c-Jun NH2-terminal kinase-dependent Fas activation contributes to etoposide-induced apoptosis in p53-mutated prostate cancer cells

Human ALKBH6 Is Required for Maintenance of Genomic Stability and Promoting Cell Survival During Exposure of Alkylating Agents in Pancreatic Cancer

Alpha-ketoglutarate-dependent dioxygenase (ALKBH) is a DNA repair gene involved in the repair of alkylating DNA damage. There are nine types of ALKBH (ALKBH1-8 and FTO) identified in humans. In particular, certain types of ALKBH enzymes are dioxygenases that directly reverse DNA methylation damage via transfer of a methyl group from the DNA adduct onto α-ketoglutarate and release of metabolic products including succinate and formaldehyde. Here, we tested whether ALKBH6 plays a significant role in preventing alkylating DNA damage and decreasing genomic instability in pancreatic cancer cells. Using an E. coli strain deficient with ALKB, we found that ALKBH6 complements ALKB deficiency and increases resistance after alkylating agent treatment. In particular, the loss of ALKBH6 in human pancreatic cancer cells increases alkylating agent-induced DNA damage and significantly decreases cell survival. Furthermore, in silico analysis from The Cancer Genome Atlas (TCGA) database suggests that overexpression of ALKBH6 provides better survival outcomes in patients with pancreatic cancer. Overall, our data suggest that ALKBH6 is required to maintain the integrity of the genome and promote cell survival of pancreatic cancer cells.

Involvement of the glutamine RF‑amide peptide and its cognate receptor GPR103 in prostate cancer

Glutamine RF‑amide peptide (QRFP) belongs to the RFamide neuropeptide family, which is involved in a wide spectrum of biological activities, ranging from food intake and cardiovascular functioning to analgesia, aldosterone secretion, locomotor activity and reproduction. Recently, QRFP has been demonstrated to exert its effects by activating the G protein‑coupled receptor GPR103. QRFP is expressed in the brain and peripherally in the adipose tissue, bladder, colon, testis, parathyroid and thyroid gland, as well as in the prostate gland. Following lung cancer, prostate cancer constitutes the second most frequently diagnosed cancer among men, whilst obesity appears to be a contributing factor for aggressive prostate cancer. In the present study, we sought to investigate the role of QRFP in prostate cancer, using two androgen‑independent human prostate cancer cell lines (PC3 and DU145) as in vitro experimental models and clinical human prostate cancer samples. The expression of both QRFP and GPR103 at the gene and protein level was higher in human prostate cancer tissue samples compared to control and benign prostatic hyperplasia (BHP) samples. Furthermore, in both prostate cancer cell lines used in the present study, QRFP treatment induced the phosphorylation of ERK1/2, p38, JNK and Akt. In addition, QRFP increased cell migration and invasion in these in vitro models, with the increased expression of MMP2. Furthermore, we demonstrated that the pleiotropic adipokine, leptin, increased the expression of QRFP and GPR103 in PC3 prostate cancer cells via a PI3K‑ and MAPK‑dependent mechanism, indicating a novel potential link between adiposity and prostate cancer. Our findings expand the existing evidence and provide novel insight into the implication of QRFP in prostate cancer.

Etoposide induces pancreatic β-cells cytotoxicity via the JNK/ERK/GSK-3 signaling-mediated mitochondria-dependent apoptosis pathway

Etoposide is widely used in the treatment of the different types of tumors such as pancreatic cancer. However, etoposide also causes several unwanted side-effects in normal viable cells, including pancreatic β-cells, which are vulnerable to chemical-induced injuries, and the molecular mechanisms underlying etoposide-induced apoptosis are still unclear. Here, the results showed that in RIN-m5F cells (a β-cell-derived cell line), the number of viable cells was significantly decreased after 24h of etoposide treatment and underwent mitochondria-dependent apoptotic signals accompanied by mitochondrial dysfunction, and increases in the population of sub-G1 hypodiploid cells and apoptotic cells, caspase-3 activity, and the activation of caspase cascades. Etoposide also increased the phosphorylation levels of glycogen synthase kinase (GSK)-3α/β in treated RIN-m5F cells. Pretreatment with LiCl, a GSK-3 inhibitor, prevented etoposide-induced mitochondria-dependent apoptosis and GSK-3 protein phosphorylation in RIN-m5F cells. Furthermore, exposure of the cells to etoposide induced the phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK)1/2 but not p38-MAPK, which was suppressed by the specific JNK inhibitor (SP600125) and ERK1/2 inhibitor (PD98059), respectively. Additionally, pretreatment with both SP600125 and PD98059 effectively suppressed etoposide-induced β-cell cytotoxicity, apoptosis, and GSK-3 protein phosphorylation; however, LiCl did not reverse JNK and ERK1/2 phosphorylation. Taken together, these results suggest that etoposide is capable of causing cytotoxicity on pancreatic β-cells by inducing apoptosis through the JNK/ERK-mediated GSK-3 downstream-triggered mitochondria-dependent signaling pathway.

Huachansu suppresses human bladder cancer cell growth through the Fas/Fasl and TNF- alpha/TNFR1 pathway in vitro and in vivo

Background

Huachansu (HCS), a class of toxic steroids extracted from toad venom, which has been shown to be a valuable anticancer drug in many kinds of cancers. However, the effect of HCS on bladder cancer has not been elucidated. In this study, we focused on the antitumor activities and related mechanisms of HCS on bladder cancer in vitro and in vivo.

