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1.
Clin Radiol ; 68(8): 837-44, 2013 Aug.
Article in English | MEDLINE | ID: mdl-23623578

ABSTRACT

This article will review the uncommon locations and morphological features of meningiomas, which are important to recognize in order to avoid misdiagnosis. Uncommon locations will be demonstrated at the cerebellopontine angle, pineal, optic, intraventricular, and intradiploic regions. Unusual imaging features including cysts, metaplastic changes, and peritumoural oedema will also be discussed.


Subject(s)
Diagnostic Imaging , Meningeal Neoplasms/diagnosis , Meningioma/diagnosis , Contrast Media , Diagnosis, Differential , Humans
2.
Clin Radiol ; 68(2): 203-13, 2013 Feb.
Article in English | MEDLINE | ID: mdl-22889460

ABSTRACT

The trigeminal nerve is the largest cranial nerve and has both sensory and motor components. Due to its extensive distribution in the head and neck, the nerve or its branches may be involved by a myriad of disease entities. Additionally, the nerve may act as a route of spread in various inflammatory and neoplastic diseases, underlining the need for a thorough understanding of its anatomy. A segmental division of the trigeminal system is preferred when interpreting imaging studies as both the type of lesion and symptoms may vary based on the site of involvement. These segments include the brainstem, cisternal, Meckel's cave, cavernous sinus, and peripheral divisions. In general, dedicated magnetic resonance imaging (MRI) is preferred to evaluate nerve dysfunction. In select cases, contrast medium administration, heavily T2-weighted sequences, or MR angiography may prove to be diagnostic. This review aims to review the anatomy of the trigeminal nerve briefly, followed by illustrations of various lesions that may present with trigeminal nerve dysfunction.


Subject(s)
Cranial Nerve Neoplasms/diagnosis , Magnetic Resonance Imaging/methods , Trigeminal Nerve Diseases/diagnosis , Trigeminal Nerve/anatomy & histology , Trigeminal Nerve/pathology , Contrast Media , Diagnosis, Differential , Female , Humans , Image Enhancement/methods , Male
3.
Clin Radiol ; 68(6): 545-54, 2013 Jun.
Article in English | MEDLINE | ID: mdl-23142023

ABSTRACT

The term encephalopathy refers to a clinical scenario of diffuse brain dysfunction, commonly due to a systemic, metabolic, or toxic derangement. Often the clinical evaluation is unsatisfactory in this scenario and imaging plays an important role in the diagnosis, assessment of treatment response, and prognostication of the disorder. Hence, it is important for radiologists to be familiar with the imaging features of some relatively frequently acquired metabolic encephalopathies encountered in the hospital setting. This study reviews the computed tomography (CT) and magnetic resonance imaging (MRI) features of a number of metabolic encephalopathies that occur as part of systemic diseases in adults. The following conditions are covered in this review: hypoglycaemic encephalopathy, hypoxic ischaemic encephalopathy, non-ketotic hyperglycaemia, hepatic encephalopathy, uraemic encephalopathy, hyperammonaemic encephalopathy, and posterior reversible encephalopathy syndrome. MRI is the imaging method of choice in evaluating these conditions. Due to their high metabolic activity, bilateral basal ganglia changes are evident in the majority of cases. Concurrent imaging abnormalities in other parts of the central nervous system often provide useful diagnostic information about the likely underlying cause of the encephalopathy. Besides this, abnormal signal intensity and diffusion restriction patterns on MRI and MR spectroscopy features may provide important clues as to the diagnosis and guide further management. Frequently, the diagnosis is not straightforward and typical imaging features require correlation with clinical and laboratory data for accurate assessment.


Subject(s)
Brain Diseases, Metabolic/diagnosis , Magnetic Resonance Imaging , Tomography, X-Ray Computed , Adult , Brain/diagnostic imaging , Brain/pathology , Brain Diseases, Metabolic/diagnostic imaging , Brain Diseases, Metabolic/pathology , Hepatic Encephalopathy/diagnosis , Hepatic Encephalopathy/diagnostic imaging , Hepatic Encephalopathy/pathology , Humans , Hyperglycemia/diagnosis , Hyperglycemia/diagnostic imaging , Hyperglycemia/pathology , Hypoglycemia/diagnosis , Hypoglycemia/diagnostic imaging , Hypoglycemia/pathology , Hypoxia-Ischemia, Brain/diagnosis , Hypoxia-Ischemia, Brain/diagnostic imaging , Hypoxia-Ischemia, Brain/pathology , Posterior Leukoencephalopathy Syndrome/diagnosis , Posterior Leukoencephalopathy Syndrome/diagnostic imaging , Posterior Leukoencephalopathy Syndrome/pathology , Wernicke Encephalopathy/diagnosis , Wernicke Encephalopathy/diagnostic imaging , Wernicke Encephalopathy/pathology
4.
Clin Radiol ; 67(4): 380-8, 2012 Apr.
Article in English | MEDLINE | ID: mdl-22137800

