Elevated NF-kappaB responses and FLIP levels in leukemic but not normal lymphocytes: reduction by salicylate allows TNF-induced apoptosis

NF-κB in biology and targeted therapy: new insights and translational implications

NF-κB signaling has been discovered for nearly 40 years. Initially, NF-κB signaling was identified as a pivotal pathway in mediating inflammatory responses. However, with extensive and in-depth investigations, researchers have discovered that its role can be expanded to a variety of signaling mechanisms, biological processes, human diseases, and treatment options. In this review, we first scrutinize the research process of NF-κB signaling, and summarize the composition, activation, and regulatory mechanism of NF-κB signaling. We investigate the interaction of NF-κB signaling with other important pathways, including PI3K/AKT, MAPK, JAK-STAT, TGF-β, Wnt, Notch, Hedgehog, and TLR signaling. The physiological and pathological states of NF-κB signaling, as well as its intricate involvement in inflammation, immune regulation, and tumor microenvironment, are also explicated. Additionally, we illustrate how NF-κB signaling is involved in a variety of human diseases, including cancers, inflammatory and autoimmune diseases, cardiovascular diseases, metabolic diseases, neurological diseases, and COVID-19. Further, we discuss the therapeutic approaches targeting NF-κB signaling, including IKK inhibitors, monoclonal antibodies, proteasome inhibitors, nuclear translocation inhibitors, DNA binding inhibitors, TKIs, non-coding RNAs, immunotherapy, and CAR-T. Finally, we provide an outlook for research in the field of NF-κB signaling. We hope to present a stereoscopic, comprehensive NF-κB signaling that will inform future research and clinical practice.

PTTG1 is involved in TNF-α-related hepatocellular carcinoma via the induction of c-myc

Hepatocellular carcinoma (HCC) is a malignant disease caused by a variety of factors. However, the genomic and molecular aberrations in HCC are largely unknown. Herein, pituitary tumor transforming gene 1 (PTTG1) was discovered as a potential inflammation‐related oncogene in HCC, and its functions and molecular mechanisms were investigated. mRNA expression microarray, real‐time polymerase chain reaction (PCR), immunohistochemistry, and western blotting analyses revealed that PTTG1 is upregulated in HCC. Further in vitro and in vivo studies indicated that the proinflammatory cytokine tumor necrosis factor‐α (TNF‐α) induces PTTG1 expression, and PTTG1 was found to upregulate c‐myc, a well‐known oncogene. Downregulation of PTTG1 reduced c‐myc and proliferating cell nuclear antigen (PCNA) expression and inhibited cell proliferation. Interestingly, inhibition of c‐myc by 10058‐F4 did not affect PTTG1, which suggests that PTTG1 regulates c‐myc expression. Furthermore, PTTG1 expression levels are inversely correlated with HCC patient survival, indicating an independent prognostic biomarker for patients with HCC. Our data demonstrate that PTTG1 is involved in TNF‐α‐related HCC via c‐myc induction and that PTTG1 may be a potential therapeutic target for HCC.

Icaritin Sensitizes Human Glioblastoma Cells to TRAIL-Induced Apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been considered to be one of the most promising candidates in research on treatments for cancer, because it induces apoptosis in a wide variety of cancer cells but not in most normal human cell types. However, many cells including glioblastoma (GBM) cells are resistant to TRAIL-induced apoptosis, which limits the potential application of TRAIL in cancer therapy. Icaritin, a hydrolytic product of icariin from Epimedium Genus, has been identified as a potential therapeutic and preventive agent in renal cell carcinoma and breast cancer. In this study, we investigated whether Icaritin treatment could modulate TRAIL-induced apoptosis in GBM. The effect of icaritin on TRAIL sensitivity was assessed in human GBM U87 and U373 cells. The underlying regulatory cascades were approached by biochemical and pharmacological strategies. We found that nontoxic concentration of icaritin alone had no significant effect on the level of apoptosis, but a combination treatment of TRAIL and icaritin caused a significantly more profound apoptosis. The sensitization was accompanied by c-FLIP down-regulation and inhibition of NF-κB activity. Studies have further demonstrated that silencing NF-κB alone was sufficient to down-regulate c-FLIP expression and sensitized both tested cells to TRAIL-induced apoptosis. These data suggest that icaritin sensitizes TRAIL-induced tumor cell apoptosis via suppression of NF-κB-dependent c-FLIP expression, providing in vitro evidence supporting the notion that icaritin is a potential sensitizer of TRAIL in anticancer therapy against human GBM.

