Recognition of neurokinin 1 receptor (NK1-R): an antibody to a peptide sequence from the third extracellular region binds to brain NK1-R

Activation of neurokinin-1 receptor by substance P inhibits melanogenesis in B16-F10 melanoma cells

Skin pigmentation plays a number of valuable roles and its regulation is a complex process that is controlled by different factors. Substance P (SP) regulates many biological functions, including neurogenic inflammation, pain, and stress. However, to date, the regulatory role of SP in the control of melanogenesis has not been elucidated. The present study was designed to investigate the effects of SP on melanogenesis and to elucidate its underlying mechanism(s). After treatment for 48 h in mouse B16-F10 melanoma cells, SP (1 and 10nM) significantly down-regulated tyrosinase activity and melanin content. Importantly, western blot analysis revealed the presence of neurokinin-1 receptor (NK-1 R) in B16-F10 cells and the activation of it after SP treatment. It was also found that preincubation with NK-1 receptor antagonist Spantide I could partially reversed SP-induced down-regulations of tyrosinase activity, melanin content and the expression of tyrosinase and tyrosinase-related protein 1. Furthermore, SP could remarkably inhibit the expressions of microphtalmia-associated transcription factor (MITF) and p-p38 MAPK and stimulated p-p70 S6K1. These effects could also be partially reversed by the pretreatment with Spantide I. These results collectively suggested that SP inhibited melanogenesis in B16-F10 cells, which might be attributed to the fact that SP induces the activation of NK-1 receptor, stimulates the phosphorylation of p70 S6K1 and inhibits that of p38 MAPK, decreases the tyrosinase and tyrosinase-related protein 1 expression through MITF, finally resulting in the suppression of melanogenesis. These observations in vitro indicated that the regulation of the SP/NK-1 receptor system might be a useful novel management for skin pigmentation.

The role of neurokinin-1 receptor in the microenvironment of inflammation and cancer

The recent years have witnessed an exponential increase in cancer research, leading to a considerable investment in the field. However, with few exceptions, this effort has not yet translated into a better overall prognosis for patients with cancer, and the search for new drug targets continues. After binding to the specific neurokinin-1 (NK-1) receptor, the peptide substance P (SP), which is widely distributed in both the central and peripheral nervous systems, triggers a wide variety of functions. Antagonists against the NK-1 receptor are safe clinical drugs that are known to have anti-inflammatory, analgesic, anxiolytic, antidepressant, and antiemetic effects. Recently, it has become apparent that SP can induce tumor cell proliferation, angiogenesis, and migration via the NK-1 receptor, and that the SP/NK-1 receptor complex is an integral part of the microenvironment of inflammation and cancer. Therefore, the use of NK-1 receptor antagonists as a novel and promising approach for treating patients with cancer is currently under intense investigation. In this paper, we evaluate the recent scientific developments regarding this receptor system, its role in the microenvironment of inflammation and cancer, and its potentials and pitfalls for the usage as part of modern anticancer strategies.

Prophylactic and therapeutic targeting of the neurokinin-1 receptor limits neuroinflammation in a murine model of pneumococcal meningitis

There is increasing evidence that the tachykinin substance P (SP) can augment inflammatory immune responses within the CNS. We have recently demonstrated that resident CNS cells express high-affinity receptors for this neuropeptide (neurokinin-1 receptors [NK-1R]), and we have shown that SP can significantly augment glial inflammatory responses to clinically relevant Gram-negative bacteria. Furthermore, we provided evidence that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation following in vivo exposure to these pathogens. In this study, we demonstrate that SP similarly enhances inflammatory glial responses to the major Gram-positive causative agent of bacterial meningitis, Streptococcus pneumoniae, and show that endogenous SP/NK-1R interactions play a critical role in the development of CNS inflammation in an in vivo model of pneumococcal meningitis. Importantly, we provide the first demonstration, to our knowledge, that pharmacological targeting of the NK-1R not only prevents the development of damaging inflammation when administered prophylactically, but can also limit or reverse neuroinflammation associated with an established streptococcal CNS infection when delivered therapeutically. We show that an NK-1R antagonist attenuates increases in CNS inflammatory cytokine levels and decreases in immunosuppressive cytokine production associated with an ongoing S. pneumoniae infection. Furthermore, we demonstrate that such a therapeutic intervention reverses infection-associated gliosis and demyelination in the absence of changes in CNS bacterial burden. Together, these results suggest that targeting SP/NK-1R interactions is a strategy worthy of further study for the treatment of microbially induced neuroinflammation.

