Differential expression of isoforms of the regulatory subunit of type II cAMP-dependent protein kinase in rat neurons, astrocytes, and oligodendrocytes

The effects of Chinese medicines on cAMP/PKA signaling in central nervous system dysfunction

Neuropathological injury in the mammalian adult central nervous system (CNS) may cause axon disruption, neuronal death and lasting neurological deficits. Failure of axon regeneration is one of the major challenges for CNS functional recovery. Recently, the cAMP/PKA signaling pathway has been proven to be a critical regulator for neuronal regeneration, neuroplasticity, learning and memory. Also, previous studies have shown the effects of Chinese medicines on the prevention and treatment of CNS dysfunction mediated in part by cAMP/PKA signaling. In this review, the authors discuss current knowledge of the role of cAMP/PKA signaling pathway in neuronal regeneration and provide an overview of the Chinese medicines that may enable CNS functional recovery via this signaling pathway.

Microtubule-associated type II protein kinase A is important for neurite elongation

Neuritogenesis is a process through which neurons generate their widespread axon and dendrites. The microtubule cytoskeleton plays crucial roles throughout neuritogenesis. Our previous study indicated that the amount of type II protein kinase A (PKA) on microtubules significantly increased upon neuronal differentiation and neuritogenesis. While the overall pool of PKA has been shown to participate in various neuronal processes, the function of microtubule-associated PKA during neuritogenesis remains largely unknown. First, we showed that PKA localized to microtubule-based region in different neurons. Since PKA is essential for various cellular functions, globally inhibiting PKA activity will causes a wide variety of phenotypes in neurons. To examine the function of microtubule-associated PKA without changing the total PKA level, we utilized the neuron-specific PKA anchoring protein MAP2. Overexpressing the dominant negative MAP2 construct that binds to type II PKA but cannot bind to the microtubule cytoskeleton in dissociated hippocampal neurons removed PKA from microtubules and resulted in compromised neurite elongation. In addition, we demonstrated that the association of PKA with microtubules can also enhance cell protrusion using the non-neuronal P19 cells. Overexpressing a MAP2 deletion construct which does not target PKA to the microtubule cytoskeleton caused non-neuronal cells to generate shorter cell protrusions than control cells overexpressing wild-type MAP2 that anchors PKA to microtubules. Finally, we demonstrated that the ability of microtubule-associated PKA to promote protrusion elongation was independent of MAP2 phosphorylation. This suggests other proteins in close proximity to the microtubule cytoskeleton are involved in this process.

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.

Nectin-like molecule 1 is a high abundance protein in cerebellar neurons

Nectins and Nectin-like molecules belong to the Ca-independent immunoglobulin superfamily of cell adhesion molecules and are mandatory for various cellular functions such as morphogenesis, differentiation and proliferation. Among them, Nectin-like molecule 1 (Necl-1) is unique for its exclusive expression in the brain where it is localized at the contact sites among axon terminals and glia cell processes, cooperatively forming synapses. We hereby aimed to unambiguously characterize Necl-1 at the protein level in rat brain. Rat cerebellar neurons were lysed, proteins extracted and run on two-dimensional gel electrophoresis with subsequent in-gel digestion and mass spectrometrical (MS/MS) analysis of protein spots. One spot at pI 5.96 with an observed molecular weight of 26 kDa was identified as Nectin-like molecule 1. MS/MS analyses of three matching peptides warranted unambiguous identification for the first time. Additionally, we verified the result by immunoblotting and detected two bands at about 48 kDa and 60 kDa. The proposed roles of Necl-1 in cerebellar morphogenesis as well as plasticity of synapses challenge further research on its function in more detail and we hereby provide a fair analytical tool for the unequivocal determination of Necl-1, independent of antibody availability and specificity.

Reduced ocular dominance plasticity and long-term potentiation in the developing visual cortex of protein kinase A RII alpha mutant mice

The cAMP-dependent protein kinase (PKA) signalling pathway has been shown to play an important role in long-term potentiation (LTP) and depression (LTD), and ocular dominance plasticity in the visual cortex. In order to investigate further the involvement of individual PKA subunits in visual cortical plasticity, LTP and LTD in vitro and ocular dominance plasticity in vivo in the developing visual cortex were examined in mice lacking the RII alpha subunit of PKA. Here we show that LTP in layers II/III was decreased in RII alpha knockout mice, but LTD was almost unaffected, and the ocular dominance shift induced by monocular deprivation was also partially blocked. These data provide evidence that RII alpha is involved in LTP and ocular dominance plasticity, and further suggest that different afferent inputs could selectively activate particular subunits of PKA and thereby direct specific aspects of visual cortical plasticity.

Regional variations in the localization of insoluble kinase A regulatory isoforms during rodent brain development

In eukaryothes, the second messenger cAMP regulates many cellular functions by binding to the regulatory subunits of cAMP-dependent protein kinases, and releasing the catalytic subunits. In the mammalian brain all four regulatory isoforms (RIalpha and beta, RIIalpha and beta) are present. Apparently, they are simple inhibitors of the catalytic subunits. It is still unclear why four isoforms are needed, but possibly they can target kinase activity at precise intracellular locations. Therefore, we examined the distribution of the insoluble regulatory isoforms in rat and mouse brains during prenatal (from embryonic day 8) and postnatal development up to senescence (13 months), via immunohistochemistry. RIIalpha labelling is always restricted to the ventricular ependyma. Punctated RIIbeta labelling is observed in the embryo from early stages of development, and is mainly localized in the cortical plate. After birth, punctate RIIbeta labelling is present throughout almost the whole brain, often observed in proximity of neurofilaments. It shows different characteristics and relationships to the other isoforms: for example in the CA1 hippocampal field, RIIbeta is substituted by RIalpha 2 weeks after birth, while in CA2 it persists for life. In other regions, as in the reticular formation, RIIbeta and RIalpha aggregates are found in the same cell, although clearly segregated. The different regulatory isoforms show distinct patterns of distribution that change consistently during development. A careful characterization of second messenger systems may be as useful as the study of neurotransmitters to understand neuronal properties and their modifications during development, so as to relate biochemical to functional properties.

