Biomedical subjects

R J Davis

Publications and source records attributed to R J Davis.

At least 91 records · Page 5Linked to original sources

PubMed1999

Epidemic of blindness in kangaroos--evidence of a viral aetiology.

OBJECTIVE: To determine the cause of an epidemic of blindness in kangaroos. DESIGN AND PROCEDURES: Laboratory examinations were made of eyes and brains of a large number of kangaroos using serological, virological, histopathological, electron microscopical, immunohistochemical methods, and PCR with cDNA sequencing. In addition, potential insect viral vectors identified during the disease outbreak were examined for specific viral genomic sequences. SAMPLE POPULATION: For histopathological analysis, 55 apparently blind and 18 apparently normal wild kangaroos and wallabies were obtained from New South Wales, Victoria, South Australia, and Western Australia. A total of 437 wild kangaroos and wallabies (including 23 animals with apparent blindness) were examined serologically. RESULTS: Orbiviruses of the Wallal and Warrego serogroups were isolated from kangaroos affected with blindness in a major epidemic in south-eastern Australia in 1994 and 1995 and extending to Western Australia in 1995/96. Histopathological examinations showed severe degeneration and inflammation in the eyes, and mild inflammation in the brains. In affected retinas, Wallal virus antigen was detected by immunohistochemical analysis and orbiviruses were seen in electron microscopy. There was serological variation in the newly isolated Wallal virus from archival Wallal virus that had been isolated in northern Australia. There were also variations of up to 20% in genotype sequence from the reference archival virus. Polymerase chain reactions showed that Wallal virus was present during the epidemic in three species of midges, Culicoides austropalpalis, C dycei and C marksi. Wallal virus nucleic acid was also detected by PCR in a paraffin-embedded retina taken from a blind kangaroo in 1975. CONCLUSION: Wallal virus and perhaps also Warrego virus are the cause of the outbreak of blindness in kangaroos. Other viruses may also be involved, but the evidence in this paper indicates a variant of Wallal virus, an orbivirus transmitted by midges, has the strongest aetiological association, and immunohistochemical analysis implicates it as the most damaging factor in the affected eyes.

Animals↗

PubMed1999

The JIP group of mitogen-activated protein kinase scaffold proteins.

Activation of the c-Jun NH(2)-terminal kinase (JNK) group of mitogen-activated protein (MAP) kinases is mediated by a protein kinase cascade. This signaling mechanism may be coordinated by the interaction of components of the protein kinase cascade with scaffold proteins. The JNK-interacting protein (JIP) group of scaffold proteins selectively mediates signaling by the mixed-lineage kinase (MLK)-->MAP kinase kinase 7 (MKK7)-->JNK pathway. The scaffold proteins JIP1 and JIP2 interact to form oligomeric complexes that accumulate in peripheral cytoplasmic projections extended at the cell surface. The JIP proteins function by aggregating components of a MAP kinase module (including MLK, MKK7, and JNK) and facilitate signal transmission by the protein kinase cascade.

Adaptor Proteins, Signal Transducing↗

PubMed1999

The MKK7 gene encodes a group of c-Jun NH2-terminal kinase kinases.

The c-Jun NH2-terminal protein kinase (JNK) is a member of the mitogen-activated protein kinase (MAPK) group and is an essential component of a signaling cascade that is activated by exposure of cells to environmental stress. JNK activation is regulated by phosphorylation on both Thr and Tyr residues by a dual-specificity MAPK kinase (MAPKK). Two MAPKKs, MKK4 and MKK7, have been identified as JNK activators. Genetic studies demonstrate that MKK4 and MKK7 serve nonredundant functions as activators of JNK in vivo. We report here the molecular cloning of the gene that encodes MKK7 and demonstrate that six isoforms are created by alternative splicing to generate a group of protein kinases with three different NH2 termini (alpha, beta, and gamma isoforms) and two different COOH termini (1 and 2 isoforms). The MKK7alpha isoforms lack an NH2-terminal extension that is present in the other MKK7 isoforms. This NH2-terminal extension binds directly to the MKK7 substrate JNK. Comparison of the activities of the MKK7 isoforms demonstrates that the MKK7alpha isoforms exhibit lower activity, but a higher level of inducible fold activation, than the corresponding MKK7beta and MKK7gamma isoforms. Immunofluorescence analysis demonstrates that these MKK7 isoforms are detected in both cytoplasmic and nuclear compartments of cultured cells. The presence of MKK7 in the nucleus was not, however, required for JNK activation in vivo. These data establish that the MKK4 and MKK7 genes encode a group of protein kinases with different biochemical properties that mediate activation of JNK in response to extracellular stimuli.

