Elevation of intracellular cAMP inhibits RhoA activation and integrin-dependent leukocyte adhesion induced by chemoattractants

Cyclic Adenosine Monophosphate in Cardiac and Sympathoadrenal GLP-1 Receptor Signaling: Focus on Anti-Inflammatory Effects

Glucagon-like peptide-1 (GLP-1) is a multifunctional incretin hormone with various physiological effects beyond its well-characterized effect of stimulating glucose-dependent insulin secretion in the pancreas. An emerging role for GLP-1 and its receptor, GLP-1R, in brain neuroprotection and in the suppression of inflammation, has been documented in recent years. GLP-1R is a G protein-coupled receptor (GPCR) that couples to Gs proteins that stimulate the production of the second messenger cyclic 3',5'-adenosine monophosphate (cAMP). cAMP, acting through its two main effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), exerts several anti-inflammatory (and some pro-inflammatory) effects in cells, depending on the cell type. The present review discusses the cAMP-dependent molecular signaling pathways elicited by the GLP-1R in cardiomyocytes, cardiac fibroblasts, central neurons, and even in adrenal chromaffin cells, with a particular focus on those that lead to anti-inflammatory effects by the GLP-1R. Fully elucidating the role cAMP plays in GLP-1R's anti-inflammatory properties can lead to new and more precise targets for drug development and/or provide the foundation for novel therapeutic combinations of the GLP-1R agonist medications currently on the market with other classes of drugs for additive anti-inflammatory effect.

A PI3Kγ mimetic peptide triggers CFTR gating, bronchodilation, and reduced inflammation in obstructive airway diseases

Cyclic adenosine 3',5'-monophosphate (cAMP)-elevating agents, such as β₂-adrenergic receptor (β₂-AR) agonists and phosphodiesterase (PDE) inhibitors, remain a mainstay in the treatment of obstructive respiratory diseases, conditions characterized by airway constriction, inflammation, and mucus hypersecretion. However, their clinical use is limited by unwanted side effects because of unrestricted cAMP elevation in the airways and in distant organs. Here, we identified the A-kinase anchoring protein phosphoinositide 3-kinase γ (PI3Kγ) as a critical regulator of a discrete cAMP signaling microdomain activated by β₂-ARs in airway structural and inflammatory cells. Displacement of the PI3Kγ-anchored pool of protein kinase A (PKA) by an inhaled, cell-permeable, PI3Kγ mimetic peptide (PI3Kγ MP) inhibited a pool of subcortical PDE4B and PDE4D and safely increased cAMP in the lungs, leading to airway smooth muscle relaxation and reduced neutrophil infiltration in a murine model of asthma. In human bronchial epithelial cells, PI3Kγ MP induced unexpected cAMP and PKA elevations restricted to the vicinity of the cystic fibrosis transmembrane conductance regulator (CFTR), the ion channel controlling mucus hydration that is mutated in cystic fibrosis (CF). PI3Kγ MP promoted the phosphorylation of wild-type CFTR on serine-737, triggering channel gating, and rescued the function of F508del-CFTR, the most prevalent CF mutant, by enhancing the effects of existing CFTR modulators. These results unveil PI3Kγ as the regulator of a β₂-AR/cAMP microdomain central to smooth muscle contraction, immune cell activation, and epithelial fluid secretion in the airways, suggesting the use of a PI3Kγ MP for compartment-restricted, therapeutic cAMP elevation in chronic obstructive respiratory diseases.

Adenosine 2A receptor and TIM3 suppress cytolytic killing of tumor cells via cytoskeletal polarization

Tumors generate an immune-suppressive environment that prevents effective killing of tumor cells by CD8⁺ cytotoxic T cells (CTL). It remains largely unclear upon which cell type and at which stage of the anti-tumor response mediators of suppression act. We have combined an in vivo tumor model with a matching in vitro reconstruction of the tumor microenvironment based on tumor spheroids to identify suppressors of anti-tumor immunity that directly act on interaction between CTL and tumor cells and to determine mechanisms of action. An adenosine 2A receptor antagonist, as enhanced by blockade of TIM3, slowed tumor growth in vivo. Engagement of the adenosine 2A receptor and TIM3 reduced tumor cell killing in spheroids, impaired CTL cytoskeletal polarization ex vivo and in vitro and inhibited CTL infiltration into tumors and spheroids. With this role in CTL killing, blocking A_2AR and TIM3 may complement therapies that enhance T cell priming, e.g. anti-PD-1 and anti-CTLA-4.

Differential responses of abomasal transcriptome to Haemonchus contortus infection between Haemonchus-selected and Trichostrongylus-selected merino sheep

Haemonchus contortus is the most prevalent and pathogenic gastrointestinal nematode infecting sheep and goats. The two CSIRO sheep resource flocks, the Haemonchus-selected flock (HSF) and Trichostrongylus-selected flock (TSF) were developed for research on host resistance or susceptibility to gastrointestinal nematode infection. A recent study focused on the gene expression differences between resistant and susceptible sheep within each flock, with lymphatic and gastrointestinal tissues. To identify features in the host transcriptome and understand the molecular differences underlying host resistance to H. contortus between flocks with different selective breeding and genetic backgrounds, we compared the abomasal transcriptomic responses of the resistant or susceptible animals between HSF and TSF flocks. A total of 11 and 903 differentially expressed genes were identified in the innate infection treatment in HSF and TSF flocks between resistant and susceptible sheep respectively, while 52 and 485 genes were identified to be differentially expressed in the acquired infection treatment, respectively. Among them, 294 genes had significantly different gene expression levels between HSF and TSF flock animals within the susceptible sheep by both the innate and acquired infections. Moreover, similar expression patterns of the 294 genes were observed, with 273 genes more highly expressed in HSF and 21 more highly expressed in the TSF within the abomasal transcriptome of the susceptible animals. Gene ontology enrichment of the differentially expressed genes identified in this study predicted the likely differing function between the two flock's susceptible lines in response to H. contortus infection. Nineteen pathways were significantly enriched in both the innate and adaptive immune responses in susceptible animals, which indicated that these pathways likely contribute to the host resistance development to H. contortus infection in susceptible sheep. Biological networks built for the set of genes differentially abundant in susceptible animals identified hub genes of PRKG1, PRKACB, PRKACA, and ITGB1 for the innate immune response, and CALM2, MYL1, COL1A1, ITGB1 and ITGB3 for the adaptive immune response, respectively. Our results offered a quantitative snapshot of host transcriptomic changes induced by H. contortus infection between flocks with different selective breeding and genetic backgrounds and provided novel insights into molecular mechanisms of host resistance.

Mitofusin-2 regulates leukocyte adhesion and β2 integrin activation

Neutrophils are critical for inflammation and innate immunity, and their adhesion to vascular endothelium is a crucial step in neutrophil recruitment. Mitofusin-2 (MFN2) is required for neutrophil adhesion, but molecular details are unclear. Here, we demonstrated that β₂ -integrin-mediated slow-rolling and arrest, but not PSGL-1-mediated cell rolling, are defective in MFN2-deficient neutrophil-like HL60 cells. This adhesion defect is associated with reduced expression of fMLP (N-formylmethionyl-leucyl-phenylalanine) receptor FPR1 as well as the inhibited β₂ integrin activation, as assessed by conformation-specific monoclonal antibodies. MFN2 deficiency also leads to decreased actin polymerization, which is important for β2 integrin activation. Mn²⁺ -induced cell spreading is also inhibited after MFN2 knockdown. MFN2 deficiency limited the maturation of β2 integrin activation during the neutrophil-directed differentiation of HL60 cells, which is indicated by CD35 and CD87 markers. MFN2 knockdown in β2-integrin activation-matured cells (CD87^high population) also inhibits integrin activation, indicating that MFN2 directly affects β2 integrin activation. Our study illustrates the function of MFN2 in leukocyte adhesion and may provide new insights into the development and treatment of MFN2 deficiency-related diseases.

