Serine/threonine protein kinases

Toxic activity and protein identification from the parotoid gland secretion of the common toad Bufo bufo

Anuran toxins released from the skin glands are involved in defence against predators and microorganisms. Secretion from parotoid macroglands of bufonid toads is a rich source of bioactive compounds with the cytotoxic, cardiotoxic and hemolytic activity. Bufadienolides are considered the most toxic components of the toad poison, whereas the protein properties are largely unknown. In the present work, we analysed the cardio-, myo-, and neurotropic activity of extract and the selected proteins from Bufo bufo parotoids in in vitro physiological bioassays carried out on two standard model organisms: beetles and frogs. Our results demonstrate a strong cardioactivity of B. bufo gland extract. The toad poison stimulates (by 16%) the contractility of the insect heart and displays the cardioinhibitory effect on the frog heartbeat frequency (a 27% decrease), coupled with an irreversible cardiac arrest. The gland extract also exhibits significant myotropic properties (a 10% decrease in the muscle contraction force), whereas its neuroactivity remains low (a 4% decrease in the nerve conduction velocity). Among identified peptides present in the B. bufo parotoid extract are serine proteases, muscle creatine kinase, phospholipid hydroperoxide glutathione peroxidase, cytotoxic T-lymphocyte protein, etc. Some proteins contribute to the cardioinhibitory effect. Certain compounds display the paralytic (myo- and neurotropic) properties. As the toad gland extract exhibits a strong cardiotoxic activity, we conclude that the poison is a potent agent capable of slaying a predator. Our results also provide the guides for the use of toad poison-peptides in therapeutics and new drug development.

Identification, characterization, and functional studies of a Pelle gene in the Chinese mitten crab, Eriocheir sinensis

The toll-like receptor/NF-κB signaling pathways play an important role in the innate immune system. In the present study, one Pelle gene (named EsPelle) was identified for the first time from the Chinese mitten crab Eriocheir sinensis. The full-length cDNA of EsPelle is 3797 bp with a 3156 bp-long open reading frame that encodes a 1051 amino acid protein. EsPelle protein contains a death domain at the N-terminal and a serine/threonine kinase domain at the C-terminal. A neighbor joining phylogenetic tree showed that the EsPelle protein, which is closest to those of Scylla paramamosain Pelle and Litopenaeus vannamei Pelle, was clustered to a group of crustacean Pelle proteins. EsPelle was expressed in all tested tissues of normal crabs, and its expression was regulated in hemocytes and hepatopancreas of crabs challenged with lipopolysaccharide, peptidoglycan, Staphyloccocus aureus, Vibrio parahaemolyticus, and Aeromonas hydrophila. Overexpression of EsPelle in Drosophila Schneider 2 cells could upregulate the expression of Drosophila antimicrobial peptides, namely, metchnikowin (Mtk), attacinA (Atta), drosomycin (Drs), and cecropinA (CecA). Moreover, EsPelle silencing by siRNA reduced the transcription of anti-lipopolysaccharide factor 1 and 2, crustin 2, and lysozyme in crabs challenged with V. parahaemolyticus. From the results, we speculated that EsPelle was involved in innate immune defense against V. parahaemolyticus in E. sinensis.

The effects of disruption of A kinase anchoring protein-protein kinase A association on protein kinase A signalling in neuroendocrine melanotroph cells of Xenopus laevis

