Purification and characterization of a rabbit liver calmodulin-dependent protein kinase able to phosphorylate glycogen synthase

Phosphorylation and Dephosphorylation of Tau Protein by the Catalytic Subunit of PKA, as Probed by Electrophoretic Mobility Retard

Background:

Tau is a microtubule associated protein that regulates the stability of microtubules and the microtubule-dependent axonal transport. Its hyperphosphorylated form is one of the hallmarks of Alzheimer’s disease and other tauopathies and the major component of the paired helical filaments that form the abnormal proteinaceous tangles found in these neurodegenerative diseases. It is generally accepted that the phosphorylation extent of tau is the result of an equilibrium in the activity of protein kinases and phosphatases. Disruption of the balance between both types of enzyme activities has been assumed to be at the origin of tau hyperphosphorylation and the subsequent toxicity and progress of the disease.

Objective:

We explore the possibility that, beside the phosphatase action on phosphorylated tau, the catalytic subunit of PKA catalyzes both tau phosphorylation and also tau dephosphorylation, depending on the ATP/ADP ratio.

Methods:

We use the shift in the relative electrophoretic mobility suffered by different phosphorylated forms of tau, as a sensor of the catalytic action of the enzyme.

Results:

The results are in agreement with the long-known thermodynamic reversibility of the phosphorylation reaction (ATP + Protein = ADP+Phospho-Protein) catalyzed by PKA and many other protein kinases.

Conclusion:

The results contribute to put the compartmentalized energy state of the neuron and the mitochondrial-functions disruption upstream of tau-related pathologies.

Functional implications of CaMKII alternative splicing

Ca²⁺ /calmodulin-dependent protein kinase II (CaMKII) is known to be a crucial regulator in the post-synapse during long-term potentiation. This important protein has been the subject of many studies centered on understanding memory at the molecular, cellular, and organismic level. CaMKII is encoded by four genes in humans, all of which undergo alternative splicing at the RNA level, leading to an enormous diversity of expressed proteins. Advances in sequencing technologies have facilitated the discovery of many new CaMKII transcripts. To date, newly discovered CaMKII transcripts have been incorporated into an ambiguous naming scheme. Herein, we review the initial experiments leading to the discovery of CaMKII and its subsequent variants. We propose the adoption of a new, unambiguous naming scheme for CaMKII variants. Finally, we discuss biological implications for CaMKII splice variants.

Characterization and expression analysis of Calmodulin (CaM) in orange-spotted grouper (Epinephelus coioides) in response to Vibrio alginolyticus challenge

Vibrio alginolyticus containing the highly toxic extracellular product is one of the most serious threats to grouper survival and its minimum lethal dose is approximately 500 CFU/g fish body weight in grouper. To study the toxic effects of V. alginolyticus on the immune system in teleost, Calmodulin (CaM), an important molecular indicator gene, was cloned from the orange-spotted grouper (Epinephelus coioides). The full-length Ec-CaM consisted of a 5'-UTR of 103 bp, an ORF of 450 bp and a 3'-UTR of 104 bp. The Ec-CaM gene encoded a protein of 149 amino acids with an estimated molecular mass of 16.4 kDa and a predicted isoelectric point of 3.93. The deduced amino acid sequence showed that Ec-CaM contained four highly conserved EF-hand domains known to be critical for the function of CaM. Ec-CaM was widely expressed and the highest expression level was observed in liver. Following V. alginolyticus challenge, a sharp increase level of respiratory burst activity and apoptosis ratio were observed. Further analyses of CaM expression and p53 expression in liver, kidney and spleen by qRT-PCR demonstrated that the up-regulated expression of CaM and p53 were observed in the vibrio challenge group. Western blotting analysis confirmed that the Ec-CaM protein was strongly induced in liver at 12 h post-injection, while a sharp increase of p53 protein expression was observed at 24 h post-injection. These results showed CaM expression serving as a potential molecular indicator may help to assess the toxicological effects of V. alginolyticus on the ROS generation and apoptotic process in grouper.

Beta(2)-Adrenergic activation increases glycogen synthesis in L6 skeletal muscle cells through a signalling pathway independent of cyclic AMP

AIMS/HYPOTHESIS

In skeletal muscle, the storage of glycogen by insulin is regulated by glycogen synthase, which is regulated by glycogen synthase kinase 3 (GSK3). Here we examined whether adrenergic receptor activation, which can increase glucose uptake, regulates glycogen synthesis in L6 skeletal muscle cells.

METHODS

We used L6 cells and measured glycogen synthesis (as incorporation of D: -[U-(14)C]glucose into glycogen) and GSK3 phosphorylation following adrenergic activation.

