Arc (protein)
Encyclopedia
Arc, for activity-regulated cytoskeleton-associated protein (also known as Arg3.1), is a plasticity
protein first characterized in 1995. Arc is a member of the immediate-early gene (IEG) family, a rapidly activated class of genes functionally defined by their ability to be transcribed
in the presence of protein synthesis inhibitor
s. Arc mRNA is localized to activated synaptic sites in an NMDA receptor
-dependent manner, where the newly translated
protein is believed to play a critical role in learning and memory-related molecular processes. Arc is widely considered to be an important protein in neurobiology because of its activity regulation, localization, and utility as a marker for plastic changes in the brain. Along with other IEGs such as zif268
and Homer 1a
, Arc is also a significant tool for systems neuroscience
as illustrated by the development of the cellular compartment analysis of temporal activity by fluorescence in situ hybridization, or catFISH technique (see fluorescent in situ hybridization
).
15 in the mouse
http://www.ensembl.org/Mus_musculus/Gene/Summary?g=ENSMUSG00000022602, chromosome 7 in the rat
http://www.ensembl.org/Rattus_norvegicus/Gene/Summary?g=ENSRNOG00000043465, and chromosome 8 in the human
http://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000198576, is conserved across vertebrate species and has low sequence homology to spectrin, a cytoskeletal protein involved in forming the actin
cellular cortex. A number of promoter and enhancer
regions have been identified that mediate activity-dependent Arc transcription: a serum response element (SRE; see serum response factor
) at ~1.5 kb upstream of the initiation site; a second SRE at ~6.5 kb; and a synaptic activity response element (SARE) sequence at ~7 kb upstream that contains binding sites for cyclic AMP response element-binding protein
(CREB), myocyte enhancer factor 2
(MEF2), and SRF.
The 3' UTR
of the mRNA contains a cis-acting element required for the localization of Arc to neuronal dendrites, as well as sites for two exon junction complex
es (EJCs) that make Arc a natural target for nonsense mediated decay
(NMD). Also important for translocation of cytoplasmic Arc mRNA to activated synapses is an 11 nucleotide binding site for heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2).
Once transported, the translated protein is 396 residues in length, with an N-terminus located at amino acids 1-25, a C-terminus at 155-396 (note that the spectrin homology located at 228-380 within the C-terminal), and a putative coiled coil
domain at amino acids 26-154. Additionally, the protein has binding sites for endophilin 3 and dynamin 2 at amino acids 89-100 and 195-214, respectively. While Arc mRNA is subject to degradation by NMD, the translated protein contains a PEST sequence
at amino acids 351-392, indicating proteasome
-dependent degradation. The translated protein can be visualized with an immunoblot as a band at 55 kDa.
. The first knockouts
(KOs) for Arc were therefore incompatible with life. Subsequent efforts produced homozygous knockout mice by targeting the entire Arc gene rather than portions of the coding region, eliminating dominant negative effects. These animals proved viable and exhibit no gross malformations in neuronal architecture, but express higher levels of the GluR1 subunit
and increased miniature excitatory postsynaptic currents
(mEPSCs) in addition to displaying deficiencies in long-term memory
.
, contextual fear conditioning, spatial memory, operant conditioning
, and inhibitory avoidance. The mRNA is notably upregulated following electical stimulation in LTP
-induction procedures such as high frequency stimulation (HFS), and is massively and globally induced by maximal electroconvulsive shock (MECS).
The Arc transcript is the first known IEG that is entirely dependent upon activation of the mitogen-activated protein kinase
or MAP kinase (MAPK) cascade, a pathway important for regulation of cell growth and survival. Extracellular signaling to neuronal dendrites activates postsynaptic sites to increase Arc levels through a wide variety of signaling molecules, including mitogens such as epidermal growth factor
(EGF), nerve growth factor
(NGF), and brain-derived neurotrophic factor
(BDNF), glutamate acting at NMDA receptors, dopamine through activation of the D1 receptor subtype
, and dihydroxyphenylglycine
(DHPG). The common factor for these signaling molecules involves activation of cyclic-AMP
and its downstream target protein kinase A (PKA). As such, direct pharmacological activation of cAMP by forskolin or 8-Br-cAMP robustly increases Arc levels while H89, a PKA antagonist, blocks these effects as does further downstream blockade of mitogen-activated protein kinase kinase [sic] (MEK). Note that the MAPK cascade is a signaling pathway involving multiple kinase
s acting sequentially [MAPKKK--> MAPKK--> MAPK].