The secretory activity of melanotroph cells from Xenopus laevis is regulated by multiple neurotransmitters that act through adenylyl cyclase. Cyclic adenosine monophosphate (cAMP), acting on protein kinase A (PKA), stimulates the frequency of intracellular Ca(2+) oscillations and the secretory activity of the melanotroph cell. Anchoring of PKA near target proteins is essential for many PKA-regulated processes, and the family of A kinase anchoring proteins (AKAPs) is involved in the compartmentalisation of PKA type II (PKA II) regulatory subunits. In the present study, we determined to what degree cAMP signalling in Xenopus melanotrophs depends on compartmentalised PKA II. For this purpose, a membrane-permeable stearated form of Ht31 (St-Ht31), which dislodges PKA II from AKAP (thus disrupting PKA II signalling), was used. The effect of St-Ht31 on both secretion of radiolabelled peptides and intracellular Ca(2+) signalling by superfused Xenopus melanotrophs was assessed. St-Ht31 stimulated secretion but had no effect on Ca(2+) signalling. We conclude Xenopus melanotrophs possess a St-Ht31-sensitive PKA II that is associated with the exocytosis machinery and, furthermore, that Ca(2+) signalling is regulated by an AKAP-independent signalling system. Moreover, our results support a recent proposal that AKAP participates in regulating PKA activity independently from cAMP.

Differential expression pattern of the novel serine/threonine kinase, STK33, in mice and men

Serine/threonine kinase 33 (STK33/Stk33) is a recently discovered gene whose inferred amino acid sequence translation displays characters typical for a calcium/calmodulin dependent kinase (CAMK). In this study we analysed the STK33/Stk33 RNA and protein distribution and the localization of the protein. The STK33/Stk33 expression pattern resembles those of some related members of the CAMK group. STK33/Stk33 displays a nonubiquitous and, in most tissues, low level of expression. It is highly expressed in testis, particularly in cells from the spermatogenic epithelia. Moreover, significant expression is detected in lung epithelia, alveolar macrophages, horizontal cells in the retina and in embryonic organs such as heart, brain and spinal cord. A possible role of STK33/Stk33 in spermatogenesis and organ ontogenesis is discussed.

Genetic approaches to the study of synaptic plasticity and memory storage

Long-term memory is believed to depend on long-lasting changes in the strength of synaptic transmission known as synaptic plasticity. Understanding the molecular mechanisms of long-term synaptic plasticity is one of the principle goals of neuroscience. Among the most powerful tools being brought to bear on this question are genetically modified mice with changes in the expression or biological activity of genes thought to contribute to these processes. This article reviews how strains of mice with alterations in the cyclic adenosine monophosphate/protein kinase A/cyclic adenosine monophosphate-response element-binding protein signaling pathway have advanced our understanding of the biological basis of learning and memory.

A novel serine/threonine kinase gene, STK33, on human chromosome 11p15.3

Human chromosomal region 11p15 is known to be associated with several diseases including predispositions to develop various tumor types. In search of candidate genes, a novel human kinase gene is described, STK33, which codes for a serine/threonine protein kinase. The gene was discovered by comparative genome analysis of human chromosome 11p15.3 and its orthologous region on distal mouse chromosome 7. Human STK33 gene contains 12 exons as has been determined by the comparison to the full-length transcript amplified from human uterus RNA. Transcripts are found in a variety of tissues in at least two alternatively spliced forms as revealed by reverse transcriptase-polymerase chain reaction, cDNA sequencing and expressed sequence tag clustering. Phylogenetic analysis suggests that STK33 may belong to the calcium/calmodulin-dependent protein kinase group, even though, like several other members of the group, it lacks the calcium/calmodulin binding domain [FASEB J. 9 (1995) 576]. STK33 shows a differential expression in a variety of normal and malignant tissues.

Na(+) channel regulation by calmodulin kinase II in rat cerebellar granule cells

The effects of specific CaM kinase II inhibitors were investigated on Na(+) channels from rat cerebellar granule cells. A maximal effect of KN-62 was observed at 20 microM and consisted of an 80% reduction of the peak Na(+) current after only a 10-min application. A hyperpolarizing shift of 8 mV in the steady-state inactivation was also observed. KN-04 (20 microM), an inactive analog, had no detectable effect. KN-62 was however inactive on Na(+) currents recorded from Chinese hamster ovary cells expressing the type II A alpha subunit. We have also analyzed the inhibitory effects of CaM kinase II 296-311 and CaM kinase II 281-309 peptides. Both peptides (75 microM) induced a maximum peak Na(+) current reduction within 30 min. Under similar conditions, a truncated peptide CaM kinase II 284-302 was ineffective. These results demonstrate that CaM kinase II acts as a modulator of Na(+) channel activity in cerebellar granule cells.