Structure and Stability of Long Rod-like Dodecyltrimethylammonium Chloride Micelles in Solutions of Hydroxybenzoates: A Molecular Dynamics Simulation Study

The relative position of the hydroxylic and carboxylic groups in the isomeric hydroxybenzoate (HB) anions is experimentally known to have a large impact on the thermodynamics of micellization of cationic surfactants, such as dodecyltrimethylammonium chloride (DTAC), and on the structure of the resulting micelles. To understand the effect of the different isomers on the molecular level, we employed atomistic molecular dynamics simulations to study systems containing infinitely long cylindrical DTAC micelles in aqueous solutions of the sodium salts of all three isomers of HB at a temperature and a pressure of 298.15 K and 1 atm. In all studied systems, the number of DTAC unimers is identical to the number of HB anions. At this concentration, the initially cylindrical micelles remain stable, irrespective of the nature of the isomer, whereas micelles rapidly disintegrated in the absence of HB anions. The HB isomers decrease the line density of unimers along the micellar axis and its concomitant thickness in the order o-HB > m-HB > p-HB. It is further observed that o-HB anions penetrate more deeply into the micellar core, induce a more ordered internal structure of the micelle, and are oriented more strongly than the other two isomers. In addition, the ortho isomer shows two different preferential orientations with respect to the radial direction of the cylindrical micelle; it can either be incorporated almost completely into the micelle or it can be attached through hydrogen bonding to one of those o-HB anions that are already incorporated into the micelle, and thus stick out of the micellar surface.

Sodium salicylate reduces the level of GABAB receptors in the rat's inferior colliculus

Previous studies have indicated that sodium salicylate (SS) can cause hearing abnormalities through affecting the central auditory system. In order to understand central effects of the drug, we examined how a single intraperitoneal injection of the drug changed the level of subunits of the type-B γ-aminobutyric acid receptor (GABAB receptor) in the rat's inferior colliculus (IC). Immunohistochemical and western blotting experiments were conducted three hours following a drug injection, as previous studies indicated that a tinnitus-like behavior could be reliably induced in rats within this time period. Results revealed that both subunits of the receptor, GABABR1 and GABABR2, reduced their level over the entire area of the IC. Such a reduction was observed in both cell body and neuropil regions. In contrast, no changes were observed in other brain structures such as the cerebellum. Thus, a coincidence existed between a structure-specific reduction in the level of GABAB receptor subunits in the IC and the presence of a tinnitus-like behavior. This coincidence likely suggests that a reduction in the level of GABAB receptor subunits was involved in the generation of a tinnitus-like behavior and/or used by the nervous system to restore normal hearing following application of SS.

The Histone Deacetylase Inhibitor Trichostatin A Sensitizes Human Renal Carcinoma Cells to TRAIL-Induced Apoptosis through Down-Regulation of c-FLIPL

