ACTH, cyclic nucleotides, and brain protein phosphorylation in vitro

Early effect of an ACTH4-9 analog (Org.2766) on regenerative sprouting demonstrated by the use of neurofilament-binding antibodies isolated from a serum raised by alpha-MSH immunization

Antibodies binding to the 150 kDa neurofilament protein NF150 have been purified from a serum raised by immunizing a rabbit with alpha-MSH. The NF150-binding antibodies were purified by affinity chromatography on a column of cytoskeletal proteins coupled to CNBr-activated Sepharose-4B. Immunocytochemical application of these antibodies, followed by a FITC-coupled second antibody, labels axons in intact and regenerating nerves and provides a means of identifying and counting small regenerating sprouts from 48 h after nerve crush. We have been able to demonstrate that treatment with the neurotrophic melanocortin analog, Org.2766, increases the number of regenerating axons present in the nerve as early as 72 h after nerve crush.

Synapsin I, a phosphoprotein associated with synaptic vesicles: possible role in regulation of neurotransmitter release

The data presented here provide evidence that the study of neuronal phosphoproteins can lead to the identification of previously unknown proteins and that these proteins may play important roles in neuronal communication. Specifically, in the case of synapsin I, direct evidence has been obtained that this phosphoprotein is involved in regulating neurotransmitter release. A tentative explanation of the results obtained in the micro-injection studies is as follows: synapsin I, in the dephosphostate, is bound to the cytoplasmic surface of synaptic vesicles and inhibits the ability of the vesicle to interact with the plasma membrane; increases in intracellular calcium activate calmodulin kinase II which in turn phosphorylates synapsin I and the phosphorylated synapsin I dissociates from the synaptic vesicle thus removing a constraint on the release of neurotransmitter. Clearly, more studies need to be done to rigorously test this hypothesis. Nevertheless these studies of synapsin I suggest that the study of previously unknown phosphoproteins will lead to the elucidation of previously unknown regulatory processes in neurons.

Comparison of a 52-kDa phosphoprotein from synaptic plasma membranes related to long-term potentiation and the major coated vesicle phosphoprotein

In the in vitro hippocampal slice preparation a short tetanus induces long-term potentiation (LTP) and an increase in the post hoc phosphorylation of a 52-kDa protein in synaptosomal plasma membranes (SPM) prepared from these slices. This 52-kDa SPM phosphoprotein closely resembles the predominant phosphoprotein in coated vesicles, pp50, with respect to the insensitivity of its phosphorylation to Ca2+/calmodulin and cyclic AMP. This resemblance prompted us to compare in rat brain the 52-kDa SPM protein with pp50 in isolated coated vesicles. Both proteins appear to be very similar on basis of the following criteria: relative molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, peptide mapping, phospho-amino acid content, and isoelectric point. Since coated vesicles are thought to be involved in receptor-mediated endocytosis and membrane recycling, our data suggest that LTP-correlated changes in 52-kDa phosphorylation may reflect increased coated vesicle activity.

Nerve growth factor enhances the level of the protein kinase C substrate B-50 in pheochromocytoma PC12 cells

Exposure of PC12 cells to nerve growth factor results in arrest of cell growth and induction of differentiation to sympathetic neuron-like cells, bearing neurites. In this study we identify a 48 kDa PC12 phosphoprotein as the neuron-specific protein kinase C substrate B-50 (Mr 48 kDa; IEP 4.5) on basis of comigration with purified B-50, immunoreactivity and phosphopeptide mapping. B-50 is present in both undifferentiated and differentiated PC12 cells. Exposure of PC12 cells to nerve growth factor for two days results in a 2.5-fold increase in the amount of B-50 as measured by RIA. Indirect immunofluorescence microscopy reveals that B-50 is mainly localized at the cell membrane and in growth cones. Our data are in line with the hypothesis that B-50 plays a role in neurite outgrowth and indicate that PC12 cells provide a suitable model to study this hypothesis.

Dioctanoylglycerol and phorbol diesters enhance phosphorylation of phosphoprotein B-50 in native synaptic plasma membranes

The short chain diacylglycerol, 1,2-dioctanoylglycerol, at concentrations of 100-300 microM stimulated phosphorylation of the nervous system-specific membrane protein B-50 (Mr 48 kDa, IEP 4.5) in isolated synaptic plasma membranes both in the presence and absence of exogenous protein kinase C. Comparable enhancement of histone phosphorylation by purified protein kinase C was achieved with 1 microM neutral lipid. Phorbol dibutyrate was 100 times more potent than the diacylglycerol in stimulating endogenous B-50 kinase in the membranes, whereas 4-alpha-phorbol was without effect. These results further confirm that B-50 is phosphorylated physiologically by a C kinase. Our data are consistent with a negative feedback mechanism in which generation of 1,2-diacylglycerol by enhanced phosphatidylinositol-4,5-bisphosphate hydrolysis could stimulate B-50 phosphorylation, thereby diminishing phosphatidylinositol-4-phosphate kinase activity and decreasing phosphatidylinositol-4,5-bisphosphate biosynthesis.

In vitro interaction of ACTH with rat brain muscarinic receptors

ACTH-(1-24) inhibits the in vitro binding of the muscarinic antagonist [3H]QNB to membranes from rat brain. The magnitude of inhibition is dependent on the concentration of ACTH-(1-24). Kinetic analysis indicates a pure competitive inhibition which is suggestive of a reversible interaction of ACTH with muscarinic receptors. A mechanism involving an interaction of ACTH-(1-24) with the phospholipid core of the receptors is suggested. Structure activity studies point to a relation with reported effects of intracerebroventricularly administered ACTH on the turnover rate of acetylcholine and the ACTH-induced stretching and yawning syndrome.