ABSTRACT

Cavernous haemangiomas (CH) are relatively uncommon non-shunting vascular malformations of the central nervous system and can present with seizures or with neurological deficits due to haemorrhage. Radiologists can often suggest the diagnosis of CH based on characteristic magnetic resonance imaging (MRI) features, thus avoiding further invasive procedures such as digital subtraction angiography or surgical biopsy. Although typical MRI appearance combined with the presence of multiple focal low signal lesions on T2*-weighted images or the presence of one or more developmental venous anomaly within the brain can improve the diagnostic confidence, serial imaging studies are often required if a solitary CH presents at a time when the imaging appearances had not yet matured to the typical "popcorn" appearance.


Subject(s)
Brain , Hemangioma, Cavernous, Central Nervous System/diagnosis , Magnetic Resonance Imaging , Spinal Cord , Cerebral Hemorrhage/diagnosis , Cerebral Hemorrhage/etiology , Hemangioma, Cavernous, Central Nervous System/complications , Hemangioma, Cavernous, Central Nervous System/congenital , Hemangioma, Cavernous, Central Nervous System/surgery , Humans
6.
Neuroscience ; 163(3): 811-24, 2009 Oct 20.
Article in English | MEDLINE | ID: mdl-19580852

ABSTRACT

Modification of synapses in the accessory olfactory bulb (AOB) is believed to underlie pheromonal memory that enables mate recognition in mice. The memory, which is acquired with single-trial learning, forms only with coincident noradrenergic and glutamatergic inputs to the AOB. The mechanisms by which glutamate and norepinephrine (NE) alter the AOB synapses are not well understood. Here we present results that not only reconcile the earlier, seemingly contradictory, observations on the role of glutamate and NE in changing the AOB synapses, but also reveal novel mechanisms of plasticity. Our studies suggest that initially, glutamate acting at Group II metabotropic receptors and NE acting at alpha(2)-adrenergic receptors inhibit N-type and R-type Ca(2+) channels in mitral cells via a G-protein. The N-type and R-type Ca(2+) channel inhibition is reversed by activation of alpha(1)-adrenergic receptors and protein kinase Calpha (PKCalpha). Based on these results, we propose a hypothetical model for a new kind of synaptic plasticity in the AOB that accounts for the previous behavioral data on pheromonal memory. According to this model, initial inhibition of the Ca(2+) channels suppresses the GABAergic inhibitory feedback to mitral cells, causing disinhibition and Ca(2+) influx. NE also activates phospholipase C (PLC) through alpha(1)-adrenergic receptors generating inositol 1,4,5-trisphosphate and diacylglycerol (DAG). Calcium and DAG together activate PKCalpha which switches the disinhibition to increased inhibition of mitral cells. Thus, PKCalpha is likely to be a coincidence detector integrating glutamate and NE input in the AOB and bridging the short-term signaling to long-term structural changes resulting in enhanced inhibition of mitral cells that is thought to underlie memory formation.


Subject(s)
Neuronal Plasticity/physiology , Olfactory Bulb/physiology , Protein Kinase C-alpha/physiology , Animals , Calcium/physiology , Calcium Channels, N-Type/physiology , Calcium Channels, R-Type/physiology , Female , GTP-Binding Proteins/physiology , Glutamic Acid/pharmacology , Glutamic Acid/physiology , In Vitro Techniques , Inhibitory Postsynaptic Potentials/drug effects , Isoenzymes/physiology , Mice , Norepinephrine/pharmacology , Norepinephrine/physiology , Patch-Clamp Techniques , Receptors, Adrenergic, alpha-1/physiology , Receptors, Adrenergic, alpha-2/physiology , Receptors, Metabotropic Glutamate/agonists , Receptors, Metabotropic Glutamate/physiology , Sex Attractants/physiology , Synapses/physiology , Type C Phospholipases/physiology
7.
Neuroscience ; 157(2): 340-8, 2008 Nov 19.
Article in English | MEDLINE | ID: mdl-18848604

