State-dependent phosphorylation of ε-isozyme of protein kinase C in adult rat dorsal root ganglia after inflammation and nerve injury

Abstract

The ε-isozyme of protein kinase C (PKCε) and the vanilloid receptor 1 (VR1) are both expressed in dorsal root ganglion (DRG) neurons and are reported to be predominantly and specifically involved in nociceptive function. Using phospho-specific antibody against the C-terminal hydrophobic site Ser729 of PKCε as a marker of enzyme activation, the state-dependent activation of PKCε, as well as the expression of VR1 in rat DRG neurons, was evaluated in different experimental pain models in vivo. Quantitative analysis showed that phosphorylation of PKCε in DRG neurons was significantly up-regulated after carrageen- and Complete Freund's Adjuvant-induced inflammation, while it was markedly downregulated after chronic constriction injury. A double-labeling study showed that phosphorylation of PKCε was expressed predominantly in VR1 immunoreactivity positive small diameter DRG neurons mediating the nociceptive information from peripheral tissue to spinal cord. The VR1 protein expression showed no significant changes after either inflammation or chronic constriction injury. These data indicate that functional activation of PKCε has a close relationship with the production of inflammatory hyperalgesia and the sensitization of the nociceptors. Inflammatory mediator-induced activation of PKCε and subsequent sensitization of VR1 to noxious stimuli by PKCε may be involved in nociceptor sensitization.