NF2 signaling pathway plays a pro-apoptotic role in ?-adrenergic receptor stimulated cardiac myocyte apoptosis.
ABSTRACT: Treatment of adult rat ventricular myocytes (ARVMs) with ?-AR agonist (isoproterenol) for 15 min increased phosphorylation (serine-518) and sumoylation of NF2. Co-immunoprecipitation assay confirmed ?-AR-stimulated sumoylation of NF2. ?-AR stimulation enhanced nuclear translocation of phosphorylated and sumoylated NF2. Specific inhibition of ?1-AR and protein kinase A (PKA) decreased ?-AR-stimulated increase in NF2 post-translational modifications, while inhibition of ?2-AR had no effect. Activation of adenylyl cyclase using forskolin (FSK) mimicked the effects of ?-AR stimulation. ?-AR stimulation and expression of wild-type (WT)-NF2 using adenoviruses increased phosphorylation of mammalian sterile like kinase-1/2 (MST1/2) and yes activated protein (YAP), downstream targets of NF2. Knockdown of NF2 using siRNA in H9C2 cardiomyocytes decreased ?-AR-stimulated increase in NF2 and YAP phosphorylation. siRNA-mediated knockdown of NF2 decreased ?-AR-stimulated increase in apoptosis, while expression of WT-NF2 induced apoptosis in ARVMs. Expression of WT-NF2 stimulated the mitochondrial death pathway as evidenced by activation of c-Jun N-terminal Kinases (JNKs), and increase in cytosolic cytochrome c levels and Bax expression.?-AR stimulation affects post-translational modifications of NF2 via the involvement ?1-AR/PKA/cAMP pathway, and NF2 plays a pro-apoptotic role in ?-AR-stimulated myocyte apoptosis via the phosphorylation (inactivation) of YAP and involvement of mitochondrial death pathway.
Project description:Merlin/NF2 is a bona fide tumor suppressor whose mutations underlie inherited tumor syndrome neurofibromatosis type 2 (NF2), as well as various sporadic cancers including kidney cancer. Multiple Merlin/NF2 effector pathways including the Hippo-YAP/TAZ pathway have been identified. However, the molecular mechanisms underpinning the growth and survival of NF2-mutant tumors remain poorly understood. Using an inducible orthotopic kidney tumor model, we demonstrate that YAP/TAZ silencing is sufficient to induce regression of pre-established NF2-deficient tumors. Mechanistically, YAP/TAZ depletion diminishes glycolysis-dependent growth and increases mitochondrial respiration and reactive oxygen species (ROS) buildup, resulting in oxidative-stress-induced cell death when challenged by nutrient stress. Furthermore, we identify lysosome-mediated cAMP-PKA/EPAC-dependent activation of RAF-MEK-ERK signaling as a resistance mechanism to YAP/TAZ inhibition. Finally, unbiased analysis of TCGA primary kidney tumor transcriptomes confirms a positive correlation of a YAP/TAZ signature with glycolysis and inverse correlations with oxidative phosphorylation and lysosomal gene expression, supporting the clinical relevance of our findings.
