The long non-coding RNA HOTAIR enhances pancreatic cancer resistance to TNF-related apoptosis-inducing ligand

Pancreatic cancer is a malignant neoplasm with a high mortality rate. Therapeutic agents that activate TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis have shown promising efficacy, but many pancreatic cancers are resistant to TRAIL therapy. Epigenetic regulation plays important roles in tumor pathogenesis and resistance, and a recent study indicated that the long non-coding RNA HOX transcript antisense RNA (HOTAIR) is overexpressed in pancreatic cancer. However, the role of HOTAIR in pancreatic cancer resistance to anticancer agents is unknown. The present study determined the role of HOTAIR in pancreatic cancer TRAIL resistance and investigated the underlying molecular mechanisms. We observed that TRAIL-resistant pancreatic cancer cells had higher levels of HOTAIR expression, whereas TRAIL-sensitive pancreatic cancer cells had lower HOTAIR levels. Overexpressing HOTAIR in TRAIL-sensitive cells attenuated TRAIL-induced apoptosis, and shRNA-mediated HOTAIR knockdown in TRAIL-resistant PANC-1 cells sensitized them to TRAIL-induced apoptosis. These results support a causative effect of HOTAIR on TRAIL sensitivity. Mechanistically, we found that increased HOTAIR expression inhibited the expression of the TRAIL receptor death receptor 5 (DR5), whereas HOTAIR knockdown increased DR5 expression. We further demonstrated that HOTAIR regulates DR5 expression via the epigenetic regulator enhancer of zeste homolog 2 (EZH2) and that EZH2 controls histone H3 lysine 27 trimethylation on the DR5 gene. Taken together, these results demonstrate that high HOTAIR levels increase the resistance of pancreatic cancer cells to TRAIL-induced apoptosis via epigenetic regulation of DR5 expression. Our study therefore supports the notion that targeting HOTAIR function may represent a strategy to overcome TRAIL resistance in pancreatic cancer.

HuR Contributes to TRAIL Resistance by Restricting Death Receptor 4 Expression in Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal cancers, in part, due to resistance to both conventional and targeted therapeutics. TRAIL directly induces apoptosis through engagement of cell surface Death Receptors (DR4 and DR5), and has been explored as a molecular target for cancer treatment. Clinical trials with recombinant TRAIL and DR-targeting agents, however, have failed to show overall positive outcomes. Herein, we identify a novel TRAIL resistance mechanism governed by Hu antigen R (HuR, ELAV1), a stress-response protein abundant and functional in PDA cells. Exogenous HuR overexpression in TRAIL-sensitive PDA cell lines increases TRAIL resistance whereas silencing HuR in TRAIL-resistant PDA cells, by siRNA oligo-transfection, decreases TRAIL resistance. PDA cell exposure to soluble TRAIL induces HuR translocation from the nucleus to the cytoplasm. Furthermore, it is demonstrated that HuR interacts with the 3'-untranslated region (UTR) of DR4 mRNA. Pre-treatment of PDA cells with MS-444 (Novartis), an established small molecule inhibitor of HuR, substantially increased DR4 and DR5 cell surface levels and enhanced TRAIL sensitivity, further validating HuR's role in affecting TRAIL apoptotic resistance. NanoString analyses on the transcriptome of TRAIL-exposed PDA cells identified global HuR-mediated increases in antiapoptotic processes. Taken together, these data extend HuR's role as a key regulator of TRAIL-induced apoptosis.

IMPLICATIONS

Discovery of an important new HuR-mediated TRAIL resistance mechanism suggests that tumor-targeted HuR inhibition increases sensitivity to TRAIL-based therapeutics and supports their re-evaluation as an effective treatment for PDA patients. Mol Cancer Res; 14(7); 599-611. ©2016 AACR.

The alkyllysophospholipid edelfosine enhances TRAIL-mediated apoptosis in gastric cancer cells through death receptor 5 and the mitochondrial pathway

The ether phospholipid edelfosine is the prototype of a group of synthetic antitumor alkyllysophospholipid (ALP) compounds that exert pro-apoptotic effects in various types of cancer cells through cell type-dependent mechanisms. In this study, we examined the antitumor effect of edelfosine in human gastric cancer cells. Edelfosine decreased cell viability and induced autophagic death at a moderate concentration (~30 μM), whereas it induced apoptotic cell death at concentrations over 30 μM. Interestingly, low concentrations of edelfosine (5-10 μM) effectively enhanced recombinant human tumor necrosis factor (TNF)-related apoptosis-inducing ligand (rhTRAIL/TNFSF10)-induced apoptosis and clonogenicity in gastric cancer cells, including TRAIL-resistant AGS cells. Edelfosine upregulated the protein level of death receptor 5 (DR5/TNFRSF10B) and/or increased DR5 upregulation in lipid rafts. In addition, edelfosine-mediated rhTRAIL sensitization was regulated by the DR5 pathway. Edelfosine also activated p38MAPK (MAPK14), and edelfosine-mediated rhTRAIL sensitization was partially regulated by a p38-mediated decrease in mitochondrial membrane potential. This study suggests a novel therapeutic strategy targeting gastric cancer cells by using the combination of edelfosine and TRAIL.

Shogaol overcomes TRAIL resistance in colon cancer cells via inhibiting of survivin

In this study, we showed the ability of representative shogaol, which as a major component of ginger, to overcome TRAIL resistance by increasing apoptosis in colon cancer cells. Shogaol increased death receptor 5 (DR5) levels. Furthermore, shogaol decreased the expression level of antiapoptotic proteins (survivin and Bcl-2) and increased pro-apoptotic protein, Bax. Shogaol treatment induced apoptosis and a robust reduction in the levels of the antiapoptotic protein survivin but did not affect the levels of many other apoptosis regulators. Moreover, knockdown of survivin sensitized colon cancer cells to resistant of TRAIL-induced apoptosis. Therefore, we showed the functions of shogaol as a sensitizing agent to induce cell death of TRAIL-resistant colon cancer cells. This study gives rise to the possibility of applying shogaol as an antitumor agent that can be used for the purpose of combination treatment with TRAIL in TRAIL-resistant colon tumor therapy.

Ursodeoxycholic acid effectively kills drug-resistant gastric cancer cells through induction of autophagic death

Carcinoma cells that have acquired drug resistance often exhibit cross-resistance to various other cytotoxic stimuli. Here, we investigated the effects of ursodeoxycholic acid (UDCA), a gastrointestinal tumor-suppressor, on a cisplatin‑resistant SNU601 gastric cancer subline (SNU601/R). While other anticancer drugs, including L-OHP, etoposide, and death ligand TRAIL, had minimal effects on the viability of these resistant cells, they were sensitive to UDCA. The UDCA‑induced reduction in the viability of the SNU601/R cells was accomplished through autophagy while the primary means of cell death in the parental SNU601 cells (SNU601/WT) was apoptosis. Previously, we demonstrated that the UDCA-triggered apoptosis of gastric cancer cells was regulated by a cell surface death receptor, TRAIL-R2/DR5, which was upregulated and re-distributed on lipid rafts. The UDCA stimulation of TRAIL-R2/DR5 also occurred in the SNU601/R cells despite the lack of apoptosis. In the present study, we found that CD95/Fas, another cell surface death receptor, was also translocated into lipid rafts in response to UDCA although it was not involved in the decrease in cell viability. Specifically, raft relocalization of CD95/Fas was triggered by UDCA in the SNU601/WT cells in which apoptosis occurred, but not in the SNU601/R cells where autophagic death occurred. Notably, UDCA reduced ATG5 levels, an essential component of autophagy, in the SNU601/WT, but not in the SNU601/R cell line. Moreover, in CD95/Fas-silenced SNU601/WT cells, UDCA did not decrease ATG5 levels and induced autophagic cell death rather than apoptosis. These results imply that raft‑distributed CD95/Fas may support UDCA-induced apoptosis via downregulation of ATG5 levels, preventing the autophagic pathway. Taken together, these results suggest that UDCA induces both apoptotic and autophagic cell death depending on the intracellular signaling environment, thereby conferring the advantage to overcome drug resistance through apoptotic defects.

Doxorubicin overcomes resistance to drozitumab by antagonizing Inhibitor of Apoptosis Proteins (IAPs)

BACKGROUND/AIM

Drozitumab is a fully human agonistic monoclonal antibody that binds to death receptor DR5 and induces apoptosis. However, drozitumab resistance is a major obstacle limiting anticancer efficacy.

MATERIALS AND METHODS

We examined the potential for the chemotherapeutic agent doxorubicin to overcome resistance against drozitumab-resistant breast cancer cells both in vitro and in vivo.

RESULTS

Treatment with doxorubicin increased cell surface expression of DR5, reduced levels of Inhibitors of Apoptosis Proteins (cIAPs) and re-sensitised cells to drozitumab-induced apoptosis. Animals implanted with resistant breast cancer cells into the mammary fat pad and treated with a combination of drozitumab and doxorubicin showed inhibition of tumor growth and a substantial delay in tumor progression compared to untreated controls and mice treated with each agent alone.

CONCLUSION

These results suggest that combination of drozitumab with chemotherapy and agents that modulate IAP levels could potentially be a useful strategy in the treatment of breast cancer.

