Protein kinase C: rapid enzyme purification and substrate-dependence of the diacylglycerol effect

Protein kinase C-beta activates tyrosinase by phosphorylating serine residues in its cytoplasmic domain

We have previously shown that protein kinase C-beta (PKC-beta) is required for activation of tyrosinase (Park, H. Y., Russakovsky, V., Ohno, S., and Gilchrest, B. A. (1993) J. Biol. Chem. 268, 11742-11749), the rate-limiting enzyme in melanogenesis. We now examine its mechanism of activation in human melanocytes. In vivo phosphorylation experiments revealed that tyrosinase is phosphorylated through the PKC-dependent pathway and that introduction of PKC-beta into nonpigmented human melanoma cells lacking PKC-beta lead to the phosphorylation and activation of tyrosinase. Preincubation of intact melanosomes with purified active PKC-beta in vitro increased tyrosinase activity 3-fold. By immunoelectron microscopy, PKC-beta but not PKC-alpha was closely associated with tyrosinase on the outer surface of melanosomes. Western blot analysis confirmed the association of PKC-beta with melanosomes. Only the cytoplasmic (extra-melanosomal) domain of tyrosinase, which contains two serines but no threonines, was phosphorylated by the serine/threonine kinase PKC-beta. These two serines at positions 505 and 509 both are present in the C-terminal peptide generated by trypsin digestion of tyrosinase. Co-migration experiments comparing synthetic peptide standards of all three possible phosphorylated tryptic peptides, a diphosphopeptide and two monophosphopeptides, to tyrosinase-phosphorylated in intact melanocytes by PKC-beta and then subjected to trypsin digestion revealed that both serine residues are phosphorylated by PKC-beta. We conclude that PKC-beta activates tyrosinase directly by phosphorylating serine residues at positions 505 and 509 in the cytoplasmic domain of this melanosome-associated protein.

Protein kinase C enhances recombinant bovine alpha 1 beta 1 gamma 2L GABAA receptor whole-cell currents expressed in L929 fibroblasts

The beta 1 and gamma 2L subunits of the gamma-aminobutyric acid type A receptor (GABAR) contain phosphorylation sites for PKC. To determine the effect of PKC on GABAR function, whole-cell recordings were obtained from mouse fibroblasts expressing recombinant alpha 1 beta 1 gamma 2L receptors, and catalytically active PKC (PKM) was applied via the recording pipette. The first experiment was a population study. Intracellular application of PKM increased GABAR currents, and the enhancement was antagonized by coapplication of the PKC inhibitory peptide. No acceleration or deceleration of GABAR desensitization was observed. The second experiment was a reimpalement study in which paired recordings were made successively from individual cells. Enhancement of GABAR currents by PKM was again obtained. PKM increased GABAR currents at high (> 10 microM) but not at low (< 10 microM) GABA concentrations, resulting in increases in both EC50 and maximal GABAR current. Thus, PKC phosphorylation enhanced recombinant alpha 1 beta 1 gamma 2L GABAR current by increasing maximal current without increasing the affinity of GABA for the GABARs.

In vitro activation of rat brain protein kinase C by polyenoic very-long-chain fatty acids

A variety of fatty acids including the cis-polyunsaturated very-long-chain fatty acids (VLCFA) (> 22 carbon atoms) common in retina, spermatozoa, and brain were examined for their ability to activate protein kinase C (PKC) purified from rat brain. Arachidonic [20:4(n-6)], eicosapentaenoic [20:5(n-3)], and docosahexaenoic [22:6(n-3)] acids as well as the VLCFA dotriacontatetraenoic [32:4(n-6)] and tetratriacontahexaenoic [34:6(n-3)] were equally capable of activating PKC in vitro with maximal activity being between 25 and 50 microM. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate further enhanced the in vitro activation of PKC when added to the protein kinase assay system with the fatty acids. The fully saturated arachidic acid (20:0) was inactive in both assay systems. The potential significance of the in vitro activation of PKC by the VLCFA is discussed.

