Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Extracellular calcium rapidly controls PTH secretion through binding to the G protein-coupled calcium-sensing receptor (CASR) expressed in parathyroid glands. Very little is known about the regulatory proteins involved in desensitization of CASR. G protein receptor kinases (GRK) and beta-arrestins are important regulators of agonist-dependent desensitization of G protein-coupled receptors. In the present study, we investigated their role in mediating agonist-dependent desensitization of CASR. In heterologous cell culture models, we found that the transfection of GRK4 inhibits CASR signaling by enhancing receptor phosphorylation and beta-arrestin translocation to the CASR. In contrast, we found that overexpression of GRK2 desensitizes CASR by classical mechanisms as well as through phosphorylation-independent mechanisms involving disruption of Galphaq signaling. In addition, we observed lower circulating PTH levels and an attenuated increase in serum PTH after hypocalcemic stimulation in beta-arrestin2 null mice, suggesting a functional role of beta-arrestin2-dependent desensitization pathways in regulating CASR function in vivo. We conclude that GRKs and beta-arrestins play key roles in regulating CASR responsiveness in parathyroid glands.
Mol Endocrinol 2005 Apr
PMID:Beta-arrestin- and G protein receptor kinase-mediated calcium-sensing receptor desensitization. 1563 45

The melanocortin 1 receptor, a G protein-coupled receptor positively coupled to adenylyl cyclase, is a key regulator of epidermal melanocyte proliferation and differentiation and a determinant of human skin phototype and skin cancer risk. Despite its potential importance for regulation of pigmentation, no information is available on homologous desensitization of this receptor. We found that the human melanocortin 1 receptor (MC1R) and its mouse ortholog (Mc1r) undergo homologous desensitization in melanoma cells. Desensitization is not dependent on protein kinase A, protein kinase C, calcium mobilization, or MAPKs, but is agonist dose-dependent. Both melanoma cells and normal melanocytes express two members of the G protein-coupled receptor kinase (GRK) family, GRK2 and GRK6. Cotransfection of the receptor and GRK2 or GRK6 genes in heterologous cells demonstrated that GRK2 and GRK6 impair agonist-dependent signaling by MC1R or Mc1r. However, GRK6, but not GRK2, was able to inhibit MC1R agonist-independent constitutive signaling. Expression of a dominant negative GRK2 mutant in melanoma cells increased their cAMP response to agonists. Agonist-stimulated cAMP production decreased in melanoma cells enriched with GRK6 after stable transfection. Therefore, GRK2 and GRK6 seem to be key regulators of melanocortin 1 receptor signaling and may be important determinants of skin pigmentation.
Mol Endocrinol 2005 Apr
PMID:Role of G protein-coupled receptor kinases in the homologous desensitization of the human and mouse melanocortin 1 receptors. 1565 23

The mouse 5-hydroxytryptamine4a (5-HT4a) receptor is an unusual member of the G protein-coupled receptor superfamily because it possesses two separate carboxyl-terminal palmitoylation sites, which may allow the receptor to adopt different conformations in an agonist-dependent manner (J Biol Chem 277:2534-2546, 2002). By targeted mutation of the proximal (Cys-328/329) or distal (Cys-386) palmitoylation sites, or a combination of both, we generated 5-HT4a receptor variants with distinct functional characteristics. In this study, we showed that upon 5-HT stimulation, the 5-HT4a receptor undergoes rapid (t(1/2) approximately 2 min) and dose-dependent (EC50 approximately 180 nM) phosphorylation on serine residues by a staurosporine-insensitive receptor kinase. Overexpression of GRK2 significantly reduced the receptor-promoted cAMP formation. The Cys328/329-Ser mutant, which is constitutively active in the absence of ligand, exhibited enhanced receptor phosphorylation under both basal and agonist-stimulated conditions and was more effectively desensitized and internalized via a beta-arrestin-2 mediated pathway compared with the wild-type 5-HT4a. In contrast, G protein activation, phosphorylation, desensitization, and internalization of the other palmitoylation-deficient receptor mutants were affected differently. These findings suggest that palmitoylation plays an important role in modulating 5-HT4a receptor functions and that G protein activation, phosphorylation, desensitization, and internalization depend on the different receptor conformations.
Mol Pharmacol 2005 May
PMID:Palmitoylation of the 5-hydroxytryptamine4a receptor regulates receptor phosphorylation, desensitization, and beta-arrestin-mediated endocytosis. 1568 70

