Reciprocal inhibition between MyoD and STAT3 in the regulation of growth and differentiation of myoblasts

The development of myoblasts is regulated by various growth factors as well as by intrinsic muscle-specific transcriptional factors. In this study, we analyzed the roles for STAT3 in the growth and differentiation of myoblasts in terms of cell cycle regulation and interaction with MyoD using C2C12 cells. Here we found that STAT3 inhibited myogenic differentiation induced by low serum or MyoD as efficiently as the Ras/mitogen-activated protein kinase cascade. As for this mechanism, we found that STAT3 not only promoted cell cycle progression through the induction of c-myc but also inhibited MyoD activities through direct interaction. STAT3 inhibited not only DNA binding activities of MyoD but also its transcriptional activities. However, the inhibited transcriptional activities were restored by the supplement of p300/CBP and PCAF, suggesting that STAT3 might deprive MyoD of these transcriptional cofactors. In addition, we found that MyoD inhibited DNA binding activities of STAT3, thereby inhibiting STAT3-dependent cell growth and survival of Ba/F3 cells. These results suggest that the development of muscle cells is regulated by the coordination of cytokine signals and intrinsic transcription factors.

Effects of p38MAPK isoforms on renal mesangial cell inducible nitric oxide synthase expression

Several related isoforms of p38MAPK have been identified and cloned in many species. Although they all contain the dual phosphorylation motif TGY, the expression of these isoforms is not ubiquitous. p38alpha and -beta2 are ubiquitously expressed, whereas p38gamma and -delta appear to have more restricted expression. Because there is evidence for selective activation by upstream kinases and selective preference for downstream substrates, the functions of these conserved proteins is still incompletely understood. We have demonstrated that the renal mesangial cell expresses the mRNA for all the isoforms of p38MAPK, with p38alpha mRNA expressed at the highest level, followed by p38gamma and the lowest levels of expression by p38beta2 and -delta. To determine the functional effects of these proteins on interleukin (IL)-1beta-induced inducible nitric oxide synthase (iNOS) expression, we transduced TAT-p38 chimeric proteins into renal mesangial cells and assessed the effects of wild-type and mutant p38 isoforms on ligand induced iNOS expression. We show that whereas p38gamma and -delta had minimal effects on iNOS expression, p38alpha and -beta2 significantly altered its expression. p38alpha mutant and p38beta2 wild-type dose dependently inhibited IL-1beta-induced iNOS expression. These data suggest that p38alpha and beta2 have reciprocal effects on iNOS expression in the mesangial cell, and these observations may have important consequences for the development of selective inhibitors targeting the p38MAPK family of proteins.

Effects of eosinophils on nerve cell morphology and development: the role of reactive oxygen species and p38 MAP kinase

The adhesion of eosinophils to nerve cells and the subsequent release of eosinophil products may contribute to the pathogenesis of conditions such as asthma and inflammatory bowel disease. In this study we have separately examined the consequences of eosinophil adhesion and degranulation for nerve cell morphology and development. Eosinophils induced neurite retraction of cultured guinea pig parasympathetic nerves and differentiated IMR32 cholinergic neuroblastoma cells. Inhibition of eosinophil adhesion to IMR32 cells attenuated this retraction. Eosinophil adhesion to IMR32 cells led to tyrosine phosphorylation of a number of nerve cell proteins, activation of p38 MAP kinase, and generation of neuronal reactive oxygen species (ROS). Inhibition of tyrosine kinases with genistein prevented both the generation of ROS in the nerve cells and neurite retraction. The p38 MAP kinase inhibitor SB-239063 prevented neurite retraction but had no effect on the induction of ROS. Thus eosinophils induced neurite retraction via two distinct pathways: by generation of tyrosine kinase-dependent ROS and by p38 MAP kinase. Eosinophils also prevented neurite outgrowth during differentiation of IMR32 cells. In contrast to their effect on neurite retraction, this effect was mimicked by medium containing products released from eosinophils and by eosinophil major basic protein. These results indicate that eosinophils modify the morphology of nerve cells by distinct mechanisms that involve adhesion and released proteins.