Dissecting interdomain communication within cAPK regulatory subunit type IIbeta using enhanced amide hydrogen/deuterium exchange mass spectrometry (DXMS)

cAMP-dependent protein kinase (cAPK) is a heterotetramer containing a regulatory (R) subunit dimer bound to two catalytic (C) subunits and is involved in numerous cell signaling pathways. The C-subunit is activated allosterically when two cAMP molecules bind sequentially to the cAMP-binding domains, designated A and B (cAB-A and cAB-B, respectively). Each cAMP-binding domain contains a conserved Arg residue that is critical for high-affinity cAMP binding. Replacement of this Arg with Lys affects cAMP affinity, the structural integrity of the cAMP-binding domains, and cAPK activation. To better understand the local and long-range effects that the Arg-to-Lys mutation has on the dynamic properties of the R-subunit, the amide hydrogen/deuterium exchange in the RIIbeta subunit was probed by electrospray mass spectrometry. Mutant proteins containing the Arg-to-Lys substitution in either cAMP-binding domain were deuterated for various times and then, prior to mass spectrometry analysis, subjected to pepsin digestion to localize the deuterium incorporation. Mutation of this Arg in cAB-A (Arg230) causes an increase in amide hydrogen exchange throughout the mutated domain that is beyond the modest and localized effects of cAMP removal and is indicative of the importance of this Arg in domain organization. Mutation of Arg359 (cAB-B) leads to increased exchange in the adjacent cAB-A domain, particularly in the cAB-A domain C-helix that lies on top of the cAB-B domain and is believed to be functionally linked to the cAB-B domain. This interdomain communication appears to be a unidirectional pathway, as mutation of Arg230 in cAB-A does not effect dynamics of the cAB-B domain.

Dynamics of cAPK type IIbeta activation revealed by enhanced amide H/2H exchange mass spectrometry (DXMS)

cAMP-dependent protein kinase (cAPK) is a key component in numerous cell signaling pathways. The cAPK regulatory (R) subunit maintains the kinase in an inactive state until cAMP saturation of the R-subunit leads to activation of the enzyme. To delineate the conformational changes associated with cAPK activation, the amide hydrogen/deuterium exchange in the cAPK type IIbeta R-subunit was probed by electrospray mass spectrometry. Three states of the R-subunit, cAMP-bound, catalytic (C)-subunit bound, and apo, were incubated in deuterated water for various lengths of time and then, prior to mass spectrometry analysis, subjected to digestion by pepsin to localize the deuterium incorporation. High sequence coverage (>99%) by the pepsin-digested fragments enables us to monitor the dynamics of the whole protein. The effects of cAMP binding on RIIbeta amide hydrogen exchange are restricted to the cAMP-binding pockets, while the effects of C-subunit binding are evident across both cAMP-binding domains and the linker region. The decreased amide hydrogen exchange for residues 253-268 within cAMP binding domain A and for residues 102-115, which include the pseudosubstrate inhibitory site, support the prediction that these two regions represent the conserved primary and peripheral C-subunit binding sites. An increase in amide hydrogen exchange for a broad area within cAMP-binding domain B and a narrow area within cAMP-binding domain A (residues 222-232) suggest that C-subunit binding transmits long-distance conformational changes throughout the protein.

MAP2 is required for dendrite elongation, PKA anchoring in dendrites, and proper PKA signal transduction

Microtubule-associated protein 2 (MAP2) is a major component of cross-bridges between microtubules in dendrites, and is known to stabilize microtubules. MAP2 also has a binding domain for the regulatory subunit II of cAMP-dependent protein kinase (PKA). We found that there is reduction in microtubule density in dendrites and a reduction of dendritic length in MAP2-deficient mice. Moreover, there is a significant reduction of various subunits of PKA in dendrites and total amounts of various PKA subunits in hippocampal tissue and cultured neurons. In MAP2-deficient cultured neurons, the induction rate of phosphorylated CREB after forskolin stimulation was much lower than in wild-type neurons. Therefore, MAP2 is an anchoring protein of PKA in dendrites, whose loss leads to reduced amount of dendritic and total PKA and reduced activation of CREB.

Localization of cAMP-dependent protein kinase in the actin and microtubule cytoskeletons in mouse hippocampal neurons

Cyclic adenosine monophosphate-dependent protein kinase (PKA) is involved in various biological functions in neurons. To investigate the subcellular localization of PKA, we stained cultured hippocampal neurons with anti-PKA catalytic subunit antisera. PKA catalytic subunit colocalized with microtubules (MTs) in dendrites as well as with the actin filaments (F-actin) in growth cones. After treatment with cytochalasin B, the colocalization of PKA catalytic subunits with MTs was enhanced, whereas the colocalization with F-actin was suppressed. This result indicates that PKA is anchored to the actin and MT cytoskeletons, and disruption of F-actin releases PKA to the cytoplasm, which then leads to an increase in the amount of PKA in MT domains in the neuron.

