Alternative titles; symbols
HGNC Approved Gene Symbol: GRK2
Cytogenetic location: 11q13.2 Genomic coordinates (GRCh38): 11:67,266,473-67,286,556 (from NCBI)
BARK is a ubiquitous cytosolic enzyme that specifically phosphorylates the activated form of the beta-2 adrenergic receptor (ADRB2; 109690) and related G protein-coupled receptors (Penn and Benovic, 1994).
Benovic et al. (1991) used the bovine Bark cDNA to screen a human retina library and isolate the human cDNA. They showed that it encodes a protein of 689 amino acids with an overall 98% amino acid and 92.5% nucleotide identity with bovine Bark.
Fan and Malik (2003) noted that desensitization of G protein-coupled receptors regulates the number of polymorphonuclear leukocytes (PMNs), as well as their motility and ability to stop upon contact with pathogens or target cells, and this desensitization is mediated by GRKs. They found that MIP2 (CXCL2; 139110) induces GRK2 and GRK5 (600870) expression in PMNs through PI3KG (PIK3CG; 601232) signaling. However, lipopolysaccharide (LPS), acting through TLR4 (603030) signaling, mediated through MEK1 (176872)/MEK2 (601263), transcriptionally downregulates expression of GRK2 and GRK5 in response to MIP2, which decreases chemokine receptor desensitization and markedly augments PMN migration. Therefore, LPS-activated TLR4 signaling regulates PMN migration by modulating the expression of chemokine receptors in a GRK2- and GRK5-dependent manner.
Lorenz et al. (2003) demonstrated that the RAF kinase inhibitor protein (RKIP; 604591) is a physiologic inhibitor of GRK2. After stimulation of G protein-coupled receptors, RKIP dissociates from its known target, RAF1 (164760), to associate with GRK2 and block its activity. This switch is triggered by a protein kinase C (PKC; see 176960)-dependent phosphorylation of RKIP on serine-153. Lorenz et al. (2003) concluded that their data delineate a new principle in signal transduction: by activating PKC, the incoming receptor signal is enhanced both by removing an inhibitor from RAF1 and by blocking receptor internalization. A physiologic role for this mechanism is shown in cardiomyocytes in which the downregulation of RKIP restrains beta-adrenergic signaling and contractile activity.
Wang et al. (2004) reported that the multidomain protein spinophilin (603325) antagonizes the multiple arrestin functions associated with G protein-coupled receptor (GPCR)-mediated signaling and trafficking. Through blocking GRK2 association with receptor-G-beta-gamma complexes, spinophilin reduces arrestin-stabilized receptor phosphorylation, receptor endocytosis, and the acceleration of mitogen-activated protein kinase (MAPK) activity following endocytosis. Spinophilin knockout mice were more sensitive than wildtype mice to sedation elicited by stimulation of alpha-2 adrenergic receptors (see 104210), whereas arrestin-3 (301770) knockout mice were more resistant, indicating that the signal-promoting, rather than the signal-terminating, roles of arrestin are more important for certain response pathways. Wang et al. (2004) concluded that the reciprocal interactions of GPCRs with spinophilin and arrestin represent a regulatory mechanism for fine-tuning complex receptor-orchestrated cell signaling and responses.
Chen et al. (2004) found that 2 molecules interact with mammalian Smoothened (SMO; 601500) in an activation-dependent manner: Grk2 leads to phosphorylation of Smo, and beta-arrestin-2 (ARRB2; 107941) fused to green fluorescent protein interacts with Smo. These 2 processes promote endocytosis of Smo in clathrin-coated pits. Ptc (601309) inhibits association of Arrb2 with Smo, and this inhibition is relieved in cells treated with Shh (600725). A Smo agonist stimulated and a Smo antagonist (cyclopamine) inhibited both phosphorylation of Smo by Grk2 and interaction of Arrb2 with Smo. Chen et al. (2004) suggested that Arrb2 and Grk2 are thus potential mediators of signaling by activated Smo.
Raveh et al. (2010) showed that GRK2 was responsible for short-term desensitization of the potassium channels GIRK1 (KCNJ3; 601534) and GIRK4 (KCNJ5; 600734). Desensitization was independent of GRK2 kinase activity, but depended upon the ability of GRK2 to bind G protein beta-gamma subunits. Sequestration of G protein beta-gamma subunits by GRK2 appeared to quench channel activity by competing for the available pool of beta-gamma subunits.