RESULTS

Insulin (negative logarithm of median effective concentration [pEC(50)] 8.2 +/- 0.3) and the beta-adrenergic agonist isoprenaline (pEC(50) 7.5 +/- 0.3) induced a twofold increase in glycogen synthesis in a concentration-dependent manner. The alpha(1)-adrenergic agonist cirazoline and alpha(2)-adrenergic agonist clonidine had no effect. Both insulin and isoprenaline phosphorylated GSK3. The beta-adrenergic effect on glycogen synthesis is mediated by beta(2)-adrenoceptors and not beta(1)-/beta(3)-adrenoceptors, and was not mimicked by 8-bromo-cyclic AMP or cholera toxin, and also was insensitive to pertussis toxin, indicating no involvement of cyclic AMP or inhibitory G-protein (G(i)) signalling in the beta(2)-adrenergic effect on glycogen synthesis. 12-O-tetra-decanoylphorbol-13-acetate (TPA) increased glycogen synthesis 2.5-fold and phosphorylated GSK3 fourfold. Inhibition of protein kinase C (PKC) isoforms with 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrollo(3,4-c)-carbazole (Gö6976; inhibits conventional and novel PKCs) or 2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl)maleimide (Gö6983; inhibits conventional, novel and atypical PKCs) inhibited the stimulatory TPA effect, but did not significantly inhibit glycogen synthesis mediated by insulin or isoprenaline. Inhibition of phosphatidylinositol 3-kinase (PI3K) with wortmannin inhibited the effects of insulin and isoprenaline on glycogen synthesis.

CONCLUSIONS/INTERPRETATION

These results demonstrate that in L6 skeletal muscle cells adrenergic stimulation through beta(2)-adrenoceptors, but not involving cyclic AMP or G(i), activates a PI3K pathway that stimulates glycogen synthesis through GSK3.

Organ-specific distribution of the calcium sensor CaMKII in Locusta migratoria

The Ca(2+)/calmodulin-dependent kinase CaMKII is a key signaling component in Ca(2+)-dependent physiological processes. The expression and function of CaMKII in insect brain is well documented but less investigated for other tissues of insects. The present study demonstrates that in the locust Locusta migratoria CaMKII is widely expressed in various tissues. Relatively high expression levels of CaMKII were found in the brain, upper part of the digestive tract (pharynx, esophagus), and the flight and leg muscles. The different expression patterns of CaMKII in various tissues, as well as different molecular masses of CaMKII between 48 and 60 kDa indicate a tissue-specific expression of CaMKII variants. The expression was monitored with a polyclonal anti-(rat)CaMKII antibody. About 60% of total CaMKII activity in flight muscle cells is associated to the myofibril-rich, particulate fraction suggesting an important role of CaMKII in sarcomeric function.

Effect of prenatal and postnatal ethanol exposure on Ca2+ /calmodulin-dependent protein kinase II in rat cerebral cortex

The ability of ethanol to influence Ca2+ /calmodulin-dependent protein kinase II (CaM kinase II)-mediated phosphorylation in rat cerebral cortex during prenatal and postnatal ethanol treatment was examined. Ethanol treatment increased protein expression of CaM kinase II alpha-subunit in membrane and cytosolic fractions during development. When specific CaM kinase II stimulators (Ca2+ /calmodulin) and inhibitor (autocamtide-2-related inhibitory peptide) were included during in vitro phosphorylation assays, three putative proteins (65, 50, and 40 kDa) were specifically phosphorylated by CaM kinase II, which might be involved in neurosignaling events associated with chronic ethanol treatment. Given that activation of CaM kinase II is a prerequisite for long-term potentiation induction through N-methyl-D-aspartate receptors, ethanol-induced increase in the levels of CaM kinase II alpha-subunit and selective phosphorylation of specific substrate proteins in cerebral cortex suggest a relation between calcium influx and increased CaM kinase II levels that might be relevant in ethanol-induced central nervous system dysfunction.

Role of COOH-terminal phosphorylation in the regulation of casein kinase I delta

Casein kinase I delta is a member of the casein kinase I (CKI) family, a group of second messenger independent protein kinases. We present evidence that the COOH-terminal domain of CKI delta has regulatory properties. CKI delta expressed in Escherichia coli was activated by heparin, as found previously, and by treatment with the catalytic subunit of type-1 protein phosphatase (CS1). Concomitant with activation by CS1, there was a reduction in the apparent molecular weight of CKI delta from 55,000 to 49,000 as judged by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Truncation of CKI delta by removal of the COOH-terminal 110 amino acids eliminated the ability of CS1 to activate or to increase electrophoretic mobility. Casein kinase I alpha, a 37-kDa isoform that lacks an extended COOH-terminal domain, was not activated by CS1 or the presence of heparin. However, a chimeric enzyme consisting of CKI alpha fused to the COOH-terminal domain of CKI delta was activated by both heparin and CS1. Analysis of the effects of CS1 on a series of CKI delta COOH-terminal truncation mutants identified an inhibitory region between His317 and Pro342, which contained six potential phosphorylation sites. From analysis of the specific activites of these truncation mutants, removal of the same region resulted in enzyme with a specific activity nearly 10-fold greater than wild-type. Thus, CKI delta activity can be regulated by phosphorylation of its COOH terminus, which may serve to create an autoinhibitory domain. This mechanism of regulation could have important consequences in vivo.

