Inhibition of Nuclear Factor κB Activation Attenuates Apoptosis Resistance in Lymphoid Cells

Current perspectives of mitochondria-targeted antioxidants in cancer prevention and treatment

Oxidative stress nearly always accompanies all stages of cancer development. At the early stages, antioxidants may help to reduce reactive oxygen species (ROS) production and exhibit anticarcinogenic effects. In the later stages, ROS involvement becomes more complex. On the one hand, ROS are necessary for cancer progression and epithelial-mesenchymal transition. On the other hand, antioxidants may promote cancer cell survival and may increase metastatic frequency. The role of mitochondrial ROS in cancer development remains largely unknown. This paper reviews experimental data on the effects of both endogenous and exogenous antioxidants on cancerogenesis focusing on the development and application of mitochondria-targeted antioxidants. We also discuss the prospects for antioxidant cancer therapy, focusing on the use of mitochondria-targeted antioxidants.

Application of the nuclear factor-kappaB inhibitor BAY 11-7085 for the treatment of endometriosis: an in vitro study

Most of the current medical treatments for endometriosis aim to downregulate estrogen activity. However, a high recurrence rate after medical treatment has been the most significant problem. BAY 11-7085, a soluble inhibitor of NK-kappaB activation, has been shown to inhibit cell proliferation and induce apoptosis of a variety of cells. To examine the potential application of BAY 11-7085 in the treatment of endometriosis, we investigated the effects of this agent on the cell proliferation and apoptosis of cultured ovarian endometriotic cyst stromal cells (ECSCs) by a modified methylthiazole tetrazolium assay, a 5-bromo-2'-deoxyuridine incorporation assay, and internucleosomal DNA fragmentation assays. The effect of BAY 11-7085 on the cell cycle of ECSCs was also determined by flow cytometry. The expression of apoptosis-related molecules was examined in ECSCs with Western blot analysis. BAY 11-7085 significantly inhibited the cell proliferation and DNA synthesis of ECSCs and induced apoptosis and the G0/G1 phase cell cycle arrest of these cells. Additionally, downregulation of the B-cell lymphoma/leukemia-2 (Bcl-2) and Bcl-X(L) expression with simultaneous activation of caspase-3, -8, and -9 was observed in ECSCs after treatment with BAY 11-7085. These results suggest that BAY 11-7085 induces apoptosis of ECSCs by suppressing antiapoptotic proteins, and that caspase-3-, -8-, and -9-mediated cascades are involved in this mechanism. Therefore, BAY 11-7085 could be used as a therapeutic agent for the treatment of endometriosis.

Constitutively activated nuclear factor-kappaB, but not induced NF-kappaB, leads to TRAIL resistance by up-regulation of X-linked inhibitor of apoptosis protein in human cancer cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in most, but not all, cancer cells. The molecular factors regulating the sensitivity to TRAIL are still incompletely understood. The transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated, but its exact role is controversial. We studied different cell lines displaying varying responses to TRAIL and found that TRAIL can activate NF-kappaB in all our cancer cell lines regardless of their TRAIL sensitivity. Inhibition of NF-kappaB via adenoviral expression of the IkappaB-alpha super-repressor only sensitized the TRAIL-resistant pancreatic cancer cell line Panc-1. Panc-1 cells harbor constitutively activated NF-kappaB, pointing to a possible role of preactivated NF-kappaB in protection from TRAIL. Furthermore, we could reduce X-linked inhibitor of apoptosis protein (XIAP) levels in Panc-1 cells by inhibition of constitutively activated NF-kappaB and sensitize Panc-1 cells to TRAIL by RNA interference against XIAP. These results implicate elevated XIAP levels caused by high basal NF-kappaB activity in TRAIL resistance and suggest that therapeutic strategies involving TRAIL can be abetted by inhibition of NF-kappaB and/or XIAP only in tumor cells with constitutively activated NF-kappaB.

