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Neurokinin A (NKA) belongs to the tachykinin neuropeptide family. Its biological functions are primarily mediated by the neurokinin (NK)-2 receptor. NKA has been implicated in several inflammatory conditions. However, there are limited data about the mechanism of its pathogenetic action. Here, we investigated proinflammatory effects of NKA on peripheral immune cells using the mouse macrophage/ monocyte cell line RAW 264.7 and primary peritoneal macrophages. The signaling mechanistic pathways involved were also studied. In mouse macrophages with no detectable NK-2 receptors, NKA induces the upregulation of NK-1 but not NK-2 receptor expression. Furthermore, NKA engages this NK-1 receptor, resulting in inflammatory-like responses involving activation of the transcription factor nuclear factor (NF)-ºB and induction of NF-ºB-responsive proinflammatory chemokine expression. NKA activates NF-ºB as evidenced by induced phosphorylation (leading to degradation) of its inhibitory protein IºBα, increased cellular levels of the transactivation-active phospho(Ser276)-p65 and its nuclear translocation, as well as enhanced DNA-binding activity of NF-ºB. These responses are specifically inhibited by selective NK-1 receptor antagonists but not NK-2 receptor antagonists, thereby excluding the role of NK-2 receptor. Further investigation on the upstream signaling mechanisms suggests that two NF-ºB-activating pathways (extracellular signal-regulated kinase 1/2 and phosphatidylinositol 3-kinase/protein kinase B) are activated by NKA. Specific inhibitors of the two pathways block NF-ºB-dependent chemokine expression. The inhibitory effects are mediated through regulation of nuclear translocation, DNA-binding activity, and/or transactivation activity of NF-ºB. Together, we provide novel evidence that NKA engages NK-1 receptors on mouse macrophages to elicit NF-ºB-dependent cellular responses. The findings reveal cellular mechanisms that may underlie NKA-mediated inflammatory and immunological conditions. [ABSTRACT FROM AUTHOR]

Interaction of the neuropeptide substance P (SP) with its high-affinity neurokinin-1 receptor (NK1R) plays an important role in the pathophysiology of acute pancreatitis. SP is known to stimulate the production of chemokines monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein (MIP)-1a, and MIP-2 in pancreatic acinar cells via the activation of NF-κB. However, the signaling mechanisms by which the SP-NK1R interaction induces NF-κB activation and chemokine production remain unclear. To that end, in the present study, we investigated the participation of PKC in SP-induced chemokine production in pancreatic acinar cells. In this study, we showed that SP stimulated an early phosphorylation of PKC isoform PKC-δ followed by increased activation of MAPKKK MEKK1 and MAPK ERK and JNK as well as transcription factor NF-κB and activator protein-1 driven chemokine production. Depletion of PKC-δ with its inhibitor rottlerin or the specific PKC-δ translocation inhibitor peptide dose dependently decreased SP-induced PKC-δ, MEKK1, ERK, JNK, NF-κB, and AP-1 activation. Moreover, rottlerin as well as PKC-δ translocation inhibitor inhibited SP-induced chemokine production in a concentration-dependent manner. We also demonstrated that PKC-δ activation was attenuated by CP96345, a selective NK1R antagonist, thus showing that PKC-δ activation was indeed mediated by SP in pancreatic acinar cells. These results show that PKC-δ is an important proinflammatory signal transducer for SP-NK1R-induced chemokine production in pancreatic acinar cells. [ABSTRACT FROM AUTHOR]