Calponin phosphorylation in vitro and in intact muscle

Calponin, a thin-filament-associated protein implicated in the regulation of smooth-muscle contraction, is phosphorylated in vitro by protein kinase C and Ca2+/calmodulin-dependent protein kinase II [Winder and Walsh (1990) J. Biol. Chem. 265, 10148-10155] and dephosphorylated by a type 2A protein phosphatase [Winder, Pato and Walsh (1992) Biochem. J. 286, 197-203]. Unphosphorylated calponin binds to actin and inhibits the actin-activated myosin MgATPase; these properties are lost on phosphorylation. Although both serine and threonine residues in calponin are phosphorylated, the major site of phosphorylation by either kinase is Ser-175. Calponin also undergoes phosphorylation when bound to actin in synthetic thin filaments, in a reconstituted actomyosin system, in washed myofibrils and in tissue extracts; this results in dissociation of calponin from actin. Tryptic phosphopeptide mapping indicates that the same sites are phosphorylated in the bound as in the isolated protein. Toad stomach calponin exists in at least three isoforms which differ in charge but exhibit the same molecular mass on SDS/PAGE. In a toad stomach extract, all three isoforms are phosphorylated by protein kinase C or Ca2+/calmodulin-dependent protein kinase II as shown by two-dimensional gel electrophoresis (non-equilibrium pH-gradient gel electrophoresis and SDS/PAGE). Calponin phosphorylation also occurs in intact toad stomach smooth-muscle strips metabolically labelled with 32Pi and stimulated to contract with carbachol. These results support the hypothesis that calponin may be regulated in vivo by phosphorylation-dephosphorylation.

Smooth-muscle caldesmon phosphatase is SMP-I, a type 2A protein phosphatase

Caldesmon phosphatase was identified in chicken gizzard smooth muscle by using as substrates caldesmon phosphorylated at different sites by protein kinase C, Ca2+/calmodulin-dependent protein kinase II and cdc2 kinase. Most (approximately 90%) of the phosphatase activity was recovered in the cytosolic fraction. Gel filtration after (NH4)2SO4 fractionation of the cytosolic fraction revealed a single major peak of phosphatase activity which coeluted with calponin phosphatase [Winder, Pato and Walsh (1992) Biochem. J. 286, 197-203] and myosin LC20 phosphatase. Further purification of caldesmon phosphatase was achieved by sequential chromatography on columns of DEAE-Sephacel, omega-amino-octyl-agarose, aminopropyl-agarose and thiophosphorylated myosin LC20-Sepharose. A single peak of caldesmon phosphatase activity was detected at each step of the purification. The purified phosphatase was identified as SMP-I [Pato and Adelstein (1980) J. Biol. Chem. 255, 6535-6538] by subunit composition (three subunits, of 60, 55 and 38 kDa) and Western blotting using antibodies against the holoenzyme which recognize all three subunits and antibodies specific for the 38 kDa catalytic subunit. SMP-I is a type 2A protein phosphatase [Pato, Adelstein, Crouch, Safer, Ingebritsen and Cohen (1983) Eur. J. Biochem. 132, 283-287; Winder et al. (1992), cited above]. Consistent with the conclusion that SMP-I is the major caldesmon phosphatase of smooth muscle, purified SMP-I from turkey gizzard dephosphorylated all three phosphorylated forms of caldesmon, whereas SMP-II, -III and -IV were relatively ineffective. Kinetic analysis of dephosphorylation by chicken gizzard SMP-I of the three phosphorylated caldesmon species and calponin phosphorylated by protein kinase C indicates that calponin is a significantly better substrate of SMP-I than are any of the three phosphorylated forms of caldesmon. We therefore suggest that caldesmon phosphorylation in vivo can be maintained after kinase inactivation due to slow dephosphorylation by SMP-I, whereas calponin and myosin are rapidly dephosphorylated by SMP-I and SMP-III/SMP-IV respectively. This may have important functional consequences in terms of the contractile properties of smooth muscle.

Inhibition of myosin light chain kinase, cAMP-dependent protein kinase, protein kinase C and of plant Ca(2+)-dependent protein kinase by anthraquinones

A variety of anthraquinone (anthracene-9,10-dione) derivatives inhibits rat brain Ca(2+)- and phospholipid-activated protein kinase C (PKC) of which the most potent inhibitors are mitoxantrone (1,4-dihydroxy-5,8-bis[2-(hydroxyethylamino)-ethylamino]-9,10- anthracenedione) (IC50 4 microM) and quinalizarin (1,2,5,8-tetrahydroxy-anthraquinone (IC50 4 microM). Anthraquinone derivatives with less polar substitution in positions 1 to 4 and 5 to 8 are less effective as inhibitors of PKC. Wheat germ Ca(2+)-dependent protein kinase (CDPK) assayed with a myosin light chain-based peptide substrate is much less sensitive to inhibition by anthraquinones, the most effective anthraquinone inhibitors being the 1,2,4-trihydroxy (IC50 14 microM), 1,8-dihydroxy-3-methyl (IC50 56 microM) and 1,2,5,8-tetrahydroxy (IC50 65 microM) derivatives. Ca(2+)-calmodulin-dependent myosin light chain kinase (MLCK) is inhibited by a range of di-, tri- and tetrahydroxylated anthraquinones (IC50 values 2 to 53 microM), the most potent inhibitors being the more polar compounds, namely mitoxantrone (IC50 2 microM) and emodin (1,3,8-trihydroxy-6-methylanthraquinone) (IC50 8 microM). Mitoxantrone interacts with calmodulin as determined from abolition of Ca(2+)-dependent fluorescence enhancement of dansyl-calmodulin (IC50 4 microM). A range of anthraquinone derivatives inhibits the catalytic subunit of cAMP-dependent protein kinase (cAK). In a number of cases compounds acting as potent inhibitors of MLCK (such as mitoxantrone and emodin) are very poor inhibitors of cAK and vice versa.

