FLICE-inhibitory Protein Expression Research Articles

The Antigastric Cancer Effect of Triptolide is Associated With H19/NF-κB/FLIP Axis.

Background and Objective: Triptolide (TP), one of the fat-soluble components extracted from the Chinese medicinal herb Tripterygium wilfordii Hook F. (TWHF), possesses strong antitumor bioactivities, but its dose-dependent side effects restrict its wide application. This study was designed to investigate whether inflammatory factors increased the antitumor effects of the nontoxic dose of TP on gastric cancer cells and tried to explore the possible molecular mechanisms. Method: AGS and MKN45 cells were treated with different doses of TP and TNF-α. Cell viability and apoptosis were detected in vitro. In addition, NF-κB mediated prosurvival signals and cytoprotective proteins, especially FLICE-inhibitory protein (FLIP), were detected to determine their effects on TP/TNF-α–induced apoptosis. Moreover, the function of lncRNA H19/miR-204-5p/NF-κB/FLIP axis was investigated in vitro, and the antigastric cancer effect of TP plus TNF-α was proved in the mice xenograft model. Result: In vitro experimental results showed that TP pretreatment promoted apoptosis in AGS and MKN45 cells upon TNF-α exposure. TP/TNF-α–mediated apoptosis was partly mediated by the inhibitory effect of NF-κB–mediated FLIP expression. Oncogene H19 lying in the upstream pathway of NF-κB played a vital role upon TNF-α exposure, and bioinformatics analysis proved that H19 participated in TP/TNF-α–induced apoptosis via binding of miR-204-5p. Lastly, a low dose of TP and TNF-α inhibited the tumor weight and tumor volume of AGS and MKN45 cells in vivo. Conclusion: TP pretreatment increased apoptosis in TNF-α–stimulated gastric cancer cells, which are dependent on the disruption of the H19/miR-204-5p/NF-κB/FLIP axis. Cotreatment of TP and TNF-α is a better option for enhancing the anticancer effect and lowering the side effect of TP.

Glutamine metabolism regulates FLIP expression and sensitivity to TRAIL in triple-negative breast cancer cells

Glutamine plays an important role in the metabolism of tumor cells through its contribution to redox homeostasis, bioenergetics, synthesis of macromolecules, and signaling. Triple-negative breast cancers (TNBC) are highly metastatic and associated with poor prognosis. TNBC cells show a marked dependence on extracellular glutamine for growth. Herein we demonstrate that TNBC cells are markedly sensitized to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis upon glutamine deprivation. Upregulation of pro-apoptotic TRAIL receptor 2 (TRAIL-R2/DR5) and downregulation of FLICE-inhibitory protein (FLIP) are observed in glutamine-deprived TNBC cells. Activation of the amino-acid-sensing kinase general control nonderepressible 2 (GCN2) upon glutamine deprivation is responsible for TRAIL-R2 upregulation through a signaling pathway involving ATF4 and CHOP transcription factors. In contrast, FLIP downregulation in glutamine-deprived TNBC occurs by a GCN2-independent mechanism. Importantly, silencing FLIP expression by RNA interference results in a marked sensitization of TNBC cells to TRAIL-induced apoptosis. In addition, pharmacological or genetic inhibition of transaminases increases TRAIL-R2 expression and downregulates FLIP levels, sensitizing TNBC cells to TRAIL. Interestingly, treatment with l-asparaginase markedly sensitizes TNBC cells to TRAIL through its glutaminase activity. Overall, our findings suggest that targeting the glutamine addiction phenotype of TNBC can be regarded as a potential antitumoral target in combination with agonists of proapoptotic TRAIL receptors.

