Ceramide accumulation is independent of camptothecin-induced apoptosis in prostate cancer LNCaP cells

We have investigated to determine the source of ceramide produced during the genotoxic apoptosis induced by the anti-cancer drug, camptothecin (CPT), in human prostate cancer LNCaP cells by measuring the activities of acid and neutral sphingomyelinases (SMase) and by using fumonisinB(1) (FB(1)), the inhibitor of ceramide synthase involving de novo synthesis of ceramide. In contrast to time-dependent elevation of intracellular ceramide level after CPT-treatment, the activities of both SMases were not increased but rather decreased. Instead, pretreatment for 3 h with FB(1) (100 microM), an inhibitor of ceramide synthase, almost completely abrogated ceramide accumulation observed in cells exposed to CPT for 18 h. These results indicate that ceramide is produced via de novo pathway but not via sphingomyelin hydrolysis pathway. Furthermore, it is to be noted that the pretreatment with FB(1) did not affect the CPT-induced apoptosis as assessed by DNA ladder formation, Hoechst 33342 staining, flow cytometry, and mitochondrial potential thereby leading us to propose that ceramide accumulation is independent of apoptosis in this system.     

Identification of organoselenium compounds that possess chemopreventive properties in human prostate cancer LNCaP cells

The process of cancer development consists of three sequential stages termed initiation, promotion, and progression. Oxidative stress damages DNA and introduces mutations into oncogenes or tumor suppressor genes, thus contributing to cancer development. Cancer chemoprevention is defined to prevent or delay the development of cancer by the use of natural or synthetic substances. In the present study, we synthesized a series of organoselenium compounds and evaluated their possible chemopreventive properties in human prostate cancer LNCaP cells. Among 42 organoselenium compounds tested, two compounds, 3-selena-1-dethiacephem 13 and 3-selena-1-dethiacephem 14 strongly activated the Nrf2/ARE (antioxidant response element) signaling and thus markedly increased expression of heme oxygenase-1 (HO-1), a phase II antioxidant enzyme. Translocation of Nrf2 to the nucleus preceded HO-1 protein induction by two compounds. The intracellular ROS level was strongly reduced immediately after treatment with these compounds, showing that they are potent antioxidants. Finally, both compounds inhibited cell growth via cell cycle arrest. Our findings suggest that compounds 13 and 14 could not only attenuate oxidative stress through Nrf2/ARE activation and direct ROS scavenging but also inhibit cell growth. Thus, these compounds possess the potential as pharmacological agents for chemoprevention of human prostate cancer.     

Proteomic analysis of STEAP1 knockdown in human LNCaP prostate cancer cells

Prostate cancer (PCa) continues to be one of the most common cancers in men worldwide. The six transmembrane epithelial antigen of the prostate 1 (STEAP1) protein is overexpressed in several types of human tumors, particularly in PCa. Our research group has demonstrated that STEAP1 overexpression is associated with PCa progression and aggressiveness. Therefore, understanding the cellular and molecular mechanisms triggered by STEAP1 overexpression will provide important insights to delineate new strategies for PCa treatment. In the present work, a proteomic strategy was used to characterize the intracellular signaling pathways and the molecular targets downstream of STEAP1 in PCa cells. A label-free approach was applied using an Orbitrap LC-MS/MS system to characterize the proteome of STEAP1-knockdown PCa cells. More than 6700 proteins were identified, of which a total of 526 proteins were found differentially expressed in scramble siRNA versus STEAP1 siRNA (234 proteins up-regulated and 292 proteins down-regulated). Bioinformatics analysis allowed us to explore the mechanism through which STEAP1 exerts influence on PCa, revealing that endocytosis, RNA transport, apoptosis, aminoacyl-tRNA biosynthesis, and metabolic pathways are the main biological processes where STEAP1 is involved. By immunoblotting, it was confirmed that STEAP1 silencing induced the up-regulation of cathepsin B, intersectin-1, and syntaxin 4, and the down-regulation of HRas, PIK3C2A, and DIS3. These findings suggested that blocking STEAP1 might be a suitable strategy to activate apoptosis and endocytosis, and diminish cellular metabolism and intercellular communication, leading to inhibition of PCa progression.     

