Transfected β3- but Not β2-Adrenergic Receptors Regulate Cystic Fibrosis Transmembrane Conductance Regulator Activity via a New Pathway Involving the Mitogen-Activated Protein Kinases Extracellular Signal-Regulated Kinases

Agonist-induced desensitisation of β3 -adrenoceptors: Where, when, and how?

β₃ -Adrenoceptor agonists have proven useful in the treatment of overactive bladder syndrome, but it is not known whether their efficacy during chronic administration may be limited by receptor-induced desensitisation. Whereas the β₂ -adrenoceptor has phosphorylation sites that are important for desensitisation, the β₃ -adrenoceptor lacks these; therefore, it had been assumed that β₃ -adrenoceptors are largely resistant to agonist-induced desensitisation. While all direct comparative studies demonstrate that β₃ -adrenoceptors are less susceptible to desensitisation than β₂ -adrenoceptors, desensitisation of β₃ -adrenoceptors has been observed in many models and treatment settings. Chimeric β₂ - and β₃ -adrenoceptors have demonstrated that the C-terminal tail of the receptor plays an important role in the relative resistance to desensitisation but is not the only relevant factor. While the evidence from some models, such as transfected CHO cells, is inconsistent, it appears that desensitisation is observed more often after long-term (hours to days) than short-term (minutes to hours) agonist exposure. When it occurs, desensitisation of β₃ -adrenoceptors can involve multiple levels including down-regulation of its mRNA and the receptor protein and alterations in post-receptor signalling events. The relative contributions of these mechanistic factors apparently depend on the cell type under investigation. Which if any of these factors is applicable to the human urinary bladder remains to be determined. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

β3-Adrenoceptor agonists for overactive bladder syndrome: Role of translational pharmacology in a repositioning clinical drug development project

β3-Adrenoceptor agonists were originally considered as a promising drug class for the treatment of obesity and/or type 2 diabetes. When these development efforts failed, they were repositioned for the treatment of the overactive bladder syndrome. Based on the example of the β3-adrenoceptor agonist mirabegron, but also taking into consideration evidence obtained with ritobegron and solabegron, we discuss challenges facing a translational pharmacology program accompanying clinical drug development for a first-in-class molecule. Challenges included generic ones such as ligand selectivity, species differences and drug target gene polymorphisms. Challenges that are more specific included changing concepts of the underlying pathophysiology of the target condition while clinical development was under way; moreover, a paucity of public domain tools for the study of the drug target and aspects of receptor agonists as drugs had to be addressed. Nonetheless, a successful first-in-class launch was accomplished. Looking back at this translational pharmacology program, we conclude that a specifically tailored and highly flexible approach is required. However, several of the lessons learned may also be applicable to translational pharmacology programs in other indications.

Biphasic Erk1/2 activation sequentially involving Gs and Gi signaling is required in beta3-adrenergic receptor-induced primary smooth muscle cell proliferation

The beta3 adrenergic receptor (B3-AR) reportedly induces cell proliferation, but the signaling pathways that were proposed, involving either Gs or Gi coupling, remain controversial. To further investigate the role of G protein coupling in B3-AR induced proliferation, we stimulated primary human myometrial smooth muscle cells with SAR150640 (B3-AR agonist) in the absence or presence of variable G-protein inhibitors. Specific B3-AR stimulation led to an Erk1/2 induced proliferation. We observed that the proliferative effects of B3-AR require two Erk1/2 activation peaks (the first after 3min, the second at 8h). Erk1/2 activation at 3min was mimicked by forskolin (adenylyl-cyclase activator), and was resistant to pertussis toxin (Gi inhibitor), suggesting a Gs protein signaling. This first signaling also required the downstream Gs signaling effectors PKA and Src. However, Erk1/2 activation at 8h turned out to be pertussis toxin-dependent, and PKA-independent, indicating a Gi signaling pathway in which Src and PI3K were required. The pharmacological inhibition of both the Gs and Gi pathway abolished B3-AR-induced proliferation. Altogether, these data indicate that B3-AR-induced proliferation depends on the biphasic activation of Erk1/2 sequentially induced by the Gs/PKA/Src and Gi/Src/PI3K signaling pathways.

