Activity-regulated cytoskeleton-associated protein is a plasticityprotein that in humans is encoded by the ARCgene. It was first characterized in 1995.[1][2] 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 inhibitors. Arc mRNA is localized to activated synaptic sites in an NMDA receptor-dependent manner,[3][4] where the newly translated protein is believed to play a critical role in learning and memory-related molecular processes.[5] 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. Dysfunctions in the production of Arc protein has been implicated as an important factor in understanding of various neurological conditions including amnesia,[6]Alzheimer's disease, Autism spectrum disorders, and Fragile X syndrome.[7] 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[8][9] (see fluorescent in situ hybridization).
The Arc gene, located on chromosome 15 in the mouse[2], chromosome 7 in the rat[3], and chromosome 8 in the human[4] genome, is conserved across vertebrate species and has low sequence homology to spectrin,[1] 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.[10][11] a second SRE at ~6.5 kb;[11] 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.[12]
It is suspected that Arc gene originated from Ty3/gypsy retrotransposons and was repurposed for mediating neuron-neuron communication.[17]
Protein
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.[18] Additionally, the protein has binding sites for endophilin 3 and dynamin 2 at amino acids 89-100 and 195-214, respectively.[19] 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.[20] The translated protein can be visualized with an immunoblot as a band at 55 kDa. The ARC protein can form virus-like capsids that package mRNA and can traffic between cells.[21][17]
Trafficking
Following transcription, Arc mRNA is transported out of the nucleus and localized to neuronal dendrites[1] and activated synapses,[22] a process dependent on the 3' UTR,[13] polymerization of actin,[23] and ERK phosphorylation.[23] The mRNA (and aggregate protein) is carried along microtubules radiating out from the nucleus by kinesin (specifically KIF5)[24] and likely translocated into dendritic spines by the actin-based motor protein myosin-Va.[25] Arc has been shown to be associated with polyribosomes at synaptic sites,[26] and is translated in isolated synaptoneurosomal fractions[27]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.[19] Consistent with this, increased Arc levels reduce AMPA currents,[28] while Arc KOs display increases in surface AMPA expression.[29]
Knockouts
Arc is critical as a ubiquitous signaling factor in early embryonic development and is required for growth and patterning during gastrulation.[30] 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.[31]
Signalling
The Arc transcript is dependent upon activation of the mitogen-activated protein kinase or MAP kinase (MAPK) cascade,[10] a pathway important for regulation of cell growth and survival.[32] 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),[1]nerve growth factor (NGF),[1] and brain-derived neurotrophic factor (BDNF),[14] glutamate acting at NMDA receptors,[3][4] dopamine through activation of the D1 receptor subtype,[33][34] and dihydroxyphenylglycine (DHPG).[35] 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[10][34] while H89, a PKA antagonist, blocks these effects[34] as does further downstream blockade of mitogen-activated protein kinase kinase [sic] (MEK).[10] Note that the MAPK cascade is a signaling pathway involving multiple kinases acting sequentially [MAPKKK--> MAPKK--> MAPK].
MAPK is able to enter the nucleus and perform its phosphotransferase activity on a number of gene regulatory components[36] that have implications for the regulation of immediate-early genes. Several transcription factors are known to be involved in regulating the Arc gene (see above), including serum response factor (SRF),[10][12]CREB,[12]MEF2,[12] and zif268.[37]
Behavioral effects
Changes in Arc mRNA and/or protein are correlated with a number of behavioral changes including cued fear conditioning,[38] contextual fear conditioning,[39] spatial memory,[40][41]operant conditioning,[42][43] and inhibitory avoidance.[5] The mRNA is notably upregulated following electrical stimulation in LTP-induction procedures such as high frequency stimulation (HFS),[40] and is massively and globally induced by maximal electroconvulsive shock (MECS).[1][3]
References
↑ 1.01.11.21.31.41.5Lyford GL, Yamagata K, Kaufmann WE, Barnes CA, Sanders LK, Copeland NG, et al. (1995). "Arc, a growth factor and activity-regulated gene, encodes a novel cytoskeleton-associated protein that is enriched in neuronal dendrites". Neuron. 14 (2): 433–45. doi:10.1016/0896-6273(95)90299-6. PMID7857651.
