Factors In Prostate Cancer Cells Research Articles

Human RecQL4 Helicase Plays Critical Roles in Prostate Carcinogenesis

Prostate cancer is the second leading cause of cancer-associated deaths among men in the western countries. Here, we report that human RecQL4 helicase, which is implicated in the pathogenesis of a subset of cancer-prone Rothmund-Thomson syndrome, is highly elevated in metastatic prostate cancer cell lines. Increased RecQL4 expression was also detected in human prostate tumor tissues as a function of tumor grade with the highest expression level in metastatic tumor samples, suggesting that RecQL4 may be a potential prognostic factor for advanced stage of prostate cancer. Transient and stable suppression of RecQL4 by small interfering RNA and short hairpin RNA vectors drastically reduced the growth and survival of metastatic prostate cancer cells, indicating that RecQL4 is a prosurvival factor for prostate cancer cells. RecQL4 suppression led to increased poly(ADP-ribose) polymerase (PARP) synthesis and RecQL4-suppressed prostate cancer cells underwent an extensive apoptotic death in a PARP-1-dependent manner. Most notably, RecQL4 knockdown in metastatic prostate cancer cells drastically reduced their cell invasiveness in vitro and tumorigenicity in vivo, showing that RecQL4 is essential for prostate cancer promotion. Observation of a direct interaction of retinoblastoma (Rb) and E2F1 proteins with RecQL4 promoter suggests that Rb-E2F1 pathway may regulate RecQL4 expression. Collectively, our study shows that RecQL4 is an essential factor for prostate carcinogenesis.

Butein suppresses the expression of nuclear factor-kappa B-mediated matrix metalloproteinase-9 and vascular endothelial growth factor in prostate cancer cells

3,4,2′,4′-Tetrahydroxychalcone (butein) has potent anti-inflammatory, anti-cancer and anti-fibrogenic effects. However, little is known about the mechanism by which butein inhibits metastasis and invasion. This study aimed to investigate the effects of butein on the expression of matrix metalloproteinase (MMP-9) and vascular endothelial growth factor (VEGF) in human prostate cancer cells. Butein in vitro resulted in a moderate inhibition of cell proliferation and viability through G 2/M phase arrest. We also analyzed the effect of butein on the activities of nuclear factor-kappa B (NF-κB)-regulated MMP-9 and VEGF since they are prominently involved in the processes of tumor cell invasion and metastasis. Our results in vitro showed that butein attenuates VEGF and MMP-9 activities via the suppression of NF-κB activity. Furthermore, butein repressed the expression of VEGF and MMP-9 induced by treatment with tumor necrosis factor-α and phorbol-12-myristate-13-acetate. Taken together, these data suggest that a blockade of NF-κB activity by butein inhibits invasion and angiogenesis in prostate cancer cells.

Abstract B45: The short-term effects of arsenic on Cdk5-dependent apoptosis of prostate cancer cells

Abstract Arsenic compounds have been used widely in medicine to treat a variety of diseases. However, it has also been believed to involve the carcinogenesis of prostate cancer and the hormone disruption might be one of the causes. Our previous results indicate that digoxin treatment leads to apoptosis of prostate cancer cells through Cdk5 overactivation, in which the regular activator of Cdk5, p35, is cleaved into more potent one, p25. Here, our latest data showed that arsenic also caused p35 cleavage and subsequently Cdk5 overactivation in prostate cancer cells. Similarly, this arsenic- induced stimulatory effect on Cdk5 resulted in apoptosis of prostate cancer cells accompanying with the degradation of androgen receptor in LNCaP cells. This result implies that androgen is no longer a trophic factor for prostate cancer cells after arsenic treatment. Although STAT3 was identified by us as a Cdk5 substrate responding to tumor growth, arsenic-triggered Cdk5 overactivation did not increase STAT3 phosphorylation. In conclusion, although long-term exposure of arsenic possibly causes prostate cancer, our present results provide evidence indicating that in vitro and short-term treatments of arsenic might lead to apoptosis of prostate cancer cell lines through Cdk5 overactivation pathway. This study may arouse the new indication for the old chemical and also shed light on the application on cancer therapy. Citation Information: Clin Cancer Res 2010;16(14 Suppl):B45.

