IkappaB kinase-dependent chronic activation of NF-kappaB is necessary for p21(WAF1/Cip1) inhibition of differentiation-induced apoptosis of monocytes

NF-κB in monocytes and macrophages - an inflammatory master regulator in multitalented immune cells

Nuclear factor κB (NF-κB) is a dimeric transcription factor constituted by two of five protein family members. It plays an essential role in inflammation and immunity by regulating the expression of numerous chemokines, cytokines, transcription factors, and regulatory proteins. Since NF-κB is expressed in almost all human cells, it is important to understand its cell type-, tissue-, and stimulus-specific roles as well as its temporal dynamics and disease-specific context. Although NF-κB was discovered more than 35 years ago, many questions are still unanswered, and with the availability of novel technologies such as single-cell sequencing and cell fate-mapping, new fascinating questions arose. In this review, we will summarize current findings on the role of NF-κB in monocytes and macrophages. These innate immune cells show high plasticity and dynamically adjust their effector functions against invading pathogens and environmental cues. Their versatile functions can range from antimicrobial defense and antitumor immune responses to foam cell formation and wound healing. NF-κB is crucial for their activation and balances their phenotypes by finely coordinating transcriptional and epigenomic programs. Thereby, NF-κB is critically involved in inflammasome activation, cytokine release, and cell survival. Macrophage-specific NF-κB activation has far-reaching implications in the development and progression of numerous inflammatory diseases. Moreover, recent findings highlighted the temporal dynamics of myeloid NF-κB activation and underlined the complexity of this inflammatory master regulator. This review will provide an overview of the complex roles of NF-κB in macrophage signal transduction, polarization, inflammasome activation, and cell survival.

Micro-RNAs in Response to Active Forms of Vitamin D3 in Human Leukemia and Lymphoma Cells

Non-coding micro-RNA (miRNAs) regulate the protein expression responsible for cell growth and proliferation. miRNAs also play a role in a cancer cells’ response to drug treatment. Knowing that leukemia and lymphoma cells show different responses to active forms of vitamin D₃, we decided to investigate the role of selected miRNA molecules and regulated proteins, analyzing if there is a correlation between the selected miRNAs and regulated proteins in response to two active forms of vitamin D₃, calcitriol and tacalcitol. A total of nine human cell lines were analyzed: five leukemias: MV-4-1, Thp-1, HL-60, K562, and KG-1; and four lymphomas: Raji, Daudi, Jurkat, and U2932. We selected five miRNA molecules—miR-27b, miR-32, miR-125b, miR-181a, and miR-181b—and the proteins regulated by these molecules, namely, CYP24A1, Bak1, Bim, p21, p27, p53, and NF-kB. The results showed that the level of selected miRNAs correlates with the level of proteins, especially p27, Bak1, NFκB, and CYP24A1, and miR-27b and miR-125b could be responsible for the anticancer activity of active forms of vitamin D₃ in human leukemia and lymphoma.

Free Radical-Mediated Protein Radical Formation in Differentiating Monocytes

Free radical-mediated activation of inflammatory macrophages remains ambiguous with its limitation to study within biological systems. U-937 and HL-60 cell lines serve as a well-defined model system known to differentiate into either macrophages or dendritic cells in response to various chemical stimuli linked with reactive oxygen species (ROS) production. Our present work utilizes phorbol 12-myristate-13-acetate (PMA) as a stimulant, and factors such as concentration and incubation time were considered to achieve optimized differentiation conditions. ROS formation likely hydroxyl radical (HO^●) was confirmed by electron paramagnetic resonance (EPR) spectroscopy combined with confocal laser scanning microscopy (CLSM). In particular, U-937 cells were utilized further to identify proteins undergoing oxidation by ROS using anti-DMPO (5,5-dimethyl-1-pyrroline N-oxide) antibodies. Additionally, the expression pattern of NADPH Oxidase 4 (NOX4) in relation to induction with PMA was monitored to correlate the pattern of ROS generated. Utilizing macrophages as a model system, findings from the present study provide a valuable source for expanding the knowledge of differentiation and protein expression dynamics.

Frutescone O from Baeckea frutescens Blocked TLR4-Mediated Myd88/NF-κB and MAPK Signaling Pathways in LPS Induced RAW264.7 Macrophages

Frutescone O was isolated from the aerial parts of Baeckea frutescens L., which was commonly used as a folk medicinal material for treating anti-inflammatory disease in South East Asia. This study aimed to investigate the anti-inflammatory activity and related signaling cascade of Frutescone O (Fru) in LPS induced RAW264.7 cells. The anti-inflammation activity of Frutescone O was determined according to the inhibitory effects on the secretion of nitric oxide (NO), expression of inducible NO synthase, and pro-inflammatory cytokines. The regulation of Myeloid differentiation factor 88 (Myd88), inhibition of NF-κB, and MAPK pathways were further investigated for molecular mechanisms. Fru significantly decreased the expression of iNOS and the production of NO in LPS-stimulated RAW264.7 cells. It also dose-dependently suppressed LPS induced expression of IL-1β, IL-6, and TNF-α. Furthermore, Fru remarkably inhibited the upregulation of NF-κB (p50) expression in the nucleus and the phosphorylation ratio of p38, JNK, ERK, and Myd88 signaling protein. The molecular docking and cellular thermal shift assay (CETSA) results indicated that Fru participated in a robust and stable interaction with the active site of TLR4-MD2. Thus, Fru suppressed the LPS induced inflammation in RAW264.7 cells by blocking the TLR4 mediated signal transduction through the NF-κB and MAPK signaling pathways and inhibiting the Myd88 and iNOS expression.

In-depth characterization of ubiquitin turnover in mammalian cells by fluorescence tracking

Despite almost 40 years having passed from the initial discovery of ubiquitin (Ub), fundamental questions related to its intracellular metabolism are still enigmatic. Here we utilized fluorescent tracking for monitoring ubiquitin turnover in mammalian cells, resulting in obtaining qualitatively new data. In the present study we report (1) short Ub half-life estimated as 4 h; (2) for a median of six Ub molecules per substrate as a dynamic equilibrium between Ub ligases and deubiquitinated enzymes (DUBs); (3) loss on average of one Ub molecule per four acts of engagement of polyubiquitinated substrate by the proteasome; (4) direct correlation between incorporation of Ub into the distinct type of chains and Ub half-life; and (5) critical influence of the single lysine residue K27 on the stability of the whole Ub molecule. Concluding, our data provide a comprehensive understanding of ubiquitin-proteasome system dynamics on the previously unreachable state of the art.

NF-κB inhibition promotes apoptosis in androgen-independent prostate cancer cells by the photothermal effect via the IκBα/AR signaling pathway

BAY 11-7082 promotes apoptosis in DU145 cells and increased the sensitivity of cells to the photothermal therapy of Au–Ag@PDA NPs.

Captopril alleviates hypertension-induced renal damage, inflammation, and NF-κB activation

Hypertensive renal damage generally occurs during the middle and late stages of hypertension, which is typically characterized by proteinuria and renal inflammation. Captopril, an angiotensin-converting enzyme (ACE) inhibitor, has been widely used for therapy of arterial hypertension and cardiovascular diseases. However, the protective effects of captopril on hypertension-induced organ damage remain elusive. The present study was designed to explore the renoprotective action of captopril in spontaneously hypertensive rats (SHR). The 6-week-old male SHR and age-matched Wistar-Kyoto rats were randomized into long-term captopril-treated (34 mg/kg) and vehicle-treated groups. The results showed that in SHR there was obvious renal injury characterized by the increased levels of urine albumin, total protein, serum creatinine, blood urea nitrogen, renal inflammation manifested by the increased mRNA and protein expression of inflammatory factors including tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and inducible nitric oxide synthase, and enhanced nuclear factor-κB (NF-κB) activation. Captopril treatment could lower blood pressure, improve renal injury, and suppress renal inflammation and NF-κB activation in SHR rats. In conclusion, captopril ameliorates renal injury and inflammation in SHR possibly via inactivation of NF-κB signaling.