Methods

Cell viability of T24, EJ, RT-4, SV-HUC-1 cells after HCS treatment was measured by MTS, whereas the changes of cell morphology were observed by transmission electron microscopy. The early apoptosis induced by HCS was evaluated by flow cytometry, and the expression level of apoptosis-related molecules (Bax, Bcl-2, XIAP, PARP, cleaved-Caspases 3, 8, 9) was detected using Western blot. We then evaluated the impact of HCS on the expression of Fas/Fasl, TNF- alpha/TNFR1, and the activation of NF-Kappa B pathway, and furthermore the effect of these pathways in HCS induced-apoptosis were also detected. At last, xenograft tumor in nude mice was used to further investigate the antitumor effect of HCS in vivo.

Results

Our results showed that HCS could efficiently inhibit proliferation and induce apoptosis in human bladder cancer cell lines. The expression of Fas, Fasl, TNF- alpha were all elevated at both mRNA and protein level after HCS treatment. Furthermore, down regulation of TNF- alpha, TNFR1, Fas or inhibition of Fas/Fasl interaction decreased the relative number of death cells induced by HCS. In vivo, HCS treatment significantly suppressed tumor growth and induced apoptosis in xenografts tumor in nude mice.

Conclusions

HCS could efficiently inhibit proliferation and induce apoptosis in human bladder cancer cells in vitro and in vivo, which is largely mediated by Fas/Fasl and TNF- alpha/TNFR1 pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0134-9) contains supplementary material, which is available to authorized users.

Phosphorylation status of Fas-associated death domain protein is associated with biochemical recurrence after radical prostatectomy

OBJECTIVE

To assess whether the phosphorylated Fas-associated death domain protein (FADD) at 194 serine (p-FADD) is valuable as a marker of biochemical recurrence in hormone-naive patients who had undergone radical prostatectomy.

MATERIALS AND METHODS

We used radical prostatectomy specimens from 106 patients. None of the patients had received neoadjuvant or adjuvant therapy. The percentage of positive p-FADD cells (nuclear staining) was immunohistochemically evaluated. The correlation between FADD phosphorylation and the clinicopathologic parameters was assessed. The correlation between the biochemical recurrence-free rate and the p-FADD expression level was analyzed using the Kaplan-Meier method.

RESULTS

Overall, 39 patients developed biochemical recurrence. We investigated the expression of p-FADD in 106 patients with prostate cancer using immunohistochemistry. We compared our findings with the clinicopathologic parameters, including the follow-up data. Patients with a greater positive p-FADD rate had a significantly lower biochemical recurrence rate than those with a lower positive p-FADD rate (P < .001). A significant inverse correlation was found between the positive p-FADD rate and the Gleason score.

CONCLUSION

A low expression of p-FADD could be a predictor of biochemical recurrence in hormone-naive patients who have undergone radical prostatectomy.

Suppression of MMP-2 attenuates TNF-α induced NF-κB activation and leads to JNK mediated cell death in glioma

Background

Abrogation of apoptosis for prolonged cell survival is essential in cancer progression. In our previous studies, we showed the MMP-2 downregulation induced apoptosis in cancer cell lines. Here, we attempt to investigate the exact molecular mechanism of how MMP-2 depletion leads to apoptosis in glioma xenograft cell lines.

Methodology/Principal Findings

MMP-2 transcriptional suppression by MMP-2siRNA (pM) induces apoptosis associated with PARP, caspase-8 and -3 cleavage in human glioma xenograft cells 4910 and 5310. Western blotting and cytokine array showed significant decrease in the cellular and secreted levels of TNF-α with concomitant reduction in TNFR1, TRADD, TRAF2, RIP, IKKβ and pIκBα expression levels resulting in inhibition of p65 phosphorylation and nuclear translocation in pM-treated cells when compared to mock and pSV controls. In addition MMP-2 suppression led to elevated Fas-L, Fas and FADD expression levels along with increased p38 and JNK phosphorylation. The JNK-activity assay showed prolonged JNK activation in pM-transfected cells. Specific inhibition of p38 with SB203580 did not show any effect whereas inhibition of JNK phosphorylation with SP600125 notably reversed pM-induced cleavage of PARP, caspase-8 and -3, demonstrating a significant role of JNK in pM-induced cell death. Supplementation of rhMMP-2 counteracted the effect of pM by remarkably elevating TNF-α, TRADD, IKKβ and pIκBα expression and decreasing FADD, Fas-L, and phospho-JNK levels. The EMSA analysis indicated significant reversal of pM-inhibited NF-κB activity by rhMMP-2 treatment which rescued cells from pM-induced cell death. In vivo studies indicated that pM treatment diminished intracranial tumor growth and the immuno histochemical analysis showed decreased phospho-p65 and enhanced phospho-JNK levels that correlated with increased TUNEL-positive apoptotic cells in pM-treated tumor sections.

Conclusion/Significance

In summary, our study implies a role of MMP-2 in the regulation of TNF-α mediated constitutive NF-κB activation and Fas-mediated JNK mediated apoptosis in glioma xenograft cells in vitro and in vivo.

ALKBH3, a human AlkB homologue, contributes to cell survival in human non-small-cell lung cancer

BACKGROUND

We have demonstrated for the first time that a novel human AlkB homologue, ALKBH3, contributes to prostate cancer development, but its clinical and biological roles in lung cancer remain unclear.