Abstract 1707: Androgen responsiveness of the NKX3.1 gene is regulated by the proto-oncogene ETS1

Abstract Expression of the prostatic homeodomain protein NKX3.1 is androgen-regulated in both the normal prostate and in prostate cancer cells. Androgen responsiveness of NKX3.1 is mediated in part by the 3’ untranslated region (3'UTR) of the NKX3.1 gene, within which we have isolated 3 discrete regions of androgen-induced transcriptional regulatory activity including 2 androgen response elements (AREs). The proximal ∼2kb of the 5’ promoter of the NKX3.1 gene is incompletely characterised, however it is not androgen-responsive using conventional luciferase reporter assays. Investigation of the NKX3.1 proximal promoter has identified regulation of promoter activity by the ETS transcription factor, ETS1, which is mediated by an ETS binding site (EBS) located at −1008 relative to the NKX3.1 transcription start site. Overexpression of ETS1 in the LNCaP prostate cancer cell line results in upregulation of NKX3.1 protein levels, supporting a functional role of ETS1 in the regulation of NKX3.1 expression. ETS1 has been reported previously to transactivate the androgen receptor (AR) in a ligand-dependent manner on a subset of androgen-responsive promoters, suggesting cooperativity or co-regulation of AR and ETS1 signalling in prostate cancer cells. Treatment of LNCaP cells with 10−8M 5α-dihydrotestosterone (DHT) results in upregulation of endogenous ETS1 protein levels, while overexpression of exogenous ETS1 causes a concomitant increase in AR expression. A cooperative interaction between ETS1 and the AR on the NKX3.1 promoter is evident in LNCaP cells whereby overexpression of ETS1 is able to induce androgen responsiveness of the initial ∼2kb of the NKX3.1 promoter sequence and in particular the 76bp region surrounding the EBS. Reversal of DHT effects by the antiandrogen bicalutamide indicates an AR-mediated mechanism. ETS1 is overexpressed in a high proportion of prostate cancers with its expression aberrantly localised in the cytoplasm of a subset of prostate tumour cells. Findings of the present study support a complex mechanism of AR-mediated regulation of NKX3.1 expression via multiple regions of the NKX3.1 gene and modified by additional transcription factors in prostate cancer cells. Abnormal expression and/or function of these factors may contribute to the transcriptional deregulation of NKX3.1 expression and the downregulation of NKX3.1 protein levels that is frequently observed in advanced prostate tumours. Similarly, it is also feasible that upregulation of ETS1 contributes to the deregulation of AR signalling in advanced prostate cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1707.

12-Lipoxygenase and the regulation of hypoxia-inducible factor in prostate cancer cells

12-Lipoxygenase, an arachidonic acid metabolizing enzyme of the lipoxygenase pathway, has been implicated as a major factor in promoting prostate cancer progression and metastasis. The ability of 12-LOX to aggravate the disease was linked to its proangiogenic role. Recent studies clearly demonstrated that 12-LOX enhances the expression and secretion of the angiogenic factor, vascular endothelial growth factor (VEGF) thus providing a direct link between this enzyme and its angiogenic properties. In the present study we have investigated the relationship between 12-LOX and hypoxia inducible factor-1α (HIF-1α), a transcription factor involved in the regulation of VEGF expression under hypoxic conditions in solid tumors. Our findings have revealed that HIF-1 is one of the target transcription factors regulated by 12-LOX and 12(S)-HETE, in hypoxic tumor cells of the prostate. Regulation of HIF-1α by 12-LOX adds to the complexity of pathways mediated by this enzyme in promoting prostate cancer angiogenesis and metastasis. We have evidence that 12-LOX increases the protein level, mRNA, and functional activity of HIF-1α under hypoxic conditions, one of the mechanisms by which it upregulates VEGF secretion and activity.

Vascular endothelial growth factor regulates myeloid cell leukemia-1 expression through neuropilin-1-dependent activation of c-MET signaling in human prostate cancer cells.