Tumor-Induced Oxidative Stress Perturbs Nuclear Factor-κB Activity-Augmenting Tumor Necrosis Factor-α–Mediated T-Cell Death: Protection by Curcumin

Cancer patients often exhibit loss of proper cell-mediated immunity and reduced effector T-cell population in the circulation. Thymus is a major site of T-cell maturation, and tumors induce thymic atrophy to evade cellular immune response. Here, we report severe thymic hypocellularity along with decreased thymic integrity in tumor bearer. In an effort to delineate the mechanisms behind such thymic atrophy, we observed that tumor-induced oxidative stress played a critical role, as it perturbed nuclear factor-kappaB (NF-kappaB) activity. Tumor-induced oxidative stress increased cytosolic IkappaBalpha retention and inhibited NF-kappaB nuclear translocation in thymic T cells. These NF-kappaB-perturbed cells became vulnerable to tumor-secreted tumor necrosis factor (TNF)-alpha (TNF-alpha)-mediated apoptosis through the activation of TNF receptor-associated protein death domain-associated Fas-associated protein death domain and caspase-8. Interestingly, TNF-alpha-depleted tumor supernatants, either by antibody neutralization or by TNF-alpha-small interfering RNA transfection of tumor cells, were unable to kill T cell effectively. When T cells were overexpressed with NF-kappaB, the cells became resistant to tumor-induced apoptosis. In contrast, when degradation-defective IkappaBalpha (IkappaBalpha super-repressor) was introduced into T cells, the cells became more vulnerable, indicating that inhibition of NF-kappaB is the reason behind such tumor/TNF-alpha-mediated apoptosis. Curcumin could prevent tumor-induced thymic atrophy by restoring the activity of NF-kappaB. Further investigations suggest that neutralization of tumor-induced oxidative stress and restoration of NF-kappaB activity along with the reeducation of the TNF-alpha signaling pathway can be the mechanism behind curcumin-mediated thymic protection. Thus, our results suggest that unlike many other anticancer agents, curcumin is not only devoid of immunosuppressive effects but also acts as immunorestorer in tumor-bearing host.

NF-kappaB and the immune response

One of the primary physiological roles of nuclear factor-kappa B (NF-kappaB) is in the immune system. In particular, NF-kappaB family members control the transcription of cytokines and antimicrobial effectors as well as genes that regulate cellular differentiation, survival and proliferation, thereby regulating various aspects of innate and adaptive immune responses. In addition, NF-kappaB also contributes to the development and survival of the cells and tissues that carry out immune responses in mammals. This review, therefore, describes the role of the NF-kappaB pathway in the development and functioning of the immune system.

Betulinic acid as new activator of NF-kappaB: molecular mechanisms and implications for cancer therapy

Recent evidence demonstrates that the anticancer activity of betulinic acid (BetA) can be markedly increased by combination protocols, for example with chemotherapy, ionizing radiation or TRAIL. Since nuclear factor-kappaB (NF-kappaB), a key regulator of stress-induced transcriptional activation, has been implicated in mediating apoptosis resistance, we investigated the role of NF-kappaB in BetA-induced apoptosis. Here, we provide for the first time evidence that BetA activates NF-kappaB in a variety of tumor cell lines. NF-kappaB DNA-binding complexes induced by BetA consisted of p50 and p65 subunits. Nuclear translocation of p65 was also confirmed by immunofluorescence microscopy. BetA-induced NF-kappaB activation involved increased IKK activity and phosphorylation of IkappaB-alpha at serine 32/36 followed by degradation of IkappaB-alpha. Reporter assays revealed that NF-kappaB activated by BetA is transcriptionally active. Interestingly, inhibition of BetA-induced NF-kappaB activation by different chemical inhibitors (proteasome inhibitor, antioxidant, IKK inhibitor) attenuated BetA-induced apoptosis. Importantly, specific NF-kappaB inhibition by transient or stable expression of IkappaB-alpha super-repressor inhibited BetA-induced apoptosis in SH-EP neuroblastoma cells, while transient expression of IkappaB-alpha super-repressor had no influence on BetA-induced apoptosis in two other cell lines. Thus, our findings that activation of NF-kappaB by BetA promotes BetA-induced apoptosis in a cell type-specific fashion indicate that NF-kappaB inhibitors in combination with BetA would have no therapeutic benefit or could even be contraproductive in certain tumors, which has important implications for the design of BetA-based combination protocols.