METHODS

Expression of both mRNA and protein of PCA-1 was examined by RT-PCR and western blotting. We also assessed association with senescence and in vivo ALKBH3 treatment on orthotopic tumour cell inoculation, and analysed it clinicopathologically.

RESULTS

We have since found novel biological roles for ALKBH3 in human lung cancers, particularly in adenocarcinoma. Our immunohistochemical analysis of human adenocarcinomas and squamous cell carcinomas of the lung not only showed overexpression of ALKBH3 in these tumours but the percentage of cells positive for ALKBH3 also correlated statistically to recurrence-free survival in adenocarcinoma. Knockdown of ALKBH3 by siRNA transfection induced expression of p21(WAF1/Cip1) and p27(Kip1) in the human lung adenocarcinoma cell line A549, resulting in cell cycle arrest, senescence and strong suppression of cell growth in vitro. In vivo, peritoneal tumour growth and dissemination was inhibited in nude mice, previously inoculated with the A549 cell line, by intraperitoneal injection of ALKBH3 siRNA + atelocollagen, as demonstrated by the reduction in both number and diameter of tumours developing in the peritoneum.

CONCLUSION

We suggest that ALKBH3 contributes significantly to cancer cell survival and may be a therapeutic target for human adenocarcinoma of the lung.

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.

Function of JunB in transient amplifying cell senescence and progression of human prostate cancer

PURPOSE

Replicative senescence in cells acts as a barrier against excessive proliferation and carcinogenesis. Transient amplifying cells (TAC) are a subset of basal cell populations within the prostate from which cancers are thought to originate; therefore, we focused on prostate TAC to investigate the molecular mechanisms by which the TAC may be able to evade senescence.

EXPERIMENTAL DESIGN

TAC clones were isolated from each zone within the whole prostate and analyzed in flow cytometry. Prostate cancer cells were transfected with junB small interfering RNA (siRNA) and examined by chorioallantoic membrane assay for cancer invasion. Immunohistochemical analysis was done in primary and metastatic prostate cancer specimens.

RESULTS

TAC populations showed increased expression of p53, p21, p16, and pRb, resulting in senescence. TAC clones with reduced p16 expression successfully bypassed this phase. We further found close correlation between the levels of junB and p16 expression. Repeated transfection of junB siRNA in prostatic TAC allowed the cells to escape senescence presumably through inactivation of p16/pRb. The chorioallantoic membrane invasion assay showed much lower in invasive cancer cells with high expression of junB; conversely, silencing of junB by transfection with junB siRNA promoted invasion. We also found that metastatic prostate cancers, as well as cancers with high Gleason scores, showed significantly low junB immunopositivity.

CONCLUSIONS

JunB is an essential upstream regulator of p16 and contributes to maintain cell senescence that blocks malignant transformation of TAC. JunB thus apparently plays an important role in controlling prostate carcinogenesis and may be a new target for cancer prevention and therapy.

Cleavage of phospholipase D1 by caspase promotes apoptosis via modulation of the p53-dependent cell death pathway

The enzymatic activity of phospholipase D (PLD) is known to be essential for cell survival and protection from apoptosis. However, the mechanisms regulating PLD activity during apoptosis remain unknown. Here we report that cleavage of PLD1 by caspases facilitates p53-mediated apoptosis. Cleavage of PLD1 into an N-terminal fragment (NF-PLD1) and a C-terminal fragment at the amino-acid sequence, DDVD(545), led to a reduction in PLD1 activity. However, a caspase-resistant mutant form of PLD1 retained significant levels of enzymatic activity and apoptotic function as compared to wild-type PLD1. Exogenous NF-PLD1 expression induced apoptosis through a dominant-negative effect on the activity of endogenous PLD1. During apoptosis, a small fraction of PLD1 is cleaved by caspases in a p53-independent manner and NF-PLD1 amplifies apoptotic signaling through inhibition of the remaining PLD1 activity. As PLD1 suppresses the ATM-Chk2-p53 pathway, elimination of PLD1 activity through NF-PLD1 or si-RNA against PLD1 increases apoptosis in a p53-dependent manner. Taken together, our results reveal that cleavage of PLD1 by caspases promotes apoptosis via modulation of the p53-dependent cell death pathway.

Induction of multinucleated cells and apoptosis in the PC-3 prostate cancer cell line by low concentrations of polyethylene glycol 1000

Polyethylene glycol (PEG) has been reported to inhibit the development of colonic lesions in carcinogen-treated rats when administered orally. However, the precise mechanism for the chemopreventive activity of PEG remains largely elusive. Based on a characteristic feature of PEG as a 'fusogen', we investigated its potential as a chemotherapeutic agent through the induction of multinucleated cell formation and apoptosis induction in PC-3 prostate cancer cells. When PC-3 cells were treated with 0.5 and 1.0% PEG 1000, multinucleated cells were induced at a frequency of 8.4 and 13%, respectively, 36 h after PEG treatment under high cell density (1 x 10(6) cells in 100 microL PEG solution) in vitro. Although abnormality of cell cycle progression was not evident in PEG-treated PC-3 cells, multinucleated cells substantially disappeared at around 38 h due to apoptosis. In contrast, no apparent growth suppression was observed when PC-3 cells were exposed to up to 1.0% PEG at a much lower cell density, namely under ordinary culture conditions. Furthermore, injection of 0.5% PEG solution in vivo into PC-3 xenografts implanted in BALB/c-nu/nu male mice significantly suppressed tumor growth compared to phosphate-buffered saline injection. Multinucleated TdT-mediated dUTP-biotin nick end-labeling (TUNEL)-positive cells were observed inside the PEG-injected tumors. PEG was here demonstrated to have anticell proliferation and antitumor effects via induction of apoptosis, possibly by cell fusion. PEG injection therapy could therefore be adopted as an alternative chemotherapeutic strategy for localized prostate cancers, including those that become refractory to androgen-deprivation therapy.