Involvement of protein kinase C in thrombin-induced translocation of Gi2 alpha from the membrane to the cytosol in mouse mastocytoma P-815 cells

Recently, we reported that in mouse mastocytoma P-815 cells the cytosol contains some factor(s) which promotes the release of GTP-activated Gi2 alpha from the membrane, and that thrombin induces the translocation of Gi2 alpha from the membrane to the cytosol (Takahashi, S., Negishi, M. and Ichikawa, A. (1991) J. Biol. Chem. 266, 5367-5370). Here we investigated the mechanism underlying the thrombin-induced translocation of Gi2 alpha in mastocytoma cells. Thrombin induced a rapid and transient increase in the intracellular Ca2+ concentration ([Ca2+]i) within 1 min, attenuated pertussis toxin-catalyzed ADP-ribosylation of Gi2 in the membrane, and caused the subsequent translocation of Gi2 alpha. Thrombin induced the translocation of protein kinase C from the cytosol to the membrane, and a protein kinase C inhibitor, staurosporine, completely inhibited the thrombin-induced translocation of Gi2 alpha. When cells were treated with thrombin, the ability of the cytosol to release Gi2 alpha from the membrane in the presence of GTP gamma S markedly increased. This stimulatory effect of thrombin on the ability of the cytosol was mimicked by 12-O-tetradecanoylphorbol 13-acetate (TPA), but not by the Ca2+ ionophore, ionomycin. The thrombin- and TPA-induced potentiation of the ability of the cytosol to release Gi2 alpha was completely abolished by staurosporine. Furthermore, phosphorylation of the cytosol by protein kinase C markedly potentiated the ability of the cytosol to release Gi2 alpha. These results together demonstrate that the thrombin-induced translocation of Gi2 alpha is due to enhancement of the ability of the cytosol to release Gi2 alpha via activation of protein kinase C.

The major endogenous bovine brain protein kinase C inhibitor is a heat-labile protein

A crude cytosolic fraction prepared from bovine brain contained protein kinase C, as shown by immunoblotting, but its activity was undetectable, suggesting the presence of interfering factors. Phosphatase, ATPase and protease activities did not account for the absence of detectable protein kinase C activity. The major contributing factor was found to be a heat-labile protein which was separated from the kinase by ion-exchange chromatography. The contribution to the total inhibitory activity of heat-stable proteins was relatively minor, suggesting that they may not function physiologically as protein kinase C inhibitors.

Phosphorylation of a Ras-related GTP-binding protein, Rap-1b, by a neuronal Ca2+/calmodulin-dependent protein kinase, CaM kinase Gr

A neuron-specific Ca2+/calmodulin-dependent protein kinase, CaM kinase Gr, phosphorylates selectively a Ras-related GTP-binding protein (Rap-1b) that is enriched in brain tissue. The phosphorylation reaction achieves a stoichiometry of about 1 and involves a serine residue near the carboxyl terminus of the substrate. Both CaM kinase Gr and cAMP-dependent protein kinase, but not CaM kinase II, phosphorylate identical or contiguous serine residues in Rap-1b. The rate of phosphorylation of Rap-1b by CaM kinase Gr is enhanced following autophosphorylation of the protein kinase. Other low molecular weight GTP-binding proteins belonging to the Ras superfamily, including Rab-3A, Rap-2b, and c-Ha-ras p21, are not phosphorylated by CaM kinase Gr. The phosphorylation of Rap-1b itself can be reversed by an endogenous brain phosphoprotein phosphatase. These observations provide a potential connection between a neuronal Ca2(+)-signaling pathway and a specific low molecular weight GTP-binding protein that may regulate neuronal transmembrane signaling, vesicle transport, or neurotransmitter release.

