Analysis of cabazitaxel‐resistant mechanism in human castration‐resistant prostate cancer

Cabazitaxel (CBZ) is approved for docetaxel‐resistant castration‐resistant prostate cancer (CRPC). However, efficacy of CBZ for CRPC is limited and there are no effective treatments for CBZ‐resistant CRPC. In order to investigate the CBZ‐resistant mechanism, the establishment of a CBZ‐resistant cell line is urgently needed. We established CBZ‐resistant CRPC cell lines DU145CR and PC3CR by incubating DU145 and PC3 cells with gradually increasing concentrations of CBZ for approximately 2 years. We analyzed the gene expression profiles and cell cycle changes using microarray and flow cytometry. Pathway analysis revealed DU145CR cells had enhanced gene clusters of cell division and mitotic nuclear division. Enhancement of ERK signaling was detected in DU145CR cells. DU145CR cells had resistance to G₂/M arrest induced by CBZ through ERK signaling activation. The MEK inhibitor PD184352 significantly inhibited cell proliferation of DU145CR. In contrast to DU145CR, PC3CR cells had enhancement of PI3K/AKT signaling. The PI3K/mTOR inhibitor NVP‐BEZ 235 had a significant antitumor effect in PC3CR cells. Cabazitaxel ‐resistant CRPC cells established in our laboratory had enhancement of cell cycle progression signals and resistance to G₂/M arrest induced by CBZ. Enhancement of ERK signaling or PI3K/AKT signaling were detected in the cell lines, so ERK or PI3K/AKT could be therapeutic targets for CBZ‐resistant CRPC.     

胱硫醚β合成酶在前列腺癌中的异常表达及其对前列腺癌细胞增殖的调控作用

目的:探讨胱硫醚β合成酶(CBS)在前列腺癌中的差异表达情况,及其对前列腺癌细胞增殖的调控作用。方法:利用GEPIA网站分析来源于TCGA和GTEx数据库的492例前列腺癌组织和152例正常组织中CBS mRNA表达情况。利用ULCAN网站分析来源于TCGA数据库的497例前列腺癌组织和52例正常组织中CBS mRNA的表达情况。用RPIM-1640培养基培养前列腺癌细胞系DU145、PC3、LNCaP和C4-2,免疫印迹实验检测CBS蛋白表达情况。shRNA转染DU145细胞,分为对照shRNA组、CBS shRNA#1组或#2组,克隆形成实验检测细胞克隆形成数量,BrdU标记实验检测细胞增殖能力,免疫印迹实验检测AKT、mTOR、S6K蛋白表达情况,以及AKT S473位点、mTOR S2448位点、S6K T421/S424位点的磷酸化水平。将稳定表达对照shRNA、CBS shRNA#1或#2的DU145细胞注射入小鼠皮下,建立小鼠前列腺癌移植瘤模型,观察肿瘤生长情况。结果:数据库分析结果显示,与正常前列腺组织比较,前列腺癌组织中CBS mRNA的表达水平显著上升。CBS蛋白在...     

Downregulation of reticulocalbin‐1 differentially facilitates apoptosis and necroptosis in human prostate cancer cells

Reticulocalbin 1 (RCN1), an endoplasmic reticulum (ER)‐resident Ca²⁺‐binding protein, is dysregulated in cancers, but its pathophysiological roles are largely unclear. Here, we demonstrate that RCN1 is overexpressed in clinical prostate cancer (PCa) samples, associated with cyclin B, not cyclin D1 expression, compared to that of benign tissues in a Chinese Han population. Downregulation of endogenous RCN1 significantly suppresses PCa cell viability and arrests the cell cycles of DU145 and LNCaP cells at the S and G2/M phases, respectively. RCN1 depletion causes ER stress, which is evidenced by induction of GRP78, activation of PERK and phosphorylation of eIF2α in PCa cells. Remarkably, RCN1 loss triggers DU145 cell apoptosis in a caspase‐dependent manner but mainly causes necroptosis in LNCaP cells. An animal‐based analysis confirms that RCN1 depletion suppresses cell proliferation and promotes cell death. Further investigations reveal that RCN1 depletion leads to elevation of phosphatase and tensin homolog (PTEN) and inactivation of AKT in DU145 cells. Silencing of PTEN partially restores apoptotic cells upon RCN1 loss. In LNCaP cells, predominant activation of CaMKII is important for necroptosis in response to RCN1 depletion. Thus, RCN1 may promote cell survival and serve as a useful target for cancer therapy.     

