Abstract
A cDNA molecule encoding a major part of the human Norepinephrine transporter(hNET) was synthesized by means of Polymerase Chain Reaction(PCR) technique and used as a probe for selecting the human genomic NET gene. A positive clone harbouring the whole gene was obtained from a human lymphocyte genomic library through utilizing the “genomic walking” technique. The clone, designated as phNET, harbours a DNA fragment of about 59 kb in length inserted into BamH I site in cosmid pWE15. The genomic clone contains 14 exons encoding all amino acid residues in the protein. A single exon encodes a distinct transmembrane domain, except for transmembrane domain 10 and 11, which are encoded by part of two exons respectively, and exon 12, which encodes part of domain 11 and all of domain 12. These results imply that there is a close relationship between exon splicing of a gene and structural domains of the protein, as is the case for the human γ-aminobutyric acid transporter(hGAT) and a number of other membrane proteins.
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Introduction
Norepinephrine(NE) is a major catecholamine neurotransmitter in the peripheral and central nervous systems1. In noradrenergic neurons, synaptic transmisslon includes three steps: release of NE into the synaptic cleft, interaction with a postsynaptic receptor, and subsequent removal of NE from the cleft into the presynaptic terminals or surrounding glial cells. This uptake process is carried out via a sodium-dependent NE transporter(NET). The NET is also apparently the initial site of action for therapeutic antidepressants and drugs such as cocaine and the amphetamines2, 3.
Over the past five years, the cDNAs for many of the known neurotransmitter transporters have been elucidated using PCR, homology screening and expression cloning techniques3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. According to their dependence on Na+/K+ or Na+/Cl−, these transporters can be divided into two families. Family I, with 6, 8 or 10 transmembrane domains, includes transporters for glutamate / aspartate4, glutamate5, certain neutral amino acids6, 7 and excitatory amino-acid carrier 18. Family II, based on the homology and other characteristics of the transport systems, can be further divided into three subfamilies: i) transporters for γ-aminobutyric acid(GABA) 9, 10, 11, 12, 13, taurine14, 15 and choline16 (enzymaticly dissolved from acetylcholine), but betaine transporter17 and creatine transporter18 can also be ineluded here, although betaine is an osmolyte and creatine is a component involved in energy exchange; ii) transporters for glycine19, 20, 21 and proline22; and iii) transporters for norepinephrine3, dopamine23, 24, 25, 26 and serotonin[27-291. All members belonging to family II have 12 constant transmembrane domains. It is noteworthy that transporters are expressed from prokaryote ie. E.coli.31 to eukaryote ie. yeast32, Drosophila29 and mammalian systems, and that the expressions of transporters during development in one species appear to be tightly programmed13.
Since neurotransmitter transporters are involved in diseases of the nervous sys- tem, drug addiction and synaptic plasticity33, 34, 35, they had been studied pharmacologically and biochemically for a long time before. In contrast, studies on the genomic structures of these transporters have been much more limited36, 37. To learn the structure, function and regulation of neurotransmitter transporters in the nervous system, we cloned and analyzed genomic NET gene. The result of this study indicated the unique characters of the biogenic amine transporters' subfamily.
Material and Methods
1. Molecular cloning of the human NET gene
To clone and analyze NET gene, a human brain stem cDNA library cloned in Lambda ZAPII(Stratagene) was amplified and its DNA molecules were extracted according to published procedures. A pair of primers were designed for PCR amplification. The sense primer was corresponding to bases 1111-1137 of NET eDNA molecule with the sequence 5′GAACACAAGGTCAACATTGAGGATGTG 3′ , the antisense primer was corresponding to bases 1911-1892 with the sequence 5′CGGAAGCTTGTGACCTGGACATTGGCATGG 3′ , HinclI and HindIII were underlined. The amplification protocol consisted of a 1 min denaturation at 94°C, a 1.5 min annealing at 55°C, and a 2 min extension at 70°C for 30 cycles on DNA Amplifier. A 801 bp DNA fragment was generated by PCR. The 801 bp fragment was cloned into pTZ19u between SmaI and HindIII. The recombinant plasmid was called pNET1. Identification was done by sequencing using the method of Guo and Wu38.
