Involvement of cAMP-dependent protein kinase and pertussis toxin-sensitive G-proteins in CGRP mediated JNK activation in human neuroblastoma cell line

Control of myeloid cell functions by nociceptors

The immune system has evolved to protect the host from infectious agents, parasites, and tumor growth, and to ensure the maintenance of homeostasis. Similarly, the primary function of the somatosensory branch of the peripheral nervous system is to collect and interpret sensory information about the environment, allowing the organism to react to or avoid situations that could otherwise have deleterious effects. Consequently, a teleological argument can be made that it is of advantage for the two systems to cooperate and form an “integrated defense system” that benefits from the unique strengths of both subsystems. Indeed, nociceptors, sensory neurons that detect noxious stimuli and elicit the sensation of pain or itch, exhibit potent immunomodulatory capabilities. Depending on the context and the cellular identity of their communication partners, nociceptors can play both pro- or anti-inflammatory roles, promote tissue repair or aggravate inflammatory damage, improve resistance to pathogens or impair their clearance. In light of such variability, it is not surprising that the full extent of interactions between nociceptors and the immune system remains to be established. Nonetheless, the field of peripheral neuroimmunology is advancing at a rapid pace, and general rules that appear to govern the outcomes of such neuroimmune interactions are beginning to emerge. Thus, in this review, we summarize our current understanding of the interaction between nociceptors and, specifically, the myeloid cells of the innate immune system, while pointing out some of the outstanding questions and unresolved controversies in the field. We focus on such interactions within the densely innervated barrier tissues, which can serve as points of entry for infectious agents and, where known, highlight the molecular mechanisms underlying these interactions.

Calcitonin Gene-Related Peptide (CGRP) and Cluster Headache

Cluster headache (CH) is a severe primary headache with a prevalence of 1/1000 individuals, and a predominance in men. Calcitonin gene-related peptide (CGRP) is a potent vasodilator, originating in trigeminal neurons and has a central role in CH pathophysiology. CGRP and the CGRP receptor complex have recently taken center stage as therapeutic targets for primary headaches, such as migraine. Multiple CGRP and CGRP receptor monoclonal antibodies, as well as small molecule antagonists (gepants) are on their way constituting a new frontier of migraine and possibly CH medication. During a CH attack, there is an activation of the trigeminal-autonomic reflex with the release of CGRP, and inversely if CGRP is administered to a CH patient in an active disease phase, it triggers an attack. Increased levels of CGRP have been found in ipsilateral jugular vein blood during the active phase of CH. This process is hypothesized to have a key role in the intense pain perception and in the associated distinctive vasodilation. So far, clinical tests of CGRP antibodies have been inconclusive in CH patients. This review summarizes the current state of knowledge on the role of CGRP in CH pathology, and as a target for future treatments.

Protective Role of α-Calcitonin Gene-Related Peptide in Cardiovascular Diseases

α-Calcitonin gene-related peptide (α-CGRP) is a regulatory neuropeptide of 37 amino acids. It is widely distributed in the central and peripheral nervous system, predominantly in cell bodies of the dorsal root ganglion (DRG). It is the most potent vasodilator known to date and has inotropic and chronotropic effects. Using pharmacological and genetic approaches, our laboratory and other research groups established the protective role of α-CGRP in various cardiovascular diseases such as heart failure, experimental hypertension, myocardial infarction, and myocardial ischemia/reperfusion injury (I/R injury). α-CGRP acts as a depressor to attenuate the rise in blood pressure in three different models of experimental hypertension: (1) DOC-salt, (2) subtotal nephrectomy-salt, and (3) L-NAME-induced hypertension during pregnancy. Subcutaneous administration of α-CGRP lowers the blood pressure in hypertensive and normotensive humans and rodents. Recent studies also demonstrated that an α-CGRP analog, acylated α-CGRP, with extended half-life (~7 h) reduces blood pressure in Ang-II-induced hypertensive mouse, and protects against abdominal aortic constriction (AAC)-induced heart failure. Together, these studies suggest that α-CGRP, native or a modified form, may be a potential therapeutic agent to treat patients suffering from cardiac diseases.

