c-Myc regulates cyclin D-Cdk4 and -Cdk6 activity but affects cell cycle progression at multiple independent points

c-myc is a cellular proto-oncogene associated with a variety of human cancers and is strongly implicated in the control of cellular proliferation, programmed cell death, and differentiation. We have previously reported the first isolation of a c-myc-null cell line. Loss of c-Myc causes a profound growth defect manifested by the lengthening of both the G1 and G2 phases of the cell cycle. To gain a clearer understanding of the role of c-Myc in cellular proliferation, we have performed a comprehensive analysis of the components that regulate cell cycle progression. The largest defect observed in c-myc-/- cells is a 12-fold reduction in the activity of cyclin D1-Cdk4 and -Cdk6 complexes during the G0-to-S transition. Downstream events, such as activation of cyclin E-Cdk2 and cyclin A-Cdk2 complexes, are delayed and reduced in magnitude. However, it is clear that c-Myc affects the cell cycle at multiple independent points, because restoration of the Cdk4 and -6 defect does not significantly increase growth rate. In exponentially cycling cells the absence of c-Myc reduces coordinately the activities of all cyclin-cyclin-dependent kinase complexes. An analysis of cyclin-dependent kinase complex regulators revealed increased expression of p27(KIP1) and decreased expression of Cdk7 in c-myc-/- cells. We propose that c-Myc functions as a crucial link in the coordinate adjustment of growth rate to environmental conditions.

Glucocorticoid-induced insulin resistance of protein synthesis is independent of the rapamycin-sensitive pathways in rat skeletal muscle

This study was designed to evaluate the role of p70 S6 kinase (p70(S6K) ), p90 S6 kinase (p90(RSK)) and mitogen-activated protein (MAP) kinase pathways in the insulin resistance of muscle protein synthesis observed during glucocorticoid treatment. Dexamethasone treatment decreased the effect of insulin on protein synthesis (-35. 2%) in epitrochlearis muscle incubated in vitro. This resistance is associated with a total blockage of the stimulation of p70(S6K) by insulin without any significant decrease in the amount of the kinase. However, the effect of rapamycin (inhibitor of several intracellular pathways including p70(S6K) pathways) on muscle protein synthesis was not modified by dexamethasone in rat muscles. This suggested that 'rapamycin-sensitive pathways' associated with the insulin stimulation of protein synthesis were not altered by glucocorticoids and thus are not responsible for the insulin resistance observed. As incubation of muscles with a MAP kinase inhibitor (PD98059) did not modify the stimulation of protein synthesis by insulin and as glucocorticoids did not alter the effect of insulin on p90(RSK )activity, our results provide evidence that glucocorticoid-induced alterations in muscle protein synthesis regulation by insulin do not involve factors or kinases that are dependent on MAP kinase and/or p90(RSK).

Target selectivity of MAPK phosphorothioate antisense ODN on p42/p44, p38 MAPK, and JNK protein expression and its inhibitory effect on VSMC DNA synthesis

AIM

To analyze the target selective and sequence-specific inhibitory effect of mitogen-activated protein kinase (MAPK) phosphorothioate antisense oligodeoxynucleotides (ODN) on p42/p44, p38 MAPK, c-jun NH2-terminal protein kinases (JNK) protein expression, and DNA synthesis in vascular smooth muscle cell (VSMC).

METHODS

Using a phosphorothioate-protected 17-mer antisense MAPK ODN directed against the initiation of translation sites of the p42/p44 MAPK isoforms by liposomal transfection to deplete cultured rat, rabbit, and fetal calf VSMC MAP kinases. The 17-mer sense and random sequence MAPK ODN were used as controls. After liposomal transfection, cells were exposed to 20% serum for 24 h, and then harvested in lysis buffer. P42/p44, p38 MAPK, and p46/p58 JNK protein expression were measured by Western blot. DNA synthesis was measured by [3H]thymidine incorporation.

RESULTS

Treatment with MAPK antisense ODN (0.1-0.8 mumol.L-1) for 48 h reduced phosphored p42/p44 MAPK protein expression but without effect on p38 MAPK and JNK expression, and inhibited cultured rat, rabbit, and fetal calf VSMC [3H]thymidine incorporation stimulated by 20% serum in a concentration-dependent manner.

CONCLUSION

The MAPK antisense ODN target-selectively and sequence-specifically reduces the p42/p44 MAPK protein expression and concentration-dependently inhibits proliferation of rat, rabbit and fetal calf VSMC.

