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)

Protein kinase C (PKC) isoforms are key mediators in hormone, growth factor, and neurotransmitter triggered pathways of cell activation (Nishizuka: Science 233:305-312, 1986; Nature 334:661-665, 1988). Stimulation of kinase activity by diacylglycerol and calcium often leads to translocation of PKC from the cytosol to a particulate fraction (Kraft and Anderson: Nature 301:621-623, 1983). The beta isoform of PKC is translocated and degraded much more rapidly than the alpha isoform in phorbolester-stimulated rat basophilic leukemia (RBL) cells (Huang et al.: J. Biol. Chem. 264:4238-4243, 1989). We report here immunofluorescence evidence that the distributions of PKC alpha and beta are strikingly different in antigen-activated RBL cells. PKC beta associates with perinuclear filaments and filaments that extend from the perinuclear area to the cell periphery whereas PKC alpha concentrates in regions of the cell periphery. This distribution of PKC beta is distinctly different from that of actin filaments and microtubules as determined by phalloidin staining and by anti-tubulin antibody labeling. In contrast, the staining patterns obtained with antibodies to PKC beta and to the intermediate filament protein vimentin are almost identical, indicating that PKC beta associates with vimentin filaments. These bundles of 100 A filaments may provide docking sites for interactions of PKC beta with its substrates and thus confer specificity to the actions of this isoform.
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PMID:Association of the beta isoform of protein kinase C with vimentin filaments. 151 48

Heat shock treatment of rat embryo fibroblasts resulted in a 60% increase in cytosolic protein kinase C activity, in contrast to phorbol ester-induced translocation to the membrane. During reversal of the cells back to the normal temperature a decrease in cytosolic PKC activity was observed and paralleled by an increase in protamine kinase activity. Cell lysates prepared from heat shock-treated cells show a marked calcium/phospholipid-dependent phosphorylation of several endogenous PKC substrate proteins, while the 28-kDa stress protein was shown to be a PKC substrate. These cells express the TYPE III-alpha isoform of PKC and, thus, the alterations induced within cells exposed to hyperthermic treatment may reflect a functional significance with regard to the regulation of this specific isoform.
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PMID:Alterations in protein kinase C type III-alpha during heat shock of rat embryo fibroblasts. 184 15

Inhibitors of protein kinases were screened for the ability to prevent the repression of cholesterol 7 alpha-hydroxylase mRNA by taurocholate in primary cultures of adult rat hepatocytes. The addition of taurocholate (25 microM) for 6 h decreased cholesterol 7 alpha-hydroxylase mRNA by 64 +/- 3%. However, after a preincubation with the protein kinase C inhibitors calphostin C or chelerythrine, taurocholate had no significant effect on cholesterol 7 alpha-hydroxylase mRNA, or decreased levels by only 23 +/- 8%, respectively. Protein kinase C activation with phorbol 12-myristate, 13-acetate (100 nM) decreased cholesterol 7 alpha-hydroxylase mRNA and transcriptional activity by 71 +/- 5% and 60 +/- 16%, respectively, within 3 h. mRNA levels recovered to control levels by 18-24 h, however, consistent with downregulation of protein kinase C. Furthermore, after depletion of protein kinase C with a 24-h preincubation with phorbol diesters, taurocholate (25 microM) repressed cholesterol 7 alpha-hydroxylase mRNA by only 14 +/- 17%. The addition of taurocholate (50 microM) to the culture medium transiently increased membrane-associated protein kinase C activity by approximately twofold, while causing a concomitant decrease in cytosolic activity. Other bile acids increased membrane-associated protein kinase C activity in approximate proportion to their relative hydrophobicity. Finally, immunoblotting experiments revealed translocation of the alpha isoform of protein kinase C to hepatocyte membranes in response to taurocholate. These data suggest that hydrophobic bile acids repress cholesterol 7 alpha-hydroxylase transcription through a protein kinase C-dependent mechanism.
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PMID:Repression of cholesterol 7 alpha-hydroxylase transcription by bile acids is mediated through protein kinase C in primary cultures of rat hepatocytes. 766 12