Tumor necrosis factor-related apoptosis-inducing ligand-mediated proliferation of tumor cells with receptor-proximal apoptosis defects

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) might represent a future cytotoxic drug to treat cancer as it induces apoptosis in tumor cells without toxicity in animal trials. We recently described that in contrast to apoptosis, TRAIL mediates tumor cell survival and proliferation in certain tumor cells. Here we studied the effect of TRAIL on 18 cell lines and 53 primary leukemia cells and classified these tumor cells into four groups: TRAIL, anti-DR4 or anti-DR5 induced apoptosis in group A cells, whereas they had no effect on group 0 cells and mediated proliferation in group P cells. To our surprise, TRAIL induced simultaneous apoptosis and proliferation in group AP cells. More than 20% of all cells tested belonged to group P and showed TRAIL-mediated proliferation even in the presence of certain cytotoxic drugs but not inhibitors of nuclear factor-kappaB. Transfection with B-cell leukemia/lymphoma protein 2 transformed group A cells into group 0 cells, whereas transfection with Fas-associated polypeptide with death domain (FADD)-like interleukin-1-converting enzyme-inhibitory protein (FLIP) transformed them into group AP cells. Loss of caspase-8 or transfection of dominant-negative FADD transformed group A cells into group P cells. Taken together, our data suggest that proliferation is a frequent effect of TRAIL on tumor cells, which is related to receptor-proximal apoptosis defects at the level of the death-inducing signaling complex and should be prevented during antitumor therapy with TRAIL.

Proteasome inhibitor therapy in multiple myeloma

Multiple myeloma remains incurable despite available therapies, and novel therapies that target both tumor cell and bone marrow microenvironment are urgently needed. Preclinical in vitro and in vivo studies show remarkable anti-multiple myeloma activity of the proteasome inhibitor bortezomib/PS-341 even in multiple myeloma cells refractory to multiple prior therapies, including dexamethasone, melphalan, and thalidomide. Based on these findings, the U.S. Food and Drug Administration recently approved the first proteasome inhibitor bortezomib (Velcade), formerly known as PS-341, for the treatment of relapsed/refractory multiple myeloma. Bortezomib therapy has set an outstanding example of translational research in the field of oncology. Genomics and proteomic studies further provide rationale for combining bortezomib with conventional and novel agents to inhibit multiple myeloma growth, overcome drug resistance, reduce attendant toxicity, and improve patient outcome in multiple myeloma.

Increased Expression of the E3-Ubiquitin Ligase Receptor Subunit βTRCP1 Relates to Constitutive Nuclear Factor-κB Activation and Chemoresistance in Pancreatic Carcinoma Cells

