Roles of the MAP kinase cascade in vertebrates

Identification of an AP1-ZFP36 Regulatory Network Associated with Breast Cancer Prognosis

It has been established that ZFP36 (also known as Tristetraprolin or TTP) promotes mRNA degradation of proteins involved in inflammation, proliferation and tumor invasiveness. In mammary epithelial cells ZFP36 expression is induced by STAT5 activation during lactogenesis, while in breast cancer ZFP36 expression is associated with lower grade and better prognosis. Here, we show that the AP-1 transcription factor components, i.e. JUN, JUNB, FOS, FOSB, in addition to DUSP1, EGR1, NR4A1, IER2 and BTG2, behave as a conserved co-regulated group of genes whose expression is associated to ZFP36 in cancer cells. In fact, a significant down-modulation of this gene network is observed in breast, liver, lung, kidney, and thyroid carcinomas compared to their normal counterparts. In breast cancer, the normal-like and Luminal A, show the highest expression of the ZFP36 gene network among the other intrinsic subtypes and patients with low expression of these genes display poor prognosis. It is also proposed that AP-1 regulates ZFP36 expression through responsive elements detected in the promoter region of this gene. Culture assays show that AP-1 activity induces ZFP36 expression in mammary cells in response to prolactin (PRL) treatment thorough ERK1/2 activation. These results suggest that JUN, JUNB, FOS and FOSB are not only co-expressed, but would also play a relevant role in regulating ZFP36 expression in mammary epithelial cells.

Development of a p38α-selective radioactive probe for qualitative diagnosis of cancer using SPECT

OBJECTIVE

p38 mitogen-activated protein (MAP) kinase (p38α) has drawn attention as a new target molecule for the treatment and diagnosis of cancer, and its overexpression and activation have been reported in various types of cancer. In this study, a single photon emission computed tomography (SPECT) imaging probe of p38α was developed to noninvasively image p38α activity for effective qualitative diagnosis of cancer.

METHODS

Pyrrolepyridine derivatives, m-YTM and p-YTM, were designed and synthesized based on the structure of the p38α-selective inhibitor. Radioactive iodine-labeled m-YTM, [¹²⁵I]m-YTM, was synthesized because m-YTM greatly inhibited the phosphorylation of p38α upon examining the inhibitory effects of the compounds. After investigating the binding affinity of [¹²⁵I]m-YTM to the recombinant p38α, a saturation binding experiment using activated p38α and inactive p38α was performed to determine the binding site. Uptake of [¹²⁵I]m-YTM into various cancer cell lines was investigated, and the pharmacokinetics was evaluated using tumor-bearing mice.

RESULTS

The inhibitory activity of m-YTM was approximately 13 times higher than that of SB203580, a p38α-selective inhibitor. The binding site of [¹²⁵I]m-YTM was estimated to be the p38α activating site, similar to that of SB203580, because the [¹²⁵I]m-YTM bound strongly to both activated p38α and inactive p38α. Various different cancer cells incorporated [¹²⁵I]m-YTM; however, its accumulation was significantly reduced by treatment with SB203580. Pharmacokinetics study of [¹²⁵I]m-YTM in B-16 tumor-bearing mice was examined which revealed high accumulation of radioactivity in tumor tissues. The ratios of radioactivity in the B-16 tumor to that in blood were 3.1 and 50 after 1 and 24 h, respectively. The ratio of radioactivity in the tumor to that in blood in the tumor-bearing mice generated using other cancer cell lines was also ≥ 1 at 1 h after the administration of the probe.

CONCLUSIONS

This study suggests that [¹²³I]m-YTM has potential as a p38α imaging probe effective for various cancer types.

Glioma growth modeling based on the effect of vital nutrients and metabolic products

Glioma brain tumors exhibit considerably aggressive behavior leading to high mortality rates. Mathematical modeling of tumor growth aims to explore the interactions between glioma cells and tissue microenvironment, which affect tumor evolution. Leveraging this concept, we present a three-dimensional model of glioma spatio-temporal evolution based on existing continuum approaches, yet incorporating novel factors of the phenomenon. The proposed model involves the interactions between different tumor cell phenotypes and their microenvironment, investigating how tumor growth is affected by complex biological exchanges. It focuses on the separate and combined effect of vital nutrients and cellular wastes on tumor expansion, leading to the formation of cell populations with different metabolic, proliferative, and diffusive profiles. Several simulations were performed on a virtual and a real glioma, using combinations of proliferation and diffusion rates for different evolution times. The model results were validated on a glioma model available in the literature and a real case of tumor progression. The experimental observations indicate that our model estimates quite satisfactorily the expansion of each region and the overall tumor growth. Based on the individual results, the proposed model may provide an important research tool for patient-specific simulation of different tumor evolution scenarios and reliable estimation of glioma evolution. Graphical Abstract Outline of the mathematical model functionality and application to glioma growth with indicative results.

YKL-40 expression in abnormal invasive placenta cases

OBJECTIVE

YKL-40 is a secreted glycoprotein and has been implicated in the proliferation and differentiation of malignant cells, extracellular tissue remodelling, neovascularisation, inhibition of cancer cell apoptosis and stimulation of tumour-associated fibroblasts. The purpose of this study was to evaluate YKL-40 tissue expression in extravillous trophoblast invasion and its possible implication in placenta creta.

METHODS

A total of 35 placenta creta cases and six control cases were included in the study, of which eight cases were placenta accreta, 12 were increta and 15 were percreta. Histological YKL-40 staining was scored in tissue as weak (1), medium (2) and strong (3).

RESULTS

YKL-40 immunoreactivity intensity in the percreta group was significantly higher compared to the increta and accreta groups (2.47±0.74, 1.33±0.49 and 1.37±0.52, respectively; P=0.000). YKL-40 immunoreactivity intensity was positively correlated with creta (r=0.6; P=0.000), depth of invasion (r=0.49; P=0.003) and depth of invasion to full thickness ratio (r=0.58; P=0.000).

CONCLUSION

This study demonstrated that YKL-40 is strongly expressed in placenta percreta and is correlated with extravillous trophoblast invasion. These findings may be informative for understanding the pathophysiology of placenta creta.

Growth, bioluminescence and shoal behavior hormetic responses to inorganic and/or organic chemicals: a review

A biphasic dose response, termed hormesis, is characterized by beneficial effects of a chemical at a low dose and harmful effects at a high dose. This biphasic dose response phenomenon has the potential to strongly alter toxicology in a broad range. The present review focuses on the progress of research into hormetic responses in terms of growth (in plants, birds, algae and humans), bioluminescence, and shoal behavior as end points. The paper describes how both inorganic and organic chemicals at a low dose show stimulatory responses while at higher doses are inhibitory. The article highlights how factors such as symbiosis, density-dependent factors, time, and contrasting environmental factors (availability of nutrients, temperature, light, etc.) affect both the range and amplitude of hormetic responses. Furthermore, the possible underlying mechanisms are also discussed and we suggest that, for every end point, different hormetic mechanisms may exist. The occurrences of varying interacting receptor systems or receptor systems affecting the assessment of hormesis for each endpoint are discussed. The present review suggests that a hormetic model should be adopted for toxicological evaluations instead of the older threshold and linear non-threshold models.