Casein kinase I gamma subfamily. Molecular cloning, expression, and characterization of three mammalian isoforms and complementation of defects in the Saccharomyces cerevisiae YCK genes

Casein kinase I, one of the first protein kinases identified biochemically, is known to exist in multiple isoforms in mammals. Using a partial cDNA fragment corresponding to an isoform termed CK1 gamma, three full-length rat testis cDNAs were cloned that defined three separate members of this subfamily. The isoforms, designated CK1 gamma 1, CK1 gamma 2, and CK1 gamma 3, have predicted molecular masses of 43,000, 45,500, and 49,700. CK1 gamma 3 may also exist in an alternatively spliced form. The proteins are more than 90% identical to each other within the protein kinase domain but only 51-59% identical to other casein kinase I isoforms within this region. Messages for CK1 gamma 1 (2 kilobases (kb)), CK1 gamma 2 (1.5 and 2.4 kb), and CK1 gamma 3 (2.8 kb) were detected by Northern hybridization of testis RNA. Message for CK1 gamma 3 was also observed in brain, heart, kidney, lung, liver, and muscle whereas CK1 gamma 1 and CK1 gamma 2 messages were restricted to testis. All three CK1 gamma isoforms were expressed as active enzymes in Escherichia coli and partially purified. The enzymes phosphorylated typical in vitro casein kinase I substrates such as casein, phosvitin, and a synthetic peptide, D4. Phosphorylation of the D4 peptide was activated by heparin whereas phosphorylation of the protein substrates was inhibited. The known casein kinase I inhibitor CK1-7 also inhibited the CK1 gamma s although less effectively than the CK1 alpha or CK1 delta isoforms. All three CK1 gamma s underwent autophosphorylation when incubated with ATP and Mg2+. The YCK1 and YCK2 genes in Saccharomyces cerevisiae encode casein kinase I homologs, defects in which lead to aberrant morphology and growth arrest. Expression of mammalian CK1 gamma 1 or CK1 gamma 3 restored growth and normal morphology to a yeast mutant carrying a disruption of YCK1 and a temperature-sensitive allele of YCK2, suggesting overlap of function between the yeast Yck proteins and these CK1 isoforms.

Autophosphorylation: a salient feature of protein kinases

Most protein kinases catalyze autophosphorylation, a process which is generally intramolecular and is modulated by regulatory ligands. Either serine/threonine or tyrosine serves as the phosphoacceptor, and several sites on the same kinase subunit are usually autophosphorylated. Autophosphorylation affects the functional properties of most protein kinases. Members of the protein kinase family exhibit diversity in the characteristics and functions of autophosphorylation, but certain common themes are emerging.

Multifunctional Ca2+/calmodulin-dependent protein kinase

Multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) is a prominent mediator of neurotransmitters which elevate Ca2+. It coordinates cellular responses to external stimuli by phosphorylating proteins involved in neurotransmitter synthesis, neurotransmitter release, carbohydrate metabolism, ion flux and neuronal plasticity. Structure/function studies of CaM kinase have provided insights into how it decodes Ca2+ signals. The kinase is kept relatively inactive in its basal state by the presence of an autoinhibitory domain. Binding of Ca2+/calmodulin eliminates this inhibitory constraint and allows the kinase to phosphorylate its substrates, as well as itself. This autophosphorylation significantly slows dissociation of calmodulin, thereby trapping calmodulin even when Ca2+ levels are subthreshold. The kinase may respond particularly well to multiple Ca2+ spikes since trapping may enable a spike frequency-dependent recruitment of calmodulin with each successive Ca2+ spike leading to increased activation of the kinase. Once calmodulin dissociates, CaM kinase remains partially active until it is dephosphorylated, providing for an additional period in which its response to brief Ca2+ transients is potentiated.

Recombinant rabbit muscle casein kinase I alpha is inhibited by heparin and activated by polylysine

The casein kinase I (CKI) family consists of widely distributed monomeric Ser/Thr protein kinases that have a preference for acidic substrates. Four mammalian isoforms are known. A full length cDNA encoding the CKI alpha isoform was cloned from a rabbit skeletal muscle cDNA library and was utilized to construct a bacterial expression vector. Active CKI alpha was expressed in Escherichia coli as a polypeptide of Mr 36,000. The protein kinase phosphorylated casein, phosvitin and a specific peptide substrate (D4). The enzyme was inhibited by the isoquinolinesulfonamide CKI-7, half-maximally at 70 microM. Heparin inhibited phosphorylation of the D4 peptide or phosvitin by CKI alpha. Polylysine activated when the D4 peptide was the substrate but had no effect on phosvitin phosphorylation. It is becoming clear that the individual CKI isoforms have different kinetic properties and hence could have quite distinct cellular functions.

Novel bovine heart calmodulin-dependent protein kinase which phosphorylates a high molecular weight calmodulin-binding protein

A novel calmodulin-dependent protein kinase has been isolated from bovine cardiac muscle by successive chromatography on DEAE-Sepharose 6B, Calmodulin-Sepharose 4B affinity and Sepharose 6B chromatography columns. The protein kinase was shown by gel filtration chromatography to have a molecular mass of 36,000 daltons. The highly purified protein kinase stoichiometrically phosphorylated the high molecular weight calmodulin-binding protein from cardiac muscle [Sharma RK (1990) J Biol Chem 265, 1152-1157] in a Ca2+/calmodulin-dependent manner. The phosphorylation resulted in the maximal incorporation of 1 mol of phosphate/mol of the high molecular weight calmodulin-binding protein. Other Ca2+/calmodulin-dependent protein kinases failed to phosphorylate the high molecular weight calmodulin-binding protein. The distinct substrate specificity of this protein kinase indicates that it is not related to the known calmodulin-dependent protein kinases and therefore constitutes a novel protein kinase.

