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FEBS Letters Apr 1992The phosphorylation and dephosphorylation of the 25 kDa mRNA cap binding protein eukaryotic initiation factor-4E (eIF-4E) is regulated during different physiologic and... (Comparative Study)
Comparative Study
The phosphorylation and dephosphorylation of the 25 kDa mRNA cap binding protein eukaryotic initiation factor-4E (eIF-4E) is regulated during different physiologic and pathophysiologic states that include cell growth and the late phase of adenovirus infection. We have found that okadaic acid is much more effective in increasing the phosphorylated fraction of eIF-4E than phorbol 12-myristate 13-acetate in Hep G2 cells. Phosphoprotein phosphatase 2A dephosphorylated eIF-4E isolated from both phorbol 12-myristate 13-acetate- or okadaic acid-treated cells, whereas alkaline and acid phosphatase were relatively ineffective. The ability of purified [35S]eIF-4E isolated from okadaic acid-treated cells to bind mRNA caps was compared to phosphoprotein phosphatase 2A-treated [35S]eIF-4E and found to be no different. This suggests that alternative explanations for the previously observed effects of eIF-4E phosphorylation on protein synthesis must be considered. In addition, our results indicate that the in vivo phosphorylation of eIF-4E is not catalyzed solely by protein kinase C.
Topics: Ethers, Cyclic; Eukaryotic Initiation Factor-4E; Humans; Liver; Models, Biological; Okadaic Acid; Peptide Initiation Factors; Phosphoprotein Phosphatases; Phosphorylation; Protein Phosphatase 2; RNA Caps; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured
PubMed: 1333409
DOI: 10.1016/0014-5793(92)80200-z -
Molecular and Cellular Biochemistry May 1998Protein Phosphatase-1 (PP-1) appears to be the key component of the insulin signalling pathway which is responsible for bridging the initial insulin-simulated... (Review)
Review
Protein Phosphatase-1 (PP-1) appears to be the key component of the insulin signalling pathway which is responsible for bridging the initial insulin-simulated phosphorylation cascade with the ultimate dephosphorylation of insulin sensitive substrates. Dephosphorylations catalyzed by PP-1 activate glycogen synthase (GS) and simultaneously inactivate phosphorylase a and phosphorylase kinase promoting glycogen synthesis. Our in vivo studies using L6 rat skeletal muscle cells and freshly isolated adipocytes indicate that insulin stimulates PP-1 by increasing the phosphorylation status of its regulatory subunit (PP-1G). PP-1 activation is accompanied by an inactivation of Protein Phosphatase-2A (PP-2A) activity. To gain insight into the upstream kinases that mediate insulin-stimulated PP-1G phosphorylation, we employed inhibitors of the ras/MAPK, PI3-kinase, and PKC signalling pathways. These inhibitor studies suggest that PP-1G phosphorylation is mediated via a complex, cell type specific mechanism involving PI3-kinase/PKC/PKB and/or the ras/MAP kinase/Rsk kinase cascade. cAMP agonists such as SpcAMP (via PKA) and TNF-alpha (recently identified as endogenous inhibitor of insulin action via ceramide) block insulin-stimulated PP-1G phosphorylation with a parallel decrease of PP-1 activity, presumably due to the dissociation of the PP-1 catalytic subunit from the regulatory G-subunit. It appears that any agent or condition which interferes with the insulin-induced phosphorylation and activation of PP-1, will decrease the magnitude of insulin's effect on downstream metabolic processes. Therefore, regulation of the PP-1G subunit by site-specific phosphorylation plays an important role in insulin signal transduction in target cells. Mechanistic and functional studies with cell lines expressing PP-1G subunit site-specific mutations will help clarify the exact role and regulation of PP-1G site-specific phosphorylations on PP-1 catalytic function.