Permanent phenotypic and genotypic changes of prostate cancer cells cultured in a three-dimensional rotating-wall vessel

A three-dimensional (3D) integrated rotating-wall vessel cell-culture system was used to evaluate the interaction between a human prostate cancer cell line, LNCaP, and microcarrier beads alone, or microcarrier beads previously seeded with either prostate or bone stromal cells. Upon coculture of LNCaP cells with microcarrier beads either in the presence or in the absence of prostate or bone stromal cells, 3D prostate organoids were formed with the expected hormonal responsiveness to androgen, increased cell growth, and prostate-specific antigen production. In this communication, we define permanent phenotypic and genotypic changes of LNCaP cells upon coculture with microcarrier beads alone, or with microcarrier beads previously seeded with either prostate or bone stromal cells. Most notably, we observed selective genetic changes, i.e., chromosomal losses or gains, as evaluated by both conventional cytogenetic and comparative genomic hybridization, in LNCaP sublines derived from the prostate organoids. Moreover, the derivative LNCaP cells appear to have altered growth profiles, and exhibit permanent and stable changes in response to androgen, estrogen, and growth factors. The derivative LNCaP sublines showed increased anchorage-independent growth rate, and enhanced tumorigenicity and metastatic potential when inoculated orthotopically in castrated athymic mice. Our results support the hypothesis that further nonrandom genetic and phenotypic changes in prostate cancer epithelial cells can occur through an event that resembles "adaptive mutation" such as has been described in bacteria subjected to nutritional starvation. The occurrence of such permanent changes may be highly contact dependent, and appears to be driven by specific microenvironmental factors surrounding the tumor cell epithelium grown as 3D prostate organoids.     

Development of a mathematical model that predicts the outcome of hormone therapy for prostate cancer

We propose a mathematical model that quantitatively reproduces the dynamics of the serum prostate-specific antigen (PSA) level under intermittent androgen suppression (IAS) for prostate cancer. Taking into account the biological knowledge that there are reversible and irreversible changes in a malignant cell, we constructed a piecewise-linear dynamical model where the testosterone dynamics are modelled with rapid shifts between two levels, namely the normal and castrate concentrations of the male hormone. The validity of the model was supported by patient data obtained from a clinical trial of IAS. It accurately reproduced the kinetics of the therapeutic reduction of PSA and predicted the future nadir level correctly. The coexistence of reversible and irreversible changes within the malignant cell provided the best explanation of early progression to androgen independence. Finally, since the model identified patients for whom IAS was effective, it potentially offers a novel approach to individualized therapy requiring the input of time sequence values of PSA only.     

Low doses of selenium specifically stimulate the repair of oxidative DNA damage in LNCaP prostate cancer cells

Epidemiological studies have demonstrated an inverse relationship between selenium (Se) intake and cancer incidence and/or mortality. However, the molecular mechanisms underlying the cancer chemopreventive activity of Se compounds remain largely unknown. The objective of this study was to investigate the effect of low doses of Se on the stimulation of DNA repair systems in response to four different qualities of DNA damage. P53-proficient LNCaP human prostate adenocarcinoma cells were grown either untreated or in the presence of low concentrations of two Se compounds (30° nM sodium selenite, or 10 μM selenomethionine) and exposed to UVA, H2O2, methylmethane sulfonate (MMS) or UVC. Cell viability as well as DNA damage induction and repair were evaluated by the alkaline Comet assay. Overall, Se was shown to be a very potent protector against cell toxicity and genotoxicity induced by oxidative stress (UVA or H2O2) but not from the agents that induce other types of deleterious lesions (MMS or UVC). Furthermore, Se-treated cells exhibited increased oxidative DNA repair activity, indicating a novel mechanism of Se action. Therefore, the benefits of Se could be explained by a combination of antioxidant activity, the reduction in DNA damage and the enhancement of oxidative DNA repair capacity.     

