Increase In Intracellular cAMP Levels Research Articles

Increase of Intracellular Cyclic AMP by PDE4 Inhibitors Affects HepG2 Cell Cycle Progression and Survival.

Type 4 cyclic nucleotide phosphodiesterases (PDE4) are major members of a superfamily of enzymes (PDE) involved in modulation of intracellular signaling mediated by cAMP. Broadly expressed in most human tissues and present in large amounts in the liver, PDEs have in the last decade been key therapeutic targets for several inflammatory diseases. Recently, a significant body of work has underscored their involvement in different kinds of cancer, but with no attention paid to liver cancer. The present study investigated the effects of two PDE4 inhibitors, rolipram and DC-TA-46, on the growth of human hepatoma HepG2 cells. Treatment with these inhibitors caused a marked increase of intracellular cAMP level and a dose- and time-dependent effect on cell growth. The concentrations of inhibitors that halved cell proliferation to about 50% were used for cell cycle experiments. Rolipram (10 μM) and DC-TA-46 (0.5 μM) produced a decrease of cyclin expression, in particular of cyclin A, as well as an increase in p21, p27 and p53, as evaluated by Western blot analysis. Changes in the intracellular localization of cyclin D1 were also observed after treatments. In addition, both inhibitors caused apoptosis, as demonstrated by an Annexin-V cytofluorimetric assay and analysis of caspase-3/7 activity. Results demonstrated that treatment with PDE4 inhibitors affected HepG2 cell cycle and survival, suggesting that they might be useful as potential adjuvant, chemotherapeutic or chemopreventive agents in hepatocellular carcinoma. J. Cell. Biochem. 118: 1401-1411, 2017. © 2016 Wiley Periodicals, Inc.

Wnt/β-catenin signaling inhibitor ICG-001 enhances pigmentation of cultured melanoma cells

BackgroundWnt/β-catenin signaling is important in development and differentiation of melanocytes. ObjectiveThe object of this study was to evaluate the effects of several Wnt/β-catenin signaling inhibitors on pigmentation using melanoma cells. MethodsMelanoma cells were treated with Wnt/β-catenin signaling inhibitors, and then melanin content and tyrosinase activity were checked. ResultsAlthough some inhibitors showed slight inhibition of pigmentation, we failed to observe potential inhibitory effect of those chemicals on pigmentation of HM3KO melanoma cells. Rather, one of powerful Wnt/β-catenin signaling inhibitors, ICG-001, increased the pigmentation of HM3KO melanoma cells. Pigmentation-enhancing effect of ICG-001 was reproducible in other melanoma cell line MNT-1. Consistent with these results. ICG-001 increased the expression of pigmentation-related genes, such as MITF, tyrosinase and TRP1. When ICG-001 was treated, the phosphorylation of CREB was significantly increased. In addition, ICG-001 treatment led to quick increase of intracellular cAMP level, suggesting that ICG-001 activated PKA signaling. The blockage of PKA signaling with pharmaceutical inhibitor H89 inhibited the ICG-001-induced pigmentation significantly. ConclusionsThese results suggest that PKA signaling is pivotal in pigmentation process itself, while the importance of Wnt/β-catenin signaling should be emphasized in the context of development and differentiation.

Molecular cloning and pharmacological characterization of giant panda (Ailuropoda melanoleuca) melanocortin-4 receptor

The melanocortin-4 receptor (MC4R) is critical in regulating mammalian food intake and energy expenditure. Giant panda (Ailuropoda melanoleuca), famous as the living fossil, is an endangered species endemic to China. We are interested in exploring the functions of the giant panda MC4R (amMC4R) in regulating energy homeostasis and report herein the molecular cloning and pharmacology of the amMC4R. Sequence analysis revealed that amMC4R was highly homologous (>88%) at nucleotide and amino acid sequences to several mammalian MC4Rs. Western blot revealed that the expression construct myc-amMC4R in pcDNA3.1 was successfully constructed and expressed in HEK293T cells. With human MC4R (hMC4R) as a control, pharmacological characteristics of amMC4R were analyzed with binding and signaling assays. Four agonists, including [Nle4, D-Phe7]-α-melanocyte stimulating hormone (NDP-MSH), α- and β-MSH, and a small molecule agonist, THIQ, were used in binding and signaling assays. We showed that amMC4R bound NDP-MSH with the highest affinity followed by THIQ, α-MSH, and β-MSH, with the same ranking order as hMC4R. Treatment of HEK293T cells expressing amMC4R with different concentrations of agonists resulted in dose-dependent increase of intracellular cAMP levels, with similar EC50s for the four agonists. The results suggested that the cloned amMC4R encoded a functional MC4R. The availability of amMC4R and its binding and signaling properties will facilitate the investigation of amMC4R in regulating food intake and energy homeostasis.