Using pNET1 insert as a probe to isolate human NET gene from a human genomic library cloned in Cosmid pWE15 (Stratagene), one positive clone harbouring 29.7 kb fragment was obtained and mapped. Far 5′terminal of the insert was used as a probe for chromosome walking. Together this technique was proceeded three times. Then the clone named as phNET contains the entire open reading frame(ORF) of NET.
2. Structural analyzing of the human NET gene
Standard protocols were used for restriction mapping, Southern hybridization, subclone and sequencing39.
Results and Discussion
A 801 bp fragment corresponding to 1111-1911 of NET cDNA molecular was obtained from a human brain stem cDNA libray (where hNET is highly expressed) by using PCR technique. After cloning and identification, it was used as a probe to isolate the human NET gene. One positive clone harbouring a 29.7 kb fragment was obtained and mapped. Southern hybridization with γ-32P-dATP labelled oligonucleotides corresponding to 5′terminal in NET cDNA showed that the clone contains only part of the gene. Far 5′terminal of the insert was used as a probe for chromosome walking. Altogether this technique was proceeded for three times, giving 11 kb, 9.5 kb and 8.6 kb extensions towards 5′direction of the gene respectively. Then the clone named as phNET with the entire open reading frame(ORF) of NET was obtained. Fourteen exons encoding all amino acids of NET were determined on ∼ 59kb genomic DNA fragment by restriction mapping, Southern hybridization, subclone, and sequencing. Exon 1 to exon 6 were determined by restriction sites in NET cDNA sequence and synthesized oligonucleotides.
The human NE transporter gene is much larger than the human GABA transporter gene36. In the NET genomic DNA, intron 1 and 2 exceed 10 kb in length, and exons are more concentrated on the 3′ terminal (Fig 1). The deduced amino acid sequence of this gene is identical to that deduced from published NET cDNA molecule.
The intron-exon junctions of this gene are shown in Tab 1. The statistics of all splice donor and acceptor sequences is.......g100t100a54a46g70t61.......c93a100g100. The twelve putative transmembrane regions of the human NET are encoded by exons 1–12. In general, each transmembrane domain is encoded by a single different exon, with the exception of transmembrane domain 10 and 11, which are encoded by parts of exon 10 and 11, and exon 11 and 12, respectively. Furthermore, exon 12 encodes part of domain 11 as well as the entire domain 12. Compared with the human GABA transporter36, the organization of these two proteins is rather similar. There are, however, three distinct differences: i) while the human GABA transporter gene is about 25 kb, consists of 16 exons, the human NE transporter is about 46 kb, consists of 14 exons; ii) in the human GABA transporter gene, the largest outside loop is encoded by a separate exon---exon 6 (the translation starting site is in exon 3), while in NE transporter gene, this loop is encoded by 3′ terminal of exon 3 and 5′terminal of exon 4; iii) in the human GABA transporter, most of the amino acid residues of the cytoplasmic carboxyl terminus are encoded by exon 16, whereas in the human NE transporter, the C terminal in cytoplasm was encoded by three exons: part of exon 12, and all of exon 13 and 14 (Fig 2).
Amino acid residues at domain boundaries are listed in Tab 2. It is noted that glycine or polar amino acid residues always occur there, except for amino acid residues between exon 11 and 12, which are inside transmembrane domain 11. This is possibly a result of evolution, since glycine, an amino acid without any branches in the residue, has the greatest flexibility.
The human NET gene(NETHG) reported here is the first human catecholamine transporter gene that has been cloned and analyzed. From the relationship between exons and domains of NETHG, we predict that for this gene, 14 exons encode 13 functional domains in the NET protein. Exon 14 only encodes seven amino acids which may not comprise an independent domain. Additionally, with the exception of domain 10 and 11, the exon-intron junctions are all located at the border of, or outside, the membrane (Fig 2). The significance of these observations is not known.
