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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fetal muscle-like acetylcholine receptors (AChRs) are composed of alpha, beta, gamma, delta subunits (gamma-AChRs) and have a rapid half life (t1/2), whereas adult muscle-like AChRs are composed of alpha, beta, epsilon, delta subunits (epsilon-AChRs) and have a slow t1/2. Two populations of AChRs, a slowly degrading population and a rapidly degrading population, have been shown to coexist in the postsynaptic membrane after denervation [In: Penn et al. (Eds.), Myasthenia Gravis and Related Disorders, Vol. 681, NY Acad. Sci., 1993, pp. 155-164]. Treatment of rat myotubes or mouse diaphragm muscle in organ culture with forskolin or cAMP analogues causes and increase in the t1/2 of the slowly degrading population of AChRs with no apparent effect on the rapidly degrading population of AChRs19. In this study, we have investigated the effect of forskolin on the cell surface half-lives of mouse gamma-AChRs, epsilon-AChRs and alpha beta delta complexes stably expressed in mouse fibroblasts. Forskolin had no significant effect on the t1/2 of gamma-AChRs or alpha beta delta complexes. The effect of forskolin on surface AChRs (alpha beta gamma delta) expressed in the C2 muscle cell line was similar to its effect on gamma-AChRs expressed in fibroblasts. In contrast, forskolin stabilized the epsilon-AChRs by approximately 2 fold. We show that the epsilon-subunit is phosphorylated in vivo, phosphorylation of epsilon increases with forskolin treatment, and the forskolin effect is reversible. Although the precise role of epsilon-subunit phosphorylation is yet to be determined, our results support the hypothesis that the slowly degrading population of AChRs consists of epsilon-AChRs and the rapidly degrading population of AChRs consists of gamma-AChRs.
Brain Res Mol Brain Res 1994 Oct
PMID:Forskolin stabilizes epsilon subunit-containing acetylcholine receptors. 785 59

To elucidate the role of protein kinase C (PKC) in nerve growth factor (NGF)-induced differentiation, PMA downregulation of pheochromocytoma (PC12) cells was undertaken. Prolonged treatment (2 d) of PC12 cells with PMA (1 microM) resulted in depleting the cells of alpha, beta, delta, and epsilon-PKC isoforms, but had no effect on the expression of the atypical PKC isoform zeta. PC12 cells, which expressed only PKC zeta, were evaluated for their responses to NGF. Removal of the PMA-sensitive PKC isoforms enhanced the ability of NGF to promote neurite extension. Both the percentage cells with neurites and length of neurites were increased in the PMA-treated cells, whereas no effect was observed on the number of neurites per cell or branching of individual neurites. In addition, PMA downregulation resulted in an increase in the incorporation of 3H-thymidine without any significant effect on the expression of c-fos. Addition of NGF to PC12 cells depleted of the PMA-sensitive PKC isoforms resulted in the activation of PKC zeta (Wooten et al., 1994). To test whether the transient activation of PKC zeta is a necessary component of the neuritogenetic pathway, antisense oligonucleotide strategy was utilized to remove this particular PKC isoform. The addition of a 20-bp antisense oligonucleotide directed against the 5' coding sequence of PKC zeta attenuated NGF-induced neurite outgrowth in PC12 cells lacking PMA-sensitive PKC isoforms. Sense oligonucleotide directed at the same site was without effect on NGF responses. These data indicate that PKC zeta comprises a portion of the NGF pathway and underscores the importance of this isoform in neuronal differentiation. Moreover, these findings demonstrate that the PMA-insensitive pathway, which was previously characterized as PKC-independent, and the neurite induction pathway are synonymous and mediated by PKC zeta.
J Mol Neurosci 1994
PMID:Nerve growth factor-induced differentiation of PC12 cells employs the PMA-insensitive protein kinase C-zeta isoform. 785 79

