The Neuropeptide Substance P Activates p38 Mitogen-Activated Protein Kinase Resulting in IL-6 Expression Independently from NF-κB

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Abstract
Substance P (SP), a member of the tachykinin peptide family, is a major mediator of neuroimmunomodulatory activities and neurogenic inflammation within the central and peripheral nervous system. SP has been shown to induce the expression of proinflammatory cytokines such as IL-6, which might be implicated in the etiopathology of several human brain disorders. We showed in a previous study that nanomolar concentrations of SP triggered activation of NF-κB, a transcription factor involved in the control of cytokine expression. However, activation of NF-κB was not involved in SP-induced expression of IL-6. Here, we describe p38 mitogen-activated protein kinase (p38 MAPK) as a signal transduction component that operates independently from NF-κB activation and that mediates SP-induced IL-6 expression in the human astrocytoma cell line U373 MG. SP induced the phosphorylation of p38 MAPK within 10 min, and this activation persisted up to 30 min and was independent from p42/44 MAPKs and protein kinase C activation, which all are induced after stimulation with SP. As shown by EMSA, p38 MAPK was not involved in SP-induced activation of NF-κB. p38 MAPK, however, mediated SP-induced IL-6 expression as shown by the use of specific inhibitors of this kinase. Our results suggest that activation of p38 MAPK is an important component controlling neurogenic inflammation within the CNS independently from NF-κB. Drugs targeting this MAPK may therefore interfere with SP-correlated neuropsychiatric disorders and may represent a therapeutic approach in these disorders.