Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P67775 (alpha isoform)
 797 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inhibitor-2 (I-2) is the regulatory subunit of the cytosolic ATP-Mg-dependent form of type 1 serine/threonine protein phosphatase and its phosphorylation at Thr-72 by glycogen synthase kinase-3 results in phosphatase activation. Activation of cytosolic type 1 phosphatase has been observed in cells treated with growth factors. Reported here is the phosphorylation and activation of the ATP-Mg-dependent phosphatase by mitogen-activated protein kinase (MAPK). Recombinant I-2 was phosphorylated by activated MAPK to an extent (approximately 0.3 mol of phosphate/mol of polypeptide) similar to that reported for phosphorylation by the alpha isoform of glycogen synthase kinase-3. The phosphorylation of I-2 by MAPK was exclusively at Thr-72, the site involved in the activation of phosphatase. Incubation of MAPK with purified ATP-Mg-dependent phosphatase resulted in phosphorylation of the I-2 component and activation of the phosphatase. Ribosomal S6 protein kinase II (p90rsk) was also able to phosphorylate the recombinant I-2; however, this phosphorylation occurred on serines and had no effect on phosphatase activation. Our data may explain growth factor-induced activation of the ATP-Mg-dependent phosphatase and suggest that MAPK may of cytosolic type 1 phosphatase in response to insulin and/or other growth factors.
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PMID:Phosphorylation and activation of the ATP-Mg-dependent protein phosphatase by the mitogen-activated protein kinase. 762 58

Following LTP induction in freely moving rats, in situ hybridization revealed discrete changes in the expression of one isoform in each of four families of serine/threonine kinases constitutively expressed in the dentate gyrus of the hippocampus. Expression of the alpha isoform of CaMKII showed a transient increase over the soma and a more persistent increase over the dendritic field of dentate granule cells. Of the PKC isoforms, only gamma PKC was up-regulated substantially 2 hr after LTP induction, declining to control levels 48 hr later. An increase in the expression of mRNA for ERK2 and raf-B was seen at 24 hr only. These results show that, during the maintenance phase of LTP in the hippocampus, there are selective increases in the expression of serine/threonine kinases and that these increases have specific and characteristic temporal and spatial profiles.
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PMID:Spatial and temporal changes in signal transduction pathways during LTP. 791 3

The ability of simian virus 40 (SV40) large T antigen to catalyze the initiation of viral DNA replication is regulated by its phosphorylation state. Previous studies have identified the free catalytic subunit of protein phosphatase 2A (PP2Ac) as the cellular phosphatase which can remove inhibitory phosphoryl groups from serines 120 and 123. The catalytic C subunit exists in the cell complexed with a 65-kDa A subunit and one of several B subunits. To determine if any of the holoenzymes could activate T antigen, we tested the ability of the heterodimeric AC and two heterotrimeric ABC forms to stimulate T-antigen function in unwinding the origin of SV40 DNA replication. Only free catalytic subunit C and the heterotrimeric form with a 72-kDa B subunit (PP2A-T72) could stimulate T-antigen-dependent origin unwinding. Both the dimeric form (PP2A-D) and the heterotrimer with a 55-kDa B subunit (PP2A-T55) actively inhibited T-antigen function. We found that PP2A-T72 activated T antigen by dephosphorylating serines 120 and 123, while PP2A-D and PP2A-T55 inactivated T antigen by dephosphorylating the p34cdc2 target site, threonine 124. Thus, alterations in the subunit composition of PP2A holoenzymes have significant functional consequences for the initiation of in vitro SV40 DNA replication. The regulatory B subunits of PP2A may play a role in regulating SV40 DNA replication in infected cells as well.
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PMID:Different oligomeric forms of protein phosphatase 2A activate and inhibit simian virus 40 DNA replication. 800 66

The immunolocalization and substrates of protein phosphatases present in nucleolus were investigated using Swiss 3T3 cells and Novikoff hepatoma ascites cells. The protein phosphatase activity was detected in the extract of the isolated nucleoli and its activity was inhibited by okadaic acid with IC50 value of 160 nM. Immunoblotting assay indicated that PP1c delta but not PP1c alpha, PP1c gamma 1, and PP2Ac was localized in the isolated nucleoli. Confocal microscopy showed that PP1c delta was localized in nucleoli, nuclei, and cytosol, though the intensity of fluorescence at the nucleoli was stronger than that of the cytosol or nuclei. PP1c delta was co-localized with the major nucleolar phosphoprotein B23 at nucleoli. The phosphatase was capable of dephosphorylating several proteins in the nucleolus, including B23. The Km of PP1 for the recombinant B23.1, phosphorylated by endogenous kinase(s), was 3.5 microM. These results indicate that PP1c delta is the major serine/threonine phosphatase present in nucleolus and it dephosphorylates nucleolar phosphoproteins, including B23.
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PMID:The delta isoform of protein phosphatase type 1 is localized in nucleolus and dephosphorylates nucleolar phosphoproteins. 970 75