MicroRNA profiling of cystic fibrosis intestinal disease in mice

Cystic fibrosis (CF) intestinal disease is characterized by alterations in processes such as proliferation and apoptosis which are known to be regulated in part by microRNAs. Herein, we completed microRNA expression profiling of the intestinal tissue from the cystic fibrosis mouse model of cystic fibrosis transmembrane conductance regulator (Cftr) deficient mice (BALBc/J Cftr(tm1UNC)), relative to that of wildtype littermates, to determine whether changes in microRNA expression level are part of this phenotype. We identified 24 microRNAs to be significantly differentially expressed in tissue from CF mice compared to wildtype, with the higher expression in tissue from CF mice. These data were confirmed with real time PCR measurements. A comparison of the list of genes previously reported to have decreased expression in the BALB×C57BL/6J F2 CF intestine to that of genes putatively targeted by the 24 microRNAs, determined from target prediction software, revealed 155 of the 759 genes of the expression profile (20.4%) to overlap with predicted targets, which is significantly more than the 100 genes expected by chance (p=1×10(-8)). Pathway analysis identified these common genes to function in phosphatase and tensin homolog-, protein kinase A-, phosphoinositide-3 kinase/Akt- and peroxisome proliferator-activated receptor alpha/retinoid X receptor alpha signaling pathways, among others, and through real time PCR experiments genes of these pathways were demonstrated to have lower expression in the BALB CF intestine. We conclude that altered microRNA expression is a feature which putatively influences both metabolic abnormalities and the altered tissue homeostasis component of CF intestinal disease.

Genistein stimulates duodenal HCO(3)(-) secretion through PI3K pathway in mice

Genistein has been proposed as a promising pharmacotherapeutic for cystic fibrosis. We recently found that genistein stimulates murine duodenal HCO(3)(-) secretion through cystic fibrosis transmembrane conductance regulator (CFTR). The aim of the present study was to determine the intracellular signal pathways involved in genistein-stimulated duodenal HCO(3)(-) secretion. Murine duodenal mucosal HCO(3)(-) secretion was examined in vitro in Ussing chambers by the pH-stat technique. The results showed that neither cAMP-dependent signal pathway inhibitors MDL-12330A and KT-5720, nor cGMP signal pathway inhibitors NS2028 and KT5823, nor calcium signal pathway inhibitors verapamil and W-13, altered genistein-stimulated duodenal HCO(3)(-) secretion. In calcium-free solution, genistein-stimulated duodenal HCO(3)(-) secretion was not altered either. Vanadate, an inhibitor of protein tyrosine phosphatase, only partially inhibited genistein-stimulated duodenal HCO(3)(-) secretion. However, both wortmannin and LY294002, two structurally and mechanistically distinct phosphatidylinositol 3-kinase (PI3K) inhibitors, markedly inhibited genistein-stimulated duodenal HCO(3)(-) secretion. Genistein increased duodenal mucosal PI3K activity and induced the phosphorylation of Akt, a signaling molecule downstream of PI3K, which was again inhibited by wortmannin. Estrogen receptor antagonist, ICI182,780, also markedly inhibited genistein-stimulated duodenal HCO(3)(-) secretion and genistein-induced PI3K activity increase in duodenal mucosa. These results demonstrate that genistein stimulates duodenal HCO(3)(-) secretion mainly through estrogen receptor and PI3K-dependent pathway. These findings contribute to the understanding of the molecular mechanism of genistein-induced anion secretion and further pharmacotherapeutic development and use of genistein or related substances in the treatment of diseases of epithelial tissues.

Cross-regulation between beta 1- and beta 3-adrenoceptors following chronic beta-adrenergic stimulation in neonatal rat cardiomyocytes

BACKGROUND AND PURPOSE

We have previously shown that beta-adrenoceptors continuously stimulated with noradrenaline induces an increase in beta(3)-adrenoceptors (G alpha(i)PCRs) and a decrease in beta(1)-adrenoceptors (G alpha(s)PCRs) at functional, genomic and protein levels. This compensatory modification induced by noradrenaline is probably one of the consequences of cardiac depression observed in heart disease. Therefore, we investigated further the interaction between beta(1)- and beta(3)-adrenoceptors in neonatal rat cardiomyocytes.