Two closely related human members of chitinase-like family, CHI3L1 and CHI3L2, activate ERK1/2 in 293 and U373 cells but have the different influence on cell proliferation

The activation of extracellular signal-regulated kinases (ERK1/2) has been associated with specific outcomes. Sustained activation of ERK1/2 by nerve growth factor (NGF) is associated with translocation of ERKs to the nucleus of PC12 cells and precedes their differentiation into sympathetic-like neurons whereas transient activation by epidermal growth factor (EGF) leads to cell proliferation. It was demonstrated that different growth factors initiating the same cellular signaling pathways may lead to the different cell destiny, either to proliferation or to the inhibition of mitogenesis and apoptosis. Thus, further investigation on kinetic differences in activation of certain signal cascades in different cell types by biologically different agents are necessary for understanding the mechanisms as to how cells make a choice between proliferation and differentiation.

It was reported that chitinase 3-like 1 (CHI3L1) protein promotes the growth of human synovial cells as well as skin and fetal lung fibroblasts similarly to insulin-like growth factor 1 (IGF1). Both are involved in mediating the mitogenic response through the signal-regulated kinases ERK1/2. In addition, CHI3L1 which is highly expressed in different tumors including glioblastomas possesses oncogenic properties. As we found earlier, chitinase 3-like 2 (CHI3L2) most closely related to human CHI3L1 also showed increased expression in glial tumors at both the RNA and protein levels and stimulated the activation of the MAPK pathway through phosphorylation of ERK1/2 in 293 and U87 MG cells. The work described here demonstrates the influence of CHI3L2 and CHI3L1 on the duration of MAPK cellular signaling and phosphorylated ERK1/2 translocation to the nucleus. In contrast to the activation of ERK1/2 phosphorylation by CHI3L1 that leads to a proliferative signal (similar to the EGF effect in PC12 cells), activation of ERK1/2 phosphorylation by CHI3L2 (similar to NGF) inhibits cell mitogenesis and proliferation.

Immunohistochemical expression of YKL-40 in peritoneal endometriosis

AIMS

To evaluate the relationship between the immunohistochemical expression of YKL-40 and peritoneal endometriosis by using paraffinized peritoneal tissue blocks.

METHODS AND MATERIALS

We retrospectively collected data from 27 patients whose pathologic reports indicated invasion of the peritoneum by endometriosis. A conventional peroxidase staining technique was performed using rabbit polyclonal antibody (Quidel corporation, Santa Clara, CA) on peritoneal tissue blocks; their histology was then reviewed by a pathologist, and data were analyzed by nonparametric and Mann-Whitney tests.

RESULTS

YKL-40 was detected immunohistochemically in 17 (63%) of 27 cases. The number of biopsies which were invaded by endometriosis (P = 0.015), with a score based on the revised classification of endometriosis (American Society for Reproductive Medicine) had statistical significance (P = 0.001). The obstetric history, age, body mass index, severity, and occurrence of dysmenorrhea, menstrual phase, preoperative CA 125, erythrocyte sedimentation rate, and white blood cell count had no statistical significance. YKL-40 immunoreactivity was recognized as brown staining, localized to the cytoplasm of epithelial cells of endometrial gland in peritoneal endometriosis. There was no positive staining on endometrial stromal cells or smooth muscle cells.

CONCLUSIONS

YKL-40 is related to severity of peritoneal endometriosis. However why a different expression level of immunohistochemical staining should occur is not known and needs further investigation.

Mechanism of copper-activated transcription: activation of AP-1, and the JNK/SAPK and p38 signal transduction pathways

Copper is an essential metal that is able to produce reactive oxygen species and to induce intracellular oxidative stress. Several studies have examined the effects of excessive copper and oxidative stress on various organisms and tissues, but few have addressed the molecular mechanisms by which copper affects transcription. Our results demonstrated that, in COS-7 cells, copper treatment caused an increase in the binding of nuclear proteins to activating protein-1 and antioxidant response elements. The level of copper-inducible nuclear protein binding was modulated by increasing or decreasing the level of intracellular oxidative stress. Copper exposure also led to an increase in the steady-state levels of c-fos, c-jun, and c-myc mRNAs. Exposure to copper resulted in an increase in the levels of phosphorylation and activation of the c-Jun N-terminal kinase/stress-activated protein kinase and p38 pathways. The activation of these pathways resulted in a concomitant increase in c-Jun phosphorylation. We investigated the hypothesis that copper-induced oxidative stress leads to the formation of stable lipid peroxidation by-products that activate mitogen-activated protein kinase (MAPK) pathways, ultimately affecting transcription. While exposure did result in the production of 4-hydroxynonenal, the timing of the increased levels of proto-oncogene mRNA, phosphorylation of c-jun, and phosphorylation and activation of MAPKs, as well as the inability of the lipophilic antioxidant vitamin E to abrogate MAPK phosphorylation, suggest that the formation of stable lipid peroxidation by-products may not be the primary mechanism by which copper activates MAPKs. These results further elucidate the effects of copper on signal transduction pathways to alter gene expression.

Iron supplementation protects against lead-induced apoptosis through MAPK pathway in weanling rat cortex

Recent studies indicate that iron (Fe) is involved in neurotoxicity caused by inorganic lead (Pb). We studied the role of Fe in the effects Pb-induced cerebral apoptosis during rat development and to explore its possible regulatory mechanism. In the present study, weanling male Sprague-Dawley rats were randomly divided into four groups. Three groups of rats received 400 microg/mL Pb acetate solution in drinking water, among which two of the groups were concurrently given 20mg/kg and 40mg/kg FeSO(4) solution, respectively, as the low and high Fe group, for 6 weeks. The Fe doses were administered orally by gavage every other day according to animal body weight. For the control group, Na acetate with an acetate concentration equivalent to the high dose of Pb acetate was prepared in the same manner. At the end of the study, exposure to Pb in drinking water significantly promoted internucleosomal DNA fragmentation, enhanced the percentage of TUNEL-positive cells and increased the caspase-3 activities in cortex as compared to the controls. At the same time, it did cause a significant decrease in cortex Fe concentrations. Concomitant supplement with different dose Fe appeared to restore brain Fe level to the normal level. Although the low dose of Fe restored brain Pb level to the normal level and the high dose of Fe did not, both of them reduced the formation of DNA fragments, showed few TUNEL-positive cells with yellow nuclei and inhibited Pb-induced procaspase-3 degradation. Western blot showed that exposure to Pb caused a significant elevation in the phosphorylation of ERK1/2, JNK1/2, and Elk-1. Low Fe supplemental treatment suppressed the phosphorylation of ERK1/2 and JNK1/2 but not Elk-1. Interestingly, high Fe treatment slightly suppressed the phosphorylation of JNK1/2, but significantly elevated the phosphorylation of ERK1/2 and Elk-1. Collectively, the current study suggests that supplementation of Fe during Pb treatment prevents against cytotoxicity and apoptosis induced by Pb insults, in which MAPK pathways play an important role in Pb-induced cerebral apoptosis by activating the MEK-ERK pathway that suppresses JNK signaling.

