The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Michael Karin - One of the best experts on this subject based on the ideXlab platform.
-
mapping of the inducible ikappab phosphorylation sites that signal its ubiquitination and degradation
Molecular and Cellular Biology, 1996Co-Authors: Joseph A Didonato, Frank Mercurio, Caridad Rosette, Jian Wuli, Helena Suyang, Sankar Ghosh, Michael KarinAbstract:Extracellular stimuli that activate the transcription factor NF-kappaB cause rapid phosphorylation of the IkappaBalpha inhibitor, which retains NF-kappaB in the cytoplasm of nonstimulated cells. Phosphorylation of IkappaBalpha is followed by its rapid degradation, the inhibition of which prevents NF-kappaB activation. To determine the relationship between these events, we mapped the inducible phosphorylation sites of IkappaBalpha. We found that two residues, Serines 32 and 36, were phosphorylated in response to either tumor necrosis factor, interleukin-1, or phorbol ester. Substitution of either Serine blocks or slows down induction of IkappaBalpha degradation. Substitutions of the homologous sites in IkappaBbeta, Serines 19 and 23, also prevent inducible IkappaBbeta degradation. We suggest that activation of a single IkappaB kinas e or closely related IkappaB kinases is the first cr itical step in NF-kappaB activation. Once phosphorylated, IkappaB is ubiquitinated. Unlike wild-type IkappaBalpha, the phosphorylation-defective mutants do not undergo inducible polyubiquitination. As substitution of a conserved lysine residue slows down the ubiquitination and degradation of IkappaBalpha without affecting its phosphorylation, polyubiquitination is required for inducible IkappaB degradation.
-
identification of an oncoprotein and uv responsive protein kinase that binds and potentiates the c jun activation domain
Genes & Development, 1993Co-Authors: Masahiko Hibi, Audrey Minden, Tod Smeal, Michael KarinAbstract:The activity of c-Jun is regulated by phosphorylation. Various stimuli including transforming oncogenes and UV light, induce phosphorylation of Serines 63 and 73 in the amino-terminal activation domain of c-Jun and thereby potentiate its trans-activation function. We identified a Serine/threonine kinase whose activity is stimulated by the same signals that stimulate the amino-terminal phosphorylation of c-Jun. This novel c-Jun amino-terminal kinase (JNK), whose major form is 46 kD, binds to a specific region within the c-jun trans-activation domain and phosphorylates Serines 63 and 73. Phosphorylation results in dissociation of the c-Jun-JNK complex. Mutations that disrupt the kinase-binding site attenuate the response of c-Jun to Ha-Ras and UV
-
identification of an oncoprotein and uv responsive protein kinase that binds and potentiates the c jun activation domain
Genes & Development, 1993Co-Authors: Masahiko Hibi, Audrey Minden, Tod Smeal, Michael KarinAbstract:: The activity of c-Jun is regulated by phosphorylation. Various stimuli including transforming oncogenes and UV light, induce phosphorylation of Serines 63 and 73 in the amino-terminal activation domain of c-Jun and thereby potentiate its trans-activation function. We identified a Serine/threonine kinase whose activity is stimulated by the same signals that stimulate the amino-terminal phosphorylation of c-Jun. This novel c-Jun amino-terminal kinase (JNK), whose major form is 46 kD, binds to a specific region within the c-Jun trans-activation domain and phosphorylates Serines 63 and 73. Phosphorylation results in dissociation of the c-Jun-JNK complex. Mutations that disrupt the kinase-binding site attenuate the response of c-Jun to Ha-Ras and UV. Therefore the binding of JNK to c-Jun is of regulatory importance and suggests a mechanism through which protein kinase cascades can specifically modulate the activity of distinct nuclear targets.
Masahiko Hibi - One of the best experts on this subject based on the ideXlab platform.