The beta(2)-adrenergic receptor (beta(2)-AR) negatively regulates T cell activity through the activation of the G(s)/adenylyl cyclase/cAMP pathway. beta(2)-AR desensitization, which can be induced by its phosphorylation, may have important consequences for the regulation of T cell function in asthma. In the present study we demonstrate that the C-C chemokine thymus and activation-regulated chemokine (TARC) impairs the ability of beta(2)-agonist fenoterol to activate the cAMP downstream effector cAMP-responsive element binding protein (CREB) in freshly isolated human T cells. The TARC-induced activation of Src kinases resulted in membrane translocation of both G protein-coupled receptor kinase (GRK) 2 and beta-arrestin. Moreover, TARC was able to induce Src-dependent serine phosphorylation of the beta(2)-AR as well as its association with GRK2 and beta-arrestin. Finally, in contrast to CREB, phosphorylation of Src and extracellular signal-regulated kinase was enhanced by fenoterol upon TARC pretreatment. In summary, we show for the first time that TARC exposure impairs beta(2)-AR function in T cells. Our data suggest that this is mediated by Src-dependent activation of GRK2, resulting in receptor phosphorylation, binding to beta-arrestin, and a switch from cAMP-dependent signaling to activation of the MAPK pathway. We propose that aberrant T cell control in the presence of endogenous beta-agonists promotes T cell-mediated inflammation in asthma.
Am J Physiol Lung Cell Mol Physiol 2005 Jul
PMID:Exposure to TARC alters beta2-adrenergic receptor signaling in human peripheral blood T lymphocytes. 1574 41

Immortalization is an early and essential step of human carcinogenesis. Amplification of chromosome 20q has been shown to be a common event in immortalized cells and cancers. We have previously reported that gain and amplification of chromosome 20q is a non-random and common event in immortalized human ovarian surface epithelial (HOSE) cells. The chromosome 20q harbors genes including TGIF2 (20q11.2-q12), AIB1 (20q12), PTPN1 (20q13.1), ZNF217 (20q13.2), and AURKA (20q13.2-q13.3), which were previously reported to be amplified and overexpressed in ovarian cancers. Some of these genes may be involved in immortalization of HOSE cells and represent crucial premalignant changes in ovarian surface epithelium. Investigation of the involvement of these genes was examined in four pairs of pre-crisis (preimmortalized) and post-crisis (immortalized) HOSE cells. Overexpression of AURKA (Aurora kinase A), also known as BTAK and STK15, by both real time-quantitative polymerase chain reaction (RT-QPCR) and Western blotting was detected in all the four immortalized HOSE cells examined while overexpression of AIB1 and ZNF217 was observed in two of four immortalized HOSE cells examined. Overexpression of TGIF2 and PTPN1 was not significant in our immortalized HOSE cell systems. The degree of overexpression of AURKA was shown to be closely associated with the amplification of chromosome 20q in immortalized HOSE cells. Fluorescence in situ hybridization (FISH) with labeled P1 artificial clone (PAC) confirmed the amplification of the chromosomal region (20q13.2-13.3) where AURKA resides. DNA amplification of AURKA was also confirmed using semi-quantitative PCR. Our study showed that amplification and overexpression of AURKA is a common and significant event during immortalization of HOSE cells and may represent an important premalignant change in ovarian carcinogenesis.
Mol Carcinog 2005 Jul
PMID:Amplification and overexpression of aurora kinase A (AURKA) in immortalized human ovarian epithelial (HOSE) cells. 1588 Jul 41