Biphasic effect of arsenite on cell proliferation and apoptosis is associated with the activation of JNK and ERK1/2 in human embryo lung fibroblast cells

Biphasic dose-response relationship induced by environmental agents is often characterized with the effect of low-dose stimulation and high-dose inhibition. Some studies showed that arsenite may induce cell proliferation and apoptosis via biphasic dose-response relationship in human cells; however, mechanisms underlying this phenomenon are not well understood. In the present study, we aimed at investigating the relationship between biphasic effect of arsenite on cell proliferation and apoptosis and activation of JNK and ERK1/2 in human embryo lung fibroblast (HELF) cells. Our results demonstrated that cell proliferation may be stimulated at lower concentrations (0.1 and 0.5 microM) arsenite but inhibited at higher concentrations (5 and 10 microM). When cell apoptosis was used as the endpoint, the concentration-response curves were changed to U-shapes. During stimulation phospho-JNK levels were significantly increased at 3, 6, and 12 h after 0.1 or 0.5 microM arsenite exposure. Phospho-ERK1/2 levels were increased with different concentrations (0.1-10 microM) of arsenite at 6, 12, and 24 h. Blocking of JNK pathway with 20 microM SP600125 or ERK1/2 by 100 microM PD98059 significantly inhibited biphasic effect of arsenite in cells. Data in the present study suggest that activation of JNK and ERK1/2 may be involved in biphasic effect of arsenite when measuring cell proliferation and apoptosis in HELF cells. JNK activation seems to play a more critical role than ERK1/2 activation in the biphasic process.

The role of transforming growth factor beta signaling in messenger RNA stability

Transforming growth factor beta (TGF-beta) is a biologically multipotent regulatory protein implicated in functions that include the regulation of cellular growth, differentiation, extracellular matrix formation, and wound healing. It also plays a role in the pathologies of Alzheimer's disease, cancer and autoimmune disorders. TGF-beta modulates gene expression by affecting transcriptional activation and mRNA turnover rate. Steady-state mRNA levels depend on both the transcriptional activity and mRNA half-life. The stability of mRNA can be modified by the binding of trans-acting factors to cis-elements on the message. These can protect the mRNA from cleavage by RNAses, or they may promote mRNA cleavage. Changes in mRNA stability can lead to changes in the proteome and subsequently in cellular metabolism. The SMAD family of proteins has been implicated in the transduction of the TGF-beta signal, where they regulate transcriptional activity. This review attempts to provide new insights into the role played by TGF-beta in the regulation of mRNA turnover.

Expression of ICAM-1, TNF-alpha, NF kappa B, and MAP kinase in tubers of the tuberous sclerosis complex

Individuals affected with tuberous sclerosis complex (TSC) develop cortical tubers characterized by disorganized cytoarchitecture and morphologically abnormal cell types, such as dysplastic neurons (DNs) and giant cells (GCs). As part of ongoing cDNA array analysis to study the molecular pathogenesis of tuber formation, we detected increased expression of intercellular adhesion molecule-1 (ICAM-1) mRNA, a cell adhesion molecule (CAM) that functions in cytokine signaling, in tubers. Western and immunohistochemical analyses revealed that ICAM-1 protein was selectively expressed in tubers, but was only minimally expressed in control cortex, adjacent nontuberal cortex, or in non-TSC focal cortical dysplasia. Increased expression of ICAM-1 was found in mice in which the Tsc1 gene was conditionally inactivated in astrocytes. Expression of molecules involved in ICAM-1 activation and cytokine signaling were increased in tubers, including tumor necrosis factor alpha (TNF-alpha), mitogen activated protein kinase (MAPK), and nuclear factor kappa B (NF-kappaB). Numerous CD68-immunoreactive macrophages were observed clustered around GCs further supporting an inflammatory response in tubers. Expression of caspase 8 and Fas support cytokine activation and detection of TUNEL reactivity suggests ongoing cell death in tubers. Specific alterations in ICAM-1, TNF-alpha, NF-kappaB1, and MAPK expression coupled with the detection of numerous CD68-immunoreactive macrophages suggests activation of proinflammatory cytokine signaling pathways in tubers that may culminate in cell death.

Vasopressin-induced intracellular redistribution of protein kinase D in intestinal epithelial cells

The spatio-temporal changes of signaling molecules in response to G protein-coupled receptors (GPCR) stimulation is a poorly understood process in intestinal epithelial cells. Here we investigate the dynamic mechanisms associated with GPCR signaling in living rat intestinal epithelial cells by characterizing the intracellular translocation of protein kinase D (PKD), a serine/threonine protein kinase involved in mitogenic signaling in intestinal epithelial cells. Analysis of the intracellular steady-state distribution of green fluorescent protein (GFP)-tagged PKD indicated that in non-stimulated IEC-18 cells, GFP-PKD is predominantly cytoplasmic. However, cell stimulation with the GPCR agonist vasopressin induces a rapid translocation of GFP-PKD from the cytosol to the plasma membrane that is accompanied by its activation via protein kinase C (PKC)-mediated process and posterior plasma membrane dissociation. Subsequently, active PKD is imported into the nuclei where it transiently accumulates before being exported into the cytosol by a mechanism that requires a competent Crm1 nuclear export pathway. These findings provide evidence for a mechanism by which PKC coordinates in intestinal epithelial cells the translocation and activation of PKD in response to vasopressin-induced GPCR activation.

Effect of space flight on the frequency of micronuclei and expression of stress-responsive proteins in cultured mammalian cells

Results of past space experiments suggest that the biological effect of space radiation could be enhanced under microgravity in some cases, especially in insects. To examine if such a synergistic effect of radiation and microgravity also exists in human cells, frequencies of chromosome instability and cellular levels of several stress-responsive proteins were analyzed in cultured human and rodent cells after space flight. Human (MCF7 and AT2KY), mouse (m5S) and hamster (SHE) cell lines were loaded on the Space Shuttle Discovery (STS-95 mission) and grown during a 9-day mission. After landing, the micronuclei resulting from abnormal nuclear division and accumulation of stress-responsive proteins such as p53 and mitogen-activated protein kinases (MAPKs), which are involved in radiation-induced signal transduction cascades, were analyzed. The frequencies of micronuclei in all the four mammalian cell strains tested were not significantly different between flight and ground control samples. Also, the cellular amounts of p53, p21 (WAF1/SDI1/CIP1) and activated (phosphorylated) forms of three distinct MAPKs in MCF7 and m5S cells of flight samples were similar to those of ground control samples. These results indicated that any effect of space radiation, microgravity, or combination of both were not detectable, at least under the present experimental conditions.