Alternative Splicing↗

PubMed1999

Requirement for transcription factor NFAT in interleukin-2 expression.

The nuclear factor of activated T cells (NFAT) transcription factor is implicated in expression of the cytokine interleukin-2 (IL-2). Binding sites for NFAT are located in the IL-2 promoter. Furthermore, pharmacological studies demonstrate that the drug cyclosporin A inhibits both NFAT activation and IL-2 expression. However, targeted disruption of the NFAT1 and NFAT2 genes in mice does not cause decreased IL-2 secretion. The role of NFAT in IL-2 gene expression is therefore unclear. Here we report the construction of a dominant-negative NFAT mutant (dnNFAT) that selectively inhibits NFAT-mediated gene expression. The inhibitory effect of dnNFAT is mediated by suppression of activation-induced nuclear translocation of NFAT. Expression of dnNFAT in cultured T cells caused inhibition of IL-2 promoter activity and decreased expression of IL-2 protein. Similarly, expression of dnNFAT in transgenic mice also caused decreased IL-2 gene expression. These data demonstrate that NFAT is a critical component of the signaling pathway that regulates IL-2 expression.

Animals↗

PubMed1999

Signal transduction by the c-Jun N-terminal kinase.

The c-Jun N-terminal kinase (JNK) group of mitogen-activated protein kinases (MAP kinases) is activated by exposure of cells to environmental stress and by the treatment of cells with cytokines. The mechanism of activation of JNK is mediated by dual phosphorylation within kinase subdomain VIII on the motif Thr-Pro-Tyr. This phosphorylation is mediated by the MAP kinase kinases MKK4 and MKK7. These MAP kinase kinases serve as signalling molecules that integrate a wide array of stimuli into the activation of the JNK signalling pathway. Studies of the physiological function of JNK have been facilitated by the molecular genetic analysis of JNK signalling in Drosophila and by the creation of mice with targeted disruption of components of the JNK pathway. These studies demonstrate that the JNK pathway regulates AP-1 (activator protein-1) transcriptional activity in vivo and indicate that JNK is required for embryonic morphogenesis, the regulation of cellular proliferation and apoptosis, and the response of cells to immunological stimuli.

Amino Acid Sequence↗

PubMed1998

Interaction of ZPR1 with translation elongation factor-1alpha in proliferating cells.

The zinc finger protein ZPR1 is present in the cytoplasm of quiescent mammalian cells and translocates to the nucleus upon treatment with mitogens, including epidermal growth factor (EGF). Homologues of ZPR1 were identified in yeast and mammals. These ZPR1 proteins bind to eukaryotic translation elongation factor-1alpha (eEF-1alpha). Studies of mammalian cells demonstrated that EGF treatment induces the interaction of ZPR1 with eEF-1alpha and the redistribution of both proteins to the nucleus. In the yeast Saccharomyces cerevisiae, genetic analysis demonstrated that ZPR1 is an essential gene. Deletion analysis demonstrated that the NH2-terminal region of ZPR1 is required for normal growth and that the COOH-terminal region was essential for viability in S. cerevisiae. The yeast ZPR1 protein redistributes from the cytoplasm to the nucleus in response to nutrient stimulation. Disruption of the binding of ZPR1 to eEF-1alpha by mutational analysis resulted in an accumulation of cells in the G2/M phase of cell cycle and defective growth. Reconstitution of the ZPR1 interaction with eEF-1alpha restored normal growth. We conclude that ZPR1 is essential for cell viability and that its interaction with eEF-1alpha contributes to normal cellular proliferation.

Amino Acid Sequence↗

PubMed1998

Defective T cell differentiation in the absence of Jnk1.