Twenty-four hour exposure to prostaglandin downregulates prostanoid receptor binding but does not alter PGE(2)-mediated sensitization of rat sensory neurons

Although the tissue levels of prostaglandins are elevated for a relatively long period during injury or inflammation, few studies have been performed to assess the effects of prolonged prostaglandin exposure on receptor binding and activity in sensory neurons. Consequently, we examined whether unilateral inflammation or a 24 h exposure to prostaglandin E2 (PGE2) altered binding of this prostanoid in spinal cord tissue or in isolated sensory neurons, respectively. To assess functional changes in EP receptors, we also examined PGE2-induced cAMP production and the prostanoid-mediated augmentation of substance P release from isolated sensory neurons after acute and 24 h pretreatment with PGE2. Injection of complete Freund's adjuvant into the hindpaw decreased binding of PGE2 in ipsilateral, but not contralateral dorsal spinal cord 24 h after injection. This decrease in Bmax was blocked by administration of intrathecal ketorolac (10 nmol/microl/h) for 24 h prior to and throughout the period of inflammation, suggesting that the inflammation-induced decrease in binding is dependent on prostaglandin synthesis. In an analogous manner, treating sensory neurons grown in culture with 1 microM PGE2 for 24 h decreased [3H]-PGE2 binding by approximately 50% without altering binding affinity. Exposing neuronal cultures to 1 microM PGE2 for 24 h also reduced, but did not abolish the ability of the prostanoid to increase the production of cAMP. This treatment, however, did not significantly alter the ability of PGE2 to augment the evoked release of immunoreactive substance P from sensory neurons. These results demonstrate that under conditions that significantly downregulate PGE2 binding, sensory neurons are still capable of maintaining PGE2-mediated sensitization.

The biological functions of A-kinase anchor proteins

cAMP-dependent protein kinase is targeted to discrete subcellular locations by a family of specific anchor proteins (A-kinase anchor proteins, AKAPs). Localization recruits protein kinase A (PKA) holoenzyme close to its substrate/effector proteins, directing and amplifying the biological effects of cAMP signaling.AKAPs include two conserved structural modules: (i) a targeting domain that serves as a scaffold and membrane anchor; and (ii) a tethering domain that interacts with PKA regulatory subunits. Alternative splicing can shuffle targeting and tethering domains to generate a variety of AKAPs with different targeting specificity. Although AKAPs have been identified on the basis of their interaction with PKA, they also bind other signaling molecules, mainly phosphatases and kinases, that regulate AKAP targeting and activate other signal transduction pathways. We suggest that AKAP forms a "transduceosome" by acting as an autonomous multivalent scaffold that assembles and integrates signals derived from multiple pathways. The transduceosome amplifies cAMP and other signals locally and, by stabilizing and reducing the basal activity of PKA, it also exerts long-distance effects. The AKAP transduceosome thus optimizes the amplitude and the signal/noise ratio of cAMP-PKA stimuli travelling from the membrane to the nucleus and other subcellular compartments.

Visualization of detergent insoluble cyclic AMP-dependent protein kinase RIalpha aggregates in the rat brain

Regulatory subunits of the cAMP dependent protein kinases are the most abundant receptor for cAMP in eukaryotic cells. Four isoforms of regulatory subunits (RIalpha and -beta, RIIalpha and -beta) have been distinguished. Distribution of the most abundant RII isoforms has been extensively studied in the brain, by immunohistochemistry and biochemical fractionation, while the least abundant RI isoforms have been neglected. In neurons most regulatory subunits are bound to the cytoskeleton. A protocol is presented that allows immunohistochemical and biochemical characterization of detergent-insoluble RI isoforms in the brain.

cAMP-dependent protein kinase type RI is found in clusters in the rat detergent-insoluble neuronal fraction

Different types of cAMP dependent regulatory subunits have been characterized in the mammalian brain: RI alpha and beta, RII alpha and beta. The subcellular distribution of RI subunits has been examined in the rat brain. Partial amino acid sequencing of tryptic fragments from the Triton insoluble pellet of the rat brain shows that cAMP dependent regulatory subunits type RI alpha are found in this fraction. Immunohistochemistry shows that Triton-insoluble RI subunits are concentrated to form clusters and this distribution is distinct from RII subunits. Immunohistochemistry and fluorescent cAMP labeling show that the clusters bind fluorescent cAMP analogues. These results suggest that the high local concentration of RI subunits can modulate cAMP distribution among different cellular compartments.

A quantitative autoradiographic study of [3H]cAMP binding to cytosolic and particulate protein kinase A in post-mortem brain staged for Alzheimer's disease neurofibrillary changes and amyloid deposits