ABSTRACT

Glutamate and norepinephrine (NE) are believed to mediate the long-lasting synaptic plasticity in the accessory olfactory bulb (AOB) that underlies pheromone recognition memory. The mechanisms by which these neurotransmitters bring about the synaptic changes are not clearly understood. In order to study signals that mediate synaptic plasticity in the AOB, we used AOB neurons in primary culture as a model system. Because induction of pheromone memory requires coincident glutamatergic and noradrenergic input to the AOB, and requires new protein synthesis, we reasoned that glutamate and NE must induce gene expression in the AOB. We used a combination of agonists that stimulate alpha1 and alpha2 adrenergic receptors in combination with N-methyl-d-aspartic acid and tested expression of the immediate-early gene (IEG) c-Fos. We found that the glutamatergic and noradrenergic stimulation caused significant induction of c-Fos mRNA and protein. Induction of c-Fos was significantly reduced in the presence of inhibitors of protein kinase C, mitogen-activated protein kinase (MAPK) and phospholipase C. These results suggest that glutamate and NE induce gene expression in the AOB through a signaling pathway mediated by protein kinase C and MAPK.


Subject(s)
Gene Expression/physiology , Olfactory Bulb/cytology , Sensory Receptor Cells/physiology , Signal Transduction/physiology , Adrenergic alpha-Agonists/pharmacology , Age Factors , Animals , Animals, Newborn , Cell Survival , Cells, Cultured , Enzyme Inhibitors/pharmacology , Female , Gene Expression/drug effects , Gene Expression Regulation, Developmental/drug effects , Gene Expression Regulation, Developmental/physiology , Imidazoles/pharmacology , Mice , Mice, Inbred BALB C , N-Methylaspartate/pharmacology , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Proto-Oncogene Proteins c-fos/genetics , Proto-Oncogene Proteins c-fos/metabolism , Signal Transduction/genetics , Type C Phospholipases/pharmacology
9.
Brain Res Mol Brain Res ; 76(2): 424-8, 2000 Mar 29.
Article in English | MEDLINE | ID: mdl-10762722

ABSTRACT

The ubiquitin-proteasome pathway, which is up-regulated in response to sensitizing treatments with serotonin (5-HT), plays a critical role in inducing long-term facilitation (LTF) of sensory-to-motor synapses in Aplysia. We characterized the structure of the polyubiquitin gene of Aplysia and studied its expression. At least six ubiquitin coding units exist in tandem, one of which encodes a protein with an amino acid sequence identical to human ubiquitin. Although the synthesis of polyubiquitin is induced by strong stimuli in many organisms, we found that the expression of ubiquitin in Aplysia is not affected by protocols that produce LTF.


Subject(s)
Aplysia/genetics , Biopolymers/genetics , Ubiquitins/genetics , Amino Acid Sequence , Animals , Base Sequence , Ganglia, Invertebrate/metabolism , Gene Expression , Humans , Molecular Sequence Data , Polyubiquitin , Restriction Mapping , Sequence Alignment , Sequence Homology, Nucleic Acid , Ubiquitins/chemistry
10.
J Neurochem ; 73(6): 2415-23, 1999 Dec.
Article in English | MEDLINE | ID: mdl-10582601

ABSTRACT

Long-term facilitation (LTF) of the sensory-to-motor synapses that mediate defensive reflexes in Aplysia requires induction of the transcription factor Aplysia CCAAT/enhancer binding protein (ApC/EBP) as an early response gene. We examined the time course of ApC/ EBP DNA binding during the induction of LTF: Binding activity was detected within 1 h of the sensitization treatment with serotonin, reached a maximum at 2 h, and decreased after 6 h. How are DNA binding and the turnover of ApC/EBP regulated? We find that phosphorylation of ApC/EBP by mitogen-activated protein (MAP) kinase is essential for binding. MAP kinase appears to be activated through protein kinase C. We also showed that ApC/EBP is degraded through the ubiquitin-proteasome pathway but that phosphorylation by MAP kinase renders it resistant to proteolysis. Thus, phosphorylation by MAP kinase is required for ApC/EBP to act as a transcription activator as well as to assure its stability early in the consolidation phase, when genes essential for the development of LTF begin to be expressed.


