Sphingosine kinase (SphK) is overexpressed by a variety of cancers, and its phosphorylation of sphingosine results in accumulation of sphingosine-1-phosphate (S1P) and activation of anti-apoptotic signal transduction. Existing data indicate a role for S1P in viral pathogenesis, but roles for SphK and S1P in virus-associated cancer progression have not been defined. Rare pathologic variants of diffuse large B-cell lymphoma arise preferentially in the setting of HIV infection, including primary effusion lymphoma (PEL), a highly mortal tumor etiologically linked to the Kaposi’s sarcoma-associated herpesvirus (KSHV). We have found that ABC294640, a novel clinical-grade small molecule selectively targeting SphK (SphK2 >> SphK1), induces dose-dependent caspase cleavage and apoptosis for KSHV+ patient-derived PEL cells, in part though inhibition of constitutive signal transduction associated with PEL cell proliferation and survival. These results were validated with induction of PEL cell apoptosis using SphK2-specific siRNA, as well as confirmation of drug-induced SphK inhibition in PEL cells with dose-dependent accumulation of pro-apoptotic ceramides and reduction of intracellular S1P. Furthermore, we demonstrate that systemic administration of ABC294640 induces tumor regression in an established human PEL xenograft model. Complimentary ex vivo analyses revealed suppression of signal transduction and increased KSHV lytic gene expression within drug-treated tumors, with the latter validated in vitro through demonstration of dose-dependent viral lytic gene expression within PEL cells exposed to ABC294640. Collectively, these results implicate interrelated mechanisms and SphK2 inhibition in the induction of PEL cell death by ABC294640 and rationalize evaluation of ABC294640 in clinical trials for the treatment of KSHV-associated lymphoma.
KSHV; sphingosine kinase; S1P; lymphoma; HIV
Phosphorylation of sphingosine by sphingosine kinases (SphK1 and SphK2) generates sphingosine-1-phosphate (S1P), a bioactive sphingolipid which promotes cancer cell survival and tumor progression in vivo. We have recently reported that targeting SphK2 induces apoptosis for human primary effusion lymphoma (PEL) cell lines infected by the Kaposi’s sarcoma-associated herpesvirus (KSHV), and this occurs in part through inhibition of canonical NF-κB activation. In contrast, pharmacologic inhibition of SphK2 has minimal impact for uninfected B-cell lines or circulating human B cells from healthy donors. Therefore, we designed additional studies employing primary human endothelial cells to explore mechanisms responsible for the selective death observed for KSHV-infected cells during SphK2 targeting. Using RNA interference and a clinically relevant pharmacologic approach, we have found that targeting SphK2 induces apoptosis selectively for KSHV-infected endothelial cells through induction of viral lytic gene expression. Moreover, this effect occurs through repression of KSHV-microRNAs regulating viral latency and signal transduction, including miR-K12-1 which targets IκBα to facilitate activation of NF-κB, and ectopic expression of miR-K12-1 restores NF-κB activation and viability for KSHV-infected endothelial cells during SphK2 inhibition. These data illuminate a novel survival mechanism and potential therapeutic target for KSHV-infected endothelial cells: SphK2-associated maintenance of viral latency.
Mechanosensory hair cells are the receptor cells of hearing and balance. Hair cells
are sensitive to death from exposure to therapeutic drugs with ototoxic side effects,
including aminoglycoside antibiotics and cisplatin. We recently showed that the
induction of heat shock protein 70 (HSP70) inhibits ototoxic drug–induced
hair cell death. Here, we examined the mechanisms underlying the protective effect of
HSP70. In response to heat shock, HSP70 was induced in glia-like supporting cells but
not in hair cells. Adenovirus-mediated infection of supporting cells with
Hsp70 inhibited hair cell death. Coculture with heat-shocked
utricles protected nonheat-shocked utricles against hair cell death. When
heat-shocked utricles from Hsp70–/– mice
were used in cocultures, protection was abolished in both the heat-shocked utricles
and the nonheat-shocked utricles. HSP70 was detected by ELISA in the media
surrounding heat-shocked utricles, and depletion of HSP70 from the media abolished
the protective effect of heat shock, suggesting that HSP70 is secreted by supporting
cells. Together our data indicate that supporting cells mediate the protective effect
of HSP70 against hair cell death, and they suggest a major role for supporting cells
in determining the fate of hair cells exposed to stress.
