Pharmacological profile of hemokinin 1: a novel member of the tachykinin family

Mouse Hemokinin-1 Decapeptide Subjected to a Brain-specific Post-translational Modification

BACKGROUND/AIM

The tachykinin mouse hemokinin-1, expressed by the mouse Tac4 gene, produces either analgesia or nociception, interacting with the neurokinin 1 receptor. TAC4 precursor processing is not identical to the processing of the TAC1 precursor, for the release of substance P (amidated undecapeptide). The characterization of the mouse hemokinin-1 sequence was required.

MATERIALS AND METHODS

We developed anti-tachykinin-specific antibodies for the immunoaffinity purification of tachykinins.

RESULTS

Using MALDI-ToF, we identified mouse hemokinin-1 as an amidated decapeptide expressed in murine brain and periphery. Furthermore, we interestingly observed an additional mass peak corresponding to acetylated mouse hemokinin-1 and this post-translational modification is brain-specific, not detected in the periphery.

CONCLUSION

We suggest that the N-terminal acetylation of the peptide provides greater potency for ligand-receptor interactions during neural cell signaling.

Role of hemokinin-1 in health and disease

Hemokinin-1 (HK-1), the newest tachykinin encoded by the Tac4 gene was discovered in 2000. Its name differs from that of the other members of this peptide family due to its first demonstration in B lymphocytes. Since tachykinins are classically found in the nervous system, the significant expression of HK-1 in blood cells is a unique feature of this peptide. Due to its widespread distribution in the whole body, HK-1 is involved in different physiological and pathophysiological functions involving pain inflammation modulation, immune regulation, respiratory and endocrine functions, as well as tumor genesis. Furthermore, despite the great structural and immunological similarities to substance P (SP), the functions of HK-1 are often different or the opposite. They both have the highest affinity to the tachykinin NK1 receptor, but HK-1 is likely to have a distinct binding site and signalling pathways. Moreover, several actions of HK-1 different from SP have been suggested to be mediated via a presently not identified own receptor/target molecule. Therefore, it is very important to explore its effects at different levels and compare its characteristics with SP to get a deeper insight in the different cellular mechanisms. Since HK-1 has recently been in the focus of intensive research, in the present review we summarize the few clinical data and experimental results regarding HK-1 expression and function in different model systems obtained throughout the 16years of its history. Synthesizing these findings help to understand the complexity of HK-1 actions and determine its biomarker values and/or drug development potentials.

Changes in the disposition of substance P in the rostral ventromedial medulla after inflammatory injury in the rat

This study examined whether peripheral inflammatory injury increases the levels or changes the disposition of substance P (SubP) in the rostral ventromedial medulla (RVM), which serves as a central relay in bulbospinal pathways of pain modulation. Enzyme immunoassay and reverse transcriptase quantitative polymerase chain reaction were used to measure SubP protein and transcript, respectively, in tissue homogenates prepared from the RVM and the periaqueductal gray (PAG) and cuneiform nuclei of rats that had received an intraplantar injection of saline or complete Freund's adjuvant (CFA). Matrix-Assisted Laser Desorption/Ionization Time of Flight analysis confirmed that the RVM does not contain hemokinin-1 (HK-1), which can confound measurements of SubP because it is recognized equally well by commercial antibodies for SubP. Levels of SubP protein in the RVM were unchanged four hours, four days and two weeks after injection of CFA. Tac1 transcripts were similarly unchanged in the RVM four days or two weeks after CFA. In contrast, the density of SubP immunoreactive processes in the RVM increased 2-fold within four hours and 2.7-fold four days after CFA injection; it was unchanged at two weeks. SubP-immunoreactive processes in the RVM include axon terminals of neurons located in the PAG and cuneiform nucleus. SubP content in homogenates of the PAG and cuneiform nucleus was significantly increased four days after CFA, but not at four hours or two weeks. Tac1 transcripts in homogenates of these nuclei were unchanged four days and two weeks after CFA. These findings suggest that there is an increased mobilization of SubP within processes in the RVM shortly after injury accompanied by an increased synthesis of SubP in neurons that project to the RVM. These findings are consonant with the hypothesis that an increase in SubP release in the RVM contributes to the hyperalgesia that develops after peripheral inflammatory injury.

Hemokinin-1(4-11)-induced analgesia selectively up-regulates δ-opioid receptor expression in mice

Our previous studies have shown that an active fragment of human tachykinins (hHK-1(4-11)) produced an opioid-independent analgesia after intracerebroventricular (i.c.v.) injection in mice, which has been markedly enhanced by a δ OR antagonist, naltrindole hydrochloride (NTI). In this study, we have further characterized the in vivo analgesia after i.c.v. injection of hHK-1(4-11) in mouse model. Our qRT-PCR results showed that the mRNA levels of several ligands and receptors (e.g. PPT-A, PPT-C, KOR, PDYN and PENK) have not changed significantly. Furthermore, neither transcription nor expression of NK₁ receptor, MOR and POMC have changed noticeably. In contrast, both mRNA and protein levels of DOR have been up-regulated significantly, indicating that the enhanced expression of δ opioid receptor negatively modulates the analgesia induced by i.c.v. injection of hHK-1(4-11). Additionally, the combinatorial data from our previous and present experiments strongly suggest that the discriminable distribution sites in the central nervous system between hHK-1(4-11) and r/mHK-1 may be attributed to their discriminable analgesic effects. Altogether, our findings will not only contribute to the understanding of the complicated mechanisms regarding the nociceptive modulation of hemokinin-1 as well as its active fragments at supraspinal level, but may also lead to novel pharmacological interventions.

