Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Exposure of beta 2-adrenergic receptors (beta 2ARs) to agonists causes a rapid desensitization of the receptor-stimulated adenylyl cyclase response. Phosphorylation of the beta 2AR by several distinct kinases plays an important role in this desensitization phenomenon. In this study, we have utilized purified hamster lung beta 2AR and stimulatory guanine nucleotide binding regulatory protein (Gs), reconstituted in phospholipid vesicles, to investigate the molecular properties of this desensitization response. Purified hamster beta 2AR was phosphorylated by cAMP-dependent protein kinase (PKA), protein kinase C (PKC), or beta AR kinase (beta ARK), and receptor function was determined by measuring the beta 2AR-agonist-promoted Gs-associated GTPase activity. At physiological concentrations of Mg2+ (less than 1 mM), receptor phosphorylation inhibited coupling to Gs by 60% (PKA), 40% (PKC), and 30% (beta ARK). The desensitizing effect of phosphorylation was, however, greatly diminished when assays were performed at concentrations of Mg2+ sufficient to promote receptor-independent activation of Gs (greater than 5 mM). Addition of retinal arrestin, the light transduction component involved in the attenuation of rhodopsin function, did not enhance the uncoupling effect of beta ARK phosphorylation of beta 2AR when assayed in the presence of 0.3 mM free Mg2+. At concentrations of Mg2+ ranging between 0.5 and 5.0 mM, however, significant potentiation of beta ARK-mediated desensitization was observed upon arrestin addition. At a free Mg2+ concentration of 5 mM, arrestin did not potentiate the inhibition of receptor function observed on PKA or PKC phosphorylation. These results suggest that distinct pathways of desensitization exist for the receptor phosphorylated either by PKA or PKC or alternatively by beta ARK.
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PMID:Desensitization of the isolated beta 2-adrenergic receptor by beta-adrenergic receptor kinase, cAMP-dependent protein kinase, and protein kinase C occurs via distinct molecular mechanisms. 134 86

Phosphorylation of the beta-adrenergic receptor (beta AR) is closely associated with homologous desensitization of the beta-adrenergic receptor-coupled adenylate cyclase system. Homologous desensitization and receptor phosphorylation also occur in cell mutants which are deficient in their cAMP-dependent protein kinase (kin- mutant of S49 lymphoma cells). beta AR phosphorylation is mediated by a cAMP-independent protein kinase which phosphorylates the receptor only when it is occupied by a beta-agonist. During the time course of desensitization the beta AR kinase (beta ARK) activity is translocated from a cytoplasmic to a plasma membrane location. beta ARK translocation can also be effected by prostaglandin E1 (PGE1) suggesting that this beta ARK may represent a more general enzyme capable of phosphorylating other adenylate cyclase-coupled receptors. Thus, beta ARK may play a key role in the process of homologous desensitization of adenylate cyclase coupled receptors. Extracellular hormones interact with specific receptors at the outer surface of the plasma membrane and thus initiate a cellular response. One of the best studied transmembrane signalling systems known to be coupled to the occupancy of cell surface receptors is adenylate cyclase. The adenylate cyclase system is composed of various components all of which have been purified to homogeneity (Shorr et al., 1982; Homcy et al., 1983; Benovic et al., 1984; Codina et al., 1984; Northup et al., 1980; Sternweis et al., 1981; Bokoch et al., 1984; Pfeuffer et al., 1985). Initially, agonist binding to the receptor promotes coupling of the occupied receptor to one of the guanine nucleotide binding regulatory proteins. These proteins are members of a family of heterotrimeric proteins consisting of alpha, beta and gamma subunits. Stimulatory receptors like the beta-adrenergic (Cerione et al., 1984) or glucagon (Iyengar et al., 1979) receptors couple to the stimulatory regulatory protein Ns (or Gs) whereas inhibitory receptors like the alpha 2-adrenergic (Jacobs et al., 1976) or M2-muscarinic (Harden et al., 1982) receptors couple to the inhibitory regulatory protein Ni (or Gi). Prolonged exposure to agonist hormones, either stimulatory or inhibitory, results in an attenuation of the response to the hormonal activation, a phenomenon called tachyphylaxis or desensitization (Harden, 1983; Sibley and Lefkowitz, 1985; Sharma et al., 1975). One of the best studied models for desensitization is the beta-adrenergic receptor-coupled adenylate cyclase system. In this system two different forms of desensitization have been characterized.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The beta-adrenergic receptor kinase: role in homologous desensitization in S49 lymphoma cells. 284 12

