Substance P (SP) enhances CCL5-induced chemotaxis and intracellular signaling in human monocytes, which express the truncated neurokinin-1 receptor (NK1R)

Substance P (SP) is a potent modulator of monocyte/macrophage function. The SP-preferring receptor neurokinin-1 receptor (NK1R) has two forms: a full-length NK1R (NK1R-F) isoform and a truncated NK1R (NK1R-T) isoform, which lacks the terminal cytoplasmic 96-aa residues. The distribution of these receptor isoforms in human monocytes is not known. We previously identified an interaction among SP, NK1R, and HIV viral strains that use the chemokine receptor CCR5 as a coreceptor, suggesting crosstalk between NK1R and CCR5. The purpose of this study was to determine which form(s) of NK1R are expressed in human peripheral blood monocytes and to determine whether SP affects proinflammatory cellular responses mediated through the CCR5 receptor. Human peripheral blood monocytes were found to express NK1R-T but not NK1R-F. SP interactions with NK1R-T did not mobilize calcium (Ca2+), but SP mobilized Ca2+ when the NK1R-F was transfected into monocytes. However, the NK1R-T was functional in monocytes, as SP enhanced the CCR5 ligand CCL5-elicited Ca2+ mobilization, a response inhibited by the NK1R antagonist aprepitant. SP interactions with the NK1R-T also enhanced CCL5-mediated chemotaxis, which was ERK1/2-dependent. NK1R-T selectively activated ERK2 but increased ERK1 and ERK2 activation by CCL5. Activation of NK1R-T elicited serine phosphorylation of CCR5, indicating that crosstalk between CCL5 and SP may occur at the level of the receptor. Thus, NK1R-T is functional in human monocytes and activates select signaling pathways, and the NK1R-T-mediated enhancement of CCL5 responses does not require the NK1R terminal cytoplasmic domain

Regulation of TNF-induced oxygen radical production in human neutrophils: role of δ-PKC

In human neutrophils, TNF-elicited O2− production requires adherence and integrin activation. How this cooperative signaling between TNFRs and integrins regulates O2− generation has yet to be fully elucidated. Previously, we identified δ-PKC as a critical early regulator of TNF signaling in adherent neutrophils. In this study, we demonstrate that inhibition of δ-PKC with a dominant-negative δ-PKC TAT peptide resulted in a significant delay in the onset time of TNF-elicited O2− generation but had no effect on Vmax, indicating an involvement of δ-PKC in the initiation of O2− production. In contrast, fMLP-elicited O2− production in adherent and nonadherent neutrophils was δ-PKC-independent, suggesting differential regulation of O2− production. An important step in activation of the NADPH oxidase is phosphorylation of the cytosolic p47phox component. In adherent neutrophils, TNF triggered a time-dependent association of δ-PKC with p47phox, which was associated with p47phox phosphorylation, indicating a role for δ-PKC in regulating O2− production at the level of p47phox. Activation of ERK and p38 MAPK is also required for TNF-elicited O2− generation. TNF-mediated ERK but not p38 MAPK recruitment to p47phox was δ-PKC-dependent. δ-PKC activity is controlled through serine/threonine phosphorylation, and phosphorylation of δ-PKC (Ser643) and δ-PKC (Thr505) was increased significantly by TNF in adherent cells via a PI3K-dependent process. Thus, signaling for TNF-elicited O2− generation is regulated by δ-PKC. Adherence-dependent cooperative signaling activates PI3K signaling, δ-PKC phosphorylation, and δ-PKC recruitment to p47phox. δ-PKC activates p47phox by serine phosphorylation or indirectly through control of ERK recruitment to p47phox

Protection against sepsis-induced lung injury by selective inhibition of protein kinase C-δ (δ-PKC)

Targeted inhibition of δ-PKC exerted a lung-protective effect and significantly attenuated pulmonary inflammatory cell infiltration, disruption of lung architecture, and pulmonary edema associated with sepsis