NFκB regulates p21 expression and controls DNA damage-induced leukemic differentiation

DNA damage exposure is a major modifier of cell fate in both normal and cancer tissues. In response to DNA damage, myeloid leukemia cells activate a poorly understood terminal differentiation process. Here, we show that the NFκB pathway directly activates expression of the proliferation inhibitor p21 in response to DNA damage in myeloid leukemia cells. In order to understand the role of this unexpected regulatory event, we ablated the NFκB binding site we identified in the p21 promoter, using CRISPR/Cas9-mediated genome editing. We found that NFκB-mediated p21 activation controls DNA damage-induced myeloid differentiation. Our results uncover a p53-independent pathway for p21 activation involved in controlling hematopoietic cell fate.

A20 restores phorbol ester-induced differentiation of THP-1 cells in the absence of nuclear factor-κB activation

A20, also referred to as tumor necrosis factor alpha (TNFα)-induced protein 3 (TNFAIP3), is an ubiquitin-editing enzyme whose expression is enhanced by NF-κB activation, and plays an important role in silencing NF-κB activity. Another well-known role for A20 is to protect cells from TNFα-induced apoptosis. Depletion of NF-κB in differentiating U937 monocytic leukemia cells is known to cause apoptotic cell death; however, much remains to be explored about the molecules that are expressed in an NF-κB-dependent manner and which support monocyte-macrophage differentiation. Using the monocytic cell line THP-1, and peripheral blood monocytes, we show here a sustained increase in A20 expression during monocyte-macrophage differentiation, which coincided with high NF-κB-dependent transcriptional activity. Depletion of NF-κB by stable expression of a super-repressor form of IκBα in THP-1 cells caused remarkable cell death during phorbol 12-myristate 13-acetate (PMA)-induced differentiation. A20 expression in these cells did not alter this NF-κB suppression, but was sufficient to protect the cells and restore the cell surface expression of a differentiation marker (CD11b) and phagocytic activity. Mutational analyses revealed that this A20 activity requires the carboxy-terminal zinc-finger domain, but not its deubiquitinase activity. Based on these findings, we conclude that A20, when ectopically expressed, can support both survival and differentiation of THP-1 cells in the absence of sustained NF-κB activity.

Suppression of Baeckea frutescens L. and its components on MyD88-dependent NF-κB pathway in MALP-2-stimulated RAW264.7 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Baeckea frutescens L. is commonly used as a folk medicinal material. There are nineteen components in its volatile oil, including Pcymol which has effects of eliminating phlegm, relieving asthma and antiviral. This study was aimed to investigate the anti-infectious inflammatory activities of Baeckea frutescens L. and its conponents and analyzing the mechanisms.

MATERIALS AND METHODS

The anti-infectious inflammation of Baeckea frutescens L. were studied by using macrophage activating lipopeptide-2 (MALP-2)-stimulated RAW264.7 cell model in vitro. Secretion of nitric oxide (NO), expression of inducible NO synthase (iNOS) and cytokines were detected as classic inflammatory index. Expression of Myeloid differentiation factor 88 (MyD88), degradation of inhibitory κBα (IκBα) and nuclear translocation of NF-κB p65 were further investigated.

RESULTS

The results suggested that Baeckea frutescens L. has effect on suppression of MALP-2-mediated inflammation in RAW264.7 cells. The secretion of NO and the expression of iNOS could be inhibited. The secretion of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) were also declined. Baeckea frutescens L. significantly decreased the expression of MyD88, therefore, inhibited the degradation of IκBα, reduced the level of nuclear translocation of p65.

CONCLUSION

The results of this study indicated that Baeckea frutescens L. and its components could inhibit the anti-infectious inflammatory events and iNOS expression in MALP-2 stimulated RAW264.7 cells. Among them, BF-2 might play a role through the inhibition of the MyD88 and NF-κB pathway. Our study might provide a new strategy to design and develop this kind of drug towards mycoplasma-infected inflammation.

Caspase-1 promotes monocyte-macrophage differentiation by repressing PPARγ

Monocyte-to-macrophage differentiation is tightly controlled in vivo, as disruption of the normal differentiation program can lead to diverse disorders. Caspase-1, the first identified member of the caspase family, regulates differentiation in various cell types such as Th17 cells and adipocytes. However, the contribution of caspase-1 in monocyte-macrophage differentiation remains elusive. Here we report that caspase-1 is significantly downregulated in leukemia cells from patients with acute monocytic leukemia. By using the phorbol 12-myristate 13-acetate-induced cell differentiation model, we found that caspase-1 activation was required for the differentiation of human monocytes to macrophages. Further analysis of peroxisome proliferator-activated receptor γ (PPARγ) protein levels revealed that the monocyte-macrophage differentiation program could be divided into two stages. Caspase-1-mediated downregulation of PPARγ was important in the late stage of monocyte-macrophage differentiation; however, PPARγ protein levels had little effect on the early stage differentiation. Accumulation of PPARγ protein by troglitazone treatment potently suppressed the late stage of macrophage differentiation, which might be linked to inhibition of nuclear factor-κB activity. The data provide a plausible mechanistic basis by which caspase-1 promotes the differentiation of macrophages from monocytes.

Metformin inhibits monocyte adhesion to endothelial cells and foam cell formation

The United Kingdom Prospective Diabetes Study (UKPDS) found that metformin reduces macrovascular complications in type 2 diabetic patients. To investigate the mechanisms involved we examined the effect of metformin on monocyte adhesion to human endothelial cells (ECs) induced by advanced glycation end-products (AGE), and on monocyte differentiation into macrophages and foam cell formation. Treatment of human ECs with AGEs (100 µg/ml) for up to 12 hours significantly increased human monocyte adhesion. Pre-treatment of the cells with metformin (0.1—2.5 µg/ml) inhibited AGE-induced monocyte adhesion and expression of endothelial cell adhesion molecules. In culture, human monocytes spontaneously differentiated into macrophages, as indicated by phenotypic changes, and increased expression of lectin-like oxidised low-density lipoprotein (LDL) receptor and scavenger receptor type A. Incubation of these cells in the presence of metformin decreased expression of all of these parameters. Metformin also inhibited foam cell formation induced by minimally modified LDL. Overall, these results suggest new mechanisms by which metformin may reduce the risk of vascular complications in patients with type 2 diabetes.

Regulation of CYBB Gene Expression in Human Phagocytes by a Distant Upstream NF-κB Binding Site

The human CYBB gene encodes the gp91-phox component of the phagocyte oxidase enzyme complex, which is responsible for generating superoxide and other downstream reactive oxygen species essential to microbial killing. In the present study, we have identified by sequence analysis a putative NF-κB binding site in a DNase I hypersensitive site, termed HS-II, located in the distant 5' flanking region of the CYBB gene. Electrophoretic mobility assays showed binding of the sequence element by recombinant NF-κB protein p50 and by proteins in nuclear extract from the HL-60 myeloid leukemia cell line corresponding to p50 and to p50/p65 heterodimers. Chromatin immunoprecipitation demonstrated NF-κB binding to the site in intact HL-60 cells. Chromosome conformation capture (3C) assays demonstrated physical interaction between the NF-κB binding site and the CYBB promoter region. Inhibition of NF-κB activity by salicylate reduced CYBB expression in peripheral blood neutrophils and differentiated U937 monocytic leukemia cells. U937 cells transfected with a mutant inhibitor of κB "super-repressor" showed markedly diminished CYBB expression. Luciferase reporter analysis of the NF-κB site linked to the CYBB 5' flanking promoter region revealed enhanced expression, augmented by treatment with interferon-γ. These studies indicate a role for this distant, 15 kb upstream, binding site in NF-κB regulation of the CYBB gene, an essential component of phagocyte-mediated host defense.