A cytotoxin isolated from Agkistrodon acutus snake venom induces apoptosis via Fas pathway in A549 cells

ACTX-6 is a protein isolated from Agkistrodon acutus snake venom and demonstrated cytotoxic activity to various cancer cells in vitro. In this paper the exact mechanism in ACTX-6-induced cell death was investigated and it was found that ACTX-6 could induce cell apoptosis. The results of Western blot and RT-PCR showed that ACTX-6 could induce Fas and FasL protein expression. When Fas signaling pathway was blocked by neutralizing antibodies to Fas or FasL, ACTX-6-induced apoptosis was inhibited. DISC formation was also detected by immunoprecipitation. These results suggested that Fas pathway was involved in ACTX-6-induced apoptosis. The activities of caspase-3, 8 and 9 were assayed and the activation of caspase-9 demonstrated that mitochondrial pathway was also involved in ACTX-6-induced apoptosis. Bid cleavage and dissipation of mitochondrial membrane potential (delta psi(m)) verified the involvement of mitochondria. ACTX-6 is an L-amino acid oxidase and can oxidize L-amino acid to generate hydrogen peroxide. The production of ROS in ACTX-6-treated cells was detected and the ROS scavenger catalase could inhibit ACTX-6-induced apoptosis. Western blot analysis showed that JNK was phosphorylated in ACTX-6-treated cells and c-Jun was also activated. JNK inhibitor SP600125 could inhibit ACTX-6-induced apoptosis and catalase could inhibit JNK and c-Jun phosphorylation. It could be concluded that JNK pathway was necessary in ACTX-6-induced apoptosis and the oxidative stress generated by ACTX-6 was responsible for the activation of JNK.

c-Jun NH2 terminal kinase activation and decreased expression of mitogen-activated protein kinase phosphatase-1 play important roles in invasion and angiogenesis of urothelial carcinomas

We here examined whether c-Jun NH(2) terminal kinase (JNK) might be involved in the progression of urothelial carcinomas. In vitro and in vivo invasion assays using Matrigel and chick embryo chorioallantoic membrane approaches showed constitutive activation of JNK to significantly increase two processes, invasion and angiogenesis, in the human urothelial carcinoma cell line kU-7, this being suppressed by a JNK inhibitor, SP600125, or cell-permeable peptides. In addition, we found that mitogen-activated protein kinase phosphatase (MKP)-1 functions as an endogenous inhibitor of JNK-mediated signals in urothelial carcinoma cells: chorioallantoic membrane assays showed UMUC14 cells with low MKP-1 expression to be more invasive and have pronounced angiogenesis compared to UMUC6 cells with high MKP-1. Furthermore, knockdown of the MKP-1 gene by siRNA transfection enhanced JNK activation in UMUC6 cells to the UMUC14 level. Immunohistochemically, JNK was found to be highly phosphorylated in high-grade and invasive carcinomas (>/=pT2) as well as carcinoma in situ but not in low-grade and noninvasive phenotypes (pTa, pT1). In contrast, MKP-1 was much more expressed in low-grade/noninvasive cancers than with the high-grade/invasive phenotype, reversely correlating with phosphorylated JNK. Taken together, JNK activation and decreased expression of MKP-1 may play important roles in progression of urothelial carcinoma.

A two-phase strategy for treatment of oxidant-dependent cancers

In many cancers, a chronic increase in oxidant stress - associated with elevated levels of hydrogen peroxide - contributes to the increased proliferative rate, diminished apoptosis, increased angiogenic and metastatic capacity, and chemoresistance that often characterize advanced malignancies. This oxidant stress often reflects up-regulation of expression and activity of NADPH oxidase, and/or decreased activity of catalase, which functions as suppressor gene in oxidant-dependent cancers. These characteristics of oxidant-dependent cancers suggest a dual strategy for treatment of these cancers. Since ascorbate can react spontaneously with molecular oxygen to generate hydrogen peroxide, high-dose intravenous ascorbate should be selectively toxic to tumors that are low in catalase activity - as suggested by numerous cell culture studies. Measures which concurrently improve the oxygenation of hypoxic tumor regions would be expected to boost the efficacy of such therapy; calcitriol and high-dose selenium might also be useful in this regard. Secondly, during the intervals between sessions of ascorbate therapy, administration of agents which can safely inhibit NADPH oxidase would be expected to slow the proliferation and spread of surviving tumor cells - while providing selection pressure for a further decline in catalase activity. In effect, cancers treated in this way would be whipsawed between lethally excessive and inadequately low oxidant stress. An additional possibility is that ascorbate-induced oxidant stress in tumors might potentiate the cell kill achieved with concurrently administered cytotoxic drugs, inasmuch as oxidant mechanisms appear to play a mediating role in the apoptosis induced by many such drugs, largely via activation of c-Jun NH(2)-terminal kinase; cell culture studies would be useful for evaluating this possibility.

