Molecular cloning and functional characterization of a mouse bradykinin B1 receptor gene

Cyclic and linear bradykinin analogues: implications for B2 antagonist design

Bradykinin (BK, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) antagonists are potentially useful for treating inflammation, pain and severe trauma. To identify what chemical features might promote effective antagonism, we replaced Arg1 and Pro7 with structurally constrained and proteolytic-resistant residues, such as Bip (biphenylalanine), Dip (diphenylalanine) or 2Ind (indane amino acid). To determine which BK folding might lead to favourable interactions with receptors, the effects of cyclo(3,8) vs. cyclo(5,8) analogues were compared. The resulting BK analogues were examined for their agonistic and antagonistic activities in guinea pig ileum, rat uterus and depressor assays. The results suggest that co-planarity of the residue-7 side chain with its backbone NH is important for potent agonism as well as antagonism, and a D-directed side chain is crucial for antagonism. For residue-1 an L-orientation is important, and Dip1 may mimic a folded Arg1 side chain to elicit agonistic activities, with Bip1 mimicking an extended Arg1 side chain to elicit inhibitory activities. However, ileal and uterine receptors appear to prefer differently folded BK. For ileum, a BK conformation in which residues-3 and -8 are proximal to each other, but apart from residue-5, led to improved pA2.

Molecular characterisation of cloned bradykinin B1 receptors from rat and human

This report describes the characterisation of cloned rat and human bradykinin B1 receptors in African green monkey kidney fibroblast (Cos-7) cells. A ligand binding assay with [3H]des-Arg10-kallidin was used to compare their pharmacology with respect to known bradykinin B1 and B2 receptor ligands. In addition, the pharmacology of T-kinin and its' derivative des-Arg11-T-kinin was investigated. The cloned rat receptor had a similar pharmacology to that of the recently described mouse receptor and differs from that described for the human receptor. The rat receptor had a higher affinity for des-Arg11-T-kinin than the human receptor. These differences in pharmacological properties may relate to the presence of T-kinin, bradykinin and their des-Arg derivatives as the major physiological peptides in rat and the predominance of kallidin and its derivatives in human. We confirm that the rat bradykinin B1 receptor gene is organised in a two exon structure and differs from the human gene which has a three exon structure and we further examine the inducible expression of this gene in a wide range of tissues using Northern blotting.

Regulation by interleukin-1beta of gene expression of bradykinin B1 receptor in MH-S murine alveolar macrophage cell line

The effects of recombinant murine interleukin (IL)-1beta on gene expression of murine bradykinin B1 receptor (BDKRB1) in MH-S murine alveolar macrophage cell line were evaluated. BDKRB1 mRNA expression in MH-S cells was increased by IL-1beta (1, 3, and 10 ng/ml) in a time-dependent manner, peaking at 3-4 h by 100-1000 fold. IL-1beta (5 ng/ml, 24h) also induced significant binding to [3H]-des-Arg10-kallidin with a dissociation constant (Kd) of 2.95 nM and a maximal binding density (Bmax) of 670 sites/cell. Des-Arg10-kallidin (10 microM), a BDKRB1 agonist, increased intracellular calcium ion ([Ca2+]i) in IL-1beta (5 ng/ml, 24 h)-exposed cells, an increase not observed in the cells not exposed to IL-1beta. A significant increase of tumor necrosis factor (TNF)-alpha secretion occurred in the IL-1beta (5 ng/ml, 24 h)-exposed cells following addition of des-Arg10-kallidin (the IL-1beta-exposed group: 57. 8 +/- 13.7 vs. the vehicle-exposed group: 16.7 +/- 4.3 pg/ml, p < 0.05 after a 100 nM des-Arg10-kallidin for 8 h), with an optimal effect at 3-100 nM. These data suggest that IL-1beta may up-regulate BDKRB1-mediated functions of alveolar macrophages via an induction of BDKRB1 gene expression.

