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R J Lefkowitz

Publications and source records attributed to R J Lefkowitz.

At least 55 records · Page 3Linked to original sources
PubMed2000

Assembly of an A kinase-anchoring protein-beta(2)-adrenergic receptor complex facilitates receptor phosphorylation and signaling.

Phosphorylation of G-protein-coupled receptors by second-messenger-stimulated kinases is central to the process of receptor desensitization [1-3]. Phosphorylation of the beta(2)-adrenergic receptor (beta(2)-AR) by protein kinase A (PKA), in addition to uncoupling adenylate cyclase activation, is obligatory for receptor-mediated activation of mitogen-activated protein kinase (MAP kinase) cascades [4] [5]. Although mechanisms for linking G-protein-coupled receptor kinases to the activated receptor are well established, analogous mechanisms for targeting second messenger kinases to the beta(2)-AR at the plasma membrane have not been elucidated. Here we show that the A-kinase-anchoring protein, AKAP79/150, co-precipitates with the beta(2)-AR in cell and tissue extracts, nucleating a signaling complex that includes PKA, protein kinase C (PKC) and protein phosphatase PP2B. The anchoring protein directly and constitutively interacts with the beta(2)-AR and promotes receptor phosphorylation following agonist stimulation. Functional studies show that PKA anchoring is required to enhance beta(2)-AR phosphorylation and to facilitate downstream activation of the MAP kinase pathway. This defines a role for AKAP79/150 in the recruitment of second-messenger-regulated signaling enzymes to a G-protein-coupled receptor.

A Kinase Anchor Proteins↗
PubMed2000

The beta(2)-adrenergic receptor mediates extracellular signal-regulated kinase activation via assembly of a multi-receptor complex with the epidermal growth factor receptor.

Many G protein-coupled receptors (GPCRs) activate MAP kinases by stimulating tyrosine kinase signaling cascades. In some systems, GPCRs stimulate tyrosine phosphorylation by inducing the "transactivation" of a receptor tyrosine kinase (RTK). The mechanisms underlying GPCR-induced RTK transactivation have not been clearly defined. Here we report that GPCR activation mimics growth factor-mediated stimulation of the epidermal growth factor receptor (EGFR) with respect to many facets of RTK function. beta(2)-Adrenergic receptor (beta(2)AR) stimulation of COS-7 cells induces EGFR dimerization, tyrosine autophosphorylation, and EGFR internalization. Coincident with EGFR transactivation, isoproterenol exposure induces the formation of a multireceptor complex containing both the beta(2)AR and the "transactivated" EGFR. beta(2)AR-mediated EGFR phosphorylation and subsequent beta(2)AR stimulation of extracellular signal-regulated kinase (ERK) 1/2 are sensitive to selective inhibitors of both EGFR and Src kinases, indicating that both kinases are required for EGFR transactivation. beta(2)AR-dependent signaling to ERK1/2, like direct EGF stimulation of ERK1/2 activity, is sensitive to inhibitors of clathrin-mediated endocytosis, suggesting that signaling downstream of both the EGF-activated and the GPCR-transactivated EGFRs requires a productive engagement of the complex with the cellular endocytic machinery. Thus, RTK transactivation is revealed to be a process involving both association of receptors of distinct classes and the interaction of the transactivated RTK with the cells endocytic machinery.

Animals↗
PubMed2000

Role of endocytosis in the activation of the extracellular signal-regulated kinase cascade by sequestering and nonsequestering G protein-coupled receptors.

Acting through a number of distinct pathways, many G protein-coupled receptors (GPCRs) activate the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) cascade. Recently, it has been shown that in some cases, clathrin-mediated endocytosis is required for GPCR activation of the ERK/MAPK cascade, whereas in others it is not. Accordingly, we compared ERK activation mediated by a GPCR that does not undergo agonist-stimulated endocytosis, the alpha(2A) adrenergic receptor (alpha(2A) AR), with ERK activation mediated by the beta(2) adrenergic receptor (beta(2) AR), which is endocytosed. Surprisingly, we found that in COS-7 cells, ERK activation by the alpha(2A) AR, like that mediated by both the beta(2) AR and the epidermal growth factor receptor (EGFR), is sensitive to mechanistically distinct inhibitors of clathrin-mediated endocytosis, including monodansylcadaverine, a mutant dynamin I, and a mutant beta-arrestin 1. Moreover, we determined that, as has been shown for many other GPCRs, both alpha(2A) and beta(2) AR-mediated ERK activation involves transactivation of the EGFR. Using confocal immunofluorescence microscopy, we found that stimulation of the beta(2) AR, the alpha(2A) AR, or the EGFR each results in internalization of a green fluorescent protein-tagged EGFR. Although beta(2) AR stimulation leads to redistribution of both the beta(2) AR and EGFR, activation of the alpha(2A) AR leads to redistribution of the EGFR but the alpha(2A) AR remains on the plasma membrane. These findings separate GPCR endocytosis from the requirement for clathrin-mediated endocytosis in EGFR transactivation-mediated ERK activation and suggest that it is the receptor tyrosine kinase or another downstream effector that must engage the endocytic machinery.