Hetero-oligomerization and Functional Interaction between Purinergic Receptors Expressed in Platelets to Regulate Platelet Shape Change

Adenosine and its precursors, ATP and ADP, exert various physiological effects via binding to purinergic receptors. We previously used co-immunoprecipitation, bioluminescence resonance energy transfer (BRET) and immunoelectron microscopy to demonstrate the hetero-oligomerization of purinergic receptor subtypes. Furthermore, pharmacological studies found significant changes in receptor-mediated signaling in human embryonic kidney (HEK) 293T cells co-transfected with these receptors. These findings suggest that heterodimers of purinergic receptors may have distinct pharmacological profiles, possibly due to dimerization-induced conformational changes, further suggesting that hetero-dimerization may be employed to "fine-tune" purinergic receptor signaling. Adenosine A(2A) receptor (A(2A)R), P2Y1 receptor (P2Y1R) and P2Y12 receptor (P2Y12R) are predominantly expressed on human platelets. ADP activates human platelets by stimulating both P2Y1R and P2Y12R, which act sequentially and in concert to achieve complete platelet aggregation. In contrast, adenosine stimulates Gs-coupled A(2A)R, followed by activativation of adenylate cyclase, leading to an increase in intracellular cAMP levels, which potently inhibits platelet activation. We examined the hetero-oligomerization and functional interactions of A(2A)R, P2Y1R, and P2Y12R. In HEK293T cells triply expressing all three receptors, hetero-oligomerization was observed among the three receptors. Additionally, P2Y1R agonist-evoked Ca(2+) signaling was significantly inhibited by co-treatment with an A(2A)R antagonist in HEK293T cells. In human platelets, we identified endogenous A(2A)R/P2Y1R and A(2A)R/P2Y12R heterodimers. We also observed functional Ca(2+)-signaling-related cross-talk similar to those found in HEK293T cells, and found that they appeared to affect platelet shape. These results collectively suggest that intermolecular signal transduction and specific conformational changes occur among components of the hetero-oligomers formed by these three receptors.

Abstract 19593: Sirtuin-3 is Essential for Glucagon-like Peptide-1-mediated Restoration of Diabetic Cardiomyopathy

Introduction: Sirtuin 3 (SIRT3) is a mitochondrial protein deacetylase and its expression is increased by fasting and exercise in skeletal muscle; however, the impact of anti-diabetic intervention on diabetic myocardium remained uncertain. Hypothesis: We hypothesized that the anti-diabetic remedy glucagon-like peptide-1 agonist (exendin-4; Ex4) may ameliorate mitochondrial remodeling observed in diabetic cardiomyopathy. Methods: Type 2 diabetic mice [T2DM; KKAy and dietary diabetes induced by high fat and high sucrose diet (HF/HS), male 14-16 w/o] and age- and gender-matched SIRT3 knockout mice with dietary diabetes (sirHF/HS) diet were allocated into Ex4 (24 nmole/kg/day for 40 days) and vehicle (CON) groups. Results: T2DM-CON and sirHF/HS-CON exhibited myocardial hypertrophy, increased fibrosis, decreased cardiac capillary density, and defragmented mitochondria, which were reversed by Ex4. Consistently with the changes in mitochondrial morphology, the mitochondrial regulatory proteins mitofusin-1 (Mfn1) and mitofusin-2 (Mfn2) ratio was reduced in T2DM-CON and sirHF/HS-CON, which were ameliorated by Ex4 treatment exclusively to T2DM-CON. T2DM-CON exhibited decrease in cardiac SIRT3 level compared to nondiabetic counterpart, which was ameliorated by Ex4. Interestingly, cardiac remodeling of sirHF/HS-CON remained unchanged by Ex4 treatment, exclusively to cardiac capillary density. T2DM-CON and sirHF/HS-CON exhibited decrease in cardiac cyclic AMP level, which were attenuated by Ex4. The GLP-1 inactive analog (Ex9-39) failed to increase cardiac cyclic AMP concentration in mouse heart. In vitro analysis using cultured cardiomyocytes revealed that increase in intracellular cAMP levels by isoprotelenol (10microM) or 8-bromo-cyclic AMP (10 microM) enhanced SIRT3 mRNA, which was reversed by protein kinase A (PKA) inhibition. Conclusions: Our results indicate that Ex4 reversed abnormal suppression of SIRT3 in mitochondria of diabetic heart via restoration of cardiac cAMP.

