Biology:Activity-regulated cytoskeleton-associated protein

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Activity-regulated cytoskeleton-associated protein is a plasticity protein that in humans is encoded by the ARC gene. The gene is believed to derive from a retrotransposon.[1] The protein is found in the neurons of tetrapods and other animals where it can form virus-like capsids that transport RNA between neurons.[1]

ARC mRNA is localized to activated synaptic sites in an NMDA receptor-dependent manner,[2][3] where the newly translated protein is believed to play a critical role in learning and memory-related molecular processes.[4] Arc protein is widely considered to be important in neurobiology because of its activity regulation, localization, and utility as a marker for plastic changes in the brain. Dysfunction in the production of Arc protein has been implicated as an important factor in understanding various neurological conditions, including amnesia,[5] Alzheimer's disease, Autism spectrum disorders, and Fragile X syndrome.[6]

ARC was first characterized in 1995[7][8] and 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. Along with other IEGs such as ZNF268 and HOMER1, ARC is 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[9][10] (see fluorescent in situ hybridization).

Gene

The ARC gene, located on chromosome 15 in the mouse,[11] chromosome 7 in the rat,[12] and chromosome 8 in the human,[13] is conserved across vertebrate species and has low sequence homology to spectrin,[7] 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.[14][15] a second SRE at ~6.5 kb;[15] 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.[16]

The 3' UTR of the mRNA contains a cis-acting element required for the localization of Arc to neuronal dendrites,[17] as well as sites for two exon junction complexes (EJCs)[18] that make Arc a natural target for nonsense mediated decay (NMD).[19] Also important for translocation of cytoplasmic Arc mRNA to activated synapses is an 11 nucleotide binding site for heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2).[20]

It is suspected that the ARC gene originated from the gag gene of a Ty3/gypsy retrotransposon and was repurposed for mediating neuron-neuron communication.[1]

Trafficking

Following transcription, Arc mRNA is transported out of the nucleus and localized to neuronal dendrites[7] and activated synapses,[21] a process dependent on the 3' UTR,[17] polymerization of actin,[22] and ERK phosphorylation.[22] The mRNA (and aggregate protein) is carried along microtubules radiating out from the nucleus by kinesin (specifically KIF5)[23] and likely translocated into dendritic spines by the actin-based motor protein myosin-Va.[24] Arc has been shown to be associated with polyribosomes at synaptic sites,[25] and is translated in isolated synaptoneurosomal fractions in vitro[26] indicating that the protein is likely locally translated in vivo.

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.[27] Additionally, the protein has binding sites for endophilin 3 and dynamin 2 at amino acids 89-100 and 195-214, respectively.[28] 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.[29] 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.[30][1]

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.[28] Consistent with this, increased Arc levels reduce AMPA currents,[31] while Arc KOs display increases in surface AMPA expression.[32]

Knockouts

Arc is critical as a ubiquitous signaling factor in early embryonic development and is required for growth and patterning during gastrulation.[33] 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.[34]

Signaling

The Arc transcript is dependent upon activation of the mitogen-activated protein kinase or MAP kinase (MAPK) cascade,[14] a pathway important for regulation of cell growth and survival.[35] 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),[7] nerve growth factor (NGF),[7] and brain-derived neurotrophic factor (BDNF),[18] glutamate acting at NMDA receptors,[2][3] dopamine through activation of the D1 receptor subtype,[36][37] and dihydroxyphenylglycine (DHPG).[38] 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[14][37] while H89, a PKA antagonist, blocks these effects[37] as does further downstream blockade of mitogen-activated protein kinase kinase [sic] (MEK).[14] 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[39] 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),[14][16] CREB,[16] MEF2,[16] and zif268.[40]

Behavioral effects

Changes in Arc mRNA and/or protein are correlated with a number of behavioral changes including cued fear conditioning,[41] contextual fear conditioning,[42] spatial memory,[43][44] operant conditioning,[45][46] and inhibitory avoidance.[4] The mRNA is notably upregulated following electrical stimulation in LTP-induction procedures such as high frequency stimulation (HFS),[43] and is massively and globally induced by maximal electroconvulsive shock (MECS).[7][2]

