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P L Han

Publications and source records attributed to P L Han.

18 recordsLinked to original sources
PubMed2001

Delayed induction of p38 MAPKs in reactive astrocytes in the brain of mice after KA-induced seizure.

Activation of p38 mitogen-activated protein kinase (p38 MAPK) has been implicated in pathological changes in inflammatory and apoptotic processes in various cell types including neurons. Here we report the delayed induction of p38 MAPKs in the brain of mice following kainic acid (KA)-induced seizure. The immunoreactivities of p38alpha and p38beta MAPKs were markedly increased in the brain 4 days after KA administration, especially in the areas undergoing selective neuronal loss. In particular, p38beta was dramatically increased in reactive astrocytes of CA3 and CA1 regions of hippocampus with its enriched localization in the nucleus of astrocytes. The induction of p38beta was sustained for more than 10 days after KA-treatment. Pre-administration of the selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI), which suppressed the delayed neuronal death as well as astrogliosis in hippocampus of seizure-experienced animals, dramatically repressed the delayed induction of p38beta MAPK in astrocytes. The repression was reversed by the co-injection with L-arginine (L-arg), a substrate for NOS, which coincided with the aggravation of neuronal death. Together, these data suggested a role of p38 MAPK signal pathway in delayed neuronal death and/or in reactive gliosis in mice with KA-induced seizure.

Animals↗
PubMed2001

Delayed induction of alpha B-crystallin in activated glia cells of hippocampus in kainic acid-treated mouse brain.

Small heat shock proteins have been implicated in playing a role in various cellular processes, including stress-induced cell death. In kainic acid (KA)-treated rat brain, the immunoreactivity of heat-shock protein 27 (HSP27) was markedly increased in glia cells of the limbic system. In the present study, we demonstrated that alpha B-crystallin, a member of the small heat-shock protein family, was strongly induced in reactive astrocytes in hippocampus after KA-induced seizure. The induction was localized mainly in the CA3 region of hippocampus, where massive neuronal loss occurred. We also demonstrated that the delayed induction of alpha B-crystallin and HSP27 immunoreactivities in the hippocampus of epileptic animals was repressed to the levels seen in control animals with preadministration of the selective nNOS inhibitor 7-nitroindazole (7-NI). This repression was reversed by coinjection of L-arginine, a substrate of NOS. Together, these data suggest a role for alpha B-crystallin and HSP27 in reactive gliosis and/or in delayed neuronal death proceeded after KA-induced seizure.

Animals↗
PubMed2001

Attenuation of Zn2+ neurotoxicity by aspirin: role of N-type Ca2+ channel and the carboxyl acid group.

Synaptically released Zn2+ ions enter into neurons primarily through voltage-gated Ca2+ channels (VGCC) or N-methyl-d-aspartate (NMDA) receptors, which can mediate pathological neuronal death. We studied the possibility (and underlying mechanisms) that aspirin, known to prevent NMDA neurotoxicity, would also attenuate Zn2+ neurotoxicity. Administration of 3 to 10 mM aspirin, in cortical cell cultures, attenuated the evolution of neuronal death following exposure to 300 microM Zn2+ for 30 min. This neuroprotective effect of aspirin was attributable to the prevention of Zn2+ ion entry. Aspirin interfered with inward currents and an increase in [Ca2+]i through VGCC and selective binding of omega-conotoxin, sensitive to N-type Ca2+ channel. The omega-conotoxins GVIA or MVIIC, the selective inhibitors of N-type Ca2+ channels, attenuated Zn2+ neurotoxicity. Aspirin derivatives lacking the carboxyl acid group did not reduce Zn2+ neurotoxicity. The present findings suggest that aspirin prevents Zn2+-mediated neuronal death by interfering with VGCC, and its action specifically requires the carboxyl acid group.

Acetylcysteine↗
PubMed2000

Vitamin D3 up-regulated protein 1 mediates oxidative stress via suppressing the thioredoxin function.