The permanent activation of the transcription factor nuclear factor-κB (NF-κB) in pancreatic cancer cells is associated with a profound resistance towards chemotherapy. In the present study, we show that chemoresistant pancreatic cancer cell lines exhibiting constitutive NF-κB activity (i.e., PancTu-1, BxPc3, and Capan-1) express significantly elevated levels of the E3-ubiquitin ligase receptor subunit βTRCP1, compared with pancreatic carcinoma cell lines lacking constitutive NF-κB activity and chemoresistance (i.e., PT45-P1 and T3M4). If transfected with βTRCP1, PT45-P1 cells exhibit an elevated NF-κB activity and become less sensitive towards anticancer drug treatment (i.e., etoposide). Conversely, blockade of βTRCP1 expression in PancTu-1 cells by transfection with a vector-expressed small interfering RNA reduces NF-κB activation and chemoresistance. In PancTu-1 cells, βTRCP1 expression is inhibited, at least in part, by the interleukin-1 (IL-1) receptor(I) antagonist, whereas stimulation of PT45-P1 cells with IL-1β resulted in an increased expression of βTRCP1, and transfection of this cell line with βTRCP1 induced IL-1β secretion in a NF-κB–dependent fashion. Thus, via its close and mutual link to IL-1β secretion, βTRCP1 expression might substantially contribute to the persistent, IL-1β–dependent activation of NF-κB in pancreatic carcinoma cells. In support of this, βTRCP1 expression is detectable at considerable levels in a great number of pancreatic ductal adenocarcinoma specimens, along with an intense staining for activated NF-κB. Altogether, our findings of the elevated βTRCP1 expression in pancreatic carcinoma cells pinpoint to another important mediator of constitutive NF-κB activation and thereby of chemoresistance.

Down-regulation of protein kinase Cη potentiates the cytotoxic effects of exogenous tumor necrosis factor–related apoptosis-inducing ligand in PC-3 prostate cancer cells

Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) is a highly promising candidate for the treatment of cancer because it elicits cell death in the majority of tumor cells while sparing most normal cells. Some cancers, however, display resistance to TRAIL, suggesting that treatment with TRAIL alone may be insufficient for cancer therapy. In the present study, we explored whether the apoptotic responsiveness of PC-3 prostate cancer cells to TRAIL could be enhanced by targeting the novel protein kinase C (PKC) isoform η. Transfection of PC-3 cells with second-generation chimeric antisense oligonucleotides against PKCη caused a time- and dose-dependent knockdown of PKCη, as revealed by real-time RT-PCR and Western blot analyses. Knockdown of PKCη resulted in a marked amplification of TRAIL's cytotoxic activity. Cell killing could be substantially prevented by the pan-caspase inhibitor z-VAD-fmk. In addition, PKCη knockdown and administration of TRAIL significantly synergized in activation of caspase-3 and internucleosomal DNA fragmentation. Knockdown of PKCη augmented TRAIL-induced dissipation of the mitochondrial transmembrane potential and release of cytochrome c from mitochondria into the cytosol, indicating that PKCη acts upstream of mitochondria. We conclude that PKCη represents a considerable resistance factor with respect to TRAIL and a promising target to exploit the therapeutic potential of TRAIL.

Death receptors in chemotherapy and cancer

Apoptosis, the cell's intrinsic death program, is a key regulator of tissue homeostasis. An imbalance between cell death and proliferation may result in tumor formation. Also, killing of cancer cells by cytotoxic therapies such as chemotherapy, gamma-irradiation or ligation of death receptors is predominantly mediated by triggering apoptosis in target cells. In addition to the intrinsic mitochondrial pathway, elements of death receptor signaling pathways have been implied to contribute to the efficacy of cancer therapy. Failure to undergo apoptosis in response to anticancer therapy may lead to resistance. Also, deregulated expression of death receptor pathway molecules may contribute to tumorigenesis and tumor escape from endogenous growth control. Understanding the molecular events that regulate apoptosis induced by anticancer therapy and how cancer cells evade apoptosis may provide new opportunities for pathway-based rational therapy and for drug development.

Transfection of a dominant-negative mutant NF-kB inhibitor (IkBm) represses p53-dependent apoptosis in acute lymphoblastic leukemia cells: interaction of IkBm and p53