Involvement of both caspase-8 and Noxa-activated pathways in endoplasmic reticulum stress-induced apoptosis in triple-negative breast tumor cells

Recent evidences indicate that triple-negative breast cancer (TNBC) cells with a mesenchymal phenotype show a basal activation of the unfolded protein response (UPR) that increases their sensitivity to endoplasmic reticulum (ER) stress although the underlying cell death mechanism remains largely unexplored. Here we show that both caspase-8-dependent and -independent apoptotic mechanisms are activated in TNBC cells undergoing sustained ER stress. Activation of the extrinsic apoptotic pathway by ER stress involves ATF4-dependent upregulation of tumor necrosis factor-related apoptosis-inducing ligand receptor 2 (TRAIL-R2/DR5). In addition, accumulation of BH3-only protein Noxa at the mitochondria further contributes to apoptosis following ER stress in TNBC cells. Accordingly, simultaneous abrogation of both extrinsic and intrinsic apoptotic pathways is required to inhibit ER stress-induced apoptosis in these cells. Importantly, persistent FLICE-inhibitory protein (FLIP) expression plays an adaptive role to prevent early activation of the extrinsic pathway of apoptosis upon ER stress. Overall, our data show that ER stress induces cell death through a pleiotropic mechanism in TNBC cells and suggest that targeting FLIP expression may be an effective approach to sensitize these tumor cells to ER stress-inducing agents.

Depletion of myeloid cells exacerbates hepatitis and induces an aberrant increase in histone H3 in mouse serum.

These findings indicate an unexpected role of myeloid cells in decreasing serum IL-6, TNFα, and histone H3 levels via the suppression of TNFα-induced hepatocyte apoptosis. (Hepatology 2017;65:237-252).

Both intrinsic and extrinsic apoptotic pathways are involved in Toll-like receptor 4 (TLR4)-induced cell death in monocytic THP-1 cells

Our previous study showed that TLR3 induces apoptosis via both death receptors and mitochondial in human endothelial cells. We report here that the activation of TLR4 induced dose- and time-dependent cell death in moncytic THP-1 cells. LPS treatment of THP-1 cells induced the activation of both caspase 8 and 9, suggesting the involvement of intrinsic and extrinsic apoptosis pathways. TNFα was induced by TLR4 activation at both mRNA and protein levels, but its neutralization did not down-regulated TLR4-induced cell death. TLR4 activation also induced the up-regulation of TRAIL and its receptors DR4 and DR5, and the neutralization of TRAIL ameliorated TLR4 induced apoptosis, suggesting the involvement of TRAIL and its receptors DR4 and DR5 in LPS-induced cell death. Meanwhile, LPS treatment down-regulated the expression of FLICE inhibitory protein (FLIP), a suppressor of death receptor-induced cell death. In addition, TLR4 activation down-regulated the anti-apoptotic protein bcl-2, and up-regulated the pro-apoptotic proteins Noxa and Puma, suggesting that mitochondrial apoptotic pathway was also involved in LPS-induced cell death. Furthermore, we found that TAP63α might confer to the activation of intrinsic and extrinsic apoptotic pathways. The treatment of THP-1 cells with LPS induced the translocation of TAP63α from cytoplasm to nucleus. Taken together, our study suggested that both death receptors and mitochondial were involved in TLR4-induced cell death, and TAP63α may be a target for the prevention of LPS-induced cell death.

Abstract C1: Harnessing the pro-inflammatory tumor microenvironment of castrate-resistant prostate cancer to promote apoptosis