Transient receptor potential melastatin 4 channel contributes to migration of androgen-insensitive prostate cancer cells

Impaired Ca²⁺ signaling in prostate cancer contributes to several cancer hallmarks, such as enhanced proliferation and migration and a decreased ability to induce apoptosis. Na⁺ influx via transient receptor potential melastatin 4 channel (TRPM4) can reduce store-operated Ca²⁺ entry (SOCE) by decreasing the driving force for Ca²⁺. In patients with prostate cancer, gene expression of TRPM4 is elevated. Recently, TRPM4 was identified as a cancer driver gene in androgen-insensitive prostate cancer.We investigated TRPM4 protein expression in cancer tissue samples from 20 patients with prostate cancer. We found elevated TRPM4 protein levels in prostatic intraepithelial neoplasia (PIN) and prostate cancer tissue compared to healthy tissue. In primary human prostate epithelial cells (hPEC) from healthy tissue and in the androgen-insensitive prostate cancer cell lines DU145 and PC3, TRPM4 mediated large Na⁺ currents. We demonstrated significantly increased SOCE after siRNA targeting of TRPM4 in hPEC and DU145 cells. In addition, knockdown of TRPM4 reduced migration but not proliferation of DU145 and PC3 cells. Taken together, our data identify TRPM4 as a regulator of SOCE in hPEC and DU145 cells, demonstrate a role for TRPM4 in cancer cell migration and suggest that TRPM4 is a promising potential therapeutic target.     

Sorafenib-induced defective autophagy promotes cell death by necroptosis

Autophagy is one of the main cytoprotective mechanisms that cancer cells deploy to withstand the cytotoxic stress and survive the lethal damage induced by anti-cancer drugs. However, under specific conditions, autophagy may, directly or indirectly, induce cell death. In our study, treatment of the Atg5-deficient DU145 prostate cancer cells, with the multi-tyrosine kinase inhibitor, sorafenib, induces mitochondrial damage, autophagy and cell death. Molecular inhibition of autophagy by silencing ULK1 and Beclin1 rescues DU145 cells from cell death indicating that, in this setting, autophagy promotes cell death. Re-expression of Atg5 restores the lipidation of LC3 and rescues DU145 and MEF atg5−/− cells from sorafenib-induced cell death. Despite the lack of Atg5 expression and LC3 lipidation, DU145 cells form autophagosomes as demonstrated by transmission and immuno-electron microscopy, and the formation of LC3 positive foci. However, the lack of cellular content in the autophagosomes, the accumulation of long-lived proteins, the presence of GFP-RFP-LC3 positive foci and the accumulated p62 protein levels indicate that these autophagosomes may not be fully functional. DU145 cells treated with sorafenib undergo a caspase-independent cell death that is inhibited by the RIPK1 inhibitor, necrostatin-1. Furthermore, treatment with sorafenib induces the interaction of RIPK1 with p62, as demonstrated by immunoprecipitation and a proximity ligation assay. Silencing of p62 decreases the RIPK1 protein levels and renders necrostatin-1 ineffective in blocking sorafenib-induced cell death. In summary, the formation of Atg5-deficient autophagosomes in response to sorafenib promotes the interaction of p62 with RIPK leading to cell death by necroptosis.     