EXPERIMENTAL APPROACH

Functional studies were performed by cyclic adenosine monophosphate (cAMP) accumulation assays in cells untreated or treated with dobutamine and ICI 118551 (beta(1)-adrenoceptor) or CL-3162436243 (beta(3)-adrenoceptor) for 24 h in the presence or absence of protein kinase inhibitors. Beta-adrenoceptor and protein kinase expression was monitored by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and by Western blotting, respectively.

KEY RESULTS

Chronic beta(1)- or beta(3)-adrenoceptor stimulation reduced beta(1)-adrenoceptor-mediated cAMP accumulation in association with a decrease in beta(1)-adrenoceptor mRNA and protein levels through protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and p38 mitogen-activated protein kinase (p38MAPK) activation. In contrast, both treatments induced an increase in beta(3)-adrenoceptor expression and beta(3)-adrenoceptor-inhibited forskolin response through PKC, extracellular-signal-regulated kinases 1 and 2 (ERK1/2) and p38MAPK phosphorylation, although no beta(3)-adrenoceptor response was observed in untreated cells. ERK1/2 and p38MAPK were activated by both treatments. The modulation of beta(1)- or beta(3)-adrenoceptor function did not require stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) although chronic beta(1)-adrenoceptor stimulation activated SAPK/JNK. Beta(3)-adrenoceptor treatment activated Akt although PI3K was not involved in beta(3)-adrenoceptor up-regulation.

CONCLUSION AND IMPLICATIONS

We show for the first time that chronic beta(1)- or beta(3)-adrenoceptor stimulation leads to the modulation of beta(1)- and beta(3)-adrenoceptors by a cross-regulation involving PKC, PI3K p38MAPK and MEK/ERK1/2 pathway, and through protein kinase A when beta(1)-adrenoceptors are chronically activated.

JNK mitogen-activated protein kinase limits calcium-dependent chloride secretion across colonic epithelial cells

Neuroimmune agonists induce epithelial Cl(-) secretion through elevations in intracellular Ca2+ or cAMP. Previously, we demonstrated that epidermal growth factor receptor (EGFR) transactivation and subsequent ERK MAPK activation limits secretory responses to Ca2+-dependent, but not cAMP-dependent, agonists. Although JNK MAPKs are also expressed in epithelial cells, their role in regulating transport function is unknown. Here, we investigated the potential role for JNK in regulating Cl(-) secretion in T(84) colonic epithelial cells. Western blot analysis revealed that a prototypical Ca2+-dependent secretagogue, carbachol (CCh; 100 microM), induced phosphorylation of both the 46-kDa and 54-kDa isoforms of JNK. This effect was mimicked by thapsigargin (TG), which specifically elevates intracellular Ca2+, but not by forskolin (FSK; 10 microM), which elevates cAMP. CCh-induced JNK phosphorylation was attenuated by the EGFR inhibitor, tyrphostin-AG1478 (1 microM). Pretreatment of voltage-clamped T(84) cells with SP600125 (2 microM), a specific JNK inhibitor, potentiated secretory responses to both CCh and TG but not to FSK. The effects of SP600125 on CCh-induced secretion were not additive with those of the ERK inhibitor, PD98059. Finally, in apically permeabilized T(84) cell monolayers, SP600125 potentiated CCh-induced K+ conductances but not Na+/K+ATPase activity. These data demonstrate a novel role for JNK MAPK in regulating Ca2+ but not cAMP-dependent epithelial Cl(-) secretion. JNK activation is mediated by EGFR transactivation and exerts its antisecretory effects through inhibition of basolateral K+ channels. These data further our understanding of mechanisms regulating epithelial secretion and underscore the potential for exploitation of MAPK-dependent signaling in treatment of intestinal transport disorders.

