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Biomedical subjects

B S Li

Publications and source records attributed to B S Li.

At least 37 records · Page 2Linked to original sources
PubMed1999

Calcium influx and membrane depolarization induce phosphorylation of neurofilament (NF-M) KSP repeats in PC12 cells.

Signals activating the kinases that phosphorylate neurofilament proteins in the axon remain unknown. In a previous study, we have demonstrated that a constitutively active form of MEK1 activates Erk1 and Erk2 kinases, which phosphorylate co-transfected NF-M in NIH 3T3 cells. In this study, we report the activation of endogenous Erk1 and Erk2 by membrane depolarization and calcium influx through L-type calcium channels, which resulted in phosphorylation of the NF-M tail domain in PC12 cells. This phosphorylation was inhibited in the presence of nifedipine, an L-type calcium channel inhibitor, and PD98059, a specific MEK1 inhibitor. Our data suggest a mechanism linking calcium influx through voltage-gated calcium channels with the MAP kinase pathway and NF-M tail domain phosphorylation in cell body and neurite. These findings may provide significant new insights into mechanisms involved in some neurological diseases.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1999

The expression of GABA(A) receptor alpha2 subunit is upregulated by testosterone in rat cerebral cortex.

The GABAergic system is sexually dimorphic in certain brain regions and can be regulated by testosterone (T). However, the contribution of T to sex-specific developmental processes in the brain is less clear. We have examined whether T regulates expression of GABA(A) receptor alpha2 subunit in the cerebral cortex of embryonic and postnatal female rats using in situ hybridization and Western blotting. We found that both alpha2 mRNA and protein levels are significantly increased by T treatment at embryonic day 20 (E20) and birth (P0). The observed modulation of the expression of GABA(A) receptor alpha2 subunit by T may be translated into changes in the levels or composition of GABA(A) receptor, either of which would be expected to alter neuronal functional response to GABA activation. As the effects of T are developmental-stage-specific, they may have an organizational impact on brain development.

Analysis of Variance↗
PubMed1999

Expression of gicerin, a novel cell adhesion molecule, is upregulated in the astrocytes after hypoglossal nerve injury in rats.

Gicerin is an integral membrane glycoprotein which mediates cell-cell and cell-extracellular matrix (ECM) interactions in the nervous system. We studied gicerin expression in the hypoglossal nucleus post transection using in situ hybridization and immunocytochemistry. We found that hypoglossal nerve injury resulted in a significant increase in gicerin expression. Its expression levels reached peak values in reactive astrocytes surrounding axotomized motoneurons of the ipsilateral hypoglossal nucleus 14 days after hypoglossal nerve injury. The results indicate that gicerin is up-regulated during nerve regeneration, suggesting that gicerin expressed in the reactive astrocytes might be involved in the processes of nerve regeneration.

Animals↗
PubMed1999

Nocistatin reverses the effect of orphanin FQ/nociceptin in antagonizing morphine analgesia.

Nocistatin is a recently characterized neuropeptide derived from the preprohormone containing nociceptin (Orphanin FQ, OFQ). Nocistatin was reported to antagonize OFQ induced allodynia, hyperalgesia and prostaglandin E2-elicited pain responses. The aim of the present study was to determine whether nocistatin, injected intracerebroventricularly (i.c.v.), would reverse the anti-morphine effect of OFQ in rats using the tail-flick latency (TFL) as the nociceptive index. I.c.v. injection of nocistatin at doses of 0.005, 0.05, 0.5, 5, 50, and 500 ng produced no significant changes in the basal TFL, nor did it affect morphine analgesia. However, it significantly reversed the antagonistic effect of OFQ on morphine analgesia when co-injected i.c.v. at doses of 0.05, 0.5, 5, 50 and 500 ng per rat with OFQ. The dose-response curve was bell-shaped and the most effective dose was 0.5 ng. The results suggest that nocistatin can reverse the anti-morphine effect of OFQ in rat brain.

Analgesia↗
PubMed1999

Activation of mitogen-activated protein kinases (Erk1 and Erk2) cascade results in phosphorylation of NF-M tail domains in transfected NIH 3T3 cells.