Caffeic acid phenethyl ester suppresses monocyte adhesion to the endothelium by inhibiting NF-κB/NOX2-derived ROS signaling

Caffeic acid phenethyl ester (CAPE), one of the major polyphenols, exhibits anti-oxidative, anti-bacterial, and anti-cancer properties. Atherosclerosis is a chronic inflammatory disease, the progression of which is closely related to the accumulated adhesion of inflammatory monocytes/macrophages to the endothelium. We herein determined whether CAPE and its derivatives suppressed THP-1 cell adhesion to human umbilical vein endothelial cells (HUVEC). Of the four polyphenols tested, CAPE significantly suppressed the 12-O-tetradecanoylphorbol 13-acetate (TPA)-elicited expression of cluster for differentiation (CD) 11b, 14, and 36, and this was accompanied by the inhibition of THP-1 cell adhesion to HUVEC. CAPE also suppressed the activation of TPA-elicited nuclear factor-κB (NF-κB) and accumulation of NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS), but did not affect extracellular signal-regulated kinase (ERK) phosphorylation. Taken together, these results demonstrated that CAPE suppressed THP-1 cell adhesion to HUVEC through, at least in part, the NF-κB, NOX2, and ROS-derived signaling axis.

Role of hexokinase-1 in the survival of HIV-1-infected macrophages

Viruses have developed various strategies to protect infected cells from apoptosis. HIV-1 infected macrophages are long-lived and considered reservoirs for HIV-1. One significant deciding factor between cell survival and cell death is glucose metabolism. We hypothesized that HIV-1 protects infected macrophages from apoptosis in part by modulating the host glycolytic pathway specifically by regulating hexokinase-1 (HK-1) an enzyme that converts glucose to glucose-6-phosphate. Therefore, we analyzed the regulation of HK-1 in HIV-1 infected PBMCs, and in a chronically HIV-1 infected monocyte-like cell line, U1. Our results demonstrate that HIV-1 induces a robust increase in HK-1 expression. Surprisingly, hexokinase enzymatic activity was significantly inhibited in HIV-1 infected PBMCs and in PMA differentiated U1 cells. Interestingly, we observed increased levels of mitochondria-bound HK-1 in PMA induced U1 cells and in the HIV-1 accessory protein, viral protein R (Vpr) transduced U937 cell derived macrophages. Dissociation of HK-1 from mitochondria in U1 cells using a pharmacological agent, clotrimazole (CTZ) induced mitochondrial membrane depolarization and caspase-3/7 mediated apoptosis. Dissociation of HK-1 from mitochondria in Vpr transduced U937 also activated caspase-3/7 activity. These observations indicate that HK-1 plays a non-metabolic role in HIV-1 infected macrophages by binding to mitochondria thereby maintaining mitochondrial integrity. These results suggest that targeting the interaction of HK-1 with the mitochondria to induce apoptosis in persistently infected macrophages may prove beneficial in purging the macrophage HIV reservoir.

The anti-inflammatory activities of Ainsliaea fragrans Champ. extract and its components in lipopolysaccharide-stimulated RAW264.7 macrophages through inhibition of NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Ainsliaea fragrans Champ. (A. fragrans) is a traditional Chinese herbal that contains components like 3,5-dicaffeoylquinic acid and 4,5-dicaffeoylquinic acid. It exhibits anti-inflammatory activities which has been used for the treatment of gynecological diseases for many years in China. The aims of the present study were to investigate the anti-inflammatory activities of A. fragrans and elucidate the underlying mechanisms with regard to its molecular basis of action for the best component.

MATERIALS AND METHODS

The anti-inflammatory effects of A. fragrans were studied by using lipopolysaccharide (LPS)-stimulated activation of nitric oxide (NO) in mouse RAW264.7 macrophages. Expression of inducible NO synthase (iNOS) and pro-inflammatory cytokines, inhibitory κBα (IκBα) degradation and nuclear translocation of NF-κB p65 were further investigated.

RESULTS

The present study demonstrated that A. fragrans could suppress the production of NO in LPS-stimulated RAW264.7 macrophages. Further investigations showed A. fragrans could suppress iNOS expression. A. fragrans also inhibited the expression of tumor necrosis factor-alpha and interleukin-6. A. fragrans significantly decreased the degradation of IκBα, reduced the level of nuclear translocation of p65. All these results suggested the inhibitory effects of A. fragrans on the production of inflammatory mediators through the inhibition of the NF-κB activation pathway.

CONCLUSION

Our results indicated that A. fragrans inhibited inflammatory events and iNOS expression in LPS-stimulated RAW264.7 cells through the inactivation of NF-κB pathway. This study gives scientific evidence that validate the use of A. fragrans in treatment of patients with gynecological diseases in clinical practice in traditional Chinese medicine.

Effects of er-miao-san extracts on TNF-alpha-induced MMP-1 expression in human dermal fibroblasts

BACKGROUND

Various health benefits have been attributed to Er-Miao-San (EMS), a traditional Chinese herbal formulation that contains equal amounts of cortex phellodendri (Phellodendron amurense Ruprecht) and rhizoma atractylodis (Atractylodes lancea D.C). However, its effect on the anti-inflammatory activity in human dermal fibroblasts (HDFs) and the mechanism underlying this effect are unknown.

RESULTS

This study investigated the effects of EMS on TNF-α-induced MMP-1 expression in HDFs. Our data show that EMS inhibited TNF-α-induced MMP-1 expression in a concentration-dependent manner. Interestingly, EMS maintained IκB content without inhibiting the phosphorylation of MAPKs, which are well-established upstream kinases of NF-κB. Moreover, EMS reduced the level of nuclear p65 protein in HDFs. Luciferase assay revealed that EMS inhibits the transcriptional activity of NF-κB by stabilizing IκB. Our results show that EMS exerts its anti-inflammatory effect by inhibiting NF-κB-regulated genes such as IL-1β and IL-8. Moreover, EMS effectively inhibited TNF-α-induced expression of MMP-1 via the NF-κB pathway.

CONCLUSIONS

Taken together, our data suggest that EMS could potentially be used as an anti-inflammatory and anti-aging treatment.

Er-Miao-San, a traditional herbal formula containing Rhizoma Atractylodis and Cortex Phellodendri inhibits inflammatory mediators in LPS-stimulated RAW264.7 macrophages through inhibition of NF-κB pathway and MAPKs activation

ETHNOPHARMACOLOGICAL RELEVANCE

Er-Miao-San (EMS) is a traditional Chinese herbal formulation that contains combinations of Rhizoma Atractylodis (RA) and Cortex Phellodendri (CP). It exhibits analgesic and anti-inflammatory activities and have been used for the treatment of various "Bi Zheng" for thousand years in China. The aims of the present study were to investigate the anti-inflammatory activities of EMS and elucidate the underlying mechanisms with regard to its molecular basis of action for the best combination.

MATERIALS AND METHODS

The anti-inflammatory effects of EMS were studied by using lipopolysaccharide (LPS)-stimulated activation of nitric oxide (NO) and pro-inflammatory cytokine production in mouse RAW264.7 macrophages. Expression of inducible NO synthase (iNOS), mitogen-activated protein kinases (MAPKs) phosphorylation, p65 phosphorylation, inhibitor-κBα (IκBα) degradation, and NF-κB DNA-binding activity were further investigated.