Lymphocytes egress from lymphoid organs in response to sphingosine-1-phosphate (S1P); minutes later they migrate from blood into tissue against the S1P gradient. Arnon et al. (2011) showed that heterotrimeric GRK2 functions in downregulation of S1P receptor-1 (S1PR1; 601974) on blood-exposed lymphocytes. T- and B-cell movement from blood into lymph nodes was reduced in the absence of GRK2 but was restored in S1P-deficient mice. In the spleen, B-cell movement between the blood-rich marginal zone and follicles was disrupted by GRK2 deficiency and by mutation of an S1PR1 desensitization motif. Moreover, Arnon et al. (2011) found that delivery of systemic antigen into follicles was impaired. Thus, GRK2-dependent S1PR1 desensitization allows lymphocytes to escape circulatory fluids and migrate into lymphoid tissues.
Penn and Benovic (1994) reported that the ADRBK1 gene spans approximately 23 kb and is composed of 21 exons interrupted by 20 introns. Exon sizes range from 52 bp (exon 7) to over 1,200 bp (exon 21); intron sizes range from 68 bp (intron L) to 10.8 kb (intron A). A major transcription start site was thought to be located approximately 246 bp upstream of the start ATG. Sequence analysis of the 5-prime flanking/promoter region shows many features characteristic of mammalian housekeeping genes: the lack of a TATA box, absent or nonstandard positioned CAAT box, high GC content, and the presence of Sp1-binding sites. The extraordinarily high GC content of the 5-prime flanking region (more than 80%) helped define this region as a CpG island that may be a principal regulator of expression of the gene.
Crystal Structure
Lodowski et al. (2003) determined the crystal structure of bovine GRK2 in complex with G protein beta-1 (139380)/gamma-2 (606981) subunits. The results demonstrated how the 3 domains of GRK2--the RGS (regulator of G protein signaling) homology, protein kinase, and pleckstrin homology domains--integrate their respective activities and recruit the enzyme to the cell membrane in an orientation that not only facilitates receptor phosphorylation, but also allows for the simultaneous inhibition of signaling by G-alpha (see 139320) and G-beta/gamma subunits.
GRK2 plays a key role in the desensitization of G protein-coupled receptor signaling by phosphorylating activated heptahelical receptors and by sequestering heterotrimeric G proteins. Tesmer et al. (2005) reported the atomic structure of GRK2 in complex with G-alpha-q (600998) and G-beta-gamma, in which the activated G-alpha subunit of Gq is fully dissociated from G-beta-gamma and dramatically reoriented from its position in the inactive G-alpha-beta-gamma heterotrimer. G-alpha-q forms an effector-like interaction with the GRK2 regulator of G protein signaling (RGS) homology domain that is distinct from and does not overlap with that used to bind RGS proteins.
By study of rodent/human hybrid cells retaining various human chromosomes and parts of chromosomes, Benovic et al. (1991) demonstrated that the ADRBK1 gene segregates with the long arm of chromosome 11, centromeric to 11q13, i.e., 11cen-q13. Benovic et al. (1991) mapped the homologous gene to mouse chromosome 19.
Heart failure is accompanied by severely impaired beta-adrenergic receptor (beta-AR) function, which includes loss of receptor density and functional uncoupling of the remaining receptors. An important mechanism for the rapid desensitization of beta-AR function is agonist-stimulated receptor phosphorylation by the beta-AR kinase (beta-ARK1), an enzyme known to be elevated in failing human heart tissue. To investigate whether alterations in beta-AR function contribute to the development of myocardial failure, Rockman et al. (1998) mated transgenic mice with cardiac-restricted overexpression of either a peptide inhibitor of beta-ARK1 or the beta-2-AR into a genetic model of murine heart failure. They found that overexpression of the inhibitor prevented the development of cardiomyopathy in this murine model of heart failure. The findings implicated abnormal coupling of beta-AR to G protein in the pathogenesis of the failing heart and pointed the way toward the development of agents to inhibit beta-ARK1 as a novel mode of therapy.