Ca2+/calmodulin-dependent phosphorylation of the 100-kDa protein in chick embryonic muscle cells in culture

The pattern of protein phosphorylation was found to change in differentiating chick embryonic myoblasts in culture. The extent of phosphorylation of 42-, 50-, and 100-kDa proteins increased while that of a 63-kDa protein declined in extracts of myoblasts that had been cultured for increasing periods. Of these, the increase in phosphorylation of the 100-kDa protein occurred most dramatically in extracts of myoblasts in an early stage of differentiation and was specifically inhibited by trifluoperazine (TFP) and other calmodulin (CaM) antagonists including chlorpromazine and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7). Treatment of increasing concentrations of TFP to culture medium also decreased the phosphorylation state of the 100-kDa protein and the degree of myoblast fusion in parallel. In addition, levels of both the kinase activity and the 100-kDa protein but not of CaM appeared to rise in the cells cultured for longer periods. These results suggest that (1) a Ca2+/CaM-dependent protein kinase is responsible for phosphorylation of the 100-kDa protein, (2) the TFP-mediated myoblast fusion block may be associated with the inhibitory effect of the drug against the kinase activity, and (3) the increase in phosphorylation state of the 100-kDa protein during myogenic differentiation is due to the rise in levels of the kinase and its substrate.

Calcium/calmodulin-dependent protein kinase II

There is a great deal known about the in vitro properties of CaM kinase II, both in terms of its substrate specificity and its regulation by calmodulin and autophosphorylation. Much of this characterization is based on experiments performed with the rat brain isozyme of CaM kinase II, although in the aspects examined to date isozymes of the kinase from other tissues appear to behave in a broadly similar manner in vitro. However, relatively little is known about the functions of the kinase in vivo. The proteins phosphorylated by the kinase (with the probable exception of synapsin I and tyrosine hydroxylase) and the role of kinase autophosphorylation in vivo remain largely unknown. Investigation of the physiological role of the kinase in brain and other tissues will be a particularly exciting area for future work. The current knowledge of the in vitro properties and the availability of cDNA clones will hopefully expedite this research.

Multifunctional Ca2+/calmodulin-dependent protein kinase: domain structure and regulation

Cells respond to many hormones, neurotransmitters and growth factors by increasing intracellular Ca2+. This second messenger, in turn, affects cellular function via activation of a novel multifunctional Ca2+/calmodulin-dependent protein kinase. The kinase displays an interesting form of biochemical 'memory'; activation elicits an autophosphorylation which converts it to a Ca2+-independent enzyme that can continue to phosphorylate cellular proteins for some time following termination of the initial Ca2+ stimulus.

The insulin receptor: structure and function

Promising progress in understanding the molecular basis of insulin action has been achieved by demonstrating that the insulin receptor is an insulin-sensitive tyrosine kinase. Here we discuss the structure of this receptor kinase and compare it with receptors for related growth factors. We review the known modes to regulate the receptor kinase activity, either through its autophosphorylation (on tyrosine residues) or through its phosphorylation by other kinases (on serine and threonine residues). We discuss the role of the receptor kinase activity in hormone signal transduction in light of results indicating a reduced kinase activity in insulin-resistant states. Finally, studies to identify natural substrates for the insulin receptor kinase are presented. The possible physiological role of these phosphorylated substrates in mediating insulin action is evaluated.

Immunohistochemical localization of Ca2+/calmodulin-dependent protein kinase II in rat brain and various tissues

Polyclonal antibodies against Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) of rat brain were prepared by immunizing rabbits and then purified by antigen-affinity column. The antibodies which recognized both subunits of the enzyme with Mrs 49K and 60K were used for the study on the distribution of CaM kinase II in formalin-fixed, paraffin-embedded tissues. In the brain, a light-microscopic study demonstrated strong immunoreactivity in neuronal somata and dendrites and weak immunoreactivity in nuclei. The densely stained regions included cerebral cortex, hippocampal formation, striatum, substantia nigra, and cerebellar cortex. In substantia nigra, neurites were stained, but not neuronal somata. Electron microscopy revealed that the immunoreactive product was highly concentrated at the postsynaptic densities. In addition to neurons, weak immunoreactivity was also demonstrated in glial cells, such as astrocytes and ependymal cells of ventricles and epithelial cells of choroid plexus. In other tissues, strong immunoreactivity was observed in the islet of pancreas and moderate immunoreactivity in skeletal muscle and kidney tubules. Immunoreactivity was demonstrated in all of the tissues tested. The results suggest that CaM kinase II is widely distributed in the tissues.