The cAMP-dependent protein kinase (PKA) has been implicated in the Alzheimer's disease pathology of abnormal tau phosphorylation leading to neurofibrillary tangle (NFT) formation, as well as in amyloid precursor protein alpha-secretase processing. In the present study, we determined whether [3H]cAMP binding to cytosolic and particulate PKA showed any relationship to the extent of Alzheimer's disease pathology at post-mortem. Autoradiographic [3H]cAMP binding to cytosolic and particulate PKA was measured in sections of entorhinal cortex/hippocampal formation from 23 cases that had been staged for Alzheimer's disease-related neurofibrillary changes and amyloid deposits according to Braak and Braak [H. Braak, E. Braak, Neuropathological staging of Alzheimer's-related changes, Acta Neuropathol. 82 (1991) 239-259]. [3H]cAMP binding to cytosolic PKA showed statistically significant reductions in the entorhinal cortex (P<0.01, ANOVA) with respect to neurofibrillary changes. Post-hoc analysis with Fisher's PLSD test showed significant reductions of [3H]cAMP binding to cytosolic PKA at the isocortical stages (V and VI), compared to the non-pathological (O) (by 55%, P<0.01), transentorhinal (I and II) (by 58%, P<0.001) and limbic (III and IV) (by 45%, P<0.05) stages. A significant reduction (by 25%, P<0.05) was also seen in the transentorhinal compared to the limbic stages. [3H]cAMP binding to cytosolic PKA showed no significant alterations with respect to neurofibrillary changes in either the subiculum, CA1-CA4 subfields of the hippocampus or the dentate gyrus. [3H]cAMP binding to cytosolic PKA also showed significant declines in the entorhinal cortex (P<0.01) and subiculum (P<0.05) with respect to staging for amyloid deposits. Post-hoc analysis with Fisher's PLSD test showed significant reductions of [3H]cAMP binding to cytosolic PKA in the entorhinal cortex at amyloid stage C compared to stages O (by 41%, P<0.01) and A (by 38%, P<0.01). In the subiculum, there were significant reductions of [3H]cAMP binding at stages C (by 41%, P<0.01) and B (by 40%, P<0.05), respectively, compared to stage O. [3H]cAMP binding to particulate PKA did not show significant relationships to staging for either neurofibrillary changes or amyloid deposits in either the entorhinal cortex or any of the hippocampal subregions. These findings suggest that whereas [3H]cAMP binding to cytosolic PKA in the entorhinal cortex is reduced with progression of neurofibrillary and amyloid pathology, other hippocampal regions show a preservation of cytosolic and particulate PKA even in late stage pathologies.

Immunochemical visualization and quantitation of cyclic AMP in single cells

Adenosine 3':5'-cyclic monophosphate (cAMP) is a key second messenger in signaling pathways governing many cellular processes. To define the subcellular localization and relative abundance of cAMP, we developed a novel immunochemical approach based on acrolein fixation to visualize cAMP within cells. We describe here the fixation and immobilization of cAMP within cells and the production of specific, high titer polyclonal antibodies that recognize cAMP. Relative levels of cAMP immunofluorescence were quantitated in glial cells (oligodendrocytes, astrocytes, Schwann cells, and glioma cells) that were either untreated or treated with activators of endogenous adenylyl cyclase to raise cAMP levels. In treated cells, cAMP immunofluorescence is strongly localized in the perinuclear cytoplasm.

Characterization of protein kinase and phosphatase systems in chick ciliary ganglion

The aim of the present study was to characterize the second messenger activated protein kinase and phosphatase systems in chick ciliary ganglion using biochemical and immunochemical techniques. Using synthetic peptide substrates cyclic-AMP-, cyclic-GMP-, Ca2+/calmodulin- and Ca2+/phospholipid-dependent protein kinase activities were detected in homogenates of ciliary ganglion dissected from 15-16-day-old embryos. Autophosphorylation of the alpha and beta subunits of Ca2+/calmodulin-dependent protein kinase II in the presence of Ca2+/calmodulin or 5 mM ZnSO4 was detected by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography. Protein kinase C was shown to be present using a monoclonal antibody. Two cyclic-AMP binding proteins whose molecular weights corresponded to the regulatory subunits of cyclic AMP-dependent protein kinase (RI and RII) were detected in ciliary ganglia using 8-azido-cyclic-AMP. The most heavily labelled band following incubation with [gamma-32P]ATP under most conditions had an apparent molecular weight of 65,000 which corresponds to the chicken form of myristoylated alanine-rich C kinase substrate, a known substrate of protein kinase C. Another substrate for protein kinase C was a 45,000 molecular weight protein which was tentatively identified as neuromodulin (B-50/GAP-43). Although no endogenous substrate proteins for cyclic-GMP-dependent protein kinase were detected, protein kinase A strongly labelled a 40,000 molecular weight protein. Using 32P(i)-labelled glycogen phosphorylase, protein phosphatases 1 and 2A were identified in ciliary ganglia homogenates at levels which were indistinguishable from forebrain at the same age. The major endogenous protein substrates in ciliary ganglion homogenates from 15-16-day-old embryos were also labelled to a similar extent in homogenates of ciliary ganglia from newly hatched chickens. Intact ciliary ganglia remained viable for several hours after dissection and, after incubation with 32P(i), responded to phorbol ester stimulation by an increased endogenous phosphorylation of several proteins, but especially myristoylated alanine-rich C kinase substrate. These results represent the first systematic characterization of the protein phosphorylation systems in chicken ciliary ganglion and provide a basis for future studies on the biochemical mechanisms responsible for regulating synaptic transmission in this tissue.

Association of the regulatory subunit of a type II cAMP-dependent protein kinase and its binding proteins with the fibrous sheath of rat sperm flagellum

Demembranated rat sperm flagellar polypeptides capable of binding the regulatory subunit (RII) of a type II cAMP-dependent protein kinase, having apparent subunit molecular masses of 120, 80 and 57 kDa were identified by an RII overlay procedure [Horowitz, J. A., Wasco, W., Leiser, M. & Orr, G. A. (1988) J. Biol. Chem. 263, 2098-2104]. In this study it is shown that all three polypeptides capable of binding RII on a solid-phase blot are tightly associated with the fibrous sheath. Purified fibrous sheath preparations were capable of binding (a) [3H]cAMP and (b) purified catalytic subunits of cAMP-dependent protein kinase forming a functional holoenzyme. The 57-kDa protein was identified as RII by photoaffinity labeling with 8-azido[32P]cAMP. This peptide was phosphorylated by the catalytic subunit of cAMP-dependent protein kinase. RII alpha was also shown to form tight, specific complexes with the fibrous sheath demonstrating the presence of functional RII alpha-binding sites. Truncated RII beta fusion proteins were used to identify the N-terminal amino acids at positions 1-50 as a primary determinant for RII-binding protein interaction. Differential extraction of adult testis with buffers containing Triton X-100, urea and sodium dodecyl sulfate revealed the presence of 80-kDa (major) and 120-kDa (minor) RII-binding proteins in particulate extracts. The 80-kDa polypeptide is only expressed at late stages of spermatogenesis, i.e. during spermiogenesis, suggesting a developmental role for RII anchoring to the sperm flagellar fibrous sheath.