Possible role of calcitonin gene-related peptide in trigeminal modulation of glomerular microcircuits of the rodent olfactory bulb

Chemosensation in the mammalian nose comprises detection of odorants, irritants and pheromones. While the traditional view assigned one distinct sub-system to each stimulus type, recent research has produced a more complex picture. Odorants are not only detected by olfactory sensory neurons but also by the trigeminal system. Irritants, in turn, may have a distinct odor, and some pheromones are detected by the olfactory epithelium. Moreover, it is well established that irritants change odor perception and vice versa. A wealth of psychophysical evidence on olfactory-trigeminal interactions in humans contrasts with a paucity of structural insight. In particular, it is unclear whether the two systems communicate just by sharing stimuli, or whether neuronal connections mediate cross-modal signaling. One connection could exist in the olfactory bulb that performs the primary processing of olfactory signals and receives trigeminal innervation. In the present study, neuroanatomical tracing of the mouse ethmoid system illustrates how peptidergic fibers enter the glomerular layer of the olfactory bulb, where local microcircuits process and filter the afferent signal. Biochemical assays reveal release of calcitonin gene-related peptide from olfactory bulb slices and attenuation of cAMP signaling by the neuropeptide. In the non-stimulated tissue, the neuropeptide specifically inhibited the basal activity of calbindin-expressing periglomerular interneurons, but did not affect the basal activity of neurons expressing calretinin, parvalbumin, or tyrosine hydroxylase, nor the activity of astrocytes. This study represents a first step towards understanding trigeminal neuromodulation of olfactory-bulb microcircuits and provides a working hypothesis for trigeminal inhibition of olfactory signal processing. This article is protected by copyright. All rights reserved.

Receptor Activity-modifying Protein-directed G Protein Signaling Specificity for the Calcitonin Gene-related Peptide Family of Receptors

The calcitonin gene-related peptide (CGRP) family of G protein-coupled receptors (GPCRs) is formed through the association of the calcitonin receptor-like receptor (CLR) and one of three receptor activity-modifying proteins (RAMPs). Binding of one of the three peptide ligands, CGRP, adrenomedullin (AM), and intermedin/adrenomedullin 2 (AM2), is well known to result in a Gα_s-mediated increase in cAMP. Here we used modified yeast strains that couple receptor activation to cell growth, via chimeric yeast/Gα subunits, and HEK-293 cells to characterize the effect of different RAMP and ligand combinations on this pathway. We not only demonstrate functional couplings to both Gα_s and Gα_q but also identify a Gα_i component to CLR signaling in both yeast and HEK-293 cells, which is absent in HEK-293S cells. We show that the CGRP family of receptors displays both ligand- and RAMP-dependent signaling bias among the Gα_s, Gα_i, and Gα_q/11 pathways. The results are discussed in the context of RAMP interactions probed through molecular modeling and molecular dynamics simulations of the RAMP-GPCR-G protein complexes. This study further highlights the importance of RAMPs to CLR pharmacology and to bias in general, as well as identifying the importance of choosing an appropriate model system for the study of GPCR pharmacology.

Calcitonin gene-related peptide mediates an inflammatory response in Schwann cells via cAMP-dependent ERK signaling cascade

AIMS

Calcitonin gene-related peptides (CGRP), an endogenous neuropeptide, play an important role in the development of neuroinflammation by acting upon its receptor. The CGRP receptor immunoreactivity was identified on Schwann cells. However the effects of CGRP on Schwann cells are unknown and the exact signaling mechanisms associated with CGRP receptor activation related to Schwann cells inflammatory responses are not well understood. We investigated the effect of CGRP on CGRP receptor activation mediates a proinflammatory signaling response in Schwann cells.

MAIN METHODS

CGRP-induced ERK-MAPK phosphorylation and proinflammatory cytokines, interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor (TNF-α) expressions were measured by immune blotting. We also used specific antagonist and inhibitors to confirm the exactly signaling pathway including CGRP (8-37), SQ 22536 and H-89.

KEY FINDINGS

Treatment with CGRP demonstrated a significant generation of IL-1β and IL-6 but not in the level of TNF-α. In addition, there was a temporal increase in the activated form of ERK caused by CGRP that was prevented after pretreatment with CGRP (8-37), SQ 22536 and H-89. Furthermore, use of the CGRP (8-37), ERK inhibitor PD 98059, SQ 22536 or H-89 abolished the CGRP mediated increase in IL-1β.

SIGNIFICANCE

This investigation provides evidence for a novel CGRP activation on Schwann cells that mediates inflammatory response by increasing of IL-1β and IL-6 expression. CGRP activates the cAMP-PKA-ERK signaling cascade leading to IL-1β production. These results support the notion that CGRP may play a direct role to initiate inflammatory processes in the peripheral nervous system.