Hemokinin-1 competitively inhibits substance P-induced stimulation of osteoclast formation and function

Hemokinin-1 (HK-1) is a novel member of the tachykinin family that is encoded by preprotachykinin 4 (TAC4) and shares the neurokinin-1 receptor (NK1-R) with substance P (SP). Although HK-1 is thought to be an endogenous peripheral SP-like endocrine or paracrine molecule in locations where SP is not expressed, neither the distribution of HK-1 in the maxillofacial area nor the role HK-1 in bone tissue have been examined. In this study, we investigated the distribution of HK-1 in trigeminal ganglion (TG) and maxillary bone, and assessed the expression of HK-1 during osteoclast differentiation. In vivo, rat molars were loaded for 5 days using the Waldo method. In vitro, rat osteoclast-like cells were induced from bone marrow cells. HK-1 distribution and expression were examined by immunofluorescence staining and reverse transcription polymerase chain reaction (RT-PCR). In vivo, HK-1 was localized in rat TG neurons; however, the number of HK-1-positive neurons was less than that of SP-positive neurons. In the maxillary bone, nerve fibers, blood vessels, and osteocytes were immunopositive for HK-1. Furthermore, HK-1-positive immunoreactivity was found in osteoclasts on the pressure side. In vitro, PCR showed that TAC4 and NK1-R mRNA was expressed in osteoclasts as well as in bone marrow cells. Although SP (10⁻⁷ M) treatment led to an increased number of osteoclasts, HK-1 (10⁻⁷ M) treatment did not. The numbers of biotin-labeled HK-1 peptides bound osteoclasts significantly decreased upon incubation with unlabeled SP and biotin-labeled HK-1 compared with biotin-labeled HK-1 alone. These results suggest that HK-1 may not stimulate the differentiation and function of osteoclasts. SP-stimulated osteoclast formation is competitively regulated by peripheral HK-1 through NK1-Rs.

Study on the distribution sites and the molecular mechanism of analgesia after intracerebroventricular injection of rat/mouse hemokinin-1 in mice

Hemokinin-1 is a peptide encoded by Pptc, which belongs to the family of mammalian tachykinins. Our previous results showed that rat/mouse hemokinin-1 (r/m HK-1) produced striking analgesia after intracerebroventricular (i.c.v.) injection in mice, and the analgesia could be blocked by the NK1 receptor antagonist and the opioid receptor antagonist, respectively. However, the precise distribution sites and the molecular mechanism involved in the analgesic effect after i.c.v. administration of r/m HK-1 are needed to be further investigated deeply. Using the fluorescence labeling method, our present results directly showed that r/m HK-1 peptides were mainly distributed at the ventricular walls and several juxta-ventricular structures for the first time. Our results showed that the mRNA expressions of NK1 receptor, PPT-A, PPT-C, KOR, PDYN, DOR and PENK were not changed markedly, as well as the protein expression of NK1 receptor was hardly changed. However, both the transcripts and proteins of MOR and POMC were up-regulated significantly, indicating that the analgesic effect induced by i.c.v. administration of r/m HK-1 is related to the activation of NK1 receptor first, then it is related to the release of endogenous proopiomelanocortin, as well as the increased expression level of μ opioid receptor. These results should facilitate further the analysis of the analgesia of r/m HK-1 in the central nerval system in acute pain and may open novel pharmacological interventions.

Expression and proliferative effect of hemokinin-1 in human B-cells

Tachykinins are a family of structurally related peptides, including substance P (SP), hemokinin-1 (HK-1), neurokinin A (NKA), and neurokinin B. SP and NKA have been shown to modulate hematopoiesis and rat/mouse HK-1 has been found to be involved in the survival and differentiation of mouse B-cells. This study was designed to assess the expression of tachykinins with a focus on human HK-1 (hHK-1) in human B lymphocytes and the role of these peptides in cell differentiation, apoptosis and proliferation. Expression of tachykinin and tachykinin receptor mRNA was determined quantitatively in human B lymphoproliferative malignancies and compared to normal B-cells. Expression of hHK-1 and NK(1) receptor, but not SP, was detected in human B-lymphocytes, and was up-regulated in B-lymphocytes from chronic lymphocytic leukemia and non-Hodgkin's lymphoma, while it was down-regulated in acute lymphoblastic leukemia. Moreover, hHK-1, in contrast to SP, was able to induce proliferation of human pre-B lymphocytes through a NK(1) receptor-independent mechanism. These data suggest a role for hHK-1 in normal and pathological B lymphopoiesis, and open the door to a better understanding of the physiopathological mechanisms leading to lymphoproliferative malignancies.

Early B-cell factor regulates the expression of Hemokinin-1 in the olfactory epithelium and differentiating B lymphocytes

Hemokinin-1, encoded by the TAC4 gene, is a tachykinin most closely related to substance P. Previous studies have shown that TAC4 distinguishes itself from other tachykinins by its predominantly non-neuronal expression profile, particularly in cells of the immune system. Here we report for the first time that the highest levels of TAC4 expression are found in the olfactory epithelium. Furthermore, we identify olfactory neuron-specific transcription factor (Olf-1), also known as early B-cell factor (EBF), as a novel regulator of TAC4 expression. EBF present in the olfactory epithelium and in B cells binds to two sites in the TAC4 promoter and modulates expression in developing B cells. Our findings suggest a role for TAC4 in cell differentiation, and represent a regulatory bridge between the nervous system and the immune system.

Expression and function of human hemokinin-1 in human and guinea pig airways

Background

Human hemokinin-1 (hHK-1) and endokinins are peptides of the tachykinin family encoded by the TAC4 gene. TAC4 and hHK-1 expression as well as effects of hHK-1 in the lung and airways remain however unknown and were explored in this study.

Methods

RT-PCR analysis was performed on human bronchi to assess expression of tachykinin and tachykinin receptors genes. Enzyme immunoassay was used to quantify hHK-1, and effects of hHK-1 and endokinins on contraction of human and guinea pig airways were then evaluated, as well as the role of hHK-1 on cytokines production by human lung parenchyma or bronchi explants and by lung macrophages.

Results

In human bronchi, expression of the genes that encode for hHK-1, tachykinin NK₁-and NK₂-receptors was demonstrated. hHK-1 protein was found in supernatants from explants of human bronchi, lung parenchyma and lung macrophages. Exogenous hHK-1 caused a contractile response in human bronchi mainly through the activation of NK₂-receptors, which blockade unmasked a NK₁-receptor involvement, subject to a rapid desensitization. In the guinea pig trachea, hHK-1 caused a concentration-dependant contraction mainly mediated through the activation of NK₁-receptors. Endokinin A/B exerted similar effects to hHK-1 on both human bronchi and guinea pig trachea, whereas endokinins C and D were inactive. hHK-1 had no impact on the production of cytokines by explants of human bronchi or lung parenchyma, or by human lung macrophages.

Conclusions

We demonstrate endogenous expression of TAC4 in human bronchi, the encoded peptide hHK-1 being expressed and involved in contraction of human and guinea pig airways.