A-kinase anchoring proteins: a key to selective activation of cAMP-responsive events?

The cAMP-dependent protein kinase (PKA) regulates a variety of diverse biochemical events through the phosphorylation of target proteins. Because PKA is a multifunctional enzyme with a broad substrate specificity, its compartmentalization may be a key regulatory event in controlling which particular target substrates are phosphorylated. In recent years it has been demonstrated that differential localization of the type II holoenzyme is directed through interaction of the regulatory subunit (RII) with a family of A-Kinase Anchoring Proteins (AKAPs). In this report, we review evidence for PKA compartmentalization and discuss the structural and functional properties of AKAPs.

Increase in [3H]cAMP binding sites and decrease in Gi alpha and Go alpha immunoreactivities in left temporal cortices from patients with schizophrenia

To search for possible alterations in second messenger systems in the temporal cortex (Brodmann's area 22) of patients with schizophrenia, we measured the binding activities of [3H]adenosine 3',5'-cyclic monophosphate ([3H]cAMP) and [3H]4 beta-phorbol 12,13-dibutyrate ([3H]PDBu) which can label the regulatory subunit of cAMP-dependent protein kinase (protein kinase A) and the regulatory domain of Ca2+/phospholipid-dependent protein kinase (protein kinase C), respectively. We also immunoquantified the variable subunits of guanine nucleotide binding proteins (G-proteins), using specific polyclonal antisera against Gs alpha, Gi alpha and Go alpha. Brains were obtained at autopsy on 10 patients with schizophrenia and 10 age-matched control subjects. Representative Scatchard plots for specific [3H]cAMP bindings to the soluble fraction consisted of a single component with high affinity (Kd = 2.36 nM, Bmax = 737 fmol/mg protein). Among the tested adenyl and guanyl nucleotides, or neuroleptics, cAMP alone potently inhibited the binding (Ki = 4.95 nM). The binding sites for [3H]cAMP were discretely localized, and were in the order of: cerebral cortex = hypothalamus = amygdala > hippocampus = neostriatum = thalamus = nucleus accumbens > globus pallidus = cerebellum. Specific [3H]cAMP bindings to the soluble fractions were about 30% greater in the left temporal cortices of schizophrenic patients, as compared to findings in the right side of the patients and the left side of the control subjects, no control brain showed this asymmetry. The specific [3H]PDBu binding in schizophrenic and control groups did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the existence of cAMP-dependent protein kinase phosphorylation system associated with specific phosphoproteins in stable microtubules from rat cerebral cortex

Cyclic AMP is a second messenger by which different extracellular signals are transduced into biological responses. Within the cell, most of the effects of cAMP are mediated through the cAMP protein kinase which appears to be localized in specific compartments of the cell near to their substrate proteins. In the present study, we have investigated the possible association of cAMP-dependent protein kinase, its substrate proteins and RII binding proteins in stable microtubules from rat cerebral cortex. The results show that in this fraction there is a cAMP binding protein of 52-54 kDa. This cAMP receptor is in the inactive holoenzyme form, since the addition of cAMP (5 microM) induces an increase in the endogenous phosphorylation of different stable microtubules polypeptides, which is completely inhibited in the presence of a specific protein kinase inhibitor (PKI 5-24 1 microM). Interestingly, overlay binding assay reveals that beside MAP2, 32P/R II is able to bind stable microtubule proteins of M(r) 150 and 75 kDa which, according to their electrophoretic mobility, can also be endogenous substrates for the enzyme. We conclude that cAMP-dependent phosphorylation system is indeed associated with stable microtubules from rat cerebral cortex.

Norepinephrine-mediated protein phosphorylation in astrocytes

Studies were conducted to determine if norepinephrine activates both protein kinase C and the cyclic AMP-dependent protein kinase in cultured rat astrocytes using phosphoproteins as markers. Norepinephrine was found to decrease 32P incorporation into an acidic 80,000 M(R) protein. A similar response was observed with isoproterenol and cyclic AMP analogs. In contrast, phorbol myristate acetate (PMA) increased 32P incorporation into this protein. Further studies looked at phosphorylation sites on glial fibrillary acidic protein and vimentin using two-dimensional tryptic phosphopeptide maps. The pattern of phosphorylation of these two proteins by norepinephrine resembles that of 8-bromo cyclic AMP and isoproterenol, and not that of PMA. Additionally, the effect of norepinephrine on the phosphorylation of GFAP and vimentin was blocked by alprenolol. One difference noted between norepinephrine and isoproterenol was the phosphorylation of an 18,000 M(R) protein. Norepinephrine increased, and isoproterenol decreased, 32P incorporation into this protein; however, the mechanism which mediates the norepinephrine effect remains to be determined. Overall, these studies indicate that the most prominent phosphorylation events mediated by norepinephrine are the consequence of the activation of cyclic AMP-dependent protein kinase.

Blotting and band-shifting: techniques for studying protein-protein interactions

The type II cAMP-dependent protein kinase (PKA) is localized in certain cellular compartments through association with specific A-kinase anchoring proteins (AKAPs). A variety of blotting and electrophoresis techniques have been developed to study the protein-protein interactions that occur between the regulatory (R) subunit of PKA and AKAPs. These methods have also been used for a variety of purposes such as detecting calmodulin-binding proteins, comparing wild-type- and mutant-form binding affinities and estimating the molecular weight of multiprotein complexes.