Adrenergic alpha-Agonists↗
PubMed2000

Multiple endocytic pathways of G protein-coupled receptors delineated by GIT1 sensitivity.

Recently, we identified a GTPase-activating protein for the ADP ribosylation factor family of small GTP-binding proteins that we call GIT1. This protein initially was identified as an interacting partner for the G protein-coupled receptor kinases, and its overexpression was found to affect signaling and internalization of the prototypical beta(2)-adrenergic receptor. Here, we report that GIT1 overexpression regulates internalization of numerous, but not all, G protein-coupled receptors. The specificity of the GIT1 effect is not related to the type of G protein to which a receptor couples, but rather to the endocytic route it uses. GIT1 only affects the function of G protein-coupled receptors that are internalized through the clathrin-coated pit pathway in a beta-arrestin- and dynamin-sensitive manner. Furthermore, the GIT1 effect is not limited to G protein-coupled receptors because overexpression of this protein also affects internalization of the epidermal growth factor receptor. However, constitutive agonist-independent internalization is not regulated by GIT1, because transferrin uptake is not affected by GIT1 overexpression. Thus, GIT1 is a protein involved in regulating the function of signaling receptors internalized through the clathrin pathway and can be used as a diagnostic tool for defining the endocytic pathway of a receptor.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Intracoronary adenovirus-mediated delivery and overexpression of the beta(2)-adrenergic receptor in the heart : prospects for molecular ventricular assistance.

BACKGROUND: Genetic modulation of ventricular function may offer a novel therapeutic strategy for patients with congestive heart failure. Myocardial overexpression of beta(2)-adrenergic receptors (beta(2)ARs) has been shown to enhance contractility in transgenic mice and reverse signaling abnormalities found in failing cardiomyocytes in culture. In this study, we sought to determine the feasibility and in vivo consequences of delivering an adenovirus containing the human beta(2)AR cDNA to ventricular myocardium via catheter-mediated subselective intracoronary delivery. METHODS AND RESULTS: Rabbits underwent percutaneous subselective catheterization of either the left or right coronary artery and infusion of adenoviral vectors containing either a marker transgene (Adeno-betaGal) or the beta(2)AR (Adeno-beta(2)AR). Ventricular function was assessed before catheterization and 3 to 6 days after gene delivery. Both left circumflex- and right coronary artery-mediated delivery of Adeno-beta(2)AR resulted in approximately 10-fold overexpression in a chamber-specific manner. Delivery of Adeno-betaGal did not alter in vivo left ventricular (LV) systolic function, whereas overexpression of beta(2)ARs in the LV improved global LV contractility, as measured by dP/dt(max), at baseline and in response to isoproterenol at both 3 and 6 days after gene delivery. CONCLUSIONS: Percutaneous adenovirus-mediated intracoronary delivery of a potentially therapeutic transgene is feasible, and acute global LV function can be enhanced by LV-specific overexpression of the beta(2)AR. Thus, genetic modulation to enhance the function of the heart may represent a novel therapeutic strategy for congestive heart failure and can be viewed as molecular ventricular assistance.

Adenoviridae↗
PubMed2000

The superfamily of heptahelical receptors.

Despite a growing appreciation of functional analogies between visual and hormonal signalling systems in the early 1980s, the discovery of the close structural relationship between rhodopsin and the beta2-adrenergic receptor, and of the existence of a larger 'superfamily' of such receptors, came as a total surprise. Here I provide a personal perspective on events leading up to and flowing from this exciting discovery that opened up a vast field of research.

Animals↗
PubMed2000

Adenovirus-mediated genetic manipulation of the myocardial beta-adrenergic signaling system in transplanted hearts.