Topics: Animals; Humans; Insulin; Models, Biological; Phosphoprotein Phosphatases; Protein Phosphatase 1; Protein Phosphatase 2; Signal Transduction; Structure-Activity Relationship
PubMed: 9609113
DOI: No ID Found -
British Journal of Pharmacology Jun 2012The MMPs and their inhibitors [tissue inhibitor of MMPs (TIMPs)] form the mainstay of extracellular matrix homeostasis. They are expressed in response to numerous... (Review)
Review
The MMPs and their inhibitors [tissue inhibitor of MMPs (TIMPs)] form the mainstay of extracellular matrix homeostasis. They are expressed in response to numerous stimuli including cytokines and GPCR activation. This review highlights the importance of adrenoceptors and phosphoprotein phosphatases (PPP) in regulating MMPs in the cardiovascular system, which may help explain some of the beneficial effects of targeting the adrenoceptor system in tissue remodelling and will establish emerging crosstalk between these three systems. Although α- and β-adrenoceptor activation increases MMP but decreases TIMP expression, MMPs are implicated in the growth stimulatory effects of adrenoceptor activation through transactivation of epidermal growth factor receptor. Furthermore, they have recently been found to catalyse the proteolysis of β-adrenoceptors and modulate vascular tone. While the mechanisms underpinning these effects are not well defined, reversible protein phosphorylation by kinases and phosphatases may be key. In particular, PPP (Ser/Thr phosphatases) are not only critical in resensitization and internalization of adrenoceptors but also modulate MMP expression. The interrelationship is complex as isoprenaline (ISO) inhibits okadaic acid [phosphoprotein phosphatase type 1/phosphoprotein phosphatase type 2A (PP2A) inhibitor]-mediated MMP expression. While this may be simply due to its ability to transiently increase PP2A activity, there is evidence for MMP-9 that ISO prevents okadaic acid-mediated expression of MMP-9 through a β-arrestin, NF-κB-dependent pathway, which is abolished by knock-down of PP2A. It is essential that crosstalk between MMPs, adrenoceptors and PPP are investigated further as it will provide important insight into how adrenoceptors modulate cardiovascular remodelling, and may identify new targets for pharmacological manipulation of the MMP system.
Topics: Adrenergic Agonists; Adrenergic Antagonists; Animals; Enzyme Activation; Enzyme Inhibitors; Gene Expression Regulation, Enzymologic; Humans; Matrix Metalloproteinase Inhibitors; Matrix Metalloproteinases; Molecular Targeted Therapy; Phosphoprotein Phosphatases; Phosphorylation; Protein Processing, Post-Translational; Protein Transport; Proteolysis; Receptors, Adrenergic; Signal Transduction
PubMed: 22364165
DOI: 10.1111/j.1476-5381.2012.01917.x -
Trends in Endocrinology and Metabolism:... 2001Protein phosphatase 5 (PP5) possesses unique biochemical properties, which include its tetratricopeptide repeat (TPR) targeting/regulatory domain and its ability to be... (Review)
Review
Protein phosphatase 5 (PP5) possesses unique biochemical properties, which include its tetratricopeptide repeat (TPR) targeting/regulatory domain and its ability to be activated by lipids. PP5 has been studied as a paradigm for TPR protein structure and function. Roles for PP5 in signal transduction are emerging: from cell cycle regulation and signaling by nuclear receptors, to possible regulation of membrane receptors and ion channels.
Topics: Animals; Cell Cycle; Humans; Nuclear Proteins; Phosphoprotein Phosphatases; Potassium Channels; Signal Transduction
PubMed: 11137038
DOI: 10.1016/s1043-2760(00)00335-0 -
Frontiers in Bioscience (Landmark... Jan 2012Wip1 (PPM1D) is a stress responsive PP2C phosphatase that plays a key role in stress signaling. Although originally identified as a gene induced by p53 after genotoxic... (Review)
Review
Wip1 (PPM1D) is a stress responsive PP2C phosphatase that plays a key role in stress signaling. Although originally identified as a gene induced by p53 after genotoxic stress, we now know that Wip1 expression is additionally regulated by other mechanisms. Wip1 is not only a target of p53, but is also a target of other transcription factors, including Estrogen Receptor-alpha and NF-kappaB. Additionally, Wip1 expression is regulated by post-transcriptional mechanisms such as mRNA stabilization and alternative splicing. Upon induction, Wip1 dampens the stress response by dephosphorylating and inactivating proteins such as p53, p38 MAPK, and ATM, usually as part of a negative feedback loop. As a result, Wip1 functions to abrogate cell cycle checkpoints and inhibit senescence, apoptosis, DNA repair, and the production of inflammatory cytokines. Furthermore, Wip1 is overexpressed in several types of human cancers and has oncogenic functions. The regulation of Wip1, the role of Wip1 in stress signaling, and the cooperation of Wip1 with oncogenes in promoting tumorigenesis will be discussed in this review.
