MEKK1 activates both IkappaB kinase alpha and IkappaB kinase beta

Cell type-specific expression of the IkappaB kinases determines the significance of phosphatidylinositol 3-kinase/Akt signaling to NF-kappa B activation

Phosphatidylinositol (PI) 3-kinase/Akt signaling activates NF-kappa B through pleiotropic, cell type-specific mechanisms. This study investigated the significance of PI 3-kinase/Akt signaling to tumor necrosis factor (TNF)-induced NF-kappa B activation in transformed, immortalized, and primary cells. Pharmacological inhibition of PI 3-kinase blocked TNF-induced NF-kappa B DNA binding in the 293 line of embryonic kidney cells, partially affected binding in MCF-7 breast cancer cells, HeLa and ME-180 cervical carcinoma cells, and NIH 3T3 cells but was without significant effect in H1299 and human umbilical vein endothelial cells, cell types in which TNF activated Akt. NF-kappa B is retained in the cytoplasm by inhibitory proteins, I kappa Bs, which are phosphorylated and targeted for degradation by I kappa B kinases (IKK alpha and IKK beta). Expression and the ratios of IKK alpha and IKK beta, which homo- and heterodimerize, varied among cell types. Cells with a high proportion of IKK alpha (the IKK kinase activated by Akt) to IKK beta were most sensitive to PI 3-kinase inhibitors. Consequently, transient expression of IKK beta diminished the capacity of the inhibitors to block NF-kappa B DNA binding in 293 cells. Also, inhibitors of PI 3-kinase blocked NF-kappa B DNA binding in Ikk beta-/- but not Ikk alpha-/- or wild-type cells in which the ratio of IKK alpha to IKK beta is low. Thus, noncoordinate expression of I kappa B kinases plays a role in determining the cell type-specific role of Akt in NF-kappa B activation.

NF-kappaB promotes survival during mitotic cell cycle arrest

By activating the mitotic checkpoint, anti-microtubule drugs such as nocodazole cause mammalian cells to arrest in mitosis and then undergo apoptosis. Microtubule depolymerization is rapid and results in the activation of the transcription factor NF-kappaB and induction of NF-kappaB-dependent gene expression. However, the functional consequence of NF-kappaB activation has remained unclear. Evidence has accumulated to suggest that NF-kappaB transcriptional activity is required to suppress apoptosis. In the present study, we confirm and extend previous findings that microtubule depolymerization leads to the rapid activation of NF-kappaB and test the hypothesis that the induction of NF-kappaB regulates cell survival during mitotic cell cycle arrest in order to define its role. Using a range of functional assays, we have shown that microtubule depolymerization correlates with the activation of IKKalpha and IKKbeta; the phosphorylation, ubiquitination, and degradation of IkappaBalpha; the translocation of native p65 (RelA) into the nucleus; and increased NF-kappaB transcriptional activity. By inhibiting either the activation of the IKKs or the degradation of IkappaBalpha, we find that the level of apoptosis is significantly increased in the mitotically arrested cells. Inhibition of NF-kappaB signaling in the nonmitotic cells did not affect their survival. We establish that although NF-kappaB is activated rapidly in response to microtubule depolymerization, its cell survival function is not required until mitotic cell cycle arrest, when the mitotic checkpoint is activated and apoptosis is triggered. We conclude that NF-kappaB may regulate the transcription of one or more antiapoptotic proteins that may regulate cell survival during mitotic cell cycle arrest.

Roles for homotypic interactions and transautophosphorylation in IkappaB kinase beta IKKbeta) activation [corrected]

The nuclear factor kappaB (NF-kappaB)/Rel family of transcription factors participates in a wide range of biological activities including inflammation, immunity, and apoptosis. NF-kappaB is kept inactive in the cytoplasm in unstimulated cells by virtue of the masking of its nuclear localization sequence by bound IkappaB protein. Cellular stimuli trigger the destruction of IkappaB proteins and the liberation of NF-kappaB to enter the nucleus and activate gene expression. A multisubunit IkappaB kinase complex (IKK) phosphorylates IkappaB proteins and mediates the activation of NF-kappaB by proinflammatory stimuli such as tumor necrosis factor alpha. Phosphorylation of IkappaB proteins triggers their polyubiquitination and their subsequent recognition and degradation by the proteasome. The IKK complex contains two catalytic subunits, IKKalpha and IKKbeta, and a noncatalytic subunit, NF-kappaB essential modifier/IKKgamma. IKK activation depends upon the phosphorylation of residues in the activation loop of IKKbeta and the subsequent activation of IKKbeta kinase activity. However, the events contributing to IKKbeta phosphorylation are not well understood. Here, we present evidence that the activation of IKKbeta depends on its ability to form homotypic interactions and to transautophosphorylate. We find that an intact leucine zipper in IKKbeta is necessary for homotypic interactions, kinase activation, and phosphorylation on its activation loop. Enforced oligomerization of an IKKbeta mutant defective in forming homotypic interactions restores kinase activation. Homotypic interactions allow IKKbeta molecules to transautophosphorylate one another on their activation loops. Finally, the oligomerization of IKKbeta is stimulated by tumor necrosis factor alpha in cultured cells. Our findings support a model whereby ligand-induced homotypic interactions between IKKbeta molecules result in IKKbeta phosphorylation and consequently IKK activation.

Inhibition of tumor necrosis factor-[alpha]-induced SHP-2 phosphatase activity by shear stress: a mechanism to reduce endothelial inflammation

OBJECTIVE

Atherosclerosis preferentially occurs in areas of turbulent flow, whereas laminar flow is atheroprotective. Inflammatory cytokines have been shown to stimulate adhesion molecule expression in endothelial cells that may promote atherosclerosis, in part, by stimulating c-Jun N-terminal kinase (JNK) and nuclear factor (NF)-kappaB transcriptional activity.

METHODS AND RESULTS

Because Src kinase family and Src homology region 2-domain phosphatase-2 (SHP-2) may regulate JNK activation, we studied the effect of shear stress on endothelial inflammation and JNK. Human umbilical vein endothelial cells preexposed to flow showed decreased tumor necrosis factor (TNF)-alpha-induced c-Jun and NF-kappaB transcriptional activation. TNF-alpha-mediated JNK, c-Jun, and NF-kappaB activation required Src and SHP-2 activity. Shear stress significantly inhibited SHP-2 phosphatase activity without affecting TNF-alpha-induced Src family kinase activation. Because MEKK3 and Gab1 are critical for TNF-alpha-induced c-Jun and NF-kappaB activation, we determined the role of SHP-2 phosphatase activity in MEKK3 signaling. A catalytically inactive form of SHP-2 increased MEKK3/Gab1 interaction and inhibited MEKK3 (but not MEKK1)-mediated c-Jun and NF-kappaB activation.

CONCLUSIONS

These results suggest that SHP-2 is a key mediator for the inhibitory effects of shear stress on TNF-alpha signaling in part via regulating MEKK3/Gab1 interaction, MEKK3 signaling, and subsequent adhesion molecule expression.

Tumor necrosis factor-alpha-induced IKK phosphorylation of NF-kappaB p65 on serine 536 is mediated through the TRAF2, TRAF5, and TAK1 signaling pathway

The activation of NF-kappaB has been shown to be regulated by multiple phosphorylations of IkappaBs and the NF-kappaB p65 subunit. Here, we characterized the intracellular signaling pathway leading to phosphorylation of p65 on Ser-536 using a novel anti-phospho-p65 (Ser-536) antibody. The Ser-536 of endogenous p65 was rapidly phosphorylated in response to a wide variety of NF-kappaB stimulants including TNF-alpha in the cytoplasm and rapidly dephosphorylated in the nucleus. The TNF-alpha-but not IL-1beta-induced Ser-536 phosphorylation was severely impaired in murine embryonic fibroblasts derived from traf2-/-traf5-/- mice. Bay 11-7082, an inhibitor of IkappaB phosphorylation, inhibited the TNF-alpha-induced phosphorylation in vivo. In addition, overexpression of TGF-beta-activated kinase 1 (TAK1), IKKalpha and IKKbeta stimulated the phosphorylation, and their dominant negative mutants blocked the TNF-alpha-induced phosphorylation. Moreover, small interfering RNAs (siRNAs) against TAK1, IKKalpha and IKKbeta blocked the phosphorylation of endogenous p65. On the other hand, calyculin-A, a protein phosphatase inhibitor, blocked the dephosphorylation in the nucleus in vivo. These results indicate that similar signaling pathways were utilized for the phosphorylations of IkappaBalpha and p65, which further support the idea that both IkappaB and NF-kappaB are substrates for the IKK complex in the activation of NF-kappaB.