The c-Jun NH2-terminal kinase (JNK) signaling pathway has been implicated in the immune response that is mediated by the activation and differentiation of CD4 helper T (TH) cells into TH1 and TH2 effector cells. JNK activity observed in wild-type activated TH cells was severely reduced in TH cells from Jnk1-/- mice. The Jnk1-/- T cells hyperproliferated, exhibited decreased activation-induced cell death, and preferentially differentiated to TH2 cells. The enhanced production of TH2 cytokines by Jnk1-/- cells was associated with increased nuclear accumulation of the transcription factor NFATc. Thus, the JNK1 signaling pathway plays a key role in T cell receptor-initiated TH cell proliferation, apoptosis, and differentiation.

Animals↗

PubMed1998

The JNK pathway regulates the In vivo deletion of immature CD4(+)CD8(+) thymocytes.

The extracellular signal-regulated kinase (ERK), the c-Jun NH2-terminal kinase (JNK), and p38 MAP kinase pathways are triggered upon ligation of the antigen-specific T cell receptor (TCR). During the development of T cells in the thymus, the ERK pathway is required for differentiation of CD4(-)CD8(-) into CD4(+)CD8(+) double positive (DP) thymocytes, positive selection of DP cells, and their maturation into CD4(+) cells. However, the ERK pathway is not required for negative selection. Here, we show that JNK is activated in DP thymocytes in vivo in response to signals that initiate negative selection. The activation of JNK in these cells appears to be mediated by the MAP kinase kinase MKK7 since high levels of MKK7 and low levels of Sek-1/MKK4 gene expression were detected in thymocytes. Using dominant negative JNK transgenic mice, we show that inhibition of the JNK pathway reduces the in vivo deletion of DP thymocytes. In addition, the increased resistance of DP thymocytes to cell death in these mice produces an accelerated reconstitution of normal thymic populations upon in vivo DP elimination. Together, these data indicate that the JNK pathway contributes to the deletion of DP thymocytes by apoptosis in response to TCR-derived and other thymic environment- mediated signals.

Animals↗

PubMed1998

Activation of p38 MAP kinase and JNK but not ERK is required for erythropoietin-induced erythroid differentiation.

p38 MAP kinase (p38) and JNK have been described as playing a critical role in the response to a variety of environmental stresses and proinflammatory cytokines. It was recently reported that hematopoietic cytokines activate not only classical MAP kinases (ERK), but also p38 and JNK. However, the physiological function of these kinases in hematopoiesis remains obscure. We found that all MAP kinases examined, ERK1, ERK2, p38, JNK1, and JNK2, were rapidly and transiently activated by erythropoietin (Epo) stimulation in SKT6 cells, which can be induced to differentiate into hemoglobinized cells in response to Epo. Furthermore, p38-specific inhibitor SB203580 but not MEK-specific inhibitor PD98059 significantly suppressed Epo-induced differentiation and antisense oligonucleotides of p38, JNK1, and JNK2, but neither ERK1 nor ERK2 clearly inhibited Epo-induced hemoglobinization. However, in Epo-dependent FD-EPO cells, inhibition of either ERKs, p38, or JNKs suppressed cell growth. Furthermore, forced expression of a gain-of-function MKK6 mutant, which specifically activated p38, induced hemoglobinization of SKT6 cells without Epo. These results indicate that activation of p38 and JNKs but not of ERKs is required for Epo-induced erythroid differentiation of SKT6 cells, whereas all of these kinases are involved in Epo-induced mitogenesis of FD-EPO cells.

Animals↗

PubMed1998

A mammalian scaffold complex that selectively mediates MAP kinase activation.

The c-Jun NH2-terminal kinase (JNK) group of mitogen-activated protein (MAP) kinases is activated by the exposure of cells to multiple forms of stress. A putative scaffold protein was identified that interacts with multiple components of the JNK signaling pathway, including the mixed-lineage group of MAP kinase kinase kinases (MLK), the MAP kinase kinase MKK7, and the MAP kinase JNK. This scaffold protein selectively enhanced JNK activation by the MLK signaling pathway. These data establish that a mammalian scaffold protein can mediate activation of a MAP kinase signaling pathway.

Animals↗

PubMed1998

Up-regulation of MET but not neural cell adhesion molecule expression by the PAX3-FKHR fusion protein in alveolar rhabdomyosarcoma.