To determine whether inhibition of BARK1 is sufficient to rescue a model of severe heart failure, Harding et al. (2001) mated transgenic mice overexpressing a peptide inhibitor of Bark1 with transgenic mice overexpressing calsequestrin (Csq, or CASQ1; 114250). Csq mice had a severe cardiomyopathy and markedly shortened survival. In contrast, Csq mice who also overexpressed the peptide inhibitor of Bark1 exhibited a significant increase in mean survival time, showed less cardiac dilation, and had significantly improved cardiac function. Enhancement of the survival rate in the doubly transgenic mice was substantially potentiated by chronic treatment with the beta-adrenergic receptor antagonist metoprolol. Thus, overexpression of the Bark1 inhibitor resulted in a marked prolongation in survival and improved cardiac function in a mouse model of severe cardiomyopathy, an effect that can be potentiated with beta-blocker therapy. The data demonstrated a significant synergy between an established heart-failure treatment and the strategy of BARK1 inhibition.
Spurney et al. (2002) determined that expression of a dominant-negative GRK construct, the C terminus of GRK2 (GRK2-CT), in cells expressing endogenous or exogenous parathyroid hormone receptor-1 (PTHR1; 168468) led to reduced agonist-induced phosphorylation of PTHR1 followed by enhanced signaling. To determine the effect of GRK inhibition on bone formation in vivo, they developed transgenic mice with expression of GRK2-CT targeted to mature osteoblasts. Transgenic mice demonstrated an increase in both osteoblastic and osteoclastic activity as well as alterations in osteoprotegerin (OPG; 602643) and OPG ligand (602642) mRNA levels in mouse calvaria. Although both bone formation and bone resorption were enhanced in transgenic mice, the net effect of the transgene was anabolic, as evidenced by an increase in bone density and trabecular bone volume.
Liu et al. (2005) presented evidence suggesting a role for GRK2 in hepatic vascular dynamics in a rat model of liver sinusoidal endothelial injury and portal hypertension induced by bile duct ligation. Sinusoidal endothelial cells isolated from the affected animals had increased levels of GRK2, reduced levels of phosphorylated protein kinase AKT (164730) and eNOS (163729), and decreased levels of the vasodilator nitric oxide (NO). Further analysis showed that the C terminus of GRK2 bound to and inhibited the phosphorylation and activation of AKT. Gene silencing of GRK2 using siRNA in injured sinusoidal endothelial cells restored AKT activity and resulted in increased NO production. Liu et al. (2005) also found that heterozygous Grk2 mice had increased levels of phosphorylated Akt and decreased portal hypertension in response to injury compared to wildtype mice. Liu et al. (2005) proposed a mechanism in which upregulation of GRK2 after endothelial cell injury directly inhibits phosphorylation of AKT, leading to reduced activation of eNOS and decreased production of NO, and resulting in portal hypertension.
In 2 models of heart failure, Csq mice and post-myocardial infarction rats, Lymperopoulos et al. (2007) found substantial alpha-2-adrenergic receptor (see 104210) dysregulation in the adrenal gland, triggered by increased expression and activity of Grk2. Adrenal gland-specific Grk2 inhibition reversed alpha-2-adrenergic receptor dysregulation, resulting in lowered plasma catecholamine levels, improved cardiac beta-adrenergic receptor signaling and function, and increased sympatholytic efficacy of an alpha-2-adrenergic receptor agonist. Lymperopoulos et al. (2007) suggested that the sympatholytic effects of GRK2 inhibition could counteract the chronic deleterious sympathetic overstimulation of the failing heart and improve its inotropic reserve.