The alpha isoform of the folate receptor (FR) is a 38-KDa glycosylphosphatidylinositol (GPI) protein which mediates the internalization of folates. The FR amino acid sequence has features typical of GPI-linked proteins, including the presence of a hydrophobic carboxyl-terminus, a hinge region, and a stretch of small and uncharged amino acids. Substitution of predicted cleavage/attachment Ser234 with arginine or threonine, or replacement of Gly235 with proline by site-directed mutagenesis had no effect on GPI processing. In fact, CHO cells transfected with each of the three cDNA variants or with FR wild-type showed comparable amounts of phosphatidylinositol-specific phospholipase C-resistant FR in double-determinant radioimmunoassay. Western blot analysis of total cell lysates from all transfectants consistently revealed the 38-KDa FR band. Deletion of residues 233-237 in the amino-terminal portion of the FR cDNA constructs derived by a polymerase chain reaction strategy abrogated GPI processing, with only a small proportion of the FR remaining in the cytoplasm in four of the five clones tested. This finding suggests that FR residues 233-237 are essential in properly juxtaposing the FR hydrophobic domain. Together, these data support the hypothesis that the postulated Ser234 is not the only potential cleavage/attachment site of the alpha isoform of FR.
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PMID:Molecular requirements for attachment of the glycosylphosphatidylinositol anchor to the human alpha folate receptor. 1002 72

Protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine-specific protein phosphatase, comprises a catalytic subunit and two distinct regulatory subunits, A and B. The primary sequence of the catalytic (C) subunit is highly conserved in evolution, and its function has been shown to be essential in yeast, Drosophila and mice. In many eukaryotes, the C subunit is encoded by at least two nearly identical genes, impeding conventional loss-of-function genetic analysis. We report here the development of a functional complementation assay in S. cerevisiae that has allowed us to isolate dominant-defective alleles of human and Arabidopsis C subunit genes. Wild-type human and Arabidopsis C subunit genes can complement the lethal phenotype of S. cerevisiae PP2A-C mutations. Site-directed mutagenesis was used to create two distinct, catalytically impaired C subunit mutants of the human and Arabidopsis genes. In both cases, expression of the mutant subunit in yeast prevented growth, even in the presence of functional C subunit proteins. This dominant growth defect is consistent with a dominant-interfering mode of action. Thus, we have shown that S. cerevisiae provides a rapid system for the functional analysis of heterologous PP2A genes, and that two mutations that abrogate phosphatase activity exhibit dominant-defective phenotypes in S. cerevisiae.
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PMID:Functional expression of human and Arabidopsis protein phosphatase 2A in Saccharomyces cerevisiae and isolation of dominant-defective mutants. 1039 36

Type 1 serine/threonine protein phosphatases (PP1) are important regulators of many cellular and developmental processes, including glycogen metabolism, muscle contraction, and the cell cycle [1] [2] [3] [4] [5]. Drosophila and humans both have multiple genes encoding PP1 isoforms [3] [6] [7]; each has one beta and several alpha isoform genes (alpha(1), alpha(2), alpha(3) in flies, alpha and gamma in humans; mammalian PP1beta is also known as PP1delta). The alpha/beta subtype differences are highly conserved between flies and mammals [6]. Though all these proteins are >85% identical to each other and have indistinguishable activities in vitro, we show here that the Drosophila beta isoform has a distinct biological role. We show that PP1beta9C corresponds to flapwing (flw), previously identified mutants of which are viable but flightless because of defects in indirect flight muscles (IFMs) [8]. We have isolated a new, semi-lethal flw allele that shows a range of defects, especially in muscles, which break away from their attachment sites and degenerate.
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PMID:Protein phosphatase 1beta is required for the maintenance of muscle attachments. 1071 8

