Epac inhibits migration and proliferation of human prostate carcinoma cells

cAMP: A master regulator of cadherin-mediated binding in endothelium, epithelium and myocardium

Regulation of cadherin-mediated cell adhesion is crucial not only for maintaining tissue integrity and barrier function in the endothelium and epithelium but also for electromechanical coupling within the myocardium. Therefore, loss of cadherin-mediated adhesion causes various disorders, including vascular inflammation and desmosome-related diseases such as the autoimmune blistering skin dermatosis pemphigus and arrhythmogenic cardiomyopathy. Mechanisms regulating cadherin-mediated binding contribute to the pathogenesis of diseases and may also be used as therapeutic targets. Over the last 30 years, cyclic adenosine 3',5'-monophosphate (cAMP) has emerged as one of the master regulators of cell adhesion in endothelium and, more recently, also in epithelial cells as well as in cardiomyocytes. A broad spectrum of experimental models from vascular physiology and cell biology applied by different generations of researchers provided evidence that not only cadherins of endothelial adherens junctions (AJ) but also desmosomal contacts in keratinocytes and the cardiomyocyte intercalated discs are central targets in this scenario. The molecular mechanisms involve protein kinase A- and exchange protein directly activated by cAMP-mediated regulation of Rho family GTPases and S665 phosphorylation of the AJ and desmosome adaptor protein plakoglobin. In line with this, phosphodiesterase 4 inhibitors such as apremilast have been proposed as a therapeutic strategy to stabilize cadherin-mediated adhesion in pemphigus and may also be effective to treat other disorders where cadherin-mediated binding is compromised.

The Role of Genetic, Metabolic, Inflammatory, and Immunologic Mediators in the Progression of Intraductal Papillary Mucinous Neoplasms to Pancreatic Adenocarcinoma

Intraductal papillary mucinous neoplasms (IPMN) have the potential to progress to pancreatic ductal adenocarcinoma (PDAC). As with any progression to malignancy, there are a variety of genetic and metabolic changes, as well as other disruptions to the cellular microenvironment including immune alterations and inflammation, that can contribute to tumorigenesis. Previous studies further characterized these alterations, revealing changes in lipid and glucose metabolism, and signaling pathways that mediate the progression of IPMN to PDAC. With the increased diagnosis of IPMNs and pancreatic cysts on imaging, the opportunity to attenuate risk with the removal of high-risk lesions is possible with the understanding of what factors accelerate malignant progression and how they can be clinically utilized to determine the level of dysplasia and stratify the risk of progression. Here, we reviewed the genetic, metabolic, inflammatory, and immunologic pathways regulating the progression of IPMN to PDAC.

Epac: A Promising Therapeutic Target for Vascular Diseases: A Review

Vascular diseases affect the circulatory system and comprise most human diseases. They cause severe symptoms and affect the quality of life of patients. Recently, since their identification, exchange proteins directly activated by cAMP (Epac) have attracted increasing scientific interest, because of their role in cyclic adenosine monophosphate (cAMP) signaling, a well-known signal transduction pathway. The role of Epac in cardiovascular disease and cancer is extensively studied, whereas their role in kidney disease has not been comprehensively explored yet. In this study, we aimed to review recent studies on the regulatory effects of Epac on various vascular diseases, such as cardiovascular disease, cerebrovascular disease, and cancer. Accumulating evidence has shown that both Epac1 and Epac2 play important roles in vascular diseases under both physiological and pathological conditions. Additionally, there has been an increasing focus on Epac pharmacological modulators. Therefore, we speculated that Epac could serve as a novel therapeutic target for the treatment of vascular diseases.

cAMP Signaling in Cancer: A PKA-CREB and EPAC-Centric Approach

Cancer is one of the most common causes of death globally. Despite extensive research and considerable advances in cancer therapy, the fundamentals of the disease remain unclear. Understanding the key signaling mechanisms that cause cancer cell malignancy may help to uncover new pharmaco-targets. Cyclic adenosine monophosphate (cAMP) regulates various biological functions, including those in malignant cells. Understanding intracellular second messenger pathways is crucial for identifying downstream proteins involved in cancer growth and development. cAMP regulates cell signaling and a variety of physiological and pathological activities. There may be an impact on gene transcription from protein kinase A (PKA) as well as its downstream effectors, such as cAMP response element-binding protein (CREB). The position of CREB downstream of numerous growth signaling pathways implies its oncogenic potential in tumor cells. Tumor growth is associated with increased CREB expression and activation. PKA can be used as both an onco-drug target and a biomarker to find, identify, and stage tumors. Exploring cAMP effectors and their downstream pathways in cancer has become easier using exchange protein directly activated by cAMP (EPAC) modulators. This signaling system may inhibit or accelerate tumor growth depending on the tumor and its environment. As cAMP and its effectors are critical for cancer development, targeting them may be a useful cancer treatment strategy. Moreover, by reviewing the material from a distinct viewpoint, this review aims to give a knowledge of the impact of the cAMP signaling pathway and the related effectors on cancer incidence and development. These innovative insights seek to encourage the development of novel treatment techniques and new approaches.

The Role of Neuropeptide-Stimulated cAMP-EPACs Signalling in Cancer Cells

Neuropeptides are autocrine and paracrine signalling factors and mainly bind to G protein-coupled receptors (GPCRs) to trigger intracellular secondary messenger release including adenosine 3′, 5′-cyclic monophosphate (cAMP), thus modulating cancer progress in different kind of tumours. As one of the downstream effectors of cAMP, exchange proteins directly activated by cAMP (EPACs) play dual roles in cancer proliferation and metastasis. More evidence about the relationship between neuropeptides and EPAC pathways have been proposed for their potential role in cancer development; hence, this review focuses on the role of neuropeptide/GPCR system modulation of cAMP/EPACs pathways in cancers. The correlated downstream pathways between neuropeptides and EPACs in cancer cell proliferation, migration, and metastasis is discussed to glimmer the direction of future research.

The Role of Epac in Cancer Progression

Cancer continues to be a prime contributor to global mortality. Despite tremendous research efforts and major advances in cancer therapy, much remains to be learned about the underlying molecular mechanisms of this debilitating disease. A better understanding of the key signaling events driving the malignant phenotype of cancer cells may help identify new pharmaco-targets. Cyclic adenosine 3',5'-monophosphate (cAMP) modulates a plethora of biological processes, including those that are characteristic of malignant cells. Over the years, most cAMP-mediated actions were attributed to the activity of its effector protein kinase A (PKA). However, studies have revealed an important role for the exchange protein activated by cAMP (Epac) as another effector mediating the actions of cAMP. In cancer, Epac appears to have a dual role in regulating cellular processes that are essential for carcinogenesis. In addition, the development of Epac modulators offered new routes to further explore the role of this cAMP effector and its downstream pathways in cancer. In this review, the potentials of Epac as an attractive target in the fight against cancer are depicted. Additionally, the role of Epac in cancer progression, namely its effect on cancer cell proliferation, migration/metastasis, and apoptosis, with the possible interaction of reactive oxygen species (ROS) in these phenomena, is discussed with emphasis on the underlying mechanisms and pathways.

Beta-adrenergic signaling on neuroendocrine differentiation, angiogenesis, and metastasis in prostate cancer progression

Prostate cancer is a complex, heterogeneous disease that mainly affects the older male population with a high-mortality rate. The mechanisms underlying prostate cancer progression are still incompletely understood. Beta-adrenergic signaling has been shown to regulate multiple cellular processes as a mediator of chronic stress. Recently, beta-adrenergic signaling has been reported to affect the development of aggressive prostate cancer by regulating neuroendocrine differentiation, angiogenesis, and metastasis. Here, we briefly summarize and discuss recent advances in these areas and their implications in prostate cancer therapeutics. We aim to provide a better understanding of the contribution of beta-adrenergic signaling to the progression of aggressive prostate cancer.