Calcitonin gene-related peptide regulates mitogen-activated protein kinase pathway to decrease transforming growth factor β1-induced hepatic plasminogen activator inhibitor-1 mRNA expression in HepG2 cells

Transforming growth factor (TGF) β1-induced plasminogen activator inhibitor (PAI)-1 is one of factors associated with the development of hepatic fibrosis. Calcitonin gene-related peptide (CGRP) shows hepatoprotective effect during hepatic injuries, including fibrosis. However, the effects of CGRP on PAI-1 expression induced by TGFβ1 are unknown. In this study, we investigated the effect of CGRP on TGFβ1-induced PAI-1 expression and its regulatory mechanisms in HepG2 cells. CGRP inhibited TGFβ1-induced PAI-1 expression. H89, a protein kinase A inhibitor, abolished the inhibition of TGFβ1-induced PAI-1 expression by CGRP. TGFβ1 activated mitogen-activated protein kinase (MAPK), including extracellular signal-regulated kinase, c-jun NH2-terminal kinase, and p38, and this activation was abolished by CGRP. These results show that the CGRP-induced cAMP/PKA activation suppresses activation of MAPK induced by TGFβ1, leading to decreased PAI-1 expression in HepG2 cells.

CGRP in the trigeminovascular system: a role for CGRP, adrenomedullin and amylin receptors?

The neuropeptide calcitonin gene-related peptide (CGRP) is reported to play an important role in migraine. It is expressed throughout the trigeminovascular system. Antagonists targeting the CGRP receptor have been developed and have shown efficacy in clinical trials for migraine. However, no CGRP antagonist is yet approved for treating this condition. The molecular composition of the CGRP receptor is unusual because it comprises two subunits; one is a GPCR, the calcitonin receptor-like receptor (CLR). This associates with receptor activity-modifying protein (RAMP) 1 to yield a functional receptor for CGRP. However, RAMP1 also associates with the calcitonin receptor, creating a receptor for the related peptide amylin but this also has high affinity for CGRP. Other combinations of CLR or the calcitonin receptor with RAMPs can also generate receptors that are responsive to CGRP. CGRP potentially modulates an array of signal transduction pathways downstream of activation of these receptors, in a cell type-dependent manner. The physiological significance of these signalling processes remains unclear but may be a potential avenue for refining drug design. This complexity has prompted us to review the signalling and expression of CGRP and related receptors in the trigeminovascular system. This reveals that more than one CGRP responsive receptor may be expressed in key parts of this system and that further work is required to determine their contribution to CGRP physiology and pathophysiology.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Naratriptan mitigates CGRP1-associated motor neuron degeneration caused by an expanded polyglutamine repeat tract

Spinal and bulbar muscular atrophy (SBMA) is a motor neuron disease caused by the expansion of the CAG triplet repeat within the androgen receptor (AR) gene. Here, we demonstrated that pathogenic AR upregulates the gene encoding calcitonin gene-related peptide α (CGRP1). In neuronal cells, overexpression of CGRP1 induced cellular damage via the activation of the c-Jun N-terminal kinase (JNK) pathway, whereas pharmacological suppression of CGRP1 or JNK attenuated the neurotoxic effects of pathogenic AR. The depletion of CGRP1 inactivated JNK and suppressed neurodegeneration in a mouse model of SBMA. Naratriptan, a serotonin 1B/1D (5-hydroxytryptamine 1B/1D, or 5-HT1B/1D) receptor agonist, decreased CGRP1 expression via the induction of dual-specificity protein phosphatase 1 (DUSP1), attenuated JNK activity and mitigated pathogenic AR-mediated neuronal damage in cellular and mouse SBMA models. These observations suggest that pharmacological activation of the 5-HT1B/1D receptor may be used therapeutically to treat SBMA and other polyglutamine-related neurodegenerative diseases.

Role of calcitonin gene-related peptide in cerebral vasospasm, and as a therapeutic approach to subarachnoid hemorrhage