As a result of identifying the regulatory proteins of thioredoxin (TRX), a murine homologue for human vitamin D3 up-regulated protein 1 (VDUP1) was identified from a yeast two-hybrid screen. Cotransfection into 293 cells and precipitation assays confirmed that mouse VDUP1 (mVDUP1) bound to TRX, but it failed to bind to a Cys32 and Cys35 mutant TRX, suggesting the redox-active site is critical for binding. mVDUP1 was ubiquitously expressed in various tissues and located in the cytoplasm. Biochemical analysis showed that mVDUP1 inhibited the insulin-reducing activity of TRX. When cells were treated with various stress stimuli such as H2O2 and heat shock, mVDUP1 was significantly induced. TRX is known to interact with other proteins such as proliferation-associated gene and apoptosis signal-regulating kinase 1. Coexpression of mVDUP1 interfered with the interaction between TRX and proliferation-associated gene or TRX and ASK-1, suggesting its roles in cell proliferation and oxidative stress. To investigate the roles of mVDUP1 in oxidative stress, mVDUP1 was overexpressed in NIH 3T3 cells. When cells were exposed to stress, cell proliferation was declined with elevated apoptotic cell death compared with control cells. In addition, c-Jun N-terminal kinase activation and IL-6 expression were elevated. Taken together, these results demonstrate that mVDUP1 functions as an oxidative stress mediator by inhibiting TRX activity.

3T3 Cells↗
PubMed2000

Constitutive activity and differential localization of p38alpha and p38beta MAPKs in adult mouse brain.

To understand the roles of p38 mitogen-activated protein kinase (p38 MAPK) isoforms in adult mouse brain, in vivo activities and detailed expression patterns of two p38 isoforms, p38alpha and p38beta, were examined by using biochemical and immunohistochemical analyses. The result indicated that the activity of both p38alpha and p38b MAPKs in normal adult mouse brain was remarkably high, and the nuclear pool of the p38 isoforms was primarily responsible for most of the constitutive p38 MAPK activity in brain. Both p38alpha and p38beta were highly expressed in brain areas including cerebral cortex, hippocampus, cerebellum, and few nuclei of the brainstem. At the subcellular level, p38alpha was distributed in dendrites and in cytoplasmic and nuclear regions of cell body of neurons, which is in contrast to p38beta, since p38beta was preferentially expressed in nucleus of neurons. These results suggest that the p38 pathway may play an important role, not only in inflammation and neuronal cell death as previously suggested, but also in normal physiology of adult mouse brain.

Animals↗
PubMed1999

Distinct localization of SAPK isoforms in neurons of adult mouse brain implies multiple signaling modes of SAPK pathway.

Various cellular and environmental stresses lead to the activation of stress-activated protein kinase (SAPK), which is also referred to as c-Jun N-terminal kinase (JNK). In mammals, multiple SAPK isoforms, encoded by three independent genes, were identified. To gain insight into the roles of SAPK pathway in adult mouse brain, detailed expression patterns of three SAPK isoforms in brain were examined by using immunohistochemical and cell biological analyses. SAPKbeta was heavily expressed in almost all regions of brain as previously reported. Interestingly, SAPKgamma was also widely expressed at high levels. SAPKgamma expression was generally overlapped with SAPKbeta although there were some exceptions such as in hippocampus, where SAPKgamma was restricted to CA3 and CA4 regions while SAPKbeta was evenly expressed. SAPKalpha was widely expressed, but at low levels. It is particularly intriguing to note the differential subcellular localization of SAPK isoforms in neurons. In brain of normally reared mice, SAPKbeta was identified in nucleus as well as in cytoplasm of neurons, while SAPKgamma was detected mainly in cytoplasm and dendrites. Biochemical and immunological analyses revealed extraordinarily high basal activities of all SAPK isoforms in brain compared to peripheral organs, indicating that SAPK pathway may play a role in normal brain physiology. In addition, differential regional and subcellular localizations of SAPK isoforms allow us to speculate multiple signaling modes for SAPK activation in brain.

Animals↗
PubMed1999

Dynamic expression of SEK1 suggests multiple roles of the gene during embryogenesis and in adult brain of mice.

Stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK), a member of the MAP kinase (MAPK) superfamily, plays a key role in a variety of cellular processes. It is well established that SAPK/JNK activation is controlled by SEK1/MKK4, an up-stream MAP kinase kinase. To gain insight into the role of SEK1 during embryonic development and in adult life, we examined the temporal and spatial patterns of sek1 expression in mice by using in situ hybridization and immunohistochemical study. Dynamic changes of sek1 expression were observed during embryogenesis. Strong sek1 expression was detected in most of the central nervous system and in liver and thymus during early stages of development. While the sek1 expression in nervous system increases over time, expression in fetal liver and thymus gradually decreases as embryogenesis proceeds. High level of the sek1 expression in the central nervous system was persisted throughout postnatal development and remained at a stable level in adult brain. These observations provide an anatomical basis for the vital role(s) of SEK1 in development, for example, in hepatogenesis and/or neurogenesis. Although SEK1 was widely expressed in adult brain, more strong expression of the sek1 was observed at layers 2 and 6 in cerebral cortex, in Purkinje cells of cerebellum, and also in hypothalamic nuclei. The strongest expression of the sek1 was found in the CA3 region of hippocampus, the region being highly vulnerable to exitotoxicity-induced apoptosis in kainate-treated animal models. Interestingly, SEK1 was localized not only in cytoplasm but in dendrites and/or in nucleus of neurons depending on the regions of adult mouse brain. Taken together, these results suggest multiple roles of the SEK1 during embryogenesis and in adult brain.

Age Factors↗
PubMed1999

Molecular cloning of multiple splicing variants of JIP-1 preferentially expressed in brain.

Stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) is activated by a variety of cellular or environmental stresses. Proper regulation of the SAPK/JNK pathway may be critical for cell survival or death under various conditions. In this study, we report the molecular cloning of novel isoforms of JIP-1, which harbor a putative phosphotyrosine interaction domain and a helix-loop-helix domain, as well as an SH3 homologous region in the C terminus. Northern analysis indicates that transcription variant jip-1 is expressed in brain and kidney and transcription variants jip-2 and jip-3 are specifically expressed in brain. In situ hybridization data showed that the hybridized jip messages were heavily concentrated in adult brain, and were particularly enriched in the cerebral cortex and hippocampus, the brain regions vulnerable to pathological states such as hypoxia-ischemia, epilepsy, and Alzheimer's disease. All the deduced protein products of the jip transcription variants appear to have a similar property in that they inhibit the SAPK/JNK stimulation when overexpressed. Inhibition of SAPK activation by overexpression of the novel isoform JIP-2a resulted in suppression of etoposide-induced cell death in a neuroglioma cell line, N18TG. These findings suggest that JIP may play an important role in regulation of the SAPK pathway that is involved in stress-induced cellular responses.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Ca2+-mediated activation of c-Jun N-terminal kinase and nuclear factor kappa B by NMDA in cortical cell cultures.

We examined the possibility that c-Jun N-terminal kinase (JNK) and nuclear factor kappaB (NF-kappaB) might be involved in intracellular signaling cascades that mediate NMDA-initiated neuronal events. Exposure of cortical neurons to 100 microM NMDA induced activation of JNK within 1 min. Activity of JNK was further increased over the next 5 min and then declined by 30 min. Similarly, ionomycin, a selective Ca2+ ionophore, induced activation of JNK. The NMDA-induced activation of JNK was abrogated in the absence of extracellular Ca2+, suggesting that Ca2+ entry is necessary and sufficient for the JNK activation. Immunohistochemistry with anti-NF-kappaB antibody demonstrated nuclear translocation of NF-kappaB within 5 min following NMDA treatment. NMDA treatment also enhanced the DNA binding activity of nuclear NF-kappaB in a Ca2+-dependent manner. Treatment with 3 mM aspirin blocked the NMDA-induced activation of JNK and NF-kappaB. Neuronal death following a brief exposure to 100 microM NMDA was Ca2+ dependent and attenuated by addition of aspirin or sodium salicylate. The present study suggests that Ca2+ influx is required for NMDA-induced activation of JNK and NF-kappaB as well as NMDA neurotoxicity. This study also implies that aspirin may exert its neuroprotective action against NMDA through blocking the NMDA-induced activation of NF-kappaB and JNK.

Animals↗
PubMed1998

The Drosophila sanpodo gene controls sibling cell fate and encodes a tropomodulin homolog, an actin/tropomyosin-associated protein.

Notch signaling is required in many invertebrate and vertebrate cells to promote proper cell fate determination. Mutations in sanpodo cause many different neuronal peripheral nervous system precursor cells to generate two identical daughter neurons, instead of a neuron and sibling cell. This phenotype is similar to that observed when Notch function is lost late in embryonic development and opposite to the numb loss-of-function phenotype. Genetic interaction studies show that sanpodo is epistatic to numb. sanpodo encodes a homolog of tropomodulin, an actin/tropomyosin-associated protein. Loss of sanpodo leads to an aberrant F-actin distribution and causes differentiation defects of actin-containing sensory structures. Our data suggest that an actin-based process is involved in Notch signaling.