Evidence for in vitro expression of B1 receptor in the mouse trachea and urinary bladder

1. Motor responses to des-Arg9-bradykinin and bradykinin were studied in the isolated mouse trachea (precontracted with carbachol, 10 microM) and the urinary bladder of either Swiss, C57B1/6J or bradykinin B2 receptor knockout (Bk2r(-/-)) mice after 1-6 h in vitro. The expression of mRNA for the mouse B1 receptor in tracheal and urinary bladder tissues was also studied by using Northern blot analysis. 2. In isolated tracheae, des-Arg9-bradykinin produced a relaxant response that increased over time: no response was observed after 1 h of incubation, whereas after 6 h the maximum response (1 microM) was 68-84% of the relaxation produced by isoproterenol (1 microM) in the three mouse strains. The relaxant response to bradykinin (1 microM) observed at 1 h (38-51% of isoproterenol) was increased (62-65% of isoproterenol) after 6 h in Swiss and C57B1/6J mice, but was absent in Bk2r(-/-) mice. In the presence of cycloheximide, des-Arg9-bradykinin did not cause any response at 6 h. 3. Similar findings were obtained in the urinary bladder: at 1 h des-Arg9-bradykinin (1 microM) did not cause any motor effect, whereas at 6 h it caused a contraction that was 28-59% of that produced by carbachol (1 microM) in the three mouse strains. Cycloheximide blocked the response to des-Arg9-bradykinin. Bradykinin (1 microM) contracted urinary bladders at 1 h (34-35% of carbachol), as well as at 6 h (66-77% of carbachol) in Swiss and C57B1/6J strains, but was without effect in Bk2r(-/-) mice. 4. Northern blot hybridization with a specific cDNA probe against mouse B1 receptor mRNA using total RNA extracted from tracheae and urinary bladders freshly removed from Swiss and Bk2r(-/-) mice revealed minimal expression. However, marked hybridization was detected 150 min after in vitro exposure in both tissues. 5. Evidence is provided that in vitro exposure of mouse trachea and urinary bladder causes a time-dependent induction of B1 receptors that cause relaxation and contraction, respectively.

B1 receptors as a new inflammatory target. Could this B the 1?

The kinins, particularly bradykinin (BK), are important mediators involved in both the initiation and progression of an inflammatory response. The pro-inflammatory effects of kinins are mediated by at least two receptors: the B2 subtype is expressed constitutively and the B1 receptor is induced following tissue inflammation and damage. The endogenous ligand for the B1 receptor is des-arg9BK, a cleavage product of the activity of carboxypeptidase on BK. Activation of B1 receptors produces a range of pro-inflammatory effects including oedema, pain and promotion of blood-borne leukocyte trafficking. In this article Amrita Ahluwalia and Mauro Perretti briefly describe the biology of BK and its receptors, and discuss the possible development of B1 receptor antagonists as novel anti-inflammatory agents.

Oral anti-inflammatory action of NPC 18884, a novel bradykinin B2 receptor antagonist

This study describes the anti-inflammatory actions of NPC 18884, a non-peptide bradykinin B2 receptor antagonist in bradykinin and carrageenan-induced inflammation in the mouse model of pleurisy. The selectivity of NPC 18884 was assessed in the pleurisy caused by histamine, substance P and des-Arg9-bradykinin. NPC 18884 given intraperitoneally or orally inhibited bradykinin-induced leukocytes influx (ID50 value of 63 nmol/kg and 141 nmol/kg, respectively). The NPC 18884 also inhibited the exudation induced by bradykinin (P < 0.05). NPC 18884 given either intraperitoneally or orally caused dose-dependent inhibition of the exudation and total and differential cell content caused by intrapleural injection of carrageenan (1%, assessed 4 h after), with mean ID50, values of 132 and 295 nmol/kg, respectively. The NPC 18884 actions installs rapidly (0.5 h), lasted for up to 4 h and were selective for the bradykinin B2 receptors; at similar doses it had no significant effect against the inflammatory responses induced by des-Arg9-bradykinin, histamine or substance P. These results indicate that the novel non-peptide bradykinin B2 receptor antagonist, NPC 18884, exhibited selective intraperitoneal and oral anti-inflammatory properties when assessed in the inflammatory reaction induced by bradykinin and carrageenan in the mice model of pleurisy.

Differential induction of functional B1-bradykinin receptors along the rat nephron in endotoxin induced inflammation

BACKGROUND

Under physiological conditions, the effects of kinins in the kidney are mainly mediated by the bradykinin B2-receptor, whereas the kinin B1-receptor is strongly induced under inflammatory conditions in a variety of tissues. Knowledge of the distribution of the B1-receptor along the nephron is of importance since the B1-receptor might replace B2-receptors under these conditions.

METHODS

Using a RT-PCR/Southern blot approach allowing relative quantification of mRNA levels, ten different microdissected rat nephron segments were analyzed for the presence of the B1- and B2-receptor before and after endotoxin treatment to induce experimental inflammation. The functionality of the expressed receptors was assessed by kinin-induced intracellular calcium ([Ca2+]i) mobilization in microdissected nephron segments.