BackgroundMyeloid cell leukemia-1 (Mcl-1) is a member of the Bcl-2 family, which inhibits cell apoptosis by sequestering pro-apoptotic proteins Bim and Bid. Mcl-1 overexpression has been associated with progression in leukemia and some solid tumors including prostate cancer (PCa). However, the regulatory mechanism for Mcl-1 expression in PCa cells remains elusive.ResultsImmunohistochemical analyses revealed that Mcl-1 expression was elevated in PCa specimens with high Gleason grades and further significantly increased in bone metastasis, suggesting a pivotal role of Mcl-1 in PCa metastasis. We further found that vascular endothelial growth factor (VEGF) is a novel regulator of Mcl-1 expression in PCa cells. Inhibition of endogenous Mcl-1 induced apoptosis, indicating that Mcl-1 is an important survival factor in PCa cells. Neuropilin-1 (NRP1), the "co-receptor" for VEGF165 isoform, was found to be highly expressed in PCa cells, and indispensible in the regulation of Mcl-1. Intriguingly, VEGF165 promoted physical interaction between NRP1 and hepatocyte growth factor (HGF) receptor c-MET, and facilitated c-MET phosphorylation via a NRP1-dependent mechanism. VEGF165 induction of Mcl-1 may involve rapid activation of Src kinases and signal transducers and activators of transcription 3 (Stat3). Importantly, NRP1 overexpression and c-MET activation were positively associated with progression and bone metastasis in human PCa specimens and xenograft tissues.ConclusionsThis study demonstrated that Mcl-1 overexpression is associated with PCa bone metastasis. Activation of VEGF165-NRP1-c-MET signaling could confer PCa cells survival advantages by up-regulating Mcl-1, contributing to PCa progression.

Caveolin-1 Promotes Autoregulatory, Akt-Mediated Induction of Cancer-Promoting Growth Factors in Prostate Cancer Cells

Caveolin-1 (cav-1) and the cancer-promoting growth factors vascular endothelial growth factor (VEGF), transforming growth factor beta1 (TGF-beta1), and fibroblast growth factor 2 (FGF2) are often found to be upregulated in advanced prostate cancer and other malignancies. However, the relationship between cav-1 overexpression and growth factor upregulation remains unclear. This report presents, to our knowledge, the first evidence that in prostate cancer cells, a positive autoregulatory feedback loop is established in which VEGF, TGF-beta1, and FGF2 upregulate cav-1, and cav-1 expression, in turn, leads to increased levels of VEGF, TGF-beta1, and FGF2 mRNA and protein, resulting in enhanced invasive activities of prostate cancer cells, i.e., migration and motility. Our results further show that cav-1-enhanced mRNA stability is a major mechanism underlying the upregulation of these cancer-promoting growth factors, and that PI3-K-Akt signaling is required for forming this positive autoregulatory feedback loop.

Androgen regulates Cdc6 transcription through interactions between androgen receptor and E2F transcription factor in prostate cancer cells

Androgen receptor plays a critical role in the development and maintenance of cancers in the prostate. Earlier, we have shown that Cdc6, a regulatory protein for initiation of DNA replication, is down regulated in androgen-insensitive prostate cancer cells. In this report, we studied the involvement of androgen, mediated through androgen receptor (AR) in regulation of Cdc6 expression. Our results demonstrated that androgen treatment stimulated Cdc6 expression in xenograft tumors and androgen-sensitive prostate cancer cells. We also showed that androgen treatment stimulated Cdc6 transcription through possible interaction of AR with the ARE sequence in the Cdc6 promoter and that the stimulatory effect of androgen required intact E2F binding sites in the promoter. Androgen treatment differentially altered nuclear availability of E2F1 and E2F3, and increased the amount of hypophosphorylated retinoblastoma protein (pRb) in the nucleus in a time dependent fashion. We further showed that AR interacted with E2F transcription factors in a ligand-independent manner and that ligand-bound AR was less efficient in interacting with E2F proteins. DNA–protein interaction assays indicated that androgen treatment altered binding of E2F1 to the Cdc6 promoter in prostate cancer cells. We conclude that AR regulates Cdc6 transcription through interaction with the Cdc6 promoter, and complex formation with E2F1 and E2F3 in a differential manner.