Abstract Introduction Castrate-Resistant Prostate Cancer (CRPC) represents a highly aggressive, currently incurable disease state. Overexpression of anti-apoptotic proteins including FLIP (FLICE-inhibitory protein) and inhibitors of apoptosis proteins (cIAP-1, cIAP-2 and XIAP) in prostate cancer have been associated with progression to castrate-resistant disease. These proteins are known to contribute to resistance to standard-of-care therapies and aid cancer progression through their anti-apoptotic activity. SMAC mimetics are small molecule compounds which mimic the activity of the endogenous inhibitor of IAPs known as SMAC (Second Mitochondrial-derived Activator of Caspase). SMAC mimetic activity is dependent on TNFα signalling and has also been shown to induce apoptosis in response to TRAIL therapy. Both TRAIL and TNFα are derived from immune cells that are frequently present in the tumour microenvironment, making SMAC mimetic therapy an attractive strategy for treating cancers associated with pro-inflammatory immune infiltrates. Methods A panel of prostate cancer cell lines were treated with SMAC mimetic alone, or in combination with exogenous TNFα or TRAIL. Cell viability was determined by MTT assay, and apoptosis was assessed using Western blotting and AnnexinV/PI flow cytometry. siRNA and Histone Deacetylase Inhbitor (HDACi) therapy were employed to reduce FLIP expression. The addition of exogenous TNFα, TRAIL or macrophage-conditioned media was used to model the pro-inflammatory microenvironment. Results Prostate cancer cells were found to be resistant to SMAC mimetic therapy alone and in the presence of TNFα or TRAIL. FLIP expression was found to be a resistance mechanism to SMAC-mimetic treatment. Depletion of FLIP expression by siRNA or HDACi therapy resulted in an increased sensitivity to TNFα, TRAIL and macrophage conditioned media alone and in combination with SMAC mimetics. Targeting FLIP alone may therefore be a more effective means of harnessing the pro-inflammatory microenvironment. Moreover, the apoptosis induced in the presence of macrophage conditioned media by SMAC mimetics in FLIP-depleted cells was demonstrated to be TNFα-dependent using TNFα neutralising antibodies. Conclusion Prostate cancer cell lines are inherently resistant to SMAC mimetic therapy even in the presence of TNFα or TRAIL. However, dual targeting of FLIP and IAPs sensitises CRPC cell lines to microenvironment-derived TNFα. Combined targeting of IAPs and FLIP, or single targeting of FLIP, may be an effective means of treating pro-inflammatory prostate cancer. Citation Format: Christopher McCann, Nyree Crawford, David Waugh, Daniel Longley. Harnessing the pro-inflammatory tumor microenvironment of castrate-resistant prostate cancer to promote apoptosis. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C1.

Iron supplementation effectively suppresses gastrocnemius muscle lesions to improve exercise capacity in chronic heart failure rats with anemia

ObjectiveFor patients with chronic heart failure (CHF), exertional fatigue is one of the most common and debilitating symptoms. However, the poor relationship between heart dysfunction and exercise capacity has been ascribed to peripheral abnormalities. Several previous studies confirmed that iron supplementation could significantly improve the exercise capacity of patients with CHF, although they did not analyze effects in the musculoskeletal system. The aim of this study was to investigate the effect of iron treatment on gastrocnemius muscles of CHF rats with anemia. MethodsMale Sprague-Dawley rats were subjected to coronary ligation to induce heart failure. At the same time, blood (1–1.5 mL) was withdrawn from the retro-orbital plexus once every week to induce anemia. After 6 wk of this process, iron dextran was administered to the CHF rats with anemia (CHFa rats) at the dose of 8, 16, 32, or 64 mg/kg every 2 d for 2 wk. ResultsIron dextran (8 mg/kg every 2 d) effectively improved hemodynamic parameters (P < 0.05) compared with CHFa rats. Similarly, this dose of iron dextran significantly reduced the ratio of heart weight to body weight (P < 0.01), whereas it significantly increased the distance run (m) to exhaustion (P < 0.01). Iron dextran effectively inhibited sarcoplasmic vacuolation and muscle atrophy of gastrocnemius muscles in CHFa rats, as evaluated by pathologic examinations. Other iron treatments, however, were found to be ineffective on the same parameters, so particular focus was placed on the iron dextran (8 mg/kg every 2 d) group in subsequent analyses. Consistently, phospho-p38 in gastrocnemius muscles of CHFa rats was markedly suppressed by iron dextran. Additionally, iron dextran significantly decreased c-fos and c-jun and up-regulated cellular FLICE-inhibitory protein expression levels.

CCT327 enhances TRAIL-induced apoptosis through the induction of death receptors and downregulation of cell survival proteins in TRAIL-resistant human leukemia cells.

