Protein Kinase C in Primary Astrocyte Cultures: Cytoplasmic Localization and Translocation by a Phorbol Ester

The distribution of calcium-activated, phospholipid-dependent protein kinase (protein kinase C) in supernatant and particulate fractions of primary cultures of rat astrocytes and its translocation by a phorbol ester were studied. We observed that 91% of protein kinase C activity in astrocytes was in the supernatant fraction, as measured by lysine-rich histone phosphorylation assay. Attempts to uncover latent activity in the particulate fraction were unsuccessful. Approximately 75% of the supernatant protein kinase C activity could be translocated to the particulate fraction by prior treatment (30-60 min) of the cultures with 100 nM 12-O-tetradecanoyl-phorbol 13-acetate (TPA), but not with 4 alpha-phorbol, an inactive phorbol ester. Investigation of endogenous substrates for protein kinase C showed that TPA treatment brought about an increase in phosphorylation in membrane proteins and a decrease in phosphorylation of supernatant proteins. These findings indicate that the distribution of protein kinase C in astrocytes differs substantially from that in whole brain tissue, where approximately two-thirds of the protein kinase C activity is associated with the particulate fraction. Because protein kinase C is concentrated in the cytosol of astrocytes and most of this activity can be translocated to membranes, astrocytes may be particularly well-suited to respond to signals that activate phosphoinositide-linked receptors in brain.     

Effect of phorbol esters on the distribution and total activity of protein kinase C in the perfused rat heart

1. The perfused rat heart was treated with the tumour-promoter and protein kinase C activator, phorbol 12-myristate 13-acetate and the distribution of protein kinase C activity between cytosolic and particulate fractions determined. 2. Phorbol ester treatment led to a rapid loss of protein kinase C activity from the cytosol (t0.5 = 2 min) with a corresponding translocation into the particulate fraction. Translocated protein kinase C activity was tightly bound to the particulate fraction, could only be extracted with buffers containing 2% Triton X-100 and could therefore be misinterpreted as being down-regulated. 3. Claims of rapid down-regulation of protein kinase C activity by phorbol esters need to be supported by rigorous procedures for extraction of the particulate material.     

Phorbol esters, but not epidermal growth factor or insulin, rapidly decrease soluble protein kinase C activity in rat hepatocytes

Exposure of freshly isolated rat hepatocytes to tumor-promoting phorbol esters like phorbol 12-myristate 13-acetate resulted in a time- and concentration-dependent translocation of protein kinase C from the soluble to the particulate fraction of the cells. No such disappearance of soluble protein kinase C activity was observed with either epidermal growth factor or insulin, indicating that activation of protein kinase C is not necessarily involved in the short-term metabolic action of physiological growth factors on rat hepatocytes.     

Modulation of aortic protein phosphorylation by benzo(a)pyrene: Implications in PAH-induced atherogenesis

The toxicity of polycyclic aromatic hydrocarbons such as benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene, and 3-methylcholanthrene has been associated with alterations in the proliferation of vascular smooth muscle cells and the development of lesions of mesenchymal origin. Because phosphorylation of endogenous substrates plays a central role in the regulation of smooth muscle cell growth, the present studies were conducted to evaluate the phosphorylation pattern of medial aortic protein upon repeated in vivo exposure of Japanese quail to benzo(a)pyrene (BaP). Medial aortic homogenates from quail treated for 10 weeks with 10 mg/kg benzo(a)pyrene or vehicle were processed for in vitro measurements of protein phosphorylation. In vitro phosphorylation of endogenous or exogenous proteins stimulated in vitro by phorbol myristate acetate/phosphatidyl-serine or cyclic AMP, known activators of protein kinase C and cyclic AMP-dependent protein kinase, respectively, was examined in the cytosolic and particulate fractions of homogenates from control and treated animals. Benzo(a)pyrene treatment significantly enhanced the basal phosphorylation of Mr 113, 35, and 23 kDa proteins in the cytosolic fraction. Modest increases in the phosphorylation of Mr 71, 52, and 38 kDa were also observed under basal conditions. No changes in the basal phosphorylation of particulate proteins were observed. Phosphorylation of endogenous protein substrates by protein kinase C in the cytosolic fraction was not altered by benzo(a)pyrene treatment. In contrast, inhibition of C-kinase-mediated phosphorylation of endogenous Mr 272, 72, and 45 kDa proteins was observed in the particulate fraction of aortic homogenates from benzo(a)pyrene-treated quail relative to controls. Exogenous histone phosphorylation by PKC in the particulate, but not cytosolic fraction, was decreased by benzo(a)pyrene treatment. The effects of benzo(a)pyrene on the C-kinase system were specific, since cAMP-mediated phosphorylation of endogenous proteins, as well as exogenous histone, was not altered by benzo(a)pyrene. Interestingly, benzo(a)pyrene treatment was associated with a selective increase of Mr 200, 80, and 67 kDa proteins in the cytosolic fraction. Collectively, these data are consistent with the hypothesis that medial protein phosphorylation is a significant molecular target of benzo(a)pyrene within the vascular wall.     