Effects of rat/mouse hemokinin-1, human hemokinin-1 and human hemokinin-1(4-11), mammalian tachykinin peptides, on rate and perfusion pressure in the isolated guinea pig heart

Rat/mouse hemokinin-1 (r/m HK-1), human hemokinin-1 (h HK-1) and human hemokinin-1(4-11) (h HK-1(4-11)) are members of the tachykinin family. In the present study, the coronary vascular activities and cardiac functions of r/m HK-1, h HK-1 and h HK-1(4-11) were investigated in isolated, spontaneously beating guinea pig hearts. Bolus injections of r/m HK-1 caused decrease in perfusion pressure indicative of coronary vasodilation, which was primarily due to the action on tachykinin NK1 receptors on vascular endothelial cells, causing the release of nitric oxide that relaxed the coronary vessels. H HK-1 caused biphasic perfusion pressure changes that were coronary vasodilation followed by coronary vasoconstriction. The mechanisms involved in the vasodilation induced by h HK-1 were similar to that of r/m HK-1 while the mechanisms for coronary vasoconstriction were mediated through the activation of tachykinin NK2 receptors on coronary sympathetic neurons to release catecholamines. H HK-1(4-11) only produced coronary vasoconstriction and the mechanisms involved in this effect were similar to that of h HK-1 in vasoconstriction. Moreover, r/m HK-1 and h HK-1 produced similar decreases in heart rate indicative of negative chronotropic responses and the decreases were mainly mediated through the activation of tachykinin NK1 receptors to release ACh acting on muscarinic receptors. H HK-1(4-11) also produced negative chronotropic response, which was mainly mediated through tachykinin NK2 receptors and muscarinic receptors. Our present results provide evidence that all of the three tachykinins could influence cardiac function and coronary vascular activity in the isolated guinea pig heart.

Targeted deletion of the tachykinin 4 gene (TAC4-/-) influences the early stages of B lymphocyte development

Hemokinin-1 (HK-1), encoded by the TAC4 gene, is a tachykinin peptide that is predominantly expressed in non-neuronal cells, such as immune cells. We have disrupted the mouse TAC4 gene to obtain a better understanding of the actions of HK-1 during hematopoiesis. We demonstrate here that TAC4(-/-) mice exhibit an increase of CD19(+)CD117(+)HSA(+)BP.1(-) "fraction B" pro-B cells in the bone marrow, whereas pre-B, immature, and mature B cells are within the normal range. We show that in vitro cultures derived from TAC4(-/-) bone marrow, sorted "fraction B" pro-B cells or purified long-term reconstituting stem cells, contain significantly higher numbers of pro-B cells compared with controls, suggesting an inhibitory role for HK-1 on developing B cells. Supporting this idea, we show that addition of HK-1 to cultures established from long-term reconstituting stem cells and the newly described intermediate-term reconstituting stem cells leads to a significant decrease of de novo generated pro-B cells. Based on our studies, we postulate that HK-1 plays an inhibitory role in hematopoiesis, and we hypothesize that it may be part of the bone marrow microenvironment that supports and regulates the proliferation and differentiation of hematopoietic cells.

The amino-terminal region of hemokinin-1 regulates the induction of thermal hyperalgesia in rats

It is known that intrathecal administration of substance P (SP) induces thermal hyperalgesia, whereas hemokinin-1 (HK-1), a member of the same tachykinin family as SP, hardly induces thermal hyperalgesia; however, the underlying mechanism remains to be elucidated. Therefore, we aimed to clarify which amino acid of these peptides contributes to the induction of thermal hyperalgesia. When two chimera peptides between the N-terminal region of SP and the C-terminal region of HK-1, and vice versa, SP (1-5)/HK-1 and HK-1 (1-5)/SP, were intrathecally administered, SP (1-5)/HK-1 induced thermal hyperalgesia whereas HK-1 (1-5)/SP had hardly any effect; furthermore, thermal hyperalgesia was induced by only C-terminal fragments of HK-1 and SP. These findings indicate that the N-terminal region of HK-1 is involved in the non-induction of thermal hyperalgesia. Next, we synthesized and intrathecally administered these chimera peptides in which part of the N-terminal region of HK-1 was replaced with that of SP, and vice versa, and all synthesized peptides induced thermal hyperalgesia. Both SP (1-2)/HK-1 and HK-1 (1-4)/SP certainly induced thermal hyperalgesia, although HK-1 and HK-1 (1-5)/SP had hardly any effect; therefore, it is probable that Ser at the 2nd position and Arg at the 5th position of HK-1 may be involved in the non-induction of thermal hyperalgesia. Furthermore, peptides in which amino acid at the 3rd and/or 4th positions of HK-1 was replaced with that of SP were synthesized. Intrathecal administration of HK-1 (1-2,4-5)/SP, but not HK-1 (1-2,5)/SP and HK-1 (1-3,5)/SP, hardly induced thermal hyperalgesia. These findings indicate that three amino acids, Ser, Thr and Arg at the 2nd, 4th and 5th positions of HK-1, respectively, regulate the induction of thermal hyperalgesia by HK-1.

Hemokinin-1 activates the MAPK pathway and enhances B cell proliferation and antibody production

Hemokinin 1 (HK-1) is a substance P-like tachykinin peptide predominantly expressed in non-neuronal tissues. In addition to a prominent function in lymphoid development, recent studies indicate a potential role for HK-1 in immunoregulation. The current study was focused on its action on mature B cells. Despite the negligible effect on its own, HK-1 exhibited a profound influence on B cell activation elicited by several classical signals, including LPS stimulation, BCR cross-linking, and CD40 ligation. Cells therefore showed enhanced proliferation, survival, and CD80/86 expression, and produced more IgM with a higher frequency of Ab-forming cells. Biochemical analysis revealed that HK-1 alone was sufficient to induce the activation of MAPKs and the expression of Blimp-1 and Xbp-1 in B cells. Nevertheless, costimulation with a known B cell activator resulted in much enhanced phosphorylation of MAPKs and transcriptional activation of Blimp-1 and Xbp-1. Overall, these data support that HK-1 provides an important costimulatory signal for B cell activation, possibly through synergistic activation of the MAPK pathway and induction of transcription factors critical for plasmacytic differentiation.