Targeting Cyclic AMP Signalling in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major healthcare problem worldwide, representing one of the leading causes of cancer mortality. Since there are currently no predictive biomarkers for early stage diagnosis, HCC is detected only in advanced stages and most patients die within one year, as radical tumour resection is generally performed late during the disease. The development of alternative therapeutic approaches to HCC remains one of the most challenging areas of cancer. This review focuses on the relevance of cAMP signalling in the development of hepatocellular carcinoma and identifies the modulation of this second messenger as a new strategy for the control of tumour growth. In addition, because the cAMP pathway is controlled by phosphodiesterases (PDEs), targeting these enzymes using PDE inhibitors is becoming an attractive and promising tool for the control of HCC. Among them, based on current preclinical and clinical findings, PDE4-specific inhibitors remarkably demonstrate therapeutic potential in the management of cancer outcomes, especially as adjuvants to standard therapies. However, more preclinical studies are warranted to ascertain their efficacy during the different stages of hepatocyte transformation and in the treatment of established HCC.

Ending Restenosis: Inhibition of Vascular Smooth Muscle Cell Proliferation by cAMP

Increased vascular smooth muscle cell (VSMC) proliferation contributes towards restenosis after angioplasty, vein graft intimal thickening and atherogenesis. The second messenger 3′ 5′ cyclic adenosine monophosphate (cAMP) plays an important role in maintaining VSMC quiescence in healthy vessels and repressing VSMC proliferation during resolution of vascular injury. Although the anti-mitogenic properties of cAMP in VSMC have been recognised for many years, it is only recently that we gained a detailed understanding of the underlying signalling mechanisms. Stimuli that elevate cAMP in VSMC inhibit G₁-S phase cell cycle progression by inhibiting expression of cyclins and preventing S-Phase Kinase Associated Protein-2 (Skp2-mediated degradation of cyclin-dependent kinase inhibitors. Early studies implicated inhibition of MAPK signalling, although this does not fully explain the anti-mitogenic effects of cAMP. The cAMP effectors, Protein Kinase A (PKA) and Exchange Protein Activated by cAMP (EPAC) act together to inhibit VSMC proliferation by inducing Cyclic-AMP Response Element Binding protein (CREB) activity and inhibiting members of the RhoGTPases, which results in remodelling of the actin cytoskeleton. Cyclic-AMP induced actin remodelling controls proliferation by modulating the activity of Serum Response Factor (SRF) and TEA Domain Transcription Factors (TEAD), which regulate expression of genes required for proliferation. Here we review recent research characterising these mechanisms, highlighting novel drug targets that may allow the anti-mitogenic properties of cAMP to be harnessed therapeutically to limit restenosis.

Synergistic effect of phosphodiesterase 4 inhibitor and serum on migration of endotoxin-stimulated macrophages

Macrophage migration is an essential step in host defense against infection and wound healing. Elevation of cAMP by inhibiting phosphodiesterase 4 (PDE4), enzymes that specifically degrade cAMP, is known to suppress various inflammatory responses in activated macrophages, but the role of PDE4 in macrophage migration is poorly understood. Here we show that the migration of Raw 264.7 macrophages stimulated with LPS was markedly and dose-dependently induced by the PDE4 inhibitor rolipram as assessed by scratch wound healing assay. Additionally, this response required the involvement of serum in the culture medium as serum starvation abrogated the effect. Further analysis revealed that rolipram and serum exhibited synergistic effect on the migration, and the influence of serum was independent of PDE4 mRNA expression in LPS-stimulated macrophages. Moreover, the enhanced migration by rolipram was mediated by activating cAMP/exchange proteins directly activated by cAMP (Epac) signaling, presumably via interaction with LPS/TLR4 signaling with the participation of unknown serum components. These results suggest that PDE4 inhibitors, together with serum components, may serve as positive regulators of macrophage recruitment for more efficient pathogen clearance and wound repair.

cAMP guided his way: a life for G protein-mediated signal transduction and molecular pharmacology-tribute to Karl H. Jakobs

Karl H. Jakobs, former editor-in-chief of Naunyn-Schmiedeberg's Archives of Pharmacology and renowned molecular pharmacologist, passed away in April 2018. In this article, his scientific achievements regarding G protein-mediated signal transduction and regulation of canonical pathways are summarized. Particularly, the discovery of inhibitory G proteins for adenylyl cyclase, methods for the analysis of receptor-G protein interactions, GTP supply by nucleoside diphosphate kinases, mechanisms in phospholipase C and phospholipase D activity regulation, as well as the development of the concept of sphingosine-1-phosphate as extra- and intracellular messenger will presented. His seminal scientific and methodological contributions are put in a general and timely perspective to display and honor his outstanding input to the current knowledge in molecular pharmacology.

cAMP regulated EPAC1 supports microvascular density, angiogenic and metastatic properties in a model of triple negative breast cancer

Breast cancer is a leading cause of cancer-related mortality in women. Triple-negative breast cancer (TNBC; HER2-, ER-/PR-) is an aggressive subtype prone to drug resistance and metastasis, which is characterized by high intratumor microvascular density (iMVD) resulting from angiogenesis. However, the mechanisms contributing to the aggressive phenotypes of TNBC remain elusive. We recently reported that down-regulation of exchange factor directly activated by cyclic AMP (cAMP), also known as EPAC1, leads to a reduction in metastatic properties including proliferation and cell migration in TNBC cell lines. Here, we report that EPAC1 supports TNBC-induced angiogenesis, tumor cell migration and invasiveness as well as pro-metastatic phenotypes in endothelial cells induced through the tumor secretome. Using an approach that integrates proteomics with bioinformatics and gene ontologies, we elucidate that EPAC1 supports a tumor-secreted network of angiogenic, cell adhesion and cell migratory pathways. Using confocal microscopy, we show that signaling molecules involved in focal adhesion, including Paxillin and MENA, are down-regulated in the absence of EPAC1, and electric cell substrate impedance sensing technique confirmed a role for EPAC1 on TNBC-induced endothelial cell permeability. Finally, to provide a translational bridge, we studied iMVD and therapy response using a primary human tumor explant assay, CANscriptTM, which suggests a link between therapy-modulated neovascularization and drug sensitivity. These data provide mechanistic insight into the role of EPAC1 in regulating the tumor microenvironment, iMVD and cancer cell-induced angiogenesis, a dynamic mechanism under drug pressure that may associate to treatment failure.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Insights into exchange factor directly activated by cAMP (EPAC) as potential target for cancer treatment

Cancer remains a global health problem and approximately 1.7 million new cancer cases are diagnosed every year worldwide. Although diverse molecules are currently being explored as targets for cancer therapy the tumor treatment and therapy is highly tricky. Secondary messengers are important for hormone-mediated signaling pathway. Cyclic AMP (cAMP), a secondary messenger responsible for various physiological processes regulates cell metabolism by activating Protein kinase A (PKA) and by targeting exchange protein directly activated by cAMP (EPAC). EPAC is present in two isoforms EPAC1 and EPAC2, which exhibit different tissue distribution and is involved in GDP/GTP exchange along with activating Rap1- and Rap2-mediated signaling pathways. EPAC is also known for its dual role in cancer as pro- and anti-proliferative in addition to metastasis. Results after perturbing EPAC activity suggests its involvement in cancer cell migration, proliferation, and cytoskeleton remodeling which makes it a potential therapeutic target for cancer treatments.