Evidence for antagonism of BMP-4 signals by MAP kinase during Xenopus axis determination and neural specification

We have previously shown that mitogen-activated protein (MAP) kinase activity is required for neural specification in Xenopus. In mammalian cells, the BMP-4 effector Smad1 is inhibited by phosphorylation at MAP kinase sites (Kretzschmar et al., 1997). To test the hypothesis that MAP kinase inhibits the BMP-4/Smad1 pathway during early Xenopus development, we have generated a Smad1 mutant lacking the MAP kinase phosphorylation sites (M4A-Smad1) and compared the effects of wild-type (WT)- and M4A-Smad1 on axial pattern and neural specification in Xenopus embryos. Although overexpression of either WT- or M4A-Smad1 produced ventralized embryos, at each mRNA concentration, M4A-Smad1 had a greater ventralizing effect than WT-Smad1. Interestingly, overexpression of either form of Smad1 in ventral blastomeres disrupted posterior pattern and morphogenesis; again, more severe defects were produced by expression of M4A-Smad1 than by equal amounts of WT-Smad1. Ectodermal expression of M4A-Smad1 disrupted expression of the anterior neural gene otx2 in vivo and inhibited neural specification in response to endogenous signals in mesoderm-ectoderm recombinates. In contrast, overexpression of WT-Smad1 at identical levels had little effect on either neural specification or otx2 expression. Comparisons of protein levels following overexpression of either WT- or M4A-Smad1 indicate that WT-Smad1 may be slightly more stable than M4A-Smad1; thus, differences in stability cannot account for the increased effectiveness of M4A-Smad1. Our results demonstrate that mutations disrupting the MAPK phosphorylation sites act collectively as a gain-of-function mutation in Smad1 and that inhibitory phosphorylation of Smad1 may be a significant mechanism for the regulation of BMP-4/Smad1 signals during Xenopus development.

Okadaic acid induces sustained activation of NFkappaB and degradation of the nuclear IkappaBalpha in human neutrophils

Human neutrophils differ from other cells by containing high amount of IkappaBalpha in the nucleus, and this increased nuclear IkappaBalpha accumulation is associated with the inhibition of NFkappaB activity and increased apoptosis. However, the mechanisms regulating NFkappaB activation and IkappaBalpha degradation in human neutrophils are little understood. The objective of this study was to provide a further insight into the mechanisms regulating NFkappaB activity and IkappaBalpha degradation in human neutrophils. We show that okadaic acid (OA), an inhibitor of protein phosphatases PP1 and PP2A, induces sustained activation of NFkappaB and degradation of the nuclear IkappaBalpha, and increases interleukin-8 expression in the neutrophils. Furthermore, inhibitors of protein kinase C-delta (PKCdelta) and IkappaB kinase (IKK) inhibit the OA-induced activation of NFkappaB. Collectively, our results indicate that in human neutrophils, the sustained activation of NFkappaB is regulated by a continuous phosphorylation and degradation of the nuclear IkappaBalpha.

Ligands of the peripheral benzodiazepine receptor induce apoptosis and cell cycle arrest in oesophageal cancer cells: involvement of the p38MAPK signalling pathway

Specific ligands of the peripheral benzodiazepine receptor (PBR) are known to induce apoptosis and cell cycle arrest in oesophageal cancer cells. However, the underlying mechanisms are still unknown. Here, we investigated the transcriptional alterations and activation of protein kinases in response to PBR-specific ligands. Using cDNA arrays, we examined the transcriptional effects of the PBR-specific ligand FGIN-1-27 in two oesophageal cancer cell lines, KYSE-140 (squamous cell carcinoma) and OE-33 (adenocarcinoma). In oesophageal cancer cells, FGIN-1-27 induced extensive changes in the expression of genes involved in the regulation of apoptosis and cell cycle. Both in oesophageal cancer cell lines (KYSE-140, OE-33) we observed a strong upregulation of the growth arrest and DNA-damage-inducible genes, gadd45 and gadd153, in response to PBR ligands. gadd genes are known to be induced by p38MAPK activation. Using Western blotting we detected a time- and dose-dependent phosphorylation of p38MAPK, which was found to be functionally involved in gadd induction, apoptosis, and cell cycle arrest. In conclusion, our data indicate that PBR-specific ligands cause apoptosis and cell cycle arrest by activation of the p38MAPK pathway and induction of gadd45 and gadd153.

Downregulation of urokinase plasminogen activator receptor expression inhibits Erk signalling with concomitant suppression of invasiveness due to loss of uPAR-beta1 integrin complex in colon cancer cells