Neurogenic exacerbation of microglial and astrocyte responses to Neisseria meningitidis and Borrelia burgdorferi

Although glial cells are recognized for their roles in maintaining neuronal function, there is growing appreciation of the ability of resident CNS cells to initiate and/or augment inflammation following trauma or infection. The tachykinin, substance P (SP), is well known to augment inflammatory responses at peripheral sites and its presence throughout the CNS raises the possibility that this neuropeptide might serve a similar function within the brain. In support of this hypothesis, we have recently demonstrated the expression of high affinity receptors for SP (Neurokinin-1 (NK-1) receptors) on microglia and shown that this tachykinin can significantly elevate bacterially induced inflammatory prostanoid production by isolated cultures of these cells. In the present study, we demonstrate that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation in vivo following exposure to two clinically relevant bacterial CNS pathogens, Neisseria meningitidis and Borrelia burgdorferi. We show that in vivo elevations in inflammatory cytokine production and decreases in the production of an immunosuppressive cytokine are markedly attenuated in mice genetically deficient in the expression of the NK-1R or in mice treated with a specific NK-1R antagonist. Furthermore, we have used isolated cultures of microglia and astrocytes to demonstrate that SP can augment inflammatory cytokine production by these resident CNS cell types following exposure to either of these bacterial pathogens. Taken together, these studies indicate a potentially important role for neurogenic exacerbation of resident glial immune responses in CNS inflammatory diseases, such as bacterial meningitis.

The NK1 receptor is involved in the antitumoural action of L-733,060 and in the mitogenic action of substance P on neuroblastoma and glioma cell lines

We have carried out an in vitro study to investigate the ability of substance P to activate cell growth and the NK1 receptor antagonist L-733,060 to inhibit cell growth in the SKN-BE(2) neuroblastoma and GAMG glioma cell lines. A coulter counter was used to determine viable cell numbers, followed by application of the tetrazolium compound [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)2-(4-sulfophenyl)-2H-tetrazolium], inner salt, colorimetric method to evaluate cell viability in this cytotoxicity assay. Nanomolar concentrations of substance P increased, and micromolar concentrations of L-733,060 inhibited the growth of both cell lines studied, with and without previous administration of substance P. In addition, we have demonstrated by immunoblot analysis that NK1 receptors are present in both cancer cell lines studied here. Thus, this study demonstrates that substance P acts as a mitogen in the SKN-BE(2) neuroblastoma and GAMG glioma cell lines, and that the antitumoural action of L-733,060 on both human cell lines occurs through the NK1 receptor. This action suggests that the NK1 receptor is a new and promising target in the treatment of human neuroblastoma and glioma.

Expression of substance P and its neurokinin-1 receptor on thymocytes: functional relevance in the regulation of thymocyte apoptosis and proliferation

Herein, we provide evidence of the expression and function of substance P (SP) and neurokinin-1 receptor (NK-1R) in the rat thymus. In situ hybridization evidenced NK-1R mRNA mainly in the thymic medulla, and Northern blot analysis of mRNA from FACS-sorted thymocytes identified NK-1R on CD4+, CD8+ and double-positive subpopulations. With flow cytometry, it could be seen that NK-1R was expressed on the majority of CD5+ thymocytes, and it was identified by Western blot analysis as two bands migrating at 44 and 54 kD. SP administration rescues thymocytes from spontaneous and NK-1R antagonist (SR140333)-induced apoptosis and stimulates concanavalin A (ConA)-induced thymocyte proliferation, CD25 expression and IL-2 production, whereas SR140333 exerts inhibitory effects on these functions. We also demonstrated the expression of mRNA for the SP precursor preprotachykinin-A in the thymic medulla and purified CD5+ thymocytes. SP protein was detected on 40% of CD5+ thymocytes and identified as a band of 1.3 kD by Western blot analysis. Finally, thymocytes spontaneously released SP, which was increased upon ConA or CD3 stimulation.