Tachykinin receptor assays

Described in this unit are methods for obtaining, preparing, and testing smooth muscle preparations bearing tachykinin receptors to study the agonist or antagonist properties of test compounds. Concentration-response curves to agonists are constructed to measure their ability to produce smooth muscle contractions and thus evaluate the potency and efficacy of the agonists. Antagonists are tested for their ability to shift the agonist concentration-response curve and to calculate their potency. Two different protocols are described for each of the three tachykinin receptors (NK(1), NK(2), and NK(3)). The NK(1) receptor assays use guinea pig ileum longitudinal muscle myenteric plexus (GPI) and rat urinary bladder (RUB), the NK(2) receptor assays use isolated endothelium-deprived rabbit pulmonary artery (RPA) and hamster trachea (HT), and the NK(3) receptor assays use GPI and rat portal vein (RPV).

Human hemokinin-1 and human hemokinin-1(4-11), mammalian tachykinin peptides, suppress proliferation and induce differentiation in HL-60 cells

Human hemokinin-1 (h HK-1) and its truncated form h HK-1(4-11) are mammalian tachykinin peptides encoded by the TAC4 gene identified in human, and the biological functions of these peptides have not been well investigated. The tachykinins have shown immuno-regulatory activities in humans. In the present study, we investigated the effects of h HK-1 and h HK-1(4-11) on the proliferation and differentiation of a human promyelocyte leukemia cell line, HL-60. It is noteworthy that h HK-1 (1-300muM) displayed inhibitory effects on the proliferation of HL-60 cells in a dose- and time-dependent manner. The effect of suppressing proliferation induced by these peptides was accompanied by an accumulation of cell cycle in the S phase. Moreover, this peptide induced differentiation of HL-60 cells by significantly increasing the NBT-reduction activity. The effects induced by h HK-1(4-11) on HL-60 cells were similar to that of h HK-1, indicating that it is the active fragment of h HK-1. However these effects induced by h HK-1 or h HK-1(4-11) were not antagonized by the NK(1) receptor antagonist SR140333 or the NK(2) receptor antagonist SR48968. All the results indicated that h HK-1 and h HK-1(4-11) were able to significantly inhibit proliferation and induce differentiation and S phase arrest of a human promyelocyte leukemia cell line HL-60, which may not be mediated through the activation of classical tachykinin NK(1) receptors and tachykinin NK(2) receptors. Our observations also implied that h HK-1 and h HK-1(4-11) could act as immunomodulatory factors in cancer chemotherapy.

In vitro characterization of the effects of rat/mouse hemokinin-1 on mouse colonic contractile activity: a comparison with substance P

Rat/mouse hemokinin-1 (r/m HK-1) has been identified as a member of the tachykinin family and its effect in colonic contractile activity remains unknown. We investigated the effects and mechanisms of actions of r/m HK-1 on the mouse colonic contractile activity in vitro by comparing it with that of substance P (SP). R/m HK-1 induced substantial contractions on the circular muscle of mouse colon. The maximal contractile responses to r/m HK-1 varied significantly among proximal-, mid- and distal-colon, suggesting that the action of r/m HK-1 was region-specific in mouse colon. The contractile response induced by r/m HK-1 is primarily via activation of tachykinin NK(1) receptors leading to activation of cholinergic excitatory pathways and with a minor contribution of NK(2) receptors, which may be on the smooth muscle itself. A direct action on colonic smooth muscles may be also involved. In contrast, SP induced biphasic colonic responses (contractile and relaxant responses) on the circular muscle, in which the contractile action of SP was equieffective with r/m HK-1. SP exerted its contractile effect predominantly through neural and muscular tachykinin NK(1) receptors, but unlike r/m HK-1 did not appear to act via NK(2) receptors. The relaxation induced by SP was largely due to release of nitric oxide (NO) produced via an action on neural NK(1) receptors. These results indicate that the receptors and the activation properties involved in r/m HK-1-induced mouse colonic contractile activity are different from those of SP.

Regulatory mechanisms in the differential expression of Hemokinin-1

Hemokinin-1, encoded by the TAC4 gene, is the most recent addition to the tachykinin family. Although most closely related to the neuropeptide Substance P, Hemokinin-1 distinguishes itself from other tachykinins by its predominantly non-neuronal expression pattern. Its expression in T and B lymphocytes, macrophages, and dendritic cells points to an important role for Hemokinin-1 in the immune system. To seek reasons for its preferential expression in the immune system and ultimately to provide clues to its function, we investigated the molecular mechanisms driving the differential expression pattern of this unique tachykinin. Our study provides the first analysis of the promoter region of the TAC4 gene, which reveals regulatory mechanism different from the Substance P promoter. We demonstrate for the first time that Hemokinin-1 initiates transcription from multiple start sites through a TATA-less promoter. Conservation of the 5' non-coding region indicates the importance of the upstream regulatory region in directing expression of Hemokinin-1 in specific cell types, during cell differentiation and activation. Furthermore, NFkappaB, a transcription factor important in the activation of immune cells was shown to be involved in promoting increased TAC4 transcription during PMA induction of a T cell line. Our studies reveal that Hemokinin-1 is regulated by a unique transcription regulation system that likely governs its differential expression pattern and suggests a role for Hemokinin-1 distinct from Substance P.

Functional characterisation of hemokinin-1 in mouse uterus

The preprotachykinin gene Tac4 expressed in murine uterus and placenta is thought to encode a peptide RSRTRQFYGLM-NH(2), mouse hemokinin 1. We have examined the uterotonic effects of mouse hemokinin 1 and its N-terminally truncated analogue, mouse hemokinin 1(2-11) on mouse uterus. Mouse hemokinin 1(2-11) was equieffective with but slightly less potent than substance P in tissues from non-pregnant Swiss mice. On myometrium from Balb C mice primed with oestrogen the positions of concentration-response curves to substance P and the mouse hemokinins were similar to those of neurokinin A, but the maximum responses were lower. The tachykinin NK(1) receptor antagonist, 1-{2-(3, 4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl) piperidin-3-yl]ethyl}-4phenyl-1-azonia-bicyclo[2.2.2]octane (SR 140333), reduced the effects of the agonists in tissues from both groups of mice. In myometria from late pregnant (Days 17-18) Balb C mice the responses to mouse hemokinin 1(2-11) were less potent than in those from oestrogen-primed mice. Human hemokinin 1, the human orthologue of mouse hemokinin 1, was more effective than mouse hemokinin 1(2-11), while endokinin D was inactive. Mouse hemokinin 1 effects were blocked by SR 140333 alone and in combination with ((S)-N-methyl-N[4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl]benzamide (SR 48968) but not by SR 48968 alone. Thus the mouse hemokinins are tachykinin NK(1) receptor-preferring uterotonic agonists in non-pregnant mice but lack action at the myometrial tachykinin NK(2) receptors present in late pregnant mice.