To investigate the possible role of inhibiting NF-kB activation in sensitizing tumor cells to chemotherapy-induced apoptosis, we transfected the dominant-negative mutant inhibitor of NF-kB (IkBm) into the EU-1 cell line, an acute lymphoblastic leukemia (ALL) line with constitutive NF-kB activation. Overexpression of IkBm significantly reduced constitutive NF-kB activity in EU-1 cells, resulting in decreased cell growth. In response to apoptosis induced by chemotherapeutic drugs, IkBm-transfected cells (EU-1/IkBm) exhibited increased sensitivity to vincristine (VCR), whereas sensitivity to doxorubicin (Dox) was not changed as compared to neo-transfected control (EU-1/neo) cells. To further evaluate the link between IkBm and sensitivity to Dox and VCR, we demonstrated that both endogenous IkBalpha and ectopic IkBm bind to p53. In response to Dox, the cytosolic p53.IkBalpha complex rapidly dissociated due to downregulation of IkBalpha. However, the p53.IkBm complex did not dissociate under these conditions. Although treatment of EU-1/IkBm cells with Dox increased the expression of p53, the nondissociating p53.IkBm complex resulted in decreased p53 function, as demonstrated by absence of cell-cycle arrest and induction of p53 target genes. Contrastingly, VCR-induced cell death neither downregulated IkBalpha nor induced p53, as shown by the lack of NF-kB activation and p53-mediated gene expression in VCR-treated cells. Our data suggest that IkBm simultaneously downregulates NF-kB activation and sequesters p53 in the cytoplasm, thus enhancing NF-kB-regulated apoptosis but blocking p53-dependent apoptosis.

TRAIL induced survival and proliferation in cancer cells resistant towards TRAIL-induced apoptosis mediated by NF-kappaB

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in cancer cells. Examining primary cells of children with untreated acute leukemia, TRAIL induced apoptosis in 50% of cells, but to our surprise attenuated spontaneous apoptosis in the remaining samples or, most importantly, even mediated proliferation. We therefore examined tumor cell lines of leukemic and nonleukemic origin with apoptosis resistance towards TRAIL because of absent Caspase-8 or dysfunctional FADD. In all cell lines tested, TRAIL treatment increased cell numbers in average to 163% within 4 days and accelerated doubling time from 24 to 19 h. TRAIL-mediated proliferation was completely abrogated by blockade of NF-kappaB activation using proteasome inhibitors or in RIP-negative, IKKgamma-negative cells or in cells overexpressing dominant-negative IkappaBalpha. Our data describe the biological significance of TRAIL-mediated activation of NF-kappaB in cancer cells resistant to TRAIL-mediated apoptosis: TRAIL leads to an increase in tumor cell count by a prosurvival and possibly mitogenic function. Given the promising therapeutic potential of TRAIL as a novel anticancer drug, TRAIL-mediated survival or proliferation of target cells may restrict its use to apoptosis-sensitive tumors.

Cellular stress response and apoptosis in cancer therapy

Anticancer treatment using cytotoxic drugs is considered to mediate cell death by activating key elements of the apoptosis program and the cellular stress response. While proteolytic enzymes (caspases) serve as main effectors of apoptosis, the mechanisms involved in activation of the caspase system are less clear. Two distinct pathways upstream of the caspase cascade have been identified. Death receptors, eg, CD95 (APO-1/Fas), trigger caspase-8, and mitochondria release apoptogenic factors (cytochrome c, Apaf-1, AIF), leading to the activation of caspase-9. The stressed endoplasmic reticulum (ER) contributes to apoptosis by the unfolded protein response pathway, which induces ER chaperones, and by the ER overload response pathway, which produces cytokines via nuclear factor-kappaB. Multiple other stress-inducible molecules, such as p53, JNK, AP-1, NF-kappaB, PKC/MAPK/ERK, and members of the sphingomyelin pathway have a profound influence on apoptosis. Understanding the complex interaction between different cellular programs provides insights into sensitivity or resistance of tumor cells and identifies molecular targets for rational therapeutic intervention strategies.

