Neuropathic pain is a complex, chronic pain state that often accompanies tissue damage, inflammation or injury of the nervous system. However the underlying molecular mechanisms still remain unclear. Here, we showed that CXCL12 and CXCR4 were upregulated in the dorsal root ganglion (DRG) after chronic compression of DRG (CCD), and some CXCR4 immunopositive neurons were also immunopositive for the nociceptive neuronal markers IB4, TRPV1, CGRP, and substance P. The incidence and amplitude of CXCL12-induced Ca2+ response in primary sensory neurons from CCD mice was significantly increased compared to those from control animals. CXCL12 depolarized the resting membrane potential, decreased the rheobase, and increased the number of action potentials evoked by a depolarizing current at 2X rheobase in neurons from CCD mice. The mechanical and thermal hypernociception after CCD was attenuated by administration of a CXCR4 antagonist AMD3100. These findings suggest that CXCL12/CXCR4 signaling contributes to hypernociception after CCD, and targeting CXCL12/CXCR4 signaling pathway may alleviate neuropathic pain.

Several members of the mitogen-activated protein kinase kinase kinase (MAP3K) family including MEKK3 and TGFβ-activating kinase (TAK1) play nonredundant roles in activation of the NF-κB transcription factor. However, the mechanism by which MEKK3 mediates NF-κB signaling is not fully understood. In this report we investigate the association of murine MEKK3 with other proteins and their roles in NF-κB activation. Using tandem affinity purification TAK1 was identified as an endogenous protein that interacts with MEKK3. MEKK3-TAK1 interactions were confirmed by fluorescence resonance energy transfer and coimmunoprecipitation. MEKK3-TAK1 complexes contain non-phosphorylated forms of both molecules. Expression of non-phosphorylated TAK1 interferes with MEKK3 phosphorylation and NF-κB reporter activity induced by transient MEKK3 expression or TNFα stimulation. Addition of TAB1 facilitates TAK1 autophosphorylation and reverses the inhibitory effects of TAK1 on MEKK3 phosphorylation and NF-κB signal transduction in human 293 cells and TAK1 deficient mouse embryonic fibroblasts. The data provide insights into the homeostatic interactions that maintain basal NF-κB levels by holding the enzymes MEKK3 and TAK1 in their inactive state.