In this study, we investigate the molecular mechanisms by which acute orphanin FQ/nociceptin (OFQ/N), acting through the nociceptin opioid peptide (NOP) receptor, desensitizes the mu-opioid receptor. We described previously the involvement of protein kinase C and G-protein-coupled receptor kinases (GRK) 2 and 3 in OFQ/N-induced mu receptor desensitization. Because phosphorylation of the mu receptor triggers the successive regulatory mechanisms responsible for desensitization, such as receptor uncoupling, internalization, and down-regulation, we investigated the ability of OFQ/N to modulate [d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO)-induced mu receptor phosphorylation in BE(2)-C human neuroblastoma cells transfected with epitope-tagged mu receptors. OFQ/N treatment (100 nM, 60 min) potentiated DAMGO-induced mu receptor phosphorylation; inhibition of GRK2 or protein kinase C concomitant with OFQ/N treatment blocked the OFQ/N-mediated increase in DAMGO-induced phosphorylation. Inclusion of the NOP antagonist peptide III-BTD during OFQ/N pretreatment blocked the potentiation of DAMGO-induced phosphorylation by OFQ/N, which is consistent with the potentiation being mediated via actions of the NOP receptor. In addition, in cells expressing mu receptors in which the GRK-mediated phosphorylation site Ser(375) was mutated to alanine, OFQ/N treatment failed to potentiate DAMGO-induced mu receptor phosphorylation and failed to desensitize the mu receptor. However, DAMGO-induced mu receptor phosphorylation and OFQ/N-induced mu receptor desensitization occurred in cells expressing mu receptors lacking non-GRK phosphorylation sites. These data suggest that OFQ/N binds to NOP receptors and activates protein kinase C, which then increases the ability of GRK2 to phosphorylate the agonist-occupied mu receptor, heterologously regulating homologous mu receptor desensitization.
Mol Pharmacol 2005 Aug
PMID:Orphanin FQ/nociceptin potentiates [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin-Induced mu-opioid receptor phosphorylation. 1589 Aug 42

G protein-coupled receptor kinases (GRKs) regulate seven-transmembrane receptors (7TMRs) by phosphorylating agonist-activated 7TMRs. Recently, we have reported that GRK2 can function as a negative regulator of insulin action by interfering with G protein-q/11 alpha-subunit (Galphaq/11) signaling, causing decreased glucose transporter 4 (GLUT4) translocation. We have also reported that chronic endothelin-1 (ET-1) treatment leads to heterologous desensitization of insulin signaling with decreased tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and Galphaq/11, and decreased insulin-stimulated glucose transport in 3T3-L1 adipocytes. In the current study, we have investigated the role of GRK2 in chronic ET-1-induced insulin resistance. Insulin-induced GLUT4 translocation was inhibited by pretreatment with ET-1 for 24 h, and we found that this inhibitory effect was rescued by microinjection of anti-GRK2 antibody or GRK2 short interfering RNA. We further found that GRK2 mediates the inhibitory effects of ET-1 by two distinct mechanisms. Firstly, adenovirus-mediated overexpression of either wild-type (WT)- or kinase-deficient (KD)-GRK2 inhibited Galphaq/11 signaling, including tyrosine phosphorylation of Galphaq/11 and cdc42-associated phosphatidylinositol 3-kinase activity. Secondly, ET-1 treatment caused Ser/Thr phosphorylation of IRS-1 and IRS-1 protein degradation. Overexpression of KD-GRK2, but not WT-GRK2, inhibited ET-1-induced serine 612 phosphorylation of IRS-1 and restored activation of this pathway. Taken together, these results suggest that GRK2 mediates ET-1-induced insulin resistance by 1) inhibition of Galphaq/11 activation, and this effect is independent of GRK2 kinase activity, and 2) GRK2 kinase activity-mediated IRS-1 serine phosphorylation and degradation.
Mol Endocrinol 2005 Nov
PMID:G protein-coupled receptor kinase 2 mediates endothelin-1-induced insulin resistance via the inhibition of both Galphaq/11 and insulin receptor substrate-1 pathways in 3T3-L1 adipocytes. 1599 3

Myocardial infarction (MI) represents an enormous clinical challenge as loss of myocardium due to ischemic injury is associated with compromised left ventricular (LV) function often leading to acute cardiac decompensation or chronic heart failure. S100A1 was recently identified as a positive inotropic regulator of myocardial contractility in vitro and in vivo. Here, we explore the strategy of myocardial S100A1 gene therapy either at the time of, or 2 h after, MI to preserve global heart function. Rats underwent cryothermia-induced MI and in vivo intracoronary delivery of adenoviral transgenes (4 x 10(10) pfu). Animals received saline (MI), the S100A1 adenovirus (MI/AdS100A1), a control adenovirus (MI/AdGFP), or a sham operation. S100A1 gene delivery preserved global in vivo LV function 1 week after MI. Preservation of LV function was due mainly to S100A1-mediated gain of contractility of the remaining, viable myocardium since contractile parameters and Ca(2+) transients of isolated MI/AdS100A1 myocytes were significantly enhanced compared to myocytes isolated from both MI/AdGFP and sham groups. Moreover, S100A1 gene therapy preserved the cardiac beta-adrenergic inotropic reserve, which was associated with the attenuation of GRK2 up-regulation. Also, S100A1 overexpression reduced cardiac hypertrophy 1 week post-MI. Overall, our data indicate that S100A1 gene therapy provides a potential novel treatment strategy to maintain contractile performance of the post-MI heart.
Mol Ther 2005 Dec
PMID:S100A1 gene therapy preserves in vivo cardiac function after myocardial infarction. 1616 14

