Subcellular alterations in cyclic AMP-binding and protein kinase activities during ontogeny in the rat cerebellum

Ontogenic relationships between levels of cyclic AMP-binding activity and protein kinase activity were examined in subcellular fractions of the cerebellum during the first 3 weeks of neonatal life. A progressive increase in cyclic AMP levels was paralleled by an increase in cyclic AMP bindign by the nuclear and cytosol fractions, but not by the mitochondrial or microsomal fractions. Utilization of heat-stable protein kinase inhibitor permtited distinction of the cyclic AMP-dependent from the cyclic AMP-independent form of the protein kinase population. Cyclic AMP-dependent protein kinase increased between days 4 and 20 to represent a progressively greater proportion of the protein kinase population. In all subcellular fractions alterations of cyclic AMP-dependent protein kinase during neonatal development paralleled changes in binding of cyclic AMP to protein in these fractions. In both the nuclear and cytosol fractions cyclic AMP-dependent protein kinase activity increased progressively between days 4 and 20, i.e. 64 ± 6 to 176 ± 16 and 79 ± 12 to 340 ± 12 pmol/min per mg protein, respectively. Cyclic AMP-dependent protein kinase activity in the mitochondrial fraction declined during the postnatal period studied, and in the microsomal fraction it rose to a non-sustained peak at 14 days and fell thereafter. Unlike the cyclic AMP-dependent form, cyclic AMP-independent protein kinase activity did not follow the ontogenetic pattern of cyclic AMP-binding activity. The specific activity of nuclear cyclic AMP-independent protein kinase did not change during days 4–20, and a non-sustained rise of cyclic AMP-independent protein kinase activity in both cytosol and microsomal fractions during the 7th–12th day tended to parallel more closely known patterns of postnatal proliferative growth. The findings reported herein indicate that the ontogenic pattern of cyclic AMP-dependent protein kinase varies between different subcellular fractions of the neonatal cerebellum, that these patterns parallel the changes in cyclic AMP-bidign activity, and suggest that the component parts of the cyclic AMP system may develop as a functional unit.     

Efficient Induction of Sporulation of Dictyostelium Prespore Cells by 8-Bromocyclic AMP under Both Submerged- and Shaken-Culture Conditions and Involvement of Protein Kinase(s) in Its Action

It is important to establish an experimental system in which sporulation of Dictyostelium can be induced at high cell densities to obtain sufficient amounts of materials for analysis of the molecular events leading to sporulation. 8-Bromo cAMP (Br-cAMP) was found to be effective for inducing sporulation by prespore cells of Dictyostelium discoideum NC4 at high cell densities under both submerged- and shaken-culture conditions. Ultrastructural studies revealed that the morphological changes associated with this sporulation proceeded normally in vitro. The effect of Br-cAMP was inhibited by two protein kinase inhibitors, K252a and staurosporine. Protein-phosphorylation experiments showed that Br-cAMP induced increased phosphorylations of a 96 kDa spore coat protein (SP96) and a protein with a mobility corresponding to a molecular weight of 50 kDa (p50-4). The protein kinase inhibitor K252a blocked the phosphorylations of both proteins. These proteins may be targets of particular protein kinase(s) that is activated by Br-cAMP. These findings indicate that the present experimental system should be useful for elucidating the molecular events involved in normal sporulation and the mechanism by which Br-cAMP induces sporulation in vitro.     

A novel role of Dma1 in regulating forespore membrane assembly and sporulation in fission yeast

In fission yeast Schizosaccharomyces pombe, a diploid mother cell differentiates into an ascus containing four haploid ascospores following meiotic nuclear divisions, through a process called sporulation. Several meiosis-specific proteins of fission yeast have been identified to play essential roles in meiotic progression and sporulation. We report here an unexpected function of mitotic spindle checkpoint protein Dma1 in proper spore formation. Consistent with its function in sporulation, expression of dma1(+) is up-regulated during meiosis I and II. We showed that Dma1 localizes to the SPB during meiosis and the maintenance of this localization at meiosis II depends on septation initiation network (SIN) scaffold proteins Sid4 and Cdc11. Cells lacking Dma1 display defects associated with sporulation but not nuclear division, leading frequently to formation of asci with fewer spores. Our genetic analyses support the notion that Dma1 functions in parallel with the meiosis-specific Sid2-related protein kinase Slk1/Mug27 and the SIN signaling during sporulation, possibly through regulating proper forespore membrane assembly. Our studies therefore revealed a novel function of Dma1 in regulating sporulation in fission yeast.     

