Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have studied the effect of protein kinase C and protein kinase A activation, and phosphatase inhibition on two different stimuli with distinct mechanisms of action. The first stimulus is compound 48/80, and its action is mediated probably by a Gi-protein, while the other is sodium fluoride, which unspecifically activates G-proteins. We established a comparative study because the action of compound 48/80 is calcium-independent, while fluoride is strictly calcium-dependent. The activation of protein kinase C was attained with the phorbol esther 12-O-tetradecanoylphorbol-13-acetate, protein kinase A was activated by increasing cAMP levels with forskolin or rolipram, and the phosphatase activity was inhibited with okadaic acid (OA), which inhibits phosphatases type 1 and 2A. Our results show that OA enhances the response to fluoride and compound 48/80 in the absence of calcium, and we conclude that calcium has a negative feedback role on the cell response. Protein kinase A activation strongly inhibits the response to fluoride, and the results show a positive regulation of protein kinase C and a negative regulation of protein kinase A over fluoride response. As previously reported by other authors for the ionophore A23187, TPA notably potentiates the response to fluoride, which supports its possible modulatory role on extracellular calcium-dependent stimuli.
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PMID:Influence of protein kinase C, cAMP and phosphatase activity on histamine release produced by compound 48/80 and sodium fluoride on rat mast cells. 128 Sep 5

We studied the effect of fasting on phosphotyrosine phosphatase (PTPase) activities in particulate (PF) and cytosolic (CF) fractions of rat adipocytes and liver. PTPase activity was assessed using [32P]tyrosine insulin receptor (IR). In adipocytes, 48 h fasting significantly inhibited PTPase activity. Dephosphorylation of IR by PF and CF PTPases was reduced by 80 and 65%, respectively. Similar reductions of lesser magnitude were observed in fasted rat livers. The effect of fasting was completely reversed by either refeeding or by incubating "fasted" adipocytes for 2 h in tissue culture medium containing 5 mM glucose. Neither 20 mM glucose nor the presence of insulin influenced phosphatase activity. Because fasting is accompanied by elevated protein kinase C (PKC) and adenosine 3',5'-cyclic monophosphate (cAMP) levels, we examined their influence on adipocyte PTPases. Neither activation (1 microM 12-O-tetradecanoylphorbol-13-acetate) nor inhibition (20 microM sphingosine) of PKC affected PTPase activity. In contrast, cAMP (2 mM) significantly inhibited PTPase activity (80% inhibition at 2 h), and its effect was prevented by a cAMP antagonist RpcAMP. Fasting- and cAMP-induced inhibition of PTPase activity was restored by incubating PF with trypsin (4 micrograms/ml for 5 min), which separated the putative inhibitors from the phosphatases. We conclude that fasting-induced inhibition of PTPases is mediated by elevated cAMP levels, most likely by activating phosphatase inhibitors.
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PMID:Role of cAMP in mediating effects of fasting on dephosphorylation of insulin receptor. 131 6

The specific phosphatase inhibitor, okadaic acid, increases the level of mRNA for the receptor for urokinase-type plasminogen activator (u-PAR) in 8 out of 13 human cell lines. The strongest increase (90-fold) was observed in A549 lung carcinoma cells, in which it was partly traced back to an increased transcription of the u-PAR gene. There was a parallel but less pronounced increase in the u-PAR protein level. These findings indicate that u-PAR gene transcription is regulated by one or more factors that are constitutively phosphorylated and are dephosphorylated by okadaic acid-sensitive phosphatases. A lack of additivity of u-PAR induction by okadaic acid and by the protein kinase C activator, PMA, in the A549 cells suggests that the regulatory factors affected by okadaic acid are phosphorylated by protein kinase C.
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PMID:Okadaic acid strongly increases gene transcription, mRNA and protein level for the urokinase receptor in human A549 cells. 131 23

1. Voltage-activated currents through calcium channels in primary cultures of murine dorsal root ganglion cells (DRG) were studied with the whole-cell and cell-attached patch recording techniques. 2. The chemical phosphatase 2,3-butanedione monoxime (BDM) reversibly reduced the amplitude of L-type calcium current (ICa) in a dose-dependent manner; at a concentration of 20 mM, BDM caused a 47% suppression of ICa. 3. Application of 10 mM-8-bromo-cyclic AMP or 50 microM-isoprenaline onto DRG treated with BDM completely restored ICa to the pre-BDM level. 4. In striking contrast, bath application of Bay K 8644 (0.5-5 microM) had no effect on the BDM-suppressed ICa. As expected, Bay K 8644 alone caused a two- to threefold increase of the maximal ICa and shifted its I-V relationship to the left. Interestingly, if a cell was first exposed to Bay K 8644 further treatment with 20 mM-BDM resulted in 100% suppression of ICa. This suggests that Bay K 8644 changes the conformation of the calcium channel to one which is more sensitive or more accessible to the action of the phosphatase. 5. Pre-treatment of DRG with an activator of protein kinase C, 12-O-tetradecanoyl-phorbol-13-acetate, did not antagonize BDM's effect on ICa. 6. The depressant action of BDM on ICa was distinct from that of nifedipine in that it did not exhibit use dependence. 7. When single calcium channel currents were recorded in cell-attached patches (barium as the charge carrier), bath application of BDM reduced the percentage of time that the channel spent in the open state. 8. Superfusion with 8-bromo-cyclic AMP restored the ensemble macroscopic 'ICa' to the pre-BDM amplitude. This was due to a dramatic enhancement of the frequency of channel openings. 9. We suggest that BDM acts through the cytoplasm to alter cyclic AMP-dependent protein kinase modulation of neuronal L-type calcium channels. The brief, high-frequency openings which 8-bromo-cyclic AMP activates in the presence of BDM may reflect a rapid phosphorylation-dephosphorylation sequence which controls channel gating.
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PMID:Novel suppression of an L-type calcium channel in neurones of murine dorsal root ganglia by 2,3-butanedione monoxime. 131 30