CXCL16 Functions as a Novel Chemotactic Factor for Prostate Cancer Cells In vitro

A variety of tumor cells produce chemokines that promote tumor cell proliferation and chemotaxis. We previously reported that CXCL16 production is increased in aggressive prostate cancer cells compared with the less aggressive tumor cells and benign cells as identified in a cytokine antibody array. The functional contribution of CXCL16 in prostate cancer development has not yet been evaluated. Accordingly, mRNA expression of CXCL16 and its receptor, CXCR6, were determined by real-time reverse transcription-PCR in various cancer cell lines, including prostate cancer and tissues obtained from localized and metastatic prostate cancer. Consistent with our finding on CXCL16 protein production by prostate cancer cells, aggressive prostate cancer C4-2B and PC3 cells, as well as bone and liver metastatic tissues, expressed higher levels of both CXCL16 and CXCR6 mRNA compared with the less aggressive prostate cancer LNCaP cells, nonneoplastic PrEC and RWPE-1 cells, and benign prostate tissues, respectively. Furthermore, CXCR6 and CXCL16 protein expressions were examined in tissue specimens by immunohistochemistry. Immunohistochemical examination of CXCR6 expression showed strong epithelial staining that correlated with Gleason score, whereas CXCL16 staining was not. Finally, we found that both interleukin-1beta and tumor necrosis factor alpha significantly induced CXCL16 production by prostate epithelial cells, thereby indicating that inflammatory cytokines may play a role in the CXCL16 induction. CXCL16 was found to promote prostate cancer cell migration and invasion in vitro. Therefore, we concluded that CXCL16 functions, through CXCR6, as a novel chemotactic factor for prostate cancer cells.

Dermcidin expression confers a survival advantage in prostate cancer cells subjected to oxidative stress or hypoxia

Dermcidin (DCD) is a candidate survival gene in breast cancer. DCD gene expression has been identified in prostate cancer cell lines and primary prostate cancer tissue. The DCD protein is composed of proteolysis-inducing factor-core peptide (PIF-CP) and the skin antimicrobial DCD-1. The aim of this work was to: (i) establish if the DCD gene confers resistance of prostate cancer cells to hypoxia and oxidative stress; (ii) identify the component of the gene transcript responsible for this effect. Site-directed mutagenesis was used to create mutant DCD vectors. PC-3M prostate cancer cells were stably transfected with pcDNA3.1+ vectors encoding the entire DCD cDNA, mutant DCD vectors, or a control empty vector. Oxidative stress was produced using menadione, glucose oxidase, or hydrogen peroxide. Cell hypoxia was induced by incubation at 0.2% oxygen. Comparison of cell growth showed a 54.5% relative-proliferative advantage for the DCD-transfected PC-3M cells compared with sham-transfected cells after 8 days of cell growth (P = 0.03). Overexpression of DCD provided upto 36% absolute survival advantage over sham-transfected cells following induction of oxidative stress or hypoxia (P = 0.004). On exposure to hypoxia or oxidative stress PC-3M cells overexpressing the entire DCD gene had upto 42% survival advantage over those transfectants lacking the PIF-CP sequence (P = 0.004). DCD and PIF-CP are proliferation and survival factors in prostate cancer cells subjected to stressors found in the prostate cancer microenvironment. Thus, DCD and specifically PIF-CP are potential targets for the treatment of prostate cancer.