Calcitonin gene-related peptide (CGRP) is one of the most potent microvascular vasodilators identified to date. Vascular relaxation and vasodilation is mediated via activation of the CGRP receptor. This atypical receptor is made up of a G protein-coupled receptor called calcitonin receptor-like receptor (CLR), a single transmembrane protein called receptor activity-modifying protein (RAMP), and an additional protein that is required for Ga(s) coupling, known as receptor component protein (RCP). Several mechanisms involved in CGRP-mediated relaxation have been identified. These include nitric oxide (NO)-dependent endothelium-dependent mechanisms or cAMP-mediated endothelium-independent pathways; the latter being more common. Subarachnoid hemorrhage (SAH) is associated with cerebral vasoconstriction that occurs several days after the hemorrhage and is often fatal. The vasospasm occurs in 30-40% of patients and is the major cause of death from this condition. The vasoconstriction is associated with a decrease in CGRP levels in nerves and an increase in CGRP levels in draining blood, suggesting that CGRP is released from nerves to oppose the vasoconstriction. This evidence has led to the concept that exogenous CGRP may be beneficial in a condition that has proven hard to treat. The present article reviews: (a) the pathophysiology of delayed ischemic neurologic deficit after SAH (b) the basics of the CGRP receptor structure, signal transduction, and vasodilatation mechanisms and (c) the studies that have been conducted so far using CGRP in both animals and humans with SAH.

Calcitonin gene related peptide (CGRP) inhibits norepinephrine induced apoptosis in cultured rat cardiomyocytes not via PKA or PKC pathways

Evidence showed overrelease of norepinephrine can induce apoptosis in ventricle myocytes. Calcitonin gene related peptide and norepinephrine could be simultaneously up-regulated in early time of acute myocardial ischemia, suggesting a co-participation of calcitonin gene related peptide and norepinephrine in the pathology. In this study, we investigated a potential anti-apoptotic effect of calcitonin gene related peptide on myocardial apoptosis induced by norepinephrine and its link with the protein kinase A (PKA) or protein kinase C (PKC) pathway in cultured neonatal rat cardiomyocytes. Cultured cardiomyocytes were exposed to one of the treatments, separately: (1) 3 ml DMEM culture medium, (2) norepinephrine (10(-5)mol/l), (3) H89 (3 x 10(-5)mol/l), a specific PKA inhibitor, with norepinephrine (10(-5)mol/l), (4) calcitonin gene related peptide at a range of concentrations (10(-9)mol/l, 10(-8)mol/l and 10(-7)mol/l) with norepinephrine (10(-5)mol/l) and (5) calcitonin gene related peptide (10(-8)mol/l) with norepinephrine (10(-5)mol/l)+CGRP(8-7) (10(-7)mol/l), a specific antagonist of calcitonin gene related peptide receptor. Then, apoptosis rate and the activity of PKA and PKC were examined. The dose of norepinephrine induced a marked increase in apoptosis of the myocytes (31+/-2%), compared to the control (17+/-4%, p<0.05). The pro-apoptotic effect of norepinephrine was attenuated by H89 (3 x 10(-5)mol/l) or by calcitonin gene related peptide which could be completely reversed by CGRP(8-37). The activities of PKA and PKC were increased by norepinephrine but no difference in the activities of PKA and PKC was detected in the presence and absence of co-treatment with calcitonin gene related peptide (10(-8)mol/l). Calcitonin gene related peptide inhibits norepinephrine induced apoptosis in cultured cardiomyocytes, which is mediated by CGRP receptor but unlikely to be mediated by PKA or PKC pathway.

Differential effects of methamphetamine and SCH23390 on the expression of members of IEG families of transcription factors in the rat striatum

Methamphetamine (METH) is a psychostimulant that can cause long-lasting neurodegenerative effects in humans and animals. These toxic effects appear to occur, in part, via activation of dopamine (DA) D1 receptors. This paper assessed the possibility that the DA D1 receptor antagonist, SCH23390, might inhibit METH-induced changes in the expression of several members of immediate early genes (IEGs) which are known to control more delayed expression of other genes. We found that injections of METH (4x10 mg/kg, given at 2 h intervals) caused significant increases in c-fos and fra-2 expression which lasted from 30 min to 4 h. Pre-treatment with SCH23390, given 30 min before each METH injection, completely blocked METH-induced expression of c-fos, but only partially inhibited fra-2 mRNA expression. These results were confirmed by Western blot analysis which showed METH-induced changes in c-Fos protein expression that were blocked by pretreatment with SCH23390. There were also delayed METH-induced DA D1 receptor-dependent effects on fosB mRNA expression. Even though fra-1 expression was not affected by pretreatment with METH alone, the repeated injections of SCH23390 caused substantial decreases in fra-1 mRNA expression in both the presence and absence of METH. The repeated injections of METH caused no changes in the mRNAs for c-jun, junB or junD. However, there were significant increases in the phosphorylation of c-Jun protein (ser63). Phosphorylation of c-Jun occurred in a delayed fashion (16 and 24 h after the last METH injections) and was attenuated by SCH23390 pretreatment. Interestingly, SCH23390 given alone caused significant decreases in phospho-c-Jun at all time-points. The METH injections also caused delayed induction in the expression of members of the Egr family of transcription factors in a DA D1 receptor-dependent fashion. Repeated injections of SCH23390 caused substantial suppression of basal striatal egr-1 and egr-2 mRNA expression but not of that of egr-3. Both crem and arc mRNA levels were induced by METH in a SCH23390-sensitive fashion. Moreover, multiple injections of SCH23390 given alone caused marked inhibition of basal arc expression. These results show that multiple injections of METH can differentially affect the expression of several IEGs, some of which occurred in a DA D1 receptor dependent fashion. The SCH23390-mediated suppression of basal fra-1, egr-1, and egr-2 mRNA levels suggests that their basal expression in the striatum might be dependent on tonic stimulation of the DA D1 receptor.