Vaccinia virus B1R kinase interacts with JIP1 and modulates c-Jun-dependent signaling

Viruses have to adjust to the host cell to guarantee their life cycle and survival. This aspect of the virus-host cell interaction is probably performed by viral proteins, such as serine-threonine kinases, that are present early during infection. Vaccinia virus has an early Ser-Thr kinase, B1R, which, although required for successful viral infection, is poorly characterized regarding its effects on cellular proteins, and thus, its potential contribution to pathogenesis is not known. Signaling by mitogen-activated protein kinase (MAPK) is mediated by the assembly of complexes between these kinases and the JIP scaffold proteins. To understand how vaccinia virus B1R can affect the host, its roles in the cellular signaling by MAPK complexes and c-Jun activation have been studied. Independently of its kinase activity, B1R can interact with the central region of the JIP1 scaffold protein. The B1R-JIP1 complex increases the amount of MAPK bound to JIP1; thus, MKK7 and TAK1 either bind with higher affinity or bind more stably to JIP1, while there is an increase in the phosphorylation state of JNK bound to JIP1. The functional consequence of these more stable interactions is an increase in the activity of transcription factors, such as c-Jun, that respond to these complexes. Furthermore, B1R is also able to directly phosphorylate c-Jun in residues different from those targeted by JNK and, thus, B1R can also cooperate by an independent route in c-Jun activation. Vaccinia virus B1R can thus modulate the signaling of pathways that respond to cellular stress.

α-TEA inhibits survival and enhances death pathways in cisplatin sensitive and resistant human ovarian cancer cells

RRR-alpha-tocopherol ether linked acetic acid analog (alpha-TEA), is a potential chemotherapeutic agent for ovarian cancer. Pro-death and pro-life signaling pathways were studied to understand the anti-cancer actions of alpha-TEA on cisplatin-sensitive (A2780S) and -resistant (A2780/cp70R) human ovarian cancer cells. Both cell lines were refractory to Fas; whereas, alpha-TEA sensitized them to Fas signaling. alpha-TEA increased levels of Fas message, protein and membrane-associated Fas. Neutralizing antibodies to Fas or Fas L partially blocked alpha-TEA-induced apoptosis. alpha-TEA induced prolonged activation of c-Jun N-terminal kinase (JNK) and its substrate c-Jun; Bax conformational change; and cleavage of Bid and caspases-8, -9 and -3. Chemical inhibitors of JNK, and caspases blocked alpha-TEA-induced apoptosis. alpha-TEA decreased phosphorylation of protein kinase B (Akt/PKB) and extracellular signal-regulated kinase (ERK1/2), as well as cellular FLICE-like inhibitory protein (c-FLIP) and Survivin protein levels. Knockdown of Akt and ERK activity using phosphoinositide- 3-kinase (PI3K) and mitogen-activated protein kinase kinase (MKK1) inhibitors enhanced alpha-TEA-induced apoptosis. Over-expression of constitutively active Akt2 and MKK1 blocked alpha-TEA-induced apoptosis. Collectively, data show alpha-TEA to be a potent apoptotic inducer of both cisplatin-sensitive and -resistant human ovarian cancer cells via activating death receptor Fas signaling and suppressing anti-apoptotic AKT and ERK targets.

Specific positive and negative effects of FLIP on cell survival in human prostate cancer

We demonstrate here for the first time novel positive and negative effects of the FLICE-like inhibitory protein (FLIP) on human prostate cancer cell survival. A proteaosome inhibitor, MG132, mediated cell cycle arrest at G2/M and apoptosis through p38 activation. Interestingly, FLIP was stabilized by MG132 and interacted with Raf-1, resulting in enhancement of p38 signals and cytotoxicity. In contrast, overexpression of FLIP inhibited ubiquitylation and proteasomal degradation of beta-catenin, resulting in increase of the target gene cyclin D1, colony formation and invasive activity. Immunohistochemical analysis and in vitro experiments in primary culture showed FLIP to be overexpressed, statistically associated with expression of beta-catenin/cyclin D1 in metastatic cells, the FLIP/beta-catenin/cyclin D1 signals contributing to colony formation and invasion, which were canceled by FLIP knock down. In contrast, MG132-induced cytotoxicity including apoptosis was strongly inhibited by reduction of FLIP. Taken together, the results indicate that FLIP plays an important role in development of metastatic prostate cancer by inhibiting proteasomal degradation of beta-catenin, whereas it is mainly involved in proteasome inhibitior-mediated cell cycle arrest and apoptosis through activating the Raf-1/p38 pathway. Furthermore, proteasome inhibitors may be effective drugs for advanced prostate cancers overexpressing FLIP.