The beta 2-adrenergic receptor (beta 2AR) belongs to the large family of G protein-coupled receptors. Mutation of tyrosine residue 326 to an alanine resulted in a beta 2AR mutant (beta 2AR-Y326A) that was defective in its ability to sequester and was less well coupled to adenylyl cyclase than the wild-type beta 2AR. However, this mutant receptor not only desensitized in response to agonist stimulation but down-regulated normally. In an attempt to understand the basis for the properties of this mutant, we have examined the ability of this regulation-defective mutant to undergo agonist-mediated phosphorylation. When expressed in 293 cells, the maximal response for phosphorylation of the beta 2AR-Y326A mutant was impaired by 75%. Further characterization of this phosphorylation, using either forskolin stimulation or phosphorylation site-deficient beta 2AR-Y326A mutants, demonstrated that the beta 2AR-Y326A mutant can be phosphorylated by cAMP-dependent protein kinase (PKA) but does not serve as a substrate for the beta-adrenergic receptor kinase 1 (beta ARK1). However, overexpression of beta ARK1 led to the agonist-dependent phosphorylation of the beta 2AR-Y326A mutant and rescue of its sequestration. beta ARK1-mediated rescue of beta 2AR-Y326A sequestration could be prevented by mutating putative beta ARK phosphorylation sites, but not PKA phosphorylation sites. In addition, both sequestration and phosphorylation of the wild-type beta 2AR could be attenuated by overexpressing a dominant-negative mutant of beta ARK1 (C20 beta ARK1-K220M). These findings implicate a role for beta ARK1-mediated phosphorylation in facilitating wild-type beta 2AR sequestration.
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PMID:Role of phosphorylation in agonist-promoted beta 2-adrenergic receptor sequestration. Rescue of a sequestration-defective mutant receptor by beta ARK1. 755 96

Effects of G proteins on the phosphorylation of muscarinic receptors (mAChRs) have been examined. Cerebral but not atrial mAChRs were phosphorylated by any one of three types of protein kinase C and 4-6 mol of phosphate were incorporated per mol of mAChR, mostly in the 12-14 kDa from the carboxyterminus. Atrial mAChRs were better substrates of cAMP-dependent protein kinase than cerebral mAChRs. Phosphorylation of mAChRs by protein kinase C or cAMP-dependent protein kinase was not dependent on the presence of agonists and G proteins except that a slight inhibition by G proteins was observed probably because G proteins were also substrates of the two kinases. Agonist-dependent phosphorylation of atrial mAChRs or recombinant human mAChRs (m2 subtype) by a kinase (mAChR kinase), which is the same or very similar to beta adrenergic receptor kinase (beta ARK), was found to be regulated by the G proteins in a dual manner; stimulation by G protein beta gamma subunits and inhibition by G protein alpha beta gamma trimer. The inhibition by the G protein trimer is restored by addition of guanine nucleotides and is considered to be due to the formation of a ternary complex of agonist, mAChR and guanine nucleotide free G proteins. The stimulation by G protein beta gamma subunits was also observed for the light- or agonist-dependent phosphorylation of rhodopsin and beta AR by the mAChR kinase but not for the light-dependent phosphorylation of rhodopsin by rhodopsin kinase. The phosphorylation by beta ARK 1 was also found to be stimulated by G protein beta gamma subunits. The beta gamma subunit is considered to interact with the extra 130 amino acid residue carboxyterminal tail of beta ARK, which does not exist in rhodopsin kinase, and the interaction results in the activation of the kinase. We may assume that the G protein coupled receptor kinase is an effector of G protein beta gamma subunits and that one of the functions of beta gamma subunits is to stimulate the phosphorylation of G protein coupled receptors thereby facilitating their desensitization.
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PMID:Phosphorylation of muscarinic receptors: regulation by G proteins. 844 23

We recently identified a novel human AMPK family member, ARK5, and discovered that is a major factor in Akt-dependent cancer cell survival and migration activity through activation of MT1-MMPs in vitro. The mRNA expression of other AMPK family members and ARK5 was measured using RT-PCR in human colorectal carcinoma cell lines DLD-1, WiDr, HCT-15, SW620, LoVo, SW480, and mRNA expression of AMPK-alpha1, SNARK, MELK and ARK5, but not AMPK-alpha2, was detected in every line. Quantitative-PCR (Q-PCR) to estimate the amount of ARK5 mRNA expression in the cell lines showed that there is a variety of ARK5 expressions among the cell lines and high expression was observed in a cell line derived from the metastatic lesion, LoVo. To determine the effect of ARK5 overexpression on metastasis in vivo, we established human pancreas cancer cell line PANC-1 stably transfected with ARK5 full-length expression vector (P/ARK) and DLD-1 stably transfected with the same vector (D/ARK). Migration assay showed a remarkable increase in the activity both in P/ARK and D/ARK, and an in vivo metastasis assay showed a marked increase of P/ARK in liver metastasis. Based on these observations, it is suggested that ARK5 expression is involved in cancer invasion and metastasis.
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PMID:Strong association of ARK5 with tumor invasion and metastasis. 1535 11