Grk6 encodes G protein-coupled receptor kinase 6, a member of the GRK4/5/6 subfamily of AGC serine/threonine protein kinases, with an N-terminal RGS-homology domain, a central protein kinase domain and a C-terminal AGC-kinase extension. It is widely expressed, including all brain regions, smooth muscle and lymphoid tissue. Palmitoylation of a C-terminal cysteine cluster anchors GRK6 to membranes and increases its catalytic activity; the non-palmitoylated pool is cytosolic. GRK6 phosphorylates agonist-occupied G protein-coupled receptors, which promotes arrestin binding, receptor uncoupling from G proteins and internalization, producing homologous desensitization. In rat cells it mediates desensitization of beta-adrenergic receptors in uterine smooth muscle and contributes to desensitization of M1 muscarinic receptors in hippocampal neurons; in mice it limits D2-like dopamine receptor signaling in striatum and regulates CXCR4 signaling and chemotaxis in T cells. It binds the ARF GAP GIT1.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0002029 desensitization of G protein-coupled receptor signaling pathway | IDA PMID:12810562 Endogenous G protein-coupled receptor kinase 6 triggers homo... | ACCEPT | Summary: Rat myometrial cells: endogenous GRK6 mediates homologous beta-adrenergic receptor desensitization. Reason: Core process. GRK6 phosphorylates agonist-occupied GPCRs, promoting arrestin binding and homologous desensitization. Rat evidence: dominant-negative K215R-GRK6 relieves beta-adrenergic desensitization in myometrial cells (PMID:12810562) and M1 muscarinic desensitization in hippocampal neurons (PMID:15115810, PMID:17908240); mouse knockouts show D2-like dopamine receptor supersensitivity (PMID:12718862). Abstract-only cache; the abstract directly supports this process claim. Supporting Evidence: PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. PMID:12810562 Expression of (K215R)GRK6 increased by approximately 70% the cAMP response to isoproterenol without effect on forskolin stimulation. |
| GO:0002029 desensitization of G protein-coupled receptor signaling pathway | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA prediction of GPCR desensitization; consistent with the experimental rat and mouse data. Reason: Core process. GRK6 phosphorylates agonist-occupied GPCRs, promoting arrestin binding and homologous desensitization. Rat evidence: dominant-negative K215R-GRK6 relieves beta-adrenergic desensitization in myometrial cells (PMID:12810562) and M1 muscarinic desensitization in hippocampal neurons (PMID:15115810, PMID:17908240); mouse knockouts show D2-like dopamine receptor supersensitivity (PMID:12718862). Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Such receptor phosphorylation initiates beta-arrestin-mediated receptor internalization, and signaling events leading to their desensitization. PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. |
| GO:0002029 desensitization of G protein-coupled receptor signaling pathway | IMP PMID:17908240 The regulation of M1 muscarinic acetylcholine receptor desen... | ACCEPT | Summary: Rat hippocampal neurons: dominant-negative GRK6 partially prevents picrotoxin-enhanced M1 muscarinic receptor desensitization. Reason: Core process. GRK6 phosphorylates agonist-occupied GPCRs, promoting arrestin binding and homologous desensitization. Rat evidence: dominant-negative K215R-GRK6 relieves beta-adrenergic desensitization in myometrial cells (PMID:12810562) and M1 muscarinic desensitization in hippocampal neurons (PMID:15115810, PMID:17908240); mouse knockouts show D2-like dopamine receptor supersensitivity (PMID:12718862). Full text read: in mature neurons the K215R-GRK6 effect is confined to picrotoxin-treated (synaptically hyperactive) cultures and GRK2 is the dominant kinase, but the result agrees with the earlier rat study (PMID:15115810) showing GRK6 regulates M1 receptor desensitization. Supporting Evidence: PMID:17908240 However, inhibition of endogenous GRK6 appeared to partially prevent picrotoxin-enhanced M1 mACh receptor desensitization (Fig. 3e). PMID:15115810 Inhibition of endogenous GRK6 (G-protein-coupled receptor kinase) activity, by the introduction of catalytically inactive (K215R)GRK6, partially reversed the attenuation of agonist-induced responsiveness, whereas overexpression of wild-type GRK6 increased receptor desensitization. |
| GO:0002029 desensitization of G protein-coupled receptor signaling pathway | ISO GO_REF:0000121 | ACCEPT | Summary: ISO from mouse Grk6; GRK6-deficient mice show D2-like dopamine receptor supersensitivity. Reason: Core process. GRK6 phosphorylates agonist-occupied GPCRs, promoting arrestin binding and homologous desensitization. Rat evidence: dominant-negative K215R-GRK6 relieves beta-adrenergic desensitization in myometrial cells (PMID:12810562) and M1 muscarinic desensitization in hippocampal neurons (PMID:15115810, PMID:17908240); mouse knockouts show D2-like dopamine receptor supersensitivity (PMID:12718862). Supporting Evidence: PMID:12718862 The present study indicates that postsynaptic D2-like dopamine receptors are physiological targets for GRK6 PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. |
