Showing papers by "Robert J. Lefkowitz published in 1999"
TL;DR: Data suggest that beta-arrestin binding, which terminates receptor-G protein coupling, also initiates a second wave of signal transduction in which the "desensitized" receptor functions as a critical structural component of a mitogenic signaling complex.
Abstract: The Ras-dependent activation of mitogen-activated protein (MAP) kinase pathways by many receptors coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) requires the activation of Src family tyrosine kinases. Stimulation of beta2 adrenergic receptors resulted in the assembly of a protein complex containing activated c-Src and the receptor. Src recruitment was mediated by beta-arrestin, which functions as an adapter protein, binding both c-Src and the agonist-occupied receptor. beta-Arrestin 1 mutants, impaired either in c-Src binding or in the ability to target receptors to clathrin-coated pits, acted as dominant negative inhibitors of beta2 adrenergic receptor-mediated activation of the MAP kinases Erk1 and Erk2. These data suggest that beta-arrestin binding, which terminates receptor-G protein coupling, also initiates a second wave of signal transduction in which the "desensitized" receptor functions as a critical structural component of a mitogenic signaling complex.
1,451 citations
TL;DR: It is suggested that inhibition of beta-arrestin 2 function might lead to enhanced analgesic effectiveness of morphine and provide potential new avenues for the study and treatment of pain, narcotic tolerance, and dependence.
Abstract: The ability of morphine to alleviate pain is mediated through a heterotrimeric guanine nucleotide binding protein (G protein)-coupled heptahelical receptor (GPCR), the mu opioid receptor (muOR). The efficiency of GPCR signaling is tightly regulated and ultimately limited by the coordinated phosphorylation of the receptors by specific GPCR kinases and the subsequent interaction of the phosphorylated receptors with beta-arrestin 1 and beta-arrestin 2. Functional deletion of the beta-arrestin 2 gene in mice resulted in remarkable potentiation and prolongation of the analgesic effect of morphine, suggesting that muOR desensitization was impaired. These results provide evidence in vivo for the physiological importance of beta-arrestin 2 in regulating the function of a specific GPCR, the muOR. Moreover, they suggest that inhibition of beta-arrestin 2 function might lead to enhanced analgesic effectiveness of morphine and provide potential new avenues for the study and treatment of pain, narcotic tolerance, and dependence.
973 citations
TL;DR: Three types of scaffolds for GPCR-directed complex assembly have been identified: transactivated receptor tyrosine kinases, integrin-based focal adhesions, and GPCRs themselves, and nonreceptor tyrosines play an important role in each case.
693 citations
TL;DR: Beta2ARs in murine cardiac myocytes couple to concurrent Gs and Gi signaling, resulting in null inotropic response, unless the Gi signaling is inhibited, and results suggest that PTX-sensitive G proteins are responsible for the unresponsiveness of mouse heart to agonist-induced beta2AR stimulation.
Abstract: -Transgenic mouse models have been developed to manipulate beta-adrenergic receptor (betaAR) signal transduction. Although several of these models have altered betaAR subtypes, the specific functional sequelae of betaAR stimulation in murine heart, particularly those of beta2-adrenergic receptor (beta2AR) stimulation, have not been characterized. In the present study, we investigated effects of beta2AR stimulation on contraction, [Ca2+]i transient, and L-type Ca2+ currents (ICa) in single ventricular myocytes isolated from transgenic mice overexpressing human beta2AR (TG4 mice) and wild-type (WT) littermates. Baseline contractility of TG4 heart cells was increased by 3-fold relative to WT controls as a result of the presence of spontaneous beta2AR activation. In contrast, beta2AR stimulation by zinterol or isoproterenol plus a selective beta1-adrenergic receptor (beta1AR) antagonist CGP 20712A failed to enhance the contractility in TG4 myocytes, and more surprisingly, beta2AR stimulation was also ineffective in increasing contractility in WT myocytes. Pertussis toxin (PTX) treatment fully rescued the ICa, [Ca2+]i, and contractile responses to beta2AR agonists in both WT and TG4 cells. The PTX-rescued murine cardiac beta2AR response is mediated by cAMP-dependent mechanisms, because it was totally blocked by the inhibitory cAMP analog Rp-cAMPS. These results suggest that PTX-sensitive G proteins are responsible for the unresponsiveness of mouse heart to agonist-induced beta2AR stimulation. This was further corroborated by an increased incorporation of the photoreactive GTP analog [gamma-32P]GTP azidoanilide into alpha subunits of Gi2 and Gi3 after beta2AR stimulation by zinterol or isoproterenol plus the beta1AR blocker CGP 20712A. This effect to activate Gi proteins was abolished by a selective beta2AR blocker ICI 118,551 or by PTX treatment. Thus, we conclude that (1) beta2ARs in murine cardiac myocytes couple to concurrent Gs and Gi signaling, resulting in null inotropic response, unless the Gi signaling is inhibited; (2) as a special case, the lack of cardiac contractile response to beta2AR agonists in TG4 mice is not due to a saturation of cell contractility or of the cAMP signaling cascade but rather to an activation of beta2AR-coupled Gi proteins; and (3) spontaneous beta2AR activation may differ from agonist-stimulated beta2AR signaling.