Neurofilaments (NFs) are neuron-specific intermediate filaments, and are the major cytoskeletal component in large myelinated axons. Lysine-serine-proline (KSP) repeats in the tail domains of high molecular weight NF proteins (NF-M and NF-H) are extensively phosphorylated in vivo in the axon. This phosphorylation in the tail domain has been postulated to play an important role in mediating neuron-specific properties, including axonal caliber and conduction velocity. Recent studies have shown that the mitogen-activated protein kinases (extracellular signal-regulated kinases, Erk1 and Erk2) phosphorylate KSP motifs in peptide substrates derived from the NF-M and NF-H tail domains in vitro. However, it is not clear whether activation of the mitogen activated protein (MAP) kinase pathway is able to phosphorylate these domains in vivo. To answer this question, a constitutively active form of mitogen-activated Erk activating kinase (MEK1) was cotransfected with an NF-M expression construct into NIH 3T3 cells. The activated mutant, but not the dominant negative mutant, induced phosphorylation of NF-M. In addition, it was shown that epidermal growth factor, which induces the MAP kinase cascade in NIH 3T3 cells, also activated endogenous Erk1 and Erk2 and NF-M tail domain phosphorylation in the transfected cells. These results present direct evidence that in-vivo activation of Erk1 and Erk 2 is sufficient for NF-M tail domain phosphorylation in transfected cells.

3T3 Cells↗
PubMed1998

Lymphotactin: a key regulator of lymphocyte trafficking during acute graft rejection.

The attraction of leucocytes to allografts is essential for rejection. The process is controlled by chemokines. In order to clarify the role of lymphotactin (a cytokine that represents a novel branch of the chemokine superfamily) in regulating leucocyte trafficking during graft rejection, we used rat renal transplantation models to examine its gene expression and the distribution of lymphotactin-expressing cells in renal grafts. Lymphotactin mRNA was upregulated strongly in acutely rejecting renal allografts. The mRNA was undetectable in isografts, chronically rejecting renal allografts or normal kidney. Once lymphotactin was expressed, large numbers of infiltrating lymphocytes were seen. Moreover extended studies demonstrated that in cultured rat spleen cells the expression of lymphotactin mRNA was markedly induced by phytohaemagglutinin (PHA) or phorbol myristate acetate (PMA), and such induction was inhibited by the immunosuppressive drugs FK506 and cyclosporin. Collectively, these observations provide new evidence demonstrating that lymphotactin is a key regulator of lymphocyte motility and adhesiveness during acute allograft rejection. FK506 and cyclosporin inhibition of lymphotactin expression is likely to represent an important molecular mechanism of the action of the drugs.

Acute Disease↗
PubMed1996

Neuron-specific expression of a chicken gicerin cDNA in transient transgenic zebrafish.

Gicerin, a novel cell adhesion molecule which belongs to the immunoglobulin superfamily, is expressed temporally and spatially in the developing chick brain and retina. The previous in vitro experiments using transfected cells showed that gicerin can function as a cell adhesion molecule which has both homophilic and heterophilic binding activities. For the in vivo analyses of gicerin in neural development, we tried to utilize a zebrafish system, a vertebrate suitable for studying early development. We generated transient transgenic animals by microinjecting DNA constructs into zebrafish embryos. Chicken gicerin, under control of the neurofilament gene promoter, was preferentially expressed in neuronal cells and gicerin-expressing neurons exhibited a fasciculation formation with neighboring gicerin-positive axons, which may be partly due to homophilic cell adhesion activity of gicerin. These experimental results suggest that this fast and efficient transgenic animal system is useful for studying the functional roles of neuron-specific genes during the development.

Animals↗
PubMed1996

Ca2+/calmodulin-dependent transcriptional activation of neuropeptide Y gene induced by membrane depolarization: determination of Ca(2+)- and cyclic AMP/phorbol 12-myristate 13-acetate-responsive elements.

Membrane depolarization stimuli (high potassium concentration and veratridine) increased neuropeptide Y (NPY) mRNA abundance time-dependently, without a change in beta-actin mRNA level, in NG108-15 and PC12 cells. Although the induction by veratridine was blocked completely by tetrodotoxin, the induction by potassium was suppressed minimally. Voltage-dependent Ca channel blockers and calmodulin antagonists inhibited the increases by both depolarization stimuli completely, suggesting involvement of Ca2+/calmodulin-dependent kinases (CaM kinases). Transient assay using chloramphenicol acetyltransferase reporter genes containing the rat NPY gene promoter indicated that membrane depolarization and Ca entry stimulate transcription of the NPY gene. The depolarization-induced transactivation was also blocked by CaM kinase inhibitors. The 200-bp 5'-upstream region (-344/-145) was localized as a Ca2+/ calmodulin-responsive element (CaMRE), which confers depolarization-induced transactivation. It is interesting that this CaMRE did not contain the canonical Ca-responsive elements such as CRE, SRE, NF-AT, or the C/EBP beta-binding site and was separated from a 64-bp cyclic AMP/ phorbol 12-myristate 13-acetate-responsive element (-144/-81). These findings suggested that membrane depolarization regulates the NPY gene transcription positively through the unique CaMRE by activation of CaM kinases following Ca entry through L-type Ca channels.

Animals↗
PubMed1995

Expression and functional analysis of a novel isoform of gicerin, an immunoglobulin superfamily cell adhesion molecule.