The substrate specificity of protein kinases which phosphorylate the alpha subunit of eukaryotic initiation factor 2

The alpha subunit of eukaryotic protein synthesis initiation factor (eIF-2 alpha) is phosphorylated at a single serine residue (Ser51) by two distinct and well-characterized protein kinase, the haem-controlled repressor (HCR) and the double-stranded RNA-activated inhibitor (dsI). The sequence adjacent to Ser51 is rich in basic residues (Ser51-Arg-Arg-Arg-Ile-Arg) suggesting that they may be important in the substrate specificity of the two kinases, as is the case for several other protein kinases. A number of proteins and synthetic peptides containing clusters of basic residues were tested as substrates for HCR and dsI. Both kinases were able to phosphorylate histones and protamines ar multiple sites as judged by two-dimensional mapping of the tryptic phosphopeptides. These data also showed that the specificities of the two kinases were different from one another and from the specificities of two other protein kinases which recognise basic residues, cAMP-dependent protein kinase and protein kinase C. In histones, HCR phosphorylated only serine residues while dsI phosphorylated serine and threonine. Based on phosphoamino acid analyses and gel filtration of tryptic fragments, dsI was capable of phosphorylating both 'sites' in clupeine Y1 and salmine A1, whereas HCR acted only on the N-terminal cluster of serines in these protamines. The specificities of HCR and dsI were further studied using synthetic peptides with differing configurations of basic residues. Both kinases phosphorylated peptides containing C-terminal clusters of arginines on the 'target' serine residue, provided that they were present at positions +3 and/or +4 relative to Ser51. However, peptides containing only N-terminal basic residues were poor and very poor substrates for dsI and HCR, respectively. These findings are consistent with the disposition of basic residues near the phosphorylation site in eIF-2 alpha and show that the specificities of HCR and dsI differ from other protein kinases whose specificities have been studied.

Difference between the calcium- and the phorbol ester-induced association of protein kinase C with phospholipid membrane

1. Membrane association of protein kinase C is thought to be a prerequisite for the activation of the enzyme. 2. We studied the association of the enzyme with liposome. 3. We show here that the mechanisms for the calcium- and the phorbol ester-induced association of protein kinase C with liposome are different from each other. 4. Diacylglycerol is not crucial for the association of the enzyme with liposome.

Substitution by fatty acids for phosphatidylserine in a reconstitution of phorbol ester binding to protein kinase C

1. Fatty acids can be substituted or phosphatidylserine in a reconstitution of phorbol ester binding to protein kinase C. 2. Phorbol ester, however, does not seem to be effectively utilized for the activation of the enzyme. 3. It is suggested that fatty acids play a role on the activation of protein kinase C in the abnormal conditions such as ischemia, while the phospholipid-dependent activation has a physiological significance in normal conditions.

Identification of the protein kinase C phosphorylation site in neuromodulin

Neuromodulin (P-57, GAP-43, B-50, F-1) is a neurospecific calmodulin binding protein that is phosphorylated by protein kinase C. Phosphorylation by protein kinase C has been shown to abolish the affinity of neuromodulin for calmodulin [Alexander, K. A., Cimler, B. M., Meier, K. E., & Storm, D. R. (1987) J. Biol. Chem. 262, 6108-6113], and we have proposed that the concentration of free CaM in neurons may be regulated by phosphorylation and dephosphorylation of neuromodulin. The purpose of this study was to identify the protein kinase C phosphorylation site(s) in neuromodulin using recombinant neuromodulin as a substrate. Toward this end, it was demonstrated that recombinant neuromodulin purified from Escherichia coli and bovine neuromodulin were phosphorylated with similar Km values and stoichiometries and that protein kinase C mediated phosphorylation of both proteins abolished binding to calmodulin-Sepharose. Recombinant neuromodulin was phosphorylated by using protein kinase C and [gamma-32P]ATP and digested with trypsin, and the resulting peptides were separated by HPLC. Only one 32P-labeled tryptic peptide was generated from phosphorylated neuromodulin. The sequence of this peptide was IQASFR. The serine in this peptide corresponds to position 41 of the entire protein, which is adjacent to or contained within the calmodulin binding domain of neuromodulin. A synthetic peptide, QASFRGHITRKKLKGEK, corresponding to the calmodulin binding domain with a few flanking residues, including serine-41, was also phosphorylated by protein kinase C. We conclude that serine-41 is the protein kinase C phosphorylation site of neuromodulin and that phosphorylation of this amino acid residue blocks binding of calmodulin to neuromodulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein phosphorylation associated with the stimulation of neutrophils. Modulation of superoxide production by protein kinase C and calcium

Neutrophils and other phagocytic cells of the immune system possess a superoxide-generating oxidase system which is essential for the efficient killing of microbes. The system is activated by a wide variety of stimuli, some of which operate through pathways involving protein kinase C (PKC), while others appear not to. The PKC-dependent pathway is probably the major signal transduction route for most of the stimuli. Alterations in cellular Ca2+ and diglyceride levels can have a pronounced stimulatory effect on this pathway by their ability to synergistically activate PKC. This review discusses PKC, the different interactions of this kinase with the plasmalemma that are important in superoxide production, the synergy between Ca2+ and diglyceride, and the nature of the phosphoproteins involved. Evidence supporting the existence of the PKC-independent pathway is also reviewed.