Two Ser/Thr protein kinases essential for efficient aggregation and spore morphogenesis in Myxococcus xanthus

Myxococcus xanthus has a complex life cycle that involves vegetative growth and development. Previously, we described the espAB locus that is involved in timing events during the initial stages of fruiting body formation. Deletion of espA caused early aggregation and sporulation, whereas deletion of espB caused delayed aggregation and sporulation resulting in reduced spore yields. In this study, we describe two genes, pktA5 and pktB8, that flank the espAB locus and encode Ser/Thr protein kinase (STPK) homologues. Cells deficient in pktA5 or pktB8 formed translucent mounds and produced low spore yields, similar in many respects to espB mutants. Double mutant analysis revealed that espA was epistatic to pktA5 and pktB8 with respect to aggregation and fruiting body morphology, but that pktA5 and pktB8 were epistatic to espA with respect to sporulation efficiency. Expression profiles of pktA5-lacZ and pktB8-lacZ fusions and Western blot analysis showed that the STPKs are expressed under vegetative and developmental conditions. In vitro kinase assays demonstrated that the RD kinase, PktA5, autophosphorylated on threonine residue(s) and phosphorylated the artificial substrate, myelin basic protein. In contrast, autophosphorylation of the non-RD kinase, PktB8, was not observed in vitro; however, the phenotype of a pktB8 kinase-dead point mutant resembled the pktB8 deletion mutant, indicating that this residue was important for function and that it likely functions as a kinase in vivo. Immunoprecipitation of Tap-tagged PktA5 and PktB8 revealed an interaction with EspA during development in M. xanthus. These results, taken together, suggest that PktA5 and PktB8 are STPKs that function during development by interacting with EspA and EspB to regulate M. xanthus development.     

Induction of cyclic AMP phosphodiesterase in Blastocladiella emersonii and its relation to cyclic AMP metabolism.

Extracts of vegetative cells of Blastocladiella emersonii contain 5% or less of the cyclic AMP phosphodiesterase activity in zoospore extracts. This difference in activity could be accounted for entirely by an increase in the differential rate of phosphodiesterase synthesis during sporulation, beginning after a lag period of about 60 min and extending for at least an additional 90 min into the 4-h sporulation process. To examine the relation between enzyme synthesis and cyclic nucleotide metabolicm, we determined the substrate specificity of phosphodiesterase synthesized during sporulation and partially purified from zoospores. Zoospore extracts contain two components, separable by gel filtration chromatography, with cyclic AMP phosphodiesterase activity. The larger component accounts for 20% of the total activity and the smaller component for 80%. Both components show essentially an absolute substrate specificity for cyclic AMP among several cyclic purine and cyclic pyrimidine nucleotides tested. Nevertheless, we found no change in the total cyclic AMP content of sporulating cells before, during, or after enzyme activity increased. We speculate that some other component of cyclic AMP metabolism or function limits the rate of cyclic AMP hydrolysis in sporulating cells.     