| GO:0002029 desensitization of G protein-coupled receptor signaling pathway | ISO GO_REF:0000121 | ACCEPT | Summary: ISO from human GRK6; consistent with rat experimental data. Reason: Core process. GRK6 phosphorylates agonist-occupied GPCRs, promoting arrestin binding and homologous desensitization. Rat evidence: dominant-negative K215R-GRK6 relieves beta-adrenergic desensitization in myometrial cells (PMID:12810562) and M1 muscarinic desensitization in hippocampal neurons (PMID:15115810, PMID:17908240); mouse knockouts show D2-like dopamine receptor supersensitivity (PMID:12718862). Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Such receptor phosphorylation initiates beta-arrestin-mediated receptor internalization, and signaling events leading to their desensitization. PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. |
| GO:0004672 protein kinase activity | IEA GO_REF:0000002 | MODIFY | Summary: Generic protein kinase activity from InterPro Ser/Thr kinase active-site signature. Reason: Correct but less specific than the evidence supports. GRK6 is a GPRK-subfamily AGC kinase whose defining substrates are agonist-activated GPCRs; refine to GO:0004703 G protein-coupled receptor kinase activity, which the gene already carries (IBA, IDA, ISO, IEA). Proposed replacements: G protein-coupled receptor kinase activity Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. GPRK subfamily. file:rat/Grk6/Grk6-uniprot.txt Specifically phosphorylates the activated forms of G protein-coupled receptors. |
| GO:0004672 protein kinase activity | ISO GO_REF:0000121 | MODIFY | Summary: ISO protein kinase activity from mouse Grk6; true but generic. Reason: Correct but less specific than the evidence supports. GRK6 is a GPRK-subfamily AGC kinase whose defining substrates are agonist-activated GPCRs; refine to GO:0004703 G protein-coupled receptor kinase activity, which the gene already carries (IBA, IDA, ISO, IEA). Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: MGI:MGI:1347078 SUPPORTS TRANSFER Donor kinase activity transfers correctly; only the term is too general. PR:O70293-1 SUPPORTS TRANSFER Donor kinase activity transfers correctly; only the term is too general. Proposed replacements: G protein-coupled receptor kinase activity Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. GPRK subfamily. file:rat/Grk6/Grk6-uniprot.txt Specifically phosphorylates the activated forms of G protein-coupled receptors. |
| GO:0004674 protein serine/threonine kinase activity | IEA GO_REF:0000002 | MODIFY | Summary: Ser/Thr kinase activity from InterPro AGC-kinase C-terminal signature; true but generic. Reason: Correct but less specific than the evidence supports. GRK6 is a GPRK-subfamily AGC kinase whose defining substrates are agonist-activated GPCRs; refine to GO:0004703 G protein-coupled receptor kinase activity, which the gene already carries (IBA, IDA, ISO, IEA). Proposed replacements: G protein-coupled receptor kinase activity Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. GPRK subfamily. file:rat/Grk6/Grk6-uniprot.txt Specifically phosphorylates the activated forms of G protein-coupled receptors. |
| GO:0004703 G protein-coupled receptor kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA GPCR kinase activity for the GRK4/5/6 clade; rat Grk6 is a member and has its own experimental support. Reason: Core activity. GRK6 phosphorylates agonist-activated GPCRs (beta2-adrenergic receptor in vitro, PMID:9819198), and in rat cells its catalytic activity is required for homologous desensitization (kinase-dead K215R mutant acts as dominant negative; PMID:12810562, PMID:15115810). The IBA node is placed on the GRK clade, which includes the target; RGD:61986 appearing among donors reflects the target's own experimental grounding. Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Specifically phosphorylates the activated forms of G protein-coupled receptors. PMID:9819198 Palmitoylated GRK6 is 10-fold more active at phosphorylating beta2-adrenergic receptor than nonpalmitoylated wild-type GRK6 or a nonpalmitoylatable mutant GRK6. |