Characterization of epitopes shared by alpha-melanocyte-stimulating hormone (alpha-MSH) and the 150-kD neurofilament protein (NF150): relationship to neurotrophic sequences

Immunoblot techniques and immunohistochemistry have been used to investigate epitopes shared by alpha-melanocyte-stimulating hormone (alpha-MSH) and the 150-kD neurofilament protein (NF150). Three anti-alpha-MSH antisera (namely 31H2T, 4394, and M5) from a total of 12 sera were found to react with NF150. The three crossreacting sera are different in their binding properties to peptide fragments related to alpha-MSH, suggesting that at least two distinct epitopes are shared by NF150 and alpha-MSH. The only known sequence common to NF150 and alpha-MSH, the N-terminal Ac-S-Y residues, appears to be essential for binding of sera 31H2T and 4394. However, the binding of antiserum M5 involves other, currently unknown, similarities between NF150 and alpha-MSH. This is shown by the binding of M5 to peptides such as ACTH(4-10), which do not contain the N-terminal Ac-S-Y sequence. Binding of M5 to tobacco mosaic virus coat protein (TMV-coat protein), which is homologous with alpha-MSH and NF150 in its Ac-S-Y residues, was negligible. The peptide structures that are recognized by M5 have previously been shown to exert neurotrophic activity. The data are discussed in the light of the hypothesis that similarity between NF150 and alpha-MSH, as illustrated by binding to M5, may be significant in the neurotrophic activity of MSH-related peptides.

Pentylenetetrazole-induced bursting activity and cellular protein phosphorylation in snail neurons

To elucidate the intracellular mechanism of seizure discharge, phosphorylation of cellular protein during pentylenetetrazole (PTZ)-induced bursting activity in snail neurons was investigated. PTZ markedly enhanced the phosphorylation of proteins of 34,000 and 50,000 molecular weight. Similar effects were observed by application of a calcium ionophore, A23187. Calmodulin antagonist, N-(6-aminohexyl)-5-chloronaphthalenesulfonamide hydrochloride (W-7), inhibited the PTZ-induced increased phosphorylation of these two proteins. Dibutyryl cyclic AMP and iosobutylmethylxanthine (IBMX) showed no significant effect on the phosphorylation pattern. Bath application of the calcium ionophore produced bursting activity followed by long-lasting hyperpolarization. Bath application of W-7 completely inhibited the PTZ-induced bursting activity. These results suggest that the phosphorylation of proteins of 34,000 and 50,000 in molecular weight is related to the generation of bursting activity by PTZ.

Characteristics of [D-Trp8]-somatostatin-sensitive B50 phosphorylation

Inhibition of the phosphorylation of the synaptic plasma membrane (SPM) protein B50 by [D-Trp8]-somatostatin in vitro is time-dependent. Increasing the time of incubation of hippocampal synaptic plasma membranes with the peptide from 15 sec to 30 min prior to addition of 7.5 microM [gamma-32P]ATP results in a complete reduction of B50 phosphorylation. Incubation of synaptic plasma membranes for 30 min in the absence of peptide does not alter basal B50 phosphorylation. Neither ACTH nor beta-endorphin produces similar effects--inhibition of B50 phosphorylation by ACTH is maximal at 15 sec and beta-endorphin produces only a small inhibition, even after 30 min. [D-Trp8]-somatostatin is not activating a membrane-bound protease, since maximal inhibition of B50 phosphorylation by the peptide is seen in the presence of leupeptin or bacitracin. Hippocampal synaptic plasma membranes contain protein phosphatase activity. Assays of B50 phosphorylation in synaptic plasma membranes done under conditions that favor either net phosphorylation or dephosphorylation are consistent with inhibition of protein phosphatase activity by [D-Trp8]-somatostatin. This evidence suggests that [D-Trp8]-somatostatin interacts with SPM binding sites in the hippocampus, which may alter the activity of an endogenous protein phosphatase to determine the degree of B50 phosphorylation.

The effect of ACTH4-10 on protein synthesis, actin and tubulin during regeneration

The effects of ACTH4-10, a peptide fragment of corticotropin, on rat dorsal root ganglia (DRG), spinal cord and sciatic nerve were studied following a crush lesion of the sciatic nerve. The in vitro total protein synthesis rate of DRG L4, L5 and L6, measured one and three days after ipsilateral nerve crush, were not altered by various ACTH4-10 treatment regimes. Likewise, neither ACTH4-10 treatment of sham-operated rats nor in vitro exposure of control ganglia to peptide, resulted in changes in synthesis rate. Four days after crush lesion, the amounts of actin and tubulin in the ventral horn L2-L5 region of the spinal cord and of actin in DRG L5 were estimated following 2-dimensional separation. No significant effect of ACTH treatment was found. Degeneration-associated changes in the protein profiles of segments of sciatic nerve were not altered by ACTH4-10 treatment. The data are discussed in relation to the possible site of action of neurotrophic ACTH-like peptides.

alpha-Melanotropin-induced changes in protein phosphorylation in melanophores

To investigate a possible role of protein phosphorylation in the mechanism of action of alpha-MSH, excised tail-fins of Xenopus tadpoles were incubated with or without alpha-MSH. After homogenization, in vitro endogenous protein phosphorylation was assayed using [gamma-32P]ATP. alpha-MSH treatment of intact tail-fins, producing full pigment dispersion, resulted in a 5-fold increase in 32P-incorporation into a 53 kDa protein band. This increase in 53 kDa phosphorylation was completely reversible. The increase was not found in homogenates from the melanophore-free part of the alpha-MSH-treated tail-fins. Phosphorylation of the 53 kDa protein could be detected in homogenates of alpha-MSH-treated primary cultured melanophores. Incubation of tail-fins with ACTH1-24, an alpha-MSH-like peptide producing full pigment dispersion, also induced an increase in 53 kDa phosphorylation. A structurally related peptide (ACTH15-24) and an unrelated peptide (LH-RH), neither of which induced pigment dispersion, were ineffective in stimulating 53 kDa phosphorylation. Injection of white adapted tadpoles with 1 micrograms of alpha-MSH or adaptation of tadpoles to a black background also resulted in a significant increase in 53 kDa phosphorylation. alpha-MSH added to the homogenates did not affect 53 kDa phosphorylation, indicating that alpha-MSH acts through a receptor-mediated mechanism. The increase in 53 kDa phosphorylation measured in vitro (post hoc), most likely reflects an alpha-MSH-induced decrease in 53 kDa phosphorylation in vivo. Our results strongly suggest that a decrease in 53 kDa phosphorylation is involved in the mechanism of action of alpha-MSH on melanophores.