OBJECTIVES: Ex vivo perfusion of the cardiac allograft during organ procurement is an ideal environment for adenoviral vectors with transgenes that target improving graft contractility. One such target is the beta-adrenergic receptor-signaling system, in which alterations in transgenic mice have elucidated novel means to improve the function of the heart in vivo. The purpose of the current study was to determine the functional consequences of beta-adrenergic receptor manipulation in a rabbit model of cardiac allograft transplantation. METHODS: New Zealand White rabbits weighing 3 kg served as recipients to 1-kg outbred donors. Donor hearts were arrested and harvested, and 1 of 3 adenoviral constructs was administered into the aortic root perfusing the graft. Transgenes delivered encoded either the human beta(2)-adrenergic receptor, a peptide inhibitor of beta-adrenergic receptor densensitization, or the marker transgene beta-galactosidase. RESULTS: Five days after cervical heterotopic transplantation, left ventricular performance was measured on a Langendorff apparatus. A moderate pattern of rejection was seen in all grafts. Biventricular myocyte expression of beta-galactosidase was observed, and beta(2)-adrenergic receptor density was elevated 10-fold in grafts that received adeno-beta(2)-adrenergic receptor. Left ventricular systolic and diastolic performance was significantly increased in grafts transfected with either adeno-beta(2)-adrenergic receptor or adeno-beta-adrenergic receptor densensitization compared with control grafts that received adeno-beta-galactosidase. CONCLUSIONS: Ex vivo adenovirus-mediated gene transfer is feasible in a rabbit allograft model and, more important, genetic manipulation of beta-adrenergic receptor signaling either by increasing beta(2)-adrenergic receptor density or blocking endogenous receptor desensitization improves graft function acutely in this allograft model.

Adenoviridae↗
PubMed2000

Platelet-derived growth factor receptor association with Na(+)/H(+) exchanger regulatory factor potentiates receptor activity.

Platelet-derived growth factor (PDGF) is a potent mitogen for many cell types. The PDGF receptor (PDGFR) is a receptor tyrosine kinase that mediates the mitogenic effects of PDGF by binding to and/or phosphorylating a variety of intracellular signaling proteins upon PDGF-induced receptor dimerization. We show here that the Na(+)/H(+) exchanger regulatory factor (NHERF; also known as EBP50), a protein not previously known to interact with the PDGFR, binds to the PDGFR carboxyl terminus (PDGFR-CT) with high affinity via a PDZ (PSD-95/Dlg/Z0-1 homology) domain-mediated interaction and potentiates PDGFR autophosphorylation and extracellular signal-regulated kinase (ERK) activation in cells. A point-mutated version of the PDGFR, with the terminal leucine changed to alanine (L1106A), cannot bind NHERF in vitro and is markedly impaired relative to the wild-type receptor with regard to PDGF-induced autophosphorylation and activation of ERK in cells. NHERF potentiation of PDGFR signaling depends on the capacity of NHERF to oligomerize. NHERF oligomerizes in vitro when bound with PDGFR-CT, and a truncated version of the first NHERF PDZ domain that can bind PDGFR-CT but which does not oligomerize reduces PDGFR tyrosine kinase activity when transiently overexpressed in cells. PDGFR activity in cells can also be regulated in a NHERF-dependent fashion by stimulation of the beta(2)-adrenergic receptor, a known cellular binding partner for NHERF. These findings reveal that NHERF can directly bind to the PDGFR and potentiate PDGFR activity, thus elucidating both a novel mechanism by which PDGFR activity can be regulated and a new cellular role for the PDZ domain-containing adapter protein NHERF.

Amino Acid Motifs↗
PubMed2000

Functional consequences of altering myocardial adrenergic receptor signaling.

From the ability to successfully manipulate the mouse genome has come important transgenic and gene-targeted knockout models that impact many areas of biomedical research. Genetically engineered mouse models geared toward the study of cardiovascular regulation have recently been described and provide powerful tools to study normal and compromised cardiac physiology. The genetic manipulation of the adrenergic receptor (AR) signaling system in the heart, including its regulation by desensitizing kinases, has shed light on the role of this signaling pathway in the regulation of cardiac contractility. One major finding, supported by several mouse models, is that in vivo contractility can be enhanced via alteration of myocardial AR signaling. Thus genetic manipulation of this critical receptor system in the heart represents a novel therapeutic approach for improving function of the failing heart.

Animals↗
PubMed1999

Enhanced morphine analgesia in mice lacking beta-arrestin 2.

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.

Analgesia↗
PubMed1999

Feedback inhibition of G protein-coupled receptor kinase 2 (GRK2) activity by extracellular signal-regulated kinases.