Human HPTP beta is unique among mammalian receptor-like protein tyrosine phosphatases in that it has only a single catalytic domain. The intracellular region of HPTP beta was expressed in bacteria, purified, and characterized. It exhibits high activity toward all substrates tested and is potently inhibited by zinc. Vanadate and polyanions also inhibited activity. The juxta-membrane segment of HPTP beta (residues 1622-1639) potentially functions as a negative regulatory sequence since its deletion can increase HPTP beta activity 5-fold. This segment contains up to two sites for protein kinase C phosphorylation, although in vitro phosphorylation by this kinase did not affect HPTP beta activity. The boundaries of the catalytic domain were delineated by truncation analyses. Successive deletion of N-terminal sequence prior to residue 1684 had little effect on substrate affinity and at most reduced activity about 6-fold. Further removal of residues 1684-1686 resulted in a marked 50-500-fold drop in activity, and loss of N-terminal sequence prior to residue 1690 abolished activity. Based on these analyses a highly conserved motif was identified in all mammalian tyrosine phosphatases (E/q) (F/y)XX(L/i), corresponding to positions 1684-1688 of HPTP beta. Mutation of residue 1684 or 1685 generally gave rise to proteins with marked temperature sensitivity. These mutant HPTP beta were active but had reduced activity compared to the wild type enzyme. In conjunction, these results suggest that this region represents the N-terminal border of the catalytic domain and is essential for correct phosphatase folding although not directly involved in catalysis. Parallel truncation studies have defined residues 1930-1939/40 as the C-terminal border of the catalytic domain.
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PMID:Expression and characterization of wild type, truncated, and mutant forms of the intracellular region of the receptor-like protein tyrosine phosphatase HPTP beta. 132 15

Chromostatin is a 20-residue peptide derived from chromogranin A (CGA), the major soluble component of secretory granules in adrenal medullary chromaffin cells. One known biological function of chromostatin is to inhibit the secretagogue-evoked catecholamine secretion from chromaffin cells. Putative receptors are present on the chromaffin-cell plasma membrane, and the activation of such receptors leads to the inhibition of L-type voltage-sensitive calcium channels. We report here that exposure of chromaffin cells to chromostatin modifies neither cAMP and cGMP levels nor protein kinase C activity but does provoke the activation of soluble protein phosphatase (PPase) type 2A in a dose-dependent manner compatible with the peptide concentration inhibiting catecholamine secretion. The activation of the PPase as well as the inhibition of both secretagogue-induced Ca2+ entry and catecholamine secretion by chromostatin were all blocked by okadaic acid, a specific PPase inhibitor. We suggest that chromostatin directly or indirectly stimulates PPase-2A, dephosphorylating a target protein and lowering its activity in the secretory process.
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PMID:Chromostatin inhibits catecholamine secretion in adrenal chromaffin cells by activating a protein phosphatase. 132 34

We have demonstrated that the alpha 2,3 sialyltransferase (alpha 2,3 ST) from C6 cultured glioma cells was inhibited in vivo by W-7 and related Ca2+/Calmodulin (Ca/CaM) antagonists while protein kinase C effectors had no effect. Dephosphorylation of alpha 2,3 ST by the wide specificity alkaline phosphatase led to inactivation indicating that the enzyme is phosphorylated. The serine/threonine protein phosphatase inhibitors okadaic acid and Calyculin A led also to an inhibition of alpha 2,3 ST activity. In addition, Ca/CaM antagonists and phosphatase inhibitors led both to an inhibition of a alpha 2,3 sialoglycoprotein from C6 glioma cells as demonstrated with lectin affinity blotting. A concerted regulatory mechanism with phosphorylation/dephosphorylation of alpha 2,3 ST is then postulated.
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PMID:Study of O-glycan sialylation in C6 cultured glioma cells: regulation of a beta-galactoside alpha 2,3 sialyltransferase activity by Ca2+/calmodulin antagonists and phosphatase inhibitors. 132 69