Heat shock protein 27 association with the I kappa B kinase complex regulates tumor necrosis factor alpha-induced NF-kappa B activation

Heat shock protein 27 (Hsp27) is a ubiquitously expressed member of the heat shock protein family that has been implicated in various biological functions including the response to heat shock, oxidative stress, and cytokine treatment. Previous studies have demonstrated that heat shock proteins are involved in regulating signal transduction pathways including the NF-kappa B pathway. In this study, we demonstrated that Hsp27 associates with the I kappa B kinase (IKK) complex and that this interaction was stimulated by tumor necrosis factor alpha treatment. Phosphorylation of Hsp27 by the kinase mitogen-activated protein kinase-activated protein kinase 2, a downstream substrate of the mitogen-activated protein kinase p38, enhanced the association of Hsp27 with IKK beta to result in decreased IKK activity. Consistent with these observations, treatment of cells with a p38 inhibitor reduced the association of Hsp27 with IKK beta and thus resulted in increased IKK activity. These studies indicate that Hsp27 plays a negative role in down-regulating IKK signaling by reducing its activity following tumor necrosis factor alpha stimulation.

Increased expression of Mcl-1 is responsible for the blockage of TRAIL-induced apoptosis mediated by EGF/ErbB1 signaling pathway

Epidermal growth factor (EGF) protects against death receptor induced apoptosis in epithelial cells. Herein, we demonstrate that EGF protection against tumor necrosis factor related apoptosis-inducing ligand (TRAIL) induced apoptosis is mediated by increased expression of the Bcl-2 family member myeloid cell leukemia 1 (Mcl-1). EGF increased the mRNA and protein levels of Mcl-1. Furthermore, expression of ErbB1 alone or in combination with ErbB2 in NIH3T3 cells up-regulates Mcl-1 following EGF treatment. In addition, up-regulation of Mcl-1 by EGF is mediated through AKT and NFkappaB activation since kinase inactive AKT and DeltaIkappaB effectively blocks this up-regulation. NFkappaB was also critical for the ability of EGF to prevent TRAIL induced apoptosis as a dominant negative IkappaB (DeltaIkappaB) blocked NFkappaB activation, and relieved EGF protection against TRAIL mediated mitochondrial cytochrome-c release and apoptosis. Finally, anti-sense oligonucleotides directed against Mcl-1 effectively reduced the protein levels of Mcl-1 and blocked EGF protection against TRAIL induced mitochondrial cytochrome-c release and apoptosis. Taken together, EGF signaling leads to increased Mcl-1 expression that is required for blockage of TRAIL induced apoptosis.

Role of double-stranded RNA-activated protein kinase R (PKR) in deoxynivalenol-induced ribotoxic stress response

Trichothecene mycotoxins and other protein synthesis inhibitors activate mitogen-activated protein kinase (MAPKs) via a mechanism that has been termed the "ribotoxic stress response." MAPKs are believed to mediate the leukocyte apoptosis that is observed following experimental exposure to these chemical agents in vitro and in vivo. The purpose of this research was to test the hypothesis that double-stranded, RNA-activated protein kinase R (PKR) is a critical upstream mediator of the ribotoxic stress response induced by the trichothecene deoxynivalenol (DON) and other translational inhibitors. DON was found to readily induce phosphorylation of JNK 1/2, ERK 1/2, and p38 in the murine macrophage RAW 264.7 cell line, within 5 min of culture addition, in a concentration-dependent fashion. Effects were maximal from 15 to 30 min and lasted up to 6 h. The translational inhibitors anisomycin and emetine also had similar effects when added to cultures at equipotent concentrations to DON. DON rapidly activated PKR within 1 to 5 min, as evidenced by autophosphorylation and by phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha). Interestingly, the latter effect was associated with rapid degradation of eIF2alpha. Pretreatment of RAW 264.7 cells with two inhibitors of PKR, 2-aminopurine (2-AP) or adenine (Ad), markedly impaired MAPK phosphorylation in RAW 264.7 cells according to the following rank order JNK>p38>ERK. The capacity of DON to induce MAPK phosphorylation was also markedly suppressed in a stable transformant of the human promonocytic U-937 cell line containing an antisense PKR expression vector. This suppression followed a rank order of JNK>p38>ERK in this PKR-deficient cell line when compared to control cells transfected with vector only. Apoptosis induction by DON and two other translational inhibitors, anisomycin and emetine, was almost completely abrogated in PKR-deficient cells. Together, the results indicate that PKR plays a critical upstream role in the ribotoxic stress response inducible by translational inhibitors.

Selective activation of the c-Jun N-terminal kinase (JNK) pathway fails to elicit Bax activation or apoptosis unless the phosphoinositide 3'-kinase (PI3K) pathway is inhibited

c-Jun N-terminal kinase (JNK) is activated when cells are exposed to noxious stimuli. The role of JNK in apoptosis is subject to considerable debate; for example, JNK activation may promote or inhibit apoptosis depending on the cell type and stimulus involved. These conflicting results have arisen in part because few studies have successfully separated JNK activation from the primary stress-induced damage or from other stress-induced signalling pathways. Here we describe a conditional mutant, deltaMEKK1:ER*, which allows selective activation of the JNK cascade in the absence of any cellular stress. Activation of deltaMEKK1:ER* in CC139 fibroblasts resulted in the rapid and sustained activation of JNK without activating ERK or p38 or promoting IkappaBalpha phosphorylation. Activation of deltaMEKK1:ER* caused a reversible halt in cell growth but failed to induce apoptosis. In contrast, treatment of cells with LY294002, to inhibit phosphoinositide 3-kinase (PI3K), caused downregulation of Bcl-2 and Mcl-1 and allowed deltaMEKK1:ER* to elicit a robust apoptotic response characterized by activation of Bax and caspases. This PI3K-inhibitable, JNK-induced death response was not impeded, but actually accelerated, by cycloheximide. This suggests that JNK-induced activation of Bax and cell death does not require the upregulation of pro-death genes such as Bim or FasL, but rather proceeds through pre-existing components. However, if the PI3K cell survival pathway is not inhibited, even sustained activation of JNK exerts no overt proapoptotic effect in CC139 cells.

Helicobacter pylori induces RANTES through activation of NF-kappa B

Helicobacter pylori-infected gastric mucosa displays a conspicuous infiltration of mononuclear cells and neutrophils. RANTES (short for "regulated upon activation, normal T cell expressed and secreted") is a chemoattractant cytokine (chemokine) important in the infiltration of T lymphocytes and monocytes. RANTES may therefore contribute to the cellular infiltrate in the H. pylori-infected gastric mucosa. The aim of this study was to analyze the molecular mechanism responsible for H. pylori-mediated RANTES expression. We observed that gastric epithelial cells produced RANTES upon coculture with H. pylori. In addition, H. pylori induced RANTES mRNA expression and an increase in luciferase activity in cells which were transfected with a luciferase reporter construct derived from the RANTES promoter, in gastric epithelial cells, indicating that the induction of RANTES production occurred at the transcriptional level. Induction of RANTES was dependent on an intact cag pathogenicity island. Activation of the RANTES promoter by H. pylori occurred through the action of NF-kappa B. Transfection of kinase-deficient mutants of I kappa B kinase (IKK) and NF-kappa B-inducing kinase (NIK) inhibited H. pylori-mediated RANTES activation. In contrast, tumor necrosis factor alpha- or interleukin-1/Toll-like receptor signaling molecules-such as mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1, MyD88, and interleukin-1 receptor-associated kinase-did not play a role in RANTES activation by H. pylori. Collectively, H. pylori induced NF-kappa B activation through an intracellular signaling pathway that involved IKK and NIK, leading to RANTES gene transcription. RANTES induction by H. pylori may play an important role in gastric inflammation.

Signal transduction mediated by the Ras/Raf/MEK/ERK pathway from cytokine receptors to transcription factors: potential targeting for therapeutic intervention

The Ras/Raf/Mitogen-activated protein kinase/ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) cascade couples signals from cell surface receptors to transcription factors, which regulate gene expression. Depending upon the stimulus and cell type, this pathway can transmit signals, which result in the prevention or induction of apoptosis or cell cycle progression. Thus, it is an appropriate pathway to target for therapeutic intervention. This pathway becomes more complex daily, as there are multiple members of the kinase and transcription factor families, which can be activated or inactivated by protein phosphorylation. The diversity of signals transduced by this pathway is increased, as different family members heterodimerize to transmit different signals. Furthermore, additional signal transduction pathways interact with the Raf/MEK/ERK pathway to regulate positively or negatively its activity, or to alter the phosphorylation status of downstream targets. Abnormal activation of this pathway occurs in leukemia because of mutations at Ras as well as genes in other pathways (eg PI3K, PTEN, Akt), which serve to regulate its activity. Dysregulation of this pathway can result in autocrine transformation of hematopoietic cells since cytokine genes such as interleukin-3 and granulocyte/macrophage colony-stimulating factor contain the transacting binding sites for the transcription factors regulated by this pathway. Inhibitors of Ras, Raf, MEK and some downstream targets have been developed and many are currently in clinical trials. This review will summarize our current understanding of the Ras/Raf/MEK/ERK signal transduction pathway and the downstream transcription factors. The prospects of targeting this pathway for therapeutic intervention in leukemia and other cancers will be evaluated.