Platelet ERK2 activation by thrombin is dependent on calcium and conventional protein kinases C but not Raf-1 or B-Raf

Extracellular signal-regulated kinase (ERK) activation pathways have been well characterized in a number of cell types but very few data are available for platelets. The thrombin-induced signaling pathway leading to ERK2 activation in platelets is largely uncharacterized. In this study, we investigated the kinases involved in thrombin-induced ERK2 activation in conditions of maximal ERK2 activation. We found that thrombin-induced mitogen-activated protein kinase/ERK kinase (MEK)1/2 activation was necessary for ERK2 phosphorylation. We obtained strong evidence that conventional protein kinase Cs (PKCs) and calcium are involved in thrombin-induced ERK2 activation. First, ERK2 and MEK1/2 phosphorylation was totally inhibited by low concentrations (1 microM) of RO318425, a specific inhibitor of conventional PKCs. Second, Ca(2+), from either intracellular pools or the extracellular medium, was necessary for ERK2 activation and conventional PKC activation, excluding the involvement of a new class of calcium-insensitive PKCs. Third, LY294002 and wortmannin had no significant effect on ERK2 activation, even at concentrations that inhibit phosphatidylinositol (PI)3-kinase (5 microM to 25 microM and 50 nM, respectively). This suggests that PI3-kinase was not necessary for ERK2 activation and therefore, that PI3-kinase-dependent atypical PKCs were not involved. Surprisingly, in contrast to proliferative cells, we found that the serine/threonine kinases Raf-1 and B-Raf were not an intermediate kinase between conventional PKCs and MEK1/2. After immunoprecipitation of Raf-1 and B-Raf, the basal glutathione S-transferase-MEK1 phosphorylation observed in resting platelets was not upregulated by thrombin and was still observed in the absence of anti-Raf-1 or anti-B-Raf antibodies. In these conditions, the in vitro cascade kinase assay did not detect any MEK activity. Thus in platelets, thrombin-induced ERK2 activation is activated by conventional PKCs independently of Raf-1 and B-Raf activation.

CNS myelinogenesis in vitro: myelin basic protein deficient shiverer oligodendrocytes

The shiverer mutant mouse is an autosomal recessive mutant characterized by incomplete myelin sheath formation in the central nervous system (CNS). Such mice contain a deletion in the MBP gene, do not produce MBP proteins, and have little or no compact myelin in the CNS. To investigate the myelin sheath formation in shiverer mutant mice resulting from the absence of compact myelin, firstly we developed new methods for generating oligodendrocyte precursor cells (OPCs) from an E17 mouse brain, and examined homozygous shiverer (shi/shi) OPCs with respect to myelinogenesis in vitro. After treatment of shi/shi OPCs in vitro with PDGF or bFGF, proliferation of shi/shi OPCs was enhanced similar to that observed in wild-type OPCs. The majority of cells from the shiverer mutant mouse, however, remained as A2B5-immunoreactive early OPCs. To determine which molecular events affect the differentiation of shi/shi OPCs, we determined the signaling pathway that could be responsible for activating myelin sheath-specific proteins. We found that the developmental schedule of shi/shi OPCs in vitro was accelerated by the addition of cyclic AMP analogs, dibutyryl cAMP (dbcAMP). Treatment of shi/shi OPCs with dbcAMP had significant effect on the differentiation of OPCs that became MAG-expressing oligodendrocytes. To further determine the possible mechanism involved in the activation of MAG by dbcAMP, we examined the cAMP-dependent signaling cascades. The activation of JNK was markedly stimulated by treatment with dbcAMP, and the phosphorylation of transcription factor ATF-2 was also stimulated by dbcAMP. We demonstrated that the MAG-positive shi/shi oligodendrocytes extend processes around axons and finally covered the axon, this was clearly observed by immunocytochemistry of shi/shi oligodendrocyte-DRG cocultures. These results suggest that ATF-2 coupled to specific signal transduction cascades plays an important regulatory role in MAG expression at a specific stage of shi/shi oligodendrocyte differentiation, and OPCs grow to become myelin-forming cells with numerous cell processes that wraps around an axon to form a thin myelin sheath.

Overexpression of extracellular superoxide dismutase decreases lung injury after exposure to oil fly ash

The mechanism of tissue injury after exposure to air pollution particles is not known. The biological effect has been postulated to be mediated via an oxidative stress catalyzed by metals present in particulate matter (PM). We utilized a transgenic (Tg) mouse model that overexpresses extracellular superoxide dismutase (EC-SOD) to test the hypothesis that lung injury after exposure to PM results from an oxidative stress in the lower respiratory tract. Wild-type (Wt) and Tg mice were intratracheally instilled with either saline or 50 microg of residual oil fly ash (ROFA). Twenty-four hours later, specimens were obtained and included bronchoalveolar lavage (BAL) and lung for both homogenization and light histopathology. After ROFA exposure, EC-SOD Tg mice showed a significant reduction in BAL total cell counts (composed primarily of neutrophils) and BAL total protein compared with Wt. EC-SOD animals also demonstrated diminished concentrations of inflammatory mediators in BAL. There was no statistically significant difference in BAL lipid peroxidation; however, EC-SOD mice had lower concentrations of oxidized glutathione in the BAL. We conclude that enhanced EC-SOD expression decreased both lung inflammation and damage after exposure to ROFA. This supports a participation of oxidative stress in the inflammatory injury after PM exposure rather than reflecting a response to metals alone.

The chitinase 3-like protein human cartilage glycoprotein 39 (HC-gp39) stimulates proliferation of human connective-tissue cells and activates both extracellular signal-regulated kinase- and protein kinase B-mediated signalling pathways

Human cartilage glycoprotein 39 (HC-gp39) is a glycoprotein secreted by articular chondrocytes, synoviocytes and macrophages. Increased levels of HC-gp39 have been demonstrated in synovial fluids of patients with rheumatoid or osteoarthritis. The increased secretion of HC-gp39 under physiological and pathological conditions with elevated connective-tissue turnover suggests its involvement in the homoeostasis of these tissues. We report here that HC-gp39 promotes the growth of human synovial cells as well as skin and fetal lung fibroblasts. A dose-dependent growth stimulation was observed when each of the fibroblastic cell lines was exposed to HC-gp39 in a concentration range from 0.1 to 2 nM, which is similar to the effective dose of the well-characterized mitogen, insulin-like growth factor-1. At suboptimal concentrations, the two growth factors work in a synergistic fashion. The use of selective inhibitors of the mitogen-activated protein kinase and the protein kinase B (AKT) signalling pathways indicates that both are involved in mediating the mitogenic response to HC-gp39. Phosphorylation of both extracellular signal-regulated kinases 1/2 and AKT occurred in a dose- and time-dependent fashion upon addition of HC-gp39. Activation of these signalling pathways could also be demonstrated in human chondrocytes. Thus HC-gp39 initiates a signalling cascade in connective-tissue cells which leads to increased cell proliferation, suggesting that this protein could play a major role in the pathological conditions leading to tissue fibrosis.