Upregulation of microRNA135a-3p and death receptor 5 plays a critical role in Tanshinone I sensitized prostate cancer cells to TRAIL induced apoptosis

Though tumor necrosis factor related apoptosis inducing ligand (TRAIL) has been used as a potent anticancer agent, TRAIL resistance is a hot-issue in cancer therapy. We investigated the antitumor mechanism of Tanshinone I to sensitize prostate cancer cells to TRAIL. Comibination of Tanshinone I and TRAIL exerted synergistic cytotoxicity, increased cleaved PARP, sub G1 population, the number of TUNELpositive cells, activated caspase 8, 9 and ROS production in PC-3 and DU145 cells. Of note, combination of Tanshinone I and TRAIL enhanced the protein expression of death receptor 5 (DR5) and attenuated anti-apoptotic proteins. RT-PCR and RT-qPCR analyses confirmed that co-treatment of Tanshinone I and TRAIL up-regulated DR5 and microRNA 135a-3p at mRNA level or activity of DR5 promoter and attenuated phosphorylation of extracellular signal regulated kinases in PC-3. Conversely, the silencing of DR5 blocked the increased cytotoxicity, sub G1 population and PARP cleavages induced by co-treatment of Tanshinone I and TRAIL. Interestingly, miR135a-3p mimic enhanced DR5 at mRNA, increased PARP cleavage, Bax and the number of TUNEL positive cells in Tanshinone I and TRAIL cotreated PC-3. Overall, our findings suggest that Tanshinone I enhances TRAIL mediated apoptosis via upregulation of miR135a-3p mediated DR5 in prostate cancer cells as a potent TRAIL sensitizer.

Poly(ADP-ribose) polymerase inhibitors sensitize cancer cells to death receptor-mediated apoptosis by enhancing death receptor expression

Recombinant human tumor necrosis factor-α-related apoptosis inducing ligand (TRAIL), agonistic monoclonal antibodies to TRAIL receptors, and small molecule TRAIL receptor agonists are in various stages of preclinical and early phase clinical testing as potential anticancer drugs. Accordingly, there is substantial interest in understanding factors that affect sensitivity to these agents. In the present study we observed that the poly(ADP-ribose) polymerase (PARP) inhibitors olaparib and veliparib sensitize the myeloid leukemia cell lines ML-1 and K562, the ovarian cancer line PEO1, non-small cell lung cancer line A549, and a majority of clinical AML isolates, but not normal marrow, to TRAIL. Further analysis demonstrated that PARP inhibitor treatment results in activation of the FAS and TNFRSF10B (death receptor 5 (DR5)) promoters, increased Fas and DR5 mRNA, and elevated cell surface expression of these receptors in sensitized cells. Chromatin immunoprecipitation demonstrated enhanced binding of the transcription factor Sp1 to the TNFRSF10B promoter in the presence of PARP inhibitor. Knockdown of PARP1 or PARP2 (but not PARP3 and PARP4) not only increased expression of Fas and DR5 at the mRNA and protein level, but also recapitulated the sensitizing effects of the PARP inhibition. Conversely, Sp1 knockdown diminished the PARP inhibitor effects. In view of the fact that TRAIL is part of the armamentarium of natural killer cells, these observations identify a new facet of PARP inhibitor action while simultaneously providing the mechanistic underpinnings of a novel therapeutic combination that warrants further investigation.

Cytokines from the tumor microenvironment modulate sirtinol cytotoxicity in A549 lung carcinoma cells

Cytokines in tumor microenvironment play an important role in the success or failure of molecular targeted therapies. We have chosen tumor necrosis factor α (TNF-α), TNF related apoptosis inducing ligand (TRAIL), insulin-like growth factor 1 (IGF-1) and transforming growth factor β (TGF-β) as representative pro-inflammatory, pro-apoptotic, anti-apoptotic and anti-inflammatory tumor derived cytokines. Analysis of Oncomine database revealed the differential expression of these cytokines in a subset of cancer patients. The effects of these cytokines on cytotoxicity of FDA approved drugs - cisplatin and taxol and inhibitors of epidermal growth factor receptor - AG658, Janus kinase - AG490 and SIRT1 - sirtinol were assessed in A549 lung cancer cells. TRAIL augmented cytotoxicity of sirtinol and IGF-1 had a sparing effect. Since TRAIL and IGF-1 differentially modulated sirtinol cytotoxicity, further studies were carried out to identify the mechanisms. Sirtinol or knockdown of SIRT1 increased the expression of death receptors DR4 and DR5 and sensitized A549 cells to TRAIL. Increased cell death in presence of TRAIL and sirtinol was caspase independent and demonstrated classical features of necroptosis. Inhibition of iNOS increased caspase activity and switched the mode of cell death to caspase mediated apoptosis. Interestingly, sirtinol or SIRT1 knockdown did not increase IGF-1R expression. Instead, it abrogated ligand induced downregulation of IGF-1R and increased cell survival through PI3K-AKT pathway. In conclusion, these findings reveal that the tumor microenvironment contributes to modulation of cytotoxicity of drugs and that combination therapy, with agents that increase TRAIL signaling and suppress IGF-1 pathway may potentiate anticancer effect.

Hexane extract from Polygonum multiflorum attenuates glutamate-induced apoptosis in primary cultured cortical neurons

ETHNOPHARMACOLOGICAL RELEVANCE

Polygonum multiflorum has traditionally had wide use as an anti-aging treatment in East Asian countries. We investigated the neuroprotective effects of Polygonum multiflorum against glutamate-induced neurotoxicity with a focus on the anti-apoptotic mechanism in primary cultured cortical neurons.

MATERIAL AND METHODS

Cell viability, cytotoxicity, morphological, flow cytometry, Western blot, and caspase activity assays were performed for examination of the neuroprotective effects of active hexane extract from Polygonum multiflorum (HEPM).

RESULTS

Pretreatment with HEPM resulted in significantly decreased glutamate-induced neurotoxicity in a concentration-dependent manner and also resulted in drastically inhibited glutamate-induced apoptosis. Treatment with HEPM resulted in decreased expression of glutamate-induced death receptor (DR)4, and enhanced expression of glutamate-attenuated anti-apoptotic proteins, including Bcl-2, XIAP, and cIAP-1, and slightly reduced glutamate-induced cleavage of Bid. In addition, treatment with HEPM resulted in suppressed glutamate-induced activation of caspase-8, caspase-9, and caspase-3, and, subsequently, decreased degradation of poly(ADP-ribose) polymerase, β-catenin, and phospholipase Cγ1 protein, which are downstream targets of activated caspase-3.

CONCLUSIONS

The results of this study demonstrated that HEPM exerts a neuroprotective effect against glutamate-induced neurotoxicity via inhibition of apoptosis. This protection may be mediated through suppression of DR4 and up-regulation of Bcl-2, XIAP, and cIAP-1, as well as inhibition of caspase activation, resulting in prevention of apoptosis of cortical neurons.

Lipoxygenase inhibitor MK886 potentiates TRAIL-induced apoptosis through CHOP- and p38 MAPK-mediated up-regulation of death receptor 5 in malignant glioma

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers specific apoptosis in tumor cells and is one of the most promising candidates for cancer gene therapy. However, resistance to TRAIL is one of the main impediments to use of TRAIL in cancer treatment. We showed previously that the lipoxygenase inhibitor MK886 in combination with TRAIL exhibits enhanced antitumor activities compared with each agent alone in human glioma cells. In this study, we elucidated the molecular mechanisms responsible for MK886-mediated sensitization to TRAIL-induced apoptosis. We found that MK886 sensitized glioma cells to TRAIL-induced apoptosis by upregulating the death receptor 5 (DR5) and that specific knockdown of DR5 attenuated cell death. The mechanisms underlying this sensitization involved activation of the MK886-induced p38 mitogen-activated protein kinase (MAPK) pathway and subsequent DR5 overexpression. However, treatment with a specific inhibitor or gene silencing of p38 MAPK abolished both the DR5 induction and the increase in apoptosis caused by TRAIL. Taken together, our findings indicate that the increased expression of DR5 in a p38 MAPK-dependent manner plays an important role in the sensitization of MK886 to TRAIL-induced apoptosis.

Capsazepine, a TRPV1 antagonist, sensitizes colorectal cancer cells to apoptosis by TRAIL through ROS-JNK-CHOP-mediated upregulation of death receptors

A major problem in clinical trials of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as cancer therapy is the development of resistance to TRAIL. Therefore, agents that can overcome TRAIL resistance have great therapeutic potential. In this study, we evaluated capsazepine, a TRPV1 antagonist, for its ability to sensitize human colon cancer cells to TRAIL-induced apoptosis. Capsazepine potentiated the effect of TRAIL, as shown by its effect on intracellular esterase activity; activation of caspase-8,-9, and -3; and colony-formation assay. Capsazepine induced death receptors (DRs) DR5 and DR4, but not decoy receptors, at the transcriptional level and in a non-cell-type-specific manner. DR induction was dependent on CCAAT/enhancer-binding protein homologous protein (CHOP), as shown by (a) the induction of CHOP by capsazepine and (b) the abolition of DR- and potentiation of TRAIL-induced apoptosis by CHOP gene silencing. CHOP induction was also reactive oxygen species (ROS)-dependent, as shown by capsazepine's ability to induce ROS and by the quenching of ROS by N-acetylcysteine or glutathione, which prevented induction of CHOP and DR5 and consequent sensitization to TRAIL. Capsazepine's effects appeared to be mediated via JNK, as shown by capsazepine's ability to induce JNK and by the suppression of both CHOP and DR5 activation by inhibition of JNK. Furthermore, ROS sequestration abrogated the activation of JNK. Finally, capsazepine downregulated the expression of various antiapoptotic proteins (e.g., cFLIP and survivin) and increased the expression of proapoptotic proteins (e.g., Bax and p53). Together, our results indicate that capsazepine potentiates the apoptotic effects of TRAIL through downregulation of cell survival proteins and upregulation of death receptors via the ROS-JNK-CHOP-mediated pathway.