Future studies will be focused on the molecular, developmental and pharmacological properties of this protein as well as the regulation of the NET gene. Such analyses should enhance our understanding of the molecular mechanisms of neurotransmitter transporters, and their relationships with synaptic plasticity, learning and certain neurological disorders such as drug addiction and depression.
References
Zygmunt LK, Christopher JP(Eds) . Neurotransmitters and Drugs. Third Edition. Chapmanl Hall. 1992.
Axelrod J . Noradrenaline: fate and control of its biosynthesis. Science 1971; 173:598–606
Pacholczyk T, Blakely R, Amara S . Expression cloning of a cocaine- and antidepressant-sensitive human noradrenaline transporter. Nature 1991; 350:350–4.
Stork T, Schulte S, Hofmann K, Stoffel W . Structure, expression, and functional analysis of a Na+-dependent glutamate/aspartate transporter from rat brain. Proc Natl Acad Sci USA 1992; 89:10955–9.
Pines G, Danbolt NC, Bjoras M, et al. Cloning and expression of a rat brain L-glutamate transporter. Nature 1992; 360:464–7.
Arriza JL, Kavanaugh MP, Fairman WA, et al. Cloning and expression of a human neutral amino acid transporter with structural similarity to the glutamate transporter gene family. J Biol Chem 1993; 268:15329–32.
Shafqat S, Tamarappoo BK, Kilberg M, et al. Cloning and expression of a novel Na+-dependent neutral amino acid transporter structurally related to mammalian Na+ /glutamate cotrans- porters. J Biol Chem 1993; 268:15351–5.
Kanai Y, Hediger MA . Primary structure and functional characterization of a high-affinity glutamate transporter. Nature 1992; 360:467–71.
Guastella J, Nelson N, Lester H, et al. Cloning and expression of a rat brain GABA transporter. Science 1990; 249:1303–6.
Nelson H, Mandiyan S, Nelson N . Cloning of the human brain GABA transporter. FEBS Lett 1990; 269:181–4.
Lopez-Corcuera B, Liu QR, Mandiyan S, Nelson H, Nelson N . Expression of a mouse brain cDNA encoding novelγ- aminobutyric acid transporter. J Biol Chem 1992; 267:17491–3.
Borden LA, Smith KE, Hartig PR, Branchek TA, Weinshank RL . Molecular heterogeneity of the γ-aminobutyric acid(GABA) transporter system, cloning of two novel high affinity GABA transporter from rat brain. Neuron 1992; 9:337–48.
Liu QR, Lopez-Corcuera B, Mandiyan S, Nelson H, Nelson N . Molecular characterization of four pharmacologically distinct γ-aminobutyric acid transporters in mouse brain. J Biol Chem 1993; 268:2106–12.
Smith KE, Borden LA, Wang CHD, Hartig PR, Branchek TA, Weinshank RL . Cloning and expression of a high affinity taurine transporter from rat brain. Mol Pharmacol 1992; 42:563–9.
Liu QR, Lopez-Corcuera B, Nelson H, Madiyan S, Nelson N . Cloning and expression of a cDNA encoding the transporter of taurine and beta-alanine in mouse brain. Proc Natl Acad Sci USA 1992; 89:12145–9.
Mayser W, Schloss P, Betz H . Primary structure and functional expression of a choline trans- porter expressed in the rat nervous system. FEBS Lett 1992; 305:31–6.
Yamauchi A, Uchida S, Kwon HM, et al. Cloning of a Na+ and C1−-dependent betaine trans-porter that is regulated by hypertonicity. J Biol Chem 1992; 267:649–52.
Guimbal C, Kilimann MW . A Na+- dependent creatine transporter in rabbit brain, muscle, heart, and kidney. J Biol Chem 1993; 268:8418–21.
Guastella J, Brecha N, Weigmann C, Lester HA . Cloning, expression, and localization of a rat brain high-affinity glycine transporter. Proc Natl Acad Sci USA 1992; 89:7189–93.
Liu QL, Nelson H, Mandiyan S, Lopez-Corcuera B, Nelson N . Cloning and expression of a glycine transporter from mouse brain. FEBS Lett 1992; 305:110–4.