Corticotropin Releasing Hormone and Urocortin 3 Stimulate Vascular Endothelial Growth Factor Expression through the cAMP/CREB Pathway

Colonic epithelium is the first line of defense against various pathological offenses in the gut. Previous studies have shown that the peptides of the corticotropin-releasing hormone (CRH) family modulate vascular endothelial growth factor (VEGF)-A production in other cells. Here we sought to investigate whether CRH and urocortin (Ucn) 3 regulate VEGF-A secretion in colonocytes through CRH receptors and to elucidate the underlying mechanism of action. CRH and Ucn 3 significantly increased the expression levels of VEGF-A mRNA and protein through CRH receptor 1 and 2, respectively, in human colonic epithelial cells and primary mouse intestinal epithelial cells. Underlying mechanisms involve activation of adenylyl cyclase with subsequent increase of intracellular cAMP level and increased DNA binding activity of transcription factor CREB on VEGF-A promoter region. Finally, genetic deficiency of CREB decreased intestinal inflammation and VEGF-A expression in a dextran sodium sulfate-induced colitis model. These results show that activation of CRH receptors by CRH ligands stimulates VEGF-A expression in intestinal epithelial cells through the cAMP/CREB pathway. Since VEGF-A boosts inflammatory responses through angiogenesis, these data suggest that CREB may be a key effector of CRH and Ucn 3-dependent inflammatory angiogenesis.

Annexin A4 is a novel direct regulator of adenylyl cyclase type 5.

Annexin A4 (AnxA4), a Ca(2+)- and phospholipid-binding protein, is up-regulated in the human failing heart. In this study, we examined the impact of AnxA4 on β-adrenoceptor (β-AR)/cAMP-dependent signal transduction. Expression of murine AnxA4 in human embryonic kidney (HEK)293 cells dose-dependently inhibited cAMP levels after direct stimulation of adenylyl cyclases (ACs) with forskolin (FSK), as determined with an exchange protein activated by cAMP-Förster resonance energy transfer (EPAC-FRET) sensor and an ELISA (control vs. +AnxA4: 1956 ± 162 vs. 1304 ± 185 fmol/µg protein; n = 8). Disruption of the anxA4 gene led to a consistent increase in intracellular cAMP levels in isolated adult mouse cardiomyocytes, with heart-directed expression of the EPAC-FRET sensor, stimulated with FSK, and as determined by ELISA, also in mouse cardiomyocytes stimulated with the β-AR agonist isoproterenol (ISO) (anxA4a(+/+) vs. anxA4a(-/-): 5.1 ± 0.3 vs. 6.7 ± 0.6 fmol/µg protein) or FSK (anxA4a(+/+) vs. anxA4a(-/-): 1891 ± 238 vs. 2796 ± 343 fmol/µg protein; n = 9-10). Coimmunoprecipitation experiments in HEK293 cells revealed a direct interaction of murine AnxA4 with human membrane-bound AC type 5 (AC5). As a functional consequence of AnxA4-mediated AC inhibition, AnxA4 inhibited the FSK-induced transcriptional activation mediated by the cAMP response element (CRE) in reporter gene studies (10-fold vs. control; n = 4 transfections) and reduced the FSK-induced phosphorylation of the CRE-binding protein (CREB) measured on Western blots (control vs. +AnxA4: 150 ± 17% vs. 105 ± 10%; n = 6) and by the use of the indicator of CREB activation caused by phosphorylation (ICAP)-FRET sensor, indicating CREB phosphorylation. Inactivation of AnxA4 in anxA4a(-/-) mice was associated with an increased cardiac response to β-AR stimulation. Together, these results suggest that AnxA4 is a novel direct negative regulator of AC5, adding a new facet to the functions of annexins.