SOCE and cancer: Recent progress and new perspectives

Ca²⁺ acts as a universal and versatile second messenger in the regulation of a myriad of biological processes, including cell proliferation, differentiation, migration and apoptosis. Store‐operated Ca²⁺ entry (SOCE) mediated by ORAI and the stromal interaction molecule (STIM) constitutes one of the major routes of calcium entry in nonexcitable cells, in which the depletion of intracellular Ca²⁺ stores triggers activation of the endoplasmic reticulum (ER)‐resident Ca²⁺ sensor protein STIM to gate and open the ORAI Ca²⁺ channels in the plasma membrane (PM). Accumulating evidence indicates that SOCE plays critical roles in cancer cell proliferation, metastasis and tumor neovascularization, as well as in antitumor immunity. We summarize herein the recent advances in our understanding of the function of SOCE in various types of tumor cells, vascular endothelial cells and cells of the immune system. Finally, the therapeutic potential of SOCE inhibitors in the treatment of cancer is also discussed.     

Dasatinib induces autophagic cell death in human ovarian cancer

BACKGROUND:

Dasatinib, an inhibitor of Src/Abl family kinases, can inhibit tumor growth of several solid tumors. However, the effect and mechanism of action of dasatinib in human ovarian cancer cells remains unknown.

METHODS:

Dasatinib‐induced autophagy was determined by acridine orange staining, punctate localization of GFP‐LC3, LC3 protein blotting, and electron microscopy. Significance of beclin 1, AKT, and Bcl‐2 in dasatinib‐induced autophagy and growth inhibition was assayed by small interfering RNA (siRNA) silencing and/or overexpression of the gene of interest.

RESULTS:

Dasatinib inhibited cell growth by inducing little apoptosis, but substantial autophagy in SKOv3 and HEY ovarian cancer cells. In vivo studies showed dasatinib inhibited tumor growth and induced both autophagy and apoptosis in a HEY xenograft model. Knockdown of beclin 1 and Atg12 expression with their respective siRNAs diminished dasatinib‐induced autophagy, whereas knockdown of p27Kip1 with specific siRNAs did not. Small hairpin RNA knockdown of beclin 1 expression reduced dasatinib‐induced autophagy and growth inhibition. Dasatinib reduced the phosphorylation of AKT, mTOR, p70S6K, and S6 kinase expression. Constitutive expression of AKT1 and AKT2 inhibited dasatinib‐induced autophagy in both HEY and SKOv3 cells. Dasatinib also reduced Bcl‐2 expression and activity. Overexpression of Bcl‐2 partially prevented dasatinib‐induced autophagy.

CONCLUSIONS:

Dasatinib induces autophagic cell death in ovarian cancer that partially depends on beclin 1, AKT, and Bcl‐2. These results may have implications for clinical use of dasatinib. Cancer 2010. © 2010 American Cancer Society.     

Ampelopsin‐induced autophagy protects breast cancer cells from apoptosis through Akt‐mTOR pathway via endoplasmic reticulum stress

Our previous study has shown that ampelopsin (AMP), a flavonol mainly found in Ampelopsis grossedentata, could induce cell death in human breast cancer cells via reactive oxygen species generation and endoplasmic reticulum (ER) stress pathway. Here, we examined whether autophagy is activated in AMP‐treated breast cancer cells and, if so, sought to find the exact role and underlying molecular profile of autophagy in AMP‐induced cell death. Our results showed that AMP treatment activated autophagy in MDA‐MB‐231 and MCF‐7 breast cancer cells, as evidenced by the accumulation of autophagosomes, an increase of microtubule‐associated protein 1 light chain 3 beta‐2 (LC3B‐II) and the conversion of LC3B‐I to LC3B‐II, the degradation of the selective autophagic target p62/SQSTM1, and the formation of green fluorescent protein (GFP)‐LC3 puncta. Blockage of autophagy augmented AMP‐induced cell death, suggesting that autophagy has cytoprotective effects. Meanwhile, AMP treatment suppressed Akt‐mammalian target of rapamycin (mTOR) pathway as evidenced by dose‐ and time‐dependent decrease of the phosphorylation of Akt, mTOR and ribosomal protein S6 kinase (p70S6K), whereas Akt activator insulin‐like growth factor‐1 (IGF‐1) pretreatment partially restored Akt‐mTOR pathway inhibited by AMP and decreased AMP‐inuduced autophagy, signifying that AMP activated autophagy via inhibition of the Akt‐mTOR pathway. Additionally, blocking ER stress not only reduced autophagy induction, but also alleviated inhibition of the Akt‐mTOR pathway induced by AMP, suggesting that activation of ER stress was involved in induction of autophagy and inhibition of the Akt‐mTOR pathway. Taken together, these findings indicate that AMP induces protective autophagy in human breast cancer cells through Akt‐mTOR pathway via ER stress.     