Developmental expression of the CaM kinase II isoforms: ubiquitous gamma- and delta-CaM kinase II are the early isoforms and most abundant in the developing nervous system

CaM kinase II constitutes a family of multifunctional protein kinases that play a major role in Ca2+-mediated signal transduction. As a first step in understanding their possible function in mouse development we characterized the expression patterns of all CaM kinase II isoforms (alpha, beta, gamma and delta) starting in prenatal development. Remarkably, only the ubiquitous gamma- and delta-CaM kinase II are expressed during early development. Their distribution suggests a special role in the developing nervous system and in mature excitable tissues. Additionally, we describe the murine betaM-CaM kinase II, a variant of the 'brain-specific' beta-CaM kinase II, which is highly expressed in skeletal muscle.

Defective regulation of Ca2+/calmodulin-dependent protein kinase II in gamma-irradiated ataxia telangiectasia fibroblasts

Recent indirect evidence suggests that a Ca2+/ calmodulin-dependent pathway, which may involve calmodulin-dependent protein kinase II (CaMKII), mediates the S-phase delay manifested by gamma-ray-exposed human fibroblasts. This pathway is severely impaired in ataxia telangiectasia (A-T) cells [Mirzayans et al. (1995) Oncogene 11, 15971. To extend these findings, we assayed CaMKII activity in irradiated normal and A-T fibroblasts. The radiation treatment induced the autonomous activity of the kinase in normal cells. In contrast, this activity was not elevated in either (i) normal cells pretreated with the selective CaMKII antagonist KN-62 or (ii) gamma-irradiated A-T cells. Moreover, A-T fibroblasts, unlike normal cells, failed to mobilize intracellular Ca2+ upon mitogenic stimulation. These findings identify a novel role for CaMKII in radiation-induced signal transduction and suggest its involvement in effecting the S-phase delay. The data also implicate ATM, the product of the gene responsible for A-T, as a key mediator of both intracellular Ca2+ mobilization and CaMKII activation in response not only to genotoxic stress but also to physiological stimuli.

An Escherichia coli expression vector that allows recovery of proteins with native N-termini from purified calmodulin-binding peptide fusions

We describe a T7-based Escherichia coli expression vector in which protein coding sequence is seamlessly fused to the N-terminal calmodulin-binding peptide (CBP) purification tag. We combined the use of the site-specific protease enterokinase (EK) and the type IIs restriction enzyme Eam1104 I, which cleave outside their respective (amino acid and nucleotide) target sequences, such that any amino acid sequence may be fused directly C-terminal to the EK cleavage site without codon constraints conferred by the cloning method. PCR products are cloned using ligation-dependent or ligation-independent methods with high cloning efficiencies (>10(6) cfu/microg vector), allowing production of insert quantities sufficient for several cloning experiments with a limited number of PCR cycles, resulting in a significant time-savings and reduced likelihood of accumulating PCR-derived mutations. CBP fusion proteins are expressed to high levels when the CBP peptide is positioned at the N-terminus. CBP binds to calmodulin with nanomolar affinity, and fusion proteins are purified to near homogeneity from crude extracts with one pass through calmodulin affinity resin using gentle binding and elution conditions. We show high efficiency seamless cloning of three inserts into the pCAL-n-EK vector, including one encoding the protein c-Jun N-terminal kinase (JNK). CBP-EK-JNK fusion protein was synthesized to 10-20 mg/liter culture and purified to near homogeneity in one step with calmodulin affinity resin. The fusion tag was efficiently removed with EK to yield active JNK with native N-terminal amino acid sequence.

Developmental expression and localization of glycogen synthase kinase-3beta in rat brain

Glycogen synthase kinase (GSK)-3beta is a protein kinase in the wingless/wnt pathway and as such is involved in the regulation of growth and development of the neural tissue in Drosophila and in vertebrates. This enzyme is also abundantly expressed in the mammal adult brain, where it might play a role in the regulation of several substrates. The expression and the neuroanatomical distribution of GSK-3beta immunoreactivity in the rat brain from embryonic up to adult stages has been studied. GSK-3beta was expressed in the developing brain with the highest expression observed from 18 days of embryonic life up to 10 days of postnatal life. Its expression decreased thereafter and was lowest in the adult. GSK-3beta was strongly expressed in developing neurons but only weakly expressed in layers containing neuroblasts. In the adult and during development, GSK-3beta was detected in the pericarya and proximal part of dendrites. In the embryo, an intense GSK-3beta immunoreactivity was also observed in axonal tracts. This axonal immunoreactivity had markedly decreased by 10 days of postnatal life and was absent at 20 days of postnatal life and in the adult. No GSK-3beta immunoreactivity was detected in astrocytes. The GSK-3beta immunoreactivity was found in most brain regions, although significant local variations of GSK-3beta expression were observed. The developmental evolution of GSK-3beta compartmentalization in neurons parallels that of phosphorylated tau, a protein considered to be a physiological substrate for the kinase.