RESULTS

The present study demonstrated that EMS could suppress the production of NO in LPS-stimulated RAW264.7 macrophages. However, CP and RA did not have significant inhibitory effect on them. EMS also inhibited the production of tumor necrosis factor-alpha, interleukin-1 beta and macrophage chemotactic protein-1. Further investigations showed EMS could suppress iNOs expression and p38 phosphorylation. EMS significantly decreased the content of IκBα, reduced the level of phosphorylated p65 and suppressed the NF-κB DNA-binding activity. All these results suggested the inhibitory effects of EMS on the production of inflammatory mediators through the inhibition of the NF-κB pathway.

CONCLUSIONS

Our results indicated that EMS inhibited inflammatory events and iNOS expression in LPS-stimulated RAW264.7 cells through the inactivation of the MAPK and NF-κB pathway. This study gives scientific evidence validating the use of EMS in treatment of patients with "Bi Zheng" in clinical practice in traditional Chinese medicine.

Regulation of reactionary dentin formation by odontoblasts in response to polymicrobial invasion of dentin matrix

Odontoblast synthesis of dentin proceeds through discrete but overlapping phases characterized by formation of a patterned organic matrix followed by remodelling and active mineralization. Microbial invasion of dentin in caries triggers an adaptive response by odontoblasts, culminating in formation of a structurally altered reactionary dentin, marked by biochemical and architectonic modifications including diminished tubularity. Scanning electron microscopy of the collagen framework in reactionary dentin revealed a radically modified yet highly organized meshwork as indicated by fractal and lacunarity analyses. Immuno-gold labelling demonstrated increased density and regular spatial distribution of dentin sialoprotein (DSP) in reactionary dentin. DSP contributes putative hydroxyapatite nucleation sites on the collagen scaffold. To further dissect the formation of this altered dentin matrix, the associated enzymatic machinery was investigated. Analysis of extracted dentin matrix indicated increased activity of matrix metalloproteinase-2 (MMP-2) in the reactionary zone referenced to physiologic dentin. Likewise, gene expression analysis of micro-dissected odontoblast layer revealed up-regulation of MMP-2. Parallel up-regulation of tissue inhibitor of metalloproteinase-2 (TIMP-2) and membrane type 1- matrix metalloproteinase (MT1-MMP) was observed in response to caries. Next, modulation of odontoblastic dentinogenic enzyme repertoire was addressed. In the odontoblast layer expression of Toll-like receptors was markedly altered in response to bacterial invasion. In carious teeth TLR-2 and the gene encoding the corresponding adaptor protein MyD88 were down-regulated whereas genes encoding TLR-4 and adaptor proteins TRAM and Mal/TIRAP were up-regulated. TLR-4 signalling mediated by binding of bacterial products has been linked to up-regulation of MMP-2. Further, increased expression of genes encoding components of the TGF-β signalling pathway, namely SMAD-2 and SMAD-4, may explain the increased synthesis of collagen by odontoblasts in caries. These findings indicate a radical adaptive response of odontoblasts to microbial invasion of dentin with resultant synthesis of modified mineralized matrix.

The human NADPH oxidase: primary and secondary defects impairing the respiratory burst function and the microbicidal ability of phagocytes

Phagocytes, such as granulocytes and monocytes/macrophages, contain a membrane-associated NADPH oxidase that produces superoxide leading to other reactive oxygen species with microbicidal, tumoricidal and inflammatory activities. Primary defects in oxidase activity in chronic granulomatous disease (CGD) lead to severe, life-threatening infections that demonstrate the importance of the oxygen-dependent microbicidal system in host defence. Other immunological disturbances may secondarily affect the NADPH oxidase system, impair the microbicidal activity of phagocytes and predispose the host to recurrent infections. This article reviews the primary defects of the human NADPH oxidase leading to classical CGD, and more recently discovered immunological defects secondarily affecting phagocyte respiratory burst function and resulting in primary immunodeficiencies with varied phenotypes, including susceptibilities to pyogenic or mycobacterial infections.

TNF-α renders macrophages resistant to a range of cancer chemotherapeutic agents through NF-κB-mediated antagonism of apoptosis signalling

The abundance of macrophages is an independent negative prognostic factor in a range of cancer types, linked to the actions of macrophage products on vasculogenesis and cancer cell survival, motility and metastasis. TNF-α is a macrophage product and a product of some cancer cell types that is also associated with adverse prognosis in clinical and experimental cancers, through enhanced tumour cell growth, survival and metastasis. Macrophages are important targets of TNF-α. We observed that TNF-α partly substituted for the macrophage growth factor, M-CSF, in maintaining macrophage survival by protecting cells from apoptosis. We found that TNF-α afforded similar protection to chemotherapeutic agents and related cytotoxic drugs that acted through a range of apoptosis-initiating pathways, but not where protein synthesis was inhibited. Protection was dependent on intact NF-κB signalling. In addition to NF-κB-dependent factors previously identified as anti-apoptotic, we found an absolute requirement for very early antagonism of mitochondrial cytochrome C release, which sufficed to prevent apoptosis in the face of activation of a range of upstream apoptosis pathways, including p53, DISC-linked, mitochondrial depolarisation and calcium-sensitive pathways. The capacity of TNF-α to preserve macrophage numbers in the face of chemotherapy drugs is a potential contributor to prognosis in TNF-α-expressing cancers, encouraging further testing of anti-TNF-α treatments in these patients.

Tumor necrosis factor-alpha promotes survival in methotrexate-exposed macrophages by an NF-kappaB-dependent pathway

Introduction

Methotrexate (MTX) induces macrophage apoptosis in vitro, but there is not much evidence for increased synovial macrophage apoptosis in MTX-treated patients. Macrophage apoptosis is reported, however, during clinical response to anti-tumor necrosis factor-alpha (TNF-α) treatments. This implies that TNF-α promotes macrophage survival and suggests that TNF-α may protect against MTX-induced apoptosis. We, therefore, investigated this proposal and the macrophage signaling pathways underlying it.

Methods

Caspase-3 activity, annexin-V binding/7-aminoactinomycin D (7-AAD) exclusion and cell-cycle analysis were used to measure steps in apoptosis of primary murine macrophages and cells of the RAW_264.7 macrophage cell line that had been exposed to clinically-relevant concentrations of MTX and TNF-α.

Results

MTX induces apoptosis in primary murine macrophages at concentrations as low as 100 nM in vitro. TNF-α, which has a context-dependent ability to increase or to suppress apoptosis, efficiently suppresses MTX-induced macrophage apoptosis. This depends on NF-κB signaling, initiated through TNF Receptor Type 1 ligation. Macrophage colony stimulating factor, the primary macrophage survival and differentiation factor, does not activate NF-κB or protect macrophages from MTX-induced apoptosis. A weak NF-κB activator, Receptor Activator of NF-κB Ligand (RANKL) is likewise ineffective. Blocking NF-κB in TNF-α-exposed macrophages allowed pro-apoptotic actions of TNF-α to dominate, even in the absence of MTX. MTX itself does not promote apoptosis through interference with NF-κB signaling.

Conclusions

These findings provide another mechanism by which TNF-α sustains macrophage numbers in inflamed tissue and identify a further point of clinical complementarity between MTX and anti-TNF-α treatments for rheumatoid arthritis.