Tumor necrosis factor-related apoptosis‑inducing ligand (TRAIL) has potential application in cancer therapy and it has the ability to selectively kill cancer cells without affecting normal cells. However, the development of resistance to TRAIL in cancer cells cannot be avoided. This study investigated the effects of 2-(5-methylselenophen‑2‑yl)‑6,7‑methylenedioxyquinolin‑4-one (CCT327), an analogue of quinolin-4-one, on the sensitization of cancer cells to TRAIL and on TRAIL‑induced apoptosis in TRAIL‑resistance human leukemia cells (HL60‑TR). We found that CCT327 enhanced TRAIL‑induced apoptosis through upregulation of death receptors DR4 and DR5. In addition to upregulating DRs (death receptors), CCT327 suppressed the expression of decoy receptor DcR1 and DcR2. CCT327 significantly downregulated the expression of FLICE inhibitory protein (cFLIP) and other antiapoptotic proteins. We also demonstrated that CCT327 could activate p38 and JNK. Moreover, CCT327-induced induction of DR5 and DR4 was mediated by reactive oxygen species (ROS), and N-acetylcysteine (NAC) blocked the induction of DRs by CCT327. Taken together, these results showed that CCT327 combined with TRAIL treatment may provide an effective therapeutic strategy for cancer.

S-nitrosylation of FLICE inhibitory protein determines its interaction with RIP1 and activation of NF-κB

Death receptor (DR) ligation can lead to divergent signaling pathways causing either caspase-mediated cell death or cell proliferation and inflammation. These variations in cellular fate are determined by adaptor proteins that are recruited to the DR signaling complex. FLICE inhibitory protein (FLIP) is an established inhibitor of caspase-8-mediated apoptosis, and it is also involved in NF-κB activation. However, the molecular mechanism that regulates FLIP within this complex is unknown. In this study, we provide new evidence for the regulation of NF-κB by FLIP through S-nitrosylation, which involves covalent modification of the protein’s cysteine thiol by nitric oxide to form S-nitrosothiol. Point mutations of FLIP at cysteine residues 254 and 259 prevent FLIP S-nitrosylation and its ability to activate NF-κB. The mechanism by which FLIP nitrosylation regulates NF-κB activity involves RIP1 binding and redistribution, whereas TRAF2 binding and distribution are unaffected. We further show that FLIP processing and cleavage is dependent on its nitrosylation status. Collectively, our study reveals a novel pathway for FLIP regulation of NF-κB through protein S-nitrosylation, which is a key posttranslational mechanism controlling DR-mediated cell death and survival. Since increased expression of FLIP and nitric oxide are frequently observed in chemotherapy-resistant tumors, S-nitrosylation of FLIP could be a key mechanism of chemoresistance and tumor growth.

Absence of FLICE-Inhibitory Protein Is a Novel Independent Prognostic Marker for Very Short Survival in Pancreatic Ductal Adenocarcinoma

Evading apoptosis is a hallmark of pancreatic cancer. In pancreatic cancer models, chemotherapy down-regulates the antiapoptotic protein cellular FLICE inhibitory protein (c-FLIP), which renders cells sensitive to apoptosis. Currently, the relevance of c-FLIP expression as a biomarker in pancreatic cancer is unknown, and here we assessed the prognostic significance of the c-FLIP expression status in a large cohort of pancreatic cancer patients with clinical follow-up. Cellular FLICE inhibitory protein expression levels were determined by immunohistochemistry in 120 surgically resected ductal pancreatic adenocarcinomas. Survival analysis by c-FLIP status was compared with established clinicopathologic biomarkers as well as Ki-67 and cyclooxygenase 2 expression levels as 2 other established independent prognostic biomarkers in pancreatic cancer. Of 120 tumors, 111 (91%) were c-FLIP positive, whereas 9 (9%) were completely c-FLIP negative. Cyclooxygenase 2 was positive in 59 cases (52%), and Ki-67 was positive in more than 10% of tumor cells in 51 cases (44%). Univariate and multivariate survival analysis (correcting for stage, grade, and proliferation index) showed that c-FLIP is an independent prognostic factor. Specifically, c-FLIP negativity identifies 9% of patients with a highly aggressive disease course (P = 0.0001). Cellular FLICE inhibitory protein expression status is a valuable prognostic biomarker in pancreatic cancer.

