Showing papers by "Robert J. Lefkowitz published in 2005"
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TL;DR: Another previously unappreciated strategy used by the receptors to regulate intracellular signaling pathways is indicated, which regulates aspects of cell motility, chemotaxis, apoptosis, and likely other cellular functions through a rapidly expanding list of signaling pathways.
Abstract: The transmission of extracellular signals to the interior of the cell is a function of plasma membrane receptors, of which the seven transmembrane receptor family is by far the largest and most versatile. Classically, these receptors stimulate heterotrimeric G proteins, which control rates of generation of diffusible second messengers and entry of ions at the plasma membrane. Recent evidence, however, indicates another previously unappreciated strategy used by the receptors to regulate intracellular signaling pathways. They direct the recruitment, activation, and scaffolding of cytoplasmic signaling complexes via two multifunctional adaptor and transducer molecules, beta-arrestins 1 and 2. This mechanism regulates aspects of cell motility, chemotaxis, apoptosis, and likely other cellular functions through a rapidly expanding list of signaling pathways.
1,592 citations
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TL;DR: It is demonstrated that, apart from its classical function in receptor desensitization, beta-arrestin 2 also acts as a signaling intermediate through a kinase/phosphatase scaffold, thus implicating beta-arsenin 2 as a positive mediator of dopaminergic synaptic transmission and a potential pharmacological target for dopamine-related psychiatric disorders.
950 citations
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TL;DR: Findings indicate distinct functional capabilities of beta-arrestins bound to receptors phosphorylated by different classes of GRKs, which are related to receptor recruitment, recruitment, and receptor endocytosis.
Abstract: β-arrestins bind to G protein-coupled receptor kinase (GRK)-phosphorylated seven transmembrane receptors, desensitizing their activation of G proteins, while concurrently mediating receptor endocytosis, and some aspects of receptor signaling. We have used RNA interference to assess the roles of the four widely expressed isoforms of GRKs (GRK 2, 3, 5, and 6) in regulating β-arrestin-mediated signaling to the mitogen-activated protein kinase, extracellular signal-regulated kinase (ERK) 1/2 by the angiotensin II type 1A receptor. Angiotensin II-stimulated receptor phosphorylation, β-arrestin recruitment, and receptor endocytosis are all mediated primarily by GRK2/3. In contrast, inhibiting GRK 5 or 6 expression abolishes β-arrestin-mediated ERK activation, whereas lowering GRK 2 or 3 leads to an increase in this signaling. Consistent with these findings, β-arrestin-mediated ERK activation is enhanced by overexpression of GRK 5 and 6, and reciprocally diminished by GRK 2 and 3. These findings indicate distinct functional capabilities of β-arrestins bound to receptors phosphorylated by different classes of GRKs.
347 citations
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TL;DR: The results suggest that beta-arrestin recruited in response to receptor phosphorylation by different GRKs has distinct functional potentials.
Abstract: Signaling through β-arrestins is a recently appreciated mechanism used by seven-transmembrane receptors. Because G protein-coupled receptor kinase (GRK) phosphorylation of such receptors is generally a prerequisite for β-arrestin binding, we studied the roles of different GRKs in promoting β-arrestin-mediated extracellular signal-regulated kinase (ERK) activation by a typical seven-transmembrane receptor, the Gs-coupled V2 vasopressin receptor. Gs- and β-arrestin-mediated pathways to ERK activation could be distinguished with H89, an inhibitor of protein kinase A, and β-arrestin 2 small interfering RNA, respectively. The roles of GRK2, -3, -5, and -6 were assessed by suppressing their expression with specific small interfering RNA sequences. By using this approach, we demonstrated that GRK2 and -3 are responsible for most of the agonist-dependent receptor phosphorylation, desensitization, and recruitment of β-arrestins. In contrast, GRK5 and -6 mediated much less receptor phosphorylation and β-arrestin recruitment, but yet appeared exclusively to support β-arrestin 2-mediated ERK activation. GRK2 suppression actually increased β-arrestin-stimulated ERK activation. These results suggest that β-arrestin recruited in response to receptor phosphorylation by different GRKs has distinct functional potentials.