Sphingosylphosphorylcholine and lysosulfatide have inverse regulatory functions in monocytic cell differentiation into macrophages

Sphingolipids act as signaling mediators that regulate a diverse range of cellular events. Although numerous sphingolipid functions have been studied, little is known about the effect of sphingolipids on monocyte differentiation into macrophages. Here, we report that two lysosphingolipids, sphingosylphosphorylcholine (SPC) and lysosulfatide (LSF), inversely affect macrophagic differentiation of monocytic cell lines, U937 and THP-1. Molecular analyses revealed that SPC enhances, whereas LSF suppresses, phorbol ester-induced classical (M1-polarized) differentiation to macrophages. The expression of CD11b, a macrophage marker, was induced in accordance with the activation status of the Raf/MEK/ERK signaling pathway in which SPC and LSF had opposite effects. Pharmacological inhibition of this pathway aborted the differentiation, indicating that this signaling pathway is required. Consistently, SPC promoted, while LSF inhibited, monocyte adhesion to fibronectin, through the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway. The effects of SPC on Raf/MEK/ERK and PI3K/Akt signaling were dependent on G(i/o), whereas the SPC-induced calcium influx was dependent on G(q). Thus SPC utilizes G-protein coupled receptor. In contrast, the effects of LSF were independent of G(i/o) and G(q). These results suggest that SPC enhances, whereas LSF suppresses, monocyte differentiation into macrophages through regulating the Raf/MEK/ERK and PI3K/Akt signaling pathways via distinct mechanisms.

Divergent effect of cobalt and beryllium salts on the fate of peripheral blood monocytes and T lymphocytes

Occupational exposure to metals such as cobalt and beryllium represents a risk factor for respiratory health and can cause immune-mediated diseases. However, the way they act may be different. We show here that the two metals have a divergent effect on peripheral T lymphocytes and monocytes: BeSO(4) induces cell death in monocytes but not in T lymphocytes, which instead respond by producing Interferon gamma (IFN-γ); conversely, CoCl(2) induces apoptosis in T lymphocytes but not in monocytes. Interestingly, both metals induce p53 overexpression but with a dramatic different outcome. This is because the effect of p53 in CoCl(2)-treated monocytes is counteracted by the antiapoptotic activity of cytoplasmic p21(Cip1/WAF1), the activation of nuclear factor κB, and the inflammasome danger signaling pathway leading to the production of proinflammatory cytokines. However, CoCl(2)-treated monocytes do not fully differentiate into macrophage or dendritic cells, as inferred by the lack of expression of CD16 and CD83, respectively. Furthermore, the expression of HLA-class II molecules, as well as the capability of capturing and presenting the antigens, decreased with time. In conclusion, cobalt keeps monocytes in a partially activated, proinflammatory state that can contribute to some of the pathologies associated with the exposure to this metal.

The orphan nuclear receptor SHP inhibits apoptosis during the monocytic differentiation by inducing p21WAF1

Small heterodimer partner (SHP) is an atypical member of nuclear receptor superfamily that lacks a DNA-binding domain. In previous study, we showed that SHP, c-jun, p65 of NF-gammaB subunits, and p21WAF1 expression was increased during monocytic differentiaton with the exposure of human leukemia cells to a differentiation agent, PMA. In this study, c-Jun and p65 were shown to mediate the transcriptional activation of the SHP promoter. In addition, SHP induced the cell cycle regulatory protein levels and cooperatively increased an induction of p21WAF1 expression with p65. Furthermore, SHP protected differentiated cells from etoposide-induced cellular apoptosis through the induction and cytoplasmic sequestration of p21WAF1. Complex formation between SHP and p21WAF1 was demonstrated by means of coimmunoprecipitation. These results suggest that SHP prolongs a cellular survival of differentiating monocytes through the transcriptional regulation of target genes of cell survival and differentiation.

Sustained NF-kappaB activation produces a short-term cell proliferation block in conjunction with repressing effectors of cell cycle progression controlled by E2F or FoxM1

NF-kappaB transcription factors induce a host of genes involved in pro-inflammatory/stress-like responses; but the collateral effects and consequences of sustained NF-kappaB activation on other cellular gene expression programming remain less well understood. Here enforced expression of a constitutively active IKKbeta T-loop mutant (IKKbetaca) drove murine fibroblasts into transient growth arrest that subsided within 2-3 weeks of continuous culture. Proliferation arrest was associated with a G1/S phase block in immortalized and primary early passage MEFs. Molecular analysis in immortalized MEFs revealed that inhibition of cell proliferation in the initial 1-2 weeks after their IKKbetaca retroviral infection was linked to the transient, concerted repression of essential cell cycle effectors that are known targets of either E2F or FoxM1. Co-expression of a phosphorylation resistant IkappaBalpha super repressor and IKKbetaca abrogated growth arrest and cell cycle effector repression, thereby linking IKKbetaca's effects to canonical NF-kappaB activation. Transient growth arrest of IKKbetaca cells was associated with enhanced p21 (cyclin-dependent kinase inhibitor 1A) protein expression, due in part to transcriptional activation by NF-kappaB and also likely due to strong repression of Skp2 and Csk1, both of which are FoxM1 direct targets mediating proteasomal dependent p21 turnover. Ablation of p21 in immortalized MEFs reduced their IKKbetaca mediated growth suppression. Moreover, trichostatin A inhibition of HDACs alleviated the repression of E2F and FoxM1 targets induced by IKKbetaca, suggesting chromatin mediated gene silencing in IKKbetaca's short term repressive effects on E2F and FoxM1 target gene expression.

cIAP1-dependent TRAF2 degradation regulates the differentiation of monocytes into macrophages and their response to CD40 ligand

Peripheral blood monocytes are plastic cells that migrate to tissues and differentiate into various cell types, including macrophages, dendritic cells, and osteoclasts. We have described the migration of cellular inhibitor of apoptosis protein 1 (cIAP1), a member of the IAP family of proteins, from the nucleus to the Golgi apparatus in monocytes undergoing differentiation into macrophages. Here we show that, once in the cytoplasm, cIAP1 is involved in the degradation of the adaptor protein tumor necrosis factor receptor-associated factor 2 (TRAF2) by the proteosomal machinery. Inhibition of cIAP1 prevents the decrease in TRAF2 expression that characterizes macrophage formation. We demonstrate that TRAF2 is initially required for macrophage differentiation as its silencing prevents Ikappa-Balpha degradation, nuclear factor-kappaB (NF-kappaB) p65 nuclear translocation, and the differentiation process. Then, we show that cIAP1-mediated degradation of TRAF2 allows the differentiation process to progress. This degradation is required for the macrophages to be fully functional as TRAF2 overexpression in differentiated cells decreases the c-Jun N-terminal kinase-mediated synthesis and the secretion of proinflammatory cytokines, such as interleukin-8 and monocyte chemoattractant protein 1 (MCP-1) in response to CD40 ligand. We conclude that TRAF2 expression and subsequent degradation are required for the differentiation of monocytes into fully functional macrophages.

Essential role of nuclear factor-kappaB for NADPH oxidase activity in normal and anhidrotic ectodermal dysplasia leukocytes

This work investigated the functional role of nuclear factor-kappaB (NF-kappaB) in respiratory burst activity and in expression of the human phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase genes CYBB, CYBA, NCF1, and NCF2. U937 cells with a stably transfected repressor of NF-kappaB (IkappaBalpha-S32A/S36A) demonstrated significantly lower superoxide release and lower CYBB and NCF1 gene expression compared with control U937 cells. We further tested Epstein-Barr virus (EBV)-transformed B cells from patients with anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID), an inherited disorder of NF-kappaB function. Superoxide release and CYBB gene expression by EDA-ID cells were significantly decreased compared with healthy cells and similar to cells from patients with X-linked chronic granulomatous disease (X91(0) CGD). NCF1 gene expression in EDA-ID S32I cells was decreased compared with healthy control cells and similar to that in autosomal recessive (A47(0)) CGD cells. Gel shift assays demonstrated loss of recombinant human p50 binding to a NF-kappaB site 5' to the CYBB gene in U937 cells treated with NF-kappaB inhibitors, repressor-transfected U937 cells, and EDA-ID patients' cells. Zymosan phagocytosis was not affected by transfection of U937 cells with the NF-kappaB repressor. These studies show that NF-kappaB is necessary for CYBB and NCF1 gene expression and activation of the phagocyte NADPH oxidase in this model system.