Subject(s)
Aplysia/metabolism , DNA-Binding Proteins/metabolism , Escape Reaction/physiology , MAP Kinase Signaling System , Memory/physiology , Nerve Tissue Proteins/metabolism , Nuclear Proteins/metabolism , Transcription, Genetic , Amino Acid Sequence , Animals , CCAAT-Enhancer-Binding Proteins , Cysteine Endopeptidases/metabolism , DNA/metabolism , Enzyme Activation , Escape Reaction/drug effects , Ganglia, Invertebrate/metabolism , Genes, Immediate-Early , Molecular Sequence Data , Multienzyme Complexes/metabolism , Peptide Fragments/immunology , Phosphorylation , Proteasome Endopeptidase Complex , Protein Kinase C/physiology , Protein Processing, Post-Translational , Serotonin/pharmacology , Ubiquitins/metabolism
11.
Neuron ; 22(1): 147-56, 1999 Jan.
Article in English | MEDLINE | ID: mdl-10027297

ABSTRACT

The formation of a persistently active cAMP-dependent protein kinase (PKA) is critical for establishing long-term synaptic facilitation (LTF) in Aplysia. The injection of bovine catalytic (C) subunits into sensory neurons is sufficient to produce protein synthesis-dependent LTF. Early in the LTF induced by serotonin (5-HT), an autonomous PKA is generated through the ubiquitin-proteasome-mediated proteolysis of regulatory (R) subunits. The degradation of R occurs during an early time window and appears to be a key function of proteasomes in LTF. Lactacystin, a specific proteasome inhibitor, blocks the facilitation induced by 5-HT, and this block is rescued by injecting C subunits. R is degraded through an allosteric mechanism requiring an elevation of cAMP coincident with the induction of a ubiquitin carboxy-terminal hydrolase.


Subject(s)
Aplysia/physiology , Cyclic AMP-Dependent Protein Kinases/biosynthesis , Long-Term Potentiation/physiology , Animals , Aplysia/metabolism , Cattle , Cyclic AMP/physiology , Cyclic AMP-Dependent Protein Kinases/metabolism , Cyclic AMP-Dependent Protein Kinases/pharmacology , Cysteine Endopeptidases/physiology , Injections , Multienzyme Complexes/physiology , Neurons, Afferent/drug effects , Neurons, Afferent/physiology , Peptide Fragments/metabolism , Peptide Fragments/pharmacology , Proteasome Endopeptidase Complex , Serotonin/pharmacology , Ubiquitins/metabolism
12.
Mol Neurobiol ; 20(2-3): 125-42, 1999.
Article in English | MEDLINE | ID: mdl-10966118

ABSTRACT

Sensitization of defensive reflexes in Aplysia is a simple behavioral paradigm for studying both short- and long-term memory. In the marine mollusk, as in other animals, memory has at least two phases: a short-term phase lasting minutes and a long-term phase lasting several days or longer. Short-term memory is produced by covalent modification of pre-existing proteins. In contrast, long-term memory needs gene induction, synthesis of new protein, and the growth of new synapses. The switch from short-term (STF) to long-term facilitation (LTF) in Aplysia sensory neurons requires not only positive regulation through gene induction, but also the specific removal of several inhibitory proteins. One important inhibitory protein is the regulatory (R) subunit of the cAMP-dependent protein kinase (PKA). Degradation of R subunits, which is essential for initiating long-term stable memory, occurs through the ubiquitin-proteasome pathway.


Subject(s)
Cysteine Endopeptidases/metabolism , Learning/physiology , Memory/physiology , Multienzyme Complexes/metabolism , Ubiquitins/metabolism , Animals , Cyclic AMP-Dependent Protein Kinases/metabolism , Humans , Long-Term Potentiation , Nerve Tissue Proteins/metabolism , Proteasome Endopeptidase Complex
13.
Cell ; 89(1): 115-26, 1997 Apr 04.
Article in English | MEDLINE | ID: mdl-9094720

ABSTRACT

The switch from short-term to long-term facilitation of the synapses between sensory and motor neurons mediating gill and tail withdrawal reflexes in Aplysia requires CREB-mediated transcription and new protein synthesis. We isolated several downstream genes, one of which encodes a neuron-specific ubiquitin C-terminal hydrolase. This rapidly induced gene encodes an enzyme that associates with the proteasome and increases its proteolytic activity. This regulated proteolysis is essential for long-term facilitation. Inhibiting the expression or function of the hydrolase blocks induction of long-term but not short-term facilitation. We suggest that the enhanced proteasome activity increases degradation of substrates that normally inhibit long-term facilitation. Thus, through induction of the hydrolase and the resulting up-regulation of the ubiquitin pathway, learning recruits a regulated form of proteolysis that removes inhibitory constraints on long-term memory storage.