Cancer invasion is regulated by cell surface proteinases and adhesion molecules. Interaction between specific cell surface molecules such as urokinase plasminogen activator receptor (uPAR) and integrins is crucial for tumour invasion and metastasis. In this study, we examined whether uPAR and beta1 integrin form a functional complex to mediate signalling required for tumour invasion. We assessed the expression of uPAR/beta1 integrin complex, Erk signalling pathway, adhesion, uPA and matrix metalloproteinase (MMP) expression, migration/invasion and matrix degradation in a colon cancer cell line in which uPAR expression was modified. Antisense inhibition of the cell surface expression of uPAR by 50% in human colon carcinoma HCT116 cells (A/S) suppressed Erk-MAP kinase activity by two-fold. Urokinase plasminogen activator receptor antisense treatment of HCT116 cells was associated with a 1.3-fold inhibition of adhesion, approximately four-fold suppression of HMW-uPA secretion and inhibition of pro-MMP-9 secretion. At a functional level, uPAR antisense resulted in a four-fold decline in migration/invasion and abatement of plasmin-mediated matrix degradation. In empty vector-transfected cells (mock), uPA strongly elevated basal Erk activation. In contrast, in A/S cells, uPA induction of Erk activation was not observed. Urokinase plasminogen activator receptor associated with beta1 integrin in mock-transfected cells. Disruption of uPAR-beta1 integrin complex in mock-transfected cells with a specific peptide (P25) inhibited uPA-mediated Erk-MAP kinase pathway and inhibited migration/invasion and plasmin-dependent matrix degradation through suppression of pro-MMP-9/MMP-2 expression. This novel paradigm of uPAR-integrin signalling may afford opportunities for alternative therapeutic strategies for the treatment of cancer.

c-Jun N-terminal kinase (JNK)-mediated modulation of brain mitochondria function: new target proteins for JNK signalling in mitochondrion-dependent apoptosis

The molecular mechanisms underlying the initiation and control of the release of cytochrome c during mitochondrion-dependent apoptosis are thought to involve the phosphorylation of mitochondrial Bcl-2 and Bcl-x(L). Although the c-Jun N-terminal kinase (JNK) has been proposed to mediate the phosphorylation of Bcl-2/Bcl-x(L) the mechanisms linking the modification of these proteins and the release of cytochrome c remain to be elucidated. This study was aimed at establishing interdependency between JNK signalling and mitochondrial apoptosis. Using an experimental model consisting of isolated, bioenergetically competent rat brain mitochondria, these studies show that (i) JNK catalysed the phosphorylation of Bcl-2 and Bcl-x(L) as well as other mitochondrial proteins, as shown by two-dimensional isoelectric focusing/SDS/PAGE; (ii) JNK-induced cytochrome c release, in a process independent of the permeability transition of the inner mitochondrial membrane (imPT) and insensitive to cyclosporin A; (iii) JNK mediated a partial collapse of the mitochondrial inner-membrane potential (Deltapsim) in an imPT- and cyclosporin A-independent manner; and (iv) JNK was unable to induce imPT/swelling and did not act as a co-inducer, but as an inhibitor of Ca-induced imPT. The results are discussed with regard to the functional link between the Deltapsim and factors influencing the permeability transition of the inner and outer mitochondrial membranes. Taken together, JNK-dependent phosphorylation of mitochondrial proteins including, but not limited to, Bcl-2/Bcl-x(L) may represent a potential of the modulation of mitochondrial function during apoptosis.

JNK/SAPK mediates doxorubicin-induced differentiation and apoptosis in MCF-7 breast cancer cells

Pharmacologic induction of cancer cell differentiation has potential in the treatment of breast cancer. Doxorubicin, a widely used anthracycline antibiotic, was previously reported to induce differentiation of MCF-7 breast cancer cells. We demonstrate in this study that inhibition of MCF-7 breast cancer cell growth by low dose doxorubicin (0.01 microg/ml) was accompanied by an increase in cytokeratin 8/18 and milk fat globule membrane protein expression, biomarkers for differentiation of breast cancer, as well as an increase in JNK/SAPK phosphorylation. High dose doxorubicin (10.0 microg/ml) induced apoptosis in these cells. Overexpression of dominant-inhibitory forms of JNK1 and c-Jun blocked both the differentiation and apoptotic effects of doxorubicin. These results suggest that JNK/SAPK pathway signaling plays a prominent role in doxorubicin-induced cell cycle withdrawal, differentiation and control of apoptosis in this cell system. These findings support the possibility that JNK/SAPK pathway activation may be a means of therapeutic intervention in breast cancer.