-
identification of an oncoprotein and uv responsive protein kinase that binds and potentiates the c jun activation domain
Genes & Development, 1993Co-Authors: Masahiko Hibi, Audrey Minden, Tod Smeal, Michael KarinAbstract:The activity of c-Jun is regulated by phosphorylation. Various stimuli including transforming oncogenes and UV light, induce phosphorylation of Serines 63 and 73 in the amino-terminal activation domain of c-Jun and thereby potentiate its trans-activation function. We identified a Serine/threonine kinase whose activity is stimulated by the same signals that stimulate the amino-terminal phosphorylation of c-Jun. This novel c-Jun amino-terminal kinase (JNK), whose major form is 46 kD, binds to a specific region within the c-jun trans-activation domain and phosphorylates Serines 63 and 73. Phosphorylation results in dissociation of the c-Jun-JNK complex. Mutations that disrupt the kinase-binding site attenuate the response of c-Jun to Ha-Ras and UV
-
identification of an oncoprotein and uv responsive protein kinase that binds and potentiates the c jun activation domain
Genes & Development, 1993Co-Authors: Masahiko Hibi, Audrey Minden, Tod Smeal, Michael KarinAbstract:: The activity of c-Jun is regulated by phosphorylation. Various stimuli including transforming oncogenes and UV light, induce phosphorylation of Serines 63 and 73 in the amino-terminal activation domain of c-Jun and thereby potentiate its trans-activation function. We identified a Serine/threonine kinase whose activity is stimulated by the same signals that stimulate the amino-terminal phosphorylation of c-Jun. This novel c-Jun amino-terminal kinase (JNK), whose major form is 46 kD, binds to a specific region within the c-Jun trans-activation domain and phosphorylates Serines 63 and 73. Phosphorylation results in dissociation of the c-Jun-JNK complex. Mutations that disrupt the kinase-binding site attenuate the response of c-Jun to Ha-Ras and UV. Therefore the binding of JNK to c-Jun is of regulatory importance and suggests a mechanism through which protein kinase cascades can specifically modulate the activity of distinct nuclear targets.
Herman Wolosker - One of the best experts on this subject based on the ideXlab platform.
-
The Neurobiology of d-Serine Signaling.
Advances in pharmacology (San Diego), 2017Co-Authors: Herman WoloskerAbstract:Abstract d -Serine is a physiological coagonist of NMDA receptors involved in synaptic plasticity, neurodevelopment, and neurodegeneration. d -Serine is synthesized by the enzyme Serine racemase, which converts l - to d -Serine. Recent studies indicate that the supply of l -Serine by astroglia fuels the neuronal synthesis of d -Serine. This pathway, named the Serine shuttle, highlights the importance of the glia–neuron metabolic crosstalk for regulating NMDA receptor activity. Dysfunction of different components of the Serine shuttle pathway leads to neurodevelopmental defects, neurodegeneration, and may be involved in psychiatric diseases. Serine racemase and other components of the Serine shuttle are therefore promising targets for neuroprotective drugs. Here we review several aspects of the neurobiology of d -Serine focusing on mechanisms regulating d -Serine signaling in health and disease.
-
Purification of Serine racemase: ) neuromodulator D-Serine
2016Co-Authors: Herman Wolosker, Kevin N. Sheth, Masaaki Takaha, Christopher D. Ferris, Solomon H. Snyder, Jean-pierre MothetAbstract:High levels of D-Serine occur in mammalian brain, where it appears to be an endogenous ligand of the glycine site of N-methyl-D-aspartate receptors. In glial cul- tures of rat cerebral cortex, D-Serine is enriched in type II astrocytes and is released upon stimulation with agonists of non-N-methyl-D-aspartate glutamate receptors. The high lev- els of D-Serine in discrete areas of rat brain imply the existence of a biosynthetic pathway. We have purified from rat brain a soluble enzyme that catalyzes the direct racemization of L-Serine to D-Serine. Purified Serine racemase has a molecular mass of 37 kDa and requires pyridoxal 5'-phosphate for its activity. The enzyme is highly selective toward L-Serine, failing to racemize any other amino acid tested. Properties such as pH optimum, Km values, and the requirement for pyridoxal phos- phate resemble those of bacterial racemases, suggesting that the biosynthetic pathway for D-amino acids is conserved from bacteria to mammalian brain.
-
Serine racemase and the Serine shuttle between neurons and astrocytes.