Arnon, T. I., Xu, Y., Lo, C., Pham, T., An, J., Coughlin, S., Dorn, G. W., Cyster, J. G. GRK2-dependent S1PR1 desensitization is required for lymphocytes to overcome their attraction to blood. Science 333: 1898-1903, 2011. [PubMed: 21960637] [Full Text: https://dx.doi.org/10.1126/science.1208248]
Benovic, J. L., Stone, W. C., Huebner, K., Croce, C., Caron, M. G., Lefkowitz, R. J. cDNA cloning and chromosomal localization of the human beta-adrenergic receptor kinase. FEBS Lett. 283: 122-126, 1991. [PubMed: 2037065] [Full Text: https://dx.doi.org/10.1016/0014-5793(91)80568-n]
Chen, W., Ren, X.-R., Nelson, C. D., Barak, L. S., Chen, J. K., Beachy, P. A., de Sauvage, F., Lefkowitz, R. J. Activity-dependent internalization of Smoothened mediated by beta-arrestin 2 and GRK2. Science 306: 2257-2260, 2004. [PubMed: 15618519] [Full Text: https://dx.doi.org/10.1126/science.1104135]
Fan, J., Malik, A. B. Toll-like receptor-4 (TLR4) signaling augments chemokine-induced neutrophil migration by modulating cell surface expression of chemokine receptors. Nature Med. 9: 315-321, 2003. Note: Erratum: Nature 9: 477 only, 2003. [PubMed: 12592402] [Full Text: https://dx.doi.org/10.1038/nm832]
Harding, V. B., Jones, L. R., Lefkowitz, R. J., Koch, W. J., Rockman, H. A. Cardiac beta-ARK1 inhibition prolongs survival and augments beta blocker therapy in a mouse model of severe heart failure. Proc. Nat. Acad. Sci. 98: 5809-5814, 2001. [PubMed: 11331748] [Full Text: https://dx.doi.org/10.1073/pnas.091102398]
Liu, S., Premont, R. T., Kontos, C. D., Zhu, S., Rockey, D. C. A crucial role for GRK2 in regulation of endothelial cell nitric oxide synthase function in portal hypertension. Nature Med. 11: 952-958, 2005. [PubMed: 16142243] [Full Text: https://dx.doi.org/10.1038/nm1289]
Lodowski, D. T., Pitcher, J. A., Capel, W. D., Lefkowitz, R. J., Tesmer, J. J. G. Keeping G proteins at bay: a complex between G protein-coupled receptor kinase 2 and G-beta/gamma. Science 300: 1256-1262, 2003. [PubMed: 12764189] [Full Text: https://dx.doi.org/10.1126/science.1082348]
Lorenz, K., Lohse, M. J., Quitterer, U. Protein kinase C switches the Raf kinase inhibitor from Raf-1 to GRK-2. Nature 426: 574-579, 2003. [PubMed: 14654844] [Full Text: https://dx.doi.org/10.1038/nature02158]
Lymperopoulos, A., Rengo, G., Funakoshi, H., Eckhart, A. D., Koch, W. J. Adrenal GRK2 upregulation mediates sympathetic overdrive in heart failure. Nature Med. 13: 315-323, 2007. [PubMed: 17322894] [Full Text: https://dx.doi.org/10.1038/nm1553]
Penn, R. B., Benovic, J. L. Structure of the human gene encoding the beta-adrenergic receptor kinase. J. Biol. Chem. 269: 14924-14930, 1994. [PubMed: 8195124] [Full Text: https://linkinghub.elsevier.com/retrieve/pii/S0021-9258(17)36554-7]
Raveh, A., Cooper, A., Guy-David, L., Reuveny, E. Nonenzymatic rapid control of GIRK channel function by a G protein-coupled receptor kinase. Cell 143: 750-760, 2010. [PubMed: 21111235] [Full Text: https://dx.doi.org/10.1016/j.cell.2010.10.018]
Rockman, H. A., Chien, K. R., Choi, D.-J., Iaccarino, G., Hunter, J. J., Ross, J., Jr., Lefkowitz, R. J., Koch, W. J. Expression of a beta-adrenergic receptor kinase 1 inhibitor prevents the development of myocardial failure in gene-targeted mice. Proc. Nat. Acad. Sci. 95: 7000-7005, 1998. [PubMed: 9618528] [Full Text: https://dx.doi.org/10.1073/pnas.95.12.7000]
Spurney, R. F., Flannery, P. J., Garner, S. C., Athirakul, K., Liu, S., Guilak, F., Quarles, L. D. Anabolic effects of a G protein-coupled receptor kinase inhibitor expressed in osteoblasts. J. Clin. Invest. 109: 1361-1371, 2002. [PubMed: 12021252] [Full Text: https://dx.doi.org/10.1172/JCI14663]
Tesmer, V. M., Kawano, T., Shankaranarayanan, A., Kozasa, T., Tesmer, J. J. G. Snapshot of activated G proteins at the membrane: the G-alpha-q-GRK2-G-beta-gamma complex. Science 310: 1686-1690, 2005. [PubMed: 16339447] [Full Text: https://dx.doi.org/10.1126/science.1118890]
Wang, Q., Zhao, J., Brady, A. E., Feng, J., Allen, P. B., Lefkowitz, R. J., Greengard, P., Limbird, L. E. Spinophilin blocks arrestin actions in vitro and in vivo at G protein-coupled receptors. Science 304: 1940-1944, 2004. [PubMed: 15218143] [Full Text: https://dx.doi.org/10.1126/science.1098274]