Vasoactive Intestinal Peptide Transactivates the Androgen Receptor through a Protein Kinase A-Dependent Extracellular Signal-Regulated Kinase Pathway in Prostate Cancer LNCaP Cells

Acquisition of androgen independence by prostate cancer is the key problem of prostate cancer progression. Vasoactive intestinal peptide (VIP), a neuropeptide, may act as a survival factor for prostate cancer cells under androgen deprivation. However, the molecular mechanisms by which VIP promotes the androgen-independent growth of androgen-sensitive prostate cancer cells have not been addressed. We therefore investigated the biological effect and signal pathway of VIP in LNCaP cells, a prostate cancer cell line that requires androgens for growth. We showed that low nanomolar concentrations of VIP, acting through G(s)-protein-coupled VIP receptors, can induce LNCaP cell growth in the absence of androgen. Blockade of androgen-receptor (AR) in these cells by AR antagonist bicalutamide or by anti-AR small interfering RNA, inhibited the proliferative effect of VIP. In addition, VIP stimulated androgen-independent activation of AR with an EC(50) of 3.0 +/- 0.8 nM. We then investigated VIP-stimulated signaling events that may interact with the AR pathway in prostate cancer cells. VIP regulation of AR activation, mediated by VIP receptors, was protein kinase A (PKA)-dependent, and extracellular signal-regulated kinase 1/2 (ERK1/2) activation contributes to VIP-mediated AR activation. Furthermore, PKA-dependent Rap1 activation is required for both ERK1/2 activation and androgen-independent AR activation in LNCaP cells upon VIP stimulation. Finally, we showed that VIP-induced AR activation was also present in prostate cancer CWR22Rv1 and PC3 cells transfected with the wild-type AR. Altogether, we demonstrate that VIP acting through its G(s)-protein-coupled receptors can cause androgen-independent transactivation of AR through a PKA/Rap1/ERK1/2 pathway, thus promoting androgen-independent proliferation of androgen-sensitive prostate cancer cells.

Critical role of acylglycerol kinase in epidermal growth factor-induced mitogenesis of prostate cancer cells.

The bioactive phospholipids, LPA (lysophosphatidic acid) and PA (phosphatidic acid), regulate pivotal processes related to the pathogenesis of cancer. Recently, we cloned a novel type of lipid kinase that phosphorylates monoacylglycerols (such as 2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand) and diacylglycerols, to form LPA and PA, respectively. This AGK (acylglycerol kinase) is highly expressed in prostate cancer cell lines and the results reviewed here suggest that AGK might be a critical player in the initiation and progression of prostate cancer. Intriguingly, down-regulation of endogenous AGK inhibited EGF (epidermal growth factor), but not LPA-induced ERK1/2 (extracellular-signal-regulated kinase 1/2) activation and progression through the S-phase of the cell cycle. In this review, we will summarize the evidence demonstrating that AGK amplifies EGF growth signalling pathways that play an important role in the pathophysiology of prostate cancer. Because LPA has long been implicated as an autocrine and paracrine growth stimulatory factor for prostate cancer cells, the identification of this novel lipid kinase that regulates its production could provide new and useful targets for preventive or therapeutic measures.

Critical role of acylglycerol kinase in epidermal growth factor-induced mitogenesis of prostate cancer cells

The bioactive phospholipids, LPA (lysophosphatidic acid) and PA (phosphatidic acid), regulate pivotal processes related to the pathogenesis of cancer. Recently, we cloned a novel type of lipid kinase that phosphorylates monoacylglycerols (such as 2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand) and diacylglycerols, to form LPA and PA, respectively. This AGK (acylglycerol kinase) is highly expressed in prostate cancer cell lines and the results reviewed here suggest that AGK might be a critical player in the initiation and progression of prostate cancer. Intriguingly, down-regulation of endogenous AGK inhibited EGF (epidermal growth factor), but not LPA-induced ERK1/2 (extracellular-signal-regulated kinase 1/2) activation and progression through the S-phase of the cell cycle. In this review, we will summarize the evidence demonstrating that AGK amplifies EGF growth signalling pathways that play an important role in the pathophysiology of prostate cancer. Because LPA has long been implicated as an autocrine and paracrine growth stimulatory factor for prostate cancer cells, the identification of this novel lipid kinase that regulates its production could provide new and useful targets for preventive or therapeutic measures.

Interleukin-6 Sequence Variants Are not Associated with Prostate Cancer Risk

Interleukin-6 Sequence Variants Are not Associated with Prostate Cancer Risk

Activation of signal transducer and activator of transcription 5 in human prostate cancer is associated with high histological grade.