AXL Mediates TRAIL Resistance in Esophageal Adenocarcinoma

The overexpression of AXL receptor tyrosine kinase is a frequent finding that has been associated with poor prognosis in esophageal adenocarcinoma (EAC). As the majority of EAC are intrinsically resistant to DNA-damaging therapies, an alternative therapeutic approach based on the activation of death receptors may be warranted. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been evaluated in clinical trials and found promising as anticancer agent with mild side effects; unfortunately, resistance to TRAIL remains a major clinical problem. Herein, we explored the role of AXL in TRAIL resistance and elucidated the underlying mechanism. Overexpression of AXL in OE33 and OE19 cells promoted cell survival and attenuated TRAIL-induced cellular and molecular markers of apoptosis. In contrast, knockdown of endogenous AXL sensitized FLO-1 cells to TRAIL. The mechanism by which AXL regulates TRAIL resistance was examined. Protein and mRNA expression of DR4 and DR5 death receptors was not downregulated by AXL. In addition, the possible involvement of FLICE-inhibitory protein (FLIP) in regulating the interaction of caspase-8 with Fas-associated death domain protein (FADD) was excluded, as AXL did not enhance FLIP expression or FLIP/FADD association. Alternatively, protein association of AXL with DR5, independent of TRAIL, was confirmed, suggesting that AXL could regulate DR5 receptor activity. The AXL/DR5 association had no negative effect on TRAIL-induced interaction with FADD. However, the AXL/DR5 interaction blocked the recruitment of caspase-8 to the death-inducing signal complex (DISC). Collectively, our findings uncover a novel mechanism of TRAIL resistance mediated by AXL through regulation of the DISC and provide strong evidence that AXL could be exploited as a therapeutic target to circumvent TRAIL resistance.

FLIP: A flop for execution signals

Resistance to apoptosis is one of the established hallmarks of cancer cells. This is a function of an imbalance between the proteins that facilitate death execution and those that inhibit apoptosis or promote cell proliferation. The anti-apoptotic protein, FLICE inhibitory protein (FLIP), first identified as a viral protein, is over-expressed in a variety of human pathologies. Initial observations linked FLIP expression to inhibition of death receptor induced apoptosis, due to its structural homology to the cysteine protease, caspase-8. FLIP impedes full processing of pro-caspase-8 to its active form and its release to the cytosol, and by doing so blocks apoptotic signaling downstream of the membrane death initiating signaling complex (DISC). Recent observations have highlighted the complex regulation of this protein and its cross talk with diverse signaling networks and metabolic processes. As FLIP expression is directly associated with chemotherapy resistance, a better understanding of its genomic organization, gene transcription, as well as post-transcriptional regulation could yield novel targets with potential therapeutic implications against drug refractory cancers. In this short review, we provide a brief overview of the structural and functional biology of this somewhat complex protein with direct relevance to carcinogenesis.

Immunohistochemical features of post‐radiation vaginal recurrences of endometrioid carcinomas of the endometrium: role for proteins involved in resistance to apoptosis and hypoxia