Elevated aggressive behavior in male mice with thyroid-specific Prkar1a and global Epac1 gene deletion

Alterations in circulating thyroid hormone concentrations are associated with several psychological and behavioral disorders. In humans, behavioral disorders such as anxiety, depression, and attention-deficit hyperactivity disorder can be associated with thyroid disease. The Tpo-Cre;Prkar1aflox/flox;Epac1-/- (R1A-Epac1KO) mice, originally bred to investigate the role of exchange protein directly activated by cAMP (Epac1) in follicular thyroid cancer, displayed self-mutilating and aggressive behaviors during casual observation. To assess these atypical responses, behavioral testing was conducted with the R1A-Epac1KO mice, as well as their single knockout counterparts, the thyroid-specific Prkar1a-/- and global Epac1-/- mice. Mice of all three genotypes demonstrated increased aggressive behavior against an intruder mouse. In addition, Epac1-/- mice increased response to an auditory stimulus, and the Prkar1a-/- and R1A-Epac1KO mice increased swimming behavior in the Porsolt forced swim test. Both Prkar1a-/- mice and R1A-Epac1KO mice have increased circulating thyroxine and corticosterone concentrations. Although hyperthyroidism has not been previously associated with aggression, increased thyroid hormone signaling might contribute to the increased aggressive response to the intruder mouse, as well as the increased swimming response. Mice with a genetic background of Tpo-Cre;Prkar1aflox/flox;Epac1-/- are aggressive, and both the thyroid-specific knockout of Prkar1a and global knockout of Epac1 likely contribute to this aggressive behavior. This study supports the hypothesis that altered thyroid signaling and aggressive behavior are linked.

Epac1 links prostaglandin E2 to β-catenin-dependent transcription during epithelial-to-mesenchymal transition

In epithelial cells, β-catenin is localized at cell-cell junctions where it stabilizes adherens junctions. When these junctions are disrupted, β-catenin can translocate to the nucleus where it functions as a transcriptional cofactor. Recent research has indicated that PGE₂ enhances the nuclear function of β-catenin through cyclic AMP. Here, we aim to study the role of the cyclic AMP effector Epac in β-catenin activation by PGE₂ in non-small cell lung carcinoma cells.

We show that PGE₂ induces a down-regulation of E-cadherin, promotes cell migration and enhances β-catenin translocation to the nucleus. This results in β-catenin-dependent gene transcription. We also observed increased expression of Epac1. Inhibition of Epac1 activity using the CE3F4 compound or Epac1 siRNA abolished the effects of PGE₂ on β-catenin. Further, we observed that Epac1 and β-catenin associate together. Expression of an Epac1 mutant with a deletion in the nuclear pore localization sequence prevents this association. Furthermore, the scaffold protein Ezrin was shown to be required to link Epac1 to β-catenin.

This study indicates a novel role for Epac1 in PGE₂-induced EMT and subsequent activation of β-catenin.

Structure-Activity Relationship Studies with Tetrahydroquinoline Analogs as EPAC Inhibitors

EPAC proteins are therapeutic targets for the potential treatment of cardiac hypertrophy and cancer metastasis. Several laboratories use a tetrahydroquinoline analog, CE3F4, to dissect the role of EPAC1 in various disease states. Here, we report SAR studies with tetrahydroquinoline analogs that explore various functional groups. The most potent EPAC inhibitor 12a exists as a mixture of inseparable E (major) and Z (minor) rotamers. The rotation about the N-formyl group indeed impacts the activity against EPAC.

Overexpression of exchange protein directly activated by cAMP-1 (EPAC1) attenuates bladder cancer cell migration

Exchange protein directly activated by cAMP (EPAC) is a mediator of a cAMP signaling pathway that is independent of protein kinase A. EPAC has two isoforms (EPAC1 and EPAC2) and is a cAMP-dependent guanine nucleotide exchange factor for the small GTPases, Rap1 and Rap2. Recent studies suggest that EPAC1 has both positive and negative influences on cancer and is involved in cell proliferation, apoptosis, migration and metastasis. We report that EPAC1 and EPAC2 expression levels were significantly lower in bladder cancer tissue than in normal bladder tissue. In addition, bladder cancer cell lines showed reduced EPAC1 mRNA expression. Furthermore, EPAC1 overexpression in bladder cancer cell lines induced morphologic changes and markedly suppressed cell migration without affecting cell viability. The overexpressed EPAC1 preferentially localized at cell-cell interfaces. In conclusion, reduced EPAC1 expression in bladder tumors and poor migration of EPAC1-overexpressing cells implicate EPAC1 as an inhibitor of bladder cancer cell migration.

Paving the Rho in cancer metastasis: Rho GTPases and beyond

Malignant carcinomas are often characterized by metastasis, the movement of carcinoma cells from a primary site to colonize distant organs. For metastasis to occur, carcinoma cells first must adopt a pro-migratory phenotype and move through the surrounding stroma towards a blood or lymphatic vessel. Currently, there are very limited possibilities to target these processes therapeutically. The family of Rho GTPases is an ubiquitously expressed division of GTP-binding proteins involved in the regulation of cytoskeletal dynamics and intracellular signaling. The best characterized members of the Rho family GTPases are RhoA, Rac1 and Cdc42. Abnormalities in Rho GTPase function have major consequences for cancer progression. Rho GTPase activation is driven by cell surface receptors that activate GTP exchange factors (GEFs) and GTPase-activating proteins (GAPs). In this review, we summarize our current knowledge on Rho GTPase function in the regulation of metastasis. We will focus on key discoveries in the regulation of epithelial-mesenchymal-transition (EMT), cell-cell junctions, formation of membrane protrusions, plasticity of cell migration and adaptation to a hypoxic environment. In addition, we will emphasize on crosstalk between Rho GTPase family members and other important oncogenic pathways, such as cyclic AMP-mediated signaling, canonical Wnt/β-catenin, Yes-associated protein (YAP) and hypoxia inducible factor 1α (Hif1α) and provide an overview of the advancements and challenges in developing pharmacological tools to target Rho GTPase and the aforementioned crosstalk in the context of cancer therapeutics.

Role of exchange protein directly activated by cAMP (EPAC1) in breast cancer cell migration and apoptosis

Despite the current progress in cancer research and therapy, breast cancer remains the leading cause of mortality among half a million women worldwide. Migration and invasion of cancer cells are associated with prevalent tumor metastasis as well as high mortality. Extensive studies have powerfully established the role of prototypic second messenger cAMP and its two ubiquitously expressed intracellular cAMP receptors namely the classic protein kinaseA/cAMP-dependent protein kinase (PKA) and the more recently discovered exchange protein directly activated by cAMP/cAMP-regulated guanine nucleotide exchange factor (EPAC/cAMP-GEF) in cell migration, cell cycle regulation, and cell death. Herein, we performed the analysis of the Cancer Genome Atlas (TCGA) dataset to evaluate the essential role of cAMP molecular network in breast cancer. We report that EPAC1, PKA, and AKAP9 along with other molecular partners are amplified in breast cancer patients, indicating the importance of this signaling network. To evaluate the functional role of few of these proteins, we used pharmacological modulators and analyzed their effect on cell migration and cell death in breast cancer cells. Hence, we report that inhibition of EPAC1 activity using pharmacological modulators leads to inhibition of cell migration and induces cell death. Additionally, we also observed that the inhibition of EPAC1 resulted in disruption of its association with the microtubule cytoskeleton and delocalization of AKAP9 from the centrosome as analyzed by in vitro imaging. Finally, this study suggests for the first time the mechanistic insights of mode of action of a primary cAMP-dependent sensor, Exchange protein activated by cAMP 1 (EPAC1), via its interaction with A-kinase anchoring protein 9 (AKAP9). This study provides a new cell signaling cAMP-EPAC1-AKAP9 direction to the development of additional biotherapeutics for breast cancer.