Cardiovascular responses to intravenous administration of human hemokinin-1 and its truncated form hemokinin-1(4-11) in anesthetized rats

Human hemokinin-1 and its carboxy-terminal fragment human hemokinin-1(4-11) have been recently identified as the members of the tachykinin family. The peripheral cardiovascular effects of these two tachykinin peptides were investigated in anesthetized rats. Lower doses of human hemokinin-1 (0.1-3 nmol/kg) injected intravenously (i.v.) induced depressor response, whereas higher doses (10 and 30 nmol/kg) caused biphasic (depressor and pressor) responses. The depressor response is primarily due to the action on endothelial tachykinin NK(1) receptor to release endothelium-derived relaxing factor (NO) and vagal reflex was absent in this modulation. The pressor response is mediated through the activation of tachykinin NK(1) receptor to release catecholamines from sympathetic ganglia and adrenal medulla. Moreover, human hemokinin-1 injected i.v. produced a dose-dependent tachycardia response along with blood pressure responses and the activation of sympathetic ganglia and adrenal medulla are involved in the tachycardia response. Human hemokinin-1(4-11) only lowered mean arterial pressure dose-dependently (0.1-30 nmol/kg) and the mechanisms involved in the depressor response are similar to that of human hemokinin-1. Additionally, human hemokinin-1(4-11) could also produce tachycardia response dose-dependently and the mechanisms involved in the tachycardia response are similar to that of human hemokinin-1 except that bilateral adrenalectomy could not affect the tachycardia markedly, indicating that the tachycardia induced by human hemokinin-1(4-11) is primarily due to the stimulation of sympathetic ganglia. In a word, to a certain extent, human hemokinin-1(4-11) is the active fragment of human hemokinin-1, however, the differences between human hemokinin-1 and hemokinin-1(4-11) involved in the effects of cardiovascular system suggest that the divergent amino acid residues at the N-terminus of human hemokinin-1 produced different activation properties for tachykinin NK(1) receptor.

Co-regulated decrease of Neurokinin-1 receptor and Hemokinin-1 gene expression in monocytes and macrophages after activation with pro-inflammatory cytokines

Hemokinin-1 (HK-1), a potent ligand for the Neurokinin-1 receptor (NK-1) is thought to play a role in the immune system. To investigate the regulation of this receptor-ligand pair, we examined the effects of pro-inflammatory cytokines on their expression in the monocyte/macrophage cell lines Wehi-3 and RAW264.7. We demonstrate co-expression of NK-1 and HK-1 mRNA in both lines, as well as functional NK-1 receptor protein in Wehi-3 cells. Stimulation with IFN-gamma, IL-1beta and TNF-alpha markedly decreased NK-1 and HK-1 mRNA as well as NK-1 receptor protein, which coincided with monocytic differentiation. A co-regulated decrease could also be observed in differentiating primary bone marrow macrophages, suggesting that this receptor-ligand pair may be controlled by cytokine networks and may serve a developmental role in the immune system.

Cardiovascular responses to rat/mouse hemokinin-1, a mammalian tachykinin peptide: systemic study in anesthetized rats

Rat/mouse hemokinin-1 is a mammalian tachykinin peptide whose biological functions have not been well characterized. In the present study, an attempt has been made to investigate the effect and mechanism of action of rat/mouse hemokinin-1 on systemic arterial pressure after intravenous (i.v.) injections in anesthetized rats by comparing it with that of substance P. Our data showed that injection of rat/mouse hemokinin-1 (0.1, 0.3, 1, 3 and 10 nmol/kg) lowered systemic arterial pressure dose-dependently. This effect was significantly blocked by pretreatment with SR140333 (a selective tachykinin NK1 receptor antagonist) and the NO synthase inhibitor L-NAME (Nomega-nitro-L-arginine methyl ester hydrochloride), respectively, but was not affected by bilateral vagotomy or the muscarinic receptor blocker atropine. Compared to rat/mouse hemokinin-1, a dose of 3 nmol/kg of substance P caused biphasic changes in systemic arterial pressure (depressor and pressor responses). The results suggest that the mechanism of the depressor response caused by substance P was similar to rat/mouse hemokinin-1 in that it was inhibited by SR140333 and L-NAME, respectively, but that there was a component of the cardiovascular change induced by rat/mouse hemokinin-1 (but not substance P) that was attenuated by SR48968 (a selective tachykinin NK2 receptor antagonist). The depressor response induced by rat/mouse hemokinin-1 (i.v.) might be explained primarily by the action on endothelial tachykinin NK1 receptors to release endothelium-derived relaxing factor (NO) and this effect was not affected by vagal components. In addition, rat/mouse hemokinin-1 could not induce the pressor response through stimulation of sympathetic ganglion like substance P in anesthetized rats.

Characterization of the gene structures, precursor processing and pharmacology of the endokinin peptides

The endokinins represent several species-divergent and peripherally located mammalian tachykinins (hemokinin-1 in mouse and rat, endokinin-1 in rabbit and endokinins A and B in humans) and also the tachykinin gene-related peptides. These peptides are all encoded on the preprotachykinin 4 (TAC4) gene. Their complementary DNA sequences, gene structures and expression profiles have been determined from a number of different mammalian species. They are all flanked by adjacent upstream and downstream dibasic cleavage sites in their respective precursor proteins, except for human EKA/B that instead possesses a N-terminal monobasic cleavage site. Evidence for differential processing in the periphery at the N-terminal cleavage site of the tachykinins could explain why in humans the evolutionary pressure to maintain the N-terminal dibasic cleavage site of EKA/B has been lost. Furthermore, the TAC4 encoded tachykinins all exhibit a remarkable selectivity and potency for the highly species conserved tachykinin NK(1) receptor, similar to that of substance P. Particular consideration is also given to the potential interactions of the endokinins with the short NK(1) receptor isoform and to speculation of whether there could be an "endokinin-sensitive" NK(1) binding site.