Apoptosis resistance in HIV-1 persistently-infected cells is independent of active viral replication and involves modulation of the apoptotic mitochondrial pathway

Background

HIV triggers the decline of CD4⁺ T cells and leads to progressive dysfunction of cell-mediated immunity. Although an increased susceptibility to cell death occurs during the acute phase of HIV infection, persistently-infected macrophages and quiescent T-cells seem to be resistant to cell death, representing a potential reservoir for virus production.

Results

Lymphoid (H9/HTLVIII_B and J1.1) and pro-monocytic (U1) HIV-1 persistently-infected cell lines were treated with hydrogen peroxide (H₂O₂) and staurosporine (STS) for 24 h, and susceptibility to apoptosis was evaluated and compared with uninfected counterparts (H9, Jurkat and U937 respectively). When exposed to different pro-apoptotic stimuli, all persistently-infected cell lines showed a dramatic reduction in the frequency of apoptotic cells in comparison with uninfected cells. This effect was independent of the magnitude of viral replication, since the induction of viral production in lymphoid or pro-monocytic cells by exposure to TNF-α or PMA did not significantly change their susceptibility to H₂O₂- or STS-induced cell death. A mechanistic analysis revealed significant diferences in mitochondrial membrane potential (MMP) and caspase-3 activation between uninfected and persistently-infected cells. In addition, Western blot assays showed a dramatic reduction of the levels of pro-apototic Bax in mitochondria of persistently-infected cells treated with H₂O₂ or STS, but not in uninfected cells.

Conclusion

This study represents the first evidence showing that resistance to apoptosis in persistently-infected lymphoid and monocytic cells is independent of active viral production and involves modulation of the mitochondrial pathway. Understanding this effect is critical to specifically target the persistence of viral reservoirs, and provide insights for future therapeutic strategies in order to promote complete viral eradication.

Anti-inflammatory interventions of NF-kappaB signaling: potential applications and risks

Signaling via NF-kappaB is a key process during inflammation and thus constitutes an attractive target for anti-inflammatory therapeutic interventions. Especially during initial hyperinflammatory states of an acute illness such as sepsis or in the course of chronic inflammation and autoimmune diseases inhibition of IKK-driven NF-kappaB activation provides a promising treatment strategy. Given its critical role in innate and adaptive immune responses, however, there is a certain amount of risk due to induced immunodeficiency that may follow inhibitory treatment. Moreover, its primary anti-apoptotic function suggests that blockade of NF-kappaB activation has dramatic effects on cell functions and survival and eventually worsens the course of an inflammatory disease. An overview of canonical and alternative NF-kappaB activation and its critical role in immune responses will be provided. A main topic focuses on recent animal studies and data derived from genetic studies in humans that provide an insight into potential effects of different therapeutic modulations of NF-kappaB inflammatory signaling. The pros and cons of NF-kappaB inhibition and treatment strategies will be critically reviewed.

Differential expression and role of p21cip/waf1 and p27kip1 in TNF-alpha-induced inhibition of proliferation in human glioma cells

Background

The role of TNF-α in affecting the fate of tumors is controversial, while some studies have reported apoptotic or necrotic effects of TNF-α, others provide evidence that endogenous TNF-α promotes growth and development of tumors. Understanding the mechanism(s) of TNF-α mediated growth arrest will be important in unraveling the contribution of tissue associated macrophages in tumor resistance. The aim of this study was to investigate the role of Cyclin Dependent Kinase Inhibitors (CDKI) – p21^cip/waf1 and p27^kip1 in TNF-α mediated responses in context with p53 and activation of NF-κB and Akt pathways. The study was done with human glioma cell lines -LN-18 and LN-229 cells, using monolayer cultures and Multicellular Spheroids (MCS) as in vitro models.

Results

TNF-α induced inhibition of proliferation and enhanced the expression of p21^cip/waf1 and p27^kip1 in LN-18 cells. p21 was induced on exposure to TNF-α, localized exclusively in the nucleus and functioned as an inhibitor of cell cycle but not as an antiapoptotic protein. In contrast, p27 was constitutively expressed, localized predominantly in the cytoplasm and was not involved in arrest of proliferation. Our data using IκBα mutant LN-18 cells and PI3K/Akt inhibitor-LY294002 revealed that the expression of p21 is regulated by NF-κB. Loss of IκBα function in LN-229 cells (p53 positive) did not influence TNF-α induced accumulation of pp53 (Ser-20 p53) suggesting that p53 was not down stream of NF-κB. Spheroidogenesis enhanced p27 expression and p21 induced by TNF-α was significantly increased in the MCS compared to monolayers.

Conclusion

This study demarcates the functional roles for CDKIs-p21^cip/waf1 and p27^kip1 during TNF-α stimulated responses in LN-18 glioma cells. Our findings provide evidence that TNF-α-induced p21 might be regulated by NF-κB or p53 independently. p21 functions as an inhibitor of cell proliferation and does not have a direct role in rendering the cells resistant to TNF-α mediated cytotoxicity.

Histone deacetylase inhibitors: signalling towards p21cip1/waf1

Chromatin-modifying enzymes such as histone deacetylases (HDAC) facilitate a closed chromatin structure and hence transcriptional repression. HDAC are commonly affected in human cancer diseases. Thus, inhibition of HDAC represents a novel therapeutic approach. Several studies have shown that HDAC inhibitors strongly activate the expression of the cyclin-dependent kinase inhibitor p21(cip1/waf1) through (i) enhanced histone acetylation around the p21(cip1/waf1) promoter and (ii) the Sp1 sites on the p21(cip1/waf1) promoter releasing the repressor HDAC1 from its binding. p21(cip1/waf1) expression is regulated in a p53-dependent and p53-independent manner. The decision if p21(cip1/waf1) up-regulation results in cell cycle arrest or apoptosis, decides about the therapeutic efficacy of an anti-cancer treatment with HDAC inhibitors.

B7-DC/PD-L2 Cross-Linking Induces NF-κB-Dependent Protection of Dendritic Cells from Cell Death

Cross-linking cell surface molecules with IgM Abs is a specific approach for activating cells in vitro or in vivo. Dendritic cells (DC) activated with a human B7-DC (PD-L2)-specific IgM Ab can induce strong antitumor responses and block inflammatory airway disease in experimental models, yet the Ab-mediated molecular events promoting these responses remain unclear. Analysis of human or mouse DC treated with the B7-DC cross-linking Ab revealed PI3K-dependent phosphorylation of AKT accompanied by mobilization of NF-kappaB. Ab-activated DC up-regulated expression of cytokine and chemokine genes in an NF-kappaB-dependent manner. Importantly, PI3K-->AKT-->NF-kappaB activation was found to be indispensable for B7-DC cross-linking Ab-mediated protection of DC from cell death caused by cytokine withdrawal. Although other DC activators similarly protect DC from cell death, a synergy between cross-linking B7-DC and ligating RANK was observed. The parallel signaling events induced in human and mouse DC demonstrate that activation of cells using IgM Ab results in a response governed by a common mechanism and support the hypothesis that B7-DC cross-linking using this Ab may provide beneficial therapeutic immune modulation in human patients similar to those seen in animal models.

Caspase-8 prevents sustained activation of NF-kappaB in monocytes undergoing macrophagic differentiation

Caspases have demonstrated several nonapoptotic functions including a role in the differentiation of specific cell types. Here, we show that caspase-8 is the upstream enzyme in the proteolytic caspase cascade whose activation is required for the differentiation of peripheral-blood monocytes into macrophages. On macrophage colony-stimulating factor (M-CSF) exposure, caspase-8 associates with the adaptor protein Fas-associated death domain (FADD), the serine/threonine kinase receptor-interacting protein 1 (RIP1) and the long isoform of FLICE-inhibitory protein FLIP. Overexpression of FADD accelerates the differentiation process that does not involve any death receptor. Active caspase-8 cleaves RIP1, which prevents sustained NF-kappaB activation, and activates downstream caspases. Together these data identify a role for caspase-8 in monocytes undergoing macrophagic differentiation, that is, the enzyme activated in an atypical complex down-regulates NF-kappaB activity through RIP1 cleavage.