Three distinct hepatocyte nuclear factor 3 (HNF-3) proteins (alpha, beta, and gamma) are known to regulate the transcription of numerous liver-specific genes. The HNF-3 proteins bind to DNA as monomers through a winged-helix motif, which is also utilized by a number of developmental regulators, including the Drosophila homeotic fork head (fkh) protein. We have previously characterized a strong-affinity HNF-3S site in the transthyretin (TTR) promoter region which is essential for expression in human hepatoma (HepG2) cells. In the current study, we identify an activating protein 1 (AP-1) site which partially overlaps the HNF-3S sequence in the TTR promoter. We show that in HepG2 cells the AP-1 sequence confers 12-O-tetradecanoylphorbol-13-acetate inducibility to the TTR promoter and contributes to normal TTR transcriptional activity. We also demonstrate that the HNF-3 proteins and AP-1 bind independently to the TTR AP-1-HNF-3 site, and cotransfection experiments suggest that they do not cooperate to activate an AP-1-HNF-3 reporter construct. In addition, 12-O-tetradecanoylphorbol-13-acetate exposure of HepG2 cells results in a reciprocal decrease in HNF-3 alpha and -3 gamma expression which may facilitate interaction of AP-1 with the TTR AP-1-HNF-3 site. In order to explore the role of HNF-3 in the liver, we have examined expression patterns of TTR and HNF-3 during the acute-phase response and liver regeneration. Partial hepatectomy produced minimal fluctuation in HNF-3 and TTR expression, suggesting that HNF-3 expression is not influenced by proliferative signals induced during liver regeneration. In acute-phase livers, we observed a dramatic reduction in HNF-3 alpha expression which correlates with a decrease in the expression of its target gene, the TTR gene. Furthermore, consistent with previous studies, the acute-phase livers are induced for c-jun but not c-fos expression. We propose that the reduction in TTR gene expression during the acute phase is likely due to lower HNF-3 alpha expression levels and that the induction of primarily c-jun homodimers, which are poor transcriptional activators, is insufficient to maintain normal TTR expression levels. We also discuss the role of reduced HNF-3 alpha expression in mediating decreased transcription of HNF-3 target genes which respond negatively to cytokine signalling.
Mol Cell Biol 1995 Mar
PMID:Decreased expression of hepatocyte nuclear factor 3 alpha during the acute-phase response influences transthyretin gene transcription. 786 29

The PKC1 gene of the budding yeast Saccharomyces cerevisiae encodes a homolog of the alpha, beta, and gamma isoforms of mammalian PKC that is essential for cell growth. Loss of PKC1 function results in a cell lysis defect that is suppressed by osmotic stabilizing agents, suggesting a defect in cell wall integrity. In this study, we show that Pkc1p-depleted cells develop holes in their cell walls positioned at their bud tips, the site to which growth is focused during polarized cell growth. This result suggests that pkc1 mutants are deficient in the process of cell wall remodeling during growth. In further support of this model, cells bearing a pkc1 delta mutation, allowed to proliferate in the presence of osmotic stabilizing agents, possessed cell walls that were only 60% as thick as wild-type cell walls. This diminution in cell wall material affected both the beta-glucan layer and the mannoprotein layer. We have exploited the cell lysis defect of pkc1 mutants to identify genes that function within the same signalling pathway at points downstream of PKC1. These genes comprise a protein kinase cascade that culminates in the activation of the MAP kinase homolog Mpk1p. The proposed order of protein kinase function, based on genetic experiments, is Pkc1p to Bck1p to Mkk1/2p to Mpk1p. Consistent with the proposed model, Pkc1p selectively phosphorylates Bck1p in vitro and Mpk1p protein kinase activity requires a functional BCK1 gene.
Cell Mol Biol Res 1994
PMID:Dissecting the protein kinase C/MAP kinase signalling pathway of Saccharomyces cerevisiae. 787

Detoxification of cyanide is catalyzed by a sulfurtransferase, rhodanese, a phosphoprotein regulated by unknown protein kinases. In this study, we determined if a Ca2+/phospholipid-modulated phosphotransferase, protein kinase C (PKC) could modify rhodanese activity. Thiocyanate (SCN-) production as an estimate of rhodanese activity in vitro was measured in the presence or absence of exogenously added purified PKC, or 12-O-tetradecanoylphorbol acetate (TPA), a pharmacologic activator of the endogenous PKC. HI-6 (1-(2-(hydroximino)methyl))pyridinium-2-(4-(aminocarbonyl) pyridinium dimethylether) is an oxime that may dephosphorylate phosphoproteins due to the proposed phosphatase-like activity of the oximes. We examined HI-6's effect on rhodanese-catalyzed SCN- production. Bovine kidney rhodanese (0.40 mg/ml protein) was reacted with 4 mM KCN and SCN- production determined spectrophotometrically following the method of Westley (1981). Preincubating rhodanese with 20 or 100 ng of purified PKC (alpha, beta, gamma isozymes) for 5 min before initiating the reaction with 4 mM KCN as the substrate increased SCN- production by 17 or 40%, respectively, over the control (P < 0.05). Rhodanese formation of SCN- decreased when the preincubation was conducted with 1 nM or 100 nM of TPA. With HI-6 at 1 or 10 microM used in place of PKC, or TPA, rhodanese activity was increased by 6 or 14% (P < 0.05), respectively, compared to control. Under the conditions examined, exogenous PKC acting as a possible phosphate acceptor, and HI-6, a potential dephosphorylating compound, increased rhodanese activity. These data are consistent with the observation that rhodanese can exist as a phosphorylated enzyme which is not active and a dephosphorylated form which is active. It is suggested that addition of purified, exogenous PKC may accept phosphate from phosphorylated rhodanese or HI-6 may dephosphorylate rhodanese, both of which stimulate the conversion of cyanide anion to the less toxic SCN-. These observations support the possibility that rhodanese may be regulated by protein phosphorylation and treatments that alter the phosphorylation state of rhodanese may affect cyanide detoxification via SCN- formation.
Res Commun Mol Pathol Pharmacol 1994 Nov
PMID:Protein kinase C modulation of rhodanese-catalyzed conversion of cyanide to thiocyanate. 788 66