High-pressure extraction of membrane-associated protein kinase C from rat brain

Extraction of rat brain membrane-associated protein kinase C with high specific activity was obtained by applying benzyl alcohol (a membrane fluidizer), EDTA, and high hydrostatic pressures. Approximately 50% of total brain-associated activity was extracted from membranes. The pressure-extracted activity had an eightfold enrichment in the lipid/protein ratio when compared with the cytosolic fraction. This may explain the inability of exogenous diacylglycerol to stimulate endogenous phosphorylation in pressure-extracted activity. The enzyme is extracted at greater than 1,300 atm, a result indicating it most likely has a portion inserted into the hydrophobic portion of the membrane bilayer. Perturbation of the native membrane induces a change in the membrane-associated protein kinase C-lipid interaction that permits extraction under conditions used for the cytosolic species. This is the first report of conversion of the endogenous membrane species to a cytosolic one and may be important in determining the role of protein kinase C in neuronal regulation.

Phosphorylation of both 47 and 49kDa proteins accompanies superoxide release by neutrophils

Neutrophils stimulated with activators of protein kinase C (i.e., 4 beta-phorbol 12-myristate 13-acetate; sn-1,2-dioctanoylglycerol) exhibit a dramatic, dose-dependent incorporation of 32P[Pi] into two proteins with molecular weights of ca. 47 and 49kDa. Proteins of the same molecular weights are also labelled when the cells are stimulated with a chemotactic peptide. However, with the latter stimulus, labelling of the 47kDa species is transient whereas that of the 49kDa entity persists. Labelling of both proteins always accompanied the release of O2-stimulated by these agents. The kinetics of labelling are compatible with the involvement of both phosphoproteins in the stimulation of these cells.

In vitro studies of the inhibition of protein kinase C from rat brain by di-(2-ethylhexyl)phthalate

The environmental contaminant di(2-ethylhexyl)phthalate (DEHP) has been shown to inhibit the phosphorylation of histone by purified protein kinase C (PK-C) from rat brain in a concentration-dependent manner. The inhibition does not involve making the substrate unavailable, although DEHP does bind to some extent to histone. DEHP displaces phorbol dibutyrate from PK-C, indicating that DEHP binds to the regulatory domain of the enzyme. Since DEHP does not affect the PK-C dependent phosphorylation of protamine, DEHP probably does not bind at the catalytic site. DEHP non-competitively blocked activation of PK-C by either phosphatidyl serine or calcium ion. Inhibition of histone phosphorylation by DEHP was enhanced if diglyceride was present, and the enhancement was stereoselective for the isomeric form of the diglyceride. The mechanism of the inhibition is thought to involve interference with the interaction between calcium ion and the regulatory domain of PK-C, and would have significance only for those PK-C substrates that require calcium activation of the enzyme. Thus the presence of DEHP in the high nanomolar concentration range alters the effective substrate specificity of PK-C.

Phosphorylation of the human erythrocyte glucose transporter by protein kinase C: localization of the site of in vivo and in vitro phosphorylation

1. The human erythrocyte glucose transporter was phosphorylated in vitro by protein kinase C. 2. Tryptic cleavage of phosphorylated native transporter produced two major unphosphorylated membrane-embedded fragments weighing 23 and 19 kDa and released numerous water-soluble peptides. 3. Ion-exchange FPLC of the soluble tryptic peptides resolved the mixture into two phosphopeptide peaks. 4. Tryptic digestion of glucose transporter that was phosphorylated in vivo in response to phorbol esters produced soluble phosphopeptides that eluted at identical salt concentrations. 5. Proteolytic digestion and peptide mapping of the transporter revealed that the site(s) of phosphorylation lie within the large cytoplasmic domain that bisects the molecule.

Purification of a 107 kilodalton (kDa) casein kinase G substrate from thyroid cytosol

A 107 kDa (pp107) casein kinase G (ck-G) substrate has been purified from mouse and beef thyroid cytosol; ck-G was purified from beef thyroid cytosol. Ck-G and pp107 were found to co-elute on DEAE cellulose chromatography at approximately 300 mM NaCl. Ck-G and pp107 were separated by spermine-agarose affinity chromatography; pp107 is eluted with a stepped gradient at 250 mM NaCl and ck-G is eluted at 500 mM NaCl. Ck-G was subsequently purified by casein-agarose and GTP-agarose affinity chromatography. The 107 kDa protein was purified using heparin-agarose affinity chromatography. Phosphorylation of purified pp107 by ck-G was stimulated by spermine (ED50 = 0.2 mM) and inhibited by low concentrations of heparin (0.1-5 micrograms/ml). The Km and Vmax for the reaction were 1.46 microM and 32.2 nmoles P transferred/20 min/mg protein, respectively; 1 mole pp107 incorporated 0.81 mole phosphorus. pp107 was found to be an acidic substrate with a pI of 3.87 and was absorbed to wheat-germ agglutinin-agarose. The specificity of pp107 phosphorylation was studied using diacylglycerol-activated calcium/phospholipid-dependent protein kinase C, calcium-activated calmodulin-dependent protein kinase, and the catalytic subunit of cAMP-dependent protein kinase A. Phosphorylation of pp107 by the other protein kinases tested never exceeded 4% of that of ck-G. Our data show that pp107 is an acidic glycoprotein which may serve as a high-affinity and specific substrate for ck-G.