The p38 mitogen-activated protein kinase pathway and its role in interferon signaling

Interferons (IFNs) are pleiotropic cytokines that exhibit multiple biological effects on cells and tissues. IFN receptors are expressed widely in mammalian cells and virtually all different cell types express them on their surface. The Type I IFN receptor has a multichain structure, composed of at least two distinct receptor subunits, IFNalphaR1 and IFNalphaR2. Two Jak-kinases, Tyk-2 and Jak-1, associate with the different receptor subunits and are activated in response to IFNalpha or IFNbeta to regulate engagement of multiple downstream signaling cascades. These include the Stat-pathway, whose function is essential for transcriptional activation of IFN-sensitive genes, and the insulin receptor substrate pathway, which regulates downstream activation of the phosphatidyl-inositol-3' kinase. Members of the Map family of kinases are also activated by the Type I IFN receptor and participate in the generation of IFN signals. The p38 Map kinase pathway appears to play a very important role in the induction of IFN responses. p38 is rapidly activated during engagement of the Type I IFN receptor, and such an activation is regulated by the small G-protein Rac1, which functions as its upstream effector in a tyrosine kinase-dependent manner. The activated form of p38 regulates downstream activation of other serine kinases, notably MapKapK-2 and MapKapK-3, indicating the existence of Type I IFN-dependent signaling cascades activated downstream of p38. Extensive studies have shown that p38 plays a critical role in Type I IFN-dependent transcriptional regulation, without modifying activation of the Stat-pathway. It is now well established that the function of p38 is essential for gene transcription via ISRE or GAS elements, but has no effects on the phosphorylation of Stat-proteins, the formation of Stat-complexes, and their binding to the promoters of IFN-sensitive genes. As Type I IFNs regulate gene expression for proteins with antiviral properties, it is not surprising that pharmacological inhibition of the p38 pathway blocks induction of IFNalpha-antiviral responses. In addition, pharmacological inhibition of p38 abrogates the suppressive effects of Type I IFNs on normal human hematopoietic progenitors, indicating a critical role for this signaling cascade in the induction of the regulatory effects of Type I IFNs on hematopoiesis. p38 is also activated during IFNalpha-treatment of primary leukemia cells from patients with chronic myelogenous leukemia. Such activation is required for IFNalpha-dependent suppression of leukemic cell progenitor growth, indicating that this pathway plays a critical role in the induction of the antileukemic effects of IFNalpha.

Local anesthetics induce human renal cell apoptosis

Renal cell apoptosis contributes significantly to the pathogenesis of acute renal failure. Local anesthetics induce apoptosis in neuronal and lymphocytic cell lines. We examined the effects of chronic (48 h) local anesthetic treatment (lidocaine, bupivacaine and tetracaine) on human proximal tubular (HK-2) cells. Apoptosis induction was assessed by detecting poly(ADP)-ribose polymerase fragmentation, caspase activation, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) staining, DNA laddering and by cellular morphology. Cell death was quantified by measuring neutral red dye uptake and lactate dehydrogenase released into the cell culture medium. All 3 local anesthetics caused concentration-dependent cell death, induced HK-2 cell apoptosis and potentiated TNF-alpha induced apoptosis. Local anesthetics induced HK-2 cell apoptosis by activation of caspases 3, 6, 7, 8 and 9. ZVAD-fmk, a pan-caspase inhibitor, blocked the local anesthetic induced HK-2 cell apoptosis. Local anesthetics also inhibited the activities of anti-apoptotic kinases protein kinase B (Akt) and extracellular signal regulated mitrogen-activated protein kinase. Local anesthetic's pro-apoptotic effects are independent of sodium channel inhibition as tetrodotoxin, a selective voltage-gated sodium channel blocker, failed to mimic local anesthetic-mediated induction or potentiation of HK-2 cell apoptosis. We conclude that local anesthetics induce human renal cell apoptotic signaling by caspase activation and via inhibition of pro-survival signaling pathways.

Recent advances in alpha1-adrenoceptor pharmacology

alpha(1)-Adrenergic receptors (ARs) mediate some of the main actions of the natural catecholamines, adrenaline and noradrenaline. They participate in many essential physiological processes, such as sympathetic neurotransmission, modulation of hepatic metabolism, control of vascular tone, cardiac contraction, and the regulation of smooth muscle activity in the genitourinary system. Here, we review recent progress on subtype-specific subcellular localization, participation in signaling cascades, and the pivotal function of alpha(1)-ARs, as delineated through studies on genetically engineered animals. Together, these findings will provide new insights into the physiological and pathophysiological roles of the alpha(1)-ARs.