Silibinin inhibits tumor growth in a murine orthotopic hepatocarcinoma model and activates the TRAIL apoptotic signaling pathway

AIM

The present study investigated the molecular mechanism of silibinin-induced antitumoral effects in hepatocarcinoma Hep-55.1C cells in vitro and in a hepatocarcinoma model in mice.

MATERIALS AND METHODS

Cell death was analyzed by flow cytometry. The genetic expression of apoptotic and inflammatory biomarkers was assessed by quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR). Orthotopic grafting of Hep-55.1C cells into the liver of C57BL/6J mice was performed, and tumor growth was followed by micro-computed imaging.

RESULTS

Silibinin activated the extrinsic apoptotic pathway in Hep55.1C cells, as attested by the up-regulation of TNF-related apoptosis-inducing ligand (TRAIL) and TRAIL Death receptor 5 (DR5) transcripts, and by the activation of caspase-3 and -8. After grafting of Hep-55.1C cells into mouse liver, the oral administration of silibinin at 700 mg/kg body weight for four weeks caused a significant reduction of tumor growth, associated with the down-regulation of inflammatory components [matrix metalloproteinase -7 and -9, (MMP-7, MMP-9), Interleukin-1 beta (IL1β)], the up-regulation of apoptotic mediators (TRAIL, DR5), and caspase-3 activation.

CONCLUSION

Silibinin treatment exerted important anticarcinogenic effects, including the activation of TRAIL death receptor apoptotic signaling pathway in Hep-55.1C hepatocarcinoma cells, both in vitro and in hepatocarcinoma grafts in mice.

CHM-1, a new vascular targeting agent, induces apoptosis of human umbilical vein endothelial cells via p53-mediated death receptor 5 up-regulation

CHM-1 (2'-fluoro-6,7-methylenedioxy-2-phenyl-4-quinolone) has been identified as a potent antitumor agent in human hepatocellular carcinoma; however, its role in tumor angiogenesis is unclear. This study investigated the effects of CHM-1 and the mechanisms by which it exerts its antiangiogenic and vascular disrupting properties. Using a xenograft model antitumor assay, we found that CHM-1 significantly inhibits tumor growth and microvessel formation. Flow cytometry, immunofluorescence microscopy, and cell death enzyme-linked immunosorbent assay kit revealed that CHM-1 inhibits growth of human umbilical vein endothelial cells (HUVEC) by induction of apoptotic cell death in a concentration-dependent manner. CHM-1 also suppresses HUVEC migration and capillary-like tube formation. We were able to correlate CHM-1-induced apoptosis in HUVEC with the cleavage of procaspase-3, -7, and -8, as well as with the cleavage of poly(ADP-ribose) polymerase by Western blotting assay. Such sensitization was achieved through up-regulation of death receptor 5 (DR5) but not DR4 or Fas. CHM-1 was also capable of increasing the expression level of p53, and most importantly, the induction of DR5 by CHM-1 was abolished by p53 small interfering RNA. Taken together, the results of this study indicate that CHM-1 exhibits vascular targeting activity associated with the induction of DR5-mediated endothelial cell apoptosis through p53 up-regulation, which suggests its potential as an antivascular and antitumor therapeutic agent.

Major histocompatibility complex class I-related chains A and B (MIC A/B): a novel role in nonalcoholic steatohepatitis

Stress-induced soluble major histocompatibility complex class I-related chains A/B (MIC A/B) are increased in chronic liver diseases and hepatocellular malignancy. We investigated the impact of these molecules on liver injury, apoptosis, and fibrosis in nonalcoholic steatohepatitis (NASH). Blood and liver tissue were obtained from 40 patients with NASH undergoing bariatric surgery for obesity. The control group consisted of 10 healthy individuals. We also investigated 10 patients with nonalcoholic fatty liver (NAFL). Polymerase chain reaction was used to measure messenger RNA (mRNA) transcripts of MIC A/B, natural killer cell receptor G2D (NKG2D), CD95/Fas, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-death receptor 5 (DR5). Apoptosis was quantified by way of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) (intrahepatic) and M30/M65 (systemic). Liver injury was assessed histopathologically and serologically (alanine aminotransferase/aspartate aminotransferase). Fibrosis was identified by Sirius red staining, quantitative morphometry, and alpha-smooth muscle actin and collagen 1alpha transcripts. Compared with controls, patients with NASH revealed significant increases in (1) NKG2D mRNA (13.1-fold) and MIC A/B mRNA (3.6-fold and 15.8-fold, respectively); (2) TRAIL-DR5 and CD95/Fas mRNA (2.7-fold and 3.6-fold, respectively); (3) TUNEL-positive hepatocytes (4.0-fold); and (4) M30 and M65 levels (4.6-fold and 3.4-fold, respectively). We found relevant correlations between MIC protein expression rates and NAS and fibrosis stages. In contrast, NKG2D and MIC A/B transcripts were attenuated in patients with NAFL compared with NASH. Histopathologically, NASH patients revealed increased NAS scores, an accumulation of natural killer cells, and 2.7-fold increased hepatic fibrosis by quantitative morphometry.

CONCLUSION

Our findings suggest an important role for MIC A/B in liver injury. Therapeutic intervention aimed at reducing MIC A/B levels may beneficially affect the progression of NASH.

Anti-DR5 mAb ameliorate adjuvant arthritis rats through inducing synovial cells apoptosis

OBJECTIVE

Study the therapeutic effects and immunoregulatory mechanisms of anti-DR5 mAb on adjuvant arthritis (AA) rats.

METHODS

AA rats induced by CFA, were treated with anti-DR5 mAb through mainline administration. Effect on the synovial membranes of the tissues was detected by H&E staining. Flow cytometry and MTT assay were used for detecting the induced apoptosis in an in vitro system and TUNEL assay was used for analysis in an in vivo system. The involvement of the apoptotic pathway was further proved by a caspase inhibition assay.

RESULTS

Anti-DR5 mAb could induce synovial cell apoptosis in an in vitro system, which was related with the mRNA expression of DR5 on the cell surface. The mRNA expressions of c-myc and bcl-2 were decreased in synovial cells and those of p21, p53, and bax were increased. The protein expressions of caspase-8/3/9, RANKL, JNK2, and c-Jun were raised and that of bcl-2 was decreased. When the caspase inhibitor was added to the synovial cells treated with anti-DR5 mAb, it showed a dose-dependence inhibition effect, indicating that anti-DR5 mAb inducing apoptosis might be through the caspase pathway.

CONCLUSION

This study shows that anti-DR5 mAb can ameliorate arthritic symptoms. The mechanisms of the treatment are related to the increase in synovial cell apoptosis by regulating the mRNA expression of DR5 and apoptosis-related genes, prolonging the duration of the cell cycle by modulation of the mRNA expression of cell cycle-related genes, and the protein expression of the molecules in the caspase pathway and RANKL, JNK2, and c-Jun.

Inhibition of ataxia telangiectasia mutated kinase activity enhances TRAIL-mediated apoptosis in human melanoma cells

The aim of the present study was to elucidate the effects of ataxia telangiectasia mutated (ATM) kinase on the regulation of the extrinsic tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 2/DR5-mediated death pathway in human melanoma cells. We revealed that total ATM protein levels were high in some human melanoma lines compared with normal cells. The basal levels of active form ATM phospho-Ser(1981) were also detectable in many melanoma lines and could be further up-regulated by gamma-irradiation. Pretreatment of several melanoma lines just before gamma-irradiation with the inhibitor of ATM kinase KU-55933 suppressed p53 and nuclear factor-kappaB (NF-kappaB) activation but notably increased radiation-induced DR5 surface expression, down-regulated cFLIP (caspase-8 inhibitor) levels, and substantially enhanced exogenous TRAIL-induced apoptosis. Furthermore, gamma-irradiation in the presence of KU-55933 rendered TRAIL-resistant HHMSX melanoma cells susceptible to TRAIL-mediated apoptosis. In addition, suppression of ATM expression by the specific short hairpin RNA also resulted in down-regulation of cFLIP levels, up-regulation of surface DR5 expression, and TRAIL-mediated apoptosis in melanoma cells. Besides p53 and NF-kappaB, crucial regulators of DR5 expression, transcription factor STAT3 is known to negatively regulate DR5 expression. Suppression of Ser(727) and Tyr(705) phosphorylation of STAT3 by KU-55933 reduced STAT3 transacting activity accompanied by elevation in DR5 expression. Dominant-negative STAT3beta also efficiently up-regulated the DR5 surface expression and down-regulated cFLIP levels in melanoma cells in culture and in vivo. Taken together, our data show the existence of an ATM-dependent STAT3-mediated antiapoptotic pathway, which on suppression sensitizes human melanoma cells to TRAIL-mediated apoptosis.