Rho GTPases are over-expressed in human tumors

Small GTPases of the Rho family are involved in the regulation of a variety of cellular processes, such as the organization of the microfilamental network, cell-cell contact and malignant transformation. To address the question of whether Rho proteins are involved in carcinogenesis in man, we compared their expression in tumors from colon, breast and lung with that of the corresponding normal tissue originating from the same patient. As shown by Rho-specific 32P-ADP-ribosylation, as well as Western-blot analysis, the amount of RhoA protein was largely increased in all 3 types of tumors tested. The most dramatic differences in the expression of Rho GTPases were observed in breast tissue. All breast tumors analyzed showed high levels of RhoA, Rac and Cdc42 proteins, whereas in the corresponding normal tissue these Rho proteins were hardly or not detectable. Progression of breast tumors from WHO grade I to grade III was accompanied by a significant average increase in RhoA protein. Overall, increase in the amount of Rho GTPases, in particular RhoA, appears to be a frequent event in different types of human tumors. This supports the view that Rho GTPases are involved in human carcinogenesis.

Induction of GADD45 and JNK/SAPK-dependent apoptosis following inducible expression of BRCA1

The breast cancer susceptibility gene BRCA1 encodes a protein implicated in the cellular response to DNA damage, with postulated roles in homologous recombination as well as transcriptional regulation. To identify downstream target genes, we established cell lines with tightly regulated inducible expression of BRCA1. High-density oligonucleotide arrays were used to analyze gene expression profiles at various times following BRCA1 induction. A major BRCA1 target is the DNA damage-responsive gene GADD45. Induction of BRCA1 triggers apoptosis through activation of c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), a signaling pathway potentially linked to GADD45 gene family members. The p53-independent induction of GADD45 by BRCA1 and its activation of JNK/SAPK suggest a pathway for BRCA1-induced apoptosis.

Repetitive electroconvulsive seizures induce activity of c-Jun N-terminal kinase and compartment-specific desensitization of c-Jun phosphorylation in the rat brain

Electroconvulsive seizures (ECS) are used for therapy of pharmacoresistent depression and are supposed to induce long-lasting neuronal alterations in morphology and gene expression. In this study, we have investigated the phosphorylation of the transcription factor protein c-Jun at its serine 73 residue by immunohistochemistry and the activity of the c-Jun N-terminal kinase 1 (JNK1) by immunocomplex assay following repetitive ECS in adult rats. In untreated controls, nuclear c-Jun immunoreactivity, but not N-terminal phosphorylation, was present in a variety of neuronal populations including the hippocampus, the temporobasal cortex and the amygdalar complex. Daily ECS for 1, 5 or 10 days (1x, 5x or 10x ECS) did not alter the expression of c-Jun but caused a substantial N-terminal phosphorylation of c-Jun (phospho-c-Jun). Nuclear phospho-c-Jun immunoreactivity was maximal within 15 min following ECS, and became absent after 30 min. The highest levels of phospho-c-Jun labeling were found after 1x ECS in the amygdalar complex, the dorsomedial hypothalamus and the piriform cortex. The inducibility of c-Jun N-terminal phosphorylation was preserved in the medial amygdala and piriform cortex, but significantly declined in the basal amygdala and medial hypothalamus with progressive ECS stimulation. One single ECS 3 or 5 days following 10x ECS yielded a pattern of phospho-c-Jun as seen following 10x ECS; thus, a lag of 5 days was not sufficient to provoke the initial level of N-terminal phosphorylation of c-Jun. In the rostral hippocampus, c-Jun was not phosphorylated at any investigated time inspite of its high constitutive expression. In some contrast with this compartment-specific phosphorylation of c-Jun, immunocomplex assays revealed that the JNK1 activity was strongly enhanced in both amygdala and hippocampus. Our findings demonstrate that rapid JNK activation and phosphorylation of c-Jun as stand-by transcription factor characterize the beginning of neuroplastic changes, e.g., following ECS, a classic treatment of mental disorders. The N-terminal phosphorylation is compartment specific and can habituate following repetitive stimulation suggesting that the differential activation of the JNK/c-Jun axis is part of the neuronal strategy to integrate transynaptic excitation.