Involvement of MEKK1/ERK/P21Waf1/Cip1 signal transduction pathway in inhibition of IGF-I-mediated cell growth response by methylglyoxal

The abnormal accumulation of methylglyoxal (MG), a physiological glucose metabolite, is strongly related to the development of diabetic complications by affecting the metabolism and functions of organs and tissues. These disturbances could modify the cell response to hormones and growth factors, including insulin-like growth factor-1 (IGF-I). In this study, we investigated the effect of MG on IGF-I-induced cell proliferation and the mechanism of the effect in two cell lines, a human embryonic kidney cell line (HEK293), and a mouse fibroblast cell line (NIH3T3). MG rendered these cells resistant to the mitogenic action of IGF-I, and this was associated with stronger and prolonged activation of ERK and over-expression of P21(Waf1/Cip1). The synergistic effect of MG with IGF-I in activation of ERK was completely abolished by PD98059 but not by a specific PI3K inhibitor, LY294002, or a specific PKC inhibitor, bisindolylmaleimide. Blocking of Raf-1 activity by expression of a dominant negative form of Raf-1 did not reduce the enhancing effect of MG on IGF-I-induced activation of ERK. However, transfection of a catalytically inactive form of MEKK1 resulted in inactivation of the MG-induced activation of ERK and partial inhibition of the enhanced activation of ERK and over-expression of p21(Waf1/Cip1) induced by co-stimulation of MG and IGF-I. These results suggested that the alteration of intracellular milieu induced by MG through a MEKK1-mediated and PI3K/PKC/Raf-1-independent pathway resulted in the modification of cell response to IGF-I for p21(Waf1/Cip1)-mediated growth arrest, which may be one of the crucial mechanisms for MG to promote the development of chronic clinical complications in diabetes.

Chondrogenesis induced by actin cytoskeleton disruption is regulated via protein kinase C-dependent p38 mitogen-activated protein kinase signaling

Disruption of the actin cytoskeleton in subconfluent mesenchymal cells induces chondrogenic differentiation via protein kinase C (PKC) alpha signaling. In this study, we investigated the role of p38 mitogen-activated protein (MAP) kinase in the chondrogenic differentiation of mesenchymal cells that is induced by depolymerization of the actin cytoskeleton. Treatment of mesenchymal cells derived from chick embryonic limb buds with cytochalasin D (CD) disrupted the actin cytoskeleton with concomitant chondrogenic differentiation. The chondrogenesis was accompanied by an increase in p38 MAP kinase activity and inhibition of p38 MAP kinase with SB203580 blocked chondrogenesis. Together these results suggest an essential role for p38 MAP kinase in chondrogenesis. In addition, inhibition of p38 MAP kinase did not alter CD-induced increased expression and activity of PKC alpha, whereas down-regulation of PKC by prolonged exposure of cells to phorbol ester inhibited CD-induced p38 MAP kinase activation. Our results therefore suggest that PKC is involved in the regulation of chondrogenesis induced by disruption of the actin cytoskeleton via a p38 MAP kinase signaling pathway.

Stimulation of the calcitonin gene-related peptide enhancer by mitogen-activated protein kinases and repression by an antimigraine drug in trigeminal ganglia neurons

Calcitonin gene-related peptide (CGRP) is involved in the underlying pathophysiology of all vascular headaches, including migraines. Elevated levels of CGRP during migraine are restored to normal coincident with headache relief after treatment with the antimigraine drug sumatriptan. We have used primary cultures of trigeminal neurons under conditions simulating migraine pathology and therapy to study the mechanisms controlling the CGRP promoter. Using reporter genes in transient transfection assays, we demonstrate that an 18 bp enhancer containing a helix-loop-helix element is both necessary and sufficient for full promoter activity. NGF treatment and cotransfection with an upstream activator of the extracellular signal-regulated MAP kinases (MAPKs) activated the enhancer. Treatment with sumatriptan repressed NGF- and MAPK-stimulated CGRP promoter activity. Repression was also observed using a synthetic MAPK-responsive reporter gene. Sumatriptan regulation of CGRP gene expression did not couple to a G(i)/G(o) pathway, but rather caused a prolonged increase in intracellular calcium. The importance of the prolonged calcium signal in repression of MAPK activity was demonstrated by using the ionophore ionomycin to mimic sumatriptan action. We propose that activation of MAPK pathways may increase CGRP gene expression during migraine, and that sumatriptan can diametrically oppose that activation via a prolonged elevation of intracellular calcium.