Phosphorylation of glycogen synthase by a bovine thymus protein-tyrosine kinase, p40

Glycogen synthase from rabbit skeletal muscle was found to be phosphorylated by a protein-tyrosine kinase, p40, purified from bovine thymus. The phosphorylation, to a stoichiometry of 0.4-0.5 mol/mol subunit, was specific for a single tyrosine residue in the sequence EEDGERYDEDEE. This acidic sequence has considerable similarity to the site recognized by p40 in erythrocyte band 3 protein. In the analysis of the phosphorylated peptide, it was noted that the sequence -RY(P)- impeded cleavage by either trypsin or automatic Edman degradation.

Substrate specificity of Ca2+/CaM-dependent multifunctional protein kinases: comparison of isoenzymes from brain, liver and skeletal muscle

Ca2+/CaM-dependent multifunctional protein kinase isoenzymes from brain, skeletal muscle and liver were compared by their phosphorylation of a number of protein substrates. Under the conditions of assay, the three isoenzymes demonstrated rapid phosphorylation of synapsin I and glycogen synthase. In contrast, rates of phosphorylation of pyruvate kinase and phenylalanine hydroxylase were almost two orders of magnitude slower. Differences in phosphorylation specifically of the latter two substrates was also observed among the three protein kinases. Phosphorylation by Ca2+/CaM-dependent protein kinases was contrasted with cAMP-dependent protein kinase, which phosphorylates these proteins in vitro and in vivo. The potential role of Ca2+/CaM-dependent multifunctional protein kinases in the Ca2+-dependent phosphorylation of these substrates is discussed.

Conserved and variable regions in the subunits of brain type II Ca2+/calmodulin-dependent protein kinase

Brain type II Ca2+/calmodulin-dependent protein kinase is a holoenzyme composed of several copies each of three subunits, alpha (50 kd), beta (60 kd), and beta' (58 kd), in varying proportions. The deduced amino acid sequences of alpha (reported here) and beta are highly similar but not identical. The major difference between them is the deletion from alpha of two short segments (residues 316-339 and 354-392 in beta). cDNAs that appear to encode beta' are identical to beta except for the deletion of a segment encoding residues 378-392. Thus, the structural differences among alpha, beta, and beta' arise primarily from deletions (or insertions) in a variable region lying immediately carboxyl to the protein kinase and calmodulin-binding domains. The alpha and beta subunits are encoded by distinct genes expressed primarily, if not exclusively, in brain. Rather than being encoded by a third gene, beta' may arise by alternative splicing of the beta gene transcript.

Heterogeneity of human liver, muscle, and adipose tissue insulin receptor

We have studied the structure and function of the human insulin receptor in liver, skeletal muscle and adipose tissue. The alpha-subunit of the insulin receptor for liver, muscle and adipose tissue migrated on SDS-PAGE with Mrs 137632 +/- 216, 134034 +/- 1080, and 133575 +/- 165, respectively (p less than 0.05). Treatment of these receptors with neuraminidase decreased their molecule sizes and eliminated the relative size differences between the receptors. Three monoclonal antibodies (5A1, 10D9, and 20H3), directed towards different epitopes of the human insulin receptor alpha-subunit were used to probe immunological differences among the receptors. Antibodies 5A1 and 20H3 recognized all the receptors, whereas 10D9 recognized muscle and adipose tissue receptors but not liver receptors. The mobility of insulin receptor beta-subunit in the absence of insulin was the same in all tissues with a similar phosphorylation-induced decrease in mobility in SDS-PAGE in the presence of insulin. However, insulin stimulated autophosphorylation per receptor was different being greatest (p less than 0.05) in muscle (334 +/- 104 32P cpm) and similar in adipose tissue (114 +/- 10) and liver (183 +/- 68). These studies indicate, therefore, that the human insulin receptor is heterogeneous among the major target tissues for insulin, and raise the possibility that this heterogeneity may account for tissues' specific differences in insulin's biological messages.

The Ca2+-pumping ATPase and the major substrates of the cGMP-dependent protein kinase in smooth muscle sarcolemma are distinct entities

It has been proposed that the plasma membrane Ca2+ pump of smooth muscle tissues may be regulated by cGMP-dependent phosphorylation [Popescu, L. M., Panoiu, C., Hinescu, M. & Nutu, O. (1985) Eur. J. Pharmacol. 107, 393-394; Furukawa, K. & Nakamura, H. (1987) J. Biochem. (Tokyo) 101, 287-290]. This hypothesis has been tested on a smooth muscle sarcolemma preparation from pig thoracic aorta. The actomyosin-extracted membranes showed ATP-dependent Ca2+ uptake as well as cGMP-dependent protein kinase (G-kinase) activity. The molecular masses of the major protein substrates of the G-kinase (G1) and that of the Ca2+ pump were compared. Electrophoretic analysis of the phosphorylated intermediate of the sarcolemmal Ca2+-ATPase and the G1 phosphoprotein showed that these two proteins are not identical. The results were confirmed by using a 125I-calmodulin overlay technique and an antibody against human erythrocyte Ca2+-ATPase. Ca2+-uptake experiments with prephosphorylated membrane vesicles were carried out to elucidate possible effects of cGMP-dependent phosphorylation of membrane proteins on the activity of the Ca2+ pump. The cGMP-dependent phosphorylation was found to be extremely sensitive to temperature leading to very low steady-state phosphorylation levels at 37 degrees C. The difficulty was overcome by ATP[gamma S], which produced full and stable thiophosphorylation of G1 during the Ca2+-uptake experiments at 37 degrees C. However, the cGMP-dependent thiophosphorylation failed to influence the Ca2+-uptake properties of sarcolemmal vesicles. The results show that the Ca2+ pump of smooth muscle plasma membrane is not a direct target of the cGMP-dependent protein kinase and is not regulated by the cGMP-dependent phosphorylation of membrane proteins.