Role of Jun and Jun kinase in resistance of cancer cells to therapy

A series of kinases, the mitogen-activated protein (MAP) kinases, serves to regulate cellular responses to various environmental influences in metazoans. Three major pathways have been described, each with some overlap in substrate specificity that causes activation of parallel pathways. The activation of one of these, the Jun kinase pathway, has been implicated in apoptotic responses to DNA damage, cell stress and cytotoxic drugs. Under most circumstances in non-malignant cells it appears that c-Jun N-terminal kinase (JNK) activation is a pro-apoptotic event that results in turn in activation of pro-apoptotic members of Bcl-2 family and cytochrome c release from mitochondria. In cells with dysregulated/mutated proliferation or cell cycle controls, the role of JNK and of c-Jun is more controversial. We distinguish between the transcriptional effects of JNK and other protein interactions in which it participates. The initiation of mitochondrial apoptosis pathways by JNK is independent of its transcriptional effects for the most part. In certain cell types, c-Jun overexpression is clearly a basis for resistance to DNA-damaging drugs, and resistance reversal has been observed using c-jun antisense. This preliminary evidence suggests that c-jun may have a role in drug resistance, but additional work with patient tumor samples is required to validate the potential of the JNK pathway as a target.

Erythroid gene suppression by NF-kappa B

NF-kappa B/Rel transcription factors play essential roles to mediate the immune response and apoptosis, and they have also been implicated in cellular differentiation such as erythropoiesis. To elucidate the possible role(s) of NF-kappa B in erythroid gene regulation and erythropoiesis, we have carried out transient transfection studies of the human embryonic/fetal erythroid cell line K562 and mouse adult erythroid MEL cells. It is shown that tumor necrosis factor-alpha represses the transcription activity directed by either alpha or zeta globin promoter in a dose-dependent manner. Furthermore, different NF-kappa B family members could effectively repress the transfected alpha-like globin promoters in K562 as well as in MEL cells. The involvement of NF-kappa B pathway is supported by the ability of a NF-kappa B-specific, dominant negative mutant to block the tumor necrosis factor-alpha or p65-mediated suppression of the alpha-like globin promoter activities. The suppression appears to be mediated through cis-linked HS-40 enhancer. Finally, stably transfected K562 cells overexpressing p65 contain reduced amounts of the p45/NF-E2 RNA and functional NF-E2 proteins. Our studies have identified a new set of targets of NF-kappa B. We suggest that the relatively high activity of the NF-kappa B pathway in early erythroid progenitors is involved in the suppression of erythroid-specific genes. Later in differentiation, together with other changes, the decline of the amounts of the NF-kappa B family of factors leads to derepression and consequent increase of NF-E2, which in turn would activate a subset of erythroid-specific genes.

Effect of caspase cleavage-site phosphorylation on proteolysis

Caspases are important mediators of apoptotic cell death. Several cellular protein substrates of caspases contain potential phosphorylation site(s) at the cleavage-site region, and some of these sites have been verified to be phosphorylated. Since phosphorylation may affect substantially the substrate susceptibility towards proteolysis, phosphorylated, non-phosphorylated and substituted oligopeptides representing such cleavage sites were studied as substrates of apoptotic caspases 3, 7 and 8. Peptides containing phosphorylated serine residues at P4 and P1' positions were found to be substantially less susceptible towards proteolysis as compared with the serine-containing analogues, while phosphoserine at P3 did not have a substantial effect. P1 serine as well as P1-phosphorylated, serine-containing analogues of an oligopeptide representing the poly(ADP-ribose) polymerase cleavage site of caspase-3 were not hydrolysed by any of these enzymes, whereas the P1 aspartate-containing peptides were efficiently hydrolysed. These findings were interpreted with the aid of molecular modelling. Our results suggest that cleavage-site phosphorylation in certain positions could be disadvantageous or detrimental with respect to cleavability by caspases. Cleavage-site phosphorylation may therefore provide a regulatory mechanism to protect substrates from caspase-mediated degradation.

Helicobacter pylori induces matrix metalloproteinase-9 through activation of nuclear factor kappaB

BACKGROUND & AIMS

Matrix metalloproteinases (MMPs), enzymes capable of degrading extracellular matrix components, are believed to be active in connective tissue remodeling associated with various physiologic processes and in pathologic conditions. The aim of this study was to analyze the molecular mechanism responsible for Helicobacter pylori-mediated MMP expression.

METHODS

Expression of MMP messenger RNA and MMP activity were assessed by reverse-transcription polymerase chain reaction and zymography, respectively. Chloramphenicol acetyltransferase assay was used to monitor activation of the MMP-9 gene promoter, and electrophoretic mobility shift assay was used to explore the binding of transcription factors to this promoter. Gastric tissue samples were immunohistochemically stained for MMP-9.

RESULTS

H. pylori induced MMP-9 expression in 2 gastric epithelial cell lines but had no effect on MMP-2. Induction of MMP-9 was dependent on an intact cag pathogenicity island. Activation of the MMP-9 promoter by H. pylori occurred through the action of nuclear factor kappaB. Transfection of kinase-deficient mutants of IkappaB kinase and nuclear factor kappaB-inducing kinase inhibited H. pylori-mediated activation of MMP-9. MMP-9 expression was higher in epithelial cells of H. pylori-positive tissue compared with those of H. pylori-negative tissue.

CONCLUSIONS

H. pylori induced activation of nuclear factor kappaB through an intracellular signaling pathway that involved IkappaB kinase and nuclear factor kappaB-inducing kinase, leading to MMP-9 gene transcription. MMP-9 induction by H. pylori may play an important role in gastric inflammation, ulcer formation, and carcinogenesis.

Up-regulation of vascular endothelial growth factor C in breast cancer cells by heregulin-beta 1. A critical role of p38/nuclear factor-kappa B signaling pathway

Vascular endothelial growth factor C (VEGF-C) is a critical activator of tumor lymphangiogenesis that recently has been strongly implicated in the tumor metastasis process. In this study, we identified that HRG-beta 1 stimulated up-regulation of VEGF-C mRNA and protein of human breast cancer cells in a dosage- and time-dependent manner and that this up-regulation was de novo RNA synthesis-dependent. The HRG-beta 1-induced increase in VEGF-C expression was effectively reduced by treatment with Herceptin, an antibody specifically against HER2. Also, when HER2 was overexpressed in MCF-7 cells that resulted in an evident increase in the VEGF-C level, suggesting an essential role of HER2 in mediating VEGF-C up-regulation by HRG-beta 1. NF-kappa B has been shown to be probably involved in interleukin-1 beta- or tumor necrosis factor-alpha-induced VEGF-C mRNA expression in human fibroblasts. Here we found that HRG-beta 1 could stimulate NF-kappa B nuclear translocation and DNA-binding activity via the I kappa B alpha phosphorylation-degradation mechanism. Blockage of the NF-kappa B activation cascade caused a complete inhibition of the HRG-beta 1-induced elevation of VEGF-C. In promoter-reporter assay, the luciferase activities of the reporter constructs, including the putative NF-kappa B site deleted and mutated form were significantly reduced after HRG-beta 1 treatment as compared with the 1.5-kb VEGF-C promoter. Although investigating the upstream kinase pathway(s) involved in HRG-beta 1-elicited NF-kappa B activation and VEGF-C up-regulation, we found that HRG-beta1 could activate extracellular signal-regulated protein kinase 1/2, phosphatidylinositol 3'-kinase, and p38 mitogen-activated protein kinase (MAPK) in MCF-7. However, only SB203580 (a specific inhibitor of p38 MAPK), not PD98059 nor LY294002, blocked the up-regulation of VEGF-C by HRG-beta 1. A similar inhibition in VEGF-C expression was obtained by cell transfection with dominant-negative p38 (p38AF). Interestingly, the HRG-beta 1-induced NF-kappa B activation cascade was also effectively blocked by SB203580 treatment or p38AF transfection. Our data thus suggests that HRG-beta 1 stimulated a NF-kappa B-dependent up-regulation of VEGF-C through the p38 MAPK signaling pathway in human breast cancer cells.