Arc in insects

It has been found that Arc may have been acquired by animals more than once. While Arc seems to be closely related among all tetrapods, the versions of Arc found in fruit flies (Drosophila melanogaster), silkworms (Bombyx mori), and Argentine ants (Linepithema humile) may have been transferred to a common ancestor of these insects by another event.[47][48][49]

References

  1. ↑ 1.0 1.1 1.2 1.3 "The Neuronal Gene Arc Encodes a Repurposed Retrotransposon Gag Protein that Mediates Intercellular RNA Transfer" (in en). Cell 172 (1–2): 275–288.e18. 2018-01-11. doi:10.1016/j.cell.2017.12.024. ISSN 0092-8674. PMID 29570995. 
  2. ↑ 2.0 2.1 2.2 "Differential intracellular sorting of immediate early gene mRNAs depends on signals in the mRNA sequence". The Journal of Neuroscience 18 (1): 26–35. 1998. doi:10.1523/jneurosci.18-01-00026.1998. PMID 9412483. 
  3. ↑ 3.0 3.1 "Selective targeting of newly synthesized Arc mRNA to active synapses requires NMDA receptor activation". Neuron 30 (1): 227–40. 2001. doi:10.1016/s0896-6273(01)00275-6. PMID 11343657. 
  4. ↑ 4.0 4.1 "Memory-influencing intra-basolateral amygdala drug infusions modulate expression of Arc protein in the hippocampus". Proceedings of the National Academy of Sciences of the United States of America 102 (30): 10718–23. 2005. doi:10.1073/pnas.0504436102. PMID 16020527. Bibcode: 2005PNAS..10210718M. 
  5. ↑ "Involvement of hippocampal Arc in amnesia and its recovery by alcoholic extract of Ashwagandha leaves". Neurobiology of Learning and Memory 106: 177–84. 2013. doi:10.1016/j.nlm.2013.08.009. PMID 24012642. 
  6. ↑ "Arc protein 'could be key to memory loss', says study". BBC News Online. 2013-06-09. https://www.bbc.co.uk/news/health-22811691. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 "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. 1995. doi:10.1016/0896-6273(95)90299-6. PMID 7857651. 
  8. ↑ "Environment-specific expression of the immediate-early gene Arc in hippocampal neuronal ensembles". Nature Neuroscience 2 (12): 1120–4. 1999. doi:10.1038/16046. PMID 10570490. 
  9. ↑ "Experience-dependent coincident expression of the effector immediate-early genes arc and Homer 1a in hippocampal and neocortical neuronal networks". The Journal of Neuroscience 22 (23): 10067–71. 2002. doi:10.1523/JNEUROSCI.22-23-10067.2002. PMID 12451105. 
  10. ↑ "Gene: Arc (ENSMUSG00000022602) - Summary - Mus musculus - Ensembl genome browser 100". http://www.ensembl.org/Mus_musculus/Gene/Summary?g=ENSMUSG00000022602. 
  11. ↑ "Gene: Arc (ENSRNOG00000043465) - Summary - Rattus norvegicus - Ensembl genome browser 100". http://www.ensembl.org/Rattus_norvegicus/Gene/Summary?g=ENSRNOG00000043465. 
  12. ↑ "Gene: ARC (ENSG00000198576) - Summary - Homo sapiens - Ensembl genome browser 100". http://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000198576. 
  13. ↑ 14.0 14.1 14.2 14.3 14.4 "Arg3.1/Arc mRNA induction by Ca2+ and cAMP requires protein kinase A and mitogen-activated protein kinase/extracellular regulated kinase activation". The Journal of Neuroscience 21 (15): 5484–93. 2001. doi:10.1523/jneurosci.21-15-05484.2001. PMID 11466419. 
  14. ↑ 15.0 15.1 "The serum response factor and a putative novel transcription factor regulate expression of the immediate-early gene Arc/Arg3.1 in neurons". The Journal of Neuroscience 29 (5): 1525–37. 2009. doi:10.1523/JNEUROSCI.5575-08.2009. PMID 19193899. 