We have recently identified signal transducer and activator of transcription 5 (Stat5) as a critical survival factor for prostate cancer cells. We now report that activation of Stat5 is associated with high histological grade of human prostate cancer. Specifically, immunohistochemical analysis demonstrated a strong positive correlation with activation of Stat5 and high Gleason score in 114 human prostate cancers. To investigate the mechanisms underlying constitutive activation of Stat5 in prostate cancer, a dominant-negative mutant of Janus kinase 2 (Jak2) was delivered by adenovirus to CWR22Rv cells. Dominant-negative-Jak2 effectively blocked the activation of Stat5 whereas wild-type Jak2 enhanced activation, indicating that Jak2 is the main kinase that phosphorylates Stat5 in human prostate cancer cells. A ligand-induced mechanism for activation of Stat5 in prostate cancer was suggested by the ability of prolactin (Prl) to stimulate activation of both Jak2 and Stat5 in CWR22Rv human prostate cancer cells and in CWR22Rv xenograft tumors. In addition, Prl restored constitutive activation of Stat5 in five of six human prostate cancer specimens in ex vivo long-term organ cultures. Finally, Prl protein was locally expressed in the epithelium of 54% of 80 human prostate cancer specimens with positive correlation with high Gleason scores and activation of Stat5. In conclusion, our data indicate that increased activation of Stat5 was associated with more biologically aggressive behavior of prostate cancer. The results further suggest that Jak2 is the principal Stat5 tyrosine kinase in human prostate cancer, possibly activated by autocrine/paracrine Prl.

Co-operative functions between nuclear factors NFkappaB and CCAT/enhancer-binding protein-beta (C/EBP-beta) regulate the IL-6 promoter in autocrine human prostate cancer cells.

IL-6 is a growth and survival factor for prostate cancer cells through autocrine pathways. Here, we have systematically examined the transcriptional regulation mechanisms of IL-6 in autocrine prostate cancer cells. RT-PCR and immunohistochemical staining were used to determine IL-6 production in the cells. Serial mutant IL-6 promoter luciferase reporters were generated and their transcriptional activities were examined. The transcription factors involved in IL-6 regulation were identified with super-shift EMSA. Overexpression of NFkappaB p65 and C/EBP-beta, and blockade of NFkappaB with IkappaBalpha or CAPE were performed to demonstrate the cooperation between NFkappaB p65 and C/EBP-beta in activation of IL-6. Transcription factor regulatory sites IL6-NFkappaB, IL6-C/EBP, IL6-CREB, and IL6-AP1, are responsive to constitutively activated IL-6 production in autocrine prostate cancer cell lines. Among these sites, IL6-AP1 and IL6-C/EBP appear most important, while IL6-NFkappaB shows the least effect for IL-6 promoter activity as determined by mutant IL-6 promoter luciferase reporter assay. Nevertheless, nuclear factor NFkappaB is activated and required. Such activation is minimally dependent upon the IL6-NFkappaB site, occurring through cooperation with other transcription factors that bind the IL-6 promoter. Cooperation between NFkappaB p65 and C/EBP-beta did not require a functional IL6-NFkappaB binding site. These data support a unique role for NFkappaB p65 as the primary trigger in autocrine production of IL-6 in prostate cancer cells. Furthermore, we describe a novel transcriptional activation mechanism for NFkappaB that is independent of its regulatory binding site, occurring through cooperation with other transcription factors that facilitate the neighboring regulatory site.