NF-kappa B p65 transactivation domain is involved in the NF-kappa B-inducing kinase pathway

NF-kappa B-inducing kinase (NIK) is involved in the signal transduction pathway leading to the NF-kappa B activation. In this report, we demonstrate that the NIK-mediated NF-kappa B activation involves the transactivation (TA) domain of p65 subunit of NF-kappa B and the nuclear translocation of IKK alpha. By using luciferase assay, we found that both IKK alpha and IKK beta could activate NF-kappa B in synergy with NIK. Interestingly, although IKK beta stimulated the NIK-mediated I kappa B degradation, IKK alpha stimulated the action of NF-kappa B without enhancing the I kappa B degradation. By using heterologous transactivation system with Gal4 DNA-binding domain in fusion with various portions of p65 TA domain, we found that the transactivation domain 1 (TA1) of p65 serves as the direct target for the NIK-IKK alpha cascade and that the serine residue at 536 within p65 TA1 is indispensable for this action. Furthermore, we found that this action of NIK depends on the energy-dependent action of Ras-related protein (Ran) since the dominant negative mutant of Ran (RanQ69L) inhibited the transcriptional activity of p65 by preventing the nuclear import of IKK alpha.

Inhibition of IkappaB kinase by a new class of retinoid-related anticancer agents that induce apoptosis

The transcription factor NF-kappaB is overexpressed or constitutively activated in many cancer cells, where it induces expression of antiapoptotic genes correlating with resistance to anticancer therapies. Small molecules that inhibit the NF-kappaB signaling pathway could therefore be used to induce apoptosis in NF-kappaB-overexpressing tumors and potentially serve as anticancer agents. We found that retinoid antagonist MX781 inhibited the activation of NF-kappaB-dependent transcriptional activity in different tumor cell lines. MX781 was able to completely inhibit tumor necrosis factor alpha-mediated activation of IkappaB kinase (IKK), the upstream regulator of NF-kappaB. Inhibition of IKK activity resulted from direct binding of MX781 to the kinase, as demonstrated by in vitro inhibition studies. Two other molecules, MX3350-1 and CD2325, which are retinoic acid receptor gamma-selective agonists, were capable of inhibiting IKK in vitro, although they exerted variable inhibition of IKK and NF-kappaB activities in intact cells in a cell type-specific manner. However, N-(4-hydroxyphenyl)-retinamide, another apoptosis-inducing retinoid, and retinoic acid as well as other nonapoptotic retinoids did not inhibit IKK. Inhibition of IKK by the retinoid-related compounds and other small molecules correlated with reduced cell proliferation and increased apoptosis. Reduced cell viability was also observed after overexpression of an IKKbeta kinase-dead mutant or the IkappaBalpha superrepressor. The induction of apoptosis by the retinoid-related molecules that inhibited IKK was dependent on caspase activity but independent of the retinoid receptors. Thus, the presence of an excess of retinoic acid or a retinoid antagonist did not prevent the inhibition of IKK activation by MX781 and CD2325, indicating a retinoid receptor-independent mechanism of action.

H-Ras-specific activation of NF-kappaB protects NIH 3T3 cells against stimulus-dependent apoptosis

Ras signaling involves the activation of several downstream pathways that exhibit isoform specificity. In this study, the basal and tumor necrosis factor alpha (TNFalpha)-induced activation of NF-kappaB has been examined in cells overexpressing H-Ras, K-Ras or N-Ras. Cells expressing H-Ras exhibited a basal kappaB activity that correlated with sustained IkappaB kinase activation and lower steady-state levels of IkappaBalpha in the cytosol. Upon activation with TNFalpha, the cells expressing the distinct Ras isoforms behaved similarly in terms of binding of nuclear proteins to a kappaB sequence and induction of a kappaB-dependent reporter gene. The basal activation of NF-kappaB in cells expressing H-Ras impaired staurosporine-induced apoptosis in these cells, through a mechanism that was NF-kappaB-dependent and inhibitable in the presence of z-VAD. Moreover, titration of caspase activation in response to staurosporine showed a significant resistance in cells expressing H-Ras when compared with the void vector or the N-Ras counterparts. These results indicate that the distinct Ras proteins have specific effects on the NF-kappaB pathway and that this action contributes to protect cells against apoptosis.

The NF-kappa B activation in lymphotoxin beta receptor signaling depends on the phosphorylation of p65 at serine 536

NF-kappaB-inducing kinase (NIK) has been shown to play an essential role in the NF-kappaB activation cascade elicited by lymphotoxin beta receptor (LTbetaR) signaling. However, the molecular mechanism of this pathway remains unclear. In this report we demonstrate that both NIK and IkappaB kinase alpha (IKKalpha) are involved in LTbetaR signaling and that the phosphorylation of the p65 subunit at serine 536 in its transactivation domain 1 (TA1) plays an essential role. We also found that NF-kappaB could be activated in the LTbetaR pathway without altering the level of the phosphorylation of IkappaB and nuclear localization of p65. By using a heterologous transactivation system in which Gal4-dependent reporter gene is activated by the Gal4 DNA-binding domain in fusion with various portions of p65, we found that TA1 serves as a direct target in the NIK-IKKalpha pathway. In addition, mutation studies have revealed the essential role of Ser-536 within TA1 of p65 in transcriptional control mediated by NIK-IKKalpha. Furthermore, we found that Ser-536 was phosphorylated following the stimulation of LTbetaR, and this phosphorylation was inhibited by the kinase-dead dominant-negative mutant of either NIK or IKKalpha. These observations provide evidence for a crucial role of the NIK-IKKalpha cascade for NF-kappaB activation in LTbetaR signaling.

Inhibition of p38 mitogen-activated protein kinase blocks activation of rat pancreatic stellate cells

Activated pancreatic stellate cells (PSCs) have recently been implicated in the pathogenesis of pancreatic fibrosis and inflammation. However, the signal transduction pathways in PSCs remain largely unknown. We examined the role of p38 mitogen-activated protein (MAP) kinase in the activation of PSCs. PSCs were isolated from rat pancreas tissue and used in their culture-activated, myofibroblast-like phenotype. Activation of p38 MAP kinase was determined by Western blotting using anti-phosphospecific antibody. The effects of two p38 MAP kinase inhibitors, 4-(4-flurophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)imidazole (SB203580) and 4-(4-flurophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)1H-imidazole (SB202190), on the parameters of PSC activation, including proliferation, expression of alpha-smooth muscle actin, alpha1(I) procollagen, and prolyl 4-hydroxylase (alpha) genes, and monocyte chemoattractant protein-1 production were evaluated. Interleukin-1beta and platelet-derived growth factor-BB activated p38 MAP kinase. Platelet-derived growth factor-induced PSC proliferation was inhibited by SB203580 and SB202190. These reagents decreased alpha-smooth muscle actin protein expression, and alpha1(I) procollagen and prolyl 4-hydroxylase (alpha) mRNA levels. Treatment with these p38 MAP kinase inhibitors also resulted in inhibition of monocyte chemoattractant protein-1 expression. In addition, SB203580 inhibited spontaneous activation of freshly isolated PSCs in culture on plastic. Thus, inhibition of p38 MAP kinase modulated profibrogenic and proinflammatory actions in PSCs, implying a potential application of p38 MAP kinase inhibitors for the treatment of pancreatic fibrosis and inflammation.

A subdomain of MEKK1 that is critical for binding to MKK4

Mitogen-activated protein kinase (MAPK) cascades are central components of signal transduction pathways induced by mitogens and stresses. They consist of a three-kinase module in which a mitogen-activated protein kinase kinase kinase (MAP3K) activates a mitogen-activated protein kinase kinase (MAP2K), which in turn activates MAPK. The molecular determinants that underlie specific MAP3K-MAP2K interactions are poorly understood. In this study, we examined the interaction between the MAP3K MEKK1 and MKK4, a MAP2K of the JNK pathway. Select point mutations in subdomain X of the catalytic domain of MEKK1 (MEKK1delta) were found to impair the ability of MEKK1delta to bind to and activate MKK4. Such mutations were also found to impair MEKK1delta-induced activation of an AP1 reporter gene. These studies point to a critical role for subdomain X in the interaction of MEKK1 with MKK4.

Mixed lineage kinase LZK and antioxidant protein-1 activate NF-kappaB synergistically

Leucine zipper-bearing kinase (LZK) is a novel member of the mixed lineage kinase (MLK) family [Sakuma, H., Ikeda, A., Oka, S., Kozutsumi, Y., Zanetta, J. P., and Kawasaki, T. (1997) J. Biol. Chem.272, 28622-28629]. We have previously shown that LZK activates the c-Jun-NH2 terminal kinase (JNK) pathway, but not the extracellular signal-related kinase (ERK) pathway, by acting as a mitogen-activated protein kinase kinase kinase (MAPKKK) [Ikeda, A., Hasegawa, K., Masaki, M., Moriguchi, T., Nishida, E., Kozutsumi, Y., Oka, S., and Kawasaki, T. (2001) J. Biochem.130, 773-781]. However, the mode of activation of LZK remains largely unknown. By means of a yeast two-hybrid screening system, we have identified a molecule localized to mitochondria, antioxidant protein-1 (AOP-1), that binds to LZK and which acts as a modulator of LZK activity. Recently, several MAPKKKs involved in the JNK pathway, such as MEKK1, TAK1 and MLK3, were shown, using over-expression assay systems, to activate a transcription factor, NF-kappaB, through activation of the IKK complex. Using similar assay systems, we demonstrated that LZK activated NF-kappaB-dependent transcription through IKK activation only weakly, but this was reproducible, and that AOP-1 enhanced the LZK-induced NF-kappaB activation. We also provided evidence that LZK was associated directly with the IKK complex through the kinase domain, and that AOP-1 was recruited to the IKK complex through the binding to LZK.