Blame the signaling: Role of cAMP for the resolution of inflammation

A complex intracellular signaling governs different cellular responses in inflammation. Extracellular stimuli are sensed, amplified, and transduced through a dynamic cellular network of messengers converting the first signal into a proper response: production of specific mediators, cell activation, survival, or death. Several overlapping pathways are coordinated to ensure specific and timely induction of inflammation to neutralize potential harms to the tissue. Ideally, the inflammatory response must be controlled and self-limited. Resolution of inflammation is an active process that culminates with termination of inflammation and restoration of tissue homeostasis. Comparably to the onset of inflammation, resolution responses are triggered by coordinated intracellular signaling pathways that transduce the message to the nucleus. However, the key messengers and pathways involved in signaling transduction for resolution are still poorly understood in comparison to the inflammatory network. cAMP has long been recognized as an inducer of anti-inflammatory responses and cAMP-dependent pathways have been extensively exploited pharmacologically to treat inflammatory diseases. Recently, cAMP has been pointed out as coordinator of key steps of resolution of inflammation. Here, we summarize the evidence for the role of cAMP at inducing important features of resolution of inflammation.

Clozapine reduces infiltration into the CNS by targeting migration in experimental autoimmune encephalomyelitis

Background

Atypical antipsychotic agents, such as clozapine, are used to treat schizophrenia and other psychiatric disorders by a mechanism that is believed to involve modulating the immune system. Multiple sclerosis is an immune-mediated neurological disease, and recently, clozapine was shown to reduce disease severity in an animal model of MS, experimental autoimmune encephalomyelitis (EAE). However, the mode of action by which clozapine reduces disease in this model is poorly understood.

Methods

Because the mode of action by which clozapine reduces neuroinflammation is poorly understood, we used the EAE model to elucidate the in vivo and in vitro effects of clozapine.

Results

In this study, we report that clozapine treatment reduced the infiltration of peripheral immune cells into the central nervous system (CNS) and that this correlated with reduced expression of the chemokines CCL2 and CCL5 transcripts in the brain and spinal cord. We assessed to what extent immune cell populations were affected by clozapine treatment and we found that clozapine targets the expression of chemokines by macrophages and primary microglia. Furthermore, in addition to decreasing CNS infiltration by reducing chemokine expression, we found that clozapine directly inhibits chemokine-induced migration of immune cells. This direct target on the immune cells was not mediated by a change in receptor expression on the immune cell surface but by decreasing downstream signaling via these receptors leading to a reduced migration.

Conclusions

Taken together, our study indicates that clozapine protects against EAE by two different mechanisms; first, by reducing the chemoattractant proteins in the CNS; and second, by direct targeting the migration potential of peripheral immune cells.

The impact of the rs8005161 polymorphism on G protein-coupled receptor GPR65 (TDAG8) pH-associated activation in intestinal inflammation

Background

Tissue inflammation in inflammatory bowel diseases (IBD) is associated with a decrease in local pH. The gene encoding G-protein-coupled receptor 65 (GPR65) has recently been reported to be a genetic risk factor for IBD. In response to extracellular acidification, proton activation of GPR65 stimulates cAMP and Rho signalling pathways. We aimed to analyse the clinical and functional relevance of the GPR65 associated single nucleotide polymorphism (SNP) rs8005161.

Methods

1138 individuals from a mixed cohort of IBD patients and healthy volunteers were genotyped for SNPs associated with GPR65 (rs8005161, rs3742704) and galactosylceramidase (rs1805078) by Taqman SNP assays. 2300 patients from the Swiss IBD Cohort Study (SIBDC) were genotyped for rs8005161 by mass spectrometry based SNP genotyping. IBD patients from the SIBDC carrying rs8005161 TT, CT, CC and non-IBD controls (CC) were recruited for functional studies. Human CD14+ cells were isolated from blood samples and subjected to an extracellular acidic pH shift, cAMP accumulation and RhoA activation were measured.

Results

In our mixed cohort, but not in SIBDC patients, the minor variant rs8005161 was significantly associated with UC. In SIBDC patients, we observed a consistent trend in increased disease severity in patients carrying the rs8005161-TT and rs8005161-CT alleles. No significant differences were observed in the pH associated activation of cAMP production between IBD (TT, CT, WT/CC) and non-IBD (WT/CC) genotype carriers upon an acidic extracellular pH shift. However, we observed significantly impaired RhoA activation after an extracellular acidic pH shift in IBD patients, irrespective of the rs8005161 allele.

Conclusions

The T allele of rs8005161 might confer a more severe disease course in IBD patients. Human monocytes from IBD patients showed impaired pH associated RhoA activation upon an acidic pH shift.

Electronic supplementary material

The online version of this article (10.1186/s12876-018-0922-8) contains supplementary material, which is available to authorized users.

cAMP-induced activation of protein kinase A and p190B RhoGAP mediates down-regulation of TC10 activity at the plasma membrane and neurite outgrowth

Cyclic AMP plays a pivotal role in neurite growth. During outgrowth, a trafficking system supplies membrane at growth cones. However, the cAMP-induced signaling leading to the regulation of membrane trafficking remains unknown. TC10 is a Rho family GTPase that is essential for specific types of vesicular trafficking. Recent studies have shown a role of TC10 in neurite growth in NGF-treated PC12 cells. Here, we investigated a mechanical linkage between cAMP and TC10 in neuritogenesis. Plasmalemmal TC10 activity decreased abruptly after cAMP addition in neuronal cells. TC10 was locally inactivated at extending neurite tips in cAMP-treated PC12 cells. TC10 depletion led to a decrease in cAMP-induced neurite outgrowth. Constitutively active TC10 could not rescue this growth reduction, supporting our model for a role of GTP hydrolysis of TC10 in neuritogenesis by accelerating vesicle fusion. The cAMP-induced TC10 inactivation was mediated by PKA. Considering cAMP-induced RhoA inactivation, we found that p190B, but not p190A, mediated inactivation of TC10 and RhoA. Upon cAMP treatment, p190B was recruited to the plasma membrane. STEF depletion and Rac1-N17 expression reduced cAMP-induced TC10 inactivation. Together, the PKA-STEF-Rac1-p190B pathway leading to inactivation of TC10 and RhoA at the plasma membrane plays an important role in cAMP-induced neurite outgrowth.

β2 adrenergic agonist suppresses eosinophil-induced epithelial-to-mesenchymal transition of bronchial epithelial cells

Background

Epithelial-mesenchymal transition is currently recognized as an important mechanism for the increased number of myofibroblasts in cancer and fibrotic diseases. We have already reported that epithelial-mesenchymal transition is involved in airway remodeling induced by eosinophils. Procaterol is a selective and full β₂ adrenergic agonist that is used as a rescue of asthmatic attack inhaler form and orally as a controller. In this study, we evaluated whether procaterol can suppress epithelial-mesenchymal transition of airway epithelial cells induced by eosinophils.

Methods

Epithelial-mesenchymal transition was assessed using a co-culture system of human bronchial epithelial cells and primary human eosinophils or an eosinophilic leukemia cell line.

Results

Procaterol significantly inhibited co-culture associated morphological changes of bronchial epithelial cells, decreased the expression of vimentin, and increased the expression of E-cadherin compared to control. Butoxamine, a specific β₂-adrenergic antagonist, significantly blocked changes induced by procaterol. In addition, procaterol inhibited the expression of adhesion molecules induced during the interaction between eosinophils and bronchial epithelial cells, suggesting the involvement of adhesion molecules in the process of epithelial-mesenchymal transition. Forskolin, a cyclic adenosine monophosphate-promoting agent, exhibits similar inhibitory activity of procaterol.

Conclusions

Overall, these observations support the beneficial effect of procaterol on airway remodeling frequently associated with chronic obstructive pulmonary diseases.