Early effects of TPA on protein kinase activity in murine thymocytes. Reduction of protein kinase C activity in the cytosol and increase of Ca2+ and phospholipid-independent kinase activity in the particulate fractions

Brief treatment of intact thymocytes with TPA and other tumor promoters causes a reduction in protein kinase C activity from the cytosol and an increase in kinase activity in the particulate fraction. In contrast to the activity in the cytosol, which is absolutely dependent on the addition of Ca2+, phosphatidylserine and diolein, the activity in the particulate fraction is independent of these agents. Analysis of target specificity of the particulate kinase activity using exogenous and endogenous substrates suggests that the increased phosphorylation in the particulate fraction is catalysed by protein kinase C with altered catalytic properties. Although interleukin-1 and TPA are both co-mitogens for murine thymocytes, interleukin-1 does not share with TPA its property to alter protein kinase activity in the cytosolic and particulate fractions.     

Survival of Chick Embryonic Sensory Neurons in Culture Is Supported by Phorbol Esters

Sensory neurons of the chick embryo are supported in culture by several neurotrophic factors, including the phorbol esters. Because phorbol esters are known to activate one of the second messengers, namely, protein kinase C, it was of interest to see if the neurotrophic action of phorbol 12,13-dibutyrate (PDB) was related to the activation of protein kinase C in sensory neurons. Sensory neurons were obtained from dorsal root ganglia of 10-day-old chick embryos and maintained in a serum-free medium for several days to quantify survival and analyze protein kinase C activity. PDB (30 nM) supported the survival of approximately 50% of the total number of neurons plated. This value was comparable to that supported by nerve growth factor (NGF; 40 ng/ml). If PDB and NGF were added together, there was no additive effect on the survival. The protein kinase C activity of the particulate and cytosolic fractions of sensory neurons supported by NGF for 3 days was 1.26 +/- 0.1 and 2.9 +/- 0.32 pmol/min/mg of protein, respectively. In contrast, neurons supported by PDB showed an approximately 500% increase in enzyme activity in their particulate fraction. The enzyme activity of the cytosolic fraction was decreased by approximately 40%. If NGF-supported neurons were treated with PDB (30 nM) for 15 min, protein kinase C activity increased greater than 400% in the particulate fraction, whereas an approximately 50% decrease was observed in the cytosolic fraction. The protein kinase C value, expressed as a ratio of the activities in the particulate to cytosol fractions, showed large increases after phorbol treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between membrane-bound protein kinase C activity and calcium-dependent proliferation of BALB/c 3T3 cells

Extracellular calcium-deprivation inhibited the proliferation of BALB/c 3T3 cells and this inhibition correlated with a loss of protein kinase C activity from the particulate fraction. Addition of calcium induced proliferation of the cells with the DNA synthetic activity returning to the control rate at 18 hours following calcium addition. The level of protein kinase C activity in the particulate fraction was monitored at various times after calcium addition and increased in parallel with the DNA synthetic activity.     