We have cloned a novel cDNA of gicerin, a cell adhesion molecule belonging to the immunoglobulin superfamily. Both gicerin isoforms share the same extracellular domain, which has five immunoglobulin-like loop structures and a transmembrane domain as s-gicerin, but differ in the cytoplasmic tail domain. As the newly identified form has a larger cytoplasmic domain than the previously reported form, we refer to them as l-gicerin and s-gicerin, respectively. l-gicerin is transcribed from a distinct mRNA containing an inserted sequence not found in s-gicerin mRNA which caused a frameshift for the coding region for a cytoplasmic domain. Previous studies demonstrated that gicerin showed a doublet band of 82 and 90 kDa in chicken gizzard smooth muscle. We report that the 82-kDa protein corresponds to s-gicerin and the 90-kDa protein to l-gicerin. We also found that the two gicerin isoforms are expressed differentially in the developing nervous system. Functional analysis of these gicerin isoforms in stable transfectants revealed that they had differ in their homophilic adhesion properties, as well as in heterophilic cell adhesion assayed with neurite outgrowth factor. In addition, these isoforms have neurite-promoting activity by their homophilic adhesion, but differ in their ability to promote neurite outgrowth.

Amino Acid Sequence↗
PubMed1995

Determination of a necdin cis-acting element required for neuron specific expression by using zebra fish.

To determine cis-acting elements required for neuron specific expression of a necdin gene, we tried to use zebra fish assay system in vivo instead of cell lines in vitro. Various expression vectors carrying upstream sequences of necdin gene fused to MEKA (lacZ) gene as a reporter were injected into fertilized zebra fish embryos and then the expression of the reporter gene was analyzed by the whole mount immunochemical method. No promoter activity was obtained with a construct carrying sequence from -63 to +63 of the necdin gene, while promoter activity with preferential skin expression was obtained with a construct having sequence from -86 to +28. Further upstream sequence from -173 to +28 exhibited neuron specific expression as well as that from -845 to +63. These results indicate that a cis-acting element responsible for neuron specific expression is located in an 87bp sequence from -173 to -87 of necdin gene.

Animals↗
PubMed1995

Depressed mood in Chinese children: relations with school performance and family environment.

A sample of primary school children in Shanghai, People's Republic of China, participated in this 2-year longitudinal project. Information on the family environment, children's social functioning, academic achievement, and depression was collected from multiple sources. The mean depression scores in the Chinese children was found to be similar to those found for children in the West. Depression was positively associated with aggressive-disruptive behavior and negatively associated with social competence. School social and academic difficulties were concurrently and positively correlated with depression. Moreover, social adjustment problems at age 8 were associated with depression at age 10. Academic difficulties were predictive of later depression only for children from families in which the mother was rejecting and parents had a conflictual relationship. Finally, decline in social and academic performance was related to depressed affect.

Child↗
PubMed1995

[Second messenger-mediated transcriptional regulation of neural genes and possible drug action sites].

Second messenger systems regulate transcription initiation of immediate-early genes (IEGs) through phosphorylation of transcriptional factors and repressors. Tissue-specific late response genes (LRGs) are induced dependently on protein synthesis slowly after IEGs, but the mechanisms of regulation of LRGs are still unknown. In this review, the mechanisms of transcriptional regulation of IEGs are summarized and possible drug action sites are discussed. As to the neuropeptide Y (NPY) gene, a typical neuronal LRG, the approach was introduced to elucidate the transcriptional regulations of the NPY gene induced by membrane depolarization and NGF-induced neuronal differentiation. The second messenger systems were Ca/calmodulin dependent protein kinases (CaM) and NGF-induced MAP kinases, respectively. The unique CaM- and NGF-responsive elements and DNA-binding factors were identified. The NDF1 protein bound to NGF-RE were cloned and characterized. NDF1 seems to a novel transcriptional factor that regulates neurotrophin-induced transcription of LRGs. Thus identification of novel regulatory factors is required to elucidate mechanisms of gene expression including transcriptional initiation, and pharmacological studies are also necessary to discover the novel drug action sites in the gene expression system.

Animals↗
PubMed1992

[Synthesis and antitumor activity of 4-alkylthio-4-deoxy-4'-demethylepipodophyllotxin derivatives].

As a continuing part of our study on the chemistry and antitumor activity of podophyllotoxin, 11 new C-4 S-substituted podophyllotoxin derivatives were synthesised and screened in vitro against L1210 leukemia and KB cells. Thus, 4'-demethylepipodophyllotoxin was reacted with thiols in the presence of BF3. Et2O or trifluroacetic acid to give thioethers. In addition, 4-bromo-4-deoxy-4'-demethylepipodophyllotoxin, when reacted with thiols, also gave rise to corresponding thioether (4-alkylthio-4-deoxy-4'-demethylepipodophyllotoxins). Compounds 10 and 12 have the same activity as etoposide in the inhibition against L1210 leukemia, and compounds 9, 10, 12 and 15 also have comparable activity with etoposide against KB cells.