Synthesis of glial fibrillary acidic protein in rat C6 glioma in chemically defined medium: cyclic AMP-dependent transcriptional and translational regulation

Glial fibrillary acidic protein (GFA) expression was induced in rat C6 glioma in chemically defined medium by the addition of N6, O2'-dibutyryl cyclic AMP (dbcAMP). Induction was dependent on the increase in intracellular cyclic AMP (cAMP), which was linearly correlated with added dbcAMP. Contrary to GFA mRNA synthesis, which can be obtained by cAMP-dependent and -independent pathways, translation of mRNA into GFA was observed only above a cellular cAMP concentration of approximately 0.2 fmol/cell. dbcAMP stimulation did not affect the vimentin concentration, which remained at a low level, but changed the cellular morphology from a bipolar to a stellate shape. A similar morphological change was observed after stimulation of C6 with lipopolysaccharide (LPS). However, LPS did not significantly increase the intracellular concentration of cAMP and the LPS-induced mRNA was not translated into GFA. Our results indicate that GFA synthesis is regulated at the mRNA level and at the translational level and that a cAMP-dependent mechanism determines the ultimate synthesis of GFA by a yet unknown mechanism.

Regional localization of the regulatory subunit (RII beta) of the type II cAMP-dependent protein kinase in human brain

The distribution of the regulatory (RII beta) subunits of type II cAMP-dependent protein kinase in cortical and subcortical areas was examined in human control and Alzheimer's disease (AD) brains. Four monoclonal antibodies generated against bovine brain RII, which cross-reacted with human brain RII beta, detected RII-immunoreactivity in pyramidal neurons of the hippocampus and frontal, occipital, parietal and superior temporal cortices and in non-pyramidal neurons of the amygdala and putamen. RII beta immunoreactivity was localized to neuronal perikarya, proximal dendrites and cell processes. With the exception of rare processes in the ventroposterior lateral nucleus, RII-immunoreactivity was not seen in the thalamus. Other areas lacking RII-immunoreactivity included the midbrain, caudate nucleus and globus pallidus. RII-immunoreactivity was not detected in endothelia or glia. Except for the neocortex, the distribution of RII beta immunoreactivity was the same in AD and non-demented control brains; however, cell bodies and their processes stained more intensely and uniformly in the neocortical regions of non-demented controls compared to AD. In the neocortex of AD, RII beta immunoreactivity was substantially decreased in the superior temporal and occipital cortices, but not in the frontal cortex. Our data suggest that RII subunits are regionally distributed in the human brain. RII-immunoreactivity was decreased in some regions of neocortex in AD, but it did not preferentially colocalize with neurofibrillary tangles (NFT), senile plaques, or neuropil threads.

Two lipid-anchored cAMP-binding proteins in the yeast Saccharomyces cerevisiae are unrelated to the R subunit of cytoplasmic protein kinase A

We show that the yeast, Saccharomyces cerevisiae, contains two cAMP-binding proteins in addition to the well-characterized regulatory (R) subunit of cytoplasmic cAMP-dependent protein kinase (PKA). We provide evidence that they comprise a new type of cAMP receptor, membrane-anchored by covalently attached lipid structures. They are genetically not related to the cytoplasmic R subunit. The respective proteins can be detected in sral mutants, in which the gene for the R subunit of PKA has been disrupted and a monoclonal antibody raised against the cytoplasmic R subunit does not cross-react with the two membrane-bound cAMP-binding proteins. In addition, they differ from the cytoplasmic species also with respect to their location and the peptide maps of the photoaffinity-labeled proteins. Although they differ from one another in molecular mass and subcellular location, peptide maps of the cAMP-binding domains resemble each other and both proteins are membrane-anchored by lipid structures, one to the outer surface of the plasma membrane, the other to the outer surface of the inner mitochondrial membrane. Both anchors can be metabolically labeled by Etn, myo-Ins and fatty acids. In addition, the anchor structure of the cAMP receptor from plasma membranes can be radiolabeled by GlcN and Man. After cleavage of the anchor with glycosylphosphatidylinositol-specific phospholipase C from trypanosomes, the solubilized cAMP-binding protein from plasma membranes reacts with antibodies which specifically recognize the cross-reacting determinant from soluble trypanosomal coat protein, suggesting similarity of the anchors. Degradation studies also point to the glycosylphosphatidylinositol nature of the anchor from the plasma membrane, whereas the mitochondrial counterpart is less complex in that it lacks carbohydrates. The plasma membrane cAMP receptor is, in addition, modified by an N-glycosidically linked carbohydrate side chain, responsible mainly for its higher molecular mass.

Cyclic AMP accumulation induces a rapid desensitization of the cyclic AMP-dependent protein kinase in mouse striatal neurons

Striatal neurons from the mouse brain embryo grown in primary culture express high levels of cyclic AMP (cAMP)-dependent protein kinase (PKA) activity. To study the modulation of PKA in intact neurons, a rapid method based on Zn(2+)-protein precipitation was developed. This strategy allowed analysis of the stimulation of PKA under conditions of intracellular cAMP concentration increases. Whereas increases up to 1 microM lead to an activation, large and sustained accumulations of cAMP result in a loss of the enzyme activity. With 8-bromo-cAMP (8-Br-cAMP) at 100 microM, the PKA refractoriness occurs within 2 min. It is rapidly reversible because incubation of treated neurons in fresh medium leads to a complete recovery of PKA activity within 30 min. The decrease in assayable PKA does not involve an activation of phosphatases because the histone dephosphorylation rate is not affected by 8-Br-cAMP treatment. Finally, not only 8-Br-cAMP- but also forskolin- and vasoactive intestinal peptide-induced increases in intracellular cAMP concentration can lead to the PKA desensitization. Altogether, these data unravel a new mechanism of PKA regulation.