Subject(s)
Aplysia/physiology , Genes, Immediate-Early/physiology , Long-Term Potentiation/genetics , Thiolester Hydrolases/genetics , Amino Acid Sequence , Animals , Antibodies/pharmacology , Base Sequence , Blotting, Northern , Cells, Cultured/drug effects , Cells, Cultured/enzymology , Cyclic AMP/pharmacology , Cyclic AMP-Dependent Protein Kinases/metabolism , Ganglia, Invertebrate/cytology , Memory/physiology , Microinjections , Molecular Sequence Data , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/immunology , Nerve Tissue Proteins/metabolism , Neurons, Afferent/drug effects , Neurons, Afferent/enzymology , Oligonucleotides, Antisense/pharmacology , Proteins/metabolism , RNA, Messenger/analysis , Serotonin/pharmacology , Substrate Specificity , Thiolester Hydrolases/immunology , Thiolester Hydrolases/metabolism , Ubiquitin Thiolesterase , Ubiquitins/metabolism
14.
J Neurosci ; 15(11): 7592-603, 1995 Nov.
Article in English | MEDLINE | ID: mdl-7472510

ABSTRACT

In response to the facilitating neurotransmitter serotonin (5-HT), the cAMP-dependent protein kinase (PKA) acquires a special mnemonic characteristic in Aplysia sensory neurons. PKA becomes persistently activated at basal cAMP concentrations owing to a decreased regulatory (R) to catalytic (C) subunit ratio. We previously implicated ubiquitin-mediated proteolysis in this selective loss of R. Here we show that ubiquitin (Ub), Ub-conjugates and proteasomes are present in cell bodies, axon, neuropil and nerve terminals of Aplysia neurons. Because R subunits are not decreased in muscle exposed to 5-HT, comparison of the two tissues provides a tractable approach to determine how the Ub pathway is regulated. We compared the structure of M1, the muscle-specific R isoform, to that of N4, a major neuronal R isoform, to rule out the possibility that the differences in their stability result from differences in structure. We present evidence that N4 and M1 are encoded by identical transcripts; they also behave similarly as protein substrates for the Ub pathway in extracts of the two tissues. Nervous tissue contains 20-times more free Ub, but we present evidence that the susceptibility of R subunits to degradation in neurons relative to muscle results from the greater capacity of neurons to degrade ubiquitinated proteins through the proteasome. Thus, factors that regulate the activity of proteasomes could underlie the enhanced degradation of R subunits in long-term sensitization.


Subject(s)
Aplysia/physiology , Cyclic AMP-Dependent Protein Kinases/metabolism , Neurons/physiology , Peptide Hydrolases/metabolism , Ubiquitins/physiology , Amino Acid Sequence , Animals , Cyclic AMP-Dependent Protein Kinases/chemistry , Cyclic AMP-Dependent Protein Kinases/genetics , Cysteine Endopeptidases/metabolism , Enzyme Activation , Immunoblotting , Isoenzymes/genetics , Isoenzymes/metabolism , Molecular Sequence Data , Multienzyme Complexes/metabolism , Muscles/chemistry , Nervous System/chemistry , Proteasome Endopeptidase Complex , Ubiquitins/analysis
15.
FEBS Lett ; 333(1-2): 103-7, 1993 Oct 25.
Article in English | MEDLINE | ID: mdl-8224144

ABSTRACT

We showed earlier that the phosphorylation of a 38 kDa protein (p38) from rat liver plasma membrane is stimulated by ras or endogenous G-proteins. We have now estimated the level of expression of p38 in liver tissues from embryos at different stages of development, regenerating liver and also in tumor cell lines of hepatic origin. Our results indicate that the expression of p38 is negatively correlated with cell division. It is suggested that the phosphorylation of p38, an event which is regulated by ras proteins and G-proteins, could be involved in signal transduction processes associated with the inhibitory regulation of cell division.