RESULTS

While under physiological conditions no B1-receptor mRNA could be detected, after 18 hours of treatment with bacterial lipopolysaccharide (LPS) the expression of B1-receptor mRNA was strongly induced in the efferent arteriole, the medullary and inner medullary thin limb, and in the distal tubule. Moderate expression was found in the glomerulus, proximal convoluted and straight tubules, and in the medullary thick ascending limb. Small but detectable expression was observed in the cortical collecting duct. The induction of B1-receptor mRNA expression resulted in functional receptor expression, since increases in [Ca2+]i were observed upon B1-agonist stimulation. LPS treatment also increased the expression of B2-receptor mRNA in all nephron segments except in the glomerulus, the inner medullary thin limb and the outer medullary collecting duct. However, no related changes in B2-agonist induced rises in [Ca2+]i were found.

CONCLUSIONS

These studies show a functional induction of the B1-kinin receptor along the rat nephron, which should be taken in account to address the effects of kinins under inflammatory conditions in the kidney.

Molecular cloning and expression of rat bradykinin B1 receptor

The gene encoding rat bradykinin B1 receptor has been cloned by using a partial rat B1 cDNA probe. The rat B1 receptor gene contains two exons and the entire coding region is within the second exon. The 5'-flanking region of the rat B1 receptor gene contains several putative transcriptional regulatory sites including TATA box, cAMP response element, NF-kappaB and AP-1. It showed promoter activity inducible by lipopolysaccharide in vascular smooth muscle cells. Rat B1 receptor mRNA was found to be alternatively spliced and induced by lipopolysaccharide treatment in a wide range of tissues, such as the salivary gland, testis, kidney, lung, heart, prostate and aorta. The deduced rat B1 receptor amino acid sequence is 71% homologous to human and rabbit counterparts, and 89% homologous to the mouse counterpart. The expressed B1 receptor in HEK293 cells displayed a rank order of affinity for the kinin peptides: des-Arg9-BK>Lys-des-Arg9-BK approximately des-Arg9, Leu8-BK>Sar-Tyr-epsilonAhx-Lys-[D-betaNal7, Ile8]-des-Arg9-BK>Sar-Tyr-epsilonAhx-Lys-des-Arg9-BK>>BK>> Hoe140. These results indicate that the cloned gene encodes a functional rat B1 receptor.

Bradykinin B1 receptors in human umbilical vein: pharmacological evidence of up-regulation, and induction by interleukin-1 beta

Bradykinin B1 receptor-mediated responses increase as a function of in vitro incubation in the human umbilical vein. When tissues were continuously treated with the protein synthesis inhibitor, cycloheximide, or with the protein trafficking inhibitor, brefeldin A, pEC50 and maximal response to the selective bradykinin B1 receptor agonist, des-Arg9-bradykinin, were significantly diminished. The anti-inflammatory steroid, dexamethasone, produced a rightward shift of the concentration-response curve to des-Arg9-bradykinin, without affecting the maximal response. Furthermore, lipopolysaccharide or recombinant human interleukin-1 beta potentiate the bradykinin B1-sensitized responses, showing a leftward shift of the concentration-response curve to des-Arg9-bradykinin, without modifying the maximal response. On the other hand, bradykinin B2 receptor-mediated responses were unaffected by continuous exposure to cycloheximide, dexamethasone or lipopolysaccharide. These results provide pharmacological evidence to support the view that the de novo synthesis of bradykinin B1 receptors is involved in the induction of vascular responses in the human umbilical vein. This up-regulation process seems to be selective for bradykinin B1 receptors. The inhibitory effect of dexamethasone and the potentiating actions of lipopolysaccharide and exogenous human recombinant interleukin-1 beta on des-Arg9-bradykinin-mediated responses, suggest the possible role of interleukin-1 beta in the bradykinin B1 receptor up-regulation phenomenon in human umbilical vein.

