Similarly, the addition of dihydrotestosterone (DHT) to androgen-deprived LNCaP cells re-established cell proliferation, through an androgen receptor/PI3K/Akt dependent stimulation of SphK1, and inhibition of SphK1 could markedly impede the effects of DHT. Conversely, long-term removal of androgen support in LNCaP and C4-2B cells resulted in a progressive increase in SphK1 expression and activity throughout the progression to androgen-independence state, which was characterized by the acquisition of a neuroendocrine (NE)-like cell phenotype. Importantly, inhibition of the PI3K/Akt pathway—by negatively impacting SphK1 activity—could prevent NE differentiation in both cell models, an event that could be mimicked by SphK1 inhibitors. Fascinatingly, the reversability of the NE phenotype by exposure to normal medium was linked with a pronounced inhibition of SphK1 activity.Conclusions/SignificanceWe report the first evidence that androgen deprivation induces a differential effect on SphK1 activity in hormone-sensitive prostate cancer cell models. These results also suggest that SphK1 activation upon chronic androgen deprivation may serve as a compensatory mechanism allowing prostate cancer cells to survive in androgen-depleted environment, giving support to its inhibition as a potential therapeutic strategy to delay/prevent the transition to androgen-independent prostate cancer.

Androgenic regulation of hedgehog signaling pathway components in prostate cancer cells

Hedgehog signaling is thought to play a role in several human cancers including prostate cancer. Although prostate cancer cells express many of the gene products involved in hedgehog signaling, these cells are refractory to the canonical signaling effects of exogenous hedgehog ligands or to activated Smoothened, the hedgehog-regulated mediator of Gli transcriptional activation. Here, we show that the expression of hedgehog ligands and some hedgehog target genes are regulated by androgen in the human prostate cancer cell line, LNCaP and its more metastatic variants (C4-2 and C4-2B). Androgen (R1881) strongly suppressed the expression of hedgehog ligands in these cells and their prolonged maintenance in androgen-deficient medium upregulated Sonic and Indian hedgehog mRNA and protein levels by up to 30,000-fold. Hedgehogs were released into the conditioned medium of androgen-deprived LNCaP cells and this medium was able to increase hedgehog target gene expression in hedgehog-responsive mouse fibroblasts (MC3T3-E1). Moreover, this activity was accompanied by increased expression of Gli target genes, Patched 1 and Gli2, in LNCaP that could be suppressed by cyclopamine, indicating that chronic androgen-deprivation also re-awakens the autocrine responsiveness of the cancer cells to hedgehog. In contrast to the suppressive effects of R1881 on hedgehog ligand and Gli2 expression, we found that Gli1 expression in LNCaP cells was induced by R1881. Given the ability of androgen to modulate the expression and release of hedgehog ligands and the activity of the autocrine hedgehog signaling pathway in these prostate cancer cells, our results imply that chronic androgen deprivation therapy (ADT) for prostate cancer might create a hedgehog signaling environment in the region of the tumor that could ultimately impact on the long term effectiveness of this treatment. This consideration supports the idea of clinically testing hedgehog-blocking drugs in conjunction with ADT in patients with advanced prostate cancer.

Phosphatidylinositol 3-Kinase-AKT-Mammalian Target of Rapamycin Pathway Is Essential for Neuroendocrine Differentiation of Prostate Cancer

Hormonal therapy of prostate cancer, by inhibiting androgen production and/or androgen function, is the treatment of choice for advanced prostate cancer. Although most patients respond initially, the effect is only temporary, and the tumor cells will resume proliferation in an androgen-deprived environment. The mechanism for androgen-independent proliferation of cancer cells is unclear. Hormonal therapy induces neuroendocrine differentiation of prostate cancer cells, which is hypothesized to contribute to tumor recurrence by a paracrine mechanism. We studied signal transduction pathways of neuroendocrine differentiation in LNCaP cells after androgen withdrawal, and we showed that both the phosphatidylinositol 3-kinase-AKT-mammalian target of rapamycin pathway and ERK are activated, but only the former is required for neuroendocrine differentiation. A constitutively active AKT promotes neuroendocrine differentiation and a dominant negative AKT inhibits it. Activation of AKT by IGF-1 leads to neuroendocrine differentiation, and neuroendocrine differentiation induced by epinephrine requires AKT activation. We also show that the AKT pathway is likely responsible for neuroendocrine differentiation in DU145, an androgen-independent prostate cancer cell line. Therefore, our study demonstrated a novel function of the AKT pathway in prostate cancer progression and identified potential targets that may be explored for the treatment of androgen-independent cancer.

ErbB1 and prostate cancer: ErbB1 activity is essential for androgen-induced proliferation and protection from the apoptotic effects of LY294002.

Androgens play a critical role in proliferation and survival of prostate cancer cells, but the mechanisms leading to these effects are poorly understood. ErbB receptor tyrosine kinases have been implicated in the development of prostate cancer. We examined the interaction between the ErbB receptors and androgens using the LNCaP androgen-sensitive prostate tumor model. In the absence of androgens, the cells have low levels of ErbB1 and relatively high levels of ErbB2. Addition of androgens to the medium reversed the ratio; ErbB1 levels rose and ErbB2 levels dropped in response to treatment with the synthetic hormone, R1881. Expression of ErbB activating ligands was found to be constitutive and androgen-independent. The androgen-induced proliferation of LNCaP cells was completely inhibited by the addition of the small molecule ErbB1 tyrosine kinase inhibitors CGP59326 and the bispecific inhibitor (PKI166) for ErbB1 and ErbB2 to the culture medium. Furthermore, in the absence of androgens the relatively low proliferative level was further significantly reduced in the presence of CGP59326. Inhibition of PI3K activity by LY294002 led to induction of apoptosis in androgen-deprived LNCaP cells. Androgen-mediated rescue from LY294002-induced apoptosis was inhibited by addition of CGP59326 to the cells. These results suggest a model whereby androgens promote an increase in the activity of the epidermal growth factor (EGF)-network by increasing ErbB1 levels, and this activity of is essential for androgen-induced proliferation and survival of the prostate cancer LNCaP cell line.

Signaling pathways that control the growth and survival of prostate tumor cells in the absence of androgens

Androgen-dependent human prostate adenocarcinoma cell line LNCaP was used to study the effect of androgen deprivation on the cell response to TNF-related cytokines. Several signaling pathways were implicated in cell survival in the absence of androgens. In androgen-deprived LNCaP cells, TNF-alpha and TRAIL stimulated the cell growth and activated the mitogenic and antiapoptotic signaling pathways involving NF-kappa B, STAT3, PI3K, and beta-catenin. The results suggested a role of cytokines in the survival of prostate adenocarcinoma cells deprived of androgens in vitro.