Histone acetylation plays a critical role in the regulation of transcription by altering the structure of chromatin, and it may influence the resistance of some tumor cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) by regulating the gene expression of components of the TRAIL signaling pathway. In this study, we investigated the effects and molecular mechanisms of trichostatin A (TSA), a histone deacetylase inhibitor, in sensitizing TRAIL-induced apoptosis in Caki human renal carcinoma cells. Our results indicate that nontoxic concentrations of TSA substantially enhance TRAIL-induced apoptosis compared with treatment with either agent alone. Cotreatment with TSA and TRAIL effectively induced cleavage of Bid and loss of mitochondrial membrane potential (MMP), which was associated with the activation of caspases (-3, -8, and -9) and degradation of poly (ADP-ribose) polymerase (PARP), contributing toward the sensitization to TRAIL. Combined treatment with TSA and TRAIL significantly reduced the levels of the cellular Fas-associated death domain (FADD)-like interleukin-1β-converting enzyme (FLICE) inhibitory protein (c-FLIP), whereas those of death receptor (DR) 4, DR5, and FADD remained unchanged. The synergistic effect of TAS and TRAIL was perfectly attenuated in c-FLIP_L-overexpressing Caki cells. Taken together, the present study demonstrates that down-regulation of c-FLIP contributes to TSA-facilitated TRAIL-induced apoptosis, amplifying the death receptor, as well as mitochondria-mediated apoptotic signaling pathways.

Understanding life and death decisions in human leukaemias

Human leukaemia cells have an often unique ability to either undergo apoptotic cell death mechanisms or, at other times, undergo proliferative expansion, sometimes to the same stimulus such as the pluripotent cytokine TNFα (tumour necrosis factor α). This potential for life/death switching helps us to understand the molecular signalling machinery that underlies these cellular processes. Furthermore, looking at the involvement of these switching signalling pathways that may be aberrant in leukaemia informs us of their importance in cancer tumorigenesis and how they may be targeted pharmacologically to treat various types of human leukaemias. Furthermore, these important pathways may play a crucial role in acquired chemotherapy resistance and should be studied further to overcome in the clinic many drug-resistant forms of blood cancers. In the present article, we uncover the relationship that exists in human leukaemia life/death switching between the anti-apoptotic pro-inflammatory transcription factor NF-κB (nuclear factor κB) and the cytoprotective antioxidant-responsive transcription factor Nrf2 (nuclear factor-erythroid 2-related factor 2). We also discuss recent findings that reveal a major role for Btk (Bruton's tyrosine kinase) in both lymphocytic and myeloid forms of human leukaemias and lymphomas.

Comparison of hematopoietic cancer stem cells with normal stem cells leads to discovery of novel differentially expressed SSRs

Tandem repeat expansion in the transcriptomics level has been considered as one of the underlying causes of different cancers. Cancer stem cells are a small portion of cancer cells within the main neoplasm and can remain alive during chemotherapy and re-induce tumor growth. The EST-SSR background of cancer stem cells and possible roles of expressed SSRs in altering normal stem cells to cancer ones have not been investigated yet. Here, SSR distributions in hematopoietic normal and cancer stem cells were compared based on the expressed EST-SSR. One hundred eighty nine and 223 EST-SSRs were identified in cancer and normal stem cells, respectively. The EST-SSR expression pattern was significantly different between normal and cancer stem cells. The frequencies of AC/GT and TA/TA EST-SSRs were about 10% higher in cancer than normal stem cells. Remarkably, the number of triplets in cancer stem cells was 1.5 times higher than that in normal stem cells. GAT EST-SSR was frequent in cancer stem cells, but, conversely, normal stem cells did not express GAT EST-SSR. We suggest this EST-SSR as a novel triplet in cancer stem cell induction. Translating EST-SSRs to amino acids demonstrated that Asp and Ile were more abundant in cancer stem cells compared to normal stem cells. Finally, Gene Ontology (GO) enrichment analysis was carried out on genes containing triplet SSRs and showed that SSRs intentionally visit some specific GO classes. Interestingly, a NF-kappa (nuclear factor-kB) binding transcription factor was significantly hit by SSR instability which is a hallmark for leukemia stem cells. NF-kappa is an over represented transcription factor during cancer progression. It seems that there is a crosstalk between the NF-kB transcription factor and expressed GAT tandem repeat which negatively regulate apoptosis. In addition to better understanding of tumorigenesis, the findings of this study offer new DNA markers for diagnostic purposes and identifying at risk populations. In addition, a new approach for gene discovery in cancer by target analysis of differentially expressed EST-SSRs between cancer and normal stem cells is presented here.