Inactivation of Id-1 in prostate cancer cells: A potential therapeutic target in inducing chemosensitization to taxol through activation of JNK pathway

Resistance to anticancer drugs is the major problem in the treatment of many advanced cancers, including androgen-independent prostate cancer. Recently, increased expression of Id-1, a basic helix-loop-helix protein, is reported in several types of advanced cancer. It is suggested that high expression of Id-1 may provide an advantage for cancer cell survival and inactivation of Id-1 may be able to increase cancer cells' susceptibility to apoptosis. To test this hypothesis, in this study, by using RNA interfering technology, we inactivated the Id-1 gene in 2 androgen-independent prostate cancer cell lines, DU145 and PC3, and investigated whether downregulation of Id-1 could lead to increased sensitivity to a commonly used anticancer drug, taxol. By using colony forming assay and MTT assay, we found that inactivation of Id-1 resulted in both decreased colony forming ability and cell viability in prostate cancer cells, after taxol treatment. In addition, the si-Id-1-induced sensitization to taxol was associated with activation of apoptosis pathway, which is demonstrated by increased apoptotic index, DNA laddering, sub-G1 phase of the cell cycle, as well as cleaved-PARP and Caspase 3. Furthermore, c-Jun N-terminal kinase (JNK), one of the common pathways responsible for taxol-induced apoptosis, was also activated in the si-Id-1 transfected cells. Inhibition of JNK activity by a specific inhibitor, SP600125, blocked the si-Id-1-induced sensitivity to taxol. These results indicate that increased Id-1 expression in prostate cancer cells may play a protective role against apoptosis, and downregulation of Id-1 may be a potential target to increase sensitivity of taxol-induced apoptosis in prostate cancer cells.

Phosphorylation status of Fas-associated death domain-containing protein (FADD) is associated with prostate cancer progression

It has recently been demonstrated that phosphorylation of FADD at serine 194 plays an important role in the induction of apoptosis by anti-cancer drugs in human prostate cancer cells. The present study has assessed whether this phosphorylation status is valuable as a marker for human prostate cancer progression, and has investigated its biological role in cell growth. Immunohistochemical studies revealed much higher phosphorylation of FADD at serine 194 in normal epithelial cells than in cancer cells, although FADD was found to be highly expressed to the same extent in both cases. The positivity for phosphorylated FADD was significantly lower for patients with a Gleason score greater than or equal to 7, a positive surgical margin, extracapsular or seminal vesicle invasion. In addition, a relationship was also apparent in cancer cells refractory to neoadjuvant hormonal therapy. Interestingly, in Gleason score 3 + 4 tumours, the positivity for FADD phosphorylation was statistically increased by neoadjuvant hormonal therapy, resulting in a reduced percentage of cases with a positive surgical margin and extracapsular invasion. In vitro data showed different functions of phosphorylated and non-phosphorylated FADD: in normal epithelial cells, overexpression of a phosphorylation-mimicking mutant FADD (S194E) caused G2/M cell-cycle arrest, while a non-phosphorylation-mimicking mutant (S194A) had no effect, whereas S194A overexpression resulted in cell cycle progression and enhanced colony-forming activity in cancer cells, but S194E FADD was without influence. These results clearly demonstrate that transition from phosphorylated FADD to the non-phosphorylated form might be associated with carcinogenesis and that induction of FADD phosphorylation could therefore be a target for chemohormonal therapy of human prostate cancer. Moreover, assessment of FADD phosphorylation may be useful as a new biomarker to predict cancer progression.

Methylseleninic acid potentiates apoptosis induced by chemotherapeutic drugs in androgen-independent prostate cancer cells

PURPOSE

To test whether and how selenium enhances the apoptosis potency of selected chemotherapeutic drugs in prostate cancer (PCA) cells.

EXPERIMENTAL DESIGN

DU145 and PC3 human androgen-independent PCA cells were exposed to minimal apoptotic doses of selenium and/or the topoisomerase I inhibitor 7-ethyl-10-hydroxycamptothecin (SN38), the topoisomerase II inhibitor etoposide or the microtubule inhibitor paclitaxel/taxol. Apoptosis was measured by ELISA for histone-associated DNA fragments, by flow cytometric analysis of sub-G(1) fraction, and by immunoblot analysis of cleaved poly(ADP-ribose)polymerase. Pharmacologic inhibitors were used to manipulate caspases and c-Jun-NH(2)-terminal kinases (JNK).

RESULTS

The methylselenol precursor methylseleninic acid (MSeA) increased the apoptosis potency of SN38, etoposide, or paclitaxel by several folds higher than the expected sum of the apoptosis induced by MSeA and each drug alone. The combination treatment did not further enhance JNK1/2 phosphorylation that was induced by each drug in DU145 cells. The JNK inhibitor SP600125 substantially decreased the activation of caspases and apoptosis induced by MSeA combination with SN38 or etoposide and completely blocked these events induced by MSeA/paclitaxel. The caspase-8 inhibitor zIETDfmk completely abolished apoptosis and caspase-9 and caspase-3 cleavage, whereas the caspase-9 inhibitor zLEHDfmk significantly decreased caspase-3 cleavage and apoptosis but had no effect on caspase-8 cleavage. None of these caspase inhibitors abolished JNK1/2 phosphorylation. A JNK-independent suppression of survivin by SN38 and etoposide, but not by paclitaxel, was also observed. In contrast to MSeA, selenite did not show any enhancing effect on the apoptosis induced by these drugs.

CONCLUSIONS

MSeA enhanced apoptosis induced by cancer therapeutic drugs in androgen-independent PCA cells. In DU145 cells, the enhancing effect was primarily through interactions between MSeA and JNK-dependent targets to amplify the caspase-8-initiated activation cascades. The results suggest a novel use of methyl selenium for improving the chemotherapy of PCA.