Acidic extracellular pH induces vascular endothelial growth factor (VEGF) in human glioblastoma cells via ERK1/2 MAPK signaling pathway: mechanism of low pH-induced VEGF

Overexpression of vascular endothelial growth factor (VEGF) is associated with disease progression in human glioblastomas. We recently showed that VEGF promoter activity is inversely correlated with tumor extracellular pH (pH(o)) in vivo in the human glioma (U87 MG) xenografts. Here we show that substitution of the neutral culture medium (pH 7.3) with acidic pH medium (pH 6.6) up-regulates VEGF mRNA and protein production in human glioblastoma cells as reflected by Northern blot analysis and enzyme-linked immunosorbent assay. Functional analysis of the VEGF promoter reveals that the sequence between -961 bp and -683 bp upstream of the transcription start site is responsible for the transcriptional activation of the VEGF gene by acidic pH. This region contains the binding site for AP-1. Consequently, AP-1 luciferase reporter gene was activated by acidic pH. Gel-shift analysis confirmed that AP-1 DNA binding activity is induced under acidic pH. While investigating the upstream signaling pathways, we found that ERK1/2 MAPK is activated and translocates to the nucleus to activate Elk-1, and inhibition of the activation of ERK by specific inhibitors of MEK1 blocks the up-regulation of VEGF by low pH. Dominant negative forms of Ras and Raf abolished the activation of VEGF promoter by acidic pH. These results show that acidic pH activates Ras and the ERK1/2 MAPK pathway to enhance VEGF transcription via AP-1, leading to increased VEGF production.

Regulated nucleocytoplasmic transport of protein kinase D in response to G protein-coupled receptor activation

Protein kinase D (PKD)/protein kinase C mu is a serine/threonine protein kinase activated by growth factors, antigen-receptor engagement, and G protein-coupled receptor (GPCR) agonists via a phosphorylation-dependent mechanism that requires protein kinase C (PKC) activity. In order to investigate the dynamic mechanisms associated with GPCR signaling, the intracellular distribution of PKD was analyzed in live cells by imaging fluorescent protein-tagged PKD and in fixed cells by immunocytochemistry. We found that PKD shuttled between the cytoplasm and the nucleus in both fibroblasts and epithelial cells. Cell stimulation with mitogenic GPCR agonists that activate PKD induced a transient nuclear accumulation of PKD that was prevented by inhibiting PKC activity. The nuclear import of PKD requires its cys2 domain in conjunction with a nuclear import receptor, while its nuclear export requires its pleckstrin homology domain and a competent Crm1-dependent nuclear export pathway. This study thus characterizes the regulated nuclear transport of a signaling molecule in response to mitogenic GPCR agonists and positions PKD as a serine kinase whose kinase activity and intracellular localization is coordinated by PKC.

Identification of new JNK substrate using ATP pocket mutant JNK and a corresponding ATP analogue

Modification of the ATP pocket on protein kinases allows selective use of an ATP analogue that exhibits high affinity for the altered kinases. Using this approach, we altered the ATP-binding site on JNK and identified N(6)-(2-phenythyl)-ATP, a modified form of ATP that exhibits high specificity and affinity for the modified, but not the wild type form, of JNK. Using modified JNK and its ATP analogue enables the detection of novel JNK substrates. Among substrates identified using this approach is heterogeneous nuclear ribonucleoprotein K, which is involved in transcription and post-transcriptional mRNA metabolism. The newly identified substrate can be phosphorylated by JNK on amino acids 216 and 353, which contribute to heterogeneous nuclear ribonucleoprotein K mediated transcriptional activities.

Apoptosis signal-regulating kinase 1 (ASK1) is an intracellular inducer of keratinocyte differentiation

Cells differentiate in response to various extracellular stimuli. This cellular response requires intracellular signaling pathways. The mitogen-activated protein (MAP) kinase cascade is a core signal transduction pathway that determines the fate of many kinds of cell. MAP kinase kinase kinase activates MAP kinase kinase, which in turn activates MAP kinase. Apoptosis signal-regulating kinase (ASK1) was identified as a MAP kinase kinase kinase involved in the stress-induced apoptosis-signaling cascade that activates the SEK1-JNK and MKK3/MKK6-p38 MAP kinase cascades. Expression of the constitutively active form of ASK1 (ASK1-DeltaN) in keratinocytes induced significant morphological changes and differentiation markers, transglutaminase-1, loricrin, and involucrin. A transient increase in p21(Cip1/WAF1) reduced DNA synthesis, and cell cycle analysis verified the differentiation. p38 MAP kinase inhibitors, SB202190 and SB203580, abolished the induction of differentiation markers, transglutaminase-1, loricrin, and involucrin. In turn, the induction of differentiation with ceramide in keratinocytes caused an increase in ASK1 expression and activity. Furthermore, normal human skin expresses ASK1 protein in the upper epidermis, implicating ASK1 in in vivo keratinocyte differentiation. We propose that the ASK1-p38 MAP kinase cascade is a new intracellular regulator of keratinocyte differentiation.

Amino-terminal-derived JNK fragment alters expression and activity of c-Jun, ATF2, and p53 and increases H2O2-induced cell death

The stress-activated protein kinase JNK plays an important role in the stability and activities of key regulatory proteins, including c-Jun, ATF2, and p53. To better understand mechanisms underlying the regulation of JNK activities, we studied the effect of expression of the amino-terminal JNK fragment (N-JNK; amino acids 1-206) on the stability and activities of JNK substrates under nonstressed growth conditions, as well as after exposure to hydrogen peroxide. Mouse fibroblasts that express N-JNK under tetracycline-off (tet-off) inducible promoter exhibited elevated expression of c-Jun, ATF2, and p53 upon tetracycline removal. This increased coincided with elevated transcriptional activities of p53, but not of c-Jun or ATF2, as reflected in luciferase activities of p21(Waf1/Cip1)-Luc, AP1-Luc, and Jun2-Luc, respectively. Expression of N-JNK in cells that were treated with H(2)O(2) impaired transcriptional output as reflected in a delayed and lower level of c-Jun-, limited ATF2-, and reduced p53-transcriptional activities. N-JNK elicited an increase in H(2)O(2)-induced cell death, which is p53-dependent, because it was not seen in p53 null cells yet could be observed upon coexpression of p53 and N-JNK. The ability to alter the activity of ATF2, c-Jun, and p53 and the degree of stress-induced cell death by a JNK-derived fragment identifies new means to elucidate the nature of JNK regulation and to alter the cellular response to stress.