Arsenic-mediated cellular signal transduction, transcription factor activation, and aberrant gene expression: implications in carcinogenesis

Arsenic is a common environmental and occupational pollutant and a well-known human carcinogen that causes cancers in many human organs. The exact molecular mechanisms of arsenic carcinogenesis, however, are not well understood. It is generally acknowledged that arsenic does not act via a classic genotoxic or mutagenic mechanism, because it is not a direct mutagen. On the other hand, a growing amount of evidence has shown that arsenic shares many properties with tumor promoters by inducing intracellular signal transduction, activating transcription factors, and changing the expression of genes that are involved in promoting cell growth, proliferation, and malignant transformation. It is postulated that arsenic-induced mitogen-activated protein kinases (MAPKs) signal transduction, which leads to activation of transcription factors such as activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappaB) (which in turn alter gene expression), is associated with the carcinogenicity of arsenic. In this article, we review the recent findings in arsenic-induced MAPKs, AP-1 and NF-kappaB activation, and aberrant gene expression; their implications in arsenic carcinogenesis are discussed. The elucidation of arsenic-induced signal transduction pathways that lead to aberrant gene expression involved in the arsenic-triggered malignant transformation could help to identify novel molecular targets for the treatment of human cancers resulting from arsenic exposure.

The molecular mechanisms of arsenic-induced cell transformation and apoptosis

Arsenic is a well-documented human carcinogen associated with cancers of the skin, lung, liver, and bladder. Interestingly, arsenic has also been used as an effective chemotherapeutic agent in the treatment of certain human cancers. However, the mechanisms by which arsenic induces proliferation of cancer cells or cancer cell death are not well understood. We found that exposure of JB6 P+ cells to low concentrations of arsenic induces cell transformation, whereas higher concentrations of arsenic induce cell apoptosis. Arsenite induces phosphorylation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH(2)-terminal kinases (JNKs). Arsenite-induced Erk activation was markedly inhibited by introduction of dominant-negative Erk2 into cells, whereas expression of dominant-negative Erk2 did not inhibit JNKs or mitogen-activated protein kinase Erk kinase 1/2. Furthermore, arsenite-induced cell transformation was blocked in cells expressing dominant-negative Erk2. In contrast, overexpression of dominant-negative JNK1 increased cell transformation even though it inhibited arsenite-induced JNK activation. Arsenic also induced AP-1 and nuclear factor kappa B (NF-kappaB) activation. Blocking NF-kappaB activation by dominant-negative inhibitory kappa Balpha inhibited arsenic-induced apoptosis and enhanced arsenic-induced cell transformation. Arsenic induced activation of JNKs at a similar dose range that was effective for induction of apoptosis in JB6 cells. In addition, we found that arsenic did not induce p53-dependent transactivation. Similarly, apoptosis induction was not different between p53 wild-type (p53(+/+)) or p53-deficient (p53(-/-)) cells. In contrast, arsenic-induced apoptosis was almost totally blocked by expression of a dominant-negative mutant of JNK. Taken together with previous findings that p53 mutations are involved in approximately 50% of all human cancers and nearly all chemotherapeutic agents kill cancer cells mainly by apoptotic induction, we suggest that arsenic may be a useful agent for the treatment of cancers with p53 mutations. These results suggest that the activation of Erks is required for arsenic-induced cell transformation, whereas the activation of JNKs and NF-kappaB is involved in arsenic-induced apoptosis of JB6 cells.

Induction of apoptosis in mammalian cells by cadmium and zinc

In various mammalian cells, two group IIb metals, cadmium and zinc, induce several morphological and biochemical effects that are salient features of programmed cell death. In C6 rat glioma cells, cadmium caused externalization of phosphatidylserine, breakdown of the mitochondrial membrane potential, activation of caspase-9, internucleosomal DNA fragmentation, chromatin condensation, and nuclear fragmentation. In NIH3T3 murine fibroblasts, cadmium-induced apoptosis was inhibited by overexpression of the antiapoptotic protein Bcl-2. Cadmium-induced DNA fragmentation in C6 cells was independent of inhibition of protein kinase A (PKA), protein kinase C (PKC), mitogen-activated protein kinase (MAPK), phosphatidylinositol-3-kinase, Ca-calmodulin-dependent protein kinase, and protein kinase G. Zinc at moderate concentrations (10-50 microM) protected against programmed cell death induced by cadmium, whereas deprivation of zinc by the membrane-permeable chelator N,N,N',N-terakis-(2-pyridylmethyl)ethylenediamine (TPEN) caused cell death with features characteristic of apoptosis. On the other hand, at elevated extracellular levels (150-200 microM), zinc alone caused programmed cell death in C6 cells. Zinc-induced apoptosis was independent of inhibition of PKA, PKC, guanylate cyclase and MAPK, but it was suppressed in the presence of 100 microM lanthanum chloride.