Protein kinase C is a common component of CGRP receptor desensitization induced by distinct agonists

The calcitonin gene-related peptide (CGRP) is a neuropeptide involved in vasodilation and other physiological functions throughout the body. The receptor for CGRP has been cloned and well studied, but the mechanism of CGRP receptor desensitization has not been fully elucidated. In the present study, we evaluated the kinetics for agonist-mediated desensitization of the adenylate cyclase response in human neuroblastoma SK-N-MC cells. Distinct CGRP receptor agonists were used, including alpha and beta isoforms of CGRP, the linearized derivative cys(Et)2,7 alphaCGRP, adrenomedullin, and adrenomedullin 2. betaCGRP was 4-600 times more potent at desensitizing the cAMP production as compared to the other receptor-activating ligands, and all of the desensitization effects were blocked by a CGRP receptor antagonist. Although the different agonists vary in their ability to induce functional desensitization, a pretreatment/washout sequence with each peptide was able to reduce the activation potency of the other members of the calcitonin/CGRP peptide family. Next we tested whether the desensitizing effects of the distinct peptides involve protein kinase C (PKC) or protein kinase A (PKA). A PKC inhibitor, Ro 31-8220, concentration-dependently reduced the desensitization induced by the 5 CGRP receptor agonists, while having little effect on their desensitization potencies. PKA inhibitors KT-5720 and H-89, on the other hand, showed little effect on the induced level of desensitization. The findings indicate that functional desensitization is produced by distinct peptides acting through the active site of CGRP receptors, and involves the activation of PKC as a common component necessary to achieve maximal desensitization of receptor signaling.

Proliferative effect of calcitonin gene-related peptide is induced by at least five proteins as identified by proteome profiling

Calcitonin gene-related peptide is a 37 amino acid neuropeptide. Although calcitonin gene-related peptide activates a G-protein-coupled receptor, recent evidence suggests that calcitonin gene-related peptide induces more complex signaling cascades including the activation of MAP kinases [Eur J Pharmacol; 389:125-130 (2000), Neuropeptides; 34:229-233 (2000)]. However, the molecular mechanisms of this activation still remain to be elucidated. For the first time we applied a proteomics approach in order to identify molecular targets of calcitonin gene-related peptide downstream signaling in the neuroblastoma cell line SK-N-MC and identified proteins that changed either their expression, location, or their post-translational modifications in a time-dependent manner after calcitonin gene-related peptide stimulation.

Localization of the calcitonin gene-related peptide receptor complex at the vertebrate neuromuscular junction and its role in regulating acetylcholinesterase expression

The calcitonin gene-related peptide (CGRP) is released by motor neurons where it exerts both short and long term effects on skeletal muscle fibers. In addition, sensory neurons release CGRP on the surrounding vasculature where it is in part responsible for local vasodilation following muscle contraction. Although CGRP-binding sites have been demonstrated in whole muscle tissue, the type of CGRP receptor and its associated proteins or its cellular localization within the tissue have not been described. Here we show that the CGRP-binding protein referred to as the calcitonin receptor-like receptor is highly concentrated at the avian neuromuscular junction together with its two accessory proteins, receptor activity modifying protein 1 and CGRP-receptor component protein, required for ligand specificity and signal transduction. Using tissue-cultured skeletal muscle we show that CGRP stimulates an increase in intracellular cAMP that in turn initiates down-regulation of acetylcholinesterase expression at the transcriptional level, and, more specifically, inhibits expression of the synaptically localized collagen-tailed form of the enzyme. Together, these studies suggest a specific role for CGRP released by spinal cord motoneurons in modulating synaptic transmission at the neuromuscular junction by locally inhibiting the expression of acetylcholinesterase, the enzyme responsible for terminating acetylcholine neurotransmission.