Persistence of effector cytotoxic T lymphocytes (CTLs) during an immunological response is critical for successfully controlling a viral infection or tumor growth. Various cytokines are known to play an important part in regulating the immune response. The IL-2 family of cytokines that includes IL-2 and IL-15 are known to function as growth and survival factors for antigen-experienced T cells. IL-2 and IL-15 possess similar properties, including the ability to induce T cell proliferation. Whereas long term IL-2 exposure has been shown to promote apoptosis and limit CD8+ memory T cell survival and proliferation, it is widely believed that IL-15 can inhibit apoptosis and helps maintain a memory CD8+ T-cell population. However, mechanisms for superior outcomes for IL-15 as compared to IL-2 are still under investigation. Our data shows that human T cells cultured in the presence of IL-15 exhibit increased expression of anti-oxidant molecules Glutathione reductase (GSR), Thioredoxin reductase 1 (TXNDR1), Peroxiredoxin (PRDX), Superoxide dismutase (SOD). An increased expression of cell-surface thiols, intracellular glutathione, and thioredoxins was also noted in IL-15 cultured T cells. Additionally, IL-15 cultured T cells also showed an increase in cytolytic effector molecules. Apart from increased level of Granzyme A and Granzyme B, IL-15 cultured T cells exhibit increased accumulation of reactive oxygen (ROS) and reactive nitrogen (RNS) species as compared to IL-2 cultured T cells. Overall, this study suggests that T cells cultured in IL-15 show increase persistence not only due to increased anti-apoptotic proteins but also due to increased anti-oxidant levels, which is further complimented by increased cytolytic effector functions.
Cytokine; thiols; apoptosis
Adenoviral gene therapy using the death receptor ligand TRAIL as the therapeutic transgene can be safely administered via intraprostatic injection but has not been evaluated for efficacy in patients. Here we investigated the efficacy of adenoviral TRAIL gene therapy in a model of castration resistant prostate cancer and found that intratumoral injections can significantly delay tumor growth but cannot eliminate established lesions. We hypothesized that an underlying cause is inefficient adenoviral delivery. Using the LNCaP progression model of prostate cancer we show that surface CAR expression decreases with increasing tumorigenicity and that castration resistant C4-2b cells were more difficult to transduce with adenovirus than castration sensitive LNCaP cells. Many genes, including CAR, are epigenetically silenced during transformation but a new class of chemotherapeutic agents, known as histone deacetylase inhibitors (HDACi), can reverse this process. We demonstrate that HDACi restore CAR expression and infectivity in C4-2b cells and enhance caspase activation in response to infection with a TRAIL adenovirus. We also show that in cells with high surface CAR expression, HDACi further enhance transgene expression from the CMV promoter. Thus HDACi have multiple beneficial effects, which may enhance not only viral but also non-viral gene therapy of castration resistant prostate cancer.