Activation of early signaling transcription factor, NF-kappaB following low-level manganese exposure

Occupational and environmental exposure to manganese (Mn(2+)) is an increasing problem. It manifests neuronal degeneration characterized by dyskinesia resembling Parkinson's disease. The study was performed to test the hypotheses whether exposure to Mn(2+) alters cellular physiology and promotes intracellular signaling mechanism in dopaminergic neuronal cell line. Since transcription factors have been shown to play an essential role in the control of cellular proliferation and survival, catecholaminergic rich pheochromocytoma (PC12) cells were used to measure changes in the DNA binding activities of nuclear factor kappa B (NF-kappaB) by electrophoretic mobility shift assay (EMSA) following Mn(2+) (0.1-10 microM) exposure. Cells that were exposed to Mn(2+) produced five-fold-activation of transcription factor NF-kappaB DNA binding activity. This remarkable increase was seen within 30-60 min period of Mn(2+) exposure. Activation of NF-kappaB DNA binding activity by Mn(2+) at 1.0 microM correlated with proteolytic degradation of the inhibitory subunit IkappaB(alpha) as evidenced in cytosol. Additional experiments on NF-kappaB reporter gene assay also showed increased NF-kappaB gene expression at 1.0 and 5.0 microM Mn(2+) and this was completely blocked in the presence of NF-kappaB translocation inhibitor, IkappaB(alpha)-DN supporting that NF-kappaB induction occurred during Mn(2+) exposure. In addition, Mn(2+) exposure to PC 12 cells led to activation of signal responsive mitogen activated protein kinase kinase (MAPKK). These results suggest that Mn(2+) at a low dose appears to induce the expression of immediate early gene, NF-kappaB through MAPKK by a mechanism in which IkappaB(alpha) phosphorylation may be involved.

Signaling by the Mpl receptor involves IKK and NF-kappaB

Binding of tumor necrosis factor-alpha (TNF-alpha) to its receptor activates IKK complex, which leads to inducement of NF-kappaB activity. Here we report that activation of Mpl ligand is also linked to IKK and NF-kappaB activity. Mpl ligand, also known as thrombopoietin (TPO) or megakaryocyte growth and development factor (MGDF), induces megakaryocyte differentiation and inhibition of mitotic proliferation, followed by induction of polyploidization and fragmentation into platelets. The latter process is often observed in megakaryocytes undergoing apoptosis. Treatment of a Mpl ligand-responding megakaryocytic cell line with this cytokine led to an immediate, transient increase in IKK activity followed by a profound decrease in this kinase activity over time. This decrease was not due to an effect on the levels of the IKK regulatory components IKKalpha and IKKbeta. Proliferating megakaryocytes displayed a constitutive DNA-binding activity of NF-kappaB p50 homodimers and of NF-kappaB p50-p65 heterodimers. As expected, reduced IKK activity in Mpl ligand-treated cells was associated with a significant reduction in NF-kappaB DNA binding activity and in the activity of a NF-kappaB-dependent promoter. Our study is thus the first to identify a constitutive NF-kappaB activity in proliferating megakaryocytes as well as to describe a link between Mpl receptor signaling and IKK and NF-kappaB activities. Since a variety of proliferation-promoting genes and anti-apoptotic mechanisms are activated by NF-kappaB, retaining its low levels would be one potential mechanism by which inhibition of mitotic proliferation is maintained and apoptosis is promoted during late megakaryopoiesis.

Signaling from toxic metals to NF-kappaB and beyond: not just a matter of reactive oxygen species

The nuclear factor kappa B (NF-kappaB) family of transcription factors controls expression of a number of early response genes associated with inflammatory responses, cell growth, cell cycle progression, and neoplastic transformation. These genes include a multitude of cytokines, chemokines, adhesion molecules, immune receptors, stress proteins, apoptotic or anti-apoptotic regulators, and several oncogenes. Accumulating evidence indicates that a variety of toxic metals are able to affect the activation or activity of NF-kappaB, but the molecular mechanisms involved in this process remain largely unknown. The signaling pathways mediating cytokine- or microorganism-induced NF-kappaB activation have been well established recently. Whether the same signaling systems are involved in metal-induced NF-kappaB activation, however, is unclear. In the present review, we have attempted to evaluate and update the possible mechanisms of metal signals on the activation and function of NF-kappaB.

Ras and relatives--job sharing and networking keep an old family together

Many members of the Ras superfamily of GTPases have been implicated in the regulation of hematopoietic cells, with roles in growth, survival, differentiation, cytokine production, chemotaxis, vesicle-trafficking, and phagocytosis. The well-known p21 Ras proteins H-Ras, N-Ras, K-Ras 4A, and K-Ras 4B are also frequently mutated in human cancer and leukemia. Besides the four p21 Ras proteins, the Ras subfamily of the Ras superfamily includes R-Ras, TC21 (R-Ras2), M-Ras (R-Ras3), Rap1A, Rap1B, Rap2A, Rap2B, RalA, and RalB. They exhibit remarkable overall amino acid identities, especially in the regions interacting with the guanine nucleotide exchange factors that catalyze their activation. In addition, there is considerable sharing of various downstream effectors through which they transmit signals and of GTPase activating proteins that downregulate their activity, resulting in overlap in their regulation and effector function. Relatively little is known about the physiological functions of individual Ras family members, although the presence of well-conserved orthologs in Caenorhabditis elegans suggests that their individual roles are both specific and vital. The structural and functional similarities have meant that commonly used research tools fail to discriminate between the different family members, and functions previously attributed to one family member may be shared with other members of the Ras family. Here we discuss similarities and differences in activation, effector usage, and functions of different members of the Ras subfamily. We also review the possibility that the differential localization of Ras proteins in different parts of the cell membrane may govern their responses to activation of cell surface receptors.

Mixed-lineage kinase control of JNK and p38 MAPK pathways

Mixed-lineage kinases (MLKs) are serine/threonine protein kinases that regulate signalling by the c-Jun amino-terminal kinase (JNK) and p38 mitogen-activated-protein kinase (MAPK) pathways. MLKs are represented in the genomes of both Caenorhabditis elegans and Drosophila melanogaster. The Drosophila MLK Slipper regulates JNK to control dorsal closure during embryonic morphogenesis. In mammalian cells, MLKs are implicated in the control of apoptosis and are potential drug targets for many neurodegenerative diseases.

Mechanisms of constitutive NF-kappaB activation in human prostate cancer cells

BACKGROUND

Activation of the NF-kappaB transcription factor has been previously demonstrated in two androgen receptor negative prostate cancer cell lines. We wished to extend this work to additional prostate cancer cells and to characterize the mechanisms responsible for constitutive NF-kappaB activation.

METHODS

Electrophoretic mobility shift assays were performed to measure NF-kappaB DNA-binding activity in prostate cancer cell lines, and immunohistochemistry was performed to detect nuclear localization of NF-kappaB in prostate cancer tissues. Western blot analysis was used to study the status of IkappaBalpha. Transient transfection assays were employed to characterize the contributions of IkappaB kinase (IKK), MAPK kinase kinases (MAPKKKs), androgen receptor (AR), and tyrosine phosphorylation to the constitutive activation of NF-kappaB in the prostate cancer cell lines.

RESULTS

Constitutive NF-kappaB activity was observed in AR-negative cell lines as well as in the prostate cancer patient samples, but was not present in AR positive cells. A "super-repressor" IkappaBalpha, as well as dominant negative forms of IKKbeta and NF-kappaB-inducing kinase (NIK), and tyrosine kinase inhibition were able to suppress NF-kappaB activity in the cells with constitutive activation.

CONCLUSIONS

The constitutive activation of NF-kappaB observed in prostate cancer cells is likely due to a signal transduction pathway involving tyrosine kinases, NIK, and IKK activation.

A role for NF-kappa B activation in perforin expression of NK cells upon IL-2 receptor signaling

Optimal NK cell development and activation as well as cytolytic activity involves IL-2R beta signals that also up-regulate expression of the pore-forming effector molecule perforin. Although the Jak/Stat pathway and specifically Stat5 transcription factors are required to promote many of the respective downstream events, the role of additional signaling pathways and transcription factors remains to be clarified. This report investigates the role of NF-kappa B activation for perforin expression by NK cells. It is demonstrated that IL-2-induced up-regulation of perforin in primary NK cells and in a model cell line is blocked by two pharmacological agents known to inhibit NF-kappa B activation. Direct evidence for the activation of the NF-kappa B pathway by IL-2R signals in NK cells involves activation of the IKK alpha kinase, inhibitory protein kappa B alpha degradation, nuclear translocation of p50/p65 complexes, and ultimately, transcriptional activation of the perforin gene via an NF-kappa B binding element in its upstream enhancer. Taken together, these observations strongly suggest that IL-2R signals can activate a pathway leading to NF-kappa B activation in NK cells and that this pathway is involved in the control of perforin expression.