Activation of α7 nicotinic acetylcholine receptors increases intracellular cAMP levels via activation of AC1 in hippocampal neurons

The activation of α7 nAChRs has been shown to improve hippocampal-dependent learning and memory. However, the molecular mechanism of α7 nAChRs' action remains elusive. We previously reported that activation of α7 nAChRs induced a prolonged enhancement of glutamatergic synaptic transmission in a PKA-dependent manner. Here, we investigated any connection between the activation of the α7 nAChR and cAMP signaling in hippocampal neurons. To address this question, we employed a FRET-based biosensor to measure the intracellular cAMP levels directly via live cell imaging. We found that application of the α7 nAChR-selective agonist choline, in the presence of the α7 nAChR positive allosteric modulator PNU-120596, induced a significant change in emission ratio of F535/F470, which indicated an increase in intracellular cAMP levels. This choline-induced increase was abolished by the α7 nAChR antagonist MLA and the calcium chelator BAPTA, suggesting that the cAMP increase depends on the α7 nAChR activation and subsequent intracellular calcium rise. The selective AC1 inhibitor CB-6673567 and siRNA-mediated deletion of AC1 both blocked the choline-induced cAMP increase, suggesting that calcium-dependent AC1 is required for choline's action. Furthermore, α7 nAChR activation stimulated the phosphorylation of synapsin, which serves as a downstream effector to regulate neurotransmitter release. Our findings provide the first direct evidence to link activation of α7 nAChRs to a cAMP rise via AC1, which defines a new signaling pathway employed by α7 nAChRs. Our study sheds light into potential molecular mechanisms of the positive cognitive actions of α7 nAChR agonists and development of therapeutic treatments for cognitive impairments.

Cyclic AMP Regulates Social Behavior in African Trypanosomes.

ABSTRACTThe protozoan parasite Trypanosoma brucei engages in surface-induced social behavior, termed social motility, characterized by single cells assembling into multicellular groups that coordinate their movements in response to extracellular signals. Social motility requires sensing and responding to extracellular signals, but the underlying mechanisms are unknown. Here we report that T. brucei social motility depends on cyclic AMP (cAMP) signaling systems in the parasite’s flagellum (synonymous with cilium). Pharmacological inhibition of cAMP-specific phosphodiesterase (PDE) completely blocks social motility without impacting the viability or motility of individual cells. Using a fluorescence resonance energy transfer (FRET)-based sensor to monitor cAMP dynamics in live cells, we demonstrate that this block in social motility correlates with an increase in intracellular cAMP levels. RNA interference (RNAi) knockdown of the flagellar PDEB1 phenocopies pharmacological PDE inhibition, demonstrating that PDEB1 is required for social motility. Using parasites expressing distinct fluorescent proteins to monitor individuals in a genetically heterogeneous community, we found that the social motility defect of PDEB1 knockdowns is complemented by wild-type parasites in trans. Therefore, PDEB1 knockdown cells are competent for social motility but appear to lack a necessary factor that can be provided by wild-type cells. The combined data demonstrate that the role of cyclic nucleotides in regulating microbial social behavior extends to African trypanosomes and provide an example of transcomplementation in parasitic protozoa.

Ex Vivo Modulation of Mobilized Peripheral Blood: Characterization of HSC and T-Cell Responses to Prostaglandin E2

16,16 dimethyl prostaglandin E2 (FT1050) was previously identified to be a critical regulator of hematopoetic stem cell (HSC) homeostasis and we hypothesized that a brief ex vivo modulation could improve patient outcomes in umbilical cord blood (UCB) transplantation by increasing the “effective dose” of HSCs. Using preclinical models, we have demonstrated that pulse treating human HSCs with FT1050 significantly enhances the homing and engraftment of donor cells to the bone marrow niche, in part by upregulating CXCR4.To date, preclinical and clinical translation of this therapeutic paradigm has focused on UCB. In an initial clinical evaluation, ex vivo modulation of UCB with FT1050 (2 hours, on site, just prior to infusion) was found to accelerate neutrophil recovery (median 17.5 vs 21 days, p = 0.045) in adult patients undergoing double UCB transplantation (Cutler, 2013). In this Phase 1b study, we also observed low rates of viral reactivation (17% incidence of CMV viremia vs. 42-67% reported in the literature) and GvHD, suggesting that FT1050 may also be having a therapeutically relevant effect on the T-cell compartment of the treated UCB units. To explore the potential therapeutic application of ex vivo modulation of other allogeneic HSC sources, we conducted a series of in vitro studies characterizing the effect of FT1050 on HSCs and T-cells derived from mobilized peripheral blood (mPB).CD34+ cells isolated from mPB or UCB were treated with 10μM FT1050 for 2 hours at 37ºC. We showed that FT1050 binds to the EP2 and EP4 receptors on the cell surface, activating adenylate cyclase which results in a rapid increase in intracellular cAMP levels. Results of a competitive antibody binding assay demonstrated robust and comparable increases in cAMP levels in CD34+ cells from both UCB and mPB. Genome-wide expression analysis of FT1050 treated CD34+ cells showed a highly similar expression response in cells isolated from mPB and UCB, including a 20-fold increase in the key HSC homing receptor CXCR4. We also observed similar FT1050-dependent increases in the surface CXCR4 protein levels and significant improvements in transwell migration rates to gradients of SDF-1. Genome-wide expression analysis within the T-cell compartments from both UCB and mPB (e.g., CD8, CD4, NK, Tregs) revealed a highly similar set of FT1050 induced genes which are involved in cell cycle (e.g., CCND1, CCNE1), tolerance (e.g., DUSP5, FLT1) and anti-viral response (e.g., CD56, EFNB2). The results of this preclinical characterization study provides the basis upon which to explore the future use of FT1050 modulated mPB in a clinical setting. DisclosuresRobbins:Fate Therapeutics: Employment, Equity Ownership. Le:Fate Therapeutics: Employment, Equity Ownership. Troung:Fate Therapeutics: Employment, Equity Ownership. Foster:Fate Therapeutics: Employment, Equity Ownership. Rezner:Fate Therapeutics: Employment, Equity Ownership. Mitchell:Fate Therapeutics: Employment, Equity Ownership. Guerrettaz:Fate Therapeutics: Employment, Equity Ownership. Multani:Fate Therapeutics: Employment, Equity Ownership. Shoemaker:Fate Therapeutics: Employment, Equity Ownership.