The profiles of the calcium-dependent protein kinase C (PKC) isozymes alpha, beta, and gamma were examined in subcellular fractions from Fischer 344 rat liver during the early stages (48 h, 96 h, 7 d, and 60 d) of diethylnitrosamine (DEN)-induced carcinogenesis, using the Solt-Farber "resistant hepatocyte" model (DEN-2-acetylaminofluorene-partial hepatectomy; DEN-AAF-PH), and then related to the presence of focal or nodular gamma-glutamyl transpeptidase (GGT)-positive morphologic changes in the liver. After DEAE and hydroxyapatite column chromatography, two peaks, immunologically identified as PKC-alpha and -beta isoforms, were detected in the liver of normal (alpha/beta ratio = 4.0) and treated rats. In DEN-AAF-PH hepatocarcinogenesis an increase in PKC-alpha expression was found after PH (+43 +/- 19% at 48 h, alpha/beta ratio = 5.1; +125 +/- 25% at 96 h, alpha/beta ratio = 4.8), whereas the PKC-beta isoform appeared less significantly modified (+11 +/- 3% at 48 h and +89 +/- 17% at 96 h). Seven and 60 days after PH, a marked increase in the PKC-alpha (+96 +/- 20% and +150 +/- 48%, respectively) and PKC-beta isoforms (+158 +/- 41%, alpha/beta ratio = 3.1 and +130 +/- 26%, alpha/beta ratio = 4.4, respectively), occurred along with the appearance of GGT-positive altered hepatic foci and nodules in the liver sections. Sham hepatectomy caused PKC-alpha and -beta isoform activities similar to those of normal controls. In contrast, saline-AAF-PH-treated rats had downregulation of PKC-alpha after PH (alpha/beta ratio = 1.8 at 96 h), possibly due to the mitoinhibitory effect of the carcinogen AAF on normal uninitiated hepatocytes. Immunohistochemical analysis with monoclonal antibodies to PKC-alpha and -beta revealed diffuse positive cytoplasmic signals in GGT-positive foci and nodules in rat liver. Taken together, these preliminary results, using the Solt-Farber model of liver carcinogenesis, suggest a role for PKC in tumor promotion. They also suggest that the PKC-alpha isoform may play a specific role in clonal expansion of DEN-initiated hepatocytes after PH.
Mol Carcinog 1993
PMID:Analysis of calcium-dependent protein kinase C isoforms in the early stages of diethylnitrosamine-induced rat hepatocarcinogenesis. 790 65

Holophosphorylase kinase was digested with Glu-C specific protease; from the peptide mixture calmodulin binding peptides were isolated by affinity chromatography and identified by N-terminal sequence analysis. Two peptides originating from the alpha subunit, having a high tendency to form a positively charged amphiphilic helix and containing tryptophane, were synthesized. Additionally, a homologous region of the beta subunit and a peptide from the alpha subunit present in a region deleted in the alpha' isoform were also selected for synthesis. Binding stoichiometry and affinity were determined by following the enhancement in tryptophane fluorescence occurring upon 1:1 complex formation between these peptides and calmodulin. Finally, Ca2+ binding to calmodulin in presence of peptides was measured. By this way, the peptides alpha 542-566, alpha 547-571, alpha 660-677 and beta 597-614 have been found to bind specifically to calmodulin. Together with previously predicted and synthesized calmodulin binding peptides four calmodulin binding regions have been characterized on each the alpha and beta subunits. It can be concluded that endogenous calmodulin can bind to two calmodulin binding regions in gamma as well as to two regions in alpha and beta. Exogenous calmodulin can bind to two regions in alpha and in beta. A binding stoichiometry of 0.8 mol of calmodulin/alpha beta gamma delta promoter of phosphorylase kinase has been determined by inhibiting the ubiquitination of calmodulin with phosphorylase kinase. Phosphorylase kinase is half maximally activated by 23 nM calmodulin which is in the affinity range of calmodulin binding peptides from beta to calmodulin. Therefore, binding of exogenous calmodulin to beta activates the enzyme. A model for switching endogenous calmodulin between alpha, beta and gamma and modulation of ATP binding to alpha as well as Mg2+/ADP binding to beta by calmodulin is presented.
Mol Cell Biochem 1993 Nov
PMID:Interaction sites on phosphorylase kinase for calmodulin. 793 51