  15. ↑ 16.0 16.1 16.2 16.3 "Synaptic activity-responsive element in the Arc/Arg3.1 promoter essential for synapse-to-nucleus signaling in activated neurons". Proceedings of the National Academy of Sciences of the United States of America 106 (1): 316–21. 2009. doi:10.1073/pnas.0806518106. PMID 19116276. Bibcode: 2009PNAS..106..316K. 
  16. ↑ 17.0 17.1 "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. 2005. doi:10.1111/j.1460-9568.2005.04508.x. PMID 16367764. 
  17. ↑ 18.0 18.1 "The EJC factor eIF4AIII modulates synaptic strength and neuronal protein expression". Cell 130 (1): 179–91. 2007. doi:10.1016/j.cell.2007.05.028. PMID 17632064. 
  18. ↑ "The ever-increasing complexities of the exon junction complex". Current Opinion in Cell Biology 16 (3): 279–84. 2004. doi:10.1016/j.ceb.2004.03.012. PMID 15145352. 
  19. ↑ "Multiplexed dendritic targeting of alpha calcium calmodulin-dependent protein kinase II, neurogranin, and activity-regulated cytoskeleton-associated protein RNAs by the A2 pathway". Molecular Biology of the Cell 19 (5): 2311–27. 2008. doi:10.1091/mbc.E07-09-0914. PMID 18305102. 
  20. ↑ "Synaptic activation causes the mRNA for the IEG Arc to localize selectively near activated postsynaptic sites on dendrites". Neuron 21 (4): 741–51. 1998. doi:10.1016/S0896-6273(00)80591-7. PMID 9808461. 
  21. ↑ 22.0 22.1 "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. 2007. doi:10.1523/JNEUROSCI.2410-07.2007. PMID 17715342. 
  22. ↑ "Kinesin transports RNA: isolation and characterization of an RNA-transporting granule". Neuron 43 (4): 513–25. 2004. doi:10.1016/j.neuron.2004.07.022. PMID 15312650. 
  23. ↑ "Myosin-Va facilitates the accumulation of mRNA/protein complex in dendritic spines". Current Biology 16 (23): 2345–51. 2006. doi:10.1016/j.cub.2006.10.024. PMID 17141617. 
  24. ↑ "Chemical stimulation of synaptosomes modulates alpha -Ca2+/calmodulin-dependent protein kinase II mRNA association to polysomes". The Journal of Neuroscience 20 (10): RC76. 2000. doi:10.1523/jneurosci.20-10-j0004.2000. PMID 10783400. 
  25. ↑ "The brain-derived neurotrophic factor enhances synthesis of Arc in synaptoneurosomes". Proceedings of the National Academy of Sciences of the United States of America 99 (4): 2368–73. 2002. doi:10.1073/pnas.042693699. PMID 11842217. Bibcode: 2002PNAS...99.2368Y. 
  26. ↑ "Activity-regulated cytoskeleton-associated protein Arc/Arg3.1 binds to spectrin and associates with nuclear promyelocytic leukemia (PML) bodies". Brain Research 1153: 20–33. 2007. doi:10.1016/j.brainres.2007.03.079. PMID 17466953. 
  27. ↑ 28.0 28.1 "Arc/Arg3.1 interacts with the endocytic machinery to regulate AMPA receptor trafficking". Neuron 52 (3): 445–59. 2006. doi:10.1016/j.neuron.2006.08.033. PMID 17088211. 
  28. ↑ "AMPA receptors regulate transcription of the plasticity-related immediate-early gene Arc". Nature Neuroscience 9 (7): 887–95. 2006. doi:10.1038/nn1708. PMID 16732277. 
  29. ↑ "Retrovirus-like Gag Protein Arc1 Binds RNA and Traffics across Synaptic Boutons". Cell 172 (1–2): 262–274.e11. 2018. doi:10.1016/j.cell.2017.12.022. PMID 29328915. 
  30. ↑ "Increased expression of the immediate-early gene arc/arg3.1 reduces AMPA receptor-mediated synaptic transmission". Neuron 52 (3): 461–74. 2006. doi:10.1016/j.neuron.2006.09.031. PMID 17088212. 