Regulation of protein kinase C activity by various lipids

Protein kinase C has recently attracted considerable attention because of its importance in the control of cell division, cell differentiation, and signal transduction across the cell membrane. The activity of this enzyme is altered by several lipids such as diacylglycerol, free fatty acids, lipoxins, gangliosides, and sulfatides. These lipids may interact with protein kinase C either directly or through calcium ions and produce their regulatory effect (activation or inhibition) on the activities of the enzymes phosphorylated by this kinase. These processes widen our perspective of the regulation of intercellular and intracellular communication.

Structure and phosphorylation of eukaryotic initiation factor 2. Casein kinase 2 and protein kinase C phosphorylate distinct but adjacent sites in the beta-subunit

Eukaryotic initiation factor 2 (eIF-2) from rabbit reticulocytes can be phosphorylated on its beta-subunit by two different protein kinases, protein kinase C and casein kinase 2. Phosphorylation by these kinases is additive, suggesting that they phosphorylate different sites (serine residues) in eIF-2 beta. Two-dimensional peptide mapping of the phosphopeptides generated from labelled eIF-2 beta by digestion with trypsin, cyanogen bromide or Staphylococcus aureus V8 proteinase showed that protein kinase C and casein kinase 2 phosphorylated distinct and different sites in this protein. This conclusion was supported by the results of analysis of the phosphopeptides on reverse-phase chromatography. Analysis of the phosphopeptides derived from eIF-2 beta labelled by both kinases together strongly suggested that the sites labelled by protein kinase C and casein kinase 2 are adjacent in the primary sequence. These data are discussed in the light of the present understanding of the sequence specificity of the kinases. Rat liver eIF-2 beta was also found to be a substrate for protein kinase C and casein kinase 2, which were again shown to label different serine residues.

Characterization of a soluble Mr-30,000 catalytic fragment of the neuronal calmodulin-dependent protein kinase II

Chymotryptic digestion of postsynaptic densities releases a soluble, catalytically active fragment of the alpha (Mr 50,000) subunit of the neuronal cytoskeletal calmodulin-dependent protein kinase II. The purified soluble form of the kinase likewise yields the fragment. Denaturation of the enzyme results in more extensive proteolytic degradation. 125I-Iodopeptide maps of the isolated catalytic portions of both forms of the enzyme are similar and are contained within the map of the isolated alpha subunit. Catalytic fragments of both forms of the enzyme comigrate on two-dimensional SDS-PAGE/isoelectric focusing with pI 6.7-7.2. The fragment phosphorylates microtubule-associated protein (MAP-2) but is not activated by Ca+2/calmodulin nor is it inhibited by trifluoperazine. Km values for MAP-2 and ATP are indistinguishable from those of the holoenzyme, while the Vmax is similar to that of the holoenzyme activated with Ca+2/calmodulin. Overlays of Western blots of fragment with 125I-calmodulin shows a loss of calmodulin binding. Both the number of phosphorylation sites and the ability to autophosphorylate are markedly reduced in the catalytic fragment. Evaluation of the hydrodynamic parameters of the purified fragment yielded Mr value of 25,600 with a frictional ratio (f/f0) of 1.12; the Mr value determined by SDS-PAGE was 30,000. Thus, the catalytic fragment appears to represent an activated form of the kinase with a monomeric, globular structure unlike the native enzyme which exhibits oligomerization and cytoskeletal association. These results are consistent with a tertiary structure for the calmodulin-dependent protein kinase that contains distinct domains responsible for catalytic activity, regulation by calmodulin, cytoskeletal association and the multimeric organization of enzyme subunits.