MAPK is able to enter the nucleus and perform its phosphotransferase activity on a number of gene regulatory components that have implications for the regulation of immediate-early genes. Several transcription factor
s are known to be involved in regulating the Arc gene (see above), including serum response factor
(SRF), CREB
, MEF2
, and zif268
.
, and ERK phosphorylation. The mRNA (and aggregate protein) is carried along microtubule
s radiating out from the nucleus by kinesin
(specifically KIF5) and likely translocated into dendritic spine
s by the actin-based motor protein myosin
-Va. Arc has been shown to be associated with polyribosomes at synaptic sites, and is translated in isolated synaptoneurosomal fractions in vitro indicating that the protein is likely locally translated in vivo.
Synaptically localized Arc protein interacts with dynamin
and endophilin, proteins involved in clathrin
-mediated endocytosis
, and facilitates the removal of AMPA receptors from the plasma membrane. Consistent with this, increased Arc levels reduce AMPA currents, while Arc KOs display increases in surface AMPA expression.
- Ensembl Arc gene information http://uswest.ensembl.org/Homo_sapiens/Gene/Summary?db=core;g=ENSG00000198576.
- Arc gene in Mus musculus http://www.informatics.jax.org/searches/accession_report.cgi?id=MGI:88067.
Neuroplasticity
Neuroplasticity is a non-specific neuroscience term referring to the ability of the brain and nervous system in all species to change structurally and functionally as a result of input from the environment. Plasticity occurs on a variety of levels, ranging from cellular changes involved in...
protein first characterized in 1995. Arc is a member of the immediate-early gene (IEG) family, a rapidly activated class of genes functionally defined by their ability to be transcribed
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
in the presence of protein synthesis inhibitor
Protein synthesis inhibitor
A protein synthesis inhibitor is a substance that stops or slows the growth or proliferation of cells by disrupting the processes that lead directly to the generation of new proteins....
s. Arc mRNA is localized to activated synaptic sites in an NMDA receptor
NMDA receptor
The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....
-dependent manner, where the newly translated
Translation (genetics)
In molecular biology and genetics, translation is the third stage of protein biosynthesis . In translation, messenger RNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein...
protein is believed to play a critical role in learning and memory-related molecular processes. Arc is widely considered to be an important protein in neurobiology because of its activity regulation, localization, and utility as a marker for plastic changes in the brain. Along with other IEGs such as zif268
Zif268
EGR-1 also known as Zif268 or NGFI-A is a protein that in humans is encoded by the EGR1 gene....
and Homer 1a
HOMER1
Homer protein homolog 1 or Homer1 is a neuronal protein that in humans is encoded by the HOMER1 gene. Other names are Vesl and PSD-Zip45.-Domain structure:...
, Arc is also a significant tool for systems neuroscience
Systems neuroscience
Systems neuroscience is a subdiscipline of neuroscience and systems biology that studies the function of neural circuits and systems. It is an umbrella term, encompassing a number of areas of study concerned with how nerve cells behave when connected together to form neural networks...
as illustrated by the development of the cellular compartment analysis of temporal activity by fluorescence in situ hybridization, or catFISH technique (see fluorescent in situ hybridization
Fluorescent in situ hybridization
FISH is a cytogenetic technique developed by biomedical researchers in the early 1980s that is used to detect and localize the presence or absence of specific DNA sequences on chromosomes. FISH uses fluorescent probes that bind to only those parts of the chromosome with which they show a high...
).