Site-specific phosphorylation of neurofilament-L is mediated by calcium/calmodulin-dependent protein kinase II in the apical dendrites during long-term potentiation

Neurofilament-L (NF-L), one subunit of the neuronal intermediate filaments, is a major element of neuronal cytoskeletons. The dynamics of NF-L are regulated by phosphorylation of its head domain. The phosphorylation sites of the NF-L head domain by protein kinase A, protein kinase C, and Rho-associated kinase have been previously identified, and those by calcium/calmodulin-dependent protein kinase II (CaMKII) were identified in this study. A series of site- and phosphorylation state-specific antibodies against NF-L was prepared to investigate NF-L phosphorylation in neuronal systems. Long-term potentiation (LTP) is a cellular model of neuronal plasticity that is thought to involve the phosphorylation of various proteins. NF-L is considered a possible substrate for phosphorylation. During LTP stimulation of mouse hippocampal slices, the series of antibodies demonstrated the increase in the phosphorylation level of Ser(57) in NF-L and the visualization of the localized distribution of Ser(57) phosphorylation in a subpopulation of apical dendrites of the pyramidal neurons. Furthermore, Ser(57) phosphorylation during LTP is suggested to be mediated by CaMKII. Here we show that NF-L is phosphorylated by CaMKII in a subpopulation of apical dendrites during LTP, indicating that Ser(57) is a novel phosphorylation site of NF-L in vivo related to the neuronal signal transduction.

Immunohistochemical analysis of the expression of two serine-threonine kinases in the maturing mouse testis

Previously we identified two intronless serine-threonine kinase genes (Tsk1 and Tsk2) located 3 kb apart on mouse chromosome 16 (Galili, N., Baldwin, H.S., Lund, J., Reeves, R., Gong, W., Wang, Z., Roe, B.A., Emanuel, B.S., Nayak, S., Mickanin, C., Budraf, M.L., Buck, C.A., 1997. A region of mouse chromosome 16 is syntenic to the DiGeorge, velocardiofacial syndrome minimal critical region. Gen. Res. 7, 17-26). Tsk1 was identical to a putative testicular kinase reported by Bielke et al. (Bielke, W., Blaschke, R.J., Miescher, G.C., Zurcher, G., Andres, A.C., Ziemiecki, A., 1994. Characterization of a novel murine testis-specific serine/threonine kinase. Gene 13, 235-239). Here we document the expression patterns of each Tsk throughout spermiogenesis showing an initial association of Tsk1 with cells in meiotic metaphase and a later association of Tsk2 with tail-like structures in the lumen of the seminiferous tubule.

Defective learning in mutants of the Drosophila gene for a regulatory subunit of cAMP-dependent protein kinase

Disruptions of a Drosophila gene encoding a regulatory subunit of cAMP-dependent protein kinase homologous to mammalian RIbeta (dPKA-RI) were targeted to the first (noncoding) exon of dPKA-RI via site-selected P element mutagenesis. Flies homozygous for either of two mutant alleles showed specific defects in olfactory learning but not in subsequent memory decay. In contrast, olfactory acuity and shock reactivity, component behaviors required for normal odor avoidance learning, were normal in these mutants. Northern and Western blot analyses of mRNA and protein extracted from adult heads have revealed a complex lesion of the PKA-RI locus, including expression of a novel product and over- or underexpression of wild-type products in mutants. Western blot analysis revealed reductions in RI protein in mutants. PKA activity in the absence of exogenous cAMP also was significantly higher than normal in homogenates from mutant adult heads. These two mutant alleles failed to complement each other for each of these phenotypic defects, eliminating second-site mutations as a possible explanation. These results establish a role for an RI regulatory subunit of PKA in Pavlovian olfactory conditioning.