The 2;13 chromosomal translocation in alveolar rhabdomyosarcoma generates the chimeric protein PAX3-FKHR, which is a powerful transcriptional activator. We hypothesize that PAX3-FKHR regulates downstream effector genes involved in rhabdomyosarcoma tumorigenesis. We evaluated alterations in expression of MET and neural cell adhesion molecule that were proposed previously as downstream targets of wild-type PAX3. We used a myogenic tumor cell culture system and rhabdomyosarcoma tumor specimens to assess candidate gene expression in relationship to various PAX3-FKHR expression levels. We demonstrate that the expression of MET, but not neural cell adhesion molecule, correlates significantly with PAX3-FKHR expression. These findings indicate that MET, which encodes a receptor involved in growth and motility signaling, is a downstream target of PAX3-FKHR in alveolar rhabdomyosarcoma.

Cells, Cultured↗

PubMed1998

Platelet-activating factor is a downstream messenger of kainate-induced activation of mitogen-activated protein kinases in primary hippocampal neurons.

Excitatory amino acids transduce physiological and pathological signals to neurons. Similarly, the neuroactive lipid platelet-activating factor (PAF) has been implicated in modulating long-term potentiation and neuronal survival. Excitatory amino acids and PAF have been shown to increase mitogen-activated protein (MAP) kinases in different cell types. Here, we have investigated the similarities and differences between PAF and kainate in activating MAP kinases in primary hippocampal neurons in vitro. Extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 kinases were activated by kainate or PAF in hippocampal neurons. This activation was blocked by the receptor antagonists CNQX and BN 50730 for kainate and PAF, respectively. The PAF receptor antagonist BN 50730 also blocked kainate activation. CNQX had no effect on PAF activation of the kinases, indicating that PAF is downstream of kainate activation. Coapplication of submaximal concentrations of PAF and kainate resulted in a less than additive activation, suggesting similar routes of activation by the two agonists. Both CNQX and BN 50730 blocked kainate-induced neurotoxicity. These results indicate that PAF and kainate activate similar kinase pathways. Therefore, PAF acts downstream of the kainate subtype of glutamate receptors, and when excessive receptor activation takes place, this bioactive lipid may contribute to neuronal cell death.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1998

Interferon-gamma expression by Th1 effector T cells mediated by the p38 MAP kinase signaling pathway.

Signal transduction via MAP kinase pathways plays a key role in a variety of cellular responses, including growth factor-induced proliferation, differentiation and cell death. In mammalian cells, p38 MAP kinase can be activated by multiple stimuli, such as pro-inflammatory cytokines and environmental stress. Although p38 MAP kinase is implicated in the control of inflammatory responses, the molecular mechanisms remain unclear. Upon activation, CD4+ T cells differentiate into Th2 cells, which potentiate the humoral immune response or pro-inflammatory Th1 cells. Here, we show that pyridinyl imidazole compounds (specific inhibitors of p38 MAP kinase) block the production of interferon-gamma (IFNgamma) by Th1 cells without affecting IL-4 production by Th2 cells. These drugs also inhibit transcription driven by the IFNgamma promoter. In transgenic mice, inhibition of the p38 MAP kinase pathway by the expression of dominant-negative p38 MAP kinase results in selective impairment of Th1 responses. In contrast, activation of the p38 MAP kinase pathway by the expression of constitutivelyactivated MAP kinase kinase 6 in transgenic mice caused increased production of IFNgamma during the differentiation and activation of Th1 cells. Together, these data demonstrate that the p38 MAP kinase is relevant for Th1 cells, not Th2 cells, and that inhibition of p38 MAP kinase represents a possible site of therapeutic intervention in diseases where a predominant Th1 immune response leads to a pathological outcome. Moreover, our study provides an additional mechanism by which the p38 MAP kinase pathway controls inflammatory responses.

Animals↗

PubMed1998

Modulation of HIV-1 infectivity by MAPK, a virion-associated kinase.

Infection of a cell by human immunodeficiency virus type 1 (HIV-1) results in the formation of a reverse transcription complex in which viral nucleic acids are synthesized. Efficient disengagement of the reverse transcription complex from the cell membrane and subsequent nuclear translocation require phosphorylation of reverse transcription complex components by a virion-associated kinase. In this study, we identify the virion-associated kinase as mitogen-activated protein kinase (ERK/MAPK). Upon density gradient fractionation, MAPK, but not its activating kinase MEK, co-sedimented with viral particles. Expression of a constitutively active, but not kinase-inactive, MEK1 in virus producer cells was able to activate virion-associated MAPK in trans. Stimulation of virion-associated MAPK activity in trans by the mitogen phorbol myristate acetate (PMA) increased viral infectivity. Conversely, suppression of virion-associated MAPK by specific inhibitors of the MAPK cascade markedly impaired viral infectivity. These studies demonstrate regulation of an early step in HIV-1 infection by the host cell MAPK signal transduction pathway.