Characterization of alpha-MSH-induced changes in the phosphorylation of a 53 kDa protein in Xenopus melanophores

alpha-Melanotropin has been shown to induce specific changes in the degree of phosphorylation of a 53 kDa melanophore protein, concomitant with pigment dispersion. To further characterize the alpha-MSH-induced changes in 53 kDa phosphorylation in melanophores from the ventral tail-fin of Xenopus tadpoles, we investigated the concentration and time dependency of the effect. A significant increase in 53 kDa phosphorylation was detectable at 5 X 10(-8) M alpha-MSH. The maximal increase in 53 kDa phosphorylation was found after an incubation time of 10-15 min, whereas pigment dispersion was optimal after 60 min. The phosphorylated 53 kDa band showed clear cross-reactivity with monoclonal anti-beta-tubulin, and migrates as a single protein after two-dimensional (2D) separation. On a 2D-separation system the 53 kDa protein (IEP 5.1) migrated in the acidic tail of purified beta-tubulin. Our data strongly indicate that the 53 kDa protein is a beta-tubulin-like protein. We suggest that the degree of 53 kDa phosphorylation may be an important factor in the regulation of microtubule function in melanophores.

Protein kinase C activation leading to protein F1 phosphorylation may regulate synaptic plasticity by presynaptic terminal growth

It has recently been proposed by the author that protein kinase C regulates the expression of synaptic plasticity. In the present review it is suggested that this regulation involves a growth of presynaptic terminals. This proposal was based on the discovery that one of the substrates of protein kinase C, protein F1 (molecular mass = 47 kDa, pI = 4.5) is increased in its phosphorylation 5 min, 1 hr, and 3 days following long-term potentiation (LTP) in the intact hippocampal formation. No other phosphoprotein studied was altered by LTP. The amplitude or persistence of synaptic plasticity was directly related to the extent of protein F1 phosphorylation. As a critical control, it was shown that protein F1 was unaltered following synaptic activation that did not alter synaptic strength. Protein F1 in the hippocampus was also altered in its phosphorylation after an experience involving memory of a spatial environment. Phosphorylation F1 may thus participate in both neurophysiological and behavioral events that evoke plasticity. The identification of the F1 substrate has recently been sought. The physical characteristics of protein F1 (mol wt., isoelectric point) indicate that it is the same as the B-50 protein and the growth protein, GAP-43. Protein F1 is then a brain-specific, synaptically enriched phosphoprotein. Recent evidence indicates that protein F1 is present in high concentration in growth cones of late embryonic rat brain in which postsynaptic specializations are not detected, suggesting a presynaptic locus. With respect to the identity of the F1 kinase, we have shown that protein F1, like B-50, is a substrate for protein kinase C, a Ca2+/phospholipid-dependent kinase. Activation of this enzyme by tumor-promoting phorbol esters can trigger cell growth and neurite extension. Recent evidence indicates a presynaptic localization of the enzyme. On the basis of the colocalization of enzyme and substrate in the presynaptic terminal it is proposed that protein kinase C control of the phosphorylation state of protein F1 may regulate the expression of synaptic plasticity via presynaptic terminal growth.

Protein phosphorylation and neuronal function

Studies in the past several years have provided direct evidence that protein phosphorylation is involved in the regulation of neuronal function. Electrophysiological experiments have demonstrated that three distinct classes of protein kinases, i.e., cyclic AMP-dependent protein kinase, protein kinase C, and CaM kinase II, modulate physiological processes in neurons. Cyclic AMP-dependent protein kinase and kinase C have been shown to modify potassium and calcium channels, and CaM kinase II has been shown to enhance neurotransmitter release. A large number of substrates for these protein kinases have been found in neurons. In some cases (e.g., tyrosine hydroxylase, acetylcholine receptor, sodium channel) these proteins have a known function, whereas most of these proteins (e.g., synapsin I) had no known function when they were first identified as phosphoproteins. In the case of synapsin I, evidence now suggests that it regulates neurotransmitter release. These studies of synapsin I suggest that the characterization of previously unknown neuronal phosphoproteins will lead to the elucidation of previously unknown regulatory processes in neurons.

Modulation of the activity of purified phosphatidylinositol 4-phosphate kinase by phosphorylated and dephosphorylated B-50 protein

To investigate the modulation of phosphatidylinositol 4-phosphate kinase activity by the degree of phosphorylation of the B-50 protein, the enzyme was purified from rat brain cytosol by ammonium sulphate precipitation and DEAE-cellulose column chromatography. Purified rat brain B-50 was phosphorylated with protein kinase C and dephosphorylated with alkaline phosphatase. Incubation of the semi-purified phosphatidylinositol 4-phosphate kinase with 1 microgram of the B-50 preparation enriched in the dephospho-form, resulted in a small reduction of phosphatidylinositol 4-phosphate kinase activity (-16%), whereas incubation with the phospho B-50 preparation inhibited the enzyme activity by 40%. The effect of exogenous B-50 was studied in the presence of 10 micrograms albumin to minimize aspecific protein-protein interactions. The present data on the effect of exogenous B-50 protein on phosphatidylinositol 4-phosphate kinase activity, further support our hypothesis that the phosphorylation state of B-50 may be a regulatory factor in phosphoinositide metabolism in rat brain.