Early effects of TPA on protein kinase activity in murine thymocytes : Reduction of protein kinase C activity in the cytosol and increase of Ca and phospholipid-independent kinase activity in the particulate fractions

Brief treatment of intact thymocytes with TPA and other tumor promoters causes a reduction in protein kinase C activity from the cytosol and an increase in kinase activity in the pariculate fraction. In contrast to the activity in the cytosol, which is absolutely dependent on the addition of Ca²⁺, phosphatidylserine and diolein, the activity in the particulate fraction is independent of these agents. Analysis of target specificity of the particulate kinase activity using exogenous and endogenous substrates suggests that the increased phosphorylation in the particulate fraction is catalysed by protein kinase C with altered catalytic properties. Although interleukin-1 and TPA are both co-mitogens for murine thymocytes, interleukin-1 does not share with TPA its property to alter protein kinase activity in the cytosolic and particulate fractions.     

The subcellular distribution of protein kinase Calpha, -epsilon, and -zeta isoforms during cardiac cell differentiation.

There is little information on the molecular events that control the subcellular distribution of protein kinase C during cardiac cell differentiation. We examined protein kinase C activity and the subcellular distribution of representatives of the "classical," "novel," and "atypical" protein kinase C's in P19 murine teratoma cells induced to undergo differentiation into cardiac myocytes by the addition of dimethylsulfoxide to the medium (Grepin et al., Development 124, 2387-2395, 1997). Differentiation was assessed by the presence of striated myosin, a morphological marker for cardiac cells. Addition of dimethyl sulfoxide to the medium resulted in the appearance of striated myosin by 10 days postincubation. Immunolocalization and Western blot studies revealed that a significant proportion of protein kinase Calpha, -epsilon, and -zeta were associated with the particulate fraction in P19 cells prior to differentiation. Differentiation into cardiac cells resulted in a translocation of protein kinase C activity from the particulate fraction to cytosol and localization of most of protein kinase Calpha, -epsilon, and -zeta to the cytoplasmic compartment. The total cellular protein kinase C activity was unaltered during differentiation. The translocation of protein kinase C activity during differentiation of P19 cells into cardiac myocytes was associated with a decrease in the levels of cellular 1, 2-diacyl-sn-glycerol. The cellular levels of phosphatidylserine and phosphatidylinositol did not change during differentiation. Addition of 1,2-dioctanoyl-sn-glycerol, a cell-permeant 1, 2-diacyl-sn-glycerol analog, reversed the differentiation-induced switch in the relative distribution of protein kinase C activity and dramatically increased the association of protein kinase Calpha with the particulate fraction. Addition of 1,2-dioctanoyl-sn-glycerol did not reverse the pattern of distribution for protein kinase Cepsilon or -zeta. The results indicate that protein kinase C activity and protein kinase Calpha, -epsilon and -zeta isoforms are redistributed from the particulate to the cytosolic fraction during differentiation of P19 cells into cardiomyocytes. The mechanism for the redistribution of protein kinase Calpha may be related to the reduction in the cellular 1,2-diacyl-sn-glycerol levels that accompany differentiation.     

Phorbol ester induces differential membrane-association of protein kinase C subspecies in human platelets

Human platelets contained proteins which cross-reacted with antisera specific for brain protein kinase C-alpha and -beta. When platelets were incubated with 12-O-tetradecanoylphorbol-13-acetate there was a rapid accumulation of protein kinase C-alpha in the particulate fraction associated with a loss of this subspecies from the soluble fraction. No particulate accumulation or soluble loss of protein kinase C-beta could be detected when platelets were incubated with the phorbol ester.     

Cell-free protein synthesis in heart and skeletal muscles from polymyopathic hamsters