Cyclosporin A, an inhibitor of calcineurin, impairs memory formation in day-old chicks

Considerable evidence exists that changes in the phosphorylation state of neuronal proteins are correlated with learning and that inhibition of various protein kinases disrupts memory formation. Given the reversible nature of protein phosphorylation, a role for protein phosphatases in memory processing also seems likely. It has been shown recently that administration of the phosphatase inhibitor, okadaic acid, disrupts memory formation in day-old chicks, with retention deficits first appearing at approximately 40 min post-training [93]. In the present study the intracranial administration of the immunosuppressant cyclosporin A was also found to produce retention deficits in day-old chicks trained on a single-trial, passive-avoidance task, but the deficits were not significant until 85 min post-training. The difference could not be attributed to differences in the pharmacokinetics of the drugs. Since okadaic acid preferentially inhibits protein phosphatases 1 and 2A, while cyclosporin A is reported to inhibit only the Ca2+/calmodulin-dependent protein phosphatase, calcineurin, it is possible that different phosphatases may be involved in distinct stages of memory formation, as has been reported previously for protein kinases. The possibility that cyclosporin A may, in addition, act through inhibition of cyclophilin's peptidyl-prolyl-cis/transisomerase activity is also canvassed.

Interaction of cyclic AMP- and calcium-dependent mechanisms in the regulation of growth hormone-releasing hormone-stimulated growth hormone release from ovine pituitary cells

Growth hormone-releasing hormone (GHRH)-stimulated growth hormone (GH) release from the sheep pituitary is mediated through Ca(2+)-and cyclic AMP-dependent mechanisms. The initial Ca2+ influx is suggested to result from depolarization, whereas a secondary Ca2+ influx is thought to result from second messengers. This study sought to determine whether there was an interaction between these two signal transduction pathways. Sheep pituitary cells were placed in culture for 4 d and were then washed and incubated for 1 hr in serum-free medium before the application of specific antagonises and/or agonists. Both KCl and forskolin stimulated GH release (P < 0.05), but neither produced an effect similar to that of GHRH. The combination of both stimuli, however, mimicked GH release, as seen with a maximal dose of GHRH. Pretreatment with H89 (protein kinase A [PKA] inhibitor) inhibited GHRH, forskolin- and KCl-stimulated GH release (P < 0.001) but had no effect on phorbol myristate acetate (PMA)-stimulated GH release. Verapamil (voltage-dependent Ca2+ channel blocker) inhibited the GHRH effects on GH release (P < 0.0002) but did not influence forskolin or PMA actions. These data suggest that Ca(2+)-dependent pathways converge with cyclic AMP-dependent pathways before or with the activation of PKA. The data also suggest that PKA activation by cyclic AMP alone is insufficient to reproduce either the effects of GHRH stimulation or the combined effects of Ca2+ influx plus PKA activation on GH release. A calmodulin blocker, W7, reduced GHRH-stimulated GH release, a reduction equivalent to the Ca2+ effect on GH release. This suggests that Ca2+ activates calmodulin, which in turn enhances adenylyl cyclase and/or PKA activity to release GH from the sheep pituitary.

Expression of constitutively active CaMKII in target tissue modifies presynaptic axon arbor growth

Calcium/calmodulin-dependent protein kinase II (CaMKII) can be regulated by synaptic activity and could therefore be involved in activity-dependent control of neuronal growth. We tested whether increased CaMKII activity in postsynaptic optic tectal neurons can modify the development of retinotectal axons in Xenopus. The elaboration of individual presynaptic retinal axons was observed in vivo before and up to 3 days after infecting the tectal cells with vaccinia virus carrying the gene for constitutively active truncated CaMKII (tCaMKII). Elevated postsynaptic CaMKII activity prevented the axons from developing the complexity of normal arbors by increasing the normal rate of branch retractions. Some effects of tCaMKII on arbor morphology were seen 1 day after infection, but they became more dramatic by the third day. The results suggest that postsynaptic CaMKII plays a role in the development of presynaptic arbor structure.