Induction of apoptosis in mammalian cells by cadmium and zinc

In various mammalian cells, two group IIb metals, cadmium and zinc, induce several morphological and biochemical effects that are salient features of programmed cell death. In C6 rat glioma cells, cadmium caused externalization of phosphatidylserine, breakdown of the mitochondrial membrane potential, activation of caspase-9, internucleosomal DNA fragmentation, chromatin condensation, and nuclear fragmentation. In NIH3T3 murine fibroblasts, cadmium-induced apoptosis was inhibited by overexpression of the antiapoptotic protein Bcl-2. Cadmium-induced DNA fragmentation in C6 cells was independent of inhibition of protein kinase A (PKA), protein kinase C (PKC), mitogen-activated protein kinase (MAPK), phosphatidylinositol-3-kinase, Ca-calmodulin-dependent protein kinase, and protein kinase G. Zinc at moderate concentrations (10-50 microM) protected against programmed cell death induced by cadmium, whereas deprivation of zinc by the membrane-permeable chelator N,N,N',N-terakis-(2-pyridylmethyl)ethylenediamine (TPEN) caused cell death with features characteristic of apoptosis. On the other hand, at elevated extracellular levels (150-200 microM), zinc alone caused programmed cell death in C6 cells. Zinc-induced apoptosis was independent of inhibition of PKA, PKC, guanylate cyclase and MAPK, but it was suppressed in the presence of 100 microM lanthanum chloride.

Menin uncouples Elk-1, JunD and c-Jun phosphorylation from MAP kinase activation

Menin, a nuclear protein encoded by the tumor suppressor gene MEN1, interacts with the AP-1 transcription factor JunD and inhibits its transcriptional activity. In addition, overexpression of Menin counteracts Ras-induced tumorigenesis. We show that Menin inhibits ERK-dependent phosphorylation and activation of both JunD and the Ets-domain transcription factor Elk-1. We also show that Menin represses the inducible activity of the c-fos promoter. Furthermore, Menin expression inhibits Jun N-terminal kinase (JNK)-mediated phosphorylation of both JunD and c-Jun. Kinase assays show that Menin overexpression does not interfere with activation of either ERK2 or JNK1, suggesting that Menin acts at a level downstream of MAPK activation. An N-terminal deletion mutant of Menin that cannot inhibit JunD phosphorylation by JNK, can still repress JunD phosphorylation by ERK2, suggesting that Menin interferes with ERK and JNK pathways through two distinct inhibitory mechanisms. Taken together, our data suggest that Menin uncouples ERK and JNK activation from phosphorylation of their nuclear targets Elk-1, JunD and c-Jun, hence inhibiting accumulation of active Fos/Jun heterodimers. This study provides new molecular insights into the tumor suppressor function of Menin and suggests a mechanism by which Menin may interfere with Ras-dependent cell transformation and oncogenesis.

AP-1, NF-kappa-B, and ERK activation thresholds for promotion of neoplastic transformation in the mouse epidermal JB6 model

The promotion-sensitive mouse epidermal JB6 cells (clone 41) have been used to identify the tumor-promoting activity of various compounds. Because treatment by tumor promoters [12-O-tetradecanoylphorbol-13-acetate (TPA), epidermal growth factor (EGF), or tumor necrosis factor alpha (TNF-alpha)] transforms clone 41 cells to anchorage-independent and tumorigenic phenotypes, they are considered to be undergoing late-stage tumor promotion. Here we address the question of how much activation of transformation-relevant transcription factors [activator protein-1 (AP-1), ternary complex factors (TCFs), or nuclear factor kappa-B (NF-kappa-B)] is required for transformation response and how much tumor promoter produces significant risk of transformation. Stable transfectants harboring a reporter construct with an AP-1 response element, serum-response element (SRE), or NF-kappa-B response element were established. We examined the relationship between concentration of tumor promoters, key signaling events, and activation of the transcription factors. A concentration of > 0.2 nM TPA or 0.12 ng/mL (0.02 nM) EGF produced a significant increase in transformation response as well as in extracellular signal-regulated protein kinase (ERK), SRE, or AP-1 activation. Treatment with > 0.4 U/mL (2.35 pM) TNF-alpha increased NF-kappa-B activity and transformation response in a dose-dependent manner. However, transformation response decreased at > 33 U/mL TNF-alpha due to a cytotoxic response. These findings suggest that the signaling pathway leading to the activation of ERK, TCF, and AP-1 proteins constitutes a major factor determining the risk of tumor promotion by TPA or EGF. Cell toxicity in addition to NF-kappa-B activation should be considered in predicting TNF-alpha-induced transformation response.