The targeted therapeutics sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and this drug combination is entering phase I evaluation. In this study we determined how CD95 is activated by treatment with this drug combination. Low doses of sorafenib and vorinostat but not the individual drugs rapidly increased ROS, Ca2+ and ceramide levels in GI tumor cells. The production of ROS was reduced in Rho zero cells. Quenching ROS blocked drug-induced CD95 surface localization and apoptosis. ROS generation, CD95 activation and cell killing was also blocked by quenching of induced Ca2+ levels or by inhibition of PP2A. Inhibition of acidic sphingomyelinase or de novo ceramide generation blocked the induction of ROS however combined inhibition of both acidic sphingomyelinase and de novo ceramide generation was required to block the induction of Ca2+. Quenching of ROS did not impact on drug-induced ceramide/dihydro-ceramide levels whereas quenching of Ca2+ reduced the ceramide increase. Sorafenib and vorinostat treatment radiosensitized liver and pancreatic cancer cells, an effect that was suppressed by quenching ROS or knock down of LASS6. Further, sorafenib and vorinostat treatment suppressed the growth of pancreatic tumors in vivo. Our findings demonstrate that induction of cytosolic Ca2+ by sorafenib and vorinostat is a primary event that elevates dihydroceramide levels, each essential steps in ROS generation that promotes CD95 activation.
Sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and the present studies have determined individually how sorafenib and vorinostat contribute to CD95 activation. Sorafenib (3-6 μM) promoted a dose-dependent increase in Src Y416, ERBB1 Y845 and CD95 Y232/Y291 phosphorylation, and Src Y527 dephosphorylation. Low levels of sorafenib (3 μM) –induced CD95 tyrosine phosphorylation did not promote surface localization whereas sorafenib (6 μM), or sorafenib (3 μM) and vorinostat (500 nM) treatment promoted higher levels of CD95 phosphorylation that correlated with DISC formation, receptor surface localization and autophagy. CD95 (Y232F, Y291F) was not tyrosine phosphorylated and was unable to plasma membrane localize or induce autophagy. Knock down / knock out of Src family kinases abolished sorafenib –induced: CD95 tyrosine phosphorylation; DISC formation; and the induction of cell death and autophagy. Knock down of PDGFRβ enhanced Src Y416 and CD95 tyrosine phosphorylation that correlated with elevated CD95 plasma membrane levels and autophagy, and with a reduced ability of sorafenib to promote CD95 membrane localization. Vorinostat increased ROS levels; and in a delayed NFκB-dependent fashion, those of FAS ligand and CD95. Neutralization of FAS-L did not alter the initial rapid drug-induced activation of CD95 however, neutralization of FAS-L reduced sorafenib + vorinostat toxicity by ~50%. Thus sorafenib contributes to CD95 activation by promoting receptor tyrosine phosphorylation whereas vorinostat contributes to CD95 activation via initial facilitation of ROS generation and subsequently of FAS-L expression.
Vorinostat; Sorafenib; CD95; c-FLIP-s; FAS-L; cell death; autophagy
Bladder cancer, the 5th most common malignancy in the USA, is often detected as a result of incidental findings or by presenting hematuria. Once diagnosed the disease is one of the costliest cancers to treat due to frequent, invasive and often lifelong follow-up procedures. Because cells are shed into urine, there has been an emerging effort to develop non-invasive tests for the detection of bladder cancer. Expression of survivin, a member of the inhibitor of apoptosis protein family, has been associated with bladder cancer. Therefore, the goal of this study was to determine the feasibility of transducing viable exfoliated cells obtained from urine with an adenoviral vector in which a reporter gene is under the control of the survivin promoter.
Exfoliated cells from urine were obtained from 36 human subjects (> 40 years old). An adenovirus in which GFP expression is under control of the survivin promoter (Ad.Surv.GFP) was generated. An adenovirus in which GFP is expressed from the CMV promoter served as a control. GFP expression was analyzed by fluorescent microscopy and quantified by flow cytometry.
Short-term cultures from exfoliated cells in urine could be established in 16 of 31 samples. These cultures were successfully transduced with Ad.CMV.GFP. Analysis of GFP expression following transduction with Ad.Surv.GFP, indicated that the survivin promoter was preferentially active in UM-UC-3 bladder cancer cells compared to non-malignant UROtsa cells. Interestingly, baseline levels of GFP expression in cultures from exfoliated cells in urine exhibited higher baseline levels than UROtsa following transduction with Ad.Surv.GFP.