Augmentation of CAR T-cell Trafficking and Antitumor Efficacy by Blocking Protein Kinase A Localization

Antitumor treatments based on the infusion of T cells expressing chimeric antigen receptors (CAR T cells) are still relatively ineffective for solid tumors, due to the presence of immunosuppressive mediators [such as prostaglandin E2 (PGE2) and adenosine] and poor T-cell trafficking. PGE2 and adenosine activate protein kinase A (PKA), which then inhibits T-cell receptor (TCR) activation. This inhibition process requires PKA to localize to the immune synapse via binding to the membrane protein ezrin. We generated CAR T cells that expressed a small peptide called the "regulatory subunit I anchoring disruptor" (RIAD) that inhibits the association of PKA with ezrin, thus blunting the negative effects of PKA on TCR activation. After exposure to PGE2 or adenosine in vitro, CAR-RIAD T cells showed increased TCR signaling, released more cytokines, and showed enhanced killing of tumor cells compared with CAR T cells. When injected into tumor-bearing mice, the antitumor efficacy of murine and human CAR-RIAD T cells was enhanced compared with that of CAR T cells, due to resistance to tumor-induced hypofunction and increased T-cell infiltration of established tumors. Subsequent in vitro assays showed that both mouse and human CAR-RIAD cells migrated more efficiently than CAR cells did in response to the chemokine CXCL10 and also had better adhesion to various matrices. Thus, the intracellular addition of the RIAD peptide to adoptively transferred CAR T cells augments their efficacy by increasing their effector function and by improving trafficking into tumor sites. This treatment strategy, therefore, shows potential clinical application for treating solid tumors. Cancer Immunol Res; 4(6); 541-51. ©2016 AACR.

cAMP effects in neuroendocrine tumors: The role of Epac and PKA in cell proliferation and adhesion

cAMP effects have been initially attributed to protein kinase A (PKA) activation. Subsequently, two exchange proteins directly activated by cAMP (Epac1/2) have been identified as cAMP targets. Aim of this study was to investigate cAMP effects in pancreatic-NET (P-NET) and bronchial carcinoids and in corresponding cell lines (QGP-1 and H727) on cell proliferation and adhesion and to determine PKA and Epac role in mediating these effects. We found that cAMP increased cyclin D1 expression in P-NET and QGP-1 cells, whereas it had opposite effects on bronchial carcinoids and H727 cells and it promoted cell adhesion in QGP-1 and H727 cells. These effects are mimicked by Epac and PKA specific analogs, activating the small GTPase Rap1. In conclusion, we demonstrated that cAMP exerted divergent effects on proliferation and promoted cell adhesion of different neuroendocrine cell types, these effects being mediated by both Epac and PKA and involving the same effector GTPase Rap1.

Comprehensive analysis of chemokine-induced cAMP-inhibitory responses using a real-time luminescent biosensor

Chemokine receptors are members of the G-protein-coupled receptor (GPCR) family coupled to members of the Gi class, whose primary function is to inhibit the cellular adenylate cyclase. We used a cAMP-related and PKA-based luminescent biosensor (GloSensor™ F-22) to monitor the real-time downstream response of chemokine receptors, especially CX3CR1 and CXCR4, after activation with their cognate ligands CX3CL1 and CXCL12. We found that the amplitudes and kinetic profiles of the chemokine responses were conserved in various cell types and were independent of the nature and concentration of the molecules used for cAMP prestimulation, including either the adenylate cyclase activator forskolin or ligands mediating Gs-mediated responses like prostaglandin E2 or beta-adrenergic agonist. We conclude that the cAMP chemokine response is robustly conserved in various inflammatory conditions. Moreover, the cAMP-related luminescent biosensor appears as a valuable tool to analyze the details of Gi-mediated cAMP-inhibitory cellular responses, even in native conditions and could help to decipher their precise role in cell function.

Multi-Inhibitory Effects of A2A Adenosine Receptor Signaling on Neutrophil Adhesion Under Flow

A2A adenosine receptor (A2AAR) signaling negatively regulates inflammatory responses in many disease models, but the detailed mechanisms remain unclear. We used the selective A2AAR agonist, ATL313, to examine how A2AAR signaling affects human and murine neutrophil adhesion under flow. Treating neutrophils with ATL313 inhibited selectin-induced, β2 integrin-dependent slow rolling and chemokine-induced, β2 integrin-dependent arrest on ICAM-1. ATL313 inhibited selectin-induced β2 integrin extension, which supports slow rolling, and chemokine-induced hybrid domain "swing-out," which supports arrest. Furthermore, ATL313 inhibited integrin outside-in signaling as revealed by reduced neutrophil superoxide production and spreading on immobilized anti-β2 integrin Ab. ATL313 suppressed selectin-triggered activation of Src family kinases (SFKs) and p38 MAPK, chemokine-triggered activation of Ras-related protein 1, and β2 integrin-triggered activation of SFKs and Vav cytoskeletal regulatory proteins. ATL313 activated protein kinase A and its substrate C-terminal Src kinase, an inhibitor of SFKs. Treating neutrophils with a protein kinase A inhibitor blocked the actions of ATL313. In vivo, ATL313-treated neutrophils rolled faster and arrested much less frequently in postcapillary venules of the murine cremaster muscle after TNF-α challenge. Furthermore, ATL313 markedly suppressed neutrophil migration into the peritoneum challenged with thioglycollate. ATL313 did not affect A2AAR-deficient neutrophils, confirming its specificity. Our findings provide new insights into the anti-inflammatory mechanisms of A2AAR signaling and the potential utility of A2AAR agonists in inflammatory diseases.

Protein tyrosine phosphatase receptor type γ is a JAK phosphatase and negatively regulates leukocyte integrin activation

Regulation of signal transduction networks depends on protein kinase and phosphatase activities. Protein tyrosine kinases of the JAK family have been shown to regulate integrin affinity modulation by chemokines and mediated homing to secondary lymphoid organs of human T lymphocytes. However, the role of protein tyrosine phosphatases in leukocyte recruitment is still elusive. In this study, we address this issue by focusing on protein tyrosine phosphatase receptor type γ (PTPRG), a tyrosine phosphatase highly expressed in human primary monocytes. We developed a novel methodology to study the signaling role of receptor type tyrosine phosphatases and found that activated PTPRG blocks chemoattractant-induced β2 integrin activation. Specifically, triggering of LFA-1 to high-affinity state is prevented by PTPRG activation. High-throughput phosphoproteomics and computational analyses show that PTPRG activation affects the phosphorylation state of at least 31 signaling proteins. Deeper examination shows that JAKs are critically involved in integrin-mediated monocyte adhesion and that PTPRG activation leads to JAK2 dephosphorylation on the critical 1007-1008 phosphotyrosine residues, implying JAK2 inhibition and thus explaining the antiadhesive role of PTPRG. Overall, the data validate a new approach to study receptor tyrosine phosphatases and show that, by targeting JAKs, PTPRG downmodulates the rapid activation of integrin affinity in human monocytes, thus emerging as a potential novel critical regulator of leukocyte trafficking.

Glucagon-like peptide 1 stimulates insulin secretion via inhibiting RhoA/ROCK signaling and disassembling glucotoxicity-induced stress fibers

Chronic hyperglycemia leads to pancreatic β-cell dysfunction characterized by diminished glucose-stimulated insulin secretion (GSIS), but the precise cellular processes involved are largely unknown. Here we show that pancreatic β-cells chronically exposed to a high glucose level displayed substantially increased amounts of stress fibers compared with β-cells cultured at a low glucose level. β-Cells at high glucose were refractory to glucose-induced actin cytoskeleton remodeling and insulin secretion. Importantly, F-actin depolymerization by either cytochalasin B or latrunculin B restored glucotoxicity-diminished GSIS. The effects of glucotoxicity on increasing stress fibers and reducing GSIS were reversed by Y-27632, a Rho-associated kinase (ROCK)-specific inhibitor, which caused actin depolymerization and enhanced GSIS. Notably, glucagon-like peptide-1-(7-36) amide (GLP-1), a peptide hormone that stimulates GSIS at both normal and hyperglycemic conditions, also reversed glucotoxicity-induced increase of stress fibers and reduction of GSIS. In addition, GLP-1 inhibited glucotoxicity-induced activation of RhoA/ROCK and thereby resulted in actin depolymerization and potentiation of GSIS. Furthermore, this effect of GLP-1 was mimicked by cAMP-increasing agents forskolin and 3-isobutyl-1-methylxanthine as well as the protein kinase A agonist 6-Bnz-cAMP-AM whereas it was abolished by the protein kinase A inhibitor Rp-Adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt. To establish a clinical relevance of our findings, we examined the association of genetic variants of RhoA/ROCK with metabolic traits in homeostasis model assessment index of insulin resistance. Several single-nucleotide polymorphisms in and around RHOA were associated with elevated fasting insulin and homeostasis model assessment index of insulin resistance, suggesting a possible role in metabolic dysregulation. Collectively these findings unravel a novel mechanism whereby GLP-1 potentiates glucotoxicity-diminished GSIS by depolymerizing F-actin cytoskeleton via protein kinase A-mediated inhibition of the RhoA-ROCK signaling pathway.