338 citations
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TL;DR: It is shown that β-arrestin 1 is required to activate the small GTPase RhoA leading to the re-organization of stress fibers following the activation of the angiotensin II type 1A receptor.
190 citations
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TL;DR: For example, β-arrestin binding blocks further G protein coupling, leading to "desensitization" of G protein-dependent signaling pathways as discussed by the authors, leading to activation of the 7-transmembrane receptor.
Abstract: Cell surface receptors are important communicators of external stimuli to the cell interior where they lead to initiation of various signaling pathways and cellular responses. The largest receptor family is the seven-transmembrane receptor (7TMR) family, with approximately 1000 coding genes in the human genome. When 7TMRs are stimulated with agonists, they activate heterotrimeric guanine nucleotide-binding proteins (G proteins), leading to the production of signaling second messengers, such as adenosine 3′,5′-monophosphate, inositol phosphates, and others. Activated receptors are rapidly phosphorylated on serine and threonine residues by specialized enzymes called G protein–coupled receptor kinases. Phosphorylated receptors bind the multifunctional adaptor proteins β-arrestin1 and β-arrestin2 with high affinity. β-arrestin binding blocks further G protein coupling, leading to "desensitization" of G protein–dependent signaling pathways. For several years, this was considered the sole function of β-arrestins. However, novel functions of β-arrestins have been discovered. β-arrestins are now designated as important adaptors that link receptors to the clathrin-dependent pathway of internalization. β-arrestins bind and direct the activity of several nonreceptor tyrosine kinases in response to 7TMR stimulation. β-arrestins also bind and scaffold members of such signaling cascades as the mitogen-activated protein kinases (MAPKs). β-arrestins are crucial components in 7TMR signaling leading to cellular responses that include cell survival and chemotaxis. β-arrestins act as endocytic adaptors and signal mediators not only for the 7TMRs, but also for several receptor tyrosine kinases.
169 citations
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TL;DR: Shenoy et al. as discussed by the authors showed that lysines at positions 11 and 12 in β-arrestin2 are specific and required sites for its AngII-mediated sustained ubiquitination.
166 citations
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TL;DR: Evidence is provided that β-arrestin, otherwise known to be involved in the regulation of G protein-coupled receptors, serves as an adaptor to bring the oncoprotein E3 ubiquitin ligase MDM2 to the IGF-1R, which acts as a crucial component in the ubiquitination and down-regulation of the receptor.
160 citations
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TL;DR: The data suggest that β-arrestin 2 can mediate chemotaxis through mechanisms which may be G-protein-independent (Ang II receptors) or -dependent (LPA receptors), and that p38 plays a role inChemotaxis that is not specific to the AT1AR in this system.
Abstract: Chemotaxis is a cellular response that directs cell migration toward a chemical gradient and is fundamental to a variety of cellular processes. The receptors for most known chemokines belong to the seven transmembrane-spanning superfamily and signal through members of the G αi family. β-Arrestins, in addition to regulating desensitization, have emerged as potential mediators of G-protein-independent signaling pathways and have been implicated in several chemotactic pathways. Here, we report a system wherein chemotaxis is stimulated in a β-arrestin 2-dependent and apparently G-protein-independent manner. Human embryonic kidney 293 cells with stable expression of the angiotensin II (Ang II) receptor type 1A (AT 1A R) undergo chemotaxis in response to Ang II. An Ang II peptide analog S 1 I 4 I 8 Ang II that is unable to activate G-protein-mediated responses induces chemotaxis in these cells that is unaffected by pertussis toxin-mediated suppression of G αi . Suppression of β-arrestin 2 expression using small interfering RNA (siRNA) essentially eliminated AT 1A R-mediated chemotaxis induced by either Ang II or the S 1 I 4 I 8 Ang II peptide but had no effect on epidermal growth factor (EGF)-induced chemotaxis. It also abolished chemotaxis induced by lysophosphatidic acid (LPA), which was completely sensitive to pertussis toxin. In contrast, reduction of G αq/11 through siRNA and inhibition of protein kinase C, extracellular signal-regulated kinases 1 and 2, or phosphatidylinositol-3-kinase did not diminish AT 1A R-mediated chemotaxis. Inhibiting p38 mitogen-activated protein kinase decreased AT 1A R-mediated chemotaxis and eliminated EGF-mediated chemotaxis, suggesting that p38 plays a role in chemotaxis that is not specific to the AT 1A R in this system. These data suggest that β-arrestin 2 can mediate chemotaxis through mechanisms which may be G-protein-independent (Ang II receptors) or -dependent (LPA receptors).