Targeting nuclear factor-kappa B to overcome resistance to chemotherapy

Intrinsic or acquired resistance to chemotherapeutic agents is a common phenomenon and a major challenge in the treatment of cancer patients. Chemoresistance is defined by a complex network of factors including multi-drug resistance proteins, reduced cellular uptake of the drug, enhanced DNA repair, intracellular drug inactivation, and evasion of apoptosis. Pre-clinical models have demonstrated that many chemotherapy drugs, such as platinum-based agents, antracyclines, and taxanes, promote the activation of the NF-κB pathway. NF-κB is a key transcription factor, playing a role in the development and progression of cancer and chemoresistance through the activation of a multitude of mediators including anti-apoptotic genes. Consequently, NF-κB has emerged as a promising anti-cancer target. Here, we describe the role of NF-κB in cancer and in the development of resistance, particularly cisplatin. Additionally, the potential benefits and disadvantages of targeting NF-κB signaling by pharmacological intervention will be addressed.

Kurarinone promotes TRAIL-induced apoptosis by inhibiting NF-κB-dependent cFLIP expression in HeLa cells

This study was designed to investigate the effects of the prenylated flavonoid kurarinone on TNF-related apoptosis inducing ligand (TRAIL)-induced apoptosis and its underlying mechanism. A low dose of kurarinone had no significant effect on apoptosis, but this compound markedly promoted tumor cell death through elevation of Bid cleavage, cytochrome c release and caspase activation in HeLa cells treated with TRAIL. Caspase inhibitors inhibited kurarinone-mediated cell death, which indicates that the cytotoxic effect of this compound is mediated by caspase-dependent apoptosis. The cytotoxic effect of kurarinone was not associated with expression levels of Bcl-2 and IAP family proteins, such as Bcl-2, Bcl-x_L, Bid, Bad, Bax, XIAP, cIAP-1 and cIAP-2. In addition, this compound did not regulate the death-inducing receptors DR4 and DR5. On the other hand, kurarinone significantly inhibited TRAIL-induced IKK activation, IκB degradation and nuclear translocation of NF-κB, as well as effectively suppressed cellular FLICE-inhibitory protein long form (cFLIP_L) expression. The synergistic effects of kurarinone on TRAIL-induced apoptosis were mimicked when kurarinone was replaced by the NF-κB inhibitor withaferin A or following siRNA-mediated knockdown of cFLIP_L. Moreover, cFLIP overexpression effectively antagonized kurarinone-mediated TRAIL sensitization. These data suggest that kurarinone sensitizes TRAIL-induced tumor cell apoptosis via suppression of NF-κB-dependent cFLIP expression, indicating that this compound can be used as an anti-tumor agent in combination with TRAIL.

BTK inhibitor ibrutinib is cytotoxic to myeloma and potently enhances bortezomib and lenalidomide activities through NF-κB

Ibrutinib (previously known as PCI-32765) has recently shown encouraging clinical activity in chronic lymphocytic leukaemia (CLL) effecting cell death through inhibition of Bruton's tyrosine kinase (BTK). In this study we report for the first time that ibrutinib is cytotoxic to malignant plasma cells from patients with multiple myeloma (MM) and furthermore that treatment with ibrutinib significantly augments the cytotoxic activity of bortezomib and lenalidomide chemotherapies. We describe that the cytotoxicity of ibrutinib in MM is mediated via an inhibitory effect on the nuclear factor-κB (NF-κB) pathway. Specifically, ibrutinib blocks the phosphorylation of serine-536 of the p65 subunit of NF-κB, preventing its nuclear translocation, resulting in down-regulation of anti-apoptotic proteins Bcl-xL, FLIP(L) and survivin and culminating in caspase-mediated apoptosis within the malignant plasma cells. Taken together these data provide a platform for clinical trials of ibrutinib in myeloma and a rationale for its use in combination therapy, particularly with bortezomib.