PKA turnover by the REGγ-proteasome modulates FoxO1 cellular activity and VEGF-induced angiogenesis

The REGγ-proteasome serves as a short-cut for the destruction of certain intact mammalian proteins in the absence of ubiquitin- and ATP. The biological roles of the proteasome activator REGγ are not completely understood. Here we demonstrate that REGγ controls degradation of protein kinase A catalytic subunit-α (PKAca) both in primary human umbilical vein endothelial cells (HUVECs) and mouse embryonic fibroblast cells (MEFs). Accumulation of PKAca in REGγ-deficient HUVECs or MEFs results in phosphorylation and nuclear exclusion of the transcription factor FoxO1, indicating that REGγ is involved in preserving FoxO1 transcriptional activity. Consequently, VEGF-induced expression of the FoxO1 responsive genes, VCAM-1 and E-Selectin, was tightly controlled by REGγ in a PKA dependent manner. Functionally, REGγ is crucial for the migration of HUVECs. REGγ(-/-) mice display compromised VEGF-instigated neovascularization in cornea and aortic ring models. Implanted matrigel plugs containing VEGF in REGγ(-/-) mice induced fewer capillaries than in REGγ(+/+) littermates. Taken together, our study identifies REGγ as a novel angiogenic factor that plays an important role in VEGF-induced expression of VCAM-1 and E-Selectin by antagonizing PKA signaling. Identification of the REGγ-PKA-FoxO1 pathway in endothelial cells (ECs) provides another potential target for therapeutic intervention in vascular diseases.

Cyclic AMP regulates the migration and invasion potential of human pancreatic cancer cells

Aggressive dissemination and metastasis of pancreatic ductal adenocarcinoma (PDAC) results in poor prognosis and marked lethality. Rho monomeric G protein levels are increased in pancreatic cancer tissue. As the mechanisms underlying PDAC malignancy are little understood, we investigated the role for cAMP in regulating monomeric G protein regulated invasion and migration of pancreatic cancer cells. Treatment of PDAC cells with cAMP elevating agents that activate adenylyl cyclases, forskolin, protein kinase A (PKA), 6-Bnz-cAMP, or the cyclic nucleotide phosphodiesterase inhibitor cilostamide significantly decreased migration and Matrigel invasion of PDAC cell lines. Inhibition was dose-dependent and not significantly different between forskolin or cilostamide treatment. cAMP elevating drugs not only blocked basal migration, but similarly abrogated transforming-growth factor-β-directed PDAC cell migration and invasion. The inhibitory effects of cAMP were prevented by the pharmacological blockade of PKA. Drugs that increase cellular cAMP levels decreased levels of active RhoA or RhoC, with a concomitant increase in phosphorylated RhoA. Diminished Rho signaling was correlated with the appearance of thickened cortical actin bands along the perimeter of non-motile forskolin or cilostamide-treated cells. Decreased migration did not reflect alterations in cell growth or programmed cell death. Collectively these data support the notion that increased levels of cAMP specifically hinder PDAC cell motility through F-actin remodeling.

Prostaglandin D2 inhibits collagen secretion from lung fibroblasts by activating the DP receptor

Lung fibroblasts are responsible for collagen secretion during normal tissue repair and the development of fibrosis. Many other prostaglandins have been reported to regulate collagen synthesis in lung fibroblasts, but the role of prostaglandin D2 (PGD2) is unknown. In this study, we investigated the effect of PGD2 on type I collagen secretion in human lung fibroblasts. Pretreatment with PGD2 (0.1 - 10 μM, 1 h) significantly attenuated type I collagen secretion to the cell supernatant induced by transforming growth factor-β (TGF-β). Although an agonist on chemoattractant receptorhomologous molecule expressed on Th2 cells (CRTH2) did not have any effect, the prostanoid DP-receptor agonist BW245C (0.01 - 1 μM) suppressed TGF-β-induced collagen secretion. PGD2 and BW245C significantly increased intracellular cAMP level. One-hour pretreatment with forskolin (0.1 - 10 μM), dibutyryl-cAMP (0.01 - 1 mM), and the protein kinase A (PKA)-activator N(6)-phenyl-cyclic AMP (100 μM) significantly reduced TGF-β-induced collagen secretion, while exchange protein activated by cAMP (Epac) activator 8-bromo-2'-O-methyladenosine-3',5'-cyclic AMP (10 μM) did not affect collagen deposition. These results suggest that PGD2 inhibits TGF-β-induced collagen secretion via intracellular cAMP accumulation through activating DP receptor.

GDNF and endothelin 3 regulate migration of enteric neural crest-derived cells via protein kinase A and Rac1

Enteric neural crest-derived cells (ENCCs) migrate from the anterior foregut in a rostrocaudal direction to colonize the entire gastrointestinal tract and to form the enteric nervous system. Genetic approaches have identified many signaling molecules regulating the migration of ENCCs; however, it remains elusive how the activities of the signaling molecules are regulated spatiotemporally during migration. In this study, transgenic mice expressing biosensors based on Förster resonance energy transfer were generated to video the activity changes of the signaling molecules in migrating ENCCs. In an organ culture of embryonic day 11.25 (E11.25) to E13 guts, ENCCs at the rostral wavefront migrated as a cellular chain faster than the following ENCCs that formed a network. The faster-migrating cells at the wavefront exhibited lower protein kinase A (PKA) activity than did the slower-migrating trailing cells. The activities of Rac1 and Cdc42 exhibited an inverse correlation with the PKA activity, and PKA activation decreased the Rac1 activity and migration velocity. PKA activity in ENCCs was correlated positively with the distribution of GDNF and inversely with the distribution of endothelin 3 (ET-3). Accordingly, PKA was activated by GDNF and inhibited by ET-3 in cultured ENCCs. Finally, although the JNK and ERK pathways were previously reported to control the migration of ENCCs, we did not find any correlation of JNK or ERK activity with the migration velocities. These results suggest that external cues regulate the migration of ENCCs by controlling PKA activity, but not ERK or JNK activity, and argue for the importance of live imaging of signaling molecule activities in developing organs.

Cyclic AMP dysregulates intestinal epithelial cell restitution through PKA and RhoA

BACKGROUND

Mucosal homeostasis is dependent on the establishment and maintenance of the cell-cell contacts that comprise the physiological barrier. Breaks in the barrier are linked to multiple diseases such as inflammatory bowel disease. While increased cyclic adenosine monophosphate (cAMP) levels limit inflammation by decreasing leukocyte infiltration, the effects of elevated cAMP on intestinal epithelial repair are unknown.

METHODS

Restitution in animals administered rolipram was monitored by microscopic examination after laser wounding of the intestinal epithelium or in mice treated with dextran sodium sulfate (DSS). In vitro analysis was conducted using IEC6 and T84 cells to determine the role of elevated cAMP in altering Rho-dependent cellular migration signaling pathways.

RESULTS

We show that treatment with rolipram, forskolin, and cAMP analogs decrease intestinal epithelial cell migration in vitro. In vivo cell imaging revealed that increased cAMP resulted in a decreased cellular migration rate, with cells at the edge displaying the highest activity. As expected, elevated cAMP elicited increased protein kinase A (PKA) activity, in turn resulting in the inactivation and sequestration of RhoA and decreased actin reorganization. The ablation of restitution by cAMP was not restricted to cell culture, as forskolin and rolipram treatment significantly decreased epithelial microwound closure induced by the two photon confocal injury model.

CONCLUSIONS

Together, these data suggest that administration of cAMP-elevating agents paradoxically decrease infiltration of damage-causing leukocytes while also preventing epithelial repair and barrier maintenance. We propose that treatment with cAMP-elevating agents severely limits mucosal reepithelialization and should be contraindicated for use in chronic inflammatory bowel disorders.