We demonstrated the feasibility of establishing and analysing short-term cultures isolated from exfoliated cells in voided urine by means of adenoviral transduction, thereby forming the foundation for future studies to determine the specificity and sensitivity of a non-invasive test based on survivin promoter activity.
The present studies determined in greater detail the molecular mechanisms upstream of the CD95 death receptor by which geldanamycin HSP90 inhibitors and MEK1/2 inhibitors interact to kill carcinoma cells. MEK1/2 inhibition enhanced 17AAG toxicity that was suppressed in cells deleted for mutant active RAS which were non-tumorigenic but was magnified in isogenic tumorigenic cells expressing H-RAS V12 or K-RAS D13. MEK1/2 inhibitor and 17AAG treatment increased intracellular Ca2+ levels and reduced GRP78/BiP expression in a Ca2+ -dependent manner. GRP78/BiP over-expression, however, also suppressed drug-induced intracellular Ca2+ levels. MEK1/2 inhibitor and 17AAG treatment increased ROS levels that were blocked by quenching Ca2+ or over-expression of GRP78/BiP. MEK1/2 inhibitor and 17AAG treatment activated CD95 and inhibition of ceramide synthesis; ROS or Ca2+ quenching blocked CD95 activation. In SW620 cells that are patient matched to SW480 cells, MEK1/2 inhibitor and 17AAG toxicity was significantly reduced that correlated with a lack of CD95 activation and lower expression of ceramide synthase 6 (LASS6). Over-expression of LASS6 in SW620 cells enhanced drug-induced CD95 activation and enhanced tumor cell killing. Inhibition of ceramide signaling abolished drug-induced ROS generation but not drug-induced cytosolic Ca2+ levels. Thus treatment of tumor cells with MEK1/2 inhibitor and 17AAG induces cytosolic Ca2+ and loss of GRP78/BiP function, leading to de novo ceramide synthesis pathway activation that plays a key role in ROS generation and CD95 activation.
Geldanamycin; 17AAG; MEK1/2 inhibitor; CD95; c-FLIP-s; GRP78/BiP; autophagy; cell death; ASMase; de novo
Cell cycling and protein synthesis are both key physiological tasks for cancer cells. Here we present a model for how the elongation phase of protein synthesis, governed by elongation factor 2 and elongation factor 2 kinase, both modulates and responds to cell cycling. Within this framework we also discuss survivin, a protein with both pro-mitotic and anti-apoptotic roles whose persistence in the cell is tied to protein synthesis due to its short half-life. Finally, we provide a brief overview of efforts of cancer researchers to target EF2 and EF2 kinase.
cell cycle; elongation factor 2; elongation factor 2 kinase; apoptosis; cancer
Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) is a novel cytokine displaying selective apoptosis-inducing activity in transformed cells without harming normal cells. The present studies focused on clarifying the mechanism(s) by which glutathione S-transferase (GST)-MDA-7 altered cell survival of human renal carcinoma cells in vitro. GST-MDA-7 caused plasma membrane clustering of CD95 and the association of CD95 with procaspase-8. GST-MDA-7 lethality was suppressed by inhibition of caspase-8 or by overexpression of short-form cellular FLICE inhibitory protein, but only weakly by inhibition of cathepsin proteases. GST-MDA-7–induced CD95 clustering (and apoptosis) was blocked by knockdown of acidic sphingomyelinase or, to a greater extent, ceramide synthase-6 expression. GST-MDA-7 killing was, in parallel, dependent on inactivation of extracellular signal–regulated kinase 1/2 and on CD95-induced p38 mitogen-activated protein kinase and c-jun NH2-terminal kinase-1/2 signaling. Knockdown of CD95 expression abolished GST-MDA-7–induced phosphorylation of protein kinase R–like endoplasmic reticulum kinase. GST-MDA-7 lethality was suppressed by knockout or expression of a dominant negative protein kinase R–like endoplasmic reticulum kinase that correlated with reduced c-jun NH2-terminal kinase-1/2 and p38 mitogen-activated protein kinase signaling and maintained extracellular signal–regulated kinase-1/2 phosphorylation. GST-MDA-7 caused vacuolization of LC3 through a mechanism that was largely CD95 dependent and whose formation was suppressed by knockdown of ATG5 expression. Knockdown of ATG5 suppressed GST-MDA-7 toxicity. Our data show that in kidney cancer cells GST-MDA-7 induces ceramide-dependent activation of CD95, which is causal in promoting an endoplasmic reticulum stress response that activates multiple proapoptotic pathways to decrease survival.