Cyclic AMP-receptor protein activity in rat preputial cells

Cells from the rat preputial gland--a type of sebaceous gland--exhibited specific responsiveness of cyclic 3',5'-adenosine monophosphate (AMP) dependent protein kinase to stimulation by agents that elevate intracellular cyclic AMP. Electron microscopy shows that the rat preputial gland resembles the human sebaceous gland, not only in terms of containing a sebocyte-like population of cells in an acinar arrangement at different maturational stages, but also in the morphology of its organelles such as abundant and sometimes atypical mitochondria, many perinuclear lysosomes with crystalline inclusions, lipid droplets of various sizes, and peroxisomes. Other cell types, among them duct and inflammatory cells, were evident in the tissue sections, but constituted a minor component. Responses to stimulation of the adenylate cyclase-protein kinase pathways were determined using preputial cells that had been both freshly dispersed and grown in monolayer culture. Stimulation with isoproterenol (IPR) or forskolin (FS) resulted in both cases in an increase of cyclic AMP binding of the regulatory (R) subunits of cyclic AMP-dependent protein kinase, as determined by photoaffinity labeling of R subunits with an azido analog of cyclic AMP ([32P]-8-azido cyclic AMP). Cells from the epidermis under comparable conditions responded to a lesser degree and with a different distribution of R subunit isoforms. There are, therefore, differences in receptor activity as well as in the transduction pathways between the two types of epithelial cell populations. These results indicate that the preputial gland contains precursor cells that differentiate in culture to retain specific molecular mechanisms of action mediated via cyclic AMP.

Immunocytochemical localization of the neural-specific regulatory subunit of the type II cyclic AMP-dependent protein kinase to postsynaptic structures in the rat brain

The cellular and subcellular distribution of a major cyclic AMP binding protein in the central nervous system, the neural-specific regulatory subunit of the type II cyclic AMP-dependent protein kinase (RII-B), was analyzed in rat brains with light and electron microscopic immunocytochemical methods. The distribution of the non-neural isoform of the regulatory subunit of the enzyme (RII-H) was also analyzed. It was found that RII-B immunoreactivity was predominantly localized to neurons whereas glial and endothelial cells were unlabeled. In the neurons the RII-B immunoreactivity occurred in the perikaryal cytoplasm and in the dendrites; there was no significant accumulation of immunoreaction product in nuclei, myelinated axons and axon terminals. Although immunoreactivity was never detected in axon terminals, it was characteristically associated with the postsynaptic densities and the surrounding non-synaptic sites in somata, dendrites and dendritic spines. The localization of RII-B antigenic sites did not show specificity to any type of neuron or synapse, but the amount of immunoreactivity varied. The distribution of RII-H immunoreactivity was similar to that of RII-B except that RII-H immunoreaction product was also observed in glial cells and occurred more frequently in myelinated axons. Our data confirm that RII-B is one of the major cyclic AMP binding proteins in neurons, and provide morphological support for the involvement of the type II cyclic AMP-dependent protein kinase in postsynaptic neural functions.

Identification of a 50-kDa Ca-, cAMP-, and cGMP-dependent epithelial phosphoprotein as a cAMP regulatory protein

Multiple second messengers, presumably acting via protein phosphorylation mechanisms, regulate flounder intestinal ion transport. We recently reported [C. Toskulkao, N. T. Nash, K. Leach, and M. C. Rao. Am. J. Physiol. 258 (Cell Physiol. 27): C879-C888, 1990] that this tissue possesses adenosine 3',5'-cyclic monophosphate (cAMP)- and guanosine 3',5'-cyclic monophosphate (cGMP)-specific protein kinases, types II and III Ca-calmodulin kinases, and very low levels of protein kinase C. These results correlate with ion transport studies in which cGMP and Ca were shown to inhibit salt absorption, cAMP to increase anion permeability, and phorbol esters to have no effect. In the present study we characterized in detail a 50-kDa protein the phosphorylation of which is regulated by more than one second messenger. The 50-kDa (pI 5.2) phosphoprotein is present in both the cytosol (50 kDa-C) and particulate (50 kDa-P) fractions and appears to be regulated by Ca, cAMP, and cGMP. Although the pI and Mr of the regulated proteins are identical, there are differences in the regulation of 50 kDa-P and 50 kDa-C. The phosphorylation of 50 kDa-P is high in the basal state, and Ca and cGMP enhance this. cAMP has a biphasic effect, increasing it at low and decreasing it at high protein concentrations. The isoquinoline derivatives H-8 [50% effective dose (ED50) approximately 2.3 microM] and H-7 (ED50 approximately 45 microM) inhibit basal 50 kDa-P phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogenetic analysis of embryonic palatal type I and type II cAMP-dependent protein kinase isozymes