Cisplatin-induced activation of mitogen-activated protein kinases in ovarian carcinoma cells: inhibition of extracellular signal-regulated kinase activity increases sensitivity to cisplatin

Cisplatin treatment activates multiple signal transduction pathways, which can lead to several cellular responses including cell cycle arrest, DNA repair, survival, or apoptosis. We investigated the response of the mitogen-activated protein kinases, extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun-N-terminal kinase 1 (JNK1), and p38, to cisplatin treatment in the ovarian carcinoma cell line SK-OV-3. Cisplatin caused a late and prolonged induction in a dose-dependent manner of both ERK1/2 and JNK1 activity. ERK1/2 and JNK1 activities continued to increase in magnitude up to 24 h following initiation of cisplatin treatment. In contrast, cisplatin treatment had no effect on p38 activity. Transplatin failed to induce either ERK1/2 or JNK1 at 24 h, which suggests that the activation of these kinases was dependent on cisplatin-specific DNA damage. Treatment with cycloheximide resulted in inhibition of cisplatin-induced ERK1/2 activation, demonstrating that ERK1/2 activity induced by cisplatin was dependent on de novo protein synthesis. Furthermore, inhibition of cisplatin-induced ERK1/2 activity by PD 98059 caused enhanced cisplatin cytotoxicity. Similar enhanced cytotoxic effects of cisplatin were also observed following treatment with PD 98059 in the ovarian carcinoma cell line UCI 101. These observations indicate that ERK1/2 activation induced by cisplatin partially protects cells from cisplatin cytotoxicity. Continued investigation into the mechanism by which the ERK pathway and other signal transduction pathways modulate the response to cisplatin may be helpful in the development of new strategies for improving the therapeutic use of platinum drugs.

Phorbol ester-induced mononuclear cell differentiation is blocked by the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059

The purpose of this study was to evaluate whether the mitogen-activated protein kinase (MAPK) signaling pathway contributes to 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mononuclear differentiation in the human myeloblastic leukemia ML-1 cells. Upon TPA treatment, the activity of ERK1 and ERK2 rapidly increased, with maximal induction between 1 and 3 h, while ERK2 protein levels remained constant. The activity of JNK1 was also significantly induced, with JNK1 protein levels increasing moderately during exposure to TPA. Treatment of cells with PD98059, a specific inhibitor of mitogen-activated protein kinase kinase (MEK), inhibited TPA-induced ERK2 activity. Furthermore, PD98059 completely blocked the TPA-induced differentiation of ML-1 cells, as assessed by a number of features associated with mononuclear differentiation including changes in morphology, nonspecific esterase activity, phagocytic ability, NADPH oxidase activity, mitochondrial respiration, and c-jun mRNA inducibility. We conclude that activation of the MEK/ERK signaling pathway is necessary for TPA-induced mononuclear cell differentiation.

Human cytomegalovirus binding to human monocytes induces immunoregulatory gene expression

To continue our investigation of the cellular events that occur following human CMV (HCMV) infection, we focused on the regulation of cellular activation following viral binding to human monocytes. First, we showed that viral binding induced a number of immunoregulatory genes (IL-1beta, A20, NF-kappaB-p105/p50, and IkappaBalpha) in unactivated monocytes and that neutralizing Abs to the major HCMV glycoproteins, gB (UL55) and gH (UL75), inhibited the induction of these genes. Next, we demonstrated that these viral ligands directly up-regulated monocyte gene expression upon their binding to their appropriate cellular receptors. We then investigated if HCMV binding also resulted in the translation and secretion of cytokines. Our results showed that HCMV binding to monocytes resulted in the production and release of IL-1beta protein. Because these induced gene products have NF-kappaB sites in their promoter regions, we next examined whether there was an up-regulation of nuclear NF-kappaB levels. These experiments showed that, in fact, NF-kappaB was translocated to the nucleus following viral binding or purified viral ligand binding. Changes in IkappaBalpha levels correlated with the changes in NF-kappaB translocation. Lastly, we demonstrated that p38 kinase activity played a central role in IL-1beta production and that it was rapidly up-regulated following infection. These results support our hypothesis that HCMV initiates a signal transduction pathway that leads to monocyte activation and pinpoints a potential mechanism whereby HCMV infection of monocytes can result in profound pathogenesis, especially in chronic inflammatory-type conditions.