Bacterial killing by Mytilus hemocyte monolayers as a model for investigating the signaling pathways involved in mussel immune defence

The signaling pathways involved in mussel immune defence were investigated utilizing a model of killing of Escherichia coli by Mytilus galloprovincialis hemocytes in a co-culture setting. In particular, the role played by different mitogen activated protein kinases (MAPKs) and by the production of eicosanoids were investigated utilising specific cell permeant, pharmacological enzyme inhibitors. Hemocyte pretreatment with the p38 MAPK inhibitor SB203580 significantly reduced bacterial killing, whereas PD98059 (an inhibitor of ERK--extracellularly regulated kinase--MAPK activation) had no significant effect. Wortmannin also inhibited bacterial killing, indicating a crucial role for PI3-kinase activation in the immune response. Killing of E. coli was also reduced by inhibitors of both PLA2 and cyclooxygenase activities, indicating that eicosanoid production is involved in mediating the response to bacterial challenge. The results demonstrate that bacterial killing by mussel hemocytes is particularly sensitive to inhibitors of the key steps involved in the transduction of bacterial signals into the host cell. Moreover, these data indicate that the hemocyte bactericidal activity can be suitably utilized not only for identifying the signaling pathways involved in the response to bacterial infection, but also as a potential investigative-toxicology model to test drugs and contaminants for their effect on the overall mussel immune defence.

Inhibition of tumor necrosis factor-alpha -induced nuclear translocation and activation of NF-kappa B by dehydroxymethylepoxyquinomicin

We previously designed and synthesized an NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), that showed anti-inflammatory activity in vivo. In the present study we looked into its mechanism of inhibition. DHMEQ inhibited tumor necrosis factor-alpha (TNF-alpha)- and 12-O-tetradecanoylphorbol-13-acetate-induced transcriptional activity of NF-kappaB in human T cell leukemia Jurkat cells. It also inhibited the TNF-alpha-induced DNA binding of nuclear NF-kappaB but not the phosphorylation and degradation of IkappaB. Moreover, DHMEQ inhibited the TNF-alpha-induced nuclear accumulation of p65, a component of NF-kappaB. It also inhibited TNF-alpha-induced nuclear transport of green fluorescent protein-tagged p65. On the other hand, DHMEQ did not inhibit the nuclear transport of Smad2 and large T antigen. Also, it did not inhibit TNF-alpha-induced activation of JNK but synergistically induced apoptosis with TNF-alpha in Jurkat cells. Taken together, these data indicate that DHMEQ is a unique inhibitor of NF-kappaB acting at the level of nuclear translocation.

Influence of epidermal growth factor receptor (EGFR), p53 and intrinsic MAP kinase pathway status of tumour cells on the antiproliferative effect of ZD1839 ("Iressa")

of ZD1839 ("Iressa") is an orally active, selective epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI), which blocks signal transduction pathways implicated in proliferation and survival of cancer cells, and other host-dependent processes promoting cancer growth. Permanent downstream activation of the mitogen-activated protein kinase pathway can theoretically bypass the upstream block of epidermal growth factor receptor-dependent mitogen-activated protein kinase activation at the epidermal growth factor receptor level. We investigated the impact of epidermal growth factor receptor content, p53 status and mitogen-activated protein kinase signalling status on ZD1839 sensitivity in a panel of human tumour cell lines: seven head and neck cancer cell lines and two colon cancer cell lines (LoVo, HT29) with derivatives differing only by a specific modification in p53 status (LoVo p53 wt + p53 mut cells, HT29 p53 mut + p53 wt rescued cells). The antiproliferative activity of ZD1839 was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test. ZD1839 concentrations ranged from 0.2-200 microM (48 h exposure). Epidermal growth factor receptor expression, p53 status and p42/p44 (for testing a constitutively active mitogen-activated protein kinase pathway status) were determined by competition analysis (Scatchard plots), denaturing gradient cell electrophoresis and Western blot, respectively. Epidermal growth factor receptor levels ranged from 388 to 33794 fmol mg(-1) protein, a range that is similar to that found in head and neck tumours. The IC(50) values for cell sensitivity to ZD1839 ranged from 6 to 31 microM and a significant inverse correlation (P=0.022, r=0.82) between IC(50) values and epidermal growth factor receptor levels was observed. There was no influence of p53 status on the sensitivity to ZD1839. In two head and neck cancer cell lines with comparably elevated epidermal growth factor receptor expression, a two-fold higher ZD1839 IC(50) value was found for the one with a constitutively active mitogen-activated protein kinase. In conclusion, ZD1839 was active against cells with a range of epidermal growth factor receptor levels, although more so in cells with higher epidermal growth factor receptor expression. Activity was unaffected by p53 status, but was reduced in cells strongly dependent on epidermal growth factor receptor signalling in the presence of an intrinsically activated mitogen-activated protein kinase pathway.