Genistein prevents hyperglycemia-induced monocyte adhesion to human aortic endothelial cells through preservation of the cAMP signaling pathway and ameliorates vascular inflammation in obese diabetic mice

Hyperglycemia-induced vascular inflammation resulting in the enhanced monocyte-endothelial cell (EC) interaction is the key event in the pathogenesis of atherosclerosis in diabetes. Here, we investigated the effect of isoflavone genistein on hyperglycemia-stimulated vascular inflammation. Human aortic EC (HAEC) were pretreated with genistein before the addition of high glucose (HG; 25 mmol/L) for 48 h. Genistein at a physiological concentration (0.1 μmol/L) significantly inhibited HG-induced adhesion of monocytes to HAEC and suppressed endothelial production of monocyte chemotactic protein-1 (MCP-1) and IL-8. Inhibition of adenylate cyclase or protein kinase A (PKA) significantly attenuated the antiadhesion effect of genistein. Consistently, genistein improved HG-impaired intracellular cAMP production and PKA activity in HAEC. Six-week-old diabetic db/db mice were untreated (db/db) or treated with a diet containing 1 g genistein/kg diet (db/db+G) for 8 wk. Their nondiabetic db/+ mice were used as normal controls. Circulating concentrations of MCP-1/JE and KC were significantly greater, whereas IL-10 concentrations were lower in db/db mice than those in normal mice. Dietary supplementation of genistein did not normalize but significantly suppressed the elevated serum concentrations of MCP-1/JE from 286 ± 30 ng/L to 181 ± 35 ng/L and KC from 321 ± 21 ng/L to 232 ± 20 ng/L while increasing that of IL-10 from 35 ± 4 ng/L to 346 ± 35 ng/L in db/db+G mice. Further, genistein treatment suppressed diabetes-induced adhesion of monocytes to EC by 87% and endothelial secretion of adhesion molecules. We conclude that genistein improves diabetes-caused vascular inflammation, which may be mediated through promoting the cAMP/PKA pathway.

An integrated stochastic model of "inside-out" integrin activation and selective T-lymphocyte recruitment

The pattern of T-lymphocyte homing is hypothesized to be controlled by combinations of chemokine receptors and complementary chemokines. Here, we use numerical simulation to explore the relationship among chemokine potency and concentration, signal transduction, and adhesion. We have developed a form of adhesive dynamics-a mechanically accurate stochastic simulation of adhesion-that incorporates stochastic signal transduction using the next subvolume method. We show that using measurable parameter estimates derived from a variety of sources, including signaling measurements that allow us to test parameter values, we can readily simulate approximate time scales for T-lymphocyte arrest. We find that adhesion correlates with total chemokine receptor occupancy, not the frequency of occupation, when multiple chemokine receptors feed through a single G-protein. A general strategy for selective T-lymphocyte recruitment appears to require low affinity chemokine receptors. For a single chemokine receptor, increases in multiple cross-reactive chemokines can lead to an overwhelming increase in adhesion. Overall, the methods presented here provide a predictive framework for understanding chemokine control of T-lymphocyte recruitment.

Control of neurite outgrowth by RhoA inactivation

cAMP induces neurite outgrowth in the rat pheochromocytoma cell line 12 (PC12). In particular, di-butyric cAMP (db-cAMP) induces a greater number of primary processes with shorter length than the number induced by nerve growth factor (NGF). db-cAMP up- and down-regulates GTP-RhoA levels in PC12 cells in a time-dependent manner. Tat-C3 toxin stimulates neurite outgrowth, whereas lysophosphatidic acid (LPA) and constitutively active (CA)-RhoA reduce neurite outgrowth, suggesting that RhoA inactivation is essential for the neurite outgrowth from PC12 cells stimulated by cAMP. In this study, the mechanism by which RhoA is inactivated in response to cAMP was examined. db-cAMP induces phosphorylation of RhoA and augments the binding of RhoA with Rho guanine nucleotide dissociation inhibitor (GDI). Moreover, RhoA (S188D) mimicking phosphorylated RhoA induces greater neurite outgrowth than RhoA (S188A) mimicking dephosphorylated form does. Additionally, db-cAMP increases GTP-Rap1 levels, and dominant negative (DN)-Rap1 and DN-Rap-dependent RhoGAP (ARAP3) block neurite outgrowth induced by db-cAMP. DN-p190RhoGAP and the Src inhibitor PP2 suppress neurite outgrowth, whereas transfection of c-Src and p190RhoGAP cDNAs synergistically stimulate neurite outgrowth. Taken together, RhoA is inactivated by phosphorylation of itself, by p190RhoGAP which is activated by Src, and by ARAP3 which is activated by Rap1 during neurite outgrowth from PC12 cells in response to db-cAMP.

Relaxant effect of prostaglandin D(2)--receptor DP agonist on liver myofibroblast contraction

Increased intrahepatic resistance causes portal hypertension in cirrhosis. Liver myofibroblasts (MFs) are now regarded as the principle cells involved in sinusoidal blood flow regulation. Many other prostaglandin-receptor agonists have been reported to regulate liver MF contraction, but the role of the prostaglandin D(2)-receptor DP is unknown. In this study, we investigated the effect of a synthetic agonist of prostanoid DP receptor, BW245C, on contractile properties of primary rat liver MFs. Collagen gel contraction assay revealed that BW245C alone (1 and 10 µM) did not induce contraction but induced cell relaxation. Pretreatment with BW245C (10 µM, 30 min) attenuated bradykinin (100 nM)-induced liver MF contraction. Elevation of [Ca(2+)](i) induced by bradykinin (100 nM) was partially suppressed by BW245C pretreatment (10 µM, 3 min). BW245C (1 and 10 µM) significantly increased intracellular cAMP level in a dose-dependent manner. Pretreatment with forskolin (30 - 300 nM, 30 min) and dibutyryl-cAMP (3 - 30 µM, 30 min) significantly reduced bradykinin-induced contraction. Furthermore, a protein kinase A (PKA) inhibitor KT5720 (10 nM to 1 µM, 30 min) blocked the relaxant effect of BW245C. These results suggest that prostanoid DP receptor agonism inhibits bradykinin-induced [Ca(2+)](i) elevation and contraction through cAMP-PKA signal activation in rat liver MFs.

Protein kinase A governs a RhoA-RhoGDI protrusion-retraction pacemaker in migrating cells

The cyclical protrusion and retraction of the leading edge is a hallmark of many migrating cells involved in processes such as development, inflammation, and tumorigenesis. The molecular identity of signaling mechanisms that control these cycles has remained unknown. Here, we used live cell imaging of biosensors to monitor spontaneous morphodynamic and signaling activities, and employed correlative image analysis to examine the role of cAMP-activated Protein Kinase A (PKA) in protrusion regulation. PKA activity at the leading edge is closely synchronized with rapid protrusion and with the activity of RhoA. Ensuing PKA phosphorylation of RhoA and the resulting increased interaction between RhoA and RhoGDI establishes a negative feedback that controls the cycling of RhoA activity at the leading edge. Thus, cooperation between PKA, RhoA, and a RhoGDI forms a pacemaker that governs the morphodynamic behavior of migrating cells.

Inverse agonism of cannabinoid CB1 receptor blocks the adhesion of encephalitogenic T cells in inflamed brain venules by a protein kinase A-dependent mechanism

It is well known that the cannabinoid system has a significant role in the regulation of the immune responses. Cannabinoid receptors CB1 and CB2 are expressed on T lymphocytes and mediate the immunomodulatory effects of cannabinoids on T cell functions. Here we show that the treatment of proteolipid protein (PLP)139-151-specific T cells with SR141716A, a CB1 inverse agonist and prototype of the diarylpyrazoles series, induced a strong inhibition of firm adhesion in inflamed brain venules in intravital microscopy experiments. In contrast, SR144528, a potent CB2 inverse agonist, had no significant effect on both rolling and arrest of activated T cells. In addition, two analogs of SR141716A and CB1 inverse agonists, AM251 and AM281 inhibited encephalitogenic T cell adhesion suggesting that selective CB1 inverse agonism interfere with lymphocyte trafficking in the CNS. Flow cytometry experiments showed that CB1 inverse agonists have no effect on adhesion molecule expression suggesting that CB1 blockade interferes with signal transduction pathways controlling T cell adhesion in inflamed brain venules. In addition, integrin clustering was not altered after treatment with CB1 inverse agonists suggesting that adhesion blockade is not due to the modulation of integrin valency. Notably, the inhibitory effect exerted by AM251 and AM281 on the adhesive interactions was completely reverted in the presence of protein kinase A (PKA) inhibitor H89, suggesting that cAMP and PKA activation play a key role in the adhesion blockade mediated by CB1 inverse agonists. To further strengthen these results and unveil a previously unknown inhibitory role of cAMP on activated T cell adhesion in vivo in the context of CNS inflammation, we showed that intracellular increase of cAMP induced by treatment with Bt2cAMP, a permeable analog of cAMP, and phosphodiesterase (PDE) inhibitor theophylline efficiently blocked the arrest of encephalitogenic T cells in inflamed brain venules. Our data show that modulation of CB1 function has anti-inflammatory effects and suggests that inverse agonism of CB1 block signal transduction mechanisms controlling encephalitogenic T cells adhesion in inflamed brain venules by a PKA-dependent mechanism.