1. Cell-free protein synthesis was studied in striated and smooth muscles in an attempt to elucidate the primary genetic defect in polymyopathic hamsters. 2. When washed membrane-free polyribosomes from myopathic and control heart muscle were individually recombined with pH5 enzymes from both types of animals, the pH5 enzymes from myopathic muscle were less active in polypeptide synthesis than those from controls, irrespective of the source of polyribosomes. 3. The same defect was present in skeletal-muscle preparations. 4. Both the initial rate and the maximum extent of incorporation were affected in the defective preparations from myopathic muscle. 5. Concentration differences, with respect to total protein and RNA, were not responsible. 6. Preincubation of the pH5 enzymes resulted in a greater degree of inhibition. 7. The defect in the pH5 enzymes from myopathic muscle was also expressed in poly(U)-directed polyphenylalanine synthesis. 8. Acid proteinase activity in extracts of control and myopathic muscle was the same but general ribonuclease activity in the latter extracts was higher. 9. The defect was also present when both types of pH5 enzymes were prepared in the presence of the ribonuclease-asborbent bentonite. 10. pH5 enzymes from uterine smooth muscle, brains and livers of myopathic animals were similarly affected in homologous and heterologous combinations. 11. It is concluded that the general tissue defect is both qualitative and quantitative in nature, implying that there is a shortage of some essential soluble component in the pH5 fraction which is accompanied by the presence of an altered substituent. This prevents the attainment of extents of polypeptide synthesis in vitro obtained in control extracts from unaffected animals.     

Tyrosine protein kinase activity of rat spleen and other tissues

Using a synthetic peptide (Glu-Asp-Ala-Glu-Tyr-Ala-Ala-Arg-Arg-Arg-Gly) as a substrate, various normal tissues from the rat were probed for tyrosine protein kinase activity. Spleen was shown to contain much higher tyrosine protein kinase activity than other rat tissues (lung, brain, testes, liver, kidney, heart, and thymus, in decreasing order of specific activity). Most of the tyrosine protein kinase activity of the various rat tissues (greater than 80%) was present in the particulate fraction, and Nonidet P-40, a nonionic detergent, could activate the particulate form of the enzyme 2-20-fold in many of the tissues. Epidermal growth factor (1 microgram/ml), cyclic AMP, cyclic GMP, or Ca2+ did not increase spleen tyrosine protein kinase activity. Half-maximal enzyme activity was observed at 60-80 microM MgATP and at 2.2 mM peptide, and both Mg2+ (10 mM) and Mn2+ (0.5-1.0 mM) were effective divalent metal ions for the expression of activity. When the particulate fraction of spleen was incubated with [gamma-32P]ATP followed by polyacrylamide gel electrophoresis in the presence of Na dodecyl SO4, a number of alkali-stable bands were identified by autoradiography. Two major bands at Mr = 53,000 and 56,000 were shown to contain phosphotyrosine. Two similar alkali-stable bands containing phosphotyrosine but with lower amounts of 32P labeling were also observed in the particulate fractions of various other tissues (lung, brain, kidney, and testes). The particulate form of tyrosine protein kinase of rat spleen could be solubilized by using high concentrations of Nonidet P-40 (5%) at an alkaline pH (pH 9.0). Partial purification and subsequent filtration on Sephacryl S-200 yielded a peak of tyrosine protein kinase activity with an apparent molecular weight of 55,000. The two major phosphorylated bands of Mr = 53,000 and 56,000 co-migrated with the peak of enzyme activity. The solubilized and partially purified enzyme preparation phosphorylated only tyrosine residues when either endogenous proteins or casein were used as substrates. These results suggest that relatively high activities of tyrosine protein kinase exist in a normal tissue (rat spleen). Major endogenous substrates of the enzyme(s) appear to be represented by two proteins of Mr = 53,000 and 56,000; one or both of these substrates may be the tyrosine protein kinase itself.     

Calcium . calmodulin-dependent protein kinase II and calcium . phospholipid-dependent protein kinase activities in rat tissues assayed with a synthetic peptide

Rat tissue levels of Ca2+ . calmodulin-dependent protein kinase II (protein kinase II) and Ca2+ . phospholipid-dependent protein kinase (protein kinase C) were selectively assayed using the synthetic peptide syntide-2 as substrate. The sequence of syntide-2 (pro-leu-ala-arg-thr-leu-ser-val-ala-gly-leu-pro-gly-lys-lys) is homologous to phosphorylation site 2 in glycogen synthase. The relative Vmax/Km ratios of the known Ca2+-dependent protein kinases for syntide-2 were determined to be as follows: protein kinase II, 100; protein kinase C, 22; phosphorylase kinase, 2; myosin light chain kinase, 0.005. Levels of protein kinase II were highest in cerebrum (3.36 units/g tissue) and spleen (0.85 units/g) and lowest in testis (0.05 units/g) and kidney (0.04 units/g). Protein kinase II activity was localized predominantly in the 100,000g particulate fraction of cerebrum and testis, in the supernatant fraction of heart, liver, adrenal, and kidney, and about equally distributed between particulate and supernatant in spleen and lung. Likewise, protein kinase C activity was highest in cerebrum (0.56 units/g) and spleen (0.47 units/g), and the majority of activity was present in the cytosolic fraction for all tissues measured except for cerebrum and testis in which the kinase activity was equal in both fractions. Finally, the ratios of protein kinase II to protein kinase C were different in various rat tissues and between particulate and supernatant fractions. These results suggest somewhat different functions for these two Ca2+-regulated, multifunctional protein kinases.     