Actins↗
PubMed1997

Nitric oxide modulates the c-Jun N-terminal kinase/stress-activated protein kinase activity through activating c-Jun N-terminal kinase kinase.

Nitric oxide is a signaling molecule that has a broad range of physiological functions, including neurotransmission, macrophage activation, and vasodilation. The mechanism by which nitric oxide regulates signal transduction mediating diverse biological activities is not fully understood, however. Here, we demonstrate that nitric oxide induced the stimulation of c-Jun NH2-terminal kinase (JNK)/stress-activated protein kinase (SAPK) in intact cells. Exposure of cultured HEK293 cells to sodium nitroprusside, a nitric oxide releasing agent, resulted in the stimulation of JNK1 activity. The sodium nitroprusside-induced stimulation of JNK1 activity was abolished by treatment of cells with N-acetylcysteine. Nitric oxide production from HEK293 cells ectopically expressing nitric oxide synthases resulted in the stimulation of JNK1 activity, while JNK1 stimulation in nitric oxide synthase-overexpressing cells was abrogated by a nitric oxide synthase inhibitor, NG-nitro-L-arginine. Furthermore, exposure of cells to sodium nitroprusside resulted in the stimulation of JNK kinase (JNKK1/SEK1). Taken together, our data suggest that nitric oxide modulates the JNK activity through activating JNKK1/SEK1.

Animals↗
PubMed1997

Activation of c-Jun N-terminal kinase antagonizes an anti-apoptotic action of Bcl-2.

Bcl-2 is an intracellular membrane-associated protein that prevents cell death induced by a variety of apoptotic stimuli. A mechanism by which Bcl-2 exerts an anti-cell death effect is, however, not fully understood. In the present study, Bcl-2 suppressed cell death of N18TG neuroglioma cells caused by various apoptotic stresses, including etoposide, staurosporine, anisomycin, and ultraviolet irradiation. Concomitantly, Bcl-2 disrupted a signaling cascade to the c-Jun N-terminal kinase activation induced by the apoptotic stresses. Bcl-2 also prevented the etoposide-induced stimulation of MEKK1. Furthermore, overexpression of c-Jun N-terminal kinase antagonized the death-protective function of Bcl-2. These data suggest that suppression of the c-Jun N-terminal kinase signaling pathway may be critical for Bcl-2 action.

Animals↗
PubMed1996

The Drosophila brain revisited by enhancer detection.

The patterns of gene expression in the Drosophila brain were studied by using the lacZ reporter gene carried on an enhancer detector element. From the analysis of serial sections of the heads of 6000 enhancer detector lines, reporter gene expression in some lines was found to generally follow boundaries established by cell type or anatomy, revealing distinct patterns of lacZ expression restricted to the lamina, the medulla, mushroom bodies, antennal lobes, or other anatomical subdivisions. About 15% of the lines showed ubiquitous expression in most or all head tissues and 25% of the lines showed expression throughout the CNS. Another quarter of the lines showed widespread expression in the CNS, with large regions of the brain showing expression. This suggests that the majority of detected genes are expressed with little spatial specificity. The expression patterns produced by 12 different insertions at the rutabaga locus were found to be extremely similar in the brain and offer strong evidence that the enhancer detector elements generally report the activity of an adjacent gene. Only 15% of the lines were judged to have relatively specific expression in one brain region, including those with preferential or specific expression in the mushroom bodies, antennal lobes, lamina, medulla, etc. The cytological insertion sites for elements showing preferential mushroom body expression were found to be dispersed in the genome at approximately 50 different chromosomal regions. In addition to providing a broad picture of the transcriptional activity in the Drosophila brain, these enhancer detector lines offer access to interesting new genes and form a novel collection of lines in which identifiable brain cells are marked in a reproducible way.

Animals↗
PubMed1993

Neuromusculin, a Drosophila gene expressed in peripheral neuronal precursors and muscles, encodes a cell adhesion molecule.