G protein-coupled receptor kinase (GRK)-mediated receptor phosphorylation and beta-arrestin binding uncouple G protein-coupled receptors (GPCRs) from their respective G proteins and initiates the process of receptor internalization. In the case of the beta(2)-adrenergic receptor and lysophosphatidic acid receptor, these processes can lead to ERK activation. Here we identify a novel mechanism whereby the activity of GRK2 is regulated by feedback inhibition. GRK2 is demonstrated to be a phosphoprotein in cells. Mass spectrometry and mutational analysis localize the site of phosphorylation on GRK2 to a carboxyl-terminal serine residue (Ser(670)). Phosphorylation at Ser(670) impairs the ability of GRK2 to phosphorylate both soluble and membrane-incorporated receptor substrates and dramatically attenuates Gbetagamma-mediated activation of this enzyme. Ser(670) is located in a peptide sequence that conforms to an ERK consensus phosphorylation sequence, and in vitro, in the presence of heparin, ERK1 phosphorylates GRK2. Inhibition of ERK activity in HEK293 cells potentiates GRK2 activity, whereas, conversely, ERK activation inhibits GRK2 activity. The discovery that ERK phosphorylates and inactivates GRK2 suggests that ERK participates in a feedback regulatory loop. By negatively regulating GRK-mediated receptor phosphorylation, beta-arrestin-mediated processes such as Src recruitment and clathrin-mediated internalization, which are required for GPCR-mediated ERK activation, are inhibited, thus dampening further ERK activation.

Cell Line↗
PubMed1999

Overexpression of the cardiac beta(2)-adrenergic receptor and expression of a beta-adrenergic receptor kinase-1 (betaARK1) inhibitor both increase myocardial contractility but have differential effects on susceptibility to ischemic injury.

Cardiac beta(2)-adrenergic receptor (beta(2)AR) overexpression is a potential contractile therapy for heart failure. Cardiac contractility was elevated in mice overexpressing beta(2)ARs (TG4s) with no adverse effects under normal conditions. To assess the consequences of beta(2)AR 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 beta(2)ARs, unlike beta(1)ARs, couple to G(i) as well as G(s), we pretreated mice with the G(i) 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 studied mice that overexpressed either betaARK1 (TGbetaARK1) or a betaARK1 inhibitor (TGbetaARKct). Recoveries of function, ATP, and phosphocreatine were higher in TGbetaARK1 hearts than in wild-type hearts. Despite basal contractility being elevated in TGbetaARKct hearts to the same level as that of TG4s, ischemic injury was not increased. In summary, beta(2)AR overexpression increased ischemic injury, whereas betaARK1 overexpression was protective. Ischemic injury in the beta(2)AR overexpressors was exacerbated by PTX treatment, implying that it was G(s) not G(i) activity that enhanced injury. 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.

Adenosine Triphosphate↗
PubMed1999

Identification of the endophilins (SH3p4/p8/p13) as novel binding partners for the beta1-adrenergic receptor.

Several G-protein coupled receptors, such as the beta1-adrenergic receptor (beta1-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 beta1-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 beta1-AR. In vitro and in human embryonic kidney (HEK) 293 cells, SH3p4 specifically binds to the third intracellular loop of the beta1-AR but not to that of the beta2-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 beta1-ARs in HEK293 cells while having no effect on beta2-ARs. Thus, our 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.

Adaptor Proteins, Signal Transducing↗
PubMed1999

The GRK4 subfamily of G protein-coupled receptor kinases. Alternative splicing, gene organization, and sequence conservation.

G protein-coupled receptor kinases (GRKs) desensitize G protein-coupled receptors by phosphorylating activated receptors. The six known GRKs have been classified into three subfamilies based on sequence and functional similarities. Examination of the mouse GRK4 subfamily (GRKs 4, 5, and 6) suggests that mouse GRK4 is not alternatively spliced in a manner analogous to human or rat GRK4, whereas GRK6 undergoes extensive alternative splicing to generate three variants with distinct carboxyl termini. Characterization of the mouse GRK 5 and 6 genes reveals that all members of the GRK4 subfamily share an identical gene structure, in which 15 introns interrupt the coding sequence at equivalent positions in all three genes. Surprisingly, none of the three GRK subgroups (GRK1, GRK2/3, and GRK4/5/6) shares even a single intron in common, indicating that these three subfamilies are distinct gene lineages that have been maintained since their divergence over 1 billion years ago. 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. The divergence of individual GRKs at vastly different rates reveals that strikingly different evolutionary pressures apply to the function of the individual GRKs.

Alternative Splicing↗
PubMed1999

G protein-coupled receptor kinase 6A phosphorylates the Na(+)/H(+) exchanger regulatory factor via a PDZ domain-mediated interaction.