Essential functions of protein tyrosine phosphatases PTP2 and PTP3 and RIM11 tyrosine phosphorylation in Saccharomyces cerevisiae meiosis and sporulation

Tyrosine phosphorylation plays a central role in eukaryotic signal transduction. In yeast, MAP kinase pathways are regulated by tyrosine phosphorylation, and it has been speculated that other biochemical processes may also be regulated by tyrosine phosphorylation. Previous genetic and biochemical studies demonstrate that protein tyrosine phosphatases (PTPases) negatively regulate yeast MAP kinases. Here we report that deletion of PTP2 and PTP3 results in a sporulation defect, suggesting that tyrosine phosphorylation is involved in regulation of meiosis and sporulation. Deletion of PTP2 and PTP3 blocks cells at an early stage of sporulation before premeiotic DNA synthesis and induction of meiotic-specific genes. We observed that tyrosine phosphorylation of several proteins, including 52-, 43-, and 42-kDa proteins, was changed in ptp2Deltaptp3Delta homozygous deletion cells under sporulation conditions. The 42-kDa tyrosine-phosphorylated protein was identified as Mck1, which is a member of the GSK3 family of protein kinases and previously known to be phosphorylated on tyrosine. Mutation of MCK1 decreases sporulation efficiency, whereas mutation of RIM11, another GSK3 member, specifically abolishes sporulation; therefore, we investigated regulation of Rim11 by Tyr phosphorylation during sporulation. We demonstrated that Rim11 is phosphorylated on Tyr-199, and the Tyr phosphorylation is essential for its in vivo function, although Rim11 appears not to be directly regulated by Ptp2 and Ptp3. Biochemical characterizations indicate that tyrosine phosphorylation of Rim11 is essential for the activity of Rim11 to phosphorylate substrates. Our data demonstrate important roles of protein tyrosine phosphorylation in meiosis and sporulation     

Opiates and cultured neuroblastoma x glioma cells. Effect on cyclic AMP and polyamine levels and on ornithine decarboxylase and protein kinase activities.

In cultured NG 108-15 neuroblastoma x glioma cells, opiates decreased cellular cyclic AMP and polyamine levels. This decrease was related to the inhibition of ornithine decarboxylase and cyclic AMP-dependent protein kinase activities during the acute exposure of the cells to the drugs. Growing the cells in the presence of opiates for several days led to drug addiction. In the tolerant-addicted cells, polyamine and cyclic AMP levels were close to normal values as were the activities of ornithine decarboxylase and cyclic AMP-dependent protein kinase. Removal of the opiate from 'addicted' cells, by either washing or by adding the antagonist naloxone, resulted in an increase in cyclic AMP and polyamine levels and the activities of ornithine decarboxylase and cyclic AMP-dependent protein kinase. The effect of opiates was closely related to their biological activities. Inactive enantiomorphs did not affect cyclic AMP or polyamine levels; neither did they decrease ornithine decarboxylase and cyclic AMP-dependent protein kinase activities.     

The dual-specificity protein phosphatase Yvh1p regulates sporulation, growth, and glycogen accumulation independently of catalytic activity in Saccharomyces cerevisiae via the cyclic AMP-dependent protein kinase cascade

Yvh1p, a dual-specific protein phosphatase induced specifically by nitrogen starvation, regulates cell growth as well as initiation and completion of sporulation. We demonstrate that yvh1 disruption mutants are also unable to accumulate glycogen in stationary phase. A catalytically inactive variant of yvh1 (C117S) and a DNA fragment encoding only the Yvh1p C-terminal 159 amino acids (which completely lacks the phosphatase domain) complement all three phenotypes as well as the wild-type allele; no complementation occurs with a fragment encoding only the C-terminal 74 amino acids. These observations argue that phosphatase activity is not required for the Yvh1p functions we measured. Mutations which decrease endogenous cyclic AMP (cAMP) levels partially suppress the sporulation and glycogen accumulation defects. In addition, reporter gene expression supported by a DRR2 promoter fragment, containing two stress response elements known to respond to cAMP-protein kinase A, decreases in a yvh1 disruption mutant. Therefore, our results identify three cellular processes that both require Yvh1p and respond to alterations in cAMP, and they lead us to suggest that Yvh1p may be a participant in and/or a contributor to regulation of the cAMP-dependent protein kinase cascade. The fact that decreasing the levels of cAMP alleviates the need for Yvh1p function supports this suggestion.     

G1 specific increases in cyclic AMP levels and protein kinase activity in Chinese hamster ovary cells.