Protein kinase C phosphorylates a 47 Mr protein (F1) directly related to synaptic plasticity

Ca2+-phospholipid-dependent protein kinase C, and activators of protein kinase C (phosphatidylserine, phorbol esters) stimulate the in vitro phosphorylation of a 47 kdalton phosphoprotein (protein F1) previously shown (Routtenberg, Lovinger and Steward, Behav. neural Biol., 43 (1985) 3-11) to be directly related to the plasticity of long-term potentiation. These data indicate that protein F1 serves as a protein kinase C substrate, and suggest the hypothesis that protein kinase C is involved in processes of long-term potentiation.

Resolution of rat brain synaptic phosphoprotein B-50 into multiple forms by two-dimensional electrophoresis: evidence for multisite phosphorylation

Phosphoprotein B-50 was extracted from rat brain membranes by alkaline extraction and purified by ammonium sulphate precipitation and flat-bed isoelectric focusing. The purified protein shows microheterogeneity upon isoelectric focusing in a narrow pH gradient (pH 3.5-5.0). As visualized by two-dimensional gel electrophoresis, B-50 resolved into four clearly separated forms which differ slightly in isoelectric point. The forms are in part mutually convertible by exhaustive phosphorylation (using protein kinase C) and dephosphorylation (using Escherichia coli alkaline phosphatase). Proteolysis with Staphylococcus aureus protease yielded two radioactive peptides. Analysis of their molecular weights and the time course of their formation suggests that B-50 was cleaved at only one specific site. Our data indicate the presence of more than one phosphorylatable site. The possibility that the heterogeneity of B-50 was in part due to a glycoprotein nature of B-50 was studied extensively. However, none of the six different methods used revealed the presence of glyco-moieties in B-50.

Regulation of phosphate incorporation into four brain phosphoproteins that are affected by experience

Various regulators of protein kinase activities were tested for their effects on the in vitro transfer of phosphate from [gamma-32P]ATP to four proteins of rat brain synaptic particulate preparations. One protein, of apparent molecular weight 44,000, accepted 32P in the presence of 8 mM EDTA and no added Mg2+. It was the major phosphoprotein of brain mitochondria. Its phosphorylation was inhibited by pyruvate and stimulated by K+, and it comigrated in electrophoretic gels with authentic alpha-subunit of pyruvate: lipoamide oxidoreductase (decarboxylating) (EC 1.2.4.1) from bovine heart. The major kinase acting on three proteins of apparent molecular weights 24,000, 21,000, and 19,000 was stimulated by Ca2+, by preincubation with phospholipase C, and by 12-tetradecanoyl 4-beta-phorbol 13-acetate. Phosphorylation of these lower-molecular-weight proteins was inhibited by ACTH1-24, by cyclic 3',5'-adenosine monophosphate, and by 50 microM trifluoperazine. The stimulatory effect of Ca2+ was antagonized by calmodulin. The kinase in question appears to be B-50 protein kinase or protein kinase C.

Modulation of phosphorylation of a 30-kD polyribosomal protein (pp30) by ACTH and spermine: comparison with modulation of brain protein synthesis

Gel electrophoretic separation of proteins phosphorylated in a postmitochondrial supernatant fraction of brain in the presence of spermine or adrenocorticotropin (ACTH) indicated modulation in only one region (30 kD) of the gel. The 30-kD (pp30) protein together with enzyme activity catalyzing its phosphorylation and sensitivity of the phosphorylation to spermine and ACTH were retained in a free polyribosomal fraction of this extract. ACTH(11-24) inhibited phosphorylation at all the spermine or Mg2+ concentrations tested. Structure-activity studies revealed that the inhibitory activity within ACTH(1-24) resides in the sequences ACTH(11-24), (5-18, 17Lys, 18Lys)-NH2, (15-24), (7-16)-NH2, and (1-16)-NH2 and can also be found in certain polylysine fragments. Phosphorylation under conditions suitable for measuring protein synthesis revealed only one phosphoprotein (pp30), sensitive to both ACTH(15-24) and spermine. The possibility of a relationship between modulation of pp30 phosphorylation and modulation of brain cell-free protein synthesis is discussed in relation to the effects of ACTH, spermine, and Mg2+.

Cross-reaction of anti-rat B-50: characterization and isolation of a "B-50 phosphoprotein" from bovine brain

Antibodies to the phosphoprotein B-50 of rat brain were used to trace cross-reacting brain proteins of vertebrates. With the SDS-gel-immunoperoxidase method, a cross-reacting protein (CP) of apparent Mr 53,000 was demonstrated in the homogenate and the synaptic plasma membrane fraction of bovine brain. Sequence 1-24 of adrenocorticotropin (ACTH1-24) (10(-5) M and 10(-4) M) inhibited endogenous phosphorylation of CP in synaptic plasma membranes. The protein was partially characterized and purified to homogeneity from bovine brain by procedures previously described for rat B-50. CP was enriched in ammonium sulfate precipitated protein (ASP) fractions and phosphorylated by an endogenous protein kinase. Two-dimensional gel analysis of bovine and rat ASP showed that the cross-reacting protein had an isoelectric point less acidic than B-50. Limited proteolysis by Staphylococcus aureus protease yielded a "peptide map" analogous to B-50. Two major fragments of Mr 30,000 and 17,000 were produced. In addition, CP exhibited other similarities to rat B-50: phosphorylation by rat brain protein kinase C, microheterogeneity observed after isoelectric focusing, and possibly degradation by endogenous proteolysis. Cross-reaction of proteins in brain homogenates of other mammalian species and of chicken was demonstrated: the Mr of the proteins ranged from 47,000 to 53,000. We conclude that (1) the cross-reacting bovine protein is a "B-50 protein," and (2) the Mr of the "B-50 protein" varies from species to species.