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 activity and expression of Ca(2+)-dependent cPKC alpha and beta isoenzymes in the particulate, soluble (cytosolic) and nuclear fractions of rat liver and the expression of Ca(2+)-independent nPKC delta and aPKC zeta were examined during the early stages (30 and 60 min, 24 and 96 h and 7 and 60 days post-hepatectomy) of the Solt-Farber 'resistant hepatocyte' model of diethylnitrosamine (DENA)-induced hepatocarcinogenesis in Fischer 344 rats and related to the presence of gamma-glutamyl transpeptidase (GGT)-positive hyperplastic cell foci and persistent nodules in rat liver. Total PKC activity was unmodified by the carcinogenic treatment. In contrast, the PKC activity in the particulate, as well as nuclear fractions increased with time, reaching a maximum 60 days post-hepatectomy, with a decrease in the cytosolic activity. In carcinogen-treated animals maximal expression of cPKC alpha and beta isoenzymes was present 7 days post-hepatectomy, while no changes in nPKC delta and aPKC zeta immunoreactivity were detected. In the nucleus, no cPKC alpha isoform expression was observed, the cPKC beta expression being maximal at 60 days. Seven and 60 days post-hepatectomy GGT-positive hyperplastic cell foci and persistent nodules were present in rat liver respectively. Taken together, the results of this study suggest a role for nuclear cPKC beta and for cPKC alpha in promoting the selective growth of carcinogen-initiated hepatocytes in rat liver. No evidence for a role of Ca(2+)-independent nPKC delta and aPKC zeta isoenzymes in the early stages of DENA-induced liver carcinogenesis could be demonstrated.
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PMID:Membrane and nuclear protein kinase C activation in the early stages of diethylnitrosamine-induced rat hepatocarcinogenesis. 805 57

Protein kinase C activity was detected in the cytosolic fraction of quiescent parotid acinar cells; the particulate fraction contained a much smaller proportion of the enzyme. Protein kinase C activity was increased in the membrane fraction and decreased in the cytosol after exposure of intact cells to phorbol 12-myristate 13-acetate (PMA) or the muscarinic-receptor agonist carbachol. The effect of PMA was potentiated by a subthreshold concentration of ionomycin. Immunoblot analysis with anti-protein kinase C antibodies revealed that the protein kinase C-alpha isoform is expressed in rat parotid cells. Other Ca(2+)-dependent isoforms were not detected. Further, agonist stimulation caused the redistribution of protein kinase C-alpha from cytosol to a membrane fraction. Agonists may promote parotid acinar cell activity, including amylase secretion, by increasing the affinity of protein kinase C-alpha for the membrane fraction, presumably via a rise in Ca2+ and diacylglycerol derived from polyphosphoinositide hydrolysis.
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PMID:Translocation of the alpha-isozyme of protein kinase C during stimulation of rat parotid acinar cells by phorbol ester and carbachol. 814 66

A decrease in protein kinase C activity caused either by treatment with inhibitors, such as staurosporine or H-7, or by prolonged exposure to phorbol diesters has been proposed to be involved in the early events of SH-SY5Y neuroblastoma cell differentiation. Because eight distinct isoforms of protein kinase C with discrete subcellular and tissue distributions have been described, we determined which isoforms are present in SH-SY5Y cells and studied their modifications during differentiation. The alpha, beta 1, delta, and epsilon isoforms were present in SH-SY5Y cells, as well as in rat brain. Protein kinase C-alpha and -beta 1 were the most abundant isoforms in SH-SY5Y cells, and immunoreactive protein kinase C-delta and -epsilon were present in much smaller amounts than in rat brain. Subcellular fractionation and immunocytochemistry demonstrated that all four isoforms are distributed bimodally in the cytoplasm and the membranes. Immunocytochemical analysis showed that the alpha isoform is associated predominantly with the plasma membrane and the processes extended during treatment with 12-tetradecanoyl-13-acetyl-beta-phorbol or staurosporine, and that protein kinase C-epsilon is predominantly membrane-bound. Its localization did not change during differentiation. Western blots of total SH-SY5Y cell extracts and of subcellular fractions probed with isoform-specific polyclonal antibodies showed that when SH-SY5Y cells acquired a morphologically differentiated phenotype, protein kinase C-alpha and -epsilon decreased, and protein kinase C-beta 1 did not change. These data suggest distinct roles for the different protein kinase C isoforms during neuronal differentiation, as well as possible involvement of protein kinase alpha and epsilon in neuritogenesis.
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PMID:Differential expression and subcellular localization of protein kinase C alpha, beta, gamma, delta, and epsilon isoforms in SH-SY5Y neuroblastoma cells: modifications during differentiation. 841 48