Project description:RATIONALE:Phosphorylation of ?(2)-adrenergic receptor (?(2)AR) by a family of serine/threonine kinases known as G protein-coupled receptor kinase (GRK) and protein kinase A (PKA) is a critical determinant of cardiac function. Upregulation of G protein-coupled receptor kinase 2 (GRK2) is a well-established causal factor of heart failure, but the underlying mechanism is poorly understood. OBJECTIVE:We sought to determine the relative contribution of PKA- and GRK-mediated phosphorylation of ?(2)AR to the receptor coupling to G(i) signaling that attenuates cardiac reserve and contributes to the pathogenesis of heart failure in response to pressure overload. METHODS AND RESULTS:Overexpression of GRK2 led to a G(i)-dependent decrease of contractile response to ?AR stimulation in cultured mouse cardiomyocytes and in vivo. Importantly, cardiac-specific transgenic overexpression of a mutant ?(2)AR lacking PKA phosphorylation sites (PKA-TG) but not the wild-type ?(2)AR (WT-TG) or a mutant ?(2)AR lacking GRK sites (GRK-TG) led to exaggerated cardiac response to pressure overload, as manifested by markedly exacerbated cardiac maladaptive remodeling and failure and early mortality. Furthermore, inhibition of G(i) signaling with pertussis toxin restores cardiac function in heart failure associated with increased ?(2)AR to G(i) coupling induced by removing PKA phosphorylation of the receptor and in GRK2 transgenic mice, indicating that enhanced phosphorylation of ?(2)AR by GRK and resultant increase in G(i)-biased ?(2)AR signaling play an important role in the development of heart failure. CONCLUSIONS:Our data show that enhanced ?(2)AR phosphorylation by GRK, in addition to PKA, leads the receptor to G(i)-biased signaling, which, in turn, contributes to the pathogenesis of heart failure, marking G(i)-biased ?(2)AR signaling as a primary event linking upregulation of GRK to cardiac maladaptive remodeling, failure and cardiodepression.
Project description:cAMP/protein kinase (PK)A activation represents a key signaling mechanism for neurohormonal stimulation of diversified physiological processes. Using real-time, fluorescence resonance energy transfer-based imaging of PKA activity in neonatal cardiac myocytes, we report that sustained activation of PKA induced by beta-adrenoceptor (betaAR) dictates signaling propagation for substrate phosphorylation and myocyte contraction. Activation of betaARs in wild-type myocytes induces strong and sustained PKA activities, which are rapidly attenuated on washing away agonist or adding antagonist to the cells. The sustained PKA activities promote signaling propagation to the sarcoplasmic reticulum for phosphorylation of phospholamban and increases in myocyte contraction. Addition of antagonist after betaAR stimulation significantly attenuates PKA phosphorylation of phospholamban and rapidly reduces contraction rate increases. Moreover, stimulation of beta(1)AR subtype induces PKA activities similar to those in wild-type cells. In contrast, stimulation of beta(2)AR subtype induces strong initial activation of PKA similar to those induced by beta(1)AR; however, the activities are rapidly decreased to baseline levels. The transient PKA activities are sufficient for phosphorylation of the overexpressed beta(2)ARs under agonist stimulation, but not phospholamban. Further analysis reveals that phosphodiesterase 4 is the major family that shapes PKA activities under betaAR stimulation. Inhibition of phosphodiesterase 4 extends beta(2)AR-induced PKA activities, promotes PKA phosphorylation of phospholamban, and ultimately enhances myocyte contraction responses. Together, our data have revealed insights into kinetics of PKA activities in signaling propagation under neurohormonal stimulation.
Project description:?-Adrenergic receptors (?-ARs) enhance cardiac contractility by increasing cAMP levels and activating PKA. PKA increases Ca²?-induced Ca²? release via phosphorylation of L-type Ca²? channels (LTCCs) and ryanodine receptor 2. Multiple cyclic nucleotide phosphodiesterases (PDEs) regulate local cAMP concentration in cardiomyocytes, with PDE4 being predominant for the control of ?-AR-dependent cAMP signals. Three genes encoding PDE4 are expressed in mouse heart: Pde4a, Pde4b, and Pde4d. Here we show that both PDE4B and PDE4D are tethered to the LTCC in the mouse heart but that ?-AR stimulation of the L-type Ca²? current (ICa,L) is increased only in Pde4b-/- mice. A fraction of PDE4B colocalized with the LTCC along T-tubules in the mouse heart. Under ?-AR stimulation, Ca²? transients, cell contraction, and spontaneous Ca²? release events were increased in Pde4b-/- and Pde4d-/- myocytes compared with those in WT myocytes. In vivo, after intraperitoneal injection of isoprenaline, catheter-mediated burst pacing triggered ventricular tachycardia in Pde4b-/- mice but not in WT mice. These results identify PDE4B in the CaV1.2 complex as a critical regulator of ICa,L during ?-AR stimulation and suggest that distinct PDE4 subtypes are important for normal regulation of Ca²?-induced Ca²? release in cardiomyocytes.