Biochimica et Biophysica Acta, 2011Co-Authors: Herman WoloskerAbstract:Abstract d -Serine is a brain-enriched d -amino acid that works as a transmitter-like molecule by physiologically activating NMDA receptors. Synthesis of d -Serine is carried out by Serine racemase (SR), a pyridoxal 5′-phosphate-dependent enzyme. In addition to carry out racemization, SR α,β-eliminates water from l - or d -Serine, generating pyruvate and NH4+. Here I review the main mechanisms regulating SR activity and d -Serine dynamics in the brain. I propose a role for SR in a novel form of astrocyte-neuron communication—the “Serine shuttle”, whereby astrocytes synthesize and export l -Serine required for the synthesis of d -Serine by the predominantly neuronal SR. d -Serine synthesized and released by neurons can be further taken up by astrocytes for storage and activity-dependent release. I discuss how SR α,β-elimination with d -Serine itself may limit the achievable intracellular d -Serine concentration, providing a mechanistic rationale on why neurons do not store as much d -Serine as astrocytes. The higher content of d -Serine in astrocytes appears to be related to increased d -Serine stability, for their low SR expression will prevent substantial d -Serine metabolism via α,β-elimination. SR and the Serine shuttle pathway are therapeutic targets in neurodegenerative diseases in which NMDA receptor dysfunction plays pathological roles. This article is part of a Special Issue entitled: Pyridoxal Phospate Enzymology.
-
Neuronal release of d-Serine: a physiological pathway controlling extracellular d-Serine concentration
The FASEB Journal, 2010Co-Authors: Dina Rosenberg, Maria Shleper, Elena Kartvelishvily, Chanda Ciriacks Klinker, Michael T. Bowser, Herman WoloskerAbstract:d-Serine is thought to be a glia-derived transmitter that activates N-methyl d-aspartate receptors (NMDARs) in the brain. Here, we investigate the pathways for d-Serine release using primary cultures, brain slices, and in vivo microdialysis. In contrast with the notion that d-Serine is exclusively released from astrocytes, we found that d-Serine is released by neuronal depolarization both in vitro and in vivo. Veratridine (50 μM) or depolarization by 40 mM KCl elicits a significant release of endogenous d-Serine from primary neuronal cultures. Controls with astrocyte cultures indicate that glial cells are insensitive to veratridine, but release d-Serine mainly by the opening of volume-regulated anion channels. In cortical slices perfused with veratridine, endogenous d-Serine release is 10-fold higher than glutamate receptor-evoked release. Release of d-Serine from slices does not require internal or external Ca2+, suggesting a nonvesicular release mechanism. To confirm the neuronal origin of d-Serine, we selectively loaded neurons in cortical slices with d-[3H]Serine or applied d-alanine, which specifically releases d-Serine from neurons. Depolarization with veratridine promotes d-Serine release in vivo monitored by high temporal resolution microdialysis of the striatum. Our data indicate that the neuronal pool of d-Serine plays a major role in d-Serine dynamics, with implications for the regulation of NMDAR transmission. Rosenberg, D., Kartvelishvily, E., Shleper, M., Klinker, C. M. C., Bowser, M. T., Wolosker, H. Neuronal release of d-Serine: a physiological pathway controlling extracellular d-Serine concentration.
-
Modulation of D-Serine levels via ubiquitin-dependent proteasomal degradation of Serine racemase.
Journal of Biological Chemistry, 2006Co-Authors: Elena Dumin, Veronika N. Foltyn, Inna Bendikov, Elena Kartvelishvily, Yoshio Misumi, Yukio Ikehara, Herman WoloskerAbstract:Abstract Mammalian Serine racemase is a brain-enriched enzyme that converts l- into d-Serine in the nervous system. d-Serine is an endogenous co-agonist at the “glycine site” of N-methyl d-aspartate (NMDA) receptors that is required for the receptor/channel opening. Factors regulating the synthesis of d-Serine have implications for the NMDA receptor transmission, but little is known on the signals and events affecting Serine racemase levels. We found that Serine racemase interacts with the Golgin subfamily A member 3 (Golga3) protein in yeast two-hybrid screening. The interaction was confirmed in vitro with the recombinant proteins in co-transfected HEK293 cells and in vivo by co-immunoprecipitation studies from brain homogenates. Golga3 and Serine racemase co-localized at the cytosol, perinuclear Golgi region, and neuronal and glial cell processes in primary cultures. Golga3 significantly increased Serine racemase steady-state levels in co-transfected HEK293 cells and primary astrocyte cultures. This observation led us to investigate mechanisms regulating Serine racemase levels. We found that Serine racemase is degraded through the ubiquitin-proteasomal system in a Golga3-modulated manner. Golga3 decreased the ubiquitylation of Serine racemase both in vitro and in vivo and significantly increased the protein half-life in pulse-chase experiments. Our results suggest that the ubiquitin system is a main regulator of Serine racemase and d-Serine levels. Modulation of Serine racemase degradation, such as that promoted by Golga3, provides a new mechanism for regulating brain d-Serine levels and NMDA receptor activity.