EPAC1 overexpression is a prognostic marker and its inhibition shows promising therapeutic potential for gastric cancer

cAMP signaling controls a variety of cellular functions. In addition to the well-known signal transducer cAMP-dependent protein kinase, a more recently discovered transducer is the exchange protein directly activated by cAMP (EPAC). EPAC responses are mediated by small G proteins, which regulate biologic functions such as cell adhesion, migration and proliferation. Recently, the clinical importance of EPAC1 has received increased attention. This study investigated the correlations between the expression of EPAC1 and various clinicopathologic parameters as well as the survival of the patients with gastric cancer (GC). The patient cohort in this study consisted of 141 cases of GC that presented from 1999 through 2011; documented clinicopathologic parameters and clinical outcomes were available for all cases. Immunoblotting, immunohistochemistry and quantitative real-time PCR were used to examine EPAC1 expression in gastric cells and tissues. siRNA technology was used to study the effect of EPAC1 knockdown on cell proliferation and invasion. An increase in EPAC1 expression was found in GC cells and tissues. The overexpression of EPAC1 was associated with the depth of invasion (P=0.0021), stage (P=0.0429), and vascular invasion (P=0.0049) and was correlated with poor disease-free survival (P=0.0029) and overall survival (P=0.0024). A univariate Cox regression analysis showed that the overexpression of EPAC1 was a prognostic marker for GC (P=0.038). Furthermore, cell studies indicated that the knockdown of EPAC1 in GC cells suppressed cell proliferation and invasion. The overexpression of EPAC1 can be used as a marker to predict the outcome of patients with GC, and EPAC1 represents a potential therapeutic modality for treating GC.

The cyclic AMP phosphodiesterase 4D5 (PDE4D5)/receptor for activated C-kinase 1 (RACK1) signalling complex as a sensor of the extracellular nano-environment

The cyclic AMP and protein kinase C (PKC) signalling pathways regulate a wide range of cellular processes that require tight control, including cell proliferation and differentiation, metabolism and inflammation. The identification of a protein complex formed by receptor for activated C kinase 1 (RACK1), a scaffold protein for protein kinase C (PKC), and the cyclic AMP-specific phosphodiesterase, PDE4D5, demonstrates a potential mechanism for crosstalk between these two signalling routes. Indeed, RACK1-bound PDE4D5 is activated by PKCα, providing a route through which the PKC pathway can control cellular cyclic AMP levels. Although RACK1 does not appear to affect the intracellular localisation of PDE4D5, it does afford structural stability, providing protection against denaturation, and increases the susceptibility of PDE4D5 to inhibition by cyclic AMP-elevating pharmaceuticals, such as rolipram. In addition, RACK1 can recruit PDE4D5 and PKC to intracellular protein complexes that control diverse cellular functions, including activated G protein-coupled receptors (GPCRs) and integrins clustered at focal adhesions. Through its ability to regulate local cyclic AMP levels in the vicinity of these multimeric receptor complexes, the RACK1/PDE4D5 signalling unit therefore has the potential to modify the quality of incoming signals from diverse extracellular cues, ranging from neurotransmitters and hormones to nanometric topology. Indeed, PDE4D5 and RACK1 have been found to form a tertiary complex with integrin-activated focal adhesion kinase (FAK), which localises to cellular focal adhesion sites. This supports PDE4D5 and RACK1 as potential regulators of cell adhesion, spreading and migration through the non-classical exchange protein activated by cyclic AMP (EPAC1)/Rap1 signalling route.

Epac1 interacts with importin β1 and controls neurite outgrowth independently of cAMP and Rap1

Exchange protein directly activated by cAMP-1 (Epac1) is a cAMP sensor that regulates multiple cellular functions including cellular migration, proliferation and differentiation. Classically, Epac1 is thought to exert its effects through binding of cAMP leading to a conformational change in Epac1 and its accumulation at the plasma membrane (PM) where it activates Rap1. In search for regulators of Epac1 activity, we show here that importin β1 (impβ1) is an Epac1 binding partner that prevents PM accumulation of Epac1. We demonstrate that in the absence of impβ1, endogenous as well as overexpressed Epac1 accumulate at the PM. Moreover, agonist-induced PM translocation of Epac1 leads to dissociation of Epac1 from impβ1. Localization of Epac1 at the PM in the absence of impβ1, requires residue R82 in its DEP domain. Notably, the PM accumulation of Epac1 in the absence of impβ1 does not require binding of cAMP to Epac1 and does not result in Rap1 activation. Functionally, PM accumulation of Epac1, an Epac1 mutant deficient in cAMP binding, or an Epac1 mutant tethered to the PM, is sufficient to inhibit neurite outgrowth. In conclusion, we uncover a cAMP-independent function of Epac1 at the PM and demonstrate that impβ1 controls subcellular localization of Epac1.

Activation of P2X7 and P2Y11 purinergic receptors inhibits migration and normalizes tumor-derived endothelial cells via cAMP signaling

Purinergic signaling is involved in inflammation and cancer. Extracellular ATP accumulates in tumor interstitium, reaching hundreds micromolar concentrations, but its functional role on tumor vasculature and endothelium is unknown. Here we show that high ATP doses (>20 μM) strongly inhibit migration of endothelial cells from human breast carcinoma (BTEC), but not of normal human microvascular EC. Lower doses (1–10 mm result ineffective. The anti-migratory activity is associated with cytoskeleton remodeling and is significantly prevented by hypoxia. Pharmacological and molecular evidences suggest a major role for P2X7R and P2Y11R in ATP-mediated inhibition of TEC migration: selective activation of these purinergic receptors by BzATP mimics the anti-migratory effect of ATP, which is in turn impaired by their pharmacological or molecular silencing. Downstream pathway includes calcium-dependent Adenilyl Cyclase 10 (AC10) recruitment, cAMP release and EPAC-1 activation. Notably, high ATP enhances TEC-mediated attraction of human pericytes, leading to a decrease of endothelial permeability, a hallmark of vessel normalization. Finally, we provide the first evidence of in vivo P2X7R expression in blood vessels of murine and human breast carcinoma. In conclusion, we have identified a purinergic pathway selectively acting as an antiangiogenic and normalizing signal for human tumor-derived vascular endothelium.

POPDC proteins as potential novel therapeutic targets in cancer

Popeye domain-containing (POPDC) proteins are a novel class of cAMP-binding molecules that affect cancer cell behaviour and correlate with poor clinical outcomes. They are encoded by the POPDC genes POPDC1, POPDC2, and POPDC3. The deletion of POPDC genes and the suppression of POPDC proteins correlate with enhanced cancer cell proliferation, migration, invasion, metastasis, drug resistance, and poor patient survival in various human cancers. Overexpression of POPDC proteins inhibits cancer cell migration and invasion in vitro. POPDC proteins present promising anticancer therapeutic targets and here we review their roles in promoting cancer progression and highlight their potential as anticancer therapeutic targets.

Epac1 knockdown inhibits the proliferation of ovarian cancer cells by inactivating AKT/Cyclin D1/CDK4 pathway in vitro and in vivo

Ovarian cancer is the leading cause of death among gynecological malignancies, and high grade serous ovarian carcinoma is the most common and most aggressive subtype. Recently, it was demonstrated that cAMP mediates protein kinase A-independent effects through Epac (exchange protein directly activated by cAMP) proteins. Epac proteins, including Epac1 and Epac2, are implicated in several diverse cellular responses, such as insulin secretion, exocytosis, cellular calcium handling and formation of cell-cell junctions. Several reports document that Epac1 could play vital roles in promoting proliferation, invasion and migration of some cancer cells. However, the expression levels and roles of Epac1 in ovarian cancer have not been investigated. In the present study, we detected the expression levels of Epac1 mRNA and protein in three kinds of ovarian cancer cells SKOV3, OVCAR3 and CAOV3. Furthermore, the effect of Epac1 knockdown on the proliferation and apoptosis of SKOV3 and OVCAR3 cells was evaluated in vitro and in vivo. The results showed that there was higher expression of Epac1 mRNA and protein in SKOV3 and OVCAR3 cells. Epac1 knockdown inhibited the proliferation of SKOV3 and OVCAR3 cells in vitro and in vivo. Decreased proliferation may be due to downregulation of Epac1-induced G1 phase arrest by inactivating the AKT/Cyclin D1/CDK4 pathway, but not to alterations in the MAPK pathway or to apoptosis. Taken together, our data provide new insight into the essential role of Epac1 in regulating growth of ovarian cancer cells and suggest that Epac1 might represent an attractive therapeutic target for treatment of ovarian cancer.