Molecular cloning and expression of a stress-responsive mitogen-activated protein kinase-related kinase from Tetrahymena cells

To identify genes responsive to cold stress, we employed the differential display mRNA analysis technique to isolate a novel gene from Tetrahymena thermophila which encodes a protein kinase of 430 amino acids. A homolog of this kinase with 90% amino acid sequence identity was also found in T. pyriformis. Both kinases contain 11 subdomains typical of protein kinases. Sequence analysis revealed that the predicted amino acid sequences resemble those of mitogen-activated protein kinase (MAPK), especially p38 and stress-activated protein kinase which are known to be involved in various stress responses. However, it should be noted that the tyrosine residue in the normally conserved MAPK phosphorylation site (Thr-X-Tyr) is replaced by histidine (Thr226-Gly-His228) in this MAPK-related kinase (MRK). The recombinant MRK expressed in Escherichia coli phosphorylated myelin basic protein (MBP) and became autophosphorylated. However, the mutated recombinant protein in which Thr226 was replaced by Ala lost the ability to phosphorylate MBP, suggesting that Thr226 residue is essential for kinase activity. The MRK mRNA transcript in T. thermophila increased markedly upon temperature downshift from 35 to 15 degrees C (0.8 degrees C/min). Interestingly, osmotic shock either by sorbitol (100-200 mM) or NaCl (25-100 mM) also induced mRNA expression of the MRK in T. pyriformis. In addition, the activity of the kinase as determined by an immune complex kinase assay using MBP as a substrate was also induced by osmotic stress. This is the first demonstration of a MAPK-related kinase in the unicellular eukaryotic protozoan Tetrahymena that is induced by physical stresses such as cold temperature and osmolarity. The present results suggest that this MRK may function in the stress-signaling pathway in Tetrahymena cells.

Defective interleukin (IL)-18-mediated natural killer and T helper cell type 1 responses in IL-1 receptor-associated kinase (IRAK)-deficient mice

Interleukin (IL)-18 is functionally similar to IL-12 in mediating T helper cell type 1 (Th1) response and natural killer (NK) cell activity but is related to IL-1 in protein structure and signaling, including recruitment of IL-1 receptor-associated kinase (IRAK) to the receptor and activation of c-Jun NH2-terminal kinase (JNK) and nuclear factor (NF)-kappaB. The role of IRAK in IL-18-induced responses was studied in IRAK-deficient mice. Significant defects in JNK induction and partial impairment in NF-kappaB activation were found in IRAK-deficient Th1 cells, resulting in a dramatic decrease in interferon (IFN)-gamma mRNA expression. In vivo Th1 response to Propionibacterium acnes and lipopolysaccharide in IFN-gamma production and induction of NK cytotoxicity by IL-18 were severely impaired in IRAK-deficient mice. IFN-gamma production by activated NK cells in an acute murine cytomegalovirus infection was significantly reduced despite normal induction of NK cytotoxicity. These results demonstrate that IRAK plays an important role in IL-18-induced signaling and function.

Identification and expression of delta-isoforms of the multifunctional Ca2+/calmodulin-dependent protein kinase in failing and nonfailing human myocardium

Despite its importance for the regulation of heart function, little is known about the isoform expression of the multifunctional Ca2+/calmodulin-dependent protein kinase (CaMKII) in human myocardium. In this study, we investigated the spectrum of CaMKII isoforms delta2, delta3, delta4, delta8, and delta9 in human striated muscle tissue. Isoform delta3 is characteristically expressed in cardiac muscle. In skeletal muscle, specific expression of a new isoform termed delta11 is demonstrated. Complete sequencing of human delta2 cDNA, representing all common features of the investigated CaMKII subclass, revealed its high homology to the corresponding rat cDNA. Comparative semiquantitative reverse transcription-polymerase chain reaction analyses from left ventricular tissues of normal hearts and from patients suffering from dilated cardiomyopathy showed a significant increase in transcript levels of isoform delta3 relative to the expression of glyceraldehyde-3-phosphate dehydrogenase in diseased hearts (101. 6+/-11.0% versus 64.9+/-9.9% in the nonfailing group; P<0.05, n=6). Transcript levels of the other investigated cardiac CaMKII isoforms remained unchanged. At the protein level, by using a subclass-specific antibody, we observed a similar increase of a delta-CaMKII-specific signal (7.2+/-1.0 versus 3.8+/-0.7 optical density units in the nonfailing group; P<0.05, n=4 through 6). The diseased state of the failing hearts was confirmed by a significant increase in transcript levels for atrial natriuretic peptide (292. 9+/-76.4% versus 40.1+/-3.2% in the nonfailing group; P<0.05, n=3 through 6). Our data characterize for the first time the delta-CaMKII isoform expression pattern in human hearts and demonstrate changes in this expression pattern in heart failure.