Prostate cancer cell proliferation is influenced by leptin 1

Background Obesity is considered a risk for many cancers. Serum leptin levels are often elevated in obese people. Leptin acts as a mitogenic agent in many tissues; therefore, it may act to promote cancer cell growth. We previously demonstrated that leptin acts as a growth factor for prostate cancer cells in vitro. The purpose of this study was to characterize leptin receptor isoform mRNA expression in leptin-treated DU145 and PC-3 prostate cancer cell lines. Expression levels of SOCS-3, a known leptin-inducible suppressor of leptin signaling, and known mitogenic signaling pathways of PI3K and ERK were also analyzed Methods DU145 and PC-3 cells were treated with 0, 4, 40, or 80 ng/ml leptin for 0, 0.5, 1, 2, 4, 24, or 48 h. Multiplex RT-PCR was performed to determine mRNA levels of the short (huOB-Ra) or the long (huOB-Rb) OB-R isoforms or SOCS-3. p-Akt and p-ERK were determined by Western blot. Cell viability and apoptosis were determined by MTT and nucleosomal fragmentation assay Results DU145 and PC-3 expressed huOB-Ra, huOB-Rb, and SOCS-3 mRNA. huOB-Ra mRNA levels increased in PC-3 at 48 h ( P < 0.01); however, no significant changes were observed in DU145. huOB-Rb mRNA levels decreased at 48 h in DU145; however, a twofold increase at 48 h ( P < 0.01) was observed with PC-3 and was dose-dependent ( P < 0.05). Leptin increased SOCS-3 mRNA in DU145 at 24 and 48 h ( P < 0.05) and in PC-3 at 1 h (2-fold) and 48 h (fivefold; P < 0.01). Leptin up-regulated p-Akt in a time- and dose-dependent manner in the DU145 prostate cancer cells via a suppression of apoptosis. Leptin up-regulated p-ERK in a time-dependent manner in PC-3 cells Conclusions In prostate cancer cells, the mitogenic effects of leptin are not a consequence of altered receptor isoform mRNA expression. No defect in SOCS-3 signaling was observed, and proliferation appears to be working through the PI3K and MAPK leptin receptor-activated pathways, depending on cell type. Leptin stimulation may be selective for either pathway to suppress apoptosis, thereby enhancing prostate cancer growth.

Saposin C promotes survival and prevents apoptosis via PI3K/Akt-dependent pathway in prostate cancer cells

BackgroundIn addition to androgens, growth factors are also implicated in the development and neoplastic growth of the prostate gland. Prosaposin is a potent neurotrophic molecule. Homozygous inactivation of prosaposin in mice has led to the development of a number of abnormalities in the male reproductive system, including atrophy of the prostate gland and inactivation of mitogen-activated protein kinase (MAPK) and Akt in prostate epithelial cells.We have recently reported that prosaposin is expressed at a higher level by androgen-independent (AI) prostate cancer cells as compared to androgen-sensitive prostate cancer cells or normal prostate epithelial and stromal cells. In addition, we have demonstrated that a synthetic peptide (prosaptide TX14A), derived from the trophic sequence of the saposin C domain of prosaposin, stimulated cell proliferation, migration and invasion and activated the MAPK signaling pathway in prostate cancer cells. The biological significances of saposin C and prosaposin in prostate cancer are not known.ResultsHere, we report that saposin C, in a cell type-specific and dose-dependent manner, acts as a survival factor, activates the Akt-signaling pathway, down-modulates caspase-3, -7, and -9 expression and/or activity, and decreases the cleaved nuclear substrate of caspase-3 in prostate cancer cells under serum-starvation stress. In addition, prosaptide TX14A, saposin C, or prosaposin decreased the growth-inhibitory effect, caspase-3/7 activity, and apoptotic cell death induced by etoposide. We also discovered that saposin C activates the p42/44 MAP kinase pathway in a pertussis toxin-sensitive and phosphatidylinositol 3-kinase (PI3K) /Akt-dependent manner in prostate cancer cells. Our data also show that the anti-apoptotic activity of saposin C is at least partially mediated via PI3K/Akt signaling pathway.ConclusionWe postulate that as a mitogenic, survival, and anti-apoptotic factor for prostate cancer cells, saposin C or prosaposin may contribute to prostate carcinogenesis at its early androgen-dependent or metastatic AI state.