Endometrioid carcinoma of the endometrium (EEC) is treated with surgery and radiotherapy. Post-radiation recurrences are associated with increased risk of metastases. Comparison of the expression of genes important in the development and progression of EEC, and others involved in resistance to apoptosis and hypoxia and adaptation to radiation, was performed between post-radiation vaginal recurrences (PVRs) and primary EECs. We tried to reproduce the results by exposing an EEC cell line to hypoxia and radiation. Immunohistochemistry and tissue microarrays were used to compare 24 PVRs with 82 primary EECs. PVRs exhibited increased expression of p53 (P < 0.0001), cytoplasmic FLICE-inhibitory protein (FLIP) (P < 0.0001), and Ki67 (P < 0.0001), and nuclear staining for FLIP, nuclear factor kappaB (NF-κB) family members (p50, P < 0.0001; c-Rel, P = 0.0077; RelB, P = 0.0157), and β-catenin (P = 0.0001). Differences regarding p50, hypoxia-inducible factor 1α (HIF-1α), and cytoplasmic FLIP were statistically significant when PVRs and primary EECs were matched for histological grade. Exposure of the EEC cell line to hypoxia induced nuclear expression of β-catenin, FLIP, and HIF-1α, as well as increased NF-κB activity. No changes in FLIP, HIF-1α or NF-κB were seen when cells were exposed to radiation. Nuclear expression of β-catenin was seen at 3 Gy, but not at 1 Gy. Genes involved in resistance to hypoxia are expressed in PVRs, and may play a role in the development of post-radiation recurrences.

FLIP regulation of HO-1 and TNF signalling in human acute myeloid leukemia provides a unique secondary anti-apoptotic mechanism.

Acute myeloid leukemia (AML) comprises a heterogeneous group of clonal disorders of hematopoietic progenitors. We previously showed that heme oxygenase-1 (HO-1/Hsp32) underlies resistance of AML to TNF-induced apoptosis. Here we show for the first time that the modulatory protein, FLICE-inhibitory protein (FLIP) indirectly regulates induction of HO-1 in response to TNF in human AML blasts, but not non-cancerous control cells. In AML cells, TNF-induced FLIP expression was an NF-κB-dependent event, and silencing of FLIP isoforms (FLIPL, FLIPS and FLIPR) induced pro-apoptotic responses to TNF, with FLIPL knock-down providing the greatest apoptotic switch. However, FLIPL knock-down consequently increased expression of HO-1; a response that occurred in AML (but not non-cancerous) cells to protect a proportion of them from apoptotic death. Our results show that increases in HO-1 induced an apoptotic-resistant form in AML cells in the absence of FLIPL. This is the first time that FLIPL has been shown to regulate the expression of HO-1. These data reveal unique regulatory networks in cancerous AML cells whereby FLIP regulation of HO-1 provides AML cells with secondary anti-apoptotic protection against extrinsic factors (eg TNF/chemotherapies) that try to switch on death signals in these highly death-resistant cells. Future AML therapies should target these mechanisms.

FLIP regulation of HO-1 and TNF signalling in human acute myeloid leukemia provides a unique secondary anti-apoptotic mechanism.

Acute myeloid leukemia (AML) comprises a heterogeneous group of clonal disorders of hematopoietic progenitors. We previously showed that heme oxygenase-1 (HO-1/Hsp32) underlies resistance of AML to TNF-induced apoptosis. Here we show for the first time that the modulatory protein, FLICE-inhibitory protein (FLIP) indirectly regulates induction of HO-1 in response to TNF in human AML blasts, but not non-cancerous control cells. In AML cells, TNF-induced FLIP expression was an NF-κB-dependent event, and silencing of FLIP isoforms (FLIPL, FLIPS and FLIPR) induced pro-apoptotic responses to TNF, with FLIPL knock-down providing the greatest apoptotic switch. However, FLIPL knock-down consequently increased expression of HO-1; a response that occurred in AML (but not non-cancerous) cells to protect a proportion of them from apoptotic death. Our results show that increases in HO-1 induced an apoptotic-resistant form in AML cells in the absence of FLIPL. This is the first time that FLIPL has been shown to regulate the expression of HO-1. These data reveal unique regulatory networks in cancerous AML cells whereby FLIP regulation of HO-1 provides AML cells with secondary anti-apoptotic protection against extrinsic factors (eg TNF/chemotherapies) that try to switch on death signals in these highly death-resistant cells. Future AML therapies should target these mechanisms.