Subject(s)
GTP-Binding Proteins/physiology , Liver/cytology , Membrane Proteins/metabolism , Proto-Oncogene Proteins p21(ras)/physiology , Animals , Blotting, Western , Cell Division/physiology , Humans , In Vitro Techniques , Liver/metabolism , Phosphorylation , Rats , Signal Transduction/physiology
16.
Proc Natl Acad Sci U S A ; 90(16): 7436-40, 1993 Aug 15.
Article in English | MEDLINE | ID: mdl-8395048

ABSTRACT

In Aplysia, behavioral sensitization of defensive reflexes and the underlying presynaptic facilitation of sensory-to-motor neuron synapses lasts for several minutes (short term) or days to weeks (long term). Short-term sensitization has been explained by modulation of ion-channel function through cAMP-dependent protein phosphorylation. Long-term facilitation requires additional molecular changes including protein synthesis. A key event is the persistent activation of the cAMP-dependent protein kinase at baseline concentrations of cAMP. This activation is due to selective loss of regulatory (R) subunits of PKA without any change in catalytic (C) subunits. To understand the molecular mechanisms that produce the loss of R subunits in long-term facilitation, we investigated how R subunits are degraded in extracts of Aplysia nervous tissue and in rabbit reticulocyte lysates. Degradation of Aplysia R subunits requires ATP, ubiquitin, and a particulate component that appears to be the proteasome complex. Degradation is blocked by hemin, which causes the accumulation of high molecular weight derivatives of R subunits that are likely to be ubiquitin conjugates of R subunits and intermediates in the degradative pathway. We also show that vertebrate RI and RII subunits can be degraded through the ubiquitin pathway. We suggest that degradation is initiated by cAMP, which causes the holoenzyme to dissociate and, further, that the altered R-to-C ratio in Aplysia sensory neurons is maintained in long-term facilitation by newly synthesized proteins that help target R subunits for accelerated degradation.


Subject(s)
Neuronal Plasticity , Neurons/physiology , Protein Kinases/metabolism , Synapses/physiology , Ubiquitins/metabolism , Animals , Aplysia , Cattle , Ganglia/physiology , In Vitro Techniques , Macromolecular Substances , Molecular Weight , Protein Binding , Protein Kinases/isolation & purification , Rabbits , Reticulocytes/metabolism , Ubiquitins/isolation & purification
17.
Mol Cell Biol ; 10(6): 2468-74, 1990 Jun.
Article in English | MEDLINE | ID: mdl-2188088

ABSTRACT

We had reported earlier the enhanced phosphorylation of a 38-kilodalton protein (p38) in rat liver plasma membrane by ras proteins. Now we show that glucagon increased the phosphorylation of the same protein. The nature and site(s) of phosphorylation were the same as those for the ras proteins. Both ATP and GTP could donate phosphate for the phosphorylation of p38. The stimulation of p38 phosphorylation by glucagon was guanine nucleotide dependent. This observation, together with our data on the stimulation of p38 phosphorylation by AIF4-, suggest the involvement of G proteins in the reaction. We also showed that glucagon stimulates the phosphorylation of p38 in vivo.


Subject(s)
Glucagon/pharmacology , Liver/metabolism , Membrane Proteins/metabolism , Oncogene Protein p21(ras)/pharmacology , Animals , Electrophoresis, Polyacrylamide Gel , Guanosine Diphosphate/metabolism , Guanosine Triphosphate/metabolism , Humans , Kinetics , Male , Molecular Weight , Peptide Mapping , Phosphoproteins/isolation & purification , Phosphorylation , Rats , Rats, Inbred Strains , Recombinant Proteins/pharmacology
18.
FEBS Lett ; 217(1): 74-80, 1987 Jun 08.
Article in English | MEDLINE | ID: mdl-3297778

ABSTRACT

Phosphorylation of a 38 kDa protein (p38) present in rat liver plasma membrane has been shown for the first time to be enhanced by ras proteins. This increase in phosphorylation is about 3-16-fold depending on the incubation time and the type of ras protein used. Acid treatment removes phosphate from this protein suggesting that the phosphorylation involves phosphoramidate derivatives of basic amino acids. Experiments carried out in the presence of diethylpyrocarbonate suggest that the phosphorylation occurs on (a) histidine residue(s). It is probable that the function of p38 in the cell is modulated by ras proteins through phosphorylation. The significance of phosphorylation of p38 in terms of malignant transformation is presently known.


Subject(s)
Liver/analysis , Membrane Proteins/metabolism , Oncogene Proteins, Viral/metabolism , Protein-Tyrosine Kinases/metabolism , Proto-Oncogene Proteins/metabolism , Animals , Diethyl Pyrocarbonate , Guanosine Diphosphate/metabolism , Histidine/analogs & derivatives , Histidine/biosynthesis , Histidine/metabolism , Male , Oncogene Protein p21(ras) , Phosphorylation , Proto-Oncogene Proteins p21(ras) , Rats , Rats, Inbred Strains
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