391 citations
TL;DR: Heptahelical receptors, so called because of their conserved structure featuring seven α-helical transmembrane spans, mediate physiological responses to a remarkably diverse array of stimuli.
Abstract: Heptahelical receptors, so called because of their conserved structure featuring seven α-helical transmembrane spans, mediate physiological responses to a remarkably diverse array of stimuli. These include hormones, neurotransmitters, small peptides, proteins, lipids and ions, as well as sensory
337 citations
TL;DR: The dependence of GPCR-mediated Erk 1/2 activation on intact focal adhesions correlates with expression of the calcium-regulated focal adhesion kinase, Pyk2.
270 citations
TL;DR: It is demonstrated that activation of β2-adrenergic receptors (β2-ARs) leads to c-Src-mediated tyrosine phosphorylation of dynamin, which is required for receptor internalization in clathrin mediated G protein-coupled receptor endocytosis.
268 citations
TL;DR: It is demonstrated that global myocardial in vivo gene delivery is possible and that genetic manipulation of beta-AR density can result in enhanced cardiac performance, and replacement of lost receptors seen in HF may represent novel inotropic therapy.
Abstract: Exogenous gene delivery to alter the function of the heart is a potential novel therapeutic strategy for treatment of cardiovascular diseases such as heart failure (HF). Before gene therapy approaches to alter cardiac function can be realized, efficient and reproducible in vivo gene techniques must be established to efficiently transfer transgenes globally to the myocardium. We have been testing the hypothesis that genetic manipulation of the myocardial β-adrenergic receptor (β-AR) system, which is impaired in HF, can enhance cardiac function. We have delivered adenoviral transgenes, including the human β2-AR (Adeno-β2AR), to the myocardium of rabbits using an intracoronary approach. Catheter-mediated Adeno-β2AR delivery produced diffuse multichamber myocardial expression, peaking 1 week after gene transfer. A total of 5 × 1011 viral particles of Adeno-β2AR reproducibly produced 5- to 10-fold β-AR overexpression in the heart, which, at 7 and 21 days after delivery, resulted in increased in vivo hemodynamic function compared with control rabbits that received an empty adenovirus. Several physiological parameters, including dP/dtmax as a measure of contractility, were significantly enhanced basally and showed increased responsiveness to the β-agonist isoproterenol. Our results demonstrate that global myocardial in vivo gene delivery is possible and that genetic manipulation of β-AR density can result in enhanced cardiac performance. Thus, replacement of lost receptors seen in HF may represent novel inotropic therapy.
219 citations
TL;DR: It is demonstrated that elimination of GRK5 results in cholinergic supersensitivity and impaired muscarinic receptor desensitization and suggested that a deficit of GPCR desensItization may be an underlying cause of behavioral supersensitivity.
199 citations
TL;DR: A novel mechanism whereby the activity of GRK2 is regulated by feedback inhibition is identified, whereby β-arrestin-mediated processes such as Src recruitment and clathrin-mediated internalization are inhibited, thus dampening further ERK activation.
188 citations
TL;DR: It is concluded that CAM-dependent activation of Erk1/2 through the 5-HT1A receptor reflects its role in endocytosis of the receptor, which is a required step in the activation of MEK and subsequently Erk 1/2.
TL;DR: The studies demonstrate a role of the SH3p4/p8/p13 protein family in beta1-AR signaling and suggest that interaction between proline-rich motifs and SH3-containing proteins may represent a previously underappreciated aspect of G-protein coupled receptor signaling.