The expression of TRAIL and its receptors in gastric cancer and the apoptotic effect of rh-TRAIL on SGC7901 cells

This study investigated the expression of TRAIL and its receptors in human gastric cancer and normal gastric tissues, the effects of rh-TRAIL with or without chemotherapeutic drugs in apoptosis of the gastric cancer cell line SGC7901 and the expression changes of DR4 and DR5 in SGC7901 cells influenced by chemotherapeutic drugs. The expression of TRAIL, DR4 and DcR1 were studied in 34 cases of human gastric cancer tissues and 15 cases of adjacent normal mucosa tissues, as well as 21 cases of distant normal mucosa tissues by means of immunohistochemistry. In addition, the expression of FasL were studied in gastric cancer tissues by immunohistochemistry. The effects of treatment with rh-TRAIL alone and/or chemotherapeutic drugs on SGC7901 cell growth inhibition were measured by MTT assay and the mRNA changes of DR4 and DR5 were detected by RT-PCR technique. The expression of TRAIL, DR4 and DcR1 in gastric cancer were lower than those of normal tissues (P<0.05). There was significant relationship between the expression of TRAIL and Borrmann type of gastric cancer (P=0.039), and so was the expression of DcR1 and tumor location (P=0.01). The correlation coefficient between the expression of TRAIL and FasL was 0.354 (P=0.04). Rh-TRAIL protein had inhibiting effect on the growth of SGC7901 cells. DDP and 5-FU increased the growth-inhibiting ability of rh-TRAIL to SGC7901 cells. DDP facilitated the induction of expression of DR4 and DR5 significantly in cell line (P<0.05), but 5-FU influenced only the expression of DR5 significantly. From the results, we concluded that the expression of TRAIL and its receptors were lower in gastric cancer than those of normal tissue, and the apoptosis-inducing effect of rh-TRAIL was enhanced when concomitant with chemotherapeutic drugs.

The Effect of N-Nitrosodimethylamine on TRAIL and DR5 Expression in Human Neutrophils—Preliminary Study

The intracellular mechanisms of NDMA-induced apoptosis of neutrophils have not yet been fully understood. The aim of this study was to explain whether the TRAIL/DR5 system is implicated in NDMA-induced apoptosis of human neutrophils. The expression of TRAIL and DR5 was examined, as well as the secretion of sTRAIL and sDR5 by human neutrophils treated with NDMA confronted with intensity apoptosis of these cells. For comparative purposes similar examinations in autologous peripheral blood mononuclear cells (PBMC) were performed. Decreased expression and secretion of TRAIL and increased expression and secretion of DR5 associated with increased intensity of apoptosis of polymorphonuclear leukocytes (PMNs) suggest that NDMA-induced apoptosis in these cells may be depend on TRAIL/DR5 system. Autologous PBMCs no exerted that changes in the expression and secretion of TRAIL as well as in the intensity of apoptosis. However, the expression and secretion of DR5 by PBMCs were similar to those by PMNs. Differences above suggest that PMNs are more sensitive to unfavorable action of NDMA than PBMCs.

Molecular mechanisms and gene regulation of melphalan- and hyperthermia-induced apoptosis in Ewing sarcoma cells

The prognosis of high-risk Ewing tumours (HR-ET) remains poor. Melphalan-containing chemotherapy regimens are commonly applied for HR-ET patients. Moreover, melphalan (Mel) is a promising agent in thermochemotherapy. Therefore, we investigated the single effects, the synergism and the gene regulation of Mel and hyperthermia (HT) in an ET cell line (RD-ES). Dose-dependent cytotoxicity by Mel was demonstrated, which was enhanced by the concomitant application of HT (42 degrees C for 2 h). Mel, HT and their combination caused a significant activation of caspase-3. Using the pan-caspase inhibitor z-VAD-fmk, we demonstrated that both stimuli mediated predominantly caspase-dependent cytotoxicity. With cDNA array analysis, 20 out of 198 apoptosis-related genes were identified to be differentially expressed by Mel and/or HT. Although a significant enhancement of three selected genes could not be proven at the protein level in subsequent experiments, this study gives insight into the complex molecular and genetic response of tumour cells to cytotoxic stimulation.

[The expression of tumor necrosis factor-related apoptosis inducing ligand and its receptors in muscle tissue of inflammatory myopathies]

OBJECTIVE

The purpose of this study is to analyse the expression of tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) and its receptors in muscle tissue from patients with idiopathic inflammatory myopathies ( IIM) and investigate the possible role of TRAIL system in the pathogenesis of IIM.

METHODS

TRAIL and its receptors DR4, DR5, DCR1 and DCR2 were detected in the muscle biopsy tissue from 36 patients with IIM (13 polymyositis, 23 dermatomyositis) and 9 healthy controls by using immunohistochemistry.

RESULTS

The expression of TRAIL and its receptors was found in muscle tissue samples from the IIM patients and healthy controls. The expression of TRAIL, DR4 and DCR2 in the muscle tissue from the IIM patients was significantly higher than those from healthy controls (all P values < 0.05). The expression of TRAIL, DCR1 and DR4 was also detected in the infiltrating lymphocytes in endomysium and in the interstitial tissue around blood vessels.

CONCLUSION

The diversity in expression of TRAIL and its receptors between patients with IIM and healthy controls suggests the hypothesis of a crucial role of TRAIL in the pathogenesis and the pathology of IIM.

Sp1 is involved in 8-chloro-adenosine-upregulated death receptor 5 expression in human hepatoma cells

8-Chloro-adenosine (8-Cl-Ado) is an adenosine derivative, which inhibits proliferation and induces apoptosis in various tumor cells. Subtoxic concentration of 8-Cl-Ado sensitizes human hepatoma cells to tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-triggered apoptosis. However, the molecular mechanism by which TRAIL cytotoxicity is amplified by 8-Cl-Ado is unknown. In the present study, we demonstrated by Western blot and real-time PCR that 8-Cl-Ado selectively up-regulated death receptor 5 (DR5), but not death receptor 4 (DR4), at both protein and RNA levels in human hepatoma cell line BEL-7402. Analysis of the transcriptional regulation of DR5 expression by using Dual-Luciferase reporter assay system demonstrated that the 5'-flanking fragment -207 to -145 upstream to the ATG site within the DR5 promoter region was responsible for the 8-Cl-Ado-upregulated DR5 expression. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) confirmed that 8-Cl-Ado treatment facilitated transcription factor Sp1 binding to its cis-element -198/-189 in the DR5 promoter, suggesting that Sp1 is at least one of the 8-Cl-Ado-responsive transcription factors. However, we observed that nuclear factor kappaB (NF-kappaB) activity remained invariable in the cells treated with 8-Cl-Ado. These data allowed us to draw a conclusion that 8-Cl-Ado-enhanced DR5 expression is regulated by Sp1 binding to the -198/-189 cis-element in DR5 promoter without affecting NF-kappaB activity in the hepatoma cells. This study may shed light on further screening the regulators of DR5 expression and developing novel therapeutic drugs for liver cancer.

Regulation of tumor cell sensitivity to TRAIL-induced apoptosis by the metastatic suppressor Raf kinase inhibitor protein via Yin Yang 1 inhibition and death receptor 5 up-regulation

Raf-1 kinase inhibitor protein (RKIP) has been implicated in the regulation of cell survival pathways and metastases, and is poorly expressed in tumors. We have reported that the NF-kappaB pathway regulates tumor resistance to apoptosis by the TNF-alpha family via inactivation of the transcription repressor Yin Yang 1 (YY1). We hypothesized that RKIP overexpression may regulate tumor sensitivity to death ligands via inhibition of YY1 and up-regulation of death receptors (DRs). The TRAIL-resistant prostate carcinoma PC-3 and melanoma M202 cell lines were examined. Transfection with CMV-RKIP, but not with control CMV-EV, sensitized the cells to TRAIL-mediated apoptosis. Treatment with RKIP small interfering RNA (siRNA) inhibited TRAIL-induced apoptosis. RKIP overexpression was paralleled with up-regulation of DR5 transcription and expression; no change in DR4, decoy receptor 1, and decoy receptor 2 expression; and inhibition of YY1 transcription and expression. Inhibition of YY1 by YY1 siRNA sensitized the cells to TRAIL apoptosis concomitantly with DR5 up-regulation. RKIP overexpression inhibited several antiapoptotic gene products such as X-linked inhibitor of apoptosis (XIAP), c-FLIP long, and Bcl-x(L) that were accompanied with mitochondrial membrane depolarization. RKIP overexpression in combination with TRAIL resulted in the potentiation of these above effects and activation of caspases 8, 9, and 3, resulting in apoptosis. These findings demonstrate that RKIP overexpression regulates tumor cell sensitivity to TRAIL via inhibition of YY1, up-regulation of DR5, and modulation of apoptotic pathways. We suggest that RKIP may serve as an immune surveillance cancer gene, and its low expression or absence in tumors allows the tumor to escape host immune cytotoxic effector cells.