The regulated expression of mannose 6-phosphate/insulin-like growth factor II (M6P/IGF II) receptors in plasma membranes has previously been shown to be accompanied by marked changes in the phosphorylation state of the receptors (Corvera, S., Folander, K., Clairmont, K. B., and Czech, M. P. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 7567-7571). In the present study we show that protein phosphatase 2A dephosphorylates the human M6P/IGF II receptor in vitro. Incubation of human fibroblasts with okadaic acid, a specific inhibitor of this phosphatase, resulted in a depletion of M6P/IGF II receptors at the cell surface without affecting their internalization kinetics. The phosphorylation state of the remaining cell surface receptors was 3-fold increased. Thus, the endocytosis rate of M6P/IGF II receptors appears to be unaltered by increased phosphorylation. While the decreased cell surface expression of receptors was reversible upon removal of okadaic acid the IGF II-induced redistribution of M6P/IGF II receptors to the plasma membrane (Braulke, T., Tippmer, S., Neher, E., and von Figura, K. (1989) EMBO J. 8, 681-686) was irreversibly inhibited by the phosphatase inhibitor. Receptor redistribution in response to protein kinase C activation was not affected by okadaic acid. These results suggest that the cell surface expression of M6P/IGF II receptor can be regulated by phosphatase-dependent and -independent pathways. In addition, the phosphorylation state and the steady-state cell surface number of transferrin receptors were not affected by okadaic acid, whereas it impaired the IGF II-stimulated receptor redistribution similarly as for M6P/IGF II receptors. The data indicate that okadaic acid-sensitive protein phosphatases may play a general role in terms of IGF II-modulated receptor recycling.
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PMID:Role of protein phosphatases in insulin-like growth factor II (IGF II)-stimulated mannose 6-phosphate/IGF II receptor redistribution. 132 32

Calponin, a thin-filament protein of smooth muscle, has been implicated in the regulation of smooth-muscle contraction, since in vitro the isolated protein inhibits the actin-activated myosin MgATPase. This inhibitory effect, and the ability of calponin to bind to actin, is lost after its phosphorylation by protein kinase C or Ca2+/calmodulin-dependent protein kinase II [Winder & Walsh (1990) J. Biol. Chem. 265, 10148-10155]. If this phosphorylation reaction is of physiological significance, there must be a protein phosphatase in smooth muscle capable of dephosphorylating calponin and restoring its inhibitory effect on the actomyosin MgATPase. We demonstrate here the presence, in chicken gizzard smooth muscle, of a single major phosphatase activity directed towards calponin. This phosphatase was purified from the soluble fraction of chicken gizzard by (NH4)2SO4 fractionation and sequential chromatography on Sephacryl S-300, DEAE-Sephacel, omega-amino-octyl-agarose and thiophosphorylated myosin 20 kDa light-chain-Sepharose columns. The purified phosphatase contained three polypeptide chains of 60, 55 and 38 kDa which were shown to be identical with the subunits of SMP-I, a smooth-muscle phosphatase capable of dephosphorylating the isolated 20 kDa light chain of myosin but not intact myosin [Pato & Adelstein (1983) J. Biol. Chem. 258, 7047-7054]. Consistent with its identity with SMP-I, calponin phosphatase was classified as a type-2A protein phosphatase. Of several potential phosphoprotein substrates examined, calponin proved to be kinetically the best, suggesting that calponin may be a physiological substrate for this phosphatase. Finally, dephosphorylation of calponin which had been phosphorylated by protein kinase C restored completely its ability to inhibit the actin-activated MgATPase of smooth-muscle myosin. These observations support the hypothesis that calponin plays a role in regulating the contractile state of smooth muscle and that this function in turn is controlled by phosphorylation-dephosphorylation.
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PMID:Purification and characterization of calponin phosphatase from smooth muscle. Effect of dephosphorylation on calponin function. 132 79

Erythropoietin stimulation of erythroid cells induces a rapid increase in c-myc and decrease in c-myb mRNA levels. The signal pathway to c-myc requires activation of protein kinase C. We now report that erythropoietin down-regulates expression of c-myb via a discrete, serine/threonine-specific phosphatase-dependent pathway. The protein kinase C-blocker H7 completely prevents the c-myc response to erythropoietin, but has no effect on the c-myb response. In contrast, the phosphatase blocker okadaic acid prevents the c-myb response but not the c-myc response. This effect of okadaic acid on the c-myb response is concentration-dependent. Both the protein kinase C-dependent signal to c-myc and the phosphatase-dependent signal to c-myb regulate gene expression by a transcriptional arrest mechanism operative within the first intron of the respective protooncogenes. In contrast, the chemical inducer of differentiation, dimethyl sulfoxide, regulates expression of c-myc and c-myb without activation of these phosphatase- and kinase-dependent pathways.
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PMID:Activation of two discrete signaling pathways by erythropoietin. 132 29


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