Myeloid cell leukemia-1 is a key molecular target for mithramycin A-induced apoptosis in androgen-independent prostate cancer cells and a tumor xenograft animal model

Mithramycin A (Mith) is a natural polyketide that has been used in multiple areas of research including apoptosis of various cancer cells. Here, we examined the critical role of Mith in apoptosis and its molecular mechanism in DU145 and PC3 prostate cancer cells and tumor xenografts. Mith decreased cell growth and induced apoptosis in DU145 and PC-3 cells. Myeloid cell leukemia-1 (Mcl-1) was over-expressed in both cell lines compared to RWPE1 cells. Mith inhibited Mcl-1 protein expression in both cells, but only altered Mcl-1 mRNA levels in PC-3 cells. We also found that Mith reduced Mcl-1 protein levels through both proteasome-dependent protein degradation and the inhibition of protein synthesis in DU145 cells. Studies using siRNA confirmed that the knockdown of Mcl-1 induced apoptosis. Mith significantly suppressed TPA-induced neoplastic cell transformation through the down-regulation of the Mcl-1 protein in JB6 cells, and suppressed the transforming activity of both cell types. Mith also inhibited tumor growth and Mcl-1 levels, in addition to inducing apoptosis, in athymic nude mice bearing DU145 cell xenografts without affecting five normal organs. Therefore, Mith inhibits cell growth and induces apoptosis by suppressing Mcl-1 in both prostate cancer cells and xenograft tumors, and thus is a potent anticancer drug candidate for prostate cancer.     

Knockdown of astrocyte-elevated gene-1 inhibits prostate cancer progression through upregulation of FOXO3a activity

Astrocyte-elevated gene-1 (AEG-1) has been reported to be upregulated in several malignancies and play a critical role in Ha-ras-mediated oncogenesis through the phosphatidylinositol 3-kinase/AKT signaling pathway. However, the role of AEG-1 in prostate cancer (PC) has never been reported. We now show that AEG-1 is overexpressed in clinical PC tissue samples and cultured PC cells compared to benign prostatic hyperplasia tissue samples and normal prostate epithelial cells. Interestingly, AEG-1 knockdown induced cell apoptosis through upregulation of forkhead box (FOXO) 3a activity. This alteration of FOXO3a activity was dependent on reduction of AKT activity in LNCaP and PC-3 cells with high constitutive AKT activity, but not in DU145 cells with low constitutive AKT activity, although AEG-1 knockdown had no impact on phosphatase and tensin homolog expression in these cells. AEG-1 knockdown also attenuated the constitutive activity of the nuclear factor kappaB (NF-kappaB) and the activator protein 1 (AP-1) with a corresponding depletion in the expression of NF-kappaB and AP-1-regulated genes (interleukin (IL)-6, IL-8 and matrix metalloproteinase-9) and significantly decreased cell invasion properties of PC-3 and DU145 cells. Overall, our findings suggest that aberrant AEG-1 expression plays a dominant role as a positive auto-feedback activator of AKT and as a suppressor of FOXO3a in PC cells. AEG-1 may therefore represent a novel genetic biomarker to serve as an attractive molecular target for new anticancer agents to prevent PC cell progression and metastasis.     