Contraction-associated translocation of protein kinase C in rat skeletal muscle

Electrical stimulation of the sciatic nerve of the anaesthetized rat in vivo led to a time-dependent translocation of protein kinase C from the muscle cytosol to the particulate fraction. Maximum activity of protein kinase C in the particulate fraction occurred after 2 min of intermittent short tetanic contractions of the gastrocnemius-plantaris-soleus muscle group and coincided with the loss of activity from the cytosol. Translocation of protein kinase C may imply a role for this kinase in contraction-initiated changes in muscle metabolism.     

Isoproterenol induces a ribosomal modification in the heart and the skeletal muscle of hamsters

The protein synthesis activity of heart, skeletal muscle and liver polysomes from isoprotenerol-treated and control hamsters has been compared in an in vitro non-inititating translation system. Heart and skeletal muscle polysomes from treated hamsters were less active than controls and required a higher magnesium concentration for optimal protein synthesis. These results suggest that there is a conformational modification in heart and skeletal muscle ribosomes from isoprotenerol-treated hamsters. No such change was observed with ribosomes from the liver of isoproterenol-treated hamsters.     

Protein kinase C activity in activated human T-lymphocytes stimulated by interleukin-2

Interleukin-2 and phorbol 12-myristate 13-acetate (PMA) are shown to induce DNA-synthesis in human T-lymphocytes activated with phytohaemagglutinin. However, whereas PMA induced a rapid and persistent translocation of protein kinase C from cytosol to particulate fraction, no translocation was observed upon stimulation with interleukin-2. Treatment with PMA for 72 h caused a slow down-regulation of protein kinase C activity to less than 10% of unstimulated T-lymphocytes and was mainly located in the particulate fraction. In contrast, stimulation with phytohaemagglutinin increased the total cellular protein kinase C activity by approx. 100% but with an unaltered subcellular distribution. However, interleukin-2-induced DNA synthesis in PMA- and phytohaemagglutinin-stimulated T-lymphocytes was comparable. Further, maximal DNA synthesis was shown to be dependent on the continuous presence of interleukin-2. These results indicate that interleukin-2-induced proliferation of activated human T-lymphocytes can occur without a translocation of protein kinase C from the cytosol to the particulate fraction and that interleukin-2 most likely functions as a progression factor.     

Compartmentalization of adenosine 3':5'-monophosphate and adenosine 3':5'-monophosphate-dependent protein kinase in heart tissue.

