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Solute carrier family 6 (neurotransmitter transporter, dopamine), member 3
Identifiers
Symbols SLC6A3; DAT; DAT1
External IDs OMIM126455 MGI94862 HomoloGene55547 GeneCards: SLC6A3 Gene
RNA expression pattern
PBB GE SLC6A3 206836 at tn.png
More reference expression data
Orthologs
Species Human Mouse
Entrez 6531 13162
Ensembl ENSG00000142319 ENSMUSG00000021609
UniProt Q01959 Q3UVW5
RefSeq (mRNA) NM_001044 NM_010020
RefSeq (protein) NP_001035 NP_034150
Location (UCSC) Chr 5:
1.45 - 1.5 Mb
Chr 13:
74 - 74.04 Mb
PubMed search [1] [2]

The dopamine transporter (also dopamine active transporter, DAT, SLC6A3) is a membrane-spanning protein that binds the neurotransmitter dopamine; DAT provides the primary mechanism through which dopamine is cleared from synapses, transporting dopamine from the synapse into a neuron. DAT is present in the peri-synaptic area of dopaminergic neurons in areas of the brain where dopamine signaling is common. DAT is implicated in a number of dopamine-related disorders, including attention deficit hyperactivity disorder, bipolar disorder, clinical depression, and alcoholism. The gene that encodes the DAT protein is located on human chromosome 5, consists of 15 coding exons, and is roughly 64 kbp long. Evidence for the associations between DAT and dopamine related disorders has come from a genetic polymorphism in the DAT gene, which influences the amount of protein expressed.

Contents

Function

DAT is an integral membrane protein that removes dopamine from the synaptic cleft and deposits it into surrounding cells, thus terminating the signal of the neurotransmitter. Dopamine underlies several aspects of cognition, including reward, and DAT facilitates regulation of that signal.[1]

Mechanism

DAT is a symporter that moves dopamine across the cell membrane by coupling the movement to the energetically-favorable movement of sodium ions moving from high to low concentration into the cell. DAT function requires the sequential binding and co-transport of two Na+ ions and one Cl- ion with the dopamine substrate. The driving force for DAT-mediated dopamine reuptake is the ion concentration gradient generated by the plasma membrane Na+/K+ ATPase.[2]

In the most widely-accepted model for monoamine transporter function, sodium ions must bind to the extracellular domain of the transporter before dopamine can bind. Once dopamine binds, the protein undergoes a conformational change, which allows both sodium and dopamine to unbind on the intracellular side of the membrane.[3]

Studies using electrophysiology and radioactive-labeled dopamine have confirmed that the dopamine transporter is similar to other monoamine transporters in that one molecule of neurotransmitter can be transported across the membrane with one or two sodium ions. Chloride ions are also needed to prevent a buildup of positive charge. These studies have also shown that transport rate and direction is totally dependent on the sodium gradient.[4]

Because of the tight coupling of the membrane potential and the sodium gradient, activity-induced changes in membrane polarity can dramatically influence transport rates. In addition, the transporter may contribute to dopamine release when the neuron depolarizes.[4]

Protein Structure

The initial determination of the membrane topology of DAT was based upon hydrophobic sequence analysis and sequence similarities with the GABA transporter. These methods predicted twelve transmembrane domains (TMD) with a large extracellular loop between the third and fourth TMDs.[5] Further characterization of this protein used proteases, which digest proteins into smaller fragments, and glycosylation, which occurs only on extracellular loops, and largely verified the initial predictions of membrane topology.[6]

Location and distribution

Regional distribution of DAT has been found in areas of the brain with established dopaminergic circuitry including: mesostriatal, mesolimbic, and mesocortical pathways.[7] The nuclei that make up these pathways have distinct patterns of expression.

DAT in the mesocortical pathway, labeled with radioactive antibodies, was found to be enriched in dendrites and cell bodies of neurons in the substantia nigra pars compacta and ventral tegmental area. This pattern makes sense for a protein that regulates dopamine levels in the synapse.

Staining in the striatum and nucleus accumbens of the mesolimbic pathway was dense and heterogeneous. In the striatum, DAT is localized in the plasma membrane of axon terminals. Double immunocytochemistry demonstrated DAT colocalization with two other markers of nigrostriatal terminals, tyrosine hydroxylase and D2 dopamine receptors. The latter was thus demonstrated to be an autoreceptor on cells that release dopamine.