Involvement of phosphatidylinositol 3-kinase in cAMP- and cGMP-induced duodenal epithelial CFTR activation in mice

Although phosphatidylinositol 3-kinase (PI3K) is essential for several cellular signal transductions, its role in the regulation of cystic fibrosis transmembrane conductance regulator (CFTR) activity in intestinal epithelial cells is poorly understood. Therefore, the possible involvement of PI3K in the regulation of cAMP- and cGMP-induced duodenal epithelial CFTR activation was investigated in the present study. Forskolin and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) markedly stimulated duodenal mucosal HCO(3)(-) secretion and short-circuit current (I(sc)) in CFTR wild-type mice, which was significantly inhibited by CFTR(inh)-172, a highly potent and specific CFTR inhibitor. Forskolin and 8-Br-cGMP failed to stimulate duodenal HCO(3)(-) secretion and I(sc) in CFTR knockout mice. Moreover, forskolin- and 8-Br-cGMP-stimulated duodenal HCO(3)(-) secretion and I(sc) were significantly reduced by wortmannin and LY294002, two selective PI3K inhibitors that are structurally and mechanistically different. Forskolin and 8-Br-cGMP induced CFTR phosphorylation and shifted CFTR proteins to the plasma membrane of duodenal epithelial cells, which were inhibited by wortmannin and LY294002. Forskolin and 8-Br-cGMP not only increased the activity of PI3K but also induced the phosphorylation of Akt, a signaling molecule downstream of PI3K, which were again inhibited by wortmannin and LY294002. Together, our results obtained from functional, biochemical, and morphological studies demonstrate that PI3K pathway plays an important role in the regulation of cAMP- and cGMP-induced duodenal epithelial CFTR channel activity and intracellular trafficking.

beta3-adrenergic receptor activation increases human atrial tissue contractility and stimulates the L-type Ca2+ current

beta3-adrenergic receptor (beta3-AR) activation produces a negative inotropic effect in human ventricles. Here we explored the role of beta3-AR in the human atrium. Unexpectedly, beta3-AR activation increased human atrial tissue contractility and stimulated the L-type Ca2+ channel current (I Ca,L) in isolated human atrial myocytes (HAMs). Right atrial tissue specimens were obtained from 57 patients undergoing heart surgery for congenital defects, coronary artery diseases, valve replacement, or heart transplantation. The I(Ca,L) and isometric contraction were recorded using a whole-cell patch-clamp technique and a mechanoelectrical force transducer. Two selective beta3-AR agonists, SR58611 and BRL37344, and a beta3-AR partial agonist, CGP12177, stimulated I(Ca,L) in HAMs with nanomolar potency and a 60%-90% efficacy compared with isoprenaline. The beta3-AR agonists also increased contractility but with a much lower efficacy (approximately 10%) than isoprenaline. The beta3-AR antagonist L-748,337, beta1-/beta2-AR antagonist nadolol, and beta1-/beta2-/beta3-AR antagonist bupranolol were used to confirm the involvement of beta3-ARs (and not beta1-/beta2-ARs) in these effects. The beta3-AR effects involved the cAMP/PKA pathway, since the PKA inhibitor H89 blocked I(Ca,L) stimulation and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) strongly increased the positive inotropic effect. Therefore, unlike in ventricular tissue, beta3-ARs are positively coupled to L-type Ca2+ channels and contractility in human atrial tissues through a cAMP-dependent pathway.

Flagellin-stimulated Cl- secretion and innate immune responses in airway epithelia: role for p38

