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

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 Zn²⁺-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)γ-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-α, -β, -γ and -δ isoforms exists, whereas PKC-ε showed a slight decrease in its soluble fraction immunoreactivity. The PKC-ζ 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, PLCγ-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 Tyr⁴⁹⁰, and antibodies against Thr/Tyr phosphorylated ERK-1/2. Moreover, PLCγ-1 phosphorylation was supported by its H_c-TeTx-induced translocation to the membranous compartment, an event related to PLCγ-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.