Molecular Profile
The Arc gene, located on chromosomeChromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
15 in the mouse
House mouse
The house mouse is a small rodent, a mouse, one of the most numerous species of the genus Mus.As a wild animal the house mouse mainly lives associated with humans, causing damage to crops and stored food....
http://www.ensembl.org/Mus_musculus/Gene/Summary?g=ENSMUSG00000022602, chromosome 7 in the rat
Brown Rat
The brown rat, common rat, sewer rat, Hanover rat, Norway rat, Brown Norway rat, Norwegian rat, or wharf rat is one of the best known and most common rats....
http://www.ensembl.org/Rattus_norvegicus/Gene/Summary?g=ENSRNOG00000043465, and chromosome 8 in the human
Human
Humans are the only living species in the Homo genus...
http://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000198576, is conserved across vertebrate species and has low sequence homology to spectrin, a cytoskeletal protein involved in forming the actin
Actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
cellular cortex. A number of promoter and enhancer
Enhancer (genetics)
In genetics, an enhancer is a short region of DNA that can be bound with proteins to enhance transcription levels of genes in a gene cluster...
regions have been identified that mediate activity-dependent Arc transcription: a serum response element (SRE; see serum response factor
Serum response factor
Serum response factor , also known as SRF, is a transcription factor.It is a member of the MADS box superfamily of transcription factors. This protein binds to the serum response element in the promoter region of target genes...
) at ~1.5 kb upstream of the initiation site; a second SRE at ~6.5 kb; and a synaptic activity response element (SARE) sequence at ~7 kb upstream that contains binding sites for cyclic AMP response element-binding protein
CREB
CREB is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements , thereby increasing or decreasing the transcription of the downstream genes....
(CREB), myocyte enhancer factor 2
Mef2
In the field of molecular biology, myocyte enhancer factor-2 proteins are a family of transcription factors which through control of gene expression are important regulators of cellular differentiation and consequently play a critical role in embryonic development. In adult organisms, Mef2...
(MEF2), and SRF.
The 3' UTR
Three prime untranslated region
In molecular genetics, the three prime untranslated region is a particular section of messenger RNA . It is preceeded by the coding region....
of the mRNA contains a cis-acting element required for the localization of Arc to neuronal dendrites, as well as sites for two exon junction complex
Exon junction complex
The exon junction complex has major influences on translation, surveillance and localization of the spliced mRNA. It is first deposited onto mRNA during splicing and is then transported into the cytoplasm. There it plays a major role in post-transcriptional regulation of mRNA. It is believed that...
es (EJCs) that make Arc a natural target for nonsense mediated decay
Nonsense mediated decay
Nonsense-mediated decay is a cellular mechanism of mRNA surveillance that functions to detect nonsense mutations and prevent the expression of truncated or erroneous proteins. Following transcription, precursor mRNA undergoes an assemblage of ribonucleoprotein components followed by regulatory...
(NMD). Also important for translocation of cytoplasmic Arc mRNA to activated synapses is an 11 nucleotide binding site for heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2).
Once transported, the translated protein is 396 residues in length, with an N-terminus located at amino acids 1-25, a C-terminus at 155-396 (note that the spectrin homology located at 228-380 within the C-terminal), and a putative coiled coil
Coiled coil
A coiled coil is a structural motif in proteins, in which 2-7 alpha-helices are coiled together like the strands of a rope . Many coiled coil type proteins are involved in important biological functions such as the regulation of gene expression e.g. transcription factors...
domain at amino acids 26-154. Additionally, the protein has binding sites for endophilin 3 and dynamin 2 at amino acids 89-100 and 195-214, respectively. While Arc mRNA is subject to degradation by NMD, the translated protein contains a PEST sequence
PEST sequence
A PEST sequence is a peptide sequence which is rich in proline , glutamic acid , serine , and threonine . This sequence is associated with proteins that have a short intracellular half-life; hence, it is hypothesized that the PEST sequence acts as a signal peptide for protein degradation.The...
at amino acids 351-392, indicating proteasome
Proteasome
Proteasomes are very large protein complexes inside all eukaryotes and archaea, and in some bacteria. In eukaryotes, they are located in the nucleus and the cytoplasm. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks...
-dependent degradation. The translated protein can be visualized with an immunoblot as a band at 55 kDa.