Heat stress-induced B1 receptor synthesis in the rat: an ex vivo study

1. This ex vivo study was performed to characterize B1 receptor induction in rats submitted to heat stress. Changes in aortic isometric tension were recorded after a 90 min in vitro incubation with [des-Arg9]-bradykinin. B1 receptor mRNA were detected in aorta and heart using RT-PCR technique. 2. Aortic rings from sham rats did not respond to [des-Arg9]-bradykinin. In contrast, this agonist induced a concentration-dependent relaxation of aortic rings from rats submitted to lipopolysaccharide (LPS) treatment or to heat stress 24 h earlier. 3. The concentration-dependent relaxation induced by [des-Arg9]-bradykinin on aortic rings from heat-stressed rats was abolished by [des-Arg10]-HOE 140, a selective B1 receptor antagonist. 4. In endothelium denuded aortic rings from heat-stress rats, [des-Arg9]-bradykinin induced a concentration-dependent constriction. 5. Pretreatment of intact aortic rings from heat-stress rats with the cyclo-oxygenase inhibitor, diclofenac (1 microM) did not prevent the concentration-dependent relaxation in response to [des-Arg9]-bradykinin. In contrast. NO synthase inhibition with N(omega)-nitro-L-arginine methyl ester (30 microM) totally prevented the vasorelaxant response. 6. B1 receptor mRNA were not detected in aorta and heart from sham animals but were present in tissue from heat-stressed and LPS-treated rats. 7. In conclusion, our results suggest that heat stress induces a transcriptional activation of the B1 receptor gene. The induction of B1 receptors leads to an endothelium- and NO-dependent vasorelaxant response to [des-Arg9]-bradykinin.

Systemic treatment with Mycobacterium bovis bacillus Calmette-Guérin (BCG) potentiates kinin B1 receptor agonist-induced nociception and oedema formation in the formalin test in mice

This study investigates the effect and some of the mechanisms involved following systemic treatment of mice with Mycobacterium bovis bacillus Calmette-Guérin (BCG) (1 dose per animal containing 6.4 x 10(4) colony-forming units (CFu) 20-60 days beforehand) on modulation of the kinin B1 receptor agonist-induced nociception and oedema formation in the formalin test. Intraplantar (i.p.l.) co-injection of des-Arg9-bradykinin (4-32 nmol/paw) or des-Arg10-kallidin (1-15 nmol/paw), together with sub-maximal concentrations of formalin (0.01 or 0.5%), potentiated (P < 0.01) both pain phases and the paw oedema caused by formalin in animals pre-treated with saline. However, when animals were pre-treated with BCG, the dose-response curves for both B1 agonists were shifted 2 to 8-fold to the left. These B1-mediated effects peaked at 30-45 days after BCG treatment and were still elevated at 60 days after BCG injection. The pain response and oedema formation caused by i.p.l. co-injection of des-Arg9-bradykinin, together with formalin in BCG-pre-treated animals, were dose-dependently antagonised by i.p.l. co-injection of the B1 antagonist des-Arg9[Leu8]bradykinin (1-15 nmol/paw), but were not affected by the B2 antagonist Hoe 140 (10 nmol/paw). The i.p.l. co-injection of tyrosine8-bradykinin (a B2 agonist, 3-15 nmol/paw) with formalin (0.01 or 0.5%) potentiated the pain response and paw oedema in BCG and saline-pre-treated animals to the same extent (P < 0.01). The actions caused by tyrosine8-bradykinin were antagonised by Hoe 140, while des- Arg9[Leu8]bradykinin (10 nmol/paw) had no effect. Dexamethasone (0.5 mg/kg, s.c.), given every 24 h, from day 0 to 30-45, inhibited significantly the potentiation of nociceptive response and oedema formation caused by i.p.l. co-injection of formalin plus des-Arg9-bradykinin, while indomethacin (2 mg/kg, i.p.) or phenidone (30 mg/kg, i.p.), given 1 h prior, caused less inhibition. These data show that the long-term systemic treatment of mice with BCG produced dose-related potentiation of B1 receptor agonist-mediated nociception and oedema formation, without affecting similar responses caused by the B2 receptor agonist tyrosine8-bradykinin. Thus, systemic treatment of mice with BCG induces upregulation of B1 receptors, without affecting B2-mediated responses, by a mechanism that seems to be secondary to cytokine release.

Molecular biology of the kallikrein-kinin system: from structure to function

The participation of the kallikrein-kinin system, comprising the serine proteases kallikreins, the protein substrates kininogens and the effective peptides kinins, in some pathological processes like hypertension and cardiovascular diseases is still a matter of controversy. The use of different experimental set-ups in concert with the development of potent and specific inhibitors and antagonists for the system has highlighted its importance but the results still lack conclusivity. Over the last few years, transgenic and gene-targeting technologies associated with molecular biology tools have provided specific information about the elusive role of the kallikrein-kinin system in the control of blood pressure and electrolyte homeostasis. cDNA and genomic sequences for kinin receptors B2 and B1 from different species were isolated and shown to encode G-protein-coupled receptors and the structure and pharmacology of the receptors were characterized. Transgenic animals expressing an overactive kallikrein-kinin system were established to study the cardiovascular effects of these alterations and the results of these investigations further corroborate the importance of this system in the maintenance of normal blood pressure. Knockout animals for B2 and B1 receptors are available and their analysis also points to the role of these receptors in cardiovascular regulation and inflammatory processes. In this paper the most recent and relevant genetic animal models developed for the study of the kallikrein-kinin system are reviewed, and the advances they brought to the understanding of the biological role of this system are discussed.