The new era in the pharmacological treatment of overactive bladder (OAB): mirabegron--a new selective beta3agonist

Overactive bladder is defined by ICS as urgency frequency and nocturia, with or without urgency urinary incontinence in the absence of urinary tract infection, or other obvious causative pathology Lower urinary tract symptoms (LUTS) are highly prevalent, especially in aging populations. Epidemiological studies reported LUTS in 62% of men and 67% of women, rising to 81% and 79%, respectively in adults over 60 years old. However the actual burden of LUTS remains relatively unrecognized. LUTS, mainly due to considerable distress including almost all aspects of social functioning, impact on sleep and mental health, may significantly affect quality of life. Management of LUTS including OAB has undergone dramatic changes since 1972, when the first antimuscarinic drug-oxybutynin, was introduced into clinical practice. In the last two decades, six new antimuscarinic drugs entered OAB field and this was accompanied by introduction of botulinum toxin into clinical practice in patients resistant to or not compliant with antimuscarinics. Nowadays, it is recognized that OAB is progressive, age-related and non sex-specific condition with most patients experiencing a combination of storage, voiding and post-micturition symptoms. In 2013, the next step was taken, with new therapeutic options for OAB, enabling an even more patient-tailored approach. This was possible for both, male and female OAB sufferers with new class of oral 3 adrenoreceptor agonist (mirabegron). This drug, by stimulation of 3-adrenoceptors, couples via Gs proteins to adenylyl cyclase, what results in an increase of intracellular cAMP levels and a subsequent activation of cAMP-dependent protein kinase A, which then phosphorylates myosin light chain kinase responsible for inhibition of calcium-calmodulin dependent interaction of myosin with actin. Moreover the cAMP increase also leads to the reduction of cytoplasmic Ca2+ concentration by removal of calcium ions from cytoplasm. These both actions result in a significant increase in the storage bladder capacity and by this interval between micturitions is prolonged. Mirabegron was evaluated in three 12-week, double blind, randomized, placebo controlled, parallel-group, multicenter clinical trials in OAB patients with symptoms of urge urinary incontinence, urgency and frequency - study 046, 047 and 074. It should be pointed out that efficacy of mirabegron was maintained through the entire 12-month period in phase Ill long-term study Discoveries on the physiology of the normal bladder and on the pathophysiology underlying OAB have led to the development of new treatment options for OAB. Pharmacological management of OAB should be tailored to patient's characteristics. New and recent options of pharmacological treatment have undoubtedly expanded treatment possibilities, what should allow physicians to select the optimal treatment for each patient.