Protein kinase C (PKC) is a gene family consisting of no less than 11 distinct isoforms. In both murine and rat fibroblasts, we detected expression of four PKC isoforms: the conventional PKC alpha, the novel PKCs delta and epsilon, and the atypical PKC zeta. With the conventional and novel PKC isoforms, membrane association has been used to show PKC activation. In cells transformed by v-Src, there was a Ca(2+)-dependent increase in membrane association of the alpha isoform relative to the nontransformed parental cells. The zeta isoform had a slightly increased membrane association in murine fibroblasts transformed by v-Src but not in rat fibroblasts transformed by v-Src. However, since it is not clear whether cellular distribution of zeta isoform correlates with activation, the data are inconclusive with regard to this isoform. Interestingly, of the Ca(2+)-independent PKC isoforms delta and epsilon, only the delta isoform was preferentially associated with membrane fractions in v-Src-transformed cells. The lack of PKC epsilon activation was not due to lack of responsiveness to diacylglycerol (DG), since exogenously supplied DG and phorbol ester were both able to induce membrane association of PKC epsilon. Thus, the differential activation of the delta and epsilon isoforms by v-Src suggests a more complex mechanism for the activation of the novel Ca(2+)-independent PKC isoforms, involving more than simply elevating DG levels. Since PKC has been implicated in the intracellular signals activated by v-Src that lead to transformation, the selective activation of PKC alpha and delta suggests a role in mitogenesis and transformation for these PKC isoforms.
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PMID:Selective activation of protein kinase C isoforms by v-Src. 856 74

Phospholipase D (PLD) which was partially purified from membranes of porcine brain could be stimulated by multiple cytosolic components; these included ADP-ribosylation factor (Arf) and RhoA, which required guanine nucleotides for activity, and an unidentified factor which activated the enzyme in a nucleotide-independent manner (Singer, W. D., Brown, H. A., Bokoch, G. M., and Sternweis, P. C. (1995) J. Biol. Chem. 270, 14944-14950). Here, we report purification of the latter factor, its identification as the alpha isoform of protein kinase C (PKCalpha), and characterization of its regulation of PLD activity. Stimulation of PLD by purified PKCalpha or recombinant PKCalpha (rPKCalpha) occurred in the absence of any nucleotide and required activators such as Ca2+ or phorbol ester. This action was synergistic with stimulation of PLD evoked by either Arf or RhoA. Dephosphorylation of rPKC alpha with protein phosphatase 1 or 2A resulted in a loss of its kinase activity, but had little effect on its ability to stimulate PLD either alone or in conjunction with Arf. Staurosporine inhibited the kinase activity of PKCalpha without affecting activation of PLD. Finally, gel filtration of PKCalpha that had been cleaved with trypsin demonstrated that stimulatory activity for PLD coeluted with the regulatory domain of the enzyme. These data indicate that PKC may regulate signaling events through direct molecular interaction with downstream effectors as well as through its well characterized catalytic modification of proteins by phosphorylation.
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PMID:Regulation of phospholipase D by protein kinase C is synergistic with ADP-ribosylation factor and independent of protein kinase activity. 862 5

These studies of a model liver cell line evaluate the mechanisms responsible for regulated release of K+ ions during metabolic stress. Metabolic inhibition of HTC hepatoma cells by exposure to 2, 4-dinitrophenol (50 microM) and 2-deoxy-D-glucose (10 mM) stimulated outward currents carried by K+ of 974 +/- 75 pA at 0 mV (n = 20, p < 0.001). Currents were inhibited by chelation of intracellular Ca2+ or exposure to apamin (50 nM), an inhibitor of SKCa channels. In cell-attached recordings from intact cells, removal of metabolic substrates (25/28 cells) or exposure to metabolic inhibitors (32/40 cells) opened K+-selective channels with a conductance of 6.5 +/- 0. 2 pS. Channels had an open probability of 0.31 +/- 0.08 and opened in bursts averaging 3.55 +/- 0.27 ms in duration (n = 6). Metabolic stress was associated with rapid translocation of the alpha isoform of protein kinase C (PKCalpha) from cytosol to membrane; and down-regulation of PKCalpha by phorbol esters or exposure to the PKC inhibitor chelerythrine (10 microM) each inhibited currents. Moreover, intracellular perfusion with purified PKCalpha activated currents in a Ca2+- and concentration-dependent manner. These findings indicate that metabolic stress leads to opening of apamin-sensitive SKCa channels in hepatoma cells through a Ca2+- and PKC-dependent mechanism and suggest that PKCalpha may be selectively involved in the response. This mechanism functionally couples the metabolic state of cells to membrane K+ permeability and represents a potential target for modification of liver injury associated with ischemia and preservation.
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PMID:Metabolic stress opens K+ channels in hepatoma cells through a Ca2+- and protein kinase calpha-dependent mechanism. 866 72


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