The B1-agonist [des-Arg10]-kallidin activates transcription factor NF-kappaB and induces homologous upregulation of the bradykinin B1-receptor in cultured human lung fibroblasts

The bradykinin B1-receptor is strongly upregulated under chronic inflammatory conditions. However, the mechanism and reason are not known. Because a better understanding of the mechanism of the upregulation will help in understanding its potential importance in inflammation, we have studied the molecular mechanism of B1-receptor upregulation in cultured human lung fibroblasts (IMR 90) in response to IL-1beta and the B1-agonist [des-Arg10]-kallidin. We show that treatment of human IMR 90 cells by IL-1beta stimulates the expression of both B1-receptor mRNA and protein. The latter was studied by Western blot analysis using antipeptide antibodies directed against the COOH-terminal part of the human B1-receptor. We furthermore report the novel observation that the B1-receptor is upregulated by its own agonist which was completely blocked by the specific B1-antagonist [des-Arg10-Leu9]-kallidin, indicating an upregulation entirely mediated through cell surface B1-receptors. The increased population of B1-receptors was functionally coupled as exemplified by an enhancement of the B1-agonist induced increase in free cytosolic calcium. Upregulation by the B1-agonist was blocked by a specific protein kinase C inhibitor. B1-agonist-induced upregulation was correlated to the induction of transcription factor nuclear factor kappaB (NF-kappaB) which efficiently bound to the NF-kappaB-like sequence located in the promoter region of the human B1-receptor gene. This correlation was further confirmed by reporter gene assays which showed that this NF-kappaB-like sequence, in the B1-receptor promoter context, could contribute to IL-1beta and DLBK-induced B1-receptor transcription activation, and by the effect of NF-kappaB inhibitor pyrrolidinedithiocarbamate which diminished both B1-receptor upregulation and NF-kappaB activation. NF-kappaB is now recognized as a key inflammatory mediator which is activated by the B1-agonist but which is also involved in B1-receptor upregulation.

Cloning, sequencing and functional expression of a guinea pig lung bradykinin B2 receptor

Kinin receptors are classified as B1 and B2 based upon agonist and antagonist potencies and cloning and expression studies. Using sequences from human and rat bradykinin B2 receptors, polymerase chain reaction (PCR) was utilized to isolate cDNA from guinea pig lung. The receptor obtained is predicted to have 372 amino acids and shares > 80% sequence homology with human, rat, rabbit and mouse B2 receptors. In competition binding experiments in Chinese hamster ovary (CHO-K1) cells in which the guinea pig cDNA was expressed, [3H]bradykinin was displaced by kinin receptor ligands with an order of potency consistent with a B2 subtype. In CHO cells expressing the guinea pig receptor, bradykinin caused a concentration 45Ca2+ efflux. A B1 receptor agonist, desArg9-bradykinin, also caused 45Ca2+ efflux but with a potency several orders of magnitude lower than bradykinin. Curiously, several B1 and B2 receptor antagonists induced 45Ca2+ efflux, indicating that this receptor may be coupled differently in CHO cells than in native tissues.

Involvement of bradykinin B1 and B2 receptors in relaxation of mouse isolated trachea