Cyclic Phosphatidic Acid Stimulates cAMP Production and Inhibits Growth in Human Colon Cancer Cells

Colon cancer is a malignancy that develops in colon and rectal tissues. The prognosis for metastatic colon cancer remains poor, and novel therapeutic options are required to reduce colon cancer mortality. Recently, intracellular cAMP levels have been suggested to influence the behavior of cancer cells. Intriguingly, cyclic phosphatidic acid (cPA) and its structural analogs inhibit growth in many cancer cell lines, and our previous work has suggested that cPA increases cAMP production. Phosphodiesterase (PDE) type 3 isoforms PDE3A and PDE3B are expressed mainly in cardiovascular tissue and adipose tissue, respectively. Moreover, increase in intracellular cAMP levels has been associated with the inhibition of growth in colon cancer cells. These findings suggest that cPA could be used in colon cancer therapy. In this study, we found that cPA inhibited the growth of HT-29 cells, which express high levels of PDE3B, but not the growth of DLD-1 cells, which express low levels of PDE3B. Furthermore, cPA inhibited the phosphorylation of Akt in HT-29 cells in a dose-dependent fashion. Our results suggest that PDE3B expression and intracellular cAMP levels are correlated with the proliferation of colon cancer cells. These findings demonstrate for the first time that cPA may serve as a useful a molecule in targeted therapy for colon cancer.

Calmodulin–CaMKII mediated alteration of oxidative stress: interplay of the cAMP/PKA–ERK 1/2-NF-κB–NO axis on arsenic-induced head kidney macrophage apoptosis

Using the head kidney macrophages (HKM) from catfish (Clarias batrachus) we earlier demonstrated the role of calcium (Ca2+) and its dependent neutral protease calpain in arsenic-induced apoptosis. Here, we report the role of the CaM–CaMKII axis as an initiator of the process. With the help of specific assay kits and inhibitors we document the pro-apoptotic role of CaM and CaMKII in arsenic-induced HKM apoptosis. CaM-induced CaMKII activity influenced superoxide ion production in exposed cells with a consequent increase in intracellular cAMP levels. Using H-89, the specific inhibitor for PKA, we show for the first time the pro-apoptotic role of the cAMP/PKA pathway in arsenic-induced HKM apoptosis. We report the cAMP/PKA pathway to be critical for initiating downstream activation of MAPKs, namely ERK 1/2. The superoxide ions generated due to arsenic-stress also induce NF-κB activation in HKM. Inducible NOS activity and consequent NO production were evident in the exposed HKM and our study implicates the involvement of ERK 1/2 and NF-κB in the process. Arsenic exposure alters mitochondrial membrane potential, releases cytochrome C and activates caspase-9 leading to caspase-3 mediated apoptosis of HKM. Our findings, thus, provide insight into the underlying mechanism of arsenic toxicity and indicate that HKM could serve as an important in vitro model for immunotoxicity assays.

Abstract 18482: cAMP-mediated Cardiac Myocyte-fibroblast Crosstalk

Cyclic adenosine monophosphate (cAMP) serves as an intracellular second messenger to transduce the effects of the stimulation of Gs-coupled receptors. Recent studies indicated that cAMP can be extruded by the multidrug resistance associated-protein 4 (MRP4) from many cell types including cardiac myocytes (CM). The present study investigated whether the cAMP extruded from CM acts as a signalling molecule. We employed a fluorescence resonance energy transfer (FRET)-based sensor (Epac2-cAMPs) to directly assay for the formation of cAMP in CM and fibroblasts (CF). We found cAMP to be extruded from neonatal and adult CM upon β-adrenergic receptor (βAR) stimulation (1µM isoproterenol, ISO), an effect that was largely sensitive to MRP inhibition. Extracellular cAMP blocked the βAR-mediated increase in intracellular cAMP in CM. This negative feedback was reversed by a non-specific adenosine receptor antagonist (DPSPX) and an A1 adenosine receptor specific antagonist (DPCPX) but not by an A2 adenosine receptor specific antagonist (ZM-241385) (FRET ratio: 12.6±0.6 after ISO treatment vs. 4.5±0.8 after ISO+ecto-cAMP, 12.6±1.3 after ISO+ecto-cAMP+DPSPX, p<0.001). In contrast, application of extracellular cAMP onto CF induced an increase in intracellular cAMP levels while A2 adenosine receptor specific antagonist blocked this effect (FRET ratio: 8.1±1.1 after ecto-cAMP treatment vs 0.07±0.3 after ecto-cAMP+ZM, p<0.001). To determine if extracellular cAMP released from CM is sufficient to stimulate cAMP formation in CF, we stimulated CF isolated from β1β2-AR-deficient mice with conditioned medium (coM) from ISO or control-treated CM. Exposure of βAR-deficient CF to coM from ISO-treated CMs yielded a significant increase in intracellular cAMP compared to control-coM. DPSPX again markedly attenuated the elevation of cAMP in response to ISO-coM (FRET ratio: control-coM: 3.1±0.6, ISO-coM: 7±1.2, ISO-coM+DPSPX: 2.2±1.3, p<0.05). In conclusion, this study provides evidence that βAR stimulation of CM induces an inside-out signaling through secreted cAMP. cAMP is exported from CM, metabolized to adenosine and in an autocrine and paracrine manner stimulates adenosine receptors on CM (A1 receptors) and CF (A2a,2b receptors).