Immature human osteoblastic MG63 cells predominantly express a subtype 1-like CGRP receptor that inactivates extracellular signal response kinase by a cAMP-dependent mechanism

Although accumulated data suggest that calcitonin gene-related peptide (CGRP) produces anabolic effects in skeletal tissue by directly acting on osteogenic cells, neither the distribution of CGRP receptor subtypes nor the associated cellular signaling pathways are well understood. In this study, we have pharmacologically and biochemically characterized CGRP-binding sites in immature human osteoblastic MG63 cells. In a [125I]CGRP whole-cell-binding assay, nonlinear regression curve-fitting analysis demonstrated a single binding site (K(D)=405+/-29 pM; 13,100+/-223 sites per cell). Immunocytochemical and Western blot analyses demonstrated that 48-, 52-, and 120-kDa forms of the calcitonin receptor-like receptor (CRLR) and a 15-kDa form of the receptor-activity-modifying protein-1 (RAMP-1) was expressed on the plasma membrane. CGRP strongly stimulated cellular cAMP production and this effect was antagonized not only by an antagonist of the subtype-1 CGRP (CGRP(1)) receptor, CGRP-(8-37), but by an agonist of the putative subtype-2 CGRP (CGRP(2)) receptor, [Cys(Acm)(2,7)]-CGRP, that also itself acted as a weak agonist. In contrast to published data, CGRP dose- and time-dependently dephosphorylated and inactivated extracellular signal response kinase (ERK). This action was blocked by CGRP-(8-37), by an inhibitor of cAMP-dependent protein kinase (H-89), or by an inhibitor of protein phosphatases (vanadate). Prolonged CGRP treatments significantly suppressed DNA synthesis at 27 h, but up-regulated type I collagen. Both these actions were blocked by CGRP-(8-37) and mimicked by a specific inhibitor of ERK (PD98059). In summary, our data suggest that the CGRP receptors in MG63 cells meet many, but not all, of the classical criteria used to define CGRP(1) receptors. These receptors that functioned in a pharmacologically distinct manner could inhibit cell proliferation, and were substantially more sensitive to a CGRP(2) receptor agonist than are typical CGRP(1) receptors. These receptor proteins were not exactly matched with the known components of a CGRP(1) receptor that have been reported. Therefore, it is possible that the CGRP receptors expressed in immature osteoblastic human MG63 cells represent a variation of the known CGRP(1) receptor.

Involvement of cyclic adenosine monophosphate-dependent protein kinase A and pertussis toxin-sensitive G proteins in the migratory response of human CD14+ mononuclear cells to katacalcin

Katacalcin (KC) belongs to a small family of polypeptides that are encoded by the calc-1 gene and also include calcitonin (CT) and procalcitonin NH2-terminal cleavage peptide (N-ProCT). Biological roles of KC or N-ProCT are unknown. To determine whether these polypeptides affect leukocyte function, forearm venous blood polymorphonuclear neutrophils and CD14+ peripheral blood mononuclear cells (PBMCs) were isolated from healthy human donors. Cell migration was assessed in a blindwell chemotaxis chamber using nitrocellulose micropore filters. Cellular levels of cyclic adenosine monophosphate (cAMP) were measured by HPLC; activation of protein kinase A was studied by Western blot. Fluorochrome-labeled peptide binding to cells was studied by fluorescence-activated cell sorting (FACS) and intracellular calcium transients were studied by confocal microscopy with FLUO-3. KC elicited concentration-dependent migration of CD14+ PBMC at concentrations from the atomolar to the micromolar range and deactivated attractant-induced chemotaxis. CT N-terminal flanking peptide had no such effect. Neutrophils did not migrate toward any of those peptides and their oxygen-free radical release was not affected as measured fluorometrically. Functional responses of CD14+ PBMC to KC correlated to forskolin-sensitive cAMP accumulation in cells and were inhibited by protein kinase A inhibitor (PKI) and Rp diastereomer of adenosine 3',5'-cyclic monophosphorothioate. Treatment of CD14+ PBMC with KC activated protein kinase A(C alpha). Intracellular calcium was decreased with CT, KC, and procalcitonin (PCT). Binding studies showed that KC might share the binding site with CT and PCT. Data indicate that KC regulates human CD14+ PBMC migration via signaling events involving protein kinase A-dependent cAMP pathways.