To unravel the molecular mechanisms of peripheral nervous system differentiation in Drosophila, we have screened for and identified genes that are expressed in sensory mother cells. Here, we describe a novel gene, neuromusculin (nrm), that is expressed in sensory mother cells and developing muscles. nrm encodes a member of the immunoglobulin superfamily. Immunoblots of Schneider 2 cells transfected with an nrm cDNA indicate that Nrm is present in a membrane-associated form and a secreted form. Cell aggregation assays suggest that Nrm is a homophilic cell adhesion molecule that is secreted or released after proteolysis, a mechanism that to our knowledge has not been described for immunoglobulin-like molecules. Genetic analyses indicate that nrm is an essential gene required for larval viability. We propose that Nrm may play a role as a cell adhesion molecule in clustering cells of the peripheral nervous system, neuronal fasciculation, and/or pathfinding.

Amino Acid Sequence↗
PubMed1992

The Drosophila learning and memory gene rutabaga encodes a Ca2+/Calmodulin-responsive adenylyl cyclase.

Four putative adenylyl cyclase genes from Drosophila melanogaster were identified by virtue of their extensive sequence homology with mammalian cyclases. One corresponds to the learning and memory gene rutabaga and is most similar to the mammalian brain Ca2+/calmodulin (CaM)-responsive cyclase. In a mammalian expression system, rutabaga cyclase activity was stimulated approximately 5-fold by the presence of Ca2+/CaM. A point mutation, identified at this locus in rut1 mutant flies, resulted in loss of detectable adenylyl cyclase activity. New P element insertion-induced rutabaga mutations mapped to within 200 nucleotides of the 5' end of the rutabaga cDNA. These data confirm the identity of the rutabaga locus as the structural gene for the Ca2+/CaM-responsive adenylyl cyclase and show that the inactivation of this cyclase leads to a learning and memory defect.

Adenylyl Cyclases↗
PubMed1992

Preferential expression of the Drosophila rutabaga gene in mushroom bodies, neural centers for learning in insects.

Seven lines were isolated with P element insertions in the cytogenetic vicinity of the learning and memory gene, rutabaga, from an enhancer detector screen designed to mark genes preferentially expressed in mushroom bodies. Six of these lines performed poorly in learning and memory tests, and several failed to complement an existing rutabaga allele. Molecular cloning revealed that the P elements were inserted in the putative promoter of the rutabaga gene. RNA in situ hybridization and immunohistochemistry demonstrated that the expression of the rutabaga gene, which encodes a Ca2+/calmodulin-responsive adenylyl cyclase, is markedly elevated in the mushroom bodies of normal flies and that the insertion elements compromised its expression in the new rutabaga mutants. The reisolation of a known learning and memory gene, but with a heretofore unknown expression pattern, strongly supports the postulate that mushroom bodies are principal sites mediating olfactory learning and memory.

Alleles↗
PubMedDate not supplied

The cyclic AMP system and Drosophila learning.

The cyclic AMP (cAMP) system plays a critical role in olfactory learning in the fruit fly, Drosophila melanogaster, as evidenced by the following: [1] The dunce gene encodes a form of cAMP phosphodiesterase (PDE). Flies carrying mutations at this gene show reduced PDE activity, high cAMP levels, and deficits in olfactory learning and memory [2]. The rutabaga gene encodes one type of adenylyl cyclase (AC) similar in properties to the Type I AC characterized from vertebrate brain. This enzyme is activated by G-protein and Ca++ and has been postulated to be a molecular coincidence detector, capable of integrating information from two independent sources such as the conditioned stimulus (CS) and the unconditioned stimulus (US) delivered to animals during Pavlovian conditioning. Rutabaga mutant flies are deficient in AC activity and show behavioral defects similar to those exhibited by dunce mutants [3]. Flies carrying mutations in the gene (DC0) that encodes the catalytic subunit of protein kinase A (PKA), the major mediator of cAMP actions, show alterations in learning performance and a loss in PKA activity. All three genes are expressed preferentially in mushroom bodies, neuroanatomical sites that mediate olfactory learning. Interestingly, the PDE and the catalytic subunit of PKA are found primarily in axonal and dendritic compartments of the mushroom body cells, whereas the AC is found primarily in the axonal compartment. The reason for this differential compartmentalization is unclear, although the hypothetical role of AC as coincidence detector would predict that CS and US stimuli are integrated in the axonal compartment. These observations suggest that cAMP is a dominant second messenger utilized by mushroom body cells to modulate their physiology while the animal is learning and consolidating memory. However, many other types of molecules are likely involved in the physiological alterations that occur in these cells during learning, including cell surface proteins, transcription factors, and synaptic proteins.

3',5'-Cyclic-AMP Phosphodiesterases↗