Age-dependent increases in protein kinase C-alpha beta immunoreactivity and activity in the human brain: possible in vivo modulatory effects on guanine nucleotide regulatory G(i) proteins

In the postmortem human brain (20 specimens of frontal cortex, Brodmann area 9) the abundance of immunoreactive protein kinase C (PKC-alpha beta) and the activity of PKC (calcium, phosphatidylserine, and phorbol ester-dependent enzymes) were determined to study the effect of aging (range 1 month to 89 years) on this regulatory enzyme. Also, the abundance of immunoreactive G protein subunits (G alpha i1/2, G alpha i3, G alpha o, G alpha s and G beta) were assessed in parallel to investigate possible relationships with PKC-alpha beta. The abundance of PKC-alpha beta was positively correlated with aging (r = 0.62, n = 20, P < 0.005). Moreover, PKC activity also showed a significant positive correlation with the age of the subject at death (r = 0.55, n = 14, P < 0.05). Because of the known in vitro modulatory role of PKC-alpha beta on G(i) proteins, the existence of an in vivo effect of brain PKC-alpha beta on various G proteins was assessed through correlation analyses. In the brain of the same subjects, there were significant negative correlations between the immunoreactivity of PKC-alpha beta and the immunoreactivities of G alpha i1/2 (r = -0.78, n = 13, P < 0.005) and G alpha i3 (r = -0.58, n = 15, P < 0.005). In the same brains, similar negative, although non-significant, correlations were found between the levels of PKC-alpha beta and those of G alpha o, G alpha s and G beta. The results demonstrate an up-regulation of brain PKC-alpha beta with aging and suggest the existence of a relevant in vivo modulatory role of this regulatory enzyme on inhibitory Gi proteins in the human brain during the process of aging.

TGF beta 2 and TGF beta 3 are potent survival factors for midbrain dopaminergic neurons

The vertebrate ventral midbrain contains 3-4 x 10(4) dopaminergic neurons that influence motor activity, emotional behavior, and cognition. Recently, glial cell line-derived neurotrophic factor (GDNF) was shown to be a potent survival factor for these dopaminergic neurons in culture. However, many midbrain dopaminergic neurons project to targets that do not express GDNF. We report here that transforming growth factors (TGFs) TGF beta 2 and TGF beta 3, which are distantly related to GDNF, also prevent the death of cultured rat embryonic midbrain dopaminergic neurons at picomolar concentrations. Furthermore, we find that TGF beta 2, TGF beta 3, and GDNF are expressed sequentially as local and target-derived trophic factors and that subpopulations of dopaminergic neurons projecting to distinct targets have access to only one of these factors. These findings are consistent with the idea that GDNF, TGF beta 2, and TGF beta 3 are physiological survival factors for developing midbrain dopaminergic neurons and may have applications as therapeutics for Parkinson's disease, a neurodegenerative disorder of dopaminergic neurons.

Postsynaptic integration of glutamatergic and dopaminergic signals in the striatum

