RIC-3 affects properties and quantity of nicotinic acetylcholine receptors via a mechanism that does not require the coiled-coil domains.
Members of the RIC-3 gene family are effectors of nicotinic acetylcholine receptor (nAChR) expression in vertebrates and invertebrates. In Caenorhabditis elegans RIC-3 is needed for functional expression of multiple nAChRs, including the DEG-3/DES-2 nAChR. Effects of RIC-3 on DEG-3/DES-2 functional expression are found in vivo and following heterologous expression in Xenopus leavis oocytes. We now show that in X. leavis oocytes RIC-3 also affects the kinetics and agonist affinity properties of the DEG-3/DES-2 receptor. Because these effects are mimicked by increasing the ratio of DEG-3 subunits within DEG-3/DES-2 receptors, this suggests that RIC-3 may preferentially promote maturation of DEG-3-rich receptors. Indeed, effects of RIC-3 on functional expression of DEG-3/DES-2 positively correlate with the DEG-3 to DES-2 ratio. All RIC-3 family members have two transmembrane domains followed by one or two coiled-coil domains. Here we show that the effects of RIC-3 on functional expression and on receptor properties are mediated by the transmembrane domains and do not require the coiled-coil domains. In agreement with this, mammals express a RIC-3 transcript lacking the coiled-coil domain that is capable of promoting DEG-3/DES-2 functional expression. Last, we show that RIC-3 affects DEG-3 quantity, suggesting stabilization of receptors or receptor intermediates by RIC-3. Together our results suggest that subunit-specific interactions of RIC-3 with nAChR subunits, mediated by the transmembrane domains, are sufficient for the effects of RIC-3 on nAChR quantity and quality.
Ben-Ami
Hagit Cohen
HC
Department of Physiology, Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
Yassin
Lina
L
Farah
Hanna
H
Michaeli
Avner
A
Eshel
Margalit
M
Treinin
Millet
M
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002794:Choline / Q000737:chemistry / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D018075:RNA, Complementary / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014981:Xenopus; D014982:Xenopus laevis
D029742:Caenorhabditis elegans Proteins; D018076:DNA, Complementary; D020033:Protein Isoforms; D018075:RNA, Complementary; D011978:Receptors, Nicotinic; C454141:ric-3 protein, C elegans; D049452:Green Fluorescent Proteins; D002794:Choline