Understanding the role of miRNA in regulating NF-κB in blood cancer

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by binding to complementary sequences in mRNAs encoding downstream target genes. A large variety of cellular processes, including differentiation, development, apoptosis and cell cycle progression, are dependent on miRNA-mediated suppression of gene expression for their regulation. As such, it is unsurprising that these small RNA molecules are associated with signaling networks that are often altered in various diseases, including many blood cancers. One such network is the nuclear factor-κB (NF-κB) pathways that universally stimulate transcription of proteins which generally promote cell survival, inhibit apoptosis, allow cellular growth, induce angiogenesis and generate many pro-inflammatory responses. The NF-κB signalling pathway is often constitutively activated in blood cell cancers including myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML), acute lymphocytic leukaemia (ALL), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), lymphomas and in multiple myeloma (MM). This review focuses on the function of miRNAs that directly target NF-κB signaling cascade. Recent findings that connect this pathway through various miRNA families to human blood cancers are reviewed, and support for using miRNA-based therapy as a novel method to counteract this tumour-promoting signalling event is discussed.

TNF alpha antagonist therapy and safety monitoring

OBJECTIVES

To develop and/or update fact sheets about TNFα antagonists treatments, in order to assist physicians in the management of patients with inflammatory joint disease.

METHODS

1. selection by a committee of rheumatology experts of the main topics of interest for which fact sheets were desirable; 2. identification and review of publications relevant to each topic; 3. development and/or update of fact sheets based on three levels of evidence: evidence-based medicine, official recommendations, and expert opinion. The experts were rheumatologists and invited specialists in other fields, and they had extensive experience with the management of chronic inflammatory diseases, such as rheumatoid. They were members of the CRI (Club Rhumatismes et Inflammation), a section of the Société Francaise de Rhumatologie. Each fact sheet was revised by several experts and the overall process was coordinated by three experts.

RESULTS

Several topics of major interest were selected: contraindications of TNFα antagonists treatments, the management of adverse effects and concomitant diseases that may develop during these therapies, and the management of everyday situations such as pregnancy, surgery, and immunizations. After a review of the literature and discussions among experts, a consensus was developed about the content of the fact sheets presented here. These fact sheets focus on several points: 1. in RA and SpA, initiation and monitoring of TNFα antagonists treatments, management of patients with specific past histories, and specific clinical situations such as pregnancy; 2. diseases other than RA, such as juvenile idiopathic arthritis; 3. models of letters for informing the rheumatologist and general practitioner; 4. and patient information.

CONCLUSION

These TNFα antagonists treatments fact sheets built on evidence-based medicine and expert opinion will serve as a practical tool for assisting physicians who manage patients on these therapies. They will be available continuously at www.cri-net.com and updated at appropriate intervals.

TNF mediates the sustained activation of Nrf2 in human monocytes

Modulation of monocyte function is a critical factor in the resolution of inflammatory responses. This role is mediated mainly by the production of TNF-α. Investigations of the actions of TNF have mostly focused on acute activation of other cell types such as fibroblasts and endothelial cells. Less is known about the effects of TNF on monocytes themselves, and little is known about the regulation of cell responses to TNF beyond the activation of NF-κB. In this study, we investigated the regulation of NF-E2-related factor 2 (Nrf2) cyctoprotective responses to TNF in human monocytes. We found that in monocytes TNF induces sustained Nrf2 activation and Nrf2 cytoprotective gene induction in a TNFR1-dependent manner. Under TNF activation, monocytes increased their expression of Nrf2-dependent genes, including NAD(P)H:quinone oxidoreductase 1 and glutamyl cysteine ligase modulatory, but not heme oxygenase-1. We also showed that autocrine TNF secretion was responsible for this sustained Nrf2 response and that Nrf2 activation by TNF was mediated by the generation of reactive oxygen species. Moreover, we showed that Nrf2-mediated gene induction can modulate TNF-induced NF-κB activation. These results show for the first time, to our knowledge, that TNF modulates prolonged Nrf2-induced gene expression, which in turn regulates TNF-induced inflammatory responses.