In rabbit heart homogenates about 50% of the cAMP-dependent protein kinase activity was associated with the low speed particulate fraction. In homogenates of rat or beef heart this fraction represented approximately 30% of the activity. The percentage of the enzyme in the particulate fraction was not appreciably affected either by preparing more dilute homogenates or by aging homogenates for up to 2 h before centrifugation. The particulate enzyme was not solubilized at physiological ionic strength or by the presence of exogenous proteins during homogenization. However, the holoenzyme or regulatory subunit could be solubilized either by Triton X-100, high pH, or trypsin treatment. In hearts of all species studied, the particulate-bound protein kinase was mainly or entirely the type II isozyme, suggesting isozyme compartmentalization. In rabbit hearts perfused in the absence of hormones and homogenized in the presence of 0.25 M NaCl, at least 50% of the cAMP in homogenates was associated with the particulate fraction. Omitting NaCl reduced the amount of particulate-bound cAMP. Most of the particulate-bound cAMP was probably associated with the regulatory subunit in this fraction since approximately 70% of the bound nucleotide was solubilized by addition of homogeneous catalytic subunit to the particulate fraction. The amount of cAMP in the particulate fraction (0.16 nmol/g of tissue) was approximately one-half the amount of the regulatory subunit monomer (0.31 nmol/g of tissue) in this fraction. The calculated amount of catalytic subunit in the particulate fraction was 0.18 nmol/g of tissue. Either epinephrine alone or epinephrine plus 1-methyl-3-isobutylxanthine increased the cAMP content of the particulate and supernatant fractions. The cAMP level was increased more in the supernatant fraction, possibly because the cAMP level became saturating for the regulatory subunit in the particulate fraction. The increase in cAMP was associated with translocation of a large percentage of the catalytic subunit activity from the particulate to the supernatant fraction. The distribution of the regulatory subunit of the enzyme was not significantly affected by this treatment. The catalytic subunit translocation could be mimicked by addition of cAMP to homogenates before centrifugation. The data suggest that the regulatory subunit of the protein kinase, at least that of isozyme II, is bound to particulate material, and theactive catalytic subunit is released by formation of the regulatory subunit-cAMP complex when the tissue cAMP concentration is elevated. A model for compartmentalized hormonal control is presented.     

Subcellular distribution of protein kinase C in rat adrenal glomerulosa cells

With the aid of a synthetic nonapeptide which is a selective substrate for protein kinase C the activity of this enzyme was determined in the crude cytosolic and particulate fractions of rat adrenal glomerulosa cells. When the cells were sonicated in the presence of Ca2+ chelators 65 per cent of their total protein kinase C activity was found in the cytosolic extract. The treatment of cells with angiotensin II under conditions where the maximal stimulation of inositol-lipid hydrolysis was observed did not cause a statistically significant change in the apparent subcellular distribution of protein kinase C. However, when the cytosolic extract was prepared in the presence of Ca2+ the protein kinase C activity was recovered nearly exclusively from the particulate fraction.     

Alterations in the creatine kinase system in the myocardium of cardiomyopathic hamsters

Immunochemical and biochemical methods were used to assess quantitatively the changes in the heart creatine kinase system in the myopathic Syrian hamsters, line CHF I46. Cardiomyopathy in I75-200 day old animals was characterized by decreased content of mitochondria and lower total creatine kinase activity. In isolated mitochondria only the creatine kinase activity was decreased while cytochromes aa3 content and respiration rate were unchanged. The share of mitochondrial creatine kinase in the total tissue enzyme activity was decreased from 33% to I8% and that of BB form was elevated from 5% in control to 20%, at unchanged relative level of MM. Immunoassay showed decreased amount of the mitochondrial creatine kinase in the tissue and its decreased ratio to cytochromes aa3. The results show altered expression of creatine kinase isoenzymes in cardiomyopathy.     

Differential mechanisms of translocation of protein kinase C to plasma membranes in activated human neutrophils

Three classes of activators of human neutrophils that induce the intracellular translocation of protein kinase C from the cytosol to the particulate fraction were compared for their effects on the properties of the particulate (membrane-bound) enzyme. In cells stimulated with 10 ng/ml of phorbol-12-myristate-13-acetate (PMA) the particulate enzyme is almost fully active in the absence of added Ca2+ or phospholipids and this activity is not released by the Ca2+-chelator EDTA. In contrast, binding of protein kinase C to the particulate fraction in cells treated with the chemotactic factor f-Met-Leu-Phe (fMLF) or with the ionophore A-23187 plus Ca2+ is observed only when the cells are lysed in the presence of 1 mM Ca2+. With these stimuli the particulate enzyme retains a nearly absolute requirement for Ca2+ and phospholipids. Thus only the full intercalation of protein kinase C caused by PMA, which is resistant to removal by chelators stabilizes an active form of protein kinase C in the neutrophil membrane. In confirmation of this conclusion, in isolated plasma membranes loaded with partially purified protein kinase C by incubation with 5 microM Ca2+ further incubation with PMA, but not with fMLF, caused a significant fraction of the bound PKC to become resistant to removal by chelators, and to be nearly fully active in the absence of added activators.