The aim of this study was to achieve a better understanding of the integration in striatal medium-sized spiny neurons (MSNs) of converging signals from glutamatergic and dopaminergic afferents. The review of the literature in the first section shows that these two types of afferents not only contact the same striatal cell type, but that individual MSNs receive both a corticostriatal and a dopaminergic terminal. The most common sites of convergence are dendritic shafts and spines of MSNs with a distance between the terminals of less than 1-2 microns. The second section focuses on synaptic transmission and second messenger activation. Glutamate, the candidate transmitter of corticostriatal terminals, via different types of glutamate receptors can evoke an increase in intracellular free calcium concentrations. The net effect of dopamine in the striatum is a stimulation of adenylate cyclase activity leading to an increase in cAMP. The subsequent sections present information on calcium- and cAMP-sensitive biochemical pathways and review the regional and subcellular distribution of the components in the striatum. The specific biochemical reaction steps were formalized as simplified equilibrium equations. Parameter values of the model were chosen from published experimental data. Major results of this analysis are: at intracellular free calcium concentrations below 1 microM the stimulation of adenylate cyclase by calcium and dopamine is at least additive in the steady state. Free calcium concentrations exceeding 1 microM inhibit adenylate cyclase, which is not overcome by dopaminergic stimulation. The kinases and phosphatases studied can be divided in those that are almost exclusively calcium-sensitive (PP2B and CaMPK), and others that are modulated by both calcium and dopamine (PKA and PP1). Maximal threonine-phosphorylation of the phosphoprotein DARPP requires optimal concentrations of calcium (about 0.3 microM) and dopamine (above 5 microM). It seems favourable if the glutamate signal precedes phasic dopamine release by approximately 100 msec. The phosphorylation of MAP2 is under essentially calcium-dependent control of at least five kinases and phosphatases, which differentially affect its heterogeneous phosphorylation sites. Therefore, MAP2 could respond specifically to the spatio-temporal characteristics of different intracellular calcium fluxes. The quantitative description of the calcium- and dopamine-dependent regulation of DARPP and MAP2 provides insights into the crosstalk between glutamatergic and dopaminergic signals in striatal MSNs. Such insights constitute an important step towards a better understanding of the links between biochemical pathways, physiological processes, and behavioural consequences connected with striatal function. The relevance to long-term potentiation, reinforcement learning, and Parkinson's disease is discussed.

Alternative splicing introduces a nuclear localization signal that targets multifunctional CaM kinase to the nucleus

Intracellular targeting may enable protein kinases with broad substrate-specificities, such as multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) to achieve a selectivity of action in vivo. We have examined the intracellular targeting of three delta-CaM kinase isoforms. The delta B-CaM kinase isoform is targeted to the nucleus in transfected cells while the delta A- and delta C-CaM kinase isoforms are cytosolic/cytoskeletal. A chimeric construct of alpha-CaM kinase containing the delta B-CaM kinase variable domain is rerouted to the nucleus while the native alpha-CaM kinase and chimeras of alpha-CaM kinase which contain the delta A- or delta C-CaM kinase variable domains are retained in the cytoplasm. Using site-directed mutagenesis, we have defined a nuclear localization signal (NLS) within an 11-amino acid sequence, likely inserted by alternative splicing, in the variable domain of delta B-CaM kinase. Isoform-specific nuclear targeting of CaM kinase is probably a key mechanism in the selective regulation of nuclear functions by CaM kinase. CaM kinase is a multimer that can be composed of several isoforms. We find that when cells express two different isoforms of CaM kinase, cellular targeting is determined by the ratio of the isoforms. When an excess of the cytoplasmic isoform of CaM kinase is coexpressed along with the nuclear isoform, both isoforms are localized in the cytoplasm. Conversely an excess of the nuclear isoform can reroute the cytoplasmic isoform to the nucleus. The nuclear isoform likely coassembles with the cytosolic isoform, to form a heteromultimeric holoenzyme which is transported into the nucleus. These experiments demonstrate isoform-specific targeting of CaM kinase and indicate that such targeting can be modified by the expression of multiple isoforms of the enzyme.

Cloning of a type I TGF-beta receptor and its effect on TGF-beta binding to the type II receptor

Transforming growth factor-beta (TGF-beta) affects cellular proliferation, differentiation, and interaction with the extracellular matrix primarily through interaction with the type I and type II TGF-beta receptors. The type II receptors for TGF-beta and activin contain putative serine-threonine kinase domains. A murine serine-threonine kinase receptor, Tsk 7L, was cloned that shared a conserved extracellular domain with the type II TGF-beta receptor. Overexpression of Tsk 7L alone did not increase cell surface binding of TGF-beta, but coexpression with the type II TGF-beta receptor caused TGF-beta to bind to Tsk 7L, which had the size of the type I TGF-beta receptor. Overexpression of Tsk 7L inhibited binding of TGF-beta to the type II receptor in a dominant negative fashion. Combinatorial interactions and stoichiometric ratios between the type I and II receptors may therefore determine the extent of TGF-beta binding and the resulting biological activities.