  31. ↑ "Arc/Arg3.1 mediates homeostatic synaptic scaling of AMPA receptors". Neuron 52 (3): 475–84. 2006. doi:10.1016/j.neuron.2006.08.034. PMID 17088213. 
  32. ↑ "Activity-regulated, cytoskeleton-associated protein (Arc) is essential for visceral endoderm organization during early embryogenesis". Mechanisms of Development 92 (2): 207–15. 2000. doi:10.1016/s0925-4773(99)00340-8. PMID 10727859. 
  33. ↑ "Arc/Arg3.1 is essential for the consolidation of synaptic plasticity and memories". Neuron 52 (3): 437–44. 2006. doi:10.1016/j.neuron.2006.08.024. PMID 17088210. 
  34. ↑ "Making new connections: role of ERK/MAP kinase signaling in neuronal plasticity". Neuron 23 (1): 11–4. 1999. doi:10.1016/s0896-6273(00)80747-3. PMID 10402188. 
  35. ↑ "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. 2008. doi:10.1093/cercor/bhm026. PMID 17395606. 
  36. ↑ 37.0 37.1 37.2 "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. 2008. doi:10.1074/jbc.M702451200. PMID 17981809. 
  37. ↑ "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. 2004. doi:10.1016/j.bbrc.2004.08.028. PMID 15336574. 
  38. ↑ "Regulation of transcription by MAP kinase cascades". Current Opinion in Cell Biology 8 (2): 205–15. 1996. doi:10.1016/s0955-0674(96)80067-6. PMID 8791420. 
  39. ↑ "The neuroplasticity-associated arc gene is a direct transcriptional target of early growth response (Egr) transcription factors". Molecular and Cellular Biology 25 (23): 10286–300. 2005. doi:10.1128/MCB.25.23.10286-10300.2005. PMID 16287845. 
  40. ↑ "Subchronic rolipram delivery activates hippocampal CREB and arc, enhances retention and slows down extinction of conditioned fear". Neuropsychopharmacology 31 (2): 278–86. 2006. doi:10.1038/sj.npp.1300813. PMID 15988467. 
  41. ↑ "Amygdala regulation of immediate-early gene expression in the hippocampus induced by contextual fear conditioning". The Journal of Neuroscience 26 (5): 1616–23. 2006. doi:10.1523/JNEUROSCI.4964-05.2006. PMID 16452685. 
  42. ↑ 43.0 43.1 "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. 2000. doi:10.1523/jneurosci.20-11-03993.2000. PMID 10818134. 
  43. ↑ "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. 2001. doi:10.1523/jneurosci.21-14-05089.2001. PMID 11438584. 
  44. ↑ "Acquisition of a novel behavior induces higher levels of Arc mRNA than does overtrained performance". Neuroscience 110 (4): 617–26. 2002. doi:10.1016/s0306-4522(01)00605-4. PMID 11934470. 
  45. ↑ "Experience-dependent regulation of the immediate-early gene arc differs across brain regions". The Journal of Neuroscience 23 (16): 6443–51. 2003. doi:10.1523/jneurosci.23-16-06443.2003. PMID 12878684. 
  46. ↑ Letzter, Rafi (2 February 2018). "An Ancient Virus May Be Responsible for Human Consciousness". Live Science. https://www.livescience.com/61627-ancient-virus-brain.html. 
  47. ↑ "A Viral (Arc)hive for Metazoan Memory". Cell 172 (1–2): 8–10. January 2018. doi:10.1016/j.cell.2017.12.029. PMID 29328922. 
  48. ↑ "The Neuronal Gene Arc Encodes a Repurposed Retrotransposon Gag Protein that Mediates Intercellular RNA Transfer". Cell 172 (1–2): 275–288.e18. January 2018. doi:10.1016/j.cell.2017.12.024. PMID 29328916. 

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