Regulation of the stimulant actions of neurokinin a and human hemokinin-1 on the human uterus: a comparison with histamine

Regulation of the contractile effects of tachykinins and histamine on the human uterus was investigated with biopsy sections of the outer myometrial layer. The effects of neurokinin A (NKA) and human hemokinin-1 (hHK-1) in tissues from pregnant but not from nonpregnant women were enhanced by the inhibition of neprilysin. The effects of NKA and eledoisin were blocked by the NK2 receptor antagonist SR 48968 but not by the NK1 receptor antagonist SR 140333 in tissues from both groups of women. Human HK-1 acted as a partial agonist blocked by SR 48968 and, to a lesser extent, by SR 140333; endokinin D was inactive. In tissues from pregnant women, responses to high potassium-containing Krebs solution were 2-3-fold higher than those from nonpregnant women. Mepyramine-sensitive maximal responses to histamine were similarly enhanced. The absolute maximum responses to NKA and its stable NK2 receptor-selective analogue, [Lys5MeLeu9Nle10]NKA(4-10), were increased in pregnancy, but their efficacies relative to potassium responses were decreased. Tachykinin potencies were lower in tissues from pregnant women than in those from nonpregnant women. These data 1) show for the first time that hHK-1 is a uterine stimulant in the human, 2) confirm that the NK2 receptor is predominant in mediating tachykinin actions on the human myometrium, and 3) indicate that mammalian tachykinin effects are tightly regulated during pregnancy in a manner that would negate an inappropriate uterotonic effect. The potencies of these peptides in tissues from nonpregnant women undergoing hysterectomy are consistent with their possible role in menstrual and menopausal disorders.

Rat/mouse hemokinin-1, a mammalian tachykinin peptide, markedly potentiates the antinociceptive effects of morphine administered at the peripheral and supraspinal level

Rat/mouse hemokinin 1 (r/m HK-1) is a mammalian tachykinin peptide whose biological functions are not fully understood. Our recent report showed that i.c.v. administration of r/m HK-1 could produce dose- and time-related antinociceptive effect at nanomole concentration, and naloxone significantly antagonized this effect. Thus, we provide indirect evidence favoring a role of NK1 supraspinal receptors in the inhibitory control of descending pain pathways, a role that seems to partially involve the activation of the endogenous opioid systems. Based on this report, the present study was conducted to further investigate the direct functional interaction between supraspinal tachykinin (r/m HK-1) and opioid systems. The results demonstrate that i.c.v. administration of r/m HK-1 (5 nmol/kg) could significantly potentiate the antinociceptive effects of morphine which was injected at peripheral and supraspinal level. These antinociceptive effects were blocked by prior treatment with the classical opioid receptors antagonist naloxone, indicating that the potentiated analgesic response is mediated by opioid-responsive neurons. Consistent with previous biochemical data, a likely mechanism underlying the peptide-mediated enhancement of opioid analgesia may center on the ability of r/m HK-1 to release endogenous opioid peptides. We suggest that there may be a cascade amplification mechanism in pain modulation when the two agents were co-administrated. The synergistic analgesic relationship of morphine and r/m HK-1 established here supports the hypothesis that supraspinal tachykinin and peripheral and central opioid systems have a direct functional interaction in the modulation of local nociceptive responses.

Neuroimmunoendocrine circuitry of the ‘brain-skin connection’

The skin offers an ideally suited, clinically relevant model for studying the crossroads between peripheral and systemic responses to stress. A 'brain-skin connection' with local neuroimmunoendocrine circuitry underlies the pathogenesis of allergic and inflammatory skin diseases, triggered or aggravated by stress. In stressed mice, corticotropin-releasing hormone, nerve growth factor, neurotensin, substance P and mast cells are recruited hierarchically to induce neurogenic skin inflammation, which inhibits hair growth. The hair follicle is both a target and a source for immunomodulatory stress mediators, and has an equivalent of the hypothalamus-pituitary-adrenal axis. Thus, the skin and its appendages enable the study of complex neuroimmunoendocrine responses that peripheral tissues launch upon stress exposure, as a basis for identifying new targets for therapeutic stress intervention.

From the brain-skin connection: the neuroendocrine-immune misalliance of stress and itch

Perceived stress has long been allied with disturbances of the dynamic equilibrium established between the nervous, endocrine and immune systems, thus triggering or aggravating disease manifestation. Several common skin diseases are now acknowledged to be worsened by psychological stress, particularly immunodermatoses such as atopic dermatitis, psoriasis, seborrheic eczema, prurigo nodularis, lichen planus, chronic urticaria, alopecia areata and pruritus sine materia. Itch (pruritus) is perhaps the most common symptom associated with a majority of these inflammatory skin diseases, and acute as well as chronic stress perceptions are recognized to trigger or enhance pruritus. A wealth of mediators released systemically or locally in the skin in response to stress increase sensory innervation, upregulate the production of other pruritogenic agents, perpetuate (neurogenic) inflammation and lower the itch threshold. In the present review, we explore recent frontiers in both stress and pruritus research and portray the perpetuation of chronic skin inflammation and itch as a neuroendocrine-immune 'misalliance'. We argue that key candidate molecules of the stress response with strong pruritogenic potential, such as nerve growth factor, corticotropin-releasing hormone and substance P, and mast cells, which may be considered as 'central cellular switchboards of pruritogenic inflammation', need to be further explored systematically in order to develop more effective therapeutic combination strategies for itch management in chronic, stress-vulnerable inflammatory skin diseases.

Effect of intrathecal administration of hemokinin-1 on the withdrawal response to noxious thermal stimulation of the rat hind paw

Hemokinin-1 (HK-1) is a new peptide described as a member of the tachykinin family. HK-1 has biological effects similar to substance P (SP), a representative of the tachykinin family, following central administration. However, the biological function of HK-1 at the spinal level has not been well characterized. Thus, we investigated the effect of intrathecal administration of HK-1 by comparing it with that of SP. Intrathecal administration of HK-1 as well as SP at 10(-3) M caused pain-related behavior such as scratching. The scratching by HK-1 administration was inhibited by pretreatment with an antagonist of substance P receptor. In addition, SP (10(-8)-10(-6) M) decreased the latency of the withdrawal response of the hind paw to noxious thermal stimulation 20-30 min after intrathecal administration, whereas administration of HK-1 had little effect on this response. These results suggest that there may exist a proper receptor related to HK-1.