Cyclic nucleotide- and calcium-independent phosphorylation of proteins in rat brain polyribosome: effects of ACTH, spermine, and hemin

The incorporation of [gamma-32P]ATP into proteins of rat brain polyribosomes was studied in vitro. The effects of cyclic nucleotides, calcium, hemin, ACTH, GTP, and spermine were examined. The incorporation of phosphate into proteins increased with time and phosphatase activity was very low; thus, the extent of phosphorylation was predominantly a reflection of protein kinase activity. Phosphorylation of proteins was not sensitive to Ca2+ in the presence or absence of either calmodulin or phosphatidylserine. Phosphorylation was also unaffected by cyclic nucleotides in the absence of exogenous enzymes. However, addition of a cAMP-dependent protein kinase together with cAMP resulted in a stimulation of the incorporation of phosphate into 4 phosphoproteins (pp70, pp58, pp43, and pp32); phosphorylation of pp32 was completely dependent on the addition of the kinase. ACTH (1-24), (11-24), and spermine inhibited the endogenous phosphorylation of one protein band (pp30). The phosphorylation of this 30 kD band was also selectively increased by hemin (5 microM). Higher concentrations of hemin exerted an inhibitory effect on the majority of the phosphoproteins. Protein phosphatase activity was not influenced by ACTH or spermine. The specific inhibition of pp30 phosphorylation by ACTH or spermine is most probably explained by an interaction with a cyclic nucleotide- and Ca2+ -independent protein kinase.

Adrenocorticotropic hormone (ACTH)-lipid interactions. Implications for involvement of amphipathic helix formation

ACTH-lipid interactions were investigated by: (1) lipid-monolayer studies using several zwitterionic and anionic phospholipids and gangliosides, (2) permeability experiments by following the swelling rate of liposomes in isotonic glycerol solutions by light scattering, using liposomes of synthetic lipids and liposomes made of lipids extracted from light synaptic plasma membranes, and (3) by steady-state fluorescence anisotropy measurements on liposomes derived from light synaptic plasma membranes employing 1,6-diphenyl-1,3,5-hexatriene as fluorescent probe. (1) The monolayer experiments demonstrated an interaction with gangliosides GT1, GM1, dioleoylphosphatidic acid and phosphatidylserine, but little or no interaction with phosphatidylcholine or sphingomyelin. The interaction with monolayers of GT1 or phosphatidic acid decreased for ACTH1-13-NH2 and ACTH1-10. (2) The liposome experiments showed that 2 X 10(-5) M ACTH1-24 increased the glycerol permeability by 20% and decreased the activation energy only when liposomes derived from light synaptic plasma membranes were used. Treatment of the liposomes with neuraminidase abolished the ACTH-induced permeability increase. (3) Steady-state fluorescence depolarization measurements revealed that ACTH1-24, ACTH1-16-NH2 and ACTH1-10 did not change the fluidity of liposomes derived from light synaptic plasma membranes as sensed by diphenylhexatriene. It is concluded that ACTH1-24 can bind to negatively charged lipids and can form an amphipathic helix aligned parallel to the membrane surface involving the N-terminal residues 1 to 12, possibly to 16. Polysialogangliosides will favorably meet the condition of a high local surface charge density under physiological circumstances. It is suggested that ACTH-ganglioside interactions will participate in ACTH-receptor interactions.

Evidence that the neurotrophic actions of alpha-MSH may derive from its ability to mimick the actions of a peptide formed in degenerating nerve stumps

The ability of alpha-MSH to facilitate the recovery of sensorimotor nerve function following crush lesion is restricted to a critical period following such a lesion. This period coincided with the initiation of sprouting and the disappearance of the 150 kD neurofilament protein from the degenerating distal stump of the nerve. Degenerating nerve contains a factor that is active in a bioassay system for MSH. This factor could not be detected in control nerves. The hypothesis is forwarded that a neurotrophic factor known to be present in degenerating nerve stumps is an alpha-MSH-like peptide formed by the breakdown of the 150 kD neurofilament protein.

Dopamine-induced changes in protein phosphorylation and polyphosphoinositide metabolism in rat hippocampus

Effects of dopamine (DA) on endogenous phosphorylation of hippocampal proteins and polyphosphoinositides were studied in subcellular fractions from a crude mitocondrial/synaptosomal preparation. DA induced a concentration-dependent decrease in the in vitro phosphorylation of the protein B-50 (-22.1% at 10(-5) M DA), whereas no changes were found in phosphoproteins in other subcellular fractions. Treatment of hippocampal slices with 5 X 10(-4) M DA resulted in a 45.8% increase in post hoc phosphorylation of B-50 in SPM and it affected post hoc phosphorylation of several proteins in a cytosolic fraction. In vitro phosphorylation of SPM with DA (5 X 10(-4) M) increased endogenous TPI phosphorylation (+51.6%), whereas treatment of slices with DA (5 X 10(-4) M) resulted in a 39.4% decrease in post hoc TPI phosphorylation. This decrease could be blocked by haloperidol. Significant changes induced by DA (5 X 10(-4) M) were also found in 32P-incorporation into PA (in vitro: -32.4% and post hoc: +39.3%), but were not found in DPI labeling. The data provide evidence for DA-induced changes in phosphorylation of proteins and polyphosphoinositides in rat hippocampal SPM.