Surprisingly, DAT was not identified within any synaptic active zones. These results suggest that striatal dopamine reuptake may occur outside of synaptic specializations once dopamine diffuses from the synaptic cleft.

In the substantia nigra, DAT appears to be specifically transported into dendrites, where it can be found in smooth endoplasmic reticulum, plasma membrane, and pre- and postsynaptic active zones. These localizations suggest that DAT modulates the intracellular and extracellular dopamine levels of nigral dendrites.

Within the perikarya of pars compacta neurons, DAT was localized primarily to rough and smooth endoplasmic reticulum, Golgi complex, and multivesicular bodies, identifying probable sites of synthesis, modification, transport, and degradation.[8]

Genetics and regulation

The gene for DAT is located on chromosome 5p15.[9] The protein encoding region of the gene is over 64 kb long and comprises 15 coding segments or exons.[10] This gene has a variable number tandem repeat (VNTR) at the 3’ end (rs28363170).[11] Differences in the VNTR have been shown to affect the basal level of expression of the transporter; consequentially, researchers have looked for associations with dopamine related disorders.[12]

Nurr1, a nuclear receptor that regulates many dopamine related genes, can bind the promoter region of this gene and induce expression.[13] This promoter may also be the target of the transcription factor Sp-1.

While transcription factors control which cells express DAT, functional regulation of this protein is largely accomplished by kinases. Both MAPK[14] and PKC[15] can modulate the rate at which the transporter moves dopamine or cause the internalization of DAT.

Biological role and disorders

The rate at which DAT removes dopamine from the synapse can have a profound effect on the amount of dopamine in the cell. This is best evidenced by the severe cognitive deficits, motor abnormalities, and hyperactivity of mice with no dopamine transporters.[16] These characteristics have striking similarities to the symptoms of ADHD.

Differences in the functional VNTR have been identified as risk factors for bipolar disorder[17] and ADHD.[18] Data has emerged that suggests there is also an association with stronger withdrawal symptoms from alcoholism, although this is a point of controversy.[19][20] Interestingly, an allele of the DAT gene with normal protein levels is associated with non-smoking behavior and ease of quitting.[21] Additionally, male adolescents particularly those in high-risk families (ones marked by a disengaged mother and absence of maternal affection) who carry the 10-allele VNTR repeat show a statistically significant affinity for antisocial peers[22].

Increased activity of DAT is associated with several different disorders, including clinical depression.[23] Decreasing levels of DAT expression are associated with aging, and likely underlie a compensatory mechanism for the decreases in dopamine release as a person ages.[24]

Pharmacology

Mechanisms of Cocaine and Amphetamine DAT blocking

DAT is also the target of several “DAT-blockers” including amphetamines and cocaine. These chemicals inhibit the action of DAT and, to a lesser extent, the other monoamine transporters, but their effects are mediated by separate mechanisms.

Cocaine blocks DAT by binding directly to the transporter and reducing the rate of transport.[5] In contrast, amphetamines trigger a signal cascade thought to involve PKC or MAPK that leads to the internalization of DAT molecules, which are normally expressed on the neuron’s surface.[25]

Both of these mechanisms result in less removal of dopamine from the synapse and increased signaling, which is thought to underlie the pleasurable feelings elicited by these substances.[1]

Interactions

Dopamine transporter has been shown to interact with TGFB1I1,[26] PICK1[27] and Alpha-synuclein.[28][29]