| GO:0004703 G protein-coupled receptor kinase activity | IDA PMID:12810562 Endogenous G protein-coupled receptor kinase 6 triggers homo... | ACCEPT | Summary: Rat myometrial cells: endogenous GRK6 kinase activity mediates homologous beta-AR desensitization. Reason: Core activity. GRK6 phosphorylates agonist-activated GPCRs (beta2-adrenergic receptor in vitro, PMID:9819198), and in rat cells its catalytic activity is required for homologous desensitization (kinase-dead K215R mutant acts as dominant negative; PMID:12810562, PMID:15115810). Cached record is abstract-only and the abstract reports inhibitor and dominant-negative experiments rather than a direct kinase assay; the curator had the full text, and GPCR kinase activity is well established for GRK6, so the row is accepted. Supporting Evidence: PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. PMID:12810562 Expression of (K215R)GRK6 increased by approximately 70% the cAMP response to isoproterenol without effect on forskolin stimulation. PMID:9819198 Palmitoylated GRK6 is 10-fold more active at phosphorylating beta2-adrenergic receptor than nonpalmitoylated wild-type GRK6 or a nonpalmitoylatable mutant GRK6. |
| GO:0004703 G protein-coupled receptor kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA (ARBA/InterPro GPCR kinase family/Rhea/EC 2.7.11.16) GPCR kinase activity. Reason: Core activity. GRK6 phosphorylates agonist-activated GPCRs (beta2-adrenergic receptor in vitro, PMID:9819198), and in rat cells its catalytic activity is required for homologous desensitization (kinase-dead K215R mutant acts as dominant negative; PMID:12810562, PMID:15115810). Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. GPRK subfamily. file:rat/Grk6/Grk6-uniprot.txt Specifically phosphorylates the activated forms of G protein-coupled receptors. |
| GO:0004703 G protein-coupled receptor kinase activity | ISO GO_REF:0000121 | ACCEPT | Summary: ISO GPCR kinase activity from mouse Grk6. Reason: Core activity. GRK6 phosphorylates agonist-activated GPCRs (beta2-adrenergic receptor in vitro, PMID:9819198), and in rat cells its catalytic activity is required for homologous desensitization (kinase-dead K215R mutant acts as dominant negative; PMID:12810562, PMID:15115810). Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Specifically phosphorylates the activated forms of G protein-coupled receptors. PMID:12718862 The present study indicates that postsynaptic D2-like dopamine receptors are physiological targets for GRK6 |
| GO:0004703 G protein-coupled receptor kinase activity | ISO GO_REF:0000121 | ACCEPT | Summary: ISO GPCR kinase activity from human GRK6. Reason: Core activity. GRK6 phosphorylates agonist-activated GPCRs (beta2-adrenergic receptor in vitro, PMID:9819198), and in rat cells its catalytic activity is required for homologous desensitization (kinase-dead K215R mutant acts as dominant negative; PMID:12810562, PMID:15115810). Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Specifically phosphorylates the activated forms of G protein-coupled receptors. PMID:9819198 Palmitoylated GRK6 is 10-fold more active at phosphorylating beta2-adrenergic receptor than nonpalmitoylated wild-type GRK6 or a nonpalmitoylatable mutant GRK6. |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: ATP binding inferred from the protein kinase domain and ATP-binding-site signature. Reason: True of an active protein kinase (the ATP-binding Lys215 is the residue mutated in the dominant-negative K215R construct), but ATP binding is part of the catalytic mechanism rather than an independent function. Supporting Evidence: PMID:12810562 Expression of (K215R)GRK6 increased by approximately 70% the cAMP response to isoproterenol without effect on forskolin stimulation. file:rat/Grk6/Grk6-uniprot.txt Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. GPRK subfamily. |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA cytoplasm; non-palmitoylated GRK6 is cytosolic, palmitoylated GRK6 is membrane-bound. Reason: GRK6 is a peripheral membrane protein: palmitoylation on C-terminal cysteines targets it to membranes where its receptor substrates are, while the non-palmitoylated pool is cytosolic. The cytoplasm row is therefore correct for part of the protein but peripheral to where the core activity is exerted (plasma membrane). Supporting Evidence: PMID:9819198 Palmitoylated GRK6 is associated with the membrane, while nonpalmitoylated GRK6 remains cytosolic. PMID:7961702 Palmitoylation of GRK6 appears essential for membrane association, since palmitoylated kinase was found only in the membrane fraction. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO signal transduction from the GPCR kinase family signature. Reason: GRK6 does not relay signals in a signal transduction pathway; it terminates GPCR signaling by receptor phosphorylation. The specific supported process is GO:0002029 desensitization of G protein-coupled receptor signaling pathway, which the gene already carries with experimental evidence. Proposed replacements: desensitization of G protein-coupled receptor signaling pathway Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Such receptor phosphorylation initiates beta-arrestin-mediated receptor internalization, and signaling events leading to their desensitization. PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. |