The pleiotropic role of exchange protein directly activated by cAMP 1 (EPAC1) in cancer: implications for therapeutic intervention

The pleiotropic second messenger adenosine 3',5'-cyclic monophosphate (cAMP) regulates a myriad of biological processes under both physiological and pathophysiological conditions. Exchange protein directly activated by cAMP 1 (EPAC1) mediates the intracellular functions of cAMP by acting as a guanine nucleotide exchange factor for the Ras-like Rap small GTPases. Recent studies suggest that EPAC1 plays important roles in immunomodulation, cancer cell migration/metastasis, and metabolism. These results, coupled with the successful development of EPAC-specific small molecule inhibitors, identify EPAC1 as a promising therapeutic target for cancer treatments.

High RhoA expression at the tumor front in clinically localized prostate cancer and association with poor tumor differentiation

Ras homolog gene family, member A (RhoA) has been reported as essential to the invasion process and aggressiveness of numerous cancers. However, there are only sparse data on the expression and activity of RhoA in clinically localised prostate cancer. In numerous cancers, tumour cells at the invasive front demonstrate more aggressive behaviour in comparison with the cells in the central regions. In the present study, the expression and activity of RhoA was evaluated in 34 paraffin-embedded and 20 frozen prostate tissue specimens obtained from 45 patients treated with radical prostatectomy for clinically localised cancer. The expression patterns of RhoA were assessed by immunohistochemical staining and western blotting. Additional comparisons were performed between the tumour centre, tumour front and distant peritumoural tissue. RhoA activity was assessed by G-LISA. Associations between RhoA expression and the clinical features and outcome of the patients were also analysed. The present study found an increasing gradient of expression from the centre to the periphery of index tumour foci. RhoA expression was significantly increased at the tumour front compared to the tumour centre, which was determined using immunohistochemistry (P=0.001). Increased RhoA expression was associated with poor tumour differentiation in the tumour front (P=0.044) and tumour centre (P=0.039). Subsequent to a median follow-up period of 52 months, the rate of prostate-specific antigen (PSA) relapse was increased in patients with higher RhoA expression at the tumour front when compared with patients with lower RhoA expression (62.5 vs. 35.0%), although the difference was not significant (P=0.09). There was no association between RhoA expression and the PSA level or pathological stage in the present study. In conclusion, RhoA expression was increased at the tumour front and was associated with poor tumour differentiation in the tumour front and tumour centre, indicating the potential role of RhoA in prostate cancer. RhoA expression may also act as a prognostic factor in prostate cancer. The present data provide a foundation for novel therapeutic approaches by targeting RhoA in prostate cancer.

Beta-Adrenoceptor Activation Reduces Both Dermal Microvascular Endothelial Cell Migration via a cAMP-Dependent Mechanism and Wound Angiogenesis

Angiogenesis is an essential process during tissue regeneration; however, the amount of angiogenesis directly correlates with the level of wound scarring. Angiogenesis is lower in scar-free foetal wounds while angiogenesis is raised and abnormal in pathophysiological scarring such as hypertrophic scars and keloids. Delineating the mechanisms that modulate angiogenesis and could reduce scarring would be clinically useful. Beta-adrenoceptors (β-AR) are G protein-coupled receptors (GPCRs) expressed on all skin cell-types. They play a role in wound repair but their specific role in angiogenesis is unknown. In this study, a range of in vitro assays (single cell migration, scratch wound healing, ELISAs for angiogenic growth factors and tubule formation) were performed with human dermal microvascular endothelial cells (HDMEC) to investigate and dissect mechanisms underpinning β-AR-mediated modulation of angiogenesis in chick chorioallantoic membranes (CAM) and murine excisional skin wounds. β-AR activation reduced HDMEC migration via cyclic adenosine monophosphate (cAMP)-dependent and protein kinase A (PKA)-independent mechanisms as demonstrated through use of an EPAC agonist that auto-inhibited the cAMP-mediated β-AR transduced reduction in HDMEC motility; a PKA inhibitor was, conversely, ineffective. ELISA studies demonstrated that β-AR activation reduced pro-angiogenic growth factor secretion from HDMECs (fibroblast growth factor 2) and keratinocytes (vascular endothelial growth factor A) revealing possible β-AR-mediated autocrine and paracrine anti-angiogenic mechanisms. In more complex environments, β-AR activation delayed HDMEC tubule formation and decreased angiogenesis both in the CAM assay and in murine excisional skin wounds in vivo. β-AR activation reduced HDMEC function in vitro and angiogenesis in vivo; therefore, β-AR agonists could be promising anti-angiogenic modulators in skin. J. Cell. Physiol. 230: 356–365, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Epac1 Deficiency Attenuated Vascular Smooth Muscle Cell Migration and Neointimal Formation

OBJECTIVE

Vascular smooth muscle cell (SMC) migration causes neointima, which is related to vascular remodeling after mechanical injury and atherosclerosis development. We previously reported that an exchange protein activated by cAMP (Epac) 1 was upregulated in mouse arterial neointima and promoted SMC migration. In this study, we examined the molecular mechanisms of Epac1-induced SMC migration and the effect of Epac1 deficiency on vascular remodeling in vivo.

APPROACH AND RESULTS

Platelet-derived growth factor-BB promoted a 2-fold increase in SMC migration in a primary culture of aortic SMCs obtained from Epac1(+/+) mice (Epac1(+/+)-ASMCs), whereas there was only a 1.2-fold increase in Epac1(-/-)-ASMCs. The degree of platelet-derived growth factor-BB-induced increase in intracellular Ca(2+) was smaller in Fura2-labeled Epac1(-/-)-ASMCs than in Epac1(+/+)-ASMCs. In Epac1(+/+)-ASMCs, an Epac-selective cAMP analog or platelet-derived growth factor-BB increased lamellipodia accompanied by cofilin dephosphorylation, which is induced by Ca(2+) signaling, whereas these effects were rarely observed in Epac1(-/-)-ASMCs. Furthermore, 4 weeks after femoral artery injury, prominent neointima were formed in Epac1(+/+) mice, whereas neointima formation was significantly attenuated in Epac1(-/-) mice in which dephosphorylation of cofilin was inhibited. The chimeric mice generated by bone marrow cell transplantation from Epac1(+/+) into Epac1(-/-) mice and vice versa demonstrated that the genetic background of vascular tissues, including SMCs rather than of bone marrow-derived cells affected Epac1-mediated neointima formation.

CONCLUSIONS

These data suggest that Epac1 deficiency attenuates neointima formation through, at least in part, inhibition of SMC migration, in which a decrease in Ca(2+) influx and a suppression of cofilin-mediated lamellipodia formation occur.

β-Adrenergic Receptor Signaling in Prostate Cancer

Enhanced sympathetic signaling, often associated with obesity and chronic stress, is increasingly acknowledged as a contributor to cancer aggressiveness. In prostate cancer, intact sympathetic nerves are critical for tumor formation, and sympathectomy induces apoptosis and blocks tumor growth. Perineural invasion, involving enrichment of intra-prostatic nerves, is frequently observed in prostate cancer and is associated with poor prognosis. β₂-adrenergic receptor (ADRB2), the most abundant receptor for sympathetic signals in prostate luminal cells, has been shown to regulate trans-differentiation of cancer cells to neuroendocrine-like cells and to affect apoptosis, angiogenesis, epithelial–mesenchymal transition, migration, and metastasis. Epidemiologic studies have shown that use of β-blockers, inhibiting β-adrenergic receptor activity, is associated with reduced prostate cancer-specific mortality. In this review, we aim to present an overview on how β-adrenergic receptor and its downstream signaling cascade influence the development of aggressive prostate cancer, primarily through regulating neuroendocrine differentiation.