Modulation of protein synthesis in a cell-free system derived from rat brain by corticotropin (ACTH), magnesium, and spermine

Modulation of protein synthesis by fragments of the ACTH molecule has been studied in a cell-free system obtained from subcortical brain tissue of rats. Both the activity of the protein-synthesizing system and its sensitivity to ACTH-like peptides appeared to be highly dependent on the Mg2+ and spermine concentrations. At optimal Mg2+ concentrations (4 mM) the peptide sequences ACTH(1-24) and (11-24) were both inhibitory, the latter being the more active. The inhibitory effect was reduced or abolished at higher (suboptimal) concMg2+ concentrations. Spermine, like ACTH, inhibited protein synthesis at the optimal Mg2+ concentration. However, at lower Mg2+ concentrations spermine had a stimulatory effect and maximal activity was obtained at 0.75-1.0 mM Mg2+. In the presence of spermine (60 microM) and Mg2+ (0.75 mM), a half-maximal inhibition of protein synthesis was obtained with a peptide concentration of 5 microM. A structure-activity study showed that the peptides ACTH(7-16)-NH2, (11-24), (5-18, 17Lys 18Lys)-NH2 and (15-24) were active in inhibiting protein synthesis, whereas the fragments ACTH(1-16)-NH2 and (17-24) were inactive. The results are discussed in terms of an interaction between ACTH, Mg2+, and spermine, and intracellular processes involved in protein synthesis.

Effects of corticotropin-(1-24)-tetracosapeptide on polyphosphoinositide metabolism and protein phosphorylation in rabbit iris subcellular fractions

Effects of the neuropeptide corticotropin-(1-24)-tetracosapeptide (ACTH) on the endogenous and exogenous phosphorylation of lipids and endogenous phosphorylation of proteins were investigated in microsomes and a 110,000 X g supernatant fraction [30-50% (NH4)2SO4 precipitate; ASP 30-50] obtained from rabbit iris smooth muscle. Subcellular distribution studies revealed that both of these fractions are enriched in diphosphoinositide (DPI) kinase. The 32P labeling of lipids and proteins was measured by incubation of the subcellular fractions with [gamma-32P]ATP. The labeled lipids, which consisted of triphosphoinositide (TPI), DPI, and phosphatidic acid (PA) were isolated by TLC. The microsomal and ASP 30-50 fractions were resolved into six and nine labeled phosphoprotein bands, respectively, by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The basal labeling of both lipids and proteins was rapid (30-60 s), and it was dependent on the presence of Mg2+ in the incubation medium; in general it was inhibited by high concentrations (greater than 0.2 mM) of Ca2+. ACTH stimulated the labeling of TPI and inhibited that of PA in a dose-dependent manner, with maximal effect observed at 50-100 microM of the peptide. ACTH appears to increase TPI labeling by stimulating the DPI kinase. Under the same experimental conditions ACTH (100 microM) inhibited significantly the endogenous phosphorylation of six microsomal phosphoproteins (100K, 84K, 65K, 53K, 48K, and 17K). In the ASP 30-50 fraction, ACTH inhibited the phosphorylation of three phosphoproteins (53K, 48K, and 17K) and stimulated the labeling of six phosphoprotein bands (117K, 100K, 84K, 65K, 42K, and 35K).(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorylation of B-50 protein by calcium-activated, phospholipid-dependent protein kinase and B-50 protein kinase

B-50 is a brain-specific phosphoprotein, the phosphorylation state of which may play a role in the regulation of (poly)phosphoinositide metabolism. Several kinases were tested for their ability to phosphorylate purified B-50 protein. Only calcium-activated, phospholipid-dependent protein kinase (kinase C) and B-50 protein kinase were able to use B-50 protein as a substrate. Furthermore, kinase C specifically phosphorylates B-50 when added to synaptic plasma membranes. We further characterized the sensitivity of kinase C and B-50 kinase to ACTH (and various fragments), phospholipids, chlorpromazine, and proteolytic activation. Since the sensitivities of both kinases were similar, we conclude that B-50 protein kinase is a calcium-dependent, phospholipid-stimulated protein kinase of the same type as kinase C.

The time course of excessive grooming after neuropeptide administration

In this paper we review the temporal pattern of excessive grooming in the hour or so following the central injection of ACTH1-24 in the rat. Changes in the grooming pattern after specific neuropharmacological manipulations of dopaminergic and opiate-related systems are presented which indicate a differential sensitivity of the grooming responses at different times after injection. The grooming affected by dopaminergic antagonists and opiate agonists and antagonists occurs in the last 30 min of the observation period while that found earlier is unaffected. It is also the grooming in this last 30 min of the observation period term tolerance to central administration of ACTH1-24. In contrast lesions of the central nervous system that affect excessive grooming, i.e., the substantia nigra and the hippocampus, reduce grooming throughout the observation period. The present analysis has provided evidence for dopamine/opiate insensitive and sensitive systems in excessive grooming, and thus temporal aspects are of extreme importance to the understanding of central neuropeptide influences on behavior.

Affinity-purified anti-B-50 protein antibody: interference with the function of the phosphoprotein B-50 in synaptic plasma membranes

Affinity-purified anti-B-50 protein antibodies were used to study the previously proposed relationship of the phosphorylation state of B-50 protein and polyphosphoinositide metabolism in synaptic plasma membranes. Antibodies were raised against a membrane extract enriched in the B-50 protein and its adrenocorticotropin-sensitive protein kinase, obtained from rat brain. Anti-B-50 protein immunoglobulins were purified by affinity chromatography on a solid immunosorbent prepared from B-50 protein isolated by an improved procedure. The purified antibodies reacted only with the B-50 and B-60 protein, a proteolysis derivative (of B-50), as assessed by the sodium dodecyl sulfate-gel immunoperoxidase method. These antibodies inhibited specifically the endogenous phosphorylation of B-50 protein in synaptic plasma membranes, without affecting notably the phosphorylation of other membrane proteins. This inhibition was accompanied by changes of the formation of phosphatidylinositol 4,5-diphosphate and phosphatidic acid in synaptic plasma membranes, whereas formation of phosphatidylinositol 4-phosphate was not altered. Inhibition by ACTH 1-24 of the endogenous phosphorylation of B-50 protein in membranes was associated only with an enhancement of the phosphorylation of phosphatidyl-inositol 4-phosphate to phosphatidylinositol 4,5-diphosphate. These data support our hypothesis on the functional interaction of B-50 protein and phosphatidylinositol 4-phosphate kinase in rat brain membranes. The evidence shows that purified anti-B-50 protein antibodies can be used to probe specifically the function of B-50 protein in membranes.