Inhibition of NF-κB Signaling by Quinacrine Is Cytotoxic to Human Colon Carcinoma Cell Lines and Is Synergistic in Combination with Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL) or Oxaliplatin

Colorectal cancer is the third most common malignancy in the United States. Modest advances with therapeutic approaches that include oxaliplatin (L-OHP) have brought the median survival rate to 22 months, with drug resistance remaining a significant barrier. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is undergoing clinical evaluation. Although human colon carcinomas express TRAIL receptors, they can also demonstrate TRAIL resistance. Constitutive NF-kappaB activation has been implicated in resistance to TRAIL and to cytotoxic agents. We have demonstrated constitutive NF-kappaB activation in five of six human colon carcinoma cell lines; this activation is inhibited by quinacrine. Quinacrine induced apoptosis in colon carcinomas and potentiated the cytotoxic activity of TRAIL in RKO and HT29 cells and that of L-OHP in HT29 cells. Similarly, overexpression of IkappaBalpha mutant (IkappaBalphaM) or treatment with the IKK inhibitor, BMS-345541, also sensitized these cells to TRAIL and L-OHP. Importantly, 2 h of quinacrine pretreatment resulted in decreased expression of c-FLIP and Mcl-1, which were determined to be transcriptional targets of NF-kappaB. Extended exposure for 24 h to quinacrine did not further sensitize these cells to TRAIL- or L-OHP-induced cell death; however, exposure caused the down-regulation of additional NF-kappaB-dependent survival factors. Short hairpin RNA-mediated knockdown of c-FLIP or Mcl-1 significantly sensitized these cells to TRAIL and L-OHP. Taken together, data demonstrate that NF-kappaB is constitutively active in colon cancer cell lines and NF-kappaB, and its downstream targets may constitute an important target for the development of therapeutic approaches against this disease.

Expression of FLICE-inhibitory Protein in Synovial Tissue and Its Association with Synovial Inflammation in Juvenile Idiopathic Arthritis

To examine the expression of FLICE-inhibitory protein (FLIP) in juvenile idiopathic arthritis (JIA) and analyze its correlation with synovial inflammation. The expression of FLIP was assessed in 11 JIA and 3 normal synovial tissue samples by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. The cell types expressing FLIP were further characterized, and the correlation of FLIP expression with the degree of synovial inflammation, as well as the activity of caspase 8 was then analyzed. RT-PCR revealed the expression of FLIP mRNA in all 11 JIA samples, but not in 3 normal synovial tissues. In JIA, FLIP expression could be found in both the lining and sublining layers, mainly in the macrophage-like cells. Moreover, the expression of FLIP in JIA synovial tissues was positively correlated with the degree of synovial inflammation (r = 0.563, P < 0.05). The expression of antiapoptotic FLIP in JIA synovial tissue and its correlation to accumulation of inflammatory cells in synovial tissue suggests that FLIP potentially extends the lifespan of synovial cells and thus contributes to the progression of joint destruction.

S-Adenosylmethionine and Methylthioadenosine Inhibit Cellular FLICE Inhibitory Protein Expression and Induce Apoptosis in Colon Cancer Cells

S-Adenosylmethionine (SAMe) and its metabolite 5'-methylthioadenosine (MTA) inhibit mitogen-induced proliferative response in liver and colon cancer cells. SAMe and MTA are also proapoptotic in liver cancer cells by selectively inducing Bcl-x(S) expression. The aims of this work were to assess whether these agents are proapoptotic in colon cancer cells, and if so, to elucidate the molecular mechanisms. We found that both SAMe and MTA are proapoptotic in HT-29 and RKO cells in a dose- and time-dependent manner. Gene microarray uncovered down-regulation of cellular FLICE inhibitory protein (cFLIP). SAMe and MTA treatment led to a decrease in the mRNA and protein levels of both the long and short cFLIP isoforms. This required de novo RNA synthesis and was associated with activation of procaspase-8, Bid cleavage, and release of cytochrome c from the mitochondria. Inhibiting caspase 8 activity or overexpression of cFLIP protected against apoptosis, whereas supplementing with polyamines did not. SAMe and MTA treatment sensitized RKO cells to tumor necrosis factor alpha-related apoptosis-inducing ligand-induced apoptosis. Although SAMe and MTA are proapoptotic in colon cancer cells, they have no toxic effects in NCM460 cells, a normal colon epithelial cell line. In contrast to liver cancer cells, SAMe and MTA had no effect on Bcl-x(S) expression in colon cancer cells. In conclusion, SAMe and MTA are proapoptotic in colon cancer cells but not normal colon epithelial cells. One molecular mechanism identified is the inhibition of cFLIP expression. SAMe and MTA may be attractive agents in the chemoprevention and treatment of colon cancer.