The Na(+)/H(+) exchanger regulatory factor (NHERF) is constitutively phosphorylated in cells, but the site(s) of this phosphorylation and the kinase(s) responsible for it have not been identified. We show here that the primary site of constitutive NHERF phosphorylation in human embryonic kidney 293 (HEK-293) cells is Ser(289), and that the stoichiometry of phosphorylation is near 1 mol/mol. NHERF contains two PDZ domains that recognize the sequence S/T-X-L at the carboxyl terminus of target proteins, and thus we examined the possibility that kinases containing this motif might associate with and phosphorylate NHERF. Overlay experiments and co-immunoprecipitation studies revealed that NHERF binds with high affinity to a splice variant of the G protein-coupled receptor kinase 6, GRK6A, which terminates in the motif T-R-L. NHERF does not associate with GRK6B or GRK6C, alternatively spliced variants that differ from GRK6A at their extreme carboxyl termini. GRK6A phosphorylates NHERF efficiently on Ser(289) in vitro, whereas GRK6B, GRK6C, and GRK2 do not. Furthermore, the endogenous "NHERF kinase" activity in HEK-293 cell lysates is sensitive to treatments that alter the activity of GRK6A. These data suggest that GRK6A phosphorylates NHERF via a PDZ domain-mediated interaction and that GRK6A is the kinase in HEK-293 cells responsible for the constitutive phosphorylation of NHERF.

Amino Acid Sequence↗
PubMed1999

In vivo inhibition of elevated myocardial beta-adrenergic receptor kinase activity in hybrid transgenic mice restores normal beta-adrenergic signaling and function.

BACKGROUND: The clinical syndrome of heart failure (HF) is characterized by an impaired cardiac beta-adrenergic receptor (betaAR) system, which is critical in the regulation of myocardial function. Expression of the betaAR kinase (betaARK1), which phosphorylates and uncouples betaARs, is elevated in human HF; this likely contributes to the abnormal betaAR responsiveness that occurs with beta-agonist administration. We previously showed that transgenic mice with increased myocardial betaARK1 expression had impaired cardiac function in vivo and that inhibiting endogenous betaARK1 activity in the heart led to enhanced myocardial function. METHODS AND RESULTS: We created hybrid transgenic mice with cardiac-specific concomitant overexpression of both betaARK1 and an inhibitor of betaARK1 activity to study the feasibility and functional consequences of the inhibition of elevated betaARK1 activity similar to that present in human HF. Transgenic mice with myocardial overexpression of betaARK1 (3 to 5-fold) have a blunted in vivo contractile response to isoproterenol when compared with non-transgenic control mice. In the hybrid transgenic mice, although myocardial betaARK1 levels remained elevated due to transgene expression, in vitro betaARK1 activity returned to control levels and the percentage of betaARs in the high-affinity state increased to normal wild-type levels. Furthermore, the in vivo left ventricular contractile response to betaAR stimulation was restored to normal in the hybrid double-transgenic mice. CONCLUSIONS: Novel hybrid transgenic mice can be created with concomitant cardiac-specific overexpression of 2 independent transgenes with opposing actions. Elevated myocardial betaARK1 in transgenic mouse hearts (to levels seen in human HF) can be inhibited in vivo by a peptide that can prevent agonist-stimulated desensitization of cardiac betaARs. This may represent a novel strategy to improve myocardial function in the setting of compromised heart function.

Adenylyl Cyclases↗
PubMed1999

Feedback regulation of beta-arrestin1 function by extracellular signal-regulated kinases.

The functions of beta-arrestin1 to facilitate clathrin-mediated endocytosis of the beta2-adrenergic receptor and to promote agonist-induced activation of extracellular signal-regulated kinases (ERK) are regulated by its phosphorylation/dephosphorylation at Ser-412. Cytoplasmic beta-arrestin1 is almost stoichiometrically phosphorylated at Ser-412. Dephosphorylation of beta-arrestin1 at the plasma membrane is required for targeting a signaling complex that includes the agonist-occupied receptors to the clathrin-coated pits. Here we demonstrate that beta-arrestin1 phosphorylation and function are modulated by an ERK-dependent negative feedback mechanism. ERK1 and ERK2 phosphorylate beta-arrestin1 at Ser-412 in vitro. Inhibition of ERK activity by a dominant-negative MEK1 mutant significantly attenuates beta-arrestin1 phosphorylation, thereby increasing the concentration of dephosphorylated beta-arrestin1. Under such conditions, beta-arrestin1-mediated beta2-adrenergic receptor internalization is enhanced as is its ability to bind clathrin. In contrast, if ERK-mediated phosphorylation is increased by transfection of a constitutively active MEK1 mutant, receptor internalization is inhibited. Our results suggest that dephosphorylated beta-arrestin1 mediates endocytosis-dependent ERK activation. Following activation, ERKs phosphorylate beta-arrestin1, thereby exerting an inhibitory feedback control of its function.

Arrestins↗