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.

High basal nuclear levels of Nrf2 in acute myeloid leukemia reduces sensitivity to proteasome inhibitors

Proteasome inhibitors such as bortezomib exhibit clinical efficacy in multiple myeloma, but studies in acute myeloid leukemia (AML) have been disappointing to date. The apparent failure in AML likely reflects a lack of biological understanding that might clarify applications of proteosome inhibitors in this disease. Here we show that AML cells are considerably less sensitive than control noncancerous cells to bortezomib-induced cytotoxicity, permitting most bortezomib-treated AML cells to survive treatment. We traced reduced bortezomib sensitivity to increased basal levels of nuclear Nrf2, a transcription factor that stimulates protective antioxidant enzymes. Bortezomib stimulates cytotoxicity through accumulation of reactive oxygen species (ROS) but elevated basal levels of nuclear Nrf2 present in AML cells reduced ROS levels, permitting AML cells to survive drug treatment. We further found that the Nrf2 transcriptional repressor Bach1 is rapidly inactivated by bortezomib, allowing rapid induction of Nrf2-regulated cytoprotective and detoxification genes that protect AML cells from bortezomib-induced apoptosis. By contrast, nonmalignant control cells lacked constitutive activation of Nrf2, such that bortezomib-mediated inactivation of Bach1 led to a delay in induction of Nrf2-regulated genes, effectively preventing the manifestation of apoptotic protection that is seen in AML cells. Together, our findings argue that AML might be rendered sensitive to proteasome inhibitors by cotreatment with either an Nrf2-inhibitory or Bach1-inhibitory treatment, rationalizing a targeted therapy against AML.

Catalase suppression-mediated H(2)O(2) accumulation in cancer cells by wogonin effectively blocks tumor necrosis factor-induced NF-κB activation and sensitizes apoptosis

Tremendous effort has been made to improve the anticancer value of tumor necrosis factor (TNF). In this study, we show that wogonin, a flavonoid isolated from Huang-Qin (Scutellaria baicalensis), synergistically sensitizes cancer cells derived from the cervix, ovary and lung to TNF-induced apoptosis, which was associated with inhibition of catalase activity and an increase of cellular hydrogen peroxide (H(2)O(2)). Wogonin-induced reactive oxygen species block TNF-induced NF-κB activation through inhibiting phosphorylation on the NF-κB p65 subunit and consequently the DNA binding of NF-κB. In addition, wogonin suppressed the expression of the antiapoptotic factor c-FLIP, which is accompanied with potentiation of TNF-induced caspase 8 activation that initiates apoptosis. Importantly, wogonin did not sensitize normal bronchial epithelial cells to TNF-induced cell death, which was associated with the defect in induction of H(2)O(2). Thus, wogonin specifically sensitizes cancer cells to TNF-induced cytotoxicity through H(2)O(2)-mediated NF-κB suppression and apoptosis activation. Our data provide important insights into the molecular mechanism underlying wogonin's anticancer activity, and suggest this common flavonoid could be used as a TNF adjuvant for cancer therapy.

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.