CD95 and TRAIL receptor-mediated activation of protein kinase C and NF-kappaB contributes to apoptosis resistance in ductal pancreatic adenocarcinoma cells

The molecular alterations in tumour cells leading to resistance towards apoptosis induced by CD95 and TRAIL-receptors are not fully understood. We report here that the stimulation of the CD95- and TRAIL-resistant human pancreatic adenocarcinoma cell line PancTuI with an agonistic anti-CD95 antibody or TRAIL resulted in activation of protein kinase C and NF-kappaB. Inhibition of protein kinase C by Gö6983 sensitized these cells to apoptotic challenges and strongly diminished activation of NF-kappaB by anti-CD95 and TRAIL. Similarly, inhibition of NF-kappaB by MG132 or by transient transfection with a dominant negative mutant of IkappaBalpha restored the responsiveness of PancTuI cells to both death ligands. In the CD95 and TRAIL-sensitive cell line Colo357 the induction of protein kinase C and NF-kappaB following activation of CD95 and TRAIL-R was very moderate compared with PancTuI cells. However, pre-incubation of these cells with PMA strongly reduced their apoptotic response to anti-CD95 and TRAIL. Taken together, we show that activation of protein kinase C operates directly in a death receptor-dependent manner in PancTuI cells and protect pancreatic tumour cells from anti-CD95 and TRAIL-mediated apoptosis by preventing the loss DeltaPsim and Cytochrome c release as well as by induction of NF-kappaB.

Constitutive activation of nuclear factor-kappaB prevents TRAIL-induced apoptosis in renal cancer cells

TRAIL has gained much attention for its specific induction of apoptosis in cancer cells but not in normal cells. This phenomenon has been explained thus: that cancer cells dominantly express death receptors while normal cells express decoy receptors. However, recent reports have shown that some cancer cell lines are resistant to TRAIL-induced apoptosis despite the absence of decoy receptors and the presence of death receptors. This suggested the existance of an inhibitory factor. We herein showed that NF-kappaB is a key molecule underlying the TRAIL-resistant mechanism in renal cell carcinoma (RCC) cell lines. We observed that NF-kappaB is constitutively activated in resistant cell lines. Forced expression of antisense cDNA of IkappaBalpha, a specific inhibitor of NF-kappaB, in TRAIL-sensitive cell lines with a low NF-kappaB activity result in constitutive activation of NF-kappaB and resistance to TRAIL-induced apoptosis. Adenoviral expression of a stable form of IkappaBalpha in the TRAIL-resistant cell lines induced apoptosis. These data suggest that RCC can be classified into two subsets: TRAIL-sensitive RCC with a low NF-kappaB activity and TRAIL-resistant RCC with constitutively activated NF-kappaB. In the former group TRAIL can be a treatment option, while in the latter group a molecular approach targeting NF-kappaB appears to be a promising therapy.

Cytotoxicity of Tumor necrosis factor related apoptosis-inducing ligand towards Ewing's sarcoma cell lines

Death ligands of the Tumor Necrosis Factor (TNF) family are known to induce apoptosis upon binding to their cognate receptors. However, the clinical utility of these cytokines as anticancer agents has been limited due to unacceptable toxicity. TRAIL is a recently isolated death ligand that possesses selective anti-tumor activity against a number of cancer cell lines without significant systemic toxicity. In this report we present evidence that cell lines derived from Ewing's Sarcoma (ES) are uniformly sensitive to TRAIL-mediated apoptosis. Furthermore, unlike TNF-alpha, treatment with TRAIL fails to induce the anti-apoptotic and pro-inflammatory NF-kappaB pathway in the ES cell lines. Our results suggest that TRAIL may prove to be a useful agent for the treatment of Ewing's sarcoma and related peripheral neuroectodermal tumors.