Influence of adrenocorticotropic hormone on the growth of isolated neurons in culture

The present study reports the influence of adrenocorticotropic hormone (ACTH) on the development of cultured neurons from chick embryo cerebral hemispheres. Cultures were initiated in serum-supplemented medium and then transferred to serum-free hormonally-defined medium containing various concentrations of ACTH1--24. The effects of ACTH on the light microscopic features, metabolic activity and permeation properties were examined. The results demonstrate that ACTH exerts a trophic action on the neurons.

Somatostatin and analogs inhibit endogenous synaptic plasma membrane protein phosphorylation in vitro

The addition of somatostatin to hippocampal synaptic plasma membrane (SPM) preparations in vitro decreased subsequent phosphorylation of specific protein bands. 10(-4)M somatostatin inhibited the phosphorylation of protein bands with apparent molecular weights between 10 000 and 20 000 daltons and, to a lesser extent, 48 000 daltons (B-50) and 52 000. Increasingly greater degrees of inhibition were seen in response to somatostatin-28 and [D-Trp8]somatostatin. Inhibition of B-50 protein phosphorylation in the presence of [D-Trp8]somatostatin was most prominent in SPM preparations from the hippocampus and amygdala, with lesser degrees of inhibition seen in the cortex and hypothalamus. Addition of [D-Trp8]somatostatin to an ammonium sulfate-precipitated fraction (ASP 55-80) from cortex only slightly inhibited endogenous B-50 phosphorylation. The injection of [D-Trp8] somatostatin intracerebroventricularly into rats did not induce excessive grooming behavior but resulted in barrel rotation. These results suggest that somatostatin and congeners affect SPM protein phosphorylation in a manner different from that of ACTH, presumably involving membrane sites that bind somatostatin.

The effect of ACTH on rat brain synaptic plasma membrane lipid fluidity

The effect of ACTH on the lipid fluidity was examined in synaptic plasma membranes from rat forebrain. ACTH1-24 increased the fluidity of the synaptic plasma membranes in a dose-dependent way, the lowest effective dose being 10(-5) M. The shorter N-terminal fragment ACTH1-10 was not effective. The significance of this finding is discussed in relation to the known effects of ACTH on synaptic membrane phosphorylation.

Characterization of infant rat cerebral cortical membrane proteins phosphorylated in vivo: identification of the ACTH-sensitive phosphoprotein B-50

This study on the phosphorylation in vivo of membrane proteins in cerebral cortices of infant rats reports the identification of the adrenocorticotropin (ACTH)-sensitive phosphoprotein B-50 as one of the substrate proteins that are rapidly phosphorylated in vivo following intracisternal administration of 2 mCi [32P]orthophosphate. Rats were sacrificed 30 min after isotope injection. A fraction enriched in membranes, designated neural membranes (NM), was isolated from the cerebral cortices according to the procedure used for preparation of synaptic plasma membranes (SPM) from adult brain. This NM fraction was characterized by electron microscopy. The proteins of NM were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. Numerous protein bands of NM in infant rat brain were phosphorylated in vivo. Attention was focussed on the 32P-labeled protein bands in the molecular weight range of 47K-67K. In this region one phosphoprotein band (MW 48K) was more highly labeled than the other bands. The electrophoretic behavior of three of these labeled bands, designated a, c, and e (MW 48K, 55K, and 62K, respectively) was compared with that of protein bands that were phosphorylated in vitro in cerebral membranes isolated from noninjected infant rats. The effects of ACTH1-24 and cyclic AMP in the in vitro system were also studied to probe for the presence of specific membrane proteins known to be sensitive to these modulators. On incubation of NM with [gamma-32P)ATP in the presence and absence of ACTH1-24 in vitro, phosphorylation of a 48K protein band was inhibited in a dose-dependent fashion by the neuropeptide. Two-dimensional electrophoretic separation of NM proteins labeled in vivo indicated that the 48K band had an isoelectric point of 4.5, identical to that of the ACTH-sensitive B-50 protein previously identified. Cyclic AMP stimulated phosphorylation in vitro of two protein bands (MW 55K and 59K) in NM preparations. This result indicates that the in vivo labeled band c may correspond to the cyclic AMP-sensitive 55K protein, whereas phosphoprotein band e, labeled in vivo, appears to be different from the cyclic AMP-sensitive 59K protein band. These observations indicate that neural membranes isolated from infant rat cerebral cortices contain a variety of proteins that can be phosphorylated in vivo. Several of these, for example, the 48K protein band, have the properties of synaptic plasma membrane proteins of adult rat brain that have been characterized by their sensitivity to neuromodulators in endogenous phosphorylating systems in vitro.