S179D prolactin increases vitamin D receptor and p21 through up-regulation of short 1b prolactin receptor in human prostate cancer cells

In this study, we further investigated the mechanisms by which pseudophosphorylated prolactin (S179D PRL) inhibits the growth of human prostate cancer cells. When treated with S179D PRL for 3 days, LnCAP cells responded by increasing expression of the vitamin D receptor (VDR) and the cell cycle regulatory molecule, p21, whereas PC3 and DU145 cells did not. After 5 days of treatment, both PC3 and DU145 cells responded. Untreated LnCAP cells express the short 1b form (SF1b) of the human prolactin receptor, but DU145 and PC3 cells express only low amounts of this receptor until elevated by treatment with S179D PRL. DU145 and PC3 cells become sensitive to the negative effects of S179D PRL on cell number after induction of the SF1b. Transfection of either SF1b or SF1a into PC3 or DU145 cells made them sensitive to S179D PRL in the 3-day time frame, a finding that was not duplicated by transfection with the long form of the receptor. Treatment of LnCAP cells with S179D PRL increased long-term activation of extracellular signal-regulated kinase 1/2 (ERK1/2). This did not occur in PC3 and DU145 cells until transfection with SF1a/SF1b. Blockade of ERK signaling eliminated S179D PRL-stimulated expression of the VDR and p21 in LnCAP cells and transfected PC3 and DU145 cells. We conclude that initiation of alternative splicing to produce SF1b, and subsequent altered signaling, contribute to the growth inhibitory mechanisms of S179D PRL. This is the first indication of a role for short prolactin receptors in the regulation of cell proliferation.     

Suppression of STIM1 inhibits human glioblastoma cell proliferation and induces G0/G1 phase arrest

Background

Depletion of calcium (Ca²⁺) from the endoplasmic reticulum (ER) activates the ubiquitous store-operated Ca²⁺ entry (SOCE) pathway which sustains long-term Ca²⁺ signals and is critical for cellular functions. Stromal interacting molecule 1 (STIM1) serves a dual role as an ER Ca²⁺ sensor and activator of SOCE. Aberrant expression of STIM1 could be observed in several human cancer cells. However, the role of STIM1 in regulating tumorigenesis of human glioblastoma still remains unclear.

Methods

Expression of STIM1 protein in a panel of human glioblastoma cell lines (U251, U87 and U373) in different transformation level were evaluated by Western blot method. STIM1 loss of function was performed on U251 cells, derived from grade IV astrocytomas-glioblastoma multiforme with a lentvirus-mediated short harpin RNA (shRNA) method. The biological impacts after knock down of STIM1 on glioblastoma cells were investigated in vitro and in vivo.

Results

We discovered that STIM1 protein was expressed in U251, U87 and U373 cells, and especially higher in U251 cells. RNA interference efficiently downregulated the expression of STIM1 in U251 cells at both mRNA and protein levels. Specific downregulation of STIM1 inhibited U251 cell proliferation by inducing cell cycle arrest in G0/G1 phase through regulation of cell cycle-related genes, such as p21^Waf1/Cip1_, cyclin D1 and cyclin-dependent kinase 4 (CDK4), and the antiproliferative effect of STIM1 silencing was also observed in U251 glioma xenograft tumor model.

Conclusion

Our findings confirm STIM1 as a rational therapeutic target in human glioblastoma, and also indicate that lentivirus-mediated STIM1 silencing is a promising therapeutic strategy for human glioblastoma.     

Secreted factors from metastatic prostate cancer cells stimulate mesenchymal stem cell transition to a pro‐tumourigenic ‘activated’ state that enhances prostate cancer cell migration

Mesenchymal stem cells (MSCs) are a heterogeneous population of multipotent cells that are capable of differentiating into osteocytes, chondrocytes and adipocytes. Recently, MSCs have been found to home to the tumour site and engraft in the tumour stroma. However, it is not yet known whether they have a tumour promoting or suppressive function. We investigated the interaction between prostate cancer cell lines 22Rv1, DU145 and PC3, and bone marrow‐derived MSCs. MSCs were ‘educated’ for extended periods in prostate cancer cell conditioned media and PC3‐educated MSCs were found to be the most responsive with a secretory profile rich in pro‐inflammatory cytokines. PC3‐educated MSCs secreted increased osteopontin (OPN), interleukin‐8 (IL‐8) and fibroblast growth factor‐2 (FGF‐2) and decreased soluble fms‐like tyrosine kinase‐1 (sFlt‐1) compared to untreated MSCs. PC3‐educated MSCs showed a reduced migration and proliferation capacity that was dependent on exposure to PC3‐conditioned medium. Vimentin and α‐smooth muscle actin (αSMA) expression was decreased in PC3‐educated MSCs compared to untreated MSCs. PC3 and DU145 education of healthy donor and prostate cancer patient‐derived MSCs led to a reduced proportion of FAP+ αSMA+ cells contrary to characteristics commonly associated with cancer associated fibroblasts (CAFs). The migration of PC3 cells was increased toward both PC3‐educated and DU145‐educated MSCs compared to untreated MSCs, while DU145 migration was only enhanced toward patient‐derived MSCs. In summary, MSCs developed an altered phenotype in response to prostate cancer conditioned medium which resulted in increased secretion of pro‐inflammatory cytokines, modified functional activity and the chemoattraction of prostate cancer cells.     