Catechol Pyrazolinones as Trypanocidals: Fragment-Based Design, Synthesis, and Pharmacological Evaluation of Nanomolar Inhibitors of Trypanosomal Phosphodiesterase B1

Trypanosomal phosphodiesterases B1 and B2 (TbrPDEB1 and TbrPDEB2) play an important role in the life cycle of Trypanosoma brucei, the causative parasite of human African trypanosomiasis (HAT), also known as African sleeping sickness. We used homology modeling and docking studies to guide fragment growing into the parasite-specific P-pocket in the enzyme binding site. The resulting catechol pyrazolinones act as potent TbrPDEB1 inhibitors with IC₅₀ values down to 49 nM. The compounds also block parasite proliferation (e.g., VUF13525 (20b): T. brucei rhodesiense IC₅₀ = 60 nM, T. brucei brucei IC₅₀ = 520 nM, T. cruzi = 7.6 μM), inducing a typical multiple nuclei and kinetoplast phenotype without being generally cytotoxic. The mode of action of 20b was investigated with recombinantly engineered trypanosomes expressing a cAMP-sensitive FRET sensor, confirming a dose-response related increase of intracellular cAMP levels in trypanosomes. Our findings further validate the TbrPDEB family as antitrypanosomal target.

Roflumilast-N-oxide Induces Surfactant Protein Expression in Human Alveolar Epithelial Cells Type II

Surfactant proteins (SPs) are important lipoprotein complex components, expressed in alveolar epithelial cells type II (AEC-II), and playing an essential role in maintenance of alveolar integrity and host defence. Because expressions of SPs are regulated by cyclic adenosine monophosphate (cAMP), we hypothesized that phosphodiesterase (PDE) inhibitors, influence SP expression and release. Analysis of PDE activity of our AEC-II preparations revealed that PDE4 is the major cAMP hydrolysing PDE in human adult AEC-II. Thus, freshly isolated human AEC-II were stimulated with two different concentrations of the PDE4 inhibitor roflumilast-N-oxide (3 nM and 1 µM) to investigate the effect on SP expression. SP mRNA levels disclosed a large inter-individual variation. Therefore, the experiments were grouped by the basal SP expression in low and high expressing donors. AEC-II stimulated with Roflumilast-N-oxide showed a minor increase in SP-A1, SP-C and SP-D mRNA mainly in low expressing preparations. To overcome the effects of different basal levels of intracellular cAMP, cyclooxygenase was blocked by indomethacin and cAMP production was reconstituted by prostaglandin E2 (PGE2). Under these conditions SP-A1, SP-A2, SP-B and SP-D are increased by roflumilast-N-oxide in low expressing preparations. Roflumilast-N-oxide fosters the expression of SPs in human AEC-II via increase of intracellular cAMP levels potentially contributing to improved alveolar host defence and enhanced resolution of inflammation.

New evidence for the involvement of prostaglandin receptor EP4b in ovulation of the medaka, Oryzias latipes

A cDNA for a prostaglandin E2 (PGE2) receptor subtype 4, EP4b (Ptger4b), was cloned from the medaka ovary. The effect of PGE2 was examined using COS-7 cells expressing the recombinant Ptger4b protein. An increase in intracellular cAMP levels was observed when the cells were incubated with PGE2, but the increase in cAMP levels was nullified by the addition of the EP4 antagonist GW627368X. The expression of ptger4b mRNA was drastically induced by the addition of pregnant mare serum gonadotropin to the in vitro culture of large preovulatory follicles. In in vitro ovulation studies of the effect of GW627368X addition on follicle ovulation, the critical timing of the PGE2/Ptger4b interaction was suggested to be between −1 and 0h of ovulation. These results further substantiate that PGE2/Ptger4b signaling is involved in follicle rupture during ovulation in the medaka ovary.