The multikinase inhibitor sorafenib potentiates TRAIL lethality in human leukemia cells in association with Mcl-1 and cFLIPL down-regulation

Interactions between the multikinase inhibitor sorafenib and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) were examined in malignant hematopoietic cells. Pretreatment (24 h) of U937 leukemia cells with 7.5 micromol/L sorafenib dramatically increased apoptosis induced by sublethal concentrations of TRAIL/Apo2L (75 ng/mL). Similar interactions were observed in Raji, Jurkat, Karpas, K562, U266 cells, primary acute myelogenous leukemia blasts, but not in normal CD34+ bone marrow cells. Sorafenib/TRAIL-induced cell death was accompanied by mitochondrial injury and release of cytochrome c, Smac, and AIF into the cytosol and caspase-9, caspase-3, caspase-7, and caspase-8 activation. Sorafenib pretreatment down-regulated Bcl-xL and abrogated Mcl-1 expression, whereas addition of TRAIL sharply increased Bid activation, conformational change of Bak (ccBak) and Bax (ccBax), and Bax translocation. Ectopic Mcl-1 expression significantly attenuated sorafenib/TRAIL-mediated lethality and dramatically reduced ccBak while minimally affecting levels of ccBax. Similarly, inhibition of the receptor-mediated apoptotic cascade with a caspase-8 dominant-negative mutant significantly blocked sorafenib/TRAIL-induced lethality but not Mcl-1 down-regulation or Bak/Bax conformational change, indicating that TRAIL-mediated receptor pathway activation is required for maximal lethality. Sorafenib/TRAIL did not increase expression of DR4/DR5, or recruitment of procaspase-8 or FADD to the death-inducing signaling complex (DISC), but strikingly increased DISC-associated procaspase-8 activation. Sorafenib also down-regulated cFLIP(L), most likely through a translational mechanism, in association with diminished eIF4E phosphorylation, whereas ectopic expression of cFLIP(L) significantly reduced sorafenib/TRAIL lethality. Together, these results suggest that in human leukemia cells, sorafenib potentiates TRAIL-induced lethality by down-regulating Mcl-1 and cFLIP(L), events that cooperate to engage the intrinsic and extrinsic apoptotic cascades, culminating in pronounced mitochondrial injury and apoptosis.

Apoptotic killing of HIV-1-infected macrophages is subverted by the viral envelope glycoprotein

Viruses have evolved strategies to protect infected cells from apoptotic clearance. We present evidence that HIV-1 possesses a mechanism to protect infected macrophages from the apoptotic effects of the death ligand TRAIL (tumor necrosis factor–related apoptosis-inducing ligand). In HIV-1–infected macrophages, the viral envelope protein induced macrophage colony-stimulating factor (M-CSF). This pro-survival cytokine downregulated the TRAIL receptor TRAIL-R1/DR4 and upregulated the anti-apoptotic genes Bfl-1 and Mcl-1. Inhibition of M-CSF activity or silencing of Bfl-1 and Mcl-1 rendered infected macrophages highly susceptible to TRAIL. The anti-cancer agent Imatinib inhibited M-CSF receptor activation and restored the apoptotic sensitivity of HIV-1–infected macrophages, suggesting a novel strategy to curtail viral persistence in the macrophage reservoir.

Much of our understanding regarding mechanisms of HIV-1 persistence has been derived from studies with lymphocytes. However, mechanisms governing persistent infection of macrophages are less well understood. We investigated whether HIV-1 modulates macrophage function in a way that promotes their persist infection. We focused on a cytokine called macrophage colony-stimulating factor (M-CSF), because this pro-survival factor is induced upon infection by HIV-1. We found that the viral envelope gene was necessary for M-CSF induction of macrophages. M-CSF upregulated anti-apoptotic genes in macrophages and restricted the expression of the death receptor (tumor necrosis factor–related apoptosis-inducing ligand [TRAIL]-R1). As a consequence, HIV-1–infected macrophages were resistant to the apoptotic effects of TRAIL. If M-CSF was blocked by antibody or if the anti-apoptotic genes were silenced by RNA interference, the apoptotic sensitivity of HIV-1–infected macrophages was restored. Also, the anti-cancer drug Imatinib, which impairs activation of the M-CSF receptor, promoted the death of HIV-1–infected macrophages but not of uninfected macrophages. We believe that HIV-1 regulates M-CSF to extend macrophage survival and promote viral persistence in the host. Agents that interfere with M-CSF signaling, such as Imatinib, warrant further examination for activity against macrophage reservoirs in vivo.

DcR2 (TRAIL-R4) siRNA and adenovirus delivery of TRAIL (Ad5hTRAIL) break down in vitro tumorigenic potential of prostate carcinoma cells

High levels of decoy receptor 2 (DcR2; TRAIL-R4) expression are correlated with TRAIL resistance in prostate cancer cells. In addition, upregulation of TRAIL death receptor (DR4 and DR5) expression, either by ionizing radiation or chemotherapy, can sensitize cancer cells to TRAIL. Considering more than half of human cancers are TRAIL resistant, modulation of surface TRAIL receptor expression appears to be an attractive treatment modality to counteract TRAIL resistance. In this study, three siRNA duplexes targeting DcR2 receptor were tested. Ad5hTRAIL infections were performed to overexpress human full-length TRAIL to induce cell death, and the in vitro tumorigenic potential of prostate cancer cells was assessed using colony-forming assays on soft agar. The DU145 and LNCaP prostate cancer cell lines, which express high levels of DcR2, were resistant to Ad5hTRAIL-induced death. Downregulation of surface DcR2 expression by siRNA sensitized these prostate cancer cell lines to Ad5hTRAIL. In addition, DcR2 siRNA-mediated knockdown of DcR2, followed by Ad5hTRAIL infection, dramatically reduced the in vitro tumorigenic potential of prostate cancer cells. Collectively, our results suggest the potential for combining receptor-specific siRNA with TRAIL in the treatment of certain cancers.

[Gene expression and primary functional characterization of human DR5 extracellular fragment]

AIM

To acquire human DR5 extracellular fragment with bioactivity.

METHODS

Total RNA was prepared from Jurkat cells by Trizol. Human DR5 extracellular fragment gene was amplified by RT-PCR, cloned into pGEM-T Easy vector, and confirmed by sequence analysis. Then the gene was subcloned into expression vector pET30a with a His-tag at the amino terminus and expressed in E.coli BL21 (DE3). The products was purified by Ni-NTA chromatography column and identified by SDS-PAGE and Western blot. ELISA method was used to detect its binding activity to anti-DR5 monoclonal antibody (mAb) mDRA-6.

RESULTS

Human DR5 extracellular fragment gene was successfully amplified and high level expression was obtained in E.coli BL21 (DE3) induced by 0.1 mmol/L IPTG. The DR5 extracellular fragment protein was identified by SDS-PAGE and Western blot analysis. ELISA results showed that the purified DR5 could be recognized by mDRA-6.

CONCLUSION

The extracellular region of DR5 with bioactivity has been successfully expressed and purified, which lay the foundation for further study.

Sequential treatment by ionizing radiation and sodium arsenite dramatically accelerates TRAIL-mediated apoptosis of human melanoma cells

Melanoma is the most lethal form of skin cancer. There is a lack of effective treatments for individuals with advanced disease. Many melanomas exhibit high levels of radioresistance. The direct consequence of gamma-irradiation for most melanoma cells is growth arrest at the G2-M phase of cell cycle. However, radiation-induced signaling pathways may affect numerous additional targets in cancer cells. We show in the present study that gamma-irradiation, as well as alpha-particle exposure, dramatically increases the susceptibility of melanoma cells to recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis via up-regulation of surface TRAIL-receptor 1/receptor 2 (DR4/DR5) levels and to Fas ligand-mediated apoptosis via up-regulation of surface Fas levels. Additionally, increased dynamin-2 expression after irradiation is critically important in the translocation of death receptor to the cell surface. Moreover, sodium arsenite treatment may up-regulate expression of endogenous TRAIL and induces its translocation to cell surface and further down-regulates cFLIP levels in melanoma cells. We have evaluated the effects of sequential gamma-irradiation and arsenite treatment of melanoma cells for the induction of death signaling. Such treatment results in an efficient TRAIL-mediated apoptosis via a paracrine mechanism. These data highlight the efficacy of combined modality treatment involving radiation and arsenite in clinical management of this often fatal form of skin cancer.

Lipoxygenase inhibitors induce death receptor 5/TRAIL-R2 expression and sensitize malignant tumor cells to TRAIL-induced apoptosis

Lipoxygenases induce malignant tumor progression and lipoxygenase inhibitors have been considered as promising anti-tumor agents. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising candidates for new cancer therapeutics. Combined treatment with nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, and TRAIL markedly induced apoptosis in Jurkat T-cell leukemia cells at suboptimal concentrations for each agent. The combined treatment efficiently activated caspase-3, -8 and -10, and Bid. The underling mechanism by which NDGA enhanced TRAIL-induced apoptosis was examined. NDGA did not change the expression levels of anti-apoptotic factors, Bcl-x(L), Bcl-2, cIAP-1, XIAP and survivin. The expression of death receptor-related genes was investigated and it was found that NDGA specifically up-regulated the expression of death receptor 5 (DR5) at mRNA and protein levels. Down-regulation of DR5 by small interfering RNA prevented the sensitizing effect of NDGA on TRAIL-induced apoptosis. Furthermore, NDGA sensitized prostate cancer and colorectal cancer cells to TRAIL-induced apoptosis. In contrast, NDGA neither enhanced TRAIL-induced apoptosis nor up-regulated DR5 expression in normal peripheral blood mononuclear cells. Another lipoxygenase inhibitor, AA861, also up-regulated DR5 and sensitized Jurkat and DU145 cells to TRAIL. These results indicate that lipoxygenase inhibitors augment the apoptotic efficiency of TRAIL through DR5 up-regulation in malignant tumor cells, and raise the possibility that the combination of lipoxygenase inhibitor and TRAIL is a promising strategy for malignant tumor treatment.