6-Gingerol suppresses cell viability,migration and invasion via inhibiting EMT,and inducing autophagy and ferroptosis in LPS-stimulated and LPS-unstimulated prostate cancer cells

6-Gingerol is a bioactive compound isolated from Zingiber officinale. 6-Gingerol has been shown to have anticancer effects in numerous types of cancer cell. The mechanisms underlying the anticancer effect of 6-Gingerol in prostate cancer requires investigation. In the present study, the effect on cell viability of 6-Gingerol on LNCaP, PC3 and DU145 prostate cancer cells were determined using the MTT and colony formation assays. 6-Gingerol significantly inhibited cell migration, adhesion and invasion in LPS-stimulated and LPS-unstimulated prostate cancer cells. Furthermore, these changes were accompanied by alterations in the protein expression levels of epithelial-mesenchymal transition biomarkers, including E-cadherin, N-cadherin, Vimentin and zonula occludens-1. 6-Gingerol also induced autophagy by significantly increasing LC3B-II and Beclin-1 protein expression levels in prostate cancer cells. Combining 6-Gingerol with LY294002, an autophagy inhibitor, significantly increased cell survival in DU145 cells. Furthermore, 6-Gingerol significantly decreased the protein expression levels of glutathione (GSH) peroxidase 4 and nuclear factor erythroid 2-related factor 2 in prostate cancer cells. Reactive oxygen species (ROS) levels were significantly increased but GSH levels were decreased following 6-Gingerol treatment in prostate cancer cells. Co-treatment with the ferroptosis inhibitor, ferrostatin-1, significantly increased cell viability and significantly decreased ROS levels in 6-Gingerol-treated cells. These results suggested that 6-Gingerol may have inhibited prostate cell cancer viability via the regulation of autophagy and ferroptosis. In addition, 6-Gingerol inhibited cell migration, adhesion and invasion via the regulation of EMT-related protein expression levels in LPS-stimulated and LPS-unstimulated prostate cancer cells. In conclusion, 6-Gingerol may induce protective autophagy, autophagic cell death and ferroptosis-mediated cell death in prostate cancer cells. These findings may provide a strategy for the treatment and prevention of prostate cancer.     

Inhibition of stromal‐interacting molecule 1‐mediated store‐operated Ca2+ entry as a novel strategy for the treatment of acquired imatinib‐resistant gastrointestinal stromal tumors

Imatinib has revolutionized the treatment of gastrointestinal stromal tumors (GIST); however, primary and secondary resistance to imatinib is still a major cause of treatment failure. Multiple mechanisms are involved in this progression. In the present study, we reported a novel mechanism for the acquired resistance to imatinib, which was induced by enhanced Ca²⁺ influx via stromal‐interacting molecule 1 (STIM1)‐mediated store‐operated Ca²⁺ entry (SOCE). We found that the STIM1 expression level was related to the acquired resistance to imatinib in our studied cohort. The function of STIM1 in imatinib‐resistant GIST cells was also confirmed both in vivo and in vitro. The results showed that STIM1 overexpression contributed to SOCE and drug response in imatinib‐sensitive GIST cells. Blockage of SOCE by STIM1 knockdown suppressed the proliferation of imatinib‐resistant GIST cell lines and xenografts. In addition, STIM1‐mediated SOCE exerted an antiapoptotic effect via the MEK/ERK pathway. The results from this study provide a basis for further research into potential novel therapeutic strategies in acquired imatinib‐resistant GIST.     