Sensitization of Glioma Cells to Fas-Dependent Apoptosis by Chemotherapy-Induced Oxidative Stress

A prominent feature of glioblastoma is its resistance to death from Fas pathway activation. In this study, we explored the modulation of Fas-induced glioblastoma death with chemotherapeutic agents. Camptothecin significantly increased the glioblastoma cell death response to Fas receptor activation regardless of p53 status. Sublethal concentrations of camptothecin reduced the IC50 of agonistic anti-Fas antibody (CH-11) 10-fold, from 500 to 50 ng/mL, in human U87 glioblastoma cells (p53 wild-type). Cell viability in response to camptothecin, CH-11 alone, and the combination of camptothecin + CH-11 was found to be 84%, 85%, and 47% (P < 0.001), respectively. A similar pattern of relative cytotoxicity was found in U373 cells (p53 mutant). We further examined the pathways and mechanisms involved in this apparent synergistic cytotoxic response. Cell death was found to be predominantly apoptotic involving both extrinsic and intrinsic pathways as evidenced by annexin V staining, cleavage of caspases (3, 8, and 9), increased caspase activities, Smac release, and cytoprotection by caspase inhibitors. Expression of Fas-associated death domain, and not Fas, Fas ligand, or caspase proteins, increased following cell treatment with camptothecin + CH-11. Camptothecin treatment enhanced c-jun-NH2-kinase activation in response to CH-11, but inhibition of c-jun-NH2-kinase did not prevent cell death induced by the combination treatment. Reactive oxygen species, especially H2O2, were elevated following camptothecin treatment; and H2O2 enhanced cell death induced by CH-11. The antioxidants glutathione and N-acetyl-cysteine prevented cell death induced by camptothecin + CH-11. These findings show that camptothecin synergizes with Fas activation to induce glioblastoma apoptosis via a mechanism involving reactive oxygen species and oxidative stress pathways.

c-Jun N-terminal kinase (JNK) is required for survival and proliferation of B-lymphoma cells

Several primary murine and human B lymphomas and cell lines were found to constitutively express high levels of the activated form of c-jun N-terminal kinase (JNK), a member of the mitogen-activated protein (MAP) kinase family. Proliferation of murine B lymphomas CH31, CH12.Lx, BKS-2, and WEHI-231 and the human B lymphomas BJAB, RAMOS, RAJI, OCI-Ly7, and OCI-Ly10 was strongly inhibited by SP600125, an anthrapyrazolone inhibitor of JNK, in a dose-dependent manner. The lymphoma cells underwent apoptosis and arrested at the G2/M phase of cell cycle. Furthermore, JNK-specific small interfering RNA (siRNA) inhibited the growth of both murine and human B lymphomas. Thus in the B-lymphoma model, JNK appears to have a unique prosurvival role. Survival signals provided by CD40 and interleukin-10 (IL-10) together reversed the growth inhibition induced by the JNK inhibitor. c-Myc protein levels were reduced in the presence of both SP600125 and JNK-specific siRNA, and CD40 ligation restored c-Myc levels. Moreover, Bcl-xL rescued WEHI-231 cells from apoptosis induced by the JNK inhibitor. The JNK inhibitor also reduced levels of early growth response gene-1 (Egr-1) protein, and overexpressing Egr-1 partially rescued lymphoma cells from apoptosis. Thus, JNK may act via c-Myc and Egr-1, which were shown to be important for B-lymphoma survival and growth.

Post-irradiation hypoxic incubation of X-irradiated MOLT-4 cells reduces apoptotic cell death by changing the intracellular redox state and modulating SAPK/JNK pathways

To elucidate radiobiological effects of hypoxia on X-ray-induced apoptosis, MOLT-4 cells were treated under four set of conditions: (1) both X irradiation and incubation under normoxia, (2) X irradiation under hypoxia and subsequent incubation under normoxia, (3) X irradiation under normoxia and subsequent incubation under hypoxia, and (4) both X irradiation and incubation under hypoxia, and the induction of apoptosis was examined by fluorescence microscopy. About 28-33% apoptosis was observed in cells treated under conditions 1 and 2, but this value was significantly reduced to around 18-20% in cells treated under conditions 3 and 4, suggesting that post-irradiation hypoxic incubation rather than hypoxic irradiation mainly caused the reduction of apoptosis. The activation and expression of apoptosis signal-related molecules SAPK/JNK, Fas and caspase-3 were also suppressed by hypoxic incubation. Effects of hypoxic incubation were canceled when cells were treated under conditions 3 and 4 with an oxygen-mimicking hypoxic cell radiosensitizer, whereas the addition of N-acetyl-L-cysteine again reduced the induction of apoptosis. From these results it was concluded that hypoxia reduced the induction of apoptosis by changing the intracellular redox state, followed by the regulation of apoptotic signals in X-irradiated MOLT-4 cells.

Activation of the Fas-FasL Signaling Pathway by MDA-7/IL-24 Kills Human Ovarian Cancer Cells