Selective loss of PMA-stimulated expression of matrix metalloproteinase 1 in HaCaT keratinocytes is correlated with the inability to induce mitogen-activated protein family kinases

Many cell types, including fibroblasts and primary keratinocytes, increase matrix metalloproteinase 1 (MMP-1) production in response to agonists such as growth factors and phorbol esters. However, the spontaneously transformed human keratinocyte cell line HaCaT, although it increases MMP-1 production in response to epidermal growth factor (EGF), does not respond similarly to stimulation with PMA. This phenomenon occurs even though HaCaT cells remain proliferatively responsive to both agonists, suggesting a HaCaT-specific defect in a PMA-mediated signal transduction pathway. Using an inside-out approach to elucidate the source of this defect, we found that EGF, but not PMA, stimulated MMP-1 promoter activity in transiently transfected HaCaT keratinocytes. In addition, an assessment of fibroblast and HaCaT c-fos and c-jun gene expression after exposure to EGF and PMA showed that although both agonists increased the expression of c-fos and c-jun mRNA in fibroblasts, only EGF did so in HaCaT keratinocytes. Finally, we looked at the activation of mitogen-activated protein (MAP) family kinases after stimulation with EGF or PMA and found that both agonists increased the phosphorylation and activation of fibroblast extracellular signal-regulated protein kinase and c-Jun N-terminal kinase, but only EGF activated the same kinase activities in HaCaT cells. Further, the EGF-mediated increase in MMP-1 gene expression was inhibited by the MAP kinase/ERK kinase (MEK)-specific inhibitor PD98059 and the p38 kinase-specific inhibitor SB203580. Our evidence indicates that although HaCaT MAP kinases are functional, they are not properly regulated in response to the activation of protein kinase C, and that the defect that bars HaCaT MMP-1 expression in response to stimulation with PMA lies before MAP kinase activation.

Differential expression and activation of p38 mitogen-activated protein kinase alpha, beta, gamma, and delta in inflammatory cell lineages

Four p38 mitogen-activated protein kinases (p38alpha, beta, gamma, delta) have been described. To understand the role of p38 family members in inflammation, we determined their relative expression in cells that participate in the inflammatory process. Expression was measured at the level of mRNA by reverse-transcriptase PCR and protein by Western blot analysis. p38alpha was the dominant form of p38 in monocytes; expression of p38delta was low and p38beta was undetected. In macrophages, p38alpha and p38delta were abundant, but p38beta was undetected. p38alpha and p38delta were also expressed by neutrophils, CD4+ T cells, and endothelial cells. Again, p38beta was not detected in neutrophils, although low amounts were present in CD4+ T cells. In contrast, p38beta was abundant in endothelial cells. p38gamma protein was not detected in any cell type, although p38gamma mRNA was present in endothelial cells. Immunokinase assays showed a strong activation of p38alpha and a lesser activation of p38delta in LPS-stimulated macrophages. Abs specific for mono- and dual-phophorylated forms of p38 suggested that LPS induces dual phosphorylation of p38alpha, but primarily mono-phosphorylation of p38delta. IL-1beta activated p38alpha and p38beta in endothelial cells. However, p38alpha was the more activated form based on kinase assays and phosphorylation analysis. Expression and activation patterns of p38alpha in macrophages and endothelial cells suggest that p38alpha plays a major role in the inflammatory response. Additional studies will be needed to define the contribution of p38delta to macrophage, neutrophil, and T cell functions, and of p38beta to signaling in endothelial cells and T cells.

