The role of Protein Kinase C in the modulation of neuronal sensitivity and neurite morphology following treatment with paclitaxel in cultured sensory neurons

Abstract

Paclitaxel is a chemotherapeutic drug that is used in the treatment of solid tumors including breast and ovarian cancer. However, a debilitating and severe side effect associated with paclitaxel treatment is peripheral neuropathy. Clinically, peripheral neuropathy is characterized by a gain and loss of sensory neuronal function with symptoms including burning pain, tingling and numbness, respectively. In addition, paclitaxel also elicits a reduction in the length of intraepidermal nerve fibers. Currently, there are no effective therapies to prevent or alleviate the symptoms of peripheral neuropathy. Further studies are needed to elucidate the mechanisms underlying the changes in neuronal function and neurite morphology induced by paclitaxel in order to develop therapeutics to address the symptoms of peripheral neuropathy. Our laboratory previously demonstrated that paclitaxel altered capsaicin stimulated release of calcitonin gene-related peptide (CGRP) from cultured sensory neurons, indicating that paclitaxel altered the function of the transient receptor potential vanilloid I (TRPV1) channels. Because protein kinase C (PKC) modulates the function of TRPV1, we questioned whether PKC mediated changes in neuronal sensitivity induced by chronic treatment with paclitaxel. We used the release of CGRP as an index of neuronal sensitivity. Our data show that paclitaxel decreased the activity and membrane localization of the conventional PKC isozymes, PKCα and PKCβI/II, to elicit a reduction in the release of CGRP from cultured sensory neurons. For our neurite morphology studies, we focused on the importance of the novel PKC isozyme, PKCε, in mediating the changes in neurite morphology induced by treatment with paclitaxel because studies have demonstrated that PKCε is important for enhancing neurite outgrowth. Since our preliminary data showed a correlative reduction in PKCε protein expression and neurite length and branching following treatment with paclitaxel, we questioned whether loss of PKCε mediated altered neurite morphology induced by paclitaxel. Unexpectedly, we found that downregulation of PKCε did not exacerbate the reduction in neurite length and branching induced by paclitaxel. Our work highlights the significance of PKCα and PKCβI/II as critical mediators of changes in neuronal sensitivity induced by paclitaxel and illuminates our understanding of the mechanisms underlying the neurotoxic effects of paclitaxel on sensory neuronal function.