By sequencing the central region of the cucumopine-type T-DNA of Agrobacterium rhizogenes strain 2659, we identified three open reading frames homologous, to different extents, to ORFs 10, 11 and 12 (rolA, B and C) of the agropine-type (1855) T-DNA. Recombinant Agrobacterium strains encompassing the ORFs of 2659 T-DNA--which we refer to as rol alpha, beta and gamma--were utilized to infect carrot discs and to obtain transgenic tobacco plants, in order to compare the morphogenetic capabilities to those of the 1855 rol genes. Moreover, a long segment of the 5' non-coding region of rol alpha and rol beta was fused to the GUS reporter gene and the pattern of expression and the responsiveness to auxin of the constructs was analysed in transgenic tobacco. Differences in the auxin requirement for root induction between the 2659 rol genes and their respective 1855 counterparts were pinpointed. These differences are not due to gene regulation and presumably reflect functional differences in the proteins encoded. Differences were also observed in the pattern of expression of rol beta in roots of transgenic plants, as compared to rolB. In addition, the pattern of expression of rol alpha-GUS construct in roots was found to be analogous to that observed for a construct driven by two of the five regulatory domains of the rolB promoter.
Plant Mol Biol 1994 Oct
PMID:rol genes of Agrobacterium rhizogenes cucumopine strain: sequence, effects and pattern of expression. 794 87

Using systematic combination of alpha 1, alpha 3, and alpha 5 with beta 1, beta 2, and beta 3, together with gamma 1, gamma 2, and gamma 3, we have investigated the contributions of the various alpha, beta, and gamma subunits to the pharmacology of gamma-aminobutyric acid (GABA)A agonists. We have characterized GABA, (RS)-dihydromuscimol, piperidine-4-sulfonic acid, and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol with recombinant human GABAA receptors expressed in Xenopus oocytes. Our observations indicate that the alpha subunit is the major determinant of efficacy for partial GABAA agonists. When alpha 1 and alpha 3 or alpha 1 and alpha 5 are coexpressed, the alpha 1 subunit determines the maximum efficacy, whereas the affinity is determined by the entire combination of subunits. Thus, the results of the present study demonstrate that the pharmacology of GABAA agonists is dependent on the subunit composition of the GABAA receptor complex. Functional GABAA receptors containing two different alpha subunits show pharmacological profiles distinctly different from those of receptors containing a single alpha subtype, indicating that two different alpha subunits can be coexpressed in one functional GABAA receptor complex.
Mol Pharmacol 1994 Nov
PMID:Molecular pharmacology of gamma-aminobutyric acid type A receptor agonists and partial agonists in oocytes injected with different alpha, beta, and gamma receptor subunit combinations. 796 86

We have used transient expression in COS cells of the subunits of the nicotinic acetylcholine receptor (AChR) from mouse skeletal muscle to investigate the role of transmembrane and cytoplasmic domains of the delta subunit in assembly of the AChR. When chimeric subunits whose extracellular amino- and carboxyl-terminal domains were from the delta subunit and whose transmembrane and cytoplasmic domains were from either the beta, gamma, or epsilon subunit were expressed with alpha, beta, and epsilon subunits, alpha-bungarotoxin-binding activity appeared on the surface of the transfected cells. The resulting receptor complexes each had sedimentation constants resembling those of the native AChR, consistent with a pentameric structure. Further investigation of the delta beta chimeric subunit showed that it formed a heterodimer with the alpha subunit and that the resulting subunit bound d-tubocurarine with an affinity similar to that of the alpha delta heterodimer; delta beta also formed a heterodimer with a form of the alpha subunit that is truncated after the first transmembrane domain. A heterodimer formed from the epsilon beta and alpha subunits also bound d-tubocurarine with an affinity similar to that of the alpha epsilon heterodimer. When both epsilon beta and delta beta subunits were substituted for the epsilon and delta subunits, respectively, a receptor complex was formed whose structure appeared to be alpha 2 beta(epsilon beta)(delta beta). These results show that, as with the epsilon subunit, the identity of the delta subunit in AChR assembly arises from the extracytoplasmic domains of the subunit.
Mol Pharmacol 1994 Nov
PMID:Amino- and carboxyl-terminal domains specify the identity of the delta subunit in assembly of the mouse muscle nicotinic acetylcholine receptor. 796 87


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