Extracellular signal-regulated kinases regulate leukotriene C4 generation, but not histamine release or IL-4 production from human basophils

Human basophils secrete histamine and leukotriene C4 (LTC4) in response to various stimuli, such as Ag and the bacterial product, FMLP. IgE-mediated stimulation also results in IL-4 secretion. However, the mechanisms of these three classes of secretion are unknown in human basophils. The activation of extracellular signal-regulated kinases (ERKs; ERK-1 and ERK-2) during IgE- and FMLP-mediated stimulation of human basophils was examined. Following FMLP stimulation, histamine release preceded phosphorylation of ERKs, whereas phosphorylation of cytosolic phospholipase A2 (cPLA2), and arachidonic acid (AA) and LTC4 release followed phosphorylation of ERKs. The phosphorylation of ERKs was transient, decreasing to baseline levels after 15 min. PD98059 (MEK inhibitor) inhibited the phosphorylation of ERKs and cPLA2 without inhibition of several other tyrosine phosphorylation events, including phosphorylation of p38 MAPK. PD98059 also inhibited LTC4 generation (IC50 = approximately 2 microM), but not histamine release. Stimulation with anti-IgE Ab resulted in the phosphorylation of ERKs, which was kinetically similar to both histamine and LTC4 release and decreased toward resting levels by 30 min. Similar to FMLP, PD98059 inhibited anti-IgE-mediated LTC4 release (IC50, approximately 2 microM), with only a modest effect on histamine release and IL-4 production at higher concentrations. Taken together, these results suggest that ERKs might selectively regulate the pathway leading to LTC4 generation by phosphorylating cPLA2, but not histamine release or IL-4 production, in human basophils.

Synaptic plasticity: regulated translation in dendrites

Synaptic activity can induce neurons to synthesize proteins important for cognition and brain development. Recent results suggest this activity-induced protein synthesis is partially mediated by regulated translation within neuronal dendrites.

Hyperoxia induces the neuronal differentiated phenotype of PC12 cells via a sustained activity of mitogen-activated protein kinase induced by Bcl-2

We previously reported that rat pheochromocytoma PC12 cells express the neuronal differentiated phenotype under hyperoxia through the production of reactive oxygen species (ROS). In the present study, we found that in this phenotype, Bcl-2, an apoptosis inhibitor, affects mitogen-activated protein (MAP)-kinase activity, which is known as a key enzyme of the signal-transduction cascade for differentiation. When PC12 cells were cultured under hyperoxia, a rapid increase in MAP-kinase activity, including that of both p42 and p44, was observed. Although the activity level then decreased quickly, activity higher than the control level was observed for 48 h. PD98059, an inhibitor of MAP kinase, suppressed the hyperoxia-induced neurite extensions, suggesting the involvement of MAP-kinase activity in the mechanism of differentiation induced by ROS. An elevation of Bcl-2 expression was observed after culturing PC12 cells for 24 h under hyperoxia. This Bcl-2 elevation was not affected by treatment with PD98059, suggesting that it did not directly induce neurite extension under hyperoxia. However, the blockade of the Bcl-2 elevation by an antisense oligonucleotide inhibited the sustained MAP-kinase activity and neurite extensions under hyperoxia. Further, in PC12 cells highly expressing Bcl-2, the sustained MAP-kinase activity and neurite extensions under hyperoxia were enhanced. These results suggested that MAP kinase is activated through the production of ROS, and the subsequent elevation of Bcl-2 expression sustains the MAP-kinase activity, resulting in the induction of the neuronal-differentiation phenotype of PC12 cells under hyperoxia.

Characterization of cellular pathways involved in glioblastoma response to the chemotherapeutic agent 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) by gene expression profiling

The effectiveness of chemotherapy for human cancers is limited by pharmacokinetic parameters such as variation in metabolism and is determined by the cellular response. In this work, we aimed to gain a more holistic understanding of the molecular basis of glioma response to the DNA-alkylating agent 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) by using a systematic approach: we investigated the expression of 588 genes with various cellular functions in a BCNU-resistant glioblastoma cell line and a BCNU-sensitive subline before and after treatment with BCNU. Our gene expression profiling revealed major differences in gene expression between these two cell lines, especially after treatment with BCNU. One striking example was that BCNU decreased the expression of six DNA-repair genes in sensitive but not in resistant cells. In sensitive cells, BCNU treatment resulted in the induction of two MAP kinase genes; this finding suggests that the specific response to BCNU in sensitive cells may involve the Jun kinase signal transduction pathway. After BCNU treatment, marked induction of tumor necrosis factor was detected only in sensitive cells, suggesting that tumor necrosis factor is a mediator of BCNU-induced cell death. Bcl-2 family members were not altered by BCNU in sensitive cells, suggesting that BCNU-induced cell death may be independent of the bcl-2 pathway. Results of the present study demonstrate that gene expression profiling may facilitate identification of cellular pathways associated with specific responses to chemotherapeutic agents and contribute to an understanding of the molecular basis of drug action.