Involvement of VILIP-1 (visinin-like protein) and opposite roles of cyclic AMP and GMP signaling in in vitro cell migration of murine skin squamous cell carcinoma

VILIP-1 (visinin-like protein 1) is downregulated in various human squamous cell carcinoma (SCC). In a mouse skin SCC model VILIP-1 expression is reduced in aggressive tumor cells, accompanied by reduced cAMP levels. Overexpression of VILIP-1 in aggressive SCC cells led to enhanced cAMP production, in turn causing a reduction in invasive properties. Moreover, in primary neurons and neuronal tumor lines VILIP-1 enhanced cGMP signaling. Here, we set out to determine whether and how cAMP and cGMP signaling contribute to the VILIP-1 effect on enhanced SCC model cell migration, and thus most likely invasiveness in vivo. We found stronger increase in cGMP levels in aggressive, VILIP-1-negative SCC cells following stimulation of guanylyl cyclases NPR-A and -B with the natriuretic peptides ANP and CNP, respectively. Incubation with ANP or 8Br-cGMP to increase cGMP levels further enhanced the migration capacity of aggressive cells, whereas cell adhesion was unaffected. Increased cGMP was caused by elevated expression levels of NPR-A and -B. However, the expression level of VILIP-1 did not affect cGMP signaling and guanylyl cyclase expression in SCC. In contrast, VILIP-1 led to reduced migration of aggressive SCC cells depending on cAMP levels as shown by use of adenylyl cyclase (AC) inhibitor 2',3'-dideoxyadenosine. Involvement of cAMP-effectors PKA and EPAC play a role downstream of AC activation. VILIP-1-positive and -negative cells did not differ in mRNA expression of ACs, but an effect on enhanced protein expression and membrane localization of ACs was shown to underlie enhancement of cAMP production and, thus, reduction in cell migration by VILIP-1.

Cyclic AMP-mediated immune regulation--overview of mechanisms of action in T cells

The canonical second messenger cAMP is well established as a potent negative regulator of T cell immune function. Through protein kinase A (PKA) it regulates T cell function at the level of transcription factors, members of the mitogen-activated protein kinase pathway, phospholipases (PLs), Ras homolog (Rho)A and proteins involved in the control of cell cycle progression. Type I PKA is the predominant PKA isoform in T cells. Furthermore, whereas type II PKA is located at the centrosome, type I PKA is anchored close to the T cell receptor (TCR) in lipid rafts by the Ezrin-ERM-binding phosphoprotein of 50 kDa (EBP50)-phosphoprotein associated with glycosphingolipid-enriched microdomains (PAG) scaffold complex. The most TCR-proximal target for type I PKA is C-terminal Src kinase (Csk), which upon activation by raft recruitment and phosphorylation inhibits the Src family tyrosine kinases Lck and Fyn and thus functions to maintain T cell homeostasis. Recently, induction of cAMP levels in responder T cells has emerged as one of the mechanisms by which regulatory T (T(R)) cells execute their suppressive action. Thus, the cAMP-type I PKA-Csk pathway emerges as a putative target for therapeutic intervention in autoimmune disorders as well as in cancer, where T(R) cell-mediated suppression contributes to suboptimal local immune responses.

Histamine regulates autoreactive T cell activation and adhesiveness in inflamed brain microcirculation

Histamine may contribute to the pathology of MS and its animal model EAE. We explored the effects of histamine and specific HR agonists on activation and migratory capacity of myelin-autoreactive T cells. We show that histamine in vitro inhibits proliferation and IFN-γ production of mouse T cells activated against PLP(139-151). These effects were mimicked by the H1R agonist HTMT and the H2R agonist dimaprit and were associated with reduced activation of ERK½ kinase and with increased levels of cell cycle inhibitor p27Kip-1, both involved in T cell proliferation and anergy. H1R and H2R agonists reduced spontaneous and chemokine-induced adhesion of autoreactive T cells to ICAM-1 in vitro and blocked firm adhesion of these cells in inflamed brain microcirculation in vivo. Thus histamine, through H1R and H2R, inhibits activation of myelin-autoreactive T cells and their ability to traffic through the inflamed BBB. Strategies aimed at interfering with the histamine axis might have relevance in the therapy of autoimmune disease of the CNS.

A PKA-Csk-pp60Src signaling pathway regulates the switch between endothelial cell invasion and cell-cell adhesion during vascular sprouting

Angiogenesis is controlled by signals that stimulate motility in endothelial cells at the tips of vascular sprouts while maintaining cell-cell adhesion in the stalks of angiogenic sprouts. We show here that Gs-linked G protein-coupled receptor activation of cAMP-dependent protein kinase (PKA) plays an important role in regulating the switch between endothelial cell adhesion and migration by activating C-terminal Src kinase, leading to inhibition of pp60Src. Activated PKA blocks pp60Src-dependent vascular endot helial-cadherin phosphorylation, thereby stimulating cell-cell adhesion while suppressing endothelial cell polarization, motility, angiogenesis, and vascular permeability. Similar to the actions of Notch and Dll4, PKA activation blocks sprouting in newly forming embryonic blood vessels, while PKA inhibition promotes excessive sprouting in these vessels. These findings demonstrate that G protein-coupled receptors and PKA regulate vascular sprouting during angiogenesis by controlling endothelial cell migration and cell-cell adhesion through their actions on pp60Src.

Prostaglandin E2 inhibits migration of colonic lamina propria fibroblasts

BACKGROUND

Migration of colonic lamina propria fibroblasts (CLPF) is an important mechanism during wound healing in inflammatory bowel disease (IBD). The concentration of prostaglandin E2 (PGE2) is increased in the intestinal mucosa of IBD patients. We therefore investigated the role of PGE2 in CLPF migration.

METHODS

Primary cultures of CLPF were isolated from healthy controls and Crohn's disease patients. Migration assays were performed in the Boyden chamber and scratch assays. EP receptors, PGE2, intracellular cyclic adenosine monophosphate (cAMP), expression and distribution of F-actin, alpha-smooth muscle actin (SMA), and myosin light chain (MLC) were determined by immunoblotting, immunocytochemistry, and enzyme-linked immunosorbent assay (ELISA).

RESULTS

All four EP receptor subtypes were present on CLPF. PGE2 and agonists to the EP2 and EP4 receptor reduced the migration of CLPF. Blockade of the EP2 and the EP4 receptor inhibited the effect of PGE2 on CLPF migration. An increase in intracellular cAMP reduced CLPF migration. PGE2 increased the concentrations of cAMP in CLPF, with abrogation after addition of EP2 and EP4 receptor antagonists. PGE2 and forskolin decreased the expression of alpha-SMA and F-actin and reduced cell polarization and lamellipodium formation in a scratch assay. In addition, forskolin reduced the phosphorylation of MLC (pMLC) and led to lack of accumulation of pMLC in the leading edge of CLPF.

CONCLUSIONS

PGE2 reduced the migration of CLPF via elevation of intracellular cAMP. Potential mechanisms are changes in expression of cytoskeletal proteins, failure of CLPF to polarize, and a decreased amount of pMLC. This might be a possible reason for the impairment of intestinal wound healing in IBD.

PDE8 regulates rapid Teff cell adhesion and proliferation independent of ICER

BACKGROUND

Abolishing the inhibitory signal of intracellular cAMP by phosphodiesterases (PDEs) is a prerequisite for effector T (Teff) cell function. While PDE4 plays a prominent role, its control of cAMP levels in Teff cells is not exclusive. T cell activation has been shown to induce PDE8, a PDE isoform with 40- to 100-fold greater affinity for cAMP than PDE4. Thus, we postulated that PDE8 is an important regulator of Teff cell functions.