Regulation of the interaction of actin filaments with microtubule-associated protein 2 by calmodulin-dependent protein kinase II

Phosphorylation of microtubule-associated protein 2 (MAP 2) by Ca2+-, calmodulin-dependent protein kinase II (protein kinase II) inhibited the actin filament cross-linking activity of MAP 2. This inhibition required the presence of ATP, Mg2+, Ca2+ and calmodulin. The minimal concentration of MAP 2 required for gel formation of actin filaments was increased with increasing amounts of phosphate incorporated into MAP 2, and the phosphorylated MAP 2, into which 10.3 mol of phosphate/mol of protein had been incorporated, did not cause actin filaments to gel under the experimental conditions used. The phosphorylation of MAP 2 by Ca2+-, phospholipid-dependent protein kinase (protein kinase C) and cAMP-dependent protein kinase also inhibited the actin filament cross-linking activity of MAP 2. The extent and rate of phosphorylation of MAP 2 by protein kinase II were higher than those of the phosphorylation by protein kinase C and cAMP-dependent protein kinase. The interaction of actin filaments with MAP 2 was inhibited more by the actions of protein kinase II and protein kinase C than by cAMP-dependent protein kinase. The actin filament cross-linking activity of MAP 2 phosphorylated either by protein kinase II, cAMP-dependent protein kinase or protein kinase C was retrieved when phosphorylated MAP 2 was treated by protein phosphatase. These results indicate that the interaction of actin filaments with MAP 2 is regulated by the phosphorylation-dephosphorylation of MAP 2.

The effect of thyroxine on the calmodulin-dependent (Ca2+-Mg2+)ATPase activity and protein phosphorylation in rabbit fast skeletal muscle sarcolemma

Enzymatic properties and the protein pattern of sarcolemma fractions isolated from three groups of rabbits: euthyroid, hyperthyroid and hypothyroid, were studied. The amount of phosphorylated intermediate formed by the calmodulin-dependent (Ca2+-Mg2+)ATPase and the activity of this enzyme as well as that of (Na+-K+)ATPase were the highest in membranes isolated at the hyperthyroid state. On the other hand, sarcolemma obtained from the hypothyroid animals exhibited a decreased activity of (Na+-K+)ATPase, while the activity of calmodulin-dependent (Ca2+-Mg2+)ATPase was the same as in the preparations obtained from euthyroid animals. Thyroid hormones also changed the protein pattern of muscle sarcolemma. Membranes isolated from hyperthyroid animals lacked peptides of apparent molecular masses of 41 kDa and 53 kDa, while a peptide of the apparent molecular mass of 63 kDa was enriched in the preparation from hypothyroid animals. Thyroid hormones affected endogenous cAMP-dependent protein phosphorylation. The sarcolemma fraction obtained from hyperthyroid animals exhibited a decreased phosphorylation of peptides of apparent molecular masses of 30 kDa and 47 kDa, while the cAMP-independent phosphorylation of several other peptides was augmented. Moreover, sarcolemma preparations isolated from hyperthyroid animals showed higher activity of cAMP-independent protein kinase(s) and lower activity of cAMP-dependent protein kinase when compared to the euthyroid preparations. It is proposed that thyroxine increases the content of calmodulin-dependent (Ca2+-Mg2+)ATPase protein and affects the activity of cAMP-independent and cAMP-dependent protein kinases bound to sarcolemma.

Identification of the multifunctional calmodulin-dependent protein kinase in the cytosol, sarcoplasmic reticulum, and sarcolemma of rabbit skeletal muscle

A multifunctional calmodulin-dependent protein kinase (calmodulin kinase) was purified from the cytosol of rabbit skeletal muscle as a subunit of 58 kDa. A 58-kDa protein in sarcoplasmic reticulum (SR) and sarcolemma (SL) of rabbit skeletal muscle was endogenously phosphorylated in a calmodulin-dependent manner. The 58-kDa protein in SR and SL was considered to be identical to the subunit of cytosol calmodulin kinase on the basis of immunoreactivity, calmodulin binding, and autophosphorylation studies and on the patterns of protease-treated phosphopeptides. Calmodulin kinase showed broad substrate specificity and phosphorylated troponins I and T.

Calcium and calmodulin-dependent phosphorylation of kappa-casein by a bovine mammary casein kinase

A calcium and calmodulin-dependent kappa-casein kinase activity has been described in the bovine mammary gland. This kinase required previously dephosphorylated kappa-casein for substrate, thus suggesting a physiological role for this enzyme. The kappa-casein kinase required magnesium and the presence of both calcium and calmodulin for full activity. Calmodulin concentrations of .32 microM achieved one-half maximal activation of this enzyme. The calcium and calmodulin-dependent kappa-casein kinase was found in preparations of mammary acini and could be localized in a membranous fraction by centrifugation. The particles containing this activity had a high density (1.309 g/cc) and cofractionated with caseins, suggesting this enzyme may be present in secretory granules.