Quantification of hemokinin-1 peptide production and secretion from mouse B cells

Hemokinin-1 is a recent addition to the family of mammalian tachykinins and is thought to play an important role in B cell and T cell lymphopoiesis. The mRNA coding for this peptide was expressed in some B lymphocyte cell lines including 70Z/3.12, ABE-8.1/2, and RAW8.1 cells, suggesting the possibility that hemokinin-1 may function in an autocrine or paracrine manner in these cells. Therefore, we quantified secretion of this peptide from the 70Z/3.12 cell line expressing hemokinin-1 mRNA. Despite a sensitive radioimmunoassay, we were surprised to find that hemokinin-1 secretion from confluent cells was below the level of detection of this assay. Furthermore, cell lysates routinely demonstrated a low or undetectable immunoreactive peptide. Collectively these studies show a limited production of hemokinin-1 peptide by transformed B cells.

The role of mast cells in migraine pathophysiology

Mast cells are critical players in allergic reactions, but they have also been shown to be important in immunity and recently also in inflammatory diseases, especially asthma. Migraines are episodic, typically unilateral, throbbing headaches that occur more frequently in patients with allergy and asthma implying involvement of meningeal and/or brain mast cells. These mast cells are located perivascularly, in close association with neurons especially in the dura, where they can be activated following trigeminal nerve, as well as cervical or sphenopalatine ganglion stimulation. Neuropeptides such as calcitonin gene-related peptide (CGRP), hemokinin A, neurotensin (NT), pituitary adenylate cyclase activating peptide (PACAP), and substance P (SP) activate mast cells leading to secretion of vasoactive, pro-inflammatory, and neurosensitizing mediators, thereby contributing to migraine pathogenesis. Brain mast cells can also secrete pro-inflammatory and vasodilatory molecules such as interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF), selectively in response to corticotropin-releasing hormone (CRH), a mediator of stress which is known to precipitate or exacerbate migraines. A better understanding of brain mast cell activation in migraines would be useful and could lead to several points of prophylactic intervention.

New challenges in the study of the mammalian tachykinins

There is an expanding repertoire of mammalian tachykinins produced by a variety of tachykinin genes, gene splicing events and peptide processing. Novel tachykinin-binding molecules/receptors are proposed, but only, three tachykinin receptors are identified with certainty. The question remains - do more tachykinin receptors exist or is there just the need to reappraise our understanding of the known receptors? The tachykinin NK1 receptor, the preferred receptor for both substance P and the peripheral SP-like endokinins, exists in several tissue-specific conformations and isoforms and may provide some clues. This review addresses recent advances in this exciting field and raises challenging new concepts.

Hemokinin-1 has Substance P-like function in U-251 MG astrocytoma cells: A pharmacological and functional study

Substance P (SP) triggers responses in astrocytoma cells, which are considered important for proliferation and neuroimmunomodulatory activity. In this study, we compared the effects of SP with those of the novel tachykinin Hemokinin-1 (HK-1) in the human astrocytoma cell line U-251 MG. We show that U-251 MG cells express high levels of Neurokinin-1 (NK-1) receptors. The binding affinities of 125I-SP and 125I-mHK-1 to these receptors were in a similar, subnanomolar range. HK-1 and SP stimulated Ca2+ mobilization and induced increased cytokine mRNA expression. A specific NK-1 receptor antagonist blocked the observed effects. We conclude that there are no qualitative differences in SP and HK-1-evoked responses, suggesting that both peptides act through NK-1 receptors in U-251 MG cells. Moreover, we show TAC4 mRNA expression in gliomas, indicating a possible involvement of HK-1 in glioma biology.

Development of an automated in vitro selection protocol to obtain RNA-based aptamers: identification of a biostable substance P antagonist

We have developed an automated SELEX (Systematic Evolution of Ligands by EXponential Enrichment) process that allows the execution of in vitro selection cycles without any direct manual intervention steps. The automated selection protocol is designed to provide for high flexibility and versatility in terms of choice of buffers and reagents as well as stringency of selection conditions. Employing the automated SELEX process, we have identified RNA aptamers to the mirror-image configuration (d-peptide) of substance P. The peptide substance P belongs to the tachykinin family and exerts various biologically important functions, such as peripheral vasodilation, smooth muscle contraction and pain transmission. The aptamer that was identified most frequently was truncated to the 44mer SUP-A-004. The mirror-image configuration of SUP-A-004, the so-called Spiegelmer, has been shown to bind to naturally occurring l-substance P displaying a K_d of 40 nM and to inhibit (IC₅₀ of 45 nM) l-substance P-mediated Ca²⁺ release in a cell culture assay.

Functional and molecular characterization of tachykinins and tachykinin receptors in the mouse uterus

The aim of this study was to analyze the function and expression of tachykinins, tachykinin receptors, and neprilysin (NEP) in the mouse uterus. A previous study showed that the uterotonic effects of substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) in estrogen-treated mice were mainly mediated by the tachykinin NK1 receptor. In the present work, further contractility studies were undertaken to determine the nature of the receptors mediating responses to tachykinins in uteri of late pregnant mice. Endpoint and real-time quantitative RT-PCR were used to analyze the expression of the genes that encode the tachykinins SP/NKA, NKB, and hemokinin-1 (HK-1) (Tac1, Tac2, and Tac4); and the genes that encode tachykinin NK1 (Tacr1), NK2 (Tacr2), and NK3 (Tacr3) receptors in uteri from pregnant and nonpregnant mice. The data show that the mRNAs of tachykinins (particularly NKB and HK-1), tachykinin receptors, and NEP are locally expressed in the mouse uterus, and their expression changes during the estrous cycle and during pregnancy. The tachykinin NK1 receptor is the predominant tachykinin receptor in the nonpregnant and early pregnant mouse and may mediate tachykinin-induced uterine contractions in the nonpregnant mouse. The tachykinin NK2 receptor is predominant in the late pregnant mouse and is the main receptor mediating uterotonic responses to tachykinins at late pregnancy. The tachykinin NK3 receptor is expressed in considerable amounts only in uteri from nonpregnant diestrous animals, and its physiological significance remains to be clarified.