1. The aim of the present study was to investigate the effects of bradykinin and [des-Arg9]-bradykinin and their relaxant mechanisms in the mouse isolated trachea. 2. In the resting tracheal preparations with intact epithelium, bradykinin and [des-Arg9]-bradykinin (each drug, 0.01-10 microM) induced neither contraction nor relaxation. In contrast, bradykinin (0.01-10 microM) induced concentration-dependent relaxation when the tracheal preparations were precontracted with methacholine (1 microM). The relaxation induced by bradykinin was inhibited by the B2 receptor antagonist, D-Arg0-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin (Hoe 140, 0.01-1 microM) in a concentration-dependent manner whereas the B1 receptor antagonist, [des-Arg9,Leu8]-bradykinin (0.01-1 microM), had no inhibitory effect on bradykinin-induced relaxation. [des-Arg9]-bradykinin (0.01-10 microM) also caused concentration-dependent relaxation after precontraction with methacholine. The relaxation induced by [des-Arg9-bradykinin was concentration-dependently inhibited by the B1 receptor antagonist, [des-Arg9,Leu8]-bradykinin (0.01-1 microM), whereas the B2 receptor antagonist, Hoe 140 (0.01-1 microM) was without effect. 3. In the presence of the cyclo-oxygenase inhibitor, indomethacin (0.01-1 microM), the relaxations induced by bradykinin and [des-Arg9]-bradykinin were inhibited concentration-dependently. 4. Two nitric oxide (NO) biosynthesis inhibitors NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) and NG-nitro-L-arginine (L-NOARG, 100 microM) had no inhibitory effects on the relaxations induced by bradykinin and [des-Arg9]-bradykinin. Neither did the selective inhibitor of the soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM) inhibit the relaxations induced by bradykinin and [des-Arg9]-bradykinin. 5. Prostaglandin E2 (PGE2, 0.01-33 microM) caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. Indomethacin (1 microM) and ODQ (10 microM) exerted no inhibitory effects on the relaxation induced by PGE2. 6. The NO-donor, sodium nitroprusside (SNP; 0.01-100 microM) also caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. ODQ (0.1-1 microM) concentration-dependently inhibited the relaxation induced by SNP. 7. These data demonstrate that bradykinin and [des-Arg9]-bradykinin relax the mouse trachea precontracted with methacholine by the activation of bradykinin B2-receptors and B1-receptors, respectively. The stimulation of bradykinin receptors induces activation of the cyclo-oxygenase pathway, leading to the production of relaxing prostaglandins. The NO pathway is not involved in the bradykinin-induced relaxation. The relaxation caused by NO-donors in the mouse trachea is likely to be mediated via activation of soluble guanylate cyclase.

B2 kinin receptor upregulation by cAMP is associated with BK-induced PGE2 production in rat mesangial cells

In the rat mesangial cell (MC), activation of the bradykinin B2 receptor (B2R) by bradykinin (BK) is associated with both phospholipase C (PLC) and A2 (PLA2) activities and with inhibition of adenosine 3',5'-cyclic monophosphate (cAMP) formation leading to cell contraction. Because cAMP plays an important role in the regulation of gene expression in general, we investigated the effect of increasing the intracellular cAMP concentration ([cAMP]i) in mesangial cells on the B2 mRNA expression, on the density of B2 receptor binding sites, on the BK-induced increase in both the free cytosolic Ca2+ concentration ([Ca2+]i), and in the prostaglandin E2 (PGE2) production. Forskolin, PGE2, and cAMP analog, 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), were used to increase [cAMP]i. Twenty-four-hour treatment with forskolin, PGE2, and 8-BrcAMP resulted in significant increases in B2 receptor binding sites, which were inhibited by cycloheximide. The maximum B2 receptor mRNA expression (160% above control) was observed in cells treated during 24 h with forskolin and was prevented by actinomycin D. In contrast, the D-myo-inositol 1,4,5-trisphosphate (IP3) formation and the BK-induced increase in [Ca2+]i, reflecting activation of PLC, were not affected by increased levels of [cAMP]i. However the BK-induced PGE2 release, reflecting PLA2 activity, was significantly enhanced. These data bring new information regarding the dual signaling pathways of B2 receptors that can be differentially regulated by cAMP.

Transcription factor nuclear factor kappaB regulates the inducible expression of the human B1 receptor gene in inflammation

Expression of the bradykinin B1 receptor gene is up-regulated in vascular smooth muscle cells (VSMCs) in response to a variety of inflammatory stimuli. We isolated the 5'-flanking region of the human bradykinin B1 receptor gene and examined its promoter activity by transient transfection analysis. This region (-2582 to +34) showed promoter activity inducible by lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF-alpha), and interleukin-1beta (IL-1beta) in VSMCs. Further deletion analysis revealed that constructs containing 111 base pairs of 5'-flanking sequence were sufficient for transcriptional induction. Mutagenesis of a nuclear factor kappaB (NF-kappaB)-like site at -64 to -55 abolished most of the LPS, TNF-alpha, and IL-1beta inducibility, whereas a mutation of a cyclic AMP response element at -50 to -43 markedly reduced the basal promoter activity, and a mutation of the activator protein 1 (AP-1) site at -78 to -72 had minimal effects. Nuclear extracts from LPS, TNF-alpha, and IL-1beta-treated VSMCs, IL-1beta-treated human hepatoma HepG2, and human lung fibroblast IMR-90 cells showed strong inducible binding activity to the NF-kappaB-like site by gel shift assays. These results demonstrated that NF-kappaB-like nuclear factor was involved in the inducible expression of the human bradykinin B1 receptor gene during inflammatory processes.