The proteasome inhibitor PS-341 (bortezomib) up-regulates DR5 expression leading to induction of apoptosis and enhancement of TRAIL-induced apoptosis despite up-regulation of c-FLIP and survivin expression in human NSCLC cells

The proteasome inhibitor PS-341 (bortezomib or Velcade), an approved drug for treatment of patients with multiple myeloma, is currently being tested in clinical trials against various malignancies, including lung cancer. Preclinical studies have shown that PS-341 induces apoptosis and enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human cancer cells with undefined mechanisms. In the present study, we show that PS-341 induced caspase-8-dependent apoptosis, cooperated with TRAIL to induce apoptosis, and up-regulated death receptor 5 (DR5) expression in human non-small cell lung cancer (NSCLC) cells. DR5 induction correlated with the ability of PS-341 to induce apoptosis. Blockage of PS-341-induced DR5 up-regulation using DR5 small interfering RNA (siRNA) rendered cells less sensitive to apoptosis induced by either PS-341 or its combination with TRAIL, indicating that DR5 up-regulation mediates PS-341-induced apoptosis and enhancement of TRAIL-induced apoptosis in human NSCLC cells. We exclude the involvement of c-FLIP and survivin in mediating these events because c-FLIP (i.e., FLIP(S)) and survivin protein levels were actually elevated on exposure to PS-341. Reduction of c-FLIP with c-FLIP siRNA sensitized cells to PS-341-induced apoptosis, suggesting that c-FLIP elevation protects cells from PS-341-induced apoptosis. Thus, the present study highlights the important role of DR5 up-regulation in PS-341-induced apoptosis and enhancement of TRAIL-induced apoptosis in human NSCLC cells.

Sanguinarine-dependent induction of apoptosis in primary effusion lymphoma cells

Primary effusion lymphoma (PEL) is an incurable, aggressive B-cell malignancy that develops rapid resistance to conventional chemotherapy. In efforts to identify novel approaches to block proliferation of PEL cells, we found that sanguinarine, a natural compound isolated from the root plant Sanguinaria canadendid, inhibits cell proliferation and induces apoptosis in a dose-dependent manner in several PEL cell lines. Our data show that sanguinarine treatment of PEL cells results in up-regulation of death receptor 5 (DR5) expression via generation of reactive oxygen species (ROS) and causes activation of caspase-8 and truncation of Bid (tBid). Subsequently, tBid translocates to the mitochondria causing conformational changes in Bax, leading to loss of mitochondrial membrane potential and release of cytochrome c to the cytosol. Sanguinarine-induced release of cytochrome c results in activation of caspase-9 and caspase-3 and poly(ADP-ribose) polymerase (PARP) cleavage, leading to induction of caspase-dependent apoptosis. In addition, we show that pretreatment of PEL cells with carbobenzoxy-Val-Ala-Asp-fluoromethylketone, a universal inhibitor of caspases, abrogates caspase and PARP activation and prevents cell death induced by sanguinarine. Moreover, treatment of PEL cells with sanguinarine down-regulates expression of inhibitor of apoptosis proteins (IAP). Finally, N-acetylcysteine, an inhibitor of ROS, inhibits sanguinarine-induced generation of ROS, up-regulation of DR5, Bax conformational changes, activation of caspase-3, and down-regulation of IAPs. Taken together, our findings suggest that sanguinarine is a potent inducer of apoptosis of PEL cells via up-regulation of DR5 and raise the possibility that this agent may be of value in the development of novel therapeutic approaches for the treatment of PEL.

The Farnesyltransferase Inhibitor R115777 Up-regulates the Expression of Death Receptor 5 and Enhances TRAIL-Induced Apoptosis in Human Lung Cancer Cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) preferentially induces apoptosis in transformed or malignant cells, thus exhibiting potential as a tumor-selective apoptosis-inducing cytokine for cancer treatment. Many studies have shown that the apoptosis-inducing activity of TRAIL can be enhanced by various cancer therapeutic agents. R115777 (tipifarnib) is the first farnesyltransferase inhibitor (FTI) that showed clinical activity in myeloid malignancies. In general, R115777, like other FTIs, exerts relatively weak effects on the induction of apoptosis in cancer cells with undefined mechanism(s). In the current study, we studied its effects on the growth of human lung cancer cells, including induction of apoptosis, and examined potential underlying mechanisms for these effects. We showed that R115777 induced apoptosis in human lung cancer cells, in addition to inducing G(1) or G(2)-M arrest. Moreover, we found that R115777 up-regulated the expression of death receptor 5 (DR5), an important death receptor for TRAIL, and exhibited an augmented effect on the induction of apoptosis when combined with recombinant TRAIL. Blockage of DR5 induction by small interfering RNA (siRNA) abrogated the ability of R115777 to enhance TRAIL-induced apoptosis, indicating that R115777 augments TRAIL-induced apoptosis through up-regulation of DR5 expression. Thus, our findings show the efficacy of R115777 in human lung cancer cells and suggest that R115777 may be used clinically in combination with TRAIL for treatment of human lung cancer.

Fenretinide up-regulates DR5/TRAIL-R2 expression via the induction of the transcription factor CHOP and combined treatment with fenretinide and TRAIL induces synergistic apoptosis in colon cancer cell lines

Fenretinide (N-[4-Hydroxyphenyl]retinamide; 4HPR) is a semisynthetic retinoid that induces apoptosis in a variety of malignancies. Fenretinide has been examined in clinical trials as a cancer chemopreventive and chemotherapeutic agent. Oxidative stress induced by fenretinide has been shown to mediate apoptosis through a mitochondrial pathway by the induction of a transcription factor CCAAT/enhancer binding protein homologous protein (CHOP) and Bak. In this study, we report that fenretinide induces death receptor 5 (DR5)/TRAIL-R2 up-regulation via the induction of the transcription factor CHOP in colon cancer cell lines. Fenretinide induced DR5 expression at protein and mRNA levels. Furthermore, fenretinide increased DR5 promoter activity and the enhanced activity decreased by mutation of the CHOP binding site. CHOP was also up-regulated by fenretinide at the promoter level. We also showed that combined treatment with fenretinide and TRAIL induced synergistic apoptosis in colon cancer cell lines. The synergistic apoptosis was markedly blocked by DR5/Fc chimeric protein. Fenretinide and TRAIL cooperatively activated caspase-3, -8, -10 and -9 and cleavage of Bid and PARP, and this activation was also blocked in the presence of DR5/Fc chimeric protein. These results indicate that fenretinide-induced apoptosis is sensitized by TRAIL. Therefore, combined treatment with fenretinide and TRAIL might be a promising model for the treatment of colorectal cancer.

Induction of death receptor 5 and suppression of survivin contribute to sensitization of TRAIL-induced cytotoxicity by quercetin in non-small cell lung cancer cells

The natural flavonoid quercetin has been suggested by epidemiological studies to have preventive activity against lung cancer; however, the mechanism of which has not been well elucidated. In this report, we demonstrate that quercetin significantly enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cytotoxicity in non-small cell lung cancer (NSCLC) cells. Quercetin increased expression of death receptor (DR) 5, whereas it had no effect on that of other components of the death-inducing signaling complex. Conversely, the expression of survivin was potently inhibited by quercetin. We further determined that Protein Kinase C (PKC) is essential for DR5 induction but is dispensable for suppression of survivin expression. In contrast, the blockage of the serine/threonine kinase Akt activity by quercetin is important for inhibition of survivin expression but not induction of DR5. These results suggest the pathways for regulation of DR5 and survivin expression by quercetin are distinct. Importantly, suppression of survivin-sensitized TRAIL-induced cell death and blockage of DR5 expression suppressed the synergistic cytotoxicity induced by quercetin and TRAIL co-treatment. On the whole, our data show that quercetin sensitizes TRAIL-induced cytotoxicity in lung cancer cells through two independent pathways: induction of DR5 and suppression of survivin expression, which may underlie the mechanism of the lung cancer preventive activity of quercetin. The potentiation of TRAIL-induced NSCLC cell death could be implicated in lung cancer therapy and prevention.

Monoclonal antibody to tumor necrosis factor-related apoptosis-inducing ligand receptor 2 (TRAIL-R2) induces apoptosis in primary renal cell carcinoma cells in vitro and inhibits tumor growth in vivo

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers apoptosis in a variety of tumor cells through two of its receptors: TRAIL-R1 and TRAIL-R2. We investigate the susceptibility of human renal cell carcinoma (RCC) cells to TRM-1 and HGS-ETR2, 2 human monoclonal agonistic antibodies specific for TRAIL-R1 and TRAIL-R2, respectively. HGS-ETR2 effectively induced apoptotic cell death in 10 of 11 cell cultures, including 2 human RCC cell lines and 9 human primary RCC cell cultures, with a more pronounced effect after preincubation with anti-human IgG Fc. In contrast, TRM-1 was effective in only 1 primary RCC cell culture. The increased effectiveness of HGS-ETR2 for inducing cell death might have been affected by differences in the cell-surface expression of the 2 TRAIL receptors, namely that TRAIL-R2 but not TRAIL-R1 was frequently expressed in most of the RCC cells tested. The activities of caspase-9, -8, -6, and -3 were increased with HGS-ETR2-induced apoptosis, and cell death could be blocked by specific caspase inhibitors for caspase-9, -8, and -3, and the general caspase inhibitor. In vivo administration of HGS-ETR2 with or without cross-linker significantly suppressed tumor growth of subcutaneously inoculated human RCC xenografts in immunodeficient mice. These results suggest the potential utility of TRAIL-R2 antibody as a novel therapeutic agent in RCC.