Chinese hamster ovary cells were synchronized by selective detachment of cells in mitosis. The adenosine 3':5'-cyclic monophosphate (cyclic AMP) intracellular concentrations and cyclic AMP-dependent protein kinase activities were measured as these cells traversed G1 phase and entered S phase. Protein kinase activity, assayed in the presence or absence of saturating exogenous cyclic AMP in the reaction mixture, was lowest in early G1 phase (2 h after mitosis), increased 2-fold (plus exogenous cyclic AMP in reaction mixture) or 3.5-fold (minus cyclic AMP in reaction mixture) to maximum values in mid to late G1 phase (4-5 h after mitosis), and then decreased as cells entered S phase. Intracellular cyclic AMP concentrations were minimal 1 h after mitosis, increased 5-fold to maximum levels at 4-6 after mitosis, and decreased as cells entered S phase. Similar to the fluctuations in intracellular cyclic AMP, the cyclic AMP-dependent protein kinase activity ratio increased more than 40% in late G1 or early S phase. Puromycin (either 10 mug/ml or 50 mug/ml) administered 1 h after mitosis inhibited cyclic AMP-dependent protein kinase activity up to 50% by 5 h after mitosis, while similar treatment (10 mug/ml) had no effect on the increase in cyclic AMP formation. These data demonstrate that: (1) total protein kinase activity changed during G1 phase and this increase was dependent on new protein synthesis; (2) the increased intracellular concentrations of cyclic AMP were not dependent on new protein synthesis; and (3) the activation of cyclic AMP-dependent protein kinase was temporally coordinated with increased intracellular concentration of cycli AMP as Chinese hamster ovary cells traversed G1 phase and entered S phase. These results suggest that cyclic AMP acts during G1 phase to regulate the activation of cyclic AMP-dependent protein kinase.     

Comparative studies on sporulation-promotive actions on cyclic AMP, theophylline and caffeine in Saccharomyces cerevisiae.

Cyclic AMP, theophylline and caffeine promoted sporulation when added to a presporulation medium containing glucose. Caffeine promoted sporulation even when added to a presporulation medium containing acetate as the carbon source, but cyclic AMP and theophylline did not. Caffeine did not increase the intracellular cyclic AMP level, while theophylline did significantly when added to a presporulation medium containing glucose. Caffeine inhibited the vegatative DNA synthesis with little effect on RNA and protein synthesis, resulting in the increase in cell volume, dry weight, and RNA and protein contents, but cyclic AMP and theophylline did not show such effects.     

Developmental regulation of expression of the regulatory subunit of the cAMP-dependent protein kinase of Blastocladiella emersonii

A monospecific polyclonal antiserum to the regulatory subunit (R) of the cAMP-dependent protein kinase of Blastocladiella emersonii has been developed by immunization with purified regulatory subunit. In Western blots, the antiserum displays high affinity and specificity for the intact R monomer of Mr = 58,000, as well as for its proteolytic products of Mr = 43,000 and Mr = 36,000, even though the antiserum has been raised against the Mr = 43,000 fragment. Western blots of cell extracts prepared at different times during the life cycle of the fungus indicate that the increase in cAMP-binding activity occurring during sporulation, as well as its decrease during germination, are associated with the accumulation of the regulatory subunit during sporulation and its disappearance during germination, respectively. Pulse labeling with [35S]methionine and immunoprecipitation indicate that the accumulation of R is due to its increased synthesis during sporulation. Two-dimensional gel electrophoresis of affinity purified cell extracts obtained after [35S]methionine pulse labeling during sporulation confirms de novo synthesis of R during this stage and furthermore shows that the protein is rapidly phosphorylated after its synthesis. In vitro translation studies using RNA isolated from different stages of the life cycle followed by immunoprecipitation have shown that the time course of expression of the mRNA coding for the regulatory subunit parallels the rate of its synthesis in vivo.     

Ontogeny of cyclic AMP-dependent protein phosphokinase during hepatic development of the rat.