↑ 3.03.13.2Wallace CS, Lyford GL, Worley PF, Steward O (1998). "Differential intracellular sorting of immediate early gene mRNAs depends on signals in the mRNA sequence". The Journal of Neuroscience. 18 (1): 26–35. PMID9412483.
↑ 4.04.1Steward O, Worley PF (2001). "Selective targeting of newly synthesized Arc mRNA to active synapses requires NMDA receptor activation". Neuron. 30 (1): 227–40. PMID11343657.
↑Gautam A, Wadhwa R, Thakur MK (2013). "Involvement of hippocampal Arc in amnesia and its recovery by alcoholic extract of Ashwagandha leaves". Neurobiology of Learning and Memory. 106: 177–84. doi:10.1016/j.nlm.2013.08.009. PMID24012642.
↑ 13.013.1Kobayashi H, Yamamoto S, Maruo T, Murakami F (2005). "Identification of a cis-acting element required for dendritic targeting of activity-regulated cytoskeleton-associated protein mRNA". The European Journal of Neuroscience. 22 (12): 2977–84. doi:10.1111/j.1460-9568.2005.04508.x. PMID16367764.
↑ 14.014.1Giorgi C, Yeo GW, Stone ME, Katz DB, Burge C, Turrigiano G, Moore MJ (2007). "The EJC factor eIF4AIII modulates synaptic strength and neuronal protein expression". Cell. 130 (1): 179–91. doi:10.1016/j.cell.2007.05.028. PMID17632064.
↑Tange TØ, Nott A, Moore MJ (2004). "The ever-increasing complexities of the exon junction complex". Current Opinion in Cell Biology. 16 (3): 279–84. doi:10.1016/j.ceb.2004.03.012. PMID15145352.
↑Rao VR, Pintchovski SA, Chin J, Peebles CL, Mitra S, Finkbeiner S (2006). "AMPA receptors regulate transcription of the plasticity-related immediate-early gene Arc". Nature Neuroscience. 9 (7): 887–95. doi:10.1038/nn1708. PMID16732277.
↑Ashley J, Cordy B, Lucia D, Fradkin LG, Budnik V, Thomson T (2018). "Retrovirus-like Gag Protein Arc1 Binds RNA and Traffics across Synaptic Boutons". Cell. 172 (1–2): 262–274.e11. doi:10.1016/j.cell.2017.12.022. PMID29328915.
↑Steward O, Wallace CS, Lyford GL, Worley PF (1998). "Synaptic activation causes the mRNA for the IEG Arc to localize selectively near activated postsynaptic sites on dendrites". Neuron. 21 (4): 741–51. doi:10.1016/S0896-6273(00)80591-7. PMID9808461.
↑ 23.023.1Huang F, Chotiner JK, Steward O (2007). "Actin polymerization and ERK phosphorylation are required for Arc/Arg3.1 mRNA targeting to activated synaptic sites on dendrites". The Journal of Neuroscience. 27 (34): 9054–67. doi:10.1523/JNEUROSCI.2410-07.2007. PMID17715342.
↑Kanai Y, Dohmae N, Hirokawa N (2004). "Kinesin transports RNA: isolation and characterization of an RNA-transporting granule". Neuron. 43 (4): 513–25. doi:10.1016/j.neuron.2004.07.022. PMID15312650.
↑Yoshimura A, Fujii R, Watanabe Y, Okabe S, Fukui K, Takumi T (2006). "Myosin-Va facilitates the accumulation of mRNA/protein complex in dendritic spines". Current Biology. 16 (23): 2345–51. doi:10.1016/j.cub.2006.10.024. PMID17141617.
↑Bagni C, Mannucci L, Dotti CG, Amaldi F (2000). "Chemical stimulation of synaptosomes modulates alpha -Ca2+/calmodulin-dependent protein kinase II mRNA association to polysomes". The Journal of Neuroscience. 20 (10): RC76. PMID10783400.