AMPK/SIRT1 signaling through p38MAPK mediates Interleukin-6 induced neuroendocrine differentiation of LNCaP prostate cancer cells

Neuroendocrine Prostate Cancer (NEPC) is an aggressive form of androgen independent prostate cancer (AIPC), correlated with therapeutic resistance. Interleukin (IL)-6 promotes proliferation and neuroendocrine differentiation (NED) of androgen dependent LNCaP cells. We treated LNCaP cells with IL-6 and observed for in vitro NED of cells and also expression of NE markers βIII tubulin, neuron-specific enolase (NSE) and chromogranin A (ChA). Here we investigated the proteins and/or pathways involved in NED of LNCaP cells induced by IL-6 and characterized their role in NED of PCa cells. We found that the altered proteins modulated AMPK signaling pathway in NE cells. Remarkably, IL-6 induces NED of LNCaP cells through activation of AMPK and SIRT1 and also both of these are co-regulated while playing a predominant role in NED of LNCaP cells. Of the few requirements of AMPK-SIRT1 activation, increased eNOS is essential for NED by elevating Nitric oxide (NO) levels. Pleiotropic effects of NO ultimately regulate p38MAPK in IL-6 induced NED. Hence, IL-6 induced AMPK-SIRT1 activation eventually transfers its activation signals through p38MAPK for advancing NED of LNCaP cells. Moreover, inactivation of p38MAPK with specific inhibitor (SB203580) attenuated IL-6 induced NED of LNCaP cells. Therefore, IL-6 promotes NED of PCa cells via AMPK/SIRT1/p38MAPK signaling. Finally, targeting AMPK-SIRT1 or p38MAPK in androgen independent PC3 cells with neuroendocrine features reversed their neuroendocrine characteristics. Taken together these novel findings reveal that targeting p38MAPK mitigated NED of PCa cells, and thus it can be a favorable target to overcome progression of NEPC.     

GLI1, a crucial mediator of sonic hedgehog signaling in prostate cancer, functions as a negative modulator for androgen receptor

Sonic hedgehog (SHH) signaling, acting in a combinatorial manner with androgen signaling, is essential for prostate patterning and development. Recently, elevated activation of SHH signaling has been shown to play important roles in proliferation, progression and metastasis of prostate cancer. In this report, we demonstrate for the first time, that GLI1, which has been shown to play a central role in SHH signaling in prostate cancer, can act as a co-repressor to substantially block androgen receptor (AR)-mediated transactivation, at least in part, by directly interacting with AR. Our observations suggest that the SHH-GLI pathway might be one of determinants governing the transition of prostate cancer from an androgen-dependent to an androgen-independent state by compensating, or even superseding androgen signaling.     

灵芝酸A对前列腺癌LNCaP细胞的生长抑制作用及机制

本研究利用alamarBlue~?测定细胞活力法、流式细胞术(annxin V-FITC)/PI双染色测定细胞凋亡法和高效液相色谱(high performance liquid chromatography,HPLC)测定5α-还原酶活性法评价灵芝酸A对前列腺癌的体外抗肿瘤活性,并进一步利用流式细胞术2’,7’-二氯荧光素二乙酸酯(2’,7’-dichlorofluorescindiacetate,H2DCFDA)染色测定ROS释放量法、实时荧光定量PCR(quantitative real-time PCR,qPCR)和蛋白质免疫印迹(western blot,WB)检测雄激素受体(androgen receptor,AR)基因和凋亡相关基因表达的方法,探讨其作用机理。研究结果表明灵芝酸A可通过抑制5α-还原酶活性,抑制睾酮诱导的前列腺癌LNCaP细胞增殖,诱发细胞早期凋亡来发挥抗肿瘤活性;进一步研究表明,灵芝酸A降低前列腺癌细胞中AR的表达,并通过引发细胞线粒体功能障碍释放过量活性氧(reactive oxygen species,ROS)诱发细胞凋亡,而qPCR和WB的数据进一步表明细胞线粒体功能障碍与抑癌基因caspase-3、bad和aifm1的高表达密切相关。     

Vitamin D inhibits G1 to S progression in LNCaP prostate cancer cells through p27Kip1 stabilization and Cdk2 mislocalization to the cytoplasm