Activation of an innate immune response in airway epithelia by the human pathogen Pseudomonas aeruginosa requires bacterial expression of flagellin. Addition of flagellin (10(-7) M) to airway epithelial cell monolayers (Calu-3, airway serous cell-like) increased Cl(-) secretion (I(Cl)) beginning after 3-10 min, reaching a plateau after 20-45 min at DeltaI(Cl) = 15-50 microA/cm(2). Similar, although 10-fold smaller, responses were observed in well-differentiated bronchial epithelial cultures. Flagellin stimulated I(Cl) in the presence of maximally stimulating doses of the purinergic agonist ATP, but had no effects following forskolin. IL-1beta (produced by both epithelia and neutrophils during infections) stimulated I(Cl) similar to flagellin. Flagellin-, IL-1beta-, ATP-, and forskolin-stimulated I(Cl) were inhibited by cystic fibrosis transmembrane conductance regulator (CFTR) blockers GlyH101, CFTRinh172, and glibenclamide. Neither flagellin nor IL-1beta altered transepithelial fluxes of membrane-impermeant dextran (10 kDa) or lucifer yellow (mol wt = 457), but both activated p38, NF-kappaB, and IL-8 secretion. Blockers of p38 (SB-202190 and SB-203580) reduced flagellin- and IL-1beta-stimulated I(Cl) by 33-50% but had smaller effects on IL-8 and NF-kappaB. It is concluded that: 1) flagellin and IL-1beta activated p38, NF-kappaB, IL-8, and CFTR-dependent anion secretion without altering tight junction permeability; 2) p38 played a role in regulating I(Cl) and IL-8 but not NF-kappaB; and 3) p38 was more important in flagellin- than IL-1beta-stimulated responses. During P. aeruginosa infections, flagellin and IL-1beta are expected to increase CFTR-dependent ion and fluid flow into and bacterial clearance from the airways. In cystic fibrosis, the secretory response would be absent, but activation of p38, NF-kappaB, and IL-8 would persist.

8-iso-PGE2Stimulates Anion Efflux from Airway Epithelial Cells via the EP4Prostanoid Receptor

Isoprostanes are biologically active molecules, produced when reactive oxygen species mediate the peroxidation of membrane polyunsaturated fatty acids. Previous work has demonstrated that the isoprostane 8-iso-prostaglandin E(2) (PGE(2)) stimulates cystic fibrosis transmembrane conductance regulator (CFTR)-mediated transepithelial anion secretion across the human airway epithelial cell line, Calu-3. Since isoprostanes predominantly achieve their effects via binding to prostanoid receptors, we hypothesized that this 8-iso-PGE(2) stimulation of CFTR activity was the result of the isoprostane binding to a prostanoid receptor. Using RT-PCR, immunoblotting, and immunofluorescence, we here demonstrate that Calu-3 cells express the EP(1-4) and FP receptors, and localize these proteins in polarized cell monolayers. Using iodide efflux as a marker for CFTR-mediated Cl(-) efflux, we investigate whether prostanoid receptor agonists elicit a functional response from Calu-3 cells. Application of the agonists PGE(2), misoprostol (EP(2), EP(3), and EP(4)) and PGE(1)-OH (EP(3) and EP(4)) stimulate iodide efflux; however, iloprost, butaprost, sulprostone, and fluoprostenol (agonists of the EP(1), EP(2), EP(3), and FP receptors, respectively) have no effect. The iodide efflux seen with 8-iso-PGE(2) is abolished by the EP(4) receptor antagonist AH23848, the CFTR inhibitor 172, and inhibition of PKA and the PI3K pathway. In conclusion, we demonstrate that although Calu-3 cells possess numerous prostanoid receptors, only the EP(4) subtype appears capable of eliciting a functional iodide efflux response, which is mediated via the EP(4) receptor. We propose that 8-iso-PGE(2), acting via EP(4) receptor, could play an important role in the CFTR-mediated response to oxidant stress, and which would be compromised in the CF airways.

EGF receptor transactivation and PI3-kinase mediate stimulation of ERK by alpha(2A)-adrenoreceptor in intestinal epithelial cells: a role in wound healing