The tumor-suppressive activity of melanoma differentiation-associated gene-7 (mda-7), also known as interleukin 24 (IL-24), has been shown in a spectrum of human cancer cells in vitro and in vivo. However, mechanisms responsible for antitumor activity of mda-7 in human ovarian cancer cells have not been identified. We investigated the therapeutic activity and underlying mechanisms of adenovirus-mediated mda-7 gene (Ad-mda7) transfer in human ovarian cancer cells. Ad-mda7 treatment resulted in overexpression of MDA-7/IL-24 protein in both ovarian cancer and normal ovarian epithelial cells. However, Ad-mda7 significantly (P = 0.001) inhibited cell proliferation and induced apoptosis only in tumor cells and not in normal cells. Studies addressing the mechanism of action of Ad-mda7-induced tumor cell apoptosis revealed early activation of the transcription factors c-Jun and activating transcription factor 2, which in turn stimulated the transcription of an immediate downstream target, the death-inducer Fas ligand (FasL), and its cognate receptor Fas. Associated with the activation of Fas-FasL was the activation of nuclear factor kappaB and induction of Fas-associated factor 1, Fas-associated death domain, and caspase-8. Promoter-based reporter gene analyses showed that Ad-mda7 specifically activated the Fas promoter. Inhibition of Fas using small interfering RNA resulted in a significant decrease in Ad-mda7-mediated tumor cell death. Additionally, blocking of FasL with NOK-1 antibody abrogated Ad-mda7-mediated apoptosis. Collectively, these results show that Ad-mda7-mediated killing of human ovarian cancer cells involves activation of the Fas-FasL signaling pathway, a heretofore unrecognized mediator of MDA-7 apoptosis induction.

Enhanced induction of apoptosis by combined treatment of human carcinoma cells with X rays and death receptor agonists

The death receptors Fas and DR5 are known to be expressed not only in immune cells but also in various tumor cells. The aim of the present study was to determine whether X irradiation enhanced induction of apoptosis in Tp53 wild type and Tp53-mutated tumor cell lines treated with agonists against these death receptors. We showed that 5 Gy of X irradiation significantly up-regulated the expression of death receptors Fas and DR5 on the plasma membrane in gastric cancer cell lines MKN45 and MKN28, lung cancer cell line A549, and prostate cancer cell line DU145, and that subsequent treatments with agonistic molecules for these death receptors, Fas antibody CH11 and TRAIL, increased the formation of active fragment p20 of caspase 3 followed by the induction of apoptosis. This death-receptor-mediated apoptosis was independent of Tp53 status since MKN28 and DU145 were Tp53-mutated. The post-irradiation treatment of the cells with N-acetyl-L-cysteine (NAC) abolished the up-regulation of the expression of Fas and DR5 on the plasma membrane. NAC also attenuated the increase in the formation of p20 and the induction of apoptosis by agonistic molecules. These results suggested that the increase in the induction of apoptosis by combined treatment with X irradiation and CH11 or TRAIL occurred through a change of the intracellular redox state independent of Tp53 status in human carcinoma cell lines.

Androgen and the blocking of radiation-induced sensitization to Fas-mediated apoptosis through c-jun induction in prostate cancer cells

PURPOSE

To clarify the key mechanism by which androgen makes prostate cancer cells highly resistant to Fas-mediated apoptosis.

MATERIALS AND METHODS

The role of c-jun induction by 10 nM dihydrotestosterone (DHT) in 5 Gy radiation-induced up-regulation of Fas and sensitization to the apoptosis was studied by using the human prostate cancer cell line LNCaP.

RESULTS

On exposure to 5 Gy radiation, LNCaP cells demonstrated high sensitization to Fas-mediated apoptosis through increased Fas expression, stabilized p53 expression and binding to p53 response elements within the promoter and first intronic region of the Fas gene. Following treatment with DHT, in vivo binding of p53 to its response elements was strongly inhibited. In addition, DHT significantly up-regulated c-jun expression through extracellular stress-regulated kinase (ERK) activation, and transfection of an antisense oligonucleotide for c-jun or ERK inhibition by PD98059 cancelled DHT-mediated suppression of radiation-induced transactivation of Fas gene and sensitization to Fas-mediated apoptosis.

CONCLUSIONS

Radiation-induced Fas sensitization in prostate cancer cell was mediated through p53-dependent transactivation of the Fas gene, which can be blocked by androgen stimulation mainly through induction of c-jun.

The molecular mechanism of sensitization to Fas-mediated apoptosis by 2-methoxyestradiol in PC3 prostate cancer cells

It is widely known that death receptor Fas-dependent apoptotic signals are associated with development of prostate cancer, but the key pathways involved in sensitivity to the apoptosis remain unclear. Here we investigated the molecular mechanism by which 2-methoxyestradiol (2-ME) effectively sensitizes a human prostate cancer cell line, PC3, to Fas-mediated apoptosis. 2-ME significantly inhibited nuclear factor-kappaB (NF-kappaB) activation and downregulated Fas-associated death domain (FADD) protein interluekin-1beta-converting enzyme inhibitory protein (FLIP). Overexpression of the dominant negative mutant form of IkappaBalpha (d/n IkappaBalpha) or treatment with Ikappa kinase-specific inhibitor Bay117082 gave the same results, although the sensitizing effect was not as pronounced. A selective inhibitor of Akt phosphorylation, LY294002, accelerated formation of the death-inducing signaling complex (DISC) not only by FLIP reduction but also by enhancement of recruitment of the FADD to Fas, thereby sensitizing PC3 cells to apoptosis similar to the case with 2-ME stimulation. Moreover, we found that inhibition of 2-ME-induced extracellular signal-regulated kinase (ERK) activation by the upstream kinase inhibitor PD98059 significantly enhanced 2-ME-mediated suppression of Akt activation, resulting in much greater sensitization to apoptosis. Taken together, the present findings indicate that 2-ME suppresses NF-kappaB/FLIP signaling and enhances DISC formation through inhibition of Akt, and that PC3 cells thereby are being sensitized to Fas-mediated apoptosis and by a process closely associated with ERK.