Mechanisms of selection mediated by interleukin-7, the preBCR, and hemokinin-1 during B-cell development

Many of the stromal-derived signals and factors that regulate B lymphopoiesis have been identified. We review recent evidence from our laboratory that shows that there are at least three phases during B-cell development when cells direct their own maturation, independent of stromal cells. Following the expression of the preB-cell receptor (preBCR), cells acquire the ability to proliferate in low levels of interleukin-7 (IL-7), which acts as a self-selecting mechanism to expand cells that have successfully expressed a preBCR in environments that are non-permissive to preBCR- cells. Second, the preBCR is required for a contact-mediated event between B-cell progenitors. Disruption at this stage prevents the further maturation of progenitors to the lipopolysaccharide (LPS)-responsive stage. Finally, the transition from IL-7 receptor to mature antigen receptor-based signaling is enhanced by a novel member of the tachykinin family, hemokinin-1. This series of maturation, survival, and differentiation signals is generated by B-lineage cells as they progress through developmental checkpoints on the way to becoming functionally mature cells.

Tachykinins and tachykinin receptors: a growing family

The peptides of the tachykinin family are widely distributed within the mammalian peripheral and central nervous systems and play a well-recognized role as excitatory neurotransmitters. Currently, the concept that tachykinins act exclusively as neuropeptides is being challenged, since the best known members of the family, substance P, neurokinin A and neurokinin B, are also present in non-neuronal cells and in non-innervated tissues. Moreover, the recently cloned mammalian tachykinins hemokinin-1 and endokinins are primarily expressed in non-neuronal cells, suggesting a widespread distribution and important role for these peptides as intercellular signaling molecules. The biological actions of tachykinins are mediated through three types of receptors denoted NK(1), NK(2) and NK(3) that belong to the family of G protein-coupled receptors. The identification of additional tachykinins has reopened the debate of whether more tachykinin receptors exist. In this review, we summarize the current knowledge of tachykinins and their receptors.

T-cell developmental blockage by tachykinin antagonists and the role of hemokinin 1 in T lymphopoiesis

Hemokinin 1 (HK-1) is a new member of the tachykinin peptide family that is expressed in hematopoietic cells. Recent reports studying mouse, rat, and human orthologs of HK-1 demonstrate a broader distribution than originally reported. Our previous studies demonstrated that HK-1, by promoting proliferation, survival, and possibly maturation of B-cell precursors, plays an important role in B lymphopoiesis. Here we present data showing that HK-1 also influences T-cell development at a similar stage of differentiation. This peptide enhanced the proliferation of T-cell precursors and increased the number of thymocytes in fetal thymus organ cultures (FTOCs). Tachykinin antagonists, on the other hand, greatly reduced the cellularity of thymi both in vivo and in vitro. The major reduction occurred in the CD4/CD8 double-positive (DP) cells and the CD44-CD25+ subset of the CD4/CD8 double-negative (DN) cells. Of note, these populations also express HK-1, raising the possibility of autocrine or paracrine pathways influencing T-cell development as we previously reported for B-cell development. Consistent with this, the detrimental effect of tachykinin antagonists could be partially overcome with exogenous HK-1 peptide.

Centrally administered hemokinin-1 (HK-1), a neurokinin NK1 receptor agonist, produces substance P-like behavioral effects in mice and gerbils

Hemokinin-1 (HK-1) is a recently described mouse tachykinin peptide whose biological functions are not fully understood. To date, a unique receptor for HK-1 has not been identified. Recent studies suggest HK-1 may have a role in immunological functions, but there has been little characterization of HK-1's effects in the central nervous system (CNS). In the present studies, we confirm that HK-1 is an endogenous agonist at all of the known tachykinin receptors, and is selective for the NK1 receptor over the NK2 and NK3 subtypes. CHO cells transfected with the human NK1 receptor released intracellular calcium in response to HK-1. In addition, HK-1 competed with substance P (SP) for binding to mouse NK1 and human NK1 receptors. In vivo central administration of HK-1 to gerbils and mice induced foot-tapping and scratching behaviors, respectively, similar to those observed following central administration of SP or the NK1 receptor agonist, GR-73632. Furthermore, these behavioral effects were blocked by the selective NK1 receptor antagonist, MK-869. Finally, a comprehensive expression analysis of HK-1 demonstrated that HK-1 mRNA is much more broadly expressed than previously reported with expression observed in many brain regions. Together these data demonstrate that HK-1 is a functional agonist at NK1 receptors and suggest that HK-1 may function both centrally and peripherally.

Characterization of the endokinins: human tachykinins with cardiovascular activity

We report four human tachykinins, endokinins A, B, C, and D (EKA-D), encoded from a single tachykinin precursor 4 gene that generates four mRNAs (alpha, beta, gamma, and delta). Tachykinin 4 gene expression was detected primarily in adrenal gland and in the placenta, where, like neurokinin B, significant amounts of EKB-like immunoreactivity were detected. EKA/B 10-mers displayed equivalent affinity for the three tachykinin receptors as substance P (SP), whereas a 32-mer N-terminal extended form of EKB was significantly more potent than EKA/B or SP. EKC/D, which possess a previously uncharacterized tachykinin motif, FQGLL-NH(2), displayed low potency. EKA/B displayed identical hemodynamic effects to SP in rats, causing short-lived falls in mean arterial blood pressure associated with tachycardia, mesenteric vasoconstriction, and marked hindquarter vasodilatation. Thus, EKA/B could be the endocrineparacrine agonists at peripheral SP receptors and there may be as yet an unidentified receptor(s) for EKC/D.

PepPat, a pattern-based oligopeptide homology search method and the identification of a novel tachykinin-like peptide

PepPat, a hybrid method that combines pattern matching with similarity scoring, is described. We also report PepPat's application in the identification of a novel tachykinin-like peptide. PepPat takes as input a query peptide and a user-specified regular expression pattern within the peptide. It first performs a database pattern match and then ranks candidates on the basis of their similarity to the query peptide. PepPat calculates similarity over the pattern spanning region, enhancing PepPat's sensitivity for short query peptides. PepPat can also search for a user-specified number of occurrences of a repeated pattern within the target sequence. We illustrate PepPat's application in short peptide ligand mining. As a validation example, we report the identification of a novel tachykinin-like peptide, C14TKL-1, and show it is an NK1 (neuokinin receptor 1) agonist whose message is widely expressed in human periphery.

AVAILABILITY

PepPat is offered online at: http://peppat.cbi.pku.edu.cn.