Because phospholipase C epsilon (PLC-epsilon) is activated by Galpha(12/13) and Rho family GTPases, we investigated whether these G proteins contribute to the increased inositol lipid hydrolysis observed in COS-7 cells after activation of certain G protein-coupled receptors. Stimulation of inositol lipid hydrolysis by endogenous lysophosphatidic acid (LPA) or thrombin receptors was markedly enhanced by the expression of PLC-epsilon. Expression of the LPA(1) or PAR1 receptor increased inositol phosphate production in response to LPA or SFLLRN, respectively, and these agonist-stimulated responses were markedly enhanced by coexpression of PLC-epsilon. Both LPA(1) and PAR1 receptor-mediated activation of PLC-epsilon was inhibited by coexpression of the regulator of G protein signaling (RGS) domain of p115RhoGEF, a GTPase-activating protein for Galpha(12/13) but not by expression of the RGS domain of GRK2, which inhibits Galpha(q) signaling. In contrast, activation of the G(q)-coupled M1 muscarinic or P2Y(2) purinergic receptor was neither enhanced by coexpression with PLC-epsilon nor inhibited by the RGS domain of p115RhoGEF but was blocked by expression of the RGS domain of GRK2. Expression of the Rho inhibitor C3 botulinum toxin did not affect LPA- or SFLLRN-stimulated inositol lipid hydrolysis in the absence of PLC-epsilon but completely prevented the PLC-epsilon-dependent increase in inositol phosphate accumulation. Likewise, C3 toxin blocked the PLC-epsilon-dependent stimulatory effects of the LPA(1), LPA(2), LPA(3), or PAR1 receptor but had no effect on the agonist-promoted inositol phosphate response of the M1 or P2Y(2) receptor. Moreover, PLC-epsilon-dependent stimulation of inositol phosphate accumulation by activation of the epidermal growth factor receptor, which involves Ras- but not Rho-mediated activation of the phospholipase, was unaffected by C3 toxin. These studies illustrate that specific LPA and thrombin receptors promote inositol lipid signaling via activation of Galpha(12/13) and Rho.
Mol Pharmacol 2006 Jun
PMID:Galpha12/13- and rho-dependent activation of phospholipase C-epsilon by lysophosphatidic acid and thrombin receptors. 1655 9

We previously found that a canine model of selective surgical ventricular denervation (VD), which does not permit increased sympathetic tone during the pathogenesis of heart failure (HF), tolerated the development of HF better than controls. To investigate the cellular mechanisms, we examined cellular contraction and L-type Ca(2+) channel currents (I(Ca)) and their responses to beta-adrenergic receptor (beta-AR) stimulation in left ventricular myocytes from 1) control, 2) VD, 3) HF induced by rapid pacing, and 4) HF induced in VD (VD-HF) dogs. The magnitude of myocyte contraction and rate of relaxation in VD were similar to control but were depressed in both HF and VD-HF. These changes were associated with reduced protein expression of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) and protein kinase A phosphorylated phospholamban (PLB), which was reduced in HF, but essentially abolished in VD-HF. beta-AR kinase (GRK2) was increased in HF but reduced in VD-HF. Basal I(Ca) density did not differ among control, VD, and HF groups, but VD-HF myocytes showed a markedly reduced I(Ca) density (approximately 40%). Compared to controls, the sensitivity of I(Ca) to isoproterenol (ISO), was significantly higher in VD, but reduced in HF. While I(Ca) responses to ISO in VD-HF were maintained at control levels, the amplitude of the ISO-stimulated I(Ca) was significantly smaller (approximately 50%) compared with HF myocytes. The relative decrease in Ca(2+) influx due to downregulation of I(Ca) density may contribute to the cardioprotective effects in VD-HF hearts by preventing Ca(2+) overload during the development of HF. These findings, in combination with the virtual abolition of phosphorylated PLB in VD-HF and the decrease in GRK2, may explain, in part, why VD dogs tolerate the development of HF better than control dogs.
J Mol Cell Cardiol 2006 May
PMID:Down regulation of the L-type Ca2+ channel, GRK2, and phosphorylated phospholamban: protective mechanisms for the denervated failing heart. 1660 Feb 89


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