Knockouts
Arc is critical as a ubiquitous signaling factor in early embryonic development and is required for growth and patterning during gastrulationGastrulation
Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.Gastrulation takes place after cleavage...
. The first knockouts
Gene knockout
A gene knockout is a genetic technique in which one of an organism's genes is made inoperative . Also known as knockout organisms or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function...
(KOs) for Arc were therefore incompatible with life. Subsequent efforts produced homozygous knockout mice by targeting the entire Arc gene rather than portions of the coding region, eliminating dominant negative effects. These animals proved viable and exhibit no gross malformations in neuronal architecture, but express higher levels of the GluR1 subunit
AMPA receptor
The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor is a non-NMDA-type ionotropic transmembrane receptor for glutamate that mediates fast synaptic transmission in the central nervous system . Its name is derived from its ability to be activated by the artificial glutamate analog AMPA...
and increased miniature excitatory postsynaptic currents
Excitatory postsynaptic potential
In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...
(mEPSCs) in addition to displaying deficiencies in long-term memory
Long-term memory
Long-term memory is memory in which associations among items are stored, as part of the theory of a dual-store memory model. According to the theory, long term memory differs structurally and functionally from working memory or short-term memory, which ostensibly stores items for only around 20–30...
.
Induction
Changes in Arc mRNA and/or protein are correlated with a number of behavioral paradigms including cued fear conditioningFear conditioning
Fear conditioning is a behavioral paradigm in which organisms learn to predict aversive events. It is a form of learning in which an aversive stimulus is associated with a particular neutral context or neutral stimulus , resulting in the expression of fear responses to the originally neutral...
, contextual fear conditioning, spatial memory, operant conditioning
Operant conditioning
Operant conditioning is a form of psychological learning during which an individual modifies the occurrence and form of its own behavior due to the association of the behavior with a stimulus...
, and inhibitory avoidance. The mRNA is notably upregulated following electical stimulation in LTP
Long-term potentiation
In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...
-induction procedures such as high frequency stimulation (HFS), and is massively and globally induced by maximal electroconvulsive shock (MECS).
The Arc transcript is the first known IEG that is entirely dependent upon activation of the mitogen-activated protein kinase
Mitogen-activated protein kinase
Mitogen-activated protein kinases are serine/threonine-specific protein kinases that respond to extracellular stimuli and regulate various cellular activities, such as gene expression, mitosis, differentiation, proliferation, and cell survival/apoptosis.-Activation:MAP kinases are activated...
or MAP kinase (MAPK) cascade, a pathway important for regulation of cell growth and survival. Extracellular signaling to neuronal dendrites activates postsynaptic sites to increase Arc levels through a wide variety of signaling molecules, including mitogens such as epidermal growth factor
Epidermal growth factor
Epidermal growth factor or EGF is a growth factor that plays an important role in the regulation of cell growth, proliferation, and differentiation by binding to its receptor EGFR...
(EGF), nerve growth factor
Nerve growth factor
Nerve growth factor is a small secreted protein that is important for the growth, maintenance, and survival of certain target neurons . It also functions as a signaling molecule. It is perhaps the prototypical growth factor, in that it is one of the first to be described...
(NGF), and brain-derived neurotrophic factor
Brain-derived neurotrophic factor
Brain-derived neurotrophic factor, also known as BDNF, is a protein that, in humans, is encoded by the BDNF gene. BDNF is a member of the "neurotrophin" family of growth factors, which are related to the canonical "Nerve Growth Factor", NGF...
(BDNF), glutamate acting at NMDA receptors, dopamine through activation of the D1 receptor subtype
Dopamine receptor D1
Dopamine receptor D1, also known as DRD1, is a protein that in humans is encoded by the DRD1 gene.- Function :This gene encodes the D1 subtype of the dopamine receptor. The D1 subtype is the most abundant dopamine receptor in the central nervous system. This G-protein-coupled receptor stimulates...
, and dihydroxyphenylglycine
Dihydroxyphenylglycine
-3,5-Dihydroxyphenylglycine or DHPG is a potent agonist of group I metabotropic glutamate receptors mGluR1 and mGluR5.DHPG was the first agonist shown to be selective for group I mGluRs...