Kinin receptors

Rapid developments are expected in the molecular pharmacology of both B1, and B2 types of kinin receptors, since the underlying genetic structures are now known and widely studied. The consequences of kinin receptor duality and physiopathological regulation have not yet been fully appreciated. Medicinal chemistry is also an active front of research in kinin pharmacology, as more effective drugs targeted at kinin receptors are regularly reported. Various complementary molecular approaches (the receptor binding, cloning, immunoreacting, mutagenesis, inactivation, the study of regulation, allelic polymorphisms, and so forth) are expanding our knowledge of the role of kinins in allergy, inflammation, and singularly, renal medicine.

Modulation of kinin B1 but not B2 receptors-mediated rat paw edema by IL-1beta and TNFalpha

The modulatory effects of IL-1beta and TNF alpha on the rat paw edema induced by B1 agonists have been analyzed. In naive rats, i.d. injection of B1 agonists, des-Arg9-bradykinin and des-Arg10-kallidin (up to 300 nmol), causes a minimal increase in paw volume, while the B2 agonist tyrosine8-bradykinin (0.3-10 nmol) induces graded paw edema. The injection of des-Arg9-bradykinin (10-100) nmol or des-Arg10-kallidin (1-100 nmol), in paws pre-treated with IL-1beta or TNF alpha (both 5 ng/paw; 60 and 30 min prior, respectively), caused a graded edema formation. The edemas induced by des-Arg9-bradykinin (100 nmol) were evident at 15 min, reaching the maximum 60 and 30 min after treatment with IL-1beta (0.64 +/- 0.06 ml) or TNF alpha (0.47 +/- 0.05 ml), respectively, being reduced at 360 min. The B1 antagonist des-Arg9-NPC 17731 (1-30 nmol), but not the B2 antagonist Hoe 140 (10 nmol), produced marked inhibition of des-Arg9-bradykinin-induced paw edema. Dexamethasone (0.5 mg/kg, s.c., 4 h) or cycloheximide (1.5 mg/kg, s.c., 6 h) significantly prevented the edema caused by des-Arg9-bradykinin (100 nmol) in rats treated with IL-1beta (81 +/- 5% and 59 +/- 3%) or TNF alpha (78 +/- 4% and 43 +/- 2%). Indomethacin (2 mg/kg, i.p.) or meloxicam (3 mg/kg, i.p.), 1 h prior, significantly reduced the edema induced by des-Arg9-bradykinin (100 nmol) in IL-1beta (40 +/- 6% and 69 +/- 8%) or TNF alpha (43 +/- 3% and 53 +/- 9%) treated rats. It is suggested that i.d. injection of the IL-1beta or TNF alpha, produced up-regulation of B1 receptor-mediated paw edema, being this effect sensitive to dexamethasone and cycloheximide and to cyclo-oxygenase pathway.

Characterization of des-Arg9-bradykinin-induced contraction in guinea-pig gallbladder in vitro