Arsène Burny - One of the best experts on this subject based on the ideXlab platform.
-
Phosphorylation of bovine leukemia virus Tax protein is required for in vitro transformation but not for transactivation
Oncogene, 1998Co-Authors: Luc Willems, Cathy Grimonpont, Pierre Kerkhofs, Carine Capiau, Dirk Gheysen, Karel Conrath, Roussi Roussef, Robert Mamoun, Daniel Portetelle, Arsène BurnyAbstract:The Tax proteins of the oncovirinae viruses are phosphorylated transcriptional activators that exhibit oncogenic potential. The role of phosphorylation in their functional activities remains unknown. As a model for the Human T-cell leukemia virus type I (HTLV-I), Bovine Leukemia Virus (BLV) permits the characterization of viral replication and leukemogenesis in vivo . Here, we show that the BLV Tax protein is phosphorylated on Serine residues 106 and 293 both in insect and in mammalian cells. These sites can also be efficiently phosphorylated by the cdc2 and MAP kinases in vitro . Mutation of these residues does not affect the capacity of the Tax protein to function as a transactivator. Indeed, the Tax proteins mutated at one or both Serines increase LTR-directed viral transcription at levels similar to those obtained with wild-type Tax in cell culture. Moreover, inhibition of Tax phosphorylation by W7, a calmodulin antagonist, does not alter its transactivation activity. Thus, phosphorylation on Serines 106 and 293 is not required for transactivation by Tax. However, simultaneous substitution of both Serines into alanine residues destroys the capacity of Tax to cooperate with the Ha- ras oncogene to transform primary rat embryo fibroblasts and induce tumors in nude mice. When the Serines were replaced with aspartic acid residues, the oncogenic potential of Tax was maintained indicating that the negative charge rather than the phosphate group itself was required for Tax oncogenicity. Finally, to assess the role of the Serine residues in vivo , recombinant viruses which express the Tax mutants were constructed and injected into sheep. It appeared that the mutated proviruses replicate at levels similar to the wild-type virus in vivo . We conclude that Tax phosphorylation is dispensable for transactivation and viral replication in vivo but is required for its oncogenic potential in vitro .
Tod Smeal - One of the best experts on this subject based on the ideXlab platform.
-
identification of an oncoprotein and uv responsive protein kinase that binds and potentiates the c jun activation domain
Genes & Development, 1993Co-Authors: Masahiko Hibi, Audrey Minden, Tod Smeal, Michael KarinAbstract:The activity of c-Jun is regulated by phosphorylation. Various stimuli including transforming oncogenes and UV light, induce phosphorylation of Serines 63 and 73 in the amino-terminal activation domain of c-Jun and thereby potentiate its trans-activation function. We identified a Serine/threonine kinase whose activity is stimulated by the same signals that stimulate the amino-terminal phosphorylation of c-Jun. This novel c-Jun amino-terminal kinase (JNK), whose major form is 46 kD, binds to a specific region within the c-jun trans-activation domain and phosphorylates Serines 63 and 73. Phosphorylation results in dissociation of the c-Jun-JNK complex. Mutations that disrupt the kinase-binding site attenuate the response of c-Jun to Ha-Ras and UV
-
identification of an oncoprotein and uv responsive protein kinase that binds and potentiates the c jun activation domain
Genes & Development, 1993Co-Authors: Masahiko Hibi, Audrey Minden, Tod Smeal, Michael KarinAbstract:: The activity of c-Jun is regulated by phosphorylation. Various stimuli including transforming oncogenes and UV light, induce phosphorylation of Serines 63 and 73 in the amino-terminal activation domain of c-Jun and thereby potentiate its trans-activation function. We identified a Serine/threonine kinase whose activity is stimulated by the same signals that stimulate the amino-terminal phosphorylation of c-Jun. This novel c-Jun amino-terminal kinase (JNK), whose major form is 46 kD, binds to a specific region within the c-Jun trans-activation domain and phosphorylates Serines 63 and 73. Phosphorylation results in dissociation of the c-Jun-JNK complex. Mutations that disrupt the kinase-binding site attenuate the response of c-Jun to Ha-Ras and UV. Therefore the binding of JNK to c-Jun is of regulatory importance and suggests a mechanism through which protein kinase cascades can specifically modulate the activity of distinct nuclear targets.