(DHPG). The common factor for these signaling molecules involves activation of cyclic-AMP
Cyclic adenosine monophosphate
Cyclic adenosine monophosphate is a second messenger important in many biological processes...
and its downstream target protein kinase A (PKA). As such, direct pharmacological activation of cAMP by forskolin or 8-Br-cAMP robustly increases Arc levels while H89, a PKA antagonist, blocks these effects as does further downstream blockade of mitogen-activated protein kinase kinase [sic] (MEK). Note that the MAPK cascade is a signaling pathway involving multiple kinase
Kinase
In chemistry and biochemistry, a kinase is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates, a process referred to as phosphorylation. Kinases are part of the larger family of phosphotransferases...
s acting sequentially [MAPKKK--> MAPKK--> MAPK].
MAPK is able to enter the nucleus and perform its phosphotransferase activity on a number of gene regulatory components that have implications for the regulation of immediate-early genes. Several transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
s are known to be involved in regulating the Arc gene (see above), including serum response factor
Serum response factor
Serum response factor , also known as SRF, is a transcription factor.It is a member of the MADS box superfamily of transcription factors. This protein binds to the serum response element in the promoter region of target genes...
(SRF), CREB
CREB
CREB is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements , thereby increasing or decreasing the transcription of the downstream genes....
, MEF2
Mef2
In the field of molecular biology, myocyte enhancer factor-2 proteins are a family of transcription factors which through control of gene expression are important regulators of cellular differentiation and consequently play a critical role in embryonic development. In adult organisms, Mef2...
, and zif268
Zif268
EGR-1 also known as Zif268 or NGFI-A is a protein that in humans is encoded by the EGR1 gene....
.
Trafficking
Following transcription, Arc mRNA is transported out of the nucleus and localized to neuronal dendrites and activated synapses, a process dependent on the 3' UTR, polymerization of actinActin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
, and ERK phosphorylation. The mRNA (and aggregate protein) is carried along microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
s radiating out from the nucleus by kinesin
Kinesin
A kinesin is a protein belonging to a class of motor proteins found in eukaryotic cells. Kinesins move along microtubule filaments, and are powered by the hydrolysis of ATP . The active movement of kinesins supports several cellular functions including mitosis, meiosis and transport of cellular...
(specifically KIF5) and likely translocated into dendritic spine
Dendritic spine
A dendritic spine is a small membranous protrusion from a neuron's dendrite that typically receives input from a single synapse of an axon. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body...
s by the actin-based motor protein myosin
Myosin
Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...
-Va. Arc has been shown to be associated with polyribosomes at synaptic sites, and is translated in isolated synaptoneurosomal fractions in vitro indicating that the protein is likely locally translated in vivo.
Synaptically localized Arc protein interacts with dynamin
Dynamin
Dynamin is a GTPase responsible for endocytosis in the eukaryotic cell. Dynamins are principally involved in the scission of newly formed vesicles from the membrane of one cellular compartment and their targeting to, and fusion with, another compartment, both at the cell surface as well as at the...
and endophilin, proteins involved in clathrin
Clathrin
Clathrin is a protein that plays a major role in the formation of coated vesicles. Clathrin was first isolated and named by Barbara Pearse in 1975. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When the triskelia interact they form a polyhedral lattice...
-mediated endocytosis
Endocytosis
Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...
, and facilitates the removal of AMPA receptors from the plasma membrane. Consistent with this, increased Arc levels reduce AMPA currents, while Arc KOs display increases in surface AMPA expression.
Database Information
- Mitocheck database http://www.mitocheck.org/cgi-bin/mtc?query=MCG_0007741&query_type=genes with video data http://www.mitocheck.org/cgi-bin/mtc?action=list_movies;query=MCO_0019700 on mitosis in Arc-silenced human cells.- Ensembl Arc gene information http://uswest.ensembl.org/Homo_sapiens/Gene/Summary?db=core;g=ENSG00000198576.
- Arc gene in Mus musculus http://www.informatics.jax.org/searches/accession_report.cgi?id=MGI:88067.