The ontogeny of protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) and cyclic AMP-binding activity in subcellular fractions of liver was examined during prenatal and postnatal development of the male rat. 1. Protein kinase activity and cyclic AMP-binding activity were found in the nuclear, microsomal, lysosomal-mitochondrial, and soluble liver fractions. 2. The protein kinase activity of the soluble (105 000 X g supernatant) fraction measured with histone F1 as substrate was stimulated by cyclic AMP. Cyclic AMP did not stimulate the protein kinase activity of the particulate fractions. 3. The protein kinase activity of all subcellular fractions increased rapidly from the activity observed in prenatal liver (3-4 days before birth) to reach maximal activity in 2-day-old rats. Thereafter, the protein kinase activity declined more slowly and regained the prenatal levels at 10 days after birth. 4. Considerable latent protein kinase activity was associated with liver microsomal fractions which could be activated by treatment of microsomes with Triton X-100. The latent microsomal protein kinase activity was highest in prenatal liver, at the time of birth, and 2 days after birth. During the subsequent postnatal development the latent microsomal protein kinase activity gradually declined to insignificantly low levels. 5. During the developmental period examined (4 days before birth to age 60-90 days) marked alterations of the cyclic AMP-binding activity were determined in all subcellular fractions of rat liver. In general, cytosol, microsomal, and lysosomal-mitochondrial cyclic AMP-binding activity was highest in 10-11 day-old rats. Nuclear cyclic AMP-binding activity was highest 3-4 days before birth and declined at birth and during the postnatal period. There was no correlation between the developmental alteration of cyclic AMP-binding activity and cyclic AMP dependency of the protein kinase activity in any of the subcellular fractions. This suggests that the measured cyclic AMP-binding activity does not reflect developmental alterations of the cyclic AMP-binding regulatory subunit of cyclic AMP-dependent protein kinase.     

Changes in the Activity of the Maturation-Promoting Factor Are Correlated with Those of a Major Cyclic AMP and Calcium-Independent Protein Kinase During the First Mitotic Cell Cycles in the Early Starfish Embryo

Many studies suggest that MPF activation depends on protein phosphorylation or that MPF is itself a protein kinase. In the present report, cyclic variations of MPF activity have been correlated in vivo with changes in the extent of protein phosphorylation or in vitro with changes of a major protein kinase during the first cell cycles of fertilized starfish eggs. This cycling protein kinase neither requires cAMP nor Ca²⁺. Neither colchicine nor aphidicoline, which inhibits cleavage and chromosome replication respectively, was found to suppress the synchronous and cyclic variations of both MPF and protein kinase activities. Protein synthesis was found to be required for both MPF and protein kinase activities to reappear after their simultaneous drop at the time of mitotic or meiotic cleavages. Production of either MPF or protein kinase activities is not the immediate result of protein synthesis since there is a delay at each cell cycle between the time when protein synthesis is required and the time when both MPF and protein kinase activities are produced. This suggests that both MPF and protein kinase activities might involve some post-translational modification of a precursor protein synthesized during the preceeding cell cycle.     

Isolation and properties of cyclic AMP-dependent protein kinase from Dictyostelium discoideum

Cyclic AMP-dependent protein kinase (ATP-protein phosphotransferase, EC 2.7.1.37) in Dictyostelium discoideum was shown to be developmentally controlled. No activity was measured in vegetative cells, but activity increased rapidly during differentiation. A simple procedure for the isolation of the catalytic subunit of the kinase from aggregating cells is presented. The cycle AMP-dependent holoenzyme could be reconstituted by adding purified D. discoideum cyclic AMP-binding protein. Molecular weight, kinetic parameters, pH dependence and affinity for cyclic AMP were determined for th enzyme. Most properties are similar to those of cyclic AMP-dependent kinase from mammalian cells.     

Comparison of cyclic nucleotide specificity of guanosine 3',5'-monophosphate-dependent protein kinase and adenosine 3',5'-monophosphate-dependent protein kinase.