In vivo and in vitro correlation of pulmonary MAP kinase activation following metallic exposure

Residual oil fly ash (ROFA) is a particulate pollutant produced in the combustion of fuel oil. Exposure to ROFA is associated with adverse respiratory effects in humans, induces lung inflammation in animals, and induces inflammatory mediator expression in cultured human airway epithelial cells (HAEC). ROFA has a high content of transition metals, including vanadium, a potent tyrosine phosphatase inhibitor that we have previously shown to disregulate phosphotyrosine metabolism and activate mitogen-activated protein kinase (MAPK) signaling cascades in HAEC. In order to study MAPK activation in response to in vivo metal exposure, we used immunohistochemical methods to detect levels of phosphorylated protein tyrosines (P-Tyr) and the MAPKs ERK1/2, JNK, and P38 in lung sections from rats intratracheally exposed to ROFA. After a 1-h exposure to 500 microg ROFA, rat lungs showed no histological changes and no significant increases in immunostaining for either P-Tyr or phospho-(P-) MAPKs compared to saline-instilled controls. At 4 h of exposure, there was mild and variable inflammation in the lung, which was accompanied by an increase in specific immunostaining for P-Tyr and P-MAPKs in airway and alveolar epithelial cells and resident macrophages. By 24 h of exposure, there was a pronounced inflammatory response to ROFA instillation and a marked increase in levels of P-Tyr and P-MAPKs present within the alveolar epithelium and in the inflammatory cells, while the airway epithelium showed a continued increase in the expression of P-ERK1/2. By comparison, HAEC cultures exposed to 100 microg/ml ROFA for 20 min resulted in marked increases in P-Tyr and P-MAPKs, which persisted after 24 h of exposure. P-Tyr levels continued to accumulate for up to 24 h in HAEC exposed to ROFA. These results demonstrate in vivo activation in cell signaling pathways in response to pulmonary exposure to particulate matter, and support the relevance of in vitro studies in the identification of mechanisms of lung injury induced by pollutant inhalation.

Molecular cloning of MINK, a novel member of mammalian GCK family kinases, which is up-regulated during postnatal mouse cerebral development

A new germinal center kinase (GCK) family kinase, Misshapen/NIKs-related kinase (MINK), has been cloned and its expression has been characterized in several tissues and various developmental stages of the mouse brain. MINK encodes a 1300 amino acid polypeptide, consisting of an N-terminal kinase domain, a proline-rich intermediate region, and a C-terminal GCK homology region. The expression of MINK is up-regulated during the postnatal development of the mouse brain. MINK activates the cJun N-terminal kinase and the p38 pathways.

Kinetic mechanism of the p38-alpha MAP kinase: phosphoryl transfer to synthetic peptides

p38 is a member of the mitogen-activated protein (MAP) kinase family. Activation (phosphorylation) of p38 acts as a switch for the transcriptional and translational regulation of a number of proteins, including the proinflammatory cytokines. Investigation of a set of small peptides revealed that, as with protein substrates, p38-alpha behaves as a proline-directed Ser/Thr MAP kinase for a peptide substrate, peptide 4 (IPTSPITTTYFFFKKK). We investigated the steady-state kinetic mechanism of the p38-alpha-catalyzed kinase reaction with EGF receptor peptide, peptide 1, as a substrate. Lineweaver-Burk analysis of the substrate kinetics yielded a family of lines intersecting to the left of the ordinate, with either ATP or peptide 1 as the varied substrate. Kinetic analysis in the presence of ADP yielded a competitive inhibition pattern when ATP was the varied substrate and a noncompetitive pattern if peptide 1 was the varied substrate. At saturating peptide substrate concentrations, inhibition by phosphopeptide product yielded an uncompetitive pattern when ATP was the varied substrate. These data are consistent with ordered binding with ATP as the initial substrate. We provide further evidence of the existence of a productive p38.ATP binary complex in that (a) activated p38-alpha has intrinsic ATPase activity, (b) ATPase and kinase activities are coupled, and (c) inhibitors of ATPase activity also inhibit the kinase activity with a similar inhibition constant. The k(cat) for the kinase reaction was lowered by 1.8-fold when ATP-gamma-S was used. Microviscosity linearly affected the k(cat) values of both the ATP and ATP-gamma-S reactions with a slope of about 0.8. These observations were interpreted to mean that the phosphoryl transfer step is not rate-limiting and that the release of product and/or enzyme isomerization is a possible rate-limiting step(s).

p38MAP kinase is a negative regulator for ERK1/2-mediated growth of AIDS-associated Kaposi's sarcoma cells

AIDS-associated Kaposi's sarcoma (KS) is a cytokine-mediated tumor, at least in the early stages of this disease; however, there is at present no definitive consensus regarding the exact role of intracellular signaling pathways involved in growth of KS cells. We found that KS cell growth factors oncostatin M, sIL-6R/IL-6, TNFalpha, and IL-1beta all activate ERK1/2, and selective blockage of this kinase by PD98059 resulted in a profound inhibition of the cytokine-induced KS cell growth. Concurrently with activation of ERK1/2, these growth factors phosphorylated and activated p38MAPK. The selective inhibition of p38MAPK by SB203580 prominently enhanced the cytokine-induced proliferation of KS cells, thereby indicating that p38MAPK has a negative feedback on mitogenic signals. As these KS cell growth factors lead to simultaneous activation of ERK1/2 and p38MAPK signaling pathways, the concerted effects of these kinase activities may well determine the intensity of cellular proliferative responses to these growth factors.

Distinct, constitutively active MAPK phosphatases function in Xenopus oocytes: implications for p42 MAPK regulation In vivo

Xenopus oocyte maturation requires the phosphorylation and activation of p42 mitogen-activated protein kinase (MAPK). Likewise, the dephosphorylation and inactivation of p42 MAPK are critical for the progression of fertilized eggs out of meiosis and through the first mitotic cell cycle. Whereas the kinase responsible for p42 MAPK activation is well characterized, little is known concerning the phosphatases that inactivate p42 MAPK. We designed a microinjection-based assay to examine the mechanism of p42 MAPK dephosphorylation in intact oocytes. We found that p42 MAPK inactivation is mediated by at least two distinct phosphatases, an unidentified tyrosine phosphatase and a protein phosphatase 2A-like threonine phosphatase. The rates of tyrosine and threonine dephosphorylation were high and remained constant throughout meiosis, indicating that the dramatic changes in p42 MAPK activity seen during meiosis are primarily attributable to changes in MAPK kinase activity. The overall control of p42 MAPK dephosphorylation was shared among four partially rate-determining dephosphorylation reactions, with the initial tyrosine dephosphorylation of p42 MAPK being the most critical of the four. Our findings provide biochemical and kinetic insight into the physiological mechanism of p42 MAPK inactivation.

Coordinated regulation of radioadaptive response by protein kinase C and p38 mitogen-activated protein kinase

Eukaryotic cells are known to have an inducible or adaptive response that enhances radioresistance after a low priming dose of radiation. This radioadaptive response seems to present a novel cellular defense mechanism. However, its molecular processing and signaling mechanisms are largely unknown. Here, we studied the role of protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) in the expression of radioadaptive response in cultured mouse cells. Protein immunoblot analysis using isoform-specific antibodies showed an immediate activation of PKC-alpha upon X-irradiation as indicated by a translocation from cytosol to membrane. A low priming dose caused a prolonged translocation, while a nonadaptive high dose dramatically downregulated the total PKC level. Low-dose X-rays also activated the p38 MAPK. The activation of p38 MAPK and resistance to chromosome aberration formation were blocked by SB203580, an inhibitor of p38 MAPK, and Calphostin C, an inhibitor of PKC. Furthermore, it was demonstrated that p38 MAPK was physically associated with delta1 isoform of phospholipase C (PLC-delta1), which hydrolyzed phosphatidylinositol bisphosphate into diacylglycerol, an activator of PKC, and that SB203580 also blocked the activation of PKC-alpha. These results indicate the presence of a novel mechanism for coordinated regulation of adaptive response to low-dose X-rays by a nexus of PKC-alpha/p38 MAPK/PLC-delta1 circuitry feedback signaling pathway with its breakage operated by downregulation of labile PKC-alpha at high doses or excess stimuli.