Topics: Gene Expression Regulation, Enzymologic; Humans; Phosphoprotein Phosphatases; Protein Phosphatase 2C; Stress, Physiological
PubMed: 22201816
DOI: 10.2741/3999 -
European Journal of Biochemistry Dec 1979A metal-ion-independent, nonspecific phosphoprotein phosphatase (Mr = 35000) which represents the major phosphorylase phosphatase activity in bovine adrenal cortex has...
A metal-ion-independent, nonspecific phosphoprotein phosphatase (Mr = 35000) which represents the major phosphorylase phosphatase activity in bovine adrenal cortex has been purified to apparent homogeneity. An alkaline phosphatase activity (p-nitrophenyl phosphate as a substrate) of the same molecular weight, which requires both a metal ion (Mg2+ greater than Mn2+ greater than Co2+) and a sulfhydryl compound for activity, has been found to co-purify with the phosphoprotein phosphatase throughout the purification procedures. Characterization of the phosphoprotein and the alkaline phosphatase activities with respect to their catalytic properties, substrate and metal ion specificities, relationship with large molecular forms of the enzymes and responses to various effectors has been carried out. The results indicate that the phosphoprotein phosphatase can be converted by pyrophosphoryl compounds (e.g. PPi and ATP) to a metal-ion-dependent form which, subsequently, can be reactivated by Co2+ greater than Mn2+ but not by Mg2+ or Zn2+. The results also indicate that, although the phosphoprotein and the alkaline phosphatase activities are closely associated, they exhibit distinct physical and catalytic properties. Discussions concerning whether these two activities represent two different forms of the same protein or two different yet very similar polypeptide chains have been presented.
Topics: Adrenal Cortex; Alkaline Phosphatase; Animals; Calcium; Cattle; Cobalt; Dithiothreitol; Kinetics; Magnesium; Manganese; Molecular Weight; Phosphoprotein Phosphatases; Phosphorylase Phosphatase
PubMed: 230963
DOI: 10.1111/j.1432-1033.1979.tb04251.x -
Molecular and Cellular Biochemistry Jan 1982The catalytic subunit of phosphoprotein phosphatase (Mr = 35,000) is inactivated by phosphate compounds such as trimetaphosphate, PPi, and ATP. The inactivation of...
The catalytic subunit of phosphoprotein phosphatase (Mr = 35,000) is inactivated by phosphate compounds such as trimetaphosphate, PPi, and ATP. The inactivation of phosphoprotein phosphatase by these phosphate compounds is time- and concentration-dependent, is not reversed by dilution or gel filtration and is protected by Pi. A dissociation constant for the enzyme-trimetaphosphate complex and a rate constant for the reaction were calculated to be 4.6 x 10(-4) M and 0.29 min-1, respectively. The inactivation of phosphatase by PPi and ATP shows more complex kinetics than that by trimetaphosphate. The addition of EDTA to PPi and ATP exhibits more potent inactivation, even though EDTA alone does not inactivate phosphatase. This phosphoprotein phosphatase is not labeled by [gamma-32P]ATP. The inactivation of phosphatase by PPi or ATP can only be reversed by Mn2+ or Co2+, among all other metals or cationic compounds tried. The reactivation also requires sulfhydryl compounds. The effectiveness of sulfhydryl compounds follows the order: dithioerythritol greater than mercaptoethanol greater than cysteine. Glutathione was without effect. Metal analysis of the catalytic subunit did not reveal any significant amounts of Ca, Cd, Co, Cu, Fe, Mg, Mn, Ni, Sn, or Zn. Phosphoprotein phosphatase activity from zinc-deficient rat livers also eliminated the possibility of this phosphatase being a zinc metalloenzyme. Inactivation does not seem to be due to a loss of a critical metal ion. Other mechanisms for inactivation are presented.