CCL2 Is a Negative Regulator of AMP-Activated Protein Kinase to Sustain mTOR Complex-1 Activation,Survivin Expression,and Cell Survival in Human Prostate Cancer PC3 Cells

CCL2 is a cytokine prevalent in the prostate cancer tumor microenvironment. Recently, we reported that CCL2 induces the mammalian target of rapamycin (mTOR) pathway to promote prostate cancer PC3 cell survival; however, the mechanism used by CCL2 to maintain mTOR complex-1 (mTORC1) activation requires clarification. This study demonstrates that upon serum starvation, CCL2 functions as a negative regulator of AMP-activated protein kinase (AMPK) by decreasing phosphorylation at its major regulatory site (Thr¹⁷²) in PC3, DU145, and C4-2B prostate cancer cells. The CCL2-mediated AMPK regulation decreased raptor phosphorylation (Ser⁷⁹²) resulting in hyperactivation of mTORC1. D942, a pharmacological activator of AMPK, stunted CCL2-induced mTORC1 activity, survivin expression, and cell survival without significantly affecting Akt activity. CCL2, however, conferred some resistance to the lethal effect of D942 compared with untreated cells. By using Akt-specific inhibitor X, it was shown that Akt inactivation did not cause an increase in AMPK phosphorylation in CCL2-stimulated cells, suggesting that CCL2-mediated negative regulation of AMPK is independent of Akt. Furthermore, bisindolylmaleimide-V, a specific inhibitor of p70^S6K, stunted survivin expression and induced cell death in CCL2-treated PC3. Altogether, these findings suggest that CCL2 hyperactivates mTORC1 through simultaneous regulation of both AMPK and Akt pathways and reveals a new network that promotes prostate cancer: CCL2-AMPK-mTORC1-survivin.     

Down?regulation of E?cadherin enhances prostate cancer chemoresistance via Notch signaling

Background: The chemoresistance of prostate cancer (PCa) is invariably associated with the aggressiveness and metastasis of this disease. New emerging evidence indicates that the epithelial-to-mesenchymal transition (EMT) may play pivotal roles in the development of chemoresistance and metastasis. As a hallmark of EMT, E-cadherin is suggested to be a key marker in the development of chemoresistance. However, the molecular mechanisms underlying PCa chemoresistance remain unclear. The current study aimed to explore the association between EMT and chemoresistance in PCa as well as whether changing the expression of E-cadherin would affect PCa chemoresistance.Methods: Parental PC3 and DU145 cells and their chemoresistant PC3-TxR and DU145-TxR cells were analyzed. PC3-TxR and DU145-TxR cells were transfected with E-cadherin-expressing lentivirus to overexpress E-cadherin; PC3 and DU145 cells were transfected with small interfering RNA to silence E-cadherin. Changes of EMT phenotype-related markers and signaling pathways were assessed by Western blotting and quantitative real-time polymerase chain reaction. Tumor cell migration, invasion, and colony formation were then evaluated by wound healing, transwell, and colony formation assays, respectively. The drug sensitivity was evaluated using MTS assay.Results: Chemoresistant PC3-TxR and DU145-TxR cells exhibited an invasive and metastatic phenotype that associated with EMT, including the down-regulation of E-cadherin and up-regulation of Vimentin, Snail, and N-cadherin,comparing with that of parental PC3 and DU145 cells. When E-cadherin was overexpressed in PC3-TxR and DU145-TxR cells, the expression of Vimentin and Claudin-1 was down-regulated, and tumor cell migration and invasion were inhibited. In particular, the sensitivity to paclitaxel was reactivated in E-cadherin-overexpressing PC3-TxR and DU145-TxR cells. When E-cadherin expression was silenced in parental PC3 and DU145 cells, the expression of Vimentin and Snail was up-regulated, and, particularly, the sensitivity to paclitaxel was decreased. Interestingly, Notch-1 expression was up-regulated in PC3-TxR and DU145-TxR cells, whereas the E-cadherin expression was down-regulated in these cells comparing with their parental cells. The use of γ-secretase inhibitor, a Notch signaling pathway inhibitor, significantly increased the sensitivity of chemoresistant cells to paclitaxel.Conclusion: The down-regulation of E-cadherin enhances PCa chemoresistance via Notch signaling, and inhibiting the Notch signaling pathway may reverse PCa chemoresistance     