Inactivation and reactivation of the multifunctional calmodulin-dependent protein kinase from brain by autophosphorylation and dephosphorylation: involvement of protein phosphatases from brain

The multifunctional calmodulin-dependent protein kinase (calmodulin-kinase) from rat brain was autophosphorylated in a Ca2+- and calmodulin-dependent manner. The activity of the autophosphorylated enzyme was independent of Ca2+ and calmodulin. Calmodulin-kinase was dephosphorylated by protein phosphatase C from bovine brain, which is the catalytic subunits of protein phosphatases 1 and 2A. The holoenzyme of protein phosphatase 2A was also involved in the dephosphorylation of the enzyme. The autophosphorylated sites of calmodulin-kinase were universally dephosphorylated by protein phosphatase C. Calmodulin-kinase was inactivated and reactivated by autophosphorylation and dephosphorylation, respectively. Furthermore, the regulation of calmodulin-kinase by autophosphorylation and dephosphorylation was observed using calmodulin-kinase from canine heart. These results suggest that the activity of calmodulin-kinase is regulated by autophosphorylation and dephosphorylation, and that the regulation is the universal phenomenon for many other calmodulin-kinases in various tissues.

Identification of membrane-bound calcium, calmodulin-dependent protein kinase II in canine heart

Phospholamban, the putative regulatory proteolipid of the Ca2+/Mg2+ ATPase in cardiac sarcoplasmic reticulum, was selectively phosphorylated by a Ca2+/calmodulin (CaM)-dependent protein kinase associated with a cardiac membrane preparation. This kinase also catalyzed the phosphorylation of two exogenous proteins known to be phosphorylated by the multifunctional Ca2+/CaM-dependent protein kinase II (Ca2+/CaM-kinase II), i.e., smooth muscle myosin light chains and glycogen synthase a. The latter protein was phosphorylated at sites previously shown to be phosphorylated by the purified multifunctional Ca2+/CaM-kinase II from liver and brain. The membrane-bound kinase did not phosphorylate phosphorylase b or cardiac myosin light chains, although these proteins were phosphorylated by appropriate, specific calmodulin-dependent protein kinases added exogenously. In addition to phospholamban, several other membrane-associated proteins were phosphorylated in a calmodulin-dependent manner. The principal one exhibited a Mr of approximately 56,000, a value similar to that of the major protein (57,000) in a partially purified preparation of Ca2+/CaM-kinase II from the soluble fraction of canine heart that was autophosphorylated in a calmodulin-dependent manner. These data indicate that the membrane-bound, calmodulin-dependent protein kinase that phosphorylates phospholamban in cardiac membranes is not a specific calmodulin-dependent kinase, but resembles the multifunctional Ca2+/CaM-kinase II. Our data indicate that this kinase may be present in both the particulate and soluble fractions of canine heart.

Purification and properties of a multifunctional calcium/calmodulin-dependent protein kinase from rat pancreas

A calcium/calmodulin-dependent protein kinase (Ca/calmodulin protein kinase) was purified from rat pancreas using hydrophobic chromatography followed by gel filtration and affinity chromatography. Ca/calmodulin protein kinase from pancreas resembled previously described multifunctional Ca/calmodulin protein kinases from other tissues with respect to substrate specificity, autophosphorylation on serine and threonine residues, and catalytic and hydrodynamic properties. While Ca/calmodulin protein kinase from other tissues contains subunits of 53-60 kDa with variable proportions of a smaller 50-52 kDa subunit, pancreatic Ca/calmodulin protein kinase was found to contain a single component of 51 kDa. Experiments mixing brain Ca/calmodulin protein kinase with pancreatic homogenate suggest that the absence of a larger subunit in the pancreatic Ca/calmodulin protein kinase is not due to proteolytic degradation during enzyme preparation. Ca/calmodulin protein kinase binding to 125I-labeled calmodulin in solution was demonstrated using the photoaffinity cross-linker, N-hydroxysuccinimidyl-4-azidobenzoate. 125I-labeled calmodulin binding to Ca/calmodulin protein kinase was also demonstrated using filters containing Ca/calmodulin protein kinase transferred from polyacrylamide gels after two-dimensional gel electrophoresis. Finally, the ribosomal substrate for Ca/calmodulin protein kinase was identified as the ribosomal protein, S6. The purification procedure presented in this study promises to be useful in characterizing Ca/calmodulin protein kinase in other tissues and in clarifying the role of these enzymes in cellular function.