LPA Is a Chemorepellent for B16 Melanoma Cells: Action through the cAMP-Elevating LPA5 Receptor

Lysophosphatidic acid (LPA), a lipid mediator enriched in serum, stimulates cell migration, proliferation and other functions in many cell types. LPA acts on six known G protein-coupled receptors, termed LPA1–6, showing both overlapping and distinct signaling properties. Here we show that, unexpectedly, LPA and serum almost completely inhibit the transwell migration of B16 melanoma cells, with alkyl-LPA(18∶1) being 10-fold more potent than acyl-LPA(18∶1). The anti-migratory response to LPA is highly polarized and dependent on protein kinase A (PKA) but not Rho kinase activity; it is associated with a rapid increase in intracellular cAMP levels and PIP3 depletion from the plasma membrane. B16 cells express LPA2, LPA5 and LPA6 receptors. We show that LPA-induced chemorepulsion is mediated specifically by the alkyl-LPA-preferring LPA5 receptor (GPR92), which raises intracellular cAMP via a noncanonical pathway. Our results define LPA5 as an anti-migratory receptor and they implicate the cAMP-PKA pathway, along with reduced PIP3 signaling, as an effector of chemorepulsion in B16 melanoma cells.

Identification and Functional Characterization of Two Orphan G-protein-coupled Receptors for Adipokinetic Hormones from Silkworm Bombyx mori

Adipokinetic hormones (AKHs) are the best studied insect neuropeptides with the function of mobilizing lipids and carbohydrates during energy-expensive activities and modulating fundamental physiological processes, such as sugar homeostasis, lipid metabolism, and reproduction. Three distinct cDNAs encoding the prepro-Bombyx AKH1-3 have been cloned and confirmed by mass spectrometric methods. Our previous research suggested the Bombyx AKH receptor is activated by AKH1 and AKH2 with high affinity but by AKH3 with quite low affinity. In this study, using stable functional expression of the receptors in HEK293 cells, we have now identified AKH3 as a specific ligand for two orphan G-protein-coupled receptors, and we therefore named them AKHR2a and AKHR2b, respectively. We demonstrated that both AKHR2a and AKHR2b were activated by AKH3 at high affinity and by AKH1 and AKH2 at low affinity, leading to an increase of intracellular cAMP levels and activation of ERK1/2 and receptor internalization, but they were not activated by Bombyx corazonin. Conversely, the Bombyx corazonin receptor was activated by corazonin but not by AKH1-3. Quantitative RT-PCR revealed that AKHR2a and AKHR2b were both highly expressed in the testis but were also detected at low levels in other tissues. These results will lead to a better understanding of the AKH/AKHR system in the regulation of fundamental physiological processes.

The Extracellular Signal-regulated Kinase Mitogen-activated Protein Kinase/Ribosomal S6 Protein Kinase 1 Cascade Phosphorylates cAMP Response Element-binding Protein to Induce MUC5B Gene Expression via d-Prostanoid Receptor Signaling

Mucus hypersecretion is a prominent feature of respiratory diseases, and MUC5B is a major airway mucin. Mucin gene expression can be affected by inflammatory mediators, including prostaglandin (PG) D(2,) an inflammatory mediator synthesized by hematopoietic PGD synthase (H-PGDS). PGD(2) binds to either D-prostanoid receptor (DP1) or chemoattractant receptor homologous molecule expressed on T-helper type 2 cells (CRTH2). We investigated the mechanisms by which PGD(2) induces MUC5B gene expression in airway epithelial cells. Western blot analysis showed that H-PGDS was highly expressed in nasal polyps. Similar results were obtained for PGD(2) expression. In addition, we could clearly detect the expressions of both H-PGDS and DP1 in nasal epithelial cells but not CRTH2. We demonstrated that PGD(2) increased MUC5B gene expression in normal human nasal epithelial cells as well as in NCI-H292 cells in vitro. S5751, a DP1 antagonist, inhibited PGD(2)-induced MUC5B expression, whereas a CRTH2 antagonist (OC0459) did not. These data suggest that PGD(2) induced MUC5B expression via DP1. Pretreatment with extracellular signal-regulated kinase (ERK) inhibitor (PD98059) blocked both PGD(2)-induced ERK mitogen-activated protein kinase (MAPK) activation and MUC5B expression. Proximity ligation assays showed direct interaction between RSK1 and cAMP response element-binding protein (CREB). Stimulation with PGD(2) caused an increase in intracellular cAMP levels, whereas intracellular Ca(2+) did not have such an effect. PGD(2)-induced MUC5B mRNA levels were regulated by CREB via direct interaction with two cAMP-response element sites (-921/-914 and -900/-893). Finally, we demonstrated that PGD(2) can induce MUC5B overproduction via ERK MAPK/RSK1/CREB signaling and that DP1 receptor may have suppressive effects in controlling MUC5B overproduction in the airway.