CD4 Antigens↗

PubMed1998

Mechanism of sodium arsenite-mediated induction of heme oxygenase-1 in hepatoma cells. Role of mitogen-activated protein kinases.

Heme oxygenase-1 is an inducible enzyme that catalyzes heme degradation and has been proposed to play a role in protecting cells against oxidative stress-related injury. We investigated the induction of heme oxygenase-1 by the tumor promoter arsenite in a chicken hepatoma cell line, LMH. We identified a heme oxygenase-1 promoter-driven luciferase reporter construct that was highly and reproducibly expressed in response to sodium arsenite treatment. This construct was used to investigate the role of mitogen-activated protein (MAP) kinases in arsenite-mediated heme oxygenase-1 gene expression. In LMH cells, sodium arsenite, cadmium, and heat shock, but not heme, induced activity of the MAP kinases extracellular-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38. To examine whether these MAP kinases were involved in mediating heme oxygenase-1 gene expression, we utilized constitutively activated and dominant negative components of the ERK, JNK, and p38 MAP kinase signaling pathways. Involvement of an AP-1 site in arsenite induction of heme oxygenase-1 gene expression was studied. We conclude that the MAP kinases ERK and p38 are involved in the induction of heme oxygenase-1, and that at least one AP-1 element (located -1576 base pairs upstream of the transcription start site) is involved in this response.

Animals↗

PubMed1998

Differential targeting of MAP kinases to the ETS-domain transcription factor Elk-1.

The activation of MAP kinase (MAPK) signal transduction pathways results in the phosphorylation of transcription factors by the terminal kinases in these cascades. Different pathways are activated by mitogenic and stress stimuli, which lead to the activation of distinct groups of target proteins. The ETS-domain transcription factor Elk-1 is a substrate for three distinct classes of MAPKs. Elk-1 contains a targeting domain, the D-domain, which is distinct from the phosphoacceptor motifs and is required for efficient phosphorylation and activation by the ERK MAPKs. In this study, we demonstrate that members of the JNK subfamily of MAPKs are also targeted to Elk-1 by this domain. Targeting via this domain is essential for the efficient and rapid phosphorylation and activation of Elk-1 both in vitro and in vivo. The ERK and JNK MAPKs use overlapping yet distinct determinants in the D-domain for targeting to Elk-1. In contrast, members of the p38 subfamily of MAPKs are not targeted to Elk-1 via this domain. Our data therefore demonstrate that different classes of MAPKs exhibit differential requirements for targeting to Elk-1.

3T3 Cells↗

PubMed1998

Selective activation of p38 mitogen-activated protein (MAP) kinase isoforms by the MAP kinase kinases MKK3 and MKK6.

The cellular response to treatment with proinflammatory cytokines or exposure to environmental stress is mediated, in part, by the p38 group of mitogen-activated protein (MAP) kinases. We report the molecular cloning of a novel isoform of p38 MAP kinase, p38 beta 2. This p38 MAP kinase, like p38 alpha, is inhibited by the pyridinyl imidazole drug SB203580. The p38 MAP kinase kinase MKK6 is identified as a common activator of p38 alpha, p38 beta 2, and p38 gamma MAP kinase isoforms, while MKK3 activates only p38 alpha and p38 gamma MAP kinase isoforms. The MKK3 and MKK6 signal transduction pathways are therefore coupled to distinct, but overlapping, groups of p38 MAP kinases.

Amino Acid Sequence↗

PubMed1998

Signal transduction by the c-Jun N-terminal kinase (JNK)--from inflammation to development.

The c-Jun amino-terminal kinase (JNK) group of MAP kinases has been identified in mammals and insects. JNK is activated by exposure of cells to cytokines or environmental stress, indicating that this signaling pathway may contribute to inflammatory responses. Genetic and biochemical studies demonstrate that this signaling pathway also regulates cellular proliferation, apoptosis, and tissue morphogenesis. A functional role for JNK is therefore established in both the cellular response to stress and in many normal physiological processes.

Animals↗