Project description:Neurofibromin 2 (NF2), a potent tumor suppressor, is reported to inhibit proliferation in several cell types. The role of NF2 in neointima hyperplasia after vascular injury is unknown. We explored the role of NF2 in proliferation, migration of vascular smooth muscle cell (VSMC) and neointima hyperplasia after vascular injury. NF2 phosphorylation was elevated in VSMC subjected to platelet-derived growth factor (PDGF)-BB and in artery subjected to vascular injury. Mice deficient for Nf2 in VSMC showed enhanced neointima hyperplasia after injury, increased proliferation and migration of VSMC after PDGF-BB treatment. Mechanistically, we observed increased nuclear p-NF2, declined p-Yes-Associated Protein (YAP), nuclear translocation of YAP after PDGF-BB treatment or injury. NF2 knockdown or YAP overexpression showed similar phenotype in VSMC proliferation, migration and neointima hyperplasia. YAP inhibition abolished the above effects mediated by NF2 knockdown. Finally, NF2 knockdown further promoted YAP-TEA Domain Transcription Factor 1 (TEAD1) interaction after PDGF-BB treatment. Inhibition of TEAD1 blocked PDGF-BB-induced VSMC proliferation and migration, which were not reversed by either NF2 knockdown or YAP overexpression. In conclusion, NF2 knockdown promotes VSMC proliferation, migration and neointima hyperplasia after vascular injury via inducing YAP-TEAD1 interaction.
Project description:Aldosterone (Aldo), when overproduced, is a cardiotoxic hormone underlying heart failure and hypertension. Aldo exerts damaging effects via the mineralocorticoid receptor (MR) but also activates the antiapoptotic G protein-coupled estrogen receptor (GPER) in the heart. G protein-coupled receptor (GPCR)-kinase (GRK)-2 and -5 are the most abundant cardiac GRKs and phosphorylate GPCRs as well as non-GPCR substrates. Herein, we investigated whether they phosphorylate and regulate cardiac MR and GPER. To this end, we used the cardiomyocyte cell line H9c2 and adult rat ventricular myocytes (ARVMs), in which we manipulated GRK5 protein levels via clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and GRK2 activity via pharmacological inhibition. We report that GRK5 phosphorylates and inhibits the cardiac MR whereas GRK2 phosphorylates and desensitizes GPER. In H9c2 cardiomyocytes, GRK5 interacts with and phosphorylates the MR upon ?2-adrenergic receptor (AR) activation. In contrast, GRK2 opposes agonist-activated GPER signaling. Importantly, GRK5-dependent MR phosphorylation of the MR inhibits transcriptional activity, since aldosterone-induced gene transcription is markedly suppressed in GRK5-overexpressing cardiomyocytes. Conversely, GRK5 gene deletion augments cardiac MR transcriptional activity. ?2AR-stimulated GRK5 phosphorylates and inhibits the MR also in ARVMs. Additionally, GRK5 is necessary for the protective effects of the MR antagonist drug eplerenone against Aldo-induced apoptosis and oxidative stress in ARVMs. In conclusion, GRK5 blocks the cardiotoxic MR-dependent effects of Aldo in the heart, whereas GRK2 may hinder beneficial effects of Aldo through GPER. Thus, cardiac GRK5 stimulation (e.g., via ?2AR activation) might be of therapeutic value for heart disease treatment via boosting the efficacy of MR antagonists against Aldo-mediated cardiac injury.