Borowsky B, Mezey E, Hoffman BJ . Two glycine transporter variants with distinct localization in the CNS and peripheral tissues are encoded by a common gene. Neuron 1993; 10:851–63.
Fremeau RT, Caron MG, Blakely RD . Molecular cloning and expression of a high affinity L- proline transporter expressed in putative glutamatergic pathways of rat brain. Neuron 1992; 8:915–26.
Shimada S, Kitayama S, Lin CL, et al. Cloning and expression of a cocaine sensitive dopamine transporter complementary DNA. Science 1991; 254:576–8.
Kilty JE, Lorang D, Amara SG . Cloning and expression of a cocaine-sentitive rat dopamine transporter. Science 1991; 254:578–9.
Giros B, Mestikawy SE, Bertrand L, Caron MG . Cloning and functional characterization of a cocaine- sensitive dopamine transporter. FEBS Lett 1991; 295:149–54.
Giros B, Mestickawy SE, Godinot N, et al. Cloning, pharmacological characterization, and chromosome assignment of the human dopamine transporter. Mol Pharmacol 1992; 42:391–7.
Hoffman B, Mezey E, Brownstein MJ . Cloning of a serotonin transporter affected by antide-pressants. Science 1991; 254:579–80.
Blakely RD, Berson HE, Fremeau RT Jr, et al. Cloning and expression of a functional serotonin transporter from rat brain. Nature 1991; 354:66–70.
Corey JL, Quick MW, Davidson N, Lester HA, Guastella J . A cocaine-sensitive drosophila serotonin transporter: cloning, expression, and electrophysiological characterization. Proc Natl Acad Sci USA 1994; 91:1188–92.
Liu QR, Mandiyan S, Lopez-Corcuera B, Nelson H, Nelson N . A rat brain cDNA encoding the neurotransmitter transporter with an unusual structure. FEBS Lett 1993; 315:114–8.
Seol W, Shatkin AJ . Escherichia coli kgtP encodes an alpha-ketoglutarate transporter. Proc Natl Acad Sci USA 1991; 88:3802–6.
Szkutnicka K, Tschopp J, Andrews L, Cirillo VP . Sequence and structure of the yeast galactose transporter. J Bacteriol 1989; 171:4486–93.
Wheal H, Thomson A (Eds). Excitatory Amino Acids and Synaptic Transmission. Academic Press. 1992.
Huang F, Fei J, Guo LH . Neurotransmitter transporters. LIFE SCIENCES (China) 1994; 6:5–8.
Iversen LL . Uptake processes for biogenic amines. In L.L. Iversen, S.D. Iversen and S.H. Sny-der(Eds.), Handbook of psychophaxmacology. Vol 3. Plenum. New York. 1978: pp.381–442.
Lam DMK, Fei J, Zhang XY, et al. Molecular cloning and structure of the human(GABATHG) GABA transporter gene. Mol Brain Res 1993; 19:227–32.
Liu QR, Mandiyan S, Nelson H, Nelson N . A family of genes encoding neurotransmitter trans- porters. Proc Natl Acad Sci USA 1992; 89:6639–43.
Guo LH, Wu R . In R. Wu, L. Grossman and K. Moldave (Eds), Recombinant DNA Methodology. Academic Press.1989. pp.73–109.
Sambrook J, Fritsch EF, Maniatis T (Eds). Molecular Cloning. Second Edition. Cold Spring Harbor Laboratory Press. 1989.
Acknowledgements
We thank Drs. Steven King and Ken Beattie for their valuable advice and Ms. Teddy Woodyard for preparation of the manuscript. This work was supported by research grants from the Retina Research Foundation (Houston) GES Pharmaceuticals Inc. (Houston) and the Croucher Foundation (Hong Kong).
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*Dedicated to Professor Yao Zhen's 80th Birthday
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Guo, L., Zhu, L., Huang, F. et al. Molecular cloning and structural analysis of human norepinephrine transporter gene(NETHG). Cell Res 5, 93–100 (1995). https://doi.org/10.1038/cr.1995.9
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DOI: https://doi.org/10.1038/cr.1995.9