Anthrax lethal factor causes proteolytic inactivation of mitogen-activated protein kinase kinase

A search of the National Cancer Institute's Anti-Neoplastic Drug Screen for compounds with an inhibitory profile similar to that of the mitogen-activated protein kinase kinase (MAPKK) inhibitor PD098059 yielded anthrax lethal toxin. Anthrax lethal factor was found to inhibit progesterone-induced meiotic maturation of frog oocytes by preventing the phosphorylation and activation of mitogen-activated protein kinase (MAPK). Similarly, lethal toxin prevented the activation of MAPK in serum stimulated, ras-transformed NIH3T3 cells. In vitro analyses using recombinant proteins indicated that lethal factor proteolytically modified the NH2-terminus of both MAPKK1 and 2, rendering them inactive and hence incapable of activating MAPK. The consequences of this inactivation upon meiosis and transformed cells are also discussed.

An inhibitor of p38 mitogen-activated protein kinase prevents insulin-stimulated glucose transport but not glucose transporter translocation in 3T3-L1 adipocytes and L6 myotubes

The precise mechanisms underlying insulin-stimulated glucose transport still require investigation. Here we assessed the effect of SB203580, an inhibitor of the p38 MAP kinase family, on insulin-stimulated glucose transport in 3T3-L1 adipocytes and L6 myotubes. We found that SB203580, but not its inactive analogue (SB202474), prevented insulin-stimulated glucose transport in both cell types with an IC50 similar to that for inhibition of p38 MAP kinase (0.6 microM). Basal glucose uptake was not affected. Moreover, SB203580 added only during the transport assay did not inhibit basal or insulin-stimulated transport. SB203580 did not inhibit insulin-stimulated translocation of the glucose transporters GLUT1 or GLUT4 in 3T3-L1 adipocytes as assessed by immunoblotting of subcellular fractions or by immunofluorescence of membrane lawns. L6 muscle cells expressing GLUT4 tagged on an extracellular domain with a Myc epitope (GLUT4myc) were used to assess the functional insertion of GLUT4 into the plasma membrane. SB203580 did not affect the insulin-induced gain in GLUT4myc exposure at the cell surface but largely reduced the stimulation of glucose uptake. SB203580 had no effect on insulin-dependent insulin receptor substrate-1 phosphorylation, association of the p85 subunit of phosphatidylinositol 3-kinase with insulin receptor substrate-1, nor on phosphatidylinositol 3-kinase, Akt1, Akt2, or Akt3 activities in 3T3-L1 adipocytes. In conclusion, in the presence of SB203580, insulin caused normal translocation and cell surface membrane insertion of glucose transporters without stimulating glucose transport. We propose that insulin stimulates two independent signals contributing to stimulation of glucose transport: phosphatidylinositol 3-kinase leads to glucose transporter translocation and a pathway involving p38 MAP kinase leads to activation of the recruited glucose transporter at the membrane.

Implication of TNF Receptor-I-Mediated Extracellular Signal-Regulated Kinases 1 and 2 (ERK1/2) Activation in Growth of AIDS-Associated Kaposi’s Sarcoma Cells: A Possible Role of a Novel Death Domain Protein MADD in TNF-α-Induced ERK1/2 Activation in Kaposi’s Sarcoma Cells

TNF-α is a key pathogenic mediator of infectious and inflammatory diseases. HIV infection stimulates and dysregulates the immune system, leading to abnormal production of TNF-α. Despite its cytotoxic effect on some tumor cell lines, TNF-α functions as a growth stimulator for Kaposi’s sarcoma (KS), a common malignancy in HIV-infected patients. However, signaling pathways linked to TNF-α-induced mitogenic responses are not well understood. We found that extracellular signal-regulated kinases 1 and 2 (ERK1/2) in KS cells were significantly activated by TNF-α through tyrosine/threonine phosphorylation. Using neutralizing anti-TNFR-I and TNFR-II mAbs, we have now obtained evidence that TNF-α-induced KS cell growth and ERK1/2 activation are mediated exclusively by TNFR-I, not by TNFR-II. A selective inhibitor for ERK1/2 activator kinases, PD98059, profoundly inhibited not only the activation of ERK1/2, but also the TNF-α-induced KS cell proliferation. We therefore propose that the TNFR-I-ERK1/2 pathway plays a pivotal role in transmitting to KS cells the mitogenic signals of TNF-α. TNFR-I possesses no intrinsic kinase activity, suggesting that TNFR-I-associated proteins may provide a link between TNFR-I and ERK1/2 activation. We found that actinomycin D treatment of KS cells selectively abolished expression of mitogen-activated protein kinase-activating death domain protein (MADD), a novel TNFR-I-associated death domain protein. TNF-α failed to induce ERK1/2 activation in the actinomycin D-treated cells. MADD may couple TNFR-I with the ERK1/2 signaling pathway required for KS cell proliferation.

Complementation of defective colony-stimulating factor 1 receptor signaling and mitogenesis by Raf and v-Src

Ras-activated signal transduction pathways are implicated in the control of cell proliferation, differentiation, apoptosis, and tumorigenesis, but the molecular mechanisms mediating these diverse functions have yet to be fully elucidated. Conditionally active forms of Raf, v-Src, and MEK1 were used to identify changes in gene expression that participate in oncogenic transformation, as well as in normal growth control. Activation of Raf, v-Src, and MEK1 led to induced expression of c-Myc and cyclin D1. Induction of c-Myc mRNA by Raf was an immediate-early response, whereas the induction of cyclin D1 mRNA was delayed and inhibited by cycloheximide. Raf activation also resulted in the induction of an established c-Myc target gene, ornithine decarboxylase (ODC). ODC induction by Raf was mediated, in part, by tandem E-boxes contained in the first intron of the gene. Activation of the human colony-stimulating factor 1 (CSF-1) receptor in NIH 3T3 cells leads to activation of the mitogen-activated protein (MAP) kinase pathway and induced expression of c-Fos, c-Myc, and cyclin D1, leading to a potent mitogenic response. By contrast, a mutated form of this receptor fails to activate the MAP kinases or induce c-Myc and cyclin D1 expression and fails to elicit a mitogenic response. The biological significance of c-Myc and cyclin D1 induction by Raf and v-Src was confirmed by the demonstration that both of these protein kinases complemented the signaling and mitogenic defects of cells expressing this mutated form of the human CSF-1 receptor. Furthermore, the induction of c-Myc and cyclin D1 by oncogenes and growth factors was inhibited by PD098059, a specific MAP kinase kinase (MEK) inhibitor. These data suggest that the Raf/MEK/MAP kinase pathway plays an important role in the regulation of c-Myc and cyclin D1 expression in NIH 3T3 cells. The ability of oncogenes such as Raf and v-Src to regulate the expression of these proteins reveals new lines of communication between cytosolic signal transducers and the cell cycle machinery.

