title: Functional consequences of homo- but not hetero-oligomerization between transporters for the biogenic amine neurotransmitters.
abstract: Before this study, the human norepinephrine transporter (hNET) was the only member of the biogenic amine neurotransmitter transporter family that had not been demonstrated to be a functional homo-oligomer. Here, using two forms of the transporter, I155C and hNET-myc, with distinct antigenicity and inhibitor sensitivity, we demonstrated that hNET exists as a homo-oligomer. hNET I155C is a functional mutant and is sensitive to inactivation by the sulfhydryl reagent [2-(trimethylammonium)ethyl]methanethiosulfonate, while hNET-myc is resistant to inactivation by this reagent. Coimmunoprecipitation of these two forms demonstrated that a physical interaction exists between norepinephrine transporter monomers. Further characterization of this physical interaction has revealed that the activity of norepinephrine transporters depends on interactions between monomers. Because norepinephrine transporters and serotonin transporters are the only two members of the neurotransmitter transporter family endogenously expressed in the cell membrane of the same cells, placental syncytiotrophoblasts, we tested the ability of norepinephrine transporters and serotonin transporters to associate and function in a hetero-oligomeric form. Similarly, coexpression of hNET-myc with serotonin transporter-FLAG showed a physical interaction in coimmunoprecipitation assays. However, coexpression of serotonin and norepinephrine transporters did not sensitize norepinephrine transporter activity to inhibition by citalopram, a selective serotonin transport inhibitor. Thus, the norepinephrine transporter-serotonin transporter physical association did not produce functional consequences. Based on this, we propose that the transporters for biogenic amine neurotransmitters interact functionally in homo- but not hetero-oligomeric forms.
authors.affiliation: Department of Biochemistry and Molecular Biology, UAMS, Little Rock, Arkansas 72205, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Kocabas
authors.forename: G
authors.initials: G
authors.lastname: Rudnick
authors.forename: F
authors.initials: F
authors.lastname: Kilic
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001483:Base Sequence; D015306:Biogenic Monoamines / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D008698:Mesylates / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins; D050484:Norepinephrine Plasma Membrane Transport Proteins; D011233:Precipitin Tests; D011485:Protein Binding / Q000502:physiology; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins; D013439:Sulfhydryl Reagents / Q000737:chemistry; D027981:Symporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D015306:Biogenic Monoamines; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008698:Mesylates; D009419:Nerve Tissue Proteins; D050484:Norepinephrine Plasma Membrane Transport Proteins; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; C493227:SLC6A2 protein, human; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; D013439:Sulfhydryl Reagents; D027981:Symporters; C109154:(2-(trimethylammonium)ethyl)methanethiosulfonate