Inhibition of NF-kappaB sensitizes human pancreatic carcinoma cells to apoptosis induced by etoposide (VP16) or doxorubicin

The transcription factor NF-kappaB has anti-apoptotic properties and may confer chemoresistance to cancer cells. Here, we describe human pancreatic carcinoma cell lines that differ in the responsiveness to the topoisomerase-2 inhibitors VP16 (20 microM) and doxorubicin (0.3 microM): Highly sensitive T3M4 [corrected] and PT45-P1 cells, and Capan-1 and A818-4 cells that were almost resistant to both anti cancer drugs. VP16, but not doxorubicin, transiently induced NF-kappaB activity in all cell lines, whereas basal NF-kappaB binding was nearly undetectable in T3M4 [corrected] and PT45-P1 cells, but rather high in Capan-1 and A818-4 cells, as demonstrated by gel-shift and luciferase assays. Treatment with various NF-kappaB inhibitors (Gliotoxin, MG132 and Sulfasalazine), or transfection with the IkappaBalpha super-repressor, strongly enhanced the apoptotic effects of VP16 or doxorubicin on resistant Capan-1 and 818-4 cells. Our results indicate that under certain conditions the resistance of pancreatic carcinoma cells to chemotherapy is due to their constitutive NF-kappaB activity rather than the transient induction of NF-kappaB by some anti-cancer drugs. Blockade of basal NF-kappaB activity by well established drugs efficiently reduces chemoresistance of pancreatic cancer cells and offers the potential for improved therapeutic strategies.

Isolation and characterization of an acute promyelocytic leukemia cell line selectively resistant to the novel antileukemic and apoptogenic retinoid 6-[3-adamantyl-4-hydroxyphenyl]-2-naphthalene carboxylic acid

6-[3-adamantyl-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) is a novel compound that represents the prototype of a new class of synthetic retinoids with apoptogenic properties in acute promyelocytic leukemia (APL) and other types of leukemia. In this article, using SCID mice xenografted with APL-derived NB4 cells, we demonstrate that CD437 has significant antileukemic activity in vivo. In addition, we report on the isolation and characterization of an APL cell line (NB4.437r) resistant to CD437. The cell line retains expression of PML-RAR and is approximately 33-fold more resistant than the parental counterpart to the apoptogenic effects of the retinoid. Resistance is relatively specific to CD437 and structural congeners because the NB4.437r cell line is still sensitive to various types of apoptogenic compounds. The CD437-resistant cell line maintains sensitivity to the antiproliferative and apoptotic action of all-trans-retinoic acid, AM580, and fenretinide, though it shows partial resistance to the cytodifferentiating effects of the first 2 compounds. Resistance to CD437 lays upstream of the CD437-induced release of cytochrome c from the mitochondria and the activation of caspase-3, -7, -8, and -9. Furthermore, NB4.437r cells are deficient in the CD437-dependent activation of nuclear NFkb and AP1-binding activities and in the phosphorylation of the protein kinase Akt. In the case of AP1, deficient assembly of the complex is not caused by the lack of activation of the Jun N-terminal kinase (JNK) family of kinases. The novel cell line will be useful in the elucidation of the molecular mechanisms underlying the apoptogenic action of CD437 and structurally related retinoids.

Overexpression of the wild-type p53 gene inhibits NF-kappaB activity and synergizes with aspirin to induce apoptosis in human colon cancer cells

The tumor suppressor gene p53 is a potent transcriptional regulator of genes which are involved in many cellular activities including cell cycle arrest, apoptosis, and angiogenesis. Recent studies have demonstrated that the activation of the transcriptional factor nuclear factor kappaB (NF-kappaB) plays an essential role in preventing apoptotic cell death. In this study, to better understand the mechanism responsible for the p53-mediated apoptosis, the effect of wild-type p53 (wt-p53) gene transfer on nuclear expression of NF-kappaB was determined in human colon cancer cell lines. A Western blot analysis of nuclear extracts demonstrated that NF-kappaB protein levels in the nuclei were suppressed by the transient expression of the wt-p53 in a dose-dependent manner. Transduced wt-p53 expression increased the cytoplasmic expression of I kappaB alpha as well as its binding ability to NF-kappaB, thus markedly reducing the amount of NF-kappaB that translocated to the nucleus. The decrease in nuclear NF-kappaB protein correlated with the decreased NF-kappaB constitutive activity measured by electrophoretic mobility shift assay. Furthermore, parental cells transfected with NF-kappaB were better protected from cell death induced by the wt-p53 gene transfer. We also found that the wt-p53 gene transfer was synergistic with aspirin (acetylsalicylic acid) in inhibiting NF-kappaB constitutive activity, resulting in enhanced apoptotic cell death. These results suggest that the inhibition of NF-kappaB activity is a plausible mechanism for apoptosis induced by the wt-p53 gene transfer in human colon cancer cells and that anti-NF-kappaB reagent aspirin could make these cells more susceptible to apoptosis.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