Pharmacological inhibition and genetic knockdown of exchange protein directly activated by cAMP 1 reduce pancreatic cancer metastasis in vivo

cAMP plays a critical role in regulating migration of various cancers. This role is context dependent and is determined by which of the two main cAMP sensors is at play: cAMP-dependent protein kinase or exchange protein directly activated by cAMP (EPAC). Recently, we have shown that the cAMP sensor protein EPAC1 promotes invasion/migration of pancreatic ductal adenocarcinoma (PDA) in vitro. In this study, we investigated the role of EPAC1 in invasion and metastasis of PDA in vivo, and evaluated the therapeutic potential of EPAC inhibitors as antimetastasis agents for this neoplasm. We employed an orthotopic metastatic mouse model in which the PDA cells MIA PaCa-2 were injected into the pancreas of athymic nude mice, and their local and distant spread was monitored by in vivo imaging and histologic evaluation of the number of metastatic foci in the liver. Either genetic suppression of EPAC1 or its pharmacologic inhibition with 3-(5-tert-butyl-isoxazol-3-yl)-2-[(3-chloro-phenyl)-hydrazono]-3-oxo-propionitrile, an EPAC-specific antagonist recently identified in our laboratory, decreased invasion and metastasis of the PDA cells. Mechanistically, EPAC1 promotes activation and trafficking of integrin β1, which plays an essential role in PDA migration and metastasis. Our data show that EPAC1 facilitates metastasis of PDA cells and EPAC1 might be a potential novel therapeutic target for developing antimetastasis agents for PDA.

Epac1 increases migration of endothelial cells and melanoma cells via FGF2-mediated paracrine signaling

Fibroblast growth factor (FGF2) regulates endothelial and melanoma cell migration. The binding of FGF2 to its receptor requires N-sulfated heparan sulfate (HS) glycosamine. We have previously reported that Epac1, an exchange protein activated by cAMP, increases N-sulfation of HS in melanoma. Therefore, we examined whether Epac1 regulates FGF2-mediated cell–cell communication. Conditioned medium (CM) of melanoma cells with abundant expression of Epac1 increased migration of human umbilical endothelial cells (HUVEC) and melanoma cells with poor expression of Epac1. CM-induced increase in migration was inhibited by antagonizing FGF2, by the removal of HS and by the knockdown of Epac1. In addition, knockdown of Epac1 suppressed the binding of FGF2 to FGF receptor in HUVEC, and in vivo angiogenesis in melanoma. Furthermore, knockdown of Epac1 reduced N-sulfation of HS chains attached to perlecan, a major secreted type of HS proteoglycan that mediates the binding of FGF2 to FGF receptor. These data suggested that Epac1 in melanoma cells regulates melanoma progression via the HS–FGF2-mediated cell–cell communication.

Dosage-dependent regulation of cell proliferation and adhesion through dual β2-adrenergic receptor/cAMP signals

The role of β-adrenergic receptors (β-ARs) remains controversial in normal and tumor breast. Herein we explore the cAMP signaling involved in β-AR-dependent control of proliferation and adhesion of nontumor human breast cell line MCF-10A. Low concentrations of a β-agonist, isoproterenol (ISO), promote cell adhesion (87.5% cells remaining adherent to the plastic dishes following specific detachment vs. 35.0% in control, P<0.001), while increasing concentrations further engages an additional 36% inhibition of Erk1/2 phosphorylation (p-Erk1/2)-dependent cell proliferation (P<0.01). Isoproterenol dose response on cell adhesion was fitted to a 2-site curve (EC50(1): 16.5±11.5 fM, EC50(2): 4.08±3.09 nM), while ISO significantly inhibited p-Erk1/2 according to a 1-site model (EC50: 0.25±0.13 nM). Using β-AR-selective agonist/antagonists and cAMP analogs/inhibitors, we identified a dosage-dependent signaling in which low ISO concentrations target a β2-AR population localized in raft microdomains and stimulate a Gs/cAMP/Epac/adhesion-signaling module, while higher concentrations engage a concomitant activation of another β2-AR population outside rafts and inhibit the proliferation by a Gs/cAMP/PKA-dependent signaling module. Our data provide a new molecular basis for the dose-dependent switch of β-AR signaling. This study also sheds light on a new cAMP pathway core mechanism with a single receptor triggering dual cAMP signaling controlled by PKA or Epac but with different cellular outputs.

cAMP inhibits migration, ruffling and paxillin accumulation in focal adhesions of pancreatic ductal adenocarcinoma cells: effects of PKA and EPAC

We demonstrated that increasing intracellular cAMP concentrations result in the inhibition of migration of PANC-1 and other pancreatic ductal adenocarcinoma (PDAC) cell types. The rise of cAMP was accompanied by rapid and reversible cessation of ruffling, by inhibition of focal adhesion turnover and by prominent loss of paxillin from focal adhesions. All these phenomena develop rapidly suggesting that cAMP effectors have a direct influence on the cellular migratory apparatus. The role of two primary cAMP effectors, exchange protein activated by cAMP (EPAC) and protein kinase A (PKA), in cAMP-mediated inhibition of PDAC cell migration and migration-associated processes was investigated. Experiments with selective activators of EPAC and PKA demonstrated that the inhibitory effect of cAMP on migration, ruffling, focal adhesion dynamics and paxillin localisation is mediated by PKA, whilst EPAC potentiates migration.

Quantitative global phosphoproteomics of human umbilical vein endothelial cells after activation of the Rap signaling pathway

The small GTPase Rap1 is required for proper cell-cell junction formation and also plays a key role in mediating cAMP-induced tightening of adherens junctions and subsequent increased barrier function of endothelial cells. To further study how Rap1 controls barrier function, we performed quantitative global phosphoproteomics in human umbilical vein endothelial cells (HUVECs) prior to and after Rap1 activation by the Epac-selective cAMP analog 8-pCPT-2'-O-Me-cAMP-AM (007-AM). Tryptic digests were labeled using stable isotope dimethyl labeling, enriched with phosphopeptides by strong cation exchange (SCX), followed by titanium(iv) immobilized metal affinity chromatography (Ti(4+)-IMAC) and analyzed by high resolution mass spectrometry. We identified 19 859 unique phosphopeptides containing 17 278 unique phosphosites on 4594 phosphoproteins, providing the largest HUVEC phosphoproteome to date. Of all identified phosphosites, 220 (∼1%) were more than 1.5-fold up- or downregulated upon Rap activation, in two independent experiments. Compatible with the function of Rap1, these alterations were found predominantly in proteins regulating the actin cytoskeleton, cell-cell junctions and cell adhesion.