Cardiac calmodulin-stimulated protein phosphatase: purification and identification of specific sarcolemmal substrates

A calmodulin-stimulated protein phosphatase has been purified from bovine myocardium. The purification procedure involves sequential DEAE-Sephacel ion exchange chromatography, calmodulin-Sepharose affinity chromatography, and high performance liquid chromatography using a Spherogel TSK DEAE 5PW column. By SDS polyacrylamide gel electrophoresis, the purified cardiac phosphatase consists of two subunits of Mr 61,000 and 19,000, similar to the brain enzyme, calcineurin. Protein phosphatase activity of the cardiac enzyme is stimulated by Ca2+-calmodulin and inhibited by the calmodulin antagonist drug, calmidazolium. Effects of a series of divalent cations on catalytic activity of the cardiac calmodulin-stimulated protein phosphatase are similar to those observed with calcineurin, when the two enzymes are assayed under identical conditions. Highly enriched preparations of bovine cardiac sarcolemma contain substrates of cAMP-dependent protein kinase of Mr 166 K, 133 K, 108 K, 79 K, 39 K, and 14 K, which are specifically dephosphorylated by the calmodulin-stimulated phosphatase with pseudofirst-order rate constants of 0.23, 0.46, 0.69, 0.35, 0.69, and 0.115 min-1, respectively. These substrates are not present in purified preparations of cardiac sarcoplasmic reticulum. These results support a role of the calmodulin-stimulated phosphatase in the Ca2+-regulation of specific sarcolemmal processes by protein dephosphorylation.

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.

Mechanisms of hormonal regulation of hepatic glucose metabolism

Acute hormonal regulation of liver carbohydrate metabolism mainly involves changes in the cytosolic levels of cAMP and Ca2+. Epinephrine, acting through beta 2-adrenergic receptors, and glucagon activate adenylate cyclase in the liver plasma membrane through a mechanism involving a guanine nucleotide-binding protein that is stimulatory to the enzyme. The resulting accumulation of cAMP leads to activation of cAMP-dependent protein kinase, which, in turn, phosphorylates many intracellular enzymes involved in the regulation of glycogen metabolism, gluconeogenesis, and glycolysis. These are (1) phosphorylase b kinase, which is activated and, in turn, phosphorylates and activates phosphorylase, the rate-limiting enzyme for glycogen breakdown; (2) glycogen synthase, which is inactivated and is rate-controlling for glycogen synthesis; (3) pyruvate kinase, which is inactivated and is an important regulatory enzyme for glycolysis; and (4) the 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase bifunctional enzyme, phosphorylation of which leads to decreased formation of fructose 2,6-P2, which is an activator of 6-phosphofructo-1-kinase and an inhibitor of fructose 1,6-bisphosphatase, both of which are important regulatory enzymes for glycolysis and gluconeogenesis. In addition to rapid effects of glucagon and beta-adrenergic agonists to increase hepatic glucose output by stimulating glycogenolysis and gluconeogenesis and inhibiting glycogen synthesis and glycolysis, these agents produce longer-term stimulatory effects on gluconeogenesis through altered synthesis of certain enzymes of gluconeogenesis/glycolysis and amino acid metabolism. For example, P-enolpyruvate carboxykinase is induced through an effect at the level of transcription mediated by cAMP-dependent protein kinase. Tyrosine amino-transferase, serine dehydratase, tryptophan oxygenase, and glucokinase are also regulated by cAMP, in part at the level of specific messenger RNA synthesis. The sympathetic nervous system and its neurohumoral agonists epinephrine and norepinephrine also rapidly alter hepatic glycogen metabolism and gluconeogenesis acting through alpha 1-adrenergic receptors. The primary response to these agonists is the phosphodiesterase-mediated breakdown of the plasma membrane polyphosphoinositide phosphatidylinositol 4,5-P2 to inositol 1,4,5-P3 and 1,2-diacylglycerol. This involves a guanine nucleotide-binding protein that is different from those involved in the regulation of adenylate cyclase. Inositol 1,4,5-P3 acts as an intracellular messenger for Ca2+ mobilization by releasing Ca2+ from the endoplasmic reticulum.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of protein kinase C in the regulation of rat liver glycogen synthase

Rat liver glycogen synthase was phosphorylated by purified protein kinase C in a Ca2+- and phospholipid-dependent fashion to 1-1.4 mol PO4/subunit. Analysis of the 32P-labeled tryptic peptides derived from the phosphorylated synthase by isoelectric focusing and two-dimensional peptide mapping revealed the presence of a major radioactive peptide. The sites in liver synthase phosphorylated by protein kinase C appears to be different from those phosphorylated by other kinases. Prior phosphorylation of the synthase by protein kinase C has no significant effect on the subsequent phosphorylation by glycogen synthase (casein) kinase-1 or kinase Fa, but prevents the synthase from further phosphorylation by cAMP-dependent protein kinase, Ca2+/calmodulin-dependent protein kinase, phosphorylase kinase, or casein kinase-2. Additive phosphorylation of liver glycogen synthase can be observed by the combination of protein kinase C with the former set of kinases but not with the latter. Phosphorylation of liver synthase by protein kinase C alone did not cause an inactivation nor did the combination of this kinase with glycogen synthase (casein) kinase-1 or kinase Fa produce a synergistic effect on the inactivation of the synthase. Based on these findings we conclude that the phorbol ester-induced inactivation of glycogen synthase previously observed in hepatocytes cannot be accounted for entirely by the activation of protein kinase C.