Project description:We previously reported in atrial myocytes that inhibition of cAMP-dependent protein kinase (PKA) by laminin (LMN)-integrin signaling activates ?2-adrenergic receptor (?2-AR) stimulation of cytosolic phospholipase A2 (cPLA2). The present study sought to determine the signaling mechanisms by which inhibition of PKA activates ?2-AR stimulation of cPLA2. We therefore determined the effects of zinterol (0.1 ?M; zint-?2-AR) to stimulate ICa,L in atrial myocytes in the absence (+PKA) and presence (-PKA) of the PKA inhibitor (1 ?M) KT5720 and compared these results with atrial myocytes attached to laminin (+LMN). Inhibition of Raf-1 (10 ?M GW5074), phospholipase C (PLC; 0.5 ?M edelfosine), PKC (4 ?M chelerythrine) or IP3 receptor (IP3R) signaling (2 ?M 2-APB) significantly inhibited zint-?2-AR stimulation of ICa,L in-PKA but not +PKA myocytes. Western blots showed that zint-?2-AR stimulation increased ERK1/2 phosphorylation in-PKA compared to +PKA myocytes. Adenoviral (Adv) expression of dominant negative (dn) -PKC?, dn-Raf-1 or an IP3 affinity trap, each inhibited zint-?2-AR stimulation of ICa,L in + LMN myocytes compared to control +LMN myocytes infected with Adv-?gal. In +LMN myocytes, zint-?2-AR stimulation of ICa,L was enhanced by adenoviral overexpression of wild-type cPLA2 and inhibited by double dn-cPLA2S505A/S515A mutant compared to control +LMN myocytes infected with Adv-?gal. In-PKA myocytes depletion of intracellular Ca2+ stores by 5 ?M thapsigargin failed to inhibit zint-?2-AR stimulation of ICa,L via cPLA2. However, disruption of caveolae formation by 10 mM methyl-?-cyclodextrin inhibited zint-?2-AR stimulation of ICa,L in-PKA myocytes significantly more than in +PKA myocytes. We conclude that inhibition of PKA removes inhibition of Raf-1 and thereby allows ?2-AR stimulation to act via PKC?/Raf-1/MEK/ERK1/2 and IP3-mediated Ca2+ signaling to stimulate cPLA2 signaling within caveolae. These findings may be relevant to the remodeling of ?-AR signaling in failing and/or aging heart, both of which exhibit decreases in adenylate cyclase activity.
Project description:AIMS:The cAMP-dependent protein kinase (PKA) mediates β-adrenoceptor (β-AR) regulation of cardiac contraction and gene expression. Whereas PKA activity is well characterized in various subcellular compartments of adult cardiomyocytes, its regulation in the nucleus remains largely unknown. The aim of the present study was to compare the modalities of PKA regulation in the cytoplasm and nucleus of cardiomyocytes. METHODS AND RESULTS:Cytoplasmic and nuclear cAMP and PKA activity were measured with targeted fluorescence resonance energy transfer probes in adult rat ventricular myocytes. β-AR stimulation with isoprenaline (Iso) led to fast cAMP elevation in both compartments, whereas PKA activity was fast in the cytoplasm but markedly slower in the nucleus. Iso was also more potent and efficient in activating cytoplasmic than nuclear PKA. Similar slow kinetics of nuclear PKA activation was observed upon adenylyl cyclase activation with L-858051 or phosphodiesterase (PDE) inhibition with 3-isobutyl-1-methylxantine. Consistently, pulse stimulation with Iso (15 s) maximally induced PKA and myosin-binding protein C phosphorylation in the cytoplasm, but marginally activated PKA and cAMP response element-binding protein phosphorylation in the nucleus. Inhibition of PDE4 or ablation of the Pde4d gene in mice prolonged cytoplasmic PKA activation and enhanced nuclear PKA responses. In the cytoplasm, phosphatase 1 (PP1) and 2A (PP2A) contributed to the termination of PKA responses, whereas only PP1 played a role in the nucleus. CONCLUSION:Our study reveals a differential integration of cytoplasmic and nuclear PKA responses to β-AR stimulation in cardiac myocytes. This may have important implications in the physiological and pathological hypertrophic response to β-AR stimulation.