Catalytic domains of the metalloenzymes protein phosphatases (PPP) 1, 2A and 2B (PP1, PP2A and PP2B, respectively) are homologous to approximately 45%, with the residues in the enzymatic centers strictly conserved. PP1, PP2A and PP2B are abundant in cells and they dephosphorylate serine and/or threonine residues in a variety of proteins serving as cellular phospho switches. The active enzymes work as invariant catalytic subunits PP1c, PP2Ac and PP2Bc, respectively, complexed with diverse regulatory subunits, dependent on the enzymes' specific location and biological function. The crystal structures of PP1c and PP2B (calcineurin) heterotetramer calcineurinA x calcineurinB x FKBP x FK506 have been determined. A comparison of the catalytic subunits of both enzymes indicates their significant structural homology and virtual identity within the catalytic centers, each including a set of conservative amino acids, two metal ions and a phosphate; thus confirming a hypothesis on their common enzymatic mechanisms. The elongated substrate cleft at the active centre is kinked by approximately 120 degrees at the active center in its middle and thus divided into a pre-phospho-Ser/Thr (ligand N-terminal) and a post-phospho-Ser/Thr (ligand C-terminal) section. In PP1c the N-terminal section is highly acidic while in PP2Bc is not. This feature is likely pertinent but not sufficient to the enzymes' selectivity, which is also controlled by regulatory subunits, diverse in various tissues. The metalloenzymes in general and PPP in particular are hard to deal with using theoretical simulations due to parameterization problems for the metal cations. In fact, there are only a few PP1c simulations reported, with the metal di-cations treated quite crudely. This is a preliminary work, in which we introduce and test against some experimental evidence a concept of pseudomolecules of proper geometry, composed of double metal (2Zn2+ or 2Mn2+) cation, and the OH- nuclephile incorporated into the PP1c catalytic site. Both models are associated with either the phosphate (a free enzyme) or the phosphorylated dodecapeptide RRRRPpTPAMLFR, an active fragment (residues 29-40) of a regulatory subunit DARPP-32 inhibitor (PP1c-inhibitor complex); four models total. We have parameterized both pseudomolecules within the AMBER force field. Subsequently, using molecular dynamic in water, we have found the free PP1c subunits to be less stable than the complexed ones and we have speculated on possible reasons for this feature.
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PMID:Molecular modeling of the catalytic domain of serine/threonine phosphatase-1 with the Zn2+ and Mn2+ di-nuclear ion centers in the active site. 1081 8

Phosphorylation by cAMP-dependent protein kinase (PKA) regulates a vast number of cellular functions. An important target for PKA in brain and heart is the class C L-type Ca(2+) channel (Ca(v)1.2). PKA phosphorylates serine 1928 in the central, pore-forming alpha(1C) subunit of this channel. Regulation of channel activity by PKA requires a proper balance between phosphorylation and dephosphorylation. For fast and specific signaling, PKA is recruited to this channel by an protein kinase A anchor protein (Davare, M. A., Dong, F., Rubin, C. S., and Hell, J. W. (1999) J. Biol. Chem. 274, 30280-30287). A phosphatase may be associated with the channel to effectively balance serine 1928 phosphorylation by channel-bound PKA. Dephosphorylation of this site is mediated by a serine/threonine phosphatase that is inhibited by okadaic acid and microcystin. We show that immunoprecipitation of the channel complex from rat brain results in coprecipitation of PP2A. Stoichiometric analysis indicates that about 80% of the channel complexes contain PP2A. PP2A directly and stably binds to the C-terminal 557 amino acids of alpha(1C). This interaction does not depend on serine 1928 phosphorylation and is not altered by PP2A catalytic site inhibitors. These results indicate that the PP2A-alpha(1C) interaction constitutively recruits PP2A to the channel complex rather than being a transient substrate-catalytic site interaction. Functional assays with the immunoisolated class C channel complex showed that channel-associated PP2A effectively reverses serine 1928 phosphorylation by endogenous PKA. Our findings demonstrate that both PKA and PP2A are integral components of the class C L-type Ca(2+) channel that determine the phosphorylation level of serine 1928 and thereby channel activity.
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PMID:Protein phosphatase 2A is associated with class C L-type calcium channels (Cav1.2) and antagonizes channel phosphorylation by cAMP-dependent protein kinase. 1098 83

Casein kinase I (CKI) are a family of conserved second messenger-independent serine/threonine protein kinases found in all eukaryotes. The avian and mammalian CKI alpha isoform has four splice variants differing in the presence or absence of 28 amino acids ('(L)' insertion) in the catalytic domain and/or 12 amino acids ('(S)' insertion) in the regulatory domain. Here we report the isolation of cDNAs encoding human CKIalpha(L) and CKIalpha(S). We find human CKIalpha(L) has a preference to phosphorylate phosvitin over casein, with a higher K(m) for casein than phosvitin, the reverse being the case for human CKIalpha(S). Both human CKIalpha(L), and CKIalpha(S) are derived from 4.2-kb mRNA transcripts and 2.4-kb transcripts, the latter probably generated by use of an alternate polyadenylation signal identified in the longer transcripts. The 4. 2-kb transcripts contain six RNA-destabilising AU-rich element (ARE) motifs in the 3'-untranslated region (UTR), while the 2.4-kb transcripts contain a single ARE motif. In vitro analysis of CKI alpha 3'-UTR RNA sequences suggests that in HeLa cells, the longer 3'-UTR transcripts are likely to degrade approximately 13 times faster than the shorter 3'-UTR transcripts. This is the first report of a kinase mRNA containing multiple RNA-destabilising AREs in the longer of two mRNA transcripts.
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PMID:Human CKIalpha(L) and CKIalpha(S) are encoded by both 2.4- and 4. 2-kb transcripts, the longer containing multiple RNA-destablising elements. 1100 13


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