Protein kinase A-dependent phosphorylation of Rap1 regulates its membrane localization and cell migration

The small G protein Rap1 can mediate "inside-out signaling" by recruiting effectors to the plasma membrane that signal to pathways involved in cell adhesion and cell migration. This action relies on the membrane association of Rap1, which is dictated by post-translational prenylation as well as by a stretch of basic residues within its carboxyl terminus. One feature of this stretch of acidic residues is that it lies adjacent to a functional phosphorylation site for the cAMP-dependent protein kinase PKA. This phosphorylation has two effects on Rap1 action. One, it decreases the level of Rap1 activity as measured by GTP loading and the coupling of Rap1 to RapL, a Rap1 effector that couples Rap1 GTP loading to integrin activation. Two, it destabilizes the membrane localization of Rap1, promoting its translocation into the cytoplasm. These two actions, decreased GTP loading and decreased membrane localization, are related, as the translocation of Rap1-GTP into the cytoplasm is associated with its increased GTP hydrolysis and inactivation. The consequences of this phosphorylation in Rap1-dependent cell adhesion and cell migration were also examined. Active Rap1 mutants that lack this phosphorylation site had a minimal effect on cell adhesion but strongly reduced cell migration, when compared with an active Rap1 mutant that retained the phosphorylation site. This suggests that optimal cell migration is associated with cycles of Rap1 activation, membrane egress, and inactivation, and requires the regulated phosphorylation of Rap1 by PKA.

The cAMP effector EPAC activates Elk1 transcription factor in prostate smooth muscle, and is a minor regulator of α1-adrenergic contraction

Background

Prostate smooth muscle tone is regulated by α1-adrenoceptor-induced contraction and cAMP-mediated relaxation. EPAC is an effector of cAMP, being involved in smooth muscle relaxation and cell cycle control outside the lower urinary tract. Here, we investigated the expression and function of EPAC in human prostate tissues from patients undergoing radical prostatectomy.

Results

mRNA and protein expression of EPAC was detected in all prostate tissues by RT-PCR and Western blot analysis. Immunoreactivity was observed in stromal cells, and colocalized with immunofluorescence for α-smooth muscle actin and calponin. Under normal conditions, noradrenaline- or phenylephrine-induced contraction of prostate strips in the organ bath was not affected by the EPAC activator pCPT (SP-8-pCPT-2^′-O-Me-cAMPS.NA) (30 μM). However, when the cyclooxygenase inhibitor indomethacin (50 μM) was added, EPAC activators pCPT and OME (8-CPT-2^′-O-Me-cAMP.Na) (30 μM) significantly reduced contractions by low concentrations of phenylephrine. These effects were not observed on noradrenaline-induced contraction. OME and pCPT caused phosphorylation of the transcription factor Elk1 in prostate tissues. Elk1 activation was confirmed by EMSA (electrophoretic mobility shift assay), where OME and pCPT incresed Elk1 binding to a specific DNA probe.

Conclusions

EPAC activation may reduce α1-adrenergic prostate contraction in the human prostate, although this effect is masked by cyclooxygenases and β-adrenoceptors. A main EPAC function in the human prostate may be the regulation of the transcription factor Elk1.

A novel interplay between Rap1 and PKA regulates induction of angiogenesis in prostate cancer

Angiogenesis inhibition is an important therapeutic strategy for advanced stage prostate cancer. Previous work from our laboratory showed that sustained stimulation of Rap1 by 8-pCPT-2'-O-Me-cAMP (8CPT) via activation of Epac, a Rap1 GEF, or by expression of a constitutively active Rap1 mutant (cRap1) suppresses endothelial cell chemotaxis and subsequent angiogenesis. When we tested this model in the context of a prostate tumor xenograft, we found that 8CPT had no significant effect on prostate tumor growth alone. However, in cells harboring cRap1, 8CPT dramatically inhibited not only prostate tumor growth but also VEGF expression and angiogenesis within the tumor microenvironment. Subsequent analysis of the mechanism revealed that, in prostate tumor epithelial cells, 8CPT acted via stimulation of PKA rather than Epac/Rap1. PKA antagonizes Rap1 and hypoxic induction of 1α protein expression, VEGF production and, ultimately, angiogenesis. Together these findings provide evidence for a novel interplay between Rap1, Epac, and PKA that regulates tumor-stromal induction of angiogenesis.

The putative tumor suppressor VILIP-1 counteracts epidermal growth factor-induced epidermal-mesenchymal transition in squamous carcinoma cells

Epithelial-mesenchymal transition (EMT) is a crucial step for the acquisition of invasive properties of carcinoma cells during tumor progression. Epidermal growth factor (EGF)-treatment of squamous cell carcinoma (SCC) cells provokes changes in the expression of lineage markers, morphological changes, and a higher invasive and metastatic potential. Here we show that chronic stimulation with EGF induces EMT in skin-derived SCC cell lines along with the down-regulation of the epithelial marker E-cadherin, and of the putative tumor suppressor VILIP-1 (visinin-like protein 1). In esophageal squamous cell carcinoma and non-small cell lung carcinoma the loss of VILIP-1 correlates with clinicopathological features related to enhanced invasiveness. VILIP-1 has previously been shown to suppress tumor cell invasion via enhancing cAMP-signaling in a murine SCC model. In mouse skin SCC cell lines the VILIP-1-negative tumor cells have low cAMP levels, whereas VILIP-1-positive SCCs possess high cAMP levels, but low invasive properties. We show that in VILIP-1-negative SCCs, Snail1, a transcriptional repressor involved in EMT, is up-regulated. Snail1 expression is reduced by ectopic VILIP-1-expression in VILIP-1-negative SCC cells, and application of the general adenylyl cyclase inhibitor 2',3'-dideoxyadenosine attenuated this effect. Conversely, EGF-stimulation of VILIP-1-positive SCC cells leads to the down-regulation of VILIP-1 and the induction of Snail1 expression. The induction of Snail is inhibited by elevated cAMP levels. The role of cAMP in EMT was further highlighted by its suppressive effect on the EGF-induced enhancement of migration in VILIP-1-positive SCC cells. These findings indicate that VILIP-1 is involved in EMT of SCC by regulating the transcription factor Snail1 in a cAMP-dependent manner.

Gβγ subunits inhibit Epac-induced melanoma cell migration

Background

Recently we reported that activation of Epac1, an exchange protein activated by cAMP, increases melanoma cell migration via Ca ²⁺ release from the endoplasmic reticulum (ER). G-protein βγ subunits (Gβγ) are known to act as an independent signaling molecule upon activation of G-protein coupled receptor. However, the role of Gβγ in cell migration and Ca ²⁺ signaling in melanoma has not been well studied. Here we report that there is crosstalk of Ca ²⁺ signaling between Gβγ and Epac in melanoma, which plays a role in regulation of cell migration.

Methods

SK-Mel-2 cells, a human metastatic melanoma cell line, were mainly used in this study. Intracellular Ca ²⁺ was measured with Fluo-4AM fluorescent dyes. Cell migration was examined using the Boyden chambers.

Results

The effect of Gβγ on Epac-induced cell migration was first examined. Epac-induced cell migration was inhibited by mSIRK, a Gβγ -activating peptide, but not its inactive analog, L9A, in SK-Mel-2 cells. Guanosine 5', α-β-methylene triphosphate (Gp(CH2)pp), a constitutively active GTP analogue that activates Gβγ, also inhibited Epac-induced cell migration. In addition, co-overexpression of β1 and γ2, which is the major combination of Gβγ, inhibited Epac1-induced cell migration. By contrast, when the C-terminus of β adrenergic receptor kinase (βARK-CT), an endogenous inhibitor for Gβγ, was overexpressed, mSIRK's inhibitory effect on Epac-induced cell migration was negated, suggesting the specificity of mSIRK for Gβγ. We next examined the effect of mSIRK on Epac-induced Ca ²⁺ response. When cells were pretreated with mSIRK, but not with L9A, 8-(4-Methoxyphenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (8-pMeOPT), an Epac-specific agonist, failed to increase Ca ²⁺ signal. Co-overexpression of β1 and γ2 subunits inhibited 8-pMeOPT-induced Ca ²⁺ elevation. Inhibition of Gβγ with βARK-CT or guanosine 5'-O-(2-thiodiphosphate) (GDPβS), a GDP analogue that inactivates Gβγ, restored 8-pMeOPT-induced Ca ²⁺ elevation even in the presence of mSIRK. These data suggested that Gβγ inhibits Epac-induced Ca ²⁺ elevation. Subsequently, the mechanism by which Gβγ inhibits Epac-induced Ca ²⁺ elevation was explored. mSIRK activates Ca ²⁺ influx from the extracellular space. In addition, W-5, an inhibitor of calmodulin, abolished mSIRK's inhibitory effects on Epac-induced Ca ²⁺ elevation, and cell migration. These data suggest that, the mSIRK-induced Ca ²⁺ from the extracellular space inhibits the Epac-induced Ca ²⁺ release from the ER, resulting suppression of cell migration.