↑Liu D, Bei D, Parmar H, Matus A (2000). "Activity-regulated, cytoskeleton-associated protein (Arc) is essential for visceral endoderm organization during early embryogenesis". Mechanisms of Development. 92 (2): 207–15. PMID10727859.
↑Plath N, Ohana O, Dammermann B, Errington ML, Schmitz D, Gross C, et al. (2006). "Arc/Arg3.1 is essential for the consolidation of synaptic plasticity and memories". Neuron. 52 (3): 437–44. doi:10.1016/j.neuron.2006.08.024. PMID17088210.
↑Impey S, Obrietan K, Storm DR (1999). "Making new connections: role of ERK/MAP kinase signaling in neuronal plasticity". Neuron. 23 (1): 11–4. PMID10402188.
↑Granado N, Ortiz O, Suárez LM, Martín ED, Ceña V, Solís JM, Moratalla R (2008). "D1 but not D5 dopamine receptors are critical for LTP, spatial learning, and LTP-Induced arc and zif268 expression in the hippocampus". Cerebral Cortex. 18 (1): 1–12. doi:10.1093/cercor/bhm026. PMID17395606.
↑ 34.034.134.2Bloomer WA, VanDongen HM, VanDongen AM (2008). "Arc/Arg3.1 translation is controlled by convergent N-methyl-D-aspartate and Gs-coupled receptor signaling pathways". The Journal of Biological Chemistry. 283 (1): 582–92. doi:10.1074/jbc.M702451200. PMID17981809.
↑Brackmann M, Zhao C, Kuhl D, Manahan-Vaughan D, Braunewell KH (2004). "MGluRs regulate the expression of neuronal calcium sensor proteins NCS-1 and VILIP-1 and the immediate early gene arg3.1/arc in the hippocampus in vivo". Biochemical and Biophysical Research Communications. 322 (3): 1073–9. doi:10.1016/j.bbrc.2004.08.028. PMID15336574.
↑Treisman R (1996). "Regulation of transcription by MAP kinase cascades". Current Opinion in Cell Biology. 8 (2): 205–15. PMID8791420.
↑Monti B, Berteotti C, Contestabile A (2006). "Subchronic rolipram delivery activates hippocampal CREB and arc, enhances retention and slows down extinction of conditioned fear". Neuropsychopharmacology. 31 (2): 278–86. doi:10.1038/sj.npp.1300813. PMID15988467.
↑Huff NC, Frank M, Wright-Hardesty K, Sprunger D, Matus-Amat P, Higgins E, Rudy JW (2006). "Amygdala regulation of immediate-early gene expression in the hippocampus induced by contextual fear conditioning". The Journal of Neuroscience. 26 (5): 1616–23. doi:10.1523/JNEUROSCI.4964-05.2006. PMID16452685.
↑ 40.040.1Guzowski JF, Lyford GL, Stevenson GD, Houston FP, McGaugh JL, Worley PF, Barnes CA (2000). "Inhibition of activity-dependent arc protein expression in the rat hippocampus impairs the maintenance of long-term potentiation and the consolidation of long-term memory". The Journal of Neuroscience. 20 (11): 3993–4001. PMID10818134.
↑Guzowski JF, Setlow B, Wagner EK, McGaugh JL (2001). "Experience-dependent gene expression in the rat hippocampus after spatial learning: a comparison of the immediate-early genes Arc, c-fos, and zif268". The Journal of Neuroscience. 21 (14): 5089–98. PMID11438584.
↑Kelly MP, Deadwyler SA (2002). "Acquisition of a novel behavior induces higher levels of Arc mRNA than does overtrained performance". Neuroscience. 110 (4): 617–26. PMID11934470.
↑Kelly MP, Deadwyler SA (2003). "Experience-dependent regulation of the immediate-early gene arc differs across brain regions". The Journal of Neuroscience. 23 (16): 6443–51. PMID12878684.