130 citations
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TL;DR: In studies of the mouse heart, Zhai et al. compare the physiologic and biochemical consequences of transgenic cardiac-specific overexpression of a mutant AT1R incapable of G protein coupling with those of a wild-type receptor and provide important and previously unappreciated clues as to the underlying molecular mechanisms.
Abstract: Classically, 7 transmembrane receptors transduce extracellular signals by coupling to heterotrimeric G proteins, although recent in vitro studies have clearly demonstrated that they can also signal via G protein-independent mechanisms. However, the physiologic consequences of this unconventional signaling, particularly in vivo, have not been explored. In this issue of the JCI, Zhai et al. demonstrate in vivo effects of G protein-independent signaling by the angiotensin II type 1 receptor (AT1R) (see the related article beginning on page 3045). In studies of the mouse heart, they compare the physiologic and biochemical consequences of transgenic cardiac-specific overexpression of a mutant AT1R incapable of G protein coupling with those of a wild-type receptor. Their results not only provide the first glimpse of the physiologic effects of this newly appreciated mode of signaling but also provide important and previously unappreciated clues as to the underlying molecular mechanisms.
102 citations
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TL;DR: It is indicated that a single cluster of hydroxy amino acids within the C-terminal seven amino acids of the orexin-1 receptor determine the sustainability of interaction with beta-arrestin-2, and an important role of beta-Arrestin scaffolding in defining the kinetics of orexIn-1 receptors-mediated ERK MAPK activation is indicated.
Abstract: The orexin-1 receptor interacts with β-arrestin-2 in an agonist-dependent manner. In HEK-293T cells, these two proteins became co-internalized into acidic endosomes. Truncations from the C-terminal tail did not prevent agonist-induced internalization of the orexin-1 receptor or alter the pathway of internalization, although such mutants failed to interact with β-arrestin-2 in a sustained manner or produce its co-internalization. Mutation of a cluster of three threonine and one serine residue at the extreme C-terminus of the receptor greatly reduced interaction and abolished co-internalization of β-arrestin-2–GFP (green fluorescent protein). Despite the weak interactions of this C-terminally mutated form of the receptor with β-arrestin-2, studies in wild-type and β-arrestin-deficient mouse embryo fibroblasts confirmed that agonist-induced internalization of this mutant required expression of a β-arrestin. Although without effect on agonist-mediated elevation of intracellular Ca2+ levels, the C-terminally mutated form of the orexin-1 receptor was unable to sustain phosphorylation of the MAPKs (mitogen-activated protein kinases) ERK1 and ERK2 (extracellular-signal-regulated kinases 1 and 2) to the same extent as the wild-type receptor. These studies indicate that a single cluster of hydroxy amino acids within the C-terminal seven amino acids of the orexin-1 receptor determine the sustainability of interaction with β-arrestin-2, and indicate an important role of β-arrestin scaffolding in defining the kinetics of orexin-1 receptor-mediated ERK MAPK activation.
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TL;DR: The data show that the level of &bgr;ARK1 inhibition determines the degree to which cardiac function can be preserved in response to pressure overload and has important therapeutic implications when &b gr;ark1 inhibition is considered as a molecular target.
Abstract: Background— Heart failure is characterized by abnormalities in β-adrenergic receptor (βAR) signaling, including increased level of myocardial βAR kinase 1 (βARK1). Our previous studies have shown that inhibition of βARK1 with the use of the Gβγ sequestering peptide of βARK1 (βARKct) can prevent cardiac dysfunction in models of heart failure. Because inhibition of βARK activity is pivotal for amelioration of cardiac dysfunction, we investigated whether the level of βARK1 inhibition correlates with the degree of heart failure. Methods and Results— Transgenic (TG) mice with varying degrees of cardiac-specific expression of βARKct peptide underwent transverse aortic constriction (TAC) for 12 weeks. Cardiac function was assessed by serial echocardiography in conscious mice, and the level of myocardial βARKct protein was quantified at termination of the study. TG mice showed a positive linear relationship between the level of βARKct protein expression and fractional shortening at 12 weeks after TAC. TG mice wit...