Project description:Ataxia telangiectasia mutated kinase (ATM) is involved in cell cycle checkpoints, DNA repair and apoptosis. ?-Adrenergic receptor (?-AR) stimulation induces cardiac myocyte apoptosis. Here we analysed basal myocardial structure and function in ATM knockout (KO) mice and tested the hypothesis that ATM modulates ?-AR-stimulated myocyte apoptosis. Left ventricular (LV) structure and function, myocyte apoptosis, fibrosis and expression of fibrosis-, hypertrophy- and apoptosis-related proteins were examined in wild-type (WT) and KO mice with or without l-isoprenaline treatment for 24 h. Body and heart weights were lower in KO mice. M-Mode echocardiography showed reduced septal wall thicknesses and LV diameters in KO mice. Doppler echocardiography showed an increased ratio of early peak velocity (E wave) to that of the late LV filling (A wave) in KO mice. Basal fibrosis and myocyte cross-sectional area were greater in KO hearts. Expression of fibrosis-related genes (connective tissue growth factor and plasminogen activator inhibitor-1) and hypertrophy-related gene (atrial natriuretic peptide) was higher in KO hearts. ?-Adrenergic receptor stimulation increased myocyte apoptosis to a similar extent in both groups. Activation of c-Jun N-terminal kinases and expression and phosphorylation of p53 in response to ?-AR stimulation were only observed in the WT group. Akt phosphorylation was lower in KO sham-treated animals and remained lower following ?-AR stimulation in the KO group. ?-Adrenergic receptor stimulation activated glycogen synthase kinase-3? to a similar extent in both groups. Thus, lack of ATM induces structural and functional changes in the heart, with enhanced myocardial fibrosis and myocyte hypertrophy. ?-Adrenergic receptor-stimulated apoptosis in WT hearts is associated with a p53- and JNKs-dependent mechanism, while decreased Akt activity may play a role in increased myocyte apoptosis in the absence of ATM.
Project description:BACKGROUND:Hepatic ischemia-reperfusion injury (IRI) is a severe complication in liver transplantation, hepatectomy, and hemorrhagic shock. As neuropeptides transmit the regulatory signal between nervous and immune systems communication, our previous study documented that pituitary adenylate cyclase-activating polypeptides (PACAP) depressed hepatic Toll-like receptor 4 immune response in liver IRI. METHODS:Here, we focused on how PACAP suppressed hepatocellular damage and enhanced hepatocyte regeneration in a murine model of partial liver warm IRI. RESULTS:Yes-associated protein (YAP), a cellular modulator of tissue regeneration, was readily induced in wild type (WT) mouse IR-livers. As its induction was failed in PACAP-deficient livers, PACAP supplement enhanced YAP expression in WT mouse and promoted its nuclear translocation and downstream antioxidative/regenerative genes expression both in vivo and in vitro. Further, verteporfin, a YAP transcriptional inhibitor, abolished PACAP-mediated hepatoprotection significantly. Meanwhile, blockade of protein kinase A (PKA)-CRE-binding protein (CREB) signaling recreated liver damage in PACAP-protected liver as well as impeded stimulation on YAP and its downstream gene expressions. Consistently, inhibition of PKA-CREB decreased PACAP-promoted YAP expression in primary hepatocytes culture, and made them vulnerable to H2O2 stress in vitro. In addition, lysophosphatidic acid, another Hippo pathway inhibitor, failed to affect PACAP-mediated hepatoprotection or hepatocellular YAP induction. This implies that PACAP regulated YAP through PKA-CREB pathway at the transcriptional level rather than canonical hippo pathway. CONCLUSIONS:Our study discovered the neural modulation of PACAP-YAP axis in hepatic cytoprotection and homeostasis in liver IRI. These reveal a novel insight of neuropeptide PACAP in combating liver IRI in clinical patients.