Cell stress and MEKK1-mediated c-Jun activation modulate NFkappaB activity and cell viability

Chemotherapeutic agents such as cisplatin induce persistent activation of N-terminal c-Jun Kinase, which in turn mediates induction of apoptosis. By using a common MAPK Kinase, MEKK1, cisplatin also activates the survival transcription factor NFkappaB. We have found a cross-talk between c-Jun expression and NFkappaB transcriptional activation in response to cisplatin. Fibroblast derived from c-jun knock out mice are more resistant to cisplatin-induced cell death, and this survival advantage is mediated by upregulation of NFkappaB-dependent transcription and expression of MIAP3. This process can be reverted by ectopic expression of c-Jun in c-jun(-/-) fibroblasts, which decreases p65 transcriptional activity back to normal levels. Negative regulation of NFkappaB-dependent transcription by c-jun contributes to cisplatin-induced cell death, which suggests that inhibition of NFkappaB may potentiate the antineoplastic effect of conventional chemotherapeutic agents.

The human papillomavirus oncoprotein E7 attenuates NF-kappa B activation by targeting the Ikappa B kinase complex

Infection with high-risk human papillomaviruses (HPV) can lead to the development of cervical carcinomas. This process critically depends on the virus-encoded E6 and E7 oncoproteins, which stimulate proliferation by manipulating the function of a variety of host key regulatory proteins. Here we show that both viral proteins dose-dependently interfere with the transcriptional activity of NF-kappaB. A variety of experimental approaches revealed that a fraction of the E7 proteins is found in association with the IkappaB kinase complex and attenuates induced kinase activity of IkappaB kinase alpha (IKKalpha) and IKKbeta, thus resulting in impaired IkappaBalpha phosphorylation and degradation. Indirect immunofluorescence shows that E7 impairs TNFalpha-induced nuclear translocation of NF-kappaB, thus preventing NF-kappaB from binding to its cognate DNA. While E7 obviates IKK activation in the cytoplasm, the E6 protein reduces NF-kappaB p65-dependent transcriptional activity within the nucleus. We suggest that HPV oncogene-mediated suppression of NF-kappaB activity contributes to HPV escape from the immune system.

Identification of a signaling cascade for interleukin-8 production by Helicobacter pylori in human gastric epithelial cells

Infecting gastric epithelial cells with Helicobacter pylori (H. pylori) has been shown to induce interleukin-8 (IL-8) production, but the signal transduction mechanism leading to IL-8 production is not defined clearly. In the present study, we investigated the molecular mechanism responsible for H. pylori-induced IL-8 release in human gastric epithelial cells. IL-8 levels in culture supernatants were determined by an enzyme linked-immunosorbent assay. Extracellular signal-regulated kinase (ERK) activity was tested using an in vitro kinase assay, which measured the incorporation of [gamma-33P]ATP into a synthetic peptide that is a specific ERK substrate. ERK phosphorylation and IkappaBalpha degradation by H. pylori infection were assessed by western blotting. In MKN45 cells, H. pylori-induced IL-8 release in a time-dependent manner. This IL-8 release was abolished by treatment with intracellular Ca2+ chelators (BAPTA-AM and TMB-8) but not by EGTA or nifedipine. The Ca2+ ionophore A23187 also induced IL-8 release to an extent similar to that of H. pylori infection. Calmodulin inhibitors (W7 and calmidazolium) and tyrosine kinase inhibitors (genistein and ST638) completely blocked IL-8 release by H. pylori and A23187. PD98059, an ERK pathway inhibitor, completely abolished H. pylori-induced IL-8 release. Moreover, BAPTA-AM, calmidazolium, and genistein, but not nifedipine, suppressed the ERK activation induced by H. pylori infection. PD98059 as well as MG132, an NF-kappaB pathway inhibitor, blocked both IL-8 production and degradation of IkappaBalpha induced by H. pylori infection, whereas only PD98059 inhibited ERK activity in response to H. pylori. There was no significant difference between IL-8 production induced by the cagA positive wild-type strain and the cagA negative isogenic mutant strain of H. pylori; therefore, CagA is not involved in the IL-8 production pathway. H. pylori-induced IL-8 production is dominantly regulated by Ca2+/calmodulin signaling, and ERK plays an important role in signal transmission for the efficient activation of H. pylori-induced NF-kappaB activity, resulting in IL-8 production.

Differential requirement for NF-kappaB-inducing kinase in the induction of NF-kappaB by IL-1beta, TNF-alpha, and Fas

In this study, we examined the role of the nuclear factor-kappaB (NF-kappaB)-inducing kinase (NIK) in distinct signaling pathways leading to NF-kappaB activation. We show that a dominant-negative form of NIK (dnNIK) delivered by adenoviral (Ad5dnNIK) vector inhibits Fas-induced IkappaBalpha phosphorylation and NF-kappaB-dependent gene expression in HT-29 and HeLa cells. Interleukin (IL)-1beta- and tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activation and kappaB-dependent gene expression are inhibited in HeLa cells but not in Ad5dnNIK-infected HT-29 cells. Moreover, Ad5dnNIK failed to sensitize HT-29 cells to TNF-alpha-induced apoptosis at an early time point. However, cytokine- and Fas-induced signals to NF-kappaB are finally integrated by the IkappaB kinase (IKK) complex, since IkappaBalpha phosphorylation, NF-kappaB DNA binding activity, and IL-8 gene expression were strongly inhibited in HT-29 and HeLa cells overexpressing dominant-negative IKKbeta (Ad5dnIKKbeta). Our findings support the concept that cytokine signaling to NF-kappaB is redundant at the level of NIK. In addition, this study demonstrates for the first time the critical role of NIK and IKKbeta in Fas-induced NF-kappaB signaling cascade.

MEKK1 plays a critical role in activating the transcription factor C/EBP-beta-dependent gene expression in response to IFN-gamma

IFN-gamma induces a number of genes to up-regulate cellular responses by using specific transcription factors and the cognate elements. We recently discovered that CCAAT/enhancer-binding protein-beta (C/EBP-beta) induces gene transcription through an IFN-response element called gamma-IFN-activated transcriptional element (GATE). Using mutant cells, chemical inhibitors, and specific dominant negative inhibitors, we show that induction of GATE-driven gene expression depends on MEK1 (mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinase kinase) and ERKs (extracellular signal-regulated protein kinases) but is independent of Raf-1. Interestingly in cells lacking the MEKK1 gene or expressing the dominant negative MEKK1, ERK activation, and GATE dependent gene expression is inhibited. A dominant negative MEKK1 blocks C/EBP-beta-driven gene expression stimulated by IFN-gamma. These studies describe an IFN-gamma-stimulated pathway that involves MEKK1-MEK1-ERK1/2 kinases to regulate C/EBP-beta-dependent gene expression.

Protein kinase C(theta) in T cell activation

The novel protein kinase C (PKC) isoform, PKC theta, is selectively expressed in T lymphocytes and is a sine qua non for T cell antigen receptor (TCR)-triggered activation of mature T cells. Productive engagement of T cells by antigen-presenting cells (APCs) results in recruitment of PKC theta to the T cell-APC contact area--the immunological synapse--where it interacts with several signaling molecules to induce activation signals essential for productive T cell activation and IL-2 production. The transcription factors NF-kappa B and AP-1 are the primary physiological targets of PKC theta, and efficient activation of these transcription factors by PKC theta requires integration of TCR and CD28 costimulatory signals. PKC theta cooperates with the protein Ser/Thr phosphatase, calcineurin, in transducing signals leading to activation of JNK, NFAT, and the IL-2 gene. PKC theta also promotes T cell cycle progression and regulates programmed T cell death. The exact mode of regulation and immediate downstream substrates of PKC theta are still largely unknown. Identification of these molecules and determination of their mode of operation with respect to the function of PKC theta will provide essential information on the mechanism of T cell activation. The selective expression of PKC theta in T cells and its essential role in mature T cell activation establish it as an attractive drug target for immunosuppression in transplantation and autoimmune diseases.