Animals↗
PubMed1990

Age-dependent decrease in the heat-inducible DNA sequence-specific binding activity in human diploid fibroblasts.

In order to gain a better understanding of the molecular mechanism of the attenuated heat shock response in aging diploid fibroblasts (Liu, A. Y.-C., Lin, Z., Choi, H.-S., Sorhage, F., and Li, B. (1989) J. Biol. Chem. 264, 12037-12045), we examined the regulation of a heat-inducible, heat shock element (HSE) sequence-specific binding protein in IMR-90 diploid fibroblasts. Using gel retardation assay, we showed that the HSE binding activity in extracts of IMR-90 cells was very dependent on heat shock of the cells; that the induction was transient with a maximal increase observed at 1 h of heat shock. Significantly, the level of this heat-inducible HSE-binding activity was age-dependent, being high in young cells and low in old cells. By Scatchard analysis, we determined that this difference in HSE binding in young and old cells was not due to a change in the affinity of the binding, rather the level of the heat-inducible HSE-binding activity was different. The equilibrium dissociation constants (Kd) were estimated to be 30, 25, and 31 pM for cells with population-doubling levels of 22, 35, and 45, respectively; the corresponding Bmax values were 0.087, 0.042, and 0.0059 pmol of 32P-HSE bound per mg of whole cell extract protein. The decreased 32P-HSE-binding activity in the old cells was not a reflection of global alteration of many transcription factors; assay of the DNA binding activity of activating transcription factor showed little difference as a function of age. Experiments of mixing extracts from young and old cells provided evidence of a dominant inhibitor of the HSE-binding activity in old cells. Probing of protein blots with 32P-HSE showed that the subunit molecular weight of the HSE-binding protein was 83,000 in both young and old cells. The pattern of regulation of this HSE-binding protein upon heat shock and cell aging as well as the identity, in DNA sequence specificity and subunit molecular weight, of this protein with that of the human heat shock gene transcription factor suggest that the HSE-binding protein is involved in the transcriptional activation of hsp genes in IMR-90 cells. We concluded that there was an age-associated decrease in the heat shock gene transcription factor DNA-binding activity and that this could account for the attenuated heat shock gene expression in aging diploid cells.

Base Sequence↗
PubMed1989

Heat shock induction of HSP 89 is regulated in cellular aging.

Induction of heat shock proteins (HSPs) was evaluated as a function of age of the IMR-90 human diploid fibroblasts. Heat shock (42 degrees C) markedly increased the synthesis of proteins with apparent molecular weights of 98, 89, 72, 50, 42 and 25 KDa, with HSP 89 and 72 being most prominent. This heat shock induction of HSPs was inversely correlated to the population doubling level (PDL) of the cell cultures used. For example, the synthesis rate of HSP 89 increased from a basal heat shock of young cells (PDL 18); in the old cells (PDL 51), the increase was from 1% to a maximum of 4% at 10-12 hrs after initiation of the heat shock. Western blot analysis showed that HSP 89 constituted approximately 2 and 10% of total cellular proteins in control and heat shocked (42 degrees C, 12-24 hrs) young cells; corresponding values for the old cells were 2 and 4.5%, respectively. Northern blot quantitation of the amount of mRNA hybridizable to cDNA probes of HSP 89 provided evidence that this age-dependent decrease in induction of HSP 89 in IMR-90 cells was attributable to a transcriptional/pre-translational mechanism.

Blotting, Northern↗
PubMed1989

[Synthesis and antimalarial as well as antitumor activities of 2,4-diamino-6-(N-methyl-substituted benzylamino) quinazolines].

Sixteen 2,4-diamino-6-(N-methyl-substituted benzylamino) quinazolines (I) were synthesized by two different methods. 2-Nitro-5-chloro-benzonitrile was treated with the appropriate N-methyl-substituted benzylamines and I was formed after reduction and cyclization. Another method was reductive methylation, i.e., 2,4-diamino-6-substituted benzylaminoquinazolines reacted with formaldehyde and sodium cyanoborohydride at pH 6.3. Suppressive therapeutic tests in mice infected with Plasmodium berghei showed that four (I6,7,10,16) out of these compounds suppressed all the parasites when administered orally at the dose of 5 mg/kg and produced more than 99% suppression at 2.5 mg/kg. Eight compounds (I1,2,4,5,8-10,15) were found to have antitumor effects against Leukemia cells in culture comparable with or superior to those of the positive control methotrexate.

Animals↗