NF-kappaB and the regulation of hematopoiesis

This review will focus on the role of nuclear factor kappaB (NF-kappaB) signaling in hematopoietic differentiation. We will also discuss several hematopoietic pathologies associated with deregulation of NF-kappaB and their potential therapies.

Nuclear factor-kappaB dimer exchange promotes a p21(waf1/cip1) superinduction response in human T leukemic cells

The nuclear factor-kappaB (NF-kappaB)/Rel transcription factors are recognized as critical apoptosis regulators. We reported previously that NF-kappaB contributes to chemoresistance of CEM human T leukemic cells in part through its ability to induce p21(waf1/cip1). Here, we provide evidence that sequential NF-kappaB-activating signals induce heightened NF-kappaB DNA binding and p21(waf1/cip1) induction in CEM and additional T leukemic cell lines. This response arises from exceedingly low basal expression of the p105/p50 NF-kappaB subunit encoded by the NFKB1 gene in these cell lines. An initial NF-kappaB activation event enhances the recruitment of p65 and ELF1 to the NFKB1 promoter, leading to p65- and ELF1-dependent synthesis of p105/p50, which promotes an exchange of NF-kappaB complexes to p50-containing complexes with an increased DNA-binding activity to certain NF-kappaB target elements. Subsequent stimulation of these cells with an anticancer agent, etoposide, results in augmented NF-kappaB-dependent p21(waf1/cip1) induction and increased chemoresistance of the leukemia cells. Thus, we propose that low basal NFKB1 expression coupled with sequential NF-kappaB activation events can promote increased chemoresistance in certain T leukemic cells.

Differentiation of androgen-independent prostate cancer PC-3 cells is associated with increased nuclear factor-kappaB activity

Recently, we have reported that inosine 5'-monophosphate dehydrogenase inhibitors, such as mycophenolic acid (MPA), induce the differentiation of PC-3 cells, which are derived from a human androgen-independent prostate cancer, into cells with a phenotype resembling maturing prostate secretory cells. Here, we describe such differentiation induced by the histone deacetylase inhibitor tributyrin. The maturation was defined by cytoplasmic vacuole production and induction of CD10, CD46, CD55, GRP78, keratin 17, and zinc-alpha-2-glycoprotein. To identify additional genes associated with tributyrin-induced PC-3 cell differentiation and to gain some insight into the mechanism that underlies this differentiation, we have, by means of microarray analyses, compared tributyrin-induced gene expression patterns with those of MPA, which initiates PC-3 cell differentiation by a dissimilar mode of action. We suggested that genes induced by both tributyrin and MPA would be most likely associated with differentiation rather than with the unique action of each particular inducer. Our results indicated that tributyrin or MPA induced the expression of a large number of common genes, including genes known or assumed to be NF-kappaB dependent. The NF-kappaB dependency of a group of these genes, which included the PC-3 cell differentiation marker keratin 17, was confirmed by using two common NF-kappaB activation inhibitors, Bay11-082 and TMB-8, and p65 subunit of NF-kappaB complex specific small interfering RNA. Taken together, our results implicate both NF-kappaB-dependent and NF-kappaB-independent genes in the processes leading to PC-3 cell differentiation induced by tributyrin and MPA.

A proapoptotic function of p21 in differentiating granulocytes

p21(waf 1/cip 1) (p21), best known for its ability to regulate the cell cycle, has been noted also to exert cell cycle-independent effects on apoptosis and differentiation. Inhibition of apoptosis by p21 has been reported in hematopoietic models, particularly in monocytes exposed to apoptogenic agents. The effect of p21 on survival has not hitherto been analyzed during the myeloblast to granulocyte transition. Using 32 Dc l3 murine myeloblasts, a cell line that proliferates in IL-3 and differentiates in G-CSF, we studied the effects of forced expression of p21 on cell survival. We hypothesized that exogenous p21 would suppress the modest levels of cell death associated with G-CSF-mediated differentiation of 32 Dc l3 cells. Contrary to expectations, we found that exogenous p21 enhanced apoptosis of cells removed from IL-3. The p21 overexpression led to decreased cell growth, caspase-3 activation and annexin positivity. These effects occurred only in the presence of G-CSF. These findings suggest that p21 is proapoptotic in granulopoiesis, and that this effect is masked by IL-3-mediated survival signals. Our results also indicate there are distinct and opposing effects of p21 on monocytic and granulocytic survival. Aberrantly high levels of p21 may contribute to disease processes involving excessive apoptosis of granulocyte precursors.

Arsenic Trioxide Induces Apoptosis of Human Monocytes during Macrophagic Differentiation through Nuclear Factor-κB-Related Survival Pathway Down-Regulation

Arsenic trioxide (As(2)O(3)) is known to be toxic toward leukemia cells. In this study, we determined its effects on survival of human monocytic cells during macrophagic differentiation, an important biological process involved in the immune response. As(2)O(3) used at clinically relevant pharmacological concentrations induced marked apoptosis of human blood monocytes during differentiation with either granulocyte-macrophage colony-stimulating factor or macrophage colony-stimulating factor. Apoptosis of monocytes was associated with increased caspase activities and decreased DNA binding of p65 nuclear factor-kappaB (NF-kappaB); like As(2)O(3), the selective NF-kappaB inhibitor (E)-3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (Bay 11-7082) strongly reduced survival of differentiating monocytes. The role of NF-kappaB in arsenic toxicity was also studied in promonocytic U937 cells during phorbol 12-myristate 13-acetate-induced macrophagic differentiation. In these cells, As(2)O(3) first reduced DNA binding of p65 NF-kappaB and subsequently induced apoptosis. In addition, overexpression of the p65 NF-kappaB subunit, following stable infection with a p65 retroviral expressing vector, increased survival of As(2)O(3)-treated U937 cells. As(2)O(3) specifically decreased protein levels of X-linked inhibitor of apoptosis protein and FLICE-inhibitory protein, two NF-kappaB-regulated genes in both U937 cells and blood monocytes during their differentiations. Finally, As(2)O(3) was found to inhibit macrophagic differentiation of monocytic cells when used at cytotoxic concentrations; however, overexpression of the p65 NF-kappaB subunit in U937 cells reduced its effects toward differentiation. In contrast to monocytes, well differentiated macrophages were resistant to low concentrations of As(2)O(3). Altogether, our study demonstrates that clinically relevant concentrations of As(2)O(3) induced marked apoptosis of monocytic cells during in vitro macrophagic differentiation likely through inhibition of NF-kappaB-related survival pathways.

Loss of p21 disrupts p14 ARF-induced G1 cell cycle arrest but augments p14 ARF-induced apoptosis in human carcinoma cells

The human INK4a locus encodes two structurally unrelated tumor suppressor proteins, p16 INK4a and p14 ARF (p19 ARF in the mouse), which are frequently inactivated in human cancer. Both the proapoptotic and cell cycle-regulatory functions of p14 ARF were initially proposed to be strictly dependent on a functional p53/mdm-2 tumor suppressor pathway. However, a number of recent reports have implicated p53-independent mechanisms in the regulation of cell cycle arrest and apoptosis induction by p14 ARF. Here, we show that the G1 cell cycle arrest induced by p14 ARF entirely depends on both p53 and p21 in human HCT116 and DU145 carcinoma cells. In contrast, neither loss of p53 nor p21 impaired apoptosis induction by p14 ARF as evidenced by nuclear DNA fragmentation, phosphatidyl serine exposure, and caspase activation, which included caspase-3/7- and caspase-9-like activities. However, lack of functional p21 resulted in the accumulation of cells in G2/M phase of the cell cycle and markedly enhanced p14 ARF-induced apoptosis that was, nevertheless, efficiently inhibited by the cell permeable broad-spectrum caspase inhibitor zVAD-fmk (valyl-alanyl-aspartyl-(O)-methyl)-fluoromethylketone). Thus, loss of cell cycle restriction point control in the absence of p21 may interfere with p14 ARF-induced apoptosis. Finally, these data indicate that the signaling events required for G1 cell cycle arrest and apoptosis induction by p14 ARF dissociate upstream of p53.