METHODOLOGY/PRINCIPAL FINDINGS

We found that Teff cells express PDE8 in vivo. Inhibition of PDE8 by the PDE inhibitor dipyridamole (DP) activates cAMP signaling and suppresses two major integrins involved in Teff cell adhesion. Accordingly, DP as well as the novel PDE8-selective inhibitor PF-4957325-00 suppress firm attachment of Teff cells to endothelial cells. Analysis of downstream signaling shows that DP suppresses proliferation and cytokine expression of Teff cells from Crem-/- mice lacking the inducible cAMP early repressor (ICER). Importantly, endothelial cells also express PDE8. DP treatment decreases vascular adhesion molecule and chemokine expression, while upregulating the tight junction molecule claudin-5. In vivo, DP reduces CXCL12 gene expression as determined by in situ probing of the mouse microvasculature by cell-selective laser-capture microdissection.

CONCLUSION/SIGNIFICANCE

Collectively, our data identify PDE8 as a novel target for suppression of Teff cell functions, including adhesion to endothelial cells.

Integrin and CD3/TCR activation are regulated by the scaffold protein AKAP450

During antigen recognition by T cells, membrane receptors and cytoskeletal molecules form a specialized structure at the T cell-antigen-presenting cell junction called the immune synapse (IS). We report a role for the scaffolding protein A-kinase anchoring protein-450 (AKAP450), a member of the A-kinase anchoring protein family, in IS formation and T-cell signaling in antigen- and superantigen-dependent T-cell activation. Suppression of AKAP450 by overexpression of a dominant-negative form or siRNA knockdown disrupted the positioning and conformational activation of lymphocyte function-associated antigen 1 at the IS and impaired associated signaling events, including phosphorylation of phospholipase C-gamma1 and protein kinase C-. AKAP450 was also required for correct activation and phosphorylation of CD3, LAT, and Vav1, key T-cell receptor-activated intracellular signaling molecules. Consistently, antigen-triggered reorientation of the microtubule-organizing center at the IS and interleukin-2 secretion were diminished in AKAP450-disrupted T cells. These results indicate key roles for AKAP450 in the organization and activation of receptor molecules at the IS during T-cell signaling events.

Selective mobilization of cytotoxic leukocytes by epinephrine

It is well-known that acute stress, presumably as a first defense against pathogens, enhances PBMC counts by mobilizing these beta2-adrenoceptor positive cells from the marginal pool. Yet, only select leukocyte subsets participate in this phenomenon of adrenergic leukocytosis and underlying mechanisms are obscure. In this study, we analyzed in human blood adhesion molecule and chemokine receptor profiles in 14 leukocyte subsets, and responsiveness of subsets to epinephrine in vivo and in vitro. Five subsets, namely, CCR7(-)CD45RA(+)CD8(+) effector T cells, CD4(-)CD8(-) gamma/delta T cells, CD3(+)CD56(+) NKT-like cells, CD16(+)CD56(dim) cytotoxic NK cells, and CD14(dim)CD16(+) proinflammatory monocytes showed a rapid and transient increase after infusion of epinephrine at physiological concentrations. These cells were characterized by a CD62L(-)CD11a(bright)CX3CR(bright) phenotype, whereby expression of both CD11a and CX3CR1 was strongly correlated with adrenergic leukocytosis in vivo (r = 0.86 and 0.78, p < 0.005). The same subsets showed highest adherence to activated endothelium in vitro, which (except for proinflammatory monocytes) was reversed by epinephrine. We conclude that these five cytotoxic effector leukocyte subsets comprise the marginal pool by a CD11a/CX3CR1-mediated attachment to the endothelium. Epinephrine rapidly attenuates this attachment to allow demargination and release of the cells into the circulation that, because of their cytotoxic effector function, provide immediate protection from invading pathogens.

Forskolin increases angiogenesis through the coordinated cross-talk of PKA-dependent VEGF expression and Epac-mediated PI3K/Akt/eNOS signaling

Forskolin, a potent activator of adenylyl cyclases, has been implicated in modulating angiogenesis, but the underlying mechanism has not been clearly elucidated. We investigated the signal mechanism by which forskolin regulates angiogenesis. Forskolin stimulated angiogenesis of human endothelial cells and in vivo neovascularization, which was accompanied by phosphorylation of CREB, ERK, Akt, and endothelial nitric oxide synthase (eNOS) as well as NO production and VEGF expression. Forskolin-induced CREB phosphorylation, VEGF promoter activity, and VEGF expression were blocked by the PKA inhibitor PKI.Moreover, phosphorylation of ERK by forskolin was inhibited by the MEK inhibitor PD98059, but not PKI. The forskolin-induced Akt/eNOS/NO pathway was completely inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, but not significantly suppressed by PKI. These inhibitors and a NOS inhibitor partially inhibited forskolin-induced angiogenesis. The exchange protein directly activated by cAMP (Epac) activator, 8CPT-2Me-cAMP, promoted the Akt/eNOS/NO pathway and ERK phosphorylation,but did not induce CREB phosphorylation and VEGF expression. The angiogenic effect of the Epac activator was diminished by the inhibition of PI3K and MEK, but not by the PKA inhibitor. Small interfering RNA-mediated knockdown of Epac1 suppressed forskolin-induced angiogenesis and phosphorylation of ERK, Akt, and eNOS, but not CREB phosphorylation and VEGF expression. These results suggest that forskolin stimulates angiogenesis through coordinated cross-talk between two distinct pathways, PKA-dependent VEGF expression and Epac-dependent ERKactivation and PI3K/Akt/eNOS/NO signaling.

Cortisol and epinephrine control opposing circadian rhythms in T cell subsets

Pronounced circadian rhythms in numbers of circulating T cells reflect a systemic control of adaptive immunity whose mechanisms are obscure. Here, we show that circadian variations in T cell subpopulations in human blood are differentially regulated via release of cortisol and catecholamines. Within the CD4(+) and CD8(+) T cell subsets, naive cells show pronounced circadian rhythms with a daytime nadir, whereas (terminally differentiated) effector CD8(+) T cell counts peak during daytime. Naive T cells were negatively correlated with cortisol rhythms, decreased after low-dose cortisol infusion, and showed highest expression of CXCR4, which was up-regulated by cortisol. Effector CD8(+) T cells were positively correlated with epinephrine rhythms, increased after low-dose epinephrine infusion, and showed highest expression of beta-adrenergic and fractalkine receptors (CX3CR1). Daytime increases in cortisol via CXCR4 probably act to redistribute naive T cells to bone marrow, whereas daytime increases in catecholamines via beta-adrenoceptors and, possibly, a suppression of fractalkine signaling promote mobilization of effector CD8(+) T cells from the marginal pool. Thus, activation of the major stress hormones during daytime favor immediate effector defense but diminish capabilities for initiating adaptive immune responses.

Spatial distribution of protein kinase A activity during cell migration is mediated by A-kinase anchoring protein AKAP Lbc

Protein kinase A (PKA) has been suggested to be spatially regulated in migrating cells due to its ability to control signaling events that are critical for polarized actin cytoskeletal dynamics. Here, using the fluorescence resonance energy transfer-based A-kinase activity reporter (AKAR1), we find that PKA activity gradients form with the strongest activity at the leading edge and are restricted to the basal surface in migrating cells. The existence of these gradients was confirmed using immunocytochemistry using phospho-PKA substrate antibodies. This observation holds true for carcinoma cells migrating randomly on laminin-1 or stimulated to migrate on collagen I with lysophosphatidic acid. Phosphodiesterase inhibition allows the formation of PKA activity gradients; however, these gradients are no longer polarized. PKA activity gradients are not detected when a non-phosphorylatable mutant of AKAR1 is used, if PKA activity is inhibited with H-89 or protein kinase inhibitor, or when PKA anchoring is perturbed. We further find that a specific A-kinase anchoring protein, AKAP-Lbc, is a major contributor to the formation of these gradients. In summary, our data show that PKA activity gradients are generated at the leading edge of migrating cells and provide additional insight into the mechanisms of PKA regulation of cell motility.

Localization and translocation of RhoA protein in the human gastric cancer cell line SGC-7901

AIM: To elucidate the localization of RhoA in gastric SGC-7901 cancer cells and its translocation by lysophosphatidic acid (LPA) and/or 8-chlorophenylthio-cAMP (CPT-cAMP).