Ethanol extract of propolis inhibits nitric oxide synthase gene expression and enzyme activity

Propolis obtained from honeybee hives has been used in Oriental folk medicine as an anti-inflammatory, anti-carcinogenic, or immunomodulatory agent. However, the molecular basis for anti-inflammatory properties of propolis has not yet been established. Since nitric oxide (NO) synthesized by inducible nitric oxide synthase (iNOS) has been known to be involved in inflammatory and autoimmune-mediated tissue destruction, modulation of NO synthesis or action represents a new approach to the treatment of inflammatory and autoimmune diseases. The present study, therefore, examined effects of ethanol extract of propolis (EEP) on iNOS expression and activity of iNOS enzyme itself. Treatment of RAW 264.7 cells with EEP significantly inhibited NO production and iNOS protein expression induced by lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma). EEP also inhibited iNOS mRNA expression and nuclear factor-kappa B (NF-kappaB) binding activity in a concentration-dependent manner. Furthermore, transfection of RAW 264.7 cells with iNOS promoter linked to a chloramphenicol acetyltransferase (CAT) reporter gene, revealed that EEP inhibited the iNOS promoter activity induced by LPS plus IFN-gamma through the NF-kappaB sites of the iNOS promoter. In addition, EEP directly interfered with the catalytic activity of murine recombinant iNOS enzyme. These results suggest that EEP may exert its anti-inflammatory effect by inhibiting the iNOS gene expression via action on the NF-kappaB sites in the iNOS promoter and by directly inhibiting the catalytic activity of iNOS.

IL-1beta during in vitro decidualization in primate

The sequence of biochemical and molecular events associated with decidualization in the primate remain unclear. In the baboon, the sequential changes during this period in vivo are characterized by the downregulation of alpha-smooth actin followed by induction of cyclooxygenase-2 (COX-2) at the implantation site and the expression of insulin growth factor binding protein-1 (IGFBP-1). IGFBP-1 is the predominant protein in decidualized cells and is considered to be biochemical marker of decidualization. In the baboon the expression of IGFBP-1 requires the presence of a conceptus in vivo or N(6), 2'-O-dibutyryladenosine 3:5'-cyclic monophosphate (dbcAMP) in the presence of hormones in vitro. In addition IL-1beta, as a possible conceptus-mediated factor, can induce IGFBP-1 expression in the presence of hormones following 3 days of incubation. However, if IL-1beta and dbcAMP are added together, IGFBP-1 expression is inhibited which resulted in IL-1beta being considered to be "inhibitory" to decidualization. Current data suggest that IL-1beta can activate multiple signaling pathways that either positively (no exogenous cAMP) or negatively (in presence of exogenous cAMP) regulate IGFBP-1 gene expression and decidualization in vitro. Signaling pathways activated by IL-1beta following 10 min of stimulation result in the phosphorylation of mitogen-activated protein kinase (MAPK, specifically p38 MAPK) and also lead to NF-kappaB activation. The expression of COX-2 and matrix metalloproteinase-3 (MMP-3) genes follows after 4-6 h. The steroid hormones, particularly progesterone, which are critical for IGFBP-1 expression, modulate the activity of IL-1beta by down-regulating MMP-3 activity. Disruption of actin filaments enhances IGFBP-1 induction during decidualization. IL-1beta induced MMP-3 may upregulate IGFBP-1 by initiation of cytoskeletal reorganization through degradation of extracellular matrix (ECM). Inhibition of IL-1beta induced pathways leads to reduction of IGFBP-1 expression, suggesting that IL-1beta may be involved in the events leading to decidualization in baboons.

African swine fever virus IAP-like protein induces the activation of nuclear factor kappa B

African swine fever virus (ASFV) encodes a homologue of the inhibitor of apoptosis (IAP) that promotes cell survival by controlling the activity of caspase-3. Here we show that ASFV IAP is also able to activate the transcription factor NF-kappaB. Thus, transient transfection of the viral IAP increases the activity of an NF-kappaB reporter gene in a dose-responsive manner in Jurkat cells. Similarly, stably transfected cells expressing ASFV IAP have elevated basal levels of c-rel, an NF-kappaB-dependent gene. NF-kappaB complexes in the nucleus were increased in A224L-expressing cells compared with control cells upon stimulation with phorbol myristate acetate (PMA) plus ionomycin. This resulted in greater NF-kappaB-dependent promoter activity in ASFV IAP-expressing than in control cells, both in basal conditions and after PMA plus ionophore stimulation. The elevated NF-kappaB activity seems to be the consequence of higher IkappaB kinase (IKK) basal activity in these cells. The NF-kappaB-inducing activity of ASFV IAP was abrogated by an IKK-2 dominant negative mutant and enhanced by expression of tumor necrosis factor receptor-associated factor 2.

Opposing roles of serine/threonine kinases MEKK1 and LOK in regulating the CD28 responsive element in T-cells

T-cell activation requires signals from both the T-cell receptor (TcR) and other co-stimulatory molecules such as CD28. TcR- and CD28-mediated signals are integrated during T-cell activation resulting in the expression of cytokine genes such as interleukin-2 (IL-2). An enhancer element (CD28RE) of the IL-2 gene specifically responsive to CD28 signals has been previously identified and characterized. This response element and an adjacent Activated Protein-1 (nuclear factor-interleukin-2B) site together (RE/AP1) were shown to complex with c-rel, AP-1 and other factors. However, details of the signal transduction pathways leading from CD28 to the composite response element remain poorly understood. We present data showing that overexpression of the serine threonine kinase, mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase kinase-1 (MEKK1), but not nuclear factor-kappa B inducing kinase, or MAP kinase/ERK kinase-1 (MEK1), can significantly increase the level of CD28RE/AP1-driven luciferase (Luc) reporter gene expression in Jurkat E6-1 cells. A MEKK1 dominant negative mutant blocked such activation induced by stimulation with Raji B cells and the superantigen staphylococcus enterotoxin E (SEE), as well as via CD3/CD28. Mutations in either site of the RE/AP1 element abolished MEKK1-induced Luc expression. Calcineurin inhibitors, CsA and FK520, or inhibitors of p38 kinase (SB 203580), or MEK1 (PD 098059), did not affect MEKK1-induced reporter activation. These results directly implicate MEKK1 in the CD28 signalling pathway that activates the CD28 response element. Co-expression of the lymphocyte-oriented kinase (LOK) kinase attenuated Raji/SEE-induced IL-2 production in Jurkat cells, as well as MEKK1 and Raji/SEE-induced reporter gene activation. These data suggest that MEKK1 and LOK may have opposing roles in regulating the CD28RE/AP1 element.

Up-regulation of inducible nitric oxide synthase and nitric oxide in Helicobacter pylori-infected human gastric epithelial cells: possible role of interferon-gamma in polarized nitric oxide secretion

BACKGROUND

Nitric oxide (NO) generated by nitric oxide synthase (NOS) is known to be an important modulator of the mucosal inflammatory response. In this study, we questioned whether Helicobacter pylori infection could up-regulate the epithelial cell inducible NOS (iNOS) gene expression and whether NO production could show polarity that can be regulated by immune mediators.

MATERIALS AND METHODS

Human gastric epithelial cell lines were infected with H. pylori, and the iNOS mRNA expression was assessed by quantitative RT-PCR. NO production was assayed by determining nitrite/nitrate levels in culture supernatants. To determine the polarity of NO secretion by the H. pylori-infected epithelial cells, Caco-2 cells were cultured as polarized monolayers in transwell chambers, and NO production was measured.

RESULTS

iNOS mRNA levels were significantly up-regulated in the cells infected with H. pylori, and expression of iNOS protein was confirmed by Western blot analysis. Increased NO production in the gastric epithelial cells was seen as early as 18 hours postinfection, and reached maximal levels by 24 hours postinfection. The specific MAP kinase inhibitors decreased H. pylori-induced iNOS and NO up-regulation. After H. pylori infection of polarized epithelial cells, NO was released predominantly into the apical compartment, and IL-8 was released predominantly into basolateral compartment. The addition of IFN-gamma to H. pylori-infected polarized epithelial cells showed a synergistically higher apical and basolateral NO release.

CONCLUSION

These results suggest that apical NO production mediated by MAP kinase in H. pylori-infected gastric epithelial cells may influence the bacteria and basolateral production of NO and IL-8 may play a role in the tissue inflammation.