NF-kappaB-inhibited acute myeloid leukemia cells are rescued from apoptosis by heme oxygenase-1 induction

Despite high basal NF-kappaB activity in acute myeloid leukemia (AML) cells, inhibiting NF-kappaB in these cells has little or no effect on inducing apoptosis. We previously showed that heme oxygenase-1 (HO-1) underlies this resistance of AML to tumor necrosis factor-induced apoptosis. Here, we describe a mechanism by which HO-1 is a silent antiapoptotic factor only revealed when NF-kappaB is inhibited, thus providing a secondary antiapoptotic mechanism to ensure AML cell survival and chemoresistance. We show that inhibition of NF-kappaB increased HO-1 expression in primary AML cells compared with that of nonmalignant cells. In addition, we observed this suppressed HO-1 level in AML cells compared with CD34(+) nonmalignant control cells. Using chromatin immunoprecipitation assay and small interfering RNA knockdown, we showed that the NF-kappaB subunits p50 and p65 control this suppression of HO-1 in AML cells. Finally, we showed that inhibition of HO-1 and NF-kappaB in combination significantly induced apoptosis in AML cells but not in noncancerous control cells. Thus, NF-kappaB inhibition combined with HO-1 inhibition potentially provides a novel therapeutic approach to treat chemotherapy-resistant forms of AML.

High expression levels of IKKalpha and IKKbeta are necessary for the malignant properties of liver cancer

IKK-NF-kappaB signaling is regarded as an important factor in hepatocarcinogenesis and a potential target for liver cancer therapy. Therefore, in this study, we analyzed the expression of mRNAs encoding components and targets of NF-kappaB signaling including IKKalpha, IKKbeta, RANK, RANKL, OPG, CyclinD3, mammary serine protease inhibitor (Maspin), CyclinD1, c-FLIP, Bcl-xl, Stat3, Cip1 and Cip2 by real-time PCR in 40 patients with liver cancer. After statistical analysis, 7 indices including IKKalpha, IKKbeta, RANK, Maspin, c-FLIP, Cip2 and cyclinD1 were found to show significant differences between tumor tissue and its corresponding adjacent tissue. When IKKalpha and IKKbeta were downregulated in the hepatocellular carcinoma (HCC) cell lines of MHCC-97L and MHCC-97H in vitro, the numbers of BrdU positive cells were decreased in both IKKalpha and IKKbeta knockdown cells. Levels of apoptosis were also investigated in IKKalpha and IKKbeta knockdown cells. The growth of HCC was inhibited in the subcutaneous implantation model, and lung metastatogenesis was also significantly inhibited in the kidney capsule transplantation model. Downregulation of IKKalpha and IKKbeta in HCC cultured in vitro revealed that increased Maspin, OPG and RANKL expression was associated with metastasis of HCC. These findings were associated with downregulation of Bcl-XL and c-FLIP, which may be the reason for increased apoptosis. The therapeutic effect of IKKalpha and IKKbeta downregulation depends on extent of NF-kappaB inhibition and the malignant nature of the HCC. We anticipate that IKK-targeted gene therapy can be used in the treatment of HCC, a cancer that is notoriously resistant to radiation and chemotherapy.

Oxaprozin-induced apoptosis on CD40 ligand-treated human primary monocytes is associated with the modulation of defined intracellular pathways

The modulation of CD40L activity might represent a promising therapeutic target to reduce monocyte inflammatory functions in chronic diseases, such as rheumatoid arthritis. In the present study, we investigated the possible influence of nonsteroidal anti-inflammatory drugs (NSAIDs) on CD40L-induced monocyte survival. Monocytes were isolated from buffy coats by using Ficoll-Percoll gradients. Monocyte apoptosis was evaluated by fluorescence microscopy on cytopreps stained with acridine orange or using flow cytometry analysis of Annexin-V and Propidium Iodide staining. Akt and NF-kappaB activation was assessed using western blot. Caspase 3 activity was determined spectrophotometrically. Among different NSAIDs, only oxaprozin dose-dependently increased apoptosis of CD40L-treated monocytes. Oxaprozin pro-apoptotic activity was associated with the inhibition of CD40L-triggered Akt and NF-kappaB phosphorylation and the activation of caspase 3. In conclusion, our data suggest that oxaprozin-induced apoptosis in CD40L-treated human monocytes is associated with previously unknown cyclooxygenase (COX)-independent pathways. These intracellular proteins might be promising pharmacological targets to increase apoptosis in CD40L-treated monocytes.