Control of apoptosis by Rel/NF-kappaB transcription factors

Apoptosis is a physiological process critical for organ development, tissue homeostasis, and elimination of defective or potentially dangerous cells in complex organisms. Apoptosis can be initiated by a wide variety of stimuli, which activate a cell suicide program that is constitutively present in most vertebrate cells. In diverse cell types, Rel/NF-kappaB transcription factors have been shown to have a role in regulating the apoptotic program, either as essential for the induction of apoptosis or, perhaps more commonly, as blockers of apoptosis. Whether Rel/NF-kappaB promotes or inhibits apoptosis appears to depend on the specific cell type and the type of inducer. An understanding of the role of Rel/NF-kappaB transcription factors in controlling apoptosis may lead to the development of therapeutics for a wide variety of human diseases, including neurodegenerative and immune diseases, and cancer.

IFN-γ Mediates a Novel Antiviral Activity Through Dynamic Modulation of TRAIL and TRAIL Receptor Expression

TNF-related apoptosis-inducing ligand (TRAIL) is able to kill many transformed cells of diverse tissue types. We show that TRAIL is inducible by IFN-γ, by TNF-α, and by infection with human CMV, and has potent antiviral activity in vitro. CMV infection and IFN-γ also reciprocally modulate TRAIL receptor (TRAIL-R) expression. CMV infection increased the expression of TRAIL-R1 and -R2, whereas IFN-γ down-regulated the expression of TRAIL-Rs on uninfected fibroblasts. Moreover, IFN-γ significantly decreased the basal level of NF-κB activation, a known survival factor that inhibits apoptosis. Thus, TRAIL selectively kills virus-infected cells while leaving uninfected cells intact, and IFN-γ potentiates these effects by dynamic modulation of TRAIL and TRAIL-R expression and by sensitizing cells to apoptosis. The regulation of TRAIL and TRAIL-R expression may represent a general mechanism that contributes to the control of TRAIL-mediated apoptosis.

The Murine Antiapoptotic Protein A1 Is Induced in Inflammatory Macrophages and Constitutively Expressed in Neutrophils

Myeloid leukocytes are thought to regulate their susceptibility to apoptosis upon migration to a site of inflammation. However, factors that determine survival have not been well characterized in these cells. We have examined the expression of murine A1, an antiapoptotic Bcl-2 relative found in activated myeloid cells, during the course of an acute inflammatory response. Intraperitoneal infection of mice with the virulent RH strain of Toxoplasma gondii led to a 5- to 10-fold increase in A1 mRNA levels in peritoneal cells after several days. Bcl-2 expression was unchanged. The increase in A1 expression depended on the dose of the organism and coincided with a sharp increase in peritoneal cellularity. A1 protein levels were also increased as determined by Western blot analysis and immunohistochemical studies. All neutrophils and approximately half of the macrophages in the inflammatory exudate contained high levels of A1 in cytoplasm. A1 expression did not correlate with intracellular parasitization. Peripheral blood neutrophils from normal mice strongly expressed A1 protein, whereas normal monocytes showed only weak staining. Bax mRNA was induced in parallel with A1 in macrophages. Exudate macrophages and granulocytes that were apoptotic by TUNEL staining occasionally appeared to display A1 throughout the cell nucleus. These studies identify A1 as a potential regulator of apoptosis during acute inflammation.