Purification and properties of protein kinase C from rabbit reticulocyte lysates

We have previously reported that addition of Ca2+ and phospholipid (PL) inhibits translation in hemin-containing reticulocyte lysates through activation of a eukaryotic protein synthesis initiation factor (eIF-2) kinase. The possibility that this activation was mediated by a Ca2+-PL-dependent protein kinase (protein kinase C, PKC) appeared unlikely by the observation that it was prevented or reversed by NADPH-generating systems. Nevertheless, reticulocyte lysates contain a potent PKC activity and we deemed it desirable to isolate this enzyme to answer unequivocally the question whether it does or does not activate eIF-2 alpha kinase. We have purified reticulocyte PKC to near homogeneity with Mr 95,500 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme absolutely depended upon both Ca2+ and phosphatidylserine for activity on histone H1 or the beta-subunit of initiation factor eIF-2 and underwent autophosphorylation in a Ca2+- and PL-dependent manner. Mild treatment with trypsin yielded an Mr 82,000 polypeptide that still required Ca2+ and PL for activity. This Mr agrees with that reported for other PKCs, suggesting that these enzymes may undergo limited degradation during isolation. Further proteolytic treatment converted the reticulocyte enzyme into a Ca2+- and PL-dependent form, as is known for PKCs from other sources. The highly purified PKC had no effect on translation in hemin-supplemented reticulocyte lysates.

A single form of protein kinase C is expressed in bovine adrenocortical tissue, as compared to four chromatographically resolved isozymes in rat brain

Protein kinase C purified to apparent homogeneity from rat brain was resolved into four active moieties following chromatography over a hydroxyapatite high resolution system. By contrast, the same procedure applied to bovine adrenocortical protein kinase C revealed that a single protein kinase C isoform could be detected in this tissue, with a chromatographic behavior identical to that of one of the brain isoenzymes. Although the isolated protein kinase C isozymes were all activated to various degrees in the presence of phospholipids and calcium, quantitative differences were observed in their catalytic properties, especially with regard to their sensitivity to diacylglycerol and TPA and to their relative affinity for different protein substrates. These observations confirmed at the protein level the heterogeneity of protein kinase C predicted on the basis of cDNA cloning studies. They also suggest that the expression of a specific set of protein kinase C isoenzyme(s) in a given cell type deserves further attention, since it may reflect a functional significance with regard to the regulation of specific cellular processes.

Substitution of phosphatidylserine by lipid A in the activation of purified rabbit brain protein kinase C

Three lipid A derivatives (hexaacyl monophosphoryl lipid A, hexaacyl diphosphoryl lipid A, and disaccharide precursor IVA) were shown to activate protein kinase C from rabbit brain. These derivatives substituted for phosphatidylserine in a concentration-dependent manner and did not compete for binding of [3H]phorbol dibutyrate to its receptor site. Instead, phorbol dibutyrate binding was increased on raising the concentration of the derivatives in a similar manner to phosphatidylserine. The phorbol ester 12-0-tetra-decanol 13-acetate augmented the activation of protein kinase C by the lipid A derivatives.

Protein kinase C binding to isolated nuclei and its activation by a Ca2+/phospholipid-independent mechanism

The direct interaction of protein kinase C with the nucleus was examined utilizing endogenous protein phosphorylation and [3H]PDBu binding to detect the enzyme. Rat brain nuclei were relatively rich in phorbol ester receptors whereas liver nuclei contained less than 10% of their brain counterpart. Purified protein kinase C from rat brain could bind to purified rat liver nuclei at 4 degrees C or at 24 degrees C reaching apparent equilibrium by 20 min. The binding was linearly dependent on protein kinase C concentration and required free Ca2+ with an EC50 of 0.5 microM. Chelation of Ca2+ with EGTA resulted in rapid loss of phorbol ester receptors from nuclei. Differential extraction experiments with Triton X-100 and NaCl suggested that about 50% of the acquired phorbol ester receptors were bound to chromatin and 25% were associated with the nuclear matrix. Protein Kinase C bound to nuclei was also able to phosphorylate several endogenous nuclear substrates in a Ca2+/phospholipid-independent reaction. These data suggest that protein kinase C can associate with nuclear components leading to the phosphorylation of nuclear substrates.

In-vitro modulation of protein kinase C activity by environmental chemical pollutants

A number of environmental chemical pollutants have been reported to cause tumors or help in the propagation of tumors in experimental animals. The in-vitro effects of a few chemical contaminants were studied on the histone phosphorylation and 3H Phorbol dibutyrate (PdBu) binding of partially purified Ca2+/phospholipid dependent protein kinase c (PKC) from the brains of Fischer F344 and B6C3F1 mice. The enzyme was prepared by a modified method which gave approximately 75-fold purification. A differential effect of various compounds was observed on the phosphorylation activity and PdBu binding of PKC from rats and mice. The reported tumor promoting ability and effect on protein kinase C activity appeared to be related in the case of the rat enzyme, although causality cannot be inferred.

A rapid preparation of human platelet calcium-activated phospholipid-dependent protein kinase

A rapid, high yield and relatively stable preparation of human platelet calcium-activated phospholipid-dependent protein kinase (protein kinase C) is described. The method is based on the calcium-dependent and reversible binding of the enzyme to platelet membranes and its success is largely due to the immediate separation of the enzyme from the soluble calcium-dependent protease as well as the platelet endogenous substrate in the first step. Different additions to the platelet lysis medium are examined and the most critical are leupeptin as an inhibitor of the protease and mercapto-ethanol to maintain enzyme activity. This protein kinase C preparation can be done in less than 24 hours and yields an enzyme which is about 90% pure with a 15-fold activation by calcium, diolein and phospholipid, and is devoid of any cAMP-dependent protein kinase or myosin light chain kinase activities.