Intestinal cells express alpha(2A)-adrenoreceptors that stimulate sodium and peptide absorption and promote cell proliferation. Involved mechanisms are poorly understood and are not fully related to inhibition of cAMP production. Previous study using a clone of CaCo2 cells expressing the human alpha(2A)-adrenoreceptor (CaCo2-3B) showed that alpha(2)-adrenoreceptor agonists cause extracellular signal-regulated kinase (ERK) phosphorylation. Present work examines the signaling pathway triggering ERK activation and investigates the consequence of alpha(2A)-adrenoreceptor stimulation on cell migration. Treatment of CaCo2-3B with the alpha(2)-adrenoreceptor agonist 5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline (UK14304) induces not only ERK, but also Akt phosphorylation. Both effects are strongly attenuated by inhibition or desensitization of epidermal growth factor (EGF) receptor, matrix metalloproteinase (MMP) blockade, heparin-binding-EGF neutralization or phosphatidylinositol 3-kinase (PI3-kinase) inhibitors. Conditioned medium from UK14304-treated CaCo2-3B stimulates ERK in parental CaCo2 by a mechanism sensitive to EGF receptor and PI3-kinase inhibitors. Exposure of CaCo2-3B to UK14304 accelerates the wound healing. This effect is abolished by heparin-binding-EGF neutralization but not by mitomycin C, indicating that it results probably from increased cell spreading and/or migration. In conclusion, alpha(2A)-adrenoreceptor activates ERK and Akt in intestinal cells by a common pathway which depends on PI3-kinase activation and results from EGF receptor transactivation, via an autocrine/paracrine pathway implying MMP activation and heparin-binding-EGF shedding. Therefore, alpha(2A)-adrenoreceptor could have a positive role in intestinal regeneration in vivo.

Enhanced IL-1beta-induced IL-8 production in cystic fibrosis lung epithelial cells is dependent of both mitogen-activated protein kinases and NF-kappaB signaling

Transcription nuclear factor-kappaB (NF-kappaB) is hyperactivated in cystic fibrosis (CF) lung epithelial cells, and participates in exaggerated IL-8 production in the CF lung. We recently found that rapid activation of NF-kappaB occurred in a CF lung epithelial IB3-1 cell line (CF cells) upon IL-1beta stimulation, which was not observed in its CFTR-corrected lung epithelial S9 cell line (corrected cells). To test whether other signaling pathways such as that of mitogen-activated protein kinases (MAPKs) could be involved in IL-1beta-induced IL-8 production of CF cells, we investigated ERK1/2, JNK, and p38MAP signaling compared to NF-kappaB. Within 30min, exposure to IL-1beta caused high activation of NF-kappaB, ERK1/2, p38MAP but not JNK in CF cells compared to corrected cells. Treatment of IL-1beta-stimulated CF cells with a series of chemical inhibitors of NF-kappaB, ERK1/2, and p38MAP, when used separately, reduced slightly IL-8 production. However, when used together, these inhibitors caused a blockade in IL-1beta-induced IL-8 production in CF cells. Understanding of the cross-talk between NF-kappaB and MAPKs signaling in CF lung epithelial cells may help in developing new therapeutics to reduce lung inflammation in patients with CF.

NHE-RF1 protein rescues DeltaF508-CFTR function

In cystic fibrosis (CF), the DeltaF508-CFTR anterograde trafficking from the endoplasmic reticulum to the plasma membrane is inefficient. New strategies for increasing the delivery of DeltaF508-CFTR to the apical membranes are thus pathophysiologically relevant targets to study for CF treatment. Recent studies have demonstrated that PDZ-containing proteins play an essential role in determining polarized plasma membrane expression of ionic transporters. In the present study we have hypothesized that the PDZ-containing protein NHE-RF1, which binds to the carboxy terminus of CFTR, rescues DeltaF508-CFTR expression in the apical membrane of epithelial cells. The plasmids encoding DeltaF508-CFTR and NHE-RF1 were intranuclearly injected in A549 or Madin-Darby canine kidney (MDCK) cells, and DeltaF508-CFTR channel activity was functionally assayed using SPQ fluorescent probe. Cells injected with DeltaF508-CFTR alone presented a low chloride channel activity, whereas its coexpression with NHE-RF1 significantly increased both the basal and forskolin-activated chloride conductances. This last effect was lost with DeltaF508-CFTR deleted of its 13 last amino acids or by injection of a specific NHE-RF1 antisense oligonucleotide, but not by NHE-RF1 sense oligonucleotide. Immunocytochemical analysis performed in MDCK cells transiently transfected with DeltaF508-CFTR further revealed that NHE-RF1 specifically determined the apical plasma membrane expression of DeltaF508-CFTR but not that of a trafficking defective mutant potassium channel (KCNQ1). These data demonstrate that the modulation of the expression level of CFTR protein partners, like NHE-RF1, can rescue DeltaF508-CFTR activity.