Sp1 and NF-kappaB transcription factor activity in the regulation of the p21 and FasL promoters during promyelocytic leukemia cell monocytic differentiation and its associated apoptosis

Treatment of human acute promyelocytic leukemia cells with phorbol 12-myristate 13-acetate (PMA) results in growth arrest and differentiation toward monocytes, which subsequently die by apoptosis. However, the relationship between terminal differentiation and apoptosis remains unclear. Here we have studied Sp1 and nuclear factor kappaB (NF-kappaB) transcription factor activity in controlling promoters of cell cycle-regulating (p21/WAF1/CIP1) and cell death (FasL) genes during monocytic differentiation and apoptosis of the human acute promyelocytic leukemia cell lines NB4 and HL-60. Using the electrophoretic mobility shift assay, we observed that PMA treatment of NB4 cells caused an early response in Sp1 binding to the p21 and FasL promoters at 8 h. The firmly adherent cell phenotype, characteristic of differentiated cells, retained Sp1-binding activity to either promoter, but it was often lost completely in detached, apoptotic cells. The association of Sp1 with the p21 promoter during monocytic differentiation correlated with the levels of expressed p21 in the cytoplasmic fraction, as detected by immunoblotting. In HL-60 cells, very weak or no Sp1 binding to either promoter was observed. Low NF-kappaB affinity for its consensus sites and to the FasL promoter was characteristic of apoptotic cells. The results of this study suggest a positive role of Sp1 and NF-kappaB, as regulators of p21 and FasL genes, in leukemic cell survival and monocytic differentiation and a negative role in apoptotic cell death.

Proapoptotic function of protein kinase CK2alpha" is mediated by a JNK signaling cascade

Protein kinase CK2 (formerly casein kinase II) is a tetrameric enzyme constitutively expressed in all eurakyotic tissues that plays a significant role in the regulation of cell proliferation, malignant transformation, and apoptosis. The catalytic alpha-subunit of the enzyme is known to exist in three isoforms CK2alpha, CK2alpha' and CK2alpha". CK2alpha" is highly expressed in liver compared with other tissues and is required for the normal trafficking of several hepatocellular membrane proteins. Initial studies of dengue virus infection indicated that the CK2alpha"-deficient membrane trafficking mutant cell line (Trf1) was resistant to virus-induced cell death compared with the parental human hepatoma (HuH)-7 hepatoma line. Expression of recombinant CK2alpha" in Trf1 was capable of reverting this resistant phenotype. This study was extended to TNF-alpha in addition to other stimuli of cell death in an attempt to uncover common death pathways that might be modulated by CK2alpha". Evaluation of different pathways involved in death signaling suggest that the regulation of a critical proapoptotic step in HuH-7 cells by CK2alpha" is mediated by a JNK signaling cascade.

Constitutive NF-kappaB DNA-binding activity in AML is frequently mediated by a Ras/PI3-K/PKB-dependent pathway

In the present study, we aimed to elucidate the mechanism responsible for constitutive NF-kappaB DNA-binding activity in AML cells. Intervening in aberrant signaling pathway provides a rational approach for in vivo targeting of AML cells. Constitutive NF-kappaB DNA-binding activity was observed in 16 of 22 (73%) investigated AML cases and was, in general, associated with resistance to spontaneous apoptosis. Indeed, inhibition of NF-kappaB activity by the NF-kappaB inhibitor SN-50 peptide resulted in enhanced chemotherapy-induced apoptosis. In the majority of cases, constitutive NF-kappaB activity was mediated by a Ras/PI3 kinase (PI3-K)/protein kinase B (PKB)-mediated pathway. The PI3-K inhibitor Ly294002 and the Ras inhibitor L-744832 both inhibited PKB phosphorylation and NF-kappaB DNA-binding activity. The constitutive activation of Ras GTP-ase was caused by mutations in the gene encoding for N-Ras in 29% of the cases. The constitutive NF-kappaB activity could so far not be ascribed to the autocrine production of growth factors or to mutations in the Flt3 receptor, since anti-GM-CSF, -IL-1, -IL6, -TNFalpha or the tyrosine kinase inhibitor AG1296 did not affect the NF-kappaB DNA-binding activity. The present study demonstrates that Ras activation is an important pathway for triggering the NF-kappaB pathway in AML cells.

Constitutive cytoplasmic localization of p21(Waf1/Cip1) affects the apoptotic process in monocytic leukaemia

In the present study, we analysed the expression and localization of p21(Waf1/Cip1) in normal and malignant haematopoietic cells. We demonstrate that in normal monocytic cells, protein kinase C (PKC)-induced p21 gene activation, which is nuclear factor-kappaB (NF-kappaB) independent, results in predominantly cytoplasmic localized p21 protein. In acute monocytic leukaemia (M4, M5), monocytic blasts (N=12) show constitutive cytoplasmic p21 expression in 75% of the cases, while in myeloid leukaemic blasts (N=10), low nuclear and cytoplasmic localization of p21 could be detected, which is also PKC dependent. Constitutive p21 expression in monocytic leukaemia might have important antiapoptotic functions. This is supported by the finding that in U937 cells overexpressing p21, VP16-induced apoptosis is significantly reduced (20.0+/-0.9 vs 55.8+/-3.8%, P<0.01, N=5), reflected by a reduced phosphorylation of p38 and JNK. Similarly, AML blasts with high cytoplasmic p21 were less sensitive to VP16-induced apoptosis as compared to AML cases with low or undetectable p21 expression (42.25 vs 12.3%, P<0.01). Moreover, complex formation between p21 and ASK1 could be demonstrated in AML cells, by means of coimmunoprecipitation. In summary, these results indicate that p21 has an antiapoptotic role in monocytic leukaemia, and that p21 expression is regulated in a PKC-dependent and NF-kappaB-independent manner.

The nuclear localization of NFkappaB and p53 is positively correlated with HPV16 E7 level in laryngeal squamous cell carcinoma

The interaction between the HPV (human papilloma virus) 16 E7 and other cell growth factors, such as p53 and NFkappaB in laryngeal cancer is not clearly understood. The aim of this study was to examine the expression of these three proteins in tumor and non-tumor laryngeal tissues from patients with laryngeal squamous cell carcinoma. These three proteins were dominantly expressed in the nucleus and their levels were higher in the tumor tissue than in the non-tumor tissue, although the comparison between the tumor and non-tumor tissues of p53 staining did not reach significance. The intensity of the nuclear stain of E7 and p53 was stronger than that of p65, a subunit of NFkappaB. Correlation analysis revealed that there was a positive relationship between the level of HPV16 E7 and the expression of p65. The correlation between E7 and p53 was also significant, although to a lesser degree. The finding of nuclear localization of p65 suggests that NFkappaB is constantly activated in the laryngeal cancer cells, whereas the sequestration of p53 in the nucleus may represent a mutated form of p53, which is probably inactivated by HPV16 oncoproteins. In conclusion, this study suggests that the nuclear localization of NFkappaB and p53 may play a role in the development of human laryngeal squamous cell carcinoma infected with HPV16.