See also

References

  1. ^ a b Schultz W (1998). "Predictive reward signal of dopamine neurons". J. Neurophysiol. 80 (1): 1–27. PMID 9658025.  
  2. ^ Torres GE, Gainetdinov RR, Caron MG (2003). "Plasma membrane monoamine transporters: structure, regulation and function". Nat. Rev. Neurosci. 4 (1): 13–25. doi:10.1038/nrn1008. PMID 12511858.  
  3. ^ Sonders MS, Zhu SJ, Zahniser NR, Kavanaugh MP, Amara SG (1997). "Multiple ionic conductances of the human dopamine transporter: the actions of dopamine and psychostimulants". J. Neurosci. 17 (3): 960–74. PMID 8994051.  
  4. ^ a b Wheeler DD, Edwards AM, Chapman BM, Ondo JG (1993). "A model of the sodium dependence of dopamine uptake in rat striatal synaptosomes". Neurochem. Res. 18 (8): 927–36. doi:10.1007/BF00998279. PMID 8371835.  
  5. ^ a b Kilty JE, Lorang D, Amara SG (1991). "Cloning and expression of a cocaine-sensitive rat dopamine transporter". Science 254 (5031): 578–9. doi:10.1126/science.1948035. PMID 1948035.  
  6. ^ Vaughan RA, Kuhar MJ (1996). "Dopamine transporter ligand binding domains. Structural and functional properties revealed by limited proteolysis". J. Biol. Chem. 271 (35): 21672–80. doi:10.1074/jbc.271.35.21672. PMID 8702957.  
  7. ^ Ciliax BJ, Drash GW, Staley JK, et al. (1999). "Immunocytochemical localization of the dopamine transporter in human brain". J. Comp. Neurol. 409 (1): 38–56. doi:10.1002/(SICI)1096-9861(19990621)409:1<38::AID-CNE4>3.0.CO;2-1. PMID 10363710.  
  8. ^ Hersch SM, Yi H, Heilman CJ, Edwards RH, Levey AI (1997). "Subcellular localization and molecular topology of the dopamine transporter in the striatum and substantia nigra". J. Comp. Neurol. 388 (2): 211–27. doi:10.1002/(SICI)1096-9861(19971117)388:2<211::AID-CNE3>3.0.CO;2-4. PMID 9368838.  
  9. ^ Vandenbergh DJ, Persico AM, Hawkins AL, et al. (1992). "Human dopamine transporter gene (DAT1) maps to chromosome 5p15.3 and displays a VNTR". Genomics 14 (4): 1104–6. doi:10.1016/S0888-7543(05)80138-7. PMID 1478653.  
  10. ^ Kawarai T, Kawakami H, Yamamura Y, Nakamura S (1997). "Structure and organization of the gene encoding human dopamine transporter". Gene 195 (1): 11–8. doi:10.1016/S0378-1119(97)00131-5. PMID 9300814.  
  11. ^ Sano A, Kondoh K, Kakimoto Y, Kondo I (May 1993). "A 40-nucleotide repeat polymorphism in the human dopamine transporter gene". Human Genetics 91 (4): 405–406. doi:10.1007/BF00217369. PMID 8500798.  
  12. ^ Miller GM, Madras BK (2002). "Polymorphisms in the 3'-untranslated region of human and monkey dopamine transporter genes affect reporter gene expression". Mol. Psychiatry 7 (1): 44–55. doi:10.1038/sj/mp/4000921. PMID 11803445.  
  13. ^ Sacchetti P, Mitchell TR, Granneman JG, Bannon MJ (2001). "Nurr1 enhances transcription of the human dopamine transporter gene through a novel mechanism". J. Neurochem. 76 (5): 1565–72. doi:10.1046/j.1471-4159.2001.00181.x. PMID 11238740.  
  14. ^ Morón JA, Zakharova I, Ferrer JV, et al. (2003). "Mitogen-activated protein kinase regulates dopamine transporter surface expression and dopamine transport capacity". J. Neurosci. 23 (24): 8480–8. PMID 13679416.  
  15. ^ Pristupa ZB, McConkey F, Liu F, et al. (1998). "Protein kinase-mediated bidirectional trafficking and functional regulation of the human dopamine transporter". Synapse 30 (1): 79–87. doi:10.1002/(SICI)1098-2396(199809)30:1<79::AID-SYN10>3.0.CO;2-K. PMID 9704884.  
  16. ^ Gainetdinov RR, Wetsel WC, Jones SR, Levin ED, Jaber M, Caron MG (1999). "Role of serotonin in the paradoxical calming effect of psychostimulants on hyperactivity". Science 283 (5400): 397–401. doi:10.1126/science.283.5400.397. PMID 9888856.  