Abstract: Several G-protein coupled receptors, such as the β1-adrenergic receptor (β1-AR), contain polyproline motifs within their intracellular domains. Such motifs in other proteins are known to mediate protein–protein interactions such as with Src homology (SH)3 domains. Accordingly, we used the proline-rich third intracellular loop of the β1-AR either as a glutathione S-transferase fusion protein in biochemical “pull-down” assays or as bait in the yeast two-hybrid system to search for interacting proteins. Both approaches identified SH3p4/p8/p13 (also referred to as endophilin 1/2/3), a SH3 domain-containing protein family, as binding partners for the β1-AR. In vitro and in human embryonic kidney (HEK) 293 cells, SH3p4 specifically binds to the third intracellular loop of the β1-AR but not to that of the β2-AR. Moreover, this interaction is mediated by the C-terminal SH3 domain of SH3p4. Functionally, overexpression of SH3p4 promotes agonist-induced internalization and modestly decreases the Gs coupling efficacy of β1-ARs in HEK293 cells while having no effect on β2-ARs. Thus, our studies demonstrate a role of the SH3p4/p8/p13 protein family in β1-AR signaling and suggest that interaction between proline-rich motifs and SH3-containing proteins may represent a previously underappreciated aspect of G-protein coupled receptor signaling.
TL;DR: It is demonstrated that β-arrestin1 phosphorylation and function are modulated by an ERK-dependent negative feedback mechanism, and the results suggest that dephosphorylated β-Arrestin 1 mediates endocytosis-dependent ERK activation.
TL;DR: It is shown that the primary site of constitutive NHERF phosphorylated in human embryonic kidney 293 (HEK-293) cells is Ser289, and that the stoichiometry of phosphorylation is near 1 mol/mol, which indicates that the endogenous “NHERF kinase” activity in HEk-293 cell lysates is sensitive to treatments that alter the activity of GRK6A.
TL;DR: The demonstration of β-arrestin1-NSF complex formation and the functional consequences of NSF overexpression suggest a hitherto unappreciated role for NSF in facilitating clathrin coat-mediated G protein-coupled receptor internalization.
TL;DR: Comparison of the amino acid sequences of GRKs from various mammalian species indicates that GRK2, GRK5, and GRK6 exhibit a remarkably high degree of sequence conservation, whereas GRK1 and particularly GRK4 have accumulated amino acid changes at extremely rapid rates over the past 100 million years.
TL;DR: In vivo results demonstrated that the presence of the betaARKct in injured rat carotid arteries significantly reduced VSM intimal hyperplasia by 70%, and targeted Gbetagamma inhibition represents a novel approach for the treatment of pathological conditions such as restenosis.
Abstract: Restenosis continues to be a major problem limiting the effectiveness of revascularization procedures To date, the roles of heterotrimeric G proteins in the triggering of pathological vascular smooth muscle (VSM) cell proliferation have not been elucidated βγ subunits of heterotrimeric G proteins (Gβγ) are known to activate mitogen-activated protein (MAP) kinases after stimulation of certain G protein-coupled receptors; however, their relevance in VSM mitogenesis in vitro or in vivo is not known Using adenoviral-mediated transfer of a transgene encoding a peptide inhibitor of Gβγ signaling (βARKct), we evaluated the role of Gβγ in MAP kinase activation and proliferation in response to several mitogens, including serum, in cultured rat VSM cells Our results include the striking finding that serum-induced proliferation of VSM cells in vitro is mediated largely via Gβγ Furthermore, we studied the effects of in vivo adenoviral-mediated βARKct gene transfer on VSM intimal hyperplasia in a rat carotid artery restenosis model Our in vivo results demonstrated that the presence of the βARKct in injured rat carotid arteries significantly reduced VSM intimal hyperplasia by 70% Thus, Gβγ plays a critical role in physiological VSM proliferation, and targeted Gβγ inhibition represents a novel approach for the treatment of pathological conditions such as restenosis
TL;DR: The results indicate that increased β-adrenergic receptor kinase-1 is not invariably associated with myocardial hypertrophy but apparently is controlled by the state of β-adsenergic receptor activation.
Abstract: Pressure overload ventricular hypertrophy is accompanied by dysfunctional beta-adrenergic receptor signaling due to increased levels of the beta-adrenergic receptor kinase-1, which phosphorylates and desensitizes beta-adrenergic receptors. In this study, we examined whether increased beta-adrenergic receptor kinase 1 expression is associated with myocardial hypertrophy induced by adrenergic stimulation. With use of implanted mini-osmotic pumps, we treated mice with isoproterenol, phenylephrine, or vehicle to distinguish between alpha1- and beta-adrenergic stimulation. Both treatments resulted in cardiac hypertrophy, but only isoproterenol induced significant increases in beta-adrenergic receptor kinase-1 protein levels and activity. Similarly, in isolated adult rat cardiac myocytes, 24 hours of isoproterenol stimulation resulted in a significant 2.8-fold increase in beta-adrenergic receptor kinase-1 protein levels, whereas 24 hours of phenylephrine treatment did not alter beta-adrenergic receptor kinase-1 expression. Our results indicate that increased beta-adrenergic receptor kinase-1 is not invariably associated with myocardial hypertrophy but apparently is controlled by the state of beta-adrenergic receptor activation.