The application of adenoviral gene therapy for cancer is limited by immune clearance of the virus as well as poor transduction efficiency, since the protein used for viral entry (CAR) serves physiological functions in adhesion and is frequently decreased among cancer cells. Cationic polymers have been used to enhance adenoviral gene delivery but novel polymers with low toxicity are needed to realize this approach. We recently identified polymers that were characterized by high transfection efficiency of plasmid DNA and a low toxicity profile. In this study we evaluated the novel cationic polymer EGDE-3,3′ for its potential to increase adenoviral transduction of the CAR-negative bladder cancer cell line TCCSUP. The amount of adenovirus required to transduce 50-60% of the cells was reduced 100-fold when Ad.GFP was pre-incubated with the EGDE-3,3′ polymer. Polyethyleneimine (pEI), a positively charged polymer currently used as a standard for enhancing adenoviral transduction, also increased infectivity, but transgene expression was consistently higher with EGDE-3,3′. In addition, EGDE-3,3′-supplemented transduction of an adenovirus expressing an apoptosis inducing transgene, Ad.GFP-TRAIL, significantly enhanced the amount of cell death. Thus, our results indicate that novel biocompatible polymers may be useful in improving the delivery of adenoviral gene therapy.
Polymer; adenovirus; gene therapy; cancer; bladder cancer
Cytolytic T lymphocytes (CTL) undergo massive expansion upon appropriate antigenic stimulation. Homeostasis is maintained by a subsequent “contraction” of these cells. Activation-induced cell death (AICD) and programmed cell death, prevent the untoward side effects arising from excessive numbers and prolonged persistence of activated CTL that occur upon uncontrolled and/or continued expansion. However, effector cell persistence has been identified as a hallmark of successful T cell-mediated adoptive immunotherapy. Thus, prevention of AICD may be critical to achieve more successful clinical results. We have previously shown that treatment with c-jun N-terminal kinase (JNK)-inhibitor, SP600125, protects human melanoma epitope Mart-127-35 reactive CTL from apoptotic death upon their re-encounter with cognate antigen. However, inhibition of JNK also interferes with the functional capability of the CTL to secrete interferon (IFN)-γ. Here, we show that reactive oxygen species (ROS) inhibitors such as the superoxide dismutase mimetic, Mn (III) tetrakis (5, 10, 15, 20-benzoic acid) porphyrin (MnTBAP), efficiently protected Mart-127-35 reactive primary CTL from AICD without impairing their functional capability. MnTBAP prevented the increase in intracellular ROS, mitochondrial membrane collapse, and DNA fragmentation observed in control treated cells upon cognate antigen encounter. Furthermore, the mechanism of AICD prevention in primary CTL included blockade of JNK activation. Finally, tumor reactive in vitro expanded tumor infiltrating lymphocytes, which are used clinically in cancer immunotherapy, also benefit from MnTBAP mediated antioxidant treatment. Thus, modulation of the redox pathway might improve CTL persistence and lead to better clinical results for T cell-based immunotherapies.