Apoptotic signaling in bufalin‐ and cinobufagin‐treated androgen‐dependent and ‐independent human prostate cancer cells

Prostate cancer has its highest incidence in the USA and is becoming a major concern in Asian countries. Bufadienolides are extracts of toxic glands from toads and are used as anticancer agents, mainly on leukemia cells. In the present study, the antiproliferative and apoptotic mechanisms of bufalin and cinobufagin on prostate cancer cells were investigated. Proliferation of LNCaP, DU145, and PC3 cells was measured by 3‐(4,5‐dimethylthiazol‐2‐yle)‐2,5‐diphenyltetrazolium bromide assay and the doubling time (tD) was calculated. Bufalin and cinobufagin caused changes in the tD of three prostate cancer cell lines, which were more significant than that of human mesangial cells. In addition, bufadienolides induced prostate cancer cell apoptosis more significantly than that in breast epithelial cell lines. After treatment, the caspase‐3 activity and protein expression of caspase‐3, ‐8, and ‐9 were elevated. The expression of other apoptotic modulators, including mitochondrial Bax and cytosolic cytochrome c, were also increased. However, expression of p53 was only enhanced in LNCaP cells. Downregulation of p53 by antisense TP53 restored the cell viability suppressed by bufalienolides. Furthermore, the increased expression of Fas was more significant in DU145 and PC3 cells with mutant p53 than in LNCaP cells. Transfection of Fas small interfering RNA restored cell viability in the bufadienolide‐treated cells. These results suggest that bufalin and cinobufagin suppress cell proliferation and cause apoptosis in prostate cancer cells via a sequence of apoptotic modulators, including Bax, cytochrome c, and caspases. The upstream mediators might be p53 and Fas in androgen‐dependent LNCaP cells and Fas in androgen‐independent DU145 and PC3 cells. (Cancer Sci 2008; 99: 2467–2476)     

Thapsigargin resistance in human prostate cancer cells

BACKGROUND: Thapsigargin (TG) is a potent inhibitor of sarcoplasmic/endoplasmic reticulum Ca2+ ATPases (SERCAs). TG-based prodrugs are being developed for the treatment of prostate cancer (PC). To develop optimal TG-based therapeutics it is important to understand the mechanisms of resistance to TG that may potentially occur in cancer cells. METHODS: DU145/TG and PC3/TG cells were derived from human PC DU145 and PC3 cells, respectively, by incremental exposure to TG. Growth assays, Western blot analyses, cDNA microarrays, semiquantitative and real-time polymerase chain reaction (PCR), Northern blot analyses, and immunohistochemistry were used to study these cells. RESULTS: DU145/TG cells are 1100-fold and PC3/TG cells are 1350-fold resistant to TG. Although expression of both SERCA and p-glycoprotein can mediate TG resistance in hamster cells, neither is modulated in DU145/TG cells. In contrast, in PC3/TG cells, SERCA, and not p-glycoprotein, is significantly overexpressed but cannot by itself account for the 1350-fold resistance to TG in these cells. Several genes not previously identified to be altered by TG selection are modulated in DU145/TG and PC3/TG cells. Furthermore, the spectrum of genes modulated in DU145/TG cells are distinct from that in PC3/TG cells, even though both cells are of prostate origin and share the same TG-resistant phenotype. CONCLUSIONS: PC cells can adapt to SERCA inhibition by TG. However, they demonstrate cell type-specific plasticity with respect to gene expression upon TG selection. Further, previously not described mechanisms of resistance appear to be recruited in the TG-resistant PC cells, which provide a novel model to study mechanisms of resistance and adaptation in PC on TG-mediated dysregulation of Ca2+ homeostasis.