We have reported that bradykinin induces graded contraction in guinea-pig gallbladder in vitro through activation of bradykinin B2 receptors and prostanoid release, while des-Arg9-bradykinin, a selective bradykinin B1 receptor agonist, causes only a weak contraction, suggesting the presence of badykinin B1 receptors in this tissue. In the present study, we attempted to characterise the receptor subtype and the possible mechanism by which des-Arg9-bradykinin induces contraction in this preparation. Contractions induced by des-Arg9-bradykinin in guinea-pig gallbladder (1 pM to 1 microM) increased significantly as a function of time elapsed after setting up of the preparation, reaching the maximum after 6 h of equilibration (EC50 16.4 pM and Emax 0.6 +/- 0.08 g). Des-Arg9-bradykinin-induced contraction in guinea-pig gallbladder was totally prevented by cycloheximide (70 microM, an inhibitor of protein synthesis), indomethacin (3 microM), ibuprofen (30 microM), phenidone (30 microM) or Ca2+-free medium plus EGTA, and was partially antagonised by MK 571 ((3-(3-(2-(7-chloro-2-quinolinyl) ethenyl) phenyl ((3-dimethyl amino-3-oxo-propyl) thio) methyl) propanoic acid, 0.1 microM) or by nicardipine (1 microM), but was not affected by dazoxiben (30 microM), staurosporine (100 nM) or L 655,240 (240 (3-[1-(4-clorobenzil)-5-fluoro-3-metilhyindol-2il] 2,2-dimetilpropanoic acid, 1 microM). Unexpectedly, des-Arg9-bradykinin-induced contraction was unaffected by the selective bradykinin B1 receptor antagonists, des-Arg9-[Leu8]-bradykinin and des-Arg9-NPC 17761 (des-Arg0-D-Arg [Hip3, D-HipE (transtiofenil)7, Oic8]-des-Arg9-bradykinin). However, the selective bradykinin B2 receptor antagonists, HOE 140 (D-Arg0-[Hyp3, Thi5, D-Tic7, Oic8]-bradykinin) and NPC 17731 (D-Arg0 [Hyp3, DHypE (transpropyl)7, Oic8]-bradykinin), completely blocked des-Arg9-bradykinin-mediated contraction. Pre-treatment of the animals with Escherichia coli endotoxin (lipopolysaccharide, 30 microg/animal, i.v., 24 h) did not significantly change the response to des-Arg9-bradykinin induction. It is concluded that des-Arg9-bradykinin-induced contractions in guinea-pig gallbladder are mediated primarily by the release of proinflammatory eicosanoid(s) derived from the cyclo-oxygenase pathway. These effects are unrelated to thromboxane A2 and do not seem to be coupled to activation of a protein kinase C-dependent mechanism. Response to des-Arg9-bradykinin increases as a function of the equilibration period of the preparation by a mechanism dependent on protein synthesis and seems to be mediated by activation of bradykinin B2 (but not B1) receptors. Finally, in contrast to that observed for bradykinin, the contraction induced by des-Arg9-bradykinin in guinea-pig gallbladder is fully dependent on the influx of extracellular Ca2+, partially through L-type Ca2+ channels.

Inducible receptors

While regulation of receptor function is known to occur at many levels (e.g. transcriptional, post-translational), it is generally perceived that a tissue either expresses or does not express a particular receptor in an all-or-none fashion. Many pathological (e.g. tissue injury) and physiological (e.g. angiogenesis) processes have, however, been shown to be associated with the transcriptional induction of specific receptors. Induced receptors are not confined to any particular class, but range from G protein-coupled receptors to receptor tyrosine kinases. The potential implications of de novo receptor expression are profound with respect to potential novel therapeutic targets in specific disease states. Further, this observation may explain unexpected side-effects in the pharmacotherapy of existing disease states. In this article Lucy Donaldson, Michael Hanley and Amparo Villablanca discuss circumstances under which de novo receptor induction has been described, potential mechanisms of induction and the implications for pharmacology.

The sixth transmembrane domains of the human B1 and B2 bradykinin receptors are structurally compatible and involved in discriminating between subtype-selective agonists

In order to investigate the molecular basis for the ability of the human B1 and B2 bradykinin (BK) receptor subtypes to discriminate between subtype-selective ligands, we constructed chimeric proteins in which the sixth transmembrane domains (TM-VI) of these receptors were exchanged. The pharmacological profiles of the constructs were analyzed by radioligand binding in particulate preparations of transiently transfected HEK293 cells using the agonist [3H]des-Arg10-kallidin and the antagonist [3H]NPC17731. The ability of these constructs to transmit an intracellular signal was measured in transiently transfected A10 cells, a vascular smooth muscle cell line, by single cell Ca2+ imaging. Substitution of B1 TM-VI into the B2 receptor (B2(B1VI)) dramatically reduced the affinity of the B2-selective agonist BK, whereas the affinity of the B2-selective antagonist NPC17731 was unaltered. High affinity BK binding was fully regained when two residues, Tyr259 and Ala263, near the extracellular surface of TM-VI in B2(B1VI), were replaced with the corresponding residues in the wild-type B2 receptor, which are Phe259 and Thr263. The construct B1(B2VI), produced by substitution of B2 TM-VI into the B1 receptor, did not support high affinity binding of the B1-selective agonist des-Arg10-kallidin. In contrast to BK and des-Arg10-kallidin, the binding of the less subtype-selective agonist kallidin showed little sensitivity to TM-VI exchange. These results show that TM-VI in the human B1 and B2 BK receptor subtypes, although only 36% identical, are structurally compatible. Furthermore, this domain contributes significantly to the ability of these receptors to discriminate between the subtype-selective agonists BK and des-Arg10-kallidin.