Topics: Animals; Cations, Divalent; Enzyme Activation; Kinetics; Macromolecular Substances; Molecular Weight; Muscles; Phosphates; Phosphoprotein Phosphatases; Rabbits; Rats; Sulfhydryl Compounds; Zinc
PubMed: 6278282
DOI: 10.1007/BF00223535 -
The Biochemical Journal Nov 1961
Topics: Brain; Phosphoprotein Phosphatases; Phosphoric Monoester Hydrolases
PubMed: 14493847
DOI: 10.1042/bj0810339 -
Biochimica Et Biophysica Acta Jul 1979Using 32P-labeled phosphocasein or phosphohistones as exogenous substrates it was possible to detect a phosphoprotein phosphatase activity on the outer surface of intact...
Using 32P-labeled phosphocasein or phosphohistones as exogenous substrates it was possible to detect a phosphoprotein phosphatase activity on the outer surface of intact normal and transformed 3T3 fibroblasts. Incubation of monolayers of intact cells in buffered salt solution with the radioactively labeled substrate resulted in the release of alkali-labile 32P counts into the surrounding medium. The reaction was: (a) linear with time (at least up to 20 min); (b) proportional to the cell density; (c) dependent on the temperature and pH of the incubation medium; (d) stimulated by K+; and (e) inhibited by sodium fluoride, inorganic pyrophosphate, zinc chloride and relatively impermeant sulfhydryl reagents. Less than 2% of the externally located phosphoprotein phosphatase activity was detectable in pooled cell-free washings of the intact cell monolayer. Phosphocasein did not cause any detectable leakage of intracellular lactate dehydrogenase or soluble phosphoprotein phosphatase activity into the external medium; incubation of the cells with phosphohistones, on the other hand, resulted in appreciable leakage of both these cytoplasmic activities. Neoplastic transformation was associated with a nearly two-fold decrease in the activity of the surface phosphoprotein phosphatase. Addition of serum to either non-transformed 3T3 or spontaneously transformed 3T6 cells resulted in a rapid and remarkeable drop in the cell surface dephosphorylating activity. Acrylamide gel electrophoresis of the dephosphorylated casein or histone substrate revealed no proteolytic degradation or change in electrophoretic mobility. The intact cells showed no damage upon microscopic examination as a result of exposure to phosphocasein or phosphohistones.
Topics: Animals; Cattle; Cell Line; Cell Membrane; Cell Transformation, Neoplastic; Cytoplasm; Enzyme Activation; Fibroblasts; L-Lactate Dehydrogenase; Membrane Proteins; Mice; Phosphoprotein Phosphatases
PubMed: 226167
DOI: 10.1016/0304-4165(79)90080-1 -
FEBS Letters Jun 2005Protein phosphatase 4 (Ppp4) is a ubiquitous serine/threonine phosphatase in the PPP family that is now recognised to regulate a variety of cellular functions... (Review)
Review
Protein phosphatase 4 (Ppp4) is a ubiquitous serine/threonine phosphatase in the PPP family that is now recognised to regulate a variety of cellular functions independently of protein phosphatase 2A (PP2A). Regulatory subunits (R1 and R2) have been identified in mammals that interact with the catalytic subunit of Ppp4 (Ppp4c) and control its activity. Ppp4c-R2 complexes play roles in organelle assembly; not only are they essential for maturation of the centrosome, but they are also involved in spliceosomal assembly via interaction with the survival of motor neurons (SMNs) complex. Several cellular signalling routes, including NF-kappaB and the target of rapamycin (TOR) pathways appear to be regulated by Ppp4. Emerging evidence indicates that Ppp4 may play a role in the DNA damage response and that Ppp4c-R1 complexes decrease the activity of a histone deacetylase, implicating Ppp4 in the regulation of chromatin activities. Antitumour agents, cantharidin and fostriecin, potently inhibit the activity of Ppp4. Orthologues of mammalian Ppp4 subunits in Saccharomyces cerevisiae confer resistance to the anticancer, DNA-binding drugs, cisplatin and oxaliplatin.
Topics: Animals; Antineoplastic Agents; Cell Nucleus; Humans; Organelles; Phosphoprotein Phosphatases; Protein Phosphatase 2; Protein Subunits; Signal Transduction
PubMed: 15913612
DOI: 10.1016/j.febslet.2005.04.070