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HC fragment (C-terminal portion of the heavy chain) of tetanus toxin activates protein kinase C isoforms and phosphoproteins involved in signal transduction.

ABSTRACT: A recent report [Gil, Chaib-Oukadour, Pelliccioni and Aguilera (2000) FEBS Lett. 481, 177-182] describes activation of signal transduction pathways by tetanus toxin (TeTx), a Zn(2+)-dependent endopeptidase synthesized by the Clostridium tetani bacillus, which is responsible for tetanus disease. In the present work, specific activation of protein kinase C (PKC) isoforms and of intracellular signal-transduction pathways, which include nerve-growth-factor (NGF) receptor trkA, phospholipase C(PLC)gamma-1 and extracellular regulated kinases (ERKs) 1 and 2, by the recombinant C-terminal portion of the TeTx heavy chain (H(C)-TeTx) is reported. The activation of PKC isoforms was assessed through their translocation from the soluble (cytosolic) compartment to the membranous compartment, showing that clear translocation of PKC-alpha, -beta, -gamma and -delta isoforms exists, whereas PKC-epsilon showed a slight decrease in its soluble fraction immunoreactivity. The PKC-zeta isoform showed no consistent response. Using immunoprecipitation assays against phosphotyrosine residues, time- and dose-dependent increases in tyrosine phosphorylation were observed in the trkA receptor, PLCgamma-1 and ERK-1/2. The effects shown by the H(C)-TeTx fragment on tyrosine phosphorylation were compared with the effects produced by NGF. The trkA and ERK-1/2 activation were corroborated using phospho-specific antibodies against trkA phosphorylated on Tyr(490), and antibodies against Thr/Tyr phosphorylated ERK-1/2. Moreover, PLCgamma-1 phosphorylation was supported by its H(C)-TeTx-induced translocation to the membranous compartment, an event related to PLCgamma-1 activation. Since H(C)-TeTx is the domain responsible for membrane binding and lacks catalytic activity, the activations described here must be exclusively triggered by the interaction of TeTx with a membrane component.

SUBMITTER: Gil C

PROVIDER: S-EPMC1221816 | biostudies-other | 2001 May

REPOSITORIES: biostudies-other

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Project description:Previous publications from our group [Gil, Chaib, Pelliccioni and Aguilera (2000) FEBS Lett. 481, 177-182; Gil, Chaib, Blasi and Aguilera (2001) Biochem. J. 356, 97-103] have reported the activation, in rat brain synaptosomes, of several phosphoproteins, such as neurotrophin tyrosine kinase (Trk) A receptor, phospholipase Cgamma-1, protein kinase C (PKC) isoforms and extracellular-signal-regulated kinases 1 and 2 (ERK-1/2). In the present study, we examined, by means of phospho-specific antibodies, the activation of the signalling cascades involving neurotrophin Trk receptor, Akt kinase and ERK pathway, in cultured cortical neurons from foetal rat brain, by tetanus toxin (TeTx) as well as by the C-terminal part of its heavy chain (H(C)-TeTx). TeTx and H(C)-TeTx induce fast and transient phosphorylation of Trk receptor at Tyr(674) and Tyr(675), but not at Tyr(490), although the potency of TeTx in this action was higher when compared with H(C)-TeTx action. Moreover, H(C)-TeTx and TeTx also induced phosphorylation of Akt (at Ser(473) and Thr(308)) and of ERK-1/2 (Thr(202)/Tyr(204)), in a time- and concentration-dependent manner. The detection of TeTx- and H(C)-TeTx-induced phosphorylation at Ser(9) of glycogen synthase kinase 3beta confirms Akt activation. In the extended analysis of the ERK pathway, phosphorylation of the Raf, mitogen-activated protein kinase kinase (MEK)-1/2 and p90Rsk kinases and phosphorylation of the transcription factor cAMP-response-element-binding protein were detected. The use of tyrphostin AG879, an inhibitor of Trk receptors, demonstrates their necessary participation in the H(C)-TeTx-induced activation of Akt and ERK pathways, as well as in the phosphorylation of phospholipase Cgamma-1. Furthermore, both pathways are totally dependent on phosphatidylinositol 3-kinase action, and they are independent of PKC action, as assessed using wortmannin and Ro-31-8220 as inhibitors. The activation of PKC isoforms was determined by their translocation from the cytosolic compartment to the membranous compartment, showing a clear H(C)-TeTx-induced translocation of PKC-alpha and -beta, but not of PKC- epsilon.

Project description:Background: Synaptic transmission is required for functional maturation of the CNS and to induce gene transcription involved in neuronal plasticity. Our aim is to identify genes that are transcriptionally regulated by synaptic transmission during development. cDNA microarrays will be used to compare gene expression in normal embryos and embryos with no synaptic transmission. Using the Gal4 UAS system, the tetanus toxin light fragment (TET) will be expressed throughout the nervous system. The effects of TET are well characterised: the synaptic protein n-Synaptobrevin is cleaved, blocking evokes vesicle fusion in TET expressing neurons and as a result synaptic transmission is blocked. Embryos expressing an inactive, mutant version of TET (iTET) show no detectable phenotype. Thus a comparison of gene expression in iTET expressing embryos and TET expressing embryos focuses our screen cleanly and specifically on genes that are regulated by synaptic transmission. At the end of larval life, during metamorphosis, there is a second phase of nervous system development with the same requirement for neural circuit differentiation and maturation as in the embryo. We will compare gene expression in TET expressing and iTET expressing pupae to identify genes which are regulated by synaptic transmission in this second phase of nervous system development. We will focus our analysis on genes which are similarly regulated in both systems. Plan: elav Gal4 (expressed in all the neurons) for the embryos and Heat Shock Gal4 (which allows a temporally controlled expression) for the pupae are used to drive UAS TET and UAS iTET throughout the nervous system. Crosses are set up with flies homozygous for Gal4 or UAS transgenes, so that all the progeny have the same genotype. Total RNA is extracted from 500 carefully staged embryos that have been collected at the time of hatching. Pupae are heat shocked at 24 hours after puparium formation, and heads are then collected 5 days after puparium formation. TET expressing pupae are paralysed but morphologically normal whereas iTET expressing pupae emerge as normal adults. Total RNA will be extracted from 250 heads of each genotype. Probes made from TET and iTET expressing embryos extracts will be hybridised together to the chip and so will be probes made from TET and iTET expressing pupae extracts. Genes regulated in both systems will be compared together.

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HC fragment (C-terminal portion of the heavy chain) of tetanus toxin activates protein kinase C isoforms and phosphoproteins involved in signal transduction.

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