Membrane phosphoproteins of rat hippocampus: sensitivity to tetanic stimulation and enkephalin

Hippocampal slices are electrically stimulated in the perforant path with a pulse-train, which can lead to long-term potentiation (LTP). Of the thus stimulated slices, subcellular fractions are prepared and used in an endogenous protein phosphorylation assay. A phosphoprotein band which was reported earlier to be sensitive to electric stimulation as well as to methionine-enkephalin is now further analyzed: it consists of two phosphoproteins only slightly differing in molecular weight: 50,000 Mr (50 K) and 52,000 Mr (52 K), but having distinct biochemical properties and subcellular localization. Their IEP is dissimilar (3.5-4.3 and 5.3, respectively), they display different sensitivity towards calcium when tested in the phosphorylation assay, but are both cAMP-independently phosphorylated. Only one of them responds to tetanic stimulation with an increased phosphorylation post hoc. This protein, the 52 K component, is localized in synaptic membranes. Moreover, this protein also responds to incubation of slices with methionine-enkephalin. The phosphorylation of the 50 K component is not influenced by electric stimulation, nor by incubations with neuropeptides; its phosphorylation takes place in material sedimenting with the mitochondrial cell fractions and is strongly calcium- and calmodulin-dependent.

The phosphorylation of proteins in hippocampal slices: effects of noradrenaline and of pretreatment with kainic acid

Hippocampal slices were incubated in the presence of [32P]P1, and protein phosphorylation was examined by means of sodium dodecyl sulfate-gel electrophoresis. Incubation for at least 30 min with 300 muCi of [32P)P1/brain slice gave rise to the phosphorylation of 8-10 protein bands. Most of these bands showed enhanced phosphorylation in response to noradrenaline. The basal phosphorylation of kainic acid-pretreated hippocampal slices was enhanced two- to threefold compared with controls. There was also an additional increase in kainic acid-pretreatment slices in the response to noradrenaline. 8-Br-Cyclic AMP and phosphodiesterase inhibitors, such as papaverine or isobutylmethylxanthine, had no effect on the phosphorylation patterns.

Evidence that the synaptic phosphoprotein B-50 is localized exclusively in nerve tissue

The localization of the phosphoprotein B-50 (molecular weight 48,000 isoelectric point 4.5) in the rat has been studied. Inspection of endogenous phosphorylation patterns of the particulate as well as the cytosolic subcellular fractions from a variety of peripheral organs failed to demonstrate phosphorylation of a molecular weight 48,000 protein. Only in the particulate fractions from brain tissue was there endogenous phosphorylation of the B-50 protein. Two-dimensional analysis (isoelectric focusing and sodium dodecyl sulfate polyacrylamide gel electrophoresis) and in immunochemical detection method employing an anti B-50 antiserum revealed the presence of B-50 in particulate material from brain, but not in that of other tissues. Therefore the data were interpreted as pointing to the localization of B-50 in nervous tissue. In addition, the regional distribution of endogenous B-50 phosphorylation was studied using synaptosomal plasma membranes (SPM) obtained from individual rat brain regions. The highest value was found in SPM of septal origin, the lowest in SPM from the medulla spinalis. The relationship of the high value for B-50 phosphorylation in the septum to the sensitivity of that brain area to ACTH1-24 is discussed.

beta-Endorphin proteolysis by guinea-pig ileum myenteric plexus membranes: increased gamma-endorphin turnover after chronic exposure to morphine

The influence of chronic morphine exposure in vitro on the biotransformation of beta-endorphin (beta E) was investigated using the myenteric plexus-longitudinal muscle of guinea-pig ileum. A membrane preparation was incubated with beta E and the degradation of beta E as well as the accumulation of several beta E fragments in the incubation medium were followed with time. The levels of peptides were determined by specific radioimmunoassays after separation by high-pressure liquid chromatography. It was found that exposure to morphine did not affect the disappearance of beta E, but altered the time course of accumulation of beta E fragments. In fact, the accumulation of gamma-endorphin, alpha-endorphin and des-tyrosine1-alpha-endorphin was enhanced, while that of des-tyrosine1-gamma-endorphin was not change. Additionally, the disappearance of gamma-endorphin appeared to be stimulated by morphine exposure. These data provide evidence that the fragmentation of beta E is changed by chronic morphine exposure in such a way that the turnover of gamma-endorphin is increased.

ACTH1--24 releases a protein from synaptosomal plasma membranes

Brain membranes contain several protein kinases, all of which appear to play a role in the regulation of neuronal functioning. These membranes also contain numerous (phospho) proteins. It has been proposed that the degree of phosphorylation of some of these proteins may affect neuronal membrane properties. In a series of previous reports we showed that ACTH1--24 inhibits the endogenous phosphorylation of several synaptosomal plasma membrane (SPM) proteins including the B-50 protein. Although we have speculated that the degree of phosphorylation of B-50 may be important in regulating the turnover of membrane (poly)-phosphoinositides, the exact nature of the interaction between ACTH1--24 and B-50/B-50 protein kinase is unknown. The purpose of the present study was to determine whether treatment of SPM with ACTH1--24 will lead to a specific release of proteins from SPM. We found that ACTH1--24 specifically releases a 41,000 Mr protein from rat brain SPM. Although we are not certain about the biological significance of the release of this polypeptide, it is of sufficient interest for further research in view of the lack of success of finding binding of labeled ACTh to brain membranes.

Specific proteolysis of a brain membrane phosphoprotein (B-50): effects of calcium and calmodulin

The membrane bound phosphoprotein B-50 (MW 48K) was isolated from rat brain tissue. The fraction containing the highest endogenous B-50 phosphorylating activity (ASP 57-82%) contains protease activity. In the absence of calcium a time-dependent decrease of the protein B-50 is observed. Under these conditions another phosphoprotein B-60 (MW 46K) appears in the incubation medium. Addition of calcium and/or calmodulin enhances the protease activity whereas the substrate specificity is lost. Results of both isoelectric focussing and peptide mapping indicate the B-50 and B-60 are related proteins. These data support our hypothesis that the recently isolated behaviorally active peptide PIP (MW approx. 1600 D) is the smaller cleavage product of the proteolytic degradation of B-50 to B-60.