AICD; CTL; Oxidative stress; ROS; JNK
Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) is a cytokine with roles in tumor surveillance and tolerance. TRAIL selectively induces apoptosis in many malignant but not normal cells but the underlying cause for spontaneous TRAIL sensitivity remains elusive. We propose a novel hypothesis that links TRAIL sensitivity to translational arrest following stresses that inactivate eukaryotic elongation factor 2 (EF2). Affected cells experience a reduction in apoptotic threshold because, due to their short half-lives, levels of anti-apoptotic proteins quickly drop off once translation elongation is inhibited leaving pro-apoptotic proteins unchallenged. This change in protein profile renders affected cells sensitive to TRAIL-mediated apoptosis and places EF2 into the role of a sensor for cellular damage.
Apoptosis; Tumor necrosis factor related apoptosis; inducing ligand (TRAIL); Eukaryotic elongation factor 2 (EF2); Free radicals; Cancer
We have previously shown that doxorubicin sensitizes prostate cancer cells to TNF-Related Apoptosis Inducing Ligand (TRAIL). Sensitization correlated with decreased expression of the anti-apoptotic protein cFLIPS. The decrease in cFLIPS could not be explained by transcriptional regulation or increased degradation, leading us to focus on translational mechanisms. In this study, we found that doxorubicin caused strong and sustained phosphorylation of elongation factor 2 (EF-2), which interferes with protein elongation. Phosphorylation of EF-2 appeared to occur in a kinase-independent manner. Treatment with hydrogen peroxide recapitulated the events observed after doxorubicin treatment. In addition, cells treated with hydrogen peroxide expressed less XIAP and survivin which, like cFLIPS, are short half-life proteins with an anti-apoptotic function while expression levels of DR5, caspases-8, -9, -3, and Bax are maintained. The doxorubicin-mediated decrease in cFLIPS and XIAP as well as TRAIL-induced apoptosis was prevented by pretreatment with an iron chelator, indicating that expression of these proteins was affected by free radical generation upon interaction of iron with doxorubicin. In conclusion, our data suggest that free radicals can affect the phosphorylation of EF-2 resulting in a net loss of short half-life proteins such as cFLIPS and XIAP, leaving a cell more vulnerable to apoptotic stimuli.
apoptosis; doxorubicin; hydrogen peroxide; translation; c-FLIP (cellular FLICE inhibitory protein); elongation factor 2; cancer
Prostate cancer is a significant health problem among American men. Treatment strategies for androgen-independent cancer are currently not available. Tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) is a death receptor ligand that can induce apoptosis in a variety of cancer cell lines, including androgen-independent PC3 prostate carcinoma cells. In vitro, TRAIL-mediated apoptosis of prostate cancer cell lines can be enhanced by doxorubicin and correlates with the downregulation of the anti-apoptotic protein c-FLIP. This study evaluated the effects of doxorubicin on c-FLIP expression and tumor growth in combination with Apo2L/TRAIL in a xenograft model.
In vitro cytotoxic effects of TRAIL were measured using a MTS-based viability assay. For in vivo studies, PC3 prostate carcinoma cells were grown subcutaneously in athymic nude mice and tumor growth was measured following treatment with doxorubicin and/or Apo2L/TRAIL. c-FLIP expression was determined by western blot analysis. Apoptosis in xenografts was detected using TUNEL. Statistical analysis was performed using the student t-test.
In vitro experiments show that PC3 cells are partially susceptible to Apo2L/TRAIL and that susceptibility is enhanced by doxorubicin. In mice, doxorubicin did not significantly affect the growth of PC3 xenografts but reduced c-FLIP expression in tumors. Expression of c-FLIP in mouse heart was decreased only at the high doxorubicin concentration (8 mg/kg). Combination of doxorubicin with Apo2L/TRAIL resulted in more apoptotic cell death and tumor growth inhibition than Apo2L/TRAIL alone.
Combination of doxorubicin and Apo2L/TRAIL is more effective in growth inhibition of PC3 xenografts in vivo than either agent alone and could present a novel treatment strategy against hormone-refractory prostate cancer. The intracellular mechanism by which doxorubicin enhances the effect of Apo2L/TRAIL on PC3 xenografts may be by reducing expression of c-FLIP.