Guanosine 3',5'-monophosphate-dependent protein kinase (cyclic GMP-dependent protein kinase) and adenosine 3',5'-monophosphate-dependent protein kinase (cyclic AMP-dependent protein kinase) exhibited a high degree of cyclic nucleotide specificity when hormone-sensitive triacylglycerol lipase, phosphorylase kinase, and cardiac troponin were used as substrates. The concentration of cyclic GMP required to activate half-maximally cyclic dependent protein kinase was 1000- to 100-fold less than that of cyclic AMP with these substrates. The opposite was true with cyclic AMP-dependent protein kinase where 1000- to 100-fold less cyclic AMP than cyclic GMP was required for half-maximal enzyme activation. This contrasts with the lower degree of cyclic nucleotide specificity of cyclic GMP-dependent protein kinase of 25-fold when histone H2b was used as a substrate for phosphorylation. Cyclic IMP resembled cyclic AMP in effectiveness in stimulating cyclic GMP-dependent protein kinase but was intermediate between cyclic AMP and cyclic GMP in stimulating cyclic AMP-dependent protein kinase. The effect of cyclic IMP on cyclic GMP-dependent protein kinase was confirmed in studies of autophosphorylation of cyclic GMP-dependent protein kinase where both cyclic AMP and cyclic IMP enhanced autophosphorylation. The high degree of cyclic nucleotide specificity observed suggests that cyclic AMP and cyclic GMP activate only their specific kinase and that crossover to the opposite kinase is unlikely to occur at reported cellular concentrations of cyclic nucleotides.     

Comparison of cyclic nucleotide specificity of guanosine 3′,5′-monophosphate-dependent protein kinase and adenosine 3′,5′-monophosphate-dependent protein kinase

Guanosine 3′,5′-monophosphate-dependent protein kinase (cyclic GMP-dependent protein kinase) and adenosine 3′,5′-monophosphate-dependent protein kinase (cyclic AMP-dependent protein kinase) exhibited a high degree of cyclic nucleotide specificity when hormone-sensitive triacylglycerol lipase, phosphorylase kinase, and cardiac troponin were used as substrates. The concentration of cyclic GMP required to activate half-maximally cyclic dependent protein kinase was 1000- to 100-folds less than that of cylic AMP with these substrates. The opposite was true with cyclic AMP-dependent protein kinase where 1000- to 100-fold less cyclic GMP was required for half-maximal enzyme activation. This contrasts with the lower degree of cyclic nucleotide specificity of cyclic GMP-dependent protein kinase of 25-fold when histone H2b was used as a substrate for phosphorylation. Cyclic IMP resembled cyclic AMP in effectiveness in stimulating cyclic GMP-dependent protein kinase but was intermediate between cyclic AMP and cyclic GMP in stimulating cyclic. AMP-dependent protein kinase. The effect of cyclic IMP on cyclic GMP-dependent protein kinase was confirmed in studies of autophosphorylation of cyclic GMP-dependent protein kinase where both cyclic AMP and cyclic IMP enhanced autophophorylation. The high degree of cyclic nucleotide specificity observed suggests that cyclic AMP and cyclic GMP activate only their specific kinase and that crossover to the opposite kinase is unlikely to occur at reported cellular concentrations of cyclic nucleotides.     

Effect of polyanions and polycations on adenosine 3',5'-monophosphate-binding and protein kinase activity.

Histone, protamine, poly-L-arginine, and poly-L-lysine enhance the binding of adenosine 3′,5′-monophosphate (cyclic AMP) to rat liver cyclic AMP-dependent protein kinase as determined by Millipore filtration assay. Poly-L-glutamic acid and poly-L-aspartic acid suppress cyclic AMP-binding stimulated by histone. Poly-L-glutamic acid and poly-L-aspartic acid are effective against protein kinase and result in decrease in initial reaction velocity when histone is used as a protein substrate. Incubation of cyclic AMP-dependent protein kinase with 6 μg poly-L-glutamic acid produces half-maximal inhibition of cyclic AMP-dependent protein kinase when 30 μg histone is used as substrate.