Stellate cell apoptosis by a soluble mediator from immortalized human hepatocytes

Activated hepatic stellate cells (HSCs) are the major source of extracellular matrix in fibrosis and cirrhosis. In this study, we have investigated the role of hepatitis C virus (HCV) core protein induced immortalized human hepatocytes (IHH) on HSC growth. Preferential growth of IHH and apoptosis of activated human hepatic stellate cells (LX2) were observed upon coculture of these two cell types in a dual chamber or in the presence of conditioned medium (CM) from IHH. CM did not display a growth inhibitory role on other hepatic (Huh-7, HepG2, Hep3B and THLE) and non-hepatic (HeLa, MCF-7, and BHK) epithelial cells, indicating that the soluble mediator from IHH does not have a generalized effect on cell lines examined in our study. Further studies suggested that CM from IHH increased the expression of TRAIL receptors on LX2 cell surface, and induced apoptosis by a caspase dependent mechanism. Peptide mass fingerprinting of the purified soluble mediator from CM suggested that gelsolin fragments may play a role in apoptosis of LX2 cells. Taken together, our results suggested that a soluble mediator secreted from immortalized human hepatocytes plays an important role in hepatic stellate cell growth regulation.

Differential Expression of TRAIL and its Receptors in Benign and Malignant Prostate Tissues

PURPOSE

Because TRAIL (tumor necrosis factor related apoptosis inducing ligand) selectively kills cancer cells without damaging normal cells, a gene therapy approach using TRAIL is feasible for treating patients with cancer. However, recent publications suggest that significant portions of human tumors appear to be TRAIL resistant. Furthermore, there is some controversy about whether TRAIL receptor composition influences TRAIL sensitivity in cancer cells. Our recent studies suggest that TRAIL receptor composition is the major modulator of TRAIL sensitivity, as demonstrated using prostate, breast and lung cancer cells. We investigated TRAIL and TRAIL receptor expression profiles during prostate carcinogenesis to evaluate their potential as biomarkers and predict the feasibility of a related gene therapy approach.

MATERIALS AND METHODS

Paraffin embedded prostate tissues of 44 patients with benign prostatic hyperplasia, 28 with organ confined prostate carcinoma and 26 with advanced prostate carcinoma were analyzed using immunohistochemical staining procedures.

RESULTS

Significant levels of TRAIL-R4 decoy receptor expression were detected in patients with benign prostatic hyperplasia, and organ confined and advanced prostate carcinoma. All TRAIL markers tested appear to be valuable markers for separating patients with benign prostatic hyperplasia from patients with organ confined prostate carcinoma or advanced prostate carcinoma.

CONCLUSIONS

Due to high TRAIL-R4 expression in all patient groups complementary gene therapy modalities might be needed to bypass potential TRAIL-R4 induced resistance.

Phytosphingosine in combination with TRAIL sensitizes cancer cells to TRAIL through synergistic up-regulation of DR4 and DR5

Sensitization of cancer cells to TRAIL could improve the effectiveness of TRAIL as an anticancer agent. We explored whether TRAIL in combination with phytosphingosine could sensitize cancer cells to TRAIL. The combined treatment enhanced synergistic apoptotic cell death of Jurkat T cells, compared to TRAIL or phytosphingosine alone. Enhanced apoptosis in response to the combination treatment was associated with caspase-8 activation-mediated Bax and Bak activation and mitochondrial dysfunction. The combination treatment also resulted in synergistic up-regulation of TRAIL receptor R1 (DR4) and R2 (DR5). siRNA targeting of DR5 significantly attenuated the combination treatment-induced caspase-8 activation, mitochondrial dysfunction, and apoptotic cell death. Upon stimulation of cells with the combination treatment, NF-kappaB was activated. Moreover, siRNA targeting of NF-kappaB significantly attenuated the combination treatment-induced DR4 and DR5 expression and receptor-mediated caspase-8 activation. These results indicate that phytosphingosine sensitizes cancer cells to TRAIL through the synergistic up-regulation of DR4 and DR5 in an NF-kappaB-dependent fashion resulting in caspase-8 activation and subsequent mitochondrial dysfunction. These findings support the potential application of combination treatment with TRAIL and phytosphingosine in the treatment of cancers that are less sensitive to TRAIL.

Nuclear factor-kappaB maintains TRAIL resistance in human pancreatic cancer cells

Although it displays promising activity in other tumor models, the effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on human pancreatic cancer cells have not been comprehensively explored. We report that a majority of human pancreatic cancer cell lines (seven of nine) underwent apoptosis when they were exposed to recombinant human TRAIL in vitro. Characterization of surface TRAIL receptors by fluorescence-activated cell sorting showed that TRAIL-resistant cells (Panc-1 and HS766T) expressed lower levels of DR4 and DR5 than did TRAIL-sensitive cells. The proteasome inhibitor bortezomib (PS-341, Velcade) further increased TRAIL responsiveness in the TRAIL-sensitive cells and synergized with TRAIL to reverse resistance in Panc-1 and HS776T cells. The effects of bortezomib were mimicked by transfection with a small interfering RNA construct specific for the p65 subunit of nuclear factor-kappaB (NF-kappaB) or exposure to a selective chemical inhibitor of IKK (PS-1145). Silencing IkappaBalpha prevented TRAIL sensitization by PS-1145, confirming that IkappaBalpha mediated the effects of PS-1145. NF-kappaB inhibition resulted in down-regulation of BCL-XL and XIAP, and silencing either restored TRAIL sensitivity in TRAIL-resistant cells. Finally, therapy with TRAIL plus PS-1145 reversed TRAIL resistance in vivo to produce synergistic growth inhibition in orthotopic Panc-1 tumors. Together, our results show that NF-kappaB inhibits TRAIL-induced apoptosis in human pancreatic cancer cells and suggest that combination therapy with TRAIL and NF-kappaB inhibitors, such as bortezomib, PS-1145, or curcumin, should be considered as a possible treatment strategy in patients with pancreatic cancer.

Novel in vivo imaging shows up-regulation of death receptors by paclitaxel and correlates with enhanced antitumor effects of receptor agonist antibodies

Susceptibility to apoptosis by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is mediated through cognate death receptor signaling. We hypothesized that auto-amplification of this apparatus would enhance antitumor effects in vivo and could be optimized using the results obtained from novel imaging techniques. We therefore imaged mice bearing human colorectal cancer (Colo205) tumor xenografts with HGS-ETR1 and HGS-ETR2 agonist antibodies to TRAIL receptor-1 (TRAIL-R1) and TRAIL-R2, respectively, after radiolabeling the antibodies. Paclitaxel significantly increased in vivo expression of TRAIL-R1 and TRAIL-R2 in a time-dependent manner. The imaging results were confirmed by immunoblots for steady-state protein levels (>20-fold increase in TRAIL-R1 and TRAIL-R2 levels in tumor xenografts by 48 h after paclitaxel administration). TRAIL-R1 and TRAIL-R2 mRNA expression did not change, suggesting that these effects were posttranscriptional. Sequential treatment with paclitaxel followed by HGS-ETR1 or HGS-ETR2 after 48 h resulted in markedly enhanced antitumor activity against Colo205 mouse xenografts. Our experiments suggest that sequential taxane treatment followed by TRAIL-R agonist antibodies could be applied in the clinic, and that novel imaging techniques using radiolabeled receptor antibodies may be exploitable to optimize sequence timing and patient selection.

Proteasome inhibition sensitizes hepatocellular carcinoma cells to TRAIL by suppressing caspase inhibitors and AKT pathway

The ubiquitin-proteasome pathway is responsible for regulating cell cycle proteins, tumor-suppressor molecules, oncogenes, transcription factors, and pro- and anti-apoptotic proteins. The aim of this study is to evaluate the effects of proteasome inhibitors on human hepatocellular carcinoma (HCC) cells. HCC cells SK-Hep1, HLE and HepG2 were treated with the proteasome inhibitors MG132 and MG115. Our data showed that both inhibitors induce apoptosis in the three cell types tested in a dose-dependent manner. Moreover, subtoxic levels of MG132 and MG115 sensitized HCC cells to TRAIL-induced apoptosis. To investigate the mechanism of increased TRAIL sensitivity in HCC cells, we first examined surface expression of TRAIL and its receptors. MG132 upregulated TRAIL and its receptors (TRAIL-R1 and -R2) in SK-Hep1 and HLE, whereas MG115 upregulated them in SK-Hep1. MG132 downregulated expression of X-linked inhibitor of apoptosis protein (XIAP) in SK-Hep1 and HLE, and of survivin in all three cell-types. MG115 downregulated expression of XIAP in SK-Hep1, and survivin in SK-Hep1 and HepG2. Furthermore, MG132 downregulated phospho-AKT and its downstream target phospho-BAD, indicating that MG132 activated the mitochondrial apoptosis pathway by inhibiting phosphorylation of AKT and BAD. In conclusion, proteasome inhibitors induced apoptosis and augmented TRAIL sensitivity via both the IAP family and AKT pathways. Thus, combining proteasome inhibitors with a TRAIL agonist may provide a new therapeutic strategy for HCC.