| GO:0009966 regulation of signal transduction | IBA GO_REF:0000033 | MODIFY | Summary: IBA regulation of signal transduction; true but general. Reason: Correct but general. GO:0002029 desensitization of G protein-coupled receptor signaling pathway is an is_a descendant of GO:0009966 (checked with OAK) and is the specific process supported by rat and mouse experiments; the gene already carries it. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: RGD:61986 SUPPORTS TRANSFER GRK clade members desensitize GPCR signaling; transfer is sound, only the term is too general. UniProtKB:P43250 SUPPORTS TRANSFER GRK clade members desensitize GPCR signaling; transfer is sound, only the term is too general. MGI:MGI:1347078 SUPPORTS TRANSFER GRK clade members desensitize GPCR signaling; transfer is sound, only the term is too general. Proposed replacements: desensitization of G protein-coupled receptor signaling pathway Supporting Evidence: PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. PMID:15115810 Inhibition of endogenous GRK6 (G-protein-coupled receptor kinase) activity, by the introduction of catalytically inactive (K215R)GRK6, partially reversed the attenuation of agonist-induced responsiveness, whereas overexpression of wild-type GRK6 increased receptor desensitization. |
| GO:0016020 membrane | IEA GO_REF:0000044 | MODIFY | Summary: Membrane, from the UniProt subcellular location "Membrane; Lipid-anchor". Reason: Correct but general. Two independent lines place GRK6 at the plasma membrane: palmitoylation of the C-terminal cysteine cluster is required for membrane association (PMID:7961702, PMID:9819198), and its substrates are agonist-activated cell-surface GPCRs whose phosphorylation at the plasma membrane triggers arrestin binding and internalization. Refine to GO:0005886 plasma membrane. Proposed replacements: plasma membrane Supporting Evidence: file:rat/Grk6/Grk6-uniprot.txt Membrane; Lipid-anchor. PMID:7961702 Palmitoylation of GRK6 appears essential for membrane association, since palmitoylated kinase was found only in the membrane fraction. file:rat/Grk6/Grk6-uniprot.txt Such receptor phosphorylation initiates beta-arrestin-mediated receptor internalization, and signaling events leading to their desensitization. |
| GO:0047696 beta-adrenergic receptor kinase activity | ISO GO_REF:0000121 | ACCEPT | Summary: ISO from human GRK6: beta-adrenergic receptor kinase activity. Reason: GRK6 phosphorylates the beta2-adrenergic receptor in vitro (PMID:9819198), and in rat myometrium endogenous GRK6 is the kinase responsible for homologous beta-AR desensitization (PMID:12810562). GO:0047696 is a sibling (not a descendant) of GO:0004703 in GO (checked with OAK), so it is retained as a substrate-specific activity. Supporting Evidence: PMID:9819198 Palmitoylated GRK6 is 10-fold more active at phosphorylating beta2-adrenergic receptor than nonpalmitoylated wild-type GRK6 or a nonpalmitoylatable mutant GRK6. PMID:12810562 These results strongly suggest that endogenous GRK6 mediate homologous beta-AR desensitization in myometrial cells. |
| GO:0071222 cellular response to lipopolysaccharide | IEP PMID:23359120 Expression of G-protein-coupled receptor kinase 6 (GRK6) aft... | MARK AS OVER ANNOTATED | Summary: GRK6 protein is upregulated in microglia after spinal cord injury and after LPS stimulation. Reason: Expression evidence only: LPS induces GRK6 protein, showing that Grk6 is regulated by the stimulus, not that GRK6 executes a cellular response to LPS. No functional test of GRK6 in the LPS response is reported in the abstract. Supporting Evidence: PMID:23359120 Western blot analysis demonstrated up-regulation in GRK6 protein expression after LPS stimulation was time- and dose-dependent |
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Download this section (compressed HTML)Q: The PMID:12810562 rows are coded IDA, but the abstract reports dominant-negative (K215R) and inhibitory-antibody experiments, which would normally be IMP. Does the full text contain a direct GRK6 kinase or localization assay that justifies IDA?
Q: Which rat GPCRs are preferential GRK6 substrates in vivo (D2-like dopamine receptors, CXCR4, M1 mAChR, beta-adrenergic receptors), and how is specificity divided with GRK2 and GRK5 in the same cells?
Q: Does the RGS-homology domain of GRK6 contribute phosphorylation-independent regulation, as the GRK2 RH domain does through Galpha q/11 binding?
Experiment: Map GRK6-dependent phosphosites on endogenous rat M1 muscarinic and beta2-adrenergic receptors by mass spectrometry after agonist stimulation in cells with Grk6 knockdown versus control.
Type: phosphoproteomics
Experiment: Compare wild-type, palmitoylation-deficient (C561/562/565S) and kinase-dead GRK6 rescue in Grk6-depleted rat myometrial cells to test whether membrane targeting is required for beta-AR desensitization.
Type: site-directed mutagenesis with functional assay
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