The developmental processes of cell growth and differentiation are important mechanisms regulating tissue and organ formation. These processes appear to be dependent on the ligand-receptor interactions of various hormones, growth factors, and extracellular matrix molecules. In turn, ligand-receptor interactions may elevate intracellular levels of second messengers. Among the second messengers, cyclic AMP (cAMP) is known to activate cAMP-dependent protein kinases (cAMP-dPK) by binding to two major regulatory subunit isoforms, RI and RII, of this enzyme. The present study examined the occurrence of changes in the cAMP-dPK isozyme patterns during the critical period of murine palatal ontogeny between days 12 and 14 of gestation. Cyclic AMP-dPK in cytosolic preparations (27,000 x g) of murine embryonic maxillary and palatal tissue were analyzed by DEAE chromatography and photoaffinity labelling with 8-azido-[32P]cAMP followed by SDS-PAGE and autoradiography. Both techniques indicated shifting patterns of expression of RI (45,000 Mr) and RII (52,000 Mr) regulatory subunits during palatal ontogeny. Immunohistochemical localization of RI and RII revealed more intense fluorescence in the palatal epithelial layer by days 13 and 14 with an apparent greater intensity of immunostaining on the basal aspect of the epithelial layer. These results suggest an important role for cAMP-dPK in epithelial-mesenchymal cell signalling during development of the murine palate.

Localization and characterization of the binding site for the regulatory subunit of type II cAMP-dependent protein kinase on MAP2

Microtubule-associated protein 2 (MAP2) binds, and is a substrate for, type II cAMP-dependent protein kinase. The structural domain in MAP2 that binds the regulatory subunit (RII) of protein kinase II was identified by expressing fragments of a human MAP2 cDNA in E. coli using the pATH11 vector. Fusion proteins were resolved by SDS-PAGE and transferred to nitrocellulose. The filters were probed with purified bovine heart or brain RII, anti-RII monoclonal antibodies, and 125I-labeled protein A. Binding of RII was localized to a 31 amino acid sequence near the N-terminus of the MAP2 molecule. Fusion proteins containing this fragment bound both heart and brain RIIs in a concentration-dependent manner, but bound heart RII with a higher apparent affinity than brain RII. The amino acid sequence of this fragment (DRETAEEVSARIVQVVTAEAVAVLKGEQEKE) is totally conserved between human and mouse MAP2, suggesting an important role for the RII binding site of MAP2 in neuronal function.

Distinct patterns of cAMP-dependent protein kinase gene expression in mouse brain

In situ hybridization was used to localize cAMP-dependent protein kinase (PKA) mRNAs in the adult mouse CNS. The PKA holoenzyme contains two catalytic (C) subunits and a regulatory (R) subunit dimer. Our studies demonstrate expression of two isoforms of C (C alpha and C beta) and four isoforms of R (RI alpha, RI beta, RII alpha, and RII beta) in the CNS. mRNAs for C alpha, RI alpha, and RI beta preferentially localize in the neocortex, caudate-putamen, hypothalamus, thalamus, and hippocampus. Hybridization with C beta and RII beta probes is clearly distinguished from the C alpha-like pattern by a reduced level of hybridization in the thalamus and by a relative increase in expression in the dentate gyrus compared with cell layers CA1-3 in the hippocampus. RII alpha transcripts are very specifically localized in the medial habenula. The differential expression of PKA subunit genes suggests that functional differences in cAMP responses within neural tissues may be mediated by the biochemical properties of specific PKA isoforms.

Autoradiographic localization of particulate cyclic AMP-dependent protein kinase in mammalian brain using [3H]cyclic AMP: implications for organization of second messenger systems

Cyclic AMP's regulatory role as an intracellular second messenger is well established. In brain and other tissues, specific proteins that bind cyclic AMP have been shown to be the regulatory subunits of cystolic and particulate cyclic AMP-dependent protein kinases. This study of the autoradiographic localization of specific [3H]cyclic AMP binding revealed the heterogeneous distribution of particulate cyclic AMP-dependent protein kinase in the mammalian central nervous system. Specific [3H]cyclic AMP binding to tissue sections was of high affinity (KD = 60 nM) and saturable (Bmax = 5 pmol/mg protein). Purine and pyrimidine nucleotide analogues demonstrated inhibition constants against [3H]cyclic AMP binding consistent with the specific labelling of cyclic AMP-dependent protein kinase (e.g. 8'-bromo-cyclic AMP: IC50 = 130 nM; inosine 3',5'-cyclic monophosphate: IC50 = 1 microM; uridine 3',5'-cyclic monophosphate: IC50 = 60 microM). Variations in the levels of [3H]cyclic AMP binding presumably reflect the presence of differing amounts of particulate cyclic AMP-dependent protein kinase in different neuronal populations. Highest densities were associated with neuronal cell layers such as the pyramidal cells of the piriform cortex and hippocampus, and granule cells of the dentate gyrus and cerebellum. High levels of binding were also found in other cortical and limbic structures, while moderate levels were found in hypothalamic, thalamic and midbrain areas. Excitotoxic lesions confirmed the localization of the enzyme in hippocampal pyramidal cells and cerebellar granule cells. Localizations reported in this study are largely consistent with results obtained using immunohistochemical methods to label cyclic AMP-dependent protein kinases. Recently, [3H]forskolin, a potent and selective activator of adenylate cyclase, the enzyme responsible for the formation of cyclic AMP from adenosine 5'-triphosphate, has been used to localize the activated catalytic component of this enzyme in rat brain. Regions described as being intensely labelled with [3H]forskolin (e.g. basal ganglia, hilus of the dentate gyrus and molecular layer of the cerebellum) were found to be associated with relatively low [3H]cyclic AMP binding levels. These findings suggest a marked difference between the localization of the two related enzyme entities. However, the distribution of the enzymes is indirectly correlated as high levels of particulate cyclic AMP-dependent protein kinase are present in the soma of neurons with high concentrations of adenylate cyclase in their terminals. Alternatively, it is possible that [3H]forskolin localizes only a subpopulation of adenylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)