Mitogen-activated protein kinase (p38-, JNK-, ERK-) activation pattern induced by extracellular and intracellular singlet oxygen and UVA

Ultraviolet A (UVA; 320-400 nm) radiation in human skin fibroblasts induces a pattern of mitogen-activated protein kinase (MAPK) activation consisting of a rapid and transient induction of p38 and c-Jun-N-terminal kinase (JNK) activity but not extracellular signal-regulated kinases (ERK). UVA activation of p38 can be inhibited by the singlet oxygen (1O2) quenchers azide and imidazole, but not by the hydroxyl radical scavengers mannitol or dimethylsulfoxide, pointing to the involvement of 1O2. The same effect has been shown for JNK. Like UVA, 1O2 generated intracellularly upon photoexcitation of Rose Bengal activates p38 and JNK but not ERK. p38 and JNK activation was also elicited by chemiexcitation for the intracellular generation of 1O2 by the lipophilic 1,4-endoperoxide of N,N'-di(2,3-dihydroxypropyl)-1, 4-naphthalene dipropionamide. In contrast, extracellular generation of 1O2, by irradiation of Rose Bengal immobilized on agarose beads or by chemiexcitation employing the hydrophilic 1,4-endoperoxide of disodium 3,3'-(1,4-naphthylidene) dipropionate, was ineffective in activating p38 or JNK. These data suggest that the activation of p38 and JNK by 1O2 occurs only when the electronically excited molecule is generated intracellularly.

Estrogen-induced activation of mitogen-activated protein kinase in cerebral cortical explants: convergence of estrogen and neurotrophin signaling pathways

We have shown that estrogen elicits a selective enhancement of the growth and differentiation of axons and dendrites (neurites) in the developing CNS. We subsequently demonstrated widespread colocalization of estrogen and neurotrophin receptors (trk) within developing forebrain neurons and reciprocal transcriptional regulation of these receptors by their ligands. Using organotypic explants of the cerebral cortex, we tested the hypothesis that estrogen/neurotrophin receptor coexpression also may result in convergence or cross-coupling of their signaling pathways. Estradiol elicited rapid (within 5-15 min) tyrosine phosphorylation/activation of the mitogen-activated protein (MAP) kinases, ERK1 and ERK2, that persisted for at least 2 hr. This extracellular signal-regulated protein kinase (ERK) activation was inhibited successfully by the MEK1 inhibitor PD98059, but not by the estrogen receptor (ER) antagonist ICI 182,780, and did not appear to result from estradiol-induced activation of trk. Furthermore, we also found that estradiol elicited an increase in B-Raf kinase activity. The latter and subsequent downstream events leading to ERK activation may be a consequence of our documentation of a multimeric complex consisting of, at least, the ER, hsp90, and B-Raf. These novel findings provide an alternative mechanism for some of the estrogen actions in the developing CNS and could explain not only some of the very rapid effects of estrogen but also the ability of estrogen and neurotrophins to regulate the same broad array of cytoskeletal and growth-associated genes involved in neurite growth and differentiation.

Inhibition of ultraviolet B--induced c-fos gene expression and p38 mitogen-activated protein kinase activation by (-)-epigallocatechin gallate in a human keratinocyte cell line

(-)-Epigallocatechin gallate (EGCG), the major polyphenol isolated from green tea, is an active chemoprevention agent against cancer. However, the molecular mechanisms that underlie the inhibitory effects of EGCG are not well understood. In this study, we tested the effects of EGCG on ultraviolet (UV) B radiation-induced c-fos gene expression in a human keratinocyte cell line, HaCaT. EGCG inhibited UVB-induced steady-state message and transcriptional activation of the c-fos gene in a dose-dependent manner. Western analyses further indicated that EGCG had an inhibitory effect on UVB-induced accumulation of the c-fos protein within the same dose range. To further examine the mechanism by which EGCG inhibits UVB-induced c-fos expression, we tested the effect of EGCG on upstream activators of the c-fos gene. We found that EGCG significantly inhibited activation of p38 mitogen-activated protein kinase but not c-jun NH2-terminal kinase or extracellular signal-regulated protein kinase activation. Our previous studies have indicated that UVB-induced c-fos expression may play a key role in UVB-induced activation of the activator protein-1 transcription factor and EGCG-inhibited, UVB-induced activation of AP-1 in HaCaT cells. Because AP-1 is important for tumor promotion and c-fos is a major component of AP-1, the inhibitory effects of EGCG on c-fos expression may further explain the anti-tumor-promoting effects of EGCG.