Isozymic forms of rat brain Ca2+-activated and phospholipid-dependent protein kinase

Three forms of rat brain Ca2+-activated and phospholipid-dependent protein kinase (EC 2.7.1.37) were separated by hydroxylapatite column chromatography. These enzymes, designated type I, II, and III protein kinase C, all have a molecular weight of 82,000, undergo autophosphorylation in the presence of Ca2+, phosphatidylserine, and diolein, and bind [3H]phorbol 12,13-dibutyrate. Autophosphorylation of these kinases resulted in an incorporation of 1-1.5 mol of 32P per mol of enzyme. Two-dimensional peptide mapping analysis revealed that these kinases had different sites of autophosphorylation. Phosphoamino acid analysis showed that type I and type III protein kinase C primarily autophosphorylated at a serine residue, whereas type II kinase autophosphorylated at both serine and threonine residues. In addition, polyclonal antibodies raised against a mixture of three types of the kinase preferentially inhibited type I and type II enzymes. Monoclonal antibodies against type I and type II kinase only recognized their respective enzymes but not the type III enzyme. These results demonstrate the presence of isozymic forms of protein kinase C in rat brain.

Studies and perspectives of protein kinase C

Protein kinase C, an enzyme that is activated by the receptor-mediated hydrolysis of inositol phospholipids, relays information in the form of a variety of extracellular signals across the membrane to regulate many Ca2+-dependent processes. At an early phase of cellular responses, the enzyme appears to have a dual effect, providing positive forward as well as negative feedback controls over various steps of its own and other signaling pathways, such as the receptors that are coupled to inositol phospholipid hydrolysis and those of some growth factors. In biological systems, a positive signal is frequently followed by immediate negative feedback regulation. Such a novel role of this protein kinase system seems to give a logical basis for clarifying the biochemical mechanism of signal transduction, and to add a new dimension essential to our understanding of cell-to-cell communication.

Retinoids stimulate the release of superoxide by neutrophils and change their morphology

All-trans-retinal stimulated the release of superoxide by human and guinea pig neutrophils 63 +/- 14 SD and 53 +/- 5 SD nmol of O2-/min/10(7) cells, respectively. Superoxide release by unstimulated cells was negligible. All-trans-retinal also induced morphological changes (i.e., evaginations) in these cells. Other retinoids were effective in instigating these phenomena. The similarities of these effects to those instigated by cis-unsaturated fatty acids (Badwey, J.A., et al., 1984, J. Biol. Chem., 259:7870-7877) are discussed in light of possible mechanisms.

Rapid purification of protein kinase C by high performance liquid chromatography

Protein kinase C was purified from rat brain cytosol by using a high performance liquid chromatography (HPLC), Pharmacia FPLC system. This procedure employed a column chromatography on DE-52, followed by three steps of HPLC procedures with threonine-Sepharose (prepared as described in this report), TSK gel Phenyl-5PW (Toyo Soda), and TSK gel G3000SW (Toyo Soda) columns. Starting from about 30 g of rat brain, approximately 200 micrograms of pure enzyme was obtained. The procedure was very simple and highly reproducible. The enzyme thus obtained was nearly pure by silver staining after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the presence of 10% (w/v) glycerol and 0.05% (w/v) Triton X-100, the enzyme could be stored at -80 degrees C for several months.

Activation of protein kinase C by lipoxin A and other eicosanoids. Intracellular action of oxygenation products of arachidonic acid

Arachidonic acid, linolenic acid and 14 different oxygenated fatty acid derivatives were tested as activators of human protein kinase C in vitro using histone as substrate. Lipoxin A (5,6,15L-trihydroxy-7,9,11,13-eicosatetraenoic activated the kinase in the presence of calcium at 30 fold lower concentration (1 microM) than did arachidonic acid or 1,3-dioleoylglycerol. The methyl ester of lipoxin A and the free acids of leukotriene B4 as well as two lipoxin B isomers were without effect. In contrast, linolenic acid, leukotriene C4, certain mono- and dihydroxylated eicosanoids and one lipoxin B isomer had stimulatory effects, albeit at higher concentrations. The substrate specificity of protein kinase C activated by lipoxin A proved to be different from that of the phosphatidylserine or phorbol ester activated kinase. Results of the present study suggest that arachidonic acid derived oxygenation products, in particular lipoxin A, may serve as intracellular activators of protein kinase C.