1,25-(OH)2 vitamin D3 (1,25-(OH)2D3) exerts antiproliferative effects via cell cycle regulation in a variety of tumor cells, including prostate. We have previously shown that in the human prostate cancer cell line LN-CaP, 1,25-(OH)2D3 mediates an increase in cyclin-dependent kinase inhibitor p27Kip1 levels, inhibition of cyclin-dependent kinase 2 (Cdk2) activity, hypophosphorylation of retinoblastoma protein, and accumulation of cells in G1. In this study, we investigated the mechanism whereby 1,25-(OH)2D3 increases p27 levels. 1,25-(OH)2D3 had no effect on p27 mRNA levels or on the regulation of a 3.5-kb fragment of the p27 promoter. The rate of p27 protein synthesis was not affected by 1,25-(OH)2D3 as measured by luciferase activity driven by the 5'- and 3'-untranslated regions of p27 that regulate p27 protein synthesis. Pulse-chase analysis of 35S-labeled p27 revealed an increased p27 protein half-life with 1,25-(OH)2D3 treatment. Because Cdk2-mediated phosphorylation of p27 at Thr187 targets p27 for Skp2-mediated degradation, we examined the phosphorylation status of p27 in 1,25-(OH)2D3-treated cells. 1,25-(OH)2D3 decreased levels of Thr187 phosphorylated p27, consistent with inhibition of Thr187 phosphorylation-dependent p27 degradation. In addition, 1,25-(OH)2D3 reduced Skp2 protein levels in LNCaP cells. Cdk2 is activated in the nucleus by Cdk-activating kinase through Thr160 phosphorylation and by cdc25A phosphatase via Thr14 and Tyr15 dephosphorylation. Interestingly, 1,25-(OH)2D3 decreased nuclear Cdk2 levels as assessed by subcellular fractionation and confocal microscopy. Inhibition of Cdk2 by 1,25-(OH)2D3 may thus involve two mechanisms: 1) reduced nuclear Cdk2 available for cyclin binding and activation and 2) impairment of cyclin E-Cdk2-dependent p27 degradation through cytoplasmic mislocalization of Cdk2. These data suggest that Cdk2 mislocalization is central to the antiproliferative effects of 1,25-(OH)2D3.     

Bcl-xL mediates a survival mechanism independent of the phosphoinositide 3-kinase/Akt pathway in prostate cancer cells

Among various molecular strategies by which prostate cancer cells evade apoptosis, phosphoinositide 3-kinase (PI3K)/Akt signaling represents a dominant survival pathway. However, different prostate cancer cell lines such as LNCaP and PC-3 display differential sensitivity to the apoptotic effect of PI3K inhibition in serum-free media, reflecting the heterogeneous nature of prostate cancer in apoptosis regulation. Whereas both cell lines are equally susceptible to LY294002-mediated Akt dephosphorylation, only LNCaP cells default to apoptosis, as evidenced by DNA fragmentation and cytochrome c release. In PC-3 cells, Akt deactivation does not lead to cytochrome c release, suggesting that the intermediary signaling pathway is short-circuited by an antiapoptotic factor. This study presents evidence that Bcl-xL overexpression provides a distinct survival mechanism that protects PC-3 cells from apoptotic signals emanating from PI3K inhibition. First, the Bcl-xL/BAD ratio in PC-3 cells is at least an order of magnitude greater than that of LNCaP cells. Second, ectopic expression of Bcl-xL protects LNCaP cells against LY294002-induced apoptosis. Third, antisense down-regulation of Bcl-xL sensitizes PC-3 cells to the apoptotic effect of LY294002. The physiological relevance of this Bcl-xL-mediated survival mechanism is further underscored by the protective effect of serum on LY294002-induced cell death in LNCaP cells, which is correlated with a multifold increase in Bcl-xL expression. In contrast to Bcl-xL, Bcl-2 expression levels are similar in both cells lines, and do not respond to serum stimulation, suggesting that Bcl-2 may not play a physiological role in antagonizing apoptosis signals pertinent to BAD activation in prostate cancer cells.     

Cannabinoid receptor agonist-induced apoptosis of human prostate cancer cells LNCaP proceeds through sustained activation of ERK1/2 leading to G1 cell cycle arrest