Molecular characterisation of plant cDNAs BnMAP4Kalpha1 and BnMAP4Kalpha2 belonging to the GCK/SPS1 subfamily of MAP kinase kinase kinase kinase

Several yeast and mammal MAP kinase modules require, upstream of their MAP kinase kinase kinase (MAP3K), a MAP3K kinase (MAP4K). An Arabidopsis thaliana EST clone, sharing identity to MAP4Ks from yeast and mammals, has been used to isolate cDNA clones from a Brassica napus microspore-derived embryo cDNA library. The BnMAP4Kalpha1 and BnMAP4K-alpha2 clones encode putative proteins possessing the 12 subdomains of the serine/threonine protein kinase catalytic domain. A detailed analysis showed that they belong to the GCK/SPS1 subfamily of MAP4K proteins which possess an amino terminal catalytic domain and a long carboxy terminal tail. A Southern blot analysis suggested that the two proteins are encoded by a small multigene family. Expression studies revealed the presence of BnMAP4Kalpha1 and -alpha2 transcripts in all the tissues examined; however, they are most abundant in roots, siliques and flower buds. The expression of BnMAP4Kalpha1 and -alpha2 at the three main developmental stages of microspore-derived embryos (i.e., globular/heart, torpedo and cotyledonary) was confirmed by northern blot and RT-PCR analysis. An expression analysis of the above genes using synchronised Arabidopsis thaliana cell suspensions showed that the homologues genes are cell cycle regulated.

Activation of MAPKs in human bronchial epithelial cells exposed to metals

We have previously shown that in vitro exposure to metallic compounds enhances expression of interleukin (IL)-6, IL-8, and tumor necrosis factor-alpha in human bronchial epithelial cells. To characterize signaling pathways involved in metal-induced expression of inflammatory mediators and to identify metals that activate them, we studied the effects of As, Cr, Cu, Fe, Ni, V, and Zn on the mitogen-activated protein kinases (MAPK) extracellular receptor kinase (ERK), c-Jun NH2-terminal kinase (JNK), and P38 in BEAS cells. Noncytotoxic concentrations of As, V, and Zn induced a rapid phosphorylation of MAPK in BEAS cells. Activity assays confirmed marked activation of ERK, JNK, and P38 in BEAS cells exposed to As, V, and Zn. Cr and Cu exposure resulted in a relatively small activation of MAPK, whereas Fe and Ni did not activate MAPK under these conditions. Similarly, the transcription factors c-Jun and ATF-2, substrates of JNK and P38, respectively, were markedly phosphorylated in BEAS cells treated with As, Cr, Cu, V, and Zn. The same acute exposure to As, V, or Zn that activated MAPK was sufficient to induce a subsequent increase in IL-8 protein expression in BEAS cells. These data suggest that MAPK may mediate metal-induced expression of inflammatory proteins in human bronchial epithelial cells.

Phosphorylation of the MAP kinase ERK2 promotes its homodimerization and nuclear translocation

The MAP kinase ERK2 is widely involved in eukaryotic signal transduction. Upon activation it translocates to the nucleus of the stimulated cell, where it phosphorylates nuclear targets. We find that nuclear accumulation of microinjected ERK2 depends on its phosphorylation state rather than on its activity or on upstream components of its signaling pathway. Phosphorylated ERK2 forms dimers with phosphorylated and unphosphorylated ERK2 partners. Disruption of dimerization by mutagenesis of ERK2 reduces its ability to accumulate in the nucleus, suggesting that dimerization is essential for its normal ligand-dependent relocalization. The crystal structure of phosphorylated ERK2 reveals the basis for dimerization. Other MAP kinase family members also form dimers. The generality of this behavior suggests that dimerization is part of the mechanism of action of the MAP kinase family.

Identification of substrates and regulators of the mitogen-activated protein kinase ERK5 using chimeric protein kinases

Extracellular signal-regulated protein kinase 5 (ERK5) is a recently discovered orphan mitogen-activated protein kinase for which no substrates or strong activators have been described. Two ERK5 chimeras were created as a novel approach to discover its substrates and upstream regulators. One chimeric protein contained the N-terminal domain of the ERK5 catalytic core (subdomains I-IV) and the C-terminal domain of the ERK2 catalytic core (subdomains V-XI). This chimera was highly responsive to stimuli that regulate ERK2 in vitro and in cells. A second chimeric protein consisted of the N-terminal domain of ERK2 (subdomains I-IV) and the C-terminal domain of the ERK5 catalytic core (subdomains V-XI). This chimera was activated in bacteria by coexpression with a constitutively active mutant of MEK1. Using the activated chimera, we identified three in vitro substrates of ERK5. Assaying ERK5 activity in immune complexes with one of these substrates, c-Myc, we determined that the ERK5 catalytic domain is activated by V12 H-Ras and to a lesser extent by phorbol ester but not by constitutively active mutants of Raf-1. Thus, ERK5 is a target of a novel Ras effector pathway that may communicate with c-Myc.

The Ig alpha/Igbeta heterodimer on mu-negative proB cells is competent for transducing signals to induce early B cell differentiation

The immunoglobulin alpha (Ig alpha)/Ig beta heterodimer was detected on the surface of mu-negative proB cell lines in association with calnexin. The cross-linking of Ig beta on proB cells freshly isolated from bone marrow of recombination activating gene (RAG)-2-deficient mice induced a rapid and transient tyrosine-phosphorylation of Ig alpha as well as an array of intracellular proteins including Syk, PI3-kinase, Vav, and SLP-76. It also elicited the phosphorylation and activation of a MAP kinase ERK but not JNK/SAPK or p38. When RAG-2-deficient mice were treated with anti-Ig beta monoclonal antibody, developmentally arrested proB cells were induced to differentiate to the small preB cell stage as observed when the mu transgene was expressed in RAG-2-deficient mice. Thus, the cross-linking of Ig beta on proB cells appears to elicit differentiation signals analogous to those delivered by the preB cell receptor in normal B cell development.

LOK is a novel mouse STE20-like protein kinase that is expressed predominantly in lymphocytes

We have identified a new gene, designated lok (lymphocyte-oriented kinase), that encodes a 966-amino acid protein kinase whose catalytic domain at the N terminus shows homology to that of the STE20 family members involved in mitogen-activated protein (MAP) kinase cascades. The non-catalytic domain of LOK does not have any similarity to that of other known members of the family. There is a proline-rich motif with Src homology region 3 binding potential, followed by a long coiled-coil structure at the C terminus. LOK is expressed as a 130-kDa protein, which was detected predominantly in lymphoid organs such as spleen, thymus, and bone marrow, in contrast to other mammalian members of the STE20 family. LOK phosphorylated itself as well as substrates such as myelin basic protein and histone IIA on serine and threonine residues but not on tyrosine residues, establishing LOK as a novel serine/threonine kinase. When coexpressed in COS7 cells with the known MAP kinase isoforms (ERK, JNK, and p38), LOK activated none of them in contrast to PAK- and GCK-related kinases. These results suggest that LOK could be involved in a novel signaling pathway in lymphocytes, which is distinct from the known MAP kinase cascades.