  17. ^ Greenwood TA, Alexander M, Keck PE, et al. (2001). "Evidence for linkage disequilibrium between the dopamine transporter and bipolar disorder". Am. J. Med. Genet. 105 (2): 145–51. doi:10.1002/1096-8628(2001)9999:9999<::AID-AJMG1161>3.0.CO;2-8. PMID 11304827.  
  18. ^ Yang B, Chan RC, Jing J, Li T, Sham P, Chen RY (2007). "A meta-analysis of association studies between the 10-repeat allele of a VNTR polymorphism in the 3'-UTR of dopamine transporter gene and attention deficit hyperactivity disorder". Am. J. Med. Genet. B Neuropsychiatr. Genet. 144 (4): 541–50. doi:10.1002/ajmg.b.30453. PMID 17440978.  
  19. ^ Sander T, Harms H, Podschus J, et al. (1997). "Allelic association of a dopamine transporter gene polymorphism in alcohol dependence with withdrawal seizures or delirium". Biol. Psychiatry 41 (3): 299–304. doi:10.1016/S0006-3223(96)00044-3. PMID 9024952.  
  20. ^ Ueno S, Nakamura M, Mikami M, et al. (1999). "Identification of a novel polymorphism of the human dopamine transporter (DAT1) gene and the significant association with alcoholism". Mol. Psychiatry 4 (6): 552–7. doi:10.1038/sj.mp.4000562. PMID 10578237.  
  21. ^ Ueno S (2003). "Genetic polymorphisms of serotonin and dopamine transporters in mental disorders". J. Med. Invest. 50 (1-2): 25–31. PMID 12630565.  
  22. ^ Beaver, Kevin M.; John Paul Wright, Matt DeLisi (2001). "Delinquent peer group formation: evidence of a gene x environment correlation.". The Journal of Genetic Psychology 169 (3): 227–44. doi:10.3200/GNTP.169.3.227-244. PMID 18788325.  
  23. ^ Laasonen-Balk T, Kuikka J, Viinamäki H, Husso-Saastamoinen M, Lehtonen J, Tiihonen J (1999). "Striatal dopamine transporter density in major depression". Psychopharmacology (Berl.) 144 (3): 282–5. doi:10.1007/s002130051005. PMID 10435396.  
  24. ^ Bannon MJ, Poosch MS, Xia Y, Goebel DJ, Cassin B, Kapatos G (1992). "Dopamine transporter mRNA content in human substantia nigra decreases precipitously with age". Proc. Natl. Acad. Sci. U.S.A. 89 (15): 7095–9. doi:10.1073/pnas.89.15.7095. PMID 1353885.  
  25. ^ Kahlig KM, Javitch JA, Galli A (2004). "Amphetamine regulation of dopamine transport. Combined measurements of transporter currents and transporter imaging support the endocytosis of an active carrier". J. Biol. Chem. 279 (10): 8966–75. doi:10.1074/jbc.M303976200. PMID 14699142.  
  26. ^ Carneiro, Ana M; Ingram Susan L, Beaulieu Jean-Martin, Sweeney Ava, Amara Susan G, Thomas Sheila M, Caron Marc G, Torres Gonzalo E (Aug. 2002). "The multiple LIM domain-containing adaptor protein Hic-5 synaptically colocalizes and interacts with the dopamine transporter". J. Neurosci. (United States) 22 (16): 7045–54. doi:20026740. PMID 12177201.  
  27. ^ Torres, G E; Yao W D, Mohn A R, Quan H, Kim K M, Levey A I, Staudinger J, Caron M G (Apr. 2001). "Functional interaction between monoamine plasma membrane transporters and the synaptic PDZ domain-containing protein PICK1". Neuron (United States) 30 (1): 121–34. ISSN 0896-6273. PMID 11343649.  
  28. ^ Wersinger, Christophe; Sidhu Anita (Apr. 2003). "Attenuation of dopamine transporter activity by alpha-synuclein". Neurosci. Lett. (Ireland) 340 (3): 189–92. ISSN 0304-3940. PMID 12672538.  
  29. ^ Lee, F J; Liu F, Pristupa Z B, Niznik H B (Apr. 2001). "Direct binding and functional coupling of alpha-synuclein to the dopamine transporters accelerate dopamine-induced apoptosis". FASEB J. (United States) 15 (6): 916–26. ISSN 0892-6638. PMID 11292651.  

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