TL;DR: Unlike beta(2)AR overexpression, basal contractility was increased by betaARK1 inhibitor expression without increasing ischemic injury, thus implicating a safer potential therapy for heart failure.
Abstract: —Cardiac β2-adrenergic receptor (β2AR) overexpression is a potential contractile therapy for heart failure. Cardiac contractility was elevated in mice overexpressing β2ARs (TG4s) with no adverse effects under normal conditions. To assess the consequences of β2AR overexpression during ischemia, perfused hearts from TG4 and wild-type mice were subjected to 20-minute ischemia and 40-minute reperfusion. During ischemia, ATP and pH fell lower in TG4 hearts than wild type. Ischemic injury was greater in TG4 hearts, as indicated by lower postischemic recoveries of contractile function, ATP, and phosphocreatine. Because β2ARs, unlike β1ARs, couple to Gi as well as Gs, we pretreated mice with the Gi inhibitor pertussis toxin (PTX). PTX treatment increased basal contractility in TG4 hearts and abolished the contractile resistance to isoproterenol. During ischemia, ATP fell lower in TG4+PTX than in TG4 hearts. Recoveries of contractile function and ATP were lower in TG4+PTX than in TG4 hearts. We also studie...
TL;DR: The results indicate that myocardial function of the transplanted heart can be enhanced by the adenovirus-mediated delivery of β2-ARs, and genetic manipulation may offer a novel therapeutic strategy to improve donor heart function in the post- operative setting.
Abstract: Gene transfer to modify donor heart function during transplantation has significant therapeutic implications. Recent studies by our laboratory in transgenic mice have shown that overexpression of beta2-adrenergic receptors (beta2-ARs) leads to significantly enhanced cardiac function. Thus, we investigated the functional consequences of adenovirus-mediated gene transfer of the human beta2-AR in a rat heterotopic heart transplant model. Donor hearts received 1 ml of solution containing 1 x 1010 p.f.u. of adenovirus encoding the beta2-AR or an empty adenovirus as a control. Five days after transplantation, basal left ventricular (LV) pressure was measured using an isolated, isovolumic heart perfusion apparatus. A subset of hearts was stimulated with the beta2-AR agonist, zinterol. Treatment with the beta2-AR virus resulted in global myocardial gene transfer with a six-fold increase in mean beta-AR density which corresponded to a significant increase in basal contractility (LV + dP/dtmax, control: 3152.1 +/- 286 versus beta2-AR, 6250.6* +/- 432.5 mmHg/s; n = 10, *P < 0.02). beta2-AR overexpressing hearts also had higher contractility after zinterol administration compared with control hearts. Our results indicate that myocardial function of the transplanted heart can be enhanced by the adenovirus-mediated delivery of beta2-ARs. Thus, genetic manipulation may offer a novel therapeutic strategy to improve donor heart function in the post- operative setting.
TL;DR: Data demonstrate that in the mouse, GRK3 may be involved in modulating the cholinergic response of airway smooth muscle and in regulating the chronotropic component of the baroreceptor reflex.
Abstract: Contraction and relaxation of airway smooth muscles is mediated, in part, by G protein-coupled receptors (GPCRs) and dysfunction of these receptors has been implicated in asthma. Phosphorylation of...
01 Sep 1999
TL;DR: The compelling finding that inhibition of beta ARK1 activity or expression significantly enhances cardiac function and potentiates beta AR signaling in failing cardiomyocytes is addressed.
Abstract: The beta-adrenergic signaling cascade is an important regulator of myocardial function. Significant alterations of this pathway are associated with several cardiovascular diseases, including congestive heart failure (CHF). Included in these alterations is increased activity and expression of G protein-coupled receptor kinases (GRKs), such as the beta-adrenergic receptor kinase (beta ARK1), which phosphorylate and desensitize beta-adrenergic receptors (beta ARs). A body of evidence is accumulating that suggests that GRKs, in particular beta ARK1, are critical determinants of cardiac function under normal conditions and in disease states. Transgenic mice with myocardial-targeted alterations of GRK activity have shown profound changes in the in vivo functional performance of the heart. Included in these studies is the compelling finding that inhibition of beta ARK1 activity or expression significantly enhances cardiac function and potentiates beta AR signaling in failing cardiomyocytes. This article summarizes the advances made in the study of beta ARK1 in the heart and addresses its potential as a novel therapeutic target for CHF.