Conclusion

We found the cross talk of Ca ²⁺ signaling between Gβγ and Epac, which plays a major role in melanoma cell migration.

Hypertension is positively associated with prostate cancer development in the TRAP transgenic rat model

Epidemiological data on the relationship between hypertension and prostate cancer development are conflicting. To cast light on this question, we performed animal experiments using hybrid rats generated by crossing the spontaneously hypertensive rat (SHR) or its normotensive control Wistar Kyoto (WKY) rat with a transgenic rat for adenocarcinoma of prostate (TRAP) that features development of adenocarcinoma at high incidence by 15 weeks of age. The number of adenocarcinomatous foci in the lateral prostate of hypertensive (TRAP × SHR)F1 rats was demonstrated to be significantly increased compared with those of normotensive (TRAP × WKY)F1 rats. In the ventral prostate, increase of carcinoma foci was also observed but did not reach significance. The number of cancer foci showing microinvasion in (TRAP × SHR)F1 rats was higher than that of (TRAP × WKY)F1 rats, but again without significance, while treatment with prazosin, an anti-hypertensive agent, tended to decrease microinvasive carcinoma foci in both the ventral and lateral prostate. In conclusion, the present study provided additional evidence that high blood pressure is associated with prostate cancer risk.

The small molecule PKA-specific cyclic AMP analogue as an inducer of osteoblast-like cells differentiation and mineralization

Osteoblastic differentiation is an important landmark for bone formation, bone repair and regeneration; however, it is a very complex process controlled by different signalling mechanisms. Several groups have reported that the cyclic adenosine monophosphate (cAMP) signalling system is responsible for regulating osteoblast cell differentiation. Nonetheless, to date, the principle role of the cAMP molecules related to this process remains controversial. Moreover, the underlying cAMP-dependent signalling cascade governing the osteoblastic differentiation has not been clarified. In this study we investigated the roles of the cAMP-dependent protein kinase A (PKA) signalling in proliferation, differentiation and mineralization of osteoblast-like MC3T3-E1 cells, using the PKA-specific small molecule cAMP analogue, 6-Bnz-cAMP, at 100 µM. Alkaline phosphatase (ALP) activity, runt transcription factor 2 (Runx2), osteopontin (OPN) and osteocalcin (OCN) protein expressions were used as osteoblast-specific markers to demonstrate osteoblastic differentiation. Further, calcium measurement of the extracellular matrix was employed as the hallmark of matrix mineralization or calcification. We report here that activation of PKA by the small molecule 6-Bnz-cAMP induces osteoblastic differentiation and matrix mineralization of osteoblast-like MC3T3-E1 cells. Moreover, 6-Bnz-cAMP does not induce cytotoxicity to the cells, as revealed by our cell proliferation studies. Therefore, based on these findings, we propose that the PKA-specific small molecule 6-Bnz-cAMP may serve as a novel bone-inducing growth factor for repairing and regenerating bone tissues during bone-regenerative engineering.

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.

Roles of cAMP and cAMP-dependent protein kinase in the progression of prostate cancer: cross-talk with the androgen receptor

Prostate carcinomas are among the most frequently diagnosed and death causing cancers affecting males in the developed world. It has become clear that the molecular mechanisms that drive the differentiation of normal prostate cells towards neoplasia involve multiple signal transduction cascades that often overlap and interact. A critical mediator of cellular proliferation and differentiation in various cells (and cancers) is the cAMP-dependent protein kinase, also known as protein kinase A (PKA), and its activating secondary messenger, cAMP. PKA and cAMP have been shown to play critical roles in prostate carcinogenesis and are the subject of this review. In particular we will focus on the cross-talk between PKA/cAMP signaling and that of the androgen receptor.

Exchange protein directly activated by cyclic AMP increases melanoma cell migration by a Ca2+-dependent mechanism

Melanoma has a poor prognosis due to its strong metastatic ability. Although Ca(2+) plays a major role in cell migration, little is known about the role of Ca(2+) in melanoma cell migration. We recently found that the exchange protein directly activated by cyclic AMP (Epac) increases melanoma cell migration via a heparan sulfate-related mechanism. In addition to this mechanism, we also found that Epac regulates melanoma cell migration by a Ca(2+)-dependent mechanism. An Epac agonist increased Ca(2+) in several different melanoma cell lines but not in melanocytes. Ablation of Epac1 with short hairpin RNA inhibited the Epac agonist-induced Ca(2+) elevation, suggesting the critical role of Epac1 in Ca(2+) homeostasis in melanoma cells. Epac-induced Ca(2+) elevation was negated by the inhibition of phospholipase C (PLC) and inositol triphosphate (IP(3)) receptor. Furthermore, Epac-induced cell migration was reduced by the inhibition of PLC or IP(3) receptor. These data suggest that Epac activates Ca(2+) release from the endoplasmic reticulum via the PLC/IP(3) receptor pathway, and this Ca(2+) elevation is involved in Epac-induced cell migration. Actin assembly was increased by Epac-induced Ca(2+), suggesting the involvement of actin in Epac-induced cell migration. In human melanoma specimens, mRNA expression of Epac1 was higher in metastatic melanoma than in primary melanoma, suggesting a role for Epac1 in melanoma metastasis. In conclusion, our findings reveal that Epac is a potential target for the suppression of melanoma cell migration, and, thus, the development of metastasis.

Functional roles of protein kinase A (PKA) and exchange protein directly activated by 3',5'-cyclic adenosine 5'-monophosphate (cAMP) 2 (EPAC2) in cAMP-mediated actions in adrenocortical cells

In the adrenal cortex, the biosynthesis of steroid hormones is controlled by the pituitary-derived hormone ACTH. The functions of ACTH are principally relayed by activating cAMP-dependent signaling pathways leading to the induction of genes encoding enzymes involved in the conversion of cholesterol to steroid hormones. Previously, protein kinase A (PKA) was thought to be the only direct effector of cAMP. However, the discovery of the cAMP sensors, exchange proteins directly activated by cAMP (EPAC1 and 2), has led to a reevaluation of this assumption. In the present study, we demonstrate the occurrence of the EPAC2 splicing variant EPAC2B in adrenocortical cancer cells. Immunocytochemistry demonstrated that EPAC2B is localized predominantly in the nucleus. EPAC2B is functional because it activates Rap1 in these cells. Using the cAMP analogs 8-p-chlorophenylthio-2'-O-methyl-cAMP and N6-benzoyl-cAMP, which specifically activate EPAC1/2 and PKA, respectively, we evaluated the contribution of these factors in steroid hormone production, cell morphology, actin reorganization, and migration. We demonstrate that the expression of cAMP-inducible factors involved in steroidogenesis (steroidogenic acute regulatory protein, cytochrome P450 11A1 and 17, and nerve growth factor-induced clone B) and the cAMP-induced biosynthesis of steroid hormones (cortisol and aldosterone) are mediated by PKA and not by EPAC2B. In contrast, both PKA- and EPAC-specific cAMP analogs induced cell rounding, loss of stress fibers, and blocked migration. Taken together, the presented data confirm PKA as the central cAMP mediator in steroid hormone production and reveal the involvement of EPAC2B in cAMP-induced effects on cytoskeleton integrity and cell migration.