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TL;DR: Using human embryonic kidney 293 (HEK-293) cells as a model system and utilizing RNA interference technology, two distinct pathways of angiotensin II-mediated ERK activation have been uncovered: a G protein– dependent pathway that produces a transient activation of nuclear ERK and a β-arrestin–dependent pathway that leads to sustained activation of ERK that is localized to the cytosol and endosomes.
Abstract: Beta-arrestin, originally identified as a protein that inhibits heterotrimeric guanine nucleotide-binding protein (G protein) coupling to cognate seven-transmembrane receptors [(7TMRs), also known as G protein-coupled receptors (GPCRs)], is currently being appreciated as a positive signaling mediator for various cell surface receptors. Activation of mitogen-activated protein kinases (MAPKs), especially extracellular signal regulated kinases 1 and 2 (ERK1/2), is a hallmark of intracellular signaling resulting from stimulation of various growth factor receptors, as well as 7TMRs. The resulting ERK activity can occur through multiple parallel or converging mechanisms. Using human embryonic kidney 293 (HEK-293) cells as a model system and utilizing RNA interference technology, two distinct pathways of angiotensin II-mediated ERK activation have been uncovered: (i) a G protein-dependent pathway that produces a transient activation of nuclear ERK and (ii) a beta-arrestin-dependent pathway that leads to sustained activation of ERK that is localized to the cytosol and endosomes. The spatial and temporal segregation of ERK activated by G protein and beta-arrestin pathways suggests that the physiological consequences may be different, and thus ligands that selectively stimulate or inhibit one of these pathways may be therapeutically valuable.
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TL;DR: β-arrestin, a protein known to regulate the signalling, trafficking and degradation of mammalian seven-transmembrane-spanning receptors, has now been identified as a regulator of ubiquitination and degrading of the Notch receptor in Drosophila melanogaster.
Abstract: β-arrestin, a protein known to regulate the signalling, trafficking and degradation of mammalian seven-transmembrane-spanning receptors, has now been identified as a regulator of ubiquitination and degradation of the Notch receptor in Drosophila melanogaster.
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TL;DR: One of the most interesting discussions concerned the possibility that a number of currently so-called orphan receptors might have no personal ligands but, rather, function to bestow novel properties on other 7TM-spanning receptors by oligomer formation.
Abstract: Listening to the talks delivered at the symposium during this 2 1/2-d meeting left me with the feeling that this was a field that has truly come of age in the past few years. Although the earliest observations, a number of them by the organizers of the meeting, on receptor-receptor interactions go back almost two decades, it is really only in the past few years that the molecular basis of these interactions has begun to be clarified. The initial skepticism is now subsiding as more and more examples of receptor oligomerization are identified. At the meeting, three types of receptor oligomerization were discussed: homo-oligomerization; hetero-oligomerization, where both partners are seven transmembrane (7TM)-spanning receptors; and hetero-oligomerization, where a 7 TM-spanning receptor is complexed with a structurally different class of molecule. Although interesting papers were presented in each area, I found myself most intrigued by the papers dealing with hetero-oligomerization between different 7TM-spanning receptors. Most striking were examples where novel functions were created by the heterodimerization process, such as novel opioid binding patterns or the acquisition of novel signaling pathways, as in the case of D1-D2 dopamine receptor heterodimerization. In this connection, to me, one of the most interesting discussions concerned the possibility that a number of currently so-called orphan receptors might have no personal ligands but, rather, function to bestow novel properties on other 7TM-spanning receptors by oligomer formation. Thus, these orphans might convey a new signaling function or an altered ligand- binding specificity on a known receptor. If this were the case then, for such an orphan, all efforts to identify its function by expressing it alone would be doomed to fail. Another potentially interesting function of some orphan receptors might be to act as chaperones for other receptors, helping to bring them to the cell surface and stabilizing their membrane expression.