Selective triggering of apoptosis of concanavalin A-activated T cells by fraxinellone for the treatment of T-cell-dependent hepatitis in mice

Selectively inducing apoptosis of activated T cells is essential for the clearance of pathogenic injurious cells and subsequent efficient resolution of inflammation. However, few chemicals have been reported to trigger apoptosis of activated T cells in the treatment of hepatitis without affecting quiescent T cells. In the present study, we found that fraxinellone, a small natural compound isolated from the root bark of Dictamnus dasycarpus, selectively facilitated apoptosis of concanavalin A (Con A)-activated CD4 + T cells rather than those non-activated, by disrupting the mitochondrial transmembrane potential, decreasing the ratio of Bcl-2/Bax, and increasing cytochrome c release from the mitochondria to the cytosol. The enhancement in Fas expression and caspase-8 activity, truncation of Bid, and down-regulation of anti-apoptotic cellular FLICE-inhibitory protein expression by fraxinellone also suggested the participation of an extrinsic apoptosis pathway. Furthermore, fraxinellone significantly alleviated Con A-induced T-cell-dependent hepatitis in mice, which was closely associated with reduced serum transaminases, pro-inflammatory cytokines, and pathologic parameters. Consistent with the in vitro results, fraxinellone dramatically induced apoptosis of activated peripheral CD4 + T cells in vivo, consequently resulting in less CD4 + T-cell activation and infiltration to the liver. These results strongly suggest fraxinellone might be a potential leading compound useful in treating T-cell-mediated liver disorders in humans.

493 POSTER Manipulating prostate cancer cell susceptibility to docetaxel and novel titanocene analogues induced apoptosis

The overexpression of AXL receptor tyrosine kinase is a frequent finding that has been associated with poor prognosis in esophageal adenocarcinoma (EAC). As the majority of EAC are intrinsically resistant to DNA-damaging therapies, an alternative therapeutic approach based on the activation of death receptors may be warranted. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been evaluated in clinical trials and found promising as anticancer agent with mild side effects; unfortunately, resistance to TRAIL remains a major clinical problem. Herein, we explored the role of AXL in TRAIL resistance and elucidated the underlying mechanism. Overexpression of AXL in OE33 and OE19 cells promoted cell survival and attenuated TRAIL-induced cellular and molecular markers of apoptosis. In contrast, knockdown of endogenous AXL sensitized FLO-1 cells to TRAIL. The mechanism by which AXL regulates TRAIL resistance was examined. Protein and mRNA expression of DR4 and DR5 death receptors was not downregulated by AXL. In addition, the possible involvement of FLICE-inhibitory protein (FLIP) in regulating the interaction of caspase-8 with Fas-associated death domain protein (FADD) was excluded, as AXL did not enhance FLIP expression or FLIP/FADD association. Alternatively, protein association of AXL with DR5, independent of TRAIL, was confirmed, suggesting that AXL could regulate DR5 receptor activity. The AXL/DR5 association had no negative effect on TRAIL-induced interaction with FADD. However, the AXL/DR5 interaction blocked the recruitment of caspase-8 to the death-inducing signal complex (DISC). Collectively, our findings uncover a novel mechanism of TRAIL resistance mediated by AXL through regulation of the DISC and provide strong evidence that AXL could be exploited as a therapeutic target to circumvent TRAIL resistance.