Identification of leptin receptor isoforms in human prostate cancer cells

Introduction: The incidence of certain cancers, including prostate cancer, is increased in obese individuals. Serum levels of the adipocyte-derived hormone leptin are elevated in obese people and leptin acts as a mitogenic agent in a number of tissues. Thus, leptin may act to promote cancer cell growth. Indeed, we have demonstrated that leptin acts as a growth factor for prostate cancer cells in vitro. Various isoforms of the leptin receptor (Ob-R) exist through which leptin may act to promote cell growth. The purpose of this study was to characterize expression of leptin receptor isoform mRNAs in the absence and presence of leptin in two prostate cancer cell lines. Methods: Two lines of prostate cancer cells (DU145 and PC3) were treated with 40ng/ml of human recombinant leptin for 48h and total RNA was isolated. This dose of leptin is similar to that observed in obese humans. Primers were designed specifically to detect the presence of either the short (huOb-Ra) or the long (huOb-Rb) Ob-R isoforms and level of mRNA expression for each was determined. The presence of leptin receptor isoforms in prostate cancer cells was assessed using RT-PCR and expected product lengths were verified by gel electrophoresis. Results: DU145 and PC3 cancer cell lines exhibited both huOb-Ra and huOb-Rb mRNA expression. Treatment of both cancer cell lines with 40ng/ml leptin reduced huOb-Rb mRNA expression to the point where it was no longer readily detectable. In contrast, huOb-Ra mRNA levels were not reduced by treatment with 40ng/ml leptin. Conclusions: Leptin is a growth factor that stimulates the proliferation of prostate cancer cells in vitro. This proliferation of prostate cancer cells by leptin is related to Ob-R isoform expression. In prostate cancer cells exposed to high levels of leptin, mRNA expression for huOb-Rb is significantly reduced whereas huOb-Ra mRNA expression is unaffected. Thus, it may be that the mitogenic activity of leptin in prostate cancer cells occurs primarily through the short isoform of the leptin receptor.

Bombesin stimulates nuclear factor kappa B activation and expression of proangiogenic factors in prostate cancer cells. Levine L, Lucci JA 3rd, Pazdrak B, Cheng JZ, Guo YS, Townsend CM Jr, Hellmich MR, Department of Obstetrics and Gynecology, The University of Texas Medical Branch, Galveston, TX 77555: Cancer Res 2003;63(13):3495–3502

The majority of deaths from prostate cancer occur in patients with androgen-insensitive metastatic disease. An important early event in the development of the metastatic phenotype is the induction of genes that promote angiogenesis, such as vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8), which are released from tumor cells into their microenvironment. Coincident with progression from prostatic carcinoma in situ to metastatic disease is an increase in the number of tumor cells exhibiting neuroendocrine (NE) differentiation. NE cells express a variety of peptide hormones, including the bombesin (BBS)-like peptide, gastrin-releasing peptide (GRP), and its cognate receptor, GRP-R. Although there is a strong positive correlation between the degree of NE differentiation and the metastatic potential of prostate cancers, a mechanistic link between increased expression of peptide hormone receptors, such as GRP-R, and proangiogenic gene expression has not been established. Here we report that BBS stimulates nuclear factor kappa B (NF kappa B) activation and proangiogenic gene expression in the androgen-insensitive prostate cancer cells lines, PC-3 and DU-145. In PC-3 cells, BBS stimulation of GRP-R resulted in the up-regulation of IL-8 and VEGF expression through a NF kappa B-dependent pathway. We show that BBS treatment induced inhibitor of NF kappa B degradation, NF kappa B translocation to the cell nucleus, increased NF kappa B binding to its DNA consensus sequence, and increased IL-8 and VEGF mRNA expression and protein secretion. Treatment with the proteasome inhibitor, MG-132, blocked BBS-stimulated NF kappa B DNA binding, and IL-8 and VEGF expression and secretion. Finally, media collected from PC-3 cell cultures, after BBS treatment, stimulated an NF kappa B-dependent migration of human umbilical vascular endothelial cells in vitro. Together, our data demonstrate a role for BBS and GRP-R in the NF kappa B-dependent up-regulation of proangiogenic gene expression, and suggest a possible molecular mechanism linking NE differentiation and the increased metastatic potential of androgen-insensitive prostate cancers.