Tumor necrosis factor and cancer, buddies or foes?

Tumor necrosis factor (TNF) is a multifunctional cytokine that plays important roles in diverse cellular events such as cell survival, proliferation, differentiation, and death. As a pro-inflammatory cytokine, TNF is secreted by inflammatory cells, which may be involved in inflammation-associated carcinogenesis. TNF exerts its biological functions through activating distinct signaling pathways such as nuclear factor-kappaB (NF-kappaB) and c-Jun N-terminal kinase (JNK). NF-kappaB is a major cell survival signal that is anti-apoptotic, whereas sustained JNK activation contributes to cell death. The crosstalk between the NF-kappaB and JNK is involved in determining cellular outcomes in response to TNF. In regard to cancer, TNF is a double-dealer. On one hand, TNF could be an endogenous tumor promoter, because TNF stimulates the growth, proliferation, invasion and metastasis, and tumor angiogenesis of cancer cells. On the other hand, TNF could be a cancer killer. The property of TNF in inducing cancer cell death renders it a potential cancer therapeutic, although much work is needed to reduce its toxicity for systematic TNF administration. Recent studies have focused on sensitizing cancer cells to TNF-induced apoptosis through inhibiting survival signals such as NF-kappaB, by combined therapy. In this article we provide an overview of the roles of TNF-induced signaling pathways in cancer biology with specific emphasis on carcinogenesis and cancer therapy.

NF-kappaB and cancer-identifying targets and mechanisms

A connection between inflammation and carcinogenesis has long been known, but the precise mechanisms are just beginning to be understood. NF-kappaB proteins, transcription factors which integrate stress signals and orchestrate immune responses, have also recently been linked to carcinogenesis. Hallmarks of cancer development include self-sufficiency in growth signals, insensitivity to growth-inhibitors, evasion of apoptosis, limitless replicative potential, tissue invasion and metastasis, and sustained angiogenesis. NF-kappaB signaling has been implicated in each of these hallmarks, and recent experimental studies have illuminated the mechanistic pathways by which NF-kappaB signaling contributes to these aspects of carcinogenesis. This review will focus on recent experimental data supporting the hypothesis that inflammation promotes carcinogenesis, and that NF-kappaB signaling is at the heart of such inflammation.

HO-1 underlies resistance of AML cells to TNF-induced apoptosis

In human monocytes, tumor necrosis factor (TNF) induces a proinflammatory response. In NF-κB–inhibited monocytes, TNF stimulates cell death/apoptosis. In the present study, we analyzed the response of acute myeloid leukemia (AML) cells to TNF stimulation in conjunction with NF-κB inhibition. In all AML-derived cells tested, NF-κB–inhibited cells were resistant to TNF-induced apoptosis. Further investigation revealed that the cytoprotective gene heme oxygenase-1 (HO-1) was induced in NF-κB–inhibited AML cells in response to TNF stimulation, and HO-1 was responsible for the resistance of AML cells to the cytotoxic actions of TNF. Moreover, after transfection with HO-1 siRNA, the resistance to TNF-induced cell death signals of AML cells was removed. The HO-1 promoter region contains antioxidant-response elements that can bind the transcription factor NF-E2–related factor 2 (Nrf2). We further demonstrated that Nrf2 was activated by TNF under NF-κB–inhibited conditions, to play the major role in up-regulating HO-1 expression and ultimately the fate of AML cells. These results demonstrate a novel mechanism by which TNF-induced cell death is inhibited in AML cells through the induction of HO-1, via Nrf2 activation.