Mechanisms of TRAIL-induced apoptosis in leukemic plasmacytoid dendritic cells

OBJECTIVE

Dendritic cells play a central role in regulating the innate and adaptive immune responses. Plasmacytoid dendritic cells (PDC) represent a newly identified kind of DC with specialized functions aimed at fighting against viral infections. Recently, we have shown that CD4+CD56+ malignancies were leukemia arising from PDC, with a particularly aggressive clinical course. Hence, we asked whether these malignant PDC could be killed via TRAIL, a death-inducing ligand that belongs to a new class of anticancer drugs currently under development.

MATERIALS AND METHODS

In this study we used a PDC line (GEN2.2) we recently developed from leukemic PDC as a model.

RESULTS

We show that GEN2.2 PDC are sensitive to TRAIL-induced apoptosis and can be killed in vitro by TRAIL-expressing NK cells. Our results suggest that TRAIL binds to Death Receptor 5 (DR5) expressed by GEN2.2 and induces apoptosis mainly via caspases 10, 8, and 3. Interestingly, during infection with influenza, DR5 decreases on GEN2.2 cell surface, which consequently become resistant to TRAIL-induced apoptosis. Moreover, we confirmed the expression of DR5 or DR4 on half of LPDC tested, suggesting the possibility to kill these cells via TRAIL. Hopefully, normal PDC expressed neither DR4 nor DR5.

CONCLUSION

These results suggest that TRAIL agonists represent a therapeutic alternative for the treatment of LPDC.

[Combined effect of recombinant mutant human TRAIL and daunorubicin in inducing apoptosis of leukemia cell and its mechanism]

The aim of study was to investigate the combined effect of recombinant mutant human TRAIL (rmhTRAIL) with daunorubicin (DNR) or alone on K562 and U937 leukemia cell lines and its mechanism. The fibroblasts (MRC-5) of normal-human embryonic lung were used as control cells. After being treated with rmhTRAIL and DNR or only with rmTRAIL, the cytotoxic effect and the apoptosis rate in K562, U937 cells were measured by MTT assay. The expression levels of TRAIL death receptor and TRAIL decoy receptor mRNA in these three cell lines were assayed by semiquantitive RT-PCR before and after treatment with DNR. The results indicated that K562 and U937 were sensitive to rmhTRIAL. DNR had synergistic inhibitory effect with rmhTRAIL on the growth of K562 and U937 cell lines (P < 0.05). The expression level of DR4 and DR5 mRNA was significantly higher in K562 and U937 with combined treatment of rmhTRAIL and DNR than that in those alone, while the expressions of DcR1 and DcR2 mRNA were not influenced. It is concluded that in vitro, rmhTRAIL alone or in combination with DNR can obviously inhibit the growth of leukemia cell lines and induce cell apoptosis, DNR and rmhTRAIL have a synergistic inhibitory effect on growth of K562 and U937. The mechanism may correlate with the up-regulation of DR4 and DR5 of K562 and U937.

[TRAIL impacts in growth and apoptosis of human ovarian carcinoma cell line SKOV3]

OBJECTIVE

To investigate the effect of TRAIL on growth and apoptosis of ovarian carcinoma cell line SKOV3.

METHODS

The effects of TRAIL alone and/or associating with DDP to treat on SKOV3 cells growth inhibition were measured by MTT assay, and the changes of DR4 and DR5 mRNA were detected by RT-PCR technique. The cell cycle and apoptosis index were analyzed by technique of Flow Cytometry (FCM).

RESULTS

The soluble TRAIL protein had the inhibiting effect on the growth SKOV3 cells. The DDP increased the ability of TRAIL to SKOV3 cell growth inhibition. The apoptotic indexes (AI) of SKOV3 cells detected by FCM were 5.9%, 13.4% and 39.5% for control group, TRAIL group and TRAIL plus DDP group, respectively. The DDP increased the DR5 expressing in SKOV3 cells by 1.95 folds than control group and by 1.54 times for the DR4 expressing than the control group (P < 0.05).

CONCLUSIONS

The soluble TRAIL has the effect on inhibiting the growth of SKOV3 cells. The combination use of TRAIL and DDP increases significantly the growth-inhibiting ratio to SKOV3 cells. The AI of SKOV3 cell is raised after TRAIL intervening in. The DDP can increase the expressions of DR4 and DR5 in SKOV3 cells.

[Relationship between death receptor 5 and apoptosis in hepatocellular carcinoma]

OBJECTIVE

To investigate the antitumor efficacy of death receptor 5, its ligand (TRAIL) and DR5mAb in human hepatocellular carcinoma.

METHODS

Expression of DR5 in the HCC cell lines HepG2, SMMC 7721 and normal human liver cell line LO2 was measured at mRNA and protein level by semi-quantitative RT-PCR and Western blot, respectively. MTT method was used to measure the cell viability and flow cytometry assay was used to detect apoptosis so as to observe the inhibitory effect of TRAIL and DR5mAb on HCC cells.

RESULTS

Death receptor 5 was highly expressed in the HCC cell lines, but rarely expressed in normal human liver cell line (P < 0.01). With the increase of TRAIL concentration, the cell viability of HCC cells decreased gradually. However, when the concentration of TRAIL was above 1000 ng/ml, HCC cells were resistant to TRAIL, but still sensitive to DR5mAb. After incubation with DR5mAb (1000 ng/ml) for 24 h, the rate of apoptosis in HCC cells reached to 52.45% +/- 0.57%, which was higher than that incubated with TRAIL under the same condition (14.74% +/- 0.48%) (P < 0.05). The cell viability of normal human liver cell line treated with TRAIL tended to decline with the increase of the concentration, which was significantly different from that of matched control group. But DR5mAb had little effect on normal human liver cell line.

CONCLUSION

Death receptor 5 as a target plays an important role in the course of HCC apoptosis induction. Agonistic monoclonal antibody specific for human DR5 can selectively and effectively kill hepatocellular carcinoma cells in vitro, while is not harmful to normal human hepatocytes. It reveals that DR5mAb might provide a new direction in hepatocellular carcinoma treatment research.

Differential susceptibility to TRAIL of normal versus malignant human urothelial cells

Comparing normal human urothelial (NHU) cells to a panel of six representative urothelial cell carcinoma (UCC)-derived cell lines, we showed that while TRAIL receptor expression patterns were similar, susceptibility to soluble recombinant crosslinked TRAIL fell into three categories. 4/6 carcinoma lines were sensitive, undergoing rapid and extensive death; NHU and 253J cells were partially resistant and HT1376 cells, like normal fibroblasts, were refractory. Both normal and malignant urothelial cells underwent apoptosis via the same caspase-8/9-mediated mechanism. Rapid receptor downregulation was a mechanism for evasion by some UCC cells. TRAIL resistance in malignant urothelial cells was partially dependent on FLIP(L) and was differentially mediated by p38(MAPK), whereas in normal cells, resistance was mediated by NF-kappaB. Importantly, extensive killing of UCC cells could be induced using noncrosslinked TRAIL after prolonged exposure, with no damage to their homologous, normal urothelial cell counterparts.

[Study of TRAIL receptors expression on the mononuclear cells from multiple myeloma patients and KM3 cells]

OBJECTIVE

To study the differential expression of four TRAIL receptors on bone marrow mononuclear cells (BMMNC) from multiple myeloma (MM) patients and myeloma cell line KM3 cells, to compare their altered expressions after chemotherapy and to explore the mechanisms by which TRAIL selectively kills tumor cells.

METHODS

Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry were used to investigate the expression of four TRAIL receptors on BMMNCs in 23 MM patients, KM3 cells and 15 controls, and the changes of their expression pattern after chemotherapy and after incubation of KM3 cells with sub-clinical concentration of doxorubicin.

RESULTS

DR4 and DR5 were highly expressed on KM3 cells with no expression of DcR1 and DcR2. Expressions of DR4 and DR5 on BMMNCs from MM patients were higher and expression of DcR1 and DcR2 were lower than that of controls (P < 0.05). The expression of DR5 on MM and KM3 cells was up-regulated after chemotherapy and exposure to doxorubicin (P < 0. 05).

CONCLUSIONS

The expressions of four TRAIL receptors on myeloma cells and normal controls were different, which might account for the selective killing effect of TRAIL on MM cells. Up-regulated DR5 on KM3 cells after incubating with doxorubicin and after chemotherapy suggests the cytotoxic agents might enhance the apoptosis of MM cells.

[Expression and its significance of TRAIL and its receptors in cells of patients with acute myeloid leukemia]

This study was aimed to detect the expression of TNF related apoptosis-inducing ligand (TRAIL) and its receptors on acute myeloid leukemic (AML) cells, and explore its possible role in leukemia therapy. RT-PCR and flow cytometry were used to detect the expression of TRAIL and its receptors on AML cells of 39 cases (patient group), AML cells of 18 cases with complete remission (CR group) and BMMNC or PBMNC of 21 normal persons (control group). The results showed that (1) TRAIL, DR4 and DR5 were highly expressed in both patient group and CR group, while the DcR1 and DcR2 were poorly expressed. (2) The level of DR5 expression in CR group was higher than that in patient group. (3) The level of DR5 was higher than DR4 in both patient group and CR group. (4) TRAIL and its receptors were expressed similarly in different subtypes of AML. In conclusion, there are differences between the expressions of TRAIL and its receptors in AML cells. DR5 may play an important role in TRAIL-inducing apoptosis of AML cells.