Bacterial lipopolysaccharides and innate immunity

Bacterial lipopolysaccharides (LPS) are the major outer surface membrane components present in almost all Gram-negative bacteria and act as extremely strong stimulators of innate or natural immunity in diverse eukaryotic species ranging from insects to humans. LPS consist of a poly- or oligosaccharide region that is anchored in the outer bacterial membrane by a specific carbohydrate lipid moiety termed lipid A. The lipid A component is the primary immunostimulatory centre of LPS. With respect to immunoactivation in mammalian systems, the classical group of strongly agonistic (highly endotoxic) forms of LPS has been shown to be comprised of a rather similar set of lipid A types. In addition, several natural or derivatised lipid A structures have been identified that display comparatively low or even no immunostimulation for a given mammalian species. Some members of the latter more heterogeneous group are capable of antagonizing the effects of strongly stimulatory LPS/lipid A forms. Agonistic forms of LPS or lipid A trigger numerous physiological immunostimulatory effects in mammalian organisms, but--in higher doses--can also lead to pathological reactions such as the induction of septic shock. Cells of the myeloid lineage have been shown to be the primary cellular sensors for LPS in the mammalian immune system. During the past decade, enormous progress has been obtained in the elucidation of the central LPS/lipid A recognition and signaling system in mammalian phagocytes. According to the current model, the specific cellular recognition of agonistic LPS/lipid A is initialized by the combined extracellular actions of LPS binding protein (LBP), the membrane-bound or soluble forms of CD14 and the newly identified Toll-like receptor 4 (TLR4)*MD-2 complex, leading to the rapid activation of an intracellular signaling network that is highly homologous to the signaling systems of IL-1 and IL-18. The elucidation of structure-activity correlations in LPS and lipid A has not only contributed to a molecular understanding of both immunostimulatory and toxic septic processes, but has also re-animated the development of new pharmacological and immunostimulatory strategies for the prevention and therapy of infectious and malignant diseases.

Caffeic acid phenethyl ester inhibits nitric oxide synthase gene expression and enzyme activity

Since nitric oxide (NO) synthesized by inducible nitric oxide synthase (iNOS) has been known to be involved in inflammatory and autoimmune-mediated tissue destruction, modulation of NO synthesis or action represents a new approach to the treatment of inflammatory and autoimmune diseases. Caffeic acid phenethyl ester (CAPE), an active component of honeybee propolis, has been identified to show anti-inflammatory, anti-viral and anti-cancer activities. The present study, therefore, examined effects of CAPE on iNOS expression and activity of iNOS enzyme itself. Treatment of RAW 264.7 cells with CAPE significantly inhibited NO production and iNOS protein expression induced by lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma). CAPE also inhibited iNOS mRNA expression and nuclear factor-kappa B (NF-kappaB) binding activity in a concentration-dependent manner. Furthermore, transfection of RAW 264.7 cells with iNOS promoter linked to a chloramphenicol acetyltransferase reporter gene, revealed that CAPE inhibited the iNOS promoter activity induced by LPS plus IFN-gamma through the NF-kappaB sites of the iNOS promoter. In addition, CAPE directly interfered with the catalytic activity of murine recombinant iNOS enzyme. These results suggest that CAPE may exert its anti-inflammatory effect by inhibiting the iNOS gene expression at the transcriptional level through the suppression of NF-kappaB activation, and by directly inhibiting the catalytic activity of iNOS.

IkappaB kinase activation is involved in regulation of paclitaxel-induced apoptosis in human tumor cell lines

Paclitaxel (Taxol), a naturally occurring antimitotic agent, has shown significant cell-killing activity against human solid tumor cells through induction of apoptosis. The molecular mechanism underlying paclitaxel-induced apoptosis is not entirely clear. Using the unique inhibitory effect of glucocorticoids on paclitaxel-induced apoptosis, we recently discovered that paclitaxel-induced inhibitor kappaBalpha (IkappaBalpha) degradation and nuclear factor-kappaB (NF-kappaB) activation might contribute to the mediation of paclitaxel-induced apoptosis. In this study, using a novel IkappaBalpha phosphorylation inhibitor, we demonstrated that the blockage of paclitaxel-induced IkappaBalpha degradation inhibited apoptotic cell death in human breast cancer BCap37 and ovarian cancer OV2008 cell lines. Furthermore, in vitro kinase assays showed that the activity of IkappaB kinase (IKK), which is responsible for the phosphorylation and degradation of IkappaB proteins, was significantly activated by paclitaxel in these paclitaxel-sensitive tumor cells. Stable transfection of a mutant IkappaBalpha lacking Ser(32) and Ser(36) that was insensitive to IKK-mediated phosphorylation and degradation resulted in reduced sensitivity of tumor cells to paclitaxel-induced apoptosis. Moreover, we also found that the expression of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 1, an upstream regulator of IKK, was up-regulated by paclitaxel. These findings suggest that the activation of IKK might play a critical role in the regulation of paclitaxel-induced NF-kappaB activation that subsequently mediates paclitaxel-induced apoptotic cell death in solid tumor cells.

The ups and downs of MEK kinase interactions

MEK kinases (MEKKs) comprise a family of related serine-threonine protein kinases that regulate mitogen-activated protein kinase (MAPK) signalling pathways leading to c-Jun NH2-terminal kinase (JNK) and p38 activation, induced by cellular stress (e.g., UV and gamma irradiation, osmotic stress, heat shock, protein synthesis inhibitors), inflammatory cytokines (e.g., tumour necrosis factor alpha, TNFalpha, and interleukin-1, IL1) and G protein-coupled receptor agonists (e.g., thrombin). These stress-activated kinases have been implicated in apoptosis, oncogenic transformation, and inflammatory responses in various cell types. At present, the signalling events involving MEKKs are not well understood. This review summarises our current knowledge concerning the regulation and function of MEKK family members, with particular emphasis on those factors capable of directly interacting with distinct MEKK isoforms.

Raf kinase inhibitor protein interacts with NF-kappaB-inducing kinase and TAK1 and inhibits NF-kappaB activation

The Raf kinase inhibitor protein (RKIP) acts as a negative regulator of the mitogen-activated protein (MAP) kinase (MAPK) cascade initiated by Raf-1. RKIP inhibits the phosphorylation of MAP/extracellular signal-regulated kinase 1 (MEK1) by Raf-1 by disrupting the interaction between these two kinases. We show here that RKIP also antagonizes the signal transduction pathways that mediate the activation of the transcription factor nuclear factor kappa B (NF-kappaB) in response to stimulation with tumor necrosis factor alpha (TNF-alpha) or interleukin 1 beta. Modulation of RKIP expression levels affected NF-kappaB signaling independent of the MAPK pathway. Genetic epistasis analysis involving the ectopic expression of kinases acting in the NF-kappaB pathway indicated that RKIP acts upstream of the kinase complex that mediates the phosphorylation and inactivation of the inhibitor of NF-kappaB (IkappaB). In vitro kinase assays showed that RKIP antagonizes the activation of the IkappaB kinase (IKK) activity elicited by TNF-alpha. RKIP physically interacted with four kinases of the NF-kappaB activation pathway, NF-kappaB-inducing kinase, transforming growth factor beta-activated kinase 1, IKKalpha, and IKKbeta. This mode of action bears striking similarities to the interactions of RKIP with Raf-1 and MEK1 in the MAPK pathway. Emerging data from diverse organisms suggest that RKIP and RKIP-related proteins represent a new and evolutionarily highly conserved family of protein kinase regulators. Since the MAPK and NF-kappaB pathways have physiologically distinct roles, the function of RKIP may be, in part, to coordinate the regulation of these pathways.

MAPK cascades in plant defense signaling

The Arabidopsis genome encodes approximately 20 different mitogen-activated protein kinases (MAPKs) that are likely to be involved in growth, development and responses to endogenous and environmental cues. Several plant MAPKs are activated by a variety of stress stimuli, including pathogen infection, wounding, temperature, drought, salinity, osmolarity, UV irradiation, ozone and reactive oxygen species. Recent gain-of-function studies show that two tobacco MAPKs induce the expression of defense genes and cause cell death. By contrast, loss-of-function studies of other MAPK pathways revealed negative regulation of disease resistance. This 'push-and-pull' regulation by different MAPK pathways might provide a more precise control of plant defense responses.

NF-kappaB and the MAP kinases/AP-1 pathways are both involved in interleukin-6 and interleukin-8 expression in fibroblast-like synoviocytes stimulated by protein I/II, a modulin from oral streptococci

As in rheumatoid arthritis (RA), it was demonstrated recently that bacterial fragments of DNA or rRNA are present in the joint and therefore could play a role in inducing or perpetuating the disease, this work was initiated to define mechanisms that account for the stimulatory activities of the oral streptococcal modulin, protein I/II, on fibroblast-like synoviocytes (FLSs) from RA patients. FLSs from RA patients were stimulated with protein I/II, and expression of interleukin (IL)-6 and IL-8 mRNA was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Immunoblotting by antibodies specific for activated forms of MAPKs and electrophoretic mobility shift assays (EMSAs) were performed to study downstream signalling, which allowed the synthesis of IL-6 and IL-8. We reported that protein I/II interactions with FLSs from RA patients trigger the synthesis and release of IL-6 and IL-8. We also demonstrated that protein I/II enhances the phosphorylation of ERK 1/2, p38 and JNKs and that ERK 1/2 and JNK MAPKs seem to play a more important role than p38 in protein I/II-mediated synthesis of IL-6 and IL-8. Our experiments also indicated that stimulation of FLSs with protein I/II induces nuclear translocation of NF-kappaB, AP-1-binding activity and that NF-kappaB plays a major role in IL-6 and IL-8 secretion from activated cells.