METHODS: Immunofluorescence microscopy was used to determine the localization of RhoA. Western blotting was used to detect both endogenous and exogenous RhoA in different cellular compartments (membrane, cytosol, nucleus) and the translocation of RhoA following treatment with LPA, CPT-cAMP, or CPT-cAMP + LPA.

RESULTS: Immunofluorescence staining revealed endogenous RhoA to be localized in the membrane, the cytosol, and the nucleus, and its precise localization within the nucleus to be the nucleolus. Western blotting identified both endogenous and exogenous RhoA within different cellular compartments (membrane, cytosol, nucleus, nucleolus). After stimulation with LPA, the amount of RhoA within membrane and nuclear extracts increased, while it decreased in the cytosol fractions. After treatment with CPT-cAMP the amount of RhoA within the membrane and the nuclear extracts decreased, while it increased within the cytosol fraction. Treatment with a combination of both substances led to a decrease in RhoA in the membrane and the nucleus but to an increase in the cytosol.

CONCLUSION: In SGC-7901 cells RhoA was found to be localized within the membrane, the cytosol, and the nucleus. Within the nucleus its precise localization could be demonstrated to be the nucleolus. Stimulation with LPA caused a translocation of RhoA from the cytosol towards the membrane and the nucleus; treatment with CPT-cAMP caused the opposite effect. Furthermore, pre-treatment with CPT-cAMP was found to block the effect of LPA.

Integrin signaling is integral to regeneration

The inability of the adult injured mammalian spinal cord to successfully regenerate is not well understood. Studies suggest that both extrinsic and intrinsic factors contribute to regeneration failure. In this review, we focus on intrinsic factors that impact regeneration, in particular integrin receptors and their downstream signaling pathways. We discuss studies that address the impact of integrins and integrin signaling pathways on growth cone guidance and motility and how lessons learned from these studies apply to spinal cord regeneration in vivo.

Alpha1-acid glycoprotein suppresses rat acute inflammatory paw edema through the inhibition of neutrophils activation and prostaglandin E2 generation

Alpha(1)-acid glycoprotein (AGP) is an acute phase protein. Whereas the expression of AGP in an inflammatory state is enhanced by inflammatory cytokines including interleukin-1, 6 (IL-1 and IL-6), and tumor necrosis factor-alpha (TNF-alpha), the biological significance of AGP remains unclear. In the current study, the anti-inflammatory effect of AGP on the acute inflammatory state was examined in vivo and in vitro. AGP suppressed carrageenan-, dextran- and kaolin-induced paw edema and vascular permeability in rat. These results suggest that both initial inflammatory mediators (serotonin and histamine) and later inflammatory mediators (prostaglandin and bradykinin) are involved in the anti-inflammatory effects of AGP. In fact, prostaglandin E(2) (PGE(2)) generation in plasma was significantly inhibited by AGP. Moreover, AGP inhibited the migration of neutrophils treated with N-formyl-methionyl-leucyl-phenylalanine (fMLP) through membrane filter. In addition, AGP significantly suppressed superoxide generation from neutrophils that has been treated with fMLP or phorbol 12-myristate 13-acetate. These results imply that the anti-inflammatory effect of AGP may involve the inhibition of neutrophils migration. The data obtained in this study support a scenario in which an increase in AGP concentration in pathological conditions suppresses inflammation reactions induced by autacoids and neutrophils activities and that AGP plays an important role in the maintenance in the body.

Regulation of VASP serine 157 phosphorylation in human neutrophils after stimulation by a chemoattractant

Vasodilator-stimulated phosphoprotein (VASP) is a cAMP-dependent protein kinase A (PKA) substrate, which links cellular signaling to cytoskeletal organization and cellular movement. VASP is phosphorylated by PKA on serine 157 (Ser 157), which is required for VASP function in platelet adhesion and fibroblast motility. Our hypothesis is that PKA regulates neutrophil migration through VASP Ser 157 phosphorylation. The objective of this study was to characterize VASP Ser 157 phosphorylation in chemoattractant-stimulated neutrophils. fMLF, IL-8, leukotriene B(4), or platelet-activating factor stimulation resulted in an initial increase in VASP Ser 157 phosphorylation, which was maximal by 30 s and was followed by a return to baseline Ser 157 phosphorylation by 10 min. In contrast, stimulation with the nonchemoattractant, proinflammatory cytokine TNF-alpha did not affect Ser 157 phosphorylation. The kinetics of fMLF-induced VASP Ser 157 phosphorylation levels closely matched the kinetics of the fold-change in F-actin levels in fMLF-stimulated neutrophils. fMLF-induced Ser 157 phosphorylation was abolished by pretreatment with the PKA inhibitor H89 and the adenylyl cyclase inhibitor SQ22536. In contrast, fMLF-induced Ser 157 phosphorylation was unaffected by the PKC inhibitors calphostin and staurosporine, the PKG inhibitors Rp-8-pCPT-cGMP and KT5823, and the calmodulin-dependent protein kinase II inhibitor KN-62. Inhibition of adhesion with EDTA or the anti-beta2-integrin antibody IB4 did not alter fMLF-induced VASP phosphorylation or dephosphorylation. These data show that chemoattractant stimulation of human neutrophils induces a rapid and transient PKA-dependent VASP Ser 157 phosphorylation. Adhesion does not appear to be an important regulator of the state of VASP Ser 157 phosphorylation in chemoattractant-stimulated neutrophils.

The pivotal role of RhoA GTPase in the molecular signaling of axon growth inhibition after CNS injury and targeted therapeutic strategies

The dogma that the adult central nervous system (CNS) is nonpermissive to axonal regeneration is beginning to fall in the face of increased understanding of the molecular and cellular biology of axon outgrowth. It is now appreciated that axon growth is regulated by a combination of extracellular factors related to the milieu of the developing or adult CNS and the presence of injury, and intracellular factors related to the "growth state" of the developing or regenerating neuron. Several critical points of convergence within the developing or regenerating neuron for mediating intracellular cell signaling effects on the growth cone cytoskeleton have been identified, and their modulation has produced marked increases in axon outgrowth within the "nonpermissive" milieu of the adult injured CNS. One such critical convergence point is the small GTPase RhoA, which integrates signaling events produced by both myelin-associated inhibitors (e.g., NogoA) and astroglial-derived inhibitors (chondroitin sulfate proteoglycans) and regulates the activity of downstream effectors that modulate cytoskeletal dynamics within the growth cone mediating axon outgrowth or retraction. Inhibition of RhoA has been associated with increased outgrowth on nonpermissive substrates in vitro and increased axon regeneration in vivo. We are developing lentiviral vectors that modulate RhoA activity, allowing more long-term expression than is possible with current approaches. These vectors may be useful in regenerative strategies for spinal cord injury, brain injury, and neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and Huntington's disease.

The PGE2-induced inhibition of the PLD activation pathway stimulated by fMLP in human neutrophils is mediated by PKA at the PI3-Kgamma level

Prostaglandin E2 (PGE2), an eicosanoid that modulates inflammation, inhibits several chemoattractant-elicited functions in neutrophils such as chemotaxis, production of superoxide anions, adhesion, secretion of cytotoxic enzymes and synthesis of leukotriene B4. We previously reported that PGE2 inhibits the fMLP signaling pathway that leads to PLD activation through suppression of PI3-Kgamma activity and the decreased recruitment to membranes of PLD activation factors, PKC, Rho and Arf-GTPases. This effect is mediated via the EP2 receptors known to raise cAMP in cells. The inhibition of most fMLP-induced functional responses by PGE2 via EP2 receptors is mediated by PKA, except the chemotactic response. We have investigated the role of PKA in the EP2-mediated inhibition of the PLD activation pathway. H-89, a selective PKA pharmacological inhibitor suppressed the inhibitory effects of PGE2 at all stages of the PLD pathway activated by fMLP, i.e. PLD activity, translocation to membranes of PKCalpha, Rho and Arf-GTPases, calcium influx, tyrosine phosphorylation of proteins and finally translocation of p110gamma catalytic subunit of PI3-K to membranes. However, neither PLD nor PI3-Kgamma was substrate of PKA. These data provide evidence that PGE2-stimulated PKA activity regulates the PLD pathway stimulated by fMLP at the level of PI3-Kgamma and that the inhibition of PI3-Kgamma activation by PKA is a complex mechanism that remains to be completely elucidated.