We have recently shown that the expression levels of both cannabinoid receptors CB(1) and CB(2) are higher in human prostate cancer cells than in normal prostate epithelial cells, and treatment of LNCaP cells with WIN-55,212-2 (a mixed CB(1)/CB(2) agonist) resulted in inhibition of cell growth and induction of apoptosis (Sarfaraz, S., Afaq, F., Adhami, V. M., and Mukhtar, H. (2005) Cancer Res. 65, 1635-1641). This study was conducted to understand the mechanistic basis of these effects. Treatment of LNCaP cells with WIN-55,212-2 (1-10 microm; 24 h) resulted in: (i) an arrest of the cells in the G(0)/G(1) phase of the cell cycle; (ii) an induction of p53 and p27/KIP1; (iii) down-regulation of cyclins D1, D2, E; (iii) decrease in the expression of cdk-2, -4, and -6; (iv) decrease in protein expression of pRb; (v) down-regulation of E2F (1-4); and (vi) decrease in the protein expression of DP1 and DP2. Similar effects were also observed when androgen-independent PC3 cells were treated with WIN-55,212-2 (5-30 microm). We further observed sustained up-regulation of ERK1/2 and inhibition of PI3k/Akt pathways in WIN-55,212-2-treated cells. Inhibition of ERK1/2 abrogated WIN-55,212-2-indued cell death suggesting that sustained activation of ERK1/2 leads to cell cycle dysregulation and arrest of cells in G(0)/G(1) phase subsequently leading to an induction of apoptosis. Further, WIN-55,212-2 treatment of cells resulted in a dose-dependent increase in Bax/Bcl-2 ratio in such a way that favors apoptosis. The induction of apoptosis proceeded through down-regulation of caspases 3, 6, 7, and 9 and cleavage of poly (ADP-ribose) polymerases. Based on these data we suggest that cannabinoid receptor agonists should be considered as novel agents for the management of prostate cancer.     

乙醇浓度对提取灵芝三萜含量的影响及提取物抗前列腺癌细胞LNCaP的活性

本研究考察乙醇浓度对灵芝子实体中三萜成分提取的影响及提取物抗前列腺癌细胞LNCaP的增殖活性和迁移能力,为提取灵芝三萜时乙醇浓度的选择和灵芝抑制前列腺相关疾病产品开发提供依据。研究采用高效液相（HPLC）色谱法测定了灵芝醇提物中目前具有代表性的9种三萜的含量;并用抑制前列腺癌细胞LNCaP的细胞活性和细胞迁移能力的实验研究灵芝提取物的抗前列腺癌的作用。HPLC测定结果显示,当乙醇浓度为50%-80%时,9种灵芝三萜的含量随着乙醇浓度的升高而增大;当乙醇浓度继续升高至95%时,提取的三萜含量反而有所降低。细胞实验结果显示,4个浓度乙醇的灵芝提取物都具有良好的抑制LNCaP肿瘤细胞增殖作用和阻滞LNCaP细胞迁移能力。因此在使用乙醇提取灵芝三萜时,乙醇浓度升高有利于三萜的提取;在生产灵芝抗前列腺相关产品时,提取灵芝子实体中抗前列腺增生的活性成分时选用80%的乙醇较为适宜。     

Induction of differentiation of leukaemic (HL-60) or prostate cancer (LNCaP, JCA-1) cells potentiates apoptosis triggered by onconase

Onconase (Onc) is a ribonuclease from amphibian oocytes that is cytostatic and cytotoxic to many tumour lines. It shows in vivo antitumour activity in mouse tumour models and is currently in Phase III clinical trials. The present study was designed to test whether cytotoxic effects of ONC can be modulated by differentiating agents. Human leukaemic HL-60 and prostate cancer LNCaP and JCA-1 cells were treated with Onc in the absence and presence of several inducers of differentiation and frequency of apoptosis was assessed using three different cytometric methods and confirmed by analysis of cell morphology. A moderate degree of apoptosis observed after 48-72 h incubation of HL-60 cells in the presence of 0.42 microM Onc alone was markedly potentiated by administration of retinoic acid (all trans), sodium butyrate or dimethylsulfoxide at concentrations known to induce differentiation but be minimally cytotoxic. Likewise, the frequency of apoptosis of LNCaP and JCA-1 cells treated with Onc was increased in the cultures to which phenylbutyrate was added. Although cell treatment with Onc alone, with each of the differentiating agents alone or with Onc in combination with the differentiating agents led to an increase in the proportion of G1 cells, no specific cell cycle phase preference in induction of apoptosis was observed. The data suggest that cells undergoing differentiation are particularly vulnerable to Onc; a combination of Onc and differentiating agents should be considered for further in vivo tests to assess its possible usefulness in the clinic.